Hexaindium Heptasulfide/Nitrogen and Sulfur Co-Doped Carbon Hollow Microspindles with Ultrahigh-Rate Sodium Storage through Stable Conversion and Alloying Reactions

Group IIIA-VA metal sulfides (GMSs) have attracted increasing attention because of their unique Na-storage mechanisms through combined conversion and alloying reactions, thus delivering large theoretical capacities and low working potentials. However, Na+ diffusion within GMSs anodes leads to severe volume change, generally representing a fundamental limitation to rate capability and cycling stability. Here, monodispersed In6S7/nitrogen and sulfur co-doped carbon hollow microspindles (In6S7/NSC HMS) are produced by morphology-preserved thermal sulfurization of spindle-like and porous indium-based metal organic frameworks. The resulting In6S7/NSC HMS anode exhibits theoretical-value-close specific capacity (546.2 mAh g(-1) at 0.1 A g(-1)), ultrahigh rate capability (267.5 mAh g(-1) at 30.0 A g(-1)), high initial coulombic efficiency (approximate to 93.5%), and approximate to 92.6% capacity retention after 4000 cycles. This kinetically favored In6S7/NSC HMS anode fills up the kinetics gap with a capacitive porous carbon cathode, enabling a sodium-ion capacitor to deliver an ultrahigh energy density of 136.3 Wh kg(-1) and a maximum power density of 47.5 kW kg(-1). The in situ/ex situ analytical techniques and theoretical calculation both show that the robust and fast Na+ charge storage of In6S7/NSC HMS arises from the multi-electron redox mechanism, buffered volume expansion, negligible morphological change, and surface-controlled solid-state Na+ transport.

Automated summary

Researchers have successfully synthesized In6S7/NSC HMS anode material with theoretical-value-close specific capacity, ultrahigh rate capability, and excellent cycling stability. When paired with a capacitive porous carbon cathode, a sodium-ion capacitor can achieve a high energy density and maximum power density.