Multifunctional additive-driven efficient critical metal recovery from spent lithium-ion batteries via all-solid-state subcritical process

The sustainable recycling of spent lithium-ion batteries (LIBs) is crucial for ensuring resource security and minimizing environmental impact. To address this challenge, we developed an innovative all-solid-state (ASS) subcritical process using FeCl₂·4H₂O as a multifunctional reaction mediator. This method achieves near-quantitative recovery of valuable metals (99.9%) from LiNi _x Co _y Mn _z O ₂ (NCM) cathode materials. In our process, spent NCM are directly mixed with solid FeCl₂·4H₂O and heated under controlled subcritical conditions. This initiates a rapid structural breakdown of the cathode material, facilitated by a synergistic redox reaction involving Fe²⁺ and in-situ generated HCl. As a result, the valuable metals are efficiently leached out in just 10 min, using an ultra-low amount of water (low liquid-solid ratio). Mechanistic investigations reveal a dual activation pathway: thermal hydrolysis of Fe²⁺ generating proton flux for lattice protonation, and chloride-assisted electron transfer inducing transition metal reduction. Molecular dynamics (MD) simulations and Density Functional Theory (DFT) calculations quantitatively demonstrate the synergistic effect of different components of FeCl₂⋅4H₂O in destabilizing the NCM lattice framework. This closed-loop process exhibits exceptional sustainability metrics, including zero acid consumption, significant energy reduction, and substantially reduced aqueous emissions. The methodology establishes a techno-economically viable paradigm for next-generation green battery recycling infrastructures.