The importance of lithium battery manufacturing site management

With the popularization of new energy vehicles and the frequent exposure of safety accidents, the safety of vehicle power batteries has attracted more and more attention. Power battery internal impurities, metal particles and so on have the possibility of power battery internal short circuit, resulting in heat out of control, a safety accident. This requires the power battery monomer production process control measures in place to ensure high quality monomer, avoid the battery internal impurities mixing. Lithium battery production is sensitive to environmental factors, and the site needs to strictly control the moisture, metal dust, temperature and so on. Here mainly for lithium battery production site foreign body management simple summary.

Metal foreign bodies do great harm to lithium batteries. Metal dust mixed into the battery is particularly easy to cause the battery internal positive and negative short circuit, this kind of short circuit according to the size of the resistance can be divided into internal short circuit and internal micro short circuit. When there is an internal short circuit, the short circuit resistance is small and the current is large. In the process of charging and discharging, the open circuit voltage of the battery is directly abnormal, and even a large amount of heat released by the short circuit discharge causes the heat to be out of control. And the internal micro-short circuit current is small, the battery in the long-term storage process of self-discharge, battery calendar life is short, poor storage performance. In the battery, there are four types of internal short circuit, which are :(1) copper foil-aluminum foil short circuit; (2) copper foil-anode material short circuit; (3) cathode material -- aluminum foil short circuit; (4) negative material - positive material short circuit. The nature of each type of short circuit is different from that of the thermal overpass 3.

The basic principle of short circuit in the battery caused by metal foreign body has two processes, as shown in figure 1. Larger metal particles Pierce the diaphragm directly, resulting in a short circuit between the positive and negative poles. This is a physical short circuit. In addition, after the metal foreign matter is mixed into the positive electrode, the positive electrode potential increases after charging, the metal above 3V dissolves, diffuses through the electrolyte, and then the metal dissolves under the negative electrode potential 1V precipitates on the negative electrode surface, and finally punctures the diaphragm, forming a short circuit, which is a chemical short circuit. The most common metal foreign bodies in battery factory are Fe, Cu, Zn, Al, Sn, SUS, etc.

In the face of such complex metal foreign bodies, the manufacturing site often takes measures to prevent foreign bodies from mixing into battery products, as shown in figure 2. Such as electrode paste with electromagnetic iron removal equipment to remove Fe and other metal impurities, pole cutting or die cutting process with brush such as cleaning cutting burr, pole ear or coating edge tape protection, easy to produce metal chips in the process (welding) with dust collector adsorption of foreign bodies, and so on. In check, liquid injection before the battery through the internal short circuit withstand voltage test detected nonconforming, aging cells through pressure drop Δ V detection nonconforming product. In addition, 5S and cleaning activities on the production site are also very important means of foreign body management on the site.

Basic principles of foreign body management in production site:

(1) do not bring: air shower is set in the buffer area. When people, materials and equipment enter the buffer area, remove dust and foreign matters and do not bring dust into the site. Items not related to production, such as metal fixtures, tools and pencils, should not be brought in as far as possible.

(2) do not produce: people working inside, processed parts, materials, equipment, etc. should not produce dust as far as possible. It is forbidden to keep semi-finished products in areas where foreign bodies are prone to occur. The cathode? The diaphragm is kept separately. Mechanical sliding, contact parts with magnets to remove metal foreign bodies.

(3) no accumulation: dust generated by the equipment or environment does not fall on, mix in and accumulate on the product.

(4) removal: timely remove the dust generated by the equipment and environment, prohibit its attachment, mixing and accumulation on the product.

Cleaning to remove dust pollution is the key, cleaning is not to eliminate pollution, but to transfer the pollution to different places: pollution -> vacuum cleaners, rags, water, air and so on -> disposal, waste and so on.

General process of cleaning (PDCA) :

Plan P: identify and understand the pollution, and decide on cleaning methods according to the type and nature of the pollution, etc. Determine the results and goals to be achieved.

D implementation: according to the previously decided cleaning method.

C inspection: check the implementation results and compare them with the goals set.

A treatment: treatment, not to achieve the effect, analysis of the reasons, again make plans, put forward measures and objectives. Good way to standardize it.

Therefore, the first step is to recognize pollution. There are three elements of pollution, namely, pollutant, surface property of pollutant, and combination of the two, as shown in FIG. 3. We should make clear the following problems. After understanding the pollution, we should choose the right cleaning tools and methods according to the characteristics of pollution:

(1) what are the types of pollutants, dust, hair, dirt, oil, sewage, materials, (welding, cutting) metal debris, etc. What is the nature of the pollution, chemical composition, form (gas, liquid, solid), specific gravity, size, weight, shape, hydrophilic or hydrophobic, what is the source?

(2) surface properties of contaminants: type (wood, brick, finishing, equipment), chemical composition, hydrophilic or hydrophobic, surface roughness, hardness and softness, shape, cleanliness required.

(3) bonding state (interface state) : chemical bonding, electrostatic adsorption, van der Waals force, gravity, etc.

The battery manufacturing site has strict requirements for dust. Generally, the battery is produced in a clean environment, and personnel, equipment, materials and so on are always more or less able to bring in or produce dust. How to remove dust is very critical. Cleaning is also a technology, want to master also need training!

The man who can sweep the floor may be an eminent monk. Do you know how to clean the battery factory?

The page contains the contents of the machine translation.