See what you’ve been missing with your battery cells
April 26, 2022
Today we have a lot more choice when it comes to analytical methods, however it can be frustrating sometimes that many of the gold standard measurements such as X-ray diffraction or in situ imaging require complex setups for a single cell or are performed at synchrotron facilities where availability of beamtime is scarce.
This means that we need to develop a strong suite of complementary, lab-based techniques that can help us understand exactly what is happening in our battery cells with good spatial and temporal resolution. But what techniques do we have now?
Techniques for measuring battery cells
CURRENT AND VOLTAGE
Of course, we have current and voltage. Given that the purpose of a battery is to be a source of current and voltage, the importance of these measurements cannot be overstated. However, using only current and voltage to estimate battery state has several shortcomings. Moreover, batteries today have exceedingly demanding applications. They need to take electric cars across countries, they need to keep our phones charged for days and they need to keep medical devices running inside patients. To improve that we really need to know what is going on inside the cells which means more than only voltage and current.
Temperature can infer a lot about the processes going on inside a battery. Overheating of batteries negatively affects performance as well as raising safety concerns so measuring the external temperature can be very important and is relatively easy to do. However, measuring local changes of the internal temperature is also very valuable. Unfortunately this is technically much more challenging. Measuring temperature can also only ever deliver limited information if it is not measured in parallel with other methods. There can be many causes of temperature changes and it is important to understand the root causes in order to maximise performance and safety, or perhaps develop the next generation of batteries.
ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY
Another powerful technique is electrochemical impedance spectroscopy or EIS. With right setup, it is possible to gather a wealth of information from your battery cells. While the information from EIS is valuable, especially when comparing to a standard control, it is often difficult to fully characterise the electrode setup to fully interpret data such as changes in impedance. Full characterisation requires access to rigid models which are not always available.
All of the aforementioned methods can be applied non-destructively. If your experimental setup permits and you can sacrifice some of your samples, destructive methods can also give important insight into your battery function. Decommissioning your battery cells can allow for a full range of visual, chemical, and electrical analysis but this comes at a cost. New and continuous measurement methods have shown us that sampling, even if done completely randomly can give misleading results. Sampling gives a valuable snapshot but if the snapshot is not representative, it can give a false perception of what is actually happening.
At Insplorion, we’ve been working on developing an alternative and complementary technology to expand the toolbox of currently available methods and can measure battery performance continuously. We use fibre optics which are electrically insulated and small enough to be integrated into most battery setups. With this we can perfect spectroscopy very locally to understand how the battery changes over time.
Using our patented NanoPlasmonic Sensing (NPS) technology, fibre optic sensors are equipped to function like optical antennae and probe their close environment for changes occurring. As various processes take place inside the battery the sensors will respond to alterations in materials it is placed next to, such as accumulated charge, morphology changes, or SEI layer formation. In doing so, a clear correlation can be observed with the optical interrogation setup.
Fibre optics offer the additional advantage that they are small, so not only can they be integrated easily to measure the inside of coin cell, but many optical fibres can be incorporated in to one instrument. Our instrument for example can take 8 measurements simultaneously. This could be used to measure on 8 cells or take 8 measurements in the same cell.
A perfect complement
Being small enough to easily integrate into small battery setups and having the ability to measure continuously makes fibre optics a great option to complement other techniques. For example, if most of the characterisation of your battery cell are performed at a synchrotron, then being able to perform more characterisations at your home lab will allow you to direct your synchrotron experiment to get the most out of your beam time and your data. Likewise, if you are always measuring voltage, current and temperature without performing other characterisations, then a fibre optic-based sensor could seamlessly fit into your lab workflow, while providing a wealth of extra information for each experiment.
Learn more about battery sensing with Insplorion’s technology
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