High-bonding-strength PVDF (polyvinylidene fluoride) coated diaphragm and preparation method thereof

Abstract

In order to solve the technical problems of how to improve the bonding strength of a water-based coated PVDF (Polyvinylidene Fluoride) diaphragm, reduce the breathable increment after the diaphragm is coated and improve the hardness and cycle performance of a battery cell, the invention provides a lithium battery coated diaphragm with high bonding strength, which comprises a basic diaphragm and a coating coated on at least one surface of the outer side of the basic diaphragm, the coating is mainly prepared from the following raw materials: PVDF (Polyvinylidene Fluoride), PMMA (Polymethyl Methacrylate) emulsion and an auxiliary agent; the auxiliaries comprise a thickening agent, a wetting agent and a binding agent. The coating is mainly prepared from the following raw materials in parts by weight: 20 to 90 parts of PVDF (Polyvinylidene Fluoride), 10 to 80 parts of PMMA (Polymethyl Methacrylate) emulsion, 0.3 to 1.35 parts of thickening agent, 3 to 13.5 parts of wetting agent and 1.4 to 6.3 parts of binding agent. The invention also provides a method for preparing the coated diaphragm with high bonding strength. The PMMA in the emulsion state is adopted, the layering phenomenon after powder is dispersed is effectively avoided, the powder is more easily and evenly dispersed in the emulsion, the batching procedure is simple and rapid, the requirement for equipment is low, and the cost is low.

Description

technical field [0001] The invention belongs to the technical field of preparation methods of separators for batteries, and in particular relates to a PVDF coated separator with high bonding strength and a preparation method thereof. Background technique [0002] As a key part in lithium-ion batteries, the separator plays an important role in isolating the positive and negative electrodes to prevent short circuits and providing channels only for lithium ions. At present, the simple polyethylene separator can no longer meet the current development needs of batteries, and the market for coated separators with functional coatings is gradually expanding. [0003] The existing polyvinylidene fluoride polymer (PVDF) coated diaphragm has low bonding strength, weak lyophilic ability of the diaphragm, and high air permeability after coating, and the internal resistance of the diaphragm increases greatly, which affects the lithium ion transmission. PMMA is commonly known as acrylic....

AI Technical Summary

Problems solved by technology

Due to its high swelling capacity, the thickness of the battery cell after winding is high, and the assembled battery takes up more space, which affects the volume and weight of the PACK, which in turn affects the energy density of the battery pack and limits its application.

[0004] The existing technology adopts PMMA powder, which is mixed with PVDF powder. When the amount of powder added is large, it is easy to disperse unevenly during the batching process, because the surface tension of PVDF powder is relatively large, and the difference between PMMA powder and PVDF powder There is a large difference in density, so there is a problem of stratification between the two in the process of mixing ingredients

However, the existing technology proposes to carry out surface modification on the two powders respectively. After the surface modification, although this problem can be solved to a certain extent, the batching process is relatively complicated and the cost is high. On the one hand, it increases the complexity of the batching process. On the other hand, the improvement of the bonding strength is limited, the cycle performance of the battery is not good enough, and there is still the risk of uneven dispersion

[0005] Due to the high requirements on equipment for the mixing of PMMA powder and PVDF powder, and the low bonding strength of the coated diaphragm, the high value-added air permeability has gradually failed to meet the needs of high-demand customers for high bonding and low cost.

There is an urgent need to solve the problem of how to improve the low bonding strength of the water-based PVDF separator, while reducing the value-added air permeability after the separator is coated, and improving the hardness and cycle performance of the battery core

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