High-voltage positive electrode material and preparation method thereof, positive plate and sodium ion battery

Abstract

The invention relates to the technical field of sodium ion batteries, in particular to a high-voltage positive electrode material and a preparation method thereof, a positive plate and a sodium ion battery. The general formula of the high-voltage positive electrode material is Naa (NiMn) x (CuTi) yM < 1-2x-2y > O < 2-delta >, and the high-voltage positive electrode material is prepared after at least two times of sintering, the sphericity rate of the material obtained after primary sintering is greater than or equal to 0.60, and the sphericity rate of the material obtained after secondary sintering is greater than or equal to 0.80; the length ratio b / a of the short axis to the long axis of the single crystal particles in the CP cross-sectional view of the material obtained after sintering is obtained, the range is [0, 1], the range is subjected to n-part equidistant segmentation, the number ratio of the single crystal particles in each segmentation section is xi, and the value of b / a of each segmentation section is wi. The morphology of the material can be controlled by controlling the sphericity rate of the material after multiple times of sintering, and the sphericity degree of the single crystal particles is improved, so that the high-voltage stability of the material is improved.

Description

TECHNICAL FIELD

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

[0002] With the advent of the era of electric vehicles and smart grids, lithium resource shortage will become an important factor restricting its development. Sodium ion batteries have low cost, unique fast charging performance and low temperature performance, so they have been paid attention again. At present, they have demonstration projects in electric two-wheel vehicles and A00 level electric vehicles. However, the relative atomic mass of sodium element is much larger than that of lithium element, and the sodium ion radius is larger than the lithium ion radius, which makes the energy density, power density and cycle life of sodium ion batteries lower than those of lithium ion batteries. Therefore, improving the energy density and prolonging the cycle life are important directions for the development of sodium ion batteries.

[0003] Among them, the layered oxide Na x TMO2(TM: transition metal) is widely concerned in high-energy-density sodium ion battery research due to its high capacity and feasible synthesis method. Generally speaking, there are two main ways to improve the capacity of the positive electrode material: one is to improve the specific capacity of the positive electrode material, and the other is to improve the sodium extraction potential of the positive electrode material. The working voltage of the positive electrode material can be improved by doping, coating modification, single crystalization, structure design, microstructure control, surface and interface engineering, etc. to improve the structure stability of the positive electrode material, so that it can work at high voltage. The positive electrode material obtained by single crystalization sintering has stable chemical properties, exhibits higher load voltage and more excellent cycle performance, and is also a more cost-effective route.

[0004] However, single crystal materials have various morphologies, such as flaky, hexagonal prismatic, elliptical and circular, etc. The single crystal material synthesized at high temperature tends to grow unevenly, and the irregular morphology formed will cause uneven extraction of sodium in different particles or even different positions in the particles, causing uneven charging and discharging, and also affecting the performance of the material.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] The first object of the present application is to provide a high-voltage positive electrode material. By controlling the sphericity of the material obtained after multiple sintering, the morphology of the material can be controlled, and the high-voltage stability of the material can be improved. The uneven extraction of sodium in different particles or even different positions in the particles caused by irregular single crystal morphology is improved, and the phenomenon of uneven charging and discharging is caused.

[0007] The second object of the present application is to provide a preparation method of a high-voltage positive electrode material, which is obtained by sintering through a single crystal strategy and can withstand a higher load voltage, exhibit a higher energy density and a more excellent cycle performance.

[0008] The third object of the present application is to provide a positive electrode sheet, and a battery prepared by using the positive electrode sheet has a high capacity, a good rate performance and an excellent cycle performance.

[0009] The fourth object of the present application is to provide a sodium ion battery, which can withstand a higher load voltage and has a high capacity, a high rate performance and a long cycle life.

[0010] In order to achieve the above objects of the present application, the following technical solutions are adopted:

[0011] The present application first provides a high-voltage positive electrode material, the general formula of the high-voltage positive electrode material is Na a (NiMn) x (CuTi) y M 1-2x-2y O 2-δ , wherein 0.8≤a≤1.05, 0.3≤x≤0.5, 0

[0012] The high-voltage positive electrode material is mainly prepared by sintering a precursor and a sodium source at least twice; wherein the sphericity of the primary sintered material obtained after the first sintering is ≥0.60, and the sphericity of the secondary sintered material obtained after the second sintering is ≥0.80.

[0013] The sphericity is m, The ratio b / a of the short axis length b to the long axis length a of each single crystal particle in the cross-sectional image of the sintered material obtained after each sintering is obtained and counted, the value of b / a ranges from [0, 1], the range is equally divided, n is the number of division, and the number of single crystal particles in each division segment accounts for x i The value of b / a of each division segment is w i .

[0014] Further, 0.85≤a≤1.0.

[0015] Further, 0.35≤x≤0.45.

[0016] Further, 0.05≤y≤0.15.

[0017] Further, 0≤1-2x-2y≤0.15.

[0018] Further, the particle size Dv50 of the high-voltage cathode material is 5-20 μm.

[0019] Further, the particle size distribution width SPAN of the high-voltage cathode material is ≤1.3.

[0020] Further, the tap density TD of the high-voltage cathode material is ≥2.0 g / cm 3 .

[0021] Further, the specific surface area BET of the high-voltage cathode material is ≤0.40 m 2 / g.

[0022] Further, the mass fraction of carbon element in the high-voltage cathode material is ≤0.15%.

[0023] The application further provides a preparation method of the high-voltage cathode material, comprising the following steps: mixing a precursor and a sodium source and then performing at least two times of sintering.

[0024] Further, the precursor comprises at least one of (NiMn) x (CuTi) y M 1-2x-2y CO3, (NiMn) x (CuTi) y M 1-2x-2y (OH)2 and (NiMn) x (CuTi) y M 1-2x-2y O 2-δ ; wherein 0.8≤a≤1.05, 0.3≤x≤0.5, 0

[0025] Further, the sodium source comprises at least one of sodium carbonate, sodium hydroxide and sodium bicarbonate.

[0026] Further, the sintering is performed in an oxygen-containing gas atmosphere, wherein the volume fraction of oxygen is 21%-30%.

[0027] Further, the sintering is performed at a temperature of 800-1050℃.

[0028] Further, the holding time of each sintering is 10-20 h.

[0029] The application further provides a cathode sheet comprising the high-voltage cathode material.

[0030] The present invention also provides a sodium ion battery comprising the above-mentioned positive electrode sheet.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The present invention can control the sphericity of the material obtained after multiple sintering to control the material morphology and improve the stability of the material under high voltage. It can also improve the phenomenon of uneven charging and discharging caused by the uneven degree of sodium insertion and extraction in different particles or even in different positions within the particles due to irregular single crystal morphology.

[0033] (2) The present invention obtains single crystal materials by sintering through a single crystalization strategy, which can withstand higher load voltages, exhibit higher energy density and better cycle performance.

[0034] (3) The battery made using the high-voltage positive electrode material provided by the present invention has high capacity, good rate performance and excellent cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 Schematic diagram of the statistical method of the b / a value of single crystal particles provided by the present invention;

[0037] Figure 2 A schematic diagram of the sphericity distribution of particles provided by the present invention;

[0038] Figure 3 This is a SEM image of the high-voltage positive electrode material prepared in Example 4 provided by the present invention;

[0039] Figure 4 This is an SEM image of the high-voltage positive electrode material prepared in Comparative Example 1 provided by the present invention. DETAILED DESCRIPTION

[0040] 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, not 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 creative labor fall within the scope of protection of the present application. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be purchased on the market.

[0041] If not specifically stated, in the present application, "first aspect", "second aspect", "third aspect", "fourth aspect" and the like are only used for description purposes, and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implying the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth" and the like only serve the purpose of non-exhaustive enumeration and description, and should be understood as not constituting a closed limitation on the quantity.

[0042] If not specifically stated, "including" and "containing" mentioned in the present application mean open-ended, and can also be closed-ended. For example, "including" and "containing" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0043] If not specifically stated, in the present application, "one or more" or "at least one" means any one, any two or any two or more of the listed items. Among them, "several" means any two or more.

[0044] In the first aspect, the present application provides a single-crystallized high-voltage cathode material for sodium-ion batteries, and the general formula of the high-voltage cathode material is Na a (NiMn) x (CuTi) y M 1-2x-2y O 2-δ0.8≤a≤1.05, 0.3≤x≤0.5, 0

[0045] The value of a includes but is not limited to any one of 0.8, 0.83, 0.85, 0.88, 0.9, 0.92, 0.95, 0.97, 1.0, 1.02, 1.03, 1.05 or a range value between any two of them; the value of x includes but is not limited to any one of 0.3, 0.33, 0.35, 0.38, 0.4, 0.42, 0.45, 0.47, 0.5 or a range value between any two of them; the value of y includes but is not limited to any one of 0.01, 0.03, 0.05, 0.08, 0.1, 0.12, 0.13, 0.15, 0.18, 0.2 or a range value between any two of them; the value of 1-2x-2y includes but is not limited to any one of 0, 0.01, 0.03, 0.05, 0.08, 0.1, 0.12, 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, 0.3 or a range value between any two of them; the value of δ includes but is not limited to any one of 0, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05 or a range value between any two of them.

[0046] The high-voltage positive electrode material is an O3 phase layered oxide positive electrode material and is a single crystal particle.

[0047] The high-voltage positive electrode material is mainly prepared from a precursor and a sodium source through at least two times of sintering. The material obtained after each sintering has a high sphericity.

[0048] The sphericity of the primary sintered material obtained after the first sintering is ≥0.60, including but not limited to any one of 0.6, 0.61, 0.63, 0.65, 0.68, 0.7, 0.73, 0.75, 0.78, 0.8, 0.85, 0.9 or a range value between any two of them.

[0049] The sphericity of the secondary sintered material obtained after the second sintering is ≥0.80, including but not limited to any one of 0.8, 0.81, 0.83, 0.85, 0.88, 0.9, 0.91, 0.93, 0.95, 0.98, 1 or a range value between any two of them.

[0050] It can be understood that the higher the sphericity, the better the sphericity of the high-voltage positive electrode material.

[0051] The sphericity m is m = x w. The ratio b / a (b / a≤1) of the short axis length (i.e. the width of the cross section of the single crystal particle) b to the long axis length (i.e. the length of the cross section of the single crystal particle) a of a plurality of single crystal particles in the CP cross section image of the material obtained after each sintering (the primary sintered material or the secondary sintered material) is calculated and statistically analyzed, the value of b / a ranges from 0 to 1 (i.e. 0-1), the range is equally divided, n is the number of partitions, and the proportion of the number of single crystal particles in each partition is x i The value of b / a of each partition is w i It can be understood that the larger n is, the more accurate the calculated sphericity is.

[0052] The CP cross section image refers to the internal cross-sectional microstructure image of the material observed by an electron microscope (such as a scanning electron microscope SEM) after the sample is prepared by argon ion cross-section polishing technology (Cross-Sectional Polishing, CP).

[0053] Specifically, NMP (N-methyl pyrrolidone) is used as a solvent, and the material obtained after each sintering (such as the primary sintered material or the secondary sintered material) is mixed with conductive carbon black SP and PVDF (polyvinylidene fluoride) at a mass ratio of 90:5:5 to prepare a slurry, the obtained slurry is coated on an aluminum foil current collector, and the cross-sectional morphology is collected by CP cross-section polishing technology and scanning electron microscopy (SEM). The long axis length and the short axis length of the single crystal particles in the cross-sectional image are counted, the long axis length is set as a, and the short axis length is set as b, the b / a value (b / a≤1) of each single crystal particle is calculated and statistically analyzed. It can be understood that the closer the value of b / a is to 1, the higher the sphericity of the single crystal particle is. According to the statistical analysis, the value of b / a is taken as the abscissa, and the range is [0, 1], the range is equally divided, and the proportion of the number of single crystal particles in each partition is x i The value of b / a of each partition is w i The sphericity m is m = x w.

[0054] For example, the CP cross-section of the once sintered material is obtained, and the long axis length and the short axis length of a plurality of single crystal particles therein are counted, the ratio b / a of the short axis length b to the long axis length a of each single crystal particle is calculated, and statistical analysis is performed. Taking the value of b / a as the abscissa, the range is [0, 1], which is equally divided, assuming that the number of partitions n = 10 (i.e. the interval of the abscissa b / a value is 1 / 10 = 0.1), assuming that the number of single crystal particles in the first partition is x1, the number of single crystal particles in the second partition is x2, the number of single crystal particles in the third partition is x3, the number of single crystal particles in the fourth partition is x4, the number of single crystal particles in the fifth partition is x5, and so on, the number of single crystal particles in the nth partition is xn. n The value of b / a of the first partition is 0.1, the value of b / a of the second partition is 0.2, the value of b / a of the third partition is 0.3, the value of b / a of the fourth partition is 0.4, the value of b / a of the fifth partition is 0.5, and so on, the value of b / a of the nth partition is n / 10. Then the sphericity of the once sintered material is m = x1x0.1 + x2x0.2 + x3x0.3 + x4x0.4 + x5x0.5 + x6x0.6 + x7x0.7 + x8x0.8 + x9x0.9 + xn x1.0. 10

[0055] The statistical method of the b / a value of the single crystal particle is shown in Figure 1 The sphericity particle distribution diagram is shown in Figure 2 .

[0056] By controlling the sphericity of the material obtained after multiple sintering, especially the sphericity of the once sintered material and the twice sintered material, the morphology of the material can be controlled, and the stability of the material at high voltage can be improved. The phenomenon of uneven charging and discharging caused by the uneven degree of sodium extraction of different particles and even different positions inside the particles due to irregular single crystal morphology is improved.

[0057] The high-voltage positive electrode material with high sphericity has a more uniform sodium ion diffusion path, and the rate performance and cycle performance are improved.

[0058] In some specific embodiments, the sphericity m1 of the once sintered material obtained after the first sintering is 0.6-1.0, and the sphericity m2 of the twice sintered material obtained after the second sintering is 0.8-1.0.

[0059] In some specific embodiments, 0.85≤a≤1.0, 0.35≤x≤0.45, and 0.05≤y≤0.15.

[0060] ​0≤1-2x-2y≤0.15, wherein a, x, y, 1-2x-2y adopt the above range, which can further improve the sphericity of the primary sintered material and the secondary sintered material.

[0061] In some specific embodiments, the particle size Dv50 of the high-voltage positive electrode material is 5-20 μm, including but not limited to any one of 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 13 μm, 15 μm, 16 μm, 18 μm, 20 μm, or a range value between any two of them, preferably 7-13 μm. Suitable single crystal size can effectively reduce the side reaction between the material and the electrolyte, and in addition, a suitable ion transport path is an effective guarantee for the rate performance.

[0062] In some specific embodiments, the particle size distribution width SPAN of the high-voltage positive electrode material is ≤1.3, including but not limited to any one of 1.3, 1.25, 1.2, 1.15, 1.1, 1.05, 1, 0.99, 0.98, 0.95, 0.9, 0.8, or a range value between any two of them. The smaller the particle size distribution width, the higher the consistency of the single crystal particles of the high-voltage positive electrode material, that is, the more uniform the particle size.

[0063] SPAN=Dv90-Dv10 / Dv50, Dv90 is the particle size Dv50 of the high-voltage positive electrode material, Dv10 is the particle size Dv10 of the high-voltage positive electrode material, and Dv50 is the particle size Dv50 of the high-voltage positive electrode material.

[0064] In some specific embodiments, the tap density TD of the high-voltage positive electrode material is ≥2.0 g / cm 3 , including but not limited to any one of 2.0 g / cm 3 , 2.03 g / cm 3 , 2.05 g / cm 3 , 2.08 g / cm 3 , 2.1 g / cm 3 , 2.13 g / cm 3 , 2.15 g / cm 3 , 2.18 g / cm 3 , 2.2 g / cm 3 , 2.3 g / cm 3 , or a range value between any two of them.

[0065] The present application can improve the tap density and the tap density of the high-voltage positive electrode material, and exhibit higher energy density.

[0066] In some specific embodiments, the specific surface area BET of the high-voltage positive electrode material is ≤0.40 m 2 / g, including but not limited to 0.40 m 2 / g, 0.39 m 2 / g, 0.38 m 2 / g, 0.37 m 2 / g, 0.36 m 2 / g, 0.35 m 2 / g, 0.34 m 2 / g, 0.33 m 2 / g, 0.31 m 2 / g, 0.30 m 2 / g, 0.28 m 2 / g, 0.25 m 2 / g. Smaller specific surface area indicates that there is little amount of fine powder in the material, which greatly reduces the side reaction with the electrolyte, and in turn reduces the probability of cell failure caused by interface problems.

[0067] In some specific embodiments, the mass fraction of carbon element in the high-voltage positive electrode material is ≤0.15%, including but not limited to any one of the point values of 0.15%, 0.13%, 0.12%, 0.11%, 0.1%, 0.09%, 0.08%, 0.05% or a range value between any two of them. Low mass fraction of carbon element indicates that the high-voltage positive electrode material has low residual alkali content, better structural stability at high voltage, and the battery made therefrom is less likely to produce gas.

[0068] In a second aspect, the present application provides a preparation method of the above high-voltage positive electrode material, comprising the following steps: weighing the precursor and the sodium source according to the stoichiometric ratio, mixing uniformly using a high-speed mixer, and then placing in an atmosphere furnace for at least two times of sintering, and after cooling, crushing by airflow mill and sieving, to obtain the high-voltage positive electrode material.

[0069] The single crystal material prepared by the method can withstand higher load voltage, exhibit higher energy density and more excellent cycle performance.

[0070] And the high-voltage positive electrode material prepared by the method has good sphericity, high stability of the material at high voltage, and is beneficial to improve the rate performance and cycle performance of the battery made of the high-voltage positive electrode material.

[0071] In some specific embodiments, the precursor includes (NiMn) x (CuTi) y M 1-2x-2y CO3carbonate precursor, (NiMn) x (CuTi) y M 1-2x-2y (OH)2hydroxide precursor and (NiMn)x (CuTi) y M 1-2x-2y O 2-δ at least one of oxide precursor; wherein, 0.8≤a≤1.05, 0.3≤x≤0.5, 0

[0072] In some specific embodiments, the preparation method of the precursor comprises: using a co-precipitation method, weighing corresponding metal salts according to stoichiometric ratio, dissolving them in an aqueous solution containing a dispersant to obtain liquid A, dissolving the obtained solution of precipitant as liquid B, using a peristaltic pump to add liquid B dropwise to liquid A, and controlling the pH of the precipitation process. Then, the obtained precipitate is washed and dried to obtain the corresponding proportion of the precursor (carbonate precursor or hydroxide precursor).

[0073] Preferably, the metal salt comprises at least one of nitrate, sulfate, hydrochloride and oxygen-containing acid salt, wherein the metal salt contains at least Ni element, Mn element, Cu element and Ti element, and the metal salt contains or does not contain M element, M comprising at least one of Fe, Al, B, Bi, Li, Ca, Co, Nb, Sr and Zr. Preferably, the molar concentration of the solution containing the metal salt is 1-3 mol / L. Preferably, the dispersant comprises at least one of soluble starch, polyvinylpyrrolidone (PVP), sodium dodecyl sulfonate (SDS) and polyethylene glycol (PEG-400). Preferably, the precipitant comprises at least one of sodium carbonate, sodium hydroxide and ammonia water; the molar concentration of the solution containing the precipitant is 0.8-1.5 mol / L. Preferably, the pH is controlled at 6-13.

[0074] Further, the carbonate precursor ((NiMn) x (CuTi) y M 1-2x-2y CO3) or the hydroxide precursor ((NiMn) x (CuTi) y M 1-2x-2y (OH)2) is sintered to obtain the oxide precursor ((NiMn) x (CuTi) y M 1-2x- 2y O 2-δ ), wherein the sintering temperature can be 400-700℃.

[0075] In some specific embodiments, the sodium source comprises at least one of sodium carbonate, sodium hydroxide and sodium bicarbonate.

[0076] In some embodiments, the sintering is performed in an oxygen-containing atmosphere, such as an air atmosphere, or a mixed atmosphere of oxygen and other gases. The volume fraction of oxygen in the atmosphere is 21% to 30%, including but not limited to any one of 21%, 22%, 23%, 25%, 26%, 28%, 30%, or a range between any two of them.

[0077] In some embodiments, the sintering is performed at a temperature of 800 to 1050℃, including but not limited to any one of 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, or a range between any two of them.

[0078] In some embodiments, the holding time of each sintering is 10 to 20h, including but not limited to any one of 10h, 12h, 14h, 15h, 16h, 18h, 20h, or a range between any two of them.

[0079] In some embodiments, the morphology of the high-voltage cathode material is controlled by multiple sintering, the temperature of each sintering, and the regulation of oxygen partial pressure during each sintering.

[0080] In a third aspect, the present application provides a cathode sheet comprising the high-voltage cathode material.

[0081] The battery prepared using the cathode sheet has high capacity, good rate performance, and excellent cycle performance.

[0082] It can be understood that the high-voltage cathode material is used as the positive active material in the cathode sheet.

[0083] In a fourth aspect, the present application provides a sodium-ion battery comprising the cathode sheet.

[0084] The sodium-ion battery can withstand a higher load voltage, and has high capacity, good rate performance, and long cycle life.

[0085] Optionally, the sodium-ion battery further comprises an anode sheet, a separator, and an electrolyte, which are not limited by the present application.

[0086] Embodiments of the present application will be described in detail below with reference to examples, but those skilled in the art will understand that the following examples are only for illustration of the present application, and should not be regarded as limiting the scope of the present application. The specific conditions not specified in the examples are carried out under conventional conditions or according to the manufacturer's recommendations. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be obtained commercially.

[0087] Example 1

[0088] The high-voltage positive electrode material Na 0.95 (NiMn) 0.36 (CuTi) 0.09 Fe 0.1 O 1.975 The preparation method comprises the following steps:

[0089] (1) Preparation of (NiMn) 0.36 (CuTi) 0.09 Fe 0.1 O 1.5 oxide precursor: weigh the corresponding mass of nickel sulfate, manganese sulfate, copper sulfate, titanium sulfate and iron sulfate according to the target chemical formula, dissolve them in an aqueous solution containing PVP (dispersing agent) to prepare a metal mixed solution with a total metal element molar concentration of 2 mol / L. Control the reaction temperature to be 35℃, and continuously stir, use peristaltic pump to add 1.0 mol / L sodium carbonate solution to the metal mixed solution, carry out coprecipitation reaction, control the pH of the coprecipitation reaction process to be 7, stop the reaction when the Dv50 of the precipitate particles is 5μm. Wash and dry the obtained precipitate, then sinter it, the sintering temperature is 650℃, the sintering time is 10h, and the oxide precursor is obtained.

[0090] (2) The oxide precursor obtained in step (1) and sodium carbonate are weighed according to the stoichiometric ratio, and a high-speed mixer is used for mixing. The material after high-speed mixing is sintered in an oxygen-containing atmosphere (the volume fraction of oxygen is controlled to be 21%). The first sintering parameters are as follows: the temperature is increased to 970℃ at a rate of 3℃ / min, and the temperature is kept for 18h, and then the temperature is naturally lowered to obtain the first sintered material. The obtained first sintered material is crushed by gas and sieved, and then sintered for the second time: the temperature is increased to 900℃ at a rate of 5℃ / min, and the temperature is kept for 15h, and then the temperature is naturally lowered to obtain the second sintered material. The second sintered material is crushed by gas and sieved to obtain the high-voltage positive electrode material.

[0091] Example 2

[0092] The high-voltage positive electrode material Na 0.95 (NiMn) 0.4 (CuTi) 0.1 O 1.975 The preparation method comprises the following steps:

[0093] (1) Preparation of (NiMn) 0.4 (CuTi) 0.1(OH)3 hydroxide precursor: according to the target chemical formula, the corresponding mass of nickel nitrate, manganese nitrate, copper nitrate and titanium nitrate was weighed, which was dissolved in an aqueous solution containing SDS (dispersing agent) to prepare a metal mixed solution with a total molar concentration of metal elements of 1.8 mol / L. The reaction temperature was controlled at 30°C, and continuous stirring was performed. A peristaltic pump was used to add 1.0 mol / L sodium hydroxide solution to the metal mixed solution to perform coprecipitation reaction. The pH value during the coprecipitation reaction process was controlled at 13. When the Dv50 of the precipitated particles was 4.5 μm, the reaction was stopped. The obtained precipitate was washed and dried to obtain the hydroxide precursor.

[0094] (2) The hydroxide precursor obtained in step (1) and sodium carbonate were weighed according to the stoichiometric ratio, and a high-speed mixer was used for mixing. The material after high-speed mixing was sintered in an oxygen-containing atmosphere (the volume fraction of oxygen was controlled at 23%). The one-time sintering parameters were as follows: the temperature was increased to 980°C at a rate of 2°C / min, and the temperature was maintained for 15 h. Then, the temperature was naturally lowered to obtain the one-time sintered material. The one-time sintered material was crushed by air and sieved, and then the two-time sintering was performed: the temperature was increased to 920°C at a rate of 5°C / min, and the temperature was maintained for 15 h. Then, the temperature was naturally lowered to obtain the two-time sintered material. The two-time sintered material was crushed by air and sieved, and then the three-time sintering was performed: the temperature was increased to 850°C at a rate of 5°C / min, and the temperature was maintained for 15 h. Then, the temperature was naturally lowered and crushed to obtain the three-time sintered material, i.e., the high-voltage positive electrode material.

[0095] Example 3

[0096] The high-voltage positive electrode material Na 0.90 (NiMn) 0.4 (CuTi) 0.095 Bi 0.01 O 1.95 The preparation method of the high-voltage positive electrode material Na

[0097] (1) Preparation of (NiMn) 0.4 (CuTi) 0.095 Bi 0.01 (CO3) 1.5 Carbonate precursor: according to the target chemical formula, the corresponding mass of nickel chloride, manganese chloride, copper chloride, titanium chloride and bismuth chloride was weighed, which was dissolved in an aqueous solution containing PEG-400 (dispersing agent) to prepare a metal mixed solution with a total molar concentration of metal elements of 2.5 mol / L. The reaction temperature was controlled at 30°C, and continuous stirring was performed. A peristaltic pump was used to add 1.2 mol / L sodium hydroxide solution to the metal mixed solution to perform coprecipitation reaction. The pH value during the coprecipitation reaction process was controlled at 6. When the Dv50 of the precipitated particles was 5.5 μm, the reaction was stopped. The obtained precipitate was washed and dried to obtain the carbonate precursor.

[0098] (2) The carbonates precursor obtained in step (1) and sodium carbonate are weighed according to stoichiometric ratio, and mixed by using a high-speed mixer. The mixed material is sintered in a ball mill under an oxygen-containing atmosphere (controlling the volume fraction of oxygen to be 28%). The sintering parameters are as follows: heating to 980°C at a rate of 2°C / min, maintaining for 15h, and then naturally cooling to obtain the primary sintered material. The primary sintered material is crushed by air jet and sieved, and then sintered again: heating to 940°C at a rate of 5°C / min, maintaining for 15h, and then naturally cooling to obtain the secondary sintered material. The secondary sintered material is crushed by air jet and sieved to obtain the high-voltage positive electrode material.

[0099] Example 4

[0100] The high-voltage positive electrode material Na 0.93 (NiMn) 0.38 (CuTi) 0.1 Co 0.04 O 1.965 of the present embodiment is basically the same as that of Example 1, except that in step (1), the corresponding mass of nickel sulfate, manganese sulfate, copper sulfate, titanium sulfate and cobalt sulfate is weighed according to the target chemical formula, and in step (2), the primary sintering parameters are as follows: heating to 950°C at a rate of 5°C / min, maintaining for 18h, and the secondary sintering parameters are as follows: heating to 950°C at a rate of 5°C / min, maintaining for 15h.

[0101] The SEM image of the high-voltage positive electrode material prepared in the present embodiment is shown in Figure 3 .

[0102] Example 5

[0103] The high-voltage positive electrode material Na 0.9 (NiMn) 0.36 (CuTi) 0.1 Zr 0.08 O 1.99 of the present embodiment is basically the same as that of Example 1, except that in step (1), the corresponding mass of nickel sulfate, manganese sulfate, copper sulfate, titanium sulfate and zirconium sulfate is weighed according to the target chemical formula, and in step (2), the primary sintering parameters are as follows: heating to 920°C at a rate of 5°C / min, maintaining for 15h, and the secondary sintering parameters are as follows: heating to 960°C at a rate of 5°C / min, maintaining for 18h.

[0104] Example 6

[0105] The high-voltage positive electrode material Na 0.95 (NiMn) 0.35 (CuTi) 0.13 Sr0.04 O 1.955 The preparation method of the high-voltage positive electrode material Na

[0106] Example 7

[0107] The high-voltage positive electrode material Na 0.96 (NiMn) 0.4 (CuTi) 0.09 Li 0.02 O 1.96 The preparation method of the high-voltage positive electrode material Na

[0108] Example 8

[0109] The high-voltage positive electrode material Na 0.94 (NiMn) 0.41 (CuTi) 0.07 Ca 0.04 O 1.95 The preparation method of the high-voltage positive electrode material Na

[0110] Example 9

[0111] The high-voltage positive electrode material Na 0.95 (NiMn) 0.43 (CuTi) 0.05 Al 0.04 O 1.975The preparation method of the high-voltage positive electrode material Na

[0112] Comparative Example 1

[0113] The high-voltage positive electrode material Na 0.95 (NiMn) 0.36 (CuTi) 0.09 Fe 0.1 O 1.975 The preparation method of the high-voltage positive electrode material Na

[0114] The SEM image of the high-voltage positive electrode material prepared in the present comparative example is shown in Figure 4 .

[0115] Comparative Example 2

[0116] The high-voltage positive electrode material Na 0.95 (NiMn) 0.4 (CuTi) 0.1 O 1.975 The preparation method of the high-voltage positive electrode material Na

[0117] Comparative Example 3

[0118] The high-voltage positive electrode material Na 0.94 (NiMn) 0.41 (CuTi) 0.07 Ca 0.04 O 1.95 The preparation method of the high-voltage positive electrode material Na

[0119] Comparative Example 4

[0120] The high-voltage positive electrode material Na 0.94 (NiMn) 0.47 (CuTi) 0.03 O 1.97The preparation method is basically the same as that of Example 2, except that: in step (1), the corresponding masses of nickel nitrate, manganese nitrate, copper nitrate and titanium nitrate are weighed according to the target chemical formula.

[0121] Comparative Example 5

[0122] The high voltage positive electrode material Na 0.95 (NiMn) 0.32 (CuTi) 0.18 O 1.98 The preparation method is basically the same as that of Example 2, except that: in step (1), the corresponding masses of nickel nitrate, manganese nitrate, copper nitrate and titanium nitrate are weighed according to the target chemical formula.

[0123] The sphericity m1 of the primary sintered material obtained after the first sintering of each embodiment and each comparative example, the sphericity m2 of the secondary sintered material, the particle size Dv10, particle size Dv50, particle size Dv90, and particle size distribution width SPAN of the high-voltage positive electrode material prepared in each embodiment and each comparative example, the tap density TD and specific surface area BET of the high-voltage positive electrode material prepared in each embodiment and each comparative example, and the mass fraction of the carbon element in the high-voltage positive electrode material prepared in each embodiment and each comparative example (abbreviated as C value) are shown in Table 1.

[0124] Among them, the sphericity m1 and the sphericity m2 are collectively referred to as m, and the calculation method is: The ratio b / a of the short axis length b to the long axis length a of several single crystal particles in the CP cross-section of the material obtained after each sintering is obtained respectively, and the values ​​of b / a are statistically analyzed. The range of the value of b / a is [0,1]. The range is divided into 10 equal parts, and the number of single crystal particles in each segment accounts for x. i , the value of b / a in each segment is w i (i.e. the value of b / a for each segment w i They are: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0).

[0125] Table 1 Physical and chemical data and sphericity results of each embodiment

[0126]

[0127]

[0128] Further, the high-voltage cathode material prepared in each example and each comparative example is used as a cathode active material, mixed in a mass ratio of 90:5:5 of the cathode active material, SP and PVDF, and NMP is added to form a viscous glue liquid, which is coated on an aluminum foil, baked in a vacuum drying oven at 120°C for 6h to obtain a cathode sheet. A 2032 button cell is assembled in an Ar protection glove box with a metal sodium sheet as a counter electrode, glass fiber (Waterman) as a separator, 1 mol / L NaPF6, EC:DMC (volume ratio) = 1:1 as an electrolyte.

[0129] Then each battery is subjected to a cycle test according to the following method: 0.1C small current is used for charge and discharge test to obtain the 0.1C discharge capacity (unit: mAh / g) in the voltage range of 2.0-4.3V and the nominal specific capacity is 150mAh / g, and 0.1C is cycled for 3 weeks, 0.5C is cycled for 3 weeks, then 1C current is used for charge and discharge test to obtain the 1C capacity (unit: mAh / g), and 1C constant current charge and discharge is used for cycle test. The test results are shown in Table 2.

[0130] And each battery is subjected to a rate performance test according to the following method: 0.1C, 0.2C, 0.5C, 1C, 2C, 5C are cycled for 4 weeks respectively, then 0.1C is cycled for 4 weeks, and the nominal specific capacity is also 150mAh / g. The test results are shown in Table 2.

[0131] Table 2: Electrochemical performance results of each battery

[0132]

[0133]

[0134] From the data of each example in Table 1 and Table 2, it can be seen that under the given ratio and sintering conditions, a high-voltage cathode material with a narrow particle size distribution width is obtained, and the tap density TD of the high-voltage cathode material is ≥2.0g / cm 3 , the specific surface area BET is ≤0.40m 2 / g, and the mass fraction of carbon element is ≤0.15%, i.e. each example obtains a spherical O3-type single crystal layered oxide with a high spherical rate, which effectively improves the phenomenon of uneven charge and discharge caused by the uneven degree of sodium extraction of different particles and even different positions inside the particles due to irregular single crystal morphology, and improves the structural stability of the high-voltage cathode material, which still has excellent rate and cycle performance under high voltage.

[0135] It can be seen from Table 1 and Table 2 that the high-voltage cathode material with a high spherical rate has better rate and cycle performance.

[0136] From Comparative Example 1, it can be seen that a suitable sintering temperature is an important condition for promoting sintering of single crystals, and if the first sintering temperature is too low, it is difficult to provide the energy required for ion diffusion in the sintering process, which is not conducive to the ordered generation of the layered structure.

[0137] From Comparative Example 2 and Example 2, it can be seen that multiple sintering can effectively improve the morphology of single crystals, and multiple sintering can promote the recrystallization and growth of small particles and the fusion and growth between particles, and the annealing process experienced multiple times can effectively eliminate defects such as dislocations in the crystal lattice, and improve the structural stability of the material.

[0138] From Comparative Example 3 and Example 8, it can be seen that when the oxygen content in the sintering process is less than 21%, the C value is significantly increased, and the capacity, the rate, and the cycle performance are significantly low. The oxygen content can significantly affect the chemical equilibrium of the sintering process, and a suitable oxygen partial pressure is conducive to the forward reaction, so that the reaction is sufficient and the morphology is good.

[0139] From Comparative Example 4 and Example 2, it can be seen that when the ratio deviates from the given range, the electrochemical performance of the material is poor, which can be attributed to the poor structural stability of the material, which is difficult to support the large crystal parameter change in the charging and discharging process at high voltage, and the reversibility is poor, resulting in structural failure and poor cycle.

[0140] From Comparative Example 5 and Example 2, it can be seen that when the ratio exceeds the given range, the structural stability of the material is poor, and the particle sphericity is low. The charging and discharging process shows a heterogeneous reaction of sodium ions in the particles, resulting in poor material performance.

[0141] In summary, by controlling the sphericity of the material obtained after multiple sintering, especially the sphericity of the first sintered material and the second sintered material, the morphology of the material can be controlled, the sphericity of the single crystal particles can be improved, and the stability of the material at high voltage can be improved. Therefore, the battery prepared by using the high-voltage positive electrode material of the present application has high capacity, high rate performance and cycle performance.

[0142] 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 technical solutions of the present application, and are not limiting thereof; it should be understood by those skilled in the art that the technical solutions described in the above embodiments can be modified, or some or all of the technical features thereof can be replaced by equivalents, 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 solutions deviate from the scope of the technical solutions of the embodiments of the present application; therefore, this means that all such replacements and modifications within the scope of the present application are included in the appended claims.

Claims

1. A high-voltage cathode material, characterized in that, The general formula of the high-voltage positive electrode material is Na a (NiMn) x (CuTi) y M 1-2x-2y O 2-δ wherein 0.8≤a≤1.05, 0.3≤x≤0.5, 0 y≤0.2, 0≤1-2x-2y≤0.3, 0≤δ≤0.05, and M includes at least one of Fe, Al, B, Bi, Li, Ca, Co, Nb, Sr, and Zr elements. The high-voltage cathode material is prepared by at least twice sintering of a precursor and a sodium source; wherein the spheroidization rate of the primary sintered material obtained after the first sintering is ≥0.60, and the spheroidization rate of the secondary sintered material obtained after the second sintering is ≥0.

80. The sphericity is m, The ratio b / a of the short axis length b to the long axis length a of each single crystal particle in the cross-sectional image of the material CP obtained after each sintering is obtained and counted, the value of b / a ranges from [0, 1], the range is equally divided, n is the number of division, and the number of single crystal particles in each division segment accounts for x i The value of b / a of each division segment is w i .

2. The high voltage positive electrode material according to claim 1, characterized in that: At least one of the following conditions is satisfied: (1)0.85≤a≤1.0； (2)0.35≤x≤0.45； (3)0.05≤y≤0.15； (4) 0≤1-2x-2y≤0.

15.

3. The high voltage cathode material of claim 1, wherein, At least one of the following conditions is satisfied: (1) the particle size Dv50 of the high-voltage cathode material is 5-20 μm; (2) the particle size distribution width SPAN of the high-voltage cathode material is ≤1.

3.

4. The high voltage cathode material of claim 1, wherein, The tap density TD of the high-voltage cathode material is ≥ 2.0 g / cm3 3 .

5. The high voltage cathode material of claim 1, wherein, The high-voltage cathode material has a specific surface area BET < 0.40 m 2 / g.

6. The high voltage cathode material of claim 1, wherein, The mass fraction of carbon element in the high-voltage cathode material is ≤0.15%.

7. The method for preparing a high voltage positive electrode material according to any one of claims 1 to 6, wherein: The method comprises the following steps: mixing a precursor and a sodium source and then sintering at least twice.

8. The method of claim 7, wherein the high-voltage cathode material is prepared by the steps of: At least one of the following conditions is satisfied: ​ (1) the precursor comprises (NiMn) x (CuTi) y M 1-2x-2y CO3, (NiMn) x (CuTi) y M 1-2x-2y (OH)2, and (NiMn) x (CuTi) y M 1-2x-2y O 2-δ at least one of; wherein 0.8≤a≤1.05, 0.3≤x≤0.5, 0 y≤0.2, 0≤1-2x-2y≤0.3, 0≤δ≤0.05, M comprises at least one of Fe, Al, B, Bi, Li, Ca, Co, Nb, Sr, and Zr elements. (2) the sodium source comprises at least one of sodium carbonate, sodium hydroxide and sodium bicarbonate; (3) the sintering is performed in an oxygen-containing atmosphere, wherein the volume fraction of oxygen is 21%-30%; (4) the sintering temperature is 800-1050℃; (5) the holding time of each sintering is 10-20 h.

9. A positive electrode sheet characterized by comprising: The high-voltage cathode material as claimed in any one of claims 1-6.

10. A sodium-ion battery, characterized in that, The cathode sheet as claimed in claim 9.

Images