Ester-mediated self-evolving electrolyte enables low-temperature aqueous zinc-ion batteries

The failure of low-concentration electrolytes in low-temperature aqueous zinc-ion batteries arises from the abundance of H₂O molecules that facilitate electrolyte freezing and induce sluggish ion transport and interfacial reaction kinetics, resulting in uneven Zn deposition and dendrite growth. Herein, we propose an ester-mediated self-evolving low-concentration electrolyte (SELC) developed through the incorporation of methyl formate (MF) and methyl heptafluorobutyrate (MH) into 1 M Zn(OTf)₂ aqueous solution. As a chemically transformable co-solvent, MF undergoes partial hydrolysis to generate formic acid and methanol in situ, which reorganize the hydrogen-bonding network of H₂O molecules, diversify Zn²⁺ coordination environments, and maintain efficient ion transport under subzero conditions. Meanwhile, MH serves as a fluorinated interfacial regulator that preferentially accumulates at the Zn interface and contributes to the formation of a H₂O-deficient organic-rich and inorganic-reinforced gradient solid electrolyte interphase, thereby suppressing side reactions and dendrite growth. Benefiting from the synergistic regulation of Zn²⁺ solvation and interfacial chemistry, the SELC electrolyte induces preferential Zn deposition along the (002) crystal plane. Consequently, Zn||Zn symmetric cells achieve stable cycling for 3800 h at room temperature, 2200 h at −30 °C, and 300 h at −50 °C, respectively, demonstrating outstanding wide-temperature adaptability. Zn||polyaniline (PANI) full cells deliver 99.6% of their initial capacity after 7000 cycles, while pouch cells maintain 81.0% capacity retention after 1200 cycles.