In order to maximize the speed of the chemical reaction of the battery,shorten the time for the battery to reach a fully charged state, and at the same time ensure that the polarization of the positive and negative plates of the battery is minimized or lightened. Fast charging technology has been rapidly developed in recent years. Several popular fast charging methods are designed around the optimal charging curve, and the purpose is to make the charging curve as close to the optimal charging curve as possible. The conventional charging method adopts the low-current slow charging method. The initial charging of the new battery requires more than 70H, and the ordinary charging also requires more than 10H. If the charging time is too long, it will not only prolong the charging detection time and cause a waste of electric energy, but also limit the cycle times of the battery and increase the maintenance workload. The fast charging method can shorten the charging time of the battery, improve the charging rate, save energy, and increase the number of battery cycles, which has great practical significance.
(1) Battery Fast Charging TechnologyIn the mid-1960s, American scientist Maas did a lot of research on the gas evolution of the battery charging process and proposed an acceptable charging current curve for the battery on the premise of the minimum gas evolution rate. In the charging process, only the charging current is required, so the charging time is greatly prolonged. In the later stage of charging, the charging current is greater than the acceptable current of the battery, so a large number of air bubbles are generated in the battery. However, if the actual charging current can always be equal to or close to the acceptable charging current of the battery during the entire charging process, the charging speed can be greatly accelerated, and the gassing rate can be controlled within a very low range. This is the basic rationale for fast charging. However, during the charging process, the polarization voltage generated in the battery will hinder its own charging and significantly increase the gassing rate and temperature rise. Therefore, the polarization voltage is an important factor affecting the charging speed. In order to achieve fast charging, we must try to eliminate the influence of polarization voltage on battery charging. From the formation mechanism of the polarization voltage, it can be inferred that the magnitude of the polarization voltage changes with the change of the charging current. When charging is stopped, the resistive polarization disappears, and the concentration polarization of a discharge channel and electrochemical scheme gradually weakens. If a discharge path is provided for the battery to discharge in reverse, concentration polarization and electrochemistry will quickly disappear, and the temperature in the battery will decrease due to discharge. Therefore, when charging is suspended during the charging process of the battery, and a discharge pulse is appropriately added, various polarization voltages can be quickly and effectively eliminated, thereby increasing the charging speed. At present, the fast charging method that everyone agrees with is pulse charging and pulse discharge depolarization method.
(2) Ways To Realize Fast Charging Technology
- Improve the battery design and reduce the ohmic internal resistance. If the battery uses a copper wire mesh negative grid, the grid resistance will be significantly reduced. This is not only beneficial to improve the utilization rate of active materials and the specific power of the battery but also can improve the fast charging performance of the battery.
- Improve the occurrence time of reactive ion diffusion current, that is, prolong the time for the battery voltage to reach the gassing voltage, thereby allowing to increase the charging current, reducingthe thickness of the electrode plate, increasingthe porosity of the active material, and increase the contact area of the grid active material.
- Reform the charging method of the battery. The theory of the pulse fast charging method is basically to superimpose a certain frequency, a high degree of negative pulse or a short-term charging stop in the charging current so that the lead ions participating in the reaction can be generated in time to increase its concentration, and the generated hydrogen ions and sulfate radicals.
- The effect of fast charging on battery life. The impact of high current fast charging on the life of the battery is still under discussion. There are also different views in the industry.