US-12620578-B2 - Positive electrode active material and lithium secondary battery comprising the same

US12620578B2US 12620578 B2US12620578 B2US 12620578B2US-12620578-B2

Abstract

The present invention relates to a positive electrode active material having improved electrochemical characteristics and improved stability, and a lithium secondary battery using a positive electrode including the positive electrode active material, and more particularly, to a positive electrode active material which may prevent decreases in electrochemical characteristics and stability of the positive electrode active material, which are caused by Li impurities, in advance by controlling the content of the Li impurities remaining on the surface of the positive electrode active material without a washing process to reduce the amount of residual lithium present on the surface thereof, and a lithium secondary battery using a positive electrode containing the positive electrode active material.

Inventors

Chang Woo Lee
Moon Ho Choi
Hyun Jong YU

Assignees

ECOPRO BM CO., LTD.

Dates

Publication Date: 20260505
Application Date: 20210616
Priority Date: 20200828

Claims (8)

1 . A positive electrode active material, comprising: a first compound enabling lithium intercalation/deintercalation; and a coating layer present on at least a part of the surface of the first compound, wherein the first compound has an Ni content of 80 mol % or more, wherein the first compound is represented by Formula 1 below: Li w Ni 1-(x+y+z) Co x M1 y M2 z O 2+α [Formula 1] wherein, M1 is at least one selected from Mn and Al, M2 is at least one selected from Mn, P, Sr, Ba, B, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W and Cu, M1 and M2 are different elements, 0.5≤w≤1.5, 0≤x≤0.20, 0≤y≤0.20, 0≤z≤0.20, and 0≤a≤0.02, wherein the coating layer comprises a second compound containing phosphorus (P) and a third compound containing tungsten (W), wherein the first compound does not include any coating layer formed thereon that comprises a compound having a crystal structure belonging to a space group Fd-3m, R3c and R-3m, wherein the second compound comprises a first oxide including LiCo(PO 4 ) and LiPO 3 , and a second oxide including Co 3 (PO 4 ) 2 , wherein a ratio of the first oxide to the second oxide in the second compound present in the coating layer is less than 0.87, and wherein a content of LiOH in the positive electrode active material is 1,789 to 2,892 ppm.
2 . The positive electrode active material of claim 1 , wherein tungsten is present in the crystal lattice of the first compound.
3 . The positive electrode active material of claim 1 , wherein the second compound is represented by Formula 2 below: Li a Co b M3 c (P β O γ ) d [Formula 2] wherein, M3 is at least one selected from Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Gd and Nd, 0≤a≤10, 0≤b≤8, 0≤c≤8, 0<d≤13, 0<β≤4, and 0<γ≤10.
4 . The positive electrode active material of claim 3 , wherein the second compound comprises a first oxide represented by Formula 3 below and a second oxide represented by Formula 4 below: Li a′ Co b′ M3′ c′ (P β′ O γ′ ) d′ [Formula 3] wherein, M3′ is at least one selected from Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Gd and Nd, 0<a′≤10, 0≤b′≤8, 0≤c′≤8, 0<d′≤13, 0≤β′≤4, and 0<γ′≤10; and Co b″ M3″ c″ (P β″ O γ″ ) d″ [Formula 4] wherein, M3″ is at least one selected from Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Gd and Nd, 0≤b″≤8, 0≤c″≤8, 0<d″≤13, 0≤β″≤4, and 0<γ″≤10.
5 . The positive electrode active material of claim 1 , wherein the third compound is represented by Formula 5 below, Li e W f M4 g O h [Formula 5] wherein, M4 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, Ce, V, Ba, Ta, Sn, Hf, Gd and Nd, 0≤e≤10, 0<f≤8, 0≤g≤8, and 2≤h≤13.
6 . The positive electrode active material of claim 5 , wherein the content of the second compound on the first compound is higher than that of the third compound.
7 . A positive electrode comprising the positive electrode active material of claim 1 .
8 . A lithium secondary battery using the positive electrode of claim 7 .

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims priority to and the benefit of Korean Patent Application No. 10-2020-0109044, filed on Aug. 28, 2020, the disclosure of which is incorporated herein by reference in its entirety. BACKGROUND 1. Field of the Invention The present invention relates to a positive electrode active material having improved electrochemical characteristics and improved stability and a lithium secondary battery using a positive electrode containing the positive electrode active material, and more particularly, to a positive electrode active material which can prevent decreases in electrochemical characteristics and stability of the positive electrode active material, which are caused by Li impurities, in advance by controlling the content of the Li impurities remaining on the surface of the positive electrode active material without a washing process to reduce the amount of residual lithium present on the surface thereof, and a lithium secondary battery using a positive electrode containing the positive electrode active material. 2. Discussion of Related Art Batteries store electrical power by using materials facilitating an electrochemical reaction at a positive electrode and a negative electrode. As a representative example of such batteries, there is a lithium secondary battery storing electrical energy due to a difference in chemical potential when lithium ions are intercalated/deintercalated into/from a positive electrode and a negative electrode. The lithium secondary battery uses materials enabling reversible intercalation/deintercalation of lithium ions as positive electrode and negative electrode active materials, and is manufactured by charging an organic electrolyte solution or a polymer electrolyte solution between the positive electrode and the negative electrode. A lithium composite oxide is used as a positive electrode active material of the lithium secondary battery, and composite oxides such as LiCoO2, LiMn2O4, LiNiO2, LiMnO2, etc. are being studied. Among the positive electrode active materials, LiCoO2 is most widely used due to excellent lifetime characteristics and charge/discharge efficiency, but it is expensive because of the limited resource of cobalt, which is used as a raw material, and thus has a disadvantage of limited price competitiveness. Lithium manganese oxides such as LiMnO2 and LiMn2O4 have advantages of excellent thermal safety and low costs, but also have problems of small capacity and poor high-temperature characteristics. In addition, while a LiNiO2-based positive electrode active material exhibits a battery characteristic such as a high discharge capacity, due to cation mixing between Li and a transition metal, it is difficult to synthesize the LiNiO2-based positive electrode active material, thereby causing a big problem in rate characteristics. In addition, depending on the intensification of such cation mixing, a large amount of Li by-products is generated, and since most of the Li by-products consist of compounds of LiOH and Li2CO3, they become a cause of gelation in preparation of a positive electrode paste and gas generation according to charge/discharge progression after the preparation of an electrode. Residual Li2CO3 increases the swelling phenomenon of a cell and thus reduces cycles and also leads to the swelling of a battery. Meanwhile, a content of the Li impurities present on the surface of the positive electrode active material tends to increase proportional to an Ni content of the positive electrode active material. Therefore, in the case of a high-Ni-type positive electrode active material recently introduced to improve the capacity characteristics of the positive electrode active material, due to the excessive presence of Li impurities in the surface, a washing process for removal thereof may be essential. However, residual lithium present on the surface of the positive electrode active material may be reduced through the washing process, but damage may be generated on the surface of the positive electrode active material. When the surface of the positive electrode active material is damaged by the washing process, the electrochemical characteristics and stability of the positive electrode active material may deteriorate. SUMMARY OF THE INVENTION The present invention relates to a positive electrode active material having improved electrochemical characteristics and improved stability to solve various problems of a conventional positive electrode active material for a lithium secondary battery. Particularly, the present invention is directed to providing a positive electrode active material which can prevent decreases in electrochemical characteristics and stability of the positive electrode active material, which are caused by Li impurities, by controlling a content of the Li impurities remaining on a surface of the positive electrode active material without a washing process to reduce an amount of the residual lit