A freestanding hierarchically structured cathode enables high sulfur loading and energy density of flexible Li–S batteries

Abstract

Due to sulfur agglomeration and drastic volume expansion during charging, a significant challenge for lithium–sulfur battery applications is to achieve favorable energy densities while realizing substantial sulfur loading. The rational design of cathode materials is therefore essential. Here we show a new type of low-cost sulfur/silica/carbon hybrid cathode by integrating carbon-coated and sulfur-encapsulated mesoporous SiO₂ nanospheres with a carbon fiber cross-linked graphene framework (denoted as 3D-GCSS). The porous morphology of SiO₂ ensures electrolyte accessibility, while the mechanical robustness of graphene and the carbon fiber contributes to structural sturdiness and flexibility. The synergistic effect exerted by polar SiO₂ together with conductive graphene and the carbon fiber helps to confine sulfur and intermediate polysulfides as well as providing abundant charge transfer paths. Benefiting from these merits, a coin cell fabricated based on the freestanding 3D-GCSS with an 8 mg cm⁻² sulfur content displayed a high capacity of 1462 mA h g⁻¹ at 0.5C, satisfactory rate performance and cycling stability. More importantly, a type of ultra-flexible soft-packaged cell was assembled utilizing the 3D-GCSS electrode. At a considerable sulfur loading of 20 mg cm⁻², the battery delivered an outstanding capacity of 2.15 A h, a gravimetric energy density of 371 W h kg⁻¹ (1055 W h kg⁻¹ based on the cathode) and a volumetric energy density of 582 W h l⁻¹.