Nanocellulose-Based Hybrid Hydrogels as Flexible Cathodes of Aqueous Zn-Ion Batteries

Cellulose nanofibers, detached from natural plants, are very promising for applications in the energy storage devices. The swelling of cellulose nanofibers provides abundant paths in the hybrid hydrogels for ion diffusion towards the active material. There is an optimal composition of 50 wt.% for cellulose nanofibers in the hybrid hydrogels due to the balance between ion diffusion and electron transport, that is, facilitated by conductive graphite nanoplatelets. The aqueous Zn-ion batteries, assembled from the optimized hybrid hydrogels, have a high-specific capacity of 149.4 mAh/g and energy density of 113.2 mWh/g, respectively. Moreover, high flexibility of the aqueous Zn-ion batteries is guaranteed by the hybrid hydrogels. There is only a little decay in the electrochemical performance under mechanical bending.