List the factors that affect the cycle performance of lithium batteries

Factors affecting the cycle performance of lithium batteries Many cycle performance is self-evident to the importance of lithium batteries; in addition, from a macro point of view, a longer life cycle means less resource consumption. Therefore, the factors that affect the cycle performance of lithium batteries are issues that every practitioner in the lithium battery industry must consider. The following article lists several factors that may affect battery cycle performance for your reference. Material type: Material selection is the primary factor affecting the performance of lithium batteries. Choose a material with poor cycle performance, the process is reasonable and complete, and the cycle of the battery cannot be guaranteed; if you choose a better material, even if some problems are subsequently created, the cycle performance may not be too bad or too outrageous (one gram of lithium cobalt acid) It can only play about 135.5mah/g, and although the 1C is more than 100 dives, the lithium battery is 0.5c, 500 times more than 90%; after the battery is disassembled, the cycle performance of the battery with black graphite particles on the negative electrode is normal. From the material point of view, The cycle performance of the full battery is determined by the poorer of the cycle performance of the positive electrode and the electrolyte and the cycle performance of the negative electrode and the electrolyte. The material cycle performance is poor. On the one hand, it may be crystals in the circulation process. The structural change is too fast to continue to complete the lithium insertion. On the one hand, it may be due to the fact that the active material and its corresponding electrolyte cannot have a dense and uniform SEI membrane active material and electrolyte premature side reactions, so that the excessive consumption of the electrolyte will affect the cycle. In the battery design, if one pole confirms that a material with poor cycle performance is selected, the other pole should not choose a material with better cycle performance, which is wasted. Positive and negative electrode compaction: The positive and negative electrode compaction is too high, although it can improve the battery Energy density, but it will also reduce the cycle performance of the material to a certain extent. From the theoretical analysis, the greater the degree of compaction, the greater the damage to the material structure, and the material structure is the basis for ensuring the recycling of lithium batteries; In addition, it is difficult for cells with higher positive and negative densities to ensure higher liquid retention, which is the basis for the cells to complete one or more normal cycles. Water: Excessive water will react with the active materials in the positive and negative electrodes. It destroys its structure and affects circulation. At the same time, too much water is not conducive to the formation of SEI film. However, although trace water is difficult to remove, trace water can also ensure the performance of cells to a certain extent. Unfortunately, Wenwu himself is here The relevant experience in this area is almost zero and can’t be said too much. If you are interested, you can search for information on this topic in the forum. Film density: It is almost impossible to consider the effect of film density on univariate cycles. Task. The inconsistency of the film density will lead to the difference in capacity or the difference in the number of winding or layering layers. For batteries of the same type, capacity and material, reducing the film density is equivalent to adding one or more winding layers or stacks The number of layers, the new membrane can absorb more electrolyte to ensure circulation. Considering more film density can improve the performance of the battery, it will be easier to remove water from the battery pole pieces and bare bake, of course, when the film is coated Density errors may be more difficult to control, active substances in larger particles may also cause negative effects on the coating, rolling, more layers means more foils and diaphragms, which means higher costs and lower energy density Therefore, the evaluation should be balanced. Excess negative electrode: The reason for excess negative electrode is not only the influence of the first irreversible capacity and the deviation of the coating density, but also the cycle performance. Regarding the cobalt-graphite lithium system, the negative electrode graphite often becomes short during the cycle Plate. If the negative electrode is too much and not enough, the battery may not be able to get rid of lithium before cycling, but the positive electrode structure does not change much after hundreds of cycles. However, the negative electrode structure is destroyed , Unable to fully receive the lithium ions supplied by the positive electrode, resulting in premature decrease in capacity. Electrolyte dosage: There are three reasons for the influence of insufficient electrolyte dosage on circulation. One is insufficient injection volume; second, insufficient injection volume leads to insufficient aging time; third, excessive compaction of positive and negative electrodes causes insufficient immersion; third, consumption of electrolyte in the circulating battery. Wenwu wrote about the impact of missing electrolyte on battery performance before, so it will not be repeated. The third point is that the microscopic performance of the compatibility of the positive electrode and the negative electrode, especially the negative electrode and the electrolyte, is the formation of dense and stable SEI, while the performance visible to the right eye is not only the consumption rate of the electrolyte during the cycle. On the one hand, the incomplete SEI film cannot effectively prevent side reactions between the negative electrode and the electrolyte, thereby consuming the electrolyte; on the other hand, the defective part of the SEI film will regenerate the SEI film as the cycle progresses, consuming the reversible lithium source and electrolyte. . Regardless of the hundreds or thousands of cell cycles and cell diving, if the previous electrolyte is fully circulated and the electrolyte is consumed after the cycle, the number of new electrolyte holdings may improve its cycle performance to a certain extent. Test of objective conditions: charge and discharge rate, cut-off voltage, charge current limit, overcharge and charge test, temperature test room, sudden interruption during the test, internal resistance test point and cell contact and other external factors More or less will affect the test results of the cycle performance. In addition, different materials have different sensitivities to the above objective factors. Therefore, it is necessary to unify test standards and know the characteristics of commonly used and important materials in daily work. Conclusion: Just like the wooden barrel principle, among many factors, the final determining factor is the shortest board. At the same time, these influencing factors also have interactive uses. With the same material and production capacity, the higher the cycle, the lower the energy density. Finding what can just meet the needs of customers and ensuring the consistency of the core as much as possible is the most important task. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: Brief analysis of 18650 lithium battery charging and discharging knowledge