SAN FRANCISCO—Researchers at Stanford University have developed a lithium-ion battery that cycles on and off based on temperature to prevent battery fires.
Traditional lithium-ion batteries can overheat if punctured or shorted, and can catch fire or explode at about 300 degrees Fahrenheit. Techniques such as adding flame retardants to an electrolyte make the battery nonfunctional and, thus, don't truly solve a problem, said Stanford engineer Yi Cui.
To solve this issue, Cui, chemical engineering professor Zhenan Bao, and postdoctoral scholar Zheng Chen turned to nanotechnology and a wearable body temperature monitor recently invented by Bao. The sensor is made of a plastic material and is embedded with tiny particles of nickel that have nanoscale spikes protruding from their surface. For use in batteries, researchers coated the spiky nickel particles with graphene, an atom-thick layer of carbon, and embedded the particles in a thin film of elastic polyethylene.
"We attached the polyethylene film to one of the battery electrodes so that an electric current could flow through it," Chen, the lead author of the study, said in a release. "To conduct electricity, the spiky particles have to physically touch one another. But during thermal expansion, polyethylene stretches. That causes the particles to spread apart, making the film non-conductive so that electricity can no longer flow through the battery."
Nanoparticles of graphene-coated nickel. (Source: Stanford/Image: postdoctoral scholar Zheng Chen)
Above 160 F, the polyethylene film expands, causing the spiky particles to separate and the battery to shut down. When the temperature drops to 160 F, the polyethylene shrunk, the particles came back into contact, and the battery started generating electricity again. Bao said they can tune the temperature based on the number of nickle particles and the type of polymer.
Researchers repeatedly applied heat to the battery with a hot-air gun to test stability. Each time, the battery shut down when it got too hot and quickly resumed operating when the temperature cooled.
The research was supported by the SLAC National Accelerator Laboratory and the Precourt Institute for Energy at Stanford. The battery study is published in the Jan. 11 issue of the journal Nature Energy.
it has the same function as a resettable switch, but tied to electrode temperature.
This can have value for series connections of cells, buried electrodes in a battery stack will have the same steady state temperature as the cells themselves, at least all the inner electrodes that have a cell on the left and the right.
It can be the P&J inside the sandwitch with a small, probably neglible for safety conserns time constant to internal cell if above Sandwich in stackup.
This idea and the original one have a basic issue of competing expansions if this is not mechanicaly solvable. Expansion of cell impiges on electode thermal switch that needs room to expand.
You have to insure the electrode thermal switch can win in an expansion fight.
Unfortunately, that only works for problems OUTSIDE the battery cells. The battery can still overheat/explode for an internal short.
I would hope that battery manufacturers are at least using thermal cutout switches between cells in their packs.
Years ago, I was on a project where we used a litihium primary (non-rechargable) battery. After some experiments with exploding batteries, we ended up using Duracell 6V (two cell) camera batteries which had a thermal cutout between the cells
Jessica....Laptops are the obvious one, not a heavy draw like cars, but there have been instances of them catching fire. Then again, you'd be pretty p...'d off if your laptop just shut down without saving your 20-page document! Phones and other small things usually have very small batteries, but might be applicable here. Then there are all the horror stories about Chinese-designed goodies catching fire. It would be a good safety net for bad design! It will be interesting to see what the developers say about this. The current capacity will have a big impact on its applicability.
The fires generally start with a failure of the separator as famously shown by the SONY laptop and Boeing Dreamliner incidents. This seems to act as a fuse for the battery discharge to an external load but would not protect against internal failures.
Taking a quick peek at \batteryuniversity.com the energy density of LiPo's are comparable to the best NiMH which don't have the problem(fire). However, LiPos are superior when it comes to self discharge rate. So if a product isn't used very often or charged, this is a significant factor, and now it can be as safe as NiMH.