Graphene-Loaded Bi2Se3: A Conversion-Alloying-type Anode Material for Ultrafast Gravimetric and Volumetric Na Storage.

Sodium-ion battery (SIB) has been a promising alternative for sustainable electrochemical energy-storage devices. However, it still needs great efforts to develop electrode materials with ultrafast gravimetric and volumetric Na-storage performance, due to difficult balance between Na-ion diffusion kinetics and pressing density of materials. In this work, Bi2Se3/graphene composites, synthesized by a selenization reaction, are investigated as anode materials for SIBs. Na-ion storage mechanism of Bi2Se3 should be attributed to a combined conversion-alloying one by a series of ex situ measurements. In the composites, Bi2Se3 particles with an average diameter of 100 nm are uniformly dispersed onto graphene with strong interfacial interaction. Despite their nanoscale size, the pressing density of Bi2Se3/graphene composite could still reach a high value of 2.07 g/cm3. Therefore, the composites can deliver a high gravimetric specific capacity of 346 mAh/g and volumetric specific capacity of 716 mAh/cm3 at a current density of 0.1 A/g. Remarkably, the composites exhibit an ultrafast Na-storage capability and a negligible capacity fading with the increasing of current density from 0.2 to 5 A/g. Even at 10 A/g (≈30 C), the composites still possess a gravimetric capacity of 183 mAh/g and volumetric capacity of 379 mAh/cm3 with ultrastable cyclability up to 1000 cycles. This work introduces a valid route to design electrode materials with both excellent gravimetric and volumetric performance of Na-ion storage.