As useful and ubiquitous as they are, lithium-ion batteries are nearing their limits, and it's unlikely we'll be able to squeeze much more juice out of them. Variations like lithium-air and lithium metal batteries are in the works to possibly replace them, and now researchers at Rice University have improved the latter with the help of an unlikely ingredient. The team found that adding asphalt to the anode made for lithium metal batteries that charge faster and are less likely to short circuit and fail.
To make their new battery, the Rice researchers used untreated gilsonite, a derivative of asphalt, and mixed it with conductive graphene nanoribbons. Then, that composite was coated in lithium metal through the process of electrochemical deposition, to create an anode. The final battery is made by combining this anode with a cathode of sulfurized carbon.
The team tested these new asphalt-lithium metal batteries over more than 500 charge-discharge cycles, and found the porous carbon material from the asphalt made the battery more stable. The batteries were found to have a power density of 1,322 watts per kg, and an energy density of 943 watt-hours per kg. Meanwhile, a high current density of 20 mA per square cm means that these batteries could be recharged from empty much faster than standard lithium-ion batteries.
"The capacity of these batteries is enormous, but what is equally remarkable is that we can bring them from zero charge to full charge in five minutes, rather than the typical two hours or more needed with other batteries," says James Tour, lead researcher on the project.
The new batteries have another vital trick up their sleeve: they prevent the formation of dendrites. These tiny tentacles of lithium often crop up on the anode during the charging process and eventually branch out throughout the device until they reach the other electrode. This short-circuits the battery and in extreme cases, can cause them to catch fire or even explode.
But the asphalt derivative helps prevent that, creating a more stable battery. The active ingredient in that process is the carbon, which the Rice researchers discovered in a previous project, using an anode of graphene and carbon nanotubes. The key difference here, the team says, is that the new design is much easier to make.
"While the capacity between the former and this new battery is similar, approaching the theoretical limit of lithium metal, the new asphalt-derived carbon can take up more lithium metal per unit area, and it is much simpler and cheaper to make," says Tour. "There is no chemical vapor deposition step, no e-beam deposition step and no need to grow nanotubes from graphene, so manufacturing is greatly simplified."
The research was published in the journal ACS Nano.
Source: Rice University