A positive electrode material precursor for a sodium ion battery, a preparation method of the positive electrode material precursor, a positive electrode material, and a sodium ion battery

Abstract

The application provides a positive electrode material precursor for a sodium ion battery, a preparation method of the positive electrode material precursor, a positive electrode material and a sodium ion battery, and relates to the technical field of new energy sources.The positive electrode material precursor for the sodium ion battery comprises a core and a shell, the core primary particles are arranged in disorder, the shell primary particles comprise skeleton primary particles staggered along the circumference of secondary particles and elongated primary particles filled between the skeleton primary particles, the skeleton primary particles improve the strength of the secondary particles, so that structural collapse is not prone to occurring in the sintering process, and the stability of the structure can be maintained; the skeleton is filled with the elongated primary particles in the middle, the tap density of the precursor can be improved, the electrochemical performance of the material can be improved, and the capacity of the battery is improved; moreover, the overall porosity of the precursor is relatively high, the elements are uniformly distributed, the infiltration of Na elements and other doped elements is facilitated in the sintering process, and the sintering temperature is reduced.

Description

Technical Field

[0001] This application relates to the field of new energy technology, and in particular to a precursor of a positive electrode material for sodium-ion batteries, its preparation method, the positive electrode material, and the sodium-ion battery. Background Technology

[0002] Sodium-ion batteries offer advantages such as low cost, low-temperature resistance, safety, and convenience, and are expected to see rapid development in various fields including electric vehicles, electric boats, home / industrial energy storage, 5G communication base stations, data centers, large-scale renewable energy integration, and smart grids. Sodium is an abundant natural resource, and sodium-ion batteries can reduce or eliminate the use of expensive metals such as lithium, cobalt, and nickel, thus lowering energy storage costs. Therefore, sodium-ion batteries are highly competitive in the energy storage field and are expected to become an excellent alternative to lithium-ion batteries.

[0003] The cycle stability and capacity of sodium-ion batteries mainly depend on the performance of the cathode material, which inherits the morphology and structural characteristics of the precursor. Currently, sodium-ion batteries prepared by sintering mixed cathode material precursors have low capacity and poor cycle performance. Cathode material precursors prepared by simple co-precipitation methods also suffer from poor elemental uniformity and low material tap, which restricts the improvement of the overall capacity and cycle stability of sodium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a precursor for a positive electrode material for sodium-ion batteries, a method for preparing the same, the positive electrode material, and a sodium-ion battery, aiming to solve the problems of poor elemental distribution uniformity and low material tap in existing precursor materials, which restrict the improvement of the overall capacity and cycle stability of sodium-ion batteries.

[0005] To achieve the above objectives, the first aspect of this application provides a cathode material precursor for sodium-ion batteries, comprising secondary particles formed by the aggregation of multiple primary particles, wherein the secondary particles include a core and a shell covering the core.

[0006] The primary particles of the core are arranged in a disordered manner, while the primary particles of the outer shell include skeletal primary particles arranged in a staggered manner along the circumference of the secondary particles and slender primary particles filling the spaces between the skeletal primary particles.

[0007] The uniform distribution of elements in the precursor of the positive electrode material for the sodium-ion battery is beneficial to improving the battery capacity and cycling performance of the positive electrode material. The primary particles in the core are arranged disorderly, which is beneficial to the diffusion of Na elements during the sintering process of the positive electrode material; the primary particles of the thick skeleton in the shell are arranged staggered along the circumferential direction of the secondary particles, forming the outer skeleton structure of the secondary particles. The primary particles of the skeleton improve the particle strength of the secondary particles, making the positive electrode material not prone to structural collapse during the processes of Na doping and batch mixing and sintering, and being able to maintain the stability of the structure; slender primary particles are filled between the primary particles of the skeleton, which can improve the tap density of the precursor and the volumetric energy density of the material, enabling the battery to have a high discharge capacity and high charge-discharge efficiency; moreover, the precursor as a whole has many pores and uniform element distribution, which is beneficial to the infiltration of Na elements and other doping elements during the sintering process and reduces the sintering temperature; the copper-containing positive electrode material prepared by sintering the precursor material of the positive electrode material for the sodium-ion battery has good air stability, which is beneficial to improving the cycle life.

[0008] Preferably, its chemical formula is (Ni x Cu y M 1-x-y )(OH)2, where 0 < x < 1, 0 < y ≤ 1, and M is one or more of the elements Mn, Fe, Ti, Zn, Mg, Ca, Al, Ag, Co, Cr, La, Ce.

[0009] Preferably, the precursor of the positive electrode material for the sodium-ion battery satisfies at least one of the following conditions (1) to (3):

[0010] (1) The thickness of the primary particles of the skeleton in the shell is 30 - 600 nm, for example, it can be 30 - 60 nm, or 50 - 100 nm, or 150 - 200 nm, or 70 - 120 nm, or 100 - 150 nm, or 20 - 300 nm, or 200 - 300 nm, or 200 - 400 nm, or 200 - 600 nm; the length of the primary particles of the skeleton is 1.0 - 4.0 μm, for example, it can be 1.0 - 2.0 μm, or 1.1 - 1.9 μm, or 2.0 - 4.0 μm;

[0011] (2) The thickness of the slender primary particles in the shell is 5 - 80 nm, for example, it can be 5 - 20 nm, or 5 - 50 nm, or 5 - 80 nm, or 10 - 30 nm, or 10 - 50 nm, or 50 - 80 nm; the length of the slender primary particles is 0.4 - 2.5 μm, for example, it can be 0.4 - 2.0 μm, or 0.4 - 2.2 μm, or 0.5 - 2.0 μm;

[0012] (3) The thickness of the primary particles in the core is 10-50 nm, for example, it can be 10-20 nm, or 15-30 nm, or 20-30 nm, or 15-25 nm, or 30-50 nm; the length of the primary particles in the core is 0.2-1.0 μm, for example, it can be 0.2-0.4 μm, or 0.3-0.5 μm, or 0.2-0.6 μm, or 0.7-1.0 μm, or 0.5-0.8 μm.

[0013] Preferably, the area ratio of primary skeleton particles to secondary particles in the shell is greater than or equal to 10%, for example, it can be 10% to 20%, or 20% to 30%, or greater than 40%, or greater than 50%.

[0014] Preferably, the area ratio of primary skeleton particles to secondary particles in the shell is greater than 40%.

[0015] Preferably, the (D90-D10) / D50 ratio of the precursor for the positive electrode material of sodium-ion batteries is 0.4 to 1.0, for example, it can be 0.4 to 0.6, or 0.6 to 0.9, or 0.8 to 0.9, or 0.85 to 1.0. (D90-D10) / D50 is the Span value. A smaller Span value results in more uniform secondary particle size, allowing for denser filling when used in the positive electrode material, thus improving the battery's discharge capacity. Preferably, the (D90-D10) / D50 ratio of the precursor for the positive electrode material of sodium-ion batteries is 0.6-0.9.

[0016] Preferably, the cathode material precursor satisfies at least one of the following conditions (4) to (5):

[0017] (4) The radius of the core is 1.0 to 2.0 μm, for example, it can be 1.0 to 1.5 μm, or 1.5 to 1.6 μm, or 1.6 to 2.0 μm, or 1.5 to 2.0 μm; the thickness of the outer shell is 1.0 to 3.0 μm, for example, it can be 1.0 to 1.5 μm, or 1.5 to 2.0 μm, or 2.0 to 3.0 μm, or 1.0 to 2.0 μm;

[0018] (5) The porosity of the core is 5-30%, for example, it can be 5%-10%, or 10%-20%, or 20%-30%, and the porosity of the shell is 20%-45%, for example, it can be 20%-30%, or 30%-40%, or 40%-45%.

[0019] Preferably, the precursor material for the positive electrode of the sodium-ion battery satisfies at least one of the following conditions (6) to (9):

[0020] (6) The D50 of the positive electrode material precursor for sodium-ion batteries is 4 to 8 μm, for example, it can be 4 to 6 μm, or 5 to 6 μm, or 5.5 to 6.5 μm, or 6 to 7 μm, or 7 to 8 μm;

[0021] (7) The TD of the positive electrode material precursor for sodium-ion batteries is 1.0–1.5 g / cm³. 3 For example, it can be 1.0 to 1.1 g / cm³. 3 or 1.1~1.2g / cm 3 or 1.2–1.5 g / cm³ 3 ;

[0022] (8) The BET of the positive electrode material precursor for sodium-ion batteries is 20-80m. 2 / g, for example, can be 20-40m 2 / g, or 30-40m 2 / g, or 30-50m 2 / g, or 50-60m 2 / g, or 60-70m 2 / g, or 50-80m 2 / g;

[0023] (9) Preferably, the BET of the positive electrode material precursor for sodium-ion batteries is 30-50m. 2 / g.

[0024] This application also provides a method for preparing the above-mentioned precursor for the positive electrode material of sodium-ion batteries, including:

[0025] Water, precipitant, and complexing agent are added to the reaction vessel and mixed to obtain the reaction base liquid;

[0026] A metal salt solution, precipitant, and complexing agent were added to the reaction substrate to carry out a coprecipitation reaction, and the pH value of the reaction system was gradually reduced.

[0027] The coprecipitation reaction also includes the addition of additives during the reaction, including at least one of ammonium sulfate and dilute sulfuric acid.

[0028] In the preparation process of the precursor material for the positive electrode of the sodium-ion battery, the precipitation rate of the metal is increased under high pH (11-12) conditions, which makes the core primary particles finer and arranged in a disordered manner. By adding complexing agents and additives, the surface potential energy of the shell primary particles is reduced, which improves the growth uniformity of the shell primary particles. At the same time, the reaction pH is reduced (10-11), which reduces the precipitation rate of the metal and increases the thickness of the shell primary particles. This results in the formation of a skeletal structure composed of thick sheet-like skeleton primary particles, with slender primary particles tightly packed between the skeleton primary particles.

[0029] Preferably, the preparation method of the positive electrode material precursor for sodium-ion batteries satisfies at least one of the following conditions a to c:

[0030] a. The complexing agent includes one or more of the following: ammonia solution, oxalic acid, sodium acetate, and EDTA-2Na;

[0031] b. Metal salt solutions include Ni, Cu, and metal salt solutions of at least one element selected from Fe, Mn, Ti, Zn, Mg, Ca, Al, Ag, Co, Cr, La, and Ce;

[0032] c. Metal salt solutions include metal salt solutions containing Ni, Cu, and at least one element selected from Fe, Mn, and Mg.

[0033] Preferably, the complexing agent is sodium acetate. When sodium acetate is used as a complexing agent and ammonium sulfate is added, the difference in the complexing ability of the complexing agent for metal elements is smaller, resulting in a smaller difference in precipitation rate and thus optimizing the uniformity of morphology. Furthermore, ammonium sulfate can further reduce the growth rate, resulting in thicker primary particles.

[0034] Preferably, the preparation method of the positive electrode material precursor for sodium-ion batteries satisfies at least one of the following conditions d to g:

[0035] d. The concentration of the additive is 0.01 to 0.5 mol / L, for example, it can be 0.01 to 0.05 mol / L, or 0.05 to 0.1 mol / L, or 0.1 to 0.5 mol / L, more specifically, it can be 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L;

[0036] e. The mass concentration of each metal ion in the metal salt solution is independently 10–50 g / L, for example, 10–30 g / L, 20–40 g / L, or 30–50 g / L;

[0037] f. The mass concentration of the complexing agent is 60–100 g / L, for example, it can be 60–90 g / L, or 70–100 g / L, or 70–90 g / L, more specifically, it can be 60 g / L, 65 g / L, 70 g / L, 72, 75 g / L, 77 g / L, 80 g / L, 82 g / L, 85 g / L, 88 g / L, 90 g / L, 95 g / L or 100 g / L;

[0038] g. The pH of the reaction substrate is 11-12, and the pH of the reaction system is reduced to 10-11.

[0039] This application also provides a sodium-ion battery cathode material, which includes an inner layer and an outer layer. The outer layer is dense, the inner layer has a hollow structure, and the outer layer includes multiple sheet-like primary particles.

[0040] Preferably, the sodium-ion battery cathode material satisfies at least one of the following conditions A to C:

[0041] A. The diameter of the inner layer of the sodium-ion battery cathode material is 0.5-2.0 μm, for example, it can be 0.5-1.0 μm, or 0.8-2.0 μm, or 0.6-1.2 μm; the thickness of the outer layer of the sodium-ion battery cathode material is 1.0-3.0 μm, for example, it can be 1.0-2.0 μm, or 2.0-3.0 μm, or 1.0-1.5 μm.

[0042] B. The D50 of the positive electrode material for sodium-ion batteries is 3.5–8 μm, for example, it can be 3.5–5.0 μm, or 4.0–6.0 μm, or 5.0–8.0 μm, or 4.0–7.0 μm;

[0043] C. The (D90-D10) / D50 ratio of the sodium-ion battery cathode material is 0.4-1 μm, for example, it can be 0.4-0.8 μm, or 0.5-1 μm, or 0.5-0.8 μm.

[0044] This application also provides a sodium-ion battery, the raw materials of which include the above-mentioned sodium-ion battery cathode material precursor or the above-mentioned sodium-ion battery cathode material.

[0045] Compared with the prior art, the beneficial effects of this application include:

[0046] The sodium-ion battery cathode material precursor provided in this application features a disordered arrangement of primary particles in the core, which facilitates the diffusion of Na elements during the sintering process. The thicker outer shell consists of primary skeleton particles arranged circumferentially along the secondary particles, forming an outer skeleton structure. These primary skeleton particles enhance the particle strength of the secondary particles, preventing structural collapse during Na doping and sintering, thus maintaining structural stability. The primary skeleton particles are filled with elongated primary particles, increasing the tap density of the precursor and the volumetric energy density of the material, resulting in high discharge capacity and high charge / discharge efficiency. Furthermore, the precursor has numerous pores and a uniform element distribution, which facilitates the infiltration of Na and other dopants during sintering, reducing the sintering temperature. The copper-containing cathode material prepared by sintering this sodium-ion battery cathode material precursor exhibits good air stability, contributing to improved cycle life. Attached Figure Description

[0047] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0048] Figure 1 Here is a SEM image of the sodium-ion battery cathode material precursor from Example 1;

[0049] Figure 2 This is a cross-sectional SEM image of the positive electrode material precursor for sodium-ion batteries in Example 1;

[0050] Figure 3 This is a cross-sectional mapping diagram of the positive electrode material precursor for sodium-ion batteries in Example 1;

[0051] Figure 4 Here is a SEM image of the positive electrode material for a sodium-ion battery in Example 1;

[0052] Figure 5 This is a cross-sectional SEM image of the positive electrode material for sodium-ion batteries in Example 1;

[0053] Figure 6 Here is a SEM image of the sodium-ion battery cathode material precursor from Example 2;

[0054] Figure 7 This is a cross-sectional SEM image of the positive electrode material precursor for sodium-ion batteries in Example 2;

[0055] Figure 8 Here is a SEM image of the sodium-ion battery cathode material precursor from Example 3;

[0056] Figure 9 This is a cross-sectional SEM image of the positive electrode material precursor for sodium-ion batteries in Example 3;

[0057] Figure 10 Here is a SEM image of the sodium-ion battery cathode material precursor from Example 4;

[0058] Figure 11 Here is a SEM image of the nickel-iron-manganese hydroxide precursor of Comparative Example 1;

[0059] Figure 12 SEM image of the nickel-iron-manganese-copper hydroxide precursor of Comparative Example 2;

[0060] Figure 13 Here is a cross-sectional SEM image of the nickel-iron-manganese-copper hydroxide precursor of Comparative Example 2;

[0061] Figure 14 This is a cross-sectional mapping diagram of the nickel-iron-manganese-copper hydroxide precursor of Comparative Example 2;

[0062] Figure 15 This is a SEM image of the positive electrode material used in the sodium-ion battery of Comparative Example 2. Detailed Implementation

[0063] As used in this article:

[0064] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0065] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0066] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0067] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0068] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (K is any number representing a multiplier). It is important to understand that, unlike the number of parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0069] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0070] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0071] Example 1

[0072] Example 1 First, a material with a D50 of 6.01 μm and the chemical formula (Ni) was prepared. 0.23 Fe 0.33 Mn 0.34 Cu 0.10 The specific preparation method of the nickel-iron-manganese-copper hydroxide precursor (OH)2 is as follows:

[0073] ① Dissolve nickel sulfate, ferrous sulfate, manganese sulfate, and copper sulfate crystals to form metal salt solutions with nickel ion concentrations of 27.7 g / L, ferrous ion concentrations of 37.9 g / L, manganese ion concentrations of 37.3 g / L, and copper ion concentrations of 13.12 g / L, respectively. The concentration of sodium hydroxide solution used is 21%, the complexing agent is sodium acetate with a concentration of 82 g / L, and the additives are ammonium sulfate and dilute sulfuric acid with concentrations of 0.1 mol / L and 0.05 mol / L, respectively. The ammonium sulfate is added to the sodium acetate solution, and the dilute sulfuric acid is added to the metal salt solution.

[0074] ② Add pure water, sodium acetate solution, and sodium hydroxide solution to the reaction vessel, mix to obtain the reaction base liquid, control the pH value of the reaction base liquid to 11.40, introduce nitrogen gas for protection, heat the reaction vessel to 60℃, and control the stirring speed at 800r / min.

[0075] ③ After the feeding conditions are met, a metal salt solution, a sodium hydroxide solution, and a sodium acetate solution are pumped into the reaction base liquid. Then, the metal salt solution (flow rate of 8% / h of the total reactor capacity), the sodium hydroxide solution (flow rate of 3.2% / h of the total reactor capacity), and the sodium acetate solution (flow rate of 0.8% / h of the total reactor capacity) are introduced at the set flow rates. The ammonium sulfate concentration is maintained at 0.025-0.01 mol / L in the reaction system, and the dilute sulfuric acid concentration is maintained at 0.01-0.05 mol / L in the reaction system. The pH value of the reaction system is controlled, and the pH is gradually reduced from 11.40 during the nucleation period to 10.20 during the control period. The reaction yields a nickel-iron-manganese-copper quaternary precursor precipitate.

[0076] ④ After the synthesis stage, the material was centrifuged, washed, dried, and demagnetized to obtain the nickel-iron-manganese-copper hydroxide precursor of Example 1, the SEM image of which is shown below. Figure 1 As shown, its cross-sectional SEM image is as follows: Figure 2 As shown, its cross-sectional mapping diagram is as follows: Figure 3 As shown.

[0077] Figure 1 It can be seen that the precursor secondary particles prepared in Example 1 are uniform in size. This is mainly because sodium acetate is used as a complexing agent and ammonium sulfate is added as an additive. The complexing ability of the complexing agent to the metal is relatively small, which reduces the difference in precipitation rate and optimizes the uniformity of the precursor secondary particle morphology. The combined effect of ammonium sulfate and dilute sulfuric acid can further reduce the growth rate and make the primary particles thicker.

[0078] from Figure 2 It can be seen that the precursor core is composed of fine primary particles arranged in a disordered manner, which is conducive to the diffusion of Na elements during the sintering process of the cathode material. The thicker skeleton primary particles are arranged in an alternating pattern along the circumference of the secondary particles, forming the outer skeleton structure of the secondary particles. The thick skeleton primary particles improve the particle strength of the secondary particles, making the cathode material less prone to structural collapse during Na doping and sintering, thus maintaining structural stability. The space between the skeleton primary particles is filled with slender primary particles, which can improve the tap density of the precursor and the volumetric energy density of the material, enabling the battery to have high discharge capacity and high charge-discharge efficiency. Moreover, the precursor has a large number of pores and uniform element distribution, which is conducive to the infiltration of Na and other dopants during the sintering process and reduces the sintering temperature. The copper-containing cathode material prepared by sintering the cathode material precursor material of this sodium-ion battery has good air stability, which is beneficial to improving cycle life.

[0079] according to Figure 3 It can be seen that the precursor prepared in Example 1 has a good uniform element distribution, which can effectively ensure the uniformity of element distribution of the cathode material prepared from the precursor material. The uniform distribution of Cu element can effectively reduce the sintering difficulty of the cathode material and reduce the post-processing cost of the material. At the same time, it is beneficial to improve the stability of the crystal structure. During the charging and discharging process, the cathode material can reduce the changes in the crystal structure and reduce the dislocation of the layered oxide crystal plane, thereby improving the cycle performance.

[0080] Example 1 also prepared a positive electrode material for sodium-ion batteries, which was prepared using the nickel-iron-manganese-copper hydroxide precursor obtained in Example 1. The preparation method was as follows: a certain weight of precursor material and refined sodium carbonate (<100 mesh) were accurately weighed at a mass ratio of 1:1.24, mixed evenly, and then transferred to a mortar, spread evenly. Finally, the mortar was transferred to a muffle furnace for sintering. The temperature was increased according to the heating curve of 1℃ / min, and the temperature was held at 500℃ for 5-8h. Then, the temperature was increased to 950-1050℃ according to the heating curve of 1℃ / min, held for 10h, and then cooled naturally to obtain the positive electrode material for sodium-ion batteries of Example 1.

[0081] Figure 4 This is a SEM image of the sodium-ion battery cathode material prepared in Example 1. Figure 5 This is a cross-sectional view of the sodium-ion battery cathode material prepared in Example 1. It can be seen that the cathode material comprises an inner layer and an outer layer. The inner layer has a diameter of 1.35 μm, and the outer layer has a thickness of 1.83 μm. The outer layer is dense and includes multiple sheet-like primary particles, while the inner layer has a hollow structure, which facilitates electrolyte penetration and increases the contact area between the electrolyte and the electrode material, thereby improving the electrochemical performance and usable capacity of the material. The secondary particles are uniform in size, with a D50 of 5.85 μm and a span value of 0.78. The secondary particles have high strength, making it difficult to generate micropowder during the mixing and sintering process. This cathode material for sodium-ion batteries can improve the capacity of sodium-ion batteries.

[0082] Example 2

[0083] Example 2 first prepared a material with a D50 of 6.17 μm and the chemical formula (Ni 0.17 Fe 0.36 Mn 0.36 Cu 0.11 The specific preparation method of the nickel-iron-manganese-copper hydroxide precursor (OH)2 is as follows:

[0084] ① Dissolve nickel sulfate, ferrous sulfate, manganese sulfate, and copper sulfate crystals to form metal salt solutions with nickel ion concentrations of 20.3 g / L, ferrous ion concentrations of 41.0 g / L, manganese ion concentrations of 40.3 g / L, and copper ion concentrations of 14.3 g / L. The sodium hydroxide solution used has a concentration of 21%, the complexing agent is sodium acetate with a concentration of 82 g / L, and the additives are ammonium sulfate and dilute sulfuric acid with concentrations of 0.1 mol / L and 0.05 mol / L, respectively. The ammonium sulfate is added to the sodium acetate solution, and the dilute sulfuric acid is added to the metal salt solution.

[0085] ② Add pure water, sodium acetate solution, and sodium hydroxide solution to the reaction vessel, mix to obtain the reaction base liquid, control the pH value of the reaction base liquid to 11.40, introduce nitrogen gas for protection, heat the reaction vessel to 60℃, and control the stirring speed at 800r / min.

[0086] ③ After the feeding conditions are met, a metal salt solution, a sodium hydroxide solution, and a sodium acetate solution are pumped into the reaction base liquid. Then, the metal salt solution (flow rate of 8% / h of the total reactor capacity), the sodium hydroxide solution (flow rate of 3.2% / h of the total reactor capacity), and the sodium acetate solution (flow rate of 0.8% / h of the total reactor capacity) are introduced at the set flow rates. The concentration of ammonium sulfate in the reaction system is maintained at 0.025-0.01 mol / L; the concentration of dilute sulfuric acid in the reaction system is maintained at 0.01-0.05 mol / L, and the pH value of the reaction system is controlled by gradually reducing the pH from 11.40 during the nucleation period to 10.20 during the control period. The reaction yields a nickel-iron-manganese-copper quaternary precursor precipitate.

[0087] ④ After the synthesis stage is completed, the material is centrifuged, washed, dried, and demagnetized to obtain the nickel-iron-manganese-copper hydroxide precursor of Example 2. Figure 6 The SEM image of the nickel-iron-manganese-copper hydroxide prepared in Example 2 is shown below, along with its cross-sectional SEM image. Figure 7 As shown. Changing the elemental ratio of nickel, iron, manganese, and copper (Ni... 0.17 Fe 0.36 Mn 0.36 Cu 0.11 The morphology of (OH)₂ remains stable, indicating that the secondary particles of the precursor are uniform in size. In the cross-sectional view, the area ratio of the primary particles with thick lamellar skeletons to the secondary particles is approximately 40%. This demonstrates that the stability and consistency of the precursor morphology prepared by this method can be guaranteed under different nickel contents.

[0088] Example 2 also prepared a positive electrode material for sodium-ion batteries, which was prepared using the nickel-iron-manganese-copper hydroxide precursor obtained in Example 2. The preparation method was the same as that of the positive electrode material for sodium-ion batteries in Example 1.

[0089] Example 3

[0090] Example 3 First, a material with a D50 of 5.99 μm and the chemical formula (Ni) was prepared. 0.23 Fe 0.33 Mn 0.34 Cu 0.10 The specific preparation method of the nickel-iron-manganese-copper hydroxide precursor (OH)2 is as follows:

[0091] ① Dissolve nickel sulfate, ferrous sulfate, manganese sulfate, and copper sulfate crystals respectively to form metal salt solutions with nickel ion concentration of 27.7 g / L, ferrous ion concentration of 37.9 g / L, manganese ion concentration of 37.3 g / L, and copper ion concentration of 13.1 g / L. The sodium hydroxide solution used has a concentration of 21%, sodium acetate is used as the complexing agent with a concentration of 82 g / L, and ammonium sulfate is used as an additive with a concentration of 0.1 mol / L. The ammonium sulfate is added to the sodium acetate solution.

[0092] ② Add pure water, sodium acetate solution, and sodium hydroxide solution to the reaction vessel, mix to obtain the reaction base liquid, control the pH value of the reaction base liquid to 11.40, introduce nitrogen gas for protection, heat the reaction vessel to 60℃, and control the stirring speed at 800r / min.

[0093] ③ After the feeding conditions are met, a metal salt solution, a sodium hydroxide solution, and a sodium acetate solution are pumped into the reaction base liquid. Then, the metal salt solution (flow rate of 8% / h of the total reactor capacity), the sodium hydroxide solution (flow rate of 3.2% / h of the total reactor capacity), and the sodium acetate solution (flow rate of 0.8% / h of the total reactor capacity) are introduced at the set flow rates. The ammonium sulfate concentration is maintained at 0.025-0.01 mol / L in the reaction system. The pH is gradually reduced from 11.40 during the nucleation period to 10.20 during the control period, according to the pH value of the reaction system. The reaction yields a nickel-iron-manganese-copper quaternary precursor precipitate.

[0094] ④ After the synthesis stage is completed, the material is centrifuged, washed, dried and demagnetized to obtain the nickel-iron-manganese-copper hydroxide precursor of Example 3.

[0095] Figure 8 The image shows the SEM image of the nickel-iron-manganese-copper hydroxide precursor prepared in Example 3. It can be seen that the secondary particles of the precursor are uniform in size. This is mainly because sodium acetate is used as a complexing agent and ammonium sulfate is added. The complexing ability of the complexing agent to the metal is relatively small, which reduces the difference in precipitation rate and optimizes the uniformity of the secondary particle morphology of the precursor. Ammonium sulfate can further reduce the growth rate and make the primary particles thicker.

[0096] Figure 9 The image shows a cross-sectional view of the nickel-iron-manganese-copper hydroxide prepared in Example 3. It can be seen that the precursor prepared by this method has a dense structure in the inner layer composed of fine primary particles arranged in a disordered manner, which is conducive to the diffusion of Na element during the sintering of the cathode material. The outer layer has a loose and porous structure, consisting of thick plate-like primary particles arranged alternately along the circumference of the secondary particles, forming the outer skeleton structure of the secondary particles. The area ratio of the thick plate-like skeleton primary particles in the outer shell to the area ratio of the secondary particles is about 40%.

[0097] Example 3 also prepared a positive electrode material for sodium-ion batteries, which was prepared using the nickel-iron-manganese-copper hydroxide precursor obtained in Example 3. The preparation method was the same as that of the positive electrode material for sodium-ion batteries in Example 1.

[0098] Example 4

[0099] Example 4 first prepared a material with a D50 of 6.0 ± 0.5 μm and the chemical formula (Ni 0.23 Fe 0.33 Mn 0.34 Cu 0.10 The specific preparation method of the nickel-iron-manganese-copper hydroxide precursor (OH)2 is as follows:

[0100] ① Dissolve nickel sulfate, ferrous sulfate, manganese sulfate, and copper sulfate crystals to form metal salt solutions with nickel ion concentrations of 27.7 g / L, ferrous ion concentrations of 37.9 g / L, manganese ion concentrations of 37.3 g / L, and copper ion concentrations of 13.1 g / L, respectively. The sodium hydroxide solution used has a concentration of 21%, the complexing agent is sodium acetate with a concentration of 82 ± 2 g / L, and the additive is dilute sulfuric acid with a concentration of 0.05 mol / L. The dilute sulfuric acid is added to the metal salt solutions.

[0101] ② Add pure water, sodium acetate solution, and sodium hydroxide solution to the reaction vessel, mix to obtain the reaction base liquid, control the pH value of the reaction base liquid to 11.40, introduce nitrogen gas for protection, heat the reaction vessel to 60℃, and control the stirring speed at 800r / min.

[0102] ③ After the feeding conditions are met, a metal salt solution, a sodium hydroxide solution, and a sodium acetate solution are pumped into the reaction base liquid. Then, the metal salt solution (flow rate of 8% / h of the total reactor capacity), the sodium hydroxide solution (flow rate of 3.2% / h of the total reactor capacity), and the sodium acetate solution (flow rate of 0.8% / h of the total reactor capacity) are introduced at the set flow rates. The concentration of dilute sulfuric acid in the reaction system is maintained at 0.01-0.05 mol / L. The pH is gradually reduced from 11.40 during the nucleation period to 10.20 during the control period, according to the pH value of the reaction system. The reaction yields a nickel-iron-manganese-copper quaternary precursor precipitate.

[0103] ④ After the synthesis stage is completed, the material is centrifuged, washed, dried and demagnetized to obtain the nickel-iron-manganese-copper hydroxide precursor of Example 4.

[0104] Figure 10The image shows a SEM image of the nickel-iron-manganese-copper hydroxide precursor prepared in Example 4. It can be seen that the precursor prepared by this method has uniform secondary particle size, a large number of primary skeletal particles, and a relatively thin thickness. Using sodium acetate as a complexing agent and adding dilute sulfuric acid to the metal salt solution reduces the difference in the complexing ability of the complexing agent for the metal, thus minimizing the difference in precipitation rate and optimizing morphological uniformity.

[0105] Example 4 also prepared a positive electrode material for sodium-ion batteries, which was prepared using the nickel-iron-manganese-copper hydroxide precursor obtained in Example 4. The preparation method was the same as that of the positive electrode material for sodium-ion batteries in Example 1.

[0106] The cathode material prepared from the nickel-iron-manganese-copper hydroxide precursor obtained in Example 4 has a low compaction density, resulting in a low 1C capacity.

[0107] Comparative Example 1

[0108] Comparative Example 1: First, a material with a D50 of 6.08 μm and the chemical formula (Ni) was prepared. 0.33 Fe 0.33 Mn 0.34 The specific preparation method of the nickel-iron-manganese hydroxide precursor (OH)2 is as follows:

[0109] ① Dissolve nickel sulfate, ferrous sulfate, and manganese sulfate crystals to form metal salt solutions with nickel ion concentrations of 39.8 g / L, ferrous ion concentrations of 37.9 g / L, and manganese ion concentrations of 37.3 g / L, respectively. The sodium hydroxide solution used has a concentration of 21%, the complexing agent is sodium acetate with a concentration of 82 g / L, and the additives are ammonium sulfate and dilute sulfuric acid with concentrations of 0.1 mol / L and 0.05 mol / L, respectively. The ammonium sulfate is added to the sodium acetate solution, and the dilute sulfuric acid is added to the metal salt solution.

[0110] ② Add pure water, sodium acetate solution, and sodium hydroxide solution to the reaction vessel, mix to obtain the reaction base liquid, control the pH value of the reaction base liquid to 11.40, introduce nitrogen gas for protection, heat the reaction vessel to 60℃, and control the stirring speed at 800r / min.

[0111] ③ After the feeding conditions are met, a metal salt solution, a sodium hydroxide solution, and a sodium acetate solution are pumped into the reaction base liquid. Then, the metal salt solution (flow rate of 8% / h of the total reactor capacity), the sodium hydroxide solution (flow rate of 3.2% / h of the total reactor capacity), and the sodium acetate solution (flow rate of 0.8% / h of the total reactor capacity) are introduced at the set flow rates. The concentration of ammonium sulfate in the reaction system is maintained at 0.025-0.01 mol / L; the concentration of dilute sulfuric acid in the reaction system is maintained at 0.01-0.05 mol / L. The pH is gradually reduced from 11.40 during the nucleation period to 10.20 during the control period, according to the pH value of the reaction system. The reaction yields a nickel-iron-manganese ternary precursor precipitate.

[0112] ④ After the synthesis stage is completed, the material is centrifuged, washed, dried and demagnetized to obtain the nickel-iron-manganese hydroxide precursor of Comparative Example 1.

[0113] Figure 11 The image shows a SEM image of the nickel-iron-manganese hydroxide precursor prepared in Comparative Example 1. Although the secondary particles of the precursor include two types of primary particles with different morphologies in the outer layer, their cross-sections are significantly different from those of the precursor prepared in the example.

[0114] Comparative Example 1 also prepared a positive electrode material for sodium-ion batteries, which was prepared using the nickel-iron-manganese hydroxide precursor obtained in Comparative Example 1. The preparation method was the same as that of the positive electrode material for sodium-ion batteries in Example 1.

[0115] Comparative Example 2

[0116] Comparative Example 2 first prepared a material with a D50 of 6.12 μm and the chemical formula (Ni) 0.23 Fe 0.33 Mn 0.34 Cu 0.10 The specific preparation method of the nickel-iron-manganese-copper hydroxide precursor (OH)2 is as follows:

[0117] ① Dissolve nickel sulfate, ferrous sulfate, manganese sulfate, and copper sulfate crystals to form metal salt solutions with nickel ion concentrations of 27.7 g / L, ferric ion concentrations of 37.9 g / L, manganese ion concentrations of 37.3 g / L, and copper ion concentrations of 13.1 g / L, respectively. The sodium hydroxide solution used has a concentration of 21%, and the complexing agent is ammonia water with a concentration of 19 g / L.

[0118] ② Add pure water and sodium hydroxide solution to the reactor, mix to obtain the reaction base liquid, control the pH value of the reaction base liquid to 11.40, introduce nitrogen gas for protection, heat the reactor to 60℃, and control the stirring speed at 800r / min.

[0119] ③ After the feeding conditions are met, a metal salt solution, sodium hydroxide solution, and ammonia solution are pumped into the reaction base liquid. Then, the metal salt solution (flow rate of 8% / h of the total capacity of the reactor), sodium hydroxide solution (flow rate of 3.2% / h of the total capacity of the reactor), and ammonia solution (flow rate of 0.8% / h of the total capacity of the reactor) are introduced at the set flow rates. The pH is gradually reduced from 11.40 during the nucleation period to 10.20 during the control period according to the pH value of the reaction system. The reaction yields a nickel-iron-manganese-copper quaternary precursor precipitate.

[0120] ④ After the synthesis stage is completed, the material is centrifuged, washed, dried and demagnetized to obtain the nickel-iron-manganese-copper hydroxide precursor of Comparative Example 2.

[0121] Figure 12 The SEM image of the nickel-iron-manganese-copper hydroxide precursor prepared in Comparative Example 2 shows that the secondary particles of the precursor prepared by this method have poor uniformity in size, and the primary particles are uneven in thickness and have significant differences in morphology, exhibiting a disordered arrangement. This is mainly because the complexing agent used in the traditional method is ammonia water, and the varying complexing ability of ammonia water to metals leads to significant differences in precipitation rates, resulting in poor morphological uniformity. The precursor prepared by this method has low particle strength due to the lack of a framework structure, making the subsequent sintering process for preparing the cathode material oxide difficult.

[0122] Figure 13 The cross-sectional view of the nickel-iron-manganese-copper hydroxide precursor prepared in Comparative Example 2 shows that the precursor shell prepared by this method is composed of disordered stacking of sheet-like primary particles, with a loose and porous structure that is prone to structural collapse.

[0123] Figure 14 The cross-sectional mapping diagram of the nickel-iron-manganese-copper hydroxide precursor prepared in Comparative Example 2 shows that the elemental distribution uniformity of the precursor prepared by this method is poor, especially the Cu element, which shows regional enrichment, thus affecting the capacitance and cycle performance of the cathode material.

[0124] Comparative Example 2 also prepared a positive electrode material for sodium-ion batteries, which was prepared using the nickel-iron-manganese-copper hydroxide precursor obtained in Comparative Example 2. The preparation method was the same as that of the positive electrode material for sodium-ion batteries in Example 1.

[0125] Figure 15 The image shows the SEM image of the sodium-ion battery cathode material prepared in Comparative Example 2. It can be seen that the particle morphology of this cathode material is irregular and the size varies greatly.

[0126] The product parameters of the sodium-ion battery cathode material precursors of Examples 1-4 and Comparative Examples 1-2 are shown in Table 1. (To evaluate the porosity characteristics, this application uses image analysis software (ImageJ) to directly calculate the pore area and cross-sectional area of ​​each region. The porosity of different regions is calculated by (porosity = pore area of ​​each region / cross-sectional area of ​​each region × 100%). The porosity of this application is characterized by this method.)

[0127] Table 1. Product parameters of cathode material precursors

[0128]

[0129] As shown in Table 1, compared to Comparative Examples 1-2, the precursors prepared in Examples 1-4 include a core and a shell. The core is composed of randomly arranged fine primary particles, while the shell consists of thicker skeletal primary particles arranged circumferentially along the secondary particles, forming an outer skeletal structure of the secondary particles. The spaces between the skeletal primary particles are filled with slender primary particles. In Examples 1 and 2, the area ratio of the skeletal primary particles to the secondary particles in the shell exceeds 40%, while in Examples 3-4, the area ratio exceeds 30%. The slender primary particles filling the spaces between the skeletal primary particles increase the tap density of the precursor; therefore, Examples 1-4 all have high tap densities.

[0130] The smaller Span values ​​of Examples 1-4 indicate that the secondary particles of the precursor are more uniform in size, allowing for more dense filling when used in the cathode, thus improving the battery's discharge capacity. Furthermore, the precursors of Examples 1-4 have appropriate ranges of D50 and specific surface area, and the core and shell of the precursors have appropriate ranges of thickness and porosity, enabling the cathode materials prepared from the precursors of Examples 1-4 to balance capacity and cycle performance.

[0131] Sodium-ion batteries were prepared using the positive electrode materials obtained in Examples 1-4 and Comparative Examples 1-2. The positive electrode material, binder polyvinylidene fluoride (PVDF), and conductive agent (SuperP) were mixed uniformly in a mass ratio of 8:1:1. This mixture was then uniformly coated onto aluminum foil to form a thin layer. After drying, the mixture was cut into circular pieces to serve as the positive electrode material. A metallic sodium sheet was used as the negative electrode, and Whatman glass fiber was used as the separator. The electrolyte was 1.0 mol L⁻¹ NaClO₄ / EC (ethylene carbonate) + DMC (dimethyl carbonate) + FEC (fluoroacetic acid) (EC to DMC volume ratio 1:1, FEC accounting for 5% of the total volume). CR2032 button cells were assembled in an argon-filled glove box. Constant current charge-discharge tests were performed on the button cells. The charge-discharge voltage range was 2–4 V, and the cells were continuously cycled for 50 cycles at a current density of 150 mA / g. The performance test results are shown in Table 2.

[0132] Table 2 Electrochemical Performance

[0133]

[0134] The batteries prepared from the precursors of Examples 1-4 exhibited high discharge capacities, all exceeding 130 mAh / g. The capacity retention rates of the batteries prepared from the precursors of Examples 1-4 were all above 82%, with the capacity retention rates of the batteries prepared from the precursors of Examples 1-2 being higher than those of Examples 3-4, reaching over 90%. The battery prepared from the precursor of Example 1 not only possessed a high discharge capacity but also a high capacity retention rate. Comparative Example 1, due to its high nickel content, exhibited a high 1C discharge capacity and first-cycle efficiency; however, due to the lack of copper and its inconsistent morphology with the examples, its 50-cycle capacity retention rate was significantly lower than that of Examples 1-4. Comparative Example 2, due to its inconsistent morphology with the examples, had relatively low 1C discharge capacity and 50-cycle capacity retention rate.

[0135] The sodium ion cathode materials prepared from precursors obtained in different embodiments and comparative examples exhibited 1C capacity retention rates after 50 weeks of exposure to air for different durations, as shown in Table 3.

[0136] Table 3. 50-week 1C capacity retention of different sodium ion cathode materials

[0137]

[0138] When exposed to air, sodium-ion cathode materials, due to their high activity, readily react with moisture and carbon dioxide in the air, causing transition metal oxides to undergo valence state changes, leading to phase changes and significant sodium precipitation. This, in turn, degrades the capacity and cycle performance of the cathode material. Furthermore, poor air stability significantly increases the costs of material storage, transportation, and battery manufacturing, thus limiting the practical application of sodium-ion cathode oxide materials. Table 3 clearly shows that the sample in Comparative Example 1, lacking copper and with an internal structure inconsistent with the examples, exhibits significantly worse air stability and cycle stability compared to Examples 1-4 and Comparative Example 2, indicating that Cu-containing cathode materials can significantly improve the air stability of the cathode material. Examples 1-2 show better cycle stability than Examples 3-4 and Comparative Example 1, suggesting that the morphology and uniform distribution of Cu in Examples 1-2 are more conducive to the cycle stability of sodium-ion battery materials. Example 2, with a 1% higher Cu content than Example 1, demonstrates a significant improvement in cycle performance.

[0139] In summary, the disordered arrangement of the primary core particles in the precursor of the sodium-ion battery cathode material provided in this application is beneficial for the diffusion of Na elements during the sintering process of the cathode material. The primary skeleton particles of the outer shell are staggered along the circumference of the secondary particles, forming an outer skeleton structure of the secondary particles. The primary skeleton particles improve the particle strength of the secondary particles, making the cathode material less prone to structural collapse during Na doping and sintering, thus maintaining structural stability. The slender primary particles filling the spaces between the primary skeleton particles can increase the tap density of the precursor and the volumetric energy density of the material, enabling the battery to have high discharge capacity and high charge-discharge efficiency. Moreover, the precursor has a large number of pores and uniform element distribution, which is conducive to the infiltration of Na and other dopants during the sintering process and reduces the sintering temperature. The copper-containing cathode material prepared by sintering the precursor material of this sodium-ion battery cathode material has good air stability, which is beneficial to improving cycle life.

[0140] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0141] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A precursor for a positive electrode material used in sodium-ion batteries, characterized in that, It includes secondary particles composed of multiple primary particles aggregated together, wherein the secondary particles include a core and a shell covering the core; The primary particles of the core are arranged in a disordered manner, and the primary particles of the shell include skeletal primary particles arranged in a staggered manner along the circumference of the secondary particles and elongated primary particles filling the spaces between the skeletal primary particles. The chemical formula of the cathode material precursor for the sodium-ion battery is (Ni x Cu y M 1-x-y )(OH)2, where 0 < x < 1, 0 < y < 1, and M is one or more of the elements Mn, Fe, Ti, Zn, Mg, Ca, Al, Ag, Co, Cr, La, Ce; The thickness of the primary skeletal particles in the outer shell is 200~600nm, and the length is 1.0~4.0μm; The thickness of the slender primary particles in the shell is 5~80nm and the length is 0.4~2.5μm.

2. The precursor for the positive electrode material of a sodium-ion battery according to claim 1, characterized in that, The thickness of the primary particles in the core is 10~50nm and the length is 0.2~1.0μm.

3. The precursor for the positive electrode material of a sodium-ion battery according to claim 1, characterized in that, The area ratio of the primary skeleton particles to the secondary particles in the outer shell is greater than or equal to 10%.

4. The sodium-ion battery cathode material precursor according to claim 3, characterized in that, The area ratio of the primary skeleton particles to the secondary particles in the outer shell is greater than 40%.

5. The precursor for the positive electrode material of a sodium-ion battery according to claim 1, characterized in that, The (D90-D10) / D50 ratio of the precursor for the positive electrode material used in the sodium-ion battery is 0.4~1.

0.

6. The sodium-ion battery cathode material precursor according to claim 5, characterized in that, The ratio (D90-D10) / D50 is 0.6-0.

9.

7. The precursor for the positive electrode material of a sodium-ion battery according to claim 1, characterized in that... The cathode material precursor satisfies at least one of the following conditions (1) to (2): (1) The radius of the core is 1.0~2.0μm; the thickness of the outer shell is 1.0~3.0μm; (2) The porosity of the core is in the range of 5-30%, and the porosity of the shell is in the range of 20%-45%.

8. The precursor for the positive electrode material of a sodium-ion battery according to claim 1, characterized in that, The sodium-ion battery cathode material precursor satisfies at least one of the following conditions (3) to (5): (3) The D50 of the precursor of the positive electrode material for the sodium-ion battery is 4~8μm; (4) The TD of the sodium-ion battery cathode material precursor is 1.0~1.5 g / cm³. 3 ; (5) The BET of the precursor of the positive electrode material for sodium-ion batteries is 20~80m. 2 / g.

9. The precursor for a sodium-ion battery cathode material according to claim 8, characterized in that, The BET of the precursor for the positive electrode material used in the sodium-ion battery is 30~50m. 2 / g.

10. A method for preparing a positive electrode material precursor for a sodium-ion battery according to any one of claims 1 to 9, characterized in that, include: Water, precipitant, and complexing agent are added to the reaction vessel and mixed to obtain the reaction base liquid; A metal salt solution, a precipitant, and a complexing agent are added to the reaction substrate to carry out a co-precipitation reaction, and the pH value of the reaction system is gradually reduced; the pH value of the reaction substrate is 11-12, and the pH value of the reaction system is reduced to 10-11; The coprecipitation reaction further includes adding an additive during the reaction, the additive including at least one of ammonium sulfate and dilute sulfuric acid; The complexing agent is sodium acetate, the ammonium sulfate is added to the sodium acetate solution, and the dilute sulfuric acid is added to the metal salt solution.

11. The method for preparing the precursor of the positive electrode material for sodium-ion batteries according to claim 10, characterized in that, The metal salt solution includes a metal salt solution containing Ni, Cu, and at least one element selected from Fe, Mn, Ti, Zn, Mg, Ca, Al, Ag, Co, Cr, La, and Ce.

12. The method for preparing the precursor of the positive electrode material for sodium-ion batteries according to claim 11, characterized in that, The metal salt solution includes a metal salt solution containing Ni, Cu, and at least one element selected from Fe, Mn, and Mg.

13. The method for preparing the precursor of the positive electrode material for sodium-ion batteries according to claim 10, characterized in that, The method for preparing the precursor of the positive electrode material for sodium-ion batteries satisfies at least one of the following conditions a to c: a. The concentration of the additive is 0.01~0.5 mol / L; b. The mass concentration of each metal ion in the metal salt solution is independently 10~50 g / L; c. The mass concentration of the complexing agent is 60~100g / L.

14. A sodium-ion battery cathode material, characterized in that, The sodium-ion battery cathode material is prepared from the precursor of the cathode material according to any one of claims 1 to 9. The cathode material includes an inner layer and an outer layer, the outer layer is dense, the inner layer has a hollow structure, and the outer layer includes a plurality of sheet-like primary particles.

15. The sodium-ion battery cathode material according to claim 14, characterized in that, The sodium-ion battery cathode material satisfies at least one of the following conditions A to C: A. The diameter of the inner layer of the sodium-ion battery positive electrode material is 0.5-2.0 μm, and the thickness of the outer layer of the sodium-ion battery positive electrode material is 1.0-3.0 μm; B. The D50 of the sodium-ion battery cathode material is 3.5~8μm; C. The ratio of (D90-D10) / D50 of the sodium-ion battery cathode material is 0.4-1.

16. A sodium-ion battery, characterized in that, The raw materials include the sodium-ion battery cathode material precursor as described in any one of claims 1 to 9 or the sodium-ion battery cathode material as described in any one of claims 14 to 15.

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