| AVS 59th Annual International Symposium and Exhibition | |
| Thin Film | Monday Sessions |
| Session TF+EN-MoA |
| Session: | ALD for Energy |
| Presenter: | X. Chen, University of Maryland |
| Authors: | X. Chen, University of Maryland H. Zhu, University of Maryland L. Hu, University of Maryland G.W. Rubloff, University of Maryland |
| Correspondent: | Click to Email |
A major challenge for Li-ion batteries is to achieve high rates (power) by overcoming the long charge/discharge time caused by low Li diffusivity in active storage materials. Nanostructured electrodes provide a potential solution by reducing the thickness of active storage layers, since the diffusion time is proportional to the square of diffusion length. Our strategy to improve the rate performance of Li-ion battery is to use atomic layer deposition (ALD) to grow thin active battery materials on highly conductive current collecting scaffolds with high surface area. The unprecedented conformality of ALD allows maximum utilization of high surface area, while the highly conductive scaffold facilitates easy electron transport and Li+ migration in electrolyte as also needed for high power. We report two embodiments of this heterogeneous nanostructure configuration, both with ALD V2O5 storage layers.
First, we used highly porous multiwall carbon nanotube (MWCNT) sponge as the scaffold. The V2O5-MWCNTcoaxial sponge achieves a stable high areal capacity as 816 µAh/cm2 over voltage range 4.0-2.1 V at current density of 1.1 mA/cm2 (i.e., 1C rate). This capacity is 450X that of a corresponding planar V2O5 thin film cathode. For the same voltage range but 50X higher current, the areal capacity of the V2O5-MWCNT sponge is 155 µAh/cm2, giving a high power density of 21.7 mW/cm2. The areal capacity increases further to 1284 µAh/cm2, when cycled over a larger voltage window (4.0-1.5 V), but this incurs deteriorated cycling performance as expected from the intrinsic properties of V2O5.
Second, we employed well-ordered anodic aluminum oxide (AAO) templates to with ALD current collecting layers as a scaffold for the storage material. ALD TiN was first deposited into the AAO nanopores to form current collecting nanostructures, after which ALD V2O5 was deposited on TiN as the active Li storage medium, with both layer thicknesses precisely controlled and highly conformal. The resulting structures, with electrolyte filling the remaining pore volume, provide test structures to understand regimes where either Li+ transport or electron transport can be rate-limiting.