Rational Design of Embedded CoTe2 Nanoparticles in Freestanding N-Doped Multichannel Carbon Fibers for Sodium-Ion Batteries with Ultralong Cycle Lifespan.

Although sodium-ion batteries (SIBs) have high potential for applications in large-scale energy storage, their limited cycle life and unsatisfactory energy density hinder their commercial applications. Here, a superior stable CoTe2/carbon anode, in which CoTe2 nanoparticles are embedded in freestanding N-doped multichannel carbon fiber (CoTe2@NMCNFs), with ultralong cycle life for SIBs, is reported. Specifically, CoTe2 nanoparticles are uniformly dispersed in the carbon matrix to inhibit its volume expansion and agglomeration during the desodiation/sodiation process, enabling a high-capacity and stable energy storage (retains 204.3 mAh g-1/612.9 mAh cm-3 at 1 A g-1 after 2000 cycles with an ultralow capacity decay of 0.016% per cycle). Moreover, a CoTe2@NMCNFs electrode exhibits a pseudocapacitive-dominated behavior, enabling the high-rate performance (152.4 mAh g-1/457.2 mAh cm-3 at 10 A g-1). The battery-capacitive dual-model reaction mechanism and outstanding reversibility of the CoTe2@NMCNFs composite are systematically investigated by ex situ XRD/SEM/TEM and a galvanostatic intermittent titration technique test, as well as surface capacitance calculations. More importantly, the fabricated sodium-ion CoTe2@NMCNFs//P2-NaNMMT-4 full cell delivers a stable reversible capacity of 445 Wh kg-1anode at 0.2 A g-1 and an excellent rate performance. The facile synthetic approach together with unique nanostructural design, provides a meaningful reference for the rational design of next-generation ultralong cycle-life SIBs anodes.