Batteries supply electricity to mobile electric appliances, such as smartphones and laptop computers. Also electric vehicles need batteries as powerful stores of electric energy. All batteries are expected to be rechargeable safely and reliably over and over again.
A major challenge is posed by the need to prolong service life and prevent fires as a result of short circuits. When lithium metal is produced during charging of a lithium ion battery, this may give rise to needle-shaped deposits, so-called dendrites. Where these dendrites become long enough to make a conductive connection between the electrodes, a short circuit is the consequence.
At present, manufacturers avoid the problem by using graphite for the negative electrode (anode). Drawbacks of graphite electrodes compared to lithium metal are the sophisticated manufacturing process and the lower specific energy density.
KIT scientists of the Institute for Applied Materials (IAM) developed a technology which can reduce dendrite growth. They use a special multilayered separator for this purpose. A separator acts as a spacer and insulator between the electrodes, and is porous in order to be impregnated by an electrolyte.
The separator developed at the KIT consists of a fine porous layer on the cathode side and a coarse porous layer on the anode side. The coarse structures offer sufficient space for controlled metal deposition, and prevent dendrite growth by the fine porous layer in the direction of the cathode.
The separator can also be positioned between two cathodes and then act as an anode at the same time, thanks to the use of electrically conducting components. The separator anode consists of fine porous layers on the outsides and one coarse porous fabric of polymer and metal filaments in the middle part. A metal, for instance lithium, can be forced into the fabric. A battery of this design is compact and has high energy density.