Heterostructure Engineering of FeS2–MoS2 with Encapsulated Architecture for Long-Term Stability and Fast Kinetics Sodium-Ion Battery Anodes

Abstract

Conversion-type transition metal sulfides (TMSs), particularly pyrite-phase FeS2, are promising anodes due to their high theoretical capacity. However, their practical application is hindered by intrinsic drawbacks such as poor electrical conductivity, severe volume expansion, sluggish reaction kinetics, and polysulfide shuttling. Herein, a FeS2–MoS2 heterostructure composite is synthesized to overcome these limitations. In this unique structure, cubic-phase FeS2 particles are encapsulated within layered MoS2 nanosheets, self-assembling into ∼2.8 μm flower-like spheres. The heterostructure effectively mitigates volume expansion and polysulfide shuttling. Electrochemical tests demonstrate that the FeS2–MoS2 anode significantly outperforms its individual constituents, delivering a high specific capacity of 762.8 mA h g–1 at 200 mA g–1 after 100 cycles. Furthermore, it exhibits exceptional long-term stability with a capacity of 620.1 mA h g–1 after 1600 cycles at 2000 mA g–1. Kinetic analysis reveals dominant capacitive behavior and accelerated Na+ diffusion kinetics compared to pure FeS2 or MoS2. Additionally, the composite displays excellent temperature adaptability, delivering 353.9 mA h g–1 at –25 °C (1800 cycles, 1000 mA g–1) and 570.4 mA h g–1 at 45 °C (1000 cycles, 2000 mA g–1). Full-cell tests employing Na3V2(PO4)3 cathode confirm the practical viability of the material, achieving 97.3 mA h g–1 at 0.5 C. This work highlights the FeS2–MoS2 heterostructure as a cost-effective and highly promising anode candidate for advanced SIBs.