Twinborn TiO2–TiN heterostructures enabling smooth trapping–diffusion–conversion of polysulfides towards ultralong life lithium–sulfur batteries

Abstract

The practical use of lithium–sulfur (Li–S) batteries is largely hindered by their poor cycling stability because of the shuttling of soluble lithium polysulfides (LiPSs) in a slow redox reaction. Physical and chemical confinement by carbon or noncarbon hosts has been used to block LiPS shuttling, but this may only be a complete solution to the problem if it combines with LiPS fast conversion into an insoluble sulfide. Here we report a twinborn TiO₂–TiN heterostructure that combines the merits of highly adsorptive TiO₂ with conducting TiN and achieves smooth trapping–diffusion–conversion of LiPSs across the interface. TiO₂ has high adsorption for LiPSs while TiN promotes their conversion into insoluble Li₂S. The fast diffusion of LiPSs from TiO₂ to TiN helps achieve both high trapping efficiency and fast conversion. By loading such a heterostructure onto graphene, which acts as a physical barrier, a compact and thin coating is fabricated on the separator, and LiPS shuttling is greatly restrained even with a high sulfur loading. A capacity of 927 mA h g⁻¹ after 300 cycles is obtained under a low current density of 0.3C. Over 2000 cycles, capacity retentions of 73% and 67% at 1C are achieved for sulfur loadings of 3.1 and 4.3 mg cm⁻². Such an interlayer is expected to promote the practical use of Li–S batteries because of the simple processing and the resulting outstanding capacity and cyclic performance. Such a heterostructure suggests a new way to produce multifunctional interlayers that improve the performance of energy storage devices.