Phosphate-based cathode materials to boost the electrochemical performance of sodium-ion batteries
The evolution of energy storage technology that can deliver high energy density with excellent rate performance is desirable all over the world. The scientific community is putting their efforts together to solve this issue and one of the best ways is to use battery technology. The studies are not only about the battery technology, the cathode materials that reveal these properties have also been getting great attention. Polyanionic compound-based electrodes offer a new perspective for improving and achieving higher capacity and energy/power density, safety, and long-life cycle stability of sodium-ion batteries (NIBs). However, in recent years, phosphate-based cathode compounds for NIBs have attracted great interest because of their improved structural diversity, stability, high ionic mobility, and better safety. This review article analyzes the recent advancements in the crystal structures of different explored Na-based phosphate compounds, their ion diffusion mechanisms, and the study of multi-electron reactions. The types of NASICONs Na-based phosphate compounds, which include orthophosphates, pyrophosphates, phosphates, and mixed phosphates, are also discussed with their drawbacks and benefits. The low electronic conductivity and moderately low-capacity performance of this class of materials are the major drawbacks to their advancement and application in NIBs. This review provides insight into the strategies to address these problems and summarizes suitable synthetic routes, dopants, and coating materials that can improve the electrochemical performance of existing phosphate-based cathode materials. The detailed analysis of crystal structures and the multi-electron reaction of phosphate-based materials are discussed. Different strategies have been discussed for enhancing their electrochemical properties, such as synthetic methodologies, compounding, and nano-structuring, which will provide insight into the important progress made in these materials and better guidance for polyanionic phosphate-based cathode materials for NIBs.