Flexible multifunctional Fe2O3/CC cathode host enables efficient adsorption and catalysis of polysulfides for lithium-sulfur batteries

Abstract

Lithium-sulfur batteries are among the most promising electrochemical energy storage devices due to their high energy density and low cost. However, the shuttle effect of polysulfides and the low conductivity of sulfur are major challenges for their commercialization. In this work, using Fe(NO3)3·9H2O as the iron source and NH4F as a surfactant, a flexible Fe2O3/CC composite was prepared by a simple hydrothermal and calcination process, in which Fe2O3 nanorods were decorated on carbon cloth (CC). The presence of mesopores in Fe2O3 facilitates electrolyte penetration and lithium-ion transport and diffusion during charge/discharge, while the abundant active sites exposed by the dense array enable efficient adsorption and rapid conversion of polysulfides, reducing the shuttle effect. Electrochemical analysis shows that the Fe2O3/CC cathode delivers a high discharge specific capacity of 1250 mAh g−1 at 0.1 C (1 C = 1672 mA g−1), and retains 789 mAh g−1 after 100 cycles. At 2 C, it still achieves a discharge capacity of 576 mAh g−1 after 1000 cycles with a capacity retention of 70%, significantly outperforming the control sample. Therefore, Fe2O3/CC effectively suppresses polysulfide shuttling and improves the rate performance and cycling stability of lithium-sulfur batteries.

1. Introduction

With the rise of the energy internet ecosystem and the power Internet of Things, the layout of the new energy industry chain has further accelerated. Under the background of 'dual carbon', the key position of energy storage technology in China's energy conversion and storage system construction has become increasingly prominent. In this situation, commercial lithium-ion batteries will not be able to meet all market demands [1]. Lithium-sulfur batteries, with their high theoretical energy density (2600 Wh kg−1), low cost, and eco-friendliness, have rapidly developed into a promising emerging secondary battery [2–3]. However, the low conductivity of elemental sulfur (5×10−30 S cm−1) and its discharge products (Li2S and Li2S2), as well as the 'shuttle effect' of soluble intermediate polysulfides (LiPSs), lead to low Coulombic efficiency and rapid capacity decay, greatly limiting the industrial application of lithium-sulfur battery cathodes [4–6].

To address these issues, researchers have proposed using carbon materials (carbon nanotubes, graphene, carbon cloth, etc.) as sulfur hosts, employing physical confinement to suppress the shuttle effect. However, due to the non-polar nature of C–C bonds, carbon materials are difficult to form strong chemical bonds with sulfur atoms, and cannot effectively anchor polar polysulfides, resulting in capacity fading during cycling [7]. To develop more effective sulfur immobilization strategies, researchers have focused on transition metal oxides. Among them, Fe2O3 has attracted much attention due to its low cost, environmental friendliness, high catalytic activity, and ideal theoretical capacity [8–9]. In addition, Fe ions have empty d orbitals that can accept lone pairs of electrons, acting as Lewis acids to form coordination bonds with sulfur atoms, chemically adsorbing LiPSs, reducing their accumulation and diffusion in the electrolyte, and lowering the shuttle effect [10]. For example, Li et al. designed defect-engineered SA-Fe2O3(Ov) porous microspheres rich in oxygen vacancies, which increased active sites and enhanced electron transfer rates, resulting in excellent electrochemical performance as lithium-sulfur battery cathodes [11]. Xu et al. reported spherical α-Fe2O3 as a cathode material, effectively promoting LiPSs conversion, delivering a high specific capacity of 1417 mAh g−1 at 0.1 C and maintaining 683 mAh g−1 after 300 cycles at 1 C [12]. However, due to the low electron transfer rate of α-Fe2O3, it exhibits low sulfur utilization and poor rate performance. Therefore, it is necessary to optimize the microstructure and electronic structure to construct novel sulfur host materials with more chemical anchoring sites and rapid electron transfer to improve sulfur utilization and conversion.

In summary, this work designs nanorod-like Fe2O3/CC as an efficient sulfur-loading composite material. The carbon-based material ensures good electrical conductivity to improve electrochemical kinetics; the interconnected Fe2O3 nanorod arrays enable efficient adsorption and rapid conversion of polysulfides, thereby reducing the shuttle effect. Furthermore, the electrochemical performance and ion diffusion kinetics of Fe2O3/CC electrode materials are studied, and the electrochemical performance of lithium-sulfur batteries with Fe2O3/CC as the cathode is evaluated, providing ideas for constructing high-performance lithium-sulfur battery cathode materials.