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Ultranarrow Bandgap Se‐Deficient Bimetallic Selenides for High Performance Alkali Metal‐Ion Batteries

Metal selenides have attracted significant attention as practically promising anode materials in alkali metal‐ion batteries because of their high theoretical capacity. However, a drawback is that these do not provide sufficient rate performance and cycle stability for large‐scale. Here, anion defect‐tuned ultra‐narrow bandgap bimetallic selenide nanoparticles anchored on honeycomb‐like N‐doped, porous carbon dominated by pyrrolic nitrogen is reported. This targeted defect chemistry and unique structure facilitate rapid diffusion of lithium‐potassium ions to provide increased pseudo‐capacitance that boosts electrochemical performance. It is demonstrated that in lithium‐ and potassium‐ion batteries (LIB and KIB), the composite exhibits high specific capacity, and excellent cycle stability with a reversible capacity of 937 mA h g−1 at 2 A g−1 for LIB and 304 mA h g−1 at 1 A g−1 for KIB following 1000 cycles, together with superior rate capability of, respectively, 499 mA h g–1 for LIB and 139 mA h g–1 for KIB at 10 A g–1. A synergistic effect of the greater lithium/potassium ion adsorption energy of the bimetallic selenide and N‐doped carbon boosts ion diffusion kinetics of the materials is confirmed. It is concluded that, these findings will be of immediate benefit to the practical development of alkali‐metal ion batteries.