METHOD OF PREPARING MATERIAL FOR LITHIUM SECONDARY BATTERY OF HIGH PERFORMANCE
Provided is a method for preparing a lithium mixed transition metal oxide, comprising subjecting Li 2 CO 3 and a mixed transition metal precursor to a solid-state reaction under an oxygen-deficient atmosphere with an oxygen concentration of 10 to 50% to thereby prepare a powdered lithium mixed transition metal oxide having a composition represented by Formula I of Li x M y O 2 wherein M, x and y are as defined in the specification. Therefore, since the high-Ni lithium mixed transition metal oxide having a given composition can be prepared by a simple solid-state reaction in air, using a raw material that is cheap and easy to handle, the present invention enables industrial-scale production of the lithium mixed transition metal oxide with significantly decreased production costs and high production efficiency. Further, the thus-produced lithium mixed transition metal oxide is substantially free of impurities, and therefore can exert a high capacity and excellent cycle stability, in conjunction with significantly improved storage stability and high-temperature stability.
1 . A method for preparing a lithium mixed transition metal oxide, comprising subjecting Li 2 CO 3 and a mixed transition metal precursor to a solid-state reaction under an oxygen-deficient atmosphere with an oxygen concentration of 10 to 50% by volume to thereby prepare a powdered lithium mixed transition metal oxide having a composition represented by Formula I below:
Li x M y O 2 (I)
wherein:
M=M′ 1−k A k , wherein M′ is Ni 1−a−b (Ni 1/2 Mn 1/2 ) a Co b , 0.65≦a+b≦0.85 and 0.1≦b≦0.4;
A is a dopant;
0≦k≦0.05; and
x+y≈2 and 0.95≦x≦1.05.
2 . The method according to claim 1 , wherein the oxygen concentration is 10% to 30% by volume.
3 . The method according to claim 2 , wherein the atmosphere is an air atmosphere.
4 . The method according to claim 1 , wherein the mixed transition metal precursor is at least one selected from the group consisting of M(OH) 2 and MOOH wherein M is as defined in Formula I.
5 . The method according to claim 4 , wherein the mixed transition metal precursor is MOOH, and is prepared by an ammonia-free process.
6 . The method according to claim 1 , wherein the mixed transition metal precursor has a tap density of 1.1 to 1.6 g/cm 3 .
7 . The method according to claim 1 , wherein a mixing ratio of Li 2 CO 3 and the mixed transition metal precursor is 0.95 to 1.04:1 wherein the ratio of Li 2 CO 3 :mixed transition metal precursor is a w/w ratio.
8 . The method according to claim 1 , wherein the solid-state reaction includes a sintering process at 600 to 1,100° C. for 3 to 20 hours.
9 . The method according to claim 8 , wherein an amount of air exceeding 2 m 3 /kg LiMO 2 during the sintering process is supplied to a reaction vessel equipped with a heat exchanger for pre-warming of the air.
10 . The method according to claim 1 , wherein the lithium mixed transition metal oxide is prepared by a large-scale process of 5 kg or more under a high rate of air circulation of at least 2 m 3 of air by volume at room temperature per 1 kg of the final lithium mixed transition metal oxide.
11 . The method according to claim 10 , wherein for the high rate of air circulation, the air is pumped into or out of the reaction vessel.
12 . The method according to claim 11 , wherein at least 10 m 3 of air per 1 kg of the final lithium mixed transition metal oxide is pumped into or out of the reaction vessel.
13 . The method according to claim 9 , wherein the heat exchanger pre-warms in-flowing air before the in-flowing air enters the reaction vessel, while cooling the out-flowing air.
14 . A lithium mixed transition metal oxide prepared by the method of claim 1 .
15 . A lithium secondary battery comprising the lithium mixed transition metal oxide of claim 14 as a cathode active material.