Revolutionizing aqueous Zn-ion batteries: Precision control of H2O activity and Zn deposition through ammonium oxalate additive

The natural reactivity of Zn metal in aqueous environments leads to surface deterioration and uncontrolled dendrite growth, posing challenges in the advancement of Zn-ion batteries. In this research, we introduce an environmentally friendly and cost-effective electrolyte additive, ammonium oxalate (AO), to significantly extend the cycle life of Zn-ion batteries with minimal usage. Oxalate ions within AO actively participate in the solvation of hydrated Zn ions and attach to the Zn anode surface prior to H2O molecules, creating a robust solid-electrolyte interface (SEI) layer. This SEI layer serves a dual purpose: it inhibits further reactions with H2O and restricts the two-dimensional movement of Zn ions, promoting the preferential growth of the (0 0 2) crystal plane. Consequently, Zn||Zn cells exhibit an impressive lifespan surpassing 1800 h (at 1 mA cm−2, 1 mAh cm−2), and Zn||Cu cells experience a tenfold increase in cycling life. Moreover, Zn||MnO2 full cells, incorporating this low-cost and highly efficient inorganic additive, maintain an outstanding 80.84 % capacity retention after 1200 cycles at 1 A g−1. This breakthrough with AO offers a promising avenue for the practical implementation of Zn-ion batteries, emphasizing their cost-effectiveness and environmental sustainability.