Composite diaphragm and secondary battery comprising same
By constructing an ion-fast-pass composite thin layer on the separator base membrane, the safety contradiction between high energy density and high rate performance of secondary batteries is resolved, and thermal runaway suppression and battery life extension are achieved under mechanical abuse, electrical abuse or thermal abuse.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-07
- Publication Date
- 2026-04-10
AI Technical Summary
In the pursuit of high energy density and high rate performance, existing rechargeable batteries face a contradiction between safety and battery performance. In particular, they are prone to thermal runaway under mechanical, electrical, or thermal abuse. Furthermore, the acidic substances produced by electrolyte decomposition can corrode electrode materials, affecting battery cycle life and reliability.
An ion-fast-pass composite thin layer is constructed on one side of the membrane base film, containing lithium-ion conductive materials, thermally diffusing fillers, conductive agents, and inorganic functional particles. Through synergistic effects, it reduces interfacial polarization, disperses hot spots, inhibits interfacial side reactions of acidic byproducts, and provides structural stability.
Without significantly sacrificing energy density, it improves 5C capacity retention, reduces peak needle current and maximum temperature rise, enhances safety consistency, mitigates impedance drift and gas generation, and achieves a synergistic improvement in high-rate performance and safety.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of secondary batteries, and particularly relates to a composite separator and a secondary battery comprising the same. BACKGROUND
[0002] Secondary batteries, especially lithium-ion batteries, are the core energy components of modern electronic devices, electric vehicles and large-scale energy storage systems, and their market demand is growing at an unprecedented rate. In order to meet the pursuit of longer mileage and more convenient use experience at the application end, high energy density and high rate (fast charging) performance have become two key directions of the development of secondary battery technology.
[0003] However, there is an inherent contradiction between energy density and safety. High energy density batteries usually mean that more chemical energy is stored in the system, and thinner and more active electrode materials and separators are used. This makes the battery more likely to have a severe internal short circuit when subjected to mechanical abuse (such as needle puncture, extrusion), electrical abuse (such as overcharging, short circuit) or thermal abuse, and quickly triggers thermal runaway, leading to serious safety accidents such as burning, explosion, etc. Currently, to improve safety, the method of coating ceramic particles on the surface of the separator is generally used to improve the heat resistance and puncture resistance of the separator. However, this traditional ceramic coated separator, although it improves the safety to some extent, also increases the tortuosity of ion transport and interface impedance, often sacrificing the rate performance of the battery, leading to serious capacity decay at high rate, and unable to meet the demand of fast charging.
[0004] At the same time, in order to achieve high rate performance, researchers have been working to reduce the resistance of lithium ion migration within the battery. The pore structure and wettability of the separator, as the key channel for ion migration, are crucial to the rate performance. Some solutions to improve the rate performance, such as using thinner base films or better pore-forming separators, often reduce the mechanical strength and thermal stability of the separator, thereby posing a hidden danger to safety.
[0005] In addition, during the long-term cycling or high-temperature storage of the battery, the electrolyte will inevitably decompose to a small extent, producing acidic substances such as hydrogen fluoride (HF). These substances will corrode the SEI film (solid electrolyte interface film) formed on the surface of the electrode material and react with the positive electrode material, leading to increased internal resistance, capacity decay, gas swelling and other problems, affecting the cycle life and reliability of the battery.
[0006] Therefore, a composite separator technology is needed that can provide efficient lithium ion fast transport, thermal diffusion and structural stability at a micron level thickness, and also has interface chemical stability, to achieve the synergistic improvement of high rate performance and needle puncture safety. SUMMARY
[0007] In view of the deficiencies of the prior art, the purpose of the present application is to provide a composite separator and a secondary battery comprising the same.
[0008] To achieve the above object, the present application provides the following technical solutions. A composite separator comprises a separator base film and an ion fast-through composite thin layer arranged on one side of the separator base film. The ion fast-through composite thin layer comprises, by mass percentage, 42-50% of a lithium ion conducting material, 38-45% of a thermal diffusion filler, 0.1-0.3% of a conductive agent, and 0.015-0.035% of inorganic functional particles, with the balance being a polymer binder phase, and the total of the components being 100%.
[0009] Optionally, the thickness of the ion fast-through composite thin layer is 0.9-1.2 microns.
[0010] Optionally, the lithium ion conducting material is a halide solid-state ion conductor selected from one or more of Li3InCl6, Li3YCl6, Li3ScCl6, and Li2ZrCl6.
[0011] Preferably, the lithium ion conducting material is Li3InCl6.
[0012] Optionally, the thermal diffusion filler is one or more of aluminum nitride, aluminum oxide, and boehmite.
[0013] Preferably, the thermal diffusion filler is aluminum nitride.
[0014] Optionally, the polymer binder phase is selected from one or more of PVDF-HFP, PVDF, PAN, and PI.
[0015] Preferably, the polymer binder phase is PVDF-HFP.
[0016] Optionally, the conductive agent is one or both of carbon nanotubes and conductive carbon black.
[0017] Preferably, the conductive agent is carbon nanotubes.
[0018] Optionally, the inorganic functional particles are one or more of inorganic particles containing Yb, La, Ce, and Zr elements.
[0019] Further, the inorganic functional particles are used to inhibit interface side reactions caused by acidic byproducts and / or to improve the structural stability of the ion fast-through composite thin layer; preferably, the inorganic functional particles are inorganic particles containing La elements, and more preferably, La2O3.
[0020] Optionally, the separator base film is selected from one of PP / PE / PP multilayer base film, PP base film, PE base film, and has a thickness of 8-12 μm.
[0021] Optionally, the composite separator has the following reversibly identifiable structural features: a) the ion fast-through composite thin layer covers the effective area of one side of the separator base film, and retains an uncoated positioning strip at at least one separator long side, the uncoated positioning strip has a width of 0.5-3.0 mm; b) the characteristic element signal of the inorganic functional particles E contained in the ion fast-through composite thin layer can be identified by XRF and / or SEM-EDX detection to distinguish the coated surface from the uncoated surface.
[0022] The present application also protects a secondary battery comprising a positive electrode, a negative electrode, an electrolyte and a composite separator as described above.
[0023] Compared with the prior art, the present application has the following beneficial effects: The composite separator provided by the present application constructs an ion fast-through composite thin layer on one side of the separator base film, reduces interface polarization and disperses hot spots through the synergistic effect of lithium ion conductive material and thermal diffusion filler, improves the 5C capacity retention rate and reduces the needle puncture peak current and the maximum temperature rise without significantly sacrificing the energy density; and the trace amount of inorganic functional particles inhibits the interface side reaction caused by acidic by-products, slows down the impedance drift and gas production, improves the safety consistency, and at the same time has a detectable element characteristic signal. DETAILED DESCRIPTION
[0024] The technical solutions of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.
[0025] Unless otherwise specified, the chemical reagents and materials in the present application are purchased through market channels or synthesized from raw materials purchased through market channels.
[0026] A composite separator comprises a separator base film and an ion fast-through composite thin layer arranged on one side of the separator base film. Wherein, the ion fast-through composite thin layer comprises the following raw materials in mass percentage: lithium ion conductive material 42-50%, thermal diffusion filler 38-45%, conductive agent 0.1-0.3%, and inorganic functional particles 0.015-0.035%, and the balance is a polymer bonding phase, and the total of the components is 100%.
[0027] In some embodiments, the ion fast-through composite thin layer has a thickness of 0.9-1.2 μm.
[0028] In some embodiments, the lithium ion conducting material is a halide solid state ion conductor selected from one or more of Li3InCl6, Li3YCl6, Li3ScCl6, Li2ZrCl6.
[0029] Preferably, the lithium ion conducting material is Li3InCl6.
[0030] In some embodiments, the thermal diffusion filler is one or more of aluminum nitride, aluminum oxide, boehmite.
[0031] Preferably, the thermal diffusion filler is aluminum nitride.
[0032] In some embodiments, the polymer binder phase is selected from one or more of PVDF-HFP, PVDF, PAN, PI.
[0033] Preferably, the polymer binder phase is PVDF-HFP.
[0034] In some embodiments, the conductive agent is one or both of carbon nanotube, conductive carbon black.
[0035] Preferably, the conductive agent is carbon nanotube.
[0036] In some embodiments, the inorganic functional particle is one or more of inorganic particles containing Yb, La, Ce, Zr elements.
[0037] Further, the inorganic functional particle is used to suppress the interface side reaction induced by acidic byproducts and / or to improve the structural stability of the ion fast-through composite thin layer; preferably, the inorganic functional particle is inorganic particle containing La element, more preferably La2O3.
[0038] In some embodiments, the separator base film is selected from one of PP / PE / PP multi-layer base film, PP base film, PE base film, and has a thickness of 8-12 μm.
[0039] In some embodiments, the composite separator has the following reversibly identifiable structural features: a) the ion fast-through composite thin layer covers the effective area of one side of the separator base film, and at least one long side of the separator, a non-coated positioning strip is reserved, the width of the non-coated positioning strip is 0.5-3.0 mm; b) the characteristic element signal of the inorganic functional particle E contained in the ion fast-through composite thin layer can be detected and identified by XRF and / or SEM-EDX, to distinguish the coated surface from the non-coated surface.
[0040] In some embodiments, the preparation method of the composite separator is as follows: Pre-drying: halide solid-state ion conductor, thermal diffusion filler, and inorganic functional particles are vacuum dried at 80-120°C for 6h.
[0041] Preparation of polymer binder phase solution: the polymer binder phase is added to NMP and stirred until completely dissolved and clear.
[0042] Pre-dispersion of conductive agent: the conductive agent is taken and added to NMP, and ultrasonic dispersion is performed for 10 min to obtain a conductive agent dispersion.
[0043] Powder addition and main dispersion: the halide solid-state ion conductor, thermal diffusion filler, and inorganic functional particles are sequentially added to the polymer binder phase solution, vacuum degassing is performed, stirring is performed at 1200 rpm for 10 min for mixing, and the conductive agent dispersion is further added for mixing.
[0044] Solid content adjustment and viscosity adjustment: the remaining NMP is added to make the solid content about 20 wt%, vacuum degassing is then performed, and large particles are removed by filtration through a 50 μm filter screen to obtain an ion fast-through composite thin layer slurry.
[0045] Single-sided coating: the ion fast-through composite thin layer slurry is subjected to slot coating on one side (defined as the side facing the positive electrode) of the separator, pre-baking is performed at 60-80°C for 2-3 min, subsequent baking is performed at 110-130°C for 3-5 min, and finally vacuum drying is performed at 60°C for 2h.
[0046] In some embodiments, the preparation method of the secondary lithium ion battery is as follows: Positive electrode sheet manufacturing method: The positive electrode active material, conductive carbon black, carbon nanotube, and polyvinylidene fluoride (PVDF) are taken and uniformly mixed by stirring in an N-methyl pyrrolidone solvent system at a mass ratio of 96:1:1:2 to obtain a positive electrode coating material, and the positive electrode coating material is then coated on an aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet.
[0047] In some embodiments, the negative electrode manufacturing method: The negative electrode sheet includes a negative electrode current collector copper foil and a negative electrode coating material coated on both sides of the copper foil, and the negative electrode coating material includes, by mass percentage, 10.0% of deposited silicon carbon, 76.0% of graphite, 0.75% of the conductive agent, 0.75% of conductive carbon black, 1.0% of the thickening agent carboxymethyl cellulose sodium (CMC), 0.75% of the binder polyacrylic acid (PAA), and 0.75% of the binder styrene-butadiene rubber (SBR), the above substances are added to deionized water to form the negative electrode coating material, the solid content is 42%, and then the negative electrode coating material is coated on both sides of the negative electrode current collector (copper foil), dried, and cold-pressed to form the negative electrode sheet, and the compacted density is 1.5 g / cm 3.
[0048] In some embodiments, the preparation of the electrolyte solution: Lithium salt lithium hexafluorophosphate (LiPF6), organic solvent ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD) and vinylene carbonate (VC) are mixed in a ratio of 10.0:22.0:53.0:3.0:7.0:5.0 by mass percentage to obtain the electrolyte solution.
[0049] In some embodiments, the assembly of the lithium ion battery: After the positive electrode sheet and the negative electrode sheet are respectively subjected to rolling and slitting treatment, they are wound together with the composite separator according to a set process to form a 21700 cylindrical battery roll core. Subsequently, the battery roll core and the pre-prepared connecting sheet are fixed by welding, and are loaded into a metal battery shell. After completing key processes such as electrolyte injection, sealing, and formation, the secondary lithium ion battery is prepared. The lithium ion battery adopts a cylindrical shell, and its outer dimensions are 21.0 mm in diameter and 70.0 mm in length, meeting the 21700 standard specification.
[0050] Example 1 A composite separator, comprising: a separator base film and an ion fast-through composite thin layer arranged on one side of the separator base film; wherein, by mass percentage, the ion fast-through composite thin layer comprises the following raw materials: Li3InCl6 45%, AlN 40%, carbon nanotube 0.2%, La2O3 0.02%, PVDF-HFP 14.78%, the thickness of the ion fast-through composite thin layer is 1 μm, and the separator base film is a PP base film with a thickness of 10 μm.
[0051] A preparation method of a composite separator, comprising the following steps: Pre-drying: 45 g of Li3InCl6, 40 g of AlN, and 0.02 g of La2O3 are vacuum dried at 80-120°C for 6 h; Preparation of a polymer binder phase solution: 14.78 g of PVDF-HFP is added to 250 g of NMP, and stirred until completely dissolved and clear; Pre-dispersion of the conductive agent: 0.2 g of carbon nanotube is added to 50 g of NMP, and ultrasonic dispersion is performed for 10 min to obtain a conductive agent dispersion liquid; Powder addition and main dispersion: 45 g of Li3InCl6, 40 g of AlN, and 0.02 g of La2O3 are sequentially added to the polymer binder phase solution, vacuum degassing is performed, stirring is performed at 1200 rpm for 10 min, and then the conductive agent dispersion liquid is added for further mixing; The viscosity of the slurry was adjusted by adding NMP to the slurry to a total amount of 500 g, so that the solid content was about 20 wt%, and then vacuum degassing, and filtering through a 50 μm filter screen to remove large particles, to obtain the ion fast-through composite thin layer slurry.
[0052] Single-sided coating: the ion fast-through composite thin layer slurry was slot-coated on one side of the separator (defined as the side facing the positive electrode), pre-baked at 60-80°C for 2-3 min, and then baked at 110-130°C for 3-5 min, and finally vacuum dried at 60°C for 2 h.
[0053] Example 2 The difference between this example and Example 1 is that the content of the lithium ion conducting material (Li3InCl6) in the ion fast-through composite thin layer is adjusted from 45 wt% to 42 wt% in this example, and other conditions remain unchanged, so that to maintain the total amount of solid components at 100 wt%, the content of the thermal diffusion filler (AlN) is adjusted from 40 wt% to 43 wt%, the polymer binder phase, the conductive agent (CNT) and the inorganic functional particles (La2O3) remain the same as in Example 1, and the others are the same as in Example 1.
[0054] Example 3 The difference between this example and Example 1 is that the content of the lithium ion conducting material (Li3InCl6) in the ion fast-through composite thin layer is adjusted from 45 wt% to 50 wt% in this example, and other conditions remain unchanged, so that to maintain the total amount of solid components at 100 wt%, the content of the thermal diffusion filler (AlN) is adjusted from 40 wt% to 35 wt%, the polymer binder phase, the conductive agent (CNT) and the inorganic functional particles (La2O3) remain the same as in Example 1, and the others are the same as in Example 1.
[0055] Example 4 The difference between this example and Example 1 is that the inorganic functional particles La2O3 in the ion fast-through composite thin layer are replaced by Yb2O3 in this example, so that the type of inorganic functional particles changes to inorganic particles containing Yb element and the content remains at 0.02 wt%, the content of the lithium ion conducting material, the polymer binder phase, the thermal diffusion filler, and the conductive agent (CNT) in the ion fast-through composite thin layer remain the same as in Example 1, and the others are the same as in Example 1.
[0056] Example 5 The difference between this embodiment and embodiment 1 is that in this embodiment, the inorganic functional particles La2O3 in the ion fast-through composite thin layer are replaced by Ce2O3, so that the type of inorganic functional particles becomes inorganic particles containing Ce element and the content is still 0.02 wt%, the contents of lithium ion conducting material, polymer binder phase, thermal diffusion filler and conductive agent (CNT) in the ion fast-through composite thin layer remain consistent with embodiment 1, and the others are the same as embodiment 1.
[0057] Embodiment 6 The difference between this embodiment and embodiment 1 is that in this embodiment, the inorganic functional particles La2O3 in the ion fast-through composite thin layer are replaced by ZrO2, so that the type of inorganic functional particles becomes inorganic particles containing Zr element and the content is still 0.02 wt%, the contents of lithium ion conducting material, polymer binder phase, thermal diffusion filler and conductive agent (CNT) in the ion fast-through composite thin layer remain consistent with embodiment 1, and the others are the same as embodiment 1.
[0058] Embodiment 7 The difference between this embodiment and embodiment 1 is that in this embodiment, the conductive agent in the ion fast-through composite thin layer is replaced by carbon nanotubes, and other conditions remain unchanged, so that the type of conductive agent becomes conductive carbon black and the content is still 0.20 wt%, the types and contents of lithium ion conducting material, thermal diffusion filler, polymer binder phase and inorganic functional particles in the ion fast-through composite thin layer remain consistent with embodiment 1, and the others are the same as embodiment 1.
[0059] Embodiment 8 The difference between this embodiment and embodiment 1 is that in this embodiment, the conductive agent in the ion fast-through composite thin layer is replaced by carbon nanotubes and conductive carbon black, and other conditions remain unchanged, so that the type of conductive agent becomes a combination of 0.10 wt% carbon nanotubes and 0.10 wt% conductive carbon black and the content is still 0.20 wt%, the types and contents of lithium ion conducting material, thermal diffusion filler, polymer binder phase and inorganic functional particles in the ion fast-through composite thin layer remain consistent with embodiment 1, and the others are the same as embodiment 1.
[0060] Embodiment 9 The difference between this embodiment and embodiment 1 is that in this embodiment, the thermal diffusion filler in the ion fast-through composite thin layer is replaced by aluminum oxide, and other conditions remain unchanged, so that the type of thermal diffusion filler becomes aluminum oxide and the content is still 40 wt%, the types and contents of lithium ion conducting material, polymer binder phase, conductive agent and inorganic functional particles in the ion fast-through composite thin layer remain consistent with embodiment 1, and the others are the same as embodiment 1.
[0061] Embodiment 10 The difference between the present example and Example 1 is that, in the present example, the thermal diffusion filler in the ion fast-through composite thin layer is replaced by boehmite from aluminum nitride, other conditions remain unchanged, so that the type of thermal diffusion filler becomes boehmite and its content is still 40 wt%, the types and contents of lithium ion conducting material, polymer binder phase, conductive agent and inorganic functional particles in the ion fast-through composite thin layer remain consistent with Example 1, and the others are the same as Example 1.
[0062] Comparative Example 1 The difference between the present example and Example 1 is that, in the present example, the content of lithium ion conducting material (Li3InCl6) in the ion fast-through composite thin layer is adjusted from 45 wt% to 70 wt%, other conditions remain unchanged, so that to keep the total amount of solid components as 100 wt%, the content of thermal diffusion filler (AlN) is adjusted from 40 wt% to 15 wt%, the polymer binder phase, conductive agent (CNT) and inorganic functional particles (La2O3) remain consistent with Example 1, and the others are the same as Example 1.
[0063] Comparative Example 2 The difference between the present example and Example 1 is that, in the present example, the content of lithium ion conducting material (Li3InCl6) in the ion fast-through composite thin layer is adjusted from 45 wt% to 30 wt%, other conditions remain unchanged, so that to keep the total amount of solid components as 100 wt%, the content of thermal diffusion filler (AlN) is adjusted from 40 wt% to 55 wt%, the polymer binder phase, conductive agent (CNT) and inorganic functional particles (La2O3) remain consistent with Example 1, and the others are the same as Example 1.
[0064] Comparative Example 3 The difference between the present example and Example 1 is that, in the present example, the inorganic functional particles La2O3 in the ion fast-through composite thin layer is replaced by MgO, so that the type of inorganic functional particles E becomes inorganic particles containing no Yb, La, Ce or Zr elements and its content is still 0.02 wt%, the contents of lithium ion conducting material, polymer binder phase, thermal diffusion filler, conductive agent (CNT) in the ion fast-through composite thin layer remain consistent with Example 1, and the others are the same as Example 1.
[0065] Comparative Example 4 The difference between the present example and Example 1 is that, in the present example, the coating step of ion fast-through composite thin layer in the separator base film is cancelled, other conditions remain unchanged, so that the thickness of ion fast-through composite thin layer becomes 0 μm and the separator is only the base film body, and the others are the same as Example 1.
[0066] Comparative Example 5 The difference between the present comparative example and Example 1 is that the thickness of the ion fast-through composite thin layer is adjusted from 1.0 μm to 0.5 μm in the present example, and other conditions remain unchanged, so that the dry film thickness parameter of the ion fast-through composite thin layer coating becomes 0.5 μm, while the types and contents of the lithium ion conducting material, thermal diffusion filler, polymer binder phase, conductive agent and inorganic functional particles in the ion fast-through composite thin layer formula remain consistent with Example 1, and other conditions are the same as Example 1.
[0067] Comparative Example 6 The difference between the present comparative example and Example 1 is that the thickness of the ion fast-through composite thin layer is adjusted from 1.0 μm to 2.0 μm in the present example, and other conditions remain unchanged, so that the dry film thickness parameter of the ion fast-through composite thin layer coating becomes 2.0 μm, while the types and contents of the lithium ion conducting material, thermal diffusion filler, polymer binder phase, conductive agent and inorganic functional particles in the ion fast-through composite thin layer formula remain consistent with Example 1, and other conditions are the same as Example 1.
[0068] Comparative Example 7 The difference between the present comparative example and Example 1 is that the conductive agent in the ion fast-through composite thin layer is replaced from carbon nanotubes to graphene in the present example, and other conditions remain unchanged, so that the type of conductive agent becomes graphene and its content remains 0.20 wt%, the types and contents of the lithium ion conducting material, thermal diffusion filler, polymer binder phase and inorganic functional particles in the ion fast-through composite thin layer remain consistent with Example 1, and other conditions are the same as Example 1.
[0069] Comparative Example 8 The difference between the present comparative example and Example 1 is that the thermal diffusion filler in the ion fast-through composite thin layer is replaced from aluminum nitride to silicon dioxide in the present example, and other conditions remain unchanged, so that the type of thermal diffusion filler becomes silicon dioxide and its content remains 40 wt%, the types and contents of the lithium ion conducting material, polymer binder phase, conductive agent and inorganic functional particles in the ion fast-through composite thin layer remain consistent with Example 1, and other conditions are the same as Example 1.
[0070] The parameters of Examples 1-10 and Comparative Examples 1-8 are as shown in Table 1 below.
[0071] Table 1 The composite separator prepared in Examples 1-10 and Comparative Examples 1-8 is used for lithium ion batteries, and electrochemical performance tests are carried out, and the performance test method is as follows: P1: 3C / 5C capacity retention rate: The battery was placed in a 45 °C constant temperature oven for 6 h and tested according to the following steps: (1) first cycle constant current constant voltage charging: constant current charging to 4.25 V at 0.1 C, then constant voltage charging until the current decreases to 0.01 C. (2) After charging, stand for 30 minutes. (3) Constant current discharge, discharge to 2.5 V at a rate of 0.5 C, record the reference capacity C1. (4) Charge-discharge process: constant current charging to 4.25 V at a rate of 3 C, then constant voltage charging until the current decreases to 0.1 C. (5) Stand for 30 minutes again. (6) Constant current discharge to 2.5 V at a rate of 5 C. (7) Stand for 30 minutes again. (8) Repeat (4)-(7) 100 times, record the capacity retention rate after 100 times C100 / C1 100%.
[0072] P2: Maximum temperature of needle puncture Tmax (°C) The cell obtained in (2) was punctured in the middle of the cell with a 3 mm steel needle at a speed of 25 mm / s at 25 °C, and the maximum temperature of the shell was recorded by an external K-type thermocouple.
[0073] P3: Peak short circuit current of needle puncture I peak (A) The (2) needle puncture test was simultaneously used to record the current curve using a Hall current sensor, and the maximum value I peak was taken. The test results are shown in Table 2.
[0074] Table 2 As shown in Table 2, compared with Comparative Examples 1-3 and Comparative Examples 1, 2, when the lithium ion conducting material content is in the middle range (Example 1, 45 wt%), a relatively continuous lithium ion transport network can be formed in the composite thin layer, while still retaining sufficient thermal diffusion filler and polymer binder phase to maintain the pore structure and film layer toughness, thereby balancing 5C rate and needle safety. When the lithium ion conducting material is too low (Example 2, 42 wt%), the volume fraction of the ion fast transport phase decreases, the equivalent ion conductivity at the interface decreases, resulting in an increase in concentration polarization and charge transfer impedance at high rate discharge, resulting in a decrease in 5C capacity retention. At the same time, local heating is more concentrated, and the temperature rise and current peak under needle working conditions are also more likely to rise. However, when Li3InCl6 is reduced to 30 wt% (Comparative Example 2), the continuous lithium ion conduction phase in the composite thin layer decreases significantly, which is close to the percolation threshold. Near the threshold, the equivalent ion conductivity does not decrease linearly, but can change by orders of magnitude, resulting in a significant decrease in 5C capacity retention. At the same time, the increase in polarization means that more irreversible heat is generated per unit time, and the temperature rise is slightly worse. Although the lithium ion conducting material is too high (Example 3, 50 wt%), it can further reduce the interface ion impedance and improve the rate, but when the lithium ion conducting material is too high (Comparative Example 1, 70 wt%), it will occupy the proportion of thermal diffusion filler and binder phase, reaching the film forming and electrode separation force threshold: insufficient binder phase will cause the composite thin layer to become brittle, and the cohesive strength and adhesion to the base film will decrease, and drying shrinkage and rolling, winding bending will more easily introduce microcracks, powdering, edge powdering, pinholes or local delamination. These defects result in a decrease in 5C instead of an increase. Under needle working conditions, thin layer defects can cause the membrane surface to be more prone to local tearing and expansion, and the short circuit contact area will be amplified to a surface contact more quickly, resulting in a lower equivalent resistance of the short circuit loop, and thus peak significantly increased, max significantly increased.
[0075] As shown in Table 2, compared with Comparative Examples 1-3 and Comparative Examples 1, 2, when the lithium ion conducting material content is in the middle range (Example 1, 45 wt%), a relatively continuous lithium ion transport network can be formed in the composite thin layer, while still retaining sufficient thermal diffusion filler and polymer binder phase to maintain the pore structure and film layer toughness, thereby balancing 5C rate and needle safety. When the lithium ion conducting material is too low (Example 2, 42 wt%), the volume fraction of the ion fast transport phase decreases, the equivalent ion conductivity at the interface decreases, resulting in an increase in concentration polarization and charge transfer impedance at high rate discharge, resulting in a decrease in 5C capacity retention. At the same time, local heating is more concentrated, and the temperature rise and current peak under needle working conditions are also more likely to rise. However, when Li3InCl6 is reduced to 30 wt% (Comparative Example 2), the continuous lithium ion conduction phase in the composite thin layer decreases significantly, which is close to the percolation threshold. Near the threshold, the equivalent ion conductivity does not decrease linearly, but can change by orders of magnitude, resulting in a significant decrease in 5C capacity retention. At the same time, the increase in polarization means that more irreversible heat is generated per unit time, and the temperature rise is slightly worse. Although the lithium ion conducting material is too high (Example 3, 50 wt%), it can further reduce the interface ion impedance and improve the rate, but when the lithium ion conducting material is too high (Comparative Example 1, 70 wt%), it will occupy the proportion of thermal diffusion filler and binder phase, reaching the film forming and electrode separation force threshold: insufficient binder phase will cause the composite thin layer to become brittle, and the cohesive strength and adhesion to the base film will decrease, and drying shrinkage and rolling, winding bending will more easily introduce microcracks, powdering, edge powdering, pinholes or local delamination. These defects result in a decrease in 5C instead of an increase. Under needle working conditions, thin layer defects can cause the membrane surface to be more prone to local tearing and expansion, and the short circuit contact area will be amplified to a surface contact more quickly, resulting in a lower equivalent resistance of the short circuit loop, and thus max and I peakLower and less fluctuant. Yb2O3, Ce2O3, ZrO2 (Examples 4-6) can also provide certain adsorption of acidic species or interface passivation, but their surface basicity, reactivity and product stability are different, resulting in a generally weaker comprehensive effect than La2O3. Comparative Example 3 uses MgO, which is also basic, but lacks the advantages of stable formation of low-solubility fluoride and traceable element characteristics, and its interface regulation effect in the composite thin layer is insufficient, which can easily result in higher needle current and temperature rise, indicating that inorganic functional particles are not only used for identification, but also have actual contribution to interface reaction inhibition and safety consistency.
[0076] As can be seen from Comparative Examples 1 and 4-6, the thickness of the thin layer determines the balance between ion transmission impedance and mechanical thermal stability enhancement. When the thickness is moderate (Example 1, 1.0 μm), the composite thin layer can provide a continuous ion fast channel and also enhance the surface of the separator and support heat diffusion, which is beneficial to inhibit the local tearing expansion of the separator and the rapid expansion of the short-circuit contact area during needle puncture, so that the T max and I peak are at a relatively optimal level. When the thin layer is thinner (Comparative Example 5, 0.5 μm), the ion transmission path is shorter and the interface impedance can be reduced, and the rate retention rate can be improved, but the mechanical reinforcement and heat diffusion capacity are insufficient, and micro-crack expansion or local damage is more likely to occur under needle puncture impact, and the short-circuit channel rapidly expands, resulting in I peak and T max rise. When the thin layer is thicker (Comparative Example 6, 2.0 μm), the anti-crack expansion and heat diffusion capacity can be more obviously improved, and the needle puncture peak current and maximum temperature can be reduced, but the increased thickness leads to an increase in the tortuosity of the pore channel and the effective transmission length, which can easily cause high-rate concentration polarization to be aggravated, and the 5C retention rate to decrease. After the thin layer is removed in Comparative Example 4, the separator lacks ion fast transmission and structural reinforcement, and the short-circuit expansion is more severe during needle puncture, and the safety indicators are significantly deteriorated.
[0077] As can be seen from Comparative Examples 1, 7, 8 and Comparative Example 7, the morphology and percolation behavior of the conductive agent directly affect the rate and needle puncture safety of the composite thin layer under the premise of maintaining electronic insulation. When CNT is used (Example 1), the high aspect ratio of CNT is beneficial to improving the inter-particle contact and micro stress transfer at a very low addition amount, and can improve the interfacial electrochemical uniformity without forming a through electronic network, which shows a good 5C retention rate and a lower needle puncture I peakControlled. When using conductive carbon black (Example 7), the carbon black is mainly in the form of point aggregates, and the efficiency of improving contact is lower than that of CNTs. At the same addition amount, the gain for high rate is weaker, but the safety of needle punching is generally more stable because it is more difficult to form long-range connected channels. When CNTs and carbon black are compounded (Example 8), the advantages of both can be taken into account when the dispersion is sufficient, so that the rate and safety performance are between single CNT and single carbon black. When graphene is used in Comparative Example 7, the two-dimensional conductive phase in the form of sheets is more likely to be oriented and stacked during coating and drying, and to form local in-plane conductive channels. When needle punched or locally compacted, it is more likely to make the electronic channels connected, thereby significantly reducing the short-circuit loop resistance, leading to I peak With T max The type of conductive agent not only affects the rate, but also determines the failure mode and risk level under needle punching.
[0078] As can be seen from Comparative Examples 1, 9, 10 and Comparative Example 8, the intrinsic thermal conductivity, particle morphology and interface compatibility of the thermal diffusion filler jointly determine the needle punching heat management capability and thin layer structure stability. When AlN is used (Example 1), AlN has high thermal diffusion capacity, which can more effectively diffuse the heat generated near the needle punching short-circuit point in the plane, reduce the local hot spot peak, and make T max and I peak lower, and AlN is an electronic insulator, which does not introduce additional electronic short-circuit paths. When Al2O3 (Example 9) or boehmite (Example 10) is used, although they also have the effects of electronic insulation and mechanical reinforcement, the overall thermal diffusion performance is generally weaker than that of AlN, and the local heat is more likely to accumulate during needle punching. Therefore, T max and I peak are often higher than those of the AlN system; at the same time, boehmite may improve the uniformity of the coating due to the surface hydroxyl and wetting properties, but its thermal diffusion advantage is not enough to completely offset. When SiO2 is used in Comparative Example 8, the thermal diffusion capacity is weaker and the interface heat transfer resistance is higher, the hot spot is more concentrated under needle punching conditions, the temperature rise is larger, and the short-circuit current and thermal runaway risk are higher.
[0079] The above is a further detailed description of the present application in combination with specific implementation examples, which cannot be considered as limiting the specific implementation of the present application to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, any modification, equivalent replacement and improvement made without departing from the concept of the present application should be considered as falling within the protection scope of the present application.
[0080] As can be understood by those skilled in the art, the above description is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.
Claims
1. A composite diaphragm, characterized in that, include: The diaphragm base membrane and the ion-fast-pass composite thin layer disposed on one side of the diaphragm base membrane; The ion-passing composite thin layer comprises, by mass percentage, the following raw materials: A. lithium-ion conductive material 42-50%, B. thermally diffusing filler 38-45%, D. conductive agent 0.1-0.3%, and E. inorganic functional particles 0.015-0.035%, with the balance being C. polymer binder phase, and the total composition is 100%.
2. The composite diaphragm according to claim 1, characterized in that, The thickness of the ion fast-pass composite thin layer is 0.9-1.2 μm.
3. The composite diaphragm according to claim 1, characterized in that, The lithium-ion conductive material is a halide solid-state ion conductor, selected from one or more of Li3InCl6, Li3YCl6, Li3ScCl6, and Li2ZrCl6.
4. The composite diaphragm according to claim 1, characterized in that, The thermally diffusing filler is one or more of aluminum nitride, alumina, and boehmite.
5. The composite diaphragm according to claim 1, characterized in that, The polymer binder phase is selected from one or more of PVDF-HFP, PVDF, PAN, and PI.
6. The composite diaphragm according to claim 1, characterized in that, The conductive agent is one or both of carbon nanotubes and conductive carbon black.
7. The composite diaphragm according to claim 1, characterized in that, The inorganic functional particles are one or more of the inorganic particles containing Yb, La, Ce, and Zr elements.
8. The composite diaphragm according to claim 1, characterized in that, The diaphragm base film is selected from one of PP / PE / PP multilayer base film, PP base film, and PE base film, and its thickness is 8-12μm.
9. The composite diaphragm according to claim 1, characterized in that, The composite diaphragm has the following reversibly identifiable structural features: a) The ion-fast composite thin layer covers the effective area of one side of the diaphragm base film, and retains an uncoated positioning strip at at least one long side of the diaphragm, wherein the width of the uncoated positioning strip is 0.5-3.0 mm; b) The characteristic element signals of the inorganic functional particles E contained in the ion fast-pass composite thin layer can be detected and identified by XRF and / or SEM-EDX to distinguish the coated surface from the uncoated surface.
10. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, an electrolyte, and a composite membrane as described in any one of claims 1–9.