Preparation And Investigation Of Gel Polymer Electrolyte Films For Magnesium Batteries

In recent years, magnesium-ion batteries are becoming a new type of potential energy due to its high energy density, low cost, non-toxic and high security. Compared with lithium-ion batteries, magnesium-ion batteries have a lot of advantages, leading very wide range of applications and good development prospects. Electrolyte is one of the most important parts of the magnesium-ion batteries. Many researchers now focus on the st udy of gel polymer electrolytes because gel polymer electrolytes have the better ionic conductivity compared to solid polymer electrolytes, better safety performance and thermal stability than liquid electrolyte.In this thesis, solid polymer electrolytes and gel polymer electrolytes are prepared by the solution casting method using PVDF-HFP as polymer, Mg(Tf)2 as salt, room temperature ionic liquid EMITf as plasticizer, the crystal structure, microstructure, thermal properties, interface performance, ioni c conductivity and electrochemical properties have been characterized by means of XRD, SEM, DSC, TGA, ac impedance and cyclic voltammograms. The performance in polymer electrolytes of different concentrations of magnesium salt, ionic liquids on the performance are studied by the results.Experimental results of the prepared solid polymer electrolytes show that when the Mg(Tf)2 is added into the polymer matrix, microporous structure begins to appear in the membrane structure, the crystallinity and thermal stability of electrolyte decrease with the increase of magnesium salt concentration, the tensile strength decreases with the increase of magnesium salt concentration. When the concentration of magnesium salt content is 10%, the ion conductivity of the polymer is the highest, which can reach 1.07×10-5 S cm-1, the electrochemical stability window can reach 4.1 V. The electrolyte has good thermal stability and mechanical properties. The melting point of the electrolyte is 126°C, the thermal decomposition temperature is 357°C, young’s modulus of the electrolyte is 167 MPa, the tensile strength is up to 6.4 MPa and the breaking strain is 686%.When the ionic liquid EMITf is added into the basis of solid polymer electrolytes, the thermal stability and mechanical pro perties of the polymer electrolytes are slightly reduced, the highly microporous structure appeares on the surface of the electrolyte, the ionic conductivity and electrochemical stability is higher. When EMITf concentration is 40%, the ionic conductivity reaches the highest value 4.63×10-3 S cm-1, which is two orders of magnitude compared to the solid polymer electrolyte. The electrochemical stabi lity window can be up to 4.8 V, which is 0.7 V higher than solid polymer electrolyte. The gel polymer electrolyte shows good thermal stability and good mechanical properties, the melting point of electrolyte is 112 °C, young’s modulus of the electrolyte is 66 MPa, the tensile strength is up to 3.4 MPa and the breaking strain is 633%, thus indicating the application in magnesium-ion batteries.