Modified diaphragm, preparation method thereof and sodium ion battery

Abstract

The invention belongs to the technical field of electrochemical energy storage materials, and discloses a modified diaphragm and a preparation method thereof, and a sodium ion battery, the preparation method comprises the following steps: S1, mixing an oxide and an ethanol aqueous solution containing a binder, and stirring to form a dispersion liquid; s2, soaking a glass fiber diaphragm in the dispersion liquid; s3, drying the soaked glass fiber diaphragm to obtain a modified diaphragm; wherein the oxide is at least one of aluminum oxide, zirconium oxide, magnesium oxide, silicon oxide, titanium oxide and cerium oxide; the binder is at least one of sodium carboxymethyl cellulose, butadiene styrene rubber, polyacrylic acid, sodium alginate and polyvinyl alcohol. The modified diaphragm has good electrolyte wettability, and when the modified diaphragm is applied to the sodium ion battery, the rate capability and the cycle stability of the battery can be effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage materials technology, specifically relating to a modified separator, its preparation method, and a sodium-ion battery. Background Technology

[0002] Lithium-ion batteries, due to their inherent advantages such as high energy density, long cycle life, high operating voltage, and low self-discharge, have been widely used in consumer electronics, electric vehicles, and energy storage systems. Meanwhile, the demand for improved battery performance is increasing. Sodium and lithium belong to the same group and have similar physicochemical properties. Furthermore, sodium is abundant, evenly distributed, and inexpensive on Earth, making it an ideal choice for next-generation large-scale energy storage technology. Sodium-ion batteries mainly consist of a positive electrode, a negative electrode, a current collector, a separator, an electrolyte, and a battery casing. Their working principle is similar to that of lithium batteries. During charging, sodium ions migrate from the positive electrode through the separator and electrolyte to the negative electrode. During discharging, sodium ions migrate from the negative electrode back to the positive electrode. The entire charge-discharge cycle is a directional migration process of sodium ions between the positive and negative electrodes. The main advantage of sodium-ion batteries over lithium-ion batteries lies in cost reduction, including the cost of sodium salt raw materials, electrolyte, and foil materials.

[0003] The separator is a crucial component of sodium-ion batteries. Its primary function is not only to prevent direct contact between the positive and negative electrodes, thus preventing short circuits, but also to provide porous channels for sodium ion transport. Therefore, the physicochemical properties of the separator have a vital impact on the battery's electrochemical performance and safety. Currently, the most commonly used separators in sodium-ion batteries are polyolefin separators and glass fiber separators. Polyolefin separators include polyethylene (PE) and polypropylene (PP) separators. These materials typically have low porosity, poor wettability to the electrolyte, and poor thermal stability. Furthermore, during charging, sodium dendrites easily form on the negative electrode surface, gradually growing and eventually piercing the separator, leading to a short circuit.

[0004] Glass fiber membranes have gradually become candidate membrane materials for sodium-ion batteries due to their high temperature resistance, high porosity and good electrolyte wettability. However, they can easily lead to a decrease in the rate performance and insufficient cycle stability of the battery. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a modified separator, which can introduce inorganic oxides on the surface of a glass fiber separator. When applied to a sodium-ion battery, this method can effectively improve the rate performance and cycle stability of the battery.

[0006] The following technical solutions are used to achieve the above objectives.

[0007] The first aspect of this invention provides a method for preparing a modified diaphragm, comprising the following steps:

[0008] S1. Mix the oxide and the ethanol aqueous solution containing the binder, and stir to form a dispersion;

[0009] S2. Immerse the glass fiber diaphragm in the dispersion;

[0010] S3. After soaking, the glass fiber diaphragm is dried to obtain the modified diaphragm.

[0011] Wherein, the oxide is at least one of aluminum oxide, zirconium oxide, magnesium oxide, silicon oxide, titanium oxide, and cerium oxide;

[0012] The adhesive is at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, sodium alginate, and polyvinyl alcohol.

[0013] In some embodiments, in step S1, the concentration of the oxide in the dispersion is 2g~10g / 100mL, preferably 3g~8g / 100mL, more preferably 4g~6g / 100mL, and even more preferably 4.5g~5.5g / 100mL.

[0014] In some embodiments, the volume ratio of ethanol to water in the aqueous ethanol solution is 1:9 to 9:1, preferably 1:1 to 4:1, and more preferably 1:1 to 1.5:1.

[0015] In some embodiments, in step S1, the stirring speed is 200 r / min to 600 r / min, and the stirring time is 30 min to 150 min, preferably 80 min to 140 min, more preferably 100 min to 130 min, and even more preferably 115 min to 125 min.

[0016] In some embodiments, the oxide is nano-alumina with a particle size of 100nm~200nm;

[0017] And / or, the binder is sodium carboxymethyl cellulose.

[0018] In some embodiments, the glass fiber diaphragm is one of GF / A, GF / B, GF / C, GF / D, and GF / F, preferably GF / D.

[0019] In some embodiments, in step S2, the soaking time is 1 min to 30 min, preferably 1 min to 5 min, and more preferably 1.5 min to 2.5 min.

[0020] In some embodiments, in step S3, the drying process is hot air drying or vacuum drying, and the drying temperature is 50~120 ℃, preferably 55℃~65℃.

[0021] A second aspect of the present invention provides a modified diaphragm prepared by the method described above.

[0022] A third aspect of the present invention provides a sodium-ion battery, the sodium-ion battery comprising a casing and a cell; the cell is encapsulated within the casing, and the cell is impregnated with an electrolyte;

[0023] The battery cell includes a positive electrode, a negative electrode, and a modified separator as described above, and the positive electrode, the modified separator, and the negative electrode are stacked in sequence.

[0024] In this invention, we discovered a method suitable for modifying glass fiber membranes with oxides. The method involves mixing oxides and a binder in an aqueous ethanol solution to obtain a dispersion, and then immersing the glass fiber membrane in the dispersion to load and modify the membrane. This allows the oxides to penetrate the pores of the glass fiber membrane and form a three-dimensional anchoring structure with the glass fibers, constructing stable ion transport channels and a mechanically reinforced network. By combining appropriate oxide concentrations, solvent ratios, and stirring times, the prepared modified membrane can ensure electrolyte wettability. Furthermore, when this modified membrane is applied to sodium-ion batteries, it can effectively improve the battery's rate performance and cycle stability.

[0025] The preparation method of this invention is simple, using a one-step process of low-temperature soaking-in-situ loading-mild drying. It can obtain modified membranes without complex coating equipment or high-temperature sintering steps, and has better advantages for large-scale application. Attached Figure Description

[0026] Figure 1 The images are scanning electron microscope (SEM) images of the diaphragms of Example 1 and Comparative Example 1.

[0027] Figure 2 The diagram shows the contact angle test results for the diaphragms of Example 1 and Comparative Example 1.

[0028] Figure 3 The first charge-discharge curves of sodium-ion batteries in Example 1 and Comparative Example 1 are shown.

[0029] Figure 4 The charge-discharge curves of sodium-ion batteries in Example 1 and Comparative Examples 1-8 after 50 cycles are shown.

[0030] Figure 5 The figures show the low-current cycling curves of sodium-ion batteries in Example 1 and Comparative Example 1.

[0031] Figure 6The rate performance of sodium-ion batteries in Example 1 and Comparative Example 1 is shown.

[0032] Figure 7 The images show the AC impedance spectra of sodium-ion batteries in Example 1 and Comparative Example 1. Detailed Implementation

[0033] To facilitate understanding of the present invention, a more complete description will be provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0034] Unless otherwise specified, experimental methods in the following examples are generally performed under standard conditions or as recommended by the manufacturer. All commonly used chemical reagents used in the examples are commercially available products.

[0035] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used in this invention includes any and all combinations of one or more of the associated listed items.

[0036] This invention provides a method for preparing a modified diaphragm, comprising the following steps:

[0037] S1. Mix the oxide and the ethanol aqueous solution containing the binder, and stir to form a dispersion;

[0038] S2. Immerse the glass fiber diaphragm in the dispersion;

[0039] S3. After soaking, the glass fiber diaphragm is dried to obtain the modified diaphragm.

[0040] Wherein, the oxide is at least one of aluminum oxide, zirconium oxide, magnesium oxide, silicon oxide, titanium oxide, and cerium oxide;

[0041] The adhesive is at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, sodium alginate, and polyvinyl alcohol.

[0042] In this invention, we discovered a method suitable for modifying glass fiber membranes with oxides. The method involves mixing oxides and a binder in an aqueous ethanol solution to obtain a dispersion, and then immersing the glass fiber membrane in the dispersion to load and modify the membrane. This allows the oxides to penetrate the pores of the glass fiber membrane and form a three-dimensional anchoring structure with the glass fibers, constructing stable ion transport channels and a mechanically reinforced network. By combining appropriate oxide concentrations, solvent ratios, and stirring times, the prepared modified membrane can ensure electrolyte wettability. Furthermore, when this modified membrane is applied to sodium-ion batteries, it can effectively improve the battery's rate performance and cycle stability.

[0043] Alumina, being nano-sized inorganic particles, has a decisive influence on the microstructure of the subsequent membrane modification layer due to its dispersion state in the dispersion solution. When the stirring time is too short, the nano-alumina particles are difficult to fully deagglomerate and tend to exist as aggregates, leading to uneven particle distribution in the dispersion solution. The resulting modified membrane exhibits localized enriched and depleted regions at the microscale, resulting in uneven ion flux and electric field distribution. During cycling, this easily induces uneven deposition of metal ions and dendrite formation, ultimately causing the membrane to be punctured and resulting in an internal short circuit, significantly shortening the stable cycling time. When the stirring time is too long, continuous mechanical stirring may disrupt the stable state of the particle surface, causing secondary agglomeration of the nano-alumina or the formation of locally dense stacked structures, while simultaneously increasing the hindering effect of the modified layer on ion transport. In this case, the effective porosity of the membrane decreases, polarization intensifies, and dendrite growth is also easily induced, leading to premature battery failure. When the stirring time is appropriate, nano-alumina particles can be uniformly and stably dispersed in the dispersion, forming a continuous and uniform modified layer on the membrane surface and within the pores. On the one hand, this alumina does not significantly block the membrane pores, maintaining good ion transport performance; on the other hand, the uniformly distributed alumina particles help homogenize the local electric field and ion flux, suppressing uneven nucleation of metal ions and dendrite growth at the membrane interface. In summary, the stirring time of the alumina dispersion directly affects the dispersion state of nano-alumina and the microstructure of the modified membrane. Only within a suitable stirring time range can a modified membrane that balances ion transport uniformity and dendrite suppression be obtained, thereby significantly improving the cycle stability of the battery and effectively suppressing the occurrence of internal short circuits.

[0044] Nano-alumina particles possess abundant hydroxyl groups and high surface energy. Their stable dispersion in the dispersion solution is highly dependent on the polarity, hydrogen bonding, and wetting ability of the solvent system. The ratio of ethanol to water as a mixed solvent significantly affects the dispersion uniformity of nano-alumina in the dispersion solution and the subsequent film quality on the separator surface. When the volume ratio of water to ethanol deviates from the appropriate range, the overall polarity and solvation ability of the solvent system change significantly. On the one hand, excessively high water content enhances hydrogen bonding and van der Waals forces between particles, easily inducing agglomeration of nano-alumina particles; on the other hand, excessively high ethanol content weakens the effective wetting and stable dispersion ability on the alumina surface, leading to uneven particle distribution in the dispersion solution. The resulting modified separator is prone to forming localized areas of particle enrichment or absence at the microscale, causing uneven pore structure and ion flux distribution in the separator. Under these conditions, local electric field and current density concentration occurs during battery cycling, leading to uneven deposition of metal ions at the separator interface. Dendrites preferentially grow and puncture the separator, resulting in a significantly shortened stable cycle time or even failure to cycle normally. Therefore, when the volume ratio of water to ethanol is within a suitable range, the mixed solvent system achieves a better balance between polarity, wettability, and dispersion stability. The nano-alumina particles can maintain a uniform and stable dispersion in the dispersion liquid. The modified separator prepared in this way has a uniform microstructure, which is beneficial for homogenizing ion flux and electric field distribution, thereby effectively suppressing uneven nucleation of metal ions and dendrite growth. Only in this way can a modified separator that balances ion transport uniformity and dendrite suppression ability be prepared, thereby significantly improving the cycle stability of the battery and effectively avoiding the occurrence of internal short circuits.

[0045] In this invention, nano-alumina is mainly used for interface modification of the separator. Its distribution and coverage on the separator surface have a significant impact on ion flux regulation and dendrite suppression. Therefore, the concentration of nano-alumina affects the modified separator structure and performance. When the concentration of nano-alumina is too low, the number of effective particles in the dispersion is insufficient, making it difficult to form a continuous and uniform modified layer on the separator surface and within the pores. At this time, the lack of interfacial regulation by alumina particles in local areas of the separator leads to uneven distribution of ion flux and electric field. During battery cycling, this easily induces uneven deposition of metal ions in local areas, thereby promoting dendrite growth and causing the separator to be punctured, significantly shortening the stable cycling time. When the concentration of nano-alumina is too high, excessive inorganic particles easily accumulate or partially block the separator surface and within the pores, reducing the effective porosity of the separator and increasing the tortuosity of the ion migration path. At the same time, alumina itself is an electrochemically inert and non-conductive material, and its excessive content will increase the interfacial transport impedance, leading to intensified polarization. Under the aforementioned conditions, batteries are also prone to uneven ion flux and localized current density concentrations during cycling, which can induce dendrite growth and cause internal short circuits. Under suitable nano-alumina concentrations, alumina particles can be uniformly distributed on the membrane surface and within the pores, effectively homogenizing the local electric field and ion flux without significantly blocking ion transport channels, thereby suppressing uneven metal ion nucleation and dendrite growth. In summary, the concentration of nano-alumina directly affects the microstructure of the modified membrane and its ability to regulate ion transport and dendrite behavior. Only within a suitable nano-alumina concentration range can a balance be achieved between the membrane modification effect and electrochemical performance, thus significantly improving the battery's cycle stability and effectively suppressing internal short circuits.

[0046] The present invention will be described below with reference to specific embodiments.

[0047] Example 1

[0048] This embodiment provides a method for preparing a modified diaphragm, comprising the following steps:

[0049] 1) Weigh out 0.5 g of nano-alumina (Huifu, particle size 150 nm) and 0.05 g of sodium hydroxymethyl cellulose, and add them to a mixed solvent of 5 mL water and 5 mL ethanol. The concentration of nano-alumina is 5 g / 100 mL. Stir with a magnetic stirrer at 400 r / min for 120 min until the nano-alumina is evenly dispersed to form a dispersion, which is a white emulsion.

[0050] 2) Immerse the GF / D membrane (Beijing Shenhe Weiye Technology Co., Ltd. (SHM)) in the dispersion for 2 minutes to ensure that the nano-alumina is uniformly loaded on the surface and pores of the GF / D membrane.

[0051] 3) The soaked diaphragm was vacuum dried at 60℃ for 12 h to obtain a surface-modified GF / D@Al2O3 glass fiber diaphragm (hereinafter referred to as the modified diaphragm). Scanning electron microscopy showed that the surface of the GF / D diaphragm was covered with a dense Al2O3 coating. Figure 1 ).

[0052] Contact angle test results show that the coating does not affect the diaphragm wettability and has good electrolyte wettability. Figure 2 .

[0053] This embodiment provides a method for assembling a sodium-ion battery, including the following steps:

[0054] 1. The electrode sheet is prepared according to conventional methods:

[0055] The positive electrode sheet is prepared by uniformly mixing active material, conductive agent, and binder in a mass ratio of 8:1:1 using conventional methods. The active material is sodium vanadium phosphate; the conductive agent is conductive carbon black; and the binder is sodium carboxymethyl cellulose. The mixed slurry is uniformly coated onto an aluminum foil current collector, dried at 80°C, rolled, and punched for later use.

[0056] The negative electrode is made of sodium metal with a diameter of 14 nm.

[0057] 2. Diaphragm preparation:

[0058] The separator used is the modified separator prepared above, which is dehydrated in a vacuum drying oven before battery assembly.

[0059] 3. Electrolyte preparation:

[0060] The electrolyte was 1M NaPF6 electrolyte dissolved in diethylene glycol dimethyl ether solution.

[0061] 4. Assemble the battery using standard methods:

[0062] Inside a glove box protected by an inert atmosphere (argon atmosphere, H2O and O2 content ≤ 0.1 ppm), the positive electrode, modified separator, and negative electrode are stacked in sequence to form a "positive electrode / separator / negative electrode" structure.

[0063] Add 150 microliters of electrolyte to the stacked structure to fully wet the separator, and then encapsulate it in a button cell casing (CR2025 type).

[0064] 5. Packaging and Formation

[0065] After assembly, the battery is initially allowed to stand, and then constant current and constant voltage charge-discharge formation treatment is performed to form a stable interface film.

[0066] The assembled sodium-ion battery was subjected to constant current charge-discharge test at a rate of 0.2 C, and the AC impedance test frequency was 0.01-100000HZ.

[0067] The test results show that the sodium-ion battery has a first-cycle discharge specific capacity of 98.7 mAh g. -1 In the first lap, Cullen's efficiency was 85.0%. Figure 3 Stable cycling for over 400 hours without short circuit, see [link / reference]. Figure 4 After 50 cycles, the specific capacity is 98.5 mAh g. -1 ,See Figure 5 The capacitance retention is close to 100%, and it exhibits good rate performance, without short-circuiting at high current densities. (See [link]). Figure 6 Furthermore, the battery's internal resistance did not increase significantly, see [reference needed]. Figure 7 .

[0068] Comparative Example 1

[0069] In this comparative example, the same GF / D membrane as in Example 1 was used, but without any treatment, for comparison. Scanning electron microscopy revealed that the GF / D membrane had numerous pores, which is detrimental to inhibiting dendrite growth and easily leads to internal short circuits. (See...) Figure 1 Contact angle test results show that the GF / D membrane has good electrolyte wettability. Figure 2 .

[0070] Sodium-ion batteries are assembled according to the assembly method of sodium-ion batteries in Example 1, wherein the separator used is an untreated GF / D separator.

[0071] The assembled sodium-ion battery was subjected to constant current charge-discharge test at a rate of 0.2 C, and the AC impedance test frequency was 0.01-100000HZ.

[0072] The test results are as follows: the first discharge specific capacity is 99.3 mAh g. -1 In the first lap, Cullen's efficiency was 87.6%. Figure 3 The cycle time is less than 100 hours, see... Figure 4 If the number of loops is less than 10, see... Figure 5 It also exhibits a tendency to short-circuit in its rate performance, see... Figure 6 Furthermore, the battery exhibits good internal resistance. Figure 7 .

[0073] Comparative Example 2

[0074] This comparative example provides a method for preparing a modified diaphragm, comprising the following steps:

[0075] 1) Weigh out 0.5 g of nano-alumina (Huifu, particle size 150 nm) and 0.05 g of sodium carboxymethyl cellulose, and add them to a mixed solvent of 5 mL water and 5 mL ethanol. The concentration of nano-alumina is 5 g / 100 mL. Stir with a magnetic stirrer at 400 r / min for 60 min until the nano-alumina is evenly dispersed to form a dispersion, which is a white emulsion.

[0076] 2) Immerse the GF / D membrane (Beijing Shenhe Weiye Technology Co., Ltd. (SHM)) in the dispersion for 2 minutes to ensure that the nano-alumina is uniformly loaded on the surface and pores of the GF / D membrane.

[0077] 3) The soaked diaphragm was vacuum dried at 60℃ for 12 h to obtain a surface-modified GF / D@Al2O3 glass fiber diaphragm (hereinafter referred to as modified diaphragm).

[0078] Sodium-ion batteries were assembled according to the assembly method of sodium-ion batteries in Example 1, wherein the separator used was the modified separator prepared in this comparative example.

[0079] The assembled sodium-ion battery was subjected to constant current charge-discharge test at a rate of 0.2 C, and the AC impedance test frequency was 0.01-100000HZ.

[0080] The test results showed that the stable cycling time was below 150 h, and dendrites caused an internal short circuit. Figure 4 .

[0081] Comparative Example 3

[0082] This comparative example provides a method for preparing a modified diaphragm, comprising the following steps:

[0083] 1) Weigh out 0.5 g of nano-alumina (Huifu, particle size 150 nm) and 0.05 g of sodium carboxymethyl cellulose, and add them to a mixed solvent of 5 mL water and 5 mL ethanol. The concentration of nano-alumina is 5 g / 100 mL. Stir with a magnetic stirrer at 400 r / min for 150 min until the nano-alumina is evenly dispersed to form a dispersion, which is a white emulsion.

[0084] 2) Immerse the GF / D membrane (Beijing Shenhe Weiye Technology Co., Ltd. (SHM)) in the dispersion for 2 minutes to ensure that the nano-alumina is uniformly loaded on the surface and pores of the GF / D membrane.

[0085] 3) The soaked diaphragm was vacuum dried at 60℃ for 12 h to obtain a surface-modified GF / D@Al2O3 glass fiber diaphragm (hereinafter referred to as modified diaphragm).

[0086] Sodium-ion batteries were assembled according to the assembly method of sodium-ion batteries in Example 1, wherein the separator used was the modified separator prepared in this comparative example.

[0087] The assembled sodium-ion battery was subjected to constant current charge-discharge test at a rate of 0.2 C, and the AC impedance test frequency was 0.01-100000HZ.

[0088] The test results were as follows: Constant current charge-discharge testing at 0.2 C rate resulted in a stable cycle time of less than 100 hours; dendrite formation caused an internal short circuit. (See attached image). Figure 4 .

[0089] Comparative Example 4

[0090] This comparative example provides a method for preparing a modified diaphragm, comprising the following steps:

[0091] 1) Weigh out 0.5 g of Huifu nano-alumina (particle size 150 nm) and 0.05 g of sodium hydroxymethyl cellulose, and add them to a mixed solvent of 2.5 mL water and 7.5 mL ethanol. The concentration of nano-alumina is 5 g / 100 mL. Stir with a magnetic stirrer at 400 rpm for 120 min until the nano-alumina is evenly dispersed to form a white emulsion.

[0092] 2) Immerse the GF / D membrane (Beijing Shenhe Weiye Technology Co., Ltd. (SHM)) in the dispersion for 2 minutes to ensure that the nano-alumina is uniformly loaded on the surface and pores of the membrane.

[0093] 3) The soaked diaphragm was vacuum dried at 60℃ for 12 h to obtain a surface-modified GF / D@Al2O3 glass fiber diaphragm (hereinafter referred to as modified diaphragm).

[0094] Sodium-ion batteries were assembled according to the assembly method of sodium-ion batteries in Example 1, wherein the separator used was the modified separator prepared in this comparative example.

[0095] The assembled sodium-ion battery was subjected to constant current charge-discharge test at a rate of 0.2 C, and the AC impedance test frequency was 0.01-100000HZ.

[0096] The test results showed that stable cycling time was below 80 hours, and dendrites caused internal short circuits. (See attached image) Figure 4 .

[0097] Comparative Example 5

[0098] This comparative example provides a method for preparing a modified diaphragm, comprising the following steps:

[0099] 1) Weigh out 0.5 g of nano-alumina (Huifu, particle size 150 nm) and 0.05 g of sodium hydroxymethyl cellulose, and add them to a mixed solvent of 7.5 mL water and 2.5 mL ethanol. The concentration of nano-alumina is 5 g / 100 mL. Stir with a magnetic stirrer at 400 r / min for 120 min until the nano-alumina is evenly dispersed to form a dispersion, which is a white emulsion.

[0100] 2) Immerse the GF / D membrane (Beijing Shenhe Weiye Technology Co., Ltd. (SHM)) in the dispersion for 2 minutes to ensure that the nano-alumina is uniformly loaded on the surface and pores of the membrane.

[0101] 3) The soaked diaphragm was vacuum dried at 60℃ for 12 h to obtain a surface-modified GF / D@Al2O3 glass fiber diaphragm (hereinafter referred to as modified diaphragm).

[0102] Sodium-ion batteries were assembled according to the assembly method of sodium-ion batteries in Example 1, wherein the separator used was the modified separator prepared in this comparative example.

[0103] The assembled sodium-ion battery was subjected to constant current charge-discharge test at a rate of 0.2 C, and the AC impedance test frequency was 0.01-100000HZ.

[0104] The test result was: unable to cycle; dendrites directly caused an internal short circuit. (See below) Figure 4 .

[0105] Comparative Example 6

[0106] This comparative example provides a method for preparing a modified diaphragm, comprising the following steps:

[0107] 1) Weigh out 0.2 g of nano-alumina (Huifu, particle size 150 nm) and 0.05 g of sodium carboxymethyl cellulose, and add them to a mixed solvent of 5 mL water and 5 mL ethanol. The concentration of nano-alumina is 2 g / 100 mL. Stir with a magnetic stirrer at 400 r / min for 120 min until the nano-alumina is evenly dispersed to form a dispersion, which is a white emulsion.

[0108] 2) Immerse the GF / D membrane (Beijing Shenhe Weiye Technology Co., Ltd. (SHM)) in the dispersion for 2 minutes to ensure that the nano-alumina is uniformly loaded on the surface and pores of the membrane.

[0109] 3) The diaphragm after soaking was vacuum dried at 60℃ for 12 h to obtain the GF / D@Al2O3 glass fiber diaphragm after soaking.

[0110] Sodium-ion batteries were assembled according to the assembly method of sodium-ion batteries in Example 1, wherein the separator used was the modified separator prepared in this comparative example.

[0111] The assembled sodium-ion battery was subjected to constant current charge-discharge test at a rate of 0.2 C, and the AC impedance test frequency was 0.01-100000HZ.

[0112] The test results showed that the stable cycling time was less than 100 hours, and dendrites caused an internal short circuit. (See attached image.) Figure 4 .

[0113] Comparative Example 7

[0114] This comparative example provides a method for preparing a modified diaphragm, comprising the following steps:

[0115] 1) Weigh 1.0 g of nano-alumina (Huifu, particle size 150 nm) and 0.05 g of sodium hydroxymethyl cellulose, and add them to a mixed solvent of 5 mL water and 5 mL ethanol. The concentration of nano-alumina is 10 g / 100 mL. Stir with a magnetic stirrer at 400 r / min for 120 min until the nano-alumina is evenly dispersed to form a dispersion, which is a white emulsion.

[0116] 2) Immerse the GF / D membrane (Beijing Shenhe Weiye Technology Co., Ltd. (SHM)) in the dispersion for 2 minutes to ensure that the nano-alumina is uniformly loaded on the surface and pores of the membrane.

[0117] 3) The soaked diaphragm was vacuum dried at 60℃ for 12 h to obtain a surface-modified GF / D@Al2O3 glass fiber diaphragm (hereinafter referred to as modified diaphragm).

[0118] Sodium-ion batteries were assembled according to the assembly method of sodium-ion batteries in Example 1, wherein the separator used was the modified separator prepared in this comparative example.

[0119] The assembled sodium-ion battery was subjected to constant current charge-discharge test at a rate of 0.2 C, and the AC impedance test frequency was 0.01-100000HZ.

[0120] The test results showed that the stable cycling time was less than 50 hours, and dendrites caused an internal short circuit. (See attached image.) Figure 4 .

[0121] Comparative Example 8

[0122] This comparative example provides a method for preparing a modified diaphragm, comprising the following steps:

[0123] (1) Prepare the dispersion according to the steps of Example 1;

[0124] (2) Coat the dispersion evenly on the surface of the GF / D membrane;

[0125] (3) The coated diaphragm was vacuum dried at 60°C for 12 h to obtain a surface-modified GF / D@Al2O3 glass fiber diaphragm (hereinafter referred to as modified diaphragm).

[0126] Sodium-ion batteries are assembled according to the assembly method of sodium-ion batteries in Example 1, wherein the separator used is the modified separator prepared above.

[0127] The assembled sodium-ion battery was subjected to constant current charge-discharge test at a rate of 0.2 C, and the AC impedance test frequency was 0.01-100000HZ.

[0128] The test results are as follows: stable cycling time is less than 100 hours, dendrites cause internal short circuits (see attached). Figure 4 .

[0129] The test results above show that in the modified separator prepared in this embodiment, the oxide can enter the pores of the glass fiber separator and form a three-dimensional anchoring structure with the glass fiber, thereby constructing a stable ion transport channel and mechanical reinforcement network inside the separator. The coating on the surface of the modified separator does not significantly affect the wettability of the separator and still maintains good electrolyte wettability. When this modified separator is applied to a sodium-ion battery, the resulting battery achieves a first-cycle coulombic efficiency of 85.0%, a capacity retention of nearly 100% after 50 cycles, and can stably cycle for more than 400 hours without short circuits within a range from 0.2C to a large current density. The above results indicate that the modified separator prepared in this embodiment has a significant effect on improving the rate performance and cycle stability of the battery.

[0130] In Comparative Example 1, a sodium-ion battery assembled using a conventional untreated GF / D separator was prone to short circuits under high-rate conditions, failed to complete 10 cycles, and failed within 100 hours of cycling. This indicates that the separator has poor interfacial stability, insufficient rate performance, and is unable to effectively suppress internal short circuits caused by dendrite growth. In contrast, Example 1, using the modified separator of this application, showed that its corresponding battery could cycle stably for over 400 hours without short circuits and maintained good rate performance even under high current density conditions. Therefore, compared to conventional GF / D separators, the modified separator of this embodiment has significant technical advantages in improving battery rate performance and cycle stability.

[0131] Compared to Comparative Examples 2-3, in the preparation of the alumina dispersion, the stirring time of Example 1 affects battery performance. Too short or too long a stirring time leads to a reduction in stable cycling time and dendrite formation causing internal short circuits. However, the battery in Example 1 achieved stable cycling for over 400 hours without short circuits, indicating that the modified separator prepared with an appropriate stirring time can improve cycle stability and inhibit dendrite growth.

[0132] Compared to Comparative Examples 4-5, in the preparation of the alumina dispersion, the ratio of ethanol to water in the solvent of Example 1 affects battery performance. When the volume ratio of water to ethanol is 1:3 or 3:1, dendrite formation leads to internal short circuits, resulting in reduced stable cycle time or even failure to cycle. However, in Example 1, when the volume ratio of water to ethanol is 1:1, the prepared battery achieved stable cycling for over 400 hours without short circuits, indicating that the modified separator prepared with a suitable solvent ratio can improve cycle stability and inhibit dendrite growth.

[0133] Compared to Comparative Examples 6-7, in Example 1, the concentration of nano-alumina affects battery performance during the preparation of the alumina dispersion. Both excessively high and low concentrations of nano-alumina lead to reduced stable cycling time and dendrite formation causing internal short circuits. However, the battery prepared in Example 1 exhibited stable cycling for over 400 hours without short circuits, indicating that a modified separator prepared with an appropriate concentration of nano-alumina can improve cycling stability and inhibit dendrite growth.

[0134] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0135] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a modified diaphragm, characterized in that, Includes the following steps: S1. Mix the oxide and the ethanol aqueous solution containing the binder, and stir to form a dispersion; S2. Immerse the glass fiber diaphragm in the dispersion; S3. After soaking, the glass fiber diaphragm is dried to obtain the modified diaphragm. Wherein, the oxide is at least one of aluminum oxide, zirconium oxide, magnesium oxide, silicon oxide, titanium oxide, and cerium oxide; The adhesive is at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, sodium alginate, and polyvinyl alcohol.

2. The method for preparing the modified diaphragm as described in claim 1, characterized in that, In step S1, the concentration of the oxide in the dispersion is 3g~8g / 100 mL, preferably 4g~6g / 100 mL, and more preferably 4.5g~5.5g / 100 mL.

3. The method for preparing the modified diaphragm as described in claim 1, characterized in that, The volume ratio of ethanol to water in the ethanol-water solution is 1:9 to 9:1, preferably 1:1 to 4:1, and more preferably 1:1 to 1.5:

1.

4. The method for preparing the modified diaphragm as described in claim 1, characterized in that, In step S1, the stirring speed is 200 r / min to 600 r / min, and the stirring time is 80 min to 140 min, preferably 100 min to 130 min, and more preferably 115 min to 125 min.

5. The method for preparing the modified diaphragm according to any one of claims 1-4, characterized in that, The oxide is nano-alumina with a particle size of 100nm~200nm; And / or, the binder is sodium carboxymethyl cellulose.

6. The method for preparing the modified diaphragm according to any one of claims 1-4, characterized in that, The glass fiber diaphragm is one of GF / A, GF / B, GF / C, GF / D and GF / F, preferably GF / D.

7. The method for preparing the modified diaphragm according to any one of claims 1-4, characterized in that, In step S2, the soaking time is 1 min to 30 min, preferably 1 min to 5 min, and more preferably 1.5 min to 2.5 min.

8. The method for preparing the modified diaphragm according to any one of claims 1-4, characterized in that, In step S3, the drying process is hot air drying or vacuum drying, and the drying temperature is 50~120 ℃, preferably 55℃~65℃.

9. A modified diaphragm prepared by the method of any one of claims 1-8.

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes a casing and a battery cell; the battery cell is encapsulated within the casing and is impregnated with an electrolyte. The battery cell includes a positive electrode, a negative electrode, and the modified separator as described in claim 9, wherein the positive electrode, the modified separator, and the negative electrode are stacked sequentially.

Images