The production process of lithium battery can be divided into three stages: front pole piece manufacturing, middle channel cell encapsulation, and rear cell activation. The purpose of battery activation stage is to fully activate the active material and electrolyte in the battery to achieve electrochemical Stable performance. The activation phase includes pre-charging, formation, aging, constant volume, etc. The purpose of pre-charging and chemical formation is to allow the positive and negative materials to be charged and discharged for the first time to activate the material to make the material in optimal use. .
There are several main purposes for aging: one is to make the electrolyte infiltration better, which is conducive to the stability of the battery performance; the second is that the active substances in the positive and negative materials can accelerate the progress of some side effects, such as gas production, electrolysis. Liquid decomposition, etc., the electrochemical performance of the lithium battery is quickly stabilized; Third, the lithium battery consistency screening after aging for a period of time. After the formation, the voltage of the battery core is unstable, and the measured value will deviate from the actual value, the electricity after aging The core voltage and internal resistance are more stable, which is convenient for screening highly consistent batteries.
There are two main factors affecting the performance of lithium batteries in the aging system, namely aging temperature and aging time. In addition, it is also important that the battery is in the state of sealing or opening when aging.
For the opening formation, if the plant can control the humidity, it can be aged and then sealed. If high temperature aging is used, the aging after sealing is better. For different battery systems, ternary positive electrode / graphite negative lithium battery, lithium iron phosphate positive electrode / graphite Negative lithium battery or lithium titanate negative battery, need to be based on material characteristics and lithium battery characteristics for targeted tests. In the experimental design, the lithium battery capacity difference, internal resistance difference, pressure drop characteristics to determine the best aging system.
One, ternary or lithium iron phosphate cathode / graphite anode lithium battery
For a lithium battery in which ternary is used as a positive electrode material and graphite is used as a negative electrode material, a solid electrolyte membrane (SEI) is formed on the surface of the graphite negative electrode during the pre-charge phase of the lithium ion battery, and the formation potential of the film is about 0.8. Around V, SEI allows ions to penetrate without allowing electrons to pass, thereby inhibiting further decomposition of the electrolyte after forming a certain thickness, and preventing battery performance degradation caused by decomposition of the electrolyte. However, the SEI film structure formed after formation Tight and small pores, aging the battery, will help the SEI structure reorganization, forming a loose porous membrane, thereby improving the performance of the lithium battery.
The aging of ternary/graphite lithium battery generally chooses normal temperature aging for 7 days to 28 days, but some factories adopt high temperature aging system, the aging time is 1-3 days, the so-called high temperature is generally between 38 ° C and 50 ° C. Aging is only to shorten the entire production cycle. Its purpose is the same as normal temperature aging. It is to balance the positive and negative electrodes, diaphragm and electrolyte to achieve a more stable state.
Second, lithium titanate negative lithium battery
The so-called lithium titanate battery is a battery using lithium titanate as the negative electrode. The positive electrode material is mainly ternary, lithium cobalt oxide and other materials. The difference between lithium titanate battery and graphite negative battery is that the lithium insertion potential of lithium titanate is 1.55V (relative to lithium metal), higher than 0.8V formed by SEI, so no solid electrolyte membrane (SEI) will form during charging and discharging, and dendritic lithium will not form, which has higher safety.
This means that during the charging process of lithium titanate, electrons react with the electrolyte continuously, generating by-products and generating hydrogen, CO, CH4, C2H4 and other gases, which will cause the drum of the battery. The problem of tying the lithium titanate is mainly Relieve by the change of material properties, such as coating the surface of the material, changing the particle size distribution, finding a suitable electrolyte, etc.
In addition, by optimizing the pre-filling, chemical formation, aging system can also properly reduce the phenomenon of lithium titanate bulging. Lithium titanate battery aging system generally prefers high temperature aging system, aging temperature is 40 ° C -55 ° C, aging time is generally 1- 3 days, after aging, negative pressure exhaust is required. Multiple high temperature aging is performed to fully react the internal moisture of the battery. After the gas is discharged, the problem of flatulence of the lithium titanate battery can be effectively suppressed and the cycle life can be improved.
Regardless of the battery of any system, aging is an indispensable process. Although the aging of lithium batteries is understood to be the loss and destruction of lithium batteries, in fact, it is a battery with high screening consistency, which is effective in eliminating defective products. Ways. Only through aging, can you choose a lithium battery suitable for grouping, improve the service life of power tools.
