Trace additives enable highly reversible zinc anode via water-deficient pH buffer layer construction

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The commercial application of aqueous zinc-ion batteries (AZIBs) is hindered by dendrite growth, side reaction of hydrogen evolution reaction (HER), and corrosion passivation of zinc anode. In this work, trace inorganic additive ammonium hydrogen borate (AB) was introduced into 2 M ZnSO₄ electrolyte to construct a water-deficient pH buffer layer with electrostatic shielding effect at anode-solution interface. The buffer layer can effectively reduce the water content at the interface and maintain the interfacial pH stable, thereby suppressing the HER and the corrosion of anode. In addition, the NH₄⁺ in the additive also demonstrates an electrostatic shielding effect, which alleviates the "tip effect" and increases the nucleation overpotential of the zinc anode. As a result, the buffer layer can induce the uniform deposition of zinc and restrict the growth of dendrites, realizing a highly reversible zinc anode. Under this electrolyte system, the zinc symmetric battery can cycle stably for 7266 h at a current density of 5 mA cm⁻², and the cumulative deposition capacity could reach 18.17 Ah cm⁻². Even under the condition of a high depth of discharge (DOD) of 78.54%, it still maintained an excellent cycle life of 450 h. The zinc-copper half-cell can stably cycle 1400 times at a current density of 10 mA cm⁻² and delivers an ultra-high Coulombic efficiency of 99.70%. The Zn||MnO₂ full cell retains a capacity retention rate of 76.68% after 900 cycles at a current density of 1 A g⁻¹, indicating its promising application potential.