US-12620590-B2 - Method of washing positive electrode active material, and positive electrode active material prepared thereby

US12620590B2US 12620590 B2US12620590 B2US 12620590B2US-12620590-B2

Abstract

A positive electrode active material includes a lithium composite transition metal oxide and a lithium by-product present on the surface of the lithium composite transition metal oxide. The lithium by-product is included at 0.3 mol % to 0.41 mol % with respect to a total mole number of the lithium composite transition metal oxide, and Li 2 CO 3 and LiOH are included at a molar ratio of 1:1.8 to 1:3. A positive electrode including the positive electrode active material and a lithium secondary battery including the positive electrode are also provided.

Inventors

Won Sig Jung
Sang Soon Choi
Hyun Ah Park

Assignees

LG CHEM, LTD.

Dates

Publication Date: 20260505
Application Date: 20240719
Priority Date: 20180504

Claims (6)

1 . A positive electrode active material, comprising: a lithium composite transition metal oxide and a lithium by-product present on a surface of the lithium composite transition metal oxide, wherein the lithium by-product is Li 2 CO 3 and LiOH and included at 0.32 mol % to 0.41 mol % with respect to a total mole number of the lithium composite transition metal oxide, and Li 2 CO 3 and LiOH are included at a molar ratio of 1:1.8 to 1:3, and wherein the lithium composite transition metal oxide includes Ni, Co, and Mn, and an Ni content is 60 mol % or more.
2 . The positive electrode active material of claim 1 , wherein the lithium composite transition metal oxide includes Li 2 CO 3 on its surface at 0.05 mol % to 0.14 mol % with respect to the total mole number of the lithium composite transition metal oxide.
3 . The positive electrode material of claim 1 , wherein the lithium composite transition metal oxide includes LiOH on its surface at 0.15 mol % to 0.27 mol % with respect to the total mole number of the lithium composite transition metal oxide.
4 . The positive electrode material of claim 1 , further comprising a coating layer including one or more metal or metalloid elements on the surface of the lithium composite transition metal oxide.
5 . A positive electrode for a lithium secondary battery, comprising the positive electrode active material of claim 1 .
6 . A lithium secondary battery, comprising the positive electrode for a lithium secondary battery of claim 5 .

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. patent application Ser. No. 17/050,919, filed on Oct. 27, 2020, which is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/KR2019/005428 filed on May 7, 2019, which claims priority to Korean Patent Application No. 10-2018-0051714, filed on May 4, 2018, the disclosures of which are incorporated herein by reference in their entirety. TECHNICAL FIELD The present invention relates to a positive electrode active material for a secondary battery, which includes a composite coating layer having excellent coatability, a method of preparing the same, and a lithium secondary battery including the same. BACKGROUND ART According to the increase in the development and demand for mobile devices, the demand for a secondary battery as an environmentally friendly alternative energy source is rapidly increasing. Among secondary batteries, a lithium secondary battery, which exhibits a high energy density and a high voltage, and has a longer cycle life and a low self-discharge rate, has been commercialized and widely used. Lithium transition metal composite oxides are used as a positive electrode active material for a lithium secondary battery, and among them, the lithium cobalt composite metal oxide LiCoO2 having a high operating voltage and an excellent capacity is mainly used. However, since LiCoO2 has very poor thermal characteristics due to destabilization of a crystal structure due to delithiation and is expensive, there is a limit to mass use as a power source in the field of electric vehicles. As an alternative for LiCoO2, a lithium-manganese composite metal oxide (LiMnO2 or LiMn2O4), a lithium iron phosphate compound (LiFePO4) or a lithium nickel composite metal oxide (LiNiO2) was developed. Among them, the research and development of lithium-nickel composite metal oxides, which easily implement a high-capacity battery due to a high reversible capacity of approximately 200 mAh/g is more actively performed. However, compared to LiCoO2, LiNiO2 has poor thermal stability and is decomposed when an internal short circuit occurs due to pressure from the outside when charging, thereby causing the battery to rupture and ignite. For this reason, as a method of retaining the excellent reversible capacity of LiNiO2 and improving low thermal stability, a nickel-cobalt-manganese-based lithium composite metal oxide in which some of nickel (Ni) is substituted with cobalt (Co) (hereinafter, simply referred to as a “NCM-based lithium oxide”) has been developed. The lithium composite transition metal oxide has lithium by-products such as LiOH and Li2CO3 which do not react in the preparation thereof. Among these lithium by-products, LiOH increases the pH of an electrode slurry to cause the gelation of an electrode slurry and generates moisture in the charging/discharging of the battery, and since Li2CO3 is the cause of the generation of gases such as CO2 and CO, it highly affects the performance of the battery. Among NCM-based lithium oxides, an NCM-based lithium oxide having an Ni content of 60% or more is washed with water to adjust the amount of a lithium by-product in the preparation. In this process, when all of the lithium by-products are removed, side reactions and corrosion of the surface of the NCM-based lithium oxide occur, and thus it is necessary to leave a certain amount of lithium by-products. However, when more than the required amount of lithium by-products remains, since it leads to the above-described problems of the lithium by-products, it is necessary to control lithium by-products at the surface of a positive electrode material to have a certain amount and a certain proportion. When LiOH and Li2CO3 are used as Li precursors in the preparation of the lithium composite transition metal oxide, LiOH/Li2CO3 proportions in the residual lithium compound are different, and the total amount of the lithium by-products will vary according to the atmosphere in sintering and the residence time of each process. In previous washing processes, the washing amount of a lithium by-product may be adjusted by adjusting a water amount and a washing time, but when a water amount increases, processability is reduced, and it is impossible to selectively remove LiOH and Li2CO3. Therefore, there is a demand for the development of a washing technique for a positive electrode active material capable of effectively adjusting the washing amount of lithium by-products and selectively removing LiOH and Li2CO3. DISCLOSURE OF THE INVENTION Technical Problem The present invention is directed to providing a method of washing a positive electrode active material, which can effectively adjust the washing amount of lithium by-products and selectively remove LiOH and Li2CO3. The present invention is also directed to providing a method of preparing a positive electrode active material, which includes the method of washing a positive electrode act