JP2010257624A - Positive electrode active material, method for manufacturing positive electrode active material, and nonaqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode active material capable of suppressing gas generation, and to provide a method for manufacturing the positive electrode active material, and a nonaqueous electrolyte battery. <P>SOLUTION: A positive electrode 13 has the positive electrode active material, and the positive electrode active material has a lithium complex oxide particle containing nickel as a main component, and a coating layer formed on at least part of the surface of the lithium complex oxide particle. The coating layer contains an oxo acid and/or an oxo acid compound, and an acidity of the surface of the lithium complex oxide particle is increased by the coating layer to a determined acidity. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a positive electrode active material, a method for producing a positive electrode active material, and a nonaqueous electrolyte battery.

  In recent years, with the widespread use of portable devices such as video cameras and notebook personal computers, the demand for small, high-capacity secondary batteries has increased. Currently used secondary batteries include nickel-cadmium batteries and nickel-hydrogen batteries using an alkaline electrolyte, but the battery voltage is as low as about 1.2 V, and it is difficult to improve the energy density. For this reason, a lithium metal secondary battery using lithium metal having a specific gravity of 0.534, which is the lightest of the solid simple substance, the potential is extremely base, and the current capacity per unit weight is the largest among the metal negative electrode materials. It was done.

  However, in a secondary battery using lithium metal as a negative electrode, dendritic lithium (dendrites) is deposited on the surface of the negative electrode during charging, and this grows by a charge / discharge cycle. The growth of dendrites not only deteriorates the charge / discharge cycle characteristics of the secondary battery, but in the worst case, it breaks through the separator (separator) arranged so that the positive electrode and the negative electrode are not in contact with each other. As a result, there is a problem that an internal short circuit occurs and the battery is destroyed due to thermal runaway.

  Thus, for example, as described in Patent Document 1 below, a secondary battery that repeats charging and discharging by using a carbonaceous material such as coke as a negative electrode and doping and dedoping alkali metal ions has been proposed. As a result, it has been found that the above-described problem of deterioration of the negative electrode due to repeated charge / discharge can be avoided.

JP 62-90863 A

  On the other hand, as a positive electrode active material, a battery with a battery voltage of around 4 V has appeared due to the search and development of an active material exhibiting a high potential, and has attracted attention. As such active materials, inorganic compounds such as transition metal oxides containing alkali metals and transition metal chalcogens are known.

In particular, when the main component is nickel or cobalt such as Li _x NiO ₂ (0 <x ≦ 1.0) or Li _x CoO ₂ (0 <x ≦ 1.0), the lithium transition metal composite oxide has a high potential. The most promising in terms of stability and long life. Among these, the lithium transition metal composite oxide containing nickel as a main component is a positive electrode active material exhibiting a relatively high potential. By using this in a battery, it is expected that the charging current capacity is high and the energy density can be increased.

  However, in a secondary battery using a lithium transition metal composite oxide containing nickel as a main component as a positive electrode active material, gas is likely to be generated inside the battery. For this reason, there has been a problem that the internal pressure of the battery tends to increase. In particular, a battery using a laminate film for the exterior has a problem that the battery easily expands due to gas generation.

  Accordingly, an object of the present invention is to provide a positive electrode active material, a method for producing a positive electrode active material, and a nonaqueous electrolyte battery that can suppress gas generation.

  In order to solve the above-described problem, the first invention has lithium composite oxide particles and a coating layer formed on at least a part of the surface of the lithium composite oxide particles. The lithium composite oxide particles mainly containing nickel, and the coating layer contains an oxo acid and / or oxo acid compound, and the acidity of the surface of the lithium composite oxide particles mainly containing nickel by the coating layer Is increased to a predetermined acidity, and the predetermined acidity is obtained by dispersing 1.0 part by weight of lithium composite oxide particles mainly composed of nickel on which a coating layer is formed in 50 parts by weight of water. The positive electrode active material is defined by the pH of the supernatant of water in which the composite oxide particles have settled, and the pH is less than 8.0.

  According to a second aspect of the present invention, there is provided a deposition step of depositing an oxo acid and / or an oxo acid compound on the lithium composite oxide particles containing nickel as a main component, and the oxo acid and / or the oxo acid compound deposited A heat treatment step of heat-treating lithium composite oxide particles containing nickel as a main component, and the surface acidity of the lithium composite oxide particles containing nickel as a main component is predetermined by the deposition step and the heat treatment step. After the heat treatment step, the predetermined acidity is obtained by adding 1.0 part by weight of lithium composite oxide particles mainly composed of nickel coated with oxo acid and / or oxo acid compound. A positive electrode active material that is defined by the pH of the supernatant of water in which the lithium composite oxide particles have settled after being dispersed in 50 parts by weight of water, and the pH is less than 8.0 It is a manufacturing method.

  The third invention has a positive electrode, a negative electrode, and an electrolyte, the positive electrode has a positive electrode active material, and the positive electrode active material is at least one of the surfaces of the lithium composite oxide particles and the lithium composite oxide particles. The lithium composite oxide particles are lithium composite oxide particles containing nickel as a main component, and the cover layer contains an oxo acid and / or an oxo acid compound, By the coating layer, the acidity of the surface of the lithium composite oxide particles mainly composed of nickel is increased to a predetermined acidity, and the predetermined acidity is mainly the nickel on which the coating layer is formed. It is defined by the pH of the supernatant of water in which lithium composite oxide particles have settled after 1.0 part by weight of lithium composite oxide particles as a component is dispersed in 50 parts by weight of water, and the pH is 8.0. Is less than It is a non-aqueous electrolyte battery.

  According to this invention, the oxidation activity on the surface of the lithium composite oxide particles containing nickel as a main component in a charged state can be suppressed. Thereby, decomposition | disassembly of the nonaqueous electrolyte etc. in the surface of a positive electrode active material can be suppressed. Moreover, the carbonate radical contained in the lithium composite oxide particle which has nickel as a main component can be reduced.

  According to the present invention, gas generation due to decomposition of a non-aqueous electrolyte component or the like can be suppressed. Moreover, gas generation from the positive electrode active material itself can be suppressed.

It is a perspective view which shows one structural example of the nonaqueous electrolyte battery by embodiment of this invention. It is sectional drawing along the II-II line of the winding electrode body 10 shown in FIG. It is sectional drawing which shows one structural example of the nonaqueous electrolyte battery by embodiment of this invention. FIG. 4 is an enlarged cross-sectional view illustrating a part of a wound electrode body 30 illustrated in FIG. 3.

Embodiments of the present invention will be described below with reference to the drawings. The embodiments described below are specific examples of the present invention, and various technically preferable limitations are given. However, the scope of the present invention is particularly limited in the following description. Unless stated to the effect, the present invention is not limited to the embodiment. The description will be given in the following order.
1. First embodiment (positive electrode active material)
2. Second Embodiment (Method for Producing Positive Electrode Active Material)
3. Third Embodiment (First Example of Nonaqueous Electrolyte Battery)
4). Fourth embodiment (second example of nonaqueous electrolyte battery)
5). Fifth embodiment (third example of nonaqueous electrolyte battery)
6). Other embodiment (modification)

1. First embodiment (positive electrode active material)
First, in order to facilitate understanding of the present invention, a technical background related to the positive electrode active material according to the first embodiment of the present invention will be described.

For example, composite oxides mainly composed of nickel, such as lithium nickelate (LiNiO ₂ ) and nickel-based oxides in which a part of nickel of lithium nickelate is replaced with other metals, are positive electrode active materials for non-aqueous electrolyte batteries. Can be used as In addition, for example, a cobalt-based composite oxide such as lithium cobaltate (LiCoO ₂ ) or a cobalt-based oxide in which a part of cobalt of lithium cobaltate is replaced with another metal is used for a non-aqueous electrolyte battery. It can be used as a positive electrode active material.

  A composite oxide containing nickel as a main component is more economical than a composite oxide containing cobalt as a main component, and is economically unstable and has a low content of expensive cobalt. Furthermore, a composite oxide containing nickel as a main component has an advantage of a large current capacity as compared with a composite oxide containing cobalt as a main component, and it is expected to further increase the advantage.

  On the other hand, in a secondary battery using a lithium composite oxide mainly composed of nickel as a positive electrode active material, internal pressure increases due to internal gas generation, and swelling tends to occur in a laminate encapsulated battery. There is a problem, and it is desired to solve this problem.

  The positive electrode active material according to the first embodiment meets the above-described requirements, and modifies a lithium composite oxide containing nickel as a main component to reduce gas generation that occurs when used in a battery. It has an effect.

[Regarding suppression of gas generation]
In battery gas generation, it is generally accepted that the factors attributable to the positive electrode active material are the following (Factor 1) and (Factor 2).
(Factor 1) Carbonic acid radicals contained in the positive electrode active material generate carbon dioxide gas from the acid component derived from the non-aqueous electrolyte.
(Factor 2) Due to the strong oxidizing power of the positive electrode active material in a charged state, organic components such as a non-aqueous electrolyte are oxidized to produce carbon dioxide or carbon monoxide.

  Considering (Factor 1) and (Factor 2), an effective treatment for reducing the carbonate radical content of the positive electrode active material, and a surface treatment of a lithium composite oxide containing nickel as a main component, the oxidation activity of the surface The generation of gas can be suppressed by performing an effective process for suppressing the above.

  Therefore, the inventors of the present application examined in detail the interaction between carbon dioxide gas and the positive electrode active material, which is one of the causes of gas generation. That is, the mechanism by which carbon dioxide gas is adsorbed on the positive electrode active material was examined in detail. This study revealed the following.

  Carbon dioxide gas is easily adsorbed on lithium basic oxide particles (positive electrode active material) having high basicity, such as lithium composite oxide containing nickel as a main component, and the adsorbed carbon dioxide gas is a residue of the positive electrode active material. It becomes carbonate.

  In a battery incorporating a positive electrode active material having a residual carbonic acid content, carbon dioxide gas is desorbed from the residual carbonic acid content due to a substitution reaction between the residual carbonic acid content and an acidic content generated from an electrolyte, etc. Cause.

  Adsorption of carbon dioxide gas on the positive electrode active material does not proceed on a basic surface, and requires adsorbed moisture. That is, in order for carbon dioxide gas to be adsorbed on the positive electrode active material, the surface of the positive electrode active material requires the presence of surface hydroxyl groups that are chemically adsorbed water, and particularly requires the presence of basic surface hydroxyl groups.

  Adsorption of carbon dioxide to the positive electrode active material proceeds by reacting the surface hydroxyl group and carbon dioxide to form a bicarbonate group, and this reaction is more likely to proceed as the basicity of the surface hydroxyl group increases. The formed bicarbonate group undergoes a dehydration reaction with an adjacent surface hydroxyl group and is adsorbed on the surface as a bidentate carbonate group. This once adsorbed carbonate group cannot be easily detached.

From the above, the following is found.
The reaction in which the surface hydroxyl group and carbon dioxide react to form a bicarbonate group is more likely to proceed as the basicity of the surface hydroxyl group of the positive electrode active material increases. From this, the low Bronsted basicity of the positive electrode active material suppresses the progress of the reaction in which the surface hydroxyl group and carbon dioxide react to form a bicarbonate group, so the process of carbon content that causes gas generation Suppress the increase in the inside.
In addition, the low Bronsted basicity of the positive electrode active material is also effective in suppressing the gelation of the binder. Further, although the expression mechanism is still unclear, the low Bronsted basicity of the positive electrode active material is It is also effective in reducing carbon dioxide generation due to the above (Factor 2).

[Relationship between basic control and discharge capacity]
As described above, the low Bronsted basicity of the positive electrode active material is effective in suppressing gas generation and the like. However, if the basicity of the surface of the positive electrode active material is reduced, charging and discharging at a high current is performed. The capacity of is reduced.

  This is because the active material is deposited on the surface of the positive electrode active material to form an inactive layer, or lithium in the surface layer loses mobility, or as a result, lithium ions diffuse in the surface layer. This is because resistance increases.

[About the positive electrode active material according to the first embodiment]
The positive electrode active material according to the first embodiment is mainly made of nickel so that the acidity of the surface of the positive electrode active material can be controlled and the effect of suppressing gas generation can be obtained under the constraint that the decrease in capacity does not increase. This is a modified lithium composite oxide particle as a component.

  That is, the positive electrode active material according to the first embodiment is obtained by subjecting particles of lithium composite oxide containing nickel as a main component to surface treatment. This positive electrode active material is obtained, for example, by applying heat treatment to a composite oxide particle containing nickel as a main component after depositing an oxo acid and / or an oxo acid compound. The positive electrode active material thus obtained has lithium composite oxide particles mainly composed of nickel and a coating layer formed on at least a part of the surface of the composite oxide particles.

  In the positive electrode active material according to the first embodiment, the decrease in discharge capacity that decreases due to the formation of the coating layer is set to a predetermined decrease rate. This predetermined reduction rate is less than 5% with respect to the discharge capacity of the lithium composite oxide particles before the coating layer is formed.

  The rate of decrease in the discharge capacity is, for example, by producing a predetermined measurement cell, charging it to 4.25 V (vs. lithium metal potential) at a predetermined charging current, and 2.50 V (vs. lithium) at a discharge current of 1 C or less. It is defined by the discharge capacity of the positive electrode active material when discharged until the metal potential. The reduction rate of the discharge capacity is determined by the above-described discharge capacity of the positive electrode active material before surface treatment (lithium composite oxide mainly composed of nickel before coating layer formation) and the positive electrode active material after surface treatment (after coating layer formation). This is the rate of decrease when the above discharge capacities of lithium composite oxides mainly composed of nickel are compared.

  Furthermore, the positive electrode active material according to the first embodiment is enhanced so that the acidity of the surface becomes equal to or higher than a predetermined acidity under the restriction of the reduction rate of the discharge capacity.

  This predetermined acidity is a state in which lithium composite oxide particles settled after 1.0 part by weight of lithium composite oxide particles mainly composed of nickel on which a coating layer is formed are dispersed in 50 parts by weight of water. Defined by the pH of the water supernatant. This pH is less than 8.0.

  In addition, in the regulation of acid basicity by pH, which is the standard of the predetermined acidity, the above prescribed value can be achieved by using an excessive acid component in the surface treatment of the positive electrode active material. However, in that case, as the ratio of the acid component to the positive electrode active material increases, the capacity decreases due to the decrease in the ratio of the positive electrode active material, and the chemical modification of the surface layer of the positive electrode active material by the acid component occurs. The accompanying capacity reduction occurs. Therefore, it is preferable to achieve the acid basicity under the restriction of the capacity reduction.

[Lium complex oxide particles]
The lithium composite oxide particles are lithium composite oxide particles containing lithium (Li) and nickel (Ni) as constituent elements. This lithium composite oxide contains nickel as a main component. Note that the phrase “containing nickel as a main component” means that the nickel component is contained most in the metal elements (excluding lithium) constituting the lithium composite oxide.

  The lithium composite oxide particles may be primary particles or secondary particles in which a plurality of primary particles are aggregated. This lithium composite oxide contains more nickel component than cobalt component. For example, the average composition is represented by the following (formula 1).

(Formula 1)
Li _a Ni _x Co _y Al _z O ₂
(However, nickel (Ni) is manganese (Mn), chromium (Cr), iron (Fe), vanadium (V) within the range of 0.1 or less of Ni when the total amount of Ni is 1. , Magnesium (Mg), titanium (Ti), zirconium (Zr), niobium (Nb), molybdenum (Mo), tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In) , Tin (Sn), lanthanum (La), cerium (Ce) can be substituted with one or more metal elements selected from the group consisting of a, x, y, and z, 0.20 ≦ a ≦ 1.40, 0.60 <x <0.90, 0.10 <y <0.40, 0.01 <z <0.20, and x, y There is a relationship of x + y + z = 1 between z and z.)

  Here, in (Formula 1), the range of a is, for example, 0.20 ≦ a ≦ 1.40. When the value is smaller than this range, the layered rock salt structure of the crystal structure that is the source of the function of the positive electrode active material is destroyed, recharging becomes difficult, and the capacity is greatly reduced. If the value increases outside this range, lithium diffuses out of the composite oxide particles described above, which hinders control of the basicity of the next processing step, and finally the gel during the kneading of the positive electrode paste. It will be a cause of the harmful effect of the promotion.

  The range of x is, for example, 0.60 <x <0.90, more preferably 0.65 <x <0.85, and still more preferably 0.70 <x <0.80. When the value decreases outside this range, the discharge capacity of the positive electrode active material decreases. If the value is increased outside this range, the stability of the crystal structure of the composite oxide particles decreases, which causes a decrease in the capacity of repeated charge / discharge of the positive electrode active material and a decrease in safety.

  The range of y is, for example, 0.10 <y <0.40, preferably 0.15 <y <0.35, and more preferably 0.20 <y <0.30. When the value is smaller than this range, the stability of the crystal structure of the composite oxide particles is lowered, which causes a reduction in the capacity of repeated charge / discharge of the positive electrode active material and a reduction in safety. When the value increases outside this range, the discharge capacity of the positive electrode active material decreases.

  The range of z is, for example, 0.01 <z <0.20, more preferably 0.02 <z <0.15, and further preferably 0.03 <z <0.10. If the value is smaller than the above range, the stability of the crystal structure of the composite oxide particles is lowered, which causes a reduction in the capacity of repeated charge / discharge of the positive electrode active material and a reduction in safety. When the value increases outside this range, the discharge capacity of the positive electrode active material decreases.

  This lithium composite oxide containing nickel as a main component is a lithium composite oxide for a lithium ion secondary battery that can realize a high voltage and high energy density substantially equal to those of a composite oxide containing cobalt as a main component. Since this lithium composite oxide is unstable in resources and has a low content of cobalt, which is an expensive material, it has the advantage of high economic efficiency. Further, this lithium composite oxide has an advantage of a large current capacity as compared with lithium cobalt oxide.

[Coating layer]
The coating layer is formed on the surface of the composite acid acid particle containing nickel as a main component, and contains an oxo acid and / or an oxo acid compound. Examples of oxo acids include silicotungstic acid, phosphotungstic acid, and phosphomolybdic acid. Examples of the oxo acid compound include ammonium metatungstate, ammonium paratungstate, and ammonium silicotungstate. The oxo acid and oxo acid compound are not limited to those exemplified.

  By this coating layer, the acidity of the surface of the composite oxide particle containing nickel as a main component is increased to a predetermined acidity. Therefore, the above-mentioned (factor 1) and Among (Factor 2), it is considered that it contributes to the elimination of (Factor 2) and can suppress the generation of carbon dioxide.

  In addition, this positive electrode active material has reduced carbonate radicals contained in a composite oxide containing nickel as a main component. That is, the details of the production method will be described later. For example, this positive electrode active material is obtained by applying heat treatment by depositing oxo acid and / or oxo acid compound on the surface of the composite oxide particle mainly composed of nickel. The carbonic acid radicals contained in the composite oxide containing nickel as a main component can be reduced.

  In the heat treatment, the oxoacid ions generated from the oxoacid and / or oxoacid compound undergo a substitution reaction with a part of the carbonate radical remaining on the surface of the lithium composite oxide particle mainly composed of nickel. A part of is released as carbon dioxide out of the system. As a result, the carbonate group content of the lithium composite oxide particles containing nickel as a main component is reduced, and a reduction in swelling associated with this can be expected. This is considered to contribute to the elimination of (Factor 1).

  For example, the carbonic acid radical content (carbonic acid component content) of the positive electrode active material is 0.15% by weight or less and 0.10% by weight as analyzed by the method shown in Japanese Industrial Standard JIS-R-9101. The following is more preferable, and 0.05% by weight or less is particularly preferable.

[Particle size]
The average particle diameter of the positive electrode active material is preferably 2.0 μm or more and 50 μm or less. When the average particle size is less than 2.0 μm, the positive electrode active material layer is peeled off when the positive electrode active material layer is pressed during the production of the positive electrode. Further, since the surface area of the positive electrode active material is increased, it is necessary to increase the amount of the conductive agent and the binder added, and the energy density per unit weight tends to be reduced. On the other hand, when the average particle diameter exceeds 50 μm, the particles tend to penetrate the separator and cause a short circuit.

[effect]
In the positive electrode active material according to the first embodiment of the present invention, the acidity of the surface of the composite oxide particles containing nickel as a main component is increased to a predetermined acidity by the coating layer. Thereby, when used for a nonaqueous electrolyte battery, the oxidation activity on the surface of the composite oxide particles in a charged state can be suppressed. Thereby, gas generation by decomposition | disassembly of a nonaqueous electrolyte component etc. can be suppressed.

  In addition, the positive electrode active material according to the first embodiment of the present invention has reduced carbonate radicals contained in lithium composite oxide particles containing nickel as a main component. Thereby, gas generation from the positive electrode active material itself can be suppressed.

2. Second Embodiment Next, a method for producing a positive electrode active material according to an embodiment of the present invention will be described. The method for producing a positive electrode active material according to the first embodiment of the present invention can be broadly classified as a deposition step of depositing oxo acid and / or oxo acid compound on composite oxide particles mainly composed of nickel. And a heating step of heat-treating the composite oxide particles mainly composed of nickel coated with oxo acid and / or oxo acid compound.

  A method for producing a positive electrode active material according to the first embodiment of the present invention includes, for example, the above-described deposition step and heating step for composite oxide particles mainly composed of nickel produced by a known method. By performing the surface treatment comprising, the characteristics of the composite oxide particles containing nickel as a main component are improved.

  Hereinafter, first, a method for producing lithium composite oxide particles containing nickel as a main component will be described. Next, the oxo acid and / or oxo acid compound deposition treatment on the lithium composite oxide particles, and heating after the deposition treatment Processing will be described sequentially.

[Method for producing lithium composite oxide particles]
The lithium composite oxide particles containing nickel as a main component can be produced by a known method. For example, the lithium composite oxide particles having the average composition represented by (Formula 1) described in the first embodiment can be produced by a known method.

  Specifically, for example, a nickel compound, a cobalt compound, an aluminum compound, a lithium compound, and a compound of a substitution element as necessary are dissolved in water, and a sodium hydroxide solution is added to the nickel-cobalt while stirring sufficiently. -Make aluminum composite coprecipitated hydroxide.

  Next, a precursor obtained by washing the nickel-cobalt-aluminum composite coprecipitated hydroxide with water and drying is fired. Thus, lithium composite oxide particles containing nickel as a main component can be produced. In addition, you may grind | pulverize the lithium nickelate after baking as needed.

  Examples of nickel compound raw materials include nickel hydroxide, nickel carbonate, nickel nitrate, nickel fluoride, nickel chloride, nickel bromide, nickel iodide, nickel perchlorate, nickel bromate, nickel iodate, nickel oxide, Use inorganic compounds such as nickel peroxide, nickel sulfide, nickel sulfate, nickel hydrogen sulfate, nickel nitride, nickel nitrite, nickel phosphate and nickel thiocyanate, or organic compounds such as nickel oxalate and nickel acetate. One or two or more of these may be used.

  Examples of the raw material of the cobalt compound include cobalt hydroxide, cobalt carbonate, cobalt nitrate, cobalt fluoride, cobalt chloride, cobalt bromide, cobalt iodide, cobalt chlorate, cobalt perchlorate, cobalt bromate, and cobalt iodate. Inorganic compounds such as cobalt oxide, cobalt phosphinate, cobalt sulfide, cobalt hydrogen sulfide, cobalt sulfate, cobalt hydrogen sulfate, cobalt thiocyanate, cobalt nitrite, cobalt phosphate, cobalt dihydrogen phosphate, cobalt hydrogen carbonate, etc. Organic compounds such as cobalt acid and cobalt acetate can be used, and one or more of these may be used.

  Examples of aluminum compound raw materials include inorganic substances such as aluminum hydroxide, aluminum nitrate, aluminum fluoride, aluminum chloride, aluminum bromide, aluminum iodide, aluminum perchlorate, aluminum oxide, aluminum sulfide, aluminum sulfate, and aluminum phosphate. An organic compound such as an aluminum compound or an aluminum oxalate can be used, and one or more of these may be used.

  Examples of lithium compound raw materials include lithium hydroxide, lithium carbonate, lithium nitrate, lithium fluoride, lithium chloride, lithium bromide, lithium iodide, lithium chlorate, lithium perchlorate, lithium bromate, and lithium iodate. Inorganic compounds such as lithium oxide, lithium peroxide, lithium sulfide, lithium hydrogen sulfide, lithium sulfate, lithium hydrogen sulfate, lithium nitride, lithium azide, lithium nitrite, lithium phosphate, lithium dihydrogen phosphate, lithium hydrogen carbonate, Alternatively, an organic compound such as methyl lithium, vinyl lithium, isopropyl lithium, butyl lithium, phenyl lithium, lithium oxalate, or lithium acetate can be used, and one or more of these may be used.

  The lithium composite oxide particles mainly composed of nickel can be used as starting materials that are usually available as positive electrode active materials. In some cases, particles obtained by crushing secondary particles using a ball mill or a crusher can also be used.

[Deposition process]
The lithium composite oxide particles containing nickel as the main component are subjected to an oxo acid and / or oxo acid compound deposition treatment. For example, an oxo acid and / or oxo acid compound deposition treatment is performed on secondary particles in which primary particles of lithium composite oxide mainly composed of nickel having layered crystals are aggregated. The coating process is performed by the following dry method.

[Dry method]
Deposition treatment of oxo acid and / or oxo acid compound by a dry method will be described. A known method can be used for the deposition of the oxo acid and / or oxo acid compound by the dry method.

  Specifically, using a dry lithium composite oxide particle and a dried oxo acid and / or oxo acid compound particle, a method of applying manually using a mortar, a method using a crusher, or a machine For example, a method using a high-speed machine with a high shearing force that causes typical adhesion may be used. The amount of oxo acid and / or oxo acid compound deposited is preferably 0.01 parts by weight or more and 5.0 parts by weight or less, based on 100 parts by weight of the composite oxide particles, and 0.02 parts by weight or more and 3.0 parts by weight or less. The following is more preferable, and 0.03 to 1.0 part by weight is further preferable. If the deposition amount is smaller than this range, the effect of suppressing gas generation in the positive electrode active material cannot be obtained. On the other hand, if the amount of deposition increases outside this range, the discharge capacity of the positive electrode active material decreases, which is not preferable.

[Heat treatment]
Next, the positive electrode active material according to the first embodiment can be obtained by firing the lithium composite oxide particles subjected to the deposition treatment by heat treatment. The particle size of the lithium composite oxide particles after the heat treatment may be adjusted by light pulverization or classification as required.

  In the heat treatment, oxo acid ions are generated from the oxo acid and / or oxo acid compound. This oxo acid ion diffuses on the surface and bulk of the lithium composite oxide particles mainly composed of nickel, and proceeds to lower the basicity of the surface of the lithium composite oxide particles mainly composed of nickel. Then, a partial substitution reaction with the carbonate radical of the lithium composite oxide particles proceeds, and the carbonate radical is released out of the system as carbon dioxide gas. Thereby, the carbonate group content of the lithium composite oxide containing nickel as a main component can be reduced.

[Heat treatment temperature]
In the heat treatment, the optimum temperature range of the heating temperature is preferably 150 ° C. or higher and 1200 ° C. or lower, more preferably 200 ° C. or higher and 1100 ° C. or lower, and more preferably 250 ° C. or higher and 1000 ° C. or lower.

  When the temperature falls outside the optimum temperature range, the reaction for producing oxo acid ions from the oxo acid and / or oxo acid compound does not proceed sufficiently. Furthermore, a diffusion reaction in which the generated oxo acid ion diffuses on the surface and bulk of the lithium composite oxide particles containing nickel as a main component cannot proceed sufficiently. Furthermore, the substitution reaction between the oxo acid and / or oxo acid compound and the carbonate group of the composite oxide containing nickel as a main component cannot sufficiently proceed.

  On the other hand, when the temperature rises outside the optimum temperature range, the crystal structure of the lithium composite oxide containing nickel as a main component is destabilized, and the tendency of the discharge capacity to decrease is conspicuous. Furthermore, when the surface concentration of the residual component of the oxo acid and / or oxo acid compound decreases, it becomes difficult to proceed with the decrease in the basicity of the surface of the lithium composite oxide particles. Furthermore, due to the strong oxidizing power of the positive electrode active material in the charged state, the organic component such as the non-aqueous electrolyte is oxidized, and the function of suppressing the gas generation mechanism (factor 2) that generates carbon dioxide gas decreases.

  As described above, the deposition treatment of oxo acid and / or oxo acid compound and the continuous heat treatment after deposition can reduce the carbonate group content of the lithium composite oxide mainly composed of nickel component. it can. The carbonate radical content to be achieved is 0.15% by weight or less, more preferably 0.10% by weight or less, and more preferably 0.05% by weight or less. Carbonic acid radical content (carbonic acid component content) can be measured by the AGK method shown in Japanese Industrial Standard JIS-R-9101. A reduction in the carbonate group content is effective in reducing gas generation inside the battery when used in a battery.

[Heat treatment atmosphere]
In the heat treatment, the atmospheric condition is usually preferably an oxidizing atmosphere used for the preparation of lithium nickelate, and preferably in an oxygen atmosphere.

  The positive electrode active material according to the first embodiment is obtained by performing the coating treatment step and the heat treatment step on the lithium composite oxide particles containing nickel as a main component. The first embodiment of the present invention satisfies the above-mentioned discharge capacity and acidity regulations by adjusting the amount of coating material in the coating process and adjusting conditions such as heating temperature and heating time in the heat treatment process. The positive electrode active material according to the form can be obtained.

<Effect>
In the method for producing a positive electrode active material according to the second embodiment of the present invention, the surface of a lithium composite oxide containing nickel as a main component is deposited with an oxo acid and / or an oxo compound. Thereby, the fall of the basicity of the surface of the lithium composite oxide which has nickel as a main component is advanced. Thereby, the oxidation activity on the surface of the lithium composite oxide particles containing nickel as a main component in a charged state can be suppressed. Therefore, gas generation due to decomposition of the non-aqueous electrolyte component or the like can be suppressed.

  In addition, the method for producing a positive electrode active material according to the second embodiment of the present invention provides a method for producing carbonate radicals remaining on the surface of the positive electrode active material by the deposition treatment of oxo acid and / or oxo acid compound and the subsequent heat treatment. Reduce some. Thereby, gas generation from the positive electrode active material itself can be suppressed.

3. Third Embodiment (First Example of Nonaqueous Electrolyte Battery)
FIG. 1 is a perspective view showing a configuration example of a nonaqueous electrolyte battery according to a third embodiment of the present invention. This nonaqueous electrolyte battery is, for example, a nonaqueous electrolyte secondary battery. This nonaqueous electrolyte battery has a configuration in which a wound electrode body 10 to which a positive electrode lead 11 and a negative electrode lead 12 are attached is housed inside a film-like exterior member 1 and has a flat shape. .

  Each of the positive electrode lead 11 and the negative electrode lead 12 has a strip shape, for example, and is led out from the inside of the exterior member 1 to the outside, for example, in the same direction. The positive electrode lead 11 is made of a metal material such as aluminum (Al), and the negative electrode lead 12 is made of a metal material such as nickel (Ni).

  The exterior member 1 is, for example, a laminate film having a structure in which an insulating layer, a metal layer, and an outermost layer are laminated in this order and bonded together by a lamination process or the like. For example, the exterior member 1 has the insulating layer side as the inner side, and the outer edge portions are in close contact with each other by fusion bonding or an adhesive.

  The insulating layer is made of, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, modified polypropylene, or a copolymer thereof. This is because moisture permeability can be lowered and airtightness is excellent. The metal layer is made of foil-like or plate-like aluminum, stainless steel, nickel, iron, or the like. The outermost layer may be made of, for example, the same resin as the insulating layer, or may be made of nylon or the like. This is because the strength against tearing and piercing can be increased. The exterior member 1 may include a layer other than the insulating layer, the metal layer, and the outermost layer.

  Between the exterior member 1 and the positive electrode lead 11 and the negative electrode lead 12, an adhesion film 2 for improving the adhesion between the positive electrode lead 11 and the negative electrode lead 12 and the inside of the exterior member 1 and preventing intrusion of outside air. Has been inserted. The adhesion film 2 is made of a material having adhesion to the positive electrode lead 11 and the negative electrode lead 12. For example, when the positive electrode lead 11 and the negative electrode lead 12 are made of the metal materials described above, polyethylene, polypropylene, It is preferably composed of a polyolefin resin such as modified polyethylene or modified polypropylene.

  FIG. 2 is a sectional view taken along line II-II of the spirally wound electrode body 10 shown in FIG. The wound electrode body 10 is obtained by stacking and winding a positive electrode 13 and a negative electrode 14 with a separator 15 and an electrolyte 16, and the outermost peripheral portion is protected by a protective tape 17.

  The positive electrode 13 includes, for example, a positive electrode current collector 13A and a positive electrode active material layer 13B provided on both surfaces of the positive electrode current collector 13A. The positive electrode current collector 13A is made of, for example, a metal foil such as an aluminum foil.

  The positive electrode active material layer 13B includes the positive electrode active material according to the first embodiment of the present invention described above. The positive electrode active material layer 13B further includes a conductive additive such as a carbon material and a binder such as polyvinylidene fluoride or polytetrafluoroethylene.

  For example, similarly to the positive electrode 13, the negative electrode 14 includes a negative electrode current collector 14 </ b> A and a negative electrode active material layer 14 </ b> B provided on both surfaces of the negative electrode current collector 14 </ b> A. The negative electrode current collector 14A is made of, for example, a metal foil such as a copper foil.

  The negative electrode active material layer 14B includes, for example, one or more negative electrode materials capable of occluding and releasing lithium as a negative electrode active material, and a conductive additive as necessary. And may contain a binder.

  Examples of the negative electrode material capable of inserting and extracting lithium include carbon materials such as graphite, non-graphitizable carbon, and graphitizable carbon. Any one of these carbon materials may be used alone, or two or more of them may be mixed and used, or two or more of them having different average particle diameters may be mixed and used.

  Further, examples of the negative electrode material capable of inserting and extracting lithium include a material containing a metal element or a metalloid element capable of forming an alloy with lithium as a constituent element. Specifically, a simple substance, alloy, or compound of a metal element capable of forming an alloy with lithium, or a simple substance, alloy, or compound of a metalloid element capable of forming an alloy with lithium, or one or more of these. The material which has these phases in at least one part is mentioned.

  Examples of such metal elements or metalloid elements include tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony (Sb), and bismuth (Bi). , Cadmium (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y) or hafnium (Hf) Is mentioned. Among them, the group 14 metal element or metalloid element in the long-period periodic table is preferable, and silicon (Si) or tin (Sn) is particularly preferable. This is because silicon (Si) and tin (Sn) have a large ability to occlude and release lithium, and a high energy density can be obtained.

  As an alloy of silicon (Si), for example, as a second constituent element other than silicon (Si), tin (Sn), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), and chromium (Cr). The thing containing 1 type is mentioned. As an alloy of tin (Sn), for example, as a second constituent element other than tin (Sn), silicon (Si), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), and chromium (Cr). The thing containing 1 type is mentioned.

  Examples of the compound of silicon (Si) or tin (Sn) include those containing oxygen (O) or carbon (C), and in addition to silicon (Si) or tin (Sn), Two constituent elements may be included.

  Any separator may be used as long as it is electrically stable, chemically stable with respect to the positive electrode active material, the negative electrode active material, or the solvent, and has no electrical conductivity. . For example, a polymer nonwoven fabric, a porous film, glass or ceramic fibers in a paper shape can be used, and a plurality of these may be laminated. In particular, a porous polyolefin film is preferably used, and a composite of this with a heat-resistant material made of polyimide, glass, ceramic fibers, or the like may be used.

The electrolyte 16 contains an electrolytic solution and a holding body containing a polymer compound that holds the electrolytic solution, and is in a so-called gel form. The electrolytic solution includes an electrolyte salt and a solvent that dissolves the electrolyte salt. Examples of the electrolyte salt include lithium salts such as LiPF ₆ , LiClO ₄ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , or LiAsF ₆ . Any one of the electrolyte salts may be used, or two or more of them may be mixed and used.

  Examples of the solvent include lactone solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, and ε-caprolactone, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Carbonate ester solvents such as 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,2-diethoxyethane, ether solvents such as tetrahydrofuran or 2-methyltetrahydrofuran, nitrile solvents such as acetonitrile, Nonaqueous solvents such as sulfolane-based solvents, phosphoric acids, phosphate ester solvents, or pyrrolidones are mentioned. Any one type of solvent may be used alone, or two or more types may be mixed and used.

  The solvent preferably contains a compound in which part or all of hydrogen of the cyclic ester or chain ester is fluorinated. As the fluorinated compound, difluoroethylene carbonate (4,5-difluoro-1,3-dioxolan-2-one) is preferably used. Even when the negative electrode 14 containing a compound such as silicon (Si), tin (Sn), or germanium (Ge) is used as the negative electrode active material, the charge / discharge cycle characteristics can be improved. In particular, difluoroethylene carbonate is used. This is because the cycle characteristic improvement effect is excellent.

  The polymer compound may be any one that gels upon absorption of a solvent. For example, a fluorine-based polymer compound such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene, polyethylene oxide or polyethylene oxide. And ether-based polymer compounds such as crosslinked products containing polyacrylonitrile, polypropylene oxide, or polymethyl methacrylate as repeating units. Any one of these polymer compounds may be used alone, or two or more thereof may be mixed and used.

In particular, from the viewpoint of redox stability, a fluorine-based polymer compound is desirable, and among them, a copolymer containing vinylidene fluoride and hexafluoropropylene as components is preferable. Furthermore, this copolymer contains monoesters of unsaturated dibasic acids such as monomethylmaleic acid ester, halogenated ethylenes such as ethylene trifluorochloride, cyclic carbonates of unsaturated compounds such as vinylene carbonate, or epoxy group-containing compounds. An acrylic vinyl monomer may be included as a component. This is because higher characteristics can be obtained.

[Method for producing non-aqueous electrolyte battery]
This non-aqueous electrolyte battery can be manufactured, for example, as follows. First, a precursor solution containing an electrolytic solution, a polymer compound, and a mixed solvent is applied to each of the positive electrode 13 and the negative electrode 14, and the mixed solvent is volatilized to form the electrolyte 16. After that, the positive electrode lead 11 is attached to the end of the positive electrode current collector 13A by welding, and the negative electrode lead 12 is attached to the end of the negative electrode current collector 14A by welding.

  Next, the positive electrode 13 and the negative electrode 14 on which the electrolyte 16 is formed are laminated via a separator 15 to form a laminated body, and then the laminated body is wound in the longitudinal direction, and the protective tape 17 is adhered to the outermost peripheral portion. Thus, the wound electrode body 10 is formed. Finally, for example, the wound electrode body 10 is sandwiched between the exterior members 1 and the outer edge portions of the exterior member 1 are brought into close contact with each other by thermal fusion or the like and sealed. At that time, the adhesion film 2 is inserted between the positive electrode lead 11 and the negative electrode lead 12 and the exterior member 1. Thereby, the nonaqueous electrolyte battery shown in FIGS. 1 and 2 is completed.

  Further, this nonaqueous electrolyte battery may be manufactured as follows. First, the positive electrode 13 and the negative electrode 14 are prepared as described above, and after the positive electrode lead 11 and the negative electrode lead 12 are attached to the positive electrode 13 and the negative electrode 14, the positive electrode 13 and the negative electrode 14 are laminated via the separator 15 and wound. Rotate and adhere the protective tape 17 to the outermost periphery to form a wound body that is a precursor of the wound electrode body 10. Next, the wound body is sandwiched between the exterior members 1, and the outer peripheral edge except for one side is heat-sealed to form a bag shape, and is stored inside the exterior member 1. Subsequently, an electrolyte composition including an electrolytic solution, a monomer that is a raw material of the polymer compound, a polymerization initiator, and other materials such as a polymerization inhibitor as necessary is prepared, and the interior of the exterior member 1 is prepared. Inject.

  After injecting the electrolyte composition, the opening of the exterior member 1 is heat-sealed in a vacuum atmosphere and sealed. Next, heat is applied to polymerize the monomer to obtain a polymer compound, thereby forming a gel electrolyte 16 and assembling the nonaqueous electrolyte battery shown in FIGS.

〔effect〕
According to the third embodiment of the present invention, the positive electrode active material according to the first embodiment described above is used as the positive electrode active material. With this configuration, gas generation of the electrolytic solution can be suppressed, and battery swelling can be suppressed.

4). Fourth embodiment (second example of nonaqueous electrolyte battery)

  Next explained is the fourth embodiment of the invention. A nonaqueous electrolyte battery according to a fourth embodiment of the present invention uses an electrolyte instead of the gel electrolyte 16 in the nonaqueous electrolyte battery of the third embodiment. In this case, the electrolytic solution is impregnated in the separator 15. As the electrolytic solution, the same one as in the third embodiment described above can be used.

  The nonaqueous electrolyte battery having such a configuration can be manufactured, for example, as follows. First, the positive electrode 13 and the negative electrode 14 are prepared, and the positive electrode lead 11 and the negative electrode lead 12 are attached to the positive electrode 13 and the negative electrode 14, and then the positive electrode 13 and the negative electrode 14 are laminated and wound via the separator 15, and the outermost peripheral part A protective tape 17 is adhered to the wound electrode body 10 to produce a wound electrode body having a configuration in which the electrolyte 16 is omitted from the configuration of the wound electrode body 10. After sandwiching the wound electrode body between the exterior members 1, the exterior member 1 is sealed by injecting an electrolytic solution.

〔effect〕
In the fourth embodiment of the present invention, the same effect as in the third embodiment described above can be obtained. That is, by using the positive electrode active material according to the first embodiment described above as the positive electrode active material, it is possible to suppress gas generation of the electrolytic solution and to suppress battery swelling.

5). Fifth embodiment (third example of nonaqueous electrolyte battery)
Next, the configuration of a nonaqueous electrolyte battery according to a fifth embodiment of the present invention will be described with reference to FIGS. FIG. 3 shows the configuration of a nonaqueous electrolyte battery according to the fifth embodiment of the present invention. This non-aqueous electrolyte battery is a so-called cylindrical type, in which a strip-shaped positive electrode 31 and a strip-shaped negative electrode 32 are wound through a separator 33 inside a substantially hollow cylindrical battery can 21. An electrode body 30 is provided. The separator 33 is impregnated with an electrolytic solution that is a liquid electrolyte. The battery can 21 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 21, a pair of insulating plates 22 and 23 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 30.

  A battery lid 24, a safety valve mechanism 25 provided inside the battery lid 24, and a heat sensitive resistance (PTC: Positive Temperature Coefficient) element 26 are caulked through a gasket 27 at the open end of the battery can 21. The inside of the battery can 21 is sealed. The battery lid 24 is made of the same material as the battery can 21, for example. The safety valve mechanism 25 is electrically connected to the battery lid 24 via the heat sensitive resistance element 26, and the disk plate 25A is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 24 and the wound electrode body 30 is cut off. When the temperature rises, the heat-sensitive resistor element 26 limits the current by increasing the resistance value, and prevents abnormal heat generation due to a large current. The gasket 27 is made of, for example, an insulating material, and asphalt is applied to the surface.

  The wound electrode body 30 is wound around a center pin 34, for example. A positive electrode lead 35 made of aluminum (Al) or the like is connected to the positive electrode 31 of the spirally wound electrode body 30, and a negative electrode lead 36 made of nickel (Ni) or the like is connected to the negative electrode 32. The positive electrode lead 35 is welded to the safety valve mechanism 25 to be electrically connected to the battery lid 24, and the negative electrode lead 36 is welded to and electrically connected to the battery can 21.

  4 is an enlarged cross-sectional view illustrating a part of the spirally wound electrode body 30 illustrated in FIG. The wound electrode body 30 is obtained by stacking and winding a positive electrode 31 and a negative electrode 32 with a separator 33 interposed therebetween.

  The positive electrode 31 includes, for example, a positive electrode current collector 31A and a positive electrode active material layer 31B provided on both surfaces of the positive electrode current collector 31A. The negative electrode 32 includes, for example, a negative electrode current collector 32A and a negative electrode active material layer 32B provided on both surfaces of the negative electrode current collector 32A. The configurations of the positive electrode current collector 31A, the positive electrode active material layer 31B, the negative electrode current collector 32A, the negative electrode active material layer 32B, the separator 33, and the electrolyte solution are respectively the positive electrode current collector 13A and the positive electrode active material in the third embodiment described above. This is the same as the material layer 13B, the negative electrode current collector 14A, the negative electrode active material layer 14B, the separator 15, and the electrolytic solution.

  Next explained is a method for manufacturing a nonaqueous electrolyte battery according to the fifth embodiment of the invention.

  The positive electrode 31 is produced as follows. The positive electrode active material layer 31B is formed on the positive electrode current collector 31A as described above to obtain the positive electrode 31. The method for forming the positive electrode active material layer 31B is the same as that described above, and a detailed description thereof will be omitted.

  The negative electrode 32 is produced as follows. First, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and this negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a negative electrode mixture slurry. Next, after applying this negative electrode mixture slurry to the negative electrode current collector 32A and drying the solvent, the negative electrode active material layer 32B is formed by compression molding using a roll press or the like, and the negative electrode 32 is obtained.

  Next, the positive electrode lead 35 is attached to the positive electrode current collector 31A by welding or the like, and the negative electrode lead 36 is attached to the negative electrode current collector 32A by welding or the like. Thereafter, the positive electrode 31 and the negative electrode 32 were wound through the separator 33, and the tip of the positive electrode lead 35 was welded to the safety valve mechanism 25, and the tip of the negative electrode lead 36 was welded to the battery can 21 and wound. The positive electrode 31 and the negative electrode 32 are sandwiched between a pair of insulating plates 22 and 23 and housed in the battery can 21. After the positive electrode 31 and the negative electrode 32 are accommodated in the battery can 21, the electrolyte is injected into the battery can 21 and impregnated in the separator 33. Thereafter, the battery lid 24, the safety valve mechanism 25, and the heat sensitive resistance element 26 are fixed to the opening end portion of the battery can 21 by caulking through the gasket 27. As described above, the nonaqueous electrolyte battery shown in FIG. 3 is manufactured.

〔effect〕
In the nonaqueous electrolyte battery according to the fifth embodiment of the present invention, by using the positive electrode active material according to the first embodiment, gas generation can be suppressed and damage due to an increase in internal pressure can be prevented.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples.

<Example 1>
A positive electrode active material and a nonaqueous electrolyte secondary battery were produced as follows.

[Preparation of positive electrode active material]
First, nickel sulfate, cobalt sulfate, and sodium aluminate were dissolved in water, and a sodium hydroxide solution was added with sufficient stirring. At this time, the nickel-cobalt-aluminum composite coprecipitated hydroxide is prepared so that the molar ratio of nickel (Ni), cobalt (Co), and aluminum (Al) is Ni: Co: Al = 77: 20: 3. Got. The produced coprecipitate was washed with water and dried, and then lithium hydroxide monohydrate was added to adjust the molar ratio to be Li: (Ni + Co + Al) = 98: 100 to prepare a precursor.

These precursors are calcined in an oxygen stream at 700 ° C. for 10 hours, cooled to room temperature, pulverized, and composite oxidation mainly composed of lithium nickelate represented by the composition formula Li _0.98 Ni _0.77 Co _0.20 Al _0.03 O ₂ Product particles were obtained. When the composite oxide particles were measured by a laser scattering method, the average particle size was 14 μm.

To 100 parts by weight of the composite oxide particles described above, 3.0 parts by weight of ammonium metatungstate [(NH ₄ ) ₆ W ₁₂ O ₃₉ ] was added and sufficiently mixed in a mortar. This mixture was calcined in an oxygen stream at 300 ° C. for 4 hours, cooled to room temperature, then taken out and pulverized to obtain a positive electrode active material.

(Preparation of non-aqueous electrolyte secondary battery)
A non-aqueous electrolyte secondary battery described below was produced using the produced positive electrode active material.

  First, 90 parts by mass of the obtained positive electrode active material, 5 parts by mass of graphite as a conductive agent, and 5 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. Next, this positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a dispersion medium to obtain a positive electrode mixture slurry. This positive electrode mixture slurry was uniformly applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 20 μm, dried, and compression molded with a roll press to form a positive electrode active material layer, thereby producing a positive electrode. Subsequently, a positive electrode terminal was attached to the exposed portion of the positive electrode current collector of the positive electrode.

  Next, 95 parts by mass of pulverized graphite powder as a negative electrode active material and 5 parts by mass of polyvinylidene fluoride as a binder are mixed to prepare a negative electrode mixture, and this is further mixed with N-methyl-2 as a dispersion medium. -Dispersed in pyrrolidone to make a negative electrode mixture slurry. Next, the negative electrode mixture slurry is uniformly applied on both sides of a negative electrode current collector made of a copper foil having a thickness of 15 μm, dried, and compression-molded with a roll press to form a negative electrode active material layer. Produced. Subsequently, a negative electrode terminal was attached to the exposed portion of the negative electrode current collector.

  Next, the prepared positive electrode and negative electrode are closely adhered via a separator made of a microporous polyethylene film having a thickness of 25 μm, wound in the longitudinal direction, and a protective tape is attached to the outermost peripheral portion, whereby a wound body is obtained. Produced. Subsequently, this wound body was loaded between exterior materials, and three sides of the exterior material were heat-sealed, and one side was not heat-sealed but had an opening. As the exterior material, a moisture-proof aluminum laminate film in which a 25 μm thick nylon film, a 40 μm thick aluminum foil, and a 30 μm thick polypropylene film were laminated in order from the outermost layer was used.

Subsequently, 1 mol / l of lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt was added to a solvent mixed so that the mass ratio was ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 5: 5. An electrolytic solution prepared by dissolving was prepared. This electrolyte solution was injected from the opening of the exterior material, and the remaining one side of the exterior material was heat-sealed under reduced pressure and sealed to produce a nonaqueous electrolyte secondary battery.

<Example 2>
In the manufacturing process of the positive electrode active material of Example 1, 3.0 parts by weight of ammonium metatungstate [(NH ₄ ) ₆ W ₁₂ O ₃₉ ] and ammonium paratungstate [(NH ₄ ) ₁₀ W ₁₂ O ₄₁ ] were added. The amount was 3.0 parts by weight. Except for the above, a positive electrode active material was obtained in the same manner as in Example 1. Using this positive electrode active material, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.

<Example 3>
In the production process of the positive electrode active material of Example 1, 3.0 parts by weight of ammonium metatungstate [(NH ₄ ) ₆ W ₁₂ O ₃₉ ] and 1. silicotungstic acid [H ₄ (SiW ₁₂ O ₄₀ )] The amount was 1 part by weight. Except for the above, a positive electrode active material was obtained in the same manner as in Example 1. Using this positive electrode active material, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.

<Example 4>
In the manufacturing process of the positive electrode active material of Example 1, 3.0 parts by weight of ammonium metatungstate [(NH ₄ ) ₆ W ₁₂ O ₃₉ ] and _3. phosphotungstic acid [H ₃ (PW ₁₂ O ₄₀ )] were used. The amount was 5 parts by weight. Except for the above, a positive electrode active material was obtained in the same manner as in Example 1. Using this positive electrode active material, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.

<Example 5>
In the production process of the positive electrode active material of Example 4, a positive electrode active material was obtained in the same manner as in Example 4 except that the heat treatment was performed in an oxygen stream at 200 ° C. for 0.5 hour. Using this positive electrode active material, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.

<Example 6>
In the production process of the positive electrode active material of Example 1, 3.0 parts by weight of ammonium metatungstate [(NH ₄ ) ₆ W ₁₂ O ₃₉ ] and 0.0% of phosphomolybdic acid [H ₃ (PMo ₁₂ O ₄₀ )] were added. The amount was 3 parts by weight. Except for the above, a positive electrode active material was obtained in the same manner as in Example 1. Using this positive electrode active material, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.

<Comparative Example 1>
In the manufacturing process of the positive electrode active material of Example 1, addition, mixing, and heat treatment of ammonium metatungstate [(NH ₄ ) ₆ W ₁₂ O ₃₉ ] were not performed. Except for the above, a positive electrode active material was obtained in the same manner as in Example 1. Using this positive electrode active material, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.

<Comparative example 2>
In the manufacturing process of the positive electrode active material of Example 6, 0.3 part by weight of phosphomolybdic acid [H ₃ (PMo ₁₂ O ₄₀ )] was 0.03 part by weight. Except for the above, a positive electrode active material was obtained in the same manner as in Example 6. Using this positive electrode active material, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.

(Evaluation)
Using the produced positive electrode active materials and non-aqueous electrolyte secondary batteries, the following measurements and tests were performed to evaluate the characteristics.

[PH measurement]
1.0 parts by weight of the prepared positive electrode active material was dispersed in 50 parts by weight of water, and the pH of the supernatant of the water on which the positive electrode active material was precipitated was measured.

[Measurement of carbonic acid content]
About each produced positive electrode active material, the carbonic acid content contained in a positive electrode active material was measured by AGK method prescribed | regulated to JISR9101.

[Charge / discharge test]
The produced nonaqueous electrolyte secondary battery was charged at a constant current of 880 mA at a constant current of 23 ° C. until the battery voltage reached 4.25 V against metallic lithium, and then at a constant voltage of 4.25 V. Constant voltage charging was performed until the current value reached 1 mA. Next, constant current discharge was performed at a constant current of 80 mA until the battery voltage reached 2.50 V with respect to metallic lithium. The charge / discharge efficiency and the discharge capacity of the positive electrode active material were obtained by the above charge / discharge test.

[High temperature storage test]
The produced nonaqueous electrolyte secondary battery was charged at a constant current of 880 mA at a constant current of 880 mA until the battery voltage reached 4.2 V in a 23 ° C. environment, and then the current value was 1 mA at a constant voltage of 4.2 V. Constant voltage charging was performed until it reached. Thereafter, the fully charged nonaqueous electrolyte secondary battery was stored in an environment of 80 ° C. for 4 days. The amount of change in the thickness of the nonaqueous electrolyte secondary battery at this time was measured as the amount of swelling during high temperature storage.

  Table 1 summarizes the measurement results.

[Evaluation]
Comparison of Examples 1 to 6 and Comparative Examples 1 and 2 revealed the following.
In Examples 1 to 6, it was found that the pH of the positive electrode active material was less than 8.0, the carbonic acid content contained in the positive electrode active material was small, and the amount of battery swelling was suppressed. Moreover, the charge / discharge efficiency also showed good characteristics.

6). Other embodiment (modification)
The present invention is not limited to the above-described embodiment of the present invention, and various modifications and applications are possible without departing from the spirit of the present invention. For example, the shape of the nonaqueous electrolyte battery is not limited to that described above. For example, a square shape or a coin shape may be used.

  Further, for example, a polymer solid electrolyte composed of an ion conductive polymer material or an inorganic solid electrolyte composed of an ion conductive inorganic material may be used as the electrolyte. Examples of the ion conductive polymer material include polyether, polyester, polyphosphazene, and polysiloxane. Examples of the inorganic solid electrolyte include ion conductive ceramics, ion conductive crystals, and ion conductive glass.

DESCRIPTION OF SYMBOLS 1 ... Exterior member 2 ... Adhesion film 10, 30, 53 ... Winding electrode body 11, 35 ... Positive electrode lead 12, 36 ... Negative electrode lead 13, 31 ... Positive electrode 13A, 31A ... Positive current collector 13B, 31B ... Positive electrode active material layer 14, 32 ... Negative electrode 14A, 32A ... Negative electrode current collector 14B, 32B ... Negative electrode active material layer 15, 33 ... Separator 16 ... Electrolyte 17 ... Protective tape 21 ... Battery can 22,23 ... Insulating plate 24 ... Battery cover 25 ... Safety valve mechanism 25A ... Disk plate 26 ... Heat feeling Resistance element 27 ... Gasket 34 ... Center pin

Claims (11)

Lithium composite oxide particles;
A coating layer formed on at least a part of the surface of the lithium composite oxide particles,
The lithium composite oxide particles are lithium composite oxide particles mainly composed of nickel,
The coating layer contains an oxo acid and / or an oxo acid compound,
By the coating layer, the acidity of the surface of the lithium composite oxide particles containing nickel as a main component is increased to a predetermined acidity,
The predetermined acidity is determined by the lithium composite oxide particles after the dispersion of 1.0 parts by weight of the lithium composite oxide particles mainly composed of nickel on which the coating layer is formed in 50 parts by weight of water. Defined by the pH of the supernatant of the water in the settling state,
The positive electrode active material whose said pH is less than 8.0. The lithium composite oxide particles have a reduced discharge capacity at a predetermined rate due to the formation of the coating layer,
2. The positive electrode active material according to claim 1, wherein the predetermined decrease rate is a decrease rate with respect to a discharge capacity of the lithium composite oxide particles before forming the coating layer, and is less than 5%. The positive electrode active material according to claim 1, wherein the lithium composite oxide particles containing nickel as a main component have an average composition represented by formula (1).
(Formula 1)
Li _a Ni _x Co _y Al _z O ₂
(However, nickel (Ni) is manganese (Mn), chromium (Cr), iron (Fe), vanadium (V) within the range of 0.1 or less of Ni when the total amount of Ni is 1. , Magnesium (Mg), titanium (Ti), zirconium (Zr), niobium (Nb), molybdenum (Mo), tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In) , Tin (Sn), lanthanum (La), cerium (Ce) can be substituted with one or more metal elements selected from the group consisting of a, x, y, and z, 0.20 ≦ a ≦ 1.40, 0.60 <x <0.90, 0.10 <y <0.40, 0.01 <z <0.20, and x, y There is a relationship of x + y + z = 1 between z and z.)   The positive electrode active material according to claim 1, wherein the carbonate ion content is 0.15 wt% or less.   The positive electrode active material according to claim 1, wherein the average particle diameter is in the range of 2.0 μm to 50 μm. A deposition step of depositing oxoacid and / or oxoacid compound on lithium composite oxide particles mainly composed of nickel;
A heat treatment step of heat treating the lithium composite oxide particles mainly composed of nickel to which the oxo acid and / or oxo acid compound is deposited,
By the deposition step and the heat treatment step, the acidity of the surface of the lithium composite oxide particles mainly composed of nickel is increased to a predetermined acidity,
The predetermined acidity is obtained by adding 50 parts by weight of water to 1.0 part by weight of the lithium composite oxide particles mainly composed of nickel to which the oxo acid and / or oxo acid compound is applied after the heat treatment step. Defined by the pH of the supernatant of the water in which the lithium composite oxide particles have settled after being dispersed in
The method for producing a positive electrode active material, wherein the pH is less than 8.0. By the deposition step and the heat treatment step, the discharge capacity of the lithium composite oxide containing nickel as a main component is reduced at a predetermined reduction rate.
The method for producing a positive electrode active material according to claim 6, wherein the predetermined decrease rate is a decrease rate with respect to the discharge capacity of the lithium composite oxide particles containing nickel as a main component before the deposition step and less than 5%. In the heat treatment step,
The method for producing a positive electrode active material according to claim 6, wherein the temperature of the heat treatment is 150 ° C. or higher and 1200 ° C. or lower. In the heat treatment step,
The method for producing a positive electrode active material according to claim 6, wherein the heat treatment is performed in an oxidizing atmosphere. In the above deposition process,
The method for producing a positive electrode active material according to claim 6, wherein 0.01 to 5.0 parts by weight of the oxo acid and / or oxo acid compound is applied to 100 parts by weight of the lithium composite oxide particles. A positive electrode, a negative electrode, and an electrolyte;
The positive electrode has a positive electrode active material,
The positive electrode active material has lithium composite oxide particles and a coating layer formed on at least a part of the surface of the lithium composite oxide particles.
The lithium composite oxide particles are lithium composite oxide particles mainly composed of nickel,
The coating layer contains an oxo acid and / or an oxo acid compound,
By the coating layer, the acidity of the surface of the lithium composite oxide particles containing nickel as a main component is increased to a predetermined acidity,
The predetermined acidity is determined by the lithium composite oxide particles after the dispersion of 1.0 parts by weight of the lithium composite oxide particles mainly composed of nickel on which the coating layer is formed in 50 parts by weight of water. Defined by the pH of the supernatant of the water in the settling state,
The non-aqueous electrolyte battery having a pH of less than 8.0.

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