Reshaping the Electrolyte Solvation Structure and Electrical Double Layer with Potassium Citrate To Stabilize the Zn Anode

Aqueous zinc-ion batteries (ZIBs) are regarded as a potential alternative to lithium-ion batteries, offering several advantages, including low cost, environmental compatibility, and high safety. However, dendrite growth and side reactions on the Zn anode surface can seriously shorten the cycle life of ZIBs. Herein, the Zn anode was significantly stabilized in the ZnSO4 electrolyte by adding potassium citrate to regulate the electrical double layer (EDL) structure. Cit3- (citrate ion) features a higher lone-pair electron density than H2O, partly replacing the H2O of the inner solvation sheath around Zn2+. In addition, Cit3- is preferentially adsorbed on the Zn metal surface rather than on the water dipole, forming an EDL structure that is poor in H2O. Both are proven to be capable of inhibiting side corrosion reactions and inducing Zn uniform deposition behavior. Encouragingly, a long cycle life (2000 h) for Zn//Zn symmetric cells has been achieved at 0.5 mA cm-2 using potassium citrate additive, with cycle life exceeding 1500 h under more severe conditions (10 mA cm-2, 2.5 mAh cm-2). The assembled Zn-ion hybrid capacitor can stably cycle for 10,000 cycles even at a high current density of 5 A g-1, further demonstrating the positive effect of potassium citrate for practical application. This study inspires the design of efficient electrolyte additives for the development of stable aqueous ZIBs.