pH modulation and molecular layer construction for stable zinc batteries

Abstract

Aqueous zinc-ion batteries (AZIBs) have regained interest due to their inherent safety and cost-effectiveness. However, the zinc anode is notorious for side reactions and dendrite growth, which plague the practical application of AZIBs. Adjusting the interfacial pH to reduce the by-products has been proven to be effective in protecting the zinc anode. Nevertheless, the dynamic regulation of the inherently unstable zinc interface during prolonged cycling remains a significant challenge. Herein, zwitterionic N-tris(hydroxymethyl)methylglycine (TMG) integrated with negative –COO⁻ and positive NH₂⁺ groups is proposed to stabilize the Zn anode and extend the lifespan as a self-regulating interfacial additive. The anionic portion serves as a trapping site to balance the interfacial pH and thus mitigate the unintended side reactions. Simultaneously, the NH₂⁺ cations are anchored on the zinc surface, forming a water-shielding, zincophilic molecular layer that guides three-dimensional diffusion and promotes uniform electro-deposition. Thus, an average plating efficiency of 99.74% over 3300 cycles at a current density of 2 mA cm⁻² is achieved. Notably, the TMG additive actualizes ultralong life in Zn||Zn symmetrical cells (5500 h, exceeding 229 days, 1 mA cm⁻²/1 mA h cm⁻²), and enables the Zn||I₂ cells to reach capacity retention rate of 89.4% after 1000 cycles at 1 A g⁻¹.