The key points of the electrolyte preparation process for lithium battery packs mainly include material preparation, environmental control, operation steps, quality control, safety protection, storage and transportation, etc. The following is a detailed introduction:

Material preparation

Solvent: Usually, ethylene carbonate (EC), dimethyl carbonate (DMC), etc. are selected, with a purity of at least 99.9% or more to avoid impurities affecting the conductivity of the electrolyte. The proportion of solvents is relatively large, usually ranging from 80% to 85%. These solvents typically feature high dielectric constant, low melting point, high boiling point, low viscosity, and good chemical stability.

Lithium salt: Lithium hexafluorophosphate (LiPF6) is commonly used. It should be stored in a dry environment. Before opening, check the sealing of the packaging. Lithium salts are the most crucial component in the electrolyte and have the highest cost proportion, accounting for approximately 10% to 12%, but their cost share is as high as 40% to 50%. The solutes are various lithium-containing compounds, as lithium salts can release a large number of active lithium ions after dissolving in the solvent, which is conducive to improving the conductivity of the electrolyte.

Additives: Such as film-forming agents or flame retardants, are prepared in proportion according to the formula requirements. They account for a relatively small proportion, approximately 3% to 5%, but the cost proportion is about 10% to 30%. Additives are substances with specific functions in electrolytes. According to their different types of action, they can be classified as film-forming additives, overcharge protection additives, high/low temperature additives, flame-retardant additives, and rate type additives, etc.

Environmental control

The operation should be carried out in an inert gas environment with a humidity of less than 1%, and an argon glove box is usually chosen. The oxygen content in the glove box should be controlled below 10ppm to prevent lithium salts from reacting with moisture and oxygen and becoming ineffective. Before operation, check the sealing of the glove box, confirm that the circulating purification system is operating normally and the data of the humidity monitor is stable. Operators should wear dust-free suits and nitrile gloves to avoid skin contact with chemicals.

Operation steps

Mixed solvent: Pour ethylene carbonate and dimethyl carbonate into the reactor in the formula ratio, control the stirring speed at 200 to 300 revolutions per minute, and maintain the temperature at 25±2℃.

Dissolving lithium salts: The addition of lithium salts should be carried out in batches, with each batch not exceeding 5% of the total mass. Only after complete dissolution should the addition continue to prevent local excessive concentration from causing crystallization.

Adding additives: The additives are slowly added dropwise after the lithium salt has dissolved, and the flow rate is controlled using a constant pressure dropwise funnel.

Filtration and purification: After stirring is completed, filtration is carried out. Undissolved particles are removed using a 0.2μm polytetrafluoroethylene filter membrane, and the filtration pressure should not exceed 0.3MPa.

Quality control

Moisture content detection: The filtered electrolyte is transferred to a sealed storage tank, filled with argon gas for protection, and left to stand for 24 hours to eliminate bubbles. Take samples to test the moisture content, and determine it by the Karl Fischer method. The standard value should be less than 20ppm.

Conductivity test: Use the four-electrode method. The value should conform to the theoretical range of the formula. If the deviation exceeds 5%, readjusting is required.

Other tests: For each batch of configuration, the operation parameters, environmental data and test results should be recorded, and the retention period should be no less than the product's validity period. Carry out the inspection of the first piece and the recheck of the last piece. In addition to the routine testing, the first sample needs to undergo high-temperature storage testing (60℃ for 7 days) to observe the sedimentation situation. Compare the data of the last sample with that of the first one to confirm the batch stability. Laboratory-level configuration can reduce the proportion for pre-experiments to verify the feasibility of the formula. The production-level configuration needs to verify the amplification effect and adjust the stirring power and heat transfer parameters.

Safety protection

The operation area is equipped with: eye wash stations and gas masks. The waste liquid collection bucket is made of corrosion-resistant materials.

Accidental leakage handling: Immediately cover with dry diatomite, collect and hand over to a professional institution for handling.

Skin contact handling: The electrolyte should be rinsed with plenty of water for 15 minutes. Seek medical attention if necessary.

Storage and transportation

Storage: Use double-layer stainless steel containers, with the outer layer filled with dry nitrogen for protection. During transportation, avoid severe vibration and maintain an ambient temperature of 10 to 30 degrees Celsius.

Filling: The filling process uses pipeline transportation to minimize air contact. The equipment for preparing electrolytes of different formulas should be independently dedicated to prevent cross-contamination. Record preservation includes raw material batch numbers, operators, environmental parameters, and test reports, with a traceability period of no less than five years.