| Batteries as high-efficiency electrochemical energy storage devices are essential for the efficient use of intermittent renewable energy sources.Among them,rechargeable liquid metal batteries(LMBs)have the potential advantages of low cost,easy assembly,and manufacturing,and long service life due to their all-liquid cell structure and abundant electrode and electrolyte material choices.Therefore,liquid metal batteries are one of the important development directions of nextgeneration large-scale energy storage technology.This paper focuses on the challenges of low energy density,poor voltage efficiency,and corrosion of anode current collector caused by high operating temperature for Li-based LMB technology.To address these issues,a novel Sbbased alloy cathodes were designed to increase the lithiation potential and improve the electrode reaction kinetics.Meanwhile,a high-voltage Te-Cu alloy cathode was designed to improve the electrical conductivity and decrease the solubility of Te in the molten salt electrolyte,finally enhancing the cycling stability of a high-voltage Te-based cathode.The graphite coating was applied on the negative electrode current collector to improve the corrosion resistance to molten lithium.The effects of material composition and structure of key components on the electrochemical performance of Li-based LMB were studied.The lithium storage mechanism of the designed new cathode materials was elucidated and the corrosion behavior of the negative collector was revealed.The main contents of the thesis include the following aspects:(1)A new Sb-Ag alloy cathode system was designed.Based on theoretical calculations and experimental investigation,a novel lithium storage mechanism for liquid metal batteries was revealed,phase formation and conversion mechanism of the ternary intermetallic Li2AgSb.The results show that Li2AgSb has a higher formation voltage(1.08 V)and a lower lithium diffusion potential barrier(0.063 eV)compared with Li2Sb.During the discharge process,a three-dimensional Li2AgSb+Li2Sb interpenetrating network structure is formed in the electrode,and the Li2AgSb network structure with fast lithium diffusivity significantly improves the reaction kinetics of the electrode.The constructed Li‖Sb70Ag30 battery with an active material cost of 96.03 $ kWh-1 exhibits high energy density(345.18 W h kg1),high voltage efficiency(86.46%),and superior power density(537.00 W kg-1).(2)A novel Sb-Cu alloy cathode material was designed,which shows a similar lithium storage mechanism with the Sb-Ag system but has a much lower material cost.In the lithium storage process,the high voltage phase Li2CuSb intermetallic was first formed at～1.0 V,which was followed by the conversion of Sb to Li2Sb,and then Li2CuSb to Li3Sb+Cu.Compared with Li3Sb,the discharge product Li2CuSb ternary intermetallic has fast lithium diffusivity ability and so the Sb-Cu cathode presents fast electrode reaction kinetics.The assembled Li‖Sb64Cu36 battery showed high power density(558.36 W kg-1),high voltage efficiency(88.04%),high energy density(353.00 W h kg-1)and low active material cost(only 38.45 $ kWh-1),which makes it a very competitive liquid metal battery system for grid-level energy storage.(3)To address the issue of dissolution of high voltage Te cathode in the molten salt electrolyte,a Te-Cu alloy cathode was proposed.The introduction of Cu significantly enhances the conductivity of the Te-based cathode,reduces its dissolubility in the molten salt electrolyte,and mitigates the self-discharge problem of the Te electrode.The Li‖Te70Cu30 battery exhibits stable cycling performance with a capacity retention of 96.90%after 250 cycles at 0.2 A cm-2,which is the best record of Te-based cathode material.Based on the excellent electrochemical performance,the Li‖Te70Cu30 battery exhibits high energy density(412.32 W h kg1),high energy efficiency(81.20%),and high capacity utilization(92.00%).(4)The chemical vapor deposition technique was used to grow a graphite protective layer in situ on the surface of the Ni-Fe anode current collector,which enhances the corrosion resistance of the current collector towards molten lithium.The graphene layer is deposited parallel to the surface of the Ni-Fe foam skeleton.The basal surface of graphite coating layers could prevent the insertion of lithium ions and enhance the corrosion resistance of the Ni-Fe anode current collector.Meanwhile,the coated graphite layer has good wettability with molten Li.The assembled Li/GNF‖Bi batteries exhibit excellent rate performance(almost no capacity change in the current density range of 0.2-2.0 A cm-2)and cycle stability(100 cycles at 0.4 A cm-2,98.10%capacity retention). |
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