F-doped LiFePO4@N/B/F-doped carbon as high performance cathode materials for Li-ion batteries

LiFePO4 (LFP) is widely considered as a practical cathode material for lithium ion batteries, however its applications are still plagued by the low ionic and electronic conductivities. To address this challenge, F-doped LFP coated with N, B, F ternary doped carbon layer (F-LFP@NBFC) was synthesized by hydrothermal method using ionic liquid [BMIM]BF4 as the sole source for C, N, B and F. The F-LFP@NBFC exhibits superior electrochemical performance compared with the pristine LFP. F-LFP@NBFC demonstrates a discharge capacity of 162.2 mAh g(-1) at 0.1 C, which is close to its theoretical capacity, and maintains a 100% of discharge capacity after 40 cycles at 0.1 C. F-LFP@NBFC also shows an excellent rate capability and delivers a discharge capacity of 71.3 mAh g(-1) at 15 C. The excellent performance is ascribed to the surface coating of LFP and heteroatom doping into the carbon and LFP. On one hand, the N, B, F ternary doped carbon film acts as conducive network for LFP particles, improves the electronic conductivity of electrode particle and consequently enhances the Li+/Li-0 reduced/oxidized kinetics. On the other hand, the crystal lattice of LFP is enlarged by the F doping, which facilitates the Li+ intercalation/deintercalation. This study provides a convenient approach to prepare a high performance cathode material for lithium ion batteries.