Preparation And Application In Supercapacitor Of Macro-thickness Porous Graphene

The development of energy-storage devices with sufficient storage capacity and flexibility has attracted widespread attention in the field of new electronic devices.Due to the rapid charge and discharge capability,long-cycle stability,and safety,flexible supercapacitors are considered to be one of the most promising energy storage devices.As the key component,the electrode materials have great impact on the electrochemical and mechanical properties of supercapacitors.Therefore,the design of electrode materials,especially the regulation of the microstructure,is an effective way to improve the electrochemical performances of supercapacitors.As an ideal energy storage material,three-dimensional(3D)porous graphene can not only be used directly as the electrodes of an electric double-layer capacitor but also can be combined with pseudocapacitance materials to form composite electrodes.Under the high temperature resulted from the photothermal effect of the laser,the polymer can be converted to 3D porous graphene.This laser induced graphene(LIG)preparation method shows broad application prospects in the preparation of flexible electrode due to its high efficiency,easy to doping,synchronous patterning,low cost,and scalability.However,the research on this method is still in its early stage,and the mechanism of controllable preparation of 3D porous graphene is unclear;besides,the energy and power densities of the prepared supercapacitors need to be improved.To tackle the above problems,the mechanism and influencing factors of the interaction between laser and polymer in generating porous graphene were analyzed.An improved laser-induced method for preparation of 3D porous graphene was developed through polymer structural design and thermal sensitivity control.This method achieves the rapid preparation,macro-thickness adjustment,and pore structure optimization of the 3D porous graphene.Furthermore,pseudocapacitive material is further introduced into the 3D porous LIG to prepare composite electrodes,which shows excellent electrochemical performance and mechanical flexibility.Accordingly,a flexible micro-supercapacitor(MSC)with ideal energy density and service life was constructed.Besides,a photothermal self-heating MSC was fabricated by optimizing the structure,so that its capacitive performance was greatly improved under sunlight,alleviating the problem of performance degradation in a low-temperature environment.The main contents of this thesis are as follows:(1)By adjusting the stoichiometric ratio of the raw materials and the imidization reaction temperature,the degree of imidization and molecular configuration of the resultant polyimide(PI)can be regulated to improve its thermal sensitivity,thereby increasing the laser penetration depth on it.Consequently,the 3D porous LIG,with thickness up to 320 ?m,were directly "grown" from the PI film.The areal and volumetric specific capacitances of the LIG were up to 132.2 mF/cm2 and 4.13 mF/cm3,respectively.(2)To further improve the capacitance and energy density,the pseudocapacitance material polypyrrole(PPy)was electrodeposited on the LIG film to prepare graphene/polypyrrole composite(LIG/PPy)electrodes.The LIG/PPy electrode delivered an areal specific capacitance of up to 2412.2 mF/cm2 after optimization of its structure.Accordingly,a flexible solid-state micro-supercapacitor(MSC)was fabricated,which has a high energy density of 134.4 ?Wh/cm2 and a high power density of 6500 ?W/cm2,as well as excellent rate capability,long cycle life,and mechanical flexibility.Furthermore,95.6%of initial capacitance was retained after 10000 cycles,indicating superior cycling stability.(3)By exploring the influence of the temperature on the electrochemical performance of MSC,the effect of the interaction between the electrode and the electrolyte at their interface on the transport and storage performance of charges(electrons,ions)was studied.Based on the revealed mechanism,a photothermal self-heating MSC with significant photothermal effect was constructed by using the LIG/PPy film as the electrode after optimizing the structure of the MSC.Under one solar irradiation and at room temperature,the areal specific capacitance and energy density of the MSC were increased by 4.8 times(to 2668.8 mF/cm2 and 626.4?Wh/cm2,respectively),which are higher than most reported graphene composite supercapacitors.When the MSC was placed in a low-temperature environment of-30? the specific capacitance under one solar irradiation has increased by 4.05 times(505.5 mF/cm2),close to the specific capacitance at room temperature(556.7 mF/cm2),achieving the substantial enhanced capacitive performance of the MSC in a low temperature environment.Overall,these results offer a highly effective method to increase the capacitance performance of supercapacitors and inspire new designs for solar-electric devices.