A core-shell structured oxide-coated separator and a method for preparing the same

Abstract

The application discloses a kind of core-shell structure oxide coated diaphragm and preparation method thereof, first obtain PVP surface treatment spherical alumina;Then the surface treatment alumina particles are added into glucose aqueous solution and hydrothermal reaction obtains carbon-coated alumina particles;Then carbon-coated spherical alumina is further coated, calcined in muffle furnace to obtain porous spherical shell structure coated alumina powder;Finally, coated alumina powder is prepared slurry with binder in NMP, slurry is coated to diaphragm using doctor blade, dried in vacuum drying oven to obtain porous oxide coated diaphragm.The spherical shell structure oxide coated diaphragm prepared by the application can avoid the situation that the diaphragm pore is reduced caused by traditional solid oxide coated diaphragm, and the thermal stability of coated diaphragm will not be lost, porous spherical shell structure is beneficial to lithium ion transmission, more uniform gap can realize lithium ion rearrangement, inhibit lithium dendrite generation, so as to improve the safety performance and cycle life of battery.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a high-safety modified separator for rechargeable batteries, and more specifically to a core-shell structure oxide-coated separator and its preparation method. Background Technology

[0002] With the rapid development of the Industrial Revolution and technological innovation, traditional energy sources such as fossil fuels (coal, oil, natural gas, etc.) are far from meeting human needs, causing problems such as the greenhouse effect and acid rain. Environmental pollution not only harms human health but also damages economic resources and ecological balance. To solve the energy problem, research and achievements in wind power, solar power, tidal power, and geothermal energy have surged, but the intermittency and uncontrollability of these sustainable energy sources cannot meet the needs of large-scale applications. Lithium-ion batteries (LIBs), a type of electrochemical storage and conversion device with high quality / volume density and low self-discharge characteristics, have attracted widespread attention due to their excellent performance. In recent years, the attractive characteristics of LIBs have promoted their widespread application in electric vehicles, electronic products, robot power supplies, military power supplies, emergency power supplies, military equipment power supplies, wind energy storage, and solar energy storage.

[0003] Lithium-ion batteries mainly consist of four parts: a positive electrode, a negative electrode, an electrolyte, and a separator. During charging, lithium ions (Li...) + The electrolyte is extracted from the positive electrode and inserted into the negative electrode through the electrolyte and membrane; this process is reversed during discharge. The membrane is made of Li. + Transfer provides a channel, avoiding direct contact between the positive and negative electrodes. The Advanced Battery Consortium (ACC) in the United States has set operating standards for lithium-ion battery separators, including suitable thickness (5-25 μm), uniform pore size (<1 μm), high wettability, excellent permeability, strong tensile mechanical strength, high thermal stability (shrinkage <5% after 60 min at 90°C), excellent dimensional stability, chemical stability, and electrochemical stability. Among the requirements for separators, the mechanical properties are mainly manifested in longitudinal (MD) and transverse (TD) tensile strength. The characteristics of the separator are closely related to the internal resistance, cycle performance, rate performance, safety, and commercial prospects of lithium-ion full batteries.

[0004] Polyolefin separators (polyethylene (PE) and polypropylene (PP)) have been widely used in commercial lithium-ion batteries due to their electrochemical stability. However, commercial polyolefin separators suffer from poor thermal stability and weak wettability, failing to meet the ever-increasing energy demands. When LIBs operate in harsh environments, the separator undergoes thermal shrinkage, which can lead to short circuits and, due to the flammability of LIBs, may cause fires. Furthermore, polyolefin separators have poor electrolyte absorption performance, resulting in incomplete electrolyte filling within the separator pores and blockage of ion channels, thus hindering the exchange of Li-ion between the positive and negative electrodes. +Uneven transport properties lead to poor compatibility between polyolefin separators and the positive and negative electrodes. Furthermore, the poor interface easily forms an unstable solid electrolyte interphase (SEI), accompanied by uneven lithium dendrite growth. These uneven lithium dendrites can puncture the separator, posing a safety hazard. In recent years, polymers such as polyvinylidene fluoride (PVDF) have attracted widespread attention due to their superior wettability. However, their thermal stability and mechanical strength still do not meet commercial requirements.

[0005] To address the aforementioned issues, organic-inorganic composite separators have been proposed, offering numerous advantages over commercially available polyolefin separators or single-component polymer separators. Commonly used materials for composite separators include oxides or nitrides with high melting points and mechanical properties, polymers with high tensile strength and high decomposition temperatures, or combinations thereof. Composite separators exhibit significantly improved wettability, electrolyte absorption, mechanical properties, thermal stability, flame retardancy, and ionic conductivity. However, composite separators also have some drawbacks. For example, their thickness is relatively large, resulting in an undesirable pore structure and increased internal resistance of the battery. This is because inorganic materials can clog the pores of the polymer separator, reducing the ionic conductivity of LIBs. To address these current problems, if a separator could be fabricated using a porous inorganic material that improves both battery safety and electrochemical performance, it would be possible to solve the practical application issues of separators. Summary of the Invention

[0006] The purpose of this invention is to prepare a novel core-shell structure oxide-modified separator that can improve the thermal stability of polyolefin separators while also enhancing the electrochemical performance of batteries.

[0007] This invention provides a method for preparing a core-shell structured oxide-coated membrane, specifically comprising the following steps:

[0008] S1) Spherical alumina with a particle size of 50-500 nm and polyvinylpyrrolidone (PVP) are added to deionized water at a mass ratio of 1:4, stirred, centrifuged, and washed to obtain PVP-treated spherical alumina.

[0009] S2) 10 mg of alumina particles treated with PVP surface were added to a glucose aqueous solution of 0.1-0.5 g / mL and stirred thoroughly. The mixture was then subjected to hydrothermal reaction at 160-220℃ for 6-10 h to obtain alumina particles with carbon coating of different thicknesses, with the carbon layer thickness being 5-200 nm.

[0010] S3) Disperse 0.1g of carbon-coated spherical alumina in a mixed solution of 80ml ethanol, 20ml deionized water, 1ml ammonia, and 0.3g CTAB. Then, weigh out the coating material, which is 3 to 10 times the mass of the carbon-coated spherical alumina, such that the coating material is tetraethyl orthosilicate, tetraethyl orthosilicate and tetrabutyl titanate, or tetraethyl orthosilicate and zirconium propoxide. Dilute the coating material in ethanol and then add it dropwise to the dispersion while stirring continuously for 6 hours. Finally, filter, wash, and dry the powder, and calcine it in a muffle furnace at 500-600℃ for 6 hours to remove the carbon layer and CTAB, obtaining porous spherical shell structure coated alumina powder.

[0011] S4) Dissolve the coated alumina powder and binder in a suitable solvent at a mass ratio of 10:1 to 5:5 to prepare a slurry. Stir for 8 to 10 hours to make the slurry uniform. Use a scraper to coat the slurry onto the diaphragm. Dry in a vacuum drying oven at 60 to 80°C for 6 to 8 hours to obtain a porous oxide-coated diaphragm.

[0012] In a preferred embodiment, the stirring in step S1 is performed at room temperature for 24–36 hours, and the centrifugation is performed at 8000 rpm for 5–10 minutes.

[0013] In a preferred embodiment, the molecular weight of PVP in step S1 is 10,000 to 160,000.

[0014] In a preferred embodiment, the hydrothermal reaction in step S2 is carried out in a polytetrafluoroethylene autoclave, and PVP-modified alumina is added under ultrasonic treatment for 10-20 minutes. After the hydrothermal reaction, a black solid product is obtained by three rounds of centrifugation / washing / ultrasonic treatment, and then dried in an oven at 60-80°C for 10 hours to obtain carbon-coated alumina.

[0015] In a preferred embodiment, the washing and drying in step S3 is as follows: washing three times with water and ethanol respectively, and then drying at 60°C for 5 hours.

[0016] In a preferred embodiment, the mass of the coating material in step S3 is four times that of carbon-coated alumina.

[0017] In a preferred embodiment, the mass ratio of tetrabutyl titanate or zirconium propoxide to tetraethyl orthosilicate in step S3 is 1:1 to 1:10.

[0018] In a preferred embodiment, the binder in step S4 is one of the following: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), poly(acrylic acid) (PAA), styrene-butadiene rubber (SBR), polyamide-imide (PAI), poly(vinyl alcohol) (PVA), polyethyleneimine (PEI), polyimide (PI), guar gum (GG), sodium alginate (Alg), carboxymethyl cellulose (CMC), gum arabic (GA), xanthan gum (XG), carrageenan, gelatin, chitosan, starch, and β-cyclodextrin.

[0019] In a preferred embodiment, the solvent in step S4 is one of N-methylpyrrolidone, dimethylformamide, dimethylacetamide, acetone, tetrahydrofuran, carbon tetrachloride, ethanol, and water.

[0020] In a preferred embodiment, the mass ratio of the coated alumina powder to the binder in step S4 is one of 9:1, 8:2, 7:3, 6:4, or 5:5.

[0021] In a preferred embodiment, the coating thickness in step S4 is 1–100 μm.

[0022] In a preferred embodiment, the diaphragm in step S4 is a PE or PP diaphragm.

[0023] In another aspect, the present invention provides a core-shell structured oxide-coated diaphragm, characterized in that the core-shell structured oxide-coated diaphragm is prepared by any of the methods described above.

[0024] Beneficial effects:

[0025] (1) The porous spherical shell structure oxide-coated diaphragm prepared in this invention has better performance than the current traditional diaphragm, can avoid the reduction of diaphragm pores caused by the traditional solid oxide-coated diaphragm, and will not lose the thermal stability of the coated diaphragm.

[0026] (2) The spherical shell structure in this invention can be constructed by using a single oxide or a mixture of multiple oxides to build an oxide network. The mixed oxide network can improve the strength of Lewis acid in the material and adsorb more anions in the electrolyte, thereby achieving better electrochemical performance with the same loading amount of coating material.

[0027] (3) The porous spherical shell structure in this invention helps lithium ion transport. The more uniform voids can realize the rearrangement of lithium ions and suppress the formation of lithium dendrites, thereby improving the safety performance and cycle life of the battery. Detailed Implementation

[0028] This invention provides a method for preparing a core-shell structured oxide-coated membrane, specifically comprising the following steps:

[0029] S1) 10 mg of spherical alumina with a particle size of 50-500 nm and 40 mg of PVP were added to 20 ml of deionized water and soaked for 24 h. After centrifugation and washing, spherical alumina with PVP surface treatment was obtained.

[0030] S2) Add 10 mg of alumina particles treated with PVP surface to 0.1-0.5 g / mL of glucose aqueous solution and stir thoroughly. Then, perform hydrothermal reaction at 160-220℃ for 6-10 h to obtain alumina particles with carbon coating of different thicknesses, with the carbon layer thickness being 5-200 nm.

[0031] S3) Disperse 0.1g of carbon-coated alumina in a mixed solution of 80ml ethanol, 20ml deionized water, 1ml ammonia and 0.3g CTAB. Dilute 0.4g of tetraethyl silicate in 20ml ethanol and add it dropwise to the dispersion to hydrolyze for 6h to coat the silica. After filtration, washing and drying, calcine in a muffle furnace at 550℃ for 6h to remove the carbon layer and CTAB, and obtain silica-coated alumina with a porous spherical shell structure.

[0032] S4) Prepare a slurry by mixing silica-coated alumina powder and PVDF binder in NMP at a mass ratio of 9:1. Stir for 8 hours to ensure uniform mixing of the slurry. Use a scraper to coat the slurry onto the PE membrane and dry it in a vacuum drying oven at 70°C for 7 hours to obtain a porous oxide-coated PE membrane.

[0033] Example

[0034] Example 1: First, 10 mg of alumina with a particle size of approximately 300 nm and 40 mg of PVP were added to 20 mL of deionized water, and then stirred at room temperature for 24 h. The PVP-modified alumina was collected by centrifugation at 8000 rpm for 5 minutes and washed three times with water. 10 g of glucose was completely dissolved in 30 mL of deionized water and then transferred to a 50 mL polytetrafluoroethylene autoclave. Then, 10 mg of PVP-modified alumina was added under ultrasonic treatment. After ultrasonic treatment for 10 minutes, the autoclave was placed in an oven at 173 °C for 7 h and then naturally cooled to room temperature. A black solid product was obtained by three rounds of centrifugation / washing / ultrasonic treatment, and then dried in an oven at 70 °C for 10 h to obtain carbon-coated alumina. Then, 0.1 g of the carbon-coated alumina prepared above was redispersed in a mixed solution containing CTAB (0.30 g), deionized water (20 mL), ammonia (1 mL), and ethanol (80 mL). The mixed solution was homogenized for 30 min to form a uniform solution. Then, 20 ml of ethanol solution containing 0.4 g tetraethyl orthosilicate was added dropwise to the mixed solution, and the mixture was stirred continuously for 6 h. The product was collected by filtration, washed three times with water and ethanol, and then dried at 60 °C for 5 h. The product was then calcined at 550 °C for 6 h to remove the carbon layer and CTAB, yielding a porous spherical shell structure powder (Si@Al2O3). Finally, Si@Al2O3 and PVDF in a mass ratio of 9:1 were added to an appropriate amount of NMP and stirred for 8 h to obtain a uniform slurry. This slurry was coated onto a PE membrane using a doctor blade, with an initial coating thickness of 30 μm. The membrane was then dried in a vacuum drying oven at 70 °C for 8 h to obtain a porous spherical shell structure coated Si-Al2O3@PE membrane.

[0035] Example 2: First, 10 mg of alumina with a particle size of approximately 100 nm and 40 mg of PVP were added to 20 mL of deionized water, and then stirred at room temperature for 24 h. The PVP-modified alumina was collected by centrifugation at 8000 rpm for 5 minutes and washed three times with water. 8 g of glucose was completely dissolved in 30 mL of deionized water and then transferred to a 50 mL polytetrafluoroethylene autoclave. 10 mg of PVP-modified alumina was then added under ultrasonic treatment. After ultrasonic treatment for 10 minutes, the autoclave was placed in an oven at 173 °C for 6 h and then allowed to cool naturally to room temperature. A black solid product was obtained by three rounds of centrifugation / washing / ultrasonic treatment, and then dried in an oven at 70 °C for 10 h to obtain carbon-coated alumina. Then, 0.1 g of the carbon-coated alumina prepared above was redispersed in a mixed solution containing CTAB (0.30 g), deionized water (20 mL), ammonia (1 mL), and ethanol (80 mL). The mixed solution was homogenized for 30 min to form a uniform solution. Then, 20 ml of ethanol solution containing tetraethyl orthosilicate and tetrabutyl titanate in a mass ratio of 2:1 was added dropwise to the mixed solution, with a total mass of 0.4 g of coating material. The mixture was stirred continuously for 6 h. The product was collected by filtration, washed three times with water and ethanol, and then dried at 60 °C for 5 h. The product was then calcined at 550 °C for 6 h to remove the carbon layer and CTAB, yielding a porous spherical shell structure powder (SiTi@Al2O3). Finally, SiTi@Al2O3 and PVDF in a mass ratio of 8:2 were added to an appropriate amount of NMP and stirred for 8 h to obtain a uniform slurry. This slurry was coated onto a PP membrane using a doctor blade, with an initial coating thickness of 35 μm. The membrane was then dried in a vacuum drying oven at 70 °C for 8 h to obtain a porous spherical shell structure coated SiTi-Al2O3@PP membrane.

[0036] Example 3: First, 10 mg of alumina with a particle size of approximately 500 nm and 40 mg of PVP were added to 20 mL of deionized water, and then stirred at room temperature for 24 h. The PVP-modified alumina was collected by centrifugation at 8000 rpm for 5 minutes and washed three times with water. 6 g of glucose was completely dissolved in 30 mL of deionized water and then transferred to a 50 mL polytetrafluoroethylene autoclave. 10 mg of PVP-modified alumina was then added under ultrasonic treatment. After ultrasonic treatment for 10 minutes, the autoclave was placed in an oven at 173 °C for 10 h and then allowed to cool naturally to room temperature. A black solid product was obtained by three rounds of centrifugation / washing / ultrasonic treatment, and then dried in an oven at 70 °C for 10 h to obtain carbon-coated alumina. Then, 0.1 g of the carbon-coated alumina prepared above was redispersed in a mixed solution containing CTAB (0.3 g), deionized water (20 mL), ammonia (1 mL), and ethanol (80 mL). The mixed solution was homogenized for 30 min to form a uniform solution. Then, 20 ml of ethanol solution of tetraethyl orthosilicate and zirconium propoxide in a mass ratio of 5:1 was added dropwise to the mixed solution, with a total mass of 0.4 g of coating material. The mixture was stirred continuously for 6 h. The product was collected by filtration, washed three times with water and ethanol, and then dried at 60 °C for 5 h. The product was then calcined at 550 °C for 6 h to remove the carbon layer and CTAB, yielding a porous spherical shell structure powder (SiZr@Al2O3). Finally, SiZr@Al2O3 and PVDF in a mass ratio of 9:1 were added to an appropriate amount of NMP and stirred for 8 h to obtain a uniform slurry. This slurry was coated onto a PE membrane using a doctor blade, with an initial coating thickness of 25 μm. The membrane was then dried in a vacuum drying oven at 70 °C for 8 h to obtain a porous spherical shell structure coated SiZr-Al2O3@PE membrane.

[0037] The porous spherical shell structure oxide-coated separator prepared by this invention exhibits superior performance compared to conventional separators. It avoids the porosity reduction common with traditional solid oxide-coated separators and maintains the thermal stability of the coated separator. The spherical shell structure can utilize a single oxide or a blend of multiple oxides to construct the oxide network. This mixed oxide network enhances the Lewis acid strength of the material and adsorbs more anions from the electrolyte, thereby achieving better electrochemical performance with the same coating material loading. The porous spherical shell structure also facilitates lithium-ion transport; the more uniform porosity allows for lithium-ion rearrangement and inhibits lithium dendrite formation, thus improving battery safety and cycle life.

Claims

1. A method for preparing a core-shell structured oxide-coated diaphragm, characterized in that, Specifically, the steps include the following: S1) Spherical alumina with a particle size of 50-500 nm and polyvinylpyrrolidone (PVP) were added to deionized water at a mass ratio of 1:4, stirred, centrifuged, and washed to obtain PVP-treated spherical alumina. S2) Add 10 mg of PVP-treated alumina particles to a 0.1-0.5 g / mL glucose aqueous solution and stir thoroughly. Then, perform a hydrothermal reaction at 160-220℃ for 6-10 h to obtain carbon-coated alumina particles with a carbon layer thickness of 5-200 nm. S3) Disperse 0.1g of carbon-coated spherical alumina in a mixed solution of 80ml ethanol, 20ml deionized water, 1ml ammonia, and 0.3g CTAB. Then, weigh out the coating material, which is 3-10 times the mass of the carbon-coated spherical alumina, such as tetraethyl orthosilicate, tetraethyl orthosilicate and tetrabutyl titanate, or tetraethyl orthosilicate and zirconium propoxide. Dilute the coating material in ethanol and add it dropwise to the dispersion while stirring continuously for 6 hours. Finally, filter, wash, and dry the powder, and calcine it in a muffle furnace at 500-600℃ for 6 hours to remove the carbon layer and CTAB, obtaining porous spherical shell structure coated alumina powder. S4) Prepare a slurry by mixing coated alumina powder and binder in N-methylpyrrolidone (NMP) at a mass ratio of 10:1 to 5:

5. Stir for 8 to 10 hours to ensure uniform mixing. Apply the slurry to the diaphragm using a scraper and dry in a vacuum drying oven at 60 to 80°C for 6 to 8 hours to obtain a porous oxide-coated diaphragm.

2. The method for preparing a core-shell structured oxide-coated diaphragm according to claim 1, characterized in that: In step S1, the stirring is performed at room temperature for 24–36 hours, and the centrifugation is performed at 8000 rpm for 5–10 minutes.

3. The method for preparing a core-shell structured oxide-coated diaphragm according to claim 1, characterized in that, Its features are: In step S1, the molecular weight of PVP is 10,000 to 160,000.

4. The method for preparing a core-shell structured oxide-coated diaphragm according to claim 1, characterized in that: In step S2, the hydrothermal reaction is carried out in a polytetrafluoroethylene autoclave. PVP-modified alumina is added under ultrasonic treatment for 10-20 minutes. After the hydrothermal reaction, a black solid product is obtained by three rounds of centrifugation / washing / ultrasonic treatment. Then, carbon-coated alumina is obtained by drying in an oven at 60-80°C for 10 hours.

5. The method for preparing a core-shell structured oxide-coated diaphragm according to claim 1, characterized in that, Its features are: The washing and drying process in step S3 involves washing the product three times with water and ethanol respectively, and then drying it at 60°C for 5 hours.

6. The method for preparing a core-shell structured oxide-coated diaphragm according to claim 1, characterized in that, Its features are: In step S3, the mass of the coating material is four times that of carbon-coated alumina.

7. The method for preparing a core-shell structured oxide-coated diaphragm according to claim 1, characterized in that, Its features are: The binder in step S4 is one of the following: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), poly(acrylic acid) (PAA), styrene-butadiene rubber (SBR), polyamide-imide (PAI), poly(vinyl alcohol) (PVA), polyethyleneimine (PEI), polyimide (PI), guar gum (GG), sodium alginate (Alg), carboxymethyl cellulose (CMC), gum arabic (GA), xanthan gum (XG), carrageenan, gelatin, chitosan, starch, and β-cyclodextrin.

8. The method for preparing a core-shell structured oxide-coated diaphragm according to claim 1, characterized in that: In step S4, the mass ratio of the coated alumina powder to the binder is one of 9:1, 8:2, 7:3, 6:4, or 5:

5.

9. The method for preparing a core-shell structured oxide-coated diaphragm according to claim 1, characterized in that, Its features are: In step S4, the diaphragm is a PE or PP diaphragm.

10. A core-shell structured oxide-coated diaphragm, characterized in that, The core-shell structure oxide-coated diaphragm is prepared using the preparation method described in any one of claims 1 to 9.