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 µmolNaCl 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 µmolNaCl 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.