Corrosion Failure Mechanism Analyses And Stabilization Strategies Of Sb-Sn Positive Electrode For Liquid Metal Battery

Large-scale energy storage technologies can efficiently store renewable energy power and solve the development bottleneck caused by its volatility and intermittency.Electrochemical energy storage is an important direction of future large-scale energy storage technology development.And it can quickly,efficiently and cost-effectively utilize the mutual conversion between chemical energy and electrical energy through electrochemical reaction.Liquid metal battery(LMB)is not restricted by special materials and technologies such as separators because of its unique three-layer all-liquid self-layered structure and conductive properties.Apart from being easy to be massively assembled and cheap,LMB could also effectively avoid degradations such as dendrite growth,phase transition,and grain size change so as to theoretically achieve long-term safe operation of the battery.Moreover,the liquid-liquid interface between the electrode-electrolyte endows the battery with ultrafast charge transfer dynamics for higher power applications.Therefore,LMB could be widely used in large-scale energy storage with the advantages of low cost,high rate performance,easy amplification and long life cycle.The present study focuses on the strong corrosion of Sb-Sn positive electrode that seriously hinders the widespread application of excellent-performing and lowcost Li‖Sb-Sn LMB.Specifically,this research includes the following three aspects:analysis of the failure mechanism underlying positive electrode corrosion,the selection and performance analysis of anti-corrosion coating materials of positive electrode,and the replacement and performance analysis of positive electrode strong corrosive elements.The main results of this study are as follows:(1)The corrosion mechanism between the Sb-Sn positive electrode and the SS304 current collector,and the battery reaction changes have been clarified by static corrosion,electrochemical testing,and ex-situ analysis.The dissolution of Fe plays a dominant role in the corrosion between Sb-Sn and SS304.During the charging-discharging process of the battery,Fe and Ni in SS304 gradually dissolves into the positive electrode to form Fe-Ni-Sb-Sn corrosion products,which gradually become the actual positive electrode,resulting in a lower battery discharge voltage plateau and a rapid capacity decay.The low discharge voltage plateau is mainly formed by the lithiation of Fe-Sb corrosion products,while the rapid capacity decay results from the incomplete lithiation of Fe-Sb and Ni-Sb low lithiation voltage corrosion products.The inert element Sn in the positive electrode can promote the mass transfer and the diffusion of the dissolved elements so as to accelerate the corrosion between the positive electrode and the current collector.(2)The anti-corrosion properties and electrochemical performance of Sb-Sn positive electrode when Ti,Mo,and W have been used respectively as positive current collectors of Li‖Sb-Sn LMBs are investigated through static corrosion,electrochemical tests,and post-event analysis.It is found that the Li‖Sb-Sn LMB exhibits excellent cycle stability using the preferred W as positive current collector.In contrast,Ti and Mo are more likely to dissolve and corrode with liquid Sb-Sn alloys to form Ti-Sb-Sn and Mo-Sb-Sn,resulting in a lower battery discharge voltage,a capacity loss and safety hazards.As a positive current collector material,W is very stable and has a low corrosion rate.The W coating prepared on the SS304 substrate by plasma thermal spraying technology is uniform,dense,and has a low oxygen content,which can effectively resist the corrosion of the Sb-Sn positive electrode.In addition,the W positive current collector coating has excellent service characteristics,which is proved in the first application of micro-CT non-destructive testing technology in the field of liquid metal batteries.(3)The ternary Sb-Bi-Sn positive electrode has been prepared by replacing some highly corrosive Sn in Sb-Sn positive electrode with Bi,which is immiscible with Fe.The corrosivity of the positive electrode is effectively inhibited,and the Li‖Sb-Bi-Sn LMBs have exhibited excellent cycle stability.The introduction of Bi can not only inhibit the dissolution of Fe in SS304 in Sb-Bi-Sn alloy,but also infiltrate and block solid particles(Li3Sb,Fe,and Fe-Cr),which makes the corrosion products of Fe-Sb and Fe-Cr-Sb decompose into Fe,Fe-Cr and Sb during lithiation.And the active component of positive electrode Sb in the corrosion products can be released.Due to the self-healing action of the positive electrode,the charge-discharge cycle of the battery is stable,almost unaffected by corrosion,and shows theoretically long cycle life,excellent rate performance,and anti-pulse interference ability.In addition,the introduction of Bi can also increase the proportion of active elements in the positive electrode,resulting in a Li‖Sb-Bi-Sn LMB with a specific capacity of up to 394 mAh g-1 and an energy density of 265 Wh kg-1,while the electrode cost of the battery is only 58.62 $ kWh-1.