Supercapacitors posses higher power density and longer lifetime than lithium-ion batteries, making them attractive power sources for electronic devices. Flexible electronics for biomedical or military applications have garnered much interest. However, for these devices to be practical, the energy storage system must also be flexible. Consequently, there has been a huge push to develop flexible supercapacitors with high power and energy densities.

Seung W. Lee, Georgia Institute of Technology, USA, Jinhan Cho, Korea University, Republic of Korea, and colleagues developed metallic cellulose paper-based supercapacitor electrodes with excellent energy storage performance. The cellulose paper was changed into metallic paper by ligand-mediated layer-by-layer assembly of tetraoctylammonium bromide (TOABr)-stabilized gold nanoparticles and tris(2-aminoethyl) amine (TREN). Here, the bulky TOABr ligands were replaced by TREN molecules which reduced the contact resistance between neighboring gold nanoparticles and converts the insulating cellulose paper substrate to a highly porous/flexible current collector.

The metallic paper has a high surface area allowing the incorporation of pseudocapacitive nanoparticles such as MnO and Fe₃O₄. This lead to flexible supercapacitors with remarkable power/energy densities. The team further demonstrated that alternated adsorption of metal nanoparticles and pseudoconductive nanoparticles onto the metallic paper substantially increased the energy storage capabilities. Indeed, the researchers estimated a power and energy density of the metallic paper-based hybrid supercapacitors of up to 15.1 mW cm^–2 and 267.3 µWh cm^–2, respectively, outperforming conventional paper or textile-type supercapacitors.

• Flexible supercapacitor electrodes based on real metal-like cellulose papers,
  Yongmin Ko, Minseong Kwon, Wan Ki Bae, Byeongyong Lee, Seung Woo Lee, Jinhan Cho,
  Nature Communic. 2017.
  DOI: 10.1038/s41467-017-00550-3