Research On Modification Of Li₄Ti₅O₁₂ As Anode Materials For Li-ion Batteries

In recent years, Lithium-ion battery anode material Lithium titanate (Li4Ti5O12) as an excellent new-type battery material is widely employed energy storage areas. Lithium titanate has the advantage of better anti-overcharge performance, high thermal stability, high level of security and great specific capacity. It is also rich in resources and friendly to environment. However, Lithium titanate synthesized at present is still poor in conductivity, high-current charge and discharge, and density. In order to improve the conductivity, reduce resistance and polarization of materials, as well as reduce the electrode potential, improve the energy density of batteries, this paper studied graphene-coated Li4Ti5O12, Sn-doped Li4Ti5O12, and Sn-doped graphene-coated Li4Ti5O12. Graphene-Coated Li4Ti5O12was compared with carbon-coated Li4Ti5O12synthesized by glucose, sucrose, graphite and carbon nanotubes. The materials were characterized by Thermogravimetry-differential thermoanalysis (TG-DTA), X-ray Diffraction (XRD), Scan electron microscope (SEM), Particle size analysis (PSA). Its electrochemical properties were investigated by constant current charge-discharge test, AC impedance, Cycle Voltammagram (CV).The effects of graphene content and synthesis process on on the structure and performance of graphene-coated Li4Ti5O12were first discussed. The results demonstrated that graphene-coated Li4Ti5O12synthesized in two-step solid-state reaction with one percent graphene has best performance, reaching the initial specific capacity of304.1mAh-g"1at the rate of0.1C. After thirty-three cycles at0.1C,0.5C,1C rate (each elven cycles in turn), the discharge capacity is about77.4%of its maximum capacity.Then the effect of carbon sources on on the structure and performance of carbon-coated Li4Ti5O12was discussed in one-step solid-state reaction. The results demonstrated that carbon-coated Li4Ti5O12synthesized with glucose has best performance, reaching the initial specific capacity of230.0mAh·g-1. But its cycle performance is poor, only keeping56.7%of its maximum capacity. Other carbon-coated Li4Ti5O12synthesized by sucrose, graphite, carbon nanotubes, graphene-coated Li4Ti5O12have similar initial specific capacity, about200 mAh·g-1. Graphene-coated Li4Ti5O12has best cycle performance, keeping75.8%of its maximum capacity.The amount of Sn has great influence on performance of the materials. Sn-doped Li4Ti5O12with n(Sn)/n(Ti)=1:15has best electrochemical properties, reaching the initial specific capacity of181.1mAh·g-1. the discharge capacity is about68.1%of its maximum capacity. Sn-doped graphene-coated Li4Ti5O12effectively improves specific capacity, its initial specific capacity got271.7mAh·g-1. But its cycling performance is poor, only keeping64.3%of its maximum capacity.