JP6435093B2 - Positive electrode active material and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a positive electrode active material and a lithium ion secondary battery.

  In recent years, in a lithium ion secondary battery, a technique using a lithium (Li) transition metal composite oxide containing nickel (Ni) as a positive electrode active material realizing high potential and high capacity has been proposed. .

For example, Patent Document 1 discloses a ratio I ₍₀₀₃₎ / I between the (003) plane diffraction peak (peak) intensity I ₍₀₀₃₎ and the (104) plane diffraction peak intensity I ₍₁₀₄₎ in X-ray diffraction. Disclosed is a technique for improving cycle characteristics by using LiMeO _{2 (104)} is 1.5 or more and 4 or less (wherein Me is one or more selected from Ni and Co) as a positive electrode active material. Has been.

Patent Document 2 discloses that Li _x Ni _1-y M _y O _{2 + α} having a diffraction peak intensity ratio (104/003) between the (104) plane and the (003) plane in X-ray diffraction of 0.80 or less is positive electrode. It is disclosed that battery characteristics are improved when used as an active material.

Japanese Patent Laid-Open No. 2001-167761 JP 2013-120676 A

  Here, in the techniques disclosed in Patent Documents 1 and 2, by increasing the ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane in X-ray diffraction, Ni ions are li sites in the crystal. The phenomenon (so-called cation mixing phenomenon) mixed in (site) is suppressed, and the crystal structure is stabilized.

  However, when a lithium nickel composite oxide having a high Ni ratio is used as a positive electrode active material in order to manufacture a lithium ion secondary battery having a higher potential and a higher capacity, the structure of the positive electrode active material increases as the Ni ratio increases. Stability is reduced. Therefore, even when the techniques disclosed in Patent Documents 1 and 2 are used, there is a problem that the structure of the positive electrode active material becomes unstable, and the cycle characteristics and initial charge / discharge efficiency of the lithium ion secondary battery decrease. there were.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to have a high discharge capacity, cycle characteristics and initial characteristics when a positive electrode active material having a high Ni ratio is used. It is an object of the present invention to provide a new and improved positive electrode active material and a lithium ion secondary battery capable of improving charge / discharge efficiency.

In order to solve the above problems, according to an aspect of the present invention, in X-ray diffraction, the diffraction peak intensity I _{(003) of the (003} ) plane and the diffraction peak intensity I ₍₁₀₄₎ of the (104) plane The ratio I _{(003) / (104)} is 1.05 or more and 1.25 or less, and the half width FWHM _{(003) of the} (003) plane is 0.12 or more and 0.155 or less, and The average secondary particle diameter D50 is 3 μm or more and 9 μm or less, the specific surface area is 0.38 m ² / g or more and 1.05 m ² / g or less, and the composition represented by the following general formula (1) There is provided a positive electrode active material comprising a lithium composite oxide having
(Chemical formula 1)
Li _a Ni _x Co _y M _z O ₂ (1)
In the general formula (1), M is selected from the group consisting of Al, Mn, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. One or more metal elements selected,
a is 0.20 ≦ a ≦ 1.20,
x is 0.80 ≦ x <1.00,
y is 0 <y ≦ 0.20,
z is 0 ≦ z ≦ 0.10,
x + y + z = 1.

  According to this aspect, the positive electrode active material according to an embodiment of the present invention can further improve cycle characteristics and initial charge / discharge efficiency.

In the general formula (1), M is Al or Mn,
x is 0.80 ≦ x <1.00,
y is 0 <y ≦ 0.15,
z is 0 <z ≦ 0.05,
x + y + z = 1 may be sufficient.

  According to this aspect, the positive electrode active material according to an embodiment of the present invention can further improve cycle characteristics and initial charge / discharge efficiency.

  Moreover, in order to solve the said subject, according to another viewpoint of this invention, the lithium ion secondary battery containing said positive electrode active material is provided.

According to this aspect, in the X-ray diffraction, the lithium ion secondary battery according to an embodiment of the present invention has a (003) plane diffraction peak intensity I ₍₀₀₃₎ and a (104) plane diffraction peak intensity I _{( 104)} I _{(003) / (104)} is not less than 1.05 and not more than 1.25, and the half width FWHM (003) of the (003) plane is not less than 0.12 and not more than 0.155. And a lithium transition metal having a high Ni ratio and having an average secondary particle diameter D50 of 3 μm to 9 μm and a specific surface area of 0.38 m ² / g to 1.05 m ² / g A composite oxide is included as a positive electrode active material. Therefore, the lithium ion secondary battery according to one embodiment of the present invention has a high discharge capacity, and improved cycle characteristics and initial charge / discharge efficiency.

  As described above, according to the present invention, even when a positive electrode active material having a high Ni ratio is used, the discharge capacity is high, and cycle characteristics and initial charge / discharge efficiency can be improved.

It is explanatory drawing explaining the structure of the lithium ion secondary battery which concerns on one Embodiment of this invention.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

<1. Overview of Lithium Ion Secondary Battery According to One Embodiment of the Present Invention>
First, an outline of a lithium ion secondary battery according to an embodiment of the present invention will be described with the background art of the present invention.

  A lithium ion secondary battery according to an embodiment of the present invention includes a lithium nickel composite oxide having a high nickel (Ni) ratio. A lithium ion secondary battery using a lithium nickel composite oxide having a high Ni ratio as a positive electrode active material can realize a high potential and a high discharge capacity. However, as the Ni ratio increases, the structural stability of the lithium-nickel composite oxide decreases, and cation mixing (the Ni site in the crystal being occupied by Ni divalent ions) is likely to occur. .

  Here, when the structural stability of the lithium-nickel composite oxide is reduced and a large amount of cation mixing occurs, the cycle characteristics and initial charge / discharge efficiency (that is, the lithium ion secondary battery is used in the lithium ion secondary battery) It is pointed out that the capacity will be reduced. Therefore, in the lithium ion secondary battery using the lithium nickel composite oxide having a high Ni ratio as the positive electrode active material, there is a problem that the initial charge / discharge efficiency and the cycle characteristics cannot be improved.

On the other hand, in the lithium nickel composite oxide, and the diffraction peak intensity _I (003) plane in X-ray diffraction _(003), (104) plane ratio of the diffraction peak intensity _{I (104)} of _{(I (003) / (104} It has been found that if ₎ ) is large, the crystallinity is high and cation mixing is less likely to occur. Accordingly, it has been proposed to use a lithium nickel composite oxide having a large diffraction peak intensity ratio I _{(003) / (104)} as a positive electrode active material to suppress cation mixing and improve initial charge / discharge efficiency and cycle characteristics. ing.

However, when a lithium nickel composite oxide having a large diffraction peak intensity ratio I _{(003) / (104)} is used as the positive electrode active material, the initial charge / discharge efficiency and cycle characteristics can be improved, while the discharge capacity decreases. Resulting in. Therefore, it has been difficult to improve all of the discharge capacity, initial charge / discharge efficiency, and cycle characteristics in the lithium nickel composite oxide having a high Ni ratio.

Therefore, the present inventor has come up with the present invention by examining the above-mentioned problems in detail. The positive electrode active material according to an embodiment of the present invention is a lithium-nickel composite oxide having a Ni ratio of 80% or more. In the X-ray diffraction, the (003) plane diffraction peak intensity I ₍₀₀₃₎ and the (104) plane The ratio I _{(003) / (104)} to the diffraction peak intensity I ₍₁₀₄₎ is 1.05 or more and 1.25 or less, and the half width FWHM _{(003) of the} (003) plane is 0.12 or more. When it is 0.155 or less, the average secondary particle diameter (D50) is 3 μm or more and 9 μm or less, and the specific surface area is 0.38 m ² / g or more and 1.05 m ² / g or less. In addition, the discharge capacity, the initial charge / discharge efficiency, and the cycle characteristics can all be improved.

That is, according to the present invention, in the lithium nickel composite oxide having a Ni ratio of 80% or more, even if the diffraction peak intensity ratio I _{(003) / (104)} is a relatively small value, the average secondary particle diameter (D50) It has been found that the discharge capacity, the initial charge / discharge efficiency and the cycle characteristics can all be improved by setting the half width FWHM ₍₀₀₃₎ of the (003) plane and the specific surface area within the scope of the present invention. .

<2. Configuration of lithium ion secondary battery>
Below, with reference to FIG. 1, the specific structure of the lithium ion secondary battery 10 which concerns on one Embodiment of this invention demonstrated above is demonstrated. FIG. 1 is an explanatory view illustrating the configuration of a lithium ion secondary battery according to an embodiment of the present invention.

  As shown in FIG. 1, a lithium ion secondary battery 10 is a lithium ion secondary battery using a lithium nickel composite oxide with a high Ni ratio as a positive electrode active material, and includes a positive electrode 20, a negative electrode 30, a separator (separator). ) Layer 40. The form of the lithium ion secondary battery 10 is not particularly limited. For example, the lithium ion secondary battery 10 may be any one of a cylindrical shape, a square shape, a laminate shape, a button shape, and the like.

  The positive electrode 20 includes a current collector 21 and a positive electrode active material layer 22. The current collector 21 is made of, for example, aluminum (Al).

  The positive electrode active material layer 22 includes at least a positive electrode active material and a conductive agent, and may further include a binder. The positive electrode active material contains a lithium nickel composite oxide having a high Ni ratio. The high nickel ratio lithium nickel composite oxide according to an embodiment of the present invention has, for example, a composition represented by the following general formula (1).

(Chemical formula 1)
Li _a Ni _x Co _y M _z O ₂ (1)

Here, in the general formula (1), M represents Al, Mn, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. One or more metal elements selected from the group consisting of:
a is 0.20 ≦ a ≦ 1.20,
x is 0.80 ≦ x <1.00,
y is 0 <y ≦ 0.20,
z is 0 ≦ z ≦ 0.10,
x + y + z = 1.

The lithium nickel composite oxide having a high Ni ratio according to an embodiment of the present invention more specifically, in the general formula (1), M is Al or Mn,
x is 0.80 ≦ x <1.00,
y is 0 <y ≦ 0.15,
z is 0 <z ≦ 0.05,
x + y + z = 1 may be sufficient.

A lithium ion secondary battery according to an embodiment of the present invention includes a high nickel ratio lithium nickel composite oxide having the above-described composition as a positive electrode active material, and the (003) plane of the lithium nickel composite oxide. And (104) plane diffraction peak intensity ratio I _{(003) / (104)} , (003) plane half width FWHM ₍₀₀₃₎ , average secondary particle diameter (D50), and specific surface area are within the scope of the present invention. By this, as demonstrated in the Example mentioned later, all of initial stage charge / discharge efficiency, discharge capacity, and cycling characteristics can be improved. In addition, the lithium ion secondary battery according to an embodiment of the present invention may further include another material as the positive electrode active material in addition to the above-described lithium nickel composite oxide having a high Ni ratio.

Further, the lithium nickel composite oxide of high Ni ratio in accordance with an embodiment of the present invention, the diffraction peak intensity _I (003) plane in X-ray diffraction _(003), (104) plane of the diffraction peak intensity _{I (104 )} I _{(003) / (104)} is 1.05 or more and 1.25 or less. As demonstrated in the examples described later, when the diffraction peak intensity ratio I _{(003) / (104)} is a value within these ranges, the discharge capacity, initial charge / discharge efficiency, and cycle characteristics are improved.

The diffraction peak intensity ratio I _{(003) / (104)} of the (003) plane and the (104) plane is a parameter serving as an index of crystallinity of the lithium nickel composite oxide, and the diffraction peak intensity ratio I _{(003) / ( The} higher the ₁₀₄₎ , the higher the crystallinity and the less likely cation mixing occurs. That is, when the diffraction peak intensity ratio I _{(003) / (104)} between the (003) plane and the (104) plane is less than 1.05, a large amount of cation mixing occurs in the lithium nickel composite oxide. Characteristics and initial charge / discharge efficiency are reduced. On the other hand, when the diffraction peak intensity ratio I _{(003) / (104) of} the (003) plane and the (104) plane exceeds 1.25, the crystallinity of the lithium nickel composite oxide becomes too high, so that the discharge capacity decreases. To do.

Further, in the lithium nickel composite oxide having a high Ni ratio according to an embodiment of the present invention, the half width FWHM ₍₀₀₃₎ of the (003) plane in X-ray diffraction is 0.12 or more and 0.155 or less. As demonstrated in the examples described later, when the half-value width FWHM ₍₀₀₃₎ of the (003) plane is a value within these ranges, the discharge capacity, the initial charge / discharge efficiency, and the cycle characteristics are improved. Specifically, when the half width FWHM ₍₀₀₃₎ of the (003) plane is less than 0.12, the discharge capacity, initial charge / discharge efficiency, and cycle characteristics are degraded. On the other hand, when the half width FWHM ₍₀₀₃₎ of the (003) plane exceeds 0.155, the cycle characteristics and the initial charge / discharge efficiency are lowered.

The diffraction peak intensity ratio I _{(003) / (104)} and the half width FWHM ₍₀₀₃₎ of the (003) plane described above are X of the lithium nickel composite oxide having a high Ni ratio according to an embodiment of the present invention. It is possible to calculate from a line diffraction pattern (pattern). The X-ray diffraction pattern of the lithium nickel composite oxide having a high Ni ratio according to an embodiment of the present invention can be measured, for example, by a known X-ray diffraction measurement method.

  Moreover, the lithium nickel composite oxide having a high Ni ratio according to an embodiment of the present invention exists as secondary particles in which fine primary particles are aggregated, and the average particle diameter (D50) of the secondary particles is 3 μm or more and 9 μm or less. As demonstrated in the examples described later, when the average secondary particle diameter (D50) is a value within these ranges, the initial charge / discharge efficiency, the discharge capacity, and the cycle characteristics are improved. Specifically, when the average secondary particle diameter (D50) of the lithium nickel composite oxide having a high Ni ratio is less than 3 μm, the discharge capacity, initial charge / discharge efficiency, and cycle characteristics are deteriorated. On the other hand, when the average secondary particle diameter (D50) of the lithium nickel composite oxide having a high Ni ratio exceeds 9 μm, the cycle characteristics are significantly deteriorated.

  Here, D50 means a particle size with an integrated value of 50% in the particle size distribution, and is also called a median diameter. The particle size distribution for calculating D50 of the secondary particles can be measured by a known measurement method, for example, a measurement method using a laser diffraction / scattering method. In one embodiment of the present invention, the particle diameter of the secondary particle is a diameter when the secondary particle is regarded as a sphere.

Furthermore, the high nickel ratio lithium nickel composite oxide according to an embodiment of the present invention has a specific surface area of 0.38 m ² / g or more and 1.05 m ² / g or less. As demonstrated in the examples described later, the initial charge / discharge efficiency, the discharge capacity, and the cycle characteristics are improved when the specific surface area is a value within these ranges (measured values of the examples + measurement error 10%). . Specifically, when the specific surface area of the lithium nickel composite oxide having a high Ni ratio is less than 0.38 m ² / g, the discharge capacity, initial charge / discharge efficiency, and cycle characteristics are degraded. On the other hand, when the specific surface area of the lithium nickel composite oxide having a high Ni ratio exceeds 1.05 m ² / g, the cycle characteristics are significantly lowered. Here, the specific surface area can be measured by a known measurement method such as a nitrogen adsorption method.

  The content of the lithium nickel composite oxide having a high Ni ratio is not particularly limited, and may be any content as long as it is applied to the positive electrode active material layer of the conventional lithium ion secondary battery.

  Examples of the conductive agent include carbon black such as ketjen black and acetylene black, natural graphite, and artificial graphite. In addition, a conductive agent will not be restrict | limited especially if it is for improving the electroconductivity of a positive electrode. The content of the conductive agent is not particularly limited, and may be any content as long as it is applied to the positive electrode active material layer of the lithium ion secondary battery.

  Examples of the binder include polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butylene rubber, acrylonitrile butadiene rubber, and acrylonitrile butadiene rubber. ), Fluoroelastomer, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, and the like. The binder is not particularly limited as long as it can bind the positive electrode active material and the conductive agent onto the current collector 21. Further, the content of the binder is not particularly limited, and may be any content as long as it is applied to the positive electrode active material layer of the lithium ion secondary battery.

  The positive electrode active material layer 22 includes, for example, a slurry in which a positive electrode active material, a conductive agent, and a binder are dispersed in a suitable organic solvent (for example, N-methyl-2-pyrrolidone). slurry) is applied onto the current collector 21, dried and rolled.

The negative electrode 30 includes a current collector 31 and a negative electrode active material layer 32. The current collector 31 is made of, for example, copper (Cu), nickel (Ni), or the like. Here, as long as the negative electrode active material layer 32 is used as a negative electrode active material layer of a lithium ion secondary battery, what kind of thing may be sufficient as it. For example, the negative electrode active material layer 32 includes a negative electrode active material, and may further include a binder. Examples of the negative electrode active material include graphite active materials (artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, etc.), silicon (Si), tin (Sn), or oxides thereof. A mixture of fine particles of graphite and a graphite active material, fine particles of silicon or tin, alloys based on silicon or tin, and titanium oxide (TiO _x ) compounds such as Li ₄ Ti ₅ O ₁₂ can be used. . Note that the oxide of silicon is represented by SiO _x (0 ≦ x ≦ 2). In addition to these, for example, metallic lithium can be used as the negative electrode active material. Further, as the binder, the same binder as that constituting the positive electrode active material layer 22 can be used. Note that the mass ratio between the negative electrode active material and the binder is not particularly limited, and the mass ratio employed in the conventional lithium ion secondary battery is also applicable in the present invention.

Separator layer 40 includes a separator and an electrolytic solution. The separator is not particularly limited, and any separator can be used as long as it is used as a separator for a lithium ion secondary battery. As the separator, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. The separator may be coated with an inorganic material such as Al ₂ O ₃ or SiO ₂ . Examples of the material constituting the separator include, for example, polyolefin resins represented by polyethylene, polypropylene, and the like, polyethylene terephthalate, and polybutylene terephthalate. Polyester resin, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-perfluorovinylether (perfluorovinylether) Polymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone (Hexafluoroacetone) copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetra Fluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-ethylene-tetra It can be used Ruoroechiren copolymer. The porosity of the separator is not particularly limited, and the porosity of the separator of the lithium ion secondary battery can be arbitrarily applied.

  As the electrolytic solution, the same non-aqueous electrolytic solution conventionally used for lithium secondary batteries can be used without any particular limitation. Here, the electrolytic solution has a composition in which an electrolyte salt is contained in a non-aqueous solvent. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, vinylene carbonate and the like. ); Cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate linear carbonates such as ethyl carbonate; chain esters such as methyl formate, methyl acetate, methyl butyrate; tetrahydrofuran or its derivatives; 3-dioxane (1,3-dioxane), 1,4-dioxane (1,4-dioxane), 1,2-dimethoxyethane (1,2-dioxyethane), 1,4-dibutoxyethane (1,4- ethers such as dibutoxyether and methyldiglyme; acetonitrile, benzonitrile (ben) nitriles such as zontrile; dioxolane or a derivative thereof; ethylene sulfide, sulfolane, sultone, a derivative thereof, or the like alone, or a mixture of two or more thereof However, the present invention is not limited to these.

Examples of the electrolyte salt include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO _4. , Inorganic ion salts containing one of lithium (Li), sodium (Na) or potassium (K), such as KSCN, LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NC _{lO 4, (n-C 4} H 9) 4 NI, (C 2 H 5) 4 N-maleate, (C 2 H 5) 4 N-benzoate, (C 2 H 5) 4 N-phtalate, stearyl acid Organic ion salts such as lithium (lithium stearyl sulfate), lithium octyl sulfonate (lithium octyl sulfate), lithium dodecylbenzene sulfonate (lithium dodecylbenzene sulfate), and the like can be used. These ionic compounds can be used alone or in admixture of two or more. Further, the concentration of the electrolyte salt may be the same as that of the nonaqueous electrolytic solution used in the conventional lithium secondary battery, and is not particularly limited. In the present invention, an electrolytic solution containing an appropriate lithium compound (electrolyte salt) at a concentration of about 0.5 to 2.0 mol / L can be used.

<3. Manufacturing method of lithium ion secondary battery>
[3-1. Method for producing lithium nickel composite oxide with high Ni ratio]
Next, a method for producing a lithium nickel composite oxide having a high Ni ratio according to an embodiment of the present invention will be described. Although the manufacturing method of the lithium nickel composite oxide which concerns on one Embodiment of this invention is not restrict | limited in particular, For example, a coprecipitation method can be used. Below, an example is given and demonstrated about the manufacturing method of lithium nickel complex oxide using this coprecipitation method.

First, nickel sulfate hexahydrate (NiSO ₄ · 6H ₂ O), cobalt sulfate pentahydrate (CoSO ₄ · 5H ₂ O), and a compound containing metal element M are dissolved in ion-exchanged water to obtain a mixed aqueous solution. Manufacturing. Here, the total mass of the compound including nickel sulfate hexahydrate, cobalt sulfate pentahydrate, and metal element M may be, for example, about 20% by mass with respect to the total mass of the mixed aqueous solution. Further, the nickel sulfate hexahydrate, cobalt sulfate pentahydrate, and the compound containing the metal element M are mixed so that the mole ratio of each element of Ni, Co, and M becomes a desired value. . In addition, the molar ratio of each element is determined according to the composition of the lithium nickel composite oxide to be produced. For example, when manufacturing LiNi _0.8 Co _0.15 Al _0.05 O ₂ , the molar ratio of each element Ni: Co: Al is 80: 15: 5.

  The metal element M is, for example, from the group consisting of Al, Mn, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. One or more elements selected. Moreover, the compound containing the metal element M is, for example, various salts such as sulfate and nitrate of the metal element M, oxides, hydroxides, and the like.

  In addition, a predetermined amount (for example, 500 ml) of ion exchange water is added to the reaction layer, and the temperature of this ion exchange water is maintained at 50 ° C. Hereinafter, the aqueous solution in the reaction layer is referred to as a reaction layer aqueous solution. Next, dissolved oxygen is removed by bubbling ion exchange water with an inert gas such as nitrogen.

  Here, while stirring the reaction layer aqueous solution and maintaining the temperature of the reaction layer aqueous solution at 50 ° C., the above-described mixed aqueous solution is dropped into the reaction layer aqueous solution. The speed of dropping is not particularly limited, but if it is too fast, a uniform precursor (coprecipitated hydroxide salt) may not be obtained. For example, the dropping speed may be about 3 ml / min.

  Further, a saturated NaOH aqueous solution in addition to the mixed aqueous solution is dropped into the reaction layer aqueous solution in an excessive amount relative to Ni and Co in the mixed aqueous solution. In addition, in this dripping, pH of reaction layer aqueous solution is maintained at 11.5, and temperature is maintained at 50 degreeC. This process is performed for a predetermined stirring time (* 2) at a predetermined stirring speed (* 1), for example. Thereby, the hydroxide salt of each metal element co-precipitates.

  Subsequently, solid-liquid separation (for example, suction filtration) is performed, the coprecipitated hydroxide salt is taken out from the aqueous reaction layer solution, and the taken out coprecipitated hydroxide salt is washed with ion-exchanged water. Further, the coprecipitated hydroxide salt is vacuum dried. The temperature at this time may be about 100 ° C., for example, and the drying time may be about 10 hours, for example.

Next, the dried coprecipitated hydroxide salt is pulverized for several minutes in a mortar to obtain a dry powder. And mixed powder is produced | generated by mixing dry powder and lithium hydroxide (LiOH). Here, the molar ratio between Li and Ni + Mn + M (= Me) is determined according to the composition of the lithium nickel composite oxide. For example, when producing LiNi _0.8 Co _0.15 Al _0.05 O ₂ , the molar ratio Li: Me between Li and Me is 1.0: 1.0.

Further, the mixed powder is fired in an oxygen atmosphere at a predetermined firing time (* 3) and a firing temperature (* 4). Thereby, a lithium nickel composite oxide with a high Ni ratio is produced. The lithium nickel composite oxide having a high Ni ratio according to an embodiment of the present invention manufactured by the above method has a diffraction peak intensity ratio I _{(003) / (104) 2} , (003) plane and (104) plane ( 003) FWHM ₍₀₀₃₎ , average secondary particle diameter (D50), and specific surface area are values within a predetermined range specified in the present invention.

The various parameters of the lithium nickel composite oxide with a high Ni ratio can be adjusted by * 1 stirring speed, * 2 stirring time, * 3 firing time, * 4 firing temperature, and the like. Among these, it is possible to adjust various parameters depending on the firing temperature. Specifically, as the firing temperature increases, the diffraction peak intensity ratio I _{(003) / (104)} between the (003) plane and the (104) plane increases, and the half-value width FWHM ₍₀₀₃₎ of the (003) plane decreases. Tend to. For example, the stirring speed is 4 to 5 m / s at the peripheral speed, the stirring time is 10 hours, and the firing time is 10 hours. The lithium nickel composite oxide having a high Ni ratio according to the embodiment can be manufactured.

[3-2. Manufacturing method of lithium ion secondary battery]
Then, the manufacturing method of the lithium ion secondary battery 10 is demonstrated. In the present invention, the lithium ion secondary battery is manufactured by the same manufacturing method as that of the conventional lithium ion secondary battery except that the positive electrode active material is changed to the lithium nickel composite oxide having a high Ni ratio by the manufacturing method described above. 10 can be manufactured. A method of manufacturing the lithium ion secondary battery 10 according to an embodiment of the present invention is schematically as follows.

  The positive electrode 20 is manufactured as follows. First, a slurry is formed by dispersing a mixture of a positive electrode active material, a conductive agent, and a binder in a desired ratio in an organic solvent (for example, N-methyl-2-pyrrolidone). Next, the positive electrode active material layer 22 is formed by forming (for example, coating) the slurry on the current collector 21 and drying the slurry. The coating method is not particularly limited, and for example, a knife coater method, a gravure coater method, or the like may be used. The following coating steps are also performed by the same method. Furthermore, the positive electrode active material layer 22 is compressed to a desired thickness by a compressor. Thereby, the positive electrode 20 is manufactured. Here, the thickness of the positive electrode active material layer 22 is not particularly limited as long as the positive electrode active material layer of the lithium ion secondary battery has a thickness.

  The negative electrode 30 is also manufactured in the same manner as the positive electrode 20. First, a slurry is formed by dispersing a mixture of a negative electrode active material and a binder in a desired ratio in an organic solvent (for example, N-methyl-2-pyrrolidone). Next, the negative electrode active material layer 32 is formed by forming (for example, coating) the slurry on the current collector 31 and drying the slurry. Further, the negative electrode active material layer 32 is compressed to a desired thickness by a compressor. Thereby, the negative electrode 30 is manufactured. Here, the thickness of the negative electrode active material layer 32 is not particularly limited as long as the negative electrode active material layer of the lithium ion secondary battery has a thickness. Further, when metal lithium is used for the negative electrode active material layer 32, a metal lithium foil may be stacked on the current collector 31.

  Subsequently, the electrode structure is manufactured by sandwiching the separator 40 between the positive electrode 20 and the negative electrode 30. Next, the electrode structure is processed into a desired shape (for example, a cylindrical shape, a square shape, a laminate shape, a button shape, etc.) and inserted into a container of the shape. Further, by injecting an electrolytic solution having a desired composition into the container, each pore in the separator 40 is impregnated with the electrolytic solution. Thereby, the lithium ion secondary battery 10 is manufactured.

  Below, the Example which concerns on one Embodiment of this invention is described.

(Production of lithium nickel composite oxides according to Examples 1 to 3 and Comparative Examples 1 to 4)
Nickel sulfate hexahydrate (NiSO ₄ · 6H ₂ O), cobalt sulfate pentahydrate (CoSO ₄ · 5H ₂ O), and aluminum nitrate (Al (NO ₃ ) ₃ ) are dissolved in ion-exchanged water and mixed. An aqueous solution was prepared. Here, the total mass of nickel sulfate hexahydrate, cobalt sulfate pentahydrate, and aluminum nitrate was 20 mass% with respect to the total mass of the mixed aqueous solution. Further, the mixing ratio of nickel sulfate hexahydrate, cobalt sulfate pentahydrate, and aluminum nitrate is such that the molar ratio of each element of Ni, Co, and Al is Ni: Co: Al = It mixed so that it might become 80-84: 15: 1-5.

  Moreover, 500 ml of ion exchange water was added to the reaction layer, and the temperature of this ion exchange water was maintained at 50 ° C. Next, dissolved oxygen was removed by bubbling ion exchange water with nitrogen gas.

  Then, while stirring the reaction layer aqueous solution and maintaining the temperature of the reaction layer aqueous solution at 50 ° C., the above-described mixed aqueous solution was dropped into the reaction layer aqueous solution at a rate of 3 ml / min.

  In addition to the mixed aqueous solution, an excessive amount of saturated NaOH aqueous solution was dropped into the reaction bath aqueous solution with respect to Ni and Co in the mixed aqueous solution, and the pH of the aqueous reaction layer solution was maintained at 11.5 and the temperature was maintained at 50 ° C. Here, the stirring speed was 4 to 5 m / s in peripheral speed, and the stirring time was 10 hours. Thereby, the hydroxide salt of each metal element coprecipitated.

  Subsequently, the coprecipitated hydroxide salt was taken out from the aqueous reaction layer solution by suction filtration, and the coprecipitated hydroxide salt was washed with ion-exchanged water. The coprecipitated hydroxide salt was then vacuum dried. The temperature for vacuum drying was 100 ° C., and the drying time was 10 hours.

  Next, the dried coprecipitated hydroxide salt was pulverized for several minutes in a mortar to obtain a dry powder. And mixed powder was produced | generated by mixing dry powder and lithium hydroxide (LiOH). Here, the molar ratio between Li and Me (= Ni + Co + Al) was 1.0: 1.0. Further, the mixed powder was fired in an oxygen atmosphere with a firing time of 10 hours and a firing temperature of 700 ° C. to 800 ° C.

(Production of lithium nickel composite oxide according to Examples 4 and 5 and Comparative Examples 5 and 6)
Examples 1 to 3 and Comparative Examples 1 to 1 described above were prepared except that the mixed aqueous solution was produced with nickel sulfate hexahydrate, cobalt sulfate pentahydrate, and manganese sulfate heptahydrate (MnSO ₄ .7H ₂ O). 4 were used to produce lithium nickel composite oxides according to Examples 4 and 5 and Comparative Examples 5 and 6. The mixing ratio of nickel sulfate hexahydrate, cobalt sulfate pentahydrate, and manganese sulfate heptahydrate is such that the molar ratio of Ni, Co, and Mn elements is Ni: Co: Mn = 80 to 85. : 10-15: Mixed so as to be 4-10.

(Measurement of lithium nickel composite oxide according to Examples 1 to 5 and Comparative Examples 1 to 6)
When the X-ray diffraction test was performed on the lithium nickel composite oxides according to Examples 1 to 5 and Comparative Examples 1 to 6 manufactured above, a peak on the (003) plane was detected near the diffraction angle (2θ) of 18 °. A peak on the (104) plane was detected near a diffraction angle (2θ) of 44 °. Based on this peak, the diffraction peak intensity ratio I _{(003) / (104) of} the (003) plane and the ( ₁₀₄ ) plane and the half width FWHM ₍₀₀₃₎ of the (003) plane were calculated.

  Moreover, the average secondary particle diameter (D50) of the manufactured lithium nickel composite oxide was measured with a laser diffraction / scattering particle size distribution meter (Microtrac MT3000 manufactured by Nikkiso Co., Ltd.). Furthermore, the specific surface area of the manufactured lithium nickel composite oxide was measured by a nitrogen adsorption method.

In the lithium nickel composite oxides according to Examples 1 to 5 and Comparative Examples 1 to 6, the diffraction peak intensity ratio I _{(003) / (104)} and (003) of the (003) plane and (104) plane The measurement results of the half width FWHM ₍₀₀₃₎ , the average secondary particle diameter (D50), and the specific surface area will be described later in Tables 2 and 3 together with the charge / discharge evaluation results.

(Manufacture of lithium ion secondary batteries)
Further, a lithium ion secondary battery was manufactured as follows. First, the lithium nickel composite oxide, acetylene black, and polyvinylidene fluoride produced by the above-described production methods were mixed at a mass ratio of 95: 2: 3. Then, this mixture was dispersed in N-methyl-2-pyrrolidone to form a slurry.

  Then, the positive electrode was manufactured by coating the slurry on an aluminum foil as a current collector and drying it to form a positive electrode active material layer.

  The negative electrode was manufactured by attaching metallic lithium to a current collector.

The separator is a porous polyethylene film (thickness 12 μm) whose front and back surfaces are coated with a coating liquid in which Al ₂ O ₃ fine particles and PVdF (polyvinylidene fluoride) are mixed at a mass ratio of 70:30. Was used. An electrode structure was produced by sandwiching the separator between the positive electrode and the negative electrode. The electrode structure was processed into a 2032 coin half cell.

On the other hand, lithium hexafluorophosphate (LiPF ₆ ) was dissolved to a concentration of 1.3 mol / L in a non-aqueous solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 3: 7, and the electrolyte solution was Manufactured. The separator was impregnated with the electrolytic solution by injecting the manufactured electrolytic solution into a 2032 coin half cell. Thereby, the lithium ion secondary battery was manufactured.

(Charge / discharge evaluation)
The charge / discharge evaluation of the lithium ion secondary batteries according to Examples 1 to 5 and Comparative Examples 1 to 6 manufactured by the method described above was performed. Specifically, a cycle test was conducted at the charge / discharge rate (rate) and cut-off voltage shown in Table 1 below.

  In Table 1, CC-CV indicates constant current constant voltage charging, and CC indicates constant current discharging. The cut-off voltage indicates a voltage at the end of charging and a voltage at the end of discharging. For example, charging in the first cycle was performed until the voltage of the lithium ion secondary battery reached 4.3 (V), and discharging was performed until the voltage of the lithium ion secondary battery reached 3.0 (V). It shows that.

  The results of such charge / discharge evaluation are shown in Tables 2 and 3.

  In Tables 2 and 3, the initial charge / discharge efficiency is a numerical value obtained by dividing the discharge capacity at the first cycle by the charge capacity at the first cycle. The discharge capacity is the discharge capacity at the second cycle. Furthermore, the capacity retention ratio is a value obtained by dividing the discharge capacity at the 52nd cycle by the discharge capacity for the third cycle.

First, in Table 2, as a positive electrode active _material, the measurement results of Examples 1 to 3 and Comparative Examples 1 to 4 using a lithium nickel composite oxide having a composition of _{LiNi x Co y Al z O 2} . The values of x, y, and z in each example and comparative example are also shown in Table 2.

Referring to Table 2, in Examples 1 to 3, the diffraction peak intensity ratio I _{(003) / (104)} , the half-width FWHM ₍₀₀₃₎ , the average secondary particle diameter (D50), and the specific surface area are within the scope of the present invention. It can be seen that the discharge capacity, the initial charge / discharge efficiency, and the cycle characteristics are all high.

On the other hand, in Comparative Examples 1 and 3, the diffraction peak intensity ratio I _{(003) / (104)} and the full width at half maximum FWHM ₍₀₀₃₎ are out of the scope of the present invention, and the cycle characteristics are deteriorated. In Comparative Example 2, D50, specific surface area, and full width at half maximum ₍ FWHM _{) (003)} are out of the scope of the present invention, and the discharge capacity, initial charge / discharge efficiency, and cycle characteristics are reduced. Further, in Comparative Example 4, D50 and diffraction peak intensity ratio I _{(003) / (104)} are out of the scope of the present invention, and the discharge capacity, initial charge / discharge efficiency, and cycle characteristics are reduced.

Next, in Table 3, measurement results of Examples 4 and 5 and Comparative Examples 5 and 6 using a lithium nickel composite oxide having a composition of LiNi _x Co _y Mn _z O ₂ as the positive electrode active material are shown. The values of x, y, and z in each example and comparative example are also shown in Table 3.

Referring to Table 3, Examples 4 and 5 show that the diffraction peak intensity ratio I _{(003) / (104)} , the full width at half maximum FWHM ₍₀₀₃₎ , the average secondary particle diameter (D50), and the specific surface area are within the scope of the present invention. It can be seen that the discharge capacity, the initial charge / discharge efficiency, and the cycle characteristics are all high.

On the other hand, in Comparative Example 5, the diffraction peak intensity ratio I _{(003) / (104)} and the full width at half maximum FWHM ₍₀₀₃₎ are out of the scope of the present invention, and the initial charge / discharge efficiency and the cycle characteristics are deteriorated. Further, in Comparative Example 6, the half width FWHM ₍₀₀₃₎ is out of the scope of the present invention, and the initial charge / discharge efficiency and the cycle characteristics are deteriorated.

As can be seen from the above results, according to one embodiment of the present invention, in the positive electrode active material containing the lithium nickel composite oxide having a high Ni ratio, the diffraction peak intensity I ₍₀₀₃ ) on the (003) plane in X-ray diffraction. ₎ And (104) plane diffraction peak intensity I ₍₁₀₄₎ ratio I _{(003) / (104)} is 1.05 or more and 1.25 or less, and (003) plane half width FWHM ₍₀₀₃₎ Of 0.12 to 0.155, an average secondary particle diameter (D50) of 3 μm to 9 μm, and a specific surface area of 0.38 m ² / g to 1.05 m ² / g. Thus, all of initial charge / discharge efficiency, discharge capacity, and cycle characteristics can be improved.

In particular, according to one embodiment of the present invention, in the lithium nickel composite oxide having a Ni ratio of 80% or more, the diffraction peak intensity ratio I _{(003) / (104)} between the (003) plane and the (104) plane is compared. Even when the average secondary particle size (D50), the half-value width FWHM _{(003) of the} (003) plane, and the specific surface area are within the scope of the present invention, the discharge capacity, initial charge / discharge efficiency and It is possible to improve all of the cycle characteristics.

  The preferred embodiment of the present invention has been described in detail above with reference to the accompanying drawings, but the present invention is not limited to this example. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery 20 Positive electrode 21 Current collector 22 Positive electrode active material layer 30 Negative electrode 31 Current collector 32 Negative electrode active material layer 40 Separator layer

Claims (2)

In X-ray diffraction, (003) plane and the diffraction peak intensity _{I (003)} of (104) plane of the diffraction peak intensity _{I (104)} ratio of _{I (003) / (104)} is 1.05 or more 1. 25 or less, and the (003) plane half-width FWHM ₍₀₀₃₎ is 0.12 or more and 0.155 or less, and the average secondary particle diameter D50 is 3 μm or more and 9 μm or less, and a specific surface area, and at 0.38 m ² / g or more 1.05 m ² / g or less,
A positive electrode active material comprising a lithium composite oxide having a composition represented by the following general formula (1).
(Chemical formula 1)
Li _a Ni _x Co _y M _z O ₂ (1)
In the general formula (1), M is Al,
a is 0.20 ≦ a ≦ 1.20,
x is 0.80 ≦ x <1.00,
y is 0 <y ≦ 0.15 ,
z is 0 <z ≦ 0.05 ,
x + y + z = 1. A lithium ion secondary battery comprising the positive electrode active material according to claim 1 .

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