I think it is related to CNTs and graphenes appropriate dielectric properties. both of these materials exhibit high amount of permitivitty in addition of high surface area and good electrical conductivity.
Also, CNTs, graphenes (as well as CNF composites[1]) as clever fillers[2] in common anode materials for a higher conductivity, applying engineering on the percolation laws (of conductivity threshold) of the composite[3] anode materials.
1. Carbon Nanofibers and Their Composites: A Review of
Synthesizing, Properties and Applications www.mdpi.com/1996-1944/7/5/3919/pdf
2. Carbon blacks are like dummy fillers, compared to clever fillers with an additional Li capacity.
3. Carbon Nanotube and Graphene Based Polyamide Electrospun Nanocomposites: A Review downloads.hindawi.com/journals/jnm/2016/3182761.pdf