The lead-acid battery was invented by the Frenchman Gaston Plante in 1895, which has undergone nearly 160 years of development. It has played an indispensable and important role in transport, communications, electricity, the military and in various economic fields such as navigation and aviation.

The gel lead-acid battery is an improvement on the ordinary lead-acid battery with liquid electrolyte, replacing the sulfuric acid electrolyte with a gel electrolyte. It improves on the safety, storage capacity, discharge performance and service life of the ordinary battery. One of the gel electrolytes is the use of fumed silica as the gel.

 

Fumed silica structure

FST fumed silica is a synthetic silica produced by a flame hydrolysis process developed by Fushite.

Untreated fumed silica aggregates with a variety of silica hydroxyl groups: one is an isolated, undisturbed free hydroxyl group; the other is a linked silica hydroxyl group that forms hydrogen bonds with each other. Part of the fumed silica particles are linked together by hydrogen bonding of the hydroxyl groups, forming a three-dimensional network structure, and part of the hydroxyl groups play a bridging role under acidic conditions with sulphate ions, resulting in the formation of silicon-oxygen-silicon-oxygen bonds between the silica microparticles, resulting in a high-strength gel.

 

Process for using fumed silica in gel lead-acid batteries

As fumed silica has a large specific surface area, the focus when using it is on how to disperse the fumed silica well. When the dispersion is good, it will greatly increase the production efficiency; if the dispersion is poor, it will affect the battery performance as well as the production efficiency (larger reduction in initial capacity, easy blockage of the gel filling machine, etc.).

 

There are currently two methods on the market: the direct method and the indirect method (also known as the mother liquor method)

 

The fumed silica is mixed directly with sulfuric acid in the final proportion by gas flushing. The mixing is not stopped. (As this method has been compared in the laboratory, it is completely impossible to disperse the fumed silica, it will cause difficulties in filling the gel, battery charging bulge, etc. Customers are advised not to use it)

 

Set the ratio of fumed silica and water, directly by the dispersion equipment for automatic powder absorption and stirring, you can get a very well-dispersed silica master batch. The mother liquor is then mixed directly with the diluted sulfuric acid.

 

Advantages: good dispersion effect, high degree of automation, easy to operate, and is the process used by most battery companies at present.

 

Factors influencing the use of fumed silica in gel lead acid batteries

As the temperature rising, the fumed silica gel time increases geometrically, so when mixing the silica dispersion with acid, cold acid needs to be used to delay the gel time and facilitate battery gelling.

The effect of temperature on gel time

Adding the fumed silica significantly increases the cycle life of the battery and also significantly improves the battery pack ratio.

FAQ

Q1: What percentage of fumed silica dispersions are usually made with what solids content? How long should can we leave it for?

Generally battery companies do 7-15% solid content of dispersion, the dispersion is best used up within the same day, if you make a batch of dispersion need to use a few days, generally placed below 10 ℃ storage, if placed for more than 7 days, you need to add a small amount of sodium hydroxide to maintain the stability of the dispersion.

 

Q2: What is the appropriate amount of fumed silica to add to small dense power batteries and energy storage batteries?

The current market mainstream 20AH small dense power battery, silica in the electrolyte sulfuric acid additive ratio is between 0.5-1%; energy storage battery according to customer demand to add 2-7% ranging.