Solid-electrolyte interphase governs zinc ion transfer kinetics in high-rate and stable zinc metal batteries

Abstract

Solid-electrolyte interphases (SEIs) enable stable zinc anodes and modify the Zn²⁺ transfer behaviors in rechargeable zinc metal batteries (ZMBs). Precisely understanding Zn²⁺ charge transfer kinetics within SEIs and benchmarking it against other essential steps is crucial for designing high-rate and efficient ZMBs. However, hitherto, such knowledge remains elusive. Herein, we identified that Zn²⁺ transport within SEIs is the rate-determining step of in-cell carrier transfer kinetics in typical intercalation-type ZMBs. By fine-tuning SEIs using an amide-based deep eutectic electrolyte with cyclic amide additives, we demonstrated that highly Zn²⁺-conductive Zn<inf>3</inf>N<inf>2</inf> species within the SEI outperform state-of-the-art ZnF<inf>2</inf> in facilitating Zn²⁺ transfer and stabilizing the Zn anode. This SEI design substantially enhances the rate capability and cycling stability of Zn||Mn-doped V<inf>2</inf>O<inf>5</inf> pouch cells upon low negative to positive capacity ratio (1.4:1), achieving high Zn anode utilization (72%) and device-level specific energy. This study features a fresh impetus on SEI design for high-performance ZMBs.