Structural damage, high humidity and high temperature.
1. Structural damage: Alkaline substances present in high nickel cathode materials damage the structure of PVDF.
2. High humidity: The moisture content is too high, especially in the case of high viscosity, and the temperature is too high.
3. High temperature: Excessive temperature of the suspension will cause gelation and the gel state is different from the gelling state.
How to convert mud into polar pieces when coating lithium batteries. What is the formula?
The relationship between rheological properties and battery mud
Battery mud is the most critical factor in the entire electrode preparation process battery. Battery slurry is formed by uniformly dispersing active materials, binders and conductive agents in a solvent by stirring.tion. This is a typical highly viscous solid-liquid two-phase suspension system. Battery sludge must meet the following requirements:
The first is uniformity of dispersion. If the suspension is unevenly dispersed and exhibits significant agglomeration, the electrochemical performance of the battery will be affected. If the conductive agent is unevenly distributed, different electrochemical reactions will occur at the negative electrode due to the different conductivities during the battery charging and discharging process. electrode. More complex SEI film may be produced, the reversible capacity is reduced, and may be accompanied by local overcharge and overdischarge, or lithium metal may precipitate, causing safety hazards;
The binder is unevenly distributed, The bonding force between the particles and between the particles and the current collector may be too strongne or too weak. If the bond strength is too weak, the internal resistance of the electrode will be large and the material may even fall off, ultimately affecting the performance. of the total battery capacity.
Secondly, the suspension must have good sedimentation stability and rheological properties to meet the requirements of the pole piece coating process and achieve uniform thickness coating. the pole piece should be Try to keep the thickness as consistent as possible with the edge, which is the difficulty of the battery mud coating process. During the coating process, drag phenomena often occur at the edges of the coating, and the trailing edges are usually trimmed to ensure that the amount of active material per unit area remains constant.
If there is drag phenomenon in other parts of the coating and it cannot be cut, lThe active material at this position will be reduced, resulting in excessive local tension. In addition, during the coating process, it is possible that even if the edges of the coating are flush, the local thickness at the edge is too high, which will cause uneven pressure distribution during the compaction process and porosity and l battery unit. pole pieces. Area capacity will be uneven. This also affects the number of layers when winding or rolling.
The question is to convert it to the length of the pole piece.
Method 1, using the calculation of the surface density, as follows;
Mass of the slurry m, net dry film covering Surface density p, solids content by weight, covering width a, total covering length b, the relationship is as follows
m * wt%=p* a*b,
< p>Pay attention to the units, all can be converted to international units, the areal density is thenet areal density of the dry film dressing;If it is an intermittent coating, after calculating b, the total length can be calculated according to the interval and the length of dressage. If the coating speed is known, the coating time can also be calculated;
Method 2: based on energy density.Calculation, but it's too rough, just a rough estimate;
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