WO2024168951A1 - Low-cost single-crystal sodium-ion battery positive electrode active substance, and preparation method therefor and use thereof - Google Patents

Abstract

Disclosed in the present invention are a low-cost single-crystal sodium-ion battery positive electrode active substance, and a preparation method therefor and the use thereof. The chemical formula of the single-crystal sodium-ion battery positive electrode active substance is NaiMxByMgzO2, wherein M is selected from multiple metal elements, 0.60≤i≤1.40, 0.6≤x≤0.9999, 0.0001≤y≤0.4, 0.0001≤z≤0.4, and 0.9≤x+y+z≤1.1. The preparation method comprises: a step of adding water to a compound containing an M metal element, a magnesium source, a compound containing boron, and a sodium source, so as to prepare a slurry, and sanding the slurry to obtain a mixed slurry; and a step of subjecting the mixed slurry to spray drying and sintering same to obtain a single-crystal sodium-ion battery positive electrode active substance. The preparation method of the present invention can improve the electrical performance of the positive electrode active substance and can also reduce the cost thereof.

Description

A low-cost single-crystal sodium ion battery positive electrode active material and its preparation method and use Technical Field

The present invention belongs to the field of sodium ion batteries, and in particular relates to a low-cost single crystal sodium ion battery positive electrode active material, a preparation method and uses thereof.

Background Art

Due to the large radius of sodium ions, the available positive active materials for sodium ion batteries are relatively limited. At present, the positive active materials for sodium ion batteries that have shown potential application prospects include three types of systems: Prussian blue, layered oxides, and polyanions. Among them, the O3 phase structure layered oxide system, similar to the ternary positive active material in lithium ion batteries, has the advantages of high capacity and high compaction density. It is regarded as the most promising positive electrode material and is adopted by sodium ion battery companies at home and abroad.

At present, the positive active material of the oxide system sodium ion battery is mainly a secondary spherical particle structure, but the traditional secondary spherical particle structure still has the following problems: 1. The particle structure has poor mechanical strength, which can easily lead to the breakage of the secondary spheres during the compaction of the electrode, affecting the compaction density and cycle performance of the electrode; 2. The active material has a large contact surface area with the electrolyte, and contact with the electrolyte leads to an increase in side reactions, affecting the cycle performance and safety performance.

In addition, it is difficult to control the cost of sodium-ion batteries. The key factor affecting their scale-up process is to achieve low-cost preparation of sodium-ion batteries. In order to replace lead-acid batteries on a large scale, the cost of sodium-ion batteries needs to be controlled within 0.5 yuan/Wh. After calculation, the price of positive electrode materials needs to be ≤50,000 yuan/ton, the price of electrolyte needs to be ≤30,000 yuan/ton, and the price of negative electrode materials needs to be ≤30,000 yuan/ton. Among them, the positive electrode material is mainly based on sodium nickel iron manganese oxide, and the nickel content is generally ≥12wt% to meet the comprehensive requirements of gram capacity and cycle. Among the main elements, the price of nickel is about RMB 220,000/ton, the price of iron is about RMB 5,000/ton, the price of manganese is about RMB 15,000/ton, and the price of sodium carbonate is about RMB 5,000/ton. The cost of nickel accounts for about 70% of the raw material cost of the positive electrode material. In order to meet the price requirements, the nickel-containing sodium positive electrode material must reduce the nickel content to ≤10wt%, but this often affects the electrical properties of the sodium ion battery, and it is difficult to meet the basic requirement of half-cell gram capacity ≥125mAh/g under 2.0-4.0V/0.1C conditions.

Preparing the positive electrode active material of the oxide system sodium ion battery into a single crystal morphology can significantly improve the disadvantages brought by the aforementioned secondary spherical particle structure. However, how to control the composition of the positive electrode active material of the sodium ion battery and what preparation process to use to synthesize a relatively perfect single crystal morphology have always been technical difficulties in this field.

Summary of the invention

The purpose of the present invention is to provide a method for preparing a single-crystal sodium ion battery positive electrode active material in view of the shortcomings and deficiencies of the prior art, which can prepare a single-crystal sodium ion battery positive electrode active material at a low cost, on a large scale and stably. The positive electrode active material has high compaction density and small specific surface area, and has excellent electrochemical performance, especially cycle performance, when used in sodium ion batteries.

In order to solve the above technical problems, a technical solution adopted by the present invention is as follows:

A method for preparing a low-cost single-crystal sodium ion battery positive electrode active material, wherein the chemical formula of the single-crystal sodium ion battery positive electrode active material is Na _i M _x B _y Mg _z O ₂ , wherein M is a combination of one or more selected from Li, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Nb, Mo, Ru, In, Sn, Sb, W, Ta, Ba, Bi, La, Ce, and Eu, 0.60≤i≤1.40, 0.6≤x≤0.9999, 0.0001≤y≤0.4, 0.0001≤z≤0.4, and 0.9≤x+y+z≤1.1; the preparation method comprises the steps of adding water to a compound containing the M metal element, a magnesium source, a compound containing the boron element, and a sodium source to prepare a slurry, sand-milling the mixture, and spray-drying the mixture, and sintering the mixture to obtain the single crystal sodium ion battery positive electrode active material.

In some specific embodiments of the present invention, in the chemical formula Na _i M _x B _y Mg _z O ₂ , 0.95≤i≤1.05, 0.8≤x≤0.9999, 0.0001≤y≤0.2, and 0.0001≤z≤0.2.

Further preferably, in the chemical formula Na _i M _x B _y Mg _z O ₂ , 0.98≤i≤1.04, 0.9≤x≤0.9999, 0.0001≤y≤0.1, and 0.01≤z≤0.15.

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

In some specific embodiments of the present invention, the compound containing the element M is selected from one or more combinations of the oxide, hydroxide, carbonate, oxalate and nitrate of the element M.

Furthermore, the compound containing the M element is selected from one or more combinations of nickel manganese hydroxide, ferric oxide, titanium dioxide, nickel oxide, manganese dioxide, zinc oxide, zinc carbonate, calcium oxide, calcium hydroxide, calcium carbonate, aluminum hydroxide, and aluminum oxide.

In some specific embodiments of the present invention, the compound containing the boron element is selected from one or more combinations of boron oxide, boric acid, borate, borohydride, boron trihalide, trifluoroboric acid, boric ester, borane, and metal boride.

Furthermore, the compound containing boron is selected from boric acid, boron oxide or a combination of both.

In some specific embodiments of the present invention, the magnesium source is selected from one or more combinations of magnesium oxide, magnesium carbonate, magnesium hydroxide, magnesium nitrate, magnesium acetate, and magnesium citrate.

Furthermore, the magnesium source is selected from magnesium oxide, magnesium carbonate, magnesium hydroxide or a combination of two thereof.

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

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

In some specific embodiments of the present invention, the molar ratio of the compound containing the M element, the compound containing the boron element, the magnesium source and the sodium source is (0.6-0.9999):(0.0001-0.4):(0.0001-0.4):(0.60-1.40).

Further preferably, the molar ratio of the compound containing the M element, the compound containing the boron element, the magnesium source and the sodium source is (0.6-0.9):(0.0001-0.1):(0.05-0.2):(0.90-1.10).

Furthermore, the molar ratio of the compound containing the M element, the compound containing the boron element, the magnesium source and the sodium source is (0.8-0.9):(0.01-0.06):(0.1-0.2):(0.95-1.05).

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

Furthermore, the sanding time is 1 to 4 hours.

In some specific embodiments of the present invention, the grinding body of the sand mill is a zirconia ball with a particle size of 0.1 to 0.8 mm.

In some specific embodiments of the present invention, the sanding speed is 800-3000 rpm.

Furthermore, the sanding speed is 1500-2500 rpm.

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

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

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

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

Furthermore, during the spray drying, the rotation speed of the atomizing disk is 1000-3000 rpm, the air inlet temperature is 150-300°C, and the air outlet temperature is 80-120°C.

In some specific embodiments of the present invention, the sintering is carried out in air, the sintering temperature is 750-1100° C., and the sintering time is 5-25 hours.

Furthermore, the sintering temperature is 850-1000° C. and the sintering time is 8-16 hours.

The present invention finds that by using magnesium to replace part of the metal element ratio, the oxide positive electrode active material can have a stable O3 type crystal structure, and when the positive electrode active material is used in a sodium ion battery, the gram capacity of the battery is improved, and the irreversible ion migration during the charge and discharge process can also be effectively suppressed, thereby stabilizing the cycle performance of the material and significantly reducing the production cost. That is, the addition of magnesium can reduce the cost while not affecting the electrical performance of the sodium ion battery. On the contrary, it can also improve the electrical performance of the battery.

Secondly, by adding compounds containing boron to the raw materials, the nano-scale primary particles quickly melt and merge during high-temperature sintering, and a single-crystal sodium-ion battery positive electrode active material of about 1-30 microns can be sintered. This material is not in a fluffy state, so it has a high compaction density, which can greatly reduce the side reactions between the positive electrode material and the electrolyte. In addition, by regulating the content of boron in the single-crystal positive electrode active material, the particle size of the single crystal particles of the positive electrode active material can be controlled.

Again, in the preparation method of the present invention, sand milling is used when preparing the mixed slurry, which can process water-soluble substances to achieve uniform mixing at the molecular level; it can also process water-insoluble raw materials to achieve nano-level uniform mixing between insoluble substances; it can also process nano-level uniform mixing between water-soluble and water-insoluble raw materials. Sand milling ensures uniform mixing of raw materials at the nanometer level, and positive electrode materials with excellent electrochemical activity can be stably obtained during high-temperature sintering. The sand milling method used in the present invention, the addition of compounds containing boron elements, and the addition of magnesium sources have a synergistic effect, and the three are indispensable for preparing low-cost single-crystal positive active materials with excellent cycle performance.

Finally, the present invention can also perform spray drying on the mixed slurry. The spray drying method can maintain uniform distribution of various raw materials in the uniformly mixed slurry during the drying process, ensuring that there is no component segregation of the various raw materials during the molding process.

The present invention further provides a single crystal sodium ion battery positive electrode active material prepared by the above preparation method. The positive electrode active material has low cost and excellent electrical properties.

Furthermore, the microscopic morphology of the single crystal sodium ion battery positive electrode active material is a single crystal structure, the average particle size D ₅₀ is 1-30 micrometers, the compaction density is 2.8-3.6 g/cm ³ , and the specific surface area is 0.3-1.0 m ² /g.

The present invention further provides the use of the above-mentioned single crystal sodium ion battery positive electrode active material in the positive electrode of the sodium ion battery.

When the low-cost single-crystal sodium ion battery positive electrode active material is applied to the positive electrode of the sodium ion battery, the obtained sodium ion battery has a capacity of 125 to 140 mAh/g at 2.0 to 4.0 V/0.1 C and 25° C., and a 100-cycle cycle retention rate of the cylindrical battery at 25° C. is above 90%.

The present invention also provides a positive electrode material for a sodium ion battery, comprising a positive electrode active material, a binder and a conductive agent, wherein the positive electrode active material comprises the above-mentioned single crystal sodium ion battery positive electrode active material.

The present invention also provides a sodium ion battery positive electrode prepared from the above-mentioned sodium ion battery positive electrode material.

The present invention also provides a sodium ion battery, comprising a positive electrode, wherein the positive electrode comprises the above-mentioned sodium ion battery positive electrode.

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

The present invention adopts magnesium element to replace the proportion of some metal elements, so that the oxide positive electrode active material can have a stable O3 type crystal structure, and when the positive electrode active material is used in a sodium ion battery, the gram capacity of the battery is improved, and the irreversible ion migration during the charge and discharge process can also be effectively suppressed, the cycle performance of the material is stabilized, and the production cost can be significantly reduced at the same time, that is, the addition of magnesium element can achieve the reduction of cost while not affecting the electrical performance of the sodium ion battery, on the contrary, it can also improve the electrical performance of the battery. Adding magnesium element can suppress the irreversible migration of iron element, so that the material has a low cost while also exerting a higher gram capacity, and ensuring the cycle performance of the sodium ion battery positive electrode material.

The preparation method of the present invention can efficiently achieve uniform mixing of multiple raw materials at the nanometer level, and a perfect layered O3 phase structure can be formed after the mixed slurry is sintered.

By doping boron on the basis of the sand milling method, large single crystals can be prepared, which overcomes the shortcomings of the prior art that the raw material particles are too fine, the sintered material is very fluffy, the specific surface area is large, the compaction density of the positive electrode active material when making the electrode is low, and the side reactions between the positive electrode material and the electrolyte are many during the battery cycle, resulting in a lot of gas production, resulting in poor battery cycle performance and safety performance.

The present invention controls the content of boron in the single-crystal positive electrode active material to prepare single-crystal particles of 1-30 microns, which have stable surface properties and few side reactions with the electrolyte. By controlling the content of magnesium in the positive electrode active material, when used in sodium ion batteries, it can still have good cycle performance while ensuring a high gram-to-weight capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a scanning electron microscope image of NaNi _0.14 Fe _0.35 Mn _0.37 Zn _0.05 B _0.02 Mg _0.07 O ₂ prepared in Example 1;

FIG2 is an XRD pattern of NaNi _0.14 Fe _0.35 Mn _0.37 Zn _0.05 B _0.02 Mg _0.07 O ₂ prepared in Example 1;

FIG3 is a charge-discharge curve of NaNi _0.14 Fe _0.35 Mn _0.37 Zn _0.05 B _0.02 Mg _0.07 O ₂ prepared in Example 1.

FIG4 is a full electrical cycle diagram of NaNi _0.14 Fe _0.35 Mn _0.37 Zn _0.05 B _0.02 Mg _0.07 O ₂ prepared in Example 1.

FIG5 is a scanning electron microscope image of NaNi _0.14 Fe _0.40 Mn _0.37 B _0.02 Mg _0.07 O ₂ prepared in Example 2;

FIG6 is an XRD pattern of NaNi _0.14 Fe _0.40 Mn _0.37 B _0.02 Mg _0.07 O ₂ prepared in Example 2;

FIG. 7 is a charge-discharge curve of NaNi _0.14 Fe _0.40 Mn _0.37 B _0.02 Mg _0.07 O ₂ prepared in Example 2.

FIG8 is a scanning electron microscope image of NaNi _0.17 Fe _0.37 Mn _0.33 B _0.02 Mg _0.11 O ₂ prepared in Example 5;

FIG9 is an XRD pattern of NaNi _0.17 Fe _0.37 Mn _0.33 B _0.02 Mg _0.11 O ₂ prepared in Example 5;

FIG10 is a charge-discharge curve of NaNi _0.17 Fe _0.37 Mn _0.33 B _0.02 Mg _0.11 O ₂ prepared in Example 5.

FIG. 11 is a full electrical cycle diagram of NaNi _0.17 Fe _0.37 Mn _0.33 B _0.02 Mg _0.11 O ₂ prepared in Example 5.

FIG12 is a scanning electron microscope image of NaNi _0.16 Fe _0.40 Mn _0.34 B _0.02 Mg _0.08 O ₂ prepared in Example 6;

FIG13 is an XRD pattern of NaNi _0.16 Fe _0.40 Mn _0.34 B _0.02 Mg _0.08 O ₂ prepared in Example 6;

FIG14 is a charge-discharge curve of NaNi _0.16 Fe _0.40 Mn _0.34 B _0.02 Mg _0.08 O ₂ prepared in Example 6.

FIG15 is a scanning electron microscope image of NaNi _1/3 Fe _1/3 Mn _1/3 O ₂ prepared in Comparative Example 1;

FIG16 is an XRD pattern of NaNi _1/3 Fe _1/3 Mn _1/3 O ₂ prepared in Comparative Example 1;

FIG. 17 is a charge-discharge curve of NaNi _1/3 Fe _1/3 Mn _1/3 O ₂ prepared in Comparative Example 1.

FIG18 is a scanning electron microscope image of NaNi _0.17 Fe _0.37 Mn _0.34 Mg _0.12 O ₂ prepared in Comparative Example 2;

FIG19 is an XRD pattern of NaNi _0.17 Fe _0.37 Mn _0.34 Mg _0.12 O ₂ prepared in Comparative Example 2;

FIG20 is a charge-discharge curve of NaNi _0.17 Fe _0.37 Mn _0.34 Mg _0.12 O ₂ prepared in Comparative Example 2.

FIG21 is a full electrical cycle diagram of NaNi _0.17 Fe _0.37 Mn _0.34 Mg _0.12 O ₂ prepared in Comparative Example 2.

DETAILED DESCRIPTION

In order to better understand the content of the present invention, the following is further described in conjunction with specific examples and accompanying drawings. It should be understood that these embodiments are only used for further explanation of the invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content of the present invention, without departing from the principle of the present invention, some improvements and adjustments made by technicians in this field to the present invention still belong to the protection scope of the present invention. In the following, unless otherwise specified, all raw materials are obtained from commercial purchase.

In the following embodiments and comparative examples, a half-cell is used for charge and discharge curve test: First, prepare a sodium ion half-cell: weigh 20g of the prepared positive electrode active material, add 0.64g of conductive agent SP and 0.64g of PVDF dissolved in NMP, mix well and coat on aluminum foil to make an electrode sheet. In an argon atmosphere glove box, a metal sodium sheet is used as the negative electrode, Celgard2700 is used as the diaphragm, and 1mol/L NaPF ₆ +EC:DEC (1:1) +5% FEC is used as the electrolyte to assemble a button cell. Then the charge and discharge curve is tested at a voltage range of 2.0-4.0V, a charge and discharge rate of 0.1C, and a test temperature of 25±2℃.

Cyclic battery was used for cycle performance test: First, cylindrical 18650 sodium ion battery was prepared: positive electrode slurry was mixed in the ratio of sodium positive electrode: SP: CNT: PVDF = 95.5: 1.7: 0.8: 2.0, and coated under the condition of relative humidity ≤ 15%, double-sided surface density 370g/ ^m2 , compacted density 3.05g/cm3, and matched with 16μm PP/PE diaphragm and hard carbon negative electrode, wound, and shelled. In an argon atmosphere glove box, 1mol/L _NaPF6 +EC:DEC (1:1) + 5% FEC was used as electrolyte to assemble 18650 batteries. Cyclic performance of 100 cycles was tested at a voltage range of 2.0-3.9V, a charge and discharge rate of 1C, and 25℃.

Example 1

This embodiment provides a sodium ion battery positive electrode active material, the chemical formula of which is NaNi _0.14 Fe _0.35 Mn _0.37 Zn _0.05 B _0.02 Mg _0.07 O ₂ (Ni content ˜7.59 wt %), and the preparation method comprises the following steps:

(1) Take 0.7 mol of NiO, 0.875 mol of Fe ₂ O ₃ , 1.85 mol of MnO ₂ , 0.25 mol of ZnO, 0.1 mol of H ₃ BO ₃ , 0.35 mol of MgO, and 2.5 mol of Na ₂ CO ₃ , add all the raw materials into 3.5 L of water to prepare a slurry;

(2) adding the slurry obtained in step (1) into a sand mill and grinding for 3 h. The grinding body is a zirconia ball with a particle size of 0.2 mm. The sand milling speed is 2500 rpm. Grinding obtains a mixed slurry with an average particle size of about 350 nm.

(3) The mixed slurry obtained in step (2) is transferred into a stirring barrel, stirred thoroughly, and pure water is added to adjust the slurry to a solid content of 30±1%. The slurry is spray-dried under the conditions of an atomization frequency of 35 Hz, an inlet air temperature of 190°C, and an outlet air temperature of 85°C in a spray drying equipment. The dried product is sintered in an air atmosphere furnace at 850-1000°C for 12 hours, cooled to below 80°C, crushed by jaw crushing, rolling, and pulverizing to obtain a positive electrode active material for a sodium ion battery. The sample is named NFMZ-BM1.

The scanning electron microscope image of NFMZ-BM1 is shown in Figure 1, and it can be seen that the material is a single crystal morphology. The XRD of NFMZ-BM1 is shown in Figure 2, and it can be seen that the material is an α-NaFeO _2- type pure phase layered structure. The charge and discharge curve of NFMZ-BM1 is shown in Figure 3, and it can be seen that in the voltage window of 2.0 to 4.0V, the discharge specific capacity at a rate of 0.1C is 130.0mAh/g. The full electric cycle diagram of NFMZ-BM1 is shown in Figure 4, and it can be seen that at 25°C, in the voltage window of 2.0 to 3.9V, at a rate of 1C, the capacity retention rate after 100 cycles is 91.3%.

Example 2

This embodiment provides a sodium ion battery positive electrode active material, the chemical formula of which is NaNi _0.14 Fe _0.40 Mn _0.37 B _0.02 Mg _0.07 O ₂ (Ni content ˜7.62 wt %), and the preparation method comprises the following steps:

(1) Take 0.7 mol of NiO, 1.0 mol of Fe ₂ O ₃ , 1.85 mol of MnO ₂ , 0.1 mol of H ₃ BO ₃ , 0.35 mol of MgO, and 2.5 mol of Na ₂ CO ₃ , add all the raw materials into 3.5 L of water to prepare a slurry;

(2) adding the slurry obtained in step (1) into a sand mill and grinding for 3 h. The grinding body is a zirconia ball with a particle size of 0.2 mm. The sand milling speed is 2500 rpm. Grinding obtains a mixed slurry with an average particle size of about 350 nm.

(3) The mixed slurry obtained in step (2) is transferred into a stirring barrel, stirred thoroughly, and pure water is added to adjust the slurry to a solid content of 30±1%. The slurry is spray-dried under the conditions of an atomization frequency of 35 Hz, an inlet air temperature of 190°C, and an outlet air temperature of 85°C in a spray drying equipment. The dried product is sintered in an air atmosphere furnace at 850-1000°C for 12 hours, cooled to below 80°C, crushed by jaw crushing, rolling, and pulverizing to obtain a positive electrode active material for a sodium ion battery. The sample is named NFM-BM2.

The SEM image of NFM-BM2 is shown in Figure 5, which shows that the material is a single crystal morphology. The XRD of NFM-BM2 is shown in Figure 6, which shows that the material is an α-NaFeO ₂ type pure phase layered structure. The charge and discharge curve of NFM-BM2 is shown in Figure 7, which shows that within the voltage window of 2.0 to 4.0 V, the discharge specific capacity at a rate of 0.1C is 126.4 mAh/g.

Example 3

This embodiment provides a sodium ion battery positive electrode active material, the chemical formula of which is NaNi _0.17 Fe _0.34 Mn _0.37 Ti _0.04 B _0.02 Mg _0.06 O ₂ (Ni content ˜9.25 wt %), and the preparation method comprises the following steps:

(1) Take 0.85 mol of NiO, 0.85 mol of Fe ₂ O ₃ , 1.85 mol of MnO ₂ , 0.2 mol of TiO ₂ , 0.1 mol of H ₃ BO ₃ , 0.30 mol of MgO, and 2.5 mol of Na ₂ CO ₃ , add all the raw materials into 3.5 L of water to prepare a slurry;

(2) adding the slurry obtained in step (1) into a sand mill and grinding for 3 h. The grinding body is a zirconia ball with a particle size of 0.2 mm. The sand milling speed is 2500 rpm. Grinding obtains a mixed slurry with an average particle size of about 350 nm.

(3) The mixed slurry obtained in step (2) is transferred into a stirring barrel, stirred thoroughly, and pure water is added to adjust the slurry to a solid content of 30±1%. The slurry is spray-dried under the conditions of an atomization frequency of 35 Hz, an inlet air temperature of 190°C, and an outlet air temperature of 85°C in a spray drying equipment. The dried product is sintered in an air atmosphere furnace at 850-1000°C for 12 hours, cooled to below 80°C, crushed by jaw crushing, rolling, and pulverizing to obtain a positive electrode active material for a sodium ion battery. The sample is named NFMT-BM3.

Example 4

This embodiment provides a sodium ion battery positive electrode active material, the chemical formula of which is NaNi _0.17 Fe _0.33 Mn _0.33 B _0.02 Mg _0.15 O ₂ (Ni content ˜9.47 wt %), and the preparation method comprises the following steps:

(1) Take 0.85 mol of NiO, 0.825 mol of Fe ₂ O ₃ , 1.65 mol of MnO ₂ , 0.1 mol of H ₃ BO ₃ , 0.75 mol of MgO, and 2.5 mol of Na ₂ CO ₃ , add all the raw materials into 3.5 L of water to prepare a slurry;

(2) adding the slurry obtained in step (1) into a sand mill and grinding for 3 h. The grinding body is a zirconia ball with a particle size of 0.2 mm. The sand milling speed is 2500 rpm. Grinding obtains a mixed slurry with an average particle size of about 350 nm.

(3) The mixed slurry obtained in step (2) is transferred into a stirring barrel, stirred thoroughly, and pure water is added to adjust the slurry to a solid content of 30±1%. The slurry is spray-dried under the conditions of an atomization frequency of 35 Hz, an inlet air temperature of 190°C, and an outlet air temperature of 85°C in a spray drying equipment. The dried product is sintered in an air atmosphere furnace at 850-1000°C for 12 hours, cooled to below 80°C, crushed by jaw crushing, rolling, and pulverizing to obtain a positive electrode active material for a sodium ion battery. The sample is named NFM-BM4.

Example 5

This embodiment provides a sodium ion battery positive electrode active material, the chemical formula of which is NaNi _0.17 Fe _0.37 Mn _0.33 B _0.02 Mg _0.11 O ₂ (Ni content ˜9.36 wt %), and the preparation method comprises the following steps:

(1) Take 0.85 mol of NiO, 0.925 mol of Fe ₂ O ₃ , 1.65 mol of MnO ₂ , 0.1 mol of H ₃ BO ₃ , 0.55 mol of MgO, and 2.5 mol of Na ₂ CO ₃ and add all the raw materials into 3.5 L of water to prepare a slurry;

(2) adding the slurry obtained in step (1) into a sand mill and grinding for 3 h. The grinding body is a zirconia ball with a particle size of 0.2 mm. The sand milling speed is 2500 rpm. Grinding obtains a mixed slurry with an average particle size of about 350 nm.

(3) The mixed slurry obtained in step (2) was transferred into a stirring barrel, stirred thoroughly, and pure water was added to adjust the slurry to a solid content of 30±1%. The slurry was spray-dried under the conditions of an atomization frequency of 35 Hz, an inlet air temperature of 190°C, and an outlet air temperature of 85°C in a spray drying equipment. The dried product was sintered in an air atmosphere furnace at 850-1000°C for 12 hours, cooled to below 80°C, crushed by jaw crushing, rolling, and pulverizing to obtain a positive electrode active material for a sodium ion battery. The sample name is NFM-BM5.

The SEM image of NFM-BM5 is shown in Figure 8, which shows that the material is a single crystal morphology. The XRD of NFM-BM5 is shown in Figure 9, which shows that the material is an α-NaFeO ₂ type pure phase layered structure. The charge and discharge curve of NFM-BM5 is shown in Figure 10. As shown in Figure 10, it can be seen that within the voltage window of 2.0 to 4.0 V, the discharge specific capacity at 0.1C rate is 138.8 mAh/g. The full electric cycle diagram of NFM-BM5 is shown in Figure 11. It can be seen that at 25°C, within the voltage window of 2.0 to 3.9 V, at 1C rate, the capacity retention rate after 100 cycles is 98.91%.

Example 6

This embodiment provides a sodium ion battery positive electrode active material, the chemical formula of which is NaNi _0.16 Fe _0.40 Mn _0.34 B _0.02 Mg _0.08 O ₂ (Ni content ˜8.73 wt %), and the preparation method comprises the following steps:

(1) Take 0.8 mol of NiO, 1.0 mol of Fe ₂ O ₃ , 1.7 mol of MnO ₂ , 1.0 mol of H ₃ BO ₃ , 0.4 mol of MgO, and 2.5 mol of Na ₂ CO ₃ and add all the raw materials into 3.5 L of water to prepare a slurry;

(2) adding the slurry obtained in step (1) into a sand mill and grinding for 3 h. The grinding body is a zirconia ball with a particle size of 0.2 mm. The sand milling speed is 2500 rpm. Grinding obtains a mixed slurry with an average particle size of about 350 nm.

(3) The mixed slurry obtained in step (2) is transferred into a stirring barrel, stirred thoroughly, and pure water is added to adjust the slurry to a solid content of 30±1%. The slurry is spray-dried under the conditions of an atomization frequency of 35 Hz, an inlet air temperature of 190°C, and an outlet air temperature of 85°C in a spray drying equipment. The dried product is sintered in an air atmosphere furnace at 850-1000°C for 12 hours, cooled to below 80°C, crushed by jaw crushing, rolling, and pulverizing to obtain a positive electrode active material for a sodium ion battery. The sample is named NFM-BM6.

The SEM image of NFM-BM6 is shown in Figure 12, which shows that the material is a single crystal morphology. The XRD of NFM-BM6 is shown in Figure 13, which shows that the material is an α-NaFeO ₂ type pure phase layered structure. The charge and discharge curve of NFM-BM6 is shown in Figure 14, which shows that within the voltage window of 2.0 to 4.0 V, the discharge specific capacity at a rate of 0.1C is 134.8 mAh/g.

Comparative Example 1

This embodiment provides a sodium ion battery positive electrode active material, the chemical formula of which is NaNi _1/3 Fe _1/3 Mn _1/3 O ₂ (Ni content ˜17.55 wt %), and the preparation method comprises the following steps:

(1) Take 1.65 mol of NiO, 0.835 mol of Fe ₂ O ₃ , 1.65 mol of MnO ₂ , and 2.5 mol of Na ₂ CO ₃ , add all the raw materials into 3.5 L of water to prepare a slurry;

(2) adding the slurry obtained in step (1) into a sand mill and grinding for 3 h. The grinding body is a zirconia ball with a particle size of 0.2 mm. The sand milling speed is 2500 rpm. Grinding obtains a mixed slurry with an average particle size of about 350 nm.

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

The scanning electron microscope image of NFM-1 is shown in Figure 15, which shows that the material is a fluffy secondary particle sphere with a primary particle size of about 0.5 microns. The XRD of NFM-1 is shown in Figure 16, which shows that the material is an α-NaFeO ₂ type pure phase layered structure. The charge and discharge curve of NFM-1 is shown in Figure 17, which shows that within the voltage window of 2.0 to 4.0 V, the discharge specific capacity at a rate of 0.1C is 125.0 mAh/g.

Comparative Example 2

This embodiment provides a sodium ion battery positive electrode active material, the chemical formula of which is NaNi _0.17 Fe _0.37 Mn _0.34 Mg _0.12 O ₂ (Ni content ˜9.31 wt %), and the preparation method comprises the following steps:

(1) Take 0.85 mol of NiO, 0.925 mol of Fe ₂ O ₃ , 1.7 mol of MnO ₂ , 0.6 mol of MgO, and 2.5 mol of Na ₂ CO ₃ , add all the raw materials into 3.5 L of water to prepare a slurry;

(2) adding the slurry obtained in step (1) into a sand mill and grinding for 3 h. The grinding body is a zirconia ball with a particle size of 0.2 mm. The sand milling speed is 2500 rpm. Grinding obtains a mixed slurry with an average particle size of about 350 nm.

(3) The mixed slurry obtained in step (2) is transferred into a stirring barrel, stirred thoroughly, and pure water is added to adjust the slurry to a solid content of 30±1%. The slurry is spray-dried under the conditions of an atomization frequency of 35 Hz, an inlet air temperature of 190° C., and an outlet air temperature of 85° C. in a spray drying equipment. The dried product is sintered in an air atmosphere furnace at 850-1000° C. for 12 hours, cooled to below 80° C., crushed by jaw crushing, rolling, and pulverizing to obtain a positive electrode active material for a sodium ion battery. The sample is named NFM-M2.

The scanning electron microscope image of NFM-M2 is shown in Figure 18, which shows that the material is a fluffy secondary particle sphere with a primary particle of about 0.5 microns in the sphere. The XRD of NFM-M2 is shown in Figure 19, which shows that the material is an α-NaFeO ₂ type pure phase layered structure. The charge and discharge curve of NFM-M3 is shown in Figure 20, which shows that in the voltage window of 2.0 to 4.0V, the discharge specific capacity at a rate of 0.1C is 138.7mAh/g. The full electric cycle diagram of NFM-M2 is shown in Figure 21, which shows that at 25°C, in the voltage window of 2.0 to 3.9V, at a rate of 1C, the capacity retention rate after 100 cycles is 85.78%.

Performance Testing

The positive electrode active materials prepared in the above Examples 1-6 and Comparative Examples 1-2 were subjected to physicochemical performance tests, and the physicochemical performance results are shown in Table 1 below.

Table 1. Physical properties of positive electrode active materials

The positive electrode active materials prepared in the above Examples 1-6 and Comparative Examples 1-2 were used for sodium ion battery performance testing, and the test results are shown in Table 2 below.

Table 2. Performance of sodium ion batteries

As can be seen from Tables 1-2 above, the present invention adds water to the precursor during grinding to form a mixed slurry, spray-dries before sintering, and adds boron-containing compounds and magnesium elements to the raw materials, so that the positive electrode active material can form a perfect layered single crystal structure, and the single crystal particles are large and densely grown. The compaction density of the positive electrode active material is significantly improved, and the specific surface area is reduced. When the positive electrode active material is used in a sodium ion battery, the cycle performance at high temperature can be significantly improved while ensuring a high gram-to-weight capacity, and the cost of the positive electrode active material is significantly reduced.

The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims (18)

1. A method for preparing a positive electrode active material for a single crystal sodium ion battery, characterized in that: the chemical formula of the single crystal sodium ion battery positive electrode active material is Na _i M _x B _y Mg _z O ₂ , wherein M is selected from a combination of one or more of Fe, Ni, Mn, Cu, Ti, Zn, Ca, and Al, 0.95≤i≤1.05, 0.8≤x≤0.9999, 0.0001≤y≤0.2, and 0.0001≤z≤0.2; the preparation method comprises the steps of adding water to a compound containing a metal element M, a magnesium source, a compound containing a boron element, and a sodium source to prepare a slurry, sand-milling the slurry, and spray-drying the slurry, and sintering the slurry to obtain the single crystal sodium ion battery positive electrode active material; the solid content of the slurry is 10% to 60%; the median particle size of the particles in the slurry is 20 to 800 nm; the compound containing the M element is selected from the oxide, hydroxide, carbonate, and hydrate of the M element; The compound containing the boron element is selected from a combination of one or more of boron oxide, boric acid, borate, borohydride, boron trihalide, trifluoroboric acid, boric ester, borane, and metal boride; the sodium source is selected from a combination of one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, sodium peroxide, sodium nitrate, sodium acetate, and sodium oxalate; the magnesium source is selected from a combination of one or more of magnesium sulfate, magnesium carbonate, magnesium hydroxide, magnesium nitrate, magnesium acetate, and magnesium citrate; the molar ratio of the compound containing the M element, the compound containing the boron element, the magnesium source, and the sodium source is (0.6-0.9999):(0.0001-0.4):(0.0001-0.4):(0.60-1.40).
2. A method for preparing a single crystal sodium ion battery positive electrode active material, characterized in that: the chemical formula of the single crystal sodium ion battery positive electrode active material is Na _i M _x B _y Mg _z O ₂ , wherein M is a combination of one or more selected from Li, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Nb, Mo, Ru, In, Sn, Sb, W, Ta, Ba, Bi, La, Ce, and Eu, 0.60≤i≤1.40, 0.6≤x≤0.9999, 0.0001≤y≤0.4, 0.0001≤z≤0.4, and 0.9≤x+y+z≤1.1; the preparation method comprises the steps of adding water to a compound containing the M metal element, a magnesium source, a compound containing the boron element, and a sodium source to prepare a slurry, sand-milling the mixture, and spray-drying the mixture, and sintering the mixture to obtain the single crystal sodium ion battery positive electrode active material.
3. The preparation method according to claim 2 is characterized in that: in the chemical formula Na _i M _x B _y Mg _z O ₂ , 0.95≤i≤1.05, 0.8≤x≤0.9999, 0.0001≤y≤0.2, and 0.0001≤z≤0.2.
4. The preparation method according to claim 2 is characterized in that the compound containing the M element is selected from a combination of one or more of the oxides, hydroxides, carbonates, oxalates and nitrates of the M element.
5. The preparation method according to claim 2 is characterized in that the compound containing the boron element is selected from one or more combinations of boron oxide, boric acid, borate, borohydride, boron trihalide, trifluoroboric acid, boric ester, borane, and metal boride.
6. The preparation method according to claim 2, characterized in that: the sodium source is selected from a combination of one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, sodium peroxide, sodium nitrate, sodium acetate, and sodium oxalate; and/or the magnesium source is selected from a combination of one or more of magnesium sulfate, magnesium carbonate, magnesium hydroxide, magnesium nitrate, magnesium acetate, and magnesium citrate.
7. The preparation method according to claim 2 is characterized in that the molar ratio of the compound containing the M element, the compound containing the boron element, the magnesium source and the sodium source is (0.6-0.9999):(0.0001-0.4):(0.0001-0.4):(0.60-1.40).
8. The preparation method according to claim 2 is characterized in that: the sand grinding time is 0.6 to 7.8 hours; and/or the grinding body of the sand grinding is a zirconia ball with a particle size of 0.1 to 0.8 mm; and/or the sand grinding speed is 800 to 3000 rpm.
9. The preparation method according to claim 2 is characterized in that: the solid content of the mixed slurry is 10% to 60%; and/or the median particle size of the particles in the mixed slurry is 20 to 800 nm.
10. The preparation method according to claim 2 is characterized in that: during the spray drying, the rotation speed of the atomizing disk is 1000-3000 rpm, the inlet air temperature is 150-300°C, and the outlet air temperature is 80-120°C.
11. The preparation method according to claim 2 is characterized in that: the sintering is carried out in air, the sintering temperature is 750-1100°C, and the time is 5-25h; and/or the mixed slurry is crushed after sintering.
12. A single crystal sodium ion battery positive electrode active material prepared by the preparation method according to any one of claims 1 to 11.
13. The single crystal sodium ion battery positive electrode active material according to claim 12 is characterized in that the single crystal sodium ion battery positive electrode active material has a single crystal structure in microscopic morphology, an average particle size D ₅₀ of 1-30 microns, a compaction density of 2.8-3.6 g/cm ³ , and a specific surface area of 0.3-1.0 m ² /g.
14. A use of the single crystal sodium ion battery positive electrode active material as claimed in claim 12 or 13 in a sodium ion battery positive electrode.
15. A positive electrode material for a sodium ion battery, comprising a positive electrode active material, a binder and a conductive agent, characterized in that the positive electrode active material comprises the single crystal sodium ion battery positive electrode active material according to claim 12 or 13.
16. A sodium ion battery positive electrode, characterized in that the sodium ion battery positive electrode is prepared from the sodium ion battery positive electrode material according to claim 15.
17. A sodium ion battery, comprising a positive electrode, characterized in that the positive electrode comprises the sodium ion battery positive electrode according to claim 16.
18. The sodium ion battery according to claim 17 is characterized in that the sodium ion battery has a capacity of 125 to 140 mAh/g at 2.0 to 4.0 V/0.1 C and 25° C., and a cylindrical battery 100 cycle retention rate at 25° C. of more than 90%.