Marcasite/pyrite nanocomposites confined in N,S-doped carbon nanoboxes for boosted alkali metal ion storage.

FeS 2 is a promising electrode material for alkali metal ion storage due to its high theoretical capacity. However, it still faces critical issues such as suboptimal rate and cycling performances owing to sluggish charge transport and significant volume variations. Herein, we constructed FeS 2 (m-FeS 2 ) and pyrite FeS 2 (p-FeS 2 ) nanocomposites embedded in N,S-doped carbon nanoboxes (m/p-FeS 2 @NSCN) to conquer such challenges. The microstructure design of nanoboxes effectively alleviates the stress caused by the volume expansion of FeS 2 during lithiation processes, thereby improving the cycling stability of the FeS 2 electrode. The marcasite/pyrite compositing design further increases the electronic conductivity of FeS 2 and optimizes ion migration. As expected, the target m/p-FeS 2 @NSCN exhibits improved rate capability (595.5 mA h g -1 at 5.0 A g -1 ) and robust cycling stability (500 cycles without significant capacity decay at 0.1 A g -1 ) in lithium-ion batteries. Furthermore, m/p-FeS 2 @NSCN also shows excellent battery performances and potential application prospects in the field of sodium-ion batteries. It achieves a capacity of 355 mA h g -1 at 10.0 A g -1 and sustains 800 cycles without noticeable capacity decay at 0.5 A g -1 . This work offers valuable guidance for rationally designing high-performance energy storage materials for alkali metal ion storage.