Q-Batteries铅酸蓄电池的工作原理

a) Discharge circuit b) charging circuit

1. Container 2. Electrolyte 3. Positive pole 4. Negative pole 5. Bulb 6. DC generator

1) Discharge

Immerse the positive and negative plates into the electrolyte of the container without contacting each other, and connect the two plates with a wire and a bulb outside the container, as shown in Figure (a). At this time, the bulb is on, because the lead dioxide plate and the lead plate have a chemical change with sulfuric acid in the electrolyte, resulting in an electromotive force (voltage) between the two plates, and there is current flowing through the wire, that is, the chemical energy becomes the electrical energy that makes the bulb glow. This process of outputting current due to chemical reaction is called battery discharge.

During discharge, the active substances on the positive and negative electrode plates undergo chemical changes with sulfuric acid to form lead sulfate PbSo4. When most of the active substances on the two plates become lead sulfate, the terminal voltage of the battery will drop. When the terminal voltage drops to 1.8-1.75V, the discharge should not continue. At this time, the voltage between the two plates is called the termination discharge voltage. During the whole discharge process, the sulfuric acid in the battery gradually decreases to form water, the concentration of sulfuric acid decreases, and the specific gravity of electrolyte decreases. The internal resistance of the battery increases, the electromotive force decreases, and the terminal voltage also decreases. At this time, the positive plate is light brown, and the negative plate is dark gray.

2) Charging

If the bulb in the external circuit is replaced with a DC power supply, that is, a DC generator or silicon rectifier, and the positive plate is connected to the positive pole of the external power supply, and the negative plate is connected to the negative pole of the external power supply, as shown in (b), when the terminal voltage of the external power supply is higher than the potential of the battery, the current of the external power supply will flow into the battery. The direction of the current is just opposite to that of the discharge current, so the opposite chemical reaction occurs in the battery, that is, sulfuric acid is separated from the electrode plate. The positive plate is converted into lead dioxide, and the negative plate is converted into pure lead, while the sulfuric acid in the electrolyte increases and the water decreases. After this transformation, the electromotive force between the two poles of the battery is restored, and the battery has the discharge conditions. At this time, the electric energy from the external power supply is charged into the battery and stored as chemical energy. This process is called battery charging. During the charging process, the small crystal blocks of lead sulfate are reduced to lead dioxide (positive plate) and lead sponge (negative plate) respectively, and the lead sulfate on the plate disappears. Because the charging reaction gradually penetrates into the active material on the electrode plate. As the concentration of sulfuric acid increases, the water content decreases, the density of the solution increases, the internal resistance decreases, the potential increases, and the terminal voltage increases.
3) Self-discharge phenomenon of power storage
Because the metal impurities contained in the electrolyte are deposited on the negative plate, and the active material of the plate itself also contains metal impurities. In this case, a local short circuit is formed on the negative plate, forming the self-discharge phenomenon of the battery. Generally, lead battery capacity will be reduced by 0.5% - 1% due to self-discharge in a day and night. The self-discharge phenomenon also increases with the increase of electrolyte temperature, specific gravity and service time.
a) 放电回路 b)充电回路

1.容器 2.电解液 3.正极 4.负极 5.灯泡 6.直流发电机

1）放电

把正、负极板互不接触而浸入容器的电解液中，在容器外用导线和灯泡把两种极板连接起来，如图(a)所示，此时灯泡亮，因为二氧化铅板和铅板都与电解液中的硫酸起了化学变化，使两种极板之间产生了电动势(电压)，在导线中有电流流过，即化学能变成了使灯泡发光的电能。这种由于化学反应而输出电流的过程称为蓄电池放电。

放电时，正负极板上的活性物质都与硫酸发生了化学变化，生成硫酸铅PbSo4。当两极板上大部分活性物质都变成了硫酸铅后，蓄电池的端电压就下降。当端电压降到1.8-1.75V以后，放电不宜继续下去，此时两极板间的电压称为终止放电电压。整个放电过程中，蓄电池中的硫酸逐渐减少而形成水，硫酸的浓度减少，电解液比重降低。蓄电池内阻增大，电动势下降，端电压也随之减小，此时，正极板为浅褐色，负极板为深灰色。

2）充电

如果把外电路中的灯泡换成直流电源，即直流发电机或硅整流设备，并且把正极板接外电源的正极，负极板接外电源的负极，如(b)所示,当外接电源的端电压高于蓄电池的电势时，外接电源的电流就会流人蓄电池。电流的方向刚好与放电时的电流方向相反，于是在蓄电池内就产生了与上述相反的化学反应，就是说硫酸从极板中析出。正极板又转化为二氧化铅，负极板又转化为纯铅，而电解液中硫酸增多，水减少。经过这种转化，蓄电池两极之间的电动势又恢复了，蓄电池又具备了放电条件。这时，外接电源的电能充进了蓄电池变成化学能而贮存了起来，这种过程称为蓄电池充电。充电过程使硫酸铅小晶块分别还原为二氧化铅(正极板)和铅绵(负极板)，极板上的硫酸铅消失。由于充电反应逐渐深入到极板上活性物质内部。硫酸浓度就增加，水分减少，溶液的密度增大，内阻减少，电势增大，端电压随之上升。

3）蓄电的自放电现象

由于电解液所含金属杂质沉淀在负极板上，以及极板本身活性物质中也含有金属杂质。此，在负极板上形成局部的短路，形成了蓄电池自放电现象。通常在一昼夜内，铅蓄电池由于自放电，将使其容量减少0.5%--1%。自放电现象也随着电解液的温度、比重和使用时间的增长而增加。