Thermally insulating and fire‐retardant bio‐mimic structural composites with a negative Poisson's ratio for battery protection

Abstract Battery safety has attracted considerable attention worldwide due to the rapid development of wearable electronics and the steady increase in the production and use of electric vehicles. As battery failures are often associated with mechanical‐thermal coupled behaviors, protective shielding materials with excellent mechanical robustness and flame‐retardant properties are highly desired to mitigate thermal runaway. However, most of the thermal insulating materials are not strong enough to protect batteries from mechanical abuse, which is one of the most critical scenarios with catastrophic consequences. Here, inspired by wood, we have developed an effective approach to engineer a hierarchical nanocomposite via self‐assembly of calcium silicate hydrate and polyvinyl alcohol polymer chains (referred as CSH wood). The versatile protective material CSH wood demonstrates an unprecedented combination of light weight (0.018 g cm⁻³), high stiffness (204 MPa in the axial direction), negative Poisson's ratio (−0.15), remarkable toughness (6.67 × 10⁵ J m⁻³), superior thermal insulation (0.0204 W m⁻¹ K⁻¹ in the radial direction), and excellent fire retardancy (UL94‐V0). When applied as a protective cover or a protective layer within battery packages, the tough CSH wood can resist high‐impact load and block heat diffusion to block or delay the spread of fire, therefore significantly reducing the risk of property damage or bodily injuries caused by battery explosions. This work provides new pathways for fabricating advanced thermal insulating materials with large scalability and demonstrates great potential for the protection of electronic devices.