Numerical Simulation Of The Effect Of CO₂ In Air On The Discharge Performance Of Nonaqueous Lithium-air Batteries

Nonaqueous lithium air battery is a new generation of high energy density,safety and environmental friendly electrochemical energy storage device.However,CO₂ in the air is difficult to be filtered clean,and it is easy to react on the surface of the air electrode skeleton to generate Li₂CO₃,which passivates the active site of the electrochemical reaction,leading to the increase of the battery’s passing point,the reduction of energy utilization efficiency,and the reduction of the specific capacity and cycle life of the battery.Therefore,this paper systematically studied the degradation of battery performance caused by the production of Li₂CO₃ by CO₂ in air on the surface of the air electrode skeleton,in order to provide theoretical guidance and technical support for the practical application of nonaqueous lithium air battery.Firstly,an electrochemical model was developed to simulate the discharge process of a nonaqueous lithium-air battery.It was found that the model developed in this paper is closer to the experimental results than the model calculated in the literature.In this paper,the influence of pore structure parameters of air electrode on discharge performance of nonaqueous lithium air battery is systematically analyzed.It is found that the discharge voltage platform and capacity of nonaqueous lithium air battery are higher with the increase of porosity.The air electrode porosity along the thickness direction is random,and its average porosity is the same as that of the air electrode with constant porosity.Compared with the latter,the discharge voltage platform and capacity of the nonaqueous lithium air battery prepared from the former are higher.With the decrease of the size of porous carbon particles forming the solid skeleton of the air electrode,the discharge platform of the nonaqueous lithium air battery increases,but the discharge capacity decreases.The discharge platform and capacity of nonaqueous lithium air battery decrease with the increase of the distortion rate of air electrode pore phase or solid skeleton.Secondly,based on the electrochemical model,the electrochemic-thermal coupling model of nonaqueous lithium air battery was successfully developed.It was found that the calculation results of the model could be closer to the experimental results by considering ion migration heat,electron ohmic heat,ion ohmic heat,irreversible electrochemical reaction heat and Li₂O₂film resistance heat.Then,using the model discussed the discharge current density and environmental temperature on the drainage lithium air batteries internal thermal behavior and the influence law of electrochemical behavior,found that with the increase of discharge current density,the solid phase at air electrode potential,electrolyte potential,air electrode Li⁺concentration are shown a declining trend.In addition,the peak value of Li₂O₂ volume fraction at air electrode also decreases with the increase of discharge current density.With the increase of ambient temperature,solid phase potential at air electrode,electrolyte potential and Li⁺concentration at air electrode all show an increasing trend.In addition,the peak value of the volume fraction of Li₂O₂ at the air electrode increases with the increase of ambient temperature.With the increase of discharge current density and ambient temperature,all kinds of heat generation at any position inside the nonaqueous lithium air battery are increasing at any time,but the proportion of each heat is different.Finally,based on the electrochemical-thermal coupling model,the electrochemical-thermal coupling model of nonaqueous lithium air battery was successfully developed,which could consider the effect of CO₂ in the air.Then,the effects of discharge rate,ambient temperature,CO₂ solubility and diffusion coefficient in electrolyte on the deposition process of Li₂CO₃ were discussed by using this model.It was found that:In the presence of CO₂,the discharge capacity of Li-O₂/CO₂ battery decreases significantly and the surface temperature increases.During the discharge process,the discharge voltage of Li-O₂/CO₂ battery is first higher than that of Li-O₂ battery and then lower than that of Li-O₂ battery.With the gradual increase of ambient temperature,the discharge capacity of Li-O₂/CO₂ battery shows a trend of increasing,while the discharge capacity of Li-O₂ battery shows a trend of decreasing.The surface temperature of Li-O₂/CO₂ battery decreases first and then decreases at low temperature.When the ambient temperature increases,the surface temperature of Li-O₂ battery increases slowly first and then increases rapidly.However,no matter how high the ambient temperature is,the surface temperature of Li-O₂ battery increases slowly first and then increases rapidly.With the increase of CO₂ solubility,the discharge voltage of the battery increased in the early stage of discharge,but decreased in the middle and late stage.In addition,with the gradual increase of the solubility of CO₂ in the electrolyte,the surface temperature of the battery increases at the initial stage of discharge,but decreases at the middle stage of discharge,and increases at the end of discharge.With the increase of CO₂ diffusion coefficient,the discharge platform of the battery gradually increases,the surface temperature gradually increases,and the discharge capacity first decreases and then increases.In addition,no matter how high the diffusion coefficient of CO₂ is,the surface temperature of the battery will rise rapidly at the end of discharge.In addition,this paper also discusses the deposition mechanism of Li₂CO₃generated by the reaction of CO₂ in air on the surface of the air electrode skeleton,which is of great significance,and provides technical guidance for the method of inhibiting Li₂CO₃deposition.