Soft/rigid SnS&TiS2 compounds with carbon nanotubes as heterostructure anode materials for high-performance sodium-ion batteries

Abstract

SnS is a promising anode material for sodium-ion batteries (SIBs) due to its high theoretical specific capacity, but the poor intrinsic conductivity, bulk expansion and shuttle effects brought by polysulfides seriously limit its practical use. Here, soft/rigid SnS&TiS2 compounds with carbon nanotubes (ST@CNTs) is designed to overcome the shortcomings. The rigid TiS2, as the strong backbone of SnS&TiS2, relieves the expansion stress caused by SnS after sodiation, together with CNTs improve the materials conductivity. TiS2 generates many sulfur defects under the synergistic effect of SnS, which can regulate the sodium-ion embedding sites to stabilize the compound structure and decrease the sodium-ion diffusion energy barrier. Moreover, rigid TiS2 can adsorb polysulfides induced by SnS, thus suppresses the shuttle effect and improves the cycling and rate performances. Fortunately, the above conclusions are confirmed by the DFT calculations. The ST@CNTs provide a specific capacity of 550 mAh/g at 1.0 A/g after 300 cycles, and a high-rate capability of 443 mAh/g at 2.0 A/g. This soft/rigid misfit strategy combines the advantages of high modulus of rigid layers and high sodium-ion storage capacity of soft layers, which gives an idea for the development of new anode candidates for SIBs.