By better understanding the intricacies of how lithium batteries operate, scientists can more easily identify opportunities to improve their performance, and scientists at the University of Cambridge have developed a powerful new tool for the job. A low-cost and novel microscopy technique has offered first-of-a-kind imagery of lithium ions in action, observations the team hopes can accelerate the development of smartphones and electric vehicles that charge in a fraction of the time.
“A better battery is one that can store a lot more energy or one that can charge much faster – ideally both,” says co-author Dr Christoph Schnedermann, from the University of Cambridge. “But to make better batteries out of new materials, and to improve the batteries we’re already using, we need to understand what’s going on inside them.”
Observing lithium batteries in action is currently possible only with expensive, sophisticated equipment such as electron microscopes or extremely powerful synchrotron X-ray machines, which are hundreds of thousands of times more intense than your typical X-rays. This isn't really a viable way for scientists to study the processes going on within actual lithium batteries in real-world conditions, in real-time, as first author of the study Alice Merryweather explains.
“To really study what’s happening inside a battery, you essentially have to get the microscope to do two things at once: it needs to observe batteries charging and discharging over a period of several hours, but at the same time it needs to capture very fast processes happening inside the battery,” she says.
In making their breakthrough, the Cambridge scientists leveraged an imaging technology known as interferometric scattering microscopy, which images tiny objects by using a reference beam to interact with and measure the light that they scatter. This enabled the team to image individual particles within a lithium cobalt oxide electrode in real-time, which revealed some interesting behaviors.
It showed the boundaries of the particles undergoing phase changes when the lithium ions traveled in and out as the battery was charged and discharged, which ultimately influenced the charging rate of the device. Simply observing this mechanism is a far cry from manipulating it to boost battery performance, but it is a key first step in the process.
“We found that there are different speed limits for lithium-ion batteries, depending on whether it’s charging or discharging,” says Dr Akshay Rao, who led the research. “When charging, the speed depends on how fast the lithium ions can pass through the particles of active material. When discharging, the speed depends on how fast the ions are inserted at the edges. If we can control these two mechanisms, it would enable lithium-ion batteries to charge much faster.”
Moreover, the study is a promising proof of concept for a novel imaging technique that will allow for far easier investigations into the finer details of battery functionality. This can allow scientists to explore advanced battery materials and track their performance, fast-tracking the route to devices that are safer, charge far more quickly and hold far more energy.
“Given that lithium-ion batteries have been in use for decades, you’d think we know everything there is to know about them, but that’s not the case,” says Schnedermann. “This technique lets us see just how fast it might be able to go through a charge-discharge cycle. What we’re really looking forward to is using the technique to study next-generation battery materials – we can use what we learned about LCO to develop new materials.”
The research was published in the journal Nature.
Source: University of Cambridge