Sn(II)-Pyrophosphate Complex with Low Plating/Stripping Potential for Sn–I Flow Battery Applications

Exploring electrolyte formulations that can effectively reduce the plating/stripping potentials of metallic electrodes holds great significance in advancing the development of high-voltage redox flow batteries. In this study, we introduce a novel Sn-based chelated electrolyte, namely, Sn(P₂O₇)₂^6–, by directly reacting the Sn²⁺ solution with an excess of P₂O₇^4– solution. Electrochemical tests prove that the incorporation of high-concentration P₂O₇^4– ligands could shift the plating/stripping potential to −0.67 V. Thus, the demonstrated Sn–I flow battery reveals an average cell voltage of nearly 1.2 V and maintains stable cycling over 250 cycles at a high current density of 80 mA cm^–2, with an average energy efficiency of about 70%. Moreover, no dendrite formation formed during the Sn deposition on the carbon felt. This study offers broad prospects for the future development of high-voltage Sn-based flow batteries.