Researchers developed an ultrasound-emitting device that brings lithium metal batteries (LMBs) one step closer to commercial viability. Although the research focused on LMBs, the device can be used in any battery, regardless of chemistry. The device is an integral part of the battery and works by emitting ultrasound waves to create a circulating current in the electrolyte liquid found between the anode and cathode. This prevents the formation of lithium metal growths, called dendrites, during charging that lead to decreased performance and short circuits in LMBs.
The device is made from off-the-shelf smartphone components that generate sound waves at extremely high frequencies — ranging from 100 million to 10 billion hertz. In phones, these devices are used mainly to filter the wireless cellular signal and identify and filter voice calls and data. Researchers used them instead to generate a flow within the battery’s electrolyte.
Currently, LMBs have not been considered a viable option to power everything from electric vehicles to electronics because their lifespan is too short. But these batteries also have twice the capacity of today’s best lithium ion batteries; for example, lithium metal-powered electric vehicles would have twice the range of lithium-ion powered vehicles for the same battery weight. A lithium metal battery equipped with the device could be charged and discharged for 250 cycles and a lithium-ion battery for more than 2,000 cycles. The batteries were charged from zero to 100% in 10 minutes for each cycle.
Most battery research efforts focus on finding the perfect chemistry to develop batteries that last longer and charge faster. By contrast, the new device solves a fundamental issue: In traditional metal batteries, the electrolyte liquid between the cathode and anode is static. As a result, when the battery charges, the lithium ion in the electrolyte is depleted, making it more likely that lithium will deposit unevenly on the anode. This in turn causes the development of needle-like dendrites that can grow unchecked from the anode towards the cathode, causing the battery to short circuit and even catch fire. Rapid charging speeds this phenomenon up.
By propagating ultrasound waves through the battery, the device causes the electrolyte to flow, replenishing the lithium in the electrolyte and making it more likely that the lithium will form uniform, dense deposits on the anode during charging.