Theoretical Prediction and Experimentally Realizing Cathodic Doping of Sulfur in Li₄Ti₅O₁₂ for Superior Lithium Storage Performance

Heteroatom doping has been considered an effective way to improve the kinetically limited Li4Ti5O12 as anode materials in lithium-ion batteries. Although a number of elements have been reported to enhance the conductivities of Li4Ti5O12, the influence of sulfur has been rarely investigated. More interestingly, the different valences of sulfur can lead to different cathodic or anodic dopings. In turn, theoretical prediction by equilibrium phase diagrams and density functional theory calculations and experimental confirmation using a facile thermal process were carried out to investigate the S-doping sites in Li4Ti5O12 using thiourea as the sulfur source. It is found that sulfur is more likely to be doped on Ti sites under oxygen-rich conditions. Meanwhile, significant influences such as decreased band gap, enhanced lattice spacing, and increased Ti3+ and oxygen vacancies are introduced by S-doping. In turn, kinetically limited performance of anode materials Li4Ti5O12 for lithium-ion batteries (LIBs) has been significantly improved, including high specific capacity (near theoretical value at 1 C), impressive rate performance, and remarkable cycle performance (126.4 mA h g–1 after 1000 cycles at 20 C with a Coulomb efficiency of up to 99.34%), indicating its wide applications in advanced LIBs.