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Several factors affecting the cycle performance of lithium ion batteries

Editor:ESTL Category:Technical information Release time:2019-08-19 Click volume:713

There is no need to talk about the importance of cycle performance for lithium-ion batteries; in addition, macroscopically, longer cycle life means less resource consumption. Therefore, the factors affecting the cycle performance of lithium-ion batteries are issues that every person involved in the lithium battery industry has to consider. Here are a few factors that may affect battery cycling performance for your reference.

1. Type of material:

The choice of materials is the first factor affecting the performance of lithium-ion batteries. The material with poor cycle performance is selected, the process is reasonable, and the process is perfected. The cycle of the battery core is inevitably impossible to guarantee; the better material is selected, and even if there are some problems in subsequent fabrication, the cycle performance may not be bad. Too ridiculous (one lithium cobaltate gram is only 135.5mAh / g and lithium battery, 1C although more than 100 times diving but 0.5C, 500 times more than 90%; after the core is disassembled, the negative electrode has black graphite particles The battery has a good cycle performance). From the material point of view, the cycle performance of a full battery is determined by the poor performance of the cycle performance after the positive electrode is matched with the electrolyte and the cycle performance after the negative electrode and the electrolyte are matched. The cycle performance of the material is poor. On the one hand, the crystal structure changes too fast during the cycle, so that lithium insertion can not be completed. On the one hand, the active substance and the corresponding electrolyte cannot form a dense and uniform SEI film to cause active substances. A side reaction occurs prematurely with the electrolyte to cause the electrolyte to be consumed too quickly to affect the cycle.

2. Positive and negative compaction:

The positive and negative compaction is too high, although the energy density of the cell can be increased, but the cycle performance of the material is also reduced to some extent. From the theory to analyze, the greater the compaction, the greater the structural damage to the material, and the structure of the material is the basis for ensuring the recycling of lithium-ion batteries; in addition, the higher the positive and negative compaction of the battery is difficult to guarantee High liquid holding capacity, while the liquid holding capacity is the basis for the cell to complete a normal cycle or more cycles.

3. Moisture:

Excessive moisture may cause side reactions with the positive and negative active materials, destroying its structure and affecting the cycle, and too much moisture is also detrimental to the formation of the SEI film. However, trace amounts of water can also ensure the performance of the cell to a certain extent while the trace amount of water is difficult to remove.

4. Coating film density:

The effect of a single variable on membrane density is almost an impossible task. Inconsistent film densities either result in a difference in capacity, or a difference in cell winding or lamination. For batteries of the same type and capacity of the same material, reducing the film density is equivalent to increasing the number of layers or layers of winding or lamination, and the corresponding diaphragm can absorb more electrolyte to ensure circulation. Considering the thinner film density, the rate performance of the cell can be increased, and the baking of the pole piece and the bare cell can be easier. In addition, the error of the film density coating which is too thin may be more difficult to control, in the active material. Large particles can also have a negative impact on coating and rolling. More layers mean more foil and separator, which means higher cost and lower energy density. Therefore, equilibrium needs to be considered in the assessment.

5. Negative anode excess:

The reason for the excess of the negative electrode is that in addition to the influence of the first irreversible capacity and the deviation of the coating film density, the influence on the cycle performance is also a consideration. For the lithium cobaltate plus graphite system, the negative graphite is more common on the "short board" side of the cycle. If the anode is not excessive enough, the cell may not dephosphorize before the cycle, but after several hundred cycles, the structure of the positive electrode changes little but the structure of the negative electrode is severely damaged, and the lithium ion provided by the positive electrode cannot be completely received, thereby causing lithium. Early decline.

6. The amount of electrolyte:

There are three main reasons why the electrolyte volume is insufficient to affect the cycle:

(1) Insufficient liquid injection,

(2) Although the amount of liquid injection is sufficient, the aging time is insufficient or the immersion liquid is insufficient due to excessive compaction of the positive and negative electrodes.

(3) The internal electrolyte of the circulating battery is consumed.

On the one hand, the incomplete SEI film can not effectively prevent the negative electrode from reacting with the electrolyte to consume the electrolyte. On the other hand, in the defective portion of the SEI film, the SEI film is regenerated as the cycle progresses, thereby consuming the reversible lithium source and electrolyte. . Whether it is a cell with hundreds or even thousands of cycles or a battery with dozens of dips, if the electrolyte is sufficient before the cycle and the electrolyte has been consumed after the cycle, it is possible to increase the amount of electrolyte. To the extent that it improves its cycle performance.

7. Objective conditions of the test:

During the test, the charge and discharge rate, the cut-off voltage, the charge cut-off current, the overcharge and overdischarge during the test, the temperature of the test room, the sudden interruption during the test, the contact resistance of the test point and the cell, etc., may or may not be external factors. Or less affect the cycle performance test results. In addition, different materials are sensitive to the above objective factors. Uniform testing standards and understanding of the characteristics of commonality and important materials should be sufficient for daily work.

to sum up:

As with the wooden barrel principle, among the many factors affecting the cycle performance of the battery, the final decisive factor is the shortest of many factors. At the same time, there are interactions between these influencing factors. Under the same material and manufacturing capacity, the higher the cycle, the lower the energy density, the more the joints that just meet the customer's needs, and the consistency of the cell core is the most important task. .

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