Preparation Of Oxygen-deficient Lithium Titanate And Its Electrochemical Performance

Lithium titanate(Li₄Ti₅O₁₂)has recently attracted considerable attentions as a potential anode material of LIBs for high power applications due to several outstanding features,including a flat charge/discharge plateaus?around 1.55 V vs.Li/Li⁺?because of the two-phase lithium insertion/extraction mechanism and minimum chance for the formation of SEI and dendritic lithium,dramatically enhance the potential for high rate capability and safety.In addition,there is almost no volume change during the lithium insertion and extraction processes,ensuring a high cycling stability and long operational life.However,the electronic conductivity of Li₄Ti₅O₁₂ is relatively low,resulting in large polarization lose,more so at higher cycling rates,and poor rate performance.In this paper,oxygen-deficient Li₄Ti₅O₁₂was prepared by different methods,and the electron conductivity and electrochemical performance of Li₄Ti₅O₁₂ were improved.Li₄Ti₅O₁₂/C composite anode material was prepared by high temperature solid phase method with citric acid as organic carbon source.The gas generated by the thermal decomposition of citric acid promotes the sublimation of Li₂O in the raw material and volatilization with the gas,resulting in excess TiO₂ in the prepared material.The surplus TiO₂ has a capacity contribution to the first discharge due to poor deintercalation of lithium cycle performance,and does not continue to deintercalate lithium in the subsequent cycle.On the contrary,the formation of impurities has a negative effect on the performance improvement of the Li₄Ti₅O₁₂/C.Due to the thermal decomposition of citric acid to produce a partial reducing gas,a part of Ti⁴⁺in Li₄Ti₅O₁₂ is reduced to Ti³⁺,so that the prepared Li₄Ti₅O₁₂/C contains oxygen defects.The residual small amount of amorphous carbon and the resulting oxygen deficiency increase the electron conduction and lithium ion diffusion of Li₄Ti₅O₁₂,resulting in electrochemical performance of the material at low rates.However,the excessive concentration of oxygen defects causes structural lattice defects to deteriorate the cycle performance of Li₄Ti₅O₁₂ at high rate charge and discharge.The pure phase Li₄Ti₅O₁₂ containing oxygen deficiency was synthesized by the high-temperature solid phase method in reducing atmosphere?N₂/H₂?with different flow rates.XRD shows that TiO₂ impurities appear in the material synthesized when the reducing atmosphere gas flow rate is too small,and negatively affect the electrochemical performance of the material;When the gas flow rate is too large,the oxygen defect concentration in the negative electrode material is too high,and the stability at the time of charging and discharging at a large rate is deteriorated.XRD and electrochemical performance test results show that when the reducing atmosphere gas flow rate is 170 ml/min,the prepared material contains an appropriate amount of oxygen defects,which can improve the electrochemical performance of the material without causing problems such as lattice defects.Successfully solved the problem that oxygen deficiency caused the instability of Li₄Ti₅O₁₂ high rate charge/discharge,the capacity reaches 116.3 mAh·g^-1 at 10 C.