A sodium-ion battery cathode material, its preparation method, and the battery cell and battery.

Abstract

This invention relates to the field of sodium-ion battery technology, specifically disclosing a sodium-ion battery cathode material, its preparation method, a battery cell, and a battery. The cathode material involves the sequential stacking of single-crystal particles, near-single-crystal particles, and aggregated particles along a vertical direction from a foil substrate. The single-crystal particles are single, blocky crystals; the near-single-crystal particles are secondary particles formed by the stacking and connection of multiple single-crystal particles, which are mixed with and fill the gaps between the single-crystal particles; the aggregated particles are secondary particles formed by the stacking of multiple micro / nano particles, used to provide a rapid migration channel for ions at the cathode, shortening the ion migration distance and enabling fast charging of the sodium-ion battery. This invention involves the sequential stacking of three layers of three types of active particles—single-crystal particles, near-single-crystal particles, and aggregated particles—starting from the vertical direction of the foil substrate. This multi-gradient cathode material design greatly improves the space utilization and energy carrying capacity of the active material on the electrode, while also providing fast charging capability.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a sodium-ion battery cathode material and preparation method, as well as a battery cell and battery. Background Technology

[0002] In recent years, sales of new energy vehicles in my country have continued to climb. Lithium iron phosphate (LFP) batteries, due to their cost advantage, have become the top-selling power battery product, accounting for over 60% of the market share. With the increasing demand for power batteries, lithium ore prices have fluctuated dramatically, with lithium carbonate prices rising from a low of 40,000 RMB / ton to a high of 600,000 RMB / ton, driving a sharp increase in the price of lithium battery cathode raw materials. Sodium resources are abundant and inexpensive, and sodium-ion batteries offer superior rate performance, low-temperature performance, safety performance, and lifespan, with an energy density already reaching 160Wh / kg, comparable to LFP batteries. In the future, they may even surpass LFP batteries to reach 200Wh / kg, making them a more ideal supplementary alternative to lithium-ion batteries.

[0003] Current research has found that the main problems restricting the development of sodium-ion batteries are low actual capacity utilization and poor cycle performance. At the same time, the energy density improvement of current sodium-ion power batteries has not yet reached the usable design target, and cycle life and cycle safety issues have always existed.

[0004] In battery design, the capacity of cathode materials is significantly related to the size of the stacked particles, directly determining the battery's capacity utilization level. The particle stacking method determines the electrode's compaction density, thus determining the charge capacity. Cycle performance, from an electrochemical perspective, improves the structural reliability of the particles; from a battery level perspective, it involves reducing side reactions and quickly eliminating cycle drops and safety issues caused by gas expansion.

[0005] Based on this technical background, this invention studies a sodium-ion battery cathode material and its preparation method, as well as a battery cell and battery. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a sodium-ion battery cathode material, a preparation method, a battery cell, and a battery. The cathode material consists of three layers of three active particles stacked sequentially from the foil substrate in the vertical direction: single-crystal particles, quasi-single-crystal particles, and aggregated particles. This multi-gradient cathode material design greatly improves the space utilization and energy carrying capacity of the active material on the electrode sheet, while also providing fast charging capability.

[0007] To achieve the above objectives, the first aspect of the present invention provides a sodium-ion battery cathode material, wherein single crystal particles, quasi-single crystal particles, and aggregate particles are sequentially stacked in a vertical direction from a foil substrate.

[0008] The single crystal particles are single block crystals used to provide structural support, high compaction, and active material accumulation for the positive electrode of the sodium-ion battery.

[0009] The quasi-single crystal particles are secondary particles formed by stacking and connecting multiple single crystal particles. The quasi-single crystal particles are mixed with the single crystal particles and fill the gaps between them, which is used to improve the compaction performance and capacity of the positive electrode.

[0010] The aggregated particles are secondary particles formed by the stacking of multiple micro and nano particles, which are used to provide a fast migration channel for the positive electrode ions, shorten the ion migration distance, and realize the fast charging capability of the sodium-ion battery.

[0011] A second aspect of the present invention provides a method for preparing the above-mentioned sodium-ion battery cathode material, comprising:

[0012] A sodium cathode precursor containing Ni, Fe, and M was prepared by co-precipitation method;

[0013] After uniformly mixing the precursor with sodium carbonate, the mixture is sintered in air at a first temperature and then pulverized and sieved to obtain single crystal particles. After sintering in air at a second temperature, quasi-single crystal particles are obtained. After sintering in air at a third temperature, agglomerated particles are obtained.

[0014] A third aspect of the present invention provides a sodium-ion battery cell having a tubular channel penetrating a sealing area;

[0015] When the battery cell is working normally, the port of the tubular channel is sealed with a sealing plug;

[0016] When the battery cell undergoes a side reaction and expands due to gas production, the sealing plug opens and the gas inside the battery cell is released and extracted through the tubular channel, so that the internal electrode plates of the battery cell are tightly attached to the diaphragm and there is no gas storage. This prevents the battery cell from being trapped by gas, which would prevent sodium ions from passing through, resulting in poor local potential and a large amount of sodium ions accumulating and precipitating in the area around the gas, causing safety problems.

[0017] When it is determined that the electrolyte inside the battery cell is insufficient, electrolyte is added through the tubular channel to solve the problem of battery cell cycle failure caused by insufficient sodium inside the battery cell.

[0018] The fourth aspect of the present invention provides a sodium-ion battery, which includes the sodium-ion battery positive electrode material described above or the sodium-ion battery positive electrode material prepared by the above method, and also includes the sodium-ion battery cell described above.

[0019] The sodium-ion battery positive electrode sheet includes a single crystal particle layer, a quasi-single crystal particle layer and an aggregate particle layer arranged in sequence.

[0020] The single-crystal particle layer, the near-single-crystal particle layer, and the agglomerate particle layer are formed by uniformly coating single-crystal particle slurry, near-single-crystal particle slurry, and agglomerate particle slurry onto aluminum foil in sequence.

[0021] The beneficial effects of this invention include:

[0022] (1) The sodium-ion battery cathode material proposed in this invention is stacked with three layers of three active particles in sequence, namely single crystal particles, quasi-single crystal particles and aggregate particles, starting from the vertical direction of the foil substrate. This multi-gradient cathode material design greatly improves the space utilization and energy carrying capacity of the active material on the electrode sheet, and at the same time has fast charging capability.

[0023] (2) The sodium-ion battery cathode material proposed in this invention provides high-pressure compaction of the bottom single-crystal particle layer, which serves as structural support and increases the amount of active material. The single-crystal particle transition layer is filled by mixing single-crystal particles and single-crystal particles, which not only improves the compaction performance but also enhances the capacity. The outermost aggregate particles contribute high capacity and provide a fast ion migration channel, shortening the ion migration distance and realizing the fast charging capability of sodium-ion batteries.

[0024] (3) The sodium-ion battery cell proposed in this invention has a tubular channel installed in the internal cavity area of ​​the cell. Under normal conditions, the internal and external environments are isolated by sealing nails. When the cell undergoes a side reaction and produces gas expansion, the internal gas is released and extracted through this channel, so that the internal electrode plates are tightly attached to the separator and there is no gas storage. This avoids the problem of sodium ions being unable to pass through due to internal gas stagnation, resulting in poor local potential. Then, a large number of sodium ions accumulate and precipitate in the gas surrounding area, causing safety problems. When it is determined that the internal electrolyte is insufficient, electrolyte is replenished through this channel to solve the problem of cell cycle failure caused by insufficient sodium.

[0025] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0026] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings.

[0027] Figure 1 This is a schematic diagram of the structure of the sodium-ion battery cathode material proposed in this invention.

[0028] Figure 2 This is a schematic diagram of the structure of the sodium-ion battery cell proposed in this invention. Detailed Implementation

[0029] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0030] This invention provides a sodium-ion battery cathode material, such as... Figure 1 As shown, the cathode material consists of single-crystal particles, near-single-crystal particles, and aggregated particles stacked sequentially in the vertical direction from the foil substrate.

[0031] Single crystal particles are single, blocky crystals used to provide structural support, high compaction, and increased active material accumulation for the positive electrode of sodium-ion batteries.

[0032] Quasi-single crystal particles are secondary particles formed by the stacking and connection of multiple single crystal particles. Quasi-single crystal particles are mixed with single crystal particles and fill the gaps between them to improve the compaction performance and capacity utilization of the positive electrode.

[0033] Aggregate particles are secondary particles formed by the stacking of multiple micro and nano particles. They are used to provide a fast migration channel for positive electrode ions, shorten the ion migration distance, and realize the fast charging capability of sodium-ion batteries.

[0034] In this invention, starting from the vertical direction of the foil substrate, three layers of three active particles—single crystal particles, quasi-single crystal particles, and aggregate particles—are stacked sequentially. This multi-gradient positive electrode material design greatly improves the space utilization and energy carrying capacity of the active material on the electrode sheet, while also providing fast charging capability.

[0035] According to the present invention, the single crystal particles have a particle size of 2.5-4.5 μm and a specific surface area of ​​0.55-1.05 m². 2 / g, compacted density is 3.6-3.7g / cm³ 3 ;

[0036] The chemical formula of the single crystal particles is Na. x Ni y Mn z M (1-y-z) O2, where 1.25≥x≥0.55, 0.85≥y≥0.05, 0.85≥z≥0.05, 0.35≥1-yz≥0, the stoichiometric sum of all elements in this chemical formula is 100%, satisfying electroneutrality;

[0037] M is a metal composite doping component, mainly composed of Fe and Cu, and also includes at least one of Mo, Ti, V, Nb, W, Ce, La, Ta, Zr, Li, W, B, Mn, V, F, Zn, Sr, Al and Co.

[0038] According to the present invention, the primary particles forming quasi-single-crystal particles have a particle size of 0.5-2.5 μm;

[0039] These are quasi-single-crystal particles, or secondary particles, with a particle size of 3-6.5 μm and a specific surface area of ​​0.45-1.35 m². 2 / g, compacted density 3.4-3.6g / cm³ 3 ;

[0040] The chemical formula of the single-crystal-like particles is Na. x Ni y Mn z M (1-y-z) O2, where 1.25≥x≥0.55, 0.85≥y≥0.05, 0.85≥z≥0.05, 0.35≥1-yz≥0, the stoichiometric sum of all elements in this chemical formula is 100%, satisfying electroneutrality;

[0041] M is a metal composite doping component, mainly composed of Fe and Cu, and also includes at least one of Mo, Ti, V, Nb, W, Ce, La, Ta, Zr, Li, W, B, Mn, V, F, Zn, Sr, Al and Co.

[0042] According to the present invention, the particle size of the primary particles forming the agglomerates is 200 nm-500 nm;

[0043] Aggregate particles, i.e., secondary particles, have a particle size of 10-18 μm and a specific surface area of ​​0.6-0.8 m². 2 / g, compacted density 3.0-3.3g / cm³ 3 ,

[0044] The chemical formula of the aggregated particles is Na x Ni y Mn z M (1-y-z) O2, where 1.25≥x≥0.55, 0.85≥y≥0.05, 0.85≥z≥0.05, 0.35≥1-yz≥0, the stoichiometric sum of all elements in this chemical formula is 100%, satisfying electroneutrality;

[0045] M is a metal composite doping component, mainly composed of Fe and Cu, and also includes at least one of Mo, Ti, V, Nb, W, Ce, La, Ta, Zr, Li, W, B, Mn, V, F, Zn, Sr, Al and Co.

[0046] In this invention, the bottom monocrystalline particle layer provides high-pressure compaction, serves as structural support, and increases the amount of active material accumulation; the semi-monocrystalline particle transition layer is a mixture of monocrystalline and semi-monocrystalline particles that fill the gaps between each other, which not only improves compaction performance but also enhances capacity utilization; the outermost aggregate particles contribute high capacity and provide a fast ion migration channel, shortening the ion migration distance and enabling fast charging capability of sodium-ion batteries.

[0047] The present invention also provides a method for preparing the above-mentioned sodium-ion battery cathode material, comprising:

[0048] A sodium cathode precursor containing Ni, Fe, and M was prepared by co-precipitation method;

[0049] After uniformly mixing the precursor with sodium carbonate, the mixture is sintered in air at a first temperature and then pulverized and sieved to obtain single crystal particles. After sintering in air at a second temperature, quasi-single crystal particles are obtained. After sintering in air at a third temperature, agglomerated particles are obtained.

[0050] According to the present invention, the molar ratio of Ni, Fe and M is y:z:1-yz, wherein 0.85≥y≥0.05, 0.85≥z≥0.05, and 0.35≥1-yz≥0.

[0051] The molar ratio of the precursor to sodium carbonate is x:y, where 1.25 ≥ x ≥ 0.55;

[0052] The precursor is uniformly mixed with sodium carbonate, and then sintered at a controlled temperature to obtain single-crystal particles, near-single-crystal particles, and agglomerated particles with the chemical formula Na. x Ni y Mn z M (1-y-z) O2, in which the stoichiometry of all elements is 100%, satisfies electroneutrality.

[0053] According to the present invention, the first temperature is 94.6-96.6℃, and the holding time for sintering at the first temperature is 23-27h;

[0054] The second temperature is 92.6-94.5℃, and the holding time at the second temperature is 18-22h;

[0055] The third temperature is 90.4-92.4℃, and the holding time at the third temperature is 18-22h.

[0056] This invention also provides a sodium-ion battery cell, such as... Figure 2 As shown, the battery cell is equipped with a tubular channel that penetrates the sealing area;

[0057] When the battery cell is working normally, the ports of the tubular channel are sealed with sealing plugs;

[0058] When a side reaction occurs in the battery cell and gas is generated and expanded, the sealing plug opens and the gas inside the battery cell is released and extracted through the tubular channel. This ensures that the internal electrode plates of the battery cell are tightly attached to the diaphragm and there is no gas storage. This prevents the battery cell from being trapped by gas, which would prevent sodium ions from passing through, resulting in poor local potential and a large amount of sodium ions accumulating and precipitating in the area around the gas, causing safety problems.

[0059] When it is determined that the electrolyte inside the cell is insufficient, electrolyte is added through a tubular channel to solve the problem of cell cycle failure caused by insufficient sodium inside the cell.

[0060] In this invention, a tubular channel is installed in the internal cavity area of ​​the battery cell. Under normal conditions, the internal and external environments are isolated by sealing pins. When the battery cell undergoes a side reaction that generates gas and expands, the internal gas is released and extracted through this channel, ensuring that the internal electrode plates are tightly bonded to the diaphragm without gas storage. This prevents internal gas from trapping sodium ions, which can lead to poor local potential and subsequent accumulation and precipitation of large amounts of sodium ions in the gas-affected area, causing safety issues. When it is determined that the internal electrolyte is insufficient, electrolyte is replenished through this channel, solving the problem of battery cell cycle failure caused by insufficient sodium.

[0061] The present invention also provides a sodium-ion battery, comprising the sodium-ion battery positive electrode material described above or the sodium-ion battery positive electrode material prepared by the above method, and further comprising the sodium-ion battery cell described above.

[0062] The positive electrode sheet of a sodium-ion battery includes a layer of monocrystalline particles, a layer of quasi-monocrystalline particles, and a layer of aggregated particles arranged in sequence.

[0063] The single-crystal particle layer, the near-single-crystal particle layer, and the agglomerate particle layer are formed by sequentially coating single-crystal particle slurry, near-single-crystal particle slurry, and agglomerate particle slurry onto aluminum foil.

[0064] According to the present invention, the single crystal particle slurry, the single crystal-like particle slurry, and the agglomerate particle slurry are formed by adding single crystal particles, single crystal-like particles, and agglomerate particles respectively to an anti-gel polyvinylidene fluoride conductive adhesive with a solid content of 2.8-4.8% and then dispersing them at high speed.

[0065] The solid components in the conductive adhesive are conductive carbon black and / or conductive carbon nanotubes;

[0066] Single crystal particles, near-single crystal particles, and agglomerated particles account for 92-97% of the total solid mass in their respective slurries.

[0067] The present invention will be described in more detail below through embodiments.

[0068] Example 1

[0069] This embodiment provides a sodium-ion battery cathode material, such as... Figure 1 As shown, the cathode material consists of single-crystal particles, near-single-crystal particles, and aggregated particles stacked sequentially in the vertical direction from the foil substrate.

[0070] Single crystal particles are single, blocky crystals used to provide structural support, high compaction, and increased active material accumulation for the positive electrode of sodium-ion batteries.

[0071] In this embodiment, the quasi-single crystal particles are secondary particles formed by stacking and connecting 2-5 single crystal particles. The quasi-single crystal particles are mixed with single crystal particles and fill the gaps between them to improve the compaction performance and capacity utilization of the positive electrode.

[0072] Aggregate particles are secondary particles formed by the stacking of multiple micro and nano particles. They are used to provide a fast migration channel for positive electrode ions, shorten the ion migration distance, and realize the fast charging capability of sodium-ion batteries.

[0073] This embodiment provides a sodium-ion battery cell, such as... Figure 2 As shown, the battery cell is equipped with a tubular channel that penetrates the sealing area;

[0074] When the battery cell is working normally, the ports of the tubular channel are sealed with sealing plugs;

[0075] When a side reaction occurs in the battery cell and gas is generated and expanded, the sealing plug opens and the gas inside the battery cell is released and extracted through the tubular channel. This ensures that the internal electrode plates of the battery cell are tightly attached to the diaphragm and there is no gas storage. This prevents the battery cell from being trapped by gas, which would prevent sodium ions from passing through, resulting in poor local potential and a large amount of sodium ions accumulating and precipitating in the area around the gas, causing safety problems.

[0076] When it is determined that the electrolyte inside the cell is insufficient, electrolyte is added through a tubular channel to solve the problem of cell cycle failure caused by insufficient sodium inside the cell.

[0077] This embodiment provides a method for preparing a sodium-ion battery cathode material, and an assembly method for a sodium-ion battery including the above-mentioned sodium-ion battery cathode material and a sodium-ion battery cell. The specific process flow is as follows:

[0078] (1) Preparation of cathode material: A sodium cathode precursor with Ni:Fe:Mn = 1:1:1 was prepared by co-precipitation method; the precursor was uniformly mixed with sodium carbonate at a molar ratio of 1:1.05, and then sintered at 955℃ for 25h in air atmosphere. After pulverization and sieving, single crystals were obtained.

[0079] Na 1.05 Ni 0.33 Fe 0.33 Mn 0.33 O2; sintering at 935℃ for 20 hours in air atmosphere to obtain a near-single crystal.

[0080] Na 1.05 Ni 0.33 Fe 0.33 Mn 0.33 O2 was used to sinter the aggregates at 915°C for 20 hours in an air atmosphere.

[0081] Na 1.05 Ni 0.33 Fe 0.33Mn 0.33 O2;

[0082] (2) Preparation of positive electrode sheet: Three types of positive electrode slurries were prepared: single crystal, single crystal-like single crystal mixture, and agglomerate. According to the designed formula, three types of sodium-ion layered oxide powders were accurately weighed, with the three types of layered oxides accounting for 95% of the total solid mass in the formula. After mixing for 30 min to ensure uniform particle mixing, the mixture was added in three batches to an anti-gelling PVDF conductive adhesive solution with a solid content of 3.8% (containing conductive carbon black SP and conductive carbon nanotubes CNT). The mixture was dispersed at high speed for 4.5 h, with the dispersion conditions being a dual planetary dispersion, with an orbital speed of 30 rpm and a rotational speed of 4000 rpm. After the slurry was dispersed, a three-layer extrusion coating die was used to simultaneously and uniformly coat the three slurries onto aluminum foil. The designed coating surface density was 500 g / m². 2 The electrode compaction design employs high-temperature hot pressing, with a designed temperature of 85℃ and a designed compaction density of 3.15 g / m³. 3 The electrodes are cut into corresponding sizes using molds and then baked in an oven at 100°C for 24 hours. During the preparation of the positive electrode, the ambient dew point is controlled to be ≤-40°C.

[0083] (3) Preparation of negative electrode sheet: According to the designed formula, accurately weigh the hard carbon powder, add 95.5% of the total solid mass, weigh the conductive carbon black graphite, mix for 30 min to ensure uniform particle mixing, then add it to CMC adhesive with a solid content of 1.5%, and disperse at high speed for 4-6 h. The dispersion conditions are dual planetary dispersion, revolution at 250 rpm, rotation at 1500-3000 rpm, and SBR binder is added and dispersed for 30 min. After the slurry is dispersed, it is uniformly coated on copper foil with a designed coating surface density of 230 g / m². 2 The electrode sheet compaction density is designed to be 0.95 g / m³. 3 Cut the electrode sheets into corresponding sizes using a mold, and then bake them in a 90℃ oven for 24 hours.

[0084] (4) Battery assembly: After the moisture content of the positive and negative electrode sheets is tested and qualified after baking, the assembly begins. The single cell is designed for 7Ah, with the moisture content of the positive electrode sheet required to be ≤150ppm and the moisture content of the negative electrode sheet required to be ≤200ppm. The separator is preferably a high porosity separator, and the electrolyte is a fast-charging electrolyte. The battery assembly method is Z-shaped stacking process. After the battery is assembled, it is packaged. At this time, a pipe with a diameter of 1.5mm is inserted into the cavity area of ​​the cell tab shoulder, and then it is baked again. The moisture content of the mixed sample is tested to be ≤200ppm. After the moisture content test is qualified, the electrolyte is injected. After formation aging and other processes, the finished battery is finally obtained.

[0085] The detailed schemes of Examples 2-6 and Comparative Examples 1-3 of this application are formulated according to the experimental scheme summary table in Table 1.

[0086] Table 1 Summary of experimental schemes for Examples 2-6 and Comparative Examples 1-3

[0087]

[0088] In this application, since the quasi-single crystal particles are mixed with single crystal particles and fill the gaps between them, the middle layer in the table is also called the single crystal-quasi-single crystal mixed particle layer.

[0089] The capacity retention and cycle performance of the batteries assembled in Examples 1-6 and Comparative Examples 1-3 were tested, and the specific test results are shown in Table 2.

[0090] Table 2 Test Results

[0091]

[0092]

[0093] A comparison of the test results of Examples 1-6 and Comparative Examples 1-3 in Table 2 shows that stacking three layers of three active particles—single crystal particles, near-single crystal particles, and agglomerate particles—starting vertically from the foil substrate, or stacking at least two layers, can greatly improve the space utilization and energy carrying capacity of the active material on the electrode, while also providing fast charging capability. Simultaneously, a tubular channel is installed in the internal cavity area of ​​the cell. Under normal conditions, sealing pins isolate the internal and external environments. When the cell undergoes a side reaction and gas expansion, the internal gas is released and extracted through this channel, ensuring a tight fit between the internal electrode and the separator without gas storage. This prevents internal gas buildup, which prevents sodium ions from passing through, leading to poor local potential and subsequent accumulation and precipitation of large amounts of sodium ions in the gas-affected area, causing safety issues. When it is determined that the internal electrolyte is insufficient, electrolyte is replenished through this channel, resolving the problem of cell cycle failure caused by insufficient sodium.

[0094] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A positive electrode sheet for a sodium-ion battery, characterized in that, The positive electrode sheet includes a single crystal particle layer, a near-single crystal particle layer and an aggregate particle layer sequentially disposed on an aluminum foil; The single crystal particles in the single crystal particle layer are single block crystals, which are used to provide structural support, high compaction and active material accumulation for the positive electrode of sodium-ion batteries. The single-crystal-like particles in the single-crystal-like particle layer are secondary particles formed by stacking and connecting multiple single-crystal particles. The single-crystal-like particles are mixed with the single-crystal particles and fill the gaps between them, which is used to improve the compaction performance and capacity of the positive electrode. The aggregate particles in the aggregate particle layer are secondary particles formed by the stacking of multiple micro and nano particles, which are used to provide a fast migration channel for ions in the positive electrode, shorten the ion migration distance, and realize the fast charging capability of sodium-ion batteries. The single-crystal particles have a particle size of 2.5-4.5 μm and a specific surface area of ​​0.55-1.05 m². 2 / g, compacted density is 3.6-3.7g / cm³ 3 ; The aforementioned quasi-single-crystal particles, i.e., secondary particles, have a particle size of 3-6.5 μm and a specific surface area of ​​0.45-1.35 m². 2 / g, compacted density is 3.4-3.6g / cm³ 3 ; The aggregated particles, i.e., secondary particles, have a particle size of 10-18 μm and a specific surface area of ​​0.6-0.8 m². 2 / g, compacted density is 3.0-3.3g / cm³ 3 ; The chemical formula of the single crystal particles, quasi-single crystal particles, and aggregate particles is Na. x Ni y Mn z M (1-y-z) O2, where 1.25≥x≥0.55, 0.85≥y≥0.05, 0.85≥z≥0.05, 0.35≥1-yz≥0, the stoichiometric sum of all elements in this chemical formula is 100%, satisfying electroneutrality; M is a metal composite doping component, mainly composed of Fe and Cu, and also includes at least one of Mo, Ti, V, Nb, W, Ce, La, Ta, Zr, Li, W, B, Mn, V, F, Zn, Sr, Al, and Co.

2. The positive electrode sheet according to claim 1, characterized in that, The primary particles that form the quasi-single crystal particles have a particle size of 0.5-2.5 μm.

3. The positive electrode sheet according to claim 1, characterized in that, The primary particles that form the aggregate particles have a particle size of 200nm-500nm.

4. A method for preparing a sodium-ion battery positive electrode sheet according to any one of claims 1-3, characterized in that, include: The monocrystalline particle slurry, the quasi-monocrystalline particle slurry, and the agglomerated particle slurry are sequentially coated onto aluminum foil to form a monocrystalline particle layer, a quasi-monocrystalline particle layer, and an agglomerated particle layer. A sodium cathode precursor containing Ni, Fe, and M was prepared by co-precipitation method; The precursor is uniformly mixed with sodium carbonate to obtain a mixture. The mixture is sintered in air at a first temperature and then crushed and sieved to obtain single crystal particles. The mixture is sintered in air at a second temperature to obtain near-single crystal particles. The mixture is sintered in air at a third temperature to obtain agglomerated particles. The first temperature is 946-966℃, and the sintering time at the first temperature is 23-27h; The second temperature is 926-945℃, and the sintering time at the second temperature is 18-22h; The third temperature is 904-924℃, and the holding time for sintering at the third temperature is 18-22h.

5. The preparation method according to claim 4, characterized in that, The molar ratio of Ni, Fe and M is y:z:1-yz, where 0.85≥y≥0.05, 0.85≥z≥0.05, and 0.35≥1-yz≥0. The molar ratio of the precursor to sodium carbonate is x:y, where 1.25 ≥ x ≥ 0.

55.

6. A sodium-ion battery, characterized in that, Includes the sodium-ion battery positive electrode sheet according to any one of claims 1-3 or the sodium-ion battery positive electrode sheet prepared by the preparation method according to claim 4 or 5; The sodium-ion battery positive electrode sheet includes a single crystal particle layer, a quasi-single crystal particle layer and an aggregate particle layer arranged in sequence. The single-crystal particle layer, the near-single-crystal particle layer, and the agglomerate particle layer are formed by uniformly coating single-crystal particle slurry, near-single-crystal particle slurry, and agglomerate particle slurry onto aluminum foil in sequence.

7. The sodium-ion battery according to claim 6, characterized in that, The monocrystalline particle slurry, the quasi-monocrystalline particle slurry, and the agglomerated particle slurry are formed by high-speed dispersion of monocrystalline particles, quasi-monocrystalline particles, and agglomerated particles respectively into an anti-gel polyvinylidene fluoride conductive adhesive with a solid content of 2.8-4.8%. The solid components in the conductive adhesive are conductive carbon black and / or conductive carbon nanotubes. The single crystal particles, quasi-single crystal particles, and agglomerated particles account for 92-97% of the total solid mass in their respective slurries.

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