Preparation method for polyimide with cross-linked structure and application of polyimide nanofiber membrane in lithium battery diaphragm

Abstract

The invention provides a preparation method for a polyimide nanofiber membrane with a cross-linked structure and application of the polyimide nanofiber membrane in a lithium battery diaphragm, belonging to the field of high polymer materials. The preparation method comprises the following steps: subjecting a polyamide acid solution to electrostatic spinning to prepare a polyamide acid nanofiber membrane; etching the polyamide acid nanofiber membrane in an aqueous ammonia solution with a pH value of 8 to 10 for 60 s to form the cross-linked structure; and carrying out washing, drying and imidization at a temperature of 300 DEG C so as to prepare the polyimide nanofiber membrane. The lithium ion battery diaphragm provided by the invention has high mechanical properties, heat stability, high porosity and excellent electrochemical performance. The battery diaphragm has the cross-linked structure and high mechanical properties, thereby overcoming the problems of low strength and an over-open pore structure of a nonwoven polyimide nanofiber membrane. Meanwhile, the diaphragm has porosity of about 80% and can resist a high temperature of 300 DEG C without any deformation, thereby overcoming the disadvantages of low porosity and poor temperature resistance of a polyolefin microporous diaphragm. In particular, the diaphragm provided in the invention has specific capacity substantially better than that of the traditional polyolefin microporous diaphragm under the conditions of high-rate rapid charging and discharging.

Description

technical field [0001] The invention belongs to the field of polymer materials, and provides a preparation method of a polyimide nanofiber membrane with a crosslinked structure and its application as a novel lithium-ion battery diaphragm. Background technique [0002] Lithium-ion battery is a high-efficiency, high-energy and green rechargeable battery developed in the 1990s. Due to its high working voltage, high specific energy, large capacity, small self-discharge, good cycle performance, long service life, The outstanding advantages of light weight and small size have attracted much attention in new power supply technologies. Today, it has become one of the indispensable necessities in today's networked and informationized digital age. In addition to being widely used in daily familiar mobile phones, notebook computers and other digital electronic products, lithium-ion batteries have gradually been widely used in aerospace, navigation, artificial satellites, small medical...

AI Technical Summary

Problems solved by technology

However, due to the structural characteristics of polyethylene and polypropylene materials, polyolefin separators have their own insurmountable problems

There are two main aspects. First, PP and PE are non-polar polymer materials, which leads to poor wettability between them and polar electrolytes when they are used as battery separators, resulting in a large internal resistance of the battery. , affecting the cycle and overall performance of the battery

Second, the melting point or softening temperature of PP and PE materials is too low, PP is 165°C, PE is 135°C, which leads to great problems in the temperature resistance and high temperature safety performance of the battery

[0006] When polyimide-based nanofiber membranes are used in lithium-ion battery separators, because the fibers in the nanofiber membranes are loosely packed together, there is no strong interaction between them, the fiber structure is loose, and there is a problem of insufficient mechanical properties.

There are literatures to improve the mechanical properties of the nanofiber membrane by increasing the thickness of the fiber membrane or molding the thicker nanofiber membrane, but increasing the thickness of the fiber membrane will increase the impedance of the battery separator at the same time, so that its electrical properties will decrease; the porosity of the nanofiber membrane after molding Lower air permeability and liquid absorption rate will decrease, neither fundamentally solve the problem of insufficient mechanical properties of nanofiber membranes used in battery separators

In addition, since the fibers in the fiber membrane are only loosely overlapped, the fiber membrane is prone to swelling and disintegration after long-term immersion in the electrolyte, resulting in poor long-term charge-discharge cycle life of the battery. More importantly, this It has a great impact on the safety performance of the battery, so that its practical and large-scale application is greatly limited

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