Electrolyte Elemental Analysis for Enhanced Lithium Battery Performance

Elemental analysis of lithium battery electrolytes is crucial for maintaining the quality and performance of current energy storage devices. Lithium batteries are essential for many technical applications, including portable electronic devices and electric vehicles.

The purity and specific composition of the electrolytes used highly influence their efficiency and longevity. The electrolyte’s primary role in batteries is to promote ion passage between the electrodes, which is critical for battery performance.

To achieve optimal performance, the electrolyte solution must be thoroughly and consistently quality-controlled. The Chinese standard HG/T 4067-2015¹ specifies thorough techniques and requirements for conducting chemical analyses of electrolytes in lithium batteries.

This standard assures that all key electrolyte constituents are correctly identified and quantified to maximize battery performance and safety. It offers a standardized procedure that makes results comparable and ensures compliance with international quality standards.

Lithium hexafluorophosphate (LiPF₆) is used in lithium-ion batteries because of its superior conducting characteristics.

The Chinese industrial standard HG/T 4067-2015¹ outlines a process for analyzing LiPF₆ electrolytes, stating that calibration and sample solutions are prepared using a mixture of methyl ethyl carbonate, ethanol, and water (1:4:5).

This article describes the practical application of the HG/T 4067-2015¹ standard, emphasizing the analytical techniques and procedures for determining various components in lithium battery electrolytes.

This investigation evaluated three electrolyte samples for 14 elements, each utilizing the high-resolution ICP-OES PlasmaQuant 9100 Elite under the aforementioned standard. Because LiPF₆ produces hydrofluoric acid, the measurement system included a hydrofluoric acid-resistant sample introduction kit.

The carbon-rich material causes spectrum overlaps along some analytical lines. This impact was rectified using the Correction of Spectral Interferences (CSI) software tool, resulting in a better baseline free of spectral disturbances, increasing the reliability of the measurement data.

Materials & Methods

Samples and Reagents

• LiPF₆ electrolytes
• Multielement standard solution for ICP (100 mg/L Al, As, Ca, Cd, Cr, Cu, Fe, Mg, Na, Ni, Pb, Zn)
• Single-element standard solutions for Hg and K (1000 mg/L each)
• Ethanol
• Ethyl methyl carbonate

Sample Preparation

The test samples were diluted by weighing by a factor of 10. The diluent was made in a 1:4:5 ratio using methyl ethyl carbonate, ethanol, and deionized water, per standard HG/T 4067-2015.

Instrumentation and Method Parameters

Due to the small amount of sample material provided, the analysis was carried out manually (without an autosampler) on the high-resolution ICP-OES PlasmaQuant 9100 Elite, which was fitted with a hydrofluoric acid-resistant sample introduction system (HF kit).

Table 1 summarizes the individual settings and components. Table 2 provides detailed information on the procedure parameters and settings.

Calibration

External calibration standards were created using single and multielement solutions diluted with methyl ethyl carbonate, ethanol, and deionized water (1:4:5). Table 3 lists the concentrations of the calibration standards, and Figure 1 shows instances of the resulting calibration functions.

Table 1. Instrument configuration and settings. Source: Analytik Jena US

Table 2. Method parameters. Source: Analytik Jena US

ABC: Automatic Baseline Correction, CSI: Correction of Spectral Interferences

Table 3. Concentrations of the calibration standards. Source: Analytik Jena US

Figure 1. Examples for calibration functions. Image Credit: Analytik Jena US

Results and Discussion

Table 4 shows the results for the three electrolyte samples. Following the sample analysis, an independent QC standard of 0.12 mg/L was also created and tested. The recovery is also included in the results table.

Table 5 shows the method-specific detection limits (MDL) for the analysis. These values were calculated using the reagent blank method (three times the standard deviation of 11 repeat measurements of the reagent blank). The findings and MDL are calculated using a sample preparation dilution factor 10.

Table 4. Measuring results and QC standard recovery. Source: Analytik Jena US

MDL/LOQ: Method-specific Detection Limit/Limit Of Quantification (3 or 9 times the standard deviation of 11 reagent blank measurements)

Table 5. Method-specific detection limits (MDL). Source: Analytik Jena US

MDL: Method specific Detection Limit

Summary

The PlasmaQuant 9100 Elite’s high matrix tolerance, resolution, and measurement sensitivity allow for an interference-free and robust study of battery electrolytes. Software techniques like automated baseline correction make it easier to evaluate spectra and produce trustworthy results.

Some of the analysis lines exhibit a spectral overlay of matrix-related emission bands. The CSI software program was used based on a mathematical technique (“Least Squares Model” or LSM) to remove the structured backdrop.

For this aim, a spectrum of a pure sample matrix solution (diluent) was captured at the relevant wavelengths and maintained in a database. The corrective spectrum is removed from the recorded sample spectra.

Figure 2. PlasmaQuant 9100 Elite. Image Credit: Analytik Jena US

The constructed correction model can be integrated into the procedure and applied automatically during routine measurements. Figure 3 shows the PlasmaQuant 9100 Elite’s high spectral resolution (2 pm @ 200 nm) and the effect of the CSI tool on mercury (184 nm).

Figure 3. Effect of the CSI software tool on the example of Hg184. Image Credit: Analytik Jena US

Recommended Device Configuration

Table 6. Overview of recommended devices, accessories, and consumables. Source: Analytik Jena US

References

1. Chinese standard Standard HG/T 4067-2015 (https://www.chinesestandard.net/PDF/English.aspx/HGT4067-2015)

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.