| Lithium-air batteries are also known as lithium-oxygen batteries（LOBs）.They are expected to be used as energy storage devices for electric vehicles due to their extremely high theoretical energy density（3,500 Wh/kg）.However,the discharge product lithium peroxide（Li2O2）of lithium-air batteries is not easy to decompose,resulting in batteries need higher charging overpotential,poor rate capability and low cycle stability.Therefore,it is very important and urgent to design efficient cathode reaction catalyst.In this paper,we investigated the decomposition of lithium peroxide on four transition metal（Co,Pd,Pt,and Ru）modified nitrogen-doped divacancy graphene（TM-N4C）catalysts.Firstly,we optimized the geometries of TM-N4C substrate and the adsorption configurations of Li2O2and LiO2molecules adsorbed on TM-N4C,respectively.After the optimal adsorption configurations were determined,we calculated the electronic structures,the Gibbs free energy.And we analyzed the catalytic effect of TM-N4C catalysts for lithium peroxide in detail.The result showed that Pt-N4C catalyst had the lowest charging overpotential（0.02 V）,indicating that Pt-N4C was suitable cathode catalyst for lithium-air batteries.Graphene oxide（GO）has the advantages of free transition metals and the raw materials are readily available.In this paper,graphene oxide is used as a cathode catalyst for lithium-air batteries to study the effect of its oxidation concentration on the dissociation of lithium peroxide.We constructed and optimized the graphene oxide model（GOn）by adsorbing n（n=1-6）oxygen atoms on the bridge site of graphene to form epoxide functional group.We further optimized and analyzed the adsorption configuration,electronic structure and the Gibbs free energy of Li2O2and LiO2molecules adsored on GOn,respectively.The result showed that under the equilibrium voltage,when 5 and 6 oxygen atoms were adsorbed on graphene,the charging overpotential was 0.06 V and 0.05 V,respectively.In practice,there are a certain number of defects on the surface of graphene oxide,so this paper also studied the VxGOy（x=0-2,y=0-4）of graphene oxide with defects.The result showed that V2GO1as the cathode catalyst of lithium-air batteries had the lowest charging overpotential（0.05 V）,and had the best catalytic effect on the dissociation of lithium peroxide.In conclusion,the dissociation of lithium peroxide on three different types of graphene-based catalysts TM-N4C,GOnand VxGOywere studied by first principles calculation in this paper.The optimal cathode catalysts for the dissociation of lithium peroxide were selected to provide some data reference and theoretical guidance for the rational design of cathode catalyst for lithium-air battery. |
