1.1.1 Ordinary lead-acid battery
In the 1950s, the production of lead batteries called ordinary batteries, when the product users are opened to have "initial charging" process link. After the electrolyte is injected into the battery, the battery heats up, and after the electrolysis temperature is lowered, the first charge is made. After charging and then discharging the capacity, this cycle is called the charge/discharge cycle. The initial charging process in the early six times charging 5 times discharging as many, after the development of technology, the number of charging and discharging cycles gradually reduced. The Ministry of Railways, the former Bureau of Machinery had provided for three charges and two discharges.
Why three charges and two discharges?
The purpose of three charges and two discharges is to detect the actual capacity of the battery.
The electrochemical reaction equation of lead battery is.
PbO+2H2SO4+Pb=PbSO4+2H2O+PbSO4......
(1.1) The conditions for discharging the battery are the three elements on the right, one is missing. The discharged electric capacity is composed according to the principle of barrel plate, but the discharge of the new battery does not get the proper capacity, which is because the negative plate Pb is oxidized before the sulfuric acid electrolyte is injected.
2Pb+O2=2PbO .....
(1.2) In the chemical process of battery production, the raw electrode plate becomes a cooked electrode plate, and the lead on the cooked negative plate is highly activated, and after being taken out from the chemical tank, it can quickly carry out the reaction of 1.2 with the oxygen in the air, and at the same time release a large amount of heat. Thus, the electrode plate is reduced from a high potential energy state to a low potential energy state, and this reaction makes the negative electrode plate inactive. Under humid conditions, the reaction proceeds very rapidly. After being washed and dried, this reaction does not stop. Assembled into a battery, it is still going on until the time of activation. After injection of sulfuric acid electrolyte. Then the electrothermal reaction occurs again.
PbO + H2SO4 = PbSO4 + H20 + Q ......
(1.3) This reaction renders the negative terminal of the battery electrically inactive. The purpose of the charge-discharge cycle of the initial charge is to activate the negative electrode plate.
1.1.2 Development to dry charge battery
In order to provide convenience to users and eliminate the initial charging process step, it is necessary to protect the negative plate from oxidation during production, storage and transportation. This requires making the negative plate active material with antioxidant capacity, and the technical measures taken now are.
①. Adding antioxidants, such as rosin and glycolic acid, to the lead paste formulation.
②. Wrap the lead particles with a layer of antioxidant, such as oil, boric acid.
As long as the negative electrode is well protected from oxidation, this gives the charge electrode plate which can keep its charge in the dry state before liquid injection, referred to as dry charge electrode plate. Once the battery is assembled with dry charge electrode plate, the battery can reach 80% capacity within 30 minutes after liquid injection, and the battery can be put into use.
1.1.3. Development to maintenance-free batteries
In the use of batteries, often need to replenish water, because once the lack of water battery is damaged. Replenish water is a very troublesome thing, because many users can not find qualified battery water when they need to replenish water.
The reasons for battery water loss are.
①Physical water loss: electrolyte will be evaporated by heat.
② Chemical water loss: due to the presence of impurities, impurities and lead constitute a microcell, so that the water is constantly decomposed into gas.
③Electrochemical water loss: When the charging voltage exceeds 2.3V during overcharge, water decomposition occurs. To reduce its power consumption, the value of the decomposition voltage of water must be increased.
In these three forms of water loss above, the last two are the main, the last cause of water loss is the largest proportion.
Now we have found a lead-calcium alloy, the use of lead-calcium alloy manufacturing battery, water decomposition voltage from 2.3 V to 2.45 V. If the charging voltage is controlled below 2.45 V, the water consumption of the battery in use can be reduced to very little, car battery charging voltage is 14.4 V ± 0.1 V, the average to each single cell is 2.4 ± 0.016 V. Now do car battery continuous loading Driving 6 months -8 months to add water, the manufacturer in order to market the convenience of this very low water consumption of the battery named "maintenance-free battery", that is, "MF" battery, which is the commercial name of this battery. In fact, this battery maintenance work includes: testing the technical status, replenishing electricity, replenishing water. Only the water refill cycle is extended, the maintenance requirements are higher, and it is not the real meaning of "maintenance-free".
From the technical point of view, there is no real maintenance-free battery.
1.1.4. Development to the closed battery
Can the water consumption of the maintenance-free battery be further reduced, so that the battery does not replenish water during the whole period of use, and the battery is allowed to be freely oriented under special circumstances, so that vertical and horizontal can work.
The key to the hermetic battery is how to re-synthesize the gas produced in the battery into water in the battery.
The closed cell was available as early as the 1950s, when the metal palladium was used as a catalyst to synthesize hydrogen and oxygen in the cell into water in a flameless state
H2+O2→H2O+Q ..... .1-4
Since the chemistry is converted from a high-energy gas to a low-energy liquid, a large amount of heat is released, and this heat can make the temperature of the palladium beads reach about 300°C. Since palladium is expensive and the conditions for battery use are very strict, this type of battery is only used in special cases, such as submarines and hydroelectric power stations.
By the 70s, and the development of a cathode absorption type closed battery, this battery to eliminate gas is to first make the battery as far as possible not to produce hydrogen H2, oxygen O2 is absorbed through the negative electrode into a liquid composition.
The conversion process is shown in equation 1-5.
Negative electrode Charging
O2+Pb→PbO+H2SO4→PbSO4+H2O→Pb+H2SO4... .1-5
The degassing process is: O2 is generated when charging on the positive PbO2, which reacts with Pb on the negative electrode to produce lead oxide PbO, PbO reacts with sulfuric acid H2SO4 in the electrolyte to produce lead sulfate PbSO4 and water, PbSO4 on the negative electrode is recharged to Pb again, and sulfate SO2-4 enters the electrolyte once again to increase the density value of the electrolyte.
In the above degassing process, the key is that the partition must be breathable. The approach now used is to use the liquid absorption of glass felt to keep the coexistence of gas phase, liquid phase and solid phase in the partition made of glass felt. In this way, O2 can be generated on the positive electrode through the gas channel on the felt, and gradually diffuse to the negative electrode. The process of O2 elimination is a dynamic equilibrium process, the amount of O2 generated and the amount of O2 eliminated to reach a balance, the battery is safe to use.
Once the overcharge occurs, the amount of O2 generated is greater than the amount of O2 eliminated, will make the gas pressure in the battery more and more, in order to avoid explosive accidents, the battery top cover are equipped with a safety valve, in case of an accident. So this kind of battery are called "valve-regulated cathode absorption closed maintenance-free battery".
It is not difficult to understand that the closed battery should be charged with a constant voltage charger with high voltage accuracy, and it is absolutely not allowed to use constant current charging for supplementary electric operation. Overcharging is the first killer for closed batteries.
