Two Birds with One Stone: FeS2@C Yolk–Shell Composite for High-Performance Sodium-Ion Energy Storage and Electromagnetic Wave Absorption

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 15.4 GHz bandwidth. This work inspires the development of high-performance bifunctional materials.