Carbon nanotubes for boosting the performance of aqueous zinc-ion battery based on vanadium hexacyanoferrate cathode materials: The impact of its structure and N-doping

Abstract

Vanadium hexacyanoferrate (VHCF) have emerged as promising cathode materials for aqueous zinc-ion batteries (AZIBs) due to their open framework and tunable redox properties. However, their low electrical conductivity and limited cycling stability hinder practical applications. To address these challenges, this study integrates VHCF with various carbon nanotubes (parallel nanotubes (P-CNTs), fishbone-like nanotubes (FB-CNTs), and N-doped bamboo-like nanotubes (N/B-CNTs)) via a one-step co-precipitation method. XRD, XPS, and FTIR results confirmed the successful synthesis of VHCF/CNT composites with negligible change of the VHCF structure and composition. Additionally, the incorporation of N-doped bamboo-like CNTs achieved a 3-5-fold increase in specific surface up to 198.2 m² g^-1. Battery evaluations demonstrated significant enhancement of capacity and cycling stability after the incorporation of CNTs: N/B-CNTs delivered the highest specific capacity (∼125 mAh g^-1 at 3.2 A g^-1), superior rate capability (85.4% capacity retention from 0.2 to 3.2 A g^-1), and exceptional cycling stability (81.4 mAh g^-1 after 1800 cycles, 65.1% retention), outperforming pristine VHCF (39.5%), P-CNTs (56.9%), and FB-CNTs (54.8%). Electrochemical analysis resolved the role of CNT structures and nitrogen doping in during battery tests. It reveals that cross-linked CNTs provided additional mechanical support and subsequently promoted charge transfer kinetics. Moreover, the highly dispersed VHCF on CNTs and improved surface area enhanced electron exchange process and Zn²⁺ storage. The superior performance of N/B-CNTs is attributed to the enhanced electronic conductivity from nitrogen doping and the unique bamboo-like structure, which further facilitates ion diffusion and provides robust mechanical stability.