|Fig. 1: The schematic representation of various shapes and sizes of bacteria which can be used to create variety of pores.(Source: Wikimedia Commons)|
Nature is a rich resource that provides tools and design inspiration for scientific discovery. The earliest recorded bioinspired design is of Leonardo da Vinci's flying machine which was inspired by flight mechanisms in birds.  Current climate change issues calls not only for environmentally friendly alternative energy sources but also for greener means to manufacture them. Advances in the study of biological systems have inspired researchers to learn from and use biology in material synthesis at intricate levels. Discussed below are some examples of bioinspired approaches as it applies to battery technologies.
Viruses and bacteria have been used to synthesize battery materials at different scales. Oh et al. have shown that highly porous cathodes for next-generation lithium-oxygen batteries can be synthesized by using different sizes and shapes of bacteria (shown in Fig.1) as a template material.  In this work, the cathodes tested were made by mixing bacteria and multi-walled carbon nanotubes (MWCNTs) followed by removal of the bacteria by heat treatment. The synthesized cathodes had tunable pore volume and shape that improved the oxygen evolution efficiency by 30% and doubled the full discharge capacity in repeated cycles compared to the compact films. Specifically for one discharge half cycle at a rate of 2 A/g the E. coli (rod shaped bacteria) templated porous cathode had a capacity of 3463 mAh/g compared to 2534 mAh/g for the compact film.  Furthermore, the growth of complex battery electrode nanoarchitecture was achieved by adding metals to naturally self-assembled viral particles.  Proteins are another set of biological molecules that were similarly shown to be used for metal oxide growth for cathodes. 
Others have used the functionality of the biomolecule such as oxygen binding capacity of heme. Hemoglobin is the part of the red blood cell that is used to transport oxygen from the lungs to the tissue. Heme is the iron containing part in hemoglobin and mainly contributes in the oxygen binding. It changes from oxygenated to deoxygenated state with changes in external environments. The researchers showed that this functionality makes heme an abundant and eco-friendly biomolecular catalyst in improving the energy efficiency of lithium-oxygen battery systems. 
Nature has evolved through millions of years to optimized structures for specific functions that aid survival. Bioinspired approaches can serve in green battery materials synthesis with desired nano archetectures and/or as a functional component in the battery technologies. Such approaches have the potential to lower cost and environmental effects of material synthesis in battery manufacturing.
© Loza Tadesse. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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 D. Oh et al., "Biotemplating Pores With Size and Shape Diversity for Li-Oxygen Battery Cathodes," Sci. Rep. 7, 45919 (2017).
 K. T. Nam et al., "Stamped Microbattery Electrodes Based on Self-Assembled M13 Viruses," Proc. Nat. Acad. Sci. (USA) 105, 17227 (2008).
 C. Rosant et al. "Biosynthesis of Co3O4 Electrode Materials By Peptide and Phage Engineering: Comprehension and Future," Energy Environ. Sci. 5, 9936 (2012).
 W.-H. Ryu et al., "Heme Biomolecule as Redox Mediator and Oxygen Shuttle For Efficient Charging of Lithium-Oxygen Batteries," Nat. Commun. 7, 1295 (2016).