Dual-Type Carbon Confinement Strategy: Improving the Stability of CoTe 2 Nanocrystals for Sodium-Ion Batteries with a Long Lifespan.

Sodium-ion batteries have great potential to become large-scale energy storage devices due to their abundant and low-cost resources. However, the lack of anode and cathode materials with both high energy density and long-term cycling performance significantly affects their commercial applications. In this work, uniform CoTe 2 nanoparticles are generated from the tellurization of Co nanoparticles, which were coated with polyvinylpyrrolidone in a three-dimensional (3D) porous carbon matrix (CoTe 2 @3DPNC). Finally, a dual-type carbon confinement structure is formed after tellurization during which citric acid is adopted as the source of the inner carbon scaffold. The hierarchical carbon matrix not only builds a robust and fast ion/electronic conductive 3D architecture but also mitigates the volume expansion and aggregation of CoTe 2 during sodium insertion/extraction. Remarkably, the CoTe 2 @3DPNC electrode displays a high reversible capacity (216.5 mAh g -1 /627.9 mAh cm -3 at 0.2 A g -1 after 200 cycles) and outstanding long-term cycling performance (118.1 mAh g -1 /342.5 mAh cm -3 even at 5.0 A g -1 after 2500 cycles). Kinetics tests and capacitance calculations clearly reveal a battery-capacitive dual-model Na-storage mechanism. Furthermore, ex situ XRD/SEM/TEM demonstrate superior stability during sodium insertion/extraction. This work provides a valuable strategy for the rational structural design of long-life electrodes for advanced rechargeable batteries.