A review on pyrophosphate framework cathode materials for sodium-ion batteries

Sodium-ion batteries (SIBs) have been considered as an attractive and promising alternative for energy storage applications due to their advantages of abundant resources, low cost and relatively high safety. However, the low electrochemical kinetics of sodium-ion batteries is a major issue limiting their large-scale application. One of the main strategies to address this shortcoming is to find or develop novel cathode materials, which has encouraged a large number of materials chemists to design and develop a variety of polyanionic compounds. Herein, the latest research progress of pyrophosphates as cathode materials for SIBs is reviewed. It is pointed out that pyrophosphate-based cathode materials have abundant crystal chemistry, are easy to synthesize and have a stable structure. The remaining challenges and opportunities of these systems are also discussed and provided. This review will provide better guidance on pyrophosphate electrode materials used in advanced rechargeable batteries.