Enhanced electrochemical performance and thermal properties of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode material via CaF2 coating

Abstract LiNi0.8Co0.1Mn0.1O2 (NCM811) is demonstrated as potential cathode material for next-generation lithium-ion batteries. However, the electrochemical performance of this material is severely inhibited by structural degradation and capacity decay, especially at elevated temperatures. Herein, we try to design an ultra-thin CaF2 coating on the surface of NCM811 and examine the electrochemical performance. Physicochemical characterization results show that a CaF2 layer with a thickness of 5–12 nm was successfully attached to the surface of microspheres, without significant changes in structure or morphology. Electrochemical tests indicate that calcium fluoride modified samples especially 3 wt% exhibit a surprising cycle capability and rate performance. What's more, Calcium fluoride coating can also improve the high temperature stability of cathode material, sample with 3 wt% CaF2-coated shows an initial discharge specific capacity of 149.6 mAhg−1 and a capacity loss of 20.32% after 50 cycles at 55 °C, whereas the pristine material is 150.4 mAhg−1 and a severely capacity loss of 40.68%. The cyclic voltammograms (CV) and electrochemical impedance spectra (EIS) tests show that coated samples deliver a smaller potential difference (ΔV) and impedance after cycles, further confirming that CaF2 coating can enhance the electrochemical performance of NCM811 material.