The basic structure of VRLA battery is shown in Figure 1. It consists of positive and negative plates, separators, electrolyte, safety valve, gas plug, shell and other parts. The active material on the positive plate is lead dioxide (PbO2), and the active material on the negative plate is sponge-like pure lead (Pb). The electrolyte is prepared by distilled water and pure sulfuric acid in a certain proportion. After a certain density of electrolyte is loaded into the VRLA battery tank, an electromotive force of about 2.1V (single VRLA battery) will be generated between the positive and negative plates due to the electrochemical reaction.
Figure 1 – Basic structure of valve-regulated maintenance-free lead-acid battery
The difficulty of sealing lead-acid batteries is the electrolysis of water during charging. When the charging reaches a certain voltage (generally above 2.30V/cell), oxygen is released on the positive electrode of the lead-acid battery, and hydrogen is released on the negative electrode. On the one hand, the released gas brings out the acid mist to pollute the environment; VRLA battery is a product developed to overcome these shortcomings. Its product features are as follows:
(1) The ordinary separator is no longer used between the plates, but the ultra-fine glass fiber is used as the separator. The electrolyte is all adsorbed in the diaphragm and the plate, and there is no free electrolyte inside the VRLA battery; due to the use of multiple high-quality grid alloys, the overpotential of gas release is increased. Ordinary lead-acid battery grid alloy releases gas when it is above 2.30V/cell (25°C). After using high-quality multi-component alloys, the gas is released only when the temperature is above 2.35V/monomer (25°C), which relatively reduces the amount of gas released.
(2) Let the negative electrode have excess capacity, that is, 10% more capacity than the positive electrode. In the later stage of charging, the oxygen released by the positive electrode contacts the negative electrode, reacts, and regenerates water, that is, O2+2Pb→2PbO+2H2SO4→2H20+2PbSO4, so that the negative electrode is in an undercharged state due to the action of oxygen, so no hydrogen is produced. The oxygen of the positive electrode is absorbed by the lead of the negative electrode, and then further converted into water, which is the new so-called cathode absorption principle.
(3) In order to allow the oxygen released by the positive electrode to flow to the negative electrode as soon as possible, a new type of ultra-fine glass fiber separator that is different from the microporous rubber separator used in ordinary lead-acid batteries must be used. The porosity of the separator is increased from 50% of the rubber separator to more than 90%, so that the oxygen can easily flow to the negative electrode and then be converted into water. In addition, the ultra-fine glass fiber separator has the function of adsorbing sulfuric acid electrolyte, so even if the VRLA purple battery is poured, there is no electrolyte overflow. Due to the special structural design, the production of gas is controlled. In normal use, the VRLA battery does not generate hydrogen, but only a small amount of oxygen, and the generated oxygen can be recombined in the VRLA battery and absorbed by the electrolyte.
(4) The valve-controlled sealing acid filter structure is adopted, the electrolyte will not leak, so that the acid mist cannot escape, so as to achieve the purpose of safety and environmental protection. The VRLA battery can be installed horizontally, which is convenient to use.
(5) There is a safety safety valve on the shell, which is automatically opened when the internal pressure of the VRLA battery exceeds the threshold of the safety valve to ensure the safe operation of the VRLA battery.
In the process of cathode absorption of VRLA battery, since the water produced cannot overflow under the condition of sealing, VRLA battery can be exempted from supplementary water maintenance, which is also the reason why VRLA battery is called “maintenance-free” battery. However, maintenance-free does not mean not doing any maintenance. On the contrary, in order to improve the service life of VRLA batteries, the maintenance of VRLA batteries is the same as that of ordinary lead-acid batteries, except that the supplementary water is exempted. The correct use method of VRLA batteries can only be explored in the use and maintenance.
If you first understand the related products of maintenance-free lithium batteries, please enter tycorun.com.