Self-Polymerized Dopamine As an Organic Cathode for Lithium-Ion Batteries

Abstract

The redox-active organic materials have been intensively investigated as promising candidates for replacing the inorganic cathodes in lithium-ion batteries (LIBs). In particular, quinone-based organic molecules, such as benzoquinone, naphthoquinone, and anthraquinone, have received considerable attention owing to their high redox potential, high theoretical capacity (up to 500 mAh g−1), and possibility of being synthesized from earth-abundant resources. However, these quinone derivatives cannot be directly used in common LIBs because of their high solubility in non-aqueous electrolytes. Dopamine, which has a similar molecular structure with adhesive proteins in mussel, can be self-polymerized on various types of substrates. It is interesting to note that one of the oxidation intermediates of dopamine, 5, 6-indolequinone, resembles the structures of benzoquinone and naphthoquinone, having a high theoretical capacity of 364 mAh/g. Despite its intrinsic redox characteristic of the quinone groups,1 the redox-active properties of the polydopamine (PDA) with lithium ions have not been reported yet. Here, we first demonstrated PDA as a promising organic cathode in LIBs. PDA showed a specific capacity of ~235 mAh/g at 0.14 C and ~140 mAh/g at ~27.4 C. We also investigated the energy storage mechanism in PDA and confirmed the existence of both electrical double-layer capacitance and pseudocapaitance. By using carbon nanotubes (CNTs) as 1D templates for the polymerization of dopamine, we prepared flexible PDA and CNT composite films. The composite films exhibited enhanced rate capability and excellent cycling stability owing to the unique combination of redox-active PDA and superior electrical conductivity of CNT.