Demand for lithium-ion (Li-ion) rechargeable batteries (LIBs) is growing rapidly due to their widespread use in portable electronic devices and electric vehicles (EVs). There is also a growing need for battery storage associated with renewable electricity generation. LIBs currently provide the best combination of cost, capacity, charging speed, and lifetime. Figure 1 illustrates the four key components of a LIB: the anode, cathode, electrolyte, and separator.

During LIB charging, Li ions are released from the cathode, migrate through the electrolyte, and are stored in the anode. During discharge, the reverse process occurs, with Li ions migrating from the anode to the cathode.

Diagram illustrating a lithium-ion battery. The anode and cathode exchange Li+ ions via an electrolyte and separator during charge/discharge

Figure 1. Schematic of a lithium-ion battery showing the migration of Li+ ions during charging and discharging cycles.

LIB component materials

The performance, lifetime, and safety of a LIB are affected by the electrochemical properties and composition of the anode, cathode, and electrolyte. Monitoring elemental contaminants in these components and the raw materials they are made from is therefore essential for manufacturing quality control (QC) and to support the development of new battery materials.

  • Electrolytes: Various Li salts are used in the LIB electrolyte, including lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium perchlorate (LiClO4). Salts such as lithium bis(fluorosulfonyl)imide (LiFSl) are also used to improve performance.
  • Cathodes: The cathode active material (CAM) is typically Li combined with a transition metal oxide such as cobalt oxide (LCO), nickel cobalt aluminum oxide (NCA), or nickel cobalt manganese oxide (NCM or NMC). Alternative cathode materials (not based on cobalt) include lithium iron phosphate (LFP) and lithium manganese oxide (LMO).
  • Anodes: Since the early days of LIB development, graphite has been used almost exclusively for the anode material in all LIBs, with the Li ions being stored in the lithiated graphite compound LiC6.

Standard methods for impurity analysis of LIB materials

LIB raw material suppliers and battery manufacturers require accurate analytical methods to determine a range of elements such as Fe, Ca, Mg, Cu, Zn, Si, Al, and Na in LIB raw materials and components. In China, standard methods YS/T 928.4, GB/T 24533-2019, GB/T 26300-202, and GB/T 26008-2020 currently specify ICP-OES as the recommended technique for determining contaminant elements. However, Chinese RoHS standard method GB/T 39560.5 specifies ICP-MS as one of the recommended analytical techniques for hazardous heavy metals such as Cd, Hg, and Pb in electrical and electronic equipment. For certain applications, such as measuring contaminants at lower levels to evaluate new and advanced battery materials, ICP-OES cannot achieve sufficiently low detection limits. Due to the sensitivity and spectral simplicity of ICP-MS, the technique is increasingly used for these purposes.

This article provides an overview of applications in LIB manufacturing using Agilent ICP-MS and ICP-QQQ instrumentation. It highlights the importance of monitoring trace elements to identify contaminants that affect product performance and safety.

Electrolytes: Trace contaminant analysis using ICP-MS

The multi-element capability of the Agilent 7900 ICP-MS was demonstrated by the measurement of 68 elements in lithium salts used in electrolytes, including LiPF6, LiBF4, LiClO4, and LiFSI. Agilent ICP-MS systems are equipped with the ORS4 collision/reaction cell, which is optimized for effective removal of polyatomic ions using helium (He) mode and kinetic energy discrimination (KED). So, to remove multiple polyatomic ion overlaps in the complex and variable sample matrices, a single set of consistent He-KED mode conditions were used for most elements. For intense background overlaps on difficult elements such as Si, Ca, and Fe, the optional hydrogen (H2) cell gas line provided even more effective interference control (see Figure 2).1

Standard addition calibration curves. Left: Si, concentration of 59.047 μg/kg. Right: Ca conc of 7.907 μg/kg. Blue data points and regression lines are shown.
Standard addition calibration curves. Left: Fe, concentration of 2.227 μg/kg. Right: Cr conc of 0.374 μg/kg. Blue data points and regression lines are shown.
Standard addition calibration curves. Left: Ni, concentration of 1.266 μg/kg. Right: Ca conc of 0.090 μg/kg. Blue data points and regression lines are shown.

Figure 2. Standard addition calibrations* for trace element contaminants in LIB electrolyte salt, LiFSl, measured using the Agilent 7900 ICP-MS. Reproduced from this Agilent application note.

*Agilent ICP-MS MassHunter software includes an automated function where the standard addition calibration is converted automatically to an external calibration during the batch analysis. This function means that subsequent samples of the same type can be run and quantified without needing to be individually spiked with standards. This capability removes one of the most significant barriers to analysts adopting standard addition for routine analysis.

Cathodes: Screening cathode materials for impurities

The combination of robust plasma conditions (CeO/Ce ratio <1%), UHMI, and He-KED mode provides effective control of spectral overlaps, enabling Agilent ICP-MS systems to fully characterize trace level contaminants in cathode materials.2 This technology also enables sample screening using Agilent IntelliQuant software. When selected as part of a quantitative method, a Quick Scan acquisition provides full mass data for every sample, requiring only two extra seconds of acquisition time per sample. Quick Scan data provides identification of any contaminants not included in the quantitative method, as illustrated for the NCM cathode material shown in Figure 3. The Quick Scan data is processed by IntelliQuant to provide semiquantitative concentrations without using element-specific standards.

ICP-MS quick scan spectrum showing peaks labeled for various elements like Na, Si, Fe, and Bi. Peaks vary in height, indicating concentrations.

Figure 3. Agilent 7900 ICP-MS He-KED mode Quick Scan spectrum showing trace elements in digested LiNiCoMn (NCM) cathode material. Intense peaks include Co and Ni, and internal standards, Sc, Ge, Rh, In, Tb, Lu, and Bi.

Anodes: determination of low-level contaminants in a graphite material

How robust are Agilent ICP-MS instruments for the analysis of complex LIB-related samples? In this work, 45 elements were measured in aqua regia digests of two graphite-based anode materials by the Agilent 7850 ICP-MS using a single set of conditions.3 The sample digests contained high acid levels and nominally 2.5% total dissolved solids (TDS).

To test the robustness of the method, the analytical sequence comprising digested samples (six digests for each of the two graphite samples), method blanks, QC checks, and spike recovery solutions was analyzed repeatedly over 10 hours. Tb, Lu, and Bi were used as the internal standards (ISTDs).

As shown in Figure 4, the ISTD recoveries remained stable throughout the run, within the ±20% limits indicated by the red dotted lines. The consistent, stable ISTD recoveries show that the robust plasma of the 7850 ICP-MS with UHMI aerosol dilution was able to decompose the matrix effectively, enabling excellent stability to be maintained over the long run. Also, the lack of drift confirms that no significant matrix deposition occurred on the interface during the sequence. The results demonstrate robustness and high matrix tolerance of the 7850 ICP-MS for the simple, routine elemental analysis of graphite anode materials.

A line graph showing internal standard recovery percentages for samples and standards, with data points clustered around 100%. Four lines in turquoise, purple, orange, and blue represent elements.

Figure 4. Recovery of ISTDs measured over 10 hours (more than 200 acquisitions) using the Agilent 7850 ICP-MS. Due to limited space, not all sample names are shown. Reproduced from this study.

Purity of LIB raw materials: Triple quadrupole ICP-MS for even lower DLs

Single quadrupole ICP-MS systems provide the low detection limits needed to comply with current industry requirements for LIB production. For advanced battery manufacturing and for research into new materials and processes, an Agilent 8900 Triple Quadrupole ICP-MS (ICP-QQQ) provides even lower detection limits. ICP-QQQ is especially useful for analytes that are affected by matrix-based spectral overlaps, enabling an extensive range of elements to be analyzed using a single multitune method. This capability is demonstrated by the analysis of 64 elements in lithium carbonate and the calculation of the percentage purity of the material—a measure manufacturers and suppliers use to grade their products.4

Table comparing Li2CO3 samples. Sample A: 58.9 mg/kg impurity, 99.994% purity. Sample B: 66.5 mg/kg impurity, 99.993% purity.

Table 1. Calculated purity level of Li2CO3 samples A and B based on concentrations of all 64 elements determined by the Agilent 8900 ICP-QQQ. Reproduced from this study.

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