Fundamental electrochemical studies on nanoarchitectured olivine phosphates and vanadium pentoxide cathodes for lithium ion batteries
Cheah, Yan Ling
Date of Issue2013
School of Materials Science and Engineering
Lithium-ion batteries (LIBs) are gaining increasing attention in the research field, due to the constantly increasing demand for energy. As compared to conventional batteries, rechargeable LIBs are smaller and lighter, as well as capable of providing higher energy density and longer life cycles. LIBs work on the basis of intercalation / deintercalation of lithium ions, bringing about the flow of electrons to the external circuit. Currently, commercial LIBs are used in powering portable devices such as laptops and handphones. In order to move on the large applications such as electric vehicles, lithium ion batteries with improved electrochemical performances, lower cost, reduced toxicity and good thermal properties are required. This thesis focuses on the study of cathode materials for LIBs for high energy density energy storage devices. Higher capacity of LIB anodes (>500 mAh g-1), as compared to conventional cathodes (~100-200 mAh g-1) results in a large mismatch in lithium storage properties. Herein, the study of high-voltage olivine phosphate (LiMPO4, where M= Fe, Mn, Co, Ni) and high-capacity vanadium pentoxide (V2O5) cathode materials were explored. Olivine phosphates LiFePO4 and LiMnPO4 have the advantages of non-toxicity and good thermal stability in general. However, the poor conductivity (~10-9 Scm-1) of olivine phosphates limits their practical capacity. On the other hand, V2O5 enables high capacity by intercalation of >2 Li into its structure, but not without the consequences of irreversible capacity fade.