Analyses methods to enhance lithium metal battery performance

Research Summary

Lithium metal batteries (LMBs) can have high energy density, however, they face issues such as dendrite formation (tree-like Li structures on the electrode surface) and electrolyte decomposition. These problems shorten battery lifespan and can lead to fires. Therefore, in this study we employed solid-state nuclear magnetic resonance (NMR) spectroscopy to explore the degradation of lithium metal electrodes of LMBs and lithium ion dynamics, aiming to understand the issues.

To clarify uncertainties in preparing NMR samples and interpreting NMR data, we optimized fundamental NMR experimental procedures for lithium metal electrodes from LMBs: refining battery sample shapes and sizes, sample cutting methods, aligning with external magnetic fields, and washing and drying samples. On this foundation, we studied electrodes prepared from LMBs with various electrode materials such as protecting-layer coated Li, bare Li, and LiAg.

The results agreed with the electrochemical data and scanning electron microscopy observations, revealing the formation of dendrites and interfaces between solid electrodes and electrolytes. In addition, the mobility of lithium ions in each constituent was observed to differ in each constituent.

Our results demonstrated the ability to observe the reversibility of metal electrodes at the atomic level and enhanced the feasibility of observing planar metal samples by utilizing magic angle spinning probes commonly used for solid-state NMR spectroscopy.

Expected Outcomes

This study is expected to serve as a valuable and practical guideline for characterizing lithium ion dynamics and lithium states within lithium-metal batteries using solid-state 7Li NMR spectroscopy.

Related Figures

• Sample preparation procedures for 7Li NMR experiments and sample orientation in the magnetic field. (Above) Photos of sample mounting in a CPMAS probe (Below) Definition of sample orientation (green: metallic sample plate) with respect to the external magnetic field: (left) parallel and (right) perpendicular. The gray PET plates (~800 μm thickness) were used to keep the thin sample flat, enhancing orientation accuracy.
• Comparison of data from lithium-metal batteries comprising bare lithium electrodes, lithium electrodes with protective coatings (Li-PL), and lithium-silver alloy electrodes (LiAg) (Above) Voltage data during charging and discharging cycles. (Below) ⁷Li NMR spectra after 50 charging-discharging cycles. (Gray signals indicate signals from samples oriented parallel to the external magnetic field.)