Engineering hollow polyhedrons structured from carbon-coated CoSe2 nanospheres bridged by CNTs with boosted sodium storage performance

Abstract

Nanostructured CoSe₂ anode materials hold great promise for sodium ion batteries (SIBs), drawing much recent research attention. However, high-performance CoSe₂ based anodes are still challenging to obtain. Herein, using zeolitic imidazolate framework-67 (ZIF-67) particles as the starting material, nondestructive hollow polyhedral hybrids have been synthesized successfully, which are structured from CNT-bridged carbon-coated CoSe₂ nanospheres (CoSe₂@C/CNTs). During the synthesis, the controlled in situ growth of CNTs introduces additional mesopores and open channels to the hybrids, and avoids serious agglomeration of the CoSe₂ nanospheres. When employed as anode materials for SIBs with ether-based electrolyte, the CoSe₂@C/CNTs show overwhelming merits over graphitic carbon-coated CoSe₂ nanosphere polyhedral hybrids (CoSe₂@GC) and bare CoSe₂ particles. Specifically, the CoSe₂@C/CNTs anode displays a high reversible capacity (∼470 mA h g⁻¹ at 0.2 A g⁻¹), a good rate capability of ∼373 mA h g⁻¹ even at 10 A g⁻¹, and an excellent cycling stability of over 1000 cycles with a capacity retention of ∼100% calculated from the 70^th cycle. In addition, the electrochemical reaction dynamics analysis indicates a considerable capacitive contribution during the discharge–charge cycles, which is beneficial to enhance the rate capability and cyclability of the CoSe₂@C/CNTs anode. Such results could be ascribed to the stable ether-based electrolyte-active material intermediates, improved electrolyte-active material contact, and shortened charge transfer paths afforded by the unique hybrid nanostructure.