Diaphragm for high thermal safety temperature lithium ion cell and preparation method thereof

A lithium-ion battery, safe temperature technology, applied in battery pack parts, circuits, electrical components, etc., can solve the problems of safety performance to be improved, inability to effectively thermally close holes, loss of protection functions, etc., to achieve good physical structure support, The effect of improving electrophilic performance and preventing battery explosion

Inactive Publication Date: 2012-07-18
WUHAN UNIV OF TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

The temperature difference of 35°C between the thermal closing temperature of PE and the thermal melting temperature of PP can be used to protect general lithium-ion batteries. However, when the separator is punctured and overcharged with high current density, the shrinkage of the film (heating at 105°C for 8 hours shrinks 2.5 -5%) or even melting will directly lead to short circuit and lose the protection function
[0004] In addition, the patent CN 200510055714.3 discloses a method for manufacturing a diaphragm for electronic components. The diaphragm can be used in lithium-ion secondary batteries. It is composed of a resin structure, but the invention uses a coating method to form a resin coating on a porous substrate and after drying, the carrier material needs to be removed, so the prepared membrane is not a composite membrane reinforced by a carrier
Moreover, the melting point of the filling resin in this invention is higher than or equal to 145°C, which cannot ensure that the thermal closure temperature of the diaphragm still remains after the thermal closure of the diaphragm, such as the PP / PE / PP three-layer diaphragm and the composite film prepared by the invention. The strength prevents the positive and negative poles of the battery from contacting and short circuiting
The melting point of the filling resin mentioned above is higher than or equal to 145°C. When the melting point is too high, the pores cannot be effectively thermally closed. When the melting point is too low, it is easy to melt directly and cause a short circuit.
It can be seen that the safety performance of the diaphragm for electronic components manufactured by the invention needs to be improved when it is used in lithium-ion secondary batteries.

Method used

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  • Diaphragm for high thermal safety temperature lithium ion cell and preparation method thereof
  • Diaphragm for high thermal safety temperature lithium ion cell and preparation method thereof
  • Diaphragm for high thermal safety temperature lithium ion cell and preparation method thereof

Examples

Experimental program
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Effect test

Embodiment 1

[0029] Dissolve PVDF-HFP (KYNAR FLEX 2801) in a mixed solvent of N-N dimethylformamide and acetone (volume ratio 4:3), and add DBP (dibutyl phthalate into Pore ​​agent), prepared into a polymer solution with a solid content of 5wt%, and stirred at 35°C for 1.5h to form a homogeneous casting solution. A porous polytetrafluoroethylene substrate with a thickness of 2 μm, a mechanical strength (machine direction) of 60 MPa, an average pore diameter of 5 μm, and a porosity of 80% was immersed in the casting solution for 0.5 h at 35° C. 10 -1 Torr, dried at 80° C. for 12 h to remove the solvent. Take out the initial composite membrane and soak it in absolute ethanol at 40°C to extract the pore-forming agent. Naturally drying to remove ethanol produces a separator for lithium-ion batteries with a high thermal safety temperature. The thermal closure temperature of the separator is 125°C, and the thermal safety temperature can reach 338°C.

[0030] The scanning electron microscope p...

Embodiment 2

[0032] PVDF-HFP (Aldrich, M w=400,000) was dissolved in the mixed solvent of N-methylpyrrolidone and acetone (volume ratio 2:1), and DBP and 0.1g P123 (polyoxypropylene-polyoxyethylene copolymer, EO / PO / EO=30 / 70 / 30, M w ==5800), prepare a polymer solution with a solid content of 8wt%, and stir at 40°C for 1.5h to form a homogeneous casting solution. A porous polytetrafluoroethylene substrate with a thickness of 5 μm, a mechanical strength (machine direction) of 150 MPa, an average pore diameter of 4 μm, and a porosity of 75% was immersed in the casting solution for 1 hour at 40° C. -1 Torr, dried at 80° C. for 12 h to remove the solvent. The initial composite membrane was taken out and soaked in absolute ethanol at 70°C for 6 hours to extract the pore-forming agent. Drying and removing ethanol produces a separator for lithium-ion batteries with a high thermal safety temperature. The thermal closure temperature of the separator is 133° C., and the thermal safety temperature ...

Embodiment 3

[0033] Example 3 Material

[0034] High-density polyethylene (Samsung general chemical, M w =2400,000) was dissolved in N-N dimethylacetamide and acetone (volume ratio 4: 1) mixed solvent, added liquid paraffin equivalent to 5wt.% of organic solvent quality, prepared a polymer solution with a solid content of 10%, at 40 Stir at ℃ for 1.5h to form a homogeneous casting solution. A porous polytetrafluoroethylene matrix with a thickness of 5 μm, a mechanical strength (machine direction) of 80 Pa, an average pore diameter of 4 μm, a porosity of 50% and a porosity of 75% was immersed in the casting solution at 40°C. 1h to fully immerse the casting solution, after taking it out in 10 -1 Torr, dried at 100° C. for 12 h to remove the solvent. Take out the initial composite membrane, extract the pore-forming agent with acetone, dry and remove the acetone to prepare a separator for lithium-ion batteries with a high thermal safety temperature. The thermal closure temperature of the se...

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Abstract

The invention which discloses a diaphragm for a high thermal safety temperature lithium ion cell and a preparation method thereof belongs to the field of diaphragm materials for lithium ion cells. The diaphragm is mainly formed by a high strength expanded polytetrafluoroethylene matrix membrane and a porous filled polymer with the melting point of 125-160DEG C, the thermal closure temperature of the diaphragm is 125-160DEG C, and the thermal safety temperature of the diaphragm reaches 338DEG C, wherein the tensile strength of the matrix membrane is 60-150MPa, the thickness of the membrane is 2-20mum, the membrane has a through dendritic pore structure, the porosity is 50-80%, and the average pore size is 1-5mum. The preparation method comprises the following steps: mixing a 125-160DEG melting point different polymerization degree polyvinylidene fluoride-hexafluoropropene, polyethylene or polypropylene resin, and a pore forming agent, preparing a homogeneous diaphragm casting liquid in an organic solvent, immersing the matrix membrane in the diaphragm casting liquid, taking out the matrix membrane, extracting the pore forming agent from the matrix membrane by an extractant, and drying the matrix membrane to obtain the diaphragm. The composite diaphragm prepared in the invention has the advantages of high infiltration performance, high thermal safety temperature and high thermomechanical performance, so the safety of the diaphragm in the power lithium ion cell is improved.

Description

technical field [0001] The invention relates to the field of lithium-ion battery diaphragm materials, in particular to a high thermal safety temperature diaphragm for lithium-ion batteries and a preparation method thereof. Background technique [0002] As lithium batteries are increasingly used as power batteries, the demand for high power output performance and safety puts forward higher requirements for lithium battery separators. During the high-power discharge process, the local temperature of the battery is too high, which can cause the solid electrolyte interface protective film of the negative electrode to decompose and release heat, which will cause the battery to further heat up and cause the decomposition of organic electrolyte and other substances and the melting of the diaphragm, resulting in a direct reaction of the positive and negative electrodes or even an explosion. . Puncture or impact during battery use can also cause a momentary drop in battery voltage. ...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H01M2/16C08J7/00C08J9/28C08L27/18
CPCY02E60/12Y02E60/10
Inventor 潘牧孙美玲熊明唐浩林尹壮飞
Owner WUHAN UNIV OF TECH
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