Foaming buffer support material between battery cells and preparation method thereof

Abstract

The invention discloses an inter-cell foaming buffer support material and a preparation method thereof, and relates to the technical field of high-molecular compound composition cell support materials. The foaming buffer support material between the battery cells is prepared from the following components in parts by mass: 40 to 60 parts of polyolefin elastomer, 10 to 30 parts of ethylene-vinyl acetate copolymer, 20 to 40 parts of flame retardant, 1 to 5 parts of foaming agent, 0.5 to 3 parts of foaming aid, 0.5 to 3 parts of cross-linking agent, 10 to 40 parts of inorganic filler, 5 to 15 parts of toughening agent, 0.1 to 0.5 part of antioxidant and 1 to 5 parts of compatilizer. The long-acting anti-oxidation performance is better, oxidation aging of the material under the working conditions of medium-high temperature and long-term mechanical stress can be inhibited, and mechanical performance attenuation is delayed. The mechanical stability is higher, internal stress concentration and interface defects are relieved through component cooperation, and the buffer resilience and tear resistance in long-term service are guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polymer compound composition cell support materials, in particular to a foamed buffer support material between cells and a preparation method. BACKGROUND

[0002] In the field of new energy vehicles, energy storage devices, etc., the safe and stable operation of the cell module directly determines the reliability and service life of the overall product. During the charging and discharging cycle, adjacent cells will continuously expand and contract due to temperature changes and lithium intercalation / deintercalation reactions, and at the same time, they will face complex working conditions such as vibration and impact during transportation and use. Therefore, a foamed buffer support material needs to be provided between the cells to absorb impact load, limit the cell spacing, and avoid cell damage due to extrusion.

[0003] Existing foamed buffer materials between cells are mostly based on polyolefin elastomers as the base material, and form a porous structure through a foaming process. Although they can meet the basic buffering requirements, they have obvious shortcomings during long-term use. On the one hand, the material is in a medium-high temperature environment generated by the cell operation for a long time, and is also subjected to repeated mechanical stress. The molecular chain of the base material is prone to oxidative degradation, leading to aging and embrittlement of the material. The key mechanical properties such as tear strength and compression resilience significantly decrease, and the material cannot effectively absorb the cell expansion stress and external impact. On the other hand, the traditional foamed material uses a single antioxidant in the antioxidant system, which has limited antioxidant efficiency and is prone to volatilization and migration during processing. This leads to insufficient long-term antioxidant capacity, and the material may fail due to oxidation and aging at the end of its service life. In addition, the support material may fail, causing cell displacement and short circuit, and even safety hazards.

[0004] In addition, in order to meet the requirements of fire resistance, buffering, and other functions, a large amount of inorganic filler and flame retardant is often added to the formula, which further aggravates the phase separation and stress concentration within the material. Under the action of oxidation and mechanical cycling, the structural stability of the material is more easily destroyed, and the mechanical properties decay faster. Therefore, it is a technical problem to be solved in the field of new energy that to develop a foamed buffer support material between cells with long-term antioxidant capacity, stable mechanical properties, and excellent fire resistance, buffering, and support performance that can adapt to complex cell working conditions. SUMMARY

[0005] The present application aims to solve the problems existing in the prior art and provides a foamed buffer support material between cells and a preparation method. The support material provided by the present application has long-term antioxidant capacity and stable mechanical properties, and excellent fire resistance, buffering, and support performance, which can adapt to complex cell working conditions.

[0006] To achieve the above object, the technical scheme adopted by the present application is: a foaming buffer support material between battery cells, comprising the following components: polyolefin elastomer 40-60 parts, ethylene-vinyl acetate copolymer 10-30 parts, flame retardant 20-40 parts, foaming agent 1-5 parts, foaming aid 0.5-3 parts, crosslinking agent 0.5-3 parts, inorganic filler 10-40 parts, toughening agent 5-15 parts, antioxidant 0.1-0.5 parts and compatibilizer 1-5 parts. The foaming agent is a mixed system of azodicarbonamide derivative and sodium bicarbonate, and the mass ratio of the two is 1:0.75.

[0007] By adopting the above technical scheme, further, the azodicarbonamide derivative is a compound represented by chemical formula 1; Chemical formula 1: ; The Chinese name of the chemical formula 1 is: (E)-N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propyl] azodicarbonamide.

[0008] By adopting the above technical scheme, further, the polyolefin elastomer is ethylene-octene copolymer and / or ethylene-propylene-diene monomer rubber.

[0009] By adopting the above technical scheme, further, the flame retardant is one or a combination of two or more of aluminum hydroxide, magnesium hydroxide, phosphorus-nitrogen flame retardant.

[0010] By adopting the above technical scheme, further, the phosphorus-nitrogen flame retardant is selected from one or more of urea phosphate, melamine phosphate, melamine pyrophosphate, and melamine polyphosphate.

[0011] By adopting the above technical scheme, further, the foaming aid is zinc oxide and / or zinc stearate.

[0012] By adopting the above technical scheme, further, the crosslinking agent is dicumyl peroxide.

[0013] By adopting the above technical scheme, further, the inorganic filler includes one or more of talc and wollastonite.

[0014] By adopting the above technical scheme, further, the toughening agent is styrene-ethylene-butylene-styrene block copolymer.

[0015] By adopting the above technical scheme, further, the antioxidant includes one or more of antioxidant RD, antioxidant A, antioxidant D, antioxidant 264, and antioxidant 1010.

[0016] By adopting the above technical scheme, further, the compatibilizer is maleic anhydride grafted polyolefin.

[0017] By adopting the technical scheme, further, 0.1-1.5 parts of polyisobutylene can be added.

[0018] A preparation method of a foamed buffer support material between battery cells, comprising the following steps: S1. The polyolefin elastomer, ethylene-vinyl acetate copolymer, flame retardant, inorganic filler, toughening agent, compatibilizer, and antioxidant are mixed at high speed to obtain a premix; S2. The premix is added to a banbury mixer or a double screw extruder, and is plasticized at 120-160℃ to uniformly disperse the flame retardant and inorganic filler in the resin matrix to obtain a melt; S3. The foaming agent, foaming aid, and crosslinking agent are added to the melt at 80-110℃, and plasticization is continued for 3-10min to control the material temperature to be lower than the initial decomposition temperature of the foaming agent to obtain a foaming masterbatch; S4. The foaming masterbatch is extruded into a sheet or plate by an extruder, and the extrusion temperature is controlled at 90-120℃, and the unfoamed crosslinked sheet is obtained after cooling and setting; S5. The unfoamed crosslinked sheet is placed in a mold and heated at 150-200℃ for 3-15min to complete crosslinking by decomposition of the crosslinking agent and to realize foaming by gas generated by decomposition of the foaming agent to obtain a closed-cell foamed support material; S6. The closed-cell foamed support material is tempered at 60-90℃ for 2-6h to obtain the foamed buffer support material between battery cells.

[0019] By adopting the technical scheme, further, the rotor speed of the banbury mixer is 30-80rpm.

[0020] By adopting the technical scheme, further, the initial decomposition temperature of the foaming agent is at least 10℃ higher than the extrusion temperature in the S4 step.

[0021] By adopting the technical scheme, further, the heating process in the S5 step adopts a segmented temperature control mode: first, 150-165℃ is maintained for 2-8min to preferentially perform crosslinking, and then the temperature is raised to 170-200℃ and maintained for 1-7min to perform foaming.

[0022] A battery cell module, comprising a plurality of battery cells and a foamed buffer support material arranged between adjacent battery cells, wherein: The foamed buffer support material is the above material; The foamed buffer support material is arranged in surface contact with the long side or short side of the battery cell to define the battery cell spacing and absorb the dimensional expansion and impact load generated by the battery cell under charging and discharging and vibration working conditions; The electric core is a square electric core or a soft package electric core, and the electric core spacing is determined by the thickness of the foamed buffer support material and the compression deformation amount.

[0023] A battery pack or battery system comprises a shell, a plurality of electric core modules, and a conductive connection structure, wherein: The electric core module is the above-mentioned electric core module; The foamed buffer support material is used for gap filling between the electric cores and between the electric cores and the shell, so as to improve the mechanical support, buffer and heat insulation performance of the electric cores under the conditions of collision, falling and thermal runaway.

[0024] The application fundamentally solves the problems of easy oxidation aging and mechanical property attenuation of the buffer material between the electric cores under the conditions of medium and high temperature and long-term cycling through the specific mass fraction formula and the molecular design of "foaming-protection integration". The continuous phase with flexibility and melt strength is constructed by 40-60 parts of polyolefin elastomer and 10-30 parts of EVA in the matrix, which provides the basis for cell formation and resilience. On this basis, the foaming agent system composed of the derivative modified by the azodicarbonamide (ADC) core skeleton and sodium bicarbonate in a mass ratio of 1:0.75 is introduced. When the ADC derivative decomposes in the foaming temperature zone, on the one hand, it releases nitrogen to form a uniform closed cell structure, and on the other hand, the hindered phenolic antioxidant functional groups in the residual fragments are converted into high-efficiency antioxidants in situ and firmly retained in the polymer matrix. The traditional antioxidant system of 0.1-0.5 parts is used to construct a double antioxidant defense line of "in-situ generation + external reinforcement" to inhibit the oxidative degradation of chain rupture and crosslinking from the source. At the same time, 20-40 parts of flame retardant and 10-40 parts of inorganic filler are combined with 0.5-3 parts of peroxide crosslinking agent, 5-15 parts of SEBS toughening agent, and 1-5 parts of maleic anhydride grafting compatibilizer to ensure flame retardation and dimensional stability, and to alleviate the stress concentration and interface defects caused by the addition of a large amount of fillers. The foaming structure can still maintain excellent compression resilience and tear resistance under long-term compression, vibration and thermal shock conditions, thereby realizing the overall synergy of foaming, thermal oxygen protection and flame retardant support, and significantly improving the safety and reliability of the electric core module in the whole life cycle.

[0025] Compared with the prior art, the application has the following advantages: 1. Long-term antioxidant performance is better, which can inhibit the oxidation aging of the material under the conditions of medium and high temperature and long-term mechanical stress, and delay the attenuation of mechanical properties.

[0026] 2. The mechanical stability is stronger, and the internal stress concentration and interface defects are alleviated through component synergy, which ensures the buffer resilience and tear resistance in long-term service.

[0027] 3. The comprehensive performance is more balanced, which takes into account the functional requirements of flame retardation, support, etc., and adapts to the complex conditions of electric core charging and discharging, vibration, impact, etc. Attached Figure Description

[0028] Figure 1 This is an infrared absorption spectrum of a foamed buffer support material between battery cells according to the present invention. Detailed Implementation

[0029] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Preparation Example 1: Preparation of azodicarbonamide derivatives: Prepare a dry round-bottom flask, add a magnetic stir bar, and add 3.0 g of the substrate amine ( Dissolve 2.03 g of carbonyl diimidazole in 30 mL of freshly opened and dried tetrahydrofuran (THF). Cool in an ice bath (0 °C) and slowly add the solution. After the addition is complete, remove the ice bath and stir at room temperature for 1-2 hours. Cool again to 0 °C and slowly add 315 mg of hydrazine hydrate dropwise using a microsyringe. After the addition is complete, stir at room temperature for 12 hours. Filter directly and wash the filter cake with a small amount of cold ethanol or ether. Dry under vacuum to obtain 5.10 g of white powder. Take a dry flask, add a magnetic stir bar, add 5.10 g of white powder to 80 mL of dichloromethane, stir well, and then accurately add 0.75 mL of pyridine with a syringe. Start stirring, wrap the flask with aluminum foil, divide 1.64 g of NBS into 4 portions (each approximately 0.41 g), add each portion and stir for 5 minutes before adding the next portion. After all NBS has been added, keep at room temperature and stir in the dark for 2 hours. Pour the reaction solution into a 250 mL separatory funnel, add 100 mL of distilled water, shake thoroughly, let stand and separate the layers, separate the lower organic phase, wash once with 50 mL of water, collect the organic phase, add an appropriate amount of anhydrous sodium sulfate, let stand and dry for 30 minutes, filter to remove the desiccant, and evaporate the filtrate to dryness under reduced pressure in a water bath at 40 °C on a rotary evaporator to finally obtain 4.62 g of orange-yellow solid ((E)-N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propyl]azodicarbonamide).

[0031] Structural identification of (E)-N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propyl]azodicarbonamide - Mass spectrometry showed: 609 [m+1]; NMR showed: 1HNMR: δ 6.86 (t, 2H), 3.25 (q, 4H), 3.07 (t, 4H), 2.96 (s, 2H), 2.50 (tt, 4H), 1.87 - 1.72 (m, 4H), 1.38 (s, 36H).

[0032] Examples 1-4, Comparative Examples 1-4: Preparation of a foamed cushioning support material between cells: 1. The raw material mass fraction component is shown in Table 1; Table 1 The polyolefin elastomer is ethylene-octene copolymer; The flame retardant is a mixture of aluminum hydroxide and melamine phosphate, and the mass fraction ratio of the two is 1:1; The foaming aid is zinc oxide; The crosslinking agent is dicumyl peroxide; The inorganic filler is talc; The toughening agent is styrene-ethylene-butylene-styrene block copolymer; The antioxidant is antioxidant RD; The compatibilizer is maleic anhydride grafted polyolefin; The foaming agent in Examples 1-4 is a mixed system of azodicarbonamide derivative and sodium bicarbonate, and the mass fraction ratio of the two is 1:0.75; The foaming agent in Comparative Example 1 is a mixed system of azodicarbonamide and sodium bicarbonate, and the mass fraction ratio of the two is 1:0.75; The foaming agent in Comparative Example 2 is a mixed system of azodicarbonamide derivative and ammonium bicarbonate, and the mass fraction ratio of the two is 1:0.75; The foaming agent in Comparative Example 3 is sodium bicarbonate; The foaming agent in Comparative Example 4 is a mixed system of azodicarbonamide derivative and sodium bicarbonate, and the mass fraction ratio of the two is 1:0.75.

[0033] 2. Preparation method: S1: The above weighed polyolefin elastomer, ethylene-vinyl acetate copolymer, flame retardant, inorganic filler, toughening agent, compatibilizer, antioxidant are added into a high-speed mixer, and high-speed mixing is carried out at a speed of 800 rpm for 15 min to obtain a uniform premix; S2: The premix is added into an internal mixer, the rotor speed of the internal mixer is set to 50 rpm, the temperature is controlled to 140°C, and the melt plasticizing is carried out for 12 min, so that the flame retardant and the inorganic filler are uniformly dispersed in the resin matrix to obtain a uniform melt; S3: Reduce the melt temperature in the internal mixer to 95°C, add foaming agent, foaming aid and crosslinking agent, continue plasticizing for 6 minutes, control the material temperature to be maintained at 90-100°C (at least 10°C lower than the initial decomposition temperature of the foaming agent), and obtain foaming masterbatch. S4: Add the foaming masterbatch to the single screw extruder and set the temperature of each section of the extruder as follows: Zone 1 of the barrel 90℃, Zone 2 100℃, Zone 3 110℃, and the die head 105℃. Extrude into sheets and cool and shape them by cooling rollers (cooling temperature 25℃) to obtain unfoamed cross-linked sheets. S5: After cutting the unfoamed cross-linked sheet, place it in the mold and heat it in a segmented temperature control manner: first, maintain it at 160℃ for 5 minutes to perform preferential cross-linking, then raise the temperature to 185℃ and maintain it for 4 minutes to perform foaming, so that the cross-linking agent is completely decomposed to achieve cross-linking. The foaming agent decomposes to produce gas to form a closed-cell structure, and obtains a closed-cell foamed support material. S6: Place the closed-cell foamed support material in a constant temperature oven and temper it at 75℃ for 4 hours. After naturally cooling to room temperature, the inter-cell foamed buffer support material is obtained. The infrared absorption spectrum of the inter-cell foamed buffer support material is shown below. Figure 1 As shown.

[0034] Performance testing: 1. Mechanical property test: Refer to GB / T6670-2008 to test the compression rebound rate. The data are shown in Table 2.

[0035] 2. Tear strength test: Tear strength was tested according to GB / T10808-2006, and the data are shown in Table 2.

[0036] 3. Thermo-oxidative aging test: Place the sample in an 80℃ thermo-aging test chamber and keep it at that temperature for 2500 hours. Then, retest the tear strength and calculate the tear strength retention rate. The data are shown in Table 2.

[0037] Table 2 Examples 1-4 utilize a specific ratio of polyolefin elastomer and ethylene-vinyl acetate copolymer to construct a continuous phase that combines flexibility and melt strength. Combined with SEBS toughening agent and maleic anhydride graft compatibilizer, this effectively mitigates interfacial defects caused by inorganic fillers and flame retardants, reducing stress concentration. Simultaneously, the foaming agent system composed of azodicarbonamide derivative and sodium bicarbonate decomposes to form a uniform closed-cell structure, providing a structural basis for compression rebound. Therefore, both compression rebound rate and initial tear strength exhibit excellent performance. More importantly, the hindered phenolic antioxidant functional groups remaining after the decomposition of the azodicarbonamide derivative, along with the added antioxidant, form a dual antioxidant defense line, inhibiting the oxidative degradation of the matrix molecular chains. This results in a tear strength retention rate of 89.5%-92.1% after thermo-oxidative aging.

[0038] Comparative Example 1 uses ordinary azodicarbonamide instead of modified derivative, lacking in-situ generated antioxidant function group, only relying on a single additional antioxidant, with limited antioxidant efficiency, and the molecular chain is easily degraded in long-term thermal and oxidative environment, so the tear strength retention rate is only 75.4%, although the initial mechanical properties are close to Example 1, but the long-term stability is significantly insufficient; Comparative Example 2 uses ammonium bicarbonate instead of sodium bicarbonate, the gas release rate does not match the crosslinking reaction during foaming, the cell structure is uneven and has open hole defects, resulting in a decrease in compression resilience and initial tear strength, although the antioxidant system is not damaged, but the structural defects exacerbate the performance decay after aging, and the retention rate is lower than the example; Comparative Example 3 only uses sodium bicarbonate as a foaming agent, the foaming efficiency is low and the cell is coarse and uneven, the internal structure of the matrix is poor in integrity, the mechanical properties are weak, and the compression resilience and initial tear strength are the lowest, and the retention rate after aging is also the worst; In Comparative Example 4, the polyolefin elastomer is excessive and does not match the corresponding proportion of other components, resulting in excessive flexibility and insufficient structural support of the matrix, the initial tear strength is lower than that of Example 1 and Example 4, although the antioxidant system is not affected, but the unbalanced formula leads to a decrease in comprehensive mechanical properties.

[0039] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and variations can be made to these embodiments without departing from the principles and spirit of the present application, the scope of the present application being defined by the appended claims and their equivalents.

Claims

1. A foamed buffer support material between battery cells, characterized in that, By weight, it comprises the following components: 40-60 parts of polyolefin elastomer, 10-30 parts of ethylene-vinyl acetate copolymer, 20-40 parts of flame retardant, 1-5 parts of foaming agent, 0.5-3 parts of foaming aid, 0.5-3 parts of crosslinking agent, 10-40 parts of inorganic filler, 5-15 parts of toughening agent, 0.1-0.5 parts of antioxidant, and 1-5 parts of compatibilizer; The foaming agent is a mixture of azodicarbonamide derivative and sodium bicarbonate, with a mass ratio of 1:0.

75.

2. The inter-cell foamed buffer support material according to claim 1, characterized in that, The azodicarbonamide derivative is a compound represented by chemical formula 1; Chemical Formula 1: ; The Chinese name of the chemical formula 1 is: (E)-N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propyl]azodicarbonamide.

3. The inter-cell foamed buffer support material according to claim 1, characterized in that, The polyolefin elastomer is an ethylene-octene copolymer and / or an ethylene-propylene-diene monomer rubber.

4. The inter-cell foamed buffer support material according to claim 1, characterized in that, The flame retardant is one or a combination of two or more of aluminum hydroxide, magnesium hydroxide, and phosphorus-nitrogen flame retardants. The phosphorus-nitrogen flame retardant is selected from one or more of the following: urea phosphate, melamine phosphate, melamine pyrophosphate, and melamine polyphosphate.

5. The inter-cell foamed buffer support material according to claim 1, characterized in that, The foaming agent is zinc oxide and / or zinc stearate.

6. The inter-cell foamed buffer support material according to claim 1, characterized in that, The crosslinking agent is dicumyl peroxide; Inorganic fillers include one or more of talc and wollastonite.

7. The inter-cell foamed buffer support material according to claim 1, characterized in that, The toughening agent is a styrene-ethylene-butene-styrene block copolymer; The antioxidants include one or more of antioxidant RD, antioxidant A, antioxidant D, antioxidant 264, and antioxidant 1010; The compatibilizer is maleic anhydride-grafted polyolefin.

8. A method for preparing a foamed buffer support material between battery cells according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1. The polyolefin elastomer, ethylene-vinyl acetate copolymer, flame retardant, inorganic filler, toughening agent, compatibilizer, and antioxidant are mixed at high speed to obtain a premix; S2. Add the premixed material to a mixer or twin-screw extruder and melt-plasticize it at 120-160°C to uniformly disperse the flame retardant and inorganic filler in the resin matrix to obtain a melt. S3. At 80-110℃, the foaming agent, foaming aid and crosslinking agent are added to the melt, and plasticizing is continued for 3-10 minutes. The material temperature is controlled to be lower than the initial decomposition temperature of the foaming agent to obtain foaming masterbatch. S4. The foaming masterbatch is extruded into sheets or boards using an extruder, with the extrusion temperature controlled at 90-120°C, and cooled and shaped to obtain unfoamed cross-linked sheets; S5. Place the unfoamed cross-linked sheet in a mold and heat it at 150-200℃ for 3-15 minutes to decompose the cross-linking agent and complete the cross-linking. The foaming agent decomposes to produce gas and achieves foaming, thus obtaining a closed-cell foamed support material. S6. Temper the closed-cell foam support material at 60-90°C for 2-6 hours to obtain the inter-cell foam buffer support material.

9. The method for preparing a foamed buffer support material between battery cells according to claim 8, characterized in that, The rotor speed of the internal mixer is 30-80 rpm; The initial decomposition temperature of the foaming agent is at least 10°C higher than the extrusion temperature in step S4. The heating process in step S5 adopts a segmented temperature control method: first, it is kept at 150-165℃ for 2-8 minutes to preferentially carry out cross-linking, and then the temperature is raised to 170-200℃ and kept for 1-7 minutes to carry out foaming.

10. A battery cell module, characterized in that, It includes multiple battery cells and foamed buffer support material arranged between adjacent battery cells, wherein: The foamed cushioning support material is the material described in any one of claims 1 to 7; The foamed buffer support material is attached to the long or short side of the battery cell to limit the spacing between the battery cells and absorb the dimensional expansion and impact load generated by the battery cells under charging, discharging and vibration conditions. The battery cell is a square battery cell or a pouch battery cell, and the spacing between the battery cells is determined by the thickness of the foamed buffer support material and the amount of compression deformation.

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