One-Step Synthesis of a Nanosized Cubic Li₂TiO₃-Coated Br, C, and N Co-Doped Li₄Ti₅O₁₂ Anode Material for Stable High-Rate Lithium-Ion Batteries

Abstract

Nanosized Li₄Ti₅O₁₂ with both a Li₂TiO₃ coating and C-N-Br co-doping (CLLTO) was successfully synthesized via a facile reverse microemulsion method in one step using hexadecyl trimethyl ammonium bromide as a surface control agent and as a carbon, nitrogen, and bromine source. A uniform Li₂TiO₃ layer was formed on the surface and strongly adhered to the host material Li₄Ti₅O₁₂ (LTO), which played an important role in improving the cyclic stability of CLLTO. The thin and stable Li₂TiO₃ layer has the same cubic structure as LTO, which provides many three-dimensional channels for ion transport. C, N, and Br co-doping in CLLTO promoted the transition of Ti⁴⁺ to Ti³⁺ in Li₄Ti₅O₁₂, which could improve the capacity and facilitate the Li⁺ ion and electron transfer at the interface. The conductive behavior induced by co-doping was estimated by UV-vis diffuse reflectance spectra and further supported by theoretical calculations. The electrical conductivity of both p-type and n-type LTO can be well improved by co-doping C, N, and Br. This improvement may be due to the band gap reduction and the increased n-type electronic modification of the entire LTO. Owing to the synergistic effect of coating, co-doping, and nanosizing at one time, the CLLTO exhibits a high discharge capacity of 177.3-153.9 mA h g^-1 at the working rate of 0.1C-20C, with a capacity retention of 86%. The stable cycling of CLLTO is also obtained after 500 cycles at 20C, with a capacity retention of 95.5% (approximately 8 times higher than that of pure LTO) and almost 100% Coulombic efficiency. With high capacity, excellent rate performance, and good cycling stability, CLLTO can be applied in high-power lithium-ion batteries.