Strength Testing of Lithium-Ion Battery Materials Using a Continuous-Testing Micro-Compression Testing Machine

Importance of the Topic

The mechanical integrity of electrode particles is a critical determinant of lithium-ion battery performance, reliability and lifetime. Particle fracture or plastic deformation during cell manufacturing and repeated charge/discharge cycles can degrade electrical contact, increase impedance, and accelerate capacity fade. Quantitative, high-throughput mechanical characterization of single particles supports materials development, process optimization, and quality control for cathode and anode materials.

Objectives and Study Overview

This Application News demonstrates use of Shimadzu's MCT-AD continuous micro-compression testing system to evaluate mechanical properties of single electrode particles representative of positive (NMC811) and negative (graphite) battery materials. The goals were to show automated particle detection and handling, to perform up to 100 continuous compression tests, and to extract statistically meaningful strength metrics while greatly reducing operator workload.

Methodology and Instrumentation

Key experimental approach:

• Samples: Positive electrode material (NMC811-type) and negative electrode material (graphite-type), particle sizes ~10–15 µm.
• Sample preparation: Particles dispersed singly on a lower compression plate using a syringe-based negative-pressure dispersion unit to avoid overlap.
• Automated workflow: Wide-area image stitching by an XY stage, automatic particle detection, length/diameter measurement, selection by user-defined criteria (size, circularity, aspect ratio), and sequential compression testing with automated indenter cleaning—enabling continuous testing of up to 100 particles.
• Analysis: Force–displacement curves recorded for each particle; fracture strength used for brittle behavior, deformation strength (force at 10% diameter reduction) used for softer samples; datasets filtered around median values for robust statistics.

Used Instrumentation

• MCT-211AD Micro Compression Testing Machine (MCT-AD series).
• Flat indenter, Ø50 µm contact geometry.
• Electric XY slide stage and wide-area imaging system for particle detection.
• Optional side-observation kit for real-time lateral imaging and video capture during compression.
• Soft-sample measurement mode and low-test-force option for compliant materials.

Test Conditions (Representative)

Positive electrode (NMC811):

• Particle diameter: ~10–15 µm.
• Test force: 50 mN; loading rate 2.2 mN/s.
• Measurement method: area → diameter of equivalent circle; circularity ≥ 85%; aspect-ratio threshold ~0.88.
• Fracture criterion: crush strength coefficient 2.8 (JIS Z8844).

Negative electrode (graphite):

• Particle diameter: ~10–15 µm.
• Test force: 8 mN; loading rate 0.07 mN/s (soft sample mode).
• Measurement method: maximum length and perpendicular diameter; circularity ≥ 70%; aspect-ratio threshold ~0.70.
• Deformation strength evaluated at 10% particle-diameter reduction due to limited fracture signatures.

Results and Discussion

Throughput and automation:

• The MCT-AD carried out 100 continuous measurements after a single manual setup step (~20 minutes), compared with >5 hours of operator time using conventional manual procedures—reducing operator active time by over an order of magnitude.

Positive electrode (NMC811):

• 100 samples tested; fracture behavior was common.
• Analysis used 70 samples near the median; average fracture strength = 125.3 MPa, standard deviation = 15.1 MPa.
• Force–displacement curves and strength vs. particle-diameter plots were generated to examine size-related trends and scatter.

Negative electrode (graphite):

• 100 samples tested; distinct fracture events were rarely observed.
• Deformation strength at 10% diameter reduction was computed and evaluated for 50 samples near the median; average deformation strength = 1.8 MPa, standard deviation = 0.5 MPa.
• Soft-sample measurement mode improved surface recognition and measurement reliability for compliant particles.

Observation capabilities:

• Side observation allowed real-time visualization and video recording of particle deformation and failure modes, supporting mechanistic interpretation of force–displacement signatures.

Benefits and Practical Applications

• High-throughput single-particle mechanical testing enables statistically robust characterization of particle populations important for R&D and QC.
• Automation of particle detection, sizing and sequential testing reduces operator bias and inter-operator variability in particle selection and measurement.
• Significant labor savings and lower requirement for highly skilled operators facilitate routine adoption in industrial laboratories.
• Capability to test both brittle (cathode) and soft (anode) particles with mode-specific settings broadens applicability across battery material classes; method is transferable to other particulate materials (ceramics, glass, powders).

Future Trends and Potential Uses

• Integration of single-particle mechanical data with electrochemical cycling and imaging (in situ or correlative SEM/optical) to directly link mechanical failure modes to capacity fade and cycle life.
• High-throughput datasets enabling machine-learning models that predict electrochemical performance from particle mechanical and morphological descriptors.
• Further automation of sample preparation and dispersion to increase throughput and reproducibility.
• Standardization of test protocols (e.g., deformation thresholds, contact geometries, data-filtering rules) across laboratories to enable benchmark datasets and material specifications.
• Development of micro-mechanical testing under controlled environments (temperature, humidity, state-of-lithiation) to simulate service conditions more closely.

Conclusion

The MCT-AD micro-compression system provides an automated, high-throughput platform for quantitative single-particle mechanical characterization of battery electrode materials. The workflow demonstrated reliable discrimination between fracture-dominated cathode particles (average fracture strength ~125 MPa) and deformation-dominated anode particles (deformation strength ~1.8 MPa), while drastically reducing operator time and subjectivity. These capabilities support accelerated materials development, improved quality control, and generation of datasets needed to correlate mechanical properties with electrochemical behavior.

References

1. Moon et al. The correlation between particle hardness and cycle performance of layered cathode materials for lithium-ion batteries. Journal of Power Sources. 486 (2021) 229359.
2. Omirkhan et al. Investigating the effect of lithiation on polycrystalline NMC811 Li-ion battery cathode cracking using in situ SEM micromechanical testing. Energy & Environmental Science. 18 (2025) 9254.