Closing the Cathode Loop in Lithium-Ion Battery Recycling: From Metal Recovery to Direct Regeneration of NMC and LFP Cathodes

Lithium-ion battery (LIB) recycling is usually compared across pyrometallurgical, hydrometallurgical and direct routes as if the optimal route were independent of the cathode being recycled. This review argues that cathode chemistry is the governing variable. Following the chain from cathode chemistry and degradation mechanism through pretreatment, recycling route and recovered product to electrochemical validation, we compare LiNixMnyCozO2 (NMC, 111 to 811) and LiFePO4 (LFP), with LiCoO2 and LiNi0.8Co0.15Al0.05O2 as references. LFP degradation is dominated by Li loss and Fe/Li anti-site defects in an intact olivine framework, which makes direct regeneration mechanistically well founded. Ni-rich NMC suffers microcracking, surface reconstruction and proton sensitivity, so its regeneration increasingly becomes upcycling into a different product, whereas hydrometallurgical resynthesis currently has the strongest industrial validation. Reported recovery efficiencies above 95% rarely demonstrate battery-grade products, and published energy estimates for the same route and chemistry differ by a factor of up to about 1.5 because of inconsistent system boundaries. We propose a cathode-to-cathode circularity framework and a minimum reporting set that link material recovery to validation in new cells.