Surface Potential Measurement at the Electrode- Electrolyte Interface of a Charged All-Solid-State Lithium-Ion Battery

Significance of the Topic

All-solid-state lithium-ion batteries (ASSLiBs) are emerging as a key technology for high-density, long-life, and safe energy storage, especially in electric vehicles. Interface resistance between electrode and solid electrolyte remains a major bottleneck, limiting ion transport, capacity, and fast charging. Advanced microscopic characterization of this interface is essential to understand degradation mechanisms and guide material improvements.

Objectives and Overview of the Study

This study demonstrates the use of a scanning probe microscope (SPM-Nanoa) in Kelvin probe force microscopy (KPFM) mode, housed in an inert‐atmosphere glove box, to visualize surface morphology and map surface potential at the electrode–electrolyte interface of a charged NASICON-type ASSLiB. The work aims to identify microstructural features and assess the charged state of active anode materials in situ.

Methodology and Instrumentation

Measurements were conducted using the SPM-Nanoa system inside an argon‐filled flow-type glove box (moisture <1 ppm, oxygen <1 ppm). Sample preparation steps included:

• Bonding stainless steel current collectors with silver paste and resin embedding.
• Cross‐section polishing and light ion milling to expose a clean electrode–electrolyte interface.
• Charging the ASSLiB cell for 50 hours under controlled moisture (10.6 ppm) and oxygen (0.4 ppm).

Key instrument settings:

• Scanner range: XY 125 µm, Z 7 µm
• Observation mode: Surface potential (KPFM)
• Fields of view: 30×30 µm and 5×5 µm
• Image resolution: 256×256 pixels

Main Results and Discussion

Topographical imaging revealed voids at the electrode–electrolyte interface, which act as barriers to lithium‐ion transport and contribute to interfacial resistance. Surface potential maps at three anode regions (current collector side, center area, electrolyte side) showed distinct charge distributions:

• Particles with lower potential (0.48 V) were identified as more heavily charged TiO₂ phases.
• Intermediate potentials (0.57 V) and higher potentials (0.67 V) indicated varying degrees of lithiation.
• The center area exhibited the highest average charge, suggesting balanced Li⁺ and electron supply.
• The collector side was limited by lithium supply and the electrolyte side by electron conductivity.

These observations highlight nonuniform conduction pathways for ions and electrons within the anode composite, directly impacting charge distribution and interface performance.

Benefits and Practical Applications

This in-situ SPM-KPFM approach offers:

• Direct visualization of morphological defects and charge heterogeneities at solid‐state interfaces.
• Quantitative assessment of active material lithiation states under realistic operating conditions.
• Guidance for engineering improved electrode microstructures and electrolyte compositions to reduce interface resistance.

Future Trends and Potential Applications

Advancements may include coupling KPFM with other SPM modes (e.g., electrochemical strain microscopy), real‐time monitoring during battery cycling, three-dimensional interface tomography, and the integration of machine learning for automated image analysis. These developments will expand insights into failure mechanisms and accelerate the design of next-generation solid-state batteries.

Conclusion

The combination of SPM-Nanoa and KPFM in an inert atmosphere enables detailed characterization of the electrode–electrolyte interface in ASSLiBs, revealing void formation and charge distribution patterns that underlie performance limitations. This methodology provides a powerful diagnostic tool to inform interface engineering strategies and support the development of high‐performance solid‐state energy storage.

References

1. E. Iida, T. Miyamoto, A. Kogure, H. Mukohara, N. Morimoto, R. Yamasaki, H. Yamada, SPM/AFM Evaluation of Interface of All-Solid-State Lithium-Ion Batteries, IVC-22, Sep 13, 2022; Sapporo, Japan.