Bioinspired Structuring

Paper-like materials for metal ion batteries

The motivation for our research is the need for better batteries, which is driven by the rapid developments in the fields of mobility and sustainable energy storage, which require a high power density, fast charging rate and long lifetime of more than several years. To overcome these limitations, intense research is directed to either finding strategies to further improve metal ion batteries or to develop alternative types of batteries. While most battery research has been focused on improving the electrode chemistry, the optimization of the electrode structure on the micro- and nanoscale is even more important. The latter task requires nanostructuring and aligning of the different components, for which the combination of material design and electrochemical engineering is essential.

The input of material science is transferring the structural concepts of biomaterials into the electrodes, resulting in self-supporting and binder-free electrodes (unlike conventional electrodes) in the form of micrometer thick flexible paper. Such papers exhibit a high mechanical flexibility, as illustrated in the video:

The envisioned electrodes comprise an alternating layer architecture combining inorganic nanostructures (i.e., SnO₂ nanowires, V₂O₅ nanofibres, or LiMnPO₄ nanoplatelets) as metal ion storage units with graphene sheets as charge transport elements of high mechanical flexibility and chemical stability. While the alternating layer structure is devised to facilitate stress distribution between the two types of constituents, the good electrical conductivity of the graphene is ideally suited to enhance the charge-discharge kinetics.

The major task is to explore the mechanical and electrochemical performance of the electrodes. Further the ratio between the inorganic and graphene layers, the microstructure and morphology of these layers, as well as the interfacial coupling between them. Our novel, paper-like electrodes are promising for different metal ion battery, where high energy density, rate capability and cycling stability is aimed.

Porous scaffolds inspired by cuttlebone

There is an increasing interest in light weight, functional materials that are suitable for applications related to sensors, filtering, gas distribution, acoustic and thermal insulators, catalysts or energy storage and conversion. In this work, the architecture of cuttlebone, a high performance structural biomaterial, shall be fully implemented into a synthetic, single-component, ceramic-based scaffold that combines a high specific surface area with high flexibility and good mechanical stability. This task is reached by an approach involving ice-templating of aqueous suspensions. The basic idea is to obtain a porosity that is a replica of the ice crystals, by freezing suspension and subsequently removing the ice crystals by sublimation.

Using the ice-templating approach we succeeded in producing V₂O₅ based scaffolds with millimeter dimensions and an extremely high porosity of 99.8%. Their microstructure is characterized by a highly ordered structure composed of stacked lamellas. Furthermore, the scaffolds deform under compression in an unusual manner for a ceramic material, as illustrated the two videos. Instead of brittle crushing, the scaffold walls elastically buckle. This behaviour is due not only to the intricate architecture, but also to the high flexibility of the nanofibers, as can be seen from their capability to bend without breaking.

This novel bioinspired, functional material not only displays unusual mechanical characteristics, but the multifunctionality of the V₂O₅ nanofibres also renders their possible applications, including catalysts, sensors and electrodes for energy storage.