Reliable and Precise Determination of Water in Lithium Ion batteries by Karl Fischer Titration

Lithium ion batteries are energising the current mega trend towards electrical mobility. One of the key requirements of lithium ion batteries is that they must be free of water, because water reacts with the conducting salt of the electrolyte. A proven and reliable method to measure the water content in the electrolyte matrix of lithium ion batteries directly is coulometric Karl Fischer titration.

All batteries consist of an anode and a cathode, a separator as well as an electrolyte. Electrical conductivity between anode and cathode is established by the electrolyte. In general, mixtures of anhydrous, aprotic solvents and lithium salts are chosen for such electrolytes. However, if there is water present in the electrolyte, it will react with the conducting salt, e.g., LiPF6. This leads to the formation of highly toxic hydrofluoric acid.

The water content of several materials used in lithium ion batteries can be determined reliably and precisely by coulometric Karl Fischer titration. Metrohm Application Bulletin 434 describes the determination of the water content in the following materials:

• raw materials for the manufacture of lithium-ion batteries (e.g., solvents for electrolytes, carbon black/graphite)
• electrode coating preparations (slurry) for anode and cathode coating
• the coated anode and cathode foils as well as in separator foil and in the combined material
• electrolytes for lithium-ion batteries