Abstract
Lithium recovery from end-of-life lithium-ion batteries involves energy- and reagent-intensive pyro- and hydrometallurgical refining, motivating electrochemical conversion of lithium-containing sulfate streams into recoverable products. A modular four-chamber electrochemical flow reactor was developed and evaluated as a proof-of-concept platform, comprising a Zn anode chamber, a Li2SO4 feed chamber, a precipitation chamber, and a cathode chamber supplied with either O2 or an O2–CO2 mixture. The reactor supported Li+ migration and spatial separation of product formation. Under galvanostatic operation, Zn oxidation at the anode and gas reduction at the cathode generated OH- or CO32-, which reacted with migrated Li+ to form LiOH·H2O or Li2CO3 in the precipitation chamber. Using synthetic Li2SO4 model solutions (0.8–1.2 mol L−1), the effects of electrolyte concentration, liquid flow rate, current density, and gas composition were systematically investigated, together with one synthetic Mn2+-competitive test; no real leachate was examined. An operating window around 1.0 mol L−1 and 1.0–2.0 mL min−1 gave relatively stable voltage profiles and effective precipitation. Under O2-CO2, LiOH·H2O and Li2CO3 were co-produced at 1479.00 and 303.00 mg h−1 cm−2, respectively, with a specific energy consumption of 6.40 Wh mol−1 Li and a Li-based FE of 66.29%. Under pure O2, LiOH·H2O formation was favored, giving the highest yield rate of 1773.75 mg h−1 cm−2 and the highest FE of 73.97% based on recovered Li, with a corresponding specific energy consumption of 16.70 Wh mol−1 Li. Additional 24 h tests included the synthetic Mn2+-competitive system, which yielded an apparent chamber-level Li/Mn enrichment factor of 3.75 and revealed Zn (OH)2/ZnO deposition near the CEM. However, under the lithium-product-forming conditions of 12.5–25 mA cm−2, precipitation-induced blockage caused the cell voltage to reach the 60 V cutoff before 24 h, whereas continuous 24 h operation at 0.25 mA cm−2 produced no clearly separable lithium-containing solid. Accordingly, under the current configuration, lithium-product recovery and 24 h continuous operation are mutually exclusive; the system does not yet possess engineering practicality, and these proof-of-concept results define boundary conditions for subsequent optimization but should not be extrapolated to real leachate systems.