Reversible Capacity and Cycling Stability of MoS ₂ /FeS/FeS ₂ Heterostructure Anodes for Lithium/Sodium-Ion Batteries

Transition metal dichalcogenides (TMDs), such as MoS 2 and FeS 2, are promising battery anodes but have performance limitations. MoS 2 facilitates efficient ion intercalation but suffers from structural degradation and poor conductivity during cycling. FeS 2 has a high theoretical capacity (894 mA h g –1 ) but undergoes significant volume changes that affect its stability. In this study, we synthesized MoS 2 /FeS/FeS 2 heterostructures to overcome these limitations. We found that the FeS 2 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 MoS 2 coating on the FeS surfaces enhanced electrolyte penetration and optimized electron/ion transport. The MoS 2 /FeS/FeS 2 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 MoS 2 /FeS/FeS 2 interface, offering valuable guidance for rational design of high-performance TMD-based anodes.