Barium sulfate nanofiber-based high-temperature-resistant battery separator and preparation method and application thereof

Abstract

The application relates to a barium sulfate nanofiber-based high-temperature-resistant battery diaphragm as well as a preparation method and application thereof. The barium sulfate nanofiber-based high-temperature-resistant battery diaphragm is a hybrid composite nanofiber network structure formed by barium sulfate nanofibers and cellulose nanofibers being wound together through hydrogen bonds and van der waals forces. The content of the barium sulfate nanofibers is 20-100 wt%, and the content of the cellulose nanofibers is 0-80 wt% in terms of mass percentage. Preferably, the content of the barium sulfate nanofibers is 40-80 wt%, and the content of the cellulose nanofibers is 20-60 wt%.

Description

Technical Field

[0001] This invention belongs to the field of battery material preparation, specifically relating to a barium sulfate nanofiber-based high-temperature resistant battery, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, lithium metal batteries, and other common lithium batteries possess advantages such as high energy density, high power density, and long cycle life, making them widely used in portable electronic devices, new power batteries, and energy storage batteries. A battery mainly consists of four parts: a positive electrode, a negative electrode, a separator, and an electrolyte. The separator, as one of the crucial components of the battery, serves two purposes: firstly, it prevents direct contact between the positive and negative electrodes, which could lead to a short circuit; secondly, it regulates and controls ion transport. The performance of the separator directly affects the battery's ion transport rate, ion transport pathway, electron transfer, interface structure, and impedance, thus influencing the battery's capacity, rate performance, and cycle life. Furthermore, the high-temperature stability of the separator directly determines the battery's safety; a separator with high-temperature stability can prevent the safety hazards of rapid battery overheating or even explosion.

[0003] With the increasing popularity of electric vehicles and new portable electronic devices in daily life, there is a demand for lithium-ion batteries to have longer cycle life, stronger range, wider operating temperature range, and be more economical and environmentally friendly. As an essential part of lithium-ion batteries, the separator can affect important parameters such as capacity, cycle performance, and working life.

[0004] Currently, commercially available battery separators can be classified into several categories, including microporous polyolefin membranes, non-woven membranes, and inorganic composite membranes. The commercially available separators widely used in lithium batteries are microporous polyolefin membranes. These membranes are inexpensive, have high tensile strength, and exhibit good electrochemical stability. However, these membranes also have significant drawbacks: (1) Polyolefin membranes have relatively weak polarity, while electrolytes often use highly polar organic solvent systems. When the electrolyte comes into contact with the polyolefin membrane, the membrane is almost impossible to wet with the electrolyte. Therefore, polyolefin membranes exhibit poor electrolyte affinity, which negatively impacts battery capacity, rate performance, and cycle life. (2) Polyolefin membranes are often obtained using a melt stretching method, which requires the membrane to have a certain mechanical strength. However, this method often results in polyolefin membranes having… The lower porosity (generally less than 60% for polyolefin separators) reduces the ion transport rate and ion transport quantity of the battery, resulting in a larger internal resistance and unsatisfactory electrochemical performance; (3) As is well known, polyolefin separators have poor high-temperature resistance. Most polyolefin separators cannot withstand temperatures above 150°C. When the temperature is high, they will shrink or melt, causing direct contact between the positive and negative electrodes, resulting in a short circuit in the battery. In severe cases, it may even cause the battery to burn or explode. Therefore, polyolefin separators have a high safety hazard. Although some separators will self-close at high temperatures, there will be safety hazards when the thermal shock is large. Therefore, it is urgent to develop a high-performance battery separator with good electrolyte wettability, uniform separator thickness, high ionic conductivity, high porosity, uniform pore structure, strong mechanical properties and excellent thermal stability. Summary of the Invention

[0005] To address the significant drawbacks of existing polyolefin-based separators, such as poor electrolyte wettability, low electrolyte absorption rate, low ionic conductivity, unsatisfactory cycle performance and rate capability, and poor thermal stability, this invention aims to provide a barium sulfate nanofiber-based high-temperature resistant battery separator, its preparation method, and its applications. This invention aims to improve the thermal stability and flame retardant properties of the battery separator, enhance its electrolyte wettability and adsorption performance, increase its ionic conductivity and ion transport capacity, thereby improving the electrochemical performance and safety of the battery.

[0006] Barium sulfate, as an inorganic compound, possesses excellent chemical stability, high-temperature resistance, and fire resistance. Membranes prepared using barium sulfate nanofibers exhibit good thermal stability and flame retardant properties. Therefore, applying barium sulfate nanofibers to battery separators can effectively enhance the separator's high-temperature resistance and flame retardant properties, significantly improving battery safety.

[0007] In a first aspect, the present invention provides a barium sulfate nanofiber-based high-temperature resistant battery separator, wherein the barium sulfate nanofiber-based high-temperature resistant battery separator is a hybrid composite nanofiber network structure formed by barium sulfate nanofibers and cellulose nanofibers being entangled together through hydrogen bonds and van der Waals forces; the content of the barium sulfate nanofibers is 20-100 wt% by mass percentage, and the content of the cellulose nanofibers is 0-80 wt%; preferably, the content of the barium sulfate nanofibers is 40-80 wt%, and the content of the cellulose nanofibers is 20-60 wt%.

[0008] Preferably, the diameter of the barium sulfate nanofibers is 5 to 200 nanometers; the length of the barium sulfate nanofibers is 20 to 2000 micrometers.

[0009] Preferably, the cellulose nanofibers are at least one of plant cellulose nanofibers and bacterial cellulose nanofibers.

[0010] Preferably, the thickness of the barium sulfate nanofiber-based high-temperature resistant battery separator is 10–200 μm.

[0011] Preferably, the barium sulfate nanofiber-based high-temperature resistant battery separator has a tensile strength of 4–100 MPa.

[0012] Preferably, the porosity of the barium sulfate nanofiber-based high-temperature resistant battery separator is 30% to 95%.

[0013] Preferably, the barium sulfate nanofiber-based high-temperature resistant battery separator has an electrolyte adsorption rate of 50% to 500%.

[0014] Secondly, the present invention provides a method for preparing a barium sulfate nanofiber-based high-temperature resistant battery separator, comprising: mixing a barium sulfate nanofiber aqueous slurry, a cellulose nanofiber dispersion and a solvent to obtain a barium sulfate nanofiber composite slurry; and subjecting the obtained barium sulfate nanofiber composite slurry to filtration to form a membrane, separation and drying to obtain the barium sulfate nanofiber-based high-temperature resistant battery separator.

[0015] Preferably, the concentration of the barium sulfate nanofiber aqueous slurry is not limited and can be any concentration.

[0016] Preferably, the solvent of the cellulose nanofiber dispersion is at least one of water and ethanol; the concentration of the cellulose nanofiber dispersion is not limited and can be any concentration.

[0017] Preferably, the concentration of the barium sulfate nanofiber aqueous slurry is not limited and can be any concentration.

[0018] Preferably, the solvent is at least one of water, ethanol, and isopropanol.

[0019] Preferably, the filtration is vacuum-assisted filtration.

[0020] Preferably, the drying temperature is 60–100°C and the time is 6–24 hours.

[0021] Thirdly, the present invention also provides a battery comprising the above-mentioned barium sulfate nanofiber-based high-temperature resistant battery separator.

[0022] Beneficial effects:

[0023] The barium sulfate nanofiber-based high-temperature resistant battery separator prepared by this invention possesses excellent properties, such as good electrolyte wetting performance, high electrolyte adsorption rate, excellent high-temperature resistance and flame retardancy, and good mechanical properties. These properties effectively improve the rate performance and cycle life of the battery, and significantly enhance battery safety. Therefore, the barium sulfate nanofiber composite high-performance high-temperature resistant separator can be applied to lithium-ion batteries, lithium metal batteries (including lithium-sulfur and lithium-air batteries), and other power and energy storage batteries. Attached Figure Description

[0024] Figure 1 Transmission electron micrograph of barium sulfate nanofibers prepared according to the present invention;

[0025] Figure 2 Transmission electron micrograph of the bacterial cellulose nanofibers used in this invention;

[0026] Figure 3 The images show the high-performance high-temperature resistant membrane (BC-BS) of barium sulfate nanofiber composite in Example 1 and the polypropylene membrane (PP) of Comparative Example 1 after being heated in ovens at 125°C, 150°C and 175°C for 30 minutes, respectively.

[0027] Figure 4 The images show the barium sulfate nanofiber composite high-performance high-temperature resistant membrane (BC-BS) of Example 1 and the polypropylene membrane (PP) of Comparative Example 1 before and after calcination for 10 seconds; wherein, (a) is a photo of the barium sulfate nanofiber composite high-performance high-temperature resistant membrane before calcination; (b) is a photo of the barium sulfate nanofiber composite high-performance high-temperature resistant membrane after calcination for 10 seconds; (c) is a photo of the polypropylene membrane before calcination; and (d) is a photo of the polypropylene membrane after calcination for 10 seconds.

[0028] Figure 5 The results show the rate performance test results of lithium iron phosphate-graphite batteries using the barium sulfate nanofiber composite high-performance high-temperature resistant separator (BC-BS) of Example 1 and the polypropylene separator (PP) of Comparative Example 1 at 0.2C, 0.5C, 1C and 2C, respectively.

[0029] Figure 6The results of the cycle tests of lithium iron phosphate-graphite batteries using the high-performance high-temperature resistant membrane (BC-BS) of barium sulfate nanofiber composite in Example 1 and the polypropylene membrane (PP) in Comparative Example 1 are shown at a 2C rate.

[0030] Figure 7 The results show the thermal runaway behavior of lithium iron phosphate-graphite batteries using the high-performance high-temperature resistant separator (BC-BS) of barium sulfate nanofiber composite in Example 1 and the polypropylene separator (PP) in Comparative Example 1; where (a) is the self-heating temperature versus time graph; and (b) is the self-heating rate versus temperature graph.

[0031] Figure 8 The lithium iron phosphate-graphite soft-pack full battery assembled using the barium sulfate nanofiber composite high-performance high-temperature resistant separator (BC-BS) of Example 1 was used to power the display screen at various bending angles. Detailed Implementation

[0032] To further illustrate the invention's content, features, and practical effects, the invention will be described in detail below with reference to embodiments. It should be noted that the modification methods of the invention are not limited to these specific implementation methods. Equivalent substitutions and modifications made by those skilled in the art based on their reading of the invention, without departing from its spirit and essence, are also within the scope of protection claimed by the invention. Unless otherwise specified, percentage content refers to mass percentage content.

[0033] In this invention, the barium sulfate nanofiber-based high-temperature resistant battery separator is prepared by combining barium sulfate nanofibers and cellulose nanofibers. The barium sulfate nanofiber-based high-temperature resistant battery separator is a hybrid composite nanofiber network structure formed by the interaction of barium sulfate nanofibers and cellulose nanofibers through hydrogen bonds and van der Waals forces. By mass percentage, the content of barium sulfate nanofibers is 20–100 wt%, and the content of cellulose nanofibers is 0–80 wt%; preferably, the content of barium sulfate nanofibers is 40–80 wt%, and the content of cellulose nanofibers is 20–60 wt%. This invention allows for the control of the tensile strength, porosity, and electrolyte adsorption rate of the barium sulfate nanofiber composite high-performance high-temperature resistant separator by adjusting the weight ratio of barium sulfate nanofibers to cellulose nanofibers. If the content of barium sulfate nanofibers is too low, the specific capacity of the battery will decrease; if the content of barium sulfate nanofibers is too high, it will affect the pore structure characteristics of the separator and the electrolyte wetting properties. The barium sulfate nanofibers have a diameter of 5–200 nanometers and a length of 20–2000 micrometers. The cellulose nanofibers are at least one of plant cellulose nanofibers and bacterial cellulose nanofibers. The diameter of the barium sulfate nanofiber-based high-temperature resistant battery separator can be controlled as needed; the thickness of the barium sulfate nanofiber-based high-temperature resistant battery separator is 10–200 μm.

[0034] The barium sulfate nanofiber composite high-temperature resistant battery separator prepared by this invention possesses excellent high-temperature resistance and electrochemical performance, good electrolyte wetting properties, high porosity, high electrolyte adsorption rate, relatively uniform pore structure, mechanical strength meeting normal use requirements, excellent thermal stability and flame retardant properties, and can effectively improve the battery's fast charging capability, rate performance, cycle life, and battery safety. The barium sulfate nanofiber-based high-temperature resistant battery separator has a tensile strength of 4–100 MPa; a porosity of 30%–95%; and an electrolyte adsorption rate of 50%–500%.

[0035] Barium sulfate, as an inorganic compound, possesses excellent chemical stability, high-temperature resistance, and fire resistance. Membranes prepared using barium sulfate nanofibers exhibit good flame-retardant properties. Therefore, applying barium sulfate nanofibers to battery separators can effectively enhance the high-temperature resistance and flame-retardant properties of the separator, significantly improving battery safety. Cellulose nanofibers have a high dielectric constant, and when a voltage is applied, barium sulfate nanofibers generate oriented dipoles. These dipoles help form a uniform electric field at the interface between the separator and the electrolyte, known as MAX-Wagner polarization. The built-in electric field formed by this polarization can effectively modulate the lithium-ion solvation structure at the separator-electrolyte interface. In this invention, the oriented electric field generated by combining barium sulfate nanofibers and cellulose nanofibers can attract coordinating solvent molecules in the solvated outer sheath through dipole-dipole interactions, making it easier for hydrated lithium ions to escape the binding of solvent molecules, thereby accelerating their transport speed between electrodes.

[0036] This invention uses a vacuum filtration method to prepare barium sulfate nanofiber-based high-temperature resistant battery separators, which has the advantages of simple operation, low cost, and easy mass production.

[0037] The following is an exemplary description of the preparation method of the barium sulfate nanofiber-based high-temperature resistant battery separator provided by the present invention.

[0038] The barium sulfate nanofibers of this invention can be prepared by a hydrothermal method, referring to the methods reported in published patents and literature, such as: Zhu Yingjie, Wu Jin, A barium sulfate fiber and its preparation method, patent number CN202010705516.1; Zhu Yingjie, Wu Jin, A barium sulfate fiber inorganic refractory paper and its preparation method and application, patent number CN202010705522.7; Jin Wu, Ying-Jie Zhu, Eur.J.Inorg, 2021, 429-499 (2020). The hydrothermal method includes: (1) using oleate as reactant and emulsifier, using water-soluble barium salt as barium source, and using water as solvent to obtain a barium oleate precursor suspension through chemical reaction. The water-soluble barium salt can be selected from at least one of barium chloride and barium nitrate. The oleate can be selected from at least one of sodium oleate, potassium oleate, and ammonium oleate. This invention selects water as the reaction solvent, which is low in cost, environmentally friendly, and conducive to large-scale production. In the barium oleate precursor suspension, the concentration of oleate is 0.01–2 mol / L, preferably 0.1–1 mol / L; the concentration of water-soluble barium salt is 0.01–2 mol / L, preferably 0.03–1 mol / L. (2) Then, water-soluble sulfate is added to the barium oleate precursor suspension to obtain a barium sulfate precursor suspension. The water-soluble sulfate can be selected from at least one of sodium sulfate, potassium sulfate, and ammonium sulfate. The concentration of water-soluble sulfate is 0.01–6 mol / L, preferably 0.1–1 mol / L. (3) The obtained barium sulfate precursor suspension is placed in a reaction vessel, sealed, and subjected to hydrothermal treatment at a temperature of 120–240°C, preferably 160–200°C. After separation, the product is washed several times with ethanol and water, and dried to obtain the barium sulfate nanofibers (e.g. Figure 1 (As shown). The network structure of barium sulfate nanofibers prepared via a hydrothermal method using calcium oleate precursors can intertwine with cellulose nanofibers to form a porous network structure, significantly improving the mechanical properties of the composite separator. As a separator material, it can enhance the performance of lithium-ion batteries by modulating ion transport properties through a polarized electric field. Other methods typically produce barium sulfate particles, which are difficult to use to prepare separators.

[0039] Preparation of barium sulfate nanofiber composite slurry. Aqueous barium sulfate nanofiber slurry, cellulose nanofiber dispersion, and solvent were mixed in a certain proportion to obtain a uniformly dispersed barium sulfate nanofiber composite slurry.

[0040] In an optional embodiment, the solvent of the cellulose nanofiber dispersion is at least one of water and ethanol; the concentration of the cellulose nanofiber dispersion is not limited and can be any concentration.

[0041] In an optional embodiment, the cellulose nanofibers include, but are not limited to, at least one of plant fibers and bacterial cellulose.

[0042] In an optional embodiment, the concentration of the barium sulfate nanofiber aqueous slurry is not limited and can be any concentration.

[0043] In an optional embodiment, the solvent includes, but is not limited to, at least one of water, ethanol, and isopropanol.

[0044] The obtained barium sulfate nanofiber composite slurry is then filtered to form a membrane. Specifically, the barium sulfate nanofiber composite slurry is filtered and separated using a vacuum filter to obtain a wet-state high-performance, high-temperature resistant barium sulfate nanofiber composite separator for batteries.

[0045] Drying and post-treatment. The above-mentioned wet barium sulfate nanofiber composite high-performance high-temperature resistant separator is dried and pressed (including roller pressing) to obtain the barium sulfate nanofiber composite high-performance high-temperature resistant separator for batteries.

[0046] In an optional embodiment, the drying temperature is 60–100°C and the time is 6–24 hours.

[0047] The high-performance, high-temperature resistant separator made of barium sulfate nanofibers for batteries prepared by this invention has applications in lithium-ion batteries, lithium metal batteries (including lithium-sulfur and lithium-air batteries), and other power and energy storage batteries.

[0048] This invention uses a micrometer (accuracy 0.01 mm) to test the thickness of the battery separator. Five points are randomly selected on the separator, and the average value is calculated. A universal testing machine (Drick, DRK-101B) is used to test the tensile strength of the barium sulfate nanofiber composite high-performance high-temperature resistant battery separator and a comparative battery separator. Specifically, the separator is cut into rectangular strips 40 mm long and 10 mm wide. The two ends of the strips are clamped on the universal testing machine for tensile strength testing. The clamping speed is 1 mm / min, and the clamp spacing is 15 mm. Porosity: The battery separator is immersed in n-butanol for 1 hour, and then the porosity is calculated according to the formula: Porosity (%) = (Δm / ρ) / V0 × 100%; where Δm is the difference between the weight of the separator after adsorbing n-butanol and the initial weight of the separator, V0 is the volume of the separator, and ρ is the density of n-butanol. Measurements are taken three times, and the average value is calculated. Electrolyte adsorption rate: Immerse the battery separator in the electrolyte for 30 minutes, and then calculate according to the following formula: Electrolyte adsorption rate (%) = (M - M0) / M0 × 100%; where M0 is the initial weight of the separator, and M is the weight of the separator after adsorbing electrolyte. Measure three times and calculate the average value.

[0049] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0050] Example 1

[0051] At room temperature, 7 mg of barium sulfate nanofiber aqueous slurry with a concentration of 6.5 mg / ml was dispersed in 50 mL of ethanol. 10.5 mg of bacterial cellulose nanofiber dispersion with a concentration of 3.5 mg / ml was added and stirred for 20 minutes. The mixture was then placed on a 40 mm diameter sand core funnel for vacuum filtration. After drying at 60 °C for 24 h, a barium sulfate nanofiber composite high-performance high-temperature resistant battery separator with a diameter of 40 mm and a thickness of 18 micrometers was obtained.

[0052] Figure 3 The images show the results of heat treatment at 125°C, 150°C, and 175°C for 30 minutes on a barium sulfate nanofiber composite high-performance high-temperature resistant battery separator and a polypropylene separator. As can be seen from the images, the polypropylene separator exhibits significant thermal shrinkage at 125°C. At 175°C, the polypropylene separator completely transforms into a transparent state, indicating that it has melted, closed its pores, and completely lost its function. In contrast, the barium sulfate nanofiber composite high-performance high-temperature resistant battery separator does not show significant shrinkage at the high temperatures of 125, 150, and 175°C, demonstrating good thermal stability. Although the barium sulfate nanofiber composite high-performance high-temperature resistant battery separator shows slight yellowing due to the oxidation of cellulose nanofibers at high temperatures, its shape and size remain intact. This indicates that the barium sulfate nanofiber composite high-performance high-temperature resistant battery separator prepared in this invention possesses excellent high-temperature resistance.

[0053] Figure 4 These are photographs of a barium sulfate nanofiber composite high-performance high-temperature resistant battery separator and a polypropylene battery separator before and after 10 seconds of burning. As shown in the figures, the surface color of the barium sulfate nanofiber composite high-performance high-temperature resistant battery separator darkens, but the complete membrane structure is still visible. In contrast, the polypropylene separator immediately curls upon contact with the flame of the alcohol lamp, is rapidly ignited, and burns completely within a very short time (2 seconds). This indicates that the barium sulfate nanofiber composite high-performance high-temperature resistant battery separator prepared in this invention has good flame-retardant properties.

[0054] Example 2

[0055] At room temperature, 8.75 mg of barium sulfate nanofiber aqueous slurry with a concentration of 6.5 mg / ml was dispersed in 50 mL of ethanol, and 8.75 mg of bacterial cellulose nanofiber dispersion with a concentration of 3.5 mg / ml was added. After stirring for 20 minutes, the mixture was placed on a 40 mm diameter sand core funnel for vacuum filtration. After drying and peeling off the membrane, a barium sulfate nanofiber composite high-performance high-temperature resistant battery separator with a diameter of 40 mm and a thickness of 23 micrometers was obtained.

[0056] Example 3

[0057] At room temperature, 10.5 mg of barium sulfate nanofiber aqueous slurry with a concentration of 6.5 mg / ml was dispersed in 50 mL of ethanol, and 7 mg of bacterial cellulose nanofiber dispersion with a concentration of 3.5 mg / ml was added. After stirring for 20 minutes, the mixture was placed on a 40 mm diameter sand core funnel for vacuum filtration. After drying and peeling off the membrane, a barium sulfate nanofiber composite high-performance high-temperature resistant battery separator with a diameter of 40 mm and a thickness of 18 micrometers was obtained.

[0058] Example 4

[0059] At room temperature, 6 mg of barium sulfate nanofiber aqueous slurry with a concentration of 6.5 mg / ml was dispersed in 50 mL of ethanol, and 9 mg of bacterial cellulose nanofiber dispersion with a concentration of 3.5 mg / ml was added. After stirring for 20 minutes, the mixture was placed on a 40 mm diameter sand core funnel for vacuum filtration. After drying and peeling off the membrane, a barium sulfate nanofiber composite high-performance high-temperature resistant battery separator with a diameter of 40 mm and a thickness of 18 micrometers was obtained.

[0060] Example 5

[0061] At room temperature, 8 mg of barium sulfate nanofiber slurry with a concentration of 6.5 mg / ml was dispersed in 50 mL of ethanol, and 12 mg of bacterial cellulose nanofiber dispersion with a concentration of 3.5 mg / ml was added. After stirring for 20 minutes, the mixture was placed on a 40 mm diameter sand core funnel for vacuum filtration. After drying and peeling off the membrane, a barium sulfate nanofiber composite high-performance high-temperature resistant battery separator with a diameter of 40 mm and a thickness of 25 micrometers was obtained.

[0062] Comparative Example 1

[0063] A commercially available polypropylene battery separator (24 micrometers thick, 42.9% porosity) was used as a comparison.

[0064] The battery separators in Examples 1-5 and Comparative Example 1 were characterized and their performance was tested. Table 1 shows the performance parameters of the barium sulfate nanofiber composite high-performance high-temperature resistant battery separators prepared in Examples 1-5 of this invention and the polypropylene separator in Comparative Example 1.

[0065] Table 1:

[0066]

[0067] As shown in Table 1, the porosity of the barium sulfate nanofiber composite high-performance high-temperature resistant battery separators prepared in Examples 1-5 of this invention is greater than that of the polypropylene separator in Comparative Example 1. This is mainly due to the drawing process in the preparation of the commercial polypropylene separator. These non-uniform, discontinuous, and serrated pore structure characteristics result in the lower porosity of the commercial polypropylene separator. The barium sulfate nanofiber composite high-performance high-temperature resistant battery separator is composed of an ordered layered structure, which gives the separator good porous properties that are beneficial for the wetting and diffusion of the liquid electrolyte. Except for Example 3, the electrolyte adsorption rate of the barium sulfate nanofiber composite high-performance high-temperature resistant battery separators prepared in Examples 1-2 and Examples 4-5 of this invention is greater than that of the polypropylene separator in Comparative Example 1. This is because the ratio of barium sulfate nanofibers to cellulose nanofibers in Example 3 is optimal.

[0068] Battery performance test

[0069] (1) Preparation of the battery cathode: The cathode material tested for both coin cell and pouch cell (lithium iron phosphate-graphite battery) was a high-load lithium iron phosphate cathode with a loading of 15.5 mg / cm³. 2 The electrode sheet was stamped to obtain a 12mm diameter coin cell positive electrode sheet. The lithium iron phosphate positive electrode sheet was cut to a size of 3cm × 3cm to serve as the positive electrode sheet for a pouch cell.

[0070] (2) Preparation of the battery anode: The anode material tested for both coin cell and pouch cell (lithium iron phosphate-graphite battery) was a high-load graphite anode with a loading of 7.5 mg / cm³. 2 The electrode sheet was stamped to obtain a 13mm diameter coin cell negative electrode sheet. The graphite negative electrode was cut to a size of 3cm × 3cm to serve as the negative electrode sheet for a pouch cell.

[0071] (3) Battery Assembly. In an argon-filled glove box, the negative electrode and battery separator were sequentially placed into the battery casing, 100 μL of electrolyte was added, the positive electrode was then placed in, and the battery casing was sealed to obtain the battery. The electrolyte used for testing at room temperature was 1.2 M LiPF6, with a solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and 2 wt.% ethylene carbonate (VC) was added. For the pouch battery, the separator was cut into 3.5 cm × 3.5 cm squares for later use. In an argon-filled glove box, the above-mentioned spare electrodes and separator were assembled according to the lithium iron phosphate / separator / graphite structure. The electrolyte was added before final packaging, and the battery was packaged with an aluminum-plastic film.

[0072] Figure 5The figures show the rate performance test results of lithium iron phosphate-graphite batteries using the barium sulfate nanofiber composite high-performance high-temperature resistant separator of Example 1 and the polypropylene separator of Comparative Example 1 at 0.2C, 0.5C, 1C, and 2C. As can be seen from the figures, the rate performance of high-load lithium iron phosphate / / graphite full cells with different separators is as follows: Compared with the battery using the polypropylene separator, the battery with the barium sulfate nanofiber composite high-performance high-temperature resistant separator exhibits a higher rate of 149.5 mAh g⁻¹ at 0.2C. -1 The discharge specific capacity is superior to that of batteries using polypropylene separators (capacity of 119.9 mAh g). -1 This indicates that the lithium iron phosphate-graphite battery prepared using a high-performance, high-temperature resistant battery separator made of barium sulfate nanofibers exhibits excellent rate performance.

[0073] Figure 6 The figures show the cycle test results of lithium iron phosphate-graphite batteries using the barium sulfate nanofiber composite high-performance high-temperature resistant separator of Example 1 and the polypropylene separator of Comparative Example 1 at 2C rate. As can be seen from the figures, the high-load lithium iron phosphate / / graphite full cells with different separators exhibit varying performance at 2C (~10.8 mA cm⁻¹). -2 The battery exhibits fast charging performance at accelerated charging / discharging current densities. The battery using a barium sulfate nanofiber composite high-performance high-temperature resistant separator demonstrates a high initial discharge capacity of 123.3 mAh g⁻¹. -1 (or ~1.91mAh cm) -2 The battery using a standard polypropylene separator exhibited a lower initial discharge capacity of 103.8 mAh g⁻¹. -1 (approximately 1.60mAh cm) -2 As can be seen, the battery using the barium sulfate nanofiber composite high-performance high-temperature resistant separator outperforms the battery using the standard polypropylene separator by 18.7%. Furthermore, the battery using the barium sulfate nanofiber composite high-performance high-temperature resistant separator maintains excellent cycle stability, achieving an impressive 70% capacity retention after up to 500 cycles. In stark contrast, the battery using the polypropylene separator exhibits significant capacity decay, with a retention rate of 49% after 150 cycles and 27% after 500 cycles. This demonstrates that the lithium iron phosphate-graphite battery prepared using the barium sulfate nanofiber composite high-performance high-temperature resistant battery separator possesses excellent cycle life.

[0074] Figure 7The results of thermal runaway behavior tests conducted using an accelerating calorimeter on the lithium iron phosphate-graphite battery using the barium sulfate nanofiber composite high-performance high-temperature resistant separator of Example 1 and the polypropylene separator of Comparative Example 1, under fully charged conditions, are shown in (a) as a graph of self-heating temperature versus time and (b) as a graph of self-heating rate versus temperature. As can be seen from the figures, the excellent thermal stability of the BS / BC separator can effectively increase the critical temperature for thermal runaway, reduce heat release, and significantly improve the thermal safety of the battery. This indicates that the lithium iron phosphate-graphite battery assembled using the barium sulfate nanofiber composite high-performance high-temperature resistant battery separator exhibits excellent high-temperature stability.

[0075] Figure 8 The lithium iron phosphate-graphite pouch cell assembled using the barium sulfate nanofiber composite high-performance high-temperature resistant separator (BC-BS) of Example 1 was tested to power a display screen at various bending angles. As shown in the figure, the lithium iron phosphate-graphite pouch cell assembled using the barium sulfate nanofiber composite high-performance high-temperature resistant separator (BC-BS) of Example 1 can illuminate the display screen at various bending angles. This indicates that the lithium iron phosphate-graphite pouch cell assembled using the barium sulfate nanofiber composite high-performance high-temperature resistant separator (BC-BS) prepared in this invention is not affected by the bending angle and can operate normally at various bending angles.

Claims

1. A barium sulfate nanofiber-based high-temperature resistant battery separator, characterized in that, The barium sulfate nanofiber-based high-temperature resistant battery separator is a hybrid composite nanofiber network structure formed by the interaction of barium sulfate nanofibers and cellulose nanofibers through hydrogen bonds and van der Waals forces; the content of barium sulfate nanofibers is 40-80 wt%, and the content of cellulose nanofibers is 20-60 wt%. The diameter of the barium sulfate nanofibers is 5-200 nanometers; the length of the barium sulfate nanofibers is 20-2000 micrometers; the barium sulfate nanofibers are network-structured barium sulfate nanofibers prepared by hydrothermal treatment of a barium sulfate precursor suspension in a reaction vessel, and the hydrothermal treatment temperature is 120-240℃. The cellulose nanofibers are at least one of plant cellulose nanofibers and bacterial cellulose nanofibers; The preparation method of the barium sulfate nanofiber-based high-temperature resistant battery separator includes: mixing barium sulfate nanofiber aqueous slurry, cellulose nanofiber dispersion and solvent to obtain barium sulfate nanofiber composite slurry; The obtained barium sulfate nanofiber composite slurry was filtered to form a membrane, separated, and dried to obtain the barium sulfate nanofiber-based high-temperature resistant battery separator.

2. The barium sulfate nanofiber-based high-temperature resistant battery separator according to claim 1, characterized in that, The thickness of the barium sulfate nanofiber-based high-temperature resistant battery separator is 10–200 micrometers.

3. The barium sulfate nanofiber-based high-temperature resistant battery separator according to claim 1, characterized in that, The tensile strength of the barium sulfate nanofiber-based high-temperature resistant battery separator is 4–100 MPa; The porosity of the barium sulfate nanofiber-based high-temperature resistant battery separator is 30%–95%. The barium sulfate nanofiber-based high-temperature resistant battery separator has an electrolyte adsorption rate of 50% to 500%.

4. The barium sulfate nanofiber-based high-temperature resistant battery separator according to claim 1, characterized in that, The solvent for the cellulose nanofiber dispersion is at least one of water and ethanol; The solvent is at least one of water, ethanol, and isopropanol.

5. The barium sulfate nanofiber-based high-temperature resistant battery separator according to claim 1, characterized in that, The filtration is vacuum-assisted filtration; The drying temperature is 60–100°C, and the time is 6–24 h.

6. A battery comprising a barium sulfate nanofiber-based high-temperature resistant battery separator according to any one of claims 1-3.

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