Dual-Electrode-Functional Covalent Organic Polymer Designed by a Capacity-Voltage-Related Descriptor for Superior and Antifreezing Lithium/Sodium Storage.

Abstract

Organic electrode materials (OEMs) show flexible structural designability, but low capacity and single function limit their application. Herein, we propose a capacity-voltage-related descriptor, namely the ratio of active to inactive atoms (<i>A</i>/<i>I</i>), to design high-capacity and multifunctional OEMs. As a proof of concept, we designed an active-site-rich covalent organic polymer (TAPT-COP). The abundant active groups (C═O and C═N) in TAPT-COP skeletons enrich it with a high <i>A</i>/<i>I</i> ratio of 0.61, providing significantly separated voltage platforms and high capacities, thus giving it the potential to be applied in different electrodes. Benefiting from the high <i>A</i>/<i>I</i> ratio, the TAPT-COP as cathode and anode both show high Li⁺/Na⁺-storage capacities (LIBs: 353.5 mAh g^-1 for cathode, 383.0 mAh g^-1 for anode; SIBs: 329.6 mAh g^-1 for cathode, 352.0 mAh g^-1 for anode), excellent rate capabilities, and superior antifreezing performance. <i>In situ</i> Raman, <i>in situ</i> Fourier transform infrared spectra, and density functional theoretical calculations reveal that the C═O and C═N groups as reaction sites can coordinate up to 60 Li⁺ ions per TAPT-COP unit, thus contributing to high cathodic and anodic capacity. Meanwhile, TAPT-COP as separated electrodes maintains higher stability than individual electrodes, accounting for its promise as a Li⁺/Na⁺-storage electrode materials.