Method for producing positive electrode active material for nonaqueous electrolyte secondary battery

Abstract

The present invention relates to a method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery. The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure includes: a first step of adding an alkali solution in which a tungsten compound is dissolved to a lithium metal complex oxide powder represented by a general formula Li z Ni 1‑x‑y Co x M y O2 (wherein 0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1, 0.97 ≤ z ≤ 1.20, and M is at least one element selected from the group consisting of Mn, W, Mg, Mo, Nb, Ti, Si, and Al) and mixing; and a second step of heat-treating the mixed alkali solution and the lithium metal complex oxide powder at 100 to 600°C. In the first step, the amount of the alkali solution added is 0.1 to 10 mass% relative to the lithium metal complex oxide powder.

Description

[0001] This application is a divisional application of the application filed on December 12, 2018, with application number 201880082277.X and invention title "Method for manufacturing positive electrode active material for non-aqueous electrolyte secondary batteries". Technical Field

[0002] This disclosure relates to a method for manufacturing positive electrode active materials for non-aqueous electrolyte secondary batteries. Background Technology

[0003] Lithium-ion secondary batteries, including those with non-aqueous electrolytes, are widely used in mobile phones, digital cameras, laptops, hybrid vehicles, and electric vehicles. Among lithium-ion secondary batteries, those using lithium metal oxides as the positive electrode active material and carbon materials such as graphite as the negative electrode active material have become the mainstream.

[0004] As a method for manufacturing positive electrode active materials, for example, Patent Document 1 discloses a method for manufacturing positive electrode active materials for non-aqueous electrolyte secondary batteries. In this manufacturing method, in the general formula Li z Ni 1-x-y Co x M y In a lithium metal composite oxide powder formed by primary particles of O2 (where 0.10≤x≤0.35, 0≤y≤0.35, 0.97≤z≤1.20, and M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti, and Al) and secondary particles formed by the aggregation of the aforementioned primary particles, an alkaline solution containing a tungsten compound is added and mixed. The resulting mixture is then heat-treated to form fine particles containing W and Li on the surface of the primary particles of the aforementioned lithium metal composite oxide powder.

[0005] Additionally, for example, Patent Document 2 discloses a method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery, in which a material of general formula Li... z Ni 1-x-y Co x M y In a lithium metal composite oxide powder formed by primary particles and secondary particles formed by the aggregation of primary particles, O2 (where 0≤x≤0.35, 0≤y≤0.35, 0.95≤z≤1.30, and M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti, and Al), tungsten compound powder without lithium is mixed, and the resulting tungsten mixture is heat-treated to form lithium tungstate compound on the surface of the primary particles of the lithium metal composite oxide.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2012-79464

[0009] Patent Document 2: Japanese Patent Application Publication No. 2016-127004 Summary of the Invention

[0010] However, although lithium metal composite oxides with a high nickel ratio and a cobalt ratio of less than 10 mol% (in other words, 0 ≤ x ≤ 0.1 in the above general formula) are excellent positive electrode active materials, they suffer from reduced discharge capacity at low temperatures.

[0011] Typically, the discharge capacity at low temperatures is improved by forming particles containing W and Li on the surface of primary particles of lithium metal composite oxides. However, even when using the methods disclosed in Patent Documents 1 and 2, forming particles containing W and Li on the surface of primary particles of lithium metal composite oxides with a high nickel ratio and a cobalt ratio of less than 10 mol%, the discharge capacity at low temperatures is not substantially improved.

[0012] Therefore, the purpose of this disclosure is to provide a method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery, which can both use a lithium metal composite oxide with a high nickel ratio and a cobalt ratio of less than 10 mol% and improve the discharge capacity at low temperatures.

[0013] The method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery, as one aspect of this disclosure, is characterized by comprising the following steps: Step 1, in the general formula Li z Ni 1-x-y Co x M y In a lithium metal composite oxide powder formed from primary particles of O2 (where 0≤x≤0.1, 0≤y≤0.1, 0.97≤z≤1.20, and M is at least one element selected from Mn, W, Mg, Mo, Nb, Ti, Si, and Al) and secondary particles formed by the aggregation of the aforementioned primary particles, an alkaline solution containing a dissolved tungsten compound is added and mixed; and, in a second step, the aforementioned alkaline solution is heat-treated with the aforementioned lithium metal composite oxide powder to form particles containing W and Li on the surface of the primary particles of the aforementioned lithium metal composite oxide powder, wherein in the aforementioned first step, the amount of the aforementioned alkaline solution added is 0.1 to 10% by mass relative to the aforementioned lithium metal composite oxide powder.

[0014] According to one aspect of this disclosure, a positive electrode active material for a non-aqueous electrolyte secondary battery that can improve discharge capacity at low temperatures can be obtained. Detailed Implementation

[0015] General formula Li zNi 1-x-y Co x M y Lithium metal composite oxides, formed from primary particles of O2 (where 0≤x≤0.1, 0≤y≤0.1, 0.97≤z≤1.20, and M is at least one element selected from Mn, W, Mg, Mo, Nb, Ti, Si, and Al) and secondary particles formed by the aggregation of the aforementioned primary particles, are excellent positive electrode active materials for achieving high energy density in non-aqueous electrolyte secondary batteries. However, they suffer from reduced discharge capacity at low temperatures (e.g., below -10°C). To improve the discharge capacity at low temperatures, it is considered to form particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide. Particles containing W and Li have high lithium-ion conductivity; therefore, by forming particles containing W and Li on the surface of the primary particles, the reaction resistance of the lithium metal composite oxide is reduced, and the discharge capacity at low temperatures is improved.

[0016] However, in the method described in Patent Document 2, where lithium metal composite oxide powder is mixed with tungsten compound powder and then heat-treated, the tungsten compound powder is difficult to disperse within the secondary particles. Therefore, it is difficult to form particles containing W and Li on the surface of the primary particles within the secondary particles, thus failing to adequately improve the discharge capacity at low temperatures. In the method described in Patent Document 1, where an alkaline solution containing a dissolved tungsten compound is added to lithium metal composite oxide powder and mixed, the alkaline solution can be dispersed within the secondary particles. Therefore, particles containing W and Li can be formed on the surface of the primary particles within the secondary particles. However, the inventors conducted in-depth research and found that using a general formula such as Li... z Ni 1-x- y Co x M y In the case of lithium metal composite oxides with a high nickel ratio and a cobalt ratio of 10 mol% or less, such as O2 (where 0≤x≤0.1, 0≤y≤0.1, 0.97≤z≤1.20, and M is at least one element selected from Mn, W, Mg, Mo, Nb, Ti, Si, and Al), if the amount of the aforementioned alkaline solution added is too large, excessive Li in the lithium metal composite oxide will dissolve into the alkaline solution side. Therefore, this results in an increase in the resistance of the lithium metal composite oxide itself, and the discharge capacity at low temperatures cannot be adequately improved. Therefore, the inventors conducted further research and thus conceived of a method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery as shown below.

[0017] The method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery according to this embodiment is characterized by comprising the following steps: Step 1, in general formula Li z Ni 1-x-y Cox M y In a lithium metal composite oxide powder formed from primary particles of O2 (where 0≤x≤0.1, 0≤y≤0.1, 0.97≤z≤1.20, and M is at least one element selected from Mn, W, Mg, Mo, Nb, Ti, Si, and Al) and secondary particles formed by the aggregation of the aforementioned primary particles, an alkaline solution containing a dissolved tungsten compound is added and mixed; and, in a second step, the mixed alkaline solution is heat-treated with the aforementioned lithium metal composite oxide powder to form particles containing W and Li on the surface of the primary particles of the aforementioned lithium metal composite oxide powder. In the aforementioned first step, the amount of the aforementioned alkaline solution added is 0.1 to 10% by mass relative to the aforementioned lithium metal composite oxide powder. Thus, by adding the aforementioned specified amount of alkaline solution containing a dissolved tungsten compound to the aforementioned lithium metal composite oxide powder and mixing it, the alkaline solution is dispersed into the interior of the secondary particles of the lithium metal composite oxide, and excessive dissolution of Li from the lithium metal composite oxide to the alkaline solution side can be suppressed. That is, according to the manufacturing method of this embodiment, the excessive dissolution of Li in the lithium metal composite oxide is suppressed. In addition, particles containing W and Li can be formed on the surface of the primary particles inside the secondary particles. Therefore, a positive electrode active material for a non-aqueous electrolyte secondary battery that can suppress the decrease in discharge capacity at low temperatures can be obtained.

[0018] The following describes in detail the manufacturing method of the positive electrode active material for the non-aqueous electrolyte secondary battery according to each step of this embodiment.

[0019] [Step 1]

[0020] The first step is as follows: A predetermined amount of an alkaline solution containing a dissolved tungsten compound (hereinafter, the alkaline solution containing the dissolved tungsten compound is referred to as alkaline solution (W)) is added to the lithium metal composite oxide powder formed by primary particles and secondary particles aggregated from the primary particles, and then mixed. This allows not only the surface of the primary particles exposed on the outer surface of the secondary particles in the lithium metal composite oxide powder to contact the alkaline solution (W), but also the surface of the primary particles inside the secondary particles to contact the alkaline solution (W).

[0021] The lithium metal composite oxide powder used is of the general formula Li z Ni 1-x-y Co x M yLithium metal composite oxide powder is formed from primary particles of O2 (where 0≤x≤0.1, 0≤y≤0.10, 0.97≤z≤1.20, and M is at least one element selected from Mn, W, Mg, Mo, Nb, Ti, Si, and Al) and secondary particles formed by the aggregation of the aforementioned primary particles. From the perspective of achieving high energy density in non-aqueous electrolyte secondary batteries, x in the general formula is preferably 0≤x≤0.06, and y in the general formula is more preferably 0≤y≤0.06.

[0022] In improving the power characteristics of non-aqueous electrolyte secondary batteries, lithium metal composite oxide powder is formed from primary particles and secondary particles aggregated from primary particles. Preferably, the secondary particles have pores and grain boundaries that allow electrolyte penetration. The average particle size of the primary particles is preferably 500 nm or less, more preferably in the range of 50 nm to 300 nm. The average particle size of the primary particles is the average of the major diameters of 10 primary particles obtained from a cross-sectional SEM image of the particle. The average particle size of the secondary particles is preferably in the range of 1 μm to 50 μm, more preferably in the range of 5 μm to 20 μm. The average particle size of the secondary particles is the volume average particle size determined by laser diffraction.

[0023] The alkaline solution (W) can be prepared, for example, by using a reaction vessel equipped with a stirrer, by adding a tungsten compound while stirring the alkaline solution until it dissolves. From the perspective of uniform dispersion, it is preferable that the tungsten compound is completely dissolved in the alkaline solution.

[0024] Tungsten compounds that can dissolve in alkaline solutions are acceptable; preferred tungsten compounds include tungsten oxide, lithium tungstate, and ammonium tungstate, which are readily soluble in alkalis.

[0025] The amount of tungsten dissolved in the alkaline solution is preferably the amount required to form particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide, for example, preferably 0.01 to 1.0 mol relative to the total molar amount of nickel, cobalt and M contained in the lithium metal composite oxide.

[0026] Furthermore, the tungsten concentration of the alkaline solution (W) is preferably 0.05 mol / L or higher, more preferably 0.05 to 2 mol / L. When it is below 0.05 mol / L, the tungsten concentration is low, and therefore, the amount of W and Li particles formed on the surface of the primary particles decreases, resulting in a decrease in discharge capacity at low temperatures compared to the case where the above range is met.

[0027] For the alkali used in the alkaline solution, a general alkaline solution that does not contain harmful impurities for the positive electrode active material is preferred in order to obtain high charge and discharge capacity. Ammonia and lithium hydroxide, which do not raise concerns about impurities, are preferred, and lithium hydroxide is particularly preferred. When using lithium hydroxide, the amount of lithium hydroxide relative to W is preferably set to 1.5 to 10.0 atomically. By using lithium hydroxide within this range, it becomes easier to form particles containing W and Li on the surface of the primary particles.

[0028] Furthermore, from the perspective of dispersing the alkaline solution (W) within the secondary particles of the lithium metal composite oxide, the alkaline solution is preferably an aqueous solution. It should be noted that highly volatile solvents such as alcohols are not limited; however, if such a solvent is used, there is a concern that the solvent may evaporate before the alkaline solution (W) penetrates into the secondary particles.

[0029] The pH of the alkaline solution only needs to be at a level where tungsten compounds can dissolve, preferably between 9 and 12. If the pH is below 9, more lithium dissolves from the lithium metal composite oxide, resulting in a reduced improvement in discharge capacity at low temperatures compared to the above-mentioned range. Furthermore, if the pH exceeds 12, excessive alkali remains in the lithium metal composite oxide, raising concerns about potential battery performance degradation.

[0030] In the first step, it is preferable to add and mix the lithium metal composite oxide powder with an alkaline solution (W) while stirring. To suppress the dissolution of lithium from the lithium metal composite oxide, the amount of alkaline solution (W) added relative to the lithium metal composite oxide powder only needs to be 0.1 to 10% by mass, preferably 0.1 to 3.0% by mass. If the amount of alkaline solution (W) added relative to the lithium metal composite oxide powder exceeds 10% by mass, excessive lithium will dissolve from the lithium metal composite oxide. Therefore, due to the increased resistance of the lithium metal composite oxide itself, the improvement in discharge capacity at low temperatures cannot be fully achieved. Furthermore, if the amount of alkaline solution (W) added relative to the lithium metal composite oxide powder is less than 0.1% by mass, the number of primary particles that cannot contact the alkaline solution (W) increases. As a result, the final positive electrode active material contains a large number of primary particles that do not form particles containing both W and Li, and the improvement in discharge capacity at low temperatures cannot be fully achieved.

[0031] Regarding the improvement of discharge capacity at low temperatures, the temperature of the alkaline solution (W) added to the lithium metal composite oxide powder is preferably in the range of 60°C to 90°C. If the temperature of the alkaline solution (W) exceeds 90°C, the drying of the alkaline solution (W) becomes faster, raising concerns about insufficient dispersion (penetration) into the secondary particles. If the temperature of the alkaline solution (W) is below 60°C, the solubility of W in the alkaline solution decreases, raising concerns about the precipitation of particles containing W and Li before sufficient dispersion into the secondary particles. In other words, under any circumstances, the final positive electrode active material contains a relatively large number of primary particles that do not form particles containing W and Li, thus resulting in a decrease in discharge capacity at low temperatures compared to the case where the temperature of the alkaline solution (W) is 60°C to 90°C.

[0032] Using a general mixer, the lithium metal composite oxide powder is mixed with the alkaline solution (W) by spraying or dripping, thereby ensuring thorough mixing with the alkaline solution (W) to the extent that the shape of the lithium metal composite oxide powder is not damaged. General mixers include, for example, TKHIVIS MIX, oscillating mixers, plowshare mixers, Julia mixers, and V-type mixers.

[0033] In the manufacturing method of this embodiment, to improve battery capacity and safety, a water washing process for the lithium metal composite oxide powder can be provided before the first step. This water washing can be performed using known methods and conditions, as long as it is carried out within a range where lithium is dissolved from the lithium metal composite oxide without deteriorating battery characteristics. During water washing, it is preferable to spray and mix the alkaline solution (W) solely by solid-liquid separation without drying. When mixing with the alkaline solution (W) solely by solid-liquid separation without drying, it is preferable that the moisture content after mixing with the alkaline solution (W) does not exceed the maximum moisture content of the mixture of the dried lithium metal composite oxide powder and the alkaline solution (W). It should be noted that if the moisture content increases, lithium will dissolve from the lithium metal composite oxide, potentially reducing the improvement effect on discharge capacity at low temperatures. When the lithium metal composite oxide is washed with water, dried, and then mixed with the alkaline solution (W), the number of drying cycles increases, thus sometimes reducing productivity.

[0034] [Step 2]

[0035] The second step involves heat-treating the mixed alkaline solution (W) and lithium metal composite oxide powder. This allows particles containing both W and Li to form on the surface of the primary particles of the lithium metal composite oxide, formed from W in the alkaline solution (W) and Li in the alkaline solution (W) or Li dissolved from the lithium metal composite oxide. It should be noted that the amount of alkaline solution (W) added is appropriate as described above, thus suppressing excessive dissolution of Li from the lithium metal composite oxide.

[0036] The heat treatment method is not particularly limited. However, to prevent degradation of electrical properties when used as a positive electrode active material in non-aqueous electrolyte secondary batteries, heat treatment is preferably performed in an oxygen atmosphere or vacuum atmosphere at a temperature of 100–600°C. When the heat treatment temperature is below 100°C, moisture evaporation is insufficient, and sometimes particles containing W and Li cannot be sufficiently formed on the surface of the primary particles of the lithium metal composite oxide. On the other hand, if the heat treatment temperature exceeds 600°C, the primary particles of the lithium metal composite oxide undergo sintering, and some of the W may sometimes dissolve in the lithium metal composite oxide. In other words, in any case, the improvement in discharge capacity at lower temperatures is sometimes reduced compared to the case where the heat treatment temperature is between 100 and 600°C.

[0037] To avoid reaction with moisture and carbonic acid in the atmosphere, an oxidizing atmosphere such as an oxygen atmosphere or a vacuum atmosphere is preferably formed during heat treatment. There is no particular limitation on the heat treatment time, but it is preferably set to 2 to 10 hours in order to allow sufficient evaporation of moisture in the alkaline solution (W) to form particles containing W and Li.

[0038] It should be noted that the non-aqueous electrolyte secondary battery of this embodiment is obtained, for example, by storing the electrode body (positive electrode, negative electrode) and the separator together with the non-aqueous electrolyte in a storage body such as a battery can or a laminate. The positive electrode, negative electrode, separator, and non-aqueous electrolyte in this embodiment are as follows.

[0039] <Positive electrode>

[0040] The positive electrode may include, for example, a positive electrode current collector such as a metal foil, and a positive electrode composite material layer formed on the positive electrode current collector. The positive electrode current collector may be a foil of a metal such as aluminum that is stable within the potential range of the positive electrode, or a thin film of the metal disposed on the surface.

[0041] The positive electrode composite material layer is suitable for containing positive electrode active material, as well as conductive material and binder material. For example, the positive electrode can be manufactured by coating a positive electrode composite material slurry containing positive electrode active material, conductive material, binder material, etc., onto a positive electrode current collector, allowing the coating to dry, and then calendering it to form a positive electrode composite material layer on both sides of the positive electrode current collector.

[0042] The positive electrode active material includes the non-aqueous electrolyte secondary battery positive electrode active material obtained by the manufacturing method of this embodiment described above. The non-aqueous electrolyte secondary battery positive electrode active material obtained by the manufacturing method of this embodiment is, for example, a material having the general formula Li... z Ni 1-x-y Co x M yThe positive electrode active material consists of primary particles of O2 (where 0≤x≤0.1, 0≤y≤0.10, 0.97≤z≤1.20, and M is at least one element selected from Mn, W, Mg, Mo, Nb, Ti, Si, and Al) and secondary particles formed by the aggregation of the aforementioned primary particles, as well as particles containing W and Li formed on the surface of the primary particles of the aforementioned lithium metal composite oxide powder.

[0043] As a conductive material, carbon black, acetylene black, Ketjen black, graphite and other carbon powders can be used alone or in combination of two or more.

[0044] Examples of adhesive materials include fluorinated polymers and rubber-based polymers. For example, examples of fluorinated polymers include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or their modified forms; examples of rubber-based polymers include ethylene-propylene-isoprene copolymers and ethylene-propylene-butadiene copolymers. They can be used alone or in combination of two or more.

[0045] <Negative electrode>

[0046] The negative electrode may include, for example, a negative electrode current collector such as a metal foil, and a negative electrode composite material layer formed on the negative electrode current collector. The negative electrode current collector may be a foil of a metal stable within the negative electrode's potential range, such as copper, or a thin film of the metal disposed on its surface. The negative electrode composite material layer preferably contains a negative electrode active material, as well as a thickening material and a binder. The negative electrode may be manufactured, for example, by dispersing the negative electrode active material, thickening material, and binder in water at a predetermined weight ratio to obtain a negative electrode composite material slurry. This slurry is then coated onto a negative electrode current collector, dried, and calendered to form negative electrode composite material layers on both sides of the negative electrode current collector.

[0047] As negative electrode active materials, carbon materials capable of absorbing / releasing lithium ions can be used. In addition to graphite, non-graphitized carbon, easily graphitized carbon, fibrous carbon, coke, and carbon black can also be used. Furthermore, as non-carbon-based materials, silicon, tin, and alloys and oxides based on them can be used.

[0048] As a binder, PTFE can be used, similar to the case for the positive electrode, as well as styrene-butadiene copolymer (SBR) or its modified forms. Carboxymethyl cellulose (CMC) can be used as a thickener.

[0049] <Non-aqueous electrolytes>

[0050] As a non-aqueous solvent (organic solvent) for non-aqueous electrolytes, carbonates, lactones, ethers, ketones, esters, etc., can be used, and two or more of these solvents can be mixed for use. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, and butyl carbonate, chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, and mixed solvents of cyclic and chain carbonates can be used.

[0051] As non-aqueous electrolyte salts, LiPF6, LiBF4, LICF3SO3, and mixtures thereof can be used. The solubility of the electrolyte salt in non-aqueous solvents can be set, for example, from 0.5 to 2.0 mol / L.

[0052] <Separator>

[0053] The separator can be a porous sheet or similar material that has ion-permeable and insulating properties. Specific examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator include olefin resins such as polyethylene and polypropylene, and cellulose. The separator can be a laminate containing a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Alternatively, a multilayer separator containing both polyethylene and polypropylene layers can be used, and materials such as aromatic polyamide resins or ceramics can also be coated on the surface of the separator.

[0054] Example

[0055] The present disclosure will be further described below with reference to embodiments, but the present disclosure is not limited to these embodiments.

[0056] <Example 1>

[0057] [Manufacturing of positive electrode active materials]

[0058] In Li 1.03 Ni 0.91 Co 0.045 Al 0.045 100g of lithium metal composite oxide powder (average particle size of secondary particles 12μm) as shown in O2 was mixed with 80g of pure water for 5 minutes, then filtered / separated to prepare lithium metal composite oxide powder with a moisture content adjusted to 5%. Separately, 1.19g of tungsten oxide (WO3) was added to an aqueous solution containing 0.21g of lithium hydroxide (LiOH) dissolved in 10ml of pure water and stirred to obtain an alkaline solution (W) containing tungsten.

[0059] Next, using a mixing apparatus (TKHIVIS MIX, Primix Corp.), 100g of the above-mentioned lithium metal composite oxide powder was stirred while 2g of an alkaline solution (W) at 25°C was sprayed to obtain a mixture of alkaline solution (W) and lithium metal composite oxide powder. The resulting mixture was placed in a magnesium oxide calcining vessel and heat-treated in a vacuum at a heating rate of 3°C / min to 180°C for 3 hours. After furnace cooling to room temperature, the positive electrode active material of Example 1 was obtained.

[0060] The obtained positive electrode active material was analyzed by SEM / EDS, which confirmed the formation of W and Li particles on the surface of the primary particles of the lithium metal composite oxide. Furthermore, the tungsten content of the obtained positive electrode active material was analyzed by ICP, and the result showed that it was 0.1 mol% relative to the total molar percentage of Ni, Co, and Al.

[0061] <Example 2>

[0062] 100g of the above-mentioned lithium metal composite oxide powder was sprayed with 2g of an alkaline solution (W) at 70°C. Otherwise, the positive electrode active material was prepared in the same manner as in Example 1. The obtained positive electrode active material was analyzed by SEM / EDS, and the results confirmed the formation of particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide. Furthermore, the tungsten content of the obtained positive electrode active material was analyzed by ICP, and the result showed that it was 0.1 mol% relative to the total molar percentage of Ni, Co, and Al.

[0063] <Example 3>

[0064] 0.3 g of an alkaline solution (W) at 25°C was sprayed onto 100 g of the aforementioned lithium metal composite oxide powder. Otherwise, the positive electrode active material was prepared in the same manner as in Example 1. The obtained positive electrode active material was analyzed by SEM / EDS, and the results confirmed the formation of particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide. Furthermore, the tungsten content of the obtained positive electrode active material was analyzed by ICP, and the result showed that it was 0.03 mol% relative to the total molar percentages of Ni, Co, and Al.

[0065] <Example 4>

[0066] In an aqueous solution containing 0.084 g of lithium hydroxide (LiOH) dissolved in 10 ml of pure water, 0.476 g of tungsten oxide (WO3) was added and stirred to obtain an alkaline solution (W) containing tungsten. 5 g of the alkaline solution (W) at 70°C was sprayed onto 100 g of the above lithium metal composite oxide powder. Otherwise, the positive electrode active material was prepared in the same manner as in Example 1. The obtained positive electrode active material was analyzed by SEM / EDS, and the results confirmed the formation of particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide. Furthermore, the tungsten content of the obtained positive electrode active material was analyzed by ICP, and the result showed that it was 0.1 mol% relative to the total molar percentages of Ni, Co, and Al.

[0067] <Comparative Example 1>

[0068] To 100g of the aforementioned lithium metal composite oxide powder, 0.5g of tungsten oxide powder was added. Otherwise, the positive electrode active material was prepared in the same manner as in Example 1. The obtained positive electrode active material was analyzed by SEM / EDS, and the results confirmed the formation of particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide. Furthermore, the tungsten content of the obtained positive electrode active material was analyzed by ICP, and the result showed that it was 0.2 mol% relative to the total molar percentages of Ni, Co, and Al.

[0069] <Comparative Example 2>

[0070] 100g of the above-mentioned lithium metal composite oxide powder was sprayed with 20g of an alkaline solution (W) at 25°C. Otherwise, the positive electrode active material was prepared in the same manner as in Example 1. The obtained positive electrode active material was analyzed by SEM / EDS, and the results confirmed the formation of particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide. Furthermore, the tungsten content of the obtained positive electrode active material was analyzed by ICP, and the result showed that it was 1.0 mol% relative to the total molar percentage of Ni, Co, and Al.

[0071] <Comparative Example 3>

[0072] In Example 1, the above-mentioned lithium metal composite oxide powder with a moisture content adjusted to 5% was placed in a calcining container made of magnesium oxide and heated to 180°C in a vacuum at a heating rate of 3°C / min for 3 hours. After that, it was furnace cooled to room temperature to obtain the positive electrode active material of Comparative Example 3.

[0073] [The production of the positive electrode]

[0074] The positive electrode active material of Example 1 was mixed in a ratio of 91 parts by mass, acetylene black as a conductive material in a ratio of 7 parts by mass, and polyvinylidene fluoride as a binder in a ratio of 2 parts by mass. The mixture was kneaded using a mixer (TKHIVISMIX, Primix Corp.) to prepare a positive electrode composite slurry. Next, the positive electrode composite slurry was coated onto a 15 μm thick aluminum foil, and the coating was dried to form a positive electrode composite layer on the aluminum foil. This was used as the positive electrode of Example 1. Positive electrodes were also prepared in the same manner in other examples and comparative examples.

[0075] [Preparation of non-aqueous electrolytes]

[0076] Ethyl carbonate (EC), methyl ethyl carbonate (MEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4. A non-aqueous electrolyte was prepared by dissolving lithium hexafluoride phosphate (LiPF6) in this mixed solvent to a concentration of 1.2 mol / L.

[0077] [Preparation of the experimental battery]

[0078] The positive electrode of Example 1 and the negative electrode formed of lithium metal foil were stacked opposite each other with a separator between them, and then wound together to form an electrode body. Next, the electrode body and the aforementioned non-aqueous electrolyte were embedded in an aluminum outer casing to form a test battery. Test batteries were also formed in the other examples and comparative examples in the same manner.

[0079] [Determination of initial discharge capacity]

[0080] At an ambient temperature of 25°C, the test batteries of each embodiment and comparative example were charged with a constant current of 0.2C until the battery voltage reached 4.3V, then charged with a constant voltage of 4.3V until the current value reached 0.05mA, and finally discharged with a constant current of 0.2C until the battery voltage reached 2.5V. The discharge capacity at this point was measured. This initial discharge capacity is shown in Table 1.

[0081] [Determination of discharge capacity at low temperatures]

[0082] For the test batteries of each embodiment and comparative example that underwent the above-described charge-discharge process, after charging at an ambient temperature of 25°C under the same conditions as described above, they were kept at an ambient temperature of -30°C for 30 minutes, and then discharged at an ambient temperature of -30°C under the same conditions as described above. The discharge capacity at this time was measured, and the results are shown in Table 1. It should be noted that for the improvement rate of discharge capacity at low temperature shown in Table 1, the discharge capacity at low temperature of the test battery of Comparative Example 3 is taken as 100% (baseline), and the discharge capacity at low temperature of the test batteries of other embodiments and comparative examples is represented in comparison.

[0083] [Table 1]

[0084]

[0085] In Examples 1-3, the positive electrode active material was manufactured as follows: in the process of adding and mixing an alkaline solution containing a tungsten compound to lithium metal composite oxide powder with a high nickel ratio and a cobalt ratio of 10 mol% or less, the amount of the alkaline solution added was in the range of 0.1 to 10% by mass relative to the lithium metal composite oxide powder, thereby manufacturing the positive electrode active material. On the other hand, in Comparative Example 1, a positive electrode active material was manufactured by adding tungsten compound powder to lithium metal composite oxide powder with a high nickel ratio and a cobalt ratio of 10 mol% or less, and in Comparative Example 2, a positive electrode active material was manufactured as follows: in the process of adding and mixing an alkaline solution containing a tungsten compound to lithium metal composite oxide powder with a high nickel ratio and a cobalt ratio of 10 mol% or less, the amount of the alkaline solution added was 20% by mass relative to the lithium metal composite oxide powder, thereby manufacturing the positive electrode active material. Comparing Examples 1-3 and Comparative Examples 1-2, the improvement rate of discharge capacity at low temperature in Examples 1-3 was significantly increased compared to Comparative Examples 1-2. In addition, among Examples 1 to 3, Example 2, in which the temperature of the alkaline solution added to the lithium metal composite oxide powder was 70°C, showed the greatest improvement in discharge capacity at low temperature.

[0086] <Example 5>

[0087] Using Li 1.03 Ni 0.91 Co 0.06 Al 0.03 The lithium metal composite oxide powder shown in O2 (with an average secondary particle size of 12 μm) was used to prepare the positive electrode active material in the same manner as in Example 1. The obtained positive electrode active material was analyzed by SEM / EDS, which confirmed the formation of W and Li particles on the surface of the primary particles of the lithium metal composite oxide. Furthermore, the tungsten content of the obtained positive electrode active material was analyzed by ICP, and the result showed it to be 0.1 mol% relative to the total molar percentages of Ni, Co, and Al.

[0088] <Example 6>

[0089] 100g of the above-mentioned lithium metal composite oxide powder was sprayed with 2g of an alkaline solution (W) at 70°C. Otherwise, the positive electrode active material was prepared in the same manner as in Example 5. The obtained positive electrode active material was analyzed by SEM / EDS, and the results confirmed the formation of particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide. Furthermore, the tungsten content of the obtained positive electrode active material was analyzed by ICP, and the result showed that it was 0.1 mol% relative to the total molar percentage of Ni, Co, and Al.

[0090] <Comparative Example 4>

[0091] 0.5 g of tungsten oxide powder was added to 100 g of the aforementioned lithium metal composite oxide powder, and the positive electrode active material was prepared in the same manner as in Example 5. The obtained positive electrode active material was analyzed by SEM / EDS, and the results confirmed the formation of particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide. Furthermore, the tungsten content of the obtained positive electrode active material was analyzed by ICP, and the result showed that it was 0.2 mol% relative to the total molar percentage of Ni, Co, and Al.

[0092] <Comparative Example 5>

[0093] In Example 5, the above-mentioned lithium metal composite oxide powder with a moisture content adjusted to 5% was placed in a calcining container made of magnesium oxide, and heat-treated in a vacuum at a heating rate of 3°C / min to 180°C for 3 hours. After that, the furnace was cooled to room temperature to obtain the positive electrode active material of Comparative Example 5.

[0094] For the test batteries of Examples 5 and 6 and Comparative Examples 4 and 5, charge and discharge were performed under the same conditions as described above, and the initial discharge capacity and discharge capacity at low temperature were measured. The results are shown in Table 2. It should be noted that for the improvement rate of discharge capacity at low temperature shown in Table 2, the discharge capacity at low temperature of the test battery of Comparative Example 5 is taken as 100% (baseline), and the discharge capacity at low temperature of the test batteries of the other examples and comparative examples is represented in contrast.

[0095] [Table 2]

[0096]

[0097] In Examples 5 and 6, the positive electrode active material was manufactured as follows: in the process of adding and mixing an alkaline solution containing a tungsten compound to lithium metal composite oxide powder with a high nickel ratio and a cobalt ratio of 10 mol% or less, the amount of the alkaline solution added was in the range of 0.1 to 10 wt% relative to the lithium metal composite oxide powder, thereby manufacturing the positive electrode active material. On the other hand, in Comparative Example 4, the positive electrode active material was manufactured as follows: tungsten compound powder was added and mixed to lithium metal composite oxide powder with a high nickel ratio and a cobalt ratio of 10 mol% or less, thereby manufacturing the positive electrode active material. Comparing Examples 5 and 6 with Comparative Example 4, the improvement rate of discharge capacity at low temperature was significantly increased in Examples 5 and 6 compared to Comparative Example 4. In addition, in Example 6, where the temperature of the alkaline solution added to the lithium metal composite oxide powder was 70°C, the improvement rate of discharge capacity at low temperature was the highest among Examples 5 and 6.

[0098] <Example 7>

[0099] Using Li 1.03 Ni 0.92 Co 0.02 Al 0.05 Mn 0.01 The lithium metal composite oxide powder shown in O2 (with an average secondary particle size of 12 μm) was used to prepare the positive electrode active material in the same manner as in Example 1. The obtained positive electrode active material was analyzed by SEM / EDS, which confirmed the formation of W and Li particles on the surface of the primary particles of the lithium metal composite oxide. Furthermore, the tungsten content of the obtained positive electrode active material was analyzed by ICP, and the result showed it to be 0.1 mol% relative to the total molar percentages of Ni, Co, and Al.

[0100] <Example 8>

[0101] 100g of the above-mentioned lithium metal composite oxide powder was sprayed with 2g of an alkaline solution (W) at 70°C. Otherwise, the positive electrode active material was prepared in the same manner as in Example 7. The obtained positive electrode active material was analyzed by SEM / EDS, and the results confirmed the formation of particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide. Furthermore, the tungsten content of the obtained positive electrode active material was analyzed by ICP, and the result showed that it was 0.1 mol% relative to the total molar percentage of Ni, Co, and Al.

[0102] <Comparative Example 6>

[0103] 0.5 g of tungsten oxide powder was added to 100 g of the aforementioned lithium metal composite oxide powder, and the positive electrode active material was prepared in the same manner as in Example 7. The obtained positive electrode active material was analyzed by SEM / EDS, and the results confirmed the formation of particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide. Furthermore, the tungsten content of the obtained positive electrode active material was analyzed by ICP, and the result showed that it was 0.2 mol% relative to the total molar percentage of Ni, Co, and Al.

[0104] <Comparative Example 7>

[0105] In Example 7, the above-mentioned lithium metal composite oxide powder with a moisture content adjusted to 5% was placed in a magnesium oxide calcining container and heat-treated in a vacuum at a heating rate of 3°C / min to 180°C for 3 hours. After that, it was furnace cooled to room temperature to obtain the positive electrode active material of Comparative Example 7.

[0106] For the test batteries of Examples 7 and 8 and Comparative Examples 6 and 7, charge and discharge were performed under the same conditions as described above, and the initial discharge capacity and discharge capacity at low temperature were measured. The results are shown in Table 3. It should be noted that for the improvement rate of discharge capacity at low temperature shown in Table 3, the discharge capacity at low temperature of the test battery of Comparative Example 7 is taken as 100% (baseline), and the discharge capacity at low temperature of the test batteries of the other examples and comparative examples is represented in contrast.

[0107] [Table 3]

[0108]

[0109] In Examples 7 and 8, the positive electrode active material was manufactured as follows: in the process of adding an alkaline solution containing a tungsten compound to lithium metal composite oxide powder with a high nickel ratio and a cobalt ratio of 10 mol% or less and mixing it, the amount of the alkaline solution added was in the range of 0.1 to 10 wt% relative to the lithium metal composite oxide powder. On the other hand, in Comparative Example 6, the positive electrode active material was manufactured as follows: tungsten compound powder was added to lithium metal composite oxide powder with a high nickel ratio and a cobalt ratio of 10 mol% or less and mixed to manufacture the positive electrode active material. Comparing Examples 7 and 8 with Comparative Example 6, the improvement rate of discharge capacity at low temperature was significantly increased in Examples 7 and 8 compared to Comparative Example 6. Furthermore, in Example 8, where the temperature of the alkaline solution added to the lithium metal composite oxide powder was 70°C, the improvement rate of discharge capacity at low temperature was the highest among Examples 7 and 8.

[0110] [<Reference Example 1>]

[0111] [Manufacturing of positive electrode active materials]

[0112] In Li1.03 Ni 0.82 Co 0.15 Al 0.03 To 100g of lithium metal composite oxide powder (average particle size of secondary particles 12μm) shown in O2, 0.5g of tungsten oxide powder was added. Otherwise, the positive electrode active material was prepared in the same manner as in Example 1. The obtained positive electrode active material was analyzed by SEM / EDS, and the results confirmed the formation of particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide. Furthermore, the tungsten content of the obtained positive electrode active material was analyzed by ICP, and the result showed that it was 0.2 mol% relative to the total molar percentage of Ni, Co, and Al. Then, using the obtained positive electrode active material, a test battery was prepared in the same manner as in Example 1.

[0113] <Reference Example 2>

[0114] In Li 1.03 Ni 0.82 Co 0.15 Al 0.03 To 100g of lithium metal composite oxide powder (average particle size of secondary particles 12μm) as shown in O2, 2g of alkaline solution (W) at 70°C was added. Otherwise, the positive electrode active material was prepared in the same manner as in Example 1. The obtained positive electrode active material was analyzed by SEM / EDS, and the results confirmed the formation of particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide. Furthermore, the tungsten content of the obtained positive electrode active material was analyzed by ICP, and the result showed that it was 0.2 mol% relative to the total molar percentages of Ni, Co, and Al. Then, using the obtained positive electrode active material, a test battery was prepared in the same manner as in Example 1.

[0115] <Reference Example 3>

[0116] Using Li 1.03 Ni 0.82 Co 0.15 Al 0.03 The lithium metal composite oxide powder shown in O2 was used as the positive electrode active material. Otherwise, the test battery was made in the same manner as in Example 1.

[0117] For the test batteries of each reference example, charging and discharging were performed under the same conditions as described above, and the initial discharge capacity and discharge capacity at low temperature were measured. The results are shown in Table 2. It should be noted that for the improvement rate of discharge capacity at low temperature shown in Table 2, the discharge capacity at low temperature of the test battery of Reference Example 3 is taken as 100%, and the discharge capacity at low temperature of the test batteries of the other reference examples is represented in contrast.

[0118] [Table 4]

[0119]

[0120] In Reference Example 1, the positive electrode active material was manufactured by adding tungsten compound powder to lithium metal composite oxide powder with a high nickel ratio and a cobalt ratio exceeding 10 mol%, and mixing the mixture. In Reference Example 2, the positive electrode active material was manufactured by adding an alkaline solution containing a tungsten compound to lithium metal composite oxide powder with a high nickel ratio and a cobalt ratio exceeding 10 mol%, and mixing the mixture. The amount of the alkaline solution added was 2% by mass relative to the lithium metal composite oxide powder. As shown in Table 2, the improvement rate of discharge capacity at low temperature in Reference Examples 1 and 2 did not increase significantly.

Claims

1. A method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising the following steps: In the first step, in the general formula Li z Ni 1-x-y Co x M y In a lithium metal composite oxide powder formed by primary particles (O2) and secondary particles aggregated from these primary particles, an alkaline solution containing dissolved tungsten compounds is added and mixed. 0 ≤ x < 0.1, 0 ≤ y ≤ 0.1, 0.97 ≤ z ≤ 1.20, M is at least one element selected from Mn, W, Mg, Mo, Nb, Ti, Si, and Al; and, In the second step, the mixed alkaline solution and the lithium metal composite oxide powder are heat-treated to form particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide powder. In the first step, the amount of alkaline solution added is 0.1-5% by mass relative to the lithium metal composite oxide powder. In the first step, the temperature of the alkaline solution added to the lithium metal composite oxide powder is in the range of 60~90°C.

2. The method for manufacturing the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein, The lithium metal composite oxide powder uses the general formula Li z Ni 1-x-y Co x M y O2 represents the element with 0 ≤ x ≤ 0.06, 0 ≤ y ≤ 0.1, 0.97 ≤ z ≤ 1.20, and M is at least one element selected from Mn, W, Mg, Mo, Nb, Ti, Si, and Al.

3. The method for manufacturing the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, Before the first step, there is a step A in which the lithium metal composite oxide powder is mixed with water and then subjected to solid-liquid separation.

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