Molybdenum boride quantum dot and graphene-based composite material for functional layer of lithium metal battery diaphragm

Abstract

The invention provides a preparation method of a molybdenum boride quantum dot and graphene composite material for a lithium metal battery diaphragm functional layer. The method comprises the following steps: performing hydrothermal reaction on tungsten chloride and graphene in ethylene glycol to prepare a precursor; centrifugally cleaning the hydrothermal product; mixing the product with boron powder and sodium chloride / potassium chloride molten salt, and performing high-temperature pyrolysis in an inert atmosphere; performing water bath treatment on the final product; and collecting a final product, and drying to obtain the molybdenum boride quantum dot-graphene composite material. The obtained molybdenum boride quantum dot and graphene material modified diaphragm has strong lithium affinity and excellent electron / ion transmission capability, can effectively inhibit the growth of lithium dendrites, improves the safety of a lithium metal battery, and prolongs the cycle life of the lithium metal battery.

Description

Technical Field

[0001] This invention relates to a composite material based on molybdenum boride quantum dots and graphene for use in the functional layer of lithium metal battery separators and its preparation method, and more particularly to a preparation method of the composite material based on molybdenum boride quantum dots and graphene, and its application in the modification of lithium metal battery separators. Background Technology

[0002] Lithium metal batteries are known for their extremely high theoretical specific capacity (3860 mAh g). -1 With its low density and low electrochemical potential, lithium metal anodes are considered ideal for next-generation high-energy-density energy storage systems. However, during cycling, lithium metal anodes are prone to dendrite growth, volume expansion, and interfacial instability, leading to short circuits, capacity decay, and safety hazards. Among these, the disordered growth of lithium dendrites and their penetration through the separator are key bottlenecks limiting their commercial application. Traditional separators are mostly made of polyolefin materials, lacking sufficient ion regulation and interfacial stabilization capabilities, making it difficult to effectively suppress dendrite formation. To address this, researchers have attempted to construct functional layers with high ion conductivity and high stability on the separator surface to regulate uniform lithium-ion deposition and improve electrode interfacial stability.

[0003] Currently, two-dimensional materials and quantum dot composite systems have attracted widespread attention due to their excellent conductivity, specific surface area, and active interfaces. Graphene possesses excellent electron transport capabilities and structural flexibility, enabling the construction of stable ion transport channels; while transition metal boride quantum dots (such as molybdenum boride quantum dots) combine metallic and polar characteristics, providing high-density lithium-ion adsorption and nucleation sites, thereby achieving homogenized electrochemical deposition. Anchoring molybdenum boride quantum dots to the graphene surface to form a composite material can not only significantly improve the electron / ion co-transport rate but also regulate the local electric field distribution through strong interfacial interactions, inducing uniform lithium-ion nucleation and smooth deposition. Therefore, developing a membrane functional layer composite material based on molybdenum boride quantum dots@graphene is expected to suppress dendrite growth at the source, enhance interfacial stability, and extend the cycle life of lithium metal batteries, which is of great significance for promoting the safety and practical application of high-energy-density energy storage systems. Summary of the Invention

[0004] This invention aims to address the problems of lithium dendrite growth, interface instability, and insufficient cycle life in existing lithium metal batteries, and provides a membrane functional layer composite material that is simple to prepare, exhibits excellent stability, and can effectively regulate lithium deposition behavior. By constructing a functional layer with high lithiophilicity and strong polarity, this invention enables commercially available membranes to guide uniform lithium ion nucleation and suppress dendrite growth, thereby significantly improving the overall performance of lithium metal batteries.

[0005] In this invention, the research team innovatively developed a functional material based on molybdenum boride quantum dots and graphene composites for use in lithium metal battery separators. The preparation process of this novel separator functional layer material utilizes the synergistic advantages of molybdenum oxide and graphene, generating ultra-small and highly dispersed molybdenum boride quantum dots in situ through a high-temperature borylation reaction, constructing a quantum dot-graphene composite structure with both strong lithiophilicity and high conductivity. Due to the extremely high polarity and abundant lithium affinity sites of the molybdenum boride quantum dots, their quantum size significantly increases the density of exposed active interfaces, enabling them to provide a large number of uniform nucleation hotspots in the initial stage of lithium deposition. Simultaneously, the quantum dots are uniformly and densely anchored to the graphene surface through strong interactions, forming a continuous two-dimensional electron conduction network and highly dispersed polar lithium adsorption sites, achieving synergistic regulation of electron transport and ion guidance. This invention opens a new path for the application of quantum dot materials in high-performance lithium metal batteries. This invention not only demonstrates the advantages of the molybdenum boride quantum dot@two-dimensional graphene synergistic interface regulation strategy, but also provides a new material basis for constructing high-safety, long-life lithium metal batteries.

[0006] To achieve the above objectives, the present invention provides a composite material based on molybdenum boride quantum dots@graphene for use in the functional layer of a lithium metal battery separator.

[0007] To achieve the above-mentioned objectives, the technical solution of this invention is as follows:

[0008] A composite material based on molybdenum boride quantum dots@graphene for use in the functional layer of a lithium metal battery separator, characterized by comprising the following steps:

[0009] Step 1: Preparation of precursor: Using 200-300 mg tungsten chloride and 100-150 mg graphene as raw materials, and 20-75 mL ethylene glycol as solvent; the tungsten chloride powder and graphene are ultrasonically dispersed in the solvent to obtain a uniform dispersion. After stirring the dispersion at room temperature, it is placed in a polytetrafluoroethylene reactor for hydrothermal reaction.

[0010] Step 2: Precursor collection: Centrifuge to collect the powder obtained in Step 1, wash and dry to obtain precursor powder.

[0011] Step 3: High-temperature pyrolysis process: Using the precursor powder obtained in step 2 and 1-5 mmol of amorphous boron powder as raw materials, and a sodium chloride / potassium chloride mixture as molten salt; first, the boron powder and molten salt are thoroughly ground and mixed, then the precursor powder is added and ground and mixed again, and then the mixture is pyrolyzed in a tube furnace.

[0012] Step 4: Water bath treatment: Immerse the black powder obtained in step 3 in deionized water for water bath treatment.

[0013] Step 5: Final product collection: Wash the product from step 4 using vacuum filtration and dry the product.

[0014] As a preferred embodiment, step 1 is further characterized by a hydrothermal reaction temperature of 160–200°C and a reaction time of 8–24 h.

[0015] As a preferred method, step 2 is further as follows: the centrifugation speed is set to 4500-8000 rpm, and the centrifugation is performed 3-5 times, each time using 25-50 mL of water and ethanol, and then the centrifugation is performed in a -60℃ freeze-drying oven for 8-24 hours.

[0016] As a preferred embodiment, step 3 is further defined as follows: the mass ratio of molten salt to raw material is 5:1 to 20:1, and the specific conditions for high-temperature pyrolysis treatment include argon atmosphere control, temperature of 800 to 1000°C, heating rate of 2 to 5°C / min, and pyrolysis time of 2 to 4 hours.

[0017] As a preferred method, step 4 is further described as follows: the volume of deionized water is 50-100 mL, the water bath temperature is 90°C, and the time is 2 h.

[0018] As a preferred embodiment, step 5 further comprises: the specific parameters of the drying process of the final product include a temperature of 60°C and a time of 8–24 h.

[0019] Compared with the prior art, the advantages of the present invention are reflected in the following aspects:

[0020] 1. The molybdenum boride quantum dot@graphene composite material of the present invention uses molybdenum oxide-graphene composite as a precursor. Through a high-temperature borylation reaction, ultra-small, high-density distributed molybdenum boride quantum dots are generated in situ, and boron atom doping of graphene is achieved, forming a composite structure with excellent lithiophilicity and conductivity. Molybdenum boride quantum dots possess strong lithiophilicity and abundant polar sites. Combined with a conductive graphene framework, they can significantly improve the uniformity of lithium-ion nucleation, suppress dendrite growth, and reduce interfacial impedance.

[0021] 2. The preparation process of this invention consists of steps such as dispersion in an ethylene glycol system, hydrothermal reaction, molten salt-assisted high-temperature boration, and vacuum filtration and drying. The process is simple, the conditions are easy to control, and the raw materials are inexpensive. The molten salt system is beneficial for the uniform nucleation and size confinement of quantum dots. Compared with traditional membrane modification methods, the preparation steps are more streamlined, and it has good prospects for scale-up and industrial application.

[0022] 3. The molybdenum boride@graphene modified separator prepared in this invention exhibits more uniform lithium-ion flux, lower polarization, and more stable cycle performance in lithium metal batteries, significantly improving battery life and safety. The synergistic interface regulation of molybdenum boride quantum dots and graphene networks provides a new material system and application approach for the design of functional layers in lithium metal battery separators. Attached Figure Description

[0023] Figure 1 The image shows a scanning electron microscope (SEM) image of a molybdenum boride quantum dot@graphene composite material for use as a functional layer in a lithium metal battery separator, prepared according to the present invention, exhibiting a distinct graphene sheet structure.

[0024] Figure 2 The transmission electron microscope (TEM) image and elemental mapping analysis diagram of a molybdenum boride quantum dot@graphene composite material for use as a functional layer of a lithium metal battery separator prepared in this invention are shown. The boride quantum dots with a diameter of 5-10 nm are uniformly distributed in the graphene sheets. This structure is beneficial to the uniformity of lithium ion flow and is crucial for improving the performance of lithium metal batteries.

[0025] Figure 3 The X-ray diffraction pattern of a molybdenum boride quantum dot@graphene composite material for the functional layer of a lithium metal battery separator prepared in this invention shows the successful synthesis of the molybdenum boride structure.

[0026] Figure 4 The charge-discharge curves of a lithium iron phosphate battery based on a molybdenum boride quantum dot@graphene composite material for the functional layer of a lithium metal battery separator prepared according to the present invention show that the battery exhibits excellent capacity retention and cycle stability at different rates, highlighting the excellent electrochemical performance and the ability of the material to homogenize the lithium ion flow. Detailed Implementation

[0027] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0028] Comparative Example 1

[0029] A molybdenum boride quantum dot@graphene-based composite material for lithium metal battery separators includes the following steps:

[0030] Step 1: Preparation of precursor: 200 mg tungsten chloride powder and 100 mg graphene were ultrasonically dispersed in 20 mL ethylene glycol to obtain a uniform dispersion. The dispersion was stirred at room temperature and then placed in a polytetrafluoroethylene reactor. The reaction was carried out at 160 °C for 12 h. After cooling, the precursor powder was obtained by centrifugation and freeze drying.

[0031] Step 2: Precursor collection: Centrifuge the precursor powder obtained in Step 1 at a speed of 8000 rpm and wash it three times, each time using 50 mL of water and ethanol.

[0032] Comparative Example 2

[0033] A molybdenum boride quantum dot@graphene-based composite material for lithium metal battery separators includes the following steps:

[0034] Step 1: Preparation of precursor: 200 mg tungsten chloride powder and 100 mg graphene were ultrasonically dispersed in 20 mL ethylene glycol to obtain a uniform dispersion. The dispersion was stirred at room temperature and then placed in a polytetrafluoroethylene reactor. The reaction was carried out at 160 °C for 8 h. After cooling, the precursor powder was obtained by centrifugation and freeze drying.

[0035] Step 2: Precursor collection: Centrifuge the precursor powder obtained in Step 1 at a speed of 8000 rpm and wash it three times, each time using 50 mL of water and ethanol.

[0036] Example 1

[0037] A molybdenum boride quantum dot@graphene-based composite material for lithium metal battery separators includes the following steps:

[0038] Step 1: Preparation of precursor: 200 mg tungsten chloride powder and 100 mg graphene were ultrasonically dispersed in 20 mL ethylene glycol to obtain a uniform dispersion. The dispersion was stirred at room temperature and then placed in a polytetrafluoroethylene reactor. The reaction was carried out at 160 °C for 12 h. After cooling, the precursor powder was obtained by centrifugation and freeze drying.

[0039] Step 2: Precursor collection: Centrifuge the precursor powder obtained in Step 1 at a speed of 8000 rpm and wash it three times, each time using 50 mL of water and ethanol.

[0040] Step 3: High-temperature pyrolysis process: Using the precursor powder obtained in step 2 and 2 mmol of amorphous boron powder as raw materials, and a sodium chloride / potassium chloride mixture with a mass ratio of 10:1 to the raw materials as molten salt; first, the boron powder and molten salt are thoroughly ground and mixed, then the precursor powder is added and ground and mixed again, and then the mixture is pyrolyzed in a tube furnace at 900℃ for 2 hours.

[0041] Step 4: Water bath treatment: Immerse the black powder obtained in step 3 in 100mL of deionized water for water bath treatment.

[0042] Step 5: Final product collection: Wash the product from step 4 using vacuum filtration and dry the product.

[0043] Example 2

[0044] A molybdenum boride quantum dot@graphene-based composite material for lithium metal battery separators includes the following steps:

[0045] Step 1: Preparation of precursor: 200 mg tungsten chloride powder and 150 mg graphene were ultrasonically dispersed in 20 mL ethylene glycol to obtain a uniform dispersion. The dispersion was stirred at room temperature and then placed in a polytetrafluoroethylene reactor. The reaction was carried out at 160 °C for 12 h. After cooling, the precursor powder was obtained by centrifugation and freeze drying.

[0046] Step 2: Precursor collection: Centrifuge the precursor powder obtained in Step 1 at a speed of 8000 rpm and wash it three times, each time using 50 mL of water and ethanol.

[0047] Step 3: High-temperature pyrolysis process: Using the precursor powder obtained in step 2 and 2 mmol of amorphous boron powder as raw materials, and a sodium chloride / potassium chloride mixture with a mass ratio of 10:1 to the raw materials as molten salt; first, the boron powder and molten salt are thoroughly ground and mixed, then the precursor powder is added and ground and mixed again, and then the mixture is pyrolyzed in a tube furnace at 900℃ for 2 hours.

[0048] Step 4: Water bath treatment: Immerse the black powder obtained in step 3 in 100mL of deionized water for water bath treatment.

[0049] Step 5: Final product collection: Wash the product from step 4 using vacuum filtration and dry the product.

[0050] Example 3

[0051] A molybdenum boride quantum dot@graphene-based composite material for lithium metal battery separators includes the following steps:

[0052] Step 1: Preparation of precursor: 300 mg tungsten chloride powder and 100 mg graphene were ultrasonically dispersed in 20 mL ethylene glycol to obtain a uniform dispersion. The dispersion was stirred at room temperature and then placed in a polytetrafluoroethylene reactor. The reaction was carried out at 160 °C for 12 h. After cooling, the precursor powder was obtained by centrifugation and freeze drying.

[0053] Step 2: Precursor collection: Centrifuge the precursor powder obtained in Step 1 at a speed of 8000 rpm and wash it three times, each time using 50 mL of water and ethanol.

[0054] Step 3: High-temperature pyrolysis process: Using the precursor powder obtained in step 2 and 3 mmol of amorphous boron powder as raw materials, and a sodium chloride / potassium chloride mixture with a mass ratio of 10:1 to the raw materials as molten salt; first, the boron powder and molten salt are thoroughly ground and mixed, then the precursor powder is added and ground and mixed again, and then the mixture is pyrolyzed in a tube furnace at 900℃ for 2 hours.

[0055] Step 4: Water bath treatment: Immerse the black powder obtained in step 3 in 100mL of deionized water for water bath treatment.

[0056] Step 5: Final product collection: Wash the product from step 4 using vacuum filtration and dry the product.

[0057] Example 4

[0058] A molybdenum boride quantum dot@graphene-based composite material for lithium metal battery separators includes the following steps:

[0059] Step 1: Preparation of precursor: 200 mg tungsten chloride powder and 100 mg graphene were ultrasonically dispersed in 20 mL ethylene glycol to obtain a uniform dispersion. The dispersion was stirred at room temperature and then placed in a polytetrafluoroethylene reactor. The reaction was carried out at 160 °C for 12 h. After cooling, the precursor powder was obtained by centrifugation and freeze drying.

[0060] Step 2: Precursor collection: Centrifuge the precursor powder obtained in Step 1 at a speed of 8000 rpm and wash it three times, each time using 50 mL of water and ethanol.

[0061] Step 3: High-temperature pyrolysis process: Using the precursor powder obtained in step 2 and 2 mmol of amorphous boron powder as raw materials, and a sodium chloride / potassium chloride mixture with a mass ratio of 10:1 to the raw materials as molten salt; first, the boron powder and molten salt are thoroughly ground and mixed, then the precursor powder is added and ground and mixed again, and then the mixture is pyrolyzed in a tube furnace at 800℃ for 2 hours.

[0062] Step 4: Water bath treatment: Immerse the black powder obtained in step 3 in 100mL of deionized water for water bath treatment.

[0063] Step 5: Final product collection: Wash the product from step 4 using vacuum filtration and dry the product.

[0064] Performance Analysis

[0065] The difference between the examples and Comparative Examples 1 and 2 is that boron powder was not used in the comparative examples.

[0066] The difference between Example 1 and Examples 2 and 3 is that the ratio of molybdenum chloride to graphene is different in step 1; and the amount of amorphous boron powder used is different in step 3.

[0067] The difference between Example 1 and Example 4 is that the pyrolysis temperature is different in step 3.

[0068] A composite material based on molybdenum boride quantum dots@graphene for lithium metal battery separators of the present invention was loaded onto a commercial polyethylene separator Celgard 2500, and then encapsulated in a CR2025 button cell. The electrochemical performance of the lithium iron phosphate battery after 250 cycles at 1C was tested, and the following electrochemical performance table was obtained:

[0069] Performance Comparison Table of Comparative Examples and Implementation Examples

[0070]

[0071] In the comparison of battery performance of the molybdenum boride quantum dot@graphene composite material, Example 1 showed significant superiority compared to Comparative Example 1 and Comparative Example 2. The initial capacity of Example 1 was 146.87 mAh g. -1 This is higher than the 140.37 mAh g of the comparative example. -1 Compared with Comparative Example 2, 140.01 mAh g -1 Meanwhile, in terms of reversible capacity, Example 1 achieved 137.55 mAh g. -1 Compared to the control group, the 1-component ratio was only 111.46 mAh g. -1 Compared to Comparative Example 2, the figure was only 99.46%. This clearly demonstrates that the molybdenum boride quantum dot@graphene material of Example 1 exhibits a significant improvement in electrochemical performance, particularly in regulating the uniformity of lithium-ion deposition / exfoliation during charge and discharge, showcasing its potential as an optimized separator material for lithium metal batteries.

[0072] Of all the embodiments, Example 1 exhibited the best battery performance. Example 1 showed the highest initial capacity, reaching 146.87 mAh g⁻¹, compared to Examples 2 and 3. -1 Example 2, however, has a capacity of 143.74 mAh g. -1 Example 3 has a capacity of 145.67 mAh g. -1 Regarding reversible capacity, Example 1 also performed best, reaching 137.55 mAh g. -1 Example 2: 115.06 mAh g -1 And 121.37 mAh g in Example 3 -1 Slightly lower. In addition, Example 1 showed an initial capacity of 146.87% compared to Example 4, while Example 4 was 142.33 mAh g. -1Regarding reversible capacity, Example 1 has a capacity of 137.55 mAh g. -1 It is also significantly higher than the 109.65 mAh g in Example 4. -1 .

[0073] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A boronated molybdenum quantum dots@graphene based composite material for functional layer of lithium metal battery separator, characterized in that The method comprises the following steps: Step 1: Preparation of the precursor: 200-300 mg of tungsten chloride and 100-150 mg of graphene are used as raw materials, and 20-75 mL of ethylene glycol is used as a solvent; the tungsten chloride powder and graphene are ultrasonically dispersed in the solvent to obtain a uniform dispersion liquid, and the dispersion liquid is stirred at room temperature and then placed in a polytetrafluoroethylene reaction kettle for hydrothermal reaction; Step 2: Collection of the precursor: the powder obtained in step 1 is collected by centrifugation, washed, and dried to obtain a precursor powder; Step 3: High-temperature pyrolysis process: the precursor powder obtained in step 2 and 1-5 mmol of amorphous boron powder are used as raw materials, and a sodium chloride / potassium chloride mixture is used as a molten salt; the boron powder and the molten salt are thoroughly ground and mixed, then the precursor powder is added and further ground and mixed, and then the mixture is subjected to pyrolysis treatment in a tube furnace; Step 4: Water bath treatment: the black powder obtained in step 3 is soaked in deionized water for water bath treatment; Step 5: Collection of the final product: the product of step 4 is washed using suction filtration, and the product is dried.

2. Step 1 in the method of claim 1, characterized in that the hydrothermal reaction temperature is 160-200°C, and the reaction time is 8-24h.

3. Step 2 in the method of claim 1, characterized in that the centrifugal speed is set to 4500-8000 rpm, and the washing is performed 3-5 times, each time using 25-50 mL of water and ethanol, and then freeze-drying in a -60°C freeze-drying box for 8-24h.

4. Step 3 in the method of claim 1, characterized in that the mass ratio of molten salt to raw material is 5:1-20:1, and the specific conditions of high-temperature pyrolysis treatment include an argon atmosphere, a temperature of 800-1000°C, a heating rate of 2-5°C / min, and a pyrolysis time of 2-4h.

5. Step 4 in the method of claim 1, characterized in that the volume of deionized water is 50-100 mL, the water bath temperature is 90°C, and the time is 2h.

6. Step 5 in the method of claim 1, characterized in that the drying process of the final product includes a temperature of 60°C and a time of 8-24h.

7. The MoB quantum dot@graphene composite material obtained by the method according to any one of claims 1 to 6, characterized in that: The prepared molybdenum boride quantum dots@graphene composite material has a quantum dot and graphene composite structure suitable for lithium metal battery separator applications after optimization, which has the ability to adjust the uniformization of lithium ion flow.

8. The application of the molybdenum boride quantum dots@graphene material in lithium metal battery separators according to claim 7, characterized in that the molybdenum boride quantum dots@graphene material exhibits excellent capacity retention rate and cycle stability.

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