Study On The Synthesis And Properties Of Low-resistance VFG-microporous Hybrid Al-based Electrodes For Supercapacitors

With the advantages of environmental friendliness, high energy density, fast charge and discharge efficiency, long cycle life, maintenance free, supercapacitor has become an ideal new-type energy storage component. Due to the its large specific surface area, graphene has been widely applied on active materials of supercapacitors. However, the stack of grapheme can not be effectively avoided by traditional preparation methods, which can lost the advantage of its huge surface area and affect charge transport. Meanwhile, compared with two kinds of widely used electrode materials: Ni and Fe, Al possesses better electricity conductivity, lower weight density and lower cost for a low-cost collector material of supercapacitor. However, Al is easily oxidized, and its dense surface oxide layer results to relatively high contact resistance, which limits its use in high-performance graphene-based supercapacitor. Therefore, in this paper, we put forward following methods to effectively solve aformentioned problems. Introduce plasma eching, regulate Al current collector to obtain three-dimensional structure, adjust the wettability between the electrolyte and active materials and synthesize Mn O₂/VFG-Al composite electrode material, which can effectively realize low-resistance and high-performance graphene-Al electrode material.In order to reduce the contact resistance of Al-active materials, we conducted plasma treatment by PECVD on Al to remove the oxide film on the surface. After that, we synthezed vertically oriented few-layer graphene（VFG） grown in situ on plasma treated Al foil, which can avoid reoxidation under atmospheric condition. During PECVD process, Al₄C₃ and carbon layer are formed at the interface of VFG-Al, which can signficantly optimize the charge transport path and reduce the contact resistance. All the surfaces of Al are coated by carbon layers during PECVD process, which is beneficial of preventing reacting with aqueous electrolytes during charge/discharge process. It suggested that VFG/Al can be promising candidate electrode materials in aqueous electrolytes.In order to enhance the specific capacitance of VFG-Al, we conducted chemical etching on Al to create a surface with a unique 3D structure（3D-Al）. Subsequently, the 3D-Al foils were etched by plasma treatment to remove the oxide film at the surface and then the VFG were grown in situ on the 3D-Al foils by PECVD to obtain VFG/3D-Al. Introducing 3D structure Al collector material can improve the quantity of active materials（VFG） per unit area. Furthermore, VFG can optimize charge transfer path and significantly increase the contact area between the electrolyte and VFG, so as to realize the good electrochemical performance. To reveal the enhancing effect of the organic electrolyte on the specific capacitance, we elucidated the correlation between the electrolyte type, wettability, and the supercapacitor performance. Results show that VFG shows excellent wettability in organic electrolytes, whereby the VFG/3D-Al electrode exhibits a high specific capacitance of 1398 μF/cm2.In order to combine the advantages of the electric double-layer capacitors（EDLCs） and pseudocapacitors to obtain high performance hybrid electrodes, hydrothermal synthesis was used to fabricate Mn O₂ nanosheets on VFG to obtained Mn O₂/VFG-Al hybrid electrodes. The results showed that Mn O₂/VFG-Al hybrid electrode with a sheet-like structure could take advantage of both Mn O₂ and VFG in the energy storage, electrical properties and morphology. Therefore, it exhibited higher performance with the specific capacitance up to 4134 μF/cm2 and a high retention rate of 107% of its initial capacitance after 4000 cycles. And the morphology of Mn O₂/VFG-Al showed no obvious changes after 4000 cycles.