Synthesis of multicore-shell FeS2@C nanocapsules for stable potassium-ion batteries

Transition-metal sulfides are widely used as anodes for potassium-ion batteries (PIBs) due to their low cost and high theoretical capacity. The practical application of such materials, however, is still impeded by their inherent low conductivity and obvious volume change during cycling. Herein, a flexible etch-assisted sulfidation strategy is reported. According to the strategy, the multicore-shell (MCS) nanocapsule structure is constructed, and then mesoporous FeS2 nanoparticles are encapsulated in the hollow carbon shell with adjustable interior space. The product, MCS-FeS2@C-20, not only features optimized inner space, but also delivers a large reversible capacity (519 mAh g−1 at a current density of 50 mA g−1), good rate capability (107 mAh g−1 at a high current density of 5 A g−1) and excellent cycling stability (capacity retention rate of 84.2% over 500 cycles at 0.5 A g−1), making it the promising anode material for PIBs. Notably, potassium-ion full cells (MCS-FeS2@C-20//K0.4CoO2) also show an improved potassium storage performance.