Positive electrode active material, positive electrode, sodium ion battery, battery assembly and electrical system

Abstract

A positive electrode active material, a positive electrode, a sodium ion battery, a battery assembly and an electrical system, wherein the positive electrode active material meets: the cross-sectional filling rate α of the positive electrode active material is 75%-99%, and the post-compression rebound rate ε of the positive electrode active material is 3%-10%; the post-compression rebound rate ε=1-(the compaction density after rebound / the maximum compaction density); the cross-sectional filling rate α and the post-compression rebound rate ε of the positive electrode active material satisfy: 8≤α / ε≤30. The positive electrode active material has high energy density and good cycle performance.

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 202410381828.X and entitled “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. Compared with lithium-ion batteries, sodium-ion batteries have a greater cost advantage. However, the system energy density of existing sodium-ion batteries is much lower than that of lithium-ion batteries, and the cycle performance is also not ideal, which limits the application of sodium-ion batteries. The energy density and cycle performance of the battery are limited by the self-filling rate and self-toughness of the battery's positive electrode active material. A higher self-filling rate of the material can increase the sodium ion content and improve the material's gram capacity; and the material's own toughness is conducive to the material maintaining structural stability and integrity during the electrochemical process. The post-compression rebound rate is a parameter standard that can fully reflect the toughness of the positive electrode active material. Therefore, how to control the cross-sectional filling rate and post-compression rebound rate of the positive electrode active material in the sodium-ion battery, as well as the coordination of the cross-sectional filling rate and post-compression rebound rate, has become 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 consumption system to solve the problems of low energy density and poor cycle performance of sodium ion batteries.

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

[0007] In a first aspect, a positive electrode active material satisfies: a cross-sectional filling rate α of the positive electrode active material is 75% to 99%; a post-compression rebound rate ε of the positive electrode active material is 3% to 10%, wherein the post-compression rebound rate ε = 1-(compaction density after rebound / maximum compaction density); the cross-sectional filling rate α and the post-compression rebound rate ε of the positive electrode active material satisfy: 8≤α / ε≤30.

[0008] 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 improved. The increase in the filling rate increases the content of ions (such as sodium ions) in the same volume and increases the specific 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. In addition, since the rebound characteristics of the material are related to the toughness of the material, which refers to the rebound change before and after a certain pressure (pressurization & decompression), the material with a greater rebound rate after compression can exhibit better plasticity. Therefore, by setting the post-compression rebound rate of the positive electrode active material within the above range, it can be ensured that the positive electrode active material is more inclined to maintain its original shape and structure during the ion deintercalation process, and the positive electrode active material itself has a certain toughness, which is beneficial to the material maintaining structural stability and integrity during the electrochemical process, thereby greatly improving the cycle performance; moreover, by limiting the ratio of the cross-sectional filling rate α and the post-compression rebound rate ε to meet the above range, it can be ensured that the positive electrode active material in the positive electrode has high compressibility, and combined with the rebound rate, the compressed positive electrode active material has a higher actual compression density, thereby increasing the content of ions (such as sodium ions) in the same volume and improving the material gram capacity. 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, and the preferred filling rate can ensure the transmission dynamics of ions (such as sodium ions).

[0009] In one embodiment, the cross-sectional filling rate of the positive electrode active material is 90% to 99%.

[0010] In one embodiment, the post-compression rebound rate ε of the positive electrode active material is 5% to 10%.

[0011] In one embodiment, the cross-sectional filling rate α and the post-compression springback rate ε of the positive electrode active material satisfy: 9≤α / ε≤20.

[0012] In one embodiment, the tap density of the positive electrode active material is 1.5 g / cm 3 ~2.5g / cm 3 .

[0013] In one embodiment, the tap density of the positive electrode active material is 2.1 g / cm 3 ~2.5g / cm 3 .

[0014] In one embodiment, the particle size dispersion K value of the positive electrode active material is between 0.9 and 3.0, wherein K=(D90-D10) / D50.

[0015] In one embodiment, the particle size dispersion K value of the positive electrode active material is between 1.2 and 2.4.

[0016] In one embodiment, the maximum compaction density of the positive electrode active material is 3.0 g / cm 3 ~3.6g / cm 3 ;

[0017] In one embodiment, the maximum compaction density of the positive electrode active material is 3.2 g / cm 3 ~3.6g / cm 3 .

[0018] In one embodiment, the positive electrode active material includes a sodium ion layered transition metal oxide.

[0019] 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.

[0020] In one embodiment, x satisfies: 0.9≤x≤1.02.

[0021] In one embodiment, the positive electrode active material is one or more of single crystal, quasi-single crystal, and polycrystalline.

[0022] In a second 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.

[0023] In a third aspect, the present application provides a sodium ion battery comprising the positive electrode described in the second aspect.

[0024] In a fourth aspect, the present application provides a battery assembly comprising the sodium ion battery described in the third aspect.

[0025] In a fifth aspect, the present application provides an electricity consumption system, comprising the sodium ion battery described in the third aspect or the battery assembly described in the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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.

[0027] FIG1 is a schematic diagram of the cross-sectional structure of a positive electrode according to an embodiment;

[0028] FIG2 is a schematic diagram of a cross-sectional structure of a positive electrode active material particle according to an embodiment;

[0029] FIG3 is a schematic diagram showing the calculation of the rebound rate ε of a positive electrode active material according to an embodiment;

[0030] FIG. 4 is a SEM image of a positive electrode active material according to an embodiment. Specific embodiments

[0031] 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.

[0032] 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.

[0033] 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.

[0034] The present application provides a positive electrode 100 , as shown in FIG. 1 and FIG. 4 , including a current collector 10 and a positive electrode active material disposed on the current collector 10 .

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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).

[0039] 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%.

[0040] Optionally, the surface density of the positive electrode 100 is not less than 340 g / m 2 , the positive electrode 100 compaction is not less than 2.9g / cm 3 .

[0041] In one embodiment, the positive electrode active material provided in the present application satisfies the following conditions: the cross-sectional filling rate α of the positive electrode active material is 75% to 99%; the post-compression rebound rate ε of the positive electrode active material is 3% to 10%, wherein the post-compression rebound rate ε = 1-(compaction density after rebound / maximum compaction density); the cross-sectional filling rate α and the post-compression rebound rate ε of the positive electrode active material satisfy: 8≤α / ε≤30.

[0042] 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 improved. The increase in the filling rate increases the sodium ion content in the same volume and increases the material's gram capacity. 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. In addition, since the rebound characteristics of the material are related to the toughness of the material, which refers to the rebound change before and after a certain pressure (pressurization & decompression), the material with a greater rebound rate after compression can exhibit better plasticity. Therefore, by setting the post-compression rebound rate of the positive electrode active material within the above range, it can be ensured that the positive electrode active material is more inclined to maintain its original shape and structure during the ion deintercalation process, and the positive electrode active material itself has a certain toughness, which is beneficial to the material maintaining structural stability and integrity during the electrochemical process, thereby greatly improving the cycle performance; moreover, by limiting the ratio of the cross-sectional filling rate α and the post-compression rebound rate ε to meet the above range, it can be ensured that the positive electrode active material in the positive electrode has high compressibility, and combined with the rebound rate, the compressed positive electrode active material has a higher actual compression density, thereby increasing the sodium ion content in the same volume and improving the material gram capacity. 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, and the preferred filling rate can ensure the transmission dynamics of sodium ions.

[0043] 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%.

[0044] 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). The solid filling in Figure 2 is the solid part, and the blank part is the pore; 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] The post-compression rebound rate ε of the positive electrode active material is 3% to 10%, and can be, but is not limited to, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0050] As you can understand, the positive electrode active material layer will rebound after rolling, meaning that part of the positive electrode active material returns to its pre-rolling state. The rebound rate of the positive electrode active material is the degree to which the density decreases when the pressure is released after the positive electrode active material is rolled to its maximum density. The greater the rebound rate, the easier it is for the positive electrode active material, deformed by compression, to return to its original state.

[0051] Among them, for the positive electrode active materials in the battery, the cross-sectional filling rate and the post-compression rebound rate ε test method 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, which can be one or more of an alcohol, ester, or ether. Scrape the powder to remove the positive electrode material powder. Ultrasonic cleaning is performed on the scraped positive electrode material powder for 10 minutes to remove the upper floating material. Solvent is added again and ultrasonic cleaning is repeated for 10 minutes. This cleaning is repeated three times. The bottom layer is removed and vacuum-dried to a moisture content of less than 500 ppm to obtain the positive electrode active material to be tested. The post-compression rebound rate of the positive electrode active material to be tested is then tested.

[0054] Testing method for post-compression rebound rate: For example, as shown in FIG3 , a predetermined mass (e.g., 1.0 g) of positive electrode active material is filled into a mold and vibrated at a frequency of 300 times / min until the density of the positive electrode active material reaches a tap density (e.g., 3 g / cm 3 ), and then compressed at a constant speed (e.g., 10 mm / min) so that the density of the positive electrode active material reaches the maximum compaction density (e.g., 3.6 g / cm 3 , T1 in Figure 3). Then, release the pressure, and when the pressing surface stops moving due to elasticity, measure the density after pressure release, i.e., the compacted density after rebound (T2 in Figure 3). The obtained value is used to calculate the post-compression rebound rate using the formula: Post-compression rebound rate ε = 1 - (compacted density after rebound / maximum compacted density).

[0055] The test method for tap density is as follows: a certain amount of powder is placed in a container and vibrated 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 weight of the powder is divided by the volume to obtain the tap density. The tap density test is carried out in accordance with GB / T 31057.2-2018 Part 2: Measurement of tap density of granular materials. Test equipment: BT-1001 intelligent powder comprehensive tester. Weigh a certain mass m of positive electrode active material and place it in the test container. Try to keep the surface horizontal. Vibrate at a frequency of 300 times / min until the volume of the positive electrode active material no longer decreases. Read out the powder volume v. Tap density = m / vg / cm 3 .

[0056] Layered sodium cathode active materials can experience cracking and pulverization during cycling due to the continuous release and insertion of sodium ions. Industrialization often involves toughening and modifying the material skeleton through doping with various elements or optimizing the sintering process, thereby improving the stability of the material structure and thus achieving improved cycling performance. However, due to the typically low levels of doping elements, macroscopic characterization of the material matrix's stability is difficult.

[0057] Since the rebound characteristics of a material are related to its toughness, representing the change in rebound before and after a certain pressure (pressurization and decompression), materials with a higher post-compression rebound rate exhibit better plasticity. Therefore, by setting the post-compression rebound rate of the positive electrode active material within the above range, it can be ensured that the positive electrode active material can maintain its original shape and structure to a certain extent during the ion insertion and extraction process. The positive electrode active material itself has a certain toughness, which helps the material maintain structural stability and integrity during the electrochemical process, thereby significantly improving cycle performance.

[0058] In one embodiment, the positive electrode active material has a post-compression springback rate ε of 5% to 10%. Optionally, the post-compression springback rate ε of the positive electrode active material may be, but is not limited to, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%. Meeting the above post-compression springback rates can further ensure the stability and integrity of the positive electrode active material, thereby achieving higher cycle performance.

[0059] The cross-sectional filling rate α and the post-compression rebound rate ε of the positive electrode active material satisfy: 8≤α / ε≤30, and can be but not limited to 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30.

[0060] The present application ensures that the positive electrode active material in the positive electrode has appropriate compressibility by limiting the ratio of the cross-sectional filling rate α and the post-compression rebound rate ε to meet the above range. In addition, the compressed positive electrode active material has a higher actual compression density in combination with the rebound rate, thereby increasing the sodium ion content in the same volume and improving the material gram capacity. At the same time, the increase in the cross-sectional filling rate helps the material density of a single particle to reach the theoretical density as much as possible. At the same time, the preferred cross-sectional filling rate can ensure the transmission dynamics of sodium ions.

[0061] Therefore, in this application, through the correlation between microstructure and macroscopic mechanical properties, by selecting positive electrode active materials with a certain degree of rebound characteristics, that is, the material structure itself has a certain toughness. This toughness is conducive to the material maintaining structural stability and integrity during the electrochemical process, thereby greatly improving the cycle performance.

[0062] In one embodiment, the cross-sectional filling ratio α and the post-compression springback ratio ε of the positive electrode active material satisfy: 9≤α / ε≤20. Optionally, the cross-sectional filling ratio α and the post-compression springback ratio ε of the positive electrode active material may be 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20.

[0063] In one embodiment, 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 / cm3 , 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] In one embodiment, 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, or 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 you can understand, D50 can be the average particle size of the positive electrode active material, indicating that particles smaller than this value and larger than this value each account for 50% of the sample. D10 and D90 can be the boundary particle sizes of the positive electrode active material, more similar to the maximum and minimum particle sizes in the common sense. For example, D10 = 8μm means that 10% of the particles have a diameter less than 8 microns, and D90 = 60μm means that 90% of the particles have a diameter less than 60 microns. A smaller dispersion K indicates a narrower particle size distribution, a smaller number of oversized and undersized particles, and a more concentrated particle size.

[0070] By limiting the particle size distribution and selecting powder materials 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 improving the volume energy density of the battery.

[0071] 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.

[0072] In one embodiment, the maximum compaction density of the positive electrode active material is 3.0 g / cm 3 ~3.6g / cm 3, can be but not limited to 3.0g / cm 3 、3.05g / cm 3 , 3.1g / cm 3 、3.15g / cm 3 、3.2g / cm 3 , 3.25g / cm 3 , 3.3g / cm 3 、3.35g / cm 3 、3.4g / cm 3 、3.45g / cm 3 、3.5g / cm 3 、3.6g / cm 3 .

[0073] During the production of power batteries, the compaction density has a significant impact on battery performance. Experiments have shown that compaction density is closely related to sheet capacity, efficiency, internal resistance, and battery cycle performance. Finding the optimal compaction density is very important for battery design. Generally speaking, the greater the compaction density, the higher the battery capacity can be, so compaction density is also considered one of the reference indicators for material energy density. The compaction density is not only related to the size and density of the particles, but also to the particle gradation. Particles with a high compaction density generally have a good normal distribution. It can be considered that under certain process conditions, the greater the compaction density, the higher the battery capacity.

[0074] In one embodiment, the maximum compaction density of the positive electrode active material is 3.2 g / cm 3 ~3.6g / cm 3 Optionally, the maximum compaction density of the positive electrode active material may be, but is not limited to, 3.2 g / cm 3 , 3.25g / cm 3 , 3.3g / cm 3 、3.35g / cm 3 、3.4g / cm 3 、3.45g / cm 3 、3.5g / cm 3 、3.55g / cm 3 、3.6g / cm 3 Meeting the above-mentioned maximum compaction density can further ensure that the positive electrode active material has a higher capacity.

[0075] In one embodiment, the positive electrode active material includes a sodium ion layered transition metal oxide.

[0076] In one embodiment, the positive electrode active material has the general structural formula: Na xAO2 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.

[0077] 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.

[0078] In one embodiment, the positive electrode active material is one or more of single crystal, quasi-single crystal, and polycrystalline.

[0079] 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.

[0080] In one embodiment, the preparation method of the above positive electrode active material includes:

[0081] a) precipitating an M source to form a first M source precursor at a temperature of 30-80° C. for 4-24 hours;

[0082] 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;

[0083] c) solid-phase sintering the second precursor at 300-800° C. for 10-24 hours.

[0084] Wherein, in step a), the M source may include one or more metal sources;

[0085] 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;

[0086] 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.

[0087] 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.

[0088] 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.

[0089] Sodium-ion battery models include but are not limited to soft-pack batteries, square batteries, and cylindrical batteries.

[0090] 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.

[0091] 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 is not less than 0.9g / cm 3 .

[0092] Optionally, the diaphragm can be a conventional polyethylene (propylene) diaphragm, a rubber-coated diaphragm, a ceramic diaphragm, etc.

[0093] Optionally, the sodium ion battery further includes an electrolyte, which includes an organic solvent, a sodium salt solute, and an electrolyte additive.

[0094] 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), 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.

[0095] Optionally, the sodium ion battery can be a wound cell, a laminated cell or a single cell.

[0096] 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.

[0097] 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.

[0098] In one embodiment, the present application further provides a method for manufacturing a sodium ion battery, comprising at least the following steps:

[0099] 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.

[0100] 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 .

[0101] 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.

[0102] 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 .

[0103] Step S3: Wind or stack the positive electrode, separator, and negative electrode in order to obtain a core.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] The positive electrode active materials or positive electrode sheets in the examples and comparative examples were subjected to cross-sectional filling rate tests, porosity tests, dispersion tests, tap density tests, post-compression rebound tests, and cycle tests, and the batteries were subjected to energy density tests. The specific test methods are as follows:

[0108] 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).

[0109] Porosity test: mercury intrusion method is used for testing, refer to GBT21650.1.

[0110] Dispersion test: using Malvern 3000 laser particle size analyzer, refer to GB / T19077.1; dispersion = (D90-D10) / D50.

[0111] 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 .

[0112] Powder compaction and post-compression rebound rate: 1 gram of powder is placed in a standard container and vibrated at a frequency of 300 vibrations / min until the density of the positive electrode active material reaches the tap density. Then, compression is continued at a constant speed (10 mm / min) until a pressure of 5 tons is reached. This is recorded as the pre-rebound compaction density, also known as the maximum compaction density. When the pressure is removed and the pressing surface stops moving, the post-rebound compaction density is measured and the post-compression rebound rate is calculated. The testing equipment used is the Sansi Zongheng UTM7305.

[0113] Cycle test: The battery was charged to 4.0 V at 1C, discharged to 1.5 V at 1C, and cycled until the SOH was 80%. The number of cycles was recorded (SOH = discharge capacity after cycle / discharge capacity of the first cycle).

[0114] 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.

[0115] Please refer to Table 1 and Table 2 for specific test results.

[0116] Table 1

[0117] Table 2

[0118] From the data in Tables 1 and 2 above, it can be concluded that increasing the particle cross-sectional filling rate and tap density will increase the sodium ion content in the same volume and increase the material's gram capacity. At the same time, the increase in the cross-sectional filling rate makes it possible for the material density of a single particle to nearly reach the theoretical density, thereby increasing the electrode compaction density and thus increasing the volume energy density.

[0119] At the same time, selecting a specific range of particle distribution can reduce the porosity between material particles, allowing as many small particles as possible to self-fill into the electrode gaps, thereby increasing the compaction density of the electrode and thus increasing the volume energy density.

[0120] The greater the change in powder rebound before and after pressing, the better the toughness of the material. Conversely, a smaller rebound rate of the material indicates stronger rigidity. Due to the large radius of sodium ions, the change in unit cell volume during the process of sodium intercalation and deintercalation aggravates the cracking of the material. Materials with a larger rebound rate can exhibit better plasticity, so that the material is more inclined to maintain its original structure during the process of sodium intercalation and deintercalation, and thus has better cycle performance.

[0121] 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 described in the accompanying drawings. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present application.

[0122] 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 α of the positive electrode active material is 75% to 99%; The post-compression rebound rate ε of the positive electrode active material is 3% to 10%, wherein the post-compression rebound rate ε=1-(compression density after rebound / maximum compression density); The cross-sectional filling rate α and the post-compression springback rate ε of the positive electrode active material satisfy the following conditions: 8≤α / ε≤30.

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 post-compression rebound rate ε of the positive electrode active material is 5% to 10%.

4. The positive electrode active material according to any one of claims 1 to 3, wherein The cross-sectional filling rate α and the post-compression rebound rate ε of the positive electrode active material satisfy the following conditions: 9≤α / ε≤20.

5. The positive electrode active material according to any one of claims 1 to 4, wherein The tap density of the positive electrode active material is 1.5 g / cm 3 ~2.5g / cm 3 .

6. The positive electrode active material according to claim 5, wherein The tap density of the positive electrode active material is 2.1 g / cm 3 ~2.5g / cm 3 .

7. The positive electrode active material according to any one of claims 1 to 6, wherein The particle size dispersion K value of the positive electrode active material is between 0.9 and 3.0, wherein K=(D90-D10) / D50.

8. The positive electrode active material according to claim 7, wherein The particle size dispersion K value of the positive electrode active material is between 1.2 and 2.

4.

9. The positive electrode active material according to any one of claims 1 to 8, wherein The maximum compaction density of the positive electrode active material is 3.0 g / cm 3 ~3.6g / cm 3 .

10. The positive electrode active material according to claim 9, wherein The maximum compaction density of the positive electrode active material is 3.2 g / cm 3 ~3.6g / cm 3 .

11. The positive electrode active material according to any one of claims 1 to 10, wherein The positive electrode active material includes a sodium ion layered transition metal oxide.

12. The positive electrode active material according to any one of claims 1 to 11, 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, V, 0.7≤x≤1.

2.

13. The positive electrode active material according to claim 12, wherein x satisfies: 0.9≤x≤1.

02.

14. The positive electrode active material according to any one of claims 1 to 13, wherein The positive electrode active material is one or more of single crystal, quasi-single crystal, and polycrystalline.

15. A positive electrode, wherein The invention comprises a current collector and the positive electrode active material according to any one of claims 1 to 14 arranged on the current collector.

16. A sodium ion battery, wherein: Comprising the positive electrode as claimed in claim 15.

17. A battery assembly, wherein: Including the sodium ion battery as claimed in claim 16.

18. An electricity system, wherein: Comprising the sodium ion battery according to claim 16 or the battery assembly according to claim 17.

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