Preparation And Modification Of High-Power Li₄ Ti₅ O₁₂ Electrode Materials

With the development of portable electronics and electric vehicles(EVs), excellent performance lithium-ion batteries are highly desirable, which should possess high energy density, high power density, safety and portable. Spinel Li₄Ti₅O₁₂ could provide three-dimensional free channels for Li+ diffusion. The Li-insertion process of Li₄Ti₅O₁₂ operates at about 1.5V (vs.Li/Li+), the relatively high potential makes the Li₄Ti₅O₁₂ electrodes intrinsically safer compared to graphite, which has an operating voltage close to Li electroplating potential and thus raises concerns over its safety. Furthermore, spinel Li₄Ti₅O₁₂ shows a very small volume variation during the charge/discharge process, so called―zero strain‖structure, consequently resulting in excellent cycle stability. However, the high power performance of Li₄Ti₅O₁₂ is still limited by its inherent insulating character (its inherent conductivity is only 10?9S·cm?1). In this manuscript, for improving its high-rate electrochemical performance, we mainly prepare nanocrystalline Li₄Ti₅O₁₂, compositing it with activated carbon, and coating it with carbon and silver simultaneously.Firstly, a facile approach was reported to synthesize nanocrystalline Li₄Ti₅O₁₂ via sol-gel process by employing a nonionic surfactant (EO)20(PO)70(EO)20 tri-block copolymer (pluronic F127) as the chelating agent. Pure-phase Li₄Ti₅O₁₂ with high crystallinity is obtained at a sintering temperature of 700℃. The sample has a cubic morphology and a uniform particle size distribution (¹00nm). The initial discharge capacity was 166mAh·g?1 at 1C rate. After 50 cycles, the discharge capacity is 162mAh·g?1, and the capacity retention rate is about 97.6%.Secondly, the Li₄Ti₅O₁₂ synthesised via sol-gel approach was composited with the activated carbon with bigger specific surface area. The effect of the content of activated carbon to the performance of the Li₄Ti₅O₁₂ electrode material was investigated. It demonstrates that the optimum mass ratio of Li₄Ti₅O₁₂ and activated carbon is 40:30. The initial discharge capacity was 195 mAh·g?1 at 0.5C. The cell also presents high-rate capacity of as high as 145mAh·g?1 at 20C.Finally, the concurrent coating modification with highly conductive carbon and silver was conducted on Li₄Ti₅O₁₂ nanocrystalline for constructing the conductive network. The TEM test confirms the existence of carbon and silver. The observation further shows that the the surface of Li₄Ti₅O₁₂ was uniformly coated by the carbon film with a thickness of approximate 7 nm, and then the silver particles with a particle size of about 10nm were homogeneously distributed at the surface of carbon film. The electrochimical test demonstrates that the modified Li₄Ti₅O₁₂ can exhibit the high discharge capacity of 207mAh·g?1 and 140mAh·g?1 at 0.5C and 20C rate, respectively.