Small but mighty: Empowering sodium/potassium‐ion battery performance with S‐doped SnO2 quantum dots embedded in N, S codoped carbon fiber network

Abstract

AbstractSnO2 has been extensively investigated as an anode material for sodium‐ion batteries (SIBs) and potassium‐ion batteries (PIBs) due to its high Na/K storage capacity, high abundance, and low toxicity. However, the sluggish reaction kinetics, low electronic conductivity, and large volume changes during charge and discharge hinder the practical applications of SnO2‐based electrodes for SIBs and PIBs. Engineering rational structures with fast charge/ion transfer and robust stability is important to overcoming these challenges. Herein, S‐doped SnO2 (S–SnO2) quantum dots (QDs) (≈3 nm) encapsulated in an N, S codoped carbon fiber networks (S–SnO2–CFN) are rationally fabricated using a sequential freeze‐drying, calcination, and S‐doping strategy. Experimental analysis and density functional theory calculations reveal that the integration of S–SnO2 QDs with N, S codoped carbon fiber network remarkably decreases the adsorption energies of Na/K atoms in the interlayer of SnO2–CFN, and the S doping can increase the conductivity of SnO2, thereby enhancing the ion transfer kinetics. The synergistic interaction between S–SnO2 QDs and N, S codoped carbon fiber network results in a composite with fast Na+/K+ storage and extraordinary long‐term cyclability. Specifically, the S–SnO2–CFN delivers high rate capacities of 141.0 mAh g−1 at 20 A g−1 in SIBs and 102.8 mAh g−1 at 10 A g−1 in PIBs. Impressively, it delivers ultra‐stable sodium storage up to 10,000 cycles at 5 A g−1 and potassium storage up to 5000 cycles at 2 A g−1. This study provides insights into constructing metal oxide‐based carbon fiber network structures for high‐performance electrochemical energy storage and conversion devices.