Preparation method and application of a composite thermal insulation material for suppressing thermal runaway propagation in lithium-ion batteries

Abstract

This invention discloses a method for preparing and applying a composite thermal insulation material to suppress the propagation of thermal runaway in lithium-ion batteries, relating to the field of battery safety protection technology. The method includes: adding nano-hydroxyapatite to a mixed solution of sodium alginate and polyvinyl alcohol; then adding acrylamide and 2-acrylamide-2-methylpropanesulfonic acid to a solution obtained through ultrasonic treatment; subsequently adding boron carbide nanosheets, glass fibers, an initiator, and a crosslinking agent. The initiator activates the active functional groups of sodium alginate, polyvinyl alcohol, acrylamide, and 2-acrylamide-2-methylpropanesulfonic acid, causing a chain reaction and forming a long-chain structure. Glass fibers are then introduced into the hydrogel system. The thermal conductivity of boron carbide and the thermal insulation properties of glass fibers form a "thermal conduction-thermal insulation" mechanism, resulting in a composite thermal insulation material. This method can improve the mechanical strength and thermal insulation effect of the composite thermal insulation material, and can more effectively suppress the risk of thermal runaway in lithium-ion battery modules.

Description

Technical Field

[0001] This invention relates to the field of battery safety protection technology, specifically to a method for preparing and applying a composite thermal insulation material that suppresses the propagation of thermal runaway in lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries (LIBs), as rechargeable batteries, have demonstrated significant advantages in mobile electronic devices and new energy vehicles due to their high energy density, long cycle life, low self-discharge rate, and excellent cycle stability. However, with rapid technological advancements, these batteries also face new challenges in terms of safety performance, particularly the increasingly prominent issue of thermal runaway. When batteries are subjected to external impacts, overcharging, over-discharging, or high-temperature environments, they are highly susceptible to triggering a chain reaction of exothermic reactions and releasing enormous amounts of heat. Simultaneously, internal short circuits caused by battery performance degradation or manufacturing defects can expose the battery management system to unpredictable thermal runaway risks. Especially in multi-battery pack applications such as electric vehicles, thermal runaway of a single battery can often trigger a chain reaction within densely packed battery modules, potentially leading to a serious accident affecting the entire power system.

[0003] How to delay and suppress the propagation of thermal runaway (TRP) between battery packs is one of the major unresolved safety-related issues in battery packs. Many scholars have proposed different methods to suppress TRP, mainly five methods: (1) Active battery cooling using coolants (e.g., water, air), usually laid in hoses, pipes or microchannels in the battery system. Due to its complexity, this method is costly and may occupy a large volume of battery modules and battery packs. In addition, it cannot provide enough cooling energy to prevent TRP. (2) Using the thermal capacity of the battery system to provide rapid heat dissipation by contacting the battery with a high thermal conductivity material. The main disadvantage of this method is the increase in battery pack weight, which reduces the energy density of the battery system and its limitation on low-capacity batteries. (3) Thermal insulation between batteries to limit thermal runaway to a single cell. However, thermal insulation cannot completely suppress TRP between batteries because the energy density of the LIB is constantly increasing, so the cells in the TR release more energy, and the thermal shock generated when the battery experiences TR will directly lead to the destruction of the insulation material, thereby reducing its continuous insulation effect. (4) Using phase change materials (PCM). In this method, the PCM partially absorbs and releases TR energy through an endothermic phase change (solid to liquid) at 50-90℃. One of the main drawbacks of this method is the flash point of the commonly used paraffin, which significantly increases the fire load in the case of TR. (5) Using hydrogel materials to suppress TRP between battery modules has many advantages in suppressing TRP due to its good biocompatibility and extremely high water content. However, hydrogels generally have poor mechanical properties and cannot effectively cope with the squeezing and collision caused by battery TR.

[0004] In summary, a single insulating material cannot effectively solve the safety issues caused by TRP (Transmission Reinforced Plastic) between batteries. Therefore, existing technologies require further improvement. Summary of the Invention

[0005] One of the objectives of this invention is to provide a method for preparing a composite thermal insulation material that suppresses the propagation of thermal runaway in lithium-ion batteries. By optimizing the method, the mechanical strength and thermal insulation effect of the composite thermal insulation material can be improved, which can more effectively suppress the risk of thermal runaway in lithium-ion battery modules.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a composite thermal insulation material to suppress the propagation of thermal runaway in lithium-ion batteries includes the following steps:

[0008] a. Mix sodium alginate solution with polyvinyl alcohol solution to obtain mixed solution one;

[0009] b. Add nano-hydroxyapatite to the first mixed solution and place it in an ultrasonic device for ultrasonic treatment. Then place the ultrasonically treated mixture in a water bath at 50-60°C to ensure that the nano-hydroxyapatite is uniformly dispersed to obtain the second mixed solution.

[0010] c. Add acrylamide and 2-acrylamide-2-methylpropanesulfonic acid sequentially to the second mixed solution, and stir until homogeneous to obtain the third mixed solution;

[0011] d. Add boron carbide nanosheets to mixed solution three and adjust the pH to 5-7. Stir thoroughly under certain temperature conditions to obtain mixed solution four. The phosphate groups in nano-hydroxyapatite and the cations on the surface of boron carbide form ionic bonds through electrostatic attraction. The boron atoms on the surface of boron carbide form coordination bonds with the oxygen in the phosphate or hydroxide groups of nano-hydroxyapatite.

[0012] e. Add glass fibers to the mixed solution four and place it in an ultrasonic device for ultrasonic treatment. Then place the ultrasonically treated mixture in a water bath at 50-60°C to ensure that the glass fibers are evenly dispersed, and obtain mixed solution five.

[0013] f. Slowly add ammonium persulfate as an initiator to the mixed solution five. Ammonium persulfate activates the active functional groups of sodium alginate, polyvinyl alcohol, acrylamide, and 2-acrylamide-2-methylpropanesulfonic acid, causing a chain reaction and forming a long-chain structure. Then, a crosslinking agent is added to the resulting hydrogel system to carry out the reaction. Glass fiber is introduced into the hydrogel system through crosslinking. The thermal conductivity of boron carbide and the thermal insulation of glass fiber form a "thermal conduction-thermal insulation" mechanism to obtain a composite thermal insulation material.

[0014] In the preparation method of the composite thermal insulation material for suppressing the propagation of thermal runaway in lithium-ion batteries, in step a, the mass fraction ratio of sodium alginate solution to polyvinyl alcohol solution is 0.8:1; the sodium alginate solution is prepared by adding sodium alginate to deionized water, the mass-volume ratio of sodium alginate to deionized water is 1.6:300 g / L, and the dissolution temperature is 70-75℃; the polyvinyl alcohol solution is prepared by adding polyvinyl alcohol to deionized water, the mass-volume ratio of polyvinyl alcohol to deionized water is 2:300 g / L.

[0015] In the above-mentioned method for preparing a composite thermal insulation material to suppress the propagation of thermal runaway in lithium-ion batteries, in step b, the mass ratio of nano-hydroxyapatite to sodium alginate is 1:1.

[0016] In the preparation method of the composite thermal insulation material for suppressing the propagation of thermal runaway in lithium-ion batteries, in step c, the mass ratio of acrylamide to sodium alginate is 1:0.4, and the mass ratio of acrylate to 2-acrylamide-2-methylpropanesulfonic acid is 2:1; the temperature is maintained at 50-60℃ during stirring.

[0017] In the above-mentioned method for preparing a composite thermal insulation material to suppress the propagation of thermal runaway in lithium-ion batteries, in step d, the mass ratio of boron carbide nanosheets to 2-acrylamide-2-methylpropanesulfonic acid is 1:1, and the stirring temperature is controlled at 50-60℃.

[0018] In the above-mentioned method for preparing a composite thermal insulation material to suppress the propagation of thermal runaway in lithium-ion batteries, in step e, the mass ratio of glass fiber to boron carbide is 5:2.

[0019] In the above-mentioned method for preparing a composite thermal insulation material to suppress the propagation of thermal runaway in lithium-ion batteries, in step f, the mixed solution is placed in a constant temperature water bath at a temperature of 60-65°C, and the mass ratio of ammonium persulfate to glass fiber is 0.009:1.

[0020] In the preparation method of the composite thermal insulation material for suppressing the propagation of thermal runaway in lithium-ion batteries, step f involves N,N-methylenebisacrylamide as the crosslinking agent, with the mass ratio of N,N-methylenebisacrylamide to ammonium persulfate being 0.38:0.045. The reaction temperature after adding the crosslinking agent is 60–65°C, and the reaction time is 2–4 h.

[0021] Another objective of this invention is to provide an application of the composite thermal insulation material prepared by the above-mentioned preparation method, characterized in that: when the composite thermal insulation material is in direct contact with a heat source, it can effectively delay the thermal runaway trigger time, reduce the peak temperature of the runaway battery, and effectively control the temperature rise rate of the non-runaway battery.

[0022] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0023] This invention proposes a method for preparing a composite thermal insulation material to suppress the propagation of thermal runaway in lithium-ion batteries. Sodium alginate and polyvinyl alcohol are used as the matrix, while acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, nano-hydroxyapatite, and glass fiber are used as the matrix. The synergistic composite of nano-hydroxyapatite and glass fiber enhances the thermal insulation performance. Boron carbide nanosheets are introduced into the hydrogel system, utilizing the high thermal conductivity of boron nitride to directionally disperse local hot spots, forming a synergistic "thermal conduction-thermal insulation" mechanism with the glass fiber. Specifically, the phosphate ions (PO43-) in the nano-hydroxyapatite react with the cations (such as B-) on the surface of boron carbide. 3+ Electrostatic attraction is generated, forming ionic bonds; boron atoms (B) on the surface of boron carbide form coordination bonds with oxygen atoms in PO43- or OH- of nano-hydroxyapatite. This synergistically enhances the thermal insulation performance of the hydrogel with nano-hydroxyapatite. The high thermal conductivity of boron carbide can directionally dissipate local hot spots, forming a synergistic "thermal conduction-thermal insulation" mechanism with glass fiber.

[0024] The composite thermal insulation material prepared by this invention has excellent mechanical strength and thermal insulation effect, which can effectively suppress the risk of thermal runaway of lithium-ion battery modules. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings:

[0026] Figure 1 This is a schematic diagram of the thermal runaway experimental device of the present invention;

[0027] Figure 2 (a) is a scanning electron microscope (SEM) image of glass fiber; (b) is a scanning electron microscope (SEM) image of hydroxyapatite; (c) is a scanning electron microscope (SEM) image of hydrogel obtained without the addition of glass fiber; (d) and (e) are scanning electron microscope (SEM) images of the composite thermal insulation material prepared in this invention; and (f) is a transmission electron microscope (TEM) image of the composite thermal insulation material prepared in this invention.

[0028] Figure 3 (a) and (b) show the thermal stability test results of composite insulation materials with different amounts of hydroxyapatite.

[0029] Figure 4 Figures (a) and (b) show the influence of different amounts of hydroxyapatite on the compressive strength of the composite thermal insulation materials.

[0030] Figure 5 The temperature response analysis diagram for the thermal runaway propagation experiment is shown. Specifically, with the heating rod at the center, the temperature change curve of each battery during the TR propagation experiment is shown as a function of time under unprotected conditions.

[0031] Figure 6 The temperature response analysis diagram for the thermal runaway propagation experiment is shown. Specifically, with the heating rod at the center and protected by the 4mm composite thermal insulation material of this invention, the temperature change curve of each battery during the TR propagation experiment is shown.

[0032] Figure 7 The temperature change over time for each battery during the TR propagation experiment under unprotected conditions with the heating rod located on the side.

[0033] Figure 8 The temperature change curve of each battery during the TR propagation experiment is shown when the heating rod is located on the side and protected by the 4mm composite heat insulation material of the present invention.

[0034] Figure 9 The temperature change over time for each battery during the TR propagation experiment under unprotected conditions when the heating rod is located at the corner.

[0035] Figure 10 The temperature change curve of each battery during the TR propagation experiment is shown when the heating rod is located at the corner and protected by the 4mm composite heat insulation material of this invention. Detailed Implementation

[0036] This invention proposes a method for preparing a composite thermal insulation material to suppress the propagation of thermal runaway in lithium-ion batteries and its application. To make the advantages and technical solutions of this invention clearer and more explicit, the invention will be further described below with reference to specific embodiments.

[0037] All the raw materials mentioned in this invention can be purchased through commercial channels.

[0038] The main technical concept of this invention lies in developing a novel composite thermal insulation material to optimize the performance of single thermal insulation materials in practical applications, addressing the limitations of such materials. Hydrogels, due to their unique three-dimensional network structure, excellent water absorption and retention capacity, and simple preparation process, exhibit significant advantages in thermal management and suppression of thermal runaway propagation. This invention significantly improves the mechanical properties and thermal stability of the composite thermal insulation material by optimizing the skeletal structure of the hydrogel. Based on this, a physical crosslinking technique is used to introduce low thermal conductivity glass fibers into the hydrogel system, successfully preparing a composite material with both excellent mechanical properties and efficient thermal protection. This composite hydrogel uses sodium alginate and polyvinyl alcohol as the matrix; the abundant hydroxyl and carboxyl groups on its molecular chains not only endow the material with good hydrophilicity but also facilitate crosslinking reactions with other monomers. Acrylamide and 2-acrylamido-2-methylpropanesulfonic acid are selected as the main monomers, and nano-hydroxyapatite is introduced as a reinforcing component. Acrylamide, as an important polymer synthesis raw material, can effectively improve the stability of composite thermal insulation materials. Nano-hydroxyapatite, with its inorganic inert structure, significantly enhances the heat resistance and flame retardant properties of the hydrogel. Furthermore, by physically cross-linking nano-hydroxyapatite and glass fibers uniformly dispersed in the hydrogel network, not only is the cross-linked structure denser, but the mechanical strength and thermal insulation effect of the insulation material are further improved, thus more effectively suppressing the risk of thermal runaway in lithium-ion battery modules. Boron carbide in the hydrogel increases thermal conductivity, providing heat dissipation, while glass fibers provide thermal insulation. Therefore, a synergistic thermal conductivity-insulation mechanism is formed to suppress the propagation of thermal runaway in lithium-ion battery modules.

[0039] like Figure 1 As shown, the thermal runaway device used in this invention mainly includes a battery module, thermocouples, heating rods, a battery cycler, an electronic balance, a GoPro camera, a temperature control chamber, an information processing system, and a computer. A three-row, three-column battery module was assembled using eight NCM811-18650 lithium-ion batteries and a cylindrical heating rod. The battery cycler was used to charge the batteries to full capacity. Overheating of the heating rod induced thermal runaway (TR) in the battery, with the heating temperature controlled by the temperature control chamber. Thermocouples were fixed to both the batteries and the heating rod to collect temperature data, and a balance was used to record the mass change of the battery module during the experiment. All data was collected by the information processing system and transmitted to the computer. The experimental phenomena were recorded by a GoPro camera.

[0040] The present invention will now be described in detail with reference to specific embodiments.

[0041] Example 1:

[0042] This embodiment discloses a method for preparing a composite thermal insulation material to suppress the propagation of thermal runaway in lithium-ion batteries, specifically including the following steps:

[0043] Step 1: Mix sodium alginate solution and polyvinyl alcohol solution to obtain mixed solution 1;

[0044] Six portions of sodium alginate (1.6g) and polyvinyl alcohol (2g) were weighed and dissolved in 300ml of deionized water. The sodium alginate was dissolved at 80℃. The temperature was then raised to 92℃ to dissolve the polyvinyl alcohol. After complete dissolution, a mixed solution was obtained.

[0045] Step 2: Cool to room temperature, add nano-hydroxyapatite to mixed solution 1, and place it in an ultrasonic device for ultrasonic treatment for 15 minutes. Then place the ultrasonically treated mixture in a water bath at 55°C to ensure that the nano-hydroxyapatite is evenly dispersed, thus obtaining mixed solution 2.

[0046] Step 3: Add 4g of acrylamide and 2g of 2-acrylamide-2-methylpropanesulfonic acid to mixed solution 2 in sequence, and stir in a water bath at 55℃ for 15 minutes until the mixture is homogeneous to obtain mixed solution 3.

[0047] Step 4: Add boron carbide nanosheets to mixed solution 3 at concentrations of 0 g / L, 1.33 g / L, 2.67 g / L, 4 g / L, 5.33 g / L, and 6.67 g / L, respectively, and adjust the pH to 5-7. Stir thoroughly under a certain temperature to obtain mixed solution 4. The phosphate groups in the nano-hydroxyapatite form ionic bonds with the cations on the surface of boron carbide through electrostatic attraction. The boron atoms on the surface of boron carbide form coordination bonds with the oxygen in the phosphate or hydroxide groups of the nano-hydroxyapatite.

[0048] Step 5: Add glass fiber to mixed solution 4 and sonicate it in an ultrasonic device for 30 minutes. Then place the ultrasonically treated mixture in a water bath at 50-60°C to ensure that the glass fiber is evenly dispersed, thus obtaining mixed solution 5.

[0049] Step Six: Place the mixed solution five into a constant temperature water bath at 55℃, stir at a certain speed, and slowly add the initiator ammonium persulfate. The ammonium persulfate activates the active functional groups of sodium alginate, polyvinyl alcohol, acrylamide, and 2-acrylamide-2-methylpropanesulfonic acid, causing a chain reaction and forming a long chain structure. After stirring for 30 minutes, add the crosslinking agent MBA to the resulting hydrogel system to react. Glass fiber is introduced into the hydrogel system through crosslinking. The thermal conductivity of boron carbide and the thermal insulation of glass fiber form a "thermal conduction-thermal insulation" mechanism to obtain a composite thermal insulation material.

[0050] The scanning electron microscope image of the raw material glass fiber in this embodiment is as follows: Figure 2 As shown in (a), the scanning electron microscope image of hydroxyapatite is as follows: Figure 2As shown in Figure (b), the scanning electron microscope image of the composite thermal insulation material prepared in this embodiment when the amount of nano-hydroxyapatite added is 5.33 g / L is as follows. Figure 2 As shown in (d) and (e), the transmission electron microscope (TEM) images of the composite thermal insulation material are as follows: Figure 2 As shown in (f).

[0051] Example 2:

[0052] This embodiment discloses a method for preparing a composite thermal insulation material to suppress the propagation of thermal runaway in lithium-ion batteries, specifically including the following steps:

[0053] Step 1: Mix sodium alginate solution and polyvinyl alcohol solution to obtain mixed solution 1;

[0054] Six portions of 1.6g sodium alginate were weighed and dissolved in 300mL of deionized water. The solutions were then magnetically stirred in an 80℃ water bath until completely dissolved. Polyvinyl alcohol was then added to each sodium alginate solution at concentrations of 5.33g / L, 6g / L, 6.67g / L, 7.33g / L, and 8g / L, respectively. The solutions were then magnetically stirred in a 92℃ water bath until completely dissolved, resulting in mixed solution one.

[0055] Step 2: Cool to room temperature, add 1.6g of nano-hydroxyapatite to mixed solution one, and place it in an ultrasonic device for ultrasonic treatment for 15min. Then place the ultrasonically treated mixture in a water bath at 55℃ to ensure that the nano-hydroxyapatite is evenly dispersed, thus obtaining mixed solution two.

[0056] Step 3: Add 4g of acrylamide and 2g of 2-acrylamide-2-methylpropanesulfonic acid to mixed solution 2 in sequence, and stir in a water bath at 55℃ for 15 minutes until the mixture is homogeneous to obtain mixed solution 3.

[0057] Step 4: Add 5.33 g / L boron carbide nanosheets to mixed solution 3 and adjust the pH to 5-7. Stir thoroughly under certain temperature conditions to obtain mixed solution 4. The phosphate groups in the nano-hydroxyapatite and the cations on the surface of boron carbide form ionic bonds through electrostatic attraction. The boron atoms on the surface of boron carbide form coordination bonds with the oxygen in the phosphate or hydroxide groups of the nano-hydroxyapatite.

[0058] Step 5: Add glass fiber to mixed solution 4 and sonicate it in an ultrasonic device for 30 minutes. Then place the ultrasonically treated mixture in a water bath at 50-60°C to ensure that the glass fiber is evenly dispersed, thus obtaining mixed solution 5.

[0059] Step Six: Place the mixed solution five into a constant temperature water bath at 55℃, stir at a certain speed, and slowly add the initiator ammonium persulfate. The ammonium persulfate activates the active functional groups of sodium alginate, polyvinyl alcohol, acrylamide, and 2-acrylamide-2-methylpropanesulfonic acid, causing a chain reaction and forming a long chain structure. After stirring for 30 minutes, add the crosslinking agent MBA to the resulting hydrogel system to react. Glass fiber is introduced into the hydrogel system through crosslinking. The thermal conductivity of boron carbide and the thermal insulation of glass fiber form a "thermal conduction-thermal insulation" mechanism to obtain a composite thermal insulation material.

[0060] Example 3:

[0061] This embodiment discloses a method for preparing a composite thermal insulation material to suppress the propagation of thermal runaway in lithium-ion batteries, specifically including the following steps:

[0062] Step 1: Mix sodium alginate solution and polyvinyl alcohol solution to obtain mixed solution 1;

[0063] Six portions of sodium alginate with concentrations of 3.33 g / L, 4 g / L, 4.67 g / L, 5.33 g / L, and 6 g / L were weighed and dissolved in 300 mL of deionized water. The solutions were then magnetically stirred in an 80°C water bath until completely dissolved. 2 g of polyvinyl alcohol was then added to each of the six sodium alginate solutions, and the solutions were magnetically stirred in a 92°C water bath until completely dissolved, resulting in mixed solution one.

[0064] Step 2: Cool to room temperature, add 1.6g of nano-hydroxyapatite to mixed solution one, and place it in an ultrasonic device for ultrasonic treatment for 15min. Then place the ultrasonically treated mixture in a water bath at 55℃ to ensure that the nano-hydroxyapatite is evenly dispersed, thus obtaining mixed solution two.

[0065] Step 3: Add 4g of acrylamide and 2g of 2-acrylamide-2-methylpropanesulfonic acid to mixed solution 2 in sequence, and stir in a water bath at 55℃ for 15 minutes until the mixture is homogeneous to obtain mixed solution 3.

[0066] Step 4: Add 5.33 g / L boron carbide nanosheets to mixed solution 3 and adjust the pH to 5-7. Stir thoroughly under certain temperature conditions to obtain mixed solution 4. The phosphate groups in the nano-hydroxyapatite and the cations on the surface of boron carbide form ionic bonds through electrostatic attraction. The boron atoms on the surface of boron carbide form coordination bonds with the oxygen in the phosphate or hydroxide groups of the nano-hydroxyapatite.

[0067] Step 5: Add glass fiber to mixed solution 4 and sonicate it in an ultrasonic device for 30 minutes. Then place the ultrasonically treated mixture in a water bath at 50-60°C to ensure that the glass fiber is evenly dispersed, thus obtaining mixed solution 5.

[0068] Step Six: Place the mixed solution five into a constant temperature water bath at 55℃, stir at a certain speed, and slowly add the initiator ammonium persulfate. The ammonium persulfate activates the active functional groups of sodium alginate, polyvinyl alcohol, acrylamide, and 2-acrylamide-2-methylpropanesulfonic acid, causing a chain reaction and forming a long chain structure. After stirring for 30 minutes, add the crosslinking agent MBA to the resulting hydrogel system to react. Glass fiber is introduced into the hydrogel system through crosslinking. The thermal conductivity of boron carbide and the thermal insulation of glass fiber form a "thermal conduction-thermal insulation" mechanism to obtain a composite thermal insulation material.

[0069] Example 4:

[0070] This embodiment discloses a method for preparing a composite thermal insulation material to suppress the propagation of thermal runaway in lithium-ion batteries, specifically including the following steps:

[0071] Step 1: Mix sodium alginate solution and polyvinyl alcohol solution to obtain mixed solution 1;

[0072] 1.6g of sodium alginate and 2g of polyvinyl alcohol were dissolved in 300ml of deionized water. The sodium alginate was dissolved at 80℃. The temperature was then raised to 92℃ to dissolve the polyvinyl alcohol. After complete dissolution, a mixed solution was obtained.

[0073] Step 2: Cool to room temperature, add different masses of nano-hydroxyapatite to mixed solution 1, namely 0, 0.4, 0.8, 1.2, 1.6 and 2.0 g respectively, and place it in an ultrasonic device for ultrasonic treatment for 15 min. Then place the ultrasonically treated mixture in a water bath at 55℃ to ensure that the nano-hydroxyapatite is uniformly dispersed, to obtain mixed solution 2.

[0074] Step 3: Add 4g of acrylamide and 2g of 2-acrylamide-2-methylpropanesulfonic acid to mixed solution 2 in sequence, and stir in a water bath at 55℃ for 15 minutes until the mixture is homogeneous to obtain mixed solution 3.

[0075] Step 4: Add boron carbide nanosheets to mixed solution 3 at concentrations of 0 g / L, 1.33 g / L, 2.67 g / L, 4 g / L, 5.33 g / L, and 6.67 g / L, respectively, and adjust the pH to 5-7. Stir thoroughly under a certain temperature to obtain mixed solution 4. The phosphate groups in the nano-hydroxyapatite form ionic bonds with the cations on the surface of boron carbide through electrostatic attraction. The boron atoms on the surface of boron carbide form coordination bonds with the oxygen in the phosphate or hydroxide groups of the nano-hydroxyapatite.

[0076] Step 5: Add glass fiber to mixed solution 4 and sonicate it in an ultrasonic device for 30 minutes. Then place the ultrasonically treated mixture in a water bath at 50-60°C to ensure that the glass fiber is evenly dispersed, thus obtaining mixed solution 5.

[0077] Step Six: Place the mixed solution five into a constant temperature water bath at 55℃, stir at a certain speed, and slowly add the initiator ammonium persulfate. The ammonium persulfate activates the active functional groups of sodium alginate, polyvinyl alcohol, acrylamide, and 2-acrylamide-2-methylpropanesulfonic acid, causing a chain reaction and forming a long chain structure. After stirring for 30 minutes, add the crosslinking agent MBA to the resulting hydrogel system to react. Glass fiber is introduced into the hydrogel system through crosslinking. The thermal conductivity of boron carbide and the thermal insulation of glass fiber form a "thermal conduction-thermal insulation" mechanism to obtain a composite thermal insulation material.

[0078] Comparative Example 1:

[0079] The preparation methods of composite thermal insulation materials include:

[0080] Step 1: Mix sodium alginate solution and polyvinyl alcohol solution to obtain mixed solution 1;

[0081] Six portions of sodium alginate (1.6g) and polyvinyl alcohol (2g) were weighed and dissolved in 300ml of deionized water. The sodium alginate was dissolved at 80℃. The temperature was then raised to 92℃ to dissolve the polyvinyl alcohol. After complete dissolution, a mixed solution was obtained.

[0082] Step 2: Cool to room temperature, add nano-hydroxyapatite to mixed solution 1, and place it in an ultrasonic device for ultrasonic treatment for 15 minutes. Then place the ultrasonically treated mixture in a water bath at 55°C to ensure that the nano-hydroxyapatite is evenly dispersed, thus obtaining mixed solution 2.

[0083] Step 3: Add 4g of acrylamide and 2g of 2-acrylamide-2-methylpropanesulfonic acid to mixed solution 2 in sequence, and stir in a water bath at 55℃ for 15 minutes until the mixture is homogeneous to obtain mixed solution 3.

[0084] Step 4: Add 5.33 g / L boron carbide nanosheets to mixed solution 3 and adjust the pH to 5-7. Stir thoroughly under certain temperature conditions to obtain mixed solution 4. The phosphate groups in the nano-hydroxyapatite and the cations on the surface of boron carbide form ionic bonds through electrostatic attraction. The boron atoms on the surface of boron carbide form coordination bonds with the oxygen in the phosphate or hydroxide groups of the nano-hydroxyapatite.

[0085] Step 5: Place the mixed solution 4 into a constant temperature water bath at 55℃, stir at a certain speed, and slowly add the initiator ammonium persulfate. The ammonium persulfate activates the active functional groups of sodium alginate, polyvinyl alcohol, acrylamide, and 2-acrylamide-2-methylpropanesulfonic acid, causing a chain reaction and forming a long chain structure. After stirring for 30 minutes, add the crosslinking agent MBA to the obtained hydrogel system to react. The thermal conductivity of boron carbide and the thermal insulation of glass fiber form a "thermal conduction-thermal insulation" mechanism to obtain a composite thermal insulation material.

[0086] Comparative Example 2:

[0087] The preparation methods of composite thermal insulation materials include:

[0088] Step 1: Mix sodium alginate solution and polyvinyl alcohol solution to obtain mixed solution 1;

[0089] Six portions of sodium alginate (1.6g) and polyvinyl alcohol (2g) were weighed and dissolved in 300ml of deionized water. The sodium alginate was dissolved at 80℃. The temperature was then raised to 92℃ to dissolve the polyvinyl alcohol. After complete dissolution, a mixed solution was obtained.

[0090] Step 2: Cool to room temperature, add nano-hydroxyapatite to mixed solution 1, and place it in an ultrasonic device for ultrasonic treatment for 15 minutes. Then place the ultrasonically treated mixture in a water bath at 55°C to ensure that the nano-hydroxyapatite is evenly dispersed, thus obtaining mixed solution 2.

[0091] Step 3: Add 4g of acrylamide and 2g of 2-acrylamide-2-methylpropanesulfonic acid to mixed solution 2 in sequence, and stir in a water bath at 55℃ for 15 minutes until the mixture is homogeneous to obtain mixed solution 3.

[0092] Step 4: Add glass fiber to mixed solution 3 and sonicate it in an ultrasonic device for 30 minutes. Then place the ultrasonically treated mixture in a water bath at 50-60°C to ensure that the glass fiber is evenly dispersed, thus obtaining mixed solution 4.

[0093] Step 6: Place the mixed solution 4 into a constant temperature water bath at 55℃, stir at a certain speed, and slowly add the initiator ammonium persulfate. The ammonium persulfate activates the active functional groups of sodium alginate, polyvinyl alcohol, acrylamide, and 2-acrylamide-2-methylpropanesulfonic acid, causing a chain reaction and forming a long chain structure. After stirring for 30 minutes, add the crosslinking agent MBA to the obtained hydrogel system to react. Glass fiber is introduced into the hydrogel system through crosslinking to obtain a composite thermal insulation material.

[0094] Comparative Example 3:

[0095] The preparation methods of composite thermal insulation materials include:

[0096] Step 1: Mix sodium alginate solution and polyvinyl alcohol solution to obtain mixed solution 1;

[0097] Six portions of sodium alginate (1.6g) and polyvinyl alcohol (2g) were weighed and dissolved in 300ml of deionized water. The sodium alginate was dissolved at 80℃. The temperature was then raised to 92℃ to dissolve the polyvinyl alcohol. After complete dissolution, a mixed solution was obtained.

[0098] Step 3: Add 4g of acrylamide and 2g of 2-acrylamide-2-methylpropanesulfonic acid to mixed solution one in sequence, and stir in a water bath at 55℃ for 15 minutes until the mixture is homogeneous to obtain mixed solution two.

[0099] Step 4: Add glass fiber to mixed solution 2 and sonicate it in an ultrasonic device for 30 minutes. Then place the ultrasonically treated mixture in a water bath at 50-60°C to ensure that the glass fiber is evenly dispersed, thus obtaining mixed solution 3.

[0100] Step 6: Place the mixed solution 3 into a constant temperature water bath at 55℃, stir at a certain speed, and slowly add the initiator ammonium persulfate. The ammonium persulfate activates the active functional groups of sodium alginate, polyvinyl alcohol, acrylamide, and 2-acrylamide-2-methylpropanesulfonic acid, causing a chain reaction and forming a long chain structure. After stirring for 30 minutes, add the crosslinking agent MBA to the obtained hydrogel system to react. Glass fiber is introduced into the hydrogel system through crosslinking to obtain a composite thermal insulation material.

[0101] Comparative Example 4:

[0102] The preparation methods of composite thermal insulation materials include:

[0103] Step 1: Mix sodium alginate solution and polyvinyl alcohol solution to obtain mixed solution 1;

[0104] Six portions of sodium alginate (1.6g) and polyvinyl alcohol (2g) were weighed and dissolved in 300ml of deionized water. The sodium alginate was dissolved at 80℃. The temperature was then raised to 92℃ to dissolve the polyvinyl alcohol. After complete dissolution, a mixed solution was obtained.

[0105] Step 2: Cool to room temperature, add nano-hydroxyapatite to mixed solution 1, and place it in an ultrasonic device for ultrasonic treatment for 15 minutes. Then place the ultrasonically treated mixture in a water bath at 55°C to ensure that the nano-hydroxyapatite is evenly dispersed, thus obtaining mixed solution 2.

[0106] Step 3: Add 4g of acrylamide and 2g of 2-acrylamide-2-methylpropanesulfonic acid to mixed solution 2 in sequence, and stir in a water bath at 55℃ for 15 minutes until the mixture is homogeneous to obtain mixed solution 3.

[0107] Step 4: Place the mixed solution 3 into a constant temperature water bath at 55℃, stir at a certain speed, and slowly add the initiator ammonium persulfate. The ammonium persulfate activates the active functional groups of sodium alginate, polyvinyl alcohol, acrylamide, and 2-acrylamide-2-methylpropanesulfonic acid, causing a chain reaction and forming a long chain structure. After stirring for 30 minutes, add the crosslinking agent MBA to the obtained hydrogel system to react and obtain the composite thermal insulation material.

[0108] Application testing:

[0109] The composite thermal insulation materials obtained in Examples 1-4 and Comparative Examples 1-4 of the present invention are adopted... Figure 1 The thermal runaway experimental setup was used for performance testing.

[0110] First, thermogravimetric testing

[0111] Thermogravimetric-differential scanning calorimetry (TG-DSC, SDT Q600) was used to characterize the pyrolysis behavior of the material. Before the experiment, the final product was dried in a vacuum drying oven. 9 mg of sample powder was accurately weighed and placed in a high-temperature thermogravimetric analyzer (TGA 11600HT) under a nitrogen atmosphere to test its thermal stability in order to evaluate the thermal decomposition characteristics of the material.

[0112] from Figure 3 From (a), it can be concluded that the main thermal decomposition temperatures of the composite hydrogel without hydroxyapatite are 314℃ and 388℃, and significant mass loss occurs when the temperature is raised to the range of 300℃-400℃. From... Figure 3 From (b), it can be concluded that the main thermal decomposition temperatures of the composite insulation material occur at 89℃, 296℃, 389℃, and 431℃, respectively. Comparing the two sets of data, it was found that the composite insulation material without hydroxyapatite retained only 30.5% of its mass at 650℃, and this mass continued to decrease. However, after introducing hydroxyapatite, the residual mass of the composite insulation material at the same temperature increased to 46.2% and tended to stabilize, with a mass loss reduction of 16.2%. This result indicates that the addition of hydroxyapatite significantly enhances the thermal stability of the composite insulation material, enabling it to maintain good structural integrity even at high temperatures, thus ensuring that its practical application performance is not affected.

[0113] Second, mechanical property testing

[0114] Traditional sodium alginate (SA)-based hydrogels have limited applications due to insufficient mechanical properties, so enhancing their mechanical strength is crucial for expanding practical applications. Figure 4Experimental data in (a) and (b) show that the compressive properties of the composite insulation material are significantly improved compared to the sample without hydroxyapatite. When the hydroxyapatite content reaches 5.3 g / L, the compressive strength of the composite insulation material reaches a peak of 36.23 MPa, a value far exceeding the mechanical properties of common insulation materials such as extruded polystyrene boards. This superior mechanical property stems from the material's unique structural design: on the one hand, hydroxyapatite enhances the skeletal stability of the hydrogel through hydrogen bonding and metal coordination effects; on the other hand, the polymer chains intertwine to form a dense three-dimensional network. This dual-network structure is similar to constructing "protective armor" for the hydrogel, where the rigid exoskeleton formed by hydroxyapatite and the flexible polymer network work synergistically to improve the overall mechanical properties of the composite insulation material.

[0115] Meanwhile, the mechanical properties of the composite thermal insulation gels prepared in Comparative Examples 3 and 4 were tested. The results showed that the maximum compressive strength of the composite thermal insulation gel in Comparative Example 3 without the addition of boron carbide and hydroxyapatite was 24.46 MPa, a decrease of 32.5% compared to the final product; while the maximum compressive strength of the composite thermal insulation gel in Comparative Example 4 without the addition of boron carbide and glass fiber was 30.78 MPa, a decrease of 15.1% compared to the final product. This indicates that the multiple raw materials in this invention can synergistically enhance the mechanical properties of the composite thermal insulation gel.

[0116] Third, battery thermal runaway propagation test

[0117] Temperature response analysis of thermal runaway propagation experiment combined with Figures 5 to 10 As shown, during the center heating test, in the module without protective measures, when the heating rod temperature continued to rise, batteries 1-2, 2-1, 2-3, and 3-2 adjacent to the heat source experienced thermal runaway between 2071 and 2112 seconds. Once thermal runaway was triggered, the temperature of other batteries in the module rose sharply within 35 seconds, such as... Figure 5 As shown, the average trigger time was 2109 s, and the peak temperature reached 894 °C. Because the heat source was located at the center and in direct contact with the four batteries, thermal runaway propagated fastest and was most severe. The results of the center heating test using 4 mm thick composite hydrogel protection showed... Figure 6 As shown, although it could not completely prevent thermal runaway from adjacent cells, it successfully blocked the propagation of thermal runaway from the far diagonal cells. The moisture in the hydrogel significantly slowed the temperature rise process through continuous heat absorption, delaying the average trigger time of adjacent cells to 3551 s (1442 s longer than the control group), reducing the maximum temperature to 584.8℃, the maximum temperature difference within the module to 485.6℃, and maintaining the corner cell temperature below 103.1℃. In the comparative experiment of the side heating mode, the control group showed that, as Figure 7As shown, the three batteries closest to the heat source experienced thermal runaway successively within 50 seconds, and subsequently, all batteries in the module were ignited within 100 seconds, with an average trigger time of 1702 seconds and a maximum temperature of 721.7℃. The test results after using hydrogel protection are different. Figure 8 As shown, only three adjacent batteries experienced thermal runaway, with the average trigger time extended to 3021s (1319s longer than the control group), the highest temperature decreased to 583.3℃, ​​and the maximum temperature difference was 477.9℃. Corner heating experiments showed that, as... Figure 9 As shown, after two batteries adjacent to the heat source triggered thermal runaway, a third battery went out of control within 100 seconds, with an average trigger time of 1975 seconds. The corner heating test results after using hydrogel protection showed that only two adjacent batteries went out of control, with the trigger time delayed to 3380 seconds (an increase of 1405 seconds), and the maximum temperature difference reaching 510.4℃. Figure 10 As shown.

[0118] Experimental data show that: (1) the number of batteries in direct contact with the heat source is positively correlated with the severity of thermal runaway; (2) composite thermal insulation materials can effectively delay the thermal runaway trigger time (extending by 1319 to 1442 s); (3) significantly reduce the peak temperature of runaway batteries (reducing by 138.9 to 309.2 °C); and (4) effectively control the temperature rise rate of non-runaway batteries.

[0119] The thermal runaway propagation suppression performance of the composite thermal insulation materials prepared in Comparative Examples 3 and 4 was tested. The test results showed that when a 4 mm thick composite thermal insulating hydrogel without boron carbide and nano-hydroxyapatite was used for protection, the thermal runaway trigger time of adjacent batteries could be delayed by 945–1134 s; while when a 4 mm thick composite thermal insulating hydrogel without boron carbide and glass fiber was used for protection, the thermal runaway trigger time of adjacent batteries could be delayed by 796–989 s. This demonstrates that boron carbide in the hydrogel system can, together with hydroxyapatite and glass fiber, significantly enhance the protective effect of the materials on the battery module, achieving a synergistic effect in suppressing the propagation of thermal runaway within the battery module.

[0120] Any parts not mentioned in this invention can be achieved by referring to existing technologies.

[0121] Those skilled in the art should recognize that the above embodiments are only used to illustrate this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the essential spirit and scope of this application fall within the scope of protection claimed in this application.

Claims

1. A method for preparing a composite thermal insulation material to suppress the propagation of thermal runaway in lithium-ion batteries, characterized in that, Includes the following steps: a. Mix sodium alginate solution with polyvinyl alcohol solution to obtain mixed solution one; b. Add nano-hydroxyapatite to the first mixed solution and place it in an ultrasonic device for ultrasonic treatment. Then place the ultrasonically treated mixture in a water bath at 50-60°C to ensure that the nano-hydroxyapatite is uniformly dispersed to obtain the second mixed solution. c. Add acrylamide and 2-acrylamide-2-methylpropanesulfonic acid sequentially to the second mixed solution, and stir until homogeneous to obtain the third mixed solution; d. Add boron carbide nanosheets to mixed solution three and adjust the pH to 5-7. Stir thoroughly under certain temperature conditions to obtain mixed solution four. The phosphate groups in nano-hydroxyapatite and the cations on the surface of boron carbide form ionic bonds through electrostatic attraction. The boron atoms on the surface of boron carbide form coordination bonds with the oxygen in the phosphate or hydroxide groups of nano-hydroxyapatite. e. Add glass fibers to the mixed solution four and place it in an ultrasonic device for ultrasonic treatment. Then place the ultrasonically treated mixture in a water bath at 50-60°C to ensure that the glass fibers are evenly dispersed, and obtain mixed solution five. f. Slowly add ammonium persulfate as an initiator to the mixed solution five. Ammonium persulfate activates the active functional groups of sodium alginate, polyvinyl alcohol, acrylamide, and 2-acrylamide-2-methylpropanesulfonic acid, causing a chain reaction and forming a long-chain structure. Then, a crosslinking agent is added to the resulting hydrogel system to carry out the reaction. Glass fiber is introduced into the hydrogel system through crosslinking. The thermal conductivity of boron carbide and the thermal insulation of glass fiber form a "thermal conduction-thermal insulation" mechanism to obtain a composite thermal insulation material.

2. The method for preparing a composite thermal insulation material for suppressing the propagation of thermal runaway in lithium-ion batteries according to claim 1, characterized in that: In step a, the mass fraction ratio of sodium alginate solution to polyvinyl alcohol solution is 0.8:1; the sodium alginate solution is prepared by adding sodium alginate to deionized water, with a mass-to-volume ratio of sodium alginate to deionized water of 1.6:300 g / L, and a dissolution temperature of 70-75℃; the polyvinyl alcohol solution is prepared by adding polyvinyl alcohol to deionized water, with a mass-to-volume ratio of polyvinyl alcohol to deionized water of 2:300 g / L.

3. The method for preparing a composite thermal insulation material for suppressing the propagation of thermal runaway in lithium-ion batteries according to claim 1, characterized in that: In step b, the mass ratio of nano-hydroxyapatite to sodium alginate is 1:

1.

4. The method for preparing a composite thermal insulation material for suppressing the propagation of thermal runaway in lithium-ion batteries according to claim 1, characterized in that: In step c, the mass ratio of acrylamide to sodium alginate is 1:0.4, and the mass ratio of acrylate to 2-acrylamide-2-methylpropanesulfonic acid is 2:1; the temperature is maintained at 50-60℃ during stirring.

5. The method for preparing a composite thermal insulation material for suppressing the propagation of thermal runaway in lithium-ion batteries according to claim 4, characterized in that: In step d, the mass ratio of boron carbide nanosheets to 2-acrylamide-2-methylpropanesulfonic acid is 1:1, and the temperature is controlled at 50-60℃ during stirring.

6. The method for preparing a composite thermal insulation material for suppressing the propagation of thermal runaway in lithium-ion batteries according to claim 5, characterized in that: In step e, the mass ratio of glass fiber to boron carbide is 5:

2.

7. The method for preparing a composite thermal insulation material for suppressing the propagation of thermal runaway in lithium-ion batteries according to claim 6, characterized in that: In step f, the mixed solution is placed in a constant temperature water bath at 60-65℃, and the mass ratio of ammonium persulfate to glass fiber is 0.009:

1.

8. The method for preparing a composite thermal insulation material for suppressing the propagation of thermal runaway in lithium-ion batteries according to claim 1, characterized in that: In step f, the crosslinking agent is N,N-methylenebisacrylamide, the mass ratio of N,N-methylenebisacrylamide to ammonium persulfate is 0.38:0.045, the reaction temperature after adding the crosslinking agent is 60-65℃, and the reaction time is 2-4 hours.

9. The application of the composite thermal insulation material prepared by any one of claims 1 to 8, characterized in that: When the composite thermal insulation material comes into direct contact with a heat source, it can effectively delay the thermal runaway trigger time, reduce the peak temperature of the runaway battery, and effectively control the temperature rise rate of the non-runaway battery.

Images