Thermal runaway protection material for lithium ion battery

Abstract

The invention discloses a lithium ion battery thermal runaway protection material, and belongs to the technical field of lithium ion battery thermal safety. According to the material, graphene and ammonium fluoride are subjected to high-temperature calcination to prepare N / F double-doped fluorinated graphene, the N / F double-doped fluorinated graphene is combined with expanded microspheres to construct an intelligent thermal response system, and a freeze-drying technology is adopted to form an alternate multi-layer structure; the expanded microspheres are packaged and molded through polydimethylsiloxane, the volume expansion of the expanded microspheres at high temperature is innovatively utilized to destroy a heat conduction network, the intelligent regulation and control characteristic that the heat conductivity is reduced along with the temperature rise is realized, the material has high heat conductivity, rapid thermal response and excellent flame retardant property, thermal runaway propagation of a battery module can be effectively blocked, and the service life of the battery module is prolonged. The preparation process is realized by a solution mixing-freeze drying-silica gel packaging three-step method, has the characteristics of simple flow, low cost and large-scale production, and solves the technical bottlenecks of response lag and low flame-retardant efficiency of the traditional flame-retardant material.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal management and thermal runaway safety protection of lithium-ion batteries, and particularly relates to a thermal runaway protection material for lithium-ion batteries. Background Art

[0002] With the accelerating global energy transformation, lithium-ion batteries have become the core technology in the fields of electric vehicles and energy storage due to their high energy density (150 - 250 Wh / kg). However, the contradiction between energy density improvement and safety has become increasingly acute, and their large-scale application in electric vehicles and energy storage systems still faces severe challenges: firstly, the high energy density leads to a significant increase in the risk of thermal runaway; secondly, the violent exothermic reaction during thermal runaway intensifies the destructiveness of explosions and fires. Research shows that there is an inherent "trade-off" relationship between energy density and safety - the higher the energy density, the lower the thermal runaway trigger temperature, the significantly higher the maximum temperature rise rate and the highest temperature, and the total mass loss can reach more than 60%. Current research mainly focuses on developing low-cost and high-efficiency thermal management materials to solve the current thermal runaway problem of lithium-ion batteries.

[0003] Regarding the thermal runaway problem, the design of the battery thermal management system (BTMS) is crucial. Existing thermal management technologies are mainly divided into two categories: active and passive. Active methods include air cooling and liquid cooling, which remove heat through forced convection or circulating media. Among them, liquid cooling is widely used due to its high thermal conductivity and excellent heat dissipation efficiency, but it has the disadvantages of complex system and high cost. Passive methods rely on phase change materials (PCM) or heat pipes, which absorb heat using the latent heat of material phase change and have the advantages of compact structure and no power consumption, but they need to solve the problems of poor thermal conductivity and latent heat recovery. In addition, composite thermal management technologies (such as the combination of PCM and heat pipes) are becoming a research hotspot, which can balance high-efficiency heat dissipation and system reliability.

[0004] In recent years, researchers have been committed to developing intelligent thermal management materials to break through the above limitations. For example, although phase change materials (PCMs) can delay the temperature rise by absorbing heat through solid-liquid phase change, the thermal conductivity of paraffin-based PCMs is only 0.2 W / (m·K), lower than the critical value of 1.5 W / (m·K) required for normal battery operation, and the cycle life is only 300 times; intumescent flame retardant coatings (such as ammonium polyphosphate / pentaerythritol system) need to trigger expansion above 250 °C, while the initial temperature of battery thermal runaway is only 120 - 150 °C, resulting in a response delay. The UL certification test in the United States shows that the carbonization time of this type of coating at 180 °C is as long as 120 seconds; although the ceramic-coated separator can extend the thermal runaway trigger time to 180 seconds, the coating cost is as high as 0.8 yuan / m², which is 5 times that of ordinary separators and causes a 15% increase in internal resistance; although the flame retardant electrolyte (such as adding 2% vinylene carbonate trifluoromethyl) can inhibit thermal decomposition, the conductivity decreases by 20%, and the cycle capacity attenuation rate increases from 0.05% / cycle to 0.12% / cycle. The team led by Gao Chao from Zhejiang University designed a hyperbolic graphene aerogel (HGA) / paraffin composite material (PGC), which achieved a thermal conductivity of 30.75 W / mK and a latent heat retention rate of 90% at a 12.5 wt% filler loading. When applied to 14500-type batteries, it can stably control the temperature at 42 °C for 10,000 cycles, but the dispersion and cost of high-thermal-conductivity fillers limit its large-scale application (Pang K, Song X, Xu Z, et al. Hydroplastic foaming of graphene aerogels and artificially intelligent tactile sensors[J]. Science advances, 2020, 6(46): eabd4045.). The team led by Dong Kaijun from the Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences constructed an embedded phase change material liquid cooling composite cold plate system, combining active and passive cooling technologies, and controlled the maximum battery temperature at 39.7 °C under 3C discharge, with the pump power consumption reduced by 80.8%. However, the rapid response ability and system lightweight under extreme conditions are still challenges. (Cai Y, Sun Q, Gu X, et al. Multi-objective optimization of battery thermal management system based on a novel embedded hybrid cooling plate considering time-based early shutdown strategy[J]. Energy, 2024, 312: 133419.).In recent years, the research focus has shifted to stimulus-responsive materials, such as temperature-sensitive shape memory alloys (Ni-Ti alloys undergo martensitic phase transformation at 60 °C to drive the deployment of heat dissipation fins, but the cost is as high as 1400 yuan / kg), photothermal conversion materials (graphene / carbon nanotube composite films require an additional light source system), magnetorheological fluids (Fe3O4 particles form a heat conduction chain under a magnetic field, but an electromagnetic device is required), etc. However, they all have problems such as high cost or complex systems.

[0005] Therefore, there is an urgent need to develop a lithium-ion battery thermal runaway protection material that combines high-efficiency heat dissipation, intelligent thermal response, and excellent flame retardancy while having a relatively low preparation cost. Summary of the Invention

[0006] Aiming at the deficiencies of existing lithium-ion battery thermal runaway protection materials, such as poor flame retardancy, low thermal conductivity, and high cost, the present invention provides a lithium-ion battery thermal runaway protection material based on fluorinated graphene, its preparation method and application. By using the characteristic of the expansion of expandable microspheres at high temperature, the heat conduction circuit between graphene layers can be destroyed, realizing intelligent thermal response to block the propagation of lithium-ion battery thermal runaway. At the same time, the flame retardancy is improved after doping graphene and ammonium fluoride, which provides guiding opinions for solving the problem of lithium-ion battery thermal runaway. The preparation process of the present invention is efficient and controllable, can be produced on a large scale, and has both intelligent thermal response and excellent flame retardancy, providing an innovative solution for the safety protection of lithium-ion batteries.

[0007] In order to achieve the above invention purpose, the technical solution adopted by the present invention is:

[0008] A lithium-ion battery thermal runaway protection material, characterized in that a fluorinated graphene matrix with an interlayer cavity structure is constructed through a fluorination process and an N / F dual-doping strategy, and is compounded with expandable microspheres to form an intelligent thermal response material.

[0009] The lithium-ion battery thermal runaway protection material according to claim 1, characterized in that it can realize rapid thermal response switching between heat conduction and heat insulation states, protect lithium-ion batteries from damage, and the preparation method includes the following steps:

[0010] (1) Prepare a certain amount of mixed powder of graphene and ammonium fluoride, and calcine it in a tubular furnace to generate N / F dual-doped fluorinated graphene;

[0011] (2) Wash the fluorinated graphene obtained in step (1) and then dry it under vacuum for later use;

[0012] (3) Prepare a mixed solution of fluorinated graphene and sodium carboxymethylcellulose, stir it evenly with a magnetic stirrer, and ultrasonically disperse it with an ultrasonic cleaner to form a slurry;

[0013] (4) Mix the slurry prepared in step (3) with expandable microspheres and stir it evenly with a magnetic stirrer;

[0014] (5) Coating the mixed solution prepared in step (4) on the surface of the copper foil, transferring it to a freeze dryer after being frozen with liquid nitrogen, and forming a fluorinated graphene matrix sample after freeze drying;

[0015] (6) Mixing polydimethylsiloxane and a curing agent, and stirring evenly with a magnetic stirrer;

[0016] (7) Coating the silicone rubber solution prepared in step (6) on the fluorinated graphene matrix obtained in step (5), placing it in a vacuum drying oven, curing, and then cooling to room temperature to obtain a lithium-ion battery thermal runaway protection material based on fluorinated graphene.

[0017] In the above solution, step (1) is: mixing 2 g of graphene and 4 g of ammonium fluoride, grinding them into powder with a mortar, placing them in the tube furnace, continuously heating to 600 °C under a nitrogen protection atmosphere, and maintaining for 1 - 3 hours.

[0018] In the above solution, step (2) is: after washing the fluorinated graphene powder with deionized water, filtering it with a suction pump, and drying it in vacuum at 40 °C - 60 °C. Step (3) is: adding 1.4 g of fluorinated graphene and 0.2 g of sodium carboxymethylcellulose to a solution of 30 mL of deionized water, magnetically stirring the solution for 2 - 3 hours, ultrasonically dispersing the solution for 40 - 60 minutes, the mass of the expandable microspheres is 1 g, magnetically stirring the solution for 2 - 3 hours, and freeze drying for 18 - 24 hours.

[0019] In the above solution, step (5) is: the temperature of freeze drying is -40 °C - -60 °C.

[0020] In the above solution, step (6) is: mixing 15 g of polydimethylsiloxane and 1.5 g of the curing agent.

[0021] In the above solution, step (7) is: the time of magnetic stirring is 10 - 20 minutes.

[0022] In the above solution, step (7) is: the temperature of vacuum drying is 60 °C - 80 °C.

[0023] In the above solution, step (7) is: the time of vacuum drying is 6 - 12 hours.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] The present invention selects graphene to prepare a thermal runaway protection material, which has a wide source and low cost. The thermal conductivity of single-layer graphene reaches 5300 W / (m·K), which is 13 times that of copper. By constructing a three-dimensional network, the overall thermal conductivity of the composite material can be significantly improved. At the same time, the specific surface area of graphene is as high as 2630 m 2 / g, which can provide sufficient anchoring sites for expandable microspheres. Moreover, graphene maintains its structural integrity in high-temperature and strongly corrosive environments and has excellent compatibility with the N / F double-doping process, avoiding the oxidation failure problem of traditional metal-based thermal conductive materials. The cost of graphene film prepared by chemical vapor deposition method has been reduced to 0.5 yuan / ㎡ (thickness 10 μm), which is more than 95% lower than that of commercial aerogel (120 yuan / ㎡). It reduces the material cost while improving the thermal conductivity.

[0026] The present invention innovatively selects ammonium fluoride as a dopant, and through the synergistic effect of its unique thermal decomposition behavior and the graphene lattice structure, a protection system with both chemical and physical dual flame retardant mechanisms is constructed. It is confirmed by XPS analysis that N / F double doping forms pyridine-type N and C-F bonds on the surface of graphene. The former enhances the polarity of the material, and the latter reduces the activity of the carbon ring through the electron-withdrawing effect of fluorine atoms, significantly improving the thermal stability. At the same time, the uniformly distributed expandable microspheres in the material expand in volume at 100 °C, and the formed cavity structure physically blocks the diffusion of oxygen and also destroys the interlayer thermal conduction circuit of graphene through mechanical stress, blocking the propagation of thermal runaway. This chemical-physical synergistic flame retardant mechanism enables the limiting oxygen index of the material to reach 28.6%, and greatly improves the flame retardant performance of the thermal runaway protection material after doping with ammonium fluoride.

[0027] The present invention utilizes the hydrophilicity difference between graphene and expandable microspheres to construct a unique "graphene-microsphere-graphene" alternating sandwich structure through the freeze-drying process. During the freeze-drying process, the highly hydrophilic graphene sheets preferentially adsorb water to form an ice crystal template, while the hydrophobic expandable microspheres (particle size 5-10 μm) are repelled to the ice crystal gaps, forming a regularly arranged microsphere array. Subsequently, freeze-drying is carried out at -60 °C for 24 hours to form a composite structure with micron-sized cavities embedded in a three-dimensional thermal conduction network. This hierarchical design endows the material with both high thermal conductivity and structural stability. This process does not require complex equipment, the preparation cycle is only 24 hours, and the cost is lower than that of the traditional aerogel process, with a significant performance improvement, verifying its industrial application potential.

[0028] The innovative application of expanding microspheres (particle size 5 - 10 μm) in this invention to expand and damage graphene layers at high temperatures, utilizes their property of expanding 300% in volume at 150 - 180 °C to achieve intelligent thermal response and block the spread of thermal runaway. This design breaks through the limitation of traditional thermal management materials relying on external triggers. When the battery temperature rises to the critical threshold, the microspheres expand autonomously to form mechanical stress, instantly damaging the heat conduction network between graphene layers, rapidly decreasing the thermal conductivity, and effectively blocking the heat transfer path. The preparation process adopts simple solution mixing and freeze-drying techniques without the need for complex equipment. This process can achieve continuous production in a standardized production line, providing a long-term and reliable thermal protection barrier for lithium-ion batteries. Description of the Drawings

[0029] Figure 1 SEM image of graphene after freeze-drying obtained in Example 1.

[0030] Figure 2 TEM image of graphene after freeze-drying obtained in Example 1.

[0031] Figure 3 SEM image of the expanding microspheres before thermal runaway of a lithium-ion battery thermal runaway protection material based on fluorinated graphene obtained in Example 1.

[0032] Figure 4 SEM image of the expanding microspheres after thermal runaway of a lithium-ion battery thermal runaway protection material based on fluorinated graphene obtained in Example 1.

[0033] Figure 5 XRD spectrum of graphene before and after fluorination obtained in Example 1.

[0034] Figure 6 Raman image of the XRD spectrum of graphene before and after fluorination obtained in Example 1.

[0035] Figure 7 XPS spectrum of C1s of a lithium-ion battery thermal runaway protection material based on fluorinated graphene obtained in Example 1.

[0036] Figure 8 XPS spectrum of N1s of a lithium-ion battery thermal runaway protection material based on fluorinated graphene obtained in Example 1.

[0037] Figure 9 XPS spectrum of F1s of a lithium-ion battery thermal runaway protection material based on fluorinated graphene obtained in Example 1.

[0038] Figure 10 Temperature - thermal conductivity graph of a lithium-ion battery thermal runaway protection material based on fluorinated graphene obtained in Example 1 Detailed Description of the Invention

[0039] The present invention will be further described below in conjunction with embodiments, but the present invention is not limited to the following embodiments.

[0040] Example 1

[0041] Mix 2 g of graphene and 4 g of ammonium fluoride, grind them into powder with a mortar, place them in a tube furnace, and constantly heat to 600 °C under a nitrogen protection atmosphere for 2 hours. Next, wash the graphene fluoride powder with deionized water, filter it with a suction pump, and then vacuum dry it at 60 °C. Add 1.4 g of graphene fluoride and 0.2 g of sodium carboxymethylcellulose to a solution of 30 mL of deionized water. After stirring with a magnetic stirrer for 2 hours and then sonicating and dispersing in an ultrasonic cleaner for 1 hour, a slurry is formed. Mix the slurry with 1 g of expandable microspheres, stir with a magnetic stirrer for 2 hours, then coat the mixed solution on the surface of a copper foil. After freezing with liquid nitrogen, transfer it to a freeze dryer and freeze-dry at -60 °C for 24 hours to form a graphene fluoride matrix sample as shown in Figure 1-2 Figure. Mix 15 g of polydimethylsiloxane and 1.5 g of curing agent, stir with a magnetic stirrer for 10 minutes, then coat it on the graphene fluoride matrix, place it in a vacuum drying oven, cure at 60 °C for 6 hours, and then cool to room temperature to obtain a lithium-ion battery thermal runaway protection material based on graphene fluoride with a fluorine content of 50%.

[0042] Example 2

[0043] Mix 2 g of graphene and 3 g of ammonium fluoride, grind them into powder with a mortar, place them in a tube furnace, and constantly heat to 600 °C under a nitrogen protection atmosphere for 2 hours. Next, wash the graphene fluoride powder with deionized water, filter it with a suction pump, and then vacuum dry it at 60 °C. Add 1.4 g of graphene fluoride and 0.2 g of sodium carboxymethylcellulose to a solution of 30 mL of deionized water. After stirring with a magnetic stirrer for 2 hours and then sonicating and dispersing in an ultrasonic cleaner for 1 hour, a slurry is formed. Mix the slurry with 1 g of expandable microspheres, stir with a magnetic stirrer for 2 hours, then coat the mixed solution on the surface of a copper foil. After freezing with liquid nitrogen, transfer it to a freeze dryer and freeze-dry at -60 °C for 24 hours to form a graphene fluoride matrix sample as shown in Figure 3-4 Figure. Mix 15 g of polydimethylsiloxane and 1.5 g of curing agent, stir with a magnetic stirrer for 10 minutes, then coat it on the graphene fluoride matrix, place it in a vacuum drying oven, cure at 60 °C for 6 hours, and then cool to room temperature to obtain a lithium-ion battery thermal runaway protection material based on graphene fluoride with a fluorine content of 40%.

[0044] Example 3

[0045] Mix 2 g of graphene and 5 g of ammonium fluoride, crush them into powder with a mortar, place them in a tube furnace, and constantly heat to 600 °C under a nitrogen protection atmosphere for 2 hours. Next, wash the graphene fluoride powder with deionized water, then filter it with a suction pump and vacuum dry it at 60 °C. Add 1.4 g of graphene fluoride and 0.2 g of sodium carboxymethylcellulose to a solution of 30 mL of deionized water. After stirring with a magnetic stirrer for 2 hours, put it into an ultrasonic cleaner and ultrasonically disperse it for 1 hour to form a slurry. Mix the slurry with 1 g of expanded microspheres, stir with a magnetic stirrer for 2 hours, then coat the mixed solution on the surface of a copper foil. After freezing with liquid nitrogen, transfer it to a freeze dryer and freeze dry it at a temperature of -60 °C for 24 hours to form a graphene fluoride matrix sample. Mix 15 g of polydimethylsiloxane and 1.5 g of curing agent, stir with a magnetic stirrer for 10 minutes, then coat it on the graphene fluoride matrix, place it in a vacuum drying oven, cure it at 60 °C for 6 hours, and then cool it to room temperature to obtain a lithium-ion battery thermal runaway protection material based on graphene fluoride with a fluorine content of 60%.

[0046] Example 4

[0047] Mix 2 g of graphene and 4 g of ammonium fluoride, crush them into powder with a mortar, place them in a tube furnace, and constantly heat to 600 °C under a nitrogen protection atmosphere for 3 hours. The XRD and Raman spectra of the obtained sample are as shown in Figure 5-6 , and the XPS spectrum is as shown in Figure 7-9 . Next, wash the graphene fluoride powder with deionized water, then filter it with a suction pump and vacuum dry it at 40 °C. Add 1.4 g of graphene fluoride and 0.2 g of sodium carboxymethylcellulose to a solution of 30 mL of deionized water. After stirring with a magnetic stirrer for 3 hours, put it into an ultrasonic cleaner and ultrasonically disperse it for 45 minutes to form a slurry. Mix the slurry with 1 g of expanded microspheres, stir with a magnetic stirrer for 3 hours, then coat the mixed solution on the surface of a copper foil. After freezing with liquid nitrogen, transfer it to a freeze dryer and freeze dry it at a temperature of -40 °C for 18 hours to form a graphene fluoride matrix sample. Mix 15 g of polydimethylsiloxane and 1.5 g of curing agent, stir with a magnetic stirrer for 20 minutes, then coat it on the graphene fluoride matrix, place it in a vacuum drying oven, cure it at 80 °C for 12 hours, and then cool it to room temperature to obtain a lithium-ion battery thermal runaway protection material based on graphene fluoride with a fluorine content of 50%.

[0048] Example 5

[0049] Mix 2 g of graphene and 4 g of ammonium fluoride, crush them into powder with a mortar, place them in a tube furnace, and constantly heat to 600 °C under a nitrogen protection atmosphere for 3 hours. Next, wash the graphene fluoride powder with deionized water, then filter it with a suction pump and vacuum dry it at 50 °C. Add 1.4 g of graphene fluoride and 0.2 g of sodium carboxymethyl cellulose to a solution of 30 mL of deionized water. After stirring with a magnetic stirrer for 2.5 hours, put it into an ultrasonic cleaner and ultrasonically disperse it for 50 minutes to form a slurry. Mix the slurry with 1 g of expanded microspheres, stir with a magnetic stirrer for 2.5 hours, then coat the mixed solution on the surface of a copper foil. After freezing with liquid nitrogen, transfer it to a freeze dryer and freeze dry it at -50 °C for 22 hours to form a graphene fluoride matrix sample. Mix 15 g of polydimethylsiloxane and 1.5 g of curing agent, stir with a magnetic stirrer for 15 minutes, then coat it on the graphene fluoride matrix, place it in a vacuum drying oven, cure it at 70 °C for 8 hours, and then cool it to room temperature to obtain a lithium-ion battery thermal runaway protection material based on graphene fluoride with a fluorine content of 50%.

[0050] Example 6

[0051] Place the thermal runaway protection material prepared in Example 1 in an assembled quadruplet 50 Ah nickel cobalt manganese lithium-ion battery module, and fill the space between the batteries with 1 mm thick thermal runaway protection material. Apply a current at a rate of 3C using a cyclic charge and discharge test system, and record the internal temperature distribution of the module through an embedded thermocouple (K-type, accuracy ±0.5 °C), comparing the no-interlayer and aerogel interlayer schemes. From the test results, it can be seen that in the module without an interlayer, all four batteries experienced thermal runaway propagation within 10 s. In the module with an aerogel interlayer, the thermal runaway propagated rapidly, and the average inter-cell diffusion time was 26 ± 8 s. As Figure 10 shown, in sharp contrast, the interlayer of the lithium-ion battery thermal runaway protection material based on graphene fluoride successfully blocked the thermal runaway propagation of the battery module.

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description and ideas. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. Lithium-ion battery thermal runaway protection material, characterized in that: A fluorinated graphene matrix with an interlayer cavity structure is constructed through a fluorination process and a N / F dual-doping strategy, and is composited with thermally expandable microspheres to form an intelligent thermal responsive material.

2. The lithium-ion battery thermal runaway protection material according to claim 1, characterized in that It can realize the rapid thermal response switching between the heat conduction state and the heat insulation state, and protect the lithium-ion battery from damage. The preparation method comprises the following steps: (1) preparing a mixed powder of graphene and ammonium fluoride, and calcining the mixed powder in a tube furnace to generate N / F dual-doped fluorinated graphene; (2) washing the fluorinated graphene obtained in step (1) with water and then vacuum drying it for later use; (3) preparing the mixed solution of the fluorinated graphene and sodium carboxymethyl cellulose in step (2), stirring evenly with a magnetic stirrer, and ultrasonically dispersing with an ultrasonic cleaner to form a slurry; (4) mixing the slurry prepared in step (3) with the expanded microspheres, and stirring them uniformly with the magnetic stirrer to obtain a mixed solution; (5) coating the mixed solution prepared in step (4) on the surface of a copper foil, freezing it with liquid nitrogen and transferring it to a freeze dryer, and forming a fluorinated graphene matrix sample after freeze drying; (6) mixing polydimethylsiloxane and a curing agent, and stirring them evenly with a magnetic stirrer to obtain a silicone rubber solution; (7) applying the silicone rubber solution prepared in step (6) to the fluorinated graphene substrate obtained in step (5), placing the substrate in a vacuum drying oven for curing, and after curing, cooling the substrate to room temperature to obtain a thermal runaway protection material for lithium-ion batteries based on fluorinated graphene.

3. The lithium-ion battery thermal runaway protection material according to claim 2, characterized in that: The step (1) is: 2 g of graphene and 4 g of ammonium fluoride are mixed, crushed into powder using a mortar, placed in the tube furnace, and continuously heated to 600° C. and maintained for 1-3 hours under a nitrogen protective atmosphere.

4. The lithium-ion battery thermal runaway protection material according to claim 2, characterized in that: The step (2) comprises: washing the fluorinated graphene powder with deionized water, filtering with a pump, and vacuum drying at 40° C. to 60° C. The step (3) comprises: adding 1.4 g of fluorinated graphene and 0.2 g of sodium carboxymethyl cellulose to a 30 mL deionized water solution, magnetically stirring the solution for 2 to 3 hours, ultrasonically dispersing the solution for 40 to 60 minutes, the mass of the expanded microspheres is 1 g, the magnetically stirring the solution for 2 to 3 hours, and freeze-drying the solution for 18 to 24 hours.

5. The lithium-ion battery thermal runaway protection material according to claim 2, characterized in that: The step (5) is as follows: the freeze-drying temperature is -40°C to -60°C.

6. The lithium-ion battery thermal runaway protection material according to claim 2, characterized in that: The step (6) is: mixing 15 g of polydimethylsiloxane and 1.5 g of a curing agent.

7. The lithium-ion battery thermal runaway protection material according to claim 2, characterized in that: The step (7) is as follows: the magnetic stirring time is 10 to 20 minutes.

8. The lithium-ion battery thermal runaway protection material according to claim 2, characterized in that: The step (7) is as follows: the vacuum drying temperature is 60°C to 80°C.

9. The lithium-ion battery thermal runaway protection material according to claim 2, characterized in that: The step (7) is as follows: the vacuum drying time is 6 to 12 hours.

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