Fluorides coated Ni-rich cathode materials with enhanced surficial chemical stability for advanced lithium-ion battery

Abstract

Ni-rich cathode materials (LiNixCoyMnzO2 denoted as NCM, where x ≥ 0.8 and x + y + z = 1) with high energy density are considered as next-generation promising cathodes for lithium-ion batteries (LIBs). However, the high surface chemical sensitivity against CO2 and H2O in air triggers serious surface degradation. Meanwhile, the notorious surficial residual lithium compounds are often prone to react with polyvinylidene fluoride (PVDF) binder, resulting in slurry gelation, and further deteriorating electrochemical performance. Herein, a facile solvothermal strategy is proposed to construct thin and uniform fluoride coating layers on NCM surface (NCM-F) via in-situ reacting trifluoroethanol with residual lithium compounds. This fluoride protective layer not only significantly suppresses the surface deterioration by inhibiting Li+/H+ exchange, but also avoids the side reactions between NCM and electrolyte. As a result, NCM-F with low pH value of 11.2 exhibits highly chemical stability against ambient air, excellent processing performance and superior cyclic stability. More importantly, even after 4 weeks air aging, NCM-F demonstrates high initial capacity and low electrode polarization compared to pristine NCM (P-NCM). This work not only opens up new perspectives on surface modification of NCM cathodes, but also provides guidance on improving air stability for other functional materials.