Aqueous solution and method for producing positive electrode active material for lithium secondary battery

Abstract

An aqueous solution containing Li, a peroxide complex of an element [alpha], ammonium ions, and nitrate ions, the element [alpha] being one or more elements selected from the group consisting of Nb, Ti, Ta, Zr, W, Mo, and V. The mass molar concentration ratio (NH4 + / [alpha]) of the ammonium ions to the element [alpha] in the aqueous solution is less than 4.5. And the mass molar concentration of nitrate ions (NO3 <->) is lower than 4.0 * 10 <-3 > ml / kg.

Description

Technical Field

[0001] The present invention relates to an aqueous solution and a method for producing a positive electrode active material for a lithium secondary battery.

[0002] This application claims priority based on Japanese Patent Application No. 2022-176415 filed in Japan on November 2, 2022, and the contents are incorporated herein by reference. Background Art

[0003] As a lithium secondary battery, there is known a battery having a structure including a positive electrode having a positive electrode active material, a negative electrode, and an electrolyte in contact with the positive electrode and the negative electrode.

[0004] As electrolytes used in lithium secondary batteries, electrolyte solutions containing organic solvents and solid electrolytes are known. In the following description, electrolyte solutions and solid electrolytes may be collectively referred to as "electrolytes".

[0005] In either a liquid lithium secondary battery using an electrolyte or a solid lithium secondary battery using a solid electrolyte, a positive electrode active material for a lithium secondary battery having a coating on the surface of particles of a lithium metal composite oxide has been developed. If the positive electrode active material has a coating, it is expected that the interface reaction caused by the positive electrode active material being in direct contact with the electrolyte while a voltage is applied can be suppressed, and the reduction in battery performance caused by the reaction product can be suppressed.

[0006] For example, Patent Document 1 discloses a method for producing active material composite powders, which includes a step of spraying a coating liquid containing hydrogen peroxide, a peroxo complex of niobium, and lithium as a coating material onto an active material for a lithium ion secondary battery.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent document 1: JP6034265B2 Summary of the invention

[0010] Problems to be solved by the invention

[0011] However, as a result of studying the covering liquid produced by the method disclosed in Patent Document 1, it was found that when the covering liquid was left to stand for 24 hours after production, a precipitate was generated or the covering liquid became colloid, indicating that the covering liquid was extremely unstable.

[0012] If a coating containing precipitate or a colloid is used to form a coating on the surface of the positive electrode active material, the coating amount of the positive electrode active material surface will be reduced, and the precipitate will adhere to the surface of the positive electrode active material as an impurity, increasing the resistance and deteriorating the battery performance.

[0013] When the positive electrode active material is covered with such a covering liquid, the target covering amount cannot be achieved, and the effect of suppressing the interface reaction during the operation of the lithium secondary battery cannot be fully exerted.

[0014] Furthermore, in order to use a covering liquid with poor storage stability in the covering process of the positive electrode active material, it is required to use it from the synthesis of the covering liquid to the precipitation or colloidation of the covering liquid in order to solve the above-mentioned problems. Therefore, it becomes difficult to keep a suitable inventory of the covering liquid, and it becomes necessary to control the covering liquid synthesis process and the positive electrode material covering process in an integrated manner, which is a manufacturing process with insufficient freedom.

[0015] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an aqueous solution that can be used as a coating liquid having excellent storage stability, and a method for producing a positive electrode active material for a lithium secondary battery using the same.

[0016] In this specification, "excellent storage stability" means that no precipitate is visually observed and no colloid is formed after storage at room temperature (20 to 25° C.) for at least 30 days after production. The detailed evaluation method is described below.

[0017] Means for solving problems

[0018] In order to solve the above-mentioned problems, the present invention includes the following means.

[0019] [1] An aqueous solution comprising Li, a peroxo complex of an element α, ammonium ions and nitrate ions, wherein the element α is one or more elements selected from the group consisting of Nb, Ti, Ta, Zr, W, Mo and V, and wherein in the aqueous solution, the molar concentration ratio of the ammonium ions to the element α (NH 4 + / α) is less than 4.5, and the mass molar concentration of nitrate ions is less than 4.0×10 -3 mоl / kg.

[0020] [2] The aqueous solution according to [1], wherein the molar concentration ratio of nitrate ions to the element α in the aqueous solution (NO 3 - / α) is less than 0.017.

[0021] [3] The aqueous solution according to [1] or [2], wherein the mass molar concentration ratio of Li to element α (Li / α) in the aqueous solution exceeds 1.0.

[0022] [4] The aqueous solution according to any one of [1] to [3], wherein the mass molar concentration of the element α is 0.10 mol / kg or more.

[0023] [5] The aqueous solution according to any one of [1] to [4], wherein the pH of the aqueous solution is 11.0 or higher, and the element α is Nb.

[0024] [6] A method for producing a positive electrode active material for a lithium secondary battery, which is a method for producing a positive electrode active material for a lithium secondary battery having metal composite particles and a covering covering at least a portion of the metal composite particles, comprising the following step X: bringing the aqueous solution described in any one of [1] to [5] into contact with the metal composite particles to cover at least a portion of the metal composite particles.

[0025] [7] The method for producing a positive electrode active material for a lithium secondary battery according to [6], wherein the metal composite particles are lithium metal composite oxides.

[0026] [8] The method for producing a positive electrode active material for a lithium secondary battery according to [6] or [7], wherein the step X comprises: contacting the aqueous solution with the metal composite particles by spraying, drying the aqueous solution attached to the surface of the metal composite particles, and then performing a heat treatment.

[0027] [9] A method for producing a positive electrode active material for a lithium secondary battery, which is a method for producing a positive electrode active material for a lithium secondary battery using metal composite particles and a covering covering at least a portion of the metal composite particles, comprising a step A for preparing a covering liquid, the step A comprising: a step A1 for mixing a compound containing an element α, a solution containing hydrogen peroxide, a solution containing ammonia, and a lithium compound to prepare a solution L having a liquid temperature exceeding 40°C; and a step A2 for cooling the solution L to below 40°C to obtain a covering liquid, wherein the element α is one or more elements selected from the group consisting of Nb, Ti, Ta, Zr, W, Mo, and V, the covering liquid comprises a peroxo complex of the element α and Li, and in the covering liquid, the mass molar concentration ratio of the element α to Li (Li / α) exceeds 1.0, and in the step A2, the average cooling rate of the solution L from the liquid temperature to 40°C is less than 0.9°C / min.

[0028]

[10] The method for producing a positive electrode active material for a lithium secondary battery according to [9], wherein the mass molar concentration of the element α in the coating liquid is 0.10 mol / kg or more.

[0029]

[11] A method for producing a positive electrode active material for a lithium secondary battery according to [9] or

[10] , wherein the step A1 comprises the following operation: adding a lithium compound to a slurry containing a compound containing the element α, a solution containing the hydrogen peroxide, and a solution containing the ammonia at a temperature of 35° C. or above.

[0030]

[12] A method for producing a positive electrode active material for a lithium secondary battery according to any one of [9] to

[11] , wherein the above-mentioned step A1 includes the following operations: heating a slurry containing a compound containing the above-mentioned element α, a solution containing the above-mentioned hydrogen peroxide, and a solution containing the above-mentioned ammonia at an average heating rate of not less than 0.9°C / min and not more than 10°C / min, and adding a lithium compound to the above-mentioned slurry at a temperature of not less than 35°C.

[0031]

[13] The method for producing a positive electrode active material for a lithium secondary battery according to any one of [9] to

[12] , wherein the element α is Nb.

[0032]

[14] The method for producing a positive electrode active material for a lithium secondary battery according to any one of [9] to

[13] , wherein the compound containing the element α is a compound containing niobium oxide, and the lithium compound is a compound containing lithium hydroxide or lithium hydroxide hydrate.

[0033]

[15] A method for producing a positive electrode active material for a lithium secondary battery according to any one of [9] to

[14] , wherein, after the above-mentioned step A, there is a step B of covering at least a portion of the above-mentioned metal composite particles with the above-mentioned covering liquid, and the above-mentioned step B comprises: spraying the above-mentioned covering liquid on the above-mentioned metal composite particles, drying the above-mentioned covering liquid attached to the surface of the above-mentioned metal composite particles, and then performing a heat treatment.

[0034] Effects of the Invention

[0035] According to the present invention, it is possible to provide an aqueous solution that can be used as a coating liquid having excellent storage stability, and a method for producing a positive electrode active material for a lithium secondary battery using the same.

[0036] Furthermore, according to the present invention, since a positive electrode active material for a lithium secondary battery is manufactured using a covering liquid with excellent storage stability, there is no need to worry about the introduction of impurities derived from precipitates of the covering liquid. In addition, a positive electrode active material for a lithium secondary battery having a desired covering can be manufactured without reducing the covering amount. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of an example of an apparatus used to produce a coating liquid. DETAILED DESCRIPTION

[0038] In this specification, lithium metal composite oxide (Lithium Metal composite Oxide) is hereinafter referred to as "LiMO".

[0039] The positive electrode active material for lithium secondary batteries (Cathode Active Material for lithium secondary batteries) is hereinafter referred to as "CAM".

[0040] Unless otherwise specified, the term "Li" means Li element rather than Li metal alone. The same applies to terms for other elements such as Ni, Co, Mn, Nb, Ti, Ta, Zr, W, Mo, and V.

[0041] Regarding the numerical range, “A to B” means “A or more and B or less”. For example, when “5 to 15 μm” is described, it means a range of 5 μm or more and 15 μm or less, and means a numerical range including 5 μm as a lower limit and 15 μm as an upper limit.

[0042] Regarding the numerical range in the present specification, the upper limit value and the lower limit value can be arbitrarily combined.

[0043] The numerical ranges of the various physical properties, compositions, and production conditions can be combined arbitrarily.

[0044] <Method for producing positive electrode active material for lithium secondary battery 1>

[0045] The present embodiment is a method for producing a CAM having metal composite particles and a cover covering at least a portion of the metal composite particles.

[0046] The metal composite particles are metal composite hydroxides, metal composite oxides, or LiMO, and are preferably LiMO.

[0047] The production method of this embodiment includes step A of preparing a coating liquid. In addition, it optionally includes step B of coating at least a portion of the metal composite particles with the coating liquid. Hereinafter, the production method including step A and optional step B will be described as "production method 1".

[0048] The cap formed in the manufacturing method 1 has a compound containing Li and the element α.

[0049] The element α is one or more elements selected from the group consisting of Nb, Ti, Ta, Zr, W, Mo, and V, and is preferably Nb.

[0050] The compound containing Li and the element α preferably contains, for example, a lithium composite oxide containing the element α as a main component. The lithium composite oxide containing the element α is, for example, selected from LiNbO 3 、LiTaO 3 , Li 2 TiO 3 , Li 2 WO4 , Li 4 WO 5 , Li 2 ZrO 3 , Li 2 MoO 4 , and LiV 3 O 6 At least one oxide of the group consisting of: The lithium composite oxide containing the element α has lithium ion conductivity.

[0051] It should be noted that, regarding the covering, the so-called "main component" of the lithium composite oxide means that the content of the lithium composite oxide is the highest in the material forming the covering. The content of the lithium composite oxide relative to the entire covering is preferably 50 mol% or more, more preferably 60 mol% or more. In addition, the content of the lithium composite oxide relative to the entire covering is preferably 90 mol% or less.

[0052] In this embodiment, the coating is preferably a coating layer or coating particles.

[0053] In the present embodiment, it is sufficient that the covering is provided on at least a portion of the surface of one particle of the metal composite particle. The entire surface of the metal composite particle may be covered with the covering, or a portion of the surface of the metal composite particle may be exposed.

[0054] In this embodiment, the composition of the covering can be confirmed by analyzing using cross-sectional STEM-EDX element linear analysis of CAM, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma emission analysis (ICP), electron probe microanalyzer (EPM A), etc.

[0055] Hereinafter, step A and optional step B will be described.

[0056] [Process A]

[0057] Step A is a step of preparing a coating liquid.

[0058] Step A includes at least step A1 and step A2 in order.

[0059] In step A1, a solution L described later is prepared, and in step A2, an operation of stably maintaining the solution L is performed to obtain a covering solution containing a peroxo complex of element α and Li.

[0060] Since the peroxo complex does not contain hydrocarbons in its chemical structure compared to the alcohol solution of metal alkoxide known as the covering liquid, no hydrocarbons remain in the covering after the covering liquid is sprayed and dried. Therefore, when the peroxo complex is used, no voids are generated due to combustion or oxidative decomposition of hydrocarbons in the covering during the heat treatment step described later, and a high-density covering can be finally formed.

[0061] The elements listed as element α are all capable of forming peroxo complexes.

[0062] In the present embodiment, the peroxo complex of element α includes niobium peroxo complex, titanium peroxo complex, tantalum peroxo complex, zirconium peroxo complex, tungsten peroxo complex, molybdenum peroxo complex, and vanadium peroxo complex. The peroxo complex of element α is preferably niobium peroxo complex.

[0063] (Process A1)

[0064] Step A1 is a step of mixing a compound containing element α, a solution containing hydrogen peroxide, a solution containing ammonia, and a lithium compound to prepare a solution L having a liquid temperature exceeding 40°C.

[0065] Examples of the compound containing the element α include compounds containing niobium oxide, compounds containing titanium oxide, compounds containing tantalum oxide, compounds containing zirconium oxide, compounds containing tungsten oxide, compounds containing molybdenum oxide, and compounds containing vanadium oxide. Examples include niobium oxide hydrate (Nb 2 O 5 ·nH 2 O), titanium oxide hydrate (TiO 2 ·nH 2 O), Tantalum Oxide Hydrate (Ta 2 O 5 ·nH 2 O), zirconium oxide hydrate (ZrO 2 ·nH 2 O), tungsten oxide hydrate (WO 3 ·nH 2 O), molybdenum oxide hydrate (MoO 3 ·nH 2 O), vanadium oxide (V 2 O 5 ). The compound containing the element α is preferably a compound containing niobium oxide.

[0066] In the present embodiment, the compound containing element α is added in such a ratio that the mass molar concentration of element α in the coating liquid becomes preferably 0.10 mol / kg or more, more preferably 0.12 mol / kg or more, and further preferably 0.14 mol / kg or more.

[0067] The upper limit of the molar concentration of the element α in the coating liquid is, for example, 0.50 mol / kg or less, 0.40 mol / kg or less, or 0.30 mol / kg or less.

[0068] The molar concentration of the element α in the coating liquid is, for example, 0.10 to 0.50 mol / kg, 0.12 to 0.40 mol / kg, or 0.14 to 0.30 mol / kg.

[0069] If the mass molar concentration of the element α in the covering liquid is greater than or equal to the above lower limit, when the metal composite particles are LiMO, a covering containing a sufficient amount of the element α to exert the effect of suppressing the interface reaction between the CAM surface and the electrolyte can be easily obtained. In addition, if the mass molar concentration of the element α in the covering liquid is greater than or equal to the above lower limit, in the step B described later, a target covering can be obtained with a small amount of covering liquid, and the covering treatment time can be shortened.

[0070] If the mass molar concentration of the element α in the covering liquid is below the above upper limit, the compound containing the element α is easily dissolved and residue is less likely to remain. In addition, if the molar concentration of the element α in the covering liquid is below the above upper limit, a thin film with uniform thickness can be easily obtained in the step B described later.

[0071] Preferred examples of the solution containing ammonia include aqueous ammonia and the like.

[0072] The amount of the solution containing ammonia added is preferably such that ammonia reacts with the compound containing element α and the solution containing hydrogen peroxide, and the coating solution (aqueous solution) obtained contains the following ratio (NH 4 + / α) falls within the range described below, and more preferably is set to a ratio that gives a pH value of 11.0 or more.

[0073] Preferred examples of the solution containing hydrogen peroxide include hydrogen peroxide solution and the like.

[0074] The amount of solution containing hydrogen peroxide added is preferably an amount that reacts with the compound containing element α and the solution containing ammonia so that the mass molar concentration of hydrogen peroxide in the obtained coating liquid (aqueous solution) falls within the range described below.

[0075] In step A1, hydrogen peroxide coordinated to element α of the compound containing element α is converted into a peroxide group by passing through a solution containing ammonia, and the counter ion generated is NH 4+ This intermediate is very unstable. For example, when the element α is Nb, the intermediate changes to Nb 2 O 5 , easy to precipitate.

[0076] However, by adding lithium compounds, the counter ions (NH 4+ ) ion exchange to Li + , becoming the counter ion Li + The counter ion is Li + The peroxo complex has a counter ion of NH 4+ The intermediate is stable.

[0077] Preferred examples of lithium compounds include lithium hydroxide (LiOH), lithium hydroxide hydrate (LiOH·nH 2 O), lithium nitrate (LiNO 3 ), lithium sulfate (Li 2 SO 4 )、Lithium carbonate (Li 2 CO 3 ) etc. Among them, lithium hydroxide or lithium hydroxide hydrate is preferred.

[0078] The lithium compound is preferably mixed with a compound containing element α, a solution containing hydrogen peroxide, and a solution containing ammonia in such a ratio that the ratio (Li / element α) contained in the resulting covering solution is within the range described below (i.e., greater than 1.0, preferably 1.1 or more).

[0079] Step A1 preferably includes adding a lithium compound to a slurry containing a compound containing element α, a solution containing hydrogen peroxide, and a solution containing ammonia at a temperature of 35° C. or higher. The temperature of the slurry when adding the lithium compound is more preferably 40° C. or higher, and even more preferably 45° C. or higher.

[0080] The temperature of the slurry when the lithium compound is added is, for example, 80° C. or lower, 70° C. or lower, or 65° C. or lower.

[0081] The temperature of the slurry when the lithium compound is added is, for example, 35 to 80°C, 40 to 70°C, or 45 to 65°C.

[0082] When the temperature of the slurry when the lithium compound is added is equal to or higher than the above lower limit, the ammonia in the slurry is easily converted into nitrous acid. In the presence of nitrous acid, the intermediate is easily stabilized, so the storage stability is easily improved.

[0083] When the temperature of the slurry when the lithium compound is added is equal to or lower than the above upper limit, precipitation is less likely to occur, and thus the storage stability of the coating liquid is likely to be improved.

[0084] In addition, if the decomposition of hydrogen peroxide progresses rapidly and generates heat, the reaction proceeds rapidly and precipitates are easily generated. If the temperature of the slurry when the lithium compound is added is below the above upper limit, the heat generated by the decomposition of hydrogen peroxide can be suppressed, so precipitates are not easily generated, and the storage stability of the covering liquid is easily improved.

[0085] It should be noted that the temperature in step A1 can be controlled by external heating or by heat generation during the reaction. Furthermore, the liquid temperature in step A1 can be controlled by preheating the mixture before mixing the raw materials and maintaining the temperature.

[0086] Step A1 preferably includes heating the slurry at an average heating rate of 0.9 to 10° C. / min and adding a lithium compound to the slurry at a temperature of 35° C. or higher. The average heating rate is preferably 1.0 to 8° C. / min, more preferably 1.5 to 6° C. / min.

[0087] The slurry temperature at the start of slurry mixing is set to T 0 (°C), the slurry temperature immediately before adding the lithium compound to the slurry is set to T 1 (℃), the temperature T 0 ~T 1 The elapsed time is set as t 1 (minutes), the average heating rate is (T 1 -T 0 ) / t 1 Calculate it using the formula.

[0088] By slowly heating the slurry at the above average heating rate, the reaction can be carried out under milder conditions. By carrying out the reaction under milder conditions, the abnormal generation of the above intermediates that may be generated in the case of a rapid exothermic reaction can be suppressed, the residual amount of the intermediates contained in the final covering liquid can be suppressed, and the storage stability can be improved.

[0089] In step A1, when the temperature of the slurry at the time of adding the lithium compound exceeds 40° C., the temperature raising operation may be omitted.

[0090] The slurry is reacted appropriately by controlling the above steps and temperature conditions, thereby gradually becoming a transparent solution L.

[0091] Next, the solution L is adjusted to have a liquid temperature exceeding 40° C. The maximum temperature of the solution L obtained in step A1 is set as T max (℃) T max It is higher than 40°C, preferably higher than 50°C, more preferably higher than 60°C, particularly preferably higher than 70°C.

[0092] T max The upper limit of the temperature is, for example, 90° C. or lower, 88° C. or lower, 86° C. or lower, or 84° C. or lower.

[0093] T max For example, it is higher than 40°C and lower than 90°C, 50 to 88°C, 60 to 86°C, or 70 to 84°C.

[0094] By T of solution L max When the temperature is higher than the lower limit, the reaction between the lithium compound contained in the solution L and the intermediate is accelerated, and unreacted components such as ammonia and hydrogen peroxide can be reduced. This makes it difficult for components that can become precipitates to be generated, and the storage stability of the covering solution is easily improved.

[0095] From the viewpoint of setting the temperature at which the solvent of solution L does not boil, T of solution L max It is preferably less than the above upper limit.

[0096] It should be noted that the T of solution L max It can be controlled by external heating or by heat release at the reaction temperature. For example, the slurry can be mixed and stirred while heating to prepare T max . Then T max The temperature can also be controlled by preliminarily heating the raw materials used in step A1 before mixing and maintaining the temperature.

[0097] (Process A2)

[0098] In step A2, after step A1, the solution L is cooled to 40°C or less while controlling the average cooling rate. In this way, a covering solution having excellent storage stability can be obtained.

[0099] In step A2, the average temperature drop rate is lower than 0.9°C / min, preferably lower than 0.8°C / min, and more preferably lower than 0.7°C / min.

[0100] The lower limit of the average temperature drop rate is, for example, 0.1° C. / minute or more, 0.2° C. / minute or more, or 0.3° C. / minute or more.

[0101] The average temperature drop rate in step A2 is, for example, 0.1° C. / minute or more and less than 0.9° C. / minute, 0.2 to 0.8° C. / minute, or 0.3 to 0.7° C. / minute.

[0102] By gently cooling the temperature so that the average cooling rate in step A2 is below the above upper limit, it becomes easy to maintain the structure of the obtained peroxo complex. As a result, components that can become precipitates, such as oxides of element α, are less likely to be generated in the covering liquid, and storage stability is easily improved. From the viewpoint of improving production efficiency, the average cooling rate in step A2 is preferably set to be above the above lower limit.

[0103] In T max (℃) Time until reaching 40℃ t 2 (minutes) cooling, the average cooling rate is (T max -40) / t2 Calculate it using the formula.

[0104] The coating liquid can be obtained by the above. The mass molar concentration ratio of the element α to Li contained in the coating liquid (Li / α) exceeds 1.0, preferably 1.1 or more. The upper limit of the ratio (Li / α) is, for example, 1.6 or less, 1.5 or less, or 1.4 or less.

[0105] The ratio (Li / α) is, for example, more than 1.0 and 1.6 or less, 1.1 to 1.5, or 1.1 to 1.4, and is particularly preferably 1.1 to 1.4.

[0106] In addition, the ratio (Li / α) can be measured by the method described in [Quantitative Analysis Method of Li and Element α] described later.

[0107] When the ratio (Li / α) of the covering solution exceeds the above lower limit, the lithium ions (Li ions) coordinated to the peroxo complex of the element α contained in the covering solution are sufficient. + ) amount. In this state, lithium ions (Li + ) is not insufficiently coordinated with the peroxo complex of element α and stabilized. Furthermore, the unstable intermediate mentioned above is basically not generated. In addition, the counter ion is Li + The peroxo complex is stable and not easily decomposed, so the generation of precipitates can be suppressed. As a result, the storage stability of the coating liquid is improved.

[0108] When the ratio of the covering liquid (Li / α) is below the upper limit, the Li contained in the obtained covering is not easy to become excessive but becomes an appropriate amount. Since the excess Li is contained in the covering, the battery performance may be reduced due to the formation of a resistance layer such as lithium carbonate on the surface of the metal composite particles. In this embodiment, since a covering containing an appropriate amount of Li can be formed, such a reduction in battery performance is not easy to occur.

[0109] An example of a schematic diagram of an apparatus used to implement Step A1 to Step A2 is shown in FIG. Figure 1 middle.

[0110] Figure 1 The device 1 shown in FIG. 1 includes a reaction tank 2 , a temperature adjustment mechanism 3 , a temperature control unit 4 , a thermometer 5 , a stirring blade 6 , a raw material input port 7 , and a gas exhaust port 8 .

[0111] The raw materials are introduced from the raw material inlet 7 of the reaction tank 2, and the reaction tank 2 is cooled or heated by the temperature adjustment mechanism 3 so that the liquid temperature reaches the target temperature. The temperature adjustment mechanism 3 is connected to the temperature adjustment unit 4, and the reaction tank 2 can be cooled by, for example, passing cooling water cooled by the temperature adjustment unit 4 through the temperature adjustment mechanism 3. The reaction tank 2 can also be heated by passing a heat medium heated by the temperature adjustment unit 4 through the temperature adjustment mechanism 3.

[0112] [Process B]

[0113] Step B is a step of covering at least a portion of the metal composite particles with the covering liquid obtained in step A. At this time, the covering liquid may be used immediately after the temperature is lowered, or may be used after further cooling.

[0114] The metal composite particles are, for example, compounds containing one or more elements of Ni, Co, Mn, Al, W, B, Mo, Zn, Sn, Zr, Ga, La, Ti, Nb, and V.

[0115] Examples of the metal composite particles include metal composite hydroxides or metal composite oxides containing the above elements, and LiMO containing the above elements and Li.

[0116] Examples of the metal composite hydroxide include nickel-cobalt-manganese composite hydroxide and nickel-cobalt-aluminum composite hydroxide, and examples of the metal composite oxide include nickel-cobalt-manganese composite oxide and nickel-cobalt-aluminum composite oxide.

[0117] The metal composite particles are preferably LiMO, and LiMO is preferably a compound containing Li, Ni and one or more elements selected from the group consisting of Co, Mn, and Al, and more preferably a lithium nickel cobalt manganese composite metal compound or a lithium nickel cobalt aluminum composite metal compound.

[0118] The metal composite hydroxide can be produced by the continuous coprecipitation method described in JP-A-2002-201028. The metal composite oxide can be produced by oxidizing the metal composite hydroxide by oxidative heat treatment, etc. LiMO can be produced by mixing a metal composite hydroxide or a metal composite oxide with a lithium compound and calcining the mixture.

[0119] The step B is preferably a step of spraying the coating liquid onto the metal composite particles.

[0120] The coating liquid is sprayed onto the metal composite particles to allow the coating liquid to adhere to the surfaces of the metal composite particles. Furthermore, in step B, drying is preferably performed in order to remove volatile components such as the solvent and hydration water contained in the coating liquid.

[0121] Step B can be performed by using a rotary flow coating device, a spray dryer or the like.

[0122] The step B is preferably performed using a tumbling flow coating apparatus that supplies high-temperature gas while flowing the metal composite particles in a tank and sprays the coating liquid using a sprayer to bring the coating liquid into contact with the metal composite particles.

[0123] As the rotary flow coating apparatus, for example, MP-01 manufactured by Powrex Corporation can be used.

[0124] Step B includes a heat treatment step after spraying the coating liquid onto the metal composite particles and drying the particles.

[0125] The heat treatment conditions may differ depending on the type of raw material contained in the coating liquid. Examples of the heat treatment conditions include the type of atmospheric gas, the heat treatment temperature, and the holding time of the heat treatment.

[0126] For example, when a material containing Nb as the element α is used, heat treatment is preferably performed in air or an atmosphere containing an oxidizing gas such as oxygen at a temperature range of 200 to 500° C. for 1 to 10 hours.

[0127] The heat treatment temperature in this specification refers to the temperature of the atmosphere in the heating furnace and is the highest temperature of the holding temperature in the heat treatment process. When the heat treatment process has multiple heating processes, the heat treatment temperature refers to the highest temperature in the process of heating at the highest temperature.

[0128] By heat treating the metal composite particles after drying the attached coating liquid under the above-mentioned heat treatment conditions, moisture and combustible components of the coating on the surface of the metal composite particles can be removed and the coating can be oxidized to form a coating on the surface of the metal composite particles.

[0129] CAM can be produced by going through step A and optionally step B. CAM may be used after being appropriately crushed or classified.

[0130] <Aqueous solution>

[0131] The aqueous solution of the present embodiment contains Li, a peroxo complex of element α, ammonium ions, and nitrate ions, and preferably further contains hydrogen peroxide.

[0132] The aqueous solution of the present embodiment is the coating liquid described in the above-mentioned production method 1.

[0133] The molar concentration ratio of ammonium ions to the above-mentioned element α in the coating solution (NH 4 + / α) is less than 4.5, and the mass molar concentration of nitrate ions is less than 4.0×10 -3 mоl / kg.

[0134] The composition and the like of the aqueous solution can be confirmed by the following method.

[0135] [Specification method for containing peroxy complex]

[0136] 10 g of the aqueous solution to be the sample is added to 100 ml of isopropanol, and the resulting precipitate is measured using a Fourier transform infrared absorption spectrometer (FT-IR) measuring device to confirm the presence or absence of a peak derived from a bond between oxygen elements (OO bond). The peak derived from the OO bond has a frequency of, for example, 850 to 900 cm -1 The peak of the range.

[0137] As the FT-IR measuring apparatus, for example, NICOLET6700 manufactured by Thermo SCIENTIFIC can be used.

[0138] [Quantitative analysis method of Li and element α]

[0139] The analysis can be performed by measuring 0.1 g of an aqueous solution serving as a sample into a container, adding hydrofluoric acid and nitric acid to a fixed volume, and using an inductively coupled plasma emission (ICP) analyzer.

[0140] As the ICP analyzer, for example, 5110 manufactured by Agilent Technologies and analysis software ICPExpert can be used.

[0141] [Hydrogen peroxide (H 2 O 2 ) quantitative analysis method]

[0142] 0.1 g of an aqueous solution serving as a sample was diluted with pure water and dispensed into a container. 1 mL of a Ti-PAR reagent and 3 mL of a pH buffer solution were added to the container, and then the total amount was adjusted to 10 mL with pure water to prepare a measurement solution.

[0143] The above Ti-PAR reagent is 3.0×10 -3 mol / L Ti solution and 3.0×10 -3 A solution obtained by mixing 10 mol / L PAR (4-(2-pyridyl azo) resorcinol) solutions at a volume ratio of 4:3.

[0144] The pH buffer solution is an ammonia buffer solution (1.5 mol / L, pH 8.6).

[0145] After the measurement solution was left to stand for 10 minutes, the absorbance at a wavelength of 508 nm was measured using a spectrophotometer, and the mass molar concentration of hydrogen peroxide contained in the aqueous solution serving as the sample was determined from a calibration curve prepared separately using a standard sample.

[0146] As the spectrophotometer, for example, V-650 manufactured by JASCO Corporation and Spectra Manager, which is analysis software, can be used.

[0147] [Ammonium ion (NH 4 + ) quantitative analysis method]

[0148] 0.1 g of the aqueous solution as a sample was weighed into a container, the aqueous solution was diluted with a 10 mM methanesulfonic acid solution, the supernatant was filtered, and the ion chromatography was used to measure. 4 + The mass molar concentration of

[0149] For the ion chromatography, for example, ICS-1000 manufactured by NIPPON DIONEX and analysis software Chromereon can be used.

[0150] [Nitrate ion (NO 3 - ) quantitative analysis method]

[0151] 0.1 g of the aqueous solution was diluted with pure water and measured by ion chromatography to determine the NO in the aqueous solution. 3 - The mass molar concentration of

[0152] For the ion chromatography, for example, ICS-1000 manufactured by NIPPON DIONEX and analysis software Chromereon can be used.

[0153] [pH measurement method]

[0154] The pH of an aqueous solution can be measured by the following method.

[0155] The aqueous solution to be a sample was placed in a container, and the container was placed in a zippered plastic bag. While nitrogen gas was blown into the zippered plastic bag, the pH was measured using a pH meter.

[0156] As the plastic bag with a zipper, for example, SANZIP manufactured by CITAKIRON Co., Ltd. can be used. As the pH meter, for example, F-52 manufactured by HORIBA, Ltd. can be used.

[0157] The aqueous solution of this embodiment is passed through the above-mentioned [ammonium ions (NH 4 + The ammonium ion (NH 4 + The ratio of the mass molar concentration of Li and element α to the mass molar concentration of element α measured by the method described in the above-mentioned [Quantitative analysis method of Li and element α] (NH4 + / α) is less than 4.5, preferably less than 4.3, and more preferably less than 4.1. 4 + / α) is, for example, 1.0 or more, 2.0 or more, or 3.0 or more.

[0158] Ratio (NH 4 + / α) is, for example, 1.0 or more and less than 4.5, 2.0 to 4.3, or 3.0 to 4.1.

[0159] NH 4 + / α) is less than the upper limit, since the amount of unreacted ammonia components relative to the peroxo complex of element α contained in the aqueous solution is small, and components that can become precipitates are less likely to be generated, which is preferred.

[0160] NH 4 + / α) is above the above lower limit, then in Li + The ammonium ion (NH 4 + ) can be coordinated and is therefore preferred from the viewpoint of obtaining a solution with excellent storage stability.

[0161] The aqueous solution of this embodiment is passed through the above-mentioned [nitrate ions (NO 3 - The mass molar concentration of nitrate ions measured by the method described in the quantitative analysis method of ) is less than 4.0×10 -3 mol / kg, preferably 3.5×10 -3 mol / kg or less, more preferably 3.0×10 -3 mol / kg or less. In addition, the mass molar concentration of nitrate ions is, for example, 1.0×10 - 3 mol / kg or more, 2.0×10 -3 mol / kg or more, 2.5×10 -3 mоl / kg or more.

[0162] The mass molar concentration of nitrate ions is, for example, 1.0×10 -3 mol / kg and above but less than 4.0×10 -3 mol / kg, 2.0~3.5×10 -3 mol / kg, 2.5~3.0×10 -3 mоl / kg.

[0163] When the mass molar concentration of nitrate ions is lower than the upper limit, the aqueous solution tends to maintain alkalinity in which the peroxo complex of the element α exists stably, and precipitation of the aqueous solution is less likely to occur, thereby tending to improve storage stability.

[0164] If the mass molar concentration of nitrate ions is above the above lower limit, then a post-treatment step of removing nitrate ions is not required, and the aqueous solution can be easily and efficiently produced. Nitrate ions are generated by oxidation of ammonia contained in the raw material by hydrogen peroxide. When the mass molar concentration of nitrate ions is set to be lower than the above lower limit, a post-treatment step of removing nitrate ions is sometimes required.

[0165] The aqueous solution of this embodiment is passed through the above-mentioned [nitrate ion (NO 3 - The ratio of the mass molar concentration of nitrate ions measured by the method described in [Quantitative Analysis Method for Li and Element α] to the mass molar concentration of element α measured by the method described in [Quantitative Analysis Method for Li and Element α] (NO 3 - / α) is less than 0.017, preferably less than 0.015, and more preferably less than 0.013. 3 - / α) is, for example, 0.010 or more, 0.011 or more, or 0.012 or more.

[0166] Than (NO 3 - / α) is, for example, 0.010 or more and less than 0.017, 0.011 to 0.015, or 0.012 to 0.013.

[0167] If compared with (NO 3 - / α) is lower than the above upper limit, the number of nitrate ions relative to the peroxy complex of element α contained in the aqueous solution is small, it becomes easier to maintain the alkaline region in which the peroxy complex of element α exists stably, it is less likely to generate a precipitate in the aqueous solution, and the storage stability is easily improved.

[0168] If compared with (NO 3 - / α) is not less than the above lower limit, nitrate ions are present appropriately in the aqueous solution containing the peroxo complex of element α, and a post-treatment step for removing nitrate ions is unnecessary, so that the aqueous solution can be easily and efficiently produced.

[0169] The aqueous solution of this embodiment is passed through the above-mentioned [hydrogen peroxide (H 2 O 2) quantitative analysis method] The mass molar concentration of the quantitative hydrogen peroxide is less than 50 mol / kg, preferably less than 48 mol / kg, and more preferably less than 47 mol / kg. In addition, the mass molar concentration of hydrogen peroxide is, for example, more than 10 mol / kg, more than 20 mol / kg, or more than 40 mol / kg.

[0170] The mass molar concentration of hydrogen peroxide is, for example, 10 mol / kg or more and less than 50 mol / kg, 20 to 48 mol / kg, or 40 to 47 mol / kg.

[0171] When the mass molar concentration of hydrogen peroxide is lower than the upper limit, the unreacted portion of hydrogen peroxide, which is one of the raw materials during synthesis, is small, and generation of precipitates after synthesis of the aqueous solution can be suppressed, so that storage stability is likely to be improved.

[0172] When the mass molar concentration of hydrogen peroxide is not less than the above lower limit, a post-treatment step of removing hydrogen peroxide is unnecessary, and thus it is easy to efficiently produce an aqueous solution.

[0173] The mass molar concentration of element α measured by the method described in the above [Quantitative Analysis Method of Li and Element α] of the aqueous solution of the present embodiment is preferably 0.10 mol / kg or more, more preferably 0.12 mol / kg or more, and further preferably 0.14 mol / kg or more. The mass molar concentration of element α is, for example, 0.50 mol / kg or less, 0.40 mol / kg or less, or 0.30 mol / kg or less. The mass molar concentration of element α is, for example, 0.10 to 0.50 mol / kg, 0.12 to 0.40 mol / kg, or 0.14 to 0.30 mol / kg.

[0174] When the mass molar concentration of the element α is below the upper limit, the compound containing the element α is easily dissolved during the synthesis of the aqueous solution, and residue is less likely to remain. In addition, in the step B described below, a thin film with uniform thickness can be easily obtained.

[0175] When the mass molar concentration of the element α is equal to or greater than the above lower limit, in the step of forming a coating on the surface of the metal composite particles using an aqueous solution as a coating liquid, a target coating can be obtained with a small amount of coating liquid, and the coating treatment time can be shortened.

[0176] The pH of the aqueous solution of the present embodiment measured by the above-mentioned [pH measurement method] is preferably 11.0 or more, more preferably 11.1 or more, and further preferably 11.2 or more. The pH of the aqueous solution is, for example, 13.0 or less, 12.5 or less, or 12.0 or less.

[0177] The pH of the aqueous solution is, for example, 11.0 to 13.0, 11.1 to 12.5, or 11.2 to 12.0.

[0178] When the pH of the aqueous solution is not less than the above lower limit, the aqueous solution is alkaline and the peroxo complex of the element α tends to be stable.

[0179] When the pH of the aqueous solution is below the upper limit, there is no excess ammonia, and, for example, an ammonium niobium complex is less likely to be generated. Therefore, the aqueous solution is less likely to become colloidal, and storage stability is likely to be improved.

[0180] The aqueous solution of this embodiment has a molar concentration ratio (Li / α) of Li to element α measured by the method described in the above [Quantitative Analysis Method of Li and Element α] of more than 1.0, preferably 1.1. The ratio (Li / α) of the aqueous solution is, for example, 1.6 or less, 1.5 or less, or 1.4 or less.

[0181] The ratio (Li / α) of the aqueous solution is, for example, more than 1.0 and 1.6 or less, 1.1 to 1.5, or 1.1 to 1.4.

[0182] When the ratio (Li / α) of the aqueous solution exceeds the above lower limit, the lithium ions (Li ions) coordinated to the peroxo complex of element α contained in the aqueous solution are + ) amount. In this state, lithium ions (Li + ) is not insufficiently coordinated with the peroxo complex of element α, and stabilized. In addition, the unstable intermediates mentioned above are basically not generated. In addition, the counter ion is Li + The peroxy complex is stable and not easily decomposed, so the formation of precipitates can be suppressed. As a result, the storage stability of the aqueous solution is easily improved.

[0183] When the ratio (Li / α) of the aqueous solution is below the above upper limit, the Li contained in the covering obtained by using the aqueous solution as the covering liquid is not easy to become excessive but becomes an appropriate amount. When the excess Li is included in the covering, the battery performance is reduced by forming a resistance layer such as lithium carbonate on the surface of the metal composite particles. In the present embodiment, a covering containing an appropriate amount of Li can be formed, so it is not easy to produce such a reduction in battery performance.

[0184] The aqueous solution of the present embodiment contains a peroxy complex of the element α. The peroxy complex of the element α may contain the same complex as the peroxy complex described in the above-mentioned production method 1.

[0185] When the aqueous solution has the above composition, the unreacted components due to the unstable intermediates are small and precipitation is less likely to occur, so the storage stability is easily improved. In addition, it is considered that a large amount of stable peroxy complexes are maintained.

[0186] The aqueous solution of the present embodiment preferably contains Nb as the element α, and more preferably contains a niobium peroxo complex.

[0187] <Method for producing positive electrode active material for lithium secondary battery 2>

[0188] The present embodiment is a method for producing a CAM having metal composite particles and a cover covering at least a portion of the metal composite particles.

[0189] The production method of the present embodiment includes the step X of bringing the aqueous solution of the present embodiment into contact with metal composite particles to cover at least a portion of the metal composite particles. The production method including the step X is referred to as “production method 2”.

[0190] The metal composite particles used in Production Method 2 are the same as the metal composite particles described in Production Method 1 above.

[0191] Step X is to bring the aqueous solution of the present invention into contact with metal composite particles to cover at least a portion of the metal composite particles. Step X preferably includes: bringing the aqueous solution into contact with the metal composite particles by spraying the aqueous solution, drying the aqueous solution attached to the surface of the metal composite particles, and then performing a heat treatment.

[0192] The apparatus and heat treatment conditions that can implement step X are the same as those described in step B.

[0193] <Liquid lithium secondary battery>

[0194] The CAM produced according to this embodiment can be suitably used as a positive electrode active material for a liquid lithium secondary battery used in contact with an electrolyte solution.

[0195] An example of a liquid lithium secondary battery includes a positive electrode and a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolyte solution disposed between the positive electrode and the negative electrode.

[0196] <Solid lithium secondary battery>

[0197] The CAM produced according to this embodiment can be suitably used as a positive electrode active material for a solid lithium secondary battery used in contact with a solid electrolyte.

[0198] An example of a solid lithium secondary battery includes a stacked body having a positive electrode, a negative electrode, and a solid electrolyte layer.

[0199] Examples of the positive electrode, negative electrode, separator, electrolyte solution, and solid electrolyte layer used in the liquid lithium secondary battery or the solid lithium battery include materials described in WO2022 / 113904A1.

[0200] Example

[0201] The present invention will be described below by way of examples, but the present invention is not limited to these examples.

[0202] <Evaluation method of storage stability>

[0203] The storage stability of the aqueous solution (covering solution) obtained by the method described below was evaluated by the following method. At three time points, immediately after production, 24 hours after production, and 30 days after production, the aqueous solution was placed in a 500 ml or more polypropylene container (Good Boy 1000 mL, manufactured by AS ONE, shell diameter Φ96 mm) and covered with a lid, and stirred by vibrating 10 times or more within 10 seconds with an amplitude of 10 cm or more.

[0204] Afterwards, the container was placed in a place where the ambient temperature was 20 to 25°C, and a laser pointer (wavelength 532nm, output power 1mW) was irradiated from the outside of the container at a position approximately half the height of the liquid level (a range of half the height of the liquid level to ±1cm is allowed as an error range). The laser after passing through the polypropylene container and the aqueous solution was confirmed on a white paper set at a position 3cm away from the opposite side of the irradiation point.

[0205] At this time, the outline of the laser can be confirmed on white paper, and its outline is defined as "transparent state" when it is contained within the range of diameter Φ5mm. If all the conditions are "transparent" at three time points: just after manufacturing, 24 hours after manufacturing, and 30 days after manufacturing, it is evaluated as "excellent storage stability".

[0206] Store in a place controlled at 20 to 25°C without direct sunlight for 24 hours and 30 days after production.

[0207] It should be noted that when the outline of the laser on the white paper cannot be confirmed by the above method, or when the outline exceeds Φ5mm, it is the result of laser scattering by particles generated inside the solution. Therefore, it can be judged that colloidization has occurred or precipitate has been generated, and it is evaluated as "poor storage stability".

[0208] <Analysis of Aqueous Solution>

[0209] The coating liquid or aqueous solution produced by the method described below is prepared by the above-mentioned [Quantitative analysis method for Li and element α], [hydrogen peroxide (H 2 O 2 )], [Ammonium ion (NH 4 + )], [Nitrate ion (NO 3 -) quantitative analysis method], [pH determination method], the determination ratio (NH 4 + / α), the mass molar concentration of nitrate ions (NO in Table 1 3 - concentration), ratio (NO 3 - / α), the mass molar concentration value of element α (α concentration in Table 1), ratio (Li / α), pH, and the mass molar concentration of hydrogen peroxide.

[0210] <Calculation of average temperature rise rate>

[0211] The slurry temperature at the start of slurry mixing is set to T 0 (°C), the slurry temperature immediately before adding the lithium compound to the slurry is set to T 1 (℃), T 0 ~T 1 The time is set to t 1 (minutes), the average heating rate is (T 1 -T 0 ) / t 1 Calculate it using the formula.

[0212] <Calculation of average temperature drop rate>

[0213] From the maximum temperature T max (℃) to 40℃ for time t 2 (minutes) for cooling, the average cooling rate is (T max -40) / t 2 Calculate it using the formula.

[0214] <Example 1>

[0215] [Process A]

[0216] In order to carry out step A, the following apparatus was used.

[0217] A cooling water jacket and a cylindrical separable flask (content 2 L) with a discharge stopcock at the bottom were fixed on the support. A four-mouth separable reactor cover was installed to fit the separable flask. Two of the openings in the separable reactor cover were used to install a stirring blade directly connected to the motor and a thermocouple for monitoring the temperature.

[0218] The remaining two openings are used as a gas exhaust port and a raw material input port respectively.

[0219] In order to prevent the pressure in the flask from increasing significantly during the liquid synthesis, the discharge port is provided with a sufficient opening area.

[0220] The pipe for circulating the temperature-controlled (cooling / heating) cooling water is installed on the cooling water jacket.

[0221] (Process A1)

[0222] 414.00 g of pure water and 364.60 g of hydrogen peroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., concentration 30% by mass) were introduced from the raw material inlet of the apparatus having the above configuration, and 27.76 g of niobium oxide hydrate (Nb 2 O 5 ·nH 2 O, manufactured by Mitsuwa Chemicals Co., Ltd., Nb 2 O 5 The content was 79%). After the addition of the niobium oxide hydrate, the temperature was adjusted to 20° C. while being sufficiently stirred. Thus, a slurry 1 was obtained.

[0223] To the obtained slurry 1 at 20° C., 55.50 g of aqueous ammonia (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., concentration 28% by mass) was added, and the mixture was sufficiently stirred.

[0224] Then, the temperature of slurry 1 was raised to 60° C. at an average temperature rise rate of 3.1° C. / min. 7.94 g of lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to slurry 1 at 60° C., and the temperature was raised to 79° C. while being sufficiently stirred to obtain solution L-1 at a liquid temperature of 79° C.

[0225] (Process A2)

[0226] Then, the liquid temperature of solution L-1 was lowered from 79°C to 40°C at an average temperature drop rate of 0.5°C / min to obtain covering liquid 1. The mass molar concentration of Nb in the obtained covering liquid 1 was 0.22 mol / kg, and the result of measurement by the method described in the above-mentioned [Specification method for containing peroxo complex] showed that it contained peroxo complex of Nb.

[0227] The ratio of covering liquid 1 (NH 4 + / α) is 4.1, nitrate ion (NO 3 - ) has a mass molar concentration of 2.8×10 -3 mole / kg, compared with (NO 3 - / α) is 0.013, pH is 11.2, ratio (Li / α) is 1.1, mass molar concentration of α is 0.22 mol / kg, and mass molar concentration of hydrogen peroxide is 44 mol / kg.

[0228] NH 4 + / α, mass molar concentration of nitrate ions (NO 3 - concentration), mass molar concentration of α (α concentration), NO 3 - / α, pH, and Li / α are respectively described in Table 1. Table 1 also describes the following Examples and Comparative Examples.

[0229] The coating liquid 1 was evaluated according to the above-mentioned <Evaluation method of storage stability>. As a result, it was confirmed that it was transparent at three points in time: immediately after production, 24 hours after production, and 30 days after production, and was a coating liquid with excellent storage stability.

[0230] <Example 2>

[0231] [Process A]

[0232] The same apparatus as in Example 1 above was used.

[0233] (Process A1)

[0234] 413.80 g of pure water and 364.50 g of hydrogen peroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., concentration 30% by mass) were introduced from the raw material inlet of the apparatus having the above configuration, and 27.78 g of niobium oxide hydrate (Nb 2 O 5 ·nH 2 O, manufactured by Mitsuwa Chemicals Co., Ltd., Nb 2 O 5 The content was 79%). After the addition of the niobium oxide hydrate, the temperature was adjusted to 20° C. while being sufficiently stirred. Thus, slurry 2 was obtained.

[0235] To the obtained slurry 2 at 20° C., 55.20 g of aqueous ammonia (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., concentration 28% by mass) was added, and the mixture was sufficiently stirred.

[0236] Then, the temperature of slurry 2 was raised to 60° C. at an average temperature rise rate of 3.6° C. / min. 7.94 g of lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to slurry 2 at 60° C., and the temperature was raised to 80° C. while being sufficiently stirred to obtain solution L-2 having a liquid temperature of 80° C.

[0237] (Process A2)

[0238] The liquid temperature of solution L-2 was lowered from 80° C. to 40° C. at an average temperature drop rate of 0.7° C. / min to obtain covering liquid 2. The mass molar concentration of hydrogen peroxide in the obtained covering liquid 2 was 44 mol / kg.

[0239] The coating liquid 2 was evaluated according to the above-mentioned <Method for evaluating storage stability>. As a result, it was confirmed that it was transparent at three points in time: immediately after production, 24 hours after production, and 30 days after production, and was a coating liquid having excellent storage stability.

[0240] <Example 3>

[0241] [Process A]

[0242] The same apparatus as in Example 1 above was used.

[0243] (Process A1)

[0244] 414.00 g of pure water and 364.78 g of hydrogen peroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., concentration 30% by mass) were introduced from the raw material inlet of the apparatus having the above configuration, and 27.77 g of niobium oxide hydrate (Nb 2 O 5 ·nH 2 O, manufactured by Mitsuwa Chemicals Co., Ltd., Nb 2 O 5 The content was 79%). After the addition of the niobium oxide hydrate, the temperature was adjusted to 16° C. while being sufficiently stirred. Thus, slurry 3 was obtained.

[0245] To the obtained slurry 3 at 16° C., 55.20 g of aqueous ammonia (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., concentration 28% by mass) was added, and the mixture was sufficiently stirred.

[0246] Then, the temperature of slurry 3 was raised to 55° C. at an average temperature rise rate of 2.3° C. / min. 7.94 g of lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to slurry 3 at a temperature of 55° C., and the temperature was raised to 75° C. while being sufficiently stirred to obtain solution L-3 at a liquid temperature of 75° C.

[0247] (Process A2)

[0248] The liquid temperature of solution L-3 was lowered from 75°C to 40°C at an average temperature drop rate of 0.5°C / min to obtain covering liquid 3. The mass molar concentration of hydrogen peroxide in the obtained covering liquid 3 was 41 mol / kg.

[0249] The coating liquid 3 was evaluated according to the above-mentioned <Evaluation method of storage stability>. As a result, it was confirmed that it was transparent at three points in time: immediately after production, 24 hours after production, and 30 days after production, and was a coating liquid with excellent storage stability.

[0250] <Example 4>

[0251] [Process A]

[0252] The same apparatus as in Example 1 above was used.

[0253] (Process A1)

[0254] 413.79 g of pure water and 364.77 g of hydrogen peroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., concentration 30% by mass) were introduced from the raw material inlet of the apparatus having the above configuration, and 27.75 g of niobium oxide hydrate (Nb 2 O 5 ·nH 2 O, manufactured by Mitsuwa Chemicals Co., Ltd., Nb 2 O 5 The content was 79%). After the addition of the niobium oxide hydrate, the temperature was adjusted to 24° C. while being sufficiently stirred. Thus, slurry 4 was obtained.

[0255] To the obtained slurry 4 at 24° C., 55.27 g of aqueous ammonia (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., concentration 28% by mass) was added, and the mixture was sufficiently stirred.

[0256] Then, the temperature of slurry 4 was raised to 45° C. at an average temperature rise rate of 3.1° C. / min. 7.94 g of lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to slurry 4 at a temperature of 45° C., and the temperature was raised to 75° C. while being sufficiently stirred to obtain solution L-4 at a liquid temperature of 75° C.

[0257] (Process A2)

[0258] The liquid temperature of solution L-4 was lowered from 75°C to 40°C at an average temperature drop rate of 0.7°C / min to obtain covering liquid 4. The mass molar concentration of hydrogen peroxide in the obtained covering liquid 4 was 41 mol / kg.

[0259] The coating liquid 4 was evaluated according to the above-mentioned <Evaluation method of storage stability>. As a result, it was confirmed that it was transparent at three points in time: immediately after production, 24 hours after production, and 30 days after production, and was a coating liquid with excellent storage stability.

[0260] <Example 5>

[0261] [Process A]

[0262] The same apparatus as in Example 1 above was used.

[0263] (Process A1)

[0264] 413.82 g of pure water and 364.72 g of hydrogen peroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., concentration 30% by mass) were introduced from the raw material inlet of the apparatus having the above configuration, and 27.76 g of niobium oxide hydrate (Nb 2 O5 ·nH 2 O, manufactured by Mitsuwa Chemicals Co., Ltd., Nb 2 O 5 The content was 79%). After the addition of the niobium oxide hydrate, the temperature was adjusted to 21° C. while being sufficiently stirred. Thus, slurry 5 was obtained.

[0265] To the obtained slurry 5 at 21° C., 55.28 g of aqueous ammonia (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., concentration 28% by mass) was added, and the mixture was sufficiently stirred.

[0266] Then, the temperature of slurry 5 was raised to 35° C. at an average temperature rise rate of 5.3° C. / min. 7.94 g of lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to slurry 5 at a temperature of 35° C., and the temperature was raised to 73° C. while being sufficiently stirred to obtain solution L-5 at a liquid temperature of 73° C.

[0267] (Process A2)

[0268] The liquid temperature of solution L-5 was lowered from 73° C. to 40° C. at an average temperature drop rate of 0.8° C. / min to obtain covering liquid 5. The mass molar concentration of hydrogen peroxide in the obtained covering liquid 5 was 47 mol / kg.

[0269] The coating liquid 5 was evaluated according to the above-mentioned <Evaluation method of storage stability>. As a result, it was confirmed that it was transparent at three points in time: immediately after production, 24 hours after production, and 30 days after production, and was a coating liquid with excellent storage stability.

[0270] <Example 6>

[0271] [Process A]

[0272] The same apparatus as in Example 1 above was used.

[0273] (Process A1)

[0274] 413.80 g of pure water and 364.78 g of hydrogen peroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., concentration 30% by mass) were introduced from the raw material inlet of the apparatus having the above configuration, and 18.50 g of niobium oxide hydrate (Nb 2 O 5 ·nH 2 O, manufactured by Mitsuwa Chemicals Co., Ltd., Nb 2 O 5 The content was 79%). After the addition of the niobium oxide hydrate, the temperature was adjusted to 23° C. while being sufficiently stirred. Thus, slurry 6 was obtained.

[0275] To the obtained slurry 6 at 23° C., 36.85 g of aqueous ammonia (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., concentration 28% by mass) was added, and the mixture was stirred thoroughly.

[0276] Then, the temperature of slurry 6 was raised to 55° C. at an average temperature rise rate of 1.4° C. / min. 5.29 g of lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to slurry 6 at 55° C., and the temperature was raised to 58° C. while being sufficiently stirred to obtain solution L-6 at a liquid temperature of 58° C.

[0277] (Process A2)

[0278] The liquid temperature of solution L-6 was lowered from 58° C. to 40° C. at an average temperature drop rate of 0.5° C. / min to obtain covering liquid 6. The mass molar concentration of hydrogen peroxide in the obtained covering liquid 1 was 44 mol / kg.

[0279] The coating liquid 6 was evaluated according to the above-mentioned <Evaluation method of storage stability>. As a result, it was confirmed that it was transparent at three points in time: immediately after production, 24 hours after production, and 30 days after production, and was a coating liquid with excellent storage stability.

[0280] <Comparative Example 1>

[0281] [Process A]

[0282] The same apparatus as in Example 1 above was used.

[0283] (Process A1)

[0284] 413.75 g of pure water and 364.77 g of hydrogen peroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., concentration 30% by mass) were introduced from the raw material inlet of the apparatus having the above configuration, and 27.76 g of niobium oxide hydrate (Nb 2 O 5 ·nH 2 O, manufactured by Mitsuwa Chemicals Co., Ltd., Nb 2 O 5 The content was 79%). After the addition of the niobium oxide hydrate, the temperature was adjusted to 23° C. while being sufficiently stirred. Thus, a slurry 11 was obtained.

[0285] To the obtained slurry 11 at 23° C., 56.26 g of aqueous ammonia (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., concentration 28% by mass) was added, and the mixture was sufficiently stirred.

[0286] The temperature of the slurry 11 reached 73° C. due to heat generation during the reaction.

[0287] 7.94 g of lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the slurry 11 cooled to 39° C., and the mixture was stirred thoroughly to obtain a covering liquid (solution) 11 having a liquid temperature of 39° C. The molar ratio of Nb to Li (Li / Nb) in the covering liquid 11 was 1.1. The mass molar concentration of Nb in the obtained covering liquid 1 was 0.21 mol / kg, and the mass molar concentration of hydrogen peroxide was 50 mol / kg.

[0288] The coating liquid 11 was evaluated according to the above-mentioned <Evaluation method of storage stability>. As a result, at three time points, namely, immediately after production, 24 hours after production, and 30 days after production, scattering of the irradiated laser light was confirmed, the outline of the transmitted laser light could not be confirmed, and white precipitates were generated. Therefore, it was confirmed that the storage stability of the coating liquid 11 was poor.

[0289] <Comparative Example 2>

[0290] [Process A]

[0291] The same apparatus as in Example 1 above was used.

[0292] (Process A1)

[0293] 413.81 g of pure water and 364.76 g of hydrogen peroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., concentration 30% by mass) were introduced from the raw material inlet of the apparatus having the above configuration, and 27.75 g of niobium oxide hydrate (Nb 2 O 5 ·nH 2 O, manufactured by Mitsuwa Chemicals Co., Ltd., Nb 2 O 5 The content was 79%). After the addition of the niobium oxide hydrate, the temperature was adjusted to 30° C. while being sufficiently stirred. Thus, a slurry 12 was obtained.

[0294] To the obtained slurry 12 at 30° C., 55.26 g of aqueous ammonia (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., concentration 28% by mass) was added, and the mixture was sufficiently stirred.

[0295] Then, the temperature of the slurry 12 was raised to 55° C. at an average temperature rise rate of 2.3° C. / min. 6.90 g of lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the slurry 12 at a temperature of 55° C., and the temperature was raised to 76° C. while being sufficiently stirred to obtain a solution L-12 having a liquid temperature of 76° C.

[0296] (Process A2)

[0297] The liquid temperature of the solution L-12 was lowered from 76°C to 40°C at an average temperature drop rate of 0.5°C / min to obtain a covering liquid 12. The mass molar concentration of hydrogen peroxide in the obtained covering liquid 12 was 50 mol / kg.

[0298] The coating liquid 12 was evaluated according to the above-mentioned <Evaluation method of storage stability>. As a result, although it was transparent immediately after production, at two points in time, 24 hours after production and 30 days after production, the irradiated laser light was scattered in the coating liquid 12, and the outline of the transmitted laser light could not be confirmed, so it was judged that white colloidation occurred. Therefore, it can be confirmed that the storage stability of the coating liquid 12 is poor.

[0299] <Comparative Example 3>

[0300] [Process A]

[0301] The same apparatus as in Example 1 above was used.

[0302] (Process A1)

[0303] 413.80 g of pure water and 364.90 g of hydrogen peroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., concentration 30% by mass) were introduced from the raw material inlet of the apparatus having the above configuration, and 27.77 g of niobium oxide hydrate (Nb 2 O 5 ·nH 2 O, manufactured by Mitsuwa Chemicals Co., Ltd., Nb 2 O 5 The content rate was 79%). After the addition of the niobium oxide hydrate, the temperature was adjusted to 20° C. Thus, a slurry 13 was obtained.

[0304] To the obtained slurry 13 at 20° C., 55.26 g of aqueous ammonia (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., concentration 28% by mass) was added, and the mixture was stirred thoroughly.

[0305] Then, the temperature of slurry 13 was raised to 61° C. at an average temperature rise rate of 2.6° C. / min. 7.95 g of lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to slurry 13 at a temperature of 61° C., and the temperature was raised to 77° C. while being fully stirred to obtain solution L-13 at a liquid temperature of 77° C.

[0306] (Process A2)

[0307] The liquid temperature of solution L-13 was lowered from 77°C to 40°C at an average temperature drop rate of 0.9°C / min to obtain covering liquid 13. The mass molar concentration of hydrogen peroxide in the obtained covering liquid 1 was 50 mol / kg.

[0308] The coating liquid 13 was evaluated according to the above-mentioned <Evaluation method of storage stability>. As a result, although it was transparent immediately after production, at two time points, 24 hours after production and 30 days after production, scattering of the irradiated laser light was confirmed, and the outline of the transmitted laser light could not be confirmed, indicating that white colloidation occurred. Therefore, it was confirmed that the storage stability of the coating liquid 13 was poor.

[0309] From Examples 1 to 6, it was confirmed that the coating liquid produced by step A of the present invention maintained a transparent state at three points in time immediately after production, 24 hours after production, and 30 days after production, and had excellent storage stability.

[0310] The effects of the present invention were specifically confirmed in the niobium peroxo complexes of Examples 1 to 6. The intermediates generated in the synthesis process of the peroxo complexes themselves have unstable properties, but in the case of peroxo complexes, the same intermediates can be generated even when an element other than Nb is used as the element α. From the results of Examples 1 to 6, it can be inferred that when an element α other than Nb is used, a coating liquid with excellent storage stability can be obtained, similarly to the case of Nb.

[0311] In Comparative Example 1, since the liquid temperature of the solution after step A1 was lower than 40° C., the reaction was not accelerated and many unreacted components remained, and therefore a white precipitate was generated immediately after the production.

[0312] It is considered that since the ratio (Li / α) was smaller in Comparative Example 2, the intermediate was converted into Nb oxide as a precipitate before reacting with the lithium compound, and thus white colloid was generated 24 hours after the production.

[0313] It is considered that in Comparative Example 3, since the average temperature drop rate in step A2 was too fast, the peroxo complex structure could not be maintained, and white colloid was generated 24 hours after the production.

[0314] <Physical properties of aqueous solution>

[0315] The coating liquids 1 to 6 produced by the above-mentioned method are described as Examples 1 to 6 in Table 1. The coating liquids 11 to 13 produced by the above-mentioned method are described as Comparative Examples 1 to 3 in Table 1.

[0316] The physical properties of the aqueous solution are described below.

[0317] [Table 1]

[0318]

[0319] From the results described in Table 1 and the results of Examples 1 to 6 and Comparative Examples 1 to 3, it was confirmed that the aqueous solution having the composition satisfying the present invention was excellent in storage stability when used as a coating liquid.

[0320] <Example 7>

[0321] [Metal Composite Particle Manufacturing Process]

[0322] A metal composite hydroxide containing Ni and Mn is obtained by the continuous coprecipitation method described in JP-A-2002-201028.

[0323] Lithium hydroxide was weighed in a ratio of 1.15 (molar ratio) in which the amount of Li contained in the metal composite hydroxide was 1 to the total amount of Ni and Mn. The metal composite hydroxide and lithium hydroxide were mixed, calcined at 650°C for 5 hours in an oxygen atmosphere, and then calcined at 1000°C for 5 hours to obtain LiMO. The central particle size of LiMO measured by a laser diffraction particle size distribution meter (MT3300EXII manufactured by MicrotracBEL) was 5.4 μm, and the BET specific surface area of ​​LiMO measured by a nitrogen adsorption specific surface area and pore distribution measuring device (BELSORP-mini manufactured by MicrotracBEL) was 0.49 m 2 / g.

[0324] (Preparation of covering solution)

[0325] After the adjustment, 310 g of the covering liquid 1 stored for 35 days in an atmosphere controlled at 20° C. to 30° C. was collected.

[0326] [Process B]

[0327] (Covering process)

[0328] In the coating step, a rotary flow coating apparatus (MP-01 manufactured by Powrex) was used. 500 g of LiMO was pre-treated by drying at 120° C. for 10 hours in a vacuum atmosphere.

[0329] Thereafter, the coating liquid 1 was sprayed onto the metal composite particles under the following conditions.

[0330] Carrier gas: decarbonated dry air (nitrogen content 78%)

[0331] Air volume: 0.23m 3 / min

[0332] Air supply temperature: 200℃

[0333] Sprayer Type: Two-fluid nozzle (Model MPXII-LP)

[0334] Two-fluid nozzle air flow: 30NL / min

[0335] Two-fluid nozzle air pressure: 0.07MPa

[0336] Two-fluid nozzle liquid flow rate: 4.5g / min

[0337] Coating liquid spray amount: 307.1g

[0338] Rotor speed: 400rpm

[0339] After spraying, the two-fluid nozzle was stopped, and drying was carried out for 10 minutes while maintaining the air supply temperature, air supply volume, and rotor rotation speed.

[0340] (Heat treatment process)

[0341] After the above-mentioned covering process, heat treatment is performed at 300°C for 5 hours in an oxygen atmosphere to obtain CAM7.

[0342] [CAM7 review]

[0343] The results of XPS analysis of CAM7 and the above-mentioned LiMO showed that, in CAM7, at least a portion of LiMO was covered with a lithium composite oxide containing Li and Nb, and the Nb coverage of CAM7 was 90% or more.

[0344] It should be noted that the XPS analysis was performed under the following conditions.

[0345] Measurement method: X-ray photoelectron spectroscopy (XPS)

[0346] X-ray source: AlKα ray (1486.6eV)

[0347] X-ray spot diameter: 100μm

[0348] Neutralization conditions: Neutralized electron gun (acceleration voltage adjusted by element, current 100μA)

[0349] From the obtained narrow scan spectrum, the Nb coverage was calculated as follows.

[0350] Li photoelectron intensity: integral value of Li1s waveform

[0351] O photoelectron intensity: integral value of O1s waveform

[0352] Nb photoelectron intensity: integral value of Nb3d waveform

[0353] Ni photoelectron intensity: integral value of Ni2p3 / 2 waveform

[0354] Photoelectron intensity of Mn: integral value of the waveform of Mn2p1 / 2

[0355] Nb coverage = (Nb photoelectron intensity) / (Nb photoelectron intensity + Ni photoelectron intensity + Mn photoelectron intensity)) × 100

[0356] Since (Li light intensity of CAM7) / (Li light intensity of LiMO) is greater than the coverage of Nb, and (O light intensity of CAM7) / (O light intensity of LiMO) is greater than the coverage of Nb, the covering material is identified as a lithium composite oxide.

[0357] The above shows that by coating the metal composite particles with the coating liquid 1 having excellent storage stability, the coating amount on the CAM surface does not decrease even after 30 days or more from the preparation of the coating liquid, and the coated CAM can be stably produced.

[0358] Explanation of symbols

[0359] 1: device, 2: reaction tank, 3: temperature adjustment mechanism, 4: temperature control unit, 5: thermometer, 6: stirring blade, 7: inlet, 8: gas outlet.

Claims

1. An aqueous solution comprising Li, a peroxo complex of an element α, ammonium ions and nitrate ions, wherein the element α is one or more elements selected from the group consisting of Nb, Ti, Ta, Zr, W, Mo and V, and wherein the molar concentration ratio of the ammonium ions to the element α (NH 4 + / α) is less than 4.5, nitrate ion (NO 3 - ) is less than 4.0×10 -3 mоl / kg.

2. The aqueous solution according to claim 1, in, The ratio of the mass molar concentration of nitrate ions in the aqueous solution to the mass molar concentration of the element α (NO 3 - / α) is less than 0.

017.

3. The aqueous solution according to claim 1 or 2, in, In the aqueous solution, the mass molar concentration ratio of Li to element α (Li / α) exceeds 1.

0.

4. The aqueous solution according to claim 1 or 2, in, The mass molar concentration of the element α is greater than 0.10 mol / kg.

5. The aqueous solution according to claim 1 or 2, in, The pH of the aqueous solution is greater than 11.0, and the element α is Nb.

6. A method for producing a positive electrode active material for a lithium secondary battery, which is a method for producing a positive electrode active material for a lithium secondary battery having metal composite particles and a covering covering at least a portion of the metal composite particles, comprising the following step X: bringing the aqueous solution described in claim 1 or 2 into contact with the metal composite particles to cover at least a portion of the metal composite particles.

7. The method for producing a positive electrode active material for a lithium secondary battery according to claim 6, in, The metal composite particles are lithium metal composite oxides.

8. The method for producing a positive electrode active material for a lithium secondary battery according to claim 6, in, The step X includes: contacting the aqueous solution to the metal composite particles by spraying, drying the aqueous solution attached to the surfaces of the metal composite particles, and then performing a heat treatment.

9. A method for producing a positive electrode active material for a lithium secondary battery, which is a method for producing a positive electrode active material for a lithium secondary battery using metal composite particles and a covering covering at least a portion of the metal composite particles, comprising a step A for preparing a covering liquid, wherein the step A comprises: a step A1 for mixing a compound containing an element α, a solution containing hydrogen peroxide, a solution containing ammonia, and a lithium compound to prepare a solution L having a liquid temperature exceeding 40° C.; and a step A2 for cooling the solution L to below 40° C. to obtain a covering liquid, wherein the element α is one or more elements selected from the group consisting of Nb, Ti, Ta, Zr, W, Mo, and V, the covering liquid comprises a peroxo complex of the element α and Li, and in the covering liquid, the mass molar concentration ratio of the element α to Li (Li / α) exceeds 1.0, and in the step A2, the average cooling rate of the solution L from the liquid temperature to 40° C. is less than 0.9° C. / min.

10. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9, in, In the coating liquid, the mass molar concentration of the element α is greater than or equal to 0.10 mol / kg.

11. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9 or 10, in, The step A1 includes the following operation: adding a lithium compound to a slurry containing the compound containing the element α, the solution containing the hydrogen peroxide, and the solution containing ammonia and having a temperature of 35° C. or higher.

12. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9 or 10, in, The step A1 includes heating a slurry containing a compound containing the element α, a solution containing hydrogen peroxide, and a solution containing ammonia at an average heating rate of 0.9° C. / min to 10° C. / min, and adding a lithium compound to the slurry at a temperature of 35° C. or higher.

13. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9 or 10, in, The element α is Nb.

14. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9 or 10, in, The compound containing the element α is a compound containing niobium oxide, and the lithium compound is a compound containing lithium hydroxide or lithium hydroxide hydrate.

15. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9 or 10, in, After the step A, a step B of covering at least a portion of the metal composite particles with the covering liquid is provided. The step B includes spraying the covering liquid onto the metal composite particles, drying the covering liquid attached to the surfaces of the metal composite particles, and then performing a heat treatment.

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