A new method of increasing lithium-ion battery energy density has been developed by an assistant professor at Columbia Engineering, according to a new press release from the university.
The assistant professor’s new method relies on the use of a tri-layer battery structure that is stable even in ambient air — leading to improved battery lifespan and potentially lower cost of manufacturing. Battery energy density could be improved by as much as 10–30% according to those involved.
“When lithium batteries are charged the first time, they lose anywhere from 5–20% energy in that first cycle,” stated assistant professor of materials science and engineering at Columbia Engineering Yuan Yang. “Through our design, we’ve been able to gain back this loss, and we think our method has great potential to increase the operation time of batteries for portable electronics and electrical vehicles.”
What Yang is referring to is the fact that, as the first charge of a lithium-ion battery is performed, some of the liquid electrolyte is reduced to a solid and ends up coated on the negative electrode. Typically, this process is forced before batteries are shipped from the factory.
The degree of the battery capacity loss that occurs relates to the type of electrode used — it’s as low as 10% when state-of-the-art negative electrodes are used in the battery, and as high as 20–30% for next-gen negative electrodes with high capacity. This last bit relates to silicon electrodes, amongst others.
Conventionally, the means of dealing with this loss has been the inclusion of lithium-rich materials in the electrode. Most of these lithium-rich materials, though, aren’t stable in ambient air. As you can probably guess, manufacturing in ambient air is far cheaper than the other options.
That’s where Yang’s new method comes in. Columbia states that he “developed a new trilayer electrode structure to fabricate lithiated battery anodes in ambient air. In these electrodes, he protected the lithium with a layer of the polymer PMMA to prevent lithium from reacting with air and moisture, and then coated the PMMA with such active materials as artificial graphite or silicon nanoparticles. The PMMA layer was then dissolved in the battery electrolyte, thus exposing the lithium to the electrode materials.”
“This way we were able to avoid any contact with air between unstable lithium and a lithiated electrode,” Yang explained, “so the trilayer-structured electrode can be operated in ambient air. This could be an attractive advance towards mass production of lithiated battery electrodes.”
Using Yang’s method, the loss capacity occurring with state-of-the-art graphite electrodes dropped from 8% to 0.3%. Additionally, the loss capacity occurring with silicon electrodes was reduced from 13% to “-15%.” The -15% figure relates to the fact that there was apparently more lithium than was needed. This “extra” lithium will apparently lead to longer working lives, through compensation for loss in subsequent cycles.
The researchers involved are now working to reduce the polymer coating’s thickness in order to limit the amount of space/volume that it takes up. The researchers are also working on the scaling up of their fabrication techniques.
The new research is detailed in a paper published in the journal Nano Letters.