Regulating the electrochemical reduction kinetics by the steric hindrance effect for a robust Zn metal anode

Abstract

The parasitic side reactions and dendrite growth of the Zn metal anode are two primary issues restricting the practical application of Zn-ion batteries (ZIBs). The contradiction between the fast electrochemical kinetics and slow mass transfer may create significant concentration gradients on the electrode surface, which in turn causes uneven growth of the metal Zn and short circuits in batteries. In this work, a modified solvation structure with a steric hindrance effect is introduced by incorporating large-sized molecules (tributyl phosphate) into the electrolyte. The steric hindrance could effectively slow the charge transfer from the anode to the solvated Zn²⁺ and moderate the fast electrochemical reduction kinetics, thereby preventing the preferential plating of Zn²⁺ on the tip region. Furthermore, a homogeneous and robust solid electrolyte interphase (SEI) layer forms on the electrode surface, mitigating the in situ electrochemical corrosion and hydrogen evolution reaction. As a result, the Zn||Cu half-cell has demonstrated stable Zn plating/stripping with an average Coulombic efficiency of ∼99.5% and cumulative capacity of 3000 mA h cm⁻², even under harsh cycling conditions of 10 mA cm⁻² and 10 mA h cm⁻². When coupling with the Mn²⁺ expanded hydrated V<inf>2</inf>O<inf>5</inf> cathode, the full cells exhibit high areal capacity (3.97 mA h cm⁻²) and maintain a high capacity retention of 91.4% after 650 cycles.