Positive electrode material and preparation method and application thereof

Abstract

The invention provides a positive electrode material as well as a preparation method and application thereof, and relates to the technical field of sodium ion batteries. Specifically, the positive electrode material provided by the invention comprises a granular material and a coating agent loaded on the surface of the granular material, wherein the molecular formula of the granules is NaxAaCuy (Ni31Fe34Mn35) (1-y) O2, A comprises at least one of La, Ca, Ce, Sr and Y, x is more than or equal to 0.98 and less than or equal to 1.05, y is more than or equal to 0.02 and less than or equal to 0.06, and a is more than or equal to 0.001% and less than or equal to 1%; the coating agent comprises an oxide containing at least one of Mg, Zr, Al, Ti, B and Y. According to the invention, element doping and surface modification are combined, and a large and small particle grading technology is matched, so that the positive electrode has good interface stability, higher electrode compaction density and volume energy density, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion batteries, in particular to a positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] At present, high-nickel layered positive electrode materials, especially single-crystal positive electrode materials, have advantages in cycle stability and structural integrity, but their ion diffusion rate is slow and the ion migration path is long, resulting in poor rate performance, which is difficult to meet the needs of high-power application scenarios. Rate performance is an important indicator for measuring the high-power output or rapid charging capacity of a battery. Poor rate performance makes it difficult for single-crystal positive electrode materials to meet the needs of application scenarios that have strict requirements for rapid energy replenishment and release, such as electric vehicle fast charging and high-power electronic devices.

[0003] On the other hand, although the traditional polycrystalline positive electrode material has good rate performance due to the small primary particles, the secondary spherical particles have poor mechanical stability and are prone to breakage during electrode preparation and cycling, exposing new active surfaces. These new surfaces will have more severe side reactions with the electrolyte, which will in turn cause a series of problems: such as the dissolution of transition metals into the electrolyte, which not only consumes the electrolyte but also may migrate to the negative electrode surface, damaging the solid electrolyte interface film of the negative electrode; such as the increase of interface impedance, which hinders ion transmission and reduces the charge and discharge efficiency of the battery; such as capacity attenuation, which leads to the gradual decrease of the available capacity of the battery with the increase of the cycle number. In addition, the large number of high-impedance grain boundaries in the polycrystalline material seriously hinder the ion conduction in the secondary particles, limiting its fast charging performance and application.

[0004] Therefore, the present application is proposed. SUMMARY

[0005] The first object of the present application is to provide a positive electrode material, which is mainly used to solve the technical defects of slow ion diffusion rate and long lithium ion migration path of traditional single-crystal positive electrode materials, or poor mechanical stability of secondary spherical particles and a large number of high-impedance grain boundaries in the interior of traditional polycrystalline positive electrode materials.

[0006] The second object of the present application is to provide a preparation method of the positive electrode material.

[0007] The third object of the present application is to provide a sodium ion battery.

[0008] The fourth object of the present application is to provide an electric device.

[0009] In order to achieve the above objects of the present application, the following technical solutions are adopted: A positive electrode material, comprising a particle material and a coating agent loaded on the surface of the particle material. The molecular formula of the particle is Na x A a Cu y (Ni 31 Fe 34 Mn 35 ) (1-y) O2, wherein A comprises at least one of La, Ca, Ce, Sr, Y, 0.98≤x≤1.05, 0.02≤y≤0.06, 0.001%≤a≤1%; The coating agent comprises an oxide of at least one of Mg, Zr, Al, Ti, B, and Y.

[0010] Preferably, the positive electrode material comprises first particles and second particles; the particle size of the first particles is R, the particle size of the second particles at 10% of the cumulative volume distribution is r1, and the particle size of the second particles at 90% of the cumulative volume distribution is r2, and at least one of the following characteristics (a) or (b) is satisfied: (a) r1>0.155R; (b) r2<0.702R.

[0011] More preferably, the mass ratio of the first particles to the second particles is 1-9.

[0012] Preferably, the mass ratio of the coating agent to the particle is 0.01%-5%.

[0013] A preparation method of the positive electrode material comprises the following steps: (1) preparing a positive electrode material precursor by a coprecipitation method; controlling the precipitation time and the pH of the reaction solution to obtain first and second precursors with different particle sizes; The molecular formula of the first precursor and the second precursor is independently selected from A a Cu y (Ni 31 Fe 34 Mn 35 ) (1-y) (OH)2, A comprises at least one of La, Ca, Ce, Sr, Y, 0.02≤y≤0.06, 0.001%≤a≤1%; (2) mixing, sintering, and crushing the first and second precursors with sodium carbonate respectively to obtain large-particle-size sintered material and small-particle-size sintered material respectively; (3) mixing, sintering, and crushing the large-particle-size sintered material, the small-particle-size sintered material, and a coating agent to obtain the positive electrode material; Or, the large particle size first sintered material and the small particle size first sintered material are respectively mixed with a coating agent, sintered, and crushed to obtain a large particle size second sintered material and a small particle size second sintered material respectively; and then the large particle size second sintered material and the small particle size second sintered material are mixed to obtain the positive electrode material.

[0014] Preferably, step (1) comprises: The metal salts of each element are weighed and mixed according to the molecular formula of the precursor, and dissolved in water, and then a complexing agent and a precipitating agent are added, and the precipitation time and the pH of the reaction solution are controlled to obtain first and second precursors with different particle sizes; More preferably, the complexing agent comprises at least one of ammonia, citric acid, ethylenediamine, sodium oxalate, and hydroxyethyl methyl acrylate, and the precipitating agent comprises at least one of sodium carbonate or sodium hydroxide; More preferably, the pH of the reaction solution of the co-precipitation method is 8-13; More preferably, the reaction time of the co-precipitation method is 12-48h.

[0015] Preferably, the sintering in step (2) comprises: When the large particle size first sintered material is a polycrystalline material, the sintering temperature is 830-880℃, and the holding time is 16-30h; When the large particle size first sintered material is a single crystal material, the sintering temperature is 950-1100℃, and the holding time is 12-20h; When the small particle size first sintered material is a polycrystalline material, the sintering temperature is 830-860℃, and the holding time is 12-20h; When the small particle size first sintered material is a single crystal material, the sintering is performed by programmed temperature rising, first holding at 970-1000℃ for 1-6h, and then lowering the temperature to 930-960℃ for 12-18h.

[0016] Preferably, the sintering temperature in step (3) is 650-850℃, and the holding time is 10-20h.

[0017] A sodium ion battery comprising the positive electrode material.

[0018] An electric device comprising the sodium ion battery.

[0019] Compared with the prior art, the present application has the following beneficial effects: The application significantly reduces the specific surface area of the positive electrode material by combining the element doping and surface modification modification strategy, effectively inhibits the interface side reaction between the electrolyte and the positive electrode material, and improves the interface stability; further, the surface modification modification improves the structural stability of the positive electrode material, while retaining the performance of the polycrystal or small single crystal ratio, slows down the structure degradation caused by repeated charge and discharge process; further, the coating agent in the application prevents the corrosion of the electrolyte on the active material, effectively reduces the interface side reaction.

[0020] At the same time, the application innovatively adopts the size particle grading technology, optimizes the particle size distribution, realizes higher electrode compaction density, thereby significantly improves the volume energy density, and also improves the electron and ion transmission efficiency.

[0021] In addition, the application benefits from the short lithium ion diffusion path and numerous fast migration channels provided by the smaller primary particles inside the material, and the application also has excellent rate performance and fast charge and discharge capacity while obtaining high energy density. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the application or the technical solutions in the prior art, the drawings needed in the specific embodiments or the prior art description will be briefly introduced below, and obviously, the drawings in the following description are some embodiments of the application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0023] Figure 1 A schematic diagram of the principle of formula (I) of the application is provided; Figure 2 A schematic diagram of the principle of formula (II) of the application is provided; Figure 3 An SEM image of the positive electrode material of Example 1 of the application is provided; Figure 4 An SEM image of the positive electrode material of Comparative Example 1 of the application is provided; Figure 5 An SEM image of the positive electrode material of Comparative Example 2 of the application is provided. DETAILED DESCRIPTION

[0024] The technical solutions of the present application will be described clearly and completely below in combination with the drawings and specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, rather than all the embodiments, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application. The specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not marked with the manufacturer, which are all conventional products that can be purchased on the market. In addition, the terms "first", "second", "third" are only used for description purposes, and cannot be understood as indicating or implying relative importance.

[0025] The first aspect of the present application is to provide a positive electrode material; the positive electrode material comprises a granular material, and a coating agent loaded on the surface of the granular material.

[0026] Specifically, the molecular formula of the granular material is Na x A a Cu y (Ni 31 Fe 34 Mn 35 ) (1-y) O2, wherein A comprises at least one of La, Ca, Ce, Sr, Y, 0.98≤x≤1.05, 0.02≤y≤0.06, 0.001%≤a≤1%; the coating agent comprises an oxide of at least one of Mg, Zr, Al, Ti, B, Y.

[0027] In some optional implementations, the values ​​of x include, but are not limited to, any one or any two of the following: 0.98, 0.981, 0.982, 0.985, 0.986, 0.988, 0.99, 0.992, 0.995, 0.996, 0.998, 0.10, 0.101, 0.102, 0.104, and 0.105; the values ​​of y include, but are not limited to, 0.02, 0.021, 0.022, 0.025, 0.028, 0.03, 0.035, 0.04, 0.045, 0.05, 0.052, 0.055, and 0.05. 8. A numerical range consisting of any one or any two of 0.059 and 0.06; the value of 'a' includes, but is not limited to, any one or any two of 0.001%, 0.0011%, 0.002%, 0.005%, 0.01%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 0.99%, and 1%.

[0028] In a preferred embodiment, the positive electrode material includes a first particle and a second particle; the particle size of the first particle is R, and the particle size of the second particle when its cumulative volume distribution accounts for 10% is r1 (Dv). 10 ), with the particle size of the second particle when it accounts for 90% of the cumulative volume distribution as r2 (Dv) 90 ), satisfying at least one of the following characteristics (a) or (b): (a) r1 > 0.155R; (b) r2 < 0.702R.

[0029] In this invention, the first particle and the second particle are considered to be spherical or near-spherical particles, with the diameter of the first particle being larger than that of the second particle; that is, the first particle can be considered a large particle, and the second particle can be considered a small particle. In terms of cross-section, the inscribed circle tangent to four circles is used as the minimum particle size to accommodate the small particles. Furthermore, when the cumulative volume distribution percentage is 10% (Dv... 10 () represents the smallest particle size, such as Figure 1 As shown, equation (I) can be obtained through calculation: Formula (I); Meanwhile, the inscribed circle tangent to the five circles is used as the maximum particle size to accommodate the small particles. Furthermore, when the cumulative volume distribution accounts for 90% (Dv... 90 () represents the maximum particle size, such asFigure 2 As shown, the formula (II) is calculated: Formula (II).

[0030] In the present application, the particle size can be measured by a particle size tester, and the best size particle grading compaction density can be obtained by the combination of the characteristics (a) or (b), so as to maximize the void filling.

[0031] As a preferred embodiment, the mass ratio of the first particles to the second particles is 1-9, including but not limited to any one of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9 or a numerical interval composed of any two of them.

[0032] As a preferred embodiment, the mass ratio of the coating agent to the particle material is 0.01%-5%, including but not limited to any one of 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 4.8%, 4.9%, 5% or a numerical interval composed of any two of them.

[0033] As a preferred embodiment, the positive electrode material is an O3 phase layered oxide material; in some embodiments, the particle material includes at least one of polycrystalline large particles and single-crystal large particles, and at least one of polycrystalline small particles or single-crystal small particles, i.e., the particle material is composed of large and small particles through grading and compounding.

[0034] The second aspect of the present application provides a preparation method of the positive electrode material according to the first aspect, mainly including the following steps: (1) preparing a positive electrode material precursor by a coprecipitation method; controlling the precipitation time and the pH of the reaction solution to obtain first and second precursors with different particle sizes; The molecular formula of the first precursor and the second precursor is independently selected from A a Cu y (Ni 31 Fe 34 Mn 35 ) (1-y) (OH)2, A includes at least one of La, Ca, Ce, Sr, Y, 0.02≤y≤0.06, 0.001%≤a≤1%; (2) mixing, sintering and crushing the first and second precursors with sodium carbonate respectively to obtain large-particle sintered material and small-particle sintered material respectively; (3) mixing, sintering and crushing the large particle size first sintered material, the small particle size first sintered material and the coating agent to obtain the positive electrode material; Alternatively, the large particle size first sintered material and the small particle size first sintered material are respectively mixed with the coating agent, sintered and crushed to obtain a large particle size second sintered material and a small particle size second sintered material respectively; and then the large particle size second sintered material and the small particle size second sintered material are mixed to obtain the positive electrode material.

[0035] As a preferred embodiment, the co-precipitation method comprises: weighing and mixing metal salts of each element according to the molecular formula of the precursor and dissolving in water, then adding a complexing agent and a precipitant, controlling the precipitation time and the pH of the reaction solution to obtain first and second precursors with different particle sizes.

[0036] As a more preferred embodiment, the metal salt includes but is not limited to hydrochloride, nitrate, oxalate, sulfate and the like, and any soluble metal salt that does not affect the precipitation reaction belongs to the theoretically feasible category.

[0037] As a more preferred embodiment, the concentration of the metal salt is 1 mol / L to 4 mol / L.

[0038] As a more preferred embodiment, the complexing agent includes at least one of ammonia, citric acid, ethylenediamine, sodium oxalate and hydroxyethyl methacrylate; in some embodiments, the concentration of the complexing agent is 0.01 mol / L to 5 mol / L.

[0039] As a more preferred embodiment, the precipitant includes at least one of sodium carbonate or sodium hydroxide; in some embodiments, the concentration of the precipitant is 1 mol / L to 4 mol / L.

[0040] As a more preferred embodiment, the pH of the reaction solution of the co-precipitation method is 8 to 13.

[0041] As a more preferred embodiment, the reaction time of the co-precipitation method is 12 h to 48 h, which can be understood as including the precipitation time and the aging time.

[0042] As a preferred embodiment, the amount of sodium carbonate is matched according to the molar amount of sodium element in the molecular formula of the granular material.

[0043] As an optional embodiment, the mixing in steps (2) and (3) is independently selected from one of a high-speed stirring mixer, a drum mixer, a V-shaped mixer, a fluidized bed and an ultrasonic vibration mixer to achieve sufficient mixing of the materials.

[0044] As a preferred embodiment, the sintering (i.e. first sintering) in step (2) is performed at a temperature selected according to the nature of the precursor, and the sintering procedure is as follows: In some embodiments, for the large-particle first-sintered material, which is a polycrystalline material, the sintering temperature is 830-880℃, the holding time is 16-30h, and the heating rate is 2℃ / min.

[0045] In other embodiments, for the large-particle first-sintered material, which is a single-crystalline material, the sintering temperature is 950-1100℃, the holding time is 12-20h, and the heating rate is 2℃ / min.

[0046] In other embodiments, for the small-particle first-sintered material, which is a polycrystalline material, the sintering temperature is 830-860℃, the holding time is 12-20h, and the heating rate is 2℃ / min.

[0047] In other embodiments, for the small-particle first-sintered material, which is a single-crystalline material, the sintering is performed in two steps: first, at 970-1000℃ for 1-6h, and then at 930-960℃ for 12-18h; and the heating rate in the first step is 2℃ / min, and the heating rate in the second step is 5℃ / min.

[0048] It is worth noting that, in the present application, when the large-particle first-sintered material is a polycrystalline material, the corresponding first precursor is also a polycrystalline material, i.e. a polycrystalline large particle generally inherits the morphology of the precursor, and when it is a polycrystalline material, the particle size of the large-particle first-sintered material is closely related to the particle size of the precursor. Correspondingly, when the large-particle first-sintered material is a single-crystalline material, the particle size of the corresponding first precursor is not limited, and it is affected by the coalescence between particles and can be controlled by the sintering temperature and holding time.

[0049] As a preferred embodiment, the sintering (i.e. second sintering) in step (3) is performed at a temperature of 650-850℃, a holding time of 10-20h, and a heating rate of 5℃ / min.

[0050] The third aspect of the present application provides a sodium-ion battery comprising the positive electrode material of the first aspect.

[0051] It can be understood that the positive electrode material needs to be mixed with a conductive agent, a binder or optional other additives, and be compounded with a current collector to obtain a positive electrode; thereby forming a positive electrode functional structure in the sodium-ion battery.

[0052] It can be understood that, in addition to the positive electrode containing the positive electrode material, the sodium-ion battery should include a negative electrode, an electrolyte, a separator, and other necessary or unnecessary functional elements or packaging components, etc., which can be selected and combined by those skilled in the art; when the positive electrode material is contained in the sodium-ion battery, whether the sodium-ion battery also uses a positive electrode structure not containing the positive electrode material, it can be used as an embodiment of the present application.

[0053] The fourth aspect of the present application is to provide a power consuming device comprising the sodium-ion battery of the third aspect.

[0054] It can be understood that the power consuming device can be any device or apparatus that relies on electrical energy for work or operation, including but not limited to new energy vehicles, building electrical equipment, industrial electrical appliances, household and agricultural electrical appliances, etc.; when the sodium-ion battery is included, any power consuming device equipped with the sodium-ion battery can belong to an embodiment of the present application.

[0055] Example 1 (1) Preparation of precursor: (1.1) Preparation of large particle size precursor (10 μm): Ca 0.01 La 0.003 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 (OH)2precursor was prepared by coprecipitation method, and the metal sulfate of the corresponding element was weighed according to the stoichiometric ratio, which was dissolved in water to obtain a mixed metal M solution of 2 mol / L, then 0.1 mol / L of complexing agent ethylenediamine solution was added to the M solution, then 1 mol / L of precipitating agent sodium hydroxide solution was added, and the pH was controlled at 12±0.1, the precipitation time was 36 h, the particle size of the precursor was tested during the precipitation process, and the reaction was stopped when the particle size was 10 μm, then the precursor was subjected to solid-liquid separation, and the precursor was subjected to drying treatment.

[0056] (1.2) Preparation of small particle size precursor (2.6 μm): basically the same as the preparation of large particle size precursor, the reaction time needs to be controlled for about 12 h, the particle size of the precursor is tested during the precipitation process, and the reaction is stopped when the particle size is >2.5 μm, then the precursor is subjected to solid-liquid separation, and the precursor is subjected to drying treatment.

[0057] (2) Preparation of one-fired material: (2.1) Preparation of large-particle-size polycrystalline samples: Sodium carbonate and a 10μm precursor (TM) were prepared at a Na:TM molar ratio of 1.02:1 and mixed using a high-speed mixer. The mixture was then placed in a sintering pan and heated to 850℃ at a rate of 2℃ / min, held for 25h, and sintered in compressed air. The naturally cooled material was then gas-crushed to obtain Dv. 10 It is 6.98μm, Dv 50 It is 10.3μm, Dv 90 It is a large-particle-size polycrystalline gas-crushed material with a particle size of 14.35μm.

[0058] (2.2) Preparation of large-particle-size single crystal samples: Sodium carbonate and a 10μm precursor (TM) were prepared at a Na:TM molar ratio of 1.02:1 and mixed using a high-speed mixer. The mixture was then packed into a sintering pan. The sintering process involved heating to 850℃ at a rate of 2℃ / min and holding for 2 hours, followed by heating to 980℃ at a rate of 2℃ / min and holding for 15 hours. The sintering atmosphere was compressed air. The naturally cooled material was then pulverized using an air-breaking device to obtain Dv. 10 It is 6.75μm, Dv 50 It is 10.56μm, Dv 90 It is a single crystal gas-broken material with a large particle size of 15.75μm.

[0059] (2.3) Preparation of small-particle-size polycrystalline samples: Sodium carbonate and a 2.6 μm precursor (TM) were prepared at a Na:TM molar ratio of 1.02:1 and mixed using a high-speed mixer. The mixture was then packed into a sintering pan and heated to 850 °C at a rate of 2 °C / min, held for 15 h, and sintered in compressed air. The naturally cooled material was then gas-crushed to obtain Dv. 10 It is 2.3μm, Dv 50 It is 4.06μm, Dv 90 It is a small-particle-size polycrystalline gas-crushed material with a particle size of 6.92μm.

[0060] (2.4) Preparation of small-particle-size single-crystal samples: Sodium carbonate and a 2.6 μm precursor (TM) were prepared at a Na:TM molar ratio of 1.02:1 and mixed using a high-speed mixer. The mixture was then packed into a sintering pan. The first stage of the sintering process involved heating to 990 °C at a rate of 2 °C / min and holding for 2 hours in a compressed air atmosphere. The naturally cooled material was then gas-crushed. Here, Dv was controlled... 50 At 3.5 μm. Next, a second stage of sintering was performed, with the temperature increased to 940 °C at a rate of 5 °C / min and held for 13 hours. The naturally cooled material was then subjected to air-crushing to obtain Dv. 101.72 μm, Dv 50 3.99 μm, Dv 90 small particle size monocrystal gas breaking material with 7.72 μm.

[0061] (3) Preparation of two-burned material: Different particle size material gradation coating sintering: the one-burned material in (2.1) and (2.3) is weighed according to the mass ratio of 8:2, and at the same time, mixed with 0.5% of coating agent Al2O3 by mass fraction in high-speed mixer, and sintered in a pot, the sintering process is heated to 750℃ at a heating rate of 5℃ / min, and the temperature is kept for 15h, and then crushed and sieved to obtain a size poly-crystal graded material as the positive electrode material Na 1.02 Ca 0.01 La 0.003 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 O2@Al2O3.

[0062] As Figure 3 shown, the SEM image of the positive electrode material of this embodiment 1 is provided.

[0063] Example 2 The same as example 1, the only difference is that the mass ratio in step (3) is 7:3.

[0064] Example 3 The same as example 1, the only difference is that in step (3), the one-burned material in (2.1) and (2.4) is weighed and graded according to the mass ratio of 8:2.

[0065] Example 4 The same as example 1, the only difference is that in step (3), the one-burned material in (2.2) and (2.4) is weighed and graded according to the mass ratio of 8:2.

[0066] Example 5 The same as example 4, the only difference is that the mass ratio in step (3) is 9:1.

[0067] Example 6 The same as example 1, the only difference is that in step (3), the one-burned material in (2.2) and (2.3) is weighed and graded according to the mass ratio of 8:2.

[0068] Example 7 The same as example 1, the only difference is that in step (1), the molecular formula of the precursor is Ca 0.01 Sr 0.003 Cu0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 (OH)2; the molecular formula of the positive electrode material obtained in step (3) is Na 1.02 Ca 0.01 Sr 0.003 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 O2@Al2O3. Example 8 The same as Example 1, except that: (2.1) the sintering temperature is 880℃, and the holding time is 16h; (2.3) the sintering temperature is 830℃, and the holding time is 20h.

[0069] Example 9 The same as Example 1, except that: (2.1) the sintering temperature is 830℃, and the holding time is 30h; (2.4) the sintering temperature of the first stage is 970℃, and the holding time is 6h; the sintering temperature of the second stage is 960℃, and the holding time is 12h.

[0070] Comparative Example 1 The same as Example 1, except that in step (3), only the sintering material of (2.1) is used, and the sintering material of (2.3) is not introduced.

[0071] Figure 4 SEM picture of the positive electrode material of Comparative Example 1.

[0072] Comparative Example 2 The same as Example 1, except that in step (3), only the sintering material of (2.3) is used, and the sintering material of (2.1) is not introduced.

[0073] Figure 5 SEM picture of the positive electrode material of Comparative Example 2.

[0074] Comparative Example 3 The same as Example 1, except that in step (3), the mass ratio is 3:7.

[0075] Comparative Example 4 The same as Example 1, except that: Step (2.4): In the first stage of the sintering process, the temperature is increased to 990℃ at a heating rate of 2℃ / min, and held for 4 hours. The sintering atmosphere is compressed air. Then, the naturally cooled material is gas-crushed and pulverized. Here, Dv is controlled. 50 At 4.5 μm; then, the second stage of sintering is carried out, with the temperature increased to 940℃ at a heating rate of 5℃ / min and held for 15 hours. The naturally cooled material is then subjected to air-crushing to obtain Dv. 10 It is 3.04μm, Dv 50 It is 5.77μm, Dv 90 It is a single crystal gas-broken material with small particles of 8.92μm.

[0076] It is worth noting that the particle size obtained from the first sintering of the material in this invention can be considered essentially the finished product particle size, because the secondary sintering temperature is relatively low and does not have a significant impact on the finished product particle size. However, the Dv in Comparative Example 4... 10 Dv 90 It does not satisfy the characteristics of r1 > 0.155R and r2 < 0.702R in this invention.

[0077] Test case (1) Particle size test: The particle size was tested using a Baxter laser particle size analyzer. The positive electrode materials of each embodiment or comparative example were dispersed in deionized water. The refractive index was set to 1.5, the absorptivity to 1.0, the pump speed to 2000 rpm, the laser intensity to be greater than 70%, and the shading to 8~20%. The particle size information was recorded and the data were recorded in Table 1.

[0078] (2) Powder compaction test: The powder compaction test was conducted using a powder compactor. The test method was in accordance with GB-T 44330-2024 Determination of compaction density of lithium-ion battery cathode material powder. The data were recorded in Table 1.

[0079] (3) Button battery assembly The positive electrode materials (SP:PVDF) of each embodiment or comparative example were homogenized and coated in a ratio of 90:5:5, and cut into electrode sheets with a diameter of φ12mm. After drying the electrode sheets overnight (10h), they were transferred to a glove box. Using a sodium metal sheet as the counter electrode, glass fiber as the separator, and a NaPF6 solution with a sodium ion concentration of 1mol / L (the solvent being a mixture of EC and DMC, with a volume ratio of EC / DMC=1:1) as the electrolyte, 2032 coin cells corresponding to each embodiment or comparative example were assembled in an Ar atmosphere-protected glove box.

[0080] Further, each button cell was subjected to charge-discharge curve test: the button cell was placed at a temperature of 25℃, and a new Wei button test cabinet was used for testing, the test voltage was 2.5-4.05V, and the charge-discharge was carried out at 0.1C and 0.5C rate in turn, and the cycle was three weeks, then the cycle test was carried out at 1C rate for 100 weeks, and the related data were recorded in Table 1.

[0081] (4) Light transmission compaction test of pole piece The light transmission compaction test of pole piece was carried out by using the basic folding test method: a series of pole piece samples with different compaction densities were prepared by gradually increasing the roll pressure, and then each sample was folded by 180 degrees; when the compaction density reached the critical value, the pole piece was not transparent at the fold after being folded once, but became transparent after being folded twice, and the compaction density of this critical point was determined as the limit compaction density, the limit compaction density of the positive electrode material of each example or comparative example was recorded, and was recorded as the light transmission compaction of the pole piece, and the data were recorded in Table 1.

[0082] Table 1

[0083] As can be seen from Table 1, the appropriate grading ratio can significantly improve the powder compaction density of the positive electrode material, and has better rate and cycle performance, which can be attributed to the optimization of particle size distribution, effectively filling the voids between large particles, thereby increasing the bulk density of the material, and further improving the efficiency of electron and ion transmission, and the 1C rate and capacity retention have excellent performance. In addition, the light transmission compaction density of the pole piece is also improved compared with the comparative example, further, the energy density of the battery can be improved by 6%-8%. As can be seen from Examples 2 and 3, by adjusting the sintering system and the broken particle size, the small single crystal or small polycrystal meets the particle size limitation condition, and the small single crystal and the small polycrystal have no obvious difference in void filling. In addition, as can be seen from Examples and Comparative Example 4, the powder compaction density of the small particle size sample is further improved under the condition that the particle size meets the particle size limitation condition, which can also be attributed to the effective filling of the voids between particles, thereby further improving the compaction density and energy density of the material.

[0084] Although the present application has been illustrated and described with reference to specific embodiments, it should be recognized that the above embodiments are merely illustrative of the present application, and are not limiting thereof; it should be understood by those skilled in the art that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced equivalently without departing from the spirit and scope of the present application; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solutions of the embodiments of the present application; therefore, this means that all these replacements and modifications within the scope of the present application are included in the appended claims.

Claims

1. A positive electrode material, characterized in that, The positive electrode material includes granules and a coating agent loaded on the surface of the granules; The molecular formula of the granular material is Na x A a Cu y (Ni 31 Fe 34 Mn 35 ) (1-y) O2, wherein A includes at least one of La, Ca, Ce, Sr, Y, 0.98≤x≤1.05, 0.02≤y≤0.06, 0.001%≤a≤1%. The coating agent includes an oxide containing at least one of Mg, Zr, Al, Ti, B, and Y.

2. The cathode material according to claim 1, characterized in that, The positive electrode material includes a first particle and a second particle; with the particle size of the first particle as R, the particle size of the second particle when it accounts for 10% of the cumulative volume distribution as r1, and the particle size of the second particle when it accounts for 90% of the cumulative volume distribution as r2, it satisfies at least one of the following characteristics (a) or (b): (a) r1 > 0.155R; (b) r2 < 0.702R.

3. The cathode material according to claim 2, characterized in that, The mass ratio of the first particle to the second particle is 1 to 9.

4. The cathode material according to claim 1, characterized in that, The mass ratio of the coating agent to the granules is 0.01% to 5%.

5. The method for preparing the cathode material according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) A cathode material precursor was prepared by co-precipitation; the precipitation time and pH of the reaction solution were controlled to obtain a first precursor and a second precursor with different particle sizes. The molecular formula of the first precursor and the second precursor are independently selected from A a Cu y (Ni 31 Fe 34 Mn 35 ) (1-y) (OH)2, A includes at least one of La, Ca, Ce, Sr, Y, 0.02≤y≤0.06, 0.001%≤a≤1%. (2) The first precursor and the second precursor are respectively mixed with sodium carbonate, sintered and crushed to obtain large-particle-size sintered material and small-particle-size sintered material respectively; (3) The large-particle-size sinter, the small-particle-size sinter, and the coating agent are mixed, sintered, and crushed to obtain the cathode material; Alternatively, the large-particle-size sinter and the small-particle-size sinter are respectively mixed with a coating agent, sintered, and crushed to obtain large-particle-size secondary sinter and small-particle-size secondary sinter respectively; then the large-particle-size secondary sinter and the small-particle-size secondary sinter are mixed to obtain the cathode material.

6. The preparation method according to claim 5, characterized in that, Step (1) includes: Weigh and mix the metal salts of each element according to the molecular formula of the precursor and dissolve them in water. Then add complexing agent and precipitant, control the precipitation time and pH of the reaction solution, and obtain the first precursor and the second precursor with different particle sizes. Preferably, the complexing agent includes at least one of ammonia, citric acid, ethylenediamine, sodium oxalate, and hydroxyethyl methacrylate, and the precipitant includes at least one of sodium carbonate or sodium hydroxide; Preferably, the pH of the reaction solution in the co-precipitation method is 8-13; Preferably, the reaction time for the co-precipitation method is 12h to 48h.

7. The preparation method according to claim 5, characterized in that, The sintering described in step (2) includes: When the large-particle-size sintering material is a polycrystalline material, the sintering temperature is 830℃~880℃ and the holding time is 16h~30h. When the large-particle-size sintering material is a single-crystal material, the sintering temperature is 950℃~1100℃ and the holding time is 12h~20h. When the small-particle-size sintering material is a polycrystalline material, the sintering temperature is 830℃~860℃ and the holding time is 12h~20h. When the small-particle-size sintering material is a single-crystal material, the sintering adopts a programmed temperature rise, first holding at 970℃~1000℃ for 1h~6h, and then cooling down to 930℃~960℃ and holding for 12h~18h.

8. The preparation method according to claim 5, characterized in that, The sintering temperature in step (3) is 650℃~850℃, and the holding time is 10h~20h.

9. A sodium-ion battery, characterized in that, Includes the cathode material as described in any one of claims 1 to 4.

10. An electrical appliance, characterized in that, Including the sodium-ion battery as described in claim 9.

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