"Dead zone" discovery could bring high

With the potential to hold many times more energy than the graphite it would replace, silicon is an enticing proposition for scientists working on next-generation lithium batteries. The trouble is that the silicon doesn't stand up so well to the stresses of battery cycling, but through first-of-a-kind observations researchers have gained new insights into the reasons why, and uncovered clues as to how this swift deterioration might be avoided.

Scientists working to integrate silicon into lithium-ion batteries hope to incorporate or entirely replace the graphite used as the anode component, where it has the potential to store as much as 10 times the energy. The trouble is, however, that as the battery is charged and discharged, the silicon swells and causes the anode to crack, ultimately ruining any chance the battery has of holding a charge.

We've seen some interesting approaches to solving this dilemma over the years, including using silicon with special nanostructures, combining it with solid state electrolytes, forming silicon sandwiches or caging the material in graphene. But a new understanding of the reasons why silicon anodes rapidly fail could greatly aid efforts to shore up their stability, with scientists at Pacific Northwest National Laboratory now witnessing the process in unprecedented detail.

As a battery is cycled, lithium ions move back and forth between the anode and the other electrode, the cathode, via a liquid electrolyte. As these ions enter a silicon anode, they push the silicon atoms aside, which is what causes the anode to swell to three or four times its size. Then when the lithium ions leave again, they create empty voids that cause the battery to quickly fail.