Degradation of High-Nickel Layered Oxide Cathodes from Surface to Bulk: A Comprehensive Structural, Chemical, and Electrical Analysis
Advanced Energy Materials
Lithium-ion batteries (LIBs) have been widely used in electronic devices and electric vehicles because of high energy density, and stable cycling performance. With the increasing demand for the higher energy density and safe LIBs, many studies have been progressed on the electrodes to achieve a higher reversible capacity, a higher output voltage and a better cycling stability. The commercialized cathode materials such as LiCoO2 and LiFePO4, have been proved to put a cap on high energy achieving due to the very limited available capacity. Therefore, the great attention is focusing on the development of layered lithium transition metal oxide materials (LTMO2, TM = Ni, Co, and Mn), including Li-rich LTMO, Li and Mn-rich xLi2MnO3·(1-x)LiMO2 and especially the Ni-rich LTMO owing to their much higher initial capacity. Recently, Ni-rich LTMO is the most notable cathode material to maintain capacity higher than 200 mAh/g. Unfortunately, the continuous capacity fading and the voltage decay due to chemical, structural, and mechanical degradation of these materials are serious for developing better cathode materials. Altogether, these degradation processes introduce irreversible changes on the surface and/or bulk properties of the active cathode and anode materials, resulting in a loss of active-mass/lithium as well as an increase in the internal cell resistance.It is very important to understand the degradation mechanism of LMO cathode for providing guidance on retaining higher energy during cycling.