As the world pivots en masse to renewed commitments to reducing greenhouse gases and harmful emissions, the demand for high-performance, inexpensive batteries will continue to grow. But the current industry-standard lithium-ion battery presents numerous technical constraints that limit its effectiveness and sustainability.
Faculty of Engineering Professor Jinhyuk Lee has been researching battery technology for more than a decade and is known as a rising star in the field. In a recent paper in Advanced Energy Materials, he and a team of researchers demonstrated a new path forward in the area of Disordered Rocksalt (DRX) cathodes.
Despite the name, DRX cathodes have nothing to do with the stuff you put on your driveway to get rid of ice. Rather, it refers to a class of battery materials that share a similar crystal structure with common table salt. Cathodes are one of the critical components of all batteries, and in current lithium-ion batteries, they are made with a significant amount of cobalt – a costly substance. The DRX cathodes open the door for other, more abundant materials to be used instead, such as manganese or iron, which are less than 1/18th the trading value of cobalt. Also, these cathodes can achieve twice the charge storage capacity than traditional types.
But despite this promise, DRX cathodes have thus far shown limited service life compared to standard cathodes, limiting their practical usage. The root of the problem is that conventional wisdom has long argued that battery cathodes should be designed to have what is referred to as ‘Li-excess’ compositions (i.e., where the lithium content is greater than the transition metal content in the materials). Other studies have shown that while Li-excess boosts the initial performance of DRX cathodes, it inevitably triggers material degradation upon extended cycling. Thus, their performance fades over time.
In stark contrast, however, Professor Lee demonstrated that Li-excess is not necessary for achieving high performance for certain DRX cathodes. In particular, he discovered that DRX cathodes made with manganese, one of the cheapest and most abundant metals to use in batteries, do not require Li-excess at all to deliver superior performance. Lead author on the study, Professor Lee explains, “This striking new finding allows researchers to remove the Li-excess constraint to significantly improve the service life of DRX cathodes, which has been the prime bottleneck of commercializing these inexpensive and high-energy materials.”
There is a potential for Li-ion batteries made with a DRX cathode to attain much-improved energy density, on the order of 300 to 400 watt hours per kilogram of battery – compared to current lithium-ion batteries, which provide 100 to 250 watt hours per kilogram. Such an improvement in energy density and cheaper cost of DRX cathode batteries would enable not only lighter, more efficient electric cars, but also airplanes and other transports. Professor Lee estimated, however, that the possible commercialization of the discovery was still a few years away.