Preparation And Performance Research Of ZIF-8/porous Epoxy Resinbased Composite Gel Electrolytes

In lithium metal battery systems,lithium metal is considered an extremely promising anode material because of its high theoretical capacity（3860 m A h/g）and the lowest electrochemical potential（-3.040 V）.However,the high reactivity of lithium metal anodes is prone to continuous side reactions with organic electrolytes,while the uncontrolled growth of lithium dendrites and the formation of dead lithium make lithium metal batteries a severe safety hazard.As a result,researchers have worked to develop new electrolytes to address the problems of leakage,flammability and volatilization associated with traditional liquid electrolytes.Among them,gel polymer electrolytes stand out among the options for solid-state systems due to their high flexibility,ease of fabrication and excellent interfacial compatibility.However,gel polymer electrolytes usually have poor mechanical strength,do not completely suppress the growth of lithium dendrites,and have unsatisfactory ionic conductivity.In this work,a bisphenol A epoxy resin（DGEBA）with excellent mechanical properties was selected as a polymer matrix with cross-linked network structure,and an epoxy resin-based gel electrolyte with controllable pore structure and excellent performance was designed.The zeolite imidazolate framework material（ZIF-8）with high porosity,high specific area,outstanding thermal stability and mechanical properties was grown in situ on this electrolyte membrane.Thus,a novel ZIF-8/porous epoxy resin matrix composite gel electrolyte with excellent comprehensive properties was designed and prepared.Firstly,a series of epoxy resin membranes with different pore structures were prepared by adjusting the ratio of curing agents D230 to PACM and their thermal stability,mechanical strength,electrochemical properties and cycling stability were compared to investigate the influencing of porous structure.The final preferred porous epoxy resin-based electrolyte（PEME-3:7）at D230:PACM=3:7（equivalent ratio）shows a continuous through mesoporous-macropore coexistence structure and the best overall performance with a tensile strength up to 42.13 MPa,the room temperature ionic conductivity of 1.34×10^-3 S/cm,the lithium ion migration number of 0.60,and the interfacial impedance of 40Ω.Moreover,it has a significant effect on inhibiting the growth of lithium dendrites（1 m A/cm² current density）,and the assembled full cell also shows excellent cycling stability（90%capacity retention and nearly 100%coulomb efficiency after 100 cycles at 0.2 C）.Secondly,to further enhance the electrochemical performance and cycling stability of the porous epoxy gel electrolyte,ZIF-8 was grown in situ on the surface of the preferred porous epoxy resin membrane and the internal pore surface to form a ZIF-8/epoxy resin-based composite gel electrolyte.With a suitable ZIF-8 growth amount,the as-prepared composite gel electrolyte exhibits the best overall performance with improved room temperature ionic conductivity of 2.2×10^-3 S/cm,lithium-ion mobility number of 0.70,and electrochemical stability window increased from 4.3 V to 5 V.At a current density of 1.5 m A/cm² and high capacity of 6 m A h/cm²,the composite gel electrolyte is significantly effective in inhibiting lithium dendrites,and the formation of Li F and Zn F₂ rich SEI film makes the cell more stable and exhibits excellent cycling stability.