A novel method to enhance rate performance of an Al-doped Li ₄Ti ₅O ₁₂ electrode by post-synthesis treatment in liquid formaldehyde at room temperature

An amenable method for improving rate performance of Li ₄Ti _4.85Al _0.15O ₁₂ electrode by post-synthesis treatment in formaldehyde aqueous solution at room temperature is introduced. The as-prepared samples are characterized by XRD, BET, SEM, HR-TEM, XPS and electronic conductivity measurement. The treatment causes no noticeable change on the phase structure and has only little effect on the specific surface area and particulate morphologies. It also only slightly decreases the lithium ion diffusion coefficient. However, it substantially increases the electronic conductivity due to the creation of Ti ³⁺ in the oxide lattice. The post-synthesis treatment for a period of 4 h effectively increases the capacity at 10 C rate for Li ₄Ti _4.85Al _0.15O ₁₂ from 125 mA h g ^-1 for the untreated sample to 160 mA h g ^-1, and the electrode performance is also fairly stable. This method is highly attractive for synthesis of high-performance Li ₄Ti ₅O ₁₂ electrodes owing to its simplicity, energy saving and efficiency. As a general method, post-synthesis treatment using formaldehyde may be applicable to other electrodes.