Coated particle manufacturing method

Abstract

To provide a coated particle manufacturing method that, when used as a positive electrode active material in a non-aqueous electrolyte secondary battery, enables the non-aqueous electrolyte secondary battery to exhibit excellent charge / discharge capacity and cycle characteristics.SOLUTION: A coated particle manufacturing method according to the present disclosure includes adding powder of an additive compound, which has a solubility in water of 0.5 g / 100 cm3 or more at at least any temperature in the range of 15°C to 25°C and contains one or more elements other than Li, Ni, Mn, and O, to a lithium metal composite oxide in the form of primary particles or secondary particles, which contains at least lithium and nickel and has a water content of 300 ppm to 10,000 ppm, and then performing a heat treatment to obtain coated particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for making coated particles. [Background technology]

[0002] Lithium-ion secondary batteries have attracted attention as power sources for electronic devices such as AV equipment and personal computers, due to their small size, light weight, high energy density, high charge / discharge voltage, and large charge / discharge capacity.

[0003] Lithium-ion secondary batteries that use layered or spinel-type lithium transition metal composite oxides as the positive electrode active material can obtain a high voltage of 4V, and are therefore being put to practical use as batteries with high energy density. The main materials that have been proposed include lithium cobalt composite oxide (LiCoO2), which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO2), which uses nickel, which is cheaper than cobalt, and lithium nickel cobalt manganese composite oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), and lithium manganese composite oxide (LiMn2O4) using manganese.

[0004] Such lithium metal composite oxides can generally be produced by mixing a lithium source and a metal source such as nickel and then firing the mixture. The positive electrode of a lithium ion secondary battery is formed, for example, by mixing a positive electrode active material with a binder such as polyvinylidene fluoride (PVDF) and a solvent such as N-methyl-2-pyrrolidone (NMP) to form a positive electrode mixture paste, which is then applied to a current collector such as aluminum foil. When lithium is liberated from the lithium metal composite oxide in the positive electrode mixture paste, it may react with moisture contained in the binder or the like to produce lithium hydroxide.

[0005] When lithium hydroxide is generated in this way, the lithium hydroxide reacts with the binder, causing the positive electrode mixture paste to gel. Gelation of the positive electrode mixture paste leads to poor operability in the manufacturing process and a decrease in yield. This tendency is particularly pronounced when the lithium relative to the transition metal in the lithium transition metal composite oxide, which is the positive electrode active material, is in excess of the stoichiometric ratio, particularly when the proportion of nickel among the transition metals is high.

[0006] Here, the liberation of lithium is thought to be due to lithium that has not been incorporated into the crystal lattice of the lithium metal composite oxide, and due to lithium that has been incorporated into the crystal lattice of the lithium metal composite oxide. When lithium that has been incorporated into the crystal lattice of the lithium metal composite oxide is eluted, the resistance of the lithium metal composite oxide increases, which can reduce the charge / discharge efficiency.

[0007] In order to remove the lithium that has not been incorporated into the crystal lattice of the lithium metal composite oxide, the fired product is subjected to a water washing treatment, as disclosed in Patent Document 1, for example.

[0008] Furthermore, in order to prevent the elution of lithium incorporated into the crystal lattice of the lithium metal composite oxide, it has been practiced to coat the oxide with a boron compound containing oxygen, as disclosed in Patent Document 2, for example. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-97087 [Patent Document 2] Japanese Patent Application Publication No. 2019-114560 Summary of the Invention [Problem to be solved by the invention]

[0010] However, according to the findings of the present inventors, when lithium metal composite oxide is subjected to a water washing treatment to remove lithium as in Patent Document 1, the lithium incorporated in the crystal lattice undergoes ion exchange with protons, causing the surface of the lithium metal composite oxide to become lithium-deficient or to form a rock salt phase, thereby reducing the charge / discharge capacity of the lithium ion secondary battery.

[0011] Furthermore, as in Patent Document 2, coating a lithium metal composite oxide with a boron compound containing oxygen has a certain effect in preventing the elution of lithium in the crystal lattice of the lithium metal composite oxide into the electrolyte solution and improving the cycle characteristics, but there is still room for improvement in order to further improve the cycle characteristics.

[0012] The present disclosure has been made in view of the above-described circumstances, and aims to provide a method for producing coated particles that, when used as a positive electrode active material for non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, enable the non-aqueous electrolyte secondary batteries using the coated particles to exhibit excellent charge / discharge capacity and cycle characteristics. [Means for solving the problem]

[0013] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have discovered a lithium metal composite oxide in the form of primary particles or secondary particles, which contains at least lithium and nickel, has a water content of 300 ppm or more and 10,000 ppm or less, and has a solubility in water of 0.5 g / 100 cm at least at any temperature in the range of 15° C. or more and 25° C. or less. 3 As described above, it has been found that by using coated particles obtained by a method for producing coated particles, in which an additive compound containing one or more elements other than Li, Ni, and O is added in powder form and then heat-treated to obtain coated particles, as a positive electrode active material for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery using the coated particles exhibits excellent charge / discharge capacity and cycle characteristics. Specifically, the present disclosure provides the following.

[0014] (1) A lithium metal composite oxide containing at least lithium and nickel, having a water content of 300 ppm or more and 10,000 ppm or less, in the form of primary particles or secondary particles, having a solubility in water of 0.5 g / 100 cm at at least any temperature in the range of 15 ° C. or more and 25 ° C. or less. 3 The above is the case, and an additive compound containing one or more elements other than Li, Ni, and O is added in powder form, and then heat treatment is performed to obtain coated particles. Method for producing coated particles.

[0015] (2) The lithium metal composite oxide has a layered rock salt structure and has the general formula Li a Ni 1-b-c Mn b M c The method for producing coated particles according to (1), wherein M is one or more elements other than Li, Ni, Mn, and O, and 0.90≦a≦1.15, 0≦b+c≦0.70.

[0016] (3) The method for producing coated particles according to (1) or (2), wherein the temperature of the heat treatment is 200°C or higher and 500°C or lower. [Effects of the Invention]

[0017] According to the present disclosure, it is possible to provide coated particles that, when used as a positive electrode active material in a non-aqueous electrolyte secondary battery, suppress gelation of the positive electrode mixture paste while causing the non-aqueous electrolyte secondary battery to exhibit excellent charge / discharge capacity and cycle characteristics. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram of a cross section of a coated particle sample according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present disclosure will be described, but the present disclosure is not limited in any way to the description of the following embodiments and can be implemented with appropriate modifications.

[0020] <Method for producing coated particles> The method for producing coated particles according to the present embodiment is a method for producing a lithium metal composite oxide in the form of primary particles or secondary particles, which contains at least lithium and nickel, has a water content of 300 ppm or more and 10,000 ppm or less, and has a solubility in water of 0.5 g / 100 cm at at least any temperature in the range of 15° C. or more and 25° C. or less. 3 As described above, an additive compound containing one or more elements other than Li, Ni, and O is added in a powder state, and then heat treatment is carried out to obtain coated particles.

[0021] In this way, by adjusting the water content of the lithium metal composite oxide to 300 ppm or more and 10,000 ppm or less, the additive compound dissolves appropriately during flow and can penetrate into the grain boundaries, resulting in coated particles with a higher coating effect and excellent charge / discharge capacity and cycle characteristics.

[0022] An example of the method for producing coated particles of this embodiment will be described in detail below for each step, but steps other than the step of adding the coating source and the step of heat treatment are not essential, and steps other than these two steps can be omitted. Furthermore, steps other than the steps described below may be included before or after each step described below, as long as they do not impair the effects of the present disclosure.

[0023] Precursor preparation step: A precursor complex compound containing at least nickel is prepared. Precursor mixing step: A precursor complex compound and a lithium compound are mixed to prepare a mixture. Pre-firing step: The mixture prepared in the precursor mixing step is pre-firing. Main firing step: The mixture prepared in the precursor mixing step or the pre-fired product fired in the pre-fire step is fired. Water washing step: The lithium metal composite oxide obtained by firing in the main firing step is subjected to a water washing treatment. Drying step: The lithium metal composite oxide that has been subjected to the water washing treatment is dried. Compound addition step: Adding a compound having a solubility in water of 0.5 g / 100 cm at at least one temperature in the range of 15°C to 25°C to the lithium metal composite oxide obtained in either the pre-baking step or the drying step. 3 As described above, an additive compound containing one or more elements other than Li, Ni, and O is mixed in powder form to obtain a mixture. Heat treatment process: The mixture is subjected to heat treatment to perform surface treatment.

[0024] [Precursor preparation step] First, a precursor composite compound containing at least a transition metal is prepared. The synthesis method of the precursor composite compound is not particularly limited, but for example, a method can be used in which an aqueous solution containing a transition metal aqueous solution and various aqueous solutions of compounds containing other elements corresponding to the composition of the lithium metal composite oxide is dropped into a reaction vessel in which an alkaline aqueous solution such as a sodium hydroxide aqueous solution or an ammonia solution is stirred as a mother liquid, and the sodium hydroxide or the like is also dropped while monitoring and controlling the pH so that it remains within an appropriate range, thereby causing coprecipitation by a wet reaction, and obtaining hydroxides, oxides obtained by calcining the hydroxides, carbonates, etc.

[0025] In the reaction for synthesizing the precursor composite compound, it is preferable to prepare an alkaline aqueous solution that serves as a mother liquid, and then create a nitrogen atmosphere in the reaction tank using an inert gas, or industrially preferably nitrogen gas, to reduce the oxygen concentration in the reaction tank system and in the solution as much as possible. By reducing the oxygen concentration, oxidation of the coprecipitated hydroxide by a predetermined amount or more of remaining oxygen can be suppressed, and the formation of the precursor composite compound by crystallization can be promoted.

[0026] The aqueous solution of the transition metal is not particularly limited, but it is preferable to use an acidic aqueous solution, and it is more preferable to use an aqueous sulfuric acid solution (for example, an aqueous nickel sulfate solution in the case of a nickel compound).Moreover, one or more kinds of aqueous solutions of the transition metal can be used.

[0027] The nickel compound is not particularly limited, but for example, one or more selected from nickel sulfate, nickel oxide, nickel hydroxide, nickel nitrate, nickel carbonate, nickel chloride, nickel iodide, metallic nickel, and the like can be used.

[0028] The cobalt compound is not particularly limited, but for example, one or more compounds selected from cobalt sulfate, cobalt oxide, cobalt hydroxide, cobalt nitrate, cobalt carbonate, cobalt chloride, cobalt iodide, and metallic cobalt can be used.

[0029] The manganese compound is not particularly limited, but for example, one or more compounds selected from manganese sulfate, manganese oxide, manganese hydroxide, manganese nitrate, manganese carbonate, manganese chloride, manganese iodide, and manganese metal can be used.

[0030] The aluminum compound is not particularly limited, but examples thereof include aluminum sulfate, aluminum oxide, aluminum hydroxide, aluminum nitrate, aluminum carbonate, aluminum chloride, aluminum iodide, sodium aluminate, and metallic aluminum.

[0031] The titanium compound is not particularly limited, but for example, one or more compounds selected from titanyl sulfate, titanium oxide, titanium hydroxide, titanium nitrate, titanium carbonate, titanium chloride, titanium iodide, and metallic titanium can be used.

[0032] The iron compound is not particularly limited, but for example, one or more selected from iron sulfate, iron oxide, iron hydroxide, iron nitrate, iron carbonate, iron chloride, iron iodide, metallic iron, and the like can be used.

[0033] The niobium compound is not particularly limited, but for example, one or more compounds selected from niobium oxide, niobium chloride, lithium niobate, niobium iodide, and the like can be used.

[0034] The tungsten compound is not particularly limited, but for example, one or more compounds selected from tungsten oxide, sodium tungstate, ammonium paratungstate, tungsten hexacarbonyl, tungsten sulfide, and the like can be used.

[0035] The magnesium compound is not particularly limited, but for example, one or more compounds selected from magnesium sulfate, magnesium oxide, magnesium hydroxide, magnesium nitrate, magnesium carbonate, magnesium chloride, magnesium iodide, and metallic magnesium can be used.

[0036] The zirconium compound is not particularly limited, but for example, one or more compounds selected from zirconium sulfate, zirconium oxide, zirconium nitrate, ammonium zirconium carbonate, zirconium chloride, zirconium iodide, and metallic zirconium can be used.

[0037] The zinc compound is not particularly limited, but for example, one or more compounds selected from zinc sulfate, zinc oxide, zinc hydroxide, zinc nitrate, zinc carbonate, zinc chloride, zinc iodide, and metallic zinc can be used.

[0038] As for other elements, one or more selected from sulfates, oxides, hydroxides, nitrates, carbonates, chlorides, iodides, metals, and the like can be used.

[0039] The blending ratio of each compound may be adjusted so that the amount of each element is in the desired ratio, taking into consideration the composition of the desired lithium metal composite oxide.

[0040] The pH range of the liquid in the reaction vessel when synthesizing the precursor complex compound is not particularly limited, and may be determined so as to obtain the desired secondary particle size and shape, such as the degree of coarseness and density, and may be, for example, in the range of about 10 to 13.

[0041] The precursor composite compound obtained by the wet reaction is preferably subjected to a washing treatment, dehydrated, and then dried.

[0042] By subjecting the precursor composite compound to a washing treatment, impurities such as sulfate groups, carbonate groups, and sodium that have been incorporated into the aggregated particles or attached to the surface during the reaction can be washed away. For small amounts of the washing, a Nutsche washing method using a Buchner funnel can be used, or a method in which the suspension after the reaction is sent to a press filter for washing and dehydration can be used. For example, pure water, an aqueous sodium hydroxide solution, an aqueous sodium carbonate solution, etc. can be used in the washing treatment, but pure water is preferred for industrial use. However, if a large amount of residual sulfate groups remains, an aqueous sodium hydroxide solution with its pH adjusted according to the amount of residual sulfate groups can also be used.

[0043] [Precursor mixing process] The precursor composite compound and the lithium compound prepared as described above are mixed in a predetermined ratio to prepare a mixture. The mixing may be a wet mixing in which the precursor composite compound and the lithium compound are each made into a solution such as an aqueous solution and these solutions are mixed in a predetermined ratio, or a powder of the precursor composite compound and a powder of the lithium compound are weighed out to a predetermined ratio and mixed in a dry mixing. Alternatively, one of them may be a solution and the other a powder.

[0044] The lithium compound is not particularly limited, and various lithium salts can be used. Specific examples of the lithium compound that can be used include one or more compounds selected from anhydrous lithium hydroxide, lithium hydroxide hydrate, lithium nitrate, lithium carbonate, lithium acetate, lithium bromide, lithium chloride, lithium citrate, lithium fluoride, lithium iodide, lithium lactate, lithium oxalate, lithium phosphate, lithium pyruvate, lithium sulfate, and lithium oxide. Among these, it is preferable to use one or more compounds selected from anhydrous lithium hydroxide and lithium hydroxide hydrate.

[0045] The mixing ratio of the lithium compound and the precursor composite compound is not particularly limited, but may be adjusted appropriately so that the amount of lithium and the total amount of each element are in the desired ratio, taking into consideration the composition of the target composite oxide.

[0046] [Pre-firing process] The pre-firing step is a step of firing the raw material mixture at a temperature lower than that of the main firing step described below to form a pre-firing product as a lithium metal composite oxide. That is, the raw material mixture is lithiated by this pre-firing step to form a lithium metal composite oxide containing at least lithium and a transition metal.

[0047] The firing step described below is generally carried out by weighing out a lithium compound, a precursor compound, and optionally compounds of other elements, mixing them in a mixer, and then filling the resulting mixed powder into a container such as a crucible or a sagger. However, particularly in the lithiation reaction, it becomes more difficult to vent the generated gas and to diffuse the necessary oxygen concentration toward the bottom of the container where the mixed powder is filled. As a result, it becomes more difficult to control the uniformity of the reaction and the primary particle size. Therefore, from this perspective, it is preferable to perform pre-firing.

[0048] In this pre-firing step, it is preferable to incorporate a firing method that particularly promotes the lithiation reaction. Specifically, one method is to make the mixture more susceptible to heat, easily expel gas generated from the lithium compound, and diffuse gas with a high oxygen partial pressure into the mixture (particles). For example, it is possible to achieve the desired properties by firing a smaller amount of the mixture.

[0049] In the pre-firing step, the mixture can be filled into a sagger or crucible and fired in a stationary furnace, a roller hearth kiln, or a pusher furnace, but it is preferable to fire the mixture while it is flowing. In such cases, a rotary kiln can be used as the firing apparatus.

[0050] The pre-baking temperature is not particularly limited, but is preferably, for example, 350°C or higher, 360°C or higher, 370°C or higher, 380°C or higher, or 390°C or higher. On the other hand, the pre-baking temperature is preferably 650°C or lower, 640°C or lower, 630°C or lower, 620°C or lower, or 610°C or lower.

[0051] The pre-baking time is not particularly limited as long as it is a time that allows the lithiation reaction to proceed reliably and uniformly, but is preferably, for example, 1 to 10 hours, or 2 to 8 hours.

[0052] In this disclosure, the baking temperature is the maximum temperature when the object to be heated is heated. The maximum temperature refers to the temperature of the hottest part of the object to be heated. The baking time refers to the time during which the baking temperature reaches a predetermined range and remains within that range. The same definitions of baking temperature and baking time apply hereinafter.

[0053] The atmosphere for the pre-baking is not particularly limited as long as it is an oxidizing atmosphere in which the lithiation reaction proceeds reliably and uniformly. For example, it is preferable to use a decarbonated oxidizing gas atmosphere with a carbon dioxide concentration of 30 ppm or less, or an oxygen atmosphere with an oxygen concentration of 80 vol% or more, 90 vol% or more, or 95 vol% or more.

[0054] The mixture thus pre-baked is then subjected to main baking in a later step to induce crystal growth and particle growth at a higher temperature.

[0055] If the lithium metal composite oxide obtained by firing is in the form of agglomerates, it may be pulverized using a disk mill, a mortar, etc. Furthermore, to ensure a uniform reaction in the firing step, the pre-fired mixed powder obtained may be mixed to homogenize it, and an additive may be added during mixing.

[0056] [Firing process] In the main firing, crystal growth is further promoted. The lithium metal composite oxide obtained by firing in this manner is in the form of primary particles or secondary particles.

[0057] The temperature of the main firing is not particularly limited as long as it is higher than the temperature of the pre-firing, and can be adjusted depending on the composition of the lithium metal composite oxide to be obtained. For example, the firing temperature is preferably 700°C or higher, 710°C or higher, 720°C or higher, 730°C or higher, 740°C or higher, or 750°C or higher. On the other hand, the temperature of the main firing is preferably 1100°C or lower, 1070°C or lower, 1050°C or lower, 1020°C or lower, 1000°C or lower, 970°C or lower, 950°C or lower, 920°C or lower, 900°C or lower, 870°C or lower, 850°C or lower, 820°C or lower, or 800°C or lower. By keeping the main firing temperature within the required range, a lithium metal composite oxide having a desired crystal structure can be obtained. Furthermore, unreacted components can be reduced, and a deterioration in the battery characteristics of a nonaqueous electrolyte secondary battery using the obtained lithium metal composite oxide as a positive electrode can be prevented.

[0058] The time for the main firing is not particularly limited as long as it is long enough to form a composite oxide having a desired crystal structure, and is preferably, for example, 1 to 15 hours, 2 to 12 hours, or 2 to 10 hours.

[0059] The firing atmosphere is not particularly limited, but it is preferable that the oxygen partial pressure ensures reliable and uniform crystal growth and does not reduce the transition metal contained in the pre-fired product to be fired. An atmosphere with a low moisture content and carbon dioxide concentration is preferred. For example, it is preferable to use a decarbonated oxidizing gas atmosphere with a carbon dioxide concentration of 30 ppm or less, or an oxygen atmosphere with an oxygen concentration of preferably 80 vol% or more, 85 vol% or more, 90 vol% or more, or 95 vol% or more.

[0060] (Lithium metal composite oxide) The lithium metal composite oxide obtained in the firing step contains at least lithium and nickel and is in the form of primary particles or secondary particles.

[0061] The chemical composition of the lithium metal composite oxide is not particularly limited, but it may have a layered rock salt structure and be represented by the general formula Li a Ni 1-b-c Mn b M c It is preferable to use one represented by O2 (wherein M is one or more elements other than Li, Ni, Mn and O, and 0.90≦a≦1.15, 0≦b+c≦0.70).

[0062] In the general formula, the value of a is not particularly limited as long as it is within the range of 0.90≦a≦1.15, and may be, for example, 0.955 or more, 0.96 or more, 0.965 or more, 0.97 or more, 0.975 or more, or 0.98 or more. On the other hand, the value of a may be 1.145 or less, 1.14 or less, 1.135 or less, 1.13 or less, 1.125 or less, 1.12 or less, 1.115 or less, 1.11 or less, 1.105 or less, 1.10 or less, 1.095 or less, 1.09 or less, 1.085 or less, 1.08 or less, 1.075 or less, or 1.07 or less.

[0063] In the general formula, the value of b+c is not particularly limited as long as it is within the range of 0≦b+c≦0.70, and may be, for example, 0.05 or more, 0.1 or more, and the value of b+c may be 0.65 or less, 0.6 or less, 0.55 or less, 0.5 or less, 0.45 or less, 0.4 or less, 0.35 or less, 0.3 or less, 0.25 or less, 0.2 or less, or 0.15 or less.

[0064] In the general formula, the element M is not particularly limited as long as it is one or more elements other than Li, Ni, Mn, and O, and examples that can be used include Co, Al, Ti, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr, and B. The type of element M may be selected depending on the purpose of addition. When multiple elements are contained as element M, the value of c represents the total amount of the multiple elements.

[0065] [Water washing process] The lithium metal composite oxide obtained in the main calcination step may contain impurities such as unreacted lithium compounds and lithium compounds that appear on the particle surface due to the crystalline structure during the pre-calcination step and the main calcination step. If the amount of such lithium compounds is large, the additive compound used in the addition step described below may form an oxide between lithium and the element contained in the additive compound (hereinafter also referred to as the "additive element"), but may not coat the lithium metal composite oxide. Therefore, water washing is performed to remove and reduce these impurities.

[0066] The solution used for washing with water is not particularly limited, and for example, an acidic solution, a neutral solution, or an alkaline solution can be used, but it is preferable to use neutral pure water. Depending on the physical properties of the lithium metal compound to be washed, if removal with pure water extracts more Li than necessary from the particle surface, a solution with an alkaline pH can also be used.

[0067] As described above, in order to produce the coated particles of the embodiment of the present disclosure, it is preferable to wash the lithium metal composite oxide obtained in the main firing step. On the other hand, if the lithium metal composite oxide is washed too much, the lithium contained in the crystal lattice of the lithium metal composite oxide may be deeply removed, which may have an adverse effect on the conductivity.

[0068] In cases where washing is not possible due to reasons such as process design, an alternative is to increase the amount of the additive compound added. The additive compound reacts with lithium not contained in the crystal lattice to form a compound, which suppresses the generation of lithium hydroxide and prevents gelation of the positive electrode mixture.

[0069] [Drying process] The lithium metal composite oxide washed in the water washing step contains the water used in the water washing. Meanwhile, in the method for producing coated particles of the present disclosure, the water content of the lithium metal composite oxide is adjusted to 300 ppm or more and 10,000 ppm or less when the additive compound is added to the lithium metal composite oxide.

[0070] Therefore, while monitoring the water content of the lithium metal composite oxide, the desired water content is adjusted by adjusting the drying temperature and drying time in the drying step or by adding water as needed.

[0071] Drying may be performed in air, oxygen, an oxidizing atmosphere (decarbonation of carbon dioxide gas of 30 ppm or less), an inert gas atmosphere such as argon gas, or in vacuum. Heating may or may not be performed. The heating temperature is not particularly limited and may be, for example, 40 to 200°C, 60 to 180°C, or 80 to 160°C.

[0072] In one embodiment, after the water washing step, the lithium metal composite oxide is subjected to a dehydration treatment and the water content of the lithium metal composite oxide is reduced to 1 mass % or less by using a dryer or the like. This makes it possible to prevent the lithium metal composite oxide from forming a rock salt structure due to the presence of water, which would otherwise cause deterioration in quality.

[0073] The dehydration treatment can be carried out by solid-liquid separation of the lithium metal composite oxide slurry after the water washing step. Specifically, solid-liquid separation can be carried out using a filter cloth. Alternatively, filtration using a press filter or vacuum filtration using a Buchner funnel can be carried out to obtain a cake-like lithium metal composite oxide having a water content of about 3 to 10 mass % from the slurry.

[0074] The water content of the lithium metal composite oxide after drying is not particularly limited, but is preferably, for example, 310 ppm or more, 320 ppm or more, 330 ppm or more, 340 ppm or more, 350 ppm or more, 360 ppm or more, 370 ppm or more, 380 ppm or more, 390 ppm or more, or 400 ppm or more. By having a water content above the required value, the additive elements dissolve at the particle surface and penetrate into the grain boundaries of secondary particles, etc., resulting in uniform dispersion and improved quality of the coated particles. On the other hand, the water content of the lithium metal composite oxide is preferably 9500 ppm or less, 9000 ppm or less, 8500 ppm or less, 8000 ppm or less, 7500 ppm or less, 7000 ppm or less, 6500 ppm or less, or 6000 ppm or less. By having a water content below the required value, the fluidity in the processes after the drying process is not impaired due to a decrease in drying efficiency, thereby suppressing a decrease in productivity.

[0075] [Compound addition process] The water content of the lithium metal composite oxide is adjusted to 300 ppm or more and 10,000 ppm or less, and the solubility in water is 0.5 g / 100 cm at least at any temperature in the range of 15 ° C or more and 25 ° C or less. 3 The above is followed by adding and mixing powder of an additive compound containing one or more elements other than Li, Ni, and O.

[0076] The solubility of the additive compound in water is not particularly limited, but is preferably 0.5 g / 100 cm 3 -More than H2O, 0.6g / 100cm 3 -More than H2O, 0.7g / 100cm 3 -H2O or more, 0.8g / 100cm 3 -More than H2O, 0.9g / 100cm 3 On the other hand, the solubility of the added compound in water is preferably 500 g / 100 cm 3 -H2O or less, 400g / 100cm 3 -H2O or less, 300g / 100cm 3 -H2O or less, 200g / 100cm 3-H2O or less. The solubility of the additive compound refers to the solubility at any temperature in the range of 15°C to 25°C, and it is sufficient that the above requirement is satisfied at at least one temperature. By having such a solubility, the additive compound dissolves in the small amount of water contained in the lithium metal composite oxide, making it easier for the additive compound to penetrate into the grain boundaries of the lithium metal composite oxide, and when used as a positive electrode active material, excellent battery performance is exhibited.

[0077] An example of an additive compound that satisfies this solubility is boric acid (4.72 g / 100 cm 3 (20°C)), magnesium hydroxide (0.97 mg / 100 cm 3 (20°C)), aluminum sulfate (100g / 100cm 3 (20°C)), ammonium dihydrogen phosphate (37.4g / 100cm 3 (20°C)), diammonium hydrogen phosphate (68.9g / 100cm 3 (20°C)), potassium phosphate (92.3g / cm 3 (20°C)), ammonium hydrogen sulfate (100g / 100cm 3 (20°C)), calcium hydroxide (0.17g / 100cm 3 (20℃)), calcium chloride (74g / 100cm 3 (25℃)), titanium chloride (62g / 100cm 3 (25°C)), manganese sulfate (62.9 g / cm 3 (20℃)), iron sulfate heptahydrate (48g / cm 3 (20°C)), cobalt sulfate (36.1 g / cm 3 (20°C)), zinc sulfate (53.8g / cm 3 (20°C)), vanadium oxide (V) (0.8g / 100cm 3 (20°C)), ammonium vanadate (0.48g / 100cm 3 (20°C)), gallium nitrate n-hydrate (46.5g / 100cm 3 (25°C)), strontium hydroxide (1.00g / 100cm 3 (25°C)), zirconium hydroxide (0.02g / 100cm 3(20°C)), zirconium oxynitrate hydrate (11.5g / 100cm 3 (20°C)), ammonium niobium oxalate (8g / 100cm 3 (25°C)), molybdenum oxide (0.11g / 100cm 3 (18°C)), tin sulfate (18.9 g / cm 3 (20°C)), barium hydroxide (3.89g / 100cm 3 (20°C)), lanthanum nitrate hexahydrate (136 g / cm 3 (20℃)), cerium nitrate hexahydrate (234g / 100cm 3 (20°C)), ammonium paratungstate (303.99g / 100cm 3 (20°C)).

[0078] [Heat treatment process] A mixture of lithium metal composite oxide and additive compound is subjected to heat treatment to obtain coated particles. Addition and mixing of the additive compound causes the additive compound to react with water or protons in the crystal, resulting in a weak acidity. The surface of the lithium metal composite oxide is partially transformed into a nickel oxide-like substance through a disproportionation reaction. Subsequent heat treatment is thought to form a mechanically and thermally stable nickel oxide layer (II). Furthermore, the additive compound reacts with lithium to form an oxide of lithium and the additive element, which has high ionic conductivity, and coats the surface of the nickel oxide layer.

[0079] The heat treatment temperature is not particularly limited, but is preferably, for example, 200° C. or higher, 210° C. or higher, 220° C. or higher, 230° C. or higher, 240° C. or higher, or 250° C. On the other hand, the heat treatment temperature is preferably 500° C. or lower, 490° C. or lower, 480° C. or lower, 470° C. or lower, 460° C. or lower, 450° C. or lower, 440° C. or lower, 430° C. or lower, 420° C. or lower, 410° C. or lower, or 400° C. or lower.

[0080] The heat treatment time is not particularly limited, and is preferably, for example, 1 hour to 15 hours, 2 hours to 12 hours, or 2 hours to 10 hours.

[0081] In this disclosure, the heat treatment temperature is the maximum temperature when the object to be heated is heated. The maximum temperature refers to the temperature of the hottest part of the object to be heated. The heat treatment time refers to the time during which the heat treatment temperature is maintained within a predetermined range after reaching that range. The same definitions of the heat treatment temperature and the heat treatment time apply hereinafter.

[0082] <Coated particles> The characteristics of the coated particles produced by the method for producing coated particles according to this embodiment will be described below, but the coated particles of this embodiment are not limited to the description given below, and coated particles not having the following structure may also be obtained. However, even coated particles not having the following structure can achieve the effects of the present disclosure. The coated particles contain at least lithium and nickel and have a lithium metal composite oxide in the form of primary or secondary particles, a first layer containing nickel(II) oxide on at least a portion of the surface of the lithium metal composite oxide, and a second layer containing an oxide containing lithium and an additional element on at least a portion of the surface of the first layer.

[0083] Fig. 1 is a schematic diagram of a cross section of a coated particle sample according to one embodiment of the present disclosure. The coated particle 1 shown in Fig. 1 includes a lithium metal composite oxide 2 containing at least lithium and nickel and in the form of a primary particle or a secondary particle, a first layer 3 containing nickel (II) oxide on at least a portion of the surface of the lithium metal composite oxide 2, and a second layer 4 containing an oxide containing lithium and an additional element on at least a portion of the surface of the first layer 3. Note that, although Fig. 1 shows the lithium metal composite oxide 2 as a circle and the outer contours of the first layer 3 and the second layer 4 as being circular, the cross-sectional shape is not limited to being circular.

[0084] In the coated particle 1, the lithium metal composite oxide serving as the positive electrode active material is coated with two layers: a first layer 3 containing thermally and mechanically stable nickel(II) oxide, and a second layer 4 containing an oxide highly resistant to leaching into the electrolyte. When this coated particle 1 is used as the positive electrode active material, the resulting nonaqueous electrolyte secondary battery can exhibit excellent charge / discharge capacity and cycle characteristics. While the reason for this is not entirely clear, it is believed that the presence of the thermally and mechanically stable first layer 3 coated on the surface of the lithium metal composite oxide 2 can prevent the coated particle 1 serving as the positive electrode active material from decomposing from the surface to a rock salt structure or a spinel structure inward when the coated particle 1 is in a highly charged state, which would otherwise result in a deterioration in cycle characteristics. It is also believed that the presence of the second layer 4 can prevent the coated particle serving as the positive electrode active material from directly contacting the electrolyte and deteriorating, which would otherwise result in a deterioration in cycle characteristics.

[0085] (Lithium metal composite oxide) The lithium metal composite oxide 2 contains at least lithium and nickel and is in the form of primary particles or secondary particles. Other features are the same as those explained in the production method section.

[0086] (First layer) The first layer 3 is disposed on at least a portion of the surface of the lithium metal composite oxide, and contains nickel (II) oxide.

[0087] Since the first layer 3 contains nickel (II) oxide, high-resolution STEM-EDS is used to confirm that it has a rock salt structure derived from nickel (II) oxide and that the layer contains nickel, and this is identified as the first layer 3. For the second layer 4, XPS is used to confirm that an oxide layer of lithium and the additional element exists on the surface, and then high-resolution STEM-EDS is used to identify the layer containing the additional element and oxygen as the second layer 4.

[0088] The average thickness of the first layer 3 is not particularly limited, but is preferably 3 nm or more, 4 nm or more, or 5 nm or more. The average thickness of the first layer 3 is preferably 100 nm or less, 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 19 nm or less, 18 nm or less, 17 nm or less, 16 nm or less, 15 nm or less, 14 nm or less, 13 nm or less, 12 nm or less, or 11 nm or less. When the average thickness of the first layer 3 is within the required range, the resistance of the battery can be reduced without becoming a resistance component that impairs lithium mobility. The average thickness is measured at a magnification of 10,000,000 times using a high-resolution STEM (JEM-ARM200F Dual-X, manufactured by JEOL Ltd.). Specifically, the boundaries between the lithium metal composite oxide 2, the first layer 3, and the second layer 4 are identified as described above, and then 22 points are set on the boundary between the lithium metal composite oxide 2 and the first layer 3, dividing the length of the boundary into 23 equal parts. The shortest distance from each of 20 points, excluding the two points at both ends, to the boundary between the first layer 3 and the second layer 4 is defined as the thickness at each point, and the average of the 20 points is defined as the average thickness.

[0089] The first layer 3 may contain a compound other than nickel (II) oxide. In one embodiment, the first layer 3 contains a lithium metal composite oxide 2 and at least one constituent element other than lithium (Ni 、 Mn 、 It is preferable that M and O) are the same (contain the same element as the lithium metal composite oxide). However, it is not excluded that the first layer 3 contains lithium, and the first layer 3 may contain lithium.

[0090] (Second layer) In one embodiment, the second layer 4 contains an additive element in at least a portion of the surface of the first layer 3 described above.

[0091] The average particle diameter of the coated particles 1 (which refers to the primary particle diameter in the case of primary particles and the secondary particle diameter in the case of secondary particles, and may be abbreviated as D50) is not particularly limited, but may be, for example, 80 nm or more, 100 nm or more, 120 nm or more, 150 nm or more, 170 nm or more, 200 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, or 450 nm or more. On the other hand, D50 is 25μm or less, 24.5μm or less, 24μm or less, 23.5μm or less, 23μm or less, 22.5μm or less, 22μm or less, 21.5μm or less, 21μm or less, 20.5μm or less, 20μm or less, 19.5μm or less, 19μm or less, 18.5μm or less, 18μm or less, 17.5μm or less, 17μm or less, 16.5μm or less, 16μm or less, 15.5μm or less, The particle size may be 15 μm or less, 14.5 μm or less, 14 μm or less, 13.5 μm or less, 13 μm or less, 12.5 μm or less, 12 μm or less, 11.5 μm or less, 11 μm or less, 10.5 μm or less, 10 μm or less, 9.5 μm or less, 9 μm or less, 8.5 μm or less, 8 μm or less, 7.5 μm or less, 7 μm or less, 6.5 μm or less, 6 μm or less, 5.5 μm or less, 5 μm or less, or 4.5 μm or less. Note that D50 is measured on a volume basis by a wet laser method using a laser particle size distribution analyzer (Microtrac HRA, manufactured by Nikkiso Co., Ltd.).

[0092] Such coated particles can be used as a positive electrode active material for non-aqueous electrolyte secondary batteries such as lithium secondary batteries. [Example]

[0093] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0094] <Sample preparation> Samples of Examples 1 to 5 and Comparative Examples 1 to 3 were produced according to the methods described below.

[0095] (Production of precursor compounds) A metal aqueous solution was obtained by mixing an aqueous nickel sulfate solution, a cobalt sulfate solution, and an aqueous manganese sulfate solution so that the molar ratio of Ni to Co to Mn was Ni:Co:Mn = 89:6:5. 10 L of pure water containing 300 g of sodium hydroxide solution and 500 g of ammonia water was prepared in advance in the reaction vessel as a mother liquid, and a nitrogen atmosphere was created in the reaction vessel by adding nitrogen gas at a flow rate of 0.73 L / min. The reaction was also carried out in a nitrogen atmosphere.

[0096] Thereafter, while rotating the stirring blade at 1000 rpm, the metal aqueous solution, sodium hydroxide aqueous solution, and ammonia water were simultaneously dropped at a predetermined rate, and the amount of the alkaline solution dropped was adjusted so that the pH became 11.4. Through a crystallization reaction, Ni, Co, and Mn were crystallized and coprecipitated to form aggregated particles, thereby obtaining a coprecipitate.

[0097] The slurry in the reactor was then subjected to solid-liquid separation and further washed with pure water to reduce residual impurities. The coprecipitate cake was then dried at 110°C for 12 hours in an air environment to obtain a precursor compound.

[0098] (Production of lithium metal composite oxide) The obtained precursor compound, anhydrous lithium hydroxide, and aluminum hydroxide were weighed out so that the ratio (molar ratio) of Al to the total amount of Ni, Co, and Mn was Al / (Ni+Co+Mn+Al) = 0.02, and the ratio (molar ratio) of Li to the total amount of Ni, Co, Mn, and Al was Li / (Ni+Co+Mn+Al) = 1.07, and these were mixed using a mixer to prepare a raw material mixture.

[0099] The mixture was then fired in an electric furnace under an oxygen atmosphere (oxygen concentration: 97% by volume) at a maximum temperature of 770°C for 5 hours, cooled, and then pulverized in a pulverizer to obtain a lithium metal composite oxide. The average particle size of the secondary particles in the lithium metal composite oxide was approximately 12.8 μm. The moisture content, as determined by the Karl Fischer method, was 131 ppm.

[0100] The obtained lithium metal composite oxide was added to pure water (water temperature 25°C) in a reaction vessel (volume 10 L) and stirred for 10 minutes to prepare a slurry. Here, the ratio of the amount of lithium metal composite oxide to the amount of pure water (solid-liquid ratio) was adjusted to 2000 g / L. The obtained slurry was filtered using a Buchner funnel to obtain a cake of lithium metal composite oxide. The water content of the cake was 6.2 mass%.

[0101] Example 1 The resulting cake of lithium metal composite oxide was dried at 100°C for 60 minutes using a vacuum dryer after reducing the pressure to -98 MPa, to obtain a dry powder of lithium metal composite oxide. The ICP measurement results showed that the composition of the lithium metal composite oxide was as per the charge ratio, and Li 1.07 Ni 0.8722 Mn 0.049 Co 0.0588 Al 0.02 The moisture content of the dried powder was 653 ppm.

[0102] Boric acid powder was weighed into the obtained dry powder of lithium metal composite oxide so that the amount of B was 1000 ppm relative to the final coated particle sample, and mixed with the lithium metal composite oxide using a mixer at 100°C to obtain a mixed powder. The obtained mixed powder was heat-treated in an oxygen atmosphere (oxygen concentration: 97% by volume) using an electric furnace for 3 hours so that the maximum temperature of the mixed powder was 300°C, and after cooling, it was pulverized in a pulverizer to obtain a coated particle sample.

[0103] Example 2 The obtained cake was subjected to a heat treatment at 100°C for 85 minutes after reducing the pressure to -98 MPa using a vacuum dryer, and the cake was dried to obtain a dried powder of lithium metal composite oxide. The moisture content of the dried powder was 336 ppm. A coated particle sample was obtained in the same manner as in Example 1 except for the above.

[0104] Example 3 The obtained cake was dried by reducing the pressure to -98 MPa using a vacuum dryer and then heat-treating it at 100°C for 20 minutes to obtain a dried powder of lithium metal composite oxide. The moisture content of the dried powder was 6130 ppm. A coated particle sample was obtained in the same manner as in Example 1.

[0105] Example 4 The obtained cake was dried by reducing the pressure to -98 MPa using a vacuum dryer and then heat-treating it at 100°C for 45 minutes to obtain a dried powder of lithium metal composite oxide. The moisture content of the dried powder was 1783 ppm. A coated particle sample was obtained in the same manner as in Example 1.

[0106] Diammonium hydrogen phosphate powder was weighed into the obtained dry powder of lithium metal composite oxide so that the amount of P in the final coated particle sample was 300 ppm, and mixed with the lithium metal composite oxide using a mixer at 100°C to obtain a mixed powder. The obtained mixed powder was heat-treated in an oxygen atmosphere (oxygen concentration: 97% by volume) using an electric furnace for 3 hours so that the maximum temperature of the mixed powder was 280°C, and after cooling, it was pulverized in a pulverizer to obtain a coated particle sample.

[0107] Comparative Example 1 The resulting cake was dried using a vacuum dryer, reducing the pressure to -98 MPa, and then heat-treated at 100°C for 60 minutes to obtain a dried powder of lithium metal composite oxide. The moisture content of the dried powder was 653 ppm.

[0108] The obtained dried powder of lithium metal composite oxide was heat-treated in an electric furnace under an oxygen atmosphere (oxygen concentration: 97% by volume) for 3 hours so that the maximum temperature of the dried powder reached 300°C, and after cooling, it was pulverized in a pulverizer to obtain a coated particle sample.

[0109] Comparative Example 2 The resulting cake was dried using a vacuum dryer, reducing the pressure to -98 MPa, and then heat-treated at 50°C for 5 minutes to obtain a dried powder of lithium metal composite oxide. The moisture content of the dried powder was 13,821 ppm.

[0110] Boric acid powder was weighed into the obtained dry powder of lithium metal composite oxide so that the amount of B was 1000 ppm relative to the final coated particle sample, and mixed with the lithium metal composite oxide using a mixer at 100°C to obtain a mixed powder. The obtained mixed powder was heat-treated in an oxygen atmosphere (oxygen concentration: 97% by volume) using an electric furnace for 3 hours so that the maximum temperature of the mixed powder was 300°C, and after cooling, it was pulverized in a pulverizer to obtain a coated particle sample.

[0111] Comparative Example 3 The resulting cake was heat-treated at 100°C for 90 minutes using a vacuum dryer to dry the cake, yielding a dry powder of lithium metal composite oxide. The moisture content of the dry powder was 198 ppm.

[0112] Boric acid powder was weighed into the obtained dry powder of lithium metal composite oxide so that the amount of B was 1000 ppm relative to the final coated particle sample, and mixed with the lithium metal composite oxide using a mixer at 100°C to obtain a mixed powder. The obtained mixed powder was heat-treated in an oxygen atmosphere (oxygen concentration: 97% by volume) using an electric furnace for 3 hours so that the maximum temperature of the mixed powder was 300°C, and after cooling, it was pulverized in a pulverizer to obtain a coated particle sample.

[0113] <Sample evaluation> The samples of Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated according to the methods described below, and the results are shown below.

[0114] [Composition of precursor compound and lithium metal composite oxide] 0.2 g of the precursor compound or lithium metal composite oxide was dissolved in 25 mL of 20% hydrochloric acid solution by heating, cooled, transferred to a 100 mL measuring flask, and purified water was added to prepare a solution. The constituent elements of this solution were quantified using ICP-AES [Optima 8300, manufactured by PerkinElmer Co., Ltd.], and it was confirmed that the precursor compound and lithium metal composite oxide had the same ratio of each metal element.

[0115] [Measurement of moisture content] The moisture content (ppm) of the sample was determined as the amount of moisture generated up to 300°C based on the Karl Fischer method (coulometric titration method).

[0116] [Productivity evaluation (loss rate)] The productivity was evaluated as follows. The loss rate due to adhesion to equipment in each process was calculated, from washing with water and drying to adding and mixing the additive element compound powder. Loss rate (%) = (actual recovered amount / input lithium active material sample before washing) × 100 At this time, the loss rate was determined as follows: A to C. A: It is fluid and almost no adhesion to equipment was observed. B: It has fluidity, but some adhesion to equipment was observed. C: No fluidity was exhibited, or fluidity was exhibited but the additives were not mixed uniformly, or aggregation of the additives was observed after the mixing process.

[0117] [Battery Characteristics of Non-Aqueous Electrolyte Secondary Battery] (Fabrication of coin cells using positive electrode active materials) A 2032-type coin cell using the positive electrode active material was fabricated using a positive electrode, a negative electrode, and an electrolyte solution prepared by the following method.

[0118] ·Positive electrode Acetylene black and graphite were used as conductive agents in a weight ratio of 1:1, and polyvinylidene fluoride was used as a binder. The sample as a positive electrode active material, conductive agent, and binder were blended in a weight ratio of 90:6:4 (positive electrode active material:conductive agent:binder). These were mixed in N-methylpyrrolidone to form a slurry, which was then applied to aluminum foil. This was dried at 110°C to produce a sheet, which was then punched out to a diameter of 15 mm. The density of the composite was 3.0 g / cm. 3 The resultant was rolled to form a positive electrode.

[0119] ·Negative electrode A lithium foil with a thickness of 500 μm and punched to 16 mm diameter was used as the negative electrode.

[0120] ·Electrolyte A mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) was prepared so that the volume ratio of EC:DMC was 1:2, and this was mixed with 1M LiPF6, which was the electrolyte, to prepare an electrolytic solution.

[0121] (Initial charge capacity and initial charge / discharge efficiency) Using the coin cell manufactured by the above method, constant current charging was performed at a current density of 0.1 C up to 4.30 V (upper voltage limit) in an environment of 25° C., followed by constant voltage charging until the current reached 0.1 C. The capacity at this time was defined as the initial charge capacity (mAh / g).

[0122] Next, after a 5-minute pause, constant-current discharge was performed at a current density of 10 C to 3.00 V under the same environment, and after a 5-minute pause, the initial discharge capacity (mAh / g) was measured. The series of steps up to the measurement of the initial discharge capacity was defined as a charge-discharge cycle under condition A.

[0123] The initial charge / discharge efficiency was calculated based on the measured values ​​of the initial charge capacity and the initial discharge capacity according to the following formula. Initial charge / discharge efficiency (%) = (initial discharge capacity / initial charge capacity) x 100

[0124] (initial reaction resistance) Using the manufactured coin cells, the initial reaction resistance was measured in an environment of 25°C under the conditions shown below. 1st cycle: Charge at a constant current of 0.1C up to 4.3V, then charge at a constant voltage of 0.01C 5 minute pause 0.1C constant current discharge to 2.5V 5 minute pause Cycle 2: Charge at a constant current of 0.1C up to 4.3V, then charge at a constant voltage of 0.01C Using the cell after the second cycle of charging, impedance measurement was carried out under the following conditions in an environment of 25° C. The result was taken as the second cycle impedance measurement result (second cycle reaction resistance (initial reaction resistance)). Frequency range: 300k~0.01Hz (76 points) Amplitude: 10mV

[0125] (Cycle maintenance rate) The coin cell manufactured by the above-mentioned method was subjected to 104 charge / discharge cycles in an environment of 60° C. under the conditions shown below. Cycles 1, 2, and 104: Charge at a constant current of 0.2C up to 4.3V, then charge at a constant voltage of 0.01C 5 minute pause 0.2C constant current discharge to 3.0V 5 minute pause Cycles 3 to 103: Charge at a constant current of 0.5C up to 4.3V, then charge at a constant voltage of 0.01C 5 minute pause 1C constant current discharge to 3.0V 5 minute pause Using the measured value of the discharge capacity at the 30th cycle and the measured value of the discharge capacity at the 103rd cycle, the cycle retention rate at 60°C was calculated according to the following formula. Cycle maintenance rate (%) = (discharge capacity at 103 cycles / discharge capacity at 30 cycles) × 100

[0126] [Quality evaluation] The quality was evaluated as follows: The cycle characteristics and initial reaction resistance of a non-aqueous electrolyte secondary battery using the obtained lithium metal composite oxide sample were evaluated for quality as follows. A: Initial reaction resistance is less than 30 Ω and cycle retention rate is 65% or more. B: Initial reaction resistance is less than 30 Ω and cycle retention rate is 65% or more. C: Initial reaction resistance is less than 30 Ω and cycle retention rate is not 65% or more.

[0127] The production conditions and evaluation results of Examples 1 to 5 and Comparative Examples 1 to 3 are shown in Table 1 below.

[0128] [Table 1] [Explanation of symbols]

[0129] 1. Coated particles 2. Lithium metal composite oxide 3. First Layer 4 Second Layer

Claims

1. A lithium metal composite oxide containing at least lithium and nickel, having a water content of 300 ppm or more and 10,000 ppm or less, and in the form of primary particles or secondary particles, has a solubility in water of 0.5 g / 100 cm at at least any temperature in the range of 15 ° C. or more and 25 ° C. or less. ３ The above is the case, and an additive compound containing one or more elements other than Li, Ni, and O is added in the form of powder, and then heat treatment is performed to obtain coated particles. Method for producing coated particles.

2. The lithium metal composite oxide has a layered rock salt structure and has the general formula Li ａ Ni １－ｂ－ｃ Mn ｂ M ｃ O ２ (wherein M is one or more elements other than Li, Ni, Mn, and O, and 0.90≦a≦1.15, 0≦b+c≦0.70) A method for producing the coated particles according to claim 1.

3. The temperature of the heat treatment is 200° C. or higher and 500° C. or lower. The method for producing the coated particles according to claim 1 or 2.

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