Preparation method of battery-grade sodium titanium phosphate negative electrode material

Abstract

The invention provides a preparation method of a battery-grade sodium titanium phosphate negative electrode material, which comprises the following steps: taking slurry subjected to alkali washing in an R seed crystal preparation process as a titanium source, and detecting the concentration of TiO2 and the content of sodium oxide in the slurry; adding a sodium source and a phosphorus source in proportion, and stirring; carrying out sanding and spray drying on the mixed solution obtained in the previous step to obtain a titanium sodium phosphate powdery precursor; performing dynamic suspension calcination on the sodium titanium phosphate powder precursor to obtain sodium titanium phosphate; the preparation method comprises the following steps: adding sodium titanium phosphate and a carbon source into softened water in proportion, stirring, sanding, and spray-drying; and sintering, cooling and crushing the sample to obtain the carbon-coated sodium titanium phosphate negative electrode material. According to the preparation method of the battery-grade sodium titanium phosphate negative electrode material, the material subjected to alkali washing in the R seed crystal preparation process is used as a titanium source, the raw material cost is low, the dynamic suspension calcination technology is adopted, the calcination temperature is reduced, the calcination time is shortened, the calcination energy consumption is reduced, and the prepared carbon-coated sodium titanium phosphate is excellent in cycle performance, rate capability and low-temperature performance.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage battery materials, and in particular to a method for preparing a battery-grade sodium titanium phosphate negative electrode material. Background Art

[0002] Lithium-ion batteries, as the current mainstream battery type, are widely used in electronic devices and electric vehicles. However, lithium-ion batteries are prone to forming lithium dendrites during charging and discharging, or react violently with the electrolyte, causing battery explosion, posing a huge safety hazard. Traditional aqueous rechargeable batteries such as lead-acid, nickel-chromium and nickel-metal hydride contain harmful heavy metal elements, which can cause serious environmental pollution. In addition, the development of nickel-metal hydride and all-vanadium liquid flow batteries is limited by high costs.

[0003] In recent years, the research on negative electrode materials of sodium ion batteries has made important progress. The negative electrode materials of sodium ion batteries reported so far mainly include carbon-based, titanium-based, organic, alloy and other negative electrode materials. Titanium-based materials have good stability in air, and Ti 4+ / Ti 3+ The redox potential is between 0-2V (Na + / Na), different structures exhibit different sodium storage potentials. Therefore, titanium-based materials have attracted widespread attention as candidates for sodium-ion battery anode materials.

[0004] As a typical representative of polyanionic titanium-based materials, NaTi2(PO4)3 has a NASICON-type three-dimensional network structure. + It can migrate in the three-dimensional channels contained in its crystal structure. + Insertion compounds have Na + Due to its advantages such as fast diffusion speed and relatively stable structure, NaTi2(PO4)3 has become one of the research focuses of titanium-based sodium storage materials in recent years.

[0005] Currently, the most common methods for preparing titanium-based sodium storage materials are the high-temperature solid-phase method and the hydrothermal method. The high-temperature solid-phase method involves uniformly mixing the required raw materials and then sintering them at high temperatures, generally requiring high temperatures and a long time. Currently available heat treatment temperatures are almost all at 750°C, and the required time is also very long, generally ranging from 2 to 20 hours. The use of prolonged high-temperature treatment not only places higher demands on equipment but also consumes a lot of energy. The hydrothermal method generates significant pressure during the preparation process, which is detrimental to production safety and results in low output efficiency. Furthermore, the main titanium sources include nano-titanium dioxide, titanyl sulfate, metatitanic acid, and titanates (such as tetraethyl titanate, isopropyl titanate, and tetraethyl titanate). These raw materials are relatively expensive, especially titanate compounds. The use of titanyl sulfate as a raw material for preparing sodium titanium phosphate not only produces a large amount of sulfur-containing waste gas, but also contains numerous impurities in the product, reducing its purity.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of the present invention is to address the deficiencies in the existing technology and provide a method for preparing a battery-grade sodium titanium phosphate negative electrode material. The material after alkali washing in the preparation process of R seed crystals is used as a titanium source, the raw material cost is low, and a dynamic suspension calcination technology is adopted to reduce the calcination temperature, shorten the calcination time, and reduce the calcination energy consumption. The obtained carbon-coated sodium titanium phosphate has excellent cycle performance, rate performance, and low-temperature performance.

[0008] In order to achieve the above-mentioned object of the present invention, the following technical solution is specially adopted: a method for preparing a battery-grade sodium titanium phosphate negative electrode material, comprising the following steps:

[0009] Step S1, taking the slurry after alkali washing in the preparation process of R seed crystals as a titanium source, and detecting the TiO2 concentration and sodium oxide content in the slurry;

[0010] Step S2: adding a sodium source and a phosphorus source to the slurry in the previous step in proportion and stirring;

[0011] Step S3, sand-milling and spray-drying the mixed solution in the previous step to obtain a sodium titanium phosphate powder precursor;

[0012] Step S4, dynamically sintering the sodium titanium phosphate powder precursor to obtain sodium titanium phosphate;

[0013] Step S5, adding sodium titanium phosphate and a carbon source into softened water in proportion, stirring, sand milling, and spray drying;

[0014] Step S6: sintering, cooling, and crushing the spray-dried sample to obtain a carbon-coated sodium titanium phosphate negative electrode material.

[0015] Furthermore, the TiO2 concentration in the slurry after alkali washing in step S1 is controlled at 130-170 g / L.

[0016] Furthermore, the amount of sodium source added in step S2 is based on the sodium oxide content in the slurry detected in step S1, and the sodium source difference is supplemented according to the molar ratio of sodium: titanium: phosphorus, and the molar ratio of sodium: titanium: phosphorus is Na:Ti:P=1~3:2~5:3~7.

[0017] Furthermore, the stirring time in step S2 is 30 to 60 minutes.

[0018] Furthermore, the sodium source is at least one of sodium carbonate, sodium bicarbonate, and sodium acetate.

[0019] Furthermore, the phosphorus source is at least one of phosphoric acid, monoammonium phosphate, diammonium phosphate, and triammonium phosphate.

[0020] Furthermore, in step S3, the sand milling is performed for 0.5 to 2 hours, and the particle size D50 of the material after sand milling is ≤ 0.7 μm.

[0021] Furthermore, in step S3, the inlet temperature of the spray drying is 200-240°C, and the outlet temperature is 90-95°C.

[0022] Furthermore, in step S4, the temperature of the dynamic suspension calcination is 400-500° C., and the calcination time is 30-90 seconds.

[0023] Furthermore, the amount of carbon source added in step S5 is based on the carbon content of 2 to 3 wt % in the finished sodium titanium phosphate product.

[0024] Furthermore, the carbon source in step S5 is at least one of starch, glucose, sucrose, and polyethylene glycol.

[0025] Furthermore, in step S5, stirring is performed for 30 to 60 minutes.

[0026] Furthermore, in step S5, the concentration of the sand grinding slurry is 50-60 wt %, and the particle size D50 of the material after sand grinding is ≤ 0.7 μm.

[0027] Furthermore, in step S6, sintering is performed in an inert atmosphere of nitrogen or argon in a muffle furnace at a temperature of 500-700° C., a heating rate of 1-2° C. / min, and a sintering time of 0.5-4 h.

[0028] Furthermore, the particle size D50 after pulverization in step S6 is 1 to 6 μm.

[0029] The invention relates to an application of a preparation method of a battery-grade sodium titanium phosphate negative electrode material in the preparation of a negative electrode material for aqueous sodium ion batteries.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The preparation method of the battery-grade sodium titanium phosphate negative electrode material of the present invention uses the material after alkali washing in the preparation process of titanium dioxide R seed crystals by the sulfuric acid method as the titanium source. Compared with titanyl sulfate or metatitanic acid, it has a low impurity content, reduces the generation of sulfur dioxide gas during the calcination process, and is more environmentally friendly; compared with titanate compounds, it is firstly cheaper, and at the same time can avoid the problem of uneven particle size and particle size distribution formed by the subsequent hydrolysis of titanate compounds, which is conducive to improving the electrochemical performance of the finished product.

[0032] 2. The present invention applies dynamic suspension calcination technology to the calcination process of sodium titanium phosphate for the first time. Compared with conventional rotary kilns or muffle furnaces, solid particles are evenly suspended in the reactor, the two-phase contact area is large, the heat and mass transfer processes are enhanced, the heat exchange coefficient between gas and material is greatly improved, sintering is reduced, the particle size and particle size distribution of the material are uniform, and it is more conducive to improving the electrochemical properties of the finished product; at the same time, the dynamic suspension calcination technology is used to significantly reduce the calcination temperature from the usual 700°C or above to 400-500°C, and the calcination time is greatly shortened from the conventional units of hours to seconds, thereby reducing the calcination energy consumption.

[0033] 3. The preparation method of the battery-grade sodium titanium phosphate negative electrode material of the present invention has cheap and easily available raw materials, simple operation, and is easy to achieve industrial production. The prepared carbon-coated sodium titanium phosphate has excellent cycle performance, rate performance, and low-temperature performance, and can be used as a negative electrode material in aqueous sodium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 This is an SEM photo of the carbon-coated sodium titanium phosphate negative electrode material of Example 1 of the present invention;

[0036] Figure 2 This is an SEM photo of the carbon-coated sodium titanium phosphate negative electrode material of Example 2 of the present invention;

[0037] Figure 3 This is an SEM photo of the carbon-coated sodium titanium phosphate negative electrode material of Example 3 of the present invention;

[0038] Figure 4 This is an SEM photo of the carbon-coated sodium titanium phosphate negative electrode material of Example 4 of the present invention;

[0039] Figure 5 This is an SEM photo of the carbon-coated sodium titanium phosphate negative electrode material of Comparative Example 1 of the present invention;

[0040] Figure 6 Cycling test results of half-cells of carbon-coated sodium titanium phosphate anode materials of Examples 1-4 and Comparative Example 1;

[0041] Figure 7 Rate test results of half-cells of carbon-coated sodium titanium phosphate anode materials of Examples 1-4 and Comparative Example 1;

[0042] Figure 8 Low temperature performance test results of the carbon-coated sodium titanium phosphate negative electrode material half-cells of Examples 1-4 and Comparative Example 1. DETAILED DESCRIPTION

[0043] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0044] The existing sulfuric acid process for titanium dioxide production involves acid hydrolysis, hydrolysis, primary washing, bleaching, secondary washing, salt treatment, calcination, and post-processing. Calcination seeds are often added during the bleaching process to promote crystal transformation and effectively control grain size.

[0045] The preparation method of rutile titanium dioxide seed crystals (R seed crystals) includes four steps: alkali boiling, alkali washing, acid adjustment and peptization. Alkali boiling is to mix the washed metatitanic acid with NaOH and heat them to react, destroying the anatase crystal structure in the metatitanic acid to form sodium orthotitanate (H2TiO3+4NaOH=Na4TiO4+3H2O). The alkali washing process washes away excess alkali and sulfate, reducing the consumption of HCl in the later peptization process. Then, the filter cake after alkali washing is pulped and the slurry is adjusted with HCl. When the pH value reaches about 3, sodium orthotitanate is converted into orthotitanic acid (Na4TiO4+4HCl=H4TiO4+4NaCl), and then HCl is added to react with orthotitanic acid to form titanium oxychloride (TiOCl2) (H4TiO4+2HCl=TiOCl2+3H2O). During the boiling process, titanium oxychloride is hydrolyzed to form rutile titanium dioxide colloid (TiOCl2+nH2O=TiO2·(n+1)H2O+HCl), which is the calcined seed crystal.

[0046] A method for preparing a battery-grade sodium titanium phosphate negative electrode material comprises the following steps:

[0047] Step S1, taking the slurry after alkali washing in the process of preparing R seed crystals, detecting the TiO2 concentration and sodium oxide content in the slurry, and using the slurry after alkali washing as the titanium source;

[0048] Preferably, R seed crystals are used in the production of titanium dioxide by the sulfuric acid process, and are usually used as a promoter for rutile conversion;

[0049] Preferably, the TiO2 concentration in the slurry after alkali washing is controlled at 130-170 g / L, because when the concentration is higher than 170 g / L, a peak of impurity phase of titanium pyrophosphate (TiP2O7) will appear in the product. The presence of the impurity phase TiP2O7 will increase the resistance to sodium ion transmission, hinder the diffusion of sodium ions, and have an adverse effect on the electrochemical properties of the material. In addition, the advantages of using the slurry after alkali washing as the titanium source are: (1) compared with titanyl sulfate or metatitanic acid, the impurity content is low, which reduces the generation of sulfur dioxide gas during the calcination process and is more environmentally friendly; (2) compared with titanate compounds, the price is cheaper; (3) the particle size and particle size distribution of titanium dioxide in the alkali washing slurry are uniform, which is equivalent to the uniform particle size and particle size distribution of the titanium source, which can avoid the problem of uneven particle size and particle size distribution formed by the subsequent hydrolysis of titanate compounds, and is conducive to improving the electrochemical properties of the finished product;

[0050] Step S2: adding a sodium source and a phosphorus source to the slurry in the previous step, respectively, and stirring for 30 to 60 minutes, including but not limited to 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, and 60 minutes;

[0051] Preferably, the amount of sodium source added is based on the sodium oxide content in the slurry detected in the previous step, and the sodium source difference is supplemented according to the molar ratio of sodium: titanium: phosphorus. The molar ratio of sodium: titanium: phosphorus is Na: Ti: P = 1 to 3: 2 to 5: 3 to 7, including but not limited to 1: 2: 3, 2: 3: 4, 3: 4: 6, 3: 5: 7;

[0052] Preferably, the sodium source is at least one of sodium carbonate, sodium bicarbonate, and sodium acetate, and the phosphorus source is at least one of phosphoric acid, monoammonium phosphate, diammonium phosphate, and triammonium phosphate;

[0053] Step S3, sand milling the mixed solution in the previous step for 0.5 to 2 hours, including but not limited to 0.5 hours, 1 hour, 1.5 hours, and 2 hours, and then spray drying to obtain a sodium titanium phosphate powder precursor;

[0054] Preferably, the particle size D50 of the material after sand milling is ≤ 0.7 μm. On the one hand, sand milling can fully react sodium / titanium / phosphorus to ensure better crystallinity during the subsequent dynamic suspension calcination process; on the other hand, after sand milling, the particle size of the material becomes smaller, and the particle size after calcination is also reduced, thereby reducing the sand milling intensity during the subsequent carbon coating and the pressure during the crushing of the finished product.

[0055] Preferably, the inlet temperature of the spray drying is 200-240°C, including but not limited to 200°C, 210°C, 220°C, 230°C, and 240°C, and the outlet temperature is 90-95°C, including but not limited to 90°C, 91°C, 92°C, 93°C, 94°C, and 95°C;

[0056] Step S4, dynamically sintering the spray-dried sodium titanium phosphate powder precursor to obtain sodium titanium phosphate;

[0057] Preferably, the temperature of dynamic suspension calcination is 400-500° C., including but not limited to 400° C., 410° C., 420° C., 430° C., 440° C., 450° C., 460° C., 470° C., 480° C., 490° C., and 500° C., and the calcination time is 30-90s, including but not limited to 30s, 35s, 40s, 45s, 50s, 55s, 60s, 65s, 70s, 75s, 80s, 85s, and 90s;

[0058] Step S5, adding sodium titanium phosphate and a carbon source to softened water, stirring for 30 to 60 minutes, wherein the stirring time includes but is not limited to 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, and 60 minutes, sand milling, and spray drying;

[0059] Preferably, the sand grinding slurry concentration is 50-60wt%, including but not limited to 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, and 60%. The high solid content can reduce energy consumption during spray drying. The particle size D50 of the material after sand grinding is ≤0.7μm. On the one hand, sand grinding can fully coat the carbon source on the surface of the sodium titanium phosphate particles, which is beneficial to improving the electrochemical properties of the finished product; on the other hand, it can reduce the pressure when the finished product is subsequently crushed.

[0060] Preferably, the amount of carbon source added is based on the carbon content of the finished sodium titanium phosphate product being 2 to 3 wt%;

[0061] Preferably, the carbon source is at least one of starch, glucose, sucrose, and polyethylene glycol;

[0062] Step S6, sintering the spray-dried sample under an inert atmosphere, cooling it, and then crushing it to obtain a carbon-coated sodium titanium phosphate negative electrode material;

[0063] Preferably, sintering is carried out in a muffle furnace under a nitrogen or argon atmosphere, at a temperature of 500-700°C, including but not limited to 500°C, 550°C, 600°C, 650°C, and 700°C, a heating rate of 1-2°C / min, including but not limited to 1.0°C / min, 1.1°C / min, 1.2°C / min, 1.3°C / min, 1.4°C / min, 1.5°C / min, 1.6°C / min, 1.7°C / min, 1.8°C / min, 1.9°C / min, and 2.0°C / min, and a sintering time of 0.5-4h, including but not limited to 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, and 4h;

[0064] Preferably, the particle size D50 after pulverization is 1 to 6 μm.

[0065] Example 1

[0066] A method for preparing a battery-grade sodium titanium phosphate negative electrode material comprises the following steps:

[0067] Step S1, taking the slurry after alkali washing in the process of preparing R seed crystals, detecting the TiO2 concentration and sodium oxide content in the slurry, controlling the TiO2 concentration in the slurry after alkali washing to be 130 g / L, and using the slurry after alkali washing as the titanium source;

[0068] Step S2, adding sodium carbonate and phosphoric acid to the slurry in the previous step respectively, stirring for 30 minutes, and the molar ratio of sodium: titanium: phosphorus after addition is 1:2:3. The amount of sodium carbonate added is based on the sodium oxide content in the slurry detected in the previous step, and the molar ratio of sodium: titanium: phosphorus is used to make up the difference in sodium carbonate;

[0069] Step S3: sand-milling the mixed solution in the previous step for 2 h, to a particle size D50 of 0.36 μm, and then spray-drying the solution at an inlet temperature of 200° C. and an outlet temperature of 90° C. to obtain a sodium titanium phosphate powder precursor;

[0070] Step S4, subjecting the spray-dried sodium titanium phosphate powder precursor to dynamic suspension calcination at a temperature of 400° C. for 90 seconds to obtain sodium titanium phosphate;

[0071] Step S5, adding sodium titanium phosphate and starch to softened water, with the amount of starch added being based on the carbon content of the finished sodium titanium phosphate product being 2 wt %, stirring for 30 min, sand milling, and spray drying, with the sand milling slurry concentration being 50 wt %, and the particle size D50 of the sand milled material being 0.54 μm;

[0072] Step S6: The spray-dried sample was sintered in a muffle furnace under a nitrogen atmosphere at a temperature of 500°C, a heating rate of 1°C / min, and a sintering time of 4 hours. After cooling, the sample was crushed to obtain a carbon-coated sodium titanium phosphate negative electrode material. The particle size after crushing was D50 = 1.05 μm.

[0073] Example 2

[0074] A method for preparing a battery-grade sodium titanium phosphate negative electrode material comprises the following steps:

[0075] Step S1, taking the slurry after alkali washing in the process of preparing R seed crystals, detecting the TiO2 concentration and sodium oxide content in the slurry, controlling the TiO2 concentration in the slurry after alkali washing to be 157 g / L, and using the slurry after alkali washing as the titanium source;

[0076] Step S2, adding sodium bicarbonate and monoammonium phosphate to the slurry in the previous step respectively, stirring for 55 minutes, and the molar ratio of sodium:titanium:phosphorus after addition is 2:3:4. The amount of sodium bicarbonate added is based on the sodium oxide content in the slurry detected in the previous step, and the molar ratio of sodium:titanium:phosphorus is used to make up the difference in sodium bicarbonate;

[0077] Step S3: sand-milling the mixed solution in the previous step for 1 hour to obtain a particle size D50 of 0.64 μm, followed by spray drying at an inlet temperature of 210° C. and an outlet temperature of 92° C. to obtain a sodium titanium phosphate powder precursor;

[0078] Step S4, subjecting the spray-dried sodium titanium phosphate powder precursor to dynamic suspension calcination at a temperature of 420° C. for 80 seconds to obtain sodium titanium phosphate;

[0079] Step S5, adding sodium titanium phosphate and glucose to softened water, with the amount of glucose added being based on the carbon content of the sodium titanium phosphate product being 2.2 wt %, stirring for 40 min, sand milling, and spray drying. The sand milling slurry concentration is 52 wt %, and the particle size D50 of the sand milled material is 0.62 μm;

[0080] Step S6: The spray-dried sample was sintered in a muffle furnace under a nitrogen atmosphere at a temperature of 550°C, a heating rate of 1.2°C / min, and a sintering time of 3h. After cooling, the sample was crushed to obtain a carbon-coated sodium titanium phosphate negative electrode material. The particle size after crushing was D50 = 2.58μm.

[0081] Example 3

[0082] A method for preparing a battery-grade sodium titanium phosphate negative electrode material comprises the following steps:

[0083] Step S1, taking the slurry after alkali washing in the preparation process of R seed crystals, detecting the TiO2 concentration and sodium oxide content in the slurry, controlling the TiO2 concentration in the slurry after alkali washing to be 168g / L, and using the slurry after alkali washing as the titanium source;

[0084] Step S2: adding sodium acetate and diammonium phosphate to the slurry from the previous step respectively, stirring for 60 minutes, so that the molar ratio of sodium:titanium:phosphorus is 3:4:6 after the addition. The amount of sodium acetate added is based on the sodium oxide content in the slurry detected in the previous step, and the difference in sodium acetate is supplemented according to the molar ratio of sodium:titanium:phosphorus;

[0085] Step S3: sand-milling the mixed solution in the previous step for 1.5 hours to a particle size D50 of 0.7 μm, and then spray-drying the solution at an inlet temperature of 220° C. and an outlet temperature of 94° C. to obtain a sodium titanium phosphate powder precursor;

[0086] Step S4, subjecting the spray-dried sodium titanium phosphate powder precursor to dynamic suspension calcination at a temperature of 450° C. for 60 seconds to obtain sodium titanium phosphate;

[0087] Step S5, adding sodium titanium phosphate and sucrose to softened water, with the amount of sucrose added being based on the carbon content of the finished sodium titanium phosphate being 2.6 wt %, stirring for 50 min, sand milling, and spray drying. The sand milling slurry concentration is 55 wt %, and the particle size D50 of the sand milled material is 0.58 μm;

[0088] Step S6: sinter the spray-dried sample in an argon atmosphere in a muffle furnace at a temperature of 600°C, a heating rate of 1.5°C / min, and a sintering time of 2h. After cooling, the sample is crushed to obtain a carbon-coated sodium titanium phosphate negative electrode material with a particle size D50 of 4.6μm.

[0089] Example 4

[0090] A method for preparing a battery-grade sodium titanium phosphate negative electrode material comprises the following steps:

[0091] Step S1, taking the slurry after alkali washing in the preparation process of R seed crystals, detecting the TiO2 concentration and sodium oxide content in the slurry, controlling the TiO2 concentration in the slurry after alkali washing to be 145g / L, and using the slurry after alkali washing as the titanium source;

[0092] Step S2, adding sodium carbonate and triammonium phosphate to the slurry in the previous step respectively, stirring for 45 minutes, and the molar ratio of sodium:titanium:phosphorus after addition is 3:5:7. The amount of sodium carbonate added is based on the sodium oxide content in the slurry detected in the previous step, and the molar ratio of sodium:titanium:phosphorus is used to make up the difference in sodium carbonate;

[0093] Step S3: sand-milling the mixed solution in the previous step for 0.5 h, to a particle size D50 of 0.55 μm, and then spray-drying the solution at an inlet temperature of 240° C. and an outlet temperature of 95° C. to obtain a sodium titanium phosphate powder precursor;

[0094] Step S4, subjecting the spray-dried sodium titanium phosphate powder precursor to dynamic suspension calcination at a temperature of 500° C. for 30 seconds to obtain sodium titanium phosphate;

[0095] Step S5, adding sodium titanium phosphate and polyethylene glycol to softened water, wherein the amount of polyethylene glycol added is based on the carbon content of 3 wt% in the finished sodium titanium phosphate product, stirring for 60 minutes, sand milling, and spray drying. The sand milling slurry concentration is 60 wt%, and the particle size D50 of the sand milled material is 0.65 μm;

[0096] Step S6: The spray-dried sample was sintered in an argon atmosphere in a muffle furnace at a temperature of 700°C, a heating rate of 2°C / min, and a sintering time of 0.5h. After cooling, the sample was crushed to obtain a carbon-coated sodium titanium phosphate negative electrode material. The particle size after crushing was D50 = 5.86μm.

[0097] Comparative Example 1:

[0098] A method for preparing a battery-grade sodium titanium phosphate negative electrode material comprises the following steps:

[0099] Step S1, preparation of TiO2: Tetrabutyl titanate is added to anhydrous ethanol at a volume ratio of tetrabutyl titanate: ethanol = 1:9, stirred for 0.5h, and then the mixture is poured into a 100mL reactor. Heat the reaction in a forced air drying oven at 160°C for 3h. After naturally cooling to room temperature, centrifuge to obtain a white product, repeatedly wash with ethanol three times and dry to obtain TiO2, slurry the TiO2, and control the TiO2 concentration in the slurry to 130g / L;

[0100] Step S2: Sodium carbonate and phosphoric acid are added to the slurry in the previous step respectively, and stirred for 30 minutes. After the addition, the molar ratio of sodium: titanium: phosphorus is 1:2:3;

[0101] Step S3 is the same as in Example 1;

[0102] Step S4, calcining the spray-dried sodium titanium phosphate powder precursor in a muffle furnace, heating at 5°C / min to 700°C, keeping at 700°C for 2h, and cooling to obtain sodium titanium phosphate;

[0103] Step S5 and step S6 are the same as in Example 1.

[0104] 1. Particle size and particle size distribution test of the materials of Examples 1-4 and Comparative Example 1.

[0105] Table 1 Particle size and particle size distribution test table of materials in Examples 1-4 and Comparative Example 1

[0106]

[0107]

[0108] From the particle size and particle size distribution data of Examples 1-4 and Comparative Example 1 in Table 1, it can be seen that the particle size distribution of the carbon-coated sodium titanium phosphate negative electrode material prepared by the method of the present invention is more uniform, which can also be seen from the SEM image.

[0109] II. Examples 1-4 and Comparative Example 1: SEM images of carbon-coated sodium titanium phosphate negative electrode materials Figures 1 to 5 As shown:

[0110] from Figure 1-5 It can be seen from the SEM photos that the synthesized NaTi2(PO4)3 samples are composed of nano-scale grains aggregated and stacked. The surface coating in Examples 1-4 is more uniform, the carbon is well dispersed and the carbon source is fully coated on the surface of the NaTi2(PO4)3 particles, while the agglomeration phenomenon in Comparative Example 1 is more serious and the carbon source coating is insufficient.

[0111] III. Examples 1-4 and Comparative Example 1: Cycling Performance, Rate Performance, and Low-Temperature Performance Tests of Carbon-Coated Sodium Titanium Phosphate Finished Products

[0112] Button cells were prepared using the carbon-coated sodium titanium phosphate described in Examples 1-4 and Comparative Example 1 as the negative electrode. The specific process was as follows: the carbon-coated sodium titanium phosphate, conductive carbon black Super-P, and binder PVDF from Examples 1-4 and Comparative Example 1 were mixed in a mass ratio of 8:1:1. An appropriate amount of NMP was added as solvent. The mixture was homogenized using a dual planetary deaerator for 21 minutes. The slurry was sieved through a 200-mesh stainless steel screen and evenly coated onto aluminum foil using a spatula. After vacuum drying at 85°C for 16 hours, a circular electrode sheet with a diameter of 12 mm was punched out using a mold. This sample electrode served as the study electrode, and a sodium metal sheet served as the counter electrode. The cells were assembled into a 2032-type button cell in a glove box.

[0113] The test environment is as follows: After the battery is assembled, constant current charge and discharge tests are performed at a voltage of 1.5-3V using a Land-2001A (Wuhan, China) to obtain information such as the material's rate performance changes, cycle performance, and low-temperature performance.

[0114] The cycle performance test results of Examples 1-4 and Comparative Example 1 are as follows: Figure 6 As shown, the rate performance results are as follows Figure 7 As shown, the low temperature performance is Figure 8 As shown:

[0115] from Figure 6It can be seen from the cycle test results that after 100 cycles at 1C, the carbon-coated sodium titanium phosphate negative electrode materials prepared in Examples 1-4 all showed good cycle stability, and the capacity retention rate was about 99%. The initial discharge specific capacity of the carbon-coated sodium titanium phosphate negative electrode material prepared in Comparative Example 1 was significantly lower than that of Examples 1-4, and after 100 cycles at 1C, the capacity retention rate was 98.5%.

[0116] from Figure 7 It can be seen from the test results at different rates that the carbon-coated sodium titanium phosphate negative electrode materials prepared in Examples 1-4 all exhibit better rate performance, and their discharge specific capacity can reach more than 98% of the initial capacity when increasing from 0.1C to 10C. Therefore, it can be explained that the carbon-coated sodium titanium phosphate negative electrode material prepared by the method of the present invention has a very small decrease in specific capacity at high test rates, showing good rate performance. The carbon-coated sodium titanium phosphate negative electrode material prepared in Comparative Example 1 has a significantly lower discharge specific capacity from 0.1C to 10C than the negative electrode material prepared by the method of the present invention. As one of the effective alternatives to lithium-ion batteries, sodium-ion batteries also face different application environments of lithium-ion batteries, including large temperature differences between day and night, temperature differences between different areas in the same place, etc. Therefore, studying the adaptability of sodium-ion electrode materials to temperature has practical application value, especially the electrochemical performance in low-temperature environments. As Figure 8 The low-temperature performance test results show that, at 1C, the discharge specific capacity changes of Examples 1-4 and Comparative Example 1 were compared at room temperature (20°C) and -20°C, respectively. The low-temperature performance test results show that the carbon-coated sodium titanium phosphate anode materials prepared in Examples 1-4 maintained a discharge specific capacity retention rate greater than 98% from room temperature (20°C) to -20°C, with only a slight decrease, demonstrating good low-temperature adaptability. However, the carbon-coated sodium titanium phosphate anode material prepared in Comparative Example 1 had relatively low discharge specific capacities at both room and low temperatures.

[0117] In summary, the carbon-coated sodium titanium phosphate negative electrode material prepared by the method of the present invention has the characteristics of excellent cycle performance, rate performance and low-temperature performance. At the same time, due to the cheap and readily available raw materials and simple operation, it is easy to realize industrial production.

Claims

1. A method for preparing a battery-grade sodium titanium phosphate negative electrode material, characterized in that: The following steps are involved: Step S1, taking the slurry after alkali washing in the preparation process of R seed crystals as a titanium source, and detecting the TiO2 concentration and sodium oxide content in the slurry; Step S2: adding a sodium source and a phosphorus source to the slurry in the previous step in proportion and stirring; Step S3, sand-milling and spray-drying the mixed solution in the previous step to obtain a sodium titanium phosphate powder precursor; Step S4, dynamically sintering the sodium titanium phosphate powder precursor to obtain sodium titanium phosphate; Step S5, adding sodium titanium phosphate and a carbon source into softened water in proportion, stirring, sand milling, and spray drying; Step S6: sintering, cooling, and crushing the spray-dried sample to obtain a carbon-coated sodium titanium phosphate negative electrode material.

2. The method for preparing the battery-grade sodium titanium phosphate negative electrode material according to claim 1, wherein: The TiO2 concentration in the slurry after alkali washing in step S1 is controlled at 130-170 g / L.

3. The method for preparing the battery-grade sodium titanium phosphate negative electrode material according to claim 2, wherein: Includes at least one of the following technical features: (1) The amount of sodium source added in step S2 is based on the sodium oxide content in the slurry detected in step S1, and the sodium source difference is supplemented according to the molar ratio of sodium: titanium: phosphorus, and the molar ratio of sodium: titanium: phosphorus is Na: Ti: P = 1-3: 2-5: 3-7; (2) The stirring time in step S2 is 30 to 60 minutes.

4. The method for preparing the battery-grade sodium titanium phosphate negative electrode material according to claim 3, characterized in that: Includes at least one of the following technical features: (1) The sodium source is at least one of sodium carbonate, sodium bicarbonate, and sodium acetate; (2) The phosphorus source is at least one of phosphoric acid, monoammonium phosphate, diammonium phosphate, and triammonium phosphate.

5. The method for preparing the battery-grade sodium titanium phosphate negative electrode material according to claim 1, characterized in that: Includes at least one of the following technical features: (1) sand milling for 0.5 to 2 hours in step S3, and the particle size D50 of the material after sand milling is ≤ 0.7 μm; (2) The inlet temperature of the spray drying in step S3 is 200-240°C, and the outlet temperature is 90-95°C.

6. The method for preparing the battery-grade sodium titanium phosphate negative electrode material according to claim 1, characterized in that: The temperature of the dynamic suspension calcination in step S4 is 400-500° C., and the calcination time is 30-90 seconds.

7. The method for preparing the battery-grade sodium titanium phosphate negative electrode material according to claim 1, characterized in that: The amount of carbon source added in step S5 is based on the carbon content of the finished sodium titanium phosphate product of 2 to 3 wt%.

8. The method for preparing the battery-grade sodium titanium phosphate negative electrode material according to claim 7, characterized in that: Includes at least one of the following technical features: (1) The carbon source in step S5 is at least one of starch, glucose, sucrose, and polyethylene glycol; (2) stirring in step S5 for 30 to 60 minutes; (3) In step S5, the sand grinding slurry concentration is 50-60 wt %, and the particle size D50 of the material after sand grinding is ≤ 0.7 μm.

9. The method for preparing the battery-grade sodium titanium phosphate negative electrode material according to claim 1, wherein: Includes at least one of the following technical features: (1) In step S6, sintering is performed in a muffle furnace under an inert atmosphere of nitrogen or argon at a temperature of 500-700° C., a heating rate of 1-2° C. / min, and a sintering time of 0.5-4 h; (2) The particle size D50 after pulverization in step S6 is 1 to 6 μm.

10. Use of the method for preparing the battery-grade sodium titanium phosphate negative electrode material according to any one of claims 1 to 9 in preparing negative electrode materials for aqueous sodium ion batteries.

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