A sodium-ion cathode material and its preparation method

Abstract

This invention discloses a sodium-ion cathode material and its preparation method, belonging to the technical field of sodium-ion battery cathode materials. The cathode material is characterized by having an O3-type polycrystalline morphology and the chemical formula: Na. x T 1 y T 2 (1‑y) O2, where 1.00≤x≤1.05, 0.7≤y≤0.98; T 1 T is a transition metal element. 2 As a doping element, the T 1 Selected from one or more of Ni, Fe, Mn, Co, Zr, and Cu; the T 2 The cathode material is selected from one or more of Ca, Cu, La, Sb, Al, Ti, Zn, Zr, Mg, Y, and W; the cathode material prepared by this invention has an O3-type polycrystalline gradation morphology, specifically a morphology with a gradation of large and small particles, and has the characteristics of high capacity and high compaction.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a sodium-ion cathode material with high compaction and high capacity obtained by controlling the particle size of the precursor, and its preparation method. Background Technology

[0002] With the increasing global demand for clean energy, energy storage technology has become a key link in achieving energy transition. Sodium-ion batteries, with their significant advantages such as abundant sodium resources and low cost, have shown great application potential in large-scale energy storage, electric vehicles, and other portable devices, and have received widespread attention in recent years.

[0003] Among the many components of a sodium-ion battery, the cathode material plays a decisive role in its performance. Layered oxides, due to their high theoretical specific capacity and relatively stable structure, have become a key research focus for sodium-ion battery cathode materials. However, traditional layered oxide sodium-ion cathode materials currently face numerous challenges in practical applications.

[0004] One key issue is the low compaction density. For example, some layered oxide sodium-ion cathode materials prepared by conventional methods can only achieve a compaction density of 3.0 g / cm³. 3 This figure results in a reduction in the mass of active material that can be filled within the limited battery space, making it difficult to improve the volumetric energy density of the battery electrodes. For example, a sodium-ion battery using traditional layered oxide cathode materials has a volumetric energy density of only 270Wh / L. Compared to other energy storage technologies such as lithium-ion batteries, it lags significantly in terms of space utilization efficiency and energy storage capacity, limiting the widespread adoption of sodium-ion batteries in applications with stringent volume requirements.

[0005] Studies have shown that the particle size of the precursor has a significant impact on the compaction density of the final layered oxide sodium-ion cathode material. An unreasonable particle size distribution in the precursor, such as an excessive amount of small particles, leads to a narrow particle size distribution in the material. According to relevant theories, compaction density is not only related to particle size but also closely linked to the normal distribution of particle size; the narrower the particle size distribution, the lower the compaction density. For example, patent CN116502564A mentions that in the manufacturing process of traditional sodium-ion batteries, an excessive amount of small particles in the cathode material precursor results in a narrower particle size distribution in the cathode material, ultimately reducing the compaction density. This leads to lower battery capacity per unit volume or weight, severely impacting discharge efficiency and overall cost.

[0006] Currently, although some studies have attempted to improve material properties by simply mixing precursors of different particle sizes, such as the patent [Application No.: 202311579288] which uses a method of mixing large-particle nickel-iron-manganese ternary precursors and small-particle nickel-iron-manganese ternary precursors in a certain proportion to improve the compaction density of the material to some extent, this method still has limitations and cannot precisely control the precursor particle size to achieve optimal material performance. Therefore, developing a method that can precisely control the precursor particle size is of great practical significance for preparing high-compact layered oxide sodium-ion cathode materials and improving the overall performance of sodium-ion batteries. Summary of the Invention

[0007] The first objective of this invention is to provide a high-compact, high-capacity sodium-ion cathode material.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A sodium-ion cathode material, characterized in that: the cathode material has an O3-type polycrystalline morphology, and its chemical formula is: Na x T 1 y T 2 (1-y) O2, where 1.00≤x≤1.05, 0.7≤y≤0.98; T 1 T is a transition metal element. 2 As a doping element, the T 1 Selected from one or more of Ni, Fe, Mn, Co, Zr, and Cu; the T 2 It is selected from one or more of Ca, Cu, La, Sb, Al, Ti, Zn, Zr, Mg, Y, and W.

[0010] Further settings are as follows:

[0011] In the chemical formula of the sodium-ion battery layered cathode material, 1.01≤x≤1.035.

[0012] The transition metal element T 1 It is a mixture of Ni, Fe, and Mn, with 0.9 ≤ y ≤ 0.98, wherein the molar ratio of Ni, Fe, and Mn is 1:1:1.

[0013] The doping element T 2 It is a mixture of Ca, Al, and Sb, wherein the molar ratio of Ca, Al, and Sb is 2-3:3-4:1-2.

[0014] The polycrystalline morphology of the cathode material is one or a mixture of two or more of the following: spherical, near-spherical, polyhedral, sheet-like, and blocky.

[0015] The polycrystalline graded morphology of the cathode material, with a particle size D v 10 represents 1-5 μm, D v 50 is 6-15μm.

[0016] The ratio of I(003):I(104) in the XRD of the cathode material is 0.40-0.75.

[0017] The BET value of the positive electrode material is 0.4-0.9m. 2 / g.

[0018] Particularly preferred is that in the chemical formula of the layered cathode material, x = 1.025; the transition metal element T 1 It is a mixture of Ni, Fe, and Mn, wherein the molar ratio of Ni, Fe, and Mn is 1:1:1, y = 0.97; dopant element T 2 It is a mixture of Ca, Al and Y, wherein the molar ratio of Ca, Al and Y is 3:2:1.

[0019] Particularly preferred is that the polycrystalline particles of the layered cathode material are spherical in shape; the particle size D v 10 is 1.5-3.5μm, D v The thickness of the layered cathode material is 8-13 μm; the I(003):I(104) ratio in XRD is 0.56-0.70; the BET value is 0.45-0.60 μm. 2 / g.

[0020] The second aspect of this invention aims to provide a method for preparing high-burst, high-capacity sodium-ion cathode materials by controlling the particle size of the precursor. By precisely controlling the particle size distribution of the precursor, a layered oxide sodium-ion cathode material with high burst density and good electrochemical performance is prepared, thereby improving the volumetric energy density and overall performance of sodium-ion batteries. The method includes the following steps:

[0021] (1) Preparation of cathode material precursor

[0022] Will contain T 1 The sulfates of elements are combined to form a transition metal salt solution of a certain concentration, which is then co-precipitated with sodium hydroxide solution as a precipitant and ammonia water as a complexing agent. The coprecipitation is divided into three stages: large particles are generated in reactor A, small particles are generated in reactor B, and the particle size in reactor A and reactor B is monitored in real time. After the particle size reaches the required level, the particles in reactor A and reactor B are graded in a certain proportion, mixed, aged, filtered, washed, and dried to obtain the cathode material precursor.

[0023] (2) Preparation of cathode materials

[0024] The cathode material precursor, sodium source, and dopant element T are used. 2 The materials are placed in a mixer in a certain proportion and stirred at a certain speed to obtain a blend. The blend is then sintered in a certain atmosphere and at a certain temperature, and pulverized to obtain sodium ion cathode material with O3 type polycrystalline gradation.

[0025] Further settings are as follows:

[0026] In step (1):

[0027] The coprecipitation reaction is preferably carried out in a high-pressure homogenizer.

[0028] The metal salt containing transition element T1 is selected from nickel sulfate, manganese sulfate, and cobalt sulfate. According to the stoichiometric ratio of the target layered oxide sodium ion cathode material (Ni:Fe:Mn = 0.33:0.33:0.33), they are dissolved in deionized water to prepare a mixed solution of metal salt with a concentration of 1-3 mol / L.

[0029] The concentration of the precipitant sodium hydroxide is 3-5 mol / L.

[0030] The concentration of the ammonia water is 4-6 g / L.

[0031] The large particle generation process is as follows: the reactor temperature is controlled at 65℃, the pH is controlled at 11.0, the transition metal salt concentration is 1.0 mol / L, the flow rate is 2 mL / min, the NaOH concentration is 4 mol / L, the stirring speed is 200 rpm, and the complexing agent (NH4OH / M) is used. 2+ =1.2), the reaction time is 8h, and the particle size is monitored in real time during the period.

[0032] The small particle generation process is as follows: the reactor temperature is controlled at 45℃, the pH is controlled at 11.5, the metal salt concentration is 3.0 mol / L, the flow rate is 10 mL / min, the NaOH concentration is 8 mol / L, the stirring speed is 600 rpm, and the complexing agent is reduced to (NH4OH / M). 2+ =0.3), the reaction time is 2h, and the particle size is monitored in real time during the process.

[0033] Preferably, the small particle generation process is started when the particle size of the large particles reaches Dv50 = 12μm.

[0034] The ratio of large particles to small particles is 6:4-8:2.

[0035] Preferably, to prevent secondary agglomeration of small particles, 0.1% citric acid (calculated as a mass fraction of the total material) can be added.

[0036] Preferably, large particles and small particles are mixed in a certain proportion for 0.5 to 1 hour. After mixing, the mixture is aged, filtered, and washed repeatedly with deionized water 3 to 5 times to remove impurity ions adsorbed on the surface. The washed precipitate is then dried at 80-120°C for 10 to 20 hours to obtain the cathode material precursor.

[0037] The particle size of the precursor powder is detected using a laser particle size analyzer to ensure that its particle size distribution is within the target range (e.g., D). v 10 at 2-4 μm, D v 50 particles with a diameter of 7-15 μm).

[0038] In step (2):

[0039] The sintering is preferably carried out in a high-temperature air furnace.

[0040] The cathode material precursor prepared in step (1) is combined with a sodium source and a dopant element T. 2 The mixture is based on the elemental molar ratio Na:T 1 :T 2 The mixture of 1.00–1.05:0.95–1:0.02–0.10 is thoroughly mixed, and then the mixture is placed in a high-temperature furnace for calcination in an air or oxygen atmosphere. The calcination process consists of two stages: the first stage involves heating from room temperature to 400–600°C at a rate of 3–5°C / min and holding at that temperature for 2–4 hours; the second stage involves heating from 400–600°C to 750–950°C at a rate of 5–8°C / min and sintering for 12–20 hours. After sintering, the material is naturally cooled to room temperature to obtain a high-pressure, high-capacity sodium-ion cathode material.

[0041] The sodium source is selected from one or more of sodium carbonate, sodium oxalate, sodium bicarbonate, sodium acetate, sodium oxalate, and sodium citrate.

[0042] The doping element T 2 It is a mixture of Ca, Al, and Sb, wherein: the compound containing Ca is one or a mixture of two or more of calcium carbonate, calcium oxide, calcium peroxide, calcium hydroxide, and calcium sulfate; the compound containing Al is one or a mixture of two or more of aluminum oxide, aluminum hydroxide, and aluminum sulfate; and the compound containing Sb is one or more of antimony trioxide, antimony pentoxide, and antimony pentafluoride.

[0043] Preferably, the sodium source is sodium carbonate, the Ca-containing compound is calcium carbonate, the Al-containing compound is aluminum oxide, and the Sb-containing compound is antimony trioxide.

[0044] The mixing process employs ball milling or mechanical stirring to ensure uniform mixing.

[0045] Particularly preferred, the above-mentioned cathode material precursor, sodium carbonate, and dopant element T are used. 2 (A mixture of calcium carbonate, aluminum oxide, and yttrium trioxide, with an elemental molar ratio of Ca:Al:Sb = 3:2:1), based on the elemental molar ratio of Na:T 1 :T 2 The ratio of 1.025:0.97:0.03 was placed in a mixer and stirred at 400 rpm to obtain a mixture. The mixture was then sintered at 600°C for 4 hours in air and at 940°C for 16 hours. After sintering, it was naturally cooled to room temperature to obtain a high-pressure, high-capacity sodium-ion cathode material.

[0046] A third objective of this invention is to provide an application of the aforementioned sodium-ion cathode material in the preparation of sodium-ion batteries.

[0047] Compared with the prior art, the present invention has the following advantages:

[0048] (1) The cathode material prepared by the present invention has an O3 type polycrystalline gradation morphology, specifically a morphology of large and small particle gradation, and has the characteristics of high capacity and high compaction.

[0049] (2) This invention achieves uniform mixing of all elements in the precursor through co-precipitation, and regulates the morphology and physicochemical properties of the precursor by controlling the pH, concentration, temperature, rotation speed, and time of the reaction system. In particular, by precisely controlling the particle size of the precursor, a more uniform particle size distribution is achieved during the precursor synthesis stage.

[0050] (3) In the process of preparing the cathode material, the synergistic doping of Ca, Al, and Sb optimizes the electron conduction path, reduces oxidation side reactions, and improves cycle stability. The main reason is:

[0051] a. Preferentially occupy sodium sites (Ca) 2+ vs.Na + Due to their high ionic radius matching, a small number of them may substitute for transition metal sites (such as Mn). 4+ ),Ca 2+ Its strong bonding ability (Ca-O bond energy > 500 kJ / mol) inhibits the collapse of the layered structure during charging and discharging, and reduces Jahn-Teller distortion;

[0052] b. Al substitution of transition metal sites (Al) 3+ vs.Mn 4+ / Ni 2+ ), enhance Mn 3+ / Mn 4+ Redox reversibility (Al) 3+ Inhibit Mn 3+ Disproportionation reaction), improves thermal stability (high strength of Al-O bond (bond energy > 510 kJ / mol) inhibits high-temperature phase transition and oxygen release);

[0053] c.Sb 3+ / Sb 5+ With Mn 3+ The radii are close, Sb + The high electronegativity enhances the MO bond, suppresses transition metal dissolution and lattice oxygen loss (especially in the high voltage region > 4.0V), and alleviates the Jahn-Teller effect;

[0054] (4) The preparation method provided by the present invention is high-temperature air furnace sintering. The preparation method is simple, suitable for industrial production, and is green and environmentally friendly.

[0055] To more clearly illustrate the technical solutions of the embodiments of the present invention and the prior art, the accompanying drawings required for the description of the relevant embodiments or technologies are briefly described below. It should be noted that the drawings shown below are merely exemplary illustrations of some embodiments of the present invention, and those skilled in the art can derive other derivative embodiments based on the drawings without creative effort. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of the synthesis route for cathode material precursors.

[0057] Figure 2 SEM images of the cathode material precursors prepared in Comparative Example 1 and Example 10.

[0058] Figure 3 SEM images of the cathode materials prepared in Comparative Example 1 and Example 10.

[0059] Figure 4 The XRD patterns are of the cathode materials prepared in Comparative Example 1 and Example 10.

[0060] Figure 5 The charge-discharge curves are for the cathode material prepared in Comparative Example 1.

[0061] Figure 6 The charge-discharge curve of the positive electrode material prepared in Example 10 is shown.

[0062] Figure 7 Cycling curves (1C) of the cathode materials prepared in Comparative Example 1 and Example 10. Specific implementation methods

[0063] The present invention will be explained in more detail below through specific embodiments. In the following embodiments, unless otherwise specified, the raw materials and equipment used are existing or commercially available products.

[0064] In the following embodiments, the process flow of the cathode material precursor is as follows: Figure 1 As shown: The transition metal salt solution / alkali solution is pumped into reactor A and reactor B sequentially through a diversion valve. The large particle generation stage is completed first in reactor A, and then the small particle generation stage is completed in reactor B. After the generation is completed, the large and small particles in reactor A and reactor B are mixed and aged in a certain proportion to obtain the cathode material precursor.

[0065] In the following embodiments: T 1 This refers to the first doping element, i.e., transition elements such as Ni, Fe, and Mn, T 2 This refers to the second doping element, i.e., Ca, Al, Sb, etc. in the blend. NH4OH / M 2+ =1.2 refers to the molar ratio of ammonia to transition metal ions.

[0066] Example 1

[0067] (1) Preparation of cathode material precursor

[0068] Nickel sulfate, ferrous sulfate, and manganese sulfate were prepared in molar ratios of Ni:Fe:Mn = 0.33:0.33:0.33, resulting in 1 mol / L and 3 mol / L transition metal salt solutions, respectively. These solutions were then co-precipitated with sodium hydroxide solution as a precipitant and ammonia water as a complexing agent. The coprecipitation process consisted of three stages:

[0069] First stage (large particle formation stage in reactor A): Temperature controlled at 65℃, pH controlled at 11.0, metal salt 1.0 mol / L, flow rate 2 mL / min, NaOH concentration 4 mol / L, stirring speed 200 rpm, complexing agent (NH4OH / M 2+ =1.2), the reaction time is 8h, and the particle size is monitored in real time during the period.

[0070] The second stage (small particle formation stage in reactor B): When the reaction in reactor A reaches Dv50 = 12 μm, reactor B (small particle formation stage) is started. The temperature is controlled at 45℃, the pH is controlled at 11.5, the metal salt concentration is 3.0 mol / L, the flow rate is 10 mL / min, 8 mol / L NaOH is added, the stirring speed is 600 rpm, and the complexing agent is reduced to (NH4OH / M). 2+ =0.3), the reaction time is 2h, and the particle size is monitored in real time during the process.

[0071] Third stage: When reactor A reaches Dv50 = 14 μm and reactor B reaches Dv50 = 3.5 μm, reactor C is simultaneously pumped in at a volume ratio of large particles:small particles = 8:2. Particle size is monitored in real time. The mixing temperature is reduced to 50℃, the mixing time is 1 hour, and the mixing speed is 400 rpm. After mixing, the mixture is aged (intermittently stirred for 2 hours), filtered, washed, and dried to obtain the cathode material precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2.

[0072] (2) Preparation of cathode materials

[0073] The precursor prepared in step (1) is mixed with sodium carbonate and a blend (a mixture of calcium carbonate, aluminum oxide, and antimony trioxide, with an elemental molar ratio of Ca:Al:Sb = 3:2:1), according to the elemental molar ratio of Na:T 1 :T 2 A mixture of 1.025:0.97:0.03 was placed in a mixer and stirred at 400 rpm to obtain a final mixture. The mixture was then sintered in air at 600°C for 4 hours, followed by sintering at 940°C for 16 hours. After sintering, the mixture was allowed to cool naturally to room temperature and then pulverized to obtain the sodium ion cathode material Na. 1.025 T 1 0.97 T 2 0.03 O2.

[0074] Example 2

[0075] (1) Preparation of cathode material precursor

[0076] Nickel sulfate, ferrous sulfate, and manganese sulfate were prepared in molar ratios of Ni:Fe:Mn = 0.33:0.33:0.33, resulting in 1 mol / L and 3 mol / L transition metal salt solutions, respectively. These solutions were then co-precipitated with sodium hydroxide solution as a precipitant and ammonia water as a complexing agent. The coprecipitation process consisted of three stages:

[0077] First stage (large particle formation stage in reactor A): Temperature controlled at 65℃, pH controlled at 11.0, metal salt 1.0 mol / L, flow rate 2 mL / min, NaOH concentration 4 mol / L, stirring speed 200 rpm, complexing agent (NH4OH / M 2+ =1.2), the reaction time is 8h, and the particle size is monitored in real time during the period.

[0078] The second stage (small particle formation stage in reactor B): When the reaction in reactor A reaches Dv50 = 12 μm, reactor B (small particle formation stage) is started. The temperature is controlled at 45℃, the pH is controlled at 11.5, the metal salt concentration is 3.0 mol / L, the flow rate is 10 mL / min, 8 mol / L NaOH is added, the stirring speed is 600 rpm, and the complexing agent is reduced to (NH4OH / M). 2+ =0.3), the reaction time is 2h, and the particle size is monitored in real time during the process.

[0079] Third stage: When reactor A reaches Dv50 = 14μm and reactor B reaches Dv50 = 3.5μm, reactor C is simultaneously pumped in at a volume ratio of large particles:small particles = 8:2. Particle size is monitored in real time. To prevent secondary agglomeration of small particles, 0.1% citric acid (calculated based on the mass fraction of the total material) can be added. The mixing temperature is reduced to 50℃, the mixing time is 1 hour, and the mixing speed is 400 rpm. After mixing, the mixture is aged (intermittently stirred for 2 hours), filtered, washed, and dried to obtain the cathode material precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2.

[0080] (2) Preparation of cathode materials

[0081] The precursor from step (1) is mixed with sodium carbonate and a blend (a mixture of calcium carbonate, aluminum oxide, and antimony trioxide, with an elemental molar ratio of Ca:Al:Sb = 2:3:1), according to the elemental molar ratio of Na:T 1 :T 2 A mixture of 1.025:0.97:0.03 was placed in a mixer and stirred at 400 rpm to obtain a final mixture. The mixture was then sintered in air at 600°C for 4 hours, followed by sintering at 940°C for 18 hours. After sintering, the mixture was allowed to cool naturally to room temperature and then pulverized to obtain a high-pressure solid layered oxide sodium-ion cathode material (Na) with a polycrystalline gradation morphology. 1.025 T 1 0.97 T 2 0.03 O2.

[0082] Example 3

[0083] (1) Preparation of cathode material precursor

[0084] Nickel sulfate, ferrous sulfate, and manganese sulfate were prepared in molar ratios of Ni:Fe:Mn = 0.33:0.33:0.33, resulting in 1 mol / L and 3 mol / L transition metal salt solutions, respectively. These solutions were then co-precipitated with sodium hydroxide solution as a precipitant and ammonia water as a complexing agent. The coprecipitation process consisted of three stages:

[0085] First stage (large particle formation stage in reactor A): Temperature controlled at 65℃, pH controlled at 11.0, metal salt 1.0 mol / L, flow rate 2 mL / min, NaOH concentration 4 mol / L, stirring speed 200 rpm, complexing agent (NH4OH / M 2+ =1.2), the reaction time is 8h, and the particle size is monitored in real time during the period.

[0086] The second stage (small particle formation stage in reactor B): When the reaction in reactor A reaches Dv50 = 12 μm, reactor B (small particle formation stage) is started. The temperature is controlled at 45℃, the pH is controlled at 11.5, the metal salt concentration is 3.0 mol / L, the flow rate is 10 mL / min, 8 mol / L NaOH is added, the stirring speed is 600 rpm, and the complexing agent is reduced to (NH4OH / M). 2+ =0.3), the reaction time is 2h, and the particle size is monitored in real time during the process.

[0087] Third stage: When reactor A reaches Dv50 = 14 μm and reactor B reaches Dv50 = 3.5 μm, reactor C is simultaneously pumped in at a volume ratio of large particles:small particles = 8:2. Particle size is monitored in real time (0.1% citric acid can be added to prevent secondary agglomeration of small particles). The mixing temperature is reduced to 50℃, the mixing time is 1 hour, and the mixing speed is 400 rpm. After mixing, the mixture is aged (intermittently stirred for 2 hours), filtered, washed, and dried to obtain the cathode material precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2.

[0088] (2) Preparation of cathode materials

[0089] The precursor prepared in step (1) is mixed with sodium carbonate and a blend (a mixture of calcium carbonate, aluminum oxide, and antimony trioxide, with an elemental molar ratio of Ca:Al:Sb = 2:3:1), according to the elemental molar ratio of Na:T 1 :T 2 A mixture of 1.025:0.97:0.03 was placed in a mixer and stirred at 400 rpm to obtain a final mixture. The mixture was then sintered in air at 600°C for 4 hours, followed by sintering at 940°C for 14 hours. After sintering, the mixture was allowed to cool naturally to room temperature and then pulverized to obtain the sodium ion cathode material Na. 1.025 T 1 0.97 T 2 0.03 O2.

[0090] Example 4

[0091] (1) Preparation of cathode material precursor

[0092] Nickel sulfate, ferrous sulfate, and manganese sulfate were prepared in molar ratios of Ni:Fe:Mn = 0.33:0.33:0.33, resulting in 1 mol / L and 3 mol / L transition metal salt solutions, respectively. These solutions were then co-precipitated with sodium hydroxide solution as a precipitant and ammonia water as a complexing agent. The coprecipitation process consisted of three stages:

[0093] First stage (large particle formation stage in reactor A): Temperature controlled at 65℃, pH controlled at 11.0, metal salt 1.0 mol / L, flow rate 2 mL / min, 4 mol / L NaOH added, stirring speed 200 rpm, complexing agent (NH4OH / M 2+ =1.2), the reaction time is 8h, and the particle size is monitored in real time during the period.

[0094] The second stage (small particle formation stage in reactor B): When the reaction in reactor A reaches Dv50 = 12 μm, reactor B (small particle formation stage) is started. The temperature is controlled at 45℃, the pH is controlled at 11.5, the metal salt concentration is 3.0 mol / L (flow rate 10 mL / min), the NaOH concentration is 8 mol / L, the stirring speed is 600 rpm, and the complexing agent is reduced to (NH4OH / M). 2+ =0.3), the reaction time is 2h, and the particle size is monitored in real time during the process.

[0095] Third stage: When reactor A reaches Dv50 = 14 μm and reactor B reaches Dv50 = 3.5 μm, reactor C is simultaneously pumped in at a volume ratio of large particles:small particles = 8:2. Particle size is monitored in real time (0.1% citric acid can be added to prevent secondary agglomeration of small particles). The mixing temperature is reduced to 50℃, the mixing time is 1 hour, and the mixing speed is 400 rpm. After mixing, the mixture is aged (intermittently stirred for 3 hours), filtered, washed, and dried to obtain the cathode material precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2.

[0096] (2) Preparation of cathode materials

[0097] The precursor prepared in step (1) is mixed with sodium carbonate and a blend (a mixture of calcium carbonate, aluminum oxide, and antimony trioxide, with an elemental molar ratio of Ca:Al:Sb = 1:3:2), according to the elemental molar ratio of Na:T 1 :T 2 A mixture of 1.025:0.97:0.03 was placed in a mixer and stirred at 400 rpm to obtain a final mixture. This mixture was then sintered in air at 600°C for 4 hours, followed by sintering at 950°C for 16 hours. After sintering, the mixture was allowed to cool naturally to room temperature and then pulverized to obtain the sodium ion cathode material Na. 1.025 T 1 0.97T 2 0.03 O2.

[0098] Example 5

[0099] (1) Preparation of cathode material precursor

[0100] Nickel sulfate, ferrous sulfate, and manganese sulfate were prepared in molar ratios of Ni:Fe:Mn = 0.33:0.33:0.33, resulting in 1 mol / L and 3 mol / L transition metal salt solutions, respectively. These solutions were then co-precipitated with sodium hydroxide solution as a precipitant and ammonia water as a complexing agent. The coprecipitation process consisted of three stages:

[0101] First stage (large particle formation stage in reactor A): Temperature controlled at 65℃, pH controlled at 11.0, metal salt 1.0 mol / L, flow rate 2 mL / min, NaOH concentration 4 mol / L, stirring speed 200 rpm, complexing agent (NH4OH / M 2+ =1.2), the reaction time is 8h, and the particle size is monitored in real time during the period.

[0102] The second stage (small particle formation stage in reactor B): When the reaction in reactor A reaches Dv50 = 12 μm, reactor B (small particle formation stage) is started. The temperature is controlled at 45℃, the pH is controlled at 11.5, the metal salt concentration is 3.0 mol / L (flow rate 10 mL / min), the NaOH concentration is 8 mol / L, the stirring speed is 600 rpm, and the complexing agent is reduced to (NH4OH / M). 2+ =0.3), and the reaction time is 2h.

[0103] Third stage: When reactor A reaches 14μm and reactor B reaches 3.5μm, reactor C is simultaneously pumped in at a volume ratio of large particles:small particles = 8:2. Particle size is monitored in real time (0.1% citric acid can be added to prevent secondary agglomeration of small particles). The mixing temperature is reduced to 50℃, the mixing time is 1 hour, and the mixing speed is 400 rpm. After mixing, the mixture is aged (intermittently stirred for 3 hours), filtered, washed, and dried to obtain the cathode material precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2.

[0104] (2) Preparation of cathode materials

[0105] The precursor prepared in step (1) is mixed with sodium carbonate and a blend (a mixture of calcium carbonate, aluminum oxide, and antimony trioxide, with an elemental molar ratio of Ca:Al:Sb = 1:2:3), according to the elemental molar ratio of Na:T 1 :T 2A mixture of 1.025:0.97:0.03 was placed in a mixer and stirred at 400 rpm to obtain a final mixture. The mixture was then sintered in air at 600°C for 4 hours, followed by sintering at 950°C for 14 hours. After sintering, the mixture was allowed to cool naturally to room temperature and then pulverized to obtain the sodium ion cathode material Na. 1.025 T 1 0.97 T 2 0.03 O2.

[0106] Example 6

[0107] (1) Preparation of cathode material precursor

[0108] Nickel sulfate, ferrous sulfate, and manganese sulfate were prepared in molar ratios of Ni:Fe:Mn = 0.33:0.33:0.33, resulting in 1 mol / L and 3 mol / L transition metal salt solutions, respectively. These solutions were then co-precipitated with sodium hydroxide solution as a precipitant and ammonia water as a complexing agent. The coprecipitation process consisted of three stages:

[0109] First stage (large particle formation stage in reactor A): Temperature controlled at 65℃, pH controlled at 10, metal salt 1.0 mol / L, flow rate 2 mL / min, NaOH concentration 4 mol / L, stirring speed 200 rpm, complexing agent (NH4OH / M 2+ =1.2), the reaction time is 8h, and the particle size is monitored in real time during the period.

[0110] The second stage (small particle formation stage in reactor B): When the reaction in reactor A reaches Dv50 = 12 μm, reactor B (small particle formation stage) is started. The temperature is controlled at 45℃, the pH is controlled at 11.5, the metal salt concentration is 3.0 mol / L (flow rate 10 mL / min), the NaOH concentration is 8 mol / L, the stirring speed is 600 rpm, and the complexing agent is reduced to (NH4OH / M). 2+ =0.3), the reaction time is 2h, and the particle size is monitored in real time during the process.

[0111] Third stage: When reactor A reaches 14μm and reactor B reaches 3.5μm, reactor C is simultaneously pumped in at a volume ratio of large particles:small particles = 7:3. Particle size is monitored in real time (0.1% citric acid can be added to prevent secondary agglomeration of small particles). The mixing temperature is reduced to 50℃, the mixing time is 1 hour, and the mixing speed is 400 rpm. After mixing, the mixture is aged (intermittently stirred for 2 hours), filtered, washed, and dried to obtain the cathode material precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2.

[0112] (2) Preparation of cathode materials

[0113] The precursor prepared in step (1) is mixed with sodium carbonate and a blend (a mixture of calcium carbonate, aluminum oxide, and antimony trioxide, with an elemental molar ratio of Ca:Al:Sb = 3:2:1), according to the elemental molar ratio of Na:T 1 :T 2 A mixture of 1.025:0.97:0.03 was placed in a mixer and stirred at 400 rpm to obtain a final mixture. The mixture was then sintered in air at 600°C for 4 hours, followed by sintering at 950°C for 14 hours. After sintering, the mixture was allowed to cool naturally to room temperature and then pulverized to obtain the sodium ion cathode material Na. 1.025 T 1 0.97 T 2 0.03 O2.

[0114] Example 7

[0115] (1) Preparation of cathode material precursor

[0116] Nickel sulfate, ferrous sulfate, and manganese sulfate were prepared in molar ratios of Ni:Fe:Mn = 0.33:0.33:0.33, resulting in 1 mol / L and 3 mol / L transition metal salt solutions, respectively. These solutions were then co-precipitated with sodium hydroxide solution as a precipitant and ammonia water as a complexing agent. The coprecipitation process consisted of three stages:

[0117] First stage (large particle formation stage in reactor A): Temperature controlled at 65℃, pH controlled at 11.0, metal salt 1.0 mol / L, flow rate 2 mL / min, NaOH concentration 4 mol / L, stirring speed 200 rpm, complexing agent (NH4OH / M 2+ =1.2), the reaction time is 10h, and the particle size is monitored in real time during the process.

[0118] The second stage (small particle formation stage in reactor B): When the reaction in reactor A reaches Dv50 = 12 μm, reactor B (small particle formation stage) is started. The temperature is controlled at 45℃, the pH at 11.5, the metal salt concentration is 3.0 mol / L (flow rate 10 mL / min), the NaOH concentration is 8 mol / L, the stirring speed is 600 rpm, and the complexing agent is reduced to (NH4OH / M). 2+ =0.3), the reaction time is 3h, and the particle size is monitored in real time during the process.

[0119] Third stage: When reactor A reaches 14μm and reactor B reaches 3.5μm, reactor C is simultaneously pumped in at a volume ratio of large particles:small particles = 7:3. Particle size is monitored in real time. The mixing temperature is reduced to 50℃, the mixing time is 1.0 h, and the mixing speed is 400 rpm. After mixing, the mixture is aged (intermittently stirred for 2 h), filtered, washed, and dried to obtain the cathode material precursor Ni.1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2.

[0120] (2) Preparation of cathode materials

[0121] The precursor prepared in step (1) is mixed with sodium carbonate and a blend (a mixture of calcium carbonate, aluminum oxide, and antimony trioxide, with an elemental molar ratio of Ca:Al:Sb = 3:2:1), according to the elemental molar ratio of Na:T 1 :T 2 A mixture of 1.025:0.97:0.03 was placed in a mixer and stirred at 400 rpm to obtain a compound. The compound was then sintered in air at 600°C for 4 hours, followed by sintering at 950°C for 16 hours. After sintering, the mixture was allowed to cool naturally to room temperature and then pulverized to obtain Na, a sodium-ion cathode material. 1.025 T 1 0.97 T 2 0.03 O2.

[0122] Example 8

[0123] (1) Preparation of cathode material precursor

[0124] Nickel sulfate, ferrous sulfate, and manganese sulfate were prepared in molar ratios of Ni:Fe:Mn = 0.33:0.33:0.33, resulting in 1 mol / L and 3 mol / L transition metal salt solutions, respectively. These solutions were then co-precipitated with sodium hydroxide solution as a precipitant and ammonia water as a complexing agent. The coprecipitation process consisted of three stages:

[0125] First stage (large particle formation stage in reactor A): Temperature controlled at 65℃, pH controlled at 11.0, metal salt 1.0 mol / L, flow rate 2 mL / min, 4 mol / L NaOH added, stirring speed 200 rpm, complexing agent (NH4OH / M 2+ =1.2), the reaction time is 8h, and the particle size is monitored in real time during the period.

[0126] The second stage (small particle formation stage in reactor B): When the reaction in reactor A reaches Dv50 = 12 μm, reactor B (small particle formation stage) is started. The temperature is controlled at 45℃, the pH is controlled at 11.5, the metal salt concentration is 3.0 mol / L (flow rate 10 mL / min), the NaOH concentration is 8 mol / L, the stirring speed is 600 rpm, and the complexing agent is reduced to (NH4OH / M). 2+ =0.3), the reaction time is 2h, and the particle size is monitored in real time during the process.

[0127] In the third stage, when reactor A reaches 14 μm and reactor B reaches 3.5 μm, reactor C is simultaneously pumped in at a volume ratio of large particles to small particles of 7:3. Particle size is monitored in real time (0.1% citric acid can be added to prevent secondary agglomeration of small particles). The mixing temperature is reduced to 50℃, the mixing time is 1 hour, and the mixing speed is 400 rpm. After mixing, the mixture is aged (intermittently stirred for 2 hours), filtered, washed, and dried to obtain the cathode material precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2.

[0128] (2) Preparation of cathode materials

[0129] The precursor prepared in step (1) is mixed with sodium carbonate and a blend (a mixture of calcium carbonate, aluminum oxide, and antimony trioxide, with an elemental molar ratio of Ca:Al:Sb = 3:2:1), according to the elemental molar ratio of Na:T 1 :T 2 A mixture of 1.04:0.97:0.03 was placed in a mixer and stirred at 400 rpm to obtain a compound. The compound was then sintered in air at 600°C for 4 hours, followed by sintering at 940°C for 16 hours. After sintering, the mixture was allowed to cool naturally to room temperature and then pulverized to obtain the sodium ion cathode material Na. 1.04 T 1 0.97 T 2 0.03 O2.

[0130] Example 9

[0131] (1) Preparation of cathode material precursor

[0132] Nickel sulfate, ferrous sulfate, and manganese sulfate were prepared in molar ratios of Ni:Fe:Mn = 0.33:0.33:0.33, resulting in 1 mol / L and 3 mol / L transition metal salt solutions, respectively. These solutions were then co-precipitated with sodium hydroxide solution as a precipitant and ammonia water as a complexing agent. The coprecipitation process consisted of three stages:

[0133] First stage (large particle formation stage in reactor A): Temperature controlled at 65℃, pH controlled at 11, metal salt 1.0 mol / L, flow rate 2 mL / min, NaOH concentration 4 mol / L, stirring speed 200 rpm, complexing agent (NH4OH / M 2+ =1.2), the reaction time is 8h, and the particle size is monitored in real time during the period.

[0134] The second stage (small particle formation stage in reactor B): When the reaction in reactor A reaches Dv50 = 12 μm, reactor B (small particle formation stage) is started. The temperature is controlled at 45℃, the pH is controlled at 11.5, the metal salt concentration is 3.0 mol / L (flow rate 10 mL / min), the NaOH concentration is 8 mol / L, the stirring speed is 600 rpm, and the complexing agent is reduced to (NH4OH / M). 2+ =0.3), the reaction time is 2h, and the particle size is monitored in real time during the process.

[0135] Third stage: When reactor A reaches 14μm and reactor B reaches 3.5μm, reactor C is simultaneously pumped in at a volume ratio of large particles:small particles = 7:3. Particle size is monitored in real time. The mixing temperature is reduced to 50℃, the mixing time is 1 hour, and the mixing speed is 400 rpm. After mixing, the mixture is aged (intermittently stirred for 3 hours), filtered, washed, and dried to obtain the cathode material precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2.

[0136] (2) Preparation of cathode materials

[0137] The precursor prepared in step (1) is mixed with sodium carbonate and a blend (a mixture of calcium carbonate, aluminum oxide, and antimony trioxide, with an elemental molar ratio of Ca:Al:Sb = 3:2:1), according to the elemental molar ratio of Na:T 1 :T 2 A mixture of 1.025:0.97:0.03 was placed in a mixer and stirred at 400 rpm to obtain a compound. The compound was then sintered in air at 600°C for 4 hours, followed by sintering at 940°C for 18 hours. After sintering, the mixture was allowed to cool naturally to room temperature and then pulverized to obtain the sodium ion cathode material Na. 1.025 T 1 0.97 T 2 0.03 O2.

[0138] Example 10

[0139] (1) Preparation of cathode material precursor

[0140] Nickel sulfate, ferrous sulfate, and manganese sulfate were prepared in molar ratios of Ni:Fe:Mn = 0.33:0.33:0.33, resulting in 1 mol / L and 3 mol / L transition metal salt solutions, respectively. These solutions were then co-precipitated with sodium hydroxide solution as a precipitant and ammonia water as a complexing agent. The coprecipitation process consisted of three stages:

[0141] First stage (large particle formation stage in reactor A): Temperature controlled at 65℃, pH controlled at 11.0, metal salt 1.0 mol / L, flow rate 2 mL / min, NaOH concentration 4 mol / L, stirring speed 200 rpm, complexing agent (NH4OH / M 2+ =1.2), the reaction time is 8h, and the particle size is monitored in real time during the period.

[0142] The second stage (small particle formation stage in reactor B): When the reaction in reactor A reaches Dv50 = 12 μm, reactor B (small particle formation stage) is started. The temperature is controlled at 45℃, the pH is controlled at 11.5, the metal salt concentration is 3.0 mol / L (flow rate 10 mL / min), the NaOH concentration is 8 mol / L, the stirring speed is 600 rpm, and the complexing agent is reduced to (NH4OH / M). 2+ =0.3), the reaction time is 2h, and the particle size is monitored in real time during the process.

[0143] Third stage: When reactor A reaches 14μm and reactor B reaches 3.5μm, reactor C is simultaneously pumped in at a volume ratio of large particles:small particles = 7:3. Particle size is monitored in real time (0.1% citric acid can be added to prevent secondary agglomeration of small particles). The mixing temperature is reduced to 50℃, the mixing time is 1 hour, and the mixing speed is 400 rpm. After mixing, the mixture is aged (intermittently stirred for 2 hours), filtered, washed, and dried to obtain the cathode material precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2.

[0144] (2) Preparation of cathode materials

[0145] The precursor prepared in step (1) is mixed with sodium carbonate and a blend (a mixture of calcium carbonate, aluminum oxide, and antimony trioxide, with an elemental molar ratio of Ca:Al:Sb = 3:2:1), according to the elemental molar ratio of Na:T 1 :T 2 A mixture of 1.025:0.97:0.03 was placed in a mixer and stirred at 400 rpm to obtain a final mixture. The mixture was then sintered in air at 600°C for 4 hours, followed by sintering at 940°C for 16 hours. After sintering, the mixture was allowed to cool naturally to room temperature and then pulverized to obtain the sodium ion cathode material Na. 1.025 T 1 0.97 T 2 0.03 O2.

[0146] Comparative Example 1

[0147] The preparation method is the same as in Example 10, except that the sintering temperature in step (2) is changed, and its effect on the morphology and properties of the material is investigated.

[0148] (2) Preparation of cathode materials

[0149] The precursor prepared in step (1) is mixed with sodium carbonate and a blend (a mixture of calcium carbonate, aluminum oxide, and antimony trioxide, with an elemental molar ratio of Ca:Al:Sb = 3:2:1), according to the elemental molar ratio of Na:T 1 :T 2 A mixture of 1.025:0.97:0.03 was placed in a mixer and stirred at 400 rpm to obtain a final mixture. The mixture was then sintered in air at 600°C for 4 hours, followed by sintering at 960°C for 16 hours. After sintering, the mixture was allowed to cool naturally to room temperature and then pulverized to obtain the sodium ion cathode material Na. 1.025 Ni 0.3233 Fe 0.3233 Mn 0.3233 Ca 0.015 Al 0.010 Sb 0.005 O2.

[0150] Comparative Example 2

[0151] The preparation method is the same as in Example 10, except that no elements are doped in step (2) to examine the effect of doping elements on the morphology and properties of the material.

[0152] (2) Preparation of cathode materials

[0153] The precursor prepared in step (1) and sodium carbonate are mixed according to the elemental molar ratio Na:T 1 A 1.025:1 ratio of sodium ions was added to a mixer and stirred at 400 rpm to obtain a mixture. The mixture was then sintered at 600°C for 4 hours in air and then at 940°C for 16 hours. After sintering, the mixture was allowed to cool naturally to room temperature and then pulverized to obtain the sodium ion cathode material Na. 1.025 Ni 0.3233 Fe 0.3233 Mn 0.323 3O2.

[0154] Comparative Example 3

[0155] The preparation method is the same as in Example 10, except that in step (2), only Ca is doped to investigate the effect of a single dopant element on the morphology and properties of the material.

[0156] (2) Preparation of cathode materials

[0157] The precursor, sodium carbonate, and calcium carbonate prepared in step (1) are mixed according to the elemental molar ratio Na:T 1A mixture of Ca (1.025:0.97:0.03) was placed in a mixer and stirred at 400 rpm to obtain a final product. The mixture was then sintered in air at 600°C for 4 hours, followed by sintering at 940°C for 16 hours. After sintering, the mixture was allowed to cool naturally to room temperature and then pulverized to obtain a high-pressure solid layered oxide sodium-ion cathode material (Na) with a polycrystalline gradation morphology. 1.025 Ni 0.3233 Fe 0.3233 Mn 0.3233 Ca 0.03 O2.

[0158] Comparative Example 4

[0159] The preparation method is the same as in Example 10, except that in step (2), only Al element is doped to investigate the effect of a single dopant element on the morphology and properties of the material.

[0160] (2) Preparation of cathode materials

[0161] The precursor, sodium carbonate, and aluminum oxide prepared in step (1) are mixed in an elemental molar ratio of Na:T 1 Al = 1.025:0.97:0.03 was placed in a mixer and stirred at 400 rpm to obtain a mixture. The mixture was then sintered at 600℃ for 4 hours in air atmosphere, followed by sintering at 940℃ for 16 hours. After sintering, it was naturally cooled to room temperature and pulverized to obtain sodium ion cathode material Na. 1.025 Ni 0.3233 Fe 0.3233 Mn 0.3233 Al 0.03 O2.

[0162] Comparative Example 5

[0163] The preparation method is the same as in Example 10, except that in step (2), only Sb element is doped to investigate the effect of a single dopant element on the morphology and properties of the material.

[0164] (2) Preparation of cathode materials

[0165] The precursor, sodium carbonate, and antimony trioxide prepared in step (1) are mixed in an elemental molar ratio of Na:T 1 A mixture of Sb (1.025:0.97:0.03) was placed in a mixer and stirred at 400 rpm to obtain a final product. The mixture was then sintered in air at 600°C for 4 hours, followed by sintering at 940°C for 16 hours. After sintering, the mixture was allowed to cool naturally to room temperature and then pulverized to obtain a high-pressure solid layered oxide sodium-ion cathode material (Na) with a polycrystalline gradation morphology. 1.025 Ni 0.3233 Fe 0.3233 Mn 0.3233 Sb 0.03 O2.

[0166] Product confirmation:

[0167] The cathode material precursors prepared in Example 10 and Comparative Example 1 of this invention were subjected to SEM analysis, as follows: Figure 2 As shown, during the preparation of the cathode material precursor, adjusting the concentration of the complexing agent ammonia, pH, temperature, stirring speed, aging time, etc., promotes the formation of the Ni cathode material precursor. 1 / 3 Fe 1 / 3 Mn 1 / 3 The Dv10 of (OH)2 is at 3.5 ± 0.5 μm, D v The particles with a diameter between 14 and 0.5 μm exhibited a secondary particle morphology with a graded particle size distribution. The synthesis process revealed that high concentrations of metal salts favored explosive nucleation and the growth of small particles. High pH combined with low reaction temperature ensured rapid crystal precipitation and growth. Furthermore, a low proportion of complexing agent reduced complexation, and high stirring speed inhibited particle agglomeration. The low pH was achieved by controlling pH, metal salt concentration, and reaction temperature. The opposite approach was applied to the growth of large particles.

[0168] Figure 3 SEM images of sodium-ion cathode materials prepared in Example 10 and Comparative Example 1 at different sintering temperatures are shown. Figure 3 (a) is the SEM image of Comparative Example 1. It can be seen that when the sintering temperature is 960℃, the morphology is similar to a single-crystal lamellar structure. This is due to the enlargement of secondary particles, which indicates over-sintering. Figure 3 (b) The sample prepared in Example 10, as shown in the figure, exhibits a polycrystalline gradation morphology with uniform distribution, indicating that reducing calcination helps suppress the growth of secondary particles and inhibits the development towards monocrystalline formation. Combined with... Figure 4 As shown, the cathode material prepared in Example 10 still has the O3 crystal form after doping with elements. This demonstrates that the present invention prepares a high-pressure solid layered oxide sodium ion cathode material with a polycrystalline gradation morphology.

[0169] Performance testing:

[0170] The sodium-ion cathode materials prepared in Examples 1-10 and Comparative Examples 1-5 were subjected to electrochemical performance, particle size, and BET method tests, respectively. The test results are shown in Tables 1 and 2.

[0171] (1) Electrochemical performance

[0172] The sodium-ion cathode material powders prepared in Examples 1-10 and Comparative Examples 1-5 were ground through a 200-mesh sieve, then mixed with SP (conductive carbon black) and PVDF (polyvinylidene fluoride) in a mass ratio of 8:1:1, and NMP (N-methylpyrrolidone) was added and stirred to form a slurry. This slurry was coated onto aluminum foil, dried, punched, and pressed to form the sodium-ion battery cathode material electrode sheet. Using metallic sodium as the negative electrode, glass fiber (Whatman GF / D brand) as the separator, and a NaPF6 (sodium hexafluorophosphate) PC (propylene carbonate) / EMC (ethyl methyl carbonate) solution as the electrolyte, CR2025 button batteries were assembled in an argon-filled glove box for charge-discharge testing. Under conditions of a current density of 100 mAh / g and a voltage range of 2.0-4.0V / 4.1V, the capacity and cycle performance were tested first at 0.2C for 2 cycles, and then at 1C.

[0173] (2) Particle size

[0174] The particle size distribution was determined according to the national standard GB / T19077-2016, wide-range diffraction method.

[0175] (3) BET

[0176] The specific surface area of ​​solid materials was determined according to the national standard GB / T 19587-2017, which specifies the gas adsorption BET method.

[0177] Table 1. Electrochemical performance of Comparative Examples 1-5 and Examples 1-10

[0178]

[0179]

[0180] Table 2. Physicochemical properties of Comparative Examples 1-5 and Examples 1-10

[0181]

[0182]

[0183] analyze:

[0184] Combining Tables 1 and 2, Figures 4-7 As shown

[0185] (1) As shown in Table 1, compared with Comparative Examples 1-5, the cathode materials prepared in Examples 1-10 have superior electrochemical performance and cycle performance. Taking Comparative Example 1 and Example 10 as examples: Comparative Example 1 is a near-single-crystal material, while Example 10 is a polycrystalline material. The 0.2C first discharge capacity and 1C first discharge capacity of the coin cell in Example 10 are significantly higher than those in Comparative Example 1. Figure 6As shown, Example 10 exhibits a significantly higher capacity retention rate after 100 cycles compared to Comparative Example 1. The main reasons for this are:

[0186] (a) Kinetic limitations: BET tests confirmed a decrease in specific surface area, i.e. a reduction in the effective electrochemical active area.

[0187] (b) Crystal structure defects: High-temperature environments induce transition metal ions to migrate to the sodium layer, leading to an increase in irreversible capacity during the first cycle. Figure 6 ).

[0188] (c) Increased interfacial side reactions: residual alkali on the surface leads to oxidative decomposition of the electrolyte, reducing capacity loss.

[0189] (2) Comparative Example 2 and Example 10 have the same preparation process, but Comparative Example 2 is not doped. Compared with Example 10, Comparative Example 2 has poorer discharge specific capacity and cycle performance. This is because the element Ca doped in Example 10 has a larger radius, which can expand the cell parameters of the cathode material, which is conducive to the diffusion of sodium ions and has a better discharge specific capacity. The doping of Al and Sb elements can further stabilize the structure and improve the cycle performance of the material. Comparative Examples 3-5 have the same preparation process as Comparative Example 2, but the difference is that Comparative Examples 3-5 are doped with different single elements. As can be seen from Table 1, the discharge specific capacity (2-4.0V 0.2C) of Comparative Example 3 is 4mAh / g higher than that of Comparative Example 2, indicating that the addition of Ca is beneficial to the increase of the discharge specific capacity of the material. The addition of Al and Sb elements makes the cycle performance of Comparative Examples 4 and 5 higher than that of Comparative Example 2, which again confirms that Al and Sb elements have the effect of stabilizing the result and improving the cycle stability.

[0190] (3) By adjusting the precursor preparation process parameters, cathode material sintering process parameters, and element ratios, a suitable temperature was achieved during cathode material sintering to optimize the material particle size (Example 10), thereby releasing a higher specific capacity. Compared to Example 10, the sodium content increased in Example 8, leading to an improvement in the material's discharge specific capacity. However, the cycle retention rate of Example 2 was lower than that of Example 10, mainly because the excessive sodium carbonate content resulted in a thicker passivation layer on the material surface. Combining Tables 1 and 2, the overall compaction density was higher than that of conventional synthesis methods (3.0 g / cm³). 3 Example 10 exhibits the best overall performance, and the crystal form of the material in Example 10 remains O3 after doping. Figure 4 Its cathode material exhibits an electrochemical performance with a discharge specific capacity of 144.54 mAh / g under conditions of 2-4.0 V and 0.2 C. Figure 6 ), the capacity retention rate after 100 cycles at 1C is 93.36% ( Figure 7 ).

[0191] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sodium-ion cathode material, characterized in that: The cathode material has an O3-type polycrystalline graded morphology, and its chemical formula is: Na x T 1 y T 2 (1-y) O2, where 1.00 ≤ x ≤ 1.05, 0.7 ≤ y ≤ 0.98; T 1 T is a transition metal element. 2 As a doping element, the T 1 The doping element is selected from one or more of Ni, Fe, Mn, Co, Zr, and Cu; the doping element T 2 It is a mixture of Ca, Al, and Sb, wherein the molar ratio of Ca, Al, and Sb is 2-3:3-4:1-2; The method for preparing the sodium ion cathode material includes the following steps: (1) Preparation of cathode material precursor Will contain T 1 The sulfates of elements are combined to form a transition metal salt solution of a certain concentration, which is then co-precipitated with sodium hydroxide solution as a precipitant and ammonia water as a complexing agent. The coprecipitation is divided into three stages: large particles are generated in reactor A, small particles are generated in reactor B, and the particle size in reactor A and reactor B is monitored in real time. After the particle size reaches the required level, the particles in reactor A and reactor B are graded in a certain proportion, mixed, aged, filtered, washed, and dried to obtain the cathode material precursor. (2) Preparation of cathode material The cathode material precursor, sodium source, and dopant element T are used. 2 The materials are placed in a mixer in a certain proportion and stirred at a certain speed to obtain a blend. The blend is then sintered in a certain atmosphere and at a certain temperature, and pulverized to obtain sodium ion cathode material with O3 type polycrystalline gradation.

2. The sodium-ion cathode material according to claim 1, characterized in that: In the chemical formula of the sodium ion cathode material, 1.01 ≤ x ≤ 1.035, and the transition metal element T... 1 It is a mixture of Ni, Fe, and Mn, with 0.9 ≤ y ≤ 0.98, wherein the molar ratio of Ni, Fe, and Mn is 1:1:

1.

3. The sodium-ion cathode material according to claim 1, characterized in that: In the chemical formula of the cathode material, x = 1.025; transition metal element T 1 It is a mixture of Ni, Fe, and Mn, wherein the molar ratio of Ni, Fe, and Mn is 1:1:1, and y=0.

97.

4. The sodium-ion cathode material according to claim 1, characterized in that: The polycrystalline morphology of the cathode material is one or a mixture of two or more of the following: spherical, near-spherical, polyhedral, sheet-like, and blocky; the particle size D of the cathode material is... v 10 represents 1-5 μm, D v The thickness of the cathode material is 6-15 μm; the I(003):I(104) ratio in the XRD of the cathode material is 0.40-0.75; the BET value of the cathode material is 0.4-0.9 μm. 2 / g.

5. The sodium-ion cathode material according to claim 4, characterized in that: The polycrystalline morphology of the cathode material particles is spherical; the particle size D v 10 is 1.5-3.5μm, D v The thickness of the layered cathode material is 8-13 μm; the I(003):I(104) ratio in XRD is 0.56-0.70; the BET value is 0.45-0.60 μm. 2 / g.

6. The sodium-ion cathode material according to claim 1, characterized in that: In step (1): the element containing transition element T 1 The sulfate is selected from nickel sulfate, manganese sulfate, and cobalt sulfate, and is prepared into a mixed solution of metal salts with a concentration of 1-3 mol / L; the concentration of the precipitant sodium hydroxide is 3-5 mol / L; and the concentration of the ammonia solution is 4-6 g / L. The large particle generation process is as follows: the reactor temperature is controlled at 65℃, the pH is controlled at 11.0, the transition metal salt concentration is 1.0 mol / L, the flow rate is 2 mL / min, the NaOH concentration is 4 mol / L, the stirring speed is 200 rpm, and the complexing agent is NH4OH / M. 2+ =1.2, reaction time is 8h, particle size is monitored in real time during the process; the small particle generation process is as follows: reactor temperature is controlled at 45℃, pH is controlled at 11.5, metal salt is 3.0 mol / L, flow rate is 10mL / min, NaOH concentration is 8mol / L, stirring speed is 600rpm, and complexing agent is reduced to NH4OH / M 2+ =0.3, reaction time is 2h, and particle size is monitored in real time during the process; when the particle size of large particles reaches Dv50=12μm, the small particle generation process is started. The ratio of large particles to small particles is 6:4-8:

2.

7. The sodium-ion cathode material according to claim 1, characterized in that: In step (2): the cathode material precursor prepared in step (1) is combined with a sodium source and a dopant element T. 2 The mixture is based on the elemental molar ratio Na:T 1 :T 2 The mixture of 1.00~1.05:0.95~1:0.02~0.10 is thoroughly mixed, and then the mixed material is placed in a high-temperature furnace and calcined in an air or oxygen atmosphere. The calcination process is divided into two stages: the first stage is to raise the temperature to 400-600℃ and hold it for 2-4 hours; the second stage is to raise the temperature to 750-950℃ and sinter for 12-20 hours. After sintering, the material is naturally cooled to room temperature to obtain sodium ion cathode material.

8. The sodium-ion cathode material according to claim 1, characterized in that: In step (2): the sodium source is selected from one or more of sodium carbonate, sodium oxalate, sodium bicarbonate, sodium acetate, sodium oxalate, and sodium citrate; the dopant element T 2 It is a mixture of Ca, Al, and Sb, wherein: the compound containing Ca is one or a mixture of two or more of calcium carbonate, calcium oxide, calcium peroxide, calcium hydroxide, and calcium sulfate; the compound containing Al is one or a mixture of two or more of aluminum oxide, aluminum hydroxide, and aluminum sulfate; and the compound containing Sb is one or more of antimony trioxide, antimony pentoxide, and antimony pentafluoride.

9. The use of the sodium-ion cathode material according to any one of claims 1-8 in the preparation of sodium-ion batteries.

Images