Reaction mechanism and additional lithium storage of mesoporous MnO_(2) anode in Li batteries

Nanostructured transition metal oxides,employed as anode materials for lithium-ion batteries,exhibit a higher capacity than the theoretical capacity based on the conversion reaction.To date,the reasons behind this phenomenon are unclear.For the one-step evolution of anode material for lithium-ion batteries,it is essential to understand the lithium storage reaction mechanism of the anode material.Herein,we provide a detailed report on the lithium storage and release mechanism of MnO2,using synchrotron-based X-ray techniques.X-ray diffraction and X-ray absorption spectroscopy results indicate that during the first discharge,MnO2 is reduced in the order of MnO2→LixMnO2(1<X<2)→MnO→Mn metal,followed by a reversible reaction between Mn metal and Mn3O4.Furthermore,soft X-ray absorption spectroscopy results indicate that additional reversible formation-decomposition of the electrolyte-derived surface layer occurs and contributes to the reversible capacity of MnO2 after the first discharge.These findings contribute to further understanding of the reaction mechanism and additional lithium storage of MnO2 and suggest practical strategies for developing high energy density anode materials for next-generation Li batteries.