Electrolytic-anion-redox adsorption pseudocapacitance in nanosized lithium-free transition metal oxides as cathode materials for Li-ion batteries

Conventional batteries (except redox flow batteries) react by involving only their electrode redox centers, with electrolyte ions shuttled between the cathode and the anode. However, this chemistry causes large electronic and structural changes in the bulk of the electrode materials, leading to performance degradation. Herein, we report that electrolytic-anion-redox adsorption pseudocapacitance, relayed by lithium intercalation in lithium-free transition metal oxide electrodes, can be exploited to boost the total energy density of a battery. Focused on the study of Mn3O4, we show that this pseudocapacitance is processed by the reversible adsorption/desorption of PF6- on the surface of transition metal oxides, with charge transfer between Mn3O4 and PF6- through Mn-F bond while fluoride ions acting as redox centers. This new electrolytic-anion-redox chemistry provides greater design freedom for high-capacity energy storage devices since it only involves a specific electrode surface and the electrolyte anion, rather than specially crystallized compounds for bulk reactions.