Performance of a ferroelectric glass electrolyte in a self-charging electrochemical cell with negative capacitance and resistance

Abstract

The ability for electrochemical cells to self-charge for extended periods of time is desirable for energy storage applications. While self-oscillation is a phenomenon found in human-made dynamic systems and in nature, its appearance in electrochemical cells has not been reported or anticipated. Here, we chose an electrochemical cell containing two electrodes separated by a self-organizing glass electrolyte containing alkali cations. The ferroelectric character of the electrolyte, with an impressively high dielectric constant of 106–107, supported self-charge and self-oscillation. After fabrication, the cells were characterized to determine the electrical impedance, dielectric spectroscopy, and electrochemical discharge. The electrochemical cells also displayed negative resistance and negative capacitance. Negative capacitance is due to the formation of an inverted capacitor between the double-layer capacitor formed at the negative electrode/electrolyte interface and the dipoles of the ferroelectric-electrolyte. Negative resistance is triggered by the formation of an interface phase, which leads to a step-change of the chemical potential of the electrode. The electrochemical cell demonstrates an entanglement between negative resistance, negative capacitance, self-charge, self-cycling, and the activation energy vs thermal energy or external work. The phenomenon of self-cycling is enhanced at low temperatures where the activation energy is higher than the thermal energy. This demonstration extends the Landau-Khalatnikov model for a ferroelectric to a bistable device in which the bistability resides in an electrode. The results reported here reveal the first report of negative capacitance and negative resistance existing in the same process, which can lead to valuable advancements in energy storage devices and in low-frequency applications.

Dynamical theory for the battery's electromotive force

“…The observations of slow self-oscillations in certain battery configurations 16,19 have clearly established that the electrochemical double layer at the electrode-electrolyte interface is a complex dynamical system, capable of generating an active cycle through the interplay of its chem-ical, electric, and mechanical properties. Together with the theoretical considerations, based on electrodynamics and thermodynamics, detailed in this article, we believe that this makes a strong case that the generation of the emf by the battery must be understood as an active periodic process, like other instances of the pumping of a macroscopic current.…”

“…Other possible signals include fast residual modulations of the battery's output voltage (much faster than those reported in Refs. 16,19) and the battery's response when subject to ultrasound signals capable of resonantly driving the double layer's oscillation. Moreover, as noted in Sec.…”

“…Similar slow self-oscillations have also been reported in the catalytic reactions 17,18 and in self-charging electrochemical cells with a ferroelectric glass electrolyte. 19 Some authors have proposed exploiting the mechanical energy of electrochemical self-oscillations to perform useful work, 20 but the experimentally observed electrochemical oscillations have not previously been connected to the pumping dynamic responsible for the battery's emf. Analogous self-oscillations, with frequencies well below that of the pump's running, are often seen in hydraulic pumps (where they can pose serious problems for the device's proper functioning).…”

Structural Batteries: A Review

“…Recently, we have been developing structural batteries. Our strategy is based on the use of a ferroelectric-electrolyte non-flammable composite (A2.99Ba0.005ClO, A = Li, Na) that polarizes spontaneously below 170 °C [ 109 , 110 ]. This spontaneous polarization is due to the ferroelectric character of the electrolyte and adds to the electrostatic storage in the battery cell.…”

Achieved High Energy Density and Excellent Thermal Stability in (1-x)(Bi0.5Na0.5)0.94Ba0.06TiO3-xBi(Mg0.5Ti0.5)O3 Relaxor Ferroelectric Thin Films

“…The development of new energy power generation technologies places high demands on devices that efficiently store, absorb, and supply electricity [1][2][3]. Dielectric capacitors play an essential role in high power applications, including pulsed power systems, hybrid vehicles, and medical defibrillators, owing to their fast charge/discharge rate, high power density, and long lifetime [4][5][6][7][8][9].…”