Modified pet-based composite foil current collector and preparation method, pole piece and lithium ion battery

Abstract

The application belongs to the field of batteries, and particularly relates to a modified PET-based composite foil current collector, a preparation method, a pole piece and a lithium ion battery. The modified PET-based composite foil current collector comprises a modified PET base material and metal layers arranged on both sides of the modified PET base material; the modified PET base material comprises a PET base material and a metal oxide arranged in the PET base material; and the application achieves the best effect in terms of forming an effective high-resistance area quickly to significantly delay temperature rise and inhibit thermal runaway through specific proportion Al2O3 / TiO2 synergistic modification and optimized PET layer thickness.

Description

Technical Field

[0001] This invention belongs to the field of batteries, specifically relating to a modified PET-based composite foil current collector and its preparation method, an electrode, and a lithium-ion battery. Background Technology

[0002] Currently, commercially available lithium-ion batteries, especially high-energy-density systems, generally use 8-12μm thick pure aluminum foil as the positive electrode current collector. This homogeneous metal structure presents a fundamental contradiction in terms of safety: on the one hand, its excellent longitudinal (thickness direction) conductivity ensures low internal resistance; on the other hand, when the battery experiences a local short circuit due to internal defects, dendrite growth, or external physical impacts (such as puncture or extrusion), this characteristic drastically accelerates the thermal runaway process.

[0003] The design of traditional PET-based composite aluminum foil, with PET as the intermediate insulating layer, has attracted much attention. Its initial design intention was to utilize the insulating properties and low melting point of the polymer layer to melt and physically isolate the aluminum layers on both sides during a short circuit, theoretically achieving a "melting" function. However, the glass transition temperature (Tg) of traditional PET is approximately 70-80℃, and its heat resistance, dimensional stability, and interfacial bonding with metals are insufficient, easily leading to insufficient intrinsic heat resistance and premature failure before melting. Furthermore, the electro-thermal-mechanical response of the traditional PET layer at the moment of a short circuit is unreliable, and its melting behavior is random and inefficient. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a modified PET-based composite foil current collector, its preparation method, electrode, and lithium-ion battery.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A modified PET-based composite foil current collector includes a modified PET substrate and metal layers disposed on both sides of the modified PET substrate; the modified PET substrate includes a PET substrate and metal oxides disposed within the PET substrate.

[0006] The metal oxides include one or a mixture of several of Al2O3, TiO2, SiO2, ZrO2, MgO, ZnO, or CeO2.

[0007] The metal oxide is a mixture of Al2O3 and TiO2; preferably, the average particle size of Al2O3 is 30-80 nm and the average particle size of TiO2 is 10-40 nm; preferably, the mass ratio of Al2O3 to TiO2 is (1-9):(1-9); more preferably, it is 4:1.

[0008] The metal oxide is pretreated with a silane coupling agent.

[0009] The metal oxide is 2.0 wt% to 15 wt% of the PET substrate; preferably 10 wt%.

[0010] The thickness of the modified PET substrate layer is 2.0 μm-8.0 μm; preferably, the thickness of the aluminum layer is 0.8 μm-1.6 μm. Preferably, the metal layer comprises a metal material or an alloy material; the metal material comprises at least one of aluminum foil and copper foil; the alloy material comprises at least one of copper alloy foil and aluminum alloy foil. The modified PET substrate and the metal layer are bonded together using an adhesive.

[0011] The present invention also includes a method for preparing the modified PET composite foil current collector, comprising the following steps: S1: The metal oxide is pretreated with a silane coupling agent; S2: The metal oxide treated with silane coupling agent in step S1 is mixed with dried PET resin chips, melt-blended, granulated and dried by a twin-screw extruder to obtain modified PET masterbatch; S3: The modified PET masterbatch is melt-extruded and cast into sheets, followed by biaxial stretching and heat setting to obtain a modified PET substrate film; S4: Using a dry lamination process, the metal layer is laminated with the modified PET substrate film obtained in step S3 through an electrolyte-resistant adhesive, and then cured to obtain a modified PET-based composite aluminum foil.

[0012] The present invention also includes an electrode sheet comprising the modified PET-based composite foil current collector and an active layer coated on the surface of the modified PET-based composite foil current collector; The electrode includes a positive electrode and a negative electrode.

[0013] When the electrode is a positive electrode, the metal layer is aluminum foil or aluminum alloy foil; the active layer includes a positive electrode active material; preferably, the positive electrode active material includes at least one of lithium cobalt oxide, medium-nickel ternary material, high-nickel ternary material, or lithium manganese oxide.

[0014] When the electrode is a negative electrode, the metal layer is copper foil or copper alloy foil; the active layer includes a negative electrode active material; preferably, the negative electrode active material includes at least one of graphite and silicon-carbon negative electrode. This invention also includes a lithium-ion battery comprising the aforementioned electrode.

[0015] Compared with the prior art, the beneficial effects of the present invention are: The technical solution of this application has excellent high temperature resistance and electrolyte resistance. By adding metal oxides to the PET substrate, the crystallinity and thermal stability of the PET matrix are significantly improved. As a preferred embodiment, by adding Al2O3 and TiO2 for synergistic modification, the thermal shrinkage rate of the modified PET substrate at 150°C can be reduced to below 1.0%. At the same time, it has a strong interface with the treated metal foil and does not delaminate after long-term immersion in electrolyte at 85°C, thus solving the environmental reliability shortcomings of traditional PET composite foil.

[0016] The technical solution of this application has excellent active safety response characteristics: through optimized filler ratio and PET layer thickness, the composite foil current collector can more reliably achieve rapid local damage to the PET layer and form an effective high-resistance area when an internal short circuit occurs. Compared with ordinary PET composite foil current collectors, its current limiting effect at the short circuit point is faster and more thorough, thus exhibiting lower temperature rise and higher safety in battery nail penetration tests.

[0017] The technical solution of this application offers a balanced overall performance and strong industrial applicability: the material formulation and structural parameters provided by this invention achieve a good balance between lightweight, mechanical strength, processability, and safety. The preparation process is compatible with existing thin-film processing and battery manufacturing processes, and can be widely applied to soft-pack lithium-ion batteries of different systems such as lithium cobalt oxide, ternary lithium, and lithium manganese oxide. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the modified PET-based composite aluminum foil of the present invention. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments.

[0020] Example 1: A method for preparing a modified PET-based composite foil current collector, comprising the following steps: S1: The metal oxides are pretreated with a silane coupling agent. In this embodiment, the metal oxides used are nano Al2O3 (average particle size 50nm) and nano TiO2 (average particle size 25nm), both of which are pretreated with KH-550 silane coupling agent to improve their dispersibility and interfacial bonding in the PET matrix.

[0021] The process of treating Al2O3 with silane coupling agent is used as an example. The preparation process of TiO2 is the same, and specifically includes the following steps: Preparation of hydrolysate: KH-550 silane coupling agent (γ-aminopropyltriethoxysilane) is mixed with anhydrous ethanol and deionized water, and stirred to allow for complete hydrolysis, forming a clear solution. The amount of water added is 1.0-1.5 times the molar amount of silane, which is 1.2 times in this example. The amount of anhydrous ethanol added is 5-10 times the volume of silane, which is 5 times in this example as an illustrative example.

[0022] Mixing and Dispersion: Nano-Al2O3 powder was added to the prepared hydrolysate. Initial mixing was performed using high-speed shear dispersion, followed by ultrasonic treatment (in an ice-water bath to prevent overheating) to further break up particle agglomeration and achieve uniform dispersion of the nanoparticles in the solution.

[0023] Surface reaction: The uniformly mixed suspension is placed in a heating device (such as a 70-80℃ water bath) and refluxed for several hours under mechanical stirring. During this process, the silanol generated by the hydrolysis of silane undergoes a condensation reaction with the hydroxyl groups on the surface of the nanoparticles to form stable Si-OM (M is Al or Ti) chemical bonds, thereby grafting organic amino functional groups onto its surface.

[0024] Cleaning and drying: After the reaction is complete, the suspension is centrifuged and the supernatant is discarded. The precipitate is washed repeatedly with anhydrous ethanol to remove physically adsorbed residues. Finally, the washed solid is dried in a vacuum oven at about 80°C to obtain surface-modified nanoparticles that are easily dispersed in organic resins.

[0025] Meanwhile, a soft aluminum foil with a thickness of 1.2 μm was used as the metal layer for illustrative purposes. The treated aluminum foil was obtained after cleaning and corona treatment (surface tension 54 mN / m). S2: The metal oxide Al2O3 (8.0 wt% of PET mass) and metal oxide TiO2 (2.0 wt% of PET mass) treated with silane coupling agent in step S2 are mixed with dried PET resin (PET resin intrinsic viscosity is 0.65 dl / g) chips, melt-blended, granulated and dried in a twin-screw extruder (260-275℃) to obtain modified PET masterbatch; S3: The modified PET masterbatch is melt-extruded and cast into sheets, followed by biaxial stretching (3.3 times longitudinal stretching and 3.5 times transverse stretching) and heat setting at 210°C to obtain a modified PET substrate film with a thickness of 6.0±0.2μm; S4: A dry lamination process is used to laminate the treated aluminum foil to the modified PET substrate film using an electrolyte-resistant adhesive, followed by curing to obtain a modified PET-based composite aluminum foil. Specifically, an electrolyte-resistant polyurethane adhesive (dry film thickness 1.0 μm) is used to dry-laminate the aluminum foil onto both sides of the modified PET substrate film, followed by curing at 50°C for 48 hours to obtain a symmetrical modified PET-based composite aluminum foil.

[0026] Modified PET-based composite aluminum foil, such as Figure 1 The diagram shows a modified PET substrate 2 and aluminum metal layers 1 disposed on both sides of the modified PET substrate; the modified PET substrate includes a PET substrate and metal oxides disposed within the PET substrate.

[0027] Comparative Example 1 (pure PET substrate): Except for the absence of any nano-metal oxide fillers, the PET film preparation and composite process were exactly the same as in Example 1, resulting in a pure PET composite aluminum foil with a PET layer thickness of 6.0 μm ± 0.2 μm.

[0028] Comparative Example 2 (Al2O3 only added; both the Al2O3 and TiO2 in the comparative example were metal oxides modified with silane coupling agents): In the preparation of modified PET masterbatch, only Al2O3 metal oxide (10.0 wt% of PET mass) was added; TiO2 was not added. The remaining processes were the same as in Example 1.

[0029] Comparative Example 3 (TiO2 only): In the preparation of modified PET masterbatch, only nano-TiO2 accounting for 10.0 wt% of the PET mass was added, and Al2O3 was not added. The rest of the process was the same as in Example 1.

[0030] Comparative Example 4 (PET layer too thick): By adjusting the biaxial stretching process, a modified PET film with a thickness of 12.0 μm was prepared, with the same formulation as in Example 1 (total addition 10.0 wt%, Al2O3:TiO2 = 4:1). A composite aluminum foil with a thicker PET layer was obtained after lamination.

[0031] Comparative Example 5 (Al2O3:TiO2=9:1): 9.0 wt% nano-Al2O3 and 1.0 wt% nano-TiO2 were added to PET, and the rest of the process was the same as in Example 1.

[0032] Comparative Example 6 (Al2O3:TiO2=1:9): 9.0wt% nano-TiO2 and 1.0wt% nano-Al2O3 were added to PET, and the rest of the process was the same as in Example 1.

[0033] Comparative Example 7: Total addition amount 5.0 wt%, Al2O3:TiO2 = 4:1, other processes are the same as in Example 1.

[0034] Comparative Example 8: Total addition amount 15.0 wt%, Al2O3:TiO2 = 4:1, other processes are the same as in Example 1.

[0035] It should be noted that the comparative examples in this application are only for setting up a comparison, and are themselves part of the embodiments.

[0036] Performance Testing and Comparative Analysis 1. Basic physical property tests: Heat shrinkage rate: According to GB / T 12027-2004, the dimensional change rate of the sample after being placed in an oven at 150℃ without tension for 30 minutes is measured.

[0037] High temperature resistance: The thermal stability of the sample was analyzed using TG-DSC.

[0038] Peel strength: According to GB / T 2792-2014, the adhesion between the aluminum layer and the PET layer was tested using the 180° peel method at a tensile speed of 100 mm / min.

[0039] Electrolyte resistance test: The sample was immersed in a 1M LiPF6 EC / DMC / EMC (volume ratio 1:1:1) electrolyte and placed in an 85℃ constant temperature oven for 168 hours. After removal, the appearance was observed, and the surface liquid was blotted dry with filter paper before testing the peel strength retention rate.

[0040] Surface resistance: The surface resistance of the composite aluminum foil was measured using a four-probe tester.

[0041] The results are shown in Table 1.

[0042] Table 1

[0043] 2. Analysis: Example 1 exhibits the best overall performance. Its extremely low thermal shrinkage rate and highest peel strength retention rate confirm the unique advantages of the synergistic modification of Al2O3 and TiO2 in improving intrinsic heat resistance and long-term interfacial durability. TiO2 optimizes the condensed-state structure of PET, improves its intrinsic heat resistance, and pre-determines the failure path; Al2O3 strengthens the matrix and manages heat flow, ensuring that failure occurs in a controllable and efficient manner. This deep synergistic effect is the fundamental material science reason why the modified PET composite aluminum foil of this invention can simultaneously overcome the two major industry challenges of "long-term reliability under high-temperature electrolyte environment" and "rapid active safety response during internal short circuit". The individual performance of Comparative Examples 2 and 3 is not as good as that of Example 1, indicating that the two are complementary and indispensable. Although Comparative Example 4 has the best heat resistance, its sheet resistivity is significantly increased. Comparative Example 5 (high Al2O3) has a lower thermal shrinkage rate, but its peel strength is slightly lower, indicating that the improvement effect of TiO2 on interfacial adhesion is indispensable. The properties of Comparative Example 6 (high TiO2) began to decline, indicating that an excessively high TiO2 ratio may be detrimental to the balance of mechanical properties. Example 1 already exhibited excellent heat resistance and offered better overall cost and processability. Comparative Example 8, with its highest filler content and strongest physical constraint, had the lowest thermal shrinkage and highest heat resistance temperature. Comparative Example 7 suffered from an imperfect filler network and insufficient reinforcement; Comparative Example 8, on the other hand, experienced severe filler agglomeration, which disrupted the matrix continuity and created defects, leading to a decrease in the actual interfacial bonding strength and deterioration after long-term immersion. Excessive filler in Comparative Example 8 may have affected the uniformity of aluminum layer deposition or introduced more interfacial scattering, resulting in a significant increase in sheet resistivity.

[0044] 3. Battery fabrication and needle penetration safety test: Electrode and battery fabrication: Composite aluminum foils prepared in each example and comparative example were used as positive electrode current collectors. A ternary positive electrode (NCM613) slurry was prepared and uniformly coated on both sides of the composite aluminum foil. After drying and rolling, the positive electrode sheet was obtained. Using graphite as the negative electrode, Celgard 2325 as the separator, and 1M LiPF6 / EC+DMC (1:1) as the electrolyte, a soft-pack lithium-ion battery with a rated capacity of 5Ah was assembled in a dry environment.

[0045] Needle penetration test: Conducted according to the needle penetration test clause in GB / T 31485-2015 "Safety Requirements and Test Methods for Power Batteries for Electric Vehicles". A 3mm tungsten carbide needle was used to pierce the center of the battery at a speed of 25mm / s. A high-speed data acquisition system was used to record the battery voltage and temperature changes within 1mm of the piercing point during the piercing process. After the test, the battery was disassembled, and the morphology of the composite aluminum foil at the short-circuit point was observed.

[0046] The results are shown in Table 2.

[0047] Table 2

[0048] The results showed that Example 1 exhibited the best synergistic modification effect. After needle puncture, the modified PET layer rapidly and completely vaporized around the short-circuit point, forming a large and complete insulating void. This was equivalent to instantly connecting a high resistor in series at the short-circuit point, rapidly suppressing the short-circuit current. Consequently, the voltage drop was rapid, heat generation was low, and the temperature rise was minimal. In Comparative Example 1 (pure PET), the PET layer underwent plastic deformation rather than brittle fracture, failing to effectively isolate the short-circuit point, leading to continuous short circuits and thermal runaway ignition. In Comparative Example 2 (Al2O3 only), heat diffusion resulted in a fragmented damage area, incomplete melting, poor current limiting effect, and a higher temperature rise. Comparative Example 3 (TiO2 only): Heat concentration leads to PET carbonization, potentially producing conductive residues, and the damage is incomplete, resulting in limited safety improvement. Comparative Example 4 (PET too thick): Increased energy required for damage and delayed response; although the final temperature rise is acceptable, the effect of delaying thermal runaway is not as rapid as in Example 1. Comparative Example 5: Excessive Al2O3 makes the material more "tough," resulting in slightly slower melting. Comparative Example 6: Excessive TiO2 leads to localized overheating and carbonization, resulting in incomplete damage and increased temperature. Conclusion: The experiment verifies that the present invention, through synergistic modification of a specific ratio of Al2O3 / TiO2 and optimization of the PET layer thickness (3.0 μm), achieves rapid formation of an effective high-resistivity region to significantly delay temperature rise and suppress... The best performance in terms of thermal runaway. Comparative Example 7 (insufficient addition): The filler network is sparse, with weak thermal diffusion (insufficient Al2O3) and insufficient control of the crystal structure (insufficient TiO2). During a short circuit, heat is concentrated, and PET mainly undergoes plastic melting and fiberization, failing to quickly form a large-size insulating area, resulting in slow current limiting and temperature rise. Comparative Example 8 (excessive addition): Excessive filler leads to excessive embrittlement of the composite material and a decrease in fracture toughness. During a short circuit, the PET layer is more prone to instantaneous brittle cracking rather than controllable vaporization and pore expansion, resulting in small and irregular insulating gaps. At the same time, filler agglomeration may become a localized thermal or electrical weakness. Therefore, its safety response is actually worse than that of Example 1.

[0049] In summary, the technical solution of this application has excellent high temperature resistance and electrolyte resistance. By adding metal oxides to the PET substrate, the crystallinity and thermal stability of the PET matrix are significantly improved. As a preferred embodiment, by adding Al2O3 and TiO2 for synergistic modification, the thermal shrinkage rate of the modified PET substrate at 150℃ can be reduced to below 1.0%, while the interface with the treated aluminum foil is firmly bonded. After long-term immersion in electrolyte at 85℃, there is no delamination, which solves the environmental reliability shortcomings of traditional PET composite foil.

[0050] The technical solution of this application has excellent active safety response characteristics: through optimized filler ratio and PET layer thickness, the composite foil current collector can more reliably achieve rapid local damage to the PET layer and form an effective high-resistance area when an internal short circuit occurs. Compared with ordinary PET composite foil current collectors, its current limiting effect at the short circuit point is faster and more thorough, thus exhibiting lower temperature rise and higher safety in battery nail penetration tests.

[0051] The technical solution of this application offers a balanced overall performance and strong industrial applicability: the material formulation and structural parameters provided by this invention achieve a good balance between lightweighting, mechanical strength, processability, and safety. The preparation process is compatible with existing thin-film processing and battery manufacturing processes, and can be widely applied to soft-pack lithium-ion batteries of different systems such as lithium cobalt oxide, ternary lithium, and lithium manganese oxide.

[0052] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A modified PET-based composite foil current collector, characterized in that it comprises a modified PET substrate and metal layers disposed on both sides of the modified PET substrate; the modified PET substrate comprises a PET substrate and metal oxides disposed within the PET substrate.

2. The modified PET-based composite foil current collector according to claim 1, characterized in that the metal oxide includes one or a mixture of several of Al2O3, TiO2, SiO2, ZrO2, MgO, ZnO or CeO2.

3. The modified PET-based composite foil current collector according to claim 1, characterized in that the metal oxide is a mixture of Al2O3 and TiO2; preferably, the average particle size of Al2O3 is 30-80 nm and the average particle size of TiO2 is 10-40 nm; preferably, the mass ratio of Al2O3 to TiO2 is (1-9):(1-9); more preferably, it is 4:

1.

4. The modified PET-based composite foil current collector according to claim 1, characterized in that the metal oxide is pretreated with a silane coupling agent.

5. The modified PET-based composite foil current collector according to claim 1, characterized in that the mass of the metal oxide is 2.0wt%-15wt% of the mass of the PET substrate; preferably 10wt%.

6. The modified PET-based composite foil current collector according to claim 1, characterized in that the thickness of the modified PET substrate layer is 2.0 μm-8.0 μm; preferably, the thickness of the aluminum metal layer is 0.8 μm-1.6 μm.

7. The modified PET-based composite foil current collector according to claim 1, characterized in that the modified PET substrate and the metal layer are connected by an adhesive; preferably, the metal layer comprises a metal material or an alloy material; the metal material comprises at least one of aluminum foil and copper foil; the alloy material comprises at least one of copper alloy foil and aluminum alloy foil.

8. A method for preparing the modified PET-based composite foil current collector according to any one of claims 1-7, characterized in that, Includes the following steps: S1: The metal oxide is pretreated with a silane coupling agent; S2: The metal oxide treated with silane coupling agent in step S1 is mixed with dried PET resin chips, melt-blended, granulated and dried by a twin-screw extruder to obtain modified PET masterbatch; S3: The modified PET masterbatch is melt-extruded and cast into sheets, followed by biaxial stretching and heat setting to obtain a modified PET substrate film; S4: Using a dry lamination process, the metal layer is laminated with the modified PET substrate film obtained in step S3 through an electrolyte-resistant adhesive, and then cured to obtain a modified PET-based composite aluminum foil.

9. An electrode sheet, characterized in that, Includes the modified PET-based composite foil current collector as described in any one of claims 1-7 and the active layer coated on the modified PET-based composite foil current collector; The electrode plates include positive electrode plates and negative electrode plates; When the electrode is a positive electrode, the active layer includes a positive electrode active material; preferably, the positive electrode active material includes at least one of lithium cobalt oxide, medium-nickel ternary material, high-nickel ternary material, or lithium manganese oxide. When the electrode is a negative electrode, the active layer includes a negative electrode active material; preferably, the negative electrode active material includes at least one of graphite and silicon-carbon negative electrode.

10. A lithium-ion battery, characterized in that, Includes the electrode sheet as described in claim 9.

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