Application Of COMSOL Multiphysics(?) To Lithium–sulfur Battery,Lithium–air Battery And Supercapacitor Study

Multiscale coupling analysis of the electrochemical power sources is required for their complicated reaction mechanism.Macroscopic processes such as diffusion,fluid flow and electrochemical reaction coupled with microscopic proliferation and migration that occur in the electrodes is also studied from multiphysics perspective.The rapid development of new energy and electric vehicle technologies pose a big pressure on high energy secondary power systems.And the power systems of Lithium-Sulfur battery,Lithium-Air battery and Supercapacitor have become the new focus for their attractive prospects.One-dimensional numerical models of Lithium-Sulfur battery,Lithium-Air battery and Supercapacitor were studied by using simulation software of COMSOL Multiphysics with finite element method.And the study took into account electrochemical reactions,mass transfer and charge transfer processes of the electrochemical power sources.The characteristics of the power systems under different discharge current rate as well as the influences of the electrode structure and physicochemical parameters were also studied.And some recommendations for performance optimization of the power sources were provided in the end.Polysulfide precipitation which significantly decreases the specific surface area of the active material,resulting in performance degradation of Lithium-Sulfur battery was found.The Nucleation-Growth model is used to describe the precipitation processes of Lithium-Sulfur battery accurately.Consistent with the experimental data,the calculation results show that high growth rate and nucleation rate of polysulfides,namely Li2 S,can increase the discharge voltage plateau and capacity.As Li2S2 dominating polysulfide precipitation process according to much more sulfur content,active substances cannot be fully converted into Li2 S which causes a decline in the specific energy of Lithium-Sulfur battery.The model of Lithium-Air battery focuses on the variation of electrode characteristics with different discharge current rate.The electrochemical reaction and oxygen diffusion limitation of Lithium-Air battery leading to serious performance degradation at high discharge current rate was found.The discharge overpotential can be reduced through oxygen solubility enhancement from suitable electrolyte solution.The great enhancement of discharge capacity for Lithium-Air battery with dual pore system was due to the improvement of oxygen transfer property and reduction of oxygen concentration polarization effect.The simulation of Pseudocapacitor mainly studies the different characteristics between model one and model two.A concentrated binary electrolyte theory is used to describe the role of proton diffusion on the metal oxide particles and the effect of asymmetrical distribution of charged species on potential.Compared to the model based on secondary current distribution,the model two can accurately describe the reduction of solid diffusion coefficient on capacitor performance,and the increased particle size led to discharge capacity degradation.