| Summary: | Taking advantage of electrode thicknesses well beyond conventional dimensions allowed us to follow the surface plasmonic THz frequency phenomenon with vacuum wavelengths of 100 μm to 1 mm, only to scrutinize them within millimeters-thicknesses insulators. Here, we analyze an Al/insulator/Cu cell in which the metal electrodes-collectors were separated by a gap that was alternatively filled by SiO<sub>2</sub>, MgO, Li<sub>2</sub>O, Na<sub>3</sub>Zr<sub>2</sub>Si<sub>2</sub>PO<sub>12</sub>–NASICON, Li<sub>1.5</sub>Al<sub>0.5</sub>Ge<sub>1.5</sub>(PO<sub>4</sub>)<sub>3</sub>–LAGP, and Li<sub>2.99</sub>Ba<sub>0.005</sub>ClO–Li<sup>+</sup> glass. A comparison was drawn using experimental surface chemical potentials, cyclic voltammetry (I-V plots), impedance spectroscopy, and theoretical approaches such as structure optimization, simulation of the electronic band structures, and <i>work functions</i>. The analysis reveals an unexpected common emergency from the cell’s materials to align their surface chemical potential, even <i>in operando</i> when set to discharge under an external resistor of 1842 Ω.cm<sub>insulator</sub>. A very high capability of the metal electrodes to vary their surface chemical potentials and specific behavior among dielectric oxides and solid electrolytes was identified. Whereas LAGP and Li<sub>2</sub>O behaved as p-type semiconductors below 40 °C at OCV and while set to discharge with a resistor in agreement with the Li<sup>+</sup> diffusion direction, NASICON behaved as a quasi n-type semiconductor at OCV, as MgO, and as a quasi p-type semiconductor while set to discharge. The capacity to behave as a p-type semiconductor may be related to the ionic conductivity of the mobile ion. The ferroelectric behavior of Li<sub>2.99</sub>Ba<sub>0.005</sub>ClO has shown surface plasmon polariton (SPP) waves in the form of surface propagating solitons, as in complex phenomena, as well as electrodes’ surface chemical potentials inversion capabilities (i.e., χ (Al) − χ (Cu) > 0 to χ (Al) − χ (Cu) < 0 vs. E<sub>vacuum</sub> = 0 eV) and self-charge (ΔV<sub>cell</sub> ≥ +0.04 V under a 1842 Ω.cm<sub>insulator</sub> resistor). The multivalent 5.5 mm thick layer cell filled with Li<sub>2.99</sub>Ba<sub>0.005</sub>ClO was the only one to display a potential bulk difference of 1.1 V. The lessons learned in this work may pave the way to understanding and designing more efficient energy harvesting and storage devices.
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