Developments of Ni-rich cathode materials for Li-ion Batteries

Abstract

The increasing demand of high-energy storage devices for fully electrical vehicles (EVs) and portable electronics have led to the development of batteries with high energy densities. Layered materials such as LiMO2 (M = Ni, Co, Mn, Al, etc.) have been extensively investigated as potential candidates for cathodes. In particular, Ni-rich (Ni mol% > 0.5) materials are considered to be the most promising candidates because of their high specific capacity than LiCoO2. Recently, it has been reported that electrochemical performance of LiNi1-x-yCoxMyO2(M=Al, Mn) cathode materials and improvement of thermal safety was strongly correlated with composition of transition metal, synthetic method and surface condition. Ni-rich have low tap density, uneven Ni distribution on the surface region and poor rate capability compared with LiCoO2 need to be overcome. Recently, it has been revealed that uneven distribution of Ni element influences rate capability and cycling stability at 60◦C. We are an optimized synthetic condition for Ni-rich precursors in order to obtain Ni-rich cathode materials with high tap density (T.D.). The final product prepared from the optimized precursor demonstrated substantially improved electrochemical performance. Another critical problem of Ni-rich cathodes is the presence of lithium impurities such as LiOH and Li2CO3 on cathode surface. Because of the exposure to CO2 and moisture in air or use of excessive amounts of lithium sources during the preparation phase. Li2CO3 has been reported to be the main source of CO2 evolution during the electrochemical process at 60 °C. Accordingly, the Ni-rich material shows poor cycle retention, especially at 60 °C. Vanadium surface treatment is enhance the cycling performance and structural stability of Ni-rich materials. Due to the coating layer can suppress the side reaction such as dissolution of transition metal on cathode surface. And the vanadium surface treatment could reduce the amount of residual lithium impurities in Ni-rich cathode material. The objective of my research projects is to develop high energy and high power cathode materials without sacrificing other important battery performances. The project can be divided into two parts:

Part 1: Experimental Section 2.1 A Study on the optimized synthetic conditions of Ni-rich via Co-Precipitation Method Part 2: Experimental Section 2.2-2.3 A Study on the surface hardening of Ni-rich by Vanadium Treatment