August 3, 2021
1.The charging voltage is the external cause of the charging reaction.
The charging voltage Ech must be higher than the battery electromotive force Qch by a certain value in order for the charging reaction to continue.When setting the charging voltage, it should be considered that as the battery power increases, its electromotive force also continues to increase. Especially when charging under low temperature conditions in winter, the fluidity of the diluted sulfuric acid in the electrolyte becomes worse, the concentration polarization becomes more obvious, the battery voltage rises rapidly, and the charging speed becomes slower.
2.The dissolution of lead sulfate is the internal cause of the charging reaction. According to the "double sulfation" theory, after the battery is discharged, both the positive and negative electrodes generate lead sulfate. When charging, the lead sulfate in the positive and negative electrodes is transformed into lead dioxide and lead respectively following the "dissolution and precipitation" mechanism to form active materials. The above figure shows that the effective dissolution of lead sulfate is a necessary link for the positive and negative electrodes to be able to charge.Under low temperature conditions, the charging speed does not always increase with the increase of the charging voltage. Too high a charging voltage does not increase the charging speed, but will promote side reactions such as water decomposition, which will damage the battery life. The solubility of lead sulfate becomes lower under low temperature conditions, which may become the bottleneck of the entire charging reaction.
The above characteristics of lead-acid batteries determine that they should be charged at a higher temperature as much as possible in winter:
Take the lead-acid battery used in automobiles as an example. If the battery is arranged far away from the engine compartment, the battery is kept at a low temperature, such as below 0°C, and the result is often that it cannot be effectively charged.
Especially for EV applications, charging strategies should be designed more specifically to avoid wasting valuable high-voltage power and sacrificing cruising range.