A porous multilayer composite diaphragm and a preparation method thereof

A multi-layer composite and diaphragm technology, which is applied to polypropylene/polyethylene/polypropylene porous multi-layer composite diaphragm and its preparation, and the field of porous multi-layer composite diaphragm and its preparation, can solve the increase of cost and the reduction of ionic conductivity , poor uniformity of micropores, etc., to achieve the effect of good uniformity and consistency, good pore size retention, and high interface consistency

Active Publication Date: 2018-12-21
深圳市博盛新材料有限公司
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0006] One is that it is impossible to make a composite diaphragm with a film with a large difference in material properties
If the materials of each film are quite different, such as the difference in material properties such as melt index and melting temperature, each film is stretched at high temperature (same time and parameters) in the stretching machine, and some layers are not fully stretched, and micropores cannot be formed. Or form uneven micropores, and some layers are overstretched to form too large micropores or tear into uneven micropores, that is, it is impossible to form a high-consistency microporous separator
[0007] Second, it is impossible to make a composite diaphragm with different micropores in each layer
First of all, the shedding of the coating layer and the addition of a large amount of binder will block some micropores, resulting in poor uniformity of micropores and reduced ion conductivity, which will reduce the cycle life and capacity of the battery
Secondly, the coating film is subjected to secondary processing on the basis of the diaphragm, and the cumbersome processing is not conducive to subsequent mass industrial production
The rise in cost does not conform to the trend of cost reduction

Method used

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  • A porous multilayer composite diaphragm and a preparation method thereof
  • A porous multilayer composite diaphragm and a preparation method thereof
  • A porous multilayer composite diaphragm and a preparation method thereof

Examples

Experimental program
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Embodiment 1

[0050] (1) Material preparation: the density is 0.91-0.93g / cm 3 , Polypropylene (PP) with a molecular weight of 300,000 is used as the surface layer polypropylene raw material. The density is 0.94-0.96g / cm 3 , High-density polyethylene (PE) with a molecular weight of 400,000 is used as the high-density polyethylene raw material for the core layer.

[0051] (2) Preparation of PP cast film: use a single-screw extruder with an aspect ratio L / D≥34 to melt and extrude polypropylene raw materials, and the extrusion temperature is between 160-230°C. After the melt is filtered and metered, it enters the flat die head, flows out from the die lip to form a sheet, and adheres to the casting roller to form a hard elastic casting film with a film thickness of 8-30 microns. Wherein the die draft ratio DDR is 80-180, and the casting roll temperature is 70-120°C.

[0052] (3) Preparation of PE casting film: use a twin-screw extruder with an aspect ratio L / D≥32 to melt and extrude high-dens...

Embodiment 2

[0059] This example uses the same materials and process steps as in Example 1, but in step (5), the stretching speed ratio of the PP layer is 2.1-2.3, and the stretching speed ratio of the PE layer is 1.8-2.0, and PP / PE / PP is obtained Porous multilayer composite separator.

[0060] The obtained porous multi-layer composite diaphragm has been determined to have an average porosity of 37%, wherein the porosity of the PP layer is 40%, the porosity of the PE layer is 35%; the air permeability is 322s / 100ml; It is 0.32% / week, and the capacity retention rate is 93% after 1C cycle for 2000 cycles.

Embodiment 3

[0062] This example uses the same materials and process steps as Example 1, but in step (5), the stretching speed ratio of the PP layer is 2.8-3, and the stretching speed ratio of the PE layer is 1.6-1.8, and PP / PE / PP is obtained Porous multilayer composite separator.

[0063] The obtained porous multi-layer composite diaphragm is measured, with an average porosity of 37%, wherein the porosity of the PP layer is 49%, the porosity of the PE layer is 30%; the air permeability is 291s / 100ml; It is 0.21% / week, and the capacity retention rate is 91% after 1C cycle for 2000 cycles.

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Abstract

The present application relates to a porous multilayer composite membrane, The porosity of at least one membrane layer in the porous multilayer composite membrane is significantly different from the porosity of other membrane layers, in particular to a PP / PE / PP porous multilayer composite membrane, wherein the porosity of the PP layer in the PP / PE / PP porous multilayer composite membrane is significantly greater than the porosity of the PE layer. The present application also relates to a method of preparing the porous multilayer composite membrane, in particular to the PP / PE / PP porous multilayer composite membrane, comprising an extrusion casting step, a stretching step and a composite shaping step. The porous multilayer composite membrane of the present invention has good ionic conductivity because each layer of the membrane has significantly different porosity, and the corresponding battery prepared has low self-discharge performance. Moreover, the porosity, pore size retention, uniformity and consistency of the porous multilayer composite membrane are good by using micro-melting heat-bonding and heat-setting method without using binder.

Description

technical field [0001] The invention belongs to the field of lithium-ion battery diaphragms, and mainly relates to a porous multilayer composite diaphragm and a preparation method thereof, in particular to a polypropylene / polyethylene / polypropylene (PP / PE / PP) porous multilayer composite diaphragm and its preparation method. Background technique [0002] Lithium-ion battery separator is one of the four key main materials (positive electrode material, negative electrode material, electrolyte, separator) of lithium-ion battery. The diaphragm is placed between the positive and negative poles of the battery, which plays the role of isolating electrons in the battery and preventing the short circuit of the positive and negative poles. At the same time, it provides ion transmission channels and conducts ions during the charging and discharging process. It is the core of lithium-ion batteries. The performance of the core components has a certain impact on the internal resistance, c...

Claims

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Application Information

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IPC IPC(8): H01M2/16H01M2/14B29C69/00H01M50/403H01M50/417H01M50/449
CPCB29C69/00B29K2023/065B29K2023/12B29L2007/00H01M50/403H01M50/411H01M50/449Y02E60/10
Inventor 陈世章
Owner 深圳市博盛新材料有限公司
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