Co-Construction of Solid Solution Phase and Void Space in Yolk–Shell Fe_0.4Co_0.6S@N-Doped Carbon to Enhance Cycling Capacity and Rate Capability for Aluminum-Ion Batteries

Rechargeable aluminum-ion batteries (AIBs), using low-cost and inherent safety Al metal anodes, are regarded as promising energy storage devices next to lithium-ion batteries. Currently, one of the greatest challenges for AIBs is to explore cathodes suitable for feasible Al³⁺ insertion/extraction with high structure stability. Herein, a facile co-engineering on solid solution phase and cavity structure is developed via Prussian blue analogues by a simple and facile sulfidation strategy. The obtained uniform yolk–shell Fe_0.4Co_0.6S@N-doped carbon nanocages (y–s Fe_0.4Co_0.6S@NC) display a high reversible capacity of 141.3 mA h g^–1 at 500 mA g^–1 after 100 cycles and a good rate capability of 100.9 mA h g^–1 at 1000 mA g^–1. The improved performance can be mainly ascribed to the dual merits of the composite; that is, more negative Al³⁺ formation energy and improved Al³⁺ diffusion kinetics favored by the solid solution phase and Al³⁺ insertion/extraction accommodable space stemmed from the yolk–shell structure. Moreover, the reaction mechanism study discloses that the reaction involves the intercalation of Al³⁺ ions into Fe_0.4Co_0.6S to generate Al_<i>l</i>Fe_<i>m</i>Co_<i>n</i>S and elemental Fe and Co.