Double‐Helix Structure in Carrageenan–Metal Hydrogels: A General Approach to Porous Metal Sulfides/Carbon Aerogels with Excellent Sodium‐Ion Storage

The metal sulfide-carbon nanocomposite is a new class of anode material for sodium ion batteries, but its development is restricted by its relative poor rate ability and cyclic stability. Herein, we report the use of double-helix structure of carrageenan-metal hydrogels for the synthesis of 3D metal sulfide (M_x S_y ) nanostructure/carbon aerogels (CAs) for high-performance sodium-ion storage. The method is unique, and can be used to make multiple M_x S_y /CAs (such as FeS/CA, Co₉ S₈ /CA, Ni₃ S₄ /CA, CuS/CA, ZnS/CA, and CdS/CA) with ultra-small nanoparticles and hierarchical porous structure by pyrolyzing the carrageenan-metal hydrogels. The as-prepared FeS/CA exhibits a high reversible capacity and excellent cycling stability (280 mA h^-1 at 0.5 A g^-1 over 200 cycles) and rate performance (222 mA h^-1 at 5 A g^-1 ) when used as the anode material for sodium-ion batteries. The work shows the value of biomass-derived metal sulfide-carbon heterostuctures in sodium-ion storage.