Determination of elemental impurities in lithium iron phosphate using ICP-OES

Importance of the topic

Lithium iron phosphate (LiFePO₄) is widely used as a cathode material in lithium-ion batteries because of its high safety profile, long cycle life and cost-effectiveness. Monitoring trace elemental impurities in LiFePO₄ is critical to ensure battery performance, stability and safety. Even low levels of contaminants can alter crystal structure integrity, reduce capacity or introduce safety hazards under high-rate charge/discharge conditions.

Study objectives and overview

This application note demonstrates a reliable analytical approach for quantifying 23 trace impurity elements and the main matrix components (Li, Fe, P) in LiFePO₄. The study employs the Thermo Scientific iCAP PRO Radial ICP-OES to develop a robust method, evaluate figures of merit (linearity, detection limits, precision) and verify performance via spike recovery and stability tests.

Methodology and instrumentation

Sample preparation involved acid digestion of a 0.2000 g LiFePO₄ sample in perchloric acid, followed by dilution to 50 mL. A blank and a series of multi-element standards were prepared covering low (0.05–1 mg/L) impurity levels and higher concentrations for matrix elements. The iCAP PRO Radial ICP-OES system was operated in radial view with a fully demountable extended matrix tolerance (EMT) torch to handle the complex phosphate matrix. Key operating parameters included 1 150 W RF power, 0.6 L/min nebulizer gas flow and continuous wavelength coverage from 167 to 852 nm. Data acquisition and processing were controlled by Qtegra ISDS software.

Main results and discussion

All calibration curves for 26 elements exhibited excellent linearity (R² ≥ 0.9991). Instrument detection limits in solution ranged from 0.19 to 35.9 µg/L, corresponding to method detection limits of 0.02–8.97 mg/kg in the solid sample. Four impurities (Cd, Mo, Se, W) were below detection. Mn was the highest at 240 mg/kg. Spike recovery tests (0.2 mg/L) yielded 90–110% recoveries, confirming accuracy. A two-hour stability experiment on Li, Fe and P (seven measurements) showed RSDs below 0.8%, demonstrating excellent precision.

Benefits and practical applications

The method provides high sensitivity, low detection limits and excellent stability for both trace impurities and major matrix elements. The robust EMT torch design minimizes maintenance and consumable costs, making routine quality control of LiFePO₄ cathode materials in battery manufacturing more efficient and reliable.

Future trends and potential applications

Advances in ICP-OES technology, such as enhanced matrix tolerance and faster simultaneous multi-element detection, will further improve throughput and lower detection limits. Integration with automated sample handling and inline monitoring could support real-time quality assurance in battery production lines. Extensions to other novel electrode materials and recycling streams are also promising.

Conclusion

The iCAP PRO Radial ICP-OES method offers a comprehensive solution for stringent elemental impurity analysis in lithium iron phosphate. Its combination of sensitivity, precision and low operating costs supports critical quality control needs in the lithium-ion battery industry.

References

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