| Liquid metal batteries have unique advantages in large-scale energy storage.The phase change of cathode in liquid metal battery is closely related to the alloying reaction of cathode.Understanding the cathode's solid-phase alloying process is essential to improve the battery performance.Because of the high working temperature of liquid metal battery,it is difficult to conduct online characterization of the battery with in-situ technology.Hence,this paper designed a room temperature liquid metal battery with Li metal as anode and Ga liquid metal as cathode.Scanning electrochemical microscopy(SECM)and ultrasonic monitoring techniques were used to monitor the Li deposition characteristics on liquid metal Ga cathode interface at a temperature of 40?.The flow behavior and temperature change of liquid electrolyte and cathode inside Li-Ga liquid metal battery were simulated by COMSOL.Firstly,SECM was used to on-line monitor cathode interface migration characteristics of Li||Ga battery.This work designed an in-situ detection platform for Li-Ga liquid metal battery system.Then mixed ionic liquid PYR14TFSI with organic solvent PC can ensure that the alloying-dealloying process of Li and Ga in the electrolyte can continue with good reproducibility.At the same time,the formation process of solid alloy compound on Ga interface at 28 m A/cm2 current density was on-line optical detected.It is found that the solids are preferentially deposited on the edge of Ga cathode,and then grow to the center area.The PAC fitting results show that the standard rate constant on the Ga surface is 5.33×10-5m/s.Meanwhile,the ultrasonic signal change law of the Ga electrolyte interface with different discharge current including 5 m A,7 m A,10 m A,and 12 m A was studied.Among them,Ga electrolyte interface is a mixture of solid-liquid interface and liquid-liquid interface after the discharge of 5 m A and 7 m A for 1000s.As the discharge capacity increases,the ultrasonic reflection signal increases linearly.After 10 m A and 12 m A discharge for1000 s,the Ga electrolyte interface has been completely covered by the lithium-gallium alloy solid,which is a solid-liquid interface.The relationship between the ultrasonic signal and the discharge capacity is a two-stage linear relationship.The ultrasonic signal increases with the discharge capacity in the first stage.The slope is relatively high;when it increases to 60%of the initial value,the slope of the ultrasonic signal decreases slightly with the increase of the discharge capacity.It is speculated that the point where the slope changes represents that the liquid Ga is completely covered by the Li-Ga solids.Because the high-density material has stronger reflection ability to the ultrasonic signal,the enhancement of the ultrasonic signal is more significant than the increase of the ultrasonic signal caused by the thickening of the solid in the solid-liquid interface at the stage of transition from the liquid-liquid interface to the solid-liquid interface.The results show that the ultrasonic signal has a certain linear relationship with the state of charge of the liquid metal battery,which can be used as one of the feasible technologies for detecting battery state of charge(So C).Secondly,the formation process of Li Ga solids on Ga cathode interface were studied by ultrasonic on-line technology.Through comparing the ultrasonic signals of batteries with different spacing between Ga and Li to ultrasonic signals with different discharge times,the fingerprint peak Ga/electrolyte interface signals has been identified between 2.030×10-6 to 2.193×10-6 s.Meanwhile,the ultrasonic signal change law of the Ga electrolyte interface with different discharge current including 5 m A,7 m A,10m A,and 12 m A was studied.Among them,Ga electrolyte interface is a mixture of solid-liquid interface and liquid-liquid interface after the discharge of 5 m A and 7 m A for 1000 s.As the discharge capacity increases,the ultrasonic reflection signal increases linearly.After 10 m A and 12 m A discharge for 1000 s,the Ga electrolyte interface has been completely covered by the Li-Ga alloy solid,which is a solid-liquid interface.The relationship between the ultrasonic signal and the discharge capacity is a two-stage linear relationship.The ultrasonic signal increases with the discharge capacity in the first stage.The slope is relatively high;when it increases to 60%of the initial value,the slope of the ultrasonic signal decreases slightly with the increase of the discharge capacity.It is speculated that the point where the slope changes represents that the liquid Ga is completely covered by the Li-Ga solids.Because the high-density material has stronger reflection ability to the ultrasonic signal,the enhancement of the ultrasonic signal is more significant than the increase of the ultrasonic signal caused by the thickening of the solid in the solid-liquid interface at the stage of transition from the liquid-liquid interface to the solid-liquid interface.The results show that the ultrasonic signal has a certain linear relationship with the state of charge of the liquid metal battery,which can be used as one of the feasible technologies for detecting battery So C.Last but not least,the internal flow process and temperature change inside Li||Ga liquid metal battery was simulated by COMSOL.It is found that the influence of ecternal magnetic field which affects the internal flow and temperature distribution of the battery is negligible.The fluid flow of cathode and electrolyte is obviously different.With the increase of discharge current,the flow direction of electrolyte fluid remains unchanged,but the flow rate increases.while the fluid distribution of cathode gradually changes to clockwise flow in the cross section direction.The flow direction of electrolyte plays an important role in the deposition of lithium gallium solids.Battery internal temperature at different current discharge basically unchanged,change less than 1K. |
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