Design And Electrochemical Properties Of Self-healing Polymer Electrolytes Based On Quadruple Hydrogen Bonding

As a critical component of the lithium-ion battery?LIBs?,the electrolyte plays the roles of regulating the interface of electrode materials and conducting lithium ion,could significantly affect the electrochemical performance of LIBs.The electrolyte used in the LIBs with high specific capacity usually contains flammable and explosive organic liquid,which is liable to cause serious safety accidents.Besides,the organic liquid electrolyte is easy to react with the lithium metal to form a solid electrolyte interface?SEI?,which could lead to nonuniform Li deposition on the surface of lithium metal,resulting in the growth of the lithium dendrite.Under the condition of repeated charge and discharge,the growing lithium dendrite can puncture the separator and bring potential safety hazard to the use of LIBs.To improve the reliability and safety of LIBs,it is urgent to develop new electrolyte and solve the problem of liquid electrolytes.Solid polymer electrolytes?SPEs?,which consist of the polymer matrix and lithium salts,can be promising alternatives to liquid electrolytes because they possess the advantages of good thermal stability and processability.However,SPEs still suffer from several disadvantages,for example,SPEs typically show relatively low ionic conductivity(10^-6-10^-88 S cm^-11 at room temperature),and it is difficult to meet the requirement of practical application in LIBs;the poor interfacial compatibility of SPEs/solid electrodes is an important factor that affects the electrochemical performance of LIBs;SPEs readily crack or break down under complex or long-term cyclic conditions,resulting in performance degradation of LIBs and even serious safety problems.In response to the above problems,this dissertation would focus on introducing ureidopyrimidinone?UPy?units into the polymer matrix to form a quadruple hydrogen bonding network and enable the self-healing property to the polymer electrolytes.The self-healing and electrochemical properties of polymer electrolytes are improved by fabricating the copolymer electrolytes,crosslinked polymer electrolytes and composite polymer electrolytes.The main contents of this dissertation are as follows:Firstly,poly?poly?ethylene glycol?methyl ether acrylate-co-2-ureido-4-pyrimidone ethyl methacrylate??PEGMA-UPyMA?containing UPy units was synthesized using reversible addition-fragmentation chain transfer?RAFT?polymerization.The self-healing polymer electrolyte?SHPE?was prepared by doping bis?trifluoromethanesulfonamide?lithium?LiTFSI?in the polymer matrix.The UPy units in a polymer matrix could form quadruple hydrogen bonding physically crosslinking network,which offers good self-healing performance to the SHPE.The results show that the SHPE can heal the cut damage within 2 h at room temperature without any external stimulus.When the self-healing temperature was elevated to 60?,the healing time was shortened to 30 min,indicating that the temperature could affect the self-healing efficiency of SHPE.Benefied from the abundant hydrogen bonding in the polymer matrix,the adhesive SHPE exhibits excellent interfacial stability between SHPE and electrodes.Also,the LIBs assembled with the SHPE exhibit stable cyclic performance.Furthermore,the self-healed sample was also used in LIBs,which maintain the high charge-discharge specific capacity.Secondly,the urethane group was introduced into the crosslinker of polyethylene glycol-bis-carbamate dimethacrylate?PEGBCDMA?.The dual-network self-healing polymer electrolyte?DN-SHPE?was prepared by RAFT polymerization of2-?3-?6-Methyl-4-oxo-1,4-dihydropyrimidin-2-yl?ureido?ethyl methacrylate?UPyMA?,polyethylene glycol methyl ether methacrylate?PEGMA?and PEGBCDMA.On the one hand,the physically-linked network fabricated by quadruple hydrogen bonding guarantees the DN-SHPE good self-healing property;on the other hand,the chemical cross-linked network could effectively improve the mechanical property of the DN-SHPE.Compared to the polymer electrolyte prepared by poly?ethylene glycol?dimethacrylate?PEGDA?,the urethane segments in PEGBCDMA improve the ionic conductivity and mechanical properties of the DN-SHPE.It was found that the DN-SHPE could heal itself after 2 h under 60?,and the tensile stress of the healed sample reached 84%of the original sample,indicating that DN-SHPE has good self-healing and mechanical properties.Meanwhile,the flexible pouch battery assembled with the DN-SHPE could light the LED bulb under the bending and folding conditions,showing the application potential in the field of the flexible wearable device.Thirdly,the UPy functionalized SiO₂?SiO₂-UPy?was synthesized by the reaction of2?6-isocyanatohexylaminocarbonylamino?-6-methyl-4[1H]pyrimidinone?UPy-NCO?and SiO₂ nanoparticles.Then the self-healing composite polymer electrolyte?SHCPE?was fabricated via the incorporation of SiO₂-UPy into the self-healing polymer matrix containing UPy units?PEG-UPy?.The supramolecular network constructed by the interactions of quadruple hydrogen bonding between SiO₂-UPy and PEG-UPy can improve the dispersity of SiO₂-UPy in the polymer matrix,and increase the interphase between the fillers and polymer matrix.Consequently,the SHCPE exhibit enhanced ionic conductivity of the electrolyte.It was found that the ionic conductivity of SHCPE was improved with the increase of SiO₂-UPy in the polymer matrix.When the addition amount of the SiO₂-UPy was 10 wt%,the ionic conductivity of the SHCPE-10 reached 8.01?10^-55 S cm^-1,which is higher than that of the CPE-10(6.20×10^-5S cm^-1).The self-healing property of the SHCPE was also improved because the addition of SiO₂-UPy increases the active cross-linking site in the polymer matrix,and can construct a more efficient cross-linked network.The SHCPE can heal the scratch within 1 hour,exhibits excellent self-healing property.In addition,the mechanical property of SHCPE increase the yield stress?120 kPa?by 110%compared with the CPE with SiO₂.Finally,the crosslinker of hexa?4-ethyl acrylate phenoxy?cyclotriphosphazene?HCP?was synthesized by the reaction of hexachlorocyclotriphosphazene?HCCP?with the tyrosol acrylate.The cyclotriphosphazene-based self-healing polymer electrolyte?CPSHPE?was prepared by the copolymerization of HCP,UPyMA,PEGMA and LiTFSI under UV irradiation.A series of CPSHPEs with different crosslink density were prepared by controlling the content of HCP.The benzene structure in polymer matrix could effectively improve the thermal stability of the electrolyte,and the thermal decomposition temperature of the CPSHPE can reach 300?.The ionic conductivity of the CPSHPE is 8.90?10^-55 S cm^-1.In addition,the CPSHPE shows good mechanical strength and flame-retardant performance due to the stable three-dimensional crosslinked network and the flame-retardant property of the cyclotriphosphazene network.Therefore,this polymer electrolyte is expected to improve the safety of LIBs under extreme conditions.