What effect does moisture have on lithium-ion batteries?

Regarding long-term storage of lithium-ion batteries, the internal resistance will increase with the increase in storage time. When the internal resistance exceeds a certain value, the performance of the battery will be greatly affected. Because the moisture content has an impact on the quality of the SEI film in a lithium-ion battery, it indirectly affects the internal resistance of the battery. 2. If the internal pressure of the battery is too high, the water will react with a component in the electrolyte and generate harmful gas. When there is enough water, the pressure inside the lithium-ion battery becomes greater, causing the battery to be deformed under force. If it is a mobile phone battery, it will behave as a drum shell; if it is our 26650 battery, it will behave as highly over-standard. If it is our 32xxx battery, the explosion-proof valve will crack and the battery will be scrapped. When the internal pressure is high, the battery is in danger, bursting causes the electrolyte to splash, and battery fragments are also easy to injure people. 3. The internal moisture of low-capacity lithium-ion batteries is too high. Hubei lithium-ion batteries consume the effective components of the electrolyte and also consume lithium ions, causing an irreversible chemical reaction of lithium ions on the battery negative plate. When lithium ions are consumed, the energy of the battery is reduced. 4. Battery leakage. When there is a lot of water inside the lithium-ion battery, the electrolyte inside the battery reacts with water, and the product will be gas and hydrofluoric acid. Hydrofluoric acid is a very corrosive acid. Corrosion of the metal parts inside the battery, which in turn causes the battery to leak. If the battery leaks, the performance of the battery will drop rapidly, and the electrolyte will also corrode the user's machine, eventually causing more dangerous failures. 5. When the battery charge and discharge capacity is less than 0.015% in the lithium-ion battery, the initial discharge capacity of the battery meets the national standard and the change is small; when the battery moisture is within the range of 0.015% to 0.04%, the battery discharge capacity changes with the new Increase and decrease. 6. The electrolyte is deteriorated, causing the rivets of the battery to rust. The electrolyte used in lithium-ion batteries cannot be used in an environment with excessive moisture. When filling the battery, it should be in an environment with a humidity of less than 1%, and the battery should be sealed as soon as possible after filling to prevent the inside of the battery from contacting the air. If the moisture is too high, the electrolyte reacts with the moisture to generate a small amount of harmful gas, which will have a negative impact on the environment of the injection room; this will also affect the quality of the electrolyte itself and make the battery performance poor; it will also make the battery rivets rust. Disadvantages of excessive moisture In the production process of the ternary/graphite system battery, the preparation of the positive electrode slurry generally uses an oil-based dispersion system, using PVDF as the binder and NMP as the solvent. When PVDF encounters excessive moisture, it will form a gelatinous substance, resulting in poor fluidity and leveling of the slurry, which is not conducive to the coating of the slurry. Therefore, when preparing the slurry, attention must be paid to the moisture content of the raw materials, the working environment, and the introduction of moisture during the operation of the personnel. In addition to having a huge impact on the preparation of lithium-ion battery slurry, excessive moisture will cause the electrolyte to decompose. The reaction is as follows: Hydrofluoric acid is a particularly corrosive acid, which can cause serious damage to the positive and negative electrode materials and current collectors of lithium-ion batteries, and ultimately lead to battery safety problems. Second, the significance of trace water However, it is not that the less water is better in lithium-ion batteries. As we all know, the solid electrolyte interface (commonly known as SEI membrane) is a selective permeable membrane that allows Li+ to permeate freely, but electrolyte molecules cannot permeate. The composition of the electrolyte and trace additives have a significant impact on the potential of the SEI film formation, the degree of compactness, the irreversible capacity loss of the battery, and the internal resistance of the battery. Water, as a trace component in the electrolyte, has a certain impact on the formation of SEI film and battery performance of lithium-ion batteries. 3. The influence of moisture on the performance of lithium-ion batteries In different material systems, the moisture content has a great influence on the performance of the battery. However, what remains unchanged is that moisture affects the first charge and discharge capacity, internal resistance, battery cycle life, and battery volume of lithium-ion batteries. Influence on the first charge and discharge capacity Moisture is related to the formation of SEI in lithium-ion batteries, and will inevitably affect the first irreversible capacity loss of lithium-ion batteries. As shown in Figure 1: Figure 1. The effect of moisture content on battery charge and discharge capacity. When the moisture in the battery is less than 0.015%, the first discharge capacity of the battery meets the national standard and the change is small; when the battery moisture is within the range of 0.015% to 0.04%, The first discharge capacity of the battery decreases with the increase of moisture in the battery. When the moisture content in the battery is less than 0.015%, the following reactions dominate. The lithium alkyl carbonate generated by the single-electron reduction process can also react with trace water in the electrolyte to generate lithium carbonate. 2ROCO2Li+H2O→Li2CO3+CO2+2ROH When CO2 is generated, a new chemical reaction occurs on the negative electrode surface at low potential: 2CO2+2Li++2e→Li2CO3+CO. It can be seen that the right amount of water helps to form Li2CO3-based, stable, uniform and dense SEI film. When the SEI film completely covers the negative electrode, the irreversible reaction stops immediately. When the moisture content is within the range of 0.0150% to 0.04%, the consumption of lithium ions increases, and the charge and discharge capacity of the battery decreases, which has a negative impact on it. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete it. Previous: Can lithium-ion batteries be charged by solar energy?