A B,N co-doped carbon nanotube array with anchored MnO2 nanosheets as a flexible cathode for aqueous zinc-ion batteries

Abstract

For rechargeable aqueous zinc-ion batteries (ZIBs), the design of nanocomposites comprised of electrochemically active materials and carbon materials with novel structures has great promise in addressing the issue of electrical conductivity and structural stability in the electrode materials during electrochemical cycling. We report the production of a novel flexible electrode material, by anchoring MnO2 nanosheets on a B,N co-doped carbon nanotube array (BNCNTs) grown on carbon cloth (BNCNTs@MnO2), which was fabricated by in-situ pyrolysis and hydrothermal growth. The generated BNCNTs were strongly bonded to the surface of the carbon fibers in the carbon cloth which provides both excellent electron transport and ion diffusion, and improves the stability and durability of the cathode. Importantly, the BNCNTs offer more active sites for the hydrothermal growth of MnO2, ensuring a uniform distribution. Electrochemical tests show that BNCNTs@MnO2 delivers a high specific capacity of 310.7 mAh g−1 at 0.1 A g−1, along with excellent rate capability and outstanding cycling stability, with a 79.7% capacity retention after 8000 cycles at 3 A g−1.

1. Introduction

The excessive consumption of traditional fossil fuels and other non-renewable energy sources has prompted researchers to look for alternative energy solutions. Therefore, improving energy storage technology has become crucial to meeting this challenge[1–4]. Currently, emerging energy storage facilities include fuel cells, secondary batteries and supercapacitors[5–7]. Among them, aqueous zinc-ion batteries (ZIBs) with the characteristics of high energy density, low cost and good safety have become the focus of attention[8–9]. At present, the focus of most researchers on positive electrode materials includes manganese-based compounds[10–11], vanadium based oxides and vanadate[12–13], prussian blue analogs[14–15], and organic compounds[16–17]. Manganese-based compounds are particularly promising in practical applications due to their high operating voltage, high theoretical capacity, environmental friendliness and low cost. Unfortunately, the poor conductivity of manganese oxide is not conducive to the conduction of electrons, resulting in problems such as poor cycle stability and unsatisfactory rate capability of aqueous ZIBs[18–20].

To address these issues, several effective strategies have been employed, such as element doping[21], defect engineering[22–23] and material composite[24]. Among these strategies, loading manganese oxides on carbon matrix (including hollow carbon spheres, graphene, carbon nanotubes, porous carbon sheets or spheres, etc.) is widely adopted for the reason that it can effectively improve the electrochemical performance[25–29]. Additionally, to avoid the impact of adding PVDF and conductive carbon black on energy density, using carbon cloth as the current collector is a choice. Zhang et al.[30] constructed an integrated array cathode by anchoring active manganese dioxide on N-doped porous carbon nanosheets (N-CNSs) array. The obtained N-CNSs@MnO2 cathode optimized the Zn ion storage kinetics, delivering a high capacity in aqueous electrolyte and an excellent long-term lifetime. Zhao et al.[31] prepared N-doped carbon nanotubes grown on carbon cloth (CC/...).