Rice University Adds Asphalt To Speed Lithium Metal Battery Charging By 20 Times (nextbigfuture.com)

schwit1 writes: The Rice lab of chemist James Tour developed anodes comprising porous carbon made from asphalt that showed exceptional stability after more than 500 charge-discharge cycles. A high-current density of 20 milliamps per square centimeter demonstrated the material's promise for use in rapid charge and discharge devices that require high-power density. The Tour lab previously used a derivative of asphalt -- specifically, untreated gilsonite, the same type used for the battery -- to capture greenhouse gases from natural gas. This time, the researchers mixed asphalt with conductive graphene nanoribbons and coated the composite with lithium metal through electrochemical deposition. The lab combined the anode with a sulfurized-carbon cathode to make full batteries for testing. The batteries showed a high-power density of 1,322 watts per kilogram and high-energy density of 943 watt-hours per kilogram. Testing revealed another significant benefit: The carbon mitigated the formation of lithium dendrites. These mossy deposits invade a battery's electrolyte. If they extend far enough, they short-circuit the anode and cathode and can cause the battery to fail, catch fire or explode. But the asphalt-derived carbon prevents any dendrite formation.

"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," Tour said. "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. 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 findings have been published in the journal ACS Nano.

Comments

Re:We read about battery improvements...

[Rei]

Meanwhile, cell phone batteries keep shrinking while their amp hours keep growing.

No, any given announcement isn't likely to ultimately play out. But some fraction of them do, and they change the world behind the scenes. The classic example is silicon anodes, which were the subject of big news stories on Slashdot years ago, then there was nothing.... but today they're commonly used in high-capacity li-ions.

As for this specific research: I read the study, and I have to admit, it's pretty impressive. One of the big things is that not only is the ion mobility high, but the coulombic efficiency is also very high (95-96% at high charge rates, 99% at low rates). If you want fast charging, having both is critical; otherwise, you'll never remove all of the waste heat at a fast enough rate.

After having read the paper, I have to add some caveats about this:

The batteries showed a high-power density of 1,322 watts per kilogram and high-energy density of 943 watt-hours per kilogram.

This is for the active materials only, not for whole cells, and only at low power density. First, the cell capacity is quite sensitive to how fast you charge it - if you charge it fast, the peak capacity is significantly reduced. That said, it's not a permanent difference; if the next time you charge it's a slow charge you go right back to the higher capacity. Secondly, when you include the inactive materials, they show about 450Wh/kg at low charge rates, and around 300Wh/kg at high charge rates. That said, it's still nice - and further refinement could probably reduce the inactive mass.

The capacity loss over 500 cycles - perhaps I'm not reading clearly, as I'm not seeing where that figure is given out. One of their graphs appears to show something like 10-15% loss over 130 cycles at 0,5C charge rate. It's hard to say how the curve will continue from there. A caveat is worth adding, in that the higher your maximum capacity, the fewer cycles you actually need, since for a given task you put fewer cycles per unit time on a higher capacity battery than a smaller capacity battery.

I see nothing about accelerated aging tests to see if there's any particular aging effect. Then again, I don't expect much of one, given their chemistry.

As for manufacture, it's a simple process, and requires no (relatively) expensive mined materials (e.g. no cobalt or the like). That said, one of their components - graphene nanoribbons - I have no clue what the current manufacturing costs are, nor what the potential is to bring them down in mass production. In theory, for something that's pure carbon, the cost should be able to go way down, since basic organic feedstocks are dirt cheap compared to most inorganic feedstocks. But that doesn't mean we've gotten it down that much at this point.

Just my takes from reading the paper :)