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Cycle life directly affects the use time and quality of lithium-ion batteries. The better the cycle performance, the longer the battery life, not only will reduce the user's cost of use, but also, the longer cycle life means less resource consumption.

What are the factors that affect the cycle performance of lithium-ion batteries?

1. Types of materials

The choice of materials is the first factor affecting the performance of lithium-ion batteries, the selection of materials with poor cycle performance, the process is reasonable, and the production is perfect, the cycle of the battery cell must not be guaranteed; If you choose a better material, even if there are some problems with subsequent production, the cycle performance may not be too bad.

From a material point of view, the cycle performance of a full battery is determined by the cycle performance after the positive electrode is matched with the electrolyte, the cycle performance after the negative electrode is matched with the electrolyte, the poor one of the two, 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 process so that it can not continue to complete the lithium delithium. On the one hand, it may be due to the inability of the active substance and the corresponding electrolyte to generate a dense and uniform SEI film, resulting in premature side reactions between the active substance and the electrolyte, resulting in excessive consumption of the electrolyte and thus affecting the circulation. In the design of the cell, if one pole confirms the selection of materials with poor cycle performance, the other pole does not need to choose materials with good cycle performance.

2, positive and negative electrode compaction

Positive and negative electrode compaction is too high, although it can improve the energy density of the cell, but also to a certain extent reduce the recycling performance of the material, from the theoretical analysis, the greater the compaction, equivalent to 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 cell with higher positive and negative electrode compaction is difficult to ensure a higher liquid retention, and the liquid retention is the basis for the cell to complete a normal cycle or more cycles.

3. Excessive negative electrode

In addition to the need to consider the impact of the first irreversible capacity and coating film density deviation, the impact on cycle performance is also a consideration, for lithium cobalt oxide plus graphite system, negative graphite becomes the "short plate" side of the cycle process is more common, if the negative electrode excess is not enough, the cell may not be lithium before the cycle. However, after several hundred cycles, the positive structure changes little, but the negative structure is seriously damaged and cannot fully receive the lithium ions provided by the positive electrode to analyze lithium, resulting in premature capacity decline.

4. Amount of electrolyte

There are three main reasons for the insufficient amount of electrolyte to affect the circulation, one is that the amount of liquid injection is insufficient, the second is that although the amount of liquid injection is sufficient, the aging time is not enough or the immersion of the positive and negative electrodes is insufficient due to high compaction, and the third is that the electrolyte inside the circulation cell is consumed. Whether it is a cell with hundreds or even thousands of cycles or a cell with dozens of dives, if the electrolyte is sufficient before the cycle and the electrolyte has been consumed after the cycle, increasing the amount of electrolyte is likely to improve its cycle performance to a certain extent.

5, coating film density

It is almost impossible to consider the effect of film density on the cycle with a single variable. Inconsistent film density either leads to a difference in capacity, or a difference in the number of cell winding or lamination. For cells of the same model with the same capacity and material, reducing film density is equivalent to increasing the number of one or more layers of winding or lamination. The corresponding increase in the diaphragm can absorb more electrolyte to ensure circulation.

6. Moisture

Too much water will have side reactions with positive and negative active substances, destroy their structure and then affect the circulation, and too much water is not conducive to the formation of SEI film, but in the trace water is difficult to remove at the same time, trace water can also ensure the performance of the cell to a certain extent.

7. Objective conditions of the test

External factors such as charge and discharge rate, cutoff voltage, charging cutoff current, overcharge and overdischarge in the test, test room temperature, sudden interruption in the test process, contact resistance between the test point and the battery cell will more or less affect the cyclic performance test results. In addition, different materials have different sensitivity to the above objective factors. Unifying test standards and understanding the commonalities and characteristics of important materials should be sufficient for daily work.