Overview of separators Separators are an important component of batteries and are not active substances. In some cases, it even plays a decisive role. Its own material is an electronic insulator, and its porosity makes it ionically conductive. The resistance of the separator is the important performance of the separator, which is determined by the thickness, porosity and tortuosity of the separator, which has an important impact on the capacity and terminal voltage level of the battery with high rate discharge; The stability of the separator in sulfuric acid directly affects the life of the battery; The elasticity of the separator can delay the shedding of the positive active material; The size of the diaphragm pore affects the degree of lead dendrite short circuit.  Due to the multifaceted role of the separator on the performance of the lead storage battery, each improvement in the quality of the development of the separator is accompanied by the improvement of the performance of the lead storage battery. The main function of the separator is to prevent the positive and negative electrodes from short circuit, but it cannot significantly increase the internal resistance of the battery. Therefore, the separator should be porous, allow free diffusion and ion migration of the electrolyte, and have a relatively small resistance. When the active substance is somewhat shed, it must not reach the opposite plate through the fine pores, that is, the pore size should be small, the number of holes should be large, and the total area of the gap should be large; In addition, it is also required to have good mechanical strength, acid corrosion resistance, oxidation resistance, and no precipitation of substances harmful to the plates.    In the 50s of the 20th century, the starting battery mainly used wooden separators, because it must be used under wet conditions, resulting in easy oxidation of the negative plate, long initial charging time, and can not be used for dry-load lead batteries. In particular, the wooden partition is not resistant to oxidative corrosion in sulfuric acid, resulting in a short battery life. In order to improve the life of lead storage battery, it is proposed that the wooden partition and the glass wool are used together to double the battery life, but the internal resistance of the battery increases, which has an adverse effect on the battery capacity, starting and discharging, and can also meet the standard requirements at that time.   In the mid-60s of the 20th century, microporous rubber separators appeared, which significantly improved the battery life due to its good acid and oxidation corrosion resistance. And promote the improvement of battery structure, reduce the center distance of the plate, so that the battery starting and discharging performance and volume specific energy have a large improvement. Because of the excellent performance of microporous rubber separators, from the 70s to the early 90s of the 20th century, it dominated the unemployed lead battery. The disadvantages of microporous rubber separators are: the rate of impregnation by the electrolyte is slow, except in the tropics, lack of resources, complex manufacturing process, and expensive cost. In addition, it is not easy to make a thinner finished product (thickness below 1mm is difficult) In the production of microporous rubber separators, sintered PVC separators and later soft polyvinyl chloride partitions appeared, which are not much different from rubber partitions, but they are very popular in the 80s.  Since 1993, due to the increase in the cost of microporous rubber partitions, the supply of PVC partitions has been in short supply. In the 90s of the 20th century, PP (polypropylene) separators, PE (polyethylene) partitions and ultra-fine glass fiber partitions (10-G each) and other composite partitions appeared. There have also been fiber paper separators, which have good resistance and porosity, but poor corrosion resistance and mechanical strength, and large pore size, so they cannot be used in large quantities. At present, internationally, especially in the United States and Western Europe, a large number of automotive batteries use polyethylene bag separators. PE separator has a small aperture, very low resistance and extremely thin substrate, easy to make into bags, suitable for continuous production of batteries. However, at present, there is no domestic mass production, and the assembly line (including the matching machine) suitable for this partition is also limited, so the use is not widespread; PP separators and 10-G are gradually accepted by automotive battery manufacturers. Closed valve regulated lead-acid battery is mainly in the use of AGM (adsorption glass fiber separator), below we mainly introduce AGM separator.2. Ultra-fine glass fiber separator At present, ultra-fine glass fiber separator (AGM) is commonly used in valve-regulated lead-acid batteries, the main function of the separator is to make ion flow between electrodes, with extremely high porosity; Large specific surface area and good wettability are the main characteristics of separators that can adsorb the largest amount of electrolyte. The separator must have long-term stable chemical and electrochemical corrosion resistance in the battery, it can not release any substances that increase the gas precipitation rate, corrosion or self-discharge, and must have good tensile strength to ensure that the separator will not be pierced by sharp edges or small particles during the production and assembly of the battery. The separator is an important component in the production of batteries, and its advantages and disadvantages directly affect the discharge capacity and charging and discharging cycle service life of the battery, so the selection and research of the battery separator must be paid attention to. The separator should generally have the following requirements in the battery: I. Prevent the positive and negative electrode plates from contacting each other and causing a short circuit inside the battery; II. Make the battery tightly assembled and reduce the battery volume; III. Prevent plate deformation, bending and shedding of active substances; IV. Store the necessary amount of electrolyte in the porous separator between the plates to ensure high conductivity and battery reaction requirements; V. Prevent the migration and diffusion of some substances harmful to the electrode through the partition.   To ensure that the separator plays the above role smoothly in the battery, there must also be certain requirements for the separator itself. The various requirements described below often have their own focus with different battery operating conditions. In general, there are some requirements for the quality of the partition: I.  The separator material itself is an insulator, but the separator must have a loose and porous structure, and can absorb and discharge a large amount of electrolyte solution; II. The chemical stability of the separator should be good and it must be resistant to sulfuric acid corrosion