Double-layer PAN-SiO2 aerogel composite diaphragm and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a double-layer PAN-SiO2 aerogel composite diaphragm and a lithium ion battery. The double-layer PAN-SiO2 aerogel composite diaphragm comprises a first surface layer, a second surface layer and a third surface layer, the first surface layer is composed of polyacrylonitrile PAN nanofibers formed by electrostatic spinning, and a PAN base membrane with uniform fiber diameter and controllable thickness is obtained by controlling the spraying rate to be 0.5 mL / h to 2.0 mL / h, the spinning voltage to be 10 kV to 20 kV and the spinning distance to be 8 cm to 20 cm in the electrostatic spinning process; the first surface layer comprises tetraethoxysilane, the second surface layer comprises a silicon dioxide SiO2 aerogel layer growing on the surface of the first surface layer in situ, the hydrolysis time of tetraethoxysilane is controlled to be 5-60 min, the crosslinking pH value is controlled to be 8-12, and a supercritical drying mode is adopted, so that the composite diaphragm is of a layered gradient structure in the thickness direction. The high-temperature stability, the electrolyte wettability and the dynamic performance of the composite diaphragm are greatly improved while the overall flexibility and the mechanical stability of the composite diaphragm are ensured.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, specifically to a composite separator of double-layer PAN-SiO2 aerogel and a lithium-ion battery. Background Technology

[0002] Currently, the separators in existing lithium-ion batteries mainly use polyolefin materials. In recent years, with the advancement of science and technology, polyacrylonitrile (PAN) nanofiber separators prepared by electrospinning have attracted attention due to their high porosity and mechanical strength.

[0003] In the process of implementing the embodiments of this disclosure, at least the following problems were found in the related art:

[0004] Polyacrylonitrile nanofiber separators in related technologies often suffer from technical problems such as poor heat resistance, poor electrolyte wettability, and unadjustable pore structure, which prevent them from meeting the requirements of high-safety and high-performance lithium-ion batteries.

[0005] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] To provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. This summary is not intended as a general commentary, nor is it intended to identify key / important components or describe the scope of protection of these embodiments, but rather as a prelude to the detailed description that follows.

[0007] This disclosure provides a composite separator and lithium-ion battery based on a double-layer PAN-SiO2 aerogel to improve the high-temperature stability, electrolyte wettability, and kinetic performance of the separator, thereby meeting the requirements for high-safety and high-performance lithium-ion batteries.

[0008] In some embodiments, the composite membrane of the bilayer PAN-SiO2 aerogel comprises:

[0009] The first surface layer is composed of polyacrylonitrile (PAN) nanofibers formed by electrospinning. The PAN base film with uniform fiber diameter and controllable thickness is obtained by controlling the spraying rate of 0.5 mL / h to 2.0 mL / h, the spinning voltage of 10 kV to 20 kV, and the spraying distance of 8 cm to 20 cm during the electrospinning process.

[0010] The second surface layer includes a silica (SiO2) aerogel layer grown in situ on the surface of the first surface layer, wherein the composite membrane exhibits a layered gradient structure in the thickness direction by controlling the hydrolysis time of tetraethoxysilane to 5-60 min and the crosslinking pH value to 8-12, and by employing supercritical drying.

[0011] The thickness of the first surface layer ranges from 4 μm to 10 μm, and the thickness of the second surface layer ranges from 2 μm to 5 μm.

[0012] Optionally, the thickness of the first surface layer ranges from 4 μm to 10 μm, the thickness of the second surface layer ranges from 2 μm to 5 μm, and the polyacrylonitrile (PAN) nanofibers have a diameter of 50 nm to 500 nm and are uniformly distributed.

[0013] Optionally, the pore size of the silica (SiO2) aerogel layer is 30 nm to 500 nm, and its mass accounts for 10% to 40% of the total mass of the composite membrane.

[0014] Optionally, in the Fourier transform infrared spectrum corresponding to the composite diaphragm, at 2930 cm⁻¹ -1 ~2940cm -1 The characteristic infrared peak of the methylene group appears in the interval, at 2240 cm⁻¹. -1 ~2245cm -1 The characteristic infrared peak of the nitrile group appears in the interval, at 1665 cm⁻¹. -1 ~1670cm -1 The characteristic infrared peak of the amide group appears in the interval, at 1560 cm⁻¹. -1 ~1570cm -1 The characteristic infrared peak of the carboxylic acid group appears in the interval, at 1075 cm⁻¹. -1 ~1085cm -1 Infrared characteristic peaks of asymmetric stretching vibrations of Si-O-Si appear in the interval.

[0015] Optionally, the composite membrane has an air permeability greater than 120 s / mL under conditions of 25°C and 100 kPa.

[0016] Optionally, the contact angle of the composite membrane in the liquid electrolyte is less than or equal to 15°, wherein the ratio of ethylene carbonate (EC) to diethyl carbonate (DEC) in the liquid electrolyte is 1:1.

[0017] Optionally, the rupture temperature of the composite diaphragm is greater than or equal to 250°C.

[0018] Optionally, the composite membrane has a dimensional shrinkage rate of less than 1.5% after being treated at 180°C for 30 minutes.

[0019] Optionally, the composite membrane has an ionic conductivity greater than 0.45 mS / cm.

[0020] Optionally, the lithium-ion battery assembled using this separator retains more than 85% of its capacity after being discharged at a 10C rate.

[0021] In some embodiments, the lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a composite separator of bilayer PAN-SiO2 aerogel as described in this application.

[0022] The composite separator and lithium-ion battery with double-layer PAN-SiO2 aerogel provided in this disclosure can achieve the following technical effects:

[0023] By constructing a double-layer PAN-SiO2 aerogel composite separator, the first surface layer of the composite separator is composed of polyacrylonitrile (PAN) nanofibers formed by electrospinning, and the second surface layer includes a silica (SiO2) aerogel layer grown in situ on the surface of the first surface layer. Furthermore, by controlling the electrospinning parameters and aerogel growth conditions, and employing supercritical drying, the composite separator exhibits a layered gradient structure in the thickness direction, with a specific thickness range. This ensures that the composite separator maintains overall flexibility and mechanical stability while significantly improving its high-temperature stability, electrolyte wettability, and kinetic performance. It achieves synergistic optimization of high thermal stability, excellent electrolyte wettability, and rapid ion transport, effectively enhancing battery safety and rate performance. Simultaneously, the process parameters are controllable, and the structure can be reverse-engineered, demonstrating good engineering practicality and meeting the requirements of high-safety, high-performance lithium-ion batteries.

[0024] The above general description and the description below are exemplary and illustrative only and are not intended to limit this application. Attached Figure Description

[0025] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations and drawings do not constitute a limitation on the embodiments. Elements having the same reference numerals in the drawings are shown as similar elements. The drawings are not to be scaled. And wherein:

[0026] Figure 1 This is a schematic diagram of the structure of a lithium-ion battery provided in an embodiment of this disclosure;

[0027] Figure 2 This is a schematic diagram of the structure of a battery core provided in an embodiment of this disclosure;

[0028] Figure 3 This is a schematic diagram of the unfolded battery core provided in an embodiment of this disclosure;

[0029] Figure 4 This is the Fourier transform infrared spectrum of the polyvinylidene fluoride-hexafluoropropylene copolymer provided in the embodiments of this disclosure.

[0030] Figure label:

[0031] 1-Positive terminal; 10-Battery core; 11-Positive terminal post; 12-Negative terminal; 2-Shell; 3-Negative electrode sheet; 4-Composite separator; 5-Positive electrode sheet. Detailed Implementation

[0032] To provide a more detailed understanding of the features and technical content of the embodiments of this disclosure, the implementation of the embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. The accompanying drawings are for illustrative purposes only and are not intended to limit the embodiments of this disclosure. In the following technical description, for ease of explanation, several details are used to provide a full understanding of the disclosed embodiments. However, one or more embodiments may still be implemented without these details. In other cases, well-known structures and devices may be simplified in their depiction to simplify the drawings.

[0033] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this disclosure are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this disclosure described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0034] In this disclosure, the terms "upper," "lower," "inner," "middle," "outer," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for better description of the embodiments of this disclosure and their implementations, and are not intended to limit the indicated devices, elements, or components to having a specific orientation, or to require them to be constructed and operated in a specific orientation. Furthermore, some of the aforementioned terms may be used to indicate other meanings besides orientation or positional relationship; for example, the term "upper" may in some cases indicate a dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in the embodiments of this disclosure according to the specific circumstances.

[0035] Furthermore, the terms "set up," "connect," and "fix" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this disclosure according to the specific circumstances.

[0036] Unless otherwise stated, the term "multiple" means two or more.

[0037] In this embodiment of the disclosure, the character " / " indicates that the objects before and after it are in an "or" relationship. For example, A / B means: A or B.

[0038] The term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0039] It should be noted that, unless otherwise specified, the embodiments and features described in the present disclosure can be combined with each other.

[0040] Combination Figure 1 As shown, this embodiment of the present disclosure provides a lithium-ion battery, including a casing 2, which houses a battery core. The top is a positive terminal 1, and the bottom is a negative terminal 12. A positive electrode post 11 is disposed on the positive terminal 1. Specifically, Figure 2 A schematic diagram of the battery core structure in this application is shown. Figure 3 A schematic diagram of the unfolded battery core in this application is shown. Wherein, as... Figure 3 As shown, the lithium-ion battery also includes a positive electrode 5, a negative electrode 3, a composite separator 4, and an electrolyte. The positive electrode 5, the negative electrode 3, and the composite separator 4 are stacked and then wound to form a... Figure 2 The cylindrical battery core 10 shown is initially wound at the electrode end along the cylinder axis, and ends at the electrode end on the outer surface of the cylinder after winding.

[0041] Furthermore, the composite membrane 4 of this application is a double-layer PAN-SiO2 aerogel composite membrane, including a first surface layer and a second surface layer. The first surface layer is composed of polyacrylonitrile PAN nanofibers formed by electrospinning. By controlling the spraying rate of 0.5 mL / h to 2.0 mL / h, the spinning voltage of 10 kV to 20 kV, and the spinneret distance of 8 cm to 20 cm during the electrospinning process, a PAN base membrane with uniform fiber diameter and controllable thickness is obtained.

[0042] The second surface layer includes a silica (SiO2) aerogel layer grown in situ on the surface of the first surface layer. The composite membrane exhibits a layered gradient structure in the thickness direction by controlling the hydrolysis time of tetraethoxysilane to be 5 min to 60 min and the crosslinking pH value to be 8 to 12, and by using supercritical drying.

[0043] Furthermore, the thickness of the first surface layer in this application ranges from 4 μm to 10 μm, and the thickness of the second surface layer ranges from 2 μm to 5 μm.

[0044] The composite separator using the bilayer PAN-SiO2 aerogel provided in this disclosure involves constructing a bilayer PAN-SiO2 aerogel composite separator. The first surface layer of the composite separator is composed of polyacrylonitrile (PAN) nanofibers formed by electrospinning. The second surface layer of the composite separator includes a silica (SiO2) aerogel layer grown in situ on the surface of the first surface layer. By controlling the parameters of electrospinning and the growth conditions of the aerogel, and employing supercritical drying, the composite separator exhibits a layered gradient structure in the thickness direction and has a specific thickness range. This ensures that the composite separator maintains overall flexibility and mechanical stability while significantly improving its high-temperature stability, electrolyte wettability, and kinetic performance. It achieves synergistic optimization of high thermal stability, excellent electrolyte wettability, and rapid ion transport, effectively improving the safety and rate performance of the battery. Furthermore, the process parameters are controllable, and the structure can be reverse-engineered, demonstrating good engineering practicality and meeting the requirements of high-safety, high-performance lithium-ion batteries.

[0045] Optionally, the thickness of the first surface layer in this application ranges from 4 μm to 10 μm, and the thickness of the second surface layer ranges from 2 μm to 5 μm. Furthermore, the polyacrylonitrile (PAN) nanofibers in this application have a fiber diameter of 50 nm to 500 nm and are uniformly distributed. Thus, by rationally controlling the thickness of the first and second surface layers, the air permeability and electrolyte conductivity of the composite membrane can be better improved.

[0046] Optionally, the pore size of the silica (SiO2) aerogel layer in this application is 30 nm to 500 nm, and its mass accounts for 10% to 40% of the total mass of the composite membrane.

[0047] Optionally, combined Figure 4 As shown, in the Fourier transform infrared spectrum corresponding to the composite diaphragm of this application, at 2930 cm⁻¹... -1 ~2940cm -1 The characteristic infrared peak of the methylene group appears in the interval, at 2240 cm⁻¹. -1 ~2245cm -1 The characteristic infrared peak of the nitrile group appears in the interval, at 1665 cm⁻¹. -1 ~1670cm-1 The characteristic infrared peak of the amide group appears in the interval, at 1560 cm⁻¹. -1 ~1570cm -1 The characteristic infrared peak of the carboxylic acid group appears in the interval, at 1075 cm⁻¹. -1 ~1085cm -1 Infrared characteristic peaks of asymmetric stretching vibrations of Si-O-Si appear in the interval.

[0048] Optionally, the composite diaphragm of this application has an air permeability greater than 120 s / mL under conditions of 25°C and 100 kPa.

[0049] Optionally, the composite diaphragm of this application has a contact angle of less than or equal to 15° in the liquid electrolyte, wherein the ratio of ethylene carbonate EC to diethyl carbonate DEC in the liquid electrolyte is 1:1.

[0050] Optionally, the membrane rupture temperature of the composite diaphragm in this application is greater than or equal to 250°C.

[0051] Optionally, the composite diaphragm of this application has a dimensional shrinkage rate of less than 1.5% after being treated at 180°C for 30 minutes.

[0052] Optionally, the composite membrane of this application has an ionic conductivity greater than 0.45 mS / cm.

[0053] Optionally, the lithium-ion battery assembled using this separator retains more than 85% of its capacity after being discharged at a 10C rate.

[0054] Furthermore, embodiments of this disclosure provide a lithium-ion battery, including a positive electrode, a negative electrode, an electrolyte, and a composite separator of bilayer PAN-SiO2 aerogel as described in any one of this application.

[0055] The technical solution of this application will be further described below with reference to specific embodiments.

[0056] 1. Method for manufacturing positive electrode plates:

[0057] Take positive electrode active material (LiNi) 0.8 Co 0.1 Mn 0.1 O2 (NMC811), conductive carbon black, carbon nanotubes, and polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 96:1:1:2. Next, the positive electrode coating material was uniformly coated onto a 12.0 μm thick aluminum foil. After the electrode was dried, cold-pressed, slit, and cut, the positive electrode sheet was obtained with a compaction density of 3.5 g / cm³. 3 .

[0058] 2. Negative electrode manufacturing method:

[0059] A negative electrode coating material was formed by mixing graphite (anode active material), carbon nanotubes, sodium carboxymethyl cellulose (CMC) (thickener), and styrene-butadiene rubber (SBR) (binder) in deionized water at a mass percentage of 96:1.5:1.0:1.5. The negative electrode coating material was then coated onto a 15 μm thick copper foil. After drying, cold pressing, slitting, and cutting, the negative electrode sheet was obtained with a compaction density of 1.5 g / cm³.

[0060] 3. Preparation of electrolyte:

[0061] An electrolyte was prepared by mixing lithium salt lithium hexafluorophosphate (LiPF6), organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), and vinylene carbonate (VC) in a mass percentage ratio of 10.0:20.0:55.0:2.0:8.0:5.0.

[0062] 4. Preparation of composite membranes:

[0063] (1) Preparation of the PAN layer (first surface layer)

[0064] 10 wt% polyacrylonitrile (PAN) was dissolved in N,N-dimethylformamide (DMF) and stirred for 12 h to form a homogeneous spinning solution. This solution was loaded into a syringe, installed in an electrospinning apparatus, and the injection rate was controlled at 0.5 mL / h. A voltage of 14 kV was applied, and the spinning distance was approximately 15 cm. Continuous spinning was performed on a rotating collecting plate covered with aluminum foil. By controlling the spinning time, a nanofiber membrane with a thickness of approximately 8 μm was obtained.

[0065] (2) PAN hydrolysis introduces polar functional groups

[0066] The PAN film obtained by electrospinning was placed in a 2M NaOH aqueous solution and heated to 50°C for 1 hour to hydrolyze the nitrile groups (–C≡N) in the PAN main chain, introducing polar functional groups such as hydroxyl groups (–OH), carboxylates (–COO-), and amides (–CONH–). The film was then thoroughly washed with deionized water until neutral and lightly dried under vacuum to obtain a modified PAN (MPAN) substrate with a surface rich in active sites.

[0067] (3) In-situ growth of SiO2 aerogel layer

[0068] Tetraethoxysilane (TEOS), ethanol, and distilled water were mixed in an appropriate ratio (e.g., 1:4:1), and the solution was adjusted to pH 4. TEOS hydrolysis was controlled for 30 minutes. The dried MPAN membrane was immersed in this sol, and the pH was adjusted to 10. The reaction was then carried out at 25°C for 30 minutes (the SiO2 layer thickness was approximately 2 μm). During this process, SiO2 nanoparticles gradually nucleated and grew on the fiber surface, forming a uniform and porous aerogel coating. Finally, the membrane was thoroughly rinsed with deionized water and removed.

[0069] (4) Drying to obtain a double-layer membrane

[0070] The impregnated PAN-SiO2 composite membrane was supercritically dried at 40℃ and 10MPa for 6 hours. The resulting membrane exhibited a distinct bilayer structure: the bottom layer consisted of a relatively coarse PAN fiber network, providing good mechanical support and ion channels; the outer layer was a dense and uniform SiO2 aerogel layer, rich in polar functional groups, which significantly improved electrolyte wettability and thermal stability. The resulting membrane thickness was approximately 10μm.

[0071] 5. Assembly of lithium-ion batteries:

[0072] The positive and negative electrode sheets are rolled and slit respectively, and then wound together with the separator to obtain a 21700 cylindrical battery core. The battery core is then welded to the connecting piece and installed into the battery casing. After completing the liquid injection, sealing and formation processes, the lithium-ion battery of Example 1 is obtained. The casing of the lithium-ion battery is cylindrical with the following dimensions: diameter: 21.0 mm, length: 70.0 mm.

[0073] Example 2

[0074] The difference between this embodiment and Embodiment 1 is that the concentration of the PAN spinning solution is 6 wt%, while everything else is the same as in Embodiment 1.

[0075] Example 3

[0076] The difference between this embodiment and Example 1 is that the concentration of the PAN spinning solution is 8 wt%, while everything else is the same as in Example 1.

[0077] Example 4

[0078] The difference between this embodiment and Embodiment 1 is that the concentration of the PAN spinning solution is 12 wt%, while all other aspects are the same as in Embodiment 1.

[0079] Example 5

[0080] The difference between this embodiment and Example 1 is that the concentration of the PAN spinning solution is 14 wt%, while everything else is the same as in Example 1.

[0081] Example 6

[0082] The difference between this embodiment and Embodiment 1 is that the voltage applied for electrospinning is 10kV, while everything else is the same as in Embodiment 1.

[0083] Example 7

[0084] The difference between this embodiment and Embodiment 1 is that the voltage applied for electrospinning is 12kV, while everything else is the same as in Embodiment 1.

[0085] Example 8

[0086] The difference between this embodiment and Embodiment 1 is that the voltage applied for electrospinning is 16kV, while all other aspects are the same as in Embodiment 1.

[0087] Example 9

[0088] The difference between this embodiment and Embodiment 1 is that the voltage applied for electrospinning is 18kV, while all other aspects are the same as in Embodiment 1.

[0089] Example 10

[0090] The difference between this embodiment and Embodiment 1 is that the TEOS hydrolysis time is 5 minutes, while all other aspects are the same as in Embodiment 1.

[0091] Example 11

[0092] The difference between this embodiment and Embodiment 1 is that the TEOS hydrolysis time is 15 minutes, while all other aspects are the same as in Embodiment 1.

[0093] Example 12

[0094] The difference between this embodiment and Embodiment 1 is that the TEOS hydrolysis time is 45 minutes, while all other aspects are the same as in Embodiment 1.

[0095] Example 13

[0096] The difference between this embodiment and Embodiment 1 is that the TEOS hydrolysis time is 60 minutes, while all other aspects are the same as in Embodiment 1.

[0097] Example 14

[0098] The difference between this embodiment and Embodiment 1 is that the MPAN membrane is immersed in a sol with a pH of 8 and reacted at a constant temperature of 25°C for 30 minutes.

[0099] Example 15

[0100] The difference between this embodiment and Embodiment 1 is that the MPAN membrane is immersed in a sol with a pH of 9 and reacted at a constant temperature of 25°C for 30 minutes.

[0101] Example 16

[0102] The difference between this embodiment and Embodiment 1 is that the MPAN membrane is immersed in a sol with a pH of 11 and reacted at a constant temperature of 25°C for 30 minutes.

[0103] Example 17

[0104] The difference between this embodiment and Embodiment 1 is that the impregnated PAN / SiO2 composite film is vacuum dried at 60°C for 6 hours; all other aspects are the same as in Embodiment 1.

[0105] Example 18

[0106] The difference between this embodiment and Embodiment 1 is that the impregnated PAN / SiO2 composite film is freeze-dried for 12 hours; otherwise, it is the same as Embodiment 1.

[0107] Comparative Example 1

[0108] The difference between this embodiment and Embodiment 1 is that the SiO2 aerogel layer is not grown in situ on the MPAN film; all other aspects are the same as in Embodiment 1.

[0109] Comparative Example 2

[0110] The difference between this embodiment and Embodiment 1 is that the impregnated PAN / SiO2 composite film is dried at 60°C and normal pressure for 6 hours. Everything else is the same as in Embodiment 1.

[0111] The treatment method for the diaphragm is as follows:

[0112] First, discharge the lithium-ion battery to a constant current of 2.5V to ensure it is in a safe state, reducing the risk of short circuits or thermal runaway during disassembly. Carefully disassemble the battery within a glove box (protected by argon or other inert atmosphere) and remove the separator from the cylindrical cell. Immerse the removed separator in anhydrous dimethyl carbonate (DMC) solution for 30 minutes to dissolve and remove residual electrolyte and possible byproducts. Then, gently wipe the surface with lint-free paper, replacing the DMC solution and repeating the immersion-wiping process three times to ensure no residual contaminants remain on the separator surface. Finally, rinse the separator with anhydrous ethanol, wipe it again, and place it in the glove box for 48 hours to ensure it is completely dry, preventing interference from solvent residues in subsequent tests.

[0113] Method for determining SiO2 content in the diaphragm:

[0114] The dried diaphragm was placed in a thermogravimetric analysis (TGA) chamber. It was heated to 600°C in a nitrogen atmosphere at a constant heating rate (e.g., 5°C / min) to completely pyrolyze the organic matter (leaving SiO2 as the residue). The SiO2 content was calculated by the ratio of the initial mass to the residual mass after high-temperature constant-weight analysis. The SiO2 mass percentage was calculated as the mass after calcination divided by the original sample mass (100%).

[0115] Methods for determining the diameter of ANF:

[0116] After cutting the aforementioned diaphragm into small pieces, the contents were placed in a test tube and sonicated with ethanol for 30 minutes. The middle diaphragm was then removed, and the remaining solution was centrifuged (at 10,000 rpm for 10 minutes). The supernatant was discarded, and the powder was redispersed with anhydrous ethanol. The mixture was sonicated again for 10 minutes, followed by another centrifugation. This process was repeated three times to ensure the purity of the powder sample. Then, high-resolution images of the ANF (elongated linear nanowires) were obtained using transmission electron microscopy (TEM). The diameters of the elongated linear nanowires were counted using image analysis software (≥100 nanowires were counted), and the average diameter of the ANF was calculated.

[0117] Method for measuring diaphragm contact angle:

[0118] A micro-electrolyte (EC / DEC = 1:1, v / v) of 2-5 μL was dropped onto the treated and cleaned diaphragm surface using a micro-syringe. A side view image of the droplet was taken, and the droplet profile was fitted using software (such as the Young-Laplace equation or ellipse fitting method). The contact angle was calculated after the baseline was automatically detected.

[0119] Method for determining the heat shrinkage rate of diaphragms:

[0120] Cut the diaphragm into rectangular samples of 10mm × 100mm. Lay the samples flat between A4 sheets of paper to prevent high-temperature curling. Place them in an oven with a temperature control accuracy of ±1℃, set the temperature to 180℃, heat for 1 hour without external force, and then cool to room temperature. Use a vernier caliper (accuracy 0.01mm) or a laser rangefinder to measure the initial length L0 (length direction) and the length L1 after heating, respectively. Calculate the shrinkage rate according to the formula (L0-L1) / L0×100%. Three samples should be tested in each direction and the average value should be taken. If the deviation exceeds 5%, the test should be repeated.

[0121] Method for determining the failure temperature (film rupture temperature) of a hot box:

[0122] The lithium-ion battery was placed in a 25°C constant temperature chamber for 4 hours and charged to 4.2V at a constant current and constant voltage of 1C, with a cutoff current of 0.01C. It was then allowed to stand for 10 minutes, followed by a temperature increase of 5°C / min, with a holding time of 10 minutes after each 5°C increase. The surface temperature of the lithium battery was monitored during the heating process. The oven temperature at which the temperature began to rise sharply was the oven failure temperature of the secondary battery.

[0123] Methods for determining ionic conductivity:

[0124] (1) Sample preparation: The prepared three-layer composite membrane was immersed in an electrolyte (such as 1M LiPF6, EC / DEC = 1:1, v / v) for at least 12 hours to ensure sufficient wetting.

[0125] (2) Assemble a symmetrical cell: In an inert atmosphere (such as a glove box), two stainless steel electrodes (SS) are sandwiched with a membrane that has been wetted with electrolyte to form an SS|membrane|SS symmetrical structure, which is an impedance testing device with "no active electrode".

[0126] (3) Test equipment and parameters: Use an electrochemical workstation (for AC impedance testing, EIS). The test conditions are as follows: frequency range: 1MHz~0.1Hz, AC disturbance voltage: 5~10mV, test temperature: 25℃ (temperature can be controlled by a constant temperature chamber).

[0127]

[0128] Formula for calculating electrical conductivity:

[0129] Where: σ is the ionic conductivity (S / cm), L is the membrane thickness (cm), R is the high-frequency semicircular intercept in the Nyquist plot (Ω), and A is the effective area of ​​the peripheral electrode (cm²). 2 ).

[0130] 10C discharge capacity retention test method:

[0131] Place the battery in a 25°C constant temperature chamber for 4 hours and test it according to the following steps:

[0132] (1) Charge the battery to 4.2V under constant current and constant voltage conditions at 0.2C, cut off the current at 0.1C, and let it stand for 30 minutes.

[0133] (2) Discharge under constant current at 1C until 2.5V cutoff, the capacitance value is Q1, and let stand for 30 minutes;

[0134] (3) Charge the battery to 4.2V under constant current and constant voltage conditions at 0.2C, with a cutoff current of 0.1C, and let it stand for 30 minutes.

[0135] (4) Discharge under constant current at 10C until 2.5V cutoff, the capacitance value is Q2, and let stand for 30 minutes;

[0136] The 10C capacity retention rate is calculated as: Q2 / Q1×100.

[0137] The specific results are as follows:

[0138] Examples 1-5 are investigations into the effect of PAN spinning solution concentration on membrane performance in this application. Specific results are shown in Table 1.

[0139] Table 1

[0140]

[0141] As shown in Table 1, comparing Examples 1 to 5, it can be seen that as the concentration of the PAN spinning solution increases from 6% to 10%, the membrane fibers become thicker, the structural uniformity is enhanced, the contact angle decreases, the membrane rupture temperature increases, the thermal shrinkage rate decreases, and the membrane ionic conductivity and 10C discharge rate capacity retention rate significantly increase. However, when the concentration continues to increase to 12% and 14%, the performance decreases due to the excessive viscosity of the spinning solution leading to fiber inhomogeneity. This phenomenon is attributed to the fact that the PAN concentration regulates the fiber diameter and network structure during the spinning process: a moderate concentration (e.g., 10 wt%) can form a network structure with mechanical stability and good pore connectivity, which is beneficial to improving thermal stability and ion channel efficiency; too low a concentration results in discontinuous fibers, while too high a concentration leads to fiber fusion and agglomeration, thereby affecting structural integrity and ion diffusion paths.

[0142] Examples 1, 6 to 9 are investigations into the effect of spinning voltage on diaphragm performance in this application. The specific results are shown in Table 2.

[0143] Table 2

[0144]

[0145] As shown in Table 2, comparing Examples 1, 6 to 9, it can be seen that as the spinning voltage increases from 10 to 14 kV, the enhanced electric field promotes uniform fiber stretching, resulting in a more rational pore structure. The contact angle, membrane ionic conductivity, and thermal stability are continuously optimized, and the battery's 10C discharge rate capacity retention rate increases. However, when the voltage continues to rise to 16 and 18 kV, excessively fine fibers and beading phenomena occur, leading to decreased membrane strength and pore structure stability, resulting in a decline in various performance characteristics. This phenomenon is attributed to the fact that the electrospinning voltage regulates the fiber forming dynamics. In this system, a moderate voltage (14 kV) can achieve a balanced fiber stretching and solvent evaporation process, forming regular channels and an interwoven fiber network. Excessively high voltage causes excessively fine fibers, increased defects, and disordered pore structure, reducing mechanical strength and thermal resistance, while also weakening the wetting and electrolyte retention capabilities.

[0146] Examples 1, 10 to 13 are examinations of the effect of TEOS hydrolysis time on membrane performance in this application. The specific results are shown in Table 3.

[0147] Table 3

[0148]

[0149] As shown in Table 3, comparing Examples 1, 10 to 13, it can be seen that the TEOS hydrolysis time determines the coverage and density of the aerogel deposition layer. A short time (≤15 min) results in the aerogel not forming a network and poor interfacial polarity; a long time (≥45 min) leads to thick SiO2 accumulation, clogging pores and causing localized stress concentration. The most stable nano-network structure is formed at 30 min, with a surface rich in Si–OH and Si–O–Si bridging bonds, providing excellent thermal insulation and electrolyte wettability. Furthermore, the network aerogel layer formed at this time point has a dual-functional synergistic effect on the ion conduction path, representing a key parameter window for improving thermal safety and rate performance. Therefore, controlling the TESO hydrolysis time to 30 min yields a membrane with optimal contact angle, membrane ionic conductivity, thermal stability, and kinetic performance.

[0150] Examples 1, 14 to 6 are studies on the effect of crosslinking pH on membrane performance in this application. The specific results are shown in Table 4.

[0151] Table 4

[0152]

[0153] As shown in Table 4, comparing Examples 1, 14 to 16, it can be seen that the electrochemical and thermal performance is optimal when the crosslinking pH increases from 8 to 10. Further increasing the pH to 12 leads to an increase in the membrane contact angle, thermal shrinkage rate, and restricted ion transport, resulting in a decrease in the kinetic and safety performance of the lithium battery. This phenomenon is attributed to the fact that the SiO2 particle size is pH-regulated: a moderate condensation rate under neutral or weakly alkaline conditions is beneficial for controlling particle uniformity and the formation of a three-dimensional network; excessively high pH leads to rapid aggregation, increased particle size, and pore structure rupture or collapse, disrupting interfacial continuity and electrolyte channel integrity, thus weakening wetting and conductivity characteristics.

[0154] Examples 1, 17 to 19 are the results of this application on the effect of drying methods on the microstructure and performance of the diaphragm. The specific results are shown in Table 5.

[0155] Table 5

[0156]

[0157] As shown in Table 5, comparing Examples 1 and 17-18 reveals that the drying process affects the porosity retention and structural integrity of the SiO2 aerogel framework. Supercritical drying avoids liquid-gas interfacial tension, maximizing the retention of nanopores and specific surface area. Vacuum drying, however, causes pore collapse and network structure shrinkage due to capillary forces, resulting in decreased membrane dynamics and safety performance. Freeze-drying retains some porosity but still suffers freeze-thaw damage, making its performance inferior to supercritical drying. Vacuum drying causes the greatest damage to the aerogel pore structure, resulting in the worst membrane performance. The overall results indicate that the drying process is a critical process window affecting the dynamic and safety performance of PAN-SiO2 membranes.

[0158] Table 6

[0159]

[0160] As shown in Table 6, comparing Example 1 and Comparative Examples 1 and 2, it can be seen that the absence of in-situ SiO2 layer growth on the PAN separator or the change of the drying process to 60°C atmospheric pressure drying both lead to a significant increase in the contact angle of the separator and a significant decrease in ionic conductivity, resulting in a severe decline in battery kinetic performance. In addition, the thermal stability of the separator is also significantly reduced. This phenomenon is attributed to the lack of a SiO2 layer, which reduces the number of polar functional groups on the separator surface, worsens the wettability of the electrolyte, and loses the thermal barrier and ion conduction channels provided by the aerogel structure. Furthermore, the capillary effect during the conventional drying process causes the aerogel channels to collapse and the specific surface area to decrease, further damaging the three-dimensional structure and ion diffusion network of the separator, thereby comprehensively weakening the interfacial contact efficiency, thermal insulation capacity, and electrochemical transport performance.

[0161] In summary, this invention constructs a bilayer PAN-SiO2 aerogel separator (M-PSA) through systematic control of key structural and process parameters such as PAN solution concentration, spinning voltage, SiO2 content (TEOS hydrolysis time), SiO2 particle size (crosslinking pH), and drying process. This separator exhibits excellent electrolyte wettability, thermal dimensional stability, and ion channel continuity, significantly improving the high-rate performance and thermal safety of the battery. The control pathway has a clear reverse verification mechanism and is suitable for high-safety lithium / sodium-ion batteries.

[0162] The foregoing description and accompanying drawings fully illustrate embodiments of the present disclosure to enable those skilled in the art to practice them. Other embodiments may include structural and other changes. The embodiments represent only possible variations. Individual components and functions are optional unless explicitly required, and the order of operation may vary. Parts and features of some embodiments may be included or substituted for parts and features of other embodiments. Embodiments of the present disclosure are not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes may be made without departing from its scope. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A composite membrane of double-layer PAN-SiO2 aerogel, characterized in that, include: The first surface layer is composed of polyacrylonitrile (PAN) nanofibers formed by electrospinning. The PAN base film with uniform fiber diameter and controllable thickness is obtained by controlling the spraying rate of 0.5 mL / h to 2.0 mL / h, the spinning voltage of 10 kV to 20 kV, and the spraying distance of 8 cm to 20 cm during the electrospinning process. The second surface layer includes a silica (SiO2) aerogel layer grown in situ on the surface of the first surface layer. The composite membrane exhibits a layered gradient structure in the thickness direction by controlling the hydrolysis time of tetraethoxysilane to be 5 min to 60 min and the crosslinking pH value to be 8 to 12, and by using supercritical drying.

2. The composite membrane of double-layer PAN-SiO2 aerogel according to claim 1, characterized in that, The thickness of the first surface layer ranges from 4 μm to 10 μm, the thickness of the second surface layer ranges from 2 μm to 5 μm, and the polyacrylonitrile (PAN) nanofibers have a diameter of 50 nm to 500 nm and are uniformly distributed.

3. The composite membrane of double-layer PAN-SiO2 aerogel according to claim 1, characterized in that, The pore size of the silica (SiO2) aerogel layer is 30 nm to 500 nm, and its mass accounts for 10% to 40% of the total mass of the composite membrane.

4. The composite membrane of double-layer PAN-SiO2 aerogel according to claim 1, characterized in that, In the Fourier transform infrared spectrum corresponding to the composite diaphragm, at 2930 cm⁻¹ -1 ~2940cm -1 The characteristic infrared peak of the methylene group appears in the interval, at 2240 cm⁻¹. -1 ~2245cm -1 The characteristic infrared peak of the nitrile group appears in the interval, at 1665 cm⁻¹. -1 ~1670cm -1 The infrared characteristic peak of the amide group appears in the interval, at 1560 cm⁻¹. -1 ~1570cm -1 The characteristic infrared peak of the carboxylic acid group appears in the interval, at 1075 cm⁻¹. -1 ~1085cm -1 Infrared characteristic peaks of the asymmetric stretching vibration of Si-O-Si appear in the interval.

5. The composite membrane of double-layer PAN-SiO2 aerogel according to claim 1, characterized in that, The composite membrane has an air permeability greater than 120 s / mL under conditions of 25℃ and 100 kPa.

6. The composite membrane of double-layer PAN-SiO2 aerogel according to claim 1, characterized in that, The composite diaphragm has a contact angle of less than or equal to 15° in the liquid electrolyte, wherein the ratio of ethylene carbonate (EC) to diethyl carbonate (DEC) in the liquid electrolyte is 1:

1.

7. The composite membrane of double-layer PAN-SiO2 aerogel according to claim 1, characterized in that, The rupture temperature of the composite diaphragm is greater than or equal to 250°C.

8. The composite membrane of double-layer PAN-SiO2 aerogel according to claim 1, characterized in that, The composite diaphragm exhibits a dimensional shrinkage rate of less than 1.5% after treatment at 180°C for 30 minutes.

9. The composite membrane of double-layer PAN-SiO2 aerogel according to claim 1, characterized in that, The composite membrane has an ionic conductivity greater than 0.45 mS / cm.

10. The composite membrane of double-layer PAN-SiO2 aerogel according to any one of claims 1 to 9, characterized in that, The lithium-ion battery assembled using this separator retains more than 85% of its capacity after being discharged at a 10C rate.

11. A lithium-ion battery, characterized in that, The composite membrane includes a positive electrode, a negative electrode, an electrolyte, and a double-layer PAN-SiO2 aerogel as described in any one of claims 1 to 10.

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