Lithium battery manufacturers explain the 7 factors that affect the cycle performance of lithium-ion batteries

Lithium battery manufacturers believe that the importance of cycle performance to lithium-ion batteries needless to say. Macroscopically speaking, longer service life means less resource consumption. Therefore, all lithium-ion battery cycle performance factors are in the industry. The focus that practitioners have to pay attention to. Next, lithium battery manufacturers briefly explain the seven major factors that affect the cycle life of lithium batteries. 1. Excessive moisture will cause side reactions with the positive and negative active materials, destroy its structure and affect the cycle. At the same time, too much moisture is not conducive to the formation of SEI film, but it is difficult to remove trace amounts of moisture at the same time. The water can also guarantee the performance of the battery to a certain extent. 2. Positive and negative electrode compaction The positive and negative electrode compaction is too high, although it can increase the energy density of the cell, but it will also reduce the cycle performance of the material to a certain extent. From the theoretical analysis, the greater the compaction, the equivalent to the material The greater the damage of the structure, and the structure of the material is the basis to ensure that the lithium-ion battery can be recycled; in addition, it is difficult to ensure a higher liquid retention capacity for batteries with higher positive and negative electrode compaction, and the liquid retention capacity is completed by the battery cell. The basis of a normal cycle or more cycles. 3. Objective conditions of the test Charge and discharge rate, cut-off voltage, charge cut-off current during the test, overcharge and overdischarge during the test, temperature of the test room, sudden interruption during the test, contact resistance between the test point and the battery cell, etc. External factors will more or less affect the cycle performance test results. In addition, different materials have different sensitivity to the above objective factors. A unified test standard and an understanding of common and important material characteristics should be enough for daily work. 4. Excessive negative electrode In addition to the influence of the first irreversible capacity and the deviation of the coating film density, the reason for the excessive negative electrode is also the influence on the cycle performance. For the lithium cobaltate plus graphite system, the negative electrode graphite becomes the cycle process. The short board is more common. If the negative electrode is excessively insufficient, the battery cell may not release lithium before the cycle, but the positive electrode structure changes little after hundreds of cycles, but the negative electrode structure is seriously damaged and cannot fully receive the lithium ions provided by the positive electrode. As a result, lithium is precipitated and the capacity drops prematurely. 5. It is almost impossible to consider the impact of the film density on the cycle of the single variable of the coating film density. Inconsistent film density will bring about the difference in capacity or the difference in the number of battery core windings or laminated layers. For batteries of the same model and capacity and material, reducing the film density is equivalent to increasing the number of one or more layers of winding or lamination. The correspondingly increased diaphragm can absorb more electrolyte to ensure circulation. Considering the thinner The film density can increase the rate performance of the cell, and the baking of the pole piece and the bare cell will be easier to remove water. Of course, the error of the film density when the film is too thin may be more difficult to control, and the large particles in the active material may also be It will have a negative impact on coating and rolling. More layers means more foils and diaphragms, which in turn means higher costs and lower energy densities. Therefore, balanced considerations are also required in the evaluation. 6. Material type The choice of material is the first element that affects the performance of lithium-ion batteries. If a material with poor cycle performance is selected, no matter how reasonable the process is, and no matter how perfect it is made, the cycle of the battery will inevitably not be guaranteed; choose a better one. The material, even if there are some problems in the subsequent production, the cycle performance may not be too bad. From the material point of view, the cycle performance of a full battery is determined by the cycle performance of the positive electrode and the electrolyte, and the negative electrode and the electrolyte. The cycle performance after matching is determined by the poorer one. The cycle performance of the material is poor. On the one hand, it may be that the crystal structure changes too fast during the cycle to continue the lithium insertion and removal. On the other hand, It may be due to the fact that the active material and the corresponding electrolyte cannot form a dense and uniform SEI film, which causes the active material and the electrolyte to have a side reaction prematurely, which causes the electrolyte to be consumed too quickly and affects the circulation. When designing the battery cell, if one pole is confirmed to choose a material with poor cycle performance, the other pole does not need to choose a material with better cycle performance, which is wasteful. 7. Electrolyte amount Insufficient amount of electrolyte affects the cycle mainly due to three reasons, one is insufficient injection volume, second, although the injection volume is sufficient but the aging time is not enough, or the positive and negative electrodes are immersed due to high compaction, etc. Insufficient, the third is that the electrolyte inside the cell is consumed with the circulation. The third point is that the microscopic performance of the matching between the positive and negative electrodes, especially the negative electrode, and the electrolyte is the formation of dense and stable SEI, while the performance visible to the right eye is the consumption rate of the electrolyte during the cycle, and the incomplete SEI On the one hand, the membrane cannot effectively prevent side reactions between the negative electrode and the electrolyte to consume the electrolyte. On the other hand, the defective part of the SEI membrane will regenerate the SEI membrane as the cycle progresses, thereby consuming the reversible lithium source and the electrolyte. Whether it is for batteries that are cycled hundreds or even thousands of times or for batteries that have dived dozens of times, if the electrolyte is sufficient before the cycle and the electrolyte has been consumed after the cycle, it is likely to increase the amount of electrolyte retention. 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