Evaluating Electrochemical Activity and Electric Potential inside Cathodes in All-Solid-State Lithium-Ion Batteries

Significance of the Topic

All‐solid‐state lithium‐ion batteries (ASSLiB) offer enhanced safety, higher energy density and longer cycle life compared with conventional liquid‐electrolyte systems. Understanding performance degradation mechanisms during charge–discharge cycling is critical to improving electron and ion transport in cathode materials and achieving reliable high‐power, fast‐charging solutions for electric vehicles and stationary storage.

Study Objectives and Overview

This study demonstrates how a scanning probe microscope (SPM/AFM) can be employed inside an inert‐atmosphere glove box to visualize and quantify localized electrochemical activity and surface electric potential within cathode cross‐sections of ASSLiBs. The primary goals were to map electron conduction pathways, assess distribution of conductive additives, and track changes in electric potential before and after cycling.

Methodology and Instrumentation

Sample Preparation and Measurement Setup:

• An ASSLiB cell containing LiCoPO₄ active material, TiO₂ anode, Li₁.₅Al₀.₅Ge₁.₅(PO₄)₃ (LAGP) solid electrolyte and acetylene black conductivity agent was assembled.
• The cell was split, embedded in epoxy resin, and the cross‐section was milled by ion beam to remove contamination.
• Measurements were conducted under argon (<1 ppm O₂/H₂O) inside a flow‐type glove box to prevent degradation.

Instrumentation Used:

• Instrument: SPM‐Nanoa scanning probe microscope
• Scanner range: XY 125 µm × Z 7 µm
• Observation modes: Current mode for local conduction mapping and Kelvin probe force microscopy (KPFM) for surface potential
• Field of view: 20 µm × 20 µm at 256 × 256 pixels
• Environmental conditions: Dew point –80 °C, O₂ concentration 0.8 ppm

Key Results and Discussion

1. Local Electrochemical Activity Mapping:

• Current images show red areas of high electron flow corresponding to regions rich in conductive agent and blue areas of low current associated with active material or solid electrolyte.
• Comparison before and after charge–discharge revealed stable electron conduction pathways but highlighted uneven distribution of conductive additive.

2. Surface Electric Potential Analysis:

• KPFM measurements showed an average potential of 0.75 V prior to cycling and 2.98 V afterward, indicating residual charge and incomplete discharge.
• The elevated post‐cycle potential implies degradation of ion conduction pathways or interface impedance between active material and solid electrolyte.

Benefits and Practical Applications

By directly imaging conduction networks and electric potential distribution within cathode layers, this approach provides:

• Insight into the impact of conductive additive distribution on cell performance.
• Diagnostic capability to detect interface deterioration and charge retention issues.
• Feedback for material formulation and electrode manufacturing processes to optimize uniformity and cycling stability.

Future Trends and Potential Applications

Advances in operando SPM techniques and coupling with spectroscopic probes will enable real‐time mapping of ion transport and chemical changes under bias. Integration of high‐throughput data analysis and machine learning could accelerate materials screening. Extending these methods to next‐generation solid‐state chemistries and complex electrode architectures promises deeper understanding of failure modes and pathway engineering for durable, fast‐charging batteries.

Conclusion

This application demonstrates the power of SPM‐based current and surface potential imaging to reveal nanoscale conduction and charging phenomena in ASSLiB cathodes. Such insights are instrumental in diagnosing performance loss mechanisms and guiding improvements in electrode design and fabrication for advanced solid‐state energy storage.

References

1. E. Iida, A. Kogure, T. Miyamoto, H. Nakajima, H. Mukohara, N. Morimoto, R. Yamasaki, H. Yamada, C. J. Macey. AFM Evaluation of Different‐Sized Active Materials and Interface of All‐Solid‐State Lithium‐Ion Batteries. M&M2023, July 23–27, 2023; Minneapolis, MN, USA.