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With their advantages of abundant raw material reserves, safety, and low toxicity and cost, sodium-ion batteries (SIBs) have gained increasing attention in recent years. Thanks to a high theoretical specific capacity (124 mAh g−1), a high operating voltage (about 3.2 V), and a very stable three-dimensional layered structure, sodium ferric fluorophosphate (Na2FePO4F, NFPF) has emerged as a strong candidate to be used as a cathode material for SIBs. However, applications are currently limited due to the low electronic conductivity and slow ion diffusion rate of NFPF, which result in a low actual specific capacity and a high rate performance. In this study, the authors used a high-temperature solid-phase technique to produce Na2−xLixFePO4F/C (0 ≤ x ≤ 2) and evaluated the impact on electrode performance of materials with different Na+ and Li+ contents (values of x). Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were also used to analyze the material's crystal structure and nanostructure. The results show that the material had the best room-temperature performance when x = 0.5. At a charge–discharge rate of 0.1 C, the first discharge-specific capacity of the resulting Na1.5Li0.5FePO4F/C cathode material was 122.9 mAh g−1 (the theoretical capacity was 124 mAh g−1), and after 100 cycles, it remained at 118 mAh g−1, representing a capacity retention rate of 96.2% and a Coulomb efficiency of 98%. The findings of this study demonstrate that combining lithium and sodium ions improves the electrochemical performance of electrode materials. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries (SIBs) work similarly to lithium‐ion batteries, but they cost less and are safer. However, the battery has some shortcomings, such as low energy density and poor stability, which hinder its development and application. The development of electrode materials with low cost and high‐performance characteristics is a hot and difficult point in the research of SIBs. In this paper, the existing sodium ion cathode and anode materials are systematically reviewed. Firstly, the electrochemical structures and properties of various cathode and anode materials were introduced, and the limitations of cathode and anode materials of SIBs were analyzed. Based this, the current modification methods were summarized, such as surface coating of materials, doping of heteroatoms and metal elements to improve the electrochemical performance. In this paper, the research progress and modification measures of SIBs are summarized and prospected. It is helpful to further improve its comprehensive performance and lay a foundation for the future application of cathode and anode materials for SIBs. [ABSTRACT FROM AUTHOR]

With their advantages of abundant raw material reserves, safety, and low toxicity and cost, sodium-ion batteries (SIBs) have gained increasing attention in recent years. Thanks to a high theoretical specific capacity (124 mAh g -1 ), a high operating voltage (about 3.2 V), and a very stable three-dimensional layered structure, sodium ferric fluorophosphate (Na 2 FePO 4 F, NFPF) has emerged as a strong candidate to be used as a cathode material for SIBs. However, applications are currently limited due to the low electronic conductivity and slow ion diffusion rate of NFPF, which result in a low actual specific capacity and a high rate performance. In this study, the authors used a high-temperature solid-phase technique to produce Na 2-x Li x FePO 4 F/C (0 ≤ x ≤ 2) and evaluated the impact on electrode performance of materials with different Na + and Li + contents (values of x). Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were also used to analyze the material's crystal structure and nanostructure. The results show that the material had the best room-temperature performance when x = 0.5. At a charge-discharge rate of 0.1 C, the first discharge-specific capacity of the resulting Na 1.5 Li 0.5 FePO 4 F/C cathode material was 122.9 mAh g -1 (the theoretical capacity was 124 mAh g -1 ), and after 100 cycles, it remained at 118 mAh g -1 , representing a capacity retention rate of 96.2% and a Coulomb efficiency of 98%. The findings of this study demonstrate that combining lithium and sodium ions improves the electrochemical performance of electrode materials.