Challenges in the Analysis, QC of Lithium-ion Batteries

In my view, there are three big challenges for lithium-ion batteries right now. The first one is how can we further reduce the cost of lithium-ion batteries, especially for electric vehicles (EV). Don't get me wrong, the cost of lithium-ion batteries has already been significantly reduced from a few thousand dollars per kilowatt hours in the 1990s to today's about $100 per kilowatt hour. That's a big achievement, already. But to accelerate the EV market penetration, we have to further reduce the lithium-ion battery cost. How? We have to reduce the cost of materials and processing technologies.

This brings up the second challenge, which is how can we quickly establish a healthy domestic manufacturing and supply chain for lithium-ion batteries? If we are talking about manufacturing batteries, we first need to manufacture battery materials and components—cathodes, anode, separators, electrolyte, current connectors, packaging materials, and even sealing glue. We’re talking about 10s of thousands of tons of those materials, which is really quite a challenge. Even if we already have sufficient amounts of materials components, we have large battery production lines. Who will be operating those production lines? We need to work with people with different backgrounds, different expertise—from operators to PhDs—to make this happen. But where are they? Who will be the trainees? That’s the third big challenge—workforce development for battery R&D and manufacturing.

There are four main parts of the battery—anode, cathode, electrolyte and separator—that get chemical analysis performed on it to check for purity of the compounds that go into these components. It’s important to have pure chemicals since purity leads to better performance and better safety. When you need pure chemicals, you need to test for impurities and therefore you need high sensitivity equipment. All of that high sensitivity test equipment exists. Where the analysis challenges lie for the components that go into the battery is really around ensuring you don't have contamination when you do the test work itself. Inside the laboratories, the chemists that are testing the precursor chemicals have to be careful not to cross-contaminate those samples. The safety aspect really comes from the purity of the chemicals, and you need high sensitivity instrumentation to check for the impurities.

The quality control of each component of the lithium-ion battery and the raw materials involves several testing and analysis challenges. Testing material purity is a crucial part, requiring sensitive detection of trace elements and impurities, as well as contaminants that can affect the performance and the lifespan of the battery. For example, lithium brines and lithium salts tend to have high concentrations of total dissolved solids, exhibit high background signals, and also contain high concentrations of easily ionized elements, which can introduce inaccurate results.

One of the main challenges to testing the stability and structure of a battery is looking at the evolved gases that are produced during cycling of the battery itself. If we can characterize what gases are being produced and at what quantities and what rates, it gives us a lot of information about what's happening inside the battery from a chemical reaction perspective. GC and GC-MS is the best technique for this analysis because you can characterize not just the quantity of the gases being produced but the identity if they are unknown.

There are additional GC detection systems that are extremely sensitive and can cover a wide range of analytes, even ones that aren't combustible. A typical flame ionization detector for GC only picks up things that combust; thus, elements like moisture and nitrogen, etc., require different technologies for the detection system. For example, a barrier ionization discharge detector is able to measure hydrogen and moisture in a variety of samples at very low detection limits. Similarly, we have sulfur chemiluminescence detector, which can speciate various sulfur compounds with a high degree of stability and sensitivity. Thermal conductivity detectors are able to detect pretty much anything but at the expense of some detection limits.

There are a couple of really valuable tools for evaluating the internal structure of a battery as it cycles and through the lifespan. A CT scanner looks through the image and that's very helpful. In addition to that, what we see with the crystal structure changing on the electrode material from lithium, oxygen and manganese, as the lithium ions travel out of it, what's left is manganese oxide. The structure of the remaining crystal needs to retain its strength in order to hold the integrity of the battery itself. The tool we use to measure that is a micro tester/micro tensile tester. With crystal structures the size of 10 microns, we can look at the force necessary to break it and test whether or not the battery is going to retain its integrity through these cycles.

The lithium-ion battery is a complex system and failure can be catastrophic. Even small contaminants can cause a fast-paced thermal runaway, which can result in a fire or an explosion. The biggest challenge is the sheer size of the lithium-ion battery components and the speed of operations. Any analytical technology needs to have a special form factor to accommodate the large size of the cells, modules and packs, as well as operate at the speed of the assembly line. Lithium-metal oxide components are used in the cathode, along with layered components. The layers must be consistent and free of contaminants in order to ensure the proper functioning of the battery and to prevent hotspots, which could result in fires. Contaminants introduced at any stage of the production can also result in a short circuit, which can cause in a fast-paced thermal runaway, a fire or an explosion. For this reason, it's very important that the cathode have 100% quality control inspection using advanced imaging spectroscopy and micro analysis methods to ensure that the structure and chemistry of the cathode is appropriate and consistent.

The anode faces similar challenges in material consistency and performance. Consistency is maintained by ensuring material uniformity and compositional integrity. The electrode composition must also be precisely controlled in order to maintain ionic connectivity and prevent degradation over time.

It's also important to have positive material identification and consistency in the separator. Inconsistencies in the separator can also result in thermal runaway, particularly under extreme conditions such as the heat in Texas or the cold in Minnesota. Because of component size, particularly when combined together into a cell module or pack, there needs to be specific form factors and customization available to be able to incorporate analytical technology into the materials production line or near the production line for spot testing.