Constructing strain-alleviated structures in ultrathin FeS/C composites for durable lithium and sodium storage

Iron sulfide (FeS) is a competitive anode material for Li-/Na-ion batteries (LIBs/SIBs) with high specific capacity and excellent environmental benignity. Nevertheless, its practical application is greatly hindered by the sluggish charge transfer dynamics and large volume variations upon cycling. Herein, by constructing a strain-alleviated (bubble film-like) structure in an ultrathin FeS/C composite, the sluggish transfer kinetics and huge volume variations of FeS were fundamentally solved. The bubble film-like carbon matrix serves as the protective shell to alleviate the huge volume changes of FeS and enhance its electronic conductivity, as verified by finite element simulation and ex-situ transmission electron microscopy results. Benefiting from this unique design, the as-designed electrode exhibited a significantly enhanced performance with a high discharge capacity of 469 mA h g−1 at 5 A g−1 for LIBs and 354 mA h g−1 after 1500 cycles at 1 A g−1 for SIBs. Moreover, the full cell with this electrode and LiFePO4 cathode can deliver outstanding cycling stability of 558 mA h g−1 even after 100 cycles. We expect that this strategy can also be applied to other anode materials plagued by poor conductivity and huge volume changes and remarkably spur the development of batteries with high rate capability and long lifespan.