Boosting fast and stable symmetric sodium-ion storage by synergistic engineering and amorphous structure

Tuning the microstructure and crystallinity of electrode materials is a great challenge and crucial for the development of high-performance sodium-ion batteries (SIBs). Herein, we develop a series of rationally designed carbon-coated V2O5 core-shell nanostructures (S-V2O5-HS, S-V2O5-HCS, P-V2O5/C-SCS, A-V2O5/C-SCS, and A-V2O5/C-WCS) in which the phase (single/polycrystalline, amorphous), microstructure (hollow, solid, porous) for the V2O5 core, and the thickness of the carbon shell are controlled via a one-pot solvothermal method followed by a single calcination process, and the performance differences between them are systematically studied. In this composite of amorphous carbon-coated V2O5 well-defined porous core-shell heterostructure (A-V2O5/C-WCS), synergistically the amorphous V2O5 core accelerates ions diffusion, carbon shell boosts the electronic conductivity, and the defect-rich porous structure lowers the binding energy compared to its counterparts as confirmed by DFT calculations and electrochemical results. Out of the ordinary, the A-V2O5/C-WCS used as a symmetric electrode for SIBs exhibits an excellent rate capability of 148 mAh g−1 at 5.0 A g−1 and outstanding ultralong cyclic stability (95% capacity retentions over 3000 cycles at 2.0 A g−1), when applied as a cathode (1.5–4.0 V) and anode (0.01–3.0 V) for SIBs. The A-V2O5/C-WCS displays a fully pseudocapacitive manner over the whole voltage thus the electrochemical performance of cathode and anode are well-matched. Impressively, the symmetric full-cell possesses a superior energy density of 219 Wh kg−1 at a high specific density of 6.0 KW kg−1 and superior cycling stability (95% capacity retained over 1200 cycles at 1.0 A g−1), demonstrating the great potential for practical application.