A single-crystal sodium-ion battery positive electrode active material, a preparation method therefor, and use thereof

Abstract

The application discloses a preparation method of a single-crystal sodium-ion battery positive electrode material, and the single-crystal sodium-ion battery positive electrode active material comprises sodium, M metal, boron and oxygen elements, and the preparation method comprises the following steps: adding water into a compound containing M elements, a compound containing boron elements and a sodium source to prepare a slurry, sand grinding to obtain a mixed slurry, and spray drying and sintering the mixed slurry to obtain the single-crystal sodium-ion battery positive electrode active material. The preparation method can be suitable for a wide variety of raw materials, can efficiently realize mixing and uniformity of a plurality of raw materials at a nanometer level, and can form a perfect layered O3 phase structure after sintering of the mixed slurry, so that the prepared single-crystal sodium-ion battery positive electrode material has excellent electrochemical performance and cycle performance when used in a sodium-ion battery.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion batteries, specifically relating to a method for preparing a positive electrode active material for a single-crystal sodium-ion battery. Background Technology

[0002] Due to the large radius of sodium ions, the selection of cathode active materials for sodium-ion batteries is relatively limited. Currently, the cathode active materials for sodium-ion batteries that have shown potential application prospects include three types of systems: Prussian blue, layered oxides, and polyanionic compounds. Among them, the O3 phase structure layered oxide system, similar to the ternary cathode active materials in lithium-ion batteries, has advantages such as high capacity and high compaction density, and is considered the most promising cathode material, adopted by sodium-ion battery companies both domestically and internationally.

[0003] Currently, the active materials for the positive electrode of oxide-based sodium-ion batteries are mainly secondary spherical particles. For example, Chinese patent CN110416521A discloses a magnesium-doped ternary positive electrode material for sodium-ion batteries and its preparation method. The preparation method includes: Step 1: Weighing 112 parts by weight of sodium carbonate, 40-50 parts by weight of nickel monoxide, 54 parts by weight of ferric oxide, 48 parts by weight of manganese monoxide, and 0.1-5.6 parts by weight of magnesium oxide, adding them to 610 parts by weight of deionized water, stirring, and obtaining a mixture; Step 2: Adding the mixture obtained in Step 1) to a nano-ball mill and ball milling for 20-80 minutes, removing the slurry and spray drying it at 80-120℃ to obtain precursor powder; Step 3: Calcining the precursor powder obtained in Step 2 at 750-1000℃ for 9-15 hours in air atmosphere at a rate of 2-5℃ / min, and then cooling it to room temperature to obtain the magnesium-doped ternary positive electrode material for sodium-ion batteries. (See this patent...) Figure 2 As shown, the method yields a fluffy secondary spherical structure with a secondary particle size of about 8 micrometers and a primary particle size of only 0.15-0.4 micrometers. This type of spherical structure is prone to crushing, has low compaction density, and a large specific surface area. During battery cycling, there are many side reactions between the positive electrode material and the electrolyte, resulting in more gas production and poor battery cycle performance and safety performance.

[0004] Chinese patent CN113471431A discloses a NaMn 0.5 Ni 0.5 B xThis O2 sodium-ion battery cathode material possesses a composite phase of P2 and O3 phases and exhibits a relatively dense secondary spherical morphology. Its preparation method is as follows: materials containing sodium, manganese, nickel, and boron sources are mixed in a molar ratio of Na:Mn:Ni:B of (1–1.05):0.5:0.5:x to obtain a mixture; the mixture is then heat-treated at 800–900°C in an oxygen-containing atmosphere to obtain the cathode material. Although this cathode material uses an O3 phase to improve the P2 phase, resulting in enhanced electrochemical performance compared to P2 phase materials, the patented method cannot produce a pure O3 phase material, and the corresponding electrochemical performance of the material requires further improvement.

[0005] The traditional secondary spherical particle structure mentioned above also has the following problems: 1. The particle structure has poor mechanical strength, which can easily lead to the breakage of the secondary spheres during the compaction of the electrode, affecting the compaction density and cycle performance of the electrode; 2. The active material has a large contact surface area with the electrolyte, which leads to an increase in side reactions and affects cycle performance and safety performance.

[0006] In response, engineers have focused on preparing oxide-based sodium-ion battery cathode active materials into single-crystal morphologies. For example, Chinese patent CN109817970A discloses a method for preparing single-crystal sodium-ion battery electrode materials. This method involves mixing and reacting a mixed aqueous solution of iron salt, manganese salt, and M salt with a precipitant, complexing agent, and dispersant to obtain a solid as the battery electrode material precursor. The precursor is then mixed with sodium salt, sintered, and cooled to obtain the single-crystal sodium-ion battery electrode material. The dispersant used is ammonium polyacrylate. However, in large-scale production, this method is prone to problems such as excessively low solubility product constants of iron salts, which tend to precipitate before other metals, leading to uneven distribution of the co-precipitated material and directly affecting electrochemical performance. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings and deficiencies of existing technologies by providing a method for preparing monocrystalline sodium-ion battery positive electrode active materials. This method can stably prepare monocrystalline sodium-ion battery positive electrode active materials with high compaction density, small specific surface area, and excellent electrochemical performance on a large scale.

[0008] To solve the above technical problems, the present invention adopts the following technical solution:

[0009] A method for preparing a single-crystal sodium-ion battery positive electrode active material, wherein the single-crystal sodium-ion battery positive electrode active material comprises sodium, M metal, boron and oxygen elements, the preparation method comprising the steps of adding water to a compound containing M element, a compound containing boron element and a sodium source to form a slurry and milling it to obtain a mixed slurry, and the steps of spray drying the mixed slurry and sintering it to obtain the single-crystal sodium-ion battery positive electrode active material.

[0010] According to some preferred and specific aspects of the present invention, the chemical formula of the single-crystal sodium-ion battery positive electrode active material is Na. x M y B z O2, where M is one or more combinations selected from Li, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Nb, Mo, Ru, In, Sn, Sb, W, Ta, Ba, Bi, La, Ce, Eu, 0.80≤x≤1.40, 0.6≤y≤0.9999, 0.0001≤z≤0.4.

[0011] Preferably, the chemical formula Na x M y B z In O2, 0.95≤x≤1.05, 0.8≤y≤0.9999, and 0.0001≤z≤0.2.

[0012] More preferably, the chemical formula Na x M y B z In O2, 0.98≤x≤1.04, 0.9≤y≤0.9999, 0.0001≤z≤0.1.

[0013] In some specific embodiments of the present invention, M is selected from one or more combinations of Fe, Ni, Mn, Cu, and Ti.

[0014] In some specific embodiments of the present invention, the compound containing element M is selected from one or more combinations of oxides, hydroxides, carbonates, oxalates, and nitrates of element M.

[0015] Furthermore, the compound containing element M is selected from one or more combinations of nickel manganese hydroxide, ferric oxide, titanium dioxide, nickel oxide, and manganese dioxide.

[0016] In some specific embodiments of the present invention, the boron-containing compound is selected from one or more combinations of boron oxide, boric acid, borates, borohydrides, boron trihalides, trifluoroboric acid, borate esters, boranes, and metal borides.

[0017] Furthermore, the boron-containing compound is selected from boric acid and boron oxide, or a combination of both.

[0018] In some specific embodiments of the present invention, the sodium source is selected from one or more combinations of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, sodium peroxide, sodium nitrate, sodium acetate, and sodium oxalate.

[0019] Furthermore, the sodium source is selected from one or more combinations of sodium carbonate, sodium bicarbonate, and sodium hydroxide.

[0020] In some specific embodiments of the present invention, the molar ratio of the compound containing element M, the compound containing element boron, and the sodium source is (0.6-0.9999):(0.4-0.0001):(0.80-1.40).

[0021] More preferably, the molar ratio of the compound containing element M, the compound containing element boron, and the sodium source is (0.9–0.9999):(0.1–0.0001):(0.90–1.10).

[0022] Furthermore, the molar ratio of the compound containing element M, the compound containing element boron, and the sodium source is 0.95:0.05:1.0.

[0023] In some specific embodiments of the present invention, the grinding time is 0.6 to 7.8 hours.

[0024] Furthermore, the grinding time is 1 to 4 hours.

[0025] In some specific embodiments of the present invention, the grinding media of the sand mill is zirconia balls with a particle size of 0.1 to 0.8 mm.

[0026] In some specific embodiments of the present invention, the grinding speed is 800 to 3000 rpm.

[0027] Furthermore, the grinding speed is 1500–2500 rpm.

[0028] In some specific embodiments of the present invention, the solid content of the mixed slurry is 10% to 60%.

[0029] Furthermore, the solid content of the mixed slurry is 20-40%.

[0030] In some specific embodiments of the present invention, the median particle size of the particles in the mixed slurry is 20–800 nm.

[0031] In some specific embodiments of the present invention, the mixed slurry is pulverized after sintering.

[0032] Furthermore, during the spray drying process, the atomizing disc rotates at 1000–3000 rpm, the inlet air temperature is 150–300°C, and the outlet air temperature is 80–120°C.

[0033] In some specific embodiments of the present invention, the sintering is carried out in air at a temperature of 750–1100°C for a time of 5–25 hours.

[0034] Furthermore, the sintering temperature is 850–1000°C, and the time is 8–16 hours.

[0035] In the preparation method of this invention, sand milling is used when preparing the mixed slurry. This can process water-soluble substances, achieving uniform mixing at the molecular level; it can also process water-insoluble raw materials, achieving uniform mixing at the nanoscale between insoluble substances; and it can also process uniform mixing at the nanoscale between water-soluble and water-insoluble raw materials. Sand milling ensures uniform mixing of raw materials at the nanoscale, and a cathode material with excellent electrochemical activity can be stably obtained during high-temperature sintering. In addition, by adding a boron-containing compound to the raw materials, the nanoscale primary particles rapidly fuse and coalesce during high-temperature sintering, resulting in a single-crystal sodium-ion battery cathode active material of about 1-30 micrometers. This material is not in a loose state, therefore it has a high compaction density, which can significantly reduce the side reactions between the cathode material and the electrolyte. Moreover, by controlling the boron content in the single-crystal cathode active material, the particle size of the single-crystal particles of the cathode active material can be controlled. Sand milling and the addition of a boron-containing compound also have a synergistic effect; both are indispensable for preparing a perfect single-crystal cathode active material.

[0036] In addition, the present invention can also spray dry the mixed slurry. The spray drying method can maintain the uniform distribution of various raw materials in the uniformly mixed slurry during the drying process, and ensure that the various raw materials do not segregate during the molding process.

[0037] The present invention further provides a single-crystal sodium-ion battery positive electrode active material prepared by the aforementioned preparation method, which has a single-crystal structure and an average particle size D. 50 Its size is 1-30 micrometers, and its compacted density is 2.8-3.6 g / cm³. 3 Its specific surface area is 0.2–1.0 m². 2 / g.

[0038] The present invention further provides the application of monocrystalline sodium-ion battery positive electrode active material in sodium-ion battery positive electrode.

[0039] When this monocrystalline sodium-ion battery positive electrode active material is applied to the positive electrode of a sodium-ion battery, the resulting sodium-ion battery has an initial coin cell capacity of 123-130 mAh / g at 0.1C and 25℃, an initial coin cell capacity of 117-127 mAh / g at 1C and 60℃ for one week, and an initial coin cell capacity of 100-120 mAh / g at 1C and 60℃ for 100 weeks. That is, the cycle retention rate after 100 cycles at a high temperature of 60℃ is 84%-92%.

[0040] Compared with the prior art, the present invention has the following technical advantages:

[0041] The preparation method of the present invention can be applied to a wide range of raw materials, and can efficiently achieve uniform mixing of multiple raw materials at the nanoscale. After sintering, the mixed slurry can form a perfect layered O3 phase structure.

[0042] By doping boron into the sand milling process, large single crystals can be prepared, overcoming the shortcomings of existing technologies where the raw material particles are too fine, resulting in a very loose and large specific surface area of ​​the sintered material. This leads to low compaction density of the positive electrode active material during electrode fabrication, and numerous side reactions and gas generation between the positive electrode material and the electrolyte during battery cycling, resulting in poor battery cycle performance and safety. This invention, by controlling the boron content in the single-crystal positive electrode active material, can produce single-crystal particles in the 1-30 micrometer range. These particles possess stable surface properties, exhibit fewer side reactions with the electrolyte, and when used in sodium-ion batteries, can significantly improve high-temperature cycle performance while maintaining a high specific capacity. Attached Figure Description

[0043] Figure 1 NaNi prepared in Example 1 0.32 Fe 0.33 Mn 0.32 B 0.03 Scanning electron microscope image of O2;

[0044] Figure 2 NaNi prepared in Example 1 0.32 Fe 0.33 Mn 0.32 B 0.03 XRD pattern of O2;

[0045] Figure 3 NaNi prepared in Example 1 0.32 Fe 0.33 Mn 0.32 B 0.03 Charge and discharge curves of O2.

[0046] Figure 4 NaNi prepared in Example 2 0.31 Fe 0.33 Mn 0.31 B 0.05 Scanning electron microscope image of O2;

[0047] Figure 5 NaNi prepared in Example 2 0.31 Fe 0.33 Mn 0.31 B 0.05 XRD pattern of O2;

[0048] Figure 6 NaNi prepared in Example 2 0.31 Fe 0.33Mn 0.31 B 0.05 Charge and discharge curves of O2;

[0049] Figure 7 NaNi prepared in Example 2 0.31 Fe 0.33 Mn 0.31 B 0.05 O2 cycling diagram at 2.0–4.0V / 1C high temperature (60℃).

[0050] Figure 8 NaNi prepared in Example 4 0.25 Fe 0.40 Mn 0.25 Ti 0.05 B 0.05 Scanning electron microscope image of O2;

[0051] Figure 9 NaNi prepared in Example 4 0.25 Fe 0.40 Mn 0.25 Ti 0.05 B 0.05 XRD pattern of O2;

[0052] Figure 10 NaNi prepared in Example 4 0.25 Fe 0.40 Mn 0.25 Ti 0.05 B 0.05 Charge and discharge curves of O2;

[0053] Figure 11 NaNi prepared in Example 4 0.25 Fe 0.40 Mn 0.25 Ti 0.05 B 0.05 O2 cycling diagram at 2.0–4.0V / 1C high temperature (60℃).

[0054] Figure 12 NaNi prepared for Comparative Example 1 1 / 3 Fe 1 / 3 Mn 1 / 3 Scanning electron microscope image of O2;

[0055] Figure 13 NaNi prepared for Comparative Example 1 1 / 3 Fe 1 / 3 Mn 1 / 3 XRD pattern of O2;

[0056] Figure 14 NaNi prepared for Comparative Example 1 1 / 3 Fe 1 / 3Mn 1 / 3 Charge and discharge curves of O2;

[0057] Figure 15 NaNi prepared for Comparative Example 1 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 cycling diagram at 2.0–4.0V / 1C high temperature (60℃).

[0058] Figure 16 NaNi prepared for Comparative Example 2 0.32 Fe 0.33 Mn 0.32 B 0.03 Scanning electron microscope image of O2;

[0059] Figure 17 NaNi prepared for Comparative Example 2 0.32 Fe 0.33 Mn 0.32 B 0.03 XRD pattern of O2;

[0060] Figure 18 NaNi prepared for Comparative Example 2 0.32 Fe 0.33 Mn 0.32 B 0.03 Charge and discharge curves of O2. Detailed Implementation

[0061] To better understand the content of this invention, further description is provided below with reference to specific embodiments and accompanying drawings. It should be understood that these embodiments are only for further illustration of the invention and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the content of this invention, any improvements and adjustments made to this invention by those skilled in the art without departing from the principles of the invention are still within the protection scope of this invention. Unless otherwise specified, all raw materials described below are commercially available.

[0062] In the following examples and comparative examples, the charge-discharge curves and high-temperature cycling performance were tested using the following methods: First, a sodium-ion battery was prepared: 20g of the prepared positive electrode active material was weighed, and 0.64g of conductive agent SP and 0.64g of PVDF dissolved in NMP were added. After mixing evenly, the mixture was coated onto aluminum foil to form an electrode sheet. In a glove box under an argon atmosphere, a button cell was assembled using a sodium metal sheet as the negative electrode, Celgard 2700 as the separator, and 1mol / L NaPF6+EC:DEC(1:1)+5%FEC as the electrolyte. Then, the charge-discharge curves were tested at a voltage range of 2.0-4.0V, a charge-discharge rate of 0.1C, a current of 13mA, and a test temperature of 25±2℃. The cycling performance was tested for 100 cycles at a voltage range of 2.0-4.0V, a charge-discharge rate of 1C, a current of 130mA, and a test temperature of 60℃.

[0063] Example 1

[0064] This embodiment provides a sodium-ion battery positive electrode active material with the chemical formula NaNi. 0.32 Fe 0.33 Mn 0.32 B 0.03 O2, the preparation method includes the following steps:

[0065] (1) Take 3.2 mol of Ni 0.5 Mn 0.5 (OH)2, 0.825 mol Fe2O3, 0.15 mol H3BO3, and 2.5 mol Na2CO3 were added to 3.5 L of water to prepare a slurry.

[0066] (2) Add the slurry obtained in step (1) to a sand mill and grind for 3 hours. The grinding media are zirconia balls with a particle size of 0.2 mm. The sand milling speed is 2500 rpm. Grind to obtain a mixed slurry with an average particle size of about 350 nm.

[0067] (3) The mixed slurry obtained in step (2) is transferred into a mixing tank and stirred thoroughly. Pure water is added to adjust the slurry to a solid content of 30±1%. The slurry is spray-dried under the conditions of atomization frequency of 35Hz, air inlet temperature of 190℃ and air outlet temperature of 85℃ in a spray drying equipment. After drying, the product is sintered in an air atmosphere furnace at 850~1000℃ for 12 hours, cooled to below 80℃, crushed by jaw crusher, roller crusher and pulverizer to obtain sodium-ion battery positive electrode active material, sample name NFM-B1.

[0068] Scanning electron microscope image of NFM-B1 as follows Figure 1 As shown, the material exhibits a single-crystal morphology. The XRD pattern of NFM-B1 is shown below. Figure 2As shown, this material exhibits a pure-phase layered structure of α-NaFeO2. The charge-discharge curves of NFM-B1 are shown below. Figure 3 As shown, within the voltage window of 2.0 to 4.0 V, the discharge specific capacity at a 0.1C rate is 128.8 mAh / g.

[0069] Example 2

[0070] This embodiment provides a sodium-ion battery positive electrode active material with the chemical formula NaNi. 0.31 Fe 0.33 Mn 0.31 B 0.05 O2, the preparation method includes the following steps:

[0071] (1) Take 3.1 mol of Ni 0.5 Mn 0.5 (OH)2, 0.825 mol Fe2O3, 0.25 mol H3BO3, and 2.5 mol Na2CO3 were added to 3.5 L of water to prepare a slurry.

[0072] (2) Add the slurry obtained in step (1) to a sand mill and grind for 3 hours. The grinding media are zirconia balls with a particle size of 0.2 mm. The sand milling speed is 2500 rpm. Grind to obtain a mixed slurry with an average particle size of about 350 nm.

[0073] (3) The mixed slurry obtained in step (2) is transferred into a mixing tank and stirred thoroughly. Pure water is added to adjust the slurry to a solid content of 30±1%. The slurry is spray-dried under the conditions of atomization frequency of 35Hz, air inlet temperature of 190℃ and air outlet temperature of 85℃ in a spray drying equipment. After drying, the product is sintered in an air atmosphere furnace at 850~1000℃ for 12 hours, cooled to below 80℃, crushed by jaw crusher, roller crusher and pulverizer to obtain sodium-ion battery positive electrode active material, sample name NFM-B2.

[0074] Scanning electron microscope image of NFM-B2 as follows Figure 4 As shown, the material exhibits a single-crystal morphology. The XRD pattern of NFM-B2 is shown below. Figure 5 As shown, this material exhibits a pure-phase layered structure of α-NaFeO2. The charge-discharge curves of NFM-B2 are shown below. Figure 6 As shown, within a voltage window of 2.0–4.0 V, the discharge specific capacity at a 0.1C rate is 129.1 mAh / g. The high-temperature cycling curve of NFM-B2 is shown below. Figure 7 As shown, within a voltage window of 2.0 to 4.0 V at 60℃ and a 1C rate, the capacity retention rate is 90.9% after 100 cycles.

[0075] Example 3

[0076] This embodiment provides a sodium-ion battery positive electrode active material with the chemical formula NaNi. 0.31 Fe 0.33 Mn 0.31 B 0.05 O2, the preparation method includes the following steps:

[0077] (1) Take 1.55 mol of NiO, 1.55 mol of MnO2, 0.825 mol of Fe2O3, 0.25 mol of H3BO3, and 2.5 mol of Na2CO3, and add all raw materials to 3.5 L of water to make a slurry;

[0078] (2) Add the slurry obtained in step (1) to a sand mill and grind for 3 hours. The grinding media are zirconia balls with a particle size of 0.2 mm. The sand milling speed is 2500 rpm. Grind to obtain a mixed slurry with an average particle size of about 350 nm.

[0079] (3) The mixed slurry obtained in step (2) is transferred into a mixing tank and stirred thoroughly. Pure water is added to adjust the slurry to a solid content of 30±1%. The slurry is spray-dried under the conditions of atomization frequency of 35Hz, air inlet temperature of 190℃ and air outlet temperature of 85℃ in a spray drying equipment. After drying, the product is sintered in an air atmosphere furnace at 850~1000℃ for 12 hours, cooled to below 80℃, crushed by jaw crusher, roller crusher and pulverizer to obtain sodium-ion battery positive electrode active material, sample name NFM-B3.

[0080] Example 4

[0081] This embodiment provides a sodium-ion battery positive electrode active material with the chemical formula NaNi. 0.25 Fe 0.40 Mn 0.25 Ti 0.05 B 0.05 O2, the preparation method includes the following steps:

[0082] (1) Take 2.5 mol of Ni 0.5 Mn 0.5 (OH)2, 1 mol Fe2O3, 0.25 mol TiO2, 0.25 mol H3BO3, and 2.5 mol Na2CO3 were added to 3.5 L of water to prepare a slurry.

[0083] (2) Add the slurry obtained in step (1) to a sand mill and grind for 3 hours. The grinding media are zirconia balls with a particle size of 0.2 mm. The sand milling speed is 2500 rpm. Grind to obtain a mixed slurry with an average particle size of about 350 nm.

[0084] (3) The mixed slurry obtained in step (2) is transferred into a mixing tank and stirred thoroughly. Pure water is added to adjust the slurry to a solid content of 30±1%. The slurry is spray-dried under the conditions of atomization frequency of 35Hz, air inlet temperature of 190℃ and air outlet temperature of 85℃ in a spray drying equipment. After drying, the product is sintered in an air atmosphere furnace at 850~1000℃ for 12 hours, cooled to below 80℃, crushed by jaw crusher, roller crusher and pulverizer to obtain sodium-ion battery positive electrode active material, sample name NFM-TB1.

[0085] Scanning electron microscope image of NFM-TB1 as follows Figure 8 As shown, the material exhibits a single-crystal morphology. The XRD pattern of NFM-TB1 is shown below. Figure 9 As shown, this material exhibits a pure-phase layered structure of α-NaFeO2. The charge-discharge curves of NFM-TB1 are shown below. Figure 10 As shown, within a voltage window of 2.0–4.0 V, the discharge specific capacity at a 0.1C rate is 124.8 mAh / g. The high-temperature cycling curve of NFM-TB1 is shown below. Figure 11 As shown, within a voltage window of 2.0 to 4.0 V at 60℃ and a 1C rate, the capacity retention rate is 89.04% after 100 cycles.

[0086] Example 5

[0087] This embodiment provides a sodium-ion battery positive electrode active material with the chemical formula NaNi. 0.25 Fe 0.40 Mn 0.25 Ti 0.05 B 0.05 O2, the preparation method includes the following steps:

[0088] (1) Take 1.25 mol of NiO, 1.25 mol of MnO2, 1 mol of Fe2O3, 0.25 mol of TiO2, 0.25 mol of H3BO3, and 2.5 mol of Na2CO3, and add all raw materials to 3.5 L of water to make a slurry;

[0089] (2) Add the slurry obtained in step (1) to a sand mill and grind for 3 hours. The grinding media are zirconia balls with a particle size of 0.2 mm. The sand milling speed is 2500 rpm. Grind to obtain a mixed slurry with an average particle size of about 350 nm.

[0090] (3) The mixed slurry obtained in step (2) is transferred into a mixing tank and stirred thoroughly. Pure water is added to adjust the slurry to a solid content of 30±1%. The slurry is spray-dried under the conditions of atomization frequency of 35Hz, air inlet temperature of 190℃ and air outlet temperature of 85℃ in a spray drying equipment. After drying, the product is sintered in an air atmosphere furnace at 850~1000℃ for 12 hours, cooled to below 80℃, crushed by jaw crusher, roller crusher and pulverizer to obtain sodium-ion battery positive electrode active material, sample name NFM-TB2.

[0091] Example 6

[0092] This embodiment provides a sodium-ion battery positive electrode active material with the chemical formula NaNi. 0.25 Fe 0.40 Mn 0.30 B 0.05 O2, the preparation method includes the following steps:

[0093] (1) Take 1.25 mol of NiO, 1.50 mol of MnO2, 1 mol of Fe2O3, 0.25 mol of H3BO3, and 2.5 mol of Na2CO3, and add all raw materials to 3.5 L of water to make a slurry;

[0094] (2) Add the slurry obtained in step (1) to a sand mill and grind for 3 hours. The grinding media are zirconia balls with a particle size of 0.2 mm. The sand milling speed is 2500 rpm. Grind to obtain a mixed slurry with an average particle size of about 350 nm.

[0095] (3) The mixed slurry obtained in step (2) is transferred into a mixing tank and stirred thoroughly. Pure water is added to adjust the slurry to a solid content of 30±1%. The slurry is spray-dried under the conditions of atomization frequency of 35Hz, air inlet temperature of 190℃ and air outlet temperature of 85℃ in a spray drying equipment. After drying, the product is sintered in an air atmosphere furnace at 850~1000℃ for 12 hours, cooled to below 80℃, crushed by jaw crusher, roller crusher and pulverizer to obtain sodium-ion battery positive electrode active material, sample name NFM-B4.

[0096] Comparative Example 1

[0097] This embodiment provides a sodium-ion battery positive electrode active material with the chemical formula NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, the preparation method includes the following steps:

[0098] (1) Take 3.33 mol of Ni 0.5 Mn 0.5 (OH)2, 0.835 mol Fe2O3, and 2.5 mol Na2CO3 were added to 3.5 L of water to prepare a slurry.

[0099] (2) Add the slurry obtained in step (1) to a sand mill and grind for 3 hours. The grinding media are zirconia balls with a particle size of 0.2 mm. The sand milling speed is 2500 rpm. Grind to obtain a mixed slurry with an average particle size of about 350 nm.

[0100] (3) The mixed slurry obtained in step (2) is transferred into a mixing tank and stirred thoroughly. Pure water is added to adjust the slurry to a solid content of 30±1%. The slurry is spray-dried under the conditions of atomization frequency of 35Hz, air inlet temperature of 190℃ and air outlet temperature of 85℃ in a spray drying equipment. After drying, the product is sintered in an air atmosphere furnace at 850~1000℃ for 12 hours, cooled to below 80℃, crushed by jaw crusher, roller crusher and pulverizer to obtain sodium-ion battery positive electrode active material, sample name NFM-1.

[0101] Scanning electron microscope image of NFM-1 as follows Figure 12 As shown, the material appears to be a loose, secondary granular sphere, with primary particles within the spheres approximately 0.5 micrometers in size. The XRD pattern of NFM-1 is shown below. Figure 13 As shown, this material exhibits a pure-phase layered structure of α-NaFeO2. The charge-discharge curves of NFM-1 are shown below. Figure 14 As shown, within a voltage window of 2.0–4.0 V, the discharge specific capacity at a 0.1C rate is 125.0 mAh / g. The high-temperature cycling curve of NFM-1 is shown below. Figure 15 As shown, within a voltage window of 2.0 to 4.0 V at 60℃ and a 1C rate, the capacity retention rate is 83% after 100 cycles.

[0102] Comparative Example 2

[0103] This embodiment provides a sodium-ion battery positive electrode active material with the chemical formula NaNi. 0.32 Fe 0.33 Mn 0.32 B 0.03 O2, the preparation method includes the following steps:

[0104] (1) Add nickel sulfate, ferrous sulfate and manganese sulfate to pure water at a molar ratio of Ni:Fe:Mn = 1:1:1 to prepare a solution with a total metal element concentration of 1.3 mol / L;

[0105] (2) Prepare a 4.0 mol / L sodium hydroxide solution and a 5.0 mol / L ammonia solution;

[0106] (3) The metal salt solution obtained in step (1) and the sodium hydroxide solution and ammonia solution obtained in step (2) are added to the reactor at rates of 2.5 L / h, 1.5 L / h and 0.2 L / h, respectively. The reaction temperature is controlled at 50℃, the reaction pH is 11.5, the stirring speed is 650 rpm, and the precursor is obtained after 12 h of reaction.

[0107] (4) The above precursor was washed with pure water, filtered, and dried to obtain Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2;

[0108] (5) The precursor, boric acid and sodium carbonate are mixed and ground. The total amount of metal elements in the precursor and the molar ratio of boron to sodium in sodium carbonate are 0.97:0.03:1. Then, the mixture is sintered in an air atmosphere furnace at 850-1000℃ for 12 hours, cooled to below 80℃, crushed by jaw crusher, roller crusher and pulverizer to obtain sodium-ion battery positive electrode active material. The sample name is NFM-B5.

[0109] In this preparation method, no water is added during the grinding of the precursor, it is not made into a mixed slurry, and it is not spray-dried before sintering.

[0110] Scanning electron microscope image of NFM-B5 as follows Figure 16 As shown, the material exhibits an irregularly shaped, single-crystal-like structure. The XRD pattern of NFM-B5 is shown below. Figure 17 As shown, this material has a composite phase structure of P2 and O3. The charge-discharge curves of NFM-B5 are shown below. Figure 18 As shown, within the voltage window of 2.0 to 4.0 V, the discharge specific capacity at a 0.1C rate is 115.2 mAh / g.

[0111] Performance testing

[0112] The physicochemical properties of the positive electrode active materials prepared in Examples 1-6 and Comparative Examples 1-2 were tested, and the results are shown in Table 1 below.

[0113] Table 1. Physical properties of positive electrode active materials

[0114]

[0115] The positive electrode active materials prepared in Examples 1-6 and Comparative Examples 1-2 were used for performance testing of sodium-ion batteries. The sodium-ion battery was prepared as follows: 20g of the prepared positive electrode active material was weighed, and 0.64g of conductive agent SP and 0.64g of PVDF dissolved in NMP were added. After mixing evenly, the mixture was coated onto aluminum foil to form an electrode sheet. In a glove box under an argon atmosphere, a button cell was assembled using a sodium metal sheet as the negative electrode, Celgard 2700 as the separator, and 1mol / L NaPF6+EC:DEC(1:1)+5%FEC as the electrolyte. The test voltage range was 2.0–4.0V, and the 0.1C current was 13mA. The test results are shown in Table 2 below.

[0116] Table 2. Performance of sodium-ion batteries

[0117]

[0118]

[0119] As shown in Tables 1-2 above, the present invention achieves a perfect layered single-crystal structure of positive electrode active material by adding water to the precursor during grinding to form a mixed slurry, spray drying before sintering, and adding boron-containing compounds to the raw materials. The single crystal particles are large and densely grown, the compaction density of the positive electrode active material is significantly improved, and the specific surface area is reduced. When this positive electrode active material is used in sodium-ion batteries, it can significantly improve the cycle performance at high temperatures while ensuring a high specific capacity.

[0120] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a single-crystal sodium-ion battery positive electrode active material, characterized in that: The preparation method includes the steps of adding water to a compound containing element M, a compound containing element boron, and a sodium source to form a slurry and milling it to obtain a mixed slurry, and then spray-drying and sintering the mixed slurry to obtain the monocrystalline sodium-ion battery positive electrode active material; the chemical formula of the monocrystalline sodium-ion battery positive electrode active material is Na. x M y B z O2, where M is one or more combinations selected from Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Nb, Sn, Sb, W, Ba, Bi, and La, 0.95≤x≤1.05, 0.8≤y≤0.9999, and 0.03≤z≤0.

2.

2. The preparation method according to claim 1, characterized in that: The compound containing element M is selected from one or more combinations of oxides, hydroxides, carbonates, oxalates, and nitrates of element M.

3. The preparation method according to claim 1, characterized in that: The boron-containing compound is selected from one or more combinations of boron oxide, boric acid, borates, borohydrides, boron trihalides, trifluoroboric acid, borate esters, boranes, and metal borides.

4. The preparation method according to claim 1, characterized in that: The sodium source is selected from one or more combinations of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, sodium peroxide, sodium nitrate, sodium acetate, and sodium oxalate.

5. The preparation method according to claim 1, characterized in that: The molar ratio of the compound containing element M, the compound containing element boron, and the sodium source is (0.8~0.9999): (0.03~0.2): (0.95~1.05).

6. The preparation method according to claim 1, characterized in that: The grinding time is 0.6 to 7.8 hours; and / or the grinding media of the sand mill is zirconia balls with a particle size of 0.1 to 0.8 mm.

7. The preparation method according to claim 1, characterized in that: The grinding speed is 800~3000 rpm.

8. The preparation method according to claim 1, characterized in that: The solid content of the mixed slurry is 10% to 60%; and / or the median particle size of the particles in the mixed slurry is 20 to 800 nm.

9. The preparation method according to claim 1, characterized in that: During the spray drying process, the atomizing disc rotates at 1000~3000 rpm, the inlet air temperature is 150~300℃, and the outlet air temperature is 80~120℃.

10. The preparation method according to claim 1, characterized in that: The sintering is carried out in air at a temperature of 750-1100°C for 5-25 hours; and / or the mixed slurry is pulverized after sintering.

11. A single-crystal sodium-ion battery positive electrode active material prepared by the preparation method according to any one of claims 1 to 10, characterized in that: The microstructure of the single-crystal sodium-ion battery positive electrode active material exhibits a single-crystal structure with an average particle size D. 50 Its micrometers range from 1 to 30 micrometers, and its compacted density is 2.8 to 3.6 g / cm³. 3 Its specific surface area is 0.2~1.0 m². 2 / g.

12. The use of the monocrystalline sodium-ion battery positive electrode active material according to claim 11 in the positive electrode of a sodium-ion battery.

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