Mesoscopic Mass Transfer And Performance Test Of Composite Positive Electrode For Lithium-air Batteries

Lithium-air battery is one of the most promising metal-air batteries and is a hot research topic in the field of new energy.However,the development of lithium-air battery has been hindered by a series of problems such as fewer cycles and higher overpotential.Selecting suitable cathode materials is an important method to promote the further development of lithium-air batteries.The problems encountered in the development of lithium-air batteries are introduced in this paper,the effects of different cathode materials on battery performance were studied,at the same time,the simulation analysis of positive mesoscopic mass transfer was carried out,The effects of graphene cathode and acetylene black cathode on the mass transfer performance of lithium-air batteries were investigated.The details are as follows:In simulation,firstly,a mesoscopic mass transfer model of graphene positive electrode for lithium-air battery was established,the effects of system temperature,number of graphene layers,graphene types and graphene content on the diffusion coefficients of DME,Li+,TFSIand O2 beads were studied by means of coarse-grained molecular dynamics simulation.Secondly,the mesoscopic mass transfer model of acetylene black positive electrode of lithium air battery was established,the effects of system temperature and acetylene black content on the diffusion coefficients of DME,Li+,TFSI-and O2 beads were studied.The simulation results of acetylene black cathode were compared with those of graphene cathode.It was found that the diffusion coefficient of each bead decreased with the increase of the number and type of graphene layers in the positive electrode system,it was also found that the diffusion coefficient of beads increased with the increase of temperature in the two systems,with the increase of positive electrode concentration,the diffusion coefficient of each bead decreases continuously,however,the diffusion coefficient of beads in the acetylene black system is always higher than that in the graphene system.Compared with acetylene black material,the zigzag degree of graphene and the complexity of the solution in the system are increased,it impedes the diffusion of the beads,Therefore,the diffusion in acetylene black positive electrode system is better than that in graphene positive electrode system.In order to further improve the performance of lithium-air battery,this paper continues to use test means to optimize the positive electrode of the battery,looking for the best composite positive electrode.In terms of experimentation,First,acetylene black,Super P,single-walled carbon nanotubes(SWCNT),carboxyl carbon nanotubes were prepared and four kinds of carbon materials and manganese dioxide in a ratio of 1:1 composite electrode.The effects of different positive electrodes on the performance of lithium-air batteries were studied,The positive electrode of acetylene black and MnO2 at a ratio of 1:1 was found,the effects of different positive electrodes on the performance of lithium-air batteries were studied,It was found that the performance of the battery was better when acetylene black and MnO2 were mixed as 1:1 positive electrode.Secondly,by changing the ratio of acetylene black to MnO2(Acetylene black was mixed with MnO2 at ratios of 1:2 and 2:1 respectively),find a compound positive electrode that is most suitable for lithium-air batteries.The study found that:when the cathode material is used as the cathode of lithium air battery,The number of cycles of acetylene black positive electrode is obviously more than the other three positive electrode,the discharge capacity is also greater than the other three materials.When the four kinds of composite cathode materials are respectively combined with MnO2 in a ratio of 1:1 as the positive electrode of lithium-air battery,compared with the other three composite materials,acetylene black and MnO2 have the largest number of cycles and the largest discharge capacity in the 1:1 composite positive electrode,The number of cycles and discharge capacity of the battery increased with the increase of MnO2 ratio in the MnO2 acetylene black cathode.It can be seen that when acetylene black and MnO2 compound 1:2 as positive electrode,the overall performance of the battery is the best.