Hierarchically structured Ti3C2T MXene paper for Li-S batteries with high volumetric capacity

Abstract

Due to the low density of sulfur and the large portion of carbon-based materials used as conducting network and lithium polysulfide (LiPS) host, the practical volumetric energy density of lithium–sulfur (Li–S) batteries barely rivals the Li-ion batteries. Here, MXene (Ti 3 C 2 T x )-based membrane with unique 3D hierarchical structure, high electronic conductivity, abundent active binding sites, fast ion transport, and high affinity for lithium polysulfides has been developed as a new host material to improve the electrochemical performance of Li-S batteries. With a density of 2.2 g cm −3 , a MXene-based cathode containing 4.0 mg cm −2 sulfur delivers a high volumetric capacity of 2.7 Ah cm −3 after 200 cycles. Based on operando XRD and ex-situ XPS results, we find that the Ti-OH bonds present on the surface of MXene membrane can effectively trigger the LiPS transformation. Furthermore, α -S 8 , as the stable charge product, is first reported in MXene-based host along with its possible important role in curtailing active mass loss and enhancing cycling capability. Our results reveal that 2D MXene with rationally-designed architecture enable high volumetric capacity Li-S batteries for practical applications. An excellent lithium-sulfur battery with high volumetric capacity is enabled by a 3D hierarchical MXene (Ti 3 C 2 T x ) electrode, which can effectively regulate the polysulfides shuttling via a dual-play immobilization mechanism of thiosulphate/polythionate redox conversion and Lewis acid-base interactions. α -S 8 is first reported as the stable charge product and its important role is studied in detail. • An efficient encapsulation strategy was developed to construct a robust hierarchically structured MXene cathode of Li-S batteries. • Combined in-situ and ex-situ measurements suggest that the thiosulphate/polythionate complex serves as key redox transfer mediator to facilitate the surface-redox reaction. • α-S 8 is firstly reported as the stable charge-stage product and its fast nucleation and stability effectively curtail active mass loss and enhances cycling capability.