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

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.