Preparation Of Cobalt-based Electrode Material By Microwave Method And Its Application In Supercapacitors

To solve the growing energy shortage problem,the development of effective energy storage equipment is extremely urgent.Supercapacitors have got the attention of scientists on account of their high power density,long cycle life and wide operating temperature range.Electrode materials,as a component of supercapacitors,play a key role in the performance of supercapacitors.As a well-known inorganic electrode material,cobalt-based compounds have brought about widespread attention due to their low price,abundant reserves and high theoretical specific capacitance.However,cobalt-based oxides,which have been studied extensively,have exposed the shortcomings of large resistance and low actual specific capacitance,limiting their practical application and development.At this time,it is particularly important to seek new cobalt-based electrode materials with excellent electrochemical performance.Compared with traditional synthesis methods（hydrothermal,electrodeposition,etc.）,the microwave method is green and environmentally friendly,convenient and fast,and has no post-treatment process.Therefore,this article uses graphite and carbon nanotubes to composite cobalt-based hydroxides via microwave method and also explores the electrochemical properties of cobalt-based selenide and cobalt-based vanadate electrode materials.1.The CoOOH/Co（OH）₂/graphite nanocomposite was successfully synthesized by the one-step microwave method,which used Co（NO₃）₂·6H₂O as the precursor,urea and ammonium fluoride as the alkali source,deionized water as the solvent and graphite as the thermal conductive material.A series of electrochemical characterization showed that the CoOOH/Co（OH）₂/graphite nanocomposite had excellent electrochemical performance.Under the optimal reaction conditions（1000 W 6 min,graphite addition amount is 10 mg）,the CoOOH/Co（OH）₂/graphite nanocomposite had high specific capacitance(402 F g^-1at 2 A g^-1)and cycling stability（86.2%capacitance retention of the highest value after 10000 cycles）,which were higher than those of the CoOOH/Co（OH）₂electrode.2.The CoOOH/Co（OH）₂/CNT nanocomposite was successfully prepared by the one-step microwave method,which took Co（NO₃）₂·6H₂O as the precursor,urea and ammonium fluoride as the alkali source,deionized water as the solvent and CNT as the thermal conductive material.By exploring microwave power,microwave time and CNT addition amount,the optimal reaction conditions of CoOOH/Co（OH）₂/CNT were determined（800 W90 s,CNT addition amount is 5 mg）.At this time,the specific capacitance of the CoOOH/Co（OH）₂/CNT nanocomposite can reach 768 F g^-1at 2 A g^-1and it still maintained77.5%of the highest value after 3000 cycles,which were significantly higher than those of the CoOOH/Co（OH）₂electrode material prepared under the same conditions.And the energy density of the assembled CoOOH/Co（OH）₂/CNT//AC can reach 25 Wh kg^-1when the power density is 0.42 k W kg^-1,and it can still reach 85%of the highest value after 20000 cycles.3.The CoV₂O₆·2H₂O nanosheets were successfully prepared by a one-step microwave method,which employed Co（NO₃）₂·6H₂O and NH₄VO₃as precursors.The optimal conditions were explored by adjusting microwave power and microwave time.The results showed that the CoV₂O₆·2H₂O nanosheets had the super electrochemical performance under the reaction conditions of 800W 90s.The CoV₂O₆·2H₂O nanosheet had a good specific capacitance of 355F g^-1at 1 A g^-1and excellent cycling durability(80.7%of the highest value after 80000 cycles at 5 A g^-1).The assembled CoV₂O₆·2H₂O//AC had an energy density of 19.0 Wh kg^-1when the power density is 0.4 k W kg^-1,and the highest value of 78.6%can still be maintained after35000 cycles.4.The CoSe₂porous nanosheets were successfully prepared and characterized by a one-step microwave method,which took Co（NO₃）₂·6H₂O as the precursor,selenium powder as the source of selenium,ethylenediamine and ethylene glycol as solvents,and copper oxide powder as the thermal conductive material to increase the reaction temperature.The results showed that CoSe₂has the best electrochemical performance under the optimal conditions（1000W 90s）.The CoSe₂nanosheet had a good specific capacitance(333 F g^-1at 1 A g^-1)and excellent cycle durability(79.8%of the highest value after 25000 cycles at 5 A g^-1).The assembled CoSe₂//AC had an energy density of 18.9 Wh kg^-1at a power density of 0.387 k W kg^-1,and exhibited excellent cycle performance.