Binary self-assembly of ordered BiSe/BiOSe lamellar architecture embedded into CNTs@Graphene as a binder-free electrode for superb Na-Ion storage.

With the development of various flexible electronic devices, flexible energy storage devices have attracted more research attention. Binder-free flexible batteries, without a current collector, binder, and conductive agent, have higher energy density and lower manufacturing costs than traditional sodium-ion batteries (SIBs). However, preparing binder-free anodes with high electrochemical performance and flexibility remains a great challenge. In this study, a binary self-assembly composite of an ordered BiSe/BiOSe lamellar architecture wrapped by carbon nanotubes (CNTs) was embedded in graphene with strong interfacial interaction to form BiOSe/BiSe@CNTs@rGO (BCG), which was used as a binder-free anode for SIBs. A unique "one-changes-into-two" phenomenon was observed: the layered BiSe was transformed into a unique layered BiSe/BiOSe heterojunction structure, which not only provides more electrochemical channels but also reduces internal stress to improve the stability of the material structure. BCG-2 showed excellent sodium-ion storage, delivering a reversible capacity of 346 mA h/g at 100 mA/g and maintaining a capacity of 235 mA h/g over 50 cycles. Even at a high current density of 1 A/g, it retains a capacity of 105 mA h/g after 1000 cycles. This unique design concept can also be employed in synthesizing other binder-free electrodes to improve their properties.