Nanofiber sandwich structure lithium battery separator with warning function

Abstract

The application discloses a lithium battery diaphragm with a warning function, which is a sandwich structure of three or more layers of nanofibers, and comprises a pure film and a conductive composite layer with a warning function in the middle. The application also includes adding functional materials to the lithium battery diaphragm with a warning function, so that the diaphragm has a composite function other than the warning function, for example, adding a flame-retardant coating to make the diaphragm have a flame-retardant function in addition to the warning function. The lithium battery diaphragm provided by the application not only has the characteristics of a natural three-dimensional nanometer network structure, good thermal stability, high liquid absorption rate, high ion conductivity and the like compared with traditional commercial polyolefin diaphragms, but also has unique warning and optional flame-retardant functions, which greatly ensures the safety of lithium batteries.

Description

Technical Field

[0001] This invention relates to a nanofiber sandwich structure lithium battery separator with warning function, belonging to the interdisciplinary field of lithium battery separators and biomaterials. Background Technology

[0002] Lithium-ion batteries, as one of the most advantageous rechargeable batteries, are widely used not only in portable electronic devices and new energy vehicles, but also in clean energy storage and smart grid construction, all of which contribute to the increasing demand for lithium-ion batteries. The separator, as a key component of lithium-ion batteries, determines not only the battery's internal resistance, capacity, and interface structure, but also its safety performance.

[0003] Current commercially available polyolefin separators rely on finite fossil fuels, which are non-renewable and non-biodegradable, making them unsuitable for sustainable development strategies. Furthermore, commercially available polyolefin separators suffer from poor electrolyte wettability, low porosity, and poor thermal stability, severely limiting battery performance and operating temperature range. At higher operating temperatures, the separator can thermally shrink or even melt, leading to short circuits between the positive and negative electrodes, potentially causing fires or explosions. In addition, lithium batteries often suffer from uneven lithium nucleation, resulting in lithium dendrite formation, which further leads to anode breakage, continuous electrolyte depletion, and even separator perforation, ultimately causing internal short circuits and potentially resulting in fires or explosions. Therefore, currently available commercially available polyolefin separators are insufficient to meet future development requirements.

[0004] With the development of nanoscience, the application of nanomaterials has become increasingly widespread. Nanofibers, due to their fine nanostructure, natural network structure, abundant surface active genes, excellent mechanical properties, and abundant and naturally renewable resources, have made groundbreaking progress in green energy storage fields such as lithium batteries, supercapacitors, and flow batteries in recent years.

[0005] Bacterial nanocellulose (BNC) is a type of cellulose produced by microorganisms. It not only possesses a natural 3D nanonetwork structure, excellent mechanical properties, thermal stability, and porosity, but also exhibits advantages such as biodegradability and green renewability. Therefore, BNC has significant market demand and application prospects as a new energy material. Summary of the Invention

[0006] The technical problem to be solved by the present invention is that existing lithium battery separators 1) have poor thermal stability and are prone to shrinkage and melting when heated; 2) cannot cope with the various safety accidents caused by lithium dendrites. Therefore, a nanofiber sandwich structure lithium battery separator with warning and flame retardant functions is provided.

[0007] To address the aforementioned technical problems, this invention provides a nanofiber sandwich structure lithium battery separator with an alarm function. The lithium battery separator is a three-layer or more sandwich structure made of nanofibers, and the sandwich structure includes a pure membrane and an intermediate conductive composite layer with an alarm function.

[0008] Preferably, the nanofibers are at least one of cellulose nanocrystals (CNC), plant nanofibers (CNF), and bacterial nanofibers (BNC).

[0009] Preferably, the conductive material used in the conductive composite layer is at least one of low-dimensional carbon material LDC, polypyrrole PPy, polyaniline PANI, and metal conductive materials (MCM).

[0010] More preferably, the low-dimensional carbon material LDC is at least one of zero-dimensional, one-dimensional and two-dimensional materials, specifically such as at least one of carbon nanotubes (CNTs), graphene, and nano-carbon powder; the metal conductive filler is at least one of metal fibers, metal oxides, and nanoparticles.

[0011] Furthermore, the carbon nanotubes (CNTs) include various types of carbon nanotubes such as single-walled carbon nanotubes, multi-walled carbon nanotubes, and carboxylated multi-walled carbon nanotubes; the graphene includes various types of graphene such as single-layer graphene, bilayer graphene, few-layer graphene, and multilayer graphene.

[0012] Functional materials can be added to the aforementioned nanofiber sandwich structure lithium battery separator with warning function to give it composite functions in addition to warning.

[0013] Preferably, the lithium battery separator further includes a flame-retardant coating with flame-retardant function, resulting in a nanofiber sandwich structure lithium battery separator that has both warning and flame-retardant functions.

[0014] More preferably, the flame retardant in the raw material of the lithium battery separator has a mass concentration of 0.1-1%.

[0015] More preferably, the flame retardant used in the flame retardant coating is at least one of bromine-based flame retardants, phosphorus-based flame retardants, nitrogen-based flame retardants, inorganic flame retardants, and bio-based flame retardants.

[0016] Furthermore, the brominated flame retardant includes at least one of decabromodiphenyl ethane, brominated epoxy resin, and brominated polystyrene; the phosphorus-based flame retardant includes at least one of red phosphorus masterbatch and diphenyl phosphate; the nitrogen-based flame retardant includes at least one of melamine, melamine cyanuric acid, and melamine phosphate; the inorganic flame retardant includes at least one of aluminum hydroxide (Al(OH)3) and magnesium hydroxide (Mg(OH)3); and the bio-based flame retardant includes at least one of cardanol (Car), phytic acid (PA), tannic acid (TA), and chitosan (CS).

[0017] Preferably, the mass concentration of conductive material in the raw materials of the lithium battery separator is 0.5-1%.

[0018] Preferably, the thickness of the lithium battery separator is 10-30 μm.

[0019] The lithium battery separators that can be prepared by this invention include: 1) lithium battery separators with a nanofiber sandwich structure and warning function: BCB (BNC-LDC-BNC), BPB (BNC-PPy-BNC), BPAB (BNC-PANI-BNC), BMCMB (BNC-MCM-BNC); 2) lithium battery separators with a nanofiber sandwich structure and warning and flame retardant function: BCBBr (BCB-bromine flame retardant), BCBP (BCB-phosphorus flame retardant), BCBN (BCB-nitrogen flame retardant), BCBAI (BCB-Al(OH)3), BCBMg (BCB-Mg(OH)3), BCBCar (BCB-Car), BCBPA (BCB-PA), BCBTA (BCB-TA), BCBCS (BCB-CS).

[0020] This invention also provides a method for preparing the above-mentioned nanofiber sandwich structure lithium battery separator with warning and flame-retardant functions, comprising the following steps:

[0021] Step 1): A 3D nano-network composite film with a sandwich structure is prepared using nanofibers, including a pure film and an intermediate conductive composite layer;

[0022] Step 2): Immerse the composite membrane prepared in Step 1) into a solution containing flame retardant to form a flame retardant coating on the surface of the 3D nano-network structure fibers;

[0023] Step 3): The composite membrane obtained in Step 1) or Step 2) is processed by mechanical extrusion and hot pressing and drying to obtain a nanofiber sandwich structure lithium battery separator with warning function or a nanofiber sandwich structure lithium battery separator with both warning and flame retardant functions.

[0024] Preferably, step 1) employs any one or a combination of the following preparation processes:

[0025] Dynamic in-situ horizontal drum fermentation: A 3D nano-network composite membrane with a sandwich structure is prepared using a horizontal drum reactor. The preparation process is divided into pure membrane fermentation, conductive composite layer fermentation, and pure membrane fermentation. For sandwich structures with three or more layers, conductive composite layer fermentation or pure membrane fermentation is carried out on the basis of this process. The process parameters for pure membrane fermentation are: rotation speed 5-8 rpm, fermentation time 2-5 days. The process parameters for conductive composite layer fermentation are: rotation speed 30-60 rpm, fermentation time 12-48 h.

[0026] Static in-situ fermentation: The preparation process is divided into pure membrane fermentation, conductive composite layer fermentation, and pure membrane fermentation. For sandwich structures with three or more layers, conductive composite layer fermentation or pure membrane fermentation is carried out on the basis of this process. The pure membrane fermentation takes 2-5 days, and the conductive composite layer fermentation takes 2-3 days.

[0027] Combining static fermentation with dynamic shaking: First, pure membranes are obtained by static culture for 3-15 days; one pure membrane is immersed in a solution containing conductive filler and shaken for 12-48 hours to obtain a conductive composite layer; the conductive composite layer is sandwiched between two pure membranes; for a sandwich structure with three or more layers, a conductive composite layer and a pure membrane are then laminated on the outside of the pure membrane.

[0028] Fiber homogenization and filtration: The cultured nanofibers and nanofibers with conductive materials are homogenized separately, and then vacuum filtered sequentially to obtain a pure nanofiber membrane layer, a conductive composite layer, and a pure nanofiber membrane layer; for sandwich structures with three or more layers, vacuum filtration is continued to obtain a conductive composite layer and a pure membrane layer; the nanofibers can be flocculent, granular, or be commercially available bacterial cellulose in membrane form;

[0029] The combination of static fermentation and fiber homogenization filtration: First, pure membranes are obtained by statically culturing nanofibers for 3-15 days; the cultured nanofibers with conductive materials are homogenized, and the nanofibers with conductive materials are filtered on a pure membrane to obtain a conductive composite layer, which is then covered with another pure membrane; for sandwich structures with three or more layers, filtration is continued on this basis to obtain a conductive composite layer and a pure membrane.

[0030] The preparation process for each of the above membranes can be selected from one or a combination of dynamic in-situ horizontal drum fermentation, static in-situ fermentation, static fermentation combined with dynamic shaking, fiber homogenization and filtration, and static fermentation combined with fiber homogenization and filtration.

[0031] The thickness of the composite membrane can be reduced by decreasing the bacterial culture time or by reducing the dry matter in the BNC homogenate; the thickness of the lithium battery separator can be as low as 5-10 μm.

[0032] Preferably, in step 2), the composite membrane is immersed in a solution containing flame retardant for 12-48 hours.

[0033] Preferably, the mechanical extrusion in step 3) specifically involves: first extruding under 0.1-0.3 MPa for 5-20 minutes, and then extruding under 0.4-0.6 MPa for 5-20 minutes; the hot pressing and drying temperature is 80℃, and the time is 3-7 days.

[0034] This invention also provides the application of the above-mentioned nanofiber sandwich structure lithium battery separator with warning and flame-retardant functions in liquid lithium batteries, semi-solid lithium batteries or all-solid lithium batteries.

[0035] Compared to traditional commercial separators, this lithium battery separator not only has excellent thermal stability, liquid absorption rate and mechanical properties, but also has controllable thickness and dendrite warning and flame retardant functions.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] (1) Compared with traditional commercial separators, this invention generates a short circuit alarm signal after lithium dendrites come into contact with the conductive layer, which has a unique warning function and greatly ensures the safety of lithium batteries.

[0038] (2) Compared with traditional commercial separators, the present invention has a flame-retardant coating, which can quickly extinguish itself when the battery is accidentally burned, thus effectively avoiding the occurrence of greater safety accidents.

[0039] (3) Compared with traditional commercial membranes, the present invention has stronger puncture mechanical properties, better thermal stability, higher specific surface area, liquid absorption performance and ionic conductivity.

[0040] (4) The present invention uses dynamic in-situ horizontal drum fermentation, static in-situ fermentation, fiber homogenization and filtration, static fermentation combined with dynamic shaking, and static fermentation combined with fiber homogenization and filtration to prepare a nanofiber sandwich structure lithium battery separator with a composite conductive layer in the middle, and its thickness is adjustable.

[0041] (5) The raw materials used in this invention are renewable and biodegradable. The raw materials can be fermented using waste wheat / rice straw, pulp waste, sugarcane / soybean residue, etc., which results in low cost.

[0042] (6) The preparation method used in this invention is green and environmentally friendly, the process is continuous and simple, the preparation time is short, the energy consumption is low, it is easy to operate, and it is easy to scale up production.

[0043] (7) The separator of the present invention has good application prospects in the fields of liquid lithium battery, semi-solid lithium battery and all-solid lithium battery, and is of great significance to environmental protection, energy recycling and energy storage. Attached Figure Description

[0044] Figure 1 This is a composite image showing the macroscopic and foldable properties of the BCB composite membrane cultured in dynamic in-situ horizontal drum in Example 1.

[0045] Figure 2 This is a conductivity diagram of the intermediate layer of the BCB composite membrane with different concentrations in the dynamic in-situ horizontal drum culture in Example 1.

[0046] Figure 3 The diagram shows the puncture conductivity of BCB composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 1.

[0047] Figure 4 This is a microscopic morphology (SEM) image of the BCB composite membrane cultured in dynamic in situ horizontal drum in Example 1.

[0048] Figure 5 The image shows the puncture intensity of BCB composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 1.

[0049] Figure 6 The image shows the longitudinal tensile strength of BCB composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 1.

[0050] Figure 7 The image shows the transverse tensile strength of BCB composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 1.

[0051] Figure 8 The graph shows the thermal shrinkage of BCB composite films with different concentrations in dynamic in-situ horizontal drum culture in Example 1.

[0052] Figure 9 The AC impedance spectra of BCB composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 1 are shown.

[0053] Figure 10 The diagram shows the contact angles of different concentrations of BCB composite membranes with deionized water and electrolyte during dynamic in-situ horizontal drum culture in Example 1.

[0054] Figure 11 The diagram shows the electrolyte absorbance of BCB composite membranes with different concentrations in the dynamic in-situ horizontal drum culture in Example 1.

[0055] Figure 12 The image shows the electrolyte wettability of BCB composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 1.

[0056] Figure 13 Thermogravimetric (TGA) diagrams of BCB composite membranes with different concentrations cultured in dynamic in situ horizontal drum in Example 1;

[0057] Figure 14 Infrared thermographic images of BCB composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 1;

[0058] Figure 15 Differential scanning calorimetry (DSC) images of BCB composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 1;

[0059] Figure 16 Macroscopic, folding, and microscopic thickness diagrams of the BCBTA composite membrane cultured in dynamic in situ horizontal drum in Example 2;

[0060] Figure 17 This is a conductivity diagram of the intermediate layer of the BCBTA composite membrane with different concentrations in dynamic in-situ horizontal drum culture in Example 2;

[0061] Figure 18 The image shows the puncture conductivity of BCBTA composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 2.

[0062] Figure 19 The image shows the flame retardant properties of BCBTA composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 2.

[0063] Figure 20 The image shows the puncture intensity of BCBTA composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 2.

[0064] Figure 21 The image shows the longitudinal tensile properties of BCBTA composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 2.

[0065] Figure 22 The image shows the transverse tensile properties of BCBTA composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 2.

[0066] Figure 23 This is a graph showing the electrolyte absorbance of BCB composite membranes with different concentrations in dynamic in-situ horizontal drum culture in Example 2.

[0067] Figure 24 This is a diagram showing the electrolyte wettability of BCB composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 2.

[0068] Figure 25 The diagram shows the contact angles of different concentrations of BCBTA composite membranes with deionized water and electrolyte during dynamic in-situ horizontal drum culture in Example 2.

[0069] Figure 26 The graph shows the thermal shrinkage of BCBTA composite films with different concentrations cultured in a dynamic in-situ horizontal drum in Example 2.

[0070] Figure 27 Infrared thermographs of BCBTA composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 2;

[0071] Figure 28 The AC impedance spectra of BCBTA composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum in Example 2 are shown.

[0072] Figure 29 Thermogravimetric (TGA) diagrams of BCBTA composite membranes with different concentrations cultured in dynamic in situ horizontal drum in Example 2;

[0073] Figure 30 This is a macroscopic view of the BCB composite membrane prepared by combining static fermentation and dynamic shaking in Example 5;

[0074] Figure 31 The tensile properties of the BCB composite membrane prepared by combining static fermentation and dynamic shaking in Example 5 are shown in the figure.

[0075] Figure 32 A macroscopic view of the BCB composite membrane prepared by the fiber homogenization and filtration method in Example 6;

[0076] Figure 33 The tensile properties of the BCB composite membrane prepared by the fiber homogenization and filtration method in Example 6 are shown in the figure.

[0077] Figure 34 This is a macroscopic view of the BPB composite membrane prepared by the method combining static fermentation and dynamic shaking in Example 10;

[0078] Figure 35 The tensile properties of the CCC composite membrane prepared by the fiber homogenization and filtration method in Example 14 are shown in the figure.

[0079] Figure 36 This is a macroscopic view of the BPB composite membrane prepared by static fermentation in Example 16. Detailed Implementation

[0080] To make the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0081] Example 1

[0082] This embodiment uses a dynamic in-situ horizontal drum fermentation method to prepare a lithium battery separator with warning function. The specific preparation method is as follows:

[0083] (1) Using *Acetobacter xylinus* (ATCC 23770, hereinafter the same) as the strain, 300 mL of fermentation medium (50 g / L glucose, C6H) was prepared. 12 O6, AR, Sinopharm Reagent Co., Ltd.; 5g / L tryptone, BR, Sinopharm Reagent Co., Ltd.; 3g / L yeast extract, BR, Sinopharm Reagent Co., Ltd. (other examples are the same) were fermented in a clean bench at a speed of 5-8 rpm in a horizontal drum for 2-5 days to obtain the first pure membrane. Then, carbon nanotubes (carboxylated multi-walled carbon nanotubes, CNT, >95%, outer diameter: 20-30nm, length: 10-30μm, 25g, Aladdin Reagent (Shanghai) Co., Ltd. (other examples are the same) with the fermentation medium were added by a peristaltic pump and the mixture was continuously fermented in a dynamic horizontal drum at a speed of 30-60 rpm for 12-48 hours. (Before sterilization, the mixed solution is dispersed for 5-10 minutes using the ultrasonic probe of an ultrasonic crusher. An appropriate amount of surfactant can be added to the aqueous solution as a dispersant, such as Tween 20, Tween 80, Tuoyile dispersant DS-195, DS-172, DS-194H, cationic surfactant cetyl dimethyl ammonium bromide (CTAB), anionic surfactant sodium dodecylbenzene sulfonate (SDBS), and nonionic surfactant polyethylene glycol octylphenyl ether (Triton X-100). In other examples, carbon nanotubes are pretreated using this method.) This forms an intermediate BNC and CNT composite membrane layer. Finally, 200 mL of fermentation medium is added using a peristaltic pump and fermented horizontally in a drum at a speed of 5-8 rpm for 2-5 days to obtain a 0.5% BCB, 0.75% BCB, and 1% BCB composite membrane with a sandwich structure.

[0084] (2) The above-mentioned BCB composite membranes of different concentrations were placed in sodium hydroxide (NaOH, analytical grade, Sinopharm Shanghai Chemical Reagent Co., Ltd., the same in other examples) solution, treated at 80°C for 2-4 hours, and then taken out and rinsed with deionized water until neutral to obtain BCB composite membranes of different concentrations.

[0085] (3) The above BCB composite membrane was extruded by two mechanical extrusions (0.1-0.3MPa, 5-20 minutes and 0.4-0.6MPa, 5-20 minutes, the same for other embodiments). Then it was placed in an oven at 80°C and dried by hot pressing with clamps for 3-7 days to finally obtain membranes with 0.5% BCB, 0.75% BCB and 1% BCB.

[0086] like Figure 1The image shows a composite diagram of the macroscopic structure and foldability of the BCB composite membrane cultured in a dynamic in-situ horizontal drum. As can be seen from the image, the composite membrane has a special sandwich structure. The middle layer is a composite layer of BNC and CNT, which is black. The surface of the composite membrane is smooth and uniform. The BCB composite membrane has good foldability after drying.

[0087] like Figure 2 The figure shows the conductivity of the interlayer of BCB composite membranes at different concentrations during dynamic in-situ horizontal drum culture. The figure indicates that the BNC membrane is non-conductive, but the interlayer becomes conductive after partially removing the top pure membrane layer of the BCB composite membrane, and its impedance decreases with increasing CNT composite concentration. The conductivity of the interlayer of the BCB-based membrane also... Figure 3 This was verified in (puncture conductivity diagrams of BCB composite membranes with different concentrations cultured in a dynamic in situ horizontal drum).

[0088] like Figure 4 This is a microscopic SEM image of the BCB composite membrane cultured in a dynamically in-situ horizontal drum. Compared with the commercial Celgard-2325 membrane, the BNC-based membrane exhibits a unique 3D nanofiber network structure. In the freeze-dried BCB composite membrane, CNTs and BNC fibers are intertwined in the intermediate layer, forming a uniform composite structure. Notably, the dynamic in-situ horizontal drum culture process allows for continuous production and the integrated formation of the BCB composite membrane, where the composite layer and the pure fiber layer are continuous yet exhibit significantly different morphologies.

[0089] like Figure 5 The figure shows the puncture strength of BCB composite membranes at different concentrations during dynamic in-situ horizontal drum culture. As can be seen from the figure, the puncture strength of both the commercial Celgard-2325 membrane and the BNC-based membrane is above 3N, and the puncture strength of the BCB membrane increases continuously with the increase of the CNT composite concentration. This is consistent with... Figure 6 (Longitudinal tensile strength diagrams of BCB composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum) and Figure 7 The tensile strength of the BCB composite membrane at different concentrations cultured in a dynamic in-situ horizontal drum is consistent with the result shown in Table 1, where the tensile strength increases with increasing CNT composite concentration. This indicates that the entanglement of CNTs and BNC fibers enhances the tensile strength; the higher the CNT concentration, the higher the tensile strength of the composite membrane, and its thickness also increases accordingly (as shown in Table 1). Notably, the transverse tensile strength of the BNC-based membrane is significantly higher than that of the commercial Celgard-2325 membrane.

[0090] Table 1. Thickness, liquid absorption rate, and porosity of BCB diaphragms during dynamic in-situ horizontal drum culture.

[0091] sample Film thickness / μm Liquid absorption rate (ethanol) / % Liquid absorption rate (electrolyte) / % Porosity / % Celgard-2325 (Commercial) 25 169.57±25.55 338.58±99.82 32.56±0.05 BNC 15 364.71±60.67 586.00±105.14 61.73±0.05 0.5% BCB 20 317.42±40.35 556.99±56.72 53.25±0.08 0.75% BCB 25 250.48±44.98 397.55±38.41 44.20±0.05 1% BCB 25 226.19±34.57 347.83±36.22 38.45±0.04

[0092] Table 1 shows the thickness, liquid uptake (ethanol and electrolyte), and porosity of BCB composite membranes with different concentrations in dynamic in-situ horizontal drum culture. In Table 1, the liquid uptake (ethanol and electrolyte) of the BNC-based membranes was higher than that of the commercial Celgard-2325 membrane; the liquid uptake of the BCB composite membrane for ethanol and electrolyte decreased with increasing CNT composite concentration; the porosity of the BNC-based membranes was higher than that of the commercial Celgard-2325 membrane; and the porosity of the BCB composite membrane decreased with increasing CNT composite concentration.

[0093] Figure 8 The figure shows the thermal shrinkage of BCB composite membranes at different concentrations cultured in a dynamic in-situ horizontal drum. The figure shows that the BNC-based membrane has zero shrinkage below 200℃, while the commercial Celgard-2325 membrane showed initial shrinkage at 120℃ (shrinkage rate of 40%); secondary shrinkage at 160℃ (shrinkage rate of 50%), and the membrane became transparent; and the shrinkage rate was >98% at 180-200℃.

[0094] Table 2 shows the specific surface area and average pore size of BCB composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum. From Table 2, it can be seen that the specific surface area of ​​BNC-based membranes is higher than that of commercial Celgard-2325 membranes, and the specific surface area of ​​BCB composite membranes gradually increases with the increase of CNT composite concentration. The average pore size of pure BNC membranes is lower than that of commercial membranes, while that of BCB membranes is not much different from that of commercial membranes.

[0095] Table 2. Specific surface area and average pore size of BCB septum cultured in a dynamic in-situ horizontal drum.

[0096] <![CDATA[Specific surface area (m 2 / g)]]> Average pore size (nm) Celgard-2325 (Commercial) 26.08 18.45 BNC 46.82 13.35 0.5% BCB 68.55 17.51 0.75% BCB 73.60 17.32 1% BCB 82.50 19.00

[0097] like Figure 9 The figure shows the AC impedance spectra of BCB composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum. The figure shows that the bulk resistance of the commercial Celgard-2325 membrane is approximately 4 Ω, while the bulk resistance of the pure BNC membrane is approximately twice that of the Celgard-2325 membrane. The bulk resistance of the BCB composite membrane decreases after the addition of CNTs. The calculated conductivity is shown in Table 3. The conductivity of the BCB composite membrane increases with increasing CNT concentration. When the CNT concentration is greater than 0.75%, the conductivity of the BCB composite membrane is greater than that of the commercial membrane.

[0098] Table 3. Conductivity of BCB diaphragms in dynamic in-situ horizontal drum culture

[0099] Celgard-2325 BNC 0.5% BCB 0.75% BCB 1% BCB Electrical conductivity (mS / cm) 2.46 0.74 1.71 3.51 4.91

[0100] like Figure 10The figure shows the contact angles of BCB composite membranes with different concentrations in dynamic in-situ horizontal drum culture with deionized water and electrolyte. It can be clearly seen from the figure that the contact angles of BNC-based membranes with both deionized water and electrolyte are smaller than those of commercial Celgard-2325 membranes, indicating that BNC-based membranes have strong absorption capacity for electrolytes. Among them, the 0.5% BCB and 0.75% BCB membranes have the best performance. Figure 11 (Electrolyte absorbance diagram of BCB composite membranes at different concentrations in dynamic in-situ horizontal drum culture) and Figure 12 (The electrolyte wettability diagram of BCB composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum) can also verify this result.

[0101] like Figure 13 The figure shows the thermogravimetric (TGA) graphs of BCB composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum. As can be seen from the figure, the BNC-based membrane has good thermal stability at temperatures below 250℃ with no mass loss. The addition of CNTs makes its performance more stable. Figure 15 (Differential scanning calorimetry of BCB composite membranes of different concentrations cultured in a dynamic in-situ horizontal drum) further verified that the BNC-based membrane had no melting or crystallization peaks within the range of 0-300℃, indicating its excellent thermal performance.

[0102] Table 4 shows the water vapor transmission coefficient of BCB membranes cultured in a dynamic in-situ horizontal drum. The commercial Celgard-2325 membrane has the highest water vapor transmission coefficient, while the BNC membrane has a lower coefficient. This is because the commercial membrane is hydrophobic, while the BNC membrane is hydrophilic, and the water vapor is absorbed, resulting in a decrease in its transmission.

[0103] Table 4. Water vapor permeability coefficient of BCB diaphragm during dynamic in-situ horizontal drum culture.

[0104]

[0105] like Figure 14 Infrared thermographic images of BCB composite membranes at different concentrations cultured in a dynamic in-situ horizontal drum. The images show... Figure 8 The same conclusion was reached: the BNC-based membrane did not shrink at 200°C, and the addition of CNTs increased the thermal insulation performance of the BNC-based membrane.

[0106] Example 2

[0107] This embodiment uses a dynamic in-situ horizontal drum fermentation method to prepare a lithium battery separator with warning and flame-retardant functions. The specific preparation method is as follows:

[0108] (1) Using Acetobacter xylinum as the strain, fermentation was carried out in 300 mL of fermentation medium in a clean bench at a speed of 5-8 rpm for 2-5 days to obtain the first pure membrane. Then, dynamic horizontal drum fermentation was carried out in a mixed solution of 0.5%, 0.75%, and 1% carbon nanotubes and fermentation medium at a speed of 30-60 rpm for 12-48 hours to form the intermediate BNC and CNT composite membrane layer. Finally, it was transferred to 200 mL of fermentation medium and fermented horizontally at a speed of 5-8 rpm for 2-5 days to obtain a 0.5% BCB, 0.75% BCB, and 1% BCB composite membrane with a sandwich structure.

[0109] (2) The above-mentioned BCB composite membranes of different concentrations were placed in sodium hydroxide solution and treated at 80°C for 2-4 hours. After that, they were taken out and rinsed with deionized water until neutral to obtain BCB composite membranes of different concentrations.

[0110] (3) The purified BCB composite membranes of different concentrations were immersed in a solution containing 0.5% tannic acid (AR, ≥98%, Shanghai Yi'en Chemical Technology Co., Ltd., the same applies to other examples) for 12-48 hours to obtain BCB through solution self-assembly. 0.5％ TA, BCB 0.75％ TA, BCB 1％ TA composite membrane.

[0111] (4) The above BCBTA composite film is extruded by mechanical extrusion, and then placed in an oven at 80°C and dried by hot pressing with clamps for 3-7 days to finally obtain BCBTA. 0.5％ TA, BCB 0.75％ TA, BCB 1％ TA's septum.

[0112] like Figure 16 The figures show macroscopic, folding, and microscopic thickness images of the BCBTA composite membrane cultured in a dynamic in-situ horizontal drum. The figures show that the BCB, after being combined with tannic acid, becomes darker in color and has a smoother surface; the dried membrane exhibits excellent folding properties; and the microscopic SEM images reveal the properties of the BCB. 1％ The thickness of the TA composite membrane is approximately 25 μm.

[0113] Figure 17 The figure shows the conductivity of the intermediate layer of the BCBTA composite membrane with different concentrations in dynamic in-situ horizontal drum culture. It can be seen from the figure that the outer layer of the BCBTA composite membrane is not conductive, while the inner layer is conductive. Moreover, the conductivity is better as the CNT concentration increases, indicating that the addition of TA does not affect the conductivity of the intermediate layer of the BCBTA composite membrane. Figure 18 (Puncture conductivity diagrams of BCBTA composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum) verified the conductivity of the intermediate layer of the BCBTA membrane.

[0114] Figure 19 The flame retardant properties of BCBTA composite membranes with different concentrations in dynamic in-situ horizontal drum culture were characterized. Firstly, the commercial Celgard-2325 membrane (made of PP-PE-PP) was tested. It is well known that both PP and PE are heat-fusible, releasing a large amount of heat during combustion, emitting black smoke and often accompanied by molten droplets, which drip rapidly and easily spread the flame, causing fires and seriously threatening people's lives and property. The BNC membrane, as shown in the figure, burned rapidly after ignition, exhibiting no flame retardancy. The BCB membrane, after ignition, showed smoldering characteristics; however, the danger of this characteristic lies in its insidious nature, making it difficult to detect and causing personal injury and property damage. In contrast, the BNC-based membrane with TA composite exhibited good flame retardancy, extinguishing rapidly after the ignition source was removed, unlike the BCB-based membrane which continued to smolder after the ignition source was removed.

[0115] Figure 20 The figure shows the puncture strength of BCBTA composite membranes at different concentrations during dynamic in-situ horizontal drum culture. As can be seen from the figure, the puncture strength of the BNC-based membrane is higher than that of the commercial Celgard-2325 membrane. TA increases the puncture strength of the BCB composite membrane, where BCB... 0.75％ TA has the highest puncture strength.

[0116] Figure 21 The figure shows the longitudinal tensile properties of BCBTA composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum. It can be seen from the figure that compared to... Figure 5 The addition of CNTs enhances the tensile properties of the BCB composite film, while the addition of TA significantly increases the toughness of the BCBTA composite film. This result is evident in… Figure 22 The transverse tensile properties of BCBTA composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum were also verified. Figure 22 It can also be seen that the transverse tensile strength of BNC-based membranes is much higher than that of commercial Celgard-2325 membranes.

[0117] Figure 23 and 24 The figures show the electrolyte absorbance and wettability of BCB composite membranes at different concentrations cultured in a dynamic in-situ horizontal drum. Both figures show the same results, confirming the strong electrolyte absorbance of the BCB-based membrane. Figure 25 This was further validated in the diagram (contact angles of BCBTA composite membranes with different concentrations in dynamic in-situ horizontal drum culture with deionized water and electrolyte). The BCBTA composite membrane exhibited strong wettability to the electrolyte and a smaller contact angle, which is attributed to the structure of the intermediate conductive composite layer, in which BCBTA... 0.75％ TA composite membranes have the best performance.

[0118] Figure 26The thermal shrinkage diagrams of BCBTA composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum show that the addition of TA did not affect the thermal shrinkage performance of the BCB composite membrane. The BNC, BNCTA, and BCBTA composite membranes did not shrink at 200℃, while the commercial membrane still shrank significantly. Figure 27 Infrared thermographic images of BCBTA composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum further verify the thermal stability of the BCBTA composite membranes.

[0119] Table 5 shows the thickness, liquid uptake, and porosity of BCBTA membranes cultured in a dynamic in-situ horizontal drum. BNCTA exhibits the highest porosity and liquid uptake. After coating with TA, the porosity and liquid uptake of BNCTA decrease, but due to the "sandwich" structure of BCB, its electrolyte absorption increases. This result is significant. Figure 23 This has also been verified, showing that the structure of BCB is beneficial for electrolyte absorption.

[0120] Table 5. Thickness, liquid absorption rate, and porosity of BCBTA diaphragms during dynamic in-situ horizontal drum culture.

[0121] sample Film thickness / μm Liquid absorption rate (ethanol) / % Liquid absorption rate (electrolyte) / % Porosity / % Celgard-2325 (Commercial) 25 169.57±25.55 338.58±99.82 32.56±0.05 BNC 15 364.71±60.67 586.00±105.14 61.73±0.05 BNCTA 15 345.57±58.17 506.99±144.24 57.85±0.07 BCB 0.5% TA 25 304.43±32.39 546.41±57.80 53.36±0.11 BCB 0.75% TA 25 302.86±98.79 550.36±37.20 54.76±0.15 BCB1%TA 28 249.29±51.34 429.89±43.08 45.73±0.15

[0122] Table 6 shows the specific surface area and average pore size of BCBTA composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum. It is noteworthy that the specific surface area of ​​BNCTA decreased after the addition of TA, which is due to the structure of TA wrapped on BNC fibers. Compared with Table 2, the specific surface area of ​​the BCBTA composite membrane decreased slightly, and its average pore size also decreased.

[0123] Table 6. Specific surface area and average pore size of BCBTA septa cultured in a dynamic in-situ horizontal drum.

[0124]

[0125]

[0126] Table 7 shows the water vapor transmission coefficient of BCBTA membranes cultured in a dynamic in-situ horizontal drum. Due to the hydrophilicity of BNC, the water vapor transmission rate of BNC-based membranes is relatively low, while the addition of TA further increases its hydrophilicity, resulting in a decrease in its water vapor transmission.

[0127] Table 7. Water vapor permeability coefficient of BCBTA membrane during dynamic in-situ horizontal drum culture.

[0128]

[0129] Figure 28The figure shows the AC impedance spectra of BCBTA composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum. As can be seen from the figure, the bulk resistance of the BCBTA membranes is lower than that of commercial membranes, and its charge transfer is significantly reduced. The calculated conductivity is shown in Table 8; the conductivity of the BCBTA composite membranes is approximately 4-6 times that of commercial membranes.

[0130] Table 8. Conductivity of BCBTA diaphragms in dynamic in-situ horizontal drum culture

[0131] Celgard-2325 BNC BNCTA <![CDATA[BCB 0.5％ THE]]> <![CDATA[BCB 0.75％ THE]]> <![CDATA[BCB 1％ THE]]> Electrical conductivity (mS / cm) 2.46 0.74 0.89 9.64 14.45 13.26

[0132] To further verify the thermal stability of the BCBTA composite membrane, thermogravimetric analysis (TGA) was performed on BCBTA composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum. Figure 29 The properties were characterized. BNC showed almost no weight loss from 0 to 250°C. The addition of TA resulted in a slight decrease in the thermal stability of the BNCTA composite film, as TA began to decompose at around 215°C. Notably, the BNCTA composite film only began to experience weight loss after 250°C, indicating that CNTs have a positive impact on the thermal stability of the BNC composite film, slowing down the thermal decomposition of TA.

[0133] Example 3

[0134] This embodiment uses a static in-situ fermentation method to prepare a lithium battery separator with warning function. The specific preparation method is as follows:

[0135] (1) Using Acetobacter xylinum as the strain, the fermentation medium was in situ statically fermented in a clean bench for 2-5 days; then, a mixture of 0.5%, 0.75%, and 1% graphene (25g, Saen Chemical Technology (Shanghai) Co., Ltd., the same below) and the fermentation medium was added and statically fermented for 2-3 days; finally, the fermentation medium was added and statically fermented in situ for 2-5 days to obtain a 0.5% BCB, 0.75% BCB, and 1% BCB composite membrane with a sandwich structure.

[0136] (2) The above-mentioned BCB composite membranes of different concentrations were placed in sodium hydroxide solution and treated at 80°C for 2-4 hours. After that, they were taken out and rinsed with deionized water until neutral to obtain BCB composite membranes of different concentrations.

[0137] (3) The above BCB composite membrane is extruded by mechanical extrusion, and then placed in an oven at 80°C and dried by hot pressing for 3-7 days to finally obtain membranes with 0.5% BCB, 0.75% BCB and 1% BCB.

[0138] Example 4

[0139] This embodiment uses a static in-situ fermentation method to prepare a lithium battery separator with warning and flame-retardant functions. The specific preparation method is as follows:

[0140] (1) Using Acetobacter xylinum as the strain, in situ static petri dish fermentation of fermentation medium was carried out in a clean bench for 2-5 days; then, a mixed solution of carbon nanotubes with mass concentrations of 0.5%, 0.75%, and 1% was added and statically fermented for 2-3 days; finally, in situ static petri dish fermentation was carried out for 2-5 days to obtain a 0.5% BCB, 0.75% BCB, and 1% BCB composite membrane with a sandwich structure.

[0141] (2) The above-mentioned BCB composite membranes of different concentrations were placed in sodium hydroxide solution and treated at 80°C for 2-4 hours. After that, they were taken out and rinsed with deionized water until neutral to obtain BCB composite membranes of different concentrations.

[0142] (3) The purified BCB composite membranes of different concentrations were immersed in a solution containing 0.5% tannic acid for 12-48 hours to obtain BCB through solution self-assembly. 0.5％ TA, BCB 0.75％ TA, BCB 1％ TA composite membrane.

[0143] (4) The above-mentioned BCB composite film is extruded by mechanical extrusion, and then placed in an oven at 80°C and dried by hot pressing with clamps for 3-7 days to finally obtain BCB. 0.5％ TA, BCB 0.75％ TA, BCB 1％ TA's septum.

[0144] Example 5

[0145] This embodiment uses a combination of static fermentation and dynamic shaking to prepare a lithium battery separator with an alarm function. The specific preparation method is as follows:

[0146] (1) Using Acetobacter xylinum as the strain, BNC membranes were obtained by in-situ static fermentation of fermentation medium in a clean bench for 3-15 days. The above BCB composite membranes of different concentrations were placed in sodium hydroxide solution and treated at 80℃ for 2-4 hours. After treatment, the membranes were taken out and rinsed with deionized water until neutral to obtain purified BNC membranes.

[0147] (2) The purified membrane was immersed in a mixture of carbon nanotubes and deionized water with mass concentrations of 0.5%, 0.75%, and 1% and shaken for 12-48 hours. The membrane was then sandwiched between two purified BNC membranes to obtain a composite membrane.

[0148] (3) The above composite membrane is extruded by mechanical extrusion, and then placed in an oven at 80°C and dried by hot pressing for 3-7 days to finally obtain membranes with 0.5% BCB, 0.75% BCB and 1% BCB.

[0149] like Figure 30The figure shows a macroscopic view of the BCB composite membrane prepared by combining static fermentation and dynamic shaking. As can be seen from the figure, the BCB membrane prepared by dynamic shaking is uniformly composited, black in color, and sandwiched between pure BNC membranes to form a sandwich structure.

[0150] Figure 31 The tensile properties of the BCB composite membrane prepared by combining static fermentation and dynamic shaking are shown in the figure. As can be seen from the figure, the tensile strength of BNC prepared by static fermentation is higher than that prepared by dynamic shaking. Furthermore, at the same membrane thickness, the tensile strength of statically cultured BNC is approximately twice that of dynamically cultured BNC. This result is reflected in Table 9 (thickness, maximum force, and tensile strength of BCB composite membranes prepared by combining static fermentation and dynamic shaking). The thickness of the BCB composite membrane prepared from BNC cultured statically for 3 days is less than 20 μm, and it exhibits excellent tensile properties.

[0151] Table 9. Thickness, maximum force, and tensile strength of BCB composite membranes prepared by combining static fermentation and dynamic shaking.

[0152]

[0153] Example 6

[0154] This embodiment uses a fiber homogenization and filtration method to prepare a lithium battery separator with warning function. The specific preparation method is as follows:

[0155] (1) Using Acetobacter xylinum as the strain, BNC membranes were obtained by in-situ static fermentation of fermentation medium in a clean bench for 3-15 days. The above BCB composite membranes of different concentrations were placed in sodium hydroxide solution and treated at 80℃ for 2-4 hours. After treatment, the membranes were taken out and rinsed with deionized water until neutral to obtain purified BNC membranes.

[0156] (2) Homogenize the purified BNC membrane to obtain a BNC homogenate.

[0157] (3) Take a homogenate containing 0.075g BNC and vacuum filter it to form the first layer of pure BNC membrane; then take a homogenate containing 0.025g BNC and mix it with 0.05g, 0.125g, and 0.25g CNT respectively and vacuum filter it to form a membrane; finally, filter another layer of pure BNC containing 0.075g BNC homogenate to obtain a sandwich structure composite membrane.

[0158] (4) The above composite film is extruded by mechanical extrusion, and then placed in an oven at 80°C and dried by hot pressing with clamps for 3-7 days to finally obtain BCB. 1:2 BCB 1:5 BCB 1:10 The diaphragm.

[0159] like Figure 32The image shows a macroscopic view of the BCB composite membrane prepared by fiber homogenization and filtration. As can be seen from the image, the filtered BCB membrane is uniformly composited, gray in color, and has a sandwich structure.

[0160] Figure 33 Tensile properties of BCB composite membranes prepared by fiber homogenization and filtration method, compared with... Figure 6 (Longitudinal tensile strength diagrams of BCB composite membranes with different concentrations cultured in a dynamic in-situ horizontal drum) and Figure 31 (Tensile properties of BCB composite membrane prepared by static fermentation and dynamic shaking) The mechanical properties of the BNC and BCB composite membrane prepared by homogenization and filtration are lower than those of the membrane prepared by dynamic and static culture. This is because homogenization destroys the hydrogen bonds inside BNC, thus reducing its mechanical properties.

[0161] Example 7

[0162] This embodiment uses a fiber homogenization and filtration method to prepare a lithium battery separator with warning and flame-retardant functions. The specific preparation method is as follows:

[0163] (1) Using Acetobacter xylinum as the strain, BNC membranes were obtained by in-situ static fermentation of fermentation medium in a clean bench for 3-15 days. The above BCB composite membranes of different concentrations were placed in sodium hydroxide solution and treated at 80℃ for 2-4 hours. After treatment, the membranes were taken out and rinsed with deionized water until neutral to obtain purified BNC membranes.

[0164] (2) Homogenize the purified BNC membrane to obtain a BNC homogenate.

[0165] (4) Take a homogenate containing 0.075g BNC and mix it with 0.5g tannic acid and then vacuum filter it to form the first layer of pure BNC membrane; then take a homogenate mixture containing BNC (0.025g) and tannic acid (0.5g) and mix it with 0.05g, 0.125g and 0.25g CNT respectively and vacuum filter it to form a membrane; finally, filter another layer of pure BNC containing 0.075g BNC homogenate to obtain a sandwich structure composite membrane.

[0166] (3) The above composite film is extruded by mechanical extrusion, and then placed in an oven at 80°C and dried by hot pressing with clamps for 3-7 days to finally obtain BCB. 1:2 TA, BCB 1:5 TA, BCB 1:10 TA's septum.

[0167] Example 8

[0168] This embodiment uses a combination of static fermentation and fiber homogenization filtration to prepare a lithium battery separator with warning function. The specific preparation method is as follows:

[0169] (1) Using Acetobacter xylinum as the strain, BNC membranes were obtained by in-situ static fermentation of fermentation medium in a clean bench for 3-15 days. The above BCB composite membranes of different concentrations were placed in sodium hydroxide solution and treated at 80℃ for 2-4 hours. After treatment, the membranes were taken out and rinsed with deionized water until neutral to obtain purified BNC membranes.

[0170] (2) Take a portion of the purified BNC membrane and homogenize it to obtain a BNC homogenate.

[0171] (3) Use a purified BNC membrane as the first membrane; then take a BNC homogenate containing 0.025g and mix it with 0.05g, 0.125g and 0.25g CNT respectively and filter it under vacuum to form a membrane; finally cover it with a purified BNC membrane and gently vacuum to remove air bubbles between the membranes to obtain a sandwich structure composite membrane.

[0172] (4) The above composite film is extruded by mechanical extrusion, and then placed in an oven at 80°C and dried by hot pressing with clamps for 3-7 days to finally obtain BCB. 1:2 BCB 1:5 BCB 1:10 The diaphragm.

[0173] Example 9

[0174] This embodiment uses a combination of static fermentation and fiber homogenization filtration to prepare a lithium battery separator with warning and flame-retardant functions. The specific preparation method is as follows:

[0175] (1) Using Acetobacter xylinum as the strain, BNC membranes were obtained by in-situ static fermentation of fermentation medium in a clean bench for 3-15 days. The above BCB composite membranes of different concentrations were placed in sodium hydroxide solution and treated at 80℃ for 2-4 hours. After treatment, the membranes were taken out and rinsed with deionized water until neutral to obtain purified BNC membranes.

[0176] (2) Take a portion of the purified BNC membrane and homogenize it to obtain a BNC homogenate.

[0177] (3) The purified BNC membrane was immersed in a solution containing 0.5% tannic acid for 12-48 hours to obtain a BNCTA composite membrane by solution self-assembly. Then, a homogenized mixture containing BNC (0.025g) and tannic acid (0.5g) was mixed with 0.05g, 0.125g, and 0.25g of CNT respectively, and then vacuum filtered on it to form a membrane. The membrane was then placed between two BNCTA composite membranes and gently vacuumed to remove air bubbles between the membranes to obtain a sandwich-structured composite membrane.

[0178] (4) The above composite film is extruded by mechanical extrusion, and then placed in an oven at 80°C and dried by hot pressing with clamps for 3-7 days to finally obtain BCB.1:2 TA, BCB 1:5 TA, BCB 1:10 TA's septum.

[0179] Example 10

[0180] This embodiment uses a combination of static fermentation and dynamic shaking to prepare a lithium battery separator with an alarm function. The specific preparation method is as follows:

[0181] (1) Using Acetobacter xylinum as the strain, BNC membranes were obtained by in-situ static fermentation of fermentation medium in a clean bench for 3-15 days. The above BNC composite membranes of different concentrations were placed in sodium hydroxide solution and treated at 80℃ for 2-4 hours. After treatment, the membranes were taken out and rinsed with deionized water until neutral to obtain purified BNC membranes.

[0182] (2) The purified membrane was immersed in a mixture of 0.5%, 1%, and 2% pyrrole (CP, 99% (GC), Sinopharm Chemical Reagent Co., Ltd., the same below) and deionized water, and shaken for 12-48 hours. Then, a certain amount of FeCl3 (CP, ≥98%, Sinopharm Chemical Reagent Co., Ltd., the same below) solution was added dropwise under ice-water bath conditions, and the reaction was carried out in situ for 2-4 hours to polymerize pyrrole on the surface of the BNC membrane and uniformly coat the BNC fibers to obtain a BNC and PPy composite membrane. This membrane was sandwiched between two purified BNC membranes to obtain a sandwich-structured composite membrane.

[0183] (3) The above composite membrane is extruded by mechanical extrusion, and then placed in an oven at 80°C and dried by hot pressing for 3-7 days to finally obtain membranes with 0.5% BPB, 1% BPB and 2% BPB.

[0184] like Figure 34 The image shows a macroscopic view of a BPB composite membrane prepared by a combination of static fermentation and dynamic shaking. As can be seen from the image, the BPB membrane prepared by dynamic shaking is uniformly composited, black in color, and sandwiched between pure BNC membranes to form a sandwich structure.

[0185] Example 11

[0186] This embodiment uses a combination of static fermentation and dynamic shaking to prepare a lithium battery separator with warning and flame-retardant functions. The specific preparation method is as follows:

[0187] (1) Using Acetobacter xylinum as the strain, BNC membranes were obtained by in-situ static fermentation of fermentation medium in a clean bench for 3-15 days. The above BCB composite membranes of different concentrations were placed in sodium hydroxide solution and treated at 80℃ for 2-4 hours. After treatment, the membranes were taken out and rinsed with deionized water until neutral to obtain purified BNC membranes.

[0188] (2) The purified membranes were immersed in a mixture of pyrrole and deionized water with mass concentrations of 0.5%, 1%, and 2% respectively and shaken for 12-48 hours. Then, a certain amount of FeCl3 solution was added dropwise under ice-water bath conditions, and the reaction was carried out in situ for 2-4 hours to allow pyrrole to polymerize on the surface of the BNC membrane and uniformly coat the BNC fibers, thus obtaining 0.5% BNC / PPy, 1% BNC / PPy, and 2% BNC / PPy composite membranes.

[0189] (3) Two pure membranes were immersed in a chitosan solution with a mass concentration of 0.5% for 12-48 hours to obtain a BNC / CS composite membrane through solution self-assembly. The BNC / PPy composite membrane was sandwiched between the two BNC / CS composite membranes to obtain a sandwich-structured BPB. 0.5％ CS, BPB 1％ CS, BPB 2％ CS composite membrane.

[0190] (4) The above-mentioned BPB composite film is extruded by two mechanical extrusions, and then placed in an oven at 80°C and dried by hot pressing with clamps for 3-7 days to finally obtain BPB. 0.5％ CS, BPB 1％ CS, BPB 2％ The diaphragm of CS.

[0191] Example 12

[0192] This embodiment uses a dynamic in-situ horizontal drum fermentation method to prepare a lithium battery separator with warning and flame-retardant functions. The specific preparation method is as follows:

[0193] (1) Using Acetobacter xylinum as the strain, 300 mL of fermentation medium was used in a clean bench at a speed of 5-8 rpm for 2-5 days to obtain the first pure membrane. Subsequently, 0.5%, 0.75%, and 1% polypyrrole (PPy, 1 g, Shanghai Maclean Biochemical Technology Co., Ltd., purity: 10-50 S / cm, the same for other examples) was added to the fermentation medium mixture using a peristaltic pump and the dynamic horizontal drum fermentation was continued at a speed of 30-60 rpm for 12-48 hours. (Before sterilization, the mixture was dispersed for 5-10 minutes using an ultrasonic probe of an ultrasonic crusher. An appropriate amount of surfactant could be added to the aqueous solution as a dispersant, such as Tween 20, Tween 80, Tuyle dispersant DS-195, DS-172, DS-194H, cationic surfactant cetyl dimethyl ammonium bromide (CTAB), anionic surfactant sodium dodecylbenzene sulfonate (SDBS), and nonionic surfactant polyethylene glycol octylphenyl ether (Triton)). X-100), and in other embodiments, carbon nanotubes were pretreated using this method to form an intermediate BNC and PPy composite membrane layer; finally, 200 mL of fermentation medium was added using a peristaltic pump and horizontal drum fermentation was continued at a speed of 5-8 rpm for 2-5 days to obtain a 0.5% BPB, 0.75% BPB, and 1% BPB composite membrane with a sandwich structure.

[0194] (2) Place the above-mentioned BPB composite membranes of different concentrations in sodium hydroxide solution, treat them at 80°C for 2-4 hours, take them out, rinse them with deionized water until neutral, and obtain BPB composite membranes of different concentrations.

[0195] (3) The purified BPB composite membranes of different concentrations were immersed in a chitosan solution with a mass concentration of 0.5% for 12-48 hours to obtain BPB through solution self-assembly. 0.5％ CS, BPB 0.75 %CS, BPB 1％ CS composite membrane.

[0196] (4) The above-mentioned BPB composite film is extruded by two mechanical extrusions, and then placed in an oven at 80°C and dried by hot pressing with clamps for 3-7 days to finally obtain BPB. 0.5％ CS, BPB 0.75 %CS, BPB 1％ The diaphragm of CS.

[0197] Example 13

[0198] This embodiment uses a combination of dynamic in-situ horizontal drum fermentation, static fermentation, and fiber homogenization filtration to prepare a lithium battery separator with warning function. The specific preparation method is as follows:

[0199] (1) Using Acetobacter xylinum as the strain, fermentation was carried out in a clean bench at 5-8 rpm for 2-5 days to obtain the first pure membrane. Then, dynamic horizontal drum fermentation was carried out in a mixed solution of 0.5%, 0.75%, and 1% carbon nanotubes and fermentation medium at 30-60 rpm for 12-48 hours to form the intermediate BNC and CNT composite membrane layer. Finally, it was transferred to 200 mL of fermentation medium and fermented in a clean bench at 5-8 rpm for 2-5 days to obtain a 0.5% BCB, 0.75% BCB, and 1% BCB composite membrane with a sandwich structure. Using Acetobacter xylinum as the strain, in-situ static plate fermentation was carried out in a clean bench at 3-15 days to obtain the BNC membrane.

[0200] (2) The BCB composite membranes and BNC pure membranes of different concentrations were placed in sodium hydroxide solution and treated at 80°C for 2-4 hours. After that, they were taken out and rinsed with deionized water until neutral to obtain BCB composite membranes and BNC pure membranes of different concentrations.

[0201] (3) Take a portion of the purified BNC membrane and homogenize it to obtain a BNC homogenate.

[0202] (4) The purified three-layer BCB composite membranes of different concentrations were used as the first layer membrane; then, a BNC homogenate containing 0.025g was mixed with 0.05g, 0.125g, and 0.25g CNT respectively and vacuum filtered on it to form a membrane; finally, a purified BNC membrane was covered on it and vacuumed to remove air bubbles between the membranes to obtain a five-layer composite membrane with a sandwich structure.

[0203] (5) The above BCBCB composite film is extruded by mechanical extrusion, and then placed in an oven at 80°C and dried by hot pressing with clamps for 3-7 days to finally obtain BCB. 0.5％ CB 1:2 BCB 0.75％ CB 1:5 BCB 1％ CB 1:10 The diaphragm.

[0204] Example 14

[0205] This embodiment uses a fiber homogenization and filtration method to prepare a lithium battery separator with warning function. The specific preparation method is as follows:

[0206] (1) Take a slurry containing 0.075g CNF (plant nanofiber, lignin-containing nanocellulose, solid content of about 1.3%, lignin content of about 2.9%, Sciencek) and vacuum filter it to form the first layer membrane; then take a slurry containing 0.025g CNF and mix it with 0.05g, 0.125g, and 0.25g CNT respectively and vacuum filter it to form a membrane; finally, filter another layer of fiber containing 0.075g CNF slurry to obtain a sandwich structure composite membrane.

[0207] (2) The above composite film is extruded by mechanical extrusion, and then placed in an oven at 80°C and dried by hot pressing with clamps for 3-7 days to finally obtain CCC. 1:2 CCC 1:5 CCC 1:10 The diaphragm.

[0208] Figure 35 The tensile properties of the CCC composite membrane prepared by fiber homogenization and filtration are shown in the figure. The figure shows that the mechanical properties of the homogenized and filtered composite membrane decrease with increasing CNT doping concentration. This result is consistent with... Figure 33 (Tensile property diagrams of BCB composite membranes prepared by fiber homogenization and filtration) show the same conclusion. Comparison Figure 33 It can be seen that the mechanical properties (tensile strength and toughness) of BNC and its composite membranes are higher than those prepared by CNF. This is because BNC fibers are longer than CNF fibers, and the force generated by fiber accumulation after filtration is stronger.

[0209] Example 15

[0210] This embodiment uses a combination of dynamic in-situ horizontal drum fermentation, static fermentation, and fiber homogenization filtration to prepare a lithium battery separator with warning function. The specific preparation method is as follows:

[0211] (1) Using Acetobacter xylinum as the strain, fermentation was carried out in a clean bench at 5-8 rpm for 2-5 days to obtain the first pure membrane. Then, dynamic horizontal drum fermentation was carried out in a mixed solution of 0.5%, 0.75%, and 1% carbon nanotubes and fermentation medium at 30-60 rpm for 12-48 hours to form the intermediate BNC and CNT composite membrane layer. Finally, it was transferred to 200 mL of fermentation medium and fermented in a clean bench at 5-8 rpm for 2-5 days to obtain a 0.5% BCB, 0.75% BCB, and 1% BCB composite membrane with a sandwich structure. Using Acetobacter xylinum as the strain, in-situ static plate fermentation was carried out in a clean bench at 3-15 days to obtain the BNC membrane.

[0212] (2) The purified three-layer BCB composite membranes of different concentrations were used as the first layer membrane; then, 20g of CNC (cellulose nanocrystals) containing 0.025g, 20g of CNT (length: 200nm, diameter: 10nm, Sciencek) slurry were mixed with 0.05g, 0.125g, and 0.25g of CNT respectively and vacuum filtered on it to form a membrane; finally, a layer of purified BNC membrane was covered on it, and the membrane was gently vacuumed to remove air bubbles between the membranes to obtain a five-layer composite membrane with a sandwich structure.

[0213] (3) The above composite film is extruded by mechanical extrusion, and then placed in an oven at 80°C and dried by hot pressing with clamps for 3-7 days to finally obtain BCB. 0.5％ CB 1:2 BCB 0.75％ CB 1:5 BCB 1％ CB 1:10 The diaphragm.

[0214] Example 16

[0215] This embodiment uses a static fermentation method to prepare a lithium battery separator with an alarm function. The specific preparation method is as follows:

[0216] (1) Using Acetobacter xylinum as the strain, BNC membranes were obtained by in-situ static fermentation of fermentation medium in a clean bench for 2-3 days. The above BNC composite membranes of different concentrations were placed in sodium hydroxide solution and treated at 80℃ for 2-4 hours. After treatment, the membranes were taken out and rinsed with deionized water until neutral to obtain purified BNC membranes.

[0217] (2) Immerse the purified membrane in a 2% FeCl3 solution for 5-10 minutes.

[0218] (3) Add 0.5-1.5 mL of pyrrole solution to an evaporating dish with a diameter of 90 mm. Take the membrane treated in step (2) above and cover it on the evaporating dish. Place it in a refrigerator at 4°C and react for 30, 60 and 90 min respectively. Pyrrole vapor polymerizes in situ on the surface of BNC and uniformly coats the BNC fibers to obtain BP30, BP60 and BP90 composite membranes.

[0219] (4) Cover the BP30, BP60 and BP90 composite membranes with a layer of purified BNC membrane, respectively, and gently vacuum to remove air bubbles between the membranes to obtain a sandwich structure composite membrane.

[0220] (5) The above composite film is extruded by mechanical extrusion, and then placed in an oven at 80°C and dried by hot pressing with clamps for 3-7 days to finally obtain BPB. 30 BPB 60 BPB 90 The diaphragm.

[0221] Figure 36 The image shows a macroscopic view of the BPB composite membrane prepared by static fermentation. As can be seen, pyrrole polymerizes uniformly on the BNC side, hence the membrane on that side appears black. By controlling the reaction time, a BNC-PPy composite membrane can be obtained, forming a BPB sandwich structure with the third layer of pure BNC membrane. It is noteworthy that the thickness of the BPB membrane prepared by this method can be as low as 10 μm.

Claims

1. A nanofiber sandwich structure lithium battery separator with warning function, characterized in that, The lithium battery separator is a sandwich structure with three or more layers made of nanofibers. This sandwich structure includes a pure membrane and a conductive composite layer with an alarm function in the middle. The conductive composite layer is produced continuously and integrally as a lithium battery separator using dynamic in-situ horizontal drum fermentation. Dynamic in-situ horizontal drum fermentation: A 3D nano-network composite membrane with a sandwich structure is prepared using a horizontal drum reactor. This preparation process is divided into pure membrane fermentation, conductive composite layer fermentation, and pure membrane fermentation. For sandwich structures with more than three layers, conductive composite layer fermentation or pure membrane fermentation is carried out on this basis. The process parameters for pure membrane fermentation are: rotation speed 5-8 rpm, fermentation time 2-5 days. The process parameters for conductive composite layer fermentation are: rotation speed 30-60 rpm, fermentation time 12-48 h.

2. The nanofiber sandwich structure lithium battery separator with warning function as described in claim 1, characterized in that, The nanofibers mentioned are bacterial nanofibers.

3. The nanofiber sandwich structure lithium battery separator with warning function as described in claim 1, characterized in that, The conductive material used in the conductive composite layer is at least one of low-dimensional carbon material LDC, polypyrrole PPy, polyaniline PANI, and metal conductive filler.

4. The nanofiber sandwich structure lithium battery separator with warning function as described in claim 3, characterized in that, The low-dimensional carbon material LDC is at least one of carbon nanotubes (CNTs), graphene, and nano-carbon powder; the metal conductive filler is at least one of metal fibers, metal oxides, and nanoparticles.

5. The nanofiber sandwich structure lithium battery separator with warning function as described in any one of claims 1-4, characterized in that, The lithium battery separator also includes a flame-retardant coating with flame-retardant function, thus obtaining a nanofiber sandwich structure lithium battery separator that has both warning and flame-retardant functions.

6. The nanofiber sandwich structure lithium battery separator with warning function as described in claim 5, characterized in that, The flame retardant used in the flame retardant coating is at least one of the following: bromine-based flame retardant, phosphorus-based flame retardant, nitrogen-based flame retardant, inorganic flame retardant, and bio-based flame retardant.

7. The nanofiber sandwich structure lithium battery separator with warning function as described in claim 6, characterized in that, The bromine-based flame retardant includes at least one of decabromodiphenyl ethane, brominated epoxy resin, and brominated polystyrene; the phosphorus-based flame retardant includes at least one of red phosphorus masterbatch and diphenyl phosphate; the nitrogen-based flame retardant includes at least one of melamine, melamine cyanuric acid, and melamine phosphate; the inorganic flame retardant includes at least one of aluminum hydroxide and magnesium hydroxide; and the bio-based flame retardant includes at least one of cashew nut shell powder, phytic acid, tannic acid, and chitosan.

8. The method for preparing the nanofiber sandwich structure lithium battery separator with warning function according to any one of claims 1-7, characterized in that, Includes the following steps: Step 1): A 3D nano-network composite membrane with a sandwich structure is prepared using nanofibers, including a pure membrane and an intermediate conductive composite layer; Step 2): Immerse the composite membrane prepared in Step 1) into a solution containing flame retardant to form a flame retardant coating on the surface of the 3D nano-network structure fibers; Step 3): The composite membrane obtained in Step 1) or Step 2) is processed by mechanical extrusion and hot pressing and drying to obtain a nanofiber sandwich structure lithium battery separator with warning function or a nanofiber sandwich structure lithium battery separator with both warning and flame retardant functions.

9. The preparation method according to claim 8, characterized in that, The mechanical extrusion in step 3) specifically involves: first extruding for 5-20 minutes under 0.1-0.3 MPa conditions, and then extruding for 5-20 minutes under 0.4-0.6 MPa conditions; the hot pressing and drying temperature is 80℃, and the time is 3-7 days.

10. The application of a nanofiber sandwich structure lithium battery separator with warning function as described in any one of claims 1-7 in liquid lithium batteries, semi-solid lithium batteries or all-solid lithium batteries.

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