Carbon materials can be classified into graphite carbon, soft carbon and hard carbon based on the different hybridization orbitals of carbon atoms. Generally speaking, graphite carbon and soft carbon have high elasticity but low strength and are prone to deformation. While hard carbon has high strength and good stability, it is brittle. How to prepare hard carbon materials into superelastic materials remains a challenge. 
Recently, the research group led by Professor Yu Shuhong from the University of Science and Technology of China was inspired by the fact that spider webs possess both high strength and high elasticity in nature. They ingeniously constructed a nano-fiber network structure using the template method, endowing traditional hard carbon materials with super elasticity. By using resorcinol-formaldehyde (RF) resin as the hard carbon source and various nanofibers, including bacterial cellulose nanofibers, tellurium nanowires, and carbon nanotubes, as structural templates to prepare RF's nano-fiber aerogel, the super elastic and fatigue-resistant hard carbon aerogel (HCA) can be obtained through high-temperature carbonization. 
By simply controlling the raw material ratio, researchers can easily regulate the physical parameters of the aerogel. Moreover, thanks to the nanofiber network structure and the hard carbon welding points between the fibers, the obtained HCAs have excellent mechanical properties. Through in-situ scanning electron microscopy, it was found that after 50% compression, the overall structure of the material returned to its original state, with no obvious structural damage or irreversible deformation. 
This material exhibits excellent elastic properties, with an elastic recovery speed of up to 860 mm·s-1 and an energy loss coefficient as low as 0.16. Compared to traditional carbon materials, it combines both elasticity and strength. 
This new type of HCA also achieves a balance between elasticity and strength. The researchers investigated its properties as a large-range piezoresistive sensor and as an extensible/curable conductor. The results showed that this elastic conductor has excellent cyclic stability, and due to the stability of its structure and composition, it can operate in harsh environments (such as in liquid nitrogen). 
The most significant aspect of this research lies in the transformation of traditional brittle and rigid resin into high-performance ultraelastic hard carbon aerogel materials through the inspiration from natural materials and meticulous design of the microstructure. Compared to traditional carbon materials, this aerogel exhibits extremely high rebound speed, extremely low energy loss, while maintaining high strength and stability. This method is expected to be extended to the preparation of other non-carbon-based nanofiber materials, providing researchers with a new idea of transforming rigid materials into elastic or flexible materials by designing the microstructure of nanofibers.