A comprehensive multiphysics approach to model solutal buoyancy, thermal convection, and electro-vortex flow phenomena for liquid metal batteries

Abstract

To alleviate the effects of pollution and global warming, the transition to renewable energy sources is taking place at an accelerating rate. The intermittent nature of renewable energy production can be addressed by an energy storage solution that is low-cost, efficient, and based on earth-abundant materials, and a liquid metal battery (LMB) is coming up as one such solution. Liquid metal battery (LMB) performance, especially its discharge voltage, depends on the concentration profile of cathode which in turn is influenced by fluid flow. In this study, we examine three significant phenomena that impact fluid behavior: solutal buoyancy, internally heated convection, and electro-vortex flow (EVF). Though several attempts have been made to model these processes individually or in a combination of two, a model that simulates all three aspects for resultant fluid flow has not been reported. Therefore, this study develops a comprehensive multiphysics model to simulate the positive electrode that is validated with experimental results for Li||Bi cell operating at 450 °C by coupling all of the aforementioned phenomena. While charging with a current density of 1 A/cm2, our model predicts an average velocity of ∼6 mm/s in the cathode solely due to solutal buoyancy. In the case of discharging, both solutal and internal thermal effects lead to an increase in overpotential to as high as ∼200 mV. Moreover, during discharging, the EVF induced a poloidal fluid flow with a maximum velocity of ∼3–5.5 mm/s at 1 A/cm2, reducing mass transport overpotential by ∼10 mV, but it could not disrupt the lighter intermetallic stratification layer on top of the cathode. Additionally, we investigated the charging overpotential phenomenon due to unstable stratification. This all-inclusive model leveraging solutal, thermal, and EVF effects not only offers insights into the fluid motion, concentration gradient, and voltage profile for a lab-scale LMB but can accurately simulate te conditions prevalent in commercial large LMBs, thereby catalysing the path to commercialization of LMBs.