Cathode active material for lithium secondary battery and lithium secondary battery including the same
The cathode active material for a lithium secondary battery according to embodiments of the present invention includes a lithium-transition metal composite oxide particle including a plurality of primary particles, and the lithium-transition metal composite oxide particle includes a lithium-sulfur-containing portion formed between the primary particles. Thereby, it is possible to improve life-span properties and capacity properties by preventing the layer structure deformation of the primary particles and removing residual lithium.
1. A method of manufacturing a cathode active material for a lithium secondary battery comprising:
preparing a preliminary lithium-transition metal composite oxide particle;
mixing the preliminary lithium-transition metal composite oxide particle with a sulfonyl-based compound aqueous solution including the sulfonyl-based compound represented by Structural Formula 1 below; and
performing a drying and a heat treatment on the mixed preliminary lithium-transition metal composite oxide particle and the sulfonyl-based compound aqueous solution, to prepare a lithium-transition metal composite oxide particle comprising a plurality of primary particles and a lithium-sulfur-containing portion formed between the primary particles,
wherein an average sulfur signal value of the lithium-sulfur-containing portion measured through energy dispersive spectroscopy (EDS) is 1.2 to 3.8 times greater than an average sulfur signal value in the primary particles measured through the EDS:
(In Structural Formula 1, n is 0≤n<3, R 1 and R 2 are O − , NH 2 , NH 3 + , OH, or a hydrocarbon group having 1 to 3 carbon atoms that can be substituted with a substituent, and the substituent includes a halogen, cyano group, hydroxyl group, phosphoric acid group, carboxyl group or a salt thereof).
2. The method of manufacturing a cathode active material for a lithium secondary battery according to claim 1 , wherein the lithium-sulfur-containing portion has a monoclinic crystal structure.
3. The method of manufacturing a cathode active material for a lithium secondary battery according to claim 1 , wherein a sulfur content in the lithium-transition metal composite oxide particle measured through a carbon-sulfur (CS) analyzer is 2,000 to 7,000 ppm based on a total weight of the lithium-transition metal composite oxide particle.
4. The method of manufacturing a cathode active material for a lithium secondary battery according to claim 1 , wherein the hydrocarbon group included in R1 and R2 in Structural Formula 1 is substituted with or connected to at least one selected from the group consisting of a carbon-carbon double bond, —O—, —S—, —CO—, —OCO—, —SO—, —CO—O—, —OCO—O—, —S—CO—, —S—CO—O—, —CO—NH—, —NH—CO—O—, —NR′—,
—S—S— and —SO 2 —, and R′ is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.
5. The method of manufacturing a cathode active material for a lithium secondary battery according to claim 1 , wherein the sulfonyl-based compound includes at least one of compounds of Formulae 1 to 3 below:
6. The method of manufacturing a cathode active material for a lithium secondary battery according to claim 1 , wherein the primary particles have a hexagonal close-packed structure.
7. The method of manufacturing a cathode active material for a lithium secondary battery according to claim 1 , wherein a content of lithium carbonate (Li 2 CO 3 ) remaining on the surface of the lithium-transition metal composite oxide particle is 2,500 ppm or less based on the total weight of the lithium-transition metal composite oxide particle, and
a content of lithium hydroxide (LiOH) remaining on the surface of the lithium-transition metal composite oxide particle is 2,000 ppm or less based on the total weight of the lithium-transition metal composite oxide particle.
8. The method of manufacturing a cathode active material for a lithium secondary battery according to claim 1 , wherein the sulfonyl-based compound aqueous solution is formed by inputting the sulfonyl-based compound into a solvent, and
a weight of the solvent is 2 to 20% by weight based on the total weight of the preliminary lithium-transition metal composite oxide particle.
9. The method of manufacturing a cathode active material for a lithium secondary battery according to claim 8 , wherein an amount of the sulfonyl-based compound input into the solvent is 0.5 to 2.5% by weight based on the total weight of the preliminary lithium-transition metal composite oxide particle.
10. The method of manufacturing a cathode active material for a lithium secondary battery according to claim 1 , wherein the heat treatment is performed at 250 to 450° C. under an oxygen atmosphere.
11. The method of manufacturing a cathode active material for a lithium secondary battery according to claim 1 , wherein the preliminary lithium-transition metal composite oxide particle is mixed with the sulfonyl-based compound aqueous solution without water washing treatment.
12. A lithium secondary battery comprising:
a cathode comprising a cathode active material layer including the cathode active material for a lithium secondary battery manufactured by the method of claim 1 ; and
an anode disposed to face the cathode.