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.