Hydrogen reduction of simulated black mass from spent lithium-ion batteries for stainless steel production

Using hydrogen, a direct reduction route is demonstrated for recycling lithium‑nickel‑cobalt‑manganese oxide (LNCMO, from cathodes of spent Li-ion batteries) into a metallic alloy which can be used as stainless-steel feedstock. Upon heating under flowing hydrogen from 25 to 950 °C, a stepwise reduction is observed via in-situ X-ray diffraction: LiNi₀ . ₆Co₀ . ₂Mn₀ . ₂O₂ (LNCMO) → Ni₀ . ₆Co₀ . ₂Mn₀ . ₂O (NCMO) → Ni₀ . ₆Co₀ . ₂Mn₀ . ₂ (metallic alloy). Additives (5% Al, 5% Cu, and 3% graphite) to the LNCMO powder, simulating black-mass recycling impurities, exert distinct effects: (i) Al accelerates LNCMO → NCMO decomposition by gettering H₂O and forming Al₂O₃, (ii) Cu enhances LNCMO reduction (consistent with catalysis of H₂ dissociation), forming a Ni-Co-Mn-Cu solid solution, and (iii) graphite shows synergy with hydrogen during reduction of LNCMO. The Ni-Co-Mn-Cu alloy created from black mass is arc-melted together with Fe and Cr, achieving a Fe–18.1Cr–8.2Ni–2.9Co–0.4Mn–1.0Cu (wt%) composition close to the value of 304 stainless steel, with additional Co and Cu in solid solution. Slag is sequestering Li–Al–O inclusions and residual oxidized Cr and Mn species. This study demonstrates the technical feasibility of upcycling black mass from spent Li-ion batteries into stainless-steel feedstock through H₂ reduction. Subject to confirmation by ongoing techno-economic and life cycle assessments, the process may provide a scalable and lower-carbon link between battery recycling and sustainable metallurgy.