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The production process of lithium batteries can be divided into three stages: front-end electrode manufacturing, back-end cell packaging, and back-end battery activation. The purpose of the battery activation stage is to fully activate the active substances and electrolyte in the battery to achieve stable electrochemical performance. The activation stage includes pre charging, formation, aging, and constant capacity stages. The purpose of pre charging and chemical conversion is to activate the positive and negative electrode materials through the first few cycles of charging and discharging, so that the materials are in their optimal state of use.

There are several main purposes of aging: firstly, to improve the infiltration of electrolyte, which is beneficial for the stability of battery performance; Secondly, after aging, the active substances in the positive and negative electrode materials can accelerate the occurrence of some side effects, such as gas production and electrolyte decomposition, which can quickly stabilize the electrochemical performance of lithium batteries; The third is to conduct consistency screening of lithium batteries after aging for a period of time. After formation, the voltage of the battery cell is unstable, and its measured value will deviate from the actual value. The voltage and internal resistance of the aged battery cell are more stable, making it easier to screen for batteries with high consistency.

There are two main factors that affect the performance of lithium batteries under the aging system, namely aging temperature and aging time. In addition, it is also important whether the battery is sealed or open during aging.

For open chemistry, if the factory can control the humidity well, it can be sealed after aging. If high-temperature aging is used, it is better to age after sealing. For different battery systems, targeted tests need to be conducted based on material properties and lithium battery characteristics, such as ternary positive/graphite negative lithium batteries, lithium iron phosphate positive/graphite negative lithium batteries, or lithium titanate negative lithium batteries. In experimental design, the optimal aging regime can be determined by the differences in capacity, internal resistance, and voltage drop characteristics of lithium batteries.

1、 Lithium ion batteries with ternary or lithium iron phosphate positive/graphite negative electrodes

For lithium-ion batteries with ternary as the positive electrode material and graphite as the negative electrode material, the pre charging stage of the lithium-ion battery will form a solid electrolyte membrane (SEI) on the surface of the graphite negative electrode. The formation potential of this membrane is about 0.8V, and SEI allows ions to penetrate but not electrons. Therefore, after forming a certain thickness, it will inhibit further decomposition of the electrolyte and prevent battery performance degradation caused by electrolyte decomposition. However, the SEI film formed after formation has a tight structure and small pores. Further aging of the battery will help to restructure the SEI structure and form a loose and porous film, thereby improving the performance of lithium batteries.

The aging of ternary/graphite lithium batteries generally chooses room temperature aging for 7-28 days, but some factories also use high-temperature aging system, with aging time of 1-3 days. The so-called high temperature is generally between 38 ℃ and 50 ℃. High temperature aging is only for shortening the entire production cycle, and its purpose is the same as room temperature aging, which is to allow the positive and negative electrodes, separators, electrolytes, etc. to undergo sufficient chemical reactions to reach equilibrium, so that lithium batteries can reach a more stable state.

2、 Lithium titanate negative electrode lithium battery

The commonly known lithium titanate battery is a battery that uses lithium titanate as the negative electrode, while the positive electrode material is mainly ternary, lithium cobalt oxide, and other materials. The difference between lithium titanate batteries and graphite negative electrode batteries is that the lithium insertion potential of lithium titanate is 1.55V (relative to lithium metal), which is higher than the 0.8V formed by SEI. Therefore, during the charging and discharging process, no solid electrolyte film (SEI) or dendritic lithium will be formed, thus having higher safety.

This means that during the charging process of lithium titanate, there are constantly electrons reacting with the electrolyte, generating by-products and gases such as hydrogen, CO, CH4, C2H4, which can cause the battery to bulge. The bulging problem of lithium titanate mainly relies on changes in material properties to alleviate, such as surface coating, changing particle size distribution, and finding suitable electrolytes.

In addition, optimizing the system of pre charging, formation, and aging can also appropriately alleviate the bulging phenomenon of lithium titanate. The aging system of lithium titanate batteries is generally preferred to be high-temperature aging system, with an aging temperature of 40 ℃ -55 ℃ and an aging time of 1-3 days. After aging, negative pressure exhaust is required. Performing multiple high-temperature aging processes to allow the internal moisture of the battery to fully react and release the gas can effectively suppress the gas swelling problem of lithium titanate batteries and improve their cycle life.

Aging is an essential process for any type of battery system. The aging of lithium batteries, although understood as the loss and damage of lithium batteries, is actually an effective way to screen for batteries with high consistency and eliminate defective products. Only through aging can suitable lithium batteries be selected for packaging, which can improve the service life of electric tools.

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