Molecular-level anchoring of polymer cathodes on carbon nanotubes towards rapid-rate and long-cycle sodium-ion storage

Abstract

Nitroxide radical polymers (NRPs) have attracted increasing research interest as promising cathode materials for sodium ion batteries, primarily owing to their high-voltage (ca. 3.47 V vs. Na⁺/Na), environment compatibility, low-cost, and rich resources. However, such NRP cathodes are subjected to low rate-capacity and poor cycling stability because of their inferior conductivity and dissolubility in the electrolyte. Herein, we report a “molecular glue” strategy to anchor pyrene functionalized NRPs on a highly condutive carbon nanotube (CNT) matrix through π–π interactions between the pyrene functional groups and CNTs. As such, the NRP layer is homogeneously “glued” on the carbon substrates and the non-covalent interaction with CNTs drastically improves the insolubility and electric conductivity of the composite. Benefiting from these structural merits, the new nanocomposite exhibits a record cyclability (92% capacity retention at a high current density of 2.2 A g⁻¹ after 6000 cycles) and remarkable rate capability (78 mA h g⁻¹ at 5.5 A g⁻¹) when evaluated as a high-voltage cathode material for SIBs. This work demonstrates the importance of rational hybridization of radical polymers and carbon substrates for enhanced electrochemical performance and provides insightful guides for designing high-performance polymer-based composites for energy storage applications.