Linkage Effects of Phenanthrene-based Polymeric Anodes for Lithium-Ion Batteries

Abstract

Organic polymer anodes are increasingly recognized as promising alternatives to graphite due to their structural tunability, surface-dominated lithium-ion storage, and intrinsic safety advantages. However, establishing clear molecular design principles that connect polymer structure to lithium-storage kinetics and electrochemical performance remains a major challenge. In particular, the role of linkage olinkage chemistry in regulating lithium-ion storage behavior is often oversimplified and poorly understood. Herein, a systematic series of polyamides (PQ-polyamide) featuring identical aryloxy-phenanthrene backbones but distinct linkages is designed to elucidate the influence of linker on lithium-ion storage behavior. By isolating linkage effects while maintaining a constant redox-active backbone, we demonstrate that linkage plays a decisive role in determining reversible capacity, rate capability, and charge-storage kinetics. Electrochemical analyses reveal that all polymers store lithium predominantly through surface-controlled processes, while the extent of pseudocapacitive contribution varies significantly with linkers. Among the series, PQ-d incorporating a diphenyl ether linker delivers the highest reversible capacity of 470 mAh g⁻¹ after 100 cycles at 0.1 A g⁻¹ and exhibits the largest surface-controlled contribution, as evidenced by b values approaching unity and dominant capacitive behavior. A comparative kinetic analysis indicates that linkages promoting conformational flexibility and balanced electronic character facilitate enhanced accessibility of redox-active sites and rapid lithium-ion storage. In contrast, excessively rigid or strongly electron-withdrawing substituents lead to diffusion limitations and reduced electrochemical utilization. This work establishes linkage engineering as an effective molecular strategy for regulating lithium-ion storage kinetics in polyamide-based anodes and provides general design guidelines for the development of organic electrode materials.