Four development courses of lead-acid batteries

Four development courses of lead-acid batteries

  1. Ordinary lead-acid battery

Lead-acid batteries produced in the 1950s are now called ordinary batteries, and users at that time had to have an “initial charging” process link when using the product. After the electrolyte is injected into the battery, the battery heats up. After the temperature of the electrolyte drops, the first charge is performed, and the capacity is released after charging. This cycle is called a charge-discharge cycle. In the process of initial charging, there are as many as 6 times of charge and 5 times of discharge in the early stage, and it takes 1 week to work continuously. With the development of technology, the number of charge-discharge cycles is gradually reduced to 3 times of charge and 2 times of discharge. Its purpose is to activate the plates and detect the actual capacity of the battery. For more battery knowledge you don’t know, please visit Tycorun Battery.

The electrochemical reaction equation of a lead-acid battery is (Figure 1):

Figure 1 - Electrochemical reaction equation of lead-acid battery
Figure 1 – Electrochemical reaction equation of lead-acid battery

The conditions for battery discharge are the three elements on the right side of the reaction equation, all of which are indispensable. The discharged electric capacity is determined according to the barrel plate principle, but the discharge of the new battery cannot obtain the proper capacity, because the Pb of the negative plate is oxidized before the sulfuric acid electrolyte is injected.

In the chemical formation process of battery production, the raw electrode plate becomes the cooked electrode plate, and the lead on the cooked negative electrode plate is highly activated. hot. As a result, the plate is reduced from a high potential energy state to a low potential energy state, and this reaction makes the negative plate inactive. Under humid conditions, the reaction proceeds very rapidly. After washing with water and drying, the reaction did not stop. Assembled into a battery that is still in progress until enabled. After injection of sulfuric acid electrolyte, the exothermic reaction occurs again (Figure 2).

Figure 2 - Exothermic reaction occurs after injection of sulfuric acid electrolyte
Figure 2 – Exothermic reaction occurs after injection of sulfuric acid electrolyte

This reaction makes the negative electrode of the battery inactive. The purpose of the charge-discharge cycle of the initial charge is to activate the negative plate.

  1. Dry charged battery

In order to provide convenience for users and cancel the initial charging process, it is necessary to protect the negative plate so that it will not be oxidized during production, storage and transportation. This requires the active material of the negative plate to have anti-oxidation ability, and the technical measures taken now are as follows.

①Add antioxidants such as rosin and oxalic acid to the lead paste formula.
②Wrap lead particles with a layer of antioxidants, such as mineral oil and boric acid.
As long as the negative electrode is well protected and not oxidized, a charged electrode plate that can maintain its charged performance in a dry state before liquid injection is obtained, which is referred to as a dry charged electrode plate. Once the battery assembled with the dry-charged electrode plate is filled with liquid, the battery can reach 80% of the capacity within 30 minutes and can be put into use.

  1. Maintenance-free battery

In the use of the battery, it is often necessary to add water, because once the water is short, the battery will be damaged. Replenishing water is a very troublesome thing, because many users can’t find qualified water when they need to replenish water.
The reasons for battery loss of water are as follows.

①Physical water loss: The electrolyte will evaporate when heated.
②Chemical water loss: Due to the existence of impurities, impurities and lead form a micro-battery, which makes water continuously decomposed into gas.
③Electrochemical water loss: During overcharging, when the charging voltage exceeds 2.3V, the water splitting reaction occurs. To reduce its power consumption, the water decomposition voltage value must be increased.
Among the above three forms of dehydration, the latter two are the main ones, and the last one causes the largest proportion of dehydration.

After the invention of lead-calcium alloy, the voltage of water decomposition in the battery is increased, and the water consumption is greatly reduced. At that time, batteries produced in the UK with lead-calcium alloys could be used for several months without adding water. That is to say, this kind of battery can be replenished with water once, and it can be “like a camel” for a long time without water replenishment, so this kind of battery is named “Camel Brand”.

The lead-calcium alloy prepared now has a unique function. When the lead-calcium alloy is used to make a battery, the decomposition voltage of water is increased from 2.3V to 2.45V. If the charging voltage is controlled below 2.45V, the water consumption of the battery during use will be reduced. It can be reduced to very little. The charging voltage of the car battery is (14.4±0.1)V, and the average is (2.400±0.016)V per cell. At present, it has been achieved that the car has been continuously loaded and driven for about 1 year. Add water to the battery. Since the main work of battery maintenance is to add water, the manufacturer named this battery with very low water consumption as “maintenance-free battery”, or “MF” battery, which is the commercial name of this kind of battery. In fact, this battery maintenance work includes checking the technical status, replenishing electricity, and replenishing water. It only prolongs the water addition cycle, and the requirements for maintenance are correspondingly higher, which is not a real “maintenance-free”.
From a technical point of view, there is no truly maintenance-free battery.

  1. Valve Regulated Battery

The key to valve-regulated batteries is how to re-synthesize the gas produced in the battery into water in the battery.
Valve-regulated batteries existed as early as the 1950s. At that time, metal palladium was used as a catalyst to convert hydrogen and oxygen in the battery into water in a flameless state. Since it is converted from a gas in a high energy state to a liquid in a low energy state, a large amount of heat is released, which can make the temperature of the palladium beads reach about 300 °C. Because palladium is expensive and the battery usage conditions are very strict, this battery is only used in special cases, such as submarines, hydropower stations, etc.

By the 1970s, a cathode absorption valve-controlled battery was developed. The method of eliminating gas in this battery is to first make the battery as little as possible to produce hydrogen (H2), and oxygen (O2) is converted into liquid through negative electrode absorption. Element. The conversion process is shown in Figure 3 below.

Figure 3 - Component conversion process of negative absorption into liquid
Figure 3 – Component conversion process of negative absorption into liquid

Outgassing process: O2 is generated when charging on the positive electrode (PbO2), which reacts with Pb on the negative electrode to generate lead oxide PbO. PbO reacts with sulfuric acid (H2SO4) in the electrolyte to generate lead sulfate (PbSO4) and water, and the PbSO4 on the negative electrode is charged. It is restored to Pb again, and the sulfate radical enters the electrolyte again, so that the density value of the electrolyte increases.

In the above-mentioned degassing process, the key is that the separator must be breathable. The current method is to use the liquid absorption property of the glass felt to keep the gas phase, the liquid phase and the solid phase coexisting in the separator made of the glass felt. In this way, the O2 generated on the positive electrode can gradually diffuse to the negative electrode through the gas channel on the felt. The process of eliminating O2 is a dynamic balance process. When the amount of O2 generated and the amount of O2 eliminated reach a balance, the battery is safe to use.

Once overcharging occurs, the amount of O2 generated is greater than the amount of O2 eliminated, which will increase the gas pressure in the battery. In order to avoid an explosion accident, a safety valve is installed on the top cover of the battery to prevent accidents. Therefore, this kind of battery was once called “valve-regulated cathode absorption battery”, and is now referred to as valve-regulated battery. It is not difficult to understand that the valve-controlled 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 power operations. Overcharging can cause serious damage to valve regulated batteries.

Read more: Outgassing and EMF in lead-acid batteries

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