Vanadium-modified hard carbon spheres with sufficient pseudographitic domains as high-performance anode for sodium-ion batteries

Hard carbons are promising anode materials for sodium-ion batteries. To meet practical requirements, searching for durable and conductive carbon with a stable interface is of great importance. Here, we prepare a series of vanadium-modified hard carbon submicrospheres by using hydrothermal carbonization followed by high-temperature pyrolysis. Significantly, the introduction of vanadium can facilitate the nucleation and uniform growth of carbon spheres and generate abundant V-O-C interface bonds, thus optimizing the reaction kinetic. Meanwhile, the optimized hard carbon spheres modified by vanadium carbide, with sufficient pseudographitic domains, provide more active sites for Na ion migration and storage. As a result, the HC/VC-1300 electrode exhibits excellent Na storage performance, including a high capacity of 420 mAh g(-1) at 50 mA g(-1) and good rate capability at 1 A g(-1). This study proposes a new strategy for the synthesis of hard carbon spheres with high tap density and emphasizes the key role of pseudographitic structure for Na storage and interface stabilization.