Power safety: I understand how the diaphragm is escorting

　　Author ：Iflowpower – Portable Power Station Supplier

Today, lithium-ion batteries have become 3C products (Computer, Conmunication, and ConsumeRelectronics) The most common energy devices, high capacity, stable charge and discharge performance have long service life, has always been the pursuit of lithium-ion batteries, and consumers Lithium-ion battery expectation. The diaphragm material is the key to these pursuits and expectations. First, the diaphragm is tightly consists of five parts: positive electrode material, an augant material, an electrolyte, a diaphragm, a package material.

The separator is electronically insulated between the positive and negative poles, and the use of the ion migration microporous channel is a key material that guarantees the safety of the battery system and affects the performance of the battery. Although the diaphragm does not participate in the electrode reaction, it affects the battery kinetic process, determines the charging and discharge, cycle life, and magnification of the battery. In recent years, researchers and related companies have a strong interest in the research and development of diaphragm materials and industry technology.

According to the patented online decomposition system of Chinese Academy of Sciences, the Chinese lithium-ion battery, the diaphragm is keyword, and the patent application is 2106 (as of September 2015), which is authorized to account for 51.19%, and 1078 patents. Taking Chinese polyethylene, diaphragm, polypropylene, diaphragm, ceramic, diaphragm, modification, diaphragm, and retrieved 419, 415, 390, 272 items, and the authorization ratios are 44.

4%, 42.4%, 32.0, respectively.

%, 33.1%, effective patents are 186,176, 125,90 respectively. Discovery.

In recent years, the hot glossary of the research and development and technical scope of technology, high security, new materials, ceramics, coating and improvement of wettability, etc. At the same time, in the last decade, especially in the last five years, the patent application involving the buried membrane is accelerated. Second, the functional diaphragm of the lithium electrical separator is in the Isoonic Battery.

The function is in two aspects: First, provide security to the battery. The diaphragm material first does not have good insulating properties, and the short circuit that occurs when the positive and negative electrode is exposed to the short circuit or the burr, particles, and dendritic thorns. Therefore, the diaphragm has a certain stretch, puncture strength, not easy to tear.

And basically maintain the stability of the size under the high temperature conditions of the burst, and the large area short circuit and thermal out of the battery will not be melted. The second is to provide an alternative battery to realize the charge and discharge function, the micro-hole channel of the magnification performance. Therefore, the diaphragm does not have a film having a higher porosity and a microporous distribution average.

The material itself is characteristic and the film formation of the film forms the migration of lithium ions in the battery, and the performance parameters of the battery are ionic conductivity. Third, the effect of the lithium electrical separator to supply safety to the battery is reflected from the basic properties of the diaphragm manufacturing materials. Safety requirements determine that the diaphragm has an outstanding insulation, mechanical strength, chemical stability, electrochemical stability, and thermal stability.

Therefore, the material of the manufacture of the diaphragm can only be good from the insulating, and has good film formation properties, mechanical properties, and easy-to-produce polymers and their composites. At present, commercialized mainstream materials are polypropylene microporous membranes and polyethylene microporous membranes, developing materials such as non-woven ceramic particles composite film, and materials such as polyimide (PI), etc. The battery of the battery is achieved by the construction of the diaphragm and the microporous structure characteristics.

There are also some material itself inherent attributes that affect this performance. The requirements for lithium ions are determined that the diaphragm has good wettability to the electrolyte, as it is only absorbed and retains the appropriate amount of electrolyte in the diaphragm pore structure to achieve the ionized migration and normal operation, and the electrode is extremely polarized. occur.

The microstructure of the diaphragm, such as aperture and its distribution, porosity, air passage (Gurley value), dimensional stability, and other factors related to ion conductivity, significantly affecting the performance of the battery. With the continuous improvement of battery safety pay attention to battery safety, the requirements of battery companies on diaphragm safety continue to increase, and in the use of certain special model batteries, the need for heat shrinkage ratio of diaphragm material has been increased to 180 ¡ã C for 60 min. After shrinking less than 2%, some foreign battery companies even maintain a stable diaphragm at 250-300c temperature zone dimensions.

The thickness of the diaphragm is of course, the thinner is, the better the safety. About the winding battery, the thinner the thickness of the diaphragm, the output of the battery, can leave more space to the electrode material, and reduce the misalignment of the pole winding process. However, if only one flaps emphasizes thickness, the mechanical performance will be affected, it is more susceptible to large particles, polar burrs and dendrites, resulting in low battery safety factor.

There is less whispering of the laminated battery, which is not high for thickness requirements. With the increasing diversity of lithium-ion battery materials, use, capacity, shape, the requirements of diaphragm performance and technical indicators are also chartered, and the processing company's understanding of the diaphragm is also more deeper. However, there is no such diaphragm in all technical parameters.

Therefore, when selecting the diaphragm to the battery, it should be focused, and which performance is to be highlighted, which is safety, power performance or life-life? According to battery design and use category, the types used are also different. Relevant reports on various technical parameters of diaphragms. Lithium electrical diaphragm performance and several commercial membrane performance parameters 4, lithium battery compact membranes are planarily developed, and the surface modification of polyolefin is added to or composite the characteristics of the characteristics such as a single layer polyolefin membrane, and high temperature resistance.

A composite diaphragm having a more excellent performance is a major research direction of high performance separators. Currently commonly used processes include coating, dip coating, spray, composite, etc. There is a research statement to coating a polyaryl ester material on a PE diaphragm to form a composite diaphragm of a porous polymer precipitate.

Since the polyarylate has good heat resistance, the composite diaphragm melting temperature is increased to greater than 180 ¡ã C. By dip coating, a polyaminer is applied to the PE diaphragm, and the obtained modified membrane has a higher adsorption electrolyte performance, effectively improving the high magnification cycle performance of the diaphragm. The polyolefin diaphragm was modified using a mixture of PVDF / SiO2, and the composite diaphragm was simultaneously provided with the parent-e-liquid performance of PVDF and the high temperature resistance of Si02, and the ionic battery was reached at 2C discharge magnification, and its charge and discharge efficiency reached 94%.

2, polyolefin-ceramic composite diaphragm polyolefin organic membrane and have better mechanical properties and low cost, but there is insufficient in terms of thermal stability, parent, etc., so as battery diaphragms, the safety performance is to be improved. Therefore, the process to which the composite film is produced by coating inorganic ceramic particles on the polyolefin organic diaphragm.

Although the impact of ceramic coating gives battery performance, more in-depth research and evaluation can lead to final conclusions, but this technology has been impending in many diaphragm companies and battery companies, and has been promoted. In the polymer ceramic composite film, the polyolefin organic microporous membrane material supplies flexibility to meet the requirements of the battery assembly process. Inorganic ceramic particles form a rigid skeleton in the composite film, and the alert separator shrinks or even melts under high temperature conditions to improve battery safety.

The adhesive has a tight effect on the surface properties, pore structure, mechanical strength of the ceramic composite film. The polymer-ceramic composite film increases the thermal stability and electrolyte moisture absorption of the polyelectric separator to a certain extent, but the maximum problem in such composite technologies is that the ceramic phase is weak and the organic combination is weak. Ceramic falling off (powder phenomenon.

By reasonable regulation of the amount of either, the inorganic ceramic particles are prejected in advance in the film-forming solution by the in-situ composite technique, and the process processes of the diaphragm by wet two-way stretching techniques or electrospinning methods can be alleviated to some extent. This phenomenon. The polyolefin membrane is a composite diaphragm product, and the polyolefin membrane is easily stretched into a hole in which the polyolefin membrane is easily stretched into a hole, and the safety of the separator is improved, and the characteristics such as the separator are improved.

Before, it will still occupy a critical market share. 3, the new material system is divided into polyolefin modified separators and new material diaphragms according to the materials used. Among them, new materials are tight to include fluoropolymer diaphragm, cellulose diaphragm, polyimide (PI) diaphragm, polyester (PET) type membrane and other polymer ceramic composite diaphragm, etc.

(1) The fluoropolymer diaphragm is tightly refers to a PVDF diaphragm material. From the angle of material, it can be divided into three categories of single polymers, multi-polymers and organic inorganic complexes. The most commonly used single polymer includes PVDF, P (VDF-HFP) (polyvinylidene fluoride-hexafluoropropene> and P (VDF-TRFE) (polyvinylidene fluoride).

Compared to the polyolefin diaphragm material, the fluoropolymer material diaphragm contains stronger polarity and higher dielectric constant, which greatly enhances the parentality of the separator, and contributes to ionization of the lithium salt. In addition, the molding method of such materials is diverse, such as casting method, electrospun, hot pressing, etc., which is conducive to regulatory porosity.

(2) The battery performance of the cellulose diaphragm is comparable to the polyolefin diaphragm, but its resources are rich and renewable. At the same time, the initial analysis temperature of the cellulosic material is high (270c), and the thermal stability is clear than the polyolefin material. The rapid charge and discharge performance of cellulose materials in early use is excellent, but there is self-discharge phenomenon, and the cycle performance is not stable, and the battery resistance is not enough.

Students have a non-woven cellulose as a substrate, P (VDF-HFP) is a coating, and the cellulose / PVDF composite diaphragm is made, and the liquid is distinct to the conventional PP film. The thermal stability is large. promote.

(3) The content of the core of the new process method diaphragm is two: First, the new material system, the second is the process of industrialization processing. Leaving an efficient process approach, good materials cannot be a widely accepted product. The method of conventional preparation of polyolefin diaphragms is dry and wet.

However, the polyolefin separator is developed in a thinner direction to meet the performance requirements of the 3C lithium ion battery, which is a large key entry point to improve the performance of the diaphragm. Relative preparation method, the coating process and equipment of the polyolefin modified diaphragm are very mature. It is used to make the coating modification of the polyolefin diaphragm, which can improve the heat resistance of the polyolefin membrane and the wettability of the electrolyte.

At present, many research units and manufacturers at home and abroad have research and development focuses on ceramic coating diaphragms. In summary, with the increasingness of the diaphragm material, the preparation process is increasingly mature, I believe that in the shortcomings, the high security of consumption demand, the strong hot resistant new diaphragm will succeed, and the far-reaching influence on our life.