Preparation Of Epoxy Resin Composite Electrolytes And Their Performance In Lithium Metal Batteries

Metal lithium(Li)is considered to be an ideal anode material for the next generation of high-energy lithium secondary batteries due to its high theoretical specific capacity(3860 mAh/g)and the lowest oxidation-reduction potential(-3.04 V vs standard hydrogen electrode).However,there are still two problems of safety and short cycle life in lithium metal batteries.Therefore,the use of the solid electrolytes instead of traditional organic liquid electrolytes has become a consensus among researchers.Considering the large interfacial impedance and poor processing performance of the inorganic ceramic electrolyte,and the low ionic conductivity and poor mechanical properties of the polymer electrolyte,the synergistic integration of the two to prepare organic-inorganic composite electrolytes with excellent comprehensive performances is considered a promising strategy to satisfy the commercial applications.In this paper,a perovskite-type fast ion conductor lithium niobium titanium oxide(Li0.33La0.557TiO3)was selected as a ceramic nanofiller,which was compounded with bisphenol A epoxy resin(DGEBA).And a variety of epoxy resin-based composite electrolytes with excellent comprehensive properties were prepared by special structural design.Firstly,a variety of porous epoxy resin membranes with different pore diameters were prepared by phase-inversion method.The effects of pore size on the thermal stability and mechanical properties of epoxy resin membranes and electrochemical properties of the epoxy-based gel electrolytes were compared.The results showed that the epoxy-based electrolyte had the best comprehensive properties when D230 was selected as the curing agent and the mass ratio of PEG200 to DGEBA was 3:1.The optimal porous epoxy resin membrane possesses a pore size of about 30 nm,a tensile strength of 13.1 MPa,and an ionic conductivity up to 5.66×10-4 S/cm at room temperature.Compared with the microporous epoxy resin membrane,the mesoporous epoxy resin-based gel electrolyte has a significant inhibition effect on the growth of lithium dendrites.Secondly,in order to increase the ionic conductivity at ambient temperature and mechanical properties of the electrolyte,Li0.33La0.557TiO3 nanoparticles(LLTO NPs)were prepared by sol-gel method and combined with the preferred epoxy resin-based polymer electrolyte.By adjusting the curing conditions of the epoxy resin,a three-layer composite electrolyte with an asymmetric structure was integrally formed.It is found that this asymmetric three-layer structure design not only isolates the side reaction between LLTO NPs and lithium metal,but also forms a close contact at the interface between the electrolyte and the electrode,which effectively reduces the interface impedance.Moreover,the fast ion channel provided by LLTO NPs makes the lithium ion transmission more uniform,which is beneficial to improve the deposition morphology of metallic lithium.Therefore,even at a high current density up to 4 mA/cm2,there is still a good inhibition of the formation of lithium dendrites.Finally,in order to further improve the ionic conductivity of the composite electrolyte by forming a long-range continuous ion transport path,a three-dimensional framework of Li0.33La0.557TiO3(3D LLTO)was prepared by the electrospinning technique.In addition,a pyrrolidine ionic liquid(Py13TFSI)was added to the mixed electrolyte to form a passivation layer on the surface of the lithium negative electrode,which enhances the interface stability between the electrolyte and the electrode.On the one hand,the formation of the passivation layer can significantly enhance the stability of the SEI layer,and on the other hand,effectively block the reaction between LLTO and lithium metal,and thus the obtained composite electrolyte exhibits excellent cycle performance and rate performance in Li/LiFePO4 batteries.