Water‐Soluble Salt Template‐Assisted Anchor of Hollow FeS₂ Nanoparticle Inside 3D Carbon Skeleton to Achieve Fast Potassium‐Ion Storage

Abstract The rationally structural engineering is an efficient strategy to improve the comprehensive performance of potassium‐ion storage anode materials. In this paper, a hybrid with hollow FeS₂ nanoparticles anchored into the 3D carbon skeleton (labeled as H‐FeS₂@3DCS) is successfully constructed through two critical steps of in situ chemical deposition and anion‐exchange reaction strategies. In the former, the water‐soluble Na₂CO₃ crystals are used as hard templates for the preparation of 3DCS, while Fe³⁺‐containing aqueous solutions are utilized to remove the Na₂CO₃ templates. Interestingly, the intense collision between Fe³⁺ and CO₃^2‐ in aqueous solution produces nanoscale Fe(OH)₃ colloidal particles, which are firmly anchored into the pores of the carbon skeleton to form a “lotus‐seed”‐like nanostructure. In the latter case, a central void space is created inside the FeS₂ nanoparticles due to the different diffusion rates of S‐anions and Fe‐cations during the subsequent sulfidation process. Thanks to this unique composition model, the H‐FeS₂@3DCS hybrid not only alleviates the volume expansion efficiently by rationally hollow structure design, but also provides spacious “roads” (3D carbon skeleton) and “houses” (hollow FeS₂ nanoparticles) for fast K‐ion transition and storage. As the anode of PIBs and PIHCs, the resultant H‐FeS₂@3DCS electrode delivers an obviously enhanced K‐ions storage performance over state‐of‐the‐art.