An engineering team comprised of experts from Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory has taken a new approach to improving lithium batteries. The team replaced the two conventional current collectors found in the battery—sheets of copper or aluminum—with collectors made of polyamide, a lightweight polymer, coated with a thin layer of copper. (A collector distributes current flowing in and out of an electrode.)
The switch lowers the collectors’ weight by 80%, which is notable because collectors account for 15 to 50% of the weight of modern lithium batteries. This gives the new batteries energy densities (energy stored for a given weight) 16 to 26% greater than today’s lithium cells in terms of how much energy they can store for a given weight.
Researchers in the battery industry have long been trying get lighter current collectors by making them thinner or more porous, but these attempts have unwanted side effects. They make the batteries more fragile or chemically unstable, or require more electrolyte, all of which raise costs.
To combat the tendency of lithium batteries catching fire, the engineers tried adding fire retardants to the battery’s electrolyte (the flammable part). They found they could only add small amounts before the electrolyte became viscous and no longer conducted ions well.
To keep their new battery from going up in flames, the team embedded triphenyl phosphate, or TPP, in the polyamide as a fire retardant. Thus, the polyamide can resist fire and withstand the high temperatures associated with fast battery charging. The thin copper layer adds another level of protection against fire.
The new collectors should be easy to manufacture and less expensive because they replace some copper with an inexpensive polymer. Scaling up the technology for commercial production seem feasible, according to the researchers, who have applied for a patent through Stanford. They also plan on contacting battery manufacturers to explore the possibilities.
If the new design becomes widely used, it could extend the driving range of electric vehicles by lowering the weight of battery packs, as well as reduce the danger that laptops, cell phones and other devices will burst into flames. This is especially important when batteries are charged fast, creating more of the damage that leads to fires.