1D supercapacitors based on graphene hybrids

Abstract

In recent years, fiber-shaped supercapacitors (FSCs) have emerged as a promising candidate in the field of power electronics due to their unique advantages in energy storage, such as high power density, good rate capability, excellent cycle life, high flexibility, and manufacturing compatibility for integration into woven textiles. Next, graphene has high specific surface area and excellent electrical conductivity, so it has been the attractive electrode material for preparing FSCs. However, the energy density of graphene-based fiber supercapacitors reported at present is generally low (generally <15 MWh cm-3), which cannot meet the requirements for further practical application. Therefore, it is very necessary to develop new kind of FSCs with both high energy density and high power density. To address these issues, first of all, 2D MXene materials exhibit excellent electrical and electrochemical properties due to their inherent two-dimensional atom-thick topology. So integrating MXene materials into graphene-based fibers is one of the efficient strategies to solve the problem of low energy density. However, their low oxygen resistance results in the loss of a large amountr of electronic performance and surface reactivity, therefore, by using a simple carbon nanoplating strategy to stablize MXenes nanosheets, which can effectively prevent MXene from spontaneous oxidation degradation and maintain its structure, and we used a closed interval hydrothermal synthesis method to insert the high quality of MXene nansheets (up to 65 wt. %) evenly into the graphene oxide (GO) hybrid fibers, which show a new type of composite fiber electrodes .This method provides a material platform for the development of MXene-graphene materials with superior structure and performances. Second, supercapacitors based on ion adsorption or fast surface redox reactions usually have high power density but low energy density. In contrast, batteries based on diffusion-controlled Faradic reactions have much higher energy storage capacity and lower power density. Thus, hybrid capacitors comprising of a battery-type negative electrode and a capacitor-type positive electrode have been explored to combine the merits of both batteries and supercapacitors. Miniaturizing such hybrid capacitors is expected to deliver FSCs with high energy densities. So based on these consideration I designed two different electrodes .The positive electrodes are composite carbon fibers assembled hydrothermally in capillary columns using carbon nanotubes (CNTs) and graphene oxide (GO). The negative electrodes are carbon (graphite) fibers plated with a thin layer of Zn metal. A new neutral ZnSO4-filled polyacrylic acid hydrogel act as the quasi-solid-state electrolyte, which offers high ionic conductivity and excellent stretchability. The assembled FSCs delivers a high energy density of 48.5 mWh cm–3 at a power density of 179.9 mW cm-3, which is one of the highest among all Zn-ion hybrid capacitors reported so far. In conclusion, this paper provides a new basic understanding for the fabrication of graphene hybrid materials. Some innovative methods have been demonstrated to synthesis high electrochemical performances of graphene-based fiber electrodes for 1D SCs.These results will benefit to realize the furture practical applications of 1D SCs based on graphene hybrid material.