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 refinement is made. The cycle of the battery core is inevitably impossible to guarantee; better materials are selected, even after There are some problems in the process, and the cycle performance may not be too far off the spectrum (the lithium cobaltate is only used for 135.5mAh/g and the lithium battery is used. 1C is more than 100 times diving but 0.5C, 500 times 90 More than %; After the battery is disassembled, the anode has black graphite particles, and the cycle performance is normal.) From the material point of view, the cycle performance of a full battery is the cycle performance after the positive electrode and the electrolyte are matched. The cycle performance after electrolyte matching is determined by one of the poorer ones. 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, it may be due to the fact that the active material and the corresponding electrolyte cannot form a dense and uniform SEI film, causing the active substance and the electrolyte to react prematurely, causing the electrolyte to be consumed too quickly and affecting the cycle. If one pole confirms the selection of materials with poor cycle performance, the other pole does not need to select materials with better cycle performance and waste.
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 theoretical analysis, the greater the compaction, the greater the structural damage to the material, and The structure of the material is the basis for ensuring that the lithium ion battery can be recycled. In addition, it is difficult to ensure a high liquid holding capacity for the battery with high positive and negative compaction, and the liquid holding amount is the normal cycle of the battery or more. The basis of the cycle.
Excessive moisture will react with the positive and negative active materials, destroying its structure and affecting the cycle. At the same time, too much moisture is not conducive to the formation of SEI film. However, trace amounts of water are difficult to remove, and trace amounts of water are also Can guarantee the performance of the battery to a certain extent. Unfortunately, Wenwu's personal experience in this aspect is almost zero, can't say too much. Everyone is interested in searching the forum for information on this topic, or quite a lot.
Coating film density
It is almost impossible to consider the effect of membrane density on the cycle of a single variable. Inconsistent membrane density either brings about a difference in capacity, or the difference in the number of layers of the core winding or lamination. In the case of cells, 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 a thinner film density, the cell can be increased. The rate performance, the baking of the pole piece and the bare cell will be easier to remove water. Of course, the error of coating film density of too thin may be more difficult to control, and the large particles in the active material may also be coated, rolled. Pressure has a negative impact, and more layers mean more foil and diaphragm, which in turn means higher cost and lower energy density. Therefore, equilibrium needs to be considered for evaluation.
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 considered. For the lithium cobaltate plus graphite system, the negative electrode graphite becomes the 'short plate in the cycle process. ' One side is more common. If the negative electrode is not enough, the battery may not be decomposed 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. Lithium, causing premature capacity decline.
Amount of electrolyte
There are three main reasons for the lack of electrolyte solution, one is that the amount of liquid injection is insufficient, and the other is that although the amount of liquid injection is sufficient, the aging time is not enough or the positive and negative electrodes are not fully immersed due to high compaction, etc. As the electrolyte inside the circulating cell is consumed, the amount of liquid injection is insufficient and the amount of liquid retention is insufficient. Wenwu wrote “The effect of electrolyte loss on the performance of the battery core” and therefore will not repeat them. For the third point, the positive and negative poles are special. The microscopic representation of the matching of the negative electrode and the electrolyte is the formation of dense and stable SEI, while the visible performance of the right eye is not only the consumption rate of the electrolyte during the cycle. The incomplete SEI film cannot effectively prevent the negative electrode from being The electrolyte reacts with the electrolyte to consume the electrolyte. On the one hand, the SEI film is regenerated in the defective portion of the SEI film to consume the reversible lithium source and the electrolyte. Whether it is a hundred or even thousands of cycles. The battery core is still for dozens of batteries that have both diving. If the electrolyte is sufficient before the cycle and the electrolyte has been consumed after the cycle, it is possible to increase the electrolyte retention to a certain extent. Its high cycle performance.
Objective conditions of testing
Charge and discharge rate during the test, cut-off voltage, charge cut-off current, overcharge and over discharge during test, test room temperature, sudden interruption during test, external contact with test point and cell, etc. Or less affect the cycle performance test results. In addition, different materials are sensitive to the above objective factors, unified test standards and understanding the characteristics of common and important materials should be enough for daily work.
Like the principle of wooden barrels, among the many factors affecting the cycle performance of batteries, the final decisive factor is the shortest of many factors. At the same time, there are interactions between these factors. In the same material and system Under the ability, the higher the cycle, the lower the energy density, the combination point that just meets the customer's needs, and the consistency of the battery core is the most important task.