Construction of a robust lithium cobalt phosphate layer for enhancement of the electrochemical performance of LiNi0.8Co0.1Mn0.1O2 at high voltage

The low cycling stability of LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) is due to structural instability during lithium insertion and removal and strong surface reactivity, and it limits widespread application. In this study, a layer of LiCoPO 4 was coated on NCM811, and electrochemical tests showed that the material had excellent high-voltage electrochemical properties. The NCM811 sample coated with 1.0 wt% LiCoPO 4 (NCM-LCP1) had a capacity of 156.5 mAh g −1 after 100 cycles at 3–4.6 V and a retention rate of 87.47%. In contrast, the capacity of unmodified NCM811 was only 96.9 mAh g −1 , with a retention rate of 55.9%. An NCM-LCP1/graphite full cell demonstrated a capacity retention rate of 87.46% over 200 cycles at 3–4.3 V. By combining EIS and postcycle analyses, the stability and protection mechanism of the LiCoPO 4 layer under high voltage was confirmed. The LiCoPO 4 layer effectively prevented particle fragmentation and kept the structure stable. It also suppressed side reactions on the cathode surface. This work offers a new methodology for modifying NCM811 materials operated at 4.6 V.