Nitrogen and sulfur co-doped carbon-coated Li₄Ti₅O₁₂ composite to enhance lithium storage properties

Using a hydrothermal method and subsequent heat treatment, a nitrogen and sulfur co-doped carbon (NSC) coated Li₄Ti₅O₁₂ composite (referred to as LTO@NSC) is successfully synthesized. Cetyltrimethylammonium bromide (CTAB) is chosen as the carbon source, thiourea as the sulfur and nitrogen sources for doping ions. The presence of C-S and C-N bonds in XPS spectrums proves that the carbon layer has been doped with sulfur and nitrogen. Some of the sulfur and nitrogen replace the oxygen, which effectively change the cell volume and lattice spacing. Consequently, LTO@NSC greatly changes the structure from the uneven large ball to the nanoparticles and nanosheets. Apart from this, it shortens the length of electron and lithium-ion transport. Among them, the LTO@NSC maintains excellent performance at the rate capability (161 mAh/g at 10 C) and stability in cycling (after 400 cycles, the capacity retention rate was 98.5% at 10 C). The LTO@NSC has a capacity of 119.79 mAh/g with a decline rate of only 0.00552% each cycle, after 1000 cycles at 20 C.