Lithium-ion batteries are composed of four main materials, namely positive electrode material, negative electrode material, separator and electrolyte.

Over the years, lithium-ion batteries have undergone rapid development, industrialization, and commercialization, and technological progress has reached a certain bottleneck. At present, lithium-ion batteries with high energy density, long cycle life and high safety performance are still the focus of attention of various countries. However, lithium-ion batteries are a contradictory complex. Safety, long life, and high energy need to be considered comprehensively. For example, while possessing high energy, the stability of lithium batteries is subject to certain challenges. When the cathode material is used, the battery energy density can reach very high, but it is also more dangerous. Among the key performances of lithium batteries, safety is the most important thing that cannot be ignored. It can be said that only by achieving safety can users be more assured.

Ceramic separators have been widely used in lithium-ion batteries to improve the safety performance and service life of the battery and reduce the self-discharge rate. After sufficient testing and verification, the ceramic separator can improve the cycle and safety performance of lithium-ion batteries.

Coating ceramics on the negative pole piece to improve the safety of lithium-ion batteries has been adopted by many manufacturers. The ceramic powder is nano-sized alumina particles. Nano alumina is one of the special functional nanomaterials with important application value and development prospects. It has a series of excellent characteristics such as high thermal stability, chemical stability, corrosion resistance，and high hardness. It is widely used in ceramic materials and biological materials. Medical materials, semiconductor materials, catalyst carriers, surface protection layer materials, and optical materials. It is precisely because of the good thermal stability of nano-alumina that it is considered to be a good thermal insulation material and has made a significant contribution to improving the safety performance of lithium-ion batteries.
Simply put, the surface of the negative electrode is coated with an alumina coating to take advantage of the thermally stable insulation properties of the alumina powder. It is foreseeable that the capacity of a lithium-ion battery is only related to the positive and negative materials, and has nothing to do with whether it is coated with a ceramic coating.

So what impact does the use of ceramic coating have on the performance of lithium-ion batteries?
1. Internal resistance
Since alumina powder is not non-conductive, coating with alumina powder reduces the self-discharge of lithium-ion batteries on the one hand, reduces the self-discharge of lithium-ion batteries on the other hand, and hinders the negative pole piece on the other hand. The internal electron transfer causes the internal resistance of the lithium battery to increase. The increase in the internal resistance of lithium batteries is also something we don't want to see. The greater the internal resistance, the greater the heat generated by the lithium battery during charging and discharging, which has an important impact on its performance. Therefore, in the actual production process, in order to reduce the internal resistance of the lithium battery, it can be achieved by reducing the coating degree of the ceramic coating.

2. Cycle life
Let me start with the conclusion that the cycle life of a battery coated with a ceramic coating is better than a battery without a ceramic coating. Everyone knows that when graphite is used as the negative electrode of a lithium-ion battery, SEL will be formed on the graphite surface during the first charge and discharge. This is a solid electrolyte membrane formed by the reaction of electrons, electrolytes, and lithium ions. This is also the source of the first efficiency of lithium batteries, that is, the formation of SEL is a process that consumes active lithium ions. In fact, during the charging and discharging process of lithium-ion batteries, especially as the number of cycles increases, the SEL will continue to be destroyed and rebuilt, and the thickness of the SEL will continue to increase, which will repeatedly consume the active lithium ions in the battery, resulting in Lithium battery capacity gradually decreases. At the same time, the increase in the thickness of the SEL may affect the insertion of lithium ions, leading to precipitation on the surface of the negative electrode, forming lithium dendrites, and causing a short circuit in the lithium battery. Coating a layer of ceramic powder on the surface of the negative electrode may be able to effectively block the growth of the negative electrode SEL film, thereby reducing the loss of lithium ions during battery recycling. In addition, the electrolyte will continue to decompose during the battery cycle, and the ceramic coating has a certain liquid absorption capacity, which can improve the capacity retention rate of the electrolyte during long-term charge and discharge cycles.

3. Self-discharge of lithium battery
The performance of Li-ion self-discharge has an important impact on the consistency of the battery pack. The battery module has a typical bucket effect. If one of the batteries fails, it will affect the performance of the entire module. Therefore, after the battery production is completed, a certain amount of
Shelved the number of days in order to select a battery with a good voltage drop consistency. During the process of shelving lithium batteries, some problems in the production process will gradually emerge, such as electrode surface defects, burrs on the edges of the positive and negative poles, the condition of the separator, the packaging is not milky, the welding is poor, and the ambient temperature and humidity.
The test found that the negatively coated ceramic coating battery has a stronger charge retention ability. This is because coating a layer of ceramic on the surface of the negative electrode is actually equivalent to using a ceramic coating separator, which is more stable and can effectively reduce internal short-circuits. Appear to reduce the self-discharge of lithium batteries.

4. Security
Whether it is a ceramic coating on the surface of the negative electrode or a ceramic separator, the most important significance for lithium-ion batteries is to improve the safety of lithium batteries. In accidents where electric vehicles catch fire, it is also consumers' trust in electric vehicles that have been burned, which is extremely detrimental to the development of the entire industry. Lithium battery companies must put safety first.
The safety of batteries coated with ceramic powder on the negative electrode surface is higher. In the compulsory safety inspection of lithium batteries, the short-circuit challenge of squeezing acupuncture is great, and squeezing acupuncture is an abuse test. For example, in the acupuncture test, after the needle penetrates into the battery, it is equivalent to the internal conduction of the positive and negative electrodes, and a very large current will be generated instantly, forming a large amount of heat, and will cause the electrolyte to decompose and generate heat. The structure of the positive electrode material will collapse and collapse. Heat, when the heat cannot be released, it will smoke, catch fire or even explode. As mentioned above, the alumina ceramic coating has good thermal stability. The ceramic coating on the surface of the electrode can delay the rapid increase of heat during the needling process, thereby delaying the thermal decomposition of the electrolyte and avoiding a short time. A large amount of gas is generated inside and the battery explodes.
Therefore, the use of ceramic coatings on the negative pole pieces can effectively improve the safety of lithium-ion batteries. Of course, to improve the safety of lithium-ion batteries, it is necessary to do a good job of control from many aspects, including lithium battery source materials, battery cell design, process methods, production process control, environmental control, and so on.