A recent article in Advanced Energy Materials discussed a method for restoring the composition of degraded LiΔNi0.6Co0.2Mn0.2O2 (NCM) cathodes using spontaneous galvanic corrosion at room temperature. The process utilized an aluminum current collector as the reducing agent.
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Background
The growing demand for lithium-ion batteries (LIBs) in electric vehicles and energy storage systems poses risks to raw material supply. Recycling end-of-life LIBs is critical to supporting the future LIB market sustainably.
Traditional recycling methods recover valuable metals but rely on hazardous chemicals and high energy consumption to break down cathodes and reproduce them. Direct cathode recycling offers a more sustainable alternative by addressing these challenges.
Direct cathode recycling strategies have been proposed for LiFePO4, LiCoO2, and Li(NixCoyMnz)O2. These involve direct recovery of the spent cathode materials to their original state, thereby reducing the process cost and environmental load compared to the cathode-destructive hydrometallurgy method, which transforms spent cathode materials into raw metal precursors.
This study introduces a solution-based restoration method for NCM cathodes utilizing galvanic corrosion with an aluminum current collector.
Methods
Commercially procured NCM622 and graphite electrodes were used as the cathode and anode, respectively. A pouch cell was prepared in an argon-filled glove box using these electrodes and an Al2O3-coated polyethylene separator to obtain a Li-deficient NCM cathode (L-NCM) and a degraded NCM cathode (D-NCM).
For L-NCM, the pouch cell was cycled at 0.1 C in the voltage range of 2.5 to 4.2 V and stopped after the 4th cycle discharge process in the discharge state. Subsequently, the pouch cell was disassembled in the argon-filled glove box, washed with dimethyl carbonate (DMC), and dried for 12 h at 80 °C under vacuum to remove the residual solvent.
For D-NCM, the pouch cell was cycled at 0.5 C in the 2.5 to 4.2 V voltage range for 600 cycles until the capacity retention reached 84.7 %. This cycled pouch cell was disassembled in an argon-filled glove box to collect the D-NCM cathode. The spent cathode was washed and dried the same as the L-NCM cathode.
The L-NCM and D-NCM cathodes were restored using LiBr/MeCN solution (both in-cell and outside). Additionally, the cathode mixture powder was collected by scraping from the aluminum foil to investigate the role of aluminum in the restoration reaction, which lasted for 1 to 24 hours.
The prepared electrode specimens were characterized via X-ray diffraction (XRD), neutron diffraction (ND), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible spectroscopy. Zero resistance ammeter analysis and electrochemical tests were also performed on the NCM electrodes.
Results and Discussion
Restored L-NCM (R-L-NCM) displayed a reversible capacity comparable to pristine NCM (P-NCM). The chemical composition of R-L-NCM, Li1.087Ni0.6Co0.2Mn0.2O2, was similar to that of P-NCM, Li1.045Ni0.6Co0.2Mn0.2O2. This restoration was achieved only when the aluminum current collector remained attached to L-NCM. In contrast, R-L-NCM detached from the aluminum current collector during restoration exhibited a composition of Li0.868Ni0.6Co0.2Mn0.2O2, with the reduced restoration level linked to bromide ion oxidation.
The restoration rate of L-NCM was influenced by reaction time and LiBr concentration. Restoring the composition to Li1.05Ni0.6Co0.2Mn0.2O2 required over 12 hours, while Li0.88Ni0.6Co0.2Mn0.2O2 was restored in less than one hour. The restoration rate decreased as the lithium content in LiΔ Ni0.6Co0.2Mn0.2O2 increased, allowing for uniform lithium content across spent cathodes with varying lithium levels.
The restored D-NCM (R-D-NCM) cathode displayed reversible capacity comparable to that of pristine NCM. Cross-sectional SEM images revealed no pits in the Al current collector after restoration, indicating that electrons for cathode restoration were provided by the sacrificial corrosion of the Al anode.
The study evaluated the environmental and economic impacts of four direct cathode recycling methods—molten-salt regeneration, solid-state regeneration, hydrothermal regeneration, and galvanic corrosion regeneration—for processing 1000 tons of NCM622 annually. Galvanic corrosion regeneration demonstrated lower water, energy, and cost requirements, highlighting its potential advantages.
Conclusion
The researchers demonstrated a room-temperature, solution-based direct cathode restoration method using the spontaneous galvanic corrosion of an aluminum current collector. This process effectively restored lithium inventory losses in NCM cathodes caused by initial-cycle irreversible capacity loss and lithium depletion during extended cycling.
Bromide ions facilitated the restoration by reducing the oxidized transition metals in the NCM cathode material and promoting aluminum corrosion. The energy released from aluminum corrosion further reduced the transition metals, while lithium ions in the solution replenished the Li-deficient cathode, restoring its composition to a near-pristine state. This method requires fewer resources and less energy, supporting more sustainable LIB recycling practices.
Lithium-Ion Battery Recycling: Transforming Materials with Raman Spectroscopy
Journal Reference
Song, J., et al. (2024). Reviving Spent NCM Cathodes via Spontaneous Galvanic Corrosion in Ambient Atmospheric Condition. Advanced Energy Materials. DOI: 10.1002/aenm.202402106, https://onlinelibrary.wiley.com/doi/10.1002/aenm.202402106
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