There is great potential for solid-state batteries to be a new lightweight, long-lasting power source for consumer electronics such as smart phones. Unlike typical lithium-ion batteries which contain liquid electrolytes, solid-state batteries are flexible, lighter, and have much longer shelf lives. However, it is widely understood that their performance is weak: they lose as much as 90 percent of their capacity after just ten charge and discharge cycles. Until recently, no one knew why.
Researchers from the National Institute of Standards and Technology (NIST), the University of Maryland, and Sandia National Laboratories have discovered why solid-state batteries lose their performance so quickly. Better yet, they have suggested a solution.
Previous efforts to understand why solid-state batteries degrade had only examined the battery before and after charging it, but new imaging followed changes on the anode’s surface while the battery was charging and discharging. Their work, which is described in the Journal of Materials Chemistry A, involved experiments using tools such as photoelectron spectroscopy, scanning electron microscopy and Auger electron microscopy under high vacuum.
Lithium-ion batteries typically have anodes made of carbon, but experimental solid-state batteries contain lightweight aluminum. The new images revealed that performance worsens because of oxidation of the surface of the aluminum anode. Aluminum-oxide—which has a lumpy appearance—captures lithium ions and prevents them from returning to the cathode during recharging. Therefore, electrons have fewer places to return to, which reduces the battery’s energy capacity with each subsequent charge. The researchers suggest solving this problem by coating aluminum electrodes with a different material that will not alloy.