A kind of composite diaphragm for lithium ion battery and preparation method thereof

Abstract

The invention discloses a composite separator for lithium ion batteries and a preparation method thereof, including a ceramic coating modification method and a ceramic lithium battery separator. The ceramic protective layer is mainly a mixture composed of ceramics graft-modified by anionic surfactants containing sodium sulfonate or sodium carboxylate groups, and a binder. The grafting is completed under the action of dehydrating agent and using the "grafting to" method. The grafting rate of ceramics is relatively high. The modified ceramic separator has greatly improved the performance of the modified ceramic separator due to the introduction of high-temperature-resistant high-specific surface area nanoceramics on the surface of the conventional PP separator. The insulation and electrolyte wettability of the separator are improved, especially at high temperatures of 130°C, 150°C and 180°C, showing excellent high-temperature thermal stability. The lithium battery composite separator avoids the heat shrinkage of conventional separators, thereby avoiding thermal runaway inside the battery caused by heat shrinkage, thereby improving the safety and reliability of lithium-ion batteries.

Description

Technical field [0001] The invention belongs to the technical field of lithium ion batteries, and specifically relates to a composite separator for lithium ion batteries and a preparation method thereof. More specifically, the invention relates to a composite separator containing an anionic surfactant and modifying the coating of ceramics through grafting, thereby improving the A method of dispersion and adhesion of ceramics. Background technique [0002] Since their commercialization, lithium-ion batteries have been widely used as power sources for various mobile devices due to their high energy density, high operating voltage, no memory effect, and long cycle life. It is very likely to become the most important power supply system in the field of energy storage and electric vehicles. However, with the large-scale application of lithium-ion batteries, battery safety issues have become increasingly prominent. [0003] One of the key factors affecting the safety of lithium-i...

AI Technical Summary

Problems solved by technology

However, there are still two shortcomings in the ceramic grafting modification method: one is that the selected monomer has a large steric hindrance and the grafting rate is low; the other is that the process operation is complicated, which is not conducive to industrial production. Ion exchange was also carried out after the neutralization, and the product loss would be caused during the ion exchange process, further reducing the yield

The steric hindrance of the monomer is specifically reflected in the steric hindrance of the benzene ring in sodium benzenesulfonate (also known as the stereo effect: mainly refers to the steric hindrance caused by certain atoms or groups in the molecule being close to each other and the deviation from the normal bond angle. The tension in the molecule) is relatively large, that is, the sodium benzenesulfonate derivatives all contain rigid benzene rings with high tension. When such reagents attack Al as a nucleophile 2 o 3 When the surface hydroxyl group, due to the influence of the larger steric hindrance of the benzene ring connected by the sulfonic acid group, the reaction rate of the two reactants is greatly reduced, thus reducing the Al 2 o 3 The number of reactions between hydroxyl groups and sodium sulfonate derivatives on the surface of ceramics, thereby reducing the grafting rate of ceramics

Al on ceramic surface 2 o 3 Only some of the hydroxyl groups in the ceramics are successfully grafted and covered, and most of the free hydroxyl groups fail to react with the surface active monomers to be grafted and covered. When the ceramics are dispersed, there will still be intramolecular hydrogen bonds of the free hydroxyl groups. resulting in a large amount of ceramic agglomeration

The result must be that the problem of difficult dispersion of ceramics has not been solved fundamentally. On the other hand, due to the low grafting rate, the degree of improvement of the hydrophilic and lipophilic properties of the hydroxyl groups on the ceramic surface is not obvious.

In the later stage of bonding with polyolefin base film, problems such as poor adhesion and easy peeling off of the ceramic coating will occur

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