A method for preparing a high-thermal-safety lithium battery separator based on magnesium-based whiskers

Abstract

The application discloses a preparation method of a high-heat-safety lithium battery diaphragm based on magnesium-based whiskers and belongs to the field of lithium battery diaphragms. The application obtains an oily mixed slurry by introducing magnesium-based whiskers, especially self-made basic magnesium sulfate whiskers. The oily mixed slurry is coated on both sides of a polyolefin porous base to form an oily coating, and a lithium battery diaphragm can be obtained after drying. The application has the advantages of simple process and the prepared composite diaphragm has excellent electrolyte wettability, high ionic conductivity, high lithium ion transference number, and excellent heat shrinkage resistance and flame retardance.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery separator technology, specifically relating to a method for preparing a high thermal safety lithium battery separator based on magnesium-based whiskers. Background Technology

[0002] The rapid development of electric vehicles and energy storage systems has driven the demand for batteries with higher energy density and greater safety. While traditional lithium-ion batteries are widely used, their capacity is limited by the graphite anode. In contrast, lithium metal boasts an ultra-high theoretical capacity (3860 mAh g⁻¹). -1 Its high energy density and extremely low reduction potential (-3.04 V vs RHE) make it an ideal anode material for next-generation batteries. However, the formation of an unstable solid electrolyte interphase (SEI) layer and the irreversible growth of lithium dendrites during cycling severely restrict the commercial application of lithium metal batteries. These problems not only shorten battery life but can also mechanically puncture the separator, causing internal short circuits and leading to rapid local temperature rise. When the temperature rises sharply, the organic electrolyte decomposes to produce flammable gases (such as H2 and CH4) and a large number of active free radicals (such as HO· and H·). These flammable substances then react violently with oxygen released from the thermally unstable cathode material at about 200°C, eventually leading to thermal runaway. In addition, the highly flammable polymer separator also produces additional flammable and toxic gases (such as hydrocarbons and CO), further increasing the risk of fire and explosion. These coupled failure modes—including uncontrolled dendrite growth, unstable SEI film formation, and serious safety hazards—constitute the main obstacles to the practical safe application of lithium metal batteries, highlighting the urgent need to develop effective strategies to develop rechargeable batteries that combine high energy density and safety.

[0003] To address the dendrite formation and instability issues of lithium metal anodes, various solutions have been developed, such as electrolyte optimization with additives, forming artificial SEI / coatings on the lithium metal surface, constructing three-dimensional porous frameworks, and employing solid-state electrolytes. However, these methods either face technological barriers or introduce new challenges, such as high cost, complex processes, or limited scalability. Compared to other strategies, functionalized membrane engineering is inherently simpler and highly scalable. However, traditional polyolefin membranes (polyethylene or polypropylene) suffer from poor electrolyte wettability and low ionic conductivity, which exacerbates concentration polarization and leads to uneven lithium deposition during electrochemical cycling. Furthermore, traditional polyolefin membranes have inherent defects: high flammability and poor resistance to thermal shrinkage. Polyolefin membranes are prone to thermal shrinkage; the melting point of commercial Celgard PP membranes is approximately 160-165°C, exceeding which will result in loss of structural integrity.

[0004] To address the aforementioned issues, existing technologies have explored the incorporation of inorganic whiskers into membrane slurry / coating systems. However, the inorganic whiskers used typically exhibit low aspect ratios and uneven distribution. Limited by industrial-scale precipitation processes, commercial whiskers often present as short rods or irregular fragments, with aspect ratios typically less than 30. During coating, these low aspect ratio particles struggle to construct an effective three-dimensional interpenetrating network framework on the polyolefin-based membrane surface. Instead, they tend to form dense deposits or severe agglomeration on the membrane surface, physically clogging the micropores of the base membrane. This directly leads to reduced porosity of the composite membrane, insufficient electrolyte uptake and retention, and consequently, significantly increased ion transport impedance, limiting improvements in ionic conductivity and lithium-ion transference number. Secondly, the surface condition of commercial whiskers is detrimental to electrochemical performance. To prevent agglomeration and facilitate storage, the surface of commercial whiskers often contains adsorbed impurities or undergoes hydrophobic treatment, lacking active polar sites. This results in poor affinity with the electrolyte, making it difficult to effectively regulate the solvation sheath structure of lithium ions. In terms of battery performance, batteries assembled using separators modified with commercial whiskers exhibit severe polarization and rapid capacity decay during long-cycle operation (e.g., capacity retention is difficult to maintain above 80%), and cannot effectively suppress lithium dendrite growth. Furthermore, commercial whiskers have limited ability to suppress thermal runaway. Due to the lack of a robust physical entanglement network formed by high aspect ratio whiskers, commercial whisker coatings cannot provide sufficient mechanical support at high temperatures (e.g., above 160°C) to counteract the thermal shrinkage stress of the base film. Simultaneously, due to excessive packing density, their "thermal barrier effect" and "labyrinth effect" in blocking heat and suppressing the release of combustible gases are limited, resulting in poor performance in reducing the heat release rate (HRR) and total heat release (THR).

[0005] Therefore, the challenge lies in obtaining inorganic whiskers with high aspect ratios and constructing whisker skeleton coatings with high porosity to maximize the thermal shrinkage resistance and flame retardant efficiency of the separator while achieving high porosity, electrolyte retention, and high ionic conductivity. This would solve the problem of balancing long cycle life and high thermal safety in high-energy-density lithium metal batteries. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method for preparing a high thermal safety lithium-ion battery separator based on magnesium-based whiskers. This invention prepares magnesium-based whiskers with a high aspect ratio and uses them in the preparation of lithium-ion battery separators. The prepared separator exhibits high electrolyte wettability, high ionic conductivity, high lithium-ion transference number, high heat resistance, and excellent flame retardant properties, thereby enhancing its market competitiveness.

[0007] The present invention relates to a method for preparing a high thermal safety lithium battery separator based on magnesium-based whiskers, comprising the following steps:

[0008] Magnesium-based whiskers are added to the binder polymer slurry and mixed evenly to obtain an oily mixed slurry; the oily mixed slurry is coated on both sides of a polyolefin porous substrate to form an oily coating, and after drying, a lithium battery separator can be obtained.

[0009] The binder polymer is one or more of styrene-butadiene rubber, acrylic resin, polyvinyl alcohol, polyacrylonitrile, polyvinylidene fluoride, carboxymethyl cellulose, polyethylene oxide, and polytetrafluoroethylene. Polyvinylidene fluoride is preferred. The binder polymer mainly serves to maintain the mechanical strength and toughness of the porous membrane, and to inhibit the shedding of non-conductive particles from the porous membrane during lithium battery winding. The binder polymer should have stable electrochemical performance, mainly manifested in the absence of other redox current peaks within a voltage range of 1-5V, except for the electrode lithium insertion / extraction redox peak.

[0010] When preparing the slurry of the binder polymer, the solvent used includes water or any organic solvent. Examples of organic solvents include: aliphatic hydrocarbons such as cyclopropane and cyclohexane; ketones such as ethyl methyl ketone and cyclohexanone; aromatic hydrocarbons such as benzene and toluene; nitriles such as acetonitrile and propionitrile; esters such as ethyl acetate and butyl acetate; alcohols such as methanol, ethanol, isopropanol, and ethylene glycol; ethers such as tetrahydrofuran and ethylene glycol diethyl ether; and amides such as N-methylpyrrolidone and N,N-dimethylformamide. These solvents can be used alone or in combination. N-methylpyrrolidone is preferred as the solvent for preparing the slurry.

[0011] The magnesium-based whiskers are basic magnesium sulfate whiskers (MOSw), which are prepared by a method including the following steps:

[0012] Step 1: Weigh 4.141 g of magnesium sulfate heptahydrate (MgSO4·7H2O) and 1.464 g of magnesium chloride hexahydrate (MgCl2·6H2O), respectively, and dissolve them in 30 mL of deionized water, controlling the molar ratio of MgSO4·7H2O to MgCl2·6H2O to be 7:3, to prepare a mixed salt solution with a total magnesium ion concentration of 0.8-1 mol / L; add 0.447 g of disodium ethylenediaminetetraacetate (EDTA-2Na) to the mixed salt solution, controlling the Mg... 2+ The molar ratio of EDTA-2Na is 20:1. After stirring for 45 min until homogeneous, this is used as solution A.

[0013] Step 2: Weigh 1.152 g of NaOH and dissolve it in 30 mL of deionized water to prepare solution B. While stirring vigorously, slowly add solution B dropwise to solution A, controlling the Mg content. 2+ With OH -The molar ratio was 1:1.2, and the mixture was stirred continuously for 30 min to form a homogeneous precursor slurry. The slurry was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and hydrothermally reacted at 160℃ for 10 h. After the reactor cooled naturally to room temperature, the product was filtered and repeatedly washed with deionized water until no SO4 was found. 2- and Cl - The residue was dried under vacuum at 80°C for 8 hours to obtain a high aspect ratio basic magnesium sulfate whisker product.

[0014] The length L of the magnesium-based whisker is 5~100μm, preferably 50-90μm; the diameter d is 0.5~1.5μm, preferably 0.6μm-1μm; and the aspect ratio L / d is 10-100, preferably 50-90.

[0015] In the above components, the mass-volume ratio of magnesium-based whiskers, binder polymer and solvent is (150~250)mg: (20~40)mg: (1~1.5)mL.

[0016] In addition to the components mentioned above, the slurry may also contain any other components. Examples include dispersants, wetting agents, and electrolyte dispersion inhibitors. There are no particular restrictions on the components mentioned above as long as they do not have an adverse effect on the lithium battery. One, two, or more of the above-mentioned components may be used.

[0017] The polyolefin porous substrate is a single layer of polyethylene (PE) or polypropylene (PP), or a mixed layer of polyethylene (PE) and polypropylene (PP), or a multilayer of polyethylene (PE) or polypropylene (PP). A polypropylene diaphragm is preferred.

[0018] The thickness of the polyolefin membrane is 1-30 μm, preferably 20-30 μm; the porosity of the membrane is 10%-70%, preferably 30%-50%.

[0019] There are no fixed restrictions on the coating method for the oily mixed slurry; methods such as coating and dipping can be selected. Examples of coating methods include doctor blade coating, reverse roller coating, direct roller coating, microgravure roller coating, extrusion coating, spraying coating, and dot coating. Doctor blade coating is preferred.

[0020] The drying temperature after coating is 40-80℃, and the drying time is 8-16 hours. There are no fixed restrictions on the drying method after coating; hot air, low humidity air, vacuum drying, spray drying, freeze drying, and other drying methods can be selected.

[0021] Electrolyte retention test method:

[0022] After drying the sample membrane, weigh it (M0, g). Immerse it in the electrolyte for 2 hours until the membrane has fully absorbed the electrolyte. Remove the membrane and gently blot off the electrolyte from the membrane surface with filter paper. Weigh it again (M1, g). Calculate the liquid absorption rate (u%) using the following formula:

[0023] u%=(M1-M0) / M0×100%.

[0024] Methods for testing ionic conductivity:

[0025] Electrochemical workstation, power supply voltage: 220V±10%, frequency range: 0.01 Hz~10 Hz 6 Hz; Test parameters: Initial voltage set to 0V, high frequency 10 Hz; 6 Hz, low frequency is 0.01Hz, amplitude is 0.005V, resting time is 2 seconds; connection method of test mold: four-electrode connection; resistance test mold; electrolyte: lithium bis(trifluoromethanesulfonylimide).

[0026] Method for measuring the heat shrinkage of diaphragms:

[0027] The coated diaphragm was cut into 18 mm round pieces. The sample was laid flat on two high-temperature glass weights and then placed in ovens at different temperatures for 0.5 hours. After heating, the sample was removed, allowed to return to room temperature, and its transverse length was measured. The shrinkage rate was calculated according to the following formula. Finally, the average value of the three samples was taken as the shrinkage rate.

[0028] Transverse heat shrinkage rate (%) = (Transverse length before heating - Transverse length after heating) / Transverse length before heating × 100

[0029] Flame retardant performance test:

[0030] The miniature combustion calorimeter (MCC, MCC-2 instrument, Govemark, USA) is used to study the heat release of the combustion of pyrolysis gases in samples. The test temperature range is 75℃-750℃, and the heating rate is 1℃ / min.

[0031] The composite diaphragm prepared by this invention has a contact angle close to 0° after immersion in electrolyte for 1 second. Under conditions of 25°C and relative humidity less than 60%, an SL200B contact angle measuring instrument (manufactured by Solon Tech. Co., Ltd.) was used to slowly drop electrolyte onto the diaphragm. After 1 second of dripping, the wetting contact angle of the electrolyte was measured. The contact angle was measured at three points on the membrane, and the average of the three measurements was taken as the contact angle.

[0032] The composite membrane prepared by this invention has an ionic conductivity as high as 1.159 mS / cm. -1The lithium-ion transference number is 0.72. After the membrane is placed at 160°C for 0.5 hours, its lateral shrinkage rate is only 10%, and the peak heat release rate of the membrane is reduced by 66% compared with commercial polyolefin membranes.

[0033] The beneficial effects of this invention are reflected in:

[0034] 1. This invention introduces magnesium-based whiskers, which are simple to prepare, have readily available raw materials, and stable performance, making them suitable for large-scale production applications.

[0035] 2. The high thermal safety lithium battery separator of the present invention has an electrolyte wetting contact angle of 0°, exhibiting excellent electrolyte wetting properties and rapid electrolyte immersion characteristics.

[0036] 3. The high thermal safety lithium battery separator of the present invention has high ionic conductivity and lithium ion transference number.

[0037] 4. The high thermal safety lithium battery separator of this invention has excellent resistance to thermal deformation.

[0038] 5. The high thermal safety lithium battery separator of this invention significantly reduces the heat release of the composite separator during thermal runaway through the synergistic effect of cooling kinetics and thermal barrier effect, thereby exhibiting excellent flame retardant properties. Attached Figure Description

[0039] Figure 1 SEM image of the basic magnesium sulfate whiskers prepared according to the present invention.

[0040] Figure 2 The image shows the XRD pattern of the basic magnesium sulfate whiskers prepared according to this invention.

[0041] Figure 3 The diagram shows the electrolyte contact angle data for comparative examples and embodiments of the present invention.

[0042] Figure 4 The graph shows the ionic conductivity and lithium-ion transport number data for the comparative examples and embodiments of the present invention.

[0043] Figure 5 This is a comparison of the adsorption energies of polypropylene and basic magnesium sulfate with anions, cations, and organic solvents in the electrolyte.

[0044] Figure 6 The graph shows the cycle performance of the LiFePO4 / separator / Li batteries assembled in the comparative examples and embodiments of this invention.

[0045] Figure 7 The diagram shows the heat shrinkage resistance test results of the comparative examples and embodiments of the present invention.

[0046] Figure 8 The graph shows the heat release rate curves of the comparative examples and embodiments of the present invention.

[0047] Figure 9 This is a graph showing the total heat release of the comparative examples and embodiments of the present invention.

[0048] Figure 10 This is a schematic diagram of the membrane manufacturing process.

[0049] Figure 11 The total pyrolysis gas release curves of the diaphragms in Comparative Example 1, Example 1, and Example 2 were obtained by TG-FTIR testing.

[0050] Figure 12 The alkane gas release curves of the membranes in Comparative Example 1, Example 1, and Example 2 were obtained by TG-FTIR testing.

[0051] Figure 13 The CO gas release curves of the membranes in Comparative Example 1, Example 1, and Example 2 were obtained by TG-FTIR testing.

[0052] Figure 14 The CO2 gas release curves of the membranes of Comparative Example 1, Example 1 and Example 2 were tested using TG-FTIR. Detailed Implementation

[0053] The following examples further illustrate the above-described content of the present invention, but it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention.

[0054] The basic magnesium sulfate whiskers used in Example 1 were prepared by the following method:

[0055] 1. Weigh 4.141 g of magnesium sulfate heptahydrate (MgSO4·7H2O) and 1.464 g of magnesium chloride hexahydrate (MgCl2·6H2O), respectively, and dissolve them in 30 mL of deionized water, controlling the molar ratio of MgSO4·7H2O to MgCl2·6H2O to be 7:3, to prepare a mixed salt solution with a total magnesium ion concentration of 0.8 mol / L; add 0.447 g of disodium ethylenediaminetetraacetate (EDTA-2Na) to the mixed salt solution, controlling the Mg... 2+ The molar ratio of EDTA-2Na is 20:1. After stirring for 45 min until homogeneous, this is used as solution A.

[0056] 2. Weigh 1.152 g of NaOH and dissolve it in 30 mL of deionized water to prepare solution B. While stirring vigorously, slowly add solution B dropwise to solution A, controlling the Mg content. 2+ With OH -The molar ratio was 1:1.2, and the mixture was stirred continuously for 30 min to form a homogeneous precursor slurry. The slurry was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and hydrothermally reacted at 160℃ for 10 h. After the reactor cooled naturally to room temperature, the product was filtered and repeatedly washed with deionized water until no SO4 was found. 2- and Cl - The residue was dried under vacuum at 80°C for 8 hours to obtain a high aspect ratio basic magnesium sulfate whisker product.

[0057] Example 1:

[0058] 2.559 g of the basic magnesium sulfate whiskers prepared according to this invention and 0.366 g of fully dried high molecular weight (battery grade) polyvinylidene fluoride were dry-ground in a mortar until uniformly mixed. Then, the mixture was slowly added dropwise in batches to 13 mL of N-methylpyrrolidone solution to dissolve the polyvinylidene fluoride and form a viscous slurry. The mixture was continuously stirred and ground until a uniform and viscous slurry was formed. The slurry was then coated on both sides of a 25 μm PP base membrane to form an oily coating. After vacuum drying in an oven at 60°C, the product was obtained, with a total membrane thickness of 45 μm.

[0059] Example 2:

[0060] 2.559 g of commercial basic magnesium sulfate whiskers and 0.366 g of fully dried high molecular weight (battery grade) polyvinylidene fluoride were dry-milled in a mortar until uniformly mixed. Then, the mixture was slowly added dropwise in batches to 13 mL of N-methylpyrrolidone solution to dissolve the polyvinylidene fluoride and form a viscous slurry. The mixture was continuously stirred and ground until a uniform and viscous slurry was formed. The slurry was then coated on both sides of a 25 μm PP base membrane to form an oily coating. After vacuum drying in an oven at 60°C, the product was obtained, with a total membrane thickness of 45 μm.

[0061] The sample testing parameters of commercial basic magnesium sulfate whiskers used in this embodiment are shown in Table 1 below. The inventors used SEM characterization and found that their aspect ratio was approximately 25-30.

[0062]

[0063] Example 3:

[0064] 2.559 g of magnesium oxide and 0.366 g of fully dried high molecular weight (battery-grade) polyvinylidene fluoride were dry-ground in a mortar until uniformly mixed. Then, the mixture was slowly added dropwise in batches to 13 mL of N-methylpyrrolidone solution to dissolve the polyvinylidene fluoride and form a viscous slurry. The mixture was continuously stirred and ground until a uniform and viscous slurry was formed. The slurry was then coated on both sides of a 25 μm PP base membrane to form an oily coating. After vacuum drying in an oven at 60°C, the product was obtained, with a total membrane thickness of 45 μm.

[0065] Summary: In this Example 2, compared with Example 1, the magnesium-based whiskers are magnesium oxide.

[0066] Example 4:

[0067] 2.559 g of magnesium hydroxide and 0.366 g of fully dried high molecular weight (battery-grade) polyvinylidene fluoride were dry-ground in a mortar until uniformly mixed. Then, the mixture was slowly added dropwise in batches to 13 mL of N-methylpyrrolidone solution to dissolve the polyvinylidene fluoride and form a viscous slurry. The mixture was continuously stirred and ground until a uniform and viscous slurry was formed. The slurry was then coated on both sides of a 25 μm PP base membrane to form an oily coating. After vacuum drying in an oven at 60°C, the product was obtained, with a total membrane thickness of 45 μm.

[0068] Summary: In this Example 3, compared with Example 1, the magnesium-based whiskers are magnesium hydroxide.

[0069] Example 5:

[0070] 2.559 g of basic magnesium carbonate and 0.366 g of fully dried high molecular weight (battery grade) polyvinylidene fluoride were dry-ground in a mortar until uniformly mixed. Then, the mixture was slowly added dropwise in batches to 13 mL of N-methylpyrrolidone solution to dissolve the polyvinylidene fluoride and form a viscous slurry. The mixture was continuously stirred and ground until a uniform and viscous slurry was formed. The slurry was then coated on both sides of a 25 μm PP base membrane to form an oily coating. After vacuum drying in an oven at 60°C, the product was obtained, with a total membrane thickness of 45 μm.

[0071] Summary: In this Example 4, compared with Example 1, the magnesium-based whiskers are basic magnesium carbonate.

[0072] Comparative Example 1:

[0073] Commercial Celgard 2500 membrane without any treatment.

[0074] Various tests were performed on the diaphragm in the comparative examples and embodiments, and the test results are shown in Table 2 below.

[0075]

[0076] SEM images of the basic magnesium sulfate whiskers prepared in this invention are as follows: Figure 1 As shown, its microstructure reveals that the basic magnesium sulfate whiskers have a diameter of 0.96 μm and an aspect ratio of approximately 48-87; through... Figure 2The XRD pattern confirms the successful synthesis of the basic magnesium sulfate whiskers prepared in this invention. Furthermore, the porosity of the membrane and the electrolyte wettability are crucial performance indicators. As shown in Table 2, the porosity of Comparative Example 1 was only 36%, while Example 2 increased the porosity to 58.65%, and the porosity of Example 1 was 62.07%, an increase of 3.42% compared to Example 2. This indicates that the prepared basic magnesium sulfate whisker coating can further improve the porosity of the composite membrane. To further evaluate electrolyte affinity, contact angle measurements were performed (…). Figure 3 Table 2 shows the contact angle data after the electrolyte has been in contact with the composite membrane for 1 second. Comparative Example 1 has a contact angle of 41.9°, reflecting poor electrolyte wettability; while Examples 1 and 2 have a contact angle of 0° after 1 second of electrolyte immersion, exhibiting superior electrolyte affinity and rapid electrolyte wetting characteristics. Such high porosity and excellent wettability directly affect the electrolyte retention rate of the composite membrane (Table 2). The electrolyte retention rate of Comparative Example 1 is 79.57%, while that of Example 1 is as high as 162.2%, representing increases of 82.63% and 24.42% compared to Comparative Example 1 and Example 2, respectively. This improvement stems from the abundant polar functional groups in the basic magnesium sulfate whiskers and the increased porosity of the coating. Therefore, the synergistic effect of high porosity and excellent wettability in Example 1 promotes the development of Li... + Rapid transmission is crucial for achieving long-term cycle stability and superior rate performance in lithium metal batteries.

[0077] The ionic conductivity and lithium-ion transference number were measured to further investigate the effect of basic magnesium sulfate whiskers on Li. + The influence of transport dynamics. For example... Figure 4 As shown in Table 2, the ionic conductivity of Example 1 (1.279 mS cm⁻¹) -1 ) is a comparison of Example 1 (0.246 mScm) -1 4.2 times that of Example 2 (1.052 mS cm⁻¹), compared to Example 2 (1.052 mS cm⁻¹). -1 The conductivity was increased by 22%, which can be attributed to the ability of polar materials in basic magnesium sulfate whiskers to enhance electrochemical kinetics, effectively mitigating the negative impact of increased thickness on ionic conductivity. This also indicates that the basic magnesium sulfate whiskers prepared in this invention have higher ionic conductivity than commercial basic magnesium sulfate whiskers. Besides ionic conductivity, lithium-ion transference number is another key indicator of high-performance lithium metal batteries. Compared with Comparative Example 1 (0.67) and other modified separators, Example 1 exhibited the highest lithium-ion transference number (0.74). Therefore, basic magnesium sulfate whiskers improve the Li-ion conductivity at the electrode-electrolyte interface. + transmission.

[0078] The adsorption energy between the electrolyte and the PP or basic magnesium sulfate whisker coating was calculated using the molecular dynamics (MD) method in the Forcite module of Materials Studio software. Figure 5 The desolvation effect of basic magnesium sulfate whisker coatings was investigated, and the lithium-affinity properties and excellent electrolyte wettability of the coating were verified. Li in the electrolyte... + TFSI - The adsorption energies for basic magnesium sulfate whiskers are -9.25 eV and -7.26 eV, respectively. Positively charged Li + It exhibits a stronger attraction to basic magnesium sulfate whiskers; this cation selectivity leads to it becoming the dominant interaction and initiating a desolvation effect. Furthermore, Li... + The adsorption energy between MOSw and basic magnesium sulfate whiskers is significantly higher than that of other components, indicating that MOSw can effectively regulate the Li at the interface. + The transport and deposition behavior of basic magnesium sulfate whiskers is used to improve the ionic conductivity and Li... + The transfer number provides a theoretical basis. Furthermore, basic magnesium sulfate whiskers contribute to the Li... + The adsorption energy of MOSw for both the electrolyte and the PP is stronger than that for PP, confirming that MOSw has lithium-philic properties and a high electrolyte adsorption rate.

[0079] Figure 6 The cycling performance of LiFePO4 / membrane / Li batteries assembled using the comparative example and the embodiment was measured at a 1C charge-discharge rate. The initial discharge capacity of the LiFePO4 / membrane / Li batteries assembled using the embodiment was 122.05 mAh g⁻¹ higher than that of the comparative example LiFePO4 / membrane / Li battery. -1 The initial discharge capacity was [not specified]. After 200 cycles, the LiFePO4 / separator / Li battery assembled using Example 1 exhibited the highest discharge capacity (135.98 mAh / g) with a capacity retention of 98.8%, while the discharge capacities of the comparative example and the LiFePO4 / separator / Li battery assembled using Example 2 were 97.97 mAh / g and 104.05 mAh / g, respectively, with capacity retention rates of 80% and 76%, respectively. This indicates that the basic magnesium sulfate whisker-coated separator prepared in this invention has excellent electrochemical performance.

[0080] The excellent heat shrinkage resistance of the separator is crucial for mitigating the safety hazards of lithium metal batteries, as it can prevent internal short circuits during thermal runaway. Figure 7In the demonstrated heat shrinkage test, Comparative Example 1 showed a shrinkage rate of 31% at 160°C and subsequently melted completely at 180°C, exhibiting severe thermal instability. In contrast, the introduction of the basic magnesium sulfate whisker coating significantly improved dimensional stability, achieving zero shrinkage below 140°C. Even under extreme conditions, Example 1 maintained a minimal shrinkage rate—only 10% at 160°C and 28% at 180°C—while maintaining structural integrity, thereby significantly reducing the risk of short circuits under thermal abuse conditions.

[0081] The flame-retardant properties of the diaphragm were evaluated using the MCC test. Figure 8 and 9 As shown, in the absence of a protective char layer, the pyrolysis of Comparative Example 1 produces a large amount of combustible volatiles, resulting in the release of the highest peak heat release rate (1139.6 Wg). -1 ) and total heat release (43.71 kJ g) -1 After modification with basic magnesium sulfate whiskers according to the present invention, the parameters of Example 1 were significantly reduced to 390.7 W g. -1 and 20.1 kJ g -1 Compared to Comparative Example 1, the flame retardancy was reduced by 66% and 54.0%, respectively, and was superior to Example 2. Therefore, the magnesium-based whisker flame-retardant composite diaphragm of the present invention has excellent flame-retardant properties.

[0082] As shown in the figures and tables, the present invention ultimately prepares a magnesium-based whisker and a magnesium-based whisker flame-retardant composite membrane, comprising: basic magnesium sulfate whiskers prepared from magnesium chloride and magnesium sulfate, a porous polyolefin substrate with a porous structure, and a porous coating containing a mixture of magnesium-based whiskers and a binder polymer. This porous active coating is applied to both sides of the polyolefin porous membrane; the wetting contact angle of the electrolyte on the coating after 1 second is close to 0°, and the resulting flame-retardant composite membrane exhibits an ionic conductivity as high as 1.279 mS / cm. -1 The lithium-ion transference number is 0.74. After the membrane is placed at 160°C for 0.5 hours, its shrinkage rate is only 10%, and the peak heat release rate and total heat release of the membrane are reduced by 66% and 54% respectively compared with commercial polyolefin membranes.

[0083] Example 6: Comparison of Smoke Suppression and Toxicity Reduction Performance

[0084] This invention employs thermogravimetric analysis-Fourier transform infrared spectroscopy (TG-FTIR) to characterize the evolution curve of pyrolysis gas release during membrane pyrolysis, thereby elucidating the smoke-suppressing and toxicity-reducing effect of self-made basic magnesium sulfate whiskers. Based on signal intensity, Figure 11 This indicates that the total pyrolysis gas release in Example 1 was significantly lower than that in Comparative Example 1 and Example 2. Furthermore, the alkane gas release in Example 1 was significantly lower than that in Comparative Example 1 and Example 2. Figure 12This limits the fuel supply to the flame front during combustion. More importantly, such as Figure 13 and Figure 14 As shown, the CO and CO2 gas release in Example 1 is still lower than that in Example 2. This indicates that the self-made basic magnesium sulfate whiskers endow the composite membrane with excellent smoke suppression and toxicity reduction properties, and the smoke suppression and toxicity reduction effect of the self-made basic magnesium sulfate whiskers is significantly better than that of commercial basic magnesium sulfate whiskers.

[0085] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high thermal safety lithium battery separator based on magnesium-based whiskers, characterized in that: Magnesium-based whiskers are added to the binder polymer slurry and mixed evenly to obtain an oily mixed slurry; the oily mixed slurry is coated on both sides of a polyolefin porous substrate to form an oily coating, and after drying, a lithium battery separator can be obtained. The magnesium-based whiskers are basic magnesium sulfate whiskers, prepared by a method including the following steps: Step 1: Dissolve magnesium sulfate heptahydrate and magnesium chloride hexahydrate in deionized water to prepare a mixed salt solution; add disodium ethylenediaminetetraacetate to the mixed salt solution and stir until homogeneous to obtain solution A; Step 2: Weigh out NaOH and dissolve it in deionized water to prepare solution B; under vigorous stirring, add solution B dropwise to solution A, and continue stirring to form a homogeneous precursor slurry; transfer the precursor slurry to a polytetrafluoroethylene-lined hydrothermal reactor for hydrothermal reaction; after the reaction, allow the reactor to cool naturally to room temperature, and filter the product and wash it repeatedly with deionized water until no SO4 is found. 2- and Cl - The residue is then vacuum dried to obtain a high aspect ratio basic magnesium sulfate whisker product. In step 1, the molar ratio of magnesium sulfate heptahydrate to magnesium chloride hexahydrate is 7:3, and the magnesium ion concentration in the mixed salt solution is 0.8-1 mol / L; In step 1, when adding disodium ethylenediaminetetraacetate, control the Mg content. 2+ The molar ratio of sodium EDTA to disodium ethylenediaminetetraacetate is 20:1; In step 2, when solution B is added dropwise to solution A, the Mg content is controlled. 2+ With OH - The molar ratio is 1:1.2; The magnesium-based whiskers have a length L of 50-90 μm, a diameter d of 0.6 μm-1 μm, and an aspect ratio L / d of 50-90.

2. The preparation method according to claim 1, characterized in that: In step 2, the hydrothermal reaction temperature is 160℃ and the reaction time is 10h.

3. The preparation method according to claim 1, characterized in that: The adhesive polymer is one or more of the following: styrene-butadiene rubber, acrylic resin, polyvinyl alcohol, polyacrylonitrile, polyvinylidene fluoride, carboxymethyl cellulose, polyethylene oxide, and polytetrafluoroethylene.

4. The preparation method according to claim 1, characterized in that: The mass-volume ratio of the magnesium-based whiskers, binder polymer, and solvent is (150~250) mg : (20~40) mg : (1~1.5) mL.

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