Regulating hydrogen-bond network via competitive coordination for cryogenic aqueous Zn-ion batteries

Aqueous zinc-ion batteries (AZIBs) are highly promising for energy storage by virtue of inherent safety and low cost. Nevertheless, aqueous electrolytes suffer from low-temperature solidification, which severely hinders ion transport and diffusion, and triggers Zn dendrite, significantly degrading the low-temperature performance of AZIBs. Herein, 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMImOTf) is utilized as an electrolyte additive to improve the cryogenic AZIBs. BMIm⁺ can compete with H₂O molecules via ion-dipole interactions, which reconstructs the hydrogen-bond network and depresses freezing point of electrolyte. Concurrently, the migratory BMIm⁺ and OTf^- serve as additional charge carriers, which improves the sluggish kinetics of AZIBs at low temperatures, thereby mitigating concentration polarization and facilitating faster Zn²⁺ migration. Consequently, the Zn||Zn symmetric cell with BMImOTf-added electrolyte delivers superior cryogenic behavior at -20 °C, with stable cycling of 2000 h and the Zn||Cu asymmetric cell exhibits high coulombic efficiency retention of 99.4% after 1500 cycles. Moreover, the Zn||active carbon full cell also achieves an outstanding performance of exceeding 9000 cycles with a capacity retention of 98% at -20 °C. Additionally, this electrolyte with BMImOTf has been proven to operate effectively at -40 °C and pouch cells. This electrolyte engineering provides a solution and design paradigm for high-performance AZIBs within a wider temperature range.