Application of an inorganic sulfur-modified expanded graphite anode for sodium storage at low temperatures

Abstract

Carbonaceous materials as anode materials are one of the candidates for commercial lithium ion batteries; meanwhile, they are potential for commercial sodium ion batteries. Graphite, as a member of them, plays an important role and needs to be further researched and modified. In this work, an inorganic sulfur-modified expanded graphite anode was prepared via both a liquid fusion process and a thermal expansion process, which presented a large interlayer distance of 3.77 Å. Furthermore, the capacity retention of more than 98% after 500 cycles at 0 °C was presented with a capacity of 245 mA h g⁻¹ at 1C. In addition, in the most cold environment of high-latitude areas, when the temperature decreases to −20 °C, a capacity of 66 mA h g⁻¹ means an actual availability. In addition, research of kinetics and cycled anodes showed a nice stability. Na⁺ diffusion coefficients show nearly the same trend and values at room and low temperatures, and even after cycling still retain the same order of magnitude. Therefore, the inorganic sulfur-modified expanded graphite anode deserves to be considered a qualified anode material for the commercial application of sodium storage.