Electro-chemo-mechanics of solid state batteries: inelastic response to lithium plating and stripping

One of the most important issues facing modern science is how to deal with the rising need for storage technologies and renewable energy sources. There is likely no cutting-edge technology that can replace lithium-ion batteries (LiBs) for such purposes. Although the high ionic conductivity allows liquid organic electrolytes (LoEs) to remain state-of-the-art for this type of technology, the safety concerns correlated with these devices induce scientists to study new types of batteries with different kinds of electrolytes. Solid-state electrolytes (SSEs) are considered promising candidates to replace LoEs, due to their higher energy density, non-flammability, mechanical properties and electrochemical stability against lithium metal. However, a few drawbacks, like high contact resistance, reduced ionic conductivity compared with a liquid electrolyte, dendritic growth and degradation at the Li-foil anode, affect contemporary SSEs. A correct mechanical characterization of SSEs becomes paramount. The current work investigates the mechanical response of an all-solid-state lithium battery (ASSB). An electro-chemo-transport-mechanics model, in the realm of continuum mechanics and thermodynamics, is here proposed to describe the behaviour of a battery cell, in which the negative electrode consists of a lithium metal foil. Lithium deposition on the anode surface, accompanied by the shrinkage and expansion of the cathode, has been considered to evaluate the outbreak of mechanical stresses. A detailed investigation of the mechanical problem of growth connected with the inelastic nature of lithium has been carried out. The problem has been originally framed using an elasto-plastic constitutive model for lithium foil, which has been later enhanced to highlight its rate-dependent nature. The electrochemical response of the cell is investigated in terms of electric potential and species concentrations to complete the model description. To substantiate the reliability of the proposed model, it was tested against experimental galvanostatic discharge curves on a commercial all-solid-state thin film battery (Raijmakers et al. 2020 Electrochim. Acta330, 135147 (doi:10.1016/j.electacta.2019.135147)) and from a mechanical perspective, against the experimental outcomes of a tensile test performed on a lithium sample. Predictive science could provide new tools to reveal the physical laws behind the pitfalls that penalize the smooth operation and the performance of the ASSBs.