.1.1 ordinary lead-acid battery
In the 1950s, the lead-acid battery produced was called an ordinary battery, and the user of the product at that time had to have an "initial charging" process. After the electrolyte is injected into the battery, the battery is heated, and after the electrolysis temperature is lowered, the first charge is performed. After charging, the capacity is released. This cycle is called a charge and discharge cycle. The initial charging process has 6 times of charging and 5 times of discharging in the early stage, and then with the development of technology, the number of charging and discharging cycles is gradually reduced. The original Bureau of the Ministry of Railways had prescribed three charges.
Why do you have to do three charge and two release?
The purpose of three charge and discharge is to detect the actual capacity of the battery.
The lead battery electrochemical reaction equation is:
PbO+2H2SO4+Pb=PbSO4+2H2O+PbSO4......(1.1)
The condition of battery discharge is the three elements on the right, which are indispensable. The discharged capacity is composed of the barrel plate principle, but the discharge of the new battery is not obtained as it is, because the negative plate Pb is oxidized before the electrolysis of the sulfuric acid.
2Pb+O2=2PbO.....(1.2)
In the formation process of the battery production, the green plate becomes a cooked plate, and the lead on the cooked negative plate is highly activating. After being taken out of the formation tank, the reaction can be rapidly reacted with oxygen in the air at the same time. Release a lot of heat. Thus, the plate is reduced from a high potential state to a low potential state, and this reaction causes the negative plate to lose its activity. The reaction proceeds very rapidly under humid conditions. After washing with water, the reaction did not stop. Assemble the battery until it is still in progress. After injecting sulfuric acid electrolyte. The electrothermal reaction occurs again.
PbO+H2SO4=PbSO4+H20+Q......(1.3)
This reaction causes the battery negative electrode to lose electrical activity. The purpose of the initial charge and discharge cycle is to activate the negative plate.
1.1.2 Development to dry charge battery
In order to provide convenience to the user, the anode charging process needs to be protected from the initial charging process, so that it is not oxidized during production, storage and transportation. This requires the active material of the negative electrode plate to have antioxidant capacity. The technical measures taken now are:
1. Add antioxidants such as rosin and oxalic acid to the lead paste formula.
2. The lead particles are coated with an antioxidant such as oil or boric acid.
As long as the negative electrode is protected and not oxidized, a charged electrode plate capable of maintaining its chargeability in a dry state before liquid injection is obtained, which is referred to as a dry load electrode plate. When the battery is assembled with the dry-charged electrode plate, the battery can reach 80% of the capacity within 30 minutes, and the battery can be put into use.
1.1.3. Developed to maintenance-free battery
In the use of batteries, it is often necessary to replenish water because the battery is damaged if it is short of water. Replenishing water is a cumbersome task because many users cannot find qualified battery water when they need to replenish water.
The reason for the battery loss is:
1 physical water loss: the electrolyte will be evaporated by heat.
2 chemical water loss: due to the presence of impurities, impurities and lead constitute a micro-battery, so that water is continuously decomposed into gas.
3 Electroless dehydration: When overcharged, when the charging voltage exceeds 2.3V, water decomposition occurs. To reduce its power consumption, the decomposition voltage of water must be increased.
Among the above three types of water loss, the latter two are the main ones, and the last one causes the largest proportion of water loss.
A lead-calcium alloy has been found. When a battery is fabricated using a lead-calcium alloy, the water decomposition voltage is increased from 2.3V to 2.45V. If the charging voltage is controlled below 2.45V, the water consumption of the battery can be reduced to a minimum. The charging voltage of the car battery is 14.4V ± 0.1V, and the average is 2.4 ± 0.016V per cell. Nowadays, the car battery has been continuously loaded for 6 months to 8 months plus water. The manufacturer has named this battery as a “maintenance-free batteryâ€, that is, “MF†battery, for the convenience of sales. This is the commercial name for this battery. In fact, this battery maintenance work includes: detecting technical status, replenishing electricity, and replenishing water. Only the watering cycle has been extended, and the maintenance requirements are high. It is not really "maintenance-free".
From a technical point of view, there is no real maintenance-free battery.
1.1.4. Developed to a sealed battery
The water consumption of the maintenance-free battery can be reduced again, so that the battery does not replenish water during the whole period of use. In special cases, the battery is allowed to be freely oriented, and the vertical and horizontal modes can work.
The key to a closed battery is how to recombine the gas produced in the battery into water in the battery.
The sealed battery was in the early 1950s, when metal palladium was used as a catalyst to convert hydrogen and oxygen in the battery to a synthetic state without flame.
H2+O2→H2O+Q......1-4
Since the compound is converted from a high-energy gas to a low-energy liquid, a large amount of heat is released, which can cause the temperature of the palladium beads to reach about 300 °C. Because palladium is expensive, the battery is used very strictly, so this kind of
The battery is only used under special circumstances, such as submarines, hydropower stations, etc.
In the 1970s, a cathode absorption type sealed battery was developed. The battery was eliminated by first making the battery produce hydrogen gas as much as possible. The oxygen O2 is a component that is converted into a liquid by absorption through the negative electrode.
The conversion process is shown in Equation 1-5:
Negative charge
O2+Pb→PbO+H2SO4→PbSO4+H2O→Pb+H2SO4....1-5
The degassing process is: O2 is generated when charging on the positive electrode PbO2, and PbO is formed by reacting with Pb on the negative electrode, PbO reacts with sulfuric acid H2SO4 in the electrolyte to form lead sulfate PbSO4 and water, and PbSO4 on the negative electrode is restored to Pb after charging. Sulfate SO2-4 enters the electro-hydraulic again, increasing the electro-liquid density.
The key to the above-described degassing process is that the separator must be gas permeable. The current method is to use the liquid absorbing property of the glass felt to maintain the coexistence of the gas phase, the liquid phase, and the solid phase in the separator made of the glass felt. Thus, O2 is generated on the positive electrode and can be gradually diffused to the negative electrode through the gas passage on the felt. The process of eliminating O2 is a dynamic balancing process. When the amount of O2 is equal to the amount of O2 eliminated, battery use is safe.
Once overcharge occurs, the amount of O2 generated is greater than the amount of O2 eliminated, which will increase the gas pressure inside the battery. In order to avoid an explosion accident, a safety valve is placed on the top cover of the battery to prevent accidents. Therefore, this type of battery is called "valve-controlled cathode absorption closed maintenance-free battery."
It is not difficult to understand that the sealed battery should be charged by a constant voltage charger with high voltage accuracy, and it is absolutely not allowed to use constant current charging for supplementary operation. Overcharging is the first killer for closed batteries.
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