Electronic structure manipulation of MoSe2 nanosheets with fast reaction kinetics toward long-life sodium-ion half/full batteries

Due to their high specific capacity, straightforward manufacture, and plentiful sources, transition metal oxides and dichalcogenides are regarded as the perfect anode materials for sodium ion batteries (SIBs). Among them, MoSe2 could be used as an SIB anode material due to its evident structural and performance benefits, including its two-dimensional layered structure with a large layer spacing (0.646 nm), a theoretical capacity of up to 422 mA h g−1, low cost, and environmental friendliness. However, the low conductivity of MoSe2 can easily lead to large impedance, resulting in poor rate performance. And the huge volume expansion in the process of sodium storage will result in the collapse and crushing of the MoSe2 structure. In this work, a Co doped MoSe2@carbon nanosheet (Co-MoSe2@CN) is fabricated by a facile liquid phase method with a subsequent pyrolytic selenization technique. Through this electronic modulation process, the energy band gap of MoSe2 is directly reduced from 1.365 eV to 0.195 eV, and the conductivity is significantly enhanced. Additionally, the volume tension brought on by sodium ion (de)insertion can be released and absorbed by the Co-MoSe2@CN structure. As an anode for SIBs, Co-MoSe2@CN exhibits outstanding performance in terms of a high specific capacity of 403 mA h g−1 at 1 A g−1 (300 cycles) and extended length cycling stability (373 mA h g−1 at 10 A g−1 after 1000 cycles), as well as the rate capability, which is better than that of MoSe2@CN in all aspects of rolling. Furthermore, the Co-MoSe2@CN anode helps sodium-ion full batteries attain a high energy density of 103 W h kg−1 (210 W kg−1). The high pseudo-capacitance and diffusion control play a leading role in the sodium storage of Co-MoSe2@CN. This electronic structure manipulation of MoSe2 and adsorption of Na ions are confirmed by theoretical calculation. This offers a viable design for the advancement of SIB anodes based on transition metal selenides.