Desert beetle-inspired MWCNT-engineered prepregs achieving coupled electrochemical and mechanical enhancement in structural battery composites

Structural battery composites (SBCs) integrate load-bearing capability with electrochemical energy storage, but polymer-composite encapsulation is still limited by the trade-off between mechanical integrity and durable hermetic sealing. Inspired by the tortuous microstructures of the Namib Desert beetle shell, we developed MWCNT-modified CFRP/GFRP prepregs as nano-engineered load-bearing barriers for SBCs. The percolated MWCNT network densifies polymer-rich regions, constrains chain relaxation, and increases diffusion tortuosity while preserving fiber-dominated stress transfer. At the optimized 0.3 S-MWCNT modification, water vapor and oxygen transmission rates (WVTR/OTR) decrease to 0.49 g/(m²·day) and 0.79 cm³/(m²·day), respectively, more than 70% lower than those of unmodified prepregs. After 5,000 bending cycles, OTR and WVTR increase by only 5.06% and 10.20%, confirming barrier retention under repeated deformation. Qualitative molecular dynamics simulations show that MWCNT-induced polymer confinement suppresses nanovoid formation and slows water penetration, while RVE-based finite-element analysis confirms that the fiber-dominated load path is retained. The resulting CFRP/GFRP@0.3 S-MWCNT-SBCs retain 70.4% of their energy density after 170 cycles at 0.3 C, compared with 36.1% for unmodified CFRP/GFRP-SBCs, while maintaining tensile and flexural strengths of 285.3 and 176.4 MPa. They also retain 84.9% energy density after 5,000 dynamic bending cycles at 0–80 MPa during 0.7 C operation, and achieve a multifunctional efficiency of 0.98 together with stable phone-charging and underwater power-supply demonstrations. These results demonstrate that MWCNT-engineered prepregs provide a scalable encapsulation strategy that balances hermeticity with mechanical and electrochemical durability in SBCs.