Synthesis Of Li₄Ti₅O₁₂ As Anode Material For Lithium Ion Battery

At present, rapid development of EV or HEV requests high power Li-ion batteries (LIBs) to have higher energy, longer life and better safety than before. Recently, Li4Ti5O12, as a new anode material for LIBs, attracts more attention of many researchers due to its better cyclability and safety resulted from "zero strain" during charge/discharge and reduction of electrolyte decomposition. However, lower conductivity limits its use. In order to improve the rate capability of Li4Ti5O12, the studies on preparation and optimization of Li4Ti5O12 by solid state reaction, preparation and electrochemical properties investigation of C/Li4Ti5O12 composite material and doped materials Li4Ti5-xNbxO12 and Li4-yMgyTi5O12 were carried out in this paper.Synthesis of spinel Li4Ti5O12 by solid state reaction using Li2CO3 and nanometer TiO2 as raw materials show that pure spinel Li4Ti5O12 can be obtained over 800℃. The particle size increases with elevation of heating temperatures and time. The sample prepared at 800～820℃show better crystal characteristics. However, heating temperatures over 850℃make particles melt and agglomerate. In addition, annealing time over 14h has no obvious effects on particle size. The sample prepared at 800℃for 14h exhibits the best electrochemical performance, with discharge capacity of 161.8 mAh.g-1 in the first cycle and capacity retention of 97.9% after 30 cycles at 0.2C. Using high energy ball-milling to mix raw materials benefits the properties of Li4Ti5O12. The preparation condition can be optimized to be that mixing raw materials by ball-milling, annealing at 800℃for 14h.Synthesis of C/Li4Ti5O12 composite materials by two-step solid state reaction using black carbon and sugar as carbon resources was investigated. The results show that all prepared samples show no impurity. The black carbon mixed material has particle size of 400-600nm, but carbon coated sample only has particle size of 100-200nm, showing better reduction effects on crystal growth. Among the black carbon mixed materials, the 5% mixed sample preheated at 650℃exhibits the best properties, with capacity of 161.4 mAh.g-1 at 1C and capacity retention of 100% after 30 cycles. Among carbon-coated samples, the 10% sugar coated sample preheated at 600℃exhibits the best properties, with capacity of 163.1 mAh.g-1 at 1C and capacity retention of 95.4% after 30 cycles. Compared with the black carbon mixed samples, carbon-coated Li4Ti5O12 materials show better rate capability. Better properties of C/Li4Ti5O12 composite materials can be attributed to reduction of crystal growth and increase of electric conductivity.Investigation of doped Li4Ti5O12 reveals that all Mg-doped sample show pure spinel phase, but the Nb-doped samples with x>0.10 show minor impure phase of Nb2O5 and LiNbO3. Doping has no obvious effects on particle sizes in this study. Among Nb-doped samples, the doped sample with x values of 0.025 and 0.05 exhibits better properties, with capacity of 164～169 mAh.g-1 at 0.2C and capacity of about 50mAh.g-1at 5C. Among Mg-doped samples, the doped sample with y values of 0.05 exhibits better properties, with capacity of about 160 mAh.g'1 at 0.2C and capacity of about 28mAh.g-1at 5C. Compared with Li4Ti5O12, the optimized doped materials show great improvement of rate capability and cycling stability. Better properties of doped Li4Ti5O12 can be attributed to reduction of charge-transfer impedance.C/Li4Ti5O12 composite materials synthesized by two-step solid state reaction using sugar as carbon resources show better electrical properties, being a promising anode material for LIBs.