Interesting but not by graphene
However, it’s quite expensive. The hemp bast Mitlin uses is much cheaper than graphene and, on top of that, Mitlin says their hemp supercapacitors have been able to store 12 watt-hours of energy per kilogram – over 2x as high as conventional supercapacitors.
https://earthtechling.com/energy-storage-supercapacitor-hemp-waste/