Upcycling of Cathode Materials from Industrial Lithium Iron Phosphate Black Mass: Process Design and Optimization

Abstract

Lithium is the principal active material for clean energy storage and transformation, and its stable supply is critical to achieving international climate objectives. Projected supply challenges and unprecedented demand for Li have revealed the necessity of developing spent Li-ion battery recycling as a secondary Li resource stream. Following the optimization of Li-selective leaching from industrial grade LiFePO4 black mass by formic acid and H2O2, this work explores the treatment of the derived liquor, with the objective of advancing the process to technology readiness level 5. Purification of the liquor was affected by multi-step precipitation of Al, Co, Ni, Mn, Fe, and Cu hydroxides. Processes for Li recovery by the addition of Na3PO4, H3PO4, and Na2CO3 were optimized. Interactions of reaction temperature, pH, and precipitant dosage were evaluated, and compared to synthetic solutions. The kinetics of Li2CO3 precipitation from the proprietary liquor were investigated. The conversion of Li3PO4 to LiOH by Ca(OH)2 causticization was explored. In 2-L validation experiments, the maximum recovery of Li3PO4 and Li2CO3 from the 6.5 g Li/L leachate were 98.92% and 74.73%, respectively. Li2CO3 recovery by antisolvent addition was investigated, increasing Li2CO3 recovery to 94.42% with the addition of 1:1 v/v isopropanol. The lithium content of Li2CO3 and Li3PO4 met 97.20% and 98.00%. Li2CO3 purity exceeded 99.50% after CO2 digestion and thermal decomposition recrystallization. Impurity concentrations met battery grade specifications in both products. This work provides a basis for the development of a continuous reactor, capable of upcycling Li-bearing black mass into different cathode precursors.