Ti3C2Tx MXenes in Lithium-Sulphur batteries to balance polysulphide adsorption and Li2S deposition

Lithium-Sulphur (Li-S) batteries are a promising post-lithium-ion energy storage technology due to sulphur high theoretical capacity, low toxicity and natural abundance. Nevertheless, sulphur multistep reduction reactions involve the formation of soluble lithium polysulphides, whose uncontrolled migration to the anode (shuttle effect) and sluggish conversion kinetics lead to capacity fading and poor cycling stability. To overcome these issues, different materials capable of binding polysulphide species, catalysing their conversion and controlling Li₂S deposition have been explored as sulphur hosts. In this context, MXenes have recently emerged owing to their good electrical conductivity and polar surface chemistry. The present work aimed at studying Ti₃C₂Tₓ MXenes as sulphur hosts for Li-S batteries. In particular, four samples of 2D titanium carbide were prepared by varying temperature, time and concentration of the classic synthesis involving the use of hydrogen fluoride. The synthesised Ti₃C₂Tₓ were characterised using physico- chemical and electrochemical techniques to evaluate their affinity to polysulphide species and their potential activity as catalysts for sulphur redox reactions. The results show that slight changes in the synthesis conditions influence the balance between polysulphides adsorption and electrochemical conversion. In particular, combining lower acid concentration and longer reaction time leads to MXenes with improved overall electro-chemical behaviour, delivering stable cycling up to 500 cycles with improved Coulombic Efficiency (>99%) and capacity retention (>70%), with a capacity loss < 0.30% per cycle at C/5. Although MXenes exhibit lower porosity and electrical conductivity than conventional carbon hosts, the present study highlights their effec- tiveness in suppressing the shuttle effect and control Li₂S deposition.