Sandwich-type N-C@CoTe2@C anode: a stress-buffer nanostructure for stable sodium-ion storage

Transition metal tellurides (TMTes) have received extensive attention for high specific energy sodium-ion batteries (SIBs) due to their high volumetric specific capacity. However, the continuous capacity attenuation arising from the huge volumetric strain during sodiation/desodiation impedes practical applications. Here, we report a "sandwich-type" carbon confinement strategy that entraps cobalt ditelluride (CoTe2) nanocrystals between two carbon layers. Porous cellulose-derived fibres were employed as the inner carbon framework to construct fast conductive circuits and provide an abundant site for anchoring CoTe2 nanocrystals. Polyvinylpyrrolidone (PVP)-derived carbon layers act as carbon armour to encapsulate CoTe2 nanocrystals, inhibiting their volume change and structural pulverization during repeated sodium intercalation/deintercalation. Benefiting from the exquisite structural design, the N-C@CoTe2@C electrode exhibits excellent cycling stability for over 3000 cycles at 2.0 A g-1 and rate performance (113.8 mA h g-1 at 5.0 A g-1). Moreover, ex situ XRD/TEM and kinetic tests revealed a multistep conversion reaction mechanism and a battery-capacitive dual-model Na-storage process. This work provides a new perspective on the development of low-cost and straightforward techniques for fabricating long-life commercial SIB anode materials.