Cathode active material, positive electrode, sodium-ion battery, battery assembly, and electric system

Abstract

A cathode active material, a positive electrode, a sodium-ion battery, a battery assembly, and an electric system. The cathode active material satisfies: the cross-sectional filling rate of the cathode active material ranging from 75% to 99%; the tap density of the cathode active material ranging from 1.5 g / cm3 to 2.5 g / cm3; and the value of the particle size distribution spread K of the cathode active material ranging from 0.9 to 3.0, wherein K＝(D90-D10) / D50. By means of making the tap density, cross-sectional filling rate and particle distribution range of the cathode active material be within the above-mentioned ranges, the compaction density of a positive electrode can be improved, thereby increasing the volumetric energy density of a battery.

Description

Positive electrode active material, positive electrode, sodium ion battery, battery component and power consumption system

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on March 29, 2024, with application number 202410381471.5 and application name “Positive electrode active material, positive electrode, sodium ion battery, battery assembly and power system”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of sodium ion batteries, and in particular to a positive electrode active material, a positive electrode, a sodium ion battery, a battery assembly, and an electricity consumption system. Background Art

[0003] The global abundance of sodium is much higher than that of lithium, and sodium-ion batteries have a significant cost advantage over lithium-ion batteries. However, the system energy density of existing sodium-ion batteries is much lower than that of lithium-ion batteries, which limits their application. The energy density of the battery is limited by the compaction density of the positive electrode active material. The compaction density is limited by the tap density, cross-sectional filling rate, and particle distribution of the positive electrode active material. Therefore, how to control the tap density, cross-sectional filling rate, and particle distribution range of the positive electrode active material in sodium-ion batteries becomes the key.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide a positive electrode active material, a positive electrode, a sodium ion battery, a battery assembly and a power system to solve the problem of poor cycle performance of sodium ion batteries.

[0006] To achieve the purpose of this application, this application provides the following technical solutions:

[0007] The purpose of this application is to provide a positive electrode active material, a positive electrode, a sodium ion battery, a battery assembly and a power system to solve the problem of low energy density of sodium ion batteries.

[0008] To achieve the purpose of this application, this application provides the following technical solutions:

[0009] In a first aspect, the present application provides a positive electrode active material, wherein the positive electrode active material satisfies: a cross-sectional filling rate of the positive electrode active material is 75% to 99%; a tap density of the positive electrode active material is 1.5 g / cm 3 ~2.5g / cm 3 ; The particle size dispersion K value of the positive electrode active material is between 0.9 and 3.0, where K = (D90-D10) / D50.

[0010] By setting the tap density of the positive electrode active material within the above range, the compaction density of the positive electrode active material can be increased, providing a higher volume energy density for the battery cell; and, by setting the cross-sectional filling rate of the positive electrode active material within the above range, the degree of compaction inside the particles and the particle filling rate can be increased. The increase in the filling rate increases the content of ions (such as sodium ions) in the same volume and increases the gram capacity of the material. At the same time, the increase in the filling rate helps the material density of a single particle to reach the theoretical density as much as possible; by selecting a powder material with a specific discreteness K, as many small particles as possible can be self-filled into the positive electrode voids, thereby increasing the compaction density of the positive electrode and thus increasing the volume energy density of the battery; by setting the tap density, cross-sectional filling rate and particle size distribution of the positive electrode active material within the above range, the cracking of the material during the charge and discharge process can be alleviated, the compaction density and gram capacity of the positive electrode active material can be increased, providing a higher volume energy density for the battery cell, and improving performance degradation problems.

[0011] In one embodiment, the cross-sectional filling rate of the positive electrode active material is 90% to 99%.

[0012] In one embodiment, the tap density of the positive electrode active material is 2.1 g / cm 3 ~2.5g / cm 3 .

[0013] In one embodiment, the particle size dispersion K value of the positive electrode active material is between 1.2 and 2.4.

[0014] In one embodiment, the positive electrode active material includes a sodium ion layered transition metal oxide.

[0015] In one embodiment, the positive electrode active material has the general structural formula: Na x AO2 wherein A is one or more of Ni, Cu, Fe, Mn, Co, Cr, Li, Mo, Sn, Zn, Zr, Nb, Ru, Y, W, Al, Mg, Ti, Ca, Sr, Ir, Ba, V, 0.7≤x≤1.2.

[0016] In one embodiment, x satisfies: 0.9≤x≤1.02.

[0017] In one embodiment, the positive electrode active material is one or more of single crystal, quasi-single crystal, and polycrystalline.

[0018] In one embodiment, D10 ≥ 1 μm, 2 μm ≤ D50 ≤ 13 μm, and D90 ≤ 21 μm.

[0019] In a second aspect, the present application provides a method for preparing the positive electrode active material according to the first aspect, comprising the following steps:

[0020] a) placing a metal source in water to precipitate a first precursor, wherein the precipitation temperature is 30-80° C. and the precipitation time is 4-24 hours;

[0021] b) mixing the first precursor with a sodium source and performing solid phase sintering at 600-1100° C. for 10-24 hours to obtain a second precursor;

[0022] c) solid-phase sintering the second precursor at 300-800° C. for 10-24 hours to obtain the positive electrode active material.

[0023] In a third aspect, the present application provides a positive electrode, comprising a current collector and the positive electrode active material described in the first aspect disposed on the current collector.

[0024] In one embodiment, the positive electrode active material layer includes the positive electrode active material, a conductive agent, and a binder.

[0025] In one embodiment, the conductive agent is one or more of carbon nanotubes, single-walled carbon nanotubes, conductive carbon black, and graphene.

[0026] In one embodiment, the binder is one or more of polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid.

[0027] In one embodiment, the surface density of the positive electrode is not less than 340 g / m 2 The compaction density of the positive electrode is not less than 2.9g / cm 3 .

[0028] In a fourth aspect, the present application provides a sodium ion battery comprising the positive electrode described in the third aspect.

[0029] In one embodiment, the battery further comprises a negative electrode, wherein the surface density of the negative electrode is 150 to 210 g / m 2 The compaction density of the negative electrode is not less than 0.9 g / cm 3 .

[0030] In one embodiment, the sodium ion battery further comprises an electrolyte;

[0031] The electrolyte comprises an organic solvent, a sodium salt solute and an electrolyte additive.

[0032] In one embodiment, the organic solvent is one or more of ethylene carbonate, propylene carbonate, butyl carbonate, γ-butyrolactone, ethylene glycol dimethyl ether, tetrahydrofuran, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl formate, methyl acetate, dioxolane, and 4-methyl-1,3-dioxolane.

[0033] In one embodiment, the sodium salt solute is one or more of NaBF4, NaClO4, NaPF6, NaAsF6, NaCF3SO3, Na(CF3SO2)2N, and NaC4F9SO3.

[0034] In a fifth aspect, the present application provides a battery assembly comprising the sodium ion battery described in the fourth aspect.

[0035] In a sixth aspect, the present application provides an electricity consumption system, comprising the sodium ion battery described in the fourth aspect or the battery assembly described in the fifth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the implementation methods of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the implementation methods or the description of the prior art. Obviously, the drawings described below are only some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] FIG1 is a schematic diagram of the cross-sectional structure of a positive electrode according to an embodiment;

[0038] FIG2 is a schematic diagram of a cross-sectional structure of a positive electrode active material particle according to an embodiment;

[0039] FIG. 3 is a SEM image of a positive electrode active material according to an embodiment. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0041] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by those skilled in the art to which this application belongs. The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used in this application includes any and all combinations of one or more of the relevant listed items.

[0042] The following describes some embodiments of the present application in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features therein may be combined with each other.

[0043] The present application provides a positive electrode 100 , as shown in FIG. 1 and FIG. 3 , including a current collector 10 and a positive electrode active material disposed on the current collector 10 .

[0044] Specifically, the positive electrode 100 can be a sodium ion positive electrode, and thus is used in a sodium ion battery. After the positive electrode 100 is formed, a positive electrode active material layer 20 is formed on the current collector 10. The positive electrode active material layer 20 includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material is the active ingredient in a sodium ion battery, used to provide sodium ions.

[0045] In the process of manufacturing the positive electrode 100, the positive electrode slurry is placed on the current collector 10, and then rolled and heated to form the positive electrode active material layer 20. The positive electrode slurry includes all the materials of the positive electrode active material layer 20.

[0046] Optionally, the current collector 10 may be a foam metal mesh, a metal film material, etc., specifically including any one of copper foil and aluminum foil.

[0047] Optionally, the conductive agent can be one or more of carbon nanotubes (CNTs), single-walled carbon nanotubes (SWCNTs), conductive carbon black (SP), and graphene; the binder can be one or more of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA).

[0048] Optionally, the mass content of the positive electrode active material in the slurry should be no less than 95%, the mass content of the conductive agent should be no more than 2%, and the mass content of the binder should be no more than 3%.

[0049] Optionally, the surface density of the positive electrode 100 is not less than 340 g / m 2 The compaction density of the positive electrode 100 is not less than 2.9g / cm 3 .

[0050] The positive electrode active material provided in this application meets the following conditions: the cross-sectional filling rate of the positive electrode active material layer is 75% to 99%; the tap density of the positive electrode active material is 1.5 g / cm 3 ~2.5g / cm 3 ; The particle size dispersion K value of the positive electrode active material is between 0.9 and 3.0, where K = (D90-D10) / D50.

[0051] Among them, for the positive electrode active materials in the battery, the tap density and particle size dispersion K value test methods can adopt the following methods:

[0052] 1) Discharge the battery to 1.5V using a low current (e.g., 0.05C / 0.1C / 0.2C), then disassemble in an inert environment and remove the positive electrode. Test the cross-sectional fill rate: Cut the electrode cross section using a plasma beam, magnify it 1000x, and take 10 SEM images. Use a machine to identify and calculate the particle fill rate (fill rate = particle cross-sectional area (non-void area) / particle cross-sectional area), which is the cross-sectional fill rate.

[0053] 2) Clean the positive electrode sheet with an organic solvent, where the solvent can be one or more of alcohols, esters, ethers, etc., and then scrape the powder to remove the powder of the positive electrode material. The scraped positive electrode material powder is ultrasonically cleaned for 10 minutes to remove the upper floating matter, and the solvent is added again and ultrasonically cleaned for 10 minutes. Repeat the cleaning three times, take the bottom material, and vacuum dry it. The powder moisture is required to be less than 500ppm to obtain the positive electrode active material to be tested. The positive electrode active material to be tested is subjected to a tap density test and a discreteness test. Among them, the tap density test and discreteness test methods are as follows:

[0054] Tap density test: Test equipment: BT-1001 intelligent powder comprehensive tester. Weigh a certain mass m of powder and place it into the test container. Try to keep the powder surface in a horizontal state. Vibrate at a frequency of 300 times / min until the powder volume no longer decreases. Read the powder volume v. Tap density = m / vg / cm 3 .

[0055] Dispersion test: using Malvern 3000 laser particle size analyzer, refer to GB / T19077.1, dispersion = (D90-D10) / D50.

[0056] By setting the tap density of the positive electrode active material within the above range, the compaction density of the positive electrode active material can be increased, providing a higher volume energy density for the battery cell; and, by setting the cross-sectional filling rate of the positive electrode active material within the above range, the degree of compaction inside the particles and the particle filling rate can be increased. The increase in the filling rate increases the sodium ion content in the same volume and increases the gram capacity of the material. At the same time, the increase in the filling rate helps the material density of a single particle to reach the theoretical density as much as possible; by selecting a powder material with a specific discreteness K, as many small particles as possible can be self-filled into the positive electrode voids, thereby increasing the compaction density of the positive electrode and thus increasing the volume energy density of the battery; by setting the tap density, cross-sectional filling rate and particle size distribution of the positive electrode active material within the above range, the cracking of the material during the charge and discharge process can be alleviated, the compaction density and gram capacity of the positive electrode active material can be increased, providing a higher volume energy density for the battery cell, and improving performance degradation problems.

[0057] The cross-sectional filling rate of the positive electrode active material is 75% to 99%, and can be but not limited to 75%, 77%, 79%, 81%, 83%, 85%, 87%, 89%, 91%, 93%, 95%, 97%, and 99%.

[0058] As shown in Figure 2, the cross-sectional filling rate of the positive electrode active material is actually the proportion of the solid part in the positive electrode active material in the cross section (the proportion of the shaded part in Figure 2 to the positive electrode active material particles). Conversely, the cross-sectional filling rate of the positive electrode active material can also be understood as the cross-sectional porosity of the positive electrode active material.

[0059] As you can understand, the cross-sectional fill rate is a key metric for measuring the performance of individual particles in positive electrode active materials. A higher cross-sectional fill rate indicates a higher degree of internal densification in the positive electrode active material, which translates to a higher sodium ion content. For the same volume of positive electrode active material, an increased sodium ion content results in a higher gram capacity, which contributes to a higher energy density.

[0060] Furthermore, the positive electrode active material with a greater cross-sectional filling rate (lower porosity) has a more stable structure. After the positive electrode active material is roll-formed into the positive electrode active material layer 20, the positive electrode active material is less likely to break, thereby reducing the pulverization and slagging of the positive electrode 100 during use.

[0061] When the value exceeds the lower limit of the range, it indicates that the internal pores of the positive electrode active material are relatively abundant, which will result in a lower capacity of the positive electrode active material and poor structural strength.

[0062] In one embodiment, the cross-sectional filling rate of the positive electrode active material is 90% to 99%. Alternatively, the cross-sectional filling rate of the positive electrode active material may be, but is not limited to, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%. Meeting the above ranges can further increase the energy density of the positive electrode active material and reduce the pulverization and slagging of the positive electrode during use.

[0063] The tap density of the positive electrode active material is 1.5 g / cm 3 ~2.5g / cm 3 , can be but not limited to 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 , 2.0g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3, 2.5g / cm 3 .

[0064] It can be understood that tap density is an important indicator of powder quality. The measurement of tap density refers to putting a certain amount of powder into a container and vibrating it under certain conditions until the volume of the powder in the container no longer decreases. The volume of the powder is read out, and then the tap density is obtained by dividing the weight of the powder by the volume.

[0065] Tap density is significantly affected by particle size distribution and particle morphology. Compacted density is also affected by tap density. Generally speaking, a high tap density can result in a high compacted density, but the particle size distribution and surface morphology of the powder must be considered.

[0066] The greater the tap density of the positive electrode active material, the less thick the coating needs to be when coating and manufacturing the electrode, while still achieving the corresponding capacity. Simply put, the greater the tap density, the more material can be packed into the battery for the same volume, and the greater the specific energy. Therefore, tap density is key to the high capacity of sodium-ion batteries. At the same time, tap density also affects processing performance, especially roller compaction. If the tap density exceeds the above range, the electrode may become brittle or break.

[0067] In one embodiment, the tap density of the positive electrode active material is 2.1 g / cm 3 ~2.5g / cm 3 Optionally, the tap density of the positive electrode active material may be, but is not limited to, 2.1 g / cm 3 , 2.15g / cm 3 , 2.2g / cm 3 , 2.25g / cm 3 , 2.3g / cm 3 , 2.35g / cm 3 , 2.4g / cm 3 , 2.45g / cm 3 , 2.5g / cm 3 When the above range is met, the thickness of the positive electrode active material layer can be further reduced, the energy density of the positive electrode can be increased, and the product defect rate of the positive electrode can be reduced.

[0068] The particle size dispersion K value of the positive electrode active material is between 0.9 and 3.0, and may be, but is not limited to, 0.9, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, and 3.0. K = (D90 - D10) / D50, where D10 represents the particle size corresponding to a 10% volume pass rate on the cumulative curve, D50 represents the particle size corresponding to a 50% volume pass rate on the cumulative curve, and D90 represents the particle size corresponding to a 90% volume pass rate on the cumulative curve.

[0069] As can be understood, D50 can be the average particle size of the positive electrode active material, indicating that particles smaller than it and larger than it each account for 50% of the sample. D10 and D90 can be the boundary particle sizes of the positive electrode active material, which are closer to the maximum and minimum particle sizes in the popular sense. For example, (D10, D90) = (8, 60) means that the number of particles with a diameter less than 8 microns accounts for 10%, and the number of particles with a diameter less than 60 microns accounts for 90%. The smaller the dispersion K, the narrower the particle size distribution range, the smaller the number of oversized and undersized particles, and the more concentrated the particle size.

[0070] In one embodiment, the particle size dispersion K value of the positive electrode active material is between 1.2 and 2.4. Optionally, the particle size dispersion K value of the positive electrode active material may be, but is not limited to, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, or 2.4. Meeting the above range can further allow as many small particles as possible to self-fill into the positive electrode voids, thereby increasing the positive electrode's compaction density and thus improving the battery's volumetric energy density.

[0071] In one embodiment, the positive electrode active material includes a sodium ion layered transition metal oxide.

[0072] In one embodiment, the positive electrode active material has the general structural formula: Na x AO2 wherein A is one or more of Ni, Cu, Fe, Mn, Co, Cr, Li, Mo, Sn, Zn, Zr, Nb, Ru, Y, W, Al, Mg, Ti, Ca, Sr, Ir, Ba, V, 0.7≤x≤1.2.

[0073] In one embodiment, x satisfies: 0.9≤x≤1.02. Optionally, the specific value of x can be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.01, or 1.02.

[0074] In one embodiment, the positive electrode active material is one or more of single crystal, quasi-single crystal, and polycrystalline.

[0075] In one embodiment, D10 ≥ 1 μm, 2 μm ≤ D50 ≤ 13 μm, and D90 ≤ 21 μm. Optionally, the specific value of D10 may be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm. Optionally, the specific value of D50 may be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or 13 μm. Optionally, the specific value of D90 may be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or 21 μm.

[0076] In one embodiment, the preparation method of the above positive electrode active material includes:

[0077] a) precipitating an M source to form a first M source precursor at a temperature of 30-80° C. for 4-24 hours;

[0078] b) mixing the M source precursor with the sodium source, and performing solid phase sintering at 600-1100° C. for 10-24 hours to obtain a second precursor;

[0079] c) solid-phase sintering the second precursor at 300-800° C. for 10-24 hours to obtain the positive electrode active material.

[0080] Wherein, in step a), the M source may include one or more metal sources;

[0081] In step b), in addition to being mixed with the sodium source, the M source may also be mixed with other doping elements, that is, step b) may further include mixing the M source precursor with the sodium source and other doping elements, and performing solid phase sintering at 600-1100° C. for 10-24 hours to obtain a second precursor;

[0082] Step c) may further include mixing the second precursor and the coating element and then performing solid phase sintering at 300-800° C. for 10-24 hours.

[0083] The cross-sectional filling rate, tap density and particle size dispersion K value can be adjusted by adjusting the reaction raw materials, the temperature and duration of each step of the reaction, and other factors.

[0084] In one embodiment, the present application further provides a sodium ion battery, comprising the positive electrode, negative electrode and separator in the above embodiment, wherein the positive electrode and negative electrode are respectively arranged on opposite sides of the separator.

[0085] Sodium-ion battery models include but are not limited to soft-pack batteries, square batteries, and cylindrical batteries.

[0086] Optionally, the negative electrode includes a current collector and a negative electrode material disposed on the current collector. After the negative electrode is formed, a negative electrode material layer is formed on the current collector, and the negative electrode material layer includes a negative electrode material, a conductive agent, and a binder. The negative electrode material can be hard carbon.

[0087] Optionally, the ratio of negative electrode material in the slurry should be no less than 93%, the conductive agent content should be no more than 3%, and the binder content should be no more than 4%. The surface density of the obtained negative electrode is 150-210 g / m 2 , the negative electrode compaction density is not less than 0.9g / cm 3 .

[0088] Optionally, the diaphragm can be a conventional polyethylene (propylene) diaphragm, a rubber-coated diaphragm, a ceramic diaphragm, etc.

[0089] Optionally, the sodium ion battery further includes an electrolyte, which includes an organic solvent, a sodium salt solute, and an electrolyte additive.

[0090] Optionally, the organic solvent in the electrolyte can be: ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), γ-butyrolactone (GBL), ethylene glycol dimethyl ether (DME), tetrahydrofuran (THF), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl formate (MF), methyl acetate (MA), dioxolane (DOL), 4-methyl-1,3-dioxolane (4MeDOL), etc., or a combination thereof; the sodium salt solute can be: NaBF4, NaClO4, NaPF6, NaAsF6, NaCF3SO3, Na(CF3SO2)2N, NaC4F9SO3, etc., or a combination thereof; the electrolyte additive can be: FEC, VC, PS, DTD, TEP, TMP, etc., or a combination thereof.

[0091] Optionally, the sodium ion battery can be a wound cell, a laminated cell or a single cell.

[0092] In one embodiment, the present application further provides a battery assembly comprising the sodium ion battery described above. The battery assembly may be a battery pack or a battery group.

[0093] In one embodiment, the present application further provides an electric power system, comprising the battery assembly and an electrical appliance as described above, wherein the battery assembly supplies power to the electrical appliance. Optionally, the electric power system may be a vehicle or an energy storage power station.

[0094] In one embodiment, the present application further provides a method for manufacturing a sodium ion battery, comprising at least the following steps:

[0095] Step S1: The positive electrode active material, the conductive agent and the binder uniformly dispersed in the solvent N-methylpyrrolidone (NMP) are uniformly coated on the surface of the aluminum foil (current collector), and the positive electrode is obtained after baking.

[0096] Specifically, the positive electrode active material and other auxiliary materials were evenly dispersed in the ratio of positive electrode active material: PVDF: CNT: SP: NMP = 97:1:1.5:0.5:30, coated on aluminum foil, baked at 120 ° C to obtain the positive electrode, and rolled to 3.0 g / cm 3 .

[0097] Step S2: The negative electrode material, the conductive agent, and the binder uniformly dispersed in the solvent deionized water are uniformly coated on the surface of the aluminum foil (current collector), and the negative electrode is obtained after baking.

[0098] Specifically, hard carbon, conductive agent SP, and binder SBR were uniformly mixed in deionized water at a ratio of 93:3:4, and evenly coated on the surface of aluminum foil. After baking at 110°C, the negative electrode was obtained and rolled to 0.95g / cm 3 .

[0099] Step S3: Wind or stack the positive electrode, separator and negative electrode in order to obtain a core.

[0100] Step S4: After the core is encased, electrolyte is injected, and a complete secondary sodium ion battery is obtained through aging, formation, aging and capacity separation.

[0101] Specifically, after the core is shelled, the electrolyte (solute is 1 mol / L NaPF6, solvent is EC:EMC=1:1 (v:v)+3% FEC) is injected, and after aging, formation, aging and capacity separation, a complete secondary sodium ion battery is obtained.

[0102] The present application is further described below with reference to Examples and Comparative Examples. This application provides Examples 1 through 10, as well as Comparative Examples 1 through 7. The types of positive electrode active materials used in these Examples and Comparative Examples are shown in Table 1. Batteries in each of these Examples were prepared according to the sodium ion battery manufacturing method described above.

[0103] The positive electrode active materials or positive electrode sheets in the examples and comparative examples were tested for cross-section filling rate, porosity, dispersion, and tap density, and the battery was tested for energy density. The specific test methods are as follows:

[0104] Cross-sectional filling rate: The cross section of the battery electrode is cut by plasma beam, magnified 1000 times, and 10 SEM images are taken. The machine is used to identify and calculate the particle filling rate (filling rate = particle cross-sectional area (non-empty area) / particle cross-sectional area).

[0105] Porosity test: The mercury intrusion method is used to test the pores between the positive electrode active material particles of the positive electrode, referring to GBT21650.1.

[0106] Dispersion test: Malvern 3000 laser particle size analyzer, refer to GB / T19077.1. Dispersion = (D90-D10) / D50.

[0107] Tap density test: Test equipment: BT-1001 intelligent powder comprehensive tester. Weigh a certain mass m of powder and place it into the test container. Try to keep the powder surface in a horizontal state. Vibrate at a frequency of 300 times / min until the powder volume no longer decreases. Read the powder volume v. Tap density = m / vg / cm 3 .

[0108] Energy density test: The battery is charged to 4.0V at 1 / 3C and discharged to 1.5V at 1 / 3C for 3 cycles. The volume energy density is calculated based on the last charge.

[0109] Please refer to Table 1 and Table 2 for specific test results.

[0110] Table 1

[0111] Table 2

[0112] From the data in Tables 1 and 2 above, it can be concluded that increasing the particle filling rate (reducing porosity) and tap density will increase the sodium ion content in the same volume and increase the material's gram capacity. At the same time, an appropriate increase in the filling rate makes the material density of a single particle as close to the theoretical density as possible, which can increase the positive electrode compaction density and thus increase the volume energy density. At the same time, selecting a specific range of particle distribution can reduce the porosity between material particles and achieve as many small particles as possible to self-fill into the positive electrode voids, thereby increasing the positive electrode compaction density and thus increasing the volume energy density.

[0113] In the description of the embodiments of the present application, it should be noted that the orientation or positional relationship of terms such as "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", and "outside" are based on the orientation or positional relationship of the accompanying drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0114] The above disclosure is only a preferred embodiment of the present application, and certainly cannot be used to limit the scope of rights of the present application. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made in accordance with the claims of the present application are still within the scope covered by the present application.

Claims

1. A positive electrode active material, wherein The cross-sectional filling rate of the positive electrode active material is 75% to 99%; The tap density of the positive electrode active material is 1.5 g / cm 3 ~2.5g / cm 3 ; The particle size dispersion K value of the positive electrode active material is between 0.9 and 3.0, wherein K=(D90-D10) / D50.

2. The positive electrode active material according to claim 1, wherein The cross-sectional filling rate of the positive electrode active material is 90% to 99%.

3. The positive electrode active material according to claim 1 or 2, wherein The tap density of the positive electrode active material is 2.1 g / cm 3 ~2.5g / cm 3 .

4. The positive electrode active material according to any one of claims 1 to 3, wherein The particle size dispersion K value of the positive electrode active material is between 1.2 and 2.

4.

5. The positive electrode active material according to any one of claims 1 to 4, wherein The positive electrode active material includes a sodium ion layered transition metal oxide.

6. The positive electrode active material according to any one of claims 1 to 5, wherein The general structural formula of the positive electrode active material is: Na x AO2, wherein A is one or more of Ni, Cu, Fe, Mn, Co, Cr, Li, Mo, Sn, Zn, Zr, Nb, Ru, Y, W, Al, Mg, Ti, Ca, Sr, Ir, Ba, and V, and 0.7≤x≤1.

2.

7. The positive electrode active material according to claim 6, wherein x satisfies: 0.9≤x≤1.

02.

8. The positive electrode active material according to any one of claims 1 to 7, wherein The positive electrode active material is one or more of single crystal, quasi-single crystal, and polycrystalline.

9. The positive electrode active material according to any one of claims 1 to 8, wherein D10≥1μm, 2μm≤D50≤13μm, D90≤21μm.

10. A method for preparing the positive electrode active material according to any one of claims 1 to 9, wherein: The following steps are involved: a) placing a metal source in water to precipitate a first precursor, wherein the precipitation temperature is 30-80° C. and the precipitation time is 4-24 hours; b) mixing the first precursor with a sodium source and performing solid phase sintering at 600-1100° C. for 10-24 hours to obtain a second precursor; c) solid-phase sintering the second precursor at 300-800° C. for 10-24 hours to obtain the positive electrode active material.

11. A positive electrode, wherein The invention comprises a current collector and the positive electrode active material according to any one of claims 1 to 9 arranged on the current collector.

12. The positive electrode according to claim 11, wherein The positive electrode active material layer includes the positive electrode active material, a conductive agent, and a binder.

13. The positive electrode according to claim 11 or 12, wherein The conductive agent is one or more of carbon nanotubes, single-walled carbon nanotubes, conductive carbon black, and graphene.

14. The positive electrode according to claim 11 or 12, wherein The binder is one or more of polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid.

15. The positive electrode according to any one of claims 11 to 14, wherein The surface density of the positive electrode is not less than 340g / m 2 The compaction density of the positive electrode is not less than 2.9g / cm 3 .

16. A sodium ion battery, wherein: The method comprises the positive electrode according to any one of claims 11 to 15.

17. The sodium ion battery according to claim 16, wherein: The battery also includes a negative electrode, the surface density of which is 150 to 210 g / m 2 The compaction density of the negative electrode is not less than 0.9 g / cm 3 .

18. The sodium ion battery according to claim 16 or 17, wherein The sodium ion battery also includes an electrolyte; The electrolyte comprises an organic solvent, a sodium salt solute and an electrolyte additive.

19. The sodium ion battery according to claim 18, wherein The organic solvent is one or more of ethylene carbonate, propylene carbonate, butyl carbonate, γ-butyrolactone, ethylene glycol dimethyl ether, tetrahydrofuran, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl formate, methyl acetate, dioxolane, and 4-methyl-1,3-dioxolane.

20. The sodium ion battery according to claim 18, wherein The sodium salt solute is one or more of NaBF4, NaClO4, NaPF6, NaAsF6, NaCF3SO3, Na(CF3SO2)2N, and NaC4F9SO3.

21. A battery assembly, wherein: Comprising the sodium ion battery according to any one of claims 16 to 20.

22. An electricity system, wherein: Comprising the sodium ion battery according to any one of claims 16 to 20 or the battery assembly according to claim 21.

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