"This was a major challenge which really consumed us these last three years," said Deng. "There's nothing like this available commercially, that can be injected. Either the batteries are too big, or they don't last long enough to be useful. That's why we had to design our own."
Deng turned to materials science expert Jie Xiao to create the new battery design.
To pack more energy into a small area, Xiao's team improved upon the "jellyroll" technique commonly used to make larger household cylindrical batteries. Xiao's team laid down layers of the battery materials one on top of the other in a process known as lamination, then rolled them up together, similar to how a jellyroll is created. The layers include a separating material sandwiched by a cathode made of carbon fluoride and an anode made of lithium.
The technique allowed her team to increase the area of the electrodes without increasing their thickness or the overall size of the battery. The increased area addresses one of the chief problems when making such a small battery keeping the impedance, which is a lot like resistance, from getting too high. High impedance occurs when so many electrons are packed into a small place that they don't flow easily or quickly along the routes required in a battery, instead getting in each other's way. The smaller the battery, the bigger the problem.
Using the jellyroll technique allowed Xiao's team to create a larger area for the electrons to interact, reducing impedance so much that the capacity of the material is ab
|Contact: Tom Rickey|
DOE/Pacific Northwest National Laboratory