Preparation Of Porous Epoxy Resin-based Gel Electrolytes And Their Performance In Lithium/sodium Metal Batteries

Lithium metal has become the most promising anode material for high specific-energy lithium secondary batteries due to their advantages of high theoretical capacity(3860 mA h/g),low oxidation-reduction potential(-3.0401 V vs.SHE),and low density(0.53 g/cm3).However,due to the shortage and the uneven distribution of lithium resources,the sodium metal with abundant reserves and lower costs has gradually attracted attention.Compared with traditional carbon-based anode materials,sodium metal has the advantages of low electrochemical potential(-2.714 V vs.SHE)and high theoretical specific capacity(1166 mA h/g).Making sodium metal batteries also become one of the most potential high energy density batteries.However,the above two batteries have safety problems,so it is inevitable to use solid electrolyte instead of liquid electrolyte.Regardless of a polymer electrolyte or an organic-inorganic composite electrolyte,the choice of the polymer matrix is crucial.At present,most commonly used polymer matrices have the disadvantages of low room temperature ionic conductivity and poor mechanical properties,which limit their commercial applications.In this paper,the cross-linked network of bisphenol A epoxy resin(DGEBA)was selected as the matrix.And porous epoxy resin-based gel electrolytes with excellent performance were prepared by designing different microscopic porous structures,which increases the diversity of choices of polymer matrix.First,a variety of porous epoxy resin electrolyte membranes(PEE)with different pore structures were prepared through changing the formulation ratio of the monomer and the pore-forming agent solvent during the preparation process of the phase inversion method.The differences in morphology,mechanical properties and thermodynamic properties caused by the different pore structures were compared visually and microscopically.The results show that when 1 ? mass ratio(pore-forming agent/epoxy resin)<3,the pore structure of the epoxy resin film changes from the honeycomb structure to the mixed structure(skeleton network and globule),and all have excellent mechanical properties.The epoxy resin films have excellent thermal stability,and its apparent size has not changed at 250?,60 min.Secondly,the epoxy resin membranes with different pore structures were fully activated in the liquid electrolyte to form gel electrolytes,in which the influences of pore structure on its mechanical performances and electrochemical properties was characterized.It was found that the gel electrolyte with a mass ratio x=2.75 has the most excellent comprehensive performance.On one hand,the membrane of PEE-2.75 with mixed structure(skeleton network and globule)has a wider ion transmission channel and more hydroxyl groups on the surface,which can lead to a higher liquid absorption rate(233%),a lower interface impedance,and an ion conductivity up to 2×10-3 S/cm.On the other hand,it promotes the uniform deposition of lithium ions.So even at a high current density of 2 mA/cm2,it still has a good inhibitory effect on lithium dendrites.Finally,it is the first time that epoxy resin is used as a polymer matrix in sodium metal batteries.The epoxy resin film is matched with four different electrolytes to further broaden the application.It came out that the epoxy resin membranes activated by the ether electrolyte swell significantly or even degrade due to”similarity-intermiscibility".While after activation by the liquid electrolyte(NaPF6+EC/DMC),the gel electrolytes had the best overall performance.Its ionic conductivity is up to 2×10-3 S/cm,the electrochemical window is 4.7 V,and it has excellent interface performance with electrodes,and the electrolyte has excellent rate and cycle performance in Na/Na3V2(PO4)3 full cells.