Halogen-free flame-retardant polypropylene material for lithium battery film and preparation method thereof

Abstract

This invention discloses a halogen-free flame-retardant polypropylene material for lithium battery films, relating to the field of polymer composite materials technology. It comprises the following components by weight: 55-65 parts copolymer polypropylene; 20-30 parts ammonium polyphosphate; 5-15 parts melamine cyanurate; 2-5 parts nano-silica; 0.3-0.8 parts antioxidant 1098 / 168; and 0.5-2.0 parts silicone masterbatch. A method for preparing the halogen-free flame-retardant polypropylene material for lithium battery films includes the following steps: S001, polypropylene, APP, MCA, nano-SiO2, and antioxidant are added to a high-speed mixer in proportion and stirred at 150±5℃ for 10-15 minutes; S002, the mixture is added to a twin-screw extruder and melt-blended at a gradient temperature of 170-200℃, with the screw speed controlled at 300-500 rpm; S003, the melt is water-cooled, pelletized, and dried to obtain masterbatch. In this invention, the surface of nanoparticles is modified at 150°C using a silane coupling agent, thereby reducing the particle size of the aggregates from 500 nm to below 80 nm.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a halogen-free flame-retardant polypropylene material for lithium battery films and its preparation method. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage power stations, the thermal safety of lithium batteries is becoming increasingly prominent. Existing lithium battery coating materials face the following technical bottlenecks: Insufficient flame retardancy: Traditional polypropylene has a limiting oxygen index of only 17.5%, and more than 60% aluminum hydroxide (ATH) needs to be added to achieve the UL94V-0 flame retardancy rating. However, excessive filling leads to material embrittlement (elongation at break <30%). Deterioration of mechanical properties: The high-filling system reduces the material's impact strength by more than 60%, making it unable to meet the requirements of battery vibration conditions; Processing performance is limited: the ultra-high filler content leads to a sharp increase in melt viscosity, making it difficult for existing casting processes to achieve ultra-thin production (<0.5mm). Furthermore, existing nano-synergists have limited functionality and struggle to achieve synergistic effects in both gas-phase and condensed-phase flame retardancy. Simultaneously, these materials generally lack the ability to actively respond to battery thermal runaway, failing to absorb significant amounts of heat through physical phase transitions in the early stages of thermal abuse and thus delay the runaway process. Therefore, developing a halogen-free flame-retardant polypropylene composite for lithium-ion battery coatings and its preparation method has become a pressing technical challenge in this field. Summary of the Invention

[0003] The present invention addresses the problem of overly simplistic solutions in existing technologies by providing a significantly different approach. Specifically, the present invention aims to provide a method for preparing halogen-free flame-retardant polypropylene for lithium battery coating films, thereby solving the technical challenges of low flame-retardant efficiency, poor mechanical properties, and narrow processing window in existing halogen-free flame-retardant polypropylene.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a halogen-free flame-retardant polypropylene material for lithium battery films, comprising the following components in parts by weight: 55-65 parts copolymer polypropylene; 20-30 parts ammonium polyphosphate (APP); 5-15 parts melamine cyanurate (MCA); 2-5 parts nano-silica (SiO2); 0.3-0.8 parts antioxidant 1098 / 168; 0.5-2.0 parts silicone masterbatch.

[0005] Preferably, the nano-SiO2 is modified with silane coupling agent KH-550, and its particle size distribution D50≤80nm.

[0006] Preferably, a nano-synergistic reinforcement system of "SiO2 + GQDs + LDHs" is also introduced: 1-3 parts of graphene quantum dots (GQDs) with a particle size ≤5nm are added to the halogen-free flame-retardant polypropylene material of the lithium battery film. 1-3 parts of layered double hydroxides (LDHs) are also added to the halogen-free flame-retardant polypropylene material of the lithium battery film.

[0007] The general chemical formula for layered double hydroxides is Mg6Al2(OH). 16 CO3·4H2O.

[0008] When graphene quantum dots (GQDs) are added, their huge specific surface area and abundant functional groups can act as "electron traps," effectively inhibiting the migration of lithium ions in the electrolyte and reducing the risk of leakage current.

[0009] GQDs, in synergy with nano-SiO2, can form a three-dimensional thermally conductive network in the matrix, rapidly diffusing heat laterally to avoid localized overheating and improve the material's thermal stability. Further addition of layered double hydroxides allows LDHs to decompose and absorb heat at high temperatures, releasing non-flammable gases (CO2 and H2O). This results in a gas-solid dual-phase flame-retardant synergistic effect with the ammonium polyphosphate / melamine cyanurate system, improving the limiting oxygen index and achieving a breakthrough in UL94V-0 flame retardant rating for thinner materials.

[0010] Preferably, the halogen-free flame-retardant polypropylene material of the lithium battery film further contains 5-8 parts of phase change material (PCM), wherein the phase change material is a shaped phase change material composed of n-octadecane and expanded graphite in a mass ratio of 7:3. The phase change material is pretreated to form PCM masterbatch, wherein the pretreatment method is as follows: n-octadecane and expanded graphite are melt-blended at 100±5℃ for 2-3 hours, followed by cooling and granulation.

[0011] By adding shape-stabilized phase change materials, the material activates its protective function in the early stages of battery thermal abuse (80-120℃). The phase change process of PCM from solid to liquid absorbs a large amount of heat (phase change enthalpy ≥180J / g), significantly slowing down the rate of temperature rise of the battery module and buying valuable time for the battery management system to trigger alarms or protective measures. Expanded graphite expands at higher temperatures and combines with the carbon layer formed by the flame-retardant system to construct a denser and more robust fire barrier.

[0012] A method for preparing a halogen-free flame-retardant polypropylene material for lithium battery films includes the following steps: S001. Add polypropylene, APP, MCA, nano-SiO2 and antioxidant to a high-speed mixer in proportion and stir at 150±5℃ for 10-15 minutes. S002. Add the mixture to a twin-screw extruder and melt-blend it at a gradient temperature of 170-200℃, while controlling the screw speed at 300-500 rpm. S003. The melt is cooled by water, pelletized, and dried to obtain masterbatch.

[0013] Preferably, the twin-screw extruder is equipped with four temperature ranges: Feeding section: 170±5℃; Compression section: 180±5℃; Metering range: 190±5℃; Machine head: 200±5℃.

[0014] Preferably, the lithium battery coating film made of the halogen-free flame-retardant polypropylene material of the above-mentioned lithium battery film has a film thickness of 0.15-0.5 mm, a longitudinal tensile strength ≥20 MPa, and a transverse elongation at break ≥120%.

[0015] Compared with the prior art, the beneficial effects of the present invention are: In this invention, the surface of nanoparticles is modified by using a silane coupling agent at 150°C, reducing the agglomerate particle size from 500nm to below 80nm; APP decomposition endothermics provide a physical barrier, and MCA releases ammonia gas upon heating to dilute combustible gases, forming a PN synergistic effect; a three-stage temperature control system of 170°C (feeding section), 185°C (compression section), and 200°C (metering section) is set up, combined with a variable frequency screw speed of 400-600rpm, to achieve uniform dispersion of nanoparticles. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of a method for preparing a halogen-free flame-retardant polypropylene material for lithium battery films according to the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only 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.

[0018] Table 1 shows the composition of each component in Examples 1-3 and Comparative Examples 1-2 of the present invention.

[0019] Table 2 shows the test results for the test items in Examples 1-3 and Comparative Examples 1-2 of the present invention.

[0020] As can be seen from Examples 1-3, the coating films prepared by this invention all achieve UL94V-0 rating, realizing highly efficient halogen-free flame retardancy. Meanwhile, their mechanical properties, especially elongation at break and impact strength, are far superior to those of Comparative Example 1 with high-filled aluminum hydroxide, exhibiting excellent flexibility and impact resistance.

[0021] The flame retardancy rating and mechanical properties of Comparative Example 2 (without compatibilizer) decreased significantly, demonstrating the key role of the pretreated nano-silica combustion aid in the system of this invention. Example

[0022] Composition: 58 parts copolymer PP, 25 parts APP, 10 parts MCA, 3 parts KH-550 modified nano-SiO2, 2 parts graphene quantum dots (3nm particle size), 2 parts layered double hydroxide, 0.5 parts antioxidant 1098 / 1680, and 1 part silicone masterbatch. Preparation method is the same as in Example 1. Example

[0023] Composition: 55 parts copolymer PP, 24 parts APP, 8 parts MCA, 3.5 parts nano SiO2, 0.5 parts antioxidant 1098 / 1680, 1 part silicone masterbatch, and 8 parts PCM masterbatch (prepared from n-octadecane: expanded graphite = 7:3). During preparation, the PCM masterbatch is premixed with the other components before twin-screw extrusion.

[0024] Comparative Example 3 (without nanosynergy and dynamic function) The composition was the same as that of Comparative Example 2 (i.e., without nano-SiO2).

[0025] Table 3 shows the test results of Examples 4-5 and Comparative Example 3.

[0026] Thermal runaway delay time test method: Cover the surface of a standard 18650 battery with the material, place it in an oven and heat it from room temperature at a rate of 5°C / min, and record the time when the battery thermal runaway occurs.

[0027] Analysis of the effects of Example 4: Table 3 shows that Example 4, even with an ultrathin thickness of 0.25 mm, still achieves a UL94V-0 rating and a limiting oxygen index as high as 35.5%, far exceeding Comparative Example 3. This demonstrates that the "SiO2-GQDs-LDHs" ternary nano-synergistic reinforcement system produces an unexpected synergistic effect of "1+1+1>3". This is because: "Electron Trapping" and Thermal Conductivity of GQDs: Nanoscale GQDs are uniformly dispersed in a polypropylene matrix, exhibiting a large specific surface area and high thermal conductivity. 2 Hybrid carbon structures can effectively adsorb and restrict the migration of lithium ions and electrons (manifested as Cl). - The migration rate is extremely low, only 2.5 × 10⁻⁶. -4 mg / cm 2 This reduces the risk of short circuits at the source. Simultaneously, GQDs and nano-SiO2 together construct a three-dimensional thermally conductive network, enabling rapid local heat dissipation and preventing premature material decomposition due to heat concentration. This enhances the overall thermal stability of the matrix, which is crucial for achieving ultra-thin flame retardant coatings.

[0028] The "dual function" of LDHs: When heated (above approximately 250°C), LDHs undergo laminar decomposition and hydroxyl dehydration, absorbing a large amount of heat and releasing CO2 and H2O. CO2 dilutes combustible gases, while H2O vapor cools the combustion interface. This works perfectly in synergy with the APP / MCA flame retardant system, functioning simultaneously in both the gas and condensation phases to construct a stronger and denser expanded char layer. This is the fundamental reason for the significant increase in the LOI value to 35.5%.

[0029] Analysis of the effects of Example 5: The most significant technical effect of Example 5 is that the thermal runaway delay time reaches 650 seconds, more than twice that of Comparative Example 3. This demonstrates that the dynamic flame-retardant mechanism introduced by the PCM plays a decisive role. Its mechanism of action is: The "thermal buffering" effect of PCM: When the battery begins to enter a state of thermal abuse, with the temperature rising to the 80-120℃ range, the n-octadecane in the halogen-free flame-retardant polypropylene material of the lithium battery film undergoes a solid-liquid phase transition. This process absorbs a large amount of heat (the phase transition enthalpy is as high as 185J / g), acting like a "thermal buffer" between the battery and the external environment, greatly slowing down the rate of temperature rise of the battery itself and buying critical time for the battery management system to issue warnings and intervene. This is a proactive and intelligent thermal management method that transcends the scope of traditional passive flame retardancy.

[0030] The "secondary barrier" function of expanded graphite: When the temperature continues to rise, the expanded graphite sheets in PCM expand rapidly due to heat, forming worm-like expanded graphite, which intertwines with the carbon layer formed by APP / MCA to form a denser and stronger protective layer, effectively isolating oxygen and heat. Therefore, its UL94 rating (V-1 at 0.25mm) is still better than Comparative Example 3 (V-2).

[0031] By comparing Examples 4 and 5 with Comparative Example 3, it is fully demonstrated that the present invention, through precise component design and synergistic mechanism, produces technical effects that cannot be achieved by a single component or traditional combination: Breaking the limits of ultra-thin halogen-free flame retardancy: achieving V-0 flame retardancy at a thickness of only 0.25mm.

[0032] It has achieved intelligent material function: upgrading from "passive protection" to "active intervention" and possessing dynamic thermal management capabilities.

[0033] The material is endowed with multiple safety features: it also has excellent flame retardancy, resistance to ion migration and thermal stability, providing comprehensive safety protection for lithium batteries.

[0034] A method for preparing a halogen-free flame-retardant polypropylene material for lithium battery films includes the following steps: S001. Add polypropylene, APP, MCA, nano-SiO2 and antioxidant to a high-speed mixer in proportion and stir at 150±5℃ for 10-15 minutes. S002. Add the mixture to a twin-screw extruder and melt-blend it at a gradient temperature of 170-200℃, while controlling the screw speed at 300-500 rpm. S003. The melt is cooled by water, pelletized, and dried to obtain masterbatch.

[0035] Preferably, the twin-screw extruder is equipped with four temperature ranges: Feeding section: 170±5℃; Compression section: 180±5℃; Metering range: 190±5℃; Machine head: 200±5℃.

[0036] The lithium battery coating film made of the halogen-free flame-retardant polypropylene material of the above-mentioned lithium battery film has a film thickness of 0.15-0.5 mm, a longitudinal tensile strength ≥20 MPa, and a transverse elongation at break ≥120%.

[0037] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A halogen-free flame-retardant polypropylene material for lithium battery films, characterized in that, Composed of the following components in parts by weight: 55-65 parts copolymer polypropylene; 20-30 parts ammonium polyphosphate; 5-15 parts melamine cyanurate; 2-5 parts nano-silica; 0.3-0.8 parts antioxidant 1098 / 168; 0.5-2.0 parts silicone masterbatch.

2. The halogen-free flame-retardant polypropylene material for lithium battery films according to claim 1, characterized in that: The nano-SiO2 was modified with silane coupling agent KH-550, and its particle size distribution D50≤80nm.

3. The halogen-free flame-retardant polypropylene material for lithium battery films according to claim 1, characterized in that: The halogen-free flame-retardant polypropylene material of the lithium battery film also contains 1-3 parts of graphene quantum dots with a particle size ≤5nm.

4. The halogen-free flame-retardant polypropylene material for lithium battery films according to claim 3, characterized in that: The halogen-free flame-retardant polypropylene material of the lithium battery film also contains 1-3 parts of layered double hydroxide, with the general chemical formula Mg6Al2(OH). 16 CO3·4H2O.

5. A halogen-free flame-retardant polypropylene material for a lithium battery film according to claim 1 or 2, characterized in that: The halogen-free flame-retardant polypropylene material of the lithium battery film also contains 5-8 parts of phase change energy storage material, which is a shaped phase change material composed of n-octadecane and expanded graphite in a mass ratio of 7:

3.

6. The halogen-free flame-retardant polypropylene material for lithium battery films according to claim 5, characterized in that: The phase change energy storage material is pretreated to form PCM masterbatch. The pretreatment method is as follows: n-octadecane and expanded graphite are melt-blended at 100±5℃ for 2-3 hours, and then cooled and granulated.

7. A method for preparing a halogen-free flame-retardant polypropylene material for lithium battery films, characterized in that, Includes the following steps: S001. Add polypropylene, APP, MCA, nano-SiO2 and antioxidant to a high-speed mixer in proportion and stir at 150±5℃ for 10-15 minutes. S002. Add the mixture to a twin-screw extruder and melt-blend it at a gradient temperature of 170-200℃, while controlling the screw speed at 300-500 rpm. S003. The melt is cooled by water, pelletized, and dried to obtain masterbatch.

8. The method for preparing a halogen-free flame-retardant polypropylene material for a lithium battery film according to claim 7, characterized in that: The twin-screw extruder is equipped with four temperature ranges: Feeding section: 170±5℃; Compression section: 180±5℃; Metering range: 190±5℃; Machine head: 200±5℃.

Images