Electrochemical-mechanical model of space charge zone at interface

The interface between solid electrolyte and electrode plays an important role in determining the physical processes controlling electrochemical performance of metal-ion batteries. In this work, we develop an electrochemical-mechanical model for the determination of net charge density, stress and electric fields in solid electrolyte, which is in contact with electrode, under the framework of thermodynamics and linear elasticity. The mobile species are cations, which occupy interstitial sites through the formation of Frenkel defects. Analytical solutions of net charge density, stress and electric fields are obtained for the linear, coupling model, which is simplified from the nonlinear, coupling system under small stress and electric fields. For a solid electrolyte sandwiched between two parallel electrodes, the numerical results predict that there exists accumulation/adsorption of a layer of charges (interstitial ions) to electrode, i.e., the presence of space charge zone, whose size is dependent on electric potential and elastic constants of the solid electrolyte. Such behavior is similar to the Stern layer for liquid electrolyte and allows for the storage of energy in a capacitive form, similar to electrical double layer. The ratio of the nominal size of space charge zone to the thickness of solid electrolyte is a decreasing function of the thickness of the solid electrolyte. The nonlinear and coupling system developed in this work lays a foundation to analyze the interface behavior of heterogeneous structures and the effects of space charge zone on the energy storage of multilayer structures. The approach developed in this work can be extended to investigate the multi-field coupling problems in solid oxide fuel cells, mixed halide quantum dots and transducers. Keyworks: Interface; Space charge zone; Gibbs free energy; Strain energy; Electric field.