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Battery (cell) test
Research and development on battery cells, especially on the lithium-ion battery (LIB), is ubiquitous these days. The battery cell, as the smallest unit in sometimes large cell assemblies (modules and packs), plays a decisive role for emission-free electromobility, long-lasting smartphones or the effective storage of renewable energy.
The numerous areas of application for battery cells result in many aspects that researchers or developers, chemists or engineers look at in their work. What they all have in common is the investigation of the cell with regard to its electrochemical processes. This is exactly where our solutions, with their origins in classical electrochemistry, come in.
Our measurement technology is based on the highly flexible electronic architecture of the potentiostat/galvanostat, i.e., laboratory instruments with high measurement accuracy and precision and very flexible application. Precision and accuracy form a symbiosis with scalability and robustness, which results in a particularly cost-effective solution for your problem.
Multi-channel potentiostats are exceptionally flexible with high measurement throughput. Especially in the research field, this versatility is appreciated in order to be able to carry out a wide variety of measurement protocols. On the one hand, cyclisation tests take several weeks, so that a high measuring station capacity is required, on the other hand, completely different measuring methods are needed for different types of battery cells. Multi-channel instruments offer the highest bandwidth of techniques, such as impedance spectroscopy, cyclic voltammetry or titration techniques (PITT/GITT). For high measurement resolution and accuracy, multi-channel potentiostats usually have several current and voltage measurement ranges and can work in all four quadrants (positive and negative current and voltage directions). The included software packages are usually very comprehensive in their range of functions, but special user interfaces for battery tests simplify the operation. Nevertheless, the full application potential of a potentiostat is always retained.
Compared to potentiostats, battery cyclisers are much simpler in terms of circuitry, so that current and voltage resolution are usually much poorer. However, cyclisers do not require high-resolution current/voltage measurement for their actual task. They are mainly used for specialised routine tests, such as end-of-line or quality assurance, where the measurement parameters hardly need to be varied and standardised measurement protocols are used. Therefore, cyclisers typically have to be optimally adapted to the application, e.g., they have to operate in the expected current range. The cost per measuring channel is significantly lower than for potentiostats, so that measuring stations with high measuring throughput can be set up cost-effectively. As a rule, cyclisers only include measuring methods for charging and discharging battery cells, so that techniques such as impedance spectroscopy or other electroanalytics cannot be used. The operating software of cyclisers is normally designed to be as simple and goal-oriented as possible.
Comparison of potentiostats and cyclisers:
|Measuring ranges voltage||several (also negativ)||one (positive)|
|Current measuring ranges||several (nA bis A)||few / one|
|Max. current||10 to 100 A||100 to 1000 A|
|Measuring methods||various||charge / discharge|
|Software||extensive/complex||simple / limited|
|Cost per measuring channel||expensive||reasonable|
For a complete battery cell measuring station, other components are necessary in addition to a multi-channel measuring system. Contacting of the battery cells in cell holders, for example, can be done in different ways. This logically depends on the cell types used, which are listed in the following section. In addition, the use of climate and environmental chambers may be necessary or useful.
Common cell types are screw cell, button cell, round cell, and prismatic cell (hardcover / pouch versions).
The choice of cell type is primarily based on the application and the corresponding energy density. Screw cells and button cells are primarily used in research applications, as they allow particularly small amounts of material and correspondingly small electrode areas to be used. Due to the particularly simple assembly and disassembly, the production is simple and flexible, as well as being suitable for subsequent, so-called post-mortem investigations.
In contrast, pouch cells are primarily used in research and development close to series production, since very practical manufacturing processes here should be used. In addition, pouch cells are also the end product in large-scale production (application). This also applies to the round cell and the prismatic cell. For development purposes, these cell types are mostly used close to production, as the production is more complex.
Areas of application for different cell types:
|Cell type||Research||Development||Application (LIB)|
Selection of cell holders
According to the different form factors of the cell types, the cell holders also differ. Some cell types have standardised dimensions and therefore standardised holders can be used. This is especially true for round and button cells. Due to the uniform nomenclature of diameter and height, standard dimensions for these two cell types have been established and corresponding holders are widely available.
For screw and pouch cells as well as prismatic cells, there are no prescribed dimensions, so that for contacting, one usually has to resort to individual solutions. Especially the screw cell, as a pure research cell format, is usually fixed and connected individually, often only by means of a screw terminal and banana plug or crocodile clip. For pouch cells, there are often ready-made clamping solutions as a 2-in-1 system for attaching and contacting the cell. In contrast, prismatic cells can be set up in the simplest case and then connected by means of a screw contact.
Climate and environmental chambers
Climate or environmental chambers are widely used in battery testing, with different objectives. In the most basic case, a climate chamber is used to create a constant temperature/environment for the cell, thereby increasing the reproducibility of the measurement or testing according to a standard. Some battery tests aim to analyse the cell behaviour at particularly high or low temperatures - also a suitable field of application for climate chambers. Especially the ageing behaviour at high temperatures or the determination of characteristics such as minimum or maximum operating temperature is determined in this way.
In general, environmental chambers with special safety features are used for test series with large-format cells. The focus here is not only on the behaviour under various environmental conditions but also on pure safety. In the event of a defect (often accompanied by the so-called thermal runaway or self-promoting fire), environmental and safety chambers can protect the laboratory environment from damage.