Stabilizing metal battery anodes through the design of solid electrolyte interphases

Summary The solid electrolyte interphase (SEI) is a chemically distinct material phase formed by a combination of electrochemical reduction and chemical reactions at both the explicit and implicit interfaces in all electrochemical cells. The structure, chemistry, and thermodynamics of the materials that accumulate in such interfacial material phases have emerged over the last decade to play crucial roles in achieving high levels of anode reversibility in secondary batteries, especially in systems where electrochemically active metals are used as anodes for high-energy-density and cost-effective storage. Here, we review the history, chemistry, formation characteristics, and approaches taken to achieve rational design of the SEI at metal anodes. Strategies that explicitly take advantage of the redox chemistry of electrolyte components to build designed, favourable SEI inside electrochemical cells, as well as those that benefit from ex situ chemistries performed outside the cell to create artificial SEI that enhance anode reversibility are highlighted. Taking advances based on these methods as a point of departure, the review also considers interphase design rules that facilitate chemical, mechanical, and electrochemical stability and fast ion transport through the SEI. Finally, we discuss differences and similarities of SEI formed on monovalent (Li, Na, and K), divalent (Mg, Ca, and Zn), and trivalent (Al) metals of contemporary interest for developing cost-effective but high-performance anodes and on that basis, underscore the urgent need for intrusive experimental tools for analyzing the SEI on metals at atomic levels.