Boron-alkene-coated sodium ion battery positive electrode material and preparation method thereof

Abstract

The invention provides a borane-coated sodium ion battery positive electrode material and a preparation method thereof. The chemical general formula of the positive electrode material is Na [NiaFebMnc] O2 (at) BL (a is greater than 0 and less than 1, b is greater than 0 and less than 1, c is greater than 0 and less than 1, and a + b + c = 1). The surface of the positive electrode material is uniformly coated with boron alkene, so that the air stability of the material is effectively improved. The preparation method comprises the following steps: growing a single layer of boron alkene on the surface of metal copper by adopting a chemical vapor deposition method, transferring by utilizing a wet method to obtain a boron alkene thin film, mixing the boron alkene thin film and the positive electrode material, vacuumizing, and heating and sintering in a muffle furnace, so that the boron alkene thin film is firmly coated on the surface of the positive electrode material. According to the technology, the advantages of unique cage-shaped structure, good conductivity and high hydrogen content of the Boron-Hash material are fully utilized, and the Boron-Hash coating layer is introduced to the surface of the positive electrode material, so that the air stability of the material can be enhanced, and the cycle life, the rate capability and the energy density of the material can be improved.

Description

Technical Field

[0001] The present invention relates to the field of sodium ion batteries, and in particular to a sodium ion battery positive electrode material and a preparation method thereof. Background Art

[0002] With the growth of energy demand and the improvement of environmental protection awareness, the performance of cathode materials of sodium-ion batteries, as key equipment for renewable energy storage, has become a research hotspot. However, cathode materials in existing technologies generally have problems such as insufficient air stability, poor structural stability and low specific capacity, which seriously limit the wide application and performance of sodium-ion batteries.

[0003] In order to overcome the above problems, researchers have adopted a variety of improvement strategies. Through surface modification technology, such as coating protective layers such as oxides or carbon materials, the air stability of positive electrode materials can be enhanced; at the same time, through the development of new structural modification and synthesis technologies, such as the preparation of porous materials and nanostructures, and the use of sol-gel method, hydrothermal synthesis method, etc., the structural stability and specific capacity of the materials can be improved. Although these strategies have made progress to a certain extent, they still cannot fully meet the needs of high-performance sodium-ion batteries. Summary of the invention

[0004] In order to overcome the deficiencies in the prior art, the present invention provides a borophene-coated sodium ion battery positive electrode material and a preparation method thereof. The present invention makes full use of the two-dimensional structure and unique properties of borophene, and effectively solves the limitations of the prior art. The present invention uses chemical vapor deposition and wet transfer technology to achieve uniform coating of borophene film on the surface of the positive electrode material, significantly improving the air stability, structural stability and energy density of the material. This innovation not only enhances the cycle life and rate performance of the battery, but also provides a new idea for the development of positive electrode materials for sodium ion batteries, and has important practical application value and market prospects.

[0005] To achieve the above object, the present invention provides a method for preparing a sodium ion battery positive electrode material coated with borane, which comprises the following steps:

[0006] Preparation of borophene 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, and the substrate is kept at about 400°C-450°C. Boron powder is sprayed onto the crucible surface with an evaporation source, and energy is applied to the graphite crucible surface with a 15keV electron beam spray to form a borophene film, which covers the substrate surface. After cooling for 4-9 hours, PMMA is spin-coated to support the borophene film. After drying, a sandwich structure of PMMA+borophene+copper substrate is formed, which is then placed in an iron salt solution to etch the copper metal, and then transferred to deionized water to heat and soften PMMA, and finally transferred to an acetone solution to remove PMMA. After standing for 12-24 hours, a pure borophene film is obtained;

[0007] Preparation of sodium ion battery positive electrode material: mixing the borophene film with the positive electrode material in a vacuum reactor, and then sintering in a muffle furnace to obtain the borophene-coated sodium ion battery positive electrode material.

[0008] Preferably, in the preparation of the borophene film, the substrate temperature is 400° C.-450° C., the evaporation power of the evaporation source is 40W-60W, the beam current is 4-6 μA, and the evaporation time is 2-4 hours.

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

[0010] Preferably, the borophene film prepared has a heating softening temperature of 100-150°C.

[0011] Preferably, in the preparation of the positive electrode material for sodium ion batteries, the sintering temperature is 450-600°C and the sintering time is 3-5h. Preferably, in the preparation of the positive electrode material for sodium ion batteries, the chemical formula of the positive electrode 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 comprises the following steps:

[0013] First, a sodium source, a nickel source, an iron source and a manganese source are mixed in a certain proportion and then ball-milled to obtain a mixture powder, and the mixture powder is heat-treated in a tubular furnace to obtain a positive electrode material; the sodium source, the nickel source, the iron source and the 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.

[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 ferroferric oxide; and the manganese source is selected from at least one of manganese dioxide, manganese acetate, manganese oxalate, and manganese trioxide.

[0015] Preferably, in step (1), the ball milling speed is 300-600rpm, and the ball milling time is 8-10h; the mass ratio of the mixed borophene film to the positive electrode material is 2-3:5; the mixed powder is placed at 400-500℃ for 3-6h, then heated to 750-950℃ and kept for 10-20h, 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 positive electrode material coated with boron nitride obtained by the above-mentioned preparation method.

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

[0018] (1) The beneficial effects of the present invention are firstly reflected in the effective solution to the problem that the positive electrode material is easily affected by moisture and oxygen in the air, resulting in performance degradation. Borophene, as a two-dimensional single-layer boron material, has a unique cage structure and excellent chemical stability. It can form a dense protective layer on the surface of the positive electrode material to isolate 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 boron olefin coating layer in the present invention not only provides protection, but also enhances the structural stability of the positive electrode material during the battery charging and discharging process due to its good mechanical properties and elasticity. During the charging and discharging process, the boron olefin layer can buffer the stress caused by volume change, reduce the generation of cracks inside the material, and maintain the integrity of the structure, thereby significantly improving the cycle stability of the positive electrode material and extending the service life of the battery;

[0020] (3) The introduction of borophene also improves the electron transport performance of the positive electrode 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. Borophene's high hydrogen content and unique electronic properties not only improve the battery energy density, but also optimize the battery's charge and discharge performance, meeting the requirements of high-performance sodium-ion batteries for high energy density and long cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the XRD pattern of the sodium ion battery positive electrode material coated with borophene prepared in Example 1 of the present invention;

[0022] Figure 2 is a SEM image of the sodium ion battery positive electrode material coated with boron nitride prepared in Example 1 of the present invention;

[0023] Figure 3 This is a half-cell cycle performance diagram of the sodium ion battery positive electrode material coated with boron nitride prepared in Example 1 of the present invention;

[0024] Figure 4 is the XRD pattern of the sodium ion battery positive electrode material coated with boron nitride prepared in Example 2 of the present invention;

[0025] Figure 5 This is a TEM image of the sodium ion battery positive electrode material coated with boron nitride prepared in Example 2 of the present invention;

[0026] Figure 6 This is the first charge and discharge curve diagram of the half-cell of the sodium ion battery positive electrode material coated with boron nitride prepared in Example 1 of the present invention;

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

[0028] Figure 8 This is a half-cell cycle performance diagram of the borophene-coated sodium ion battery positive electrode material prepared in Comparative Example 2. DETAILED DESCRIPTION

[0029] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present application will be further described below in conjunction with specific embodiments.

[0030] Example 1

[0031] First, weigh appropriate amounts of sodium carbonate, nickel oxalate, iron oxide and manganese dioxide and mix them in a molar ratio of 1.0:0.3:0.2:0.2. Put the mixed materials into a ball mill, set the speed to 400rpm, and ball mill for 8h to obtain a uniform mixture powder. Then, put the mixture powder into a tube furnace and carry out a heat treatment process, first at 400℃ for 3h, and then at 750℃ for 15h to prepare the positive electrode material.

[0032] A single crystal Cu(110) substrate with a size of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth. +Sputtering and annealing to obtain clean and smooth Cu(110), the copper substrate thickness should be less than 1mm, and then placed in a graphite crucible of the same size and 20mm high. 16g of pure boron powder is evenly spread to cover the copper substrate, while the substrate is kept at about 430℃. The boron powder is sprayed onto the crucible surface with an evaporation source. The power during evaporation is about 50W, the beam current is 5.5μA, and the evaporation time is 2h. The boron powder is accelerated along the magnetic field direction of the electron array, forming a huge electron flow, and applying energy to the graphite crucible surface with a high-energy electron beam spray of 15keV, so that it is in a molten state, forming a boron film covering the substrate surface. After cooling for 4 hours, the sample was transferred to a glove box and the borophene film was spin-coated with 2% PMMA at a rotation speed of 2000 rpm for 30 seconds for support. After drying, a sandwich structure of PMMA + borophene + copper substrate was formed. The structure was then placed in a 3% ferric chloride solution to etch the copper metal for 20 minutes. The structure was then transferred to deionized water to heat and soften the PMMA, and finally transferred to an acetone solution to remove the PMMA. After standing for 12 hours, a pure borophene film was obtained.

[0033] Finally, 2 g of borophene film and 5 g of the upper and lower layers of the positive electrode material were mixed into a vacuum reactor, and then sintered in a muffle furnace with the sintering temperature set to 500 ° C and the time set to 4 h to obtain the final product.

[0034] The product of this example was analyzed by X-ray powder diffraction. Figure 1 As shown in FIG. 1 , the phases thereof contain boride phases and O3 phases, indicating that the core positive electrode material is successfully synthesized. The product of this example is scanned by a transmission electron microscope, and the results are as follows: Figure 2 As shown, the surface of the positive electrode material is uniformly coated with a borophene film and no positive electrode material is exposed, indicating that the borophene coating effect meets theoretical expectations.

[0035] Weigh 0.08 g of the product prepared above, 0.01 g of acetylene black (conductive agent), and 0.01 g of PVDF (HSV900, binder), grind them thoroughly, add 0.6 mL of NMP to disperse and mix, slurry them evenly, and draw them on aluminum foil to make sheets. After drying at 85°C with air blowing, cut them into discs with a diameter of 12 mm, and assemble them in a glove box with an argon atmosphere, using a metal sodium sheet as the counter electrode, a 1 M NaPF6 solution (solvent EC:DEC volume ratio of 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the diaphragm to assemble into a CR2032 button battery. Figure 3 The cycling performance diagram in the figure shows that at 25°C, the -1 When the constant current charge and discharge test was carried out at a rate between 2-4.3V, the first discharge capacity of the product was 108.8mA hg -1 After 100 cycles, the discharge capacity is 102.59 mA h g-1 , the capacity retention rate is 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 mixture powder was heat-treated in a tube furnace at 450°C for 4 hours and 900°C for 18 hours to prepare the positive electrode material.

[0038] A single crystal Cu(110) substrate with a size of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth. + Sputtering and annealing are performed to obtain clean and smooth Cu(110), which is then placed in a graphite crucible of the same size and 20 mm high. 16 g of pure boron powder is evenly spread to cover the copper substrate, while the substrate is kept at about 400°C. Boron powder is sprayed onto the surface of the crucible using an evaporation source, with an evaporation power of about 40 W, a beam current of 4 μA, and an evaporation time of 3 h. Boron powder is accelerated along the magnetic field direction of the electron array, forming a huge electron flow, and applying energy to the surface of the graphite crucible with a high-energy electron beam spray of 15 keV, making it in a molten state, forming a boronene film that covers the surface of the substrate. After cooling for 5 hours, the sample was transferred to a glove box and the borophene film was spin-coated with 3% PMMA at a rotation speed of 2500 rpm for 20 seconds for support. After drying, a sandwich structure of PMMA + borophene + copper substrate was formed. The structure was then placed in a 4% ferric sulfate solution to etch the copper metal for 25 minutes. The structure was then transferred to deionized water to heat and soften the PMMA, and finally transferred to an acetone solution to remove the PMMA. After standing for 15 hours, a pure borophene film was obtained.

[0039] Finally, 3 g of borophene film was mixed with 5 g of the upper and lower layers of the positive electrode material and placed in a vacuum reactor, and sintered at 450 ° C for 3 h to obtain the final product.

[0040] The product of this example was analyzed by X-ray powder diffraction. Figure 4 As shown in FIG. 1 , the phases thereof include boride phase and O3 phase, indicating that the core positive electrode material is successfully synthesized. The product of this example is scanned by a scanning tunneling microscope, and the result is as follows: Figure 5 As shown, the lattice of its surface coating layer exhibits a honeycomb arrangement, consisting of nearly planar B7 clusters, with an extra boron atom on the top of each hexagon, which can be identified as borophene, indicating that the borophene coating was successful.

[0041] Weigh 0.08 g of the product prepared above, 0.01 g of acetylene black (conductive agent), and 0.01 g of PVDF (HSV900, binder), grind them thoroughly, add 0.6 mL of NMP to disperse and mix, slurry them evenly, and draw them on aluminum foil to make sheets. After drying at 85°C with air blowing, cut them into discs with a diameter of 12 mm, and assemble them in a glove box with an argon atmosphere, using a metal sodium sheet as the counter electrode, a 1 M NaPF6 solution (solvent EC:DEC volume ratio of 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the diaphragm to assemble into a CR2032 button battery. Figure 6 The cycling performance diagram in the figure shows that at 25°C, the -1 When the constant current charge and discharge test was carried out at a rate between 2-4.3V, the first discharge capacity of the product was 110.6mA hg -1 After 100 cycles, the discharge capacity is 103.9 mA h g -1 , the capacity retention rate is 93.8%.

[0042] Example 3

[0043] First, appropriate amounts of sodium acetate, nickel acetate, ferroferric 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 a good mixing effect. The mixture powder was heat treated in a tube furnace at 400°C for 4 hours and 800°C for 15 hours to obtain the positive electrode material.

[0044] A single crystal Cu(110) substrate with a size of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth. + Sputtering and annealing are performed to obtain clean and smooth Cu(110), which is then placed in a graphite crucible of the same size and 20 mm high. 16 g of pure boron powder is evenly spread to cover the copper substrate, while the substrate is kept at about 450°C. Boron powder is sprayed onto the surface of the crucible using an evaporation source. The power during evaporation is about 60 W, the beam current is 5.5 μA, and the evaporation time is 4 hours. The boron powder is accelerated along the magnetic field direction of the electron array, forming a huge electron flow, and applying energy to the surface of the graphite crucible with a high-energy electron beam spray of 15 keV, making it in a molten state, forming a boronene film that covers the surface of the substrate. After cooling for 6 hours, the sample was transferred to a glove box and the borophene film was spin-coated with 4% PMMA at a rotation speed of 3000 rpm for 30 seconds. After drying, a sandwich structure of PMMA + borophene + copper substrate was formed. The structure was then placed in a 5% ferric nitrate solution to etch the copper metal for 30 minutes. The structure was then transferred to deionized water to heat and soften the PMMA. Finally, the structure was transferred to an acetone solution to remove the PMMA. After standing for 20 hours, a pure borophene film was obtained.

[0045] Finally, 2 g of borophene film was mixed with 5 g of the upper and lower layers of the positive electrode material and placed in a vacuum reactor, and sintered at 600 ° C for 5 hours 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, add 0.6mL of NMP to disperse and mix, slurry evenly, draw the slurry on aluminum foil to make sheets, dry at 85℃ with air blast, cut into discs with a diameter of 12mm, and assemble in a glove box with argon atmosphere, using metal sodium sheet as the counter electrode, 1M NaPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the diaphragm to assemble into CR2032 button cells. At 25℃, 1A g -1 When the constant current charge and discharge test was carried out at a rate between 2-4.3V, the first discharge capacity of the product was 112.3mA hg -1 After 100 cycles, the discharge capacity is 104.8 mA h g -1 , the capacity retention rate is 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 mixture powder was heat treated in a tube furnace at 400°C for 3 hours and 850°C for 16 hours to prepare the positive electrode material.

[0049] A single crystal Cu(110) substrate with a size of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth. +Sputtering and annealing are performed to obtain clean and smooth Cu(110), which is then placed in a graphite crucible of the same size and 20 mm high. 16 g of pure boron powder is evenly spread to cover the copper substrate, while the substrate is kept at about 450°C. Boron powder is sprayed onto the surface of the crucible using an evaporation source, with an evaporation power of about 40 W, a beam current of 6 μA, and an evaporation time of 3 h. Boron powder is accelerated along the magnetic field direction of the electron array, forming a huge electron flow, and applying energy to the surface of the graphite crucible with a high-energy electron beam spray of 15 keV, making it in a molten state, forming a boronene film that covers the surface of the substrate. After cooling for 7 hours, the sample was transferred to a glove box and the borophene film was spin-coated with 5% PMMA at a rotation speed of 2000 rpm for 30 seconds for support. After drying, a sandwich structure of PMMA + borophene + copper substrate was formed. The structure was then placed in a 3% ferric chloride solution to etch the copper metal for 20 minutes. The structure was then transferred to deionized water to heat and soften the PMMA, and finally transferred to an acetone solution to remove the PMMA. After standing for 24 hours, a pure borophene film was obtained.

[0050] Finally, 3 g of borophene film was mixed with 5 g of the upper and lower layers of the positive electrode material and placed in a vacuum reactor, and sintered at 500 ° C for 4 hours 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, add 0.6mL of NMP to disperse and mix, slurry evenly, draw the slurry on aluminum foil to make sheets, dry at 85℃ with air blast, cut into discs with a diameter of 12mm, and assemble in a glove box with argon atmosphere, using metal sodium sheet as the counter electrode, 1M NaPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the diaphragm to assemble into CR2032 button cells. At 25℃, 1A g -1 When the constant current charge and discharge test was carried out at a rate between 2-4.3V, the first discharge capacity of the product was 114.3mA hg -1 After 100 cycles, the discharge capacity is 106.3 mA h g -1 , the capacity retention rate is 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 mixture powder was heat treated in a tube furnace at 450°C for 3 hours and 750°C for 17 hours to obtain a positive electrode material.

[0054] A single crystal Cu(110) substrate with a size of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth. + Sputtering and annealing are performed to obtain clean and smooth Cu(110), which is then placed in a graphite crucible of the same size and 20 mm high. 16 g of pure boron powder is evenly spread to cover the copper substrate, while the substrate is kept at about 430°C. Boron powder is sprayed onto the surface of the crucible using an evaporation source, with an evaporation power of about 45 W, a beam current of 5 μA, and an evaporation time of 2 h. Boron powder is accelerated along the magnetic field direction of the electron array, forming a huge electron flow, and applying energy to the surface of the graphite crucible with a high-energy electron beam spray of 15 keV, making it in a molten state, forming a boronene film that covers the surface of the substrate. After cooling for 8 hours, the sample was transferred to a glove box and the borophene film was spin-coated with 3% PMMA at a rotation speed of 2000 rpm for 25 seconds for support. After drying, a sandwich structure of PMMA + borophene + copper substrate was formed. The structure was then placed in a 4% ferric sulfate solution to etch the copper metal for 25 minutes. The sample was then transferred to deionized water to heat and soften the PMMA. Finally, the sample was transferred to an acetone solution to remove the PMMA. After standing for 12 hours, a pure borophene film was obtained.

[0055] Finally, 2 g of borophene film was mixed with 5 g of the upper and lower layers of the positive electrode material and placed in a vacuum reactor, and sintered at 450 ° C for 3 h 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, add 0.6mL of NMP to disperse and mix, slurry evenly, draw the slurry on aluminum foil to make sheets, dry at 85℃ with air blast, cut into discs with a diameter of 12mm, and assemble in a glove box with argon atmosphere, using metal sodium sheet as the counter electrode, 1M NaPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the diaphragm to assemble into CR2032 button cells. At 25℃, 1A g -1 When the constant current charge and discharge test was carried out at a rate between 2-4.3V, the first discharge capacity of the product was 114.6mA hg -1 After 100 cycles, the discharge capacity is 107.15 mA h g -1 , the capacity retention rate is 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 a speed of 500 rpm for 9 hours. The mixture powder was heat treated in a tube furnace at 400°C for 4 hours and 800°C for 14 hours to obtain a positive electrode material.

[0059] A single crystal Cu(110) substrate with a size of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth. + Sputtering and annealing are performed to obtain clean and smooth Cu(110), which is then placed in a graphite crucible of the same size and 20 mm high. 16 g of pure boron powder is evenly spread to cover the copper substrate, while the substrate is kept at about 430°C. Boron powder is sprayed onto the surface of the crucible using an evaporation source, with an evaporation power of about 40 W, a beam current of 4.5 μA, and an evaporation time of 2 h. Boron powder is accelerated along the magnetic field direction of the electron array, forming a huge electron flow, and applying energy to the surface of the graphite crucible with a high-energy electron beam spray of 15 keV, making it in a molten state, forming a boronene film that covers the surface of the substrate. After cooling for 9 hours, the sample was transferred to a glove box and the borophene film was spin-coated with 4% PMMA at a rotation speed of 2500 rpm for 20 seconds for support. After drying, a sandwich structure of PMMA + borophene + copper substrate was formed. The structure was then placed in a 5% ferric nitrate solution to etch the copper metal for 30 minutes. The structure was then transferred to deionized water to heat and soften the PMMA, and finally transferred to an acetone solution to remove the PMMA. After standing for 15 hours, a pure borophene film was obtained.

[0060] Finally, 2 g of borophene film was mixed with 5 g of the upper and lower layers of the positive electrode material and placed in a vacuum reactor, and sintered at 600 ° C for 5 h 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, add 0.6mL of NMP to disperse and mix, slurry evenly, draw the slurry on aluminum foil to make sheets, dry at 85℃ with air blast, cut into discs with a diameter of 12mm, and assemble in a glove box with argon atmosphere, using metal sodium sheet as the counter electrode, 1M NaPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the diaphragm to assemble into CR2032 button cells. At 25℃, 1A g -1 When the constant current charge and discharge test was carried out at a rate between 2-4.3V, the first discharge capacity of the product was 113.5mA hg -1 After 100 cycles, the discharge capacity is 106.3 mA h g -1, the capacity retention rate is 94%.

[0062] Example 7

[0063] First, appropriate amounts of sodium oxalate, nickel acetate, ferroferric 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 a speed of 550 rpm for 8 hours. The mixture powder was heat treated in a tube furnace at 450°C for 3 hours and 850°C for 16 hours to obtain the positive electrode material.

[0064] A single crystal Cu(110) substrate with a size of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth. + After sputtering and annealing, clean and smooth Cu(110) is obtained, which is then placed in a graphite crucible of the same size and 20 mm high. 16 g of pure boron powder is evenly spread to cover the copper substrate, while the substrate is kept at about 450°C. Boron powder is sprayed onto the surface of the crucible using an evaporation source. The power during evaporation is about 50 W, the beam current is 4 μA, and the evaporation time is 2.5 h. The boron powder is accelerated along the magnetic field direction of the electron array, forming a huge electron flow, and applying energy to the surface of the graphite crucible with a high-energy electron beam spray of 15 keV, making it in a molten state, forming a boron film that covers the surface of the substrate. After cooling for 4 hours, the sample was transferred to a glove box and the borophene film was spin-coated with 2% PMMA at a rotation speed of 3000 rpm for 25 seconds for support. After drying, a sandwich structure of PMMA + borophene + copper substrate was formed. The structure was then placed in a 3% ferric chloride solution to etch the copper metal for 20 minutes. The structure was then transferred to deionized water to heat and soften the PMMA. Finally, the structure was transferred to an acetone solution to remove the PMMA. After standing for 20 hours, a pure borophene film was obtained.

[0065] Finally, 3 g of borophene film was mixed with 5 g of the upper and lower layers of the positive electrode material and placed in a vacuum reactor, and sintered at 500 ° C for 4 hours 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, add 0.6mL of NMP to disperse and mix, slurry evenly, draw the slurry on aluminum foil to make sheets, dry at 85℃ with air blast, cut into discs with a diameter of 12mm, and assemble in a glove box with argon atmosphere, using metal sodium sheet as the counter electrode, 1M NaPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the diaphragm to assemble into CR2032 button cells. At 25℃, 1A g -1When the constant current charge and discharge test was carried out at a rate between 2-4.3V, the first discharge capacity of the product was 111.9mA hg -1 After 100 cycles, the discharge capacity is 104.9 mA h g -1 , the capacity retention rate is 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 mixture powder was heat treated in a tube furnace at 400°C for 4 hours and 750°C for 17 hours to obtain a positive electrode material.

[0069] A single crystal Cu(110) substrate with a size of 60mm*30mm*1mm was placed in an ultra-high vacuum system with interconnect growth. + Sputtering and annealing are performed to obtain clean and smooth Cu(110), which is then placed in a graphite crucible of the same size and 20 mm high. 16 g of pure boron powder is evenly spread to cover the copper substrate, while the substrate is kept at about 400°C. Boron powder is sprayed onto the surface of the crucible using an evaporation source, with an evaporation power of about 60 W, a beam current of 5.5 μA, and an evaporation time of 4 h. Boron powder is accelerated along the magnetic field direction of the electron array, forming a huge electron flow, and applying energy to the surface of the graphite crucible with a high-energy electron beam spray of 15 keV, making it in a molten state, forming a boronene film that covers the surface of the substrate. After cooling for 5 hours, the sample was transferred to a glove box and the borophene film was spin-coated with 3% PMMA at a rotation speed of 2500 rpm for 30 seconds for support. After drying, a sandwich structure of PMMA + borophene + copper substrate was formed. The structure was then placed in a 4% ferric sulfate solution to etch the copper metal for 25 minutes. The structure was then transferred to deionized water to heat and soften the PMMA, and finally transferred to an acetone solution to remove the PMMA. After standing for 24 hours, a pure borophene film was obtained.

[0070] Finally, 3 g of borophene film and 5 g of the upper and lower layers of the positive electrode material were mixed and placed in a vacuum reactor, and sintered at 500°C 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, add 0.6mL of NMP to disperse and mix, slurry evenly, draw the slurry on aluminum foil to make sheets, dry at 85℃ with air blast, cut into discs with a diameter of 12mm, and assemble in a glove box with argon atmosphere, using metal sodium sheet as the counter electrode, 1M NaPF6 solution (solvent EC:DEC volume ratio is 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the diaphragm to assemble into CR2032 button cells. At 25℃, 1A g -1 When the constant current charge and discharge test was carried out at a rate between 2-4.3V, the first discharge capacity of the product was 113.7mA hg -1 After 100 cycles, the discharge capacity is 107.4 mA h g -1 , the capacity retention rate is 94.5%.

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

[0073] First, weigh appropriate amounts of sodium carbonate, nickel oxalate, iron oxide and manganese dioxide and mix them in a molar ratio of 1.0:0.3:0.2:0.2. Put the mixed materials into a ball mill, set the speed to 400rpm, and ball mill for 8h to obtain a uniform mixture powder. Then, put the mixture powder into a tube furnace and carry out a heat treatment process, first at 400℃ for 3h, and then at 750℃ for 15h to prepare the positive electrode material.

[0074] Weigh 0.08 g of the product prepared above, 0.01 g of acetylene black (conductive agent), and 0.01 g of PVDF (HSV900, binder), grind them thoroughly, add 0.6 mL of NMP to disperse and mix, slurry them evenly, and draw them on aluminum foil to make sheets. After drying at 85°C with air blowing, cut them into discs with a diameter of 12 mm, and assemble them in a glove box with an argon atmosphere, using a metal sodium sheet as the counter electrode, a 1 M NaPF6 solution (solvent EC:DEC volume ratio of 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the diaphragm to assemble into a CR2032 button battery. Figure 7 The cycling performance diagram in the figure shows that at 25°C, the -1 When the constant current charge and discharge test was carried out at a rate between 2-4.3V, the first discharge capacity of the product was 95.8mA hg -1 After 100 cycles, the discharge capacity is 27.7 mA h g -1 , the capacity retention rate is 28.9%.

[0075] Comparative Example 2: Borene is prepared by the conventional growth method of borane-based composite materials and coated with positive electrode materials to compare the differences in battery performance after different coating schemes.

[0076] First, weigh appropriate amounts of sodium carbonate, nickel oxalate, iron oxide and manganese dioxide and mix them in a molar ratio of 1.0:0.3:0.2:0.2. Put the mixed materials into a ball mill, set the speed to 400rpm, and ball mill for 8h to obtain a uniform mixture powder. Then, put the mixture powder into a tube furnace and carry out a heat treatment process, first at 400℃ for 3h, and then at 750℃ for 15h to prepare the positive electrode material.

[0077] Solid sodium borohydride and copper powder are mixed in a molar ratio of 1:10, and hydrogen gas is introduced at a flow rate of 300sccm under vacuum conditions. The initial gas pressure in the furnace is adjusted to 300Pa, and then the temperature is raised to 450°C for the first time and kept for 150 minutes to fully decompose the sodium borohydride. The temperature is raised to 500°C for the second time and kept for 150 minutes to obtain an intermediate reactant. Finally, it is heated to 800°C and kept for 150 minutes to achieve the in-situ growth of borophene on the surface of metal particles. The three heating rates are all 5°C / min. The reaction product is washed with acetone to remove impurities and then dried at 80°C to obtain borophene / copper composite powder. The powder is then immersed in a 3% ferric chloride solution to etch metallic copper for 30 minutes, and then vacuum filtered and allowed to stand for 24 hours to obtain pure borophene.

[0078] Finally, 2 g of borophene was mixed with 5 g of the positive electrode material, placed in a vacuum reactor, and sintered in a muffle furnace. The sintering temperature was set to 500 ° C and the time was 4 h to obtain the final product.

[0079] Weigh 0.08 g of the product prepared above, 0.01 g of acetylene black (conductive agent), and 0.01 g of PVDF (HSV900, binder), grind them thoroughly, add 0.6 mL of NMP to disperse and mix, slurry them evenly, and draw them on aluminum foil to make sheets. After drying at 85°C with air blowing, cut them into discs with a diameter of 12 mm, and assemble them in a glove box with an argon atmosphere, using a metal sodium sheet as the counter electrode, a 1 M NaPF6 solution (solvent EC:DEC volume ratio of 1:1) as the electrolyte, and glass fiber (Grade GF / F) as the diaphragm to assemble into a CR2032 button battery. Figure 8 The cycling performance diagram in the figure shows that at 25°C, the -1 When the constant current charge and discharge test was carried out at a rate between 2-4.3V, the first discharge capacity of the product was 101.5mA hg -1 After 100 cycles, the discharge capacity is 77.6 mA h g -1 , the capacity retention rate is 76.5%.

[0080] Comparative Example 2 uses copper powder to achieve in-situ growth of borophene on the surface of metal particles. The borophene finally formed is relatively dispersed. After being mixed and sintered with an equal amount of positive electrode material, the effect is not as good as the theoretical coating effect, and part of the positive electrode material will be exposed. The electron beam evaporation coating process can grow borophene on a large area of ​​single crystal copper surface. The borophene film is finally formed, and the effect of mixing and sintering it with an equal amount of positive electrode material for coating will be more obvious. The present invention overcomes the key problems of sodium ion battery positive electrode materials in air stability, structural stability and energy density. Through the unique borophene coating technology, it effectively isolates the corrosion of moisture and oxygen to the material, and improves the air stability of the material; at the same time, it enhances the structural stability of the material during the charging and discharging process, and reduces the performance attenuation during the cycle process; and by optimizing the electron transmission efficiency, it significantly improves the energy density of the material, 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 solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a sodium ion battery positive electrode material coated with boron nitride, characterized in that: The following steps are involved: Preparation of borophene 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 crucible surface by an evaporation source, and energy is applied to the graphite crucible surface by a 15keV electron beam spray to form a borophene film, which covers the substrate surface, and after cooling for 4-9 hours, PMMA is spin-coated to support the borophene film, and after drying, a sandwich structure of PMMA+borophene+copper substrate is formed, and then it is placed in an iron salt solution to etch the copper metal, and then transferred to deionized water to heat and soften PMMA, and finally transferred to an acetone solution to remove PMMA, and after standing for 12-24 hours, a pure borophene film is obtained; Preparation of sodium ion battery positive electrode material: mixing the borophene film with the positive electrode material in a vacuum reactor, and then sintering in a muffle furnace to obtain the borophene-coated sodium ion battery positive electrode material.

2. The preparation method according to claim 1, characterized in that: In the preparation of the borophene film, the substrate temperature is 400° C.-450° C., the evaporation power of the evaporation source is 40W-60W, the beam current is 4-6 μA, and the evaporation time is 2-4 hours.

3. The preparation method according to claim 1, characterized in that: The method for preparing the borophene film comprises: using the PMMA solution with a mass fraction of 2-5%, a rotation speed of 2000-3000rpm, and a rotation time of 20-30s; 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 20-30min.

4. The preparation method according to claim 1, characterized in that: The prepared borophene film has a heating softening temperature of 100-150°C.

5. The preparation method according to claim 1, characterized in that: In the preparation of the sodium ion battery positive electrode material, the sintering temperature is 450-600° C. and the sintering time is 3-5 hours.

6. The preparation method according to claim 2, characterized in that: In the preparation of the positive electrode material for sodium ion batteries, the chemical formula of the positive electrode 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 positive electrode material includes the following steps: first, a sodium source, a nickel source, an iron source and a manganese source are mixed in a certain proportion and then ball-milled to obtain a mixture powder; the mixture powder is heat-treated in a tubular furnace to obtain a positive electrode material; the sodium source, the nickel source, the iron source and the 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 ferroferric oxide; the manganese source is selected from at least one of manganese dioxide, manganese acetate, manganese oxalate, and manganese trioxide.

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

10. A sodium ion battery positive electrode material coated with boron nitride obtained according to the preparation method according to any one of claims 1 to 9.

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