JP2015115105A - Lithium ion secondary battery, production method of positive electrode active material for lithium ion secondary battery, and manufacturing method of positive electrode for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress gas generation during high temperature storage.SOLUTION: A lithium ion secondary battery includes a positive electrode containing lithium nickel composite oxide particles of high Ni ratio, and a separator. On the surface of the lithium composite oxide particles, a coating layer containing at least one oxo acid ion represented by any one of general formulae (2)-(6) is formed, and at least any one of the positive electrode and separator has a coating layer containing at least an inorganic filler. In the general formulae (2)-(6), X is any one of P or Si, n is a natural number of 7 or less, and m is a natural number.

Description

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

  In recent years, a technique using a lithium nickel composite oxide containing nickel as a positive electrode active material that achieves a high potential and a high capacity in a lithium ion secondary battery has been proposed.

  Here, in a lithium ion secondary battery using a lithium nickel composite oxide as a positive electrode active material, a large amount of gas is generated when stored at a high temperature in a fully charged state, and the internal pressure in the battery increases. It became a problem.

For example, Patent Document 1 discloses that lithium carbonate (Li ₂ CO ₃ ) produced by a reaction between lithium hydroxide (LiOH) remaining on the surface of a lithium nickel composite oxide and carbon dioxide (CO ₂ ) has a high temperature. It is described that gas is sometimes generated. Patent Document 1 discloses a technique for reducing the above-described lithium compound, which is a cause of gas generation existing on the surface, and suppressing gas generation by cleaning the lithium nickel composite oxide.

JP 2013-026199 A

  However, the technique described in Patent Document 1 has a problem that the initial discharge capacity of the lithium ion secondary battery is reduced because the lithium (Li) of the lithium nickel composite oxide is reduced by the cleaning. . Further, in the lithium nickel composite oxide after cleaning, a phenomenon that nickel (Ni) is mixed into a Li site (that is, cation mixing phenomenon) occurs in a large amount. There was also a problem that the cycle characteristics were also lowered.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is a new and improved lithium capable of suppressing gas generation without deteriorating battery characteristics. An object of the present invention is to provide an ion secondary battery, a method for producing a positive electrode active material for a lithium ion secondary battery, and a method for producing a positive electrode for a lithium ion secondary battery.

In order to solve the above-described problems, according to an aspect of the present invention, the lithium battery includes a positive electrode including lithium composite oxide particles having a composition represented by the following general formula (1), and a separator. The composite oxide particles have a coating layer containing at least one oxo acid ion represented by any one of the following general formulas (2) to (6) formed on the surface, and at least one of the positive electrode and the separator. On the other hand, a lithium ion secondary battery having a coating layer including an inorganic filler is provided.
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.
In the general formulas (2) to (6), X is either P or Si, n is a natural number of 7 or less, and m is a natural number.

  According to this aspect, the lithium ion secondary battery according to one embodiment of the present invention can suppress gas generation when stored at a high temperature in a fully charged state.

  The coverage of the coating layer may be 1% or more and 20% or less.

  According to this aspect, the lithium ion secondary battery according to an embodiment of the present invention can further suppress gas generation when stored at a high temperature in a fully charged state.

The inorganic filler may include at least one of Mg (OH) ₂ and Al ₂ O ₃ .

  According to this aspect, the lithium ion secondary battery according to an embodiment of the present invention can further suppress gas generation when stored at a high temperature in a fully charged state.

  The separator may have a coating layer containing the inorganic filler.

  According to this aspect, the lithium ion secondary battery according to an embodiment of the present invention can further suppress gas generation when stored at a high temperature in a fully charged state.

  The lithium ion secondary battery may further include a negative electrode including graphite.

  According to this aspect, the lithium ion secondary battery according to an embodiment of the present invention can suppress gas generation when stored at a high temperature in a fully charged state while maintaining battery characteristics.

In order to solve the above problem, according to another aspect of the present invention, a mechanical shearing force is applied to the surface of the lithium composite oxide particles having the composition represented by the following general formula (1). A step (step) of forming a coating layer having at least one selected from the group consisting of oxo acid ions represented by any one of the following general formulas (2) to (6); And a step of heating the lithium composite oxide particles. A method for producing a positive electrode active material for a lithium ion secondary battery is provided.
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.
In the general formulas (2) to (4), X is either P or Si, n is a natural number of 7 or less, and m is a natural number.

  According to this aspect, it is possible to produce a positive electrode active material for a lithium ion secondary battery that can suppress gas generation when stored at a high temperature in a fully charged state.

  The step of heating the lithium composite oxide particles may be performed in an oxidizing atmosphere.

  According to this aspect, it is possible to manufacture a positive electrode active material for a lithium ion secondary battery that can further suppress gas generation when stored at a high temperature in a fully charged state.

  Furthermore, in order to solve the above problem, according to another aspect of the present invention, the method includes a step of applying a positive electrode active material for a lithium ion secondary battery manufactured by the above manufacturing method to a current collector, The step of applying to the electric body is performed at a dew point temperature of −40 ° C. or lower, and a method for producing a positive electrode for a lithium ion secondary battery is provided.

  According to this aspect, it is possible to manufacture a lithium ion secondary battery capable of suppressing gas generation when stored at a high temperature in a fully charged state.

  As described above, according to the present invention, it is possible to suppress gas generation without deteriorating the battery characteristics of the lithium ion secondary battery.

It is explanatory drawing explaining the structure of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is the graph which made each histogram the amount of generated gas of Example 1, Comparative Examples 1 and 2, and a reference example. It is the graph which plotted the discharge capacity with respect to each C rate in Example 13, Comparative example 3, and a reference example. 4 is an EDX image of Mo of the lithium nickel composite oxide particles according to Example 1. FIG. 2 is an EDX image of Ni of the lithium nickel composite oxide particles according to Example 1. FIG. 3 is an EDX image of lithium nickel composite oxide particles according to Example 2 with respect to W. FIG. 4 is an EDX image of Ni of the lithium nickel composite oxide particles according to Example 2. FIG.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<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.

  The lithium ion secondary battery which concerns on one Embodiment of this invention contains lithium nickel complex oxide as a positive electrode active material. A lithium ion secondary battery using a lithium nickel composite oxide as a positive electrode active material can realize a high potential and a high discharge capacity. On the other hand, a lithium ion secondary battery using a lithium nickel composite oxide as a positive electrode active material has a problem that a large amount of gas is generated and the internal pressure of the battery rises when stored at a high temperature in a fully charged state. It was.

  In particular, when a lithium nickel composite oxide represented by the following general formula (1) having a high nickel (Ni) ratio is used as the positive electrode active material, the energy density of the lithium ion secondary battery is increased. The above problem was remarkable.

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.

Here, as disclosed in Patent Document 1, as a method for solving the above problems, for example, by washing lithium nickel composite oxide, LiOH, which is an alkali component remaining on the surface, and LiOH A method for removing Li ₂ CO ₃ has been proposed. However, the above method has a problem that the initial discharge capacity of the lithium ion secondary battery is reduced because Li is reduced by washing the lithium nickel composite oxide.

  Therefore, the present inventor has come up with the present invention by examining the above-mentioned problems in detail. The lithium ion secondary battery according to an embodiment of the present invention includes at least an oxoacid ion represented by any one of the following general formulas (2) to (6) on the surface of the lithium nickel composite oxide particle. A coating layer including one or more is formed, and at least one of the positive electrode and the separator has a coating layer including an inorganic filler.

  In the above general formulas (2) to (6), X is either P or Si, n is a natural number of 7 or less, and m is a natural number.

Here, the acid and the compound containing the oxo acid ion act as a strong oxidizing agent. Therefore, in the lithium nickel composite oxide particles having a coating layer containing oxo acid ions on the surface, LiOH and Li ₂ CO ₃ remaining on the surface are oxidized by the heat treatment after the coating layer is formed, and CO ₂ is released. Is done. According to such a configuration, CO ₂ generated in the battery when the lithium ion secondary battery is stored at a high temperature can be released in advance, so that gas generation occurs when the lithium ion secondary battery is stored at a high temperature in a fully charged state. Can be suppressed.

Further, the lithium ion secondary battery according to one embodiment of the present invention removes alkaline components such as LiOH and Li ₂ CO ₃ remaining on the surface by the oxidizing action of the acid or compound containing the oxo acid ion, Li is not reduced. Therefore, according to the lithium ion secondary battery which concerns on one Embodiment of this invention, the fall of initial stage discharge capacity can be prevented.

  Furthermore, the lithium ion secondary battery which concerns on one Embodiment of this invention has a coating layer containing an inorganic filler in at least any one of a positive electrode or a separator. In a general lithium ion secondary battery, when stored at a high temperature in a sufficiently charged state, the electrolytic solution may be oxidized and decomposed on the positive electrode surface to generate gas. In the lithium ion secondary battery according to an embodiment of the present invention, in order to prevent the positive electrode and the separator from coming into direct contact with the coating layer containing the inorganic filler, the electrolyte solution is decomposed at the high oxidation state positive electrode / separator interface. Can be suppressed. Therefore, according to the lithium ion secondary battery which concerns on one Embodiment of this invention, gas generation | occurrence | production at the time of high-temperature storage in a full charge state can be suppressed.

  In particular, in the lithium ion secondary battery according to an embodiment of the present invention, the coating layer containing the oxo acid ion that is an oxidant is formed on the surface of the lithium nickel composite oxide particles, so that the electrolytic solution is decomposed on the surface of the positive electrode. Likely to happen. Therefore, by forming the coating layer containing the inorganic filler described above on the separator, it is possible to more suitably suppress the decomposition of the electrolytic solution.

  As described above, according to the lithium ion secondary battery according to an embodiment of the present invention, gas is generated when stored at a high temperature in a fully charged state while maintaining initial discharge capacity, output characteristics, and charge / discharge cycle characteristics. Can be suppressed.

<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 mentioned 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 as a positive electrode active material, and includes a positive electrode 20, a negative electrode 30, and a 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.

  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). In addition, the lithium ion secondary battery which concerns on one Embodiment of this invention may contain several active material as a positive electrode active material other than lithium nickel complex oxide of a high Ni ratio.

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.

  Moreover, in the lithium ion secondary battery which concerns on one Embodiment of this invention, the particle | grain surface of the lithium nickel complex oxide of the high Ni ratio which has the composition shown above has the following general formula (2)-(6). The coating layer containing the oxo acid ion represented by either is formed.

  Here, in the general formulas (2) to (6), X is either P or Si, n is a natural number of 7 or less, and m is a natural number.

  The oxo acid ions represented by the general formulas (2) to (6) are specifically polyoxo acid ions formed by condensation of oxo acid ions. More specifically, the polyoxoacid ion includes an isopolyacid ion composed of one kind of transition metal ion, and a heteroatom (phosphorus (P), silicon (Si), etc.) in the polyacid skeleton. Heteropoly acid ions included.

  The compounds containing oxo acid ions represented by the general formulas (2) to (6) include, for example, ammonium molybdate, silicotungstic acid, phosphomolybdic acid, It may be ammonium phosphotungstate, ammonium phosphomolybdate, or ammonium metavanadate.

The oxo acid ions represented by the general formulas (2) to (6) have a high oxidation number of the central element because a plurality of oxygen atoms are bonded to each other, and function as a powerful oxidant. Therefore, in the lithium nickel composite oxide particles in which the coating layer containing oxo acid ions represented by the general formulas (2) to (6) is formed, alkali such as LiOH and Li ₂ CO ₃ remaining on the surface by the heat treatment The components are oxidized and a gas such as CO ₂ is released. According to such a configuration, the lithium ion secondary battery according to an embodiment of the present invention can release CO ₂ gas generated when stored at high temperature out of the battery in advance. Gas generation can be suppressed.

Furthermore, the coverage of the coating layer in the lithium nickel composite oxide particles may be 1% or more and 20% or less. As demonstrated in the examples described later, when the coverage of the coating layer is a value within these ranges, gas generation can be further suppressed. For example, when the coating rate of the coating layer is less than 1%, alkali components such as LiOH and Li ₂ CO ₃ present on the surface cannot be oxidized by oxo acid ions, and the amount of gas generated increases. On the other hand, when the coverage of the coating layer exceeds 20%, the entry and exit of lithium ions from the lithium nickel composite oxide particles is hindered by the coating layer, so that battery characteristics such as initial discharge capacity deteriorate.

  Here, the coverage of the coating layer in the lithium nickel composite oxide particles can be measured by, for example, X-ray photoelectron spectroscopy (XPS).

  Specifically, the XPS measurement is performed on the surface of the lithium nickel composite oxide particles coated with the coating layer, and a spectrum for binding energy is obtained. Next, the background is subtracted from the acquired spectrum, and the area of each peak is calculated. Further, which peak corresponds to which element is calculated from the binding energy of each element. For example, the values described in Table 1 below can be used as the binding energy of each element.

  Further, the peak area for each element is corrected by the photoelectron emission efficiency (sensitivity factor) for each element, and the atomic ratio for each element is calculated. Subsequently, the atomic ratio of elements contained in oxo acid ions (excluding oxygen and hetero elements) is included in elements (excluding lithium and oxygen) contained in lithium nickel composite oxide and oxo acid ions. The coverage can be calculated by dividing by the sum of the atomic ratios of the elements (except oxygen and heteroelements).

For example, when the oxoacid ion contained in the coating layer is [Mo ₇ O ₂₄ ] ⁶⁻ and the composition of the lithium nickel composite oxide particles is LiNi _0.8 Co _0.15 Al _0.05 O ₂ , Mo Is divided by the sum of the atomic ratios of Ni, Co, Al, and Mo. Thus, the coverage can be calculated.

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

  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, nickel, or the like.

The negative electrode active material layer 32 may be any material as long as it is used as a negative electrode active material layer of a lithium ion secondary battery. 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.

  In one embodiment of the present invention, the negative electrode active material is more preferably graphite. According to such a configuration, as demonstrated in the examples described later, it is possible to suppress gas generation when stored at a high temperature in a fully charged state while maintaining battery characteristics.

  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 according to one embodiment of the present invention may have a coating layer containing an inorganic filler. Specifically, the coating layer may contain at least one of Mg (OH) _{2 and} Al ₂ O ₃ as an inorganic filler. According to such a configuration, the coating layer containing the inorganic filler prevents the direct contact between the positive electrode and the separator, thereby preventing the oxidation and decomposition of the electrolytic solution generated on the surface of the positive electrode during high temperature storage, and the decomposition generation of the electrolytic solution. It is possible to suppress the generation of gas that is a product.

  Here, the coating layer containing an inorganic filler may be formed on both surfaces of the separator, or may be formed only on one surface of the separator on the positive electrode side. If the coating layer containing an inorganic filler is formed at least on the positive electrode side, direct contact between the positive electrode and the electrolytic solution can be prevented.

  The present invention is not limited to the above examples. For example, the coating layer containing an inorganic filler may be formed on the positive electrode instead of on the separator. In such a case, the coating layer containing the inorganic filler can be formed on both surfaces of the positive electrode, thereby preventing direct contact between the positive electrode and the separator. Needless to say, the coating layer containing the inorganic filler may be formed on both the positive electrode and the separator.

  In addition, the structure except the coating layer of the separator which concerns on one Embodiment of this invention is not restrict | limited in particular. Any separator body according to an embodiment of the present invention can be used as long as it is used as a separator of a lithium ion secondary battery. For example, 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. 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-hexafluoro Acetone (hexafluoroacetone) copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride- Tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-ethylene-teto It can be used fluoroethylene copolymer. Note that 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 (vinyl 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 derivatives thereof; ethylene sulfide, sulfolane, sultone, or derivatives thereof 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, although the molar ratio of each element is determined according to the composition of the lithium nickel composite oxide to be manufactured, for example, when manufacturing LiNi _0.8 Co _0.15 Al _0.05 O ₂ , The molar ratio 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 with respect 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 at a predetermined stirring speed, 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 coprecipitate 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 oxidizing atmosphere at a predetermined firing time and firing temperature. In addition, since Ni in lithium nickel complex oxide is easy to be reduced, the above-described firing is preferably performed in an oxidizing atmosphere. The oxidizing atmosphere is, for example, an oxygen atmosphere. The firing temperature at this time may be, for example, about 700 to 800 ° C., and the firing time may be, for example, about 10 hours.

  Further, a compound containing an oxo acid ion represented by any one of the above general formulas (2) to (6) is added to 100 parts by mass of the fired lithium nickel composite oxide, and the lithium nickel composite oxide A coating layer is formed by depositing on the surface of the particles. Specifically, a method using mechanical shearing force can be used as a method for depositing a compound containing oxo acid ions on the surface of the lithium nickel composite oxide particles. For example, by processing at 3000 rpm for 15 minutes in a powder processing apparatus (NOB MINI manufactured by Hosokawa Micron), a compound containing oxo acid ions is deposited on the surface of lithium nickel composite oxide particles using mechanical shearing force. Can be made. Here, the compound containing an oxo acid ion to be deposited may be an oxo acid or a salt with ammonium ion or the like.

  The method for depositing the compound containing oxo acid ions on the surface of the lithium nickel composite oxide particles is not limited to the above, for example, only mixing the compound containing oxo acid ions and the lithium nickel composite oxide particles. It may be. However, in order to uniformly deposit a compound containing oxo acid ions on the surface of the lithium nickel composite oxide to form a uniform coating layer, it is preferable to deposit using a mechanical shearing force.

Moreover, the addition amount of the compound containing an oxo acid ion can use arbitrary addition amount, but 0.25 mass part or more and 2 mass parts or less are set as 100 mass parts of lithium nickel complex oxides before addition. It is preferable to do. By adding the compound containing oxo acid ions within the above range, the coverage of the coating layer containing oxo acid ions formed on the surface of the lithium nickel composite oxide can be 1% or more and 20% or less. When the coverage is in the above range, the compound containing oxo acid ions can sufficiently oxidize LiOH, Li ₂ CO _{3 and the} like present on the surface of the lithium nickel composite oxide particles, and lithium ions It is more preferable because it does not hinder the entry and exit of.

Subsequently, the lithium nickel composite oxide particles on which the coating layer containing a compound containing oxo acid ions is formed are heat-treated at a heating temperature for a predetermined heating time in an oxidizing atmosphere. In this process, the compound containing oxo acid ions contained in the coating layer of the lithium nickel composite oxide particles is decomposed, and CO ₂ gas is released by oxidizing the alkaline components such as LiOH and Li ₂ CO ₃ remaining on the surface. Let Thereafter, the lithium nickel composite oxide particles are dried.

  Note that since the Ni in the lithium nickel composite oxide is easily reduced, the heat treatment is preferably performed in an oxidizing atmosphere. The oxidizing atmosphere is, for example, an oxygen atmosphere.

In addition, the heating temperature at this time is set to a temperature at which the oxidation reaction on the surface of the lithium nickel composite oxide sufficiently proceeds based on the melting point of the deposited compound containing oxo acid ions. On the other hand, when the heating temperature is too high, the crystal structure of the lithium nickel composite oxide becomes unstable (rock chloride) and the discharge capacity decreases, so that the melting point of the compound containing the deposited oxoacid ion It is desirable not to be too high. Specifically, the temperature is preferably about 100 ° C. higher than the melting point of the deposited compound containing oxoacid ions. For example, when the deposited compound containing an oxo acid ion is (NH ₄ ) ₆ Mo ₇ O ₂₄ (melting point 190 ° C.), the heating temperature may be about 300 ° C. The heating time may be about 4 hours, for example.

  By the above method, producing lithium nickel composite oxide particles in which a coating layer containing an oxo acid ion represented by any one of the general formulas (2) to (6) according to one embodiment of the present invention is formed. Is possible.

[3-2. Manufacturing method of lithium ion secondary battery]
Then, the manufacturing method of the lithium ion secondary battery 10 is demonstrated. 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.

Note that the step of applying the positive electrode active material to the current collector is performed in a dry environment with a dew point temperature of −40 ° C. or lower. When moisture or the like adheres to the positive electrode active material, gas may be generated due to the reaction of moisture or the like with LiOH and Li ₂ CO _{3 on} the surface of the positive electrode active material during high temperature storage. Therefore, it is more preferable that the step of applying the positive electrode active material to the current collector is performed in a dry environment having a dew point temperature of −40 ° C. or less with a very low water content.

  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, both surfaces of the separator are coated with a coating liquid in which an inorganic filler and polyvinylidene fluoride are mixed at a mass ratio of 70:30. An electrode structure is manufactured by sandwiching the separator 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. Furthermore, by injecting an electrolytic solution having a desired composition into the container, each pore in the separator 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.

(Example 1)
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: 15: 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. Furthermore, this mixed powder was fired under an oxygen atmosphere with a firing time of 10 hours and a firing temperature adjusted in the range of 700 ° C to 800 ° C.

Furthermore, 1 part by mass of ammonium molybdate ((NH ₄ ) ₆ Mo ₇ O ₂₄ ) is added to 100 parts by mass of the lithium nickel composite oxide after firing, and a powder processing apparatus (NOB MINI manufactured by Hosokawa Micron) And 3000 rpm for 15 minutes to deposit ammonium molybdate on the surface of the lithium nickel composite oxide particles to form a coating layer.

  Subsequently, the lithium nickel composite oxide particles after the coating layer was formed were heated in an oxygen atmosphere at a heating time of 4 hours and a heating temperature of 300 ° C. Thereafter, the lithium nickel composite oxide particles were dried. Here, the average secondary particle diameter (D50) of the produced lithium nickel composite oxide was measured with a laser diffraction / scattering particle size distribution meter (Microtrac MT3000 manufactured by Nikkiso Co., Ltd.) and defined as the average particle diameter. The average secondary particle diameter (D50) means a particle diameter at which the integrated value is 50% in the particle diameter distribution of the diameter when the secondary particles of the lithium nickel composite oxide are regarded as spheres. The average particle diameter of the lithium nickel composite oxide produced in Example 1 was 7 μm.

  Subsequently, the lithium nickel composite oxide produced above, acetylene black, and polyvinylidene fluoride were mixed at a mass ratio of 95: 2: 3. Then, this mixture was dispersed in N-methyl-2-pyrrolidone to form a slurry.

  Subsequently, the positive electrode was manufactured by coating the slurry on an aluminum foil as a current collector in a dry environment having a dew point temperature of −40 ° C. or less, and drying to form a positive electrode active material layer.

  The negative electrode was manufactured using graphite.

The separator is a porous polyethylene film (thickness 12 μm) coated on both sides with a coating solution in which Mg (OH) ₂ and PVdF (polyvinylidene fluoride) are mixed at a mass ratio of 70:30. Using. The thickness of the coating layer was 2 μm. An electrode structure was produced by sandwiching the separator between the positive electrode and the negative electrode. Moreover, the electrode structure was processed into a shape that can be accommodated in a pouch full cell and inserted into the pouch full 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 pouring the manufactured electrolytic solution into the pouch full cell. Thus, a lithium ion secondary battery according to Example 1 was manufactured.

(Examples 2 to 6 and Comparative Examples 1 and 2)
In the same manner as in Example 1, lithium ion secondary batteries according to Examples 2 to 6 and Comparative Examples 1 and 2 were manufactured. Here, Examples 2-6 differ from Example 1 in the compounds containing oxo acid ions deposited on the lithium nickel composite oxide. The deposited compounds containing oxo acid ions are shown in Table 3.

  Further, Comparative Example 1 is different from Example 1 in that a compound containing an oxo acid ion is not deposited on the lithium nickel composite oxide and a coating layer is not formed. Further, Comparative Example 2 is different from Comparative Example 1 in that a coating layer containing an inorganic filler is not formed on the separator.

(Examples 7 to 12)
Lithium ion secondary batteries according to Examples 7 to 12 were produced in the same manner as in Example 1. Here, Examples 7-12 differ from Examples 1-6 only in that the inorganic filler contained in the coating layer formed on both sides of the separator is Al ₂ O ₃ instead of Mg (OH) _2. Different.

(Examples 13 to 16, Comparative Example 3)
In the same manner as in Example 1, lithium ion secondary batteries according to Examples 13 to 16 and Comparative Example 3 were produced. Here, Example 13 is different from Example 2 in that the composition of the lithium nickel composite oxide is changed to LiNi _0.8 Co _0.15 Al _0.05 O ₂ and LiNi _0.83 Co _0.15 Al. _The only difference is that it is _0.02 O ₂ . In addition, Examples 14 to 16 are different from Example 13 in the amount of the compound containing the deposited oxo acid ion. The amount of the compound containing the oxo acid ion deposited is shown in Table 4. Further, Comparative Example 3 is different from Example 13 in that the lithium nickel composite oxide was not coated with a compound containing oxo acid ions, and the separator was not formed with a coating layer containing an inorganic filler. Only the difference.

(Examples 17 to 22 and Comparative Example 4)
The lithium ion secondary battery which concerns on Examples 17-22 was manufactured by the method similar to Examples 1-6. Here, in Examples 17 to 22, compared to Examples 1 to 6, the composition of the lithium nickel composite oxide is changed to LiNi _0.8 Co _0.15 Al _0.05 O ₂ , and LiNi _0.8 Co _The only difference is _0.15 Mn _0.05 O ₂ . The deposited compounds containing oxo acid ions are shown in Table 5.

(Reference example)
A lithium ion secondary battery according to the reference example was manufactured in the same manner as in Comparative Example 1. Here, Comparative Example 1 is different from Comparative Example 1 in that the composition of the lithium nickel composite oxide is changed to LiNi _0.8 Co _0.15 Al _0.05 O ₂ and LiNi _0.5 Co _0.2 Mn. _The only difference is that it is _0.3 O ₂ .

(High temperature storage test)
Then, the high temperature storage test was done with respect to the lithium ion secondary battery which concerns on Examples 1-22 manufactured above, Comparative Examples 1-4, and a reference example. Specifically, after charging / discharging at the charge / discharge rate (rate) and cut-off voltage shown in Table 2 below, a high-temperature storage test was performed at 85 ° C. for 40 hours, and then stored at high temperature. The subsequent discharge capacity was measured.

  In Table 2, CC-CV indicates constant current and constant voltage charge, and CC indicates constant current discharge. The cut-off voltage indicates a voltage at the end of charging and a voltage at the end of discharging.

  Specifically, in the first cycle, constant current and constant voltage charging is performed at 0.1 C until the voltage of the lithium ion secondary battery reaches 4.2 V, and the voltage of the lithium ion secondary battery is set to 2. Constant current discharge was performed at 0.1 C until 5 V was reached. In the second cycle, constant-current constant-voltage charging is performed at 0.2 C until the voltage of the lithium ion secondary battery reaches 4.2 V, and the voltage of 0. 0 until the voltage of the lithium ion secondary battery reaches 2.5 V. Constant current discharge was performed at 2C. The discharge capacity measured at the second cycle was defined as the discharge capacity of the lithium ion secondary battery. Furthermore, about Example 3, the comparative example 3, and the reference example, discharge capacity was measured for every charging / discharging rate (C rate).

  Next, constant-current constant-voltage charging was performed at 0.2 C until the voltage of the lithium ion secondary battery reached 4.2 V, and then a high-temperature storage test at 85 ° C. for 40 hours was performed. In addition, after high temperature storage, constant current constant voltage charging is performed at 0.2 C until the voltage of the lithium ion secondary battery becomes 4.2 V, and 0.2 C until the voltage of the lithium ion secondary battery becomes 2.5 V. A constant current discharge was performed at

  In addition, the amount of gas generated was measured by the Archimedes method after the high temperature storage test. The gas generation amount was divided by the discharge capacity to obtain a value per positive electrode discharge capacity.

The results of the high temperature storage test are shown in Tables 3 to 5 and FIGS. Table 3 and FIG. 2 show the results of a high-temperature storage test of a lithium ion secondary battery in which the positive electrode active material is LiNi _0.8 Co _0.15 Al _0.05 O ₂ . FIG. 3 is a result of comparison of battery characteristics between the lithium ion secondary battery according to the present embodiment and the lithium ion secondary batteries according to the comparative example and the reference example. Further, Table 4 shows that the addition amount of the compound containing oxo acid ions to be deposited is changed with respect to the lithium ion secondary battery in which the positive electrode active material is LiNi _0.83 Co _0.15 Al _0.02 O _2. It is a result. Table 5 shows the results of the lithium ion secondary battery in which the positive electrode active material is LiNi _0.8 Co _0.15 Mn _0.05 O ₂ . In Tables 3 to 5, “-” represents that a compound containing an oxoacid ion is not deposited or a coating layer is not formed.

First, in Table 3 and Figure 2, the high-temperature storage test of the lithium ion secondary battery positive electrode active material is _{LiNi 0.8 Co 0.15 Al 0.05 O 2} , and the results of the battery characteristics. FIG. 2 is a graph showing the amount of gas generated in Example 1, Comparative Examples 1 and 2, and Reference Example in Table 3 as a histogram.

  Referring to Table 3, it can be seen that in Examples 1 to 12, the amount of generated gas was greatly suppressed as compared with Comparative Examples 1 and 2. Moreover, Examples 1-12 have comparable discharge capacity with respect to Comparative Examples 1 and 2, and it turns out that gas generation | occurrence | production can be suppressed, without deteriorating battery characteristics, such as discharge capacity. .

Further, when Examples 1 to 6 and Examples 7 to 12 are compared, it is possible to similarly suppress gas generation during high-temperature storage regardless of whether Mg (OH) ₂ or Al ₂ O ₃ is used as the inorganic filler. Recognize.

Further, with reference to FIG. 2, the description will be given focusing on Example 1, Comparative Examples 1 and 2, and Reference Example. The reference example is a lithium ion secondary battery using LiNi _0.5 Co _0.2 Mn _0.3 O ₂ which is a lithium nickel composite oxide having a lower Ni ratio and an extremely small amount of gas generation. .

Comparing Comparative Examples 1 and 2 with the Reference Example, it can be seen that Comparative Examples 1 and 2 having a high Ni ratio in the lithium nickel composite oxide have a larger amount of gas generation during high-temperature storage than the Reference Example. On the other hand, in Example 1 according to this embodiment, a coating layer containing oxo acid ions is formed, and a coating layer containing an inorganic filler is formed on one of the separator and the positive electrode, whereby a lithium nickel composite oxide It can be seen that, despite using LiNi _0.8 Co _0.15 Al _0.05 O ₂ with a large gas generation amount, the gas generation amount is suppressed more than in the reference example. In particular, referring to FIG. 2, Example 1 according to the present embodiment has the effect that the coating layer containing the inorganic filler is formed on either the separator or the positive electrode (the effect of Comparative Example 2 with respect to Comparative Example 1), and It can be seen that the gas generation amount below the reference example could be achieved by synergistic effect of the formation of the coating layer containing oxoacid ions (the effect of Example 1 with respect to Comparative Example 2).

  Furthermore, with reference to FIG. 3, the battery characteristic of the lithium ion secondary battery which concerns on this embodiment is demonstrated. FIG. 3 is a graph plotting the discharge capacity for each C rate in Example 13, Comparative Example 3 and Reference Example.

Referring to FIG. 3, it can be seen that Example 13, which is a lithium ion secondary battery according to this embodiment, has substantially the same discharge capacity for each C rate as compared to Comparative Example 3. In addition, it can be seen that the discharge capacity of Example 13 is improved compared to the reference example using LiNi _0.5 Co _0.2 Mn _0.3 O ₂ with a very small amount of gas generation. Therefore, it turns out that the lithium ion secondary battery which concerns on this embodiment can suppress gas generation amount, maintaining a battery characteristic with respect to each comparative example. In addition, the lithium ion secondary battery according to the present embodiment can improve the discharge capacity while suppressing the gas generation amount to be equal to or less than that of the reference example using the positive electrode active material with a small gas generation amount. Recognize.

Next, in Table 4, the high-temperature storage tests of Examples 13 to 16 and Comparative Example 3 produced by changing the amount of the compound containing oxoacid ion to be deposited (silicotungstic acid) and the results of battery characteristics Indicates. In Examples 13 to 16 and Comparative Example 3, the composition of the lithium nickel composite oxide is LiNi _0.83 Co _0.15 Al _0.02 O ₂ . Moreover, in Table 4, the addition amount of coating | covering material was described in the ratio which made the total mass of the lithium nickel composite oxide before making it adhere 100 mass parts.

  Referring to Table 4, it can be seen that in Examples 13 to 16, the amount of generated gas was suppressed compared to Comparative Example 3. Moreover, it turns out that Examples 13-16 have comparable discharge capacity with respect to the comparative example 3, and can suppress gas generation | occurrence | production, without deteriorating battery characteristics, such as discharge capacity. Therefore, when the compound containing oxo acid ions is added in an amount of 0.25 parts by mass to 2 parts by mass with respect to 100 parts by mass of the total mass of the lithium nickel composite oxide before being deposited, the coverage of the coating layer It can be seen that the amount of generated gas can be suppressed while maintaining the battery characteristics more suitably.

Subsequently, in Table 5, _LiNi 0.8 _Co 0.15 _{Mn 0.05} high-temperature storage test of O ₂ Example using 17 to 22 and Comparative Examples 4, and the results of the battery characteristics as the lithium nickel composite oxide Indicates.

  Referring to Table 5, it can be seen that in Examples 17 to 22, the amount of generated gas was suppressed with respect to Comparative Example 4. Moreover, Examples 17-22 have comparable discharge capacity with respect to the comparative example 4, and it turns out that gas generation | occurrence | production can be suppressed, without deteriorating battery characteristics, such as discharge capacity.

  Therefore, referring to the results of the high-temperature storage tests and battery characteristics shown in Tables 3 to 5 described above, the lithium ion secondary battery according to one embodiment of the present invention has a high Ni ratio of lithium nickel. It can be seen that gas generation can be similarly suppressed for the composite oxide.

(Evaluation of coverage)
Below, in Examples 1, 2, 13, 14, and 16 manufactured above, the coverage of the coating layer containing the oxo acid ion formed on the surface of the lithium nickel composite oxide particles was evaluated. Specifically, the lithium nickel composite oxide particles after forming the coating layer were observed with SEM and EDX (Energy Dispersive X-ray spectroscopy), and then the coating rate of the coating layer was calculated by XPS measurement.

  First, EDX observation results of the lithium nickel composite oxide according to Examples 1 and 2 are shown in FIGS. 4A and 4B and FIGS. 5A and 5B.

  4A is an EDX image of the lithium nickel composite oxide particles according to Example 1 with respect to molybdenum (Mo), and FIG. 4B is a diagram of nickel (Ni) of the lithium nickel composite oxide particles according to Example 1. It is an EDX image. 5A is an EDX image of tungsten (W) of the lithium nickel composite oxide particles according to Example 2, and FIG. 5B is an EDX of nickel (Ni) of the lithium nickel composite oxide particles according to Example 1. It is a statue.

  In FIG. 4A, Mo contained in ammonium molybdate is displayed in white, and in FIG. 4B, Ni contained in the lithium nickel composite oxide is displayed in white. 4A and 4B, it can be seen that the region where Mo is present coincides with the region where Ni is present, and ammonium molybdate is uniformly distributed on the surface of the lithium nickel composite oxide.

  In FIG. 5A, W contained in silicotungstic acid is displayed in white, and in FIG. 5B, Ni contained in the lithium nickel composite oxide is displayed in white. 5A and 5B, it can be seen that the region where W is present and the region where Ni is present coincide with each other, and silicotungstic acid is uniformly distributed on the surface of the lithium nickel composite oxide.

  Further, XPS measurement was performed on the lithium nickel composite oxide particles according to Examples 1, 2, 13, 14, and 16, and as described above, background subtraction, peak area calculation, peak identification, and sensitivity factor The atomic ratio for each element was calculated with the correction according to the above. Furthermore, the coverage of the coating layer of the lithium nickel composite oxide particles was evaluated from the calculated atomic ratio for each element. The evaluation results are shown in Table 6.

  Referring to Table 6, it can be seen that the coverage of the coating layer of the lithium nickel composite oxide according to one embodiment of the present invention is 1% or more and 20% or less. Moreover, it turns out that Example 1, 2, 13, 14, 16 in which a coverage is contained in said range has suppressed the amount of generated gas. Furthermore, Examples 1, 2, 13, 14, and 16 in which the coverage is included in the above range have a discharge capacity comparable to that of Comparative Examples 1 to 4, and battery characteristics such as discharge capacity. It can be seen that gas generation can be suppressed without deteriorating the gas.

  As can be seen from the above results, according to the lithium ion secondary battery according to one embodiment of the present invention, the positive electrode including the lithium nickel composite oxide particles on which the coating layer containing oxo acid ions is formed, and the separator It is possible to suppress gas generation when stored at a high temperature in a fully charged state without deteriorating battery characteristics by forming a coating layer containing an inorganic filler on one of the separator and the positive electrode. .

  Moreover, the lithium ion secondary battery which concerns on one Embodiment of this invention can be used more suitably when the lithium nickel complex oxide with a high Ni ratio is used as a positive electrode active material.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. 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 (8)

A positive electrode including lithium composite oxide particles having a composition represented by the following general formula (1);
A separator,
A coating layer containing at least one or more oxo acid ions represented by any of the following general formulas (2) to (6) is formed on the surface of the lithium composite oxide particles,
At least one of the positive electrode and the separator is a lithium ion secondary battery having a coating layer containing an inorganic filler.
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.
In the general formulas (2) to (6), X is either P or Si, n is a natural number of 7 or less, and m is a natural number.   The lithium ion secondary battery according to claim 1, wherein a coverage of the coating layer is 1% or more and 20% or less. The lithium ion secondary battery according to claim 1, wherein the inorganic filler includes at least one of Mg (OH) ₂ and Al ₂ O ₃ .   The lithium ion secondary battery according to any one of claims 1 to 3, wherein the separator has a coating layer containing the inorganic filler.   The said lithium ion secondary battery is a lithium ion secondary battery as described in any one of Claims 1-4 further provided with the negative electrode containing a graphite. The oxoacid ion represented by any one of the following general formulas (2) to (6) by applying mechanical shearing force to the surface of the lithium composite oxide particles having the composition represented by the following general formula (1) Forming a covering layer having at least one selected from the group consisting of:
Heating the lithium composite oxide particles on which the coating layer is formed. A method for producing a positive electrode active material for a lithium ion secondary battery.
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.
In the general formulas (2) to (4), X is either P or Si, n is a natural number of 7 or less, and m is a natural number.   The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 6, wherein the step of heating the lithium composite oxide particles is performed in an oxidizing atmosphere. Applying a positive electrode active material for a lithium ion secondary battery produced by the production method according to claim 6 or 7 to a current collector,
The step of applying to the current collector is a method for producing a positive electrode for a lithium ion secondary battery, which is performed at a dew point temperature of −40 ° C. or lower.