| The potential safety issues of liquid lithium-ion batteries?LIBs?threaten the lives and property of the public.Designing and developing new solid electrolytes can fundamentally solve the safety problems.Lots of global high-tech enterprises have started the researches and developments of solid electrolytes.The number of related patents is increasing year by year.In the field of energy storage,solid electrolyte has become a research hotspot.Although solid electrolyte products at home and abroad have made great progress in recent years,there are still some problems,such as low ion conductivity,poor mechanical properties,poor interface compatibility and high cost.To overcome the above shortcomings,this thesis aims to design several composite solid electrolyte membranes with high ionic conductivity,stable chemical property,high strength and good thermal stability.Therefore,polyethylene oxide?PEO?,polypropylene carbonate?PPC?and lactic acid and trimethylene carbonate copolymer?P?LA-co-TMC??were selected as composite solid electrolyte membrane matrixes,owing to their low cost,excellent film forming property,electrochemical stability,environmental friendliness.Four new high performance composite reinforced solid electrolytes were prepared by solution casting support film method,self-reinforced ultraviolet in-situ polymerization method and double-sides dip coating method.The ionic conductivities,mechanical strengths,chemical stabilities and thermal stabilities of the prepared composite solid electrolyte membranes reached the design goals.These researches provided powerful theoretical basis and technical support for accelerating the large-scale production and application of solid lithium batteries.The research contents are as follows:1.In order to improve the ionic conductivity,mechanical strength,chemical stability and thermal stability of traditional PEO-based solid electrolytes,the ceramic/fiber non-woven film modified PEO-based composite solid electrolyte membrane?CLASP?was prepared by solution casting method.To improve the mechanical strength and thermal stability of the CLASP membrane,the double-coated Al2O3 ceramic non-woven membrane?FS-25?was applied as the support film.The addition of self-made inorganic solid electrolyte Li1.5Al0.5Ge1.5?PO4?3?LAGP?particles,succinonitrile?SN?and lithium bistrifluoromethylsulfonimide?LiTFSI?effectively enhanced the ionic conductivity of the CLASP membrane.Through the IR,XRD and SEM tests on the CLASP film,it was proved that PEO,SN,LiTFSI and LAGP were completely embedded in the pores of the support film to form a homogeneous structure.The thermal stability of the CLASP film was very good,and it hardly deformed below 170°C.CLASP also had good mechanical properties,and its tensile strength was 10.06 MPa.The room temperature ionic conductivity of the CLASP film was up to 3.66×10-5 S cm-1,the ionic conductivity at 55°C was 1.24×10-4 S cm-1,and the electrochemical stability window was 5.4 V.The solid-state battery?LiFePO4/CLASP/Li?was assembled with CLASP film,it could be stably cycled at 55°C,0.1 C,with 140 mA h g-1 average discharge specific capacity and more than 96%coulombic efficiency.2.Since ethoxylated trimethylolpropane triacrylate?ETPTA?could be in-situ polymerized under ultraviolet?UV?light to form three-dimensional?3D?network polymer with high strength,a novel self-reinforced PEO-based composite solid electrolyte membrane?PEO-CSPE?was designed and prepared by in-situ polymerization of ETPTA under UV light.In PEO-CSPE,PEO was applied as the solid electrolyte matrix,LiTFSI was served as the lithium salt,SN was used as the plasticizer,ETPTA was applied as the polymerization monomers,and?-hydroxyisobutyrylbenzene?HMPP?was served as the initiator.The results showed that when the ratio between ETPTA and PEO was 1:4,the PEO-CSPE performanced best in all aspects.It was demonstrated that PEO-CSPE was a kind of homogeneous amorphous structure by IR,XRD and SEM.Due to the formation of network polymer after the polymerization of ETPTA,the tensile strength of PEO-CSPE was increased to 3.5 MPa,about 20 times of the PEO-SPE film without EPTTA.And it also had good thermostability.Because EPTTA molecule was rich in oxygen atoms that could help dissociate lithium salts,the ionic conductivity of PEO-CSPE at 55°C increased to 1.326×10-4 S cm-1,its electrochemical stability window was 5.6 V,and its lithium ion migration number was 0.61.At 55°C the solid-state battery?LiFePO4/PEO-CSPE/Li?had good cycle stability,low interface resistance?380??,high coulombic efficiency?>98%?,high average specific discharge capacity(>135 mA h g-1 at 0.1 C)and excellent C-rate performance.3.In order to broaden the use temperature of solid electrolyte,a novel self-reinforced PPC-based room temperature composite solid electrolyte membrane?PPC-CSPE?was successfully designed and prepared.In PPC-CSPE,PPC was used as the electrolyte matrix owing to its low crystallinity at room temperature,SN was applied as the plasticizer,LiTFSI was served as the lithium salt,ETPTA was used as the reaction monomers,and HMPP was applied as the photoinitiator.PPC-CSPE was prepared by in-situ polymerization of ETPTA under UV light.The results of IR,XRD and SEM showed that the PPC-CSPE was the homogeneous amorphous structure.When the ratio between ETPTA and PPC was 1:3,PPC-CSPE had the optimal physicochemical properties.The tensile strength of PPC-CSPE was up to 2.6 MPa,which was 18 times that of PPC-SPE film without EPTTA.PPC-CSPE also had good thermal stability and low glass transition temperature.The ionic conductivity of PPC-CSPE at 25°C was up to 2.63×10-4 S cm-1,which was greatly improved compared with PEO-CSPE.Its electrochemical stability window was about5.0 V,and its lithium ion migration number was 0.654.The solid-state battery?LiFePO4/PPC-CSPE/Li?was assembled with PPC-CSPE,it could stably charge and discharge at room temperature.The solid-state battery had low interface impedance?250??,high coulombic efficiency?>97.5%?,and improved average specific discharge capacity(>134 mA h g-1 at 0.1 C).The all-solid battery also had high C-rate performance and capacity retention?>99%?at room temperature.4.The oxygen-rich copolymer P?LA-co-TMC?was firstly applied in the field of solid electrolyte system.A novel composite solid polymer electrolyte membrane?CSPE?was successfully prepared by double-sides dip-coating method.It used P?LA-co-TMC?as the matrix,LiTFSI as the conductive lithium salt,SN as the plasticizer,and Celgard 2325 as the support membrane.The results of IR,XRD and FESEM showed that CSPE had a dense continuous structure,and Celgard 2325 film was completely impregnated with P?LA-co-TMC?-SPE.The optimum ratio of each component of CSPE was obtained by testing the ionic conductivity of CSPE,namely P?LA-co-TMC?:SN:LiTFSI=3:1:1.The ionic conductivities of the CSPE film at 25°C and 55°C reached 3.64×10-4 S cm-1 and 5.21×10-4 S cm-1,respectively.The CSPE film had high thermostability,high tensile strength?17.9 MPa?,and it was very soft.The t+Li of CSPE membrane was up to 0.64,and the electrochemical stability window of CSPE was 5.2 V.The solid-state battery?LiFePO4/CSPE/Li?could cycle stably at 55°C under 0.1 C.Its coulombic efficiency was close to100%,and also had high discharge specific capacity. |
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