Research On Preparation And Lithium Metal Battery Properties Of Inert Filler Modified Polymer Electrolytes

Li metal is considered the ideal anode material for high energy density lithium batteries due to its ultra-high theoretical capacity and the lowest electrochemical reduction potential.However,the chemically active lithium tends to deposit in the form of lithium dendrite on the anode surface of lithium metal,which causes safety risks such as short circuit and combustion.In addition,lithium batteries with liquid electrolyte also face leakage of organic solvents.To solve the aforementioned problems,researchers have begun to develop solid electrolytes.Compared with liquid state batteries,solid state batteries without flammable organic solvents can fundamentally solve safety risks.In the solid electrolyte,compared to inorganic solid electrolytes,solid polymer electrolytes possess good workability and flexibility,low production cost,and can form a better contact interface with the electrode,but the low ionic conductivity at room temperature limits their application.To solve this problem,this paper studies the filler structure of solid polymer electrolyte.Hydroxyapatite（HAP）,ZIF-90 and asbestos（ASB）with ion selectivity were respectively introduced to prepare composite solid polymer electrolytes.The interactions between the filler and lithium salt were analyzed,and the physicochemical properties,ionic conductivity and electrochemical performances of the composite polymer electrolyte with ion selective fillers were investigated.The density functional theory calculation and ab initio molecular dynamics simulation were used to analyze the influence of the filler on the ion transport of the polymer solid electrolyte.The main research contents are summarized as follows:A compound solid polymer electrolyte is prepared by using HAP with negative potential vacancy as a filler to directly introduce polyethylene oxide（PEO）polymer electrolyte.The adsorption of vacancy with negative potential to cation can improve the performance of solid polymer electrolytes.Density functional theory indicates that HAP filler with negative potential vacancies can attract lithium ions in the electrochemical reaction,which promotes the dissociation of Li TFSI.In addition,lithium ions are preferentially adsorbed on HAP in the process of lithium deposition.The migration barrier of lithium ion on HAP is lower than PEO,which shows that the lithium ions adsorbed by HAP are easily diffused and evenly distributed.XRD patterns indicate that HAP reduces the crystallinity of composite polymer electrolyte,which is conducive to improving the ionic conductivity of the electrolyte(0.064 m S cm^-1 at 30℃).In addition,FLIR and tensile tests indicate that HAP improves the thermal stability and mechanical property of PEO composite polymer electrolyte.The discharge specific capacity of Li Fe PO4/Li battery using this composite electrolyte is maintained at 112 m Ah g^-1 at 30℃and 1 C current density after 300 cycles.In order to improve the ionic conductivity of the polymer electrolyte,based on the idea of the filler of unique surface structures can selectively interact with ions in lithium salts,we selected the anion-selective filler ZIF-90 and introduced it directly into poly（vinylidene fluoride）（PVDF）to prepared compound solid polymer electrolyte.Compared to the PEO solid polymer electrolyte,PVDF has small van der Waals radius fluorine atoms and strong polar-C-F bond functional groups,which can effectively form a stable interface on the surface of lithium metal.In addition,the high polarization of PVDF can effectively dissociate lithium salts.Density functional theory and ab initio molecular dynamics indicate that the metal ion sites of ZIF-90adsorb TFSI^-,which promotes the dissociation of Li TFSI,and releases lithium ions.The interaction between the ZIF-90 and TFSI^-limits the migration of TFSI^-anions,and improves the ionic conductivity and Li⁺transference number.Raman spectra indicate that there is molecular interaction between ZIF-90 and PVDF,the N atom in ZIF-90 can provide lone pair electrons as Lewis base,inducing dehydrogenation fluoride,promoting the PVDF chain segment movement in the amorphous region,which accelerates the ion transport in the PVDF polymer electrolyte.XRD patterns indicate that ZIF-90 reduces the crystallinity of composite polymer electrolyte,which is conducive to improving the ionic conductivity of the electrolyte(0.62 m S cm^-1 at30℃).In addition,FLIR and tensile tests indicate that ZIF-90 improves the thermal stability and mechanical property of PVDF composite polymer electrolyte.The discharge specific capacity of Li Fe PO4/Li battery using this composite electrolyte is maintained at 118 m Ah g^-1 at 30℃and 1 C(0.44 m A cm^-2)after 300 cycles.In order to improve the ion distribution and evenly deposit the lithium ions,we selected the cation-selective filler ASB and introduced it directly into the Poly（vinylidene fluoride-co-hexafluoropropylene）（PVDF-HFP）to prepare compound solid polymer electrolyte.As a polymer matrix,PVDF-HFP polymer possesses a higher density of strong electron withdrawing fluoride group,which is beneficial to protect the lithium anode/electrolyte interface.Density functional theory indicates that lithium ions are preferentially adsorbed on ASB.ASB can improve the distribution of lithium ions in solid polymer electrolyte,which is beneficial to the uniform deposition of lithium ions.Raman spectra indicate that the introduction of ASB is conducive to the dissociation of lithium salt.XRD patterns indicate that ASB reduces the crystallinity of composite polymer electrolyte,which is conducive to improving the ionic conductivity of the electrolyte(0.77 m S cm^-1 at 30℃).The discharge specific capacity of Li Fe PO4/Li battery using this composite electrolyte is maintained at 133 m Ah g^-1 at 30℃and 1 C after 300 cycles.In addition,scanning electron microscopy,3D optical digital microscope images and X-ray photoelectron spectroscopy of the surface of the lithium metal after cycling indicate that the introduction of ASB can effectively inhibit the growth of lithium dendrites and ensure the safety of the battery.