Metal-based sodium phosphate salt as cathode material for sodium-ion battery and preparation method thereof

Abstract

The application discloses a sodium ion battery positive electrode material metal-based sodium phosphate salt and a preparation method thereof, and the preparation method comprises the following steps: first precursor solution preparation, second precursor solution preparation, precursor powder preparation and high-temperature sintering. The preparation method of the sodium ion battery positive electrode material metal-based sodium phosphate salt has the characteristics of uniform dispersion, high material purity, simple process operation, green pollution-free and excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, and particularly relates to a sodium ion battery positive electrode material metal-based sodium phosphate salt and a preparation method thereof. BACKGROUND

[0002] The core of an electric vehicle is a power battery. In the past two years, the installed capacity of the power battery has rapidly increased, leading to a surge in the price of lithium carbonate. At present, more than 90% of global lithium resources are mainly distributed in salt marshes in countries such as Bolivia, Argentina and Chile in South America, and the geographical distribution is uneven, and the mining difficulty of salt marshes with different components is different. The lithium resource reserves in China rank sixth in the world, and most of them are distributed in salt lake brine. The magnesium-lithium ratio in the brine resources in China is large, the mining is difficult, the cost is high, and more than 80% of the lithium resources in China depend on import. The increase in the price of lithium resources will inevitably affect the development of the new energy electric vehicle field in China, and it is impossible to meet the cheap requirements of large-scale energy storage. Therefore, developing sodium ion batteries without resource constraints will be a better alternative.

[0003] Sodium resources are abundant and low in cost, and the working principle is the same as that of lithium ion batteries. For sodium ion batteries, the positive electrode material plays a decisive role in the energy density and cost of the system. At present, sodium ion positive electrode materials include layered oxides, prussian blue and its analogues, and polyanion materials. Related researches show that in the process of sodium extraction, the layered oxides have problems such as multi-stage structure phase change, interface rock rockization, lattice distortion, transition metal ion migration and the like, thereby leading to a decrease in the stability of the material. In the synthesis process of the prussian blue material, more than 10% of lattice water exists in the structure, which will decompose to generate a large amount of gas at a high potential, causing the battery to swell and fail. Compared with the first two types of materials, the polyanion material undoubtedly is the best choice for the sodium battery positive electrode due to its stable 3D framework structure and excellent electrochemical stability.

[0004] At present, the polyanion materials mainly researched on the market include V-based phosphates such as Na3V2(PO4)3 and NaVPO4F, Fe-based phosphates such as Na2FeP2O7, Na4Fe3(PO4)2P2O7 and NaFePO4, and Fe-based sulfates such as Na2Fe(SO4)2 and Na2Fe2(SO4)3. The V-based phosphates have a high redox potential (3.4-3.6 V) and a suitable discharge capacity, and are the first choice for constructing a high-energy-density battery system. The Fe-based phosphates are non-toxic, pollution-free and inexpensive, which lays a good foundation for their application in the field of large-scale energy storage.

[0005] Take Fe phosphate system as an example, in Fe-based phosphate system, NaFePO4 is an electrochemically inert material, so this material does not have the prospect of industrialization application. Na4Fe3(PO4)2P2O7 has a high theoretical specific capacity of 129 mAh / g, a suitable discharge potential (3.2 V), a low raw material cost, and a high market application value. At present, the main preparation methods of Na4Fe3(PO4)2P2O7 are as follows:

[0006] (1) A water-soluble ferrous sulfate, iron nitrate and other iron salts are mixed with sodium salt and phosphorus salt, dried and sintered to obtain the final product. However, this process is accompanied by a large amount of S and N emissions during material sintering, which will cause serious pollution to the environment.

[0007] (2) Iron metal is reacted with acid, and then sodium salt and phosphorus salt are added, and the final product is obtained by spray drying and sintering. However, this process has low efficiency and high comprehensive production cost, and does not have the prospect of industrialization application.

[0008] Taking the iron-based phosphate as an example, Na4Fe 3-x Φ x P4O 15 contains Na, Fe, PO4, P2O7 and other elements and functional groups, and the uneven mixing between elements can easily lead to the generation of NaFePO4 or Na2FeP2O7 impurities, affecting the performance of the main phase. 3-x Φ x P4O 15 In liquid phase synthesis, water-soluble FeSO4, Fe(NO3)3 and other raw materials are often used, and liquid phase synthesis can ensure the uniform mixing of Na, Fe and P elements, but this process has serious S and N pollution and cannot realize batch production. 3-x Φ x P4O 15 In solid phase synthesis, water-insoluble FeC2O4, FePO4, FeO, Fe2O3 and other raw materials are often used, and the uniform mixing of Na, Fe and P elements cannot be guaranteed during solid phase homogenization, and the phase separation is serious. SUMMARY

[0009] The object of the present application is to provide a sodium ion battery positive electrode material metal-based sodium phosphate and a preparation method thereof, which has the characteristics of uniform dispersion, high material purity, simple process operation, green and pollution-free, and excellent electrochemical performance.

[0010] The application can be implemented by the following technical scheme:

[0011] The application discloses a preparation method of a metal-based sodium phosphate salt positive electrode material of a sodium ion battery.

[0012] S1, preparation of a first precursor solution: uniformly mixing a sodium source, a phosphorus source, a carbon source and water to obtain the first precursor solution;

[0013] S2, preparation of a second precursor solution: dissolving an insoluble metal M source and a proton H + acid in a mechanical force to obtain the second precursor solution;

[0014] S3, preparation of a precursor powder: uniformly mixing the first precursor solution obtained in the step S1 and the second precursor solution, and drying to obtain the precursor powder;

[0015] S4, high-temperature sintering: high-temperature sintering the precursor powder obtained in the step S3, and cooling to obtain the corresponding metal-based sodium phosphate salt positive electrode material.

[0016] Further, the mechanical force is a particle collision, friction and / or cutting interaction force generated by rotation of a mechanical device.

[0017] Further, the mechanical force is generated in a sand milling, ball milling and / or mechanical milling manner.

[0018] Further, the proton H + is an organic acid and / or an inorganic acid, and the organic acid and / or the inorganic acid is one or more than two selected from formic acid, acetic acid, citric acid, malic acid, oxalic acid, lactic acid and / or phosphoric acid.

[0019] Further, in the step S2, the molar ratio of the metal M source and the proton H + acid ranges from 0.01 to 1; and the pH ranges from 1 to 5.

[0020] Further, in the step S2, the termination condition of the chemical ablation dissolution is that the solid particle size D 50 is lower than 0.3 microns, and the D max is lower than 2.0 microns.

[0021] Further, in the step S3, the drying manner is flash drying, vacuum drying and / or spray drying.

[0022] Further, in the step S4, the high-temperature sintering condition is that the sintering temperature ranges from 500 to 800 DEG C, and the sintering time ranges from 2 to 15 hours.

[0023] Further, the sodium salt is an inorganic sodium salt / organic sodium salt, and the inorganic sodium salt / organic sodium salt is selected from one or two of sodium carbonate, sodium oxalate, sodium phosphate, sodium acetate and / or sodium citrate.

[0024] Preferably, the phosphorus source is selected from one or two or more of phosphoric acid, sodium phosphate, ammonium dihydrogen phosphate and / or sodium dihydrogen phosphate.

[0025] Preferably, the carbon source is an organic carbon source / inorganic carbon source, and the organic carbon source / inorganic carbon source is selected from one or two or more of citric acid, glucose, sucrose, carbon nanotubes, graphene and carbon black.

[0026] Preferably, the molar ratio of the organic carbon source to the sodium source is 0.1-1, or the weight ratio of the inorganic carbon source to the sodium source is 0.01-0.1; and the molar ratio of the sodium source to the phosphorus source is 0.5-2.0:1.

[0027] Further, the metal base is an iron base, a manganese base, a cobalt base, a nickel base or a vanadium base.

[0028] When the metal base is an iron base, the metal M source is selected from one or two or more of iron phosphate, ferrous oxalate, iron oxide and / or magnetite.

[0029] When the metal base is a manganese base, the metal M source is selected from one or two or more of manganese carbonate, manganese phosphate, manganese oxide, manganese sesquioxide and / or manganese sesquioxide.

[0030] When the metal base is a cobalt base, the metal M source is selected from one or two or more of cobalt carbonate, cobalt oxalate, cobalt oxide and / or cobalt sesquioxide.

[0031] When the metal base is nickel, the metal M source is selected from one or two or more of nickel carbonate, nickel hydroxide and / or nickel oxide.

[0032] When the metal base is a vanadium base, the metal M source is selected from one or two or more of vanadium phosphate, vanadium oxide, vanadium sesquioxide and / or vanadium sesquioxide.

[0033] Another aspect of the present application is to protect the above-prepared sodium-ion battery cathode material metal base sodium phosphate salt, and the metal base is Fe, Mn, Co, Ni or V:

[0034] When the metal base is Fe, Mn, Co or Ni, the structural formula of the metal base sodium phosphate salt is Na2MP2O7 or Na4M 3-x Φ x P4O 15 , wherein Φ refers to a vacancy defect, and x is in the range of 0-0.15.

[0035] When the metal base is V, the structural formula of the metal base sodium phosphate salt is Na3V2(PO4)3.

[0036] The sodium ion battery positive electrode material metal base sodium phosphate salt and the preparation method thereof have the following beneficial effects:

[0037] The metal base sodium phosphate salt is synthesized by a mechanochemical ablation method, wherein the metal M source is a water-insoluble raw material, the raw material particles are crushed by mechanical force, and the etching of protons H + further reduces the particle size of the material, promotes the uniform mixing of Na, M, P and other elements, and improves the phase purity of the metal base sodium phosphate salt material. Compared with the traditional liquid phase method for preparing the metal base sodium phosphate salt, the solid content of the precursor solution is increased by about 4 times, reaching about 45%, which greatly reduces the energy consumption required for later spraying. In addition, this method does not introduce polluting elements such as N and S, and there is no environmental pollution problem.

[0038] Compared with the traditional solid phase method for preparing the metal base sodium phosphate salt, due to the etching of protons H + , the particle size is smaller, the content of free metal ions is higher, the mixing of Na, M, P and other elements is more uniform, and the production efficiency and material performance are more excellent under the same mechanical crushing time.

[0039] The material prepared by the mechanochemical ablation method has a high sodium storage capacity (such as the capacity of the iron base sodium iron phosphate is 117 mAh / g); excellent long cycle stability (such as the iron base sodium iron phosphate maintains 100% at 10C rate for 1000 cycles); and excellent rate performance (such as the iron base sodium iron phosphate maintains a capacity of 95 mAh / g at 20C rate). BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is the XRD pattern of the Na4Fe 2.95 Φ 0.05 P4O 15 material of application example 1;

[0041] Figure 2 is the SEM pattern of the Na4Fe 2.95 Φ 0.05 P4O 15 material of application example 1;

[0042] Figure 3 is the first cycle charge-discharge curve of the Na4Fe 2.95 Φ 0.05 P4O 15 electrode;

[0043] Figure 4 is the first cycle charge-discharge curve of the Na4Fe 2.95 Φ 0.05P4O 15 Electrode rate performance curves;

[0044] Figure 5 Na4Fe 2.95 Φ 0.05 P4O 15 Electrode cycle stability curves;

[0045] Figure 6 Na4Fe 2.95 Φ 0.05 P4O 15 Material XRD pattern;

[0046] Figure 7 Na4Fe 2.95 Φ 0.05 P4O 15 Material SEM pattern. DETAILED DESCRIPTION

[0047] In order to make the person skilled in the art better understand the technical solutions of the present application, the product of the present application will be further described in detail below in combination with embodiments and drawings.

[0048] The application discloses a preparation method of a metal-based sodium phosphate salt positive electrode material of a sodium ion battery.

[0049] S1, preparation of a first precursor solution: uniformly mixing a sodium source, a phosphorus source, a carbon source and water to obtain the first precursor solution;

[0050] S2, preparation of a second precursor solution: dissolving an insoluble metal M source and a proton H + acid in a mechanical force to obtain the second precursor solution;

[0051] S3, preparation of a precursor powder: uniformly mixing the first precursor solution and the second precursor solution obtained in step S1, and drying to obtain the precursor powder;

[0052] S4, high-temperature sintering: high-temperature sintering the precursor powder obtained in step S3, and cooling to obtain the corresponding metal-based sodium phosphate salt positive electrode material.

[0053] Further, the mechanical force is a particle collision, friction and / or cutting interaction force generated by rotation of a mechanical device.

[0054] Further, the mechanical force is generated in a sand mill, a ball mill and / or a mechanical mill.

[0055] Further, the proton H +The organic acid and / or inorganic acid is selected from one or more of formic acid, acetic acid, citric acid, malic acid, oxalic acid, lactic acid and / or phosphoric acid.

[0056] Further, in step S2, the metal M source and the proton H + The molar ratio of the acid ranges from 0.01 to 1, and the pH ranges from 1 to 5.

[0057] Further, in step S2, the termination condition of the chemical ablation dissolution is that the solid particle size D 50 is less than 0.3 μm, D max is less than 2.0 μm.

[0058] Further, in step S3, the drying method is flash drying, vacuum drying and / or spray drying.

[0059] Further, in step S4, the high-temperature sintering condition is that the sintering temperature is 500-800°C, and the sintering duration is 2-15 h.

[0060] Further, the sodium salt is an inorganic sodium salt / organic sodium salt, which is selected from one or more of sodium carbonate, sodium oxalate, sodium phosphate, sodium acetate and / or sodium citrate.

[0061] Preferably, the phosphorus source is selected from one or more of phosphoric acid, sodium phosphate, ammonium dihydrogen phosphate and / or sodium dihydrogen phosphate.

[0062] Preferably, the carbon source is an organic carbon source / inorganic carbon source, which is selected from one or more of citric acid, glucose, sucrose, carbon nanotubes, graphene and carbon black.

[0063] Preferably, the molar ratio of the organic carbon source to the sodium source is 0.1-1, or the weight ratio of the inorganic carbon source to the sodium source is 0.01-0.1, and the molar ratio of the sodium source to the phosphorus source is 0.5-2.0:1.

[0064] Further, the metal base is an iron base, a manganese base, a cobalt base, a nickel base or a vanadium base.

[0065] When the metal base is an iron base, the metal M source is selected from one or more of iron phosphate, ferrous oxalate, iron oxide and / or magnetite.

[0066] When the metal base is a manganese base, the metal M source is selected from one or more of manganese carbonate, manganese phosphate, manganese oxide, manganese sesquioxide and / or manganese sesquioxide.

[0067] When the metal base is a cobalt base, the metal M source is selected from one or more of cobalt carbonate, cobalt oxalate, cobalt oxide and / or cobalt sesquioxide.

[0068] when the metal base is nickel, the metal M source is selected from one or more of nickel carbonate, nickel hydroxide or / and nickel oxide;

[0069] when the metal base is vanadium base, the metal M source is selected from one or more of vanadium phosphate, vanadium oxide, divanadium trioxide and / or divanadium pentoxide;

[0070] Another aspect of the present application is to protect the above prepared sodium ion battery cathode material metal base sodium phosphate salt, the metal base is Fe, Mn, Co, Ni or V:

[0071] when the metal base is Fe, Mn, Co or Ni, the structural formula of the metal base sodium phosphate salt is Na2MP2O7 or Na4M 3-x Φ x P4O 15 , wherein Φ refers to a vacancy defect, and x ranges from 0 to 0.15;

[0072] when the metal base is V, the structural formula of the metal base sodium phosphate salt is Na3V2(PO4)3.

[0073] when the metal base is iron base, the structural formula of the iron base phosphate salt is Na4Fe 3-x Φ x P4O 15 , wherein Φ refers to a vacancy defect, and x ranges from 0 to 0.15, and specifically including Na4Fe3P4O 15 , Na4Fe 2.95 Φ 0.05 P4O 15 , Na4Fe 2.90 Φ 0.1 P4O 15 , Na4Fe 2.85 Φ 0.15 P4O 15 , Na4Fe 3-x Φ x P4O 15 , and the structural formula belongs to the orthorhombic Pn21a space group, is composed of FeO6 octahedron and PO4 tetrahedron, and the cell parameters are 16.5 ≦ a (Å) ≦ 17.9, 6.0 ≦ b (Å) ≦ 6.9, 9.8 ≦ c (Å) ≦ 11.5, 1248.0 ≦ V 3 (Å) ≦ 1275.9. The following is Na4Fe 3-x Φ x P4O 15 The main combination will be specifically introduced in the detailed description of the present application.

[0074] The application discloses an acid-promoted mechanochemical method for preparing a positive material of a sodium-ion battery of an iron-based ferric phosphate salt 3-x Φ x P4O 15 , wherein the value range of x is 0-0.15. The preparation method is that an iron source insoluble in water and a proton H + acid are mixed and ball milled, under mechanical force breaking, solid particles are crushed, under proton H+ acid etching, the particle size is further reduced, and the iron source dissolution amount is increased, which is beneficial to the uniform mixing of Na, Fe and P. A sodium source, a phosphorus source and a carbon source are added, spray drying is carried out, and then sintering is carried out to obtain a pure phase Na4Fe 3-x Φ x P4O 15 material. The acid-promoted mechanochemical method has high efficiency, is different from a traditional ball milling method which only depends on physical action, and can uniformly mix Na, Fe and P in a short time. Meanwhile, the solid content of the precursor slurry can reach more than 45 %, and the energy consumption in the later drying process is greatly reduced. Finally, due to the stable 3D open frame structure, the large sodium ion diffusion channel and the pure phase structure, the material exhibits high capacity, excellent long cycle stability and excellent rate performance.

[0075] Meanwhile, the method is also suitable for solid phase synthesis of V-based materials such as Na3V2 (PO4) 3, and solid phase synthesis of M-based materials such as Na2MP2O7, Na4M 3-x Φ x P4O 15 (M is Fe, Mn, Co, Ni and the like).

[0076] Application Example 1 Synthesis of Na4Fe 2.95 Φ 0.05 P4O 15 and electrochemical performance thereof

[0077] The specific synthesis steps are as follows:

[0078] Step 1: glucose and sodium dihydrogen phosphate are weighed according to a molar ratio of 0.2, and a proper amount of water is added for dissolution, and the solid content is controlled to be 60 % (a first precursor solution);

[0079] Step 2: FeC2O4 and acetic acid are weighed according to a molar ratio of 0.05, a proper amount of water is added for dilution, and the solid content is controlled to be 30 %, and sand milling is carried out until the particle size D50 is less than 0.2 μm (a second precursor solution);

[0080] Step 3: the first precursor solution and the second precursor solution are mixed to obtain a precursor mixed solution;

[0081] Step 4: the precursor mixed solution is spray dried to obtain a precursor powder;

[0082] Step 5: The precursor powder was kept at 550℃ for 10H, and then naturally cooled to obtain Na4Fe 2.95 Φ 0.05 P4O 15 material.

[0083] Figure 1 Na4Fe 2.95 Φ 0.05 P4O 15 The XRD of the powder has strong diffraction peaks and exhibits a single pure phase with good crystallinity. In the pure phase structure, the material has a high specific capacity, smooth sodium ion diffusion, and a low energy barrier, and excellent electrochemical performance. Figure 2 Na4Fe 2.95 Φ 0.05 P4O 15 The morphology of the material shows nanoscale agglomerated particles, and small particle size can effectively reduce the distance of sodium ion deintercalation, thereby improving the rate of sodium deintercalation.

[0084] Na4Fe 2.95 Φ 0.05 P4O 15 After mixing the slurry according to a mass ratio of 7:2:1, the black slurry was coated on an aluminum foil using a 150um four-side coater, and then the film was dried in a 100℃ vacuum drying oven for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6mm using a sheet puncher, and a metal sodium was used as the counter electrode, 1mol / L NaClO4EC+DEC (1:1vol%)+5%FEC was used as the electrolyte, and a PP / PE / PP three-layer separator was used to assemble a CR2016 type button cell in a glove box.

[0085] The button cell was subjected to constant current charge and discharge test, and the current density was 0.1C (1C=129mAh / g). Figure 3 Na4Fe 2.95 Φ 0.05 P4O 15 The first cycle charge and discharge curve of the electrode showed that the reversible specific capacity was 117mAh / g in the voltage range of 2.0-4.3V, and the average discharge potential was 3.1V. Figure 4 Na4Fe 2.95 Φ 0.05 P4O 15 The rate performance of the electrode, as shown in the figure, the capacity of the material was 95mAh / g at a rate of 20C, showing excellent rate performance. Figure 5 Na4Fe 2.95 Φ 0.05 P4O 15The long cycle stability of the electrode, which has almost no capacity decay after 1000 cycles at 10C, demonstrates good structural stability.

[0086] Application Example 2 Na4Fe 2.90 Φ 0.1 P4O 15 Synthesis and Electrochemical Performance

[0087] The specific synthesis steps are as follows:

[0088] Step 1: Weigh the materials according to the molar ratio of 0.2, dissolve them in water, and control the solid content at 50% (first precursor solution);

[0089] Step 2: Weigh the materials according to the molar ratio of 0.07, dilute them with water, and control the solid content at 40%, then sand mill until the particle size D50 is less than 0.2 μm (second precursor solution);

[0090] Step 3: Mix the first precursor solution and the second precursor solution to obtain a precursor mixed solution;

[0091] Step 4: Spray dry the precursor mixed solution to obtain a precursor powder;

[0092] Step 5: Heat the precursor powder at 550°C for 10H, and then naturally cool to obtain Na4Fe 2.90 Φ 0.1 P4O 15 material.

[0093] Na4Fe 2.90 Φ 0.1 P4O 15 , AB, and PVDF are mixed into a slurry according to a mass ratio of 7:2:1, then the black slurry is coated on an aluminum foil using a 150um four-side coater, and then the film is dried in a vacuum drying oven at 100°C for 2 hours. The electrode film is punched into a circular sheet with a radius of 0.6mm using a sheet puncher, a metal sodium is used as the counter electrode, a 1 mol / L NaClO4 EC+DEC (1:1 vol%) +5% FEC is used as the electrolyte, and a PP / PE / PP three-layer separator is used as the separator, and then a CR2016 type button cell is assembled in a glove box.

[0094] The above button cell was subjected to constant current charge-discharge test, and the current density was 0.1C (1C = 129 mAh / g). The reversible specific capacity was 115 mAh / g in the voltage range of 2.0-4.3 V, and the average discharge potential was 3.1 V. The capacity of the electrode was 98 mAh / g at a rate of 20C, and the capacity almost did not decay after 1000 cycles, showing good structural stability.

[0095] Application Example 3 Na4Fe 2.85 Φ 0.15 P4O 15 , and its electrochemical performance

[0096] The synthesis steps are as follows:

[0097] Step 1: The glucose and sodium dihydrogen phosphate were weighed according to the molar ratio of 0.2, dissolved in an appropriate amount of water, and the solid content was controlled at 50% (first precursor solution);

[0098] Step 2: FeO and citric acid were weighed according to the molar ratio of 0.07, diluted with an appropriate amount of water, and the solid content was controlled at 40%, and sand grinding was performed until the particle size D50 was less than 0.2 μm (second precursor solution);

[0099] Step 3: The first precursor solution and the second precursor solution were mixed to obtain a precursor mixed solution;

[0100] Step 4: The precursor mixed solution was spray dried to obtain a precursor powder;

[0101] Step 5: The precursor powder was kept at 550°C for 10H, and after natural cooling, Na4Fe 2.85 Φ 0.15 P4O 15 material was obtained.

[0102] Na4Fe 2.85 Φ 0.15 P4O 15 , AB and PVDF were mixed into a slurry according to the mass ratio of 7:2:1, and then the black slurry was coated on an aluminum foil using a 150um four-side coater. The film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6mm using a sheet punching machine, and a metal sodium was used as a counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) +5% FEC was used as an electrolyte, and a PP / PE / PP three-layer separator was used to assemble a CR2016 type button cell in a glove box.

[0103] The above button cell was subjected to constant current charge and discharge test, and the current density was 0.1C (1C = 129 mAh / g). The reversible specific capacity was 112 mAh / g in the voltage range of 2.0-4.3V, and the average discharge potential was 3.1V. The capacity of the electrode was 90 mAh / g at 20C rate. And at 10C rate, the capacity almost did not decay after 1000 cycles, showing good structural stability.

[0104] Application Example 4 Synthesis of Na3V2(PO4)3 and its electrochemical performance

[0105] The synthesis steps are as follows:

[0106] Step 1: The sucrose and sodium dihydrogen phosphate were weighed according to the molar ratio of 0.3, dissolved in appropriate amount of water, and the solid content was controlled at 40% (first precursor solution);

[0107] Step 2: V2O5 and citric acid were weighed according to the molar ratio of 0.05, diluted with appropriate amount of water, and the solid content was controlled at 30%, and sand grinding was carried out until the particle size D50 was less than 0.2μm (second precursor solution);

[0108] Step 3: The first precursor solution and the second precursor solution were mixed to obtain a precursor mixed solution;

[0109] Step 4: The precursor mixed solution was spray dried to obtain a precursor powder;

[0110] Step 5: The precursor powder was kept at 650℃ for 8H, and after natural cooling, Na3V2(PO4)3 material was obtained.

[0111] Na3V2(PO4)3, AB, and PVDF were mixed into a uniform slurry according to the mass ratio of 7:2:1, and then the black slurry was coated on an aluminum foil using a 150um four-side coater. The film was then dried in a vacuum drying oven at 100℃ for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6mm using a sheet puncher. The CR2016 type button cell was assembled in a glove box using metallic sodium as the counter electrode, 1mol / L NaClO4 EC+DEC (1:1vol%) +5% FEC as the electrolyte, and PP / PE / PP three-layer separator.

[0112] The above button cell was subjected to constant current charge and discharge test, and the current density was 0.1C (1C = 120 mAh / g). The reversible specific capacity was 115 mAh / g in the voltage range of 2.0-4.0V, and the average discharge potential was 3.3V. The capacity of the electrode was 100 mAh / g at 20C rate. And at 10C rate, the capacity almost did not decay after 1000 cycles, showing good structural stability.

[0113] Synthesis of Na2MnP2O7 and its electrochemical performance

[0114] The synthesis steps are as follows:

[0115] Step 1: Weigh the materials according to the molar ratio of 0.7, dissolve in water, and control the solid content at 50% (first precursor solution);

[0116] Step 2: Weigh the materials according to the molar ratio of 0.08, dilute with water, and control the solid content at 40%, sand mill until the particle size D50 is less than 0.2 μm (second precursor solution);

[0117] Step 3: Mix the first precursor solution and the second precursor solution to obtain a precursor mixed solution;

[0118] Step 4: Spray dry the precursor mixed solution to obtain a precursor powder;

[0119] Step 5: Heat the precursor powder at 500°C for 5H, and then naturally cool to obtain Na2MnP2O7 material.

[0120] Mix Na2MnP2O7, AB, and PVDF according to the mass ratio of 7:2:1 to form a uniform slurry, then use a 150um four-side coater to coat the black slurry on an aluminum foil, and then dry the film in a 100°C vacuum drying oven for 2 hours. Use a sheet puncher to punch the electrode film into a circular sheet with a radius of 0.6mm, use metallic sodium as the counter electrode, 1mol / L NaClO4 EC+DEC (1:1 vol%) +5% FEC as the electrolyte, and PP / PE / PP three-layer separator, and assemble into a CR2016 type button cell in a glove box.

[0121] The above button cell was subjected to constant current charge and discharge test, and the current density was 0.1C (1C=90mAh / g). The reversible specific capacity was 89mAh / g in the voltage range of 2.0-4.5V, and the average discharge potential was 3.0V. The capacity of the electrode at 5C rate was 75mAh / g, and the rate performance was excellent.

[0122] Comparative Example 1 Na4Fe 2.95 Φ 0.05 P4O 15 Synthesis and electrochemical performance of

[0123] The synthesis steps are as follows:

[0124] Step 1: Weigh the materials according to the molar ratio of 0.2, dissolve in water, and control the solid content at 60% (first precursor solution);

[0125] Step 2: FeC2O4 was diluted with appropriate amount of water, solid content was controlled at 30%, sanding time was the same as application example 1 (second precursor solution);

[0126] Step 3: the first precursor solution and the second precursor solution were mixed to obtain a precursor mixed solution;

[0127] Step 4: the precursor mixed solution was spray dried to obtain a precursor powder;

[0128] Step 5: the precursor powder was kept at 550°C for 10H, and after natural cooling, Na4Fe 2.95 Φ 0.05 P4O 15 material.

[0129] Figure 6 Na4Fe 2.95 Φ 0.05 P4O 15 XRD of the powder, the diffraction intensity was not high, and the crystallinity was poor, and the marked NaFePO4 impurity peak was directly related to the uneven distribution between Na, Fe and P caused by the too large particle size of FeC2O4 in the sanding process. The existence of the impurity phase reduces the capacity of the main phase and affects the diffusion of sodium ions in the material, reducing the rate performance. Figure 7 Na4Fe 2.95 Φ 0.05 P4O 15 The morphology of the material showed that it presented large agglomerated particles, and the porosity between the particles was low, which was not conducive to the infiltration of the electrolyte and affected the diffusion of sodium ions between the materials.

[0130] Na4Fe 2.95 Φ 0.05 P4O 15 , AB, PVDF were mixed into a slurry at a mass ratio of 7:2:1, then a black slurry was coated on an aluminum foil using a 150um four-side coater, and then the film was dried in a 100°C vacuum drying oven for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6mm using a sheet puncher, and a metal sodium was used as a counter electrode, 1mol / L NaClO4 EC+DEC (1:1vol%) +5% FEC was used as an electrolyte, and a PP / PE / PP three-layer separator was used as a separator, and a CR2016 type button cell was assembled in a glove box.

[0131] The button cell was subjected to constant current charge and discharge test, and the current density was 0.1C (1C=129mAh / g). Figure 3 Na4Fe 2.95 Φ 0.05 P4O 15The charge-discharge curve of the electrode during the first cycle shows a reversible specific capacity of 87 mAh / g and an average discharge potential of 3.1 V within a voltage range of 2.0-4.3 V. This is much lower than the discharge capacity in Application Example 1, indicating that the presence of impurity phases occupies part of the material mass and reduces the specific capacity of the material. Figure 4 Na4Fe 2.95 Φ 0.05 P4O 15 As shown in the figure, the capacity of the material at 20C rate is 40mAh / g, which is much lower than the capacity in Application Example 1. This indicates that the presence of impurity phase is not conducive to the diffusion of sodium ions between particles, thus reducing its rate performance. Figure 5 Na4Fe 2.95 Φ 0.05 P4O 15 The electrode exhibits long-term cycling stability. After 1000 cycles at 10C, its capacity only slightly decreases, indicating that impurities have little impact on structural stability.

[0132] Comparative Example 2 Na4Fe 2.90 Φ 0.1 P4O 15 Synthesis and electrochemical properties

[0133] The synthesis steps are as follows:

[0134] Step 1: Weigh out glucose and sodium dihydrogen phosphate in a molar ratio of 0.2, add an appropriate amount of water to dissolve, and control the solid content at 50% (first precursor solution).

[0135] Step 2: Dilute FePO4 with an appropriate amount of water, control the solid content at 40%, and mill it until the particle size D50 is the same as that in Application Example 2 (second precursor solution).

[0136] Step 3: Mix the first precursor solution and the second precursor solution to obtain a precursor mixture solution;

[0137] Step 4: Spray dry the precursor mixture solution to obtain precursor powder;

[0138] Step 5: The precursor powder is kept at 550℃ for 10 hours, and then naturally cooled to obtain Na4Fe. 2.90 Φ 0.1 P4O 15 Material.

[0139] Na4Fe 2.90 Φ 0.1 P4O 15, AB, PVDF were mixed into homogenate with the mass ratio of 7:2:1, then the black slurry was coated on the aluminum foil using 150um four-side coater, and then the film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6mm using a puncher, and a CR2016 type button cell was assembled in a glove box using metal sodium as the counter electrode, 1mol / L NaClO4EC+DEC(1:1vol%)+5%FEC as the electrolyte, and PP / PE / PP three-layer separator.

[0140] The above button cell was subjected to constant current charge and discharge test, and the current density was 0.1C (1C=129mAh / g). The reversible specific capacity was 73mAh / g in the voltage range of 2.0-4.3V, and the average discharge potential was 3.1V. The capacity of the electrode was 25mAh / g at 20C rate, and the capacity attenuation was not obvious after 1000 cycles, indicating that the existence of the mixed phase had little effect on the structure of the main phase.

[0141] Comparative Example 3 Na4Fe 2.85 Φ 0.15 P4O 15 Synthesis and electrochemical performance thereof

[0142] The specific synthesis steps are as follows:

[0143] Step 1: Weigh the materials according to the molar ratio of 0.2, add an appropriate amount of water to dissolve, and control the solid content at 50% (first precursor solution);

[0144] Step 2: Dilute FeO with an appropriate amount of water, control the solid content at 40%, and sand mill to the same particle size D50 as Application Example 3 (second precursor solution);

[0145] Step 3: Mix the first precursor solution and the second precursor solution to obtain a precursor mixed solution;

[0146] Step 4: Spray dry the precursor mixed solution to obtain a precursor powder;

[0147] Step 5: Heat the precursor powder at 550°C for 10H, and then naturally cool to obtain Na4Fe 2.85 Φ 0.15 P4O 15 material.

[0148] Na4Fe 2.85 Φ 0.15 P4O 15AB, PVDF were mixed into homogenate with the mass ratio of 7:2:1, then the black slurry was coated on the aluminum foil using 150um four-side coater, and then the film was dried in a vacuum drying oven at 100℃ for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6mm using a puncher, and a CR2016 type button cell was assembled in a glove box using metal sodium as the counter electrode, 1mol / L NaClO4EC+DEC (1:1vol%) +5%FEC as the electrolyte, and PP / PE / PP three-layer separator as the separator.

[0149] The above button cell was subjected to constant current charge and discharge test, and the current density was 0.1C (1C=129mAh / g). The reversible specific capacity was 90mAh / g in the voltage range of 2.0-4.3V, and the average discharge potential was 3.1V. The capacity of the electrode was 20mAh / g at a rate of 20C. And the capacity retention rate was only 85% after 1000 cycles at a rate of 10C, and the structural stability was poor.

[0150] It should be noted that Fe, Co and Ni are all divalent first transition series elements, and have similar properties to each other. Therefore, on the basis of the specific introduction of Fe-based in the examples, no additional specific examples of Co-based and Ni-based are introduced. However, this does not affect the understanding of those skilled in the art, and the introduction of Fe-based specific examples is not a constraint on the scope of protection.

[0151] The above examples are only specific embodiments of the present application, which are described in more detail and in more detail, but should not be construed as limiting the scope of the patent range of the present application. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, and these obvious alternative forms all belong to the protection scope of the present application. The present application relates to the technical field of sodium ion batteries, and specifically relates to a metal-based sodium phosphate salt as a positive electrode material of a sodium ion battery and a preparation method thereof.

Claims

1. A method for preparing a metal-based sodium phosphate salt positive electrode material for sodium-ion batteries, characterized in that The method comprises the following steps: S1, preparation of a first precursor solution: uniformly mixing a sodium source, a phosphorus source, a carbon source and water to obtain a first precursor solution; S2, preparation of the second precursor solution: the insoluble metal M source, the proton H + containing acid are subjected to chemical ablation dissolution in the presence of mechanical force to obtain the second precursor solution; the molar ratio of the metal M source and the proton H + containing acid ranges from 0.01 to 1; the pH ranges from 1 to 5; the termination condition of the chemical ablation dissolution is that the solid particle size D 50 is lower than 0.3 μm, D max is lower than 2.0 μm; the mechanical force is the particle-particle collision, friction and / or cutting interaction force generated by the rotation of the mechanical equipment; S3, preparation of a precursor powder: uniformly mixing the first precursor solution obtained in step S1 with a second precursor solution, and drying to obtain a precursor powder; S4, high-temperature sintering: high-temperature sintering of the precursor powder obtained in step S3, and cooling to obtain a corresponding metal-based sodium phosphate salt positive electrode material.

2. The method for preparing the sodium-ion battery cathode material metal-based sodium phosphate according to claim 1, characterized in that: The mechanical force is generated by sanding, ball milling and / or mechanical grinding.

3. The method for preparing the sodium-ion battery cathode material metal-based sodium phosphate according to claim 1, characterized in that: said proton-containing H + The acid is an organic acid and / or an inorganic acid selected from one or more of formic acid, acetic acid, citric acid, malic acid, oxalic acid, lactic acid, phosphoric acid.

4. The method for preparing the sodium-ion battery cathode material metal-based sodium phosphate according to claim 3, characterized in that: In step S3, the drying method is flash drying, vacuum drying and / or spray drying; In step S4, the high-temperature sintering conditions are: a sintering temperature of 500-800℃ and a sintering time of 2-15h.

5. The method for preparing the sodium-ion battery cathode material metal-based sodium phosphate according to claim 4, characterized in that: The sodium source is an inorganic sodium salt and / or an organic sodium salt, and the inorganic sodium salt and / or the organic sodium salt is selected from one or two of sodium carbonate, sodium oxalate, sodium phosphate, sodium acetate and sodium citrate; The phosphorus source is selected from one or more of phosphoric acid, sodium phosphate, ammonium dihydrogen phosphate and sodium dihydrogen phosphate; The carbon source is an organic carbon source and / or an inorganic carbon source, and the organic carbon source and / or the inorganic carbon source is selected from one or more of citric acid, glucose, sucrose, carbon nanotubes, graphene and carbon black; The molar ratio of the organic carbon source to the sodium source is 0.1-1, or the weight ratio of the inorganic carbon source to the sodium source is 0.01-0.1; The molar ratio of the sodium source to the phosphorus source is 0.5-2.0:

1.

6. The method for preparing the sodium-ion battery cathode material metal-based sodium phosphate according to claim 5, characterized in that: The metal base is iron-based, manganese-based, cobalt-based, nickel-based or vanadium-based; When the metal base is iron-based, the metal M source is selected from one or more of iron phosphate, ferrous oxalate, iron oxide and magnetite; When the metal base is manganese-based, the metal M source is selected from one or more of manganese carbonate, manganese phosphate, manganese oxide, manganese sesquioxide and manganese sesquioxide; When the metal base is cobalt-based, the metal M source is selected from one or more of cobalt carbonate, cobalt oxalate, cobalt oxide and cobalt sesquioxide; When the metal base is nickel, the metal M source is selected from one or more of nickel carbonate, nickel hydroxide and nickel oxide; When the metal base is vanadium-based, the metal M source is selected from one or more of vanadium phosphate, vanadium oxide, vanadium sesquioxide and vanadium sesquioxide.

7. A sodium ion battery positive electrode material metal-based sodium phosphate salt prepared by the method of claim 1, characterized in that: The metal base is Fe, Mn, Co, Ni or V, When the metal base is Fe, Mn, Co or Ni, the structural formula of the metal base sodium phosphate salt is Na2MP2O7 or Na4M 3-x Φ x P4O 15 wherein Φ refers to a vacancy defect, and x has a value ranging from 0 to 0.15; When the metal base is V, the structural formula of the metal-based sodium phosphate salt is Na3V2(PO4)3.

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