Initial losses of up to 20% in battery energy density has been solved, claim Columbia University researchers
Increasing the energy density of lithium-ion batteries is vital if the uptake of EVs is to increase. While other chemistries and architectures will likely supersede li-ion cells eventually, at present they have proven to be the most effective commercial technology.
However, the potential capacity of current li-ion batteries is not being reached. Batteries have to be produced in a discharged state in order for the electrode materials to be air-stable. According to researchers at Columbia Engineering, the amount of positive lithium ions lost in the initial charge of the battery can equate to 5-20% of the total available capacity of a lithium battery. This figure could rise to a substantial 50% in the future as higher capacity anodes are rolled out. This is because higher capacity anodes require a large volume expansion and a high surface area.
Getting around this problem has been the focus of Yuan Yang and his colleagues at the US’ Columbia University, who last week published an article in Nano Letters claiming to have found a solution to manufacturing li-ion batteries in air.
“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,” said Yang.
The group has developed a new trilayer electrode structure allowing them to fabricate lithiated battery anodes in ambient air. By coating the lithium electrodes with a layer of polymer PMMA, the metal is prevented from reacting with air and moisture.
To expose the lithium to the electrode materials, the PMMA is coated in active materials such as artificial graphite or silicon nanoparticles, before being dissolved in the battery electrolyte. According to the results of the study, Yang’s method lowered the loss capacity in state-of-the-art graphite electrodes from 8% to 0.3%, and in silicon electrodes, from 13% to -15%.
This process is a very cheap option when compared with manufacturing the batteries in dry air, the current process used to compensate for the loss in capacity of batteries.
Increasing the energy density of existing production methods could squeeze valuable mileage out of EV battery packs, without greatly increasing their cost of manufacture.
Yang’s group is now trying to reduce the thickness of the polymer coating so that it will occupy a smaller volume in the lithium battery, and to scale up his technique.