A hard carbon anode material for sodium-ion batteries and its preparation method, and sodium-ion batteries

Abstract

This invention discloses a hard carbon anode material for sodium-ion batteries, its preparation method, and a sodium-ion battery. The hard carbon anode material is prepared from the following raw materials: polyvinylpyrrolidone, polyvinyl chloride, solvent, and crosslinking agent. The sodium-ion battery anode material and its anode sheet of this invention provide numerous micropores and surface defect potentials for sodium ion insertion / extraction. This effectively improves the compaction and flexibility of the electrode sheet, while also increasing its areal density. The compaction of the sodium-ion battery anode sheet of this invention can be increased to (1.2-1.5) g / cm³. 3 Sodium-ion batteries made from these electrodes have high energy density and good rate performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and relates to sodium-ion battery anodes, particularly to a hard carbon anode material for sodium-ion batteries, its preparation method, and sodium-ion batteries. Background Technology

[0002] Among the many types of rechargeable batteries, lithium-ion batteries are considered the most valuable energy storage technology due to their outstanding advantages in high energy density and power density. However, because lithium is low in abundance and unevenly distributed in the Earth's crust, concerns have arisen regarding the sustainability of future lithium resource supply as the demand for lithium-ion batteries continues to grow. In contrast, sodium is abundant and exhibits similar chemical properties to lithium, making sodium-ion batteries an ideal alternative to lithium-ion batteries.

[0003] Currently, research on carbon materials with different degrees of graphitization for sodium-ion batteries has been widely reported, such as graphite, hard carbon, and soft carbon. Among them, hard carbon, due to its larger interplanar spacing, is currently the most promising anode material for sodium-ion batteries. However, hard carbon anodes suffer from numerous defects, large specific surface area, and low tap density, resulting in problems such as low specific capacity, low initial efficiency, low tap density, excessive hardness and brittleness leading to easy breakage, and poor rate performance in practical applications. This makes it difficult to increase the surface density of sodium-ion battery anodes, which directly limits the energy density. Summary of the Invention

[0004] To address the bottlenecks in the use of hard carbon anodes in sodium-ion batteries, the first objective of this invention is to provide a hard carbon anode material and preparation method for sodium-ion batteries. This invention is based on the synthesis of hard carbon anode material and preparation method using polyvinylpyrrolidone and synthetic resin polyvinyl chloride as precursors, aiming to solve the problems of low compaction density, brittle and easily broken electrode sheets, and low initial efficiency in the application of hard carbon anodes in existing sodium-ion batteries.

[0005] The second objective of this invention is to provide a negative electrode sheet and a sodium-ion battery prepared from the aforementioned hard carbon negative electrode material. The hard carbon negative electrode material and its sheet provide numerous micropores and surface defect potentials for sodium ion insertion / extraction. This effectively improves the compaction and flexibility of the electrode sheet, while also increasing its areal density. The compaction of the sodium-ion battery negative electrode sheet prepared from the aforementioned hard carbon negative electrode material can be increased to (1.2-1.5) g / cm³. 3 Sodium-ion batteries made from these electrodes have high energy density and good rate performance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a hard carbon anode material for sodium-ion batteries, wherein the hard carbon anode material for sodium-ion batteries is prepared from the following raw materials: polyvinylpyrrolidone, polyvinyl chloride, solvent and crosslinking agent, wherein the mass ratio of polyvinylpyrrolidone to polyvinyl chloride is 10:1-10, the amount of crosslinking agent added is 3%-10%, and the solid-liquid ratio is 1:10-80.

[0008] As a preferred embodiment of the present invention, the solvent includes one or more of isopropanol, N,N dimethylformamide, ethanol, and N-methylpyrrolidone.

[0009] As a preferred embodiment of the present invention, the crosslinking agent includes one or more of copper nitrate, copper oxide, and copper sulfate.

[0010] In this invention, commonly used anodes for sodium-ion batteries include metallic sodium, titanium dioxide, carbon-based materials, and phosphorus-based materials. Each material has its advantages and disadvantages, with carbon-based materials receiving widespread attention due to their wide distribution and ease of acquisition. While traditional graphite materials exhibit excellent lithium storage performance in lithium-ion batteries, their large sodium ion radius and thermodynamic limitations make them difficult to use in sodium batteries. Hard carbon, with its large interlayer spacing, numerous pores, and many sodium-intercalation defects, is considered the most promising anode material. To improve the compaction density of hard carbon anodes and address the hardness and brittleness issues, this invention employs a novel hard carbon and anode material preparation principle. This involves using polyvinylpyrrolidone and polyvinyl chloride as carbon source materials in the precursors, one or more of isopropanol, N,N-dimethylformamide, ethanol, and N-methylpyrrolidone as solvents, and one or more of copper nitrate, copper oxide, and copper sulfate as crosslinking agents / copper sources. Nanofibers are prepared by electrospinning, followed by carbon dioxide ball milling or microwave treatment to create pores, and then a short-time high-temperature annealing process to obtain the resulting hard carbon material.

[0011] Secondly, the present invention provides a method for preparing the above-mentioned hard carbon anode material for sodium-ion batteries, the method comprising the following steps:

[0012] 1) Add polyvinylpyrrolidone to the solvent according to the formula amount, stir magnetically to react and dissolve, and obtain mixture A;

[0013] 2) In the mixture obtained in step 1), crosslinking agent and polyvinyl chloride are gradually added and magnetically stirred to obtain mixture B;

[0014] 3) Transfer the mixture B obtained in step 2) into a plastic syringe, and attach the film for electrospinning to a clean brush. After energizing, perform electrostatic spraying, and the nanofibers will gather on the collector.

[0015] 4) Let the nanofibers obtained in step 3) stand still, and then use carbon dioxide ball milling or microwave treatment to create pores;

[0016] 5) Anneal the nanofibers obtained in step 4) to obtain the hard carbon anode material for sodium-ion batteries.

[0017] In a preferred embodiment of the present invention, the magnetic stirring time in steps 1) and 2) is 3 hours.

[0018] As a preferred embodiment of the present invention, in step 3), the rotational speed of the electrostatic spray is 0.03-0.05 mm / min.

[0019] As a preferred embodiment of the present invention, in step 4), the annealing treatment is as follows: the nanofibers are calcined in a crucible at a temperature of 300-500°C for 3 hours, and then heated to 500-700°C in a box furnace under a protective atmosphere for 3 hours.

[0020] Thirdly, the present invention provides a method for preparing a sodium-ion battery negative electrode sheet, the method comprising the following steps:

[0021] The sodium-ion battery hard carbon anode material described above or prepared by the above method is mixed with a conductive agent and a binder, and then uniformly coated onto the current collector using a transfer or extrusion coating machine. The anode sheet is then formed by roll pressing and slicing.

[0022] As a preferred embodiment of the present invention, the mass ratio of conductive agent to binder in the sodium-ion battery hard carbon anode material is 92-95:2-3:2-6.

[0023] Fourthly, the present invention provides a sodium-ion battery, comprising the above-mentioned sodium-ion battery hard carbon anode material or the anode sheet prepared by the above-mentioned preparation method, a positive electrode sheet, and an electrolyte.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) The high-compact, high-capacity hard carbon anode, sodium-ion anode sheet and sodium-ion battery provided by the present invention improve the application window of the hard carbon anode by improving the synthesis process. The compaction density and specific capacity of the hard carbon prepared by the method of the present invention are improved.

[0026] 2) The sodium-ion battery anode material and anode sheet of the present invention provide numerous micropores and surface defect potentials for sodium ion insertion / extraction. This effectively improves the compaction and flexibility of the electrode sheet, while also increasing the areal density of the anode sheet.

[0027] 3) The compaction density of the sodium-ion battery negative electrode sheet of the present invention can be increased to (1.2-1.5) g / cm³. 3Sodium-ion batteries made from these electrodes have high energy density and good rate performance. Attached Figure Description

[0028] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0029] To facilitate understanding of the technical means, creative features, objectives, and effects of this invention, the invention is further described below with reference to specific embodiments. However, the following embodiments are merely preferred embodiments of this invention and not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments described herein without creative effort are all within the scope of protection of this invention. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods, and the materials and reagents used in the following embodiments are commercially available unless otherwise specified.

[0030] This invention provides a hard carbon anode material for sodium-ion batteries, which is prepared from the following raw materials: polyvinylpyrrolidone, polyvinyl chloride, solvent and crosslinking agent, wherein the mass ratio of polyvinylpyrrolidone to polyvinyl chloride is 10:1-10, the amount of crosslinking agent added is 3%-10%, and the solid-liquid ratio is 1:10-80.

[0031] Preferably, the solvent includes one or more of isopropanol, N,N dimethylformamide, ethanol, and N-methylpyrrolidone.

[0032] Preferably, the crosslinking agent includes one or more of copper nitrate, copper oxide, and copper sulfate.

[0033] In this invention, commonly used anodes for sodium-ion batteries include metallic sodium, titanium dioxide, carbon-based materials, and phosphorus-based materials. Each material has its advantages and disadvantages, with carbon-based materials receiving widespread attention due to their wide distribution and ease of acquisition. While traditional graphite materials exhibit excellent lithium storage performance in lithium-ion batteries, their large sodium ion radius and thermodynamic limitations make them difficult to use in sodium batteries. Hard carbon, with its large interlayer spacing, numerous pores, and many sodium-intercalation defects, is considered the most promising anode material. To improve the compaction density of hard carbon anodes and address the hardness and brittleness issues, this invention employs a novel hard carbon and anode material preparation principle. This involves using polyvinylpyrrolidone and polyvinyl chloride as carbon source materials in the precursors, one or more of isopropanol, N,N-dimethylformamide, ethanol, and N-methylpyrrolidone as solvents, and one or more of copper nitrate, copper oxide, and copper sulfate as crosslinking agents / copper sources. Nanofibers are prepared by electrospinning, followed by carbon dioxide ball milling or microwave treatment to create pores, and then a short-time high-temperature annealing process to obtain the resulting hard carbon material.

[0034] Example 1

[0035] See Figure 1 This embodiment provides a hard carbon anode material for sodium-ion batteries, a sodium-ion battery anode sheet, and the preparation of the sodium-ion battery thereof, including the following steps:

[0036] Step 1: Precursor Pretreatment

[0037] Add an appropriate amount of polyvinylpyrrolidone to the solvent and react and dissolve it for 3 hours under magnetic stirring.

[0038] Step 2: Precursor Mixing

[0039] In the solution obtained in step 1, crosslinking agent copper sulfate and polyvinyl chloride are gradually added, and the mixture is magnetically stirred for 3 hours.

[0040] The mass ratio of polyethylene to pyrrolidone to polyvinyl chloride is 1:1, the amount of crosslinking agent added is 10%, and the solid-liquid ratio is 1:80.

[0041] Step 3: Preparation of nanofibers

[0042] Take the mixed solution obtained in step 2 and transfer it into a plastic syringe. Then, attach all the films to a clean brush and electrospin them. After turning on the power, electrostatic spraying is performed at a speed of 0.03-0.05 mm / min, and the nanofibers are gathered on the collector.

[0043] Step 4: Ball milling to create holes

[0044] After the nanofibers obtained in step 3 were placed for 24 hours, they were rapidly ball-milled for 1 hour under a carbon dioxide atmosphere.

[0045] Step 5: Heat treatment

[0046] Take the nanofibers obtained in step 4 and place them in a crucible for dry firing at (300-500)℃ for 3 hours. Then transfer them to a box furnace and heat them to (500-700)℃ under a protective atmosphere for 3 hours to continue annealing.

[0047] Step 6: Preparation of sodium-ion battery negative electrode

[0048] Take the hard carbon material obtained in step 5, select a suitable formulation ratio, mix it with a conductive agent, and then uniformly coat it onto the current collector using a transfer or extrusion coating machine. The current collector can be one or more of copper foil, aluminum foil, titanium foil, etc. After conducting different compaction experiments, select a suitable compaction method for rolling, and obtain the negative electrode sheet after forming.

[0049] Step 7: Sodium-ion battery preparation

[0050] The negative electrode obtained in step 6 is assembled with a suitable positive electrode and separator. The positive electrode material can be one or more of polyanionic compounds, Prussian blue, oxides, etc. After encapsulation, liquid injection and formation processes are performed to obtain a sodium-ion battery.

[0051] Example 2

[0052] This embodiment provides a hard carbon anode material for sodium-ion batteries, a sodium-ion battery anode sheet, and the preparation of a sodium-ion battery thereof, including the following steps:

[0053] Step 1: Precursor Pretreatment

[0054] Add an appropriate amount of polyvinylpyrrolidone to the solvent and react and dissolve it for 3 hours under magnetic stirring.

[0055] Step 2: Precursor Mixing

[0056] In the solution obtained in step 1, copper sulfate, a crosslinking agent, is gradually added and the mixture is magnetically stirred for 3 hours.

[0057] The crosslinking agent is added at a rate of 3%, and the solid-liquid ratio is 1:10.

[0058] Steps 3-7 are the same as in Example 1.

[0059] Example 3

[0060] This embodiment provides a hard carbon anode material for sodium-ion batteries, a sodium-ion battery anode sheet, and the preparation of a sodium-ion battery thereof, including the following steps:

[0061] Step 1: Precursor Pretreatment

[0062] Add an appropriate amount of polyvinylpyrrolidone to the solvent and react and dissolve it for 3 hours under magnetic stirring.

[0063] Step 2: Precursor Mixing

[0064] In the solution obtained in step 1, crosslinking agent copper nitrate and polyvinyl chloride are gradually added, and the mixture is magnetically stirred for 3 hours.

[0065] The mass ratio of polyethylene to pyrrolidone to polyvinyl chloride is 10:1, the amount of crosslinking agent added is 5%, and the solid-liquid ratio is 1:50.

[0066] Step 3: Preparation of nanofibers

[0067] Take the mixed solution obtained in step 2 and transfer it into a plastic syringe. Then, attach all the films to a clean brush and electrospin them. After turning on the power, electrostatic spraying is performed at a speed of 0.03-0.05 mm / min, and the nanofibers are gathered on the collector.

[0068] Step 4: Microwave treatment for hole creation

[0069] After the nanofibers obtained in step 3 were placed for 24 hours, they were microwaved for 1 hour in a modified microwave heating furnace.

[0070] Steps 5-7 are the same as in Example 1.

[0071] Comparative Example 1

[0072] Hard carbon anode, sodium-ion battery anode sheet and its sodium-ion battery preparation

[0073] Step 1: Precursor Pretreatment

[0074] Add an appropriate amount of polyvinylpyrrolidone to the solvent and react and dissolve it for 3 hours under magnetic stirring.

[0075] Step 2: Preparation of nanofibers

[0076] Take the solution obtained in step 1 and transfer it into a plastic syringe. Then, attach all the films to a clean brush and electrospin them. After turning on the power, electrostatic spraying is performed at a speed of 0.03-0.05 mm / min. The nanofibers are then gathered on the collector.

[0077] Step 3: Ball milling to create holes

[0078] After the nanofibers obtained in step 2 were placed for 24 hours, they were rapidly ball-milled for 1 hour under a carbon dioxide atmosphere.

[0079] Step 4: Heat treatment

[0080] Take the nanofibers obtained in step 3, place them in a crucible and calcine them at (300-500)℃ for 3 hours. Then transfer them to a box furnace and heat them to (500-700)℃ under a protective atmosphere for 3 hours to continue annealing.

[0081] Step 5: Preparation of sodium-ion battery negative electrode

[0082] Take the hard carbon material obtained in step 4, select a suitable formulation ratio, mix it with a conductive agent, and then uniformly coat it onto the current collector using a transfer or extrusion coating machine. The current collector can be one or more of copper foil, aluminum foil, titanium foil, etc. After conducting different compaction experiments, select a suitable compaction method for rolling, and obtain the negative electrode sheet after forming.

[0083] Step 6: Sodium-ion battery preparation

[0084] The negative electrode obtained in step 5 is assembled with a suitable positive electrode and separator. The positive electrode material can be one or more of polyanionic compounds, Prussian blue, oxides, etc. After encapsulation, liquid injection and formation processes are performed to obtain a sodium-ion battery.

[0085] Comparative Example 2

[0086] Hard carbon anode, sodium-ion battery anode sheet and its sodium-ion battery preparation

[0087] Step 1: Precursor Pretreatment

[0088] Add an appropriate amount of polyvinylpyrrolidone to the solvent and react and dissolve it for 3 hours under magnetic stirring.

[0089] Step 2: Precursor Mixing

[0090] In the solution obtained in step 1, crosslinking agent and polyvinyl chloride are gradually added and magnetically stirred for 3 hours.

[0091] Step 3: Preparation of nanofibers

[0092] Same as step 3 in Example 1.

[0093] Steps 4-6 are the same as in Comparative Example 1.

[0094] Comparative Example 3

[0095] Hard carbon anode, sodium-ion battery anode sheet and its sodium-ion battery preparation

[0096] Steps 1-2 are the same as in Comparative Example 1.

[0097] Step 3: Heat treatment

[0098] Take the nanofibers obtained in step 2 and place them in a crucible for dry firing at (300-500)℃ for 3 hours. Then transfer them to a box furnace and heat them to (500-700)℃ under a protective atmosphere for 3 hours to continue annealing.

[0099] Step 4: Preparation of sodium-ion battery negative electrode

[0100] Take the hard carbon material obtained in step 3, select a suitable formulation ratio, mix it with a conductive agent, and then uniformly coat it onto the current collector using a transfer or extrusion coating machine. The current collector can be one or more of copper foil, aluminum foil, titanium foil, etc. After conducting different compaction experiments, select a suitable compaction method for rolling, and obtain the negative electrode sheet after forming.

[0101] Step 5: Sodium-ion battery preparation

[0102] The negative electrode obtained in step 4 is assembled with a suitable positive electrode and separator. The positive electrode material can be one or more of polyanionic compounds, Prussian blue, oxides, etc. After encapsulation, liquid injection and formation processes are performed to obtain a sodium-ion battery.

[0103] The hard carbon anodes obtained from the three embodiments and three comparative examples were subjected to different compaction experiments and coin cell tests. The results are shown in Table 1.

[0104] Table 1. Test Results

[0105] Sample number <![CDATA[Compaction (g / cm 3 )]]> Capacity (mAh / g) Example 1 1.0-1.5, no cracking during roller pressing 351 Example 2 1.0-1.4 349 Example 3 1.0-1.5 352 Comparative Example 1 1.0-1.2 350 Comparative Example 2 1.0-1.36 342 Comparative Example 3 0.9-1.0, coating breakage band 328

[0106] Figure 1 This is the complete synthesis process of the hard carbon anode in Example 1.

[0107] As shown in Table 1, the pore-forming and coating methods used in the three embodiments can significantly improve the compaction and specific capacity of the hard carbon anode. Specifically, electrospinning allows the crosslinking agent to be coated within the precursor, and then the pore-forming method constructs different micropores in the microstructure of the hard carbon anode, enhancing its processing performance, providing more insertion channels for sodium ions, and further improving the capacity of the sodium-ion battery.

[0108] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A sodium-ion battery hard carbon anode material, characterized in that, The sodium ion battery hard carbon negative electrode material is prepared from the following raw materials: polyvinylpyrrolidone, polyvinyl chloride, a solvent and a crosslinking agent, wherein the mass ratio of polyvinylpyrrolidone to polyvinyl chloride is 10:1-10, the addition amount of the crosslinking agent is 3%-10%, and the solid-liquid ratio is 1:10-80. The preparation method of the sodium ion battery hard carbon negative electrode material comprises the following steps: 1) A polyvinylpyrrolidone is added in a solvent according to a formula amount, and magnetic stirring is performed for reaction and dissolution to obtain a mixed solution A; 2) A crosslinking agent and polyvinyl chloride are gradually added in the mixed solution A obtained in step 1), and magnetic stirring is performed to obtain a mixed solution B; 3) The mixed solution B obtained in step 2) is transferred to a plastic syringe, a film used for electrospinning is installed on a clean brush, electrospinning is performed after power-on, and nanofibers are gathered on a collector; 4) The nanofibers obtained in step 3) are left to stand, and carbon dioxide ball milling or microwave treatment is performed to form pores; 5) The nanofibers obtained in step 4) are annealed to obtain the sodium ion battery hard carbon negative electrode material. 2.The sodium-ion battery hard carbon negative material of claim 1, characterized in that, The solvent comprises one or more of isopropyl alcohol, N-N dimethylformamide, ethanol and N-methyl pyrrolidone. 3.The sodium-ion battery hard carbon anode material of claim 1, characterized in that, The crosslinking agent comprises one or more of copper nitrate, copper oxide and copper sulfate.

4. A method of producing a sodium-ion battery hard carbon anode material as claimed in any one of claims 1 to 3, characterized in that, The preparation method comprises the following steps: 1) A polyvinylpyrrolidone is added in a solvent according to a formula amount, and magnetic stirring is performed for reaction and dissolution to obtain a mixed solution A; 2) A crosslinking agent and polyvinyl chloride are gradually added in the mixed solution A obtained in step 1), and magnetic stirring is performed to obtain a mixed solution B; 3) The mixed solution B obtained in step 2) is transferred to a plastic syringe, a film used for electrospinning is installed on a clean brush, electrospinning is performed after power-on, and nanofibers are gathered on a collector; 4) The nanofibers obtained in step 3) are left to stand, and carbon dioxide ball milling or microwave treatment is performed to form pores; 5) The nanofibers obtained in step 4) are annealed to obtain the sodium ion battery hard carbon negative electrode material.

5. The method for preparing the hard carbon anode material for sodium-ion batteries according to claim 4, characterized in that, In steps 1) and 2), the magnetic stirring time is 3h.

6. The method of claim 4, wherein the sodium-ion battery hard carbon anode material is prepared by the method comprising: mixing a sodium source and a carbon source to form a mixture; and heating the mixture at a temperature of 800-1,200 °C for 1-10 hours under an inert atmosphere. In step 3), the rotation speed of electrospinning is 0.03-0.05mm / min.

7. The method of claim 6, wherein the sodium-ion battery hard carbon anode material is prepared by the method comprising: mixing a sodium source and a carbon source to form a mixture; and heating the mixture at a temperature of 800-1,200 °C for 1-10 hours under an inert atmosphere. In step 4), the annealing treatment is that the nanofibers are air-burned in a crucible at a temperature of 300-500℃ for 3h, and then the temperature is increased to 500-700℃ under a protective atmosphere in a box-type furnace, and the holding time is 3h.

8. A method for producing a sodium-ion battery negative electrode sheet, characterized by, The preparation method comprises the following steps: The sodium ion battery hard carbon negative electrode material obtained by the preparation method of any one of claims 4-7 is mixed with a conductive agent and a binder, is uniformly coated on a current collector by using a transfer type or extrusion type coating machine, is rolled and sliced to prepare a negative electrode sheet.

9. The method of claim 8, wherein the sodium-ion battery anode sheet is prepared by a process comprising: The mass ratio of the sodium ion battery hard carbon negative electrode material, the conductive agent and the binder is 92-95:2-3:2-6. ​ 10. A sodium-ion battery, characterized in that, The negative electrode sheet prepared from the sodium ion battery hard carbon negative electrode material of any one of claims 1-3 or the sodium ion battery hard carbon negative electrode material obtained by the preparation method of any one of claims 4-7, a positive electrode sheet and an electrolyte.

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