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

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 TiO2 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 Mg2+. Theoretical calculations verify that the introduction of oxygen vacancies in TiO2, not only increases the intrinsic electronic conductivity, but also improves the adsorption capability for MgCl+, which enhances the surface-redox pseudocapacitance of TiO2. Moreover, in situ Raman measurements, ex situ XPS spectra and XRD patterns demonstrate the structural integrity of TiO2 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, TiO2 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).

Automated summary

This study proposes a strategy of interface reconstruction for the anatase TiO2 cathode, which combines ultrathin carbon coating and oxygen vacancies, to achieve fast surface-redox pseudocapacitance charge storage mechanism. The reconstructed cathode/electrolyte interface promotes the kinetics of active cations and induces the less potential-dependent charge storage process, resulting in remarkable rate performance and long lifespan.