Careful finishing: the coating process and the impact of the slurry on the battery that NMP particip

Ten days ago, the editor published an article, which is an analysis of common problems of lithium batteries suitable for NMP. Today, we continue to discuss the influence of the coating process and slurry on the production of lithium batteries in which NMP participates. For this piece, the editor is still familiar with it, after all, we WIT FENGZE & ZESHENG are specialized in the production of NMP solvent. From production and supply of NMP solvent to NMP waste liquid recovery system, tailor-made industry solutions for partners, one-stop service; solve all problems about NMP for partners! Therefore, relevant professional articles are also developed around NMP solvents, and industry friends are welcome to come and have friendly exchanges.

The electrode peel strength of lithium-ion batteries has a significant impact on battery performance, and this involves the baking process, coating process and slurry problems in the battery manufacturing process. Next, we analyze the influence of these factors on the degree of electrode peeling in detail.

[Drying process will cause changes in the internal structure of the electrode]

In the initial stage of drying, in fact, the various components of the battery are still evenly distributed. However, during the drying process, NMP and other solvents are regularly evaporated, and the electrode film shrinks accordingly; a solubility gradient begins to appear at the gas-liquid interface, forming a meniscus on the surface of the consolidated particle layer. When the NMP solvent evaporated from the wet film with a uniform pore size at a steady rate, the shrinkage of the electrode film stopped, and a well-distributed porous microelectrode structure was gradually formed. As a result, the internal structure of the electrode has completed a change.

[Baking rate also affects the distribution of components inside the electrode]

During the baking stage of the electrode sheet, the SBR binder and carbon black in the negative electrode material will migrate to the surface as the solvent evaporates. In the case of low bake rate (LDR), the binder distribution at different locations is relatively uniform; but at high bake rate (HDR), the binder concentration from the current collector to the gas-liquid interface changes continuously However, the distribution of binder in the current collector and dressing area is relatively small, which directly leads to the continuous increase of electrode resistance, thus affecting the peel strength of the electrode.

【Influence of coating area density on electrode structure】

During the coating stage, the NMP solvent is present in order to make the slurry more evenly and uniformly coated on the metal substrate. However, if the fixation of the particles within the electrode structure is faster than the flow rate of the solvent to the electrode surface to compensate, the fluidity of the binder will be greatly reduced; the lower the amount of solvent in the wet coating, the more wet the metal substrate will be. The lower the temperature, the higher the temperature, which will speed up the evaporation of the solvent, affect the electrode structure, increase the electrode resistance, and is not conducive to electrode peeling.

【Effect of slurry on electrode peel strength】

The reduction of the solid content of the slurry has an impact on the electrode peel strength. Because after the solid content of the slurry is reduced, it takes longer time or higher temperature to dry; this will lead to the instability of the binder, which directly leads to the deterioration of the peel strength of the electrode.

The electrode peel strength of lithium-ion batteries changes, which has a significant impact on the performance of the produced batteries. Therefore, for the production of lithium-ion batteries, refinement is the main purpose. The NMP solvent is used as the auxiliary solvent for the PVDF binder of the cathode material. Its purity, its production capacity, and its interaction with various materials have a small to large impact on battery production.

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