Synergistic Interfacial Charge Storage and Transfer Mechanisms for Extra Capacity in Mn-Based Oxide Anodes

Manganese-based transition metal oxides have attracted significant interest as promising lithium-ion battery anodes due to their extra capacity beyond theoretical limits. However, the intrinsic origin of extra capacity has remained controversial, particularly the interface electron-transfer mechanisms that have long eluded direct experimental verification owing to the difficulty of electrochemical interface characterization. In this work, we employ advanced operando magnetometry to dynamically analyse spin-dependent electronic behavior in Mn 3 O 4 anode during electrochemical cycling. Our findings identify two synergistic interfacial energy-storage modes underlying the extra capacity, in addition to solid electrolyte interphase (SEI) formation, reversible space-charge storage at the Mn/Li 2 O interface coupled with charge exchange at the Mn/SEI interface. Specifically, electrons first populate spin-split states in metallic Mn at the Mn/Li 2 O interface. With further accumulation, charge transfers across the Mn/SEI interface into the SEI, facilitating SEI growth and contributing to the extra capacity. This study provides the direct magnetic evidence of a multiple-interface cooperative storage mechanism in Mn-based materials, offering a new physical perspective and design strategy for developing high-capacity anode materials through the lens of interfacial electronic structures and spin regulation. Graphical Using operando magnetometry, this work unravels the five-stage electron transfer of Mn 3 O 4 upon Li + insertion/extraction. Interfacial space-charge storage dominates its extra capacity, offering guidance for rational design of Mn-based electrode materials.