Transition metal sulfides (TMSS) still face the challenges of capacity decay and poor fast charging capacity in sodium storage. Rational design of heterostructures is a new way to overcome these shortcomings. 
Figure 1Schematic representation of material preparation.
Hou Hongshuai of Central South University, Wu Naiteng of Luoyang Normal University, Sun Guang of Henan Polytechnic UniversityA three-phase heterostructure composed of pyrite FeS2, diaspore Fes2 and SNS2 was constructed by combining the secondary growth route on the surface of the MIL-88A precursor and the vulcanization process. The strategy of secondary growth on the surface of MOF precursors ensures a large number of contact sites between iron and tin sources, thus facilitating the formation of heterogeneous interfaces. Interestingly, the presence of tin in the FeS2 structure reduces the formation energy of the pyrite phase and inhibits the formation trend of diaspore FeS2. By adjusting the amount of tin source, three types of heterogeneous interfaces with three-phase structures can be achieved (the sample obtained by optimizing the ratio is expressed as FFS-TH). 
Figure 2Electrochemical performance of FFS-TH electrodes.
When used as an anode material for sodium-ion batteries (SiBs), the FFS-TH electrode exhibits excellent electrochemical properties compared to its counterparts (pyrite martensitic FeS2 two-phase heterostructure, pyrite Fes2 SNS2 two-phase heterostructure, and common SNS2), including a high reversible capacity of 901 mAh G1 and 82Initial coulombic efficiency of 7%, capacity of 827 mAh g1 after 200 cycles at 1 A g 1, and capacity of 742 mAh g 1 after 700 cycles at 5 A g L. In addition, the Na3V2(PO3)3 FFS-TH snap-on full cell showed a high capacity of 618 mAh G1 and 987% capacity retention. 
Figure 3Full battery performance
introduction of sns2 to regulate the ferrous disulfide phase evolution for the construction of triphasic heterostructures enabling kinetically accelerated and durable sodium storage. advanced functional materials 2024. doi: 10.1002/adfm.202314679