Enhanced Charge Accumulation in Activated Carbon via the Dielectric Interface

An architecture enabling activated charge accumulation into activated carbon (AC) micropores was achieved by loading the appropriate amount of BaTiO3 (BT) nanoparticles as an interfacial layer between AC and liquid electrolyte. The effects of dielectric interface incorporation on charge transfer at the AC were investigated by a series of electrochemical assessments and by computational analysis using density functional theory combined with molecular dynamics. The optimized capacity of the BT-AC composite (annealed at 300 degrees C for 20 h) was 35% higher than the capacity of the bare AC. The addition of BT significantly decreased both the charge-transfer resistance (R-ct) and diffusion resistance Z(w). Their activation energies, E-a(CT) and E-a(Diff.), were also considerably reduced by BT loading. Cyclic voltammetry analysis revealed that both the electric double-layer (EDL) current and diffusion current increased with BT loading. The improved capacity characteristics were responsible for enhanced charge-transfer reaction activity at the EDL, involving adsorption/desorption and solvation/desolvation processes, as well as ion diffusion within the AC's micropores, through the BT interface. The activated electrochemical reactions via the dielectric layer proceeded in six steps. In the Li+-(EC)(4) case (during discharging), solvated Li+ ions (i) diffused in the electrolyte solution and (ii) were preferentially adsorbed on the dielectric surface. (iii) The naked Li+ ions then underwent desolvation on the same surface. (iv) The desolvated Li+ ions diffused across the dielectric surface and reached the active materials-dielectric-electrolyte triple-phase interface (TPI). Finally, the naked Li+ ions (v) diffused through micropores near the TPI and (vi) accumulated in the inner pores. The TPI was the dominant structural parameter determining the charge-transfer activity.