Spherical aluminum oxide coating material for lithium battery diaphragm and preparation method of spherical aluminum oxide coating material

Abstract

The invention discloses a spherical aluminum oxide coating material for a lithium battery diaphragm and a preparation method of the spherical aluminum oxide coating material, and belongs to the technical field of lithium battery diaphragms.The spherical aluminum oxide coating material for the lithium battery diaphragm comprises, by weight, 40-70 parts of spherical aluminum oxide, 1-10 parts of lithiated PEEK and 50-100 parts of solvent, PEEK of the lithiated PEEK is hyperbranched PEEK, polymeric monomers of the hyperbranched PEEK comprise hexahydric phenol, diphenolic acid and 4, 4 '-dihydroxy-4, 4'-biphenyl. According to the present invention, the surface of the conventional polyethylene diaphragm is coated with the coating material composed of the lithiated PEEK and the spherical alumina particles, such that the electrochemical performance and the stability of the lithium metal battery can be easily improved, and the coating diaphragm has characteristics of excellent thermal stability, excellent wettability and excellent electrolyte absorption rate.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery separator technology, specifically relating to a spherical alumina coating material for lithium battery separators and its preparation method. Background Technology

[0002] As the "third electrode" in a battery, the separator is a key component that ensures the safety of the battery system and affects battery performance. The separator plays two main roles in the battery. First, the material itself has good insulation and certain mechanical strength, which can effectively prevent direct contact between the positive and negative electrodes, avoid lithium dendrite puncture leading to battery short circuit, and maintain dimensional stability under high temperature conditions, thereby ensuring battery safety. Second, its porous structure provides a good migration channel for lithium ions, ensuring stable and efficient operation of the battery. High-temperature resistant polymer separators for lithium metal batteries with the ability to inhibit lithium dendrite growth play a key role in improving battery safety and electrochemical performance. They should meet the following characteristics: (1) Excellent thermal stability, the separator can maintain structural integrity under high temperature conditions, avoid battery short circuit due to thermal shrinkage or melting, and significantly improve the thermal safety of the battery; (2) Excellent mechanical properties, with sufficient tensile and puncture resistance, effectively resisting lithium dendrite puncture and ensuring stable operation of the battery; (3) Suitable thickness and dimensional stability, the thickness of the separator is usually between 20 and 25 μm, ensuring that the battery is stable during assembly and operation. Maintain good dimensional stability to prevent performance degradation due to deformation; (4) High porosity and uniform pore size distribution: The separator should have high porosity and appropriate pore size distribution to provide effective lithium-ion channels, promote electrolyte absorption and penetration, improve ionic conductivity, and enhance the electrochemical performance of the battery; (5) Good electrolyte wettability: Ensure uniform electrolyte distribution, reduce interfacial resistance, promote ion conduction, and improve the cycle life and coulombic efficiency of the battery; (6) Excellent chemical stability: Under high voltage and long-term cycling, the separator can maintain chemical stability and not react with the electrolyte or electrodes, ensuring the safe operation of the battery. Currently, most commercial lithium-ion batteries use microporous polyolefin separators. Their biggest advantage is that they have good tensile strength and puncture strength and suitable thickness. However, polyolefins have poor thermal stability. The battery generates a lot of heat during repeated charge and discharge cycles. The softening and melting temperatures of polyolefin materials are low. When the temperature rise is not significant, the polyolefin separator can protect the battery by closing the pore structure. However, when the temperature inside the battery is too high, the polyolefin separator will continue to shrink and melt, which can even lead to short circuits or explosions, causing safety problems. To solve these problems, polyolefin-based separators coated with thermally stable ceramic particles have become a research hotspot. Studies have shown that PE separators coated with silica nanoparticles, alumina powder, and PP separators coated with alumina / titanium dioxide all exhibit superior thermal stability, good wettability, and higher electrolyte absorption rates compared to bare separators. Coating commercial polyolefin separators with ceramic particles has become one of the ways to improve the temperature resistance of polyolefin separators and thus enhance battery safety. However, a simple ceramic particle coating can only improve the thermal stability and structural support of the separator, and its effect on electrolyte wettability and ion conduction is not significant. Summary of the Invention

[0003] To overcome the shortcomings of the prior art, the present invention provides a spherical alumina coating material for lithium battery separators and its preparation method. The coating material is prepared by mixing lithium-ionized hyperbranched PEEK with spherical alumina and coating it onto a conventional polyolefin-based separator. This method is beneficial to improving the electrochemical performance and stability of lithium metal batteries, exhibiting superior thermal stability, wettability and electrolyte absorption rate.

[0004] The technical solution for achieving the objective of this invention is as follows: A spherical alumina coating material for lithium battery separators, comprising, by weight, 40-70 parts spherical alumina, 1-10 parts lithiated PEEK, and 50-100 parts solvent, wherein the lithiated PEEK is hyperbranched PEEK, and the polymer monomers of the hyperbranched PEEK include hexaphenol, bisphenolic acid, and 4,4'-difluorobenzophenone, wherein the hexaphenol is as shown in Formula 1: Formula 1.

[0005] In one specific embodiment, the amount of lithium-ionized PEEK is 3 to 10 parts.

[0006] In one specific embodiment, the preparation method of the lithium-ionized PEEK includes the following steps: adding bisphenol acid, hexaphenol, potassium carbonate, toluene and N,N-dimethylacetamide (DMAc) to a reaction vessel, heating to 100-120°C, stirring and azeotropically distilling to remove water for a period of time, then heating to 150-170°C, adding 4,4'-difluorobenzophenone, stirring, and maintaining the temperature for homogeneous polymerization reaction, after the reaction is completed, cooling to room temperature, pouring into methanol to produce a precipitate, filtering, repeatedly washing with lithium hydroxide aqueous solution and methanol, and then drying under vacuum conditions to obtain lithium-ionized PEEK.

[0007] In one specific embodiment, the molar ratio of the hydroxyl groups of bisphenolic acid and hexaphenol to the F of 4,4'-difluorobenzophenone in the polymer monomer of the hyperbranched PEEK is (1.05~1.15):1.

[0008] In one specific embodiment, the molar ratio of bisphenolic acid to hexaphenol is (2~4):(1~2).

[0009] In one specific embodiment, the polymer monomer of the hyperbranched PEEK also includes hydroquinone.

[0010] In one specific embodiment, the preparation method of the hexaphenol includes the following steps: reacting 1,3,5-tris(4-bromophenyl)benzene with 3,5-dimethoxyphenylboronic acid under palladium catalyst and solid base conditions to obtain tris(4-(3,5-dimethoxyphenyl)phenyl)benzene intermediate; and removing the methoxy group from the tris(4-(3,5-dimethoxyphenyl)phenyl)benzene intermediate under the action of pyridine hydrochloride to obtain hexaphenol.

[0011] In one specific embodiment, the palladium catalyst is Pd(PPh3)4, and the solid base is K2CO3 or Na2CO3.

[0012] In one specific embodiment, the number-average molecular weight Mn of the lithium-ionized PEEK is 5000~10000, the weight-average molecular weight Mw is 20000~50000, and the testing method is gel permeation chromatography.

[0013] In one specific embodiment, the degree of branching of the lithium-ionized PEEK is 40-60%.

[0014] In one specific embodiment, the average particle size of the spherical alumina is 100~1000 nm; the solvent is N,N-dimethylacetamide.

[0015] Another objective of this invention is to provide a method for preparing a protective spherical alumina coating material, comprising the following steps: dissolving lithium-ionized PEEK in a solvent to prepare a solution with a mass fraction of 10-20%, stirring for a period of time, adding spherical alumina to the solution, supplementing with additional solvent, and mixing evenly to obtain the spherical alumina coating material.

[0016] Another object of the present invention is to protect a lithium battery separator, comprising a polyolefin separator and a spherical alumina coating material coated on the surface of the polyolefin separator, wherein the spherical alumina coating material is the aforementioned spherical alumina coating material.

[0017] In one specific embodiment, the thickness of the polyolefin separator is 20-30 μm, the thickness of the coating is 5-10 μm, and the polyolefin is polyethylene or polypropylene, preferably polyethylene.

[0018] More preferably, the polyolefin separator has a thickness of 20 μm, and the coating has a thickness of 5 μm.

[0019] Another objective of the present invention is to provide a method for preparing the lithium battery separator, comprising the following steps: pouring a spherical alumina coating material onto the surface of a polyolefin separator, using a scraper to control the coating thickness, uniformly scraping the coating, and placing the coated separator into a convection oven to dry at 60~80℃ for 2~4 hours.

[0020] Beneficial effects

[0021] This invention provides a spherical alumina coating material for lithium battery separators and its preparation method, which has the following beneficial effects: (1) The addition of high proportion of spherical alumina ensures the thermal stability and physical support of the coating, reduces the risk of short circuit of lithium battery caused by shrinkage of polyolefin separator at high temperature, and the fluidity of spherical alumina is better than that of ordinary alumina, ensuring that the coating can be uniformly coated on polyolefin separator to form a coating of uniform thickness, while maintaining the uniform pore size of the separator, so as not to block the pores or cause cracks.

[0022] (2) Hyperbranched PEEK was prepared by reacting hexaphenol, bisphenol acid, and 4,4'-difluorobenzophenone with lithium and then subjected to lithiation. The terminal hydroxyl groups and side-chain carboxyl groups introduced by the hexaphenol and bisphenol acid monomers can coordinate with lithium ions, thereby building lithium-ion bridges inside the separator. This reduces the random diffusion during lithium-ion transport, promotes the rapid migration of lithium ions, increases the lithium-ion transference number, and improves the lithium-ion conductivity of the lithium battery separator. In addition, the side-chain carboxyl groups are basically uniformly distributed in the PEEK polymer, which can not only uniformly distribute the lithium-ion flux, but also avoid the local enrichment of lithium ions on the electrode surface, thus preventing the growth of lithium dendrites. The lithiation-treated coordination groups can participate in the electrode interface reaction, inducing the formation of a dense SEI film to further block dendrites from penetrating the separator, thereby extending the cycle life of the lithium battery.

[0023] (3) The hyperbranched PEEK structure reduces the viscosity of the coating and introduces abundant terminal hydroxyl groups, which together with carboxyl groups enhance the hydrophilicity of the membrane surface, significantly reducing the contact angle of the electrolyte and achieving a fully wetted state. This can accelerate electrolyte penetration and increase electrolyte adsorption. Furthermore, it can interact with hydroxyl groups on the surface of spherical alumina and the membrane substrate to form hydrogen bonds, thereby enhancing the coating adhesion and making the coating less prone to peeling or cracking during battery cycling. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the synthetic pathway of hexahydrols; Figure 2 The 1H NMR spectrum of the intermediate tris(4-(3,5-dimethoxyphenyl)phenyl)benzene and the hexaphenol; Figure 3 The carbon NMR spectra of tris(4-(3,5-dimethoxyphenyl)phenyl)benzene intermediate and hexaphenol are shown. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Unless otherwise specified, the experimental methods used in the embodiments are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0027] The raw materials and equipment used in the embodiments and comparative examples are described below: Hexahydrol: Prepared in-house, preparation method is as follows: S1. Under argon protection, 50 mmol of 1,3,5-tris(4-bromophenyl)benzene, 225 mmol of 3,5-dimethoxyphenylboronic acid, 5 mmol of palladium catalyst Pd(PPh3) 43-5 mol%, 600 mmol of solid base K2CO3, and a mixed solvent consisting of 400 ml toluene, 100 ml ethanol, and 100 ml water were added sequentially to a dry Srank flask. The reaction system was purged with argon three times, heated to 90 °C in an oil bath, and stirred under reflux for 24-48 hours. The reaction progress was monitored by thin-layer chromatography (TLC). After the reaction was complete, the mixture was cooled to room temperature. The organic phases were extracted with water and dichloromethane, combined, dried over anhydrous magnesium sulfate, filtered, and the solvent was removed by rotary evaporation to obtain the crude product. The intermediate tris(4-(3,5-dimethoxyphenyl)phenyl)benzene was purified by silica gel column chromatography (eluting with a gradient of petroleum ether / ethyl acetate) in 88% yield. The 1H NMR spectrum (¹H NMR 400MHz, CDCl₃+5 %v / vDMAc-d7) and 1C NMR spectrum were also obtained. 13 The structure was confirmed by C NMR (100 MHz, CDCl3 + 5 %v / vDMAc-d7) as follows. Figure 1 and Figure 2 As shown.

[0028] S2. Preparation: Under argon protection, 30 mmol of tris(4-(3,5-dimethoxyphenyl)phenyl)benzene intermediate and 900 mmol of pyridine hydrochloride were added to a dry reaction flask. The mixture was melt-stirred at 190 °C for 4 h, cooled to 80 °C, and 1000 mL of ice water was added. The mixture was extracted twice with ethyl acetate (100 mL each time). The extracts were combined and dried over anhydrous magnesium sulfate. After evaporation to remove the solvent, the mixture was purified by silica gel column chromatography (eluent: dichloromethane and ethyl acetate, v / v ratio 1:1) to obtain hexaphenol, yield: 95%. The 1H NMR (¹H NMR 400 MHz, CDCl₃+5 %v / v DMAc-d₇) and 1C NMR were then analyzed.13 The structure was confirmed by C NMR (100MHz, CDCl3+5 %v / vDMAc-d7) as follows. Figure 1 and Figure 2 As shown.

[0029] Lithiumized PEEK-1: Self-made, preparation method as follows: 15 mmol of bisphenol A, 9 mmol of hexahydrol, 102 mmol of potassium carbonate, 100 ml of toluene, and 200 ml of N,N-dimethylacetamide (DMAc) were added to a reaction vessel and stirred at 120 °C for 30 min. Water generated during the reaction (forming an azeotrope with toluene) was removed by azeotropic distillation. The temperature was then raised to 165 °C, and 40 mmol of 4,4'-difluorobenzophenone was added in a single addition. The mixture was stirred and stirred for another 6 hours at this temperature to carry out homogeneous polymerization. After the reaction was complete, the mixture was cooled to room temperature and poured into 300 ml of methanol. The precipitated polymer was collected by filtration, washed thoroughly with 1 mol / L lithium hydroxide aqueous solution and methanol, and then dried under vacuum to obtain hyperbranched PEEK-Li with a yield of 88%. The product was a white powder with a number-average molecular weight (Mn) of 6100 and a weight-average molecular weight (Mw) of 25600 (calibrated with polystyrene standards) as determined by GPC, and a branching degree of 43%.

[0030] Lithium-based PEEK-2: The difference between lithium-based PEEK and lithium-based PEEK is that bisphenol A is replaced with hydroquinone.

[0031] Non-lithiated PEEK: Compared with lithium-based PEEK, the difference is that the 1 mol / L lithium hydroxide aqueous solution is replaced with deionized water; Lithium-based non-hyperbranched PEEK: The difference between lithium-based PEEK and PEEK is that the hexaphenol is replaced with hydroquinone.

[0032] Unless otherwise specified, all components and raw materials used in the embodiments and comparative examples of this invention are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0033] Examples and Comparative Examples A spherical alumina coating material for lithium battery separators is prepared by dissolving PEEK in a solvent to prepare a 10% (w / w) solution. After stirring for a period of time, spherical alumina (particle size 200-400 nm) or ordinary alumina (particle size 300-500 nm) is added to the solution, and solvent is added to replenish the solvent. The mixture is then stirred evenly to obtain the spherical alumina coating material. The specific formulation is shown in Table 1. Table 1. Composition and proportions (parts by weight) of spherical alumina coating materials

[0034] In Examples 1-4, the content of spherical alumina was maintained at around 39%, and the content of lithium-ionized PEEK was 1 wt%, 4.5 wt%, 3.1 wt%, and 2.0 wt%, respectively.

[0035] Application examples A lithium battery separator is prepared by pouring the spherical alumina coating material obtained in Examples 1-4 and Comparative Examples 1-5 onto the surface of a polyethylene separator Celgard 2325 (20 μm thick), using a scraper to control the coating thickness to 5 μm, uniformly scraping the coating, and then placing the coated separator into a convection oven to dry at 60°C for 4 hours.

[0036] The membranes prepared in the examples and comparative examples were subjected to the following tests, and the results are shown in Table 2: (1) Thermal dimensional stability: The diaphragm was cut into 2cm×2cm pieces using a cutting machine, and the samples were placed in a 140℃ oven for 10min to keep warm and record the shrinkage state of the diaphragm.

[0037] (2) Liquid absorption rate: Weigh the dry mass M0 of the diaphragm, soak the weighed diaphragm in the electrolyte for 2 hours, and then take it out. Wipe off the excess electrolyte on the surface with filter paper, and weigh the diaphragm after soaking in the electrolyte M. The liquid absorption rate is calculated using the formula ξ=(M-M0) / M0×100%.

[0038] (3) Wettability: The wettability of the diaphragm is measured by a contact angle tester. The contact angle is tested after the electrolyte is dropped onto the diaphragm surface for 5 seconds.

[0039] (4) Ionic conductivity: The separator was used to assemble SUS / separator / SUS symmetric lithium-ion batteries. Electrochemical impedance spectroscopy (EIS) of the battery samples was detected using an electrochemical workstation at frequencies of 0.1 MHz to 65 kHz and amplitudes of 10 mV. The ionic conductivity (σ, mS / cm) of the separator was calculated using the following formula: σ = L / AR, where L (cm) is the thickness of the separator, and A (cm) is the thickness of the separator. 2 ) is the area of ​​the stainless steel sheet electrode, and R(Ω) is the resistance obtained through the Nyquist plot.

[0040] (5) Lithium-ion transport number: After assembling a Li / separator / Li symmetric cell, the transport number was calculated using the formula tLi by chronoamperometry (applying a polarization voltage of 10mV) and EIS testing: + = [I ss (ΔV-I0R0)] / [I0(ΔV-I ss R ss )]. Among them, I0 and I ssRepresent the initial current and steady-state current obtained by the chronoamperometry method, respectively; R0 and R ss These represent the initial interface resistance and steady-state resistance obtained through EIS, respectively.

[0041] (6) Battery cycle life: The NCM811 / / Li half cell was assembled and its cycle stability was tested after 120 cycles at a C-rate of 0.5C within a voltage range of 3.0~4.2V.

[0042] Table 2 Performance Tests of Examples and Comparative Examples

[0043] As can be seen from the examples and comparative examples, the coating prepared by hyperbranched lithiated PEEK and spherical alumina can effectively improve the thermal stability and electrolyte affinity of polyolefin lithium battery separators. Furthermore, the high-temperature resistant polymer coating can inhibit the growth of lithium dendrites, thereby improving the battery cycle life. In Example 1, the amount of lithiated PEEK added was not high, resulting in slightly poorer thermal stability, electrolyte affinity, and electrochemical performance. When lithiated PEEK was replaced with non-lithiated or non-hyperbranched PEEK, the polymer and Li... + The number of coordinating groups decreases, Li + Insufficient density resulted in a decrease in electrochemical performance.

[0044] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A spherical alumina coating material for lithium battery separators, characterized in that, The spherical alumina coating material, by weight, comprises 40-70 parts spherical alumina, 1-10 parts lithiated PEEK, and 50-100 parts solvent. The lithiated PEEK is hyperbranched PEEK, and the polymer monomers of the hyperbranched PEEK include hexaphenol, bisphenolic acid, and 4,4'-difluorobenzophenone. The hexaphenol is shown in Formula 1. Formula 1.

2. The spherical alumina coating material as described in claim 1, characterized in that, The preparation method of the lithium-ionized PEEK includes the following steps: adding bisphenol acid, hexaphenol, potassium carbonate, toluene and N,N-dimethylacetamide (DMAc) to a reaction vessel, heating to 100-120°C, stirring and azeotropically distilling to remove water for a period of time, then heating to 150-170°C, adding 4,4'-difluorobenzophenone, stirring, and maintaining the temperature for homogeneous polymerization reaction, after the reaction is completed, cooling to room temperature, pouring into methanol to produce a precipitate, filtering, repeatedly washing with lithium hydroxide aqueous solution and methanol, and then drying under vacuum to obtain lithium-ionized PEEK.

3. The spherical alumina coating material as described in claim 1, characterized in that, The preparation method of the hexaphenol includes the following steps: reacting 1,3,5-tris(4-bromophenyl)benzene with 3,5-dimethoxyphenylboronic acid under palladium catalyst and solid base conditions to obtain tris(4-(3,5-dimethoxyphenyl)phenyl)benzene intermediate; and removing the methoxy group from the tris(4-(3,5-dimethoxyphenyl)phenyl)benzene intermediate under the action of pyridine hydrochloride to obtain hexaphenol.

4. The spherical alumina coating material as described in claim 1, characterized in that, The number-average molecular weight (Mn) of the lithium-ionized PEEK is 5000~10000, and the weight-average molecular weight (Mw) is 20000~50000. The test method is gel permeation chromatography.

5. The spherical alumina coating material as described in claim 1, characterized in that, The degree of branching of the lithium-ionized PEEK is 40-60%.

6. The spherical alumina coating material as described in claim 1, characterized in that, The average particle size of the spherical alumina is 100~1000 nm; the solvent is N,N-dimethylacetamide.

7. The method for preparing the spherical alumina coating material according to any one of claims 1 to 6, characterized in that, Lithium-ionized PEEK is dissolved in a solvent to prepare a solution with a mass fraction of 10-20%. After stirring for a period of time, spherical alumina is added to the solution, and more solvent is added. The mixture is then stirred evenly to obtain a spherical alumina coating material.

8. A lithium battery separator, characterized in that, The invention includes a polyolefin separator and a spherical alumina coating material coated on the surface of the polyolefin separator, wherein the spherical alumina coating material is the spherical alumina coating material according to any one of claims 1 to 6.

9. The lithium battery separator as described in claim 8, characterized in that, The polyolefin membrane has a thickness of 20-30 μm, the coating has a thickness of 5-10 μm, and the polyolefin is polyethylene.

10. The method for preparing the lithium battery separator as described in claim 8, characterized in that, Includes the following steps: Pour the spherical alumina coating material onto the surface of the polyolefin separator, use a scraper to control the coating thickness, and scrape evenly. Place the coated separator into a convection oven and dry at 60~80℃ for 2~4 hours.

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