In situ built interphase with high interface energy and fast kinetics for high performance Zn metal anodes

Abstract

In situ construction of a multifunctional solid electrolyte interphase (SEI) for Zn anodes is promising to address the dendrite growth and side reactions (corrosion and hydrogen evolution) in aqueous Zn-ion batteries. However, there is a lack of constructive methods for choosing suitable SEI compounds and feasible implementation routes. Here, inspired by the SEI-design for Li-metal batteries, we identified that Zn₃(PO₄)₂ with high interface energy could suppress Zn dendrite growth effectively and ZnF₂ could accelerate the kinetics of Zn²⁺ transference and deposition, and thus constructing a composite SEI mainly composed of Zn₃(PO₄)₂ and ZnF₂ (ZCS) is likely to improve interface deposition and electrode kinetics comprehensively. However, the high redox potential of Zn/Zn²⁺ and H₂/H⁺ makes it difficult to develop an in situ SEI for Zn anodes in aqueous electrolytes via traditional electrochemical routes. Considering this dilemma, we take advantage of the instability of KPF₆ in an aqueous environment and build in situ ZCS on the Zn anode through the PF₆⁻ anion-induced chemical strategy. Surprisingly, ZCS-Zn exhibits enhanced reversibility with a smooth and compact structure during long-term cycling. Both cumulative capacity (2020 mA h cm⁻²) and the product of the largest current density and areal capacity (10 mA cm⁻² × 20 mA h cm⁻²) applied to ZCS-Zn reach the highest levels compared with those reported in recent reports under mildly acidic conditions. This work paves a new way for designing a desirable SEI on the Zn anode and may also guide the interface engineering of other systems to overcome the intrinsic defects in constructing favorable interphases.