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Cost-effective material with a rational design is significant for both sodium-ion batteries (SIBs) and electromagnetic wave (EMW) absorption. Herein, we report an elaborate yolk–shell FeS₂@C nanocomposite as a promising material for application in both SIBs and EMW absorption. When applied as an anode material in SIBs, the yolk–shell structure not only facilitates a fast electron transport and shortens Na ion diffusion paths but also eases the huge volume change of FeS₂ during repeated discharge/charge processes. The as-developed FeS₂@C exhibits a high specific capacity of 616 mA h g^–1 after 100 cycles at 0.1 A g^–1 with excellent rate performance. Furthermore, owing to the significant cavity and interfacial effects enabled by yolk–shell structuring, the FeS₂@C nanocomposite delivers excellent EMW absorption properties with a strong reflection loss (−45 dB with 1.45 mm matching thickness) and a broad …