Research On Lithium-based Liquid Metal Batteries

Energy storage with low cost,long lifetime and large scale performs a crucial role in stability,reliability,and security enhancements for electricity grid.The demand for large scale energy storage has significantly increased as a result of rapid development in renewable energy technologies in recent years.In 2006,Donald Sadoway at MIT proposed the concept of "all-liquid metal battery"(LMB)mass storage,which was widely concerned by researchers at home and abroad.An all-liquid metal batter design involves no any separation and membrane.The advantages of LMB include high current density,long cycle life,simple fabrication and easy to enlarge.Therefore,the LMB has broad application prospect in the field of large scale energy storage.In this work,we determined the proper components proportion of low melting point lithium salts suitable for lithium based LMB using mixed design method,and characterized the physical properties for the molten salt(LiF-LiCl-LiBr).We discussed the effects of different electrode couples in lithium based battery system with a metallic lithium negative electrode.We also performed the electrical chemical properties characterizations for a prototype battery system having capacity of 1.2Ah and an amplified battery system having capacity of 10Ah.The design and assembly for the sealing construction of the 10Ah battery system was also discussed.The minimum liquidus temperature of 416.586℃for the LiF-LiCl一LiBr molten salt system having a molar ratio 21.2:30.8:48.0 was calculated using Simplex lattice design in mixture design techniques of Design-Expert.Our measured value of liquidus temperature(melting point)of this component was 444℃.This component has anionic conductivity higher than3.0S.cm-1 and a density from 2.17 to 2.42 g.cm-3 in a temperature range from 460 to 520 ℃,which meets the requirements of lithium based LMBs.With a theoretical capacity of 1.2Ah and a full-discharge composition of 45:38:17mol%of Li-Pb-Sb,cells containing an electrolyte of LiF-LiCl-LiBr eutectic(Tm=444℃)were assembled and tested at 490℃under different current densities(150mA/cm2,300mA/cm2,500mA/cm2).The cells achieved impressive 98%Coulombic and 87.5%voltage efficiencies.The average discharge voltage was 0.8V and energy efficiency was 85.8%at the current density of 150mA/cm2.Those results revealed ultrafast charge-transfer kinetics at the interface between the liquid metal electrode and molten salt,as well as,a rapid mass transfer inside the liquid metal electrodes.In this paper,we designed and tested the 10Ah hermetically sealed battery and proposed the design concept of built-in lithium current collector.We found that the metal Li reduced on the positive electrode during discharge process was unable to penetrate through the thick Pb-Sb alloy layer,and Li3Sb intermetallics produced on Pb-Sb alloy layer easily.