Titanium-doped high-density spherical nanometer pyrophosphate ferric sodium sodium-ion battery cathode material and preparation method thereof

Abstract

The application relates to the technical field of sodium ion battery positive electrode materials, in particular to a titanium-doped high-density spherical nanometer pyrophosphoric acid ferric sodium sodium ion battery positive electrode material and a preparation method thereof. 3‑x Ti x (PO4)2P2O7, wherein 0.05<=x<=0.2, and the particle size of the positive electrode material is 20-300 nm, and the surface is coated with a layer of carbon. Through multi-dimensional innovation of materials-process-structure, the application provides a high-performance positive electrode solution for commercialization of sodium ion batteries, and has advanced technology and engineering potential.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion battery positive electrode materials, and particularly relates to a titanium-doped high-density spherical nanometer sodium iron pyrophosphate positive electrode material for sodium ion batteries and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries are limited in large-scale application due to uneven distribution of lithium resources and high cost. Sodium ion batteries become a substitute technology due to abundant sodium resources and low cost. Sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7, NFPP for short) has advantages of high theoretical capacity, high working voltage (3.1 V) and low volume expansion (<4 %), but has problems of low intrinsic conductivity and poor cycle performance. Existing technologies modify NFPP by carbon coating or introducing crystal defects, but the effect is limited, and it is difficult to balance capacity, rate and cycle stability. Therefore, a new modification method is needed to improve the comprehensive performance of NFPP. SUMMARY

[0003] In order to solve the problems of easy generation of impurities and poor rate performance of intrinsic NFPP during the synthesis of NFPP, the application provides a titanium-doped high-density spherical nanometer sodium iron pyrophosphate positive electrode material for sodium ion batteries and a preparation method thereof. Titanium metal is doped in NFPP through a series of processes of "wet mixing-coarse grinding-pre-sintering-ultrafine grinding-spray drying-sintering". The titanium doping reduces the proportion of iron in NFPP, inhibits the generation of impurities, optimizes the crystal structure through titanium doping, and improves the electron / ion transmission efficiency. The prepared titanium-doped high-density spherical nanometer sodium iron pyrophosphate positive electrode material for sodium ion batteries has high conductivity, high cycle stability and excellent rate performance. The discharge specific capacity is greater than or equal to 107 mAh / g at 1C rate, and the capacity retention rate is greater than or equal to 90 % after 500 cycles.

[0004] In the first aspect, the application provides a titanium-doped high-density spherical nanometer sodium iron pyrophosphate positive electrode material for sodium ion batteries, which adopts the following technical scheme:

[0005] The chemical general formula of the titanium-doped high-density spherical nanometer sodium iron pyrophosphate positive electrode material for sodium ion batteries is Na4Fe3-xTix(PO4)2P2O7, wherein 0.05≤x≤0.2, and the particle size of the positive electrode material is 20-300 nm, and the surface is coated with a layer of carbon.

[0006] By adopting the above technical scheme, Ti 4+ partially replaces Fe 2+ (0.05≤x≤0.2), the concentration of Fe 2+ is reduced; and Fe 2+ is inhibited from being oxidized to Fe 3+The generation of heterogeneous phases (such as FePO4) ensures the purity of the material crystallinity while stabilizing the lattice structure. The doping of Ti adjusts the connection mode of FeO6 octahedron and PO4 tetrahedron, widens the sodium ion diffusion channel, and reduces the Na + diffusion energy barrier. By two-step wet grinding (final particle size 20-300 nm), nanoscale particles are formed, and Na + The solid-phase diffusion path is shortened to the nanoscale, significantly improving the rate performance (1C discharge capacity ≥ 107mAh / g). The Ti-O bond is stronger than the Fe-O bond, which alleviates the lattice volume change caused by Na + insertion / extraction during charging and discharging, and reduces particle breakage (capacity retention rate ≥ 90% after 500 cycles). In summary, the positive electrode material is optimized by chemical doping and nanoscale structure, solving the key bottleneck of traditional NFPP materials, and providing a feasible technical path for high-power, long-life sodium ion batteries.

[0007] Preferably, the specific surface area of the positive electrode material is 14-20m 2 / g, and the tap density is ≥ 2.2g / cm 3 .

[0008] In a second aspect, the application provides a preparation method of a titanium-doped high-density spherical nanometer sodium iron pyrophosphate sodium ion battery positive electrode material, which adopts the following technical scheme:

[0009] As a general technical concept, the application also provides the preparation method of the above-mentioned titanium-doped high-density spherical nanometer sodium iron pyrophosphate sodium ion battery positive electrode material, which includes the following steps:

[0010] S31, a sodium source compound, an iron source compound, a phosphorus source compound, a titanium source compound, and a carbon source compound are put into a solvent and uniformly mixed to obtain a mixture A;

[0011] S32, the mixture A is wet ground by a sand mill to a particle size of 200-600 nm to obtain a mixture B;

[0012] S33, the mixture B is pre-fired at 300-450°C in an argon atmosphere for 4-6h to obtain a mixture C, preferably pre-fired at 350°C in an argon atmosphere for 5h;

[0013] S34, the mixture C is put into a sand mill and wet ground with 1-2 times the mass of the mixture C of solvent to a particle size of 20-300 nm to obtain a mixture D; preferably wet ground to a particle size of 150 nm;

[0014] S35, the mixture D is spray dried to form a precursor;

[0015] S36, sintering the precursor in 450-600℃ argon-hydrogen mixed gas for 8-12h to obtain a titanium-doped high-density spherical nanometer ferric sodium pyrophosphate sodium-ion battery cathode material, preferably sintering in 550℃ argon-hydrogen mixed gas for 10h.

[0016] By adopting the above technical scheme, S31 raw material mixing, through the solvent such as (water / ethanol) to realize sodium source (such as sodium bicarbonate), iron source (such as ferric nitrate), titanium source (such as titanium tetrachloride), phosphorus source (such as ammonium dihydrogen phosphate) and carbon source (such as glucose) molecular dispersion, the addition of ethanol reduces the surface tension, promotes the dispersion of nanoparticles; the carbon source (such as glucose) is pre-embedded to lay the foundation for the subsequent construction of the conductive network. S32 rough grinding treatment, the mixture is ground to 200-600nm by sand mill, high-energy mechanical force breaks the raw material agglomerates, increases the reaction contact area, makes Ti 4+ With Fe 2+ Atomic mixing is realized, S33 pre-burning treatment, eliminating organic residues and forming primary crystal nucleus. S34 ultrafine grinding, secondary sanding to 20-300nm (preferably 150nm), adopting the pre-burning grinding strategy to avoid surface defects caused by direct nanometer grinding, the specific surface area is increased to 14-20m 2 / g, shortening the Li+ diffusion path. S35 spray drying, such as inlet temperature 200-350℃, atomization pressure 0.4-0.6MPa, outlet temperature 60-120℃, spherical particles are formed by surface tension induction, the tap density is increased to 2.2-2.5g / cm 3 . S36 high-temperature sintering, Ti 4+ Substitutes Fe 2+ , Ar / H2(95:5) reducing atmosphere maintains Fe 2+ Valence state, carbon thermal reduction forms a 3D conductive network, in-situ carbon coating improves electronic conductivity. In summary, the process chain realizes the synergistic optimization of material intrinsic properties and macroscopic morphology through "particle size gradient control-stepwise crystallization-defect engineering" triple regulation, finally makes the material discharge specific capacity≥107mAh / g at 1C rate, capacity retention≥90% after 500 cycles.

[0017] Preferably, the titanium source compound is selected from one or more of titanium hydroxide, titanium sulfide, titanium halide, titanium tetrachloride, titanium dichloride, titanium dichloride oxide, titanium fluoride, titanium bromide, titanium iodide, titanium silicide, titanium oxide, titanium oxychloride and titanium carbide.

[0018] Preferably, the sodium source compound is selected from one or more of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium nitrate, sodium fluoride, sodium fluorophosphate, sodium trifluoroacetate, sodium oxalate, sodium acetate, sodium persulfate, sodium hydroxide, sodium formate, sodium citrate, sodium pyrophosphate, sodium dihydrogen pyrophosphate and sodium alginate.

[0019] Preferably, the iron source compound is selected from one or more of reduced iron powder, ferric oxide, iron oxide, ferrous oxide, ferric nitrate, ferric chloride, ferric sulfate, ferric phosphate, ferric oxalate, ferrous oxalate, ferric acetate and ferric citrate, and ferric fluoride.

[0020] Preferably, the phosphorus source compound is selected from one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium dihydrogen pyrophosphate, phosphoric acid, ammonium dihydrogen phosphate and ammonium phosphate; and the carbon source compound is selected from one or more of glucose, sucrose, citric acid, malic acid, polyaniline, polyethylene glycol, adipic acid, phenol formaldehyde resin, polypyrrole, ascorbic acid, chitosan and soluble starch.

[0021] Preferably, the solvent is selected from at least one of water and ethanol, and preferably consists of water and ethanol in a molar ratio of 1:1.

[0022] Preferably, the spray drying is performed using one of centrifugal spray and two-fluid spray, with an inlet temperature of 200-350°C, an outlet temperature of 60-120°C, and an atomization pressure of 0.4-0.6 MPa for the two-fluid spray.

[0023] By using the above technical solution, the centrifugal spray disperses the liquid mixture into fine droplets by the high-speed rotating centrifugal disc. Advantages: the droplet size distribution is narrow, which is beneficial to the formation of uniform spherical particles; it is suitable for high solid content slurry. Combined with the subsequent sintering process, the material density and structural consistency can be improved. The two-fluid spray utilizes compressed gas (such as air or inert gas) to mix with the liquid at the nozzle, achieving droplet atomization. By adjusting the gas-liquid ratio, the droplet size is optimized, and the final nanoparticle morphology is controlled in cooperation with the ultra-fine grinding step (S34). The inlet temperature (200-350°C) rapidly evaporates the solvent (water / ethanol), preventing the aggregation of precursor particles; high temperature promotes solvent removal, avoiding the influence of residual organic matter on subsequent sintering. It is connected with the pre-sintering step (S33) to avoid low temperature leading to solvent residue or high temperature causing pre-decomposition. The atomization pressure (0.4-0.6 MPa) controls the droplet size and distribution, which directly affects the particle size (20-300 nm target range) of the precursor particles. Combined with the nano-sized slurry after wet grinding (S34), it ensures that the particles after spray drying still maintain ultra-fine characteristics. The outlet temperature (60-120°C) balances the drying efficiency and the protection of heat-sensitive components, avoiding excessive temperature leading to oxidation or structural damage of the precursor. In cooperation with the argon-hydrogen mixed atmosphere sintering (S36), the reducing environment is maintained to prevent Fe 2+ oxidation to Fe 3+Spray mode + atomization pressure: Through the combination of centrifugal or two-fluid spray and medium-high pressure atomization, the uniformity of droplet size and composition is realized, and the sphericity and high density of precursor particles are ensured. Temperature gradient control: Gradient design of high temperature at the inlet (fast drying) → low temperature at the outlet (gentle termination of drying) to prevent particle cracking or agglomeration caused by thermal stress. The porous spherical precursor formed by spray drying (step S35) cooperates with subsequent sintering (step S36) to promote grain densification and optimize the electron / ion transmission path. Through the fine regulation of the above spray drying process, the positive electrode material is significantly optimized in terms of microstructure, composition uniformity and electrochemical performance, meeting the needs of high energy density and long cycle life of sodium-ion batteries.

[0024] Preferably, the volume ratio of argon and hydrogen in the argon-hydrogen mixed gas is 19:1.

[0025] In summary, the beneficial technical effects of the present application are:

[0026] I. Material performance optimization

[0027] 1. High electron / ion conductivity: Titanium element doping optimizes the lattice structure by replacing part of the Fe sites, expands the Li + / Na + diffusion channel, reduces the ion diffusion energy barrier, introduces the high electronegativity of Ti 4+ , enhances the intrinsic electronic conductivity of the material, and shortens the ion transmission path by combining with nano-sized particles (20-300nm), making the discharge specific capacity ≥107mAh / g at 1C rate.

[0028] 2. Significant improvement in cycle stability: Titanium doping suppresses lattice distortion during charging and discharging, reduces volume expansion (capacity retention rate ≥90% @500 cycles), and the two-stage heat treatment of pre-burning (300-450℃) and sintering (450-600℃) forms a stable crystal framework

[0029] 3. Breakthrough in rate performance: Ultrafine grinding (to 150nm) combined with spherical morphology optimizes the electrode-electrolyte interface contact, and the carbon source compound generates a conductive carbon network during sintering, strengthening the charge transfer dynamics.

[0030] II. Preparation process innovation

[0031] 1. Heterogeneous phase suppression mechanism: Wet grinding (200-600nm→20-300nm) realizes atomic-level uniform mixing, reduces local component segregation, and Ar / H2(19:1) reducing atmosphere sintering suppresses the generation of heterogeneous phases (such as FePO4) caused by Fe 2+ oxidation.

[0032] 2. Morphology and structure control: sand mill gradient grinding technology (coarse grinding + ultra-fine grinding) precisely regulates the particle size distribution to the nanometer level, and the spray drying process constructs high-density spherical particles to improve the tap density.

[0033] 3. Process synergy effect: the pre-burning stage (such as 350℃×5h) eliminates organic residues and forms primary crystal nuclei; the sintering stage (550℃×10h) promotes crystal grain directional growth and Ti-doped site ordering.

[0034] III. Techno-economic advantage

[0035] 1. Cost control: using water / ethanol mixed solvent (1:1) to reduce raw material cost and environmental pressure, titanium doping amount is low (0.05≤x≤0.2), avoiding excessive consumption of precious metal resources.

[0036] 2. Mass production feasibility: wet grinding + spray drying process is compatible with existing lithium battery material production line equipment, argon-hydrogen mixed gas ratio (19:1) balances safety and reduction effect, suitable for industrial production. DETAILED DESCRIPTION

[0037] The embodiments of the present application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. If the specific conditions are not specified in the examples, they are carried out under conventional conditions or according to the manufacturer's recommendations. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0038] Example 1

[0039] A preparation method of a titanium-doped high-density spherical nanometer sodium iron phosphate pyrophosphate sodium battery positive electrode material, comprising the following steps: S31, weighing 0.4 mol of sodium bicarbonate, 0.285 mol of ferric nitrate, 0.4 mol of ammonium dihydrogen phosphate, 0.005 mol of titanium fluoride, and 0.02 mol of glucose, and adding them into 500 mL of water / ethanol (molar ratio of ethanol to water is 1:1) solution, mixing uniformly to obtain a mixture A;

[0040] S32, grinding the mixture A to a particle size of 600 nm at a speed of 2000 r / min by using a sand mill to obtain a mixture B;

[0041] S33, pre-burning the mixture B in an argon atmosphere at 300℃ for 6h to obtain a mixture C;

[0042] S34, putting the mixture C into a sand mill and adding a solvent (molar ratio of ethanol to water is 1:1) with 1 times the mass of the mixture C for wet grinding to a particle size of 20 nm to obtain a mixture D;

[0043] S35, spray drying the mixture D to form a precursor, the spray drying using centrifugal spraying, the inlet temperature being 200 DEG C, the outlet temperature being 60 DEG C, the atomization pressure of the spray being 0.6 MPa;

[0044] S36, placing the precursor into an atmosphere tube furnace, sintering in argon-hydrogen mixed gas (the volume ratio of argon to hydrogen being 19:1) at 450 DEG C for 12 h to obtain a titanium-doped high-density spherical nanometer pyrophosphate ferric sodium sodium-ion battery cathode material, marked as Na4Fe 2.95 Ti 0.05 (PO4)2P2O7.

[0045] Example 2

[0046] A preparation method of a titanium-doped high-density spherical nanometer pyrophosphate ferric sodium sodium-ion battery cathode material, comprising the following steps: S31, taking 0.4 mol of sodium bicarbonate, 0.285 mol of ferric nitrate, 0.4 mol of ammonium dihydrogen phosphate, 0.015 mol of titanium oxide and 0.02 mol of glucose according to the proportion, and adding them into 500 mL of water / ethanol (the molar ratio of ethanol to water being 1:1) solution, mixing uniformly to obtain a mixture A;

[0047] S32, grinding the mixture A to a particle size of 200 nm by using a sand mill at a speed of 2000 r / min to obtain a mixture B;

[0048] S33, pre-sintering the mixture B in an argon atmosphere at 450 DEG C for 4 h to obtain a mixture C;

[0049] S34, placing the mixture C into a sand mill and adding a solvent (the molar ratio of ethanol to water being 1:1) with a mass of 2 times that of the mixture C to carry out wet grinding to a particle size of 300 nm to obtain a mixture D;

[0050] S35, spray drying the mixture D to form a precursor, the spray drying using two-fluid spraying (the gas introduced being argon and hydrogen, the volume ratio of argon to hydrogen being 19:1), the inlet temperature being 350 DEG C, the outlet temperature being 120 DEG C, the atomization pressure of the two-fluid spray being 0.4 MPa;

[0051] S36, placing the precursor into an atmosphere tube furnace, sintering in argon-hydrogen mixed gas (the volume ratio of argon to hydrogen being 19:1) at 600 DEG C for 8 h to obtain a titanium-doped high-density spherical nanometer pyrophosphate ferric sodium sodium-ion battery cathode material, marked as Na4Fe 2.85 Ti 0.15 (PO4)2P2O7.

[0052] Example 3

[0053] A preparation method of a titanium-doped high-density spherical nanometer pyrophosphate ferric sodium sodium-ion battery positive electrode material, comprising the following steps: S31, weighing 0.4 mol of sodium bicarbonate, 0.285 mol of ferric nitrate, 0.4 mol of ammonium dihydrogen phosphate, 0.020 mol of titanium tetrachloride, and 0.02 mol of glucose, and adding them into 500 mL of a water / ethanol (the molar ratio of ethanol to water is 1:1) solution, uniformly mixing to obtain a mixture A;

[0054] S32, grinding the mixture A to a particle size of 400 nm by using a sand mill at a speed of 2000 r / min to obtain a mixture B;

[0055] S33, pre-burning the mixture B in an argon atmosphere at 350 DEG C for 5 h to obtain a mixture C;

[0056] S34, putting the mixture C into a sand mill and adding a solvent (the molar ratio of ethanol to water is 1:1) with a mass of 1.5 times that of the mixture C to wet-grind to a particle size of 150 nm to obtain a mixture D;

[0057] S35, spray drying the mixture D to form a precursor, wherein the spray drying is performed by using a centrifugal spray, the inlet temperature is 300 DEG C, the outlet temperature is 80 DEG C, and the atomization pressure of the spray is 0.5 MPa;

[0058] S36, putting the precursor into a gas atmosphere tube furnace and sintering it in an argon-hydrogen mixed gas (the volume ratio of argon to hydrogen is 19:1) at 550 DEG C for 10 h to obtain a titanium-doped high-density spherical nanometer pyrophosphate ferric sodium sodium-ion battery positive electrode material, marked as Na4Fe 2.8 Ti 0.2 (PO4)2P2O7.

[0059] Comparative Example 1

[0060] The same as Example 3, except that no titanium tetrachloride is added, and the amount of ferric nitrate added is 0.3 mol, and Na4Fe3(PO4)2P2O7 is obtained.

[0061] Comparative Example 2

[0062] The same as Example 3, except that 0.27 mol of ferric nitrate and 0.030 mol of titanium tetrachloride are used.

[0063] Comparative Example 3

[0064] A preparation method of a titanium-doped high-density spherical nanometer pyrophosphate ferric sodium sodium-ion battery positive electrode material, comprising the following steps: S31, weighing 0.4 mol of sodium bicarbonate, 0.285 mol of ferric nitrate, 0.4 mol of ammonium dihydrogen phosphate, 0.020 mol of titanium tetrachloride, and 0.02 mol of glucose, and adding them into a 500 mL water / ethanol (molar ratio of ethanol to water is 1:1) solution, mixing uniformly to obtain a mixture A;

[0065] S32, grinding the mixture A to a particle size of 150 nm at a speed of 2000 r / min by using a sand mill to obtain a mixture B;

[0066] S35, spray drying the mixture B to form a precursor, wherein the spray drying is performed by using a centrifugal spray, the inlet temperature is 300 DEG C, the outlet temperature is 80 DEG C, and the atomization pressure of the spray is 0.5 MPa;

[0067] S36, placing the precursor into an atmosphere tube furnace, sintering in argon-hydrogen mixed gas (volume ratio of argon to hydrogen is 19:1) at 550 DEG C for 10 h to obtain a titanium-doped high-density spherical nanometer pyrophosphate ferric sodium sodium-ion battery positive electrode material, marked as Na4Fe 2.8 Ti 0.2 (PO4)2P2O7.

[0068] Performance test

[0069] The titanium-doped high-density spherical nanometer pyrophosphate ferric sodium sodium-ion battery positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-3 are sampled and tested as follows, and the test results are shown in Table 1.

[0070] The particle size of the above positive electrode material is tested by using a laser particle size analyzer (DLS); the specific surface area is tested by using a Belsorp-Instrument full-automatic nitrogen adsorption BET specific surface area tester BSD-BET400; and the tap density is tested according to the GB / T 5162-2021 standard;

[0071] Battery performance test:

[0072] The titanium-doped high-density spherical nanometer pyrophosphate ferric sodium sodium-ion battery positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-3 are respectively prepared into the following sodium-ion batteries:

[0073] The positive electrode material, the conductive agent Super P and the carboxymethyl cellulose are mixed into a slurry according to a ratio of 8:1:1 with water, stirred for 24 h, coated on a carbon-coated aluminum foil, and dried in an oven at 80 DEG C for 24 h. The dried electrode sheet is cut into 12 mm round pieces, and the loading amount is 1-1.4 mg / cm 2The sodium-ion battery was pressed with sodium foil as the counter electrode. The charge-discharge test conditions were as follows: constant current charge-discharge at 1C rate, voltage range 1.5V to 4.2V.

[0074] Electronic conductivity test: AC impedance test was performed on the impedance / gain-phase analyzer Zhi Li Qiang 1260A, with the frequency range of 1mHz-0.1Hz. The positive electrode material was pressed into a round sheet with a diameter of 10mm, and carbon-coated aluminum foil was attached to both sides, placed in the PEEK sleeve of the mold battery, then inserted into the stainless steel column blocking electrode on both sides, tested under the pressure of 360MPa, and the electronic conductivity was calculated.

[0075] Table 1 Performance test

[0076]

[0077] Analyzing the data in Table 1, it can be seen that:

[0078] 1) The performance test results of the titanium-doped high-density spherical nanometer sodium iron pyrophosphate sodium battery positive electrode material prepared in Examples 1-3 show that by doping titanium metal in NFPP through the series process of "wet mixing-coarse grinding-pre-sintering-ultrafine grinding-spray drying-sintering", the titanium doping reduces the proportion of iron in NFPP, inhibits the generation of impurities, and at the same time, the titanium doping optimizes the lattice structure and improves the electron / ion transmission efficiency. The prepared titanium-doped high-density spherical nanometer sodium iron pyrophosphate sodium battery positive electrode material has high conductivity, high cycle stability and excellent rate performance, with a discharge specific capacity of ≥107mAh / g at 1C rate and a capacity retention rate of ≥90% after 500 cycles.

[0079] 2) Comparative analysis of the performance of the titanium-doped high-density spherical nanometer sodium iron pyrophosphate sodium battery positive electrode material prepared in Example 3 and Comparative Examples 1-2 shows that by replacing part of Fe 4+ with Ti 2+ (0.05≤x≤0.2), the concentration of Fe 2+ is reduced, and the generation of impurities (such as FePO4) caused by the oxidation of Fe 2+ to Fe 3+ during high-temperature sintering is inhibited, ensuring the crystalline purity of the material and stabilizing the lattice structure. The doping of Ti adjusts the connection mode of FeO6 octahedron and PO4 tetrahedron, widens the sodium ion diffusion channel, and reduces the Na + diffusion energy barrier. However, when titanium is not doped or the amount of titanium doping is too much, the performance of the positive electrode material obtained is significantly reduced.

[0080] 3) Comparative analysis of the performance of the titanium-doped high-density spherical nanometer sodium iron pyrophosphate sodium battery anode material prepared in Example 3 and Comparative Example 3 shows that, by using the "wet mixing-coarse grinding-pre-sintering-ultra-fine grinding-spray drying-sintering" series process, the titanium doping reduces the proportion of iron in the NFPP, inhibits the generation of impurities, optimizes the lattice structure by titanium doping, and improves the electron / ion transmission efficiency. The titanium-doped high-density spherical nanometer sodium iron pyrophosphate sodium battery anode material prepared has high conductivity, high cycle stability and excellent rate performance. The coarse grinding and pre-sintering processes play an important role in the preparation process of the present application.

[0081] The above examples are only used to explain the technical solutions of the present application and not to limit them. Although the above examples have been specifically described, it should be understood by those skilled in the art that the specific embodiments of the present application can still be modified or replaced by equivalents without departing from the spirit and scope of the present application. Any modification and equivalent replacement that does not depart from the spirit and scope of the present application should be covered in the protection scope of the present application.

Claims

1. A method for preparing a titanium-doped high-density spherical nanoscale pyrophosphate ferric sodium sodium-ion battery cathode material, characterized in that, The method comprises the following steps: S31, placing a sodium source compound, an iron source compound, a phosphorus source compound, a titanium source compound and a carbon source compound into a solvent, mixing uniformly to obtain a mixture A; S32, wet grinding the mixture A by a sand mill to a particle size of 200-600 nm to obtain a mixture B; S33, pre-sintering the mixture B in an argon atmosphere at 300-450 DEG C for 4-6 h to obtain a mixture C; S34, placing the mixture C into a sand mill and adding a solvent with a mass of 1-2 times that of the mixture C to wet grind to a particle size of 20-300 nm to obtain a mixture D; S35, spray drying the mixture D to form a precursor; the spray drying is performed by one of centrifugal spraying and two-fluid spraying, the inlet temperature is 200-350 DEG C, the outlet temperature is 60-120 DEG C, and the atomization pressure of the two-fluid spraying is 0.4-0.6 MPa; S36, sintering the precursor in an argon-hydrogen mixed gas at 450-600 DEG C for 8-12 h to obtain a titanium-doped high-density spherical nanometer pyrophosphate iron phosphate sodium sodium-ion battery positive electrode material; The chemical general formula of the titanium-doped high-density spherical nano pyrophosphate ferric sodium sodium-ion battery cathode material is Na4Fe 3-x Ti x (PO4)2P2O7, wherein 0.05≤x≤0.2, and a surface is coated with a layer of carbon.

2. The method of claim 1, wherein the method of preparing titanium-doped high-density spherical nanoferric pyrophosphate sodium phosphate sodium-ion battery cathode material is characterized by, The titanium source compound is selected from one or more of titanium hydroxide, titanium sulfide, titanium tetrachloride, titanium dichloride, titanium dichloride oxide, titanium fluoride, titanium bromide, titanium iodide, titanium silicide, titanium oxide, titanium oxychloride and titanium carbide.

3. The method of claim 1, wherein the method of preparing titanium-doped high-density spherical nanoferric pyrophosphate sodium phosphate sodium-ion battery cathode material is characterized by, The sodium source compound is selected from one or more of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium nitrate, sodium fluoride, sodium fluorophosphate, sodium trifluoroacetate, sodium oxalate, sodium acetate, sodium persulfate, sodium hydroxide, sodium formate, sodium citrate, sodium pyrophosphate, sodium dihydrogen pyrophosphate and sodium alginate.

4. The process for the preparation of titanium doped high density spherical nanoferric pyrophosphate sodium phosphate sodium ion battery cathode material as claimed in claim 1, wherein, The iron source compound is selected from one or more of reduced iron powder, magnetite, iron oxide, ferrous oxide, iron nitrate, iron chloride, iron sulfate, iron phosphate, iron oxalate, ferrous oxalate, iron acetate and iron citrate, and iron fluoride.

5. The process for the preparation of titanium doped high density spherical nanoferric pyrophosphate sodium phosphate sodium ion battery cathode material as claimed in claim 1 wherein, The phosphorus source compound is selected from one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium dihydrogen pyrophosphate, ammonium dihydrogen phosphate and ammonium triphosphate; and the carbon source compound is selected from one or more of glucose, sucrose, citric acid, malic acid, polyaniline, polyethylene glycol, adipic acid, phenolic resin, polypyrrole, ascorbic acid, chitosan and soluble starch.

6. The process for the preparation of titanium doped high density spherical nanoferric pyrophosphate sodium phosphate sodium ion battery cathode material as claimed in claim 1, wherein, The solvent is at least one of water and ethanol.

7. The method of claim 6, wherein the method of preparing titanium-doped high-density spherical nanoferric pyrophosphate sodium phosphate sodium-ion battery cathode material is characterized by, The solvent is composed of water and ethanol in a molar ratio of 1:

1.

8. The process for the preparation of titanium doped high density spherical nanoferric pyrophosphate sodium phosphate sodium ion battery cathode material as claimed in claim 1 wherein, The volume ratio of argon to hydrogen in the argon-hydrogen mixed gas is 19:

1.

9. A titanium doped high-density spherical nanoferric pyrophosphate sodium phosphate sodium-ion battery cathode material, characterized by: The method is used to prepare the titanium-doped high-density spherical nanometer pyrophosphate iron phosphate sodium sodium-ion battery positive electrode material.

10. The titanium doped high-density spherical nanoferric pyrophosphate sodium phosphate sodium-ion battery cathode material of claim 9, wherein, The specific surface area of the positive electrode material is 14-20 m² / g, and the tap density is greater than or equal to 2.2 g / cm³.

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