Abstract
To solve the environmental concern for global issue and to enhance the efficiency of energy storage system, lithium-ion batteries have been used for large-scale energy storage system and hybrid electric vehicle (HEV) to save oil and to decrease exhaust emissions. Therefore, the increasing demands for high energy density and high power density of batteries have attracted investigators to develop new materials for lithium-ion batteries. In this study, the concept of surface modification and composite are introduced to explore advanced negative materials. Spinel Li4Ti5O12 is a promising anode material, due to its stable working voltage and negligible structure change during charge-dscharge process. Nevertheless, the relatively low electronic conductivity will limit the commercialization of spinel Li4Ti5O12. Hereafter, improving electronic conductivity via ion doping approach to promote the rate capability of spinel Li4Ti5O12 anodes is investigated in the first section. Lithium titanate was successfully doped by N3- ions into O2- sites through Ar/N2 plasma irradiation at atmospheric pressure. The electrochemical behavior of plasma-treated lithium titanate will be systematically investigated; it also exhibits a desirable discharge capacity of 132 mAh g-1 with almost 100% capacity retention after 100 cycling life at a high rate of 10C. Afterwards, to suppress irreversible reaction and to greatly accelerate their rate capability, carbon passivation layer is introduced via sputtering process. The carbon overlayer-coated lithium titanate shows desirable rate capability. The reversible capacity at 10 C even remains over 91 % of that at initial cycles. Besides, the carbon passivation layer successfully alleviates the irreversible interfacial reaction between active material and electrolyte. In the last section, the Li4Ti5O12/porous carbon matrices was synthesized under reducing atmosphere, the aim of which was to realize the excellent chemical performance of Li4Ti5O12-based anodes, based on the concept of designing continuous conductive network and inducing oxygen vacancies. Li4Ti5O12/porous carbon matrices can retain both remarkable rate capability and superior cycling stability. The c-CMC-LTO exhibits a superior capacity of 92 mAh g-1 and retains its initial value with no obviously capacity decay over 200 cycles under an ultra-high C rate (50 C). Furthermore, for sodium ion batteries, the c-CMC-LTO also showed an excellent cycling stability with a discharge capacity of 127.6 mA g-1 even after 100 cycles at 1C. In summary, the c-CMC-LTO is expected to be a promising anode material for integrating both ultrahigh rate and extremely stable cycling performance for next-generation Li-ion batteries and Na-ion batteries.