Development And Study Of Lithium Titanate New Type Of Electrode Material

Lithium Titanate (Li₄Ti₅O₁₂) is the"zero-strain"and perfect insertion electrode materials. It is the hopeful negative material of lithium-ion battery, due to its more excellent characteristic of reversibility, fast kinetics of charge-discharge process, and safety than usual electrodes. But the low inherent conductance (10-9S/cm) restricts its application. The purpose of the experiment is to synthesize Li₄Ti₅O₁₂ materials with high specific capacity, steady cyclability, good high rate cycle performance and low cost. The main testing methods including constant current charge-discharge test, AC impedance, Cycle Voltammagram (CV) and X-ray Diffraction (XRD), Scan electron microscope (SEM), Thermogravimetry- differential thermoanalysis (TG-DTA).The infection of the synthesis conditions of Li₄Ti₅O₁₂ prepared by traditional solid-state reaction were investigated, The CV behavior and AC impedance of the product were studied to discuss the electrode reaction course and dynamics parameter of Li₄Ti₅O₁₂. The results demonstrated that the characteristic of raw materials, sinter temperature, sinter time, proportion of materials, method of mixing and sinter atmosphere were importance influence factors of product; there is not passivation film on the surface of Li₄Ti₅O₁₂ indicated that Li₄Ti₅O₁₂ was safer than carbon as Li-ion battery negative material.Carbon doping, carbon coating and ball milling were adopted to improve the performance of Li₄Ti₅O₁₂. The results showed that 10%¹5%wt was the better range of graphite doping. Reaction materials mixed by ball milling could obviously improve the capacity and cyclability of the product, its cycle capacity at 0.5C and 1C rate was also good, but there was notable capacity decline. The charge transfer resistances of carbon coated Li₄Ti₅O₁₂ reduced as the content of dextrose and sucrose increased, but when the content exceeded 20%wt, the charge transfer resistances don't reduce anymore. Two steps solid-state reaction was used to gain ion-doped Li₄Ti₅O₁₂. The results indicated that the ions of Mg²⁺,Fe³⁺,Al³⁺,Cr³⁺,La³⁺,Zr⁴⁺,Nb⁵⁺,V⁵⁺,F- were doped availably. The materials doped by Mg²⁺,Zr⁴⁺ got best performance, with same doping content, their charge transfer resistances were reduced distinctly, and had fast kinetics of charge-discharge process, that made the polarization reduce, reversible capacity and cyclability improve, especially doped by Zr⁴⁺. The research of doping content demonstrated that substitute quantity (x) equated 0.15 was preferable.Through prolonging ball milling time (about 20h) to enhance the uniformity and reactivity of raw materials, then coated with carbon or multi-doped with Mg²⁺. The final product had better high rate cycle performance than that of single modification, at 0.5C rate, after cycling 45 times the reversible capacity was about 120mAh/g.Li₄Ti₅O₁₂ was synthesized by sol-gel method, the kind of chelate reagent, mix method, dosage of solvent and water were investigated to get the ideal experimental flow. The results showed that the materials sintered with nitrogen gas flow got higher capacity and better high rate cycle performance than sintered with airflow. Mg²⁺,Zr⁴⁺ could also be doped by sol-gel method, the material doped with Zr⁴⁺ was better than Mg²⁺ doped. The cyclic stability of doped Li₄Ti₅O₁₂ was preferable than pure Li₄Ti₅O₁₂...