Synergistic upcycling of mixed spent cathodes to in situ phosphate-protected alloys for durable seawater electrolysis

The simultaneous escalation of lithium-ion battery (LIB) waste and the global demand for green hydrogen necessitates synergistic technologies that close the loop on critical materials. However, the heterogeneity of spent cathodes, coexistence of layered oxides (NCM) and olivine phosphates (LFP), renders conventional separation-dependent recycling processes economically burdensome. Herein, we report a mechanochemical strategy that bypasses separation by directly upcycling mixed cathode streams into a high-performance alloy/phosphate core–shell electrocatalyst (NF–P) for seawater oxidation. Distinct from approaches relying on external phosphorus sources, this method leverages intrinsic phosphate groups and transition metals from spent LFP/NCM to in situ construct a FeCoNiMnLi alloy core encapsulated by a phosphate protective layer. The waste-derived phosphate shell effectively suppresses chloride-induced corrosion, enabling NF–P to deliver stable operation for over 300 h in alkaline seawater, far exceeding the unprotected NF counterpart. In a practical seawater membrane electrode assembly electrolyzer, NF–P sustains 100 mA cm⁻² for over 200 h. This work demonstrates a scalable waste-to-hydrogen pathway, transforming mixed LIB waste into functional electrocatalysts for sustainable seawater electrolysis. © 2026 The Authors.