The mechanism of side reaction induced capacity fading of Ni-rich cathode materials for lithium ion batteries

Abstract

Optimized domain size endows Ni-rich cathode with both sufficient electrolyte infiltration and modest side reaction. Surface structure degradation caused by HF erosion is the main reason of the capacity fading, rather than LiF deposition. • The domain size of Ni-rich cathode influences the side reaction with electrolyte. • LiF deposition from side reaction shows little impact on cycling stability. • HF erosion caused surface phase transition is the main reason for capacity fading. Ni-rich cathode materials show great potential of applying in high-energy lithium ion batteries, but their inferior cycling stability hinders this process. Study on the electrode/electrolyte interfacial reaction is indispensable to understand the capacity failure mechanism of Ni-rich cathode materials and further address this issue. This work demonstrates the domain size effects on interfacial side reactions firstly, and further analyzes the inherent mechanism of side reaction induced capacity decay through comparing the interfacial behaviors before and after MgO coating. It has been determined that LiF deposition caused thicker SEI films may not increase the surface film resistance, while HF erosion induced surface phase transition will increase the charge transfer resistance, and the later plays the dominant factor to declined capacity of Ni-rich cathode materials. This work suggests strategies to suppress the capacity decay of layered cathode materials and provides a guidance for the domain size control to match the various applications under different current rates.