Study On The Mass Transfer Characteristics Of The Positive Electrode Of Lithium Air Battery

With the development of society,the demand for energy of human beings is increasing.However,while using these energy sources,accompanied by the generation of large amounts of CO2 and other greenhouse gases,it has a great impact on the environment.Therefore,it is very important to find a clean and environmentally friendly energy source.Since the reaction principle of the organic electrolyte lithium-air battery is the reaction of metal lithium and oxygen,the generated lithium peroxide is clean and environmentally friendly.At the same time,its theoretical specific energy is as high as 11140Wh/kg,which is 6-9 times that of lithium ion batteries.It is expected to replace lithium ion batteries and become the first choice for electric vehicles.The current research on lithium-air batteries is still in its infancy,and many problems remain to be solved.The biggest problem is that the reaction product of the lithium-air battery clogs the porous electrode,resulting in a decrease in battery performance.Therefore,it is necessary to study the mass transfer problem of the positive electrode and porous electrode to boost the development of lithium-air battery.This article first described the classification,structural composition,working principle and current development status of lithium-air batteries.Secondly,through the combination of experiment and numerical simulation,the effect of the thickness and porosity of the porous electrode of the lithium-air battery on the battery performance was studied.At the same time,under different pressure and electrode porosity conditions,the battery performance,the distribution of products in the porous electrode,and the oxygen concentration distribution were analyzed.The details are as follows.In terms of testing,an organic electrolyte lithium air battery test platform was built.Under different electrode thickness conditions,deep discharge test,cyclic discharge test,specific surface area test,SEM electron microscope scan,CV voltammetry analysis,electrochemical impedance test,etc.The test results showed that the thickness of the air electrode of the lithium-air battery had a great influence on the specific capacity of the battery.As the thickness of the air electrode gradually increased,the specific capacity of the battery gradually decreased.When the electrode thickness reached 200?m,the specific capacity was as high as 3760 mAh/g.The thickness of the air electrode of a lithium-air battery also had a great influence on the number of battery cycles.When the thickness of the air electrode was 200?m,the cycle of the battery reached the peak value.Less lithium peroxide that blocked the air electrode was generated,and the reversibility of the porous electrode was also the best.At the same time,the thinner porous electrode is conducive to oxygen transport and helps electrochemical reactions,providing new ideas for improving the performance of lithium-air batteries.In terms of simulation,by coupling the charge conservation equation,electrode reaction kinetics equation and mass transfer equation,a two-dimensional transient model of a lithium-air battery was established.The discharge performance of the organic electrolyte lithium-air battery under the influence of different gas pressures,different thicknesses and gradient porosity of porous electrodes was studied.The results showed that when the thickness of the air electrode was 80?m,the specific capacity of the battery during deep discharge was the largest.And stable oxygen diffusion,uniform porosity distribution and Li2O2 deposition distribution was achieved.As the air pressure increased,the specific capacity of the battery increased,and the distribution of the product inside the porous medium became more uniform.After the porous electrode had a gradually changing porosity,oxygen can entered the interior of the electrode more easily,providing a larger space for the reaction to accommodate the deposit lithium peroxide,the battery specific capacity was doubled,and performance was optimized.This model has a certain reference function for the performance improvement of organic electrolyte lithium-air batteries.