Analysis of Elemental Impurities in Lithium Iron Phosphate Cathode Materials for LIBs by ICP-OES

Význam tématu

The rapid growth of the lithium-ion battery market, driven by electric vehicles and grid-scale energy storage, underscores the need for strict quality control of cathode materials. Lithium iron phosphate (LFP) offers a cobalt-free alternative prized for safety, cycle life, and thermal stability. Precise measurement of elemental impurities in LFP is essential to ensure battery performance, longevity, and safety.

Cíle a přehled studie

This study develops and validates a robust, accurate ICP-OES method for simultaneous quantification of 31 elements—including both major matrix constituents (Li, Fe, P) and trace impurities—in high-purity LiFePO4 cathode powders. The method employs Agilent 5800 Vertical Dual View (VDV) ICP-OES and IntelliQuant Screening to optimize wavelength selection and calibration ranges.

Použitá metodika a instrumentace

Sample Preparation:

• Approximately 0.1 g of LFP powder digested in 5% aqua regia (6 mL HCl, 2 mL HNO3) using a Mars 6 microwave system at 200 °C for 20 minutes.
• Spiked samples prepared at 0.1 mg/L for recovery studies; long-term stability samples at 0.1 mg/L in 100 mL final volume.

Calibration and Standards:

• Multi-element and single-element standards diluted in 5% AR for traces (0–0.5 mg/L) and higher ranges for Li (0–100 mg/L), Fe (0–1000 mg/L), and P (0–500 mg/L).
• Internal standard solution of Y (5 mg/L) and Rb (75 mg/L) added online.

Instrumentation:

• Agilent 5800 VDV ICP-OES with SSRF 27 MHz generator, Cooled Cone Interface, and vertical plasma for axial (traces) and radial (matrices) views.
• SeaSpray nebulizer, cyclonic spray chamber, argon humidifier, and Intelligent Rinse for optimized washout.
• Fitted background correction (FBC) and FACT spectral deconvolution to eliminate interferences.

Hlavní výsledky a diskuse

Calibration and Detection Limits:

• Excellent linearity (R>0.9999) across all elements and working ranges.
• Method detection limits below 1 mg/kg for most trace elements in the solid sample.

Accuracy and Precision:

• Spike recoveries for LFP samples between 90 % and 110 % for all 31 elements, confirming digestion and analytical accuracy.
• Lab-fortified blank recoveries within ±10 %, demonstrating minimal matrix effects.

Long-Term Stability:

• Over nine hours and 236 measurements without recalibration, spike recoveries displayed %RSD≤2.2 %, evidencing instrumental robustness.

Background Correction:

• FACT effectively resolved close spectral overlaps (e.g., P interference on Cr), ensuring accurate trace quantification.

Přínosy a praktické využití metody

This ICP-OES method enables high-throughput, simultaneous quantification of both major elements and trace impurities in LFP cathode materials. Its accuracy, precision, and stability make it ideal for routine quality control in battery manufacturing and recycling, supporting product safety and performance specifications.

Budoucí trendy a možnosti využití

Future developments may extend this approach to advanced cathode chemistries (NMC, NCA), incorporate automated sample handling and AI-driven data analysis for real-time monitoring, and integrate with battery recycling workflows to ensure compliance with environmental regulations.

Závěr

The validated Agilent 5800 VDV ICP-OES method provides reliable, precise, and stable measurements of 31 elements in LFP cathode materials. Its robust performance and minimal drift support stringent quality control and R&D efforts in the evolving lithium-ion battery industry.

Reference

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5. EVlithium, LiFePO4 Batteries VS Ternary(NMC) lithium batteries, accessed September 2023.
6. Agilent Technologies, A Practical Guide to Elemental Analysis of Lithium Ion Battery Materials Using ICP-OES, publication 5994-5489EN.