Li-ion battery charging time and life span has been the bottleneck of electric vehicle use, traditional fast charging skills may shorten the cycle life of lithium-ion batteries, polarization voltage is the external manifestation of the effect of charging current in the battery internal electrochemical reactions. The polarization voltage during the charging process will shorten the life span of Li-ion batteries, and pulse charging is the optimal charging strategy to reduce the polarization voltage buildup. What is lithium battery pulse charging? What is the effect of pulse charging on lithium batteries?
According to incomplete statistics pulse charging is divided into: negative pulse, positive pulse, positive and negative pulse. Pulse charging can be used to charge with pulse current with adjustable amplitude and duty cycle. Positive pulse charging as shown in the figure below, charging a section, placing a section, and so on in a cycle. Adding placement to the charging process can eliminate ohmic polarization and electrochemical polarization to a certain extent, but the effect of eliminating dense polarization is limited.
In order to deal with this problem, the positive and negative pulse approach can be used, adding a discharge pulse after the positive pulse charging, using the discharge pulse and placement to enhance the depolarization effect.
What is the pulse charging of lithium batteries and what is the effect of pulse charging on lithium batteries
Pulse charging contains three primary stages: pre-charging, constant current charging and pulse charging. Compared with the conventional charging method, pulse charging can charge at a higher current, and the concentration polarization and ohmic polarization of the battery will be eliminated during the stop charging period, so that the next round of charging will proceed more smoothly, with fast charging speed, small changes in temperature, and little impact on battery life, thus it is now widely used. However, the drawback is obvious: a power supply with limited current capability is required, which increases the cost of the pulse charging approach.
Lithium battery in high-current pulse operation mode, more simply make the lithium salt LiPF6 in the electrolyte decomposed into LiF, the presence of LiF makes the battery's ion dispersion impedance and charge exchange impedance rapidly increased, making the battery in high-current charging, the battery polarization voltage rapidly increased, beyond the constraint voltage of lithium batteries, so that the battery can not finish charging.
Due to the simple polarization of NiCd battery during conventional charging, conventional constant voltage or constant current charging will cause the electrolyte to continue to generate hydrogen and oxygen gas, and its oxygen will penetrate to the negative electrode and cadmium plate effect to generate CdO under the effect of internal high pressure, forming the effective capacity of the pole plate decreases. Pulse charging generally uses the method of charging and discharging, i.e. charging for 5 seconds, then discharging for 1 second.
In this way the oxygen occurred in the charging process will be mostly reduced to electrolyte under the discharge pulse. Not only the amount of internal electrolyte vaporization is restrained, but also for those old batteries that have been severely polarized, they will gradually recover or approach the original capacity after 5-10 times of charging and discharging using this charging method. The width of charging and discharging pulses should be chosen to ensure the recovery of the original crystal structure of the electrode plate, and then eliminate the memory effect. After choosing the discharge depolarization method, the charging power can be improved and high current fast charging is promised.
Intelligent chargers can give different charging modes and corresponding algorithms for the characteristics of each kind of battery to achieve good charging effect. Rechargeable batteries have high performance to price ratio, high discharge current, long life and other characteristics, and are widely used in various communication equipment, instruments and meters, and electrical measuring equipment. But different types of batteries such as NiCd batteries, NiMH batteries and Li-ion batteries have different charging characteristics and processes.
Pulse is a type of current, which is different from simple DC, and the charging current is pulsating current; excellent intelligent chargers first charge the battery with constant current, and change to constant voltage when it is close to the end of charging. Charging ends automatically when the battery is full. This charging method can be charged more abundantly and is beneficial to the battery life extension.
Pulse charging uses pulsating current for charging current. Pulse charging can also be made into an intelligent type. Intelligent charging, not only can control the charging current, excellent intelligent chargers also have temperature monitoring, so you can not find intelligent pulse chargers, you can directly use intelligent chargers.
Pulse fast charging is the primary treatment is how to quickly reduce the polarization effect, so that the charging power is improved, and then reach the intention of a faster speed to reach a full charge, pulse charging method can be used to improve the charging speed without sacrificing the life of the lithium battery. In order to better confirm the amplitude and width of the pulse, progress in speed and power, the polarization characteristics of the lithium battery itself needs to have a better grasp, so as to plan a suitable charging strategy.
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