Research On Molten Salt Iron-Air Battery And The Key Materials

Environmental pollution and the shortage of fossil energy increased demand for renewable energy generation.Battery technology plays an important role in energy conversion and utilization.It is urgent to research high energy density,high power density,high safety and low cost battery technology.High temperature molten salt battery displays great application potential in large-scale electrochemical energy storage,such as Na-S battery,ZEBRA battery and liquid metal battery.Molten salt has very high ionic conductivity and material dispersion ability,which would contribute to fast charge transfer dynamics,excellent mass transport and low ohmic loss for electrochemical reaction.It would realize a rapid and efficient conversion between chemical energy and electrical energy.Iron-air battery would be a candidate of energy storage device because of its high theoretical energy density,simple and safe battery structure,cheap and wide raw materials.Combining high temperature molten salt battery and iron air battery will be an effective way to develop a new deneration energy storage device.Our research object is a rechargeable molten air battery,which was made of iron negative electrode,air positive electrode and molten salt electrolyte.The high tendency to evaporate and flow for molten salt challenges the long time stability of battery.We designed quasi-solid-state electrolyte battery and all-solid-state molten salt battery respectively.In detail,the reaction mechanism of negative electrode with different electrolyte was also studied.Specifically divided into the following four parts:（1）the quasi-solid molten salt electrolyte was prepared by adding solid oxide nano powder into liquid molten salt.We concluded that there is strong interaction between molten salt and solid particles via characterizing the composition,morphology and thermodynamic quality of the quasi-solid-state molten salt.The adsorption of nanomaterials on molten salt would effectively alleviate the volatilization and flow of molten salt.The electrolyte was used to fabricate an iron air battery,which performed113 h cycle life,high columbic（>90%）and energy（～60%）efficiencies.We also confirmed a redox mechanism between Fe O₂^-and Fe at the three-phase interlines in the interface of negative electrode and electrolyte.（2）we confirmed a simple and efficient battery assembly process.Ceramic glaze was used to seal negative electrode.We finally determined the condition of glaze sealing by adjusting the the glaze concentration,heating rate and calcination times.The glaze layer would cover negative electrode fully and combined with electrolyte closely when a high concentration of glaze sizing agent was heated to 900℃for 3 h with rate5℃/min.There is no connerted pores and cracks on the cross section of glaze layer.（3）we synthesized pure KFe O₂ negative material via solid-phase method.We observed and explained the process of K⁺extraction after exposing KFe O₂ to air.The extracted K interacted with H₂O and CO₂ forming K₂CO₃·1.5H₂O outside KFe O₂ and lattice expansion of KFe O₂.It formed amorphousβ-Fe₂O₃ after K⁺was extracted completely.Molecular dynamics simulation results also confirmed the water sensitivity of KFe O₂ surface.We also successfully reinserted K⁺into KFe O₂ lattice by high-temperature calcination.Moreover,all-solid-state battery with KFe O₂ negative electrode obtained high cycle performance.（4）an all-solid-state iron-air battery was assembled with Ti O₂ as the negative electrode additive.It could be recharged up to 338 cycle.Coulombic efficiency of this battery was maintained at～100%,and energy efficiency was close to 70%.Ti O₂additive significantly improved the conductivity of negative electrode.The redox procee of negative electrode was realized by the interaction between Fe（III）,Fe（II）and Fe（0）.It occurred on the Fe aggregation layer between the negative and electrolyte interface.