Date: 2025-01-03 hits: 160
The edge voltage of lithium batteries specifically refers to the voltage of the aluminum layer between the positive electrode ear of soft pack batteries and the aluminum-plastic film.
In theory, the aluminum layer between the positive electrode and the aluminum-plastic film is insulated, which means their voltage should be 0.
In fact, during the processing of aluminum-plastic film, the inner PP layer will be locally damaged, resulting in local conductivity (including electronic and ion channels) between them, forming a micro battery and thus creating a potential difference (voltage).
The edge voltage standards vary among manufacturers, but most industries set them below 1.0V. The voltage standards are based on the dissolution potential of aluminum lithium alloys.
Why control the edge voltage?
Because if the PP film inside the aluminum-plastic film is damaged, there will be corrosion damage to the capacity.
There must be two conditions for corrosion:
1. The electronic pathway is formed by the negative electrode and the aluminum layer of the aluminum-plastic film
2. Ionic pathway, formed by the aluminum layer of aluminum-plastic film and electrolyte; Without any of them, corrosion cannot be established.
After both conditions are met, lithium ions will react with the aluminum layer of the aluminum-plastic film to form lithium aluminum alloy; Lithium aluminum alloy is a powdery substance that causes holes in aluminum-plastic films; That is to say, there are some black spots inside the aluminum-plastic film that we often see; These black spots will become increasingly prominent over time and with an increase in the number of charge and discharge cycles.
How to conduct testing?
There are currently three types of detection methods known:
1. Test the resistance between the aluminum-plastic film and the negative electrode ear. If it is greater than 5M ohms, it is relatively safe. Some companies define it as relatively low. Based on the final PPm of the defective product that everyone can tolerate, some data can be calculated and their own standards can be defined; This resistance test mainly selects the electronic path;
2. To test the current between the positive electrode and the aluminum film, a DC source can be used. It is generally believed that if the current is greater than 0.001mA, it is a defective product and needs to be picked out;
3. Testing the voltage between the positive electrode and the aluminum film, it is generally considered that a voltage greater than 1V is a defective product.
The above three methods can be tested in combination with 1 and 2, or 1 and 3.
