As wireless-enabled electronics are becoming smaller and more common, researchers worldwide are finding ways for batteries to store more power in less space and save weight. However, energy density gets exponentially harder to improve upon as a battery gets smaller, partially because larger portions of a battery’s footprint must be devoted to the protective packaging.
Engineers at the University of Pennsylvania have found a new way to build and package microbatteries that drastically improve energy and power density even at the smallest sizes. They developed a new kind of current collector and cathode that increases the fraction of materials that store energy while simultaneously serving as a protective shell. This reduces the need for non-conductive packaging that normally protects a battery’s sensitive internal chemicals.
Microbatteries have historically required ultra-thin electrodes that allow for fast transport of electrons and ions, but this slim profile limits the amount of energy-storing chemicals they can contain. Conventional cathodes – one of a battery’s two electrodes – consist of crushed particles compressed together, a process that results in large spaces between electrodes and a random internal configuration that slows ions as they move through the battery.
Now, the engineers are 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 James Pikul, a leader of the study. “They act as both an electron conductor and as the packaging that prevents water and oxygen from getting into the battery.“
This microbattery design also aligns the cathode’s ‘atomic highways,’ which allows lithium ions to move via the fastest and most direct routes through the cathode and into the device. These redesigned components are so efficient at transporting ions that they can be made thick enough to double the amount of energy-storing chemicals without sacrificing the speed necessary to actually power the devices they’re connected to.
Combined with the new packaging, these microbatteries have an energy density four times that of current state-of-the-art designs. The battery weighs about as much as two grains of rice but has the energy and power density of batteries that are a hundred times larger and heavier.
The researchers’ packing-free microbattery design opens the door for smaller flying microrobots, implanted medical devices with longer lifespans, and a variety of otherwise impossible devices for the Internet of Things.
The team will continue to study chemical and physical features that can be tuned to further improve the performance while also building wearable devices and microrobots that take advantage of these new power sources.