A circular economy approach to lithium iron phosphate/carbon cathode production from iron scrap: Effect of carbon coating strategy on physicochemical and electrochemical characteristics

Iron scrap is an abundant and chemically stable urban waste resource that offers a viable alternative iron source for lithium iron phosphate (LiFePO 4 , LFP) cathode synthesis, bypassing the handling challenges of ferrous sulfate in high-humidity tropical environments.This work establishes a complete scrap-to-cathode route and couples selective sulfuric acid leaching and pH-controlled oxalate precipitation of heterogeneous domestic scrap (∼87 wt% Fe) with a systematic study of carbon-coating strategies. Leaching in 1.5 M H 2 SO 4 at 60–70°C, followed by pH-controlled precipitation at pH 3 recovered phase-pure β-FeC 2 O 4 ·2 H 2 O precursor with quantitative ferric and chromium removal. The precursor was confirmed by XRD, FTIR, and TG-DTA, and its oxidative stability enables direct gravimetric stoichiometric control during LFP formulation. Four LFP/C samples were synthesized via solid-state sintering under a nitrogen atmosphere, varying the carbon source (activated carbon, AC; stearic acid, SA; and their 50:50 mixture) and sintering duration (6 h and 12 h). XRD confirmed single-phase olivine LFP (Pnma) for the mixed-carbon samples (LFP-C, LFP-D), while single-source samples (LFP-A, LFP-B) exhibited Li 3 PO 4 as a secondary phase due to non-uniform local reducing conditions. LFP-C (AC:SA 50:50, 6 h) delivered the best electrochemical performance: specific discharge capacity of 121.2 mAh g −1 , Coulombic efficiency of 79.51%, and superior rate capability across 0.05C–0.2 C, consistent with its finest pore texture (S BET = 7.94 m 2 g −1 ; mean pore radii = 92.8 Å) and most uniform carbon coating arising from the synergistic AC–SA mechanism. Techno-economic analysis on an LFP-C basis yielded an economic potential of USD 9.25 kg −1 LFP with a CO 2 emission intensity of 6.5–7.0 kg CO 2 kg −1 LFP, within the literature range for the oxalate synthesis route. These results demonstrate that scrap-derived LFP is technically feasible, economically rational, and practically deployable as a domestically sourced cathode material for battery manufacturing in developing countries.