In Situ Strain Measurements on LAGP Solid Electrolyte in Symmetrical Li/LAGP/Li Battery during Li Plating and Stripping

Abstract

Solid electrolytes have potential to dramatically improve energy density of batteries for demanding applications such as electrical vehicles by allowing the utilization of high energy density-Li metal anodes. However, harvesting the benefits of the solid electrolytes for Li-metal batteries is limited to due to interfacial instabilities, dendrite formation and large impedance. Chemo-mechanical deformations in the electrode- solid electrolyte interface are still the bottleneck to improve performance of solid-state batteries. Investigation of the solid electrolyte - electrode interface during battery cycling is must to elucidate the governing forces behind the deformations and associated electrochemical performance loss in all-solid-state batteries. Various in situ characterization techniques such as Micro CT, XPS, and TEM have provided crucial information about the deformation mechanisms in the solid electrolyte1.In this study, we utilized digital image correlation (DIC) to monitor chemo-mechanical deformations in solid-state batteries during battery cycling. DIC computes strains with spatial and temporal resolution by tracking the changes in the speckle patterns in small neighborhoods called subsets during deformation2. In situ strain measurements previously utilized to investigate the driving forces behind the structural and interfacial instabilities in alkali metal-ion battery electrodes3,4.A custom cell was designed to operate in operando strain measurements on solid electrolytes while cycling the all-solid-state battery. Shortly, symmetrical Li | LAGP | Li cells were fabricated, and stainless-steel disks were used as a current collector. Li1.5,Al0.5Ge1.5P3O12 (LAGP) powder was used to prepare LAGP solid electrolyte. In order to obtain a flat surface for the DIC measurements, the solid electrolyte was cut in half to obtain a semi-circle. Carbon black was used to decorate the flat side of the solid electrolyte as speckle pattern. In situ strain measurements demonstrated the impact of the early non-uniform deformations on the spatial distribution of Li plating and stripping on the solid electrolyte – electrode interface. The strain measurements provided quantitative analysis of the mechanical deformations and its coupling with the electrochemical behavior of the symmetrical battery cell. The measurements demonstrated the correlation between mechanical deformation in Li anode – LAGP interphase and the overpotential. Large amount of deformations in the center of the LAGP electrolyte was recorded at higher current densities and the fracture in the solid electrolyte was verified with ex-situ Micro-CT measurement. In this talk, we will present the spatial and temporal distribution of the strains in the LAGP solid electrolyte during battery cycling and we will discuss its coupling with the electrochemical performance.Acknowledgement:This work was supported by the NASA EPSCoR Research Initiation Grant. We are grateful for the valuable discussions with Dr. Behrad Koohbor and Dr. James Wu.