The influence of moisture in the lithium battery manufacturing process
Apr 10, 2024
During the manufacturing process of lithium-ion batteries, there are three crucial items that must be strictly controlled: dust, metal particles, and moisture. If dust and metal particles are not properly controlled, it will directly lead to safety accidents such as internal short circuits and fires in the battery. If moisture is not effectively controlled, it will also cause significant harm to battery performance and lead to serious quality accidents! Therefore, it is crucial to strictly control the water content of main materials such as electrodes, separators, and electrolytes during the manufacturing process. There must be no relaxation and constant vigilance! The following is a detailed explanation from three aspects: the harm of moisture to lithium batteries, the source of moisture during the manufacturing process, and the control of moisture during the manufacturing process. 1. The harm of moisture to lithium batteries (1) Battery swelling and leakage: If there is excessive moisture in lithium-ion batteries, it reacts chemically with the lithium salt in the electrolyte, generating HF: H2O + LiPF6 → POF3 + LiF + 2HF Hydrofluoric acid (HF) is a highly corrosive acid that can cause significant damage to battery performance: HF corrodes the metal components, battery shell, and sealing within the battery, eventually leading to cracks, ruptures, and leakage. HF also destroys the SEI (Solid-Electrolyte-Interface) film inside the battery by reacting with its main components: ROCO2Li + HF → ROCO2H + LiF Li2CO3 + 2HF → H2CO3 + 2LiF Eventually, LiF precipitates form inside the battery, causing irreversible chemical reactions in the negative electrode that consume active lithium ions, thereby reducing the battery's energy capacity. When there is a sufficient amount of moisture, more gas is generated, increasing the internal pressure of the battery. This can lead to deformation, swelling, and even leakage, posing a safety risk. Many instances of battery swelling and cover popping encountered in mobile phones or digital electronic products on the market are often attributed to high moisture content and gas generation inside the lithium battery. (2) Increased battery internal resistance: Battery internal resistance is one of the most critical performance parameters, serving as a primary indicator of the ease with which ions and electrons can travel within the battery. It directly affects the battery's cycle life and operating state. A lower internal resistance means less voltage is consumed during discharge, resulting in higher energy output. An increase in moisture content can lead to the formation of POF3 and LiF precipitates on the surface of the SEI film (Solid-Electrolyte-Interface). This degrades the density and uniformity of the SEI film, gradually increasing the battery's internal resistance and decreasing its discharge capacity. (3) Shortened cycle life: Excessive moisture can damage the SEI film, leading to a gradual increa...
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