Lithium battery is a new battery approved by the public in recent years that can extend battery life, but will appear after multiple charge and discharge cycles Phenomenon that the performance of the battery capacity and so on is degraded. Under the same conditions, the faster the battery capacity decays, the worse the battery quality. The cycle performance of the lithium battery pack is an important indicator to measure its quality. Many standards on lithium battery packs have a cycle life item.

　The cycle process of charging and discharging the lithium battery pack is a complex physical and chemical reaction process, and its cycle life affecting factors are various. The following will analyze the factors that affect the cycle life of the lithium battery pack.

　In the battery design process, the choice of materials is the most important factor. Different materials have different performance characteristics, and the performance of the developed batteries also has gaps. The cycle performance of the positive and negative electrode materials is good, and the cycle life of the battery will be long. In general, the design and assembly process generally requires that the capacity of the negative electrode is more than that of the positive electrode. If it is not excessive, the negative electrode will precipitate lithium during the charging process, forming lithium dendrites and affecting safety. The negative electrode has too much excess relative to the positive electrode, and the positive electrode may be excessively delithiated, causing the structure to collapse.

　The type of electrolyte and the amount of liquid injection also affect the battery life. The manufacturing process flow of the lithium battery pack mainly includes: positive and negative electrode ingredients, coating, tableting, winding, shell insertion, liquid injection, sealing, chemical formation, etc. In the battery production process, the requirements for each step of the process are very strict. If any process is not well controlled, it may affect the battery cycle performance.

　The process of the charge and discharge cycle of the lithium battery pack is a process in which lithium ions are deintercalated and moved between positive and negative materials through the electrolyte. During the cycle of the lithium battery pack, in addition to the redox reactions at the positive and negative electrodes, there are also a large number of side reactions. If the side reaction of the lithium ion battery can be reduced to a low level, so that lithium ions can always smoothly travel between the positive and negative electrode materials through the electrolyte, the cycle life of the lithium ion battery can be increased.

　　The nature of the positive and negative current collectors will also affect the battery capacity and cycle life. The current collector materials commonly used for positive and negative electrodes of lithium battery packs are aluminum and copper, both of which are easily corroded metal materials. After the current collector is corroded, the formation of a passive film, poor adhesion, local corrosion (pitting corrosion) and overall corrosion will increase the internal resistance of the battery, resulting in capacity loss and reduced discharge efficiency. The adhesion and corrosion resistance can be enhanced by acid-alkali etching, conductive coating and other pretreatment methods.

　The use process of the lithium battery pack is the process of the charge and discharge cycle, the size of the charge and discharge current, the selection of the charge and discharge cut-off voltage, and the charge and discharge system used, which also has a very important impact on the cycle life of the lithium ion battery. Any blindly increasing the battery's operating current, increasing the charge cut-off voltage, and reducing the discharge cut-off voltage will reduce the performance of the lithium battery pack.

　　Lithium-ion batteries with different electrochemical systems have different charge-discharge cut-off voltages. During the charging process of a lithium ion battery, it is considered that overcharging has occurred when the charging cut-off voltage is exceeded. When a lithium-ion battery is overcharged, excess lithium ions that are released from the positive electrode will be deposited or inserted into the negative electrode. The deposited active lithium easily reacts with the solvent and releases heat to increase the battery temperature. When the discharge voltage of the lithium battery is lower than the discharge cut-off voltage, overdischarge is formed.

　During the over-discharge process, lithium ions will be excessively extracted from the negative electrode, and it will be more difficult to re-insert it during the next charge. The discharge capacity and charge-discharge efficiency of lithium batteries are greatly reduced during the cycle after overdischarge. In addition, lithium batteries are likely to blow under high current conditions, and equipment components may also be damaged.

　The impact of the use environment of the lithium battery pack on its cycle life is also very important. Among them, the ambient temperature is a very important factor. Ambient temperature is too low or too high will affect the cycle life of lithium batteries.

The working temperature of the conventional lithium battery: -20 ℃ ~ 60 ℃, but generally the performance of the lithium battery will drop after 0 ℃, and the discharge capacity will be reduced accordingly. Therefore, the full operating temperature of the lithium battery performance is usually 0 ~ 40 ℃ . The temperature of lithium batteries required by some special environments is different. In addition, pay attention to good ventilation, which is conducive to heat dissipation and keeps the environment clean.

　The charge-discharge cycle of a lithium-ion battery is unstable at high temperatures. The high temperature causes the electrochemical polarization of the electrodes of the battery to increase and the generation of gas, causing bulging. At the same time, the charge transfer resistance increases and the ion transfer dynamics performance decreases. At low temperature, the constant voltage charging time increases, and the charging performance also deteriorates significantly. Devices using lithium-ion batteries may withstand the test of vibration, shock, collision and other conditions during transportation or normal operation. Some lithium batteries charge and discharge when communicating with the system and receive data information according to a certain frequency.

　There are many factors that affect the cycle life of lithium battery packs. The application of lithium-ion batteries is becoming more and more extensive, and the demand for lithium batteries puts forward higher requirements in terms of quantity and quality. The cycle life directly affects the use time and quality of lithium batteries, so it is necessary for manufacturers to study their influencing factors.