Encapsulating sulphur inside Magnéli phase Ti₄O₇ nanotube array for high performance lithium sulphur battery cathode

The lithium–sulphur battery is a promising system for next-generation energy storage because of its high energy density and the abundant supply of sulphur. In this study, Magnéli phase Ti₄O₇ nanotube arrays (NTA) were grown on titanium nitride mesh substrates via anodization of titanium mesh followed by high-temperature reduction under a hydrogen atmosphere. When prepared into a composite material with sulphur via electrodeposition, Ti₄O₇ NTA provides sulphur with high electronic conductivity and strong polysulphide chemisorption during battery operation. The structure of NTA allows sufficient access of incorporated sulphur to the liquid electrolyte and supports high sulphur loadings per unit area of the electrode. The application of an additional layer of conductive carbon coating to confine electrodeposited sulphur inside the NTA further improved the cell cycling performance. Under sulphur loadings of around 2.0 mg/cm², high values of specific capacity (1604 mAh/g at a 1/20 C rate), ultra-low capacity decay rate (0.03% per cycle for 1800 cycles), and versatile rate capability (660 mAh/g at 2 C and 500 mAh/g at 4 C) were achieved. Under high sulphur loadings of around 5.0 mg/cm², stable cycling (decay rate below 0.10% per cycle) and high areal capacity (4.97 mAh/cm²) were attained.