Electrochemical direct lithium extraction from brines: performance evaluation of LiFePO4 || ACnAg electrodes pairs

Direct lithium extraction offers an alternative to conventional brine evaporation by enabling controlled lithium removal from saline solutions using electrochemical methods. This study evaluated how counter electrode composition influenced lithium removal in the cell system using lithium iron phosphate as the working electrode. Activated carbon and silver-modified activated carbon were prepared on nickel foam and tested in a three-electrode cell with an Ag/AgCl reference electrode. Electrochemical characterization was performed using cyclic voltammetry, chronoamperometry and potentiostatic electrochemical impedance spectroscopy. Cell tests were conducted in synthetic brine containing Li⁺, Na⁺ and K⁺ at a molar ratio of 1:15.2:2.2. Lithium concentration changes were quantified by inductively coupled plasma optical emission spectroscopy. The 3 wt.% silver modified activated carbon electrode showed the most favorable balance between electrochemical response and mechanical stability. Its isolated electrode resistance decreased from 10.61 to 9.28 Ω relative to unmodified activated carbon, while its voltammetric response showed additional faradaic behavior consistent with Ag/AgCl reaction. The LFP||AC cell removed 1.56 mg of lithium from 100 mL of brine whereas the LFP||AC3Ag removed 1.70 mg. These results show that silver modification changes counter electrode charge compensation behavior and increases lithium removal.