Quality control of cathode materials

The IEA (International Energy Agency) expects demand for electric vehicle batteries to increase between four and a half and seven times by 2030 compared to 2023 [1]. The biggest part of the battery production cost is the materials, and cathode production is the most expensive part of the material costs [2]. A good quality control program for cathode production is important to avoid high scrap rates and achieve high production efficiency. This article presents several key analytical parameters throughout the cathode production process.

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Analysis of lithium salts for cathode production

Assay of lithium salts
Ionic impurities in lithium salts

Composition analysis of cathode active materials by titration

Main component analysis
Residual lithium hydroxide and lithium carbonate content

Determining water content in cathodes and raw materials

Measuring fluorine content in cathode black mass for recycling

Analysis of lithium salts for cathode production

Lithium hydroxide (LiOH) and lithium carbonate (Li₂CO₃) are the main lithium salts used in the production of cathode active materials (CAM) [2]. Lithium hydroxide is preferred because lithium hydroxide-based CAMs have better storage capacity and longer life cycles [3].

Therefore, it is important to assess the quality of lithium salts. This includes determining the content of the main lithium salts (assay) as well as ionic impurities to ensure this raw material does not exceed nor fall short of specific production requirements.

Titration for the assay of lithium salts

Titration with hydrochloric acid is ideal to analyze the content of lithium hydroxide and lithium carbonate. This simple method can distinguish between both salts and thus detect carbonate impurities in lithium hydroxide. The International Organization for Standardization (ISO) proposes titration to analyze lithium carbonate as well as lithium hydroxide and its carbonate impurities, respectively [4,5].

To analyze lithium hydroxide, it is crucial to protect the sample from exposure to CO₂. Otherwise, carbonate impurities will form. Figure 1 shows the results of a fully automated analysis of lithium hydroxide. One sample series ran covered with a lid to prevent exposure to CO₂, while the other series ran uncovered. The uncovered series showed a clear increase in carbonate impurities.

For more information about the assay of lithium hydroxide and lithium carbonate, take a look at our Application Note.

Application Note: Assay of lithium hydroxide and lithium carbonate – Precise and reliable determination by potentiometric titration

Figure 1. Results of the automated lithium hydroxide assay (0.1227 g for each titration) for six samples. The uncovered samples exhibit increased carbonate content over time because of carbon dioxide uptake from the air, while covered samples remain stable [6].

Ion chromatography for ionic impurities

Battery-grade lithium salts must be extremely pure, since ionic impurities can negatively affect the finished battery. One challenge when processing lithium brine is the removal of magnesium [7,8]. Ion chromatography (IC) is ideal for determining the efficiency of the magnesium removal process. In addition, other ionic impurities such as potassium, sodium, or calcium can be analyzed simultaneously.

In contrast to other techniques, such as spectroscopic methods, ion chromatography is a very easy and economical way to determine ionic impurities. An additional benefit of using IC is its robustness when analyzing samples with complex matrices—for example, high loads of salts.

Take a look at our related Application Notes to learn more about the analysis of lithium brines and ores using ion chromatography.

Application Note: Online determination of lithium in brine streams with ion chromatography

Application Note: Cations in lithium ore

Figure 2. Ion chromatography is ideally suited to determine trace cations and anions in raw materials for lithium-ion batteries.

Composition analysis of cathode active materials by titration

Main component analysis in precursor cathode active materials production by titration

The proper composition of the starting solutions is essential for producing CAMs as errors cannot be corrected [9], resulting in high scrap rates. Potentiometric titration can be used to analyze the solution used to produce the precursor cathode active material (pCAM).

Titration can handle much higher metal concentrations than other methods such as ICP-OES (inductively coupled plasma - optical emission spectrometry). Therefore, there is no need to dilute the sample, reducing potential measuring errors.

Analysis of layered oxides is straightforward with a single titration. Ternary metal oxides require more than one titration to differentiate between the metals. Table 1 summarizes the titration of the different metals in cathode active materials.

Our free Application Note below describes the fully automated analysis of the nickel, cobalt, and manganese (NCM) content in an NCM pCAM starting solution.

Application Note: Analysis of Li-ion battery cathode materials made from Co, Ni, and Mn – Fully automated determination including sample preparation using the OMNIS pipetting equipment

**Table 1.** List of cathode materials and the metal components which can be analyzed by titration.
Cathode material	Metal	Titration	Remarks
NCM	Total metal content	Complexometric titration with EDTA	Standard YS/T 1006.1 describes this analysis.
	Nickel	N/A	Value calculated from total metal content, manganese, and cobalt contents.
	Manganese	Redox titration with KMnO₄	Standard YS/T 1472.1 describes this analysis.
	Cobalt	Redox titration with ferricyanide [Fe(CN)₆]^3-	Standard YS/T 1472.2 describes this analysis.
LFP	(Total) Iron	Redox titration with potassium dichromate K₂Cr₂O₇	Standard YS/T 1028.1 describes this analysis.
LCO	Cobalt	Complexometric titration with EDTA	Standard GB/T 23367.1 describes this analysis.
LMO	Manganese	Redox titration with ferrous ammonium sulfate (FAS) (NH₄)₂Fe(SO₄)₂
NCA	Cobalt	Redox titration with ferricyanide [Fe(CN)₆]^3-	Standard YS/T 1263.2 describes this analysis.
LNMO	Manganese		Standard YS/T 1569.2 describes this analysis.

Residual alkali content

Figure 3. Titration curve for the analysis of the residual alkali content of a cathode material. EP1 corresponds to the titration of lithium hydroxide and lithium carbonate and EP2 corresponds to the titration of lithium bicarbonate. Hydrochloric acid is used as titrant.

Unreacted lithium on the surface of cathode active materials can form lithium hydroxides and carbonates. These surface hydroxides and carbonates are also called residual alkali or soluble base content. High residual alkali content can cause gelation in the cathode slurry [10,11], which will significantly impact the electrode coating process.

The residual alkali content can be determined by an acid-base titration with hydrochloric acid (HCl). Figure 4 shows the titration curve for the analysis of a cathode material. It is essential to protect the samples from CO₂ as this would falsify the result. Also, see Figure 1 under the section «Titration for the assay of lithium salts».

Figure 4. A fully automated OMNIS system equipped with Dis-Cover lids to protect the samples from uptake of atmospheric carbon dioxide.

Determining water content in cathodes and raw materials

Lithium-ion batteries should be virtually water-free as traces of water can also negatively impact the performance of these batteries. More than 1000 µg/L (ppm) water can cause capacity loss and swelling of the battery cell [12]. Furthermore, water will react with lithium hexafluorophosphate (LiPF₆) in the electrolyte, forming toxic hydrofluoric acid (HF). Therefore, it is important to monitor the water content during the entire production process of the cathode active material.

One consideration is to ensure that the workshop environment is as dry as possible during cathode production [13]. Others include measuring the water content in the purchased raw materials and during production of the cathode. Coulometric Karl Fischer titration is an established method for determining the water content in battery materials [12].

Solid samples cannot be added directly to the coulometric titration cell, therefore an indirect method with an oven is used [12]. The sample is weighed and sealed in an air-tight vial. The vial is then placed in the oven and the evaporated water is transferred to the titration cell. There the water content is determined.

Learn more about the oven method in our blog article.

Oven method for sample preparation in Karl Fischer titration

For more information on the analysis of cathode samples, download our Application Bulletin below.

Application Bulletin: Water in lithium ion battery materials

Measuring fluorine content in cathode black mass for recycling

As demand for electric vehicles (EVs) and thus lithium-ion batteries increases, recycling of spent batteries becomes more important. The recycling process typically targets nickel, cobalt and copper, but now there is increased emphasis on lithium recovery [14].

The lithium recovery process is hampered because the PVDF binder releases fluoride during calcination of the black mass. The fluoride reacts with the lithium, resulting in lithium fluoride, which is insoluble [15]. Fixation of fluoride can help with recovering lithium. To determine the amount of fixing agent required, combustion ion chromatography (CIC) can be used to measure the fluorine content in the black mass.

During combustion in chromatography, the sample (cathode black mass) undergoes pyrohydrolysis. The PVDF decomposes and the released fluorine is absorbed in ultrapure water. The resulting fluoride content is then measured by ion chromatography. Figure 5 shows the chromatogram for the analysis of a cathode material.

Figure 5. Chromatogram for the analysis of the fluorine content of a LIB cathode active material with an expected fluorine content of 2000 mg/kg. This analysis used a Metrosep A Supp 19 - 150/4.0 column in combination with a sodium carbonate/bicarbonate eluent (c(sodium carbonate) = 8.0 mmol/L c(sodium bicarbonate) = 0.25 mmol/L).

Learn more about combustion ion chromatography in our blog post.

History of Metrohm IC – Part 6

Conclusion

Monitoring the quality of the incoming raw materials and other key quality parameters during the production process, such as water content or CAM composition, can reduce the risk of quality failure of the finished battery. As recycling of batteries becomes more important, it is essential to implement analytical methods to ensure efficient and effective recycling processes.

[1] Outlook for battery and energy demand – Global EV Outlook 2024 – Analysis. IEA. https://www.iea.org/reports/global-ev-outlook-2024/outlook-for-battery-and-energy-demand (accessed 2024-07-18).

[2] Heimes, H.; Kampker, A.; Hemdt, A.; et al. Manufacturing of Lithium-Ion Battery Cell Components; 2019.

[3] Bogossian, J. Hard Rock Lithium Deposits | Geology for Investors. https://www.geologyforinvestors.com/hard-rock-lithium-deposits/ (accessed 2024-07-11).

[4] International Organization for Standardization. ISO/WD 10662 - Determination of main content of lithium carbonate - Potentiometric titration. https://www.iso.org/standard/83740.html (accessed 2024-07-11).

[5] International Organization for Standardization. ISO/AWI 11045-1 - Methods for chemical analysis of lithium salts — Part 1: Quantitative determination of lithium hydroxide and lithium carbonate content in lithium hydroxide monohydrate — Potentiometric titration method. https://www.iso.org/standard/83764.html (accessed 2024-07-11).

[6] Meier, L. Quality Control of Analytical Parameters in Battery Production, 2022.

[7] Li, Z.; Mercken, J.; Li, X.; et al. Efficient and Sustainable Removal of Magnesium from Brines for Lithium/Magnesium Separation Using Binary Extractants. ACS Sustainable Chem. Eng. 2019, 7 (23), 19225–19234. DOI:10.1021/acssuschemeng.9b05436

[8] Lalasari, L. H.; Fatahillah, F. R.; Rahmat, D. R. G.; et al. Magnesium Removal from Brine Water with Low Lithium Grade Using Limestone, Rembang, Indonesia. IOP Conf. Ser.: Mater. Sci. Eng. 2019, 578 (1), 012067. DOI:10.1088/1757-899X/578/1/012067

[9] Lithium-Ion Batteries: Basics and Applications, 1st ed. 2018.; Korthauer, R., Ed.; Springer Berlin Heidelberg : Imprint: Springer: Berlin, Heidelberg, 2018. DOI:10.1007/978-3-662-53071-9

[10] Schuer, A. R.; Kuenzel, M.; Yang, S.; et al. Diagnosis Tools for Humidity-Born Surface Contaminants on Li[Ni_0.8Mn_0.1Co_0.1]O₂ Cathode Materials for Lithium Batteries. Journal of Power Sources 2022, 525, 231111. DOI:10.1016/j.jpowsour.2022.231111

[11] Bresser, D.; Buchholz, D.; Moretti, A.; et al. Alternative Binders for Sustainable Electrochemical Energy Storage – the Transition to Aqueous Electrode Processing and Bio-Derived Polymers. Energy Environ. Sci. 2018, 11 (11), 3096–3127. DOI:10.1039/C8EE00640G

[12] Kosfeld, M.; Westphal, B.; Kwade, A. Correct Water Content Measuring of Lithium-Ion Battery Components and the Impact of Calendering via Karl-Fischer Titration. Journal of Energy Storage 2022, 51, 104398. DOI:10.1016/j.est.2022.104398

[13] Kosfeld, M.; Westphal, B.; Kwade, A. Moisture Behavior of Lithium-Ion Battery Components along the Production Process. Journal of Energy Storage 2023, 57, 106174. DOI:10.1016/j.est.2022.106174

[14] IEA. Batteries and Secure Energy Transitions; IEA: Paris, 2024.

[15] Kuzuhara, S.; Yamada, Y.; Igarashi, A.; et al. Fluorine Fixation for Spent Lithium-Ion Batteries toward Closed-Loop Lithium Recycling. J Mater Cycles Waste Manag 2024. DOI:10.1007/s10163-024-01991-x