The importance of humidity control during lithium-ion battery production
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The importance of humidity control during lithium-ion battery production

Posted Date: 2024-01-26

Lithium-ion batteries have very high humidity requirements during the production process, mainly because out-of-control or coarsening control of moisture will have adverse effects on the electrolyte. The electrolyte is the carrier for ion transmission in the battery. It is composed of lithium salt and organic solvent. It is the guarantee for the lithium-ion battery to obtain the advantages of high voltage and high specific energy. Excessive moisture content will have adverse effects on the electrolyte:

Electrolyte deterioration

The electrolyte is the carrier for ion transport in the battery and consists of lithium salts and organic solvents. The electrolyte plays a role in conducting ions between the positive and negative electrodes of lithium batteries, which is the guarantee for lithium-ion batteries to obtain the advantages of high voltage and high specific energy. When filling the battery, it must be in an environment with a humidity of less than 1%, and it must be sealed immediately after filling to prevent the inside of the battery from contacting the air. If the moisture content is too high, the electrolyte will react with the moisture to generate trace amounts of harmful gases, which will have a negative impact on the environment of the injection room. This will also affect the quality of the electrolyte itself, causing poor battery performance.

Battery capacity becomes smaller

The first discharge capacity of the battery decreases as the moisture in the battery increases. Excessive moisture content will damage the active components of the electrolyte and also consume lithium ions, causing irreversible chemical reactions of lithium ions in the negative electrode of the battery. As lithium ions are consumed, the battery's energy is reduced.

Internal resistance increases

As the battery moisture increases, the internal resistance shows an upward trend. When the battery is in use, only when the internal resistance is small can it be discharged with a large current, and the power of the battery will be very high; if the internal resistance is large, it cannot be discharged with a large current, and the power of the battery will be relatively low. Excessive moisture will affect the quality of the SEI film in lithium batteries, thereby affecting the internal resistance of the battery.

The internal pressure of the battery is too high

Moisture will react with LiPF6 in the electrolyte to generate harmful gases. When there is too much water, the pressure inside the battery increases, causing the battery to be deformed due to stress. If it is a mobile phone battery, it will appear as a drum shell; when the internal pressure is higher, the battery will be in danger. The burst will cause the electrolyte to splash, and the battery fragments can easily injure people.

Battery leaking

In addition to generating gas, LiPF6 in the electrolyte reacts with moisture to produce hydrofluoric acid, which is a highly corrosive acid that can corrode the metal parts inside the battery, causing the battery to eventually leak. If the battery leaks, the battery's performance will drop rapidly, and the electrolyte will corrode the user's machine.

The electrolyte and positive and negative electrode materials are very sensitive to water. To ensure the quality of the battery, the moisture in the workshop and glove box must be strictly controlled. In particular, some key processes, such as battery cell baking, liquid injection, sealing, etc., must be carried out in Carry out in a low humidity environment of less than 1% to avoid moisture entering the electrolyte. At this time, it is necessary to use changes in the dew point temperature value to reflect humidity fluctuations. Generally, the dew point temperature should be controlled below -45°C, or even drier.


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