Binding MoSe2 with carbon constrained in carbonous nanosphere towards high-capacity and ultrafast Li/Na-ion storage

Most of the reported MoSe2 electrode materials are suffered from tended stacking, large volume expansion and relatively low capacity. As shown the experiences of Li/Na-Se batteries, the encapsulating of the exfoliated MoSe2 into carbon nanospheres are successfully constructed with the introduction of C-O-Mo bonds and larger layer distance (0.89 nm). Interestingly, the C-O-Mo bonds stayed on the surface of the Se-O insulation layer can improve the rate of ions transfer and also promote the reversible conversion of MoSe2. The first-principles calculations demonstrated that the frontier molecular orbitals of C-O-Mo interface structure are mainly localized on the MoSe2 sheet fragment with an appropriate HOMO-LUMO gap (< 4 eV), proving that its conductivity is being greatly enhanced with higher stability. Utilized as an anode for LIBs, it delivers Li-storage capacities of 1208 mAh g(-1) after 150 cycles at 1.0 A g(-1) and 519 mAh g(-1) after 200 cycles at 4.0 A g(-1). Also note that the Na-storage capacities are found to be 543, 491 mAh g(-1) after 120 cycles at 0.1, 1.0 A g(-1), respectively. Through the analysis of CV, the reduced particles might improve the capacitive behaviors, further leading to the higher rate performances. Ex-situ techniques showed that the emerging Se during the electrochemical process was constrained uniformly in the carbon matrix. More greatly, the controlling of by-product Se plays key roles in achieving high-rate capability and cycling stability, which would open up a potential avenue for these metal-selenide anodes designs of battery storage systems.