Factors affecting the cycling performance of lithium batteries

It goes without saying how important recycling performance is for lithium-ion batteries. In addition, at the macro level, longer cycle life means less resource consumption. Therefore, the factors that affect the cycle performance of lithium ion battery are the problems that every person related to the lithium battery industry has to consider. The following Wenwu listed a few may affect the battery cycle performance factors, for your reference.

Material type: material selection is the first factor that affects the performance of lithium ion batteries. Choose the material with poor cycle performance, the process is again reasonable, make again perfect, the cycle of the cell also cannot guarantee necessarily; Even if there are some problems in the subsequent production, the cycling performance may not be too bad (the lithium cobalt oxide gram plays only about 135.5mah /g at a time, and the lithium cell is analyzed. Although 1C dives for more than 100 times, it is 0.5c and over 90% for 500 times. The negative electrode has black graphite particles after a battery is disassembled, the circulation performance is normal. From the perspective of materials, the cycling performance of an entire battery is determined by the cycling performance of the anode matched with the electrolyte or the cycling performance of the anode matched with the electrolyte. Material cycle performance is poorer, on the one hand, is likely to be in circulation in the process of crystal structure change too fast to continue to complete the intercalated lithium, on the one hand may be due to the active substance and its corresponding electrolyte can't generate dense and uniform SEI film active material and electrolyte premature side reaction and make the electrolyte excessive consumption will affect cycle. In cell design, if one pole is confirmed to choose materials with poor cycling performance, the other pole does not need to choose materials with better cycling performance, which is a waste.

Positive and negative electrode compaction: the positive and negative electrode compaction is too high. Although it can improve the energy density of the cell, it will also reduce the cyclic performance of the material to a certain extent. From the theoretical analysis, the greater the compaction, the greater the damage to the structure of the material, and the structure of the material is to ensure that the lithium ion battery can be recycled basis; In addition, the cells with higher positive and negative electrode compaction cannot guarantee a higher liquid retention, which is the basis for the cells to complete the normal cycle or more cycles.

Moisture: excess moisture will have side effects with positive and negative active substances, damage its structure and affect circulation, and excess moisture is not conducive to the formation of SEI film. But it is difficult to remove trace water at the same time, trace water can also guarantee the performance of the cell to a certain extent. Unfortunately, Wenwu's personal experience in this field is almost zero, and he can't say much. If you are interested, you can search BBS for some information about this topic.

Coating film density: considering the impact of a single variable of film density on circulation is almost an impossible task. The inconsistency in film density results in either a difference in capacity or in the number of coils or laminates. For the same type of cell with the same capacity and material, reducing the film density is equivalent to increasing the number of one or more layers of winding or lamination layer, corresponding to the increased membrane can absorb more electrolyte to ensure circulation. Considering more thin film density can increase rate performance of the batteries, the pole piece and naked batteries baked in addition to the water will be easier, too, of course, when the density of thin film coating of error may be more difficult to control, active substances in the larger particles may also cause negative effect to coating, rolling, more layer means more foil and diaphragm, which means higher costs and lower energy density. Therefore, the assessment also needs to be balanced.

Negative overdose: the causes of negative overdose in addition to the need to consider the impact of the first irreversible capacity and coating film density deviation, the impact of cyclic performance is also a consideration. For the lithium cobalt ate-graphite system, it is common for negative graphite to be the "short plate" in the circulation process. If the negative electrode is excessive and insufficient, the cell may not analyze lithium before the cycle, but after several hundred cycles, the positive electrode structure changes a little, but the negative electrode structure is damaged seriously and cannot fully receive the lithium ions provided by the positive electrode, thus lithium can be analyzed, resulting in premature capacity decline.

Electrolyte quantity: there are three main reasons for the influence of insufficient electrolyte quantity on the circulation. One is insufficient liquid injection; the other is insufficient immersion due to insufficient liquid injection quantity but insufficient aging time or high compaction of positive and negative electrodes; the third is that the electrolyte inside the circulating cell is consumed. Insufficient liquid injection and insufficient liquid retention wenwu previously wrote "the influence of electrolyte loss on cell performance", so it is unnecessary to elaborate. For the third point, the microscopic match between the positive and negative electrodes, especially the negative electrode and the electrolyte is characterized by the formation of a dense and stable SEI, while the visible one in the right eye is the consumption rate of the electrolyte during the circulation process. On the one hand, the incomplete SEI film cannot effectively prevent the negative electrode from reacting with the electrolyte, thus consuming the electrolyte; on the other hand, the SEI film will regenerate the SEI film in the defective part along with the circulation, thus consuming the reversible lithium source and electrolyte. Whether for a cell with hundreds or even thousands of cycles, or for a cell with dozens of dives, if the electrolyte before the cycle is sufficient and the electrolyte after the cycle has been consumed, it is likely to increase the amount of the electrolyte to improve its cycle performance to some extent.

Objective conditions of the test: external factors such as charge and discharge ratio, cut-off voltage, cut-off current, over-charge and over-discharge in the test, temperature in the test room, sudden interruption in the test process, contact resistance between the test point and the cell, etc., will more or less affect the test result of cyclic performance. In addition, different materials have different degrees of sensitivity to the above objective factors, so it should be sufficient for daily work to unify testing standards and understand the commonality and characteristics of important materials.

Summary: just like the principle of wooden barrel, among the many factors affecting the cycle performance of the cell, the final decisive factor is the shortest board among them. At the same time, these influencing factors are also interactive. In the same material and manufacturing capacity, the higher the cycle, often means the lower the energy density, to find just meet the customer needs of the junction, try to ensure the consistency of the cell made, is the most important task.

The page contains the contents of the machine translation.