Long-duration aqueous Zn-ion batteries achieved by dual-salt highly-concentrated electrolyte with low water activity

Aqueous Zn-ion batteries have attracted much attention due to their unique high safety and low-cost merits. However, their practical applications are at a slow pace due to their short cycle life, which fundamentally results from the instability of the positive/negative electrode interface in the traditional dilute aqueous electrolytes with high water activity. Developing highly concentrated electrolyte (HCE) has been considered as an effective solution. Unlike previous studies of single salt-based HCE (SS-HCE), herein, a new dual-salt HCE (15 m ZnCl₂ + 10 m NH₄NH₂SO₃ DS-HCE) was proposed for the first time. DS-HCE was proven to simultaneously possess higher conductivity than traditional dilute electrolytes and ultralow water activity of SS-HCE by the regulation of dual high-concentration salts on the solvation structure, which renders the Zn||Zn symmetric cell the record-long cycling life of 2200 h compared with those with SS-HCE (30 m ZnCl₂, 300 h) and other reported HCEs. Additionally, the Zn||NH₄V₄O₁₀ full cell with DS-HCE demonstrated impressed rate capability within a wide-range current densities from 0.1 to 10 A g⁻¹. Moreover, at the high current density of 5 A g⁻¹, the full cell shows almost 100% capacity retention after 4000 cycles, which indicates the promising future of the DS-HCE system for long-duration aqueous Zn-ion batteries.