Lithium battery science | Ten production problems and solutions (Part 2)
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2023/10/19 14:27:27
As an efficient and environmentally friendly energy storage device, lithium batteries are widely used in electric vehicles, mobile devices and energy storage systems. There are some problems in the production process of lithium batteries, such as high material costs, complex production processes, safety risks, etc., which restrict the development of the lithium battery industry. This paper will summarize the problems existing in the production process of lithium batteries, and put forward the corresponding solutions.
What is the effect of material particle size on discharge current?
Simply put, the smaller the particle size, the better the conductivity, on the contrary, the larger the particle size, the worse the conductivity. However, high-rate materials are generally small particles with high structure and high conductivity.
Theoretically, improving the conductivity of small particle size materials is indeed a difficult thing, especially nanoscale materials, and the material compaction of small particles will be relatively small, that is, the volume capacity is small.
Why does the positive and negative pole sheet bounce 10um after baking for 12 hours and storing for a day after rolling?
The most essential factors: materials and processes
1. The performance of the material determines the rebound index, and the rebound coefficient of different materials is different; The same material, different formulations, rebound coefficient is different; The same material, the same formula, the thickness of the tablet is different, the rebound coefficient is different.
2. If the process is not well controlled, it will also lead to rebound. Storage time, temperature, pressure, humidity, packing method, internal stress, equipment, etc.
How to solve the problem of cylindrical battery leakage?
Cylinder battery sealing has the following ways:
1. Laser welding sealing
2. Sealing ring
3. Seal with glue
4. Ultrasonic vibration sealing
5. Two or more combinations of the above sealing types
6. Other sealing methods
Several factors that cause leakage
1. The seal is not strong, resulting in leakage, generally deformation of the seal, the seal is polluted, which is a bad seal.
2. The stability of the seal is also a factor, that is, the acceptance of the seal is qualified, but the seal is easy to damage, resulting in leakage.
3. When forming or testing, gas is produced to achieve the maximum stress that the sealing can bear, and the impact sealing will lead to leakage. Different from the second point, the second point belongs to bad leakage, and the third point belongs to destructive leakage, that is, the sealing is qualified, but the internal pressure is too bad.
4. Other leakage methods.
The specific solution depends on the cause of the leakage, as long as the cause is found, it is easy to solve, the difficulty is difficult to find the cause, because the cylinder sealing effect is more difficult to test, most of them belong to the damage type, for sampling.
Does excess electrolyte affect battery performance without overflow?
There are the following conditions for no overflow
1. The electrolyte is just right (ideally, no problem).
2. The electrolyte is slightly excessive (slightly excessive is sometimes a precision problem, sometimes a design problem, usually design too much).
3. A large amount of electrolyte is excessive, but it has not reached the limit (there is no problem, but it wastes some costs, and it is easy to cause the drum shell of the battery or leakage, increasing the safety risks of the battery).
4. A large amount of electrolyte is excessive, which is close to the limit (somewhat dangerous). Due to the battery in use or testing process, due to a variety of reasons: resulting in the decomposition of the electrolyte, some gases; The battery heats up and expands. It is easy to cause the drum shell of the battery or leakage, increasing the safety risks of the battery).
5. It is full to the limit and can be sealed (very dangerous). To exaggerate, liquid can also be battery. That is, both positive and negative are inserted into a container equipped with a large amount of electrolyte. At this time, the positive and negative electrodes can be charged and discharged, and it is also a battery, so the electrolyte excess here is not a little bit. The electrolyte is only a conductive medium. However, the volume of the battery is limited, and in a limited volume, it is natural to consider the problem of space utilization and deformation.
The amount of liquid injection is too small, will the battery lead to a bulging shell?
How little liquid is injected
1. If the cell is completely infiltrated by the electrolyte, but there is no residue, the battery will not bulge after the partition.
(2) If the battery cell is completely immersed in the electrolyte, there is a small amount of residue, but it is less than the required amount of liquid injection (of course, this requirement is not necessarily the best value, a slight deviation), this time the battery will not bulge.
3. If the cell is completely immersed in the electrolyte, there is a large amount of electrolyte residue, but the demand for the amount of liquid injection is higher than the actual. At this time, the so-called insufficient liquid injection is only a concept, and can not really reflect the appropriate degree of the actual amount of liquid injection of the battery, and the partitioned battery does not drum the shell.
4. Insufficient substantial liquid injection. This is also a matter of degree. If the electrolyte can barely infiltrate the cell, the shell may or may not bulge after the parting, but the probability of the parting battery shell is greater.
5. The amount of liquid injected into the cell is seriously insufficient, so the electrical energy of the battery can not be converted into chemical energy at the time of formation, at this time, the probability of the drum shell of the capacitance cell is almost 100%.
The amount of liquid injection is small, divided into the following situations
1. Liquid injection amount =M: The battery is normal
2. The amount of liquid injection is slightly less than M: the battery capacity is not drum shell, the capacity may be normal, or slightly lower than the design value, the probability of circulating drum shell increases, and the cycle performance deteriorates
3. The amount of liquid injection is much less than M: the battery capacity drum shell rate is quite high, the battery has low capacity, and the cycle stability is very poor, and the capacity is generally less than 80% for dozens of weeks
4. If M=0, the battery does not bulge and has no capacity
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