Direct LiOH Production from Battery Cathode Leachate with Nanofiltration and Bipolar Membrane Electrodialysis

With a growing global interest in environmental protection, the importance of lithium-ion batteries (LIBs) is rapidly increasing. As a result of their quick charging, longevity, and high power density, LIBs are the leading choice in powering portable devices like smartphones, laptops, and electric vehicles. Unfortunately, domestic supplies of lithium, cobalt and manganese are limited, and current extraction methods are energy-intensive and generate large volumes of chemical waste. Lithium can be secured from primary sources, such as solid ore mining—an environmentally harmful process—or from brine evaporation, which is a very time intensive procedure. <br/>The supply of lithium, cobalt, and manganese can also be augmented through secondary sources, namely by recycling spent cathodes from LIBs. Battery recycling is the process by which valuable metals are recovered from spent LIBs to manufacture pristine LIBs. Lithium, cobalt, and manganese make up the cathode layer of the majority of LIBs. The prominent cathode chemical composition includes: LiCoO₂ (LCO), LiMn₂O₄ (LMO), and LiNi_0.33Mn_0.33Co_0.33O₂(NMC). Inorganic acid leaching—the process of soaking used batteries in inorganic acids like sulfuric acid and hydrochloric acid—is a highly effective method of recovering lithium, cobalt, and manganese from the spent cathodes. In this process, a highly concentrated acid leachate that comprises Li⁺, Mn²⁺ and Co²⁺ is produced, and electrochemical reactions are commonly leveraged to reduce the metal ions into their respective solid forms. <br/>In this work, we investigate membrane processes for direct LiOH production from battery cathode leachates. First, the battery leachate is pressurized and passed into a Donnan-enhanced nanofiltration process. Conventional polyamide nanofiltration (NF) membranes possess negative volumetric charge densities as a result of the high concentration of carboxyl moieties, leading to poor monovalent selectivity for cations. To enhance cation separations from battery leachates, a highly crosslinked layer of polyethyleneimine (PEI) is covalently bonded with the polyamide substrate through a condensation reaction between the perfluorosulfonic acid and amine moieties. The composite NF membrane acquires a positive zeta potential and exhibits passive selectivity for monovalent cations from the enhanced Donnan exclusion effect. Our preliminary results indicate that the Mn²⁺ and Co²⁺ rejections increase from 65% to 99%, between the experiments involving the pristine and composite NF membranes. Conversely, the Li⁺rejection only increased incrementally from 5% to 13%, and the Li product stream has purity rating of at least 98%. <br/>Second, the Li-rich permeate stream from NF is used as the input to a bipolar membrane electrodialysis (BMED) process. In BMED, a bipolar ion exchange membrane facilitates water dissociation, while the inherent cation and anion exchange membranes inhibit co-ion transport. As a consequence, BMED produces a basic LiOH, an acidic HCl and a desalinated stream. Here, we leverage high current densities to promote efficient water dissociation, enabling highly concentrated (1M or greater) HCl and LiOH streams to be produced from the NF permeate. The HCl can be recycled for acid leaching of battery cathodes, reducing acid consumption and chemical waste generation while promoting a closed atom economy. The concentrated LiOH can be used as a feedstock for direct battery manufacturing.