Metallic lithium, which is a critical and strategic metal for the world’s production of energy storage devices, is mainly produced from molten salt electrolysis. To increase the efficiency of the process, it is of utmost importance to prevent lithium recombination during the process to avoid energy waste. This research studies the behavior of the main variables involved in the reaction inside a Li-production experimental cell from the mass transfer, electrochemical and fluid dynamics standpoints. Simulations were done for a total electrolysis time interval of 600 s using a turbulent (k-ε) approach to solve the two-phase flow coupled to the lithium electrolysis process. To analyze the influence of cathode fluid dynamics in relation with the amount of recombined lithium, two configurations of the diaphragm were evaluated including the incorporation of a baffle at the bottom of the cell and the inclination of the diaphragm. The baffle reduced the amount of recombined lithium by 7 %, and the diaphragm with an inclination < 90° reduced the total recombined mass by 77 %, although it increased the energy consumption by 10 % with respect to the base case of a vertical diaphragm.
A mass transfer study in a lithium production electrolysis cell is carried out. The numerical domain is a 2D axis-symmetric wedge of 5 o. The bulk of the cell is filled with an electrolytic solution consisting of an eutectic mixture of LiCl − KCl. Lithium ions reduce at the cathode while Cl − oxidize at the anode releasing bubbles of chlorine gas. Those are moving upward due to their light density dragging the nearby electrolyte. The induced convection is responsible for the transport of ions, together with the migration and diffusion mechanisms. The result is a turbulent two-phase flow accounting for the transport of ions, potential drop and polarization concentration. The highly non-linear coupled mathematical model is solved using an OpenFOAM solver designed to use predictor-corrector loops for both the fluid dynamics and the electrochemistry coupling. Non-linear mixed boundary conditions complete the set of governing equations.
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