CN114709404B - NASICON titanium sodium phosphate coated sodium iron phosphate cathode material and preparation method thereof - Google Patents

Abstract

The invention provides a NASICON sodium titanium phosphate coated sodium iron phosphate cathode material and a preparation method thereof, which belong to the technical field of sodium ion batteries. The preparation process of the invention includes the preparation of sodium titanium phosphate precursor slurry, the uniform coating of sodium iron phosphate by sodium titanium phosphate, the drying of the precursor, and the solid-phase synthesis of NASICON sodium titanium phosphate-coated sodium iron phosphate cathode material. The lithium titanium phosphate fast ion conductor coating can prevent the direct contact between the electrolyte and the sodium iron phosphate, and reduce the interface side reaction. The introduction of the fast ion conductor can accelerate the transport rate of sodium ions, and improve the cycle stability and rate performance of the sodium iron phosphate. In addition, wet coating can improve the uniformity of sodium iron phosphate surface coating and ensure the consistency of coated products.

Description

A kind of NASICON sodium titanium phosphate coated sodium iron phosphate positive electrode material and preparation method thereof

technical field

The invention relates to the technical field of sodium ion batteries, in particular to a NASICON sodium titanium phosphate-coated sodium iron phosphate cathode material and a preparation method thereof.

Background technique

Sodium-ion batteries have a similar working mechanism and battery structure to lithium-ion batteries, and can be produced directly using existing lithium-ion battery production lines. Compared with lithium resources, sodium resources are rich in reserves, which are 1353 times that of lithium resources. The reserves in the earth's crust are as high as 2.36%, and the price is cheap. The price of industrial grade sodium is currently about 23,000 yuan/ton. However, the global reserves of lithium resources are limited, and the distribution is extremely uneven. 70% of lithium is distributed in South America, and the superimposed mining cycle is long. The mismatch between supply and demand leads to huge fluctuations in lithium prices, and the overall price is high. The current price of industrial-grade lithium metal is about 1.15 million yuan / ton, the increase in lithium prices will speed up the application of sodium batteries. Therefore, the application of sodium-ion batteries can alleviate the limited development of lithium batteries caused by the shortage of lithium resources to a certain extent.

Among the currently known cathode sodium storage materials, iron-based phosphate has attracted widespread attention due to its low cost and environmental friendliness. Among them, NaFePO ₄ stands out because of its high theoretical specific capacity (154mAh g ^-1 ) and suitable working potential. Given the great success of the olivine structure of LiFePO ₄ in Li-ion batteries, olivine-type NaFePO ₄ has been widely attempted as a cathode material for Na-ion batteries. However, olivine-type NaFePO ₄ is not a thermodynamically stable phase and often needs to be prepared from olivine-structured LiFePO ₄ through complex ion-exchange processes, which limits its practical application. In contrast, the thermodynamically stable phase osmanthite _NaFePO4 is generally considered to be electrochemically inactive due to the lack of sodium ion transport channels. In addition, the low intrinsic conductivity of NaFePO ₄ and the large lattice difference during the de/intercalation process affect its rate performance and cycle stability, which need to be improved. At present, the cycle stability and rate performance of sodium iron phosphate cathode materials are mainly improved by means of coating (such as carbon coating/inorganic substances), doping (F, P or metal ions, etc.), and particle nanosizing.

The NASICON structure is a sodium ion superconductor structure, which has a large three-dimensional channel structure, which can quickly deintercalate sodium ions, and the NASICON-type phosphate material has a high operating voltage and a good structural thermal conductivity. stability. The uniform coating of sodium iron phosphate surface by sodium titanium phosphate nanoparticles has not been reported yet.

Contents of the invention

The object of the present invention is to provide a positive electrode material in which sodium titanium phosphate nanoparticles uniformly coat the surface of sodium iron phosphate and a preparation method thereof.

In order to achieve the above-mentioned purpose of the invention, the present invention provides the following technical solutions:

The invention provides a preparation method of NASICON sodium titanium phosphate coated sodium iron phosphate cathode material, comprising the following steps:

1) mixing phosphorus source, titanium source, sodium source and dispersant solution and then grinding to obtain sodium titanium phosphate precursor slurry;

2) sodium iron phosphate slurry is obtained after mixing sodium iron phosphate with a dispersant solution;

3) After mixing the sodium iron phosphate slurry and the sodium titanium phosphate precursor slurry, the NASICON sodium titanium phosphate-coated sodium iron phosphate positive electrode material is obtained by shearing dispersion, spray drying, and roasting in sequence.

Further, the phosphorus source includes one or more of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate and disodium hydrogen phosphate; the titanium source includes anatase titanium dioxide, brookite One or more of titanium dioxide, rutile titanium dioxide and amorphous titanium dioxide; the sodium source includes anhydrous sodium acetate, sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium oxalate, sodium dihydrogen phosphate, dihydrogen phosphate One or more of sodium, sodium citrate and anhydrous sodium sulfate.

Further, in the step 1) and step 2), the dispersant in the dispersant solution is independently a polymer surfactant or a quaternary ammonium salt cationic surfactant; the polymer surfactant comprises polyethylene glycol , polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polyacrylonitrile and sodium carboxymethyl cellulose or one or more; the quaternary ammonium salt cationic surfactant contains tetradecyltrimethylammonium bromide , one or more of cetyltrimethylammonium bromide, 3-alkoxy-2-hydroxypropyltrimethylammonium bromide and cetyltrimethylammonium salicylate;

The mass concentration of the dispersant solution is independently 0.5-5%.

Further, in step 1), the linear velocity of the grinding is ≥15m/s, the grinding time is 4-10h, and the grinding medium is a zirconia ball with a diameter of 0.1-0.3mm;

The particle size of the sodium titanium phosphate precursor slurry is 80-250 nm.

Further, in step 1), the molar ratio of phosphorus, titanium and sodium in the sodium titanium phosphate precursor slurry is 0.5-2:0.2-1.5:0.2-1.0; the mass of the dispersant solution is 2 to 5 times the total mass of phosphorus source, titanium source and sodium source.

Further, in step 2), the molar ratio of phosphorus to iron in the sodium iron phosphate is 1:0.940-0.999, and the mass of the dispersant solution is 1-5 times the mass of the sodium iron phosphate;

The particle size of the sodium iron phosphate slurry is 100-300nm;

In step 3), the added amount of the sodium titanium phosphate precursor slurry is 1-10% of the mass of the sodium iron phosphate slurry.

Further, the frequency of the shear dispersion is 25-30 Hz, and the time of the shear dispersion is 1-3 hours.

Further, the spray drying is centrifugal spray drying or two-fluid spray drying; the inlet temperature of the spray drying is 220-260°C, the outlet temperature of the spray drying is 90-130°C, and the temperature of the spray-dried material is The particle size is 5-12 μm.

Further, the temperature of the calcination treatment is 750-850°C, the heating rate to the calcination treatment temperature is 3-10°C/min, the time of the calcination treatment is 4-10h, and the calcination treatment is carried out under a protective atmosphere. The protective atmosphere is nitrogen and/or argon.

The invention provides a NASICON sodium titanium phosphate coated sodium iron phosphate positive electrode material, the median particle size of the NASICON sodium titanium phosphate coated sodium iron phosphate positive electrode material is 8-15 μm, and the specific surface area is 3-20 m ² /g , the tap density is 0.5~1.5g/cm ³ .

Beneficial effects of the present invention:

The invention realizes the uniform coating of the sodium ferric phosphate by the sodium titanium phosphate nano-particles through technologies such as nanometer ultra-fine grinding, uniform dispersion, spray drying and roasting treatment (solid phase reaction). This preparation method has the following advantages:

(1) The uniform coating of nano-sodium titanium phosphate on sodium iron phosphate hinders the direct contact between the electrolyte and sodium iron phosphate, reduces the occurrence of side reactions, and improves the cycle stability of the battery;

(2) The sodium fast ion conductor (NASICON) provided by sodium titanium phosphate can accelerate the migration rate of sodium ions and enhance the rate performance;

(3) Wet coating can improve the uniformity and consistency of coated products, and improve the batch stability of products.

Detailed ways

The invention provides a preparation method of NASICON sodium titanium phosphate coated sodium iron phosphate cathode material, comprising the following steps:

1) mixing phosphorus source, titanium source, sodium source and dispersant solution and then grinding to obtain sodium titanium phosphate precursor slurry;

2) sodium iron phosphate slurry is obtained after mixing sodium iron phosphate with a dispersant solution;

3) After mixing the sodium iron phosphate slurry and the sodium titanium phosphate precursor slurry, the NASICON sodium titanium phosphate-coated sodium iron phosphate positive electrode material is obtained by shearing dispersion, spray drying, and roasting in sequence.

In the present invention, the phosphorus source comprises one or more of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate and disodium hydrogen phosphate, preferably phosphoric acid, ammonium monohydrogen phosphate and dibasic One or more of ammonium hydrogen.

In the present invention, the titanium source includes one or more of anatase titanium dioxide, brookite titanium dioxide, rutile titanium dioxide and amorphous titanium dioxide, preferably anatase titanium dioxide, brookite titanium dioxide and rutile One or several types of titanium dioxide.

In the present invention, the sodium source comprises one of anhydrous sodium acetate, sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium oxalate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium citrate and anhydrous sodium sulfate One or more, preferably one or more of anhydrous sodium acetate, sodium hydroxide and sodium carbonate.

In the present invention, in the step 1) and step 2), the dispersant in the dispersant solution is independently preferably a polymer surfactant or a quaternary ammonium salt cationic surfactant; One or more of ethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polyacrylonitrile and sodium carboxymethylcellulose, preferably polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone and polyacrylic acid one or more of them.

In the present invention, the quaternary ammonium salt cationic surfactant comprises tetradecyl trimethyl ammonium bromide, cetyl trimethyl ammonium bromide, 3-alkoxy-2-hydroxypropyl trimethyl One or more of ammonium bromide and cetyltrimethylammonium salicylate, preferably tetradecyltrimethylammonium bromide, cetyltrimethylammonium bromide and 3- One or more of alkoxy-2-hydroxypropyltrimethylammonium bromide.

In the present invention, the mass concentration of the dispersant solution is independently 0.5-5%, preferably 1.0-3.0%, more preferably 2.0%.

In the present invention, in step 1), the linear velocity of the grinding is ≥15m/s, the grinding time is 4-10h, and the grinding medium is a zirconia ball with a diameter of 0.1-0.3mm; preferably, the linear velocity of the grinding is ≥20m/s, the grinding time is 5-8h, and the grinding medium is a zirconia ball with a diameter of 0.2mm; more preferably, the grinding line speed is ≥35m/s, the grinding time is 6h, and the grinding medium is a diameter of 0.2mm mm of zirconia balls.

In the present invention, the particle size of the sodium titanium phosphate precursor slurry is 80-250 nm, preferably 100-240 nm, more preferably 230 nm.

In the present invention, in step 1), the molar ratio of phosphorus, titanium and sodium in the sodium titanium phosphate precursor slurry is 0.5-2:0.2-1.5:0.2-1.0, preferably 0.8-1.5: 0.5 to 1.2:0.3 to 0.8, more preferably 1.5:1:0.5.

In the present invention, the mass of the dispersant solution is 2-5 times, preferably 3-4 times, more preferably 3 times the total mass of the phosphorus source, titanium source and sodium source.

In the present invention, in step 2), the molar ratio of phosphorus to iron in the sodium iron phosphate is 1:0.940-0.999, preferably 1:0.955.

In the present invention, in step 2), the mass of the dispersant solution is 1-5 times, preferably 2-4 times, more preferably 3 times the mass of sodium iron phosphate.

In the present invention, in step 2), shear dispersion is carried out after mixing sodium ferric phosphate with the dispersant solution. The shear dispersion is first dispersed at a frequency of 5-15 Hz for 2-6 minutes, and then at a frequency ≥ 20 Hz Disperse at low temperature for 1-3 hours; preferably, shear dispersion is to disperse at a frequency of 10 Hz for 5 min, and then disperse at a frequency ≥ 25 Hz for 2 h.

In the present invention, the particle size of the sodium iron phosphate slurry is 100-300 nm, preferably 120-280 nm, more preferably 150-250 nm.

In the present invention, in step 3), the added amount of the sodium titanium phosphate precursor slurry is 1-10% of the mass of the sodium iron phosphate slurry, preferably 2-8%, more preferably 4-6%.

In the present invention, the frequency of shear dispersion is 25-30 Hz, and the time of shear dispersion is 1-3 h; preferably, the frequency of shear dispersion is 26-28 Hz, and the time of shear dispersion is 2-3 h; Further preferably, the frequency of shear dispersion is 27 Hz, and the time of shear dispersion is 2 hours.

In the present invention, the spray drying is centrifugal spray drying or two-fluid spray drying, preferably centrifugal spray drying.

In the present invention, the inlet temperature of the spray-drying is 220-260°C, the outlet temperature of the spray-drying is 90-130°C, and the particle size of the spray-dried material is 5-12 μm; preferably, the spray-drying The inlet temperature of the spray drying is 230-250°C, the outlet temperature of the spray drying is 100-120°C, and the particle size of the material after spray drying is 6-10 μm; further preferably, the inlet temperature of the spray drying is 240°C , the outlet temperature of the spray drying is 110° C., and the particle size of the material after spray drying is 8 μm.

In the present invention, the temperature of the calcination treatment is 750-850°C, the heating rate to the calcination treatment temperature is 3-10°C/min, the time of the calcination treatment is 4-10h, and the calcination treatment is carried out under a protective atmosphere, The protective atmosphere is nitrogen and/or argon; preferably, the temperature of the calcination treatment is 800-850°C, the heating rate to the calcination treatment temperature is 4-8°C/min, and the time of the calcination treatment is 5-8h, The firing treatment was performed under a nitrogen atmosphere.

The invention provides a NASICON sodium titanium phosphate coated sodium iron phosphate positive electrode material, the median particle size of the NASICON sodium titanium phosphate coated sodium iron phosphate positive electrode material is 8-15 μm, and the specific surface area is 3-20 m ² /g , the tap density is 0.5~1.5g/cm ³ .

In the present invention, the median particle size of the NASICON sodium titanium phosphate-coated sodium iron phosphate positive electrode material is preferably 10-12 μm, the specific surface area is preferably 5-15 m ² /g, and the tap density is preferably 0.8-1.2 g/ cm ³ .

The technical solutions provided by the present invention will be described in detail below in conjunction with the examples, but they should not be interpreted as limiting the protection scope of the present invention.

Example 1

The preparation method of NASICON sodium titanium phosphate coated sodium iron phosphate cathode material comprises the following steps:

1) Dissolve 6.0g of CMC powder in 520g of ultrapure water, shear and disperse for 5 minutes to make it completely dispersed, then add 172.5g of ammonium dihydrogen phosphate, 79.9g of anatase titanium dioxide and 26.5g of sodium carbonate in sequence, and continue to shear and disperse 5min, then transfer the mixed slurry to a sand mill containing zirconia balls with a diameter of 0.1mm, and grind for 6h at a linear speed of 20m/s to obtain a sodium titanium phosphate precursor slurry with a particle size of 230nm;

2) Disperse 300.0g of sodium iron phosphate cathode material with an iron-phosphorus ratio of 0.955:1 in 450.0g of 2% CMC solution, add 35.6g of sodium titanium phosphate precursor slurry after shearing and dispersing for 5 minutes, and disperse at a low speed of 10Hz 5min, then continue to disperse at 25Hz frequency for 2h to obtain sodium iron phosphate slurry;

3) After mixing the slurry in step 1) and step 2), carry out two-fluid spray treatment, control the temperature of the spray inlet to 240°C, and the temperature of the discharge port to 110°C, and control the particle size of the material after spray drying to 10 μm. The material is transferred to a nitrogen-protected box furnace for roasting treatment at a temperature of 550°C, raised to 800°C at a heating rate of 5°C/min, kept at 800°C for 6 hours, and passed through a 100-mesh sieve after cooling at room temperature to obtain phosphoric acid Titanium sodium coated sodium iron phosphate cathode material.

In this example, the NASICON sodium titanium phosphate-coated sodium iron phosphate cathode material has a median particle size of 12 μm, a specific surface area of 6.73 m ² /g, and a tap density of 1.2 g/cm ³ .

Example 2

The preparation method of NASICON sodium titanium phosphate coated sodium iron phosphate cathode material comprises the following steps:

1) Dissolve 6.0g of CMC powder in 520g of ultrapure water, shear and disperse for 5 minutes to make it completely dispersed, then add 97.9g of ammonium dihydrogen phosphate, 79.9g of brookite-type titanium dioxide and 67.2g of sodium bicarbonate in sequence, and continue to shear Cut and disperse for 5 minutes, then transfer all the mixed slurry to a sand mill containing 0.15mm zirconia balls, and grind for 7 hours at a linear speed of 16m/s to obtain a sodium titanium phosphate precursor slurry with a particle size of 230nm;

2) Disperse 300.0g of sodium iron phosphate cathode material with an iron-phosphorus ratio of 0.955:1 in 450.0g of 2% CMC solution, add 59.2g of sodium titanium phosphate precursor slurry after shear dispersion for 5min, and disperse at a low speed of 10Hz 5min, then continue to disperse at 25Hz frequency for 2h to obtain sodium iron phosphate slurry;

3) After mixing the slurry in step 1) and step 2), carry out two-fluid spray treatment, control the temperature of the spray inlet to 240°C, and the temperature of the discharge port to 110°C, and control the particle size of the material after spray drying to 10 μm. The materials were transferred to a nitrogen-protected box-type furnace for roasting treatment at a temperature of 550°C, raised to 800°C at a heating rate of 5°C/min, and kept at 800°C for 6 hours. After cooling at room temperature, sieve through a 100-mesh sieve. Sodium titanium phosphate-coated sodium iron phosphate cathode material is obtained.

In this example, the NASICON sodium titanium phosphate-coated sodium iron phosphate cathode material has a median particle size of 10 μm, a specific surface area of 5.66 m ² /g, and a tap density of 1.3 g/cm ³ .

Example 3

The preparation method of NASICON sodium titanium phosphate coated sodium iron phosphate cathode material comprises the following steps:

1) Dissolve 6.0g of CMC powder in 520g of ultrapure water, shear and disperse for 5 minutes to make it completely dispersed, then add 97.9g of ammonium dihydrogen phosphate, 79.9g of rutile titanium dioxide and 60g of sodium dihydrogen phosphate in sequence, and continue to shear and disperse 5min, then the mixed slurry was transferred to a sand mill containing 0.2mm zirconia balls, and ground for 6h at a linear speed of 15m/s to obtain a sodium titanium phosphate precursor slurry with a particle size of 230nm;

2) Disperse 300.0g of sodium iron phosphate cathode material with an iron-phosphorus ratio of 0.955:1 in 450.0g of 2% CMC solution, add 23.7g of sodium titanium phosphate precursor slurry after shear dispersion for 5min, and disperse at a low speed of 10Hz 5min, then continue to disperse at 25Hz frequency for 2h to obtain sodium iron phosphate slurry;

3) After mixing the slurry in step 1) and step 2), carry out two-fluid spray treatment, control the temperature of the spray inlet to 240°C, the temperature of the discharge port to 110°C, control the spray-dried particle size to 10μm, and the spray-dried material Transfer to a nitrogen-protected box furnace for roasting treatment, raise the temperature to 800°C at a heating rate of 5°C/min, keep it at 800°C for 6 hours, and pass through a 100-mesh sieve after cooling at room temperature to obtain a sodium titanium phosphate-coated sodium iron phosphate positive electrode Material.

In this example, the NASICON sodium titanium phosphate-coated sodium iron phosphate cathode material has a median particle size of 11 μm, a specific surface area of 5.32 m ² /g, and a tap density of 1.35 g/cm ³ .

Example 4

The preparation method of NASICON sodium titanium phosphate coated sodium iron phosphate cathode material comprises the following steps:

1) Dissolve 6.0g of CMC powder in 520g of ultrapure water, shear and disperse for 5 minutes to make it completely dispersed, then add 172.5g of ammonium dihydrogen phosphate, 79.9g of amorphous titanium dioxide and 26.5g of sodium carbonate in sequence, and continue to shear and disperse for 5 minutes , and then transfer all the mixed slurry to a sand mill containing 0.25mm zirconia balls, and grind for 5h at a linear speed of 18m/s to obtain a sodium titanium phosphate precursor slurry with a particle size of 230nm;

2) Disperse 300.0g of sodium iron phosphate cathode material with an iron-phosphorus ratio of 0.955:1 in 450.0g of 2% CMC solution, add 59.2g of sodium titanium phosphate precursor slurry after shear dispersion for 5min, and disperse at a low speed of 10Hz 5min, then continue to disperse at 25Hz frequency for 2h to obtain sodium iron phosphate slurry;

3) After mixing the slurry in step 1) and step 2), carry out two-fluid spray treatment, control the temperature of the spray inlet to 240°C, and the temperature of the discharge port to 110°C, and control the particle size of the material after spray drying to 8 μm. Transfer the material to a nitrogen-protected box-type furnace for roasting treatment at a temperature of 850°C, a heating rate of 5°C/min to 850°C, and a holding time of 4 hours. After cooling at room temperature, sieve through a 100-mesh sieve to obtain sodium titanium phosphate package Sodium iron phosphate coated cathode material.

In this example, the NASICON sodium titanium phosphate-coated sodium iron phosphate cathode material has a median particle size of 13 μm, a specific surface area of 4.96 m ² /g, and a tap density of 1.40 g/cm ³ .

Example 5

The preparation method of NASICON sodium titanium phosphate coated sodium iron phosphate cathode material comprises the following steps:

1) Dissolve 6.0g of CMC powder in 520g of ultrapure water, shear and disperse for 5 minutes to make it completely dispersed, then add 172.5g of ammonium dihydrogen phosphate, 79.9g of anatase titanium dioxide and 26.5g of sodium carbonate in sequence, and continue to shear and disperse 5min, then transfer all the mixed slurry to a sand mill containing 0.3mm zirconia balls, and grind for 6h at a linear speed of 20m/s to obtain a sodium titanium phosphate precursor slurry with a particle size of 230nm;

2) Disperse 300.0g of sodium iron phosphate cathode material with an iron-phosphorus ratio of 0.955:1 in 450.0g of 2% CMC solution, add 35.6g of sodium titanium phosphate precursor slurry after shearing and dispersing for 5 minutes, and disperse at a low speed of 10Hz 5min, then continue to disperse at 25Hz frequency for 2h to obtain sodium iron phosphate slurry;

3) After mixing the slurry in step 1) and step 2), carry out two-fluid spray treatment, control the temperature of the spray inlet to 240°C, and the temperature of the discharge port to 110°C, and control the particle size of the material after spray drying to 8 μm. The material was transferred to a nitrogen-protected box furnace for roasting treatment at a temperature of 450°C, and the temperature was raised to 700°C at a heating rate of 5°C/min, and the holding time was 10h. After cooling at room temperature, it was sieved through a 100-mesh sieve to obtain sodium titanium phosphate. Coated sodium iron phosphate cathode material.

In this example, the NASICON sodium titanium phosphate-coated sodium iron phosphate cathode material has a median particle size of 8 μm, a specific surface area of 8.53 m ² /g, and a tap density of 0.96 g/cm ³ .

Comparative example 1

Sodium iron phosphate with an iron-phosphorus ratio of 0.955:1 was used as the cathode material.

Comparative example 2

With embodiment 1, difference is:

In step 2), 300.0 g of sodium iron phosphate cathode material with an iron-phosphorus ratio of 0.955:1 is dispersed in 450.0 g of 2% CMC solution, and 71.1 g of sodium titanium phosphate precursor slurry is added after shearing and dispersing for 5 minutes, first at 10 Hz Disperse at a low speed for 5 minutes, and then continue to disperse at a frequency of 25 Hz for 2 hours to obtain a sodium iron phosphate slurry.

Comparative example 3

With embodiment 1, difference is:

In step 2), 300.0 g of sodium iron phosphate cathode material with an iron-phosphorus ratio of 0.955:1 is dispersed in 450.0 g of 2% CMC solution, and 11.8 g of sodium titanium phosphate precursor slurry is added after shearing and dispersing for 5 minutes, first at 10 Hz Disperse at a low speed for 5 minutes, and then continue to disperse at a frequency of 25 Hz for 2 hours to obtain a sodium iron phosphate slurry.

Comparative example 4

With embodiment 1, difference is:

In step 3), mix the slurries in step 1) and step 2) and carry out two-fluid spray treatment, control the temperature of the spray inlet to 240°C, the temperature of the discharge port to 110°C, control the spray drying particle size to 10 μm, and spray dry The final material was transferred to a nitrogen-protected box furnace for roasting treatment at a temperature of 900°C, a heating rate of 5°C/min, and a holding time of 2h. After cooling at room temperature, it was sieved through 100 meshes to obtain a sodium titanium phosphate-coated sodium iron phosphate positive electrode. Material.

Comparative example 5

With embodiment 1, difference is:

In step 3), mix the slurries in step 1) and step 2) and carry out two-fluid spray treatment, control the temperature of the spray inlet to 240°C, the temperature of the discharge port to 110°C, control the spray drying particle size to 10 μm, and spray dry The final material was transferred to a nitrogen-protected box furnace for roasting treatment at a temperature of 650°C, a heating rate of 5°C/min, and a holding time of 12 hours. After cooling at room temperature, it was sieved with 100 meshes to obtain a sodium titanium phosphate-coated sodium iron phosphate positive electrode Material.

Mix the positive electrode materials obtained in Examples 1-5 and Comparative Examples 1-5 according to the mass ratio of positive electrode material: PVDF: Super P 80:10:10, then dissolve and disperse them evenly with N-methylpyrrolidone, and then coat them on aluminum foil After being dried, it is rolled and pressed into a positive electrode sheet. The positive pole piece is used as the working electrode, the metal sodium piece is used as the counter electrode and the reference electrode, 1mol/L NaPF ₆ (EC: DMC: EMC = 1:1:1v/v/v) is used as the electrolyte, and the Whatman glass fiber As the separator, the battery was assembled in a glove box. The assembled battery is activated by cycling 5 cycles at 1C current, setting the charge and discharge range at 2.0-4.5V, and then cycling 100 cycles at 1C. In the rate performance test of the positive electrode material, after 5 cycles of 1C cycle, 5 cycles of 2C, 3C, 5C, and 10C were respectively cycled, and then 1C cycle was resumed for 5 cycles. The results of 10C/1C capacity retention rate are shown in Table 1.

Table 1 Example 1～5 and comparative example 1～5 battery performance test prepared by cathode material

It can be seen from the above examples that the present invention provides a NASICON sodium titanium phosphate coated sodium iron phosphate positive electrode material and a preparation method thereof. The invention prevents the direct contact between the electrolyte and the sodium iron phosphate through the uniform coating of the nano-sodium titanium phosphate on the sodium iron phosphate, reduces the occurrence of side reactions, and improves the cycle stability of the battery. It can be seen from the performance test that the present invention uses nano Sodium titanium phosphate is uniformly coated on sodium iron phosphate, and the 1C 100-cycle capacity retention rate of the battery prepared by the positive electrode material is significantly improved, up to 95.82%, and the 10C/1C capacity retention rate is also as high as 93.36%. Compared with the battery with sodium iron phosphate alone as the positive electrode material, the capacity retention rate is significantly improved. As can be seen from Comparative Example 4 and Comparative Example 5, the temperature of the final calcination treatment has a great influence on the retention rate of the battery capacity. If the temperature is too high or too low, the capacity retention rate of the battery will decrease. Therefore, the present invention is preferably 750 ~850°C.

The above is only a preferred embodiment of the present invention, it should be pointed out that, for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (8)

1. A preparation method of a NASICON titanium sodium phosphate coated sodium iron phosphate cathode material is characterized by comprising the following steps:

1) Mixing a phosphorus source, a titanium source, a sodium source and a dispersing agent solution, and grinding to obtain sodium titanium phosphate precursor slurry;

2) Mixing sodium ferric phosphate with a dispersant solution to obtain sodium ferric phosphate slurry;

3) Mixing the sodium ferric phosphate slurry and the sodium titanium phosphate precursor slurry, and then sequentially carrying out shearing dispersion, spray drying and roasting treatment to obtain the NASICON sodium titanium phosphate coated sodium ferric phosphate cathode material;

in the step 2), the molar ratio of phosphorus to iron in the sodium iron phosphate is 1: 0.940-0.999, wherein the mass of the dispersant solution is 1-5 times of that of the sodium iron phosphate;

the particle size of the sodium ferric phosphate slurry is 100-300 nm;

in the step 3), the addition amount of the sodium titanium phosphate precursor slurry is 1-10% of the mass of the sodium iron phosphate slurry;

the roasting treatment temperature is 800-850 ℃, the heating rate of heating to the roasting treatment temperature is 3-10 ℃/min, the roasting treatment time is 4-10 h, and the roasting treatment is carried out in a protective atmosphere, wherein the protective atmosphere is nitrogen and/or argon.

2. The method according to claim 1, wherein the phosphorus source comprises one or more of phosphoric acid, monoammonium phosphate, monosodium phosphate, and disodium phosphate; the titanium source comprises one or more of anatase titanium dioxide, brookite titanium dioxide, rutile titanium dioxide and amorphous titanium dioxide; the sodium source comprises one or more of anhydrous sodium acetate, sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium oxalate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium citrate and anhydrous sodium sulfate.

3. The method according to claim 1 or 2, wherein in the step 1) and the step 2), the dispersant in the dispersant solution is independently a polymeric surfactant or a quaternary ammonium cationic surfactant; the high molecular surfactant comprises one or more of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polyacrylonitrile and sodium carboxymethylcellulose; the quaternary ammonium salt cationic surfactant comprises one or more of tetradecyltrimethyl ammonium bromide, hexadecyltrimethyl ammonium bromide, 3-alkoxy-2-hydroxypropyl trimethyl ammonium bromide and hexadecyltrimethyl ammonium salicylate;

the mass concentration of the dispersant solution is independently 0.5-5%.

4. The preparation method according to claim 3, wherein in the step 1), the linear velocity of the grinding is more than or equal to 15m/s, the grinding time is 4-10 h, and the grinding medium is zirconia balls with the diameter of 0.1-0.3 mm;

the particle size of the sodium titanium phosphate precursor slurry is 80-250 nm.

5. The preparation method according to claim 2 or 4, wherein in the step 1), the molar ratio of phosphorus element, titanium element and sodium element in the titanium sodium phosphate precursor slurry is 0.5-2: 0.2 to 1.5:0.2 to 1.0; the mass of the dispersant solution is 2-5 times of the total mass of the phosphorus source, the titanium source and the sodium source.

6. The method according to claim 5, wherein the frequency of the shear dispersion is 25 to 30Hz and the time of the shear dispersion is 1 to 3 hours.

7. The method of claim 6, wherein the spray drying is centrifugal spray drying or two-fluid spray drying; the temperature of the feed inlet of the spray drying is 220-260 ℃, the temperature of the discharge outlet of the spray drying is 90-130 ℃, and the grain diameter of the spray-dried material is 5-12 mu m.

8. Claim 1 of the oilThe NASICON sodium titanium phosphate coated sodium ferric phosphate cathode material obtained by any one of the preparation methods of about 7 is characterized in that the median particle diameter of the NASICON sodium titanium phosphate coated sodium ferric phosphate cathode material is 8-15 mu m, and the specific surface area of the NASICON sodium titanium phosphate coated sodium ferric phosphate cathode material is 3-20 m ² The tap density is 0.5-1.5 g/cm ³ 。