Solid State Synthesis And Carbon Modification Of Li₄Ti₅O₁₂ Anode Material For Lithium Batteries

The ever-growing demand for lithium batteries with high power and high safety has motivated scientific efforts dedicated to improving existing battery systems and developing new electrode materials. Current commercial carbonaceous anode materials can’t meet satisfactorily the requirement of long cycle life and high safety needed for lithium battery. Spinel Li4Ti5O12has been demonstrated to be a candidate anode material for lithium battery. Due to the negligible volume change during charge and discharge, Li4Ti5O12has good structure stability ensuring its exceptional cycle life. Besides, it has a flat and high charge/discharge potential platform around1.5V (vs. Li/Li+), which is sufficiently high to avoid the decomposition of most organic electrolyte as well as the formation of dendritic lithium. Thus the electrode can be preserved from safety issues carbonaceous materials suffered.However, the widely use of Li4Ti5O12in lithium ion battery requires that its poor rate capability arising from its insulating property, has to be overcome. In this study, carbon was applied to improve the rate performance of Li4Ti5O12. Carbon can lead to a decrease of grain size and an increase of electric conductivity of particles.The conclusions have been summarized as following:1. Stearic acid was introduced as the source of carbon coating for the first time to prepare Li4Ti5O12/C by a simple one-step solid state method. The effect of different amount of added stearic acid was investigated. The grain growth of Li4Ti5O12was suppressed significantly by the formation of carbon coating during the calcination process. It was found that among the three samples of various carbon content the LTO-S0.5with2.75%carbon exhibits optimal electrochemical performance. The LTO-S0.5electrode can deliver a capacity of169.3mAh g-1at0.5C and167.7mAh g-1at1C. Furthermore, the discharge capacity of the sample can still be remained at96.8%after300cyles at20C.2.Li4TiO12/C was synthesized via two-step calcination. Carbon coated TiO2was obtained at500℃with stearic acid as carbon source in the first step. Different carbon source was employed to enhance the conductivity in the second step calcination. It is found that the sample with Super-p as the second carbon source show the optimal performance, with capacities of149.2mAh g-1and132mAh g-1at10C and15C. At30C, the sample still can deliver a capacity of101.5mAh g-1after1800cycles, with capacity retention of81.2%, exhibiting excellent high rate performance.3. The optimal Li4TisO12/C sample synthesized in this study was coupled with LiFePO4material to constitute a full cell. The mass ratio of negative electrode and positive was investigated. At the current density of30mA/g, the cell can deliver a desirable capacity of74.5mAh g-1(based on the total weight of two electrode materials), and the capacity retention can is72%after500cycles at the current density of200mA/g.