Surface‐Redox Pseudocapacitance‐Dominated Charge Storage Mechanism Enabled by the Reconstructed Cathode/Electrolyte Interface for High‐Rate Magnesium Batteries

Abstract

Abstract Th all phenyl complex (APC) electrolyte is generally accepted to be compatible with Mg metal anodes, offering excellent plating/stripping reversibility. However, the large Cl desolvation penalty of the MgCl + solvation structure in APC electrolyte causes a high reaction energy barrier at the cathode/electrolyte interface, resulting in unsatisfactory rate performance. Herein, the interface reconstruction strategy of an anatase TiO 2 cathode is proposed by the combination of ultrathin carbon coating and oxygen vacancies, which realizes the fast surface‐redox pseudocapacitance charge storage mechanism via MgCl + , circumventing the sluggish solid‐phase migration of Mg 2+ . Theoretical calculations verify that the introduction of oxygen vacancies in TiO 2 , not only increases the intrinsic electronic conductivity, but also improves the adsorption capability for MgCl + , which enhances the surface‐redox pseudocapacitance of TiO 2 . Moreover, in situ Raman measurements, ex situ XPS spectra and XRD patterns demonstrate the structural integrity of TiO 2 without undergoing phase change and the rapid reversible storage of MgCl + . Furthermore, in situ electrochemical impedance spectra reveal that the reconstructed cathode/electrolyte interface promotes the kinetics of active cations and induces the less potential‐dependent charge storage process. Consequently, TiO 2 exhibits a remarkable rate performance (discharge capacity of 68.9 mAh g −1 at 1 A g −1 ) and long‐lifespan over 3000 cycles at 0.5 A g −1 .