Difficulties for domestic soft plastic lithium battery aluminum plastic film technology

Difficulties for domestic soft plastic lithium battery aluminum plastic film technology

Compared with other batteries, soft-pack lithium batteries are widely used in consumer electronics, automotive, military, medical, power tools and other industries because of their safety performance, light weight, large capacity, small internal resistance and flexible design.

The essence of the soft-packed lithium battery is that the liquid lithium-ion battery is covered with a polymer shell, and its performance is so excellent, among which the aluminum plastic film in the polymer shell is indispensable. Then I will analyze the magic aluminum film for everyone.

First, the introduction of aluminum plastic film

The aluminum plastic film is a multilayer film composed of an outer nylon layer, a binder, an intermediate layer aluminum foil, an adhesive, and an inner layer heat seal layer, and is a packaging material for a soft lithium battery. Compared with other common plastic films, aluminum plastic film has the following advantages:

1) Aluminum plastic film has extremely high barrier property: 10,000 times higher than that of ordinary aluminum-plastic composite film;

2) Good cold stamping formability: It can meet the new battery model according to customer's product requirements.

3) It has good puncture resistance: due to the pitting corrosion caused by copper and aluminum mesh burrs around the polymer lithium battery core, accelerating electrification, when vacuuming and collecting, the burr will spur the inner membrane and may pierce the inner membrane until Aluminum foil, the hydrofluoric acid in the battery will be directly corroded by aluminum foil, changing the electrolyte composition. In severe cases, the aluminum foil will be corroded and leaked, and at the same time, it will cause a short circuit and cause the battery to be scrapped. Therefore, puncture resistance is particularly important.

4) Good resistance to electrolyte stability: A variety of organic solvents usually swell, dissolve and absorb soft packaging materials, they are good solvents for adhesives, which will destroy the bonding effect of the composite layer and change the concentration of the components in the electrolyte., which in turn affects the electrical performance of the battery. The presence of highly corrosive hydrofluoric acid will severely corrode the aluminum foil, separating the inner film from the aluminum foil, and then corroding and perforating the aluminum foil, thereby destroying the entire package, and the aluminum plastic film has good resistance to electrolyte stability, ensuring the entire battery. Safety

5) Aluminum plastic film is resistant to high temperature and strong insulation: the thickness of the metal electrode sheet is about 100u. When heat sealing at 170°C and pressure of about 3kg/cm2, if there is no high temperature resistant insulating layer in the inner film, the metal electrode is often Overwhelming the packaging of the aluminum foil, causing a short circuit, the battery is scrapped, the yield is reduced, so high temperature resistance, insulation resistance is an essential attribute of the outer casing.

Second, the structure and classification of aluminum plastic film

The main component of the aluminum-plastic film is composed of three layers of ON/ALCPP. The surface layer of ON (nylon layer) is a decorative ON layer, which also protects the AL layer from scratching. The middle is formed by AL and prevents moisture intrusion. The inner layer CPP (polypropylene) layer is an electrolyte resistant layer.

According to the different preparation processes, the aluminum plastic film can be divided into the following two categories. The following is a schematic diagram of the typical Japanese printing (DNP) and Showa electric aluminum film:

Dry method is widely used. The production of Showa ALF is 95% dry, mainly used in high energy and heavy batteries such as mobile phone batteries, MP3 and MP4. In addition, it is also widely used in electric vehicles, RC airplanes, and other large-capacity, high-capacity power batteries; thermal methods can only be applied to batteries that do not require high capacity.

Third, the preparation process of aluminum plastic film

The preparation methods of aluminum plastic film are divided into two types: dry method and heat sealing:

Dry method: After bonding with AL and CPP with an adhesive, it is directly pressed. The advantage lies in reproducible molding performance, short-circuit proof performance, appearance (impurities, pinholes, fisheyes), and cutting performance. In addition, it has good resistance to electrolyte and water barrier.

Heat sealing: MPP is then used between AL and CPP, and then thermally synthesized under conditions of slow temperature rise and pressure, and the production process is long. Moreover, due to the long-time high-temperature baking action, the ALF is embrittled, resulting in deterioration of the penetration performance. The advantage lies only in the resistance to electrolyte and water resistance, and its deep forming performance, short-circuit proof performance, appearance and cutting performance are not satisfactory.

Fourth, the difficulties faced by domestic aluminum plastic film manufacturers

At present, the performance of China's aluminum plastic film products, only a few of the company's several technical indicators can reach the level of Japanese companies, the main problem is the resistance to electrolyte and deep penetration, the domestic aluminum plastic film penetration is about 5mm, Foreign countries are 8mm, or even 15mm, and there is still a certain gap between them and foreign products. Especially in the reaction conditions and precision control, this high-precision material manufacturing process is often a thousand miles away, and the difficulty of process control is reflected in the difference. At present, domestic aluminum plastic film manufacturers have the following five major difficulties:

1) The surface treatment process of aluminum foil is backward and polluted: due to the use of water-washing oil and "chromic anhydride" passivation treatment, the pollution is large. At the same time, due to the surface tension of water, the oil in the micropores of the aluminum foil cannot be cleaned, resulting in defects in subsequent processes;

2) The water treatment process of aluminum foil will produce "hydrogen embrittlement", so the domestic aluminum plastic film has poor resistance to dismantling;

3) The surface of the aluminum foil is coated with a UV layer, the aluminum foil is not stiff enough, the dry method is easy to fold when it is composited, the wide-width product cannot be produced, and the yield is poor;

4) For CPP, it is mainly coated with a laminating machine in China, which is easy to curl and produce layered crystal when it is combined with the surface of high-heat-conducting aluminum foil;

5) Due to the domestic adhesive formulation technology, the product is prone to delamination.

Domestic lithium battery manufacturers have huge cost pressures and urgently demand to reduce raw materials cost for lithium batteries. Therefore, demand for aluminum-plastic film have import substitution and localization has become increasingly prominent.

The page contains the contents of the machine translation.