Positive electrode material and preparation method and application thereof

Abstract

The invention discloses a positive electrode material and a preparation method and application thereof and belongs to the technical field of positive electrode materials. The positive electrode material disclosed by the invention comprises a positive electrode active substance, wherein the positive electrode active substance comprises xNa < 3.64-a > Fe < 2.64-a > Ma (PO4) < 1.64-b > (BO3) P2O7. YNa < 4-2c > Fe < 2 + c > (P2O7) 2; in the formula, Na < 3.64-a > Fe < 2.64-a > Ma (PO4) < 1.64-b > (BO3) P2O7 is an NFPP superlattice solid solution phase; m comprises one or more of La, Ce and Mo, x is more than or equal to 80 wt% and less than or equal to 100 wt%, y is more than or equal to 0 wt% and less than or equal to 20 wt%, and 0 lt; a is less than 0.1, 0lt; blt; 0 < = c < = 1, and x + y = 100 wt%. The capacity and the working voltage of the positive electrode material are remarkably improved.

Description

Technical Field

[0001] This application relates to the technical field of cathode materials, and specifically relates to a cathode material, a preparation method thereof, and their uses. Background Art

[0002] Sodium iron pyrophosphate phosphate (NFPP) cathode material has become a research hotspot for the cathode active material of sodium ion energy storage, especially large-scale energy storage batteries, in the battery cell application system due to its advantages such as stable structure, good thermal stability, long cycle life, and good safety performance.

[0003] However, there are 4 sodium sites and 3 iron sites with different chemical environments and crystal structures in NFPP, which leads to easy polarization of the NFPP material during charge and discharge, resulting in a decrease in reversible capacity and discharge voltage.

[0004] In view of this, how to effectively reduce the sodium ion diffusion polarization of the NFPP material, so as to efficiently prepare a sodium secondary battery with high reversible capacity and high working voltage has become a research direction worthy of attention. Summary of the Invention

[0005] This application provides a cathode active material, a preparation method thereof, and their uses to solve the problem that the sodium ion mixed phosphate material in the prior art is prone to polarization, resulting in a decrease in the reversible capacity and working voltage of the sodium secondary battery.

[0006] In the first aspect, this application provides a cathode material, including a cathode active substance, and the cathode active substance includes xNa 3.64-a Fe 2.64-a M a (PO4) 1.64-b (BO3) b P2O7·yNa 4-2c Fe 2+c (P2O7)2;

[0007] In the formula: Na 3.64-a Fe 2.64-a M a (PO4) 1.64-b (BO3) b P2O7 is a NFPP superlattice solid solution phase; M includes one or more of La, Ce, Mo, 80wt% ≤ x ≤ 100wt%, 0wt% ≤ y ≤ 20wt%, 0 < a < 0.1, 0 < b < 0.1, 0 ≤ c ≤ 1, and x + y = 100wt%.

[0008] In a possible implementation manner, 90wt% ≤ x ≤ 100wt%, 0wt% ≤ y ≤ 10wt%;

[0009] In one possible implementation, 0 <a<0.06;

[0010] In one possible implementation, 0 <b<0.06;

[0011] In one possible implementation, Na 4-2c Fe 2+c (P2O7)2 is the NFPO defect solid solution phase.

[0012] In one possible implementation, a nanoheterostructure is formed at the interface between the NFPP superlattice solid solution phase and the NFPO defect solid solution phase.

[0013] In one possible implementation, the cathode material further includes carbon;

[0014] In one possible implementation, the carbon content is 1 wt% to 2 wt% based on the mass of the cathode material.

[0015] In one possible implementation, the cell volume of the NFPP superlattice solid solution phase satisfies

[0016] In one possible implementation, a first diffraction peak exists at a diffraction angle 2θ of 9.6 ± 0.1° in the X-ray diffraction pattern, and a second diffraction peak exists at a diffraction angle 2θ of 33.5 ± 0.1°, wherein the interplanar spacing and full width at half maximum (FWHM) of the first diffraction peak are respectively... And 0.40±0.10°, the interplanar spacing and full width at half maximum (FWHM) of the second diffraction peak are respectively and 0.35±0.05°.

[0017] In one possible implementation, the secondary particle size D of the positive electrode material V 50 is 3-50μm, and can be selected as 10-20μm;

[0018] In one possible implementation, the secondary particles are formed by the agglomeration of multiple primary particles, wherein the average particle size of the primary particles is ≤500nm, and may be 50-300nm.

[0019] Secondly, this application provides a method for preparing a cathode material, comprising the following steps:

[0020] S1. In a protective atmosphere, water, iron salt, sodium salt, phosphorus salt, boron source, M source and carbon source are mixed to obtain a mixture, and the mixture is milled to obtain a dispersion.

[0021] S2. Spray dry the dispersion to obtain precursor powder;

[0022] S3. The precursor powder is heat-treated to obtain the cathode material.

[0023] In one possible implementation, the boron source is selected from one or more of boric acid, borax, sodium borohydride, boron trifluoride, and borosilicate;

[0024] In one possible implementation, the M source is selected from one or more of the nitrates, sulfates, and oxides of the M element;

[0025] In one possible implementation, the inlet air temperature of the spray dryer is 180-220°C, the outlet air temperature is 100-150°C, and the temperature difference between the inlet and outlet air temperatures is 60-110°C.

[0026] In one possible implementation, the air inlet temperature is 190–210°C;

[0027] In one possible implementation, the outlet air temperature is 110–140°C;

[0028] In one possible implementation, the temperature difference between the inlet air and the outlet air is 70–100°C.

[0029] In one possible implementation, the heat treatment process conditions include a first stage and a second stage:

[0030] In one possible implementation, the programmed temperature rise rate in the first stage is 1 to 5 °C / min, and can be selected as 2 to 4 °C / min;

[0031] In one possible implementation, the temperature in the first stage is increased to 200–500°C, optionally 300–400°C;

[0032] In one possible implementation, the heat preservation time for the first stage is 0.5 to 5 hours, and can be selected as 1 to 4 hours;

[0033] In one possible implementation, the temperature ramp rate in the second stage is 1–5 °C / min, and can be selected as 2–4 °C / min;

[0034] In one possible implementation, the second stage of the temperature program is increased to 400–700°C, optionally to 500–600°C;

[0035] In one possible implementation, the heat preservation time in the second stage is 6 to 15 hours, and can be selected as 8 to 12 hours.

[0036] Thirdly, this application provides a positive electrode sheet, comprising:

[0037] Positive current collector, and

[0038] A positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer including the positive electrode material or the positive electrode material prepared by the preparation method.

[0039] In a fourth aspect, the present application provides a sodium secondary battery including the positive electrode sheet.

[0040] In a fifth aspect, the present application provides an electrical device including the sodium secondary battery.

[0041] The technical solution of the present application has the following advantages:

[0042] The positive electrode material provided by the present application includes a positive electrode active substance, and the positive electrode active substance includes xNa 3.64- a Fe 2.64-a M a (PO4) 1.64-b (BO3) b P2O7·yNa 4-2c Fe 2+c (P2O7)2; where: Na 3.64-a Fe 2.64-a M a (PO4) 1.64-b (BO3) b P2O7 is a NFPP superlattice solid solution phase; M includes one or more of La, Ce, and Mo, 80wt% ≤ x ≤ 100wt%, 0wt% ≤ y ≤ 20wt%, 0 < a < 0.1, 0 < b < 0.1, 0 ≤ c ≤ 1, and x + y = 100wt%.

[0043] The NFPP superlattice solid solution phase in this application contains borate and M ions. Due to the balance of occupancy and charge in the crystal structure, the occupancy of sodium, iron, and phosphorus sites is reduced, introducing appropriate sodium and iron defects to create a certain lattice distortion and increase the entropy of the system. Simultaneously, the high-valence M ions create appropriate oxygen vacancies, promoting the formation of non-stoichiometric anionic groups filling the superlattice solid solution mixed phosphate material from borate ions occupying small spaces. The lattice distortion brought about by the superlattice structure widens the metal-oxygen octahedral interstices, providing a wider sodium ion diffusion pathway and reducing sodium ion diffusion polarization within the lattice, thereby significantly improving the rate performance and operating voltage of the material. The presence of anionic and sodium ion defects in this application also inhibits the formation of the high sodium-iron ratio and high iron-phosphorus ratio m-NFP inert phase, ensuring a high proportion of the NFPP superlattice solid solution phase. In this application, the NFPP superlattice solid solution phase accounts for more than 80%, ensuring the capacity utilization of the cathode material. The hybridization of the 3d-4f orbitals of M ions and ferrous ions, along with the oxygen-bridged (BO₂PO₄) superlattice structure of borate and phosphate ions, further optimizes the electronic band gap of the cathode material, thereby significantly improving its electronic conductivity. Therefore, the cathode material provided in this application exhibits higher specific capacity, rate performance, and operating voltage compared to traditional sodium-ion polyanionic materials. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0045] Figure 1 This is a SEM image of the cathode material prepared in Example 1 of this application;

[0046] Figure 2 This is the XRD pattern of the cathode material prepared in Example 1 of this application. Detailed Implementation

[0047] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0049] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0050] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0052] Traditional NFPP materials are prone to polarization during charge and discharge processes, resulting in a decrease in reversible capacity and discharge voltage. To solve the problems existing in the above related technologies, according to the first aspect of the present application, a positive electrode material is provided, including a positive electrode active material, and the positive electrode active material includes xNa 3.64-a Fe 2.64-a M a (PO4) 1.64-b (BO3) b P2O7·yNa 4-2c Fe 2+c (P2O7)2; where: Na 3.64-a Fe 2.64-a M a (PO4) 1.64-b (BO3) b P2O7 is a NFPP superlattice solid solution phase; M includes one or more of La, Ce, Mo, 80wt% ≤ x ≤ 100wt%, 0wt% ≤ y ≤ 20wt%, 0 < a < 0.1, 0 < b < 0.1, 0 ≤ c ≤ 1, and x + y = 100wt%.

[0053] The NFPP superlattice solid solution phase of the present application contains borate and M ions. Due to the balance of crystal structure occupancy rate and charge balance, the occupancy rates of sodium sites, iron sites and phosphorus sites are reduced to introduce appropriate sodium defects and iron defects to create certain lattice distortion and increase the entropy value of the system; at the same time, the high-valence M ions create appropriate oxygen vacancies, promoting the formation of non-stoichiometric anion group interstitial superlattice solid solution mixed phosphate materials by borate ions with small space occupancy. The lattice distortion brought by the superlattice structure broadens the metal-oxygen octahedron gap, provides a wider sodium ion diffusion path, reduces the sodium ion diffusion polarization in the lattice, and thus significantly improves the rate performance and working voltage of the material.

[0054] Traditional sodium iron pyrophosphate usually contains m-NFP (sodium iron phosphate ore phase) heterophase. m-NFP has no electrochemical activity due to the too high sodium diffusion barrier, resulting in the deterioration of the performance of the positive electrode material such as capacity, rate and cycle. The presence of anion defects and sodium defects in the present application also inhibits the formation of m-NFP inert phases with high sodium-iron ratio and high iron-phosphorus ratio, ensuring a high proportion of the NFPP superlattice solid solution phase. In the present application, the proportion of the NFPP superlattice solid solution phase is more than 80%, ensuring the capacity performance of the positive electrode material.

[0055] The 3d-4f orbital hybridization of M ions and ferrous ions and the formation of a (BO2PO4) superlattice structure by borate ions and phosphate ions bridged by oxygen ions further optimize the electronic band gap of the positive electrode material, thus significantly improving the electronic conductivity of the positive electrode material.

[0056] Therefore, the cathode material provided in this application has higher specific capacity, rate performance and operating voltage compared with traditional sodium polyanionic materials.

[0057] A superlattice structure is a periodic structure formed by the alternating growth of two nanomaterials with good lattice matching; a solid solution is a homogeneous crystal structure formed by the mutual dissolution of different types of atoms or ions in the solid state. In this application, non-stoichiometric borate, phosphate, and pyrophosphate ions alternately form a Pn21a space group NFPP phase crystal structure in a mutually soluble manner.

[0058] x is Na 3.64-a Fe 2.64-a M a (PO4) 1.64-b (BO3) b The mass content of P2O7 in the positive electrode active material, y is the Na 4- 2c Fe 2+c The mass content of (P2O7)2 in the positive electrode active material. For example, x can be 80wt%, 85wt%, 90wt%, 95wt%, 100wt%, or any two of the above values. y can be 0, 5wt%, 15wt%, 20wt%, or any two of the above values. a can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.07, 0.09, 0.10, or any two of the above values. b can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.07, 0.09, 0.10, or any two of the above values. c can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or any two of the above values. For example, Na 4-2c Fe 2+c (P₂O₇)₂ can be Na 3.12 Fe 2.44 (P2O7)2.

[0059] In one possible implementation, 90wt%≤x≤100wt%, 0wt%≤y≤10wt%;

[0060] In one possible implementation, 0 <a<0.06;

[0061] In one possible implementation, 0 <b<0.06;

[0062] In one possible implementation, Na 3.64-a Fe 2.64-a M a (PO4) 1.64-b (BO3)b P2O7 belongs to the Pn21a space group;

[0063] In one possible implementation, Na 4-2c Fe 2+c (P2O7)2 belongs to the P-1 space group;

[0064] In one possible implementation, Na 4-2c Fe 2+c (P2O7)2 is the NFPO defect solid solution phase.

[0065] Non-stoichiometric ratios suppress the formation of the m-NFP phase, but lead to the formation of the NFPO phase (sodium iron pyrophosphate). Traditional NFPO, due to the large volume of its pyrophosphate groups, possesses the highest crystal structure and cycling stability, but its specific capacity and rate performance are relatively poor. In this application, the NFPO phase is a defective solid solution phase, and this defective NFPO phase forms a nano-heterojunction with the NFPP superlattice solid solution phase. An appropriate NFPO defective solid solution phase can optimize the electronic structure of the material through nano-heterojunction and superlattice interaction, improving electronic and ionic conductivity, thereby reducing polarization and improving capacity, rate performance, and operating voltage performance.

[0066] In one possible implementation, a nanoheterojunction is formed at the interface between the NFPP superlattice solid solution phase and the NFPO defect solid solution phase; that is, a nanoheterojunction is formed at the part where the two phases are in contact.

[0067] From a structural perspective, the lattice structure enhances the integrity of the crystal structure and suppresses volume changes during cycling. The nanostructure acts as a grain boundary toughening agent, mitigating stress cracking during cycling and thus improving cycle life. From a polarization perspective, polarization is a significant factor leading to stress concentration due to volume changes during charging and discharging. The significant increase in operating voltage and the reduction in powder resistance in this application indicate that the polarization of the material is effectively suppressed, thereby avoiding particle cracking caused by stress concentration and improving cycling performance.

[0068] In one possible implementation, the cathode material further includes carbon;

[0069] In one possible implementation, the carbon content is 1 wt% to 2 wt% based on the mass of the cathode material.

[0070] Carbon forms a conductive network by connecting nanoparticles and nanocrystal domains, thereby improving the electronic conductivity of the cathode material. The carbon content within the scope of this application can form an effective conductive network while avoiding a decrease in the compaction density of the cathode material, preventing sodium diffusion from being hindered, and improving the ionic conductivity of the cathode material.

[0071] In one possible implementation, the carbon is selected from one or more of amorphous carbon and / or graphite.

[0072] In one possible implementation, carbon is distributed in the NFPP superlattice solid solution phase, the NFPO defect solid solution phase, and the nano-heterojunction. That is, carbon is uniformly dispersed in the positive electrode active material.

[0073] In one possible implementation, the cell volume of the NFPP superlattice solid solution phase satisfies

[0074] In one possible implementation, a first diffraction peak exists at a diffraction angle 2θ of 9.6 ± 0.1° in the X-ray diffraction pattern, and a second diffraction peak exists at a diffraction angle 2θ of 33.5 ± 0.1°, wherein the interplanar spacing and full width at half maximum (FWHM) of the first diffraction peak are respectively... And 0.40±0.10°, the interplanar spacing and full width at half maximum (FWHM) of the first diffraction peak are respectively and 0.35±0.05°.

[0075] In one possible implementation, the secondary particle size D of the positive electrode material V 50 is 3-50μm, and can be selected as 10-20μm;

[0076] The secondary particles are self-assembled from the primary particles;

[0077] In one possible implementation, the average particle size of the primary particles is ≤500nm, and can be selected as 50-300nm.

[0078] Secondary particle size D V 50 was measured using a laser particle size analyzer. The average particle size of primary particles is the average of the particle sizes of all primary particles in the SEM field of view.

[0079] Secondly, this application provides a method for preparing a cathode material, comprising the following steps:

[0080] S1. In a protective atmosphere, water, iron salt, sodium salt, phosphorus salt, boron source, M source and carbon source are mixed to obtain a mixture, and the mixture is milled to obtain a dispersion.

[0081] S2. Spray dry the dispersion to obtain precursor powder;

[0082] S3. The precursor powder is heat-treated to obtain the cathode material.

[0083] In one possible implementation, the iron salt is selected from one or more of the following: iron sulfate, iron nitrate, iron hydrochloride, iron acetate, iron oxalate, iron phosphate, iron acetylacetonate, ferrous sulfate, ferrous nitrate, ferrous hydrochloride, ferrous acetate, ferrous oxalate, ferrous phosphate, and ferrous acetylacetonate.

[0084] In one possible implementation, the phosphate salt is selected from one or more of phosphoric acid, ferric phosphate, ferric pyrophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and monoammonium phosphate.

[0085] In one possible implementation, the sodium salt is selected from one or more of sodium oxide, sodium hydroxide, sodium carbonate, sodium fluoride, sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate;

[0086] In one possible implementation, the carbon source is selected from one or more of citric acid, acetic acid, oxalic acid, glucose, sucrose, ascorbic acid, carbon black, graphite, polyethylene glycol, and polyether.

[0087] In one possible implementation, the boron source is selected from one or more of boric acid, borax, sodium borohydride, boron trifluoride, and borosilicate;

[0088] In one possible implementation, the M source is selected from one or more of the nitrates, sulfates, and oxides of the M element; the M element includes one or more of La, Ce, and Mo.

[0089] In one possible implementation, the solid content in the mixture is 0.1–0.6 wt%, optionally 0.2–0.4 wt%.

[0090] In one possible implementation, the molar ratio of sodium:iron:phosphorus:boron:M:carbon in the dispersion is 3.54–3.64:2.54–2.64:3.54–3.64:0–0.1:0–0.1:2.54–5.28, and the contents of boron and M are both ≠0, and can be selected as 3.58–3.64:2.58–2.64:3.58–3.64:0–0.06:0–0.06:3.18–4.62.

[0091] In one possible implementation, the step of sand milling the mixture includes: adding the mixture into a sand mill at a rate of 0.5 to 1.5 L / min, adding sand milling beads, sand milling to a suitable particle size, and then collecting and discharging the material.

[0092] In one possible implementation, the filling rate of the mixture in the sand mill is 70-90%, optionally 75-85%; the diameter of the sand beads is 0.05-0.5 mm, optionally 0.1-0.4 mm;

[0093] In one possible implementation, the dispersion is pumped into the spray drying equipment by a peristaltic pump at a flow rate of 0.6–1 L / min;

[0094] In one possible implementation, spray drying is performed in a protective atmosphere.

[0095] In one possible implementation, the inlet air temperature of the spray drying equipment is 180–220°C, optionally 190–210°C; the outlet air temperature is 100–150°C, optionally 110–140°C; and the temperature difference between the inlet and outlet air temperatures is 60–110°C, optionally 70–100°C.

[0096] The atmosphere for the heat treatment is selected from one or more of nitrogen, argon, hydrogen, a hydrogen-argon mixture, and vacuum, and may be nitrogen; and / or

[0097] In one possible implementation, the heat treatment process conditions include:

[0098] The temperature ramp rate for the first stage is 1–5 °C / min, and can be selected as 2–4 °C / min;

[0099] The first stage of the program involves heating up to 200–500℃, with an option of 300–400℃.

[0100] The heat preservation time for the first stage is 0.5 to 5 hours, and can be selected as 1 to 4 hours;

[0101] The temperature ramp rate for the second stage is 1–5 °C / min, and can be selected as 2–4 °C / min;

[0102] The second stage involves a temperature increase to 400–700℃, with an option of 500–600℃.

[0103] The second stage of heat preservation time is 6 to 15 hours, and can be selected as 8 to 12 hours.

[0104] Thirdly, this application provides a positive electrode sheet, comprising:

[0105] Positive current collector, and

[0106] A positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer comprising the aforementioned positive electrode material or a positive electrode material prepared according to the aforementioned preparation method.

[0107] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0108] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0109] In some embodiments, the binder may optionally comprise 0.1-3.5% of the total weight of the positive electrode active material layer, and optionally 0.5-2.5%.

[0110] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0111] In some embodiments, the conductive agent may optionally account for 0.05-5% of the total weight of the positive electrode active material layer, and optionally 0.5-3%.

[0112] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0113] Fourthly, this application provides a sodium secondary battery, including the aforementioned positive electrode plate.

[0114] [Negative electrode plate]

[0115] In a sodium battery, the negative electrode typically includes a negative current collector and a layer of negative active material disposed on the negative current collector, wherein the negative active material layer includes a negative active material.

[0116] The negative electrode sheet may also consist only of a negative current collector, i.e., without a negative electrode active material. The negative electrode sheet may also include a pre-deposited metallic phase on the negative current collector. The negative current collector can be made of conventional metal foil, carbon-coated metal foil, or porous metal plate, etc. As an example, the negative current collector can be made of copper foil or aluminum foil.

[0117] The specific type of the negative electrode active material is not limited, and any active material known in the art that can be used as a negative electrode in sodium batteries can be used. Those skilled in the art can select according to actual needs. As an example, the negative electrode active material may include, but is not limited to, one or more of sodium metal, carbon materials, alloy materials, transition metal oxides and / or sulfides, phosphorus-based materials, and titanate materials. Specifically, the carbon material may include one or more of hard carbon, soft carbon, amorphous carbon, and nanostructured carbon materials; the alloy material may include alloys formed from one or more of Si, Ge, Sn, Pb, and Sb; the general formula of the transition metal oxides and sulfides is M. x N y M includes one or more of Fe, Co, Ni, Mn, Sn, Mo, Sb, and V, and N includes O or S; the phosphorus-based material may include one or more of red phosphorus, white phosphorus, and black phosphorus; the titanate material may include Na2Ti3O7 and Na2Ti6O7. 13 Na4Ti5O 12 Li4Ti5O 12 One or more of NaTi2(PO4)3. These materials are all commercially available.

[0118] The negative electrode active material layer may also optionally include a binder and a conductive agent. The conductive agent is used to improve the conductivity of the negative electrode active material layer, and the binder is used to firmly bond the negative electrode active material and the conductive agent to the negative electrode current collector. This application does not specifically limit the types of conductive agents and binders, which can be selected according to actual needs.

[0119] As an example, conductive agents may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0120] As an example, the adhesive may include one or more of styrene-butadiene rubber (SBR), styrene-butadiene rubber (SBCs), water-based acrylic resin, and carboxymethyl cellulose (CMC).

[0121] The negative electrode active material layer may also optionally include a thickener, such as carboxymethyl cellulose (CMC). However, this application is not limited to this, and other materials that can be used as thickeners for sodium battery negative electrode sheets may also be used.

[0122] [Isolation membrane]

[0123] As for the aforementioned separator, this application does not have any particular limitations. Any known porous structure separator with electrochemical and mechanical stability can be selected according to actual needs. For example, it can be a single-layer or multi-layer film containing one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0124] [Electrolytes]

[0125] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0126] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution may include an electrolyte salt and a solvent.

[0127] As an example, the electrolyte sodium salt includes at least one of sodium hexafluorophosphate, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium dioxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonyl)imide.

[0128] As an example, the solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), and methyl butyrate. One or more of the following: (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), diethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, 1,3-dioxopentane, 1,3-dioxane, 1,4-dioxane, tetrahydropyran, methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0129] In some embodiments, the electrolyte also includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0130] In some embodiments, the electrolyte is a sodium ion solid electrolyte.

[0131] As an example, the sodium ion solid electrolyte includes, but is not limited to: NASICON type: Na (1+x9+2y5) Zr (2-y5) M y5 P (3-x9) Si x9 O 12 , 0 ≤ x9 ≤ 3, 0 ≤ y5 ≤ 1, M includes at least one of Zn, Mg, Ca; Na-β-Alumina type: Na2O·2Al2O3 or Na2O·3Al2O3, etc.; Na (3+x10) M y6 A (1-y6) Q (4-z6) T z6 type, where -1 < x10 < 2, 0 ≤ y6 ≤ 1, 0 ≤ z6 ≤ 2, M includes at least one of B, Al, In, Si, Ge, Sn, Ti, W, Mo, A includes at least one of P, As, Sb, Bi, Q includes at least one of S, Se, T includes at least one of F, Cl, Br, I; Na (11+x11) M (2-y7) A (1+y7) Q (12-z7) T z7 type where -1 < x11 < 1, 0 ≤ y7 ≤ 2, 0 ≤ z7 ≤ 2, M includes at least one of B, Al, In, Si, Ge, Sn, Ti, W, Mo, A includes P, As, Sb, Bi; Q = at least one of S, Se, T includes at least one of F, Cl, Br, I; inverse perovskite type Na3OX, X includes at least one of Cl, Br, I, BH4.

[0132] In some embodiments, the positive electrode sheet, negative electrode sheet, and separator can be made into an electrode assembly by a winding process or a stacking process.

[0133] In some embodiments, the secondary battery may include an outer package. The outer package can be used to encapsulate the above electrode assembly and electrolyte.

[0134] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed, etc.

[0135] This application does not particularly limit the shape of the secondary battery, and it can be cylindrical, square, or any other arbitrary shape.

[0136] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0137] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0138] Fifthly, this application provides an electrical device including the aforementioned sodium secondary battery.

[0139] In some embodiments, the aforementioned electrical device may also include a battery module or battery pack assembled from the aforementioned secondary batteries. The secondary batteries, battery modules, or battery packs can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0140] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements. An example electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0141] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0142] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0143] Example 1

[0144] This embodiment provides a method for preparing a positive electrode material, including the following steps:

[0145] S1. Weigh out solid samples of ferric phosphate, sodium dihydrogen phosphate, sodium carbonate, lanthanum nitrate, boric acid, and glucose according to the stoichiometric ratio of sodium:iron:phosphorus:boron:lanthanum:carbon element of 3.61:2.61:3.61:0.03:0.03:3.92. The total mass of the added solid sample is in a mass ratio of 1:3 to pure water. Stir the solid sample in pure water to disperse it evenly to obtain a mixture.

[0146] Under nitrogen atmosphere protection, the mixture is injected into a sand mill at a flow rate of 1 L / min using a peristaltic pump. Sand milling beads with a particle size of 0.2-0.3 mm are added, and the equipment is kept at a filling rate of 80%. The mixture is sand milled at a linear velocity of 20 m / s until the particle size D50 is about 250 nm to obtain a mixed salt molecular-level dispersion.

[0147] S2, spray drying granulation:

[0148] Under nitrogen atmosphere protection, the mixed salt dispersion was injected into the spray drying equipment at a flow rate of 1L / min using a peristaltic pump, with the inlet air temperature maintained at 200℃ and the outlet air temperature at 120℃, to obtain precursor powder with a particle size D50 of about 12μm.

[0149] S3. The precursor powder is subjected to sintering heat treatment, that is, the temperature is increased to 325°C at a programmable heating rate of 3°C / min under a nitrogen atmosphere and held for 3 hours; then the temperature is increased to 570°C at a programmable heating rate of 3°C / min and held for 10 hours; then it is naturally cooled to obtain the cathode material.

[0150] XRD and ICP characterization confirmed that its composition was 96.9 wt% Na. 3.61 Fe 2.61 La 0.03 (PO4) 1.61 (BO3) 0.03 P2O7·1.3wt% Na 3.12 Fe 2.44 (P₂O₇)₂·1.8wt%C, its first diffraction peak interplanar spacing and half-maximum width are respectively And 0.41°, the interplanar spacing and full width at half maximum (FWHM) of the second diffraction peak are respectively And 0.36°, the cell volume is XRD diagram as follows Figure 2 As shown.

[0151] Figure 1 The SEM image of the cathode material prepared in this embodiment shows that the cathode material has a micron-sized secondary particle morphology formed by the self-assembly of primary nanoparticles. The average particle size of the primary particles is 250 nm, and the particle size D of the secondary particles is... V 50 represents 15μm.

[0152] Example 2

[0153] This embodiment provides a method for preparing a cathode material, including the following steps:

[0154] S1. Iron phosphate, sodium dihydrogen phosphate, sodium carbonate, lanthanum nitrate, boric acid, and glucose are weighed accurately according to the stoichiometric ratio of sodium:iron:phosphorus:boron:lanthanum:carbon element of 3.63:2.63:3.63:0.01:0.01:3.95. The solid sample is added to pure water at a mass ratio of 1:3 and then stirred and dispersed evenly to prepare a mixed solution.

[0155] Under nitrogen atmosphere protection, the mixture is injected into the sand mill at a flow rate of 1L / min using a peristaltic pump. Sand milling beads with a particle size of 0.2-0.3mm are added, and the equipment is kept at a filling rate of 80%. The mixture is sand milled at a linear velocity of 20m / s until the particle size D50 is about 250nm to obtain a mixed salt molecular-level dispersion.

[0156] S2, spray drying granulation:

[0157] Under nitrogen atmosphere protection, the mixed salt dispersion was injected into the spray drying equipment at a flow rate of 1L / min using a peristaltic pump, with the inlet air temperature maintained at 200℃ and the outlet air temperature at 120℃, to obtain precursor powder with a particle size D50 of about 12μm.

[0158] S3. The precursor powder is subjected to sintering heat treatment, that is, the temperature is increased to 325°C at a programmable heating rate of 3°C / min under a nitrogen atmosphere and held for 3 hours; then the temperature is increased to 570°C at a programmable heating rate of 3°C / min and held for 10 hours; then it is naturally cooled to obtain the cathode material.

[0159] XRD and ICP characterization confirmed that its composition was 94.0 wt% Na. 3.63 Fe 2.63 La 0.01 (PO4) 1.63 (BO3) 0.01 P2O7·4.2wt% Na 3.12 Fe 2.44 (P₂O₇)₂·1.8wt%C, its first diffraction peak interplanar spacing and half-maximum width are respectively And 0.33°, the interplanar spacing and full width at half maximum (FWHM) of the second diffraction peak are respectively And 0.32°, the cell volume is

[0160] Example 3

[0161] This embodiment provides a method for preparing a cathode material, including the following steps:

[0162] S1. Iron phosphate, sodium dihydrogen phosphate, sodium carbonate, lanthanum nitrate, boric acid, and glucose are weighed accurately according to the stoichiometric ratio of sodium:iron:phosphorus:boron:lanthanum:carbon element of 3.59:2.59:3.59:0.05:0.05:3.89. The solid sample is added to pure water at a mass ratio of 1:3 and then stirred and dispersed evenly to prepare a mixed solution.

[0163] Under nitrogen atmosphere protection, the mixture is injected into the sand mill at a flow rate of 1L / min using a peristaltic pump. Sand milling beads with a particle size of 0.2-0.3mm are added, and the equipment is kept at a filling rate of 80%. The mixture is sand milled at a linear velocity of 20m / s until the particle size D50 is about 250nm to obtain a mixed salt molecular-level dispersion.

[0164] S2, spray drying granulation:

[0165] Under nitrogen atmosphere protection, the mixed salt dispersion was injected into the spray drying equipment at a flow rate of 1L / min using a peristaltic pump, with the inlet air temperature maintained at 200℃ and the outlet air temperature at 120℃, to obtain precursor powder with a particle size D50 of about 12μm.

[0166] S3. The precursor powder is subjected to sintering heat treatment, that is, the temperature is increased to 325°C at a programmable heating rate of 3°C / min under a nitrogen atmosphere and held for 3 hours; then the temperature is increased to 570°C at a programmable heating rate of 3°C / min and held for 10 hours; then it is naturally cooled to obtain the cathode material.

[0167] XRD and ICP characterization confirmed that its composition was 95.2 wt% Na. 3.59 Fe 2.59 La 0.05 (PO4) 1.59 (BO3) 0.05 P2O7·3.0wt%Na 3.12 Fe 2.44 (P₂O₇)₂·1.8wt%C, its first diffraction peak interplanar spacing and half-maximum width are respectively And 0.44°, the interplanar spacing and full width at half maximum (FWHM) of the second diffraction peak are respectively And 0.38°, the cell volume is

[0168] Example 4

[0169] This embodiment provides a method for preparing a cathode material, including the following steps:

[0170] S1. Weigh out solid samples of ferric phosphate, sodium dihydrogen phosphate, sodium carbonate, lanthanum nitrate, boric acid, and glucose according to the stoichiometric ratio of sodium:iron:phosphorus:boron:lanthanum:carbon element of 3.55:2.55:3.55:0.09:0.09:3.83. The total mass of the added solid sample is 1:3 with the mass ratio of pure water. Stir the solid sample in pure water to disperse it evenly to obtain a mixture.

[0171] Under nitrogen atmosphere protection, the mixture is injected into a sand mill at a flow rate of 1 L / min using a peristaltic pump. Sand milling beads with a particle size of 0.2-0.3 mm are added, and the equipment is kept at a filling rate of 80%. The mixture is sand milled at a linear velocity of 20 m / s until the particle size D50 is about 250 nm to obtain a mixed salt molecular-level dispersion.

[0172] S2, spray drying granulation:

[0173] Under nitrogen atmosphere protection, the mixed salt dispersion was injected into the spray drying equipment at a flow rate of 1L / min using a peristaltic pump, with the inlet air temperature maintained at 200℃ and the outlet air temperature at 120℃, to obtain precursor powder with a particle size D50 of about 12μm.

[0174] S3. The precursor powder is subjected to sintering heat treatment, that is, the temperature is increased to 325°C at a programmable heating rate of 3°C / min under a nitrogen atmosphere and held for 3 hours; then the temperature is increased to 570°C at a programmable heating rate of 3°C / min and held for 10 hours; then it is naturally cooled to obtain the cathode material.

[0175] XRD and ICP characterization confirmed that its composition was 80.6 wt% Na. 3.55 Fe 2.55 La 0.09 (PO4) 1.55 (BO3) 0.09 P2O7·17.6wt% Na 3.12 Fe 2.44 (P₂O₇)₂·1.8wt%C, its first diffraction peak interplanar spacing and half-maximum width are respectively And 0.49°, the interplanar spacing and full width at half maximum (FWHM) of the second diffraction peak are respectively And 0.39°, the cell volume is

[0176] Example 5

[0177] This embodiment provides a method for preparing a cathode material, including the following steps:

[0178] S1. Weigh out solid samples of ferric phosphate, sodium dihydrogen phosphate, sodium carbonate, lanthanum nitrate, boric acid, and glucose according to the stoichiometric ratio of sodium:iron:phosphorus:boron:lanthanum:carbon element of 3.57:2.57:3.57:0.07:0.07:3.86. The total mass of the added solid sample is 1:3 with the mass ratio of pure water. Stir the solid sample in pure water to disperse it evenly to obtain a mixture.

[0179] Under nitrogen atmosphere protection, the mixture is injected into a sand mill at a flow rate of 1 L / min using a peristaltic pump. Sand milling beads with a particle size of 0.2-0.3 mm are added, and the equipment is kept at a filling rate of 80%. The mixture is sand milled at a linear velocity of 20 m / s until the particle size D50 is about 250 nm to obtain a mixed salt molecular-level dispersion.

[0180] S2, spray drying granulation:

[0181] Under nitrogen atmosphere protection, the mixed salt dispersion was injected into the spray drying equipment at a flow rate of 1L / min using a peristaltic pump, with the inlet air temperature maintained at 200℃ and the outlet air temperature at 120℃, to obtain precursor powder with a particle size D50 of about 12μm.

[0182] S3. The precursor powder is subjected to sintering heat treatment, that is, the temperature is increased to 325°C at a programmable heating rate of 3°C / min under a nitrogen atmosphere and held for 3 hours; then the temperature is increased to 570°C at a programmable heating rate of 3°C / min and held for 10 hours; then it is naturally cooled to obtain the cathode material.

[0183] XRD and ICP characterization confirmed that its composition was 90.3 wt% Na. 3.57 Fe 2.57 La 0.07 (PO4) 1.57 (BO3) 0.07 P2O7·7.9wt% Na 3.12 Fe 2.44 (P₂O₇)₂·1.8wt%C, its first diffraction peak interplanar spacing and half-maximum width are respectively And 0.46°, the interplanar spacing and full width at half maximum (FWHM) of the second diffraction peak are respectively And 0.39°, the cell volume is

[0184] Example 6

[0185] This embodiment is basically the same as Embodiment 1, except that in S1, iron phosphate, sodium dihydrogen phosphate, sodium carbonate, molybdenum nitrate, boric acid, and glucose are weighed in a stoichiometric ratio of sodium:iron:phosphorus:boron:molybdenum:carbon elements of 3.61:2.61:3.61:0.03:0.03:3.92.

[0186] XRD and ICP characterization confirmed that its composition was 91.2 wt% Na. 3.61 Fe 2.61 Mo 0.03 (PO4) 1.61 (BO3) 0.03 P2O7·7.0wt%Na 3.12 Fe 2.44 (P₂O₇)₂·1.8wt%C, its first diffraction peak interplanar spacing and half-maximum width are respectively And 0.38°, the interplanar spacing and full width at half maximum (FWHM) of the second diffraction peak are respectively And 0.34°, the cell volume is

[0187] Example 7

[0188] This embodiment is basically the same as Embodiment 1, except that in S1, iron phosphate, sodium dihydrogen phosphate, sodium carbonate, cerium nitrate, boric acid, and glucose are weighed in a stoichiometric ratio of sodium:iron:phosphorus:boron:cerium:carbon elements of 3.61:2.61:3.61:0.03:0.03:3.92.

[0189] XRD and ICP characterization confirmed that its composition was 92.1 wt% Na. 3.61 Fe 2.61 Mo 0.03 (PO4) 1.61 (BO3) 0.03 P2O7·6.1wt% Na 3.12 Fe 2.44 (P₂O₇)₂·1.8wt%C, its first diffraction peak interplanar spacing and half-maximum width are respectively And 0.45°, the interplanar spacing and full width at half maximum (FWHM) of the second diffraction peak are respectively And 0.32°, the cell volume is

[0190] Example 8

[0191] This embodiment is basically the same as Embodiment 1, except that in S1, the particle size of the milled zirconium beads is 0.1 mm; in S2, the inlet air temperature of the spray drying is 190°C and the outlet air temperature is 110°C; in S3, the sintering heat treatment is to raise the temperature to 325°C at a programmable heating rate of 3°C / min under a nitrogen atmosphere and hold it for 3 hours; then raise the temperature to 500°C at a programmable heating rate of 3°C / min and hold it for 10 hours.

[0192] XRD and ICP characterization confirmed that its composition was 91.4 wt% Na. 3.61 Fe 2.61 La0.03 (PO4) 1.61 (BO3) 0.03 P2O7·6.8wt%Na 3.12 Fe 2.44 (P₂O₇)₂·1.8wt%C, its first diffraction peak interplanar spacing and half-maximum width are respectively And 0.39°, the interplanar spacing and full width at half maximum (FWHM) of the second diffraction peak are respectively And 0.33°, the cell volume is

[0193] Example 9

[0194] This embodiment is basically the same as Embodiment 1, except that in S1, the particle size of the milled zirconium beads is 0.1 mm; in S2, the inlet air temperature of the spray drying is 220°C and the outlet air temperature is 140°C; in S3, the sintering heat treatment is to raise the temperature to 325°C at a programmable heating rate of 3°C / min under a nitrogen atmosphere and hold it for 3 hours; then raise the temperature to 600°C at a programmable heating rate of 3°C / min and hold it for 10 hours.

[0195] XRD and ICP characterization confirmed that its composition was 91.8 wt% Na. 3.61 Fe 2.61 La 0.03 (PO4) 1.61 (BO3) 0.03 P2O7·6.4wt%Na 3.12 Fe 2.44 (P₂O₇)₂·1.8wt%C, its first diffraction peak interplanar spacing and half-maximum width are respectively And 0.37°, the interplanar spacing and full width at half maximum (FWHM) of the second diffraction peak are respectively And 0.34°, the cell volume is

[0196] Comparative Example 1

[0197] This comparative example provides a method for preparing a cathode material, including the following steps:

[0198] S1. Iron phosphate, sodium dihydrogen phosphate, sodium carbonate, boric acid, and glucose are added in a stoichiometric ratio of sodium:iron:phosphorus:boron:carbon of 3.64:2.64:3.61:0.03:3.96. The solid sample is accurately weighed and mixed with pure water at a mass ratio of 1:3 to prepare a mixed salt dispersion.

[0199] Under nitrogen atmosphere protection, the mixed salt dispersion was injected into a sand mill at a flow rate of 1 L / min using a peristaltic pump. 0.1 mm sand beads were added, and the equipment was kept at a loading rate of 80%. The mixture was sand milled at a linear speed of 20 m / s until the particle size D50 was about 250 nm to obtain a mixed salt molecular-level dispersion.

[0200] S2 spray drying granulation

[0201] Under nitrogen atmosphere protection, the mixed salt dispersion was injected into the spray drying equipment at a flow rate of 1L / min using a peristaltic pump, with the inlet air temperature maintained at 200℃ and the outlet air temperature at 120℃, to obtain precursor powder with a particle size D50 of about 12μm.

[0202] S3 performs sintering heat treatment on the precursor powder, that is, it is heated to 325°C in air at a heating rate of 3°C / min and held for 3 hours; then it is heated to 570°C at a heating rate of 3°C / min and held for 10 hours; then it is naturally cooled to obtain the cathode material.

[0203] XRD and ICP characterization confirmed that its composition was 85.6 wt% Na. 3.64 Fe 2.64 (PO4) 1.61 (BO3) 0.03 P2O7·12.6wt%Na 3.12 Fe 2.44 (P₂O₇)₂·1.8wt%C, its first diffraction peak interplanar spacing and half-maximum width are respectively And 0.30°, the interplanar spacing and full width at half maximum (FWHM) of the first diffraction peak are respectively And 0.28°, the cell volume is

[0204] Comparative Example 2

[0205] This comparative example provides a method for preparing a cathode material, including the following steps:

[0206] S1. Iron phosphate, sodium dihydrogen phosphate, sodium carbonate, lanthanum nitrate, and glucose are added in a stoichiometric ratio of sodium:iron:phosphorus:lanthanum:carbon elements of 3.61:2.61:3.64:0.03:3.92. The solid sample is accurately weighed and mixed with pure water at a mass ratio of 1:3 to obtain a mixed solution.

[0207] Under nitrogen atmosphere protection, the mixture was injected into a sand mill at a flow rate of 1 L / min using a peristaltic pump. 0.1 mm sand beads were added, and the equipment was kept at a filling rate of 80%. The mixture was sand milled at a linear speed of 20 m / s until the particle size D50 was about 250 nm to obtain a mixed salt molecular-level dispersion.

[0208] S2, spray drying granulation

[0209] Under nitrogen atmosphere protection, the mixed salt dispersion was injected into the spray drying equipment at a flow rate of 1L / min using a peristaltic pump, with the inlet air temperature maintained at 200℃ and the outlet air temperature at 120℃, to obtain precursor powder with a particle size D50 of about 12μm.

[0210] S3. The precursor powder is subjected to sintering heat treatment, that is, the temperature is increased to 325°C in air at a heating rate of 3°C / min and held for 3 hours; then the temperature is increased to 570°C at a heating rate of 3°C / min and held for 10 hours; then it is naturally cooled to obtain the cathode material.

[0211] XRD and ICP characterization confirmed that its composition was 82.3 wt% Na. 3.61 Fe 2.61 La 0.03 (PO4) 1.64 P2O7·15.9wt%Na 3.12 Fe 2.44 (P₂O₇)₂·1.8wt%C, its first diffraction peak interplanar spacing and half-maximum width are respectively And 0.29°, the interplanar spacing and full width at half maximum (FWHM) of the first diffraction peak are respectively And 0.26°, the cell volume is

[0212] Comparative Example 3

[0213] This comparative example provides a method for preparing a cathode material, including the following steps:

[0214] S1. Iron phosphate, sodium dihydrogen phosphate, sodium carbonate, and glucose are weighed accurately according to the stoichiometric ratio of sodium:iron:phosphorus:carbon elements of 3.64:2.64:3.64:3.96. The solid sample is added to pure water at a mass ratio of 1:3 and then stirred and dispersed evenly to prepare a mixed solution.

[0215] Under nitrogen atmosphere protection, the mixture was injected into a sand mill at a flow rate of 1 L / min using a peristaltic pump. 0.1 mm sand beads were added, and the equipment was kept at a filling rate of 80%. The mixture was sand milled at a linear speed of 20 m / s until the particle size D50 was about 250 nm to obtain a mixed salt molecular-level dispersion.

[0216] S2, spray drying granulation

[0217] Under nitrogen atmosphere protection, the mixed salt dispersion was injected into the spray drying equipment at a flow rate of 1L / min using a peristaltic pump, with the inlet air temperature maintained at 200℃ and the outlet air temperature at 120℃, to obtain precursor powder with a particle size D50 of about 12μm.

[0218] S3. The precursor powder is subjected to sintering heat treatment, that is, the temperature is increased to 325°C in air at a heating rate of 3°C / min and held for 3 hours; then the temperature is increased to 570°C at a heating rate of 3°C / min and held for 10 hours; then it is naturally cooled to obtain the cathode material.

[0219] XRD and ICP characterization confirmed that its composition was 75.4 wt% Na. 3.64 Fe 2.64 (PO4) 1.64 The interplanar spacing and full width at half maximum (FWHM) of the first diffraction peak of P₂O₇·22.8wt%NaFePO₄·1.8wt%C are respectively... And 0.29°, the interplanar spacing and full width at half maximum (FWHM) of the first diffraction peak are respectively And 0.19°, the cell volume is

[0220] Test case

[0221] (1) XRD diffractometer manufacturer: Bruker, model D8 ADVANCE. Specific XRD testing procedure: The sample is passed through a 200-mesh steel sieve and then evenly and smoothly filled into a glass sample cell; using an XRD diffractometer, X-ray selection is based on a Cu target. Set the voltage to 40kV and the current to 40mA; the scanning range is 5-55°, the scanning speed is 0.5° / min, and the step size is 0.02° to obtain the XRD pattern.

[0222] (2) ICP analyzer manufacturer: Thermo Fisher Scientific, model: ICAP PRO. Specific ICP testing process: The sample needs to be digested with aqua regia to become a liquid, and the sample concentration is adjusted to the instrument's detection range; a series of standard solutions (containing the analyte) are prepared, and a concentration-signal intensity relationship is established; the sample is introduced into the nebulizer via a peristaltic pump, forming an aerosol before entering the plasma; test parameters are set as follows: RF power 1500W, nebulizer flow rate 0.5L / min, observation height selected as axial observation mode, integration time adjusted to 1-10 seconds; plasma excites the element to generate characteristic spectra, and the detector CCD records the signal; background interference is eliminated, and the element concentration is calculated based on the standard curve.

[0223] (3) The volumetric particle size Dv50 was determined using a laser particle size analyzer (MalvernMaster Size 2000) in accordance with the standard GB / T19077-2016.

[0224] (4) Sodium 2032 coin cells of the same specifications were prepared by using the positive electrode materials prepared in the examples and comparative examples, combined with the same sodium sheet negative electrode, electrolyte, and separator. Specifically: the positive electrode material, conductive agent super P, and binder PVDF were added to an appropriate amount of solvent NMP at a mass ratio of 90:5:5 and stirred into a uniform slurry; the slurry was coated on carbon-coated aluminum foil and vacuum dried at 100°C for 12 hours to remove the solvent; it was cut into 14mm diameter round pieces by a punching machine as positive electrode pieces; 30μL of electrolyte (1M NaPF6 dissolved in EC / DEC / EMC (volume ratio 1:1:1)) was added to the positive electrode piece to wet the positive electrode, and a glass fiber separator (diameter slightly larger than the electrode piece) was covered. Then 1μL of electrolyte was added to wet the separator, and the sodium sheet negative electrode was placed.

[0225] The electrical performance of the prepared 2032 button cells was tested under the following conditions: voltage range of 2.0 to 4.0V; ① 0.2C / 0.2C charge-discharge test at 25℃; ② 0.2C / 2.0C rate charge-discharge test at 25℃; ③ 0.5C / 0.5C cycle test at 25℃.

[0226] (5) Powder resistivity meter manufacturer: Haver & Boecker, model: Hosokawa Powder Tester PT-X. Specific testing procedure for powder resistivity: Control the ambient humidity ≤40%RH and temperature 25±2℃, disperse the sample in the test container; calibrate the instrument using a standard 100Ω resistor; load the powder into a special test mold, apply a constant pressure of 8MPa to eliminate air gaps; use the four-probe method, apply a constant current of 1mA to the two outer probes, measure the voltage difference between the two inner probes, and record the resistance value R, sample thickness L, and cross-sectional area A; calculate the resistivity according to the formula ρ=R×A / L; take at least 3 measurements and average the results.

[0227] The test results are shown in Table 2.

[0228] Table 1

[0229]

[0230]

[0231] Table 2

[0232]

[0233] The increased 0.2C discharge voltage indicates that the operating voltage of the sodium secondary battery has been improved.

[0234] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A positive electrode material, characterized in that, Includes a positive electrode active material, wherein the positive electrode active material includes xNa 3.64- a Fe 2.64-a M a (PO4) 1.64-b (BO3) b P2O7·yNa 4-2c Fe 2+c (P2O7)2; Where: Na 3.64-a Fe 2.64-a M a (PO4) 1.64-b (BO3) b P2O7 is the NFPP superlattice solid solution phase; M includes one or more of La, Ce, and Mo, 80 wt% ≤ x ≤ 100 wt%, 0 wt% ≤ y ≤ 20 wt%, 0 < a < 0.1, 0 < b < 0.1, 0 ≤ c ≤ 1, and x + y = 100 wt%.

2. The cathode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1)90wt%≤x≤100wt%, 0wt%≤y≤10wt%; (2)0<a＜0.06； (3)0<b<0.06； (4) Na 4-2c Fe 2+c (P2O7)2 is the NFPO defect solid solution phase.

3. The cathode material according to claim 2, characterized in that, Nanostructures are formed at the interface between the NFPP superlattice solid solution phase and the NFPO defective solid solution phase. and / or The cathode material also includes carbon; Optionally, the carbon content is 1 wt% to 2 wt% based on the mass of the cathode material.

4. The cathode material according to any one of claims 1-3, characterized in that, The cell volume of the NFPP superlattice solid solution phase satisfies and / or In the X-ray diffraction pattern, a first diffraction peak exists at a diffraction angle of 2θ of 9.6 ± 0.1°, and a second diffraction peak exists at a diffraction angle of 2θ of 33.5 ± 0.1°. The interplanar spacing and full width at half maximum (FWHM) of the first diffraction peak are as follows: And 0.40±0.10°, the interplanar spacing and full width at half maximum (FWHM) of the second diffraction peak are respectively and 0.35±0.05°.

5. The cathode material according to any one of claims 1-3, characterized in that, The secondary particle size D of the positive electrode material V 50 is 3-50μm, and can be selected as 10-20μm; Optionally, the secondary particles are formed by the aggregation of multiple primary particles, and the average particle size of the primary particles is ≤500nm, optionally 50~300nm.

6. A method for preparing the positive electrode material according to any one of claims 1-5, characterized in that, Includes the following steps: S1. In a protective atmosphere, water, iron salt, sodium salt, phosphorus salt, boron source, M source and carbon source are mixed to obtain a mixture, and the mixture is milled to obtain a dispersion. S2. Spray dry the dispersion to obtain precursor powder; S3. The precursor powder is heat-treated to obtain the cathode material.

7. The method for preparing the cathode material according to claim 6, characterized in that, At least one of the following conditions must be met: (1) The boron source is selected from one or more of boric acid, borax, sodium borohydride, boron trifluoride, and borosilicate; (2) The M source is selected from one or more of the nitrates, sulfates, and oxides of the M element; (3) The inlet air temperature of the spray dryer is 180-220℃, the outlet air temperature is 100-150℃, and the difference between the inlet air temperature and the outlet air temperature is 60-110℃. Optionally, the inlet air temperature is 190–210°C; Optionally, the outlet air temperature is 110–140°C; Optionally, the temperature difference between the inlet air and the outlet air is 70–100°C; (4) The heat treatment process conditions include a first stage and a second stage: Optionally, the temperature ramp rate for the first stage is 1–5 °C / min, and can be selected as 2–4 °C / min; Optionally, the first stage of the program can be heated to 200–500℃, or optionally 300–400℃; Optionally, the insulation time for the first stage is 0.5 to 5 hours, or 1 to 4 hours. Optionally, the temperature ramp rate for the second stage is 1–5 °C / min, and can be selected as 2–4 °C / min; Optionally, the second stage of the temperature program can be increased to 400–700℃, or optionally 500–600℃; Optionally, the insulation time for the second stage is 6 to 15 hours, or 8 to 12 hours.

8. A positive electrode sheet, characterized in that, include: Positive current collector, and A positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer comprising the positive electrode material according to any one of claims 1-6 or the positive electrode material prepared according to the preparation method of claim 7.

9. A sodium secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 8.

10. An electrical appliance, characterized in that, Including the sodium secondary battery as described in claim 9.

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