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

Abstract 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.