CuInSe ₂ /N‐Doped Carbon Nanofibers Enable Durable and Fast Sodium Storage via a Multifunctional InSe Framework

Metal selenides are attractive anode candidates for sodium‐ion batteries due to their superior theoretical capacity and weak metal–Se bonds. However, their practical deployment is hampered by sluggish kinetics and severe volume expansion during cycling. Herein, strongly bonded InSe motifs are integrated into the Cu _{2− x} Se lattice to form CuInSe ₂ , which synergistically enhances sodium storage kinetics and durability. During the conversion reaction, the InSe motifs evolve into intercalative In ₆ Se ₇ framework, converting sluggish bonding breaking/reforming behavior into rapid ion insertion/extraction. Additionally, this framework provides a robust space‐confinement and conductive platform, ensuring high reversibility and fast kinetics of the redox reactions. The well‐designed CuInSe ₂ /N‐doped carbon nanofibers composite demonstrates superior cycling stability of 84.8% capacity retention after 5000 cycles and decent rate performance of 234.3 mAh ⁻¹ at 10 A g ⁻¹ . Even at −20 °C, it exhibits fast‐charging performance at 2 A g ⁻¹ and durability over 900 cycles. The in situ incorporation of a multifunctional framework offers a new solution for developing advanced conversion‐based anode materials.