Mitlin admits that his hemp fiber can’t do everything that graphene can, but for energy storage it works just as well – and at a tiny fraction of the price. The first step, he explains, “is to cook it – almost like a pressure cooker. It’s called hydrothermal synthesis. Once you dissolve the lignin and the semicellulose, it leaves these carbon nanosheets – a pseudo-graphene structure.” These sheets are then assembled into electrodes and an ionic liquid added as the electrolyte, resulting in super-capacitors which operate at a broad range of temperatures and a high energy density.
The American Chemical Society Journal ranks the hemp based material “on par with or better than commercial graphene-based devices”. It says the hemp fiber’s properties work down to 0 C and display some of the best power-energy combinations reported in the literature for any carbon. Fully assembled, their energy density is 12 Wh/kg, which can be achieved at a charge time of less than six seconds.
Why is this important?
We reported just yesterday that Tesla is working on a battery that uses graphene anodes to double the range of its cars. Elon Musk is quoted as saying the new technology could find its way into Tesla automobiles “soon”, if they make economic sense.
Substitute Mitlin’s new hemp based material for the graphene in Musk’s experimental battery and you have a device with high energy storage ability and fast recharge times. Which means the lowly hemp plant, so long despised and vilified, may be the key to unlocking the the secret of affordable, practical electric cars.