Among the limitations of electric vehicles (EVs) is the lack of a long-lasting, high-energy-density battery that reduces the need to fuel up on long-haul trips. The same is true for houses during blackouts and power grid failures— small, efficient batteries able to power a home for more than one night without electricity don’t yet exist. A major issue is that while rechargeable lithium metal anodes play a key role in how well this new wave of lithium batteries functions, during battery operation, they are highly susceptible to the growth of dendrites — microstructures that can lead to dangerous short-circuiting, catching on fire, and even exploding.
Researchers have found that alkali metal additives, such as potassium ions, can prevent lithium microstructure proliferation during battery use. They used a combination of microscopy, nuclear magnetic resonance (similar to an MRI), and computational modeling to discover that adding small amounts of potassium salt to a conventional lithium battery electrolyte produces unique chemistry at the lithium/electrolyte interface. Specifically, they found that potassium ions mitigate the formation of undesirable chemical compounds that deposit on the surface of lithium metal and prevent lithium-ion transport during battery charging and discharging, ultimately limiting microstructural growth.
The discovery that alkali metal additives suppress the growth of nonconductive compounds on the surface of lithium metal differs from traditional electrolyte manipulation approaches, which have focused on depositing conductive polymers on the metal’s surface.
Commercial electrolytes are a combination of carefully selected molecules. Using NMR and computer simulations, the researchers were able to understand how the electrolyte formulations improve lithium metal battery performance at the molecular level. The team is now testing alkali metal additives that stop the formation of deleterious surface layers in combination with more traditional additives that encourage the growth of conductive layers on lithium metal. They are also actively using NMR to directly measure the rate of lithium transport through this layer.