A chromium oxide solution modified lithium titanium oxide with much improved rate performance

Abstract

A simple surface modification of Li₄Ti₅O₁₂ powder is made with an aqueous CrO₃ solution to improve its electrochemical properties. At a high current rate of 30 C, the specific capacity of the Li₄Ti₅O₁₂ increases by about 60% from its original 80 to 130 mA h g⁻¹. After the modification with the CrO₃ solution, a few surface phases including lithium chromate (Li₂CrO₄), Cr₂O₅ and anatase are found to co-exist in the final product. Among these three phases, Li₂CrO₄ and Cr₂O₅ can improve while anatase deteriorates the rate performance of Li₄Ti₅O₁₂. The AC impedance spectra and electron spin resonance (ESR) spectra reveal that the improvement of rate performance is correlated with the presence of Ti³⁺, which can increase the conductivity of the Li₄Ti₅O₁₂ sample. Lithium chromate (Li₂CrO₄) and Cr₂O₅ react with lithium to form lithium rich phases (Li_3+xCrO₄ and Li_yCr₂O₅) of low potential, which stabilize Li₇Ti₅O₁₂ with high electric conductivity and result in better rate performance. Besides improved rate performance, the cycle performance of the modified Li₄Ti₅O₁₂ samples is almost at the same level with the original Li₄Ti₅O₁₂, suggesting that this proposed modification method is efficient and harmless.