Scientists from MIT have grown thin, pure and dense carbon nanotubes that in combination with additives can be used as electrodes to store a higher amount of capacity in batteries and super capacitors.
Carbon nanotubes are able to store and carry a higher amount of charge because of the large structural area but the question of making them into films has still lots of gaps. That’s because conventional methods leave spaces between individual nanotubes or need additives to bind.
MIT group used layer-by-layer assembly method to make the new nanotube films. A water solution of two kinds of nanotubes is made. The first type has positively charged molecules attached and the other one has negatively charged molecules attached. The alternately dip a very thin substrate like silicon wafer into the solutions and because of the differences in potential the nanotubes are attracted to each other and stick together. Similar charged nanotubes reject each other in the solution, forming thin, uniform layers.
These films will be next detached from the substrate and baked in a hydrogen cloud to remove the charged molecules. 70% of the films are nanotubes, rest being empty space and pores that could be used to store lithium or liquid electrolytes in future battery electrodes. The capacitance of the films is one of the highest ever measured for carbon nanotubes.