Cathode active material for lithium secondary battery and lithium secondary battery including the same
Embodiments of the present invention provide a cathode active material for a lithium secondary battery. The cathode active material for a lithium secondary battery includes lithium-transition metal composite oxide particles, and a coating formed on each of the lithium-transition metal composite oxide particles. The coating includes a lithium-sulfur compound and a metal hydroxide. A residual lithium on a surface of the cathode active material is sufficiently removed to improve an ionic conductivity and low-resistance.
1 . A cathode active material for a lithium secondary battery, comprising:
lithium-transition metal composite oxide particles; and
a coating formed on each of the lithium-transition metal composite oxide particles, the coating comprising a lithium-sulfur compound and a metal hydroxide,
wherein the lithium-sulfur compound includes at least one selected from the group consisting of lithium sulfate (Li 2 SO 4 ), lithium sulfate monohydrate (Li 2 SO 4 ·H 2 O), lithium ammonium sulfate (Li(NH 4 )SO 4 ), lithium hydroxylammonium sulfate (Li(NH 3 )(OH)SO 4 ), lithium fluorosulfate (LiSO 3 F), lithium hydrogen sulfate (LiHSO 4 ) and lithium sulfide (Li 2 S),
and wherein a content of the metal hydroxide is in a range from 0.1 mol % to 0.5 mol % based on a total number of moles of the lithium-transition metal composite oxide particles.
2 . The cathode active material for a lithium secondary battery of claim 1 , wherein a binding energy measured through an X-ray Photoelectron Spectroscopy (XPS) of the metal hydroxide is greater than a binding energy measured through the XPS of an oxide of the metal included in the metal hydroxide by at least 0.4 V.
3 . The cathode active material for a lithium secondary battery of claim 1 , wherein the metal hydroxide includes at least one selected from the group consisting of LiOH, Al(OH) 3 , Ti(OH) 2 , Zr(OH) 2 , Sr(OH) 2 , Ba(OH) 2 , W(OH) 6 , Mg(OH) 2 , Ta(OH) 5 and Nb(OH) 5 .
4 . The cathode active material for a lithium secondary battery of claim 1 , wherein each of the lithium-transition metal composite oxide particles comprises a plurality of primary particles therein, and the lithium-sulfur compound is present on an outer surface of the lithium-transition metal composite oxide particle and between the primary particles.
5 . The cathode active material for a lithium secondary battery of claim 4 , wherein an amount of the metal hydroxide present on the outer surface of the lithium-transition metal composite oxide particle is greater than an amount of the metal hydroxide present between the primary particles.
6 . The cathode active material for a lithium secondary battery of claim 1 , wherein a sulfur content in the cathode active material measured through a CS (Carbon-Sulfur) analyzer is in a range from 1,500 ppm to 4,500 ppm based on a total weight of the cathode active material.
7 . The cathode active material for a lithium secondary battery of claim 1 , wherein the lithium-sulfur compound has a monoclinic crystal structure.
8 . A method for manufacturing a cathode active material for a lithium secondary battery, comprising:
mixing lithium-transition metal composite oxide particles and a metal oxide to form a pre-coating on a surface of each of the lithium-transition metal composite oxide particles;
mixing the lithium-transition metal composite oxide particles having the pre-coating thereon and an aqueous solution of a sulfur-containing compound to form a mixture; and
performing a calcination of the mixture to form a coating that comprises a lithium-sulfur compound and a metal hydroxide on the surface of the lithium-transition metal composite oxide particles, wherein the lithium-sulfur compound includes at least one selected from the group consisting of lithium sulfate (Li 2 SO 4 ), lithium sulfate monohydrate (Li 2 SO 4 ·H 2 O), lithium ammonium sulfate (Li(NH 4 ) SO 4 ), lithium hydroxylammonium sulfate (Li(NH 3 )(OH) SO 4 ), lithium fluorosulfate (LiSO 3 F), lithium hydrogen sulfate (LiHSO 4 ) and lithium sulfide (Li 2 S).
9 . The method of claim 8 , wherein forming the pre-coating is performed by dry-mixing of the lithium-transition metal composite oxide particles and the metal oxide.
10 . The method according to claim 8 , wherein the metal oxide includes at least one selected from the group consisting of Al 2 O 3 , TiO 2 , Ti 2 O 3 , ZrO 2 , B 2 O 3 , SrO 2 , SrAl 2 O 4 , SrTiO 3 , SrWO 4 , BaO, WO 3 , (NH 4 ) 10 H 2 (W 2 O 7 ) 6 , MgO, Ta 2 O 5 , Nb 2 O 5 , MoO 3 , H 4 [W 12 SiO 40 ], H 4 SiO 4 ·12MoO 3 and (NH 4 ) 2 MoO 4 .
11 . The method of claim 8 , wherein the sulfur-containing compound includes a sulfonyl-based compound, and a weight of a solvent in the aqueous solution is in a range from 2 wt % to 20 wt % based on a total weight of the lithium-transition metal composite oxide particles.
12 . The method of claim 8 , wherein the calcination is performed at a temperature in a range from 250° C. to 550° C.
13 . The method of claim 8 , wherein the lithium-transition metal composite oxide particles are mixed with the aqueous solution without a water-washing treatment.
14 . A lithium secondary battery, comprising:
a cathode comprising a cathode active material layer, the cathode active material layer comprising the cathode active material for a lithium secondary battery of claim 1 ; and
an anode facing the cathode.