1, lithium-ion battery separator Overview
With lithium batteries with high energy density, long cycle life, light weight, small size and other characteristics, but also a reliable, safe and can quickly charge and discharge, etc., to become the new power technology in the recent years, the hot spot of research in the field of high power and high-energy folk reserved. In the structure of the lithium battery, the inner membrane is a key component of the. Diaphragm plastic film is able to isolate the Laptop battery positive and negative, to prevent short circuits; also be overheating of the battery, through closed-cell function to block cell in the current conduction.
Depending on the physical and chemical characteristics, the lithium battery separator materials ion can be divided into: film weaving, non-woven membrane (non woven), microporous membrane, and composite membrane, paper separator material various film categories. Polyolefin materials have excellent mechanical properties, chemical stability and relatively inexpensive, and therefore, polyethylene, polypropylene, microporous polyolefin membranes for lithium-ion batteries will be used as a research and early development of lithium – ion IBM ThinkPad T41 battery separator. Today, the marketing of lithium-ion battery separator is still microporous polyolefin membrane. In recent years, solid electrolytes and gel began to be used as a specific component, while playing the role of electrolyte and battery separator is a new technology.
Cost Li-Ion Battery Battery separator reflect the cost of a / 3. Membrane determines the performance of the interface structure of the battery resistance and so a direct impact on the battery capacity, the cycle efficiency, and safety features such as the membrane of high performance in the improvement of the overall performance of the battery has an important role. At present 60% to 70% of the market for membranes, especially in wet bi-oriented process, because the wet, bi-lateral vertical stretch more balanced. It is mainly used for the method of high-end diaphragm wet, dry, has been applied in the low range.
2, diaphragm production process
The current market-based lithium-ion Dell Inspiron 1420 battery separators are mainly made of polyethylene, polypropylene based polyolefin membrane, including the PE single layer, single layer PP, three-layer PP / PE / PP composite film. Polyolefin membrane current process of production under dry and wet divided into two categories, while dry process design can also be decomposed into one-way and two-way stretching process.
Dry-way stretching process is the production method of hard-elastic fibers were prepared by a low degree of crystallinity of highly oriented polypropylene or polyethylene film, high temperature annealing to achieve a high degree of crystallinity of film orientation. This film is stretched at low temperature, before the formation of mania and other defects of micro-enterprises, and then opened under high temperature so that the defects form a pore. This approach was first seen in USPatent3426754 Patent U.S. Celanse 1970 for the production of mono-layer membranes of porous polypropylene. The process after decades of development in the United States, Japan is already very mature, and now the U. S. Celgard Inc., Japan’s use of these boats UBE unique production PP, PE, and three PP / PE / PP composite film. This method of producing the BATBL50L6 porous membrane has an elongated structure, because it covered a stretch event, the horizontal force of diaphragm relatively poor, but it is not conducted due to the transverse tensile, transverse almost no shrinking heat.
Due to the protection of foreign patents and constraints of intellectual property, the domestic one-way membrane traction determined by industrialization progressed very slowly. China has already started in 2004 in this patent relates to technology and foreign patents difference is that in the polypropylene has a crystallization promoting effect of adding nucleating agents, and agent additive for oil has accelerated the rate crystallization during annealing. The technology is now used in Hangzhou, a production line, using a method how to stretch the production of PP single-layer diaphragm, has made this type of membrane on the market.
Wet-phase method of separation is also known as the separation of thermally induced phase, the high boiling small molecules as pore-forming added to polyolefins to merge into a uniform, then the cooling phase separation occurs The stretch after the ecprice extraction of organic solvents with small molecules can be interconnected prepared material of the microporous membrane, the material widely applicable. Adoption of the law, a company representative Asahi Kasei of Japan, Tonen and the United States Entek, currently used primarily for single-layer membranes of the PE. Wet bi-directed path to produce the membrane after a double meaning because of tensile strength of high vertical and horizontal. China Foshan Plastics Group was established in 2004, using a wet process production of two channels by membrane stretch production line PE by the end of 2005 has started selling products on the market.
3, the major international manufacturers diaphragm
Portable power tools, mobile phones, laptops, video camera lithium rechargeable ion batteries, power tools, small batteries used mainly polyolefin membrane, technology and markets are already very mature, the largest supplier of Asahi (Asahi Chemical Industry), U. S. Celgard and Tonen (Tonen Chemical), Asahi Kasei 5 in the main supply to the membrane over Sanyo, while the Celgard and MBI is a leading provider of BYD; With Sony, SDI, LGC and other clients, Tonen Chemical to become the world This membrane third largest supplier. The United States and produced three UBE Celgard polypropylene / / polyethylene polypropylene (PP / PE / PP) composite film. This type of material characteristics of the membrane is its higher resistance, lower cost, but also in the temperature of the internal hp 367759-001 battery is high, PE melt at 130 ℃ or so, when, while the high melting point of PP (150 ℃ or so) to form the obturator membrane, so that the battery internal circuitry, greatly improve the safety performance of the battery, but the complicated manufacturing process, and these are particularly difficult to achieve Ultra-thin 16um. Asahi Kasei, Tonen, the United States Companies ENTEK such that only the polyethylene (PE) membrane. This type of membrane material because it is single-PE, and therefore the cost of production but the production of ultra-thin membrane under specific conditions 16um, so popular with major battery manufacturers such as Sanyo, Sony, Panasonic, Maxell, etc. favor.
4, the internal status of development of membrane industry
With the development of lithium-ion battery industry, the market on the separator internal lithium battery lithium battery has gradually entered the ring, Xinxiang, Henan, China and the Sino-Kuwaiti Douglas.Ryan Technology, Foshan Jin Hui Hi-tech Taiwan and raised the money represented by the manufacturers internal lithium ion toshiba PA3421U-1BRS battery separator to grow rapidly in the years, the diaphragm, compared with imports of their products, the import price gap is just 1 / 3 ~ period from 1 / 2 mineral products is also relatively short, but the thickness of the inner membrane, the strength, the absorption hole can not be get the overall balance, and batch production volume is less stable, manufacturers of lithium battery internal chose the great majority of the imported membrane. Therefore, research and development costs, production process is simple, the adequate opening size, high porosity, mechanical strength to meet the requirements of the porous polymer separator to improve battery performance and reduce costs Battery has an important practical significance. How to further improve the membrane quality indicators is the battery industry in China is now pressing problems.
5. Lithium-ion battery development trends of separation
Battery separator is mainly the development of lithium-ion batteries with the changing needs and continue to grow, in terms of volume, lithium-ion batteries are moving in the small and large two distinct meanings. In some, such as mobile phones, digital cameras and other electronic products to meet the beautiful and simple formula to bring the application on the factory batteries apple A1060 battery was very low. In pursuit of high energy density, the small size of the electrode can accommodate more equipment, battery manufacturers are seeking to divide the thickness of the thinner, the better. Small cap is a challenge because of the need to make a thin membrane, but to be able to maintain the capacity of the original battery, the cycle efficiency, and safety features and more power, more design easy.
In contrast, electric bicycles, electric vehicles and power tools used by battery power, to achieve high capacity, high power, usually a battery needs to use dozens or even hundreds of batteries to the concatenation. Because lithium batteries have the danger of explosion, the safety diaphragm is important. Due to become increasingly large, technically demanding more efficient and reduce emissions of greenhouse gas emissions, higher power.