Reuse for Photocatalytic and Pseudocapacitor Applications and Electrochemical Relithiation of the Cathode from Spent LiFePO4 Lithium-Ion Batteries
Name: MARCELA DE CAMARGO CHAVES
Publication date: 27/08/2026
Examining board:
Name |
Role |
|---|---|
| MARCOS BENEDITO JOSE GERALDO DE FREITAS | Presidente |
| MARIA DE FATIMA FONTES LELIS | Examinador Interno |
| PEDRO VITOR MORBACH DIXINI | Examinador Externo |
Summary: The use of lithium iron phosphate (LiFePO, LFP) batteries has increased significantly in the field of electric mobility. At the end of their service life, these batteries contribute to the growing generation of waste, highlighting the need for sustainable strategies for their reuse and recycling. In this work, the spent LFP cathode material was reused in new applications and directly regenerated through an electrochemical relithiation route. The spent LFP cathode material was characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TG/DTG), specific surface area analysis, inductively coupled plasma optical emission spectrometry (ICP-OES), and energy-dispersive X-ray spectroscopy (EDS). The results revealed the predominance of the LiFePO and FePO phases, a specific surface area of 24.44 m² g¹, a mesoporous structure, and partial lithium deficiency resulting from battery aging. The reuse of the spent LFP cathode material was achieved through a simple mechanical route with low cost and reduced environmental impact. The recovered cathode material was applied as both a photocatalyst and a pseudocapacitor electrode. As a photocatalyst in the heterogeneous photo-Fenton process for methylene blue decolorization, it achieved a degradation efficiency of 93.4% within 30 minutes of reaction. The catalytic performance was maintained over four consecutive reuse cycles. Raman, FTIR, and XRD analyses confirmed the preservation of the material's structural characteristics after repeated photocatalytic cycles. ICP-OES analysis showed that the concentrations of leached metals remained below the limits established by CONAMA Resolution No. 430/2011, confirming the material's chemical stability and low environmental contamination potential after the photocatalytic process. As a pseudocapacitor electrode in 1.0 mol L¹ KOH electrolyte, the material exhibited a specific capacitance of 113 F g¹ after 500 charge-discharge cycles at a current density of 1.0 A g¹, an energy density of 46.99 Wh kg¹, and a power density of 850 W kg¹, demonstrating excellent electrochemical stability. Kinetic analysis based on the Dunn method indicated that the charge storage mechanism was predominantly diffusion-controlled at low scan rates, with an increasing capacitive contribution at higher scan rates. The second part of the study focused on the direct regeneration of the cathode material through electrochemical relithiation using different current densities. XRD, FTIR, and Raman analyses demonstrated the structural regeneration of LiFePO through the conversion of the FePO phase into LiFePO via the intercalation of Li ions into the FePO crystal structure. These results demonstrate that the reuse and direct regeneration of spent LiFePO cathode materials are viable,
environmentally sustainable strategies aligned with the principles of the circular economy. The reuse approach enables applications in environmental remediation and electrochemical energy storage, while electrochemical relithiation promotes structural regeneration of the cathode material, representing a promising alternative for the recovery of spent LiFePO batteries.
