Accurate analysis of major components and trace level impurities in cathode active materials used in lithium ion battery production

Significance of the topic

Lithium-ion battery performance, lifetime and safety are strongly dependent on the chemical composition and purity of cathode active materials. Quantitative control of major components (Li, Ni, Mn, Co in NMC-type cathodes) together with trace-level elemental impurities is essential for quality control of precursor materials and finished cathodes used in consumer electronics and electric vehicles. Analytical techniques must therefore deliver high sensitivity, interference-free results and robust operation with high total dissolved solids (TDS) resulting from acid digests of these materials.

Goals and overview of the study

This application note demonstrates a robust analytical workflow for simultaneous quantification of major components and trace impurities in acid-digested NMC cathode materials using triple quadrupole ICP-MS (Thermo Scientific iCAP MTX). The study aims to show accurate quantification, interference removal for difficult analytes (e.g., As, S, Se), and practical benefits of Argon Gas Dilution (AGD) for direct analysis of high-TDS digests without laborious off-line dilutions.

Used instrumentation

• ICP-MS: Thermo Scientific iCAP MTX (triple quadrupole ICP-MS)
• Autosampler: Thermo Scientific iSC-65
• Sample introduction: iCAP MX series nebulizer, cyclonic quartz spray chamber, quartz injector and torch
• Collision/reaction cell: QCell operated with pure oxygen as reactive gas (TQ-O2 mode)
• Matrix handling: Argon Gas Dilution (AGD), intelligent matrix handling features to reduce matrix exposure
• Digestion: Microwave-assisted digestion (Milestone ETHOS One) using aqua regia (HNO3/HCl Optima grade)

Methodology and sample preparation

• Samples: Two NMC cathode materials were analyzed: NMC 111 (equal Ni:Mn:Co) and NMC 811 (Ni-rich).
• Sample prep: ~0.1 g aliquots were digested by microwave-assisted digestion in aqua regia (program ramp to 230 °C, hold 25 min) and gravimetrically diluted to 100 mL in 2% HNO3.
• Calibration and QC: Multi-level calibration was prepared to cover major components at mg·L-1 to %-level equivalents and trace impurities down to sub-µg·L-1; QC samples measured every 10 samples.
• Internal standards: Sc, Rh, Tb, Tl continuously introduced online (Y-connector) to track matrix suppression and instrument stability.
• Instrument settings (representative): AGD Level 5, QCell O2 flow ~0.26 mL·min-1, RF power 1550 W, nebulizer flow ~0.497 L·min-1, cool gas 14 L·min-1, sampling depth 8 mm, spray chamber temperature ~2.7 °C.
• Interference control: Triple quadrupole operation with oxygen reaction chemistry in the cell removed polyatomic interferences (e.g., 59Co16O+ on As) and enabled interference-free measurement of S and other challenging analytes.

Main results and discussion

• Linearity and detection limits: Calibration exhibited excellent linearity (R2 generally >0.999) across targeted ranges. Instrumental detection limits (IDLs) for trace elements were at sub-µg·L-1 to single µg·L-1 levels (examples: Li ~1.7 µg·L-1; Ni ~0.065 µg·L-1; Co ~0.026 µg·L-1), sufficient for impurity monitoring.
• Major component accuracy: For NMC 111 measured values matched certified values with recoveries near 100% (Li 7.8% measured vs 7.6% certified, Mn 16.3% vs 16.0%, Co 20.1% vs 20.3%, Ni 20.8% vs 20.2%). For NMC 811 results also agreed within expected ranges (e.g., Ni ~51.4% measured vs 51.6% certified). One noted case: Mn in NMC 811 showed elevated nominal recovery (~127%) consistent with a known high variability of the certified value.
• Trace impurities: Measured trace elements in both materials were at low mg·L-1 levels or below typical limit values. Examples: Na 121.5 mg·L-1 (NMC 111) and 54.9 mg·L-1 (NMC 811), S 1130 mg·L-1 (NMC 111) and 295 mg·L-1 (NMC 811), Fe 5.0 and 3.8 mg·L-1 respectively. Most impurities were well below the stated limit thresholds for these materials.
• Accuracy and precision: Spike recoveries for trace analytes (50 µg·L-1 level) averaged within 80–120% with relative standard deviation <5% across replicates. QC samples run periodically returned within ±10% of target, and internal standards tracked between 80–120% of expected response during multi-hour sequences.
• Robustness: Use of AGD and intelligent matrix handling minimized matrix deposition and reduced the need for frequent maintenance. Continuous monitoring of internal standards showed stable performance over extended runs without downtime.

Benefits and practical applications of the method

• Direct analysis of high-TDS digests: AGD enabled direct placement of digests on the autosampler, avoiding manual dilutions and accelerating throughput while reducing operator error.
• Superior interference removal: Triple quadrupole ICP-MS operated with oxygen removed common polyatomic interferences, enabling reliable quantification of As, S and other problematic analytes without species-specific corrections.
• High sensitivity and low IDLs: The method provided detection limits appropriate for both major component quantification and trace impurity control, supporting raw material qualification and final product QC.
• Operational robustness: Intelligent matrix handling and AGD lowered interface contamination and maintenance frequency, improving laboratory uptime for routine battery materials analysis.

Future trends and potential applications

• Wider adoption of TQ-ICP-MS for battery materials: As cathode chemistries diversify (high-nickel, nickel-free alternatives, solid-state precursors), triple quadrupole ICP-MS will be increasingly valuable for robust interference management and trace-level impurity control.
• Integration with automated sample prep and data workflows: Combining AGD-enabled direct analysis with automated digestion and LIMS connectivity can further increase throughput and traceability in production and R&D labs.
• Expanded speciation and surface analysis linkages: Complementary methods (e.g., XPS, LIBS, single-particle ICP-MS) integrated with bulk elemental data can better relate trace impurities to electrochemical performance and degradation mechanisms.
• Regulatory and supply-chain testing: Reliable, interference-free elemental analysis will be needed for incoming material screening, supplier audits and regulatory compliance as battery recycling and resource sourcing become more regulated.

Conclusion

The presented triple quadrupole ICP-MS workflow demonstrates accurate, sensitive and robust analysis of both major components and trace impurities in acid-digested NMC cathode materials. Key enabling factors are the use of AGD for direct analysis of high-TDS samples, oxygen reaction chemistry in the QCell for interference removal, and continuous internal standard monitoring for stability. The method supports efficient QC and R&D needs in battery materials laboratories by reducing manual dilution steps, limiting maintenance, and delivering reliable quantitation across a wide concentration range.

References

• Thermo Fisher Scientific. Application note AN003968-EN (2025): Accurate analysis of major components and trace level impurities in cathode active materials used in lithium ion battery production.