Sodium ferric pyrophosphate positive electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of batteries, in particular to a sodium ferric pyrophosphate positive electrode material and a preparation method and application thereof. The sodium ferric pyrophosphate positive electrode material comprises a positive electrode matrix and doping elements, the chemical general formula of the positive electrode substrate is NaxFey (PO4) 2P2O7, and y / x is more than or equal to 0.2 and less than or equal to 1; the doping elements are Ti and Co, the doping amount of Co is m, m is larger than or equal to 1000 ppm and smaller than or equal to 30000 ppm, the doping amount of Ti is n, and n is larger than or equal to 200 ppm and smaller than or equal to 30000 ppm. The sodium ferric pyrophosphate positive electrode material disclosed by the invention has high compaction, high conductivity, high capacity, high first efficiency and high rate performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a sodium pyrophosphate positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] The positive electrode material of the sodium ion battery does not have sodium resource limitation, and in the background of trade barriers and globalization decoupling, it is ushered in rapid development. The positive electrode material is mainly divided into sodium nickel iron manganese acid, sodium nickel iron copper manganese acid and the like with a layered structure; the positive electrode material with a polyatomic anion mainly includes sodium iron phosphate and sodium iron sulfate; and the positive electrode material of the Prussian blue type.

[0003] The sodium iron phosphate and the lithium iron phosphate both belong to the olivine crystal structure, but the sodium ion migration channel of the sodium iron phosphate with a positive ratio of Fe / Na is blocked, and there are problems such as no electrochemical activity. Researchers found that adjusting the Fe / Na ratio and introducing a pyrophosphate anion group can solve the sodium ion migration channel blockage while maintaining the stable crystal structure of the olivine tree type.

[0004] At present, the sodium ion battery with the sodium pyrophosphate as the positive electrode material is mainly applied in the low-speed vehicle and energy storage field. The existing sodium pyrophosphate positive electrode material has low capacity, poor initial efficiency and poor rate performance.

[0005] How to obtain a sodium pyrophosphate positive electrode material with high capacity, high initial efficiency and rate performance is crucial for the development of the sodium ion battery.

[0006] Therefore, the present application is proposed. SUMMARY

[0007] One object of the present application is to provide a sodium pyrophosphate positive electrode material with high compaction, high capacity, high initial efficiency and high rate performance.

[0008] Another object of the present application is to provide a preparation method of the sodium pyrophosphate positive electrode material. The mixing effect and performance of the slurry are adjusted through the cooperation of the step of grading grinding and other steps, so as to improve the electrochemical performance of the obtained sodium pyrophosphate positive electrode material.

[0009] Another object of the present application is to provide a battery.

[0010] Another object of the present application is to provide an electric device.

[0011] In order to achieve the above objects of the present application, the following technical solutions are adopted: A sodium pyrophosphate positive electrode material includes a positive electrode matrix and a doping element; the chemical general formula of the positive electrode matrix is Na x Fe y(PO4)2P2O7, wherein 0.2≤y / x≤1; the doping elements are Ti and Co, the doping amount of the Co is m, 1000ppm≤m≤30000ppm, and the doping amount of the Ti is n, 200ppm≤n≤30000ppm.

[0012] In some embodiments, the sum of the m and the n satisfies: 2000ppm≤m+n≤50000ppm.

[0013] In some embodiments, the surface of the positive electrode substrate is further provided with a carbon coating layer. In some embodiments, the compaction density of the sodium iron pyrophosphate positive electrode material is 2.31-2.4g / cm 3 .

[0014] In some embodiments, the battery prepared from the sodium iron pyrophosphate positive electrode material has a discharge gram capacity≥110mAh / g under the condition of 0.1C, 1.5-3.8V, a first circle efficiency≥90%, and a discharge gram capacity≥89mAh / g under the condition of 3C, 1.5-3.8V.

[0015] A preparation method of a sodium iron pyrophosphate positive electrode material, comprising the following steps: The mixture of the phosphorus source, the iron source, the sodium source, the carbon source, the titanium source, the cobalt source and the solvent is subjected to a grading grinding treatment, the grading grinding treatment comprising coarse grinding treatment, medium grinding treatment and fine grinding treatment, to obtain coarse grinding slurry, medium grinding slurry and fine grinding slurry respectively; the coarse grinding slurry, the medium grinding slurry and the fine grinding slurry are mixed to obtain a first system; and the first system is subjected to heat treatment.

[0016] In some embodiments, the grading grinding treatment specifically comprises: subjecting the mixture to the coarse grinding treatment to obtain first slurry, taking part of the first slurry as the coarse grinding slurry, subjecting the remaining first slurry to the medium grinding treatment to obtain second slurry, taking part of the second slurry as the medium grinding slurry, and subjecting the remaining second slurry to the fine grinding treatment to obtain fine grinding slurry.

[0017] In some embodiments, the coarse grinding treatment comprises coarse grinding medium, the diameter of the coarse grinding medium is 1.2-2.0mm; the medium grinding treatment adopts medium grinding medium, the diameter of the medium grinding medium is 0.4-1.0mm; and the fine grinding treatment adopts fine grinding medium, the diameter of the fine grinding medium is 0.2-0.4mm.

[0018] In some embodiments, the coarse grinding treatment comprises coarse grinding medium, the medium grinding treatment adopts medium grinding medium, and the fine grinding treatment adopts fine grinding medium, the filling rate of the coarse grinding medium, the medium grinding medium and the fine grinding medium is independently 80%-90%.

[0019] In some embodiments, the coarse grinding treatment is performed for 1-2.5 hours at a speed of 2000-3000 rpm; the medium grinding treatment is performed for 2.5-3.5 hours at a speed of 2000-3000 rpm; and the fine grinding treatment is performed for 3-4.5 hours at a speed of 2000-3000 rpm.

[0020] In some embodiments, the volume of the coarse grinding slurry is a, the volume of the medium grinding slurry is b, and the volume of the fine grinding slurry is c, 0.1≤a / (a+b+c)≤0.3, 0.2≤b / (a+b+c)≤0.5, and 0.3≤c / (a+b+c)≤0.7.

[0021] In some embodiments, the mixing treatment is performed at a speed of 300-800 rpm for 30-120 minutes.

[0022] In some embodiments, the cobalt source comprises at least one of cobalt oxalate, cobalt oxide, cobalt nitrate, cobalt carbonate, cobalt sulfate, cobalt chloride, cobalt bromide, cobalt phosphate, and cobalt hydroxide.

[0023] In some embodiments, the titanium source comprises at least one of titanium oxalate, titanium oxide, titanium sulfate, and titanium chloride.

[0024] In some embodiments, the iron source comprises at least one of iron phosphate and iron oxide.

[0025] In some embodiments, the sodium source comprises at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, and disodium hydrogen pyrophosphate.

[0026] In some embodiments, the phosphorus source comprises at least one of a phosphate, a pyrophosphate, phosphoric acid, and ammonium dihydrogen phosphate.

[0027] In some embodiments, the carbon source comprises at least one of polypyrrine, sucrose, polyethylene glycol, glucose, polyethylene, and polyvinylpyrrolidone.

[0028] In some embodiments, the molar ratio of the phosphorus source to the iron source is 0.95-1.2; the molar ratio of the iron source to the sodium source is 0.7-1; the mass percentage of the carbon source with respect to the iron source is 8%-12%; the mass of the titanium source with respect to the total mass of the phosphorus source, iron source, sodium source, carbon source, titanium source, and cobalt source is 0.1%-3%; and the mass of the cobalt source with respect to the total mass of the phosphorus source, iron source, sodium source, carbon source, titanium source, and cobalt source is 0.02%-3%. In some embodiments, the solvent comprises water and / or an alcohol solvent.

[0029] In some embodiments, the solid content of the mixture is 30% to 48%.

[0030] In some embodiments, the preparation of the mixture specifically includes: premixing the phosphorus source, iron source, sodium source, carbon source, titanium source, cobalt source and solvent, wherein the premixing time is 30~120 min.

[0031] In some embodiments, the heat treatment includes drying and gradient sintering.

[0032] In some embodiments, the drying temperature is 100~300℃; preferably, the drying process includes spray drying, wherein the inlet air temperature of the spray drying is 160~300℃, the outlet air temperature is 100~150℃, and the rotation speed of the atomizer is 20000~22000rpm.

[0033] In some embodiments, the gradient sintering temperature is 400~800℃, and the total holding time of the gradient sintering is 8~18h; preferably, the gradient sintering includes a first sintering and a second sintering performed sequentially, the temperature of the first sintering is 400~500℃, the holding time of the first sintering is 1~6h, the temperature of the second sintering is 580~800℃, and the holding time of the second sintering is 3~12h; preferably, the atmosphere of the gradient sintering is a protective atmosphere.

[0034] In some embodiments, the heat-treated material is further subjected to crushing, sieving, and demagnetization.

[0035] A battery comprising the sodium iron pyrophosphate cathode material described above, or the sodium iron pyrophosphate cathode material prepared by the method described above.

[0036] An electrical device, including the battery.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The sodium iron pyrophosphate cathode material of the present invention uses Ti and Co co-doping to improve the rate performance of the cathode material. An appropriate amount of Ti can stabilize the crystal structure, broaden the sodium ion migration channel, and reduce the diffusion barrier of sodium ions. An appropriate amount of Co doping can effectively reduce the band gap of the cathode material and improve the electronic conductivity of the material. An appropriate amount of Ti and Co can play a synergistic role and cooperate with the sodium iron pyrophosphate cathode matrix to make the obtained sodium iron pyrophosphate cathode material have high compaction, high conductivity, high first efficiency and high rate performance.

[0038] (2) The preparation method of sodium iron pyrophosphate cathode material of the present invention, by setting up a graded grinding process, performs particle size distribution before heat treatment. Compared with the mixed distribution of large and small particles after crushing, the mixing degree is more uniform under solution system conditions, ensuring the uniform distribution of Ti and Co in the matrix. The graded grinding process can control the particle size more stably and more controllably, and obtain a precursor material with suitable particle size distribution and good sphericity, which is beneficial to subsequent heat treatment, and obtain sodium iron pyrophosphate cathode material with high capacity and high rate performance.

[0039] (3) The battery of the present invention has the characteristics of high capacity, high initial efficiency and high rate performance, and good safety performance. Attached Figure Description

[0040] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0041] Figure 1 This is a flowchart of the preparation method of sodium iron pyrophosphate cathode material of the present invention; Figure 2 This is a scanning electron microscope image of the sodium iron pyrophosphate cathode material of Example 2 of the present invention; Figure 3 The charge-discharge curves of the battery prepared using the sodium iron pyrophosphate cathode material of Example 2 of the present invention under conditions of 0.1C and 1.5~3.8V. Detailed Implementation

[0042] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0043] According to one aspect of the present invention, the present invention relates to a sodium iron pyrophosphate cathode material, comprising a cathode matrix and a doping element; the general chemical formula of the cathode matrix is ​​Na. x Fe y(PO4)2P2O7, wherein 0.2≤y / x≤1; the doping elements are Ti and Co, wherein the doping amount of Co is m, 1000ppm≤m≤30000ppm, for example 1000ppm, 1500ppm, 2000ppm, 3000ppm, 5000ppm, 8000ppm, 10000ppm, 15000ppm, 20000ppm, 30000ppm, etc., and the doping amount of Ti is n, 200ppm≤n≤30000ppm, for example 200ppm, 500ppm, 1000ppm, 1500ppm, 2000ppm, 3000ppm, 5000ppm, 8000ppm, 10000ppm, 15000ppm, 20000ppm, 30000ppm, etc.

[0044] The sodium iron pyrophosphate cathode material of the present invention uses Ti and Co co-doping to improve the rate performance of the cathode material. An appropriate amount of Ti can stabilize the crystal structure, widen the sodium ion migration channel, and reduce the sodium ion diffusion barrier; an appropriate amount of Co doping can effectively reduce the band gap of the cathode material and improve the electronic conductivity of the material; an appropriate amount of Ti and Co can play a synergistic role, working together with the sodium iron pyrophosphate cathode matrix to give the obtained sodium iron pyrophosphate cathode material high compaction, high conductivity, high capacity, high initial efficiency, and high rate performance.

[0045] In some embodiments, the sum of m and n satisfies: 2000ppm ≤ m + n ≤ 50000ppm, such as 2000ppm, 3000ppm, 5000ppm, 8000ppm, 10000ppm, 20000ppm, 30000ppm, 50000ppm, etc. Further optimizing the total doping amount of Ti and Co can better guarantee the performance improvement of the positive electrode matrix, iron pyrophosphate. If the total doping amount of Ti and Co is too low, the improvement effect is not significant; if the doping amount is too high, it is not conducive to the performance of the iron pyrophosphate material.

[0046] In some embodiments, a carbon coating layer is further disposed on the surface of the positive electrode substrate. The carbon coating layer on the surface of the positive electrode substrate in this invention helps to improve the interfacial stability of the material and increase its electronic conductivity.

[0047] In some embodiments, the compaction density of the sodium iron pyrophosphate cathode material is 2.31~2.4 g / cm³. 3 For example, 2.31 g / cm³ 3 2.35g / cm 3 2.37 g / cm 3 2.38g / cm 3 2.4g / cm 3The sodium iron pyrophosphate cathode material of this application has a suitable compaction density, which is beneficial for improving the volumetric energy density of the battery.

[0048] In some embodiments, the battery prepared from the sodium iron pyrophosphate cathode material has a discharge capacity ≥110mAh / g under 0.1C and 1.5~3.8V conditions, such as 110mAh / g, 115mAh / g, 120mAh / g, 130mAh / g, etc., and an initial cycle efficiency ≥90%, such as 90%, 91%, 92%, 93%, 95%, etc., and a discharge capacity ≥89mAh / g under 3C and 1.5~3.8V conditions, such as 89mAh / g, 91mAh / g, 95mAh / g, 98mAh / g, etc.

[0049] According to another aspect of the present invention, the present invention also relates to a method for preparing a sodium iron pyrophosphate cathode material, comprising the following steps: A mixture of phosphorus source, iron source, sodium source, carbon source, titanium source, cobalt source and solvent is subjected to graded grinding, which includes coarse grinding, medium grinding and fine grinding to obtain coarse grinding slurry, medium grinding slurry and fine grinding slurry respectively; the coarse grinding slurry, medium grinding slurry and fine grinding slurry are mixed to obtain a first system; the first system is then subjected to heat treatment.

[0050] The method for preparing sodium iron pyrophosphate cathode material of the present invention involves a graded grinding process, which performs particle size distribution before heat treatment. Compared with the mixed distribution of large and small particles after crushing, the mixing degree is more uniform under solution conditions, ensuring the uniform distribution of Ti and Co in the matrix. The graded grinding process allows for more stable and controllable particle size control, resulting in precursor materials with suitable particle size distribution and good sphericity, which is beneficial for subsequent heat treatment and yields sodium iron pyrophosphate cathode materials with high capacity and high rate performance.

[0051] In some embodiments, the cobalt source includes at least one of cobalt oxalate, cobalt oxide, cobalt nitrate, cobalt carbonate, cobalt sulfate, cobalt chloride, cobalt bromide, cobalt phosphate, and cobalt hydroxide. The present invention employs a suitable cobalt source to improve the doping effect, such as a combination of cobalt oxide, cobalt nitrate, and cobalt carbonate, a combination of cobalt bromide and cobalt phosphate, a combination of cobalt phosphate and cobalt hydroxide, etc.

[0052] In some embodiments, the titanium source includes at least one of titanium oxalate, titanium oxide, titanium sulfate, and titanium chloride. The present invention employs a suitable titanium source to improve the doping effect, such as a combination of titanium oxalate and titanium oxide, or a combination of titanium sulfate and titanium chloride.

[0053] In some embodiments, the iron source includes at least one of iron phosphate and iron oxide. The present invention employs a suitable iron source to ensure the performance of the positive electrode substrate.

[0054] In some embodiments, the sodium source includes at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, and disodium dihydrogen pyrophosphate, such as a combination of sodium carbonate and sodium bicarbonate, or a combination of sodium hydroxide and disodium dihydrogen pyrophosphate. This invention employs a suitable sodium source to ensure the performance of the positive electrode substrate.

[0055] In some embodiments, the phosphorus source includes at least one of phosphate, pyrophosphate, phosphoric acid, and ammonium dihydrogen phosphate, such as a combination of phosphate and pyrophosphate, or a combination of phosphoric acid and ammonium dihydrogen phosphate. This invention employs a suitable phosphorus source to ensure the performance of the cathode substrate.

[0056] In some embodiments, the carbon source includes at least one selected from polypyrrole, sucrose, polyethylene glycol, glucose, polyethylene, and polyvinylpyrrolidone, such as a combination of polypyrrole and sucrose, or a combination of polyethylene glycol and glucose. The carbon source of the present invention undergoes subsequent heat treatment to carbonize and form a carbon coating layer, thereby improving the conductivity and interfacial stability of the positive electrode substrate.

[0057] In some embodiments, the molar ratio of the phosphorus source to the iron source is 0.95 to 1.2 (e.g., 0.95, 0.97, 1, 1.01, 1.05, 1.1, 1.15, 1.2, etc.); the molar ratio of the iron source to the sodium source is 0.7 to 1 (e.g., 0.7, 0.75, 0.8, 0.85, 0.9, or 1, etc.); and the carbon source accounts for 8% to 12% of the iron source by mass (e.g., 8%, 8.5%, 9%, 9.5%). The titanium source comprises 0.1% to 3% of the total mass of the phosphorus, iron, sodium, carbon, titanium, and cobalt sources (e.g., 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%), and the cobalt source comprises 0.02% to 3% of the total mass of the phosphorus, iron, sodium, carbon, titanium, and cobalt sources (e.g., 0.02%, 0.1%, 0.5%, 1%, 1.5%, 2%, or 3%). Appropriate proportions of each material are used to coordinate their effects and optimize the performance of the sodium iron pyrophosphate cathode material.

[0058] In some embodiments, the solvent includes water and / or alcohol solvents, such as ethanol. By using water and / or alcohol solvents as the dispersion medium, this invention ensures effective dispersion and mixing of materials, thereby improving the efficiency of wet classification and grinding.

[0059] In some embodiments, the solid content of the mixture is 30% to 48% (i.e., the total mass percentage of the phosphorus source, iron source, sodium source, carbon source, titanium source, cobalt source, and solvent to the mass of the mixture), for example, 30%, 35%, 40%, 45%, 48%, etc. The present invention uses a suitable solid content in the mixture to ensure appropriate fluidity, which is beneficial for the efficiency and effect of graded grinding. If the solid content is too low, the grinding efficiency is too low and the energy consumption is too high; if the solid content is too high, the fluidity of the slurry is poor, which is not conducive to the grinding of the grinding media.

[0060] In some embodiments, the preparation of the mixture specifically includes: premixing the phosphorus source, iron source, sodium source, carbon source, titanium source, cobalt source, and solvent for a time of 30-120 minutes, such as 30 minutes, 40 minutes, 50 minutes, 70 minutes, 100 minutes, 110 minutes, or 120 minutes. Appropriate premixing lays a good foundation for the subsequent graded grinding process.

[0061] In some embodiments, the graded grinding process specifically includes: subjecting the mixture to coarse grinding to obtain a first slurry; taking a portion of the first slurry as the coarse-ground slurry; subjecting the remaining first slurry to medium grinding to obtain a second slurry; taking a portion of the second slurry as the medium-ground slurry; and subjecting the remaining second slurry to fine grinding to obtain a fine-ground slurry. In the graded grinding method of the present invention, the coarse-ground slurry obtained from the coarse grinding process contains large particles, which can provide the main framework of the precursor material; the medium particles obtained from the medium grinding process can fill some of the large particles; and the fine-ground slurry obtained from the fine grinding process can better fill the voids formed by the large and medium particles.

[0062] In some embodiments, the coarse grinding process includes coarse grinding media with a diameter of 1.2~2.0 mm, such as 1.2 mm, 1.4 mm, 1.5 mm, 1.8 mm, or 2 mm; the medium grinding process uses medium grinding media with a diameter of 0.4~1.0 mm, such as 0.4 mm, 0.5 mm, 0.6 mm, 0.8 mm, or 1 mm; and the fine grinding process uses fine grinding media with a diameter of 0.2~0.4 mm, such as 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, or 0.4 mm. This invention uses grinding media of different particle sizes for coarse grinding, medium grinding, and fine grinding processes, enabling targeted crushing and thus ensuring the performance of the slurry obtained from each stage of grinding.

[0063] In some embodiments, the filling rates of the coarse grinding media, the medium grinding media, and the fine grinding media are each independently 80%~90%, for example, 80%, 83%, 85%, 90%, etc. In some embodiments, the graded grinding process uses agate balls and / or zirconium balls as the grinding media for each stage. This invention uses an appropriate filling rate of fine grinding media to ensure grinding efficiency and grinding effect. If the filling rate of fine grinding media is too low, the contact between the fine grinding media and the material is insufficient, resulting in low grinding efficiency. If the filling rate of fine grinding media is too high, it will increase energy consumption, which is also detrimental to the grinding effect.

[0064] In some embodiments, the coarse grinding process takes 1 to 2.5 hours, such as 1 hour, 1.5 hours, 2 hours, or 2.5 hours, and the grinding speed is 2000 to 3000 rpm, such as 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm, or 3000 rpm; the medium grinding process takes 2.5 to 3.5 hours, such as 2.5 hours, 3 hours, or 3.5 hours, and the grinding speed is 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm, or 3000 rpm; the fine grinding process takes 3 to 4.5 hours, such as 3 hours, 3.5 hours, 4 hours, or 4.5 hours, and the grinding speed is 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm, or 3000 rpm. The present invention employs appropriate processing times and speeds for each grinding stage to ensure the grinding effect on the material.

[0065] The graded grinding process of this invention uses grinding media of appropriate diameter, filling rate, processing speed and processing time. The various parameters are coordinated to ensure the grinding effect of each stage of coarse grinding, medium grinding and fine grinding, so as to obtain coarse grinding slurry, medium grinding slurry and fine grinding slurry with appropriate particle size.

[0066] In some embodiments, the mixing speed is 300-800 rpm, such as 300 rpm, 400 rpm, 500 rpm, 600 rpm, 800 rpm, etc. The mixing time is 30-120 min, such as 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 100 min, 120 min, etc. This invention employs suitable mixing conditions to ensure the mixing effect of each slurry.

[0067] In some embodiments, the coarse, medium, and fine grinding slurries obtained from the graded grinding process are respectively fed into a batch mixing tank for mixing.

[0068] In some embodiments, the volume of the coarse grinding slurry is 'a', the volume of the medium grinding slurry is 'b', and the volume of the fine grinding slurry is 'c', with 0.1 ≤ a / (a+b+c) ≤ 0.3, 0.2 ≤ b / (a+b+c) ≤ 0.5, and 0.3 ≤ c / (a+b+c) ≤ 0.9. 0.1 ≤ a / (a+b+c) ≤ 0.3 means that the ratio of the volume of the coarse grinding slurry to the total volume of the coarse, medium, and fine grinding slurries is 0.1 to 0.3, for example, 0.1, 0.15, 0.2, 0.25, or 0.3. 0.2≤b / (a+b+c)≤0.5 means that the volume ratio of the medium-ground slurry to the total volume of the coarse, medium, and fine-ground slurries in this invention is 0.2~0.5, for example, 0.2, 0.25, 0.3, 0.4, or 0.5. 0.3≤c / (a+b+c)≤0.7 means that the volume ratio of the medium-ground slurry to the total volume of the coarse, medium, and fine-ground slurries in this invention is 0.3~0.7, for example, 0.3, 0.4, 0.5, 0.6, or 0.7. The coarse, medium, and fine-ground slurries of this invention have suitable volume ratios, which can form a good gradation effect, thereby optimizing compaction density and processing performance.

[0069] In some embodiments, the heat treatment includes drying and gradient sintering. The present invention uses drying to initially remove moisture and form precursor particles, followed by gradient sintering to form a high-capacity, high-conductivity, and high-stability cathode material.

[0070] In some embodiments, the drying temperature is 100~300℃, for example, 100℃, 150℃, 200℃, 300℃, etc.; preferably, the drying process includes spray drying, wherein the inlet air temperature of the spray drying is 160~300℃, for example, 160℃, 200℃, 250℃, 280℃, 300℃, etc., the outlet air temperature is 100~150℃, for example, 100℃, 110℃, 120℃, 130℃, 150℃, etc., and the atomizer rotation speed is 20000~22000rpm, for example, 20000rpm, 21000rpm, 22000rpm, etc. This invention employs a suitable spray drying process to obtain precursor particles with good flowability and high sphericity.

[0071] In some embodiments, the temperature of the gradient sintering treatment is 400~800℃, such as 400℃, 500℃, 600℃, 700℃, 800℃, etc. The total holding time of the gradient sintering treatment is 8~18h, such as 8h, 10h, 12h, 15h, 18h, etc. In some embodiments, the gradient sintering process includes a first sintering and a second sintering performed sequentially. The temperature of the first sintering is 400-500℃, e.g., 400℃, 450℃, 500℃, etc.; the holding time of the first sintering is 1-6 hours, e.g., 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, etc.; the temperature of the second sintering is 580-800℃, e.g., 580℃, 600℃, 650℃, 700℃, 800℃, etc.; the holding time of the second sintering is 3-12 hours, e.g., 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 10 hours, 12 hours, etc. In some embodiments, the heating rate is 1-5℃ / min. In some embodiments, the atmosphere of the gradient sintering process is a protective atmosphere, such as nitrogen or argon. The first sintering of the present invention employs a suitable low-temperature pretreatment to pre-carbonize the carbon source, form and grow the matrix crystal nuclei; the second sintering employs a suitable treatment to promote crystal growth, form a uniform carbon coating layer, and obtain a cathode material with good electrochemical performance.

[0072] In some embodiments, the process further includes crushing, sieving, and demagnetizing the heat-treated material to obtain a high-purity cathode material with a suitable particle size.

[0073] In a preferred embodiment, a method for preparing a sodium iron pyrophosphate cathode material is illustrated in the schematic diagram below. Figure 1 As shown, it includes the following steps: (a) Phosphorus source, iron source, sodium source, carbon source, titanium source, cobalt source and solvent are premixed to obtain a mixture with a solid content of 30% to 48%.

[0074] (b) After the mixture from step (a) is mixed evenly in a premixing tank, it is subjected to graded grinding. This includes three stages of grinding: coarse grinding, medium grinding, and fine grinding. For coarse grinding, 1.2~2.0mm coarse grinding media is used, with a filling rate of 80%~90%, a grinding time of 1~2.5h, and a grinding speed of 2000~3000rpm. The first slurry after coarse grinding is divided into two parts. One part (coarse grinding slurry) is directly fed into the batch mixing tank at 10%~30% of the total slurry volume, and the remaining slurry is subjected to medium grinding. The intermediate grinding uses 0.4~1.0mm grinding media with a filling rate of 80%~90%, a grinding time of 2.5~3.5h, and a grinding speed of 2000~3000rpm. The second slurry after intermediate grinding is divided into two parts. One part (intermediate grinding slurry) is fed into the batch mixing tank at a volume of 20%~50% of the original slurry. The remaining slurry is then finely ground using 0.2~0.4mm grinding media with a filling rate of 80%~90%, a grinding time of 3~4.5h, and a grinding speed of 2000~3000rpm. The finely ground slurry is then fed into the batch mixing tank, where the dispersing disc rotates at 300~800rpm.

[0075] (c) After the sand milling process is completed, spray drying is carried out. The inlet air temperature is 160~300℃, the feed rate is adjusted to control the outlet air temperature at 100~150℃, and the centrifugal atomizer speed is 20000~22000rpm.

[0076] (d) After completing the spray drying process, a gradient sintering treatment is carried out. The sintering atmosphere is nitrogen, the heating temperature is 1~5℃ / min, the holding time is 400~500℃ for 1~6h, and then the temperature is raised to 580~800℃ and held for 3~12h.

[0077] (e) After sintering, the sodium iron phosphate cathode material is obtained by airflow crushing, sieving and demagnetizing.

[0078] (f) Packaging the sodium iron phosphate cathode material.

[0079] According to another aspect of the present invention, the present invention also relates to a battery comprising the aforementioned sodium iron pyrophosphate cathode material, or the sodium iron pyrophosphate cathode material prepared by the aforementioned method for preparing the sodium iron pyrophosphate cathode material.

[0080] The battery of this invention features high capacity, high initial efficiency, and high rate performance, and has good safety performance.

[0081] According to another aspect of the invention, the invention also relates to an electrical device including the aforementioned battery. The electrical devices of the invention include electric vehicles, power tools, computers, etc.

[0082] The following explanation, in conjunction with specific embodiments and comparative examples, further clarifies the situation.

[0083] Example 1 A method for preparing sodium iron pyrophosphate cathode material includes the following steps: (1) Weigh 3.967 kg of disodium dihydrogen pyrophosphate, 1.483 kg of sodium bicarbonate, 4.044 kg of ferric phosphate, 0.57 kg of glucose, 38.4 g of chelating agent citric acid, 2.631 g of additive cobalt oxalate, 6.01 g of titanium oxalate, 3.45 g of dispersant polyvinylpyrrolidone, and 16.0 kg of deionized water. The solid content is 39%.

[0084] (2) After the materials from step (1) are mixed evenly in the premix tank, they are sand milled. The sand milling is divided into three stages: coarse grinding, medium grinding and fine grinding. For coarse grinding, 1.4mm zirconium balls are used with a filling rate of 80% and a grinding time of 2 hours. The sand milling speed is 2400 rpm. The first slurry after coarse grinding is divided into two parts. One part (15% of the total slurry volume, coarse grinding slurry) is directly fed into the batch mixing tank, and the remaining 85% of the slurry is subjected to medium grinding. The intermediate mill uses 0.6mm zirconium balls with a filling rate of 82%, and the grinding time is 3 hours at a mill speed of 2400 rpm. The second slurry after intermediate milling is divided into two parts. 25% of the original slurry volume (intermediate mill slurry) is fed into the batch mixing tank. The remaining slurry is then finely milled using 0.3mm zirconium balls with a filling rate of 85%, and the grinding time is 3.5 hours at a mill speed of 2500 rpm. The finely milled slurry is then fed into the batch mixing tank for mixing. The dispersion disc speed is 600 rpm to obtain the first system.

[0085] (3) Spray dry the first system described above, with an inlet air temperature of 180°C, adjust the feed rate to control the outlet air temperature at 108°C, and set the centrifugal atomizer speed at 21000 rpm.

[0086] (4) After completing the spray drying process, the gradient sintering process is carried out. The sintering atmosphere is nitrogen, the heating temperature is 3℃ / min, the holding time is 430℃ for 4 hours, and then the temperature is raised to 640℃ for 9 hours.

[0087] (5) After sintering, the material is obtained by air-flow crushing, sieving and demagnetizing to obtain sodium iron phosphate cathode material. The chemical formula of sodium iron pyrophosphate is Na4Fe3(PO4)2P2O7, in which the doping amount of titanium is 2000ppm and the doping amount of cobalt is 3000ppm.

[0088] Example 2 A method for preparing sodium iron pyrophosphate cathode material includes the following steps: (1) Weigh 3.967 kg of disodium dihydrogen pyrophosphate, 1.483 kg of sodium bicarbonate, 4.044 kg of ferric phosphate, 0.57 kg of glucose, 38.4 g of chelating agent citric acid, 3.946 g of additive cobalt oxalate, 6.513 g of additive titanium oxalate, 3.45 g of dispersant polyvinylpyrrolidone, and 16.0 kg of deionized water. The solid content is 39%.

[0089] (2) After the materials from step (1) are mixed evenly in the premix tank, they are then sand-milled. The sand milling is divided into three stages: coarse grinding, medium grinding, and fine grinding. For coarse grinding, 1.4 mm zirconium balls are used with a filling rate of 80%, the grinding time is 2 hours, and the sand milling speed is 2400 rpm. The first slurry after coarse grinding is divided into two parts. One part (15% of the total slurry volume, coarse grinding slurry) is directly fed into the batch mixing tank, and the remaining 85% of the slurry is subjected to medium grinding. For medium grinding, 0.6 mm zirconium balls are used with a filling rate of 82%, the grinding time is 3 hours, and the sand milling speed is 2400 rpm. The second slurry after medium grinding is divided into two parts. One part (25% of the original total slurry volume, medium grinding slurry) is fed into the batch mixing tank, and the remaining slurry is subjected to fine grinding. For fine grinding, 0.3mm zirconium balls with a filling rate of 85% were used. The grinding time was 3.5 hours and the grinding speed was 2500 rpm. After fine grinding, the fine slurry was fed into a batch mixing tank for mixing. The dispersion disc rotated at 600 rpm to obtain the first system.

[0090] (3) Spray dry the first system described above, with an inlet air temperature of 180°C, adjust the feed rate to control the outlet air temperature at 108°C, and set the centrifugal atomizer speed at 21000 rpm.

[0091] (4) After completing the spray drying process, the gradient sintering process is carried out. The sintering atmosphere is nitrogen, the heating rate is 3℃ / min, the holding time is 430℃ for 4h, and then the temperature is raised to 640℃ for 9h.

[0092] (5) After sintering, the material is obtained by air-flow crushing, sieving and demagnetizing to obtain sodium iron phosphate cathode material. The chemical formula of sodium iron pyrophosphate is Na4Fe3(PO4)2P2O7, in which the doping amount of titanium is 4000ppm and the doping amount of cobalt is 3000ppm.

[0093] The scanning electron microscope image of the sodium iron pyrophosphate cathode material in this embodiment is shown below. Figure 2 As shown.

[0094] Example 3 A method for preparing sodium iron pyrophosphate cathode material includes the following steps: (1) Weigh 3.967 kg of disodium dihydrogen pyrophosphate, 1.483 kg of sodium bicarbonate, 4.044 kg of ferric phosphate, 0.57 kg of glucose, 38.4 g of chelating agent citric acid, 5.262 g of additive cobalt oxalate, 8.142 g of additive titanium oxalate, 3.45 g of dispersant polyvinylpyrrolidone, and 16.0 kg of deionized water. The solid content is 39%.

[0095] (2) After the materials from step (1) are mixed evenly in the premix tank, they are subjected to graded grinding, including three stages of grinding: coarse grinding, medium grinding, and fine grinding. For coarse grinding, 1.4 mm zirconium balls are used with a filling rate of 80%, the grinding time is 2 hours, and the grinding speed is 2400 rpm. The first slurry after coarse grinding is divided into two parts. One part (15% of the total slurry volume, coarse grinding slurry) is directly fed into the batch mixing tank, and the remaining 85% of the slurry is ground in the medium grinding tank. For the medium grinding tank, 0.6 mm zirconium balls are used with a filling rate of 82%, the grinding time is 3 hours, and the grinding speed is 2400 rpm. The second slurry after medium grinding is divided into two parts. One part (25% of the original total slurry volume, medium grinding slurry) is fed into the batch mixing tank, and the remaining slurry is ground in the fine grinding tank. For fine grinding, 0.3mm zirconium balls with a filling rate of 85% were used. The grinding time was 3.5 hours and the grinding speed was 2500 rpm. After fine grinding, the fine slurry was fed into a batch mixing tank for mixing. The dispersion disc rotated at 600 rpm to obtain the first system.

[0096] (3) Spray dry the first system described above, with an inlet air temperature of 180°C, adjust the feed rate to control the outlet air temperature at 108°C, and set the centrifugal atomizer speed at 21000 rpm.

[0097] (4) After completing the spray drying process, gradient sintering is carried out. The sintering atmosphere is nitrogen, the heating rate is 3℃ / min, the holding time is 430℃ for 4h, and then the temperature is raised to 640℃ for 9h.

[0098] (5) After sintering, the material is obtained by air-flow crushing, sieving and demagnetizing to obtain sodium iron phosphate cathode material. The chemical formula of sodium iron pyrophosphate is Na4Fe3(PO4)2P2O7, in which the doping amount of titanium is 5000ppm and the doping amount of cobalt is 4000ppm.

[0099] Example 4 A method for preparing a sodium iron pyrophosphate cathode material differs from Example 2 in that: In step (2), 1.2mm zirconium balls were used for coarse grinding, with a filling rate of 90%, a grinding time of 1 hour, and a grinding speed of 3000 rpm. The first slurry after coarse grinding was divided into two parts. One part (coarse grinding slurry) was directly fed into the batch mixing tank at 10% of the total slurry volume, and the remaining 90% of the slurry was subjected to intermediate grinding. 0.4mm zirconium balls were used for intermediate grinding, with a filling rate of 90%, a grinding time of 2.5 hours, and a grinding speed of 3000 rpm. The second slurry after intermediate grinding was divided into two parts. One part (intermediate grinding slurry) was fed into the batch mixing tank at 50% of the original total slurry volume, and the remaining slurry was subjected to fine grinding. 0.2mm zirconium balls were used for fine grinding, with a filling rate of 80%, a grinding time of 3 hours, and a grinding speed of 3000 rpm.

[0100] Example 5 A method for preparing a sodium iron pyrophosphate cathode material differs from Example 2 in that: In step (2), 2mm zirconium balls are used for coarse grinding, with a filling rate of 80%, a grinding time of 2.5 hours, and a grinding speed of 2000 rpm. The first slurry after coarse grinding is divided into two parts. One part (30% of the total slurry volume, coarse grinding slurry) is directly fed into the batch mixing tank, and the remaining 70% of the slurry is ground for intermediate grinding. 1mm zirconium balls are used for intermediate grinding, with a filling rate of 80%, a grinding time of 3.5 hours, and a grinding speed of 2000 rpm. The second slurry after intermediate grinding is divided into two parts. One part (20% of the original total slurry volume, intermediate grinding slurry) is fed into the batch mixing tank, and the remaining slurry is ground for fine grinding. 0.4mm zirconium balls are used for fine grinding, with a filling rate of 90%, a grinding time of 4.5 hours, and a grinding speed of 2000 rpm.

[0101] Example 6 A method for preparing a sodium iron pyrophosphate cathode material differs from Example 2 in that: In step (4), the temperature is kept at 500℃ for 2 hours, and then raised to 800℃ and kept for 3 hours.

[0102] Comparative Example 1 The method for preparing a positive electrode material differs from that in Example 2 in that: The materials in step (1) do not contain titanium oxalate or cobalt oxalate.

[0103] Comparative Example 2 The method for preparing a positive electrode material differs from that in Example 2 in that: The material in step (1) does not contain titanium oxalate.

[0104] Comparative Example 3 The method for preparing a positive electrode material differs from that in Example 2 in that: The material in step (1) does not contain cobalt oxalate.

[0105] Comparative Example 4 A method for preparing a cathode material differs from that in Example 1 in that: In step (2), the material from step (1) is directly ground using 0.6mm zirconium balls with a filling rate of 92%, a grinding time of 5 hours, and a grinding speed of 2400 rpm to obtain the first system.

[0106] Experimental Example Coin cells were prepared by using sodium iron phosphate cathode materials from each embodiment and cathode materials from the comparative example, including: preparing cathode sheets using sodium iron phosphate cathode materials, conductive agent SP, and binder PVDF, with a mass ratio of sodium iron phosphate cathode material, conductive agent, and binder of 90:5:5; using sodium metal sheet as the anode, and coin cell test voltage of 1.5~3.8V.

[0107] The test results are shown in Table 1. The charge-discharge curves of the battery prepared using the sodium iron pyrophosphate cathode material in Example 2 under 0.1C and 1.5~3.8V conditions are shown in the figure. Figure 3 As shown.

[0108] Table 1 Test Results

[0109] As shown in Table 1, the sodium iron phosphate cathode material preparation methods of the various embodiments of the present invention, through the combination of raw materials and the coordinated operation of each step, result in sodium iron phosphate cathode materials with suitable compaction density, around 2.30 g / cm³. 3 The batteries prepared from the sodium iron phosphate cathode materials in the various embodiments of the present invention have high capacity, high initial efficiency and high rate performance. The discharge capacity of the batteries under 0.1C and 1.5~3.8V conditions is ≥110mAh / g, the first-cycle efficiency is ≥90%, and the discharge capacity under 3C and 1.5~3.8V conditions is ≥89mAh / g.

[0110] The cathode material preparation method of Comparative Example 1 does not add cobalt and titanium sources. The battery prepared with the cathode material has reduced discharge capacity under 0.1C, 1C, 2C and 3C conditions, and the first-cycle efficiency is reduced.

[0111] Comparative Example 2 did not add a titanium source, and Comparative Example 3 did not add a cobalt source. Through coin cell test data analysis, the rate performance and initial specific capacity of the materials were reduced to a certain extent compared with the examples. It can be seen that the doping of cobalt or titanium alone is not as good as the co-doping of cobalt and titanium for stabilizing the crystal structure of the material and broadening the sodium ion migration channels.

[0112] The method of Comparative Example 4 did not perform the graded grinding of the present invention. The resulting battery prepared from the cathode material had reduced discharge capacity and first-cycle efficiency under 0.1C, 1C, 2C and 3C conditions.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sodium iron pyrophosphate cathode material, characterized in that, Including the positive electrode substrate and doping elements; The general chemical formula of the positive electrode substrate is Na. x Fe y (PO4)2P2O7, where 0.2≤y / x≤1; The doping elements are Ti and Co, the doping amount of Co is m, 1000ppm≤m≤30000ppm, and the doping amount of Ti is n, 200ppm≤n≤30000ppm.

2. The sodium iron pyrophosphate cathode material according to claim 1, characterized in that, The sum of m and n satisfies: 2000ppm≤m+n≤50000ppm.

3. The sodium iron pyrophosphate cathode material according to claim 1, characterized in that, The surface of the positive electrode substrate is also provided with a carbon coating layer.

4. The sodium iron pyrophosphate cathode material according to claim 1, characterized in that, It includes at least one of the following features (1) to (2): (1) The compaction density of the sodium iron pyrophosphate cathode material is 2.31~2.4 g / cm³. 3 ; (2) The battery prepared by the sodium iron pyrophosphate cathode material has a discharge capacity ≥110mAh / g and a first-cycle efficiency ≥90% under 0.1C and 1.5~3.8V conditions, and a discharge capacity ≥89mAh / g under 3C and 1.5~3.8V conditions.

5. A method for preparing a sodium iron pyrophosphate cathode material, characterized in that, Includes the following steps: A mixture of phosphorus source, iron source, sodium source, carbon source, titanium source, cobalt source and solvent is subjected to graded grinding treatment, which includes coarse grinding treatment, medium grinding treatment and fine grinding treatment to obtain coarse grinding slurry, medium grinding slurry and fine grinding slurry respectively; The coarse grinding slurry, medium grinding slurry and fine grinding slurry are mixed to obtain the first system; The first system is subjected to heat treatment.

6. The method for preparing sodium iron pyrophosphate cathode material according to claim 5, characterized in that, It includes at least one of the following features (1) to (6): (1) The graded grinding process specifically includes: performing the coarse grinding process on the mixture to obtain a first slurry, taking a portion of the first slurry as the coarse grinding slurry, and performing the medium grinding process on the remaining first slurry to obtain a second slurry, taking a portion of the second slurry as the medium grinding slurry, and performing the fine grinding process on the remaining second slurry to obtain a fine grinding slurry; (2) The coarse grinding process includes a coarse grinding medium with a diameter of 1.2~2.0 mm; the medium grinding process uses a medium grinding medium with a diameter of 0.4~1.0 mm; the fine grinding process uses a fine grinding medium with a diameter of 0.2~0.4 mm. (3) The coarse grinding process includes coarse grinding media, the medium grinding process uses medium grinding media, and the fine grinding process uses fine grinding media. The filling rates of the coarse grinding media, the medium grinding media, and the fine grinding media are each independently 80%~90%. (4) The coarse grinding process takes 1 to 2.5 hours and the coarse grinding speed is 2000 to 3000 rpm; the medium grinding process takes 2.5 to 3.5 hours and the medium grinding speed is 2000 to 3000 rpm; the fine grinding process takes 3 to 4.5 hours and the fine grinding speed is 2000 to 3000 rpm. (5) The volume of the coarse grinding slurry is a, the volume of the medium grinding slurry is b, and the volume of the fine grinding slurry is c, 0.1≤a / (a+b+c)≤0.3, 0.2≤b / (a+b+c)≤0.5, 0.3≤c / (a+b+c)≤0.7; (6) The mixing speed is 300~800 rpm and the mixing time is 30~120 min.

7. The method for preparing sodium iron pyrophosphate cathode material according to claim 5, characterized in that, It includes at least one of the following features (1) to (10): (1) The cobalt source includes at least one of cobalt oxalate, cobalt oxide, cobalt nitrate, cobalt carbonate, cobalt sulfate, cobalt chloride, cobalt bromide, cobalt phosphate, and cobalt hydroxide; (2) The titanium source includes at least one of titanium oxalate, titanium oxide, titanium sulfate, and titanium chloride; (3) The iron source includes at least one of iron phosphate and iron oxide; (4) The sodium source includes at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide and disodium dihydrogen pyrophosphate; (5) The phosphorus source includes at least one of phosphate, pyrophosphate, phosphoric acid and ammonium dihydrogen phosphate; (6) The carbon source includes at least one of polypyrrole, sucrose, polyethylene glycol, glucose, polyethylene and polyvinylpyrrolidone; (7) The molar ratio of the phosphorus source to the iron source is 0.95 to 1.2; the molar ratio of the iron source to the sodium source is 0.7 to 1; the carbon source accounts for 8% to 12% of the mass of the iron source; the titanium source accounts for 0.1% to 3% of the total mass of the phosphorus source, iron source, sodium source, carbon source, titanium source and cobalt source; and the cobalt source accounts for 0.02% to 3% of the total mass of the phosphorus source, iron source, sodium source, carbon source, titanium source and cobalt source. (8) The solvent includes water and / or alcohol solvents; (9) The solid content of the mixture is 30%~48%; (10) The preparation of the mixture specifically includes: premixing the phosphorus source, iron source, sodium source, carbon source, titanium source, cobalt source and solvent, wherein the premixing time is 30~120min.

8. The method for preparing sodium iron pyrophosphate cathode material according to claim 5, characterized in that, It includes at least one of the following features (1) to (2): (1) The heat treatment includes drying treatment and gradient sintering treatment; Preferably, the drying temperature is 100~300℃; preferably, the drying process includes spray drying, wherein the inlet air temperature of the spray drying is 160~300℃, the outlet air temperature is 100~150℃, and the rotation speed of the atomizer is 20000~22000rpm; Preferably, the gradient sintering temperature is 400~800℃, and the total holding time of the gradient sintering is 8~18h; preferably, the gradient sintering includes a first sintering and a second sintering performed sequentially, the temperature of the first sintering is 400~500℃, the holding time of the first sintering is 1~6h, the temperature of the second sintering is 580~800℃, and the holding time of the second sintering is 3~12h; preferably, the atmosphere of the gradient sintering is a protective atmosphere. (2) It also includes: crushing, screening and demagnetizing the material after heat treatment.

9. A battery, characterized in that, The sodium iron pyrophosphate cathode material includes any one of claims 1 to 4, or the sodium iron pyrophosphate cathode material prepared by any one of claims 5 to 8.

10. An electrical appliance, characterized in that, Includes the battery as described in claim 9.

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