With the widespread use of lithium-ion batteries in people’s daily lives. The safety function of lithium-ion batteries is attracting more and more attention. These accidents have caused huge losses in property and personal safety. For larger power battery modules, storage performance is more important. These accidents are usually caused by a short circuit of the battery during use. Therefore, storage performance is also an obstacle that hinders the development of high-capacity lithium-ion batteries.
The needle insertion test uses a metal needle with a diameter of 3mm to 5mm to insert the battery. It causes a short circuit in the battery, thus studying the safety function and heat generation of the battery. This report introduces the sensitivity of needle penetration testing of lithium-ion batteries.
Factors Affecting Battery Needle Penetration Tests
Safety accidents of lithium-ion batteries are often caused by chemical reactions between the positive and negative elements in the electrolyte. Such chemical reactions are dominated by exothermic reactions and the heat released promotes the chemical reaction. The gas produced during the reaction causes the pressure inside the battery to increase, which eventually causes the battery to explode. The key system makes a forced short circuit in the battery, to reduce the chemical reaction in the battery to avoid explosion.
We describe the factors that affect the battery demand test through the following four sections:
1)Diaphragm
2)Electrolyte corrosion retardant
3)Conductor/Coordinator
4)Battery structure
Battery diaphragm
The main function of the distributor in lithium-ion batteries is to separate the positive and negative electrodes of the battery and to prevent short circuits caused by contact between the two poles. The materials used are PP film, PE film, PE/PP double-composite film or PP/PE/PP triple-composite film. These materials do not conduct electricity, but they can pass electrolyte ions. Diaphragm thickness, closed cell temperature, film termination temperature, hole size, direction of stretching, wettability and lack of insulation all affect battery safety and bulk.
Meanwhile, to meet the requirements of low internal resistance and strong stability. The film thickness of lithium-ion batteries used in power tools is chosen to be less than 25μm. Also, the porosity is 40%-50% and the pore diameter is 0.03-0.12μm. Although the porosity is very high, the resistance of the battery can be reduced. However, the mechanical strength of the diaphragm is poor.
Importance
In a pressure test, the diaphragm breaks easily. As a result, the large contact area between the positive and negative electrodes of the battery causes a short circuit. At the same time, when the battery temperature is high, the diaphragm is easy to break, which is dangerous.
When the porosity is small, the internal stability of the battery is small. This will reduce the battery performance to some extent.
The diaphragm has a large opening, which makes it easy to short circuit between the contacts of the positive and negative poles.
However, if the gap is small, it will affect the ion conduction of the battery and affect the performance of the battery. Therefore, choosing a separator with appropriate porosity and pore size plays a very important role in battery performance.
The effect of burning electrolyte on battery needs
When the battery makes a violent action in the needle, the reaction of the conductor and the person connected to the electrolyte in the electrode has a large part. It also determines the performance of the battery saver to some extent. Therefore, choosing the right conductor and connector is very important for battery protection.
The effect of the electrode conductor on the adhesive and the need of the battery
In addition to improving the internal components of the battery to improve battery protection. We can also improve the stability and safety of the battery by improving the design of the battery. Cylindrical and smooth batteries have different needle penetration test results.
Cylindrical batteries are easily broken at different needle speeds, causing the battery to short and explode.
Because the positive and negative electrodes of the cylindrical battery and the diaphragm use a high voltage system. When the battery meets the needle punch, the diaphragm cannot expand. PIN PEC works as a driver to connect negative electrode, so resulting in small circuit.
The fint is affected by the needle application that affects and is easier to pass. Because the soft pack battery is a flat system, the difference between the positive and negative electrodes is large. When the battery meets the need, the diaphragm can expand or even cover the steel needle. This will prevent the positive and negative poles from lighting up and will not cause the battery to short out or explode.
Therefore, in order to improve the safety performance of the battery needle during battery manufacturing, battery cables can be used as follows:
1)Appropriately increase the difference between the positive and negative electrodes.
2)Try to increase the ductility of the diaphragm.
Summary
In order to improve the safety performance of the battery, the battery does not have explosions or similar things in the case of acupuncture. Battery manufacturers can improve their products in the above four areas. To improve battery safety, it is important to ensure the safety of battery testing equipment. If the tester uses bad battery testing equipment to test, which is easy to crack. Worse, the risk of the person working in the research process is very high.
