Monocrystalline sodium ion battery positive electrode material and preparation method and application thereof

Abstract

The invention relates to a single crystal sodium ion battery positive electrode material and a preparation method and application thereof. The sodium ion battery positive electrode material contains a chemical formula as shown in Na1 + aNi1-x-y-z-cMnxFeyMzNcO2, a is more than or equal to-0.40 and less than or equal to 0.25, x is more than or equal to 0.08 and less than or equal to 0.5, y is more than or equal to 0.05 and less than or equal to 0.5, z is more than 0 and less than 0.26, and c is more than 0 and less than 0.05; m is Zn, and N is selected from one or two of Al or Nb elements. The single crystal sodium ion battery positive electrode material has specific chemical composition, single crystal morphology, good structural stability and integrity, and does not generate particle fragmentation in the cycle process, thereby improving the cycle stability of the sodium ion battery.

Description

[0001] Related Application

[0002] This application is a divisional application of the parent application with the application number 202210841843.9, the invention name of "A Single Crystal Sodium Ion Battery Cathode Material and Its Preparation Method and Application", and the application date of July 18, 2022. Technical Field

[0003] The present invention belongs to the technical field of sodium ion batteries, and specifically relates to a single crystal sodium ion battery cathode material and its preparation method and application. Background Art

[0004] With the intensification of the development of lithium ion batteries, coupled with the supply-demand relationship and resource and geographical restrictions, the price of lithium salts has skyrocketed, making sodium ion batteries with cost advantages gradually become a research hotspot for major enterprises and universities. The working principle of sodium ion batteries is the same as that of lithium ion batteries. However, relatively speaking, sodium ions have a larger ionic radius and slower diffusion kinetics, resulting in certain disadvantages in energy density and cycling characteristics for sodium ion batteries.

[0005] After nearly a decade of extensive research by various parties, sodium ion batteries have formed products mainly based on systems such as transition metal oxides, Prussian blue, and polyanionic phosphates. Among them, transition metal oxides have received much favor due to their relatively high specific capacity. However, poor cycling performance and low energy density have always been important factors affecting the application of sodium ion battery cathode materials.

[0006] Currently, the transition metal oxides available on the market are mainly divided into two types. One is nickel-manganese-iron-copper-based oxides containing copper elements, and the other is nickel-iron-manganese-based oxides. For either of these two types, different sodium ion battery cathode materials with different properties can be obtained by changing the different ratios of nickel, iron, manganese, and copper elements. Also, due to different element ratios, the stability of the material when contacting the electrolyte also changes accordingly. The factors affecting the cycle life of sodium ion battery cathode materials are: 1. The reconstruction of the surface crystal structure during the cycle; 2. The rupture of agglomerated particles caused by anisotropic volume expansion during the cycle. It has been found that the connection structure between particles inside the agglomerated particles will cause a local increase in current density, thereby generating a large stress, which affects the cycling performance of the material; at the same time, there is also a phenomenon of inconsistent charging states between different parts inside the particles, which will affect the electrochemical performance of the electrode.

[0007] In addition, when the amount of sodium removed from the cathode material of a sodium-ion battery is large, the structure becomes very fragile, the active metal and oxygen in the lattice are displaced, and at a certain high temperature and high pressure, the atomic rearrangement and reconstruction gradually intensify, and the grain volume and phase change greatly; on the other hand, when the cathode material is desodiated, its oxidizing property increases, and it is extremely easy to chemically and electrochemically react with the electrolyte, resulting in easy deoxidation of the material and dissolution of transition metals. Especially at high voltages, the electrolyte will be oxidized to produce H + , which increases the acidity of the electrolyte, thereby damaging the surface film of the electrode material by HF, further changing the composition and structure of the interface, and seriously affecting the electrochemical performance and cycling performance of the material. SUMMARY OF THE INVENTION

[0008] The technical problem to be solved by the present invention is to provide a single-crystal cathode material for a sodium-ion battery to improve the cycling performance of the sodium-ion battery.

[0009] In response to the above technical problem, the inventors of the present application have obtained through in-depth research a single-crystal cathode material for a sodium-ion battery with a single-crystal morphology. By using surface coating or simultaneously performing bulk doping and surface coating modification, it can effectively avoid direct contact between the material and the electrolyte, especially HF in the electrolyte, thereby preventing side reactions from occurring, inhibiting the crystal phase transformation of the material, and thus improving the cycling stability of the material. When applied to a sodium-ion battery, especially a power-type sodium-ion battery, it can effectively improve the high-temperature and high-voltage cycling performance of the battery, especially the high-temperature stability.

[0010] The technical solution of the present invention:

[0011] The present invention provides a single-crystal cathode material for a sodium-ion battery, and the single-crystal cathode material for a sodium-ion battery contains elements with the composition shown in Chemical Formula 1;

[0012] The Chemical Formula 1 is: Na 1+a Ni 1-x-y-z-c Mn x Fe y M z N c O 2 , where, -0.40 ≤ a ≤ 0.25, 0.08 ≤ x ≤ 0.5, 0.05 ≤ y ≤ 0.5, 0 ≤ z < 0.26, 0 < c < 0.1; M is a doping element, and N is a coating element;

[0013] Both M and N are selected from one or more of the elements Ti, Zn, Co, Mn, Al, Zr, Y, Ca, Li, Rb, Cs, W, Ce, Mo, Ba, Mg, Ta, Nb, V, Sc, Sr, B, F, P or Cu.

[0014] Preferably, in the above-mentioned single-crystal sodium-ion battery cathode material, -0.40 ≤ a ≤ 0, 0.15 ≤ x ≤ 0.5, 0.15 ≤ y ≤ 0.5.

[0015] Preferably, in the above-mentioned single-crystal sodium-ion battery cathode material, M is selected from one or more of Zn, Ti, Co, Al, Zr, Y, Ca, Li, Rb, Cs, W, Ce, Mo, Ba, Mg, Ta, Nb, V, Sc, Sr, B, F, P, or Cu, preferably one or more of Zn, Al, B, Ti, Ca, Y, Mg, Nb, Zr, or Cu, more preferably Zn; preferably, 0 ≤ z ≤ 0.13.

[0016] Preferably, in the above-mentioned single-crystal sodium-ion battery cathode material, N is selected from one or more of Al, Ti, Co, Mn, Y, B, F, P, Nb, Zr, W, Sr, or Mg, preferably one or more of Al, Ti, B, Nb, or Mg; preferably, 0 < c < 0.05.

[0017] Preferably, under a scanning electron microscope, the microscopic morphology of the sodium-ion battery cathode material is a single-crystal morphology; preferably, the shape of the single-crystal morphology particles is one or more of spherical, quasi-spherical, polygonal, or lamellar.

[0018] Preferably, in the powder X-ray diffraction spectrum (XRD) of the above-mentioned single-crystal sodium-ion battery cathode material, the full width at half maximum FWHM(110) of the diffraction peak near the diffraction angle 2θ of 64.9° (110) is 0.08 - 0.35.

[0019] Preferably, the powder compaction density of the above-mentioned single-crystal sodium-ion battery cathode material under a pressure of 7000 - 9000 kg is 2.8 - 4.2 g / cm 3 .

[0020] Preferably, the moisture mass content of the above-mentioned single-crystal sodium-ion battery cathode material is less than 1500 ppm, preferably less than 1000 ppm, and more preferably less than 900 ppm.

[0021] Preferably, the pH value of the above-mentioned single-crystal sodium-ion battery cathode material is within 12.6.

[0022] Preferably, the specific surface area of the above-mentioned single-crystal sodium-ion battery cathode material is 0.35 - 1.2 m 2 / g.

[0023] Preferably, the particle size D V 50 of the above-mentioned single-crystal sodium-ion battery cathode material is 2.00 - 16.0 μm, preferably 2.50 - 12.0 μm.

[0024] The present invention also provides a method for preparing the above-mentioned single-crystal sodium-ion battery cathode material, which comprises the following steps:

[0025] (1) Mix raw materials including a sodium source compound, a manganese source compound, and an iron source compound, and optionally mix with a nickel source compound and an M source compound, then perform a first sintering and pulverize to obtain a semi-finished product;

[0026] (2) Mix the semi-finished product obtained in step (1) with an N source compound and then perform a second sintering and pulverize to obtain the single-crystal sodium-ion battery cathode material.

[0027] Preferably, in the above preparation method, the first sintering temperature in step (1) is 860-990 °C, preferably 880-980 °C; preferably, the constant temperature time is 6-40 hours.

[0028] Preferably, in the above preparation method, the second sintering temperature in step (2) is 350-900 °C, preferably 350-800 °C; preferably, the constant temperature time is 2-15 hours.

[0029] Preferably, in the above preparation method, the pulverizing pressure in both step (1) and step (2) is 0.1-1 MPa.

[0030] Preferably, in the above preparation method, the sodium source compound includes a sodium-containing salt and / or hydroxide; preferably, the sodium source compound is selected from one or more of sodium carbonate, sodium formate, sodium hydroxide, sodium acetate, sodium chloride, and sodium fluoride.

[0031] Preferably, in the above preparation method, the manganese source compound includes one or more of manganese-containing oxides, hydroxides, or salts; preferably, the manganese source compound is selected from one or more of manganese(III) oxide, manganese(II,III) oxide, manganese(II) oxide, manganese carbonate, manganese oxalate, manganese sulfate, manganese acetate, manganese chloride, and manganese nitrate.

[0032] Preferably, in the above preparation method, the nickel source compound includes one or more of nickel-containing oxides, hydroxides, or salts; preferably, the nickel source compound is selected from one or more of nickel carbonate, nickel oxalate, nickel sulfate, nickel acetate, nickel chloride, and nickel nitrate.

[0033] Preferably, in the above preparation method, the iron source compound includes one or more of iron-containing oxides, hydroxides, or salts; preferably, the iron source compound is selected from one or more of iron(III) oxide, iron(II) oxalate, iron(II) sulfate, iron(II) acetate, and iron(II) nitrate.

[0034] Preferably, the M-source compound includes an oxide and / or a salt containing the M element; preferably, the M-source compound includes one or more of calcium oxide, calcium hydroxide, boron trioxide, boric acid, niobium oxide, aluminum oxide, titanium oxide, magnesium oxide, copper oxide, yttrium trioxide, zirconium oxide, sodium fluoride, lithium fluoride, copper oxide, zinc oxide, and copper sulfate.

[0035] Preferably, the N-source compound includes an oxide and / or a salt containing the N element; preferably, the N-source compound includes one or more of calcium oxide, boron trioxide, boric acid, niobium oxide, aluminum oxide, aluminum acetate, aluminum nitrate, titanium oxide, magnesium oxide, magnesium acetate, magnesium nitrate, copper oxide, yttrium trioxide, zirconium oxide, zirconium acetate, sodium fluoride, lithium fluoride, titanium dioxide, titanium oxide dispersion, zinc oxide, and copper sulfate.

[0036] The present invention also provides a single-crystal sodium-ion battery cathode material prepared by the above preparation method.

[0037] The present invention also provides a sodium-ion battery cathode, the active material of which is the above single-crystal sodium-ion battery cathode material.

[0038] The present invention also provides a sodium-ion battery, which includes the above sodium-ion battery cathode.

[0039] The present invention also provides the application of the above single-crystal sodium-ion battery cathode material, or the above sodium-ion battery cathode, or the above sodium-ion battery in solar power generation, wind power generation, smart grid, distributed power station, home energy storage battery, low-end two-wheeler battery, or low-energy-density power battery.

[0040] In addition, in order to solve the above-mentioned problems of the prior art, the present invention also provides the following second set of technical solutions.

[0041] The present application provides a single-crystal sodium-ion battery cathode material, which contains the elements with the composition shown in Chemical Formula 1;

[0042] The Chemical Formula 1 is: Na 1+a Ni 1-x-y-z-c Mn x Fe y M z N c O 2 , where, -0.40 ≤ a ≤ 0.25, 0.08 ≤ x ≤ 0.5, 0.05 ≤ y ≤ 0.5, 0 < z < 0.26, 0 < c < 0.05; M is a doping element, and N is a coating element;

[0043] The M is Zn, and the N is selected from one or two of the elements Al or Nb;

[0044] In the powder X-ray diffraction spectrum (XRD) of the single-crystal sodium-ion battery cathode material, the full width at half maximum FWHM(110) of the diffraction peak near the diffraction angle 2θ of 64.9° (110) is 0.08 - 0.35;

[0045] The pH value of the single-crystal sodium-ion battery cathode material is within 12.6;

[0046] The single-crystal sodium-ion battery cathode material is prepared by a method comprising the following steps:

[0047] (1) Mix raw materials including a sodium source compound, a manganese source compound, and an iron source compound, and add a nickel source compound and an M source compound as needed, then perform a first sintering and airflow pulverization to obtain a semi-finished product;

[0048] (2) Mix the semi-finished product obtained in step (1) and an N source compound, then perform a second sintering and airflow pulverization to obtain the single-crystal sodium-ion battery cathode material;

[0049] Among them, the airflow pulverization pressure in both step (1) and step (2) is 0.1 - 1 MPa; the first sintering temperature in step (1) is 860 - 990 °C.

[0050] In some embodiments of the present application, -0.40 ≤ a ≤ 0, 0.15 ≤ x ≤ 0.5, 0.15 ≤ y ≤ 0.5; in some embodiments, 0 < z ≤ 0.13.

[0051] In some embodiments of the present application, under a scanning electron microscope, the micro-morphology of the single-crystal sodium-ion battery cathode material is a single-crystal morphology; preferably, the shape of the single-crystal morphology particles is one or more of spherical, quasi-spherical, polygonal, or lamellar.

[0052] In some embodiments of the present application, the powder compaction density of the single-crystal sodium-ion battery cathode material under a pressure of 7000 - 9000 kg is 2.8 - 4.2 g / cm 3 .

[0053] In some embodiments of the present application, the moisture mass content of the single-crystal sodium-ion battery cathode material is less than 1500 ppm, preferably less than 1000 ppm, and more preferably less than 900 ppm.

[0054] In some embodiments of the present application, the specific surface area of the single-crystal sodium-ion battery cathode material is 0.35 - 1.2 m 2 / g.

[0055] In some embodiments of the present application, the particle size D of the single-crystal sodium-ion battery cathode material V50 is 2.00 to 16.0 μm, preferably 2.50 to 12.0 μm.

[0056] This application also provides a method for preparing the above-mentioned single-crystal sodium-ion battery cathode material, which includes the following steps:

[0057] (1) Mix the raw materials including sodium source compound, manganese source compound and iron source compound, and add nickel source compound and M source compound as needed, then conduct the first sintering and air-flow pulverization to obtain semi-finished products;

[0058] (2) Mix the semi-finished products obtained in step (1) and N source compound, then conduct the second sintering and air-flow pulverization to obtain the single-crystal sodium-ion battery cathode material;

[0059] The air-flow pulverization pressure in both step (1) and step (2) is 0.1 - 1 MPa; the first sintering temperature in step (1) is 860 - 990 °C.

[0060] In some embodiments of this application, the first sintering temperature in step (1) is 880 - 980 °C; preferably, the constant temperature time is 6 - 40 hours.

[0061] In some embodiments of this application, the second sintering temperature in step (2) is 350 - 900 °C, preferably 350 - 800 °C; preferably, the constant temperature time is 2 - 15 hours.

[0062] In some embodiments of this application, the sodium source compound includes salts and / or hydroxides containing sodium element; preferably, the sodium source compound is selected from one or more of sodium carbonate, sodium formate, sodium hydroxide, sodium acetate, sodium chloride and sodium fluoride.

[0063] In some embodiments of this application, the manganese source compound includes one or more of oxides, hydroxides or salts containing manganese element; preferably, the manganese source compound is selected from one or more of manganese(III) oxide, manganese(II,III) oxide, manganese(II) oxide, manganese carbonate, manganese oxalate, manganese sulfate, manganese acetate, manganese chloride and manganese nitrate.

[0064] In some embodiments of this application, the nickel source compound includes one or more of oxides, hydroxides or salts containing nickel element; preferably, the nickel source compound is selected from one or more of nickel carbonate, nickel oxalate, nickel sulfate, nickel acetate, nickel chloride and nickel nitrate.

[0065] In some embodiments of this application, the iron source compound includes one or more of oxides, hydroxides or salts containing iron element; preferably, the iron source compound is selected from one or more of iron(III) oxide, ferrous oxalate, ferrous sulfate, ferrous acetate and ferrous nitrate.

[0066] In some embodiments of the present application, the M-source compound includes an oxide and / or a salt containing the M element; preferably, the M-source compound includes zinc oxide.

[0067] In some embodiments of the present application, the N-source compound includes an oxide and / or a salt containing the N element; preferably, the N-source compound includes one or more of niobium oxide, aluminum oxide, aluminum acetate or aluminum nitrate.

[0068] The present application also provides a positive electrode for a sodium-ion battery, the active material of which is the above-mentioned single-crystal sodium-ion battery positive electrode material or the single-crystal sodium-ion battery positive electrode material prepared by the above-mentioned preparation method.

[0069] The present application also provides a sodium-ion battery, which includes the above-mentioned positive electrode for a sodium-ion battery.

[0070] The present application also provides the above-mentioned single-crystal sodium-ion battery positive electrode material, or the single-crystal sodium-ion battery positive electrode material prepared by the above-mentioned preparation method, or the above-mentioned sodium-ion battery electrode, or the application of the above-mentioned sodium-ion battery, and the application is in solar power generation, wind power generation, smart grid, distributed power station, home energy storage battery, low-end two-wheeler battery or low-energy density power battery.

[0071] Advantages of the present invention

[0072] (1) The single-crystal sodium-ion battery positive electrode material of the present invention has a specific chemical composition and a single-crystal morphology, so that the sodium-ion battery positive electrode material has good structural stability and will not undergo obvious structural changes due to the frequent insertion and extraction of sodium ions during the charge and discharge process of the sodium-ion battery. In addition, the material has a complete structure and good processing performance, and will not show particle fragmentation during the cycling process, effectively preventing the direct contact between the material surface and the electrolyte, especially the contact with HF in the electrolyte, preventing side reactions from occurring, and improving the cycle stability of the sodium-ion battery.

[0073] (2) Through the coating treatment, the single-crystal sodium-ion battery positive electrode material of the present invention has a low pH value, a low residual alkali content, and a low moisture content, so that the single-crystal sodium-ion battery positive electrode material will not gel due to water absorption during the battery slurry mixing process, improving the stability of the sodium-ion battery electrode slurry, and further improving the cycle stability of the sodium-ion battery. Description of the drawings

[0074] Figure 1 SEM image (magnification: 5000 times) of the single-crystal sodium-ion battery positive electrode material prepared in Example 1;

[0075] Figure 2SEM image of the single-crystal sodium-ion battery cathode material prepared in Example 2 (Magnification: 5000 times);

[0076] Figure 3 SEM image of the single-crystal sodium-ion battery cathode material prepared in Example 3 (Magnification: 5000 times);

[0077] Figure 4 SEM image of the single-crystal sodium-ion battery cathode material prepared in Example 4 (Magnification: 5000 times);

[0078] Figure 5 SEM image of the single-crystal sodium-ion battery cathode material prepared in Example 5 (Magnification: 5000 times);

[0079] Figure 6 SEM image of the single-crystal sodium-ion battery cathode material prepared in Example 6 (Magnification: 5000 times);

[0080] Figure 7 SEM image of the single-crystal sodium-ion battery cathode material prepared in Example 7 (Magnification: 5000 times);

[0081] Figure 8 SEM image of the single-crystal sodium-ion battery cathode material prepared in Example 8 (Magnification: 5000 times);

[0082] Figure 9 SEM image of the electrode sheet containing the single-crystal sodium-ion battery cathode material prepared in Example 1 (Magnification: 5000 times);

[0083] Figure 10 SEM image of the electrode sheet containing the single-crystal sodium-ion battery cathode material prepared in Example 2 (Magnification: 5000 times);

[0084] Figure 11 SEM image of the electrode sheet containing the single-crystal sodium-ion battery cathode material prepared in Example 3 (Magnification: 5000 times);

[0085] Figure 12 SEM image of the electrode sheet containing the single-crystal sodium-ion battery cathode material prepared in Example 4 (Magnification: 5000 times);

[0086] Figure 13 SEM image of the electrode sheet containing the single-crystal sodium-ion battery cathode material prepared in Example 5 (Magnification: 5000 times);

[0087] Figure 14 SEM image of the electrode sheet containing the single-crystal sodium-ion battery cathode material prepared in Example 6 (Magnification: 5000 times);

[0088] Figure 15 SEM image (magnification:) of the electrode sheet containing the single-crystal sodium-ion battery cathode material prepared in Example 7;

[0089] Figure 16 SEM image (magnification: 5000 times) of the electrode sheet containing the single-crystal sodium-ion battery cathode material prepared in Example 8;

[0090] Figure 17 SEM image (magnification: 5000 times) of the single-crystal sodium-ion battery cathode material prepared in Example 9;

[0091] Figure 18 SEM image (magnification: 5000 times) of the electrode sheet containing the single-crystal sodium-ion battery cathode material prepared in Example 9;

[0092] Figure 19 SEM image (magnification: 5000 times) of the positive electrode sheet of the BA-C1 battery after 50 cycles;

[0093] Figure 20 Charge-discharge cycle curve of Examples 1-9. Detailed implementation manners

[0094] To make the objectives, technical solutions and technical effects of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below. The following described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Combining the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0095] The present invention D v D50 refers to the particle size corresponding to when the cumulative volume particle size distribution percentage in a sample reaches 50%.

[0096] To improve the cycle performance of the sodium-ion battery, the present invention prepares the sodium-ion battery cathode material into single-crystal particles, improves the structural stability of the material, effectively inhibits the structural change, and enhances the reversibility of the material; at the same time, the sodium-ion battery cathode material is surface-coated or simultaneously subjected to bulk doping and surface coating modification, effectively avoiding the direct contact between the material and the electrolyte, especially HF in the electrolyte, thereby preventing the occurrence of side reactions and inhibiting the crystal phase transformation of the material, thus improving the cycle stability of the material.

[0097] In a specific implementation manner of the present invention, the present invention provides a single-crystal sodium-ion battery cathode material, and the material contains elements with the composition shown in Chemical Formula 1;

[0098] The Chemical Formula 1 is: Na1+a Ni 1-x-y-z-c Mn x Fe y M z N c O 2 where: -0.40 ≤ a ≤ 0.25, 0.08 ≤ x ≤ 0.5, 0.05 ≤ y ≤ 0.5, 0.0 ≤ z < 0.26, 0 < c < 0.1; M is a doping element and N is a coating element;

[0099] The M and N are selected from one or more of the elements Ti, Zn, Co, Mn, Al, Zr, Y, Ca, Li, Rb, Cs, W, Ce, Mo, Ba, Mg, Ta, Nb, V, Sc, Sr, B, F, P or Cu.

[0100] In a preferred embodiment of the present invention, in the above chemical formula 1, -0.40 ≤ a ≤ 0, 0.15 ≤ x ≤ 0.5, 0.15 ≤ y ≤ 0.5.

[0101] In a preferred embodiment of the present invention, the above M is selected from one or more of Zn, Ti, Co, Al, Zr, Y, Ca, Li, Rb, Cs, W, Ce, Mo, Ba, Mg, Ta, Nb, V, Sc, Sr, B, F, P or Cu, preferably one or more of Zn, Al, B, Ti, Ca, Y or Cu, more preferably Zn; preferably, 0 ≤ z ≤ 0.13.

[0102] In another preferred embodiment of the present invention, the above N is selected from one or more of Al, Ti, Co, Mn, Y, B, F, P, Nb, Zr, W, Sr or Mg, preferably one or more of Al, Ti, B, Nb or Mg; preferably, 0 < c < 0.05.

[0103] In the present invention, under a scanning electron microscope, the microscopic morphology of the above sodium ion battery cathode material is a single crystal morphology; the shape of the single crystal morphology particles is one or more of spherical, quasi-spherical, polygonal or lamellar.

[0104] In the present invention, in the powder X-ray diffraction spectrum (XRD) of the above single crystal sodium ion battery cathode material, the full width at half maximum FWHM(110) of the diffraction peak near the diffraction angle 2θ of 64.9° (110) is 0.08 - 0.35.

[0105] In the present invention, the powder compaction density of the above single crystal sodium ion battery cathode material under a pressure of 7000 - 9000 kg is 2.8 - 4.2 g / cm 3 between.

[0106] In the present invention, the specific surface area of the above-mentioned single-crystal sodium-ion battery cathode material is 0.35 to

[0107] 1.2 m 2 / g.

[0108] In the present invention, the particle size D N 50 of the above-mentioned single-crystal sodium-ion battery cathode material is 2.00 to 16.0 μm, preferably 2.50 to 12.0 μm.

[0109] Due to the above-mentioned specific chemical composition and morphology of the single-crystal sodium-ion battery cathode material of the present application, the specific surface area (BET) of the material is within a reasonable range, and the intermolecular force on the material surface is in a relatively balanced position. Even in an environment with relatively high humidity, it is not easy to self-aggregate, and the moisture content of the material is at a relatively low level.

[0110] In the present invention, the moisture content of the above-mentioned single-crystal sodium-ion battery cathode material is less than 1500 ppm, preferably less than 1000 ppm, and more preferably less than 900 ppm.

[0111] In the present invention, the pH value of the above-mentioned single-crystal sodium-ion battery cathode material is within 12.6.

[0112] Due to the above-mentioned specific chemical composition and morphology of the single-crystal sodium-ion battery cathode material of the present application, combined with the coating treatment, the sodium material has a low pH value, a low residual alkali content, and a low water content, so that the sodium material will not gel due to water absorption during the battery slurry mixing process, improving the stability of the sodium battery electrode slurry.

[0113] The present invention also provides a preparation method of the above-mentioned single-crystal sodium-ion battery cathode material, which includes at least two sinterings and two grindings.

[0114] In a preferred embodiment of the present invention, the above-mentioned preparation method includes the following steps:

[0115] (1) Mix the raw materials including sodium source compound, manganese source compound and iron source compound, and add the raw materials of nickel source compound and M source compound as required, and then carry out the first sintering and grinding to obtain a semi-finished product;

[0116] (2) Mix the raw materials including the semi-finished product obtained in step (1) and N source compound, and then carry out the second sintering and grinding to obtain the single-crystal sodium-ion battery cathode material.

[0117] In the above-mentioned preparation method, the first sintering in step (1) is carried out at a temperature of 860-990 °C for 6-40 hours. Preferably, the first sintering temperature is 880-980 °C; the atmosphere used for sintering is air, oxygen or a mixture of air and oxygen;

[0118] The second sintering described in step (2) is carried out at a temperature of 350 - 900 °C for 2 - 15 hours. Preferably, the temperature of the second sintering is 350 - 800 °C; the atmosphere used for sintering is air, oxygen, or a mixture of air and oxygen;

[0119] The crushing pressure in both step (1) and step (2) is 0.1 - 1 MPa.

[0120] In the above preparation method, the sodium source compound is a sodium-containing salt and / or hydroxide, such as including one or more of sodium carbonate, sodium formate, sodium hydroxide, sodium acetate, sodium chloride, and sodium fluoride.

[0121] In the above preparation method, the manganese source compound is one or more of manganese-containing oxides, hydroxides, or manganese-containing salts, such as including one or more of manganese(III) oxide, manganese(II,III) oxide, manganese(II) oxide, manganese carbonate, manganese oxalate, manganese sulfate, manganese acetate, manganese chloride, and manganese nitrate.

[0122] In the above preparation method, the nickel source compound is one or more of nickel-containing oxides, hydroxides, or nickel-containing salts, such as including one or more of nickel carbonate, nickel oxalate, nickel sulfate, nickel acetate, nickel chloride, and nickel nitrate.

[0123] In the above preparation method, the iron source compound is one or more of iron-containing oxides, hydroxides, or iron-containing salts, such as including one or more of iron(III) oxide, ferrous oxalate, ferrous sulfate, ferrous acetate, and ferrous nitrate.

[0124] In the above preparation method, the M source compound includes M element-containing oxides and / or salts, such as including one or more of calcium oxide, calcium hydroxide, boron(III) oxide, boric acid, niobium(V) oxide, aluminum oxide, titanium(IV) oxide, magnesium oxide, copper(II) oxide, yttrium(III) oxide, zirconium(IV) oxide, sodium fluoride, lithium fluoride, copper(II) oxide, zinc oxide, and copper(II) sulfate.

[0125] In the above preparation method, the N source compound includes N element-containing oxides and / or salts, such as including one or more of calcium oxide, boron(III) oxide, boric acid, niobium(V) oxide, aluminum oxide, aluminum acetate, aluminum nitrate, titanium(IV) oxide, magnesium oxide, magnesium acetate, magnesium nitrate, copper(II) oxide, yttrium(III) oxide, zirconium(IV) oxide, zirconium acetate, sodium fluoride, lithium fluoride, titanium dioxide, titanium(IV) oxide dispersion, zinc oxide, and copper(II) sulfate.

[0126] The present invention also provides a positive electrode for a sodium-ion battery, the active material of which is the above single-crystal sodium-ion positive electrode material.

[0127] The present invention also provides a sodium-ion battery, which includes the above positive electrode for a sodium-ion battery.

[0128] The sodium-ion battery of the present invention further includes a negative electrode, an electrolyte containing a sodium salt, a separator, and an aluminum-plastic film. Specifically, the positive electrode is made of a positive electrode current collector, a positive electrode active material coated on the positive electrode current collector, and materials such as a binder and a conductive additive. The positive electrode active material is the positive electrode material of the present invention. The negative electrode is a sodium metal sheet or is made of a current collector, a negative electrode active material coated on the current collector, and materials such as a binder and a conductive additive; the separator is a PP / PE film commonly used in this industry and is used to separate the positive electrode from the negative electrode; the aluminum-plastic film is an enclosure for the positive electrode, negative electrode, separator, and electrolyte.

[0129] The binder in the present invention is mainly used to improve the adhesion characteristics between the positive electrode active material particles and between the positive electrode active material particles and the current collector. The binder in the present invention can be selected from conventional binders sold on the market and used in this industry. Specifically, the binder can be selected from polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or a combination thereof.

[0130] The conductive additive in the present invention can be selected from conventional conductive additives sold on the market and used in this industry. Specifically, the conductive additive can be selected from carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, or carbon fiber), metal-based materials (such as metal powders or metal fibers including copper, nickel, aluminum, silver, etc.), conductive polymers (such as polyphenylene derivatives), or a combination thereof.

[0131] The present invention also provides the application of the above-mentioned single-crystal sodium-ion positive electrode material, or the above-mentioned sodium-ion electrode, or the above-mentioned sodium-ion battery in solar power generation, wind power generation, smart grid, distributed power station, household energy storage battery, low-end two-wheeler battery, or low-energy density power battery.

[0132] The beneficial effects of the present invention are further illustrated by specific examples below.

[0133] The raw materials or reagents used in the present invention are all purchased from mainstream manufacturers in the market. Those without indicating the manufacturer or concentration are all raw materials or reagents of analytical pure grade that can be obtained conventionally. As long as they can play the expected role, there is no special limitation. The instrument and equipment used in this example are all purchased from major manufacturers in the market. As long as they can play the expected role, there is no special limitation. For those not indicating specific techniques or conditions in this example, they are carried out according to the techniques or conditions described in the literature in this field or according to the product instructions.

[0134] The raw materials and instruments used in the following examples and comparative examples are shown in Table 1:

[0135] Table 1 Raw materials used in examples and comparative examples

[0136]

[0137]

[0138] Table 2 Equipment information used in examples

[0139]

[0140] Example 1

[0141] Weigh the corresponding weights of sodium carbonate, manganese carbonate, nickel carbonate, iron(III) oxide and boron oxide according to the molar ratio of elements Na:Mn:Ni:Fe:B = 0.87:0.33:0.33:0.33:0.01 and the total weight of 1.59 kg, and then add them to a super-high-speed multi-functional mixer and mix at a rotation speed of 4000 r / min for 20 min. Place the uniformly mixed material in a muffle furnace under an air atmosphere, keep it at a constant temperature of 870 °C for 12 hours, then cool it naturally, and pulverize it with a jet mill under a pulverizing pressure of 0.62 MPa to obtain a semi-finished product;

[0142] Weigh 1.08 kg of the above semi-finished product and 0.0097 kg of alumina, add them to a ball mill jar, ball mill at 40 Hz for 10 min, then place the uniformly mixed material in a muffle furnace under an air atmosphere, keep it at a constant temperature of 800 °C for 4 hours, then cool it naturally, and pulverize it with a jet mill under a pulverizing pressure of 0.58 MPa, and sieve it to obtain the single-crystal sodium-ion battery cathode material C1.

[0143] Characterize and analyze the above cathode material according to the following method:

[0144] 1) Composition analysis

[0145] Perform composition analysis on the above cathode material by ICP

[0146] (1) Sample pretreatment

[0147] Weigh 0.2000 - 0.2100 (accurate to 0.001 g) of the sample into a 100 mL quartz beaker, add 10 mL of aqua regia (prepared according to the volume ratio of 37 wt% concentrated hydrochloric acid and 65 wt% concentrated nitric acid of 1:1) along the wall of the beaker, cover it with a watch glass, and heat it at 180 °C for 30 min; transfer all the solution to a 50 mL volumetric flask, dilute it to the mark with deionized water and shake well; pipette 1 mL of the solution from the shaken 50 mL volumetric flask into a 100 mL volumetric flask, add 5 mL (25%) nitric acid to the volumetric flask, and dilute it to the mark with deionized water;

[0148] (2) The component analysis test is carried out using the standard curve method.

[0149] According to the above method, the chemical formula of the single-crystal sodium-ion battery cathode material C1 is found to be Na 0.87 Ni 0.32 Mn 0.32 Fe 0.3 3 B 0.01 Al 0.02 O 2

[0150] 2) Specific surface area

[0151] The specific surface area of solid substances is measured according to the gas adsorption BET method of the national standard GB / T19587-2006.

[0152] Analytical instrument: TristarⅡ3020 full-automatic specific surface area and porosity analyzer;

[0153] Test parameters: adsorbate N2, 99.999%, coolant liquid nitrogen, P0 measured actually, volume measurement mode, adsorption pressure deviation 0.05 mmHg, equilibrium time 5 s, selection of relative pressure points P / P0: 0.05; 0.1; 0.15; 0.2; 0.25; 0.30;

[0154] Sample pretreatment: Weigh the mass of the empty sample tube + stopper and record it as M1. The sample weighing amount is 3.8 - 4.2 g. Add a 3 / 8-inch specific surface tube with a 9.5-mm ball bubble. Use the FlowPrep 060 degassing station to set the temperature at 200 °C, and purge and heat the sample with inert gas for 0.5 h. Take it down and cool it to room temperature, then weigh the mass of the sample tube + stopper + sample and record it as M2. The sample mass M = M2 - M1, and record the BET value during the on-machine test. The results are shown in Table 3.

[0155] 3) Particle size

[0156] It is measured according to the laser diffraction method for particle size distribution of the national standard GB / T19077-2016, and the results are shown in Table 3.

[0157] Test instrument: Malvern, Master Size 2000 laser particle size analyzer.

[0158] Test procedure: Weigh 1 g of the powder, add it to 60 ml of pure water, ultrasonicate it externally for 5 min, pour the sample into the injector, conduct the test, and record the test data. Test conditions: The test principle is the Mie (light scattering) theory, the detection angle is 0 - 135°, the external ultrasonic intensity is 40 KHz and 180 w, the particle refractive index is 1.692, the particle absorption rate is 1, the sample test time is 6 s, the number of background test snaps is 6,000 times, and the obscuration is 8 - 12%.

[0159] 4) pH value

[0160] It was measured using a PHSJ-3F Leici pH meter, and the specific method is as follows: Accurately weigh 5 g ± 0.05 g of the sample, add deionized water according to the mass ratio of the material to water of 1:9, prepare a 10% suspension, put in a magnetic stirrer bar, place it on the tray of the magnetic stirrer, and the rotation speed of the magnetic stirrer is 880 r / min, stir for 5 min; filter the mixed solution with qualitative filter paper and a funnel, put it into a constant temperature water bath set at 25°C, and keep it at a constant temperature for filtration for 20 ± 5 min; rinse the electrode with the sample solution, and after rinsing, insert the electrode and the temperature sensor into the sample solution. When the reading is stable and the temperature shows 25°C, record the pH value. The results are shown in Table 3.

[0161] 5) XRD test

[0162] In the embodiment of the present invention, the XRD test of the sodium ion cathode material is carried out using an X'Pert PRO MPD analyzer.

[0163] Test principle: The Bragg equation reflects the relationship between the direction of the diffracted ray and the crystal structure. Diffraction must satisfy the Bragg formula: 2dsinθ = nλ (d: interplanar spacing; θ: Bragg angle; λ: wavelength of X-ray; n: reflection order). When X-rays irradiate the sample, the scattered X-rays from each atom in the crystal interfere, and strong X-ray diffracted rays will be generated in specific directions. When X-rays irradiate the sample from different angles, diffraction will occur on different crystal planes, and the detector will receive the number of diffracted photons reflected from this crystal plane, thereby obtaining a spectrum of the relationship between the angle and the intensity.

[0164] Test conditions: The X-ray tube is a Cu target, the wavelength is 1.54060, and the Be window; incident optical path: Soller slit 0.04 rad, divergence slit 1 / 2°, aperture mask 10 mm, anti-scattering slit 1°; diffraction optical path: anti-scattering slit 8.0 mm, Soller slit 0.04 rad, large Ni filter; scanning range 10 - 90°, scanning step 0.013°, dwell time per step 30.6 s, voltage 40 kV, current 40 mA.

[0165] Sample preparation of powder sample: Use a clean sampling spoon to put the powder into the groove of the glass slide (for large particle samples, they need to be ground into powder <50μm). Place one side (>20mm) of the scraping blade against the surface of the glass slide, and slightly lift the other end (the included angle <10°). Use the edge of the scraping blade to scrape the surface of the powder sample flat. Rotate the glass slide by 90°, and scrape it flat again. Scrape several times in two directions repeatedly until there are no textures on the sample surface. Remove the excess powder around the glass slide and put it into the powder X-ray diffractometer.

[0166] Sample analysis: Open the tested sample file with the analysis software High-Score Plus; first determine the background, select peak searching for peak confirmation, repeat fitting, record the grain size calculated by the Williamson-Hall plot, select the corresponding phase for phase matching and unit cell refinement, and record the full width at half maximum of the (110) diffraction peak near the diffraction angle 2θ of 64.9°. The results are shown in Table 3.

[0167] 6) Moisture

[0168] Determined by the Karl Fischer coulometric titration method with reference to GB / T 11133-2015, tested with an 899 Coulometer + 885 Compact Oven SC coulometric moisture analyzer. Weigh 0.5 - 0.8g of the sample using a moisture bottle, accurate to 0.0001g. The gas flow rate is 50 - 60ml / min, the heating temperature is 170°C, the initial drift ≤10μg / min, the final drift is 20μg / min, and the extraction time is 400s. The test results are retained to one decimal place, and the results are shown in Table 3.

[0169] 7) Powder compaction density

[0170] ① Place the sample circular mold on the workbench of the electronic pressure testing machine, and slowly manually increase the pressure to 1000kg, then zero the displacement and deformation.

[0171] ② Place the sample bag on the electronic balance, tare it, and use a spoon to add (5.0000 ± 0.1000) powder into the circular mold. After gently leveling it, place the upper gasket of the mold on the sample. Note that both gaskets need to have the non-cutting surface facing the sample to prevent the sample from overflowing.

[0172] ③ After loading the sample, place the mold on the workbench of the electronic pressure testing machine, edit the program to increase the pressure to 8000kg at a speed of 5mm / min, keep the pressure constant for 30s, and then relieve the pressure to zero.

[0173] ④ When the sample is under constant pressure of 8000 ± 10kg (about 15 - 25s after the pressure reaches 8000kg), record the sample pressure and read the sample height h, accurate to 0.001cm.

[0174] ⑤ After the reading is completed, manually lower the workbench surface of the electronic pressure testing machine, and use the extractor to take out the sample.

[0175] ⑥ After taking out the sample, clean the inside of the sample mold with lint-free paper dipped in alcohol to ensure that the inside of the mold is clean, and the experiment is completed.

[0176] ⑦ Calculate the results according to the following formula, and the results are shown in Table 3.

[0177]

[0178] In the formula:

[0179] m——mass of the sample, g;

[0180] 1.0——radius of the circular mold, cm;

[0181] h——height of the sample, cm.

[0182] Take the cathode material of the single-crystal sodium-ion battery in Example 1 for SEM testing, as Figure 1 shown. It can be seen from Figure 1 that the material is single-crystal particles, and the morphology is polygonal and lamellar.

[0183] Mix the cathode material of the single-crystal sodium-ion battery in Example 1 with the binder polyvinylidene fluoride (PVDF) and conductive carbon black (S.P) in a weight ratio of 90:5:5, stir to form a uniform slurry, coat it on the aluminum foil current collector, dry and cold press it into a pole piece, and take the pole piece for SEM testing, as Figure 9 shown. It can be seen from Figure 9 that the material is still single-crystal particles, and there are no cracks on the surface of the material particles.

[0184] Example 2

[0185] Weigh sodium carbonate, manganese carbonate, nickel carbonate, iron(III) oxide and copper oxide respectively according to the element molar ratio of Na:Mn:Ni:Fe:Cu = 0.79:0.30:0.18:0.30:0.22 and the total weight of 1.46 kg, and then add them to a super-high-speed multi-functional mixer and mix at a rotation speed of 4000 r / min for 20 min. Place the uniformly mixed material in a muffle furnace under an air atmosphere, keep it at a constant temperature of 905 °C for 12 hours, then cool it naturally, and crush it with a jet mill at a crushing pressure of 0.58 MPa to obtain a semi-finished product.

[0186] Weigh 1.08 kg of the above semi-finished product and 0.005 kg of titanium oxide, add them into a ball mill, and ball mill them at 35 Hz for 20 minutes. Then, place the evenly mixed materials in a muffle furnace under an air atmosphere at a constant temperature of 400° C. for 3 hours, then cool them naturally, and crush them with a jet mill at a crushing pressure of 0.54 MPa. Sieve them to obtain single crystal sodium ion battery positive electrode material C2.

[0187] The chemical formula of the single crystal sodium ion battery positive electrode material C2 measured by the component analysis method in Example 1 is Na 0.79 Ni 0.18 Mn 0.295 Fe 0.30 Cu 0.22 Ti 0.005 O 2 .

[0188] The positive electrode material was tested using the method in Example 1. The test results are shown in Table 3.

[0189] The single crystal sodium ion battery positive electrode material of Example 2 was subjected to SEM testing. Figure 2 As shown by Figure 2 It can be seen that the material is a single crystal particle, and the morphology is polygonal and lamellar.

[0190] The single crystal sodium ion battery positive electrode material of Example 2 was fully mixed with the binder polyvinylidene fluoride (PVDF) and the conductive carbon black (SP) in a weight ratio of 90:5:5, stirred to form a uniform slurry, coated on an aluminum foil current collector, dried and cold pressed to form a pole piece, and the pole piece was taken for SEM testing. Figure 10 As shown, from Figure 10 It can be seen that the material is still a single crystal particle and there are no cracks on the surface of the material particles.

[0191] Example 3

[0192] According to the element molar ratio of Na:Mn:Ni:Fe:Zn=0.85:0.30:0.18:0.30:0.22 and the total weight of 1.844kg, sodium carbonate, manganese trioxide, nickel oxalate, ferrous oxalate and zinc oxide were weighed respectively, and then added into the ultra-high-speed multifunctional mixer at a speed of 3500r / min and mixed for 30min. The mixed materials were placed in a muffle furnace under air atmosphere at a constant temperature of 910℃ for 10 hours, then cooled naturally, and crushed with a jet mill at a crushing pressure of 0.63MPa to obtain a semi-finished product;

[0193] Weigh 1.11 kg of the above-mentioned semi-finished product and 0.0025 kg of magnesium oxide, add them to a ball milling jar, ball mill at 45 Hz for 15 min, place the uniformly mixed material in a muffle furnace, keep it at a constant temperature of 500 °C for 5 hours in an air atmosphere, then cool it naturally, and use a jet mill to crush it at a crushing pressure of 0.56 MPa, and screen it to obtain the single-crystal sodium-ion battery cathode material C3.

[0194] Using the component analysis method in Example 1, the chemical formula of the single-crystal sodium-ion battery cathode material C3 is found to be Na 0.88 Ni 0.18 Mn 0.30 Fe 0.297 Zn 0.22 Mg 0.003 O 2 。

[0195] Using the method in Example 1 to test the above cathode material, the test results are shown in Table 3.

[0196] Take the single-crystal sodium-ion battery cathode material of Example 3 for SEM testing, as Figure 3 shown, it can be seen from Figure 3 that the material is single-crystal particles, and the morphology is polygonal and lamellar.

[0197] Mix the single-crystal sodium-ion battery cathode material of Example 3 with the binder polyvinylidene fluoride (PVDF) and conductive carbon black (S.P) in a weight ratio of 90:5:5, stir to form a uniform slurry, coat it on an aluminum foil current collector, dry and press it into a pole piece, take the pole piece for SEM testing, as Figure 11 shown, it can be seen from Figure 11 that the material is still single-crystal particles, and there are no cracks on the surface of the material particles.

[0198] Example 4

[0199] According to the element molar ratio of Na:Mn:Ni:Fe:Zn = 0.88:0.30:0.18:0.30:0.22 and the total weight of 1.844 kg, weigh sodium carbonate, manganese(III) oxide, nickel oxalate, iron(II) oxalate and zinc oxide respectively, and then add them to a super-high-speed multi-functional mixer and mix at a rotation speed of 3500 r / min for 30 min. Place the uniformly mixed material in a muffle furnace, keep it at a constant temperature of 920 °C for 15 hours in an air atmosphere, then cool it naturally, and use a jet mill to crush it at a crushing pressure of 0.68 MPa to obtain a semi-finished product.

[0200] Weigh 0.025 kg of aluminum nitrate, and prepare an aluminum nitrate solution by mixing the weighed aluminum nitrate and pure water in a mass ratio of 1:3 for standby use; weigh 1.11 kg of the above semi-finished product, add it into water and stir for 10 minutes, add the prepared aluminum nitrate solution thereto, continue stirring for 10 minutes, filter and dry; place the dried material in a muffle furnace under an air atmosphere at a constant temperature of 600°C for 6 hours, then cool naturally, and crush it with a jet mill at a crushing pressure of 0.60 MPa, sieve to obtain single crystal sodium ion battery positive electrode material C4.

[0201] The chemical formula of the single crystal sodium ion battery positive electrode material C4 measured by the component analysis method in Example 1 is Na 0.88 Ni 0.18 Mn 0.297 Fe 0.291 Zn 0.22 Al 0.012 O 2 .

[0202] The positive electrode material was tested using the method in Example 1. The test results are shown in Table 3.

[0203] The single crystal sodium ion battery positive electrode material of Example 4 was subjected to SEM testing. Figure 4 As shown by Figure 4 It can be seen that the material is a single crystal particle, and the morphology is polygonal and lamellar.

[0204] The single crystal sodium ion battery positive electrode material of Example 4 was fully mixed with the binder polyvinylidene fluoride (PVDF) and the conductive carbon black (SP) in a weight ratio of 7:2:1, stirred to form a uniform slurry, coated on an aluminum foil current collector, dried and pressed into a pole piece, and the pole piece was taken for SEM testing. Figure 12 As shown, from Figure 12 It can be seen that the material is still a single crystal particle and there are no cracks on the surface of the material particles.

[0205] Example 5

[0206] According to the element molar ratio of Na:Mn:Ni:Fe:Al=0.81:0.33:0.33:0.33:0.01 and the total weight of 1.56kg, weigh the corresponding weight of sodium carbonate, manganese carbonate, nickel carbonate, ferric oxide and aluminum oxide respectively, and then add them into the ultra-high-speed multifunctional mixer at a speed of 2800r / min and mix for 30min. Put the mixed materials in a muffle furnace under air atmosphere at a constant temperature of 930℃ for 10 hours, then cool naturally, and crush them with a jet mill at a crushing pressure of 0.65MPa to obtain a semi-finished product;

[0207] Weigh 1.068 kg of the above-mentioned semi-finished product and 0.0074 kg of boron oxide, add them to a ball mill jar, ball mill for 10 min at 40 Hz, then place the uniformly mixed material in a muffle furnace, keep it at a constant temperature of 500 °C for 3 hours in an air atmosphere, and then cool it naturally. Use an air flow pulverizer to pulverize at a pulverizing pressure of 0.56 MPa, and sieve to obtain the single-crystal sodium-ion battery cathode material C5.

[0208] Using the component analysis method in Example 1, the chemical formula of the single-crystal sodium-ion battery cathode material C5 was measured to be Na 0.81 Ni 0.33 Mn 0.33 Fe 0.31 Al 0.01 B 0.02 O 2. 。

[0209] Using the method in Example 1 to test the above cathode material, the test results are shown in Table 3.

[0210] Take the single-crystal sodium-ion battery cathode material of Example 5 for SEM testing, as Figure 5 shown, from Figure 5 it can be seen that the material is single-crystal particles, and the morphology is polygonal and lamellar.

[0211] Mix the single-crystal sodium-ion battery cathode material of Example 5 with the binder polyvinylidene fluoride (PVDF) and conductive carbon black (S.P) in a weight ratio of 7:2:1, stir to form a uniform slurry, coat it on an aluminum foil current collector, dry and press it into a pole piece, and take the pole piece for SEM testing, as Figure 13 shown, from Figure 13 it can be seen that the material is still single-crystal particles, and there are no cracks on the surface of the material particles.

[0212] Example 6

[0213] According to the element molar ratio of Na:Mn:Ni:Fe:Zn = 0.84:0.34:0.25:0.30:0.11 and the total weight of 1.77 kg, weigh sodium carbonate, manganese carbonate, nickel carbonate, ferrous oxalate and zinc oxide respectively, and then add them to a super-high-speed multi-functional mixer at a rotation speed of 3000 r / min and mix for 30 min. Place the uniformly mixed material in a muffle furnace in an air atmosphere, keep it at a constant temperature of 980 °C for 9 hours, and then cool it naturally. Use an air flow pulverizer to pulverize at a pulverizing pressure of 0.66 MPa to obtain a semi-finished product.

[0214] Weigh 1.086 kg of the above-mentioned semi-finished product and 0.048 kg of niobium pentoxide, add them to a ball mill jar, ball mill for 20 min at 40 Hz, place the uniformly mixed material in a muffle furnace under an air atmosphere, keep it at a constant temperature of 600 °C for 7 hours, then cool it naturally, and use a jet mill to crush it under a crushing pressure of 0.58 MPa, and sieve it to obtain the single-crystal sodium-ion battery cathode material C6.

[0215] Using the component analysis method in Example 1, the chemical formula of the single-crystal sodium-ion battery cathode material C6 was measured to be Na 0.84 Ni 0.25 Mn 0.34 Fe 0.295 Zn 0.11 Nb 0.005 O 2 。

[0216] Using the method in Example 1 to test the above cathode material, the test results are shown in Table 3.

[0217] Take the single-crystal sodium-ion battery cathode material of Example 6 for SEM testing, as Figure 6 shown, it can be seen from Figure 6 that the material is single-crystal particles, and the morphology is polygonal and lamellar.

[0218] Mix the single-crystal sodium-ion battery cathode material of Example 6 with the binder polyvinylidene fluoride (PVDF) and conductive carbon black (S.P) in a weight ratio of 7:2:1, stir to form a uniform slurry, coat it on an aluminum foil current collector, dry and press it into a pole piece, take the pole piece for SEM testing, as Figure 14 shown, it can be seen from Figure 14 that the material is still single-crystal particles, and there are no cracks on the surface of the material particles.

[0219] Example 7

[0220] According to the element molar ratio of Na:Mn:Fe = 0.84:0.5:0.5 and the total weight of 1.61 kg, weigh sodium carbonate, manganese carbonate, and iron(III) oxide respectively, and then add them to an ultra-high-speed multifunctional mixer at a rotation speed of 3700 r / min and mix for 25 min. Place the uniformly mixed material in a muffle furnace under an air atmosphere, keep it at a constant temperature of 875 °C for 9 hours, then cool it naturally, and use a jet mill to crush it under a crushing pressure of 0.66 MPa to obtain a semi-finished product.

[0221] Weigh 1.072 kg of the above semi-finished product and 0.045 kg of zirconium oxide, add them into a ball mill, and ball mill them at 45 Hz for 15 minutes. Put the evenly mixed materials in a muffle furnace under air atmosphere at a constant temperature of 730° C. for 7 hours, then cool them naturally, and crush them with a jet mill at a crushing pressure of 0.58 MPa. Sieve them to obtain single crystal sodium ion battery positive electrode material C7.

[0222] The chemical formula of the single crystal sodium ion battery positive electrode material C7 measured by the component analysis method in Example 1 is Na 0.84 Mn 0.497 Fe 0.5 Zr 0.003 O 2 .

[0223] The single crystal sodium ion battery positive electrode material of Example 7 was subjected to SEM testing. Figure 7 As shown by Figure 7 It can be seen that the material is a single crystal particle, and the morphology is polygonal and lamellar.

[0224] The single crystal sodium ion battery positive electrode material of Example 7 was fully mixed with the binder polyvinylidene fluoride (PVDF) and the conductive carbon black (SP) in a weight ratio of 7:2:1, stirred to form a uniform slurry, coated on an aluminum foil current collector, dried and pressed into a pole piece, and the pole piece was taken for SEM testing. Figure 15 As shown, from Figure 15 It can be seen that the material is still a single crystal particle and there are no cracks on the surface of the material particles.

[0225] Example 8

[0226] According to the element molar ratio of Na:Mn:Ni:Fe:Ti=0.91:0.1:0.42:0.32:0.16 and the total weight of 1.79kg, sodium carbonate, manganese carbonate, nickel carbonate, ferrous oxalate, and titanium dioxide were weighed respectively, and then added into the ultra-high-speed multifunctional mixer at a speed of 3300r / min and mixed for 35min. The mixed materials were placed in a muffle furnace under an oxygen atmosphere at a constant temperature of 890℃ for 10 hours, then cooled naturally, and crushed with a jet mill at a crushing pressure of 0.62MPa to obtain a semi-finished product.

[0227] Weigh 0.025 kg of aluminum nitrate, and prepare an aluminum nitrate solution by mixing the weighed aluminum nitrate with pure water in a mass ratio of 1:3 for standby use; weigh 1.072 kg of the above semi-finished product, add it into water and stir for 10 minutes, add the prepared aluminum nitrate solution thereto, continue stirring for 10 minutes, filter and dry, place the dried material in a muffle furnace under an oxygen atmosphere at a constant temperature of 550° C. for 4 hours, then cool naturally, and crush it with a jet mill at a crushing pressure of 0.60 MPa, sieve to obtain single crystal sodium ion battery positive electrode material C8.

[0228] The chemical formula of the single-crystal sodium-ion battery cathode material C8 measured by the component analysis method in Example 1 is Na 0.91 Ni 0.42 Mn 0.1 Fe 0.308 Ti 0.16 Al 0.012 O 2 .

[0229] Take the single-crystal sodium-ion battery cathode material of Example 8 for SEM testing, as Figure 8 shown. It can be seen from Figure 8 that the material is single-crystal particles, and the morphology is polygonal and lamellar.

[0230] Mix the single-crystal sodium-ion battery cathode material of Example 8 with the binder polyvinylidene fluoride (PVDF) and conductive carbon black (S.P) in a weight ratio of 7:2:1, stir to form a uniform slurry, coat it on an aluminum foil current collector, dry and press it into a pole piece, and take the pole piece for SEM testing, as Figure 16 shown. It can be seen from Figure 16 that the material is still single-crystal particles, and there are no cracks on the surface of the material particles.

[0231] Example 9

[0232] Weigh sodium carbonate, manganese(III) oxide, nickel oxalate, iron oxalate and zinc oxide according to the element molar ratio of Na:Mn:Ni:Fe:Zn = 0.88:0.30:0.18:0.30:0.22 and the total weight of 1.844 kg, and then add them to a super-high-speed multi-functional mixer and mix at a rotation speed of 3500 r / min for 30 min. Place the uniformly mixed material in a muffle furnace under an air atmosphere, keep it at 900 °C for 10 hours, then cool it naturally, and crush it with a jet mill under a crushing pressure of 0.63 MPa, and sieve it to obtain the single-crystal sodium-ion battery cathode material C9.

[0233] The chemical formula of the single-crystal sodium-ion battery cathode material C9 measured by the component analysis method in Example 1 is Na 0.88 Ni 0.18 Mn 0.30 Fe 0.30 Zn 0.22 O 2 .

[0234] Test the above cathode material by the method in Example 1, and the test results are shown in Table 3.

[0235] Take the single-crystal sodium-ion battery cathode material of Example 9 for SEM testing, as Figure 17 shown. It can be seen from Figure 17It can be seen that the material is single-crystal particles, and the morphology is polygonal and lamellar.

[0236] The single-crystal sodium-ion battery cathode material of Example 9 was fully mixed with the binder polyvinylidene fluoride (PVDF) and conductive carbon black (S.P) in a weight ratio of 7:2:1, stirred to form a uniform slurry, coated on an aluminum foil current collector, dried and pressed into a pole piece. The pole piece was taken for SEM testing, as Figure 18 shown. It can be seen from Figure 18 that the material is still single-crystal particles, and there are no cracks on the surface of the material particles.

[0237] Table 3 Performance test results of the single-crystal sodium-ion battery cathode material of the examples

[0238]

[0239]

[0240] As can be seen from Table 3, in the powder X-ray diffraction spectrum (XRD) of the single-crystal sodium-ion battery cathode materials prepared in Examples 1-8, the full width at half maximum FWHM(110) of the (110) diffraction peak near the diffraction angle 2θ of 64.9° is 0.15 - 0.27, the moisture mass content is less than or equal to 1200 ppm, the pH is less than 12.60, the specific surface area is 0.31 - 0.69 m 2 / g, the particle size D V 50 is 3.4 - 10.2 μm, and the powder tap density is 2.95 - 3.83 g / cm 3 . In Example 9, no coating treatment was carried out, the moisture mass content was 2145 ppm, far greater than 1500 ppm, and the pH was 12.92, greater than 12.6.

[0241] Experimental Example 1

[0242] Preparation and performance evaluation of sodium-ion batteries.

[0243] The CR2430 button cell was prepared according to the following method:

[0244] Cathode preparation: The single-crystal sodium-ion battery cathode materials prepared in Examples 1-9 of the present invention were respectively fully mixed with the binder polyvinylidene fluoride (PVDF) and conductive carbon black (S.P) in a weight ratio of 7:2:1, stirred to form a uniform slurry, coated on an aluminum foil current collector, dried and pressed into pole pieces, denoted as PE-C1, PE-C2, PE-C3, PE-C4, PE-C5, PE-C6, PE-C7, PE-C8 and PE-C9.

[0245] The pressed positive electrode sheet is punched, weighed, baked, and then battery assembly is carried out in a glove box under vacuum. First, place the bottom of the button cell, then put nickel foam (2.5 mm) and a negative sodium metal sheet (manufacturer: Shenzhen Youyan Technology Co., Ltd.) on the bottom of the shell. Inject 0.5 g of electrolyte in an environment with a relative humidity of less than 1.5%. The electrolyte is a mixed solvent with a mass ratio of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) of 1:1:1, and the electrolyte is a 1 mol / L sodium hexafluorophosphate solution. Place the separator and the positive electrode sheet, and then cover the shell cover of the button cell and seal it to obtain a button cell of model CR2430, denoted as BA-C1, BA-C2, BA-C3, BA-C4, BA-C5, BA-C6, BA-C7, BA-C8, and BA-C9.

[0246] The battery is subjected to performance testing on a battery testing system according to the following method, and the results are shown in Table 4;

[0247] 1) Capacity test

[0248] Connect the prepared button cell to the test rack position and start the test program. Setting steps: Set the test temperature to 25 °C, let it stand for 4 hours, charge at a constant current of 0.1C until 4.0V, pause, let it stand, and then discharge at a constant current of 0.1C until 2.0V to obtain the capacity at this current and voltage.

[0249] 2) Cycle test

[0250] Connect the battery that has undergone the above capacity test to the test rack position and start the test program. Setting steps: Set the test temperature to 45 °C, let it stand for 4 hours, charge at a constant current of 0.5C until 4.0V, then switch to constant voltage charging at 4.0V for 2h, let it stand for 5 minutes, and then discharge at a constant current of 0.5C until the cut-off voltage of 2.0V, let it stand for 5 minutes, and repeat the steps starting from constant current charging to conduct a cycle test, and the capacity retention rate at different cycle numbers can be obtained.

[0251] Table 4 Battery performance test results

[0252]

[0253] As can be seen from Table 4, for the sodium-ion batteries prepared with the single-crystal sodium-ion battery positive electrode materials obtained in Examples 1-8, the capacity at a current of 0.1C and a voltage of 4.2V (cut-off voltage of 2.0V) is 115.9 - 164.0 mAh / g, and the capacity retention rate after 50 cycles under the conditions of 4.0V - 2.0V, 0.5C / 0.5C is 80.2 - 90.5%. In Example 9, no coating treatment was carried out, and the capacity retention rate after 50 cycles under the conditions of 4.0V - 2.0V, 0.5C / 0.5C was only 74.84%. From Figure 20It can also be seen that the capacity retention rate during the cycle test of the sodium-ion battery prepared from the single-crystal sodium-ion battery cathode material prepared in Examples 1-8 is significantly better than that of Example 9.

[0254] After the battery BA-C1 was cycled 50 times, the battery was disassembled and the positive electrode sheet was taken for SEM testing. As Figure 19 shown, it can be seen from Figure 19 that after cycling, the single-crystal particles did not show particle fragmentation and were still intact particles.

[0255] The above are only the preferred embodiments of the implementation of the present invention, and do not impose any form of limitation on the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A single-crystal sodium-ion battery cathode material, characterized in that, the sodium-ion battery cathode material contains elements with the composition shown in Chemical Formula 1; The chemical formula 1 is: Na 1+a Ni 1-x-y-z-c Mn x Fe y M z N c O 2 , where, -0.40 ≤ a ≤ 0.25, 0.08 ≤ x ≤ 0.5, 0.05 ≤ y ≤ 0.5, 0 < z < 0.26, 0 < c < 0.05; M is a doping element, and N is a coating element; wherein M is Zn, and N is selected from one or two of Al or Nb elements; in the powder X-ray diffraction spectrum (XRD) of the single-crystal sodium-ion battery cathode material, the full width at half maximum FWHM(110) of the diffraction peak near the diffraction angle 2θ of 64.9°(110) is 0.08 - 0.35; the pH value of the single-crystal sodium-ion battery cathode material is within 12.6; the single-crystal sodium-ion battery cathode material is prepared by a method including the following steps: (1) Mix raw materials including a sodium source compound, a manganese source compound, and an iron source compound, and add a nickel source compound and an M source compound as needed, then perform a first sintering and air jet milling to obtain a semi-finished product; (2) Mix the semi-finished product obtained in step (1) with an N source compound and then perform a second sintering and air jet milling to obtain the single-crystal sodium-ion battery cathode material; wherein, the air jet milling pressure in both step (1) and step (2) is 0.1 - 1 MPa; the first sintering temperature in step (1) is 860 - 990 °C.

2. The single-crystal sodium-ion battery cathode material according to claim 1, characterized in that, -0.40 ≤ a ≤ 0, 0.15 ≤ x ≤ 0.5, 0.15 ≤ y ≤ 0.5; preferably 0 < z ≤ 0.

13.

3. The single-crystal sodium-ion battery cathode material according to claim 1 or 2, characterized in that, under a scanning electron microscope, the microscopic morphology of the single-crystal sodium-ion battery cathode material is a single-crystal morphology; preferably, the shape of the single-crystal morphology particles is one or more of spherical, quasi-spherical, polygonal, or lamellar.

4. The single-crystal sodium-ion battery cathode material according to any one of claims 1 to 3, characterized in that, The powder compaction density of the single-crystal sodium-ion battery cathode material is 2.8-4.2 g / cm under a pressure of 7000-9000 kg 3 ; and / or, the mass content of moisture in the single-crystal sodium-ion battery cathode material is less than 1500 ppm, preferably less than 1000 ppm, more preferably less than 900 ppm; and / or, The specific surface area of the positive electrode material of the single crystal sodium ion battery is 0.35 to 1.2 m 2 / g; and / or, The particle size D of the single crystal sodium ion battery cathode material V is 2.00 to 16.0 μm, preferably 2.50 to 12.0 μm.

5. The preparation method of the single-crystal sodium-ion battery cathode material according to any one of claims 1 to 4, characterized in that, it includes the following steps: (1) Mix raw materials including a sodium source compound, a manganese source compound, and an iron source compound, and add a nickel source compound and an M source compound as needed, then perform a first sintering and air jet milling to obtain a semi-finished product; (2) Mix the semi-finished product obtained in step (1) with an N source compound and then perform a second sintering and air jet milling to obtain the single-crystal sodium-ion battery cathode material; the air jet milling pressure in both step (1) and step (2) is 0.1 - 1 MPa; the first sintering temperature in step (1) is 860 - 990 °C.

6. The preparation method according to claim 4, characterized in that, the first sintering temperature in step (1) is 880 - 980 °C; preferably, the constant temperature time is 6 - 40 hours; and / or, the second sintering temperature in step (2) is 350 - 900 °C, preferably 350 - 800 °C; preferably, the constant temperature time is 2 - 15 hours.

7. The preparation method according to claim 5 or 6, characterized in that, the sodium source compound includes a salt and / or hydroxide containing sodium element; preferably, the sodium source compound is selected from one or more of sodium carbonate, sodium formate, sodium hydroxide, sodium acetate, sodium chloride and sodium fluoride; and / or, the manganese source compound includes one or more of an oxide, hydroxide or salt containing manganese element; preferably, the manganese source compound is selected from one or more of manganese sesquioxide, manganese tetroxide, manganese oxide, manganese carbonate, manganese oxalate, manganese sulfate, manganese acetate, manganese chloride and manganese nitrate; and / or, the nickel source compound includes one or more of an oxide, hydroxide or salt containing nickel element; preferably, the nickel source compound is selected from one or more of nickel carbonate, nickel oxalate, nickel sulfate, nickel acetate, nickel chloride and nickel nitrate; and / or, the iron source compound includes one or more of an oxide, hydroxide or salt containing iron element; preferably, the iron source compound is selected from one or more of iron(III) oxide, ferrous oxalate, ferrous sulfate, ferrous acetate and ferrous nitrate; and / or, the M source compound includes an oxide and / or salt containing M element; preferably, the M source compound includes zinc oxide; and / or, the N source compound includes an oxide and / or salt containing N element; preferably, the N source compound is selected from one or more of niobium oxide, aluminum oxide, aluminum acetate or aluminum nitrate.

8. A positive electrode for a sodium-ion battery, the active material of which is the single-crystal sodium-ion battery cathode material according to any one of claims 1 to 4 or the single-crystal sodium-ion battery cathode material prepared by the preparation method according to any one of claims 5 to 7.

9. A sodium-ion battery, characterized in that, it comprises the positive electrode for a sodium-ion battery according to claim 8.

10. The application of the single-crystal sodium-ion battery cathode material according to any one of claims 1 to 4 or the single-crystal sodium-ion battery cathode material prepared by the preparation method according to any one of claims 5 to 7, or the sodium-ion battery electrode according to claim 8, or the sodium-ion battery according to claim 9 in solar power generation, wind power generation, smart grid, distributed power station, household energy storage battery, low-end two-wheeler battery or low-energy density power battery.

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