| With global warming,increased environmental pollution,and depletion of fossil fuels,energy and environmental issues are receiving increasing attention,and there is an urgent need to research and apply new technologies for green,efficient energy storage and conversion devices.Lithium-ion batteries,supercapacitors and fuel cells are three important research directions and solutions in the field of energy application.Supercapacitor is an energy storage device between a secondary battery and a conventional capacitor.It is a clean and efficient new energy storage device with high power density,long cycle life and fast charge and discharge capability.A typical supercapacitor is mainly composed of an electrode,a diaphragm and an electrolyte.According to the energy storage mechanism of the electrode material,the supercapacitor can be roughly divided into two types:electrical double layer capacitor that relies on electrostatic adsorption energy storage on the surface of the material,and pseudocapacitor that store energy in the near-surface redox reaction.The performance of supercapacitors depends largely on the choice of electrode materials.The development of high-performance capacitor materials is an important part of the current research work on capacitors.In this paper,SiC low-dimensional nanomaterials are studied,and the excellent stability of SiC materials is taken as the starting point.The research on the ambient temperature variation,size and energy density requirements encountered in the application of supercapacitors is carried out.The main work is as follows:1.A SiC nanochannel arrays with an array structure was formed by etching on a4H-SiC single wafer by a simple two-step anodization method.The two-step anodization was to solve the effect of the cap layer on the performance of the electrode.The prepared electrode is unique in that both the electrode active material and the current collector are single crystal 4H-SiC,and the generated SiC nanostructure is a vertical pore array structure.Such a structure is advantageous for shortening the ion transport path of the electrolyte,improving the electrochemical performance of the electrode,and improving the stability of the electrode at a wide temperature operation.The three-electrode test at room temperature shows that the specific capacitance of the electrode can reach 14.8 mF cm-2 when the scan rate is 10mV s-1.This capacitance value is at a higher level of the current SiC-based electrode material.The specific capacitance retention of SiC nanopore array electrodes after10,000 CV cycles was 96%.In addition,in order to study the application prospect of the electrode in a wide temperature environment,the electrode was subjected to 11000CV cycle stability tests under high temperature,low temperature and variable temperature conditions.The specific capacitance retention of the electrode after the cycle was 97.3%,96.8%and 95.5%respectively.These excellent electrochemical properties indicate that the SiC nanochannel arrays electrode is a very promising wide temperature supercapacitor electrode.2.The SiC nanostructures were prepared by simple anodization process,and the SiC nanostructured films with self-supporting properties were obtained after simple face-lifting method.SiC thin film electrodes with different mass loads were prepared by controlling the etching time during the etching process.Electrochemical tests showed that the specific capacitance of the electrodes increased with the increase of mass loading.When the mass loading increased up to 5.6 mg cm-2.the specific capacitance increased to 23.6 mF cm-22 and 14.8 F cm-3e at 10 mV s-1.Moreover,the SiC film and the solid electrolyte PVA/KCl are assembled into a chip-level sandwich structure of symmetrical supercapacitors with a total thickness of about 40?m.The assembled device has a specific capacitance of 22.3 mF cm-2 at a scan rate of 10 mV s-1.The specific capacitance retention of the capacitor after 10,000 cycles is 94.8%.In addition,the device exhibits a high energy density with an area energy density of 5.24?Wh cm-2 at the area power density of 5.24?Wh cm-2and a volumetric energy density of 1.31 mWh cm–3at the volume power density of 2.8W cm-3.This not only provides new ideas for increasing the energy density of micro-supercapacitors,but also provides a simple and fast method for assembling on-chip supercapacitors.3.The SiC nanowire array was deposited by chemical vapor deposition,and then the SiC porous structure was etched on the surface of the SiC nanowire by anodization.The newly formed SiC porous structure and the original SiC nanowire array structure formed a layered structure.The advantages of the electrode are mainly three points:?1?The anodizing process increases the specific surface area of the material and also increases the specific capacitance and energy density of the material.After 8 minutes of etching,the specific capacitance of the electrode was increased to26.7 mF cm-2,and the specific capacitance before etching was 5.2 mF cm-2.At the same time,according to the CV test results,the energy density of the electrode is calculated to be 1.55?Wh cm-2.?2?The etching process preserves the structure and rate performance of the SiC nano-array,and the scan rate increases from 10 mV s-1 to1500 mV s-1,the ratio of specific capacitance is still 75.3%,which is comparable to76%before etching.?3?The etching process has little effect on the internal resistance of the electrode.The internal resistance only increases by 0.4?from the change of internal resistance.And the change of the resistance value indicates that the power density of the etching loss is limited.Therefore,the anodic oxidation method increases the specific surface area of the material,satisfies the power density of the capacitor without increasing the power density of the capacitor,and exhibits great potential in the preparation of the material of the supercapacitor.4.SiC/PANI composites with core-shell structure were successfully fabricated on SiC nanowire arrays by electrochemical deposition.The formed structure is advantageous for improving the utilization ratio of PANI,shortening the diffusion path of ions,and maintaining good mechanical stability.It was prepared by a piecewise galvanostatic method during the deposition process,and PANI was uniformly distributed on the surface of SiC nanowires.The SiC/PANI composites with different PANI pore structures were prepared by controlling deposition time.Samples deposited for 80 minutes clearly had higher mass loading and porosity.Therefore,the three-electrode test results in the 1M H2SO4 electrolyte show that the electrode has a very high specific capacitance(the specific capacitance of the electrode is 225.6 mF cm-2 at a current density of 1 mA cm-2),high rate performance(80.9%of the specific capacitance retention of the electrode when the current density is increased to 40 mA cm-2),good cycle stability?after 3000 stability tests,specific capacitance retention rate of 88%?.In summary,this paper takes the requirements of temperature,size and energy density in capacitor practical application as the starting point,and adopts simple and efficient anodizing method and electrochemical deposition method to successfully prepare the array structure of SiC and its composite materials.This makes the SiC material electrode more suitable for the practical requirements of supercapacitor,and these improved materials are expected to be applied in the industrial production of supercapacitors. |
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