Conjugated cyclized-polyacrylonitrile encapsulated carbon nanotubes as core–sheath heterostructured anodes with favorable lithium storage

Abstract

Redox-active conjugated polymers are promising alternatives to inorganic electrode materials, whereas such organic electrodes usually suffer from low practical capacity, poor conductivity, high cost, and industrial incompatibility. Many commercial polymers with abundant heteroatoms in their constitutional units hold great potential for serving as inexpensive active materials in rechargeable batteries but remain unexplored largely. Here, conductive carbon nanotubes (CNTs) were fully encapsulated in highly conjugated cyclized-polyacrylonitrile (CPAN) by facile in situ free-radical polymerization in combination with subsequent thermal cyclization. The resultant poly(N-heteroacene)-like CPAN sheath layers are composed of repeated heterocyclic rings that contain aromatic C and N atoms capable of offering multi-electron active sites. Such quasi-1D CPAN-encapsulated CNT (CNT@CPAN) core–sheath heterostructures are intertwined to build robust 3D hierarchical networks, which are favorable for efficient electron transport, full exposure of active sites, and creating porous internal channels accessible to electrolytes. Remarkably, the CNT@CPAN anode delivers an ultra-large reversible capacity (1176 mA h g⁻¹ at 0.1 A g⁻¹), high rate capability (439 mA h g⁻¹ at 2 A g⁻¹), and excellent cycling stability (retaining 330 mA h g⁻¹ at 10 A g⁻¹ over 5000 cycles with a coulombic efficiency of almost 100%). This work would provide new insights into the development of low-cost polyacrylonitrile for metal-free sustainable electrode materials with industrial compatibility and flexible processability as well as the exploration of high added-value energy applications by capitalizing on other recyclable plastics.