Method for manufacturing positive electrode active material for lithium ion secondary battery

Abstract

To provide a method for manufacturing a positive electrode active material for a lithium ion secondary battery which can provide a high capacity and large output.SOLUTION: A method for manufacturing a positive electrode active material for a lithium ion secondary battery of the present invention includes: a mixing step of mixing a lithium nickel composite oxide as a start material and tungsten compound powder not including lithium while heating the lithium nickel composite oxide and the tungsten compound powder, thereby obtaining a tungsten mixture; and a thermal processing step of performing thermal processing on the tungsten mixture. The lithium nickel composite oxide includes Li, Ni, and an element M. A ratio of the number of atoms of the tungsten to a total number of the atoms of the nickel in the lithium nickel composite oxide as the start material and the atoms of the element M is at least 0.05 atom% and 3.00 atom% at most. A ratio of water in the water in the start material and the lithium nickel composite oxide is at least 3.0 mass%. A temperature in the mixing step is in the range of 30°C to 65°C.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing a positive electrode active material for a lithium ion secondary battery, a positive electrode active material for a lithium ion secondary battery, and a lithium ion secondary battery. [Background technology]

[0002] In recent years, with the widespread use of portable electronic devices such as mobile phones and notebook computers, there is a strong demand for the development of small, lightweight secondary batteries with high energy density, as well as high-output secondary batteries for use in electric vehicles, including hybrid vehicles.

[0003] A lithium-ion secondary battery is one example of a secondary battery that meets these requirements. This lithium-ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, etc., and the active materials for the negative electrode and the positive electrode are materials that can extract and insert lithium.

[0004] Such lithium-ion secondary batteries are currently the subject of vigorous research and development. In particular, lithium-ion secondary batteries that use layered or spinel-type lithium-nickel composite oxides as the positive electrode material are capable of achieving a high voltage of around 4 V, and are therefore being put into practical use as batteries with high energy density.

[0005] The main materials that have been proposed so far include lithium cobalt composite oxide (LiCoO2), which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO2), which uses nickel, which is cheaper than cobalt, and lithium nickel cobalt manganese composite oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2) and lithium manganese composite oxide (LiMn2O4) that uses manganese.

[0006] Among these, lithium nickel composite oxide has been attracting attention as a material with good cycle characteristics and capable of obtaining high output with low resistance. With regard to the positive electrode active material for lithium ion secondary batteries, in recent years, importance has been placed on achieving low resistance, which is necessary for achieving high output when used in lithium ion secondary batteries.

[0007] The addition of foreign elements is used as a method for achieving the above-mentioned low resistance, and transition metals that can assume high valence, such as W, Mo, Nb, Ta, and Re, are considered to be particularly useful.

[0008] For example, Patent Document 1 proposes a lithium transition metal compound powder for use as a positive electrode material for lithium secondary batteries, which satisfies a predetermined composition formula and contains one or more elements selected from Mo, W, Nb, Ta, and Re in a ratio of 0.1 mol % to 5 mol % relative to the total molar amount of Mn, Ni, and Co in the composition formula. Patent Document 1 also discloses a method for producing a lithium transition metal compound powder for use as a positive electrode material for lithium secondary batteries, which includes a spray drying step in which lithium carbonate, a Ni compound, a Mn compound, a Co compound, and a metal compound containing at least one element selected from Mo, W, Nb, Ta, and Re are pulverized in a liquid medium, and the resulting slurry is spray-dried to uniformly disperse the pulverized powder, and a firing step in which the resulting spray-dried product is fired.

[0009] According to Patent Document 1, it is possible to achieve both low cost, high safety, high load characteristics, and improved powder handling properties of lithium transition metal compound powder for use as a positive electrode material for lithium secondary batteries.

[0010] However, according to the manufacturing method disclosed in Patent Document 1, the lithium transition metal compound powder is obtained by pulverizing the raw materials in a liquid medium, spray-drying the slurry in which the raw materials are uniformly dispersed, and firing the resulting spray-dried body. Therefore, there is a problem that some of the foreign elements such as Mo, W, Nb, Ta, and Re are substituted for Ni arranged in layers, resulting in a decrease in battery characteristics such as the capacity and cycle characteristics of the battery.

[0011] Patent Document 2 also proposes a positive electrode active material for non-aqueous electrolyte secondary batteries having at least a layered lithium transition metal composite oxide, the lithium transition metal composite oxide being present in the form of particles consisting of one or both of primary particles and secondary particles which are aggregates thereof, and having a compound containing at least one selected from the group consisting of molybdenum, vanadium, tungsten, boron and fluorine on at least the surface of the particles. Patent Document 2 also discloses a method for producing the positive electrode active material for non-aqueous electrolyte secondary batteries, in which a raw material mixture is a mixture of a compound of an additive element such as a molybdenum compound, a lithium compound, and a compound obtained by co-precipitating cobalt or the like and then heat-treating the compound, and then pulverizing the mixture.

[0012] According to the positive electrode active material for non-aqueous electrolyte secondary batteries disclosed in Patent Document 2, in particular, by having a compound having at least one selected from the group consisting of molybdenum, vanadium, tungsten, boron and fluorine on the surface of the particles, it is said that the initial characteristics are improved without impairing the improvements in thermal stability, load characteristics and output characteristics.

[0013] However, in Patent Document 2, the effect of at least one additive element selected from the group consisting of molybdenum, vanadium, tungsten, boron, and fluorine is said to be in improving initial characteristics, i.e., initial discharge capacity and initial efficiency, but not in improving output characteristics. In addition, according to the manufacturing method disclosed in Patent Document 2, a raw material mixture that is a mixture of a compound of an additive element such as a molybdenum compound, a lithium compound, and a compound obtained by coprecipitation of cobalt or the like and then heat treatment is fired, so there is a problem that a part of the additive element is replaced with nickel arranged in layers, resulting in a deterioration of battery characteristics.

[0014] Patent Document 3 proposes a positive electrode active material having a carbonate ion content of 0.15 mass% or less, which is obtained by coating composite oxide particles having a predetermined composition with a tungstic acid compound and then performing a heat treatment. Patent Document 3 also discloses a method for producing a positive electrode active material, which includes a coating step of coating composite oxide particles containing lithium (Li) and nickel (Ni) with a tungstic acid compound, and a heating step of heat treating the composite oxide particles coated with the tungstic acid compound.

[0015] According to Patent Document 3, it is said that gas generation due to decomposition of the non-aqueous electrolyte solution etc. can be suppressed. Alternatively, it is said that gas generation from the positive electrode active material itself can be suppressed. However, it does not improve the output characteristics.

[0016] Additionally, improvements are being made to increase the output of lithium nickel composite oxides.

[0017] For example, Patent Document 4 proposes a positive electrode active material for non-aqueous electrolyte secondary batteries, which is a lithium metal composite oxide consisting of primary particles and secondary particles formed by aggregation of the primary particles, and has fine particles containing lithium tungstate expressed as any one of Li2WO4, Li4WO5, and Li6W2O9 on the surface of the lithium metal composite oxide, and is said to be able to obtain high capacity as well as high output.

[0018] However, although the output has been increased while maintaining a high capacity, there is a demand for even higher capacity.

[0019] Patent Document 5 discloses a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: a mixing step of mixing lithium-nickel composite oxide particles, a lithium-free tungsten compound powder, and water to obtain a tungsten mixture; and a heat treatment step of heat-treating the tungsten mixture, the heat treatment step including a first heat treatment step of heat-treating the tungsten mixture to cause a lithium compound present on the surfaces of the primary particles of the lithium-nickel composite oxide particles to react with the tungsten compound particles, thereby dissolving the tungsten compound particles, thereby forming lithium-nickel composite oxide particles having tungsten dispersed on the surfaces of the primary particles; and a second heat treatment step of performing heat treatment at a temperature higher than that of the first heat treatment step, subsequent to the first heat treatment step, to form lithium-nickel composite oxide particles having a compound containing tungsten and lithium provided on the surfaces of the primary particles of the lithium-nickel composite oxide particles. [Prior art documents] [Patent documents]

[0020] [Patent Document 1] Japanese Patent Application Publication No. 2009-289726 [Patent Document 2] Japanese Patent Application Publication No. 2005-251716 [Patent Document 3] Japanese Patent Publication No. 2010-40383 [Patent Document 4] Japanese Patent Application Publication No. 2013-125732 [Patent Document 5] Japanese Patent Application Publication No. 2017-063003 Summary of the Invention [Problem to be solved by the invention]

[0021] However, in the examples of Patent Document 5, only an example is disclosed in which the mixed powder of the tungsten mixture is placed in an aluminum bag and purged with nitrogen gas in the first heat treatment step, and there is a problem that such a method would be very costly when applied to mass production.

[0022] In Patent Document 5, a mixing step, a first heat treatment step, and a second heat treatment step are required, which increases the number of steps and also increases the manufacturing cost. Furthermore, the use of aluminum bags and a vacuum dryer makes it impossible to perform the mixing and heat treatment steps continuously, which is also disadvantageous in terms of cost.

[0023] In view of the problems associated with the above-described conventional techniques, an object of one aspect of the present invention is to provide a method for producing a positive electrode active material for a lithium ion secondary battery, which is low-cost and provides high capacity and high output when used in a positive electrode of a lithium ion secondary battery. [Means for solving the problem]

[0024] In order to solve the above problem, according to one aspect of the present invention, A mixing step of mixing the starting materials, lithium nickel composite oxide and a lithium-free tungsten compound powder, while heating to obtain a tungsten mixture; and a heat treatment step of heat treating the tungsten mixture, The lithium nickel composite oxide contains lithium (Li), nickel (Ni), and an element M (M), where M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti, Co, and Al; a ratio of the number of tungsten atoms to the total number of atoms of nickel and the element M contained in the lithium nickel composite oxide in the starting material is 0.05 atomic % or more and 3.00 atomic % or less; a moisture content, which is a ratio of the water in the starting material and the water in the lithium nickel composite oxide, is 3.0% by mass or more; The present invention provides a method for producing a positive electrode active material for a lithium ion secondary battery, wherein the temperature of the mixing step is 30° C. or higher and 65° C. or lower. Effect of the Invention

[0025] According to one aspect of the present invention, it is possible to provide a method for producing a positive electrode active material for a lithium ion secondary battery at low cost, which, when used in a positive electrode of a lithium ion secondary battery, provides high capacity and high output. [Brief description of the drawings]

[0026] [Figure 1] 1 shows an example of an SEM image when measuring segregated particles. [Diagram 2] 1 is a SEM photograph of segregated particles. [Diagram 3] 1 is a SEM photograph of segregated particles. [Figure 4] FIG. 2 is an explanatory diagram of a cross-sectional configuration of a coin battery produced in Examples and Comparative Examples. [Figure 5A] 1 is a measurement example of impedance evaluation. [Figure 5B] FIG. 2 is a schematic explanatory diagram of an equivalent circuit used in the analysis. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, the form for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiment, and various modifications and substitutions can be made to the following embodiment without departing from the scope of the present invention. [Method of manufacturing positive electrode active material for lithium ion secondary batteries] The method for producing a positive electrode active material for a lithium ion secondary battery according to this embodiment (hereinafter also simply referred to as a "method for producing a positive electrode active material") can include the following steps.

[0028] A mixing step in which the starting materials, the lithium nickel composite oxide and the lithium-free tungsten compound powder, are mixed while being heated to obtain a tungsten mixture. A heat treatment process in which the tungsten mixture is heat treated. The lithium nickel composite oxide may contain lithium (Li), nickel (Ni), and an element M. The element M is preferably at least one element selected from Mn, V, Mg, Mo, Nb, Ti, Co, and Al.

[0029] The ratio of the number of tungsten atoms to the total number of atoms of nickel and element M contained in the lithium nickel composite oxide in the starting material can be 0.05 atomic % or more and 3.00 atomic % or less. It is also preferable that the moisture content, which is the ratio of water to water in the starting material and the lithium nickel composite oxide, is 3.0 mass % or more, and the temperature in the mixing step is 30° C. or more and 65° C. or less.

[0030] Hereinafter, each step of the method for producing a positive electrode active material for a lithium ion secondary battery according to this embodiment will be described in detail. (Mixing process) In the mixing step, the starting materials, the lithium nickel composite oxide and the tungsten compound not containing lithium (hereinafter also simply referred to as "tungsten compound"), can be mixed while being heated. In the mixing step, a tungsten mixture is obtained, which is a mixture of the lithium nickel composite oxide and the tungsten compound not containing lithium. As will be described later, in the mixing step, at least a part of the tungsten compound is thought to react with the excess lithium compound present on the surface of the primary particles of the lithium nickel composite oxide to generate a compound containing tungsten and lithium. For this reason, the tungsten mixture can further contain a compound containing tungsten and lithium instead of or in addition to the tungsten compound.

[0031] The starting materials to be subjected to the mixing step preferably contain moisture, and for example, when neither the starting materials, the lithium nickel composite oxide nor the lithium-free tungsten compound, contain moisture, water can be added in the mixing step. Also, when at least one of the lithium nickel composite oxide and the lithium-free tungsten compound contains sufficient moisture, there is no need to add water separately in the mixing step.

[0032] When the starting material contains moisture, excess lithium compound present on the surface of the primary particles of the lithium nickel composite oxide is eluted. Therefore, when a tungsten compound that is soluble in a water-soluble or alkaline solution is used, dissolution of the tungsten compound and dispersion of the tungsten component can be promoted in the mixing step.

[0033] The mixing step is preferably carried out without being placed in a closed container such as an aluminum pouch.

[0034] By mixing the lithium nickel composite oxide with the tungsten compound while heating, the excess lithium compound present on the surface of the primary particles of the lithium nickel composite oxide can be reacted with the tungsten compound. The compound containing tungsten and lithium obtained by reacting the excess lithium compound present on the surface of the primary particles of the lithium nickel composite oxide with the tungsten compound can be dissolved in water, and the compound containing tungsten and lithium can be dispersed on the surface of the primary particles of the lithium nickel composite oxide.

[0035] The composition of the lithium nickel composite oxide to be subjected to the mixing step is not particularly limited, but it is preferable that the lithium (Li), nickel (Ni), and element M (M) are contained in a ratio of Li:Ni:M=y:1-x:x (where 0≦x≦0.70, 0.95≦y≦1.20) in terms of the ratio of the amounts of substances. The element M can be at least one element selected from Mn, V, Mg, Mo, Nb, Ti, Co, and Al. It is more preferable that the above y is 0.97≦y≦1.15. The lithium nickel composite oxide is preferably a compound having a layered structure, i.e., a layered compound.

[0036] Lithium nickel composite oxide is, for example, represented by the general formula Li y Ni 1-x M x O 2+α It should be noted that x, y, and the element M have already been explained, and therefore the explanation will be omitted here. It is preferable that α satisfies, for example, −0.2≦α≦0.2.

[0037] The lithium nickel composite oxide can be in the form of a powder having, for example, primary particles and secondary particles formed by agglomeration of the primary particles.

[0038] The lithium nickel composite oxide to be subjected to the mixing step can be prepared by calcining a mixture of a nickel composite compound, such as a nickel composite oxide or a nickel composite hydroxide, and a lithium compound. In addition, for example, the lithium nickel composite oxide obtained after calcination can be further washed with water to reduce excess lithium components and the like attached to the particle surfaces of the lithium nickel composite oxide, and then subjected to the mixing step. Note that when the lithium nickel composite oxide is subjected to the mixing step after being made into a washed cake, the washed cake contains moisture, and therefore, depending on the degree of moisture content, it is not necessary to add moisture in the mixing step as described above.

[0039] However, it is preferable that the lithium nickel composite oxide to be subjected to the mixing step is added in a calcined state, i.e., without washing with water. The calcined lithium nickel composite oxide, i.e., not washed with water, has a particularly sufficient amount of lithium compound on the surface of its primary particles to react with the tungsten compound. Therefore, by using the calcined lithium nickel composite oxide, the amount of lithium extracted from the inside of the particles of the lithium nickel composite oxide during the reaction with the tungsten compound in the mixing step or the like can be reduced, and the formation of a deteriorated layer on the surface of the primary particles of the lithium nickel composite oxide can be suppressed.

[0040] The tungsten compound used is preferably water-soluble and dissolves in the moisture contained in the starting material in order to penetrate the surface of the primary particles inside the secondary particles of the lithium nickel composite oxide. In addition, since the moisture in the starting material becomes alkaline due to the elution of lithium, the tungsten compound may be a compound that is soluble in an alkaline environment. In addition, since the starting material is heated in the mixing process, even if the tungsten compound is difficult to dissolve in water at room temperature, it can be suitably used as long as it dissolves in water by heating during the mixing process, or reacts with the lithium compound on the surface of the lithium nickel composite oxide particles to form a compound containing tungsten and lithium and dissolve in water.

[0041] Furthermore, since the dissolved tungsten compound only needs to be in an amount that can penetrate to the surfaces of the primary particles inside the secondary particles of the lithium nickel composite oxide, for example, when an excessive amount of tungsten compound is added, a part of the tungsten compound may be in a solid state after mixing and further after heating.

[0042] Thus, the tungsten compound is preferably lithium-free and in a state that is soluble in water when heated in the mixing step, etc. The lithium-free tungsten compound to be subjected to the mixing step is not particularly limited, but is preferably at least one selected from, for example, tungsten oxide, tungstic acid, ammonium tungstate, sodium tungstate, etc., and more preferably at least one selected from tungsten oxide (WO3) and tungstic acid (WO3·H2O), which are less likely to be contaminated with impurities, can be used.

[0043] The amount of tungsten contained in the starting material is not particularly limited, but for example, the tungsten compound is added so that the number of tungsten atoms is 0.05 atomic % or more and 3.00 atomic % or less, more preferably 0.05 atomic % or more and 2.00 atomic % or less, even more preferably 0.10 atomic % or more and 1.00 atomic % or less, and particularly preferably 0.10 atomic % or more and 0.50 atomic % or less, relative to the total number of atoms of nickel and element M contained in the lithium nickel composite oxide in the starting material.

[0044] By adding the tungsten compound so that the amount of tungsten in the starting material is within the above range, the amount of tungsten contained in the compound containing tungsten and lithium formed on the surface of the lithium nickel composite oxide particles in the obtained positive electrode active material can be set to a preferred range. Therefore, when the positive electrode active material is used as a material for the positive electrode of a lithium ion secondary battery, the charge / discharge capacity and the output characteristics can be particularly improved and can be compatible with each other.

[0045] Note that even after the mixing step or the heat treatment step, the ratio of the number of tungsten atoms to the total number of atoms of nickel and element M contained in the product does not change. For this reason, it is preferable that the ratio of the number of tungsten atoms to the total number of atoms of nickel and element M in the tungsten mixture obtained after the mixing step and the positive electrode active material obtained after the heat treatment step also satisfy the same range as in the case of the starting material.

[0046] The moisture content, which is the ratio of water to the water in the starting materials and the lithium nickel composite oxide, i.e., the moisture content, is not particularly limited, but is preferably, for example, 3.0 mass% or more, more preferably 3.0 mass% or more and 7.0 mass% or less, and even more preferably 4.0 mass% or more and 6.0 mass% or less.

[0047] By making the moisture content 3.0% by mass or more, the starting material contains a sufficient amount of moisture, and the tungsten compound can be sufficiently dispersed on the surface of the primary particles of the lithium nickel composite oxide. This allows the tungsten compound to react sufficiently with the lithium compound on the surface of the lithium nickel composite oxide particles. In addition, by making the moisture content 7.0% by mass or less, excessive elution of lithium from the lithium nickel composite oxide can be suppressed.

[0048] In the mixing step, in order to react the excess lithium compound present on the surface of the primary particles of the lithium nickel composite oxide with the tungsten compound, it is preferable to mix while heating. Note that, by mixing while heating, the tungsten compound and the compound containing tungsten and lithium can be sufficiently dispersed on the surface of the primary particles of the lithium nickel composite oxide.

[0049] The heating temperature in the mixing step, i.e., the mixing temperature, is not particularly limited. The mixing temperature in the mixing step is, for example, preferably 30°C or higher and 65°C or lower, more preferably 45°C or higher and 60°C or lower, and even more preferably 50°C or higher and 60°C or lower.

[0050] The temperature of the tungsten mixture may rise slightly due to the reaction between the lithium compound and the tungsten compound present on the surface of the lithium nickel composite oxide particles during mixing. However, by keeping the mixing temperature at 65°C or less, the tungsten compound can be uniformly dispersed in the lithium nickel composite oxide particles while suppressing the decrease in the amount of water in the tungsten mixture during the mixing process. In addition, by uniformly dispersing the tungsten compound, the excess lithium compound present on the surface of the primary particles of the lithium nickel composite oxide can be sufficiently reacted with the tungsten compound. However, if the mixing temperature is set to a temperature exceeding 65°C, the tungsten mixture may dry out and the amount of water required to promote the reaction between the lithium compound and the tungsten compound may not be obtained.

[0051] By setting the mixing temperature to 30° C. or higher, the dispersion of the tungsten compound can be particularly promoted, and the reaction between the tungsten compound and the excess lithium compound can also be particularly promoted.

[0052] The time for carrying out the mixing step is not particularly limited, and can be arbitrarily selected according to the mixing temperature and the like. The time for carrying out the mixing step, i.e., the mixing time, is preferably, for example, 15 minutes or more and 60 minutes or less, more preferably 25 minutes or more and 45 minutes or less. By making the mixing time 15 minutes or more, it is possible to particularly promote the dispersion of the tungsten compound and the reaction between the tungsten compound and the excess lithium compound. In addition, even if the mixing time is excessively long, there is no significant difference in the degree of the dispersion of the tungsten compound and the reaction between the tungsten compound and the excess lithium compound, so from the viewpoint of increasing productivity and reducing costs, it is preferable to make the mixing time 60 minutes or less.

[0053] The atmosphere in the mixing step is not particularly limited, but in order to avoid a reaction between carbon dioxide in the atmosphere and the lithium component on the surface of the lithium nickel composite oxide particles, the atmosphere in the mixing step is preferably either decarbonated air or an inert gas. Note that decarbonated air means an atmosphere of air with reduced carbon dioxide, i.e., carbon dioxide. An inert gas means an atmosphere of one or more gases selected from rare gases and nitrogen gas.

[0054] In addition, the atmosphere in the mixing step is desirably evacuated in order to remove moisture from the lithium nickel composite oxide. The exhaust speed is not particularly limited, but it is set to 0.15 m for a charging speed (feed amount) of the lithium nickel composite oxide to the mixing step of 1 kg / min. 3 / min or more 0.30m 3 It is preferable to exhaust the atmosphere of the mixing process at a rate of 100 / min or less. When exhausting the atmosphere of the mixing process, it is preferable to supply decarbonated air or inert gas within a range in which the atmosphere of the mixing process does not become negative pressure, that is, to adjust the flow rate of decarbonated air or inert gas. If the atmosphere of the mixing process becomes negative pressure, air may flow into the atmosphere of the mixing process, causing a reaction between the lithium component and carbon dioxide. On the other hand, by controlling the atmosphere of the mixing process not to become negative pressure as described above, the reaction between the lithium component and carbon dioxide can be suppressed, and the deterioration of the characteristics of the finally produced positive electrode active material can be particularly prevented.

[0055] A general mixer can be used to mix the lithium-nickel composite oxide and the lithium-free tungsten compound. For example, a shaker mixer, a Loedige mixer, a Julia mixer, a V blender, or the like can be used to mix the lithium-nickel composite oxide sufficiently so that the lithium-nickel composite oxide is not destroyed. (Heat treatment process) In the heat treatment step, the tungsten mixture can be heat-treated. In the heat treatment step, the moisture in the tungsten mixture can be sufficiently evaporated, and the compound containing tungsten and lithium can be fixed, i.e., fixed, on the surfaces of the primary particles of the lithium nickel composite oxide particles.

[0056] The heat treatment temperature in the heat treatment step is not particularly limited, but is preferably 100° C. or higher and 200° C. or lower. This is because, by setting the heat treatment temperature to 100° C. or higher, the moisture in the tungsten mixture can be sufficiently evaporated, and the compound containing tungsten and lithium can be sufficiently fixed on the particle surfaces of the lithium nickel composite oxide.

[0057] Furthermore, by setting the heat treatment temperature to 200° C. or less, it is possible to prevent the lithium nickel composite oxide particles from forming necking via the compound containing tungsten and lithium, and to prevent the lithium nickel composite oxide particles from decreasing in specific surface area. Therefore, when the obtained positive electrode active material is used as a material for the positive electrode of a lithium ion secondary battery, the battery characteristics can be particularly improved.

[0058] The heat treatment time in the heat treatment step is not particularly limited, but is preferably from 1 hour to 5 hours in order to sufficiently evaporate moisture and fix the compound containing tungsten and lithium.

[0059] The atmosphere in the heat treatment step is preferably either decarbonated air or an inert gas in order to avoid a reaction between carbon dioxide in the atmosphere and lithium on the particle surfaces of the lithium nickel composite oxide.

[0060] According to the manufacturing method of the positive electrode active material of the present embodiment described above, the tungsten compound can be uniformly dispersed in the lithium nickel composite oxide particles by performing mixing while heating in the mixing step. In addition, the excess lithium compound present on the surface of the lithium nickel composite oxide particles is reacted with the tungsten compound to form a compound containing tungsten and lithium, which can be uniformly dispersed. Then, by sufficiently evaporating the moisture in the heat treatment step, the compound containing tungsten and lithium, for example, lithium tungstate, can be uniformly fixed on the surface of the lithium nickel composite oxide particles. Therefore, the ratio of segregated particles in which the compound containing tungsten and lithium is more precipitated than other particles on the surface of the lithium nickel composite oxide particles can be suppressed. By suppressing the ratio of segregated particles, the cycle characteristics can be improved and the positive electrode resistance can be suppressed.

[0061] In addition, by setting the amount of tungsten in the tungsten mixture formed in the mixing step to a predetermined range, the amount of tungsten contained in the compound containing tungsten and lithium formed on the surface of the lithium nickel composite oxide particles in the obtained positive electrode active material can be set to a preferred range. Therefore, when the positive electrode active material obtained by the method for producing a positive electrode active material of this embodiment is used as a material for the positive electrode of a lithium ion secondary battery, the charge / discharge capacity and the output characteristics can be particularly improved and can be compatible. That is, high capacity and high output can be obtained.

[0062] Furthermore, according to the method for producing a positive electrode active material of the present embodiment, a desired positive electrode active material can be produced by the above-mentioned mixing step and heat treatment step without the need for sealing in an aluminum container, etc. Therefore, a positive electrode active material with high capacity and high output as described above can be obtained at low cost. [Positive electrode active material for lithium-ion secondary batteries] Next, a configuration example of the positive electrode active material for lithium ion secondary batteries (hereinafter, also referred to as "positive electrode active material") of this embodiment will be described. Note that the positive electrode active material for lithium ion secondary batteries of this embodiment can be manufactured by, for example, the manufacturing method of the positive electrode active material already described, so that some of the matters already described will be omitted.

[0063] The positive electrode active material for a lithium ion secondary battery of this embodiment can include a plurality of composite particles having particles of a lithium nickel composite oxide containing lithium (Li), nickel (Ni), and an element M (M) in a substance amount ratio of Li:Ni:M=y:1-x:x, and a compound containing tungsten and lithium arranged on the surface of the lithium nickel composite oxide particle.

[0064] The above x and y preferably satisfy 0≦x≦0.70 and 0.95≦y≦1.20, and the element M can be at least one element selected from Mn, V, Mg, Mo, Nb, Ti, Co, and Al. The above y more preferably satisfies 0.97≦y≦1.15.

[0065] Among the multiple composite particles, the ratio of segregated particles in which the compound containing tungsten and lithium is arranged on the surface of the lithium nickel composite oxide particle in a larger amount than the other composite particles can be 0.1% or less in terms of number ratio. Also, it is preferable that the ratio of the number of tungsten atoms contained in the compound containing tungsten and lithium to the total number of atoms of nickel and element M contained in the lithium nickel composite oxide is 0.05 atomic % or more and 3.0 atomic % or less.

[0066] The positive electrode active material of this embodiment can have a plurality of composite particles having the above-mentioned lithium nickel composite oxide particles and a compound containing tungsten and lithium arranged on the surface of the lithium nickel composite oxide particles. The positive electrode active material of this embodiment can also be composed of the above-mentioned composite particles.

[0067] Lithium nickel composite oxide is, for example, represented by the general formula Liy Ni 1-x M x O 2+α It can be expressed by the following formula. x, y, and element M have already been explained, so the explanation will be omitted here. α is preferably, for example, -0.2≦α≦0.2. The lithium nickel composite oxide can have, for example, a layered structure. That is, it can be a layered compound.

[0068] The lithium nickel composite oxide particles may include primary particles and secondary particles formed by agglomeration of the primary particles.

[0069] By using such a lithium nickel composite oxide, a high charge / discharge capacity can be obtained.

[0070] As described above, a compound containing tungsten and lithium, such as lithium tungstate, can be arranged on the surface of the lithium nickel composite oxide particles.

[0071] In general, if the surface of the positive electrode active material is completely covered with a different compound, the movement (intercalation) of lithium ions is greatly restricted, and as a result, it is considered that the advantage of the high capacity of the lithium nickel composite oxide is eliminated. However, in the positive electrode active material of this embodiment, a compound containing tungsten and lithium is formed on the surface of the lithium nickel composite oxide particles, and the compound containing tungsten and lithium has excellent lithium ion conductivity and has the effect of promoting the movement of lithium ions. Therefore, by disposing a compound containing tungsten and lithium on the surface of the lithium nickel composite oxide particles, a lithium conduction path can be formed at the interface with the electrolyte, and the reaction resistance of the positive electrode active material (hereinafter, sometimes referred to as "positive electrode resistance") can be reduced to improve the output characteristics.

[0072] That is, by reducing the positive electrode resistance, the voltage loss in the battery is reduced, and the voltage actually applied to the load side is relatively high, so that high output can be obtained. In addition, by increasing the voltage applied to the load side, lithium is sufficiently inserted and extracted at the positive electrode, so that the battery capacity is improved. Furthermore, by reducing the reaction resistance, the load on the active material during charging and discharging is also reduced, so that the cycle characteristics can be improved.

[0073] Such a compound containing tungsten and lithium has excellent lithium ion conductivity and promotes the movement of lithium ions by containing tungsten and lithium, and its specific composition is not particularly limited. However, it is preferably lithium tungstate, and for example, in terms of the ratio of the number of atoms, it is preferable that 50% or more of the tungsten contained in the compound containing tungsten and lithium exists in the form of Li4WO5.

[0074] This is because, among compounds containing tungsten and lithium, Li4WO5 has many conductive paths for lithium ions and is highly effective at promoting the movement of lithium ions, so when more than 50% of W is present in the form of Li4WO5, an even greater reduction in reaction resistance can be achieved.

[0075] Here, since the contact between the electrolyte and the lithium nickel composite oxide occurs on the surface of the primary particles of the lithium nickel composite oxide, it is preferable that a compound containing tungsten and lithium is formed on the surface of the primary particles of the lithium nickel composite oxide.

[0076] The primary particle surface of the lithium nickel composite oxide in this embodiment includes the primary particle surface exposed on the outer surface of the secondary particle of the lithium nickel composite oxide and the primary particle surface exposed in the vicinity of the surface and in the internal void of the secondary particle through which the electrolyte can permeate and communicate with the outside of the secondary particle. Furthermore, even the grain boundary between the primary particles is included in the primary particle surface if the bonding of the primary particles is incomplete and the electrolyte can permeate therethrough.

[0077] That is, the contact between the lithium nickel composite oxide and the electrolyte occurs not only on the outer surfaces of the secondary particles formed by agglomeration of the primary particles of the lithium nickel composite oxide, but also in the vicinity of the surfaces of the secondary particles, in the internal voids, and in the imperfect grain boundaries. Therefore, it is preferable to form and arrange a compound containing tungsten and lithium on the surfaces of the primary particles to promote the movement of lithium ions.

[0078] Therefore, by forming a compound containing tungsten and lithium on many of the surfaces of the primary particles of the lithium nickel composite oxide that can come into contact with the electrolyte, it is possible to further reduce the reaction resistance of the lithium nickel composite oxide particles.

[0079] Here, the compound containing tungsten and lithium does not need to be completely formed on the entire surface of the primary particles that can be in contact with the electrolyte, and may be partially coated or scattered. Even if it is partially coated or scattered, as long as the compound containing tungsten and lithium is formed on the surface of the primary particles that can be in contact with the electrolyte, the effect of reducing the positive electrode resistance can be obtained.

[0080] The particles of the lithium nickel composite oxide contained in the positive electrode active material of this embodiment preferably have a compound containing tungsten and lithium uniformly formed on the surface thereof.

[0081] Here, the positive electrode active material contains a plurality of composite particles having a lithium nickel composite oxide particle and a compound containing tungsten and lithium arranged on the surface of the lithium nickel composite oxide particle. The lithium nickel composite oxide particles may include primary particles containing the lithium nickel composite oxide and secondary particles formed by agglomeration of the primary particles.

[0082] Furthermore, if a compound containing tungsten and lithium is formed unevenly on the particle surface of the lithium nickel composite oxide between the above-mentioned composite particles, the movement of lithium ions between the composite particles will be uneven, which may impose a load on certain composite particles, leading to a deterioration in long-term cycle characteristics and an increase in positive electrode resistance.

[0083] When the positive electrode active material of the present embodiment includes segregated particles, the positive electrode active material is observed with a scanning electron microscope (SEM), and the segregated particles are white, whereas the other composite particles are gray. The segregated particles refer to particles in which a compound containing tungsten and lithium is precipitated and arranged unevenly on the surface of a lithium nickel composite oxide particle, in a larger amount than the other composite particles.

[0084] Therefore, by observing the positive electrode active material of this embodiment with a scanning electron microscope, the presence or absence of segregated particles, the number ratio of the segregated particles, and the like can be calculated.

[0085] As described above, in the positive electrode active material of the present embodiment, the ratio of segregated particles, in which a compound containing tungsten and lithium is arranged on the surface of a lithium nickel composite oxide particle in a larger amount than other composite particles, is preferably 0.1% or less, more preferably 0.01% or less, by number ratio among the multiple composite particles. By making the ratio of segregated particles among the multiple composite particles 0.1% or less, the cycle characteristics can be improved and the positive electrode resistance can be suppressed.

[0086] Although there is no particular lower limit for the proportion of segregated particles among the multiple composite particles, it can be set to 0% or more since it is preferable that no segregated particles exist.

[0087] The method for calculating the ratio of segregated particles among the multiple composite particles of the positive electrode active material of this embodiment is not particularly limited, but for example, the positive electrode active material is observed with a scanning electron microscope at a magnification of 10 times or more and 1000 times or less, and 3 to 20 visual fields are observed, and the ratio of segregated particles among the composite particles in the images of the multiple visual fields obtained can be calculated. The observation conditions of the scanning electron microscope are not particularly limited, but for example, it is preferable to set the acceleration voltage to 1 kV or more and 20 kV or less.

[0088] The uniformity of the compound containing tungsten and lithium in the obtained composite particles can also be evaluated and confirmed, for example, by the variation in the tungsten content when the composite particles are sampled from the positive electrode active material multiple times and the tungsten content is analyzed.

[0089] In addition, the ratio of the number of tungsten atoms contained in the compound containing tungsten and lithium to the total number of atoms of nickel and element M contained in the lithium nickel composite oxide (hereinafter also referred to as "tungsten amount") is preferably 0.05 atomic % or more and 3.00 atomic % or less, more preferably 0.05 atomic % or more and 2.00 atomic % or less, even more preferably 0.10 atomic % or more and 1.00 atomic % or less, and particularly preferably 0.10 atomic % or more and 0.50 atomic % or less. By setting the tungsten amount in the above range, when the positive electrode active material is used as a positive electrode material for a lithium ion secondary battery, it is possible to achieve both high charge / discharge capacity and output characteristics.

[0090] In the positive electrode active material of this embodiment, for example, tungsten is derived from a compound containing tungsten and lithium arranged on the particle surface of the lithium nickel composite oxide, and nickel and element M are derived from the lithium nickel composite oxide. Therefore, with regard to the amount of tungsten, it can be said that the ratio of the number of tungsten atoms to the total number of atoms of nickel and element M contained in the positive electrode active material of this embodiment is preferably 0.05 atomic % or more and 3.00 atomic % or less, as described above.

[0091] By setting the amount of tungsten to 0.05 atomic % or more, the output characteristics can be particularly improved, which is preferable.

[0092] Furthermore, by setting the tungsten content to 3.00 atomic % or less, the generation of segregated particles can be particularly suppressed. Furthermore, by setting the tungsten content to 3.00 atomic % or less, the lithium conductivity between the lithium nickel composite oxide and the electrolyte can be increased, and the charge / discharge capacity can be increased.

[0093] The form of the compound containing tungsten and lithium arranged on the surface of the lithium nickel composite oxide particles is not particularly limited. However, when the surface of the lithium nickel composite oxide particles is covered with a layered material that is a thick film of the compound containing tungsten and lithium, the thick film on the grain boundary of the lithium nickel composite oxide particles may be filled, and the specific surface area may decrease. In addition, when a layered material that is a thick film of the compound containing tungsten and lithium is formed, the compound containing tungsten and lithium may be formed in a concentrated manner on the particle surface of a specific lithium nickel composite oxide, and may not be formed on the particle surface of many other lithium nickel composite oxides. Therefore, the contact area between the lithium nickel composite oxide and the electrolyte via the compound containing tungsten and lithium may be reduced.

[0094] Therefore, in order to obtain a higher effect, it is preferable that the compound containing tungsten and lithium is present on the surface of the lithium nickel composite oxide particles as particles having a particle diameter of 1 nm or more and 300 nm or less.

[0095] By making the particle size of the compound containing tungsten and lithium 1 nm or more, it is possible to exhibit particularly sufficient lithium ion conductivity. Also, by making the particle size of the compound containing tungsten and lithium 300 nm or less, it is possible to form the particles of the compound containing tungsten and lithium particularly uniformly on the surface of the particles of the lithium nickel composite oxide, and it is possible to particularly reduce the reaction resistance.

[0096] When the particles of the compound containing tungsten and lithium have the above-mentioned form, the contact area with the electrolyte can be made sufficient, and lithium ion conductivity can be effectively improved, thereby particularly improving the charge / discharge capacity and more effectively reducing the reaction resistance.

[0097] However, it is not necessary that all particles of the compound containing tungsten and lithium are present as particles having a particle diameter of 1 nm or more and 300 nm or less. For example, it is preferable that 50% or more of the number of particles of the compound containing tungsten and lithium formed on the surface of the lithium nickel composite oxide particles satisfy the above range in terms of obtaining a particularly high effect.

[0098] On the other hand, when the particle surface of the lithium nickel composite oxide is coated with a thin film of a compound containing tungsten and lithium, a conductive path of Li can be formed at the interface with the electrolyte while suppressing the decrease in the specific surface area, and the effect of improving the charge / discharge capacity and reducing the reaction resistance can be obtained. When the primary particle surface is coated with such a thin film of a compound containing tungsten and lithium, it is preferable that the compound containing tungsten and lithium is present on the primary particle surface of the lithium nickel composite oxide as a coating having a thickness of 1 nm to 200 nm.

[0099] By making the film thickness of the compound containing tungsten and lithium 1 nm or more, the thin film can have particularly sufficient lithium ion conductivity. Also, by making the film thickness of the compound containing tungsten and lithium 200 nm or less, the lithium ion conductivity can be particularly increased and the reaction resistance can be particularly reduced, which is preferable.

[0100] The thin film of the compound containing tungsten and lithium does not have to be formed on the entire particle of the lithium nickel composite oxide, and may be formed partially on the surface of the particle of the lithium nickel composite oxide, and the thickness range of all the coatings does not have to be 1 nm or more and 200 nm or less. If a thin film of the compound containing tungsten and lithium is formed at least partially on the surface of the primary particles with a thickness of 1 nm or more and 200 nm or less, the above-mentioned high effect can be obtained. Note that, for example, when a compound containing tungsten and lithium is formed as a coating, the amount of tungsten contained in the compound can be controlled within the above-mentioned range to form a coating with a thickness of 1 nm or more and 200 nm or less sufficient to obtain the effect.

[0101] Furthermore, even when a compound containing tungsten and lithium is formed on the surface of the particles of the lithium nickel composite oxide in a mixture of particulate form and thin film form, a high effect can be obtained in terms of battery characteristics.

[0102] In addition, the amount of lithium in the entire positive electrode active material is not particularly limited, but the ratio of the sum of the numbers of atoms of nickel and element M in the positive electrode active material (Me) to the number of lithium atoms (Li), "Li / Me ratio," is preferably 0.95 or more and 1.20 or less, and more preferably 0.97 or more and 1.15 or less.

[0103] By setting the Li / Me ratio at 0.95 or more, when the obtained positive electrode active material is used as a material for the positive electrode of a lithium ion secondary battery, it is possible to suppress the reaction resistance of the positive electrode and increase the output of the battery. Also, by setting the Li / Me ratio at 1.20 or less, it is possible to suppress the excess lithium component on the particle surface of the lithium nickel composite oxide, so that when the positive electrode active material is used as a material for the positive electrode of a lithium ion secondary battery, it is possible to increase the initial discharge capacity and suppress the reaction resistance of the positive electrode.

[0104] In addition, since the lithium contained in the compound containing tungsten and lithium is supplied from the lithium nickel composite oxide serving as the base material, the amount of lithium in the entire positive electrode active material does not change before and after the formation of the compound containing tungsten and lithium.

[0105] That is, after the compound containing tungsten and lithium is formed, the Li / Me ratio of the lithium nickel composite oxide particles as the base material (core material) is decreased from that before the formation. Therefore, by making the Li / Me ratio 0.97 or more, better charge / discharge capacity and reaction resistance can be obtained.

[0106] Therefore, the Li / Me ratio of the entire positive electrode active material is more preferably 0.97 or more and 1.15 or less.

[0107] The positive electrode active material of the present embodiment improves output characteristics and cycle characteristics by providing a compound containing tungsten and lithium on the surfaces of the secondary particles and the surfaces of the primary particles of the lithium nickel composite oxide particles. The powder characteristics of the positive electrode active material, such as particle size and tap density, are not particularly limited and may be within the range of, for example, a commonly used positive electrode active material.

[0108] Furthermore, the effect of providing a compound containing tungsten and lithium on the surfaces of the secondary particles and the surfaces of the primary particles of the lithium nickel composite oxide can be applied to, for example, powders of lithium cobalt-based composite oxides, lithium manganese-based composite oxides, lithium nickel cobalt manganese-based composite oxides, and further not only to the positive electrode active materials set forth in the present invention but also to commonly used positive electrode active materials for lithium secondary batteries. [Lithium-ion secondary battery] The lithium ion secondary battery (hereinafter also referred to as "secondary battery") of this embodiment can have a positive electrode containing the above-mentioned positive electrode active material.

[0109] Hereinafter, an example of the configuration of the secondary battery of this embodiment will be described for each component. The secondary battery of this embodiment includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte, and is composed of the same components as a general lithium-ion secondary battery. Note that the embodiment described below is merely an example, and the lithium-ion secondary battery of this embodiment can be embodied in various forms that have been modified and improved based on the knowledge of those skilled in the art, including the following embodiment. In addition, the secondary battery is not particularly limited in its use. (positive electrode) The positive electrode of the secondary battery of this embodiment can contain the above-mentioned positive electrode active material.

[0110] An example of a method for manufacturing a positive electrode is described below. First, the positive electrode active material (powder), conductive material, and binder are mixed to prepare a positive electrode mixture, and activated carbon and a solvent for viscosity adjustment, etc. are added as necessary, and the mixture is kneaded to prepare a positive electrode mixture paste.

[0111] The mixing ratio of each material in the positive electrode mixture is a factor that determines the performance of the lithium ion secondary battery, and can be adjusted depending on the application. The mixing ratio of the materials can be the same as that of the positive electrode of a known lithium ion secondary battery, and for example, when the total mass of the solid content of the positive electrode mixture excluding the solvent is 100 mass%, the positive electrode active material can be contained in a ratio of 60 mass% to 95 mass%, the conductive material can be contained in a ratio of 1 mass% to 20 mass%, and the binder can be contained in a ratio of 1 mass% to 20 mass%.

[0112] The obtained positive electrode composite paste is applied to the surface of a current collector made of, for example, aluminum foil, and dried to remove the solvent, thereby producing a sheet-like positive electrode. If necessary, pressure can be applied by a roll press or the like to increase the electrode density. The sheet-like positive electrode thus obtained can be cut to an appropriate size according to the desired battery and used for the production of the battery.

[0113] As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and Ketjen Black (registered trademark) can be used.

[0114] The binder serves to bind the active material particles together, and may be, for example, one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose-based resin, polyacrylic acid, etc.

[0115] If necessary, a solvent for dispersing the positive electrode active material, conductive material, etc. and dissolving the binder can be added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Activated carbon can also be added to the positive electrode mixture to increase the electric double layer capacity.

[0116] The method for producing the positive electrode is not limited to the above-mentioned example, and other methods may be used. For example, the positive electrode may be produced by press-molding the positive electrode mixture and then drying it in a vacuum atmosphere. (Negative electrode) The negative electrode may be made of metallic lithium, a lithium alloy, etc. Alternatively, the negative electrode may be made by mixing a binder with a negative electrode active material capable of absorbing and desorbing lithium ions, adding an appropriate solvent to make a paste-like negative electrode mixture, applying the paste to the surface of a metal foil current collector such as copper, drying it, and compressing it to increase the electrode density as necessary.

[0117] As the negative electrode active material, for example, natural graphite, artificial graphite, sintered organic compounds such as phenol resin, and powder of carbon material such as coke can be used. In this case, as with the positive electrode, fluorine-containing resin such as PVDF can be used as the negative electrode binder, and an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent for dispersing these active materials and binders. (Separator) A separator may be sandwiched between the positive electrode and the negative electrode as necessary. The separator separates the positive electrode and the negative electrode and holds the electrolyte, and a known separator may be used, such as a thin membrane made of polyethylene or polypropylene having many minute pores. (Non-aqueous electrolyte) As the non-aqueous electrolyte, for example, a non-aqueous electrolytic solution can be used.

[0118] As the non-aqueous electrolyte, for example, a solution in which a lithium salt as a supporting salt is dissolved in an organic solvent can be used. Alternatively, as the non-aqueous electrolyte, a solution in which a lithium salt is dissolved in an ionic liquid can be used. Note that the ionic liquid refers to a salt that is composed of cations and anions other than lithium ions and is liquid even at room temperature.

[0119] The organic solvent may be one selected from cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethyl methyl sulfone and butane sultone; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate. Two or more of these organic solvents may be used in combination.

[0120] The supporting salt may be LiPF6, LiBF4, LiClO4, LiAsF6, LiN(CF3SO2)2, or a composite salt thereof. Furthermore, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

[0121] The non-aqueous electrolyte may be a solid electrolyte. The solid electrolyte has a property of being able to withstand high voltage. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes.

[0122] Examples of the inorganic solid electrolyte include oxide-based solid electrolytes and sulfide-based solid electrolytes.

[0123] The oxide-based solid electrolyte is not particularly limited, and for example, an oxide-based solid electrolyte containing oxygen (O) and having lithium ion conductivity and electronic insulation can be suitably used. Examples of the oxide-based solid electrolyte include lithium phosphate (Li3PO4), Li3PO4N X , LiBON X , LiNbO3, LiTaO3, Li2SiO3, Li4SiO4-Li3PO4, Li4SiO4-Li3VO4, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3-ZnO, Li 1+X Al X Ti 2-X (PO4)3(0≦X≦1), Li 1+X Al X Ge 2-X (PO4)3(0≦X≦1), LiTi2(PO4)3, Li 3X La 2 / 3-X TiO3(0≦X≦2 / 3), Li5La3Ta2O 12 , Li7La3Zr2O 12 , Li6BaLa2Ta2O 12 , Li 3.6 S 0.6 P 0.4 One or more types selected from O4, etc. can be used.

[0124] The sulfide-based solid electrolyte is not particularly limited, and for example, one containing sulfur (S) and having lithium ion conductivity and electronic insulation can be suitably used. For example, the sulfide-based solid electrolyte can be one or more selected from Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2, LiPO4-Li2S-SiS, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, etc.

[0125] As the inorganic solid electrolyte, materials other than those mentioned above may be used, for example, Li3N, LiI, Li3N-LiI-LiOH, etc. may be used.

[0126] The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ion conductivity, and examples of the organic solid electrolyte that can be used include polyethylene oxide, polypropylene oxide, copolymers thereof, etc. The organic solid electrolyte may also contain a supporting salt (lithium salt). (Shape and structure of secondary battery) The lithium ion secondary battery of the present embodiment described above can be made into various shapes such as a cylindrical shape, a laminated shape, etc. Regardless of the shape, if the secondary battery of the present embodiment uses a non-aqueous electrolyte solution as the non-aqueous electrolyte, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolyte solution, and the positive electrode current collector and the positive electrode terminal connected to the outside, and the negative electrode current collector and the negative electrode terminal connected to the outside are connected using a current collecting lead or the like, and the battery case is sealed to form a structure.

[0127] As described above, the secondary battery of the present embodiment is not limited to a form using a non-aqueous electrolyte solution as a non-aqueous electrolyte, and may be, for example, a secondary battery using a solid non-aqueous electrolyte, i.e., an all-solid-state battery. When making an all-solid-state battery, the configuration other than the positive electrode active material may be changed as necessary.

[0128] In the secondary battery of this embodiment, since the above-mentioned positive electrode active material is used as the positive electrode material, the battery has a high capacity and a high output.

[0129] In particular, when the lithium ion secondary battery using the above-mentioned positive electrode active material is used in the positive electrode of a 2032-type coin battery, it has a high initial discharge capacity, i.e., high capacity and low positive electrode resistance, for example 210 mAh / g or more, depending on the composition, and also has high output. It also has high thermal stability and excellent safety.

[0130] The secondary battery of the present embodiment can be used for various purposes, but since it can be a high-capacity, high-output secondary battery, it is suitable, for example, as a power source for small portable electronic devices (such as notebook personal computers and mobile phone terminals) that always require high capacity, and is also suitable as a power source for electric automobiles that require high output.

[0131] In addition, the secondary battery of this embodiment can be made compact and have high output, making it suitable as a power source for electric vehicles that are limited in installation space. The secondary battery of this embodiment can be used not only as a power source for electric vehicles that are driven purely by electrical energy, but also as a power source for so-called hybrid vehicles that are used in conjunction with combustion engines such as gasoline engines and diesel engines. EXAMPLES

[0132] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. The methods for evaluating the positive electrode active material and the battery in the examples and comparative examples are as follows. (Evaluation of Positive Electrode Active Material) (a) Proportion of segregated particles In calculating the ratio of segregated particles contained in the composite particles in the positive electrode active material, first, 10 arbitrary points of the powder of the positive electrode active material were photographed with a scanning electron microscope at an applied voltage of 5 kV and a magnification of 100 times. In other words, observation was performed in 10 fields of view. In this case, a scanning electron microscope photograph such as that shown in Figure 1 was obtained in one field of view. Then, the number of segregated particles, which are white particles, that appeared in the 10 SEM photographs was counted, and the ratio of the segregated particles among the composite particles contained in the 10 SEM photographs was calculated.

[0133] As shown in Figures 2 and 3, the segregated particles A can be observed as white particles, and the other composite particles B can be observed as gray particles. (Battery manufacturing and evaluation) (a) Battery manufacturing For evaluation of the positive electrode active material, a 2032 type coin battery 11 (hereinafter referred to as a coin battery) shown in FIG. 4 was used.

[0134] As shown in FIG. 4, the coin battery 11 is composed of a case 12 and an electrode 13 housed in the case 12.

[0135] Case 12 has a positive electrode can 12a that is hollow and has one open end, and a negative electrode can 12b that is placed in the opening of positive electrode can 12a. When negative electrode can 12b is placed in the opening of positive electrode can 12a, a space for accommodating electrode 13 is formed between negative electrode can 12b and positive electrode can 12a.

[0136] The electrode 13 is composed of a positive electrode 13a, a separator 13c, and a negative electrode 13b, which are laminated in this order, and are housed in the case 12 so that the positive electrode 13a contacts the inner surface of the positive electrode can 12a via the current collector 14, and the negative electrode 13b contacts the inner surface of the negative electrode can 12b via the current collector 14. A current collector 14 is also disposed between the positive electrode 13a and the separator 13c.

[0137] Case 12 is equipped with gasket 12c, which prevents relative movement between positive electrode can 12a and negative electrode can 12b so that they are kept out of contact with each other. Gasket 12c also has the function of sealing the gap between positive electrode can 12a and negative electrode can 12b to provide an airtight and liquidtight barrier between the inside of case 12 and the outside.

[0138] The coin battery 11 shown in FIG. 4 was fabricated as follows.

[0139] First, 52.5 mg of the positive electrode active material for lithium ion secondary batteries prepared in each Example and Comparative Example, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene (PTFE) resin were mixed and pressed under a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm to prepare a positive electrode 13a. The prepared positive electrode 13a was dried in a vacuum dryer at 120° C. for 12 hours.

[0140] The above-mentioned coin-type battery 11 was fabricated using this positive electrode 13a, the negative electrode 13b, the separator 13c, and the electrolyte solution in a glove box in an Ar atmosphere with a dew point controlled at -80°C.

[0141] For the negative electrode 13b, a negative electrode sheet was used in which graphite powder having an average particle size of about 20 μm and polyvinylidene fluoride were applied to copper foil and punched into a disk having a diameter of 14 mm.

[0142] A polyethylene porous film having a thickness of 25 μm was used for the separator 13c. An equal mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1M LiClO4 as the supporting electrolyte (manufactured by Toyama Pharmaceutical Co., Ltd.) was used for the electrolyte. (b) Evaluation The initial discharge capacity, positive electrode resistance, and cycle characteristics, which indicate the performance of the manufactured coin-type battery 11, were evaluated as follows. (b1)Initial discharge capacity The initial discharge capacity was measured by leaving the coin battery 11 for about 24 hours after production, and after the open circuit voltage OCV (Open Circuit Voltage) had stabilized, applying a current density of 0.1 mA / cm to the positive electrode. 2 The battery was charged to a cut-off voltage of 4.3 V, and after one hour of rest, the capacity at which the battery was discharged to a cut-off voltage of 3.0 V was defined as the initial discharge capacity. (b2) Positive electrode resistance When the positive electrode resistance is measured by an AC impedance method using a frequency response analyzer and a potentiogalvanostat (Solartron, 1255B) while charging the coin battery 11 at a charging potential of 4.1 V, the Nyquist plot shown in FIG. 5A is obtained.

[0143] This Nyquist plot is expressed as the sum of characteristic curves showing the solution resistance, the negative electrode resistance and its capacity, and the positive electrode resistance and its capacity.

[0144] The battery reaction at the electrodes consists of a resistive component associated with charge transfer and a capacitive component due to the electric double layer; when these are represented as an electrical circuit, it becomes a parallel circuit of resistance and capacitance, and the entire battery can be represented as an equivalent circuit in which the solution resistance and the parallel circuits of the negative and positive electrodes are connected in series.

[0145] For this reason, fitting calculations were performed using the equivalent circuit shown in Fig. 5B based on the Nyquist plot shown in Fig. 5A to calculate the positive electrode resistance value. The results are shown in Table 1 as the positive electrode resistance before cycling. (b3) Cycle characteristics The cycle characteristics were evaluated by the capacity retention rate after the cycle test. After the initial discharge capacity was measured, the cycle test was paused for 10 minutes, and the charge / discharge cycle was repeated 500 times (charge / discharge) in the same manner as in the initial discharge capacity measurement, including the initial discharge capacity measurement. The discharge capacity at the 500th cycle was measured, and the percentage of the discharge capacity at the 500th cycle to the discharge capacity at the 1st cycle (initial discharge capacity) was calculated as the capacity retention rate (%). (b4) Carbon content The carbon content was measured using a carbon-sulfur analyzer (manufactured by LECO, model number: CS-600).

[0146] In the present examples, the positive electrode active material and secondary battery were prepared using respective samples of special grade reagents manufactured by Wako Pure Chemical Industries, Ltd., unless otherwise specified. [Example 1] A positive electrode active material and a lithium ion secondary battery were produced and evaluated according to the following procedures. (Mixing process) Li obtained by a known technique using an oxide mainly composed of Ni and lithium hydroxide 0.98 Ni 0.91 Co 0.06 Al 0.03A powder of lithium nickel composite oxide particles, which is a layered compound represented by O2, was used as the base material. Note that the lithium nickel composite oxide, which is a layered compound, is also used as the base material in the following other examples and comparative examples. Water was then added to the base material, and the moisture content, which is the ratio of water to the lithium nickel composite oxide and water in the starting materials to be subjected to the mixing step (hereinafter also simply referred to as "moisture content"; this is also expressed in the same way in Table 1), was set to 3.2 mass%.

[0147] The base material to which water had been added was placed in a paddle-type mixer, and tungsten oxide (WO3) was added onto the base material so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.12 atomic %. These starting materials were mixed at 60°C for 30 minutes to obtain a tungsten mixture.

[0148] During the mixing process, the inside of the mixer was evacuated and decarbonated air was supplied. Specifically, the feed rate of the base material to which water was added was 0.20 m per 1 kg / min. 3 The pressure inside the mixing device was controlled so as not to become negative by exhausting the air at a rate of 1 / min and supplying decarbonated air at the same flow rate.

[0149] In addition, the ratio of the number of W atoms to the total number of atoms of the base material Ni and element M in the starting material is shown as "W amount" in Table 1. (Heat treatment process) Thereafter, the product was heat-treated at 190° C. for 120 minutes using a steam tube dryer, and then cooled in the furnace.

[0150] The atmosphere in the mixing step and the heat treatment step was decarbonated air.

[0151] Finally, the mixture was crushed and sieved through a sieve with 38 μm mesh to obtain a positive electrode active material having particles of a compound containing tungsten and lithium on the surfaces of primary particles of lithium nickel composite oxide.

[0152] For the obtained positive electrode active material, the ratio of segregated particles was calculated.

[0153] The amount of tungsten, which is the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms, of the obtained positive electrode active material was evaluated using ICP. As a result, it was confirmed that the amount of tungsten in the obtained positive electrode active material was equal to the amount of W, which is the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms of the base material in the starting material subjected to the mixing process.

[0154] In the other examples and comparative examples described below, it was also confirmed that the tungsten amount, which is the ratio of the number of W atoms to the total number of Ni and element M atoms in the obtained positive electrode active material, was equal to the ratio of the number of W atoms to the total number of Ni and element M atoms in the base material in the starting material (W amount).

[0155] The tungsten contained in the obtained positive electrode active material comes from the compound containing tungsten and lithium arranged on the particle surface of the lithium nickel composite oxide, and the nickel and element M come from the lithium nickel composite oxide. Therefore, the amount of tungsten in the positive electrode active material corresponds to the ratio of the number of tungsten atoms contained in the compound containing tungsten and lithium to the total number of atoms of nickel and element M contained in the lithium nickel composite oxide in the positive electrode active material.

[0156] The battery characteristics of a coin-type battery 11 shown in Fig. 4 having a positive electrode produced using the obtained positive electrode active material were evaluated. The positive electrode resistance before the cycle test (positive electrode resistance before cycle) was evaluated as a relative value with the positive electrode resistance of Example 1 taken as 1.00.

[0157] The carbon content was measured by the above-mentioned method.

[0158] The test conditions and evaluation results are shown in Table 1. [Example 2] A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1, except that the moisture content was 3.4 mass % and the temperature during mixing was 55°C.

[0159] The test conditions and evaluation results are shown in Table 1. [Example 3] The moisture content was set to 5.7 mass%, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.24 atomic %, and the mixing temperature was 50° C., the heat treatment temperature was 150° C., and the heat treatment time was 180 minutes. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1 except for the above points.

[0160] The test conditions and evaluation results are shown in Table 1. [Example 4] The composition of the base material is Li 0.97 Ni 0.91 Co 0.04 Al 0.05 The mixing temperature was set to 100°C, the moisture content was set to 6.9 mass%, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.06 atomic %. During the mixing process, the inside of the mixing device was evacuated and decarbonated air was supplied. Specifically, the feeding rate of the base material to which water was added was 0.15 m per 1 kg / min. 3 The pressure in the mixing device was controlled so as not to become negative by exhausting the air at a flow rate of 1 / min and supplying decarbonated air at the same flow rate. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1, except for the above points.

[0161] The test conditions and evaluation results are shown in Table 1. [Example 5] The composition of the base material is Li 0.97 Ni 0.91 Co 0.04 Al 0.05 The mixing temperature was set to 0.15 m3 / kg / min, the water content was set to 4.1 mass%, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.27 atomic %. During the mixing process, the inside of the mixing device was evacuated and decarbonated air was supplied. Specifically, the feeding rate of the base material to which water was added was set to 0.15 m3 / kg / min. 3 The pressure in the mixing device was controlled so as not to become negative by exhausting the air at a flow rate of 1 / min and supplying decarbonated air at the same flow rate. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1, except for the above points.

[0162] The test conditions and evaluation results are shown in Table 1. [Example 6] The composition of the base material is Li 0.97 Ni 0.91 Co 0.04 Al 0.05 The mixing temperature was 45°C and the mixing time was 45 minutes. During the mixing process, the inside of the mixing device was evacuated while decarbonated air was supplied. Specifically, the feeding rate of the water-added base material was 0.25 m per kg / min. 3 The pressure in the mixing device was controlled so as not to become negative by exhausting the air at a flow rate of 1 / min and supplying decarbonated air at the same flow rate. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1, except for the above points.

[0163] The test conditions and evaluation results are shown in Table 1. [Example 7] The composition of the base material is Li 0.97 Ni 0.91 Co 0.04 Al 0.05 The mixing temperature was 30°C, the mixing time was 60 minutes, the heat treatment temperature was 175°C, and the heat treatment time was 150 minutes. During the mixing process, the inside of the mixing device was evacuated while decarbonated air was supplied. Specifically, the feeding rate of the water-added base material was 0.30 m per kg / min. 3 The pressure in the mixing device was controlled so as not to become negative by exhausting the air at a flow rate of 1 / min and supplying decarbonated air at the same flow rate. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1, except for the above points.

[0164] The test conditions and evaluation results are shown in Table 1. [Example 8] The composition of the base material is Li 0.98 Ni 0.88 Co 0.09 Al 0.03The moisture content was 4.3 mass%, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.18 atomic %. Except for the above, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1.

[0165] The test conditions and evaluation results are shown in Table 1. [Example 9] The composition of the base material is Li 0.98 Ni 0.88 Co 0.09 Al 0.03 The moisture content was set to 3.6 mass%, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.30 atomic %. Except for the above, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1.

[0166] The test conditions and evaluation results are shown in Table 1. [Example 10] The composition of the base material is Li 0.97 Ni 0.88 Co 0.07 Al 0.05 The moisture content was set to 6.4 mass%, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.15 atomic %. Except for the above, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1.

[0167] The test conditions and evaluation results are shown in Table 1. [Example 11] The composition of the base material is Li 0.97 Ni 0.88 Co 0.07 Al 0.05 The mixing temperature was set to 100°C, the moisture content was set to 5.8 mass%, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.30 atomic %. During the mixing process, the inside of the mixing device was evacuated and decarbonated air was supplied. Specifically, the feeding rate of the base material to which water was added was 0.15 m per 1 kg / min. 3The pressure in the mixing device was controlled so as not to become negative by exhausting the air at a flow rate of 1 / min and supplying decarbonated air at the same flow rate. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1, except for the above points.

[0168] The test conditions and evaluation results are shown in Table 1. [Example 12] The composition of the base material is Li 0.97 Ni 0.91 Co 0.04 Al 0.05 The moisture content was set to 8.6 mass%, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.18 atomic %. Except for the above, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1.

[0169] The test conditions and evaluation results are shown in Table 1. [Example 13] The composition of the base material is Li 0.98 Ni 0.88 Co 0.09 Al 0.03 The moisture content was 7.9 mass %, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.15 atomic %. Except for the above, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1.

[0170] The test conditions and evaluation results are shown in Table 1. [Example 14] The base material to which water had been added and WO3 were continuously fed into a continuous paddle mixer, the mixture was continuously fed from the continuous paddle mixer to a continuous steam dryer, and the dried mixture was continuously discharged from the continuous steam dryer. That is, the mixing process and the heat treatment process were carried out continuously. Aside from the above, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1.

[0171] The test conditions and evaluation results are shown in Table 1. [Example 15] The base material to which water had been added and WO3 were continuously fed into a continuous paddle type mixer, the mixture was continuously fed from the continuous paddle type mixer to a continuous steam type dryer, and the dried mixture was continuously discharged from the continuous steam type dryer. That is, the mixing process and the heat treatment process were carried out continuously. Aside from the above, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 5.

[0172] The test conditions and evaluation results are shown in Table 1. [Example 16] The composition of the base material is Li 0.98 Ni 0.55 Co 0.20 Mn 0.25 A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1, except that O2 was used.

[0173] The test conditions and evaluation results are shown in Table 1. [Example 17] A positive electrode active material and a secondary battery were prepared and evaluated in the same manner as in Example 16, except that the moisture content was set to 4.9 mass%, WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Mn atoms in the base material was 0.18 atomic %, and the temperature during mixing was set to 55°C.

[0174] The test conditions and evaluation results are shown in Table 1. [Example 18] The composition of the base material is Li 0.97 Ni 0.91 Co 0.04 Al 0.05 The mixing temperature was set to 100°C, the moisture content was set to 5.2 mass%, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.15 atomic %. During the mixing process, the inside of the mixing device was evacuated and decarbonated air was supplied. Specifically, the feeding rate of the base material to which water was added was 0.10 m per 1 kg / min. 3 The pressure in the mixing device was controlled so as not to become negative by exhausting the air at a flow rate of 1 / min and supplying decarbonated air at the same flow rate. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1, except for the above points.

[0175] The test conditions and evaluation results are shown in Table 1. [Example 19] The composition of the base material is Li 0.97 Ni 0.91 Co 0.04 Al 0.05 The mixing temperature was set to 100°C, the moisture content was set to 5.5 mass%, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.19 atomic %. During the mixing process, the inside of the mixing device was evacuated and decarbonated air was supplied. Specifically, the feeding rate of the base material to which water was added was 0.35 m per 1 kg / min. 3 The pressure in the mixing device was controlled so as not to become negative by exhausting the air at a flow rate of 1 / min and supplying decarbonated air at the same flow rate. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1, except for the above points.

[0176] The test conditions and evaluation results are shown in Table 1. [Example 20] The composition of the base material is Li 0.97 Ni 0.88 Co 0.07 Al 0.05 The mixing temperature was set to 100°C, the moisture content was set to 4.9 mass%, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.18 atomic %. During the mixing process, the inside of the mixing device was evacuated and decarbonated air was supplied. Specifically, the feeding rate of the base material to which water was added was 0.10 m per 1 kg / min. 3 The pressure in the mixing device was controlled so as not to become negative by exhausting the air at a flow rate of 1 / min and supplying decarbonated air at the same flow rate. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1, except for the above points. [Example 21] The composition of the base material is Li 0.97 Ni 0.88 Co 0.07 Al 0.05 The mixing temperature was set to 0.02, the moisture content was set to 5.3 mass%, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.18 atomic %. During the mixing process, the inside of the mixing device was evacuated and decarbonated air was supplied. Specifically, the feeding rate of the base material to which water was added was 0.35 m per 1 kg / min. 3The pressure in the mixing device was controlled so as not to become negative by exhausting the air at a flow rate of 1 / min and supplying decarbonated air at the same flow rate. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1, except for the above points. [Example 22] The composition of the base material is Li 0.98 Ni 0.55 Co 0.20 Mn 0.25 The mixing temperature was set to 100°C, the moisture content was set to 5.3 mass%, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.19 atomic %. During the mixing process, the inside of the mixing device was evacuated and decarbonated air was supplied. Specifically, the feeding rate of the base material to which water was added was 0.10 m per 1 kg / min. 3 The pressure in the mixing device was controlled so as not to become negative by exhausting the air at a flow rate of 1 / min and supplying decarbonated air at the same flow rate. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1, except for the above points.

[0177] The test conditions and evaluation results are shown in Table 1. [Example 23] The composition of the base material is Li 0.98 Ni 0.55 Co 0.20 Mn 0.25 The mixing temperature was set to 100°C, the moisture content was set to 4.8 mass%, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.17 atomic %. During the mixing process, the inside of the mixing device was evacuated and decarbonated air was supplied. Specifically, the feeding rate of the base material to which water was added was 0.35 m per 1 kg / min. 3 The pressure in the mixing device was controlled so as not to become negative by exhausting the air at a flow rate of 1 / min and supplying decarbonated air at the same flow rate. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1, except for the above points.

[0178] The test conditions and evaluation results are shown in Table 1. [Comparative Example 1] The composition of the base material is Li 0.97 Ni 0.91 Co 0.04 Al 0.05A positive electrode active material and a secondary battery were prepared and evaluated in the same manner as in Example 1, except that O was used, the moisture content was 5.2 mass%, and WO was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.03 atomic %.

[0179] The test conditions and evaluation results are shown in Table 1. [Comparative Example 2] A positive electrode active material and a secondary battery were prepared and evaluated in the same manner as in Example 1, except that the moisture content was set to 2.7 mass % and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.15 atomic %.

[0180] The test conditions and evaluation results are shown in Table 1. [Comparative Example 3] The composition of the base material is Li 0.97 Ni 0.88 Co 0.07 Al 0.05 The moisture content was set to 2.8 mass%, and WO3 was added so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.15 atomic %. Except for the above, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1.

[0181] The test conditions and evaluation results are shown in Table 1. [Comparative Example 4] The composition of the base material is Li 0.98 Ni 0.91 Co 0.06 Al 0.03 The mixture was mixed at 25° C. for 90 minutes. A positive electrode active material and a secondary battery were prepared and evaluated in the same manner as in Example 1, except for the above points.

[0182] The test conditions and evaluation results are shown in Table 1. [Comparative Example 5] The composition of the base material is Li 0.98 Ni 0.91 Co 0.06 Al 0.03The composition was O2, the moisture content was 4.4 mass%, the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.15 atomic %, the temperature during mixing was 70° C., and the mixing time was 30 minutes. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1 except for the above points.

[0183] The test conditions and evaluation results are shown in Table 1. [Comparative Example 6] The composition of the base material is Li 0.98 Ni 0.88 Co 0.09 Al 0.03 The composition was O2, the moisture content was 4.5 mass%, the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.18 atomic %, the temperature during mixing was 70° C., and the mixing time was 30 minutes. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1 except for the above points.

[0184] The test conditions and evaluation results are shown in Table 1. [Comparative Example 7] The composition of the base material is Li 0.97 Ni 0.88 Co 0.07 Al 0.05 The composition was O2, the moisture content was 4.2 mass%, the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was 0.18 atomic %, the mixing temperature was 75° C., and the mixing time was 30 minutes. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1 except for the above points.

[0185] The test conditions and evaluation results are shown in Table 1. [Comparative Example 8] The moisture content was 3.4 mass%, the ratio of the number of W atoms to the total number of Ni, Co, and Mn atoms in the base material was 0.13 atomic %, and the temperature during mixing was 70° C. Except for the above, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 16.

[0186] The test conditions and evaluation results are shown in Table 1. [Comparative Example 9] The moisture content was 3.9 mass%, the ratio of the number of W atoms to the total number of Ni, Co, and Mn atoms in the base material was 0.14 atomic %, the temperature during mixing was 25° C., and the mixing time was 90 minutes. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 16 except for the above points.

[0187] The test conditions and evaluation results are shown in Table 1.

[0188] [Table 1] [evaluation] As is clear from Table 1, the positive electrode active materials of Examples 1 to 17 have higher initial discharge capacity, lower positive electrode resistance, and higher capacity retention rate than the comparative examples having the corresponding base material compositions. In addition, the proportion of segregated particles is also small, resulting in batteries with excellent characteristics.

[0189] In Examples 1, 2, 9, 14, and 16, the water content, which is the ratio of water to the water in the starting materials and the lithium nickel composite oxide used in the mixing process, was low at less than 4.0 mass%, so WO3 was not completely dispersed, and unreacted WO3 was likely to remain. Therefore, the proportion of segregated particles was somewhat higher than in other Examples, and it is believed that the battery characteristics were somewhat inferior to those of other Examples.

[0190] In Examples 4, 12, and 13, the moisture content was significantly higher than 6.0%, so the lithium in the lithium nickel composite oxide dissolved in the excess moisture, and the lithium reacted more with tungsten in the locally increased areas, resulting in the generation of segregated particles. For this reason, the number of segregated particles was larger than in other Examples, and it is believed that the battery characteristics were somewhat inferior to those of other Examples.

[0191] In Examples 6 and 7, since the temperature during mixing was low, it was necessary to use a longer mixing time than in the other Examples, but the evaluation results were good.

[0192] In Examples 18, 20, and 22, the carbon content was higher than in other Examples, although it was not a problematic level. This is because the exhaust speed and the flow rate of the decarbonated air were low, which increased the carbon dioxide gas concentration in the atmosphere during the mixing process and promoted the carbonation of the lithium component in the lithium nickel composite oxide. This carbon dioxide may turn into gas in the battery and degrade its characteristics. For this reason, it is preferable to keep carbonation as low as possible.

[0193] In Examples 19, 21, and 23, the exhaust speed and the flow rate of the decarbonated air were high, so the lithium component of the lithium nickel composite oxide was not carbonated to a great extent. However, the air flow promoted drying to some extent, so that the amount of unreacted WO3 was relatively large, although this was not a problematic level.

[0194] In contrast, in Comparative Example 1, the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was less than 0.05 atomic %, so it is believed that a compound containing sufficient tungsten and lithium was not formed, resulting in significantly inferior battery characteristics.

[0195] In Comparative Examples 2 and 3, the moisture content was low, so WO3 could not be sufficiently dispersed, and a large amount of unreacted WO3 remained. This also resulted in a large amount of surplus lithium component, which is thought to have deteriorated the battery characteristics.

[0196] In Comparative Examples 4 and 9, the mixing temperature was below 30°C, so that WO3 could not be sufficiently dispersed, and a large amount of unreacted WO3 remained. In addition, a large amount of surplus lithium component also remained, which is thought to have deteriorated the battery characteristics.

[0197] In Comparative Examples 5 to 8, since the mixing temperature exceeded 65°C, the moisture content from the tungsten mixture was rapidly reduced, and the moisture content required for dispersing WO3 could not be maintained, leaving a large amount of unreacted WO3. In addition, this resulted in a large amount of surplus lithium component, which is believed to have deteriorated the battery characteristics.

[0198] Moreover, in Comparative Examples 2 to 9, it was confirmed that since WO3 could not be sufficiently dispersed as described above, the ratio of segregated particles was high, and the battery characteristics were deteriorated.

[0199] Thus, it was revealed that the positive electrode active material of this embodiment has high capacity and high output while being low cost. In addition, in Examples 14 and 15, continuous processing was performed, and the evaluation results were good, the productivity was high, and it was revealed that further cost reduction can be expected.

[0200] The manufacturing method of the positive electrode active material for lithium ion secondary batteries, the positive electrode active material for lithium ion secondary batteries, and the lithium ion secondary batteries have been described above in terms of embodiments and examples, but the present invention is not limited to the above embodiments and examples. Various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

[0201] This application claims priority based on Japanese Patent Application No. 2019-029870, filed with the Japan Patent Office on February 21, 2019, the entire contents of which are incorporated herein by reference.

Claims

1. a mixing step of mixing, under heating, a lithium-nickel composite oxide as a starting material and a lithium-free tungsten compound powder to obtain a tungsten mixture; a heat treatment step of heat treating the tungsten mixture, The lithium nickel composite oxide contains lithium (Li), nickel (Ni), and an element M (M), where M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti, Co, and Al; a ratio of the number of tungsten atoms to the total number of atoms of nickel and the element M contained in the lithium nickel composite oxide in the starting material is 0.05 atomic % or more and 3.00 atomic % or less; a moisture content, which is a ratio of water to water in the starting materials and the lithium nickel composite oxide, is 3.0% by mass or more; The method for producing a positive electrode active material for a lithium ion secondary battery, wherein the temperature in the mixing step is 30° C. or higher and 65° C. or lower, and the atmosphere in the mixing step is either decarbonated air or an inert gas.

2. A method for producing a positive electrode active material for a lithium ion secondary battery as described in claim 1, wherein the temperature of the mixing process is higher than 50°C and lower than 65°C.

3. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1 or claim 2, wherein the lithium nickel composite oxide is a layered compound containing lithium (Li), nickel (Ni), and the element M (M) in a ratio of substance amounts of Li:Ni:M = y:1 - x:x (where 0≦x≦0.70, 0.95≦y≦1.20).

4. A method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the moisture content is 3.0 mass% or more and 7.0 mass% or less.

5. A method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the moisture content is 4.0 mass% or more and 6.0 mass% or less.

6. A method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the heat treatment temperature in the heat treatment step is 100°C or higher and 200°C or lower.

7. A method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 6, wherein the atmosphere in the heat treatment step is either decarbonated air or an inert gas.

8. A method for producing a positive electrode active material for a lithium ion secondary battery described in any one of claims 1 to 7, wherein the lithium-free tungsten compound is one or more types selected from tungsten oxide (WO 3 ) and tungstic acid (WO 3 .H 2 O).

9. A method for producing a positive electrode active material for a lithium ion secondary battery described in any one of claims 1 to 8, wherein lithium tungstate is fixed to the surface of lithium nickel composite oxide particles in the heat treatment process.

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