Controllable Preparation Of Co Based Electrodes And Investigation On Their Planar Micro-supercapacitive Properties

The rapid development of integrated electronics and portable devices have increased the demand for miniaturized and on-chip energy storage units.In particular,the micro-supercapacitor is a new type of supercapacitor with unique in-plane electrode finger.The active layer thickness is usually between tens of nanometers and several microns,which can effectively shorten the diffusion path of electrolyte ions.At the same time,more active material edges are exposed,thus providing more active sites.However,there are still many problems in the reported planar MSCs,such as easy stacking,poor electrochemical activity,low specific capacitance and energy density.Therefore,it is still a great challenge to develop planar MSCs with high electrochemical performance.Faraday pseudocapacitive materials,such as metal hydroxide and transition metal chalcogenide?TMDs?,usually have the advantages of good pseudocapacitive performance,abundant active sites,stable structure,etc.Compared with the carbon-based planar MSCs,the specific capacitance and energy power density of the device with pseudocapacitive materials,can be improved effectively.Based on this,we prepared cobalt-based hydroxides and their composite electrode materials with raised electrical conductivity through composited with carbon-based materials and TMDs,and studied the electrochemical properties of the composite materials and their planar MSCs.The purpose of this paper is to study and prepare metal-hydroxides and their composite electrode materials of supercapacitors with multiple electrochemical active sites,large specific capacity and long cycle life,and apply them to planar micro-supercapacitors.The main research contents of this paper are as follows:?1??-/?-Co?OH?₂ were prepared by reflux heating,and tested the electrochemical properties.The composite were prepared by recombination of?-Co?OH?₂ with rGO through physical mixing with different blend ratios,which were used as the electrode material.In addition,all-solid?-Co?OH?₂/rGO composite film sandwich MSC and in-plane MSC with high performance were successfully prepared by mask spraying on Au/PET films.Among them,symmetrical?-Co?OH?₂/rGO composite film based sandwich MSC showed high area and volume specific capacitance?77 mF/cm²@39F/cm³ at 0.1 mA/cm²?,and the planar MSC showed high area specific capacitance?30mF/cm²@144 F/cm³ at 0.1 mA/m²?,high energy density and power density?0.018mWh/cm²@0.05 mW/cm²?and superior cycle stability?93%capacity retention after2000 cycles?.This is a new type of sheet-sheet composite film,which utilizes the synergy of the ultra-thin pseudo-capacitive?-Co?OH?₂/rGO nanoplates and capacitive rGO to achieve rapid ion diffusion and electron transfer on the non-binder dense film electrode.?2??-Co?OH?₂ flower-like clusters with hexamethylenetetramine?HMT?as adscititious alkali are fabricated via a facile reflux heating route.Then,the?-Co?OH?₂was partially in-suit transformed into CoSe₂ on surface to synthesize?-Co?OH?₂/CoSe₂ composite with hierarchical structures.By regulating the amount of Se powder,the complex of?-Co?OH?₂/CoSe₂ with different selenization degrees was prepared,and its electrochemical test was carried out to find the optimal conversion ratio.The combination of?-Co?OH?₂ and CoSe₂ provides a larger specific surface area,which facilitates efficient ion adsorption and transport.Due to the unique flower-like cluster structure composed of ultrathin hexagonal nanocrystals and the combination of small CoSe₂ nanocrystals with good electrical conductivity,the composite has a large specific surface area.In-suit transformation of CoSe₂,not only can improve the conductivity of?-Co?OH?₂,and prevent the re-stacking of?-Co?OH?₂ and CoSe₂ nanosheets but also short the transport routes of electrons and ions between the electrode and the electrolyte.The optimized?-Co?OH?₂/CoSe₂electrode material presents high specific capacitance?1221 mF/cm² at 1 A/g?,advanced rate capability,and excellent coulombic efficiency.Moreover,as-fabricated solid-state flexible in-plane MSCs composed of?-Co?OH?₂/CoSe₂ displayed efficient areal capacitance of 24 mF/cm²,energy density of 3.3 mWh/cm²,and stable cycling performance of 85%capacitance holding after 5000 cycles,respectively.In addition,as-fabricated solid-state flexible in-plane MSC showed outstanding stable electrochemical response towards the mechanical deformation.Therefore,the electrode composed of?-Co?OH?₂/CoSe₂ is a potential candidate for high performance energy storage device application.?3?A new Ni element was introduced to improve the multiplicative performance of the material.Ni-Co-LDH was prepared as the precursor by simple reflux heating.Then,Co_xNi_ySe₂ nanoparticles were grown on the Ni-Co-LDH by second step of reflux heating methods,and Ni-Co-LDH/Co_xNi_ySe₂ composite was successfully prepared with optimum degree of selenation.The regular and uniform Ni-Co-LDH nanosheet has fully exposed active site,and the growth of Co_xNi_ySe₂ nanoparticles on its surface jointly promotes the efficient Faraday reaction,so that the Ni-Co-LDH/Co_xNi_ySe₂ composite electrode has excellent specific capacitance?1276F/g at 2 A/g?.The optimized material was applied to symmetric planar MSCs and asymmetric planar MSCs with F-rGO as a negative electrode.At the same time,the performance of the two types of planar MSCs was compared,in which the asymmetric MSC showed higher energy density?87.1 mWh/cm²@0.685 mW/cm²?and excellent cyclic stability?85%capacity retention after 5000 cycles?.