Flame-retardant sheet and secondary battery module structure using same

Abstract

The invention provides a flame-retardant plate and a secondary battery module structure using the flame-retardant plate, the flame-retardant plate structurally comprises a plate and a flame-retardant intumescent coating attached to the surface of the plate, and the flame-retardant intumescent coating comprises expanded graphite; in one aspect, the flame-retardant plate is used for forming a shell of the secondary battery module, and the flame-retardant expansion coating is located on the inner side of the shell; the flame-retardant intumescent coating can be attached to a metal or plastic plate in a spraying or brushing manner, is not limited by the shape of the plate or the shell of the secondary battery module, and can be easily constructed and manufactured; when meeting high temperature, the flame-retardant expansion coating starts to expand to form carbides, the maximum expansion rate can reach 200 times, the inner layer (close to the plate side) of the expanded carbides is of a hollow structure, the compact carbonization layer can resist impact, the outer layer is velvet-shaped carbides, the kinetic energy of impact can be reduced, and melting damage to the plate is reduced.

Description

Technical Field

[0001] The present application relates to a composite material and a secondary battery module manufactured using the composite material, in particular to a flame retardant board and a secondary battery module structure using the flame retardant board. Background Art

[0002] In the early 1860s, Brodie discovered a new functional material, Expanded Graphite (EG), by heating natural graphite with chemical reagents such as sulfuric acid and nitric acid. Expanded graphite is a new type of functional carbon material, also known as worm graphite because of its worm-like structure.

[0003] The published Chinese invention patent CN85103917 proposes an expandable graphite and a method for manufacturing the same, which solves the problems of the prior art, such as small and unstable expansion multiples and high precision requirements for graphite raw materials. The graphite particles are soaked in sulfuric acid and sulfuric acid in sequence, washed with water and then dried at low temperature until the filling amount is less than 10%, and then calcium oxide powder is added for treatment and screening, so that the prepared expandable graphite has a stable high expansion multiple.

[0004] In the published Chinese invention patent announcement number CN103333422B, a flame retardant expandable polystyrene particle doped with low-sulfur expanded graphite and a preparation method thereof are proposed; by the dispersion effect of ultrafine graphite, 0.1-10wt% low-sulfur expanded graphite (or sulfur-free expanded graphite) based on styrene monomer is uniformly dispersed into the styrene polymerization system, and 0.1-1wt% halogen flame retardant (such as hexabromocyclododecane) and related additives are added at the same time, and a 0.3mm-4.5mm diameter expandable polystyrene bead is prepared by a one-step expandable polystyrene suspension polymerization process, which can make the expanded polystyrene product reach B1 and B2 flame retardant grades. It is characterized in that under the condition of achieving the same flame retardant ability in the expandable styrene polymer; the purpose is to reduce the amount of halogen flame retardant to 10wt% to 80wt% of the original amount by adding low-sulfur expanded graphite, and also reduce the content of environmentally harmful components in the expandable polystyrene flame retardant product.

[0005] Lithium batteries have been widely used in various electronic products and electric vehicles due to their advantages such as fast charging, high energy density, small size and mature technology. However, due to the active chemical activity of "lithium", it is also accompanied by a considerable degree of risk. Lithium battery fire news is often heard. In particular, the recent occurrence of multiple electric vehicle fires and the difficulty of extinguishing them have made people pay more attention to the safety of lithium batteries. It is known that thermal runaway is one of the main factors causing lithium battery fires. Lithium battery thermal runaway is caused by the fact that the heat generation rate of the internal short circuit of the battery is much higher than the heat dissipation rate, and a large amount of heat accumulates and is not dissipated in time. And when the temperature increases, the changes caused by the increase in temperature further increase the temperature, resulting in a vicious thermal cycle and spread. The thermal runaway of lithium batteries will trigger a series of irreversible chain reactions, and the internal temperature will rise rapidly within a few milliseconds. The energy stored in the lithium battery is suddenly released, resulting in a high temperature of about 500℃ to 1000℃ inside. At the same time, some materials of the lithium battery form combustible high-temperature gas due to the high temperature, which will erupt and release pressure and overflow, thus causing a fire that is almost impossible to extinguish in conventional ways.

[0006] Known means of preventing thermal runaway of lithium batteries include: using high-temperature resistant plastic materials as isolation to increase the spacing between battery cells; using carbon steel materials to form lithium batteries to form battery packs as a means to prevent thermal runaway and spread; and using heat-insulating two-dimensional planar materials, such as mica, ceramic plates, silica plates, carbon fiber cloth, steel plates, etc. as heat-insulating and heat-insulating materials to transmit prevention and control. As for the application of heat-insulating two-dimensional planar materials, their function cannot prevent lithium battery cells from generating impact gas under thermal runaway. For high-temperature resistant and anti-melting two-dimensional planar materials that are only attached to the inside of the outer shell, once they are impacted by the internal explosion of the lithium battery core, the covering battery shell is prone to material being broken / punctured, causing external air such as oxygen to enter the lithium battery and cause re-ignition or deflagration of open flames. In addition, this material also lacks the ability to prevent high-temperature gas from spreading and diffusing in lithium batteries (stacks). Summary of the invention

[0007] The technical problem to be solved by the present application is to provide a flame retardant plate with excellent thermal insulation, impact resistance and passive flame retardant functions and a secondary battery module structure using the flame retardant plate.

[0008] In order to solve the above-mentioned technical problems, an embodiment of the flame retardant plate of the present application and a secondary battery module structure using the flame retardant plate is constructed, including: a plate, and a flame retardant expansion coating attached to the surface of the plate, wherein the composition of the flame retardant expansion coating includes expanded graphite, and the flame retardant expansion coating can be attached to the surface of the plate by spraying or brushing.

[0009] One aspect of the present application proposes a secondary battery module structure using the flame-retardant board. An embodiment of the secondary battery module structure includes: a fan, at least one secondary battery, and a shell. The shell is composed of the flame-retardant board. The flame-retardant expansion coating attached to the board is located on the inner side of the shell. The secondary batteries are arranged inside the shell. There is a gap between the secondary batteries and the flame-retardant expansion coating on the inner side of the shell to form an airflow channel. The fan is arranged at one end of the shell to deliver airflow into the airflow channel.

[0010] As a preferred embodiment of the present application, the material of the plate is metal or plastic.

[0011] As a preferred embodiment of the present application, the flame retardant intumescent coating comprises: 10% to 30% of graphite, 30% to 45% of polybutadiene, 20% to 30% of silicon dioxide, and 15% to 30% of methylcyclohexane, accounting for 10% to 30% of the weight percentage (wt%) of the flame retardant intumescent coating.

[0012] As a preferred embodiment of the present application, the flame retardant intumescent coating comprises: 5% to 30% of graphite, 10% to 15% of solid acrylic polymer, 5% to 10% of chlorinated paraffin, 5% to 10% of titanium dioxide, 25% to 30% of xylene, 5% to 10% of melamine, 5% to 10% of pentaerythritol, and 25% to 30% of ammonium polyphosphate, based on the weight percentage (wt%) of the flame retardant intumescent coating.

[0013] As a preferred embodiment of the present application, the flame retardant intumescent coating comprises: 10% to 20% of graphite, 10% to 15% of rubber, 30% to 35% of ethylcyclohexane, 20% to 30% of an environmentally friendly solvent, 10% to 15% of a resin, and 1% to 3% of an additive, accounting for 10% to 20% of the weight percentage (wt%) of the flame retardant intumescent coating.

[0014] As a preferred embodiment of the present application, the flame retardant intumescent coating comprises: 10% to 20% graphite, 60% to 75% methyl acrylate, 15% to 25% xylene, 1% to 2% dimethyl ketone, and 10% to 15% triphosphate, accounting for 10% to 20% of the weight percentage (wt%) of the flame retardant intumescent coating.

[0015] As a preferred embodiment of the present application, the flame retardant intumescent coating comprises: 10% to 15% of graphite, 40% to 60% of styrene-acrylic latex, 5% to 15% of hydrophobic aerogel powder, 10% to 20% of glass fiber, 15% to 25% of deionized water, and 0.1% to 3% of 1,2-propylene glycol, accounting for 10% to 15% of the weight percentage (wt%) of the flame retardant intumescent coating.

[0016] The advantages and functions of the flame retardant board and the secondary battery module structure using the flame retardant board of the present application are as follows: the flame retardant expansion coating can be attached to the metal or plastic plate by spraying or brushing, and is not restricted by the shape of the plate or the shell of the secondary battery module, and can be easily constructed and manufactured; when exposed to high temperature, the flame retardant expansion coating begins to expand to form carbide, and the expansion ratio can reach up to 200 times. In addition to blocking the air flow channel in the secondary battery module to prevent the internal gas from contacting with the external air or oxygen, the inner layer of the expanded carbide (close to the plate side) is a hollow structure and the compact carbonized layer is impact-resistant, and the outer layer is a velvety carbide that can reduce the kinetic energy of the impact and reduce the melting damage to the plate.

[0017] The details of other effects and embodiments of the present application are described below with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 It is a schematic diagram of the cross-sectional structure of an embodiment of the flame retardant board of the present application;

[0020] Figure 2 It is a schematic diagram of the cross-sectional structure of a secondary battery module made of a flame retardant board in the present application;

[0021] Figure 3 yes Figure 2 A side view of the embodiment of the structure;

[0022] Figure 4 yes Figure 2 A schematic diagram of a usage state of the embodiment structure;

[0023] Figure 5 It is a schematic diagram of the performance test structure of the flame retardant board of the present application;

[0024] Figures 6 to 10 It is a schematic diagram of the temperature-time curve of this application.

[0025] Explanation of symbols

[0026] 10 sheet 20 flame retardant expansion coating

[0027] 30 fans 40 secondary batteries

[0028] 50 housing 51 air flow channel

[0029] 60 straight-up blowtorch P temperature measurement point

[0030] Type 61K (Ni-Cr alloy) thermocouple wire DETAILED DESCRIPTION

[0031] The positional relationships described in the following embodiments include: up, down, left and right. Unless otherwise specified, they are all based on the directions in which the components are drawn in the drawings.

[0032] First see Figure 1 , is a schematic diagram of the cross-sectional structure of an embodiment of the flame retardant board of the present application. The structure of the flame retardant board of the present application includes: a board 10, and a flame retardant expansion coating 20 attached to the surface of the board 10, the composition of the flame retardant expansion coating 20 includes expanded graphite, in a preferred embodiment, the flame retardant expansion coating 20 can be attached to the surface of the board 10 by spraying or brushing.

[0033] In a preferred embodiment, the flame retardant intumescent coating 20 is prepared into a fluid liquid, preferably in a paint state, so that it can be attached to the surface of the plate 10 by spraying or brushing, thereby making a flame retardant plate. Moreover, it is not limited by the shape and material of the plate 10, and can be easily constructed and manufactured. Even the shell of a secondary battery module with a complex shape can be easily constructed, and is not limited to the requirement of a flat surface. Preferably, the material of the plate 10 can be metal or plastic.

[0034] See also Figure 2 , Figure 3, is a schematic diagram of the cross-sectional structure of an embodiment of a secondary battery module made using the aforementioned flame retardant board and its side view. An embodiment of the secondary battery module comprises: a fan 30, at least one secondary battery 40, and a shell 50, the shell 50 is composed of the aforementioned flame retardant board, wherein the flame retardant expansion coating 20 attached to the board 10 is located on the inner side of the shell 50, and the secondary battery 40 is arranged inside the shell. In a preferred application example, the secondary battery 40 is a lithium electron (or lithium ion battery), and there is a gap between these secondary batteries 40 and the flame retardant expansion coating 20 on the inner side of the shell 50 to form an airflow channel 51. The fan 30 is arranged at one end of the shell 50 to send airflow into the airflow channel 51, and the airflow is used to dissipate heat from the secondary battery 40 to prevent the secondary battery 40 from thermal runaway. Figure 2 The illustrated embodiment includes a plurality of secondary batteries 40 connected in series and / or in parallel, and is used as an example of an embodiment of a secondary battery module made of the aforementioned flame retardant board to illustrate the present application, but is not limited thereto. The series or parallel connection of the secondary batteries 40 should be changed according to the actual use and design. Under normal conditions, the flame retardant expansion coating 20 does not touch the positive and negative electrodes of the secondary battery 40, so that the airflow channel 51 remains unobstructed.

[0035] Generally speaking, the operating temperature range of lithium-ion batteries is generally between -20℃ and 50℃, and the optimal operating temperature is between 20℃ and 40℃. When working stably, there will be no sudden temperature rise and material vaporization. If the lithium battery is in abnormal conditions, such as overcharging, insufficient heat dissipation mechanism, material change and short circuit, it is easy to have thermal runaway. At this time, the lithium battery may first eject the internal vaporized materials and the gases produced by the gas release valve at the positive electrode. Because these gases are flammable and have high temperatures, once they meet with the combustion-supporting gases in the external environment, such as oxygen, the lithium battery is prone to high-temperature combustion and continuous open flames of 500℃ to 1000℃, and even more violent explosions caused by the combustible materials inside the lithium battery cell and the gas produced by it.

[0036] See also Figure 4 ,yes Figure 2 The figure shows a schematic diagram of the use status of a secondary battery module made of the aforementioned flame retardant board. Figure 4 The schematic diagram of the use state shown in FIG. 1 shows the situation inside the housing 50 of the secondary battery module when the secondary battery 40 has thermal runaway. Figure 4In the illustrated situation, when the secondary battery 40 experiences thermal runaway, the expanded graphite contained in the flame retardant intumescent coating 20 begins to expand due to heat or high temperature to form carbides, and the expansion ratio can be up to 200 times; the expanded carbide inner layer (close to the shell 50 side) is a hollow and compact carbonized layer, and the outer layer is a velvety carbide, so there will be two expansion effects; the chemical substances ejected by the thermal runaway of the lithium battery are more resistant to impact, and the shock wave first encounters the outer velvety and soft carbide, thereby reducing the kinetic energy, and then even if it contacts the inner hollow and hard carbonized layer, it will be blocked, reducing the melting damage to the shell 50; on the other hand, after a large expansion, the flame retardant intumescent coating 20 will block the airflow channel 51 to prevent the internal gas from contacting the external air or oxygen, and has excellent thermal insulation, impact resistance and passive flame retardant effects.

[0037] Embodiment 1 of the flame retardant expansion coating 20 is a PU flame retardant expansion coating

[0038] The flame retardant intumescent coating 20 comprises: 10% to 30% of graphite, 30% to 45% of polybutadiene, 20% to 30% of silicon dioxide, and 15% to 30% of methylcyclohexane, accounting for 10% to 30% of the weight percentage (wt%) of the flame retardant intumescent coating.

[0039] For the flame retardant and heat insulation effects of the flame retardant board made using the flame retardant intumescent coating 20, see Figure 5 The performance test framework and the test results are shown in Table 1. Figure 5 In the test structure shown, the flame retardant plate 10 is made of 304 stainless steel, and the flame retardant intumescent coating 20 is coated on the front of the plate 10; the test equipment includes: (1) a straight-up blowtorch 60 using butane fuel (temperature of about 800°C); (2) a K-type (nickel-chromium alloy) thermocouple wire 61, and the temperature measurement point P is located on the back of the plate 10. The experimental environment is a closed space (no airflow) and a constant temperature of 27.5°C.

[0040] The test steps are as follows: 1. Use a straight-up blowtorch to heat the front side of the plate 10 at the temperature measuring point, with the height of the blowtorch flame being about 5 cm; 2. Measure the temperature of the temperature measuring point on the back side every 10 seconds, heat continuously for 60 seconds, and record the test results obtained as shown in the line 2 data in the following (Table 1).

[0041] For comparison, 304 stainless steel not coated with the flame retardant intumescent coating 20 was heated by the same equipment and steps, and the test results were recorded as the data of line 1 listed below (Table 1). In addition, after completing the data of line 2, the plate 10 (304 stainless steel) coated with the flame retardant intumescent coating 20 was cooled to 27.5° C., and the target to be tested, on which the flame retardant intumescent coating 20 had been thermally expanded, was heated for the second time by the same steps and equipment, and the test results were recorded as the data of line 3 listed below (Table 1).

[0042] 10(s) 20(s) 30(s) 40(s) 50(s) 60(s) Line 1 117℃ 214℃ 318℃ 389℃ 440℃ 487℃ Line 2 48℃ 67℃ 104℃ 120℃ 131℃ 141℃ Line 3 32℃ 42℃ 60℃ 89℃ 104℃ 115℃

[0043] Table 1: Test results of Example 1 (see Figure 6 )

[0044] From the test results in Table 1, it can be found that, compared with the data of Line 1, the temperature measured by the data of Line 2 is significantly lower, and the difference is obvious; then, by comparing the data of Line 2 with the data of Line 3, the flame retardant intumescent coating 20 that has expanded due to heat is heated for the second time, and the temperature at the same temperature measuring point is significantly lower than the temperature of the first heating, which shows that the flame retardant intumescent coating 20 that has expanded due to heat can absorb more heat energy and reduce the temperature behind the heat source.

[0045] As a preferred embodiment of the present application, the composition of the flame retardant intumescent coating 20 further includes the following multiple preferred embodiments. Embodiments (II) to (V) listed below are also tested with the same test framework and test steps as embodiment (I) and the test results are listed together.

[0046] Embodiment 2 of the flame retardant expansion coating 20 is an oily flame retardant expansion coating

[0047] The flame retardant intumescent coating comprises: 5% to 30% of graphite, 10% to 15% of solid acrylic polymer, 5% to 10% of chlorinated paraffin, 5% to 10% of titanium dioxide, 25% to 30% of xylene, 5% to 10% of melamine, 5% to 10% of pentaerythritol, and 25% to 30% of ammonium polyphosphate, accounting for 5% to 30% of the weight percentage (wt%) of the flame retardant intumescent coating.

[0048] 10(s) 20(s) 30(s) 40(s) 50(s) 60(s) Line 1 117℃ 214℃ 318℃ 389℃ 440℃ 487℃ Line 2 40℃ 75℃ 102℃ 113℃ 117℃ 124℃ Line 3 32℃ 40℃ 51℃ 64℃ 76℃ 89℃

[0049] Table 2: Test results of Example 2 (see Figure 7 )

[0050] Embodiment 3 of the flame retardant expansion coating 20 is a rubber flame retardant expansion coating

[0051] The flame retardant intumescent coating comprises: 10% to 20% of graphite, 10% to 15% of rubber, 30% to 35% of ethylcyclohexane, 20% to 30% of environmentally friendly solvent, 10% to 15% of resin, and 1% to 3% of additives, accounting for 10% to 20% of the weight percentage (wt%) of the flame retardant intumescent coating.

[0052] 10(s) 20(s) 30(s) 40(s) 50(s) 60(s) Line 1 117℃ 214℃ 318℃ 389℃ 440℃ 487℃ Line 2 105℃ 130℃ 157℃ 184℃ 209℃ 227℃ Line 3 68℃ 128℃ 178℃ 228℃ 271℃ 306℃

[0053] Table 3: Test results of Example 3 (see Figure 8 )

[0054] Embodiment 4 of the flame retardant expansion coating 20 is an acrylic flame retardant expansion coating

[0055] The flame retardant intumescent coating comprises: 10% to 20% of graphite, 60% to 75% of methyl acrylate, 15% to 25% of xylene, 1% to 2% of dimethyl ketone, and 10% to 15% of triphosphate, accounting for 10% to 20% of the weight percentage (wt%) of the flame retardant intumescent coating.

[0056] 10(s) 20(s) 30(s) 40(s) 50(s) 60(s) Line 1 117℃ 214℃ 318℃ 389℃ 440℃ 487℃ Line 2 69℃ 102℃ 116℃ 125℃ 137℃ 150℃ Line 3 33℃ 50℃ 74℃ 99℃ 123℃ 141℃

[0057] Table 4: Test results of Example 4 (see Fig. 9 )

[0058] Embodiment 5 of the flame retardant expansion coating 20 is a modified aerogel flame retardant expansion coating

[0059] The flame retardant expansion coating comprises: 10% to 15% of graphite, 40% to 60% of styrene-acrylic latex, 5% to 15% of hydrophobic aerogel powder, 10% to 20% of glass fiber, 15% to 25% of deionized water, and 0.1% to 3% of 1,2-propylene glycol, accounting for 10% to 15% of the weight percentage (wt%) of the flame retardant expansion coating.

[0060] 10(s) 20(s) 30(s) 40(s) 50(s) 60(s) Line 1 117℃ 214℃ 318℃ 389℃ 440℃ 487℃ Line 2 65℃ 100℃ 113℃ 123℃ 138℃ 155℃ Line 3 48℃ 69℃ 86℃ 106℃ 122℃ 138℃

[0061] Table 5: Test results of Example 5 (see Fig.10 )

[0062] The embodiments and / or implementation methods described above are only used to illustrate the preferred embodiments and / or implementation methods for realizing the technology of the present application, and are not intended to limit the implementation methods of the technology of the present application in any form. Any technical personnel in this field may make slight changes or modifications to other equivalent embodiments without departing from the scope of the technical means disclosed in the content of the present application, but they should still be regarded as technologies or embodiments that are essentially the same as the present application.

Claims

1. A flame retardant board, characterized in that: The flame retardant board comprises: a board and a flame retardant expansion coating attached to the surface of the board. The flame retardant expansion coating comprises expanded graphite and can be attached to the surface of the board by spraying or brushing.

2. The flame retardant board according to claim 1, characterized in that: The material of the plate is metal or plastic.

3. The flame retardant board according to claim 1, characterized in that: The flame retardant expansion coating comprises: 10% to 30% by weight of graphite, 30% to 45% of polybutadiene, 20% to 30% of silicon dioxide, and 15% to 30% of methylcyclohexane.

4. The flame retardant board according to claim 1, characterized in that: The flame retardant expansion coating comprises: 5% to 30% by weight of graphite, 10% to 15% of acrylic resin, 5% to 10% of chlorinated wax, 5% to 10% of titanium dioxide, 25% to 30% of xylene, 5% to 10% of melamine, 5% to 10% of pentaerythritol, and 25% to 30% of ammonium polyphosphate.

5. The flame retardant board according to claim 1, characterized in that: The flame retardant expansion coating comprises: 10% to 20% by weight of graphite, 10% to 15% of rubber, 30% to 35% of ethylcyclohexane, 20% to 30% of environmentally friendly solvent, 10% to 15% of resin, and 1% to 3% of auxiliary agent.

6. The flame retardant board according to claim 1, characterized in that: The flame retardant expansion coating comprises: 10% to 20% of graphite, 60% to 75% of methyl acrylate, 15% to 25% of xylene, 1% to 2% of dimethyl ketone, and 10% to 15% of triphosphate, which accounts for 10% to 20% of the weight percentage of the flame retardant expansion coating.

7. The flame retardant board according to claim 1, characterized in that: The flame retardant expansion coating comprises: 10% to 15% by weight of graphite, 40% to 60% by weight of acrylic copolymer latex, 5% to 15% by weight of hydrophobic aerogel powder, 10% to 20% by weight of glass fiber, 15% to 25% by weight of deionized water, and 0.1% to 3% by weight of 1,2-propylene glycol.

8. A secondary battery module structure using the flame retardant plate according to claim 1, characterized in that: The secondary battery module structure includes: a fan, at least one secondary battery, and a shell, the shell is composed of the flame retardant board, the flame retardant expansion coating attached to the board is located on the inner side of the shell, the secondary batteries are arranged inside the shell, there is a gap between the secondary batteries and the flame retardant expansion coating on the inner side of the shell to form an airflow channel, and the fan is arranged at one end of the shell to send airflow into the airflow channel.

9. The secondary battery module structure according to claim 8, characterized in that: The material of the plate of the flame retardant plate is metal or plastic.

10. The secondary battery module structure according to claim 8, characterized in that: The flame retardant expansion coating comprises: 10% to 30% by weight of graphite, 30% to 45% of polybutadiene, 20% to 30% of silicon dioxide, and 15% to 30% of methylcyclohexane.

11. The secondary battery module structure according to claim 8, characterized in that: The flame retardant expansion coating comprises: 5% to 30% by weight of graphite, 10% to 15% of acrylic resin, 5% to 10% of chlorinated wax, 5% to 10% of titanium dioxide, 25% to 30% of xylene, 5% to 10% of melamine, 5% to 10% of pentaerythritol, and 25% to 30% of ammonium polyphosphate.

12. The secondary battery module structure according to claim 8, characterized in that: The flame retardant expansion coating comprises: 10% to 20% by weight of graphite, 10% to 15% of rubber, 30% to 35% of ethylcyclohexane, 20% to 30% of environmentally friendly solvent, 10% to 15% of resin, and 1% to 3% of auxiliary agent.

13. The secondary battery module structure according to claim 8, characterized in that: The flame retardant expansion coating comprises: 10% to 20% of graphite, 60% to 75% of methyl acrylate, 15% to 25% of xylene, 1% to 2% of dimethyl ketone, and 10% to 15% of triphosphate, which accounts for 10% to 20% of the weight percentage of the flame retardant expansion coating.

14. The secondary battery module structure according to claim 8, characterized in that: The flame retardant expansion coating comprises: 10% to 15% by weight of graphite, 40% to 60% by weight of acrylic copolymer latex, 5% to 15% by weight of hydrophobic aerogel powder, 10% to 20% by weight of glass fiber, 15% to 25% by weight of deionized water, and 0.1% to 3% by weight of 1,2-propylene glycol.

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