Regulations of Bulk and Interfacial Chemistry of Mn-Based Cathode Materials for Sodium Ion Batteries

Abstract

Sodium ion batteries (SIBs) show the great potential to achieve large-scale energy storage due to their low cost and good safety as well as abundant resources of sodium. Among the cathode materials for SIBs, manganese-based layered oxides with adjustable structure have been attached great interest for the high energy density and low-cost SIBs. . Particularly, P2-type Mn-based materials exhibit anionic redox during charge and discharge processes, which can not only elevate the battery potential but also provide extra capacity, drastically boosting the energy density of the batteries. However, the irreversible phase transition, Jahn-Teller effect of manganese and interphase degradation at high charge cutoff voltage during anionic redox largely affect the cyclic stability of the cathodes. Therefore, it is essential to develop effective strategies to regulate the structural and interfacial chemistry for suppressing the phase transition and voltage hysteresis as well as increasing the cycle life of cathode materials. In this work, various electrochemical inert/active elements have been introduced into Mn-based P2 type cathode materials for regulating the electronic structure of the cathodes to promote more anionic redox and improve the structural stability. In addition, a new type of ionic liquid is introduced to build a stable interphase and improve the high voltage stability of the cathode material. Multi-model synchrotron-based X-ray characterization techniques combined with first-principles calculation are used to reveal the effectiveness of different strategies on the electrochemical properties of SIBs. The results provide valuable information for the development of high-performance cathode materials. Acknowledgement This work at Shanghai Jiao Tong University was financially supported by the National Natural Science Foundation of China (No. 22209106).