Start with the detection method and principle of the electrolyte to understand the detection process of the electrolyte.

Related detection methods and techniques for lithium battery electrolytes

The previous article mainly introduced the principles and methods of some detection techniques for lithium-ion battery separators. The last one, as one of the four key materials—electrolyte—is often referred to as the "blood" of a lithium-ion battery. It plays a crucial role between the positive and negative electrodes, enabling the conduction of ions and ensuring the high performance of the battery in terms of voltage and power. Electrolytes are typically composed of organic solvents, lithium salts, and additives, mixed in specific proportions under controlled conditions. This article will explore the detection methods and principles of the electrolyte, guiding readers through the process of analyzing this vital component.

Start with the detection method and principle of the electrolyte to understand the detection process of the electrolyte.

1. Appearance: The appearance of the electrolyte is usually checked by observing its color. Most electrolytes are clear and colorless, but there are specific standards for testing appearance, such as GB/T 9282.1-2008. This standard uses a platinum-cobalt color scale to determine the color of transparent liquids. A series of standard solutions are prepared and measured using a spectrophotometer at different wavelengths. These solutions are then compared with the sample to determine its color grade.

Start with the detection method and principle of the electrolyte to understand the detection process of the electrolyte.

Start with the detection method and principle of the electrolyte to understand the detection process of the electrolyte.

2. Moisture content: Determined using the Karl Fischer method, which was previously discussed and will not be repeated here.

3. Free acid: Due to the presence of LiPF6 in the electrolyte, trace amounts of HF may form when exposed to moisture. To test for free acid, a simple titration method using acid and base is commonly used. Some recent patents have focused on optimizing the choice of alkali, but the basic principle remains similar.

4. Iron content: During the production and transportation of electrolytes, iron impurities can be introduced, affecting battery performance. The porphyrin spectrophotometric method is widely used, based on reducing Fe³⁺ to Fe²⁺ with ascorbic acid. At pH 2–9, Fe²⁺ reacts with phenanthroline to form an orange-red complex. The absorbance at 510 nm is measured, and the concentration is determined from a standard curve.

Start with the detection method and principle of the electrolyte to understand the detection process of the electrolyte.

Start with the detection method and principle of the electrolyte to understand the detection process of the electrolyte.

5. Density: Measured according to GB/T 2540 using a pycnometer. The sample is placed in a calibrated pycnometer, heated in a constant temperature bath, and weighed after removing excess liquid. The density is calculated using a specific formula.

Start with the detection method and principle of the electrolyte to understand the detection process of the electrolyte.

6. Conductivity: Measures the ability of the electrolyte to conduct electric current, which is essential for determining the battery’s power performance. A conductivity meter is typically used for this purpose.

Start with the detection method and principle of the electrolyte to understand the detection process of the electrolyte.

7. Color: Evaluated using the platinum-cobalt scale (GB/T 3143). The color is measured using a spectrophotometer, similar to the appearance test, and compared with standard samples.

Start with the detection method and principle of the electrolyte to understand the detection process of the electrolyte.

8. Chloride ion content: Determined using a silver nitrate titration method, which is straightforward and commonly applied.

9. Sulfate ion content: In hydrochloric acid medium, sulfate ions react with barium to form a precipitate. The turbidity of the solution is visually compared with a standard to determine the sulfate content.

10. Impurity content: For elements like K, Na, Fe, Ca, Pb, Cu, Zn, Ni, and Cr, inductively coupled plasma optical emission spectroscopy (ICP-OES) is used. The sample is atomized and excited in a plasma, emitting characteristic light that corresponds to the element concentration.

11. Electrochemical properties: Tested by assembling batteries and conducting electrical performance tests. This process is well-known among most professionals in the lithium-ion battery field.

Summary:

With the advancement of lithium-ion battery technology, electrolytes are expected to evolve from liquid to semi-solid or solid states, and from conventional to high-voltage systems. Research is also ongoing into flame-retardant, low-calorific, and high-safety electrolytes. As the industry progresses, more advanced electrolytes will likely be adopted in future battery designs. This series has covered the detection methods of the four major components, and we hope you continue to follow along. Thank you!

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