Cellulose Nanofiber/Carbon Nanotube-Based Bicontinuous Ion/Electron Conduction Networks for High-Performance Aqueous Zn-Ion Batteries

Despite their potential as a next-generation alternative to current state-of-the-art lithium (Li)-ion batteries, rechargeable aqueous zinc (Zn)-ion batteries still lag in practical use due to their low energy density, sluggish redox kinetics, and limited cyclability. In sharp contrast to previous studies that have mostly focused on materials development, herein, a new electrode architecture strategy based on a 3D bicontinuous heterofibrous network scaffold (HNS) is presented. The HNS is an intermingled nanofibrous mixture composed of single-walled carbon nanotubes (SWCNTs, for electron-conduction channels) and hydrophilic cellulose nanofibers (CNFs, for electrolyte accessibility). As proof-of-concept for the HNS electrode, manganese dioxide (MnO₂) particles, one of the representative Zn-ion cathode active materials, are chosen. The HNS allows uniform dispersion of MnO₂ particles and constructs bicontinuous electron/ion conduction pathways over the entire HNS electrode (containing no metallic foil current collectors), thereby facilitating the redox kinetics (in particular, the intercalation/deintercalation of Zn²⁺ ions) of MnO₂ particles. Driven by these advantageous effects, the HNS electrode enables substantial improvements in the rate capability, cyclability (without structural disruption and aggregation of MnO₂), and electrode sheet-based energy (91 Wh kg_electrode⁻¹)/power (1848 W kg_electrode⁻¹) densities, which lie far beyond those achievable with conventional Zn-ion battery technologies.