Research On The Surface Modification Of Porous Magnesium Oxide Fiber Used In Thermal Battery

The thermal battery is primary cell using solid salt as electrolyte.In working condition,because of melting,the solid electrolyte in the thermal battery become liquid and it is easy to leak out,which leads to a series of adverse effects.Therefore,it is necessary to add binder into the electrolyte to inhibit the flow of molten salt.Porous magnesium oxide fiber has complex network structure and porous morphology.Using porous MgO fiber as binder,its ability to inhibit the flow of molten salt is better than that of the traditional binder material with the same quality.In order to further improve the inhibition ability of porous MgO fiber and electric properties of the electrolyte-binder powder(EB powder),use physical and chemical method to modify porous MgO fiber.First,the porous MgO fiber was prepared by hydrothermal reaction,and the fiber obtained by this method was used as the base material.The chemical modification used hydrofluoric acid to react with MgO.The physical modification used the atmospheric plasma spraying method to coat a layer of alumina oxide on the surface of the porous MgO fibe.Relatively adding fiber modified by physical and chemical method into binary electrolyte(LiCl-KCl)and ternary electrolyte(Li F-LiCl-LiBr)fiber as binder,the electric conductivity,discharge capacity,electrolyte leakage and deformation was evaluated.After modification by chemical method,fiber surface was covered with magnesium fluoride.The specific surface area of the fiber was improved significantly,which would increase the contact area between the electrolyte and binder and reduce both deformation and electrolyte leakage effectively.With the increase of hydrofluoric acid,the ionic conductivity of EB powder is decreased,while the discharge capacity of EB powder significantly improved.Overall,chemical modification led to inhibition ability and better electric properties.The improvement of both inhibition ability and electrical properties were confirmed both in binary or ternary electrolyte system.After modification by chemical method,the surface of fiber was coated a layer of aluminum oxide.Compared with magnesium oxide,alumina oxide owned better affinity to molten salt,which reduced the electrolyte leakage and deformation.The alumina oxide coating on the fiber surface would decrease the ionic conductivity of the system slightly.However,the model thermal battery had larger discharge capacity with similar conductivity,so generally electrical performance had also been improved.Overall,physical modification led to better inhibition ability and electric properties.The improvement of both inhibition ability and electrical properties were also confirmed both in binary or ternary electrolyte system.