| Because the liquid electrolyte is highly flammable,easy to leak and toxic,it leads to the internal thermal instability of lithium batteries and easily causes safety problems such as runaway heating and explosion,which hinders the further development of lithium batteries.Therefore,the solid electrolyte materials become the inevitable choice for future lithium-ion batteries due to their high safety characteristics.The perovskite-type li0.33la0.557tio3(LLTO)has attracted much attention due to its high ionic conductivity among all solid-state ceramic electrolyte materials.However,they still have problems such as excessive interfacial impedance and weak interfacial effective contact.Poly(ethylene carbonate)(PEC)is also popular because of its good flexibility and high solubility in lithium salts.The conductivity of PEC based solid polymer electrolyte increases with the increase of lithium concentration,but its mechanical properties are sacrificed,which seriously affects its safety and practical performance as electrolyte materials.The key to the study of PEC based solid polymer electrolyte is how to improve the ionic conductivity of PEC based solid polymer electrolyte without affecting its mechanical properties.The purpose of this thesis is to study and develop high performance composite solid electrolyte.By optimizing the content ratio of each component in the electrolyte and the microstructure of inorganic filler,the composite solid electrolyte with complementary advantages can be designed and constructed to reduce the large interface impedance of inorganic solid electrolyte and improve the low ionic conductivity of polymer electrolyte at room temperature,so as to promote the practical application of composite electrolyte.In this paper,a composite electrolyte material with excellent performance was constructed by combining LLTO and PEC.The specific research contents are as follows:(1)The LLTO ceramic nanowires were prepared by electrospinning technology.The effects of spinning solution concentration and heat treatment process on the morphology of LLTO nanowires were investigated.The composite solid-state electrolyte was prepared by combining LLTO nanowires and PEC-25 wt.% Li TFSI.The optimal content ratio of ceramic filler components in the composite solid electrolyte was explored mainly from the two parameters of ionic conductivity and electrochemical stability window.The results show that the electrolyte membrane composed of PEC-25 wt.% Li TFSi-5 wt.%LLTO has the best room temperature lithium-ion conductivity of 6.21×10-5 S·cm-1,and the lithium-ion conductivity of the polymer electrolyte composed of PEC-25 wt.% Li TFSI increases by 50.44% compared with that of pure PEC-25 wt.% Li TFSI polymer electrolyte without LLTO ceramics.It shows that with the compounding of LLTO ceramic wires,because of the excellent lithium ion conductivity of LLTO,the fillers enhance the chain movement of the polymer,and the linear appearance provides a longer lithium ion transport path,which improves the lithium ion conductivity,resulting in the increase of lithium ion conductivity of the electrolyte membrane.(2)Ceramic composite polymer electrolyte with excellent conductivity of lithium ion at room temperature was prepared by using LLTO nanowires with the polymer electrolyte.With the increase of the diameter of LLTO nanowires,the lithium-ion conductivity of electrolyte film decreases gradually.The results show that the electrolyte membrane with PEC-25 wt.%Li TFSI-5 wt.%LLTO(d=250 nm)has the best room temperature lithium-ion conductivity of 7.91×10-5 S·cm-1,while the polymer electrolyte membrane with pec-25 wt.%litfsi-5wt.% LLTO(d = 750 nm)prepared under the same conditions has only a room temperature lithium-ion conductivity of 5.80 × 10-5 S.cm-1.(3)The hollow LLTO ceramic nanotubes were successfully prepared by coaxial spinning technology.The composite polymer electrolyte was prepared by solution casting method using PEC-50 wt.% Li TFSi as the electrolyte matrix material.Due to its special hollow morphology,nanotubes can provide more continuous rapid transport C channels of lithium ions,which can effectively enhance the ionic conductivity of the composite polymer electrolyte.The results of AC impedance test showed that the lithium ion conductivity of the composite solid electrolyte reached 1.73×10-4 S·cm-1 at room temperature and the oxidation decomposition potential reached 5.5 V(vs.Li+/Li).In addition,the lithium ion migration number is 0.77.Further test results of mechanical properties show that the tensile strength of the composite material increases from 1.10 MPa to 1.83 MPa,indicating that the electrolyte filled with hollow nanotubes can improve the mechanical properties of the composite electrolyte on the premise of improving the ionic conductivity. |
PDF Full Text Request