In-situ produced three-dimensional hierarchical porous Cu@Bi enables ultra-long sodium storage

Bismuth (Bi) is considered as one promising alloying-based anode for sodium-ion batteries due to its suitable electrode potential and high theoretical capacity, however suffered an unsatisfied cycle lifespan caused by tremendous volumetric changes, unstable electrode/electrolyte interface and sluggish ionic transport. Herein, a 3D Cu@Bi electrode is synthesized by electrodepositing Bi layer in self-synthesized three-dimensional porous copper (3D Cu). The hierarchical porous structure consists of micrometer-sized pores of 3D Cu and in-situ formed nanopores of Bi layer during sodium insertion/extraction can provide rapid ionic transferring channels, and simultaneous provides sufficient free space for volumetric changes of Bi electrode to enable active materials integrity, and avoid the active materials crushing and losing electrical contact of Bi with the current collector. Additionally, a uniform solid electrolyte interphase (SEI) layer forms on the electrode surface during cycling, further optimizing the electrochemistry performance. As a result, the 3D Cu@Bi electrode exhibits ultra-long sodium storage cyclability (260 mAh g^-1 after 15,500 cycles at 10 A g^-1 with a retention of 67.5 %) and exceptional rate capability (352 mAh g^-1 at 40 A g^-1). This work provides a novel thought combing the hierarchical porous structure and interface modification to construct Bi anode for ultralong cyclability sodium-ion battery.