Low-internal-stress polyolefin microporous membrane for lithium ion battery, and preparation method thereof

Abstract

The invention aims to provide a low-internal-stress polyolefin microporous membrane for a lithium ion battery, and a preparation method thereof. The polyolefin microporous membrane is prepared through a wet process, a diaphragm is cooled before extraction, the diaphragm retracts in an MD direction by means of the thermal expansion and cold contraction performance of the diaphragm, it is guaranteed that the speed of the rear section of a microporous membrane production line is lower than that of the front section of the microporous membrane production line, orientation in the MD direction is reduced, and internal stress is reduced; a retraction device is mainly composed of a low-temperature cooling roller and a floating roller; and the microporous membrane also has the characteristic of high mechanical strength of wet process production. Therefore, the preparation method is suitable for preparing high-capacity lithium ion batteries.

Description

technical field

[0001] The invention relates to a polyolefin microporous membrane with low internal stress and a preparation method thereof; the invention uses the polyolefin microporous membrane to cool down before extraction, and uses the thermal expansion and contraction properties of the polyolefin microporous membrane to make the diaphragm return in the MD direction. Shrinkage, to ensure that the speed of the rear section of the polyolefin microporous film production line is lower than that of the front section, the diaphragm will not rewind, and at the same time, the polyolefin is crystallized at a low temperature, reducing the orientation of the MD direction and reducing the internal stress; the polyolefin microporous membrane The porous membrane has good membrane surface smoothness, and is not prone to warping, deformation, edge collapse and other abnormalities during long-term storage, which can improve the assembly performance and safety performance of the battery mad...

Examples

Embodiment 1

[0043] Use ultra-high molecular weight polyethylene with an intrinsic viscosity of 800 milltr / gm as component I, and paraffin oil with a kinematic viscosity of (7-8) mm2 / s at 100°C as component II. The contents of component I and component II are respectively 30% by weight and 70% by weight. Adjust the parameters in the cooling and retracting device to finally form a film with a thickness of 12 ± 1 μm.

Embodiment 2

[0045] Repeat the steps of Example 1, using the ultra-high molecular weight polyethylene with an intrinsic viscosity of 1000 milltr / gm as component I, component II is constant, keep the parameters of the cooling and retracting device the same as in Example 1, and finally form a thickness of 12 ± 1 μm film.

Embodiment 3

[0047] Repeat the steps of Example 1, using ultra-high molecular weight polyethylene with an intrinsic viscosity of 1200 milltr / gm as component I, component II is constant, keep the parameters of the cooling and retracting device the same as in Example 1, and finally form a thickness of 12 ± 1 μm film.

technical field

[0001] The invention relates to a polyolefin microporous membrane with low internal stress and a preparation method thereof; the invention uses the polyolefin microporous membrane to cool down before extraction, and uses the thermal expansion and contraction properties of the polyolefin microporous membrane to make the diaphragm return in the MD direction. Shrinkage, to ensure that the speed of the rear section of the polyolefin microporous film production line is lower than that of the front section, the diaphragm will not rewind, and at the same time, the polyolefin is crystallized at a low temperature, reducing the orientation of the MD direction and reducing the internal stress; the polyolefin microporous membrane The porous membrane has good membrane surface smoothness, and is not prone to warping, deformation, edge collapse and other abnormalities during long-term storage, which can improve the assembly performance and safety performance of the battery mad...

Examples

Embodiment 1

[0043] Use ultra-high molecular weight polyethylene with an intrinsic viscosity of 800 milltr / gm as component I, and paraffin oil with a kinematic viscosity of (7-8) mm2 / s at 100°C as component II. The contents of component I and component II are respectively 30% by weight and 70% by weight. Adjust the parameters in the cooling and retracting device to finally form a film with a thickness of 12 ± 1 μm.

Embodiment 2

[0045] Repeat the steps of Example 1, using the ultra-high molecular weight polyethylene with an intrinsic viscosity of 1000 milltr / gm as component I, component II is constant, keep the parameters of the cooling and retracting device the same as in Example 1, and finally form a thickness of 12 ± 1 μm film.

Embodiment 3

[0047] Repeat the steps of Example 1, using ultra-high molecular weight polyethylene with an intrinsic viscosity of 1200 milltr / gm as component I, component II is constant, keep the parameters of the cooling and retracting device the same as in Example 1, and finally form a thickness of 12 ± 1 μm film.

Images