Intumescent flame retardant applied to lithium ion battery pack and preparation method of intumescent flame retardant

Abstract

The invention relates to an intumescent flame retardant applied to a lithium ion battery pack and a preparation method of the intumescent flame retardant, the intumescent flame retardant is of a disordered stacking structure of flaky materials with different sizes, the intumescent flame retardant mainly comprises a phosphine amine copper compound obtained by complexing melamine, amino trimethylene phosphonic acid and copper ions, and Cu-N and Cu-O coordinate bonds exist in the complex. When the intumescent flame retardant encounters flame, a compact and continuous carbon layer can be rapidly formed on the surface of a material, the intumescent flame retardant is excellent in intumescent performance, and compared with a traditional flame retardant material, the intumescent flame retardant can more efficiently prevent heat and oxygen from being transferred into the material, so that combustion of the material is slowed down or prevented, and the service life of the material is prolonged. In addition, the sheet-shaped structure also has a large specific surface area and a strong adsorption effect, and can better adsorb some free radicals generated in the combustion process, so that the chain reaction of combustion is interrupted, and the flame-retardant effect is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of fire prevention, suppression or extinguishment applicable to special objects or spaces, and particularly relates to an intumescent flame retardant for a lithium-ion battery pack and a preparation method thereof. Background Art

[0002] Due to its high energy density, high cycle times, no memory effect and other characteristics, lithium-ion batteries are widely used in fields such as mobile phones, computers, electric vehicles, etc., and have become an essential part of people's lives and industrial production. A lithium-ion battery mainly consists of a positive electrode material, a negative electrode material, an electrolyte, a separator, etc. Its working principle is based on the process of lithium-ion transfer movement between the two electrodes, and the charging and discharging of the battery continuously repeat this process. The environmental temperature where the battery is located can be divided into three categories: low temperature (<0 °C), normal temperature (0 - 50 °C) and high temperature (>50 °C). Thermal runaway rarely occurs in the battery during low-temperature and normal-temperature processes, but serious heat accumulation problems will occur when the battery operates in a high-temperature environment, causing irreversible damage to the internal materials and structures, and reducing the battery capacity and cycle service life. Therefore, relevant personnel in this field often set a flame-retardant and heat-insulating coating on the battery surface to reduce the heat absorbed by the battery interior from the outside in a high-temperature environment, and reduce the losses caused by damage to surrounding batteries or other facilities due to thermal runaway.

[0003] The existing flame-retardant and heat-insulating coatings for battery packs are mainly composed of materials such as epoxy resin, charring agents (pentaerythritol, aniline), curing agents (polyamide curing agents), foaming agents (melamine, dicyandiamide) and flame retardants (magnesium hydroxide, ammonium polyphosphate), etc. However, such flame-retardant and heat-insulating coatings have problems such as low expansion rate and unstable carbon layer, and are insufficient in terms of heat insulation and flame retardancy, thus restricting the commercialization and large-scale application of lithium-ion batteries in fields such as electric vehicles. Therefore, it is urgent to develop a new type of intumescent flame-retardant coating to effectively solve the problem of battery thermal runaway. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an intumescent flame retardant (MAP-Cu) for a lithium-ion battery pack and a preparation method thereof in view of the above deficiencies in the prior art. This intumescent flame retardant has both good heat insulation and flame retardancy, and can be mixed with a halogen-free epoxy resin (EP) to obtain an intumescent flame-retardant coating material, which is suitable for the flame retardancy and heat insulation of lithium-ion battery packs.

[0005] The technical solution provided by the present invention is as follows:

[0006] Provided is an intumescent flame retardant for a lithium ion battery pack. The intumescent flame retardant has a disordered stacking structure of flaky materials of different sizes, and the main component is a phosphine amine copper complex (MAP-Cu) obtained by complexing melamine, aminotrimethylphosphonic acid and copper ions. There are Cu—N and Cu—O coordination bonds in the complex. The intumescent flame retardant can form a heat-insulating and flame-retardant coating with a halogen-free epoxy resin. The coating absorbs heat and expands, and forms a char layer by using a carbon source (charring agent), an acid source (dehydrating agent) and a gas source (foaming agent) and the like, so as to hinder the transmission of heat and substances and achieve the flame-retardant effect.

[0007] According to the above scheme, the thickness of the flaky material is less than 200 nm, and the size of more than 80% of the flaky materials is 1-5 μm.

[0008] The present invention also includes a preparation method of the above-mentioned intumescent flame retardant for a lithium ion battery pack, and the specific steps are as follows:

[0009] 1) Add melamine (MA) into water, stir while heating until the melamine is dissolved to obtain a melamine solution;

[0010] 2) Dissolve aminotrimethylphosphonic acid (ATMP) in water, add a divalent copper salt after stirring and dissolving, and stir until the copper nitrate is completely dissolved to obtain a light blue transparent mixed solution;

[0011] 3) Add the mixed solution obtained in step 2) into the melamine solution obtained in step 1), then carry out a hydrothermal reaction, carry out suction filtration after the reaction is completed, and obtain a light blue flocculent solid, and obtain the intumescent flame retardant after drying.

[0012] According to the above scheme, the heating temperature in step 1) is 85-95 °C, and the concentration of the melamine solution is 0.1-0.3 mol / L.

[0013] According to the above scheme, the concentration of aminotrimethylphosphonic acid in the mixed solution in step 2) is 0.10-0.25 mol / L, and the molar ratio of aminotrimethylphosphonic acid to the copper salt is 3-7:1.

[0014] According to the above scheme, the divalent copper salt in step 2) is one or a combination of two or more of copper nitrate (Cu(NO3)2) and basic copper carbonate (Cu2(OH)2CO3), and preferably copper nitrate.

[0015] According to the above scheme, the molar ratio of aminotrimethylphosphonic acid in the mixed solution to melamine in the melamine solution in step 3) is 0.15-0.20:1.

[0016] According to the above scheme, the hydrothermal reaction temperature in step 3) is 85-90 °C, and the hydrothermal reaction time is 2-3 h.

[0017] According to the above scheme, the drying temperature in step 3) is 80 - 85°C, and the drying time is 7 - 8h.

[0018] The structural schematic diagram of the phosphine amine copper complex of the present invention is as follows:

[0019]

[0020] The present invention also includes an intumescent flame retardant coating material containing the above intumescent flame retardant. The raw materials of the intumescent flame retardant coating material include a halogen-free epoxy resin (EP), an amine curing agent, and the above intumescent flame retardant. The mass percentage content of the intumescent flame retardant in the intumescent flame retardant coating material is 8 - 25%. The halogen-free epoxy resin and the amine curing agent form a film-forming system of the coating. The intumescent flame retardant expands rapidly at high temperatures (800 - 1200°C), reaching dozens of times or more for endothermic absorption, preventing further heat accumulation, and providing excellent flame retardant effects.

[0021] According to the above scheme, the mass percentage content of the intumescent flame retardant in the intumescent flame retardant coating material is preferably 10 - 20%.

[0022] According to the above scheme, the halogen-free epoxy resin is one of bisphenol A diglycidyl ether (DGEBA), dicyclopentadiene phenol type epoxy resin, and bisphenol F type epoxy resin.

[0023] According to the above scheme, the amine curing agent is one of phenolic aldehyde amine T31 curing agent, aliphatic amine NX-2040 curing agent, and Hengsite-1550 curing agent.

[0024] According to the above scheme, the mass ratio of the halogen-free epoxy resin to the amine curing agent is 2.5 - 8:1.

[0025] According to the above scheme, the raw materials of the intumescent flame retardant coating material further include a foaming and expanding agent. The foaming and expanding agent is any one or more of melamine, dicyandiamide, ammonium carbonate, azodicarbonamide, and diisopropyl azodicarboxylate. The mass percentage content of the foaming and expanding agent in the intumescent flame retardant coating material is 4 - 20%.

[0026] The preparation method of the above intumescent flame retardant coating material is: mixing and stirring the halogen-free epoxy resin and the intumescent flame retardant at 40 - 60°C for 0.5 - 1h, then adding the amine curing agent, adding the foaming and expanding agent as needed, and continuing to stir for 10 - 30min to obtain the intumescent flame retardant coating material.

[0027] The present invention also includes an intumescent flame retardant coating obtained after curing the above intumescent flame retardant coating material. The specific curing process conditions are: first curing at 60 - 80°C for 1 - 2h, and then curing at normal temperature (15 - 35°C) for 24 - 48h.

[0028] The present invention also includes the application of the above intumescent flame retardant coating material in the preparation of flame retardant lithium ion batteries.

[0029] According to the above application, the specific usage method is as follows: coat the intumescent flame retardant coating material on the inner plate or the surface of the metal outer plate of the lithium battery pack housing, adjust the coating thickness to 1-3 mm according to actual requirements, and obtain the intumescent flame retardant coating after curing, pore formation, and drying.

[0030] The present invention uses melamine, aminotrimethylphosphonic acid, and copper salt as raw materials. Melamine and aminotrimethylphosphonic acid undergo a chelation reaction with copper ions to form a chelate phosphineamine copper complex (MAP-Cu). Fill the MAP-Cu into a halogen-free epoxy resin to form an EP / MAP-Cu intumescent flame retardant coating material. During combustion, the halogen-free epoxy resin and melamine serve as carbon sources, and metaphosphoric acid generated by aminotrimethylphosphonic acid and phosphorus-containing substances at high temperatures serves as an acid source to promote the dehydration of the matrix material and the formation of a cross-linked carbon layer. Nitrogen-containing substances generate non-combustible gases such as ammonia when heated (gas source, while diluting combustible gases). The addition of Cu 2+ strengthens the carbonization ability of the material, improves the strength, stability, and expansion rate of the carbon layer. The above factors work together to promote the material to absorb heat and expand to form a porous carbonized layer. This porous carbonized layer can still maintain a stable structure at high temperatures. On the one hand, it hinders the transmission of heat, oxygen, combustible gases, and other substances in the condensed phase. In addition, it can efficiently capture smoke particles generated during combustion and play a flame retardant role.

[0031] The beneficial effects of the present invention are as follows:

[0032] 1. When the intumescent flame retardant of the present invention encounters a flame, it can quickly form a dense and continuous carbon layer on the material surface, with excellent expansion performance. Compared with traditional flame retardant materials, it can more efficiently prevent the transfer of heat and oxygen to the interior of the material, thereby slowing down or preventing the combustion of the material. Its flaky structure also has a large specific surface area and strong adsorption effect, and can better adsorb some free radicals generated during combustion, thereby interrupting the chain reaction of combustion and achieving the flame retardant effect. The intumescent flame retardant of the present invention is a non-halogen flame retardant material. Compared with traditional halogen flame retardant materials, when the intumescent flame retardant decomposes at high temperatures or during combustion, it will not release toxic gases and is environmentally friendly.

[0033] 2. The intumescent flame retardant of the present invention does not generate any waste or pollutants during the preparation process. The preparation steps are simple, the reaction conditions are mild, and it is easy to industrialize production.

[0034] 3. In the present invention, an intumescent flame retardant is added to a halogen-free epoxy resin system to obtain an intumescent flame retardant coating material. In the case of thermal runaway of the battery, under the combined action of the intumescent flame retardant and the halogen-free epoxy resin in the intumescent flame retardant coating material, it rapidly expands by 30 to 100 times, forming a carbon layer with good heat insulation and flame retardant effects, effectively preventing the spread of flames or quickly extinguishing the flames, so as to achieve the purpose of fire prevention and flame retardancy and blocking the spread of battery thermal runaway. Moreover, the expanded material fills the space inside the shell, blocking the supply of oxygen outside and the transmission of heat, solving the problems of unstable carbon layer, low carbon layer density, low coating expansion rate, and unsatisfactory heat absorption effect of the current flame retardant coating material for the lithium battery shell. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a scanning electron microscope (SEM) image of MAP-Cu prepared in Example 1 of the present invention;

[0036] Figure 2 It is a scanning electron microscope image of MAP-Cu prepared in Example 1;

[0037] Figure 3 It is a physical photograph (a) of MAP prepared in the control example and MAP-Cu prepared in Example 1, and the FTIR spectra of the raw materials MA, ATMP used in Example 1, the obtained product MAP-Cu, and MAP prepared in the control example;

[0038] Figure 4 It shows EP / MAP-Cu prepared in Example 3 20％ The sample and EP / MAP-Fe prepared in Comparative Example 1 20％ A comparison diagram of the process of burning the samples with a 1200 °C butane torch for 60 s;

[0039] Figure 5 It is a comparison diagram of the data obtained from the combustion experiments of the coatings prepared in Examples 1-3 and Comparative Example 2;

[0040] Figure 6 It is EP / MAP prepared in the control example 20％ and EP / MAP-Cu prepared in Example 3 20％ and the charred residue photos of the EP cured products prepared in Comparative Example 2 after the above combustion experiment;

[0041] Figure 7 It is EP / MAP prepared in the control example 20％ and EP / MAP-Cu prepared in Example 3 20％ and the FTIR spectra of the charred residues of the EP cured products prepared in Comparative Example 2 after the above combustion experiment;

[0042] Figure 8 It is EP / MAP prepared in the control example 20％, EP / MAP-Cu prepared in Example 2 15％ , EP / MAP-Cu prepared in Example 3 20％ And the comparison chart of the temperature change of the back side of the steel plate with time under the burning of a butane torch at 1200 °C for the EP cured product prepared in Comparative Example 2;

[0043] Figure 9 For the EP cured product prepared in Comparative Example 2 and the EP / MAP prepared in the control example 20％ , EP / MAP-Cu prepared in Example 3 20％ Photos of the ablation process during the coating burning experiment;

[0044] Figure 10 For the EP / MAP prepared in the control example 20％ , EP / MAP-Cu prepared in Example 3 20％ And the schematic diagram of battery assembly for the experiment of inhibiting battery thermal runaway for the EP cured product prepared in Comparative Example 2;

[0045] Figure 11 For the EP / MAP prepared in the control example in the experiment of inhibiting battery thermal runaway 20％ , EP / MAP-Cu prepared in Example 3 20％ And the comparison chart of the surface temperature change rate curves of three groups of test batteries for the EP cured product prepared in Comparative Example 2. Detailed implementation manners

[0046] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0047] Example 1

[0048] An expansion flame retardant applied to a lithium-ion battery pack, and its preparation method is as follows:

[0049] S1. Add 12.6 g of melamine to 500 mL of water, heat it in a water bath at 90 °C while stirring until the melamine solid is completely dissolved to obtain a melamine solution;

[0050] S2. Add 10.5 g of an aqueous solution of aminotrimethylphosphonic acid with a concentration of 50 wt% (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) to 100 mL of water and stir. After becoming a homogeneous solution, add 0.73 g of copper nitrate and stir until the copper nitrate is completely dissolved to obtain a light blue transparent mixed solution;

[0051] S3. Add the mixed solution in Step S2 to the melamine solution obtained in S1, and then carry out a hydrothermal reaction at 90 °C for 2 h. During the reaction process, a large amount of light blue flocculants continuously generate on the upper layer of the solution. After the reaction ends, stop stirring. The reaction solution shows a layering phenomenon. Then, filter the reaction solution by suction. The obtained light blue flocculant solid is washed 3 times with deionized water and dried at a constant temperature of 80 °C in a vacuum oven for 8 h to obtain 15.7 g of light blue solid powder, which is the intumescent flame retardant (MAP-Cu).

[0052] Figure 1 and Figure 2 is the scanning electron microscope image of the intumescent flame retardant prepared in this example. It can be seen that the microstructure of the intumescent flame retardant is an aggregate obtained by stacking nanosheets of different sizes. The thickness of the nanosheets is less than 200 nm, and the size of more than 80% of the nanosheets is 1 - 5 μm.

[0053] Use the above intumescent flame retardant to further prepare an intumescent flame retardant coating material: Stir and mix 100.8 g of bisphenol A diglycidyl ether (epoxy value 0.44 mol / 100 g) and 14 g of the above intumescent flame retardant at 40 °C for 1 h, then add 25.2 g of the curing agent phenolic amine T31, and continuously stir for 10 min to obtain the intumescent flame retardant coating material. Then, pour the obtained intumescent flame retardant coating material into a preheated plastic mold with a mold depth of 3 mm. First, cure at 60 °C for 1 h, and then cure at room temperature (30 °C) for 24 h. Remove the mold to obtain the intumescent flame retardant coating (MAP-Cu content 10 wt%, denoted as EP / MAP-Cu 10％ ).

[0054] Control example

[0055] Preparation of intumescent flame retardant (MAP) and intumescent flame retardant coating material (EP / MAP 20％ )

[0056] The preparation method of the intumescent flame retardant MAP is similar to that of Example 1, except that copper nitrate is not added during the preparation process.

[0057] Use the above intumescent flame retardant to further prepare an intumescent flame retardant coating material: Stir and mix 44.8 g of bisphenol A diglycidyl ether and 14 g of the above intumescent flame retardant at 40 °C for 1 h, then add 11.2 g of the curing agent phenolic amine T31, and continuously stir for 10 min to obtain the intumescent flame retardant coating material. Then, pour the obtained intumescent flame retardant coating material into a preheated mold with a mold depth of 3 mm. First, cure at 60 °C for 1 h, and then cure at room temperature (30 °C) for 24 h. Remove the mold to obtain the intumescent flame retardant coating (EP / MAP 20％ ).

[0058] Figure 3(a) is a physical photo of the MAP prepared in this comparative example and the MAP-Cu prepared in Example 1. It can be observed from the figure that the MAP is white and the MAP-Cu is light blue.

[0059] The FTIR spectra of the raw materials MA, ATMP used in Example 1, the obtained product MAP-Cu, and the MAP prepared in this comparative example are as Figure 3 (b) shown. By comparing and analyzing the absorption peaks of the FTIR spectra of MAP-Cu and the main raw materials, the stretching vibrations of NH2 / OH and the asymmetric -NH3 + and symmetric -NH3 + shift from 3423 cm -1 , 1635 cm -1 and 1532 cm -1 to 3435 cm -1 , 1641 cm -1 and 1547 cm -1 , respectively indicating the formation of Cu—N and Cu—O coordination bonds after adding Cu 2+ , indicating the synthesis of the complex of MAP and Cu. The structural schematic diagram of the product phosphine amine copper complex is as follows:

[0060]

[0061] Example 2

[0062] An intumescent flame retardant coating (EP / MAP-Cu 15％ ), its composition and preparation method are similar to those of Example 1, except that the content of the intumescent flame retardant MAP-Cu is 15 wt%.

[0063] Example 3

[0064] An intumescent flame retardant coating (EP / MAP-Cu 20％ ), its composition and preparation method are similar to those of Example 1, except that the content of the intumescent flame retardant MAP-Cu is 20 wt%.

[0065] Comparative Example 1

[0066] An intumescent flame retardant (MAP-Fe), its preparation method is similar to that of Example 1, except that copper nitrate is replaced with an equimolar amount of ferric chloride.

[0067] Using MAP-Fe as the intumescent flame retardant, an intumescent flame retardant coating (EP / MAP-Fe 20％ ) is prepared by a method similar to that of Example 1, where the content of the intumescent flame retardant MAP-Fe is 20 wt%.

[0068] As Figure 4Shown is the EP / MAP-Cu prepared in Example 3 20％ sample (cut into 130 mm × 13 mm × 3 mm, Figure 4 above) and the EP / MAP-Fe prepared in this comparative example 20％ sample (cut into 130 mm × 13 mm × 3 mm, Figure 4 below) during the process of burning with a 1200 °C butane torch for 60 s. It can be seen from the figure that for the EP / MAP-Cu 20％ sample, only a small amount of coke was generated at the end when burned with the butane torch for 30 s, and there was no obvious ignition phenomenon. For the EP / MAP-Fe 20％ sample, an obvious ignition phenomenon occurred at 30 s. At 60 s, for the EP / MAP-Cu 20％ sample, a weak ignition phenomenon occurred. For the EP / MAP-Fe 20％ sample, the flame became larger compared to that at 30 s, showing a flame spread phenomenon. Thus, it is judged that MAP-Cu has better flame retardancy than MAP-Fe.

[0069] Comparative Example 2

[0070] A coating without a flame retardant was prepared as follows: 100.8 g of bisphenol A diglycidyl ether and 25.2 g of the curing agent phenolic amine T31 were stirred and mixed at 40 °C for 1 h. Then the obtained coating material was poured into a preheated mold with a depth of 3 mm. It was first cured at 60 °C for 1 h, and then cured at room temperature (30 °C) for 24 h. The mold was removed to obtain the coating (EP cured product).

[0071] Experiment 1: Vertical burning test

[0072] The flame retardancy of the intumescent flame retardant coatings in Examples 1 - 3, the intumescent flame retardant coating in the control example, and the coating prepared in Comparative Example 2 was evaluated by the LOI and UL-94 vertical burning tests.

[0073] Table 1

[0074]

[0075] Note: In Table 1, av-t1 and av-t1 are the burning times of the sample strip after the first ignition and the second ignition in the vertical burning test.

[0076] It can be seen from Table 1 that the EP cured product can be quickly ignited and accompanied by melting and dripping, with an LOI of 18.2%. When 20% of MAP is added, the LOI of the EP coating is significantly improved (27.1%), but in the vertical burning test, there is still partial dripping and the flammability of EP cannot be completely inhibited. When the addition amount of MAP-Cu is 10%, for the Cu-containing EP / MAP-Cu 10％Can achieve EP / MAP 20％ The effects are equivalent and slightly better; at the same 20% addition amount, EP / MAP-Cu containing Cu 20％ has a significantly improved effect, the combustion rating reaches V-0, and the LOI also reaches a maximum of 28.7%. It shows that the EP / MAP-Cu of the present invention can achieve good flame retardant effects at a dosage of 10-20%.

[0077] Experiment 2: TGA thermogravimetric analysis

[0078] The thermal decomposition properties of the coatings prepared in Examples 1-3 and Comparative Example 2 were detected by TGA (thermogravimetric analyzer) under N2 atmosphere. The specific test results are shown in Table 2. The EP cured product has high thermal stability, and T 5％ (temperature at 5% mass loss) is 251 °C, T 50％ (temperature at 50% mass loss) is 385 °C, T max (temperature at the maximum decomposition rate) is 371 °C, but the carbon residue is less, where wt R 700 represents the char residue rate at 700 °C. When MAP-Cu (addition amount 10-20%) is added, the char residue rate can be significantly increased. The char residue rate of the coating sample with 10 wt% MAP-Cu added is 19 wt%, which is about 2 times that of the EP cured product; the char residue rate of the coating sample with 15 wt% MAP-Cu added is 22 wt%, and the char residue rate of the coating sample with 20 wt% MAP-Cu added is 26 wt%. And when the addition amount of MAP-Cu is 20%, both the thermal stability and the char residue rate of the coating are significantly improved.

[0079] Table 2

[0080]

[0081] Experiment 3: Combustion experiment

[0082] The combustion behaviors of the coatings prepared in Examples 1-3 and Comparative Example 2 were tested by a cone calorimeter (Kunshan Modisco Combustion Technology Instruments Co., Ltd.) (sample size: 100 mm × 100 mm × 3 mm), and the external radiant heat flux was 35 kw / m 2 ), and the test results are shown in Table 3.

[0083] Table 3

[0084]

[0085] In Table 3, PHRR (kW / m 2) represents the peak heat release rate (the maximum heat release rate per unit area during the combustion process of the material), PHRR(s) is the time to reach the maximum heat release rate per unit area during the combustion process of the material, FGI is the fire growth index (the smaller the better), HRR is the heat release rate, THR is the total heat release, PCORR is the peak carbon monoxide (CO) yield released during the combustion process, and PCO2RR is the peak carbon dioxide (CO2) yield released during the combustion process.

[0086] PHRR (kW / m 2 ) As the peak heat released during the combustion process of the material, it is an important indicator for evaluating the fire hazard of polymer combustion. The PHRR (kW / m 2 ) of the EP cured product is as high as 618 kW / m 2 , and the PHRR (kW / m 2 ) of the coating added with MAP-Cu shows a significant decrease compared to the EP cured product. The PHRR value of EP / MAP-Cu 20％ is reduced by about 76.7% compared to the EP cured product. THR is another important parameter for measuring the combustion performance of polymers. The THR value of the coating added with MAP-Cu decreases significantly, and the HRR value, PCOPR, and PCO2PR also decrease significantly.

[0087] The fire growth index (FGI) is the ratio of PHRR to the time required to reach PHRR, which is used to evaluate the fire hazard. Compared with HRR and THR, it can more intuitively represent the fire risk of polymer materials. The FGI value of the EP cured product is 5.518, while the FGI value of EP / MAP-Cu 20％ is 1.066, indicating that the addition of MAP-Cu effectively reduces the fire risk of the coating material.

[0088] The comparison chart of the data obtained from the above combustion experiments is shown in Figure 5 , Figure 5 In it, (a) is the comparison chart of the heat release rate HRR of the coatings prepared in Examples 1-3 and Comparative Example 2, (b) is the comparison chart of the total heat release THR of the coatings prepared in Examples 1-3 and Comparative Example 2, (c) is the comparison chart of the smoke production rate (the amount of smoke generated per unit time during the combustion of the material, SPR) of the coatings prepared in Examples 1-3 and Comparative Example 2, (d) is the comparison chart of the total smoke production (TSP) of the coatings prepared in Examples 1-3 and Comparative Example 2, (e) is the comparison chart of the CO production rate (PCOPR) of the coatings prepared in Examples 1-3 and Comparative Example 2, and (f) is the comparison chart of the CO2 production rate (PCO2PR) of the coatings prepared in Examples 1-3 and Comparative Example 2. From Figure 5As can be seen from (c) and (d), the presence of MAP-Cu can significantly reduce TSP and SPR. The TSP value of EP / MAP-Cu 20％ is 3.5 m 2 , which is 76% lower than that of the EP cured product. It can also be seen from the figure that as the content of MAP-Cu increases, TSP further decreases, which is due to the Cu 2+ strengthened expanded carbon layer being a good smoke release barrier and being able to well inhibit the release of flue gas. From Figure 5 (e) and (f), it can be seen that the PCOPR and PCO2PR of the EP cured product are 0.094% and 1.613% respectively. In contrast, the corresponding values of the EP / MAP-Cu 20％ expansion coating are 0.041% and 0.359% respectively, a decrease of 56.4% and 77.7% respectively, indicating that MAP-Cu significantly inhibits the generation of CO and CO2 during combustion.

[0089] The EP / MAP prepared in the control example 20％ was subjected to a combustion experiment under the same above conditions and compared with the EP / MAP-Cu prepared in Example 3 20％ and the EP cured product prepared in Comparative Example 2. The EP / MAP prepared in the control example 20％ , the EP / MAP-Cu prepared in Example 3 20％ and the EP cured product prepared in Comparative Example 2 after the above combustion experiment are shown in the char photos as Figure 6 (a-f). Among them, a and d are the top view and side view of the carbon layer after the EP cured product burns, b and e are the top view and side view of the carbon layer after EP / MAP 20％ burns, c and f are the top view and side view of the carbon layer after EP / MAP-Cu 20％ burns. It can be seen that only a very small number of residues remain after the EP cured product burns. The addition of MAP makes the EP / MAP 20％ coating material retain a large amount of expanded coke after burning, with a height of 5.5 cm (see Figure 6 e), but there are some relatively large cavities in the middle of the carbon layer, and there are a large number of cracks and holes on the outer surface of the char (see Figure 6 b), indicating that its structure is prone to collapse. It can be seen from the figure that the carbon layer height of EP / MAP-Cu 20％ reaches 11.3 cm( Figure 6 f), and there is a dense and complete carbon layer on the outer surface of the char of EP / MAP-Cu 20％ , indicating that it has stronger flame retardancy and carbon layer stability, which also corresponds to the results of the above analysis of the thermal stability of the material (Table 2). The results show that: EP / MAP-Cu 20％ is better than EP / MAP 20％The char layer expansion rate is higher and more stable, and there are no cracks or cavities in the internal structure, making it a good barrier to heat, O2, and pyrolysis products (preventing further heat transfer and also isolating oxygen to prevent the combustion reaction on the battery surface from occurring further), fully reflecting the flame retardant advantage of the EP / MAP-Cu of the present invention.

[0090] By measuring the expansion height of the char layer after the above combustion experiment with a ruler and comparing it with the coating thickness to calculate the char layer expansion rate of the coating. The original coating thickness was 3 mm. It can be seen that the EP cured product only expanded 4 times, while EP / MAP 20％ expanded 18 times, and EP / MAP-Cu 20％ expanded 38 times.

[0091] Raman spectroscopy analysis was performed on the char residues of the above different coatings after the combustion experiment, and the results are as Figure 6 (g) shown. In the figure, the comprehensive intensity ratio (I D / I G ) represents the lattice size of the char layer. Among them, the higher the I D / I G value, the smaller the lattice size of the char layer material, thus forming a more effective protective shield. For the EP cured product, EP / MAP 20％ and EP / MAP-Cu 20％ char residue layers, the calculated I D / I G values are 4.80, 3.91, and 3.19 respectively. This result indicates that due to the presence of Cu 2+ , the char layer defects of the EP / MAP-Cu 20％ coating after combustion are reduced, and the degree of graphitization increases.

[0092] Figure 7 FTIR spectra of the char residues of EP / MAP 20％ prepared as a control example, EP / MAP-Cu 20％ prepared in Example 3, and the EP cured product prepared in Comparative Example 2 after the above combustion experiment. Among them, the char layer spectra of EP / MAP 20％ and EP / MAP-Cu 20％ added with flame retardants showed characteristic absorption peaks of P=O, P-O-C, and P-O-P at 1245 cm -1 , 1112 cm -1 and 1001 cm -1 , and the peak intensities of P=O and P-O-C of EP / MAP-Cu 20％ were significantly higher than those of EP / MAP 20％。The presence of a relatively large number of high-quality carbon layers formed by P=O can effectively prevent heat from transferring into the material and slow down the thermal decomposition rate of the material; the presence of P-O-C bonds can improve the stability and compactness of the carbon layer, making the material less likely to decompose and deform at high temperatures, which helps to maintain the integrity and heat insulation performance of the material and extend its service life. At the same time, EP / MAP-Cu 20％ The carbon layer also showed a new characteristic peak at 550 cm -l which may represent Cu-PO4. This is because the presence of Cu 2+ promoted the generation of phosphoric acid during the pyrolysis of ATMP and formed a phosphoric acid complex with it, indicating that Cu 2+ participated in the formation of the cross-linked carbon layer, improving the strength of the carbon layer and thus enhancing the flame retardant performance of the coating. The phosphorus element in MAP-Cu can capture highly active free radicals such as ·OH and ·H in the gas phase to interrupt the combustion chain reaction, and the synergistic effect of Cu 2+ and P-N enhanced this gas-phase flame retardant effect to inhibit heat release. In addition, MAP-Cu can also catalyze the oxidation reaction of CO and consume oxygen. CO is a toxic gas that can cause asphyxiation. Inhibiting its generation can significantly reduce the toxicity of the flue gas generated after the combustion of the EP coating material, and the generated CO2 can also act as an inert gas to dilute the combustible gas, thereby reducing the intensity of combustion.

[0093] Experiment 4: Ignition experiment

[0094] The coating materials of the control example, Examples 3-4, and Comparative Example 2 were respectively coated on stainless steel plates (100 mm × 100 mm in length and width, 1 mm in thickness), with a coating thickness of 1 mm, and cured according to the curing process conditions of each example to obtain the corresponding coatings, that is, EP / MAP prepared in the control example on the stainless steel plate 20％ 、EP / MAP-Cu prepared in Example 2 15％ 、EP / MAP-Cu prepared in Example 3 20％ and the EP cured product prepared in Comparative Example 2. The simulation coatings were coated on the surface of the battery box, and the comparison chart of the temperature change with time on the back of the steel plate under the burning of a butane spray gun at 1200 °C for the obtained coatings is as shown in Figure 8 . At the beginning, the initial temperatures of the backs of all steel plates were rising rapidly. Among them, the temperature of the steel plate coated with the EP cured product coating rose the fastest and quickly reached a peak temperature of 289 °C, while the peak temperatures of the other three coating groups (EP / MAP 20％ 、EP / MAP-Cu 15％ 、EP / MAP-Cu 20％ ) were all less than 200 °C. As time passed, the temperatures of each group began to decline, and the temperature of the EP cured product group decreased the fastest. After 50 s, it had dropped by nearly 100 °C, while EP / MAP20％ , EP / MAP-Cu 15％ and EP / MAP-Cu 20％ The temperature of the EP cured coating group also decreased by 65 °C 50 s after the combustion stopped. By comparison, it can be seen that the temperature of the EP cured coating group rose fastest and had the highest heating rate in the initial stage, but the temperature also dropped rapidly after the burning stopped, indicating that its heat insulation effect was the worst. In contrast, the temperature of the EP / MAP 20％ coating group slowed down after the carbon layer was formed, and its heat insulation effect was better than that of the EP cured product. For the EP / MAP-Cu 15％ and EP / MAP-Cu 20％ coating groups, both the heating rate in the initial stage and the subsequent cooling were relatively slow. It can be inferred that the strengthened carbon layer formed by the ablation of the EP / MAP-Cu coating under high temperature has a good heat insulation and protection effect. Especially for the EP / MAP-Cu 20％ coating group, the entire temperature rise process was the gentlest, and the temperature peak on the back of the steel plate was only 159 °C, with the best heat insulation effect. In summary, under the burning of a 1200 °C butane torch, the EP / MAP-Cu 20％ group had the best heat insulation effect, followed by EP / MAP-Cu 15％ , EP / MAP 20％ , while the EP cured coating had the worst heat insulation effect.

[0095] During the above burning experiment process, the EP cured product prepared in Comparative Example 2, the EP / MAP prepared in the Control Example 20％ , and the EP / MAP-Cu prepared in Example 3 20％ photos of the coating ablation process are shown in Figure 9 . As Figure 9 (a-c) shows the photos of the EP cured product during the burning process. The EP cured product was quickly ignited by the butane flame within 30 s and burned out within 60 s. Figure 9 (d-f) are the photos of the EP / MAP 20％ coating during the burning process. After about 120 s of continuous combustion, almost the entire surface layer of the EP / MAP 20％ was burned into coke. Due to the low strength of the carbon layer, the carbon layer was easily damaged when it was continuously ablated by the flame subsequently. Figure 9 (g-i) are the photos of the EP / MAP-Cu 20％ coating during the burning process. It can be seen that when the EP / MAP-Cu 20％ coating was burned by the butane flame for about 150 s, only the surface layer of the material was burned. A large number of expanded carbon layers were quickly generated on the coating surface, slowing down the further combustion of the bottom material, and the generated carbon layer had high strength and was not easily damaged, making it have excellent high-temperature ablation resistance.

[0096] Experiment 5: Experiment on Coating Inhibiting Thermal Runaway of Battery

[0097] Test the EP cured product prepared in Comparative Example 2 and the EP / MAP prepared in the Control Example 20％ , and the EP / MAP-Cu prepared in Example 3 20％ for their performance in inhibiting the thermal runaway of the battery. The specific test method is as follows: Select 3 pairs of 100% SOC batteries (lithium iron phosphate lithium-ion batteries, model IFR18650-20FE). Each pair of batteries is placed side by side with a heating rod (200W, the same size as the battery). The schematic diagram is as shown in Figure 10 . The heating rod is in contact with Battery 1 (the battery directly connected to the heating rod) and Battery 2 side by side. On the surface of each pair of batteries, the coating materials prepared in the Control Example, Example 3, and Comparative Example 2 are respectively coated with a thickness of 1 mm, and the corresponding coatings are cured according to the curing process conditions of each example, that is, between the heating rod and Battery 1, and between each pair of batteries, the EP / MAP prepared in the Control Example 20％ , the EP / MAP-Cu prepared in Example 3 20％ and the EP cured product prepared in Example 5 are obtained. Use the heating rod to heat to mimic the state when the battery undergoes thermal runaway. Stop heating when the surface temperature of Battery 1 reaches 140°C, and study and analyze various parameters of the temperature change of Battery 1 when different coatings are coated between the heating rod and the battery, and compare the inhibition effects of different coatings. The test data of the thermal runaway experiments corresponding to each coating are shown in Table 4 below

[0098] Table 4

[0099]

[0100] where t1 represents the time for Battery 1 to start heating to thermal runaway (the surface of Battery 1 reaches 140°C), and T max represents the peak temperature on the surface of Battery 1, and R max represents the peak value of the surface heating rate of Battery 1, and Δm represents the mass loss rate of Battery 1 before and after thermal runaway. From the data in Table 4, it can be seen that the t1 values of each group are 449 s, 601 s, and 752 s respectively. The larger the t1 value, the longer the time for Battery 1 to start heating to thermal runaway, that is, the better the effect of the coating in inhibiting the occurrence of thermal runaway. The R 20％ corresponding to EP / MAP-Cu max is also the lowest among the three groups of experiments, and R maxThe lower it is, the better the coating is in suppressing the battery temperature rise rate. In the three groups of experiments, the mass loss rates Δm of Battery 1 were 10.11%, 9.97%, and 9.85% respectively. The experiment corresponding to the EP cured product experienced thermal runaway first and had the most mass loss, and most of the lost mass was converted into toxic and harmful substances. As can be seen from Table 4, the addition of MAP-Cu significantly improved the effect of the EP material in suppressing battery thermal runaway, more effectively prevented heat from transferring to the battery surface, and thus better suppressed the rise of the battery surface temperature.

[0101] Figure 11 It is a comparison chart of the surface temperature change rate curves of the three groups of test batteries in the above-mentioned experiment on the coating's suppression of battery thermal runaway. Combining with Table 4, it can be obtained that the temperature rise rate measured by the test group corresponding to EP / MAP-Cu 20％ showed a relatively obvious downward trend compared with the other two groups, and the temperature peak decreased by 9.6% and 15.6% respectively compared with the EP cured product and EP / MAP 20％ and the time to reach the temperature peak also shifted, which further proved that the expansion coating played a role in suppressing temperature propagation and heat insulation when coated on the battery surface.

Claims

1. An expansion flame retardant applied to a lithium-ion battery pack, characterized in that, The intumescent flame retardant has a disordered stacking structure of flaky materials with different sizes. The main component is a phosphine-amine copper complex obtained by complexing melamine, aminotrimethylenephosphonic acid and copper ions. There are Cu—N and Cu—O coordination bonds in the complex.

2. The expansion flame retardant applied to the lithium-ion battery pack according to claim 1, wherein The thickness of the flaky material is less than 200 nm, and the size of more than 80% of the flaky materials is 1 - 5 μm.

3. A preparation method of the expansion flame retardant applied to a lithium-ion battery pack according to claim 1 or 2, characterized in that, The specific steps are as follows: 1) Add melamine to water, stir while heating until melamine is dissolved to obtain a melamine solution. 2) Dissolve aminotrimethylenephosphonic acid in water, add a divalent copper salt after stirring and dissolving, and stir until copper nitrate is completely dissolved to obtain a light blue transparent mixed solution. 3) Add the mixed solution obtained in step 2) to the melamine solution obtained in step 1), then carry out a hydrothermal reaction. After the reaction is completed, carry out suction filtration to obtain a light blue flocculent solid, and the intumescent flame retardant is obtained after drying.

4. The preparation method of the expansion flame retardant applied to the lithium ion battery pack according to claim 3, wherein, In step 1), the heating temperature is 85 - 95 °C, and the concentration of the melamine solution is 0.1 - 0.3 mol / L.

5. The preparation method of the expansion flame retardant applied to the lithium-ion battery pack according to claim 3, characterized in that, In step 2), the concentration of aminotrimethylenephosphonic acid in the mixed solution is 0.10 - 0.25 mol / L, and the molar ratio of aminotrimethylenephosphonic acid to the copper salt is 3 - 7:1; the divalent copper salt in step 2) is one or a combination of two or more of copper nitrate and basic copper carbonate.

6. The preparation method of the expansion flame retardant applied to the lithium ion battery pack according to claim 3, wherein, In step 3), the molar ratio of aminotrimethylenephosphonic acid in the mixed solution to melamine in the melamine solution is 0.15 - 0.20:1; the hydrothermal reaction temperature in step 3) is 85 - 90 °C, and the hydrothermal reaction time is 2 - 3 h.

7. An intumescent flame retardant coating material containing the intumescent flame retardant described in claim 1 or 2, characterized in that, The raw materials of the intumescent flame retardant coating material include a halogen-free epoxy resin, an amine curing agent and the intumescent flame retardant described in claim 1 or 2. The mass percentage content of the intumescent flame retardant in the intumescent flame retardant coating material is 8 - 25%.

8. A method for preparing the intumescent flame-retardant coating material according to claim 7, characterized in that, The specific steps are as follows: Mix and stir the halogen-free epoxy resin and the intumescent flame retardant at 40 - 60 °C for 0.5 - 1 h, then add the amine curing agent, add a foaming and expanding agent as needed, and continue to stir for 10 - 30 min to obtain the intumescent flame retardant coating material.

9. An intumescent flame retardant coating obtained after curing of the intumescent flame retardant coating material according to claim 7, characterized in that, The specific curing process conditions are: First cure at 60 - 80 °C for 1 - 2 h, and then cure at room temperature for 24 - 48 h.

10. Use of the intumescent flame retardant coating material according to claim 7 in the preparation of a flame retardant lithium-ion battery.

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