Lithium ion batteries (LIBs) are the battery of choice for electric vehicles (EVs) at present and for the foreseeable future. Adoption of EVs at a rate as high as possible is highly desirable since EVs have no direct emissions of green-house gases, smog causing chemicals, or particulate matter. The IEA has developed a roadmap to achieve 50% electrification of passenger vehicles by 2050. Unfortunately the literature shows that by the mid 2020’s lithium producers will not be able to keep up with the demand forecasted by the roadmap without recycling of EV LIBs [1]. To avoid a bottleneck, we calculated that depleated EV LIBs should be recycled and the lithium contained therein be used to make new LIBs at a rate of 28% and 75% in 2025 and 2040 (if the batteries last 5 years) or 40% and 96% in 2025 and 2035 respectively (if the batteries last 10 years).

Currently, LIB cathodes are recycled by leaching the cathodes in acid, recovering transition metals one at a time by solvent extraction, and recovering lithium as lithium carbonate by precipitation with sodium carbonate. Leaching efficiencies of ~100% have been reported, but precipitation efficiencies for lithium have stagnated at 80% for the last 17 years [2], [3]. Additionally the highest purity lithium carbonate purity reported is 99.18% [3]. The purity required for EV LIBs is 99.9 to 99.99%. 

We are developing a novel process to recover lithium from leachate (see the figure below) based on Donnan dialysis with cation exchange membranes (CEM). Lithium ions are extracted first with a monovalent CEM ({1} in the figure) then ions of the other cathode metals (Co, Mn, and Ni) with a polyvalent CEM ({2} in the figure). Lithium is recovered by: neutralizing the acidic Li solution obtained from the first monovalent CEM ({1} in the figure); exchanging Li ions with K ions from a potassium bicarbonate solution pressurized with CO₂ with another monovalent CEM ({3} in the figure); depressurizing the Li enriched KHCO₃ solution, which results in the precipitation of lithium carbonate (the desired product); adding KHCO₃ to make up the K ions exchanged; re-pressurising; and recycling the entire solution past the monovalent cation exchange membrane ({3} in the figure). The transition metal salts recovered in step {2} may be separated by solvent extraction or crystalized and used mixed in making new cathodes with the same chemistry as the leached cathodes.  

The work we have performed so far is equilibrium calculations on each of the stages and preliminary experiments to determine the mass transfer coefficients across the membranes. For steps {1} and {2} we assumed three counter-current equilibrium stages and stripping acid [H⁺] =0.90 M. We assumed a leach solution concentration of [Li⁺] = 0.285 M, [Co⁺⁺] = [Ni⁺⁺] = [Mn⁺⁺] = 0.095 M for step {1} and [Co⁺⁺] = [Ni⁺⁺] = [Mn⁺⁺] = 0.095 M for step {2}. We obtained a theoretical lithium recovery of 97.6% in step {1}, and a Co, Ni, and Mn theoretical recoveries of 99.1% in step {2}. For step {3} we assumed an incoming [Li⁺] = 0.278 M, a stripping solution of [KHCO₃] =2 M and [Li⁺] =0.0935 M (this is the solubility limit of LiHCO₃ prior to re-pressurization with CO₂). The theoretical lithium recovery using three counter-current equilibrium stages was calculated to be 95.3%. Thus the theoretical overall maximum lithium recovery rate given by the process is 93.0%, which is superior to values presented in literature and is achievable in a process free of sodium, where leaching solution is recyclable, and where there is no heating.

Our preliminary experiments reveal that using a Neosepta CMS monovalent cation exchange membrane the transmembrane mass transfer coefficients of  Mn⁺⁺, Co⁺⁺, Ni⁺⁺, when these ions are present at concentrations between 0.005 and 0.095 M and when the stripping acid [H⁺] is between 0.10 and 0.90 M, are less than 1% of the coefficient of lithium. Thus, the Neosepta CMS monovalent CEM provides an excellent separation of lithium from cobalt, nickel, and manganese.

[1]        H. Vikström, S. Davidsson, and M. Höök, “Lithium availability and future production outlooks,” Appl. Energy, vol. 110, pp. 252–266, Oct. 2013.

[2]        P. Zhang, T. Yokoyama, O. Itabashi, Y. Wakui, T. M. Suzuki, and K. Inoue, “Hydrometallurgical process for recovery of metal values from spent lithium-ion secondary batteries,” Hydrometallurgy, vol. 47, no. 2–3, pp. 259–271, 1998.

[3]        X. Chen, Y. Chen, T. Zhou, D. Liu, H. Hu, and S. Fan, “Hydrometallurgical recovery of metal values from sulfuric acid leaching liquor of spent lithium-ion batteries,” Waste Manag., vol. 38, pp. 349–356, 2015.