Several factors that may affect battery cycle performance

Material type: The choice of material is the first element that affects the performance of lithium batteries. Choose a material with poor cycle performance, no matter how reasonable the process is, and no matter how perfect the production is, the cycle of the battery cell will inevitably not be guaranteed; if a better material is selected, even if there are some problems in the subsequent production, the cycle performance may not be bad. Too outrageous (Lithium cobalt oxide gram only plays about 135.5mAh/g and lithium-evolved batteries, 1C although more than a hundred dives but 0.5C, 500 times more than 90%; after a battery is disassembled, the negative electrode has black graphite particles The battery cell, the cycle performance is normal). From a material point of view, the cycle performance of a full battery is determined by the poorer of the cycle performance after the positive electrode and the electrolyte are matched, 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 to continuously complete the lithium insertion and removal. On the other hand, it may be because the active material and the corresponding electrolyte cannot form a dense and average SEI film, which causes the active material. Premature side reactions with the electrolyte will cause the electrolyte to be consumed too quickly and affect the circulation. When designing the battery cell, if one pole is confirmed to choose a material with poor cycle performance, the other pole does not need to choose a material with good cycle performance, which is wasteful. Positive and negative electrode compaction: The positive and negative electrode compaction is too high, although it can increase the energy density of the battery, it will also reduce the cycle performance of the material to a certain extent. Decomposing from theory, the greater the compaction, the greater the damage to the structure of the material, and the structure of the material is the basis to ensure that the lithium battery can be recycled; in addition, it is difficult to guarantee the higher the positive and negative electrodes of the battery The liquid retention capacity of the battery is the basis for the battery cell to complete the normal cycle or more cycles. Moisture: Too much moisture will cause side reactions with the positive and negative active materials, destroy its structure and affect circulation. At the same time, too much moisture is not conducive to the formation of SEI film. But while the trace amount of water is difficult to remove, the trace amount of water can also guarantee the performance of the battery to a certain extent. Unfortunately, Wenwu’s personal experience in this area is almost zero, and I 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 influence of film density on the cycle of a single variable. Inconsistent film density will either bring about a difference in capacity, or a difference in the number of battery core windings or laminated layers. For batteries of the same model, capacity, and material, reducing the film density is equivalent to adding one or more layers of winding or lamination. The new diaphragm can absorb more electrolyte to ensure circulation. Taking into account the thinner film density, the rate performance of the new cell can be added, and the baking of the pole piece and the bare cell will be easier to remove the water. Of course, the error of the film density when the film is too thin may be more difficult to control, and the active material Large particles in the medium may also have a negative impact on coating and rolling. More layers means more foils and diaphragms, which in turn means higher costs and lower energy density. Therefore, the evaluation should also be balanced. Excessive negative electrode: In addition to the influence of the first irreversible capacity and the density deviation of the coating film, the reason for the excessive negative electrode is also a consideration for the impact on the cycle performance. Regarding the lithium cobaltate plus graphite system, it is more common for negative graphite to become the weaker side in the cycle. If the negative electrode is excessively insufficient, the battery cell may not release lithium before cycling, but the structure of the positive electrode changes little after hundreds of cycles, but the structure of the negative electrode is severely damaged and cannot completely receive the lithium ions supplied by the positive electrode, resulting in an overcapacity. Drop early. Electrolyte volume: There are three reasons for the lack of electrolyte volume to affect the circulation. One is that the injection volume is insufficient, and the second is that although the injection volume is sufficient, the aging time is not enough, or the positive and negative electrodes are not immersed due to high compaction. Sufficient, and thirdly, the electrolyte inside the battery cell is consumed as the circulating battery is completed. Insufficient liquid injection and insufficient liquid retention. Wenwu wrote 'The Influence of Missing Electrolyte on Cell Performance' before, so I won't repeat it. Regarding the third point, the microscopic performance of the matching between the positive and negative electrodes, especially the negative electrode, and the electrolyte is the formation of dense and stable SEI, while the performance visible to the right eye is the consumption rate of the electrolyte during the cycle. On the one hand, an incomplete SEI film cannot effectively prevent side reactions between the negative electrode and the electrolyte to consume the electrolyte. On the other hand, the defective part of the SEI film will regenerate the SEI film as the cycle progresses, thereby consuming the reversible lithium source and the electrolyte. . Regardless of whether it is a battery that is cycled hundreds or even thousands of times or a battery that has been diving for dozens of times, if the electrolyte is sufficient before the cycle and the electrolyte has been consumed after the cycle, it is likely to be able to increase the amount of electrolyte retained. Improve its cycle performance to a certain extent. The objective conditions of detection: charge-discharge rate, cut-off voltage, charge cut-off current during detection, overcharge and overdischarge during detection, temperature of detection room, sudden interruption during detection, contact internal resistance between detection point and cell, etc. Factors will more or less affect the cycle performance detection results. In addition, different materials have different sensitivity to the above-mentioned objective factors. A unified detection standard and knowledge of common and critical material characteristics should be enough for daily work. 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