Seven factors of lithium battery cycle performance

Excessive moisture will cause side reactions with the positive and negative active materials, destroy its structure and affect the cycle. At the same time, too much moisture is not conducive to the formation of SEI film. However, while trace amounts of moisture are difficult to remove, trace amounts of water also Can guarantee the performance of the battery to a certain extent. 2. Positive and negative electrode compaction The positive and negative electrode compaction is too high, although it can increase the energy density of the cell, it will also reduce the cycle performance of the material to a certain extent. From the theoretical point of view, the greater the compaction, the equivalent to the material The greater the damage of the structure, and the structure of the material is the basis to ensure that the lithium battery can be recycled; in addition, it is difficult to ensure a higher liquid retention capacity for batteries with higher positive and negative electrode compaction, and the liquid retention capacity is that the batteries are completed normally The basis for loops or more loops. 3. The objective conditions of detection. Charge and discharge rate, cut-off voltage, charge cut-off current during detection, overcharge and overdischarge during detection, room temperature detection, sudden interruption during detection, contact resistance between detection point and cell, etc. External factors will more or less affect the cycle performance detection results. In addition, different materials have different sensitivity to the above objective factors. A unified detection standard and knowledge of common and critical material characteristics should be enough for daily work. 4. 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 the influence on the cycle performance. Regarding the lithium cobaltate plus graphite system, the negative electrode graphite becomes the cycle process. The short board is more common. If the negative electrode is excessively insufficient, the battery cell may not release lithium before the cycle, but the positive electrode structure changes little after hundreds of cycles, but the negative electrode structure is seriously damaged and cannot fully receive the lithium ions supplied by the positive electrode. Thereby, lithium is analyzed, causing a premature decrease in capacity of large-capacity lithium batteries. 5. It is almost impossible to consider the impact of the film density on the cycle of the single variable of the coating film density. Inconsistent film density will bring about the difference in capacity or the difference in the number of battery core windings or laminated layers. For batteries of the same type and 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. Thin film density can increase the rate performance of the cell, and it will be easier to bake the pole piece and bare cell to remove water. Of course, the error of coating with too thin film density may be more difficult to control, and the large amount of active material Particles 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 Consider. 6. Material type The choice of material is the first element that affects the performance of lithium batteries. If a material with poor cycle performance is selected, no matter how reasonable the process is and no matter how perfect it is made, the cycle of the battery will inevitably not be guaranteed; a better material is selected Even if there are some problems in the subsequent production, the cycle performance may not be too bad. From the material point of view, the cycle performance of a full battery is determined by the cycle performance of the positive electrode and the electrolyte, and the negative electrode and the electrolyte. The later cycle performance of the two is determined by the poorer one. The cycle performance of the material is poor. On the one hand, it may be that the crystal structure changes too fast during the cycle to continuously complete lithium insertion and removal. On the other hand, it may The reason is that the active material and the corresponding electrolyte cannot form a dense and average SEI film, which causes the active material and the electrolyte to have side reactions prematurely, which causes the electrolyte to be consumed too quickly and affects the circulation. When designing the battery cell, if one pole confirms that a material with poor cycle performance is selected, the other pole does not need to choose a material with better cycle performance, which will waste large-capacity lithium batteries. 7. Electrolyte amount Insufficient amount of electrolyte has three main reasons for the circulation. One is insufficient injection volume, and second, although the injection volume is sufficient, the aging time is not enough or the positive and negative electrodes are immersed due to high compaction. Insufficient, the third is that the electrolyte inside the battery cell is consumed with the circulation. The third point is that 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, and the incomplete SEI On the one hand, the membrane 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 membrane will regenerate the SEI membrane as the cycle progresses, thereby consuming the reversible lithium source and the electrolyte. Whether it’s for cells that circulate hundreds or even thousands of times or for cells that have already dived 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 possible to increase the amount of electrolyte retained. 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