MoSe2-Covered N,P-Doped Carbon Nanosheets as a Long-Life and High-Rate Anode Material for Sodium-Ion Batteries

MoSe2 grown on N,P-co-doped carbon nanosheets is synthesized by a solvothermal reaction followed with a high-temperature calcination. This composite has an interlayer spacing of MoSe2 expanded to facilitate sodium-ion diffusion, MoSe2 immobilized on carbon nanosheets to improve charge-transfer kinetics, and N and P incorporated into carbon to enhance its interaction with active species upon cycling. These features greatly improve the electrochemical performance of this composite, as compared to all the controls. It presents a specific capacity of 378 mAh g(-1) after 1000 cycles at 0.5 A g(-1), corresponding to 87% of the capacity at the second cycle. Ex situ Raman spectra and high-resolution transmission electron microscopy images confirm that it is element Se, rather than MoSe2, formed after the charging process. The interaction of the active species with modified carbon is simulated using density functional theory to explain this excellent stability. The superior rate capability, where the capacity at 15 A g(-1) equals approximate to 55% of that at 0.5 A g(-1), could be associated with the significant contribution of pseudo-capacitance. By pairing with homemade Na3V2(PO4)(3)/C, this composite also exhibits excellent performances in full cells.