All Two-Dimensional Pseudocapacitive Sheets Based Asymmetric Planar Microsupercapacitors:Design,Construction And Electrochemical Applicaitons

With the explosive development of miniaturized,man-pack and highly integrated devices,the research of miniaturized energy storage devices with high energy conversion has become an interesting issue.Planar microsupercapacitors have gradually become competitive energy storage devices due to their small size,electrodes with open edges,no diaphragms,and integration.But they generally have the problem of low energy density per unit area,the main reasons for this problem are the low loading of active material,the small capacity,and the small potential interval In the planar microsupercapacitor,ions were transmitted in the horizontal direction.The two-dimensional material can be stacked in parallel due to the planar shape to reduce the hindrance of the ions diffusion in the planar microsupercapacitor in the horizontal direction,so that the ion transmission is not affected by the thickness of the electrode.The utilization rate of materials reaches the maximum.In addition,pseudocapacitive materials with high capacity and complementary potentials can effectively increase the capacitance and widen the potential range of asymmetric planar microsupercapacitors,thereby increasing the energy density of the device.In this paper,two-dimensional pseudocapacitive Ti3C2 and MnO2 sheets are used to fabricate flexible interdigitated electrodes by vacuum filtration and film transfer.Since the parallel stacking of two-dimensional materials provides a two-dimensional channel for transmission ions in the horizontal direction,the electrodes are pseudocapacitive in Lewis acids and have high capacitance and complementary potential intervals,the energy density per unit area of microsupercapacitors is effectively improved.The contents of the study are as follows(1)Preparation and characterization of electrodesTwo-dimensional MnO2 and Ti3C2 nanosheets with pseudocapacitance characteristics were selected as electrode materials,which were prepared into MnO2-based and Ti3C2 flexible films by vacuum suction filtration,and then the films were transferred to interdigitated stainless steel mesh substrate under mechanical pressure.The four-probe test shows that the conductivity of the film electrode can fully meet the requirements of the device.Through X-ray diffraction,scanning electron microscope and other characterization,it was found that the prepared film electrode has a layered stacking structure.The two-dimensional channel generated between the layers in this structure provides a high-speed channel for the transmission of ions in the horizontal direction.In addition,the small gap between the open edge of the interdigitated electrode and the interdigitated fingers allows the electrode material to fully contact the electrolyte while shortening the ion transmission distance.This research solved the problem of limited lateral transmission of ions in granular materials by assembling two-dimensional pseudocapacitive nanosheets into a parallel stack structure with two-dimensional channels and expanded the application of two-dimensional materials in the field of energy storage(2)Electrochemical performance characterization of electrodesIn order to give full play to the electrochemical performance of the film electrode,a Lewis acid(LiCl)that can exhibit both the excellent pseudocapacitance characteristics of the MnO2-based and Ti3C2 film electrode was selected as the electrolyte.By observing the response potential of voltammetry curve of the electrode in this electrolyte,it is proved that the two electrodes have a large and complementary potential interval,which can effectively improve the energy density of the assembled supercapacitor.Due to the fast and reversible pseudocapacitance reaction of the nanosheets and the two-dimensional channels existing between the layers,the ions can be quickly transmitted,and the film electrode exhibits high capacitance and excellent dynamic performance.This exploration solves the problems of low electrode capacity and narrow potential window by screening electrode electrochemical reaction parameters,and provides advantages for the preparation of electrodes with high electrochemical performance for two-dimensional pseudocapacitive materials.(3)Construction and performance research of the asymmetric planar microsupercapacitorsTaking the MnO2-based interdigitated electrode as the positive electrode and the Ti3C2 interdigitated electrode as the negative electrode,the PVA/LiCl gel electrolyte with high safety is used to assemble the asymmetric planar microsupercapactior.As the thickness of the electrode increases,the area capacitance of the planar microsupercapacitor increases proportionally.On the contrary,the area capacitance of the sandwich structure supercapacitor increases to a certain extent and then begins to decrease sharply.This is because in a planar microsupercapacitor,ions can be quickly transmitted along the two-dimensional channel between the nanosheet layers in the horizontal direction,so that the transmission of ions is not affected by the thickness of the electrode.Therefore,the energy density of the planar microsupercapacitor is increased to 162 ?W h cm-2(58 W h kg-1)through thickness adjustment,while maintaining a high power density(2.7 mW cm-2,985 W kg-1).In addtion,it ialso exhibits extremely high rate performance(maintains 83%even if the current is expanded by 20 times)and flexibility,the device can still work normally even under bending conditions.This study solves the problem of low mass loading of electrode by perfectly combining two-dimensional pseudocapacitive materials with planar microsupercapacitors and enriches the application of two-dimensional pseudocapacitive materials in micro wearable energy storage devices.