Positive electrode material and preparation method thereof, positive plate, battery, battery pack and electric equipment

Abstract

The invention provides a positive electrode material and a preparation method thereof, a positive plate, a battery, a battery pack and electric equipment. The positive electrode material comprises an inner core and a shell layer coating at least part of the surface of the inner core, the inner core comprises a first sodium-based compound; the shell layer comprises a second sodium-based compound and a carbon material; the chemical formula of the first sodium-based compound is Na < 2 + 2x > Fe < 2-x > (SO4) 3; the chemical formula of the second sodium-based compound is Na < 4 > Fe < y-z > M < z > P < 4 > O < 12 + y >; wherein M comprises metal, 0 < x < 2, z > = 0, and y > = z. The positive electrode material provided by the invention is stable in shell structure and small in volume strain, can inhibit structural degradation in the charge-discharge process, can also block a Fe dissolution path, and reduces the loss of iron ions in the cycle process. Therefore, the NFS is synergistically coated by the NFPP and the carbon material, so that the battery prepared from the positive electrode material has excellent cycle life.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of batteries, and particularly relates to a positive electrode material, a preparation method thereof, a positive electrode sheet, a battery, a battery pack and an electrical equipment. BACKGROUND

[0002] Sodium ferric sulfate (NFS, Na 2+2x Fe 2-x (SO4)3) is considered as one of the most potential sodium-ion battery positive electrode materials due to its high working voltage and rich resources of iron and sulfur elements and low cost. However, the actual application of the material faces a key challenge: poor cycle life, which seriously affects the service life of the battery. At present, the performance optimization of sodium ferric sulfate mainly includes carbon coating technology and element doping modification technology, but the cycle performance of the battery is very limited.

[0003] Therefore, how to improve the cycle life of sodium ferric sulfate becomes a technical problem to be solved in the field. SUMMARY

[0004] The first aspect of the present application provides a positive electrode material, which is helpful to improve the cycle life of the battery.

[0005] The second aspect of the present application provides a preparation method of a positive electrode material, which can prepare the above-mentioned positive electrode material, and the positive electrode material is beneficial to improve the cycle life of the battery.

[0006] The third aspect of the present application provides a positive electrode sheet, which is prepared from the above-mentioned positive electrode material, and therefore, the positive electrode sheet is beneficial to improve the capacity retention rate of the battery and improve the cycle life of the battery.

[0007] The fourth aspect of the present application provides a battery, since the battery comprises the above-mentioned positive electrode material or the above-mentioned positive electrode sheet, the capacity retention rate of the battery is high, and the service life is long.

[0008] The fifth aspect of the present application provides a battery pack, since the battery pack is prepared from the above-mentioned battery, the capacity retention rate of the battery pack is high, and the service life is long.

[0009] The sixth aspect of the present application provides an electrical equipment, since the electrical equipment is prepared from the above-mentioned battery pack, the electrical equipment has the advantage of long service life.

[0010] The first aspect of the present application provides a positive electrode material, comprising: a core and a shell layer coated on at least part of the surface of the core; the core comprises a first sodium-based compound, and the shell layer comprises a second sodium-based compound and a carbon material; the chemical formula of the first sodium-based compound is Na 2+2x Fe 2-x (SO4)3; the chemical formula of the second sodium-based compound is Na4Fey- z M z P4O 12+y ; wherein M comprises a metal, 0 < x < 2, z ≥ 0, and y ≥ z.

[0011] The positive electrode material as described above, wherein the positive electrode material satisfies: 0.1 ≤ K ≤ 0.52, wherein K is the ratio of Dv50 of the second sodium-based compound and Dv50 of the first sodium-based compound.

[0012] The positive electrode material as described above, wherein Dv50 of the first sodium-based compound is 2 μm-115 μm, preferably 2 μm-100 μm;

[0013] and / or, Dv50 of the second sodium-based compound is 0.1 μm-45 μm, preferably 0.1 μm-20 μm;

[0014] and / or, the thickness of the shell layer is 0.23 μm-56 μm, preferably 1 μm-50 μm.

[0015] The positive electrode material as described above, wherein the mass percentage of the carbon material in the positive electrode material is m, wherein 0 < m ≤ 10 wt%, preferably 3 wt% ≤ m ≤ 5 wt%;

[0016] and / or, the mass percentage of the second sodium-based compound in the positive electrode material is n, wherein 1 wt% ≤ n ≤ 30 wt%, preferably 5 wt% ≤ n ≤ 20 wt%.

[0017] The positive electrode material as described above, wherein 0 < x ≤ 0.44, preferably 0.1 ≤ x ≤ 0.28; and / or, 2 ≤ y ≤ 4, preferably 2.5 ≤ y ≤ 3.

[0018] The second aspect of the present application provides a preparation method of the positive electrode material, comprising the following steps:

[0019] sintering the mixture of the first sodium-based compound, the second sodium-based compound and the carbon source under inert atmosphere to obtain the positive electrode material.

[0020] The preparation method as described above, wherein the sintering temperature is 300℃-450℃; and / or, the sintering time is 6h-24h.

[0021] The third aspect of the present application provides a positive electrode sheet, comprising the positive electrode material of the first aspect described above, or the positive electrode material prepared by the preparation method of the second aspect described above.

[0022] The fourth aspect of the present application provides a battery comprising the positive electrode material according to the first aspect, or the positive electrode material prepared by the preparation method according to the second aspect, or the positive electrode sheet according to the third aspect.

[0023] The battery as described above, wherein the battery comprises a sodium-ion battery.

[0024] The fifth aspect of the present application provides a battery pack comprising the positive electrode material according to the first aspect, or the positive electrode material prepared by the preparation method according to the second aspect, or the positive electrode sheet according to the third aspect, or at least two batteries according to the fourth aspect.

[0025] The sixth aspect of the present application provides an electrical equipment comprising the positive electrode material according to the first aspect, or the positive electrode material prepared by the preparation method according to the second aspect, or the positive electrode sheet according to the third aspect, or the battery according to the fourth aspect, or the battery pack according to the fifth aspect.

[0026] The positive electrode material provided by the present application comprises a core and a shell layer coated on at least part of the surface of the core; the unique shell layer structure is stable, has small volume strain, can inhibit structural degradation during charging and discharging, and can also block the Fe dissolution path, thereby reducing the loss of iron ions during the cycle process. Therefore, the battery prepared from the positive electrode material has excellent cycle life by the synergistic coating of NFPP and carbon material on NFS. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0028] Figure 1 Structure schematic diagram of the positive electrode material provided for the first embodiment of the present application;

[0029] Figure 2 XRD diagram of the positive electrode material provided for the first embodiment of the present application.

[0030] REFERENCE NUMERALS:

[0031] 1-core; 2-second sodium-based compound; 3-carbon material.

[0032] The specific embodiments of the present application have been shown by the above drawings, and will be described in more detail hereinafter. These drawings and textual descriptions are not intended to limit the scope of the concept of the present application by any means, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0034] Sodium iron sulfate (NFS) is considered one of the most promising cathode materials for sodium-ion batteries due to its high operating voltage, abundant iron and sulfur resources, and low cost. However, its practical application faces a key challenge: poor cycle life, which severely impacts battery lifespan. Currently, performance optimization for NFS mainly involves carbon coating and elemental doping modification, but both have limited effects on improving battery cycle performance. Carbon coating is prone to NFS decomposition due to the high temperatures required for carbon source cracking, leading to impurity phase formation and capacity decay. Furthermore, the high rate of organic carbon layer shedding fails to suppress volume expansion. While elemental doping can delay structural degradation, the doping process significantly increases the original cost of NFS material and can induce crack-derived phases due to lattice stress redistribution, further reducing NFS cycle performance.

[0035] To improve the cycle life of NFS, the inventors conducted in-depth research on the failure mechanism of sodium ferric sulfate during charge and discharge processes. They discovered that NFS failure during charge and discharge has two main causes: one is Fe... 3+ Dissolution leads to the loss of sodium ferric sulfate. On the other hand, mechanical stress is easily generated inside the particles, causing volume expansion and resulting in particle pulverization.

[0036] Based on this, the inventors proposed the cathode material of the present invention.

[0037] like Figure 1 As shown, a first aspect of the present invention provides a cathode material comprising a core 1 and a shell covering at least a portion of the surface of the core 1; the core 1 comprises a first sodium-based compound, and the shell comprises a second sodium-based compound 2 and a carbon material 3; the first sodium-based compound has the chemical formula Na. 2+2x Fe 2-x (SO4)3; the chemical formula of the second sodium-based compound 2 is Na4Fe y-z M z P4O 12+y ; where M includes metals, 0 < x < 2, z ≥ 0, y ≥ z.

[0038] It should be noted that the shell in the cathode material can partially or completely cover the core surface; preferably, the shell completely covers the core surface.

[0039] The specific type of M is not limited in the present application, and can be adjusted according to actual needs. In an embodiment, M includes at least one of cobalt, manganese, nickel, aluminum, and magnesium, and preferably, M is manganese, aluminum, or magnesium.

[0040] The positive electrode material provided by the present application has excellent cycle life and conductivity. The reasons are as follows: on the one hand, the shell layer (NFPP and carbon material) has high structural stability, small volume strain, effectively inhibits the structural degradation in the charging and discharging process, prevents the material from deforming during the cycle process, thereby prolonging the service life of the material; at the same time, because the phosphate in the NFPP has a strong bonding effect with iron, the iron dissolution amount is reduced, the shell layer also acts as a physical barrier to block the Fe dissolution path, reduces the loss of iron ions during the cycle process, maintains the chemical stability of the material, and further improves the cycle performance of the battery; on the other hand, the metal elements (such as Mg, Al, Zn, Ti, Mn, etc.) doped by the second sodium-based compound can effectively improve the structural stability, the metal elements occupy the lattice sites, introduce more stable chemical bonds, optimize the unit cell volume change, inhibit the phase change during the cycle process, and stabilize Fe 2+ / Fe 3+ redox pair; the above three points jointly alleviate the structural degradation in the repeated intercalation / deintercalation process of sodium ions, and improve the cycle life and rate performance of the battery.

[0041] In addition, the shell structure composed of the carbon material and the second sodium-based compound effectively improves the electronic conductivity of the material. In the shell layer, the carbon material and the second sodium-based compound are interwoven to form a three-dimensional conductive network, which significantly enhances the overall electrical conductivity of the positive electrode material. This synergistic effect not only optimizes the charge transport path, but also greatly improves the conductivity of the positive electrode material.

[0042] In summary, the positive electrode material realizes the multiple advantages of "structural stability-electronic conduction-ion diffusion" through the synergistic effect of NFPP and carbon material, and the battery prepared from the positive electrode material has excellent cycle life and conductivity.

[0043] In a specific embodiment, the positive electrode material satisfies: 0.1≤K≤0.52, wherein K is the ratio of Dv50 of the second sodium-based compound 2 to Dv50 of the first sodium-based compound.

[0044] Exemplarily, K is 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or 0.52, or a range formed by two of the above values. When the value of K is in the range, the shell layer is more closely connected with the core, and iron dissolution is less likely to occur.

[0045] Dv50 in the present application refers to the particle size corresponding to the cumulative volume distribution percentage of 50%, i.e. 50% of the material has a particle size less than or equal to the particle size Dv50, and 50% of the material has a particle size greater than the particle size Dv50. The Dv50 of the first sodium-based compound refers to the Dv50 of the secondary particles, which are agglomerates formed by agglomeration of a plurality of primary particles; the Dv50 of the second sodium-based compound refers to the Dv50 of the secondary particles, which are agglomerates formed by agglomeration of a plurality of primary particles.

[0046] In one specific embodiment, the Dv50 of the first sodium-based compound is 2 μm-115 μm, preferably 2 μm-100 μm.

[0047] For example, the Dv50 of the first sodium-based compound is 2 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm or 115 μm, or a range formed by any two of the above values. When the Dv50 of the first sodium-based compound (the Dv50 of the inner core) is within the above range, the inner core has stronger compression resistance and more stable structure during charging and discharging. When the Dv50 of the first sodium-based compound is within the preferred range, the effect is better. In one specific embodiment, the Dv50 of the second sodium-based compound 2 is 0.1 μm-45 μm, preferably 0.1 μm-20 μm.

[0048] For example, the Dv50 of the second sodium-based compound is 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm or 45 μm, or a range formed by any two of the above values. When the Dv50 of the second sodium-based compound is within the above range, the second sodium-based compound can be better coated on the inner core and is less likely to fall off the inner core, and the core-shell structure formed is more stable. When the Dv50 of the second sodium-based compound is within the preferred range, the effect is better.

[0049] In one specific embodiment, the thickness of the shell layer is 0.23 μm-56 μm, preferably 1 μm-50 μm.

[0050] For example, the thickness of the shell layer is 0.23 μm, 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm or 56 μm, or a range formed by any two of the above values. When the thickness of the shell layer is within the above range, the dissolution of iron is inhibited and the transmission efficiency of sodium ions is ensured. When the thickness of the shell layer is within the preferred range, the effect is better.

[0051] The Dv50 and the thickness of the shell in the present application are tested by Tecnai-G2-F20 field emission transmission electron microscope, and the specific operation is as follows: a proper amount of sample is dispersed in a dispersing agent, ultrasonic treatment is performed to form a uniform suspension, a part of the sample is extracted by a dropper and loaded on a supporting film, and after sufficient drying, the sample preparation is completed, and then electron microscope observation is performed, 50 regions are randomly selected under 10k to 50k magnification, the particle size of the first sodium-based compound, the particle size of the second sodium-based compound and the thickness of the shell are counted, and the Dv50 of the first sodium-based compound, the Dv50 of the second sodium-based compound and the average thickness of the shell are calculated. Among them, the data statistics can select the particle size of different angles of the same particle, or the particle size of different particles, and this is not limited.

[0052] In a specific embodiment, the mass percentage of the carbon material 3 in the positive electrode material is m, wherein 0 < m < 10wt%, preferably 3wt% < m < 5wt%.

[0053] Exemplarily, the mass percentage of the carbon material in the positive electrode material is 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%, or a range formed by two of them. When the mass percentage of the carbon material in the positive electrode material is within the range, the structural stability of the positive electrode material can be further improved, and the iron dissolution amount in the cycle process is reduced. When the mass percentage of the carbon material in the positive electrode material is in the preferred range, the material can achieve a balance of cost and performance.

[0054] The test method of the mass percentage m of the carbon material in the positive electrode material is tested by an infrared (carbon sulfur) analyzer. The specific operation is as follows: the sample is burned to generate carbon dioxide and sulfur dioxide gas in a high-temperature furnace with oxygen, so as to separate the carbon and sulfur elements from the metal elements and compounds, and then the content of carbon dioxide and sulfur dioxide is measured, and the content of carbon and sulfur is converted. Therefore, the value of m can be measured. In a specific embodiment, the mass percentage of the second sodium-based compound 2 in the positive electrode material is n, wherein 1wt% < n < 30wt%, preferably 5wt% < n < 20wt%.

[0055] Exemplarily, the mass percentage of the second sodium-based compound in the positive electrode material is 1wt%, 3wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 24wt%, 26wt% or 30wt%, or a range formed by two of them. When the mass percentage of the second sodium-based compound in the positive electrode material is within the above range, the shell material and the core material can achieve a better balance, which not only reduces the iron dissolution amount, but also inhibits the volume strain of NFS, and also ensures the ion transmission efficiency.

[0056] The test method of the second sodium-based compound accounts for the mass percentage n of the positive electrode material: ICP test is performed using Thermo Fisher Scientific ICAP PRO X, and the specific operation is as follows: an appropriate amount of sample is placed in a sample bottle, an appropriate amount of aqua regia is added to heat and dissolve the sample until there is no residual particle, and after cooling, it is placed in a sample bin, and the content of each component element is tested and analyzed to obtain the concentration of the corresponding element in the sample. Combined with the results of infrared (carbon and sulfur) test of the sample and EDS spectrum test of the sample, the value of n is calculated.

[0057] In order to further improve the cycle life of the battery, the range of x and y of the positive electrode material can also be controlled.

[0058] In a specific embodiment, 0 < x < 0.44; preferably, 0.1 < x < 0.28.

[0059] Illustratively, x is 0.01, 0.1, 0.14, 0.18, 0.2, 0.24, 0.28, 0.3, 0.34, 0.38, 0.4 or 0.44, or a range formed by two of the above values. When x is within the range, the volume expansion of NFS in the core during charging and discharging is smaller, and the structural stability of NFS is better, so that the structural stability of the positive electrode material is good, thereby improving the cycle performance of the battery. The value of x affects the ease of controlling the specific capacity of NFS and the stability of the finished product during synthesis. Within the preferred range, x has both high specific capacity and good batch stability.

[0060] In a specific embodiment, 2 < y < 4, preferably, 2.5 < y < 3.

[0061] Illustratively, y is 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9 or 4, or a range formed by two of the above values. NFPP is used to provide a stable shell structure. When y is within the above range, the stability of the Fe-O-P framework in the crystal structure of NFPP is higher, which can further reduce the iron dissolution amount. The stability of the Fe-O-P framework also ensures that the volume change of NFPP is small, ensuring the structural stability of the positive electrode material, and thereby improving the cycle life of the battery. The NFPP in the preferred range has better structural stability and better electrical performance.

[0062] The test method of x of the first sodium-based compound and y of the second sodium-based compound: the test is performed using a Hitachi cold field scanning electron microscope-SU8600 SEM, and the specific operation is as follows: an appropriate amount of dry powder is adhered to a carbon tape, and then the carbon tape is placed on a sample table, and after vacuumizing, SEM scanning electron microscope test and energy spectrum EDS test are performed to determine the element ratio of the first sodium-based compound and the second sodium-based compound, and to determine the values of x and y.

[0063] The second aspect of the present application provides a preparation method of a positive electrode material, comprising the following steps:

[0064] The mixture of the first sodium-based compound, the second sodium-based compound and the carbon source is sintered under an inert atmosphere to obtain the positive electrode material.

[0065] It should be noted that the inert atmosphere of the present application includes at least one of argon, nitrogen and argon-hydrogen mixed gas. The present application does not make specific limitation to the equipment used for sintering, which can be a crucible, a sintering furnace, etc.

[0066] The preparation method of the positive electrode material provided by the present application sintering the mixture of the sodium source, the iron source, the sulfur source, the carbon source, the phosphorus source and the M source to perform in-situ surface coating to obtain the positive electrode material. The positive electrode material prepared by the method is beneficial to improve the cycle life of the battery.

[0067] The present application does not make specific limitation to the type of carbon source, and a conventional carbon source in the art can be used. For example, the carbon source can be at least one of carbon nanotubes, graphene, glucose and polyethylene glycol. Graphene can significantly improve the electron transmission efficiency due to its high conductivity and two-dimensional structure, and is particularly suitable for high-rate application scenarios; glucose as a low-cost biomass carbon source can form a porous carbon layer through low-temperature carbonization, and has the functions of conductivity and buffering volume expansion; the carbon layer formed after carbonization of PEG has an elastic network structure, which can buffer the volume change of NFS during charging and discharging, and improve the cycle life.

[0068] The raw materials of the first sodium-based compound include a sodium source, an iron source and a sulfur source, and the types of the sodium source, the iron source and the sulfur source are not limited herein, for example: the sodium source includes one or more than one combination of sodium sulfate, sodium carbonate and sodium sulfate decahydrate; the iron source includes one or more than one combination of ferrous sulfate monohydrate, ferrous sulfate tetrahydrate, ferrous sulfate heptahydrate and anhydrous ferrous sulfate; and the sulfur source includes at least one of sodium sulfate, ferrous sulfate, ferrous sulfate tetrahydrate, ferrous sulfate heptahydrate and anhydrous ferrous sulfate.

[0069] When the above-mentioned sodium source, iron source and sulfur source are mixtures of the aforementioned substances, the present application does not make specific limitation to the proportion of each specific substance in the mixture.

[0070] In one embodiment, the element ratio of the first sodium-based compound can meet Na 2+2xFe 2-x The sodium source, iron source and sulfur source of (SO4)3 are mixed with grinding balls after drying, and NFS precursor is obtained after ball milling, and then the NFS precursor is mixed with a carbon source, Na4Fe y-z M z P4O 12+y And then sintering.

[0071] The ball milling time is not specifically limited in the present application, and in an embodiment, the ball milling time is 6h-24h.

[0072] Further, in order to mix the NFS precursor, the carbon source, Na4Fe y-z M z P4O 12+y The NFS precursor, the carbon source, Na4Fe y- z M z P4O 12+y The NFS precursor, the carbon source, Na4Fe

[0073] The method for preparing the nanoscale suspension liquid comprises the following steps:

[0074] The NFS precursor, the carbon source, Na4Fe y-z M z P4O 12+y The NFS precursor, the carbon source, Na4Fe

[0075] The type of the grinding liquid is not specifically limited in the present application, and for example, can be at least one of anhydrous ethanol, isopropyl alcohol, ethyl acetate, cyclohexane and acetone.

[0076] The mass ratio of the NFS precursor, the carbon source, Na4Fe y-z M z P4O 12+y The mass ratio of the NFS precursor, the carbon source, Na4Fe y-z M z P4O 12+y The mass ratio of the NFS precursor, the carbon source, Na4Fe

[0077] The type of the grinding ball is not specifically limited in the present application, and for example, can be at least one of stainless steel, alumina, zirconia, agate and tungsten carbide.

[0078] The ball-to-material ratio is not specifically limited in the present application, and can be adjusted as required. In an embodiment, the ball-to-material ratio is 1:5-20.

[0079] This invention does not impose a specific limit on the grinding time, which can be adjusted as needed. In one embodiment, the grinding time is 3-12 hours.

[0080] This invention relates to Na4Fe y-z M z P4O 12+y The preparation method is not specifically limited; any conventional preparation method in this field may be used.

[0081] In one embodiment, Na4Fe y-z M z P4O 12+y The preparation methods include:

[0082] Sodium source, iron source, phosphorus source, M source, and oxidant were dissolved in water to obtain aqueous solutions. After thorough mixing, the pH was adjusted to 1.5-5, and the mixture was aged for 1-24 hours with stirring. After centrifugation or filtration, washing, and drying, an amorphous iron-phosphorus compound precursor, Na₄Fe, was obtained. y-z M z P4O 12+y Precursor.

[0083] The above amorphous iron phosphorus compound precursors were thoroughly mixed into a homogeneous slurry, with elemental proportions matching the target product Na4Fe. y-z M z P4O 12+y The elemental composition was determined. After spray drying the slurry, precursor powder was obtained. The precursor powder was then sintered under an inert atmosphere to obtain Na₄Fe₂O₃. y-z M z P4O 12+y .

[0084] This invention relates to the preparation of Na4Fe y-z M z P4O 12+y The conditions for sintering are not specifically limited. In one embodiment, the sintering temperature is 450℃-600℃ and the sintering time is 8h-24h.

[0085] For example, the sintering temperature is 450℃, 455℃, 460℃, 465℃, 470℃, 475℃, 480℃, 485℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, or 600℃, or a range of any two of these values. When the sintering temperature is within the above range, the resulting Na4Fe... y- z M z P4O 12+yThe structure is more stable. For example, the sintering time is 8h, 10h, 12h, 15h, 18h, 20h or 24h, or a range formed by any two of the above values. When the sintering time is within the above range, the Na4Fe y-z M z P4O 12+y The structure is more stable. In an embodiment, the molar ratio of Fe / P in the amorphous phosphorus-iron compound precursor satisfies 0.5≤Fe / P≤1.

[0086] The Na4Fe y-z M z P4O 12+y In the preparation method of the Na4Fe

[0087] In an embodiment, the sodium source includes one or more combinations of sodium acetate, sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium oxalate, and sodium citrate; the iron source includes one or more combinations of soluble +2 valence iron salt and +3 valence iron salt, such as ferric nitrate, ferrous nitrate, ferrous sulfate, ferric sulfate, ferric chloride, ferrous chloride, ferrous acetate, and ferrous phosphate; the phosphorus source includes one or more combinations of soluble phosphate or pyrophosphate, such as phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, and sodium pyrophosphate; and the M source includes one or more combinations of metal acid salt, such as manganese carbonate, magnesium oxalate, and aluminum oxalate.

[0088] The present application does not limit the source of the sodium source, the iron source, the phosphorus source, and the M source. Commercially available products or products prepared by conventional methods known to those skilled in the art can be used.

[0089] The present application does not specifically limit the type of oxidizing agent, which can be at least one of hydrogen peroxide, nitric acid, potassium permanganate, and potassium chlorate. In an embodiment, the oxidizing agent is hydrogen peroxide.

[0090] In an embodiment, when spray drying, the solid content of the above-mentioned precursor powder is controlled to be 20%-50%, the target particle size of the droplets is 2-100 μm, the outlet temperature is controlled to be 40-200°C, and the pressure is 1.0-2.0 bar.

[0091] The present application does not make specific limitations on the above drying methods, for example, can be at least one of oven air drying, vacuum drying, spray drying, flash evaporation, spin evaporation.

[0092] In one embodiment, the sintering temperature is 300-450 DEG C. Illustratively, the sintering temperature is 300 DEG C, 310 DEG C, 320 DEG C, 330 DEG C, 340 DEG C, 350 DEG C, 360 DEG C, 370 DEG C, 380 DEG C, 390 DEG C, 400 DEG C, 410 DEG C, 420 DEG C, 430 DEG C, 440 DEG C or 450 DEG C, or a range between any two of them. Within the above range, the carbon source, Na4Fe y-z M z P4O 12+y The inner core is more tightly coated, and the structure of the obtained positive electrode material is more stable; at the same time, sintering at low temperature further ensures the structural stability of NFS.

[0093] In one embodiment, the sintering time is 6-24h. Illustratively, the sintering time is 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h, or a range between any two of them. Within the above range, the carbon source, Na4Fe y-z M z P4O 12+y The inner core is more tightly coated, and the structure of the obtained positive electrode material is more stable; at the same time, sintering at low temperature further ensures the structural stability of NFS.

[0094] The third aspect of the present application provides a positive electrode sheet comprising the positive electrode material of the first aspect or prepared by the preparation method of the second aspect. The positive electrode sheet has the technical effects corresponding to the positive electrode material, which will not be repeated here.

[0095] The positive electrode sheet of the present application specifically comprises a positive electrode current collector and a positive electrode active layer formed by the positive electrode active material (the positive electrode material of the present application) arranged on the surface of the positive electrode current collector.

[0096] In the preparation of the positive electrode sheet, for example, the positive electrode material of the present application, a conductive agent and a binder can be dispersed in an appropriate amount of N-methyl pyrrolidone (NMP) solvent, and stirred thoroughly to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector, and then dried, rolled and cut to obtain the positive electrode sheet. In one embodiment, the positive electrode active layer comprises 70-99wt% of the positive electrode active material (the positive electrode material of the present application), 0.5-15wt% of the conductive agent and 0.5-15wt% of the binder, further comprising 80-98wt% of the positive electrode active material (the positive electrode material of the present application), 1-10wt% of the conductive agent and 1-10wt% of the binder.

[0097] The material of the positive electrode current collector can be at least one of an aluminum foil and a nickel foil; the conductive agent can be at least one of carbon black, acetylene black, graphene, ketjen black, carbon fiber, carbon nanotube, and conductive graphite; and the binder can be at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, an oxirane-containing polymer, polyvinylpyrrolidone, and polyurethane.

[0098] The fourth aspect of the present application provides a battery comprising the positive electrode material of the first aspect, or the positive electrode material prepared by the preparation method of the second aspect, or the positive electrode sheet of the third aspect. The battery has excellent cycle life and conductivity.

[0099] The battery of the present application comprises, in addition to the positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. Hereinafter, the preparation method of a sodium-ion battery is taken as an example.

[0100] The present application does not strictly limit the negative electrode active material in the negative electrode sheet, which can be at least one of the negative electrode active materials commonly used in current sodium-ion batteries, such as hard carbon, soft carbon, titanium-based materials, metal oxides, and sulfides.

[0101] The present application does not strictly limit the selection of the electrolyte, for example, it can include one or more of the solvents commonly used in the electrolyte of the current sodium-ion battery, and the electrolyte sodium salt commonly used in the current sodium-ion electrolyte, for example: the solvent can be ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, gamma-butyrolactone, etc.; the electrolyte can be selected from one or more of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, and sodium fluorotri-fluoromethylsulfonylimide.

[0102] The present application does not strictly limit the material selection of the separator, which can be one of the separator materials commonly used in the current sodium-ion battery, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene three-layer composite membrane (PP / PE / PP), cellulose non-woven separator, and ceramic-coated separator.

[0103] In one specific embodiment, the battery comprises a sodium-ion battery.

[0104] In the preparation of the sodium ion battery, the positive electrode sheet, the separator and the negative electrode sheet are wound or laminated to obtain a bare battery cell, and the bare battery cell is packaged into an aluminum plastic film bag which is pre-punched and formed. After the packaged battery is dried at 85 DEG C, the electrolyte is injected into the dried battery, and the battery is completed after standing, formation and secondary sealing.

[0105] The specific type of the battery of the present application is not particularly limited, for example, from the perspective of shape, the battery includes but is not limited to square cell, soft pack battery and cylindrical battery, etc., and the present application does not make special limitation. From the perspective of the core structure, the core of the battery can be a wound core (i.e. the positive electrode sheet, the negative electrode sheet and the separator are stacked and then wound to form the core), or a laminated core (i.e. a plurality of positive electrode sheets, negative electrode sheets and separators are stacked to form the core). The shell can be a hard shell (such as a steel shell, a hard plastic shell, etc.), or a soft shell (such as an aluminum plastic film, a bag type soft shell, etc.). The present application does not make special limitation.

[0106] The fifth aspect of the present application provides a battery pack comprising the positive electrode material of the first aspect, or the positive electrode material prepared by the preparation method of the second aspect, or the positive electrode sheet of the third aspect, or at least two batteries of the fourth aspect.

[0107] The battery of the present application can include battery monomer form, battery module form and battery pack form. In some embodiments, the battery monomer can be assembled into a battery module. In some embodiments, the battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0108] The sixth aspect of the present application provides a power consuming device comprising the positive electrode material of the first aspect, or the positive electrode material prepared by the preparation method of the second aspect, or the positive electrode sheet of the third aspect, or the battery of the fourth aspect, or the battery pack of the fifth aspect. The power consuming device has the advantage of long service life. The power consuming device provided by the present application can be a conventional power consuming device in the art, for example, a power device (such as an electric vehicle, an electric car), a power consuming device (such as a mobile phone, a tablet computer, a notebook computer, a digital camera, etc.), a wearable device (such as a watch, a bracelet, VR glasses, etc.), a power storage station, etc., which is not particularly limited.

[0109] In the following, the present application is further introduced through specific embodiments.

[0110] Example 1

[0111] (1) Preparation of NFS precursor

[0112] Accurately weigh 5.0 mmol of ferrous sulfate heptahydrate (FeS04-7H20) and 3.2 mmol of anhydrous sodium sulfate (Na2S04), and place them in a drying oven for drying at 120 °C for 8 h to remove the crystal water and surface adsorbed water. Then, the dried ferrous sulfate heptahydrate and anhydrous sodium sulfate are loaded into a ball mill tank together with zirconium oxide grinding balls (ball-to-material ratio of 1:10), 30 mL of anhydrous ethanol is added as a grinding liquid, and a planetary ball mill is used for grinding at a speed of 450 rpm for 8 h to obtain NFS precursor powder.

[0113] (2) Preparation of NFPP

[0114] Dissolve 10 mmol of Na4P207, 30 mmol of FeC204, and 20 mmol of NH4H2P04 in 50 mL of deionized water, respectively, mix them, add 10 mL of 30% hydrogen peroxide (H202) as an oxidant, stir for 30 min, adjust the pH to 2.5 with 0.1 M hydrochloric acid, and age for 3 h under magnetic stirring. Then, centrifugal washing is performed (at a speed of 8000 rpm for 3 times), and the obtained amorphous phosphorus-iron precursor is dried to obtain a dry powder by spray drying (nozzle diameter of 1.5 mm, pressure of 1.2 bar, inlet temperature of 180 °C, and outlet temperature of 90 °C). Finally, the dry powder is sintered at a temperature of 550 °C under an argon-hydrogen mixed gas (5% H2+Ar) atmosphere at a heating rate of 5 °C / min, and sintered at this temperature for 6 h (i.e., a first sintering treatment) to obtain NFPP, i.e., a second sodium-based compound.

[0115] (3) Preparation of the positive electrode material

[0116] Mix 10 g of NFPP with 200 mL of isopropyl alcohol (mass ratio of 1:80), add zirconium oxide grinding balls (ball-to-material ratio of 1:15), and ball mill for 6 h to prepare a NFPP suspension. Mix the NFS precursor powder, the NFPP suspension, and the carbon nanotubes according to a mass ratio of 81.5:15:3.5, and keep the mixture under magnetic stirring for 2 h to obtain a mixed solution. The mixed solution is spray dried (solid content of 30%, droplet size of 10-50 pm, inlet temperature of 160 °C, outlet temperature of 80 °C, and pressure of 1.5 bar) to obtain a precursor powder. Finally, the precursor powder is sintered at a temperature of 400 °C under a nitrogen atmosphere at a heating rate of 5 °C / min for 10 h (i.e., a second sintering treatment) to obtain Na 2.2 Fe 1.9 (SO4)3@Na4Fe3P4O 15 , i.e., a positive electrode material.

[0117] Example 2

[0118] This example is basically the same as Example 1, except that:

[0119] In step (1), the ball milling time was 12 h;

[0120] In step (3), the ball milling time was 18 h.

[0121] Example 3

[0122] This example is essentially the same as Example 1, except that:

[0123] In step (1), the ball milling time was 2 h;

[0124] In step (3), the ball milling time was 3 h.

[0125] Example 4

[0126] This example is essentially the same as Example 1, except that:

[0127] In step (1), the ball milling time was 4 h;

[0128] In step (3), the ball milling time was 1.5 h.

[0129] Example 5

[0130] This example is essentially the same as Example 1, except that:

[0131] In step (1), the ball milling time was 0.2 h;

[0132] In step (3), the ball milling time was 1.5 h.

[0133] Example 6

[0134] This example is essentially the same as Example 1, except that:

[0135] In step (1), the ball milling time was 5 h;

[0136] In step (3), the ball milling time was 0.8 h.

[0137] Example 7

[0138] This example is essentially the same as Example 1, except that:

[0139] In step (1), the ball milling time was 0 h;

[0140] In step (3), the ball milling time was 0.8 h.

[0141] Example 8

[0142] This example is essentially the same as Example 1, except that:

[0143] In step (1), ferrous sulfate heptahydrate (FeS04-7H20): 3.94 mmol, anhydrous sodium sulfate (Na2S04): 2.07 mmol.

[0144] Example 9

[0145] This example is basically identical with Example 1, except that:

[0146] In step (1), ferrous sulfate heptahydrate (FeS04-7H20): 3.16 mmol, anhydrous sodium sulfate (Na2S04): 2.84 mmol.

[0147] Example 10

[0148] This example is basically identical with Example 1, except that:

[0149] In step (1), ferrous sulfate heptahydrate (FeS04-7H20): 3.12 mmol, anhydrous sodium sulfate (Na2S04): 2.88 mmol.

[0150] Example 11

[0151] This example is basically identical with Example 1, except that:

[0152] In step (2), Na4P207: 10 mmol, FeC204: 10 mmol, NH4H2P04: 20 mmol.

[0153] Example 12

[0154] This example is basically identical with Example 1, except that:

[0155] In step (2), Na4P207: 15 mmol, FeC204: 15 mmol, NH4H2P04: 30 mmol.

[0156] Example 13

[0157] This example is basically identical with Example 1, except that:

[0158] In step (2), Na4P207: 10 mmol, FeC204: 25 mmol, NH4H2P04: 20 mmol.

[0159] Example 14

[0160] This example is basically identical with Example 1, except that:

[0161] In step (2), FeC204: 40 mmol, NaH2P04: 40 mmol.

[0162] Example 15

[0163] This example is basically identical with Example 1, except that:

[0164] In Step (3), the ball-milling time is 20h.

[0165] Example 16

[0166] This example is basically identical with Example 1, except that:

[0167] In Step (1), the ball-milling time is 2h;

[0168] In Step (3), the ball-milling time is 2h.

[0169] Example 17

[0170] This example is basically identical with Example 1, except that:

[0171] In Step (1), the ball-milling time is 0.2h;

[0172] In Step (3), the ball-milling time is 0.2h.

[0173] Example 18

[0174] This example is basically identical with Example 1, except that: In Step (1), the ball-milling time is 0.2h;

[0175] In Step (3), the ball-milling time is 0h.

[0176] Example 19

[0177] This example is basically identical with Example 1, except that: The mass percentage of carbon nanotubes in the positive electrode material is 1wt%.

[0178] Example 20

[0179] This example is basically identical with Example 1, except that: The mass percentage of carbon nanotubes in the positive electrode material is 3wt%.

[0180] Example 21

[0181] This example is basically identical with Example 1, except that: The mass percentage of carbon nanotubes in the positive electrode material is 5wt%.

[0182] Example 22

[0183] This example is basically identical with Example 1, except that: The mass percentage of carbon nanotubes in the positive electrode material is 8wt%.

[0184] Example 23

[0185] This example is substantially identical to Example 1, except that the mass percentage of carbon nanotubes in the positive electrode material is 10 wt%.

[0186] Example 24

[0187] This example is substantially identical to Example 1, except that the mass percentage of the second sodium-based compound in the positive electrode material is 1 wt%.

[0188] Example 25

[0189] This example is substantially identical to Example 1, except that:

[0190] y = 2.5, Dv50 of the second sodium-based compound is 2.47 pm, K = 0.46, and the mass percentage of the second sodium-based compound in the positive electrode material is 5 wt%.

[0191] Example 26

[0192] This example is substantially identical to Example 1, except that:

[0193] Dv50 of the second sodium-based compound is 2.47 pm, K = 0.46, and the mass percentage of the second sodium-based compound in the positive electrode material is 20 wt%.

[0194] Example 27

[0195] This example is substantially identical to Example 1, except that:

[0196] Dv50 of the second sodium-based compound is 2.47 pm, K = 0.46, and the mass percentage of the second sodium-based compound in the positive electrode material is 30 wt%.

[0197] Example 28

[0198] This example is substantially identical to Example 1, except that:

[0199] In step (2), 10 mmol Na4P207, 24 mmol FeC204, 20 mmol NH4H2PO4, 2 mmol MnCO3 were dissolved in 50 mL deionized water, respectively, mixed and then 10 mL 30% hydrogen peroxide (H2O2) was added as oxidant, stirred for 30 min, and then pH was adjusted to 2.5 with 0.1 M hydrochloric acid, and aged for 3 h under magnetic stirring. Subsequently, centrifugal washing was performed (8000 rpm for 3 times), and then the amorphous phosphorus-iron precursor was obtained after drying. The obtained amorphous phosphorus-iron precursor was dissolved in deionized water to prepare a slurry with solid content of 35%, and then dry powder was obtained by spray drying (nozzle diameter 1.5 mm, pressure 1.2 bar, inlet temperature 180 °C, outlet temperature 90 °C). Finally, the dry powder was sintered at 550 °C under argon-hydrogen mixed gas (5% H2+Ar) atmosphere at a heating rate of 5 °C / min, and then sintered at this temperature for 8 h (i.e. first sintering treatment), to obtain Na4Fe 2.4 Mn 0.2 P4O 15 , i.e. the second sodium-based compound.

[0200] Example 29

[0201] This example is basically the same as Example 1, except that:

[0202] In step (2), 10 mmol Na4P207, 24 mmol FeC204, 20 mmol NH4H2PO4, 2 mmol MnCO3 were dissolved in 50 mL deionized water, respectively, mixed and then 10 mL 30% hydrogen peroxide (H2O2) was added as oxidant, stirred for 30 min, and then pH was adjusted to 2.5 with 0.1 M hydrochloric acid, and aged for 3 h under magnetic stirring. Subsequently, centrifugal washing was performed (8000 rpm for 3 times), and then the amorphous phosphorus-iron precursor was obtained after drying. The obtained amorphous phosphorus-iron precursor was dissolved in deionized water to prepare a slurry with solid content of 35%, and then dry powder was obtained by spray drying (nozzle diameter 1.5 mm, pressure 1.2 bar, inlet temperature 180 °C, outlet temperature 90 °C). Finally, the dry powder was sintered at 550 °C under argon-hydrogen mixed gas (5% H2+Ar) atmosphere at a heating rate of 5 °C / min, and then sintered at this temperature for 8 h (i.e. first sintering treatment), to obtain Na4Fe 2.5 Mg 0.5 P4O 15 , i.e. the second sodium-based compound.

[0203] Example 30

[0204] This example is basically the same as Example 1, except that in step (2), 10 mmol of Na4P2O7, 25 mmol of FeC2O4, 20 mmol of NH4H2PO4, and 1.67 mmol of Al2(C2O4)3 were dissolved in 50 mL of deionized water, respectively, mixed, and then 10 mL of 30% hydrogen peroxide (H2O2) was added as an oxidant. After stirring for 30 min, the pH was adjusted to 2.5 with 0.1 M hydrochloric acid, and the mixture was aged under magnetic stirring for 3 h. Subsequently, centrifugal washing (8000 rpm, 3 times) was performed, and the obtained amorphous phosphorus-iron precursor was dried to obtain a dry powder. Finally, the dry powder was sintered at 550°C at a temperature increase rate of 5°C / min under an argon-hydrogen mixed gas (5% H2+Ar) atmosphere (i.e., a first sintering treatment) to obtain Na4Fe 2.5 Al 0.33 P4O 15 , i.e., a second sodium-based compound.

[0205] The second sodium-based compound accounts for 0.1 wt% of the mass percentage of the positive electrode material.

[0206] Comparative Example 1

[0207] 5 mmol of FeSO4·7H2O was accurately weighed and dried in a muffle furnace at 200°C for 12 h to remove the crystal water. Subsequently, the dried ferrous sulfate was mixed with 3.2 mmol of anhydrous sodium sulfate (Na2SO4). The above-mentioned raw materials (ferrous sulfate, anhydrous sodium sulfate) were transferred to a zirconium oxide jar, and 30 mL of anhydrous ethanol was added as a grinding liquid. The zirconium oxide balls used had a diameter of 0.5 mm, and the ball-to-material ratio was 5:1. A planetary ball mill was used to perform ball milling on the mixture at a speed of 400 rpm to obtain a precursor mixture, and the ball milling time was 2 h. Subsequently, the precursor mixture was pumped into a spray dryer at a speed of 300 mL·h -1 -1 to obtain a bluish-gray precursor powder. The nozzle diameter of the spray dryer was 2 mm, the pressure was 0.4 MPa, the inlet temperature was set to 200°C, and the outlet temperature was 100°C. Finally, the precursor powder was calcined in a quartz tube furnace at 350°C for 12 h (heating rate of 5°C / min -1 , under an Ar+5% H2 atmosphere), to obtain Na 2.2 Fe 1.9 (SO4)3.

[0208] Comparative Example 2

[0209] 5 mmol of FeSO4·7H2O was accurately weighed and dried in a muffle furnace at 200℃ for 12 h to remove the crystal water. Then, the dried ferrous sulfate was mixed with 3.2 mmol of anhydrous sodium sulfate (Na2SO4). Ascorbic acid was added as a reducing agent and carbon source, and carbon nanotubes (CNTs); the ascorbic acid accounted for 5 wt% of the total mass of the positive electrode active material, and the carbon nanotubes accounted for 3 wt% of the total mass of the positive electrode active material. The above raw materials (ferrous sulfate, anhydrous sodium sulfate, ascorbic acid, carbon nanotubes) were transferred to a zirconium oxide jar, and 30 mL of anhydrous ethanol was added as a grinding liquid, and the zirconium oxide balls used had a diameter of 0.5 mm, and the ball-to-material ratio was 5:1. A planetary ball mill was used to ball mill the mixture at a speed of 400 rpm to obtain a precursor mixture, and the ball milling time was 2 h. Then, the precursor mixture was pumped into a spray dryer at a speed of 300 mL·h -1 -1 to obtain a gray precursor powder. The nozzle diameter of the spray dryer was 2 mm, the pressure was 0.4 MPa, the inlet temperature was set to 200℃, and the outlet temperature was 100℃. Finally, the precursor powder was calcined in a quartz tube furnace at 350℃ for 12 h (heating rate 5℃ / min -1 under an Ar+5% H2 atmosphere) to obtain Na 2.2 Fe 1.9 (SO4)3@C.

[0210] Comparative Example 3

[0211] This comparative example is basically the same as Example 1, except that:

[0212] No carbon nanotubes were added in step (3) to obtain Na 2.2 Fe 1.9 (SO4)3@Na4Fe3P4O 15 .

[0213] Test Example

[0214] 1. Physical property test The positive electrode material prepared in Example 1 was subjected to XRD test, and the results are shown in Figure 2 .

[0215] (1) Dv50, thickness of shell layer

[0216] Test using Tecnai-G2-F20 field emission transmission electron microscope: disperse an appropriate amount of sample in dispersant, ultrasonic treatment to form a uniform suspension, extract part of the sample with a dropper to load on a support film, complete sample preparation after sufficient drying, then electron microscope observation, randomly select 50 regions under 10k to 50k magnification, count the particle size of the first sodium-based compound, the second sodium-based compound, the thickness of the shell layer, and calculate the Dv50 of the first sodium-based compound, the Dv50 of the second sodium-based compound, and the average thickness of the shell layer. Among them, data statistics can select particle sizes at different angles of the same particle, or particle sizes of different particles without limitation.

[0217] (2) The mass percentage m of the carbon material in the positive electrode material

[0218] Test by infrared (carbon sulfur) analyzer, specific operation as follows: burn the sample in a high-temperature furnace with oxygen to generate carbon dioxide and sulfur dioxide gas, separate carbon and sulfur elements from metal elements and compounds, then measure the content of carbon dioxide and sulfur dioxide, and convert the content of carbon and sulfur. Therefore, the m value can be measured.

[0219] (3) x of the first sodium-based compound and y of the second sodium-based compound

[0220] Test using Hitachi cold field scanning electron microscope-SU8600SEM, specific operation as follows: take an appropriate amount of dry powder and stick it on a carbon tape, and place it on a sample stage, vacuumize, then perform SEM scanning electron microscope test and energy spectrum EDS test to determine the element ratio of the first sodium-based compound and the second sodium-based compound, and determine the x and y values.

[0221] (4) The mass percentage n of the second sodium-based compound in the positive electrode material

[0222] ICP test using Thermo Fisher ScientificICAP PRO X, specific operation as follows: put an appropriate amount of sample into a sample bottle, add an appropriate amount of aqua regia to heat and dissolve the sample until there is no residual particle, then put it into the sample bin after cooling, test and analyze the content of each component element, obtain the concentration of the corresponding element in the sample, and combine the results of infrared (carbon sulfur) test of the sample and EDS spectrum test of the sample to calculate the n value.

[0223] (5) XRD test method: using Rigaku intelligent multifunctional X-ray diffractometer Smartlab SE, specific operation as follows: take 0.1g sample and load it into the sample stage, take another carrier and press it on the sample to flatten the surface, turn on the X-ray diffractometer, set the scanning range to 10°-60°, step size to 0.02°, and scanning speed to 2° / min.

[0224] The parameters of different embodiments and comparative examples are shown in Table 1.

[0225] Table 1

[0226]

[0227]

[0228] 2. Electrochemical performance test

[0229] The positive electrode materials prepared in the above examples and comparative examples were respectively prepared into sodium ion batteries, and the specific capacity, the Fe content on the negative electrode side after 2000 cycles, and the cycle number before the capacity retention rate decays to 70% of the initial value were tested. The test results are shown in Table 2.

[0230] Preparation of sodium ion battery:

[0231] After the positive electrode materials prepared in all examples and the positive electrode materials prepared in the comparative example were prepared into positive electrode sheets, and the negative electrode sheet, the electrolyte and the separator were assembled into sodium ion batteries according to the following method. The method comprises:

[0232] 1) The positive electrode materials prepared in the examples and the positive electrode materials prepared in the comparative example were respectively mixed with conductive carbon black and PVDF at a weight ratio of 96%:2%:2%, and the positive electrode slurry was obtained by dispersion. The slurry was coated on an aluminum foil current collector, and the positive electrode sheet was prepared by rolling at a positive electrode surface density of 4.12 g / cm 3 Rolling to prepare the positive electrode sheet;

[0233] 2) The artificial graphite, styrene diene rubber (SBR), sodium carboxymethyl cellulose and conductive carbon black were mixed at a weight ratio of 94%:3%:2%:1%, and the mixture was dispersed in water to obtain a negative electrode slurry by double planetary mixing. The slurry was coated on a copper current collector, and then rolling and drying were performed to obtain a negative electrode sheet;

[0234] 3) The positive electrode sheet, the negative electrode sheet and the separator were assembled into a sodium ion battery, and a non-aqueous electrolyte was injected. The electrolyte was mixed at a mass ratio of ethylene carbonate (abbreviated as EC): diethyl carbonate (abbreviated as DEC): propylene carbonate (abbreviated as PC) = 2:5:3, and then 5% of fluoroethylene carbonate (abbreviated as FEC) and 13% of sodium hexafluorophosphate were added, accounting for 2% of the total content of the electrolyte.

[0235] Test method:

[0236] 1) Specific capacity: for the assembled button cell, the 2.0V-4.2V, 0.1C cycle curve was tested using an electrochemical workstation, and the specific capacity of the positive electrode active material was calculated by the first cycle capacity value and the measured weight of the electrode sheet.

[0237] 2) Fe content on negative side after 2000 cycles: after cycling, the battery was disassembled, the negative electrode sheet was soaked and cleaned with DMC and dried. The negative powder on the surface of the current collector was scraped and tested by ICP. The test was in accordance with EPA6010D-2018 inductively coupled plasma atomic emission spectrometry, GB / T 9723-2007 general rule for chemical reagent flame atomic absorption spectrometry.

[0238] 3) Cycle number before capacity retention decayed to 70% of initial capacity: the battery prepared above was tested for cycle performance at room temperature of 25°C. The test process was as follows: first 1C constant current charging to 4.2V, and finally 1C constant current discharging to 2.0V. The cycle test was continued until the capacity decayed to 70%.

[0239] Table 2

[0240]

[0241] As can be seen from Table 1, compared with the comparative examples, the examples of the present application significantly reduce iron dissolution, prolong the cycle life of the battery, and improve the capacity and rate performance of the battery.

[0242] Finally, it should be noted that: other embodiments of the present application will be readily apparent to those skilled in the art upon considering the specification and practicing the application disclosed herein. The present application is intended to cover any variations, uses or adaptive changes to the present application that follow the general principles of the present application and include common knowledge or conventional technical means in the art that are not disclosed by the present application, and are not limited to the precise structures described above and shown in the drawings, and various modifications and changes can be made without departing from the scope thereof. The scope of the present application is only limited by the appended claims.

Claims

1. A positive electrode material, characterized in that, It includes a core and a shell covering at least a portion of the surface of the core; the core comprises a first sodium-based compound, and the shell comprises a second sodium-based compound and a carbon material; the first sodium-based compound has the chemical formula Na. 2+2x Fe 2-x (SO4)3; the chemical formula of the second sodium-based compound is Na4Fe y-z M z P4O 12+y ; where M includes metals, 0 < x < 2, z ≥ 0, y ≥ z.

2. The cathode material according to claim 1, characterized in that, The positive electrode material satisfies: 0.1≤K≤0.52, where K is the ratio of the Dv50 of the second sodium-based compound to the Dv50 of the first sodium-based compound.

3. The cathode material according to claim 1 or 2, characterized in that, The particle size Dv50 of the first sodium-based compound is 2μm-115μm, preferably 2μm-100μm; And / or, the particle size Dv50 of the second sodium-based compound is 0.1 μm-45 μm, preferably 0.1 μm-20 μm; And / or, the thickness of the shell layer is 0.23μm-56μm, preferably 1μm-50μm.

4. The cathode material according to any one of claims 1-3, characterized in that, The carbon material accounts for m of the mass percentage of the cathode material, where 0 < m ≤ 10 wt%, and preferably, 3 wt% ≤ m ≤ 5 wt%. And / or, the second sodium-based compound accounts for n% of the mass of the cathode material, wherein 1wt%≤n≤30wt%, preferably, 5wt%≤n≤20wt%.

5. The cathode material according to any one of claims 1-4, characterized in that, The condition 0 < x ≤ 0.44 is preferred; more preferably, 0.1 ≤ x ≤ 0.

28. And / or, wherein 2≤y≤4, preferably, 2.5≤y≤3.

6. A method for preparing the cathode material according to any one of claims 1-5, characterized in that, Includes the following steps: The cathode material is obtained by sintering a mixture of a first sodium-based compound, a second sodium-based compound, and a carbon source under an inert atmosphere.

7. The preparation method according to claim 6, characterized in that, The sintering temperature is 300℃-450℃; and / or the sintering time is 6h-24h.

8. A positive electrode plate, characterized in that, This includes the cathode material according to any one of claims 1-5, or the cathode material prepared by the preparation method according to claim 6 or 7.

9. A battery, characterized in that, It includes the positive electrode material according to any one of claims 1-5, or the positive electrode material prepared by the preparation method according to claim 6 or 7, or the positive electrode sheet according to claim 8.

10. The battery according to claim 9, characterized in that, The battery includes a sodium-ion battery.

11. A battery pack, characterized in that, It includes the positive electrode material according to any one of claims 1-5, or the positive electrode material prepared by the preparation method according to claim 6 or 7, or the positive electrode sheet according to claim 8, or at least two batteries according to claims 9 or 10.

12. An electrical appliance, characterized in that, This includes the positive electrode material according to any one of claims 1-5, or the positive electrode material prepared by the preparation method according to claim 6 or 7, or the positive electrode sheet according to claim 8, or the battery according to claim 9 or 10, or the battery pack according to claim 11.

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