Understanding TIC Analysis for Lithium Recovery

Recovering lithium from lithium-ion batteries (LIBs) is becoming more important because of the growth of electrification, particularly in the mobility industry. Lithium’s classification from the EU as a critical raw material increased raw material prices and demand; new legal recycling quotas also lead to increased research activities and industrial recycling plant construction.¹

Such projects focus on recovering lithium from LIBs and other valuable battery components. Lithium carbonate is a target product that could be used as a raw material in battery production.

Lithium’s recovery in contemporary recycling processes remains difficult; it is either not performed or done so with low recovery rates.² To bypass this issue, the Institute for Metallurgical Process Technology at RWTH Aachen University is studying methods for early lithium recovery from the active mass.^3,4

This method involves the recycled battery material (whole cells or pre-shredded batteries) being exposed to a defined thermal pretreatment (TPT). This removes organic substances from the battery cells’ electrolytes, separators, and binders. It is also utilized for phase transformations of the lithium in the LIB through the targeted adjustment of process parameters.

Constant reduction reactions form lithium carbonate. To selectively recover lithium from the active mass, a wash-out process with deionized water dissolves the formed lithium carbonate.

Because lithium fluoride is also made during thermal pre-treatment, a certain amount of this salt (depending on the selected process parameters) is also carried into solution. The lithium salt product can be recovered from the solution by evaporation.

The purity and type of lithium compound present are significant in evaluating the process parameters of TPT, leaching, and the product produced.

As the target phase in the case described is lithium carbonate, total inorganic carbon (TIC) measurement with the multi N/C analyzer offers a quick and reliable technique for comparing carbonate contents within a series of tests. It allows conclusions regarding the ratio of lithium fluoride to carbonate.

The measurement of the total organic carbon (TOC) also allows operatives to inspect for the contamination of the sample with organic residues from the TPT process. Analytik Jena’s multi N/C 2100S was used for this study to assess carbonate concentrations.

Measurements were performed on aqueous samples from a series of tests at the Institute for Metallurgical Process Technology.³ The samples originate from the water-washing process of four active compounds that have endured different TPTs.

Fluorine measurements were carried out for confirmation purposes. X-ray diffraction images of the precipitated salts were recorded, allowing qualitative conclusions regarding the phase fractions of lithium fluoride and carbonate.

Materials and Methods

The TIC determination was carried out by the multi N/C and the auto-sampler AS 60, according to the TIC determination defined in DIN EN 1484.

The samples and reagents used were the following: four samples after the water-washing process of active mass from four different TPT processes (610 °C, 1 h holding time, under N₂ atmosphere, N₂ + 2.5 % O₂, N₂ + 5 % O₂, resp. CO₂ atmosphere); 10 % phosphoric acid for automatic TIC determination and TIC calibration standard solutions sodium carbonate and sodium hydrogen carbonate in water.

The samples were diluted in a 1:8 ratio with deionized water to minimize matrix effects from metal cations. They were then transferred into vials set on the sample rack.

For direct TIC measurement, a micro-liter syringe fed a representative sample aliquot of 500 µL into the analyzer’s TIC reactor, and an aliquot of 10 % phosphoric acid was automatically transferred to the TIC reactor.

The acid CO₃^2- was converted to HCO₃ (the dissolved form of CO₂) and released from the solution by purging with clean carrier gas, either pure oxygen or synthetic air free of hydrocarbons and CO₂. After the drying and purification stage, the measurement gas was moved to the detector.

Quantification was carried out via a focus radiation non-dispersive infrared detector.

Calibration

The multi N/C was standardized with sodium carbonate and sodium hydrogen carbonate, standard solutions for the concentration range of 0.25 to 25 mg/L TIC, in a 1:1 ratio. All calibration solutions were prepared in line with DIN EN1484. A linear calibration function was used.

Fig. 1. Example of a calibration curve TIC 0.25 - 25 mg/L. Image Credit: Analytik Jena US

Method settings are shown in Table 1.

Table 1. Method parameters for multi N/C 2100S, resp. multi N/C 2300. Source: Analytik Jena US

Results and Discussion

Table 2 and Figure 2 show examples of analytical results. TIC measurements were taken through multiple injections from a sample vessel.

Further fluorine analyses with ion-selective electrodes, in addition to semi-quantitative determinations of the lithium carbonate and lithium fluoride fractions from the precipitated lithium salt, were performed via XRD measurement to assess the qualitative statement.

Because measurement of carbonate content by XRD is time-consuming (an additional process step is required to precipitate the lithium salt) and phase-fraction determination by XRD is a semi-quantitative methodology, the TIC method from solution offers the benefit of being very accurate, with low standard deviation and short measurement times.

Table 2. Comparison of the results of TIC and fluorine determination based on undiluted original sample and semiquantitative XRD evaluation of the precipitation product. Source: Analytik Jena US

Fig. 2. Examples of measurement curves of samples with different content of carbonates. Image Credit: Analytik Jena US

The example measurement curves in Figure 2 demonstrate the superb reproducibility of the measured values within multiple injections from the sample vessel. The lithium recovery rate in the aqueous eluate solution could be quantitatively determined by TIC examination.

Through comparison with the semi-quantitative XRD assessment of the proportions of lithium fluoride and carbonate in the ensuing precipitate product, it was demonstrated that samples with a higher lithium carbonate content in the salt product display higher TIC readings in solution than samples with a lower carbonate content.

The TIC measurement offers an appropriate time-saving alternative to the semi-quantitative phase determination via XRD for comparing the samples and estimating the process success regarding the yield of lithium carbonate during TPT and the corresponding lithium recovery in the elution step.

Conclusions

TIC determination via the multi N/C series is an appropriate method for assessing lithium carbonate generation in the context of LIB recycling. The data shows that this method can reliably enable the qualitative assessment of lithium carbonate recovery.

The measurement also takes less time than the semi-quantitative XRD method. The multi N/C 2300 TOC analyzer’s direct injection technique and the AS 60 offer very low sample consumption per analysis; 5 mL of sample or less is usually adequate for a triplicate determination of the TIC parameter.

A further added value is the option to analyze the sample for any TOC brought into solution, which negatively influences the product quality of the lithium salt.

Fig. 3. multi N/C 2300. Image Credit: Analytik Jena US

Table 3. Overview of devices, accessories, and consumables. Source: Analytik Jena US

References and Further Reading

1. Directorate-General for Internal Market, I., Blengini, G.A., et al. (2020). Study on the EU’s list of critical raw materials (2020): final report. [online] Publications Office of the European Union. LU: Publications Office of the European Union. Available at: https://op.europa.eu/en/publication-detail/-/publication/c0d5292a-ee54-11ea-991b-01aa75ed71a1/language-en.
2. Harper, G., et al. (2022). Roadmap for a sustainable circular economy in lithium-ion and future battery technologies. Journal of Physics: Energy. https://doi.org/10.1088/2515-7655/acaa57.
3. Stallmeister, C. and Friedrich, B. (2023). Influence of Flow-Gas Composition on Reaction Products of Thermally Treated NMC Battery Black Mass. Metals, [online] 13(5), pp.923–923. https://doi.org/10.3390/met13050923.
4. Stallmeister, C., Schwich, L. and Friedrich, B. (2020). Early-Stage Li-Removal -Vermeidung von Lithiumverlusten im Zuge der Thermischen und Chemischen Recyclingrouten von Batterien. [online] https://doi.org/10.13140/RG.2.2.35812.12167.

This information has been sourced, reviewed, and adapted from materials provided by Analytik Jena US.

For more information on this source, please visit Analytik Jena US.