What factors affect the service life of lithium batteries?
In the RV power system, there is a very important module part, that is, the lithium battery, which involves the charge-storage-discharge link in the entire power system, and as a RV power storage device, it is often necessary to install multiple batteries on the RV. Therefore, the service life of lithium batteries has become a topic of close concern.
So, what factors affect the service life of lithium batteries?
The service life of lithium batteries is mainly affected by two aspects, one is the external use conditions, and the other is the factors of the internal batteries.
From the perspective of external use conditions, the factors that affect the service life of lithium batteries mainly include charge and discharge methods, charge and discharge cut-off voltage, charge and discharge rate, service temperature and storage conditions.
From the perspective of internal battery factors, the use of lithium batteries on RVs is often in the form of battery packs. Battery packs generally connect hundreds of battery cells in series and parallel. The consistency of the cells is another important factor that affects the service life. factor. The main performance is the inconsistency of parameters such as voltage, capacity, and internal resistance.
The influence of battery external use conditions on the service life of lithium batteries
Charge and discharge method: At present, the research on charging methods of lithium batteries is mostly carried out based on Maas theory, that is, to make the charging current as close as possible to the "best charging curve" of Maas theory, without causing damage to the battery. Some researchers made a comprehensive comparison of several common charging methods and found that constant current and constant voltage charging and step constant current charging overcome the shortcomings of constant current charging and constant voltage charging. This charging method has the least damage to the battery and can widely used.
Charge and discharge rate, charge and discharge cut-off voltage: Under different charge and discharge rates, after the lithium battery cycles for the same time, the capacity decay loss rate of the lithium battery is different. After changing the charge-discharge cut-off voltage, it was found through testing that the structure of the electrode material also changed. The change in the structure of the positive electrode material and the thickening of the negative electrode surface film will lead to the reduction of the number of lithium ions and the blockage of the diffusion channel, which will cause the battery capacity to decay.
Operating temperature: Different lithium batteries have different optimal operating temperatures, too high or too low temperature will affect the service life of the battery. Studies have shown that the capacity decay of the cycled battery is relatively slow at room temperature, but the battery exhibits rapid failure behavior under high temperature conditions of 55°C and 65°C. When the temperature is lower than -10°C, the capacity of the battery will decline sharply, and at the same time, the performance of the lithium battery will also deteriorate at low temperatures, which is related to the decrease in the ionic conductivity of the electrolyte and the electrode material.
Shelving conditions: When lithium batteries are left unused, self-discharge, passivation of positive and negative electrode materials, and decomposition of electrolytes will occur due to the nature of the battery itself. However, the unstable SEI performance of the negative electrode will lead to the rapid decline of the negative electrode active material, and the precipitation of lithium metal is easy to occur. At the same time, different electrolyte components have different effects on the decline of the electrode material.
The influence of the inconsistency of internal battery cells on the service life of lithium batteries
The inconsistency of the monomer is mainly manifested in the inconsistency of parameters such as voltage, capacity, and internal resistance. If inconsistent single cells are used in series, the life of the battery pack will always be shorter than that of the shortest single cell. Similar to the "barrel principle", the life of the battery pack is determined by the single battery with the shortest life. It is very likely that the single battery with the shortest life is the battery with a small capacity. Small-capacity batteries are fully charged every time, and the output is too strong. It is very likely that the battery will reach the end of its life first. When the life of a single battery ends, a group of battery packs welded together will also die.