① Water loss, vulcanization, imbalance, thermal runaway (bulging)

The first two accounts for 97% of battery damage in the market.

(1) Analysis ①: The main reasons for water loss in lead-acid batteries

Electronic Car Charger 

The electrolyte in lead-acid batteries is as precious as blood in the human body. Once the electrolyte is lost, it means the battery is scrapped. The electrolyte is composed of dilute sulfuric acid and water. During the charging process, it is difficult to avoid water loss, and different charging modes result in different levels of water loss. The normal three-stage charging mode causes more than twice the amount of water loss during the charging process compared to the Colin pulse mode! In addition to its natural lifespan, batteries also have a water loss lifespan: if a single battery loses more than 90 grams of water, it is scrapped. At room temperature (25 ℃), the water loss of a regular charger is about 0.25 grams, while the Colin pulse is 0.12 grams. At high temperatures (35 ℃), the water loss of a regular charger is 0.5 grams, while the Corinthian pulse is 0.23 grams. According to this calculation, a regular charger will dry up after 250 cycles, while the Colin pulse will only dry up after 600 cycles. Therefore, Colin pulses can extend the lifespan of batteries by more than twice. (Present the report of Chaowei Company and draw a curve chart.)

The biggest problem with lead-acid batteries during charging is gas evolution.

According to the study by American scientist J.A. Mas on the causes and patterns of gas evolution during the charging process of lead-acid batteries, in order to achieve the lowest gas evolution rate, the charging current curve that lead-acid batteries can accept is as follows:

The formula for the critical gas evolution curve is: I=I0e at% h ^ 2

During the charging process, the part of the charging current that exceeds the critical gas evolution curve can only cause the battery to undergo water electrolysis reaction, resulting in gas and temperature rise, and cannot increase the battery capacity

① During the constant current charging stage, the charging current remains constant, and the amount of charge increases rapidly, resulting in an increase in voltage;

② During the constant voltage charging stage, the charging voltage remains constant, and the amount of charge continues to increase, resulting in a decrease in charging current;

③ The battery is fully charged, and the current drops below the float charging conversion current, and the charging voltage drops to the float charging voltage;

④ During the float charging stage, the charging voltage is maintained at the float charging voltage;

The first stage of ordinary three-stage charging is constant current charging, which is mainly designed for the convenience of the circuit and not for the best performance of the battery.

In the later stage of constant current charging and the early stage of constant voltage charging (shaded area), the current exceeds the critical gas evolution curve, causing the battery to gas out and leading to a decrease in lifespan.

The current exceeding the critical gas evolution curve only produces gas and temperature rise in the battery, which is not converted into battery charge and therefore reduces charging efficiency.

(2) Analysis 2: Reasons for Sulfurization of Lead Acid Batteries

Long term retention of batteries, long-term overcharging and undercharging during the charging process, and high current discharge during use can easily cause battery vulcanization. Its appearance is that it will light up as soon as it is released and fill up as soon as it is charged, which we call "false damage" to the battery. Sulfide substances such as sulfates adhere to the electrode plate, reducing the reaction area between the electrolyte and the electrode plate, resulting in a rapid decline in battery capacity. Loss of water will increase the sulfurization of the battery; Sulfurization can also increase the water loss of the battery, easily forming a vicious cycle.

(3) Analysis ③: The imbalance problem of lead-acid batteries

A set of batteries consists of three to four. Due to manufacturing process issues, it is not possible to achieve absolute balance for each battery. Ordinary chargers use average current to allow small capacity batteries to be fully charged first and form overcharging. When discharging, this small capacity battery is discharged first and forms overcharging. In the long run, this vicious cycle leads to the entire set of batteries falling behind, resulting in the entire set of batteries being scrapped. The float charging stage of the three-stage charger has a small current of 500mA, which is used to compensate for charging and make the battery fully charged. But it also brings two side effects: 1. After being fully charged, the excess current is not turned off, and electrical energy is converted into heat energy for water decomposition, accelerating the emission of water; 2. Low current charging generates a large current fork, which is more likely to cause imbalance in the battery pack.

(4) Analysis ④: Thermal runaway problem of lead-acid batteries

Battery deformation is not sudden, often a process. When the battery is charged to about 80% of its capacity, it enters the high-voltage charging zone. At this time, oxygen is first precipitated on the positive electrode plate, which passes through the hole in the partition and reaches the negative electrode. Oxygen reactivation reaction is carried out on the negative electrode plate: 2Pb+O2 (oxygen)=2PbO+Q (heat); PbO+H2SO4=PbSO4+H2O+Q (heat). Heat is generated during the reaction. When the charging capacity reaches 90%, the rate of oxygen generation increases, and the negative electrode begins to produce hydrogen gas. The increase in a large amount of gas causes the internal pressure of the battery to exceed the valve pressure, the safety valve opens, and the gas escapes, ultimately resulting in water loss. 2H2O=2H2 ↑+O2 ↑. As the number of battery cycles increases, the moisture content gradually decreases, resulting in the following situations in the battery:

The oxygen channel becomes unobstructed, and the oxidation generated by the positive electrode can easily reach the negative electrode through the channel;

⑵ The heat capacity decreases. In a battery, water has the largest heat capacity. After the loss of water, the heat capacity of the battery greatly decreases, and the generated heat causes the temperature of the battery to rise quickly;

Due to the shrinkage of the ultra-fine glass fiber partition in the battery after dehydration, the adhesion between it and the positive and negative plates decreases, the internal resistance increases, and the heat generated during charging and discharging increases. After the above process, the heat generated inside the battery can only be dissipated through the battery compartment. If the heat dissipated is less than the heat generated, a temperature rise phenomenon occurs. As the temperature rises, the overpotential of battery gas evolution decreases, the amount of gas evolution increases, and a large amount of oxidation on the positive electrode reacts on the negative electrode surface through the "channel", emitting a large amount of heat, causing the temperature to rise rapidly and forming a vicious cycle, known as "thermal runaway".