Determination of Elemental Impurities in Silicon-Carbon Anode Materials for Lithium-Ion Batteries by ICP-OES

Significance of the Topic

The rapid expansion of the lithium-ion battery (LIB) market, driven by electric vehicles and renewable energy storage, places stringent demands on anode materials. Silicon-carbon composites offer higher specific capacity than traditional graphite but require rigorous control of elemental impurities and dopants to maintain electrochemical performance and long-term stability. Reliable, sensitive analytical methods are essential for quality assurance in material production.

Objectives and Study Overview

This study aimed to develop and validate a robust multi-element analysis method for 25 trace and major elements in high-purity graphite, pure silicon, and silicon-carbon composite anode materials. The procedure follows Chinese national standards GB/T 24533-2019 and GB/T 38823-2020, employing microwave digestion and inductively coupled plasma optical emission spectrometry (ICP-OES) on the Agilent 5800 Vertical Dual View (VDV) system.

Methodology

Sample preparation and calibration protocols:

• Microwave digestion of solids (graphite, silicon, and 9:1 graphite:silicon composite) in aqua regia at 200 °C for 30 min using a Mars 6 system.
• Dilution to a 28.8 % aqua regia matrix; 10× dilution for silicon-carbon digests, followed by post-digestion spiking at three concentration levels.
• Calibration standards from multi-element (0–0.2 mg/L) and single-element stock solutions for Al, Fe, Ca, K, Mg, and Na up to 2 mg/L.
• Internal standards (Y, Rb) and continuing calibration blank/verification checks every 10–12 samples.
• Quality control via spike recovery tests in graphite (pre-digestion) and silicon-carbon (post-digestion) matrices.

Used Instrumentation

• Agilent 5800 VDV ICP-OES with SeaSpray concentric nebulizer, cyclonic spray chamber, and Easy-Fit fully demountable torch.
• Solid-state RF generator (27 MHz) and Cooled Cone Interface (CCI) for plasma stability and reduced interferences.
• Agilent SPS 4 autosampler and ICP Expert software for method control and data processing.
• Mars 6 Microwave Digestion System for reproducible sample dissolution.

Main Results and Discussion

Calibration linearity (R≥0.999) was achieved across all 25 elements with limits of detection/quantitation well below 1 mg/kg (graphite basis). The Fast Automated Curve-fitting Technique (FACT) effectively resolved spectral overlaps (e.g., Na 589.592 nm vs. Ba 589.612 nm). Spike recoveries ranged from 90 % to 110 %, confirming digestion and measurement accuracy. Long-term stability tests over 7.5 h showed measurement drift within ±10 % and replicates’ RSDs under 5 %. Elemental impurity profiling revealed low levels in 99.99 % graphite (Na ~32 mg/kg; Ca, K, Fe, Al <1 mg/kg), higher concentrations in pure silicon (Fe, Al >3000 mg/kg; Ca ~867 mg/kg), and proportionally reduced levels in the silicon-carbon composite (~10 % of silicon values).

Benefits and Practical Applications

• Provides a standardized, high-throughput QC method for LIB anode materials that meets industry and national standards.
• Enables reliable detection of critical dopants and contaminants for performance optimization.
• Supports material suppliers and battery manufacturers in ensuring consistency and regulatory compliance.

Future Trends and Potential Applications

• Extension to other battery components (cathode materials, electrolytes) and new chemistries.
• Integration with ICP-MS for ultratrace analysis and isotopic studies.
• Automation and data analytics for real-time process monitoring in manufacturing.
• Development of portable/lightweight plasma instruments for field-based testing.

Conclusion

The Agilent 5800 VDV ICP-OES combined with microwave digestion delivers accurate, precise, and stable multi-element determination in graphite and silicon-carbon anode materials. The method aligns with GB/T standards, offering a robust QC tool to support the growing demand for high-performance LIBs.

References

1. Markets and Markets. (2022). Lithium-ion battery market – Global forecast to 2031.
2. Nzereogu P.U., et al. (2022). Anode materials for lithium-ion batteries: A review. Applied Surface Science Advances, 9, 100233.
3. Cheng H., et al. (2021). Advanced anode materials of lithium-ion batteries. Journal of Energy Chemistry, 57, 451–468.
4. Li X., et al. (2020). Silicon/carbon anode materials for lithium-ion batteries. ChemElectroChem, 7(200), 4289–4302.
5. GB/T 24533-2019. Graphite negative electrode materials for lithium-ion battery (China National Standard).
6. GB/T 38823-2020. Silicon-carbon anode materials for lithium-ion battery (China National Standard).