Cumulative cationic and anionic redox reaction in Mg3V2(SiO4)(3) and impact on the battery performance

Abstract

A cumulative cationic and oxygen anionic redox reaction receives much attention for enhancing battery capacity in intercalant-excess cathode materials. However, such combinatorial electrochemical reactions are studied mostly for Li-containing cathode active materials so far, and multivalent systems remain unexplored from this perspective. Here, we examine the redox chemistry in the garnet-type Mg3V2(SiO4)(3) based on first-principles density functional theory calculations. Our calculations demonstrate the occurrence of a cumulative reversible cationic and anionic redox reaction without additional magnesium atoms, which offers an average discharge voltage of 3.23 V vs. Mg/Mg2+ with an energy density of as high as 1152 Wh/kg. Moreover, the unique three-dimensional corner-shared polyanionic framework in Mg3V2(SiO4)(3) only provides marginal structural changes, unlike layered Li-rich cathodes, which implies that irreversible O-2 gas release is highly unlikely. Together with a low energy barrier for Mg migration, our finding provides a new insight to develop high-performance multivalent cathode active materials for which a cumulative cationic and oxygen anionic redox reaction plays an important role.