Po-Hsiu Chien1 Xuyong Feng1 Jens Rosenberg2 Samuel Grant2 Yan-Yan Hu1 2

1, Florida State University, Tallahassee, Florida, United States
2, National High Magnetic Field Laboratory, Tallahassee, Florida, United States

Two basic needs for the development of high-performance solid-state batteries: the discovery of fast Li-ion conductors to use as solid electrolytes and the mitigation of large interfacial resistance. Both theoretical and experimental efforts have dedicated to the discovery of lithium fast ion conductors with ionic conductivity > 1 mS cm–1. In situ monitoring of the synthesis process will make the discovery process more efficient compared with traditional trial-and-error approach. In situ X-ray/Neutron Diffraction are often employed. In this contribution, we demonstrate in situ high-temperature NMR for following the synthesis process of solid electrolytes. The advantages of NMR over diffraction techniques are: 1) it unveils local structural disorder and defects that are not accessible by diffraction; 2) it is capable of determining ion dynamics and phase evolution at the same time. This is critical to the establishment of real time structure-property correlation and facilitate real time screening of candidates for fast ion conductors.
The heterogeneity of Li distribution in Li solid electrolytes results in both interfacial resistance and metallic Li microstructure formation. The ability to non-destructively probe Li distribution in solid electrolytes is important but challenging. 2D 7Li MRI was employed to monitor the distribution of Li ion concentration in a symmetric Li/c-LLZO/Li battery cell. Li deficiency layers (LDLs) near electrolyte-electrode interfaces upon electrochemical cycling were observed. The LDLs at the interfaces were associated with large interfacial impedance, which gradually increased with electrochemical cycling, and resulted in the malfunction of battery cells. In this work, we demonstrate the capabilities of 7Li NMR/MRI for capturing the salient facts of solid-state batteries which are inaccessible by other techniques.