JP2018170240A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

Provided is a nonaqueous electrolyte secondary battery that includes a positive electrode and a negative electrode including a lithium titanium composite oxide as a negative electrode active material, and has high durability while improving high-rate characteristics.
A positive electrode 12 has a positive electrode mixture layer containing a first positive electrode active material and a second positive electrode active material, each of which has a pore volume of 100 nm or less and whose volume per mass is specified. The content of the first positive electrode active material is 30% by mass or less based on the total amount of the first positive electrode active material and the second positive electrode active material. The amount of nonaqueous electrolyte retained by the positive electrode 12 is 0.49 g / cm ³ or more per unit volume of the positive electrode mixture layer.
[Selection] Figure 1

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  In recent years, environmentally friendly vehicles such as hybrid vehicles and electric vehicles have become widespread. At the same time, idling stop systems aimed at improving fuel efficiency at low cost are also widely used, and there is an increasing need for low-cost batteries that can be used for vehicle electrification and power assist functions.

2. Description of the Related Art A battery using lithium titanium composite oxide as a negative electrode active material is known as a battery for realizing vehicle electrification and power assist function enhancement at a low cost. For example, Patent Document 1 includes a positive electrode having a positive electrode active material made of a lithium composite metal oxide having a BET specific surface area of ² to 30 m ² / g, and lithium titanate represented by the formula Li _{4 + a} Ti ₅ O _12. When a non-aqueous electrolyte secondary battery having a negative electrode having a negative electrode active material is charged at a higher current rate (high rate) than a non-aqueous electrolyte secondary battery using a negative electrode having a negative electrode active material made of graphite. It is disclosed that it has excellent charging characteristics and can be rapidly charged.

JP 2011-181367 A

  A non-aqueous electrolyte secondary battery comprising a positive electrode including a lithium composite metal oxide as a positive electrode active material and a negative electrode including a lithium titanium composite oxide as a negative electrode active material. There is a need for water electrolyte secondary batteries.

  The objective of this indication is providing the nonaqueous electrolyte secondary battery which is excellent in durability, improving a high rate characteristic.

A nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure includes a positive electrode having a positive electrode mixture layer including a first positive electrode active material and a second positive electrode active material, and a negative electrode composite including a lithium titanium composite oxide as a negative electrode active material. A negative electrode having an agent layer and a nonaqueous electrolyte, wherein the first positive electrode active material has a pore diameter of 100 nm or less and a volume per mass of pores of 8 mm ³ / g or more, and a second positive electrode active material The material has a volume per mass of pores having a pore diameter of 100 nm or less and 5 mm ³ / g or less, and a volume per mass of pores having a pore diameter of 100 nm or less in the first positive electrode active material is 2nd The positive electrode active material has a pore diameter of 4 times or more with respect to the volume per mass of pores of 100 nm or less, and the content of the first positive electrode active material is the total amount of the first positive electrode active material and the second positive electrode active material. 30 mass% or less with respect to the positive electrode The amount of nonaqueous electrolyte to be retained is 0.49 g / cm ³ or more per unit volume of the positive electrode mixture layer.

  With the nonaqueous electrolyte secondary battery of the present disclosure, it is possible to provide a nonaqueous electrolyte secondary battery with excellent durability while improving high rate characteristics.

It is a perspective view which shows the structure of the nonaqueous electrolyte secondary battery which is an example of embodiment. It is sectional drawing of the electrode body with which a nonaqueous electrolyte secondary battery is provided.

In the nonaqueous electrolyte secondary battery including a negative electrode containing a lithium-titanium composite oxide as a negative electrode active material, the present inventor has identified the positive electrode and the volume per mass of the pores having a pore diameter of 100 nm or less, respectively. It has a positive electrode mixture layer containing a first positive electrode active material and a second positive electrode active material, and the content of the first positive electrode active material is 30% by mass or less based on the total amount of the first positive electrode active material and the second positive electrode active material. When the amount of the nonaqueous electrolyte retained by the positive electrode is 0.49 g / cm ³ or more per unit volume of the positive electrode mixture layer, the nonaqueous electrolyte is excellent in durability while improving the high rate characteristics. It has been found that a secondary battery can be provided.

  Hereinafter, an example of an embodiment of the present disclosure will be described in detail with reference to the drawings. In addition, the nonaqueous electrolyte secondary battery of this indication is not limited to embodiment described below. The drawings referred to in the description of the embodiments are schematically described, and the dimensions and the like of each component should be determined in consideration of the following description.

[Nonaqueous electrolyte secondary battery]
The structure of the nonaqueous electrolyte secondary battery 10 will be described with reference to FIG. FIG. 1 is a perspective view showing a configuration of a nonaqueous electrolyte secondary battery 10 (hereinafter also referred to as “battery 10”) as an example of the present embodiment. The battery 10 includes, for example, an outer can 24 having a bottom and an opening, and a sealing plate 22 that closes the opening. The outer can 24 is a flat container having a substantially rectangular parallelepiped shape. In the outer can 24, for example, an electrode body 26 including the positive electrode 12, the negative electrode 14, and the separator 16 is accommodated together with a nonaqueous electrolyte (not shown). The electrode body 26 is accommodated in the outer can 24 in a state covered with a resin insulating sheet, for example.

  The outer can 24 has a bottom portion 28 and is provided with an opening at a position facing the bottom portion 28. The sealing plate 22 is a lid that closes the opening of the outer can 24, and the sealing plate 22 is provided with, for example, a positive electrode terminal 18, a negative electrode terminal 20, a liquid injection port 30, and a gas discharge valve 32. The positive electrode terminal 18 has a function of electrically connecting an external element and the positive electrode 12 and is attached in a state of being electrically insulated from the sealing plate 22 by an insulating gasket. The negative electrode terminal 20 has a function of electrically connecting an external element and the negative electrode 14 and is attached in a state of being electrically insulated from the sealing plate 22 by an insulating gasket. The liquid injection port 30 is for injecting a nonaqueous electrolyte, and the gas discharge valve 32 is for discharging gas inside the battery to the outside of the battery.

  FIG. 2 is a cross-sectional view of the electrode body 26 provided in the battery 10. As shown in FIG. 2, the electrode body 26 has, for example, a winding structure in which the positive electrode 12 and the negative electrode 14 are wound through a separator 16, and is press-molded from a direction orthogonal to the central axis of the winding structure. The structure is as follows.

  The positive electrode 12 includes, for example, a positive electrode core and a positive electrode mixture layer formed on both surfaces of the positive electrode core. The positive electrode mixture layer is formed, for example, such that a positive electrode core exposed portion where the positive electrode core body is exposed in a strip shape is formed along the longitudinal direction at an end portion on at least one side in the width direction. The negative electrode 14 includes, for example, a negative electrode core and a negative electrode mixture layer formed on both surfaces of the negative electrode core. The negative electrode mixture layer is formed, for example, such that the negative electrode core exposed portion where the negative electrode core is exposed in a strip shape is formed along the longitudinal direction at the end on at least one side in the width direction. The positive electrode core exposed portion is electrically connected to the positive electrode terminal 18, and the negative electrode core exposed portion is electrically connected to the negative electrode terminal 20.

  Next, the positive electrode 12, the negative electrode 14, the separator 16, and the nonaqueous electrolyte that are included in the battery 10 will be described.

[Positive electrode]
As described above, the positive electrode 12 includes a positive electrode core body such as a metal foil and a positive electrode mixture layer formed on the positive electrode core body. For the positive electrode core, for example, a metal foil that is stable in the potential range of the positive electrode such as aluminum, a film in which the metal is disposed on the surface layer, or the like can be used. The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive material, and a binder.

The positive electrode mixture layer includes a first positive electrode active material and a second positive electrode active material as a positive electrode active material. In the first positive electrode active material, the volume per mass of pores having a pore diameter of 100 nm or less (hereinafter also referred to as “pore volume V _100N ”) is 8 mm ³ / g or more. The pore volume V _100N is 5 mm ³ / g or less. Further, the ratio of the pore volume V _100N in the first cathode active material to the pore volume V _100N in the second cathode active material (hereinafter also referred to as “first / second pore volume ratio”) is 4 times or more. is there. Furthermore, the content rate of the 1st positive electrode active material with respect to the total amount of a 1st positive electrode active material and a 2nd positive electrode active material is 30 mass% or less. A method for measuring the pore volume V _100N in the positive electrode active material will be described later.

  Both the first positive electrode active material and the second positive electrode active material are lithium-containing transition metal oxides. The lithium-containing transition metal oxide is a metal oxide containing at least lithium (Li) and a transition metal element. The lithium-containing transition metal oxide may contain an additive element other than lithium (Li) and the transition metal element.

  The battery 10 includes a negative electrode 14 including a lithium titanium composite oxide as a negative electrode active material. Since the lithium titanium composite oxide has high charge / discharge efficiency, the lower limit of the potential that can be discharged at the positive electrode 12 is lower than when a negative electrode active material made of a conventional carbon material is used. When charging / discharging is performed at a higher depth, the positive electrode active material particles expand and contract more. Therefore, repeated charging / discharging cycles at higher depths accelerate the generation of cracks in the positive electrode active material particles. It is thought that the width of the cracks will also increase. Due to this, in the battery 10 using the lithium titanium composite oxide as the negative electrode active material, the conduction path in the positive electrode active material layer becomes complicated as compared with the case where the negative electrode active material made of a conventional carbon material is used. Thus, the internal resistance of the battery 10 is considered to increase. Since the positive electrode active material having a small pore volume is likely to be affected by expansion and contraction, the problem of resistance increase due to particle cracking is more serious.

On the other hand, the battery 10 includes, as a positive electrode active material, a first positive electrode active material and a second positive electrode active material in which the pore volume V _100N is specified at a specific content ratio. When the positive electrode active material has pores having a pore diameter of 100 nm or less, the positive electrode active material increases the effective reaction area and significantly reduces the diffusion distance of Li ions in the solid, thereby reducing the resistance. The high rate characteristics of the battery 10 can be improved. Since the positive electrode 12 contains a first positive electrode active material having a pore volume V _100N of 8 mm ³ / g or more and a second positive electrode active material having a pore volume V _100N of 5 mm ³ / g or less, It is considered that the charging reaction occurs preferentially in the first positive electrode active material, and as a result, the first positive electrode active material is in a higher oxidation state than the second positive electrode active material, and the reaction activity is increased.

  At this time, the nonaqueous electrolyte existing in the vicinity of the first positive electrode active material is oxidatively decomposed by coming into contact with the first positive electrode active material in a highly oxidized state. Then, the oxidative decomposition product of the nonaqueous electrolyte diffuses and adheres to the surrounding positive electrode active material, thereby forming a film on the surface of the positive electrode active material. This coating suppresses the occurrence and expansion of cracks in the positive electrode active material particles due to the repetition of the charge / discharge cycle, thereby suppressing the increase in resistance of the positive electrode active material caused by the repetition of the charge / discharge cycle, and It is considered that the durability against the discharge cycle can be improved.

On the other hand, when the positive electrode active material contains only the first positive electrode active material having a pore volume V _100N of 8 mm ³ / g or more, the reaction easily occurs uniformly in the entire region of the positive electrode mixture layer. A situation in which the reaction is biased to only some of the positive electrode active materials is less likely to occur. Therefore, when only the first positive electrode active material is contained as the positive electrode active material, the amount of the positive electrode active material that is in a highly oxidized state is very small, so that the oxidative decomposition of the nonaqueous electrolyte and the formation of a film by the oxidized decomposition product hardly occur. As a result, the occurrence and expansion of cracks in the positive electrode active material particles are not suppressed, and the durability of the battery 10 with respect to the charge / discharge cycle is not improved. Even when the positive electrode 12 contains only the second positive electrode active material as the positive electrode active material, it is considered that the durability with respect to the charge / discharge cycle of the battery 10 is not improved for the same reason as described above.

In the battery 10, the first / second pore volume ratio is four times or more for the first positive electrode active material and the second positive electrode active material. When the first / second pore volume ratio is less than 4 times, since the pore volume V _{100 N} of the first positive electrode active material and the pore volume V _{100 N} of the second positive electrode active material are close, the first positive electrode active It is considered that the charge reaction is unlikely to occur preferentially in the material, and the first positive electrode active material is unlikely to be in a highly oxidized state.

  In the battery 10, the content of the first positive electrode active material with respect to the total amount of the first positive electrode active material and the second positive electrode active material in the positive electrode mixture layer is 30% by mass or less, and preferably 20% by mass or less. When the content of the first positive electrode active material is too large, in the positive electrode mixture slurry used for producing the positive electrode 12, the viscosity may be increased and the dispersibility may be decreased, for example, particles may be aggregated in spots. As a result, it is considered that the coating amount of the positive electrode mixture slurry partially increases, and the quality of the electrode plate after rolling is lowered.

  Although the minimum of content of the 1st positive electrode active material with respect to the total amount of a 1st positive electrode active material and a 2nd positive electrode active material is not specifically limited, For example, 3 mass% or more is preferable and 5 mass% or more is more preferable. When the content of the first positive electrode active material is in the above range, the positive electrode active material that is preferentially reacted and becomes highly oxidized is not unevenly distributed in the positive electrode mixture layer, and the film is formed by oxidative decomposition of the nonaqueous electrolyte. It is considered that the formation is promoted and a uniform film can be formed on the positive electrode mixture layer.

Furthermore, in the battery 10, the amount of nonaqueous electrolyte retained by the positive electrode 12 is preferably 0.49 g / cm ³ or more per unit volume of the positive electrode mixture layer. If the amount of the non-aqueous electrolyte retained by the positive electrode 12 is too small, the electrolyte solution around the positive electrode active material particles inside the positive electrode mixture layer is insufficient, and the reaction resistance increases due to a decrease in Li in-solid diffusibility, This is because the high rate characteristic is degraded. Further, if the amount of the nonaqueous electrolyte retained by the positive electrode 12 is too small, when the charge / discharge cycle is repeated in the battery 10, the nonaqueous electrolyte is consumed due to the oxidative decomposition reaction of the nonaqueous electrolyte, and the durability performance is insufficient. This is because it greatly decreases.

  Here, for example, the amount of nonaqueous electrolyte retained by the positive electrode 12 is the nonaqueous electrolyte retained in the positive electrode 12 in a state where the positive electrode mixture layer is impregnated out of the nonaqueous electrolyte contained in the battery 10. The amount of the electrolyte is indicated, and the amount is expressed by mass per unit volume of the positive electrode mixture layer. Hereinafter, the amount of the nonaqueous electrolyte retained by the positive electrode 12 / negative electrode 14 is also referred to as the “electrolyte retained amount” of the positive electrode 12 / negative electrode 14.

The upper limit of the electrolyte solution holding amount of the positive electrode 12 is not particularly limited. According to the knowledge of the present inventor, for example, even when the amount of electrolyte retained in the cathode 12 exceeds 0.70 g / cm ³ per unit volume of the cathode mixture layer, the interface where the cathode active material and the electrolyte are in contact with each other It is considered that there is little influence on the resistance of the non-aqueous electrolyte secondary battery 10, that is, on the high rate characteristics and durability of the nonaqueous electrolyte secondary battery 10. On the other hand, when charging / discharging of the non-aqueous electrolyte secondary battery 10 having a large amount of electrolyte solution held by the positive electrode 12 is repeated particularly in a severe environment such as a high temperature, the generation of gas may be facilitated. Therefore, when reliability is considered together, the electrolyte solution holding amount of the positive electrode 12 is preferably 0.70 g / cm ³ or less.

The positive electrode mixture layer of the positive electrode 12 includes, as a positive electrode active material, a first positive electrode active material having a pore volume V _100N of 8 mm ³ / g or more and a second positive electrode having a pore volume V _{100 N} of 5 mm ³ / g or less. And at least an active material. The upper limit of the pore volume V _100N of the first positive electrode active material is not particularly limited, but is preferably, for example, 50 mm ³ / g or less, and more preferably 20 mm ³ / g or less. About the pore volume _V100N of a 2nd positive electrode active material, a minimum in particular is not restrict _| limited, Preferably it is 2 mm < ³ > / g or less.

For the pore volume V _100N in the positive electrode active material, for example, a pore distribution curve is created by the BJH method based on the measurement result of the adsorption amount with respect to the pressure of nitrogen gas by the nitrogen adsorption method, and the pore diameter is 100 nm or less. It can be calculated by summing the volume of pores in the range. The BJH method is a method of determining the pore distribution by calculating the pore volume with respect to the pore diameter using a cylindrical pore as a model. The pore distribution based on the BJH method can be measured using, for example, a gas adsorption amount measuring device (manufactured by Cantachrome).

The first positive electrode active material and the second positive electrode active material are preferably layered lithium transition metal oxides having a layered crystal structure. For example, a layered lithium transition metal oxide represented by the general formula (1) Li _{1 + x} M _a O _{2 + b} can be mentioned. In the general formula (1), x, a, and b are x + a = 1, −0.2 ≦ x ≦ 0.2 and −0.1 ≦ b ≦ 0.1 are satisfied, and M is selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). A metal element containing at least one element. Since the layered lithium transition metal oxide is likely to be in a highly oxidized state when lithium ions are extracted during the charging reaction, the above-described oxidative decomposition and film formation of the nonaqueous electrolyte are likely to occur. The effect of improving the durability against the charge / discharge cycle is remarkably exhibited. As the layered lithium transition metal oxide, lithium nickel cobalt manganate represented by the above general formula (1) and containing Ni, Co and Mn as M is particularly preferable.

  The layered lithium transition metal oxide may contain other additive elements other than Ni, Co, Mn, and Al. For example, alkali metal elements other than Li, transition metal elements other than Mn, Ni, and Co, alkaline earth Metal group elements, Group 12 elements, Group 13 elements other than Al, and Group 14 elements. Specific examples of other additive elements include, for example, zirconium (Zr), boron (B), magnesium (Mg), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), tin (Sn). ), Sodium (Na), potassium (K), barium (Ba), strontium (Sr), calcium (Ca), tungsten (W), molybdenum (Mo), niobium (Nb) and silicon (Si). .

  In addition, the composition of the compound used as the positive electrode active material and the negative electrode active material in the battery 10 can be measured using an ICP emission spectroscopic analyzer (for example, product name “iCAP6300” manufactured by Thermo Fisher Scientific).

  An example of a method for synthesizing the layered lithium transition metal oxide used as the first positive electrode active material and the second positive electrode active material will be described. For example, by mixing a lithium-containing compound such as lithium hydroxide and a hydroxide obtained by firing a hydroxide containing a metal element M other than lithium at a target mixing ratio, and firing the mixture Secondary particles obtained by aggregating primary particles of the layered lithium transition metal oxide represented by the general formula (1) can be synthesized. The mixture is fired in the air or in an oxygen stream. The firing temperature is, for example, about 500 to 1100 ° C., and the firing time is, for example, about 1 to 30 hours when the firing temperature is 500 to 1100 ° C.

The pore volume V _100N in the layered lithium transition metal oxide used as the first positive electrode active material and the second positive electrode active material can be adjusted, for example, when preparing the hydroxide containing the metal element M. The hydroxide containing the metal element M is obtained, for example, by dropping an aqueous alkali solution such as sodium hydroxide into an aqueous solution containing the compound of the metal element M and stirring, and the temperature of the aqueous solution at this time, the dropping time of the aqueous alkali solution. By adjusting the stirring speed, pH and the like, the pore volume V _100N in the obtained layered lithium transition metal oxide can be adjusted.

  The average particle diameters of the first positive electrode active material and the second positive electrode active material are not particularly limited, but are preferably 2 μm or more, and more preferably 3 μm or more, for example. When the average particle diameter of the first positive electrode active material and the second positive electrode active material is less than 2 μm, the conductive path by the conductive material in the positive electrode mixture layer may be hindered, and the cycle characteristics at high rate may be deteriorated. Although the upper limit of the average particle diameter of the first positive electrode active material and the second positive electrode active material is not particularly limited, for example, 30 μm or less is preferable. When it exceeds 30 micrometers of a 1st positive electrode active material and a 2nd positive electrode active material, a load characteristic may fall by the fall of the reaction area. When the first positive electrode active material and the second positive electrode active material are secondary particles formed by agglomerating primary particles, the average particle diameter of the secondary particles of the first positive electrode active material and the second positive electrode active material is 2 μm. It is preferably in the range of 30 μm or less.

  The average particle diameter of the positive electrode active material and the negative electrode active material in the present disclosure is a volume average particle diameter measured by a laser diffraction method, and means a median diameter at which the volume integrated value is 50% in the particle diameter distribution. The average particle diameter of the positive electrode active material and the negative electrode active material can be measured using, for example, a laser diffraction / scattering particle size distribution measuring apparatus (manufactured by Horiba, Ltd.).

  The positive electrode 12 according to the present embodiment includes, for example, (1) after mixing a first positive electrode active material, a second positive electrode active material, a conductive material, and a binder, and then dispersing N-methyl-2-pyrrolidone (NMP) or the like. A slurry preparation step of preparing a positive electrode mixture slurry by adding a medium; (2) a slurry application step of applying a positive electrode mixture slurry to the surface of the positive electrode core to form an application layer; (3) on the positive electrode core The coating layer formed on the substrate is dried to produce a positive electrode mixture layer, and (4) the positive electrode mixture layer is produced by a rolling process using a rolling means such as a rolling roll. Good. The method for applying the slurry to the surface of the positive electrode core in the application step is not particularly limited, and may be performed using a known application device such as a gravure coater, a slit coater, or a die coater.

  Examples of the conductive material contained in the positive electrode mixture layer include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. These may be used alone or in combination of two or more.

  Examples of the binder contained in the positive electrode mixture layer include fluorine resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, and polyolefin. These resins may be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like. These may be used alone or in combination of two or more.

  In the battery 10, as described above, the positive electrode 12 holds a specific range of non-aqueous electrolyte in the positive electrode mixture layer. Examples of the method for measuring the electrolyte solution holding amount of the positive electrode 12 include the following methods.

  The battery 10 is discharged, for example, in an atmosphere of 25 ° C. with a discharge current of 1 C until the SOC (depth of charge) becomes 0%. The discharge at this time may be performed, for example, until the voltage is reduced to 1.5V, and when a carbon-based material is mainly included as the negative electrode active material, the discharge may be performed until the voltage is decreased to 2.5V. In a state where the SOC becomes 0%, the battery 10 is disassembled, the electrode body 26 is taken out, and further separated into the positive electrode 12, the negative electrode 14, and the separator 16. A certain range is cut out of the separated positive electrode 12 to obtain a sample having a positive electrode core and a positive electrode mixture layer on both surfaces thereof. By immersing the obtained sample in an extraction solvent (for example, water) and shaking, the nonaqueous electrolyte impregnated in the positive electrode mixture layer of the positive electrode 12 can be extracted into the extraction solvent. The above-mentioned shaking may be performed using a known shaking device such as a shaking device (manufactured by ASONE Corporation, trade name “SHAKER SRR-2”).

  Next, the concentration of the non-aqueous electrolyte in the extraction solvent is measured using a known analyzer such as an ICP emission spectroscopic analyzer (Thermo Fisher Scientific iCAP6300). As will be described later, the non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, and the ICP emission spectroscopic analyzer can quantify both the non-aqueous solvent and the electrolyte salt in the extraction solvent. The weight of the nonaqueous electrolyte (nonaqueous solvent and electrolyte salt) determined as described above and the volume of the positive electrode mixture layer in the sample separately measured (or the weight of the positive electrode mixture layer and the positive electrode mixture in the sample) Based on the density of the layer), the nonaqueous electrolyte per unit volume of the positive electrode mixture layer can be calculated as the electrolyte solution holding amount of the positive electrode 12.

  The measuring method of the electrolyte solution holding amount of the positive electrode 12 is not limited to the above. For example, the nonaqueous electrolyte contained in the extraction solvent after shaking can be quantified by a known analysis method such as ion chromatography or gas chromatography. Further, the amount of the non-aqueous electrolyte extracted from the sample may be specified from the amount of change in the weight of the extraction solvent before and after the sample of the positive electrode 12 is extracted.

  The amount of electrolyte solution retained by the positive electrode 12 can be adjusted by, for example, the density of the positive electrode mixture layer, and can also be adjusted by a conductive agent, a binder, a liquid absorbent, a combination thereof, and the like used for the positive electrode 12. The density of the positive electrode mixture layer is, for example, the viscosity of the positive electrode mixture slurry, the content of the positive electrode active material, the conductive material and the binder in the positive electrode mixture slurry, the positive electrode mixture in the method for manufacturing the positive electrode 12 described above. It can be adjusted by adjusting the amount of slurry applied, the pressure during rolling, and the like. In addition, the mixture ratio of the total weight of the 1st positive electrode active material and the 2nd positive electrode active material in the said positive mix layer is 80 mass% or more and 94.5 mass% or less, for example. The blending ratio of the conductive material in the positive electrode mixture layer is, for example, 5% by mass or more and 15% by mass or less. The blending ratio of the binder in the positive electrode mixture layer is, for example, 0.5% by mass or more and 5% by mass or less.

[Negative electrode]
The negative electrode 14 includes a negative electrode core made of a metal foil or the like and a negative electrode mixture layer formed on the negative electrode core. For the negative electrode core, a metal foil that is stable in the potential range of the negative electrode such as aluminum, a film in which the metal is disposed on the surface layer, or the like can be used. The negative electrode mixture layer includes a negative electrode active material and a binder. The negative electrode 14 can be manufactured according to the above-described method for manufacturing the positive electrode 12. For example, a negative electrode mixture slurry containing a negative electrode active material and a binder is applied and dried on the negative electrode core to form a negative electrode mixture layer. Then, the negative electrode 14 in which the negative electrode mixture layer is formed on both surfaces of the negative electrode core can be manufactured by rolling the negative electrode mixture layer with a rolling means such as a rolling roll.

The negative electrode active material used for the negative electrode 14 contains a lithium titanium composite oxide. The lithium titanium composite oxide is represented by the general formula (2) Li _{4 + y} Ti ₅ O ₁₂ (in the general formula (2), y is 0 or more and 1 or less) and has a spinel crystal structure.

  What is necessary is just to synthesize | combine the negative electrode active material which consists of lithium titanium complex oxides by the method according to the synthesis | combination method of a layered lithium transition metal oxide, for example. For example, a lithium-containing compound such as lithium hydroxide and a titanium-containing compound such as titanium dioxide and titanium hydroxide are mixed at a target mixing ratio, and the mixture is fired, whereby the general formula (2) Secondary particles obtained by agglomerating primary particles of the lithium-titanium composite oxide can be synthesized. Firing of the mixture of the lithium-containing compound and the titanium-containing compound may be performed, for example, in the atmosphere (or in an oxygen stream), and the firing temperature at that time is, for example, about 500 to 1100 ° C., and the firing temperature is 500 to 1100. When the temperature is about ° C, the firing time is, for example, 1 to 30 hours.

  As the negative electrode active material, in addition to the lithium titanium composite oxide, a compound capable of reversibly occluding and releasing lithium ions, for example, a carbon material such as natural graphite and artificial graphite, a metal that can be alloyed with lithium such as Si and Sn Etc. may be contained.

  As the binder used for the negative electrode 14, known binders can be used. As in the case of the positive electrode 12, a fluorine resin such as PTFE, PAN, polyimide resin, acrylic resin, and polyolefin resin. Etc. can be used. Moreover, as a binder used when preparing a negative mix slurry using an aqueous solvent, for example, CMC or a salt thereof, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or a salt thereof, polyvinyl Alcohol (PVA) etc. are mentioned.

In the nonaqueous electrolyte secondary battery 10 according to the present embodiment, the amount of the electrolyte solution retained in the negative electrode 14 is preferably 0.58 g / cm ³ or more per unit volume of the negative electrode mixture layer. This is because the high-rate characteristics and durability of the non-aqueous electrolyte secondary battery 10 can be further improved when the electrolyte solution holding amount of the negative electrode 14 is in the above range.

  The measurement of the electrolyte solution holding amount of the negative electrode 14 may be performed, for example, in the same manner as the method for measuring the electrolyte solution holding amount of the positive electrode 12 described above. Further, the adjustment of the electrolyte solution holding amount of the negative electrode 14 may be performed in the same manner as the method for adjusting the electrolyte solution holding amount of the positive electrode 12 described above.

[Nonaqueous electrolyte]
The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent used for the non-aqueous electrolyte, for example, esters, ethers, nitriles, amides such as dimethylformamide, a mixed solvent of two or more of these, and the like can be used. A halogen-substituted product in which at least a part of hydrogen is substituted with a halogen atom such as fluorine can also be used.

  Examples of the esters contained in the nonaqueous electrolyte include cyclic carbonates, chain carbonates, and carboxylic acid esters. Specifically, for example, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, vinylene carbonate; dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl Chain carbonates such as propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate; chain carboxylic acid esters such as methyl propionate (MP), ethyl propionate, methyl acetate, ethyl acetate, propyl acetate; and γ-butyrolactone ( GBL) and cyclic carboxylic acid esters such as γ-valerolactone (GVL). Examples thereof include cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL).

  Examples of ethers contained in the non-aqueous electrolyte include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3- Cyclic ethers such as dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineol, crown ether; diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl Ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether O-Dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene Examples thereof include chain ethers such as glycol dimethyl ether and tetraethylene glycol dimethyl.

  Examples of nitriles contained in the non-aqueous electrolyte include acetonitrile, propionitrile, butyronitrile, valeronitrile, n-heptanenitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, 1,2,3-propanetricarbox. Nitriles, 1,3,5-pentanetricarbonitrile and the like can be mentioned.

  Examples of halogen-substituted substances contained in the non-aqueous electrolyte include fluorinated cyclic carbonates such as 4-fluoroethylene carbonate (FEC), fluorinated chain carbonates, methyl 3,3,3-trifluoropropionate (FMP). ) And the like.

The electrolyte salt used for the non-aqueous electrolyte is preferably a lithium salt. _Examples of the lithium _{salt, LiBF 4, LiClO 4, LiPF} 6, LiAsF 6, LiSbF 6, LiAlCl 4, LiSCN, LiCF 3 SO 3, LiC (C 2 F 5 SO 2), LiCF 3 CO 2, Li (P (C ₂ O ₄ ) F ₄ ), Li (P (C ₂ O ₄ ) F ₂ ), LiPF _6-x (C _n F _{2n + 1} ) _x (1 ≦ x ≦ 6, n is 1 or 2), LiB ₁₀ Cl _10, LiCl, LiBr, LiI, chloroborane lithium, lower aliphatic carboxylic acid _{lithium, Li 2 B 4 O 7,} Li (B (C 2 O 4) 2) [ lithium - bis (oxalato) borate (LiBOB)], _{li (B (C 2 O 4} ) F 2) boric acid salts such _{as, LiN (FSO 2) 2,} LiN (C 1 F 2l + 1 SO 2) (C m F 2m + 1 SO 2 {L, m is an integer of at least 1} imido salts such as. Only one type of lithium salt may be used, or a mixture of two or more types may be used.

As described above, the nonaqueous electrolyte comes into contact with the first positive electrode active material in a highly oxidized state in the positive electrode mixture layer and undergoes oxidative decomposition to form a film of the oxidative decomposition product on the surface of the positive electrode active material. From this viewpoint, it is preferable to use LiPF ₆ as the nonaqueous electrolyte.

[Separator]
For the separator 16, for example, a porous sheet having ion permeability and insulating properties is used. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. As a material of the separator 16, an olefin resin such as polyethylene and polypropylene, cellulose and the like are preferable. The separator 16 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Moreover, the multilayer separator containing a polyethylene layer and a polypropylene layer may be sufficient, and what applied resin, such as an aramid resin, and inorganic fine particles, such as an alumina and a titania, to the surface of the separator 16 can also be used.

  In the above description, the battery 10 has been described using the electrode body 26 having a winding structure. However, the configuration of the nonaqueous electrolyte secondary battery of the present disclosure is not limited to this configuration. For example, an electrode body in which the positive electrode 12 and the negative electrode 14 are folded ninety-nine with the belt-like positive electrode 12 and the belt-like negative electrode 14 facing each other may be configured. Alternatively, a plurality of sheet-like positive electrode plates and a plurality of sheet-like negative electrode plates may be alternately laminated via the separator 16 to form a laminated electrode body. Further, the exterior body is not limited to a square exterior body. For example, a cylindrical metal exterior body or coin-shaped exterior body may be used, or the electrode body may be covered with a laminate film. The material of the exterior body need not be made of a conductive material as long as the exterior body and the electrode body are not electrically connected. For example, a resin exterior body may be used.

<Example 1>
[Production of positive electrode]
A lithium-containing compound and an oxide obtained by firing a hydroxide containing a metal element other than lithium including nickel (Ni), cobalt (Co), and manganese (Mn) at a target mixing ratio. By mixing and firing the mixture, secondary particles formed by agglomerating primary particles of the layered lithium transition metal oxide are synthesized, and the layered lithium transition metal oxidation used as the first positive electrode active material and the second positive electrode active material I got a thing.

By the above method, the layered lithium transition metal oxide (first positive electrode active material) represented by the composition formula Li _1.054 Ni _0.199 Co _0.597 Mn _0.199 Zr _0.005 O ₂ , and the composition formula A layered lithium transition metal oxide (second positive electrode active material) represented by Li _1.067 Ni _0.498 Co _0.199 Mn _0.299 Zr _0.005 O ₂ was mixed at a mass ratio of 3: 7. A mixture was obtained. The composition of the positive electrode active material and the compound used as the negative electrode active material described later was measured using an ICP emission spectroscopic analyzer (trade name “iCAP6300” manufactured by Thermo Fisher Scientific).

Moreover, the pore volume _V100N of the 1st positive electrode active material measured using BJH method was 8 mm < ³ > / g, and the pore volume _V100N of the 2nd positive electrode active material was 2 mm < ³ > / g. As a result of measuring the volume average particle diameters of the first positive electrode active material and the second positive electrode active material using a laser diffraction scattering type particle size distribution measuring apparatus (manufactured by Horiba, Ltd.), the volume average particle diameter of the first positive electrode active material is obtained. Was 5.0 μm, and the volume average particle size of the second positive electrode active material was 2.0 μm.

  A positive electrode active material (a mixture of a first positive electrode active material and a second positive electrode active material), carbon black (conductive material), and polyvinylidene fluoride (PVDF) (binder) produced by the above method was 91: 7. : Mixed at a mass ratio of 2. N-methyl-2-pyrrolidone (NMP) was added as a dispersion medium to the mixture, and the mixture was stirred using a mixer (Primix Co., Ltd., TK Hibismix) to prepare a positive electrode mixture slurry. The viscosity (unit: mPa · s) of the prepared positive electrode mixture slurry was measured using a B-type viscometer (manufactured by Eiko Seiki Co., Ltd., product name “Brookfield Viscometer”).

  The slurry was applied onto an aluminum foil as a positive electrode core, and the coating film was dried to form a positive electrode mixture layer. Next, the positive electrode mixture layer was rolled with a rolling roll to produce a positive electrode 12 having a positive electrode mixture layer formed on both surfaces of an aluminum foil. The slurry was applied onto an aluminum foil as a positive electrode core, and the coating film was dried to form a positive electrode mixture layer. Next, the positive electrode mixture layer was rolled with a rolling roll to produce a positive electrode 12 having a positive electrode mixture layer formed on both surfaces of an aluminum foil. As a rolling method in the present embodiment, for example, by adjusting the rolling so that the thickness of the positive electrode mixture layer after rolling is in the range of 70 to 90 μm with respect to the thickness of the positive electrode mixture layer before rolling of 110 to 115 μm. The holding amount of the positive electrode mixture layer can be adjusted to the above range. In addition, the method of controlling the quantity which hold | maintains the electrolyte solution in the positive mix layer used for the nonaqueous electrolyte secondary battery of this indication is not limited to said rolling method.

[Production of negative electrode]
A lithium titanium composite oxide represented by a composition formula Li ₄ Ti ₅ O ₁₂ , carbon black (conductive material), and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 90: 8: 2. NMP was added to the mixture, and the mixture was stirred using a mixer (manufactured by PRIMIX Corporation, TK Hibismix) to prepare a negative electrode mixture slurry. Next, after applying the negative electrode mixture slurry on the aluminum foil as the negative electrode core and drying the coating film, the coating film is rolled with a rolling roll to form a negative electrode mixture layer on both surfaces of the aluminum foil. A negative electrode 14 was prepared.

[Preparation of non-aqueous electrolyte]
Propylene carbonate (PC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 25:35:40 to prepare a mixed solvent. LiPF ₆ was dissolved in the mixed solvent to a concentration of 1.2 mol / L to prepare a non-aqueous electrolyte. In addition, the mixture ratio of the negative electrode active material in the said negative mix layer is 80 mass% or more and 95 mass% or less, for example. The blending ratio of the conductive material in the negative electrode mixture layer is, for example, 5% by mass or more and 15% by mass or less. The blending ratio of the binder in the negative electrode mixture layer is, for example, 1% by mass or more and 5% by mass or less.

[Production of battery]
The positive electrode 12 and the negative electrode 14 obtained above were spirally wound through a polypropylene microporous membrane separator 16 and then press-molded to produce a flat electrode body 26. The current collector portion was welded to each of the positive electrode core exposed portion and the negative electrode core exposed portion formed at both ends in the width direction of the electrode body 26. Next, the electrode body 26 to which the current collector portion is welded is accommodated in an aluminum outer can 24, and the nonaqueous electrolyte is injected from the injection port 30, and then the opening is sealed with the sealing plate 22. Thus, a non-aqueous electrolyte secondary battery 10 having a rated capacity of 10 Ah shown in FIG. 1 was produced.

[Measurement of electrolyte retention]
As a result of discharging the battery 10 in a 25 ° C. atmosphere at a discharge current of 1 C until the SOC (depth of charge) reached 0%, the voltage dropped to 1.5V. Next, the battery 10 was disassembled, the electrode body was taken out, and further separated into a positive electrode 12, a negative electrode 14, and a separator 16. A certain range was cut out of the obtained positive electrode 12 to obtain a sample having a positive electrode core and a positive electrode mixture layer on both surfaces thereof. The obtained sample is immersed in water (extraction solvent) and shaken using a shaker (trade name “SHAKER SRR-2” manufactured by AS ONE Co., Ltd.), whereby the positive electrode 12 is held in the positive electrode mixture layer. An extract obtained by extracting the nonaqueous electrolyte into water was obtained. Next, the concentration of the nonaqueous electrolyte in the extract was quantified using an ICP emission spectroscopic analyzer (Thermo Fisher Scientific iCAP6300), and the weight of the nonaqueous electrolyte extracted from the positive electrode 12 sample was calculated. Based on the calculated weight of the nonaqueous electrolyte and the volume of the positive electrode mixture layer in the sample separately measured, the amount of electrolyte retained in the positive electrode 12 was determined. Similarly, the amount of electrolyte solution retained in the negative electrode 14 was determined. As a result, in the battery 10 of Example 1, the electrolytic solution holding amount of the positive electrode 12 was 0.655 g / cm ³ , and the electrolytic solution holding amount of the negative electrode 14 was 0.628 g / cm ³ .

<Example 2>
A battery 10 having the same configuration as that of Example 1 was produced except that the pressure for rolling the positive electrode mixture layer and the pressure for rolling the negative electrode mixture layer were adjusted in the production of the battery 10. In the battery 10 of Example 2, the electrolyte solution holding amount of the positive electrode 12 was 0.662 g / cm ³ , and the electrolyte solution holding amount of the negative electrode 14 was 0.618 g / cm ³ .

<Example 3>
A battery 10 having the same configuration as that of Example 1 was produced except that the pressure for rolling the positive electrode mixture layer was adjusted in the production of the nonaqueous electrolyte secondary battery 10. In the battery 10 of Example 3, the electrolyte solution holding amount of the positive electrode 12 was 0.490 g / cm ³ , and the electrolyte solution holding amount of the negative electrode 14 was 0.628 g / cm ³ .

<Comparative Example 1>
A non-aqueous electrolyte secondary battery having the same configuration as that of Example 1 except that the first positive electrode active material was not used as the positive electrode active material and only the second positive electrode active material was used in the positive electrode production process. Produced. In the nonaqueous electrolyte secondary battery of Comparative Example 1, the amount of electrolyte retained on the positive electrode was 0.655 g / cm ³ , and the amount of electrolyte retained on the negative electrode was 0.628 g / cm ³ .

<Comparative example 2>
The same configuration as in Example 1 except that in the positive electrode preparation step, the first positive electrode active material and the second positive electrode active material were mixed at a mass ratio of 4: 6 to prepare a mixture, and a positive electrode mixture slurry was prepared. A non-aqueous electrolyte secondary battery having was produced. In the nonaqueous electrolyte secondary battery of Comparative Example 2, the amount of electrolyte retained on the positive electrode was 0.655 g / cm ³ , and the amount of electrolyte retained on the negative electrode was 0.628 g / cm ³ .

<Comparative Example 3>
In the production process of the positive electrode, a layered lithium transition metal represented by a composition formula Li _1.054 Ni _0.199 Co _0.597 Mn _0.199 Zr _0.005 O ₂ and having a pore volume V _100N of 5 mm ³ / g A non-aqueous electrolyte secondary battery having the same configuration as in Example 1 was produced except that the oxide was used as the first positive electrode active material. In the nonaqueous electrolyte secondary battery of Comparative Example 3, the amount of electrolyte retained on the positive electrode was 0.655 g / cm ³ , and the amount of electrolyte retained on the negative electrode was 0.628 g / cm ³ .

<Comparative example 4>
In the production of the nonaqueous electrolyte secondary battery, a nonaqueous electrolyte secondary battery having the same configuration as in Example 1 was produced, except that the pressure for rolling the positive electrode mixture layer was adjusted. In the nonaqueous electrolyte secondary battery of Comparative Example 4, the electrolytic solution retention amount of the positive electrode was 0.450 g / cm ³ , and the electrolytic solution retention amount of the negative electrode 14 was 0.620 g / cm ³ .

<Comparative Example 5>
In the production of the nonaqueous electrolyte secondary battery, a nonaqueous electrolyte secondary battery having the same configuration as in Example 1 was produced, except that the pressure for rolling the positive electrode mixture layer was adjusted. In the nonaqueous electrolyte secondary battery of Comparative Example 5, the electrolyte retention amount of the positive electrode was 0.400 g / cm ³ , and the electrolyte retention amount of the negative electrode was 0.620 g / cm ³ .

[Battery test]
The following evaluation tests were carried out using the nonaqueous electrolyte secondary batteries of Examples and Comparative Examples prepared as described above.

(1) High-rate characteristic test Each battery was charged to a SOC (charging depth) of 20% with a charging current of 1 C in a temperature atmosphere of 25 ° C. Thereafter, the charging / discharging current is increased in the order of 5C discharging step → 5C charging step → 10C discharging step → 10C charging step → 15C discharging step → 15C charging step → 20C discharging step → 20C charging step → 25C discharging step → 25C charging step. I let you. At this time, the charging or discharging time in each step was 30 seconds, and a pause period of 15 minutes was provided between each step. That is, the charge / discharge cycle was performed in the order of 30 seconds of discharge → 15 minutes of rest → 30 seconds of charge → 15 minutes of rest. Then, the battery voltage at the time when the discharge time of 10 seconds has elapsed in this charge / discharge cycle is plotted against the discharge current, and the current value when reaching 1.5 V from the straight line obtained by the least square method is calculated, The resistance value obtained from the current value was obtained as the output value of each non-aqueous electrolyte secondary battery. Based on the resistance value obtained for each non-aqueous electrolyte secondary battery, the durability against the high-rate characteristic test was evaluated according to the following criteria.

○: The resistance value after the high-rate characteristic test is less than 104% when Example 1 is 100. ×: The resistance value after the high-rate characteristic test is 104% or more when Example 1 is 100. The evaluation result of the resistance value and high rate characteristic which were obtained about the nonaqueous electrolyte secondary battery of the example and each comparative example is shown.

(2) Durability test It charged to the voltage which becomes SOC80% with the charging current of 1C in the temperature atmosphere of 25 degreeC. Next, a partial charge / discharge cycle test was performed in which a cycle of discharging to a voltage at which SOC became 20% at a discharge current of 5C in a temperature atmosphere of 60 ° C. and then charging to SOC 80% at a charge current of 5C was repeated. . This partial charge / discharge cycle was repeated until the ratio of output to output at the start of the partial charge / discharge cycle (output initial ratio) reached 80%, and the total discharge amount until the output initial ratio reached 80% was determined. Based on the total discharge amount at this time, the durability against charge / discharge cycles was evaluated according to the following criteria.

○: The total discharge amount after the durability test when Example 1 is set to 100 is 95% or more ×: The total discharge amount after the durability test when Example 1 is set to 100 is less than 95% Table 1 The total discharge amount and evaluation result obtained about the nonaqueous electrolyte secondary battery of each comparative example except each example and comparative example 5 are shown.

(3) Winding non-defective rate test For the purpose of confirming the uniformity of the thickness of the positive electrode and the negative electrode, the winding non-defective rate of the electrode bodies produced in the examples and comparative examples was evaluated. More specifically, the maximum value (winding deviation) of the deviation width in the axial direction of the winding structure of the positive electrode, the negative electrode, and the separator was measured for the electrode bodies produced in each Example and each Comparative Example. The smaller the winding deviation, the higher the thickness of the positive electrode or the negative electrode, that is, the uniformity of the thickness of the positive electrode mixture layer and the negative electrode mixture layer. As described above, when the thicknesses of the positive electrode and the negative electrode are not uniform, it is considered that the deterioration of the active material is locally accelerated and the durability of the nonaqueous electrolyte secondary battery is lowered. Therefore, it is considered that by measuring the winding deviation of the electrode body, the uniformity of the thickness of each mixture layer in the positive electrode and the negative electrode can be confirmed, and the durability of the nonaqueous electrolyte secondary battery can be evaluated.

In this measurement test, each electrode body was evaluated as “pass” if the winding deviation was within ± 1 mm, and “failed” if it was not in the range. For each example and each comparative example, the winding deviation of 50 electrode bodies was measured, and the ratio (winding non-defective product ratio) to the total number of electrode bodies for which the evaluation of the winding deviation was “pass” was obtained. . Based on the obtained winding non-defective rate, the durability of the nonaqueous electrolyte secondary batteries of Examples and Comparative Examples was evaluated according to the following criteria.

○: Winding non-defective rate is 95% or more when Example 1 is 100. ×: Winding non-defective rate is less than 95% when Example 1 is 100. Table 1 shows each example and each comparative example. The evaluation results of the durability based on the viscosity of the positive electrode mixture slurry, the winding good product rate of the electrode body, and the winding good product rate are shown.

  In Comparative Example 5, the result of the high rate characteristic is shown, but the result of the durability test is omitted. As for the non-aqueous electrolyte batteries of Comparative Examples 1, 3, and 4, when the result of the high rate characteristic (resistance) in Table 1 exceeds 100% compared to Example 1, the durability is also less than 100%. In Comparative Example 5, the result of the high rate characteristic (resistance) is more than 100%. Therefore, it is estimated that the durability is less than 100% of Example 1, and thus the durability test is omitted.

As is clear from the results in Table 1, in the nonaqueous electrolyte secondary battery using the lithium titanium composite oxide as the negative electrode active material, the first positive electrode active material having a pore volume V _100N of 8 mm ³ / g or more; And a second positive electrode active material having a pore volume V _100N of 5 mm ³ / g or less, a first / second pore volume ratio is 4 times or more, and the content of the first positive electrode active material is the first positive electrode The amount of the nonaqueous electrolyte retained by the positive electrode is 0.49 g / cm ³ or more per unit volume of the positive electrode mixture layer with respect to the total amount of the active material and the second positive electrode active material. The non-aqueous electrolyte secondary batteries of Examples 1 to 3 have higher rate characteristics, durability after charge / discharge cycles, and good winding rate than Comparative Examples 1 to 5 that do not satisfy any of the above-described configurations. It was found to be remarkably superior. A non-aqueous electrolyte secondary battery having a good winding yield rate is considered to be excellent in the durability of the non-aqueous electrolyte secondary battery because the thickness of the positive electrode and the negative electrode is excellent in uniformity.

  DESCRIPTION OF SYMBOLS 10 Nonaqueous electrolyte secondary battery, 12 Positive electrode, 14 Negative electrode, 16 Separator, 18 Positive electrode terminal, 20 Negative electrode terminal, 22 Sealing plate, 24 Outer can, 26 Electrode body, 28 Bottom part, 30 Injection port, 32 Gas discharge valve.

Claims (3)

A positive electrode having a positive electrode mixture layer including a first positive electrode active material and a second positive electrode active material;
A negative electrode having a negative electrode mixture layer containing a lithium titanium composite oxide as a negative electrode active material;
A non-aqueous electrolyte,
The first positive electrode active material has a pore volume of 100 mm or less and a volume per mass of pores of 8 mm ³ / g or more,
The second positive electrode active material has a volume per mass of pores having a pore diameter of 100 nm or less and 5 mm ³ / g or less,
The volume per mass of pores having a pore diameter of 100 nm or less in the first positive electrode active material is 4 times or more than the volume per mass of pores having a pore diameter of 100 nm or less in the second positive electrode active material. And
The content of the first positive electrode active material is 30% by mass or less based on the total amount of the first positive electrode active material and the second positive electrode active material,
The amount of the non-aqueous electrolyte retained by the positive electrode is 0.49 g / cm ³ or more per unit volume of the positive electrode mixture layer.
Non-aqueous electrolyte secondary battery.   2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the first positive electrode active material and the second positive electrode active material both have an average particle diameter of 2 μm or more. Both the first positive electrode active material and the second positive electrode active material are represented by the general formula (1) Li _{1 + x} M _a O _{2 + b} (in the general formula (1), x, a and b are x + a = 1, −0. Satisfying the condition of 2 ≦ x ≦ 0.2 and −0.1 ≦ b ≦ 0.1, and M is a metal element containing at least one element selected from the group consisting of Ni, Co, Mn and Al The nonaqueous electrolyte secondary battery according to claim 1, which is a layered lithium transition metal oxide represented by: