Mesoporous CoSe₂ nanoclusters threaded with nitrogen-doped carbon nanotubes for high-performance sodium-ion battery anodes

Currently, a great challenge to the design of durable sodium-ion batteries (SIBs) is the need for the architecture of nanostructured transition metal-selenide electrodes with high capacity and excellent cycling stability. In this paper, we describe a novel metal-organic framework (MOF)-induced approach to construct necklace-like carbon nanotube (CNT)– CoSe₂@N-doped carbon (NC) with excellent sodium ion storage performance. In this strategy, CNT-threaded zeolitic imidazolate framework-67 (ZIF-67) polyhedra, synthesized by wet chemical methods, are used as the precursor. During the selenization step, ZIF-67 polyhedra transform into mesoporous nanoclusters consisted of CoSe₂@NC nanoparticles, forming CNT-CoSe₂@NC composites with a necklace-like morphology. Such structures facilitate ion and electron transport, and inhibit the aggregation and pulverization of active materials during cycling processes via the intimate contact between the CNTs and CoSe₂@NC. The as-designed composites show significantly improved electrochemical properties including high discharge capacity (404 mA·h·g⁻¹ after 120 cycles at 0.2 A·g⁻¹), excellent rate performance (363 mA·h·g⁻¹ at 5.0 A·g⁻¹), and reasonable capacity retention (80% when calculated from the 2nd cycle).