Positive electrode material, positive electrode piece, sodium ion secondary battery and power consumption device

Abstract

To provide a positive electrode material to enhance the electrochemical properties of a sodium-ion secondary battery.SOLUTION: The positive electrode material contains a base material of Na2Fe2(SO4)3. The surface of the base material has poly-anion and carbon materials. The poly-anion material contains at least one of the following: a phosphate-based compound, a NASICON-based compound, a pyrophosphate-based compound, or a phosphoric acid fluoride-based compound. When the molar ratio of the base material to the poly-anion material is (1-a):a, 0<a≤0.1 is satisfied. When the mass percentage of the carbon material is C% relative to the mass of the positive electrode material, 0.5≤C≤5 is satisfied.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to the technical field of electrochemistry, and in particular to positive electrode materials, positive electrode strips, sodium ion secondary batteries and power consuming devices. [Background technology]

[0002] In recent years, secondary batteries such as sodium-ion secondary batteries have attracted widespread attention due to their abundant resources, low cost, environmental friendliness, and electrochemical properties similar to those of lithium-ion secondary batteries, providing a new option for electrochemical energy storage, especially for large-scale energy storage.

[0003] Na2Fe2(SO4)3 (abbreviated as NFSO) material is an ideal cathode material for sodium-ion secondary batteries because it has a high operating voltage of 3.8 V. However, NFSO material has problems with air sensitivity, and the material surface is prone to water absorption and oxidation. Therefore, new NFSO-based cathode materials are needed to minimize the risks of water absorption and oxidation and improve the electrochemical properties of sodium-ion secondary batteries. Summary of the Invention

[0004] The objective of the present invention is to provide a positive electrode material, a positive electrode strip, a sodium ion secondary battery, and a power consumption device, so as to improve the electrochemical properties of the sodium ion secondary battery. The specific technical solutions are as follows:

[0005] The first aspect of the present invention includes Na2Fe2(SO4)3 as a base material, and has a polyanion material and a carbon material on the surface of the base material. The polyanion material includes at least one of a phosphate-based compound, a NASICON-based compound, a pyrophosphate-based compound, and a fluorophosphate-based compound. When the molar ratio of the base material to the polyanion material is (1 - a):a, 0 < a ≤ 0.1. When the mass percentage of the carbon material with respect to the mass of the positive electrode material is C%, 0.5 ≤ C ≤ 5. A positive electrode material is provided. By adjusting the types of the base material and the polyanion material in the positive electrode material, and synergistically adjusting the molar ratio of the base material to the polyanion material and the mass percentage of the carbon material in the positive electrode material within the scope of the present invention, the positive electrode material can be made to have a high specific capacity and stability, so that the electrochemical characteristics of the sodium-ion secondary battery can be improved.

[0006] In some embodiments of the present invention, at least a part of the surface of the base material is coated with the polyanion material and the carbon material, and the coating degree of the polyanion material and the carbon material on the base material is 50% or more. Thereby, the stability of the coated NFSO against air can be improved, and the discharge specific capacity of NFSO can be increased.

[0007] In some embodiments of the present invention, when the specific surface area of the positive electrode material is BET m 2 / g, 0.5 ≤ BET ≤ 15. Thereby, on the one hand, the contact area between the positive electrode material and air can be reduced, so that the hygroscopicity of the positive electrode material can be reduced. On the other hand, the contact area between the positive electrode material and the electrolyte can be reduced, and the side reaction between the positive electrode material and the electrolyte can be reduced, so that the generation of gas in the sodium-ion secondary battery can be reduced.

[0008] In some embodiments of the present invention, the particle diameter Dv50 of the positive electrode material is 2 μm to 8 μm, which is advantageous for exhibiting the specific capacity and rate characteristics of the positive electrode material and for improving processing characteristics. If the particles are too small, stirring and dispersion is difficult, and if the particles are too large, it is disadvantageous for exhibiting the specific capacity and rate characteristics.

[0009] In some embodiments of the present invention, the tap density of the cathode material is ρ g / cm 3 When ρ≧0.8, the compressed density of the positive electrode material can be increased so as to increase the energy density of the sodium-ion secondary battery.

[0010] In some embodiments of the present invention, the phosphate-based compound comprises NaMPO4, where M is Fe or Mn, and the NASICON-based compound comprises Na x The pyrophosphate-based compound comprises Q2(XO4)3, where 1≦x≦4, Q comprises at least one of V, Fe, Ni, Mn, and Ti, and X comprises at least one of P, S, and Si, and the pyrophosphate-based compound is Na m Z(PO4) n (P2O7) q wherein 2≦m<10, 0≦n≦4, 1≦q<10, Z includes at least one of Fe, Mn, and Co, and the fluorophosphate-based compounds are NaVPO4F and Na3(VO 1-y PO4)2F 1+2y The phosphate compound selected from the above ranges contains at least one of the following: 0≦y≦1. The environmental stability of the substrate can be improved, and the Na content of the substrate can be reduced during charging and discharging. +The effect on the release of ions is small. By selecting a NASICON-based compound within the above range, not only can the environmental stability of the substrate be improved, but the effect on the ionic conductivity of the substrate be small and the thermal stability of the substrate can be improved. By selecting a pyrophosphate-based compound within the above range, not only can the environmental stability of the substrate be improved, but the cycle characteristics and thermal stability of the positive electrode material can be improved. By selecting a fluorophosphate-based compound within the above range, not only can the stability of the substrate against air be improved, but also the effect on the energy density of the substrate be small.

[0011] In some embodiments of the present invention, the polyanionic material has a Dv50 of 20 nm to 100 nm and a Dv99 of 20 nm to 200 nm. By adjusting the Dv50 and Dv99 of the polyanionic material within the ranges of the present invention, Na + Furthermore, adjusting the Dv50 and Dv99 of the polyanionic material within the ranges of the present invention is advantageous for the electrochemical properties of the polyanionic material itself and of NFSO to be exhibited, and the polyanionic material layer made of the polyanionic material can be made thinner and have a high coverage with respect to NFSO.

[0012] A second aspect of the present invention provides a cathode piece comprising the cathode material according to any one of the above embodiments, and thus the cathode piece provided by the present invention has good electronic and ionic conductivity.

[0013] In some embodiments of the present invention, the pressed density of the positive electrode pieces is 1000 kJ / cm 3 When the value is 0.01, CD≧1.6. Adjusting the compressed density of the positive electrode pieces to fall within the range of the present invention is advantageous in obtaining a sodium ion secondary battery having a high energy density.

[0014] The third aspect of the present invention provides a sodium-ion secondary battery including the positive electrode sheet described in any one of the above embodiments. Therefore, the sodium-ion secondary battery provided by the present invention has good electrochemical characteristics.

[0015] The fourth aspect of the present invention provides a power consumption device including the sodium-ion secondary battery described in any one of the above embodiments. Therefore, the power consumption device provided by the present invention has good use characteristics.

[0016] The beneficial effects of the present invention are as follows. The present invention provides a positive electrode material, a positive electrode sheet, a sodium-ion secondary battery, and a power consumption device. The positive electrode material includes Na2Fe2Fe2(SO4)3 as a base material, and has a polyanion material and a carbon material on the surface of the base material. The polyanion material includes at least one of a phosphate-based compound, a NASICON-based compound, a pyrophosphate-based compound, and a fluorophosphate-based compound. When the molar ratio of the base material to the polyanion material is (1 - a):a, 0 < a ≤ 0.1, and when the mass percentage of the carbon material with respect to the mass of the positive electrode material is C%, 0.5 ≤ C ≤ 5. By adjusting the types of the base material and the polyanion material in the positive electrode material, and synergistically adjusting the molar ratio of the base material to the polyanion material and the mass percentage of the carbon material in the positive electrode material within the scope of the present invention, the positive electrode material can be provided with high specific capacity and stability. Therefore, the electrochemical characteristics of the sodium-ion secondary battery can be improved. Of course, when implementing any one of the products or methods of the present invention, it is not necessarily required to achieve all of the above advantages simultaneously.

Embodiments for Carrying Out the Invention

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art based on the present invention shall be included in the protection scope of the present invention.

[0018] The first aspect of the present invention includes Na2Fe2(SO4)3 (i.e., NFSO) as a substrate, and has a polyanion material and a carbon material on the surface of the substrate. The polyanion material includes at least one of phosphate-based compounds, NASICON-based compounds, pyrophosphate-based compounds, and fluorophosphate-based compounds. When the molar ratio of the substrate to the polyanion material is (1 - a):a, 0 < a ≤ 0.1, and when the mass percentage of the carbon material is C% with respect to the mass of the positive electrode material, 0.5 ≤ C ≤ 5, a positive electrode material is provided. Specifically, the molar ratio of the substrate to the polyanion material may be 0.99:0.01, 0.97:0.03, 0.95:0.05, 0.93:0.07, 0.91:0.09, 0.9:0.1, or a range consisting of any two of the above values. The mass percentage C% of the carbon material may be 0.5%, 0.7%, 0.9%, 1%, 1.5%, 1.7%, 1.9%, 2%, 2.5%, 2.7%, 2.9%, 3%, 3.5%, 3.7%, 3.9%, 4%, 4.5%, 4.7%, 4.9%, 5%, or a range consisting of any two of the above values. Without being limited to any theory, if the molar ratio of the substrate to the polyanion material is too small (for example, less than 0.9:0.1), it will affect the energy density of the sodium-ion secondary battery. If the molar ratio of the substrate to the polyanion material is too large (for example, more than 0.99:0.01), the polyanion material cannot effectively coat the substrate, cannot effectively block the substrate from air, and cannot enhance the stability of the substrate. If the mass percentage of the carbon material is too small (for example, less than 0.5%), it will affect the electronic conductivity of NFSO. If the mass percentage of the carbon material is too large (for example, more than 5%), since the carbon material itself is inert, Na + ions cannot escape and be occluded, which affects the specific capacity of NFSO. By synergistically adjusting the molar ratio of the substrate to the polyanion material and the mass percentage of the carbon material within the scope of the present invention, the substrate can be effectively blocked from air, so that the electrochemical characteristics of the sodium-ion secondary battery can be enhanced. Moreover, NFSO can be given good electronic conductivity, which is advantageous for the exhibition of the specific capacity of NFSO.

[0019] The positive electrode material of the present invention has a polyanion material and a carbon material on the surface of a substrate. On the one hand, the polyanion material is also one of the positive electrode materials for sodium ion secondary batteries, so it has electronic conductivity and ionic conductivity, and has little effect on the electronic conductivity and ionic conductivity of NFSO. At the same time, it has a better barrier effect between NFSO and air, so it has better air stability. On the other hand, the polyanion material is Na + Because it is possible to release cations, it can function as an active material as a positive electrode material, and the effect on the specific capacity of NFSO is small. In addition, having a carbon material on the surface of the substrate can increase the electronic conductivity of the positive electrode material. The synergistic effect between the polyanion material and the carbon material is advantageous for the electrochemical properties of NFSO.

[0020] According to the above research, it has been found that in the positive electrode material provided by the present invention, the positive electrode material includes a substrate, and has a polyanion material and a carbon material on the surface of the substrate, and by synergistically adjusting the molar ratio between the substrate and the polyanion material and the mass percentage of the carbon material in the positive electrode material within the range of the present invention, the positive electrode material can be endowed with high specific capacity and stability, thereby improving the electrochemical properties of sodium ion secondary batteries.

[0021] In some embodiments of the present invention, at least a portion of the surface of the substrate is coated with a polyanionic material and a carbon material, and the coverage of the substrate with the polyanionic material and the carbon material is 50% or more. Exemplarily, the coverage of the substrate with the polyanionic material and the carbon material may be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or a range consisting of any two of the above values. The substrate may have the polyanionic material and the carbon material present on only a portion of its surface, or the entire surface. By adjusting the coverage of the polyanionic material and the carbon material on the substrate within the range of the present invention, the contact area between the NFSO and air is reduced, thereby improving the stability of the coated NFSO to air, reducing the hygroscopicity of the NFSO when left in air, reducing the amount of dissolved NFSO, and increasing the discharge specific capacity of the NFSO.

[0022] In some embodiments of the present invention, the specific surface area of ​​the positive electrode material is BET m 2 / g, 0.5≦BET≦15. Illustratively, the BET may be 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range consisting of any two of the above values. By adjusting the BET value within the range of the present invention, on the one hand, the contact area between the positive electrode material and air can be reduced, thereby reducing the hygroscopicity of the positive electrode material, and on the other hand, the contact area between the positive electrode material and the electrolyte can be reduced, thereby reducing side reactions between the positive electrode material and the electrolyte, thereby reducing gas generation in sodium ion secondary batteries. In some embodiments of the present invention, the particle diameter Dv50 of the positive electrode material is 2 μm to 8 μm. Illustratively, the particle diameter Dv50 of the positive electrode material may be 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, or a range consisting of any two of the above values. Adjusting the particle diameter Dv50 of the positive electrode material within the range of the present invention is advantageous for exhibiting the specific capacity and rate characteristics of the positive electrode material, as well as for improving processing characteristics. If the particles are too small, stirring and dispersion are difficult, and if the particles are too large, it is disadvantageous for exhibiting the specific capacity and rate characteristics.

[0023] In the present invention, Dv50 refers to the particle size at which the cumulative volume of the smallest particle size is 50% in the volume-based particle size distribution of the material.

[0024] In some embodiments of the present invention, the tap density of the positive electrode material is ρ g / cm 3 When the tap density of the positive electrode material is within the range of the present invention, the pressed density of the positive electrode material can be increased so as to increase the energy density of the sodium-ion secondary battery. Illustratively, ρ may be 0.8, 0.9, 1, 1.2, or a range consisting of any two of the above values. In some embodiments of the present invention, 0.9≦ρ≦1.2. By adjusting the tap density of the positive electrode material to fall within the range of the present invention, the pressed density of the positive electrode material can be increased so as to increase the energy density of the sodium-ion secondary battery.

[0025] In some embodiments of the present invention, the phosphate-based compound comprises NaMPO4, where M is Fe or Mn, and the NASICON-based compound comprises Na x The pyrophosphate-based compound includes Q2(XO4)3, where 1≦x≦4, Q includes at least one of V, Fe, Ni, Mn, and Ti, and X includes at least one of P, S, and Si. m Z(PO4) n (P2O7) q wherein 2≦m<10, 0≦n≦4, 1≦q<10, Z includes at least one of Fe, Mn, and Co, and the fluorophosphate compounds include NaVPO4F and Na3(VO 1-y PO4)2F 1+2yThe phosphate compound selected from the above ranges contains at least one of the following: 0≦y≦1. The environmental stability of the substrate can be improved, and the Na content of the substrate can be reduced during charging and discharging. + The effect on the release of sodium ions is small. By selecting a NASICON-based compound, which is a fast ion conductor of sodium, within the above range, such a compound has an open three-dimensional framework structure, high ionic conductivity, and good thermal stability, thereby not only improving the environmental stability of the substrate, but also having a small effect on the ionic conductivity of the substrate and improving the thermal stability of the substrate. By selecting a pyrophosphate-based compound within the above range, the pyrophosphate-based compound has good structural stability, thermal stability, and fast sodium ion mobility, thereby not only improving the environmental stability of the substrate but also improving the cycle characteristics and thermal stability of the positive electrode material. By selecting a fluorophosphate-based compound within the above range, the fluorophosphate-based compound has good stability against air and introduces F, which has strong electronegativity, into the material, thereby enhancing the inductive effect and increasing voltage. 3- It has a high voltage platform because it is used to replace O in the substrate. Having a fluorophosphate compound on the surface of the substrate not only increases the stability of the substrate against air, but also has little impact on the energy density of the substrate.

[0026] In some embodiments of the present invention, the Dv50 of the polyanionic material is 20 nm to 100 nm, and the Dv99 of the polyanionic material is 20 nm to 200 nm. By adjusting the Dv50 and Dv99 of the polyanionic material within the ranges of the present invention, Na + Furthermore, adjusting the Dv50 and Dv99 of the polyanionic material within the ranges of the present invention is advantageous for the electrochemical properties of the polyanionic material itself and of NFSO to be exhibited, and the polyanionic material layer made of the polyanionic material can be made thinner and have a high coverage with respect to NFSO.

[0027] In the present invention, Dv99 is the particle size that accounts for 99% cumulative volume from the smallest diameter side in the volume-based particle size distribution of a material.

[0028] The present invention does not impose any particular limitations on the method for producing a positive electrode material. For example, the method for producing a positive electrode material may include, but is not limited to, the following steps: dissolving raw materials in deionized water according to the stoichiometric ratio of NaFe(SO), adding an antioxidant and a carbon source to the solution, and stirring to obtain a precursor solution; spray-drying the precursor solution using a spray dryer to obtain a dried precursor; calcining, crushing, and sieving the dried precursor to obtain a NaFe(SO)-carbon composite material; weighing raw materials according to the stoichiometric ratio of a polyanionic material, mixing the weighed raw materials, and drying, calcining, crushing, and sieving the resulting mixture to obtain a polyanionic material; and mixing the NaFe(SO)-carbon composite material and the polyanionic material in a certain molar ratio and mechanically mixing them to obtain a positive electrode material. The present invention does not impose any particular limitations on the carbon source, as long as the objective of the present invention can be achieved. For example, the carbon source may be acetylene black. The present invention is not particularly limited to the antioxidant, as long as the object of the present invention can be achieved. For example, the antioxidant may be ascorbic acid (C6H8O6).

[0029] Generally, the specific surface area and coverage of the positive electrode material can be adjusted by adjusting the mechanical mixing time of the substrate and polyanionic material. For example, increasing the mechanical mixing time decreases the specific surface area, while decreasing the mechanical mixing time increases the specific surface area. Increasing the mechanical mixing time increases the coverage, while decreasing the mechanical mixing time decreases the coverage. The particle size Dv50 of the positive electrode material can be adjusted by changing the inlet temperature and / or feed rate of the spray dryer. For example, increasing the inlet temperature increases the particle size Dv50 of the positive electrode material, while decreasing the inlet temperature decreases the particle size Dv50 of the positive electrode material. Increasing the feed rate increases the particle size Dv50 of the positive electrode material, resulting in looser particles and a lower tap density. Decreasing the feed rate decreases the particle size Dv50 of the positive electrode material, resulting in a denser particle interior and an increased tap density.

[0030] The present invention is not particularly limited to a method for adjusting the particle size of a polyanionic material, as long as the object of the present invention can be achieved. For example, since the particle size of a polyanionic material generally increases with increasing baking temperature, the particle size of the polyanionic material can be adjusted by adjusting the baking temperature, and polyanionic materials with different average particle sizes can be obtained by passing the polyanionic material through a sieve.

[0031] The packing density of the positive electrode pieces generally increases with increasing cold pressure. In the present invention, the packing density of the positive electrode pieces can be adjusted by adjusting the cold pressure during the manufacturing process of the positive electrode pieces.

[0032] A second aspect of the present invention provides a cathode piece comprising the cathode material according to any one of the above embodiments, and thus the cathode piece provided by the present invention has good electronic and ionic conductivity.

[0033] In some embodiments of the present invention, the pressed density of the positive electrode pieces is preferably 1000 kJ / cm. 3When C D is 1.6 or greater, C D is 1.6 or greater. Illustratively, C D may be 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, or a range consisting of any two of the above values. In some embodiments of the present invention, 1.7≦C D ≦1.9. Adjusting the pressed density of the positive electrode pieces to fall within the range of the present invention is advantageous for obtaining a sodium-ion secondary battery with high energy density.

[0034] In the present invention, the positive electrode piece includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer provided on at least one surface of the positive electrode current collector" means that the positive electrode material layer may be provided on one surface of the positive electrode current collector in the thickness direction, or may be provided on both surfaces of the positive electrode current collector in the thickness direction. Note that the "surface" here may refer to the entire area of ​​the positive electrode current collector or a part of the area of ​​the positive electrode current collector, and the present invention is not particularly limited as long as the object of the present invention can be achieved.

[0035] The present invention is not particularly limited to the positive electrode current collector, as long as the object of the present invention can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector).

[0036] The positive electrode material layer further includes a conductive agent and a binder. The present invention does not limit the types of conductive agent and binder as long as the objectives of the present invention can be achieved. For example, the binder may include, but is not limited to, at least one of polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, polystyrene butadiene copolymer (styrene butadiene rubber), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethylcellulose, potassium carboxymethylcellulose, sodium hydroxymethylcellulose, and potassium hydroxymethylcellulose. The conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fiber, flake graphite, Ketjen black, graphene, metal material, and conductive polymer. The carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The carbon fiber may include, but is not limited to, vapor-grown carbon fiber (VGCF) and / or carbon nanofiber. The metal material may include, but is not limited to, metal powder and / or metal fiber. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, and silver. The conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, and polypyrrole. The present invention does not place any particular restrictions on the mass ratio of the positive electrode material, conductive agent, and binder in the positive electrode material layer, and those skilled in the art can select the appropriate ratio as long as the object of the present application can be achieved.

[0037] In the present invention, there are no particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the object of the present invention can be achieved. For example, the thickness of the positive electrode current collector is 6 μm to 12 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm. In the present invention, there are no particular limitations on the thickness of the positive electrode piece, as long as the object of the present invention can be achieved. For example, the thickness of the positive electrode piece is 36 μm to 250 μm.

[0038] The positive electrode piece may optionally include a conductive layer. The conductive layer is located between the positive electrode current collector and the positive electrode material layer. The present invention does not particularly limit the composition of the conductive layer, and the conductive layer may be a conductive layer common in the art. The conductive layer includes a conductive agent and a binder. The present invention does not particularly limit the conductive agent and binder in the conductive layer, and the conductive layer may be, for example, at least one of the above-mentioned conductive agents and binders.

[0039] The third aspect of the present invention provides a sodium ion secondary battery, comprising the positive electrode piece according to any one of the above embodiments, and therefore the sodium ion secondary battery provided by the present invention has good electrochemical properties.

[0040] In the present invention, the sodium ion secondary battery further includes a negative electrode piece. The negative electrode piece may include a negative electrode current collector and a negative electrode material layer formed on at least one surface of the negative electrode current collector. The present invention is not particularly limited to the negative electrode current collector, as long as the objective of the present invention can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector. The negative electrode material layer in the present invention includes a negative electrode active material, a conductive agent, and a thickener. The negative electrode active material of the present invention may include at least one of metal oxide, metal sulfide, metal phosphide, Sb-based negative electrode material, hard carbon, soft carbon, and metallic sodium. The metal oxide may include at least one of cobalt oxide, iron oxide, nickel oxide, and copper oxide. The metal sulfide may include at least one of tungsten disulfide, molybdenum disulfide, and tin disulfide. The metal phosphide may include at least one of lithium phosphide and sodium phosphide. The Sb-based negative electrode material may include at least one of an Sb-C composite material, a NiSb alloy, Sb2O3, and Sb2O4. In the present invention, there are no particular limitations on the thickness of the negative electrode current collector and the negative electrode material layer, as long as the objective of the present invention can be achieved. For example, the thickness of the negative electrode current collector is 6 μm to 10 μm, and the thickness of the negative electrode material layer is 30 μm to 120 μm. In the present invention, there are no particular limitations on the thickness of the negative electrode piece, as long as the objective of the present invention can be achieved. For example, the thickness of the negative electrode piece is 36 μm to 250 μm.

[0041] In the present invention, the sodium ion secondary battery further includes a separator that separates the positive and negative electrode pieces, prevents internal short circuits within the sodium ion secondary battery, allows free passage of electrolyte ions, and does not affect the electrochemical charge and discharge process. The present invention does not limit the type of separator as long as it achieves the objectives of the present invention. For example, the separator material may include at least one of polyolefin (PO)-based materials such as polyethylene (PE) and polypropylene (PP), polyester (e.g., polyvinyl terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, and aramid, but is not limited thereto. The type of separator may include at least one of woven film, nonwoven film, microporous film, composite film, compressed film, or spun film.

[0042] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a porous nonwoven fabric, film, or composite film. The material of the substrate layer may include at least one of polyethylene, polypropylene, polyvinyl terephthalate, and polyimide. Optionally, the substrate layer may be a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film. Optionally, a surface treatment layer may be provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or may be a layer formed by mixing a polymer and an inorganic material. For example, the inorganic layer may include inorganic particles and a binder. The inorganic particles are not particularly limited and may include, for example, at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is not particularly limited and may be, for example, at least one of the binders described above. The polymer layer includes a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0043] In the present invention, the sodium ion secondary battery further includes an electrolyte. The electrolyte includes a sodium salt and a non-aqueous solvent. The sodium salt may include at least one of NaPF6, NaOTF, NaFSI, NaTFSI, NaBF4, NaBOB, NaDFOB, and NaClO4. The present invention is not particularly limited by the concentration of the sodium salt in the electrolyte, as long as the objective of the present invention can be achieved. For example, the concentration of the sodium salt in the electrolyte is 0.9 mol / L to 1.5 mol / L. Illustratively, the concentration of the sodium salt in the electrolyte may be 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.3 mol / L, 1.5 mol / L, or a range consisting of any two of the above values. The present invention is not particularly limited by the non-aqueous solvent, as long as the objective of the present invention can be achieved. For example, the non-aqueous solvent may include at least one of a carbonate compound, a carboxylic acid ester compound, an ether compound, and another organic solvent, but is not limited thereto. The carbonate compound may include, but is not limited to, at least one of a linear carbonate compound, a cyclic carbonate compound, and a fluorocarbonate compound. The linear carbonate compound may include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and methyl ethyl carbonate (MEC). The cyclic carbonate may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinyl ethylene carbonate (VEC).The fluorocarbonate compound may include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate. The carboxylic acid ester compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, pentanolactone, and hexanolactone. The ether compound may include, but is not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. The other organic solvent may include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, and trioctyl phosphate.

[0044] The sodium ion secondary battery of the present invention further includes a packaging bag for containing the positive electrode pieces, separator, negative electrode pieces, and electrolyte, as well as other components known in the field of sodium ion secondary batteries. The present invention is not limited to the above other components. The packaging bag of the present invention is not particularly limited, and any packaging bag known in the field may be used as long as it can achieve the object of the present invention.

[0045] The manufacturing process for the sodium ion secondary battery of the present invention is well known to those skilled in the art, and the present invention is not particularly limited thereto. The manufacturing process for the sodium ion secondary battery of the present invention may include, but is not limited to, stacking positive electrode pieces, separators, and negative electrode pieces in this order, and optionally winding and folding the stack to obtain a wound electrode assembly, placing the electrode assembly in a packaging bag, pouring an electrolyte into the packaging bag, and sealing the bag to obtain a sodium ion secondary battery; or stacking positive electrode pieces, separators, and negative electrode pieces in this order, securing the four corners of the entire stack with tape to obtain a stacked electrode assembly, placing the electrode assembly in a packaging bag, pouring an electrolyte into the packaging bag, and sealing the bag to obtain a sodium ion secondary battery. Furthermore, to prevent internal pressure buildup and overcharging and discharging of the sodium ion secondary battery, an overcurrent protection element, lead plates, etc. may be provided in the packaging bag as needed.

[0046] A fourth aspect of the present invention provides a power consumption device including the sodium ion secondary battery according to any one of the above embodiments, and therefore the power consumption device provided by the present invention has good usage characteristics.

[0047] The power consuming device of the present invention is not particularly limited and may be any power consuming device known in the art. In some embodiments, the power consuming device may include, but is not limited to, a notebook computer, a pen-based computer, a mobile computer, an electronic book player, a mobile phone, a portable facsimile machine, a portable copier, a portable printer, a stereo headset, a video recorder, an LCD television, a portable vacuum cleaner, a portable CD player, a minidisc, a walkie-talkie, an electronic notebook, a calculator, a memory card, a portable tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash light, a camera, a large household storage battery, a sodium ion capacitor, and the like. [Example]

[0048] Hereinafter, the embodiments of the present invention will be described in more detail with reference to examples and comparative examples. Measurements and evaluations are carried out as follows. Unless otherwise specified, "parts" and "%" are based on mass.

[0049] Measurement method and equipment: Specific surface area measurement Based on the national standard "Measurement of the specific surface area of ​​solid materials by the gas adsorption BET method" (GB / T 19587-2017), the specific surface area of ​​the initial positive electrode material described in each example and comparative example was measured by nitrogen adsorption or desorption using a specific surface area analyzer (model: Tristar II 3020M).

[0050] Coverage measurement The initial cathode pieces described in each Example and Comparative Example were cut using an ion polishing machine (model: JEOL-IB-09010CP) to obtain cross sections. The cross sections were observed at an appropriate magnification (e.g., 1,000x to 30,000x) using a scanning electron microscope (SEM, model: Zeiss Sigma 02-33). The perimeter L1 of the substrate and the total perimeter L2 of the uncoated area were determined using Image J software, and the coverage M was calculated as 1-L2 / L1.

[0051] Measurement of particle size of positive electrode material Based on the national standard "Particle size distribution laser diffraction method" (GB / T19077-2016), the particle size distribution of the initial positive electrode material was measured using a Marvin particle size analyzer to obtain the median diameter Dv50 of the positive electrode material.

[0052] Measurement of particle size of polyanionic materials Based on the national standard "Particle size distribution by laser diffraction method" (GB / T19077-2016), the particle size distribution of the polyanionic material was measured using a Marvin particle size analyzer, and the particle sizes Dv50 and Dv99 of the polyanionic material were obtained.

[0053] Tapped density measurement 50 g of positive electrode material powder was weighed and placed in a measuring cylinder. The measuring cylinder containing the powder was then attached to a vibrating machine. After the vibration was complete, the volume was measured visually according to the surface height of the powder, and the tap density was calculated. The equipment used for the measurement was a Bettersize BT-301.

[0054] Measurement of compressed density Compressed density of positive electrode piece = Mass of positive electrode material layer per unit area (g / mm 2 ) / Thickness of the positive electrode material layer (mm) After disassembling the discharged sodium ion secondary battery to be measured, the positive electrode piece was removed and immersed in DMC (dimethyl carbonate) for 30 minutes to remove the electrolyte and by-products from the surface of the positive electrode piece. After that, the positive electrode piece was dried in a draft at a temperature of 25°C for 4 hours. The dried positive electrode piece was removed and the thickness of the positive electrode material layer on the positive electrode piece was measured with a micrometer. The thickness was 1540.25 mm 2 The positive electrode piece was punched out to obtain a small disk, and the mass m1 of this small disk was weighed on a balance. The mass m2 of a current collector with the same area as the small disk was also weighed, and the weight of the positive electrode material was calculated as m1 - m2. The compressed density of the positive electrode piece was then calculated based on the above formula.

[0055] Specific capacitance measurement In a drying chamber at 25°C and humidity ≤ 2%, the positive electrode materials described in each Example and Comparative Example, the binder polyvinylidene fluoride, and the conductive agent acetylene black were mixed in a mass ratio of 80:10:10. An appropriate amount of solvent N-methylpyrrolidone (NMP) was added and thoroughly stirred to form a homogeneous positive electrode slurry. The positive electrode slurry was applied to a 10 μm-thick aluminum foil (positive electrode current collector), dried, cold-pressed, and punched into small disks with a diameter of 14 mm to form positive electrode pieces. A coin-type half-cell was assembled using a sodium sheet as the negative electrode piece, a 12 μm-thick polypropylene separator, and a mixture of 1 mol / L NaPF6 and ethylene carbonate / propylene carbonate (EC / PC, 1:1 volume ratio) as the electrolyte.

[0056] A charge-discharge test was performed on the half-cell using a LAND battery test system (LAND CT2001A). The charge-discharge test was performed at a current density of 10 mA / g in the operating voltage range of 2.0 V to 4.2 V, and the initial discharge specific capacity was recorded. The discharge specific capacity of the positive electrode material in the initial state was measured and designated as C1, and the discharge specific capacity of the positive electrode material in the A2 state was measured and designated as C2.

[0057] Example 1 <Production of cathode materials> A solution of anhydrous Na2SO4 and FeSO4·7H2O was prepared in deionized water according to the stoichiometric ratio of Na2Fe2(SO4)3. C6H8O6 (3% by mass of C6H8O6 in the solution) and acetylene black (2:98 mass ratio of acetylene black to Na2Fe2(SO4)3) were added to the solution, and the mixture was stirred at 1500 r / min for 6 hours at room temperature to obtain the precursor solution. The precursor solution was spray-dried in a spray dryer at an inlet temperature of 180 °C, an outlet temperature of 80 °C, and a feed rate of 350 mL / h to obtain the dried precursor. The dried precursor was calcined at 350 °C for 24 hours under an argon gas atmosphere, crushed, and sieved to obtain a Na2Fe2(SO4)3-carbon composite (Na2Fe2(SO4)3 / C) with a Dv50 of 4.2 μm.

[0058] The raw materials Na2CO3, NH4VO3, and NH4H2PO4 were weighed according to the stoichiometric ratio of Na3V2(PO4)3 (NVP). The weighed raw materials were placed in a ball mill jar and wet-milled in a planetary ball mill at a ball mill speed of 300 r / min for 3 hours (using acetone as the ball milling medium). After the milling was completed, the material was placed in a vacuum drying box and dried at 60°C. It was then placed in a vacuum tube furnace filled with nitrogen gas and calcined at 350°C for 4 hours, then at 800°C for 8 hours. After that, the material was crushed and sieved to obtain an NVP polyanion material with a Dv50 of 30nm and a Dv99 of 200nm.

[0059] The Na2Fe2(SO4)3 / C and NVP polyanion material were mixed in a molar ratio of 0.95:0.05 and mechanically mixed for 60 minutes in a three-dimensional vibration ball mill at 1200 rpm to obtain a cathode material having NVP polyanion material and carbon material on its surface. The particle diameter Dv50 of the cathode material is shown in Table 1. The material at this time was considered to be in its initial state.

[0060] 10g of the above initial material is 2 The material was placed flat on a surface tray, and the surface tray containing the material was left in a humidity box at a temperature of 25°C and RH 50% for 10 days, and then removed.The material treated in the humidity box was designated as A2 state.

[0061] <Production of positive electrode pieces> In a drying chamber at 25°C and humidity ≦2%, the above initial cathode material, the binder polyvinylidene fluoride, and the conductive agent acetylene black were mixed in a mass ratio of 80:10:10, and the solvent N-methylpyrrolidone (NMP) was added. The mixture was thoroughly stirred to prepare a cathode slurry with a solids content of 68%. A 100 μm coating was applied to a 10 μm thick aluminum foil using a scraper, dried at 70°C for 12 hours, and then cold-pressed at a cold pressure of 50 T. The resulting mixture was then punched into small disks with a diameter of 14 mm to obtain initial cathode pieces.

[0062] In a drying chamber at 25°C and humidity ≦ 2%, the above-mentioned A2-state positive electrode material, polyvinylidene fluoride binder, and acetylene black conductive agent were mixed in a mass ratio of 80:10:10, and N-methylpyrrolidone (NMP) solvent was added. The mixture was thoroughly stirred to prepare a positive electrode slurry with a solids content of 68%. A 100 μm coating was applied to a 10 μm-thick aluminum foil using a scraper, dried at 70°C for 12 hours, and then cold-pressed at a cold pressure of 50 T. The resulting mixture was then punched into small disks with a diameter of 14 mm to form A2-state positive electrode pieces.

[0063] <Production of negative electrode pieces> The sodium sheet was punched out into a small disk with a diameter of 14 mm to form a negative electrode piece.

[0064] <Preparation of electrolyte> In a dry room at 25°C and humidity ≦ 2%, ethylene carbonate and propylene carbonate were mixed in a volume ratio of 1:1 as non-aqueous solvents, and then NaPF6 was added to the non-aqueous solvent, dissolved, and mixed uniformly to obtain an electrolyte solution with a molar concentration of 1 mol / L.

[0065] <Separator manufacturing> A porous polyvinyl film (Celgard) with a thickness of 12 μm was used.

[0066] <Manufacturing sodium ion coin-type half cells> The negative electrode piece, separator, and initial positive electrode piece were stacked in this order and assembled into a coin-type half cell in a glove box to obtain an initial coin-type half cell. The negative electrode piece, separator, and positive electrode piece in the A2 state were stacked in this order and assembled into a coin-type half cell in a glove box to obtain an A2-type coin-type half cell.

[0067] Example 2 The <Production of the positive electrode material> was the same as in Example 1, except that it was different from Example 1. <Production of cathode materials> A solution of anhydrous Na2SO4 and FeSO4·7H2O was prepared in deionized water according to the stoichiometric ratio of Na2Fe2(SO4)3. C6H8O6 (3% by mass of C6H8O6 in the solution) and acetylene black (2:98 mass ratio of acetylene black to Na2Fe2(SO4)3) were added to the solution, and the mixture was stirred at 1500 r / min for 6 hours at room temperature to obtain the precursor solution. The precursor solution was spray-dried in a spray dryer at an inlet temperature of 180 °C, an outlet temperature of 80 °C, and a feed rate of 350 mL / h to obtain the dried precursor. The dried precursor was calcined at 350 °C for 24 hours under an argon gas atmosphere, crushed, and sieved to obtain a Na2Fe2(SO4)3-carbon composite (Na2Fe2(SO4)3 / C) with a Dv50 of 4.2 μm.

[0068] The raw materials, FePO4 and NaPO4 from which water of crystallization had been removed, were weighed out according to the stoichiometric ratio of Na4Fe3(PO4)2P2O7 (N4FPP). The weighed raw materials were placed in a ball mill jar and wet-milled (using acetone as the ball milling medium) in a planetary ball mill at a ball mill speed of 300 r / min for 3 hours. After ball milling was completed, the material was placed in a vacuum drying box and dried at 60°C. It was then calcined in a vacuum tube furnace filled with nitrogen gas (calcination temperature 500°C, calcination time 10 hours), and then crushed and sieved to obtain N4FPP polyanion material with a Dv50 of 30 nm and a Dv99 of 200 nm.

[0069] The Na2Fe2(SO4)3 / C and N4FPP were mixed in a molar ratio of 0.95:0.05, mechanically mixed for 60 minutes in a three-dimensional vibration ball mill at 1200 rpm, and then calcined at 300°C for 2 hours to obtain a cathode material having N4FPP polyanion material and carbon material on its surface. The particle diameter Dv50 of the cathode material is shown in Table 1. The material at this time was considered to be in its initial state.

[0070] 10g of the above initial material is 2 The material was placed flat on a surface tray, and the surface tray containing the material was left in a humidity box at a temperature of 25°C and RH 50% for 10 days, and then removed.The material treated in the humidity box was designated as A2 state.

[0071] Example 3 The <Production of the positive electrode material> was the same as in Example 1, except that it was different from Example 1. <Production of cathode materials> A solution of anhydrous Na2SO4 and FeSO4·7H2O was prepared in deionized water according to the stoichiometric ratio of Na2Fe2(SO4)3. C6H8O6 (3% by mass of C6H8O6 in the solution) and acetylene black (2:98 mass ratio of acetylene black to Na2Fe2(SO4)3) were added to the solution, and the mixture was stirred at 1500 r / min for 6 hours at room temperature to obtain the precursor solution. The precursor solution was spray-dried in a spray dryer at an inlet temperature of 180 °C, an outlet temperature of 80 °C, and a feed rate of 350 mL / h to obtain the dried precursor. The dried precursor was calcined at 350 °C for 24 hours under an argon gas atmosphere, crushed, and sieved to obtain a Na2Fe2(SO4)3-carbon composite (Na2Fe2(SO4)3 / C) with a Dv50 of 4.2 μm.

[0072] The raw materials, FePO4 and NaPO4 from which water of crystallization had been removed, were weighed out according to the stoichiometric ratio of Na3Fe2(PO4)P2O7 (N3FPP). The weighed raw materials were placed in a ball mill jar and wet-milled (using acetone as the ball milling medium) in a planetary ball mill at a ball mill speed of 300 r / min for 3 hours. After ball milling was completed, the material was placed in a vacuum drying box and dried at 60°C. It was then calcined in a vacuum tube furnace filled with nitrogen gas (calcination temperature 500°C, calcination time 24 hours), and then crushed and sieved to obtain N3FPP polyanion material with a Dv50 of 30 nm and a Dv99 of 200 nm.

[0073] The Na2Fe2(SO4)3 / C and the N3FPP polyanion material were mixed in a molar ratio of 0.95:0.05 and mechanically mixed for 60 minutes in a three-dimensional vibration ball mill at 1200 rpm to obtain a cathode material having N3FPP polyanion material and carbon material on its surface. The particle diameter Dv50 of the cathode material is shown in Table 1. The material at this time was considered to be in its initial state.

[0074] 10g of the above initial material is 2The material was placed flat on a surface tray, and the surface tray containing the material was left in a humidity box at a temperature of 25°C and RH 50% for 10 days, and then removed.The material treated in the humidity box was designated as A2 state.

[0075] Example 4 <Production of positive electrode material> was the same as in Example 2, except that the molar ratio of Na2Fe2(SO4)3 / C to N4FPP was adjusted to 0.99:0.01.

[0076] Example 5 <Production of positive electrode material> was the same as in Example 2, except that the molar ratio of Na2Fe2(SO4)3 / C to N4FPP was adjusted to 0.9:0.1.

[0077] Example 6 In <Production of Positive Electrode Material>, the mechanical mixing time of Na2Fe2(SO4)3 / C and N4FPP was adjusted to 20 minutes, and parameters such as BET and coverage were adjusted as shown in Table 1, except that the procedure was the same as in Example 2.

[0078] Example 7 In <Production of Positive Electrode Material>, the mechanical mixing time of Na2Fe2(SO4)3 / C and N4FPP was adjusted to 100 minutes, thereby adjusting parameters such as BET and coverage as shown in Table 1, and the other processes were the same as in Example 2.

[0079] Example 8 In <Production of Positive Electrode Material>, the mechanical mixing time of Na2Fe2(SO4)3 / C and N4FPP was adjusted to 30 minutes, and parameters such as BET and coverage were adjusted as shown in Table 1, except that the procedure was the same as in Example 2.

[0080] Example 9 In <Production of Positive Electrode Material>, the mechanical mixing time of Na2Fe2(SO4)3 / C and N4FPP was adjusted to 10 minutes, and parameters such as BET and coverage were adjusted as shown in Table 1, except that the procedure was the same as in Example 2.

[0081] Example 10 In <Production of Positive Electrode Material>, the procedure was the same as in Example 2, except that the precursor solution was spray-dried using a spray dryer, and the particle diameter Dv50 of the positive electrode material was adjusted by adjusting the inlet temperature to 160°C and the feeding rate to 180 mL / h.

[0082] Example 11 <Production of positive electrode material> was the same as in Example 2, except that the mass ratio of acetylene black to Na2Fe2(SO4)3 was adjusted to 0.5:99.5.

[0083] Example 12 <Production of positive electrode material> was the same as in Example 2, except that the mass ratio of acetylene black to Na2Fe2(SO4)3 was adjusted to 5:95.

[0084] Example 13 In <Production of positive electrode material>, the inlet temperature was adjusted to 200°C, and the mechanical mixing time of Na2Fe2(SO4)3 / C and N4FPP was adjusted to 120 minutes, thereby adjusting the BET as shown in Table 1, and the procedure was the same as in Example 2.

[0085] Example 14 <Production of positive electrode material> was the same as in Example 2, except that the feeding rate was adjusted to 200 mL / h.

[0086] Example 15 The <Production of the positive electrode material> was the same as in Example 1, except that it was different from Example 1. <Production of cathode materials> A solution of anhydrous Na2SO4 and FeSO4·7H2O was prepared in deionized water according to the stoichiometric ratio of Na2Fe2(SO4)3. C6H8O6 (3% by mass of C6H8O6 in the solution) and acetylene black (2:98 mass ratio of acetylene black to Na2Fe2(SO4)3) were added to the solution, and the mixture was stirred at 1500 r / min for 6 hours at room temperature to obtain the precursor solution. The precursor solution was spray-dried in a spray dryer at an inlet temperature of 180 °C, an outlet temperature of 80 °C, and a feed rate of 350 mL / h to obtain the dried precursor. The dried precursor was calcined at 350 °C for 24 hours under an argon gas atmosphere, crushed, and sieved to obtain a Na2Fe2(SO4)3-carbon composite (Na2Fe2(SO4)3 / C) with a Dv50 of 4.2 μm.

[0087] NaMnPO4 was prepared using the ion exchange method. KMnPO4 solution was added to MnSO4 solution, and the mixture was maintained at 70°C for 48 hours. The resulting mixture was then filtered to obtain the precursor, KMnPO4·H2O. The precursor, KMnPO4·H2O, was then mixed with excess NaCH3COO·3H2O to obtain a mixture. This mixture was heated to 200°C at a rate of 10°C / min and calcined at this temperature for 15 hours. The mixture was then cooled to room temperature and the unreacted salts were washed with water to obtain a solid product. Finally, the solid product was washed with a small amount of ethanol, filtered, and air-dried for 5 hours to obtain a NaMnPO4 polyanionic material with a Dv50 of 30 nm and a Dv99 of 200 nm.

[0088] The Na2Fe2(SO4)3 / C and NaMnPO4 were mixed in a molar ratio of 0.95:0.05, mechanically mixed for 60 minutes in a three-dimensional vibration ball mill at 1200 rpm, and then calcined at 300°C for 2 hours to obtain a cathode material having a NaMnPO4 polyanion material and a carbon material on its surface. The particle diameter Dv50 of the cathode material is shown in Table 1. The material at this time was considered to be in its initial state.

[0089] 10g of the above initial material is 2The material was placed flat on a surface tray, and the surface tray containing the material was left in a humidity box at a temperature of 25°C and RH 50% for 10 days, and then removed.The material treated in the humidity box was designated as A2 state.

[0090] Example 16 The <Production of the positive electrode material> was the same as in Example 1, except that it was different from Example 1. <Production of cathode materials> A solution of anhydrous Na2SO4 and FeSO4·7H2O was prepared in deionized water according to the stoichiometric ratio of Na2Fe2(SO4)3. C6H8O6 (3% by mass of C6H8O6 in the solution) and acetylene black (2:98 mass ratio of acetylene black to Na2Fe2(SO4)3) were added to the solution, and the mixture was stirred at 1500 r / min for 6 hours at room temperature to obtain the precursor solution. The precursor solution was spray-dried in a spray dryer at an inlet temperature of 180 °C, an outlet temperature of 80 °C, and a feed rate of 350 mL / h to obtain the dried precursor. The dried precursor was calcined at 350 °C for 24 hours under an argon gas atmosphere, crushed, and sieved to obtain a Na2Fe2(SO4)3-carbon composite (Na2Fe2(SO4)3 / C) with a Dv50 of 4.2 μm.

[0091] The initial intercalation compound, Na2FeP2O7, was synthesized by conventional solid-state synthesis using the raw materials NaHCO3, FeC2O4·2H2O, and (NH4)2HPO4 (stoichiometric ratio 2:1:2) in accordance with the stoichiometric ratio of Na2FeP2O7. The mixture was then milled in a wet planetary ball mill (400 rpm) for 3 hours in acetone using Cr-SS stainless steel ball mill media and containers. After vacuum drying, the mixture was ground into agate mortar and pressed into cylindrical particles (12 mm diameter). The mixture was then annealed at 600°C (heating rate 10°C / min) in a tube furnace under a stable Ar / H2 (volume ratio 95:5) atmosphere to maintain a reducing atmosphere for 12 hours. The mixture was then cooled to room temperature and finally sieved to obtain a pure-phase Na2FeP2O7 polyanion material with a Dv50 of 30 nm and a Dv99 of 200 nm.

[0092] The Na2Fe2(SO4)3 / C and Na2FeP2O7 were mixed in a molar ratio of 0.95:0.05, mechanically mixed for 60 minutes in a three-dimensional vibration ball mill at 1200 rpm, and then calcined at 300°C for 2 hours to obtain a cathode material having a Na2FeP2O7 polyanion material and a carbon material on its surface. The particle diameter Dv50 of the cathode material is shown in Table 1. The material at this time was considered to be in its initial state. 10g of the above initial material is 2 The material was placed flat on a surface tray, and the surface tray containing the material was left in a humidity box at a temperature of 25°C and RH 50% for 10 days, and then removed.The material treated in the humidity box was designated as A2 state.

[0093] Example 17 The <Production of the positive electrode material> was the same as in Example 1, except that it was different from Example 1. <Production of cathode materials> A solution of anhydrous Na2SO4 and FeSO4·7H2O was prepared in deionized water according to the stoichiometric ratio of Na2Fe2(SO4)3. C6H8O6 (3% by mass of C6H8O6 in the solution) and acetylene black (2:98 mass ratio of acetylene black to Na2Fe2(SO4)3) were added to the solution, and the mixture was stirred at 1500 r / min for 6 hours at room temperature to obtain the precursor solution. The precursor solution was spray-dried in a spray dryer at an inlet temperature of 180 °C, an outlet temperature of 80 °C, and a feed rate of 350 mL / h to obtain the dried precursor. The dried precursor was calcined at 350 °C for 24 hours under an argon gas atmosphere, crushed, and sieved to obtain a Na2Fe2(SO4)3-carbon composite (Na2Fe2(SO4)3 / C) with a Dv50 of 4.2 μm.

[0094] Cetyltrimethylammonium bromide (abbreviated as CTAB, molecular formula CH3(CH2) 151.0 mol of NBr(CH3)3 was placed in a glass bottle with pure ethanol and deionized water (volume ratio 12:1). The solution was stirred for 90 minutes to form micelles. Sodium fluoride was then added, followed by oxalic acid dihydrate (C2H2O4 2H2O) and vanadium oxide (VO5). Oxalic acid acts as a reducing agent, and the addition of oxalic acid results in the formation of V2O5. 5+ V 3+ The solution was stirred for 30 minutes. NH4H2PO4:V2O5 (2:1 molar ratio) was then added to the solution. The green solution was magnetically stirred at room temperature for 24 hours to obtain a homogeneous mixture of precursors. The solvent was then evaporated using a rotary evaporator (model: Heidolph Hei-VAP Expert Control mL / G3). The dried green solid was polished and then calcined in a tube furnace (model: Carbolite Limited, UK) at 780 °C under an argon gas atmosphere for 6 hours. Finally, it was sieved to obtain a NaVPO4F polyanion material with a Dv50 of 30 nm and a Dv99 of 200 nm.

[0095] The Na2Fe2(SO4)3 / C and NaVPO4F were mixed in a molar ratio of 0.95:0.05, mechanically mixed for 60 minutes in a three-dimensional vibration ball mill at 1200 rpm, and then calcined at 300°C for 2 hours to obtain a cathode material having a NaVPO4F polyanion material and a carbon material on its surface. The particle diameter Dv50 of the cathode material is shown in Table 1. The material at this time was considered to be in its initial state.

[0096] 10g of the above initial material is 2 The material was placed flat on a surface tray, and the surface tray containing the material was left in a humidity box at a temperature of 25°C and RH 50% for 10 days, and then removed.The material treated in the humidity box was designated as A2 state.

[0097] Example 18 <Production of positive electrode material> was the same as in Example 2, except that the feeding rate was adjusted to 450 mL / h.

[0098] Example 19 In <Production of Positive Electrode Pieces>, the same procedure as in Example 1 was carried out, except that the cold pressure was adjusted to 45 T to adjust the compressed density of the positive electrode pieces as shown in Table 1.

[0099] Comparative Example 1 The <Production of the positive electrode material> was the same as in Example 1, except that it was different from Example 1. <Production of cathode materials> A solution of the raw materials, anhydrous Na2SO4 and FeSO4·7H2O, was prepared in deionized water according to the stoichiometric ratio of Na2Fe2(SO4)3. C6H8O6 (3% by mass of C6H8O6 in the solution) and acetylene black (2:98 mass ratio of acetylene black to Na2Fe2(SO4)3) were added to the solution and stirred at 1500 r / min for 6 hours at room temperature to obtain the precursor solution. The precursor solution was spray-dried in a spray dryer at an inlet temperature of 180 °C, an outlet temperature of 80 °C, and a feed rate of 350 mL / h to obtain the dried precursor. The dried precursor was calcined at 350 °C for 24 hours under an argon gas atmosphere, crushed, and sieved to obtain a Na2Fe2(SO4)3-carbon composite (Na2Fe2(SO4)3 / C) with a Dv50 of 4.2 μm. This material was designated as the initial state.

[0100] 10g of the above initial material is 2 The material was placed flat on a surface tray, and the surface tray containing the material was left in a humidity box at a temperature of 25°C and RH 50% for 10 days, and then removed.The material treated in the humidity box was designated as A2 state.

[0101] Comparative Example 2 In <Production of Positive Electrode Material>, the same procedure as in Example 2 was carried out except that the mass ratio of acetylene black to Na2Fe2(SO4)3 was adjusted to 0.1:99.9.

[0102] Comparative Example 3 In <Production of Positive Electrode Material>, the same procedure as in Example 2 was carried out except that the mass ratio of acetylene black to Na2Fe2(SO4)3 was adjusted to 7:93.

[0103] Comparative Example 4 <Production of positive electrode material> was the same as in Example 2, except that the molar ratio of Na2Fe2(SO4)3 / C to N4FPP was adjusted to 0.8:0.2. Table 1 shows the manufacturing parameters and electrical characteristic parameters of each of the examples and comparative examples.

[0104] [Table 1] Note: In Table 1, " / " indicates that there is no related manufacturing parameter.

[0105] Referring to Table 1, as can be seen from Examples 1 to 19 and Comparative Examples 1 to 4, sodium ion secondary batteries produced by having the polyanionic material and carbon material of the present invention on the surface of a substrate and adjusting the types of substrate and polyanionic material in the positive electrode material, the molar ratio between the substrate and polyanionic material, and the mass percentage of the carbon material within the ranges of the present invention, have high specific capacity. This demonstrates that sodium ion secondary batteries produced using the positive electrode material provided by the present invention have good electrochemical properties.

[0106] The degree of coverage of the substrate with the polyanionic material and carbon material, the specific surface area of ​​the positive electrode material, the particle diameter Dv50 of the positive electrode material, the tap density of the positive electrode material, and the compressed density of the positive electrode pieces generally affect the electrochemical properties of a sodium-ion secondary battery. As can be seen from Examples 1 to 19, adjusting the degree of coverage of the substrate with the polyanionic material and carbon material, the specific surface area of ​​the positive electrode material, the particle diameter Dv50 of the positive electrode material, the tap density of the positive electrode material, and the compressed density of the positive electrode pieces within the ranges of the present invention is advantageous in further improving the electrochemical properties of a sodium-ion secondary battery.

[0107] Specific surface area usually correlates to some extent with particle size. Materials synthesized under the same conditions have larger specific surface areas as particle size decreases. In the present invention, the surface of NFSO contains a polyanionic material and a carbon material. The polyanionic material is a nanomaterial, and the nanomaterial particles are small and have a large specific surface area, while the carbon material has a large specific surface area. When the mixing time is short, the coverage of the polyanionic material and the carbon material on NFSO is low. The polyanionic material and the carbon material exist independently of NFSO, and their specific surface areas are relatively large. Therefore, the specific surface areas of both the polyanionic material and the carbon material have a dominant influence on the measurement results of the specific surface area of ​​the positive electrode material.

[0108] The above description is merely a preferred embodiment of the present application, and is not intended to limit the scope of protection of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application are included in the scope of protection of the present application.

Claims

1. A positive electrode material, The positive electrode material is a base material, Na ２ Fe ２ (SO ４ ) ３ Including, a polyanionic material and a carbon material on the surface of the substrate; the polyanion material includes at least one of a phosphate-based compound, a NASICON-based compound, a pyrophosphate-based compound, and a fluorophosphate-based compound; The phosphate-based compound includes NaMPO 4 , where M is Fe or Mn; The NASICON-based compound includes Na x Q 2 (XO 4 ) 3 , where 1≦x≦4, Q includes at least one of V, Fe, Ni, Mn, and Ti, and X includes at least one of P, S, and Si; The pyrophosphate-based compound includes Na m Z(PO 4 ) n (P 2 O 7 ) q , where 2≦m<10, 0≦n≦4, and 1≦q<10, and Z includes at least one of Fe, Mn, and Co; The fluorophosphate-based compound includes at least one of NaVPO 4 F and Na 3 (VO 1-y PO 4 )F 1+2y , where 0≦y≦1; when the molar ratio of the substrate to the polyanionic material is (1-a):a, 0<a≦0.1; A positive electrode material, characterized in that, when the mass percentage of the carbon material is C % with respect to the mass of the positive electrode material, 0.5≦C≦5.

2. 2. The cathode material according to claim 1, wherein at least a portion of a surface of the substrate is coated with the polyanionic material and the carbon material, and a coverage of the substrate with the polyanionic material and the carbon material is 50% or more.

3. The specific surface area of ​​the positive electrode material is BET m ２ 2. The cathode material according to claim 1, wherein BET satisfies 0.5≦BET≦15 when .beta. / g.

4. 2. The positive electrode material according to claim 1, wherein the particle diameter Dv50 of the positive electrode material is 2 μm to 8 μm.

5. The tap density of the positive electrode material is ρ g / cm ３ 2. The cathode material according to claim 1, wherein ρ≧0.8 when

6. 2. The positive electrode material according to claim 1, wherein the polyanionic material has a Dv50 of 20 nm to 100 nm and a Dv99 of 20 nm to 200 nm.

7. A positive electrode piece comprising the positive electrode material according to any one of claims 1 to 6.

8. The compressed density of the positive electrode piece is CD g / cm ３ 8. The cathode piece of claim 7, wherein CD≧1.

6.

9. A sodium ion secondary battery comprising the positive electrode piece according to claim 8.

10. A power consuming device comprising the sodium ion secondary battery according to claim 9.

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