The importance of cycle function for lithium-ion batteries needs no elaboration; in addition, on a macro level, longer cycle life means less resource consumption. Therefore, the factors that affect the cycle function of lithium-ion batteries is a problem that every person related to the lithium-ion industry has to consider. The following Wen Wu listed several elements that may affect the battery cycle function for your reference.
Material variety: the selection of materials is the first element that affects the function of lithium-ion batteries. The selection of the cycle function of the poor material, the process is reasonable, made and perfect, the cycle of the battery cell is bound to be unable to ensure; selected a better material, even if the subsequent made a little problem, the cycle function may not be too bad (a lithium cobalt acid gram play only about 135.5mAh/g and lithium analysis of the battery cell, 1C although more than a hundred dives but 0.5C, 500 times 90% or more. (A battery cell with black graphite particles in the negative electrode after disassembly, the cycle function is normal). From the perspective of the material, the cycle function of a full battery is determined by the cycle function of the positive electrode after matching with the electrolyte, the negative electrode after matching with the electrolyte of the two, the worse one. The poor cycle function of the material may be due to the fact that the crystal structure changes too fast during the cycle and then cannot continue to finish the embedded lithium de-lithium, on the other hand, it may be due to the fact that the active material and the corresponding electrolyte cannot generate a fine and uniform SEI film to form a premature side reaction between the active material and the electrolyte and then the electrolyte is consumed too fast and then affects the cycle. In the core design, if one pole confirms to choose the material with poor circulation function, the other pole does not need to choose the material with better circulation function, which is spoiled.
Positive and negative pole compaction: positive and negative pole compaction is too high, although it can improve the energy density of the core, but it will also reduce the cycle function of the material to a certain extent. From the theoretical analysis, the greater the compaction, 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; in addition, the positive and negative electrode compaction of higher cells is difficult to ensure a higher amount of liquid retention, and the amount of liquid retention is the basis for the completion of the normal cycle or more repeated cycles of the cell.
Moisture: too much moisture will react with the positive and negative electrode active material, damage its structure and then affect the cycle, together with too much moisture is not conducive to the composition of SEI film. However, while traces of water are difficult to get rid of, traces of water can also ensure the function of the core to a certain extent. Unfortunately, Wen Wu's personal experience in this area is simply zero, can not say much. Everyone interested can search the forum on this topic, or a lot of information.
Coated film density: a single variable to consider the impact of film density on the cycle is simply an unlikely task. Inconsistencies in film density either bring about differences in capacity, or differences in the number of layers of core winding or lamination. For the same type of cell with the same capacity and material, lowering the film density is equivalent to adding one or more layers of winding or stacking, which corresponds to an increased barrier that can absorb more electrolyte to ensure cycling. Considering that a thinner film density can increase the multiplier function of the cell, the baking and water removal of the electrode and bare cell will be easier, of course, the errors in the coating of a too thin film density may be more difficult to control, and the large particles in the active material may also have a negative impact on the coating and rolling, more layers means more foil and dividers, which means higher cost and lower energy density. Therefore, a balanced consideration is also needed when evaluating.
Negative electrode overload: In addition to the impact of the initial irreversible capacity and the deviation of the coated film density, the impact on the cycling function is also a consideration for the reason of negative electrode overload. For lithium cobaltate plus graphite system, it is more common that the negative graphite becomes the "short board" in the cycle process. If the negative electrode is not enough, the core may not precipitate lithium before cycling, but after cycling hundreds of times, the structure of positive electrode has changed very little, but the structure of negative electrode is severely damaged and cannot fully receive lithium ions provided by positive electrode and then precipitate lithium, resulting in premature capacity decline.
Electrolyte quantity: The lack of electrolyte quantity affects the cycle mainly for three reasons, one is the lack of liquid injection, the second is that although the liquid injection is sufficient but the aging time is not enough or the positive and negative electrodes are not sufficiently dipped due to the high level of compaction, and the third is that the electrolyte inside the core is consumed after the cycle. The lack of liquid injection and the lack of liquid retention have been written by Wen Wu before, "the impact of electrolyte deficiency on the function of the core", so I will not repeat it. For the third point, the microscopic performance of the positive and negative electrodes, especially the matching of the negative electrode with the electrolyte, is the composition of a fine and stable SEI, and the visible performance of the right eye is both the rate of electrolyte depletion during the cycle. Incomplete SEI film can not effectively prevent the negative electrode from reacting with electrolyte and then consume electrolyte, on the other hand, the defective part of SEI film will generate SEI film from scratch and consume reversible lithium source and electrolyte as the cycle progresses. Whether it is for hundreds or even thousands of cycles or for dozens of diving cells, if the electrolyte is sufficient before the cycle and the electrolyte has been depleted after the cycle, adding electrolyte retention may be able to improve the cycle function to some extent.
Objective conditions of the test: charge/discharge rate, cut-off voltage, charge cut-off current, overcharge and over-discharge in the test, temperature of the test room, sudden suspension in the test process, internal resistance of the test point and the touch of the core and other external factors will more or less affect the cycle function test results. In addition, the sensitivity of different materials to the above objective factors varies, consistent test standards and understanding of common and important data characteristics should be sufficient for daily operation.
Conclusion: As with the barrel principle, the final decisive factor in many factors affecting the cyclic function of the battery core is the shortest of many factors. Together, these influencing factors, also have an interactive effect. In the same material and made ability, the higher the cycle, often means the lower the energy density, to find just the right combination of customer demand, try to ensure that the consistency of the core is made, the most important task.
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