Confined-space synthesis of nanostructured anatase, directed by genetically engineered living organisms for lithium-ion batteries

Biomineral formation processes in nature are temporally and spatially regulated under the functions of biomolecules in a confined space. It is potentially very productive to rationally design a mineralized system by taking into account confined space as well as biomolecules. The laboratory technique of "bacterial cell surface display" is an ideal platform to host catalytically active proteins in a three-dimensionally confined space. In the present study, aiming to regulate the synthesis of nanostructured TiO₂ anatase, repeating segments of silaffin were displayed on Escherichia coli surfaces through genetic manipulation. The displayed protein electrostatically interacted with a titanium source and catalyzed the hydrolysis of titanium dioxide precursors through hydrogen bonding interactions on the cell surface. In the subsequent calcination process, the genetically modified cells not only served as a framework for producing rod-shaped TiO₂ assembled by nanoparticles, but also provided a carbon source in situ. The size of nanoparticles was controlled by changing the number of tandem repeats of the protein segment. The as prepared TiO₂ anatase exhibited unique characteristics including nanosized anatase crystals, mesoporous structure and carbon coating. When tested as the anode electrode of a lithium-ion battery, it showed excellent lithium storage performance. The carbon coated anatase anode shows a higher specific capacity of 207 mA h g^-1 after 200 cycles at a current rate of 1C and an ultra-long cycling lifetime of 5000 cycles with an outstanding retention capacity of 149 mA h g^-1 at a higher rate of 10C. This bioprocess-inspired approach may help broaden the scope and impact of nanosized biominerals.