Density Functional Theory (DFT) Study Of Ion Transport In Electrical Double Layer Capacitors

As the intermediate form of blue energy,the acquisition and storage technologies of electric energy has received great attentions in many countries.Ion transport in electrical double layer capacitors(EDLCs)is explored in this thesis,aiming to provide fundmental insights towards the rational design and development of efficient supercapacitor and CapMix technology.(1)Ion transport in aqueous electrolyte has influence on the microstructure and dielectric constant of solution,and however,the dynamic change of dielectric environment in turn affects the ion transport.Firstly,the primitive model is modified by coupling the local dielectric constant with ion density.Then,an extended version of dynamic density functional theory(DDFT)is proposed by incorporating with the modified primitive model(MPM).(2)Taking the charging process in electric double layer system as a case study,we conduct a multiscale investigation of ion diffusion in aqueous electrolytes by using the extended DDFT.The evolutions of local dielectric constant and ion concentration with time and in space are predicted.We find that the coupling effect between the energy density and power density decreases when the hydration ability of the cation is strong,in a good agreement with the relevent experimental reports.(3)Thereafter the extraction of electricity in Capacitive Mixing(CapMix)technology is explored.We compute the maxium output work and charge time of CapMix process upon the MPM model.The variation curves of the thermodynamic work and mean power versus the applied electric potential are predicted.The results show that the thermodynamic work and mean power increases in the beginning and then decreases as increasing the applied electric potential.The positions of their peaks shift towards small electric potential when the dielectric attenuation effect of ions is additionally considered.