High performance of phosphorus and fluorine co-doped LiNi0.8Co0.1Mn0.1O2 as a cathode material for lithium ion batteries

Abstract

LiNi0.8Co0.1Mn0.1O2 (NCM811) is one of the promising cathode materials for high energy lithium ion batteries (LIBs). However, there is still ample room to improve its cycling stability. Herein, LiPF6 has been smartly employed as a doping agent to realize the P and F codoping into the structure of NCM811 material. As a result, the d-spacing of the material was enlarged, which facilitated the Li+ ions insersion/deinsersion, and the surface of NCM811 particles was stabilized as well. Thus, the cycling performance of the NCM811 material was effectively improved, although slightly lowered the initial capacity. After 100 cycles, capacity retention rates of 88.8% (159.5 mAh g−1) and 94.4% (162.3 mAh g−1) were achieved at 0.5C for doped NCM811 samples by 0.5 wt% and 1 wt% LiPF6 solution, respectively, which is much higher compared with that of the pristine NCM811 (77.7%, 143.6 mAh g−1). Similar trend has also been obtained at 1 C, in that, the 0.5% sample has the optimum capacity enhancement of 87.6%. The improved cycling stability is attributed to the enhanced reversibility of Li+ intercalation/deintercalation and reduced electrode polarization, due to the P and F codoping. Overall, the P and F codoped NCM811 material is promising for high energy LIBs application as a cathode material.