A self-supporting graphene-based carbon microsphere negative electrode frame and a preparation method thereof

Abstract

This invention provides a self-supporting graphene-based carbon microsphere anode framework and its preparation method. A chitin microsphere aqueous dispersion is mixed with a metal salt and ammonia, stirred, and filtered. The resulting chitin microspheres doped with metal hydroxide are dispersed in water. A surface charge modifier is added dropwise, and the mixture is stirred again. An aqueous solution of graphene oxide is added and stirred further. After filtration and annealing, graphene-coated metal / nitrogen co-doped carbon microspheres are obtained. These microspheres are then dispersed uniformly in water with a binder and a conductive agent, filtered to form a film, and dried to obtain a metal-doped self-supporting graphene-based carbon microsphere anode framework. This self-supporting graphene-based carbon microsphere lithium anode framework exhibits high specific capacity and excellent electrochemical performance, improving both energy density and electrode cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of anode material technology, and particularly relates to a self-supporting graphene-based carbon microsphere anode framework and its preparation method. Background Technology

[0002] With the rapid development and widespread application of long-range electric vehicles, long-life electronic products, and power tools, the development of high-energy-density lithium-ion batteries has become one of the current hot demands in society. Lithium metal anodes (LMA) possess ultra-high theoretical specific capacity (3860 mA hg). -1 It has the lowest redox potential (-3.04 V vs. standard hydrogen electrode) and extremely low density (0.534 g / cm³). -3 Lithium metal anodes are an ideal choice for next-generation high-energy-density batteries. However, the large-scale industrial application of lithium metal anodes faces two fundamental challenges: First, lithium metal is highly reactive, and the growth of lithium dendrites can lead to problems such as internal short circuits and thermal runaway. Second, lithium metal anodes undergo uncontrollable volume changes during cycling, which can easily lead to the collapse of the anode structure and damage the stability of the solid electrolyte interface (SEI), resulting in the loss of active lithium. These problems cause capacity loss and a series of safety issues in lithium metal batteries, limiting their large-scale practical application.

[0003] To address these issues, researchers have developed various methods, such as constructing artificial solid electrolyte interphase (SEI) layers, optimizing electrolyte composition, constructing lithium metal anodes, and introducing solid electrolytes. Among these, introducing three-dimensional (3D) carbon-based lithiophilic framework materials with large specific surface area and abundant internal pores is one of the most effective means to simultaneously achieve uniform lithium deposition, mitigate extreme volume fluctuations, and suppress dendrite growth during cycling.

[0004] It is of great significance to prepare a suitable three-dimensional lithiophilic anode framework through precise structural design and reasonable assembly methods to stabilize the lithium metal anode and effectively improve the specific capacity of the anode. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a self-supporting graphene-based carbon microsphere anode framework and its preparation method, wherein the anode framework prepared by this method has excellent cycle stability.

[0006] This invention provides a method for preparing a self-supporting graphene-based carbon microsphere anode framework, comprising the following steps:

[0007] a) Mix the aqueous dispersion of chitin microspheres with metal salt and ammonia, stir, and filter to obtain chitin microspheres doped with metal hydroxide;

[0008] b) Disperse the chitin microspheres doped with metal hydroxide into water, add a surface charge modifier, stir again, add an aqueous solution of graphene oxide and continue stirring, filter and anneal to obtain graphene-coated metal / nitrogen co-doped carbon microspheres.

[0009] c) The graphene-coated metal / nitrogen co-doped carbon microspheres, binder, and conductive agent are uniformly dispersed in water, filtered to form a film, and dried to obtain a metal-doped self-supporting graphene-based carbon microsphere anode framework.

[0010] Preferably, the metal salt is selected from one or more of magnesium acetate tetrahydrate, zinc acetate dihydrate, and ferric acetate tetrahydrate.

[0011] Preferably, the surface charge modifier is selected from polydiallyldimethylammonium chloride and / or hexadecyltrimethylammonium bromide.

[0012] Preferably, the stirring time is 3 to 8 hours;

[0013] The re-stirring time is 12–24 hours;

[0014] The stirring time is 4 to 12 hours.

[0015] Preferably, the binder is cyanoethyl cellulose;

[0016] The mass ratio of the graphene-coated metal / nitrogen co-doped carbon microspheres, binder, and conductive agent is (6-9):(0.5-2):(0.5-2).

[0017] Preferably, the annealing temperature is 800–900°C; the annealing time is 110–130 min.

[0018] The annealing atmosphere is a mixture of hydrogen and argon.

[0019] Preferably, the chitin microspheres have a particle size of 5–60 μm;

[0020] The concentration of the graphene oxide aqueous solution is 3–25 mg / mL.

[0021] Preferably, the metal in the metal-doped self-supporting graphene-based carbon microsphere anode framework exists in the form of an element or a metal oxide.

[0022] Preferably, based on 1L of water in the aqueous dispersion of chitin microspheres, the content of chitin microspheres is 500-1000mg; and the molar content of the metal salt is 1-4mmol.

[0023] The content of graphene oxide in the system of step b) is 0.05-0.5 mg / mL;

[0024] The mass ratio of the chitin microspheres doped with metal hydroxide to graphene oxide is 20:1 to 4:1.

[0025] This invention provides a self-supporting graphene-based carbon microsphere anode framework, which is prepared by the method described in the above technical solution.

[0026] This invention provides a method for preparing a self-supporting graphene-based carbon microsphere lithium anode framework. A unique graphene-coated magnesium / nitrogen co-doped carbon fiber microsphere (NC / Mg@RGO) structure is constructed through a bottom-up hierarchical assembly method. The internally cross-linked conductive carbon fiber network has a large specific surface area, thereby accelerating ion transport, promoting uniform charge distribution, and facilitating uniform lithium metal deposition; the abundant porosity provides ample lithium storage space. The tightly coated outer RGO layer effectively stabilizes the SEI layer while ensuring ion transport, reducing side reactions, and suppressing lithium dendrite growth. Furthermore, the introduction of lithiophilic metal nanoparticles and nitrogen doping into the microspheres effectively lowers the lithium nucleation barrier, guiding the spatially selective deposition of lithium metal within the microspheres, thus improving specific capacity and cycle stability. The self-supporting graphene-based carbon microsphere lithium anode framework prepared through simple, continuous vacuum filtration and hot-press drying exhibits high specific capacity and excellent electrochemical performance, improving both energy density and electrode cycle stability. This invention provides a new approach for the application of graphene-based materials in advanced high-energy-density lithium metal batteries from the perspective of microstructure design, and has important research value and significance. Attached Figure Description

[0027] Figure 1 The image shows a scanning electron microscope (SEM) image of the NCMs prepared in Example 1 of this invention.

[0028] Figure 2 This is a scanning electron microscope image of the NC / Mg@RGO microspheres prepared in Example 1 of this invention;

[0029] Figure 3 The XRD patterns of NCMs and NC / Mg@RGO microspheres prepared in Example 1 of this invention are shown below.

[0030] Figure 4 XPS spectra of the NC / Mg@RGO microspheres prepared in Example 1 of this invention;

[0031] Figure 5 An optical photograph of the self-supporting NC / Mg@RGO anode frame prepared in Example 1 of this invention;

[0032] Figure 6 This is a scanning electron microscope image of the self-supporting NC / Mg@RGO anode frame prepared in Example 1 of the present invention;

[0033] Figure 7 The diagram shows the symmetrical battery cycle performance of the NC / Mg@RGO-Li composite electrode prepared in Example 1 of this invention.

[0034] Figure 8 The cycling performance diagram of the NC / Mg@RGO-Li / / LFP full cell prepared in Example 1 of this invention is shown.

[0035] Figure 9 The diagram shows the rate performance of the NC / Mg@RGO-Li / / LFP full cell prepared in Example 1 of this invention. Detailed Implementation

[0036] This invention provides a method for preparing a self-supporting graphene-based carbon microsphere anode framework, comprising the following steps:

[0037] a) Mix the aqueous dispersion of chitin microspheres with metal salt and ammonia, stir, and filter to obtain chitin microspheres doped with metal hydroxide;

[0038] b) Disperse the chitin microspheres doped with metal hydroxide into water, add a surface charge modifier, stir again, add an aqueous solution of graphene oxide and continue stirring, filter and anneal to obtain graphene-coated metal / nitrogen co-doped carbon microspheres.

[0039] c) The graphene-coated metal / nitrogen co-doped carbon microspheres, binder, and conductive agent are uniformly dispersed in water, filtered to form a film, and dried to obtain a metal-doped self-supporting graphene-based carbon microsphere anode framework.

[0040] This invention introduces metal doping into chitin microspheres, then coats the surface of the resulting metal-doped chitin microspheres with a layer of flexible graphene oxide. After high-temperature carbonization and reduction, metal / nitrogen co-doped carbon microspheres coated with reduced graphene oxide are obtained. This invention constructs a unique self-supporting microsphere framework structure through micro-nano-scale structural design, possessing advantages such as light weight, high specific capacity, and stable mechanical properties. It effectively alleviates the volume changes caused by lithium deposition / deposition, suppresses lithium dendrite growth, and improves the energy density and cycle stability of the battery, providing a new strategy for solving the problems existing in the practical application of lithium metal anodes.

[0041] This invention involves mixing an aqueous dispersion of chitin microspheres with metal salts and ammonia, stirring, and filtering to obtain chitin microspheres doped with metal hydroxides.

[0042] The present invention preferably employs a sol-gel method to self-assemble chitin microspheres; specifically, the chitin microspheres are preferably prepared according to the following method:

[0043] The purified chitin was dissolved at low temperature in a sodium hydroxide-urea aqueous solution system, and isooctane and surfactant were added and stirred. The fibers were then self-assembled into chitin microspheres under a hot water bath.

[0044] In this invention, the surfactants are Span 85 and Tween 85; Span 85 must be added first, followed by Tween 85. The low-temperature dissolution temperature is -25 to -35°C; in a specific embodiment, the low-temperature dissolution temperature is -30°C; the stirring speed is 500 to 1000 rpm. The purified chitin is purchased chitin powder purified to remove impurities such as calcium carbonate and protein according to existing literature (Angew. Chem. Int. Ed. 2015, 54, 5152). Specifically, this invention synthesizes chitin microspheres via the sol-gel method according to the following literature, with a particle size range of 5 to 60 μm and an average particle size of approximately 21 μm (Angew. Chem. Int. Ed. 2015, 54, 5152; Nano Energy 2016, 27, 482).

[0045] In this invention, the metal salt is selected from one or more of magnesium acetate tetrahydrate, zinc acetate dihydrate, and ferric acetate tetrahydrate. This invention controls the doping amount of metal nanoparticles in the microspheres by adjusting the proportion of the added metal salt; based on 1 L of water in the aqueous dispersion of chitin microspheres, the content of chitin microspheres is 500–1000 mg; the molar content of the metal salt is 1–4 mmol. The stirring temperature is 60–90°C, and the stirring time is 3–8 h.

[0046] After obtaining chitin microspheres doped with metal hydroxide, the present invention disperses the chitin microspheres doped with metal hydroxide in water, adds a surface charge modifier, stirs again, adds an aqueous solution of graphene oxide and continues stirring, filters and anneals to obtain graphene-coated metal / nitrogen co-doped carbon microspheres.

[0047] In this invention, the surface charge modifier is selected from polydiallyldimethylammonium chloride (PDDA) and / or hexadecyltrimethylammonium bromide. The surface charge modifier is added dropwise. After dropwise addition, the mixture is stirred again for 12–24 h, and then an aqueous solution of graphene oxide is added. Stirring continues for 4–12 h to coat the graphene oxide. The concentration of the aqueous solution of graphene oxide is 3–25 mg / mL; the aqueous solution of graphene oxide is a concentrated slurry that is purchased or synthesized according to existing literature (e.g., Sci. Rep. 2012, 2, 613; Nat Commun. 2016. 7, 13684; Adv. Mater. 2018, 30, 1706435). This invention adjusts the degree of graphene coating on the outer layer of microspheres by adjusting the amount of graphene oxide added during the coating process. The content of graphene oxide in the system of step b) is 0.05-0.5 mg / mL; the mass ratio of the chitin microspheres doped with metal hydroxide to graphene oxide is 20:1-4:1; and the amount of surface charge modifier used is 0.5-1.5 mL.

[0048] After coating with graphene oxide, the mixture is filtered, dried, and then annealed. The annealing temperature is 800–900°C, and the annealing time is 110–130 min. The annealing atmosphere is a hydrogen-argon mixture. In a specific embodiment, the volume ratio of argon to hydrogen is 95:5.

[0049] This invention involves uniformly dispersing graphene-coated metal / nitrogen co-doped carbon microspheres, a binder, and a conductive agent in water, followed by filtration to form a film, and drying to obtain a metal-doped self-supporting graphene-based carbon microsphere anode framework. In this invention, the mass ratio of the graphene-coated metal / nitrogen co-doped carbon microspheres, binder, and conductive agent is (6–9):(0.5–2):(0.5–2). Uniform dispersion is achieved using ultrasonication. Drying is performed by hot-pressing at a temperature of 110–180°C. The binder is added to increase viscosity and facilitate electrode shaping; the conductive agent is added to improve the electrode's conductivity.

[0050] This invention provides a self-supporting graphene-based carbon microsphere anode framework, prepared by the method described above. The self-supporting graphene-based carbon microsphere anode framework is a self-supporting graphene-based carbon microsphere film.

[0051] This invention applies the aforementioned self-supporting graphene-based carbon microsphere anode framework to the anode of lithium metal batteries. The self-supporting graphene-based carbon microsphere anode framework film is cut into 12mm discs and assembled into a 2025-type button cell according to the standard button cell manufacturing process.

[0052] The full cell prepared using the above-mentioned negative electrode framework has excellent cycle stability and rate performance.

[0053] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, of a self-supporting graphene-based carbon microsphere anode framework and its preparation method, should not be construed as limiting the scope of protection of the present invention.

[0054] Example 1

[0055] 100g of chitin powder was mixed with 400g of 5wt% NaOH and stirred vigorously for 10h. The suspension was then washed with deionized water and filtered. Subsequently, the treated chitin powder was dissolved in 400g of 7% hydrochloric acid aqueous solution for 1 day to remove residual protein. The mixture was then washed with deionized water and filtered. The resulting sample was again dispersed in 400g of 5wt% NaOH solution for 24h. Finally, the powder was treated with 1.7wt% sodium chlorite solution in 400g of 0.3M sodium acetate buffer solution at 80℃ for 6h to remove pigments. The sample was then washed with deionized water and dried to obtain purified chitin powder.

[0056] The preparation process of the self-supporting graphene-based carbon microsphere lithium anode framework is as follows: 85g of deionized water, 11g of sodium hydroxide, and 4g of urea were added to a 250mL beaker and dissolved and mixed thoroughly. Then, 7g of purified chitin powder was added and stirred until homogeneous. The resulting suspension was kept at -30℃ for 2 hours, then removed and dissolved at room temperature for 30 minutes. This freeze-dissolve process was repeated twice until the suspension was completely dissolved into a transparent solution. A mixed solution of 50g isooctane and 5.5g Span 85 was prepared and rapidly poured into the above chitin solution at 0℃. The mixture was stirred vigorously in an ice bath for 1 hour. Then, a mixed solution of 5g isooctane and 3g Tween 85 was added, and stirring continued for 1 hour. Finally, chitin microspheres (CBNMs) self-assembled from chitin fibers were obtained in a hot water bath at 100℃. The pH of the suspension was adjusted to 7.0 by adding dilute hydrochloric acid solution. The mixture was washed several times with deionized water, ethanol, and tert-butanol, respectively. Chitosan microspheres were dispersed in tert-butanol and freeze-dried to obtain chitosan microsphere powder. 700 mg of chitosan microsphere powder was dispersed in 1 L of deionized water, and 2 mM magnesium acetate tetrahydrate and 20 mL of ammonia were added. The mixture was stirred at 80 °C for 3 h, filtered, and dried to obtain chitosan / magnesium hydroxide microspheres. 200 mg of chitosan / magnesium hydroxide microspheres were dispersed in 100 mL of deionized water, and 1 mL of polydiallyldimethylammonium chloride (PDDA) was added and stirred for 24 h. After washing with deionized water, the PDDA-coated microspheres were redispersed in 100 mL of pure water, and 0.1 mg / mL of graphene oxide (GO) aqueous solution was added dropwise. The mixture was stirred for another 12 h to complete the graphene coating. After filtration, washing, and drying, the microspheres were annealed at 900℃ for 2 hours in a hydrogen-argon atmosphere at a heating rate of 5℃ / min to obtain graphene-coated magnesium / nitrogen co-doped carbon microspheres (NC / Mg@RGO MSs). NC / Mg@RGO MSs, cyanoethyl cellulose, and multi-walled carbon nanotubes were uniformly dispersed in water at a mass ratio of 8:1:1. Self-supporting graphene-based carbon microsphere films (NC / Mg@RGO) were prepared by vacuum filtration and hot-pressing at 110℃ for application as a negative electrode in lithium metal batteries.

[0057] The self-supporting membrane was cut into small circular pieces with a diameter of 12 mm and assembled into corresponding 2025 button batteries according to the standard button battery manufacturing process. A composite lithium metal anode (NC / Mg@RGO-Li) was prepared by electrochemical deposition using the Xinwei multi-channel electrochemical testing system, and constant current charge-discharge and rate charge-discharge performance tests were conducted.

[0058] To characterize the elemental doping and the morphological changes before and after graphene coating, nitrogen-doped carbon microspheres (NCMs) were obtained by annealing chitin microspheres under the same conditions as control samples. The corresponding samples were characterized using a Gemini SEM 450 scanning electron microscope (SEM), a Philips X'Pert PRO SUPER X-ray diffractometer (XRD), and an ESCA Lab MKII X-ray photoelectron spectroscopy (XPS), respectively.

[0059] Through SEM photos ( Figure 1 It can be observed that NCMs are microsphere structures formed by the cross-linking of nanofibers, with a large number of voids between the fibers to provide lithium storage space; the NC / Mg@RGO surface is tightly coated with a soft, wrinkled RGO layer. Figure 2 XRD patterns Figure 3 ) and XPS maps ( Figure 4 Analysis confirmed magnesium / nitrogen co-doping in NC / Mg@RGO; the NC / Mg@RGO-Li symmetric cell achieved a 0.5 mA cm⁻¹ ampere-co-ampere temperature. -2 Current density and 1.0 mA h cm -2 The electrode can be stably cycled for over 2500 hours at its rated capacity, while the Cu-Li electrode, in contrast, short-circuited after only 1200 hours of cycling. Figure 7 This indicates that the unique self-supporting NC / Mg@RGO anode framework effectively suppresses lithium dendrite growth and improves the cycle stability of the electrode; further full-cell testing shows that the NC / Mg@RGO-Li composite electrode effectively improves the cycle stability and rate performance of the battery. Figure 8 and Figure 9 ).

[0060] Example 2

[0061] The difference between this embodiment and Embodiment 1 is that the annealing temperature is 800℃ and the time is 2 hours.

[0062] Example 3

[0063] The difference between this embodiment and Example 1 is that the polydiallyl dimethylammonium chloride (PDDA) is changed to hexadecyltrimethylammonium bromide (CTAB).

[0064] Example 4

[0065] The difference between this embodiment and Example 1 is that magnesium acetate tetrahydrate is replaced with zinc acetate dihydrate, and the product obtained is graphene-coated zinc oxide / nitrogen co-doped carbon microspheres.

[0066] As shown in the above embodiments, this invention provides a method for preparing a self-supporting graphene-based carbon microsphere anode framework. A unique graphene-coated magnesium / nitrogen co-doped carbon fiber microsphere (NC / Mg@RGO) structure was constructed through a bottom-up hierarchical assembly method. The internally cross-linked conductive carbon fiber network has a large specific surface area, thereby accelerating ion transport, achieving uniform charge distribution, and promoting uniform lithium metal deposition; the abundant porosity provides ample lithium storage space. The tightly coated outer RGO layer effectively stabilizes the SEI layer while ensuring ion transport, reducing side reactions, and suppressing lithium dendrite growth. Furthermore, the introduction of lithiophilic metal nanoparticles and nitrogen doping into the microspheres effectively lowers the lithium nucleation barrier, guiding the spatially selective deposition of lithium metal within the microspheres, thus improving specific capacity and cycle stability. The self-supporting graphene-based carbon microsphere lithium anode framework prepared through simple, continuous vacuum filtration and hot-press drying exhibits high specific capacity and excellent electrochemical performance, improving both energy density and electrode cycle stability. This invention provides a new approach for the application of graphene-based materials in advanced high-energy-density lithium metal batteries from the perspective of microstructure design, and has important research value and significance.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a self-supporting graphene-based carbon microsphere anode framework, comprising the following steps: a) Mix the aqueous dispersion of chitin microspheres with metal salt and ammonia, stir, and filter to obtain chitin microspheres doped with metal hydroxide; the metal salt is selected from one or more of magnesium acetate tetrahydrate, zinc acetate dihydrate, and iron acetate tetrahydrate. b) Disperse the chitin microspheres doped with metal hydroxide in water, add a surface charge modifier dropwise, stir again, add an aqueous solution of graphene oxide and continue stirring, filter, and anneal to obtain graphene-coated metal / nitrogen co-doped carbon microspheres; the surface charge modifier is selected from polydiallyldimethylammonium chloride and / or hexadecyltrimethylammonium bromide; the annealing temperature is 800-900℃; the annealing time is 110-130 min; the annealing atmosphere is a hydrogen-argon mixed atmosphere; c) The graphene-coated metal / nitrogen co-doped carbon microspheres, binder and conductive agent are evenly dispersed in water, filtered to form a film, and dried to obtain a metal-doped self-supporting graphene-based carbon microsphere negative electrode framework. The binder is cyanoethyl cellulose; the mass ratio of the graphene-coated metal / nitrogen co-doped carbon microspheres, binder and conductive agent is (6-9):(0.5-2):(0.5-2).

2. The preparation method according to claim 1, characterized in that, The stirring time is 3 to 8 hours; The re-stirring time is 12–24 hours; The stirring time is 4 to 12 hours.

3. The preparation method according to claim 1, characterized in that, The chitin microspheres have a particle size of 5–60 μm; The concentration of the graphene oxide aqueous solution is 3–25 mg / mL.

4. The preparation method according to claim 1, characterized in that, In the metal-doped self-supporting graphene-based carbon microsphere anode framework, the metal exists in the form of elemental or metal oxide.

5. The preparation method according to claim 1, characterized in that, If we take 1L of water in the aqueous dispersion of chitin microspheres as a reference, the content of chitin microspheres is 500-1000mg; the molar content of metal salt is 1-4mmol. The content of graphene oxide in the system of step b) is 0.05-0.5 mg / mL; The mass ratio of the chitin microspheres doped with metal hydroxide to graphene oxide is 20:1 to 4:

1.

6. A self-supporting graphene-based carbon microsphere anode framework, prepared by the method described in any one of claims 1 to 5.

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