Batteries continue to be the leading technology for storing energy from renewable sources, powering modern electric vehicles, and supporting consumer demand for wearable personal electronics and devices. Despite incredible technological advances over the past decade, researchers around the world are constantly faced with the challenge of developing the next generation of high-performance batteries that are cheaper, last longer, charge faster, are safer and also greener.
Leading the way is the lithium-ion battery, which was first developed in the second half of the 20th century and is so widespread that its developers received the Nobel Prize for Chemistry in 2019 brought. Traditionally, a cell was manufactured and then measured as a finished unit for its cycle performance, discharge rate and energy density, among other things. The disadvantage of this approach is that it does not allow identification of the specific component responsible for changes in battery performance and can significantly slow down innovation.
Within [the battery] , the calorimeter can measure very, very small amounts of heat even with the smallest reactions
However, with increasingly sophisticated characterization techniques, researchers can more thoroughly analyze entire functioning batteries and their individual components, thereby more accurately monitoring battery performance over time and under expected operating conditions. The ability to analyze batteries and their individual components more thoroughly enables chemists to select the best formulations for use in the battery in order to optimize their performance early in the development phase.
Electrochemical reactions can generate heat – and the thermodynamics of these ongoing reactions are an important tool for battery researchers. TA Instruments, a subsidiary of Waters, has a family of microcalorimeters that can do just that. The newest member of the family, the TAM IV microXL isothermal microcalorimeter, offers the sensitivity researchers need, says Neil Demarse, product manager for microcalorimetry at TA Instruments. A whole battery cell can be inserted into the device for testing. “It is one of the few instruments that can test the entire battery,” says Demarse, “it just needs to be built into the device.” And once inside, the calorimeter can measure very, very small amounts of heat, even with the smallest reactions, and provide information about how much energy is coming from the battery.
The data collected enables researchers to validate both the quality and performance of the battery during the R&D phase, explains Demarse – all of which are critical to optimizing new battery formulations and testing component compatibility. According to Demarse, the TAM portfolio of microcalorimeters was used by researchers at 3M in St. Paul, Minnesota to track parasitic reactions in a lithium-ion battery pouch. By testing the heat flow in these battery systems and changing the additives used in the electrolyte, the team was able to find the best additives that would help stabilize the battery and make it more efficient. Optimizing the battery at an early stage ultimately brings more benefits and makes batteries safer in the long term, says Demarse.
To be able to use AFM in real time during an actual electrochemical cycle of a battery is a remarkable achievement
In a recent webinar with Chemistry World, Larry Krause and Vincent Chevrier of Cyclikal provided insight into how using precise combinations of electrochemical and thermal signals can quantify parasitic responses, identify phase changes, entropic events, and even system-level events such as li Coating. Such insights can enable more accurate lifetime predictions, a new understanding of battery materials, and better cell designs.
Another recent development, looking at the battery as a whole, was done at Oxford Instruments (OI) in the UK, who have developed a version of their Atomic Force Microscope (AFM) Cypher to operate with a sealed electrochemical cell in a glove box. This AFM enabled Kumar Virwani and his colleagues at the IBM Almaden Research Center in the US to monitor the electrochemical reactions in one of the most promising next-generation battery technologies – the lithium-oxygen battery. The ability to use AFM during an actual real-time electrochemical cycle of a battery is a notable achievement. Since the electrochemical AFM cell was completely sealed in a glove box, the oxygen in the battery did not escape. Over 10 hour cycles, the AFM was able to show that lithium ions were dissolving and moving. A boundary layer then grew covering the electrodes until it began to dissolve halfway through the charge cycle. This in-situ imaging was critical evidence that the battery would likely survive many charge / discharge cycles. AFM is the only way this real-time monitoring can take place and will become another important tool in the battery development toolbox.
Mass spectrometry can also help refine entire battery systems. When batteries are used, they age. And as they get older, much like people who start wrinkling, breaking down, cracking, and underperforming, they start to do. Waters’ ultra-sensitive time-of-flight mass spectrometers, coupled with their chromatographic capability, enable researchers to monitor the aging process at every stage of battery life. A 2019 study with the Waters ACQUITY UPLC / APGC Xevo G2-XS QToF instrument shows how the system can be used to characterize changes in a pouch cell containing a promising electrode material – nickel-rich layered oxide and graphite SiOx – over the period of use.1
when is sustainable technology unsustainable?
The resulting analysis, performed at four different stages of battery life, looked at what was happening in the electrolyte. When using a lithium-ion battery, a layer forms around the anode which consumes part of the electrolyte. This layer, the SEI or solid electrolyte interphase layer, can stabilize the system, but it can also reduce its performance. A better understanding of how the SEI and anode ages will ultimately enable the development of longer-lasting batteries.
Mass spectrometry also plays a role in tracking how various electrolyte additives affect battery performance. For example, a 2018 study found2 The Waters Xevo G2-XS QTof tracked changes in the organic components of an electrolyte with various additives – here, too, we provided information about which type of SEI was formed with each composition. This kind of detailed characterization during development enables optimization at an early stage of battery development.
As more and more batteries are manufactured, resources inevitably become scarce. Against this background, we ask ourselves: When is a sustainable technology no longer sustainable? Unless every battery is recycled, the effects of replacing fossil fuels with renewables could show a darker side. Recycling will therefore be a crucial step towards the future of a battery-powered sustainable society.
As you start designing batteries that will last longer, the materials need to last longer
Neil Demarse, Microcalorimetry Product Manager, TA Instruments
To help with recycling, characterization is key. An example of promoting the recovery of valuable minerals is the work of a group in China in 2018.3rd The team, led by Hongying Hou from Kunming University of Science and Technology, wanted to find a way to recycle the lithium foils used in prototyping and developing next-generation batteries – lithium-air and lithium-sulfur solid-state batteries . When a new technology is developed, there is inevitably a lot of waste. Working out the best way to recycle these prototypes will support major recycling efforts once these batteries are fully commercialized. House’s team took the foils from their experimental button cells and quickly dissolved them in deionized water. Further treatment followed by vacuum drying and calcination in an oven left a black powder of LiFePO4th/ C. A number of techniques, including OI’s SEM-based microanalysis equipment, have analyzed this powder and interrogated myriad nano and microstructures. The team then took the powder and used it as the cathode in another electrochemical cell with promising results.
This circular economy approach, supported by high-tech characterization and other modern analytical tools, may have to become part of the battery development process in order to maintain supply.
Electric vehicle poster child Tesla announced last year that they plan to introduce a million-mile battery for their next line of electric cars. Details remain a secret, but there is no doubt that some interesting materials science will be involved. “When you start making batteries that last longer, the materials have to last longer,” says Demarse. And with the help of sophisticated characterization tools, these materials will unlock that ability to go further on a single charge, store more energy, and lead us to a more sustainable society.