Tannic Acid-a Bridge and Suspending Agent for Lithium Cobalt Oxide and Reduced Graphene Oxide: A Lodestar for Lithium-Ion Batteries.

Lithium cobalt oxide (LCO) has been employed as cathode material for forty years. However, the low solubility of LCOs in water and strong electrostatic force and H-bonding between the LCOs particles limited the use of the aqueous binders in the LCO system. We report a feasible and universal approach to fabricating a complex cathode of LCO and reduced graphene oxide (RGO). Tannic acid (TA) could simultaneously disperse LCO and RGO particles. Meanwhile, the branched polyphenol TA acts as a "bridge" molecule for connecting the LCO and RGO, confirmed by the SEM test. The rheology properties of the PVDF slurry of cathode materials (LCO, LCO/, RGO, and TA/LCO/RGO) were also determined. It could be found that the TA could act as a crosslinking agent for the LCO and RGO particles, increasing the viscosity and storage modulus of the slurry. The cell employed the TA/LCO/RGO slurry as the cathode material, have a higher areal capacity, and had a higher redox potential than employed LCO/RGO and LCO as cathode materials, all of which could be attributed to the addition of the TA. This green molecule can be used to fabricate environmentally friendly and possibly biodegradable electrochemical energy storage devices.