关键词: 钠离子电池, 正极材料, 磷酸盐, 材料结构, 电化学性能, 能量存储

Abstract:

Lithium-ion batteries have been widely used in portable electronic devices and electric vehicles because of their high energy density and long cycle life. Sodium-ion batteries have broad application prospects in the areas of large-scale electrochemical energy storage systems and low-speed electric vehicles because of their abundant raw materials, low resource cost, safety, and environmental friendliness. However, the development of sodium-ion batteries has been hindered by the low reversibility, sluggish ion diffusion, and large volume variations of the host materials. Suitable electrode materials with decent electrochemical performance must be primarily explored for the successful use of sodium-ion batteries. Since the electrochemical potential and specific capacities of cathode materials have a major impact on the energy densities of sodium-ion batteries, the development of cathode materials is critical. To date, various Na-insertable frameworks have been proposed, and some cathode materials have been reported to deliver reversible capacities approaching their theoretical values. Among them, transition metal oxides show a high reversible capacity and high working potential, but most of them still possess problems such as irreversible phase transition, air instability, and insufficient battery performance. Another type is the Prussian blue analogs. These materials exhibit a favorable operating voltage, cycling stability, and rate capability; however, the main obstacles to their practical application are the control of lattice defects, thermal instability, and low tap density. Polyanionic phosphates are the most promising cathode materials for sodium-ion batteries and have great research value and application prospects because of their stable framework structure, suitable operating voltage, and fast ion diffusion channels. However, their inherent defects, such as poor electronic conductivity and low theoretical energy density, considerably limit their practical applications. Researchers have conducted modification studies through bulk structure adjustment and micro-nano structural control with the goal of improving the performance of phosphate cathode materials and promoting the research and development of sodium-ion energy storage systems. This study reviews the recent advances in phosphate cathode materials for sodium-ion batteries, including orthophosphates, pyrophosphates, fluorophosphates, and mixed phosphate compounds. In this study, the intrinsic relationships among material composition, structure, and electrochemical properties are identified through analyses of the crystal structures, sodium storage mechanisms, and modification strategies of phosphate materials, thereby providing a reference for the continuous modification of polyanion phosphate cathode materials and exploration of high-voltage phosphate cathode materials. Some directions for future research and possible strategies for building advanced sodium-ion batteries are also proposed.

Key words: Sodium ion battery, Cathode material, Phosphate, Material structure, Electrochemical performance, Energy storage