Pure phase polyanion type sulfate sodium ion battery positive electrode material and its manufacturing method

Abstract

A pure-phase polyanionic sulfate sodium-ion battery cathode material is disclosed. The general formula of the pure-phase polyanionic sulfate sodium-ion battery cathode material is NaxMyAzSO4, where M is one or more of Mn, Fe, Co, Ni, Cu, and / or Zn, A is one or more of Li, K, and / or Na, and the range of values that each variable can take is 0.75 ≦ x ≦ 0.85, 0.52 ≦ y ≦ 0.58, 0 < z ≦ 0.1, and x + 2y + z = 2. The pure-phase polyanionic sulfate sodium-ion battery cathode material has the characteristics of good structural stability, excellent rate performance, good cycle performance, and a simple and low-cost manufacturing method.

Description

[Technical Field]

[0001] The present invention relates to the technical field of sodium ion batteries, and specifically refers to a pure phase polyanion type sulfate sodium ion battery positive electrode material and its preparation method. [Background technology]

[0002] The establishment of carbon dioxide emission reduction targets has promoted the rapid development of the new energy industry. In recent years, the number of new energy electric vehicles has increased year by year, and this rapid development has been accompanied by innovations in secondary battery technology. Due to their technological maturity and high energy conversion efficiency, secondary batteries have become the ideal choice in the current power and energy storage fields. There are various types of secondary batteries, including lead-acid batteries, nickel-metal hydride batteries, nickel-cadmium batteries, alkaline manganese batteries, and lithium / sodium-ion batteries. However, due to their process maturity, environmental adaptability, and energy conversion efficiency, lithium / sodium-ion batteries will undoubtedly become the mainstream choice in the new energy field in the future.

[0003] However, lithium-ion batteries are heavily dependent on lithium resources, and due to limited reserves of lithium resources, they cannot meet the low-cost requirements of the energy storage field in the long term.On the other hand, sodium resources are abundant and low-cost, and the operating principle of sodium-ion batteries is the same as that of lithium-ion batteries, so they have the potential and feasibility to partially replace lithium-ion batteries.

[0004] Currently, sodium-ion cathode materials include layered oxides, Prussian blue and its analogs, and polyanion-type materials, each with its own advantages and disadvantages. For example, layered oxides often undergo multiple phase transitions during the redox-induced sodium desorption / insertion process, which can cause structural collapse and affect the cycling stability of the material. Furthermore, during the synthesis of Prussian blue-type materials, a large amount of crystalline water is present within the crystal lattice, which decomposes under high potentials to generate large amounts of gas, leading to battery swelling and failure. Compared to these two types of materials, polyanion-type materials have good potential for use as sodium battery cathode materials due to their stable 3D framework structure and excellent electrochemical properties.

[0005] Currently, the main polyanion-type materials include V-based phosphates such as Na3V2(PO4)3 and NaVPO4F, and Fe-based phosphates such as Na2FeP2O7, Na4Fe3(PO4)2P2O7, and NaFePO4. V-based phosphates have a high redox potential (3.4-3.6 V) and adequate discharge capacity, but the toxicity of V makes large-scale use of V-based materials difficult. On the other hand, Fe-based phosphates are non-toxic, non-polluting, and low cost, providing a basis for large-scale use. However, Fe-based phosphates have drawbacks such as a relatively low redox potential (~3 V) and low energy density of the battery system. Based on this, iron-based sulfate cathode materials, which offer extremely low cost and high operating potential, are considered the most ideal cathode material for sodium-ion batteries. However, iron-based sulfate cathode materials suffer from drawbacks such as low conductivity, strong hygroscopicity, poor storage stability, poor stability, and poor rate performance.

[0006] Patent Document 1 discloses a sodium ion cathode material and its manufacturing method and use, which improves the performance deficiencies of the iron sulfate cathode material by combining a carbonaceous material with an iron sulfate cathode material in the prior art. The sodium ion cathode material includes a core and a coating layer covering the core surface. The core includes a polyanion type sodium ion cathode material, whose general formula is Na x M yThe formula is (SO4)3, where M is one or a combination of at least two of Ni, Co, Mn, Fe, Cu, and Zn, and 2≦x≦3, 1.5≦y≦2, and x+2y=6. The coating layer material includes a carbon material coated with a conductive polymer. This improves the electronic conductivity of the material, increases the crystal lattice parameter of the coated material, contributes to stabilizing the material structure, and effectively improves the capacity, rate performance, and cycle performance of the sodium-ion positive electrode material. However, from the crystal lattice perspective, the disclosed polyanion-type sodium-ion positive electrode material belongs to the monoclinic Pnma space group and exhibits good crystallinity, but also contains many impurities. For example, the XRD pattern in Figure 1 shows multiple diffraction peaks (theoretical two main diffraction peaks) in the 2θ range of 20-24°. A search revealed that some of these diffraction peaks (e.g., 21° and 23°) are due to the Na6Fe(SO4)4 impurity. The presence of this impurity indicates an imbalance in the ratio of Na, Fe, and SO4. Furthermore, the presence of these impurities not only reduces the content of the active material and is detrimental to the capacity per weight, but also brings about uncertainty in the discharge potential, rate performance, cycle performance, etc., due to the uncontrollable nature of the impurities, which is detrimental to actual large-scale production and use. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Chinese Patent Publication No. 114400309 Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to provide a pure-phase polyanion-type sulfate sodium ion battery positive electrode material having good structural stability, excellent rate performance, good cycle performance, and a simple and low-cost manufacturing method, and a manufacturing method thereof. [Means for solving the problem]

[0009] The present invention can be realized by the following technical solutions.

[0010] The present invention discloses a pure phase polyanion type sulfate sodium ion battery positive electrode material, the general formula of which is Na x M y A z SO4, where M is one or more of Mn, Fe, Co, Ni, Cu and / or Zn, A is one or more of Li, K and / or Na, and the ranges that each variable can take are 0.75≦x≦0.85, 0.52≦y≦0.58, 0.75≦x≦0.85, 0.52≦y≦0.58, 0.75≦x≦0.85, 0.52≦y≦0.58, 0.75≦y ... <z≦0.1、x+2y+z=2である。

[0011] Furthermore, the pure phase polyanionic sulfate sodium ion battery cathode material is in the triclinic P21 / c space group.

[0012] Furthermore, in the site division, Na, S, and O are located in the 4e site, M and A are located in the 8f site, Na / S-O4 is a tetrahedron, and M / A-O6 is an octahedron, and the tetrahedron and octahedron are connected by common points / common faces.

[0013] Furthermore, in the triclinic P21 / c space group, the range of variation of the crystal lattice parameters is 11.10 Å≦a≦12.20 Å, 11.40 Å≦b≦12.60 Å, 5.20 Å≦c≦6.90 Å, 910.01 Å 3 ≦V≦940.4 Å 3 is.

[0014] Another aspect of the present invention claims protection for a method for preparing the above-mentioned pure phase polyanion-based sulfate sodium ion battery cathode material, the method comprising the steps of uniformly mixing a sodium source, a metal source, an alkali metal source, an anion source and a carbon source in a stoichiometric ratio, and sintering the mixture under an inert atmosphere to prepare the corresponding pure phase polyanion-based sulfate sodium ion battery cathode material.

[0015] Further, the sodium source is an inorganic sodium source and / or an organic sodium source, and the inorganic sodium source is one or more of sodium hydroxide, sodium chloride, sodium sulfate, sodium nitrate, and / or sodium carbonate, and the organic sodium source is one or more of sodium formate, sodium acetate, sodium ethoxide, and / or sodium benzoate.

[0016] Furthermore, the metal source is a manganese source, an iron source, a cobalt source, a nickel source, a copper source, and / or a zinc source, the manganese source is one or more of manganese sulfate, manganese carbonate, manganese chloride, and / or manganese acetate, the iron source is one or more of ferrous sulfate, iron chloride, ferrous oxide, and / or ferrous acetate, the cobalt source is one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, and / or cobalt acetate, the nickel source is one or more of nickel sulfate, nickel nitrate, nickel chloride, and / or nickel acetate, the copper source is one or more of copper sulfate, copper chloride, and / or copper acetate, and the zinc source is one or more of zinc sulfate, zinc chloride, and / or zinc acetate.

[0017] Further, the alkali metal source is a sodium source, a lithium source and / or a potassium source.

[0018] Furthermore, the sodium source as the alkali metal source is an inorganic sodium source and / or an organic sodium source, and the inorganic sodium source is one or more of sodium hydroxide, sodium chloride, sodium sulfate, sodium nitrate, and / or sodium carbonate, and the organic sodium source is one or more of sodium formate, sodium acetate, sodium ethoxide, and / or sodium benzoate.

[0019] Additionally, the lithium source is one or more of lithium sulfate, lithium carbonate, and / or lithium hydroxide.

[0020] Furthermore, the potassium source is one or more of potassium sulfate, potassium hydroxide, potassium chloride, potassium nitrate, and / or potassium carbonate.

[0021] Furthermore, the anion source is one or more of sulfuric acid, sodium sulfate, ammonium ferrous sulfate, ferrous sulfate, and / or ammonium sulfate.

[0022] Furthermore, the carbon source is one or more of carbon materials such as SurpP, KB, carbon nanotubes, graphene, glucose, citric acid, and / or sucrose.

[0023] Furthermore, the method of uniformly mixing is a liquid-phase mixing method or a solid-phase mixing method, the inert atmosphere is argon, nitrogen, or a mixed gas of argon-hydrogen or nitrogen-hydrogen, and the sintering temperature is 200 - 400 °C.

Advantages of the Invention

[0024] The positive electrode material of the polyanion-type sodium sulfate ion battery and its manufacturing method of the present invention have the following beneficial effects.

[0025] The positive electrode material Na x M y A z SO4 of the polyanion-type sodium sulfate ion battery of the present invention shows a single pure phase within the range of 0.75 ≦ x ≦ 0.85, 0.52 ≦ y ≦ 0.58, 0 < z ≦ 0.1, and x + 2y + z = 2, and has optimal electrochemical properties.

[0026] The material is in the triclinic system and the P21 / c space group. Since M and A in its structure occupy the same 8f site, the Coulomb force between adjacent M-M is effectively weakened, the structural stability of the material is improved, and it has a high sodium deinsertion / insertion rate.

[0027] The material has a high discharge potential (3.7V vs Na / Na +) and sodium storage capacity (110 mAh / g), and exhibits excellent long cycle stability (100% retention for 1000 cycles at 10 C rate) and excellent rate performance (60 mAh / g at 30 C rate).

[0028] The manufacturing process of this material is simple, compatible with conventional solid-phase, liquid-phase and solid-liquid mixing methods, and the raw materials are abundant and the material cost is low. [Brief explanation of the drawings]

[0029] [Figure 1] Figure 1 shows the XRD pattern of the Na0.82Fe0.55Na0.08SO4 material. [Figure 2] Figure 2 is an SEM photograph of the Na0.82Fe0.55Na0.08SO4 material. [Figure 3] Figure 3 shows the initial charge-discharge curve of the Na0.82Fe0.55Na0.08SO4 electrode. [Figure 4] Figure 4 shows the rate performance curve of the Na0.82Fe0.55Na0.08SO4 electrode. [Figure 5] Figure 5 shows the cycle curves of the Na0.82Fe0.55Na0.08SO4 electrode. [Figure 6] Figure 6 shows the XRD pattern of the Na0.85Fe0.53Li0.09SO4 material. [Figure 7] Figure 7 shows the XRD pattern of the Na0.78Fe0.57K0.08SO4 material. [Figure 8] Figure 8 shows the XRD pattern of the Na0.92Fe0.50K0.08SO4 material. [Figure 9] Figure 9 shows the XRD pattern of the Na0.74Fe0.59Li0.08SO4 material. [Figure 10] Figure 10 shows the initial charge-discharge curves of the Na0.92Fe0.50K0.08SO4 / Na0.74Fe0.59Li0.08SO4 electrode. [Figure 11] Figure 11 shows the cycle curves of the Na0.92Fe0.50K0.08SO4 / Na0.74Fe0.59Li0.08SO4 electrode. DETAILED DESCRIPTION OF THE INVENTION

[0030] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the product of the present invention will be described in more detail below with reference to examples and drawings.

[0031] The present invention discloses a pure phase polyanion type sulfate sodium ion battery positive electrode material, the general formula of which is Na x M y A z SO4, where M is one or more of Mn, Fe, Co, Ni, Cu and / or Zn, A is one or more of Li, K and / or Na, and the ranges that each variable can take are 0.85≦x≦0.95, 0.52≦y≦0.58, 0.85≦x≦0.95, 0.52≦y≦0.58, 0.85≦x≦0.95, 0.52≦y≦0.58, 0.85≦y ... <z≦0.1、x+2y+z=2である。

[0032] Furthermore, the pure phase polyanionic sulfate sodium ion battery cathode material is in the triclinic P21 / c space group.

[0033] Furthermore, in the site division, Na, S, and O are located in the 4e site, M and A are located in the 8f site, Na / S-O4 is a tetrahedron, and M / A-O6 is an octahedron, and the tetrahedron and octahedron are connected by common points / common faces.

[0034] Furthermore, in the triclinic P21 / c space group, the range of variation of the crystal lattice parameters is 11.10 Å≦a≦12.20 Å, 11.40 Å≦b≦12.60 Å, 5.20 Å≦c≦6.90 Å, 910.01 Å 3 ≦V≦940.4 Å 3 is.

[0035] Another aspect of the present invention claims protection for a method for preparing the above-mentioned pure phase polyanion-based sulfate sodium ion battery cathode material, the method comprising the steps of uniformly mixing a sodium source, a metal source, an alkali metal source, an anion source and a carbon source in a stoichiometric ratio, and sintering the mixture under an inert atmosphere to prepare the corresponding pure phase polyanion-based sulfate sodium ion battery cathode material.

[0036] Further, the sodium source is an inorganic sodium source and / or an organic sodium source, and the inorganic sodium source is one or more of sodium hydroxide, sodium chloride, sodium sulfate, sodium nitrate, and / or sodium carbonate, and the organic sodium source is one or more of sodium formate, sodium acetate, sodium ethoxide, and / or sodium benzoate.

[0037] Furthermore, the metal source is a manganese source, an iron source, a cobalt source, a nickel source, a copper source, and / or a zinc source, the manganese source is one or more of manganese sulfate, manganese carbonate, manganese chloride, and / or manganese acetate, the iron source is one or more of ferrous sulfate, iron chloride, ferrous oxide, and / or ferrous acetate, the cobalt source is one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, and / or cobalt acetate, the nickel source is one or more of nickel sulfate, nickel nitrate, nickel chloride, and / or nickel acetate, the copper source is one or more of copper sulfate, copper chloride, and / or copper acetate, and the zinc source is one or more of zinc sulfate, zinc chloride, and / or zinc acetate.

[0038] Further, the alkali metal source is a sodium source, a lithium source and / or a potassium source.

[0039] Furthermore, the sodium source as the alkali metal source is an inorganic sodium source and / or an organic sodium source, and the inorganic sodium source is one or more of sodium hydroxide, sodium chloride, sodium sulfate, sodium nitrate, and / or sodium carbonate, and the organic sodium source is one or more of sodium formate, sodium acetate, sodium ethoxide, and / or sodium benzoate.

[0040] Additionally, the lithium source is one or more of lithium sulfate, lithium carbonate, and / or lithium hydroxide.

[0041] Additionally, the potassium source may be one or more of potassium sulfate, potassium hydroxide, potassium chloride, potassium nitrate, and / or potassium carbonate.

[0042] Additionally, the anion source may be one or more of sulfuric acid, sodium sulfate, ferrous ammonium sulfate, ferrous sulfate, and / or ammonium sulfate.

[0043] Furthermore, the carbon source is one or more of carbon materials such as SurpP, KB, carbon nanotubes, graphene, glucose, citric acid, and / or sucrose.

[0044] Furthermore, the method for uniformly mixing is a liquid phase mixing method or a solid phase mixing method, the inert atmosphere is argon, nitrogen or argon-hydrogen, or nitrogen-hydrogen mixed gas, and the sintering temperature is 200 to 400°C.

[0045] Specifically, the liquid-phase mixing method involves dissolving a sodium source, a metal source, an alkali metal source, an anion source, and a carbon source in an organic or inorganic solvent and drying the resulting solution to obtain a homogeneously mixed precursor. The drying method can be one or more selected from high-temperature drying methods such as air drying and spray drying, low-temperature drying methods such as freeze drying, and low-pressure drying methods such as vacuum drying. The inorganic solvent is water, and the organic solvent is one or more of methanol, ethanol, acetonitrile, etc.

[0046] Specifically, the solid-phase mixing method refers to the uniform mixing of the sodium source, metal source, alkali metal source, anion source, and carbon source by mechanical force, which can be achieved by techniques such as a sand mill or a ball mill.

[0047] Example 1

[0048] In this example, Na 0.82 Fe 0.55 Na 0.08 This is about the synthesis of SO4 and its electrochemical properties, specifically as follows:

[0049] Sodium hydroxide, ferrous acetate, sodium acetate, and ammonium sulfate were added to a ball mill in a molar ratio of 0.82:0.55:0.05:1. KB was added as a carbon source, and 20 mL of acetone was poured into the ball mill (under N2 protection). The ball-to-material ratio was 20:1, the rotation speed was 400 r / min, and the total ball milling time was 7 h with 10 min of rest time. Finally, the ball-milled precursor gel was heated to 100 °C at a heating rate of 1 °C / min under an Ar / H2 (90:10) atmosphere for 3 h, then to 200 °C at a heating rate of 1 °C / min for 3 h, and then to 350 °C at a heating rate of 1 °C / min and held at this temperature for 5 h. After cooling to room temperature, Na was added. 0.82 Fe 0.55 Na 0.08 The SO4 material was extracted. 0.82 Fe 0.55 Na 0.08 The XRD pattern of the SO4 powder is shown, and the diffraction peaks are in perfect agreement with the theoretically calculated diffraction peak positions, indicating a single pure phase with high crystallinity. In the pure phase structure, ions move easily along specific crystal planes, resulting in high speed and excellent rate performance. Furthermore, the pure phase structure contains a very high proportion of active material, and its capacity utilization rate is close to the actual theoretical capacity. Figure 2 shows the Na 0.82 Fe 0.55 Na 0.08The SO4 material shows a morphology, forming nano-sized aggregated particles. The small particle size can effectively shorten the distance of the sodium ion deintercalation process and improve the sodium deintercalation rate of the material.

[0050] Na 0.82 Fe 0.55 Na 0.08 SO4, AB, and PVDF were mixed in a mass ratio of 7:2:1 to prepare a uniform slurry. The black slurry was then applied to aluminum foil using a 150 μm four-sided applicator, and the resulting film was dried in a vacuum oven at 100°C for 2 hours. The electrode film was punched into a 0.6 mm radius disk using a punching machine. A CR2016 button battery was assembled in a glove box using metallic sodium as the counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%)+5% FEC as the electrolyte, and a PP / PE / PP three-layer separator.

[0051] A constant current charge / discharge test was carried out on the button battery, and the current density was set to 0.1 C (1 C = 100 mAh / g). 0.82 Fe 0.55 Na 0.08 The initial charge-discharge curve of the SO4 electrode shows that the reversible specific capacity was 110 mAh / g and the average discharge potential was 3.7 V within the voltage range of 2.0 to 4.3 V. 0.82 Fe 0.55 Na 0.08 Figure 5 shows the rate performance of the SO4 electrode, which exhibited a capacity of 60 mAh / g at a rate of 30 C. 0.82 Fe 0.55 Na 0.08 This demonstrates the long-term cycle stability of the SO4 electrode, with almost no capacity decay even after 1000 cycles at 10 C, demonstrating excellent structural stability.

[0052] Example 2

[0053] In this example, Na 0.85 Fe 0.53 Li 0.09This is about the synthesis of SO4 and its electrochemical properties, specifically as follows:

[0054] Lithium sulfate, ferrous acetate, and sodium sulfate were added to a ball mill container in a molar ratio of 0.045:0.53:0.425. KB was added as a carbon source, and 20 mL of acetone was poured into the ball mill container (under N2 protection). The ball-to-material ratio was 20:1, the rotation speed was 400 r / min, and the total ball milling time was 7 h with 10 min of rest time. Finally, the ball-milled precursor gel was heated to 100 °C at a heating rate of 1 °C / min under an Ar / H2 (90:10) atmosphere for 3 h, then heated to 200 °C at a heating rate of 1 °C / min for 3 h, and then heated to 350 °C at a heating rate of 1 °C / min and held at this temperature for 5 h. After cooling to room temperature, Na was added. 0.85 Fe 0.53 Li 0.09 The SO4 material was extracted. 0.85 Fe 0.53 Li 0.09 The XRD pattern of the SO4 powder is shown, and the diffraction peaks are in perfect agreement with the theoretically calculated diffraction peak positions, indicating that it is a single pure phase with high crystallinity.

[0055] Na 0.85 Fe 0.53 Li 0.09 SO4, AB, and PVDF were mixed in a mass ratio of 7:2:1 to prepare a uniform slurry. The black slurry was then applied to aluminum foil using a 150 μm four-sided applicator, and the resulting film was dried in a vacuum oven at 100°C for 2 hours. The electrode film was punched into a 0.6 mm radius disk using a punching machine. A CR2016 button battery was assembled in a glove box using metallic sodium as the counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%)+5% FEC as the electrolyte, and a PP / PE / PP three-layer separator.

[0056] A constant current charge / discharge test was carried out on the button battery, with the current density set to 0.1 C (1 C = 100 mAh / g). Within the voltage range of 2.0 to 4.3 V, the reversible specific capacity was 109 mAh / g.

[0057] Example 3

[0058] In this example, Na 0.78 Fe 0.57 K 0.08 This is about the synthesis of SO4 and its electrochemical properties, specifically as follows:

[0059] Potassium sulfate, ferrous sulfate, and sodium sulfate were added to a ball mill container in a molar ratio of 0.04:0.285:0.39. KB was added as a carbon source, and 20 mL of acetone was poured into the ball mill container (under N2 protection). The ball-to-material ratio was 20:1, the rotation speed was 400 r / min, and the total ball milling time was 7 h with 10 min of rest time. Finally, the ball-milled precursor gel was heated to 100 °C at a heating rate of 1 °C / min under an Ar / H2 (90:10) atmosphere for 3 h, then heated to 200 °C at a heating rate of 1 °C / min for 3 h, and then heated to 350 °C at a heating rate of 1 °C / min and held at this temperature for 5 h. After cooling to room temperature, Na was added. 0.78 Fe 0.57 Na 0.08 The SO4 material was extracted. 0.78 Fe 0.57 Na 0.08 The XRD pattern of the SO4 powder is shown, and the diffraction peaks are in perfect agreement with the theoretically calculated diffraction peak positions, indicating that it is a single pure phase with high crystallinity.

[0060] Na 0.78 Fe 0.57 Na 0.08SO4, AB, and PVDF were mixed in a mass ratio of 7:2:1 to prepare a uniform slurry. The black slurry was then applied to aluminum foil using a 150 μm four-sided applicator, and the resulting film was dried in a vacuum oven at 100°C for 2 hours. The electrode film was punched into a 0.6 mm radius disk using a punching machine. A CR2016 button battery was assembled in a glove box using metallic sodium as the counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%)+5% FEC as the electrolyte, and a PP / PE / PP three-layer separator.

[0061] A constant current charge / discharge test was carried out on the button battery, with the current density set to 0.1 C (1 C = 100 mAh / g). Within the voltage range of 2.0 to 4.3 V, the reversible specific capacity was 109 mAh / g.

[0062] Example 4

[0063] In this example, Na 0.86 Fe 0.52 K 0.1 This is about the synthesis of SO4 and its electrochemical properties, specifically as follows:

[0064] Sulfuric acid, sodium carbonate, ferrous oxalate, and potassium chloride were added to a flask in a molar ratio of 1.0:0.425:0.52:0.1, and 50 mL of deionized water was added to the flask. Glucose was used as the carbon source and ascorbic acid as the antioxidant. After complete dissolution, a light green solution was obtained. The solution was spray-dried. The inlet air temperature was set to 250°C, the peristaltic pump rotation speed was 15 r / min, and the exhaust temperature was controlled at 110°C to obtain a pure white precursor powder. Finally, under an Ar atmosphere, the temperature was raised to 200°C at a rate of 1°C / min for 3 hours, then raised to 350°C at a rate of 2°C / min and maintained at this temperature for 6 hours. After cooling to room temperature, a black NaCl solution was obtained. 0.86 Fe 0.52 Na 0.1 The SO4 material was removed.

[0065] Na 0.86 Fe 0.52Na 0.1 SO4, surpP, and PVDF were mixed uniformly in a mass ratio of 8:1:1, then coated onto aluminum foil using a 200μm four-sided coater. The resulting electrode film was then dried in a vacuum oven at 100℃ for 3 hours. The electrode film was punched into a 0.6mm radius disk using a punching machine. CR2016 button batteries were assembled in a glove box using metallic sodium as the counter electrode, 1mol / L NaClO4EC+DEC (1:1vol%)+5% FEC as the electrolyte, and a glass fiber separator.

[0066] A constant current charge / discharge test was carried out on the button battery, with the current density set to 0.1 C (1 C = 100 mAh / g). Within the voltage range of 2.0 to 4.3 V, the reversible specific capacity was 105 mAh / g.

[0067] Example 5

[0068] In this example, Na 0.83 Fe 0.58 Li 0.01 This is about the synthesis of SO4 and its electrochemical properties, specifically as follows:

[0069] Ferrous sulfate, lithium carbonate, ammonium sulfate, and sodium hydroxide were added to a beaker in a molar ratio of 0.58:0.01:0.42:0.83 and dissolved in 50 mL of deionized water. After complete dissolution, a pale green solution was obtained. The solution was then spray-dried. The inlet air temperature was set to 250 °C, the peristaltic pump rotation speed was 15 r / min, and the exhaust temperature was controlled at 110 °C to obtain a pure white precursor powder. The precursor powder was then dried in a vacuum dryer at 200 °C for 10 hours. The precursor powder and KB were then mixed and subjected to high-energy ball milling. The ball-to-material ratio was 20:1, the frequency was 50 Hz, and the time was approximately 3 hours. The homogeneously mixed black powder material was then heated to 200 °C at a heating rate of 1 °C / min under a N2 atmosphere, held at this temperature for 3 hours, and then heated to 350 °C at a heating rate of 2 °C / min and held at this temperature for 6 hours. After cooling to room temperature, black Na 0.83 Fe 0.58 Na0.01 The SO4 material was removed.

[0070] Na 0.83 Fe 0.58 Li 0.01 SO4, KB, and PVDF were mixed uniformly in a mass ratio of 8:1:1 and applied to aluminum foil using a 100μm four-sided applicator. The resulting electrode film was then dried in a vacuum oven at 100℃ for 3 hours. The electrode film was punched into a 0.6mm radius disk using a punching machine. A CR2016 button battery was assembled in a glove box using metallic sodium as the counter electrode, 1mol / L NaClO4EC+DEC (1:1vol%)+5% FEC as the electrolyte, and a PP / PE / PP three-layer separator.

[0071] A constant current charge / discharge test was carried out on the button battery, with the current density set to 0.1 C (1 C = 100 mAh / g). Within the voltage range of 2.0 to 4.3 V, the reversible specific capacity was 107 mAh / g.

[0072] Example 6

[0073] In this example, Na 0.86 Mn 0.54 Na 0.06 This is about the synthesis of SO4 and its electrochemical properties, specifically as follows:

[0074] Manganese acetate, sodium acetate, ammonium sulfate, and sodium chloride were added to a beaker in a molar ratio of 0.54:0.86:1.0:0.06 and dissolved in 50 mL of deionized water. After complete dissolution, a pale green solution was obtained. The solution was then spray-dried. The inlet air temperature was set to 250 °C, the peristaltic pump rotation speed was 15 r / min, and the exhaust temperature was controlled at 110 °C to obtain a pure white precursor powder. The precursor powder was then dried in a vacuum dryer at 200 °C for 10 hours. The precursor powder and KB were then mixed and subjected to high-energy ball milling. The ball-to-material ratio was 20:1, the frequency was 50 Hz, and the time was approximately 3 hours. The homogeneously mixed black powder material was then heated to 200 °C at a heating rate of 1 °C / min under a N2 atmosphere, held at this temperature for 3 hours, and then heated to 350 °C at a heating rate of 2 °C / min and held at this temperature for 6 hours. After cooling to room temperature, black Na 0.86 Mn 0.54 Na 0.06 The SO4 material was removed.

[0075] Na 0.86 Mn 0.54 Na 0.06 SO4, KB, and PVDF were mixed uniformly in a mass ratio of 8:1:1 and applied to aluminum foil using a 100μm four-sided applicator. The resulting electrode film was then dried in a vacuum oven at 100℃ for 3 hours. The electrode film was punched into a 0.6mm radius disk using a punching machine. A CR2016 button battery was assembled in a glove box using metallic sodium as the counter electrode, 1mol / L NaClO4EC+DEC (1:1vol%)+5% FEC as the electrolyte, and a PP / PE / PP three-layer separator.

[0076] A constant current charge / discharge test was carried out on the button battery, with the current density set to 0.1 C (1 C = 100 mAh / g). Within the voltage range of 2.0 to 4.8 V, the reversible specific capacity was 100 mAh / g.

[0077] Example 7

[0078] In this example, Na 0.88 Co 0.55 Li0.02 This is about the synthesis of SO4 and its electrochemical properties, specifically as follows:

[0079] Sodium hydroxide, cobalt sulfate, lithium acetate, and ammonium sulfate were added to a ball mill in a molar ratio of 0.88:0.55:0.02:0.45. KB was added as a carbon source, and 20 mL of acetone was poured into the ball mill (under N2 protection). The ball-to-material ratio was 20:1, the rotation speed was 400 r / min, and the total ball milling time was 7 h with 10 min of rest time. Finally, the ball-milled precursor gel was heated to 100 °C at a heating rate of 1 °C / min under an Ar / H2 (90:10) atmosphere for 3 h, then to 200 °C at a heating rate of 1 °C / min for 3 h, and then to 350 °C at a heating rate of 1 °C / min and held at this temperature for 5 h. After cooling to room temperature, Na was added. 0.88 Co 0.55 Li 0.02 The SO4 material was removed.

[0080] Na 0.88 Co 0.55 Li 0.02 SO4, KB, and PVDF were mixed uniformly in a mass ratio of 8:1:1 and applied to aluminum foil using a 100μm four-sided applicator. The resulting electrode film was then dried in a vacuum oven at 100℃ for 3 hours. The electrode film was punched into a 0.6mm radius disk using a punching machine. A CR2016 button battery was assembled in a glove box using metallic sodium as the counter electrode, 1mol / L NaClO4EC+DEC (1:1vol%)+5% FEC as the electrolyte, and a PP / PE / PP three-layer separator.

[0081] A constant current charge / discharge test was carried out on the button battery, with the current density set to 0.1 C (1 C = 100 mAh / g). Within the voltage range of 2.0 to 4.8 V, the reversible specific capacity was 90 mAh / g.

[0082] In the present invention, the structural formula of the pure phase polyanion type sulfate sodium ion battery positive electrode material is Na x M y A zIt is SO4, where the range of x is 0.85 ≦ x ≦ 0.95, the range of y is 0.52 ≦ y ≦ 0.58, A is an alkali metal element such as Li, K, Na, etc., the range of z is 0 < z ≦ 0.1, and x + 2y + z = 2. The manufacturing method is to uniformly mix a sodium source, a metal source, an alkali metal source, an anion source (SO4 2- ) and a carbon source in a certain ratio, and sinter in an inert atmosphere to obtain the corresponding material. This material has a high redox potential (3.7V vs Na / Na + ) and a sodium storage capacity. Due to the stable 3D open framework structure and large sodium ion diffusion channels, this material exhibits excellent long cycle stability and outstanding rate performance. Compared with other sodium-ion battery cathode materials, the elements Na, Fe, alkali metal elements, and SO4 contained in this material are rich in natural resources, have low mining costs, and Na x M y A z SO4 material is promising as an industrialized sodium-ion battery cathode material because of its simple manufacturing process and excellent performance.

[0083] Comparative Example 1

[0084] This example relates to the synthesis of Na 0.92 Fe 0.50 K 0.08 SO4 and its electrochemical properties, specifically as follows.

[0085] Sodium sulfate, ferrous sulfate, and potassium sulfate were added to a ball mill container in a molar ratio of 0.46:0.50:0.04, KB was added as a carbon source, and 20 mL of acetone was poured into the above ball mill container (under N2 protection). The ratio of balls to materials was 20:1, the rotation speed was 400 r / min, the total ball milling time was 7 hours, and the intermittent stop time was 10 minutes. Finally, the ball milled precursor gel was held at 100 °C for 3 hours at a heating rate of 1 °C / min in an Ar / H2 (90:10) atmosphere, then held at 200 °C for 3 hours at a heating rate of 1 °C / min, and then heated to 350 °C at a heating rate of 1 °C / min and held at this temperature for 5 hours. After cooling to room temperature, Na 0.92 Fe0.50 Na 0.08 The SO4 material was extracted. 0.92 Fe 0.50 K 0.08 The XRD pattern of SO4 powder shows that the diffraction peaks are consistent with the theoretical diffraction curve, with many impurity peaks in the 2θ range of 20-25°. A search revealed that these corresponded to the diffraction peaks of the Na6Fe(SO4)4 impurity phase, indicating an imbalance in the ratios of elements such as Na, Fe, and SO4. The presence of impurity phases reduces the active material fraction and reduces the specific capacity of the material. On the other hand, the presence of impurities hinders ion diffusion at the material interface, increasing electrode polarization and reducing rate performance.

[0086] Na 0.92 Fe 0.50 Na 0.08 SO4, AB, and PVDF were mixed in a mass ratio of 7:2:1 to prepare a uniform slurry. The black slurry was then applied to aluminum foil using a 150 μm four-sided applicator, and the resulting film was dried in a vacuum oven at 100°C for 2 hours. The electrode film was punched into a 0.6 mm radius disk using a punching machine. A CR2016 button battery was assembled in a glove box using metallic sodium as the counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%)+5% FEC as the electrolyte, and a PP / PE / PP three-layer separator.

[0087] A constant current charge / discharge test was carried out on the button battery, and the current density was set to 0.1 C (1 C = 100 mAh / g). 0.92 Fe 0.50 K 0.08 The initial charge-discharge curve of the SO4 electrode is shown. Within the voltage range of 2.0 to 4.3 V, the reversible specific capacity is 92 mAh / g and the average discharge potential is 3.5 V. Compared to Example 1, the capacity and potential are lower, indicating that the presence of impurity phases adversely affects the electrochemical properties of the material. 0.92 Fe 0.50 K 0.08The cycle stability of the SO4 electrode is shown, and the capacity retention of this electrode after 500 cycles at 10C is only 85%, indicating that the presence of impurity phases reduces the stability of the material interface, leading to severe cycle degradation.

[0088] Comparative Example 2

[0089] In this example, Na 0.74 Fe 0.59 Li 0.08 This is about the synthesis of SO4 and its electrochemical properties, specifically as follows:

[0090] Sodium sulfate, ferrous sulfate, and lithium sulfate were added to a ball mill container in a molar ratio of 0.37:0.59:0.04. KB was added as a carbon source, and 20 mL of acetone was poured into the ball mill container (under N2 protection). The ball-to-material ratio was 20:1, the rotation speed was 400 r / min, and the total ball milling time was 7 h with 10 min of rest time. Finally, the ball-milled precursor gel was heated to 100 °C at a heating rate of 1 °C / min under an Ar / H2 (90:10) atmosphere for 3 h, then heated to 200 °C at a heating rate of 1 °C / min for 3 h, and then heated to 350 °C at a heating rate of 1 °C / min and held at this temperature for 5 h. After cooling to room temperature, Na was added. 0.74 Fe 0.59 Li 0.08 The SO4 material was extracted. 0.74 Fe 0.59 Li 0.08 The XRD pattern of SO4 powder shows that the diffraction peaks are consistent with the theoretical diffraction curve, with many impurity peaks in the 2θ range of 20-25°. Search results revealed that these corresponded to the diffraction peaks of Na6Fe(SO4)4 and FeSO4 impurity phases, indicating an imbalance in the ratios of elements such as Na, Fe, and SO4. On the one hand, the presence of impurity phases reduces the proportion of active material and decreases the specific capacity of the material. On the other hand, the presence of impurities hinders ion diffusion at the material interface, increasing electrode polarization and reducing rate performance.

[0091] Na 0.74 Fe0.59 Li 0.08 SO4, AB, and PVDF were mixed in a mass ratio of 7:2:1 to prepare a uniform slurry. The black slurry was then applied to aluminum foil using a 150 μm four-sided applicator, and the resulting film was dried in a vacuum oven at 100°C for 2 hours. The electrode film was punched into a 0.6 mm radius disk using a punching machine. A CR2016 button battery was assembled in a glove box using metallic sodium as the counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%)+5% FEC as the electrolyte, and a PP / PE / PP three-layer separator.

[0092] A constant current charge / discharge test was carried out on the button battery, and the current density was set to 0.1 C (1 C = 100 mAh / g). 0.74 Fe 0.59 Li 0.08 The initial charge-discharge curve of the SO4 electrode shows that within the voltage range of 2.0 to 4.3 V, the reversible specific capacity is 80 mAh / g and the average discharge potential is 3.45 V. Compared to Example 1, the capacity and potential are lower, indicating that the presence of impurity phases adversely affects the electrochemical properties of the material. 0.74 Fe 0.59 Li 0.08 The cycle stability of the SO4 electrode is shown, and the capacity retention of this electrode after 500 cycles at 10C is only 78%, indicating that the presence of impurity phases reduces the stability of the material interface, leading to severe cycle degradation.

[0093] It is necessary to explain and emphasize that, although the above examples only illustrate the case where M is Fe and A is Na, based on the fundamentally similar properties, the case where M is Mn, Co, Ni, Cu and / or Zn and A is Li and / or K also has similarly predictable performance and effects and falls within the scope of the present invention.

[0094] The above-mentioned embodiments are merely specific embodiments of the present invention, and although the description is specific and detailed, it should not be construed as limiting the scope of the claims of the present invention. Furthermore, a person skilled in the art can make some modifications and improvements without departing from the spirit of the present invention, and all of these obvious substitutions belong to the scope of the claims of the present invention.

Claims

1. A pure phase polyanionic sulfate sodium ion battery cathode material, the general formula of which is Na ｘ M ｙ A ｚ SO ４ wherein M is one or more of Mn, Fe, Co, Ni, Cu, and / or Zn, and A is one or more of Li, K, and / or Na, and the ranges that each variable can take are 0.75≦x≦0.85, 0.52≦y≦0.58, 0<z≦0.1, and x+2y+z=2.

2. 2. The pure phase polyanion-type sulfate sodium ion battery cathode material according to claim 1, wherein the pure phase polyanion-type sulfate sodium ion battery cathode material is in the triclinic P21 / c space group.

3. In the site division, Na, S, and O are located at the 4e site, M and A are located at the 8f site, and Na / S-O ４ is a tetrahedron, M / A-O ６ is an octahedron, and the tetrahedron and the octahedron are connected by common points / common faces.

4. In the triclinic P21 / c space group, the ranges of variation of the crystal lattice parameters are 11.10 angstroms≦a≦12.20 angstroms, 11.40 angstroms≦b≦12.60 angstroms, 5.20 angstroms≦c≦6.90 angstroms, and 910.01 angstroms. ３ ≦V≦940.4 Å ３ 4. The pure phase polyanionic sulfate sodium ion battery cathode material of claim 3, wherein:

5. 5. A method for producing a pure phase polyanion-type sulfate sodium-ion battery cathode material according to any one of claims 1 to 4, comprising the steps of: uniformly mixing a sodium source, a metal source, an alkali metal source, an anion source, and a carbon source in a stoichiometric ratio; and sintering the mixture under an inert atmosphere to produce a corresponding pure phase polyanion-type sulfate sodium-ion battery cathode material.

6. 6. The method for producing a pure phase polyanionic sulfate sodium ion battery positive electrode material according to claim 5, wherein the sodium source is an inorganic sodium source and / or an organic sodium source, the inorganic sodium source being one or more of sodium hydroxide, sodium chloride, sodium sulfate, sodium nitrate and / or sodium carbonate, and the organic sodium source being one or more of sodium formate, sodium acetate, sodium ethoxide and / or sodium benzoate.

7. the metal source is a manganese source, an iron source, a cobalt source, a nickel source, a copper source, and / or a zinc source; the manganese source is one or more of manganese sulfate, manganese carbonate, manganese chloride, and / or manganese acetate; the iron source is one or more of ferrous sulfate, ferrous chloride, ferrous oxide, and / or ferrous acetate; the cobalt source is one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, and / or cobalt acetate; the nickel source is one or more of nickel sulfate, nickel nitrate, nickel chloride, and / or nickel acetate; the copper source is one or more of copper sulfate, copper chloride, and / or copper acetate; 6. The method for producing a pure phase polyanionic sulfate sodium ion battery positive electrode material according to claim 5, wherein the zinc source is one or more of zinc sulfate, zinc chloride and / or zinc acetate.

8. the alkali metal source is a sodium source, a lithium source, and / or a potassium source; the sodium source is an inorganic sodium source and / or an organic sodium source, the inorganic sodium source being one or more of sodium hydroxide, sodium chloride, sodium sulfate, sodium nitrate and / or sodium carbonate, and the organic sodium source being one or more of sodium formate, sodium acetate, sodium ethoxide and / or sodium benzoate; the lithium source is one or more of lithium sulfate, lithium carbonate, and / or lithium hydroxide; 6. The method for producing a pure phase polyanionic sulfate sodium ion battery cathode material according to claim 5, wherein the potassium source is one or more of potassium sulfate, potassium hydroxide, potassium chloride, potassium nitrate and / or potassium carbonate.

9. the anion source is one or more of sulfuric acid, sodium sulfate, ferrous ammonium sulfate, ferrous sulfate, and / or ammonium sulfate; 6. The method for producing a pure phase polyanion sulfate sodium ion battery positive electrode material according to claim 5, wherein the carbon source is one or more of SurpP, KB, carbon nanotubes, graphene, glucose, citric acid and / or sucrose.

10. The method for producing a pure phase polyanion type sulfate sodium ion battery positive electrode material according to claim 5, characterized in that the uniform mixing method is a liquid phase mixing method or a solid phase mixing method, the inert atmosphere is argon, nitrogen or argon-hydrogen, nitrogen-hydrogen mixed gas, and the sintering temperature is 200-400°C.

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