In this interview, AZoMaterials speaks with Jeremy May, Senior Application Scientist at TA Instruments, about advances in battery testing and how electrochemical calorimetry can help researchers better understand lithium-ion battery performance, safety, and long-term stability. He discusses how combining high-sensitivity heat-flow measurements with electrochemical cycling can reveal physical and chemical changes that conventional testing may overlook, enabling researchers to evaluate battery formulations, investigate failure mechanisms, and accelerate material development.
Can you please introduce yourself and your role at TA Instruments?
My name is Jeremy May, and I'm a Senior Application Scientist at TA Instruments. My work involves battery testing solutions, including thermal analysis, rheology, and electrochemical calorimetry.
At TA Instruments, we offer a range of technologies that support different stages of battery research and development. Our thermal analysis instruments, including differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), help researchers understand the thermal stability and safety of battery materials.
We also have rheology solutions for studying electrode slurries and powders, which are particularly important for optimizing formulations during battery manufacturing.
One of the technologies I focus on is our Battery Cycler Microcalorimeter Solution, or BCMS. This combines electrochemical cycling with highly sensitive heat-flow measurements to provide a more comprehensive understanding of the changes occurring within lithium-ion batteries.
What are the main challenges associated with conventional battery testing, and how can electrochemical calorimetry address them?
Electrochemical testing is really a cornerstone of battery research, but there are limitations to what we can learn from electrochemistry alone.
Traditionally, researchers are often forced to cycle their cells all the way to failure to differentiate between formulations. This is because they're primarily looking at changes in electrochemical performance, such as capacity retention or voltage behavior.
In reality, there are several different processes occurring inside a battery as it ages. There are electrochemical changes, but we also see physical changes such as phase transitions, structural changes, particle cracking, and cell expansion. Then we have chemical reactions, including lithium metal plating, reactions between lithium metal and the electrolyte, and spontaneous electrolyte decomposition.
All of these processes can contribute to battery degradation, but they aren't necessarily apparent from the electrochemical data alone.
Calorimetry is uniquely positioned to measure these changes because it acts as a universal detector. Physical, chemical, and electrochemical processes can all produce heat-flow signals.
By measuring heat flow during electrochemical cycling, we can correlate these events with changes in battery performance. This gives us a much more comprehensive understanding of what's happening inside the cell and can allow us to differentiate between formulations without waiting for the batteries to reach the end of their cycle life.
How does TA Instruments' Battery Cycler Microcalorimeter Solution work, and what makes it particularly useful for lithium-ion battery research?
The Battery Cycler Microcalorimeter Solution combines our TAM IV isothermal microcalorimeter with a potentiostat, in this case a VSP-300 from BioLogic.
The two instruments are integrated physically through electrically wired sample holders, which we call battery lifters, and they're also integrated through the software. This allows us to simultaneously measure heat flow while charging and discharging the battery.
The real advantage is that we're collecting both electrochemical and thermal information during the same experiment.
With conventional electrochemical testing, you might measure the cell's voltage and capacity. With our system, we're adding a highly sensitive heat-flow measurement that provides information on the physical and chemical changes occurring during electrochemical processes.
The TAM IV is designed to provide highly sensitive heat-flow measurements under stable, isothermal conditions. Its oil bath maintains the temperature within approximately 100 microdegrees Celsius of the set point, which allows us to maintain a very stable baseline during long-duration experiments.
The system is also modular, with up to four independent calorimeter channels. We offer different calorimeters for coin cells, small- and medium-sized pouch cells, and larger cylindrical cells.
The battery lifters use spring-clip connections, so no soldering is required. These connections are designed to maximize heat transfer between the sample and the calorimeter sensors while making sample loading straightforward.
Overall, it's a flexible, non-destructive technique that allows researchers to perform true in operando measurements on commercially relevant battery formats.
How can high-sensitivity heat-flow measurements improve battery safety and help researchers understand potential failure mechanisms?
When we're looking at battery safety, one of the important questions is what happens inside the cell before it eventually fails.
There are a number of physical and chemical events that can contribute to failure. These might include structural changes, lithium plating, reactions with the electrolyte, or material decomposition.
Each of these processes can generate heat, and a high-sensitivity calorimeter allows us to detect changes in heat flow that might not yet be apparent in the electrochemical performance.
This is particularly useful because it gives us an earlier indication that something may be changing inside the cell.
It is important to recognize that the Battery Cycler Microcalorimeter Solution isn't designed for thermal-runaway testing itself. However, it can provide valuable information about the events that may eventually lead to thermal runaway.
Rather than simply observing that a battery has failed, we're trying to understand how and why that failure develops.
That information is important for researchers developing safer materials, evaluating new formulations, and understanding the mechanisms underlying long-term degradation.
How can electrochemical calorimetry help researchers evaluate electrolyte additives and identify more stable battery formulations?
One of the really useful applications of electrochemical calorimetry is screening different electrolyte formulations and additives.
Generally speaking, heat flow is more sensitive to changes in formulation than electrochemical performance. That means we can often identify differences between materials much earlier than we would through conventional cycling tests.
For example, we looked at the effect of adding vinylene carbonate to an electrolyte formulation by comparing a control cell without the additive against a cell containing 4% vinylene carbonate.
When we looked at the voltage profiles, there wasn't really a significant difference between the two formulations. There was a slight shift associated with capacity, but nothing particularly obvious.
However, when we looked at the heat flow, there was a clear difference.
The cell containing vinylene carbonate generated less heat during cycling and also under open-circuit storage conditions. This reduction in heat flow was associated with the suppression of parasitic reactions.
We could also see differences in the upper voltage range. The control cell underwent significant changes between the first three cycles, whereas the formulation containing vinylene carbonate was much more stable.
That's exactly the kind of information we're looking for. Less change between cycles indicates greater stability and fewer parasitic reactions.
In another example, we isolated the heat associated with parasitic reactions and plotted it as a function of voltage. Without the additive, the parasitic heat increased with voltage; when vinylene carbonate was added, those reactions were suppressed.
We then compared those results with a conventional cycle-life experiment, which took three months to complete. This longer experiment confirmed the same trend: the cells containing the additive showed better capacity retention.
So, we're obtaining a similar correlation between formulation and long-term performance using a much shorter electrochemical calorimetry experiment. This can be extremely valuable when researchers are screening multiple formulations and trying to identify promising materials efficiently.
How can battery testing under different storage temperatures and charging conditions help predict long-term performance?
One of the important questions in battery research is how end-use conditions affect the cell's lifetime and performance.
For example, during open-circuit storage, we ideally don't want anything to happen inside the battery. Any heat flow we measure indicates that some type of process may be occurring, such as self-discharge or parasitic reactions.
We can measure heat flow at various temperatures to assess the cell's stability under different ambient conditions.
By integrating the heat-flow signal, we obtain the total heat generated over time. In one example, we could differentiate between cells after just 24 hours of measurement.
We also looked at the effect of cycling temperature by comparing the same cell chemistry at 25 °C and 40 °C.
At the higher temperature, parasitic heat increased significantly, even though the total heat flow changed only slightly. This tells us that more parasitic reactions are occurring at higher temperatures, which can contribute to a reduction in cell lifetime.
Charging rate is another important consideration: as you might expect, faster charging produces more heat. However, what's particularly interesting is that the heat isn't distributed uniformly across the state of charge.
In one experiment, the heat flow was approximately 15 milliwatts in some regions and exceeded 50 milliwatts in others. Near the beginning of charging, we even observed endothermic behavior.
This type of high-resolution heat-flow information could be valuable for developing more advanced battery thermal management systems. Rather than assuming that heat generation is constant throughout charging, researchers can identify the states of charge where additional cooling or different operating conditions may be beneficial.
Can microcalorimetry detect the early signs of battery failure before they become apparent through conventional electrochemical measurements?
Yes; this is one of the particularly interesting applications of high-sensitivity calorimetry.
To demonstrate this, we conducted an experiment examining the heat flow and voltage profile during the coin-cell formation protocol. On day four, we observed a rapid increase in heat flow, a behavior that typically precedes cell failure.
When we examined the voltage profile, however, there wasn't an obvious indication of a problem until the final cycle. At that point, we saw voltage drops during open-circuit periods, higher capacity during charging, and lower capacity during discharge.
These observations suggested that an internal short circuit was developing, most likely due to lithium dendrite growth. But when I went back and examined the heat-flow data more closely, I could actually identify signs of instability approximately two and a half days before that major event.
On day two, there were small spikes in the heat-flow signal, potentially associated with lithium metal plating or reactions between lithium metal and the electrolyte. That instability continued to increase until the cell reached the critical failure point on day four.
So, by using a more sensitive calorimeter, we were able to observe the evolution of the failure mechanism much earlier than we could from the voltage data alone.
In this way, microcalorimetry helps us not only identify that a failure has occurred, but also gain information about the processes leading up to it.
How can calorimetry be used to investigate material compatibility when developing new battery chemistries?
Material compatibility is another important application, and it doesn't necessarily require electrochemical cycling.
With the TAM IV, we can conduct experiments with static ampules to measure heat flow across different materials.
The principle is fairly straightforward. We first measure the heat flow of the individual components and then mix them together. If the heat flow of the mixture exceeds what we would expect from the individual components, it indicates that some type of reaction is occurring.
For battery materials, we generally don't want spontaneous reactions happening between components unless we're intentionally charging or discharging the cell.
For example, if we're introducing a new electrode material, binder, or electrolyte additive, we want to understand whether it will react with the materials already present in the formulation. A high-sensitivity calorimeter allows us to detect even very slow reactions that might otherwise be difficult to identify.
We can also investigate how these interactions change under different environmental conditions.
Experiments can involve solid-solid, solid-liquid, or liquid-liquid combinations, as well as materials exposed to gases or controlled humidity.
This is particularly relevant for battery manufacturing, where exposure to moisture or different atmospheric conditions can influence material stability.
The technique allows researchers to understand these interactions before scaling up a new battery chemistry.
What are some of the key advantages of using microcalorimetry for battery testing?
One of the advantages of the system is its flexibility. We can test different cell formats, including coin, cylindrical, and pouch cells, provided they fit within the dimensions of the selected calorimeter.
We can also evaluate half cells. From the calorimeter's perspective, the measurement is essentially the same as for a full cell. The main difference is in the materials used during cell preparation.
For pouch cells, it's also possible to apply pressure during measurement. With the Micro XL calorimeter, for example, a pressure plate can be placed over the pouch cell, and the applied force can be controlled and measured.
Another key consideration is temperature. The TAM IV thermostat operates over a range of approximately 4 °C to 150 °C. However, when testing batteries, we need to remain within the chemistry's safe operating limits.
For a typical lithium-ion battery, that might mean operating up to around 60 °C, although some more thermally stable materials can tolerate higher temperatures.
I would recommend evaluating the battery's thermal stability separately before introducing it into the calorimeter, particularly when operating at elevated temperatures.
In terms of software, we don't need multiple programs to control the experiment. Our TAM Assistant software communicates with the BioLogic potentiostat through its API, allowing simultaneous instrument control and data acquisition.
The data is imported in real time, and various analyses can be automated. Researchers can also export the data for additional processing.
Ultimately, the objective is to make it easier to obtain detailed thermal and electrochemical information without introducing unnecessary complexity into the experimental workflow.
Looking ahead, what role do you see advanced battery testing techniques playing in the development of next-generation battery materials?
I think one of the most important contributions of electrochemical calorimetry is the ability to understand new battery chemistries at a much more fundamental level.
When we're developing new materials, we need to understand not only how much energy a cell can store, but also how those materials behave throughout charging, discharging, and storage.
With calorimetry, we can investigate phase transitions, thermal stability, spontaneous chemical reactions, and electrochemical energy storage processes. We can also study how these events vary with temperature and lithiation.
The ability to measure side reactions is particularly important because these processes can significantly affect long-term battery performance. For researchers developing new cell chemistries, this additional information can help identify promising formulations and understand their limitations before moving toward larger-scale production.
As I've started using this technique more extensively, I've become increasingly reliant on heat-flow data to interpret how different battery chemistries behave. I would consider it an essential tool for fundamental battery research because it provides information that simply isn't available from electrochemical measurements alone.
The broader opportunity is to combine these measurements to enable researchers to make better-informed decisions about materials, operating conditions, and cell design.
By integrating physical, chemical, and electrochemical processes, we can accelerate battery development while improving our understanding of performance, stability, and safety.
About Dr. Jeremy May
Dr. Jeremy May is a Senior Applications Scientist at TA Instruments, part of Waters Materials Sciences, based in New Castle, Delaware, USA. He specializes in battery material characterization and in operando electrochemical calorimetry, supporting research and development across battery and green energy applications.
May earned his Bachelor of Arts in Chemistry from Pacific Lutheran University in 2013 before pursuing a PhD in Chemistry at the University of Idaho. His academic background provided a foundation in electrochemistry and materials characterization, which he has applied to energy storage research and analytical instrumentation.
With experience spanning electroanalytical chemistry, hydrogen fuel cells, and lithium-ion batteries, May works to advance researchers' understanding of the physical and chemical processes influencing battery performance. His expertise includes integrating electrochemical measurements with sensitive thermal analysis techniques to investigate battery degradation, material stability, and cell behavior during cycling.
His research contributions include work on solid electrolyte interphase evolution in lithium-ion battery electrodes and the use of isothermal microcalorimetry to accelerate the screening of emerging battery chemistries.
Through his role at TA Instruments, May helps researchers apply advanced characterization techniques to evaluate battery materials, investigate failure mechanisms, and improve the efficiency of battery research and development.
This information has been sourced, reviewed, and adapted from materials provided by TA Instruments.
For more information on this source, please visit TA Instruments.
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