Hetero-Nanonet Rechargeable Paper Batteries: Toward Ultrahigh Energy Density and Origami Foldability

Forthcoming smart energy era is in strong pursuit of full-fledged rechargeable power sources with reliable electrochemical performances and shape versatility. Here, as a naturally abundant/environmentally friendly cellulose-mediated cell architecture strategy to address this challenging issue, a new class of hetero-nanonet (HN) paper batteries based on 1D building blocks of cellulose nanofibrils (CNFs)/multiwall carbon nanotubes (MWNTs) is demonstrated. The HN paper batteries consist of CNF/MWNT-intermingled heteronets embracing electrode active powders (CM electrodes) and microporous CNF separator membranes. The CNF/MWNT heteronet-mediated material/structural uniqueness enables the construction of 3D bicontinuous electron/ion transport pathways in the CM electrodes, thus facilitating electrochemical reaction kinetics. Furthermore, the metallic current collectors-free, CNF/MWNT heteronet architecture allows multiple stacking of CM electrodes in series, eventually leading to user-tailored, ultrathick (i.e., high-mass loading) electrodes far beyond those accessible with conventional battery technologies. Notably, the HN battery (multistacked LiNi_0.5Mn_1.5O₄ (cathode)/multistacked graphite (anode)) provides exceptionally high-energy density (=226 Wh kg^-1 per cell at 400 W kg^-1 per cell), which surpasses the target value (=200 Wh kg^-1 at 400 W kg^-1) of long-range (=300 miles) electric vehicle batteries. In addition, the heteronet-enabled mechanical compliance of CM electrodes, in combination with readily deformable CNF separators, allows the fabrication of paper crane batteries via origami folding technique. CNFs/CNTs-based hetero-nanonet paper batteries are presented as a 1D material-mediated cell architecture strategy to enable ultrahigh energy density and shape versatility far beyond those achievable with conventional battery technologies. Owing to the 3D bicontinuous electron/ion transport pathways and exceptional mechanical compliance, the hetero-nanonet paper batteries provide unprecedented improvements in the electrochemical reaction kinetics, energy density, and origami foldability.