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.