Organic electrodes have been promising candidate for large-scale electrical energy storage applications thanks to several advantages, such as low cost, high theoretical capacity, and chemical diversities. However, their high solubility in organic electrolytes and poor electrical conductivity have limited their cycling stability as well as rate capability. A promising strategy to address these issues is to polymerize organic molecules onto conductive carbon substrates.¹ In composite structure, the covalent bonds between the monomers can prevent the dissolution of molecules, while conductive carbon can support the fast redox reactions in the polymer.¹ Tremendous efforts have been devoted in developing nanocomposite by polymerizing carbonyl compounds on various nanocarbons such as graphene or carbon nanotubes.¹ The electrochemical performance of the composites strongly dependents on their microstructures, which indicates that the interface between the redox-active polymer and nanocarbon support should be optimized for maximizing the electrochemical performance of the composite electrodes.¹

In our recent study, we investigated the electrochemical properties of polydopamine by both computational and experimental methods. The density functional theory (DFT) calculations show that polydopamine can interact with both electrolyte ions (cations and anions) at high voltage region of 2.5~4.1 V vs. Li, and the interactions are also confirmed by cyclic voltammetry measurements.¹ Comparing with the complicated polymerization process for most polymer cathode materials, dopamine can be spontaneously polymerized in weak alkaline solutions.¹ We fabricate the free-standing and flexible hybrid electrodes by spontaneously coating polydopamine onto few-walled carbon nanotubes.¹ The hybrid electrodes delivered a gravimetric capacity of ~133 mAh/g in Li-cells utilizing double layer capacitance from FWNTs and multiple redox-reactions from polydopamine.¹ In addition, for further improving the performance of the composite electrodes, we utilized reduced graphene oxide as a redox-active and conductive substrate for the growth of polydopamine. During the hydrothermal treatment, dopamine can reduce and functionalize the graphene oxide simultaneously, which results in a 3D structured functionalized graphene hydrogel. The functionalized graphene shows a significantly enhanced capacity up to 200 mAh/g.

Reference:

1. T. Liu, K. C. Kim, B. Lee, Z. Chen, S. Noda, S. S. Jang and S. W. Lee, Energy & Environmental Science, 2016. DOI: 10.1039/C6EE02641A