Production and performances examination of new generation sodium ion batteries containing heteroatom doped graphene based anode

Rapidly increasing energy demand worldwide, environmental problems and population growth lead humanity to use energy correctly and efficiently. Na-ion batteries are the biggest alternative to Li-ion batteries among rechargeable batteries due to their acceptable capacity value and long life. One of the most likely candidates to be used as anode active material in Na-ion batteries is graphene. Graphene is a promising electroactive material for these systems thanks to its extraordinary properties in electrochemical energy storage devices. In this thesis, nitrogen doped graphenes (N-GN1, N-GN7 and N GN13), silicon-nitrogen doped graphene (Si-N-GN) and iron-nitrogen doped graphene (Fe-N-GN) produced at different pH values by solvothermal method were synthesised and their anode performances in Na-ion batteries were tested. The synthesised electroactive materials were firstly physicochemically characterised. The morphological structures of the materials were determined by energy dispersive scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM) and N2 adsorption/desorption method and their crystal structures were determined by X-ray diffraction (XRD). The surface chemical structures, elemental compositions and elemental bonding configurations of the samples were determined by X-ray photoelectron spectrometry (XPS) and Raman spectrometry. When the obtained data were analysed, it was understood that N-GNs consisted of densely stacked graphene sheets and regular micro- and mesopores. Si-N-GN has an amorphous structure consisting of dispersed multiple graphene plates, while Fe-N-GN has large spherical particles inside the graphene structure in addition to the wrinkled leaf structure. The specific surface areas (SBET) for N-GN1, N-GN7, N-GN13, Si-N-GN and Fe-N-GN were calculated as 212, 1049, 1289, 523 and 482 m2.g-1, respectively. XPS and Raman data are described in detail in the relevant sections. Electrochemical analyses were carried out within the scope of studies on the usability of the materials as anodes in Na-ion batteries. The electrochemical properties of N-GNs were evaluated in their half-cells by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) in different binder and different electrolite combinations. The anode materials (N-GN13/Na-CMC, N-GN13/PVdF, Si-N-GN/PVdF and Fe-N-GN/PVdF) with the highest capacity values in GCD tests were selected and further electrochemical tests (Dunn&Trassati method, long-term durability and performance characteristics and EISs) were performed. In the longevity tests of the determined optimum parameter and cell components, 174 mAh.g-1 capacity was found for N-GN13/PVdF with its high stability and high capacity values, while 170 mAh.g-1 value was found for Fe-N-GN. Due to the high stability of these materials, they exhibited >98% Columbic efficiency for 250 cycles.