Waterborne polymer composites with surface-charge-modulated bentonite nanosheets for high-energy storage

Despite significant progress in high-energy dielectric polymer composites, conventional fabrication methods involving melt blending or solvent processing are often energy-intensive and environmentally unfriendly. Developing sustainable and waterborne dielectric materials has remained a long-standing challenge. In this work, we report a waterborne approach to fabricate high-energy dielectric films by electrostatically complexing negatively charged bentonite nanosheets (BNTs) with protonated chitosan (CTS), effectively neutralizing the surface charges and suppressing ionic conductivity. The resulting associative complexes promote the formation of densely packed, electrically heterogeneous structures. To enhance film flexibility and integrity, poly(vinyl alcohol) (PVA) was incorporated at varying amounts. Remarkably, at a CTS content of 10 wt%, corresponding to the isoelectric point of the BNT@CTS complexes, the composite exhibited significantly improved breakdown strength, despite a modest decrease in permittivity. An optimal energy storage density of 8.53 J cm −3 was achieved at 570 MV m −1 with a BNT:PVA mass ratio of 5:5. This optimum is attributed to the effective charge neutralization of BNTs, the improved BNT alignment, and the efficient buffering effect of the PVA matrix. This work offers a low-cost and sustainable route for processing inorganic colloids into high-energy dielectric materials without the use of hazardous solvents or energy-intensive processing. • A waterborne and sustainable route was developed to fabricate high-energy dielectric nanocomposites. • Bentonite nanosheets were electrostatically complexed with protonated chitosan to suppress ionic conductivity. • Poly(vinyl alcohol) enhanced film flexibility and enabled dense, electrically heterogeneous structures. • The optimized composite achieved 8.53 J cm −3 energy density at 570 MV m −1 with no hazardous solvents.