Solid-Phase Synthesis of Poly(imino anthraquinone)s for Low-Cost and High-Performance Bipolar Organic Cathode Materials

Abstract

Organic polymer cathode materials have emerged as promising candidates for constructing sustainable lithium and post-lithium batteries. However, it remains a significant challenge to synthesize electroactive polymers with the desired energy density and cycling stability in a cost-effective manner. Herein, we present a simple yet effective solid-phase method for synthesizing a series of bipolar quinone-amine polymers, specifically, poly(imino anthraquinone)s (PIAQs). The dehydration polycondensation reaction, occurring at 350 °C between the amino and hydroxy groups of low-cost diaminoanthraquinone and dihydroxyanthraquinone monomers, yields four PIAQ samples with identical repeating units but varied connection patterns. As cathode materials for lithium batteries employing ester-type electrolytes, they exhibit comparable charge–discharge curves and energy densities within 1.5–4.3 V but varying cycling stabilities proportional to their polymerization degrees. For example, despite its lowest-cost monomers, PIAQ-44 demonstrates one of the most outstanding electrochemical performances among polymer cathode materials, boasting a reversible capacity of 248 mA h g^–1, an average discharge voltage of 2.53 V, and a high cycling stability (75% capacity retention after 2000 cycles). Moreover, the slight differences in electrochemical performance among the four PIAQs, pertaining to bipolar redox, irreversible deprotonation, and capacity fade, have been thoroughly elucidated to provide constructive insights into quinone-amine polymers.