Electric field reconfiguration enables co-ion management by induced charge granular electrodes for stable...

Co-ion expulsion is an intrinsic bottleneck of electric double-layer capacitive deionization because it dissipates charge into counterproductive ion exchange rather than net salt removal. Here we report a membrane-free induced-charge capacitive deionization system in which packed granular activated carbon operates as a bipolar ion-storage medium. By physically decoupling the carbon granules from the current collectors, the applied electric field polarizes conductive granules, generating spatially separated charge domains and redirects co-ions toward oppositely polarized storage regions. This redistribution of the electric field reduces interfacial co-ion accumulation and limited reverse re-adsorption during polarity switching. In 1000 mg l^-1 NaCl, the bipolar system achieved 3.44 mg g^-1 SAC within 30 min at 0.5 × 10³ V m^-1, and reached ∼16.75 mg g^-1 as the field strength increased to 1.2 × 10³ V m^-1. After 100 cycles, the system retained >75% of its capacity, whereas the unipolar CDI retained 29%. The bipolar system showed better tolerance to scaling conditions and complex water matrices. Finite-element simulations, current-response analysis, and post-cycling electrochemical characterization indicate that field redistribution mitigates co-ion accumulation, limits localized Faradaic reactions and modifies pore evolution of activated carbon. These findings provide a practical framework for designing stable membrane-free CDI systems through electric-field control.