Foldable and free-standing 3D network electrodes based on cellulose nanofibers, carbon nanotubes and elongated TiO2 nanotubes

• The foldable and free-standing film was successfully prepared for the first time.
• The film has a porous 3D network structure.
• The film electrode exhibited high performance without binder.
• TiO2 nanotubes can enhance charge transport along the longitudinal dimension.

Foldable and free-standing electrodes were fabricated using the macroporous cellulose nanofibers (CNFs) as the scaffold. Multi-walled carbon nanotubes (MCNTs) wrapped around the CNFs as the conductive skin, while the elongated (tens of microns) TiO2 nanotubes (TNTs) were interpenetrated within the MCNTs and macroporous CNFs network. Electrochemical analysis indicated that the hybrid electrodes displayed a high discharge capacity of 62.5 mF/cm2 at 10 mV/s and a good cyclability with a capacity loss 5% after 1000 cycles at 0.5 mA/cm2. The hybrid electrodes possessed highly mechanical property and could be folded back and forth as a paper airplane without mechanical failure. Therefore the low-cost, light-weight and foldable electrodes can be well applied as foldable all-solid-state supercapacitors.