Sheet-to-layer structure of SnSe2/MXene composite materials for advanced sodium ion battery anodes

Abstract

SnSe₂ is regarded as an auspicious anode material for sodium-ion batteries owing to its high theoretical capacity and large interlayer spacing. However, the moderate conductivity, inevitable aggregation, and tremendous volumetric expansion (more than 300%) of SnSe₂ still plague its large-scale use. Thus, a sheet-to-layer structure SnSe₂/Ti₃C₂T_x (MXene) composite material has been synthesized in this work using an electrostatic assembling procedure. The SnSe₂/Ti₃C₂T_x composite electrode delivered a superior sodium storage performance in a high specific capacity of 245 mA h g⁻¹ at 1 A g⁻¹ (5.4 times that of SnSe₂ and 4.1 times that of Ti₃C₂T_x) with a capacity attenuation rate of only ∼0.06% per cycle after 445 cycles. This electrode material not only combines the advantages (high theoretical capacity SnSe₂ and high conductivity of Ti₃C₂T_x) of these two components, but also shows synergistic effects; these are: (i) the inserted SnSe₂ nanosheets can inhibit the self-stacking problem of Ti₃C₂T_x and Ti₃C₂T_x and can prevent the aggregation of SnSe₂ nanosheets and alleviate the volume expansion of SnSe₂ nanosheets during cycling; (ii) the increased surface area with the mesoporous structure is favorable for sodium ion kinetics and simultaneously conducive to electrolyte penetration and rapid ion diffusion during cycling.