Enhancement In Electrochemical Performance Of Advanced Battery Electrodes Using Carbon- Nanomaterial Composites

ENHANCEMENT IN ELECTROCHEMICAL PERFORMANCE OF LiFePO4-CARBONNANO COMPOSITE MATERIALS FOR LITHIUM ION BATTERIESbyKULWINDER S. DHINDSAMay 2015Advisor:Dr. Zhixian ZhouCo Advisors: Dr. Ratna Naik and Dr. Gholam-Abbas NazriMajor:Physics (Condensed Matter)Degree:Doctor of PhilosophyLiFePO4 has attracted great interest as a cathode material for lithium ion batteries due toits reasonably high theoretical capacity (170mAh/g), thermal stability, high Li ion reversibilityand low cost. However, prohibitively low electronic conductivity (~10 S/cm) of LiFePO4 leadsto high impedance, low capacity and low rate capability. To overcome this bottleneck, we havedeveloped multiple approaches to improve the conductivity of LiFePO4. Motivated by theoutstanding electronic and mechanical properties as well as high surface area of graphene, weprepared LiFePO4/graphene nano-composites by a sol-gel method. The phase purity of the nanoLiFePO4/Graphene composite was confirmed by X-Ray diffraction. Addition of grapheneimproved the electronic conductivity of LiFePO4 by six orders of magnitude. Scanning electronmicroscopy and transmission electron microscope images show LiFePO4 particles being covereduniformly by graphene sheets throughout the material forming a three-dimensional conductingnetwork. At low currents and charging rate of C/3, the capacity of the composite cathode reaches160 mAh/g, which is very close to the theoretical limit. More significantly, the LiFePO4-graphene composite shows a dramatically improved rate capability up to 27C and excellent