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CN-122025995-A - Composite diaphragm and preparation method and application thereof

CN122025995ACN 122025995 ACN122025995 ACN 122025995ACN-122025995-A

Abstract

The invention relates to the technical field of batteries, in particular to a composite diaphragm and a preparation method and application thereof. A composite diaphragm comprises a base film, a heat-resistant layer and a low-closed-cell composite flame-retardant layer, wherein the heat-resistant layer is positioned on one side surface of the base film, the low-closed-cell composite flame-retardant layer is positioned on the other side surface of the base film, the rupture temperature T1 of the heat-resistant layer and the rupture temperature T0 of the base film are respectively 30 ℃ less than or equal to T1-T0 and less than or equal to 350 ℃, and the melting temperature T2 of the low-closed-cell composite flame-retardant layer and the closure temperature T0 of the base film are respectively 5 ℃ less than or equal to T0-T2 and less than or equal to 50 ℃. The composite diaphragm can prevent oxygen from generating heat by crosstalk between the anode and the cathode, improve the rupture temperature of the diaphragm, reduce short circuit heat generation between the anode and the cathode, has a certain flame retardant effect, and can greatly improve the thermal safety performance of the battery on the premise of ensuring the normal electrochemical performance of the battery.

Inventors

  • HU WEIDONG
  • ZHOU YUNLONG
  • Tu Ruixuan
  • CHEN ZHENGXU
  • JIA SHAOHUA

Assignees

  • 蜂巢能源科技股份有限公司

Dates

Publication Date
20260512
Application Date
20260210

Claims (10)

  1. 1. The composite diaphragm is characterized by comprising a base film, a heat-resistant layer and a low-closed-cell composite flame-retardant layer, wherein the heat-resistant layer is positioned on one side surface of the base film, and the low-closed-cell composite flame-retardant layer is positioned on the other side surface of the base film; the rupture temperature T1 of the heat-resistant layer and the rupture temperature T0 of the base film meet the conditions that the temperature T1 is less than or equal to 30 ℃ and less than or equal to 350 ℃ and the temperature T0 is less than or equal to 0; The melting temperature T2 of the low-closed-cell composite flame-retardant layer and the closed-cell temperature T0 of the base film are equal to or less than 5 ℃ and equal to or less than 0-T2 and equal to or less than 50 ℃.
  2. 2. The composite membrane of claim 1, comprising at least one of the following features (1) to (4): (1) The thickness H1 of the heat-resistant layer and the thickness H2 of the low-closed-cell composite flame-retardant layer and the thickness H0 of the base film meet the relational expression that (H1 + H2)/H0 is more than or equal to 0.2 and less than or equal to 0.75,1/3 and less than or equal to H1/H2 and less than or equal to 3; (2) The thickness of the base film is 5-12 mu m; (3) The thickness of the heat-resistant layer is 1-3 mu m; (4) The thickness of the low-closed-pore composite flame-retardant layer is 1-3 mu m.
  3. 3. The composite membrane of claim 1 comprising at least one of the following features (1) to (3): (1) The heat-resistant layer comprises at least one of para-aramid fiber, meta-aramid fiber, nanofiber and polyimide; (2) The rupture temperature T1 of the heat-resistant layer is 180 ℃ or more and T1 or less than 460 ℃; (3) The base film comprises polyethylene.
  4. 4. The composite membrane of claim 1, wherein the low-closed cell composite flame-retardant layer comprises a low-closed cell material, a flame-retardant material and a bonding material, the mass ratio of the low-closed cell material to the flame-retardant material is (6-22): (2-22), and the bonding material accounts for 1% -5% of the mass of the low-closed cell composite flame-retardant layer.
  5. 5. The composite membrane of claim 4 comprising at least one of the following features (1) to (4): (1) The low closed cell material comprises at least one of polyethylene, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-octene copolymer, ethylene-butyl acrylate copolymer, polyethylene oxide, and nylon; (2) The melting point of the low-closed-pore material is 100-135 ℃; (3) The flame retardant material comprises at least one of magnesium hydroxide, aluminum hydroxide, and polyphosphate; (4) The bonding material includes at least one of polyvinylidene fluoride, polyvinyl alcohol, and polymethyl methacrylate.
  6. 6. The composite membrane of claim 1, wherein the composite membrane has an air permeability of greater than 200s/100cc after baking at 100 ℃ for 30 s; the composite separator has an air permeability of greater than 10000s/100cc after baking at 120 ℃ for 30 s.
  7. 7. The method for preparing the composite membrane according to any one of claims 1 to 6, comprising the steps of: preparing a first system comprising a refractory material, a first pore former, and a first solvent; Preparing a second system comprising a low closed cell material, a flame retardant material, a bonding material, a second pore former, and a second solvent; and coating the first system on one side surface of the base film, coating the second system on the other side surface of the base film, and performing heat treatment to obtain the composite diaphragm.
  8. 8. The method of producing a composite separator according to claim 7, comprising at least one of the following features (1) to (6): (1) The total mass of the heat-resistant material and the first pore-forming agent accounts for 10-30% of the mass of the first system, and the mass ratio of the heat-resistant material to the first pore-forming agent is (18-20): 1; (2) The second pore-forming agent accounts for 3-8% of the second system by mass; (3) The low-closed-cell material, the flame-retardant material and the bonding material account for 5-30% of the mass of the first system, the mass ratio of the low-closed-cell material to the flame-retardant material is (6-22) ((2-22)), and the bonding material accounts for 1-5% of the mass of the low-closed-cell composite flame-retardant layer; (4) The first pore-forming agent and the second pore-forming agent each independently comprise at least one of ammonium carbonate, ammonium bicarbonate, calcium chloride, and polyvinyl alcohol; (5) The first solvent and the second solvent each independently comprise at least one of N-methylpyrrolidone, acetone, and dimethylformamide; (6) The temperature of the heat treatment is 60-100 ℃, and the time of the heat treatment is 1-3 hours.
  9. 9. A battery comprising the composite separator, a positive electrode sheet and a negative electrode sheet according to any one of claims 1 to 6, wherein a heat-resistant layer in the composite separator faces the positive electrode sheet, and a low-closed-pore composite flame-retardant layer faces the negative electrode sheet.
  10. 10. A powered device comprising the battery of claim 9.

Description

Composite diaphragm and preparation method and application thereof Technical Field The invention relates to the technical field of batteries, in particular to a composite diaphragm and a preparation method and application thereof. Background The lithium ion secondary battery is the most promising and competitive secondary battery at present due to the advantages of high energy density, long cycle life, environmental protection, safety and the like. With the wide application of lithium ion batteries, battery safety accidents occur at times, and safety problems are becoming more and more interesting to industry personnel. In the process of heating, the positive electrode of the lithium ion battery can generate oxygen, and the oxygen generated by the positive electrode can react with the electrolyte on one hand, and on the other hand, can cross-talk to the negative electrode through the pores of the diaphragm to react with the LiC 6. When the inside of the battery cell reaches a certain temperature, the membrane is subjected to melting membrane rupture (the current conventional battery cell membrane rupture temperature is about 150 ℃), so that the positive electrode and the negative electrode are directly shorted. The heat generated by the above reaction eventually causes thermal runaway of the battery cell, so that the safety of the battery cell is reduced. In view of this, the present invention has been made. Disclosure of Invention The invention aims to provide a composite diaphragm which is beneficial to preventing crosstalk heat generation between positive and negative electrodes of oxygen, improving the rupture temperature of the diaphragm, reducing short circuit heat generation between positive and negative electrodes, and simultaneously has a certain flame retardant effect, so that the safety of a battery cell is improved. The invention also aims to provide a preparation method of the composite diaphragm, which is simple and easy to implement. Another object of the present invention is to provide a battery. It is another object of the present invention to provide a powered device. In order to achieve the above object of the present invention, the following technical solutions are specifically adopted: The composite diaphragm comprises a base film, a heat-resistant layer and a low-closed-cell composite flame-retardant layer, wherein the heat-resistant layer is positioned on one side surface of the base film, the low-closed-cell composite flame-retardant layer is positioned on the other side surface of the base film, the rupture temperature T1 of the heat-resistant layer and the rupture temperature T0 of the base film are respectively 30 ℃ and less than or equal to T1-T0 and less than or equal to 350 ℃, and the melting temperature T2 of the low-closed-cell composite flame-retardant layer and the closure temperature T0 of the base film are respectively 5 ℃ and less than or equal to T0-T2 and less than or equal to 50 ℃. In some embodiments, the thickness H1 of the heat resistant layer and the thickness H2 of the low closed cell composite flame retardant layer and the thickness H0 of the base film satisfy the relationship of 0.2≤H1+H2)/H0≤ 0.75,1/3≤H2≤3. In some embodiments, the base film has a thickness of 5-12 μm. In some embodiments, the thickness of the heat-resistant layer is 1-3 μm. In some embodiments, the low closed cell composite flame retardant layer has a thickness of 1 to 3 μm. In some embodiments, the heat resistant layer includes at least one of para-aramid, meta-aramid, nanofiber, and polyimide. In some embodiments, the rupture temperature T1 of the heat-resistant layer is 180 ℃ less than or equal to T1 less than or equal to 460 ℃. In some embodiments, the base film comprises polyethylene. In some embodiments, the low-closed-cell composite flame-retardant layer comprises a low-closed-cell material, a flame-retardant material and a bonding material, wherein the mass ratio of the low-closed-cell material to the flame-retardant material is (6-22): (2-22), and the bonding material accounts for 1% -5% of the mass of the low-closed-cell composite flame-retardant layer. In some embodiments, the low closed cell material comprises at least one of polyethylene, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-octene copolymer, ethylene-butyl acrylate copolymer, polyethylene oxide, and nylon. In some embodiments, the low closed cell material has a melting point of 100-135 ℃. In some embodiments, the flame retardant material comprises at least one of magnesium hydroxide, aluminum hydroxide, and polyphosphate. In some embodiments, the bonding material comprises at least one of polyvinylidene fluoride, polyvinyl alcohol, and polymethyl methacrylate. In some embodiments, the composite separator has an air permeability of greater than 200s/100cc after baking at 100 ℃ for 30 seconds and an air permeability of greater than 10000s/100cc after baking at 120 ℃ for 30 seconds. The prepa