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WO2012008559A1 - Séparateur pour batterie secondaire au lithium-ion et batterie secondaire au lithium-ion l'utilisant - Google Patents

Séparateur pour batterie secondaire au lithium-ion et batterie secondaire au lithium-ion l'utilisant Download PDF

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Publication number
WO2012008559A1
WO2012008559A1 PCT/JP2011/066172 JP2011066172W WO2012008559A1 WO 2012008559 A1 WO2012008559 A1 WO 2012008559A1 JP 2011066172 W JP2011066172 W JP 2011066172W WO 2012008559 A1 WO2012008559 A1 WO 2012008559A1
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Prior art keywords
fiber
separator
ion secondary
lithium ion
secondary battery
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Ceased
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PCT/JP2011/066172
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English (en)
Japanese (ja)
Inventor
松岡　昌伸
友洋 佐藤
加寿美 加藤
誉子 笠井
緑川　正敏
伯志 松田
裕夫 鍛冶
山本　浩和
宏明 渡邉
佃　貴裕
郁夫 藤田
兵頭　建二
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Mitsubishi Paper Mills Ltd
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Mitsubishi Paper Mills Ltd
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Priority to JP2012524600A priority Critical patent/JP5767222B2/ja
Priority to CN201180034584.9A priority patent/CN102986060B/zh
Publication of WO2012008559A1 publication Critical patent/WO2012008559A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/429—Natural polymers
    • H01M50/4295—Natural cotton, cellulose or wood
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/429—Natural polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/44—Fibrous material
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a separator for a lithium ion secondary battery and a lithium ion secondary battery using the separator.
  • a lithium ion secondary battery using an organic electrolyte (non-aqueous electrolyte) has attracted attention.
  • the average voltage of the lithium ion secondary battery is 3.7 V, which is about three times that of the alkaline secondary battery, and the energy density is high.
  • an aqueous electrolyte solution cannot be used unlike the alkaline secondary battery.
  • a nonaqueous electrolytic solution having sufficient oxidation-reduction resistance is used.
  • a film-like porous film made of polyolefin is often used (see, for example, Patent Document 1), but has low ionic conductivity due to low electrolyte retention. There was a problem that the internal resistance increased.
  • a paper separator for example, see Patent Document 2 mainly composed of regenerated cellulose fiber beats has been proposed.
  • Lithium ion secondary batteries have a negative effect on battery characteristics if even a small amount of water is mixed in. Therefore, if a paper separator with a high moisture content is used for the separator, it will dry for a long time when producing lithium ion secondary batteries. Processing is required. Moreover, since the separator strength was weak, there was a problem that the separator could not be thinned.
  • separators for lithium ion secondary batteries nonwoven fabric separators made of synthetic fibers (see, for example, Patent Documents 3 to 5) have also been proposed.
  • these separators have low electrolyte retention and internal resistance. There is a problem that the high short-circuiting rate is high, the internal short-circuit defect rate is high, and the high rate characteristics and discharge characteristics are inferior.
  • JP 2002-105235 A Japanese Patent No. 3661104 JP 2003-123728 A JP 2007-317675 A JP 2006-19191 A International Publication No. 2005/101432 Pamphlet International Publication No. 1996/030954 Pamphlet JP 2004-146137 A
  • the present invention has been made in view of the above circumstances, and has a low moisture content, high mechanical strength, and excellent internal resistance and internal short-circuit failure rate, in particular, high-rate discharge characteristics and variations, and cycle characteristics.
  • the object is to provide a lithium ion secondary battery separator and a lithium ion secondary battery using the same.
  • the modified freeness measured in accordance with JIS P8121 is 0 ⁇ except that an 80 mesh wire net having a wire diameter of 0.14 mm and an aperture of 0.18 mm is used as the sieve plate, and the sample concentration is 0.1%.
  • a separator for a lithium ion secondary battery comprising a porous sheet containing 250-ml solvent-spun cellulose fiber of 10 to 90% by mass and synthetic fiber of 10 to 90% by mass.
  • the solvent-spun cellulose fiber has a maximum frequency peak between 0.00 and 1.00 mm in the length-weighted fiber length distribution histogram, and a fiber having a length-weighted fiber length of 1.00 mm or more.
  • the slope of the ratio of fibers having a length-weighted fiber length of 0.05 mm between 1.00 and 2.00 mm is ⁇ 3.0 or more
  • the separator for lithium ion secondary batteries according to (3) which is ⁇ 0.5 or less.
  • the solvent-spun cellulose fiber has a maximum frequency peak between 0.00 and 1.00 mm in the length-weighted fiber length distribution histogram, and a fiber having a length-weighted fiber length of 1.00 mm or more.
  • the porous sheet was measured according to JIS P8121, except that an 80 mesh wire net having a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as the sieve plate, and the sample concentration was 0.1%.
  • (11) The separator for a lithium ion secondary battery according to (10), wherein the core of the core-sheath type heat-sealing fiber is polyethylene terephthalate and the sheath is a polyester copolymer.
  • the value measured by the method defined in JIS B7502 is 6 to 50 ⁇ m.
  • the porous sheet has a multilayer structure, and at least two layers are layers containing solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml as essential components. Separator for use.
  • the separator for a lithium ion secondary battery of the present invention comprises a nonwoven fabric containing solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml and synthetic fibers.
  • the solvent-spun cellulose fiber having a modified freeness of 0 to 250 ml and the synthetic fiber are entangled with each other, so that the liquid retaining property of the lithium ion secondary battery separator can be improved.
  • the resistance can be lowered, and the discharge characteristics at a particularly high rate can be made excellent.
  • the lithium ion secondary battery separator can be made dense, variations in internal short-circuit failure rate and discharge characteristics can be suppressed.
  • the moisture content of a separator can be restrained low by containing a synthetic fiber, and the drying process time at the time of battery manufacture can be shortened more.
  • the synthetic fiber is easily entangled with synthetic fibers and solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml, and a fiber network is formed, whereby the strength of the separator can be increased, and the separator can be more dense and The internal resistance can be lowered, the internal short-circuit failure rate and the variation in discharge characteristics can be suppressed, and the cycle characteristics can be improved.
  • the lithium ion secondary battery separator of the present invention (hereinafter also referred to as “separator”) and a lithium ion secondary battery using the same will be described in detail.
  • the solvent-spun cellulose fiber in the present invention is different from the so-called regenerated cellulose fiber in which cellulose is once chemically converted into a cellulose derivative and then returned to cellulose like conventional viscose rayon or copper ammonia rayon.
  • This refers to a fiber in which cellulose is precipitated by dry and wet spinning of a spinning stock solution dissolved in amine oxide in water without chemical change, and is also referred to as “lyocell fiber”.
  • Solvent-spun cellulose fibers have a higher molecular arrangement in the fiber long axis direction than natural cellulose fibers, bacterial cellulose fibers, and rayon fibers, so when mechanical forces such as friction are applied in a wet state, It is easy to form, and fine and long fine fibers are formed.
  • the solvent-spun cellulose fibers that are refined are superior in liquid retention of the electrolyte solution compared to the refined products of natural cellulose fibers, bacterial cellulose fibers, and rayon fibers.
  • solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml are used.
  • the modified drainage degree of the solvent-spun cellulose fiber is more preferably 0 to 200 ml, and further preferably 0 to 160 ml.
  • the modified freeness is more than 250 ml, the density of the separator becomes insufficient and the internal short circuit defect rate becomes high.
  • the modified freeness in the present invention was measured in accordance with JIS P811, except that an 80 mesh wire net having a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as a sieve plate, and the sample concentration was 0.1%. It is a value.
  • the fiber length becomes shorter as the microfabrication progresses.
  • the sample concentration is low
  • the entanglement between fibers decreases and it becomes difficult to form a fiber network. Will slip through the holes in the sieve plate.
  • an accurate freeness cannot be measured by the measuring method of JIS P8121.
  • natural cellulose fibers are in a state where many fine fibrils are torn apart from the trunk of the fiber as the degree of refinement progresses. Therefore, the fibers are easily entangled with each other through the fibrils, and a fiber network is easily formed.
  • the solvent-spun cellulose fiber is easily finely divided in parallel to the long axis of the fiber by the refining treatment, and since the uniformity of the fiber diameter in each fiber after division is high, the shorter the average fiber length, It is considered that the fibers do not easily entangle with each other and it is difficult to form a fiber network. Therefore, in the present invention, in order to measure the exact freeness of the solvent-spun cellulose fiber, an 80-mesh wire mesh having a wire diameter of 0.14 mm and an opening of 0.18 mm is used as a sieve plate, and the sample concentration is 0.1%. A modified freeness measured in accordance with JIS P8121 was used.
  • the length weighted average fiber length of solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml is preferably 0.20 to 3.00 mm, more preferably 0.20 to 2.00 mm, and 0.20 to 1. 60 mm is more preferable. If the length-weighted average fiber length is shorter than 0.20 mm, the separator may fall off, and if it is longer than 3.00 mm, the fibers may be tangled and become lumpy, resulting in uneven thickness.
  • 1 and 2 are length-weighted fiber length distribution histograms of solvent-spun cellulose fibers. As shown in FIGS. 1 and 2, in the length-weighted fiber length distribution histogram of solvent-spun cellulose fibers, the maximum frequency peak is between 0.00 and 1.00 mm, and the length-weighted fiber length is 1.00 mm or more. In the lithium ion secondary battery separator (3) in which the ratio of the fibers having 10% or more is easy to entangle the fibers and easily form a fiber network, the separator strength is increased and the internal short circuit rate is low. It is preferable.
  • the maximum frequency peak is between 0.30 and 0.70 mm, and the fiber having a length-weighted fiber length of 1.00 mm or more in terms of a decrease in internal short-circuit failure rate. More preferably, the ratio is 12% or more. A higher ratio of fibers having a length-weighted fiber length of 1.00 mm or more is preferable, but about 50% is sufficient.
  • the proportion of fibers having a length-weighted fiber length of every 0.05 mm between 1.00 and 2.00 mm The lithium ion secondary battery separator (4) having a slope of ⁇ 3.0 or more and ⁇ 0.5 or less is more preferable because of high mechanical strength of the separator and less variation in discharge capacity.
  • the inclination of the ratio of fibers having a length-weighted fiber length of 0.05 mm between 1.00 and 2.00 mm is ⁇ 2.5 or more and ⁇ 0.
  • the mechanical strength may be lowered.
  • the inclination exceeds ⁇ 0.5, the variation in discharge capacity may increase.
  • “large inclination” means that the length-weighted fiber length distribution of the solvent-spun cellulose fiber is wide, and “small inclination” means the length of the solvent-spun cellulose fiber.
  • the weighted fiber length distribution is narrow and the length weighted fiber lengths are more uniform.
  • the slope of the solvent-spun cellulose fiber [I] in FIG. 1 is ⁇ 2.9
  • the slope of the solvent-spun cellulose fiber [II] in FIG. 2 is ⁇ 0.6.
  • the “inclination of the proportion of fibers having a fiber length of every 0.05 mm between 1.00 and 2.00 mm” is 0 between 1.00 and 2.00 mm, as shown in FIG.
  • Approximate straight line is calculated by the method of least squares with respect to the value of the ratio of fibers having a length-weighted fiber length every .05 mm, and the inclination of the obtained approximate straight line is meant.
  • the length-weighted fiber length distribution histogram of solvent-spun cellulose fibers has a maximum frequency peak between 0.00 and 1.00 mm.
  • the proportion of fibers having a length-weighted fiber length of 00 mm or more is preferably 50% or more.
  • the porous sheet has a dense structure, the separator strength is strong, the internal short circuit failure rate is low, and the variation in discharge capacity can be reduced.
  • FIG. 4 shows the length weight of solvent-spun cellulose fibers having a maximum frequency peak between 0.00 and 1.00 mm, and the proportion of fibers having a length-weighted fiber length of 1.00 mm or more is 50% or more. It is a fiber length distribution histogram.
  • the ratio of fibers having a maximum frequency peak between 0.30 and 0.70 mm and having a length-weighted fiber length of 1.00 mm or more is It is preferable that it is 55% or more.
  • a higher proportion of fibers having a length-weighted fiber length of 1.00 mm or more is desirable, but about 70% is sufficient.
  • the lithium ion secondary battery separator (6) having a peak at 5 is preferable because the mechanical strength is increased and the variation in discharge capacity is reduced. Further, it preferably has a peak between 1.75 and 3.25 mm, and more preferably has a peak between 2.00 and 3.00 mm.
  • the length-weighted fiber length of peaks other than the maximum frequency peak is shorter than 1.50 mm, the mechanical strength may decrease. Moreover, when it exceeds 3.50 mm, the variation in discharge capacity may increase.
  • the solvent-spun cellulose fiber preferably has a length weighted average fiber length of 0.50 to 1.25 mm and an average curl degree of 25 or less. .
  • Good solvent retention of lithium-ion secondary battery separator by entanglement of solvent-spun cellulose fiber and synthetic fiber with length-weighted average fiber length of 0.50 to 1.25 mm and average curl of 25 or less As a result, the internal resistance can be lowered, and in particular, the discharge characteristics at a high rate can be made excellent. Furthermore, since the lithium ion secondary battery separator can be made dense, variations in internal short-circuit failure rate and discharge characteristics can be suppressed.
  • the solvent-spun cellulose fiber having a weight-weighted average fiber length of 0.50 to 1.25 mm and an average curl degree of 25 or less is easily entangled with the synthetic fiber, and a fiber network is formed.
  • the separator can be made denser and thinner, the internal resistance can be lowered, the internal short-circuit failure rate and the variation in discharge characteristics can be suppressed, and the cycle characteristics can be improved. It can be excellent.
  • the average curl degree of the solvent-spun cellulose fiber is more preferably 20 or less, and further preferably 15 or less. If the average curl degree of the solvent-spun cellulose fiber is larger than 25, the uniformity of the separator is impaired, and the internal short circuit defect rate may be increased, or the strength of the separator may be decreased.
  • the small numerical value of the average curl degree indicates that the degree of bending of the solvent-spun cellulose fiber is small, that is, closer to a straight line, and therefore there is no particular limitation on the lower limit of the average curl degree.
  • the length-weighted fiber length and length-weighted fiber length distribution histogram, length-weighted average fiber length, and average curl degree of the solvent-spun cellulose fiber of the present invention are as follows. According to 52 “Paper and pulp fiber length test method (optical automatic measurement method)”, it was measured using Kajaani Fiber Lab V3.5 (manufactured by Metso Automation).
  • the total true length (L) of the bent fiber and the shortest length (l) of both ends of the bent fiber are determined. Can be measured.
  • the “length-weighted average fiber length” is an average fiber length obtained by measuring and calculating the shortest length (l) of both ends of the bent fiber.
  • “Average curl degree” is calculated for each individual fiber by measuring the total true length (L) of the bent fiber and the shortest length (l) of both ends of the bent fiber, and calculating by the following formula: This is the average curl degree. As the degree of bending of the fiber increases, the “curl degree” increases.
  • a method for producing solvent-spun cellulose fibers having a degree of 0 to 250 ml, a length-weighted fiber length of 0.50 to 1.25 mm, and an average curl degree of 25 or less a refiner, a beater, a mill, or grinding Equipment, rotary blade homogenizer that applies shear force with a high-speed rotary blade, double-cylindrical high-speed homogenizer that generates shear force between a cylindrical inner blade that rotates at high speed and a fixed outer blade, by ultrasonic Ultrasonic crusher that is refined by impact, giving a pressure difference of at least 20 MPa to the fiber suspension, passing through a small-diameter orifice to a high speed, and colliding with this to rapidly decelerate
  • a method using a refiner is particularly preferable.
  • the type of beating / dispersing equipment and processing conditions fiber concentration, temperature, pressure, rotation speed, refiner blade shape, gap between refiner disks, number of treatments, etc.
  • the desired modified freeness Solvent-spun cellulose length-weighted fiber length, length-weighted fiber length distribution, and average curl degree can be achieved.
  • the separator for a lithium ion secondary battery of the present invention contains 10 to 90% by mass of solvent-spun cellulose fiber having a modified freeness of 0 to 250 ml.
  • the content of the solvent-spun cellulose fiber is more preferably 20 to 70% by mass, and further preferably 30 to 60% by mass.
  • the content of the solvent-spun cellulose fiber is less than 10% by mass, the liquid retainability of the electrolytic solution is insufficient and the internal resistance is increased, or the separator is insufficiently dense and the internal short circuit defect rate is increased. To do.
  • the content of the solvent-spun cellulose fiber exceeds 90% by mass, the mechanical strength of the separator becomes weak and the moisture content of the separator increases.
  • the separator for a lithium ion secondary battery of the present invention contains 10 to 90% by mass of synthetic fiber.
  • the content of the synthetic fiber is more preferably 30 to 80% by mass, and further preferably 40 to 70% by mass.
  • the synthetic fiber content is less than 10% by mass, the strength of the separator is weakened.
  • the synthetic fiber content exceeds 90% by mass, the electrolyte retainability is insufficient and the internal resistance is high, the separator is insufficiently dense, and the internal short circuit failure rate and the variation in discharge characteristics are high. It becomes.
  • the porous sheet preferably contains 20% by mass or less of fibrillated natural cellulose fibers having a modified freeness of 0 to 400 ml.
  • the content of the fibrillated natural cellulose fiber is more preferably 10% by mass or less, and further preferably 5% by mass or less.
  • Fibrilized natural cellulose fibers tend to be less uniform in thickness of one fiber than solvent-spun cellulose fibers, but are characterized by strong physical entanglement between fibers and hydrogen bonding strength.
  • the content of the fibrillated natural cellulose fiber exceeds 20% by mass, a film is formed on the separator surface, and the ionic conductivity is inhibited, so that the internal resistance may be increased or the discharge characteristics may be decreased. .
  • Fibrilization refers to a fiber that is not film-like but has a fiber portion that is mainly finely divided in a direction parallel to the fiber axis, and at least a portion of which has a fiber diameter of 1 ⁇ m or less.
  • the aspect ratio of length to width is preferably in the range of about 20 to about 100,000.
  • the length-weighted plain fiber length is preferably in the range of 0.10 to 2.00 mm, more preferably 0.1 to 1.5 mm, and still more preferably 0.10 to 1.00 mm.
  • Natural cellulose fibers can be fibrillated by refiners, beaters, mills, milling devices, rotary blade homogenizers that apply shearing force with high-speed rotary blades, cylindrical inner blades that rotate at high speed, and outer blades that are fixed. Double-cylindrical high-speed homogenizer that generates a shearing force between the two, an ultrasonic crusher that is refined by ultrasonic shock, and a high pressure by passing a small-diameter orifice by applying a pressure difference of at least 20 MPa to the fiber suspension.
  • a method using a high-pressure homogenizer or the like that applies a shearing force or a cutting force to the fiber by causing it to collide with it and rapidly decelerate it. Among these, a method using a high-pressure homogenizer is particularly preferable.
  • Synthetic fibers include polyester, acrylic, polyolefin, wholly aromatic polyester, wholly aromatic polyester amide, polyamide, semi-aromatic polyamide, wholly aromatic polyamide, wholly aromatic polyether, wholly aromatic polycarbonate, polyimide, polyamideimide ( PAI), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), poly-p-phenylenebenzobisoxazole (PBO), polybenzimidazole (PBI), polytetrafluoroethylene (PTFE), ethylene-vinyl alcohol copolymer
  • PAI polyamideimide
  • PES polyetheretherketone
  • PPS polyphenylene sulfide
  • PBO poly-p-phenylenebenzobisoxazole
  • PBI polybenzimidazole
  • PTFE polytetrafluoroethylene
  • ethylene-vinyl alcohol copolymer examples thereof include single fibers and composite fibers made of a resin such as coalescence. These synthetic fibers may be used
  • polyester, acrylic, polyolefin, wholly aromatic polyester, wholly aromatic polyester amide, polyamide, semi-aromatic polyamide, and wholly aromatic polyamide are preferable, and polyester, acrylic, and polyolefin are more preferable.
  • polyester, acrylic, and polyolefin are used, each fiber and fibrillated solvent-spun cellulose fibers are more easily entangled with each other than other synthetic fibers to easily form a network structure.
  • a separator for a lithium ion secondary battery having excellent mechanical strength can be obtained.
  • the average fiber diameter of the synthetic fiber is preferably 0.1 to 20 ⁇ m, more preferably 0.1 to 15 ⁇ m, and further preferably 0.1 to 10 ⁇ m. If the average fiber diameter is less than 0.1 ⁇ m, the fibers may be too thin and fall off from the separator. If the average fiber diameter is larger than 20 ⁇ m, it may be difficult to reduce the thickness of the separator.
  • the average fiber diameter is an average value of 100 randomly selected fibers obtained by measuring the fiber diameter of the fibers forming the separator from a scanning electron micrograph of the separator.
  • the fiber length of the synthetic fiber is preferably 0.1 to 15 mm, more preferably 0.5 to 10 mm, and further preferably 2 to 5 mm.
  • the separator may fall off, and when the fiber length is longer than 15 mm, the fiber may be entangled, resulting in uneven thickness.
  • the separator for a lithium ion secondary battery of the present invention contains solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml and synthetic fibers, and fibers other than fibrillated natural cellulose fibers having a modified freeness of 0 to 400 ml. Also good.
  • the porous sheet preferably contains carboxymethyl cellulose.
  • solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml and synthetic fibers are allowed to contain carboxymethyl cellulose so that the carboxymethyl cellulose is adsorbed on these fibers, particularly cellulose fibers. While dispersibility improves, fiber twist is suppressed, the formation at the time of using a separator improves, and mechanical strength becomes strong.
  • the dehydrating property of the fibers can be adjusted moderately, the pores of the separator sheet can be easily controlled, the pore diameter distribution can be brought close to the desired value, and the separator can be made dense and homogeneous, so that the internal short circuit failure rate, discharge Variations in characteristics can be suppressed.
  • solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml and synthetic fibers are easily entangled with each other, and carboxymethylcellulose improves the strength of the separator by forming a more homogeneous fiber network.
  • the separator can be made denser and thinner, the internal resistance can be lowered, the internal short-circuit failure rate and the variation in discharge characteristics can be suppressed, and the cycle characteristics can be improved. It has an excellent effect to make it better.
  • Carboxymethyl cellulose is a cellulose derivative synthesized by reacting monochloroacetic acid and the like using wood pulp, linter pulp and the like as raw materials, and is industrially obtained by a known production method such as a water medium method or a solvent method. is there.
  • Carboxymethylcellulose can be produced in various degrees of polymerization depending on the properties and production methods of the pulp fibers used, but the viscosity of a 1% by weight aqueous solution is 5 to 16,000 mPa ⁇ s (0.1 N-NaCl solvent, 25 ° C, B-type viscometer), average degree of polymerization of 100 to 4,500, and average molecular weight of 20,000 to 1,000,000.
  • carboxymethyl cellulose is a carboxylic acid sodium salt or potassium salt. To be precise, it is carboxymethyl cellulose sodium or carboxymethyl cellulose potassium, but the description of sodium or potassium is conventionally omitted, and carboxymethyl cellulose is simply used. Is displayed. In the present invention, it is preferable to use a sodium salt of carboxymethyl cellulose which is inexpensive and easily obtains the effects of the present invention.
  • a method in which fibers are added or dispersed sequentially or simultaneously in a solution in which carboxymethyl cellulose is dissolved in a solvent, usually water in advance, 1 in a solution in which carboxymethyl cellulose is dissolved in advance examples thereof include a method in which more than one type of fiber is introduced and mixed with another type of fiber slurry prepared elsewhere, or a method in which carboxymethyl cellulose is added to a slurry containing at least one type of fiber.
  • a method of preparing a fiber slurry in a solution in which carboxymethyl cellulose is dissolved is preferable.
  • the fibers may be added after forming a high-concentration slurry.
  • the concentration of carboxymethyl cellulose is preferably 0.5 to 5% by mass, more preferably 0.5 to 3% by mass. preferable.
  • an organic solvent for example, methanol, ethanol, etc.
  • an electrolyte such as mirabilite may be mixed within a range in which carboxymethylcellulose is stable.
  • Carboxymethylcellulose is particularly effective for the dispersion of cellulosic fibers such as solvent-spun cellulose fibers and fibrillated natural cellulose fibers, so even when carboxymethylcellulose is added in advance to the fiber slurry preparation liquid, Even when it is added during the preparation of the fiber slurry, it is preferably used in combination with at least a cellulosic fiber.
  • the addition rate of carboxymethylcellulose is preferably 0.5 to 2.0 mass%, more preferably 0.8 to 1.5 mass%, based on the total fiber mass used in the separator for lithium ion secondary batteries of the present invention.
  • the addition rate of carboxymethyl cellulose is less than 0.5% by mass, the effect of improving the formation may not be recognized.
  • the addition rate of carboxymethyl cellulose exceeds 2.0% by mass, the water retention of carboxymethyl cellulose Therefore, there is a case where a longer drying process is required or the moisture content of the lithium ion secondary battery separator is increased, which may adversely affect the battery characteristics. Furthermore, since the drainage is reduced, the productivity during papermaking may be reduced.
  • carboxymethylcellulose is synthesized by reacting monochloroacetic acid or the like with a pulp raw material, but polar carboxyl groups solubilize cellulose and facilitate chemical reaction.
  • the introduction ratio of monochloroacetic acid or the like to cellulose is represented by “degree of etherification”.
  • the dispersibility of the fiber can be improved by adsorbing carboxymethylcellulose to the fiber according to the present invention, particularly the cellulosic fiber, but the higher the degree of etherification in carboxymethylcellulose is, the better the dispersibility of the fiber is.
  • the degree of etherification of carboxymethylcellulose is preferably 0.5 or more, more preferably 0.7 or more.
  • a core-sheath type heat-fusible fiber having a non-thermal adhesive component in the core and a thermal adhesive component in the sheath is used as at least one synthetic fiber. It is preferable to contain.
  • the fibers can be bonded to each other with the core-sheath type heat-sealable fiber, and as a result, the self generated when stored for a long time in a charged state at a high voltage Since discharge can be suppressed, a separator having excellent voltage maintenance ratio characteristics can be obtained. Also.
  • a core-sheath type heat-sealing fiber is used to create a porous fiber network formed by entanglement between synthetic fibers and solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml and synthetic fibers, and hydrogen bonds between solvent-spun celluloses. It is possible to increase the separator strength by heat bonding without damaging the quality structure.
  • the heat-fusible fiber examples include a core-sheath type, an eccentric type, a split type, a side-by-side type, a sea-island type, an orange type, a multi-bimetal type, a single component fiber (single fiber), and the like.
  • the core-sheath type heat-sealable fiber maintains the fiber shape of the core part, and softens, melts or wet-heat dissolves only the sheath part to thermally bond the fibers to each other, so that the porous structure of the separator is not impaired. It is suitable for adhering.
  • the resin component constituting the core and sheath of the core-sheath type heat-sealing fiber is not particularly limited, and any resin having fiber-forming ability may be used.
  • the core / sheath combination includes polyethylene terephthalate / polyester copolymer, polyethylene terephthalate / polyethylene, polyethylene terephthalate / polypropylene, polyethylene terephthalate / ethylene-propylene copolymer, polyethylene terephthalate / ethylene-vinyl alcohol copolymer. , Polypropylene / polyethylene, and high melting point polylactic acid / low melting point polylactic acid.
  • the melting point, softening point or wet heat melting temperature of the resin component in the core part is preferably 20 ° C. or more higher than the melting point or softening point of the resin component in the sheath part from the viewpoint of easy production of the nonwoven fabric.
  • the core-sheath type heat-sealing fiber used for the lithium ion secondary battery separator of the present invention a combination of core: polyethylene terephthalate / sheath: polyester copolymer is preferable because the separator strength becomes higher.
  • the polyester copolymer used for the sheath is a copolymer of polyethylene terephthalate and one or more compounds selected from isophthalic acid, sebacic acid, adipic acid, diethyl glycol, 1,4-butadiol and the like. preferable.
  • the core-sheath type heat-sealing fiber preferably has a fineness of 0.007 to 1.7 dtex, more preferably 0.02 to 1.1 dtex, and even more preferably 0.05 to 0.5 dtex. If the fineness is less than 0.007 dtex, it may be too thin and fall off from the separator. If the fineness exceeds 1.7 dtex, it will be difficult to get entangled with the fibrillated solvent-spun cellulose fiber, ensuring the required denseness. It may not be possible.
  • the fiber length of the core-sheath type heat-sealing fiber is preferably 0.1 to 15 mm, more preferably 0.5 to 10 mm, and further preferably 2 to 5 mm.
  • the separator may fall off, and when the fiber length is longer than 15 mm, the fiber may be entangled, resulting in uneven thickness.
  • the content of the core-sheath-type heat fusion fiber is preferably 5 to 40% by mass, and more preferably 8 to 30% by mass. Is more preferably 10 to 20% by mass. If the content is less than 5% by mass, the voltage maintenance rate characteristics and mechanical strength of the separator may be insufficient. If it exceeds 40% by mass, a film is formed on the separator surface, and the ion conductivity is inhibited, so that the internal resistance may increase or the discharge characteristics may decrease.
  • the separator for the lithium ion secondary battery of the present invention is a circular paper machine, a long paper machine, a short paper machine, an inclined paper machine, a combination paper machine formed by combining the same or different types of paper machines from these, and the like Can be produced by a wet method of wet paper making.
  • a dispersant, a thickener, an inorganic filler, an organic filler, an antifoaming agent, and the like are appropriately added to the raw material slurry as necessary, and a solid content concentration of about 5 to 0.001% by mass is added.
  • a raw material slurry is prepared. This raw slurry is further diluted to a predetermined concentration to make paper.
  • the separator for a lithium ion secondary battery obtained by papermaking is subjected to calendering, thermal calendering, heat treatment and the like as necessary.
  • the separator for lithium ion secondary battery obtained by blending the core-sheath-type heat-sealing fiber and heat-treating is subjected to heat treatment to increase the mechanical strength.
  • the heat treatment method include a heat treatment method using a heating device such as a hot air dryer, a heating roll, an infrared (IR) heater, or the like while continuously performing the heat treatment or pressurizing.
  • the heat treatment temperature is equal to or higher than the temperature at which the sheath portion of the core-sheath fiber is melted or softened, and lower than the temperature at which the core portion of the core-sheath fiber and other contained fibers are melted, softened or decomposed. It is preferable.
  • the thickness of the lithium ion secondary battery separator of the present invention is preferably 6 to 50 ⁇ m, more preferably 8 to 45 ⁇ m, and even more preferably 10 to 40 ⁇ m. If the thickness is less than 6 ⁇ m, sufficient mechanical strength cannot be obtained, insulation between the positive electrode and the negative electrode is insufficient, internal short-circuit failure rate, variation in discharge characteristics, and capacity maintenance ratio and cycle characteristics are low. It may get worse. If it is thicker than 50 ⁇ m, the internal resistance of the lithium ion secondary battery may increase or the discharge characteristics may decrease.
  • the thickness of the separator of the present invention means a value measured by a method defined in JIS B7502, that is, a value measured by an outer micrometer at a load of 5N.
  • the average pore diameter is 0.10 ⁇ m or more and the maximum pore diameter is 6.0 ⁇ m or less.
  • This pore diameter can be achieved by entanglement of solvent-spun cellulose fibers with a modified freeness of 0-250 ml with synthetic fibers. If the average pore diameter is less than 0.10 ⁇ m, the internal resistance of the lithium ion secondary battery may be high, or the discharge characteristics may be low. When the maximum pore diameter is 6 ⁇ m or more, the internal short-circuit failure rate and the variation in discharge characteristics of the lithium ion secondary battery may increase.
  • the average pore diameter is 0.10 ⁇ m or more and the maximum pore diameter is 4.0 ⁇ m or less, more preferably the minimum pore diameter is 0.15 ⁇ m or more and the maximum pore diameter is 3.0 ⁇ m or less. .
  • the basis weight of the lithium ion secondary battery separator of the present invention is preferably 5 ⁇ 40g / m 2, more preferably 7 ⁇ 30g / m 2, more preferably 10 ⁇ 20g / m 2. If it is less than 5 g / m 2 , sufficient mechanical strength may not be obtained, or insulation between the positive electrode and the negative electrode may be insufficient, resulting in increased internal short-circuit failure rate and variation in discharge characteristics. If it exceeds 40 g / m 2 , the internal resistance of the lithium ion secondary battery may increase or the discharge characteristics may decrease.
  • the layer structure of the lithium ion secondary battery separator of the present invention is not particularly limited, and may be a single layer structure or a multilayer structure such as two layers or three layers. From the viewpoint of suppression of generation, a multilayer structure such as two layers or three layers is more preferable. In the case of a multilayer structure, there are no particular restrictions on the method of laminating each layer, but since there is no delamination between the layers, a weaving method can be suitably used.
  • Wet-making method is a papermaking slurry in which fibers are dispersed in water to form a uniform papermaking slurry, and this papermaking slurry is made using a papermaking machine having at least two wires such as a circular net, a long net, and an inclined type.
  • each layer may have the same blending composition or may be different, but at least each layer is solvent-spun with a modified freeness of 0 to 250 ml.
  • a layer containing cellulose fibers as an essential component is preferred. If there is a layer containing no solvent-spun cellulose fiber having a modified freeness of 0 to 250 ml, the peel strength between the layers is inferior, sufficient mechanical strength is not obtained, or the electrolyte retainability is insufficient.
  • the internal resistance may be high, or the separator may be insufficiently dense, resulting in a high internal short-circuit failure rate.
  • Examples of the negative electrode active material of the lithium ion secondary battery include carbon materials such as graphite and coke, metallic lithium, aluminum, silica, tin, nickel, and an alloy of lithium and lithium, SiO, SnO, Metal oxides such as Fe 2 O 3 , WO 2 , Nb 2 O 5 , Li 4/3 Ti 5/3 O 4 , and nitrides such as Li 0.4 CoN are used.
  • As the positive electrode active material lithium cobaltate, lithium manganate, lithium nickelate, lithium titanate, lithium nickel manganese oxide, or lithium iron phosphate is used.
  • the lithium iron phosphate may further be a composite with one or more metals selected from manganese, chromium, cobalt, copper, nickel, vanadium, molybdenum, titanium, zinc, aluminum, gallium, magnesium, boron, and niobium.
  • an electrolytic solution for a lithium ion secondary battery a solution obtained by dissolving a lithium salt in an organic solvent such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, dimethoxymethane, or a mixed solvent thereof is used.
  • the lithium salt include lithium hexafluorophosphate (LiPF 6 ) and lithium tetrafluoroborate (LiBF 4 ).
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium tetrafluoroborate
  • solid electrolyte what melt
  • Synthetic fiber B1 Polyethylene terephthalate fiber having an average fiber diameter of 3 ⁇ m and a fiber length of 3 mm was designated as synthetic fiber B1.
  • Synthetic fiber B2 An acrylic fiber having an average fiber diameter of 5 ⁇ m and a fiber length of 3 mm was designated as synthetic fiber B2.
  • ⁇ Synthetic fiber B3> A polypropylene fiber having an average fiber diameter of 4 ⁇ m and a fiber length of 3 mm was defined as a synthetic fiber B3.
  • Polyester core-sheath type heat-sealable fiber having an average fiber diameter of 10 ⁇ m, a fiber length of 5 mm, a polyethylene terephthalate (melting point: 253 ° C.) sheath and a polyethylene terephthalate-isophthalate copolymer (softening point: 75 ° C.) sheath B4.
  • Synthetic fiber B5 Polyethylene terephthalate fiber having an average fiber diameter of 20 ⁇ m and a fiber length of 5 mm was designated as synthetic fiber B5.
  • ⁇ Synthetic fiber B6> A polyethylene terephthalate fiber having an average fiber diameter of 22 ⁇ m and a fiber length of 5 mm was defined as a synthetic fiber B6.
  • ⁇ Synthetic fiber B7> A polyethylene terephthalate fiber having an average fiber diameter of 0.1 ⁇ m and a fiber length of 2 mm was defined as a synthetic fiber B7.
  • Synthetic fiber B8 A polyethylene terephthalate fiber having an average fiber diameter of 0.08 ⁇ m and a fiber length of 2 mm was designated as synthetic fiber B8.
  • ⁇ Fibrylated natural cellulose fiber C1> The linter was treated using a high-pressure homogenizer to produce a fibrillated natural cellulose fiber C1 having a modified freeness of 0 ml.
  • ⁇ Fibrylated natural cellulose fiber C2> The linter was treated with a high-pressure homogenizer to produce a fibrillated natural cellulose fiber C2 having a modified freeness of 270 ml.
  • ⁇ Fibrylated natural cellulose fiber C3> The linter was treated with a high-pressure homogenizer to produce a fibrillated natural cellulose fiber C3 having a modified freeness of 400 ml.
  • ⁇ Fibrylated natural cellulose fiber C4> The linter was treated using a high-pressure homogenizer to produce a fibrillated natural cellulose fiber C4 having a modified freeness of 500 ml.
  • fiber D1 Using a refiner, para-type wholly aromatic polyamide having an average fiber diameter of 10 ⁇ m and fiber length of 3 mm was treated, and fibrillated para-type wholly aromatic polyamide fiber having a modified freeness of 500 ml was designated as fiber D1.
  • Fiber E1 The hemp fiber having an average fiber diameter of 7 ⁇ m was designated as fiber E1.
  • Examples 1 to 24 and Comparative Examples 1 to 10 ⁇ Separator> According to the raw materials and contents shown in Table 1, a papermaking slurry was prepared, and wet papermaking was performed using a circular paper machine to prepare separators of Examples 1 to 24 and Comparative Examples 1 to 9. The thickness was adjusted by calendaring at room temperature. In addition, a porous polyethylene film (thickness 22 ⁇ m, porosity 40%) was used as the separator of Comparative Example 10.
  • ⁇ Lithium ion secondary battery A> [Preparation of Negative Electrode 1] A slurry in which 97% by mass of natural graphite and 3% by mass of polyvinylidene fluoride were mixed and dispersed in N-methyl-2-pyrrolidone was prepared, applied to both sides of a copper foil having a thickness of 15 ⁇ m, and rolled. A negative electrode for a lithium ion secondary battery having a thickness of 100 ⁇ m was produced by vacuum drying at a temperature of 2 ° C. for 2 hours.
  • a slurry in which 95% by mass of LiMn 2 O 4 , 2 % by mass of acetylene black and 3% by mass of polyvinylidene fluoride are mixed and dispersed in N-methyl-2-pyrrolidone is prepared, and both surfaces of an aluminum foil having a thickness of 20 ⁇ m are prepared. After being applied and rolled onto the substrate, it was vacuum-dried at 150 ° C. for 2 hours to produce a positive electrode for a lithium ion secondary battery having a thickness of 100 ⁇ m.
  • the negative electrode 1 and the positive electrode 1 are wound so that the separators of Examples 1 to 24 and Comparative Examples 1 to 7 and 9 are interposed between the electrodes, respectively, and stored in a cylindrical container made of aluminum alloy, and the lead body is welded. Went. Next, the whole cylindrical container was vacuum-dried at 150 ° C. for 10 hours. This was allowed to cool to room temperature in a vacuum, and then an electrolyte solution was injected and sealed up, and lithium ion secondary batteries A of Examples 1 to 24 and Comparative Examples 1 to 7 and 9 were produced.
  • the electrolytic solution a solution obtained by dissolving LiPF 6 in a mixed solvent composed of 30% by mass of ethylene carbonate and 70% by mass of diethyl carbonate so as to be 1.2M was used.
  • the negative electrode 1 and the positive electrode 1 were each wound so that the separator of Comparative Example 8 was interposed between the electrodes, housed in a cylindrical container made of aluminum alloy, and the lead body was welded. Next, the whole cylindrical container was vacuum-dried at 110 ° C. for 24 hours. This was allowed to cool to room temperature in a vacuum, and then an electrolytic solution was injected and sealed to prepare a lithium ion secondary battery A of Comparative Example 8.
  • the electrolytic solution a solution obtained by dissolving LiPF 6 in a mixed solvent composed of 30% by mass of ethylene carbonate and 70% by mass of diethyl carbonate so as to be 1.2M was used.
  • the negative electrode 1 and the positive electrode 1 were wound so that the separator of Comparative Example 10 was interposed between the electrodes, accommodated in a cylindrical container made of aluminum alloy, and the lead body was welded.
  • the whole cylindrical container was vacuum-dried at 80 ° C. for 10 hours. This was allowed to cool to room temperature in a vacuum, and then an electrolytic solution was injected and sealed to prepare a lithium ion secondary battery A of Comparative Example 10.
  • the electrolytic solution a solution obtained by dissolving LiPF 6 in a mixed solvent composed of 30% by mass of ethylene carbonate and 70% by mass of diethyl carbonate so as to be 1.2M was used.
  • ⁇ Lithium ion secondary battery B> [Preparation of Negative Electrode 2] A slurry in which 81% by mass of mesocarbon microbeads, 14% by mass of acetylene black and 5% by mass of polytetrafluoroethylene were mixed and dispersed in N-methyl-2-pyrrolidone was prepared, and both sides of a copper foil having a thickness of 15 ⁇ m After being applied and rolled onto the substrate, it was vacuum-dried at 150 ° C. for 2 hours to produce a negative electrode for a lithium ion secondary battery having a thickness of 100 ⁇ m.
  • the separator of Comparative Example 8 the positive electrode 2, and the negative electrode 2 were bonded together in this order, and the lead wire was drawn out to produce a battery body.
  • the separator of Comparative Example 10 the positive electrode 2 and the negative electrode 2 were bonded together in this order, and the lead wires were drawn out to produce a battery body.
  • the battery body was vacuum-dried at 80 ° C. for 15 hours, allowed to cool to room temperature in a vacuum, and then inserted into an aluminum laminate film, and from 1M-LiPF 6 / EC + DEC (3: 7 vol%).
  • Basis weight The basis weight was measured in accordance with JIS P8124.
  • the thickness was measured by the method defined in JIS B7502, that is, by an outer micrometer at 5N load.
  • A The difference in discharge capacity is 1.0% or less with respect to the average value.
  • ⁇ The difference in discharge capacity is more than 1.0% and 2.5% or less with respect to the average value.
  • delta The difference of discharge capacity exceeds 2.5% with respect to an average value, and is 5.0% or less.
  • X The difference of discharge capacity is over 5.0% with respect to the average value.
  • the separators for lithium ion secondary batteries of Examples 1 to 24 were 10 to 90% by mass of solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml and 10 to 90% by mass of synthetic fibers. Since it contained, the moisture content was low, the mechanical strength was strong, and it was excellent.
  • the separators for lithium ion secondary batteries of Examples 1 to 24 contain 10 to 90% by mass of synthetic fiber, they are contained in comparison with the paper separator made of solvent-spun cellulose and hemp fiber of Comparative Example 8. The moisture content could be kept low. Furthermore, the strength of the separator has increased because the fibers are easily entangled and a fiber network is easily formed.
  • the separator for the lithium ion secondary battery of Comparative Example 1 the content of the solvent-spun cellulose fiber having a modified freeness of 0 to 250 ml in the separator is more than 90% by mass, and the synthetic fiber contained in the separator is 10% by mass. Since it was less, the moisture content was high and the separator strength was weak.
  • the separator for the lithium ion secondary battery of Comparative Example 4 had a synthetic fiber content of less than 10% by mass in the separator, the separator strength was weak. Although the separator for the lithium ion secondary battery of Comparative Example 9 contained fibrillated heat-resistant fibers, the strength of the separator was weak because the modified freeness of solvent-spun cellulose fibers exceeded 250 ml.
  • the lithium ion secondary batteries of Examples 1 to 24 contain 10 to 90% by mass of solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml and 10 to 90% by mass of synthetic fibers. Since a separator made of a porous sheet is used, the internal resistance and internal short-circuit failure rate, in particular, the discharge characteristics at high rates, the variations thereof, and the cycle characteristics were excellent.
  • the separator contains 10 to 90% by mass of solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml, the liquid retention of the electrolyte is good. Since the ion conductivity can be improved, the internal resistance is low, and the discharge characteristics and the cycle characteristics are particularly excellent at a high rate. On the other hand, in the lithium ion secondary batteries of Comparative Examples 2 and 3, the content of the solvent-spun cellulose fiber having a modified freeness of 0 to 250 ml is less than 10% by mass. In the secondary battery, since the separator did not contain solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml, the electrolyte solution was inferior in liquid retention and had a high internal resistance.
  • the separator can be made dense. Therefore, the internal short circuit failure rate and the variation in discharge capacity were low and excellent.
  • the content of the solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml in the separator is less than 10% by mass, and the separator is insufficiently dense. , Internal short-circuit defect rate and discharge capacity variation increased.
  • the modified drainage degree of the solvent-spun cellulose fiber in the separator was larger than 0 to 250 ml, and the density of the separator was insufficient, so the internal short circuit defect rate was slightly increased. .
  • the separator does not contain solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml, the separator is insufficiently dense, and the internal short-circuit failure rate, Dispersion of discharge capacity became high.
  • the lithium ion secondary battery of Comparative Example 10 using a porous polyethylene film had a high internal resistance and a high rate discharge capacity.
  • the lithium ion secondary battery of Example 8 contains 5% by mass of fibrillated natural cellulose fibers having a modified freeness of 0 to 400 ml in the separator.
  • the separator contains 10% by mass of fibrillated natural cellulose fibers having a modified freeness of 0 to 400 ml.
  • 20% by mass of fibrillated natural cellulose fiber having a modified freeness of 0 to 400 ml was contained in the separator. Therefore, the separator can be made denser and thinner, and the lithium ion secondary batteries of Examples 8 to 13 have lower internal resistance and higher rate than the lithium ion secondary batteries of Examples 1 to 7 and 15 to 18. The discharge capacity of was high.
  • the lithium ion secondary batteries of Examples 9 to 12 use separators that are blended with fibrillated natural cellulose fibers C1 to C4 having the same basis weight and the same thickness and different modified drainage degrees.
  • the lithium ion secondary battery of Example 12 using the separator containing the fibrillated natural cellulose fiber C4 having a modified freeness greater than 400 ml was slightly lacking in denseness when the thickness of the separator was reduced.
  • the internal short circuit defect rate was slightly higher than that of the lithium ion secondary batteries of Examples 9 to 11 using separators containing fibrillated natural cellulose fibers C1 to C3 having a freeness of 0 to 400 ml.
  • the separator becomes slightly dense and the ion conductivity is increased.
  • the internal resistance was slightly higher than those of the lithium ion secondary batteries of Examples 1 to 13, 15 to 17, 19, and 20, and the high rate discharge capacity was slightly lower.
  • the lithium ion secondary battery of Example 18 has a slightly larger basis weight, a separator having a slightly larger thickness, and an average pore diameter slightly smaller, the lithium ion secondary batteries of Examples 1 to 13, 15 to 17, 19, and 20
  • the internal resistance was slightly higher than that of the battery, and the high-rate discharge capacity was slightly lower.
  • the lithium ion secondary battery of Example 20 has a slightly smaller basis weight, a thickness of the separator is slightly thinner, and the maximum pore diameter is slightly larger. Therefore, the internal short circuit is greater than that of the lithium ion secondary batteries of Examples 1 to 11 and 13 to 19. The variation in defective rate and discharge capacity was slightly increased.
  • the lithium ion secondary battery of Example 22 has a slightly larger average fiber diameter of the synthetic fibers used, so the separator strength is slightly weaker and the discharge capacity variation is slightly higher than that of the lithium ion secondary battery of Example 21. became.
  • the separator strength was slightly weaker than the lithium ion secondary battery of Example 23, and the cycle characteristics were slightly inferior.
  • Ratio of fibers having a length-weighted fiber length of 1.00 mm or more with respect to the solvent-spun cellulose fiber produced by the above method “Fiber ratio of 1.00 mm or more”
  • Length weighted fiber length of maximum frequency peak in length weighted fiber length distribution histogram “fiber length of maximum frequency peak”
  • Weighted fiber length “Fiber length of second peak”
  • Length-weighted average fiber length “Average fiber length” (5) Freeness measured according to JIS P8121, except that an 80-mesh wire mesh having a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as the sieve plate, and the sample concentration was 0.1% by mass. Freeness " As shown in Table 5.
  • ⁇ Fibrylated natural cellulose fiber> The linter was treated using a high-pressure homogenizer to produce fibrillated natural cellulose fibers having a modified freeness of 0 ml, 270 ml, 400 ml, and 500 ml.
  • ⁇ Separator> A papermaking slurry was prepared according to the raw materials and contents shown in Tables 6 and 7, and wet papermaking was performed using a circular paper machine to produce separators of Examples and Comparative Examples. The thickness was adjusted by calendaring at room temperature.
  • Lithium ion secondary battery C The negative electrode 1 and the positive electrode 1 were wound so that the separators of Examples and Comparative Examples were interposed between the electrodes, respectively, and housed in a cylindrical container made of aluminum alloy, and the lead body was welded. Next, the whole cylindrical container was vacuum-dried at 110 ° C. for 15 hours. This was allowed to cool to room temperature in a vacuum, and then an electrolytic solution was injected and sealed to prepare lithium ion secondary batteries C of Examples and Comparative Examples. As the electrolytic solution, a solution obtained by dissolving LiPF 6 in a mixed solvent composed of 30% by mass of ethylene carbonate and 70% by mass of diethyl carbonate so as to be 1.2M was used.
  • Liquid retention (%) (Separator mass before immersion in propylene carbonate / Separator mass after holding for 15 minutes) ⁇ 100 As a result, the liquid retention rate was calculated and evaluated according to the following criteria.
  • the liquid retention rate is 200% or more.
  • ⁇ The liquid retention rate is 150% or more and less than 200%.
  • ⁇ The liquid retention rate is 50% or more and less than 150%.
  • X The liquid retention rate is less than 50%.
  • discharge capacity variation A: The difference in discharge capacity is 1.0% or less with respect to the average value.
  • ⁇ The difference in discharge capacity is more than 1.0% and 2.5% or less with respect to the average value.
  • delta The difference of discharge capacity exceeds 2.5% with respect to an average value, and is 5.0% or less.
  • X The difference of discharge capacity is over 5.0% with respect to the average value.
  • the separators for lithium ion secondary batteries of Examples 26 to 59 have a modified freeness of 0 to 250 ml and a length weighted average fiber length of 0.20 to 2.00 mm. Since 10 to 90% by mass of a certain solvent-spun cellulose fiber and 10 to 90% by mass of a synthetic fiber are contained, the fibers are easily entangled and a fiber network is easily formed. Became stronger. Further, in the lithium ion secondary batteries of Examples 26 to 59, 10 solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml and a length weighted average fiber length of 0.20 to 2.00 mm were used.
  • the electrolyte solution of the separator has a high liquid retentivity and good ion conductivity. Excellent discharge characteristics and cycle characteristics. Further, since the separator can be made dense, the internal short-circuit defect rate and the variation in discharge capacity were low and excellent.
  • the separator for the lithium ion secondary battery of Example 25 had a slightly weaker separator strength because the average fiber length of solvent-spun cellulose fibers in the separator was shorter than 0.20 mm.
  • the separator for the lithium ion secondary battery of Example 25 since the weighted average fiber length of the solvent-spun cellulose fiber in the separator is shorter than 0.20 mm, the fibers are hardly entangled and the fiber network is not easily formed. The short-circuit defect rate and discharge capacity variation were slightly higher.
  • the modified drainage of the solvent-spun cellulose fiber in the separator exceeds 250 ml and the average fiber length exceeds 2.00 mm.
  • the lithium ion secondary batteries of Comparative Examples 11 and 12 had high internal short-circuit failure rates and variations in discharge capacity. Since the separators for lithium ion secondary batteries of Comparative Examples 13 to 16 did not contain solvent-spun cellulose fibers, the liquid retention rate was low. In addition, since the lithium ion secondary batteries of Comparative Examples 13 to 16 used separators that did not contain solvent-spun cellulose fibers, the denseness of the separators became insufficient and the internal short-circuit defect rate increased.
  • the lithium ion secondary battery of Comparative Example 17 contained synthetic fibers in excess of 90% by mass, sufficient density was not obtained, the internal short circuit failure rate was high, and the liquid retention rate was low. Since the lithium ion secondary battery of Comparative Example 18 had a synthetic fiber content of less than 10% by mass, the separator strength was weak.
  • the lithium ion secondary batteries of Examples 36 and 39 have a maximum frequency peak longer than 0.00 to 1.00 mm in the fiber length distribution histogram of solvent-spun cellulose fibers.
  • the internal short-circuit defect rate was slightly higher than in Examples 26 to 35, and the variation in discharge capacity increased.
  • the lithium ion secondary batteries of Examples 37 and 38 in the fiber length distribution histogram of the solvent-spun cellulose fiber, the ratio of fibers having a fiber length of 1.00 mm or more is less than 10%, so the separator strength is slightly weakened.
  • the 5C discharge capacity was slightly lowered.
  • the lithium ion secondary batteries of Examples 26 to 29 and 31 to 34 were 0.05 mm between 1.00 and 2.00 mm in the fiber length distribution histogram of solvent-spun cellulose fibers. Since the inclination of the ratio of the fiber having each fiber length is ⁇ 3.0 or more and ⁇ 0.5 or less, the separator strength is high and the variation in the discharge capacity is small. In the lithium ion secondary battery of Example 30, in the fiber length distribution histogram of the solvent-spun cellulose fiber, the slope of the ratio of fibers having a fiber length of every 0.05 mm between 1.00 and 2.00 mm is ⁇ 3.
  • the lithium ion secondary batteries of Examples 40 to 48 had a maximum frequency peak between 0.00 and 1.00 mm in the fiber length distribution histogram of the solvent-spun cellulose fiber, Since the ratio of the fibers having a fiber length of 1.00 mm or more is 50% or more, it has a dense structure, a strong separator strength, a low internal short-circuit failure rate, and a small variation in discharge capacity. In the lithium ion secondary battery of Example 49, since the maximum frequency peak was longer than 0.00 to 1.00 mm in the fiber length distribution histogram of the solvent-spun cellulose fiber, the internal short circuit rate was slightly inferior.
  • the lithium ion secondary battery of Example 50 has a maximum frequency peak between 0.00 and 1.00 mm in the fiber length distribution histogram of the solvent-spun cellulose fiber, but the fiber having a fiber length of 1.00 mm or more. Since the ratio was less than 50%, the separator strength was weaker than in Examples 40 to 48.
  • the lithium ion secondary batteries of Examples 40 to 42 and 44 to 47 are 1.50 to 3.50 mm in addition to the maximum frequency peak in the fiber length distribution histogram of solvent-spun cellulose fibers. Since there is a peak between them, a fiber network is more easily formed, so the strength of the separator is strong, the internal short-circuit failure rate is low, and the variation in discharge capacity is small.
  • the lithium ion secondary battery of Example 43 has a peak other than the maximum frequency peak smaller than 1.50 mm, so compared with Examples 40 to 42 and 44 to 47, The separator strength was slightly weak and the discharge capacity variation was slightly large.
  • the lithium ion secondary battery of Example 48 is compared with Examples 40 to 42 and 44 to 47.
  • the internal short circuit failure rate was slightly high, and the variation in discharge capacity was slightly increased.
  • the separator can be made denser.
  • the internal short circuit defect rate was lower than that of the lithium ion secondary batteries of Examples 58 and 59.
  • the lithium ion secondary battery of Example 55 uses a separator having a modified freeness of 0 to 400 ml of fibrillated natural cellulose fiber of more than 20% by mass. The discharge capacity at a high rate and the capacity retention rate after 100 cycles showed slightly low values.
  • the modified drainage of the fibrillated natural cellulose fiber is larger than 400 ml, so that the density of the separator is slightly lowered, and the separator strength is higher than that of Examples 40 and 53. Declined.
  • ⁇ Separator> A papermaking slurry was prepared according to the raw materials and contents shown in Table 11, and wet papermaking was performed using a circular paper machine to produce separators of Examples 60 to 88 and Comparative Examples 19 to 21. The thickness was adjusted by calendaring at room temperature.
  • the “type” of the synthetic fiber is as follows.
  • PET Polyethylene terephthalate fiber
  • AA Acrylic fiber
  • PP Polypropylene fiber
  • PET / PEs-C Polyester-based sheath-heat-bonded fiber
  • Lithium ion secondary battery E The negative electrode 1 and the positive electrode 1 are wound so that the separators of Examples 60 to 88 and Comparative Examples 19 to 21 are interposed between the electrodes, respectively, and housed in a cylindrical container made of aluminum alloy, and the lead body is welded. It was. Next, the whole cylindrical container was vacuum-dried at 150 ° C. for 10 hours. This was allowed to cool to room temperature in a vacuum, and then an electrolyte solution was injected and sealed up, and lithium ion secondary batteries E of Examples 60 to 88 and Comparative Examples 19 to 21 were produced.
  • the electrolytic solution a solution obtained by dissolving LiPF 6 in a mixed solvent composed of 30% by mass of ethylene carbonate and 70% by mass of diethyl carbonate so as to be 1.2M was used.
  • A The difference in discharge capacity is 1.0% or less with respect to the average value.
  • ⁇ The difference in discharge capacity is more than 1.0% and 2.5% or less with respect to the average value.
  • delta The difference of discharge capacity exceeds 2.5% with respect to an average value, and is 5.0% or less.
  • X The difference of discharge capacity is over 5.0% with respect to the average value.
  • the separators for lithium ion secondary batteries of Examples 60 to 86 are solvent-spun cellulose fibers having a length-weighted average fiber length of 0.50 to 1.25 mm and an average curl degree of 2.5 or less. Since 10 to 90% by mass and 10 to 90% by mass of synthetic fiber were contained, the moisture content was low, and the mechanical strength was strong and excellent.
  • the solvent-spun cellulose fiber has a length-weighted average fiber length of 0.50 to 1.25 mm. It becomes easy to form and it turns out that separator strength becomes strong.
  • the solvent-spun cellulose fiber has a length-weighted average fiber length of less than 0.50 mm (Example 87), the fiber is likely to fall off the paper machine wire during the manufacture of the separator, and the strength of the separator is hardly exhibited.
  • the average curl degree of the solvent-spun cellulose fiber is 25 or less, so that the fiber network is easily entangled with each other, and the maximum pore diameter of the separator is increased. It can be seen that it is adjusted to be smaller.
  • the lithium ion secondary batteries of Examples 60 to 86 contain 10 to 90% by mass of solvent-spun cellulose fibers having a length weighted average fiber length of 0.50 to 1.25 mm and an average curl degree of 25 or less. Therefore, since the electrolyte solution has good liquid retention and good ion conductivity, it has a low internal resistance and is particularly excellent in discharge characteristics and cycle characteristics at a high rate.
  • the lithium ion secondary battery of Comparative Example 20 has a length weighted average fiber length of 0.50 to 1.25 mm, and the content of solvent-spun cellulose fibers having an average curl degree of 25 or less is less than 10% by mass. The liquid retention was inferior and the internal resistance was high.
  • the average curl degree of the solvent-spun cellulose fiber was greater than 25.
  • the uniformity of the mass of the separator was impaired, and the internal short circuit failure rate and the variation in discharge capacity were increased.
  • the lithium ion secondary batteries of Examples 80 to 83 10% by mass of fibrillated natural cellulose fibers having a modified freeness of 0 to 400 ml are contained in the separator. In this way, by adding fibrillated natural cellulose having a modified freeness of 0 to 400 ml to the separator, the strength of the separator can be increased and the separator can be made thinner. Compared to the secondary battery, the lithium ion secondary batteries of Examples 80 to 83 had a low internal resistance and a high discharge capacity at a high rate.
  • the separator is slightly too dense.
  • the average pore diameter is also reduced, the ion conductivity is slightly deteriorated, the internal resistance is slightly higher than those of the lithium ion secondary batteries of Examples 81 and 85, and the discharge rate at a high rate is slightly lower. The value is shown.
  • the lithium ion secondary batteries of Examples 64, 65, and 69 have a maximum pore diameter larger than 6.0 ⁇ m. Therefore, the lithium ions of Examples 60 to 63 and 70 to 71 were used. The internal short circuit failure rate and the variation in discharge capacity were slightly higher than those of the ion secondary battery.
  • the lithium ion secondary battery of Example 76 has a slightly larger average fiber diameter of the synthetic fibers used, so the separator strength is slightly weaker than that of the lithium ion secondary battery of Example 75, and the discharge capacity variation is slightly higher. became.
  • Carboxymethylcellulose having a degree of etherification of 0.7 (trade name: 1205, manufactured by Daicel Chemical Industries, Ltd.) was designated as CMC2.
  • ⁇ CDS cationic starch-based paper strength enhancer
  • a cationic starch-based paper strength enhancer (trade name: DD4280, manufactured by Seiko PMC) was used as CDS.
  • GGS Guar gum paper strength enhancer
  • PET Polyethylene terephthalate fiber
  • ⁇ Separator> A papermaking slurry was prepared according to the raw materials and blending amounts (based on the total fiber amount) shown in Table 13, and wet papermaking was performed using a circular paper machine to produce separators of Examples 89 to 103 and Comparative Examples 22 to 23. did. The thickness was adjusted by calendaring at room temperature.
  • ⁇ Lithium ion secondary battery G> The negative electrode 1 and the positive electrode 1 were wound so that the separators of Examples 89 to 103 and Comparative Examples 22 to 23 were interposed between the electrodes, respectively, and stored in a cylindrical container made of aluminum alloy, and the lead body was welded. It was. Next, the whole cylindrical container was vacuum-dried at 150 ° C. for 10 hours. This was allowed to cool to room temperature in a vacuum, and then an electrolyte solution was injected and sealed up, and lithium ion secondary batteries G of Examples 89 to 103 and Comparative Examples 22 to 23 were produced.
  • the electrolytic solution a solution obtained by dissolving LiPF 6 to 1.2 M in a mixed solvent composed of 30% by mass of ethylene carbonate (EC) and 70% by mass of diethyl carbonate (DEC) was used.
  • A The difference in discharge capacity is 1.0% or less with respect to the average value.
  • ⁇ The difference in discharge capacity is more than 1.0% and 2.5% or less with respect to the average value.
  • delta The difference of discharge capacity exceeds 2.5% with respect to an average value, and is 5.0% or less.
  • X The difference of discharge capacity is over 5.0% with respect to the average value.
  • the separator for the lithium ion secondary battery of Example 89 is 10% by mass of solvent-spun cellulose fiber having a modified freeness of 0 ml per total fiber, 90% by mass of synthetic fiber per total fiber, and Since 1% by mass of carboxymethylcellulose having a degree of etherification of 0.5 was contained, the separator strength was superior to that of Example 1 in Table 1 that did not contain carboxymethylcellulose.
  • the separator for the lithium ion secondary battery of Example 90 has a modified freeness of 120 ml of solvent-spun cellulose fiber of 50% by mass per total fiber, a synthetic fiber of 50% by mass per total fiber, and a degree of etherification of 0.5. Since 1% by mass of carboxymethylcellulose is contained, the maximum pore diameter is reduced, the internal resistance and the internal short-circuit failure rate are reduced, the variation in discharge capacity is improved, and no carboxymethylcellulose is contained. Compared to Example 3 in Table 1, the separator strength was excellent.
  • the separator for the lithium ion secondary battery of Example 91 is 90 mass% of solvent-spun cellulose fibers having a modified freeness of 250 ml per total fiber, 10 mass% of synthetic fibers per total fiber, and a degree of etherification of 0.5. Since 1% by mass of carboxymethylcellulose is contained, the pore diameter and internal resistance are improved as in Example 90, and the separator strength is superior to Example 3 in Table 1 that does not contain carboxymethylcellulose. It was.
  • the separator for the lithium ion secondary battery of Example 92 has a modified freeness of 120 ml of solvent-spun cellulose fiber of 50 mass% per total fiber, a synthetic fiber of 50 mass% per total fiber, and a degree of etherification of 0.7. Since 1% by mass of carboxymethylcellulose was contained, the pore diameter and separator strength were further improved as compared with Example 90. Moreover, since the separator for lithium ion secondary batteries of Example 92 contains 1% by mass of carboxymethyl cellulose having a degree of etherification of 0.7, 1 each of cationic starch-based paper strength enhancer and guar gum paper strength enhancer. Compared to the lithium ion secondary battery separators of Example 102 and Example 103 containing mass%, it is understood that not only the separator strength is excellent, but also the discharge capacity at high rate and the variation in discharge capacity are excellent. .
  • the solvent-spun cellulose fiber having a modified freeness of 120 ml was 50% by mass per total fiber
  • the synthetic fiber was 50% by mass per total fiber
  • the degree of etherification was 0. No. 5 carboxymethyl cellulose was contained, and the moisture content of the separator, the strength of the separator, the battery characteristics and the like were satisfactory.
  • Example 93 when the content of carboxymethyl cellulose is 0.2% by mass relative to the total fiber mass, the effect of improving formation during papermaking is small, the separator strength is slightly lower, and the pore diameter is also small. There was a tendency to increase slightly.
  • Example 96 when the content of carboxymethyl cellulose is 3.0% by mass with respect to the total fiber mass, each separator performance reaches its peak, which is disadvantageous in terms of cost. Since the dehydration property was insufficient, the production efficiency was not good.
  • the separators for lithium ion secondary batteries of Examples 97 to 101 45 to 25% by mass of solvent-spun cellulose fiber having a modified freeness of 120 ml is used as the separator, 50% by mass of synthetic fiber per total fiber, and carboxymethyl cellulose. Is contained in an amount of 1.0% by mass based on the total fiber mass, and further, 5-25% by mass of fibrillated natural cellulose fiber having a modified freeness of 0 to 400 ml is contained per total fiber. Therefore, a high separator strength can be obtained even at a low basis weight, and thus the separator can be made denser and thinner. Therefore, the embodiment 97 is more preferable than the lithium ion secondary battery separator of the embodiment 90.
  • the ⁇ 101 lithium ion secondary battery separator had a low internal resistance and a high discharge capacity at a high rate.
  • the separator since the content of the fibrillated natural cellulose fiber having a modified freeness of 0 to 400 ml in the separator is more than 20% by mass per total fiber, the separator is slightly too dense, The ion conductivity was slightly deteriorated, the internal resistance was slightly higher than those of the lithium ion secondary batteries of Examples 97 to 99, and the high rate discharge capacity was slightly lower.
  • the solvent-spun cellulose fiber having a modified freeness of 120 ml is 40% by mass per total fiber
  • the synthetic fiber is 50% by mass per total fiber
  • the degree of etherification is 0.00.
  • 7 carboxymethyl cellulose is contained in an amount of 1.0% by mass relative to the total fiber mass
  • fibrillated natural cellulose fibers having a modified freeness of 270 ml are contained in an amount of 10% by mass. Therefore, the maximum pore diameter was smaller than in Example 98, and the separator strength was also increased.
  • the separator for the lithium ion secondary battery of Comparative Example 22 contains carboxymethyl cellulose in the separator, the content of solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml in the separator is more than 90% by mass per total fiber. Many synthetic fibers were less than 10% by mass per total fiber, so the moisture content was high and the separator strength was weak.
  • the separator for the lithium ion secondary battery of Comparative Example 23 contains carboxymethyl cellulose in the separator, the content of solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml in the separator is more than 10% by mass per total fiber. Since the amount of synthetic fibers is less than 90% by mass per total fiber, the maximum pore diameter is increased, and the internal short circuit defect rate is extremely increased.
  • ⁇ Heat-bonding fiber M1> A polyester core-sheath type heat-sealable fiber having a fineness of 0.5 dtex, a fiber length of 5 mm, a core of polyethylene terephthalate (melting point 253 ° C.), and a sheath of polyethylene terephthalate-isophthalate copolymer (softening point 75 ° C.) is heated. A fusion fiber M1 was obtained.
  • ⁇ Heat-bonding fiber M2> A polyester core-sheath type heat-sealable fiber having a fineness of 1.1 dtex, a fiber length of 5 mm, a core part of polyethylene terephthalate (melting point 253 ° C.), and a sheath part of a polyethylene terephthalate-isophthalate copolymer (softening point 75 ° C.) is heated. A fusion fiber M2 was obtained.
  • Heat-bonding fiber M3 A polyolefin core-sheath type heat-seal fiber having a fineness of 0.8 dtex, a fiber length of 5 mm, a core part of polypropylene (melting point 165 ° C.), and a sheath part of high-density polyethylene (melting point 135 ° C.) was designated as heat-seal fiber M3.
  • the fusing fiber was designated as heat fusing fiber M4.
  • Heat-bonding fiber M5 An unstretched polyethylene terephthalate fiber (melting point: 130 ° C.) having a fineness of 1.1 detex and a fiber length of 5 mm was designated as a heat-sealing fiber M5.
  • Heat-bonding fiber M6 An unstretched polyethylene terephthalate fiber (hot-pressure melting temperature 200 ° C.) having a fineness of 0.5 dtex and a fiber length of 5 mm was used as a heat-sealing fiber M6.
  • Heat-bonding fiber M7 Polyvinyl alcohol fiber (wet heat melting temperature 100 ° C.) having a fineness of 0.8 dtex and a fiber length of 5 mm was used as the heat fusion fiber M7.
  • Heat-bonding fiber M8 A split type composite fiber (16 splits) made of polypropylene (melting point 165 ° C.) and an ethylene-vinyl alcohol copolymer (wet heat melting temperature 100 ° C.) having a fineness of 2.2 dtex and a fiber length of 5 mm was used as a heat sealing fiber M8.
  • Papermaking slurries 1 to 16 were made up by a wet method using a circular paper machine, and heat-bonded fibers were thermally bonded by a cylinder dryer at 140 ° C. to prepare a nonwoven fabric. Next, supercalender treatment was performed to obtain lithium ion secondary battery separators of Examples 104 to 119.
  • Examples 120 and 121 The papermaking slurries 17 and 18 were made up by a wet method using a circular paper machine, and a heat-bonded fiber was thermally bonded by a cylinder dryer at 140 ° C. to produce a nonwoven fabric. Next, the nonwoven fabric was brought into contact with a heat roll having a diameter of 1.2 m heated to 200 ° C. at a speed of 20 m / min and heat-treated. Next, a super calendar process was performed to obtain lithium ion secondary battery separators of Examples 120 and 121.
  • Examples 122 to 124, Comparative Examples 24 to 29 The papermaking slurries 19 to 27 were made up by a wet method using a circular net paper machine, and heat-bonded fibers were thermally bonded by a cylinder dryer at 140 ° C. to prepare a nonwoven fabric. Next, supercalender treatment was performed to obtain lithium ion secondary battery separators of Examples 122 to 124 and Comparative Examples 24 to 29.
  • Example 125 The papermaking slurry 28 was made up using a wet method using a circular paper machine and dried with a cylinder dryer at 140 ° C. to produce a nonwoven fabric. Next, using a heat roll having a diameter of 1.2 m heated to 200 ° C., pressure heat treatment was performed at a pressure of 2 MPa and a speed of 10 m / min to thermally bond the heat-fusible fiber, and the lithium ion secondary battery of Example 125 A separator was used.
  • Example 126 Comparative Examples 30 and 31
  • the papermaking slurries 29 to 31 were made up using a wet method with a circular paper machine and dried with a cylinder dryer at 140 ° C. to produce a nonwoven fabric.
  • supercalender treatment was performed to obtain lithium ion secondary battery separators of Example 126 and Comparative Examples 30 and 31.
  • Lithium ion secondary battery I> The negative electrode 1 and the positive electrode 1 are wound so that the separators of Examples 104 to 126 and Comparative Examples 24 to 31 are interposed between the electrodes, respectively, and housed in a cylindrical container made of aluminum alloy, and the lead body is welded. It was. Next, the whole cylindrical container was vacuum-dried at 110 ° C. for 24 hours. This was allowed to cool to room temperature in a vacuum, and then an electrolytic solution was injected and sealed up, and lithium ion secondary batteries I of Examples 102 to 124 and Comparative Examples 24 to 31 were produced.
  • the electrolytic solution a solution obtained by dissolving LiPF 6 in a mixed solvent composed of 30% by mass of ethylene carbonate and 70% by mass of diethyl carbonate so as to be 1.2M was used.
  • A The difference in discharge capacity is 1.0% or less with respect to the average value.
  • ⁇ The difference in discharge capacity is more than 1.0% and 2.5% or less with respect to the average value.
  • delta The difference of discharge capacity exceeds 2.5% with respect to an average value, and is 5.0% or less.
  • X The difference of discharge capacity is over 5.0% with respect to the average value.
  • the voltage maintenance rate is 95% or more.
  • the voltage maintenance ratio is less than 95% and 90% or more.
  • X The voltage maintenance rate is less than 90%.
  • the separators for lithium ion secondary batteries of Examples 104 to 121 were 10 to 90% by mass of solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml and 10 to 90% by mass of synthetic fibers. Since it contains a low moisture content, it contains a core-sheath type heat-sealing fiber composed of a heat-sealing component and a non-heat-sealing component as at least one synthetic fiber, so the separator strength is strong. Was excellent.
  • the separators for lithium ion secondary batteries of Examples 104 to 121 contain 10 to 90% by mass of synthetic fiber, compared with the paper separator made of solvent-spun cellulose fiber and hemp fiber of Comparative Example 31, The moisture content could be kept low. Furthermore, the fibers are easily entangled with each other, and a fiber network is formed. The fiber is firmly heat-bonded with the core-sheath type heat-sealing fiber, so that the separator strength is increased.
  • the separator strength tends to increase.
  • the separators for lithium ion secondary batteries of Examples 120 and 121 subjected to the heat treatment tended to have higher strength. Since the separators for lithium ion secondary batteries of Examples 122 to 125 used heat fusion fibers other than the core-sheath type, the separators for lithium ion secondary batteries of Example 124 contained core-sheath type heat fusion fibers. As a result, the separator strength was slightly weakened.
  • the separators for lithium ion secondary batteries of Comparative Examples 24 and 25 the content of solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml in the separator is more than 90% by mass, and the separator contains 10 synthetic fibers. Since it is less than mass%, the moisture content is high and the separator strength is weak. Since the separator for the lithium ion secondary battery of Comparative Example 31 had a synthetic fiber content of less than 10% by mass in the separator, the separator strength was weak.
  • the lithium ion secondary batteries of Examples 104 to 121 contain 10 to 90% by mass of solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml and 10 to 90% by mass of synthetic fibers. Since a separator made of a porous sheet containing a core-sheath-type heat-sealing fiber composed of a heat-sealing component and a non-heat-sealing component is used as at least one kind of synthetic fiber, internal resistance, internal short-circuit failure rate In particular, the discharge characteristics at a high rate and its variation, cycle characteristics, and voltage maintenance ratio characteristics were excellent.
  • the separator contains 10 to 90% by mass of solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml, the electrolyte solution retainability is good. Since the ion conductivity can be improved, the internal resistance is low, and the discharge characteristics and the cycle characteristics are particularly excellent at a high rate.
  • the lithium ion secondary batteries of Comparative Examples 26 and 27 have a content of solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml of less than 10% by mass.
  • the lithium ion secondary battery of Comparative Example 28 is Since the separator did not contain solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml, the electrolyte solution was inferior in liquid retention and had a high internal resistance.
  • the separator can be made dense. Therefore, the internal short circuit failure rate and the variation in discharge capacity were low and excellent.
  • the content of the solvent-spun cellulose fiber having a modified freeness of 0 to 250 ml in the separator is less than 10% by mass, and the separator is insufficiently dense. , Internal short-circuit defect rate and discharge capacity variation increased.
  • the separator does not contain solvent-spun cellulose fibers having a modified freeness of 0 to 250 ml, the separator is insufficiently dense, the internal short circuit failure rate, the discharge capacity The variation of was high.
  • the modified drainage degree of the solvent-spun cellulose fiber in the separator is larger than 0 to 250 ml, and the separator is insufficiently dense. Was slightly higher.
  • the lithium ion secondary batteries of Examples 104 to 121 contain 10 to 90% by mass of a synthetic fiber, and are core-sheath type heat fusion made of at least one synthetic fiber and comprising a heat fusion component and a non-heat fusion component. In order to heat-bond the fibers together without impairing the dense structure of the fiber network, the fibers had a low internal resistance and a high voltage retention rate.
  • the lithium ion secondary batteries of Examples 122 to 125 use a heat-sealable fiber other than the core-sheath-type heat-sealable fiber for the separator, so that the shape of the heat-sealable fiber is lost during thermal bonding.
  • the porosity of the separator was locally obstructed, so that the value of the internal resistance was slightly high and the discharge rate at a high rate was slightly low. Since the lithium ion secondary battery of Example 126 did not contain the core-sheath type fusion-bonded fiber in the separator, the voltage maintenance rate was slightly low.
  • Synthetic fiber B9 Polyethylene terephthalate fiber having a fiber diameter of 2.5 ⁇ m and a fiber length of 6 mm was designated as synthetic fiber B9.
  • Papermaking slurries were prepared according to the raw materials and contents shown in Table 18, and wet papermaking was performed using a circular paper machine to produce separators of Examples 127 to 132 and Comparative Examples 32 to 34. The thickness was adjusted by calendaring at room temperature.
  • Lithium ion secondary battery K The negative electrode 1 and the positive electrode 1 were wound so that the separators of Examples and Comparative Examples were interposed between the electrodes, respectively, and housed in a cylindrical container made of aluminum alloy, and the lead body was welded. Next, the whole cylindrical container was vacuum-dried at 110 ° C. for 15 hours. This was allowed to cool to room temperature in a vacuum, and then an electrolytic solution was injected and sealed, to prepare lithium ion secondary batteries K of Examples and Comparative Examples.
  • the electrolytic solution a solution obtained by dissolving LiPF 6 in a mixed solvent composed of 30% by mass of ethylene carbonate and 70% by mass of diethyl carbonate so as to be 1.2M was used.
  • A The difference in discharge capacity is 1.0% or less with respect to the average value.
  • ⁇ The difference in discharge capacity is more than 1.0% and 2.5% or less with respect to the average value.
  • delta The difference of discharge capacity exceeds 2.5% with respect to an average value, and is 5.0% or less.
  • X The difference of discharge capacity is over 5.0% with respect to the average value.
  • the separator for the lithium ion secondary battery of Example 127 has a two-layer structure, and a solvent-spun cellulose fiber having a modified freeness of 125 ml in each layer. Is 60% by mass per total fiber and 40% by mass of synthetic fiber per total fiber, the 5C discharge capacity and capacity retention rate were excellent.
  • the separator for the lithium ion secondary battery of Example 128 has a two-layer structure, and the layer A is 6% by mass of solvent-spun cellulose fiber having a modified freeness of 125 ml and 6% by mass of synthetic fiber per total fiber.
  • the layer B contains solvent-spun cellulose fibers having a modified freeness of 125 ml of 100% by mass per total fiber, so that the separator has a slightly lower separator strength than the example 125, but the maximum pore diameter The internal resistance was slightly improved.
  • the separator for the lithium ion secondary battery of Example 129 has a two-layer structure, and the layer A is a solvent-spun cellulose fiber having a modified freeness of 125 ml of 60% by mass per total fiber, and the synthetic fiber is 40% by mass per total fiber.
  • the layer B contains 90 mass% of solvent-spun cellulose fibers having a modified freeness of 125 ml per total fiber, and 40 mass% of synthetic fibers per total fiber.
  • the separator for the lithium ion secondary battery of Example 130 has a two-layer structure, and the layer A is 60% by mass of solvent-spun cellulose fibers having a modified freeness of 125 ml and 60% by mass of synthetic fibers per total fiber.
  • the layer B contains solvent-spun cellulose fibers having a modified freeness of 125 ml of 10% by mass per total fiber and 90% by mass of synthetic fibers per total fiber, compared to Example 125, Although the separator strength was slightly improved, the 5C discharge capacity and the capacity retention rate were slightly inferior.
  • the separator for the lithium ion secondary battery of Example 131 has a two-layer structure, and the layer A is 60% by mass of solvent-spun cellulose fibers having a modified freeness of 125 ml and 60% by mass of synthetic fibers per total fiber. Since the layer B contains 100% by mass of synthetic fiber per total fiber, the separator strength is slightly improved as compared with Example 125, but the 5C discharge capacity and capacity retention rate are slightly inferior. It was.
  • the separator for the lithium ion secondary battery of Comparative Example 32 has a two-layer structure
  • the content of the solvent-spun cellulose fiber having a modified freeness of 0 to 250 ml in the separator is more than 90% by mass
  • the synthetic fiber Is less than 10% by mass per total fiber the moisture content is high and the separator strength is weak.
  • the separator for the lithium ion secondary battery of Comparative Example 33 has a two-layer structure, the content of the solvent-spun cellulose fiber having a modified freeness of 0 to 250 ml in the separator is less than 10% by mass, and the synthetic fiber Is more than 90% by mass per total fiber, the maximum pore diameter is increased, and the internal short circuit defect rate is extremely increased.
  • the lithium ion secondary battery separator of Comparative Example 34 has a two-layer structure, it uses a solvent-spun cellulose fiber with a fiber diameter of 2.5 ⁇ m and a fiber length of 6 mm. Also, the discharge capacity at high rate was greatly inferior.
  • a lithium ion secondary battery separator and a lithium ion polymer secondary battery separator are suitable.

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Abstract

L'invention porte sur un séparateur qui est destiné à une batterie secondaire au lithium-ion et qui présente une faible teneur en eau, une forte résistance mécanique et une excellente résistance interne, ainsi qu'un excellent taux de défaillance de court-circuit interne, en particulier d'excellentes caractéristiques en termes de cycle et de décharge, et de variation de ceux-ci à des vitesses élevées. Le séparateur comporte une feuille poreuse contenant 10 à 90 % en masse d'une fibre synthétique et 10 à 90 % en masse d'une fibre de cellulose filée avec solvant ayant un indice d'égouttage de 0 à 250 ml mesuré conformément à la norme JIS P8121 lorsque la concentration de l'échantillon n'est pas de 0,1 %, et utilise un tamis métallique de 80 mailles ayant des ouvertures de 0,18 mm et un diamètre de fil métallique de 0,14 mm comme tamis à plaque. L'invention porte en outre sur une batterie secondaire au lithium-ion l'utilisant.
PCT/JP2011/066172 2010-07-14 2011-07-08 Séparateur pour batterie secondaire au lithium-ion et batterie secondaire au lithium-ion l'utilisant Ceased WO2012008559A1 (fr)

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