Charge-engineered cellulose nanofibril binders for PFAS-free, high-loading lithium battery positive electrodes

The increasing demand for sustainable high-energy lithium-ion batteries has heightened concerns over the environmental and health impacts of per- and polyfluoroalkyl substances, used in current battery components. In particular, polyvinylidene fluoride, a synthetic resin used as the dominant electrode binder, relies on fluorinated chemicals and toxic solvents such as N-methyl-2-pyrrolidone, while also suffering from limited structural integrity under high-mass-loading conditions. Here, we show that a PFAS- and N-methyl-2-pyrrolidone-free binder based on charge-engineered cellulose nanofibrils derived from natural wood offers a renewable and sustainable alternative to polyvinylidene fluoride. The charge-engineered cellulose nanofibril binder, leveraging its cationic functional groups, promotes particle dispersion in the slurry through electrostatic repulsion and subsequently forms strong hydrogen bonds with electrode components after drying, reinforcing structural integrity. Additionally, its nanofibrous architecture forms robust, interconnected networks that facilitate electrolyte infiltration and ion transport. When implemented in LiNi_0.8Co_0.1Mn_0.1O₂ positive electrodes, this binder enables a mass loading of 113 mg cm^-2 and an electrode density of 3.65 g cm^-3, achieving an areal capacity of 22.5 mAh cm^-2 and a volumetric energy density of 1781.5 Wh L^-1 at 0.05 C (corresponding to 1.13 mA cm^-2), demonstrating competitive cell performance relative to electrodes based on conventional synthetic polymer binders. Moreover, the charge-engineered cellulose nanofibril binder enables N-methyl-2-pyrrolidone-free slurry processing, reducing the environmental footprint of electrode fabrication.