Revealing An Intercalation‐Conversion‐Heterogeneity Hybrid Lithium‐Ion Storage Mechanism in Transition Metal Nitrides Electrodes with Jointly Fast Charging Capability and High Energy Output

Abstract The performance of electrode materials depends intensively on the lithium (Li)‐ion storage mechanisms correlating ultimately with the Coulombic efficiency, reversible capacity, and morphology variation of electrode material upon cycling. Transition metal nitrides anode materials have exhibited high‐energy density and superior rate capability; however, the intrinsic mechanism is largely unexplored and still unclear. Here, a typical 3D porous Fe 2 N micro‐coral anode is prepared and, an intercalation–conversion–heterogeneity hybrid Li‐ion storage mechanism that is beyond the conventional intercalation or conversion reaction is revealed through various characterization techniques and thermodynamic analysis. Interestingly, using advanced in situ magnetometry, the ratio (ca. 24.4%) of the part where conversion reaction occurs to the entire Fe 2 N can further be quantified. By rationally constructing a Li‐ion capacitor comprising 3D porous Fe 2 N micro‐corals anode and commercial AC cathode, the hybrid full device delivers a high energy‐density (157 Wh kg −1 ) and high power‐density (20 000 W kg −1 ), as well as outstanding cycling stability (93.5% capacitance retention after 5000 cycles). This research provides an original and insightful method to confirm the reaction mechanism of material related to transition metals and a fundamental basis for emerging fast charging electrode materials to be efficiently explored for a next‐generation battery.