Hierarchical FeS₂ cathode with suppressed shuttle effect for high performance magnesium-ion batteries

2D transition metal sulfides (such as FeS2) are promising cathode materials for magnesium-ion batteries due to their high capacity, low cost, and abundance. However, unexpected side effects of the electrochemical process result in poor cycling performance, which hamper their widespread use. Herein, we demonstrate the shuttle effects of metal sulfide cathodes in magnesium-ion batteries for the first time and propose a strategy of phase engineering to retard such side effects, improving the magnesium storage performance of the FeS2 cathode. We also show the correlation between structure evolution of FeS2 and electrochemical performance using cryogenic transmission electron microscopy, time-of-flight secondary ion mass spectrometry and X-ray diffraction. The stress caused by the magnesiation-induced expansion of FeS2 is shown to be alleviated in porous hierarchical spheres, which has been verified by finite element simulations. This boosts the electrochemical performance of FeS2, with a respectable capacity of 556 mAh g-1 maintained after 80 cycles at 25 mA g-1. Our results can guide the use of other metal sulfides in magnesium-ion batteries.