| Energy storage technology is a key technology to eliminate bottlenecks in the large-scale development and utilization of renewable energy.It can relieve the contradiction between supply and demand,reduce the peak-valley difference,and improve security and stability of the power grid.Among the many energy storage technologies,electrochemical energy storage(EES)has the characteristics of high energy density,fast response time,low maintenance cost,and convenient installation,which has become the development direction of grid energy storage(GES)technology.However,the existing mature EES technology cannot fully meet the requirements of large-scale GES applications for energy storage cost and cycle life.The liquid metal battery(LMB)has a new three-layer self-separated battery structure without diaphragms.It is not only conducive to scale-up and mass production,but also not affected by the degradation mechanisms such as electrode deformation and dendrite growth in traditional batteries.In principle,LMB can operate safely for a long time.At the same time,due to the liquid-liquid interface between electrode and electrolyte,the battery has ultra-fast charge transfer kinetics.Therefore,LMBs have broad application prospects in large-scale GES with the advantages of low cost,long life and excellent high rate performance.Aiming at the current problem of low energy density of LMBs,this thesis designs new cathode materials for Li-based LMBs,and studies the charge-discharge performance and reaction mechanism.To reduce the operating temperature,the electrode materials matched with the low-temperature Li-based battery electrolyte are developed,and the cycle stability mechanism is studied.The charge-discharge behavior and mechanism of low-temperature Zn-based LMBs are explored.The main research results are as follows:(1)A new type of Li?Sb-Bi-Sn LMB system with high energy density has been designed and studied.The Sb and Bi components in the ternary alloy cathode determine the voltage plateau,and Sn has no effect on the voltage.The Sn element decreases melting point of the alloy and provides rapid liquid lithium diffusion paths.Because Sb and Bi have different lithiation potentials,the lithiation procese of the alloy presents a stepwise reaction characteristic.During charge and discharge,the microstructure of the discharge product changes dynamically,and the cracks in the product layer provide a new Li diffusion path.The fast atom diffusion,small ohmic resistance and charge transfer resistance in the electrode work together to improve the dynamic performance of the electrode,making the Li?Sb-Bi-Sn battery exhibit excellent rate performance.The design of low melting point ternary alloy reduces the content of inert component Sn and increases the content and utilization of Sb and Bi active components.The energy density of Li?Sb-Bi-Sn battery is 260 Wh kg-1,and the electrode material cost of the battery is only 59 $ kWh-1.(2)By matching the low melting point LiCl-KCl electrolyte,a series of low melting point cathode materials are designed and charge-discharge performance of Li-based battery at low temperature are studied.The melting temperature of the designed Sb-Bi-Sn and Sb-Bi-Pb alloys is lower than 400?.Sb and Bi in the alloy determine the voltage plateau,and Sn or Pb decreases the melting point of the alloy and has no effect on the voltage.The displacement reaction between LiCl-KCl molten salt and Li will lead to a decrease in K content.The addition of K can inhibit the displacement reaction and help maintain the stability of molten salt.The battery with LiCl-KCl as electrolyte,LiK as negative electrode,and the low melting point alloy as positive electrode can be cycled stably at 400?.The discharge energy density of LiK?Sb30Bi40Sn30 battery can reach 241 Wh kg-1,and the material cost is 68.8 $ kWh-1.The energy density of LiK?Sb30Bi40Pb30 battery is slightly reduced to 194 Wh kg-1,while the material cost is 62.8 $ kWh-1.Substituting Pb for Sn reduces the material cost of the battery by 8.7%.(3)The Zn-based LMB with Zn,Sn or Zn5Sn5 alloy as negative electrode,Bi as positive electrode,and LiCl-KCl-ZnCl2 as electrolyte has been systematically studied,and a new charge-discharge mechanism based on multiple displacement reactions is proposed.Zn-based batteries can be stably charged and discharged at 375?.The discharge process is mainly dominated by the displacement reaction between Zn and Bi ions,that is,Zn in the negative electrode and Bi ions near the positive electrode undergo oxidation and reduction reactions respectively.The charging process is the opposite.Based on this displacement reaction mechanism,the voltage plateau of Zn-based batteries reaches 0.79-0.88 V.Benefit from the molten salt electrolyte with optimized composition,the average coulombic efficiency is greater than 96%. |
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