Method for producing lithium metal composite oxide

Abstract

To provide a method for producing a lithium metal complex oxide that can improve the performance of lithium secondary batteries.SOLUTION: A method for producing a lithium metal complex oxide comprises a firing step in which a mixed gas is introduced into the inside of a firing furnace and a product to be fired is fired in the firing furnace at a temperature exceeding 600°C. The product to be fired is a mixture raw material containing a mixture of a metal complex compound and a lithium compound or a reaction product of the metal complex compound and the lithium compound. The mixed gas before introduced contains oxygen, has a moisture content of 8 to 85 volume% and a carbon dioxide content of less than 4 volume%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a lithium metal composite oxide. [Background technology]

[0002] A lithium metal composite oxide is used as a positive electrode active material for a lithium secondary battery. A method for producing a lithium metal composite oxide includes a firing step of firing a material to be fired, such as a mixture of a metal composite compound and a lithium compound, or a reaction product of a metal composite compound and a lithium compound.

[0003] In order to control the physical properties of lithium metal composite oxides, the firing conditions, such as the firing temperature and the firing atmosphere, have been investigated. For example, Patent Document 1 describes a method for producing a positive electrode active material for lithium secondary batteries with the aim of improving cycle characteristics. Patent Document 1 discloses a method in which a mixture of nickel oxyhydroxide and lithium hydroxide is heat-treated at a temperature of 100°C to 500°C in the presence of water vapor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-102054 Summary of the Invention [Problem to be solved by the invention]

[0005] Improving the crystallinity of lithium metal composite oxides is expected to improve the cycle characteristics of lithium secondary batteries. To improve the crystallinity of lithium metal composite oxides, the firing conditions need to be further investigated. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a lithium metal composite oxide that can provide a lithium secondary battery with a high cycle retention rate. [Means for solving the problem]

[0006] The present invention includes [1] to [6]. [1] A method for producing a lithium metal composite oxide, comprising a calcination step of introducing a mixed gas into a calcination furnace and calcining an object to be calcined in the calcination furnace at a temperature exceeding 600°C, wherein the object to be calcined is a mixture of a metal composite compound and a lithium compound, or a mixture raw material containing a reaction product of the metal composite compound and the lithium compound, and the mixed gas before being introduced contains oxygen, has a moisture content of 8% by volume or more and 85% by volume or less, and a carbon dioxide content of less than 4% by volume. [2] The method for producing a lithium metal composite oxide according to [1], wherein the mixed gas before being introduced has an oxygen content of 10% by volume or more and 92% by volume or less. [3] The total amount of water (m) introduced into the firing furnace relative to the powder mass (kg) of the fired material. 3 ) to 0.1m 3 / kg or more 20m 3 The method for producing a lithium metal composite oxide according to [1] or [2], wherein the amount of lithium metal composite oxide is 1 / kg or less. [4] The method for producing a lithium metal composite oxide according to any one of [1] to [3], wherein the calcination step is carried out for a calcination time of 1 hour or more and 24 hours or less. [5] The method for producing a lithium metal composite oxide according to any one of [1] to [4], further comprising a cooling step of cooling the fired product inside the firing furnace after the firing step, wherein a gas having a dew point of −15° C. or lower is supplied into the firing furnace in the cooling step. [6] The method for producing a lithium metal composite oxide according to any one of [1] to [5], wherein the lithium metal composite oxide satisfies the following general formula (I): Li x (Ni (1-y-z) Co y X z ) 1-x ]O2(I) (In formula (I), X represents one or more elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, B, Si, S, and P, and satisfies −0.1≦x≦0.2, 0≦y≦0.4, and 0≦z≦0.5. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a method for producing a lithium metal composite oxide that can provide a lithium secondary battery with a high cycle retention rate. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a lithium secondary battery. [Figure 2] FIG. 1 is a schematic diagram illustrating an example of an all-solid-state lithium secondary battery. [Figure 3] FIG. 2 is a schematic diagram showing an example of a baking means. DETAILED DESCRIPTION OF THE INVENTION

[0009] In this specification, metal composite compound will be hereinafter referred to as "MCC". Lithium metal composite oxide will be referred to hereinafter as "LiMO." Cathode active material for lithium secondary batteries will be referred to as "CAM" hereinafter.

[0010] "Ni" refers to nickel atoms, not nickel metal. Similarly, "Co" and "Li" refer to cobalt atoms and lithium atoms, respectively.

[0011] In this specification, the cycle retention rate of a lithium secondary battery is measured by the following method.

[0012] <Measurement of cycle maintenance rate> (Production of positive electrodes for lithium secondary batteries) Using the LiMO produced by the manufacturing method of this embodiment, LiMO, a conductive material, and a binder are mixed and kneaded in a ratio of LiMO:conductive material:binder=92:5:3 (mass ratio) to prepare a paste-like positive electrode mixture. When preparing the positive electrode mixture, N-methyl-2-pyrrolidone is used as the organic solvent. Acetylene black is used as the conductive material. Polyvinylidene fluoride is used as the binder.

[0013] The resulting positive electrode mixture is applied to a 40 μm thick Al foil as a current collector and dried in a vacuum at 150°C for 8 hours to obtain a positive electrode for a lithium secondary battery. The positive electrode area of ​​this positive electrode for a lithium secondary battery is 1.65 cm2. 2 Let's say.

[0014] (Fabrication of lithium secondary batteries) The following operations are carried out in a glove box under an argon atmosphere. The lithium secondary battery positive electrode prepared in (Preparation of a lithium secondary battery positive electrode) is placed on the bottom cover of a coin-type battery R2032 part (manufactured by Hosen Co., Ltd.) with the aluminum foil side facing down, and a separator (porous polyethylene film) is placed on top of that. 300 μl of electrolyte is poured into this. The electrolyte used is a 30:35:35 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, with LiPF6 dissolved at a ratio of 1.0 mol / l.

[0015] Next, metallic lithium is used as the negative electrode, and the negative electrode is placed on top of the laminated film separator. The top lid is then placed on top via a gasket and crimped with a crimping machine to prepare a lithium secondary battery (coin-type half cell R2032).

[0016] (Cycle maintenance rate) Using the lithium secondary battery produced by the above method, the cycle retention rate is measured by the following method. A cycle retention rate of 90% or more measured by the following method is evaluated as "high cycle retention rate."

[0017] After the lithium secondary battery is fabricated, it is left standing at room temperature for 12 hours to allow the separator and the positive electrode mixture layer to be sufficiently impregnated with the electrolyte. At a test temperature of 25°C, the current setting for both charging and discharging is 0.2 CA, and constant current / constant voltage charging and constant current discharging are performed, respectively. The maximum charging voltage is 4.3 V, and the minimum discharging voltage is 2.5 V.

[0018] Next, at 25°C, the current setting value for both charging and discharging was 1 CA, and a charge-discharge test was performed 50 cycles in which a constant current constant voltage charge was performed up to 4.3 V, followed by a constant voltage charge at 4.3 V, followed by a constant current discharge down to 2.5 V, and the discharge capacity (mAh / g) of each charge-discharge cycle was measured.

[0019] The cycle retention rate is calculated using the following formula from the discharge capacity at the 1st cycle and the discharge capacity at the 50th cycle obtained in the charge / discharge test. The higher the cycle retention rate, the more suppressed the decrease in battery capacity after repeated charge / discharge, which indicates desirable battery performance. Cycle retention rate (%) = 50th cycle discharge capacity (mAh / g) / 1st cycle discharge capacity (mAh / g) × 100

[0020] <Method of manufacturing lithium metal composite oxide> The LiMO manufacturing method of this embodiment requires a firing step in which a material to be fired is fired in a firing furnace. The LiMO manufacturing method preferably includes a step of obtaining MCC and a step of obtaining a mixture. The following describes the steps of obtaining MCC, obtaining the mixture, and firing in that order.

[0021] <Process for obtaining MCC> MCC may be any of a metal composite hydroxide, a metal composite oxide, and a mixture thereof. The metal composite hydroxide and metal composite oxide contain, for example, Ni, Co, and an element X in a molar ratio represented by the following formula (A): Ni:Co:X=(1-yz):y:z (A) (In formula (A), element X is one or more elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, B, Si, S, and P, and satisfies 0≦y≦0.4 and 0≦z≦0.5.)

[0022] The production method will be described in detail below, taking MCC containing Ni, Co, and Mn as metals as an example: First, a metal composite hydroxide containing Ni, Co, and Mn is prepared. The metal composite hydroxide can be produced by a commonly known batch coprecipitation method or continuous coprecipitation method.

[0023] First, a nickel salt solution, a cobalt salt solution, a manganese salt solution, and a complexing agent are reacted by a coprecipitation method, particularly a continuous method described in JP-A-2002-201028, to obtain Ni (1-y-z) Co y Mn z A metal composite hydroxide represented by (OH)2 (where y+z<1) is produced.

[0024] The nickel salt that is the solute of the nickel salt solution is not particularly limited, but for example, at least one of nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate can be used.

[0025] As the cobalt salt that is the solute of the cobalt salt solution, for example, at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate can be used.

[0026] As the manganese salt that is the solute of the manganese salt solution, for example, at least one of manganese sulfate, manganese nitrate, and manganese chloride can be used.

[0027] The above metal salts are (1-y-z) Co y Mn z It is used in a ratio corresponding to the composition ratio of (OH)2. Water is also used as the solvent.

[0028] The complexing agent is a compound capable of forming a complex with nickel ions, cobalt ions, and manganese ions in an aqueous solution, such as ammonium ion donors, hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracildiacetic acid, and glycine.

[0029] Examples of the ammonium ion donor include ammonium salts such as ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, and ammonium fluoride.

[0030] When a complexing agent is contained, the amount of the complexing agent contained in the mixed solution containing the nickel salt solution, the cobalt salt solution, the manganese salt solution and the complexing agent is, for example, in a molar ratio to the total number of moles of the metal salts of more than 0 and not more than 2.0.

[0031] In the coprecipitation method, to adjust the pH of the mixture containing the nickel salt solution, cobalt salt solution, manganese salt solution, and complexing agent, an alkaline aqueous solution is added to the mixture before the pH of the mixture changes from alkaline to neutral. The alkaline aqueous solution can be sodium hydroxide or potassium hydroxide.

[0032] The pH value in this specification is defined as the value measured when the temperature of the mixed solution is 40°C. The pH of the mixed solution is measured when the temperature of the mixed solution sampled from the reaction tank reaches 40°C.

[0033] If the temperature of the sampled mixed liquid is lower than 40°C, heat the mixed liquid and measure the pH when it reaches 40°C.

[0034] If the temperature of the sampled mixed liquid is higher than 40°C, cool the mixed liquid to 40°C and measure the pH.

[0035] When the nickel salt solution, cobalt salt solution, and manganese salt solution as well as a complexing agent are continuously supplied to the reaction vessel, Ni, Co, and Mn react with each other to produce Ni. (1-y-z) Co y Mn z(OH)2 is produced.

[0036] During the reaction, the temperature of the reaction vessel is controlled within the range of, for example, 20°C or higher and 80°C or lower, preferably 30°C or higher and 70°C or lower.

[0037] During the reaction, the pH value in the reaction vessel is controlled within the range of, for example, pH 9 or more and pH 13 or less, preferably pH 11 or more and pH 13 or less.

[0038] The materials in the reaction vessel are mixed by suitable stirring. The reaction vessel used in the continuous coprecipitation method may be a type that allows the formed reaction precipitate to overflow for separation.

[0039] In addition to controlling the above conditions, various gases, for example, inert gases such as nitrogen, argon, and carbon dioxide, oxidizing gases such as air and oxygen, or a mixture thereof, may be supplied into the reaction vessel.

[0040] After the above reaction, the obtained reaction precipitate is washed with water, dehydrated, and then dried to obtain a metal composite hydroxide containing Ni, Co, and Mn. If necessary, the reaction precipitate may be washed with weak acid water or an alkaline solution containing sodium hydroxide or potassium hydroxide.

[0041] In the above example, a metal composite hydroxide containing Ni, Co, and Mn is produced as MCC, but a metal composite oxide containing Ni, Co, and Mn may also be prepared.

[0042] For example, a metal composite hydroxide containing Ni, Co, and Mn can be heated at 400° C. or higher and 700° C. or lower to prepare a metal composite oxide containing Ni, Co, and Mn.

[0043] <Step of obtaining a mixture> The MCC obtained by the above method is mixed with a lithium compound to obtain a mixture of MCC and the lithium compound. As the lithium compound, one or more compounds selected from the group consisting of lithium carbonate, lithium hydroxide, and lithium hydroxide monohydrate can be used.

[0044] The lithium compound and MCC are mixed to obtain a mixture, taking into consideration the composition ratio of the final target product. Specifically, the lithium compound and MCC are preferably mixed in a ratio corresponding to the composition ratio of composition formula (I).

[0045] The mixture of MCC and a lithium compound may be heated before the firing step described below. By heating the mixture, a mixture raw material containing a reaction product of MCC and a lithium compound can be obtained. That is, the mixture raw material may contain a reaction product formed by the reaction of some of the MCC and the lithium compound contained in the mixture, and may further contain MCC and a lithium compound. The mixture is heated to a temperature of, for example, 300°C or higher and 700°C or lower.

[0046] The mixture of MCC and a lithium compound, or the mixture raw material containing a reaction product of MCC and a lithium compound, can be used as the material to be fired in the firing step described below.

[0047] <Firing process> The object to be fired is fired using a firing furnace. The firing means suitable for use in this embodiment will be described with reference to Fig. 3. Fig. 3 shows firing means 30 suitable for use in this embodiment. The firing means 30 includes a gas supply device 32, a moisture supply means 36, and a firing furnace 37.

[0048] The gas supply device 32 includes an oxygen gas supply means 33, an inert gas supply means 34, and an optional carbon dioxide gas supply means 35. The inert gas supply means 34 is a means for supplying an inert gas other than carbon dioxide gas (for example, nitrogen or argon). The gas supply device 32 may or may not include the carbon dioxide gas supply means 35.

[0049] The supply means are connected to supply paths 40a, 40b, and 40c, respectively. Valves 39a, 39b, 39c, 39d, 39e, and 39f may be provided upstream and downstream of the supply paths 40a, 40b, and 40c, respectively, to select between gas flow and cut-off.

[0050] Each supply line 40a, 40b and 40c may be equipped with a flow meter 38a, 38b and 38c, respectively.

[0051] The supply paths 40a, 40b, and 40c are joined together at the downstream side into a single supply path 42, to which the moisture supply means 36 is connected.

[0052] The gas supplied to the moisture supplying means 36 is, for example, oxygen gas or a gas containing oxygen gas and an inert gas. For convenience, the gas supplied to the moisture supplying means 36 is referred to as a "raw material gas."

[0053] For example, when the valves 39b, 39c, 39e and 39f are closed and the valves 39a and 39d are opened, oxygen gas is supplied to the moisture supply means 36 as the raw material gas.

[0054] Furthermore, when the valves 39c and 39f are closed and the valves 39a, 39d, 39b and 39e are opened, a gas containing oxygen gas and an inert gas is supplied to the moisture supply means 36 as a raw material gas.

[0055] The moisture supply means 36 is connected to a firing furnace 37. The firing furnace 37 is a furnace for accommodating and firing an object to be fired. The connecting portion between the moisture supply means 36 and the firing furnace 37 may be heated, for example, to around 100°C to prevent condensation due to moisture in the mixed gas.

[0056] The moisture supplying means 36 supplies moisture to the raw material gas supplied from the supply path 42. As the moisture supplying means 36, the moisture supplying means of Examples A to C below can be mentioned.

[0057] (Example A) The moisture supplying means of Example A supplies moisture to the raw material gas by bubbling. The moisture supplying means of Example A includes a water tank containing water and a heating means for heating the water in the water tank.

[0058] Specifically, first, the water temperature in the water tank is adjusted to between 41°C and 96°C by heating the water using a heating means. Next, the raw material gas is bubbled through the water whose temperature has been adjusted. This results in a mixed gas in which moisture has been supplied to the raw material gas. Increasing the water temperature can increase the moisture content in the mixed gas (hereinafter sometimes referred to as "moisture concentration"), and decreasing the water temperature can decrease the moisture concentration in the mixed gas.

[0059] [Moisture concentration] The moisture concentration [volume %] of a gas at atmospheric pressure (101325 Pa) is expressed by the following formula (X) using the water vapor pressure p (Pa).

[0060] Water concentration [volume %] = (p [Pa] / 101325 [Pa]) × 100 (X)

[0061] The relationship between saturated water vapor pressure and temperature (i.e., dew point) of a one-component liquid is expressed by the following equation (Y) described by the AICHE Design Institute for Physical Properties (DIPPR): where p is water vapor pressure (Pa) and t is dew point (K).

[0062] p=EXP (73.649-7258.2 / t-7.3037×ln(t)+0.0000041653×t 2 ) ··· expression (Y)

[0063] Using the above formula (X), the water vapor pressure p at which the moisture concentration in the mixed gas becomes the target value is calculated, and by substituting this into the above formula (Y), the dew point t at which the mixed gas having the target moisture concentration is obtained is calculated. Then, the water temperature in the water tank is controlled to the calculated dew point t, and the raw material gas is bubbled in the water at the controlled temperature to obtain a mixed gas that satisfies the target moisture concentration.

[0064] ·(Example B) The moisture supply means in Example B includes a bubble column. The bubble column is filled with water maintained at a predetermined temperature, and the raw material gas is supplied to the bubble column, thereby obtaining a mixed gas in which moisture has been supplied to the raw material gas. The moisture concentration of the mixed gas can be adjusted by adjusting the temperature of the water filled in the bubble column.

[0065] ·(Example C) The moisture supplying means of Example C includes a spraying device. The spraying device sprays atomized water into the raw material gas, thereby obtaining a mixed gas in which moisture has been supplied to the raw material gas. When the moisture supplying means of Example C is used, the moisture concentration of the mixed gas can be adjusted by increasing or decreasing the amount of water sprayed.

[0066] The mixed gas is supplied to the firing furnace 37 .

[0067] The mixed gas has a composition before being introduced into the firing furnace 37 such that the moisture concentration in the total amount of the mixed gas is 8% by volume or more and 85% by volume or less, preferably 10% by volume or more and 60% by volume or less, and more preferably 20% by volume or more and 40% by volume or less.

[0068] It is believed that the crystallinity of the resulting LiMO is improved by supplying a mixed gas with a water concentration adjusted to the above range into the firing furnace 37 and firing the material to be fired. A lithium secondary battery using such LiMO as CAM is likely to have an improved cycle retention rate. Here, "improved crystallinity" means a high degree of crystallinity.

[0069] In the composition before being introduced into the firing furnace 37, the content of carbon dioxide in the total amount of the mixed gas is less than 4% by volume, preferably 2% by volume or less, and more preferably 0% by volume.

[0070] By supplying a mixed gas with a carbon dioxide content adjusted to the above range into the firing furnace 37 and firing the material, LiMO with a small amount of residual lithium carbonate can be obtained. When such LiMO is used as CAM, a lithium secondary battery that is less likely to generate carbon dioxide gas during operation and has a high cycle retention rate can be obtained.

[0071] In the composition before being introduced into the firing furnace 37, the oxygen content in the total amount of the mixed gas is preferably 10% by volume or more and 92% by volume or less, and more preferably more than 11% by volume and 92% by volume or less.

[0072] By supplying a mixed gas with an oxygen content adjusted to the above range into the firing furnace 37 and firing the material, the reaction is promoted and LiMO is easily obtained. A lithium secondary battery using such LiMO as CAM is likely to have an improved cycle retention rate.

[0073] The oxygen and carbon dioxide contents and the moisture concentration in the mixed gas are values ​​when the total volume of the mixed gas is 100% by volume.

[0074] The oxygen and carbon dioxide contents and the moisture concentration in the mixed gas can be controlled by adjusting the flow rates of the gases supplied from the oxygen gas supply means 33, the inert gas supply means 34, and the carbon dioxide gas supply means 35, as well as the temperature of the water in the moisture supply means. The flow rate of each gas can be adjusted by using a float flow meter with a valve or the like when supplying each gas from each supply means.

[0075] In the composition before being introduced into the firing furnace 37, the mixed gas is preferably the mixed gas shown in (Example 1), (Example 2), or (Example 3) below. (Example 1) A mixed gas having a water concentration of 8% by volume or more and 85% by volume or less, a carbon dioxide content of less than 4% by volume, and an inert gas content of more than 11% by volume and 92% by volume or less. (Example 2) A mixed gas with a moisture concentration of 8% by volume or more and 85% by volume or less, an oxygen content of more than 11% by volume and 92% by volume or less, and a carbon dioxide content of less than 4% by volume. (Example 3) A mixed gas having a moisture concentration of 8% by volume or more and 85% by volume or less, an oxygen content of 10% by volume or more and 92% by volume or less, an inert gas content of 1% by volume or more and 30% by volume or less, and a carbon dioxide content of less than 4% by volume.

[0076] In any of the mixed gases in (Example 1) to (Example 3) above, the carbon dioxide content is preferably 0% by volume.

[0077] The total amount of water introduced into the firing furnace (m 3 ) to 0.1m 3 / kg or more 20m 3 / kg or less. The total amount of water (m 3 ) to the "moisture powder ratio (m 3 / kg).

[0078] The "charged powder mass of the material to be fired" is the mass of the material to be fired that is charged into the firing furnace before firing. The "total amount of moisture introduced into the firing furnace" is the total amount of moisture introduced into the firing furnace 37 by the mixed gas. 3 / kg) can be controlled by adjusting the flow rate of each gas supplied from each gas supply means and the temperature of water in the moisture supply means.

[0079] By controlling the moisture-powder ratio within the above range and firing the material, crystal growth is promoted, making it easier to obtain LiMO with high crystallinity. Lithium secondary batteries using such LiMO as CAM tend to have improved cycle retention.

[0080] The firing temperature in the firing furnace 37 is set to a temperature exceeding 600°C, preferably 700°C or higher, and more preferably 800°C or higher. The upper limit of the firing temperature can be, for example, 1300°C or lower, 1200°C or lower, or 1100°C or lower. When multiple firing steps with different firing temperatures are performed, it is preferable that the firing temperature of the firing step performed at the highest temperature be within the above range.

[0081] Firing the material at temperatures above 600°C promotes crystal growth, making it easier to obtain highly crystalline LiMO. Lithium secondary batteries using such LiMO as CAM tend to have improved cycle retention.

[0082] In this embodiment, when a plurality of firing steps with different firing temperatures are performed, it is preferable that all of the firing steps are performed at a temperature exceeding 600°C.

[0083] The firing temperature is the maximum temperature that the atmosphere in the firing furnace can be maintained at. The time for which the firing temperature is maintained is referred to as the firing time. The firing time is preferably from 1 hour to 24 hours, and more preferably from 3 hours to 12 hours.

[0084] The total time from the start of temperature increase to the end of temperature maintenance after reaching the temperature is preferably 1 hour to 30 hours. The temperature increase rate in the firing step is preferably 15°C / hour or more, more preferably 30°C / hour or more, and particularly preferably 45°C / hour or more.

[0085] The temperature rise rate in this specification is calculated from the time from when the temperature rise starts until the maximum temperature is reached in the firing device, and the temperature difference from the temperature at the start of the temperature rise in the firing furnace of the firing device to the maximum temperature.

[0086] The fired product obtained in the firing step is washed and pulverized as appropriate to obtain LiMO.

[0087] ·Cooling process It is preferable to provide a cooling step after the firing step. The cooling step is a step of cooling the fired product inside the firing furnace. At this time, it is preferable to supply a gas with a dew point of -15°C or less into the firing furnace. Furthermore, it is preferable to cool the fired product to room temperature in this step. Examples of gases with a dew point of -15°C or less include oxygen-containing gases and inert-containing gases with a dew point of -15°C or less.

[0088] In the cooling step, the timing for supplying gas with a dew point of -15°C or lower is, for example, immediately after the firing is completed for the firing time. For example, a means for supplying gas with a dew point of -15°C or lower is connected to the firing furnace 37 in advance via a supply line and a valve, and immediately after the firing is completed, the supply of mixed gas from the moisture supply means is stopped and the valve on the side of the means for supplying gas with a dew point of -15°C or lower is opened, thereby supplying gas with a dew point of -15°C or lower to the firing furnace.

[0089] LiMO is obtained by supplying gas with a dew point of -15°C or lower into the furnace and cooling the fired material. The LiMO produced through the cooling process has a low water content. Lithium secondary batteries using such LiMO as CAM tend to have improved cycle retention.

[0090] <Lithium metal composite oxide> ≪Composition≫ The LiMO produced by the production method of this embodiment preferably satisfies the following general formula (I). Li x (Ni (1-y-z) Co y X z ) 1-x ]O2(I) (In formula (I), X represents one or more elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, B, Si, S, and P, and satisfies −0.1≦x≦0.2, 0≦y≦0.4, and 0≦z≦0.5.

[0091] (x) From the viewpoint of obtaining a lithium secondary battery with a high cycle retention rate, x is preferably greater than 0, more preferably 0.01 or greater, and even more preferably 0.02 or greater. Also, from the viewpoint of obtaining a lithium secondary battery with a high initial coulombic efficiency, x is preferably 0.1 or less, more preferably 0.08 or less, and even more preferably 0.06 or less. The upper and lower limits of x can be combined arbitrarily. Examples of combinations of x include those in which x is greater than 0 and equal to or less than 0.1, 0.01 or greater and equal to or less than 0.08, and 0.02 or greater and equal to or less than 0.06.

[0092] (y) From the viewpoint of obtaining a lithium secondary battery with low internal resistance, y is preferably greater than 0, more preferably 0.005 or greater, even more preferably 0.01 or greater, and even more preferably 0.05 or greater. 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. The upper and lower limits of y can be combined arbitrarily. Examples of combinations of y include: greater than 0 and equal to or less than 0.4; 0.005 or greater and equal to or less than 0.4; 0.01 or greater and equal to or less than 0.35; and 0.05 or greater and equal to or less than 0.33.

[0093] (z) From the viewpoint of obtaining a lithium secondary battery with a high cycle retention rate, 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 excellent storage characteristics at high temperatures (e.g., in a 60°C environment), z is preferably 0.49 or less, and more preferably 0.48 or less. The upper and lower limits of z can be combined arbitrarily. Examples of combinations of z include 0.01 to 0.5, 0.02 to 0.49, and 0.03 to 0.48.

[0094] (y+z) From the viewpoint of obtaining a lithium secondary battery with a high cycle retention rate, y+z preferably exceeds 0, more preferably exceeds 0 and is 0.8 or less, and even more preferably exceeds 0 and is 0.78 or less.

[0095] X represents one or more elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, B, Si, S and P.

[0096] Furthermore, from the viewpoint of obtaining a lithium secondary battery with a high cycle retention rate, X is preferably one or more elements selected from the group consisting of Mn, Ti, Mg, Al, W, B, Zr, and Nb, and from the viewpoint of obtaining a lithium secondary battery with high thermal stability, X is preferably one or more elements selected from the group consisting of Mn, Al, W, B, Zr, and Nb.

[0097] <Composition analysis> The composition of LiMO can be analyzed by dissolving the obtained LiMO powder in hydrochloric acid and then measuring it using an ICP optical emission spectrometer. As an ICP optical emission spectrometer, for example, SPS3000 manufactured by SII NanoTechnology Inc. can be used.

[0098] <Positive electrode active material for lithium secondary batteries> The LiMO produced by the production method of this embodiment can be suitably used as CAM. The CAM of this embodiment contains LiMO. The CAM may contain LiMO other than that of the present invention as long as the effects of the present invention are not impaired.

[0099] <Lithium secondary battery> The structure of a lithium secondary battery suitable for using LiMO manufactured by the manufacturing method of this embodiment as a CAM will be described. Furthermore, a description will be given of a positive electrode for a lithium secondary battery suitable for use when LiMO produced by the production method of this embodiment is used as CAM. Hereinafter, the positive electrode for a lithium secondary battery may be referred to as a positive electrode. Furthermore, a lithium secondary battery suitable for use as a positive electrode will be described.

[0100] An example of a suitable lithium secondary battery when LiMO manufactured by the manufacturing method of this embodiment is used as a CAM includes a positive electrode, 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.

[0101] An example of a lithium secondary battery has a positive electrode, 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.

[0102] 1 is a schematic diagram showing an example of a lithium secondary battery. For example, a cylindrical lithium secondary battery 10 is manufactured as follows.

[0103] First, as shown in FIG. 1 , a pair of strip-shaped separators 1, a strip-shaped positive electrode 2 having a positive electrode lead 21 at one end, and a strip-shaped negative electrode 3 having a negative electrode lead 31 at one end are stacked in this order: separator 1, positive electrode 2, separator 1, negative electrode 3, and then wound to form an electrode group 4.

[0104] Next, the electrode group 4 and an insulator (not shown) are placed in the battery can 5, the bottom of the can is sealed, the electrode group 4 is impregnated with an electrolyte solution 6, and the electrolyte is disposed between the positive electrode 2 and the negative electrode 3. Furthermore, the top of the battery can 5 is sealed with a top insulator 7 and a sealing member 8, whereby a lithium secondary battery 10 can be manufactured.

[0105] The shape of the electrode group 4 can be, for example, a columnar shape such that the cross section of the electrode group 4 cut perpendicular to the winding axis is a circle, an ellipse, a rectangle, or a rectangle with rounded corners.

[0106] The shape of a lithium secondary battery having such an electrode group 4 can be any shape specified by IEC60086, a standard for batteries established by the International Electrotechnical Commission (IEC), or JIS C 8500. Examples of shapes include a cylindrical shape and a rectangular shape.

[0107] Furthermore, the lithium secondary battery is not limited to the above-mentioned wound type configuration, and may be a laminated type configuration in which a laminated structure of a positive electrode, a separator, a negative electrode, and a separator is repeatedly stacked. Examples of laminated lithium secondary batteries include so-called coin type batteries, button type batteries, and paper type (or sheet type) batteries.

[0108] Each component will be described below in order. (positive electrode) The positive electrode can be produced by first preparing a positive electrode mixture containing CAM, a conductive material, and a binder, and then supporting the positive electrode mixture on a positive electrode current collector.

[0109] (Conductive material) The conductive material of the positive electrode can be a carbon material, such as graphite powder, carbon black (e.g., acetylene black), or a fibrous carbon material.

[0110] The proportion of the conductive material in the positive electrode mixture is preferably 5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of CAM.

[0111] (binder) The binder in the positive electrode can be a thermoplastic resin, such as a polyimide resin, a fluororesin, a polyolefin resin, or a resin described in WO2019 / 098384A1 or US2020 / 0274158A1.

[0112] The fluororesin is, for example, polyvinylidene fluoride (hereinafter sometimes referred to as PVdF) or polytetrafluoroethylene.

[0113] The polyolefin resin is, for example, polyethylene or polypropylene.

[0114] (Positive electrode current collector) The positive electrode current collector of the positive electrode can be a strip-shaped member made of a metal material such as Al, Ni, or stainless steel.

[0115] A method for supporting the positive electrode mixture on the positive electrode current collector includes forming the positive electrode mixture into a paste using an organic solvent, applying the resulting positive electrode mixture paste to at least one side of the positive electrode current collector, drying the paste, and then performing an electrode pressing step to fix the paste.

[0116] When the positive electrode mixture is made into a paste, an organic solvent that can be used is N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP).

[0117] Examples of methods for applying the positive electrode mixture paste to the positive electrode current collector include slit die coating, screen coating, curtain coating, knife coating, gravure coating, and electrostatic spraying.

[0118] The positive electrode can be produced by the above-mentioned methods.

[0119] (Negative electrode) The negative electrode of a lithium secondary battery may be any electrode capable of doping and dedoping lithium ions at a lower potential than the positive electrode, for example, an electrode in which a negative electrode mixture containing a negative electrode active material is supported on a negative electrode current collector, or an electrode made solely of a negative electrode active material.

[0120] (Negative electrode active material) Examples of the negative electrode active material contained in the negative electrode include carbon materials, chalcogen compounds (oxides, sulfides, etc.), nitrides, metals, and alloys, which can be doped and dedoped with lithium ions at a lower potential than the positive electrode.

[0121] Examples of carbon materials that can be used as the negative electrode active material include graphite such as natural graphite and artificial graphite, cokes, carbon black, carbon fiber, and baked organic polymer compounds.

[0122] Oxides that can be used as negative electrode active materials include SiO2, SiO, and the like, which are compounds of the formula SiO x(where x is a positive real number) oxides of silicon; SnO2, SnO, etc., with the formula SnO x (where x is a positive real number); tin oxide represented by Li4Ti5O 12 and metal composite oxides containing lithium and titanium, such as:

[0123] The electrode made of the negative electrode active material may be made of a metal that can be used as the negative electrode active material, such as lithium metal, silicon metal, or tin metal. Materials that can be used as the negative electrode active material may be materials described in WO2019 / 098384A1 or US2020 / 0274158A1.

[0124] These metals and alloys are mainly used alone as electrodes after being processed into foils, for example.

[0125] Among the above-mentioned negative electrode active materials, carbon materials containing graphite as a main component, such as natural graphite or artificial graphite, are preferably used. This is because the potential of the negative electrode hardly changes from an uncharged state to a fully charged state during charging (good potential flatness), the average discharge potential is low, and the capacity retention rate after repeated charge and discharge is high (good cycle characteristics). The shape of the carbon material may be, for example, flakes like natural graphite, spherical like mesocarbon microbeads, fibrous like graphitized carbon fiber, or aggregates of fine powder.

[0126] The negative electrode mixture may contain a binder as needed. Examples of the binder 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.

[0127] (Negative electrode current collector) The negative electrode current collector of the negative electrode may be a strip-shaped member made of a metal material such as copper, nickel, or stainless steel.

[0128] As a method for supporting the negative electrode mixture on such a negative electrode current collector, as in the case of the positive electrode, there are a method using pressure molding, a method in which a paste is formed using a solvent or the like, which is applied to the negative electrode current collector, dried, and then pressed to bond the paste.

[0129] (separator) The separator of a lithium secondary battery may be, for example, a porous film, nonwoven fabric, woven fabric, or other material made of a polyolefin resin such as polyethylene or polypropylene, a fluororesin, or a nitrogen-containing aromatic polymer. The separator may be formed using two or more of these materials, or may be formed by laminating these materials. Separators described in JP-A-2000-030686 or US20090111025A1 may also be used.

[0130] (electrolyte) The electrolyte solution in the lithium secondary battery contains an electrolyte and an organic solvent.

[0131] The electrolyte contained in the electrolytic solution may be a lithium salt such as LiClO4, LiPF6, or LiBF4, and a mixture of two or more of these may also be used.

[0132] The organic solvent contained in the electrolytic solution may be, for example, a carbonate such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate.

[0133] As the organic solvent, it is preferable to use a mixture of two or more of these. Among them, a mixed solvent containing a carbonate is preferable, and a mixed solvent of a cyclic carbonate and an acyclic carbonate and a mixed solvent of a cyclic carbonate and an ether are more preferable.

[0134] Furthermore, it is preferable to use an electrolyte solution containing a fluorine-containing lithium salt such as LiPF6 and an organic solvent having a fluorine substituent, as this increases the safety of the resulting lithium secondary battery. The electrolyte and organic solvent contained in the electrolytic solution may be the electrolyte and organic solvent described in WO2019 / 098384A1 or US2020 / 0274158A1.

[0135] <All-solid-state lithium secondary battery> Next, the configuration of the all-solid-state lithium secondary battery will be described, along with a positive electrode using LiMO manufactured by the manufacturing method of this embodiment as a CAM for the all-solid-state lithium secondary battery, and an all-solid-state lithium secondary battery having this positive electrode.

[0136] Fig. 2 is a schematic diagram showing an example of an all-solid-state lithium secondary battery. The all-solid-state lithium secondary battery 1000 shown in Fig. 2 includes a laminate 100 having a positive electrode 110, a negative electrode 120, and a solid electrolyte layer 130, and an exterior body 200 that houses the laminate 100. The all-solid-state lithium secondary battery 1000 may also have a bipolar structure in which a CAM and a negative electrode active material are disposed on both sides of a current collector. A specific example of a bipolar structure is the structure described in JP-A-2004-95400. The materials constituting each component will be described later.

[0137] The laminate 100 may have an external terminal 113 connected to the positive electrode current collector 112 and an external terminal 123 connected to the negative electrode current collector 122. In addition, the all-solid-state lithium secondary battery 1000 may have a separator between the positive electrode 110 and the negative electrode 120.

[0138] The all-solid-state lithium secondary battery 1000 further includes an insulator (not shown) that insulates the laminate 100 from the exterior body 200 , and a sealing body (not shown) that seals the opening 200 a of the exterior body 200 .

[0139] A container molded from a highly corrosion-resistant metal material such as aluminum, stainless steel, or nickel-plated steel can be used as exterior body 200. Alternatively, a container formed into a bag shape from a laminate film with corrosion resistance applied to at least one surface can also be used as exterior body 200.

[0140] The all-solid-state lithium secondary battery 1000 may have any shape, such as a coin shape, a button shape, a paper shape (or a sheet shape), a cylindrical shape, a square shape, or a laminate shape (pouch shape).

[0141] The all-solid-state lithium secondary battery 1000 is illustrated as having one laminate 100 as an example, but the present embodiment is not limited to this. The all-solid-state lithium secondary battery 1000 may have a configuration in which the laminate 100 is used as a unit cell, and a plurality of unit cells (laminated bodies 100) are sealed inside an exterior body 200.

[0142] Each component will be described below in order.

[0143] (positive electrode) The positive electrode 110 includes a positive electrode active material layer 111 and a positive electrode current collector 112 .

[0144] The positive electrode active material layer 111 contains the above-mentioned CAM and solid electrolyte, and may also contain a conductive material and a binder.

[0145] (solid electrolyte) A solid electrolyte having lithium ion conductivity and used in known all-solid-state lithium secondary batteries can be used as the solid electrolyte contained in the positive electrode active material layer 111. Examples of such a solid electrolyte include inorganic electrolytes and organic electrolytes.

[0146] Examples of inorganic electrolytes include oxide-based solid electrolytes, sulfide-based solid electrolytes, and hydride-based solid electrolytes.

[0147] The organic electrolyte may be a polymer-based solid electrolyte.

[0148] Examples of each electrolyte include the compounds described in WO2020 / 208872A1, US2016 / 0233510A1, US2012 / 0251871A1, and US2018 / 0159169A1. For example, the following compounds are included.

[0149] (oxide-based solid electrolyte) Examples of oxide-based solid electrolytes include perovskite-type oxides, NASICON-type oxides, LISICON-type oxides, garnet-type oxides, and the like. Specific examples of each oxide include the compounds described in WO2020 / 208872A1, US2016 / 0233510A1, and US2020 / 0259213A1.

[0150] Examples of perovskite-type oxides include Li a La 1-a TiO3 (0 < a < 1) and other Li-La-Ti-based oxides, Li b La 1-b TaO3 (0 < b < 1) and other Li-La-Ta-based oxides, and Li c La 1-c NbO3 (0 < c < 1) and other Li-La-Nb-based oxides.

[0151] Examples of NASICON-type oxides include Li 1+d Al d Ti 2-d (PO4)3 (0 ≤ d ≤ 1) and the like. A NASICON-type oxide is an oxide represented by Li m M 1 n M 2 o P p O q (where M 1 is one or more elements selected from the group consisting of B, Al, Ga, In, C, Si, Ge, Sn, Sb, and Se. M 2 is one or more elements selected from the group consisting of Ti, Zr, Ge, In, Ga, Sn, and Al. m, n, o, p, and q are arbitrary positive numbers.)

[0152] LISICON-type oxides include Li4M 3 O4-Li3M 4 O4(M 3 is one or more elements selected from the group consisting of Si, Ge, and Ti. 4 is one or more elements selected from the group consisting of P, As and V.)

[0153] Garnet-type oxides include Li7La3Zr2O 12 Examples include Li-La-Zr oxides such as (also known as LLZ).

[0154] The oxide-based solid electrolyte may be a crystalline material or an amorphous material.

[0155] (Sulfide solid electrolyte) The sulfide-based solid electrolytes include Li2S-P2S5-based compounds, Li2S-SiS2-based compounds, Li2S-GeS2-based compounds, Li2S-B2S3-based compounds, LiI-Si2S-P2S5-based compounds, LiI-Li2S-P2O5-based compounds, LiI-Li3PO4-P2S5-based compounds, and Li 10 GeP2S 12 Examples include:

[0156] In this specification, the expression "sulfide-based compound" referring to a sulfide-based solid electrolyte is used as a general term for solid electrolytes that mainly contain raw materials such as "LiS" and "P2S5" described before "sulfide-based compound." For example, LiS-P2S5-based compounds include solid electrolytes that mainly contain LiS and P2S5 and also contain other raw materials.

[0157] The proportion of Li2S contained in the Li2S-P2S5-based compound is, for example, 50 to 90 mass % relative to the entire Li2S-P2S5-based compound.

[0158] The proportion of P2S5 contained in the Li2S-P2S5-based compound is, for example, 10 to 50 mass % with respect to the entire Li2S-P2S5-based compound.

[0159] The proportion of other raw materials contained in the Li2S-P2S5-based compound is, for example, 0 to 30 mass % relative to the entire Li2S-P2S5-based compound.

[0160] The Li2S-P2S5 based compounds also include solid electrolytes with different mixing ratios of Li2S and P2S5.

[0161] Li2S-P2S5-based compounds include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-LiI-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, and Li2S-P2S5-Z m S n (m and n are positive numbers. Z is Ge, Zn or Ga).

[0162] Li2S-SiS2-based compounds include Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-SiS2-P2S5-LiCl, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li2SO4, and Li2S-SiS2-Li x MO y (x and y are positive numbers. M is P, Si, Ge, B, Al, Ga, or In.)

[0163] Examples of Li2S-GeS2 based compounds include Li2S-GeS2 and Li2S-GeS2-P2S5.

[0164] The sulfide-based solid electrolyte may be a crystalline material or an amorphous material.

[0165] (hydride-based solid electrolyte) Examples of hydride-based solid electrolyte materials include LiBH4, LiBH4-3KI, LiBH4-PI2, LiBH4-P2S5, LiBH4-LiNH2, 3LiBH4-LiI, LiNH2, Li2AlH6, Li(NH2)2I, Li2NH, LiGd(BH4)3Cl, Li2(BH4)(NH2), Li3(NH2)I, and Li4(BH4)(NH2)3.

[0166] (polymer-based solid electrolyte) Examples of polymer-based solid electrolytes include organic polymer electrolytes such as polyethylene oxide-based polymer compounds and polymer compounds containing at least one selected from the group consisting of polyorganosiloxane chains and polyoxyalkylene chains. Also, so-called gel-type electrolytes, in which a non-aqueous electrolyte solution is held in a polymer compound, can be used.

[0167] Two or more solid electrolytes can be used in combination as long as the effects of the invention are not impaired.

[0168] (Conductive material and binder) The conductive material contained in the positive electrode active material layer 111 can be the material described above in (Conductive material). The proportion of the conductive material in the positive electrode mixture can also be the proportion described above in (Conductive material). The binder contained in the positive electrode can be the material described above in (Binder).

[0169] (Positive electrode current collector) The positive electrode current collector 112 of the positive electrode 110 can be made of the materials described above in (positive electrode current collector).

[0170] One method for supporting the positive electrode active material layer 111 on the positive electrode current collector 112 is to pressure-mold the CAM layer 111 on the positive electrode current collector 112. Cold pressing or hot pressing can be used for pressure-mold.

[0171] Alternatively, a mixture of the CAM, the solid electrolyte, the conductive material, and the binder may be made into a paste using an organic solvent to form a positive electrode mixture, and the obtained positive electrode mixture may be applied to at least one surface of the positive electrode current collector 112, dried, and pressed to adhere the positive electrode active material layer 111 to the positive electrode current collector 112.

[0172] Alternatively, a mixture of the CAM, the solid electrolyte, and the conductive material may be made into a paste using an organic solvent to form a positive electrode mixture, and the obtained positive electrode mixture may be applied to at least one surface of the positive electrode current collector 112, dried, and sintered to cause the positive electrode active material layer 111 to be supported on the positive electrode current collector 112.

[0173] As the organic solvent that can be used for the positive electrode mixture, the same organic solvent that can be used when making the positive electrode mixture into a paste as explained above in (positive electrode current collector) can be used.

[0174] The method for applying the positive electrode mixture to the positive electrode current collector 112 includes the methods described above in (Positive electrode current collector).

[0175] The positive electrode 110 can be manufactured by the methods mentioned above. Specific combinations of materials used for the positive electrode 110 include the above-mentioned CAM and the solid electrolyte, binder, and conductive material shown in Tables 1 to 3.

[0176] [Table 1]

[0177] [Table 2]

[0178] [Table 3]

[0179] (Negative electrode) 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. 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 those described above.

[0180] As in the case of the positive electrode 110, methods for supporting the negative electrode active material layer 121 on the negative electrode current collector 122 include a pressure molding method, a method in which a paste-like negative electrode mixture containing a negative electrode active material is applied to the negative electrode current collector 122, dried, and then pressed to bond the layer, and a method in which a paste-like negative electrode mixture containing a negative electrode active material is applied to the negative electrode current collector 122, dried, and then sintered.

[0181] (solid electrolyte layer) The solid electrolyte layer 130 includes the above-described solid electrolyte.

[0182] 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 above-mentioned positive electrode 110 by sputtering.

[0183] The solid electrolyte layer 130 can be formed by applying a paste mixture containing a solid electrolyte to the surface of the positive electrode active material layer 111 of the above-described positive electrode 110, and then drying the mixture. After drying, the mixture may be press-molded and further pressed by cold isostatic pressing (CIP) to form the solid electrolyte layer 130.

[0184] The laminate 100 can be produced by stacking the negative electrode 120 on the solid electrolyte layer 130 provided on the positive electrode 110 as described above, using a known method, in such a manner that the negative electrode active material layer 121 contacts the surface of the solid electrolyte layer 130. [Example]

[0185] Next, the present invention will be described in more detail with reference to examples. In the following, Examples 1 and 2 are referred to as Reference Examples 1 and 2.

[0186] <Composition analysis> The composition of LiMO was analyzed by the method described above in <Composition Analysis>.

[0187] <Measurement of cycle maintenance rate> The cycle retention rate of the lithium secondary battery using LiMO was measured by the method described in <Measurement of cycle retention rate> above.

[0188] Example 1 Water was placed in a reaction vessel equipped with a stirrer and an overflow pipe, and then an aqueous solution of sodium hydroxide was added thereto, and the liquid temperature was maintained at 50°C.

[0189] A mixed raw material liquid was prepared by mixing an aqueous nickel sulfate solution, an aqueous cobalt sulfate solution, and an aqueous manganese sulfate solution in such a ratio that the atomic ratio of Ni, Co, and Mn satisfied 60:20:20.

[0190] Next, this mixed raw material liquid and an aqueous solution of ammonium sulfate as a complexing agent were continuously added to a reaction vessel under stirring. An aqueous solution of sodium hydroxide was added dropwise at appropriate times so that the pH of the solution in the reaction vessel became 11.6 (measured at a liquid temperature of 40°C), thereby obtaining a nickel-cobalt-manganese composite hydroxide. The nickel-cobalt-manganese composite hydroxide was washed, then dehydrated using a centrifuge, isolated, and dried at 105°C to obtain nickel-cobalt-manganese composite hydroxide 1.

[0191] Nickel-cobalt-manganese composite hydroxide 1 and lithium hydroxide monohydrate powder were weighed and mixed in a molar ratio of Li / (Ni+Co+Mn)=1.05 to obtain a material to be calcined 1.

[0192] The object to be fired 1 was fired using firing means 30 shown in FIG.

[0193] The moisture concentration in the mixed gas was adjusted by supplying moisture to the raw material gas by bubbling using the moisture supply means 36 of Example A. Specifically, the dew point at which the moisture concentration in the total amount of the mixed gas becomes 8% by volume was calculated using the formulas (X) and (Y). The water temperature in the water tank was set to 42°C so as to achieve this dew point, and the raw material gas was bubbled into water at a temperature of 42°C. Oxygen gas was bubbled as the raw material gas. As a result, the mixed gas introduced into the firing furnace 37 had a moisture concentration of 8% by volume and an oxygen content of 92% by volume in the composition before introduction.

[0194] At this time, the moisture to powder ratio is 0.25m 3 / kg.

[0195] The fired material 1 was fired in the firing furnace 37 at 955°C for 5 hours to obtain a fired material. At this time, the temperature rise rate was 175°C / hour.

[0196] Immediately after the completion of the 5-hour calcination, a gas with a dew point of −15° C. or less was supplied, and the calcined product was cooled to room temperature inside the calcination furnace 37 to obtain LiMO-1. The gas with a dew point of −15° C. or less supplied at this time was a gas in which essentially only moisture had been removed from the mixed gas.

[0197] When LiMO-1 was assigned to the composition formula (I), x=0.02, y=0.20, and z=0.20.

[0198] <Example 2> The mixed gas introduced into the firing furnace 37 was changed to a gas having a moisture concentration of 11% by volume, an oxygen content of 84% by volume, and a nitrogen content of 5% by volume, and the moisture-powder ratio was changed to 0.40 m 3 / kg, LiMO-2 was obtained in the same manner as in Example 1. The water concentration in the mixed gas was adjusted by setting the water temperature to 47°C using the water supply means 36 of Example A.

[0199] When LiMO-2 was assigned to the composition formula (I), x=0.02, y=0.20, and z=0.20.

[0200] Example 3 The mixed gas introduced into the firing furnace 37 was changed to a gas having a moisture concentration of 36% by volume, an oxygen content of 32% by volume, and a nitrogen content of 32% by volume, and the moisture-powder ratio was changed to 3.9 m 3 LiMO-3 was obtained in the same manner as in Example 1, except that the firing temperature was changed to 925°C and the amount of water used was changed to 1 / kg. The water concentration in the mixed gas was adjusted by setting the water temperature to 74°C using the water supply means 36 of Example A.

[0201] When LiMO-3 was assigned to the composition formula (I), x=0.00, y=0.20, and z=0.20.

[0202] Example 4 Water was placed in a reaction vessel equipped with a stirrer and an overflow pipe, and then an aqueous solution of sodium hydroxide was added thereto, and the liquid temperature was maintained at 50°C.

[0203] A mixed raw material liquid was prepared by mixing an aqueous solution of nickel sulfate, an aqueous solution of cobalt sulfate, and an aqueous solution of manganese sulfate in such a ratio that the atomic ratio of Ni to Co to Mn was 31.5:33:35.5.

[0204] Next, this mixed raw material liquid and an aqueous solution of ammonium sulfate as a complexing agent were continuously added to a reaction vessel under stirring. An aqueous solution of sodium hydroxide was added dropwise at appropriate times so that the pH of the solution in the reaction vessel became 11.6 (measured at a liquid temperature of 40°C), thereby obtaining a nickel-cobalt-manganese composite hydroxide. The nickel-cobalt-manganese composite hydroxide was washed, then dehydrated using a centrifuge, isolated, and dried at 105°C to obtain nickel-cobalt-manganese composite hydroxide 2.

[0205] Nickel-cobalt-manganese composite hydroxide 2 and lithium hydroxide monohydrate powder were weighed and mixed in a molar ratio of Li / (Ni+Co+Mn)=1.10 to obtain a material to be calcined 2.

[0206] The object to be baked 2 was baked using the baking means 30 shown in FIG. The moisture concentration in the mixed gas was adjusted by supplying moisture to the raw material gas by bubbling using the moisture supply means 36 of Example A. Specifically, the dew point at which the moisture concentration in the total amount of the mixed gas becomes 41% by volume was calculated using the formulas (X) and (Y). The water temperature in the water tank was set to 77°C so as to achieve this dew point, and the raw material gas was bubbled into water at a temperature of 77°C. A gas containing oxygen and nitrogen was bubbled as the raw material gas. The mixed gas introduced into the firing furnace 37 had a moisture concentration of 41% by volume, an oxygen content of 18% by volume, and a nitrogen content of 41% by volume in the composition before introduction.

[0207] The moisture to powder ratio is 8.2m 3 / kg.

[0208] The fired material 2 was fired in the firing furnace 37 at 690°C for 4 hours and then at 935°C for 4 hours, to obtain a fired material. At this time, the temperature rise rate was 175°C / hour.

[0209] Immediately after the second 4-hour firing, a gas with a dew point of -15°C or less was supplied, and the fired product was cooled to room temperature inside the firing furnace 37 to obtain LiMO-4. The gas with a dew point of -15°C or less supplied at this time was a gas in which essentially only moisture had been removed from the mixed gas.

[0210] When LiMO-4 was assigned to the composition formula (I), x=0.06, y=0.33, and z=0.35.

[0211] <Example 5> The mixed gas introduced into the firing furnace 37 was changed to a gas having a moisture concentration of 60% by volume, an oxygen content of 20% by volume, and a nitrogen content of 20% by volume, and the moisture to powder ratio was changed to 8.8 m 3 / kg, LiMO-5 was obtained in the same manner as in Example 3. The water concentration in the mixed gas was adjusted by setting the water temperature to 86°C using the water supply means 36 of Example A.

[0212] When LiMO-5 was assigned to the composition formula (I), x=-0.01, y=0.20, and z=0.20.

[0213] Example 6 The mixed gas introduced into the firing furnace 37 was changed to a gas having a moisture concentration of 80% by volume and an oxygen content of 20% by volume, and the moisture to powder ratio was changed to 13 m 3 LiMO-6 was obtained in the same manner as in Example 4, except that the calcination temperature was set to 690°C / kg, and the calcination material 2 was calcined at 690°C for 4 hours in a calcination furnace 37, and then calcined at 905°C for 4 hours. The water concentration in the mixed gas was adjusted by setting the water temperature to 94°C using the water supply means 36 of Example A.

[0214] When LiMO-6 was assigned to the composition formula (I), x=0.06, y=0.33, and z=0.35.

[0215] <Comparative Example 1> LiMO-11 was obtained in the same manner as in Example 1, except that the mixed gas introduced into the firing furnace 37 was changed to a gas having an oxygen content of 80% by volume and a nitrogen content of 20% by volume in the composition before introduction. At this time, the water powder ratio was 0 m 3 / kg.

[0216] When LiMO-11 was assigned to the composition formula (I), x=0.02, y=0.20, and z=0.20.

[0217] <Comparative Example 2> LiMO-12 was obtained in the same manner as in Example 1, except that the mixed gas introduced into the sintering furnace 37 was changed to a gas having an oxygen content of 20% by volume and a nitrogen content of 80% by volume in the composition before introduction, and the sintering temperature was changed to 925°C. At this time, the moisture powder ratio was 0 m 3 / kg.

[0218] When LiMO-12 was assigned to the composition formula (I), x=0.03, y=0.20, and z=0.20.

[0219] <Comparative Example 3> The mixed gas introduced into the firing furnace 37 was changed to a gas having a moisture concentration of 6% by volume and an oxygen content of 94% by volume in the composition before introduction, and the moisture powder ratio was changed to 0.20 m 3 LiMO-13 was obtained in the same manner as in Example 1, except that the water content was changed to 1 / kg. The water concentration in the mixed gas was adjusted by setting the water temperature to 36°C using the water supply means 36 of Example A.

[0220] When LiMO-13 was assigned to the composition formula (I), x=0.01, y=0.20, and z=0.20.

[0221] <Comparative Example 4> The mixed gas introduced into the firing furnace 37 was changed to a gas having a moisture concentration of 11% by volume, an oxygen content of 3% by volume, a nitrogen content of 77% by volume, and a carbon dioxide content of 9% by volume, in the composition before introduction, and the moisture powder ratio was changed to 10 m 3 LiMO-14 was obtained in the same manner as in Example 1, except that the water content was set to 1 / kg. The water concentration in the mixed gas was adjusted by setting the water temperature to 48°C using the water supply means 36 of Example A.

[0222] When LiMO-14 was assigned to the composition formula (I), x=-0.03, y=0.20, and z=0.20.

[0223] Table 4 shows the results of the cycle retention rate of the lithium secondary batteries when LiMO-1 to LiMO-6 and LiMO-11 to LiMO-14 obtained in Examples 1 to 6 and Comparative Examples 1 to 4 were used.

[0224] [Table 4]

[0225] As shown in Table 4, it was confirmed that the lithium secondary batteries using LiMO obtained by introducing a specific mixed gas into a firing furnace and firing the batteries all had a cycle retention rate of 90% or more. [Explanation of symbols]

[0226] 1: separator, 3: negative electrode, 4: electrode group, 5: battery can, 6: electrolyte, 7: top insulator, 8: sealing body, 10: lithium secondary battery, 21: positive electrode lead, 31: negative electrode lead, 100: laminate, 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 element, 130: solid electrolyte layer, 200: exterior body, 200a: opening, 1000: all-solid-state lithium secondary battery, 30: firing means, 32: gas supply device, 33: oxygen gas supply means, 34: inert gas supply means, 35: carbon dioxide gas supply means, 36: moisture supply means, 37: firing furnace, 38a to 38c: flow meters, 39a to 39f: valves, 40a to 40c: supply channels, 42: supply channel

Claims

1. A method for producing a lithium metal composite oxide, comprising: a calcination step of introducing a mixed gas into a calcination furnace and calcining an object to be calcined in the calcination furnace at a temperature exceeding 600°C, wherein the object to be calcined is a mixture of a metal composite compound and a lithium compound, or a mixed raw material containing a reaction product of the metal composite compound and the lithium compound, and the mixed gas before being introduced contains oxygen, has a moisture content of 36 vol% or more and 85 vol% or less, and a carbon dioxide content of less than 4 vol%.

2. 2. The method for producing a lithium metal composite oxide according to claim 1, wherein the oxygen content in the mixed gas before being introduced is 10% by volume or more and 92% by volume or less.

3. The total amount of moisture (m) introduced into the firing furnace relative to the powder mass (kg) of the fired material ３ ) to 0.1 m ３ / kg or more 20m ３ 3. The method for producing a lithium metal composite oxide according to claim 1, wherein the amount of the lithium metal composite oxide is 1 / kg or less.

4. The method for producing a lithium metal composite oxide according to any one of claims 1 to 3, wherein the calcination step is carried out for a calcination time of 1 hour or more and 24 hours or less.

5. The method for producing a lithium metal composite oxide according to any one of claims 1 to 4, further comprising a cooling step of cooling the fired product inside the firing furnace after the firing step, wherein a gas having a dew point of -15°C or less is supplied into the firing furnace in the cooling step.

6. The method for producing a lithium metal composite oxide according to any one of claims 1 to 5, wherein the lithium metal composite oxide satisfies the following general formula (I): L[L) ｘ (N （１－ｙ－ｚ） Co ｙ X ｚ ) １－ｘ ]O ２ (I) In formula (I), X represents one or more elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, B, Si, S, and P, and satisfies −0.1≦x≦0.2, 0≦y≦0.4, and 0≦z≦0.5.

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