Enhanced Rate Capability and Low-Temperature Performance of Li₄Ti₅O₁₂ Anode Material by Facile Surface Fluorination

A commercial Li₄Ti₅O₁₂ material was modified by NH₄F using a facile and dry method at a low temperature in air. X-ray diffraction reveals that the fluorination did not change the bulk structure of Li₄Ti₅O₁₂. X-ray photoelectron spectroscopy demonstrates that LiF was formed at the surface and Ti⁴⁺ was partially changed into Ti³⁺. Microscopic images show that some nanoislands were formed on the surface, which enlarged the surface area. Consequently, the NH₄F-modified Li₄Ti₅O₁₂ material exhibited significantly enhanced capacities and rate capabilities, even at low temperatures. The discharge capacity was increased from 149 to 167 mA h g^-1 at 1 C, and the capacity retention was increased from 17.8 to 52.0% at 15 C. The capacity retention of NH₄F-modified Li₄Ti₅O₁₂ was greater than that of Li₄Ti₅O₁₂ at each low-temperature point. Additionally, the introduction of F can protect the Li₄Ti₅O₁₂ material from side reactions with the electrolyte and the atmosphere, enhancing the surface stability and reducing the release of gaseous products. It is believed that the NH₄F-modified Li₄Ti₅O₁₂ with enhanced electrochemical performance is a promising anode material for lithium ion batteries. Furthermore, this facile surface fluorination strategy is amenable to large-scale production.