Synthesis and Electrochemical Properties of Na₂Fe_0.8Mg_0.15Ni_0.05PO₄F/C Composite as Cathode Materials for Sodium-ion Batteries

抄録

Due to the abundance and low cost of sodium, sodium-ion batteries have received renewed attention in large-scale applications. At present, the primary task is to explore a new generation of cathode materials with excellent performance. Herein, ascorbic acid was used as a carbon source, Na₂Fe_0.85Mg_0.15PO₄F/C (NFMPF/C) and Na₂Fe_0.8Mg_0.15Ni_0.05PO₄F/C (NFMNPF/C) cathode materials were prepared by conventional solid-state reaction method on the basis of Na₂FePO₄F/C (NFPF/C). The electrochemical performance of the cathode material was improved by doping Mg and Ni on the Fe site, which was confirmed by the volt-ampere characteristic test and charge-discharge test. Compared with NFPF/C, the electrochemical performance of NFMPF/C has been greatly improved. After further doping of Ni, NFMNPF/C shows a stable discharge capacity, which can still maintain 91.3 % of the initial specific capacity after 50 cycles at 0.1 C-rate, while the rate capability shows a great improvement. The optimized NFMNPF/C sample can deliver a specific discharge capacity of 53 mAh/g at 5 C-rate. In general, the simple doping of NFPF/C optimizes the cycle life and rate capability at the same time. As a low-cost cathode material, this study provides more possibilities for the development of sodium-ion batteries.