A boronene-coated sodium-ion battery cathode material and its preparation method

Abstract

This invention provides a boronene-coated sodium-ion battery cathode material and its preparation method, wherein the general chemical formula of the cathode material is Na[Ni]. a Fe b Mn c O2@BL (0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1). This cathode material is uniformly coated with borene, effectively improving its air stability. The preparation method first involves growing a monolayer of borene on a copper surface using chemical vapor deposition, then obtaining a borene film using a wet transfer process. Finally, the borene film is mixed with the cathode material, vacuum-sealed, and sintered in a muffle furnace, ensuring the borene film is firmly coated onto the cathode material surface. This technology fully utilizes the unique cage-like structure, good conductivity, and high hydrogen content of borene materials. Introducing a borene coating layer onto the cathode material surface not only enhances its air stability but also improves its cycle life, rate performance, and energy density.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, and specifically to a sodium-ion battery cathode material and its preparation method. Background Technology

[0002] With increasing energy demand and growing environmental awareness, sodium-ion batteries, as a key device for renewable energy storage, have seen their cathode materials' performance become a research hotspot. However, existing cathode materials generally suffer from insufficient air stability, poor structural stability, and low specific capacity, which severely limit the widespread application and performance of sodium-ion batteries.

[0003] To overcome these problems, researchers have adopted various improvement strategies. Surface modification techniques, such as coating with protective layers of oxides or carbon materials, are used to enhance the air stability of the cathode material. Simultaneously, structural modification and the development of new synthesis technologies, such as the preparation of porous materials and nanostructures, and the use of sol-gel and hydrothermal synthesis methods, are employed to improve the material's structural stability and specific capacity. Although these strategies have made some progress, they still fail to fully meet the requirements of high-performance sodium-ion batteries. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a boronene-coated cathode material for sodium-ion batteries and its preparation method. This invention fully utilizes the two-dimensional structure and unique properties of boronene, effectively overcoming the limitations of existing technologies. Through chemical vapor deposition and wet transfer techniques, this invention achieves uniform coating of the cathode material surface with a boronene film, significantly improving the material's air stability, structural stability, and energy density. This innovation not only enhances the battery's cycle life and rate performance but also provides new insights for the development of sodium-ion battery cathode materials, possessing significant practical application value and market potential.

[0005] To achieve the above objectives, the present invention provides a method for preparing a borene-coated sodium-ion battery cathode material, comprising the following steps:

[0006] Preparation of boronene thin film: A clean and smooth single-crystal Cu substrate is placed in a graphite crucible. Pure boron powder is evenly spread to cover the copper substrate. The substrate is kept at about 400℃-450℃. Boron powder is sprayed onto the surface of the crucible using an evaporation source. Energy is applied to the surface of the graphite crucible by electron beam spraying at 15keV to form a boronene thin film covering the substrate surface. After cooling for 4-9 hours, PMMA is spin-coated to support the boronene thin film. After drying, a sandwich structure of PMMA+borene+copper substrate is formed. The structure is then placed in an iron salt solution to etch copper metal. Subsequently, it is transferred to deionized water and heated to soften PMMA. Finally, it is transferred to an acetone solution to remove PMMA. After standing for 12-24 hours, a pure boronene thin film is obtained.

[0007] Preparation of sodium-ion battery cathode material: Boroene film and cathode material are mixed in a vacuum reactor and then sintered in a muffle furnace to obtain boroene-coated sodium-ion battery cathode material.

[0008] Preferably, the substrate temperature for preparing the boronene thin film is 400℃-450℃, the evaporation power of the evaporation source is 40W-60W, the beam current is 4-6μA, and the evaporation time is 2-4h.

[0009] Preferably, in the preparation of the boronene film, the PMMA solution has a mass fraction of 2-5%, the rotation speed is 2000-3000 rpm, and the rotation time is 20-30 s; the iron salt solution is at least one of ferric chloride, ferric sulfate, and ferric nitrate solutions, with a concentration of 3-5%, and the etching time is 20-30 min.

[0010] Preferably, the heating softening temperature of the boronene film is 100-150℃.

[0011] Preferably, in the preparation of the sodium-ion battery cathode material, the sintering temperature is 450-600℃ and the sintering time is 3-5h. Preferably, in the preparation of the sodium-ion battery cathode material, the general chemical formula of the cathode material is Na[NiaFebMnc]O2@BL (0<a<1, 0<b<1, 0<c<1, a+b+c=1).

[0012] Preferably, the preparation of the positive electrode material includes the following steps:

[0013] First, sodium, nickel, iron, and manganese sources are mixed in a certain proportion and then ball-milled to obtain a mixture powder. The mixture powder is then heat-treated in a tube furnace to obtain the cathode material. The sodium, nickel, iron, and manganese sources are mixed in a molar ratio of 0.5-1.5:0.1-0.5:0.05-0.3:0.05-0.3.

[0014] Preferably, in step (1), the sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium citrate, sodium oxalate, and sodium acetate; the nickel source is selected from at least one of nickel oxide, nickel oxalate, and nickel acetate; the iron source is selected from at least one of iron oxide, iron acetate, and iron(II,III) oxide; and the manganese source is selected from at least one of manganese dioxide, manganese acetate, manganese oxalate, and manganese(II,III) oxide.

[0015] Preferably, in step (1), the ball milling speed is 300-600 rpm and the ball milling time is 8-10 h; the mass ratio of the mixed boronene film to the positive electrode material is 2-3:5; the mixed powder is kept at 400-500℃ for 3-6 h, then heated to 750-950℃ and kept at that temperature for 10-20 h, the heating rate during sintering is 3-5℃ / min, and heat treatment is carried out in an oxygen atmosphere.

[0016] The present invention provides a sodium-ion battery cathode material coated with boronene obtained by the above preparation method.

[0017] The beneficial effects of the present invention are as follows:

[0018] (1) The beneficial effects of this invention are primarily reflected in its effective solution to the problem that cathode materials are susceptible to moisture and oxygen in the air, leading to performance degradation. Boronene, as a two-dimensional single-layer boron material, has a unique cage-like structure and excellent chemical stability. It can form a dense protective layer on the surface of the cathode material, isolating moisture and oxygen in the air, thereby significantly improving the air stability of the material and ensuring the reliability and safety of the battery under normal conditions;

[0019] (2) The boronene coating layer in this invention not only provides protection, but also enhances the structural stability of the cathode material during battery charging and discharging due to its excellent mechanical properties and elasticity. During charging and discharging, the boronene layer can buffer the stress caused by volume changes, reduce the generation of internal cracks in the material, maintain the integrity of the structure, thereby significantly improving the cycle stability of the cathode material and extending the battery's service life;

[0020] (3) The introduction of borene also improves the electron transport performance of the cathode material. Due to its high conductivity and unique electronic structure, it helps to improve the ion transport efficiency of the battery, thereby increasing the specific capacity and energy density of the material. The high hydrogen content and unique electronic properties of borene not only improve the energy density of the battery, but also optimize the charge and discharge performance of the battery, meeting the requirements of high-performance sodium-ion batteries for high energy density and long cycle life. Attached Figure Description

[0021] Figure 1 This is the XRD pattern of the borene-coated sodium-ion battery cathode material prepared in Example 1 of this invention;

[0022] Figure 2 This is a SEM image of the borene-coated sodium-ion battery cathode material prepared in Example 1 of this invention;

[0023] Figure 3 This is a half-cell cycle performance diagram of the borene-coated sodium-ion battery cathode material prepared in Example 1 of this invention;

[0024] Figure 4 This is the XRD pattern of the borene-coated sodium-ion battery cathode material prepared in Example 2 of this invention;

[0025] Figure 5 This is a TEM image of the borene-coated sodium-ion battery cathode material prepared in Example 2 of this invention;

[0026] Figure 6 This is a graph showing the first charge-discharge curve of the half-cell of the borene-coated sodium-ion battery cathode material prepared in Example 1 of this invention.

[0027] Figure 7 This is a half-cell cycle performance diagram of the sodium-ion battery cathode material prepared in Comparative Example 1;

[0028] Figure 8 This is a half-cell cycle performance diagram of the borene-coated sodium-ion battery cathode material prepared in Comparative Example 2. Detailed Implementation

[0029] To better illustrate the purpose, technical solution, and advantages of this invention, the following will provide further explanation of this application in conjunction with specific embodiments.

[0030] Example 1

[0031] First, appropriate amounts of sodium carbonate, nickel oxalate, iron oxide, and manganese dioxide were weighed and mixed in a molar ratio of 1.0:0.3:0.2:0.2. The mixed material was then placed in a ball mill and milled at 400 rpm for 8 hours to obtain a uniform powder. Next, the powder was placed in a tube furnace for heat treatment, first held at 400℃ for 3 hours, and then held at 750℃ for 15 hours to prepare the cathode material.

[0032] A single-crystal Cu(110) substrate with dimensions of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth, and Ar was repeatedly circulated. +Sputtering and annealing yielded a clean, smooth Cu(110) substrate with a copper substrate thickness of less than 1 mm. The substrate was then placed in a 20 mm high graphite crucible of the same size. 16 g of pure boron powder was uniformly spread to cover the copper substrate while maintaining the substrate at approximately 430 °C. The boron powder was sprayed onto the crucible surface using an evaporation source with a power of approximately 50 W, a beam current of 5.5 μA, and an evaporation time of 2 h. The boron powder was accelerated along the magnetic field of the electron array, forming a large electron beam. This high-energy electron beam (15 keV) applied energy to the graphite crucible surface, molten it, and formed a boronene film covering the substrate surface. After cooling for 4 hours, the sample was transferred to a glove box and spin-coated with 2% PMMA at a rotation speed of 2000 rpm for 30 seconds. After drying, a sandwich structure of PMMA + borene + copper substrate was formed. The sample was then placed in a 3% ferric chloride solution to etch the copper metal for 20 minutes. Subsequently, the sample was transferred to deionized water and heated to soften the PMMA. Finally, the sample was transferred to an acetone solution to remove the PMMA. After standing for 12 hours, a pure borene film was obtained.

[0033] Finally, 2g of boronene film and 5g of cathode material were mixed in a vacuum reactor and then sintered in a muffle furnace at 500℃ for 4 hours to obtain the final product.

[0034] The product of this embodiment was analyzed by X-ray powder diffraction, and the results are as follows: Figure 1 As shown, the product exhibits both boride and O3 phases, indicating successful synthesis of the core cathode material. The product of this embodiment was scanned using a transmission electron microscope, and the results are as follows... Figure 2 As shown, the surface of the cathode material is uniformly coated with a boronene film without any exposed cathode material, indicating that the boronene coating effect has achieved the theoretical expectation.

[0035] Weigh 0.08g of the product prepared above, 0.01g of acetylene black (conductive agent), and 0.01g of PVDF (HSV900, binder). Grind them thoroughly and add 0.6mL of NMP to disperse and mix. After the slurry is uniform, stretch it onto aluminum foil to form a sheet. After drying at 85℃ with a forced air supply, cut it into round pieces with a diameter of 12mm. Assemble the sheet in a glove box under an argon atmosphere. Use a sodium metal sheet as the counter electrode, a 1M NaPF6 solution (solvent EC:DEC volume ratio of 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the separator to assemble a CR2032 coin cell. Figure 3 The cycling performance graph shows that at 25°C, with 1A g -1 When constant current charge-discharge tests were conducted at rates between 2-4.3V, the initial discharge specific capacity of the product was 108.8 mA hg. -1 The specific discharge capacity after 100 cycles is 102.59 mA hg.-1 The capacity retention rate was 94.3%.

[0036] Example 2

[0037] First, appropriate amounts of sodium citrate, nickel oxide, ferric acetate, and manganese trioxide were weighed and mixed in a molar ratio of 0.9:0.4:0.1:0.1. The mixture was ball-milled at 500 rpm for 10 hours to ensure thorough mixing. The powder mixture was then heat-treated in a tube furnace at 450℃ for 4 hours and 900℃ for 18 hours to prepare the cathode material.

[0038] A single-crystal Cu(110) substrate with dimensions of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth, and Ar was repeatedly circulated. + Sputtering and annealing yielded a clean, smooth Cu(110) substrate, which was then placed in a 20 mm high graphite crucible. 16 g of pure boron powder was uniformly spread to cover the copper substrate while maintaining the substrate at approximately 400 °C. The boron powder was sprayed onto the crucible surface using an evaporation source with a power of approximately 40 W, a beam current of 4 μA, and an evaporation time of 3 h. The boron powder was accelerated along the magnetic field of the electron array, forming a large electron beam. This high-energy electron beam (15 keV) applied energy to the graphite crucible surface, molten it, and formed a boronene film covering the substrate surface. After cooling for 5 hours, the sample was transferred to a glove box and spin-coated with 3% PMMA at a rotation speed of 2500 rpm for 20 seconds. After drying, a sandwich structure of PMMA + borene + copper substrate was formed. The sample was then placed in a 4% ferric sulfate solution to etch the copper metal for 25 minutes. Subsequently, the sample was transferred to deionized water and heated to soften the PMMA. Finally, the sample was transferred to an acetone solution to remove the PMMA. After standing for 15 hours, a pure borene film was obtained.

[0039] Finally, 3g of boronene film and 5g of positive electrode material were mixed in an upper and lower sandwich and placed in a vacuum reactor, and sintered at 450℃ for 3h to obtain the final product.

[0040] The product of this embodiment was analyzed by X-ray powder diffraction, and the results are as follows: Figure 4 As shown, the product exhibits both boride and O3 phases, indicating successful synthesis of the core cathode material. Scanning the product of this embodiment using a scanning tunneling microscope yielded the following results: Figure 5 As shown, the lattice of its surface coating layer exhibits a honeycomb arrangement, composed of near-planar B7 clusters, with an additional boron atom on the top of each hexagon, which can be identified as borene, indicating that the borene coating was successful.

[0041] Weigh 0.08g of the product prepared above, 0.01g of acetylene black (conductive agent), and 0.01g of PVDF (HSV900, binder). Grind them thoroughly and add 0.6mL of NMP to disperse and mix. After the slurry is uniform, stretch it onto aluminum foil to form a sheet. After drying at 85℃ with a forced air supply, cut it into round pieces with a diameter of 12mm. Assemble the sheet in a glove box under an argon atmosphere. Use a sodium metal sheet as the counter electrode, a 1M NaPF6 solution (solvent EC:DEC volume ratio of 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the separator to assemble a CR2032 coin cell. Figure 6 The cycling performance graph shows that at 25°C, with 1A g -1 When constant current charge-discharge tests were conducted at rates between 2 and 4.3V, the initial discharge specific capacity of the product was 110.6 mA hg. -1 The specific discharge capacity after 100 cycles is 103.9 mA hg. -1 The capacity retention rate was 93.8%.

[0042] Example 3

[0043] First, appropriate amounts of sodium acetate, nickel acetate, ferric oxide, and manganese oxalate were weighed and mixed in a molar ratio of 1.2:0.2:0.2:0.2. The mixture was ball-milled at 550 rpm for 10 hours to achieve good mixing. The powder mixture was then heat-treated in a tube furnace at 400℃ for 4 hours and 800℃ for 15 hours to obtain the cathode material.

[0044] A single-crystal Cu(110) substrate with dimensions of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth, and Ar was repeatedly circulated. + Sputtering and annealing yielded a clean, smooth Cu(110) substrate, which was then placed in a 20 mm high graphite crucible. 16 g of pure boron powder was uniformly spread to cover the copper substrate while maintaining the substrate at approximately 450 °C. The boron powder was sprayed onto the crucible surface using an evaporation source with a power of approximately 60 W, a beam current of 5.5 μA, and an evaporation time of 4 h. The boron powder was accelerated along the magnetic field of the electron array, forming a large electron beam. This high-energy electron beam (15 keV) applied energy to the graphite crucible surface, molten it, and formed a boronene film covering the substrate surface. After cooling for 6 hours, the sample was transferred to a glove box and spin-coated with 4% PMMA at a rotation speed of 3000 rpm for 30 seconds. After drying, a sandwich structure of PMMA + borene + copper substrate was formed. The sample was then placed in a 5% ferric nitrate solution to etch the copper metal for 30 minutes. Subsequently, the sample was transferred to deionized water and heated to soften the PMMA. Finally, the sample was transferred to an acetone solution to remove the PMMA. After standing for 20 hours, a pure borene film was obtained.

[0045] Finally, 2g of boronene film and 5g of positive electrode material were mixed in an upper and lower sandwich and placed in a vacuum reactor, and sintered at 600℃ for 5h to obtain the final product.

[0046] Weigh 0.08g of the product prepared above, 0.01g of acetylene black (conductive agent), and 0.01g of PVDF (HSV900, binder). Grind thoroughly and add 0.6mL of NMP for dispersion and mixing. After uniform mixing, stretch the slurry onto aluminum foil to form a sheet. After drying at 85℃ with a forced air supply, cut into 12mm diameter discs. Assemble in an argon-atmosphere glove box, using a sodium metal sheet as the counter electrode, 1M NaPF6 solution (solvent EC:DEC volume ratio 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the separator to assemble a CR2032 coin cell. At 25℃, with 1A g... -1 When constant current charge-discharge tests were performed at rates between 2-4.3V, the initial discharge specific capacity of the product was 112.3 mA hg. -1 The specific discharge capacity after 100 cycles is 104.8 mA hg. -1 The capacity retention rate was 93.4%.

[0047] Example 4

[0048] First, appropriate amounts of sodium oxalate, nickel oxalate, iron oxide, and manganese acetate were weighed and mixed in a molar ratio of 1.0:0.5:0.1:0.2. The mixture was ball-milled at 300 rpm for 9 hours. The powder mixture was then heat-treated in a tube furnace at 400℃ for 3 hours and 850℃ for 16 hours to prepare the cathode material.

[0049] A single-crystal Cu(110) substrate with dimensions of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth, and Ar was repeatedly circulated. +Sputtering and annealing yielded a clean, smooth Cu(110) substrate, which was then placed in a 20 mm high graphite crucible. 16 g of pure boron powder was uniformly spread to cover the copper substrate while maintaining the substrate at approximately 450 °C. The boron powder was sprayed onto the crucible surface using an evaporation source with a power of approximately 40 W, a beam current of 6 μA, and an evaporation time of 3 h. The boron powder was accelerated along the magnetic field of the electron array, forming a large electron beam. This high-energy electron beam (15 keV) applied energy to the graphite crucible surface, molten it, and formed a boronene film covering the substrate surface. After cooling for 7 hours, the sample was transferred to a glove box and spin-coated with 5% PMMA at a rotation speed of 2000 rpm for 30 seconds. After drying, a sandwich structure of PMMA + borene + copper substrate was formed. The sample was then placed in a 3% ferric chloride solution to etch the copper metal for 20 minutes. Subsequently, the sample was transferred to deionized water and heated to soften the PMMA. Finally, the sample was transferred to an acetone solution to remove the PMMA. After standing for 24 hours, a pure borene film was obtained.

[0050] Finally, 3g of boronene film and 5g of positive electrode material were mixed in an upper and lower sandwich and placed in a vacuum reactor, and sintered at 500℃ for 4h to obtain the final product.

[0051] Weigh 0.08g of the product prepared above, 0.01g of acetylene black (conductive agent), and 0.01g of PVDF (HSV900, binder). Grind thoroughly and add 0.6mL of NMP for dispersion and mixing. After uniform mixing, stretch the slurry onto aluminum foil to form a sheet. After drying at 85℃ with a forced air supply, cut into 12mm diameter discs. Assemble in an argon-atmosphere glove box, using a sodium metal sheet as the counter electrode, 1M NaPF6 solution (solvent EC:DEC volume ratio 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the separator to assemble a CR2032 coin cell. At 25℃, with 1A g... -1 When constant current charge-discharge tests were conducted at rates between 2 and 4.3V, the initial discharge specific capacity of the product was 114.3 mA hg. -1 The specific discharge capacity after 100 cycles is 106.3 mA hg. -1 The capacity retention rate was 93.2%.

[0052] Example 5

[0053] First, appropriate amounts of sodium acetate, nickel oxide, ferric acetate, and manganese trioxide were weighed and mixed in a molar ratio of 0.8:0.3:0.1:0.1. The mixture was ball-milled at 600 rpm for 8 hours. The powder mixture was then heat-treated in a tube furnace at 450℃ for 3 hours and 750℃ for 17 hours to obtain the cathode material.

[0054] A single-crystal Cu(110) substrate with dimensions of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth, and Ar was repeatedly circulated. + Sputtering and annealing yielded a clean, smooth Cu(110) substrate, which was then placed in a 20 mm high graphite crucible. 16 g of pure boron powder was uniformly spread to cover the copper substrate while maintaining the substrate at approximately 430 °C. The boron powder was sprayed onto the crucible surface using an evaporation source with a power of approximately 45 W, a beam current of 5 μA, and an evaporation time of 2 h. The boron powder was accelerated along the magnetic field of the electron array, forming a large electron beam. This high-energy electron beam (15 keV) applied energy to the graphite crucible surface, molten it, and formed a boronene film covering the substrate surface. After cooling for 8 hours, the sample was transferred to a glove box and spin-coated with 3% PMMA at a rotation speed of 2000 rpm for 25 seconds. After drying, a sandwich structure of PMMA + borene + copper substrate was formed. The sample was then placed in a 4% ferric sulfate solution to etch the copper metal for 25 minutes. Subsequently, the sample was transferred to deionized water and heated to soften the PMMA. Finally, the sample was transferred to an acetone solution to remove the PMMA. After standing for 12 hours, a pure borene film was obtained.

[0055] Finally, 2g of boronene film and 5g of positive electrode material were mixed in an upper and lower sandwich and placed in a vacuum reactor, and sintered at 450℃ for 3h to obtain the final product.

[0056] Weigh 0.08g of the product prepared above, 0.01g of acetylene black (conductive agent), and 0.01g of PVDF (HSV900, binder). Grind thoroughly and add 0.6mL of NMP for dispersion and mixing. After uniform mixing, stretch the slurry onto aluminum foil to form a sheet. After drying at 85℃ with a forced air supply, cut into 12mm diameter discs. Assemble in an argon-atmosphere glove box, using a sodium metal sheet as the counter electrode, 1M NaPF6 solution (solvent EC:DEC volume ratio 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the separator to assemble a CR2032 coin cell. At 25℃, with 1A g... -1 When constant current charge-discharge tests were conducted at rates between 2-4.3V, the initial discharge specific capacity of the product was 114.6 mA hg. -1 The discharge specific capacity after 100 cycles is 107.15 mA hg. -1 The capacity retention rate was 93.5%.

[0057] Example 6

[0058] In Example 6, appropriate amounts of sodium bicarbonate, nickel oxalate, iron oxide, and manganese oxalate were first weighed and mixed in a molar ratio of 1.1:0.2:0.2:0.1. The mixture was ball-milled at 500 rpm for 9 hours. The powder mixture was then heat-treated in a tube furnace at 400°C for 4 hours and 800°C for 14 hours to obtain the cathode material.

[0059] A single-crystal Cu(110) substrate with dimensions of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth, and Ar was repeatedly circulated. + Sputtering and annealing yielded a clean, smooth Cu(110) substrate, which was then placed in a 20 mm high graphite crucible. 16 g of pure boron powder was uniformly spread to cover the copper substrate while maintaining the substrate at approximately 430 °C. The boron powder was sprayed onto the crucible surface using an evaporation source with a power of approximately 40 W, a beam current of 4.5 μA, and an evaporation time of 2 h. The boron powder was accelerated along the magnetic field of the electron array, forming a large electron beam. This high-energy electron beam (15 keV) applied energy to the graphite crucible surface, molten it, and formed a boronene film covering the substrate surface. After cooling for 9 hours, the sample was transferred to a glove box and spin-coated with 4% PMMA at a rotation speed of 2500 rpm for 20 seconds. After drying, a sandwich structure of PMMA + borene + copper substrate was formed. The sample was then placed in a 5% ferric nitrate solution to etch the copper metal for 30 minutes. Subsequently, the sample was transferred to deionized water and heated to soften the PMMA. Finally, the sample was transferred to an acetone solution to remove the PMMA. After standing for 15 hours, a pure borene film was obtained.

[0060] Finally, 2g of boronene film and 5g of positive electrode material were mixed in an upper and lower sandwich and placed in a vacuum reactor, and sintered at 600℃ for 5h to obtain the final product.

[0061] Weigh 0.08g of the product prepared above, 0.01g of acetylene black (conductive agent), and 0.01g of PVDF (HSV900, binder). Grind thoroughly and add 0.6mL of NMP for dispersion and mixing. After uniform mixing, stretch the slurry onto aluminum foil to form a sheet. After drying at 85℃ with a forced air supply, cut into 12mm diameter discs. Assemble in an argon-atmosphere glove box, using a sodium metal sheet as the counter electrode, 1M NaPF6 solution (solvent EC:DEC volume ratio 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the separator to assemble a CR2032 coin cell. At 25℃, with 1A g... -1 When constant current charge-discharge tests were conducted at rates between 2-4.3V, the initial discharge specific capacity of the product was 113.5 mA hg. -1 The specific discharge capacity after 100 cycles is 106.3 mA hg. -1The capacity retention rate is 94%.

[0062] Example 7

[0063] First, appropriate amounts of sodium oxalate, nickel acetate, ferric oxide, and manganese acetate were weighed and mixed in a molar ratio of 0.9:0.5:0.1:0.1. The mixture was ball-milled at 550 rpm for 8 hours. The powder mixture was then heat-treated in a tube furnace at 450℃ for 3 hours and 850℃ for 16 hours to obtain the cathode material.

[0064] A single-crystal Cu(110) substrate with dimensions of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth, and Ar was repeatedly circulated. + Sputtering and annealing yielded a clean, smooth Cu(110) substrate, which was then placed in a 20 mm high graphite crucible. 16 g of pure boron powder was uniformly spread to cover the copper substrate while maintaining the substrate at approximately 450 °C. The boron powder was sprayed onto the crucible surface using an evaporation source with a power of approximately 50 W, a beam current of 4 μA, and an evaporation time of 2.5 h. The boron powder was accelerated along the magnetic field of the electron array, forming a large electron beam. This high-energy electron beam (15 keV) applied energy to the graphite crucible surface, molten it, and formed a boronene film covering the substrate surface. After cooling for 4 hours, the sample was transferred to a glove box and spin-coated with 2% PMMA at a rotation speed of 3000 rpm for 25 seconds. After drying, a sandwich structure of PMMA + borene + copper substrate was formed. The sample was then placed in a 3% ferric chloride solution to etch the copper metal for 20 minutes. Subsequently, the sample was transferred to deionized water and heated to soften the PMMA. Finally, the sample was transferred to an acetone solution to remove the PMMA. After standing for 20 hours, a pure borene film was obtained.

[0065] Finally, 3g of boronene film and 5g of positive electrode material were mixed in an upper and lower sandwich and placed in a vacuum reactor, and sintered at 500℃ for 4h to obtain the final product.

[0066] Weigh 0.08g of the product prepared above, 0.01g of acetylene black (conductive agent), and 0.01g of PVDF (HSV900, binder). Grind thoroughly and add 0.6mL of NMP for dispersion and mixing. After uniform mixing, stretch the slurry onto aluminum foil to form a sheet. After drying at 85℃ with a forced air supply, cut into 12mm diameter discs. Assemble in an argon-atmosphere glove box, using a sodium metal sheet as the counter electrode, 1M NaPF6 solution (solvent EC:DEC volume ratio 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the separator to assemble a CR2032 coin cell. At 25℃, with 1A g... -1When constant current charge-discharge tests were conducted at rates between 2 and 4.3V, the initial discharge specific capacity of the product was 111.9 mA hg. -1 The specific discharge capacity after 100 cycles is 104.9 mA hg. -1 The capacity retention rate was 93.8%.

[0067] Example 8

[0068] First, appropriate amounts of sodium citrate, nickel oxide, ferric acetate, and manganese trioxide were weighed and mixed in a molar ratio of 1.2:0.2:0.2:0.2. The mixture was ball-milled at 300 rpm for 9 hours. The powder mixture was then heat-treated in a tube furnace at 400℃ for 4 hours and 750℃ for 17 hours to obtain the cathode material.

[0069] A single-crystal Cu(110) substrate with dimensions of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth, and Ar was repeatedly circulated. + Sputtering and annealing yielded a clean, smooth Cu(110) substrate, which was then placed in a 20 mm high graphite crucible. 16 g of pure boron powder was uniformly spread to cover the copper substrate while maintaining the substrate at approximately 400 °C. The boron powder was sprayed onto the crucible surface using an evaporation source with a power of approximately 60 W, a beam current of 5.5 μA, and an evaporation time of 4 h. The boron powder was accelerated along the magnetic field of the electron array, forming a large electron beam. This high-energy electron beam (15 keV) applied energy to the graphite crucible surface, molten it, and formed a boronene film covering the substrate surface. After cooling for 5 hours, the sample was transferred to a glove box and spin-coated with 3% PMMA at a rotation speed of 2500 rpm for 30 seconds. After drying, a sandwich structure of PMMA + borene + copper substrate was formed. The sample was then placed in a 4% ferric sulfate solution to etch the copper metal for 25 minutes. Subsequently, the sample was transferred to deionized water and heated to soften the PMMA. Finally, the sample was transferred to an acetone solution to remove the PMMA. After standing for 24 hours, a pure borene film was obtained.

[0070] Finally, 3g of boronene film and 5g of positive electrode material were mixed in the upper and lower layers and placed in a vacuum reactor, and sintered at 500℃ for 4 hours to obtain the final product.

[0071] Weigh 0.08g of the product prepared above, 0.01g of acetylene black (conductive agent), and 0.01g of PVDF (HSV900, binder). Grind thoroughly and add 0.6mL of NMP for dispersion and mixing. After uniform mixing, stretch the slurry onto aluminum foil to form a sheet. After drying at 85℃ with a forced air supply, cut into 12mm diameter discs. Assemble in an argon-atmosphere glove box, using a sodium metal sheet as the counter electrode, 1M NaPF6 solution (solvent EC:DEC volume ratio 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the separator to assemble a CR2032 coin cell. At 25℃, with 1A g... -1 When constant current charge-discharge tests were conducted at rates between 2 and 4.3V, the initial discharge specific capacity of the product was 113.7 mA hg. -1 The specific discharge capacity after 100 cycles is 107.4 mA hg. -1 The capacity retention rate was 94.5%.

[0072] Comparative Example 1: Only the core cathode material was synthesized to compare the performance differences before and after coating.

[0073] First, appropriate amounts of sodium carbonate, nickel oxalate, iron oxide, and manganese dioxide were weighed and mixed in a molar ratio of 1.0:0.3:0.2:0.2. The mixed material was then placed in a ball mill and milled at 400 rpm for 8 hours to obtain a uniform powder. Next, the powder was placed in a tube furnace for heat treatment, first held at 400℃ for 3 hours, and then held at 750℃ for 15 hours to prepare the cathode material.

[0074] Weigh 0.08g of the product prepared above, 0.01g of acetylene black (conductive agent), and 0.01g of PVDF (HSV900, binder). Grind them thoroughly and add 0.6mL of NMP to disperse and mix. After the slurry is uniform, stretch it onto aluminum foil to form a sheet. After drying at 85℃ with a forced air supply, cut it into round pieces with a diameter of 12mm. Assemble the sheet in a glove box under an argon atmosphere. Use a sodium metal sheet as the counter electrode, a 1M NaPF6 solution (solvent EC:DEC volume ratio of 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the separator to assemble a CR2032 coin cell. Figure 7 The cycling performance graph shows that at 25°C, with 1A g -1 When constant current charge-discharge tests were conducted at rates between 2 and 4.3V, the initial discharge specific capacity of the product was 95.8 mA hg. -1 The specific discharge capacity after 100 cycles is 27.7 mA hg. -1 The capacity retention rate was 28.9%.

[0075] Comparative Example 2: Boron-based composite materials were prepared using conventional growth methods and coated onto the cathode material to compare the differences in battery performance after different coating schemes.

[0076] First, appropriate amounts of sodium carbonate, nickel oxalate, iron oxide, and manganese dioxide were weighed and mixed in a molar ratio of 1.0:0.3:0.2:0.2. The mixed material was then placed in a ball mill and milled at 400 rpm for 8 hours to obtain a uniform powder. Next, the powder was placed in a tube furnace for heat treatment, first held at 400℃ for 3 hours, and then held at 750℃ for 15 hours to prepare the cathode material.

[0077] Solid sodium borohydride and copper powder were mixed at a molar ratio of 1:10. Hydrogen gas was introduced under vacuum at a flow rate of 300 sccm, and the initial gas pressure in the furnace was adjusted to 300 Pa. Then, the temperature was raised to 450℃ for the first time and held for 150 min to fully decompose the sodium borohydride. The temperature was raised to 500℃ for the second time and held for 150 min to obtain an intermediate reactant. Finally, the temperature was raised to 800℃ and held for 150 min to achieve in-situ growth of borene on the surface of metal particles. The heating rate was 5℃ / min for all three heating processes. After washing the reaction product with acetone to remove impurities, it was dried at 80℃ to obtain borene / copper composite powder. Then, the powder was immersed in a 3% ferric chloride solution to etch metallic copper for 30 min. After vacuum filtration and standing for 24 h, pure borene was obtained.

[0078] Finally, 2g of borene was mixed with 5g of cathode material, placed in a vacuum reactor, and sintered in a muffle furnace at a temperature of 500℃ for 4 hours to obtain the final product.

[0079] Weigh 0.08g of the product prepared above, 0.01g of acetylene black (conductive agent), and 0.01g of PVDF (HSV900, binder). Grind them thoroughly and add 0.6mL of NMP to disperse and mix. After the slurry is uniform, stretch it onto aluminum foil to form a sheet. After drying at 85℃ with a forced air supply, cut it into round pieces with a diameter of 12mm. Assemble the sheet in a glove box under an argon atmosphere. Use a sodium metal sheet as the counter electrode, a 1M NaPF6 solution (solvent EC:DEC volume ratio of 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the separator to assemble a CR2032 coin cell. Figure 8 The cycling performance graph shows that at 25°C, with 1A g -1 When constant current charge-discharge tests were conducted at rates between 2-4.3V, the initial discharge specific capacity of the product was 101.5 mA hg. -1 The specific discharge capacity after 100 cycles is 77.6 mA hg. -1 The capacity retention rate was 76.5%.

[0080] Comparative Example 2 uses copper powder to achieve in-situ growth of borene on the surface of metal particles. The resulting borene is relatively dispersed, and the effect after mixing and sintering with an equal amount of cathode material is not as good as the theoretical coating effect, with some cathode material exposed. In contrast, electron beam evaporation coating can grow borene on a large-area single-crystal copper surface, forming a borene film. The effect of mixing and sintering this film with an equal amount of cathode material for coating is much more significant. This invention overcomes the key problems of sodium-ion battery cathode materials in terms of air stability, structural stability, and energy density. Through a unique borene coating technology, it effectively isolates the material from the erosion of moisture and oxygen, improving the material's air stability; it also enhances the structural stability of the material during charge and discharge, reducing performance degradation during cycling; and by optimizing electron transport efficiency, it significantly improves the material's energy density, meeting the technical requirements of high-performance sodium-ion batteries.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a borene-coated sodium-ion battery cathode material, characterized in that: Includes the following steps: Preparation of boronene thin film: A clean and smooth single-crystal Cu substrate is placed in a graphite crucible. Pure boron powder is evenly spread to cover the copper substrate. Boron powder is sprayed onto the surface of the crucible using an evaporation source. Energy is applied to the surface of the graphite crucible by electron beam spraying at 15keV to form a boronene thin film covering the substrate surface. After cooling for 4-9 hours, PMMA is spin-coated to support the boronene thin film. After drying, a sandwich structure of PMMA + boronene + copper substrate is formed. Then, it is placed in an iron salt solution to etch copper metal. Subsequently, it is transferred to deionized water and heated to soften PMMA. Finally, it is transferred to an acetone solution to remove PMMA. After standing for 12-24 hours, a pure boronene thin film is obtained. Preparation of sodium-ion battery cathode material: Boroene film and cathode material are mixed in a vacuum reactor and then sintered in a muffle furnace to obtain boroene-coated sodium-ion battery cathode material.

2. The preparation method according to claim 1, characterized in that: The boronene thin film is prepared with a substrate temperature of 400℃-450℃, an evaporation power of 40W-60W, a beam current of 4-6 μA, and an evaporation time of 2-4 h.

3. The preparation method according to claim 1, characterized in that: The preparation of the boronene film involves using a PMMA solution with a mass fraction of 2-5%, a rotation speed of 2000-3000 rpm, and a rotation time of 20-30 s; the iron salt solution is at least one of ferric chloride, ferric sulfate, and ferric nitrate solutions, with a concentration of 3-5%, and an etching time of 20-30 min.

4. The preparation method according to claim 1, characterized in that, The boronene thin film is prepared at a heating softening temperature of 100-150℃.

5. The preparation method according to claim 1, characterized in that: In the preparation of the sodium-ion battery cathode material, the sintering temperature is 450-600℃ and the sintering time is 3-5h.

6. The preparation method according to claim 2, characterized in that: In the preparation of the sodium-ion battery cathode material, the general chemical formula of the cathode material is Na[Ni]. a Fe b Mn c ]O2@BL, 0<a<1, 0<b<1, 0<c<1, a+b+c=1.

7. The preparation method according to claim 6, characterized in that: The preparation of the cathode material includes the following steps: First, sodium source, nickel source, iron source and manganese source are mixed in a certain proportion and then ball-milled to obtain a mixture powder. The mixture powder is then heat-treated in a tube furnace to obtain the cathode material. The sodium source, nickel source, iron source and manganese source are mixed in a molar ratio of 0.5-1.5:0.1-0.5:0.05-0.3:0.05-0.

3.

8. The preparation method according to claim 7, characterized in that: The sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium citrate, sodium oxalate, and sodium acetate; the nickel source is selected from at least one of nickel oxide, nickel oxalate, and nickel acetate; the iron source is selected from at least one of iron oxide, iron acetate, and iron(II,III) oxide; and the manganese source is selected from at least one of manganese dioxide, manganese acetate, manganese oxalate, and manganese(II,III) oxide.

9. The preparation method according to claim 7, characterized in that: The ball milling speed is 300-600 rpm, and the ball milling time is 8-10 h; the mass ratio of the boronene film to the positive electrode material is 2-3:5; the mixed powder is placed at 400-500℃ for 3-6 h, then heated to 750-950℃ and held for 10-20 h, the heating rate during sintering is 3-5℃ / min, and the heat treatment is carried out in an oxygen atmosphere.

10. The borene-coated sodium-ion battery cathode material obtained by the preparation method according to any one of claims 1-9.

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