Graphene-based Conducting Network In Lithium-ion Battery And Its Large-scale Application

The performance of lithium ion battery （LIB） is required to be further improvedto meet fast-increasing energy needs. Graphene nanosheet （GN）, composed by asingle layer of sp²carbon atoms, is characterized by unique physical, chemicalproperties and geometrical structure. In this thesis, GN is introduced into LIB systemboth for anode and cathode as an effective additive component. Electrochemicalanalysis method and theoretical simulation are both employed to investigate the effectof GN additive on the electrochemical process of LIB. Then, the application potentialof GN in real large capacity commercial LIBs is also investigated in details.GN is firstly introduced into graphite/carbon black system to construct higheffective energy-storing/conductive network. Then energy-oriented and power-oriented composite anode material is designed based on the electrochemicalperformance of GN. The results suggest that the as-obtained power-oriented anode ischaracterized by the specific capacity of300mAh/g at5C, while the specific capacityof energy-oriented is above400mAh/g with good cycle performance. The resultssuggest that the performance of the composite anode material is improved greatly dueto the introduction of GN.Due to the most exfoliate and most flexible carbon structure, GN can bridge theactive material particles together using a unique “plane-to-point” contact model.Further considering the large specific area and electronic conductivity, the usageefficiency of GN will be much higher than other commercial conductive additives.The preliminary results based on experimental coin cells shows that even with muchlower addition fraction, GN can enhance the capacity performance of LiFePO₄to alarge extent as compared to the commercial additive. However, the rate performanceis not good as expected. The electrode pore structure becomes more tortuous with GNintroduction, and hence the transport performance of Li+ion becomes worse. In orderto ameliorate this process, the geometrical structure of GN such as its size, aspectratio and the electrode structure should be modified accordingly.Commercial2.0Ah,2.6Ah and10Ah LiFePO₄/graphite LIBs are used as modelsto investigate the effect of GN on the electrochemical performance of commercial battery. Through enhancing the conductivity of GN and using GN/carbon blackcomposite additive, the performance of LIB is improved to a large extent. Based onthe results, a GN-introduced energy-storing LIB with large capacity （up to10Ah） isfabricated. The results suggest that, with only1wt%GN, the energy density of theLIB using GN is117Wh/kg at0.5C, much higher than that of the LIB using10wt%common conductive （102Wh/kg）. At the same time, compared with the latter one, thecapacity of the former LIB increases up to10%at1C. In this sense, GN may find itsreal commercial applications as a conductive additive in energy-storing LIB in thenear future; while, for a high-power LIB, not only effective electron conductingnetwork but also fast ion transport channel is required to be effectively constructed inthe GN-based cathode system before a real application.