Cycling stability of LiNi0.80Co0.15Al0.05O2 cathode modified by solid-state electrolyte film

Abstract

Ni-rich LiNi0.80Co0.15Al0.05 (NCA) cathode material with high energy density always suffers from structural degradation during cycles, resulting in rapid capacity fading and severe voltage decay. In this study, a solid-state electrolyte film of Li1.8Sc0.8Ti1.2(PO4)3 (LSTP) is constructed on the surface of NCA cathode via a chemical route to enhance the cycling stability of NCA cathode. The Ex-situ XRD, EIS, dQ/dV, and SEM analyses show that the structural degradation of NCA derives mainly from the corrosion of electrolyte rather than H2-H3 phase transition, which gives rise to the extremely weak phase transitions of H1-M−H2−H3 after cycles. Besides the isolation role of LSTP film, it is found that Ti4+ ions in LSTP incorporate into the subsurface structure of NCA, which can accelerate the Li+ diffusion, reduce the Li+/Ni2+ disorder, reinforce the crystal structure, and enlarge the inter-slab spacing of NCA. Consequently, the coated NCA-2 %LSTP cathode reveals well structural integrity and evident phase transition behavior, delivering stable cycling performance with a superior capacity retention of 96.8 % at 1.0C after 100 cycles. This study not only deeply analyzes the mechanism of the structural degradation of NCA, but also demonstrates an efficient improving approach through LSTP modification.