Scientists have come up with a new design for small batteries, overcoming a fundamental problem by developing much denser cathodes that can be “electrolyzed” directly onto thin metal foil, according to a recent study published in the journal Advanced Materials.
The research was carried out by engineers at the University of Pennsylvania, who were investigating new designs for batteries that are compact and durable enough to power increasingly small wearables and electronic devices.
To keep these types of devices running, the batteries need to be protected from damage by impacts, water and oxygen, but this involves casing that adds to their weight and size, while doing nothing for their electrochemical performance.
To overcome this limitation, the scientists reimagined the way tiny batteries are typically designed. These devices usually feature ultra-thin electrodes that allow for fast transport of electrons and ions, but this slim profile limits the amount of chemicals they can contain, and therefore the amount of energy they can store.
Cathodes are one of a battery’s two electrodes, and are typically made of crushed particles that are compressed together in a way that creates a porous structure with air gaps, which influences the speed ions can move through the battery.
The scientists overcome this problem by developing a far denser cathode material that could be “electroplated” directly onto thin metal foils, which also act as the casing.
“We essentially made current collectors that perform double duty,” says study leader James Pikul. “They act as both an electron conductor and as the packaging that prevents water and oxygen from getting into the battery.”
According to the researchers, this microbattery design also aligns the cathode’s “atomic highways”, which allows lithium ions to travel quickly and directly through the cathode and into the device.
Because the ions can travel far more efficiently through the cathode, it can be made far thicker without compromising on this key attribute, which in turn doubles the amount of energy-storing chemicals it can contain.
Ultimately, this allows for a microbattery with an energy density four times that of the current-state-of-the-art designs.
The tiny battery weighs the same as two grains of rice but has the energy and power density of a battery 100 times its size, and the researchers imagine it finding use in a number of areas.
These include tiny flying robots, wearables, medical implants that offer longer lifespans, or the countless wireless devices that make up the Internet of Things.