Polyimide-based composite aerogel material PI@SiO2 and application thereof

Abstract

The application belongs to the technical field of lithium ion batteries, and discloses a polyimide-based composite aerogel material PI@SiO2 and application thereof. The polyimide-based composite aerogel material PI@SiO2 is prepared by introducing silica aerogel with super-strong heat insulation function into a porous aerogel structure framework with high-temperature resistance and flame retardant characteristics, which is composed of polyimide, hydroxyapatite and ammonium polyphosphate through freeze-drying, high-temperature calcination and other methods. The lithium ion battery group heat insulation and flame retardant plate made by packaging the polyimide-based composite aerogel material provided by the application with epoxy resin film or polyurethane film with flame retardant effect can effectively block the spread of battery thermal runaway and ensure that the internal materials of the battery not in thermal runaway are not damaged to a large extent.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a polyimide-based composite aerogel material PI@SiO2 and application thereof in manufacturing a lithium ion battery pack heat-insulating and flame-retardant plate. BACKGROUND

[0002] At present, lithium ion batteries are the core components of electric vehicle energy storage systems, and consumers have always paid close attention to the key features such as power performance, battery capacity and safety issues. However, the safety accidents of new energy vehicles caused by thermal runaway of lithium ion batteries seriously restrict the development of the industry.

[0003] Due to the "domino" effect of lithium ion battery thermal runaway propagation, if the battery pack is not protected in advance, the thermal runaway of one battery can induce the fire and explosion accidents of the entire battery system, and therefore it is necessary to develop a method for blocking the thermal runaway propagation between batteries. The existing methods for blocking the thermal runaway propagation of lithium ion batteries mainly focus on three aspects of fire extinguishing after thermal runaway, improvement of the internal structure of the battery pack and placement of heat insulation materials. Literature shows that the existing lithium ion battery fire extinguishing methods mainly include perfluorohexone, heptafluoropropane, carbon dioxide, dry powder, water-based extinguishing agent and the like, most of which need to be equipped with corresponding power supply devices to release the extinguishing agent, and have certain limitations for the application in closed space scenes such as lithium ion battery packs. In addition, due to the halogen elements contained in part of the extinguishing agents, the environment may be polluted in the process of fire extinguishing. At the same time, most of the water-based extinguishing agents contain alkali metal salts, which can easily enhance the conductivity of the solution, easily cause battery short circuit and corrosion problems. For the design of a new battery pack structure, most of them are through isolating the battery from air or adding fire extinguishing medium to the inside of the battery pack, which needs to modify the battery pack or even the battery, and does not have universality.

[0004] In recent years, to solve the problem of thermal runaway propagation of the battery pack, a thermal insulation layer can be added in the battery pack to block the thermal runaway from the runaway monomer to the surrounding monomer, and to reduce the damage of the battery pack and the accompanying destructive effect. Traditional power battery thermal insulation materials include foam, foamed plastic, high-silicon oxygen cotton, ultra-fine glass cotton, vacuum insulation board, etc. The foam that can be used for cell thermal insulation mainly includes PU and PI foam. Compared with traditional battery thermal insulation materials, aerogel thermal insulation sheet has the advantages of super-hydrophobicity, V0-level flame retardancy, wide use temperature range, low thermal conductivity, long service life, light weight, non-toxicity, etc. Under the same thermal insulation effect, the thickness of the aerogel material is only 1 / 5 to 1 / 2 of the thickness of the traditional thermal insulation material. In the lithium ion power battery module, when the cell is in thermal runaway, the aerogel thermal insulation sheet can play a thermal insulation role and delay or block the accident; when the cell is overheated and burns, the main component of the aerogel thermal insulation sheet, nano-SiO2 structure, can effectively block or delay the spread of fire, providing enough time for escape. For example, see

Preparation and Application of Aerogel Thermal Insulation Sheet for New Energy Vehicle Battery[J]. Electric Bicycle, 2020(4): 26-27.

[0005] Based on the above technical background, in view of the limitations of the prior art, the present application provides a polyimide-based composite aerogel material PI@SiO2, in particular, a polyimide composite aerogel that can be used to block the thermal runaway propagation of a lithium ion battery pack. The material is mainly composed of polyimide, hydroxyapatite, and ammonium polyphosphate to form a porous aerogel structure framework with high-temperature resistance and flame retardant properties through freeze-drying and high-temperature calcination. The framework pores are introduced into the silica aerogel with super-strong thermal insulation function. The polyimide-based composite aerogel PI@SiO2 material provided by the present application has good thermal insulation effect and high safety, and can be used to make lithium ion battery pack thermal insulation and flame retardant materials, and can delay the thermal runaway propagation time.

[0006] To solve the above technical problems, the present application adopts the following scheme:

[0007] In a first aspect, the present application provides a polyimide-based composite aerogel PI@SiO2, which is a high-heat-insulation silica-filled aerogel obtained by freeze-drying a PI composite aerogel completely immersed in a filling liquid to form a PI@SiO2 wet gel;

[0008] The PI composite aerogel is a polyimide material skeleton with flame-retardant properties prepared by freeze-drying; the filling liquid is prepared by mixing and stirring HCl, cetyltrimethylammonium bromide, deionized water and methyltrimethoxysilane uniformly, and then adding NH3·H2O.

[0009] Specifically, the preparation of the PI composite aerogel comprises the following steps: dissolving polyamic acid PAA in deionized water, adding triethylamine (99%) dropwise to form a PAA salt with a concentration of 3%-5%; adding hydroxyapatite HAP and ammonium polyphosphate APP to the PAA salt solution, and ultrasonically stirring to form a uniform and stable solution; placing it in a freeze dryer and freezing at -50℃ for 72-96h; drying the frozen material to obtain a composite PAA aerogel; and placing the aerogel in a tube furnace under an argon atmosphere for thermal annealing, starting from room temperature 25℃ and increasing the temperature at a rate of 5℃ / min, and holding at 100℃, 200℃ and 300℃ for 30-60min respectively, to finally obtain a PI composite aerogel; preferably, the mass ratio of polyamic acid to HAP is (1:1)-(6:1); and the mass ratio of HAP to APP is (1:1)-(2:1).

[0010] Specifically, the synthesis of the hydroxyapatite HAP comprises the following steps: alternately adding an aqueous solution of CaCl2 and an aqueous solution of NaOH to a mixture of ethanol and oleic acid at room temperature 25℃ by magnetic stirring to form a precursor; then adding an aqueous solution of NaH2PO4·2H2O dropwise into the precursor solution, stirring for 30min, and then transferring it to an autoclave for heating at 160-200℃ for 23h, preferably at 180℃; after the solution cools to room temperature, adding ethanol to the solution to reduce the viscosity of the reaction system, and then fully stirring to obtain a uniform solution; the product is collected by centrifugation and washed with deionized water and ethanol, and then vacuum dried at 45℃ for 24h to obtain a linear nanostructured hydroxyapatite; preferably, the volume ratio of the aqueous solution of CaCl2 to the aqueous solution of NaOH is 1:1; the volume ratio of the aqueous solution of CaCl2 to ethanol to oleic acid is 50:38:33.5; and the volume ratio of the aqueous solution of CaCl2 to the aqueous solution of NaH2PO4·2H2O is 2:1; in the step of adding ethanol to the solution to reduce the viscosity of the reaction system, the volume of ethanol added is 10 times that of the aqueous solution of CaCl2.

[0011] Specifically, the preparation method of the filling liquid comprises the steps of mixing HCl, cetyltrimethylammonium bromide CTAB, deionized water, and methyltrimethoxysilane MTMS, magnetically stirring at room temperature 25 DEG C for at least 20 minutes, then adding NH3H2O with a concentration of 0.5-1 mol / L for stirring and mixing, and configuring into a filling liquid. -1 Preferably, the volume-mass ratio of HCl and cetyltrimethylammonium bromide CTAB is 0.5 ml:0.02 g; the volume ratio of HCl and deionized water is 1:20; and the volume ratio of deionized water, methyltrimethoxysilane MTMS, and NH3H2O is 1:1:1.

[0012] In a second aspect, the application further provides application of the polyimide composite aerogel PI@SiO2 in preparation of a lithium ion battery heat insulation and flame retardant plate, that is, a lithium ion battery thermal runaway barrier plate, which is composed of an intermediate layer and flame retardant films adhered to both sides of the intermediate layer, the intermediate layer is composed of the polyimide composite aerogel, and the flame retardant film is an epoxy resin film or a polyurethane film to which a flame retardant is added, and the flame retardant includes but is not limited to ammonium polyphosphate, aluminum diethyl phosphite, zirconium phosphate, melamine cyanurate, clay, black phosphorus, molybdenum disulfide, and boron nitride.

[0013] As a preferred embodiment of the application, the flame-retardant epoxy resin material prepared by high-temperature curing, that is, the flame-retardant epoxy resin, encapsulates the polyimide composite aerogel PI@SiO2 as a whole, and the encapsulation steps specifically include the following: first, uniformly apply the flame-retardant epoxy resin before curing to each surface of the PI@SiO2, and then heat and cure at 100 DEG C and 150 DEG C for 2 hours respectively, to obtain the flame-retardant aerogel composite PI@SiO2 / EP as the lithium ion battery thermal runaway barrier plate, which can effectively solve the powder shedding caused by the poor mechanical properties of the SiO2 aerogel.

[0014] Beneficial effects: The polyimide composite aerogel PI@SiO2 provided by the application can effectively block the propagation of thermal runaway between batteries when the maximum temperature of the first battery reaches 689.88 DEG C, and the temperature of the adjacent battery is only 137.01 DEG C. After disassembling the battery that does not occur thermal runaway, it is found through analysis of the morphology and phase transformation of the internal materials of the battery that the structure and morphology of the cathode material and the XRD pattern do not change obviously, and the XPS data of the cathode material of the battery show that the Ni 2+ / Ni 3+ peak intensity ratio of the battery internal cation rearrangement phenomenon is 0.43. The above results collectively show that the lithium ion battery heat insulation and flame retardant material PI@SiO2 / EP can effectively block the propagation of battery thermal runaway and ensure that the internal materials of the battery that does not occur thermal runaway are not damaged to a large extent. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 Micro-morphology image of HAP prepared in Example 1;

[0016] Figure 2 Micro-morphology image of PI aerogel prepared in Example 1;

[0017] Figure 3 Micro-morphology image of PI / SiO2 aerogel prepared in Example 1;

[0018] Figure 4 Micro-morphology image of MoO3-EDA prepared in Example 1;

[0019] Figure 5 Micro-morphology image of MoS2 prepared in Example 1;

[0020] Figure 6 Micro-morphology image of PR-MoS2 prepared in Example 1;

[0021] Figure 7 Micro-morphology image of PI@SiO2 / EP prepared in Example 1;

[0022] Figure 8 TGA and DTG images of PI@SiO2 / EP and part of its single component materials (HAP, PI, EP / 3.0 PR-MoS2) under nitrogen atmosphere in Test Example 1;

[0023] Figure 9 TGA and DTG images of PI@SiO2 / EP and part of its single component materials (HAP, PI, EP / 3.0 PR-MoS2) under air atmosphere in Test Example 1;

[0024] Figure 10 PI and PI@SiO2 / EP fire safety performance test in Test Example 2;

[0025] Figure 11 Lithium-ion battery thermal runaway and its propagation experimental platform in Test Example 3;

[0026] Figure 12 Battery thermal runaway propagation temperature change curve using different thickness of PI aerogel in Test Example 3;

[0027] Figure 13 Battery thermal runaway propagation temperature change curve using different thickness of PI@SiO2 / EP aerogel composite board in Test Example 3;

[0028] Figure 14The microstructure diagram of the battery after the PI aerogel blocked the thermal runaway of the battery (a and d are anode materials; b and e are separator materials; c and f are cathode materials) ;

[0029] Figure 15 The microstructure diagram of the battery after the PI@SiO2 / EP aerogel composite plate blocked the thermal runaway of the battery (a and d are anode materials; b and e are separator materials; c and f are cathode materials) ;

[0030] Figure 16 The XRD pattern of the cathode material of the battery after the PI@SiO2 / EP blocked the thermal runaway of the battery;

[0031] Figure 17 The product physical diagram of the preparation process of the PI@SiO2 / EP, wherein (a) is a frozen 3% PAA composite solution; (b) is a composite PAA aerogel; (c) is a composite PI aerogel; (d) is a PI@SiO2 wet gel; (e) is a PI@SiO2 aerogel section; (f) is a packaged composite material PI@SiO2 / EP. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0033] Meanwhile, the raw materials or reagents mentioned below without detailed description are all commercially available products, and the process steps or methods not mentioned in detail are all known to those skilled in the art.

[0034] The specifications and sources of the main raw materials and reagents of the present application are shown in Table 1 below:

[0035] Table 1

[0036] Name Specification Manufacturer Ammonium molybdate tetrahydrate AR, 99wt% Merck Aniline AR, 99wt% Efa Concentrated hydrochloric acid 37wt% solution National Pharmaceutical Group Chemical Reagent Co., Ltd. Thioacetamide AR, 99wt% Mcclin Biochemical Technology Anhydrous ethanol AR, 99wt% National Pharmaceutical Group Chemical Reagent Co., Ltd. Sodium dihydrogen phosphate AR, 99wt% National Pharmaceutical Group Chemical Reagent Co., Ltd. Calcium chloride AR, 99.5wt% Mcclin Biochemical Technology Sodium hydroxide AR, 99wt% Adamas Oleic acid AR, 99wt% Mcclin Biochemical Technology Epoxy resin AR, 99wt% Mcclin Biochemical Technology Ammonium polyphosphate AR, 98wt% Mcclin Biochemical Technology Sodium dihydrogen phosphate monohydrate AR, 98wt% Adamas Polyamide acid AR, 99wt% Sigma Aldrich Cetyltrimethylammonium bromide (CTAB) AR, 99wt% Mcclin Biochemical Technology Trimethyl trimethoxysilane (MTMS) 65-80wt% Merck Ammonia AR, 25-28wt% National Pharmaceutical Group Chemical Reagent Co., Ltd. Epoxy resin Epoxy equivalent 0.44mol / 100g Wuxi Qianwang Chemical Raw Material Co., Ltd.

[0037] Example 1: Preparation of polyimide-based composite aerogel PI@SiO2

[0038] (1) Synthesis of HAP

[0039] The aqueous solution of CaCl2 (50 ml, 0.55 g) and the aqueous solution of NaOH (50 ml, 2.50 g) were alternately added dropwise to a mixture of ethanol (38 ml) and oleic acid (33.5 ml), and the precursor was formed at room temperature 25℃ by magnetic stirring.

[0040] Then 25ml of NaH2PO4·2H2O (0.6g) aqueous solution was added dropwise into the precursor solution, after stirring for 30 minutes, the mixture was transferred into a hydrothermal kettle and heated at 180℃ for 23 hours. After the solution was cooled to room temperature, 500ml of ethanol was added to the solution to reduce the viscosity of the reaction system, after stirring evenly, the product was collected by deionized water and ethanol washing and vacuum dried at 45℃ for 24 hours to obtain hydroxyapatite, the micro-morphology thereof is shown as nanowires in Figure 1 .

[0041] (2) Preparation of PI composite aerogel

[0042] Firstly, 1.5g of polyamide acid (PAA) was dissolved in 49ml of deionized water and stirred evenly, 1ml of triethylamine (99%) was added dropwise, and ultrasonic stirring was carried out for 1 hour to form 3% PAA salt as shown in Figure 17 (a) figure. Then 0.25g of HAP and 0.25g of APP were added into the 3% PAA salt solution, and ultrasonic stirring was carried out for 20min to form a uniform and stable solution. Then the mixed solution was poured into a culture dish (Φ=9cm, h=2.5cm), and placed in a freeze dryer, and frozen at-50℃ for 72 hours, then the vacuum pump was started, and the frozen material was dried to obtain a composite PAA aerogel as shown in Figure 17 (b) figure. The above aerogel was placed in a tube furnace under argon environment for thermal annealing, and the temperature was increased at a rate of 5℃ / min from room temperature 25℃, and the temperature was kept at 100, 200, 300℃ for 60min respectively, and finally a PI composite aerogel as shown in Figure 17 (c) figure was obtained, and the micro-morphology thereof is shown as Figure 2 . The thickness of the aerogel can be controlled by the volume of the solution, and the thickness of the aerogel prepared by the solution with a volume of 30ml, 40ml and 50ml is 1.07±0.2mm, 1.80±0.2mm and 2.59±0.2mm respectively.

[0043] (3) Preparation of PI@SiO2 aerogel

[0044] 0.5ml of HCl, 0.02g of cetyltrimethylammonium bromide CTAB, 10ml of deionized water and 10ml of methyltrimethoxysilane MTMS were mixed in a beaker, after magnetic stirring at room temperature 25℃ for 20 minutes, 10ml of NH3·H2O with a concentration of 0.5mol L -1 was added to the beaker, after stirring for 2min, the PI composite aerogel was completely immersed with the above solution, until a wet gel PI@SiO2 as shown in Figure 17 (d) figure was formed; then the PI@SiO2 wet gel was freeze-dried for 36 hours to obtain a PI@SiO2 aerogel as shown in Figure 17PI@SiO2 aerogel shown in (e) of FIG. 1, the micro-morphology of which is shown in FIG. 2. Figure 3

[0045] Preparation of PI@SiO2 / EP thermal runaway barrier plate for lithium ion battery

[0046] (1) Preparation of flame-retardant epoxy resin (EP / 3.0PR-MoS2)

[0047] The flame-retardant epoxy resin can be prepared by adding inorganic nanoparticles in the epoxy resin material to protect the inside of the material by promoting catalytic charring to inhibit the pyrolysis reaction. In this embodiment, the preparation method of the flame-retardant epoxy resin is as follows by taking the doped and modified molybdenum disulfide particles as an example:

[0048] Preparation of MoO3-EDA: 2.48 g of ammonium molybdate tetrahydrate ((NH)6MoO2·4H2O) and 3.34 g of aniline were dissolved in 50 ml of distilled water to form a uniform solution. Then, a 1 mol / L HCl solution was prepared, and the above mixture was slowly added dropwise, and stirring was continued until a white precipitate was formed and the pH reached 4-5. Then the mixture was continuously stirred at 50°C for 2h, and the precipitate was collected, washed with deionized water and ethanol, and finally dried in an oven at 70°C for 24 hours to obtain MoO3-EDA inorganic-organic hybrid nanowire powder. The micro-morphology image of MoO3-EDA is shown in FIG. 3. Figure 4

[0049] Preparation of MoS2: 0.25 g of MoO3-EDA and 0.4 g of thioacetamide were uniformly dispersed in 50 ml of ethanol solution, and then the mixed solution was transferred to a 100 ml iron fluorine lined stainless steel hydrothermal kettle, which was placed in a constant temperature heating box at 180°C for 12 hours. After the solution was cooled, the solid product obtained after centrifugal washing in ethanol and deionized water was placed in a constant temperature drying oven at 70°C for 12 hours to obtain the MoS2 product. The micro-morphology image of MoS2 is shown in FIG. 4. Figure 5

[0050] Preparation of PR-MoS2: 0.15 g of MoS2 and 0.15 g of sodium dihydrogen phosphate monohydrate (NaH2PO2·H2O) were loaded into a tube furnace, the argon flow was controlled at 50 ml / min, the tube furnace was heated at a rate of 5°C / min, and the temperature was kept at 350°C for 4h. The NaH2PO2·H2O was decomposed to generate sodium hydrogen phosphate (Na2HPO4) and phosphine (PH3) gas by high temperature, so that the phosphorus element was doped in the MoS2 nanowire under the action of PH3 gas flow, and the phosphorus-doped molybdenum disulfide nanowire (PR-MoS2) was synthesized. The micro-morphology image of PR-MoS2 is shown in FIG. 5. Figure 6

[0051] ​​​​Preparation of EP / 3.0 PR-MoS2: 3 g of PR-MoS2 prepared above was added for the preparation of EP / 3.0 PR-MoS2; the epoxy resin itself is in a gel form, which is generally cured by adding a curing agent under high temperature conditions, and the ratio of epoxy resin (EP) to 4,4-diaminodiphenyl methane (DDM) is controlled to be 4.58:1. The specific preparation steps are as follows: first, 79.6 g of EP was placed in a constant temperature drying box at 100°C for softening, and 17.4 g of 4,4-diaminodiphenyl methane (DDM) was ground into powder and placed in a constant temperature drying box at 120°C for melting. Then 3 g of PR-MoS2 prepared in step 3 was placed in a 250 ml three-necked flask, 40 ml of acetone solution was added, and ultrasonic stirring was carried out for 1 h to make PR-MoS2 fully dissolved. The stopper of the three-necked flask was removed, and the softened EP was added. After continuous ultrasonic stirring for 1 h, the three-necked flask was placed in an oil bath at 90°C, and mechanical stirring was continued for 4 h to make the acetone fully volatilize. The melted DDM was added, and after 30 s of thorough stirring, it was poured into a tetrafluoroethylene mold. Then the mold was placed in a constant temperature drying box at 100°C for 2 hours, and the temperature was adjusted to 150°C for continued incubation for 2 hours. After the mold cooled down, it was demolded to obtain the EP / 3.0 PR-MoS2 cured material.

[0052] (2) Preparation of PI@SiO2 / EP material

[0053] The PI@SiO2 aerogel prepared in Example 1 was coated and packaged with the EP / 3.0 PR-MoS2 material prepared above. The specific coating and packaging operation was as follows: first, the surfaces of PI@SiO2 were uniformly coated with EP / 3.0 PR-MoS2 before curing by brushing, and then placed in an electric heating constant temperature heating box. After incubation and curing at 100 and 150°C for 2 hours respectively, the flame-retardant aerogel composite PI@SiO2 / EP was obtained, as shown in (f) of Figure 17 , which can effectively solve the problem of powder falling off due to the poor mechanical properties of SiO2 aerogel. The micro-morphology image of PI@SiO2 / EP is shown in Figure 7 . After coating and packaging of PI@SiO2 with different thicknesses in Example 1 with EP / 3.0 PR-MoS2, the thicknesses were 1.51±0.2 mm, 2.37±0.2 mm and 3.01±0.2 mm respectively, and the thickness of the coating layer was about 0.5 mm, and the mass density was about 1 g / 12.5 cm 2 .

[0054] Test Example 1:

[0055] The PI@SiO2 / EP prepared in Example 2 and part of the single component materials including HAP, PI in Example 1 and EP / 3.0 PR-MoS2 prepared in Example 2 were subjected to a dual atmosphere thermogravimetric test, and the specific test object and specific method were as follows:

[0056] (1) Thermogravimetric test under nitrogen atmosphere: 5-10 mg of PI@SiO2 / EP and part of the single component materials HAP, PI, and EP / 3.0 PR-MoS2 were respectively placed in a crucible and placed in a thermogravimetric instrument. The temperature range was selected to be 30-800℃, and the nitrogen flow rate was controlled to be 50 ml / min. According to the TGA and DTG curves shown in FIG. 1, the initial thermal decomposition temperature, the temperature corresponding to the maximum heat release rate, and the residual carbon rate of the characteristic parameters shown in Table 1 were obtained to determine the thermal weight loss of the materials under nitrogen atmosphere. Figure 8

[0057] The T 5％ of HAP was 230℃, the maximum thermal weight loss rate was reached at 250.5℃, and the residual mass percentage was 71.37% after 800℃. It can be seen that HAP has high thermal stability. Since HAP is well wrapped in PI and PI@SiO2, the maximum thermal weight loss rate peak curve presents a double peak coupling phenomenon, which makes the maximum thermal weight loss temperature of HAP increase. The T max1 of PI, PI@SiO2 / EP were 384.9, 388.5℃ respectively, and the T max1 of EP / 3.0 PR-MoS2 was similar to 376.7℃, so the first thermal weight loss occurred due to the combined thermal decomposition of HAP and EP / 3.0 PR-MoS2. The second maximum thermal weight loss temperature of PI and PI@SiO2 was 592.7 and 578.6℃ respectively, at which time the heat release should be due to the breaking of the ether bond in PI which is prone to thermal decomposition. Due to the breaking of the carbon chain of the epoxy resin-based material inside PI@SiO2 / EP, the residual carbon content of PI@SiO2 / EP decreased by 4.46% compared with that of PI.

[0058] Table 1 Key parameters of nitrogen atmosphere thermal weight loss characteristics of PI and PI@SiO2 / EP

[0059]

[0060]

[0061] ​(2) Thermogravimetric test in air atmosphere: Similar to nitrogen atmosphere, 5-10 mg of PI@SiO2 / EP and its partial single component materials HAP, PI, and EP / 3.0PR-MoS2 were respectively placed in a crucible and placed in a thermogravimetric instrument. The temperature range was selected to be 30-800℃, and the air flow rate was controlled to be 50 ml / min. According to the TGA and DTG shown in FIG. 6, the thermal decomposition initial temperature, the temperature corresponding to the maximum heat release rate, and the residual carbon rate of the materials in air atmosphere can be obtained, as shown in Table 2. Figure 9

[0062] The T 5％ and T 30％ of HAP in the composite material were 221.7 and 348.7℃, respectively. The maximum heat release rate of HAP was reached at 289.7℃ due to the thermal decomposition of residual oleate on the surface of the material. The PI composite aerogel also experienced thermal weight loss due to the thermal decomposition of oleate ions on the surface of HAP in the PI composite aerogel. The T 5％ and T 30％ of the PI composite aerogel were 312.3 and 497.3℃, respectively. The T max1 and T max2 were 554.7 and 641.9℃, respectively, indicating that PI has high heat resistance. The T 5％ and T 30％ of PI@SiO2 / EP were 324.0 and 367.7℃, respectively. The initial thermal decomposition temperature of HAP was delayed due to the immersion of the aerogel material in the super thermal insulation material SiO2, and thus increased by 11.7℃ compared to the PI composite. PI@SiO2 / EP had two maximum thermal decomposition temperatures. The first maximum thermal decomposition temperature of PI@SiO2 / EP was reached at 328.6℃, which was 231.1℃ lower than that of the PI composite. The second maximum thermal decomposition temperature was reached at 509.9℃, which was 132℃ lower than that of the PI composite, which may be due to the addition of EP / 3.0PR-MoS2 epoxy resin material in the material, which made the arrival time of the maximum heat release temperature of the material advance. As can be seen from the thermogravimetric curve in the figure, the residual carbon content of PI@SiO2 / EP composite material was about 14.5 times that of EP / 3.0PR-MoS2, so the overall thermal stability of PI@SiO2 / EP3.0 composite material was higher than that of EP / 3.0PR-MoS2.

[0063] Table 2 Key parameters of air atmosphere thermal weight loss characteristics of PI and PI@SiO2 / EP

[0064]

[0065] Test Example 2:​

[0066] The fire safety performance of PI and PI@SiO2 / EP was tested using a micro calorimeter (MCC). The specific method is as follows:

[0067] A certain amount of PI and PI@SiO2 / EP were placed in an MCC, and their fire safety performance was determined by the obtained heat release rate and heat release amount. Figure 10 As shown, the PI composite aerogel remained in a slow exothermic state before reaching 296℃, which may be due to the thermal decomposition of oleate ions on the HAP surface and APP contained in the PI composite material. Since the PI@SiO2 / EP surface is coated with EP / 3.0PR-MoS2, when the temperature reaches approximately 296℃, the EP / 3.0PR-MoS2 on the surface begins to decompose thermally, subsequently exposing the internal PI composite aerogel, which also undergoes thermal decomposition, thus causing a sharp increase in the total heat release. MCC results for PI and PI@SiO2 / EP show that the PI composite aerogel with added SiO2 / EP exhibits increased heat release, reaching its maximum heat release rate at 303℃. Compared to the PI composite aerogel, its total heat release increased by 15.14%, and the maximum heat release rate increased to 4.5 times the original. The presence of EP / 3.0PR-MoS2 slightly increases the heat release of PI@SiO2 / EP. However, without EP / 3.0PR-MoS2, the overall mechanical properties of the material would be greatly reduced, causing SiO2 to fall off from the PI skeleton, thus reducing the overall thermal insulation and reusability of the material.

[0068] Test Example 3:

[0069] A commercially available 2000mAh soft-pack ternary lithium-ion battery was selected as the experimental subject. Figure 11 The experimental platform for lithium-ion battery thermal runaway and its propagation shown was used to conduct experiments on the blocking effect of PI aerogel on battery thermal runaway and its propagation.

[0070] The PI aerogels prepared in Example 1 Step 2 were obtained by changing the solution volume to obtain PI aerogels of different thicknesses. In Example 1, the solution volumes were 30 ml, 40 ml, and 50 ml, and the thicknesses of the prepared aerogels were 1.07 ± 0.2 mm, 1.80 ± 0.2 mm, and 2.59 ± 0.2 mm, respectively. According to the thickness of the material, the three PI aerogels obtained by changing the thickness were named PI-1, PI-2, and PI-3, in order from thin to thick. Then, the three PI aerogels obtained by changing the thickness were placed between two batteries. The batteries, heating copper blocks, and barrier materials were fixed on the experimental table by a fixed support, and the heating blocks, batteries, and barrier materials were tightly fitted by adjusting the bolts. The heating copper blocks were powered by a temperature control instrument to generate heat, which was transferred to the surface of the first lithium ion battery by heat conduction to induce thermal runaway of the first battery, and then to induce the thermal runaway propagation process of the battery (the power of the heating block was turned off at the moment of thermal runaway of the first battery). The thermocouples were placed at the central position of the side of the battery, heating copper block, and barrier material to measure the surface temperature of each component. The voltage data acquisition crocodile clamp was tightly clamped at the tab of the lithium ion battery to determine the voltage change of the lithium ion battery (group) during the entire thermal runaway and propagation process.

[0071] The temperature curves of the battery thermal runaway and its propagation process were measured as shown in Figure 12 , wherein the key parameters are shown in Table 3. The initial temperature T1 of the thermal runaway of the first battery, the maximum temperature T 1max , and the corresponding times t1 and t 1max , respectively; the initial temperature T2 of the thermal runaway of the second battery, the maximum temperature T 2max , and the corresponding times t2 and t 2max , respectively; the time difference Δt1 of the initial temperature of the thermal runaway of the two batteries, the time difference Δt2 of the first thermal runaway battery reaching the maximum temperature and the initial temperature of the thermal runaway of the second battery, and the time difference Δt3 of the two batteries reaching the maximum temperature, respectively.

[0072] Figure 12Figures (a), (b), and (c) show that as the thickness increases, the initial thermal runaway time of battery 2 is delayed. When using PI-3 composite aerogel, battery 2 did not experience thermal runaway, with a maximum temperature of 141.6℃. However, in the shaded area of ​​figure (c), it can be seen that although the second battery did not experience thermal runaway, its voltage fluctuated severely until it reached 0, indicating battery failure. When using PI-1, the first battery experienced thermal runaway at 757s, reaching the maximum thermal runaway temperature at 767s. After 37s of heat transfer, the second battery experienced thermal runaway at 794s. Due to the thinness and high porosity of the PI-1 composite aerogel, it was almost ineffective in preventing the propagation of thermal runaway. When PI-2 is used, the time interval Δt1 between the thermal runaway of the two batteries is extended to 76s, which is also lower than that of 2mm air medium with the same spacing (the time interval Δt1 between the thermal runaway of the two batteries is 128s). Therefore, PI needs to be modified to enhance its flame retardant and heat insulation properties.

[0073] Table 3 Key parameters of PI aerogel of different thicknesses used in the thermal runaway propagation process of lithium-ion batteries

[0074]

[0075] Test Example 4:

[0076] Similar to Example 4, a commercially available 2000mAh soft-pack ternary lithium-ion battery was selected as the experimental subject, and the following methods were used: Figure 11 The lithium-ion battery thermal runaway and propagation experimental platform shown conducted experiments on the barrier effect of composite materials PI@SiO2 / EP-1, PI@SiO2 / EP-2, and PI@SiO2 / EP-3 on battery thermal runaway and propagation. PI@SiO2 / EP-1, PI@SiO2 / EP-2, and PI@SiO2 / EP-3 represent the increase in the thickness of the intermediate layer, while the thickness of the outer protective film remains unchanged.

[0077] The temperature and voltage change curves during battery thermal runaway and its propagation are as follows: Figure 13The key parameters of the batteries 2 are shown in FIGS. (a), (b) and (c) of the drawings, and are shown in Table 4. When PI@SiO2 / EP-1 and PI@SiO2 / EP-2 are applied, the initial thermal runaway time of the batteries 2 is delayed with the increase of the thickness of the material, and when PI@SiO2 / EP-3 is applied, the batteries 2 do not have thermal runaway, the maximum temperature is 137°C, and the battery voltage is continuously stable at 4.136V. When the PI@SiO2 / EP-1 composite aerogel is used, the second battery has thermal runaway after 210s of heat transfer, and compared with the PI-1 composite aerogel, the initial thermal runaway time is effectively delayed by 173s. When the PI@SiO2 / EP-2 composite aerogel is applied, the time interval At1 of the thermal runaway of the two batteries is extended to 215s, and compared with the PI-2 composite aerogel, the initial thermal runaway temperature is delayed by 139s. The addition of the PR-MoS2 / EP coating can not only prevent the shedding of SiO2 in the PI@SiO2 aerogel, but also effectively improve the barrier effect of the PI composite aerogel on the thermal runaway propagation of the lithium ion battery.

[0078] Table 4 Key parameters of PI@SiO2 / EP composite materials with different thicknesses for thermal runaway propagation process of lithium ion batteries

[0079]

[0080] Test Example 5

[0081] Micro-morphology characterization of PI and PI@SiO2 / EP composite plates and the batteries after thermal runaway

[0082] Since PI@SiO2 / EP-3 has the best battery thermal runaway barrier effect, the subsequent thermal runaway experiments are all aimed at the internal materials of the batteries after the PI@SiO2 / EP-3 barrier, and are compared with the internal materials of the batteries after the PI-3 barrier.

[0083] The batteries 2 after the PI-3 aerogel barrier and without thermal runaway are disassembled, and part of the cathode and anode surface materials are taken, respectively, to obtain the micro-morphology of the internal materials of the batteries as shown in FIGS. Figure 14 As shown in FIGS. (a) and (d), the micro-morphology of the anode material shows that cracks appear in the internal material, and a layer of white oxide is attached to the surface of the graphite sheet, losing the original layered structure. As shown in FIGS. (b) and (e), the overall structure of the separator collapses due to high temperature, the original pores are closed, and a large number of cracks appear. As shown in FIG. (c), the cathode material is broken and forms a large ravine, and as shown in FIG. (f), part of the nickel-cobalt-manganese ternary layered oxide (LiNi 1-x Co x Mn yO2) that is, the NCM microspheres are broken and scattered on the surface of the lithium manganate block structure. As can be seen, although the battery does not have a severe thermal runaway reaction, the cathode has a relatively serious side reaction, thus causing the voltage fluctuation of the battery 2 to decrease and eventually fail.

[0084] Figure 15 For the battery 2 that does not have a thermal runaway reaction after being blocked by PI@SiO2 / EP-3, as can be seen from (a) and (d), part of the graphite sheets in the anode lose the layered structure and a small amount of cracks are generated. As can be seen from (b) and (e), the battery separator still has a good hole structure and almost no deformation and collapse occurs. As can be seen from (c) and (f), the NCM microsphere structure on the surface of the cathode material is complete and does not break. Although the surface temperature of the battery 2 (137℃) is similar to the surface temperature of the battery 2 blocked by PI-3 (141.6℃), the micro-morphology of the material shows that the use of PI@SiO2 / EP can effectively reduce the damage degree of the cathode material, and thus the blocking effect of the PI@SiO2 / EP aerogel composite material on the thermal runaway and propagation of the lithium ion battery is more prominent than that of the PI aerogel.

[0085] Test Example 6:

[0086] XRD characterization of the cathode material of the battery that does not have a thermal runaway reaction after being blocked by PI@SiO2 / EP-3

[0087] In a ternary lithium ion battery, the main component of the cathode material is NCM. In NCM, only Ni and Co are chemically active, and Mn mainly plays a role in stabilizing the structure, so in order to make the battery have higher electrochemical performance, the content of Ni is usually increased. Because and have similar ionic radii, cation mixing often occurs in ternary materials with a high content of Ni, that is, Ni 2+ occupies the position of Li ions in the lattice under the action of external factors, thereby causing changes in the lattice on the surface of the material. Generally speaking, the atomic scattering ability of transition metals is stronger than that of lithium atoms, so if the nickel ions jump from the (003) crystal plane to the (104) crystal plane, the overall atomic scattering ability of the (104) crystal plane will be enhanced and the (003) crystal plane will be weakened, and the intensity of the X-ray diffraction peak is proportional to the scattering ability of the diffraction plane, so that the intensity of the (104) crystal plane is increased and the intensity of the (003) crystal plane is weakened, and thus the ratio of I 003 to I 104 is generally used as a scale to judge the degree of cation mixing of layered ternary materials.

[0088] XRD characterization experiments were carried out on the cathode material of the battery that does not have a thermal runaway reaction after being blocked by PI@SiO2 / EP-3, and the following results were obtained:Figure 16 The XRD images are shown. Table 5 shows the lattice constants and cation mixing coefficients I of the unblocked material, the PI@SiO2 / EP-3 barrier, and the fresh cell cathode material. 003 with I 004 The ratio changes. Among them, the I of the fresh battery... 003 / I 004 With a ratio of 1.15, the battery without barrier material has already experienced thermal runaway, and its internal structure has changed significantly. Therefore, there is no ratio of 003 and 004 peaks. After using PI@SiO2 / EP-3 as a barrier, the internal cathode material of the battery is I... 003 / I 004 The ratio is 0.69, which shows that the degree of damage to the layered structure of the battery cathode material is reduced after using PI@SiO2 / EP-3 as a barrier, indicating that the PI@SiO2 / EP-3 composite material has a good barrier effect.

[0089] Table 5. Lattice constants of cathode materials for batteries that did not experience thermal runaway after PI@SiO2 / EP-3 barrier treatment.

[0090]

[0091] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A polyimide-based composite aerogel PI@SiO2, characterized in that, The polyimide-based composite aerogel is a high-heat-insulation silica-filled aerogel obtained by freeze-drying a PI@SiO2 wet aerogel formed by completely impregnating a PI composite aerogel as a skeleton in a filling liquid; the PI composite aerogel is a polyimide material skeleton with flame-retardant properties prepared by freeze-drying and high-temperature calcination of polyimide, hydroxyapatite and ammonium polyphosphate; and the filling liquid is prepared by mixing and stirring HCl, cetyltrimethylammonium bromide, deionized water and methyltrimethoxysilane uniformly, and then adding NH3·H2O. The preparation of the PI composite aerogel comprises the steps of dissolving polyamic acid PAA in deionized water, adding triethylamine to the solution to form a PAA salt with a concentration of 3-5%, adding hydroxyapatite HAP and ammonium polyphosphate APP to the PAA salt solution, and ultrasonic stirring to form a uniform and stable solution; the solution is placed in a freeze dryer and frozen at-50℃ for 72-96 hours, and then the frozen material is dried to obtain a composite PAA aerogel; and the aerogel is placed in a tube furnace in an argon environment for thermal ammoniation, the temperature is raised at a rate of 5℃ / min from room temperature 25℃, and the temperature is kept at 100℃, 200℃ and 300℃ for 30-60 minutes respectively, to finally obtain a PI composite aerogel. The synthesis process of the hydroxyapatite HAP comprises the steps of alternately adding an aqueous solution of CaCl2 and an aqueous solution of NaOH to a mixture of ethanol and oleic acid to form a precursor at room temperature 25℃ by magnetic stirring; then adding an aqueous solution of NaH2PO4·2H2O to the precursor solution, stirring for 30 minutes, and then transferring the solution to an autoclave for heating at 160-200℃ for 23 hours; after the solution is cooled to room temperature, ethanol is added to the solution to reduce the viscosity of the reaction system, and the solution is stirred uniformly and then washed with deionized water and ethanol, and the product is collected by centrifugation and vacuum dried at 45℃ for 24 hours to obtain a linear nanostructured hydroxyapatite. The mass ratio of the polyamic acid to the HAP is (1:1)-(6:1), and the mass ratio of the HAP to the APP is (1:1)-(2:1).

2. The polyimide-based composite aerogel PI@SiO2 of claim 1, wherein, The volume ratio of the aqueous solution of CaCl2 to the aqueous solution of NaOH is 1:1; the volume ratio of the aqueous solution of CaCl2 to ethanol to oleic acid is 50:38:33.5; the volume ratio of the aqueous solution of CaCl2 to the aqueous solution of NaH2PO4·2H2O is 2:1; and in the step of adding ethanol to the solution to reduce the viscosity of the reaction system, the volume of the added ethanol is 10 times the volume of the aqueous solution of CaCl2.

3. The polyimide-based composite aerogel PI@SiO2 of claim 1, wherein, The heating temperature in the autoclave is 180℃.

4. The polyimide-based composite aerogel PI@SiO2 of claim 1, wherein, The HCl, cetyltrimethylammonium bromide CTAB, deionized water, methyltrimethoxysilane MTMS are mixed at room temperature 25°C under magnetic stirring for at least 20 minutes, then NH3·H2O with a concentration of 0.5-1 mol / L is added and stirred to mix, configured as a filling liquid. -1 ​ 5. The polyimide-based composite aerogel PI@SiO2 of claim 4, wherein, The volume-to-mass ratio of HCl to cetyltrimethylammonium bromide is 0.5ml:0.02g; the volume ratio of HCl to deionized water is 1:20; and the volume ratio of deionized water to methyltrimethoxysilane MTMS to NH3·H2O is 1:1:

1.

6. The application of the polyimide composite aerogel PI@SiO2 in the preparation of a lithium ion battery heat-insulating and flame-retardant plate according to any one of claims 1-5, wherein the application method is as follows: the polyimide composite aerogel is used as an intermediate layer, and a flame-retardant film is adhered to both sides of the intermediate layer to prepare a thermal runaway group separator plate, and the flame-retardant film is an epoxy resin film or a polyurethane film to which a flame retardant is added.

7. The use according to claim 6, wherein the compound is ###0002### The thickness of the intermediate layer is 1-4 mm.

8. The use according to claim 6, characterized in that, The flame retardant is any one of ammonium polyphosphate, aluminum diethyl phosphite, zirconium phosphate, melamine cyanurate, clay, black phosphorus, molybdenum disulfide, and boron nitride.

9. The use according to claim 6, characterized in that, The flame-retardant film is an epoxy resin film to which a flame retardant is added, and the polyimide composite aerogel PI@SiO2 is packaged by using a high-temperature curing method to prepare a lithium ion battery heat-insulating and flame-retardant plate, and the packaging steps are as follows: the surfaces of PI@SiO2 are uniformly coated with flame-retardant epoxy resin before curing, and then each is cured at a temperature of 100℃ and 150℃ for 2 hours.

Images