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Several factors that affect the cycle of the intelligent robot lithium battery?
The importance of cycling performance for Li-Ion batteries does not need to be rumored; in addition, in terms of macro terms, longer cycle life means less resource consumption. Therefore, the factors that affect the cycling performance of lithium-ion batteries are issues that each and every person involved in the lithium battery industry has to consider. The following are some of the factors that may affect the battery cycle performance for reference.
Material type: The choice of materials is the first factor that affects the performance of lithium-ion batteries. The material with poor cycle performance was selected, the process was reasonable, and the process was perfected. The cycle of the cell core must not be guaranteed; better materials were selected, and if the subsequent process was slightly problematic, the cycle performance may not be poor. Extremely outrageous (Lithium cobalt oxide plays only about 135.5mAh/g and the lithium core is evolved. Although 1C is more than 100 times diving, it is 0.5C and 500 times is more than 90%. After the first core is disassembled, the negative electrode has black graphite particles. Batteries, normal cycle performance). From the material point of view, the cycle performance of a full battery is determined by the poor one of the cycle performance of the positive electrode and the electrolyte matched, and the cycle performance of the negative electrode and the electrolyte matched. The cycle performance of the material is poor. On the one hand, the crystal structure may change too fast during cycling so that Li-lithium delithiation can no longer be completed. On the one hand, the active material and the corresponding electrolyte may not generate a dense and uniform SEI film. The premature reaction with the electrolyte causes excessive consumption of the electrolyte and further affects the cycle. In the design of the cell, if one pole confirms that the material with poor cycle performance is used, the other pole does not need to select a material with good cycle performance and waste. Positive and negative electrode compaction: If the positive and negative electrodes are compacted too high, although the energy density of the cell can be increased, the cycle performance of the material can be reduced to some extent. From the theoretical analysis, the greater the compaction, the equivalent to the structural damage to the greater the material, and the structure of the material is to ensure that the lithium-ion battery can be recycled based on the use; In addition, the positive and negative electrode compaction of the higher battery is difficult to guarantee the The high liquid holding capacity, and the liquid holding capacity is the basis for the cell to complete a normal cycle or more cycles.
Moisture: Excessive moisture can cause side reactions with positive and negative active materials, destroy their structure and affect circulation, and too much moisture is not conducive to the formation of SEI film. However, while trace amounts of water are difficult to remove, trace amounts of water can also guarantee the performance of the cell to some extent. Unfortunately, Wenwu’s immediate experience in this area is almost zero and there is not much to say. Everyone is interested in searching information on this topic in the forum. It is still quite a lot.
Coating film density: single variable considerations The effect of film density on the cycle is almost an impossible task. Inconsistent film density either results in a difference in capacity, or is a difference in the number of core wraps or laminations. For the same type and capacity of the same material, reducing the film density is equivalent to adding one or more layers of windings or laminations, and the corresponding increase in the separator can absorb more electrolyte to ensure circulation. Taking into account that the thinner film density can increase the rate performance of the core, and the baking of the pole pieces and the bare cells can be easier to remove water. Of course, when the film density is too thin, the error in coating may be more difficult to control. Large particles can also have a negative impact on coating and rolling. More layers means more foil and membrane, which in turn means higher costs and lower energy density. Therefore, balanced considerations are also needed in the assessment.
Excessive negative electrode: Excessive negative electrode causes aside from considering the influence of the first irreversible capacity and the deviation of the coating film density, the influence on the cycle performance is also a consideration. For the lithium cobalt oxide plus graphite system, the negative graphite becomes more and more common in the “short board” side of the cycle. If the negative electrode is not sufficient, the cell may not precipitate lithium before the cycle, but after a few hundred cycles, the positive electrode structure changes little but the negative electrode structure is seriously damaged, and the lithium ions provided by the positive electrode cannot be completely received thereby to cause lithium to be dissipated. Drop early.
The amount of electrolyte: There are three main reasons for insufficient circulation of electrolyte: First, the amount of liquid injected is insufficient; second, although the amount of liquid injection is sufficient, the aging time is not enough, or the immersion of positive and negative electrodes due to excessive compaction is not Sufficient, the third is with the electrolyte inside the circulating core is consumed. Insufficient liquid injection volume and insufficient liquid retention volume Before Wenwu wrote “Effect of lack of electrolyte on the performance of the cell”, it will not be repeated. For the third point, the microscopic appearance of the positive and negative electrodes, particularly the matching of the negative electrode and the electrolytic solution, is the formation of a dense and stable SEI, and the visible behavior of the right eye is the consumption rate of the electrolyte during the cycle. The incomplete SEI membrane cannot effectively prevent the negative electrode and the electrolyte from undergoing side reactions and consume the electrolyte. On the one hand, the SEI membrane will regenerate the SEI membrane as the cycle proceeds to consume the reversible lithium source and the electrolyte. . Whether it is for a cell that circulates hundreds or even thousands of times, or for a cell that does not hop for several tens of times, if the electrolyte is sufficient before the circulation and the electrolyte is consumed after the cycle, it is possible to increase the amount of electrolyte retained. To improve its cycle performance.
Objective conditions of the test: Charge/discharge rate, cut-off voltage, charge cut-off current during test, overcharge/discharge during test, temperature of test room, abrupt interruption during test, contact resistance between test point and cell, etc. Factors, will more or less affect the cycle performance test results. In addition, different materials have different sensitivities to the above-mentioned objective factors. Uniform test standards and knowledge of commonalities and characteristics of important materials should be sufficient for routine work.
Summary: As with the barrel principle, among the many factors that affect the cycle performance of the cell, the final decisive factor is the shortest of many factors. At the same time, there are interactions between these influencing factors. With the same material and ability to make, the higher the cycle time, the lower the energy density. It is the most important task to find the binding points that exactly meet the needs of customers and try to ensure the consistency of the batteries. .
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