Reasons for the short life of the battery pack

Electric bicycles are popular with users for their lightness, environmental protection, economy and practicality, and have developed rapidly in recent years. According to relevant statistics, domestic production reached 20 million vehicles in 2006, and domestic inventory was about 50 million vehicles. The market is vast and the development prospects are very broad. However, in actual use, the life of the battery pack is short and the mileage is rapidly reduced. Its statistical average life expectancy is only about one year, far from reaching its rated life. This is a long-standing problem in the use of electric vehicles. At present, the technology development and manufacturing of the four major electrical components of electric vehicles-motors, batteries, controllers and chargers are relatively mature. Therefore, the short life of the battery pack has become the most prominent problem in the use of electric vehicles, which not only affects in the long run, but also affects and limits the further development and application of electric vehicles to a certain extent.

The analysis of battery performance degradation and damage under various conditions shows that the main reasons for failure (such as powder removal, water loss, plate bending, plate rupture and plate short circuit) are the main reasons for overcharging and overdischarging. At the end of charging, the polarization voltage of the battery increases, the water electrolysis phenomenon will produce bubbles, the internal loss will increase, the temperature rise will increase, and overcharging will damage the battery; at the end of the discharge, the effective chemical reaction will be exhausted, and the internal micro The hole will be blocked and the internal resistance of the battery will increase. Over-discharge at this time will also damage the battery. Therefore, overcharging and overdischarging should be avoided as much as possible.

Electric bicycles use battery packs connected in series, which must be charged and discharged frequently during use. Due to differences in materials and manufacturing processes, there will inevitably be differences in capacity and performance between battery packs during use, that is, battery imbalance. . When charging, the battery with small capacity and poor performance will overcharge; when discharging, the battery with small capacity and poor performance will overdischarge. Continuous overcharging and overdischarging make the capacity of the bad battery become smaller and smaller, and the performance becomes worse and worse. This frequent vicious cycle process will accelerate the damage of the bad battery, thereby degrading the performance of the entire battery pack, thereby affecting the battery pack. The main reason for the service life. In the practice of battery pack maintenance and replacement, in most cases, the damage of the battery pack is actually only one battery (a very few two) is damaged, which also proves that the above analysis is correct.

  No matter how accurately the battery pack is assembled at the factory, the imbalance between the batteries is absolute during use and will definitely occur. Poor overcharging and overdischarging of batteries caused by imbalance is a vicious circle. Accelerate the damage, thereby greatly reducing the available capacity of the entire battery pack, which is the main reason that affects the life of the battery pack. Therefore, how to technically solve the problem of imbalance between batteries and perform real-time online balance adjustment during battery use to achieve the purpose of balance, so as to effectively prevent overcharge and overdischarge, is the key to solving the problem of battery short circuit. Clean up life.