Development of advanced materials for rechargeable lithium-ion batteries

As well as being one of the most promising candidates for power sources in electric vehicles (EVs) and hybrid electric vehicles (HEVs), lithium-ion batteries (LIBs) have been widely used as power sources for portable electronic devices due to their high voltage, long cycle life, and operation at ambient temperature. Compared to portable electronic devices, largescale energy storage systems, used for EVs or HEVs, require high power and high energy density, and need to be further improved by solving problems related to safety issues, high costs, and low rate capability. The electrode materials play a decisive role in the performance of LIBs. For enhancing the lithium diffusion coefficient and conductivity, preparing nanosized materials and surface modification are the most popular and highly effective methods to achieve improved electrochemical performance. In this doctoral work, several nanosized materials and conductive (electronic and ionic conductivity) composites have been synthesized, including LiNbO3 coated Li1.08Mn1.92O4 composite, LiNbO3/LiNi0.5Mn1.5O4 composite, polypyrrole-coated α-LiFeO2 nanocomposite, V2O3/C composite, and threedimensional (3D) TiO2 nanotube/Ti mesh (TiO2/Ti mesh). The high ionic conductivity LiNbO3, and electronically conductive polypyrrole and amorphous carbon were also introduced into these electrode materials to form composites. Furthermore, the effects of the structure, morphology, and physical and chemical properties of these composites towards improvement of electrochemical performance have also been systematically investigated.