Simulation And Optimization Of Electrochemical Capacitors Based On Electrochemical Model

Electrochemical capacitors,also called supercapacitors,have been increasingly attractive as electrical energy storage devices for having the advantages of high power densities,long cycling life and environmental friendliness.However,the relatively lower energy density of electrochemical capacitors,compared with electrochemical batteries,prevents them from wider applications in energy storage devices and power devices.Therefore,numerous efforts have been made both in industry and in academia to enhance their energy densities.The most effective ways are to develop nanostructured electrode materials and new electrolytes.However,the experiment qualitative results,which lack the deep understanding of electrode process,could not provide adequate fundamentals for the rational design of electrode materials and the efficient screening of electrolytes.Therefore,in order to provide useful information both on the working mechanism and on the performance optimization of electrochemical capacitor,we focus mainly on studying both quantitative effects of material nanostructures and electrolyte properties on the energy density of electrochemical capacitors,based on the electrochemical model.The results revealed here could provide useful strategies for the optimal design of nanostructured electrode material and electrolyte for electrochemical capacitors.The main results are summarized as follows:(1)The effect of electrode spatial nanostructure on specific surface capacitance of electric double capacitors is quantitatively investigated using a steady-state double layer continuum model.For the electrochemical double layer capacitors composed of carbon materials and organic electrolytes,the simulation results indicate that the stern layer dominates the total capacitance.When the particle size of carbon material is larger than 20 nm and the pore size is larger than 40 nm,the total specific surface capacitance remains nearly unchanged with curvature radius.When the curvature radius is smaller than 4 nm,the total total specific surface capacitance changes significantly with curvature radius.And the convex surface structure is helpful to improve the specific surface capacitance,especially the convex spherical surface.(2)The effect of organic electrolyte composition on specific surface capacitance of electric double capacitors is quantitatively investigated using a steady-state double layer continuum model.For organic electrolytes of the electrochemical double layer capacitors,there is a saturation phenomenon of dielectric permittivity within Stern layer that determines the total capacitance.And polar solvent with high saturated dielectric permittivity improves the capacitance performance distinctly.Moreover,the electrode spatial nanostructure is of more concern compared with solvent polarity when aiming at enhancing the total specific capacitance.(3)The electrochemical capacitor dynamic models are developed based on different energy storage mechanisms of electrode materials.The effect of organic electrolyte composition on capacitance performance of electric double capacitors is quantitatively investigated by CV simulation based on its dynamic model.The simulation results indicate that the smaller solvated ions could make the electric double layer capacitance lager because that the smaller size make lager accumulation concentration and lead to a larger potential gradient near the interface of electrode and electrolyte.And at higher scanning rate,the large diffusion coefficient of organic electrolyte can effectively improve the capacitance performance.