Method for producing lithium metal composite oxide

Abstract

A method for manufacturing a lithium metal composite oxide includes a firing process in which a workpiece is fired using a firing mechanism. The workpiece is a raw material comprising a mixture of a metal composite compound and a lithium compound, or a mixture of reactants of the metal composite compound and the lithium compound. The content of Li in the workpiece is more than 5% by mass and less than 10% by mass. The firing mechanism has an inner wall, the main material of which is an alloy containing Ni and Al. The content of Ni relative to the total amount of the alloy is more than 93% by mass and less than 95% by mass, and the content of Al relative to the total amount of the alloy is more than 3% by mass and less than 5% by mass.

Description

Technical Field

[0001] This invention relates to a method for manufacturing lithium metal composite oxides.

[0002] This application claims priority based on Japanese Patent Application No. 2020-194235 filed on November 24, 2020, the contents of which are incorporated herein by reference. Background Technology

[0003] For the positive electrode active material used in the positive electrode of lithium secondary batteries, lithium metal composite oxides are used. The manufacturing method of lithium metal composite oxides includes, for example, a calcination step of calcining a mixture of a metal composite compound and a lithium compound, or a reactant of a metal composite compound and a lithium compound, etc.

[0004] In the firing process, a continuous firing furnace or a mobile firing furnace can be used.

[0005] For example, Patent Document 1 describes a method of firing using a firing mechanism with a nickel inner wall.

[0006] Existing technical documents

[0007] Patent Literature

[0008] Patent Document 1: JP-A-2019-75253 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] Conventional metal firing furnaces suffer from the problem of corrosion affecting the contact components that come into contact with the workpiece. If these components corrode, they need to be replaced, reducing production efficiency. Specifically, the contact components are the inner walls of the firing furnace. Therefore, there is a need for a method to efficiently manufacture lithium metal composite oxides that can provide high-performance lithium-ion secondary batteries.

[0011] The present invention was made in view of the above circumstances, and the object is to provide a method for efficiently manufacturing lithium metal composite oxides that can produce lithium secondary batteries with high initial discharge capacity.

[0012] Methods for solving problems

[0013] This invention includes [1] to [8].

[0014] [1] A method for manufacturing a lithium metal composite oxide, wherein in a firing process of firing a work to be fired using a firing mechanism, the work to be fired is a raw material comprising a mixture of a metal composite compound and a lithium compound, or a mixture of the reactants of the metal composite compound and the lithium compound, wherein the content of Li in the work to be fired is more than 5% by mass and less than 10% by mass, the firing mechanism has an inner wall, the main material of the inner wall is an alloy, the alloy contains Ni and Al, the content of Ni relative to the total amount of the alloy is more than 93% by mass and less than 95% by mass, and the content of Al relative to the total amount of the alloy is more than 3% by mass and less than 5% by mass.

[0015] [2] According to the manufacturing method described in [1], the lithium metal composite oxide is represented by the following general formula (I).

[0016] Li[Li x (Ni (1-y-z) Co y M z ) 1-x O2(I)

[0017] (-0.1≤x≤0.2, 0≤y≤0.5, 0≤z≤0.9, y+z<1, M represents one or more elements selected from the group consisting of Mn, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga, and V.)

[0018] [3] The manufacturing method according to [1] or [2], wherein the alloy comprises either or both of Si or Mn.

[0019] [4] According to the manufacturing method described in [3], the content of Si relative to the total amount of the alloy is 0.5% by mass or more and 2.5% by mass or less.

[0020] [5] According to the manufacturing method described in [3], the content of Mn relative to the total amount of the alloy is more than 0% by mass and less than 1.0% by mass.

[0021] [6] The manufacturing method according to any one of [1] to [5], wherein the firing temperature in the firing process is 100°C or higher and 900°C or lower.

[0022] [7] The manufacturing method according to any one of [1] to [6], wherein the firing mechanism is a rotary kiln.

[0023] [8] The manufacturing method according to any one of [1] to [7], wherein the firing process includes a pre-firing process and a formal firing process, and at least in the pre-firing process, the firing mechanism is used for firing, the firing temperature of the pre-firing process is 100°C or more and 700°C or less, and the firing temperature of the formal firing process is more than 700°C and less than 1000°C.

[0024] Invention Effects

[0025] According to the present invention, a method for efficiently manufacturing lithium metal composite oxides that yield lithium secondary batteries with high initial discharge capacity can be provided. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating an example of a lithium secondary battery.

[0027] Figure 2 This is a schematic diagram illustrating an example of an all-solid-state lithium secondary battery. Detailed Implementation

[0028] In this specification, the metal composite compound will be referred to as "MCC" below.

[0029] The lithium metal composite oxide will be referred to as "LiMO" below.

[0030] The cathode active material for lithium secondary batteries is referred to as "CAM" below.

[0031] "Ni" does not refer to nickel metal, but rather to nickel atoms. Similarly, "Co" and "Li" refer to cobalt atoms and lithium atoms, respectively.

[0032] In this specification, the initial discharge capacity of the lithium secondary battery is determined by the following method.

[0033] <Determination of Initial Discharge Capacity>

[0034] (Making of the positive electrode for lithium secondary batteries)

[0035] The LiMO manufactured by the method of this embodiment is used as a CAM. A paste-like positive electrode mixture is prepared by adding and mixing the CAM, conductive material, and binder in a ratio of CAM:conductive material:binder = 92:5:3 (mass ratio). N-methyl-2-pyrrolidone is used as the organic solvent in the preparation of the positive electrode mixture. Acetylene black is used for the conductive material. Polyvinylidene fluoride is used as the binder.

[0036] The obtained positive electrode mixture was coated onto a 40 μm thick Al foil to serve as the current collector and then vacuum-dried at 150°C for 8 hours to obtain a positive electrode for lithium secondary batteries. The electrode area of ​​this positive electrode for lithium secondary batteries was set to 1.65 cm². 2 .

[0037] (The fabrication of lithium secondary batteries)

[0038] Perform the following operations inside a glove box under an argon atmosphere.

[0039] The positive electrode for a lithium-ion secondary battery, prepared in the (Preparation of Positive Electrode for Lithium-ion Secondary Batteries) step, is placed with the aluminum foil side down on the lower cover of a component for a coin-shaped battery R2032 (manufactured by Hosen Co., Ltd.), and a separator (a porous polyethylene membrane) is placed on top. 300 μl of electrolyte is then injected. The electrolyte is prepared by dissolving LiPF6 in a 30:35:35 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate at a ratio of 1.0 mol / L.

[0040] Next, using metallic lithium as the negative electrode, the negative electrode is placed on the upper side of the laminated membrane separator, and the top cover is covered by a gasket. The lithium secondary battery (coin-shaped half-cell R2032) is then fabricated by using a seam sealing machine.

[0041] Using the lithium secondary battery manufactured by the method described above, the first discharge capacity was determined by the following method.

[0042] (Determination Method)

[0043] The electrolyte is fully impregnated into the separator and positive electrode compound layer by letting the lithium secondary battery stand at room temperature for 12 hours.

[0044] At the test temperature of 25℃, the current setting was set to 0.2CA for both charging and discharging, and constant current and constant voltage charging and discharging were performed respectively. The negative electrode was set to metallic Li, the maximum charging voltage was set to 4.3V, and the minimum discharging voltage was set to 2.5V. The discharge capacity was measured, and the obtained value was set as the "initial discharge capacity" (mAh / g).

[0045] The criteria for determining discharge capacity vary depending on the composition of the lithium metal composite oxide. Specifically, it is determined by either criterion A or criterion B described below.

[0046] Judgment Criterion A: If the initial discharge capacity is above 180mAh / g, it is evaluated as having a high initial discharge capacity.

[0047] Judgment Criterion B: If the initial discharge capacity is above 170mAh / g, it is evaluated as having a high initial discharge capacity.

[0048] In the total amount of LiMO, criterion A is used when the Ni content is above 80%, and criterion B is used when it is below 80%.

[0049] <Determination of Corrosion Rate and Growth Rate of Corrosion Products>

[0050] The feasibility of effectively manufacturing LiMO in this specification is confirmed by measuring the corrosion rate and corrosion product growth rate of a metal test piece. The metal test piece is a model of the alloy, the main material of the inner wall of the sintering apparatus. Lower values ​​for the corrosion rate and corrosion product growth rate of the metal test piece indicate higher manufacturing efficiency. The corrosion rate and corrosion product growth rate are measured using the following methods.

[0051] First, prepare a metal test piece as a model of the alloy, which is the main material of the inner wall of the firing mechanism.

[0052] Next, a predetermined amount of material to be fired is loaded onto one side of the metal test piece and fired. The material to be fired is, for example, a mixture containing MCC and lithium compounds, or a mixture of reactants of MCC and lithium compounds.

[0053] Metal test pieces are, for example, set as plate-shaped test pieces with a thickness of a few millimeters.

[0054] The firing conditions were maintained at 680°C for 12 hours under an oxygen atmosphere.

[0055] Firing is performed once or multiple times under the same conditions. In the case of multiple firings, the same conditions are performed more than twice but less than ten times. The same conditions refer to the same firing temperature, firing time, and firing atmosphere. After each firing, the resulting fired material is recovered, and the fired material is loaded before the next firing. The fired material loaded this time is the same as the fired material loaded in the first firing, which is a mixture of MCC and lithium compounds, or a mixture of reactants of MCC and lithium compounds.

[0056] The wall thickness of the unfired metal test piece and the wall thickness of the metal test piece after multiple firings were measured respectively.

[0057] The thickness of the unfired metal test piece was measured using a micrometer. This thickness was then set as L1 (mm).

[0058] The thickness of a metal test piece refers to the value measured at the center of the test piece.

[0059] When determining the wall thickness of a metal test piece after multiple firings, the metal test piece is first cut along the thickness direction at its center to obtain a cross-section. The obtained cross-section is then observed using a microscope to determine the wall thickness. This thickness is set as L2 (mm). L2 refers to the value used when measuring the wall thickness.

[0060] The difference between L1 and L2 (L1-L2) is set as the wall thickness variation (mm).

[0061] In addition, the thickness (mm) of the corrosion products formed on the surface of the metal test piece was measured using a microscope in the obtained cross-section. The thickness of the corrosion products refers to the value when the thickness of the corrosion products is measured.

[0062] (Corrosion rate)

[0063] Then, the corrosion rate is calculated from the obtained wall thickness change using the following formula.

[0064] Corrosion rate (mm / year) = [Wall thickness change (mm) × 24 × 365] / [Holding time (h) × Number of firings]

[0065] If the corrosion rate is less than 5 mm / year, it is evaluated as a slow corrosion rate, and the inner wall of the firing mechanism is not easily corroded.

[0066] (Growth rate of corrosion products)

[0067] Furthermore, the growth rate of the corrosion products can be calculated from the thickness of the obtained corrosion products using the following formula.

[0068] Corrosion product growth rate (mm / year) = [corrosion product thickness (mm) × 24 × 365] / [holding time (h) × number of firings]

[0069] The growth rate of corrosion products is sometimes determined by different criteria depending on the composition of the lithium metal composite oxide. Specifically, it is determined by either criterion 1 or criterion 2 described below.

[0070] Judgment Criterion 1: If the growth rate of corrosion products is less than 0.9 mm / year, it is evaluated as slow corrosion rate and the inner wall of the firing mechanism is not easily corroded.

[0071] Judgment Criterion 2: If the growth rate of corrosion products is less than 2.6 mm / year, it is evaluated as slow corrosion rate and the inner wall of the firing mechanism is not easily corroded.

[0072] For the total amount of LiMO, criterion 1 is used when the Li content is less than 6.5% by mass, and criterion 2 is used when the Li content is greater than 6.5% by mass.

[0073] <Method for manufacturing lithium metal composite oxides>

[0074] The LiMO manufacturing method of this embodiment includes a firing process, in which the workpiece is fired using a firing mechanism, as an essential step. Preferably, the LiMO manufacturing method includes a process for obtaining MCC and a process for obtaining a mixture. Hereinafter, the process for obtaining MCC, the process for obtaining the mixture, and the firing process will be described sequentially.

[0075] The Process of Obtaining MCC

[0076] First, prepare MCC containing metal elements other than lithium, namely Ni, and optional metals such as Co, Al, and element M.

[0077] MCC can be manufactured using either the commonly known intermittent coprecipitation method or the continuous coprecipitation method. The following section details the manufacturing method using a metal complex hydroxide containing Ni, Co, and Al as an example.

[0078] First, Ni is produced by reacting nickel salt solution, cobalt salt solution, aluminum salt solution, and complexing agent through a co-precipitation method, particularly the continuous method described in JP-A-2002-201028. (1-y-z) Co y Al z (OH)2 (where y+z<1) represents a metal complex hydroxide.

[0079] The nickel salt used as the solute in the above-mentioned nickel salt solution is not particularly limited, but for example, any one or more of nickel sulfate, nickel nitrate, nickel chloride and nickel acetate can be used.

[0080] The cobalt salt, or cobalt salt, can be one or more of the following: cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate.

[0081] The solute used in the above aluminum salt solution is the aluminum salt, such as aluminum sulfate or sodium aluminate.

[0082] The above metal salts are used in conjunction with the above Ni. (1-y-z) Co y Al z It is used in proportions corresponding to the composition of (OH)2. In addition, water is used as a solvent.

[0083] Complexing agents are compounds that can form complexes with Ni, Co, and Al ions in aqueous solution. Examples include ammonium ion donors, hydrazine, ethylenediaminetetraacetic acid, nitric acid triacetic acid, uracil diacetic acid, and glycine.

[0084] Ammonium salts such as ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, and ammonium fluoride can be listed as ammonium ion donors.

[0085] The complexing agent may be omitted. In the case where the complexing agent is included, the molar ratio of the amount of complexing agent contained in the mixture containing the nickel salt solution, cobalt salt solution, aluminum salt solution and the complexing agent, for example, relative to the total number of moles of the metal salt, is greater than 0 and less than 2.0.

[0086] In the coprecipitation method, to adjust the pH of the mixture containing nickel salt solution, cobalt salt solution, aluminum salt solution, and complexing agent, an alkaline aqueous solution is added to the mixture before the pH changes from alkaline to neutral. Sodium hydroxide or potassium hydroxide can be used as the alkaline aqueous solution.

[0087] It should be noted that the pH value in this instruction manual is defined as the value measured at a temperature of 40°C. The pH of the mixture is measured when the temperature of the mixture sampled from the reaction tank reaches 40°C.

[0088] When the temperature of the sampled mixture is below 40°C, the pH is measured by heating the mixture to 40°C.

[0089] When the temperature of the sampled mixture is above 40°C, the pH is measured after the mixture is cooled to 40°C.

[0090] If, in addition to the aforementioned nickel salt solution, cobalt salt solution, and aluminum salt solution, a complexing agent is continuously supplied to the reaction vessel, Ni, Co, and Al react to generate Ni. (1-y-z) Co y Al z (OH)2.

[0091] It can also be achieved by manufacturing Ni (1-y-z) Co y Al z The same method as (OH)2 is used to react nickel salt solution, cobalt salt solution, manganese salt solution, and complexing agent to produce Ni. (1-y-z) Co y Mn z (OH)2 (where y+z<1) represents a metal complex hydroxide.

[0092] The solute used in the above manganese salt solution is the manganese salt, and for example, any one of manganese sulfate, manganese nitrate, and manganese chloride can be used.

[0093] During the reaction, the temperature of the reaction tank is controlled within a range of, for example, above 20°C and below 80°C, preferably above 30°C and below 70°C.

[0094] Furthermore, during the reaction, the pH value in the reaction tank is controlled within a range, for example, pH 9 or higher and pH 13 or lower, preferably pH 11 or higher and pH 13 or lower.

[0095] The substances in the reaction tank should be stirred and mixed appropriately.

[0096] The reaction tanks used in continuous coprecipitation methods can be of the type that overflow in order to separate the formed reaction precipitates.

[0097] The reaction vessel can also contain an inert atmosphere. An inert atmosphere can suppress the aggregation of elements more easily oxidized than nickel, resulting in a homogeneous metal composite hydroxide.

[0098] In addition, an inert atmosphere can be maintained in the reaction tank, and in the presence of a moderate oxygen-containing atmosphere or oxidant.

[0099] When the atmosphere in the reaction tank is controlled by a gas, it is sufficient to simply circulate the specified gas in the reaction tank or directly bubble the reaction liquid.

[0100] In addition to controlling the conditions mentioned above, various gases, such as inert gases like nitrogen, argon, and carbon dioxide, oxidizing gases like air and oxygen, or mixtures thereof, can be supplied to the reaction tank to control the oxidation state of the obtained reaction products.

[0101] As the compound used to oxidize the obtained reaction product, peroxides such as hydrogen peroxide, peroxide salts such as permanganate, perchlorate, hypochlorite, nitric acid, halogen, ozone, etc. can be used.

[0102] As compounds to reduce the obtained reaction products, organic acids such as oxalic acid and formic acid, sulfites, hydrazine, etc., can be used.

[0103] After the above reaction, the resulting reaction product is washed with water and then dried to obtain MCC. Alternatively, if impurities from the mixture remain in the reaction product after washing with water alone, the reaction product may be washed with a weak acid solution or an alkaline solution containing sodium hydroxide or potassium hydroxide, as needed.

[0104] It should be noted that in the above example, nickel-cobalt-aluminum metal composite hydroxide was manufactured as an MCC, but nickel-cobalt-aluminum metal composite oxide can also be prepared.

[0105] For example, nickel-cobalt-aluminum metal composite oxides can be prepared by oxidizing nickel-cobalt-aluminum metal composite hydroxides.

[0106] The process of obtaining a mixture

[0107] The MCC obtained by the above method is mixed with a lithium compound to obtain a mixture of MCC and lithium compound.

[0108] As a lithium compound, one or more can be selected from the group consisting of lithium carbonate, lithium hydroxide, and lithium hydroxide monohydrate.

[0109] The lithium compound and MCC are mixed to obtain a mixture, taking into account the composition ratio of the final target analyte. Specifically, the lithium compound and MCC are preferably mixed in a ratio corresponding to the composition ratio of the compositional formula (I) described later.

[0110] The mixture of MCC and lithium compounds can also be heated before the firing process described later. By heating the above mixture, a mixture of raw materials containing reactants of MCC and lithium compounds can be obtained. That is, the above mixture of raw materials can also contain a portion of the reactants obtained by reacting a portion of the MCC contained in the mixture of MCC and lithium compounds with lithium compounds, and further contain MCC and lithium compounds.

[0111] The heating temperature when heating the mixture of MCC and lithium compound is, for example, above 300°C and below 700°C.

[0112] Raw materials containing a mixture of MCC and lithium compounds, or a mixture of reactants of MCC and lithium compounds, can be used as the material to be fired in the firing process described later.

[0113] The Li content of the calcined material is more than 5% by mass and less than 10% by mass, preferably more than 5.1% by mass and less than 9.9% by mass, and more preferably more than 5.2% by mass and less than 9.8% by mass.

[0114] Furthermore, in one aspect of the present invention, the preferred content of Li in the calcined material can be listed as more than 5% by mass and less than 9.0% by mass, more than 5% by mass and less than 8.0% by mass, and more than 5% by mass and less than 7.0% by mass.

[0115] If the Li content of the calcined material exceeds the aforementioned lower limit, it is possible to manufacture a LiMO with increased lithium-ion conductivity. Such a LiMO can improve the initial efficiency of a lithium secondary battery.

[0116] If the Li content of the material being fired is below the aforementioned upper limit, the inner wall of the firing mechanism becomes less prone to corrosion. This reduces the need for component replacements in the firing mechanism, thus improving production efficiency.

[0117] The Li content in the calcined material was determined by the following method.

[0118] <Determination of Li content in calcined material>

[0119] Compositional analysis of the calcined product can be performed by dissolving the powder in hydrochloric acid and then measuring it using an ICP emission spectrometer. For example, the SPS3000 manufactured by SII Nano Technology Co., Ltd. can be used as an ICP emission spectrometer. The content of Li in the calcined product is determined by ICP emission spectrometry. The "Li content in the calcined product" is the ratio of Li to the total amount of metallic elements contained in the calcined product.

[0120] Firing Process

[0121] The above-mentioned material is fired using a firing mechanism.

[0122] (Firing mechanism)

[0123] The firing mechanism has an inner wall that is in direct contact with the object being fired.

[0124] Firing mechanisms can be exemplified by rotary kilns or roller hearth furnaces. In the case of a rotary kiln, the inner wall is, for example, a cylindrical furnace wall. In the case of a roller hearth furnace, the inner wall is, for example, the inner wall of a firing vessel.

[0125] The firing mechanism is preferably a rotary kiln. The rotary kiln can be either continuous or intermittent.

[0126] The main material of the inner wall is an alloy.

[0127] In this manual, "main material" refers to the material that makes up the largest portion of the inner wall.

[0128] The following is an explanation of the main material of the inner wall, namely the alloy.

[0129] The alloy contains Ni and Al.

[0130] The Ni content relative to the total alloy content is 93% by mass or more and 95% by mass or less. The Al content relative to the total alloy content is 3% by mass or more and 5% by mass or less.

[0131] If the content of Ni relative to the total amount of the alloy is above the lower limit and below the upper limit, the inner wall of the sintering mechanism becomes less susceptible to corrosion by lithium compounds.

[0132] It can be assumed that if the Al content relative to the total alloy content is above the aforementioned lower limit, an alumina film will form on the surface of the inner wall. This alumina film functions as a protective film, making the inner wall of the firing mechanism less susceptible to corrosion by lithium compounds. If the Al content relative to the total alloy content is below the aforementioned upper limit, it becomes easier to alloy with Ni.

[0133] If the main material is an alloy containing Ni and Al in a specific ratio, the inner wall of the firing mechanism becomes less susceptible to corrosion by lithium compounds contained in the material being fired. Therefore, it is less necessary to replace inner wall components or repair the firing mechanism, enabling the efficient and long-term production of LiMO that can provide lithium secondary batteries with high initial discharge capacity.

[0134] The alloy may also contain either or both of Si or Mn.

[0135] When the alloy contains Si, the content of Si relative to the total amount of the alloy as the main material is preferably 0.5% by mass or more and 2.5% by mass or less, more preferably 0.7% by mass or more and 2.3% by mass or less.

[0136] When the alloy contains Mn, the content of Mn relative to the total amount of the alloy as the main material is preferably more than 0% by mass and less than 1.0% by mass, more preferably more than 0.2% by mass and less than 0.8% by mass.

[0137] When the alloy contains both Si and Mn, the total amount of Si and Mn relative to the total amount of the alloy as the main material is preferably more than 0.5% by mass and less than 3.5% by mass. It can be considered that if Si or Mn is included, the film formed on the surface of the inner wall is less likely to be damaged.

[0138] The following are examples of alloys used as the main material.

[0139] Alloys formed from Ni and Al

[0140] Alloys formed from Ni, Al and Si

[0141] Alloys formed from Ni, Al and Mn

[0142] Alloys formed from Ni, Al, Si and Mn

[0143] The composition of the alloy was determined by the following method.

[0144] <Compositional Analysis of Alloys>

[0145] The compositional analysis of the main material of the inner wall of the firing mechanism, i.e., the alloy, was performed using a fluorescence X-ray analysis device. This allowed for the quantitative determination of the amount of metallic elements in the alloy. Examples of metallic elements contained in the alloy include, for example, Ni, Al, Si, and Mn.

[0146] As a fluorescence X-ray analysis device, for example, the X-MET8000, manufactured by Hitachi High-Tech, can be used. Alternatively, a glow discharge quality analyzer can be used for quantification.

[0147] The firing conditions can be either single-stage or two-stage firing. LiMO is obtained through either single-stage or two-stage firing.

[0148] A single firing is a firing process in which the object to be fired is held at a specific firing temperature for a certain period of time.

[0149] Two-stage firing, for example, involves firing the object to be fired through a pre-firing process, and then firing the pre-fired object through a formal firing process. The firing temperatures of the pre-firing process and the formal firing process are different. The firing process at a higher temperature than the pre-firing process is designated as the formal firing process.

[0150] The pre-firing process preferably uses the aforementioned firing mechanism. By using the aforementioned firing mechanism in the pre-firing process, LiMO that can provide high initial discharge capacity for lithium secondary batteries can be produced efficiently over a long period of time.

[0151] The formal firing process can be carried out using the firing mechanism described above, or it can be changed to other firing mechanisms. Since the formal firing is performed at a higher temperature than the pre-firing, the inner wall is easily damaged during firing. In this case, the inner wall is easily corroded by lithium compounds contained in the workpiece. Therefore, the formal firing process is preferably carried out using the firing mechanism described above.

[0152] In the case of a single firing, the firing temperature is preferably above 100℃ and below 1000℃.

[0153] In the case of two-stage firing, the firing temperature in either the pre-firing process or the formal firing process is preferably above 100°C and below 1000°C.

[0154] The firing temperature of the pre-firing process is preferably above 100℃ and below 700℃, and the firing temperature of the formal firing process is preferably set above 700℃ and below 1000℃.

[0155] The firing time is preferably set to a total time of 1 hour or more and 30 hours or less, from the start of heating to the end of holding the temperature. The heating rate for the heating process to reach the maximum holding temperature is preferably 180°C / hour or more and 2000°C / hour or less, more preferably 200°C / hour or more and 1900°C / hour or less, and particularly preferably 250°C / hour or more and 1800°C / hour or less.

[0156] The maximum holding temperature mentioned in this specification is the highest temperature at which the atmosphere inside the firing furnace is held during the firing process; it refers to the firing temperature during the firing process. In the case of a firing process with multiple heating steps, the maximum holding temperature refers to the highest temperature in each firing step.

[0157] The heating rate in this specification is calculated from the time from the start of heating in the firing apparatus to the time until the maximum holding temperature is reached, and the temperature difference from the initial temperature at the start of heating in the firing furnace of the firing apparatus to the maximum holding temperature.

[0158] The oxygen concentration of the firing atmosphere in the firing process is preferably 10% by volume or more. Examples of oxygen concentrations in the firing atmosphere during the firing process include 50% by volume or more and 60% by volume or more.

[0159] In the case of two-stage firing, the firing conditions for the pre-firing process and the formal firing process are preferably implemented in the following combination.

[0160] (Pre-firing process)

[0161] Firing temperature: above 600℃ and below 700℃

[0162] Firing time: 1 hour or more but less than 15 hours

[0163] Firing atmosphere: Oxygen atmosphere

[0164] (Formal firing process)

[0165] Firing temperature: above 700℃ but below 800℃

[0166] Firing time: 5 hours or more but less than 7 hours

[0167] Firing atmosphere: Oxygen atmosphere

[0168] Washing process

[0169] After firing, the resulting product can be washed. For washing, pure water or an alkaline washing solution can be used.

[0170] "composition"

[0171] The LiMO produced by the manufacturing method of this embodiment is preferably a substance represented by the following general formula (I).

[0172] Li[Li x (Ni (1-y-z) Co y M z ) 1-x O2(I)

[0173] (-0.1≤x≤0.2, 0≤y≤0.5, 0≤z≤0.9, y+z<1, M represents one or more elements selected from the group consisting of Mn, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga, and V.)

[0174] (x)

[0175] From the viewpoint of obtaining a lithium secondary battery with high cycle characteristics, x is preferably greater than 0, more preferably greater than 0.01, and even more preferably greater than 0.02. Furthermore, from the viewpoint of obtaining a lithium secondary battery with a higher initial coulombic effect, x is preferably less than 0.1, more preferably less than 0.08, and even more preferably less than 0.06.

[0176] The upper and lower limits of x can be combined arbitrarily.

[0177] As examples of combinations, x can be listed as greater than 0 and less than 0.1, greater than 0.01 and less than 0.08, and greater than 0.02 and less than 0.06.

[0178] High cycle performance refers to high discharge capacity retention.

[0179] (y)

[0180] From the viewpoint of obtaining a lithium secondary battery with low internal resistance, y is preferably 0.005 or more, more preferably 0.01 or more, and even more preferably 0.05 or more. Furthermore, from the viewpoint of obtaining a lithium secondary battery with high thermal stability, y is preferably 0.4 or less, more preferably 0.35 or less, and even more preferably 0.33 or less.

[0181] The upper and lower limits of y can be combined arbitrarily.

[0182] As examples of combinations, y can be listed as greater than 0.005 and less than 0.4, greater than 0.01 and less than 0.35, and greater than 0.05 and less than 0.33.

[0183] (z)

[0184] Furthermore, from the viewpoint of obtaining a lithium secondary battery with high cycle characteristics, z is preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.03 or more. Furthermore, from the viewpoint of obtaining a lithium secondary battery with high storage characteristics at high temperatures (e.g., 60°C), z is preferably 0.89 or less, more preferably 0.88 or less, and even more preferably 0.87 or less.

[0185] The upper and lower limits of z can be combined arbitrarily.

[0186] As examples of combinations, z can be listed as 0.01 or higher and 0.89 or lower, 0.02 or higher and 0.88 or lower, and 0.03 or higher and 0.87 or lower.

[0187] M represents one or more elements selected from the group consisting of Mn, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga, and V.

[0188] Furthermore, from the viewpoint of obtaining a lithium secondary battery with high cycle characteristics, M is preferably selected from one or more elements selected from the group consisting of Mn, Ti, Mg, Al, W, B, Zr and Nb. From the viewpoint of obtaining a lithium secondary battery with high thermal stability, M is preferably selected from one or more elements selected from the group consisting of Mn, Al, W, B, Zr and Nb.

[0189] <Composition Analysis>

[0190] Compositional analysis of LiMO can be performed by dissolving the obtained LiMO powder in hydrochloric acid and then using an ICP emission spectrometer.

[0191] As an ICP emission spectroscopy analysis device, for example, the SPS3000 manufactured by SII Nano Technology Co., Ltd. can be used.

[0192] <Lithium Metal Composite Oxides>

[0193] The LiMO manufactured by the manufacturing method of this embodiment can be used as a CAM.

[0194] <Lithium-ion secondary batteries>

[0195] The structure of a suitable lithium secondary battery when using LiMO manufactured by the manufacturing method of this embodiment as a CAM will be described.

[0196] Furthermore, a suitable positive electrode for a lithium secondary battery will be described when using LiMO manufactured by the manufacturing method of this embodiment as a CAM. Hereinafter, the positive electrode for a lithium secondary battery will sometimes be referred to as a positive electrode.

[0197] Furthermore, a suitable lithium secondary battery for use as a positive electrode will be explained.

[0198] An example of a suitable lithium secondary battery using LiMO manufactured by the manufacturing method of this embodiment as a CAM has a positive electrode and a negative electrode, a separator sandwiched between the positive and negative electrodes, and an electrolyte disposed between the positive and negative electrodes.

[0199] An example of a lithium secondary battery includes a positive electrode and a negative electrode, a separator sandwiched between the positive and negative electrodes, and an electrolyte disposed between the positive and negative electrodes.

[0200] Figure 1 This is a schematic diagram illustrating an example of a lithium secondary battery. For example, a cylindrical lithium secondary battery 10 is manufactured as shown below.

[0201] First, such as Figure 1 As shown, an electrode assembly 4 is formed by stacking and winding a pair of strip-shaped diaphragms 1, a strip-shaped positive electrode 2 with a positive electrode lead 21 at one end, and a strip-shaped negative electrode 3 with a negative electrode lead 31 at one end in the order of diaphragm 1, positive electrode 2, diaphragm 1, and negative electrode 3.

[0202] Next, after accommodating the electrode assembly 4 and an insulator (not shown) in the battery can 5, the bottom of the can is sealed, and the electrolyte 6 is impregnated into the electrode assembly 4, with the electrolyte disposed between the positive electrode 2 and the negative electrode 3. Furthermore, by sealing the upper part of the battery can 5 with a top insulator 7 and a sealing body 8, a lithium secondary battery 10 can be manufactured.

[0203] As for the shape of the electrode assembly 4, for example, the cross-sectional shape when the electrode assembly 4 is cut perpendicularly to the winding axis can be a circle, an ellipse, a rectangle, or a columnar shape such as a rectangle obtained by rounding the corners.

[0204] Furthermore, the shape of the lithium secondary battery having such an electrode assembly 4 can adopt the shape specified in the International Electrotechnical Commission (IEC) standard for batteries, namely IEC 60086, or JIS C 8500. For example, cylindrical or square shapes can be listed.

[0205] Furthermore, lithium secondary batteries are not limited to the above-described wound type configuration, but can also be of a stacked type configuration obtained by repeatedly overlapping a positive electrode, a separator, a negative electrode, and a separator. Examples of stacked lithium secondary batteries include so-called coin-type batteries, button-type batteries, or paper-type (or sheet-type) batteries.

[0206] The following sections will explain each component in turn.

[0207] (positive electrode)

[0208] The positive electrode can be manufactured by first adjusting the positive electrode mixture containing CAM, conductive material and binder, and then loading the positive electrode mixture onto the positive electrode current collector.

[0209] (Conductive materials)

[0210] For the conductive material in the positive electrode, carbon materials can be used. Examples of carbon materials include graphite powder, carbon black (e.g., acetylene black), and fibrous carbon materials.

[0211] The proportion of conductive material in the positive electrode mixture is preferably 5 parts by mass and 20 parts by mass relative to CAM100.

[0212] (Adhesive)

[0213] Thermoplastic resins can be used as the binder in the positive electrode. Examples of such thermoplastic resins include polyimide resins, fluoropolymers, polyolefin resins, and resins described in WO2019 / 098384A1 or US2020 / 0274158A1.

[0214] Polyimide resins, for example, are polyvinylidene fluoride (hereinafter, sometimes referred to as PVdF).

[0215] Fluoropolymers, for example, are polytetrafluoroethylene (PTFE).

[0216] Polyolefin resins include, for example, polyethylene and polypropylene.

[0217] (Positive current collector)

[0218] For the positive current collector of the positive electrode, a strip-shaped component made of metal materials such as Al, Ni, and stainless steel can be used.

[0219] As a method for supporting a positive electrode agent on a positive current collector, the following method can be listed: the positive electrode agent is pasteurized using an organic solvent, the resulting positive electrode agent paste is applied to at least one side of the positive current collector and dried, and then an electrode pressing process is performed to bond it.

[0220] In the case of pasteurizing the positive electrode mixture, N-methyl-2-pyrrolidone (hereinafter, sometimes referred to as NMP) can be listed as a usable organic solvent.

[0221] Methods for applying a paste of positive electrode agent to the positive electrode current collector include, for example, slot extrusion coating, screen coating, curtain coating, scraper coating, gravure coating, and electrostatic spraying.

[0222] The positive electrode can be manufactured using the methods listed above.

[0223] (negative electrode)

[0224] The negative electrode of a lithium secondary battery only needs to be capable of lithium-ion doping and dedoping at a lower potential than that of the positive electrode. Examples include electrodes formed by a negative electrode mixture containing negative electrode active material supported on a negative electrode current collector, and electrodes formed solely by negative electrode active material.

[0225] (Negative electrode active material)

[0226] Examples of negative electrode active materials include carbon materials, chalcogenides (oxides, sulfides, etc.), nitrides, metals or alloys, and materials that can be doped and dedoped with lithium ions at a lower potential than that of the positive electrode.

[0227] Carbon materials that can be used as negative electrode active materials include natural graphite, artificial graphite, coke, carbon black, carbon fiber, and sintered organic polymer compounds.

[0228] Oxides that can be used as negative electrode active materials include SiO2, SiO, and SiO2. x (where x is a positive real number) represents the oxide of silicon; SnO2, SnO, etc. x (where x is a positive real number) represents the tin oxide; Li4Ti5O 12 Metal composite oxides containing lithium and titanium, etc.

[0229] In addition, lithium metal, silicon metal, and tin metal can be listed as metals that can be used as negative electrode active materials.

[0230] The materials described in WO2019 / 098384A1 or US2020 / 0274158A1 can also be used as materials that can be used as negative electrode active materials.

[0231] These metals or alloys, for example, after being processed into foil, are primarily used as electrodes on their own.

[0232] Among the aforementioned negative electrode active materials, carbon materials with natural graphite, artificial graphite, or other graphite as the main component are preferred. This is because: during charging, the potential of the negative electrode remains essentially unchanged from the uncharged state to the fully charged state (good potential flatness), the average discharge potential is low, and the capacity retention rate during repeated charge and discharge is high (good cycle characteristics). The shape of the carbon material can be, for example, any of the following: flakes like natural graphite, spheres like mesophase carbon microspheres, fibers like graphitized carbon fibers, or aggregates of micropowder.

[0233] The aforementioned negative electrode mixture may also contain a binder as needed. Examples of binders include thermoplastic resins, specifically PVdF, thermoplastic polyimide, carboxymethyl cellulose (hereinafter, sometimes referred to as CMC), styrene-butadiene rubber (hereinafter, sometimes referred to as SBR), polyethylene, and polypropylene.

[0234] (Negative current collector)

[0235] As a negative electrode current collector, examples include strip-shaped components made of metallic materials such as Cu, Ni, and stainless steel.

[0236] As a method for loading the negative electrode agent onto such a negative electrode current collector, similar to the case of the positive electrode, methods such as press molding, paste formation using solvents, coating onto the negative electrode current collector, drying, pressing, and crimping can be listed.

[0237] (Septum)

[0238] For example, the separator used in lithium-ion batteries can be made of materials such as polyethylene, polypropylene, or other polyolefin resins, fluoropolymers, or nitrogen-containing aromatic polymers, forming porous membranes, nonwoven fabrics, or woven fabrics. Furthermore, two or more of these materials can be used to form the separator, or these materials can be layered to form the separator. Additionally, the separators described in JP-A-2000-030686 and US20090111025A1 can also be used.

[0239] (Electrolyte)

[0240] The electrolyte in a lithium secondary battery contains electrolytes and organic solvents.

[0241] Lithium salts such as LiClO4, LiPF6, and LiBF4 can be used as electrolytes in electrolyte solutions, or mixtures of two or more of these can be used.

[0242] In addition, as organic solvents contained in the electrolyte, carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate can be used.

[0243] As organic solvents, it is preferable to use a mixture of two or more of them. Among them, a mixed solvent containing carbonates is preferred, and a mixed solvent of cyclic carbonates and non-cyclic carbonates and a mixed solvent of cyclic carbonates and ethers is even more preferred.

[0244] Furthermore, as an electrolyte, since the safety of the resulting lithium secondary battery is improved, it is preferable to use an electrolyte containing fluorine-containing lithium salts such as LiPF6 and organic solvents with fluorine substituents.

[0245] The electrolytes and organic solvents contained in the electrolyte may also be those described in WO2019 / 098384A1 or US2020 / 0274158A1.

[0246] <All-solid-state lithium secondary battery>

[0247] Next, the structure of the all-solid-state lithium secondary battery will be explained, and the all-solid-state lithium secondary battery having LiMO manufactured by the manufacturing method of this embodiment as the positive electrode of the CAM of the all-solid-state lithium secondary battery and the all-solid-state lithium secondary battery having the positive electrode will also be explained.

[0248] Figure 2 This is a schematic diagram illustrating an example of an all-solid-state lithium secondary battery. Figure 2 The all-solid-state lithium secondary battery 1000 shown includes a laminate 100 having a positive electrode 110, a negative electrode 120, and a solid electrolyte layer 130, and an outer packaging 200 housing the laminate 100. Furthermore, the all-solid-state lithium secondary battery 1000 can also be a bipolar structure with a current collector and a negative electrode active material disposed on both sides of the current collector. As a specific example of a bipolar structure, the structure described in JP-A-2004-95400 can be cited. The materials constituting each component are described below.

[0249] The laminate 100 may also have an external terminal 113 connected to the positive current collector 112 and an external terminal 123 connected to the negative current collector 122. In addition, the all-solid-state lithium secondary battery 1000 may also have a separator between the positive electrode 110 and the negative electrode 120.

[0250] The all-solid-state lithium secondary battery 1000 further includes an insulator (not shown) that insulates the laminate 100 from the outer packaging 200, and a seal (not shown) that seals the opening 200a of the outer packaging 200.

[0251] The outer packaging 200 can be a container formed from a highly corrosion-resistant metal material such as aluminum, stainless steel, or nickel-plated steel. Alternatively, the outer packaging 200 can also be a container formed by processing a laminated film with at least one side treated to be corrosion-resistant into a bag shape.

[0252] The shapes of the all-solid-state lithium secondary battery 1000 can include, for example, coin type, button type, paper type (or sheet type), cylindrical type, square type, or laminated type (bag type).

[0253] The all-solid-state lithium secondary battery 1000 is illustrated as an example having a single stack 100, but this embodiment is not limited to this. The all-solid-state lithium secondary battery 1000 may also be configured such that the stack 100 is used as a unit cell and multiple unit cells (stacks 100) are sealed inside the outer packaging 200.

[0254] The following sections will explain each component in turn.

[0255] (positive electrode)

[0256] The positive electrode 110 has a positive electrode active material layer 111 and a positive electrode current collector 112.

[0257] The positive electrode active material layer 111 includes the aforementioned CAM and solid electrolyte. Furthermore, the positive electrode active material layer 111 may also include conductive materials and adhesives.

[0258] (Solid electrolyte)

[0259] The solid electrolyte contained in the positive electrode active material layer 111 can be a solid electrolyte that is known to be used in all-solid-state lithium secondary batteries and has lithium-ion conductivity. Inorganic electrolytes and organic electrolytes can be listed as such solid electrolytes.

[0260] As inorganic electrolytes, examples include oxide-based solid electrolytes, sulfide-based solid electrolytes, and hydride-based solid electrolytes.

[0261] Polymer-based solid electrolytes can be listed as examples of organic electrolytes.

[0262] As electrolytes, compounds described in WO2020 / 208872A1, US2016 / 0233510A1, US2012 / 0251871A1, and US2018 / 0159169A1 can be listed, for example, the following compounds.

[0263] (Oxide-based solid electrolyte)

[0264] Examples of oxide-based solid electrolytes include perovskite oxides, NASICON oxides, LISICON oxides, and garnet oxides. Specific examples of each oxide can be found in compounds described in WO2020 / 208872A1, US2016 / 0233510A1, and US2020 / 0259213A1, such as the following compounds.

[0265] As a garnet-type oxide, Li7La3Zr2O can be listed as an example. 12 Li-La-Zr oxides, such as LLZ (also known as LLZ).

[0266] Oxide-based solid electrolytes can be either crystalline or amorphous materials.

[0267] (Sulfide-based solid electrolyte)

[0268] As sulfide-based solid electrolytes, examples include Li₂S-P₂S₅ compounds, Li₂S-SiS₂ compounds, Li₂S-GeS₂ compounds, Li₂S-B₂S₃ compounds, LiI-Si₂S-P₂S₅ compounds, LiI-Li₂S-P₂O₅ compounds, LiI-Li₃PO₄-P₂S₅ compounds, and Li 10 GeP2S 12 wait.

[0269] It should be noted that in this specification, the term "liquid-based solid electrolyte" is used as a general term for solid electrolytes that mainly contain raw materials such as "Li2S" and "P2S5" as described before "liquid-based electrolyte". For example, for Li2S-P2S5-based compounds, it includes solid electrolytes that mainly contain Li2S and P2S5, and further contain other raw materials. The proportion of Li2S contained in Li2S-P2S5-based compounds is, for example, 50 to 90% by mass relative to the total Li2S-P2S5-based compounds. The proportion of P2S5 contained in Li2S-P2S5-based compounds is, for example, 10 to 50% by mass relative to the total Li2S-P2S5-based compounds. In addition, the proportion of other raw materials contained in Li2S-P2S5-based compounds is, for example, 0 to 30% by mass relative to the total Li2S-P2S5-based compounds. Furthermore, for Li2S-P2S5-based compounds, it also includes solid electrolytes with different mixing ratios of Li2S and P2S5.

[0270] As compounds in the Li2S-P2S5 series, examples include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, and Li2S-P2S5-LiI-LiBr.

[0271] Examples of Li2S-SiS2 compounds include Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, and Li2S-SiS2-P2S5-LiCl.

[0272] Examples of Li2S-GeS2 compounds include Li2S-GeS2 and Li2S-GeS2-P2S5.

[0273] Sulfide-based solid electrolytes can be either crystalline or amorphous materials.

[0274] Two or more solid electrolytes may be used together without impairing the effectiveness of the invention.

[0275] (Conductive materials and adhesives)

[0276] As the conductive material in the positive electrode active material layer 111, the materials described in the above-described (conductive material) section can be used. Furthermore, the proportion of the conductive material in the positive electrode mixture can also be the proportion described in the above-described (conductive material) section. Additionally, as the binder in the positive electrode, the materials described in the above-described (binder) section can be used.

[0277] (Positive current collector)

[0278] The positive current collector 112 of the positive electrode 110 can be made of the material described above (positive current collector).

[0279] One method for loading the positive electrode active material layer 111 onto the positive electrode current collector 112 is to press-form CAM111 onto the positive electrode current collector 112. For press-forming, cold pressing or hot pressing can be used.

[0280] Alternatively, a positive electrode paste can be prepared by using an organic solvent to paste a mixture of CAM, solid electrolyte, conductive material and adhesive. The obtained positive electrode paste is then coated on at least one surface of the positive electrode current collector 112 and dried, pressed and bonded, thereby enabling the positive electrode active material layer 111 to be supported on the positive electrode current collector 112.

[0281] Alternatively, a positive electrode paste can be prepared by using an organic solvent to paste a mixture of CAM, solid electrolyte, and conductive material. The obtained positive electrode paste is then coated onto at least one surface of the positive electrode current collector 112 and dried and sintered, thereby enabling the positive electrode active material layer 111 to be supported on the positive electrode current collector 112.

[0282] The organic solvent that can be used in the positive electrode mixture is the same organic solvent that can be used in the case of pasteurizing the positive electrode mixture as described above in (positive electrode current collector).

[0283] As a method for coating the positive electrode mixture onto the positive electrode current collector 112, the method described above (positive electrode current collector) can be cited as an example.

[0284] The positive electrode 110 can be manufactured using the methods listed above. Examples of specific material combinations used in the positive electrode 110 include the CAM described above combined with the solid electrolyte, binder, and conductive material listed in Tables 1-3.

[0285] [Table 1]

[0286]

[0287] [Table 2]

[0288]

[0289] [Table 3]

[0290]

[0291] (negative electrode)

[0292] The negative electrode 120 has a negative electrode active material layer 121 and a negative electrode current collector 122. The negative electrode active material layer 121 contains a negative electrode active material. In addition, the negative electrode active material layer 121 may also contain a solid electrolyte and a conductive material. The negative electrode active material, negative electrode current collector, solid electrolyte, conductive material, and binder may be the substances described above.

[0293] As a method for loading the negative electrode active material layer 121 onto the negative electrode current collector 122, similar to the case of the positive electrode 110, the following methods can be listed: using a pressure molding method; applying a paste-like negative electrode mixture containing the negative electrode active material onto the negative electrode current collector 122, drying it, pressing and bonding it; and applying a paste-like negative electrode mixture containing the negative electrode active material onto the negative electrode current collector 122, drying it, and then sintering it.

[0294] (Solid electrolyte layer)

[0295] The solid electrolyte layer 130 has the aforementioned solid electrolyte.

[0296] The solid electrolyte layer 130 can be formed by depositing an inorganic solid electrolyte on the surface of the positive electrode active material layer 111 of the positive electrode 110 by sputtering.

[0297] Furthermore, the solid electrolyte layer 130 can be formed by coating the surface of the positive electrode active material layer 111 of the positive electrode 110 with a paste-like mixture containing solid electrolyte and then drying it. Alternatively, after drying, it can be pressed and further pressed by cold isostatic pressing (CIP) to form the solid electrolyte layer 130.

[0298] The laminate 100 can be manufactured by laminating a negative electrode 120 in such a way that the surface of the negative electrode active material layer 121 is in contact with the surface of the solid electrolyte layer 130, which is disposed on the positive electrode 110 as described above, using a known method.

[0299] Example

[0300] The present invention will now be described in further detail through embodiments.

[0301] <Composition Analysis>

[0302] The compositional analysis of LiMO was performed using the methods described in the above section on compositional analysis.

[0303] <Determination of Li content in calcined material>

[0304] The Li content in the calcined product is determined by the method described in the above-mentioned <Determination of Li content in the calcined product>.

[0305] <Compositional Analysis of Alloys>

[0306] The compositional analysis of the alloys or metals contained in the firing mechanism is carried out by the methods described in the above-mentioned <Compositional Analysis of Alloys>.

[0307] <Determination of Corrosion Rate and Growth Rate of Corrosion Products>

[0308] The corrosion rate was determined using the method described in the section on "Determination of Corrosion Rate and Growth Rate of Corrosion Products".

[0309] Specifically, as metal test pieces, prepare the following metal test pieces 1 to 3.

[0310] Metal test pieces 1 to 3 are set to dimensions of 20 mm in length, 25 mm in width, and 3 mm in thickness.

[0311] Metal test piece 1 is a metal test piece containing 94% by mass of Ni, 4% by mass of Al, 1.5% by mass of Si, and 0.5% by mass of Mn.

[0312] Metal test piece 2 is a metal test piece containing 62% by mass of Ni, 22% by mass of Cr, 14% by mass of W, and 2% by mass of Mo.

[0313] Metal test piece 3 is a metal test piece with a Ni content of 100% by mass.

[0314] <Determination of Initial Discharge Capacity>

[0315] The initial discharge capacity of the lithium secondary battery was determined by the method described in the above-mentioned "Determination of Initial Discharge Capacity".

[0316] <Example 1>

[0317] After adding water to the reaction tank equipped with a stirrer and an overflow pipe, add an aqueous solution of sodium hydroxide and maintain the liquid temperature at 50°C.

[0318] A mixed raw material solution was prepared by mixing nickel sulfate aqueous solution, cobalt sulfate aqueous solution and aluminum sulfate aqueous solution in an atomic ratio of Ni:Co:Al of 88:9:3.

[0319] Next, the mixed raw material solution and ammonium sulfate aqueous solution were continuously added to the reaction tank under stirring as a complexing agent. Sodium hydroxide aqueous solution was added dropwise in a timely manner to make the pH of the solution in the reaction tank 11.6 (measured at a liquid temperature of 40°C) to obtain nickel-cobalt-aluminum composite hydroxide.

[0320] Nickel-cobalt-aluminum composite hydroxide 1 was obtained by washing the nickel-cobalt-aluminum composite hydroxide, dehydrating it with a centrifuge, separating it, and drying it at 105°C.

[0321] Nickel-cobalt-aluminum composite hydroxide 1 and lithium hydroxide monohydrate powder were weighed and mixed in a molar ratio of Li / (Ni+Co+Al)=1.10 to obtain calcined material 1.

[0322] The Li content in calcined product 1 was 6.3% by mass.

[0323] Then, using the inner wall model of the firing mechanism, the workpiece 1 is fired in a firing furnace with plates of alloy 1 inside.

[0324] Alloy 1 uses an alloy with Ni content of 94% by mass, Al content of 4% by mass, Si content of 1.5% by mass, and Mn content of 0.5% by mass.

[0325] The object to be fired 1 is placed on the alloy 1 and pre-fired. At this time, the object to be fired 1 is fired in a state that is in contact with the alloy 1 but not in contact with the inner wall of the firing furnace.

[0326] The pre-firing conditions were set as follows: oxygen atmosphere, 680°C, 12 hours. Then, the obtained pre-firing material was formally fired at 740°C for 6 hours in an oxygen atmosphere, and then sieved to obtain the LiMO of Example 1.

[0327] (Evaluation of corrosion rate and growth rate of corrosion products)

[0328] Furthermore, 3g of the aforementioned calcined material 1 was placed on one side of a metal test piece 1 and calcined at 680°C for 12 hours in an oxygen atmosphere. After calcination, the resulting calcined material was recovered, and a new calcined material 1 was loaded and calcined under the same conditions. This process was repeated 7 times to evaluate the corrosion rate and the growth rate of corrosion products. In Example 1, the total number of calcinations was 8.

[0329] <Comparative Example 1>

[0330] LiMO of Comparative Example 1 was obtained in the same manner as in Example 1, except that Alloy 1 was replaced with Alloy 2. Alloy 2 used an alloy with a Ni content of 62% by mass, a Cr content of 22% by mass, a W content of 14% by mass, and a Mo content of 2% by mass. Furthermore, except that metal test piece 1 was replaced with metal test piece 2, the corrosion rate and the growth rate of corrosion products were measured in the same manner as in Example 1.

[0331] <Comparative Example 2>

[0332] Except that alloy 1 was replaced with a metal containing 100% Ni by mass, Comparative Example 2 LiMO was obtained in the same manner as in Example 1. Furthermore, except that metal test piece 1 was replaced with metal test piece 3, the corrosion rate and the growth rate of corrosion products were measured in the same manner as in Example 1.

[0333] <Comparative Example 3>

[0334] Except that the calcined material 1 was replaced with calcined material 2 containing 0.7% by mass of Li, Comparative Example 3 was obtained in the same manner as in Example 1. In addition, using 3g of calcined material 2, the number of firings was set to a total of 4 times, and the corrosion rate and the growth rate of corrosion products were measured in the same manner as in Example 1.

[0335] <Comparative Example 4>

[0336] Except for replacing the fired material 1 with the fired material 3 containing 10.9% by mass of Li, the LiMO of Comparative Example 4 was obtained in the same manner as in Example 1. In addition, using 3g of the fired material 3, the firing number was set to a total of 3 times, and the corrosion rate and the growth rate of corrosion products were measured in the same manner as in Example 1.

[0337] Table 4 shows the composition of the LiMO produced in Examples 1 and Comparative Examples 1-4, the Li content of the calcined product, the composition of the alloy, the corrosion rate of the metal test piece, and the growth rate of the corrosion product. Furthermore, Table 4 shows the initial discharge capacity of the lithium secondary battery using the LiMO produced in Examples 1 and Comparative Examples 1-4 as the CAM.

[0338] In Examples 1 and Comparative Examples 1-4, since the Ni content in the total LiMO is over 80%, the above-mentioned criterion A is used to evaluate the first discharge capacity.

[0339] In Examples 1 and Comparative Examples 1-3, since the Li content in the total LiMO was less than 6.5% by mass, the above-mentioned judgment criterion 1 was used to evaluate the growth rate of corrosion products.

[0340] In Comparative Example 4, since the Li content in the total LiMO exceeds 6.5% by mass, the above-mentioned criterion 2 is used to evaluate the growth rate of corrosion products.

[0341]

[0342] As shown in Table 4, it was confirmed that the corrosion rate of the metal test piece in Example 1 was less than 5 mm / year, and the growth rate of corrosion products was less than 0.9 mm / year. The corrosion rate was slow, and the alloy was not easily corroded. Therefore, Example 1 demonstrates that it is an effective method for manufacturing LiMO. Furthermore, Example 1 enables the initial charge capacity of the lithium secondary battery to be set to 180 mAh / g or more, thereby improving the performance of the lithium secondary battery.

[0343] The firing conditions for pre-firing and formal firing in Example 1 reproduced the firing process using a firing mechanism with an inner wall made primarily of alloy 1. That is, based on the results of Example 1, it can be reasonably inferred that LiMO can be effectively manufactured when firing using a firing mechanism with an inner wall made primarily of alloy 1, and the initial charge capacity of the lithium secondary battery can be set to 180 mAh / g or higher, thereby improving the performance of the lithium secondary battery.

[0344] On the other hand, while Comparative Examples 1 and 2 improved the initial charge capacity of lithium-ion batteries, the corrosion rate of the metal test piece in Comparative Example 2 exceeded 5 mm / year, and the growth rate of corrosion products in Comparative Example 1 exceeded 0.9 mm / year. This indicates that even when firing is performed using a firing mechanism with Alloy 2 as the main material of the inner wall, the inner wall of the firing mechanism is also prone to corrosion. Therefore, it is clear that Comparative Examples 1 and 2 are not efficient manufacturing methods compared to Example 1.

[0345] In Comparative Example 3, the low Li content in the sintered material reduced the corrosion rate and corrosion product growth rate of the metal test piece. However, it can be assumed that the initial charge capacity of the lithium secondary battery was reduced due to the smaller lithium conductive layer of the obtained LiMO.

[0346] In Comparative Example 4, due to the high Li content in the sintered material, the corrosion rate of the alloy reached 43.8 mm / year. Furthermore, the growth rate of corrosion products was also as high as 41.4 mm / year. This indicates that even when sintering is performed using a sintering mechanism with Ni metal as the main material of the inner wall, the inner wall of the sintering mechanism is also prone to corrosion. Therefore, Comparative Example 4 is found to be an inefficient manufacturing method compared to Example 1. In Comparative Example 4, the sintered material adhered to the model, alloy 1, on the inner wall of the sintering mechanism, making LiMO recovery impossible and hindering battery evaluation.

[0347] <Example 2>

[0348] After adding water to the reaction tank equipped with a stirrer and an overflow pipe, add an aqueous solution of sodium hydroxide and maintain the liquid temperature at 50°C.

[0349] A mixed raw material solution was prepared by mixing nickel sulfate aqueous solution, cobalt sulfate aqueous solution and manganese sulfate aqueous solution in an atomic ratio of Ni:Co:Mn of 60:20:20.

[0350] Next, the mixed raw material solution and ammonium sulfate aqueous solution were continuously added to the reaction tank under stirring as a complexing agent. Sodium hydroxide aqueous solution was added dropwise in a timely manner to make the pH of the solution in the reaction tank 11.6 (measured at a liquid temperature of 40°C) to obtain nickel-cobalt-manganese composite hydroxide.

[0351] After washing, the nickel-cobalt-manganese composite hydroxide was dehydrated by centrifugation, separated, and dried at 105°C to obtain nickel-cobalt-manganese composite hydroxide 1.

[0352] Nickel-cobalt-manganese composite hydroxide 1 and lithium hydroxide monohydrate powder were weighed and mixed in a molar ratio of Li / (Ni+Co+Mn)=1.10 to obtain calcined material 11.

[0353] The Li content in the calcined product 11 was 6.6% by mass.

[0354] Using the calcined material 11, the formal firing conditions were set to 955°C for 5 hours under an oxygen atmosphere. Otherwise, the LiMO of Example 2 was obtained in the same manner as in Example 1. Furthermore, except that 3g of the calcined material 11 was used, the corrosion rate and the growth rate of corrosion products were measured in the same manner as in Example 1.

[0355] Table 5 shows the composition of the LiMO produced in Example 2, the Li content of the calcined material, the composition of the alloy, the corrosion rate of the metal test piece, and the growth rate of the corrosion products. Furthermore, Table 5 shows the initial discharge capacity of the lithium secondary battery using the LiMO produced in Example 2 as a CAM.

[0356]

[0357] In Example 2, since the Ni content in the total LiMO is less than 80%, the above-mentioned criterion B is used for evaluating the first discharge capacity.

[0358] In Example 2, since the Li content in the total LiMO exceeds 6.5% by mass, the above-mentioned criterion 2 is used to evaluate the growth rate of corrosion products.

[0359] As shown in Table 5, it was confirmed that the corrosion rate of the metal test piece in Example 2 was less than 5 mm / year, and the growth rate of corrosion products was less than 2.6 mm / year. The corrosion rate was slow, and the alloy was not easily corroded. Therefore, Example 2 demonstrates that it is an effective method for manufacturing LiMO. Furthermore, Example 2 enables the initial charge capacity of the lithium secondary battery to be set to 170 mAh / g or more, thereby improving the performance of the lithium secondary battery.

[0360] Symbol Explanation

[0361] 1: Separator; 3: Negative electrode; 4: Electrode assembly; 5: Battery can; 6: Electrolyte; 7: Top insulator; 8: Sealing body; 10: Lithium secondary battery; 21: Positive electrode lead; 100: Laminated structure; 110: Positive electrode; 111: Positive electrode active material layer; 112: Positive electrode current collector; 113: External terminal; 120: Negative electrode; 121: Negative electrode active material layer; 122: Negative electrode current collector; 123: External terminal; 130: Solid electrolyte layer; 200: Outer packaging; 200a: Opening; 1000: All-solid-state lithium secondary battery

Claims

1. A method for manufacturing a lithium metal composite oxide, wherein in a firing process of firing a workpiece using a firing mechanism, the workpiece is a raw material comprising a mixture of a metal composite compound and a lithium compound, or a mixture of reactants of the metal composite compound and the lithium compound, wherein the content of Li in the workpiece is more than 5% by mass and less than 10% by mass, the firing mechanism has an inner wall, the main material of the inner wall being an alloy containing Ni and Al, wherein the content of Ni relative to the total amount of the alloy is more than 93% by mass and less than 95% by mass, and the content of Al relative to the total amount of the alloy is more than 3% by mass and less than 5% by mass.

2. The method for manufacturing lithium metal composite oxide according to claim 1, wherein, The lithium metal composite oxide is represented by the following general formula (I). Li[Li x (Ni (1-y-z) Co y M z ) 1-x ]O2(I) -0.1≤x≤0.2、0≤y≤0.5、0≤z≤0.9、y+z<1、M represents one or more elements selected from the group consisting of Mn, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga and V.

3. The method for manufacturing lithium metal composite oxide according to claim 1 or 2, wherein, The alloy contains either or both of Si or Mn.

4. The method for manufacturing lithium metal composite oxide according to claim 3, wherein, The content of Si relative to the total amount of the alloy is more than 0.5% by mass and less than 2.5% by mass.

5. The method for manufacturing lithium metal composite oxide according to claim 3, wherein, The content of Mn relative to the total amount of the alloy is greater than 0% by mass and less than 1.0% by mass.

6. The method for manufacturing lithium metal composite oxide according to claim 1 or 2, wherein, The firing temperature in the firing process is above 100°C and below 900°C.

7. The method for manufacturing lithium metal composite oxide according to claim 1 or 2, wherein, The firing mechanism is a rotary kiln.

8. The method for manufacturing lithium metal composite oxide according to claim 1 or 2, wherein, The firing process includes a pre-firing process and a formal firing process. At least in the pre-firing process, the firing mechanism is used for firing. The firing temperature of the pre-firing process is above 100°C and below 700°C, and the firing temperature of the formal firing process is above 700°C and below 1000°C.

9. The method for manufacturing lithium metal composite oxide according to claim 1 or 2, wherein, The lithium metal composite oxide is used as the positive electrode active material for lithium secondary batteries.

Images