40
The analysis of the various solid or pasty components of the batteries can be carried out very reproducibly, since no sample preparation steps are usually necessary for the introduction of the sample into the heating oven. Various vial sizes are available, which also allow larger components, preforms or pieces of membrane to be positioned in the vial without crushing or grinding. Any kind of sample pre-treatment would bring moisture from the room air to the surface of the sample.
Figure 6 shows examples of different sizes of sample containers. Different inserts and sample trays are available for each vail size. The adjustments to the headspace oven and the autosampler can be carried out very easily by the user. It should be noted that the larger the sample container, the more humidity it contains, so that the blank value of the container also increases.
Figure 8 shows a series of tests to determine the water content in freshly dried LiCoO2 powder. The powder was dried at 600°C.
The periods of time between sampling and measurement have been varied. Just three minutes of exposure to air increases the water content threefold again. Such investigations show the great importance of the procedure both in the production process and in the sampling for the analysis of such materials.
Figure 6: Different sample containers for different sample types.
Table 1 shows measurements for different electrode materials. They show the high reproducibility of the analysis, although different weights were used. The samples are partly piece plates of electrode faces. Nevertheless, the measurement time is very short at 10-20 minutes.
Table 1: Reproducibility of measurements of the water content for powdered electrode material (100°C) using headspace technology.
Meas. -No. Sample name
1 2 3
Sample amount [mg]
Li-Ni-CO-Mn-Oxide 221.07 153.80 220.80
Mean value
4 5 6
Li-Fe-Phosphate
Rel. Standard deviation 132.15 178.50 246.45
Mean value Rel. Standard deviation
532.2 734.6
1008.6
result - absolute [µg]
223.5 149.8 216.6
Result [%]
0.10 0.10 0.10
0.10% 2.00% 0.40 0.41 0.41
0.41% 1.12%
The aim of battery manufacture is to use all components with as little water as possible so that the water content in the finished product is as low as possible and storage up to 60°C does not lead to water release. Accordingly, the materials are intensively pre-dried. The resulting water content not only depends on the conditions of the process dryer, but in particular on the subsequent processes, as can be seen in the following example.
for complete release of the trapped water. The water released from the samples is transported into the titrator with the aid of a pre-dried stream of argon or nitrogen. The samples are weighed into ceramic sample boats. This means that up to 5 g of sample can be used. The determination is blank-free.
A high-temperature furnace capable of heating samples up to a temperature of 1300°C (Figure 7) was used for the analyses. LiCoO2
and graphite require high temperatures 5. Summary
The coulometric Karl Fischer titration is the most suitable method for investigating the water content of battery materials. By coupling a heating technique with sealed sample vials, the highly hygroscopic materials can also be analysed successfully. The variation of the heating parameters enables the water content to be determined in the entire range of the electrode, electrolyte and foil materials used. The procedure for representative sampling is the key to accurate and correct analyses for process monitoring.
References:
1.
https://www.volkswagen-classic.de/de/Magazine/Electromobility/Model-History-of- Volkswagen-Electromobility-since-1972.html#
2. Effect of Humidity on Properties of Lithium-ion Batteries; Xiao Han, Saisai Xia, Jie Cao, Chris Wang, Ming-gong Chen, Int. J. Electrochem. Sci., 16 (2021) Article ID: 210554, 3. Lithium-Ion Batteries; M. Yoshio, R. Brodd, A. Kozawa (Eds.), Springer2009, Chapter 19 4. Lithium-Ion Batteries; M. Yoshio, R. Brodd, A. Kozawa (Eds.), Springer 2009, Chapter 4
5. The effects of humidity on the self-discharge properties of Li(Ni1/3Co1/3Mn1/3)O2/graphite and LiCoO2/graphite lithium-ion batteries during storage; Seoungwoo Byun, Joonam Park, Williams Agyei Appiah, Myung-Hyun Ryou and Yong Min Lee; RSC Adv., 2017, 7, 10915-10921
6. Accurate Water Determination in Lithium-Ion Batteries with Hydranal™ NEXTGEN Coulomat A-FA and C-FA 231568_AM | 10/21 © 2021 Honeywell International Inc
Figure 7: High-temperature oven coupled with coulometric Karl Fischer titration.
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Figure 8: Measurements of the water content of powdered electrode material (LiCoO2 removal from the drying process (20 min, 600°C).
) after
Glove boxes are used to avoid any falsifying influence of humidity on the battery materials. In these miniature rooms, the atmosphere can be pre-dried in a controlled manner and made oxygen-free. The example shown in Figure 9 is precisely adapted to the measurement task. An analytical balance and the Karl Fischer titrator with headspace technology are positioned in the closed room. The processes inside can be carried out from the outside using up to four glove box gloves. An airlock on the side of the glove box is used for loading and unloading the materials. With this technique, the blank value in the analyses is reduced to < 10 µg, so that highly sensitive trace analyses in the battery materials are possible.
Figure 9: Arrangement of the Karl Fischer titrator and the analytical balance in a customised glove box with four glove ports
INTERNATIONAL LABMATE - FEBRUARY 2023
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