Development of sodium and potassium ion batteries with greater energy density is gaining great attention. Although recently proposed alloying anodes (e.g., Sn, Bi) demonstrate much higher capacity than classic carbon anodes, their severe capacity fading hinders their practical applications. The failure mechanism has traditionally been attributed to the large volumetric change and/or their fragile solid electrolyte interphase (SEI). However, herein we present a completely new cogitation and approach based on electrolyte engineering to stabilize alloying anodes. This approach results in unprecedented high capacity (>650 mAh g-1) and stability (>500 cycles) of alloying anodes by simply tuning the electrolyte compositions, without the needy for nano-structural control and/or carbon modification. We confirm that the cation solvation structure, particularly the type and location of the anions in the electrolyte, plays a critical role in alloying anode stabilization. We further present a new anionic and alloying anode reaction model showing that the root cause of the capacity fading in these alloys is dictated by the properties of the anions and not only the volume change or fragile SEI effect. Our model elucidates the failure mechanism in alloying anodes and provides a new guideline for electrolyte design that stabilizes alloying anodes in emerging mobile ion batteries.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This work is supported by the National Natural Science Foundation of China (21978281,21975250) and National Key R&D Program of China (SQ2017YFE9128100). The authors also thank the Independent Research Project of the State Key Laboratory of Rare Earth Resources
Utilization (110005R086), Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. The research was also supported by King Abdullah University of Science and Technology (KAUST) and Hanyang University. The authors also acknowledege fruitful discussions with the research scientists at Huzhou Kunlun Power Battery Materials Co., LTD.