LEGO‐Like Granular‐Electrode Capacitive Deionization with Ultrahigh Mass Loading for Ultrafast Electrochemical Ion Capture

Advancing capacitive deionization (CDI) toward practical deployment requires moving beyond low‐mass‐loading, material‐focused demonstrations to high‐volumetric‐loading architectures with high system efficiency. Here, we report a membrane‐free LEGO‐like granular‐electrode CDI (GCDI) system, in which ultrahigh mass loading is achieved by assembling carbon granular electrodes (GE) rather than continuously thickening monolithic electrodes. This design avoids the conventional trade‐off between increased loading and impaired ion transport caused by longer transport distances and inaccessible internal active sites. Under forced convection, GCDI induces an ion‐entrainment effect that renews ions in both inter‐GE and intra‐GE domains. Hydrodynamic and electrochemical kinetic analyses confirm effective ion transport throughout the electrode volume. Consequently, GCDI reaches an ultrahigh mass loading of ∼274 mg cm −2 and an areal ion flux of 0.59 µmol NaCl cm −2 min −1 , outperforming most flow‐by and flow‐through CDI systems. Even at a high areal flux of 7338 L h −1 m −2 , it maintains an areal ion‐capture capacity of 16.74 µmol NaCl cm −2 . GCDI operates for over 500 cycles with ∼60% capacity retention. Cost analysis and carbon footprint estimates further indicate reduced electrode, membrane, and electricity‐related burdens for membrane‐free GCDI. These results establish membrane‐free GCDI as a scalable structural strategy for improving CDI system efficiency in practical saline and complex water treatment.