Cobalt telluride/graphene composite nanosheets for excellent gravimetric and volumetric Na-ion storage

The exploration of new anode materials with high gravimetric and volumetric Na-ion storage performances is urgent and advantageous, but it remains a great challenge. In this study, CoTe2/G composite nanosheets are prepared to achieve this goal by a solvothermal method due to the good properties and high density of 7.92 g cm−3 of bulk CoTe2. In the composite, CoTe2 nanoparticles with a size of 39 nm are uniformly anchored on graphene with strong interfacial interactions. The tap density of the composite can be as high as 1.82 g cm−3. As an anode material for SIBs, the CoTe2/G composite exhibits a high initial reversible gravimetric capacity of 382 mA h g−1 and a volumetric capacity of 695.2 mA h cm−3 along with excellent rate performance. Even at 1, 2 and 5 A g−1, the CoTe2/G composite still delivers gravimetric capacities as high as 295, 272 and 246 mA h g−1 and volumetric capacities of 536.9, 495.1 and 447.7 mA h cm−3. After 1000 cycles at 2 A g−1, the reversible gravimetric and volumetric capacities remain at 245 mA h g−1 and 445.9 mA h cm−3, respectively. The electrochemical dynamic analyses indicate that the Na-ion storage behaviour in the CoTe2/G composite is a surface-controlled capacitive process, which is helpful for higher rate performance. Besides, the enhanced performance of the CoTe2/G anode is ascribed to strong interfacial interaction between CoTe2 and graphene, which can effectively improve electron transfer and alleviate the volume changes of CoTe2 during the discharge/charge processes in SIBs. Accordingly, the CoTe2/G composite has great application prospect as a promising anode candidate for smart SIBs.