One: What is the reason of pinhole in negative electrode coating? Is it because the material is not well dispersed? Is it possible that the material particle size distribution is not good?
The appearance of pinholes should be caused by the following factors:
1. Foil material is not clean.
2. The conductive agent is not dispersed.
3. Negative electrode body material is not dispersed.
4. There are impurities in some components of the formula.
5. Uneven particles of conductive agent, dispersing difficulties.
6. Negative electrode particles are not uniform, difficult to disperse.
7. There are quality problems in the formula material itself.
8. Stirring pot is not clean, resulting in dry powder residue in the pot. What are the specific reasons, they can go to the process monitoring and analyze it.
In addition, about the diaphragm black spot I encountered many years ago, I first briefly answer the question, please correct me if it is not right. According to the analysis, it is determined that the black spot is due to the battery polarization discharge caused by the diaphragm local high temperature, negative electrode powder bonded to the diaphragm caused by polarization discharge is due to the material and process reasons, the battery roll core there is an active substance attached to the powder, resulting in the battery into a charging after the polarization discharge. To avoid the above problems, first of all, we need to use the appropriate and paste process to solve the active substance and metal collective bonding, in the battery pole plate making, battery assembly to avoid artificially caused by the de-powdering.
Adding some additives that do not affect the performance of the battery in the coating process can indeed improve some of the properties of the pole piece. Of course, adding these ingredients in the electrolyte can achieve the effect of consolidation. The localized high temperature of the diaphragm is caused by the unevenness of the pole piece, which strictly belongs to the micro-short circuit, and the micro-short circuit will cause the localized high temperature, which may result in the depowdering of the negative pole.
Two: What are the reasons for the excessive internal resistance of the battery?
Process.
1. Too little conductive agent in the positive electrode dosage (the conductivity between the material and the material is not good, because the conductivity of lithium and cobalt itself is very poor)
2. Too much binder in the anode dosage. (Binders are generally polymer materials with strong insulating properties)
3. Too much binder for negative electrode material. (Binders are generally polymer materials with strong insulating properties)
4. Uneven dispersion of ingredients.
5. Incomplete solvent of binder during dosing. (Can not be completely dissolved in NMP, water)
6. The design of coating cloth slurry surface density is too large. (Ion migration distance is large)
7. Compaction density is too large, roll pressure is too solid. (Roller pressure is too dead, some of the active substance structure is destroyed)
8. Positive pole ear welding is not secure, false welding.
9. Negative pole ear welding or riveting is not secure, appearing false welding, desoldering.
10. The winding is not tight, and the core is slack. (Make the distance between positive and negative pole pieces increase)
11. Positive pole ear is not firmly welded to the shell.
12. Negative pole lugs are not securely welded to the poles.
13. Battery baking temperature is too high, diaphragm shrinkage. (Diaphragm aperture shrinkage)
14. The amount of liquid injection is too small (the conductivity is reduced, and the internal resistance increases quickly after the cycle!)
15. Liquid injection after the shelf time is too short, the electrolyte is not fully infiltrated
16. Not fully activated during the formation.
17. Too much electrolyte leakage in the formation process.
18. Production process moisture control is not strict, battery expansion.
19. Battery charging voltage is set too high, resulting in overcharging.
20. Battery storage environment is unreasonable.
Material.
21. Positive electrode material resistance. (Poor conductivity, such as lithium iron phosphate)
22. Diaphragm material impact (diaphragm thickness, porosity, small pore size)
23. Electrolyte material impact. (small conductivity, large viscosity)
24. Influence of anode PVDF material. (high quantity or high molecular weight)
25. Positive conductive agent material influence. (poor conductivity, high resistance)
26. Positive and negative pole lug material influence (thin thickness poor conductivity, uneven thickness, poor material purity)
27. Poor conductivity of copper foil, aluminum foil or oxide on the surface.
28. Large internal resistance of riveted contact of cover pole column.
29. Large resistance of negative electrode material. Other aspects
30.Deviation of internal resistance testing instrument.
31.Human operation.
Three: the electrode piece is not uniformly coated, should pay attention to those problems?
This problem is relatively common, it would have been easier to solve, but many coating staff are not good at summarizing, resulting in the existence of a number of problematic points default to normal, unavoidable phenomenon. First of all, we should know clearly, the factors affecting surface density and the factors affecting the stability value of surface density, can be targeted to solve the problem.
Factors affecting the coated surface density are:
1. The material itself
2. Formulation
3. Stirring and mixing
4. Coating environment
5. Knife edge
6.Viscosity of slurry
7.Pole piece going speed
8.Surface water level
9.Coating machine precision
10.Oven wind
11.Coating tension and so on...
Factors affecting the uniformity of pole piece:
1. Paste quality
2.Paste viscosity
3.Traveling speed
4.Foil tension
5. Tension balance mode
6. Coating haul-off length
7.Noise
8.Surface flatness
9. Cutting edge flatness
10. Foil flatness and so on...
The above is also just a list of factors, specific but also their own analysis of the reasons, targeted to exclude the factors that cause abnormal surface density.
Four: The positive and negative electrode collectors are aluminum foil and copper foil respectively, is there any special reason? What is the problem with the reverse? See a lot of literature directly with stainless steel mesh, is there a difference?
1, The use of both do collector are because both conductivity is good, the texture is relatively soft (may also be conducive to bonding), but also relatively common and relatively inexpensive, at the same time both surfaces can form a layer of oxide protective film.
2, Copper surface oxide layer belongs to the semiconductor, electronic conduction, the oxide layer is too thick, the impedance is greater; and aluminum surface oxide layer of alumina is an insulator, the oxide layer can not conduct electricity, but because of its thin, through the tunnel effect to achieve the electronic conduction, if the oxide layer is thicker, the aluminum foil conductivity level is poor, or even insulated. General collector in the use of the best before the surface cleaning, on the one hand, wash away the oil, at the same time can remove the thick oxide layer.
3, High positive potential, aluminum thin oxide layer is very dense, can prevent the collector oxidation. Copper foil oxide layer is more loose, in order to prevent its oxidation, the potential is lower and better, at the same time, Li is difficult to form embedded lithium alloy with Cu at low potential, but if the surface of copper is oxidized a lot, Li will be embedded lithium with copper oxide at a slightly higher potential should occur.AL foil can not be used as a negative electrode, and LiAl alloying will occur at low potential.
4, The collector is required to be pure, the impurity of AL will lead to the surface film is not dense and pitting corrosion occurs, or even due to the destruction of the surface film leads to the generation of LiAl alloy. Copper mesh cleaned with bisulfate with deionized water after cleaning and baking, aluminum mesh cleaned with ammonia salt with deionized water after cleaning and baking, and then spray net conductive effect.
Five: Measure the short circuit of the core, the battery short circuit tester used, how high the voltage, you can accurately test the short-circuit core, and, short circuit tester of high voltage breakdown principle is what kind of?
How high the voltage to test the short circuit of the battery cell, and the following factors are related:
1. the technology level of your company.
2. The structural design of the battery itself
3. The diaphragm material of the battery
4. The use of the battery
Different companies use different voltages, but many companies are regardless of the size of the model capacity of the same voltage. The above factors can be arranged in this order from the heaviest to the lightest: 1>4>3>2, that is to say, the level of your company's technology to determine the size of the short-circuit voltage.
The principle of breakdown is simply put, is due to the pole piece and the diaphragm, if there are some potential short-circuit factors, such as dust, particles, larger diaphragm holes, burrs, etc., we can call it a weak link. In the fixed, higher voltage, these weak links make the contact resistance between the positive and negative pole pieces to be smaller than other places, easy to ionize the air to produce an arc; or positive and negative poles have been short-circuited, the contact point is small, in high-pressure conditions, these small contact points instantly have a large current through the electric energy instantly converted into heat, resulting in the diaphragm melting or instant breakdown.
Six: The material particle size on the discharge current effect is how?
Simply put, the smaller the particle size, the better the conductivity, the larger the particle size, the worse the conductivity, naturally, the high rate of materials are generally high structural small particles of high conductivity.
Just from the theoretical analysis, how to achieve in practice, that can only be made to do materials friends to explain, improve the conductivity of small particle size materials is a very difficult thing, especially nanoscale materials, and small particles of material compaction will be relatively small, that is, the volume capacity is small.
Seven: Positive and negative electrode pole piece in the roll after the baking 12 hours storage day rebound 10um, why is there such a big rebound?
There are two most essential influencing factors: material and process.
1. The performance of the material determines the rebound coefficient, different materials rebound coefficient is not the same; the same material, different formulas, rebound coefficient is different; the same material, the same formula, the thickness of the film is not the same, the rebound coefficient is different.
2. If process procedures are not well controlled, it will also cause rebound. Storage time, temperature, pressure, humidity, stacking method, internal stress, equipment and so on.
Eight: Cylinder battery leakage problem how to solve?
Cylindrical for the closed mouth into the liquid in the injection after the closure, therefore, the closure naturally becomes a cylindrical closure of the difficulty of the current cylindrical battery closure probably have the following ways:
1. Laser welding sealing
2. Seal ring sealing
3. Glue sealing
4. Ultrasonic vibration sealing
5. The above types of sealing two or more combinations of two types of sealing
6. Other sealing methods
Several causes of liquid leakage:
1. Poor sealing causes liquid leakage, usually there is deformation of the sealing place, the sealing place is contaminated, belongs to the poor sealing.
2. The stability of sealing is also a factor, i.e. the sealing inspection is qualified, but the sealing place is easily destroyed, resulting in liquid leakage.
3. Gas is produced during the formation or testing, which reaches the maximum stress that the seal can withstand, and impacts the seal, resulting in liquid leakage. The difference with the 2nd point is that the 2nd point belongs to defective product leakage, and the 3rd point belongs to destructive leakage, i.e., the seal is qualified, but the internal pressure is too high to destroy the seal.
4. Other ways of liquid leakage.
Specifically how to solve, depending on the cause of the leakage, as long as the reasons, it is easy to solve, difficult to find the reason is difficult to find, because the sealing effect of the cylinder is more difficult to test, most of them are destructive type, used for sampling.
Nine: Do the experiment, the electrolyte are excess, may I ask in the case of no spillage, electrolyte excess on the battery performance has an impact?
No spillage? There are several cases:
1. The electrolyte is just right
2. Slightly overfilled with electrolyte
3. A large excess of electrolyte, but not to the limit
4. A large amount of electrolyte is overfilled and is close to the limit.
5. Already full to the limit, can be sealed
The first situation is ideal, there is no problem.
The second situation, a slight excess is sometimes a precision problem, sometimes a design problem, generally will design some excess.
The third situation, there is no problem, just a little waste of cost.
The fourth case is a bit dangerous. Because the battery in the use or test process, will be due to various reasons: cause the electrolyte decomposition, resulting in some of the gas; battery heat, resulting in thermal expansion; the above two situations can easily cause the battery bulge (can also be called deformation) or leakage, increasing the battery's safety hazards.
The fifth situation, in fact, is a strengthened version of the fourth situation, the danger is even greater.
Plus a little more exaggerated, the liquid can also become a battery. That is, the positive and negative poles at the same time inserted into a container containing a large amount of electrolyte (for example, 500ML beaker), at this time, the positive and negative poles can be charged and discharged, but also a battery, and that here is not a little bit of excess electrolyte. Electrolyte is just a conductive medium. But the volume of the battery is limited, within a limited volume, naturally, we must consider the use of space and deformation.
Ten:The amount of liquid injection is small, the battery will lead to bulging after the division of the shell?
It can only be said that not necessarily, depending on what degree of liquid injection is small.
1. If the cell is completely infiltrated by the electrolyte, but there is no residue, the battery will not bulge after this time; 2.
2. If the battery cell is completely wetted by the electrolyte, there is a small part of the residue, but less than your company's requirements for the amount of liquid injection (of course, this requirement is not necessarily the optimal value, a slight deviation), at this time, the battery will not bulge after discharging.
3. If the cell is completely infiltrated by the electrolyte, there are a lot of electrolyte residue, but your company's requirements for the amount of liquid injection than the actual high, at this time the so-called insufficient amount of liquid injection is just a company's concept, and can not truly respond to the battery's actual amount of liquid injection of the appropriate degree of compartmentalized batteries do not bulge shells.
4. Substantial liquid filling volume is insufficient. This also depends on the degree. If the electrolyte is barely able to infiltrate the battery cell, after the division of capacity may drum shell, may not drum, just divided into capacity battery drum shell chances are greater;.
If the amount of liquid in the cell is seriously insufficient, then, the battery in the formation of electrical energy can not be converted into chemical energy, at this time, the chance of bulging shells of capacitor batteries is almost 100%.
Then, it can be summarized as follows: Assuming that the battery's actual optimal amount of liquid injection is Mg, with a small amount of liquid injection, divided into the following cases:
1. Liquid injection volume = M: battery normal
2. Liquid injection volume is slightly less than M: the battery capacity is not bulging, the capacity may be normal, may also be slightly lower than the design value, the cycle of bulging shells increase the chance of cycle performance deterioration.
3. Liquid injection volume is far less than M: the rate of battery compartmentalization and shell drumming is quite high, the battery has low capacity, and the cycle stability is very poor, generally the capacity is lower than 80% in tens of weeks.
4.M=0, the battery does not bulge, no capacity.
