Carbon Nanotube-Modified Electrode for a Highly Active and Reversible Sn⁴⁺/Sn Anode

Abstract

Tin (Sn) is an attractive anode for high energy density batteries owing to its four-electron redox process (Sn⁴⁺→Sn²⁺→Sn) without dendrite formation. However, the sluggish kinetics and poor reversibility of Sn⁴⁺/Sn²⁺ process hindered its practical implementation. Herein, we propose a surface-engineering strategy to accelerate the Sn⁴⁺/Sn²⁺ redox kinetics and enable highly reversible Sn⁴⁺/Sn reactions. Specifically, carbon nanotubes (CNTs) enriched with edge defects and oxygen-containing groups are grown in situ on carbon felt (CF) via chemical vapor deposition (CVD), forming a high surface area electrode (denoted as CC–T). These CNTs provide abundant active sites for Sn⁴⁺ adsorption and facilitate charge transport, thereby enhancing electron transfer kinetics and redox reversibility. Consequently, the charge-transfer resistance (Rct) of the CC–T decreases by more than 55-fold compared with pristine CF (0.27 vs. 14.89 Ω). When assembled in a Sn/Br flow battery, the battery delivers an energy efficiency (EE) of 80% at 40 mA·cm⁻², outperforming that of pristine CF (63%), and maintains stable cycling for over 650 hours. Even with 4 M electrolyte, the battery achieves a discharge capacity of 373 Ah·L⁻¹ and an areal capacity of 614 mAh·cm⁻². This work provides a promising approach for developing high-capacity, dendrite-free metal anodes for next-generation flow batteries.