Synergistically Designed Carbon-Free MoS2/MoO2 Heterostructure Anodes with Interfacial Covalent Bonds for High-Rate Sodium-Ion Batteries

The development of hierarchical heterostructured materials for sodium-ion batteries (SIBs) remains hindered by suboptimal high-rate cycling performance, primarily due to phase interface pulverization and separation during charge–discharge processes. To address these challenges, we designed a carbon-free hierarchical structure comprising few-layered MoS₂ nanosheets and MoO₂ nanocrystals through precise compositional optimization and rational structural engineering. The heterogeneous components are interconnected through robust S─O covalent bonds, which theoretical calculations and experimental results confirm generate a built-in electric field at the heterointerfaces, significantly enhancing reaction kinetics. Crucially, these covalent bonds stabilize the heterointerfaces, improving structural integrity and mitigating electrode material agglomeration and pulverization. Additionally, the MoS₂/MoO₂ heterostructure enhances Na⁺ adsorption energetics and reduces Na⁺ diffusion barriers, facilitating efficient ion transport. Leveraging its abundant heterointerfaces and stable architecture, the composite delivers exceptional rate performance (432.7 mAh·g⁻¹ at 10 A·g⁻¹) and outstanding cycling stability (nearly 100% capacity retention over 400 cycles at 5 A·g⁻¹). This work provides a strategic framework for designing heterostructured materials with stable interface-rich architectures, advancing the development of high-performance conversion/alloy-type anodes for energy storage applications.