Products | Application of fumed silica in colloidal batteries
Release time:
2021-02-26
Lead-acid batteries were invented by Frenchman Gaston Plante in 1859 and have gone through nearly 160 years of development. Lead-acid batteries have played an indispensable and important role in various economic fields, including transportation, communications, electricity, military, navigation, and aviation.
The colloidal lead-acid battery is an improvement on the ordinary lead-acid battery with liquid electrolyte. The colloidal electrolyte replaces the sulfuric acid electrolyte, which is better than ordinary batteries in terms of safety, storage capacity, discharge performance and service life. The colloidal electrolyte uses fumed silica as the colloid.
Valve-regulated sealed lead-acid battery structure diagram
one
The structure of fumed silica
Fumed silica is a nanometer-sized white powder generated by high-temperature hydrolysis of silicon halides in a hydrogen-oxygen flame, commonly known as white carbon black.
The surface-untreated fumed silica aggregates contain a variety of silanol groups: one is isolated, undisturbed free hydroxyl groups; the other is bonded silanol groups that are linked and form hydrogen bonds with each other. Some of the fumed silica particles are linked together by hydrogen bonds of hydroxyl groups to form a three-dimensional network structure, and some of the hydroxyl groups act as bridges under acidic conditions with sulfate ions, ultimately forming silicon-oxygen bonds between the silica particles, thereby achieving a high-strength gel.
Electron microscope photo of AEROSIL® 200
Thickening mechanism of fumed silica in colloidal batteries
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The use of fumed silica in colloidal batteries
Since fumed silica has a large specific surface area, the key point in its use is how to disperse the fumed silica. When the dispersion effect is good, the production efficiency will be greatly increased; if the dispersion effect is poor, it will affect the battery performance and production efficiency (the initial capacity is greatly reduced, the glue filling machine is easy to be blocked, etc.).
There are currently two methods on the market: direct method and indirect method (also known as mother liquor method)
01Direct method
Direct Method
Directly mix the fumed silica with sulfuric acid in the final ratio and mix by gas impingement. Stirring does not stop. (Since this method has been compared in the laboratory by Degussa, it is completely unable to disperse the fumed silica, which will cause difficulties in glue filling and battery charging bulging. Customers are advised not to use it)
02
Indirect method
After setting the ratio of fumed silica and water, the dispersing equipment can automatically absorb the powder and stir it to obtain a silica mother liquor with good dispersibility. Then the mother liquor can be directly mixed with the diluted sulfuric acid.
Advantages: good dispersing effect, high degree of automation, easy operation, and it is also the process used by most battery companies at present.
three
Factors affecting the use of fumed silica in colloidal batteries
As the temperature rises, the gel time of fumed silica will increase geometrically, so cold acid needs to be used when mixing silica dispersion with acid to delay the gel time and facilitate battery filling
.
Adding silicon dioxide can significantly increase the cycle life of the battery and significantly improve the battery packing rate.
Electrical performance test of AERSIL 200 with different addition ratios
Product Q&A Time
Q1: What percentage of solid content is usually required for the fumed silica dispersion? How long should it be left to stand?
A1: Generally, battery companies make dispersions with a solid content of 7-15%. The prepared dispersions should be used up on the same day. If a batch of dispersions needs to be used for several days, they are generally stored below 10°C. If the storage time exceeds 7 days, a small amount of sodium hydroxide needs to be added to maintain the stability of the dispersion.
Q2: What is the appropriate amount of fumed silica to be added to small-density power batteries and energy storage batteries?
A2: For the mainstream 20AH small-density power batteries on the market, the proportion of silicon dioxide added to the electrolyte sulfuric acid is between 0.5-1%; for energy storage batteries, the proportion varies from 2 to 7% depending on customer needs.
Q3: Does Haiyi have any recommendations for decentralized equipment?
A3: Currently, most of the equipment used in the market is Germany's BRT dispersing and emulsifying homogenizer, which can fully achieve high-quality dispersion of AEROSIL® 200.
Q4: How is the progress of the fumed silica plant jointly built by Evonik and Wynca Chemical in Zhenjiang? Has the quality of AEROSIL® 200 produced changed after completion?
A4: AEROSIL® 200 produced by the joint venture between Evonik and Wynca Chemical is expected to be available for shipment in the third quarter of 2021. The quality of the AEROSIL® 200 grade produced will be fully in accordance with Evonik's corporate standards.
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