In-Cell Electropolymerization of 10-(N-Pyrrolyl)phenoxazine into a Phenoxazine-Grafted Polypyrrole Cathode for High-Voltage and Ultrastable Li-Ion Batteries

Abstract

Organic electrode materials face critical challenges of dissolution in electrolytes and limited operating voltage, which hinder their practical application. To overcome these barriers, we designed a novel electropolymerizable molecule, phenoxazine-functionalized polypyrrole (PPyPOZ), as a high-voltage cathode. Through a one-step in-cell electropolymerization process that concurrently activates the electrode, the monomer is directly transformed into a stable, π-conjugated polymer framework on the current collector. This approach fundamentally inhibits dissolution and establishes an intrinsic conductive pathway. The resulting PPyPOZ cathode exhibits a high discharge plateau (~3.6 V) and a specific capacity of 174 mAh g-1, yielding an impressive energy density of 626.4 Wh kg-1, which ranks among the highest for organic cathodes. It also demonstrates excellent rate capability and outstanding cycling stability, retaining 95% capacity after 1170 cycles at 3 A g-1 and achieving a capacity retention of nearly 100% over 1200 cycles at 0.2 A g-1. Furthermore, the cathode delivers stable performance under practical conditions, including high mass loading (> 2 mg cm-2) and sub-zero temperature (−7 °C), demonstrating its potential for real-world applications. The charge storage mechanism, identified as a dominant capacitive process with reversible PF6− doping/dedoping at the phenoxazine sites, was elucidated via comprehensive electrochemical analysis, DFT simulations, and ex situ characterizations. This work validates the strategy of integrating redox-active units into conjugated polymers via in situ electropolymerization, paving the way for high-energy, durable organic batteries.