Co3O4 Nanoneedle Array Grown on Carbon Fiber Paper for Air Cathodes towards Flexible and Rechargeable Zn–Air Batteries

An economical and efficient method is developed for preparing flexible cathodes. In this work, a dense mesoporous Co3O4 layer was first hydrothermally grown in situ on the surface of chopped carbon fibers (CFs), and then carbon fiber paper (Co3O4/CP) was prepared by a wet papermaking process as a flexible zinc-air battery (ZAB). The high-performance air cathode utilizes the high specific surface area of a single chopped carbon fiber, which is conducive to the deposition and adhesion of the Co3O4 layer. Through the wet papermaking process, Co3O4/CP has ultra-thin, high mechanical stability and excellent electrical conductivity. In addition, the assembled ZAB exhibits relatively excellent electrochemical performance, with a continuous cycle of more than 180 times at a current density of 2 mA·cm−2. The zinc-air battery can maintain a close fit and work stably and efficiently even under high bending conditions. This process of combining single carbon fibers to prepare ultra-thin, high-density, high-conductivity carbon fiber paper through a papermaking process has huge application potential in the field of flexible wearables.

EXPERIMENTAL STUDY OF LIGHTNING DAMAGE RESISTANCE OF UNPROTECTED AND PROTECTED STITCHED WARP-KNIT CARBON-EPOXY COMPOSITES

In-flight lightning strike damage to aircraft composite structures may compromise aircraft airworthiness. Hence, it is crucial to incorporate adequate protection systems to mitigate the lightning current. Most lightning strike protection (LSP) techniques involve bonding a metallic conductive layer to the cured laminate exterior. In this study, a novel LSP integration technique was used to develop unitized panels with three different protection layers: pitch carbon fiber paper (PCFP), graphene paper (GP), and copper mesh (CM). Each LSP layer was overlaid on through-the-thickness VectranHT stitched warp-knit multiaxial dry carbon fabric stacks, resin-infused, and oven-cured. A series of lightning strike tests to protected and unprotected stitched carbonepoxy laminates were conducted at a nominal peak current of 150 kA. Visual inspection was used to investigate each panel’s lightning damage resistance, understand the damage mechanisms, and evaluate the surface morphology at the strike locations. The size and severity of the damaged area depended on several factors: the outermost ply fiber direction, the strike location relative to VectranHT and polyester knitting treads, the lightning peak current, and the conductivity of the protection layers. The CM and GP protection layers effectively dissipated the lightning current in-plane and showed no damage to the underlying composite. The degree of lightning damage on an unprotected laminate was significantly lower than for a similar panel with PCFP protection. The presence of VectranHT structural stitches and polyester warp-knitting threads profoundly reduced the size and severity of lightning damage. These threads appeared to promote close contact between adjacent carbon fiber tows, resulting in better in-plane and through-thickness electrical/thermal conductivities and reduced lightning damage.