Brief description of the cycle performance of lithium-ion batteries

The importance of cyclic properties to lithium-ion batteries need not be repeated; In addition, at the macro level, longer cycle life means less resource consumption. Therefore, the factors that affect the recycling performance of lithium ion batteries are problems that every person associated with the lithium power industry has to consider. The following civil and military lists several factors that may affect the battery cycle performance for everyone's reference.

Material type: material selection is the first factor affecting the performance of lithium-ion batteries. The material with poor circulation performance is selected, and the process is reasonable and manufactured again. The cycle of the core can not be guaranteed. Select a better material, even if there are some problems with subsequent manufacture, the cyclic performance may not be too ridiculous(Lithium cobalt acid plays only about 135.5 mAh/g and lithium-precipitates the core, 1C Although more than 100 dives but 0.5 C, 500 times more than 90 %; After the primary core is opened, the negative electrode has a black graphite particle core with normal circulation performance.) From the material point of view, the cyclic performance of a full battery is determined by the poor one of the cyclic performance of the positive electrode and the electrolyte after the negative electrode and the electrolyte match. The material has poor cyclic performance. On the one hand, it may be that the crystal structure changes too quickly during the cycle and it is impossible to continue to complete lithium delithium. On the one hand, it may be that because the active substance and the corresponding electrolyte can not produce a dense and uniform SEI membrane, the active substance and the electrolyte react prematurely to cause the electrolyte to consume too quickly and affect the circulation. In the core design, if one pole confirms the selection of materials with poor cyclic performance, the other pole does not need to select materials with better cyclic performance and waste.

Positive and negative electrode compaction: Positive and negative poles compaction is too high, although it can increase the energy density of the core, but it will also reduce the material's cyclic performance to a certain extent. From the theoretical point of view, the greater the compaction, the greater the damage to the structure of the material, and the structure of the material is the basis for ensuring that the lithium ion battery can be recycled; In addition, it is difficult for a positive and negative core to guarantee a higher amount of retention fluid, which is the basis for the core to complete normal circulation or more cycles.

Water: Too much water will react with positive and negative active substances, destroy its structure, and affect the circulation. At the same time, too much water is not conducive to the formation of SEI membranes. However, while trace amount of water is difficult to remove, trace amount of water can also ensure the performance of the core to a certain extent. Unfortunately, civil and military experience in this area is almost zero, can not say too much. Everyone is interested in searching the forum for information on this topic, or a lot.

Coating membrane density: considering the effect of membrane density on the circulation of a single variable is almost an impossible task. The film density is inconsistent either with the difference in capacity or with the difference in the number of coiled or laminated layers. For the same type of core with the same capacity as the material, reducing the membrane density is equivalent to increasing the number of layers or layers of winding or lamination. The corresponding increased diaphragm can absorb more electrolytes to ensure circulation. Considering that thinner membrane density can increase the doubling performance of the core, it is easier to bake and remove water from the electrode and naked core, of course, the error of too thin membrane density coating may be more difficult to control. Large particles in active substances may also have a negative impact on coating and rolling pressure. More layers mean more foil and diaphragm, which in turn means higher costs and lower energy density. Therefore, the assessment also needs to be balanced.

Negative overload: The reason for the negative overload is not only the impact of the first irreversible capacity and the film density deviation, but also the impact on the cycling performance. For lithium cobalt acid plus graphite system, negative graphite becomes a "short plate" in the cycle process is more common. If the negative electrode is too much, the core may not analyze lithium before the cycle, but after a few hundred cycles, the positive polar structure changes little but the negative polar structure is severely damaged and can not fully receive lithium ions supplied by the positive electrode. Lithium, resulting in premature decline in capacity.

Electrolytic fluid quantity: There are three main reasons for the effect of insufficient electrolytic fluid quantity on the circulation. One is the insufficient amount of liquid injection. The other is that although the amount of liquid injection is sufficient, the aging time is not enough or the positive and negative poles are insufficient due to the cause of high compaction. Third, the inner electrolyte of the circulating core is consumed. Insufficient fluid injection and insufficient liquid retention The influence of the lack of electrolytic fluid on the performance of the core has been written by Wenwu before and is not repeated. For the third point, the microscopic performance of the positive and negative poles, especially the matching of the negative poles and the electrolytes, is the formation of a dense and stable SEI, and the visible performance of the right eye is both the consumption speed of the electrolyte during the cycle. On the one hand, the incomplete SEI membrane can not effectively prevent the side reaction between the negative electrode and the electrolyte from consuming the electrolyte. On the other hand, the defective part of the SEI membrane will regenerate the SEI membrane as the cycle progresses, thus consuming reversible lithium sources and electrolytes. Whether it is the core of hundreds or even thousands of cycles or the core of dozens of diving, if the electrolyte is sufficient before the cycle and the electrolyte has been consumed after the cycle, increasing the amount of electrolytes is likely to increase to a certain extent. Its recycling performance.

Objective conditions for testing: charge and discharge ratio, cut-off voltage, charging and cut-off current, overcharge and over discharge in test, temperature in test room, sudden interruption in test process, internal resistance to contact between test point and core, and other external factors, Will more or less affect the cyclic performance test results. In addition, the sensitivity of different materials to the above objective factors varies, and unified testing standards and understanding of the characteristics of common and important materials should be sufficient for daily use.

Summary: Like the barrel principle, among the many factors that affect the performance of the core cycle, the final decisive factor is the shortest of many factors. At the same time, there are also interactions between these influencing factors. Under the same material and manufacturing capabilities, the higher the cycle, often means the lower the energy density, find the junction point that just meets the customer's needs, and try to ensure the consistency of the core production. The party is the most important task.

The page contains the contents of the machine translation.