Gabriel Oltean

High energy and power density TiO2 nanotube electrodes for 3D Li-ion microbatteries

Highly ordered anodic TiO2 nanotube arrays with a tube length of 9 μm are shown to provide areal capacities of 0.24 mA h cm−2 (i.e. 96 mA h g−1) at a charge/discharge current density of 2.5 mA cm−2 (corresponding to a rate of 5 C) and 0.46 mA h cm−2 (i.e. 184 mA h g−1) at 0.05 mA cm−2, when used as 3D free-standing anodes in Li-ion microbatteries. The present nanotube electrodes, which could be cycled for 500 cycles with only 6% loss of capacity, exhibited significantly higher energy and power densities, as well as an excellent cycling stability compared to previously reported TiO2-based Li-ion microbattery electrodes. The influence of parameters such as ordering, geometry and crystallinity of the nanotubes on the microbattery performance was investigated. A two-step anodization process followed by annealing of the nanotubes was found to yield the best microbattery performance. It is also demonstrated that the rate capability of the electrode depends mainly on the rate of the structural rearrangements associated with the lithiation/delithiation reaction and that the areal capacity at various charge/discharge rates can be increased by increasing the tube wall thickness or the length of the nanotubes, up to 0.6 mA h cm−2 for 100 cycles.

Electrochemical elaboration of electrodes and electrolytes for 3D structured batteries

The challenges associated with the fabrication of three-dimensional (3D) electrode and electrolyte materials for Li-ion batteries are discussed. The basic issues for achieving a solid 3D cell foundation, which can simultaneously offer sufficient electronic conductivity to enable stable cycling, as well as enough compatibility with the incorporation of complementary components, have been addressed. Various electrochemical strategies for elaborating such systems are discussed and critically examined. Several current collector systems are presented including electrochemically prepared Cu and Al nanorods and commercial aperiodic carbon structures. Further electrochemical coating approaches then provide a direct method for the deposition of thin layers of active materials successfully demonstrated here as coatings on both 3D metal structures and commercially available 3D-structured carbon substrates. Enhanced capacities per foot print area are demonstrated for a number of 3D electrode materials, namely polyaniline on reticulated vitreous carbon, Cu2O on copper nanorods and TiO2 on Al nanorods. The crucial points for achieving a thin conformal coating of the corresponding 3D electrode structures with solid polymer electrolytes are also carefully analysed and discussed. In this context electro-polymerisation is proposed as a viable route to form thin electrolyte layers with promising characteristics. The high versatility of electro-polymerisation in combination with the various structures and methodologies adopted here represents a further step towards the development of cost-effective 3D microbattery devices.