| Spinel Li4Ti5O12 is a "zero strain" material, which has been demonstrated to be one of the most promising next-generation anode materials for lithium ion battery, because it has low price, good cycle performance, extremely flat charge and discharge plateaus, and so on. However, low conductivity of Li4Ti5O12 affects the actual electrochemical properties, limiting its commercial application. In this paper, the structure, features, methods of preparation and modification of Li4Ti5O12 were reviewed in detail, based on the summary about the development of lithium ion battery and anode materials. Li4Ti5O12 was synthesized by solid-state reaction at high temperature and modified by coating carbon and doping Zr4+. The related properties of anode materials were investigated by using various electrochemical methods in combination with modern physical testing techniques such as TG/DTA, SEM, XRD, and EDS analysis.Li4Ti5O12 was prepared by solid-state reaction. The influences of raw materials and synthesis conditions on the crystal structure, morphology and electrochemical performance of Li4Ti5O12 were investigated. The results show that the reaction temperature, sintering time, raw materials and the ingredient of lithium carbonate are important factors affecting material properties. The material with the best performance was sintered at 800℃for 16h by using TiO2 and Li2CO3 as raw materials when lithium was excessive by 2%. The sample has complete spinel crystal structure, homogenous size distribution, and good electrochemical performance. The reversible specific capacity is 160.0,149.2,140.4,114.9,91.1 mAh-g"1 at 0.1C,1C,2C,5C,10C rates, respectively. At room temperature, the capacity retains 97.0% after 50 cycles at 1 Crate.In order to improve the conductivity of Li4Ti5O12, and enhance electrochemical performance, it was modified by coating, using carbon nano-tubes and organic alcohol as carbon sources, respectively. The effect of carbon contents was studied. The results show that the crystallinity and morphology of Li4Ti5O12/C composite sample are different, and different electrochemical performances are exhibited, owing to different carbon sources. The effect of organic carbon on the improvement of material is batter. When organic alcohol was used as the carbon source, the sample with 3% carbon (nominal content) displayed the best performance. The sample has spinel structure, smaller particles, and the actual carbon content is 1.61%. The reversible specific capacity is 165.0,161.0,156.6, 146.0,125.6 mAh·g-1 at 0.1C,1C,2C,5C, 10C rates, respectively, and the sample shows excellent cycle performance.Li4Ti5-xZrxO12(x=0,0.05,0.10,0.15,0.20) was prepared by solid-state reaction using Zr4+as doping cation. The effect of doping Zr4+ on Li4Ti5O12 modified was discussed. It is found that doping a small amount of Zr4+help stabilize the structure and improve electrochemical performance. Li4Ti4.95Zr0.05O12 has good morphology, stable structure, and homogenous element distribution. The reversible specific capacity is 163.9,157.5,146.9,120.7,96.0 mAh·g-1 at 0.1C,1C,2C,5C,10C rates, respectively, which has increased compared with the pure Li4Ti5O12, but not obviously.The kinetics behavior of part synthesized materials was characterized by cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS). The lithium ion intercalation/deintercalation process was studied, and a matching equivalent circuit was proposed. The difference between pure Li4Ti5O12 and modified materials was further proved in electrochemical performance from the aspect of kinetics. |
PDF Full Text Request