Study On Energy Storage Of Variable Valence Metal-mellitic Acid Complexes And Their Derivatives

With the promulgation and implementation of the"carbon peak,carbon neutral"policy,people’s demand for renewable and clean energy is increasing.Among various energy storage devices,supercapacitors have been considered to be the first choice due to their high power density,low cost,long cycle life,and environmental protection.Supercapacitors are composed of electrode materials,diaphragms,electrolytes,and etc.Moreover,electrode materials are the main factors affecting their electrochemical performance.In recent years,coordination polymers,as a new type of porous materials,have attracted extensive attention in the exploration of electrode materials.In this work,a variety of coordination polymers and derivatives were prepared by using pyromellitic acid as organic ligands through simple and efficient synthesis methods,and the energy storage properties were studied as electrode materials for supercapacitors.The specific research contents are as follows:（1）Three novel nickel-based metal-organic coordination polymers（Ni-MOF,Co Ni-MOF,Mn Co Ni-MOF）were prepared by hydrothermal method and used as electrode materials for supercapacitors.Benefiting from the synergistic effect and abundant redox active sites,Mn Co Ni-MOF can provide a specific capacitance of 655 F g^-1 at 1 A g^-1.After 10,000 cycles,the capacitance retention rate can reach 92.3%.The assembled device can deliver a power density of844 W kg^-1 at an energy density of 61 Wh kg^-1.After 2000 cycles,the capacitence retention rate can reach 98.3%.（2）NiMo bimetallic coordination polymers were prepared by hydrothermal method,and NiMo O₄materials were obtained by calcining at different temperatures in air.The abundant mesopores facilitate the diffusion of the electrolyte,which in turn enhances the electrochemical performance.The best electrochemical performance was obtained when the calcination temperature was 600°C（named NiMo O₄-600）.At 1 A g^-1,the specific capacitance can reach 790F g^-1,and the retention rate reaches 88.7%after 10,000 cycles.The assembled device can deliver a power density of 566 W kg^-1 at an energy density of 25 Wh kg^-1.After 2000 cycles,the capacity retention rate was 92.5%.（3）Nickel-containing coordination polymers were prepared by microwave method,and NiS materials were prepared by vulcanization at different temperatures.Benefiting from the in-situ doping of carbon and nitrogen,the electrochemical performance is also enhanced.When the calcination temperature is 500°C,the energy storage effect is the best.At 1 A g^-1,its specific capacitance is 525 F g^-1,and the retention rate is 85.2%after 10,000 cycles.After 2000 cycles,the assembled device showed a capacity retention rate of 91.6%and a voltage window of 1.75 V,demonstrating good cycling stability.