Abstract: Polymer lithium-ion batteries are known as chemical energy sources for the 21st century. Soft packaging technology has an important influence on battery capacity and cycle life. This article focuses on the general requirements of polymer lithium-ion batteries for flexible packaging technology, describes the difficulties of software packaging technology in this field, describes the difficulties of flexible packaging technology in the field of polymer lithium-ion batteries, and describes the development of flexible packaging materials in the field of polymer lithium-ion batteries. The trend predicts the potential of flexible packaging materials in the field of batteries.
Keywords: Flexible Packaging Technology, Packaging Design, Flexible Packaging Materials, Polymer Lithium-Ion Batteries Introduction The energy output of a battery depends on the specific capacity of the active material and the voltage of the individual cells. Lithium metal is the specific capacity of all metals and the voltage of the cell. Lithium metal is the material with the highest specific capacity among all metals, and the output voltage of the battery pair composed of C is as high as 3.6 V. These properties cannot be compared with other metals. Therefore, people began to pay attention to lithium battery research very early. Because lithium metal is very lively, using it directly to make the battery very poor safety, so people mainly study lithium ion rechargeable batteries. In 1990, the world’s first production line for producing lithium-ion secondary batteries was established in Japan. In a short period of seven or eight years, lithium-ion batteries will soon be used in mobile phones and laptops due to their light weight, large capacity, long cycle life (greater than 1,000), and no memory effect (which can be used with charge without affecting performance). Such areas as the use of batteries have expanded and are living in absolute advantages. In 1996, the polymer lithium-ion battery was successfully developed in the laboratory. Given its almost all advantages, the polymer lithium-ion battery has better advantages in terms of weight, shape, and safety, and thus has a wider range of applications. Immediately caused a sensation in the world's battery industry, known as the chemical energy of the 21st century. Countries around the world, especially Japan and the United States, have invested heavily in research and industrialization. Xiamen Baolong Industry is the first company in China to engage in the production of polymer lithium-ion batteries. The current battery production scale and the level of applied soft packaging technology are equivalent to the most developed countries.
Polymer lithium-ion batteries From the perspective of electrochemical reactions, there is no difference between polymer lithium-ion batteries and lithium-ion batteries, and even electrode materials and electrolytes used in polymer lithium-ion batteries are the same as lithium-ion batteries. However, there is no mobile electrolyte inside the polymer lithium-ion battery. The battery can be made into very thin sheets and various shapes. The single-cell battery can be made 0, 6mm thick, so that the battery is required to be lightweight, small-quantity, or In fields where there are strict requirements on the shape, such as mobile phones, notebook computers, camcorders, military portable tools, DVD players, and even electric vehicles, polymer batteries have more extensive application advantages and prospects.
The successful development of polymer lithium-ion batteries is mainly due to three major technologies and solutions, namely membrane technology, lamination technology and flexible packaging technology. Membrane technology solves the problem that batteries cannot contain liquid electrolytes; lamination technology solves the problem of monolithic battery formation and monolithic battery assembly; flexible packaging technology makes the cell sheet a battery and the battery has a polymer lithium All the advantages of ion batteries.
The impact of flexible packaging materials on polymer lithium-ion batteries Polymer batteries ultimately rely on the use of flexible packaging materials to form batteries. Strictly speaking, it cannot be called “packaging†because in the field of polymer lithium-ion batteries, the “soft packaging material†forms a battery core together with the contents, and the battery core is assembled to form a battery. Therefore, the “soft packaging material†can be Think of it as a part of the battery. However, the material it uses is the common packaging material for people, and it really does play a role in protecting the contents. Therefore, people are still used to calling it "packaging." Just because the flexible packaging material can be seen as an integral part of the battery, it has an important influence on the performance of the battery. When the content of water and oxygen in the battery reaches a certain level, the capacity of the polymer lithium-ion battery will become smaller, the voltage drop will increase, the battery will not be charged, the battery will not be discharged, and the cycle life will decline. This may eventually lead to the failure of the battery. . The flexible packaging material achieves the maintenance of the battery performance by blocking water and oxygen. Therefore, the barrier property of the flexible packaging material has an important influence on the battery. In addition, some of the organic substances in the flexible packaging material may dissolve in the electrolyte to generate an electrochemical reaction and destroy the performance of the battery; if the electrolyte is swollen by the flexible packaging material, the mixing ratio of the electrolyte will be changed, which is unfavorable for the battery performance.
General Requirements for Polymeric Lithium-Ion Batteries for Flexible Packaging Materials The flexible packaging material for lithium-ion batteries of polymers is an aluminum-plastic composite film. The general requirements are as follows:
(1) Excellent heat sealability The polymer lithium ion battery is very sensitive to high temperatures, and the general use temperature is lower than 60°C. It is required that the heat seal temperature be as low as possible when the heat seal strength of the flexible packaging material is sufficient. In general, the heat sealing temperature should not exceed 150°C. When a higher heat sealing temperature is used, appropriate edge cooling measures must be used to prevent conduction and radiation during heat sealing from damaging the battery.
(2) The heat sealable material does not dissolve in the electrolyte, and it cannot swell with the electrolyte. If the flexible packaging material is dissolved by the electrolyte, since the working voltage of the battery is as high as 3.6V or more, the dissolved components will undergo electrochemical reaction and generate gas. If the flexible packaging material swells the electrolyte, the concentration of the electrolyte will change and affect the battery. performance.
(3) High water barrier and oxygen barrier performance The water vapor permeability coefficient is required to reach 10-4~10-6g/m2.d.latm
Oxygen permeability coefficient requirements to reach 10-1 ~ 10-3cm3/m2.d.latm
(4) High flexibility and mechanical strength The production and assembly of polymer lithium-ion batteries places high demands on the flexibility of software packaging materials, and the safety of the use of the process guarantees the mechanical strength of flexible packaging materials. The heat seal strength raises high demands.
(5) Ability to withstand good electrolyte soaking After the flexible packaging material is packaged in the cell, the electrolyte cannot leak during long-term storage and turnover.
Difficulties in flexible packaging technology From the general requirements of the above-mentioned polymer lithium-ion batteries for flexible packaging materials, it can be found that the flexible packaging materials required for manufacturing have a high degree of difficulty:
First of all, the requirement for barrier properties of flexible packaging materials is 10,000 times more difficult than that of ordinary aluminum-plastic composite materials. Such high barrier properties are difficult to meet with the requirements of ordinary composite materials and composite technologies. It is generally necessary to use extremely thick aluminum foil and use a composite material of 4 to 7 layers in order to apply a variety of composite technologies. For example, in the same material production process, it may be necessary to adopt the dry complex method, the extrusion method, the continuous extrusion compound method, the triple extrusion method, the thermal compound method or the rogue compound method, and the multi-layer co-extrusion method. In this way, higher requirements are placed on the production technology of flexible packaging materials.
Secondly, the requirement for barrier properties of flexible packaging materials is 10,000 times higher than that of ordinary aluminum-plastic composite materials. Such high barrier properties are difficult to meet with the requirements of ordinary composite materials and composite technologies. It is generally necessary to use extremely thick aluminum foil and use a composite material of 4 to 7 layers in order to apply a variety of composite technologies. For example, in the same material production process, it may be necessary to adopt the dry complex method, the extrusion method, the continuous extrusion compound method, the triple extrusion method, the thermal compound method or the rogue compound method, and the multi-layer co-extrusion method. In this way, higher requirements are placed on the production technology of flexible packaging materials.
Second, the choice of composite inner heat seal material. The electrolyte used in polymer lithium-ion batteries consists of a variety of ester organic electrolytes, in which the electrolyte is hydrolyzed in the presence of moisture to acidic materials that are swellable. Low melting point heat seal materials that do not react with the electrolyte and must have sufficiently strong acid resistance are more difficult to find.
In addition, the design of flexible packaging materials is difficult. In the process of designing flexible packaging materials, it is necessary to ensure that the above five requirements are satisfied, but also to ensure that the production of flexible packaging materials can be achieved, but also to take into account the impact of packaging materials on polymer lithium-ion batteries and the development of polymer lithium-ion batteries Trends (below to develop the required flexible packaging materials ahead of time) are more difficult.
Finally, the quality of flexible packaging materials has a long period of time. Since the water-repelling and oxygen-barrier properties required for polymer lithium-ion batteries exceed the minimum accuracy required for testing in the packaging field, it is difficult to quantitatively test the developed flexible packaging materials. What is generally used today is the final determination of the realized packaging battery. According to the inspection characteristics of the battery and the degree of influence of the flexible packaging material on the battery and the rate of influence, it is generally determined that the soft packaging material is ultimately qualified for more than three months.
The development trend of flexible packaging materials The development trend of flexible packaging materials is determined by the development trend of polymer lithium-ion batteries and the expansion of their application areas. There are two trends in the development of polymer lithium ions: one trend is the development of batteries in the direction of miniaturization and thinning; the other is the development of large-capacity and high-power charge and discharge. The former requires flexible packaging materials to be developed in a thinner and more flexible direction under the premise of barrier property; one is to develop in the direction of large capacity and high power charge and discharge. The former requires that the required flexible packaging material develop in a thinner and more flexible direction under the premise of barrier property; the latter requires that the barrier property of the flexible packaging material develops to a higher direction and the degree of interaction with the electrolyte is smaller. The direction of development. These two development trends have a higher demand for the selection of packaging materials, the requirements for packaging composite technology, and especially the structural design of packaging materials. Since soft packaging materials are the last quality assurance gate for battery molding, the impact on battery performance is extremely great. Therefore, in addition to the progress of active materials and manufacturing processes required for batteries, the development and application of polymer lithium-ion batteries are expanding. Depending on the development of flexible packaging technology and its materials.
The development potential of China's flexible packaging materials At present, China's mobile phone users have exceeded 50 million; in 1999 the country's notebook computers have all used lithium-ion batteries; portable camcorders, DVD players and other batteries are very large. If the polymer lithium-ion battery is used, the value of the flexible packaging material required for each year will be 200-300 million yuan; the battery for electric vehicles (electric vehicles, electric motorcycles, and electric bicycles) is a huge market for batteries, and the lithium ion polymer The battery is the most popular type of battery in development. If it can be successfully developed, the amount of flexible packaging material consumed in the domestic battery industry will reach 3 to 5 billion yuan each year. Now, although only the polymer lithium-ion battery of Xiamen Baolong Industrial Co., Ltd. has achieved industrial scale production, nearly ten companies have already invested in projects or are in pilot production stage. Soft packaging technology is an important technical issue that restricts the development of these enterprises. Whether it is to promote the research process of lithium polymer batteries or as a flexible packaging material market, the research of flexible packaging technology in this field is very necessary. There are specialized research institutes for flexible packaging technology for polymer lithium batteries in foreign countries, and only a handful of people in China have studied from this perspective. The research and application of flexible packaging materials should become an important part of the research and production of polymer lithium-ion batteries. (Xiamen Baolong Industrial Co., Ltd. Shi Baoqing) (Extracted from "China Packaging")