January 8, 2021
Want to know what factors will affect the service life of mobile phone batteries?
Our mobile phones, pads, and notebooks use lithium-ion batteries, and their battery life has always been a key direction of HOPPT research. Needless to say, the importance of cycle performance to lithium-ion batteries is not much to say. From a macro perspective, longer cycle life means less resource consumption. Therefore, the factors that affect lithium-ion batteries' cycle performance are all related to the lithium battery industry. People have to consider issues.
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 and the battery's performance can be guaranteed to a certain extent.
2. Compaction of positive and negative poles
The positive and negative electrode compaction is too high; however, it can increase the cell's energy density; it will also reduce the material's cycle performance to a certain extent. From the theoretical analysis, the greater the compaction, the greater the structural damage to the material. The material structure is the basis to ensure that lithium-ion batteries can be recycled; also, batteries with higher positive and negative electrode compaction are difficult to ensure a higher liquid retention capacity, and the retention capacity is the battery that completes normal cycles or more The basis of circulation.
3. The objective conditions of the test
During the test, the charge and discharge rate, cut-off voltage, charge cut-off current, overcharge and over-discharge during the test, test room temperature, sudden interruption during the test, and the test point's contact resistance and the cell, and other external factors will be more or less. It may less affect the cycle performance test results. Also, different materials have different sensitivity to the above objective factors. A unified test standard and an understanding of common and important material characteristics should be enough for daily work.
4. Excessive negative electrode
In addition to the influence of the first irreversible capacity and the coating film's density deviation, the reason for the excessive negative electrode is also a consideration on the cycle performance. For the lithium cobaltate plus graphite system, the negative electrode graphite becomes the "shortboard" in the cycle process. "One side is more common. Suppose the negative electrode is not excessively large. In that case, the battery cell may not degenerate lithium before cycling. Still, the positive electrode structure changes little after hundreds of cycles. Still, the negative electrode structure is seriously damaged and cannot fully receive the positive electrode's lithium ions. Lithium causes the capacity to drop prematurely.
5. 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 incapacity or a difference in the number of layers of battery core windings or laminates. For the same model, the same capacity, the same material, For the battery cell, reducing the film density is equivalent to increasing the number of one or more layers of winding or lamination. The correspondingly increased diaphragm can absorb more electrolytes to ensure circulation. Considering the thinner film density can increase the battery cell, It will also be easier to remove water from pole pieces and bare cells. Of course, the error of coating with too thin film density may be more difficult to control, and large particles in the active material may also affect the coating, and rolling Pressure has a negative impact. More layers mean more foils and diaphragms, which in turn means higher costs and lower energy density. Therefore, the evaluation also needs to be balanced.
6. Types of materials
The choice of materials is an element that affects the performance of lithium-ion batteries. If materials with poor cycle performance are selected, no matter how reasonable the process is and no matter how perfect they are made, the battery cell cycle will inevitably not be guaranteed; better materials are selected, even if they are subsequently made. There are some problems, and the cycle performance may not be too bad. From a material point of view, a full battery's cycle performance is determined by the cycle performance of the positive electrode and the electrolyte and the cycle performance of the negative electrode and the electrolyte. The poorer of the two is determined by, the poorer cycle performance of the material. On the one hand, the crystal structure may change too fast during the cycle to continue lithium insertion and removal. On the other hand, it may be due to the active material. The Corresponding electrolyte cannot produce a dense and uniform SEI film, which causes premature side reactions between the active material and the electrolyte, which causes the electrolyte to be consumed too quickly and affects 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 better cycle performance, which is wasteful.
7. The amount of electrolyte
There are three main reasons for the insufficient amount of electrolyte to affect circulation. One is insufficient injection volume; the second is that although the injection volume is sufficient, the aging time is not enough, or the positive and negative electrodes are not fully immersed due to high compaction, etc.; the third is With the circulation of the internal electrolyte of the battery cell is consumed. 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 SE. In contrast,e the performance visible to the right eye is the electrolyte's consumption rate during the cycle. 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 SEI membrane's defective part will regenerate the SEI membrane as the cycle progresses to consume the reversible lithium source and the electrolyte. Whether it is for batteries that are cycled hundreds or even thousands of times or for batteries that have 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 increase the amount of electrolyte retained. To improve its cycle performance.
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