Correlations of Li Deficiency, Diffusion, and Interfacial Impedance in Solid-State Batteries Probed by In Situ Tracer Exchange NMR and Depth-Profiling MRI Combined with Modeling

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NON-TECHNICAL SUMMARYAll-solid-state rechargeable batteries promise high energy density, low cost, and improved safety. Therefore, they are considered as the next-generation battery technology for electric vehicles and expected to meet other critical needs for safer, more compact, and higher-capacity energy storage devices. However, low power density and poor long-term stability limit their practical applications and market competitiveness. This research, funded by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, uses new NMR and MRI techniques to provide new insights into the cause of these limitations and helps to develop high-performance solid-state rechargeable batteries. It also generates new knowledge that promotes in-depth understanding of fundamental interface chemistry, where the bottleneck lies for improved performance of other technologies including fuel cells, super-capacitors, and solar cells. The new NMR and MRI methodologies developed as part of this project not only facilitate the discovery of novel functional materials for technological applications, but might also benefit biomedical research. Additionally, the principle investigator actively recruits students from a HBCU institution and engages women and minority students in the ongoing research, thereby educating and training a diverse next generation of STEM researchers. Outreach activities aimed at engaging the general public in scientific discussions include the development of an app with the title "The Sound of NMR".TECHNICAL SUMMARYLarge resistance for mass and energy transport at electrode-solid electrolyte interfaces impedes the success of high-performance solid-state rechargeable batteries. Understanding Li-ion diffusion across these interfaces and its relationships with structures and compositions of interfaces is critical to addressing the challenges associated with interfacial impedance. This project, funded by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, probes ion transport through electrode-solid electrolyte interfaces by employing the tracer-exchange NMR method, to quantify Li deficiency with high-resolution depth-profiling magnetic resonance imaging (MRI), and determines interfacial resistance with electrochemical impedance spectroscopy, under both ex and in situ conditions. This study provides insight into the critical factors that limit ion transport at the interfaces, which aids interface design for optimal electrode-electrolyte compatibility with minimized interfacial impedance. The researchers establish real time correlations among Li deficiency, diffusion, and interfacial resistance. Two model systems, Li/Li7La3ZrO12/Li and Li/Li10GeP2S12/Li, are chosen for their representativeness of oxide and sulfide electrolytes and their distinct differences at the Li electrode-solid electrolyte interfaces. Based on the experimental investigation, an analytical model is developed to quantitatively elucidate the impact of Li deficiency and diffusion on interfacial impedance. This model is implemented in the RandFlux software, for predicting the electrochemical processes and performance of all-solid-state rechargeable batteries. For this project, the principle investigator actively recruits students from a HBCU institution and engages women and minority students in the ongoing research. Outreach activities aimed at engaging the general public in scientific discussions include the development of an app with the title "The Sound of NMR".This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.