Method for preparing positive active material for rechargeable lithium battery and positive active material prepared by same
Disclosed is a method of preparing a positive active material for a rechargeable lithium battery including adding first and second compounds to a solvent to prepare an acidic solution with a pH from 0.01 to 3, the first compound including an element that is capable of forming a double bond with an oxygen of a lithium metal oxide, and the second compound including at least one element selected from the group consisting of alkali metals, alkali earth metals, group 13 elements, group 14 elements, transition metals and rare-earth elements; adding a lithium-containing compound to the acidic coating solution to coat the lithium-containing compound; and heat-treating the coated lithium-containing compound to form a surface-treatment layer comprising a compound represented by the formula MXO k where M is an element selected from the group consisting of alkali metals, alkali earth metals, group 13 elements, group 14 elements, transition metals, rare-earth elements and combinations thereof; X is an element that is capable of forming a double bond with oxygen; and k is an integer from 2 to 4.
1. A method of preparing a positive active material for a rechargeable lithium battery comprising:
adding first and second compounds to a solvent to prepare an acidic coating solution with a pH of from 0.01 to 3, the first compound including an element that is capable of forming a double bond with an oxygen of a lithium metal oxide, and the second compound including at least one element selected from the group consisting of alkali metals, alkali earth metals, group 13 elements, group 14 elements, transition metals, and rare-earth elements;
coating a lithium-containing compound with the acidic coating solution to produce a coated lithium-containing compound; and
heat-treating the coated lithium-containing compound to form a surface-treatment layer comprising a compound represented by formula 1,
MXO k (1)
where, M is at least one element selected from the group consisting of alkali metals, alkali earth metals, group 13 elements, group 14 elements, transition metals, and rare-earth elements, X is an element that is capable of forming a double bond with oxygen, and k is a numerical value from 2 to 4.
2. The method of claim 1 , wherein element M is selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Si, Ti, B, Al, Sn, Mn, Cr, Fe, V, Zr, and combinations thereof.
3. The method of claim 1 , wherein element X is selected from the group consisting of P, S, W, and combinations thereof.
4. The method of claim 1 , wherein the pH of the acidic coating solution is from 0.8 to 1.3.
5. The method of claim 1 , wherein a molar mixing ratio of the first compound to the second compound is from 0.5 to 2:1.0 to 1.2.
6. The method of claim 1 , wherein the heat-treating step is performed at 450 to 900° C.
7. The method of claim 1 , wherein the heat-treating step is performed for 1 to 20 hours.
8. The method of claim 1 , wherein the surface-treatment layer further comprises a solid solution comprising an element selected from elements that are capable of forming a double bond with an oxygen of a lithium metal oxide, alkali metals, alkali earth metals, group 13 elements, group 14 elements, transition metals, and rare-earth elements.
9. The method of claim 1 , wherein the lithium-containing compound is represented by one of formulae 2 or 3,
Li x Ni y N 1-y A 2 (2)
Li x Ni y N 1-y O 2-z Y z (3)
where, 0.90≦x≦1.1, 0.1≦y≦0.9, 0≦z≦0.5, N is at least one element selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, and rare-earth elements, A is an element selected from the group consisting of O, F, S and P; and Y is selected from the group consisting of F, S, and P.