Now you know the influencing factors of the cycle performance of lithium electronic batteries! Let's take a look at the factors affecting the cycle performance of lithium electronic batteries! Needless to say, the importance of cycle performance to lithium-ion batteries is a macro point of view, which means longer cycle life. With less resource consumption, the factors that affect the cycle performance of lithium-ion batteries are issues that everyone involved in the lithium battery industry has to consider.
1. Compaction of positive and negative poles
The positive and negative electrode compaction is too high, although it can increase the energy density of the cell, it will also reduce the cycle performance of the material to a certain extent. From the theoretical analysis, the greater the compaction, the greater the structural damage to the material. The structure of the material is the basis to ensure that lithium-ion batteries can be recycled; in addition, batteries with higher positive and negative electrode compaction are difficult to ensure a higher liquid retention capacity, and the retention capacity is the battery that completes the normal cycle or more times. The basis of the cycle.
2. Moisture
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. However, while trace amounts of moisture are difficult to remove, trace amounts of water also The performance of the battery can be guaranteed to a certain extent.
3. Coating film density
It is almost impossible to consider the influence of film density on the cycle of a single variable. Inconsistent film density will bring about a difference in capacity, or a difference in the number of layers of battery core windings or laminated layers. For the same model, the same capacity, and the same material, For batteries, 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 film density can increase the battery core It will be easier to remove water from the baking of pole pieces and bare cells. Of course, the error of coating with too thin film density may be more difficult to control, and large particles in the active material may also affect the coating and rolling Pressure has a negative impact. More layers means more foils and diaphragms, which in turn means higher costs and lower energy density. Therefore, a balanced consideration is also required in the evaluation.
4. The objective conditions of the test
During the test, the charge and discharge rate, cut-off voltage, charge cut-off current, overcharge and overdischarge during the test, temperature of the test room, sudden interruption during the test, contact internal resistance between the test point and the battery, and other external factors, will be more or less It may 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.
5. Excessive negative electrode
In addition to the influence of the first irreversible capacity and the density deviation of the coating film, the reason for the excess of the negative electrode is also a consideration for the cycle performance. For the lithium cobaltate plus graphite system, the negative electrode graphite becomes the "short board" in the cycle process. "One side is more common. If the negative electrode is excessively insufficient, the battery cell may not release lithium before cycling, but the positive electrode structure changes little after hundreds of cycles, but the negative electrode structure is severely damaged and cannot fully receive the lithium ions provided by the positive electrode. Lithium causes the capacity to drop prematurely.
6. The amount of electrolyte
There are three main reasons for the insufficient amount of electrolyte to affect the circulation. One is insufficient injection volume; the other is insufficient aging time although the injection volume is sufficient, or insufficient immersion of the positive and negative electrodes due to high compaction, and the third is With the circulation of the internal electrolyte of the battery cell is consumed. 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. To improve its cycle performance.
7. Types of materials
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 cell will inevitably not be guaranteed; a better material is selected, even if it is followed There are some problems, and 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 cycle after the negative electrode and the electrolyte are matched. The performance of the two 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 and cannot continue to complete the lithium insertion and removal. On the other hand, it may be due to the activity Substances and corresponding electrolytes cannot form a dense and uniform SEI film, causing premature side reactions between the active material and the electrolyte, causing the electrolyte to be consumed too quickly and affecting 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.