Leapfrogging to Sustainable Lithium Hydroxide Production through Chlor-Alkali Electrolysis

The demand for lithium-ion batteries (LIBs) has surged due to a wide variety of applications, ranging from electric vehicles to energy storage systems. With cobalt scarcity posing challenges, nickel-rich cathodes like NMC 811 are gaining popularity, driving up the demand for lithium hydroxide (LiOH) as a key precursor material. This increased demand for LiOH as raw material for high nickel NMC cathode material is due to its low decomposition temperature which enables better lithium incorporation into crystal structure, enhancing phase purity and crystallinity. Traditionally, LiOH is produced by a combination of precipitation and acid-base reactions involving sulphuric acid, sodium carbonate and calcium hydroxide. Electrochemical processes such as membrane electrolysis, offer a more streamlined approach for producing battery-grade LiOH directly from lithium chloride (LiCl) salt, bypassing the need for multiple purification steps and reducing chemical usage compared to traditional chemical routes. In this regard, knowledge from the well-established chlor-alkali process for chlorine (Cl 2 ) and caustic (NaOH) production is transferable as Li and Na belong to the alkali metal group in the periodic table. Hence, similar behavior can be expected for LiCl electrolysis. One challenge in the current industrial chlor-alkali processes is unwanted hydroxide (OH - ) crossover from the cathodic to the anodic compartment, which leads to an increase in pH of the anolyte and consequently enhances the undesired oxygen evolution reaction. This mandates acid addition to the anolyte, an important step for maintaining both caustic and Cl 2 production rates. Although Li and Na belong to the alkali metal group, significant differences exist in their properties ranging from its hydration shell, cation size and solubilities of its corresponding chloride and hydroxide salts. In particular, the solubility of LiOH is 5 times lower than NaOH (5.3 M vs 25 M) in water (at room temperature). The lower solubility should in principle reduce energy consumption for evaporation and subsequent crystallization of LiOH salts produced from electrolysis of LiCl. In this work, we perform direct electrochemical conversion of LiCl to LiOH in a membrane separated finite gap flow reactor. Expanded nickel mesh was used as cathode and dimensionally stable anode (Ti-RuO 2 mixture) as anode separated by a Nafion bilayer membrane. We achieve a faradaic efficiency of 94% for LiOH at 200 mA/cm 2 with hydroxide transport numbers of 0.06, demonstrating the effectiveness of bi-layer Nafion membranes in minimizing unwanted hydroxide crossover. Furthermore, electrochemical impedance spectroscopy results show decreasing ohmic resistances with an increase in current density due to pore opening and enhanced water transport at higher current densities. These results enable advanced understanding of water transport in lithium chlor-alkali electrolyzers and paves the way for an alternative LiOH production route, vital for the production of lithium ion batteries. Figure 1