Composite current collector base film and method of making same

Abstract

The present application relates to the field of thin film current collector manufacturing, and particularly relates to a composite current collector base film and a preparation method thereof. The method comprises the following steps: mixing octamercaptopropyl cage polysilsesquioxane with a solvent, adding a polymerization inhibitor and a catalyst, heating and adding glycidyl methacrylate dropwise to carry out constant-temperature reaction in the dark; through concentration, precipitation, suction filtration and drying, a cage polysilsesquioxane derivative containing carbon-carbon double bonds and / or epoxy groups is obtained; the modifier is mixed with a base resin, a free radical initiator and an antioxidant at high speed to prepare a master batch through reactive melt extrusion, cooling and granulation; the master batch is extruded and cast into a thick sheet, and then bidirectional stretching, heat setting and winding are carried out to obtain the composite current collector base film; the present application endows the composite current collector base film with excellent surface chemical activity, effectively solving the industry problems of strong surface inertness and poor bonding force of the subsequent metal layer of the traditional resin base film.

Description

Technical Field

[0001] This invention relates to the field of thin-film current collector manufacturing, and specifically to a composite current collector base film and its preparation method. Background Technology

[0002] The continuous charge-discharge cycles of batteries place extremely high demands on ensuring the safety of their internal operation. The ease of peeling off traditional pure metal foils and the thermal runaway caused by high-temperature thermal shrinkage of polymer base films are key factors leading to decreased battery safety. Therefore, effectively improving the high-temperature dimensional stability and interfacial adhesion of composite current collector base films is a crucial foundation for ensuring the long-term safe and efficient operation of batteries. In existing composite current collector technologies, the bonding between the polymer base film and the metal layer mainly relies on physical interactions, resulting in poor interfacial adhesion. Simultaneously, traditional pure metal foils are prone to fatigue fracture during charge-discharge cycles, while polymer base films suffer from high-temperature thermal shrinkage. Furthermore, existing composite current collectors are highly susceptible to phase separation and interfacial debonding between the metal layer and the matrix under high-temperature stress fields, and the aggregation effect of nanoparticles severely weakens the mechanical coherence of the base film.

[0003] This invention uses a matrix resin and a multifunctional modifier as its core components. Through physical melt blending and chemical reactive extrusion processes, a dense physicochemical dual crosslinking network is constructed within the matrix. This invention also uses in-situ reactive grafting and free thiol coordination to enrich thiol-containing segments on the surface and provide metal binding sites, thereby improving the bonding force between the composite current collector base film and the metal layer and the high-temperature dimensional stability, ensuring the long-term stable service of the composite current collector. Summary of the Invention

[0004] The purpose of this invention is to provide a composite current collector base film and its preparation method. Existing modified base film preparation technologies have significant shortcomings in the face of battery charge-discharge cycles and high-temperature stress fields. These shortcomings include the tendency for phase separation and interfacial debonding between the metal layer and the base film, and the potential for thermal runaway caused by high-temperature thermal shrinkage of the polymer base film. This invention improves interfacial adhesion and high-temperature dimensional stability by constructing a physicochemical dual crosslinking network and inducing the enrichment of thiol-containing segments on the surface. Specifically, the technical solution of this invention includes the following steps:

[0005] The base resin, multifunctional modifier, free radical initiator and antioxidant are mixed at high speed to obtain a homogeneous mixture; the homogeneous mixture is added to an extruder for reactive melt extrusion, cooled and pelletized to obtain modified composition masterbatch; the modified composition masterbatch is extruded, cast into thick sheets, cooled and fed into a biaxial stretching machine for biaxial stretching, heat setting and winding to obtain a composite current collector base film.

[0006] The preparation of the multifunctional modifier includes the following steps:

[0007] Octadecyl-mercaptopropyl cage-type polysilsesquioxane is mixed with a solvent and stirred to dissolve. A polymerization inhibitor and a catalyst are added, and the mixture is heated to 40-60°C under a protective gas atmosphere. Glycidyl methacrylate is added dropwise, and the reaction is carried out under constant temperature and in the dark. After the reaction is completed, the reaction solution is concentrated, added dropwise to a precipitant to precipitate, filtered, washed, and dried to obtain a multifunctional modifier. The multifunctional modifier is a cage-type polysilsesquioxane derivative containing carbon-carbon double bonds and hydroxyl groups in its molecular structure.

[0008] Optionally, the weight ratio of the matrix resin, multifunctional modifier, free radical initiator and antioxidant is 100:(1.0-10.0):(0.01-0.05):(0.1-0.5).

[0009] Optionally, the matrix resin is selected from any one or more of polypropylene, polyethylene terephthalate, polyimide and polyphenylene sulfide;

[0010] The free radical initiator is selected from any one of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, dicumyl peroxide, and benzoyl peroxide;

[0011] The antioxidant is a mixture of the hindered phenolic antioxidant pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and the phosphite antioxidant tris(2,4-di-tert-butylphenyl) phosphite, and the mass ratio of the hindered phenolic antioxidant pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] to the phosphite antioxidant tris(2,4-di-tert-butylphenyl) phosphite is 1:(1-2).

[0012] Optionally, the mass ratio of octamercaptopropyl cage-type polysilsesquioxane, solvent, polymerization inhibitor, catalyst and glycidyl methacrylate is (8-12):(70-100):(0.05-0.15):(0.2-0.5):(4-8).

[0013] Optionally, the solvent is anhydrous tetrahydrofuran; the polymerization inhibitor is hydroquinone; the catalyst is triethylamine; the precipitant is n-hexane; and the protective gas is nitrogen.

[0014] Optionally, the heating temperature is 40-60℃; the reaction time is 10-14h in the dark and at a constant temperature; the drying temperature is 25℃ and the drying time is 20-28h.

[0015] Optionally, the temperature of reactive melt extrusion is 180-210℃, and the screw speed is 180-220rpm;

[0016] Biaxial stretching includes longitudinal stretching and transverse stretching. The longitudinal stretching ratio is 4-6 times and the longitudinal stretching temperature is 110-130℃; the transverse stretching ratio is 5-7 times and the transverse stretching temperature is 145-165℃.

[0017] The heat setting temperature is 155-175℃.

[0018] Optionally, a co-rotating twin-screw extruder is used for reactive melt extrusion;

[0019] The modified composition masterbatch was extruded using a single-screw extruder and cast into thick sheets through a T-die.

[0020] The casting temperature is 210-230℃; the thickness of the composite current collector base film is 4-5μm.

[0021] A composite current collector base membrane prepared by a method for preparing a composite current collector base membrane.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. This invention prepares cage-type polysilsesquioxane derivatives containing carbon-carbon double bonds and hydroxyl groups as multifunctional modifiers, and performs reactive melt extrusion with matrix resins to successfully graft or introduce active groups into the matrix network; this endows the composite current collector base film with excellent surface chemical activity, effectively solving the technical defects of traditional resin base films with strong surface inertness and poor adhesion of subsequent metal layers.

[0024] 2. This invention employs a biaxial stretching process that combines longitudinal and transverse stretching, along with the reinforcing effect of a cage-type polysilsesquioxane rigid framework. This process not only produces an ultra-thin base film with a thickness of only four to five micrometers, but also significantly improves the mechanical strength and dimensional stability of the film. This effectively overcomes the defects of ultra-thin current collectors that are prone to breakage or severe deformation during battery processing and cycling.

[0025] 3. The formula scientifically combines hindered phenolic antioxidants and phosphite antioxidants, which work synergistically to resist oxidation in the system. This not only effectively inhibits the thermal degradation and oxidative chain scission of the matrix resin and modifier during reactive extrusion and casting at temperatures as high as 180 to 230 degrees Celsius, but also significantly improves the heat aging resistance and long-term structural stability of the final composite current collector base film.

[0026] 4. In terms of process, a step-by-step processing strategy is adopted, which first prepares the modified composition masterbatch by reactive melt extrusion through a co-rotating twin-screw extruder, and then performs casting molding through a single-screw extruder. This method utilizes the strong shear and efficient dispersion capabilities of the twin screw to achieve uniform dispersion of the multifunctional modifier in the base resin, avoids the agglomeration phenomenon that is easy to occur by direct addition, and ensures the high consistency of the performance of each area of ​​the entire roll of base film.

[0027] 5. In the synthesis of the multifunctional modifier, the reaction is strictly controlled under nitrogen protection, light-proof and constant temperature conditions, and hydroquinone is introduced as a polymerization inhibitor. These specific process conditions reduce the premature self-polymerization or cross-linking failure of highly active carbon-carbon double bonds during the synthesis and purification process, which helps to stabilize the preparation of high-purity modifiers and provides a reliable raw material guarantee for subsequent base film modification. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a comprehensive durability trend chart for the present invention; Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] Example 1: A method for preparing a composite current collector base film, comprising the following steps: mixing a matrix resin, a multifunctional modifier, a free radical initiator, and an antioxidant at high speed to obtain a homogeneous mixture; adding the homogeneous mixture to an extruder for reactive melt extrusion, cooling, and pelletizing to obtain a modified composition masterbatch; extruding the modified composition masterbatch, casting it into a thick sheet, cooling it, and then feeding it into a biaxial stretching machine for biaxial stretching, heat setting, and winding to obtain a composite current collector base film;

[0032] The preparation of the multifunctional modifier includes the following steps: mixing octamercaptopropyl cage-type polysilsesquioxane with a solvent, stirring to dissolve, adding a polymerization inhibitor and a catalyst, heating to 40-60℃ in a protective gas atmosphere, adding glycidyl methacrylate dropwise, and reacting at a constant temperature in the dark; after the reaction is completed, concentrating the reaction solution, adding it dropwise to a precipitant to precipitate, filtering, washing, and drying to obtain the multifunctional modifier, which is a cage-type polysilsesquioxane derivative containing carbon-carbon double bonds and hydroxyl groups in its molecular structure;

[0033] The preparation method of composite current collector base film organically combines physical melt blending with chemical reactive extrusion to improve the problems of easy peeling of traditional pure metal foil during charge and discharge cycles and thermal runaway caused by high temperature thermal shrinkage of polymer base film.

[0034] In the preparation method of composite current collector base film, the matrix resin and multifunctional modifier and other components are first mixed at high speed to achieve preliminary uniform dispersion of each component, so as to reduce physical entanglement and aggregation between the macromolecular chains of the matrix resin. The high speed mixing speed is controlled at 1000 rpm and the mixing time is 10 min to ensure that each component is fully dispersed and that the initiator does not decompose prematurely due to excessive frictional heat generation.

[0035] The homogeneous mixture triggers a reactive melt extrusion process in the strong shear field of the extruder. During this process, the free radical initiator is thermally decomposed and induces the carbon-carbon double bonds of the multifunctional modifier to undergo an in-situ grafting reaction with the main chain of the matrix resin. The cooling after reactive melt extrusion is water-cooled, and the cooling water temperature is controlled at 25°C.

[0036] After extrusion granulation, the modified composition masterbatch obtained is subjected to casting and biaxial stretching. The cooling after casting into thick sheets is achieved by cooling rollers, with the temperature of the cooling rollers controlled at 70°C. The orientation movement of the molecular chains promotes the migration and enrichment of mercapto-containing segments to the surface of the base film under the action of orientation stress. In the preparation step of the multifunctional modifier, octamercaptopropyl cage-type polysilsesquioxane is used as a precursor, and the epoxy groups of glycidyl methacrylate undergo nucleophilic ring-opening addition under the alkaline environment of the catalyst.

[0037] The addition of glycidyl methacrylate was controlled to take 1 hour to prevent excessive exothermic reactions. This addition process generated a cage-like polysilsesquioxane derivative containing both free thiol groups and reactive double bonds. The reaction solution was obtained by reacting in the dark at a constant temperature. In this embodiment, the multifunctional modifier was clearly identified as a cage-like polysilsesquioxane derivative containing both carbon-carbon double bonds and hydroxyl groups in its molecular structure, providing a unique and definite reaction product.

[0038] After the reaction is completed, the reaction solution is concentrated in a rotary evaporator at a controlled temperature of 40°C and a vacuum of -0.09 MPa to gently remove most of the solvent. After concentration, precipitation, and filtration, anhydrous ethanol is used as the washing solvent, with an amount three times the mass of the precipitate, and the washing is performed three times to fully remove unreacted monomers and catalysts.

[0039] The room temperature in the subsequent drying step is a single value of 25°C, which is carried out in a vacuum drying oven to avoid double bond crosslinking caused by high temperature. The introduction of this nanoframework not only avoids the phase separation defects caused by conventional physical blending, but also endows the base film with excellent high-temperature dimensional stability through a dual crosslinking network of physical and chemical properties.

[0040] The weight ratio of the matrix resin, multifunctional modifier, free radical initiator and antioxidant is 100:1.0:0.01:0.1;

[0041] The weight ratio of the matrix resin, multifunctional modifier, free radical initiator and antioxidant is set to the lower limit value mentioned above to reflect the interfacial anchoring effect under the low concentration modifier system. This weight ratio ensures that sufficient free mercapto groups are provided for the coordination bonding of the subsequent metal conductive layer while minimizing the interference of exogenous additives on the bulk mechanical properties of the matrix resin.

[0042] The lower content of free radical initiator reduces the β-chain scission degradation side reaction of polymer chains under high temperature shear environment, and maintains the critical threshold of melt rheological properties; this embodiment reflects the process adaptability under the basic ratio and demonstrates the stability of this technical solution in conventional application scenarios;

[0043] The matrix resin is selected from polypropylene; the free radical initiator is selected from 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane; the antioxidant is a mixture of hindered phenolic antioxidant pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and phosphite antioxidant tris(2,4-di-tert-butylphenyl) phosphite, with a mass ratio of 1:1;

[0044] The matrix resin is selected from polypropylene to utilize its excellent insulation and processing flowability as the carrier matrix for the composite base film; the free radical initiator is selected from 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane to match the melt processing temperature range of polypropylene. Its half-life matches the processing temperature, so that the grafting reaction is mainly concentrated in the middle and later sections of the extruder screw, avoiding gelation defects caused by premature crosslinking.

[0045] A compound antioxidant system composed of hindered phenolic antioxidants and phosphite antioxidants in a specific mass ratio synergistically inhibits the oxidative degradation of polymer chains through a cascade mechanism of capturing carbon center free radicals and decomposing hydrogen peroxides. This antioxidant system helps to improve the chemical stability of the base film in long-term electrochemical service environments.

[0046] The mass ratio of octamercaptopropyl cage-type polysilsesquioxane, solvent, polymerization inhibitor, catalyst, and glycidyl methacrylate is 8:70:0.05:0.2:4.

[0047] The mass ratio of octamercaptopropyl cage-type polysilsesquioxane, solvent, polymerization inhibitor, catalyst, and glycidyl methacrylate was configured at the lower limit, which strictly controlled the stoichiometric ratio of the nucleophilic ring-opening reaction. This mass ratio setting ensures that a limited number of carbon-carbon double bonds are attached to each cage-type polysilsesquioxane backbone on average, while retaining most of the unreacted free mercapto groups. This asymmetric distribution state optimizes the density of metal coordination binding sites on the base film surface while ensuring the activity of the grafting reaction, effectively overcoming the problem of low grafting rate caused by kinetic mismatch.

[0048] The solvent is anhydrous tetrahydrofuran; the polymerization inhibitor is hydroquinone; the catalyst is triethylamine; the precipitant is n-hexane; and the protective gas is nitrogen.

[0049] Anhydrous tetrahydrofuran was used as the solvent to provide suitable dielectric constant and solubility parameters, ensuring sufficient collision of reactants in a homogeneous system. The introduction of hydroquinone as a polymerization inhibitor aimed to competitively consume trace amounts of thermogenic free radicals, preventing glycidyl methacrylate from undergoing self-polymerization during heating. The basic center provided by the catalyst triethylamine effectively lowered the activation energy barrier for ring opening of epoxy groups. The precipitant n-hexane utilized its polarity difference to promote the rapid crystallization and precipitation of the target product, while the protective gas nitrogen isolated oxygen from unintended oxidative interference to thiol groups. The combined use of this series of reagents ensured the purity of the molecular structure of the multifunctional modifier.

[0050] The heating temperature was 40℃; the reaction time was 10 hours under constant temperature in the dark; the drying temperature was 25℃ and the drying time was 20 hours.

[0051] The heating temperature and the time for the light-shielded isothermal reaction were set to these low-temperature, short-time conditions to suppress the side reactions of thioether bond breakage or double bond thermal cross-linking that may be induced at high temperatures. The combination of drying temperature and drying time effectively removed residual volatile solvent molecules and avoided the generation of bubbles during the subsequent high-temperature extrusion process. The synergistic control of these thermodynamic and kinetic parameters indicates that the reaction system still achieved stable conversion of the target product under mild conditions, demonstrating the mildness and efficiency of the preparation process.

[0052] The reactive melt extrusion temperature is 180℃, and the screw speed is 180rpm; the longitudinal stretching ratio is 4 times, and the longitudinal stretching temperature is 110℃; the transverse stretching ratio is 5 times, and the transverse stretching temperature is 145℃; the heat setting temperature is 155℃.

[0053] Setting the temperature and screw speed of reactive melt extrusion to this lower limit range allows for sufficient plasticization of the polymer melt while providing a longer residence time for the macromolecular chain segments to complete the grafting reaction. The longitudinal and transverse stretching parameters of biaxial stretching induce polypropylene crystals to deform and rearrange along the direction of force by applying a moderate mechanical stress field. The heat setting temperature effectively eliminates the internal stress accumulated during stretching. The precise control of this set of process parameters suppresses the high-temperature thermal shrinkage tendency of the base film, demonstrating the synergistic improvement effect of physical orientation and chemical crosslinking on dimensional stability.

[0054] Reactive melt extrusion was performed using a co-rotating twin-screw extruder; the modified composition masterbatch was extruded using a single-screw extruder and cast into thick sheets through a T-die; the temperature for casting into thick sheets was 210℃; the thickness of the composite current collector base film was 4μm;

[0055] The co-rotating twin-screw extruder used for reactive melt extrusion, with its excellent surface renewal capability and mixing efficiency, ensures the nanoscale uniform dispersion of the multifunctional modifier in the matrix resin. The relatively low temperature setting for casting into thick sheets helps to mitigate the thermal hysteresis effect after the melt leaves the die, preventing excessive crystallinity from causing subsequent stretching and film breakage. The thickness of the composite current collector base film is controlled at the micrometer level, which effectively improves the internal space utilization of the battery while ensuring puncture resistance and mechanical strength, highlighting the advantages of this technical solution in the engineering application of thin-film current collector manufacturing.

[0056] Example 2: The weight ratio of matrix resin, multifunctional modifier, free radical initiator, and antioxidant was 100:5.0:0.03:0.3. This weight ratio was set at a median level to balance the mechanical toughness and surface coordination activity of the base film. This weight ratio, by moderately increasing the abundance of the multifunctional modifier, constructed a denser physicochemical double crosslinking node in the matrix resin network. The appropriately increased free radical initiator provided sufficient active primary free radicals during the reactive extrusion stage, ensuring a steady increase in the carbon-carbon double bond grafting rate.

[0057] This embodiment verifies the robustness of the formulation system under normal operating conditions. This formulation state enables the composite current collector base film to achieve a good performance balance between peel strength and thermal shrinkage rate.

[0058] The reactive melt extrusion temperature is 195℃, and the screw speed is 200rpm; the longitudinal stretching ratio is 5 times, and the longitudinal stretching temperature is 120℃; the transverse stretching ratio is 6 times, and the transverse stretching temperature is 155℃; the heat setting temperature is 165℃.

[0059] The median combination of temperature and screw speed in reactive melt extrusion provides ideal shear heat and mixing strength for the polymer melt, effectively avoiding modifier agglomeration caused by local overheating. The synergistic effect of biaxial stretching parameters and heat setting temperature promotes the efficient enrichment of thiol-containing segments onto the base film surface at a suitable molecular chain relaxation rate. This set of process parameters overcomes the risk of kinetic mismatch and ensures the stability of continuous roll-to-roll production.

[0060] Example 3: The weight ratio of the matrix resin, multifunctional modifier, free radical initiator and antioxidant is 100:10.0:0.05:0.5;

[0061] The weight ratio of matrix resin, multifunctional modifier, free radical initiator and antioxidant was set as the upper limit critical threshold, and the crosslinking kinetics of the high-concentration hybrid nanoframework system were investigated. This weight ratio promotes the formation of a rigid three-dimensional cage-like polysilsesquioxane interpenetrating network inside the polymer matrix, which significantly restricts the free volume expansion of amorphous molecular chain segments at high temperature.

[0062] The increased antioxidant content effectively quenched the deep oxidation chain reaction that may be induced by excessive free radical initiators. This formulation system verified that the base film can still maintain excellent dimensional stability under high thermodynamic shock.

[0063] The heating temperature was 60℃; the reaction time was 14 hours under constant temperature in the dark; the drying temperature was 25℃ and the drying time was 28 hours.

[0064] The upper limits set for heating temperature and the time for isothermal reaction in the dark are intended to accelerate the nucleophilic ring-opening addition process of sterically hindered epoxy groups, ensuring that the precursor conversion rate approaches the thermodynamic limit. The extension of drying temperature and drying time eliminates the plasticizing effect caused by trace solvents in the system. This heat treatment strategy indicates that the crystal structure integrity of the multifunctional modifier has reached a better state, laying the material basis for subsequent efficient grafting.

[0065] Example 4: The mass ratio of octamercaptopropyl cage-type polysilsesquioxane, solvent, polymerization inhibitor, catalyst, and glycidyl methacrylate was 9:80:0.08:0.3:5;

[0066] The mass ratio of octamercaptopropyl cage-type polysilsesquioxane, solvent, polymerization inhibitor, catalyst and glycidyl methacrylate was configured to be relatively low. By fine-tuning the stoichiometric ratio of the precursor and the reactant monomer, the distribution density of free mercapto groups and carbon-carbon double bonds on the surface of the multifunctional modifier was optimized.

[0067] This mass ratio not only reduces the viscosity of the reaction system to promote mass and heat transfer, but also enhances the flexibility of the thiol-containing segments while ensuring sufficient crosslinking density, making it easier for them to overcome steric hindrance and migrate to the surface during film formation, demonstrating the robustness of the synthesis process under different material concentrations.

[0068] Reactive melt extrusion was performed using a co-rotating twin-screw extruder; the modified composition masterbatch was extruded using a single-screw extruder and cast into thick sheets through a T-die; the temperature for casting into thick sheets was 215℃; the thickness of the composite current collector base film was 4.2μm;

[0069] Setting the temperature for casting to a relatively low value helps to slow down the relaxation rate of polymer chain segments at the die head, preserving more of the extrusion orientation memory effect; the thickness of the composite current collector base film is controlled at 4.2 micrometers, which reduces the absolute thermal shrinkage deformation of the material while ensuring the base film's resistance to heat penetration during subsequent magnetron sputtering; this set of forming parameters effectively avoids the defect of uneven film thickness, marking the high adaptability of the casting process to nanocomposite systems.

[0070] Example 5: The matrix resin is selected from polyethylene terephthalate; the free radical initiator is selected from dicumyl peroxide; the antioxidant is a mixture of hindered phenolic antioxidant pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and phosphite antioxidant tris(2,4-di-tert-butylphenyl) phosphite, with a mass ratio of 1:2;

[0071] The matrix resin is selected from polyethylene terephthalate, which utilizes the inherent rigidity and heat resistance brought by the benzene ring structure in its molecular chain. Combined with the high decomposition activation energy of the free radical initiator dicumyl peroxide, precise grafting control is achieved at higher processing temperatures. The higher antioxidant mass ratio enhances the auxiliary antioxidant function of phosphite antioxidants in decomposing hydrogen peroxide.

[0072] In this embodiment, the antioxidant adopts the standard chemical nomenclature, specifically the hindered phenolic antioxidant pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and the phosphite antioxidant tris(2,4-di-tert-butylphenyl) phosphite with standard structural symbols and parentheses. This clarifies the chemical linkage relationship and effectively inhibits the transesterification and thermal degradation side reactions of polyethylene terephthalate under high-temperature shear. This matrix resin system expands the application boundaries of composite current collectors in high-voltage real-density batteries.

[0073] The reactive melt extrusion temperature is 205℃, and the screw speed is 210 rpm; the longitudinal stretch ratio is 5.5 times, and the longitudinal stretching temperature is 125℃; the transverse stretch ratio is 6.5 times, and the transverse stretching temperature is 160℃; the heat setting temperature is 170℃.

[0074] The combination of high temperature and high screw speed in reactive melt extrusion matched the high melting enthalpy and viscous flow activation energy of polyethylene terephthalate, ensuring in-situ deagglomeration and uniform dispersion of the multifunctional modifier in the polar matrix. The increase in longitudinal and transverse stretching ratios promoted deeper slip and reconstruction of the polymer crystal planes. With the increase in heat setting temperature, the orientation structure was further solidified and deep surface enrichment of mercapto-containing segments was induced. This process path verified the feasibility of thermodynamically controlling interfacial coordination activity in polar polymer systems.

[0075] Comparative Example 1: This comparative example provides a preparation scheme for a pure polypropylene base film and a composite current collector, which is intended as a control group to highlight the chemical anchoring effect of the multifunctional modifier. The scheme completely excludes the multifunctional modifier and free radical initiator in the formulation system, and only uses 100 parts of isotactic polypropylene chips and 0.2 parts of compound antioxidant for simple physical melt extrusion.

[0076] The subsequent casting, biaxial stretching, and vacuum magnetron sputtering copper plating processes were all kept highly consistent with the conditions in Example 2. Since the base film surface exhibits typical chemical inertness and lacks polar coordination groups, the copper seed layer and the polypropylene matrix can only be bonded by weak van der Waals forces and physical-mechanical interlocking caused by surface roughness.

[0077] This control design demonstrates the problem of insufficient interfacial adhesion of traditional polymer-based films when dealing with electrolyte swelling and thermal stress.

[0078] In addition, to examine the trend of the core raw material ratio outside the defined range, an additional control group with a low modifier concentration was set up in this comparative example, in which the amount of multifunctional modifier was reduced to 0.5 parts. The results showed that due to the low content of modifier, the base film surface could not form a sufficiently dense number of coordination binding sites, resulting in an initial peel strength of only 0.85 N / mm, and the peel strength retention rate after aging dropped to 65.4%, which is difficult to meet the interfacial bonding force requirements of high-strength current collectors, demonstrating the necessity of limiting the lower limit of multifunctional modifier.

[0079] Comparative Example 2: This comparative example provides a conventional physical blending modified base film preparation scheme, which aims to verify the irreplaceability of in-situ reactive grafting and free thiol coordination mechanism; the scheme replaces the multifunctional modifier in the formulation of Example 2 with an equal amount of ordinary octamethyl cage-type polysilsesquioxane that does not have reactive carbon-carbon double bonds and free thiol groups, and simultaneously eliminates the free radical initiator.

[0080] Due to the lack of chemical bonding mechanism, ordinary octamethyl cage-type polysilsesquioxane can only be dispersed in polypropylene matrix by physical filling. Under high temperature tensile stress field, it is very easy to undergo phase separation and interfacial debonding. The base film surface lacks active sites that can coordinate covalently bond with metal atoms, resulting in relatively limited improvement in the adhesion of subsequent copper plating layer.

[0081] This physical blending scheme cannot effectively improve the problem of metal layer detachment, and the agglomeration effect of nanoparticles reduces the mechanical coherence of the base film. Meanwhile, in order to examine the impact of changes in process parameter boundaries, this comparative example additionally sets up a control group with tensile parameters exceeding the limits. Based on Example 2, the longitudinal tensile ratio is increased to 8 times and the transverse tensile ratio is increased to 9 times.

[0082] Tests revealed that excessively high stretching ratios led to over-orientation of polypropylene macromolecular chains and severe stress concentration. This not only resulted in frequent film breakage and band rupture during stretching, but also caused the base film, after barely forming a film, to experience a surge in longitudinal and transverse thermal shrinkage rates of 4.2% and 3.8% respectively under 150℃ / 1h conditions, resulting in a loss of dimensional stability. This strongly supports the critical effect of the stretching parameter range setting in this invention.

[0083] Verification test: In order to systematically evaluate the comprehensive service performance of the composite current collector base film and the composite current collector of the present invention, multi-dimensional environmental tests were carried out on the samples prepared in Examples 1 to 5 and Comparative Examples 1 to 2. The purpose of this verification test is to quantitatively analyze the evolution of technical indicators in three core dimensions after the introduction of the multifunctional modifier: interfacial peel strength, electrolyte chemical stability and high temperature thermal shrinkage rate, so as to confirm the synergistic gain effect brought about by the physicochemical dual crosslinking network and the mercapto coordination mechanism.

[0084] Testing standards: The interface bonding performance is standardized and determined according to the GB / T2790-1995 test method for peel strength of adhesives at 180 degrees Celsius; the resistance to electrolyte chemical stability is based on the actual service environment inside commercial lithium-ion batteries, and a 1.0 mol / L lithium hexafluorophosphate solution is used as the aging immersion medium; the high temperature dimensional stability assessment strictly follows the 150℃ stress-free heat shrinkage test standard commonly used in the battery separator and base film industry to ensure that the test data is scientific, objective and comparable.

[0085] The specific testing process is as follows: In the peel strength test, a high-precision electronic tensile testing machine was used to peel the interface between the copper layer and the base film at a constant rate. The steady-state peel force was recorded and the initial peel strength was calculated. In the electrolyte aging test, the cut standard composite current collector sample was completely immersed in a 1:1 volume ratio of ethylene carbonate and diethyl carbonate mixed electrolyte and placed in a 60°C constant temperature aging chamber for 30 days. After the aging cycle was completed, the sample was taken out, washed with deionized water and vacuum dried. Then, a 180° peel strength test was performed again to examine the anti-swelling and attenuation ability of the interfacial coordination bonds.

[0086] In the heat shrinkage rate test, the base film was precisely cut into 10 cm x 10 cm square samples, which were then placed flat on a heat-resistant glass plate covered with talc to eliminate the frictional resistance of the substrate. They were then pushed into a forced convection oven at 150°C for 1 hour of stress-free heat treatment. After the samples cooled naturally to room temperature, the longitudinal and transverse dimensional changes were read using a two-dimensional image measuring instrument, and the corresponding heat shrinkage rate percentages were calculated. In the thermo-oxidative aging resistance test, the oxidation induction period was determined using a differential scanning calorimeter.

[0087] Approximately 5 mg of sample was placed in an aluminum crucible and heated to 200 °C at a rate of 20 °C / min under a nitrogen atmosphere and held at that temperature for 5 min. Then, the atmosphere was quickly switched to oxygen. The time from the introduction of oxygen to the start of the exothermic oxidation peak in the DSC curve was recorded as the oxidation induction period, in order to investigate the effect of different antioxidant ratios on the long-term antioxidant performance of the base film.

[0088]

[0089] Table 1 Performance test data of Examples 1-5 and Comparative Examples 1-2

[0090] Combining Table 1 and Figure 1 Experimental data show that the preparation method of the composite current collector base film effectively improves the performance bottleneck of traditional polymer base films; as shown in Table 1, the initial peel strength of Examples 1 to 5 all exceeded the critical threshold of 1.5 Newtons per millimeter, and maintained a retention rate of over 95% after electrolyte aging. The trend of peel strength retention rate is as follows. Figure 1 As shown, this confirms that the free thiol groups enriched on the surface and the in-situ coordinated covalent bonds between metal atoms have good resistance to swelling and chemical corrosion, effectively eliminating the risk of delamination failure caused by physical and mechanical bonding in the comparative example.

[0091] Regarding high-temperature dimensional stability, the longitudinal and transverse thermal shrinkage rates of all embodiments were suppressed to below 1.0%, especially Example 5, which used polyethylene terephthalate, exhibited good heat resistance rigidity. This heat shrinkage resistance effect is attributed to the cage-like polysilsesquioxane three-dimensional rigid skeleton introduced by reactive grafting. The physicochemical double crosslinking network formed by this skeleton inside the matrix resin effectively anchors the molecular chain segments in the amorphous region, suppressing their thermodynamic relaxation and shrinkage under high-temperature conditions.

[0092] This series of embodiments demonstrates the performance evolution under different process parameter gradients, verifying the robustness and process adaptability of this technical solution under different material systems and processing windows; furthermore, from Table 1 and... Figure 1 As can be seen, the oxidation induction period of each embodiment is significantly longer than that of the comparative example, further confirming the significant effect of the scientific combination of hindered phenolic and phosphite antioxidants in the formulation on improving the long-term thermo-oxidative aging resistance of the base film.

[0093] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a composite current collector-based membrane, characterized in that, Includes the following steps: The base resin, multifunctional modifier, free radical initiator and antioxidant are mixed at high speed to obtain a homogeneous mixture; the homogeneous mixture is added to an extruder for reactive melt extrusion, cooled and pelletized to obtain modified composition masterbatch; the modified composition masterbatch is extruded, cast into thick sheets, cooled and fed into a biaxial stretching machine for biaxial stretching, heat setting and winding to obtain a composite current collector base film. The preparation of the multifunctional modifier includes the following steps: Octapercaptopropyl cage-type polysilsesquioxane is mixed with a solvent and stirred to dissolve. A polymerization inhibitor and a catalyst are added, and the mixture is heated to 40-60°C under a protective gas atmosphere. Glycidyl methacrylate is added dropwise, and the reaction is carried out under constant temperature in the dark. After the reaction is completed, the reaction solution is concentrated, precipitated by adding dropwise to a precipitant, filtered, washed, and dried to obtain a multifunctional modifier. The multifunctional modifier is a cage-type polysilsesquioxane derivative containing carbon-carbon double bonds and hydroxyl groups in its molecular structure. The matrix resin is selected from any one or more of polypropylene, polyethylene terephthalate, polyimide and polyphenylene sulfide; The antioxidant is a mixture of the hindered phenolic antioxidant pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and the phosphite antioxidant tris(2,4-di-tert-butylphenyl) phosphite, and the mass ratio of the hindered phenolic antioxidant pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] to the phosphite antioxidant tris(2,4-di-tert-butylphenyl) phosphite is 1:(1-2); The mass ratio of octamercaptopropyl cage-type polysilsesquioxane, solvent, polymerization inhibitor, catalyst and glycidyl methacrylate is (8-12):(70-100):(0.05-0.15):(0.2-0.5):(4-8); The temperature for reactive melt extrusion is 180-210℃, and the screw speed is 180-220 rpm; Biaxial stretching includes longitudinal stretching and transverse stretching. The longitudinal stretching ratio is 4-6 times and the longitudinal stretching temperature is 110-130℃; the transverse stretching ratio is 5-7 times and the transverse stretching temperature is 145-165℃. The heat setting temperature is 155-175℃; Reactive melt extrusion is performed using a co-rotating twin-screw extruder; The modified composition masterbatch was extruded using a single-screw extruder and cast into thick sheets through a T-die. The casting temperature is 210-230℃; the thickness of the composite current collector base film is 4-5μm.

2. The method for preparing a composite current collector-based membrane according to claim 1, characterized in that, The weight ratio of the matrix resin, multifunctional modifier, free radical initiator and antioxidant is 100:(1.0-10.0):(0.01-0.05):(0.1-0.5).

3. The method for preparing a composite current collector-based membrane according to claim 1, characterized in that, The free radical initiator is selected from any one of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, dicumyl peroxide, and benzoyl peroxide.

4. The method for preparing a composite current collector-based membrane according to claim 1, characterized in that, The solvent is anhydrous tetrahydrofuran; the polymerization inhibitor is hydroquinone; the catalyst is triethylamine; the precipitant is n-hexane; and the protective gas is nitrogen.

5. The method for preparing a composite current collector-based membrane according to claim 1, characterized in that, The heating temperature is 40-60℃; the reaction time is 10-14h in the dark and at a constant temperature; the drying temperature is 25℃ and the drying time is 20-28h.

6. A composite current collector base film prepared by the method of any one of claims 1-5.

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