Reversible Capacity and Cycling Stability of MoS2/FeS/FeS2 Heterostructure Anodes for Lithium/Sodium-Ion Batteries

Transition metal dichalcogenides (TMDs), such as MoS2 and FeS2, are promising battery anodes but have performance limitations. MoS2 facilitates efficient ion intercalation but suffers from structural degradation and poor conductivity during cycling. FeS2 has a high theoretical capacity (894 mA h g–1) but undergoes significant volume changes that affect its stability. In this study, we synthesized MoS2/FeS/FeS2 heterostructures to overcome these limitations. We found that the FeS2 contained highly conductive mackinawite FeS nanoflakes, which formed spontaneously at the interface. This enhanced the electrode conductivity and reduced the Li/Na ion diffusion pathways. The MoS2 coating on the FeS surfaces enhanced electrolyte penetration and optimized electron/ion transport. The MoS2/FeS/FeS2 anodes exhibited outstanding cycling stability in both lithium-ion and sodium-ion batteries (LIBs and SIBs, respectively). The anodes delivered reversible capacities of 1077 mA h g–1 at 0.2 C and ∼714 mA h g–1 at 1 C after 100 cycles in LIBs and 687 mA h g–1 at 0.2 C after 50 cycles in SIBs. Notably, this study not only shows that the in situ-formed FeS contributes to enhanced reversible capacity and cycling stability but also provides structural insights into the metastable FeS phase at the MoS2/FeS/FeS2 interface, offering valuable guidance for rational design of high-performance TMD-based anodes.