Spherical sodium ion battery positive electrode material and preparation method thereof

Abstract

The invention provides a preparation method of a spherical layered oxide positive electrode material formed by compactly stacking primary particles, the chemical general formula of the spherical layered oxide positive electrode material is NaxNi < 0.4-y > Fe < 0.2 + y + z > Mn < 0.4-z > O < 2 >, the value range of x is 0.8-1, and the value ranges of y and z are 0-0.1. The preparation method comprises the following steps: dissolving a sodium source precursor and a transition metal source precursor in water, stirring to obtain slurry, sanding, spray-drying and granulating to obtain spherical precursor powder, and finally calcining at high temperature to obtain the spherical layered oxide positive electrode material. The spherical layered oxide positive electrode material is spherical secondary particles formed by agglomerating cuboid-shaped primary nano particles, the particle size of the particles is 4-8 microns, the specific surface area is 0.40-0.55 m < 2 > / g, the tap density is 1.50-1.65 g / cm < 3 >, and the interlayer spacing is 1.50-1.65 g / cm < 3 >. The preparation process is simple and easy to implement; the prepared positive electrode material has relatively high tap density and specific capacity and excellent cycling stability, shows good performance when being applied to the sodium-ion battery, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery positive electrode materials, and in particular to a spherical layered oxide positive electrode material composed of densely stacked primary nanoparticles with high capacity and stable cycle performance, and a preparation method thereof. Background Art

[0002] The sharp contradiction between surging energy demand and shrinking fossil energy reserves necessitates the development of a new renewable energy architecture for human civilization. Carbon-free energy technologies, centered around photovoltaic conversion, wind power generation, and ocean energy development, are reshaping the energy landscape. However, the intermittent power supply and regional dependence of these technologies place a rigid demand on the construction of large-scale energy storage facilities. Among existing electrochemical energy storage technologies, lithium-based battery systems have achieved large-scale application in energy storage due to their high specific energy and long-lasting cycle performance. However, due to supply chain risks and volatile prices caused by the geographical concentration of lithium resources, academic circles are focusing on advancing the research and development of sodium-based energy storage systems. As the sixth most abundant element in the Earth's crust (2.3-2.8 wt.%), sodium's widespread distribution and abundant reserves provide a key material foundation for the development of economical energy storage devices. Current innovative research on sodium cathode materials focuses on three key technological paths: layered transition metal oxides, polyanionic compounds, and Prussian blue analogs. Layered oxide systems, due to their unique crystal engineering properties, offer significant advantages. Through various manipulations, they can achieve discharge capacities exceeding 180 mAh / g, laying a crucial scientific foundation for their industrial application. However, traditional solid-phase synthesis of layered oxide materials suffers from irregular particle morphology, resulting in low tap density and slow ion diffusion kinetics. A simpler, morphology-controllable synthesis method is urgently needed. Summary of the Invention

[0003] Purpose of the Invention

[0004] The present invention provides a method for preparing a spherical layered oxide cathode material composed of densely packed primary nanoparticles. The cathode material prepared by the method has high tap density, high capacity and stable cycle performance, and the process is simple and easy to implement.

[0005] Technical Solution

[0006] The present invention is achieved in the following ways:

[0007] A method for preparing a spherical layered oxide cathode material composed of densely packed primary nanoparticles, wherein the chemical formula of the spherical layered oxide cathode material can be expressed as Na x Ni 0.4-y Fe 0.2+y+z Mn 0.4-zO2. wherein the value range of x is 0.8-1, and the value range of y and z is 0-0.1, and the characteristic is that the preparation process of the spherical layered oxide positive electrode material comprises:

[0008] (1) weighing the precursors of the sodium source and the transition metal source according to the above stoichiometric ratio, dissolving them in water, and stirring to obtain a slurry;

[0009] (2) Precursor sand milling: sand milling the slurry obtained in step (1) using water as the sand milling medium to obtain a molecularly dispersed slurry;

[0010] (3) spray drying and granulation: spray drying and granulating the slurry obtained in step (2) to obtain a spherical precursor powder;

[0011] (4) High-temperature solid-phase reaction: The spherical precursor powder in step (3) is placed in a tube furnace and calcined at high temperature to obtain a spherical layered oxide positive electrode material.

[0012] The spherical layered oxide cathode material is a spherical secondary particle formed by the aggregation of rectangular primary nanoparticles, with a particle size of 4 to 8 μm and a specific surface area of ​​0.40 to 0.55 m 2 / g, tap density is 1.50-1.65g / cm 3 , the interlayer spacing is

[0013] The sodium source is selected from one or more of sodium carbonate, sodium nitrate, sodium acetate or sodium hydroxide, and the transition metal source is selected from oxides, sulfates, carbonates, acetates or nitrates corresponding to transition metals.

[0014] The sanding speed is 2000-3000 rpm, and the time is 6-15 hours.

[0015] The spray drying outlet temperature is 90-110 degrees; the spray drying inlet temperature is 200-240 degrees, and the feed rate is 400-600 ml / h.

[0016] The heating rate in the high-temperature calcination treatment is 2 to 5°C / min, the final temperature range is controlled at 950 to 1050°C, and the holding time is controlled at 12 to 18 hours.

[0017] The present invention also provides a method for preparing a positive electrode sheet for a sodium ion battery, which is characterized by comprising the following preparation steps:

[0018] 80 wt% of the layered positive electrode material prepared by the above preparation method, 10 wt% of conductive carbon, and 10 wt% of a binder were dispersed in N-methylpyrrolidone (NMP) solvent. A uniform slurry was formed by mechanical grinding for 10 minutes. The slurry was evenly coated on a pretreated 20 μm aluminum foil surface using a doctor blade method, with a wet film thickness of 150 μm. The coated electrode was vacuum-dried at 80°C for 10 hours to remove the solvent. A 10 mm diameter disc electrode was punched out using a precision mold to obtain the corresponding layered positive electrode sheet.

[0019] The conductive carbon is Super P and the binder is PVDF.

[0020] Beneficial effects

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention provides a method for preparing a spherical layered oxide cathode material composed of densely packed primary nanoparticles, the general chemical formula of which is Na x Ni 0.4-y Fe 0.2+y+z Mn 0.4- z O2, wherein the value range of x is 0.8-1, and the value range of y and z is 0-0.1. The O3 type layered positive electrode material provided by the present invention is spherical, and the sand grinding process can fully refine the raw materials to obtain a molecular-level dispersed slurry. This process makes the primary nanoparticles formed subsequently uniform and small in size. The spherical morphology after further spray drying has a lower surface energy, and the contact between particles is closer, which can further increase the tap density. The spherical structure can also reduce the mechanical stress concentration of the particles during the battery charging and discharging process, avoid particle breakage, maintain structural stability, and extend the cycle life. The application of this positive electrode material in sodium ion batteries can enable sodium ion batteries to exhibit higher specific capacity and excellent cycle stability, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The microscopic morphology characteristics (SEM microstructure) of the layered cathode material prepared in Example 1

[0023] Figure 2 The crystal structure analysis (X-ray diffraction spectrum characteristics) of the product of Example 1

[0024] Figure 3 The first-week electrochemical behavior (charge and discharge curve) of the half-cell system assembled based on the electrodes of Example 1

[0025] Figure 4 Long-term cycle stability evaluation (capacity retention evolution) of the electrode in Example 1 DETAILED DESCRIPTION

[0026] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The present invention can be embodied in many different forms of embodiments, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0027] The present invention provides a synthesis process for a spherical layered oxide cathode material composed of densely packed primary nanoparticles. The layered oxide cathode material is further applied to sodium-ion batteries, where the batteries exhibit high capacity and stable cycle performance. The present invention specifically includes the following embodiments:

[0028] Example 1

[0029] (1) According to the stoichiometric NaNi 0.4 Fe 0.2 Mn 0.4 Accurately weigh sodium carbonate, nickel oxide, ferric oxide, and manganese dioxide precursors, dissolve them in water, and stir for 2 h.

[0030] (2) The slurry obtained in step (1) was sand-milled at a rotation speed of 2000 rpm using water as the medium for 8 hours to obtain a molecularly dispersed slurry.

[0031] (3) The slurry obtained in step (2) was spray-dried and granulated at an inlet temperature of 240°C, an outlet temperature of 105°C, and a feed rate of 500 ml / h.

[0032] (4) The spherical precursor powder obtained in step (3) was then transferred to a box-type resistance furnace for heat treatment: the target temperature reached 1000°C at a heating rate of 5°C / min, and calcined for 15 hours to complete the lattice construction and obtain a layered positive electrode active material.

[0033] (5) Take the layered positive electrode active material (80% by mass), conductive carbon (Super P, 10%) and binder (PVDF, 10%), add N-methylpyrrolidone (NMP) solvent to disperse. After mechanical grinding for 10 minutes, a uniform slurry is formed. The slurry is evenly coated on the surface of the pretreated 20μm aluminum foil using a scraper method, and the wet film thickness is controlled to be 150μm. The coated electrode is vacuum dried at 80℃ for 10 hours to remove the solvent, and a 10mm diameter disc electrode is obtained by punching using a precision mold. The active material loading is controlled at 2.0mg / cm 2 .

[0034] The particle size of the prepared positive electrode material is 4.2 μm and the specific surface area is 0.51 m 2 / g, and the tap density is 1.52g / cm 3 , the interlayer spacing is Under 2C charge and discharge conditions, the specific capacity is 127mAh / g. The specific capacity of the prepared electrode after 100 cycles at 2C is as follows: Figure 4 As shown, its specific capacity retention rate is 75%.

[0035] Example 2

[0036] (1) According to the stoichiometric NaNi 0.333 Fe 0.333 Mn 0.333 Accurately weigh sodium nitrate, nickel oxide, ferric oxide, and manganese dioxide precursors, dissolve them in water, and stir for 2 h.

[0037] (2) The slurry obtained in step (1) was sand-milled at a rotation speed of 2000 rpm using water as the medium for 8 hours to obtain a molecularly dispersed slurry.

[0038] (3) The slurry obtained in step (2) was spray-dried and granulated at an inlet temperature of 220°C, an outlet temperature of 100°C, and a feed rate of 600 ml / h.

[0039] (4) The spherical precursor powder obtained in step (3) was then transferred to a box-type resistance furnace for heat treatment: the target temperature was reached at a heating rate of 5°C / min and calcined for 12 hours to complete the lattice construction.

[0040] (5) Take the layered positive electrode active material (80% by mass), conductive carbon (Super P, 10%) and binder (PVDF, 10%), add N-methylpyrrolidone (NMP) solvent to disperse. After mechanical grinding for 10 minutes, a uniform slurry is formed. The slurry is evenly coated on the surface of the pretreated 20μm aluminum foil using a scraper method, and the wet film thickness is controlled to be 150μm. The coated electrode is vacuum dried at 80℃ for 10 hours to remove the solvent, and a 10mm diameter disc electrode is obtained by punching using a precision mold. The active material loading is controlled at 2.0mg / cm 2 .

[0041] The particle size of the prepared positive electrode material is 6 μm and the specific surface area is 0.44 m 2 / g, and the tap density is 1.58g / cm 3 , the interlayer spacing is Under 2C charge and discharge conditions, the specific capacity is 125mAh / g.

[0042] Example 3

[0043] (1) According to the stoichiometric Na 0.9 Ni 0.4 Fe 0.2 Mn 0.4Accurately weigh sodium hydroxide, nickel oxide, ferric oxide, and manganese dioxide precursors, dissolve them in water, and stir for 2 h.

[0044] (2) The slurry obtained in step (1) was sand-milled at a rotation speed of 2500 rpm using water as the medium for 10 hours to obtain a molecularly dispersed slurry.

[0045] (3) The slurry obtained in step (2) was spray-dried and granulated at an inlet temperature of 230°C, an outlet temperature of 100°C, and a feed rate of 500 ml / h.

[0046] (4) The spherical precursor powder obtained in step (3) was then transferred to a box-type resistance furnace for heat treatment: the target temperature was reached at a heating rate of 5°C / min and calcined for 15 hours to complete the lattice construction.

[0047] (5) Take the layered positive electrode active material (80% by mass), conductive carbon (Super P, 10%) and binder (PVDF, 10%), add N-methylpyrrolidone (NMP) solvent to disperse. After mechanical grinding for 10 minutes, a uniform slurry is formed. The slurry is evenly coated on the surface of the pretreated 20μm aluminum foil using a scraper method, and the wet film thickness is controlled to be 150μm. The coated electrode is vacuum dried at 80℃ for 10 hours to remove the solvent, and a 10mm diameter disc electrode is obtained by punching using a precision mold. The active material loading is controlled at 2.0mg / cm 2 .

[0048] The particle size of the prepared positive electrode material is 7.3 μm and the specific surface area is 0.41 m 2 / g, and the tap density is 1.67g / cm 3 , the interlayer spacing is Under 2C charge and discharge conditions, the specific capacity is 129mAh / g.

[0049] Example 4

[0050] (1) According to the stoichiometric Na 0.9 Ni 0.333 Fe 0.333 Mn 0.333 Accurately weigh sodium hydroxide, nickel oxide, ferric oxide, and manganese dioxide precursors, dissolve them in water, and stir for 2 h.

[0051] (2) The slurry obtained in step (1) was sand-milled at a rotation speed of 3000 rpm using water as the medium for 8 hours to obtain a molecularly dispersed slurry.

[0052] (3) The slurry obtained in step (2) was spray-dried and granulated at an inlet temperature of 240°C, an outlet temperature of 100°C, and a feed rate of 600 ml / h.

[0053] (4) The spherical precursor powder obtained in step (3) was then transferred to a box-type resistance furnace for heat treatment: the target temperature reached 1000°C at a heating rate of 5°C / min and calcined for 12 hours to complete the lattice construction.

[0054] (5) Take the layered positive electrode active material (80% by mass), conductive carbon (Super P, 10%) and binder (PVDF, 10%), add N-methylpyrrolidone (NMP) solvent to disperse. After mechanical grinding for 10 minutes, a uniform slurry is formed. The slurry is evenly coated on the surface of the pretreated 20μm aluminum foil using a doctor blade method, and the wet film thickness is controlled to be 150μm. The coated electrode is vacuum dried at 80℃ for 10 hours to remove the solvent, and a 10mm diameter disc electrode is obtained by punching using a precision mold, thus obtaining the corresponding layered positive electrode material electrode sheet.

[0055] The particle size of the prepared positive electrode material is 6.9 μm and the specific surface area is 0.48 m 2 / g, and the tap density is 1.62g / cm 3 , the interlayer spacing is Under 2C charge and discharge conditions, the specific capacity is 124mAh / g.

[0056] The preparation method of the layered oxide material of the present application uses a one-step sintering method of sand milling + spray drying, which produces a morphology, particle size and tap density that are different from the prior art. The sand milling process can fully refine the raw materials to obtain a molecularly dispersed slurry. This process makes the primary nanoparticles formed subsequently uniform and small in size. The spherical morphology after further spray drying has a lower surface energy, and the contact between particles is closer, which can further increase the tap density. The spherical structure can also reduce the mechanical stress concentration of the particles during the battery charging and discharging process, avoid particle breakage, maintain structural stability, and extend the cycle life.

Claims

1. A method for preparing a spherical layered oxide cathode material composed of densely packed primary nanoparticles, wherein the chemical formula of the spherical layered oxide cathode material can be expressed as Na x Ni 0.4-y Fe 0.2+y+z Mn 0.4-z O2, where The value range of x is 0.8-1, and the value range of y and z is 0-0.

1. The process for preparing the spherical layered oxide positive electrode material comprises: (1) weighing the precursors of the sodium source and the transition metal source according to the above stoichiometric ratio, dissolving them in water, and stirring to obtain a slurry; (2) Precursor sand milling: sand milling the slurry obtained in step (1) using water as the sand milling medium to obtain a molecularly dispersed slurry; (3) spray drying and granulation: spray drying and granulating the slurry obtained in step (2) to obtain a spherical precursor powder; (4) High-temperature solid-phase reaction: placing the spherical precursor powder in step (3) in a tube furnace for high-temperature calcination to obtain a spherical layered oxide positive electrode material; The spherical layered oxide cathode material is a spherical secondary particle formed by the aggregation of rectangular primary nanoparticles, with a particle size of 4 to 8 μm and a specific surface area of ​​0.40 to 0.55 m 2 / g, tap density is 1.50-1.65g / cm 3 , the interlayer spacing is 2. The preparation method according to claim 1, characterized in that The sodium source is selected from one or more of sodium carbonate, sodium nitrate, sodium acetate or sodium hydroxide, and the transition metal source is selected from oxides, sulfates, carbonates, acetates or nitrates corresponding to transition metals.

3. The preparation method according to claim 2, characterized in that The sanding speed is 2000-3000 rpm, and the sanding time is 6-15 hours.

4. The preparation method according to claim 2, characterized in that The spray drying outlet temperature is 90-110 degrees; the spray drying inlet temperature is 200-240 degrees, and the feed rate is 400-600 ml / h.

5. The preparation method according to claim 2, characterized in that The heating rate in the high-temperature calcination treatment is 2 to 5°C / min, the final temperature range is controlled at 950 to 1050°C, and the holding time is controlled at 12 to 18 hours.

6. A method for preparing a positive electrode sheet for a sodium ion battery, characterized in that: The method comprises the following preparation steps: 80 wt% of the spherical layered oxide positive electrode material prepared by the preparation method of claims 1-5, 10 wt% of conductive carbon, and 10 wt% of a binder are dispersed in N-methylpyrrolidone (NMP) solvent. A uniform slurry is formed by mechanical grinding for 10 minutes. The slurry is then evenly coated onto a pretreated 20 μm aluminum foil surface using a doctor blade method, with a wet film thickness of 150 μm. The coated electrode sheet is vacuum-dried at 80°C for 10 hours to remove the solvent, and then punched using a precision mold to obtain a 10 mm diameter disc electrode, thereby obtaining the corresponding layered positive electrode sheet.

7. The method for preparing a positive electrode sheet for a sodium ion battery according to claim 6, wherein: The conductive carbon is Super P and the binder is PVDF.

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