Thermal response diaphragm based on thermal polymerization monomer coating, preparation and application

Abstract

The invention relates to a thermal response diaphragm based on thermal polymerization monomer coating, preparation and application, and relates to the technical field of thermal response diaphragms. According to the temperature response diaphragm disclosed by the invention, free radical polymerization is carried out at high temperature through the coated thermal polymerization monomer, and an ion path is blocked, so that battery shutdown is realized. The solubility of the thermal polymerization monomer in the electrolyte changes along with the temperature, when the temperature is low, the solubility of the monomer is low, and when the temperature is high, the solubility of the monomer is high. During thermal abuse of the battery, the thermally polymerizable monomer undergoes a dissolution-polymerization process, achieving thermal protection of the battery. The thermal response diaphragm disclosed by the invention is low in thermal response temperature, can realize integral curing of a battery cell during thermal abuse, can effectively avoid direct contact between a positive electrode and a negative electrode, and improves the thermal safety of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoresponsive diaphragms, and more specifically, to a thermoresponsive diaphragm based on thermopolymerizable monomer coating, preparation and application thereof. Background Art

[0002] Lithium-ion batteries are widely used in fields such as electric vehicles, energy storage systems, and portable electronic devices. However, the battery is prone to thermal runaway under overcharge, short circuit, or high-temperature environments, resulting in electrolyte decomposition, gas expansion, and even fire and explosion. The thermal shutdown diaphragm is an intelligent protective layer that realizes temperature response through material design, which can quickly close the ion channels at the critical temperature, block the internal reaction of the battery, and prevent the spread of thermal runaway.

[0003] The development of thermal runaway inside a lithium-ion battery generally includes three temperatures: self-heating temperature (T1), thermal runaway temperature (T2), and maximum temperature (T3). Once the temperature inside the battery reaches T2, the temperature rises rapidly, and it becomes difficult to contain the thermal runaway. Therefore, shutting down the battery during thermal abuse to prevent the continuous progress of chemical reactions is one of the effective ways to avoid battery thermal runaway.

[0004] In view of the above problems, the existing solutions mainly focus on the following several methods.

[0005] Method 1: Using an electrolyte that thermopolymerizes at high temperatures to shut down the battery. The disadvantage of this technology is that a small amount of thermopolymerizable monomers dissolved in the electrolyte cannot achieve the thermal shutdown of the battery, and an excessive amount of thermopolymerizable monomers will reduce the cycle performance of the battery. At the same time, the thermoresponsive temperature is generally relatively high (exceeding 80 °C), making it difficult to prevent the early heat accumulation inside the battery (see: Electrochemistry Communications 25(2012)98–100; eScience 2(2022)201–208).

[0006] Method 2: Preparing a thermoresponsive current collector, which is a polymer composite film prepared by mixing conductive particles in a polymer matrix with a high coefficient of thermal expansion. The polymer matrix can expand when the temperature rises, separating the originally interconnected conductive particles and blocking the electronic path. The disadvantage of this technology is that it cannot prevent the direct contact between the positive and negative electrodes caused by the shrinkage of the diaphragm (see: Nat Energy 1,15009(2016); Adv.Funct.Mater.2020,30,1910328; ACS Appl.EnergyMater.2022,5,5236-5244).

[0007] In addition to the above two common methods, there is another method which is to prepare a thermoresponsive separator to achieve battery thermal protection. For example, Patent CN 113809476A designs a polyimide battery separator with a thermal closed-pore function to improve battery safety; as in Patent CN 113078414A, by using polyethylene microspheres to melt and fill the micropores of a polypropylene-based film when heated, the lithium-ion transport is blocked, and the safety performance of the lithium-ion battery is improved; and again, as in Patent CN 114039168A, etc., a thermal closed-pore layer slurry is gravure-coated on a base film, and then a ceramic layer slurry is gravure-coated to obtain a thermal closed-pore separator, which can improve the rate performance, cycle life, safety and heat resistance stability of the battery and is easy to achieve large-scale and high-quality production. However, the safety brought by using only a single-layer closed-pore separator to shut off the battery is very limited, because once the separator shrinks, it will cause the positive and negative electrodes to come into direct contact, resulting in a serious exothermic reaction. In contrast, the cross-linking polymerization of the electrolyte will solidify the entire battery cell, which can more effectively prevent gas crosstalk between the positive and negative electrodes. However, the reported response temperatures of the thermoresponsive electrolytes are generally high (exceeding 80 °C), making it difficult to quickly prevent early heat accumulation. Summary of the Invention

[0008] The present invention provides a thermoresponsive separator, its preparation method and application. The solubility of the thermal polymerization monomer in the carbonate-based electrolyte increases with the increase of temperature. The solubility of the thermal polymerization monomer in the electrolyte is less than 2 wt% under the temperature condition below 30 °C and greater than 10 wt% under the temperature condition above 60 °C; the thermoresponsive separator of the present invention can, under the condition that the temperature is higher than 60 °C, undergo a dissolution-polymerization process to block the ion path. The thermoresponsive separator in the present invention has a low thermoresponse temperature, can achieve the overall solidification of the battery cell during thermal abuse, can effectively avoid the direct contact between the positive and negative electrodes, and improves the thermal safety of the battery. Thus, the technical problems of high thermoresponse temperature and poor thermal safety faced in the prior art are solved.

[0009] According to the first aspect of the present invention, there is provided a thermoresponsive separator based on the coating of a thermal polymerization monomer, wherein the thermal polymerization monomer is coated on the separator; the solubility of the thermal polymerization monomer in the electrolyte increases with the increase of temperature, and the solubility of the thermal polymerization monomer in the electrolyte is less than 2 wt% under the temperature condition below 30 °C and greater than 10 wt% under the temperature condition above 60 °C in this electrolyte;

[0010] The thermoresponsive separator based on the coating of the thermal polymerization monomer can, under the condition that the temperature is higher than 60 °C, undergo a dissolution-polymerization process to block the ion path.

[0011] Preferably, the thermal polymerization monomer is one or more of maleimide-PEG8-succinimide ester, N-(4-fluorophenyl) maleimide, 3-maleimide propionic acid succinimide ester, and 6-maleimide hexanoic acid pentafluorophenyl ester.

[0012] Preferably, the base material of the separator is polyethylene, polypropylene, ceramic-coated polyolefin film, polyimide or polyamide film;

[0013] The electrolyte is a carbonate-based electrolyte.

[0014] According to another aspect of the present invention, there is provided a method for preparing the thermoresponsive separator coated with the thermal polymerization monomer as described in any one of the above, comprising the following steps:

[0015] (1) Add the thermal polymerization monomer to the binder solution to obtain a mixed solution;

[0016] (2) Coat the mixed solution obtained in step (1) on the separator base material to form a coating;

[0017] (3) Dry the coating to obtain the thermoresponsive separator coated with the thermal polymerization monomer.

[0018] Preferably, the concentration of the binder in the binder solution is 3-8 wt%, and the mass of the thermal polymerization monomer is 2-5 times the mass of the binder.

[0019] Preferably, the drying temperature is 50-80 °C and the time is 4-24 h.

[0020] Preferably, after the coating is dried, the thickness is 1-10 μm.

[0021] According to another aspect of the present invention, there is provided the application of the thermoresponsive separator coated with the thermal polymerization monomer as described in any one of the above, for preventing thermal runaway of the battery.

[0022] Preferably, the electrolyte of the battery is a carbonate-based electrolyte.

[0023] Preferably, the battery is a lithium-ion battery or a sodium battery.

[0024] Generally speaking, compared with the prior art by the above technical solutions conceived by the present invention, the following technical advantages are mainly possessed:

[0025] (1) A monomer that is insoluble at room temperature and soluble at high temperature is coated on the separator in the present invention. When thermal abuse occurs, the thermally polymerizable monomer can also initiate the free radical polymerization of the electrolyte to block the ion path. This can not only avoid the degradation of battery performance caused by excessive free monomers in the solvent, but also achieve the overall solidification inside the battery cell, improving battery safety. At the same time, the thermally polymerizable monomer can dissolve and undergo free radical polymerization at a relatively low temperature (60 °C), avoiding early heat accumulation, and is used to achieve reversible protection of the battery under thermal abuse conditions, significantly enhancing battery safety. The thermally responsive separator in the present invention can achieve the overall solidification of the battery cell during thermal abuse, effectively avoiding direct contact between the positive and negative electrodes and improving thermal safety.

[0026] (2) For the thermally responsive separator prepared in the present invention, using the thermally polymerizable monomer as a temperature response switch, the response effect is significant, and the discharge capacity of the thermally responsive battery is close to zero.

[0027] (3) The preparation process of the present invention is simple, with high reproducibility, suitable for large-scale industrial production. The prepared thermally responsive separator can achieve effective thermal shutdown of the battery, significantly enhancing battery safety.

[0028] (4) Preferably, the selected thermally polymerizable monomer in the present invention is poorly soluble in carbonate-based electrolytes at room temperature and has no adverse effect on the battery cycle performance. Description of the Drawings

[0029] Figure 1 is the cycle performance graph of the Li|liquid electrolyte|NCM811 battery using the thermally responsive separator and the commercial separator in Example 1 of the present invention.

[0030] Figure 2 is the response effect graph of the Li|liquid electrolyte|NCM811 battery using the prepared thermally responsive separator in Example 1 of the present invention.

[0031] Figure 3 is the response effect graph of the Li|liquid electrolyte|NCM811 battery using the commercial separator in Example 1 of the present invention.

[0032] Figure 4 is the R value of the AC impedance of the Li|liquid electrolyte|NCM811 battery using the prepared thermally responsive separator before and after heating in Example 1 of the present invention. ct value.

[0033] Figure 5 is the R value of the AC impedance of the Li|liquid electrolyte|NCM811 battery using the commercial separator before and after heating in Example 1 of the present invention. ct value.

[0034] Figure 6 is the R value of the AC impedance before and after heating of the thermoresponsive separator prepared using the Li|liquid electrolyte|NCM811 battery in Example 2 of the present invention. ct value.

[0035] Figure 7 is the R value of the AC impedance before and after heating of the thermoresponsive separator prepared using the Li|liquid electrolyte|NCM811 battery in Example 3 of the present invention. ct value.

[0036] Figure 8 is the R value of the AC impedance before and after heating of the thermoresponsive separator prepared using the Li|liquid electrolyte|NCM811 battery in Example 4 of the present invention. ct value. Detailed implementation manners

[0037] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various implementation manners of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] Coating a thermopolymerizable monomer that is insoluble at room temperature and soluble at high temperature on the separator can not only avoid the decline in battery performance caused by excessive free monomers in the electrolyte, but also achieve the overall solidification of the electrolyte; the monomer coated on the separator is insoluble in the electrolyte at room temperature, and a large amount of polymerizable monomer can be added to the battery to achieve rapid thermal shutdown of the battery. That is to say, the thermoresponsive separator described in the present invention uses a thermopolymerizable monomer as a thermal switch, and during thermal abuse, the overheat response of the battery is achieved through the dissolution, cross-linking polymerization process of the monomer. The thermoresponsive separator can be prepared through the following steps:

[0039] Step 1:

[0040] Prepare a mixed solution of a thermopolymerizable monomer by mixing one or more of maleimide-PEG8-succinimide ester, N-(4-fluorophenyl) maleimide, 3-maleimidepropionic acid succinimide ester, and 6-maleimidocaproic acid pentafluorophenyl ester, wherein the binder is polyvinylidene fluoride and the binder concentration is 3-8 wt%.

[0041] Step 2:

[0042] Coat the mixed solution on one of polyethylene (PE), polypropylene (PP), ceramic-coated polyolefin film, polyimide (PI), and polyamide (PA) film, and the coating thickness is 1-10 μm.

[0043] Step 3:

[0044] Dry the diaphragm substrate coated in Step 2 in a vacuum oven at 50 - 80 °C for 4 - 24 h to prepare the thermoresponsive diaphragm.

[0045] The following further elaborates on the present invention in conjunction with the drawings and embodiments:

[0046] Example 1

[0047] Prepare a mixed solution of maleimide - PEG8 - succinimide ester as a thermopolymerizable monomer, where the binder is polyvinylidene fluoride and the binder concentration is 4 wt%. The mass of the thermopolymerizable monomer is twice the mass of the binder. Subsequently, coat the mixed solution on a polypropylene (PP) diaphragm with a coating thickness of 5 μm. Dry the coated diaphragm in a vacuum oven at 60 °C for 18 h to prepare the thermoresponsive diaphragm.

[0048] (2) Comparative test. Select a commercial PP diaphragm as a comparative sample.

[0049] The cycling performance of the Li|liquid electrolyte|NCM811 battery assembled using the thermoresponsive diaphragm and the commercial diaphragm is as Figure 1 shown. The battery using the thermoresponsive diaphragm exhibits stable cycling performance, indicating that the thermoresponsive diaphragm does not affect the battery performance.

[0050] Meanwhile, Figure 2 when the temperature reaches 60 °C, the battery using the temperature - responsive current collector exhibits a specific capacity close to 0 mAh / g, demonstrating that the thermoresponsive diaphragm has excellent response effects. In contrast, Figure 3 the battery using the commercial diaphragm shown in

[0051] Figure 4 cannot achieve temperature response at high temperatures. ct In Figure 5 , for the battery assembled using the thermoresponsive diaphragm, R ct increased by approximately 3000 times after heating, while for the battery using the commercial diaphragm in

[0052] Example 2

[0053] Prepare a mixed solution of N-(4-fluorophenyl) maleimide as a thermal polymerization monomer, where the binder is polyvinylidene fluoride, the binder concentration is 3 wt%, and the mass of the thermal polymerization monomer is 3 times the mass of the binder. Subsequently, coat the mixed solution on a polyethylene (PE) separator, with a coating thickness of 10 μm. Dry the coated separator in a vacuum oven at 50 °C for 24 h to prepare the thermal-responsive separator.

[0054] Figure 6 For the battery assembled with the thermal-responsive separator, the R ct value increased by approximately 2600 times after heating, demonstrating that the thermal-responsive separator has excellent response effects.

[0055] Example 3

[0056] Prepare a mixed solution of 3-maleimidopropionic acid N-hydroxysuccinimide ester as a thermal polymerization monomer, where the binder is polyvinylidene fluoride, the binder concentration is 8 wt%, and the mass of the thermal polymerization monomer is 2 times the mass of the binder. Subsequently, coat the mixed solution on a polyimide (PI) separator, with a coating thickness of 1 μm. Dry the coated separator in a vacuum oven at 80 °C for 4 h to prepare the thermal-responsive separator.

[0057] Figure 7 For the battery assembled with the thermal-responsive separator, the R ct value increased by approximately 2700 times after heating, demonstrating that the thermal-responsive separator has excellent response effects.

[0058] Example 4

[0059] Prepare a mixed solution of 6-maleimidohexanoic acid pentafluorophenyl ester as a thermal polymerization monomer, where the binder is polyvinylidene fluoride, the binder concentration is 5 wt%, and the mass of the thermal polymerization monomer is 5 times the mass of the binder. Subsequently, coat the mixed solution on a polyamide (PA) separator, with a coating thickness of 3 μm. Dry the coated separator in a vacuum oven at 70 °C for 10 h to prepare the thermal-responsive separator.

[0060] Figure 8 For the battery assembled with the thermal-responsive separator, the R ct value increased by approximately 2900 times, demonstrating that the thermal-responsive separator has excellent response effects.

[0061] In summary, for the thermoresponsive separator prepared by the present invention, the thermopolymerizable monomer is used as a temperature-responsive switch, and the response effect is remarkable; the selected thermopolymerizable monomer is poorly soluble in carbonate electrolytes at room temperature and has no adverse effect on the battery cycle performance; the prepared thermoresponsive separator can achieve the overall solidification of the battery cell during thermal abuse and can effectively avoid the direct contact between the positive and negative electrodes; the thermoresponsive separator has stable performance, can match a variety of positive and negative electrode materials, and does not affect the battery cycle performance; the preparation process of the present invention is simple, has high repeatability, is suitable for large-scale industrial production, and the prepared thermoresponsive separator can achieve effective thermal shutdown of the battery, significantly improving the safety of the battery.

[0062] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A thermally responsive membrane based on thermally polymerized monomer coating, characterized in that: The solubility of the thermally polymerizable monomer in the electrolyte increases with the increase of temperature, and the solubility of the thermally polymerizable monomer in the electrolyte is less than 2 wt % at a temperature below 30° C. and greater than 10 wt % at a temperature above 60° C.; The thermally responsive membrane coated with a thermally polymerizable monomer can undergo a dissolution-polymerization process at a temperature above 60° C., thereby blocking the ion passage.

2. The thermally responsive membrane based on thermal polymerizable monomer coating according to claim 1, characterized in that: The thermal polymerization monomer is one or more of maleimide-PEG8-succinimide ester, N-(4-fluorophenyl) maleimide, 3-maleimidopropionic acid succinimide ester, and 6-maleimidocaproic acid pentafluorophenol ester.

3. The thermally responsive membrane based on thermal polymerizable monomer coating according to claim 1, characterized in that: The base material of the diaphragm is polyethylene, polypropylene, ceramic-coated polyolefin film, polyimide or polyamide film; The electrolyte is a carbonate electrolyte.

4. The method for preparing a thermally responsive membrane based on thermal polymerization monomer coating according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) adding a thermally polymerizable monomer to a binder solution to obtain a mixed solution; (2) coating the mixed solution obtained in step (1) on the diaphragm substrate to form a coating; (3) Drying the coating to obtain the thermally responsive membrane coated with thermally polymerizable monomers.

5. The method for preparing a thermally responsive membrane based on thermal polymerization monomer coating according to claim 4, characterized in that: The concentration of the binder in the binder solution is 3-8wt%, and the mass of the thermally polymerizable monomer is 2-5 times the mass of the binder.

6. The method for preparing a thermally responsive membrane based on thermal polymerization monomer coating according to claim 5, characterized in that: The drying temperature is 50-80°C and the drying time is 4-24h.

7. The method for preparing a thermally responsive membrane based on thermal polymerization monomer coating according to claim 5, characterized in that: After the coating is dried, the thickness is 1-10 μm.

8. The use of a thermally responsive membrane coated with a thermally polymerizable monomer according to any one of claims 1 to 3, characterized in that: Used to prevent battery thermal runaway.

9. The use according to claim 8, characterized in that The electrolyte of the battery is a carbonate electrolyte.

10. The use according to claim 8, characterized in that The battery is a lithium ion battery or a sodium battery.

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