Bi3Se4 nanodots in porous carbon: A new anode candidate for fast lithium/sodium storage

•A new Bi3Se4-based anode material is successfully developed and firstly applied in lithium and sodium ion batteries.•For the first time, in-situ XRD is employed to disclose the lithium storage mechanism of Bi3Se4/C-800 anode.•C-Se bonds are proved to strengthen the heterointerface and improve reaction knietics via experiments and theoretical calculations.•Bi3Se4/C-800 electrode exhibits ultra-long cycling life and fast-charging capability.