Method for producing positive electrode active material for lithium ion secondary battery, positive electrode active material for lithium ion secondary battery, and lithium ion secondary battery

Abstract

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; and a heat treatment step of heat treating the tungsten mixture, The lithium nickel composite oxide contains Li, Ni, and an element M, 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 the ratio of water to water in the starting materials and the lithium nickel composite oxide, of 3.0 mass% or more; A 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.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing 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 Art

[0002] In recent years, with the spread of portable electronic devices such as mobile phones and notebook computers, the development of small and lightweight secondary batteries having a high energy density has been strongly desired. In addition, the development of high-output secondary batteries as batteries for electric vehicles including hybrid vehicles has also been strongly desired.

[0003] As a secondary battery that satisfies such requirements, there is a lithium ion secondary battery. This lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, etc., and materials capable of desorbing and inserting lithium are used as the active materials of the negative electrode and the positive electrode.

[0004] Although such lithium ion secondary batteries are currently being actively researched and developed, among them, lithium ion secondary batteries using layered or spinel-type lithium nickel composite oxides as the positive electrode material are being put into practical use as batteries having a high energy density because a high voltage of 4V class can be obtained.

[0005] Materials that have been mainly proposed so far include lithium cobalt composite oxide (LiCoO 2 ) which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO 2 ) using nickel that is cheaper than cobalt, lithium nickel cobalt manganese composite oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 ), lithium manganese composite oxide (LiMn 2 O 4 ) using manganese, etc.

[0006] Among these, lithium nickel composite oxides have attracted attention as materials with good cycle characteristics, low resistance, and high output. In recent years, regarding the positive electrode active material for lithium-ion secondary batteries, reducing the resistance, which is necessary for increasing the output of lithium-ion secondary batteries, has been emphasized.

[0007] As a method for realizing the above-mentioned resistance reduction, addition of different elements is used, and in particular, transition metals that can take a high valence number such as W, Mo, Nb, Ta, and Re are considered useful.

[0008] For example, Patent Document 1 proposes a lithium transition metal-based compound powder for a positive electrode material of a lithium secondary battery that satisfies a predetermined composition formula and contains one or more elements selected from Mo, W, Nb, Ta, and Re in a proportion of 0.1 mol% or more and 5 mol% or less with respect to the total molar amount of Mn, Ni, and Co in the above composition formula. Further, Patent Document 1 discloses a method for producing a lithium transition metal-based compound powder for a positive electrode material of a lithium secondary battery, including a spray drying step of pulverizing lithium carbonate, a Ni compound, a Mn compound, a Co compound, and a metal compound containing at least one or more elements selected from Mo, W, Nb, Ta, and Re in a liquid medium and spray drying a slurry in which these are uniformly dispersed, and a firing step of firing the obtained spray-dried product.

[0009] According to Patent Document 1, it is said that it is possible to achieve both cost reduction and high safety of the lithium transition metal-based compound powder for a positive electrode material of a lithium secondary battery, and high load characteristics and improved powder handleability.

[0010] However, according to the above manufacturing method disclosed in Patent Document 1, the above lithium transition metal-based compound powder is obtained by pulverizing raw materials in a liquid medium, spray drying a slurry in which these are uniformly dispersed, and firing the obtained spray-dried product. Therefore, there has been a problem that a part of different elements such as Mo, W, Nb, Ta, and Re replaces Ni arranged in a layered manner, resulting in deterioration of battery characteristics such as the capacity and cycle characteristics of the battery.

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

[0012] According to the positive electrode active material for a non-aqueous electrolyte secondary battery disclosed in Patent Document 2, particularly by having a compound containing at least one selected from the group consisting of molybdenum, vanadium, tungsten, boron and fluorine on the surface of the particles, the initial characteristics are improved without impairing the 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 the improvement of the initial characteristics, that is, the initial discharge capacity and the initial efficiency, and does not improve the output characteristics. Further, according to the production method disclosed in Patent Document 2, since the raw material mixture which is a mixture of a compound of an additive element such as a molybdenum compound, a lithium compound, and a compound obtained by coprecipitating cobalt or the like followed by heat treatment is fired, there is a problem that a part of the additive element substitutes for nickel in which the layers are arranged, leading to a decrease in battery characteristics.

[0014] Further, Patent Document 3 discloses a positive electrode active material obtained by depositing a tungstic acid compound on composite oxide particles having a predetermined composition and performing heat treatment, and the positive electrode active material has a carbonate ion content of 0.15 mass% or less. Patent Document 3 also discloses a method for producing a positive electrode active material, which includes a deposition step of depositing a tungstic acid compound on composite oxide particles containing lithium (Li) and nickel (Ni), and a heat treatment step of heat treating the composite oxide particles on which the tungstic acid compound has been deposited.

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

[0016] In addition, improvements regarding increasing the output of lithium nickel composite oxides have also been made.

[0017] For example, Patent Document 4 discloses a lithium metal composite oxide composed of primary particles and secondary particles formed by aggregation of the primary particles, and on the surface of the lithium metal composite oxide, fine particles containing lithium tungstate represented by any one of Li 2 WO 4 、Li 4 WO 5 、Li 6 W 2 O 9 are proposed as a positive electrode active material for a non-aqueous electrolyte secondary battery, and it is said that high capacity and high output can be obtained.

[0018] However, although the high output is achieved while maintaining the high capacity, further increase in capacity is required.

[0019] Patent Document 5 discloses a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which includes a mixing step of mixing lithium nickel composite oxide particles, a tungsten compound powder that does not contain lithium, and water to obtain a tungsten mixture, and a heat treatment step of heat-treating the tungsten mixture. The heat treatment step includes a first heat treatment step of reacting a lithium compound present on the surface of primary particles of the lithium nickel composite oxide particles with tungsten compound particles by heat-treating the tungsten mixture to dissolve the tungsten compound particles and disperse tungsten on the surface of the primary particles to form lithium nickel composite oxide particles, and a second heat treatment step of heat-treating at a temperature higher than that of the first heat treatment step performed next to the first heat treatment step to form lithium nickel composite oxide particles provided with a compound containing tungsten and lithium on the surface of the primary particles of the lithium nickel composite oxide particles.

Prior Art Documents

Patent Documents

[0020]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems 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 put into an aluminum bag and purged with nitrogen gas in the first heat treatment step, and there is a problem that it becomes extremely costly when such a method is 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, and the number of steps is large, which also increases the manufacturing cost. Furthermore, by using an aluminum bag or a vacuum dryer, continuous processing of mixing and heat treatment cannot be achieved, which is also disadvantageous in terms of cost in this regard.

[0023] Therefore, in view of the problems of the above prior art, one aspect of the present invention aims to provide a method for manufacturing a positive electrode active material for a lithium-ion secondary battery that can obtain high capacity and high output at low cost when used for the positive electrode of a lithium-ion secondary battery.

Means for Solving the Problems

[0024] According to one aspect of the present invention for solving the above problems, a mixing step of obtaining a tungsten mixture by mixing a lithium nickel composite oxide as a starting material and a tungsten compound powder not containing lithium while heating; a heat treatment step of heat-treating the tungsten mixture, and the lithium nickel composite oxide contains lithium (Li), nickel (Ni), and element M (M) (however, The element M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti, Co, and Al), the ratio of the number of atoms of tungsten to the total number of atoms of nickel and 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, the moisture content, which is the ratio of water in the starting material to the lithium nickel composite oxide, is 3.0 mass% or more, the temperature of the mixing step is 30°C or more and 65°C or less, and the atmosphere of the mixing step is either decarburized air or an inert gas and The atmosphere of the mixing step is exhausted at a rate of 0.15 m 3 / min or more and 0.30 m 3 / min or less with respect to the charging rate of the lithium nickel composite oxide into the mixing step, and the decarburized air or the inert gas is supplied within a range where the atmosphere of the mixing step does not become negative pressure. Provided is a method for manufacturing a positive electrode active material for a lithium ion secondary battery.

Effects of the Invention

[0025] According to one aspect of the present invention, it is possible to provide a method for manufacturing a positive electrode active material for a lithium ion secondary battery, which can obtain a high output together with a high capacity when used for the positive electrode of a lithium ion secondary battery at low cost.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

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Figure 5A

Figure 5B

Modes for Carrying Out the Invention

[0027] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and various modifications and substitutions can be made to the following embodiments without departing from the scope of the present invention. [Method for Manufacturing Positive Electrode Active Material for Lithium Ion Secondary Battery] The method for manufacturing a positive electrode active material for a lithium ion secondary battery of the present embodiment (hereinafter, also simply referred to as "method for manufacturing a positive electrode active material") can include the following steps.

[0028] A mixing step of obtaining a tungsten mixture by mixing a lithium nickel composite oxide as a starting material and a tungsten compound powder not containing lithium while heating. A heat treatment step of heat-treating a tungsten mixture. And the lithium nickel composite oxide can contain lithium (Li), nickel (Ni), and element M (M). 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 atoms of tungsten 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. Also, the water ratio, which is the ratio of water in the starting material to the lithium nickel composite oxide, is preferably 3.0 mass % or more, and the temperature of the mixing step is preferably 30°C or more and 65°C or less.

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

[0031] The starting materials to be used in the mixing process preferably contain moisture. For example, when neither the lithium nickel composite oxide as the starting material nor the tungsten compound containing no lithium contains moisture, water can be added in the mixing process. Further, when at least one of the lithium nickel composite oxide and the tungsten compound containing no lithium contains sufficient moisture, it is not necessary to separately add water in the mixing process.

[0032] Since the starting materials contain moisture, the excess lithium compound present on the surface of the primary particles of the lithium nickel composite oxide elutes. Therefore, when using a tungsten compound that is water-soluble or soluble in an alkaline solution, the dissolution of the tungsten compound and the dispersion of the tungsten component can proceed in the mixing process.

[0033] The mixing process is preferably carried out without placing it in a closed container such as an aluminum pouch.

[0034] By mixing the lithium nickel composite oxide and 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. Then, 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 used in the mixing process is not particularly limited. For example, it preferably contains lithium (Li), nickel (Ni), and element M (M) in a molar ratio of Li:Ni:M = y:1−x:x (where 0≦x≦0.70 and 0.95≦y≦1.20). Note that element M can be at least one element selected from Mn, V, Mg, Mo, Nb, Ti, Co, and Al. Further, it is more preferable that 0.97≦y≦1.15. The lithium nickel composite oxide is preferably a compound having a layered structure, that is, a layered compound.

[0036] The lithium nickel composite oxide can be represented, for example, by the general formula Li y Ni 1-x M x O 2+α Here, since x, y, and element M have already been described, the description is omitted here. α is preferably, for example, −0.2≦α≦0.2.

[0037] The lithium nickel composite oxide can have, for example, a powder form having primary particles and secondary particles in which the primary particles are aggregated.

[0038] The lithium nickel composite oxide used in the mixing process can be prepared, for example, by firing a mixture of a nickel composite compound such as a nickel composite oxide or a nickel composite hydroxide and a lithium compound. Further, for example, the lithium nickel composite oxide obtained after firing can be further washed with water and used in the mixing process as a washed cake in which excess lithium components and the like attached to the particle surface of the lithium nickel composite oxide are reduced. When the lithium nickel composite oxide is used in the mixing process as a washed cake, since the washed cake contains moisture, depending on the degree of moisture content and the like, it may not be necessary to add moisture in the mixing process as described above.

[0039] However, it is preferable that the lithium nickel composite oxide used in the mixing step be added as it is in the fired state, that is, without performing water washing. The lithium nickel composite oxide in the fired state, that is, the one that has not been water washed, has a sufficient amount of lithium compound on the surface of its primary particles to react with the tungsten compound. Therefore, by using the lithium nickel composite oxide in the fired state, the 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 and 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 to be used is preferably water-soluble so as to dissolve in the moisture contained in the starting materials in order to penetrate to the surface of the primary particles inside the secondary particles of the lithium nickel composite oxide. Further, since the moisture in the starting materials becomes alkaline due to the elution of lithium, the tungsten compound may be a compound that can be dissolved in an alkaline solution. Further, since the starting materials are heated in the mixing step, even if it is difficult to dissolve the tungsten compound in water at room temperature, it can be dissolved in water by heating during the mixing step, or it can react with the lithium compound on the particle surface of the lithium nickel composite oxide to form a compound containing tungsten and lithium and dissolve in water, and thus can be preferably used.

[0041] Furthermore, since it is sufficient that the dissolved tungsten compound has an amount that can penetrate to the surface of the primary particles inside the secondary particles of the lithium nickel composite oxide, for example, when the tungsten compound is added in excess, even if a part thereof is in a solid state after mixing and further after heating, it may be acceptable.

[0042] Thus, it is preferable that the tungsten compound does not contain lithium and is in a state soluble in water when heated in a mixing step or the like. The tungsten compound containing no lithium to be used in the mixing step is not particularly limited, but for example, one or more selected from tungsten oxide, tungstic acid, ammonium tungstate, sodium tungstate, etc. are preferable, and tungsten oxide (WO 3 ) with low possibility of impurity mixing, and one or more selected from tungstic acid (WO 3 ·H 2 O) can be more preferably used.

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

[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 particle surface of the lithium nickel composite oxide in the obtained positive electrode active material can be made within a preferable 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 compatible with each other.

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

[0046] The water content ratio, that is, the contained water ratio, which is the ratio of water in the starting materials to the lithium nickel composite oxide, is not particularly limited. For example, it is preferably 3.0% by mass or more, more preferably 3.0% by mass or more and 7.0% by mass or less, and even more preferably 4.0% by mass or more and 6.0% by mass or less.

[0047] By setting the water content ratio to 3.0% by mass or more, a sufficient amount of water can be contained in the starting materials, and the tungsten compound can be sufficiently dispersed on the surface of the primary particles of the lithium nickel composite oxide. Therefore, the tungsten compound and the lithium compound on the surface of the lithium nickel composite oxide particles can react sufficiently. Further, by setting the water content ratio to 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 and the tungsten compound present on the surface of the primary particles of the lithium nickel composite oxide, it is preferable to mix while heating. By mixing while heating, the tungsten compound and the compound containing tungsten and lithium can also be sufficiently dispersed on the surface of the primary particles of the lithium nickel composite oxide.

[0049] The temperature at which heating is performed in the mixing step, that is, the mixing temperature, is not particularly limited. The mixing temperature in the mixing step is preferably, for example, 30°C or more and 65°C or less, more preferably 45°C or more and 60°C or less, and even more preferably 50°C or more and 60°C or less.

[0050] The temperature of the tungsten mixture may slightly increase due to the reaction between the lithium compound and the tungsten compound present on the particle surface of the lithium nickel composite oxide during mixing. However, by setting the mixing temperature to 65°C or lower, the tungsten compound can be uniformly dispersed in the particles of the lithium nickel composite oxide while suppressing the decrease in the water content in the tungsten mixture during the mixing process. Also, 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 react sufficiently with the tungsten compound. However, if the mixing temperature exceeds 65°C, the required amount of water for promoting the reaction between the lithium compound and the tungsten compound may not be obtained due to the drying of the tungsten mixture.

[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, that is, the mixing time, is preferably, for example, 15 minutes or more and 60 minutes or less, and more preferably 25 minutes or more and 45 minutes or less. By setting the mixing time to 15 minutes or more, the dispersion of the tungsten compound and the reaction between the tungsten compound and the excess lithium compound can be particularly promoted. Also, even if the mixing time is excessively long, there is no significant difference in the degree of dispersion of the tungsten compound or the reaction between the tungsten compound and the excess lithium compound. Therefore, from the viewpoint of enhancing productivity and reducing costs, the mixing time is preferably 60 minutes or less.

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

[0054] Also, in order to discharge the moisture emitted from the lithium nickel composite oxide, it is desirable to exhaust the atmosphere of the mixing process. The exhaust rate is not particularly limited, but with respect to the charging rate (charging amount) of the lithium nickel composite oxide into the mixing process of 1 kg / min, it is preferable to exhaust the atmosphere of the mixing atmosphere at a rate of 0.15 m 3 / min or more and 0.30 m 3 / min or less. When exhausting the atmosphere of the mixing process, it is preferable to supply decarburized air or an inert gas within a range where the atmosphere of the mixing process does not become negative pressure, that is, to adjust the flow rate of decarburized air or an inert gas. If the atmosphere of the mixing process becomes negative pressure, there is a risk that air will flow into the atmosphere of the mixing process and the lithium component and carbon dioxide will react. On the other hand, by controlling the atmosphere of the mixing process so as not to become negative pressure as described above, the reaction between the lithium component and carbon dioxide can be suppressed, and in particular, a decrease in the characteristics of the finally produced positive electrode active material can be prevented.

[0055] For mixing the lithium nickel composite oxide and the tungsten compound containing no lithium, a general mixer can be used. For example, a shaker mixer, a Lodige mixer, a Julia mixer, a V blender, etc. can be used to mix sufficiently without destroying the morphology of the lithium nickel composite oxide particles. (Heat treatment process) In the heat treatment process, the tungsten mixture can be heat treated. In the heat treatment process, the moisture in the tungsten mixture can be sufficiently evaporated, and the compound containing tungsten and lithium can be fixed, that is, immobilized, on the surface 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 it 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 surface of the lithium nickel composite oxide.

[0057] Also, by setting the heat treatment temperature to 200°C or lower, it is possible to suppress the formation of necking between the particles of the lithium nickel composite oxide through the compound containing tungsten and lithium, and to suppress the decrease in the specific surface area of the particles of the lithium nickel composite oxide. 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 enhanced.

[0058] The heat treatment time in the heat treatment step is not particularly limited, but it is preferably 1 hour or longer and 5 hours or shorter in order to sufficiently evaporate the 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 the reaction between carbon dioxide in the atmosphere and lithium on the particle surface of the lithium nickel composite oxide.

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

[0061] Further, by setting the amount of tungsten in the tungsten mixture formed in the mixing step within a predetermined range, the amount of tungsten contained in the compound containing tungsten and lithium formed on the particle surface of the lithium nickel composite oxide in the obtained positive electrode active material can be set within a preferable range. Therefore, when the positive electrode active material obtained by the method for manufacturing a positive electrode active material of the present 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 compatible. That is, high capacity and high output can be obtained.

[0062] Furthermore, according to the method for manufacturing a positive electrode active material of the present embodiment, a desired positive electrode active material can be manufactured by the above-described mixing step and heat treatment step without requiring operations such as sealing in an aluminum container or the like. 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 Battery] Next, a configuration example of the positive electrode active material for a lithium ion secondary battery according to the present embodiment (hereinafter also referred to as "positive electrode active material") will be described. Note that since the positive electrode active material for a lithium ion secondary battery according to the present embodiment can be manufactured, for example, by the above-described method for manufacturing a positive electrode active material, some of the matters already described will be omitted from the description.

[0063] The positive electrode active material for a lithium ion secondary battery according to the present embodiment includes particles of a lithium nickel composite oxide containing lithium (Li), nickel (Ni), and element M (M) in a ratio of Li:Ni:M = y:1 - x:x in terms of the molar ratio, and a plurality of composite particles having a compound containing tungsten and lithium disposed on the surface of the particles of the lithium nickel composite oxide.

[0064] Note that it is preferable that the above x and y 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. More preferably, the above y satisfies 0.97 ≤ y ≤ 1.15.

[0065] Among the plurality of composite particles, the ratio of the segregation particles in which the compound containing tungsten and lithium is disposed more on the surface of the particles of the lithium nickel composite oxide than in other composite particles can be 0.1% or less in terms of the number ratio. Further, the ratio of the number of tungsten atoms in the compound containing tungsten and lithium to the total number of nickel atoms contained in the lithium nickel composite oxide and the number of atoms of element M is preferably 0.05 atomic% or more and 3.0 atomic% or less.

[0066] The positive electrode active material according to the present embodiment can have a plurality of composite particles having the above-described particles of the lithium nickel composite oxide and a compound containing tungsten and lithium disposed on the surface of the particles of the lithium nickel composite oxide. Note that the positive electrode active material according to the present embodiment can also be composed of the above composite particles.

[0067] The lithium nickel composite oxide has, for example, the general formula Liy Ni 1-x M x O 2+α It can be represented by. Since x, y, and the element M have already been described, the description is 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] Also, the particles of the lithium nickel composite oxide can have primary particles and secondary particles in which the primary particles are aggregated.

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

[0070] And, it can have a configuration in which a compound containing tungsten and lithium as described above, for example, lithium tungstate, is disposed on the particle surface of the lithium nickel composite oxide.

[0071] Generally, 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 lost. However, in the positive electrode active material of the present embodiment, a compound containing tungsten and lithium is formed on the surface of the particles of the lithium nickel composite oxide. Such a compound containing tungsten and lithium has excellent lithium ion conductivity and has an effect of promoting the movement of lithium ions. Therefore, by disposing a compound containing tungsten and lithium on the surface of the particles of the lithium nickel composite oxide, a lithium conduction path can be formed at the interface with the electrolyte, and the reaction resistance of the positive electrode active material (hereinafter, may also be 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 lost within the battery decreases, and the voltage actually applied to the load side becomes relatively higher, so that high output can be obtained. Further, since the applied voltage to the load side increases and the insertion and extraction of lithium at the positive electrode are sufficiently performed, the battery capacity is also improved. Furthermore, by reducing the reaction resistance, the load on the active material during charge and discharge is also reduced, so that the cycle characteristics can be improved.

[0073] Such a compound containing tungsten and lithium, by containing tungsten and lithium, has excellent lithium ion conductivity and can have the effect of promoting the movement of lithium ions, and its specific composition is not particularly limited. However, it is preferably lithium tungstate. For example, in terms of the atomic ratio, 50% or more of the tungsten contained in the compound containing tungsten and lithium is in the form of Li 4 WO 5 It is preferably present in this form.

[0074] This is because Li 4 WO 5 has many lithium ion conduction paths among the compounds containing tungsten and lithium and has a high effect of promoting the movement of lithium ions. Therefore, when 50% or more of W is in the form of Li 4 WO 5 in terms of atomic ratio, a higher effect of reducing the reaction resistance can be obtained.

[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 surface of the primary particles of the lithium nickel composite oxide in this embodiment includes the surface of the primary particles exposed on the outer surface of the secondary particles of the lithium nickel composite oxide and the surface of the primary particles exposed in the vicinity and inside the voids of the secondary particles through which the electrolyte can penetrate to the outside of the secondary particles. Further, even the grain boundaries between the primary particles are included in the surface of the primary particles if the bonding of the primary particles is incomplete and the electrolyte can penetrate.

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

[0078] Therefore, by forming a compound containing tungsten and lithium on most of the surface of the primary particles of the lithium nickel composite oxide that can contact the electrolyte, it becomes 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 formed on the entire surface of the primary particles that can completely contact the electrolyte, and it may be in a state of partially covering or being scattered. Even in a state of partial coverage or scattering, if a compound containing tungsten and lithium is formed on the surface of the primary particles that can contact the electrolyte, the effect of reducing the anode resistance can be obtained.

[0080] It is preferable that a compound containing tungsten and lithium is uniformly formed on the surface of the particles of the lithium nickel composite oxide included in the positive electrode active material of this embodiment.

[0081] Here, the positive electrode active material contains a plurality of composite particles having particles of a lithium nickel composite oxide and a compound containing tungsten and lithium disposed on the surface of the particles of the lithium nickel composite oxide. Note that the particles of the lithium nickel composite oxide can have primary particles containing the lithium nickel composite oxide or secondary particles formed by aggregation of the primary particles.

[0082] When a compound containing tungsten and lithium is formed unevenly on the surface of the particles of the lithium nickel composite oxide among the above composite particles, the movement of lithium ions among the composite particles becomes uneven, so a specific composite particle is loaded, which may lead to deterioration of cycle characteristics over a long period and an increase in positive electrode resistance.

[0083] When the positive electrode active material of the present embodiment contains segregated particles, when the positive electrode active material is observed with a scanning electron microscope (SEM), while other composite particles are gray, such segregated particles become white. Note that the segregated particles mean particles in which a compound containing tungsten and lithium is precipitated and disposed more preferentially on the surface of the particles of the lithium nickel composite oxide than other composite particles.

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

[0085] And in the positive electrode active material of the present embodiment, as described above, among a plurality of composite particles, the ratio of segregated particles in which a compound containing tungsten and lithium is disposed more than other composite particles on the surface of the particles of the lithium nickel composite oxide is preferably 0.1% or less, and more preferably 0.01% or less in terms of the percentage of the number. By setting the ratio of the segregated particles among the plurality of composite particles to 0.1% or less, the cycle characteristics can be improved and the positive electrode resistance can be suppressed.

[0086] Among the plurality of composite particles, the lower limit of the ratio of the segregated particles is not particularly limited, but since it is preferable that there are no segregated particles, it can be set to 0% or more.

[0087] The method for calculating the ratio of the segregated particles among the plurality of composite particles included in the positive electrode active material of the present embodiment is not particularly limited. For example, by using a scanning electron microscope, the positive electrode active material is observed at a magnification of 10 times or more and 1000 times or less, and 3 fields of view or more and 20 fields of view or less, and the ratio of the segregated particles among the composite particles in the images obtained in the plurality of fields of view can be calculated. The observation conditions of the scanning electron microscope are not particularly limited, but for example, it is preferable that the acceleration voltage is 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 multiple times from the positive electrode active material and the tungsten content is analyzed.

[0089] In addition, the ratio of the number of atoms of tungsten contained in the compound containing tungsten and lithium to the total number of atoms of nickel contained in the lithium nickel composite oxide and element M (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, further 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 within the above range, when the positive electrode active material is used as the positive electrode material of a lithium ion secondary battery, high charge and discharge capacity and output characteristics can be achieved simultaneously.

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

[0091] Setting the above-mentioned tungsten amount to 0.05 atomic% or more is preferable because the output characteristics can be particularly enhanced.

[0092] Also, by setting the above-mentioned tungsten amount to 3.00 atomic% or less, the generation of segregated particles can be particularly suppressed. And by setting the tungsten amount to 3.00 atomic% or less, the lithium conductivity between the lithium nickel composite oxide and the electrolyte can be enhanced, and the charge-discharge capacity can be enhanced.

[0093] The form of the compound containing tungsten and lithium disposed on the surface of the particles of the lithium nickel composite oxide is not particularly limited. However, when the surface of the particles of the lithium nickel composite oxide is coated with a layer-like material that is a thick film of a compound containing tungsten and lithium, the thick film related to the grain boundaries of the particles of the lithium nickel composite oxide may be filled, and there is a risk of a decrease in the specific surface area. Further, when a layer-like material that is a thick film of a compound containing tungsten and lithium is formed, such a compound containing tungsten and lithium may be concentrated and formed on the surface of specific particles of the lithium nickel composite oxide and not formed on the surfaces of many other particles of the lithium nickel composite oxide. For this reason, there is a risk that the contact area between the lithium nickel composite oxide and the electrolyte via the compound containing tungsten and lithium will become small.

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

[0095] By setting the particle diameter of the compound containing tungsten and lithium to 1 nm or more, particularly sufficient lithium ion conductivity can be exhibited. Further, by setting the particle diameter of the compound containing tungsten and lithium to 300 nm or less, the particles of the compound containing tungsten and lithium can be formed particularly uniformly on the surface of the particles of the lithium nickel composite oxide, and the reaction resistance can be particularly reduced.

[0096] When the particles of the compound containing tungsten and lithium adopt the above form, the contact area with the electrolyte is made sufficient, and the lithium ion conductivity can be effectively improved. Therefore, the charge-discharge capacity can be particularly improved and the reaction resistance can be more effectively reduced.

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

[0098] On the other hand, when the surface of the particles of the lithium nickel composite oxide is coated with a thin film of a compound containing tungsten and lithium, a Li conduction path can be formed at the interface with the electrolyte while suppressing a decrease in the specific surface area, and effects such as a higher improvement in the charge-discharge capacity and a reduction in the reaction resistance can be obtained. When coating the surface of the primary particles with such a thin film-like compound containing tungsten and lithium, the compound containing tungsten and lithium preferably exists on the surface of the primary particles of the lithium nickel composite oxide as a coating film having a film thickness of 1 nm or more and 200 nm or less.

[0099] By setting the film thickness of the thin film of the compound containing tungsten and lithium to 1 nm or more, the thin film can particularly have sufficient lithium ion conductivity. Further, by setting the film thickness of the thin film of the compound containing tungsten and lithium to 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 necessarily need to be formed over the entire particles of the lithium nickel composite oxide. For example, it may be partially formed on the surface of the particles of the lithium nickel composite oxide, and the film thickness range of all the coatings does not necessarily need to be 1 nm or more and 200 nm or less. If a thin film of a compound containing tungsten and lithium with a film thickness of 1 nm or more and 200 nm or less is at least partially formed on the surface of the primary particles, the above-described high effect can be obtained. Incidentally, for example, when a compound containing tungsten and lithium is formed as a coating, by controlling the amount of tungsten contained in the compound within the above-described range, it is also possible to form a coating with a film thickness of 1 nm or more and 200 nm or less in a sufficient amount to obtain the effect.

[0101] Furthermore, even when a compound containing tungsten and lithium is formed on the surface of the lithium nickel composite oxide with a mixed particle form and thin film form, a high effect can be obtained with respect to battery characteristics.

[0102] In addition, although the amount of lithium in the entire positive electrode active material is not particularly limited, the ratio "Li / Me ratio" of the number of atoms of lithium (Li) to the sum of the number of atoms of nickel and element M in the positive electrode active material (Me) 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 to 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, the reaction resistance of the positive electrode can be particularly suppressed and the output of the battery can be increased. Further, by setting the Li / Me ratio to 1.20 or less, the excess lithium component on the particle surface of the lithium nickel composite oxide can be suppressed. Therefore, when the positive electrode active material is used as a material for the positive electrode of a lithium-ion secondary battery, the initial discharge capacity can be particularly increased and the reaction resistance of the positive electrode can be suppressed.

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

[0105] That is, after the formation of the compound containing tungsten and lithium, the Li / Me ratio of the lithium nickel composite oxide particles as the base material (core material) decreases compared to before the formation. Therefore, by setting the above-mentioned Li / Me ratio to 0.97 or more, better charge and discharge capacity and reaction resistance can be obtained.

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

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

[0108] In addition, the effect of providing a compound containing tungsten and lithium on the surface of the secondary particles and the surface of the primary particles of the lithium nickel composite oxide can be applied to powders such as lithium cobalt-based composite oxides, lithium manganese-based composite oxides, lithium nickel cobalt manganese-based composite oxides, etc., and not only the cathode active material described in the present invention but also cathode active materials for lithium secondary batteries generally used. [Lithium Ion Secondary Battery] The lithium ion secondary battery of this embodiment (hereinafter also referred to as "secondary battery") can have a cathode containing the aforementioned cathode active material.

[0109] Hereinafter, a configuration example of the secondary battery of this embodiment will be described for each component. The secondary battery of this embodiment includes, for example, a cathode, an anode, and a non-aqueous electrolyte, and is composed of the same components as a general lithium ion secondary battery. It should be noted that the embodiments described below are merely examples, and the lithium ion secondary battery of this embodiment can be implemented in various modified and improved forms based on the knowledge of those skilled in the art, including the following embodiments. Also, the use of the secondary battery is not particularly limited. (Cathode) The cathode of the secondary battery of this embodiment can contain the aforementioned cathode active material.

[0110] An example of the method for manufacturing the cathode will be described below. First, the aforementioned cathode active material (powder form), conductive material, and binder are mixed to form a cathode composite material. Further, if necessary, activated carbon or a solvent for the purpose of viscosity adjustment is added, and this is kneaded to produce a cathode composite material paste.

[0111] Since the mixing ratio of each material in the positive electrode composite material is a factor that determines the performance of the lithium-ion secondary battery, it can be adjusted according to 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. For example, when the total mass of the solid content of the positive electrode composite material excluding the solvent is 100% by mass, the positive electrode active material can be contained in a proportion of 60% by mass or more and 95% by mass or less, the conductive material can be contained in a proportion of 1% by mass or more and 20% by mass or less, and the binder can be contained in a proportion of 1% by mass or more and 20% by mass or less.

[0112] The obtained positive electrode composite material paste is applied, for example, to the surface of a current collector made of aluminum foil, dried to scatter the solvent, and a sheet-shaped positive electrode is produced. If necessary, it can also be pressed by a roll press or the like to increase the electrode density. The sheet-shaped positive electrode obtained in this way can be cut to an appropriate size according to the target battery and used for the production of the battery.

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

[0114] The binder serves to connect the active material particles. 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. can be used.

[0115] If necessary, a solvent that dissolves the binder can be added to the positive electrode composite material by dispersing the positive electrode active material, conductive material, etc. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. In addition, activated carbon can also be added to the positive electrode composite material to increase the electric double layer capacitance.

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

[0117] As the negative electrode active material, for example, natural graphite, artificial graphite, fired products of organic compounds such as phenolic resin, and powder bodies of carbon materials such as coke can be used. In this case, as the negative electrode binder, a fluorine-containing resin such as PVDF can be used as in the case of the positive electrode, and as the solvent for dispersing these active materials and binders, an organic solvent such as N-methyl-2-pyrrolidone can be used. (Separator) A separator can be disposed between the positive electrode and the negative electrode as needed. The separator separates the positive electrode and the negative electrode and holds the electrolyte, and a known one can be used. For example, a thin film such as polyethylene or polypropylene having a large number of minute pores can be used. (Non-aqueous electrolyte) As the non-aqueous electrolyte, for example, a non-aqueous electrolyte solution can be used.

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

[0119] Examples of the organic solvent include 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; phosphorus compounds such as triethyl phosphate and trioctyl phosphate. One of them may be used alone, or two or more of them may be mixed and used.

[0120] Examples of the supporting salt include LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiN(CF 3 SO 2 ) 2 , and composite salts thereof. Further, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

[0121] In addition, as the non-aqueous electrolyte, a solid electrolyte may be used. The solid electrolyte has a property of withstanding a 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. For example, those containing oxygen (O) and having lithium ion conductivity and electron insulation can be preferably used. Examples of the oxide-based solid electrolyte include lithium phosphate (Li 3 PO 4 ), Li 3 PO 4 N X , LiBO 2 N X , LiNbO 3 , LiTaO 3 , Li2 SiO 3 、Li 4 SiO 4 -Li 3 PO 4 、Li 4 SiO 4 -Li 3 VO 4 、Li 2 O-B 2 O 3 -P 2 O 5 、Li 2 O-SiO 2 、Li 2 O-B 2 O 3 -ZnO、Li 1+X Al X Ti 2-X (PO 4 ) 3 (0≦X≦1)、Li 1+X Al X Ge 2-X (PO 4 ) 3 (0≦X≦1)、LiTi 2 (PO 4 ) 3 、Li 3X La 2 / 3-X TiO 3 (0≦X≦2 / 3)、Li 5 La 3 Ta 2 O 12 、Li 7 La 3 Zr 2 O 12 、Li 6 BaLa 2 Ta 2 O 12 、Li 3.6 Si 0.6 P 0.4 O 4 One or more selected from the following can be used.

[0124] The sulfide solid electrolyte is not particularly limited. For example, those containing sulfur (S) and having lithium ion conductivity and electronic insulation can be preferably used. Examples of the sulfide solid electrolyte include, for example, Li 2 S-P2 S 5 , Li 2 S - SiS 2 , LiI - Li 2 S - SiS 2 , LiI - Li 2 S - P 2 S 5 , LiI - Li 2 S - B 2 S 3 , Li 3 PO 4 -Li 2 S - Si 2 S, Li 3 PO 4 -Li 2 S - SiS 2 , LiPO 4 -Li 2 S - SiS, LiI - Li 2 S - P 2 O 5 , LiI - Li 3 PO 4 -P 2 S 5 etc., one or more selected from these can be used.

[0125] In addition, as the inorganic solid electrolyte, those other than the above may be used. For example, Li 3 N, LiI, Li 3 N - LiI - LiOH, etc. may also be used.

[0126] As the organic solid electrolyte, there is no particular limitation as long as it is a polymer compound showing ion conductivity. For example, polyethylene oxide, polypropylene oxide, copolymers thereof, etc. can be used. Also, the organic solid electrolyte may contain a supporting salt (lithium salt). (Shape and configuration of the secondary battery) As described above, the lithium-ion secondary battery of the present embodiment can have various shapes such as cylindrical or laminated. Regardless of the shape adopted, 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, and the obtained electrode body is impregnated with the non-aqueous electrolyte solution. The positive current collector and the positive electrode terminal communicating with the outside, and the negative current collector and the negative electrode terminal communicating with the outside are connected using a current collecting lead or the like, and can be structured to be sealed in a battery case.

[0127] Note that, as described above, the secondary battery of the present embodiment is not limited to the form using a non-aqueous electrolyte solution as the non-aqueous electrolyte. For example, a secondary battery using a solid non-aqueous electrolyte, that is, an all-solid-state battery can also be used. In the case of an all-solid-state battery, the configuration other than the positive electrode active material can be changed as necessary.

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

[0129] In particular, a lithium-ion secondary battery using the above-described positive electrode active material, for example, when used for the positive electrode of a 2032-type coin battery, although it depends on the composition, for example, a high initial discharge capacity of 210 mAh / g or more, that is, a high capacity and a low positive electrode resistance can be obtained, and it has a higher output. Also, it has high thermal stability and can be said to be excellent in safety.

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

[0131] In addition, since the secondary battery of this embodiment can be miniaturized and have high output, it is suitable as a power source for electric vehicles that are restricted in mounting space. Note that the secondary battery of this embodiment can be used not only as a power source for electric vehicles that are purely driven by electric energy, but also as a power source for so-called hybrid vehicles that are used in combination with combustion engines such as gasoline engines and diesel engines.

Examples

[0132] Hereinafter, the present invention will be described in more detail by way of examples and comparative examples, but the present invention is not limited to these examples in any way. The methods for evaluating various positive electrode active materials and batteries in the examples and comparative examples are as follows. (Evaluation of positive electrode active material) (a) Ratio of segregated particles When calculating the ratio of segregated particles contained in the composite particles in the positive electrode active material, first, any 10 locations of the powder of the positive electrode active material were imaged with a scanning electron microscope at an applied voltage of 5 kV and a magnification of 100 times. That is, observations were made in 10 fields of view. At this time, in one field of view, for example, a scanning electron microscope photograph as shown in FIG. 1 can be obtained. Then, the number of white particles, which are segregated particles, shown in the 10 SEM photographs was counted, and the ratio of segregated particles among the composite particles contained in the 10 SEM photographs was measured by the method of calculating.

[0133] Note that, as shown in FIGS. 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. (Manufacture and evaluation of battery) (a) Manufacture of battery For the evaluation of the positive electrode active material, a 2032-type coin battery 11 (hereinafter referred to as a coin-type battery) shown in FIG. 4 was used.

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

[0135] The case 12 has a hollow positive electrode can 12a with one end open, and a negative electrode can 12b disposed at the opening of the positive electrode can 12a. When the negative electrode can 12b is disposed at the opening of the positive electrode can 12a, a space for accommodating the electrode 13 is formed between the negative electrode can 12b and the positive electrode can 12a.

[0136] The electrode 13 is composed of a positive electrode 13a, a separator 13c, and a negative electrode 13b, and is laminated in this order so as to be arranged in line. The positive electrode 13a is in contact with the inner surface of the positive electrode can 12a via the current collector 14, and the negative electrode 13b is in contact with the inner surface of the negative electrode can 12b via the current collector 14 and is accommodated in the case 12. A current collector 14 is also disposed between the positive electrode 13a and the separator 13c.

[0137] Note that the case 12 is provided with a gasket 12c, and the relative movement is fixed by this gasket 12c so that the space between the positive electrode can 12a and the negative electrode can 12b is maintained in a non-contact state. Further, the gasket 12c also has a function of sealing the gap between the positive electrode can 12a and the negative electrode can 12b and hermetically blocking the inside of the case 12 from the outside in terms of airtightness and liquid tightness.

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

[0139] First, 52.5 mg of a positive electrode active material for a lithium-ion secondary battery, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene (PTFE) resin prepared in each of the examples and comparative examples were mixed and press-molded at a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm to fabricate the positive electrode 13a. The fabricated positive electrode 13a was dried in a vacuum dryer at 120°C for 12 hours.

[0140] Using this positive electrode 13a, the negative electrode 13b, the separator 13c, and the electrolytic solution, the above-described coin-type battery 11 was fabricated in a glove box with an Ar atmosphere whose dew point was controlled to -80°C.

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

[0142] For the separator 13c, a polyethylene porous membrane with a thickness of 25 μm was used. For the electrolytic solution, an equal - volume mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (manufactured by Toyama Chemical Co., Ltd.) with 1 M LiClO 4 as a supporting electrolyte was used. (b) Evaluation The initial discharge capacity, positive - electrode resistance, and cycle characteristics indicating the performance of the manufactured coin - type battery 11 were evaluated as follows. (b1) Initial discharge capacity The initial discharge capacity was obtained by leaving the coin - type battery 11 standing for about 24 hours after fabrication. After the open - circuit voltage OCV (Open Circuit Voltage) became stable, the current density with respect to the positive electrode was set to 0.1 mA / cm 2 and the battery was charged up to a cut - off voltage of 4.3 V. After a 1 - hour rest, the capacity when discharging to a cut - off voltage of 3.0 V was defined as the initial discharge capacity. (b2) Positive - electrode resistance When the coin - type battery 11 was charged at a charging potential of 4.1 V and the positive - electrode resistance was measured by the alternating - current impedance method using a frequency - response analyzer and a potentiostat (manufactured by Solartron, 1255B), a Nyquist plot shown in Fig. 5A was obtained.

[0143] This Nyquist plot represents the sum of the solution resistance, the negative - electrode resistance and its capacitance, and the positive - electrode resistance and its capacitance as characteristic curves.

[0144] The battery reaction at the electrode consists of a resistance component associated with charge transfer and a capacitance component due to the electric double layer. When these are represented by an electric circuit, it becomes a parallel circuit of resistance and capacitance. As a whole battery, it is represented by an equivalent circuit in which the solution resistance and the parallel circuits of the negative electrode and the positive electrode are connected in series.

[0145] Therefore, fitting calculations were performed using the equivalent circuit shown in FIG. 5B based on the Nyquist plot shown in FIG. 5A, and the value of the positive electrode resistance was calculated. 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. In the cycle test, after measuring the initial discharge capacity, a 10-minute rest was taken, and the charge-discharge cycle was repeated 500 times (charge-discharge), including the initial discharge capacity measurement, in the same manner as 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 with respect to the discharge capacity at the 1st cycle (initial discharge capacity) was determined as the capacity retention rate (%). (b4) Carbon content The carbon content was measured using a carbon-sulfur analyzer (manufactured by LECO Corporation, model number: CS-600).

[0146] In this example, for the production of the positive electrode active material and the secondary battery, reagent-grade samples manufactured by Wako Pure Chemical Industries, Ltd. were used unless otherwise specified. [Example 1] According to the following procedure, a positive electrode active material and a lithium-ion secondary battery were produced and evaluated. (Mixing step) Using an oxide mainly composed of Ni and lithium hydroxide, Li obtained by a known technique 0.98 Ni 0.91 Co 0.06 Al 0.03 O 2 Powder of lithium nickel composite oxide particles, which is a layered compound represented by, was used as the base material. In the following other examples and comparative examples, a layered compound lithium nickel composite oxide is also used as the base material. Then, water was added to the base material, and the moisture rate, which is the ratio of water in the starting materials for the mixing step to the lithium nickel composite oxide and water, was set to 3.2 mass% (hereinafter, simply referred to as "moisture rate". The same notation is used in Table 1).

[0147] The base material added with water was put into a paddle-type mixing device, and tungsten oxide (WO such that the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Al in the base material was 0.12 atomic%3 ) was put on the base material, and these starting materials were mixed at 60 °C for 30 minutes to obtain a tungsten mixture.

[0148] During the mixing process, decarburized air was supplied while evacuating the inside of the mixing device. Specifically, the evacuation was carried out at a rate of 0.20 m 3 / min for every 1 kg / min of the input rate of the base material added with water, and decarburized air was supplied at the same flow rate to control so that the inside of the mixing device did not become negative pressure.

[0149] In addition, in Table 1, the ratio of the number of atoms of W to the total number of atoms of Ni and element M in the base material in the starting materials is described as "W content". (Heat treatment process) Thereafter, heat treatment was performed at 190 °C for 120 minutes using a steam tube dryer, and then furnace cooling was carried out.

[0150] Note that the atmospheres in the mixing process and the heat treatment process were decarburized air.

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

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

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

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

[0155] Note that the tungsten contained in the obtained positive electrode active material is in a compound containing tungsten and lithium disposed on the particle surface of the lithium nickel composite oxide, and nickel and element M are derived from the lithium nickel composite oxide. For this reason, the tungsten content of the positive electrode active material corresponds to the ratio of the number of atoms of tungsten 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 the coin-type battery 11 shown in FIG. 4 having a positive electrode prepared using the obtained positive electrode active material were evaluated. Note that the relative value with Example 1 being 1.00 for the positive electrode resistance before the cycle test (positive electrode resistance before cycle) was used as the evaluation value.

[0157] Also, the carbon content was measured by the measurement method described above.

[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% by 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 5.7% by mass, and WO was added so that the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Al in the base material was 0.24 atomic%. 3 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, with the temperature during mixing being 50°C, the heat treatment temperature being 150°C, and the heat treatment time being 180 minutes.

[0160] The test conditions and evaluation results are shown in Table 1. [Example 4] The composition of the base material was Li 0.97 Ni 0.91 Co 0.04 Al 0.05 O 2 and the moisture content was 6.9% by mass. WO 3 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%. Also, during the mixing process, decarbonated air was supplied while exhausting the inside of the mixing device. Specifically, the inside of the mixing device was exhausted at a rate of 0.15 m 3 / min per 1 kg / min of the input rate of the base material to which water was added, and decarbonated air was supplied at the same flow rate to control so that the inside of the mixing device did not become negative pressure. Except for the above points, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1.

[0161] The test conditions and evaluation results are shown in Table 1. [Example 5] The composition of the base material was Li 0.97 Ni 0.91 Co 0.04 Al 0.05 O 2 and the moisture content was 4.1% by mass. WO 3 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%. Also, during the mixing process, decarbonated air was supplied while exhausting the inside of the mixing device. Specifically, the inside of the mixing device was exhausted at a rate of 0.15 m 3 / min per 1 kg / min of the input rate of the base material to which water was added, and decarbonated air was supplied at the same flow rate to control so that the inside of the mixing device did not become negative pressure. Except for the above points, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1.

[0162] The test conditions and evaluation results are shown in Table 1. [Example 6] The composition of the base material was Li 0.97 Ni 0.91 Co 0.04 Al 0.05 O 2Set the moisture content to 5.5% by mass, and add WO so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material is 0.15 atomic%. 3 was added, and the temperature during mixing was 45°C and the mixing time was 45 minutes. During the mixing process, decarburized air was supplied while evacuating the inside of the mixing device. Specifically, the inside of the mixing device was controlled so as not to become negative pressure by evacuating at a rate of 0.25 m 3 / min per 1 kg / min of the feeding rate of the base material to which water was added, and supplying decarburized air at the same flow rate. Except for the above points, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1.

[0163] The test conditions and evaluation results are shown in Table 1. [Example 7] Set the composition of the base material to Li 0.97 Ni 0.91 Co 0.04 Al 0.05 O 2 Set the moisture content to 4.9% by mass, and add WO so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material is 0.18 atomic%. 3 was added, and the temperature during mixing 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, decarburized air was supplied while evacuating the inside of the mixing device. Specifically, the inside of the mixing device was controlled so as not to become negative pressure by evacuating at a rate of 0.30 m 3 / min per 1 kg / min of the feeding rate of the base material to which water was added, and supplying decarburized air at the same flow rate. Except for the above points, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1.

[0164] The test conditions and evaluation results are shown in Table 1. [Example 8] Set the composition of the base material to Li 0.98 Ni 0.88 Co 0.09 Al 0.03 O 2 Set the moisture content to 4.3% by mass, and add WO so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material is 0.18 atomic%. 3was added. Except for the above points, 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 was Li 0.98 Ni 0.88 Co 0.09 Al 0.03 O 2 and the moisture content was 3.6% by mass. WO 3 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 points, 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 was Li 0.97 Ni 0.88 Co 0.07 Al 0.05 O 2 and the moisture content was 6.4% by mass. WO 3 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 points, 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 was Li 0.97 Ni 0.88 Co 0.07 Al 0.05 O 2 and the moisture content was 5.8% by mass. WO 3 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, decarboxylated air was supplied while exhausting the inside of the mixing device. Specifically, 0.15 m 3Exhausted at a rate of / and supply decarbonated air at the same flow rate to control so that the inside of the mixing device does not become negative pressure. Except for the above points, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1.

[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 O 2 and the moisture content is 8.6 mass%, and WO is added so that the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Al in the base material is 0.18 atomic%. Except for the above points, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1. 3

[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 O 2 and the moisture content is 7.9 mass%, and WO is added so that the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Al in the base material is 0.15 atomic%. Except for the above points, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1. 3

[0170] The test conditions and evaluation results are shown in Table 1. [Example 14] The base material added with water and WO 3 were continuously charged into a continuous paddle type mixing device, the mixture was continuously supplied from the continuous paddle type mixing device 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 continuously carried out. Except for the above points, 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 added with water and WO 3 were continuously fed into a continuous paddle-type mixing device, the mixture was continuously supplied from the continuous paddle-type mixing device to a continuous steam dryer, and the dried mixture was continuously discharged from the continuous steam dryer. That is, the mixing step and the heat treatment step were continuously carried out. Except for the above points, 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 was Li 0.98 Ni 0.55 Co 0.20 Mn 0.25 O 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 composition of the base material was set as such.

[0173] The test conditions and evaluation results are shown in Table 1. [Example 17] The moisture content was 4.9% by mass, and WO was added such that the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Mn in the base material was 0.18 atomic%. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 16, except that the temperature during mixing was set to 55°C. 3 A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 16, except that the moisture content was 4.9% by mass, WO was added such that the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Mn in the base material was 0.18 atomic%, and the temperature during mixing was 55°C.

[0174] The test conditions and evaluation results are shown in Table 1. [Example 18] The composition of the base material was Li 0.97 Ni 0.91 Co 0.04 Al 0.05 O 2 and the moisture content was 5.2% by mass. WO was added such that the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Al in the base material was 0.15 atomic%. During the mixing step, decarbonated air was supplied while exhausting the inside of the mixing device. Specifically, 0.10 m per 1 kg / min of the feeding rate of the base material added with water 3 was added. During the mixing process, while exhausting the inside of the mixing device, decarbonated air was supplied. Specifically, 0.10 m per 1 kg / min of the feeding rate of the base material added with water 3Exhausted at a speed of / minute and supplied with decarburized air at the same flow rate to control so that the inside of the mixing device does not become negative pressure. Except for the above points, the positive electrode active material and the secondary battery were produced and evaluated in the same manner as in Example 1.

[0175] The test conditions and evaluation results are shown in Table 1. [Example 19] The composition of the base material was Li 0.97 Ni 0.91 Co 0.04 Al 0.05 O 2 and the moisture content was 5.5% by mass. WO 3 was added so that the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Al in the base material was 0.19 atomic %. During the mixing process, decarburized air was supplied while exhausting the inside of the mixing device. Specifically, it was exhausted at a speed of 0.35 m 3 / minute per 1 kg / minute of the input speed of the base material added with water, and decarburized air was supplied at the same flow rate to control so that the inside of the mixing device did not become negative pressure. Except for the above points, the positive electrode active material and the secondary battery were produced and evaluated in the same manner as in Example 1.

[0176] The test conditions and evaluation results are shown in Table 1. [Example 20] The composition of the base material was Li 0.97 Ni 0.88 Co 0.07 Al 0.05 O 2 and the moisture content was 4.9% by mass. WO 3 was added so that the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Al in the base material was 0.18 atomic %. During the mixing process, decarburized air was supplied while exhausting the inside of the mixing device. Specifically, it was exhausted at a speed of 0.10 m 3 / minute per 1 kg / minute of the input speed of the base material added with water, and decarburized air was supplied at the same flow rate to control so that the inside of the mixing device did not become negative pressure. Except for the above points, the positive electrode active material and the secondary battery were produced and evaluated in the same manner as in Example 1. [Example 21] The composition of the base material was Li 0.97 Ni 0.88 Co0.07 Al 0.05 O 2 The moisture content was set to 5.3 mass%, and the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was set to 0.18 atomic %. 3 During the mixing process, the inside of the mixing device was evacuated while 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. [Example 22] The composition of the base material is Li 0.98 Ni 0.55 Co 0.20 Mn 0.25 O 2 The moisture content was set to 5.3 mass%, and the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was set to 0.19 atomic %. 3 During the mixing process, the inside of the mixing device was evacuated while 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 O 2 The moisture content was set to 4.8 mass%, and the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material was set to 0.17 atomic %. 3 During the mixing process, the inside of the mixing device was evacuated while 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. 3It was controlled so that the inside of the mixing device would not become negative pressure by exhausting at a speed of / minute and supplying decarbonated air at the same flow rate. Except for the above points, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1.

[0178] The test conditions and evaluation results are shown in Table 1. [Comparative Example 1] The composition of the base material was Li 0.97 Ni 0.91 Co 0.04 Al 0.05 O 2 and the moisture content was 5.2 mass%. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1, except that WO 3 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] The moisture content was 2.7 mass%. A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1, except that WO 3 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 was Li 0.97 Ni 0.88 Co 0.07 Al 0.05 O 2 and the moisture content was 2.8 mass%. WO 3 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 points, 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 was Li 0.98 Ni 0.91 Co 0.06Al 0.03 O 2 and set the moisture content to 4.5% by mass, and add WO so that the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Al in the base material is 0.18 atomic%. 3 The positive electrode active material and the secondary battery were produced and evaluated in the same manner as in Example 1, except for the above points. The temperature during mixing was 25°C and the mixing time was 90 minutes.

[0182] The test conditions and evaluation results are shown in Table 1. [Comparative Example 5] The composition of the base material was Li 0.98 Ni 0.91 Co 0.06 Al 0.03 O 2 and set the moisture content to 4.4% by mass, and set the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Al in the base material to 0.15 atomic%, the temperature during mixing was 70°C, and the mixing time was 30 minutes. The positive electrode active material and the 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 was Li 0.98 Ni 0.88 Co 0.09 Al 0.03 O 2 and set the moisture content to 4.5% by mass, and set the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Al in the base material to 0.18 atomic%, the temperature during mixing was 70°C, and the mixing time was 30 minutes. The positive electrode active material and the 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 was Li 0.97 Ni 0.88 Co 0.07 Al 0.05 O 2The moisture content was set to 4.2% by mass, the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Al in the base material was set to 0.18 atomic%, the temperature during mixing was set to 75°C, and the mixing time was set to 30 minutes. Except for the above points, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 1.

[0185] The test conditions and evaluation results are shown in Table 1. [Comparative Example 8] The moisture content was set to 3.4% by mass, the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Mn in the base material was set to 0.13 atomic%, and the temperature during mixing was set to 70°C. Except for the above points, 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 set to 3.9% by mass, the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Mn in the base material was set to 0.14 atomic%, the temperature during mixing was set to 25°C, and the mixing time was set to 90 minutes. Except for the above points, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in Example 16.

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

[0188]

Table 1

[0189] In Examples 1, 2, 9, 14, and 16, since the moisture content, which is the ratio of water in the starting materials to the lithium nickel composite oxide in the water used in the mixing process, was less than 4.0% by mass and relatively low, WO 3 was not completely dispersed, and unreacted WO 3It was likely to remain. For this reason, the ratio of segregation particles became somewhat higher compared to other examples, and it is considered that the battery characteristics were somewhat inferior compared to other examples.

[0190] In Examples 4, 12, and 13, since the moisture content significantly exceeded 6.0%, lithium in the lithium nickel composite oxide dissolved out into the excess moisture, and the reaction with tungsten increased in the part where lithium was locally increased, resulting in the generation of segregation particles. For this reason, the number of segregation particles became larger compared to other examples, and it is considered that the battery characteristics were somewhat inferior compared to other examples.

[0191] In Examples 6 and 7, since the temperature during mixing was low, it was necessary to extend the mixing time compared to other examples, but the evaluation results were good.

[0192] In Examples 18, 20, and 22, although it was at a non-problematic level, the carbon content was higher compared to other examples. This is because the exhaust speed and the flow rate of decarboxylated air were low, so the carbon dioxide concentration in the atmosphere of the mixing process became higher, promoting the carbonation of the lithium component in the lithium nickel composite oxide. This carbon content may become gas in the battery and deteriorate the characteristics. For this reason, it is preferable that carbonation is minimized.

[0193] In Examples 19, 21, and 23, since the exhaust speed and the flow rate of decarboxylated air were high, the carbonation of the lithium component of the lithium nickel composite oxide was low, but drying was somewhat promoted by the airflow. Although it was at a non-problematic level, unreacted WO 3 became more.

[0194] On the other hand, in Comparative Example 1, since the ratio of the number of atoms of W to the total number of atoms of Ni, Co, and Al in the base material was less than 0.05 atomic%, a compound sufficiently containing tungsten and lithium was not formed, and it is considered that the battery characteristics significantly deteriorated.

[0195] In Comparative Examples 2 and 3, since the moisture content was low, sufficient WO 3could not be dispersed, and a large amount of unreacted WO 3 remained, and as a result, a large amount of excess lithium component also remained, which is considered to have deteriorated the battery characteristics.

[0196] In Comparative Examples 4 and 9, since the mixing temperature was below 30°C, WO 3 could not be dispersed sufficiently, and a large amount of unreacted WO 3 remained, and as a result, a large amount of excess lithium component also remained, which is considered to have deteriorated the battery characteristics.

[0197] In Comparative Examples 5 to 8, since the mixing temperature exceeded 65°C, the decrease in moisture from the tungsten mixture was rapid, and the moisture necessary for the dispersion of WO 3 could not be maintained, and a large amount of unreacted WO 3 remained, and as a result, a large amount of excess lithium component also remained, so it is considered that the battery characteristics were deteriorated.

[0198] Also, in Comparative Examples 2 to 9, as described above, since WO 3 could not be dispersed sufficiently, the segregation particle ratio increased, and it was confirmed that the battery characteristics deteriorated.

[0199] Thus, it became clear that the positive electrode active material of this embodiment is high-capacity and high-output while being low-cost. In Examples 14 and 15, continuous processing was performed, but it was clear that the evaluation results were good, the productivity was high, and a further significant cost reduction was expected.

[0200] The method for manufacturing a positive electrode active material for a lithium-ion secondary battery, the positive electrode active material for a lithium-ion secondary battery, and the lithium-ion secondary battery have been described in the embodiments and examples, etc., but the present invention is not limited to the above embodiments and examples, etc. 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, and incorporates the entire contents of Japanese Patent Application No. 2019-029870 into this international application.

Claims

1. A mixing step of obtaining a tungsten mixture by mixing a lithium nickel composite oxide as a starting material and a tungsten compound powder not containing lithium while heating; A heat treatment step of heat treating the tungsten mixture; and having, The lithium nickel composite oxide contains lithium (Li), nickel (Ni), and element M (M) (however, the element M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti, Co, and Al), In the starting material, the ratio of the number of atoms of tungsten 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 3.00 atomic % or less, The moisture rate, which is the ratio of water in the starting material to the lithium nickel composite oxide, is 3.0 mass % or more, The temperature of the mixing step is 30° C. or more and 65° C. or less, and the atmosphere of the mixing step is either decarburized air or an inert gas, A method for producing a positive electrode active material for a lithium ion secondary battery, wherein the atmosphere of the mixing step is exhausted at a rate of 0.15 m3 / min or more and 0.30 m3 / min or less with respect to the charging rate of 1 kg / min of the lithium nickel composite oxide into the mixing step, and the decarburized air or the inert gas is supplied within a range where the atmosphere of the mixing step does not become negative pressure.

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

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 moisture rate is 3.0 mass % or more and 7.0 mass % or less.

4. The 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 rate is 4.0 mass % or more and 6.0 mass % or less.

5. The 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 heat treatment temperature of the heat treatment step is 100° C. or more and 200° C. or less.

6. The 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 atmosphere in the heat treatment step is either decarburized air or an inert gas.

7. The tungsten compound that does not contain lithium is tungsten oxide (WO ３ ), and tungstic acid (WO ３ ·H ２ O), and the method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 6, which is one or more selected from the group consisting of

8. The method for producing a positive electrode active material for a lithium-ion secondary battery according to any one of claims 1 to 7, wherein lithium tungstate is fixed on the surface of the lithium nickel composite oxide particles in the heat treatment step.

9. Containing a plurality of composite particles having particles of a lithium nickel composite oxide containing lithium (Li), nickel (Ni), and element M (M) in a molar ratio of Li:Ni:M = y:1−x:x (where 0≦x≦0.70, 0.95≦y≦1.20, and the element M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti, Co, and Al), and a compound containing tungsten and lithium disposed on the surface of the particles of the lithium nickel composite oxide. Among the plurality of composite particles, the proportion of segregated particles in which the compound containing tungsten and lithium is disposed more on the surface of the particles of the lithium nickel composite oxide than on the surface of the other composite particles is 0.1% or less by number ratio. A positive electrode active material for a lithium-ion secondary battery, wherein the atomic ratio of tungsten contained in the compound containing tungsten and lithium to the total number of atoms of nickel contained in the lithium nickel composite oxide and element M is 0.05 atomic % or more and 3.0 atomic % or less.

10. A lithium-ion secondary battery having a positive electrode containing the positive electrode active material for a lithium-ion secondary battery according to claim 9.

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