Numerical Study On Discharge Process Of Li||bi Liquid Metal Battery

Large-scale energy storage is the technical bottleneck for the efficient integration of renewable energy into the grid.Among various energy storage technologies,liquid metal battery(LMB)is of great potential for development due to its low cost,long lifespan and high efficiency.LMB features a three-layer fully liquid structure,which not only endows LMB with excellent kinetics and transport properties,but also makes LMB suffer from electromagnetohydrodynamic instability.However,the in-situ monitoring on the multi-field driven flow,mass transport,interfacial electrochemistry and their interactions are quite difficult due to the closed high temperature operating environment of 300-700 ℃.Given this,numerical study has become an effective method to research the operating mechanism of LMB.So far,the reported simulation works mostly only focused on the electromagnetohydrodynamics in the idealized three-layer LMB or a liquid electrode layer.There is still no comprehensive LMB model fully coupling thermally-magnetically driven flow and electrochemistry.So developing the comprehensive LMB model has become a challenging hot work.In view of that,several two-dimensional axisymmetric LMB models,which firstly coupling thermally and magnetically driven flow and electrochemistry,were established in this dissertation.Based on the LMB models,the discharge process of LMB represented by Li||Bi system was numerically analyzed.The research content included the influence mechanism of the multi-field coupled flow on the discharge process,the discharge behaviors at different rates and performance discrepancies at different capacity designs and negative electrode structures.The main researches are summarized as following:First,an idealized tri-layer self-stratification fully liquid LMB model was established by firstly coupling electrochemistry and thermally-magnetically driven flow and the mass transport in the molten salt was also firstly taken into account in the LMB model.Based on the LMB,interaction mechanism between electrochemical behavior and thermally-magnetically driven flow was firstly studied.The comparative simulation results of different models manifested that the thermally driven flow dominants the flow field and could reduce the concentration polarization,while the magnetically driven flow was too weak to influence the discharge process.Meanwhile,the discharge process at different rates were numerically analyzed and the simulation results indicated that the discharge voltage would decrease with the increasing current,in spite of the enhanced convection effect.Next,based on the aforementioned physical model and the practical topology of LMB,the 20 Ah practical LMB models were firstly established,to investigate the effect of the thermally-magnetically driven flow on the discharge process more accurately.Based on the model,the effect of Marangoni convection and background magnetic field on electrochemical discharge process was firstly discussed.The simulation results illustrated that Marangoni effect had a weaker influence on the whole flow intensity but a notable inhibition of the flow at the positive electrode||molten salt interface,which led to a slightly larger concentration polarization and generated almost no effect on the discharge voltage.Besides,an appropriate external magnetic field was found to facilitate the convection effect and increase the discharge voltage by numerical study.Finally,different capacities and negative electrode aspect ratios of LMB models were constructed to numerically study the effect of geometry structure on the discharge process of LMB.The simulation results revealed that the capacity amplification and the increasing in negative electrode thickness could both promote the convection,but also aggravated ohmic drop slightly,which resulted in a slightly reduced discharge voltage.The simulation results theoretically demonstrated the practical phenomena occurring in the process of capacity amplification and a negative electrode structural design was also proposed by the simulation at last.