A single-crystal layered sodium-ion positive electrode material and a preparation method thereof

Abstract

The application discloses a single-crystal layered sodium-ion positive electrode material and a preparation method thereof, the single-crystal layered sodium-ion positive electrode material is O3 phase; the single-crystal layered sodium-ion positive electrode material is a single-crystal layered sodium-ion positive electrode material with (003) crystal face preferred growth; the preparation method comprises the following steps: step one, weighing a transition metal salt, adding deionized water to stir, and forming a uniform transition metal salt suspension; step two, adding a complexing agent to the transition metal salt suspension, and adjusting the pH of the transition metal salt suspension; step three, placing the transition metal salt suspension with the adjusted pH into a reaction kettle, washing with deionized water after reaction in the reaction kettle, and forming a precursor with (003) crystal face preferred growth, and the precursor has a particle size D50 of 2-4 microns; and step four, adding the prepared precursor, a sodium salt, a boron-containing molten salt and a polymer into a high-speed mixer, uniformly mixing, and then sintering to form a single-crystal layered sodium-ion positive electrode material with (003) crystal face preferred growth and a hydrophobic skeleton.

Description

A single-crystal layered sodium-ion cathode material and its preparation method Technical Field

[0001] This invention relates to the technical field, and in particular to a single-crystal layered sodium-ion cathode material and its preparation method. Background Technology

[0002] High-nickel ternary cathode materials (NCM / NCA), lithium-rich manganese layered oxide (LLO), and layered sodium cathode materials in the new energy field have become research hotspots due to their high energy density and abundant resources. However, high residual alkali on the material surface and a pH ≥ 11 result in poor air stability and gelation during electrode slurry processing (residual alkali can cause defluorination of the PVDF binder during slurry preparation, leading to slurry flocculation). Furthermore, the LiOH / Li2CO3 / NaOH / Na2CO3 on the material surface reacts with H2O / CO2 in the air to generate non-electrochemically active products such as carbonates, making the material prone to structural collapse and crack propagation in air, leading to capacity decay and decreased electrochemical performance.

[0003] To address the air stability issue of layered oxides, various solutions have been proposed in existing technologies, but these methods still have some limitations. The following are the solutions offered by existing technologies and their associated problems:

[0004] Existing technological solutions: Existing methods for improving the air stability of high-alkalinity cathode materials, such as surface coating, element doping, surface modification, and structural control, have achieved certain results, but still have problems such as complex processes, high costs, and difficulty in balancing performance and stability. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a single-crystal layered sodium ion cathode material and its preparation method.

[0006] The objective of this invention is achieved through the following technical solution: a single-crystal layered sodium ion cathode material, wherein the single-crystal layered sodium ion cathode material is an O3 phase; the single-crystal layered sodium ion cathode material is a single-crystal layered sodium ion cathode material preferentially grown on the (003) crystal plane, wherein a hydrophobic framework is formed in the tetrahedral gaps and on the surface of the single-crystal layered sodium ion cathode material, and the hydrophobic framework is obtained by sintering boron-containing molten salt and polymer;

[0007] In the X-ray diffraction pattern of the single-crystal layered sodium ion cathode material, there are diffraction peaks of the (003) crystal plane in the range of diffraction angle of 16° to 19°, and the diffraction intensity I (003) is 350.

[0008] The general formula for single-crystal layered sodium ion cathode materials is Na x Mg y Fe z Mnt Ni h Al m O2; where x = 0.8 to 1.0, and the sum of the values ​​of y, z, t, h, and m equals 1.

[0009] The present invention also provides a method for preparing the above-mentioned single-crystal layered sodium-ion cathode material, comprising:

[0010] Step 1: Weigh two or more of the transition metal salts magnesium salt, iron salt, manganese salt, nickel salt, and aluminum salt, add deionized water and stir to form a uniform suspension of transition metal salts.

[0011] Step 2: Add a complexing agent to the transition metal salt suspension from Step 1 to adjust the pH of the transition metal salt suspension;

[0012] Step 3: Place the transition metal salt suspension with pH adjusted in Step 2 into the reaction vessel. After the reaction in the reaction vessel is completed, wash with deionized water to form a precursor that preferentially grows along the (003) crystal plane. The precursor particle size D50 = 2~4μm.

[0013] Step 4: Add sodium salt, boron-containing molten salt, and polymer to the precursor prepared in step 3, mix them evenly, and then sinter them to form a (003) crystal plane preferentially grown, single-crystal layered sodium ion cathode material with a hydrophobic framework, wherein the molar ratio of sodium salt to precursor metal element is 0.8 to 1.0:1.

[0014] In step one, the magnesium salt is any one of magnesium carbonate, magnesium nitrate, and magnesium hydroxide; the iron salt is any one of iron carbonate, iron nitrate, and iron hydroxide; the manganese salt is any one of manganese carbonate, manganese nitrate, and manganese hydroxide; the nickel salt is any one of nickel carbonate, nickel sulfate, and nickel hydroxide; and the aluminum salt is any one of aluminum carbonate, aluminum nitrate, and aluminum hydroxide. In step two, the complexing agent is any one of ammonium carbonate and ammonium bicarbonate.

[0015] In step one, the concentration of the transition metal salt suspension is 0.05 mol / L to 0.2 mol / L; in step two, the pH of the transition metal salt suspension is 10 to 12.

[0016] In step three, the reaction temperature inside the reactor is 200℃~500℃, the pressure is 0.05MPa~0.2MPa, and the reaction time is 4h~8h;

[0017] In step four, the sodium salt is either sodium carbonate or sodium bicarbonate; the boron-containing molten salt is a boron-containing molten salt with a melting point of less than 500℃, selected from either ammonium hydrogen borate, boric acid, or ammonium pentaborate; the amount of boron-containing molten salt used is 0.1% to 0.5% of the precursor; the polymer is a polymer that synergistically interacts with boron to form a hydrophobic framework, selected from either N,N-dimethyldodecylamine treated with sodium chloroacetate or dimethylamino-dodecyl-dodecylamine; the amount of polymer used is 0.1% to 0.5% of the precursor.

[0018] In step four, the sintering temperature is 800℃~1000℃, and the holding time is 6h~10h.

[0019] The present invention has the following advantages:

[0020] 1. Formation of single crystal particles arranged in an orderly manner along the (003) crystal plane: By controlling the pH and reaction pressure during the precursor preparation process, the grains with different orientations compete for growth during the reaction. At the same time, the particle size range of the prepared precursor, D50, is controlled to be 2-4 μm, and finally, single crystal particles arranged in an orderly manner along the

[003] crystal plane are obtained; since the single crystal growth direction is consistent with Na + The diffusion channels are parallel, forming a narrower edge plane, which is beneficial for expanding the Na₂O₃ diffusion range. + The exposed area where the reaction occurs is increased, thereby improving cycle stability; in addition, since sodium ions have high reactivity with water, after being arranged in an orderly manner along the

[003] crystal plane, sodium ions accumulate less on the surface of the cathode material, thereby reducing the water absorption of the cathode material and improving its stability to humid air.

[0021] 2. Formation of a hydrophobic framework centered on tetrahedral interstices: The formation of this hydrophobic framework significantly reduces the reaction between sodium ions and water in the cathode material, greatly improving its stability in humid air. Furthermore, the small radius of boron ions allows for the formation of stable boron-bode bonds within the tetrahedral interstices, significantly reducing the band gap and inhibiting the reaction of sodium ions with water. + The displacement of tetrahedral sites causes slippage of the metal layer, which stabilizes the hydrophobic framework and the sodium ion cathode material structure. This creates a synergistic effect with the single-crystal structure, which helps to further reduce the water absorption of the cathode material.

[0022] 3. Controlling the molar ratio of sodium salt to precursor metal element to 0.8-1.0:1 is beneficial to forming O3 type sodium ion cathode material. O3 type sodium ion cathode material has a higher theoretical capacity and faster interlayer ion transport. Compared with P2 type structure, O3 type sodium ion cathode material has stronger structural stability and longer cycle life. Attached Figure Description

[0023] Figure 1 is a SEM image of Example 2.

[0024] Figure 2 shows the charge-discharge curves of Example 2 and Comparative Example 1 at a rate of 0.1C.

[0025] Figure 3 shows the XRD patterns of the single-crystal layered sodium ion cathode materials prepared in Example 2 and Comparative Example 1.

[0026] Figure 4 shows the capacity retention of Example 4 and Comparative Example 3 after 100 cycles at a 0.1C rate. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0028] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0029] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0030] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0031] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0032] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0033] Example 1

[0034] A single-crystal layered sodium-ion cathode material, wherein the single-crystal layered sodium-ion cathode material is an O3 phase; the single-crystal layered sodium-ion cathode material is a single-crystal layered sodium-ion cathode material preferentially grown on the (003) crystal plane;

[0035] In the X-ray diffraction pattern of the single-crystal layered sodium ion cathode material, there are diffraction peaks of the (003) crystal plane in the range of diffraction angle of 16° to 19°, and the diffraction intensity I (003) is 350.

[0036] The general formula for single-crystal layered sodium ion cathode materials is Na x Mg y Fe z Mn t Ni h Al m O2; where x = 0.8 to 1.0, and the sum of the values ​​of y, z, t, h, and m equals 1.

[0037] This embodiment also provides a method for preparing sodium-ion cathode material, used to prepare the above-mentioned single-crystal layered sodium-ion cathode material, specifically including the following steps:

[0038] Step 1: Weigh two or more of the transition metal salts magnesium salt, iron salt, manganese salt, nickel salt, and aluminum salt, add deionized water and stir to form a uniform suspension of transition metal salts.

[0039] Step 2: Add a complexing agent to the transition metal salt suspension from Step 1 to adjust the pH of the transition metal salt suspension;

[0040] Step 3: Place the transition metal salt suspension with pH adjusted in Step 2 into the reaction vessel. After the reaction in the reaction vessel is completed, wash with deionized water to form a precursor that preferentially grows along the (003) crystal plane. The precursor particle size D50 = 2~4μm.

[0041] Step 4: Add sodium salt, boron-containing molten salt, and polymer to the precursor prepared in step 3, mix them evenly, and then sinter them to form a (003) crystal plane preferentially grown, single-crystal layered sodium ion cathode material with a hydrophobic framework, wherein the molar ratio of sodium salt to precursor metal element is 0.8 to 1.0:1.

[0042] In step one, the magnesium salt is any one of magnesium carbonate, magnesium nitrate, and magnesium hydroxide; the iron salt is any one of iron carbonate, iron nitrate, and iron hydroxide; the manganese salt is any one of manganese carbonate, manganese nitrate, and manganese hydroxide; the nickel salt is any one of nickel carbonate, nickel sulfate, and nickel hydroxide; the aluminum salt is any one of aluminum carbonate, aluminum nitrate, and aluminum hydroxide; and the complexing agent is any one of ammonium carbonate and ammonium bicarbonate.

[0043] In step one, the concentration of the transition metal salt suspension is 0.05 mol / L to 0.2 mol / L; in step two, the pH of the transition metal salt suspension is 10 to 12.

[0044] In step three, the reaction temperature inside the reactor is 200℃~500℃, the pressure is 0.05MPa~0.2MPa, and the reaction time is 4h~8h;

[0045] In step four, the sodium salt is either sodium carbonate or sodium bicarbonate; the boron-containing molten salt is a boron-containing molten salt with a melting point of less than 500℃, selected from either ammonium hydrogen borate, boric acid, or ammonium pentaborate; the amount of boron-containing molten salt used is 0.1% to 0.5% of the precursor; the polymer is a polymer that synergistically interacts with boron to form a hydrophobic framework, selected from either N,N-dimethyldodecylamine treated with sodium chloroacetate or dimethylamino-dodecyl-dodecylamine; the amount of polymer used is 0.1% to 0.5% of the precursor.

[0046] In step four, the sintering temperature is 800℃~1000℃, and the holding time is 6h~10h.

[0047] The SEM image of the single-crystal layered sodium ion cathode material provided in this embodiment is shown in Figure 1. It can be seen that its microstructure exhibits uniformly sized particles with a clear growth orientation.

[0048] Example 2:

[0049] Preparation of single-crystal layered sodium-ion cathode material with preferred growth of (003) crystal planes: O3-Na 0.8 Mg 0.2 Fe 0.4 Mn 0.4 O2.

[0050] Magnesium carbonate, iron carbonate, and magnesium carbonate were weighed according to a Mg:Fe:Mn molar ratio of 0.2:0.4:0.4, and added to deionized water to prepare a suspension with a concentration of 0.05 mol / L. After mixing evenly, ammonium carbonate was added to adjust the pH of the suspension to 10, and then it was placed in a reaction vessel. The reaction temperature was set at 200℃, the pressure at 0.2 MPa, and the reaction time at 8 h. A (003) crystal plane preferential growth precursor with a particle size D50=4 μm was obtained. The precursor was washed 4 times with deionized water. Then, sodium carbonate was weighed according to a sodium to precursor metal element molar ratio of 0.8:1, and N,N-dimethyldodecylamine treated with 0.5% ammonium borate and 0.5% sodium chloroacetate was mixed with the precursor. After mixing evenly, the mixture was placed in a box furnace and kept at 800℃ for 10 h to obtain a (003) crystal plane preferentially grown single crystal O3-Na. 0.8 Mg 0.2 Fe 0.4 Mn 0.4 O2. Air stability: After 120 hours of exposure to air, the material's water absorption is 0.12%. When the material is used to make a battery, the zeta potential is -32.5 mV. The discharge capacity at 0.1C current (2-4V) is 148 mAh / g, and the capacity retention after 100 cycles is 93%.

[0051] Example 3:

[0052] Preparation of single-crystal layered sodium-ion cathode material with preferred growth of (003) crystal plane: O3-NaNi 0.5 Mn 0.5 O2.

[0053] Nickel nitrate and manganese nitrate were weighed according to a Ni:Mn molar ratio of 0.5:0.5, added to deionized water, and a suspension with a concentration of 0.2 mol / L was prepared. After mixing evenly, ammonium carbonate was added to adjust the pH of the suspension to 12. Then, the suspension was placed in a reaction vessel, and the reaction temperature was set to 500℃, the pressure to 0.05 MPa, and the reaction time to 4 h. A (003) crystal plane preferential growth precursor with a particle size D50=2 μm was obtained. The precursor was washed 4 times with deionized water. Then, sodium bicarbonate was weighed according to a sodium:precursor metal element molar ratio of 1:1, and 0.1% boric acid and 0.1% dimethylamino-dodecyl-dodecaneamine (by mass of the precursor) were mixed with the precursor. After mixing evenly, the mixture was placed in a box furnace and kept at 1000℃ for 6 h to obtain a (003) crystal plane preferentially grown single crystal O3-NaNi. 0.5 Mn 0.5O2. Air stability: After being exposed to air for 120 hours, the material's water absorption is 0.08%. When the material was made into a battery, the zeta potential was -36.8 mV, the discharge capacity at 0.1C current (2-4V) was 145 mAh / g, and the capacity retention after 100 cycles was 95%.

[0054] Example 4:

[0055] (003) Single-crystal layered sodium-ion cathode material with preferential crystal plane growth: O3-NaNi 0.45 Al 0.1 Mn 0.45 O2.

[0056] Nickel hydroxide, aluminum hydroxide, and manganese hydroxide were weighed according to a Ni:Al:Mn molar ratio of 0.45:0.1:0.45, and added to deionized water to prepare a suspension with a concentration of 0.1 mol / L. After mixing evenly, ammonium carbonate was added to adjust the pH of the suspension to 11, and then it was placed in a reaction vessel. The reaction temperature was set at 300℃, the pressure at 0.1 MPa, and the reaction time at 6 h. A (003) crystal plane preferential growth precursor with a particle size D50=3 μm was obtained. The precursor was washed 4 times with deionized water. Then, sodium bicarbonate was weighed according to a sodium to precursor metal element molar ratio of 1:1, and 0.3% ammonium pentaborate and 0.3% dimethylamino-dodecyl-dodecaneamine were mixed with the precursor. After mixing evenly, the mixture was placed in a box furnace and kept at 900℃ for 8 h to obtain a (003) crystal plane preferentially grown single crystal O3-NaNi. 0.45 Al 0.1 Mn 0.45 O2.

[0057] Air stability: After being exposed to air for 120 hours, the material's water absorption rate was 0.13%. When the material was made into a battery, the zeta potential was -34.7 mV, the discharge capacity at 0.1C current (2-4V) was 142 mAh / g, and the capacity retention rate after 100 cycles was 93%.

[0058] Preparation of O3-Na 0.8 Mg 0.2 Fe 0.4 Mn 0.4 O2 sodium ion cathode material. Preparation of O3-Na 0.8 Mg 0.2 Fe 0.4 Mn 0.4 O2 sodium ion cathode material. Preparation of O3-Na 0.8 Mg 0.2 Fe 0.4 Mn 0.4 O2 sodium ion cathode material.

[0059] Comparative Example 1:

[0060] Magnesium carbonate, ferric carbonate, and magnesium carbonate were weighed according to a Mg:Fe:Mn molar ratio of 0.2:0.4:0.4, and added to deionized water to prepare a suspension with a concentration of 0.05 mol / L. After mixing thoroughly, ammonium carbonate was added to adjust the pH of the suspension to 10, and then the suspension was placed in a reaction vessel. The reaction temperature was set at 600℃, the pressure at 0 MPa, and the reaction time at 10 h. A precursor with a particle size D50 of 10 μm was obtained. The precursor was washed four times with deionized water. Then, sodium carbonate was weighed according to a sodium to precursor metal element molar ratio of 0.8:1, and 0.5% of the precursor mass of ammonium borate and 0.5% of sodium chloroacetate-treated N,N-dimethyldodecylamine were mixed with the precursor. After mixing thoroughly, the mixture was placed in a box furnace and kept at 800℃ for 10 h to obtain O3-Na. 0.8 Mg 0.2 Fe 0.4 Mn 0.4 O2. Air stability: After being exposed to air for 120 hours, the material's water absorption is 0.52%. When the material was made into a battery, the zeta potential was +18.7 mV, the discharge capacity at 0.1C current (2-4V) was 129 mAh / g, and the capacity retention after 100 cycles was 82%.

[0061] Comparative Example 2:

[0062] Nickel nitrate and manganese nitrate were weighed according to a Ni:Mn molar ratio of 0.5:0.5, added to deionized water, and a suspension with a concentration of 0.2 mol / L was prepared. After mixing evenly, ammonium carbonate was added to adjust the pH of the suspension to 12. Then, the suspension was placed in a reaction vessel, and the reaction temperature was set to 500℃, the pressure to 0.05MPa, and the reaction time to 4h. A (003) crystal plane preferential growth precursor with a particle size D50=2um was obtained. The precursor was washed 4 times with deionized water. Then, sodium bicarbonate was weighed according to a sodium:precursor metal element molar ratio of 1:1, mixed evenly, and placed in a box furnace and kept at 1000℃ for 6h to obtain O3-NaNi with (003) crystal plane preferential growth. 0.5 Mn 0.5 O2. Air stability: After being exposed to air for 120 hours, the material's water absorption is 0.55%. When the material was made into a battery, the zeta potential was +19.3 mV, the discharge capacity at 0.1C current (2-4V) was 130 mAh / g, and the capacity retention after 100 cycles was 80%.

[0063] Comparative Example 3:

[0064] Nickel hydroxide, aluminum hydroxide, and manganese hydroxide were weighed according to a Ni:Al:Mn molar ratio of 0.45:0.1:0.45, and added to deionized water to prepare a suspension with a concentration of 0.1 mol / L. After mixing evenly, ammonium carbonate was added to adjust the pH of the suspension to 11. Then, the suspension was placed in a reaction vessel, and the reaction temperature was set at 300℃, the pressure at 0.1 MPa, and the reaction time at 6 h. A (003) crystal plane preferential growth precursor with a particle size D50=3 μm was obtained. The precursor was washed 4 times with deionized water. Then, sodium bicarbonate precursor was weighed according to a sodium to precursor metal element molar ratio of 1:1 and mixed evenly. The mixture was then placed in a box furnace and kept at 900℃ for 8 h to obtain a (003) crystal plane preferentially grown single crystal O3-NaNi. 0.45 Al 0.1 Mn 0.45 O2. Air stability: After being exposed to air for 120 hours, the material's water absorption is 0.45%. When the material was made into a battery, the zeta potential was +23.4 mV, the discharge capacity at 0.1C current (2-4V) was 133 mAh / g, and the capacity retention after 100 cycles was 85%.

[0065] Comparative Example 4:

[0066] Nickel nitrate and manganese nitrate were weighed according to a Ni:Mn molar ratio of 0.5:0.5, and added to deionized water to prepare a suspension with a concentration of 0.2 mol / L. After mixing evenly, ammonium carbonate was added to adjust the pH of the suspension to 12. Then, the suspension was placed in a reaction vessel, and the reaction temperature was set to 500℃, the pressure to 0.05 MPa, and the reaction time to 4 h. A (003) crystal plane preferential growth precursor with a particle size D50=2 μm was obtained. The precursor was washed 4 times with deionized water. Then, sodium bicarbonate was weighed according to a sodium:precursor metal element molar ratio of 0.5:1, and 0.1% boric acid and 0.1% dimethylamino-dodecyl-dodecaneamine (by mass of the precursor) were mixed with the precursor. After mixing evenly, the mixture was placed in a box furnace and kept at 1000℃ for 6 h to obtain a (003) crystal plane preferentially grown single crystal NaNi. 0.5 Mn 0.5 O2. Air stability: After being exposed to air for 120 hours, the material's water absorption is 0.10%. When the material was made into a battery, the zeta potential was -28.5 mV, the discharge capacity at 0.1C current (2-4V) was 130 mAh / g, and the capacity retention after 100 cycles was 81%.

[0067] Comparative Example 5:

[0068] Magnesium carbonate, ferric carbonate, and magnesium carbonate were weighed according to a Mg:Fe:Mn molar ratio of 0.2:0.4:0.4, and added to deionized water to prepare a suspension with a concentration of 0.05 mol / L. After mixing thoroughly, ammonium carbonate was added to adjust the pH of the suspension to 10. The suspension was then placed in a reaction vessel, and the reaction temperature was set at 600℃, the pressure at 0 MPa, and the reaction time at 10 h. A precursor with a particle size D50 of 10 μm was obtained. The precursor was washed four times with deionized water. Then, sodium carbonate was weighed according to a sodium to precursor metal element molar ratio of 0.5:1, mixed thoroughly, and placed in a box furnace at 800℃ for 10 h to obtain Na. 0.8 Mg 0.2 Fe 0.4 Mn 0.4 O2. Air stability: After being exposed to air for 120 hours, the material's water absorption is 0.66%. When the material was made into a battery, the zeta potential was +27.4 mV, the discharge capacity at 0.1C current (2-4V) was 122 mAh / g, and the capacity retention after 100 cycles was 76%.

[0069] The performance test results of the sodium ion cathode materials prepared in Examples 2-4 and Comparative Examples 1-3 are shown in Table 1 and Figures 2-4 below.

[0070] Table 1 shows the performance test results of sodium ion cathode materials in Examples 2-4 and Comparative Examples 1-5.

[0071] After 120 hours of exposure, the following parameters were observed: water absorption, zeta potential (0.1C), discharge capacity, and capacity retention after 100 cycles: Example 2: 0.12% -32.5 (mV) 148 mAh / g 93%; Example 3: 0.08% -36.8 (mV) 145 mAh / g 95%; Example 4: 0.13% -34.7 (mV) 142 mAh / g 93%; Comparative Example 1: 10.52% +18.7 (mV) 129 mAh / g 82%; Comparative Example 2: 0.55% +19.3 (mV) 130 mAh / g 80%; Comparative Example 3: 0.45% +23.4 (mV) 133 mAh / g 85%; Comparative Example 4: 0.10% -28.5 (mV) 130 mAh / g 81%; Comparative Example 5: 0.66% +27.4 (mV) 122 mAh / g 76%. surface

[0072] As can be seen, the water absorption of the single-crystal layered sodium-ion cathode material provided in this embodiment of the invention is greatly reduced due to the introduction of the hydrophobic framework, with water absorption not exceeding 0.15% after 120 hours of exposure. Meanwhile, in the 0.1C discharge capacity test, it can reach over 142 mAh / g, and the capacity retention rate after 100 cycles can reach over 93%, which is a significant improvement compared to comparative examples 1-5.

[0073] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a single-crystal layered sodium-ion cathode material, characterized in that, include: Step 1: Weigh two or more of the transition metal salts (magnesium, iron, manganese, nickel, and aluminum), add deionized water and stir to form a homogeneous transition metal salt suspension; Step 2: Add a complexing agent to the transition metal salt suspension from Step 1 to adjust the pH of the suspension; Step 3: Place the pH-adjusted transition metal salt suspension from Step 2 into a reaction vessel. After the reaction is complete, wash with deionized water to form a precursor preferentially grown along the (003) crystal plane, with a precursor particle size D50 = 2-4 μm; Step 4: The precursor prepared in Step 3... Sodium salt, boron-containing molten salt, and polymer are added to the mixture, and after uniform mixing, sintering is carried out to form a (003) crystal plane preferentially grown, single-crystal layered sodium ion cathode material with a hydrophobic framework. The molar ratio of sodium salt to precursor metal element is 0.8 to 1.0:

1. The boron-containing molten salt is a boron-containing molten salt with a melting point of less than 500℃, selected from any one of ammonium hydrogen borate, boric acid, and ammonium pentaborate. The polymer is a polymer that synergistically interacts with boron to form a hydrophobic framework, selected from any one of N,N-dimethyldodecylamine treated with sodium chloroacetate and dimethylamino-dodecyl-dodecylamine.

2. The preparation method according to claim 1, characterized in that, In step one, the magnesium salt is any one of magnesium carbonate, magnesium nitrate, and magnesium hydroxide; the iron salt is any one of iron carbonate, iron nitrate, and iron hydroxide; the manganese salt is any one of manganese carbonate, manganese nitrate, and manganese hydroxide; the nickel salt is any one of nickel carbonate, nickel sulfate, and nickel hydroxide; and the aluminum salt is any one of aluminum carbonate, aluminum nitrate, and aluminum hydroxide. In step two, the complexing agent is any one of ammonium carbonate and ammonium bicarbonate.

3. The preparation method according to claim 1, characterized in that, In step one, the concentration of the transition metal salt suspension is 0.05 mol / L to 0.2 mol / L; in step two, the pH of the transition metal salt suspension is 10 to 12.

4. The preparation method according to claim 1, characterized in that, In step three, the reaction temperature inside the reactor is 200℃~500℃, the pressure is 0.05MPa~0.2MPa, and the reaction time is 4h~8h.

5. The preparation method according to claim 1, characterized in that, In step four, the sodium salt is either sodium carbonate or sodium bicarbonate; the amount of the boron-containing molten salt is 0.1% to 0.5% of the precursor; and the amount of the polymer is 0.1% to 0.5% of the precursor.

6. The preparation method according to claim 1, characterized in that, In step four, the sintering temperature is 800℃~1000℃, and the holding time is 6h~10h.

7. A single-crystal layered sodium-ion cathode material, characterized in that: The single-crystal layered sodium ion cathode material is prepared by the preparation method according to any one of claims 1 to 6, wherein the single-crystal layered sodium ion cathode material is an O3 phase; the single-crystal layered sodium ion cathode material is a single-crystal layered sodium ion cathode material preferentially grown on the (003) crystal plane, wherein a hydrophobic framework is formed in the tetrahedral gaps and on the surface of the single-crystal layered sodium ion cathode material, wherein the hydrophobic framework is obtained by sintering boron-containing molten salt and polymer.

8. The single-crystal layered sodium-ion cathode material according to claim 7, characterized in that: The X-ray diffraction pattern of the single-crystal layered sodium ion cathode material contains diffraction peaks of the (003) crystal plane in the range of diffraction angles of 16° to 19°, and the diffraction intensity I (003) is 350.

9. The single-crystal layered sodium-ion cathode material according to claim 7, characterized in that: The general formula of the single-crystal layered sodium ion cathode material is Na. x Mg y Fe z Mn t Ni h Al m O2; where x = 0.8~1.0, y+z+t+h+m=1.

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