Preparation method of phase change composite diaphragm with thermal closing function

Abstract

The invention discloses a preparation method of a phase-change composite diaphragm with a thermal closing function. Main components in the diaphragm are an electrostatic spinning fiber membrane and a phase-change microcapsule. According to the diaphragm, the fiber membrane serves as a base membrane to play a role in framework supporting and has the characteristic of being not prone to shrinkage at the high temperature; the phase-change material in the diaphragm can control the temperature to enable the battery to run stably, and when the battery is abnormal and the temperature is continuously increased to a certain degree, the microcapsules can be broken to block micropores of the base membrane, and an ion channel is cut off before thermal runaway of the battery, so that the safety of the battery is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, and in particular to a method for preparing a phase change composite separator with thermal shut-off function. Background Technology

[0002] The safety and reliability of lithium-ion batteries have always been issues requiring continuous attention and improvement. The separator, as a key component, plays a crucial role in providing ion migration channels, ensuring battery safety, and improving battery performance. Currently, commercially available polyolefin separators are prone to softening, deformation, and even melting at high temperatures, potentially leading to thermal runaway, fire, and other safety issues, posing a serious threat to the safety of the battery system. Therefore, there is an urgent need for new materials or technologies to address the battery separator safety issues caused by drastic temperature changes. Chinese patent application 201920593724.X discloses a functional composite separator for secondary batteries, which consists of a commercially available polyolefin separator, an inorganic oxide coating, and a conductive coating. The inorganic oxide coating does indeed improve the thermal stability of the separator, while the conductive coating helps promote electron transfer efficiency at the interface. However, simply enhancing the heat resistance of the separator is insufficient to effectively address the problems of heat accumulation and release within the battery, and cannot fundamentally prevent thermal runaway. In contrast, giving the separator a thermal shut-off function is particularly crucial in addressing the thermal runaway problem. Phase change materials, as a novel type of thermally responsive material, offer an effective solution for diaphragm modification due to their ability to absorb or release heat during phase change. Summary of the Invention

[0003] To address the need for improvements in existing technologies, this invention provides a method for preparing a phase change composite separator with a heat-shutdown function. The heat-shutdown phase change composite separator is obtained by coating phase change microcapsules onto a polymer membrane, and this separator replaces commercially available polyolefin separators in lithium batteries. The phase change material effectively captures heat generated inside the battery, and under abnormally high temperatures, the microcapsules rupture, causing significant leakage of the internal core material that blocks the separator's micropores and hinders lithium-ion transport. The electrolyte affinity of the polymer membrane promotes electrolyte penetration into the micropores, thereby improving battery performance.

[0004] To achieve the above objectives, according to one aspect of the present invention, a phase change composite membrane with a heat-shutting function is provided, the heat-shutting phase change composite membrane being composed of phase change microcapsules and an electrospun fiber membrane. The phase change microcapsules are phase change materials with heat storage function, and the electrospun fiber membrane is a polymer membrane with electrolyte affinity; the phase change microcapsules are coated on the polymer membrane.

[0005] More preferably, the core layer of the phase change microcapsule is a phase change material that is immiscible with the electrolyte and has a melting temperature of 20 to 100°C, such as one or more of n-dodecane, n-tetracosane, 1-tetradecane alcohol, 1-hexadecane alcohol, methyl stearate or ethyl stearate solution.

[0006] More preferably, the sheath of the phase change microcapsule is a polymer material that can melt or transform into a viscous flow state in the range of 50 to 150°C, such as a copolymer of one or two monomers of polymethyl methacrylate, polyethyl methacrylate, polystyrene, etc.

[0007] More preferably, the polymer is one of polyvinylidene fluoride-co-hexafluoropropylene, polyethersulfone, and poly(m-phenylene isophthalamide), and its excellent high-temperature stability provides a skeletal support for the composite membrane.

[0008] More preferably, the coating thickness of the phase change microcapsules is 5–20 μm, and the mass percentage is 10%–40%.

[0009] According to another aspect of the present invention, an application of the phase change composite fiber separator with heat shut-off function described above is provided in a battery, wherein the separator is disposed between the positive and negative electrodes of the battery, and wherein the phase change material in the phase change composite fiber separator with heat shut-off function regulates the heat inside the battery and stops the battery from operating when necessary.

[0010] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0011] 1. The phase change composite separator with thermal shutdown function provided by the present invention has the phase change material having the characteristics of absorbing and releasing heat, so as to ensure that the battery operates stably within the optimal operating temperature range.

[0012] 2. The phase change composite membrane with thermal shut-off function provided by the present invention can release the phase change material in time when the temperature exceeds 105°C, thereby blocking the membrane pores and cutting off lithium ion transport.

[0013] 3. The polymer film provided by this invention, as a base film, exhibits excellent heat resistance and plays a crucial role in providing skeletal support. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of the phase change composite membrane prepared in the embodiments of the present invention.

[0015] Figure 2 This is an infrared thermal imaging comparison of the phase change composite membrane prepared in step 3 of Example 1 of the present invention and a commercial polyolefin membrane after being treated on a heating stage at 100°C for a period of time.

[0016] Figure 3 This is a cycle performance diagram of a lithium-sulfur coin cell assembled with the phase change composite membrane prepared in step 3 of Example 2 of the present invention.

[0017] Figure 4 This is a scanning electron microscope image of the phase change microcapsules prepared in step 1 of Example 3 of the present invention, heated at 105°C.

[0018] Figure 5 This is a scanning electron microscope image of the phase change composite membrane prepared in step 3 of Example 4 of the present invention, showing micropore blockage at 105°C. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0020] A phase change composite membrane with thermal shut-off function, such as Figure 1 As shown, the heat-shutdown phase change composite fiber diaphragm is composed of phase change microcapsules and electrospun fiber membrane. The phase change microcapsules are phase change materials with heat storage function, and the electrospun fiber membrane is a polymer membrane with electrolyte affinity. The phase change microcapsules are coated on the polymer membrane.

[0021] The core layer of the phase change microcapsule is a phase change material that is immiscible with the electrolyte and has a melting temperature of 20–100°C, such as one or more of the following: n-docosane, n-tetracosane, n-hexacosane, 1-tetradecane alcohol, 1-hexadecane alcohol, methyl stearate, and ethyl stearate solution.

[0022] The sheath of phase change microcapsules is a polymer material that can melt or transform into a viscous flow state in the range of 50 to 150°C, such as a copolymer of one or two monomers of polymethyl methacrylate, polyethyl methacrylate, and polystyrene.

[0023] The polymer material is one of polyvinylidene fluoride-co-hexafluoropropylene, polyethersulfone, and poly(m-phenylene isophthalamide).

[0024] This invention provides a method for preparing a thermally shut-off phase change composite membrane, characterized in that the method includes the following steps:

[0025] (1) Weigh 4g of polyvinyl alcohol and dissolve it in 200mL of distilled water. Heat to 85℃ and stir until completely dissolved. Control the stirring speed at 300-600rpm to obtain the aqueous phase. Weigh 0.6g of crosslinking agent and 0.3g of initiator and dissolve them in 2-8g of methyl methacrylate. Stir until completely dissolved. Weigh 2-8g of n-dodecane and add it to the solution. Stir until completely mixed to obtain the oil phase. Pour the oil phase into the aqueous phase and emulsify for 5-10min at a speed of 5000-10000rpm to obtain an O / W emulsion. Transfer the emulsion to a three-necked flask and react at 82℃ for 3-5h to obtain the product. Separate the microcapsules using filter paper and wash several times with ethanol to remove adsorbed organic impurities.

[0026] The crosslinking agent is pentaerythritol tetraacrylate, and the initiator is benzoyl peroxide.

[0027] (2) Weigh 2.6 g of polyvinylidene fluoride (polyvinyl difluoroethylene-co-hexafluoropropylene) and dissolve it in 10 mL of N,N'-dimethylformamide and acetone (N,N'-dimethylformamide and acetone volume ratio 7:3). Stir for 12 h to obtain the spinning solution. The electrospinning flow rate is set to 0.6 mL / h. -1 An 18kV potential difference is applied between the nozzles of the collector syringe, and the base film is obtained by spinning for 6-8 hours.

[0028] (3) Coat the phase change microcapsule slurry onto the electrospun base film of (2) with a coating thickness of 5-20 μm and dry it in an oven at 60°C for 12 h.

[0029] The phase change microcapsule slurry includes phase change microcapsules, a binder, and distilled water.

[0030] The present invention will be further described below with reference to specific embodiments.

[0031] Example 1

[0032] A method for preparing a phase change composite membrane with thermal shut-off function includes the following steps:

[0033] (1) Weigh 4g of polyvinyl alcohol and dissolve it in 200mL of distilled water. Heat to 85℃ and stir until completely dissolved. Control the stirring speed at 300-600rpm to obtain the aqueous phase. Weigh 0.6g of crosslinking agent and 0.3g of initiator and dissolve them in 8g of methyl methacrylate. Stir until completely dissolved. Weigh 2g of n-dodecane and add it to the solution. Stir until completely mixed to obtain the oil phase. Pour the oil phase into the aqueous phase and emulsify for 5min at a speed of 5000-10000rpm to obtain an O / W emulsion. Transfer the emulsion to a three-necked flask and react at 82℃ for 3h to obtain the product. Separate the microcapsules using filter paper and wash several times with ethanol to remove adsorbed organic impurities.

[0034] (2) Weigh 2.6 g of polyvinylidene fluoride (polyvinyl difluoroethylene-co-hexafluoropropylene) and dissolve it in 10 mL of N,N'-dimethylformamide and acetone (N,N'-dimethylformamide and acetone volume ratio 7:3). Stir for 12 h to obtain the spinning solution. The electrospinning flow rate is set to 0.6 mL / h. -1 An 18kV potential difference was applied between the nozzles of the collector syringe, and the base film was obtained by spinning for 8 hours.

[0035] (3) The phase change microcapsule slurry was coated onto the electrospun base film with a coating thickness of 5 μm and a mass ratio of 10%, and dried in an oven at 60°C for 12 h.

[0036] Figure 2 The infrared thermal image of the phase change composite membrane prepared in this embodiment after heat treatment at 100°C shows that the phase change membrane exhibits a lower temperature than the polyolefin membrane, demonstrating excellent temperature regulation capabilities.

[0037] Example 2

[0038] A method for preparing a phase change composite membrane with thermal shut-off function includes the following steps:

[0039] (1) Weigh 4g of polyvinyl alcohol and dissolve it in 200mL of distilled water. Heat to 85℃ and stir until completely dissolved. Control the stirring speed at 300-600rpm to obtain the aqueous phase. Weigh 0.6g of crosslinking agent and 0.3g of initiator and dissolve them in 8g of ethyl methacrylate. Stir until completely dissolved. Weigh 4g of n-tetracosane and add it to the solution. Stir until completely mixed to obtain the oil phase. Pour the oil phase into the aqueous phase and emulsify for 10min at a speed of 5000-10000rpm to obtain an O / W emulsion. Transfer the emulsion to a three-necked flask and react at 82℃ for 3h to obtain the product. Separate the microcapsules using filter paper and wash several times with ethanol to remove adsorbed organic impurities.

[0040] (2) Weigh 2.6 g of polyacrylonitrile and dissolve it in 10 mL of N,N'-dimethylformamide and acetone (N,N'-dimethylformamide and acetone volume ratio 5:5). Stir for 12 h to obtain the spinning solution. The electrospinning flow rate is set to 1.2 mL / h. -1 A potential difference of 16 kV was applied between the nozzles of the collector syringe, and the base film was obtained by spinning for 8 hours.

[0041] (3) The phase change microcapsule slurry was coated onto the electrospun base film with a coating thickness of 10 μm and a mass ratio of 20%, and dried in an oven at 60°C for 12 h.

[0042] The above-mentioned separator was used to assemble a lithium-sulfur coin cell, with a sulfur-carbon positive electrode, and electrochemical tests were performed. Figure 3As shown, at room temperature and a current density of 0.2C, the initial specific capacity is 1231 mAh / g, and after 200 cycles it is 738.6 mAh / g.

[0043] Example 3

[0044] A method for preparing a phase change composite membrane with thermal shut-off function includes the following steps:

[0045] (1) Weigh 4g of polyvinyl alcohol and dissolve it in 200mL of distilled water. Heat to 85℃ and stir until completely dissolved. Control the stirring speed at 300-600rpm to obtain the aqueous phase. Weigh 0.6g of crosslinking agent and 0.3g of initiator and dissolve them in 8g of methyl methacrylate. Stir until completely dissolved. Weigh 6g of n-hexadecane and add it to the solution. Stir until completely mixed to obtain the oil phase. Pour the oil phase into the aqueous phase and emulsify for 5min at a speed of 5000-10000rpm to obtain an O / W emulsion. Transfer the emulsion to a three-necked flask and react at 82℃ for 3h to obtain the product. Separate the microcapsules using filter paper and wash several times with ethanol to remove adsorbed organic impurities.

[0046] (2) Weigh 2.6 g of polyacrylonitrile and dissolve it in 10 mL of N,N'-dimethylformamide and acetone (N,N'-dimethylformamide and acetone volume ratio 7:3). Stir for 12 h to obtain the spinning solution. The electrospinning flow rate is set to 0.6 mL / h. -1 An 18kV potential difference was applied between the nozzles of the collector syringe, and the base film was obtained by spinning for 8 hours.

[0047] (3) The phase change microcapsule slurry was coated onto the electrospun base film with a coating thickness of 15 μm and a mass ratio of 30%, and dried in an oven at 60°C for 12 h.

[0048] Figure 4 The image shows a scanning electron microscope image of the microcapsule under a heating condition of 105°C. The microcapsule shell ruptures, releasing a large amount of phase change core material.

[0049] Example 4

[0050] A method for preparing a phase change composite membrane with thermal shut-off function includes the following steps:

[0051] (1) Weigh 4g of polyvinyl alcohol and dissolve it in 200mL of distilled water. Heat to 85℃ and stir until completely dissolved. Control the stirring speed at 300-600rpm to obtain the aqueous phase. Weigh 0.6g of crosslinking agent and 0.3g of initiator and dissolve them in 8g of styrene. Stir until completely dissolved. Weigh 8g of 1-hexadecyl alcohol and add it to the solution. Stir until completely mixed to obtain the oil phase. Pour the oil phase into the aqueous phase and emulsify for 5min at a speed of 5000-10000rpm to obtain an O / W emulsion. Transfer the emulsion to a three-necked flask and react at 82℃ for 3h to obtain the product. Separate the microcapsules using filter paper and wash several times with ethanol to remove adsorbed organic impurities.

[0052] (2) Weigh 2.8 g of polyethersulfone and dissolve it in 10 mL of N,N'-dimethylformamide and acetone (N,N'-dimethylformamide and acetone volume ratio 7:3). Stir for 12 h to obtain the spinning solution. The electrospinning flow rate is set to 1.0 mL / h. -1 A potential difference of 15 kV was applied between the nozzles of the collector syringe, and the base film was obtained by spinning for 8 hours.

[0053] (3) The phase change microcapsule slurry was coated onto the electrospun base film with a coating thickness of 20 μm and a mass ratio of 30%, and dried in an oven at 60°C for 12 h.

[0054] Figure 5 This is a scanning electron microscope cross-sectional image of the above-mentioned separator after heating it on a hot stage at 105°C. The pores of the separator are blocked by the phase change material. This indicates that the battery is thermally shut down.

[0055] Example 5

[0056] A method for preparing a phase change composite membrane with thermal shut-off function includes the following steps:

[0057] (1) Weigh 4g of polyvinyl alcohol and dissolve it in 200mL of distilled water. Heat to 85℃ and stir until completely dissolved. Control the stirring speed at 300-600rpm to obtain the aqueous phase. Weigh 0.6g of crosslinking agent and 0.3g of initiator and dissolve them in 8g of styrene. Stir until completely dissolved. Weigh 8g of paraffin wax and add it to the solution. Stir until completely mixed to obtain the oil phase. Pour the oil phase into the aqueous phase and emulsify for 5min at a speed of 5000-10000rpm to obtain an O / W emulsion. Transfer the emulsion to a three-necked flask and react at 82℃ for 3h to obtain the product. Separate the microcapsules using filter paper and wash several times with ethanol to remove adsorbed organic impurities.

[0058] (2) Weigh 2.6 g of poly(m-phenylene isophthalamide) and dissolve it in 10 mL of N,N'-dimethylacetamide and acetone (N,N'-dimethylacetamide and acetone volume ratio 7:3). Stir for 12 h to obtain the spinning solution. The electrospinning flow rate is set to 0.6 mL / h.-1 An 18kV potential difference was applied between the nozzles of the collector syringe, and the base film was obtained by spinning for 8 hours.

[0059] (3) The phase change microcapsule slurry was coated onto the electrospun base film with a coating thickness of 20 μm and a mass ratio of 40%, and dried in an oven at 60°C for 12 h.

[0060] The above-mentioned separator was used to assemble a lithium-sulfur coin cell, with a sulfur-carbon cathode, and electrochemical tests were conducted. At room temperature, the initial specific capacity was 1125 mAh / g at a current density of 1C, and it was 724.6 mAh / g after 200 cycles.

[0061] Example 6

[0062] A method for preparing a phase change composite membrane with thermal shut-off function includes the following steps:

[0063] (1) Weigh 4g of polyvinyl alcohol and dissolve it in 200mL of distilled water. Heat to 85℃ and stir until completely dissolved. Control the stirring speed at 300-600rpm to obtain the aqueous phase. Weigh 0.6g of crosslinking agent and 0.3g of initiator and dissolve them in 8g of styrene. Stir until completely dissolved. Weigh 6g of stearic acid solution and add it to the solution. Stir until completely mixed to obtain the oil phase. Pour the oil phase into the aqueous phase and emulsify for 5min at a speed of 5000-10000rpm to obtain an O / W emulsion. Transfer the emulsion to a three-necked flask and react at 82℃ for 3h to obtain the product. Separate the microcapsules using filter paper and wash several times with ethanol to remove adsorbed organic impurities.

[0064] (2) Weigh 2.6 g of poly(m-phenylene isophthalamide) and dissolve it in 10 mL of N,N'-dimethylacetamide and acetone (N,N'-dimethylacetamide and acetone volume ratio 7:3). Stir for 12 h to obtain the spinning solution. The electrospinning flow rate is set to 0.6 mL / h. -1 An 18kV potential difference was applied between the nozzles of the collector syringe, and the base film was obtained by spinning for 8 hours.

[0065] (3) The phase change microcapsule slurry was coated onto the electrospun base film with a coating thickness of 20 μm and dried in an oven at 60 °C for 12 h.

[0066] The above-mentioned separator was used to assemble a lithium-sulfur coin cell, with a sulfur-carbon cathode, and electrochemical tests were conducted. At room temperature, the initial specific capacity was 1125 mAh / g at a current density of 1C, and it was 724.6 mAh / g after 200 cycles.

[0067] Comparative Example 1

[0068] Commercially available polyolefin membranes without any modification were used as Comparative Example 1.

[0069] Comparative Example 2

[0070] 2.6 g of polyvinylidene fluoride (polyvinyl difluoroethylene-co-hexafluoropropylene) was dissolved in 10 mL of N,N'-dimethylformamide and acetone (N,N'-dimethylformamide and acetone volume ratio 7:3) and stirred for 12 h to obtain the spinning solution. The electrospinning flow rate was set to 0.6 mL / h. -1 An 18kV potential difference was applied between the nozzles of the collector syringe, and the base film was obtained by spinning for 8 hours, as a comparative example 2.

[0071] Compared with Comparative Example 1 and Comparative Example 2, the composite separator prepared in Example 4 of this invention with thermally shut-off phase change microcapsules coated with electrospun base film showed excellent electrochemical performance. The initial discharge specific capacity and the remaining specific capacity after 200 cycles are shown in Table 1.

[0072]

[0073] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention.

Claims

1. A method for preparing a phase change composite membrane with thermal shut-off function, characterized in that, It includes a polymer base film and a phase change microcapsule slurry on the surface of the base film, wherein the phase change microcapsule slurry includes phase change microcapsule particles, a binder, and distilled water.

2. The method for preparing a phase change composite membrane with thermal shut-off function according to claim 1, characterized in that, The core layer of the phase change microcapsule is a phase change material that is immiscible with the electrolyte and has a melting temperature of 20–100°C, such as one or more of n-docosane, n-tetracosane, 1-tetradecane, 1-hexadecane, methyl stearate, or ethyl stearate.

3. The method for preparing a phase change composite membrane with thermal shut-off function according to claim 1, characterized in that, The sheath of the phase change microcapsule is a polymer material that can melt or transform into a viscous flow state in the range of 50 to 150°C, such as a copolymer of one or two monomers of polymethyl methacrylate, polyethyl methacrylate, polystyrene, etc.

4. The method for preparing a phase change composite membrane with thermal shut-off function according to claim 1, characterized in that, The polymer is made of one of polyvinylidene fluoride (PVDF-co-hexafluoropropylene), polyethersulfone, or poly(m-phenylene isophthalamide), and its excellent high-temperature stability provides a skeletal support for the composite membrane.

5. The method for preparing a phase change composite membrane with thermal shut-off function according to any one of claims 1 to 4, characterized in that, The phase change microcapsule coating has a thickness of 5–20 μm and a mass percentage of 10%–40%.

6. The method for preparing a phase change composite fiber diaphragm with thermal shut-off function according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Preparation of phase change microcapsules; (2) Preparation of electrospun base membrane; (3) Preparation of composite membrane.

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