"
Lithium Battery" is a type of battery that uses lithium metal or lithium alloy as the negative electrode material and uses a non-aqueous electrolyte solution. Due to the very active chemical properties of lithium metal, the processing, storage and use of lithium metal have very high environmental requirements. Therefore, lithium batteries have not been used for a long time. With the development of science and technology, lithium batteries have now become the mainstream.
Lithium batteries can be roughly divided into two categories: lithium metal batteries and lithium ion batteries. Lithium-ion batteries do not contain metallic lithium and are rechargeable. The fifth generation of rechargeable batteries, lithium metal batteries, was born in 1996, and its safety, specific capacity, self-discharge rate, and performance-price ratio are superior to those of lithium-ion batteries. Due to its own high-tech requirements, only a few companies in a few countries are producing such lithium metal batteries.
Safeguard
After the lithium battery cell is overcharged to a voltage higher than 4.2V, side effects will begin to occur. The higher the overcharge voltage, the higher the risk. When the voltage of the lithium battery cell is higher than 4.2V, the number of lithium atoms remaining in the positive electrode material is less than half. At this time, the cell often collapses, causing a permanent decrease in battery capacity. If you continue to charge, since the cell of the negative electrode is already filled with lithium atoms, subsequent lithium metal will accumulate on the surface of the negative electrode material. These lithium atoms will grow dendrites from the surface of the negative electrode toward the direction of the lithium ions. These lithium metal crystals will pass through the separator paper and short-circuit the positive and negative electrodes. Sometimes the battery explodes before the short circuit occurs. This is because during the overcharging process, the electrolyte and other materials will crack to produce gas, causing the battery shell or pressure valve to swell and rupture, allowing oxygen to enter and react with the lithium atoms accumulated on the surface of the negative electrode. And then exploded.
Therefore, when charging a lithium battery, the upper voltage limit must be set so that the battery life, capacity, and safety can be taken into account at the same time. The ideal upper limit of the charging voltage is 4.2V. There is also a lower voltage limit when discharging lithium batteries. When the cell voltage is lower than 2.4V, some materials will begin to be destroyed. And because the battery will self-discharge, the longer it is left, the lower the voltage will be. Therefore, it is best not to stop when the battery is discharged to 2.4V. During the period when the lithium battery is discharged from 3.0V to 2.4V, the energy released only accounts for about 3% of the battery capacity. Therefore, 3.0V is an ideal discharge cut-off voltage. When charging and discharging, in addition to the voltage limit, the current limit is also necessary. When the current is too large, lithium ions will not have time to enter the cell and will accumulate on the surface of the material.
After these lithium ions obtain electrons, they will produce lithium atom crystals on the surface of the material, which is the same as overcharging, which is dangerous. If the battery casing ruptures, it will explode. Therefore, the protection of lithium-ion batteries must include at least three items: the upper limit of the charging voltage, the lower limit of the discharge voltage, and the upper limit of the current. Generally, in the lithium battery pack, in addition to the lithium battery core, there will be a protective board, which mainly provides these three protections. However, these three protections of the protection board are obviously not enough, and there are still frequent explosions of lithium batteries around the world. To ensure the safety of the battery system, the cause of the battery explosion must be analyzed more carefully.
Cause of explosion
1. Large internal polarization;
2. The pole piece absorbs water and reacts with the electrolyte.
3. The quality and performance of the electrolyte itself;
4. The amount of liquid injected cannot meet the technological requirements when injecting liquid;
5. In the assembly process, laser welding has poor sealing performance, and air leakage when measuring air leakage;
6. Dust and pole piece dust are likely to cause micro short circuits first;
7. The positive and negative plates are thicker than the process range, making it difficult to enter the shell;
8. The problem of liquid injection sealing, poor sealing performance of the steel ball, resulting in air bulging;
9. The shell wall is too thick in the incoming shell material, and the shell deformation affects the thickness;
10. Excessive ambient temperature outside is also the main cause of explosion.
Conductive layer:
Conductive coating is also called pre-coating. In the lithium battery industry, it usually refers to a conductive coating applied to the surface of the positive electrode current collector-aluminum foil. The aluminum foil coated with conductive coating is called pre-coating aluminum foil or coating for short. Layer aluminum foil, its earliest experiments in batteries can be traced back to the 1970s, and with the development of the new energy industry, especially the development of lithium iron phosphate batteries, it has become a hot new technology or new material in the industry.
The conductive coating can effectively improve the adhesion of the pole piece in the lithium battery, reduce the amount of binder used, and significantly improve the electrical performance of the battery. The products of large foreign companies will not be introduced. Let me introduce the only domestic product that is promoted in the market and has independent intellectual property rights-WX112, which is developed and produced by Shanghai Zhongxing Paineng Energy Technology Co., Ltd., a subsidiary of Zhongxingxin. According to the samples received, the technical requirements such as full coating, margins, and gaps can all be achieved. The performance is as follows:
1. Contact resistance decreased by 40%
2. Reduce the amount of adhesive by 50%
3. Under the same magnification, the battery voltage platform increases by 20%
4. The adhesion between the material and the current collector is increased by 30%, and there will be no delamination after long-term circulation
Carbon coated aluminum foil:
Carbon-coated aluminum foil is made of conductive carbon-based composite slurry and high-purity electronic aluminum foil, which is made by a transfer coating process.
Scope of application
Power type lithium battery with fine particle active material
The positive electrode is lithium iron phosphate
The positive electrode is fine particle ternary/lithium manganate
Used for supercapacitors, lithium primary batteries (lithium, lithium manganese, lithium iron, button type, etc.) instead of etching aluminum foil
effect
Suppress battery polarization, reduce thermal effects, and improve rate performance;
Reduce the internal resistance of the battery, and significantly reduce the dynamic internal resistance increase in the cycle process;
Improve consistency and increase the cycle life of the battery;
Improve the adhesion between the active material and the current collector and reduce the manufacturing cost of the pole piece;
Protect the current collector from being corroded by the electrolyte;
Improve the high and low temperature performance of lithium iron phosphate batteries, and improve the processing performance of lithium iron phosphate and lithium titanate materials
