The asphalt-derived material before (left) and after it has been coated with lithium. (credit: Tour Group, Rice University)
Most of the batteries we use, from our cell phones to our cars, rely on using lithium ions. As a result, their capacity is largely a product of how much lithium you can stuff into a given volume. Obviously, using a pure lithium electrode would provide the highest density possible. But there has been no way to control where the lithium ends up as a battery goes through charge/discharge cycles. The typical result is a set of lithium metal spines that short the whole system out.
As a result, a lot of effort has been put into finding other materials that can incorporate lithium into their structure. This lowers the total lithium content but keeps the battery from shorting out. However, a new paper suggests an intriguing alternative, describing a material that ensures lithium forms a smooth coating on its surface with no spines. What’s this wonder material? A slightly modified version of asphalt.
Pavement from a chemistry perspective
Although the term “asphalt” is often used as a general term for blacktop pavement, it has a technical meaning as well: a viscous, semi-liquid hydrocarbon that’s one of the components of the paving material. There are several different types of asphalt, but the team here worked with something called gilsonite, which is close enough to a solid to be mined. Like other hydrocarbons, it’s a complex mix of molecules rather than a pure substance, and it contains things like nitrogen and sulfur due to its origin in biological material.
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