What are the factors that affect the cycle performance of CR2430 battery?

Material types:

Material selection is the first factor that affects the performance of lithium-ion batteries. If you choose a material with poor cycle performance, no matter how reasonable the process is or how perfect the manufacturing is, the cycle of the battery cell cannot be guaranteed; if you choose a better material, even if there are some problems in the subsequent manufacturing, the cycle performance may not be too bad (a battery cell with a primary cobalt oxide gram performance of only about 135.5mAh/g and lithium deposition, although 1C has a drop of more than 100 times, it is more than 90% at 0.5C and 500 times; a battery cell with black graphite particles on the negative electrode after the primary battery cell is disassembled, has normal cycle performance). From the perspective of materials, the cycle performance of a full battery is determined by the cycle performance after the positive electrode and electrolyte are matched, and the cycle performance after the negative electrode and electrolyte are matched, whichever is worse. The poor cycle performance of the material may be due to the fact that the crystal structure changes too quickly during the cycle and thus cannot continue to insert and remove lithium. On the other hand, it may be due to the inability of the active material and the corresponding electrolyte to form a dense and uniform SEI film, which causes the active material and the electrolyte to react prematurely and consume the electrolyte too quickly, thus affecting the cycle. When designing the battery cell, if one pole is confirmed to use a material with poor cycle performance, the other pole does not need to use a material with better cycle performance, which is a waste.

Positive and negative electrode compaction:

Although the positive and negative electrode compaction is too high, it can increase the energy density of the battery cell, but it will also reduce the cycle performance of the material to a certain extent. From a theoretical analysis, the greater the compaction, the greater the damage to the material structure, and the material structure is the basis for ensuring that lithium-ion batteries can be recycled; in addition, the battery cell with high positive and negative electrode compaction is difficult to ensure a high liquid retention, and the liquid retention is the basis for the battery cell to complete normal cycles or more cycles.

Water:

Excessive water will react with the positive and negative active materials, destroy their structure and affect the cycle. At the same time, excessive water is not conducive to the formation of SEI film. But while trace amounts of water are difficult to remove, trace amounts of water can also guarantee the performance of the battery to a certain extent. Unfortunately, Wenwu has almost zero personal experience in this area and can't say much. If you are interested, you can search the forum for information on this topic, there are still quite a few.

Coating film density:

It is almost impossible to consider the impact of membrane density on the cycle as a single variable. Inconsistent membrane density either leads to differences in capacity or differences in the number of layers of battery winding or lamination. For batteries of the same model, capacity and material, reducing the membrane density is equivalent to adding one or more layers of winding or lamination, and the corresponding increased diaphragm can absorb more electrolyte to ensure circulation. Considering that a thinner membrane density can increase the rate performance of the battery, it will be easier to bake and remove water from the pole piece and bare battery. Of course, the error of too thin a membrane density during coating may be more difficult to control, and large particles in the active material may also have a negative impact on coating and rolling. More layers mean more foil and diaphragm, which means higher cost and lower energy density. Therefore, a balanced consideration is also needed during evaluation.

Negative electrode excess:

In addition to the influence of the first irreversible capacity and the coating film density deviation, the influence on the cycle performance is also a consideration for the cause of the negative electrode excess. For the lithium cobalt oxide plus graphite system, it is common for the negative electrode graphite to become the "short board" in the cycle process. If the negative electrode excess is insufficient, the battery cell may not precipitate lithium before the cycle, but after hundreds of cycles, the positive electrode structure changes little, but the negative electrode structure is severely damaged and cannot fully receive the lithium ions provided by the positive electrode, thereby precipitating lithium, causing the capacity to decrease prematurely.

Electrolyte volume:

There are three main reasons why insufficient electrolyte volume affects the cycle. One is insufficient injection volume. The second is that although the injection volume is sufficient, the aging time is not enough or the positive and negative electrodes are not fully immersed due to excessive compaction. The third is that the electrolyte inside the battery cell is consumed as the cycle progresses. Insufficient injection volume and insufficient liquid retention Wenwu has previously written "The Impact of Electrolyte Lack on Battery Performance" so I will not repeat it here. For the third point, the microscopic performance of the matching of positive and negative electrodes, especially the negative electrode and the electrolyte, is the formation of a dense and stable SEI, and the performance visible to the right eye is the consumption rate of the electrolyte during the cycle. On the one hand, the incomplete SEI film cannot effectively prevent the negative electrode from reacting with the electrolyte and consuming the electrolyte. On the other hand, the defective parts of the SEI film will regenerate the SEI film as the cycle progresses, thereby consuming the reversible lithium source and electrolyte. Whether it is for batteries that have been cycled hundreds or even thousands of times or for batteries that have been drained dozens of times, 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.

Objective conditions of the test:

External factors such as charge and discharge rate, cut-off voltage, charge cut-off current, overcharge and over-discharge during the test, test room temperature, sudden interruption during the test, and contact internal resistance between the test point and the battery cell will more or less affect the cycle performance test results. In addition, different materials have different sensitivities to the above objective factors. Unifying the test standards and understanding the commonalities and characteristics of important materials should be sufficient for daily work.

Summary:

Just like the barrel principle, among the many factors that affect the cycle performance of the battery cell, the final decisive factor is the shortest board among many factors. At the same time, these influencing factors also have interactive effects. Under the same material and manufacturing capacity, the higher the cycle, the lower the energy density. Finding the combination point that just meets customer needs and trying to ensure the consistency of battery cell manufacturing is the most important task.

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