Water in lithium ion battery materials

Importance of the topic

Water in lithium-ion battery components must be tightly controlled because even trace moisture can degrade electrolyte salts such as LiPF6, generate hydrofluoric acid and compromise performance and safety. Reliable determination of water content below 20 mg/kg in solvents, electrodes and separators supports quality assurance in battery manufacturing.

Objectives and study overview

This bulletin presents validated procedures for quantifying water by Karl Fischer titration in key lithium-ion battery materials. It covers:

• Electrolyte solvents by direct coulometric titration
• Carbon black and graphite by gas‐extraction titration
• Anode and cathode slurries with NMP and additives
• Coated electrode foils, separators and combined assemblies

Methodology and Instrumentation

The methods employ coulometric Karl Fischer titration with two sample introduction modes:

• Direct titration for aprotic solvents that do not react with reagents
• Gas extraction (vial oven) for solids and viscous slurries using inert carrier gas and elevated temperatures

Coulometric KF titrator with double-platinum electrodes (with or without diaphragm), magnetic stirrer, vial oven and nitrogen supply are used. Reagents include methanol-free anolyte/catholyte solutions and specialized KF media for challenging matrices. Conditioning of the cell to dryness, controlled drift stopping criteria (relative drift ≤ 5 μg/min, down to 2 μg/min for high accuracy) and compensation for reagent capacity are critical.

Main results and discussion

Key observations:

• Direct titration delivers fast, precise water values in aprotic solvents when hydrogen bonding does not impede reaction kinetics.
• Gas extraction at temperatures between 120 °C and 180 °C ensures complete water release from carbon materials, slurries and coated foils.
• Addition of xylene improves water release and reproducibility in NMP-based anode slurries.
• Reagent capacity must be monitored to avoid extended titration times; regular replacement and methanol compensation prevent biases.
• Proper sealing and handling of vials, along with routine maintenance of needles and tubing, reduce drift and improve reproducibility.

Benefits and practical applications

This approach enables rapid, accurate water content measurement for raw materials and finished battery components. It supports:

• Quality control of electrolyte purity
• Process optimization in electrode coating and module assembly
• Safety validation by preventing moisture‐induced degradation

Future trends and potential applications

Advances may include:

• Integration of automated valve and oven systems for high throughput analysis
• Miniaturized KF titrators for inline moisture monitoring
• Enhanced reagents tailored to emerging battery chemistries (solid‐state, high‐voltage electrolytes)
• Coupling with spectroscopic detectors for multiparameter characterization

Conclusion

Coulometric Karl Fischer titration with direct and gas-extraction modes provides a robust and versatile toolkit for water determination in lithium-ion battery materials. Adoption of optimized protocols ensures reliable data for product development, quality assurance and safety assurance.

Reference

• Metrohm Application Bulletin 280