| With the rapid depletion of fossil fuels and the environmental pollution caused by huge fossil fuel consumption,which requires us to use the clean and renewable energy sources efficiently,thereby promoting our economic growth and social sustainability.Supercapacitor is an efficient energy storage device that can be applied to portable electronic products,electric vehicles and various micro-devices due to its large power density,fast charge-discharge capability and excellent long cycle stability.In recent years,transition metal phosphate has been widely studied as the perfect electrode material for capacitors because of its low cost,abundant resources,environmental protection,and higher specific capacitance.Therefore,our paper will use nickel-based,cobalt-based,manganese-based transition metal phosphates to study the effect of electrode materials on the electrochemical performance of supercapacitors.First,the effect of the size and crystallinity of the electrode material on its electrochemical stability was investigated.For the electrode material,a small-sized material is easily destroyed during continuous charge and discharge,and the conductivity of the material is easily attenuated to affect the capacitance when the size is too large.The difference in crystallinity of the electrode material may affect the stability of the electrode material in the redox reaction.In this paper,we use a simple hydrothermal method to obtain nickel phosphate materials with different crystallinities and sizes by adjusting temperature and time.In the electrochemical performance test,we have learned that the electrode material with high crystallinity can exhibit excellent durability(continuous charge and discharge of 5000 cycles at a current density of 5 A g-1 can maintain 89%of the original capacity)and high capacitance performance(At a current density of 2 A g-1,the specific capacitance can reach 1053 F g-1).Secondly,the effect of the difference in the morphology of the material on the rate performance of the supercapacitor was studied.At present,the hierarchical self-assembled materials as electrodes can accelerate the transmission of electrons and shorten the diffusion path of ions,which may increase the charge accumulation and the degree of redox reaction thereby improving the rate performance of the supercapacitor.The morphology of the ammonium nickel phosphate electrode material was adjusted by using urea?additive?.Finally,we obtained the hierarchical self-assembled flower-like ammonium nickel phosphate electrode material,which showed good rate performance and long cycle stability(continuous charge and discharge of 3000 cycles at a current density of5 A g-1 can maintain 83%of the original capacity).Finally,we prepared the pure ammonium cobalt phosphate,ammonium manganese phosphate and the mixture of ammonium manganese cobalt phosphate by adjusting the different molar ratios of manganese and cobalt?1:3,1:1,3:1?.In order to explore its impact on the electrochemical performance of supercapacitors,through electrochemical tests,we found that the pure ammonium cobalt phosphate has the highest specific capacitance(the specific capacitance could reach 353 F g-1 at a current density of 1 A g-1).when a certain ratio of ammonium manganese phosphate is added,the specific capacitance of the electrode material is gradually lowered,which may be caused by the poor conductivity of the manganese-based electrode material,but the stability of the composite material was remarkably improved.Electrochemical tests have also shown that the sample?Co/Mn 1:1?with a layered microplate structure has large capacity of 304 F g-1 at 1 A g-1and the long cycle stability?maintain 89.2%of the original capacity?,which was higher than the stability of one-component ammonium cobalt phosphate.This remarkable performance is attributed to the synergistic effect of the lamellar mixed transition metals,which provide a large amount of internal space,high mechanical stability and abundant ion diffusion channels. |
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