Analysis of Ionic Compounds in Recycled Lithium-Ion Battery Material

Importance of the Topic

Rapid growth in lithium‐ion battery use has intensified concerns over resource scarcity and environmental hazards from battery waste. Effective identification and quantification of ionic compounds in recycled “black mass” are critical for ensuring purity, optimizing recycling processes, and recovering valuable elements while minimizing harmful discharges.

Goals and Study Overview

This study presents a straightforward ion chromatography (IC) approach for both qualitative and quantitative assessment of anionic species in black mass generated by a hydro‐washing recycling process. It aims to verify the method’s reliability for quality control and to highlight major ionic contaminants formed during recycling.

Methodology and Instrumentation

Sample Preparation:

• Weighed 1 g of black mass into polypropylene tubes and brought to 50 mL with ultrapure water.
• Ultrasonicated for 30 minutes, then centrifuged at 4500 rpm for 10 minutes.
• Filtered 2 mL of supernatant through a 0.2 µm PES syringe filter into vials.

IC Conditions:

• Instrument: Shimadzu HIC‐ESP ion chromatograph
• Column: Shim-pack IC-SA2 with SA2(G), maintained at 25 °C (28 °C in conductivity cell)
• Eluent: 1.8 mM Na2CO3 / 1.7 mM NaHCO3, flow rate 1 mL/min
• Detection: Suppressed conductivity

Main Results and Discussion

Qualitative Findings:
The chromatogram of three black mass samples revealed nearly identical profiles. Fluoride emerged as the dominant peak, in line with hydrolysis of LiPF6. Sulfate appeared in unexpected high amounts, likely introduced during sulfuric acid use in recycling. Minor peaks included PO2F2−, PO3F−, and H2PO4−, while some organic P‐based ions coeluted but remained unidentified.

Quantitative Findings:
External calibration (5–100 ppm) yielded R2 > 0.999 for fluoride, phosphate, and sulfate. Measured concentrations:

• Fluoride: 5.8–9.5 g/kg
• Phosphate (H2PO4−): 0.4–1.1 g/kg
• Sulfate: 4.5–6.5 g/kg

Coelution of PO3F− with sulfate prevented its accurate quantification. PO2F2− quantitation was not attempted due to reactive instability. A simpler one‐point standard calibration can suffice for non‐critical confirmatory analyses.

The formation mechanism traces back to LiPF6 equilibrium and stepwise hydrolysis under elevated temperature and moisture, accelerating the generation of fluoride and polyfluorophosphate species. Sulfate likely derives from sulfuric acid treatment rather than native battery additives.

Benefits and Practical Applications

Ion chromatography offers a rapid, reliable screening tool for ionic impurities in recycled black mass. Monitoring fluoride, phosphate, and sulfate levels informs process control, ensuring recycled materials meet stringent purity requirements for reuse in new batteries. This facilitates resource recovery, reduces demand for virgin raw materials, and lowers environmental risk.

Future Trends and Applications

Emerging directions include:

• Integration of multi-element detectors (e.g., ICP-MS coupling) to monitor metal ions alongside anions.
• Automated inline sampling and analysis for real-time process optimization.
• Advanced separation strategies to resolve coeluting species and trace organo-ionic degradation products.
• Development of robust calibration protocols using isotope or standard addition methods to handle reactive analytes.

Conclusion

The demonstrated IC method effectively characterizes and quantifies key ionic species in recycled lithium‐ion battery black mass. Its simplicity and precision support quality control and process development in battery recycling, promoting sustainable material recovery.