Confinement−Adsorption Synergy in Hybrid Carbon‐Coated Separator Enables Stable High‐Rate Quinone Cathode for Magnesium Batteries

Organic cathodes offer great promise for rechargeable magnesium batteries (RMBs) owing to their structural tunability and fast Mg 2+ transport, yet their dissolution in ether‐based electrolytes leads to rapid capacity fading and poor rate performance. Herein, we design a high‐performance sulfur‐containing heterocyclic quinone cathode, benzo[b]naphtho[2′,3′:5,6][1,4]dithiino[2,3‐i]thianthrene‐5,7,9,14,16,18‐hexone (BNDTH), coupled with a functional carbon‐coated separator composed of graphene oxide (GO) and carboxylated multi‐walled carbon nanotubes (MWCNTs−COOH) at an optimized 1:9 mass ratio. In this architecture, GO provides physical confinement to suppress BNDTH diffusion, while MWCNTs−COOH offer abundant chemical adsorption sites to immobilize soluble species. This synergistic confinement–adsorption mechanism effectively mitigates active‐material loss and promotes charge transfer. As a result, the Mg//BNDTH cell exhibits significantly improved rate capability, delivering cathode capacities rising from 153 to 261 mAh g −1 at 1 C and from 26 to 100 mAh g −1 at 10 C over 500 cycles, along with cell‐level power and energy densities of 4517 W kg −1 and 222 Wh kg −1 , respectively—surpassing most reported RMBs employing organic cathodes. This work presents a viable separator‐engineering strategy for achieving stable and high‐rate operation of soluble organic cathodes in RMBs.