Counterion-interference-free lignosulfonic acid additive stabilizes zinc anode interfacial behavior

Aqueous zinc-ion batteries (AZIBs) have attracted extensive attention owing to their high safety, low cost, and environmental benignity. However, water-induced parasitic reactions severely compromise the stability of Zn metal anodes, limiting their practical application. Electrolyte additives with functional anions provide an effective strategy to regulate the interfacial reaction microenvironment and construct a durable Zn/electrolyte interface. Nevertheless, conventional polyanionic additives contain counterions that can interact with their functional groups and influence interfacial Zn²⁺ transport. Herein, a biomass-derived lignosulfonic acid additive was prepared from calcium lignosulfonate via an H-type cation-exchange strategy. This process removes interfering Ca²⁺ counterions and releases abundant polar functional groups, including -SO₃H, -OH, and -COOH. The activated lignosulfonic acid preferentially adsorbs on the Zn surface and reconstructs the original water-rich electric double layer into a water-deficient inner Helmholtz layer dominated by organic molecular adsorption. This interfacial layer effectively blocks the direct contact between active water molecules and Zn metal, thereby suppressing hydrogen evolution, corrosion and the formation of basic zinc sulfate byproducts. As a result, the lignosulfonate additive enables the assembled Zn||Zn symmetric cell to operate stably for 1600 h at 1 mA cm^-2 and 1 mAh cm^-2, and allows the Zn||Cu cell to sustain 1500 plating/stripping cycles at 2 mA cm^-2 with an average Coulombic efficiency of 99.59%. Furthermore, the Zn||MnO₂ full cell delivers stable cycling performance over 2000 cycles at 0.5 A g^-1 with an average Coulombic efficiency of 99.63%.