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Tuesday, 29 October 2013 06:58

The Factors to Lithium Battery's Cycle Life

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Cycle performance of the lithium ion battery goes without saying that the degree of importance ; additional terms of the macro, longer cycle life means less consumption of resources. Thus, the impact of lithium-ion battery cycle performance factor is every personnel associated with the lithium industry have had to consider the issue. The following are a few civil and military might affect battery cycle performance factors, for your reference.
       Type of material: the choice of materials that affect the performance of lithium-ion battery of the first element. Select the poor performance of the loop material, process and then reasonable to prepare for further improvement, batteries can not be guaranteed circulation is bound ; choose a better material, even made ​​up a slight problem, the cycle of poor performance may not too outrageous ( lithium cobalt g once played only 135.5mAh / g or so and analysis of lithium batteries, 1C although over a hundred times diving but 0.5C, 500 times more than 90% ; once the batteries apart and negative black graphite particles the batteries, normal cycle performance ). From the material point of view, a full- cycle performance of the battery, the positive electrode and the electrolyte by the cycle performance after the match, a negative electrode and the electrolyte performance matched in both of the cycle, one of the poor determined. The cycling performance is poor, one may be in the cycle of rapid change in the crystal structure and thus can not proceed lithium de lithium, one may be due to the active material and the electrolyte can not generate a corresponding SEI film caused dense, homogeneous active substance side reaction with the electrolyte leaving premature excessive consumption thereby affecting electrolyte circulation. The design of the electric cell, if the cycle performance of a pole poor recognition of the material used, the other need to choose a very good cycle performance materials waste.
       Compaction is negative: positive and negative high compaction, although they could improve the energy density of batteries, but also to some extent reduce the cycling performance. From the theoretical analysis, the greater the compaction, the material equivalent to the greater structural damage, and structure of the material is to ensure that the lithium -ion battery can be used for base; addition, the positive and negative cell compaction is difficult to ensure a higher power than the high packing liquid, and the liquid holding capacity is normal cycle batteries or more times to complete the cycle basis.
       Moisture: Excessive water with positive and negative active material side reactions, thereby affecting its structure destruction cycle, while too much water is not conducive to the formation of the SEI film. But difficult to remove traces of water, while traces of water can also be to some extent to ensure the performance of batteries. Unfortunately, civil and military aspects of this personal experience is almost zero, say too many things. We are interested can search a search forum inside information on this topic, or a lot.
       Coated film density: a single variable to consider the impact on circulation film density is almost an impossible task. Capacity to bring the film density differences or inconsistencies, either wound or laminated layers batteries differences. On the same model with the same capacity in terms of materials, batteries, reducing the film density is equivalent to an additional layer or multi-layer wound or laminated layers, corresponding to the increase in electrolyte membrane can absorb more to ensure that cycle. Considering thinner film density can be increased rate performance of batteries, a pole piece and baking the bare cell will be easier to remove water, of course, the thin coating film density of the error can be difficult to control, the active substance large particles may also be coated, rolled a negative impact, more layers means more foil and diaphragm, in turn means higher costs and lower energy density. Therefore, the assessment also requires a balanced consideration.
       Excessive negative: negative excess because in addition to consider the impact of initial irreversible capacity and the coating film density deviation, the effect of the cycle performance is also a consideration. For lithium cobalt plus graphite system, the negative cycle of graphite as the " short board" one more common. If the negative excess is not sufficient, the batteries may not be in the loop before the analysis of lithium, but hundreds of times loop structure has changed little, but the negative cathode structure is severely damaged and can not fully received positive analysis thus provides a lithium ion, lithium, resulting in over- capacity early fall.
       The amount of electrolyte: electrolyte insufficient impact on circulation there are three main reasons, first, insufficient liquid injection, two liquid injection, although adequate, but aging is negative due to lack of time or other causes excessive compaction does not extract full, three cycles, with the internal batteries the electrolyte is consumed completed. Insufficient liquid injection and before Paul wrote Wenwu insufficient liquid " electrolyte deficiency on batteries performance" and therefore not repeat them. On the third point, the positive and negative anode and the electrolyte in particular microscopic matching dense and stable performance of the formation of the SEI, the performance of right eye can see, both the cycle rate of consumption of the electrolyte. SEI film on the one hand incomplete anode and electrolyte can effectively prevent the occurrence of side reactions which consume the electrolyte, while the SEI film defective parts will be with the loop and thereby regenerate the SEI film is consumed and the electrolyte Lithium reversible. Whether the circulating hundreds or even thousands of times both batteries or for dozens of diving batteries, the electrolyte is sufficient and if the cycle before the cycle after the electrolyte has been consumed, increase the amount of electrolyte is likely to be able to maintain a certain extent to improve their cycling performance.
       Test objective conditions: the testing process charge-discharge rate, cut-off voltage, the charging cut-off current, tests overcharge and over discharge, test room temperature, the sudden interruption during the test, the test point and the contact resistance of batteries and other external factors will more or less affect the cycle performance test results. In addition, different materials on the degree of sensitivity of the objective factors varies, uniform testing standards and understand the similarities and important properties of the materials should be sufficient daily use.
       Summary: As cask principles, many of the affected batteries cycling performance factors, the ultimate decisive factor is the number of factors in the shortest board. Meanwhile, among these factors, but also have a mutual influence. Made of the same material and the ability, the higher the circulation, often means lower energy density, to find exactly the point of integration to meet customer needs, try to ensure the consistency of batteries made ​​,  which is the most important task lies ahead.

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