Positive electrode active material for lithium secondary battery and method of preparing the same
The present invention relates to a positive electrode active material for a lithium secondary battery, which includes two types of layered structure materials and may improve properties by controlling an optimum cation (lithium and transition metals) distribution capable of increasing activity of oxygen ions, as anions, in the layered structure materials, and a method of preparing the same.
1 . A method of preparing a positive electrode active material for a lithium secondary battery, the method consisting essentially of:
mixing two or more metal precursors consisting essentially of lithium and at least one of transition metals selected from manganese (Mn), nickel (Ni), chromium (Cr), vanadium (V), and iron (Fe),
forming pellets after ball milling the mixture,
performing primary sintering of the mixed material,
grinding the sintered material to reduce a particle size,
performing secondary sintering at 700° C. to 1,000° C., and
quenching the secondary sintered material at 800° C. to 1,000° C., and at a cooling rate of 500° C./min to 900° C./min,
wherein the positive electrode active material for a lithium secondary battery is a composite represented by [Formula 1 ],
wherein the composite consists essentially of two phases having a layered structure,
inter-diffusion of lithium and transition metals is performed between the two phases having the layered structure, and
a lithium excess region and a cation-disordered region, where distinction between a lithium layer and a transition metal layer is not clear, are formed in both of the two layered structures,
a Li 2-x M1M2 y O 3 +b Li 1+x′ M2 (1−y′) O [Formula 1]
(wherein, 0<a<1, 0<b<1, a+b=1, 0.1≤x≤0.3, 0.1≤x′≤0.3, 0.1≤y≤0 0.3, 0.1≤y′≤0.3, ax=bx′, ay=by′, and each of M1 and M2 consists essentially of one or more elements independently selected from manganese (Mn), nickel (Ni), chromium (Cr), vanadium (V), and iron (Fe), and the composition satisfies electrical neutrality according to an amount of lithium and type and oxidation number of M1 and M2 which are inter-diffused between the two layered structures).
2 . The method of claim 1 , wherein the grinding is performed by at least one method selected from ball milling, water milling, air-jet milling, and roller milling.
3 . The method of claim 1 , wherein the primary sintering is performed at 800° C. to 1,000° C.