Unraveling the Beneficial Microstructure Evolution in Pyrite for Boosted Lithium Storage Performance

Pyrite FeS₂ as a high-capacity electrode material for lithium-ion batteries (LIBs) is hindered by its unstable cycling performance owing to the large volume change and irreversible phase segregation from coarsening of Fe. Here, the beneficial microstructure evolution in MoS₂-modified FeS₂ is unraveled during the cycling process; the microstructure evolution is responsible for its significantly boosted lithium storage performance, making it suitable for use as an anode for LIBs. Specifically, the FeS₂/MoS₂ displays a long cycle life with a capacity retention of 116 % after 600 cycles at 0.5 A g⁻¹, which is the best among the reported FeS₂-based materials so far. A series of electrochemical tests and structural characterizations substantially revealed that the introduced MoS₂ in FeS₂ experiences an irreversible electrochemical reaction and thus the in situ formed metallic Mo could act as the conductive buffer layer to accelerate the dynamics of Li⁺ diffusion and electron transport. More importantly, it can guarantee the highly reversible conversion in lithiated FeS₂ by preventing Fe coarsening. This work provides a fundamental understanding and an effective strategy towards the microstructure evolution for boosting lithium storage performances for other metal sulfide-based materials.