Negative Current Collector Materials For Na-Zn Liquid Metal Battery

Energy storage technology plays a revolutionary role in the development and operation of future energy systems.Solar energy and wind energy,which are renewable energy sources,all have intermittent supply problems.Among the many energy storage technologies,electrochemical energy storage is flexible and highly effective.As a new type of membrane-less electrochemical energy storage technology,liquid metal batteries have the advantages of high efficiency,low cost,and long life,and have broad application prospects in large-scale energy storage systems.In this paper,the negative current collector material of Mo,W and stainless steel for Na-Zn liquid metal battery is studied.The research contents include the influence of charge and discharge current density,electrolyte composition,battery temperature on charge and discharge process and electrode behavior.The results of this study are summarized as follows:(1)The anode current collector material is molybdenum,when the charge current density is 20 mA/cm2,and the discharge current density is 10 mA/cm2,the discharge flat voltage is in the range of about 1.5 V-1.65 V and the energy efficiency achieved is 54%.When the charge-discharge current density is 100 mA/cm2,the coulombic efficiency achieved is 96%.When the discharge current density was 200 mA/cm2,the discharge voltage of the Na-Zn liquid metal battery dropped rapidly and there was no discharge voltage flat.(2)When the anode current collector material is tungsten,the discharging platform voltage is the highest.When the discharge current density is 40 mA/cm2,and reaches a voltage of 1.3 V.When the discharge current density is 100 mA/cm2,the Coulomb ic efficiency is the highest,reaching 80%,and the energy efficiency reaches 30%.(3)The anode current collector material is stainless steel,when discharge current density is 40 mA/cm2,the discharge platform voltage is in the range of about 0.5 V-0.75 V,Coulombic efficiency reaches 40%,while energy efficiency reaches 30%.When the discharge current density is 100 mA/cm2,the discharge platform voltage is in an interval of 0.5 V-0.8 V,the coulombic efficiency reaches 80%,and the energy efficiency reaches 20%.(4)When the electrolyte composition is NaCl-CaCl2-BaCl2,and the electrode material is molybdenum,the Coulombic efficiency increases to 86%.When the electrode material is stainless steel,the discharge voltage flat is in the range of 0.4 V-0.8 V and the Coulombic efficiency reaches 55%.(5)It is found that the cathode reaction in the system not only includes the reduction of sodium metal,but also has the competitive deposition of zinc,calcium with sodium,which forms molybdenum zinc or calcium alloy.Zinc alloys and zinc metal fall back to the bottom of the battery due to density.The solubility of calcium is partially dissolved in the molten salt electrolyte.It is found that the diffusion coefficient of zinc ion was 2×10-6 cm2/s.(6)When the negative current collector material is molybdenum wire,Na-Zn liquid metal batteries are operated at temperatures of 543℃,560℃,and 582℃,respectively,when the discharge current density is 40 mA/cm2.During the course of discharge,the discharge platform voltage was 1.25 V-1.5 V,1.3 V-1.5 V,and 1.5 V-1.6 V,respectively,and the coulombic efficiency was 65%,55%,and 55%,respectively.When the discharge current density is 100 mA/cm2,the discharge voltage flats are 0.9 V,0.8 V,and 1.0 V,respectively,and the coulombic efficiencies are 70%,80%,and 60%,respectively.