Carbon Nanotube Intertwined Nano‐Nested Heterojunction Cubes with Double Shell Layers FeSe2‐CoSe2@NC for Efficient Lithium/Sodium Ion Storage Anode

Abstract Transition metal selenides (TMSes) have been extensively researched as anode materials of lithium/sodium‐ion batteries (LIBs/SIBs). However, the serious volume expansion, unsatisfying initial coulombic efficiency (ICE), and ion diffusion extremely limited their further application. Therefore, nanostructure design and construction of heterogeneous structures can effectively alleviate the above problems. Herein, elaborately designed carbon nanotube‐intertwined nano‐nested heterojunction cubes, FeSe 2 ‐CoSe 2 @NC (FeSe 2 ‐CoSe 2 @NC/CNT), with unique double shell layers, are successfully prepared. Electrochemical tests and theoretical calculations show that the construction of double transition metal selenide heterostructures and CNTs inter‐transfer networks promotes ion transport kinetics. Furthermore, the double‐layer nested cubic structure contributes to alleviating the volume expansion over charging/discharging. Thanks to these merits, the FeSe 2 ‐CoSe 2 @NC/CNT composite exhibits enhanced Li + storage capacity (1479.7 mAh g −1 after 500 cycles at a high current density of 2 A g −1 ), and outstanding rate capabilities. When used in SIB, the capacity is maintained at 300.1 mAh g −1 for 500 cycles at 1 A g −1 . In addition, the FeSe 2 ‐CoSe 2 @NC/CNT as anode in the full cell displays a nice reversible capacity of 100.1 mAh g −1 at 0.5 C cycling for 115 cycles, demonstrating vast potential for feasible synthesis, superior performance, and efficient lithium/sodium ion storage anodes.