Principal Investigator Yang Shao-Horn
Novel layer-by-layer (LbL) all-carbon electrodes can be assembled by repeated, sequential immersion of substrates into aqueous solutions containing positively and negatively charged nano-carbons. LbL electrodes have an interpenetrating network structure that can achieve high electronic conductivity, whereas the well-developed porous structure can facilitate fast ion diffusion. We recently reported an alternative approach based on the redox reactions of oxygen functional groups on the surfaces of carbon nanotubes. The electrode, which is several microns thick, can store lithium up to a reversible gravimetric capacity of ~200 mAh/gelectrode while also delivering 100 kW/kgelectrode of power and lifetimes in excess of thousands of cycles, both of which are comparable to electrochemical capacitor electrodes.
A device using the nanotube electrode as the positive electrode and lithium titanium oxide as a negative electrode had gravimetric energy ~5 times higher than conventional electrochemical capacitors, and power delivery ~10 times higher than conventional lithium ion batteries. Finally, binder-free and self-standing carbon nanotube (CNT) electrodes of tens of microns in thickness have been assembled via a vacuum-filtration process of oxidized few-walled CNTs (FWNTs), with different amounts of oxygen functional groups on FWNTs. These self-standing FWNT electrodes (free of binder/additive and current collector) can provide a high gravimetric energy of ~200 Wh/kg at a high power of ~10 kW/kg, showing promise as the positive electrode for light-weight, high-power lithium batteries.