Carbon-coated Li₄Ti₅O₁₂ optimized by fluorine regulation strategy for high-rate lithium-ion batteries with mixed diffusion and capacitive effects

Spinel lithium titanate (LTO) has attracted much attention due to its good stability, but its low electronic and ionic conductivities limit its application in high rate/low temperature devices. Herein, an internal and external combination strategy is reported for the preparation of fluorine-doped optimized carbon-coated LTO core-shell structures (3F-LTO@NC). The external strategy of nitrogen-doped carbon layer limits the LTO particle size to a few tens of nanometers and generates oxygen vacancies inside the bulk LTO, whereas the internal strategy of fluorine doping increases the carbon layer defects and oxygen vacancy concentration, which improves the electronic conductivity of the material. Meanwhile, the material has a pseudocapacitive diffusion energy storage mechanism due to the active sites provided by the carbon matrix defects and oxygen vacancies. For lithium-ion batteries (LIBs), 3F-LTO@NC provides outstanding cycling stability and rate performance (165.8 mAh g⁻¹ at 500 mA g⁻¹ for 2000 cycles, capacity retention of 95.0%; 136.2 mAh g⁻¹ at 10 A g⁻¹). Furthermore, a high specific capacity of 124.5 mAh g⁻¹ can be obtained after 100 cycles at −20 °C at 0.5 A g⁻¹. Our work suggests an effective way to develop high-rate and low-temperature anode materials for LIBs.