Research On The Mechanical Properties And Application Of Two Kinds Of MOFs In Battery Separator Modification

Metal-Organic Frameworks（MOFs）,also known as porous coordination polymers,are a new kind of functional materials made of multifunctional rigid organic ligands and metal clusters through bond coordination.Due to the significant advantages of MOFs,such as large porosity,high surface area,high crystallinity,tunable pore properties,abundant active sites,high mechanical and thermal stability,etc.they are widely used in gas storage and separation,solar cells,drug delivery,catalysis,sensing and thin film systems.Although the physical properties of MOFs have been extensively studied,its micromechanical properties are poorly characterized.At present,the rapid improvement of computer performance has made molecular simulation to be used for exploring the relationship between the properties and structure of MOFs.The computational simulation can provide guidance for the synthesis and application of MOF materials by saving a lot of time and experimental resources.The mechanical properties of MOFs are of great significance to the application of materials.Therefore,it is necessary to carry out computational simulation on the mechanical properties of MOFs.As typical MOF materials,DUT-49 and ZIF-8 can improve the performance of separators of lithium ion battery to a certain extent.The results indicate that the mechanical properties of materials affect the application of separator.Therefore,the above two MOFs are taken as research objects in this paper.First,the elastic constants of these two MOFs were estimated using the UFF force field of the Materials Studio.The results show that the elastic modulus of ZIF-8 is significantly higher than that of DUT-49.And then three criteria（Born criterion,real-time molecular dynamics method and P-V EOS method）were used with the MOFF-FF force field by LAMMPS software,which show that the mechanical stability of ZIF-8 under high pressure is higher than that of DUT-49.Finally,to evaluate the thermal stability of MOFs,the elastic constants of MOFs were calculated at 300K,450K,600K,800K and 900K,respectively.The results show that ZIF-8 had better thermal and mechanical stability than DUT-49.Finally,ZIF-8 crystals have been successfully synthesized in this paper,which were subsequently doped in a mixed gel of polyacrylonitrile（PAN）and polyvinylidene fluoride-hexafluoropropylene（PVDF-HFP）.The ZIF-8 modified polymer composite separator was prepared by electrospinning technique.We further explored the physical properties of the composite separator through experimental tests.The test results show that the ZIF-8 modified polymer composite separator has extremely high tensile strength and excellent thermal stability.The test cells with the as-prepared composite separators exhibit excellent electrochemical performance and can maintain a high capacity of 159 m Ahg^-1 after 100 cycles at 0.2 C.