Electrochemical Performances Of Manganese-Cobalt Hydroxides Based Asymmetric Micro-supercapacitors

With the improvement of technology,the demand for hybrid electric vehicles,portable and wearable electronic equipments and other products is increasing.Therefore,micro energy storage devices with excellent electrochemical performance and small-scale mass/volume have become the focus of research for scientists on the world.As one of the most efficient energy storage devices,micro-supercapacitors?MSCs?have great potential applications in the fields of microelectronics integrated systems and implantable medical sensors due to their high power density,long charge-discharge time and good cycling stability.However,the practical application of micro supercapacitors is limited by the problem of low energy density,so how to improve the energy density of devices is an urgent problem to be solved.In this context,asymmetric micro-supercapacitors?A-MSCs?have a wider operating voltage window than symmetric supercapacitors,which can provide higher energy density to the device while maintaining high power density.In addition,one of the key factors affecting the specific capacity of the MSCs is the active electrode material of the device.Therefore,the electrode material with excellent performance is the main source of the capacity of the micro energy storage device.In view of the above problems,this paper combines the method of electrochemical deposition with the micro-fabrication technology to fabricate the Mn-Co-H transition metal hydroxides?Mn-Co-H?and Fe₃O₄ electrodes.In addition,an A-MSC is fabricated by using Mn-Co-H nanosheets as positive electrode and Fe₃O₄ nanoparticles as negative electrode,respectively.The results are as follows:?1?In this thesis,Fe₃O₄ nanoparticles,Co?OH?₂ nanosheets and Mn-Co-H nanosheets were synthesized by electrochemical deposition on the pre-prepared Cr/Au collectors.The uniform distribution of these three electrode materials on the collector surface was observed by scanning images.?2?The electrochemical performances of the Fe₃O₄,Co?OH?₂ and Mn-Co-H electrodes were tested,and the area specific capacity of them are 150 mC cm^-2,32mC cm^-2 and 78 mC cm^-2,respectively.Compared with Co?OH?₂ electrode,the area specific capacity of Mn-Co-H electrode has increased by 1.4 times.Under the scanning rate of 1000 mV s^-1,the capacitance retention is 98%after 2000 cycles of charging and discharging,which reflects the good electrochemical performance and cycle stability of Mn-Co-H electrode.?3?The working voltage window,area specific capacity and energy density of the A-MSC is 1.7 V,35 mC cm^-2,7.78 mWh cm^-2,respectively.Under the scanning rate of 1000 mV s^-1,the capacity retention is over 79%after 2000 cycles of charging and discharging,which shows good cycling stability.In addition,it is concluded that the outstanding electrochemical performance of A-MSCs is mainly attributed to the synergistic effect between Mn-Co-H and Fe3O4.