High performance of phosphorus and fluorine co-doped nickel-rich cathode material for lithium ion batteries

Nick-rich lithium metal oxides with the virtues of high capacity and relative low-cost are considered as the promising cathode materials for high energy lithium ion batteries (LIBs). Herein, the P and F ions are introduced to co-dope into the crystal structure of commercial LiNi0.6Co0.2Mn0.2O2 (NCM622) at transition-metal layers and oxygen sites, respectively. Thus, the lattice parameters of NCM622 are enlarged, and its surface structure is stabilized as well, leading to enhanced cycling performance and rate capability. The co-doped samples using 3% and 6% LiPF6 solution have a capacity retention of 143.1 mAh g(-1) and 143 mAh g(-1) (88.5% and 88.3% of the initial capacities) at 56 mA g(-1) in 100 cycles, which are of 7.3% higher than that of undoped NCM622 (133.3 mAh g(-1), 81.3%). Further increasing the current density to 280 mA g(-1), the capacity retention ratio as high as 93.8% (134.5 mAh g(-1)) are achieved in 100 cycles for the 6% sample, corresponding to 17.4% of capacity enhancement as compared with that of undoped one. Moreover, we discovered that P and F codoping can also largely improve the cycle stability of the LiNi1/3Co1/3Mn1/3O2 and LiCoO2. Overall, P and F codoping is an effective technique to improve the electrochemical performance of NCM622 and others layered materials.