Recycling of Spent Lithium-Ion Batteries through Sustainable and Advanced Processing Technologies

Lithium-ion batteries (LIBs) are rapidly gaining acceptance in electric vehicles, energy storage systems and portable electronics, and have brought the need for sustainable end-of-life management to a new level. Again, there is significant recovery value for spent batteries: NMC and NCA cathodes contain 8-15% cobalt and nickel and 1.3-1.9% lithium by mass and LFP cells contain over 43% iron/steel with virtually no cobalt content; therefore, recycling operations need to be chemistry-specific. Hydrometallurgical leaching with 1–4 M inorganic acid (H₂SO₄, HCl, HNO₃) and H₂O₂ as a reductant is able to recover 95–100% of Li, Co, Ni and Mn under moderate conditions (70-95°C and 60-240 min), although pyrometallurgical (smelting) process works above 1000C and tolerates feedstock but losses a substantial amount of lithium and manganese to the slag phase. A number of organic acids (citric, oxalic, lactic and malic acid), which enable comparable Li recovery of 80–100% at 60–100°C, and Co recovery of 80–98%, can also reduce the toxicity of the reagents, but the emergence of deep eutectic solvents (DESs) allows for lower generation of by-products and reactions at even milder conditions (60–90°C), while also presenting challenges in solvent regeneration and selectivity. The use of acidophilic microorganisms like Acidithiobacillus ferrooxidans and Aspergillus niger is an alternative technology for bioleaching, which can extract 85-95% of Li and Co at ambient conditions with a pH range of 1.2-3.5 and with slower processing time. Selective chemical precipitation is achieved in a controlled pH process, allowing for the ability to separate valuable metals from complex leachates in an economical and scalable fashion downstream. This review brings together the above process routes and compares their recovery efficiencies, consumptions of reagents/energy and scalability, and proposes a hybrid thermal-hydrometallurgical route as the most promising one to reach an economically viable, low carbon LIB recycling.