Core-shell heterostructured composites of carbon nanotubes and imine-linked hyperbranched polymers as metal-free Li-ion anodes

An in situ Schiff-base condensation between p-phthalaldehyde (PPD) and 1,3,5-tris(4-aminophenyl)benzene (TAPB) or 1,3,5-tris(4-aminophenyl)triazine (TAPT) was actualized in the presence of carbon nanotubes (CNTs), producing imine-linked hyperbranched poly(PPD-TAPB) and poly(PPD-TAPT)-coated CNTs (abbreviated as CNT@HBP-1 and CNT@HBP-2, respectively). Such quasi-1D core-shell heterostructures are interleaved to build robust 3D networks with porous internal channels, which are favorable for efficient electron transport and ion diffusion, exposing active sites, fast redox kinetics, and high electrochemical utilization. When used as Li-ion anodes, both CNT@HBP-1 and CNT@HBP-2 exhibit larger specific capacity, better rate performance, and higher cycling stability compared to their pure polymers. Furthermore, CNT@HBP-2 delivers higher reversible capacities of 351 mA h g(-1) at 0.05 A g(-1), and 81 mA h g(-1) at 1.0 A g(-1), respectively, compared to CNT@HBP-1 (335 and 56 mA h g(-1)). Besides, CNT@HBP-2 retains 268 mA h g(-1) over 100 cycles at 0.1 A g(-1), and 617 mA h g(-1) in the 500th cycles at 0.5 A g(-1), respectively, outperforming CNT@HBP-1 (155 and 256 mA h g(-1)). Further improvements in the electrochemical performance for CNT@HBP-2 relative to CNT@HBP-1 are attributable to the incorporation of additional redox-active triazine units into HBP-2. This work would unlock insights into the rational development of metal-free polymer-based electrodes for rechargeable batteries.