Sodium succinate as functional electrolyte additive to achieve highly reversible zinc-ion batteries

Abstract

Zn-ion batteries (ZIBs) have gained great traction due to their low cost and improved safety when compared with Li-ion batteries (LIBs). However, dendrite formation and side reactions involving Zn corrosion and hydrogen evolution at the Zn electrode restrict the practical application of ZIBs. In this study, sodium succinate (SS), a common leveler and brightener in Zn electroplating, is explored as a functional electrolyte additive in ZIBs. Theoretical and experimental results indicate succinate ions can preferentially adsorb on the Zn electrode surface compared with water molecules. The adsorbed succinate ions can beneficially affect Zn²⁺ diffusion and cover the active sites for side reactions, resulting in more uniform Zn deposition and a protected Zn electrode. With the addition of 0.04 M SS to 2 M ZnSO₄, the lifetime of the ZIB is significantly improved. A cycling stability of over 7100 h at 1 mA cm⁻² is achieved, along with an ultrahigh average Coulombic efficiency of 99.6% in Zn||Cu cells, as well as a stable plating/stripping behavior of over 1800 h at 2 mA cm⁻² in Zn||Zn cells. Even at a high current of 10 mA cm⁻², both Zn||Zn and Zn||Cu cells employing the newly designed electrolyte demonstrate much improved performance. Full cells with Zn and I₂@activated carbon electrodes in the designed electrolyte exhibit both higher capacity and capacity retention (87%) compared with batteries using pure 2 M ZnSO₄ electrolyte. The exploration of SS as a functional electrolyte additive for ZIBs connects the use of levelers and brighteners in Zn electroplating with the study of ZIBs.