Core-Shell CoSe /WSe Heterostructures@Carbon in Porous Carbon Nanosheets as Advanced Anode for Sodium Ion Batteries.

Heterojunction, with the advantage of fast charge transfer dynamics, is considered to be an effective strategy to address the low capacity and poor rate capability of anode materials for sodium-ion batteries (SIBs). As well, carbonaceous materials, as a crucial additive, can effectively ameliorate the ion/electron conductivity of integrated composites, realizing the fast ion transport and charge transfer. Here, motivated by the enhancement effect of carbon and heterojunction on conductivity, it is proposed that the CoSe /WSe heterojunction as inner core is coated by carbon outer shell and uniformly embedded in porous carbon nanosheets (denoted as CoSe /WSe @C/CNs), which is used as anode material for SIBs. Combining with density functional theoretical calculations, it is confirmed that the structure of heterojunction can introduce built-in electric-field, which can accelerate the transportation of Na and improve the conductivity of electrons. Moreover, the introduction of porous carbon nanosheets (CNs) can provide a channel for the transportation of Na and avoid the volume expansion during Na insertion and extraction process. As it is expected, CoSe /WSe @C/CNs anode displays ultrastable specific capacity of 501.9 mA h g at 0.1 A g over 200 cycles, and ultrahigh rate capacity of 625 mA h g at 0.1 A g after 100 cycles.