Science and Technology Change Life, Graphene Helps Planar Supercapacitors
With the continuous development of miniaturization and wearable electronic products, the demand for Micro-storage systems has become increasingly urgent, such as mobile phones, computers and robots. There is an increasingly urgent need for miniaturization, integration and environmental protection. On the basis of ensuring high energy storage density, high charging and discharging rate and good cycle stability, planar supercapacitors meet the practical requirements for energy storage units of mobile phones, computers, robots and other precision instruments. They are highly compatible with portable electronic products and achieve the requirements of functional integration of micro-energy storage devices.
Carbonaceous materials are often used as electrode materials, such as activated carbon, carbon nanotubes, carbon aerogels and mixed carbons. Graphene, a single-layer film bonded by two-dimensional SP2 hybrid carbon atoms, has higher conductivity, larger specific surface area and stronger mechanical stability than previous carbon materials, and can meet all the requirements of energy storage devices for electrode materials.
The graphene and collector of the traditional sandwich graphene supercapacitor are in a parallel state. In order to avoid short circuit, the distance between the electrodes should not be too small, but the ion must be transported along the direction perpendicular to the collector, resulting in low ion transport efficiency. Graphene and collector in graphene planar supercapacitors are in vertical state, which can provide more transmission sites for ions and effectively reduce the thickness of capacitors, thus greatly shortening the transmission path of ions. Ions can make full use of the interstitial space of graphene for rapid transmission, thus effectively improving the power density of supercapacitors. The vertical junction between the melene and the collector can reduce their contact resistance well, and can better ensure the performance of the capacitor under the condition of folding and bending. Wu Changzheng's group of China University of Science and Technology formed a layer-by-layer supercapacitor by compounding MnO2 nanosheets onto graphene sheets. Its specific capacitance at current densities of 0.2A/g and 10 A/g was 267F/g and 208 F/g, respectively. The retention rate was 92% after 7,000 cycles, and 90% after 1,000 full-angle folding and bending.
For supercapacitors, graphene electrodes have better charge-discharge performance than other carbon material electrodes. The planar structure has better performance than the double-layer structure. By changing the parallel structure of graphene and fluid collector in traditional supercapacitors, planar supercapacitors with higher power density and better flexibility can be manufactured, which makes supercapacitors more compact and flexible.