Conductive polymer-coated nanocellulose enables dual-gradient thick electrodes for redox-homogeneous ultrahigh-areal-capacity Li-ion batteries

High-areal-capacity thick electrodes are essential for enhancing the energy density of lithium-ion batteries, yet their deployment is limited by redox heterogeneity caused by sedimentation-induced material segregation during electrode thickening. Here, we overcome this challenge by constructing a sedimentation-guided, redox-homogeneous thick electrode enabled by conducting polymer-coated nanocellulose. Unlike intrinsically insulating nanocellulose, this modified nanocellulose combines high electronic conductivity with enhanced ion transport, thereby unifying the roles of binders, conductive additives, and mechanical scaffolds in a single-phase network. This eliminates the binder/carbon domain inhomogeneity characteristic of conventional nanocellulose-based systems and transforms sedimentation from a fabrication challenge into a structural design advantage. The resulting thick paper electrodes exhibit an active material-porosity dual-gradient structure, in which active materials are densely and uniformly embedded within an interconnected conductive nanocellulose matrix, supporting fast, bicontinuous ion/electron transport and spatially uniform Li⁺ flux and current density. Using LiFePO₄ as a model, the electrodes deliver high areal and volumetric capacities of 16.7 mAh cm⁻² and 431.9 mAh cm⁻³, respectively, at a loading of 110 mg cm⁻² and a density of 2.9 g cm⁻³. This strategy not only redefines sedimentation as a tool for electrode engineering but also expands the functionality of sustainable cellulose materials for next-generation high-energy batteries.