A New Choice for Balanced Lithium Battery Packs -Lithium - Ion Battery Equipment

A New Choice for Balanced Lithium Battery Packs -Lithium - Ion Battery Equipment

The poor consistency of lithium battery cells has plagued the design of lithium battery packs for a long time. The consistency we are talking about here not only refers to parameters such as capacity and voltage in the traditional sense, but also includes the capacity decay speed of single cells, Factors such as the decay rate of internal resistance and the temperature distribution of the battery pack. Ideally, lithium batteries from the same batch should have the same electrochemical performance, but in practice there are inconsistencies between lithium-ion cells due to errors in the manufacturing process. The battery pack is often composed of hundreds or even thousands of single cells in series and parallel, so the capacity of the battery pack is greatly affected by the inconsistency of the single cells (the inconsistency factors that have the greatest impact on the performance of the battery pack include coulombs). Inconsistency in efficiency, inconsistency in self-discharge rate, inconsistency in the increase of internal resistance, etc.), research shows that even if the cycle life of a single battery reaches more than 1000 times, the life of the battery pack may be less than 200 times after forming a battery pack.(Lithium - Ion Battery Equipment)

Therefore, balancing equipment is necessary for a battery pack composed of a large number of single cells. At present, the common balancing method on the market is to use electronic equipment to achieve voltage balance between single cells. Therefore, both technically Much the same. Recently, Alexander U.Sch et al. of the University of Stuttgart in Germany used Ni metal hydride batteries (NiMH) and Ni-Zn batteries to realize the electrochemical balance of the battery pack, which provides a new idea for the balance of the battery pack.

Due to the limitation of the working principle of lithium batteries, their ability to resist overcharge is very weak, and problems such as electrolyte decomposition and lithium precipitation may occur in the case of overcharge. In the case of NiMH battery overcharging, H2O in the electrolyte will decompose O2 and H2 in the positive and negative electrodes, and O2 and H2 can be recombined to form water under the use of catalysts, thus forming a complete cycle. At a small rate of C/3-C/10, the rate of gas emergence is almost the same as the rate of its recombination, so the NiMH battery has a very good anti-overcharge performance. Based on the above principles, AlexanderU.Sch used NiMH batteries and similar Ni-Zn batteries to balance lithium battery packs. When using this electrochemical equalization method, the traditional voltage monitoring and electronic equalization units can be omitted, which effectively reduces the complexity of battery pack management and improves the reliability of the battery pack.

AlexanderU.Sch selected LiFePO4 and Li4Ti5O12 materials as the experimental objects, because these two materials have a certain tolerance to overcharge, and the voltage will rise rapidly after complete delithiation. At this time, NiMH and Ni-Zn batteries are responsible for For the purpose of the current bypass, the excess current will flow into the NiMH and Ni-Zn batteries, thereby preventing the lithium battery from being overcharged.

Its working principle is shown in the figure below. The NiMH battery or Ni-Zn battery used for balancing is connected to the lithium battery in parallel. When a group of low-capacity batteries in series in the battery pack is fully charged, the voltage reaches the threshold value. At this time, the NiMH battery connected in parallel with it assumes the purpose of shunting, and all the current basically flows through the NiMH battery and no longer flows through the lithium battery, thereby preventing the lithium battery from being overcharged. The changes in the voltage and current of the Li-battery and NiMH during this process are shown in Figure b below, and in the case of perfect matching, the Li-battery current is shown as the red curve.

The following table is the information of the batteries used in the experiment. The LFP/graphite, LMO/LTO, LFP/LTO, Ni-Zn and NiMH batteries were mainly used in the experiment.

The figure below shows the capacity-voltage curves of several batteries used in the experiment. 2´NiZn means that two Ni-Zn batteries are connected in series. It can be seen that the maximum voltage of two Ni-Zn batteries in series is 3.95V. (I=150mA), just enough to be used on LFP/C batteries to prevent overcharging. A Ni-Zn battery can be connected in parallel with an LFP/LTO battery to prevent overcharging of the battery, or two NiMH batteries can be connected in series with LMO/LTO, the maximum voltage will reach more than 3V, while the maximum voltage of the LMO/LTO battery is 2.8 V is about V, but as long as the LMO/LTO battery voltage does not exceed 3.2V, it is acceptable, and the new capacity of the LMO/LTO battery from 2.8-3.2V is only 0.65Ah.



Contact Us

24 hours online service