Vol:.(1234567890) MRS Advances (2021) 6:154–161 https://doi.org/10.1557/s43580-021-00014-3 1 3 ORIGINAL PAPER An investigation into compressive deformation and failure mechanisms in a novel Li‑ion solid‑state electrolyte Tofunmi Ogunfunmi 1  · Nnaemeka Ebechidi 2  · Ridwan Ahmed 1  · Oluwaseun Oyewole 1,3  · John Obayemi 3  · Wole Soboyejo 1,2,3 Received: 16 December 2020 / Accepted: 20 January 2021 / Published online: 5 February 2021 © This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply 2021 Abstract Solid-state batteries are generally considered to be safer than their liquid-state counterparts due to their decreased potential for fre or short circuiting. The fabrication of solid-state batteries relies on the application of stack crimping pressure that increases the interfacial surface contacts between electrolytes and the electrodes. However, excessive compressive crimping stresses (that occur in cell assembly) can give rise to cracking phenomena that can degrade battery performance and lead to thermal runaway or failure. It is, therefore, important to develop an understanding of failure mechanisms in solid-state Li- ion electrolytes. In this paper, we use a combination of in-situ optical microscopy and Digital Imaging Correlation (strain mapping) techniques to study compressive deformation and cracking phenomena in a novel solid-state Li-ion electrolyte. The stress states associated with the diferent stages of compressive deformation are also presented along with those due to charge–discharge cycles. The implications of the results are discussed for the material design of robust solid-state Li ion batteries. Keywords Microstructure · Energy storage · Stress/strain relationship · Electrical properties · Crystallographic structure Introduction Li-ion batteries have been one of the leading technologies in the battery industry. The remarkable properties of Li-ion batteries have been attributed to the presence of lithium, a light solid with large energy density [1]. The solid elec- trolytes are theoretically safer because of the increased mechanical stability in their solid state which decreases the probability of a short circuit. Ceramic electrolytes are of interest because of their high temperature resistance and good mechanical stability. They also have more promise for efcient transportation Li-ion compared to their polymer electrolytes counterparts [1]. Li+ ion conduction used in complex hydrides have often been potential materials for hydrogen storage but have made recent strides as potential materials for solid-state electro- lytes in lithium ion batteries [2]. These complex hydrides are abundant, lightweight, have low resistance and electronic conduction elements that allow it to be good materials for electrolytes [2, 3]. A common example of the complex hydride is lithium borohydride (LiBH 4 ). LiBH 4 has a struc- tural phase transition from an orthorhombic to hexagonal structure that occurs above 100 °C with high Li-ion con- ductivity. It has been shown that this high temperature phase that occurs can be stabilized at room temperature with the incorporation of lithium halides such as Cl, Br and I. Maekawa et al. [4] have shown that introduction of lithium iodide to lithium hydride increases Li-ion conduc- tivity at lower temperatures. It has also been reported that a combination of LiBH 4 and lithium amide (LiNH 2 ), in a Li(BH 4 ) 1−x (NH 2 ) x system (where x = 2/3 or at a stoichiom- etry ratio of LiBH 4 :LiNH 2 of 1:2), has high conductivity of 6.4 × 10 –3  S cm −1 at 40 °C. This is comparable to that of organic liquid electrolytes, which demonstrates prom- ising battery application. The electrolyte shows excellent interfacial stability and rate capability performance when * Tofunmi Ogunfunmi togunfunmi@wpi.edu 1 Department of Materials Science and Engineering, Worcester Polytechnic Institute, Worcester, MA 01609, USA 2 Department of Materials Science and Engineering, African University of Science and Engineering, Km 10 Airport Road, Galadimawa, Abuja, Federal Capital Territory, Nigeria 3 Department of Mechanical Engineering, Worcester Polytechnic Institute, Worcester, MA 01609, USA