Piotr Zawadzki
Lithium-ion batteries (LIBs) are one of the most popular secondary batteries for consumer electronics and, lately, for electric vehicles application. Their main advantages over other rechargeable batteries are high energy density, good cycle life, high coulombic efficiency, low self-discharge rate, low maintenance and high cell voltage. The increasing demand for high performance LIBs entails large number of scientific researches focused on developing new electrode materials with better cyclability and high-energy storage capacity.
In terms of capacity enhancement, the most promising material for the anode is silicon which theoretical capacity is 4200 mAhg-1 (in comparison to 372 mAhg-1 for the commercially most widely used graphite). Unfortunately, its implementation is limited due to the safety issue related to the huge volume expansion that takes place during charge/discharge cycle. One approach that addresses the mentioned problem is nanotechnology. Recently, in situ HRTEM observation of Si nanoparticles during lithiation process showed that there is a critical particle size for which the mechanical fracturing of the SEI layer can be avoided.
Graphene, a single layer of hexagonally arranged sp2 carbon atoms, attracts a great interest as a material that can replace graphite as an active material in anodes of LIBs. Its properties like high theoretical specific surface area, intrinsic carrier mobility, great mechanical strength could significantly increase performance of batteries. In this research graphene-based nanocomposite was synhtesized for application as the anode active materials in lithium-ion battery. Three methods were employed: (a) mechanical mixing of reduced graphene oxide (rGO) powder with silicon nanopowder, (b) mixing of rGO with Si nanopowder in isopropyl alcohol and (c) spatial functionalization of graphene oxide using hydrazine. The molecular systems with variable silicon content and, in the case of cross-linked structures, variable hydrazine content were produced. FTIR, Raman, SEM, TEM investigations as well as galvanostatic charge/discharge and cyclic voltammetry measurements.
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