As the production of lithium ion (Li-ion) batteries grows due to increasing demand for electric vehicles, the development of recycling processes for end of life (EOL) batteries as well as cell production scraps, has become increasingly important to enable the recovery of valuable metals such as cobalt, nickel, and lithium. In a closed loop recycling process, the production of lithium hydroxide is often preferred for use in Li-ion cathode materials due to its ease of use in manufacturing and superior electrochemical performance.
In the recycling of EOL Li-ion batteries, a complex material known as ‘black mass’ is produced following mechanical processing. The black mass contains the active materials from the battery electrodes. Black mass can be further processed via a hydrometallurgical route where value metals are leached with sulfuric acid in the presence of a reductant. Value metals are recovered sequentially or simultaneously (pCAM direct recycling) from the leach solution via precipitation, ion exchange, and/or solvent extraction (SX). Lithium is often recovered in the final processing step where it is present as a simplified solution of lithium and sodium sulfate following the upstream removal of divalent impurities and other value metals(1). Sodium is typically present in the lithium-containing solution in a large excess due to the addition of NaOH for neutralization and precipitation in prior processing steps. Highly efficient lithium/sodium separation is required to produce battery-grade lithium hydroxide monohydrate (LiOH•H2O) in a closed loop process.
Syensqo’s CYANEX® 936P solvent extraction reagent was developed for the separation of lithium from sodium, potassium and boron from brines(2-4). CYANEX 936P can also be used to separate lithium and sodium from battery recycling solutions(5,6). A bench-scale study was conducted to define the SX operating parameters required to optimize lithium/sodium selectivity for the production of battery-grade LiOH•H2O from a simulated battery recycling process feed. An SX pilot plant was operated using the optimized parameters, demonstrating the production of a high-purity lithium sulfate solution containing a lithium:sodium selectivity greater than 1000:1 on a mass basis. The lithium sulfate solution produced in the SX pilot plant was converted to lithium hydroxide using electrolysis and then crystallized as battery grade LiOH•H2O. This presentation will review the SX process design and operation of the pilot plant.