Positive active material, method of preparing the same, positive electrode, and lithium battery
A positive active material, a method of preparing the same, and a lithium battery including the positive active material, the positive active material including a core, the core including an overlithiated lithium transition metal oxide; and a coating layer on the core, the coating layer including Li 3 VO 4 .
1. A positive active material, comprising:
a core, the core including an overlithiated lithium transition metal oxide; and
a coating layer on the core, the coating layer including Li 3 VO 4 ,
wherein an amount of vanadium in Li 3 VO 4 of the coating layer is greater than 0 and less than about 1.25 mole %, based on 1 mole of total transition metal in the core,
wherein the coating layer includes coating particles that include the Li 3 VO 4 , and
wherein the coating particles have an average particle diameter of about 10 nm to about 100 nm.
2. The positive active material as claimed in claim 1 , wherein the overlithiated lithium transition metal oxide is represented by Formula 1:
Li[Li a Ni b Co c Mn d M f ]O 2-x F x [Formula 1]
wherein, in Formula 1, M comprises at least one selected from titanium (Ti), vanadium (V), aluminum (Al), magnesium (Mg), chromium (Cr), iron (Fe), zirconium (Zr), rhenium (Re), boron (B), germanium (Ge), ruthenium (Ru), tin (Sn), niobium (Nb), molybdenum (Mo), and platinum (Pt), and
a, b, c, d, f, and x satisfy the following relations: a+b+c+d+f=1; 0<a<1; 0<b<1; 0<c<1; 0<d<1; 0≤f<1; and 0<x<0.1.
3. The positive active material as claimed in claim 2 , wherein, in Formula 1, f>0 and M comprises at least one selected from Ti, V, Al, Mg, Cr, Fe, and Zr.
4. The positive active material as claimed in claim 2 , wherein, in Formula 1, a, b, c, d, and f satisfy the following relations: 0.1<a<0.25, 0.1<b<0.4, 0<c<0.2, f=0, and 0.8<(2a+b)/d<1.2.
5. The positive active material as claimed in claim 1 , wherein the overlithiated lithium transition metal oxide has an average particle diameter of about 10 nm to about 500 μm.
6. The positive active material as claimed in claim 1 , wherein the coating layer is an island-type discontinuous coating layer.
7. The positive active material as claimed in claim 1 , wherein the core includes secondary particles including agglomerated primary particles.
8. The positive active material as claimed in claim 1 , wherein the coating layer is on a defective surface region of primary particles of the core.
9. A lithium battery comprising a positive electrode, the positive electrode including the positive active material as claimed in claim 1 .
10. A method of preparing the positive active material as claimed in claim 1 , the method comprising:
mixing a transition metal precursor, a lithium precursor, a fluorine compound, and a vanadium source to prepare a mixed starting material for preparing the overlithiated lithium transition metal oxide; and
thermally treating the mixed starting material to form the positive active material.
11. The method as claimed in claim 10 , wherein the transition metal precursor includes Ni b Co c Mn d M f (OH) y , where b+c+d++f=1, 0<b<1, 0<c<1, 0<d<1, 0≤f<1, y=2±0.2, and M comprises at least one selected from titanium (Ti), vanadium (V), aluminum (Al), magnesium (Mg), chromium (Cr), iron (Fe), zirconium (Zr), rhenium (Re), boron (B), germanium (Ge), ruthenium (Ru), tin (Sn), neodymium (Nb), molybdenum (Mo), and platinum (Pt).
12. The method as claimed in claim 11 , wherein, in the Ni b Co c Mn d M f (OH) y , f=0.
13. The method as claimed in claim 10 , wherein the lithium precursor includes at least one selected from LiOH and Li 2 Co 3 .
14. The method as claimed in claim 10 , wherein the fluorine compound includes at least one selected from lithium fluoride (LiF), magnesium fluoride (MgF 2 ), strontium fluoride (SrF 2 ), beryllium fluoride (BeF 2 ), calcium fluoride (CaF 2 ), ammonium fluoride (NH 4 F), ammonium bifluoride (NH 4 HF 2 ), and ammonium hexafluoroaluminate ((NH 4 ) 3 AlF 6 ).
15. The method as claimed in claim 10 , wherein the vanadium source includes at least one selected from ammonium metavanadate (NH 4 VO 3 ), sodium metavanadate (NaVO 3 ), potassium metavanadate (KVO 3 ), vanadium oxide (V 2 O 5 , V 2 O 4 , V 2 O 3 , or V 3 O 4 ), vanadium oxytrichloride (VOCl 3 ), vanadium tetrachloride (VCl 4 ), and vanadium trichloride (VCl 3 ).
16. The method as claimed in claim 10 , wherein thermally treating the mixed starting material is performed in air and at a temperature of about 400° C. to about 1,000° C.
17. The method as claimed in claim 16 , wherein thermally treating the mixed starting material is performed at a temperature of about 650° C. to about 900° C.
18. A positive active material, comprising:
a core, the core including an overlithiated lithium transition metal oxide; and
a coating layer on the core, the coating layer including Li 3 VO 4 ,
wherein the coating layer includes coating particles that include the Li 3 VO 4 , and
wherein the coating particles have an average particle diameter of about 10 nm to about 100 nm.