A robust gradient solid electrolyte interphase enables fast Zn dissolution and deposition dynamics

The construction of a robust solid-electrolyte interphase (SEI) on zinc anode is an effective approach for tackling the high thermodynamic instability and side reactions of Zn-metal anode (ZMA), particularly at high current densities and high utilization ratios. Herein, a ternary aqueous electrolyte with N,N-dimethyltrifluoroacetamide (DMTFA), dimethylformamide (DMF), and H2O is developed to build a stable SEI. DMTFA is introduced as a functional solvent, which is preferentially decomposed to form a gradient rigid-soft coupling SEI layer. Meanwhile, DMF is added as a co-solvent to suppress the water activity by forming an intermolecular hydrogen bond, thus protecting the as-formed SEI against corrosion. It is found that a 31 nm-thick SEI film with a -CF3-rich-organic outer layer and a gradient zinc salts-rich-inorganic (e.g., ZnF2, Zn3N2, ZnSO3, ZnS, ZnO) inner layer delivers excellent structural integrity to block the direct contact of water and ZMA. Moreover, the as-formed SEI exhibits a high compression modulus (23.5 GPa), which is strong enough for extreme stress, such as dendrite puncture. Scanning electrochemical microscopy reveals the electron-insulating feature of the SEI, which can promote the uniform spherical zinc deposition underneath it. Consequently, AZIBs with the gradient SEI achieve ultra-long cycling stability of 4100 h in harsh conditions of 20 mA cm-2 and 20 mA h cm-2, super-high cumulative capacity of 41 A h cm-2, excellent reversibility with average coulombic efficiency of 99.8%, and an 11 000-cycle lifespan for Zn||NaV3O8 cell. A robust gradient rigid-soft coupling SEI layer on the Zn surface results in the ultra-long cycling stability and the high zinc utilization rate of AZIBs.

Automated summary

The construction of a stable solid-electrolyte interphase (SEI) on the zinc anode using a ternary aqueous electrolyte with DMTFA and DMF has been developed in this study. The gradient SEI layer formed provides excellent structural integrity, prevents direct contact between water and the zinc anode, and exhibits high compression modulus and electron-insulating feature. AZIBs with the gradient SEI demonstrate ultra-long cycling stability and high utilization rate under harsh conditions.