The influence of lithium battery activation stage on battery performance

The production process of Lithium Batteries can be divided into three stages: front pole piece manufacturing, middle battery cell packaging, and rear battery activation. The purpose of the battery activation stage is to fully activate the active substances and electrolyte in the battery to achieve electrochemistry. Stable performance.

The activation stage includes pre-charging, formation, aging, constant volume and other stages. The purpose of pre-charging and forming is to allow the positive and negative materials to be charged and discharged for the first few times to activate the material and make the material in the best state of use.

There are several main purposes of aging:

➤One is to make the electrolyte infiltration better, which is conducive to the stability of battery performance;

➤Secondly, after the active material in the positive and negative materials is aged, it can promote the acceleration of some side effects, such as gas production and electrolyte decomposition, so that the electrochemical performance of the Lithium Battery can quickly stabilize;

➤The third is to screen the consistency of lithium batteries after a period of aging. The voltage of the cell after formation is unstable, and the measured value will deviate from the actual value. The voltage and internal resistance of the cell after aging are more stable, which is convenient for screening batteries with high consistency.

The aging system has two main influence factors on the performance of lithium batteries, namely, aging temperature and aging time. In addition, it is also important whether the battery is sealed or opened during aging.

For opening formation, if the factory can control the humidity, it can be sealed after aging. If high temperature aging is used, it is better to age after sealing. For different battery systems, ternary positive/graphite negative lithium batteries, lithium iron phosphate positive/graphite negative lithium batteries, or lithium titanate negative batteries, targeted tests need to be carried out according to the material characteristics and lithium battery characteristics. In the experimental design, the best aging system can be determined through the difference in capacity, internal resistance, and pressure drop characteristics of lithium batteries.

1. Ternary or lithium iron phosphate cathode/graphite anode lithium battery

For lithium batteries with ternary as the positive electrode material and graphite as the negative electrode material, a solid electrolyte membrane (SEI) is formed on the surface of the graphite negative electrode during the pre-charge formation stage of the lithium ion battery, and the formation potential of this membrane is about 0.8 Around V, SEI allows ions to penetrate but not electrons, so that after a certain thickness is formed, it will inhibit the further decomposition of the electrolyte, which can prevent the degradation of battery performance caused by the decomposition of the electrolyte.

However, the SEI film formed after chemical conversion has a compact structure and small pores. Re-aging the battery will help the SEI structure to reorganize and form a loose and porous film, thereby improving the performance of the lithium battery.

The aging of the ternary/graphite lithium battery generally chooses room temperature aging for 7 days to 28 days, but some factories use high temperature aging system, the aging time is 1-3 days, the so-called high temperature is generally between 38℃-50℃. High-temperature aging is only to shorten the entire production cycle. The purpose is the same as room-temperature aging, which is to allow the positive and negative electrodes, diaphragm, electrolyte, etc. to fully carry out chemical reactions to balance, so that the lithium battery can reach a more stable state.

2. Lithium titanate anode lithium battery

The commonly known lithium titanate battery is a battery that uses lithium titanate as the negative electrode, and the positive electrode material is mainly ternary, lithium cobaltate and other materials.

The difference between lithium titanate battery and graphite anode battery is that the lithium intercalation potential of lithium titanate is 1.55V (relative to lithium metal), which is higher than the 0.8V formed by SEI, so no solid electrolyte membrane will be formed during charge and discharge ( SEI) will not form dendritic lithium, so it has higher safety.

This means that during the charging process of lithium titanate, electrons constantly react with the electrolyte to generate by-products and produce hydrogen, CO, CH4, C2H4 and other gases, which will cause the battery to bulge. The bulging problem of lithium titanate mainly depends on the change of material properties to alleviate, such as material surface coating, changing the particle size distribution, and finding a suitable electrolyte.

In addition, the bulging phenomenon of lithium titanate can be appropriately reduced by optimizing the pre-charge, chemical conversion, and aging system. The high temperature aging system is generally preferred for the aging system of lithium titanate batteries. The aging temperature is 40℃-55℃, and the aging time is generally 1-3 days. After aging, negative pressure exhaust is required. Carry out multiple high-temperature aging to fully react the moisture inside the battery, and after the gas is discharged, the flatulence problem of the lithium titanate battery can be effectively suppressed, and its cycle life can be improved.

Regardless of the battery system, aging is an essential process. Although the aging of lithium batteries is understood to be the loss and destruction of lithium batteries, in fact it is an effective way to screen batteries with high consistency and eliminate defective products. Only through the aging method can the lithium battery suitable for packing be selected and the service life of the electric tool can be improved.