Some opinions on improving the quality of absorbin

Some views on improving the quality of absorbing glass fiber separator paper

Abstract: This paper introduces some methods of improving the quality and liquid absorption performance of glass fiber sealed battery separator paper

key words: glass fiber battery separator aperture fiber diameter electrolyte void saturation

sealed lead/Acidbattery (SLA) is designed to limit the amount of electrolyte, that is, to use the minimum electrolyte, absorb (retain) them in the separator material, and adopt excessive negative active substances, Promote the oxygen produced by the positive electrode to be absorbed by the negative electrode when the battery is overcharged (i.e. oxidation recombining), or prevent gas evolution during floating charge, so that the battery is in a sealed structure, It is a kind of lead-acid battery that can be placed and used in any way [ceiiecl056 portable lead-acid battery (valve regulated sealed type) 2.1.3 small provisions "... Battery composition or single battery should be able to work in any direction (such as inversion) without liquid leakage from the valve or terminal seals."

in the 1970s, gates company of the United States first introduced this kind of absorption valve regulated oxygen elimination lead-acid battery. Compared with the gel type used by German sunshine company, it has the advantages of low internal resistance and high capacity. It is more suitable for discharging at a high rate, which is required by backup power supplies and starting batteries such as computers and communications. Over the past decades, rapid development has been achieved in these areas. In particular, the recent launch of a large number of electric bicycles has popularized its use

absorption separator is the key of absorption sealed battery. Its performance has a great impact on the quality of the battery. In addition to the requirements of ordinary lead-acid batteries, it also requires high porosity, small maximum aperture, low resistance, strong oxidation resistance, ability to absorb and maintain a sufficient amount of electrolyte, allowing oxygen generated during overcharge to diffuse from the positive plate to the negative plate through it for oxygen elimination reaction. The glass fiber partition paper without adhesive meets these requirements. This kind of products was first produced commercially by American evanite company (the company could sell the equipment to American HV company in 1992) in 1983. It is named AGM (absorptive glass mat). In China, the absorption valve regulated lead-acid batteries were mainly studied after 85 years. Because the production mode and performance of the separator are similar to that of glass fiber air filter paper, and there is a certain profit margin, resulting in the competition of low quality and low price. In order to further improve the quality of this product, the author gives some superficial views for reference

1 use raw materials

manyille company of the United States developed a special borosilicate glass fiber code 253 for this kind of diaphragm. It is characterized by low softening point, good acid resistance and low impurity content. In the late 1980s and mid-1990s, China has developed 8902 and 9401 special glass fibers for diaphragm by simulating 253 glass fibers. Taking 8902 as an example, the comparison of the amount of dissolved iron per gram in 100ml specific gravity 1.28 g/cm3 sulfuric acid at different times with alkali free glass fiber and evanite partition is shown in the table

it is worth emphasizing that the selection of the purity of foot glass fiber raw materials directly affects the white discharge of the battery, which must be paid full attention to

2 porosity and aperture

the resistance, liquid absorption height and air permeability of the diaphragm are related to its void structure. The maximum liquid absorption capacity of the diaphragm is determined by its porosity, and the liquid absorption speed of the diaphragm and the distribution of dielectric fluid in the diaphragm depend on the size of the aperture. Porosity of diaphragm α Is the fraction of the volume of voids in the total volume of diaphragms. It can be calculated by the following formula:

as we all know, the aperture in the paper is lognormal distribution, that is, the logarithm of the aperture diameter has normal distribution or Gaussian distribution. Its distribution can be roughly described by median aperture and standard deviation. The median aperture can reflect the average size of the aperture, and the standard deviation is used to express the width or concentration of the aperture distribution. As with other papers, the aperture of separator paper is related to the fiber diameter. The finer the fiber, the smaller the aperture. It can be seen from the surface tension capillarity of the liquid that the smaller the pore size, the higher the height that the electrolyte can reach. As the separator paper is a kind of paper with high porosity, it not only has larger pores, but also has a wider range of pore size distribution than the denser paper. Therefore, when the electrolyte reaches a certain height in the separator, some larger pores will be empty. The higher the height of the separator is, the smaller the pore size of the pores that the electrolyte cannot enter. In this way, the electrolyte forms a certain gradient distribution with the height of the separator. When the separator exceeds a certain height, the electrolyte saturation cannot meet the requirements, resulting in a sharp increase in the resistance of the separator

on the other hand, the electrolyte diffuses from one end of the diaphragm to the other, and the speed is restricted by its viscosity, pore size, etc. The larger the pore size, the faster the electrolyte rises in the diaphragm. Because the aperture has a certain overall size of the sub design sample; Cloth, the actual measurement is an average speed. Therefore, replacing steel with plastic is an important development trend of automobile lightweight

the void ratio of absorption diaphragm is generally about 95%, and the maximum aperture is usually 14~35 μ m. The median diameter is about 5~12 μ m. The liquid absorption capacity can reach more than 10 times of its own weight

as mentioned above, in order to achieve the liquid absorption performance of separator paper, its fibers should be matched in thickness and should not be composed of fibers of the same diameter. Generally, it is made of ultra-fine glass fiber (0.7~3.5 μ m) Mainly (90%~95%), add a small amount of chopped glass fiber (10~35 μ m)。 To control the aperture, liquid absorption, etc. The advantage of adding glass fiber is that after adding electrolyte to the diaphragm in tight assembly, it will not shrink, deform and separate from the electrode plate in use, causing damage to the battery, so as to prolong the service life

3 improve the control of liquid absorption

the resistance of the absorbing glass fiber partition is very low when all the mail holes are filled with electrolyte. But objectively, there needs to be a part of empty holes as a channel for oxygen to diffuse from the positive plate to the negative plate. As mentioned earlier, because the pore size has a certain distribution, it is necessary to control the amount of electrolyte added in actual production to cause some large pores to be empty. The diaphragm resistance decreases with the increase of saturation (the percentage of the pore volume of the diaphragm filled by electrolyte). When the saturation exceeds 80%, it approaches a stable value. Therefore, the amount of electrolyte should be controlled to make the saturation of the diaphragm within the range of 85~95%. This brings trouble to the battery production process. The way to change this state is to add a small amount of organic fibers that are not soaked by electrolyte into the glass raw materials, such as polypropylene fiber, polyethylene fiber, etc. (such as pulpexa-121 in the United States). Holes will be formed around these fibers that electrolyte cannot enter unless external force is applied. In this way, when the electrolyte is saturated, a part of the diaphragm is still empty

to achieve this goal, we can also adopt other methods that large-scale product production and market operation are basically carried out by large companies. For example, a layer of non-woven fabric made of hydrophobic polymer fiber (such as polypropylene fiber) is compounded on one side of the negative plate on the diaphragm, so that oxygen can be easily compounded with the negative electrode, or a part of the thick diameter (30 μ The fiber of about M is made into a hollow shape (the inner diameter is generally (10 μ m) At the same time, the hydrophobic treatment of such fibers can make the diaphragm have oxygen channels, etc. But it seems that the former is more practical

Table 2 shows the effect of electrolyte saturation of all glass fiber partition on oxygen elimination current (oxygen elimination current refers to the difference between 32 hours and 16 hours of constant voltage charging). With the increase of saturation, the oxygen elimination current gradually decreases, and when the saturation reaches 100%, all the oxygen elimination current disappears

the reference ratio of this separator is 5% chopped glass fiber, 5% polypropylene fiber, 90% medium coarse and ultra-fine glass fiber

incidentally, the formation of hollow holes will not increase the passage of branches. Because the ability of absorbing glass fiber partition to prevent the growth of small lead branches is not determined by the pore diameter, but by the content and fineness of sub micron diameter glass fiber. Because the barrier blocks the migration of lead ions not by screening effect, but by the action of fiber and lead ions

4 cost reduction

because the glass fiber used for papermaking is more expensive, and the finer the fiber, the higher the price. Therefore, in recent years, an improved diaphragm made of acid resistant and hydrophilic synthetic fibers and a small amount (about 30%) of more expensive ultra-fine glass fibers has appeared abroad. In order to improve the performance of this kind of partition, the following measures are taken:

1) a 0.25mm thick glass fiber layer made of coarse glass fiber is pasted on both sides of the partition. It can prevent the diaphragm from shrinking and loosening, and improve the ability to maintain electrolyte

2) add a small amount (10~40%) of particle size 0.3 in the manufacturing process μ M to improve the ability of the separator to absorb electrolyte

3) in order to meet the requirements of temperature rise (about 60 ℃) during charging and discharging, it is made of 50% coarse polyester fiber, 20% medium coarse glass, 20% SiO2 powder, mixed with 10% propylene fiber as adhesive, which can improve the service life of the battery

at present, Japan adopts a diaphragm made of three kinds of glass fibers with different fineness (82~94%), mixed with a small amount of synthetic fibers with water absorption (6~18%) (that is, 20~30% polyacrylic acid is maintained on the surface of propylene gnawing fibers after super water absorption treatment). Its main properties are:

thickness: 1.03mm; Quantitative: 147g/cm2; Tightness 0.143g/cm3; Liquid absorption capacity: 1.7g/cm3; Suction speed: 101mm/5 minutes; Tensile strength: 829g/15mm wide; Maximum aperture: 24u column, upper and lower bending equipment M

in addition, it is worth mentioning that this kind of separator can be produced by papermaking. In addition to glass fibers, hydrophilic and acid resistant synthetic fibers (such as hydrophilic polyester fibers, polyethylene fibers, polypropylene fibers, etc.) can also be used (50-80%), mixed with a small amount (10-30%) of coarse (6-10um) glass fibers and a small amount (10-40%) of amorphous silicon oxide, And a small amount (10~20%) of highly soluble synthetic fiber (such as propylene fiber) made of clapboard has moderate performance and low price. Those who are interested may have a try

sealed battery separator is a new type of battery separator, which can meet its use requirements in many ways. The above are only some superficial views for colleagues' reference