Method for producing lithium-metal composite oxide

Abstract

This invention provides a method for producing a lithium-metal composite oxide using a two-stage firing process comprising a preliminary firing step for heating a precursor compound of a lithium-metal composite oxide and a lithium compound at a temperature of 500ºC to 650ºC to obtain a preliminary fired product; a pelletizing step for producing a pellet of the preliminary fired product; and a firing step for firing the pellet at a temperature of 700ºC to 1000ºC, such method is capable of minimizing the difference between a raw material metal ratio and the metal composition in a lithium-metal composite oxide, which occurs as a result of lithium element volatilization, and minimizing corrosion of a furnace body by lithium hydroxide.

Description

[0001] METHOD FOR PRODUCING LITHIUM-METAL COMPOSITE OXIDE

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a method for producing a lithium-metal composite oxide.

[0004] BACKGROUND

[0005] Lithium ion secondary batteries are small and lightweight and have a high energy density, a high charge / discharge voltage and a substantial charge / discharge capacity, and have garnered attention as power sources for operating electronic devices such as AV devices and personal computers. For example, positive electrode active materials comprising lithium-metal composite oxides represented by the basic formula Lia(NixCoyMz)O2 (M is a metal such as Mn, Mg or Al) have been proposed as positive electrode active materials that are useful for such lithium ion secondary batteries.

[0006] Lithium-metal composite oxides are generally obtained by preparing a metal composite hydroxide from a nickel compound, a cobalt compound and a compound of a metal such as n, Mg or Al, firing to obtain a metal composite oxide as a precursor, and then firing a precursor mixture of this metal composite oxide and a lithium compound (see JP 2020-198195 A).

[0007] SUMMARY OF THE INVENTION

[0008] In the method described in Patent Document 1 , because the lithium-metal composite oxide is first formed in a reaction between lithium and the metal composite hydroxide in the firing step, the bulk density after firing is reduced to approximately 70% of the original bulk density. This reduction in bulk density is a possible cause of a reduction in productivity.

[0009] Therefore, the inventors of the present disclosure focused on a method comprising using a metal composite hydroxide as is as a precursor, mixing this precursor with lithium hydroxide, carrying out preliminary firing to obtain a lithium-metal composite oxide, and then carrying out main firing. Because a lithium-metal composite oxide is formed before the main firing in such a method, there is almost no change in bulk density before and after the main firing, and productivity is not impaired by changes in bulk density.

[0010] However, in a method for producing a lithium-metal composite oxide using this type of two-stage firing process, lithium metal, which has a low boiling point, volatilizes in the main firing step, and this causes a difference between the raw material metal ratio and the metal composition in the obtained lithium-metal composite oxide. In addition, lithium hydroxide, which is produced as a result of the preliminary fired product melting in the main firing step, can cause corrosion of a furnace body.

[0011] In view of the circumstances mentioned above, the purpose of the present disclosure is to provide a method for producing a lithium-metal composite oxide using a two-stage firing process comprising preliminary firing and main firing, the method being capable of minimizing the difference between a raw material metal ratio and the metal composition in a lithium-metal composite oxide, which occurs as a result of lithium element volatilization, and minimizing corrosion of a furnace body by lithium hydroxide. The inventors of the present disclosure engaged in extensive research to solve the problems noted above. As a result, the inventors of the present disclosure found that according to a method for producing a lithium-metal composite oxide which includes: a preliminary firing step for heating a precursor compound of a lithium-metal composite oxide and a lithium compound at a temperature of 500°C to 650°C to obtain a preliminary fired product; a pelletizing step for producing a pellet of the preliminary fired product; and a firing step for firing the pellet at a temperature of 700°C to 1000°C, it is possible to minimize the difference between a raw material metal ratio and the metal composition in a lithium-metal composite oxide, which occurs as a result of lithium element volatilization, and minimize corrosion of a furnace body by lithium hydroxide, and thereby completed the present disclosure. Specifically, the present disclosure provides the following.

[0012] (1) A method for producing a lithium-metal composite oxide, the method including: a preliminary firing step for heating a precursor compound of a lithium-metal composite oxide and a lithium compound at 500°C to 650°C to obtain a preliminary fired product; a pelletizing step for producing a pellet of the preliminary fired product; and a firing step for firing the pellet at 700°C to 1000°C.

[0013] (2) The method for producing a lithium-metal composite oxide according to (1), wherein the lithium-metal composite oxide is represented by the general formula LiaNii-x-y-zCoxl\ / lnyl\ / lzO2+a (in the formula, M is an element other than Li, Ni, Co, Mn and O, 0.95<a<1.20, 0<x<0.4, 0<y<0.4, 0<z<0.1 , -0.5<a<0.5, and 1-x-y-z>0.3).

[0014] (3) The method for producing a lithium-metal composite oxide according to (1) or (2), wherein the average maximum length of the pellet is 1 mm to 350 mm.

[0015] The present disclosure is capable of providing a method for producing a lithium-metal composite oxide using a two-stage firing process comprising preliminary firing and main firing, the method being capable of minimizing the difference between a raw material metal ratio and the metal composition in a lithium-metal composite oxide, which occurs as a result of lithium element volatilization, and minimizing corrosion of a furnace body by lithium hydroxide.

[0016] Embodiments of the present disclosure (hereinafter referred to as “the present embodiment”) will now be explained, but the present disclosure is in no way limited by statements in the embodiments below, and the present disclosure can be carried out by adding appropriate modifications.

[0017] The method for producing a lithium-metal composite oxide according to the present embodiment includes: a preliminary firing step for heating a precursor compound of a lithium- metal composite oxide and a lithium compound at a temperature of 500°C to 650°C to obtain a preliminary fired product; a pelletizing step for producing a pellet of the preliminary fired product; and a firing step for firing the pellet at a temperature of 700°C to 1000°C.

[0018] This type of production method can form a lithium-metal composite oxide as a result of a reaction between lithium hydroxide and a hydroxide containing a transition metal in the preliminary firing step. Therefore, there is almost no change in bulk density in the firing step, in which firing is carried out at a high temperature, and it is possible to increase production efficiency in the firing step. This is because if bulk density decreases in a firing step carried out at a higher temperature, the amount of material that can be loaded in a furnace decreases due to this reduction in bulk density.

[0019] In addition, in a production method in which productivity is increased in this way, by pelletizing a preliminary fired product formed in a preliminary firing step, it is possible to reduce the amount of volatilization of lithium in a firing step carried out at a higher temperature than in the preliminary firing step. In addition, because a pellet has a lower contact area with a furnace body than a powder, damage to the furnace body is lower even if heating is carried out at a higher temperature in the firing step.

[0020] A lithium-metal composite oxide produced using the production method of the present embodiment is not particularly limited as long as this contains a transition metal, but is preferably represented by the general formula LiaNii-x-y-zCoxMnyl\ / lzO2+a (in the formula, M is an element other than Li, Ni, Co, Mn and O, 0.95<a<1.20, 0<x<0.4, 0<y<0.4, 0<z<0.1, -0.5<a<0.5, and 1-x-y-z>0.3).

[0021] In the general formula, the value of a may be 0.95 or more, 0.955 or more, 0.96 or more, 0.965 or more, 0.97 or more, 0.975 or more, or 0.98 or more. Meanwhile, the value of a may be 1.20 or less, 1.195 or less, 1.19 or less, 1.185 or less, 1.18 or less, 1.175 or less, 1.17 or less, 1.165 or less, 1.16 or less, 1.155 or less, 1.15 or less, 1.145 or less, 1.14 or less, 1.135 or less, 1.13 or less, 1.125 or less, 1.12 or less, 1.115 or less, 1.11 or less, 1.105 or less, 1.10 or less, 1.095 or less, 1.09 or less, 1.085 or less, 1.08 or less, 1.075 or less, 1.07 or less, 1.065 or less, 1.06 or less, 1.055 or less, or 1 .05 or less.

[0022] In the general formula, the value of x is not particularly limited as long as this falls within the range 0<x<0.4, but is, for example, preferably more than 0, 0.001 or more, 0.0015 or more, 0.002 or more, 0.0025 or more, 0.003 or more, 0.0035 or more, 0.004 or more, 0.0045 or more,

[0023] 0.005 or more, 0.0055 or more, 0.006 or more, 0.0065 or more, 0.007 or more, 0.0075 or more,

[0024] 0.008 or more, 0.0085 or more, 0.009 or more, 0.0095 or more, 0.01 or more, 0.015 or more,

[0025] 0.02 or more, 0.025 or more, 0.03 or more, 0.035 or more, 0.04 or more, 0.045 or more, 0.05 or more, 0.055 or more, 0.06 or more, 0.065 or more, 0.07 or more, 0.075 or more, 0.08 or more, 0.085 or more, 0.09 or more, 0.095 or more, 0.1 or more, 0.102 or more, 0.105 or more, 0.107 or more, 0.11 or more, 0.112 or more, 0.115 or more, 0.117 or more, 0.12 or more, 0.122 or more, 0.125 or more, 0.127 or more, 0.13 or more, 0.132 or more, 0.135 or more, 0.137 or more, 0.14 or more, 0.142 or more, 0.145 or more, 0.147 or more, 0.15 or more, 0.152 or more, 0.155 or more, 0.157 or more, 0.16 or more, 0.162 or more, 0.165 or more, 0.167 or more, 0.17 or more, 0.172 or more, 0.175 or more, 0.177 or more, 0.18 or more, 0.182 or more, 0.185 or more, 0.187 or more, 0.19 or more, 0.192 or more, 0.195 or more, 0.197 or more, 0.2 or more, 0.202 or more, 0.205 or more, 0.207 or more, 0.21 or more, 0.212 or more, 0.215 or more, 0.217 or more, 0.22 or more, 0.222 or more, 0.225 or more, 0.227 or more, 0.23 or more, 0.232 or more, 0.235 or more, 0.237 or more, 0.24 or more, 0.242 or more, 0.245 or more, 0.247 or more, 0.25 or more, 0.252 or more, 0.255 or more, 0.257 or more, 0.26 or more, 0.262 or more, 0.265 or more, 0.267 or more, 0.27 or more, 0.272 or more, 0.275 or more, 0.277 or more, 0.28 or more, 0.282 or more, 0.285 or more, 0.287 or more, 0.29 or more, 0.292 or more, 0.295 or more, 0.297 or more, 0.3 or more, 0.302 or more, 0.305 or more, 0.307 or more, 0.31 or more, 0.312 or more, 0.315 or more, 0.317 or more, 0.32 or more, 0.322 or more, 0.325 or more, 0.327 or more, 0.33 or more, 0.332 or more, 0.335 or more, 0.337 or more, 0.34 or more, 0.342 or more, 0.345 or more, 0.347 or more, 0.35 or more, 0.352 or more, 0.355 or more, 0.357 or more, 0.36 or more, 0.362 or more, 0.365 or more, 0.367 or more, 0.37 or more, 0.372 or more, 0.375 or more, 0.377 or more, 0.38 or more, 0.382 or more, 0.385 or more, 0.387 or more, 0.39 or more, 0.392 or more, 0.395 or more, or 0.397 or more. Meanwhile, the value of x is preferably 0.397 or less, 0.395 or less, 0.392 or less, 0.39 or less, 0.387 or less, 0.385 or less, 0.382 or less, 0.38 or less, 0.377 or less, 0.375 or less, 0.372 or less, 0.367 or less, 0.365 or less, 0.362 or less, 0.36 or less, 0.357 or less, 0.355 or less, 0.352 or less, 0.35 or less, 0.347 or less, 0.345 or less, 0.342 or less, 0.34 or less, 0.337 or less, 0.335 or less, 0.332 or less, 0.33 or less, 0.327 or less, 0.325 or less, 0.322 or less, 0.32 or less, 0.317 or less, 0.315 or less, 0.312 or less, 0.31 or less, 0.307 or less, 0.305 or less, 0.302 or less, 0.3 or less, 0.297 or less, 0.295 or less, 0.292 or less, 0.29 or less, 0.287 or less, 0.285 or less, 0.282 or less, 0.28 or less, 0.277 or less, 0.275 or less, 0.272 or less, 0.27 or less, 0.267 or less, 0.265 or less, 0.26 or less, 0.257 or less, 0.255 or less, 0.252 or less, 0.25 or less, 0.247 or less, 0.245 or less, 0.242 or less, 0.24 or less, 0.237 or less, 0.235 or less, 0.232 or less, 0.23 or less, 0.227 or less, 0.225 or less, 0.222 or less, 0.22 or less, 0.217 or less, 0.215 or less, 0.212 or less, 0.21 or less, 0.207 or less, 0.205 or less, 0.202 or less, 0.2 or less, 0.197 or less, 0.195 or less, 0.192 or less, 0.19 or less, 0.187 or less, 0.185 or less, 0.182 or less, 0.18 or less, 0.177 or less, 0.175 or less, 0.172 or less, 0.17 or less, 0.167 or less, 0.165 or less, 0.162 or less, 0.16 or less, 0.155 or less, 0.152 or less, 0.15 or less, 0.147 or less, 0.145 or less, 0.142 or less, 0.14 or less, 0.137 or less, 0.135 or less, 0.132 or less, 0.13 or less, 0.127 or less, 0.125 or less, 0.122 or less, 0.12 or less, 0.117 or less, 0.115 or less, 0.112 or less, 0.11 or less, 0.107 or less, 0.105 or less, 0.102 or less, 0.1 or less, 0.095 or less, 0.09 or less, 0.085 or less, 0.08 or less, 0.075 or less, 0.07 or less, 0.065 or less, 0.06 or less, 0.055 or less, 0.05 or less, 0.045 or less, 0.04 or less, 0.035 or less, 0.03 or less, 0.025 or less, 0.02 or less, 0.015 or less, 0.01 or less, 0.0095 or less, 0.009 or less, 0.0085 or less, 0.008 or less, 0.0075 or less, 0.007 or less,

[0026] 0.0065 or less, 0.006 or less, 0.0055 or less, 0.005 or less, 0.0045 or less, 0.004 or less, 0.0035 or less, 0.003 or less, 0.0025 or less, 0.002 or less, 0.0015 or less, or 0.001 or less.

[0027] In the general formula, the value of y is not particularly limited as long as this falls within the range 0<y<0.4, but is, for example, preferably more than 0, 0.001 or more, 0.0015 or more, 0.002 or more, 0.0025 or more, 0.003 or more, 0.0035 or more, 0.004 or more, 0.0045 or more, 0.005 or more, 0.0055 or more, 0.006 or more, 0.0065 or more, 0.007 or more, 0.0075 or more, 0.008 or more, 0.0085 or more, 0.009 or more, 0.0095 or more, 0.01 or more, 0.015 or more, 0.02 or more, 0.025 or more, 0.03 or more, 0.035 or more, 0.04 or more, 0.045 or more, 0.05 or more, 0.055 or more, 0.06 or more, 0.065 or more, 0.07 or more, 0.075 or more, 0.08 or more, 0.085 or more, 0.09 or more, 0.095 or more, 0.1 or more, 0.102 or more, 0.105 or more, 0.107 or more, 0.11 or more, 0.112 or more, 0.115 or more, 0.117 or more, 0.12 or more, 0.122 or more, 0.125 or more, 0.127 or more, 0.13 or more, 0.132 or more, 0.135 or more, 0.137 or more, 0.14 or more, 0.142 or more, 0.145 or more, 0.147 or more, 0.15 or more, 0.152 or more, 0.155 or more, 0.157 or more, 0.16 or more, 0.162 or more, 0.165 or more, 0.167 or more, 0.17 or more, 0.172 or more, 0.175 or more, 0.177 or more, 0.18 or more, 0.182 or more, 0.185 or more, 0.187 or more, 0.19 or more, 0.192 or more, 0.195 or more, 0.197 or more, 0.2 or more, 0.202 or more, 0.205 or more, 0.207 or more, 0.21 or more, 0.212 or more, 0.215 or more, 0.217 or more, 0.22 or more, 0.222 or more, 0.225 or more, 0.227 or more, 0.23 or more, 0.232 or more, 0.235 or more, 0.237 or more, 0.24 or more, 0.242 or more, 0.245 or more, 0.247 or more, 0.25 or more, 0.252 or more, 0.255 or more, 0.257 or more, 0.26 or more, 0.262 or more, 0.265 or more, 0.267 or more, 0.27 or more, 0.272 or more, 0.275 or more, 0.277 or more, 0.28 or more, 0.282 or more, 0.285 or more, 0.287 or more, 0.29 or more, 0.292 or more, 0.295 or more, 0.297 or more, 0.3 or more, 0.302 or more, 0.305 or more, 0.307 or more, 0.31 or more, 0.312 or more, 0.315 or more, 0.317 or more, 0.32 or more, 0.322 or more, 0.325 or more, 0.327 or more, 0.33 or more, 0.332 or more, 0.335 or more, 0.337 or more, 0.34 or more, 0.342 or more, 0.345 or more, 0.347 or more, 0.35 or more, 0.352 or more, 0.355 or more, 0.357 or more, 0.36 or more, 0.362 or more, 0.365 or more, 0.367 or more, 0.37 or more, 0.372 or more, 0.375 or more, 0.377 or more, 0.38 or more, 0.382 or more, 0.385 or more, 0.387 or more, 0.39 or more, 0.392 or more, 0.395 or more, or 0.397 or more. Meanwhile, the value of y is preferably 0.397 or less, 0.395 or less, 0.392 or less, 0.39 or less, 0.387 or less, 0.385 or less, 0.382 or less, 0.38 or less, 0.377 or less, 0.375 or less, 0.372 or less, 0.367 or less, 0.365 or less, 0.362 or less, 0.36 or less, 0.357 or less, 0.355 or less, 0.352 or less, 0.35 or less, 0.347 or less, 0.345 or less, 0.342 or less, 0.34 or less, 0.337 or less, 0.335 or less, 0.332 or less, 0.33 or less, 0.327 or less, 0.325 or less, 0.322 or less, 0.32 or less, 0.317 or less, 0.315 or less, 0.312 or less, 0.31 or less, 0.307 or less, 0.305 or less, 0.302 or less, 0.3 or less, less than 0.3, 0.299 or less, 0.297 or less, 0.295 or less, 0.292 or less, 0.29 or less, 0.287 or less, 0.285 or less, 0.282 or less, 0.28 or less, 0.277 or less, 0.275 or less, 0.272 or less, 0.27 or less, 0.267 or less, 0.265 or less, 0.26 or less, 0.257 or less, 0.255 or less, 0.252 or less, 0.25 or less, 0.247 or less, 0.245 or less, 0.242 or less, 0.24 or less, 0.237 or less, 0.235 or less, 0.232 or less, 0.23 or less, 0.227 or less, 0.225 or less, 0.222 or less, 0.22 or less, 0.217 or less, 0.215 or less, 0.212 or less, 0.21 or less, 0.207 or less, 0.205 or less, 0.202 or less, 0.2 or less, 0.197 or less, 0.195 or less, 0.192 or less, 0.19 or less, 0.187 or less, 0.185 or less, 0.182 or less, 0.18 or less, 0.177 or less, 0.175 or less, 0.172 or less, 0.17 or less, 0.167 or less, 0.165 or less, 0.162 or less, 0.16 or less, 0.155 or less, 0.152 or less, 0.15 or less, 0.147 or less, 0.145 or less, 0.142 or less, 0.14 or less, 0.137 or less, 0.135 or less, 0.132 or less, 0.13 or less, 0.127 or less, 0.125 or less, 0.122 or less, 0.12 or less, 0.117 or less, 0.115 or less, 0.112 or less, 0.11 or less, 0.107 or less, 0.105 or less, 0.102 or less, 0.1 or less, 0.095 or less, 0.09 or less, 0.085 or less, 0.08 or less, 0.075 or less, 0.07 or less, 0.065 or less, 0.06 or less, 0.055 or less, 0.05 or less, 0.045 or less, 0.04 or less, 0.035 or less, 0.03 or less, 0.025 or less, 0.02 or less, 0.015 or less, 0.01 or less, 0.0095 or less, 0.009 or less, 0.0085 or less, 0.008 or less, 0.0075 or less, 0.007 or less, 0.0065 or less, 0.006 or less, 0.0055 or less, 0.005 or less, 0.0045 or less, 0.004 or less, 0.0035 or less, 0.003 or less, 0.0025 or less, 0.002 or less, 0.0015 or less, or 0.001 or less.

[0028] In the general formula, the value of z is not particularly limited as long as this falls within the range 0<z<0.1 , but is, for example, preferably more than 0, 0.001 or more, 0.0012 or more, 0.0015 or more, 0.0017 or more, 0.002 or more, 0.0022 or more, 0.0025 or more, 0.0027 or more, 0.003 or more, 0.0032 or more, 0.0035 or more, 0.0037 or more, 0.004 or more, 0.0042 or more, 0.0045 or more, 0.0047 or more, 0.005 or more, 0.0052 or more, 0.0055 or more, 0.0057 or more, 0.006 or more, 0.0062 or more, 0.0065 or more, 0.0067 or more, 0.007 or more, 0.0072 or more, 0.0075 or more, 0.0077 or more, 0.008 or more, 0.0082 or more, 0.0085 or more, 0.0087 or more, 0.009 or more, 0.0092 or more, 0.0095 or more, 0.0097 or more, 0.01 or more, 0.012 or more, 0.015 or more, 0.017 or more, 0.02 or more, 0.022 or more, 0.025 or more, 0.027 or more, 0.03 or more, 0.032 or more, 0.035 or more, 0.037 or more, 0.04 or more, 0.042 or more, 0.045 or more, 0.047 or more, 0.05 or more, 0.052 or more, 0.055 or more, 0.057 or more, 0.06 or more, 0.062 or more, 0.065 or more, 0.067 or more, 0.07 or more, 0.072 or more, 0.075 or more, 0.077 or more, 0.08 or more, 0.082 or more, 0.085 or more, 0.087 or more, 0.09 or more, 0.092 or more, 0.095 or more, or 0.097 or more. Meanwhile, the value of z is preferably 0.097 or less, 0.095 or less, 0.092 or less, 0.09 or less, 0.087 or less, 0.085 or less, 0.082 or less, 0.08 or less, 0.077 or less, 0.075 or less, 0.072 or less, 0.07 or less, 0.067 or less, 0.065 or less, 0.062 or less, 0.06 or less, 0.057 or less, 0.055 or less, 0.052 or less, 0.05 or less, 0.047 or less, 0.045 or less, 0.042 or less, 0.04 or less, 0.037 or less, 0.035 or less, 0.032 or less, 0.03 or less, 0.027 or less, 0.025 or less, 0.022 or less, 0.02 or less, 0.017 or less, 0.015 or less, 0.012 or less, 0.01 or less, 0.0097 or less, 0.0095 or less, 0.0092 or less, 0.009 or less, 0.0087 or less, 0.0085 or less, 0.0082 or less, 0.008 or less, 0.0077 or less, 0.0075 or less, 0.0072 or less, 0.007 or less, 0.0067 or less, 0.0065 or less, 0.0062 or less, 0.006 or less, 0.0057 or less, 0.0055 or less, 0.0052 or less, 0.005 or less, 0.0047 or less, 0.0045 or less, 0.0042 or less, 0.004 or less, 0.0037 or less, 0.0035 or less, 0.0032 or less, 0.003 or less, 0.0027 or less, 0.0025 or less, 0.0022 or less, 0.002 or less, 0.0017 or less, 0.0015 or less, 0.0012 or less, or 0.001 or less.

[0029] In the general formula, the element M is not particularly limited as long as this is one or more elements other than Li, Ni, Co, Mn and O, but can be, for example, Al, Ti, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr, B, or the like. Note that the type of element M should be selected depending on the purpose for which the element is being added. In addition, when a plurality of elements are included as the element M, the value of z represents the total amount of the plurality of elements.

[0030] The configuration of the produced lithium-metal composite oxide is not particularly limited, and may be, for example, in the form of particles. These particles may be in the form of secondary particles formed by aggregation of primary particles, may be primary particles as is, and may be a mixture of secondary particles and primary particles.

[0031] The average particle size of primary particles of the lithium-metal composite oxide is not particularly limited, but is, for example, preferably 80 nm or more, 100 nm or more, 120 nm or more, 150 nm or more, 170 nm or more, 200 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, or 450 nm or more. Meanwhile, the average particle size of primary particles is preferably 15 pm or less, 14.5 pm or less, 14 pm or less, 13.5 pm or less, 13 pm or less, 12.5 pm or less, 12 pm or less, 11.5 pm or less, 11 pm or less, 10.5 pm or less, 10 pm or less, 9.5 pm or less, 9 pm or less, 8.5 pm or less, 8 pm or less, 7.5 pm or less, 7 pm or less, 6.5 pm or less, 6 pm or less, 5.5 pm or less, 5 pm or less, or 4.5 pm or less. By ensuring that the average particle size of the primary particles falls within the prescribed range, it is possible to increase the energy density and to suppress cycle-associated particle destruction or a deterioration in rate characteristics. Note that the average particle size of the primary particles of the lithium-metal composite oxide is calculated by observing electron micrographs taken using a field emission scanning electron microscope (JSM-7100F: produced by JEOL Ltd.) at an accelerating voltage of 10 kV and at a magnification of 3000-20,000 times. Specifically, a field of view in which 100 or more primary particles (confirmed particle outline) are visible is randomly selected, and electron micrographs of all particles (confirmed particle outline) among the particles in the field of view are obtained, with the magnification changed as needed within the range noted above. These electron micrographs are then used to calculate the equivalent spherical diameter via image processing software (such as ImageJ) to determine the particle size of the primary particles.

[0032] In addition, the average particle size (D50) of the lithium-metal composite oxide is not particularly limited, but is, for example, preferably 80 nm or more, 100 nm or more, 120 nm or more, 150 nm or more, 170 nm or more, 200 nm or more, 250 nm or more, 300 nm or more,

[0033] 350 nm or more, 400 nm or more, or 450 nm or more. By ensuring that the D50 value is at least the prescribed value, it is possible to increase the electrode density. Meanwhile, the D50 value is preferably 25 pm or less, 24.5 pm or less, 24 pm or less, 23.5 pm or less, 23 pm or less, 22.5 pm or less, 22 pm or less, 21.5 pm or less, 21 pm or less, 20.5 pm or less, 20 pm or less, 19.5 pm or less, 19 pm or less, 18.5 pm or less, 18 pm or less, 17.5 pm or less, 17 pm or less, 16.5 pm or less, 16 pm or less, 15.5 pm or less, 15 pm or less, 14.5 pm or less, 14 pm or less, 13.5 pm or less, 13 pm or less, 12.5 pm or less, 12 pm or less, 11.5 pm or less, 11 pm or less, 10.5 pm or less, 10 pm or less, 9.5 pm or less, 9 pm or less, 8.5 pm or less, 8 pm or less, 7.5 pm or less, 7 pm or less, 6.5 pm or less, 6 pm or less, 5.5 pm or less, 5 pm or less, or 4.5 pm or less.

[0034] By ensuring that the D50 value is no greater than the prescribed value, it is possible to increase the energy density of a non-aqueous electrolyte secondary battery in which this lithium-metal composite oxide is used, and also possible to suppress cycle-associated particle destruction and a reduction in rate characteristics. Note that the D50 value is determined on a volume basis by a wet laser method using a laser type particle size distribution analyzer (Microtrac HRA produced by Nikkiso Co., Ltd.).

[0035] The BET specific surface area of the lithium-metal composite oxide powder is not particularly limited as long as this is 0.3 m2 / g or more, but is, for example, preferably 0.31 m2 / g or more, 0.32 m2 / g or more, 0.33 m2 / g or more, 0.34 m2 / g or more, 0.35 m2 / g or more, 0.36 m2 / g or more, 0.37 m2 / g or more, 0.38 m2 / g or more, 0.39 m2 / g or more, or 0.4 m2 / g or more. Meanwhile, the BET specific surface area of the lithium-metal composite oxide powder may be 5 m2 / g or less, 4.5 m2 / g or less, 4 m2 / g or less, 3.5 m2 / g or less, 3 m2 / g or less, 2.5 m2 / g or less, 2 m2 / g or less, 1.5 m2 / g or less, or 1 m2 / g or less.

[0036] Specifically, the method for producing a lithium-metal composite oxide according to the present embodiment can include the following steps.

[0037] Precursor preparation step: a precursor compound containing at least nickel is prepared.

[0038] Mixing step: a precursor mixture is prepared by mixing the precursor compound prepared in the precursor preparation step with a lithium compound.

[0039] Preliminary firing step: the precursor mixture prepared in the precursor mixing step is fired. Firing step: the precursor mixture is fired in the firing step.

[0040] Water washing step: if necessary, the lithium-metal composite oxide obtained by firing in the firing step is washed with water.

[0041] First, a precursor compound containing at least nickel is synthesized. In one embodiment, an aggregate can be obtained through aggregation of primary particles. The method for synthesizing a precursor compound is not particularly limited, and it is possible to use a method comprising, for example, adding an aqueous solution, which includes an aqueous solution containing a transition metal and aqueous solutions of compounds containing other elements according to the composition of the target lithium-metal composite oxide, dropwise to a reaction tank in which a base liquid comprising an alkaline aqueous solution such as an aqueous solution of sodium hydroxide or an ammonia solution is being stirred, monitoring and controlling the pH within a suitable range while adding sodium hydroxide or the like dropwise, coprecipitating by means of a wet reaction, and obtaining a precursor composite compound as, for example, a hydroxide, an oxide formed by calcining the hydroxide, a carbonate, or the like. Note that the precursor preparation step is not an essential process, and a precursor compound prepared using a process other than the precursor preparation step can be used in the method for producing a lithium-metal composite oxide.

[0042] In synthesis-related reactions, after the alkaline aqueous solution that serves as the base liquid is prepared, the interior of the reaction tank is preferably purged with an inert gas, or preferably nitrogen gas for industrial purposes, to create a nitrogen atmosphere in order to lower the oxygen concentration within the reaction tank system or in the solution. If the oxygen concentration is excessively high, there is a risk that the coprecipitated hydroxide will be overoxidized by any oxygen remaining over a predetermined amount, and a risk that the formation of agglomerates due to crystallization will be compromised.

[0043] The aqueous solutions of metal sources are not particularly limited, but use of acidic aqueous solutions, for example, is preferred, and in the case of a nickel compound, use of an aqueous sulfate solution such as an aqueous solution of nickel sulfate is more preferred. In addition, it is possible to use one or more aqueous solutions of metal sources.

[0044] Examples of nickel compounds that can be used include, but are not particularly limited to, one or more compounds selected from among nickel sulfate, nickel oxide, nickel hydroxide, nickel nitrate, nickel carbonate, nickel chloride, nickel iodide, metallic nickel, and the like.

[0045] Examples of cobalt compounds that can be used include, but are not particularly limited to, one or more compounds selected from among cobalt sulfate, cobalt oxide, cobalt hydroxide, cobalt nitrate, cobalt carbonate, cobalt chloride, cobalt iodide, metallic cobalt, and the like.

[0046] Examples of manganese compounds that can be used include, but are not particularly limited to, one or more compounds selected from among manganese sulfate, manganese oxide, manganese hydroxide, manganese nitrate, manganese carbonate, manganese chloride, manganese iodide, metallic manganese, and the like.

[0047] Examples of titanium compounds that can be used include, but are not particularly limited to, one or more compounds selected from among titanyl sulfate, titanium oxide, titanium hydroxide, titanium nitrate, titanium carbonate, titanium chloride, titanium iodide, metallic titanium, and the like.

[0048] Examples of aluminum compounds that can be used include, but are not particularly limited to, aluminum sulfate, aluminum oxide, aluminum hydroxide, aluminum nitrate, aluminum carbonate, aluminum chloride, aluminum iodide, sodium aluminate, metallic aluminum, and the like.

[0049] Examples of iron compounds that can be used include, but are not particularly limited to, one or more compounds selected from among iron sulfate, iron oxide, iron hydroxide, iron nitrate, iron carbonate, iron chloride, iron iodide, metallic iron, and the like.

[0050] Examples of niobium compounds that can be used include, but are not particularly limited to, one or more compounds selected from among niobium oxide, niobium chloride, lithium niobate, niobium iodide, and the like.

[0051] Examples of tungsten compounds that can be used include, but are not particularly limited to, one or more compounds selected from among tungsten oxide, sodium tungstate, ammonium para-tungstate, hexacarbonyl tungsten, tungsten sulfide, and the like.

[0052] Examples of magnesium compounds that can be used include, but are not particularly limited to, one or more compounds selected from among magnesium sulfate, magnesium oxide, magnesium hydroxide, magnesium nitrate, magnesium carbonate, magnesium chloride, magnesium iodide, metallic magnesium, and the like.

[0053] Examples of zirconium compounds that can be used include, but are not particularly limited to, one or more compounds selected from among zirconium sulfate, zirconium oxide, zirconium nitrate, ammonium zirconium carbonate, zirconium chloride, zirconium iodide, metallic zirconium, and the like.

[0054] Examples of other elements that can be used include one or more selected from among sulfates, oxides, hydroxides, nitrates, carbonates, chlorides, iodides, metals, and the like.

[0055] In view of the composition of the target lithium-metal composite oxide, the mixing proportions of these compounds should be adjusted so that the amounts of these elements are prescribed proportions.

[0056] When synthesizing a precursor compound, a suitable pH range is not particularly limited, and can be decided so as to achieve a desired form in terms of secondary particle size and coarseness / fineness, and the pH should generally fall within the range of approximately 10-13.

[0057] The precursor compound obtained by means of a wet reaction is preferably washed and then dried after being de-watered.

[0058] By washing the precursor compound, impurities such as sulfate radicals, carbonate radicals and sodium components, which are taken into an aggregated particle or adsorbed at a surface layer during the reaction, can be washed away. Washing treatments that can be used for small amounts of impurities include a procedure in which Nutsche washing using a Buchner funnel is carried out, or a procedure in which a reacted suspension is pumped through a press filter, washed with water, and de-watered. Note that the washing treatment can be carried out using, for example, pure water, an aqueous solution of sodium hydroxide, an aqueous solution of sodium carbonate, or the like, but use of pure water is industrially preferable. For a sizeable amount of residual sulfate radicals, however, a sodium hydroxide aqueous solution in which the pH is controlled according to the amount that remains may be used.

[0059] The mixing step is a step for mixing at least lithium hydroxide and the precursor compound obtained in the precursor preparation step to prepare a precursor mixture. Note that the mixing step is not an essential step.

[0060] It is preferable for raw materials such as lithium hydroxide and the precursor compound to be thoroughly mixed. If mixing is insufficient, variations may occur in terms of the ratio of lithium to other metals in some parts, and this leads to concerns that satisfactory battery characteristics cannot be achieved. Note that an ordinary mixer can be used for the mixing. For example, it is possible to use a shaker mixer, a Lbdige mixer, a Julia Mixer, a V-type blender, or the like.

[0061] Note that the ratio of raw materials is not particularly limited, and should generally be specified according to the ratio of elements in the lithium-metal composite oxide being produced, but in a case where the ratio of elements will change in a subsequent step, this change should be taken into account.

[0062] The preliminary firing step is a step for heating the precursor mixture at 500°C to 650°C to obtain a preliminary fired product as a lithium-metal composite oxide.

[0063] A lithium-metal composite oxide containing at least lithium and a transition metal is formed from the precursor mixture in this preliminary firing step.

[0064] The precursor compound contained in the precursor mixture may, or may not, contain nickel. In a case where the precursor compound contains nickel, the nickel may be divalent or trivalent, but the precursor compound preferably contains divalent nickel. The content of divalent nickel is not particularly limited, but is preferably 1 at% or more, 2 at% or more, 5 at% or more, 10 at% or more, 15 at% or more, 20 at% or more, 25 at% or more, 30 at% or more, 35 at% or more, 40 at% or more, 45 at% or more, 50 at% or more, 55 at% or more, 60 at% or more, 65 at% or more, 70 at% or more, 75 at% or more, 80 at% or more, 85 at% or more, 90 at% or more, 95 at% or more, 97 at% or more, or 99 at% or more relative to the total amount of nickel of all valencies. Meanwhile, the content of divalent nickel may be 100 at% or less.

[0065] In the preliminary firing step, it is preferable to include a firing means for promoting lithiation of the lithium-metal composite oxide. A specific example thereof is a method comprising enabling heat to be applied to the precursor mixture more easily, enabling gas generated by the lithium source to be easily discharged, and allowing gas having a high oxygen partial pressure to diffuse into the precursor mixture (into particles). In the preliminary firing step, it is possible to load the precursor mixture in a sagger or a crucible as a device used for the firing and fire the precursor mixture in a static furnace, a roller hearth kiln, a pusher furnace, or the like, but it is possible to use a rotary kiln to carry out the firing while the precursor mixture is flowing.

[0066] The firing temperature in the preliminary firing step is not particularly limited as long as this temperature is 500°C to 650°C. By ensuring that the firing temperature in the preliminary firing step falls within the range mentioned above, the lithium hydroxide in the precursor mixture reacts with the metal composite hydroxide, and it is possible to suppress generation of heterophases and obtain a lithium-metal composite oxide. The firing temperature in the preliminary firing step is preferably 510°C or higher, 520°C or higher, or 530°C. In addition, the firing temperature in the preliminary firing step is preferably 640°C or lower, 630°C or lower, 620°C or lower, 610°C or lower, 600°C or lower, 590°C or lower, or 580°C or lower. Note that the firing temperature in the present disclosure is the maximum temperature when an object to be heated is heated. The maximum temperature means the temperature of a part having the highest temperature in the object to be heated. Similar definitions are used hereinafter.

[0067] The gas atmosphere in the preliminary firing step is not particularly limited, and may be an oxidizing atmosphere in which a lithiation reaction and an oxidation reaction can progress reliably. For example, it is preferable to use a decarburized oxidizing gas atmosphere having a carbon dioxide gas concentration of 30 ppm or less, or an oxygen atmosphere having an oxygen concentration of 80 vol% or more, 90 vol% or more, or 95 vol% or more.

[0068] The firing duration in the preliminary firing step is not particularly limited as long as this is a duration that allows a lithiation reaction to take place, but is, for example, preferably 1 hour or longer, 2 hours or longer, or 3 hours or longer. Meanwhile, the firing duration in the preliminary firing step is, for example, preferably 10 hours or less, 9 hours or less, or 8 hours or less. Note that the firing duration means the duration for which the maximum temperature is held within the temperature range mentioned above. Similar definitions are used hereinafter.

[0069] The pelletizing step is a step for producing a pellet of the preliminary fired product.

[0070] Specifically, the pelletizing step can be a method for producing a pellet by compressing the powdered preliminary fired product in a mold.

[0071] The compression pressure is not particularly limited, but is preferably 20 MPa or more, 21 MPa or more, 22 MPa or more, 23 MPa or more, 24 MPa or more, 25 MPa or more, 26 MPa or more, 27 MPa or more, 28 MPa or more, 29 MPa or more, 30 MPa or more, 31 MPa or more, 32 MPa or more, 33 MPa or more, 34 MPa or more, 35 MPa or more, 36 MPa or more, 37 MPa or more, 38 MPa or more, 39 MPa or more, or 40 MPa or more. Meanwhile, the compression pressure may be 500 MPa or less, 450 MPa or less, 400 MPa or less, 350 MPa or less, 300 MPa or less, 250 MPa or less, 200 MPa or less, 150 MPa or less, 120 MPa or less, 100 MPa or less, 90 MPa or less, 80 MPa or less, or 70 MPa or less.

[0072] During the compression, moldability may be improved by adding water, a solvent, a resin binder, or the like, to the preliminary fired product.

[0073] The maximum length of the pellet is not particularly limited, but may be, for example, 1 mm or more, 2 mm or more, 3 mm or more, 4 mm or more, 5 mm or more, 6 mm or more, 7 mm or more, 8 mm or more, 9 mm or more, or 10 mm or more. Meanwhile, the maximum length of the pellet may be 350 mm or less, 320 mm or less, 300 mm or less, 270 mm or less, 250 mm or less, 220 mm or less, 200 mm or less, 170 mm or less, 150 mm or less, 120 mm or less, 100 mm or less, 70 mm or less, 60 mm or less, 50 mm or less, 47 mm or less, 45 mm or less, 42 mm or less, 40 mm or less, 37 mm or less, 35 mm or less, 32 mm or less, or 30 mm or less. Note that “maximum length” means the distance at which the distance from one end to the other end of a pellet is at a maximum.

[0074] The density of the pellet is not particularly limited, but is preferably 2 g / cm3or more, 2.1 g / cm3or more, 2.2 g / cm3or more, 2.3 g / cm3or more, 2.4 g / cm3or more, 2.5 g / cm3or more, 2.6 g / cm3or more, 2.7 g / cm3or more, 2.8 g / cm3or more, 2.9 g / cm3or more, or 3 g / cm3or more. Meanwhile, the density of the pellet may be 5 g / cm3or less, 4.9 g / cm3or less, 4.8 g / cm3or less, 4.7 g / cm3or less, 4.6 g / cm3or less, 4.5 g / cm3or less, 4.4 g / cm3or less, 4.3 g / cm3or less, 4.2 g / cm3or less, 4.1 g / cm3or less, or 4 g / cm3or less.

[0075] The shape of the pellet is not particularly limited, but may be, for example, a sphere, an elongated sphere, a circular cylinder, a disk, a polyhedron, or the like.

[0076] Note that the pelletizing step is not limited to the method described above as long as this is a method capable of molding the preliminary fired product.

[0077] The firing step is a step in which the pellet obtained in the pelletizing step is fired at a temperature of 700°C to 1000°C.

[0078] In the firing step, the lithium-metal composite oxide formed in the preliminary firing step is heated at a higher temperature to bring about crystal growth. Due to this configuration, a lithium-metal composite oxide having higher crystallinity can be obtained.

[0079] The firing temperature in the firing step is not particularly limited as long as this is 700°C to 1000°C, but is, for example, preferably 710°C or higher, 720°C or higher, or 730°C or higher. Meanwhile, the firing temperature in the firing step is preferably 980°C or lower, 950°C or lower, 920°C or lower, 880°C or lower, 850°C or lower, 820°C or lower, 810°C or lower, 800°C or lower, 790°C or lower, or 780°C or lower. By ensuring that the firing temperature falls within the prescribed range, it is possible to reduce the amount of unreacted parts and obtain a lithium- metal composite oxide having high crystallinity, and it is therefore possible to prevent a reduction in battery characteristics of a non-aqueous electrolyte secondary battery in which the obtained lithium-metal composite oxide is used in a positive electrode.

[0080] The gas atmosphere in the firing step is not particularly limited, and should be a non-reducing atmosphere in which crystal growth occurs and transition metals contained in the lithium-metal composite oxide are not reduced, and is preferably an atmosphere in which the amount of moisture and the carbon dioxide gas concentration are low. For example, it is preferable to use a decarburized oxidizing gas atmosphere having a carbon dioxide gas concentration of 30 ppm or less, or an oxygen atmosphere having an oxygen concentration of 80 vol% or more, 90 vol% or more, or 95 vol% or more.

[0081] The firing duration in the firing step is not particularly limited as long as this is a duration that allows crystal growth to take place in the lithium-metal composite oxide, but is, for example, preferably 1 hour or longer, 2 hours or longer, or 3 hours or longer. Meanwhile, the firing duration in the firing step is, for example, preferably 15 hours or less, 14 hours or less, 13 hours or less, 12 hours or less, 11 hours or less, 10 hours or less, 9 hours or less, or 8 hours or less.

[0082] A washing step may be provided in the method for producing a lithium-metal composite oxide according to the present embodiment. The washing step is a step for washing the lithium-metal composite oxide obtained in the firing step. In the lithium-metal composite oxide obtained in the firing step, generation of lithium carbonate is suppressed because lithium carbonate is absorbed by the action of the added compound, but a small amount of lithium carbonate may still be generated. In addition, unreacted lithium hydroxide and lithium compounds generated by lithium ions migrating from within crystals to the particle surface layer during firing may be present. Therefore, in order to remove or deplete these impurities, it is possible to carry out, for example, water washing, a heat treatment and drying. Note that the washing step is not an essential feature.

[0083] A surface treatment step may be provided in the method for producing a lithium-metal composite oxide according to the present embodiment. The surface treatment step is a step for carrying out a surface treatment on the lithium-metal composite oxide obtained in the firing step or the washing step. It is possible to add and mix compounds of prescribed elements with the lithium-metal composite oxide obtained in the firing step or the washing step, and then carry out a heat treatment so as to subject surfaces of primary particles and / or secondary particles of the lithium-metal composite oxide to a surface treatment with compounds of lithium and added elements. As a result, it is possible to achieve effects such as lowering the amount of lithium compounds remaining in a particle surface layer, improving lithium ion conductivity and lowering reactive resistance. Note that the surface treatment step is not an essential step.

[0084] Compounds of elements added for the surface treatment mentioned above can be one or more compounds selected from among, for example, aluminum compounds, boron compounds, tungsten compounds, manganese compounds, cobalt compounds, phosphorus compounds, niobium compounds, strontium compounds, antimony compounds, zirconium compounds, titanium compounds, and the like.

[0085] The heat treatment temperature is not particularly limited, but is, for example, preferably 200°C or higher, 210°C or higher, 220°C or higher, 230°C or higher, 240°C or higher, or 250°C or higher. Meanwhile, the heat treatment temperature is preferably 500°C or lower, 490°C or lower, 480°C or lower, 470°C or lower, 460°C or lower, 450°C or lower, 440°C or lower, 430°C or lower, 420°C or lower, 410°C or lower, or 400°C or lower. The heat treatment duration is not particularly limited, but is, for example, preferably 1-15 hours, 2-12 hours, or 2-10 hours.

[0086] A non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure is provided with a positive electrode that contains the lithium-metal composite oxide described above as a positive electrode active material, and the non-aqueous electrolyte secondary battery is constituted from the positive electrode, a negative electrode and an electrolyte solution containing an electrolyte.

[0087] When producing the positive electrode, an electrically conductive agent and a binder are added to, and mixed with, the lithium-metal composite oxide according to an embodiment of the present disclosure. The electrically conductive agent is, for example, preferably acetylene black, carbon black, graphite, or the like. The binder is, for example, preferably polytetrafluoroethylene, poly(vinylidene fluoride), or the like.

[0088] The negative electrode is not particularly limited, but can be, for example, not only a negative electrode active material such as lithium metal, graphite or a low crystallinity carbon material, but also one or more non-metallic or metallic elements selected from among Si, Al, Sn, Pb, Zn, Bi and Cd, alloys containing these, and chalcogen compounds containing these.

[0089] The solvent in the electrolyte solution is not particularly limited, but can be, for example, an organic solvent including one or more types selected from among carbonates, such as ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate, and ethers such as dimethoxyethane.

[0090] The electrolyte can be one or more types selected from among lithium salts such as lithium perchlorate and lithium tetrafluoroborate, in addition to lithium hexafluorophosphate (LiPF6) in particular, dissolved in a solvent.

[0091] Embodiments of the present disclosure have been explained above using specific examples, but the present disclosure can be carried out by adding appropriate modifications as long as the effect of the present invention is not impaired.

[0092] EXAMPLE

[0093] The present disclosure will now be explained in greater detail through the use of examples, but is not limited to these examples.

[0094] Note that in the examples, firing (the step for firing the pellet at a temperature of 700°C to 1000°C) may be referred to as “main firing” for the sake of convenience in order to distinguish from the preliminary firing.

[0095] Samples of lithium-metal composite oxides of Examples 1 and 2 and Comparative Examples 1 and 2 were prepared using the method shown below. First, an explanation will be given of a method for preparing a precursor compound used as a raw material of the lithium-metal composite oxides of the examples and comparative examples.

[0096] A mixed aqueous solution was obtained by mixing an aqueous solution of nickel sulfate, an aqueous solution of cobalt sulfate and an aqueous solution of manganese sulfate at an Ni:Co:Mn ratio (molar ratio) of 90:4:6. 300 g of an aqueous solution of sodium hydroxide and 500 g of aqueous ammonia added to 10 L of pure water was prepared in advance as a base liquid in a reaction tank, a nitrogen atmosphere was created in the reaction tank using nitrogen gas at a flow rate of 0.7 L / min, and a reaction was carried out in the nitrogen atmosphere.

[0097] Next, while rotating a stirring blade at 1000 rpm, the mixed aqueous solution, the aqueous solution of sodium hydroxide and the aqueous ammonia were simultaneously added dropwise at prescribed speeds, and a crystallization reaction was carried out by adjusting the dropwise addition amounts of the alkaline solutions so that the pH was 11.7, thereby obtaining a coprecipitate by coprecipitating so as to form aggregated particles in which Ni, Co and Mn were crystallized.

[0098] Next, the slurry in the reaction vessel was subjected to solid-liquid separation and then washed with pure water to reduce the amount of residual impurities, after which the cake-like coprecipitate was dried for 10 hours at 100°C in an air environment to obtain a nickel-cobalt- aluminum composite hydroxide represented by the compositional formula N i0.90Co0.04M nooe(OH)2.

[0099] The obtained metal composite hydroxide and anhydrous lithium hydroxide were weighed out at a Li / (Ni+Co+Mn) molar ratio of 1.08, and mixed to obtain a precursor mixture. The obtained precursor mixture was loaded in a sheath and subjected to preliminary firing in an electric furnace for 2 hours at 620°C in an oxygen atmosphere (oxygen concentration: 97 vol%) to obtain a powdered preliminary fired product.

[0100] Note that the precursor mixture obtained in the manner described above had a powder density of 1.00 g / cc and a repose angle of 55.0°, and the preliminary fired product had a powder density of 1.92 g / cc and a repose angle of 35.1°.

[0101] Example 1

[0102] 5 g of the preliminary fired product was loaded in a mold (made of SUS304) having a diameter of 15 mm, and compressed for 30 seconds at a pressure of 64 MPa using a hydraulic jack. Next, the hydraulic jack pressure was released, and a molded pellet was removed from the mold. At this point, the density of the pellet (hereinafter also referred to as the “loaded product density before main firing”) was calculated by measuring the volume and mass of the pellet, and found to be 3.16 g / cc.

[0103] Next, the obtained pellet was placed in a crucible (on an alumina setter) and fired for 4 hours at a maximum temperature of 750°C in an oxygen atmosphere (oxygen concentration: 99 vol%). After the firing, the shape of the molded body was maintained. A sample of a lithium-metal composite oxide was obtained by crushing and then pulverizing the obtained fired product. Example 2

[0104] A sample of a lithium-metal composite oxide was obtained in the same way as in Example 1 , except that a powder obtained by adding and mixing 2 mass% of water with the preliminary fired product was used.

[0105] Comparative Example 1

[0106] A sample of a lithium-metal composite oxide was obtained by loading the preliminary fired product in a crucible without carrying out pelletization, carrying out main firing for 4 hours at a maximum temperature of 750°C in an oxygen atmosphere (oxygen concentration: 99 vol%), and pulverizing the obtained fired product. Note that in Comparative Example 1, the density of the sample when loaded in the crucible was taken to be the loaded product density before main firing.

[0107] Comparative Example 2

[0108] The preliminary fired product was loaded in a crucible without carrying out pelletization, then held for 2 hours at a temperature of 600°C (at an oxygen concentration of 99 vol%), the temperature was increased to 750°C without being allowed to fall, and firing was carried out for 4 hours at a maximum temperature of 750°C. A sample of a lithium-metal composite oxide was obtained by pulverizing the obtained fired product. Note that in Comparative Example 2, the density of the sample when loaded in the crucible was taken to be the loaded product density before main firing.

[0109] The obtained samples were evaluated using the following methods.

[0110] <Compositional analysis of precursor compound and lithium-metal composite oxide>

[0111] The composition of the precursor compound and of the lithium-metal composite oxide were identified using the following method. 0.2 g of a sample of the precursor compound or the lithium-metal composite oxide was heated and dissolved in 25 mL of a 20% hydrochloric acid solution, cooled, and transferred to a 100 mL volumetric flask, and pure water was added to produce a preparation liquid. The obtained preparation liquid was subjected to elemental quantification using ICP-AES (Optima 8300 produced by PerkinElmer Japan).

[0112] Measurement of loose bulk density, repose angle of powder and loaded product density> The loose bulk density of the sample of the lithium-metal composite oxide and the powder repose angle were measured using a powder tester (produced by Hosokawa Micron Corp.).

[0113] The loose bulk density is the packing density (g / cm3) calculated by allowing a powder sample to drop naturally into a cup having a volume of 100 cm3and weighing the mass at this point.

[0114] The powder repose angle is the angle (angle of elevation) of a peak of the powder, which is formed by allowing the powder sample to drop naturally.

[0115] The loaded product density means the density (g / cm3) of a pellet when the sample of lithium- metal composite oxide is pelletized before the main firing. In addition, in a case where a pellet is not formed before the main firing, the loaded product density is the density (g / cm3) calculated by weighing out the powder sample by allowing the powder sample to drop naturally into a crucible having a volume of 100 cm3and measuring the mass at this point.

[0116] Productivity evaluations>

[0117] Productivity was evaluated in terms of the mass of sample before the main firing in the firing furnace for the same firing duration by assessing: ease of pelletizing, which was determined by assessing the loose density of the sample of lithium-metal composite oxide before the main firing and fluidity by means of powder repose angle; assessing productivity by means of loadability in a sheath; and taking into account the state of the sample before the main firing (high powder density caused by molding, ratio of sheath packing density caused by loading in the sheath). Specifically, evaluations were carried out using a three-point scale based on criteria A to C shown below.

[0118] A: All of requirements (1) to (3) below are satisfied.

[0119] B: One or two of requirements (1) to (3) below are satisfied.

[0120] C: None of requirements (1) to (3) below is satisfied.

[0121] (1) The loose bulk density of the powder before the main firing is 1.5 g / cm3to 2.6 g / cm3

[0122] (2) The powder repose angle before the main firing is 20° to 45°

[0123] (3) The ratio of the loaded product density before the main firing relative to the loose bulk density of the powder before the main firing (also referred to as “density ratio before main firing” hereinafter) is 1.2 times to 2.5 times

[0124] When the main firing was carried out, the Li / Me charging ratio (denoted by M) in the precursor mixture of the precursor compound and the lithium compound and the Li / Me ratio (denoted by N) in the lithium-metal composite oxide after the main firing were calculated using compositional analysis. At this point, the value of (M-N) / M was calculated, and quality was evaluated using a three-point scale based on criteria A to C below.

[0125] A: The value of (M-N) / M is not more than 0.03

[0126] B: The value of (M-N) / M is more than 0.03 and not more than 0.043

[0127] C: The value of (M-N) / M is more than 0.043

[0128] Table 1 below shows results for the loose bulk density of the powder before the main firing, the powder repose angle before the main firing, the packing density before the main firing, the density ratio before the main firing, the Li / Me ratio in the sample of lithium-metal composite oxide, the value of (M-N) / M, quality evaluations and productivity evaluations.

Claims

CLAIMS1. A method for producing a lithium-metal composite oxide, the method including: a preliminary firing step for heating a precursor compound of a lithium-metal composite oxide and a lithium compound at 500°C to 650°C to obtain a preliminary fired product; a pelletizing step for producing a pellet of the preliminary fired product; and a firing step for firing the pellet at 700°C to 1000°C.

2. The method for producing a lithium-metal composite oxide according to claim 1, wherein the lithium-metal composite oxide is represented by the general formula LiaNii-x-y-zCoxM nyMzO2+a (in the formula, M is an element other than Li, Ni, Co, Mn and O, 0.95<a<1.20, 0<x<0.4, 0<y<0.4, 0<z<0.1 , -0.5<a<0.5, and 1-x-y-z>0.3).

3. The method for producing a lithium-metal composite oxide according to claim 1 or claim 2, wherein the average maximum length of the pellet is 1 mm to 350 mm.

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