This could overcome the current constraints of lithium-ion batteries which reach a natural limit of how much charge can be packed into any given space and provide electric vehicle (EV) drivers with longer-range driving.
By using aggressive electrodes and then stabilising these electrode materials with a highly-fluorinated electrolyte, the researchers at the University of Maryland (UMD), the U.S. Army Research Laboratory (ARL), and Argonne National Laboratory (ANL) believe to have achieved this feat.
"We have created a fluorine-based electrolyte to enable a lithium-metal anode, which is known to be notoriously unstable, and demonstrated a battery that lasts up to a thousand cycles with high capacity," says co-first authors Xiulin Fan and Long Chen, postdoctoral researchers at UMD's A. James Clark School of Engineering.
This enables the batteries to be charged and discharged many times over without losing the ability to provide a reliable and high quality stream of energy, says the team. Even after a thousand charge cycles, the fluorine enhanced electrolytes ensured 93% of battery capacity, which the authors call "unprecedented." This means that a car running on this technology would reliably drive the same number of miles for many years.
The team demonstrated the batteries in coin-cell shape like a watch battery for testing and is working with industry partners to use the electrolytes for a high voltage battery.
These aggressive materials, such as the lithium-metal anode and nickel and high-voltage cathode materials, are called such because they react strongly with other material, meaning that they can hold a lot of energy but also tend to "eat up" any other elements they're partnered with, rendering them unusable.
Fluorine was identified as a key ingredient to ensure the aggressive chemistries behaved reversibly to yield long battery life. It also makes usually combustible electrolytes completely unable to catch on fire, according to the team.
The researchers captured video of several battery cells catching on fire in instants, but the fluorine battery was impervious.
The high population of fluorine-containing species in the interphases is the key to making the material work, even though results have varied for different researchers in the past regarding the fluorination.
"You can find evidences from literature that either support or disapprove fluorine as good ingredient in interphases," explains Kang Xu of ARL. "What we learned in this work is that, in most cases, it is not just what chemical ingredients you have in the interphase, but how they are arranged and distributed."