The Assemblies And Properties Of Multi-Dimensional Graphene Based Materials

Due to the unique two-dimensional?2D?planar structure and outstanding physicochemical properties,graphene exhibits great potential for applications in sensors,wearable electronics,supercapacitors and lithium-ion batteries,etc.Therefore,it is of fundamental and practical significance to integrate the outstanding physical and chemical properties of individual graphene nanosheets into the macroscopic architectures,such as 1D graphene fibers,2D graphene films,3D graphene architectures.Therefore,in this thesis,various graphene based multi-dimensional assembles have been assembled,and their applications in pressure sensors,supercapacitors and lithium-ion batteries and so on have been explored.The detailed research contents are highlighted as follows:1.Firstly,graphene oxide ribbons have been prepared through a“spraying-rapid freezing”process.After that,all-graphene-based fibers composed of graphene ribbons coupled with graphene sheets are fabricated by directly hydrothermally assembling.Due to their interconnected structure and the synergistic effect of graphene ribbons and sheets,the graphene hybrid fiber exhibits a high strength of 223 MPa,and an ultra-high toughness of 30MJ/cm³.2.A simple strategy has been developed for the fabrication of vertically oriented graphene nanoribbon fiber with highly exposed surface area through confined hydrothermal treatment of interconnected graphene oxide nanoribbons and consequent laser irradiation process.Due to its highly-exposed surface area and high electrical conductivity,the as-obtained fiber shows high length capacitance and excellent rate performance.More importantly,the assembled all-solid-state asymmetric supercapacitor using graphene ribbon fiber as a negative electrode and MnO₂ coated graphene ribbon fiber as a positive electrode,and PVP/Na₂SO₄ as gel electrolyte,exhibits high volumetric energy density of 5.7 mWh/m³and excellent cycling stability with 88%of capacitance retention after 10 000 cycles.3.Free-standing graphene ribbon film has been fabricated through blade-coating of interconnected graphene oxide ribbons and subsequent thermal treatment process.The thick graphene ribbon film could be readily processed into flexible and free-standing films with tunable thickness via cut,fold and compression and directly utilized as a supercapacitor electrode without any binder or current collector.With an extremely high areal mass loading?21 mg/cm²?,large ion-accessible surface area,efficient electron and ion transport pathways as well as high packing density,the graphene ribbon film shows ultrahigh areal capacitance and high gravimetric/volumetric capacitance as well as excellent rate performance and cycling stability.Importantly,the assembled symmetric supercapacitor with compressible and flexible characteristics,can deliver an ultrahigh areal energy density of 0.52 mWh/m².4.Bubbles decorated honeycomb-like film?BHGF?has been fabricated through blade-coating of graphene oxide and followed by thermal treatment process.The free-standing flexible BHGF pressure sensor exhibits a high resistance variation?89%?and an ultra-high sensitivity(-161.6 kPa^-1)due to“point to point”contact mode,which can monitor a human motions such as finger bending and pulse.Moreover,such sensor has a low operating voltage of 10 mV that can be powered by energy-harvesting devices,such as triboelectric generators.5.Three-dimensional densely layered graphene/MnO₂ and graphene?DSG?architectures as positive and negative electrode materials respectively for asymmetric supercapacitors have been prepared with MnO₂-intercalated graphite oxide as the precursor.Due to their densely stacked structure with continuous ion transport network in-between the sheets,the resulting electrodes show high gravimetric and volumetric capacitances.As a result,the as-assembled ASC delivers ultra-high volumetric energy density of 54.4 Wh/L.6.Three-dimensional densely graphene/MnO?G/MnO?has been prepared through direct annealing of MnO₂-intercalated graphite oxide block in H₂/Ar atmosphere.Due to the improvement of electron/ion transfer and interfacial stability,the obtained G/MnO exhibits ultra-high volumetric capacity of 2288 mAh/m³,ultra-low volume expansion of 18%and outstanding cycling stability.