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Factors affecting the cycle performance of lithium-ion batteries

From:CTECHI GROUP Limited     Release time:2019-10-14

Overview:The factors affecting the cycle performance of lithium-ion batteries are issues that every person involved in the lithium battery industry has to consider

Factors affecting the cycle performance of lithium-ion batteries

The factors affecting the cycle performance of lithium-ion batteries are issues that every person involved in the lithium battery industry has to consider:

1. Objective conditions of testing

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 test standards and understanding the characteristics of common and important materials should be sufficient for daily work.

2, the anode is excessive

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 a "short plate" in the cycle. "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 causes a premature decline in capacity.

3, coating film density

Considering the effect of membrane density on the cycle is almost an impossible task. Inconsistent membrane density either brings about the 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. The corresponding diaphragm can absorb more electrolyte to ensure circulation, and the cell can be increased in consideration of a thinner film density. The rate performance, pole piece and bare cell baking will also be easier to remove water. Of course, too thin film density coating error may be more difficult to control, large particles in the active material may also be coated, rolled The pressure has a negative impact, and more layers mean more foil and diaphragm, which means higher cost and lower energy density, so the balance needs to be evaluated.

4, the type of material

The choice of materials is the first factor affecting the performance of lithium-ion batteries. The materials with poor cycle performance are selected. The process is reasonable and finished, and the cycle of the cells is inevitably guaranteed. The better materials are selected, even after the follow-up. There are some problems in the process, and the cycle performance may not be too outrageous. 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, and the cycle after the negative electrode and the electrolyte are matched. In terms of performance, the poorer one determines that 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 activity. The material and the corresponding electrolyte cannot form a dense and uniform SEI film, causing the active material and the electrolyte to react prematurely, causing the electrolyte to be consumed too quickly and affecting the circulation. In the design of the battery core, 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.

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