Can gel batteries be filled with water?
The colloidal battery uses a type of gel-like electrolyte. There is no free liquid inside, but there is a certain amount of "free water". The main components of the colloidal electrolyte are gelling agent and sulfuric acid, so can water be added to the colloidal battery? In fact, due to the airtightness of the colloidal battery, the water emitted is very rare and can be ignored. What if you add water blindly?
Gel battery
After the organic additives of the colloidal electrolyte are added in an appropriate amount, on the one hand, the gel network structure can be made elastic, and on the other hand, the dosage of the gelling agent can be appropriately reduced. This is not only conducive to the migration and diffusion of ions and gases, slowing down the phenomenon of hydration and stratification, but also preventing sulfation to a certain extent and prolonging the life of colloidal lead-acid batteries. If the additive content is too large, the gel network structure is too dense, which hinders the migration of ions in the electrolyte and the diffusion of gas, and the electrode polarization is intensified, resulting in a decrease in the discharge capacity of the battery. Moreover, when the additive content reaches a certain limit, the "free water" encapsulated in the spatial network structure is squeezed out due to the compactness and contraction of the network structure, and the colloidal electrolyte appears hydration and stratification. Conversely, if the additive content is too small, it cannot have a favorable effect on the colloidal electrolyte and the battery.
Therefore, adding water will be harmful to the colloidal battery.
The gelling agent forms hydrogen bonds through the hydroxyl groups on its surface, forming a space network structure in the system, and wrapping sulfuric acid and water in it, so the colloidal electrolyte is solid when it is stationary. When subjected to a certain shearing force, its three-dimensional network structure disintegrates rapidly, and the colloidal electrolyte is in the form of an aqueous solution. When the shear force stops, the colloidal electrolyte will return to the original spatial network structure. This thixotropy endows colloidal lead-acid batteries with the advantages of easy transportation and less leakage.
The colloidal battery gel is fumed silica. Fumed silica is a high-purity white and odorless nano-powder material, which has the functions of thickening, anti-caking, controlling system rheology and thixotropy. In addition to the application, it has been widely used in gel batteries in recent years.
Fumed silica is a nano-scale white powder generated by high temperature hydrolysis of silicon halide in a hydrogen-oxygen flame, commonly known as fumed silica, which is an amorphous silica product with a primary particle size of 7-40nm. The aggregate particle size is about 200-500 nanometers, the specific surface area is 100-400 m2/g, the purity is high, and the SiO2 content is not less than 99.8%. The untreated fumed silica aggregates contain a variety of silanol groups, one is an isolated, undisturbed free hydroxyl group; the other is a bonded silanol group that is continuous and forms hydrogen bonds with each other. The untreated fumed silica aggregates are aggregates containing multiple -OH, which are easy to form a uniform three-dimensional network structure (hydrogen bond) in the liquid system. This three-dimensional network structure (hydrogen bond) will be destroyed when there is external force (shear force, electric field force, etc.), the medium will become thinner, and the viscosity will decrease. This thixotropy is reversible.
In colloidal batteries, fumed silica mainly uses its excellent thickening and thixotropic properties. The colloidal electrolyte is composed of fumed silica and a certain concentration of sulfuric acid solution in a certain proportion. The sulfuric acid and water in this electrolyte It is "stored" in the silica gel network, and it is a "soft solid-like gel", which is solid when stationary. When the battery is charged, due to the increase in the concentration of sulfuric acid in the electrolyte, it is "thickened" and accompanied by cracks. The "electrolyzed water" reaction in the later stage of charging causes the oxygen generated by the positive electrode to be absorbed by the negative electrode through the countless cracks, and further It is reduced to water, so as to realize the battery sealing cycle reaction. During discharge, the sulfuric acid concentration in the electrolyte decreases to make it "thinned", and it becomes the thin gel state before filling the battery. Therefore, the gel battery has a "maintenance-free" effect.
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