Positive electrode material of sodium-ion battery and preparation method for positive electrode material, and sodium-ion battery

Abstract

A positive electrode material of a sodium-ion battery and a preparation method for a positive electrode material, and a sodium-ion battery. In an XRD spectrum of the positive electrode material, a characteristic diffraction peak A and a characteristic diffraction peak B of a crystal plane (003) and a crystal plane (104) are respectively present when 2θ ranges from 15° to 19° and from 39° to 44°, wherein the crystallite size DA at the characteristic diffraction peak A and the crystallite size DB at the characteristic diffraction peak B satisfy: 1.3≤DA / DB≤2.5, where DA and DB are respectively equivalent to the crystallite sizes of the crystal plane (003) and the crystal plane (104) in a vertical direction. The air stability and structural stability of the positive electrode material are improved while ensuring the high volumetric energy density of the positive electrode material; and by means of applying the positive electrode material to a sodium-ion battery, the electrochemical performance of the sodium-ion battery can be effectively improved.

Description

Sodium ion battery positive electrode material and preparation method thereof, sodium ion battery Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery positive electrode material and a preparation method thereof, and a sodium ion battery containing the sodium ion battery positive electrode material. Background Art

[0002] In recent years, with the production and use of electric vehicles, lithium-ion batteries are being used extensively in the new energy vehicle industry. However, as the price of lithium resources continues to rise rapidly, sodium-ion batteries, which are abundant in resources and low in price, have received widespread attention. Sodium battery technology can significantly reduce battery manufacturing costs and is expected to be widely used in low-speed electric vehicles and energy storage fields.

[0003] In the sodium ion battery system, currently, layered oxides (Na x MO2 (M=Ni, Fe, Mn, etc.) is a cathode material that meets the needs of both power and energy storage battery applications. It offers advantages such as low cost, excellent low-temperature performance, high thermal stability, good safety, high energy density, and environmental friendliness. It holds great potential in the low- and mid-range passenger vehicle and energy storage battery markets.

[0004] However, Na x MO2 material is not only very sensitive to air humidity and easy to absorb water and convert, resulting in poor air stability, but also in the process of charge and discharge with the Na + The insertion / extraction of the structure will cause a large volume change, resulting in poor stability of the structure collapse cycle. x The shortcomings of MO2 materials, such as improving air stability and structural stability, become the subject to be studied and solved by the present invention.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to overcome the above-mentioned technical problems and provide a sodium ion battery positive electrode material and a preparation method thereof and a sodium ion battery. The positive electrode material improves the air stability and structural stability of the positive electrode material while ensuring a high volume energy density; at the same time, the positive electrode material is used in a sodium ion battery to effectively improve the electrochemical performance of the sodium ion battery.

[0007] In order to achieve the above-mentioned object, the first aspect of the present invention provides a sodium ion battery positive electrode material, wherein the XRD spectrum of the positive electrode material has characteristic diffraction peaks A and B of (003) crystal plane and (104) crystal plane at 2θ of 15-19° and 39-44°, respectively; wherein the crystallite size D of the characteristic diffraction peak A is A and the crystallite size D of the characteristic diffraction peak B B Satisfy: 1.3≤DA / D B ≤2.5, where D A and D B These correspond to the crystallite sizes in the directions perpendicular to the (003) and (104) crystal planes, respectively.

[0008] In the present invention, unless otherwise specified, the positive electrode material for sodium ion batteries is referred to as positive electrode material.

[0009] Preferably, the cathode material has an O3 type single crystal structure, and the c value is selected from

[0010] Preferably, the cathode material has a composition as shown in Formula I: Na a (Ni x Fe y Mn z M m M' n )O2 (I), wherein, 0.8≤a≤1.1, 0≤x≤0.5, 0≤y≤0.5, 0≤z≤0.5, 0≤m≤0.5, 0≤n≤0.2, 0.05≤m+n≤0.5, m and n are not 0 at the same time, x+y+z+m+n=1; M and M' are each independently selected from at least one element of Li, Cu, Co, V, Cr, Ti, Mg, Sn, Zn, Al, Zr, Sr, Nb, B, Y, W and La.

[0011] A second aspect of the present invention provides a method for preparing a positive electrode material for a sodium ion battery, the method comprising the following steps:

[0012] (1) Ni α Fe β Mn γ M δ O a H b (II) pre-calcining the precursor to obtain a pre-calcined precursor;

[0013] (2) mixing the pre-calcined precursor, the Na source and an optional dopant containing M' and calcining the mixture to obtain a positive electrode material; wherein M and M' in the positive electrode material are not both 0;

[0014] Wherein, in Formula II, 0≤α≤0.5, 0≤β≤0.5, 0≤γ≤0.5, 0≤δ≤0.5, 1≤a≤2, 0≤b≤2, α+β+γ+δ=1, and M and M′ are each independently selected from at least one element of Li, Cu, Co, V, Cr, Ti, Mg, Sn, Zn, Al, Zr, Sr, Nb, B, Y, W and La;

[0015] In which, the pre-firing includes a first heating stage, a second heating stage and a heat preservation stage. The conditions of the first heating stage include: heating to T1 at a heating rate of v1 in an oxygen-poor atmosphere with an oxygen concentration ≤10vol%; the conditions of the second heating stage include: heating to T2 at a heating rate of v2 in an oxygen-poor atmosphere with an oxygen concentration ≤20vol%; the conditions of the heat preservation stage include: heat preservation t within a temperature range of (T2-10)≤T≤(T2+10); wherein v1 is selected from 5-10℃ / min, v2 is selected from 1-3℃ / min, T1 is selected from 200-300℃, T2 is selected from 450-750℃; t is selected from 3-10h.

[0016] The third aspect of the present invention provides a sodium ion battery containing the positive electrode material provided by the first aspect, or the positive electrode material prepared by the preparation method provided by the second aspect.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) The positive electrode material provided by the present invention is defined as having characteristic diffraction peaks A and B of the (003) crystal plane and the (104) crystal plane, and combined with D A / D B Within a reasonable range, Na + The transmission distance is shorter and easier to transmit during the charge and discharge process, which improves the rate performance. In addition, by limiting the optimal range of the c value, the sodium interlayer spacing is kept in a relatively small range, which does not affect the Na + The normal insertion / extraction process also prevents water and carbon dioxide in the air from entering the interlayer and reacting with Na. That is, the cathode material not only has high sodium ion mobility and significantly improved air stability, but also has a significantly improved compaction density through the precursor gradation design with a wide distribution of large and small particles, thereby improving the volume energy density of the material.

[0019] (2) The preparation method provided by the present invention improves the tap density of the precursor by subjecting the precursor having the composition shown in Formula II to a specific pre-calcination treatment (i.e., a first heating stage, a second heating stage, and a heat preservation stage), thereby increasing production capacity and completely removing the moisture contained in the precursor, thereby solving the problem of different phases of precursors of different compositions and greatly facilitating the subsequent compounding and roasting process; in addition, the treated pre-calcined precursor can increase the porosity and specific surface area while maintaining its own morphology, thereby improving the reaction activity and making it easier to react completely with the sodium source in the subsequent sodium roasting process, thereby reducing the residual alkali on the surface of the positive electrode material and improving the air stability;

[0020] The present invention also regulates the particle size distribution and composition of the precursor, as well as the doping elements of the dopant, by alleviating the Na +The volume change caused by the insertion / extraction process can regulate the compaction density, volume energy density and structural stability of the cathode material;

[0021] In summary, the preparation method provided by the present invention obtains a pre-calcined precursor with high density and high reactivity. The pre-calcined precursor is calcined to obtain a positive electrode material that has high air stability and good structural stability while ensuring high volume energy density, and can overcome the problems of poor air stability and low cycle life of existing layered oxide sodium ion battery positive electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG1 is a SEM image of the precursor prepared in Example 1;

[0023] FIG2 is a SEM image of the calcined precursor obtained in Example 1;

[0024] FIG3 is a SEM image of the O3-type single crystal cathode material S1 prepared in Example 1;

[0025] FIG4 is an XRD pattern of the precursor prepared in Example 1;

[0026] FIG5 is an XRD pattern of the pre-calcined precursor obtained in Example 1;

[0027] FIG6 is an XRD pattern of the O3-type single crystal positive electrode material S1 prepared in Example 1. DETAILED DESCRIPTION

[0028] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0029] In the present invention, unless otherwise specified, the terms "first" and "second" do not indicate a sequential order or limit the materials or steps. They are used only to distinguish or indicate that they are not the same materials or steps. For example, "first heating stage" and "second heating stage" are used only to indicate that they are not the same heating stages.

[0030] A first aspect of the present invention provides a sodium ion battery positive electrode material, wherein the positive electrode material has a characteristic diffraction peak A and a characteristic diffraction peak B of a (003) crystal plane and a (104) crystal plane at 2θ of 15-19° and 39-44°, respectively.

[0031] Among them, the crystallite size D of the characteristic diffraction peak A is A and the crystallite size D of the characteristic diffraction peak BB Satisfy: 1.3≤D A / D B ≤2.5, where D A and D B These correspond to the crystallite sizes in the directions perpendicular to the (003) and (104) crystal planes, respectively.

[0032] In the present invention, unless otherwise specified, the microcrystalline structure characteristics (e.g., D A and D B ) refers to the vertical distance from the crystal plane to the center of the crystallite. For example, D A is the vertical distance from the (003) crystal plane to the center of the crystallite; D B It is the vertical distance from the (104) crystal plane to the center of the crystallite.

[0033] In the present invention, the crystallite size is measured by the following method: using the powder X-ray diffraction pattern comprehensive analysis software JADE6.5, the half-peak width is calculated from the characteristic diffraction peak A in the range of 2θ = 15-19° and the characteristic diffraction peak B in the range of 2θ = 39-44° from the powder X-ray diffraction pattern obtained by the powder X-ray diffraction measurement; using the obtained half-peak width, the crystallite size D is calculated according to the Scherrer formula. A and crystallite size D B .

[0034] In the present invention, D A / D B The larger the ratio, the greater the difference in the size of the crystallite in different directions, and the crystallite is anisotropically grown; the closer the ratio is to 1, the closer the size of the crystallite in different directions is, and the crystallite is isotropically grown. When the crystallite volume is the same, the degree of anisotropic growth of the crystallite will affect the sodium ion deintercalation and the stability of the crystallite. Therefore, the present invention limits 1.3≤D A / D B ≤2.5, making Na + During the charging and discharging process, the transmission distance is shorter and easier to transmit, which improves the rate performance.

[0035] In some embodiments of the present invention, preferably, the cathode material has an O3 type single crystal structure, and the c value is selected from In the present invention, by limiting the range of c values, it is shown that the positive electrode material has a smaller interlayer spacing, which greatly inhibits the entry of water and carbon dioxide in the air into the interlayer and reaction with Na when the material is exposed to an environment with high relative humidity, and its air stability is significantly improved.

[0036] In the present invention, the term "O3-type single crystal structure" refers to a single crystal positive electrode material having an O3-type crystal form, that is, the positive electrode material has an O3-type sodium-electrolyte layered oxide unit cell structure parameter.

[0037] In the present invention, unless otherwise specified, the characteristic diffraction peak A has a single broad peak with 2θ ranging from 15 to 19°; the characteristic diffraction peak B has a single broad peak with 2θ ranging from 39 to 44°.

[0038] In some embodiments of the present invention, preferably, in the XRD pattern of the positive electrode material, the 2θ of the characteristic diffraction peak A is 16.5±1°, and the 2θ of the characteristic diffraction peak B is 41.5±1°.

[0039] In one embodiment of the present invention, the cathode material has a crystallite size D at a characteristic diffraction peak A within the range of 2θ=16.5±1° in an X-ray diffraction measurement using CuKα rays. A The crystallite size D at the characteristic diffraction peak B in the range of 2θ=41.5±1° B Satisfy: 1.3≤D A / D B ≤2.5.

[0040] In some embodiments of the present invention, the crystallite size D of the characteristic diffraction peak A is A and the crystallite size D of the characteristic diffraction peak B B Satisfy: 1.3≤D A / D B ≤2.5, for example, 1.3, 1.5, 1.8, 2, 2.5, and any value in the range of any two values, preferably 1.3≤D A / D B ≤ 2. The value meeting the preferred range is more conducive to improving the high volume energy density, air stability and structural stability of the positive electrode material.

[0041] In some embodiments of the present invention, preferably, the cathode material has a composition shown in Formula I: Na a (Ni x Fe y Mn z M m M' n )O2(I), wherein, 0.8≤a≤1.1, 0≤x≤0.5, 0≤y≤0.5, 0≤z≤0.5, 0≤m≤0.5, 0≤n≤0.2, 0.05≤m+n≤0.5, m and n are not 0 at the same time, x+y+z+m+n=1; M and M' are each independently selected from at least one element of Li, Cu, Co, V, Cr, Ti, Mg, Sn, Zn, Al, Zr, Sr, Nb, B, Y, W and La.

[0042] In some embodiments of the present invention, further preferably, in Formula I, 0.85≤a≤1.05; more preferably, 0.93≤a≤1.03.

[0043] In some embodiments of the present invention, further preferably, in Formula I, M is selected from at least one element of Cu, Co, V, Cr, Ti, Mg, Sn, Zn, Al, Zr, Nb, Y, W and La, and M' is selected from at least one element of Li, Al, Mg, Ti, Zr, Sr, La, Nb, B and W; more preferably, M and M' are different.

[0044] In some embodiments of the present invention, preferably, the average particle size D of the positive electrode material is 50 It is 7-20 μm, preferably 8-16 μm, and more preferably 9-12 μm.

[0045] In the present invention, the positive electrode material has a wide particle size distribution. Preferably, the particle size distribution of the positive electrode material satisfies: 1.2≤(D 90 -D 10 ) / D 50 ≤1.8, for example, 1.2, 1.4, 1.5, 1.6, 1.8, and any value in the range of any two values, preferably 1.4≤(D 90 -D 10 ) / D 50 ≤1.6. Meeting the particle size distribution within the above range is beneficial to improving the compaction density and volume energy density of the positive electrode material.

[0046] In some embodiments of the present invention, preferably, the compaction density of the positive electrode material is 3-3.6 g / cm 3 , for example, 3g / cm 3 , 3.3g / cm 3 、3.4g / cm 3 、3.5g / cm 3 、3.6g / cm 3 , and any value in the range of any two values, preferably 3.3-3.6 g / cm 3 .

[0047] In some embodiments of the present invention, preferably, the water increment of the positive electrode material is Δ(H2O)=H2O(t x -t0) / H2O(t0), 0h<t x ≤6h, t0=0h, satisfying: 0%≤Δ(H2O)≤120%, preferably 0%≤Δ(H2O)≤100%.

[0048] In some embodiments of the present invention, preferably, the residual alkali conversion rate of the positive electrode material Δ(Na2CO3+NaOH)=Na2CO3(t x -t0) / Na2CO3(t0)+NaOH(t x -t0) / NaOH(t0), 0h<t x ≤6h, t0=0h, satisfying: 0%≤Δ(Na2CO3+NaOH)≤200%, preferably 0%≤Δ(Na2CO3+NaOH)≤150%.

[0049] When the interlayer spacing of the positive electrode material is large, water and carbon dioxide in the air are more likely to enter the laminate structure and react with Na, resulting in an increase in the water absorption of the material, Na2CO3 and NaOH conversion, showing a significant forward shift of the (003) crystal plane diffraction peak. In the present invention, the interlayer spacing of the positive electrode material provided by the present invention is reasonable. While ensuring that the insertion / extraction of sodium ions is easier, water and carbon dioxide in the air can also be avoided from entering the interlayer, and the degree of water absorption in the air is smaller, and Na2CO3 and NaOH conversion are less. Therefore, the positive electrode material provided by the present invention has excellent air stability.

[0050] A second aspect of the present invention provides a method for preparing a positive electrode material for a sodium ion battery, the method comprising the following steps:

[0051] (1) Ni α Fe β Mn γ M δ O a H b (II) pre-calcining the precursor to obtain a pre-calcined precursor;

[0052] (2) mixing the pre-calcined precursor, the Na source and an optional dopant containing M' and calcining the mixture to obtain a positive electrode material; wherein M and M' in the positive electrode material are not both 0;

[0053] Wherein, in Formula II, 0≤α≤0.5, 0≤β≤0.5, 0≤γ≤0.5, 0≤δ≤0.5, 1≤a≤2, 0≤b≤2, α+β+γ+δ=1, and M and M′ are each independently selected from at least one element of Li, Cu, Co, V, Cr, Ti, Mg, Sn, Zn, Al, Zr, Sr, Nb, B, Y, W and La;

[0054] In which, the pre-firing includes a first heating stage, a second heating stage and a heat preservation stage. The conditions of the first heating stage include: heating to T1 at a heating rate of v1 in an oxygen-poor atmosphere with an oxygen concentration ≤10vol%; the conditions of the second heating stage include: heating to T2 at a heating rate of v2 in an oxygen-poor atmosphere with an oxygen concentration ≤20vol%; the conditions of the heat preservation stage include: heat preservation t within a temperature range of (T2-10)≤T≤(T2+10); wherein v1 is selected from 5-10℃ / min, v2 is selected from 1-3℃ / min, T1 is selected from 200-300℃, T2 is selected from 450-750℃; t is selected from 3-10h.

[0055] In the present invention, a specific pre-firing process is adopted to specifically limit the oxygen content, heating rate, temperature, time, etc. of the first heating stage, the second heating stage and the insulation stage, thereby improving the tap density of the precursor, increasing production capacity, and completely removing the moisture contained in the precursor, solving the problem of different phases of precursors with different compositions, and greatly facilitating the subsequent compounding and roasting process; at the same time, by adopting the specific pre-firing process, the pre-firing precursor obtained can increase the porosity and specific surface area while maintaining its own morphology, thereby improving the reaction activity, making it easier to react completely with the sodium source in the subsequent sodium compounding and roasting process, reducing the residual alkali on the surface of the positive electrode material, and improving the air stability.

[0056] In the present invention, unless otherwise specified, the fact that M and M' in the positive electrode material are not 0 at the same time means that in the preparation method of the positive electrode material, when the M superscript in the precursor composed of Formula II is 0, then the dopant containing M' must be added; or, when the dopant containing M' is not added, then the M superscript in the precursor composed of Formula II is not 0; or, when the M superscript in the precursor composed of Formula II is not 0, then the dopant containing M' is optional.

[0057] In some embodiments of the present invention, preferably, the average particle size D of the precursor 50 7.5-8.5μm, particle size distribution satisfies: 1≤(D 90 -D 10 ) / D 50 ≤1.5. Meeting the above parameters improves the compaction density and volume energy density of the positive electrode material.

[0058] In some embodiments of the present invention, preferably, the tap density of the precursor is 0.7-1.5 g / cm 3 , with a specific surface area of ​​30-100m 2 / g.

[0059] In the present invention, the primary particles of the precursor are arranged in a uniform sheet-like manner and have a dense surface. 50, particle size distribution, tap density and specific surface area, so that the positive electrode material has maximum compatible cycle performance and capacity.

[0060] In the present invention, the source of the precursor has a wide range of options, as long as the precursor has the composition of Formula II. Preferably, the precursor is prepared by the following method: a mixed metal salt solution containing a Ni source, an Fe source, a Mn source, and an M source, a precipitant solution, and a complexing agent solution are subjected to a coprecipitation reaction in a non-oxidizing atmosphere to obtain the precursor.

[0061] In the present invention, the non-oxidizing atmosphere includes but is not limited to nitrogen atmosphere, helium atmosphere, argon atmosphere, etc., and is preferably a nitrogen atmosphere.

[0062] In some embodiments of the present invention, in the mixed metal salt solution, the amounts of Ni source, Fe source, Mn source and M source satisfy n(Ni):n(Fe):n(Mn):n(M), wherein 0≤n(Ni)≤0.5, 0≤n(Fe)≤0.5, 0≤n(Mn)≤0.5, and 0≤n(M)≤0.5.

[0063] In some embodiments of the present invention, the concentration of the mixed metal salt solution is 1-5 mol / L, preferably 1-3 mol / L, calculated as metal elements.

[0064] In a specific embodiment of the present invention, the Ni source is selected from at least one of nickel sulfate, nickel nitrate and nickel chlorate, the Fe source is selected from at least one of iron sulfate, iron nitrate and iron chlorate; the Mn source is selected from at least one of manganese sulfate, manganese nitrate and manganese chlorate, and the M source is selected from at least one of sulfates, nitrates and chlorates containing M, that is, selected from at least one of sulfates, nitrates and chlorates containing Li, Cu, Co, V, Cr, Ti, Mg, Sn, Zn, Al, Zr, Sr, Nb, B, Y, W and La; preferably selected from at least one of sulfates, nitrates and chlorates containing Cu, Co, V, Cr, Ti, Mg, Sn, Zn, Al, Zr, Nb, Y, W and La.

[0065] In some embodiments of the present invention, the concentration of the precipitant solution is 3-10 mol / L. In the present invention, the precipitant in the precipitant solution is selected from conventional options in the art, including but not limited to NaOH, KOH, LiOH, etc.

[0066] In some embodiments of the present invention, the concentration of the complexing agent is 2-11 mol / L. In the present invention, the complexing agent in the complexing agent solution is selected from conventional options in the art, including but not limited to ammonia, ammonium bicarbonate, ammonium carbonate, citric acid and disodium edetate.

[0067] According to some embodiments of the present invention, the co-precipitation reaction preferably employs a batch method, specifically comprising: introducing the mixed metal salt solution containing the Ni source, Fe source, Mn source, and M source, the precipitant solution, and the complexing agent solution into a reactor using a metering pump over a predetermined period of time, and discharging the precipitate after sufficient crystallization and growth in the reactor. Using a batch method for the co-precipitation reaction facilitates obtaining a precursor with a wide particle size distribution.

[0068] In some embodiments of the present invention, preferably, the coprecipitation reaction conditions include: pH value of 10-12.5, temperature of 40-80° C., time of 48-120 h, and stirring speed of 100-800 rpm.

[0069] In some embodiments of the present invention, preferably, the precursor and the pre-fired precursor each independently have a spherical structure.

[0070] In the present invention, the product of the coprecipitation reaction is filtered, and the obtained filter cake is dried at a temperature of 100-140° C. and then sieved to obtain the precursor.

[0071] In some embodiments of the present invention, preferably, in step (1), the pre-calcined product is filtered, washed, and dried in sequence to obtain the pre-calcined precursor.

[0072] In some embodiments of the present invention, preferably, in step (2), the amounts of the pre-calcined precursor and the Na source satisfy n(Ni+Fe+Mn+M):n(Na)=0.8-1.1:1, for example, 0.8:1, 0.85:1, 0.93:1, 0.95:1, 1:1, 1.03:1, 1.05:1, 1.1:1, and any value in the range of any two values, preferably satisfying n(Ni+Fe+Mn+M):n(Na)=0.85-1.05:1, more preferably satisfying n(Ni+Fe+Mn+M):n(Na)=0.93-1.03:1.

[0073] In some embodiments of the present invention, preferably, in step (2), the Na source is selected from at least one of sodium carbonate, sodium hydroxide, sodium nitrate and sodium oxide.

[0074] In some embodiments of the present invention, preferably, the dopant is selected from at least one of oxides, phosphates, carbonates, fluorides, chlorides, hydroxides and silicides containing M' elements, that is, at least one of sulfates, nitrates and chlorates containing Li, Cu, Co, V, Cr, Ti, Mg, Sn, Zn, Al, Zr, Sr, Nb, B, Y, W and La, preferably selected from at least one of sulfates, nitrates and chlorates containing Li, Al, Mg, Ti, Zr, Sr, La, Nb, B, At least one of the sulfates, nitrates and chlorates of W, more preferably at least one selected from Li2CO3, Al2O3, AlPO4, AlCl3, MgO, Mg3(PO4)2, MgCO3, MgSi2, MgF2, MgCl2, TiO2, ZrO, Zr(HPO4)2, ZrSi2, Sr(OH)2, SrCO3, SrSi2, SrF2, SrCl2, La2O3, Nb2O5, B2O3, WO3.

[0075] In some embodiments of the present invention, preferably, in step (2), the calcination conditions include: a temperature selected from 900-1100° C.; and a time selected from 5-15 h.

[0076] In some embodiments of the present invention, it is further preferred that the roasting includes: a heating stage I, a heating stage II and a constant temperature stage, the difference between the oxygen concentration in the atmosphere of the heating stage II and the oxygen concentration in the atmosphere of the heating stage I is 10-100 vol%, and the difference between the heating rate of the heating stage I and the heating rate of the heating stage II is 2-15°C / min.

[0077] In the present invention, unless otherwise specified, the difference between the oxygen concentration in the atmosphere of the heating stage II and the oxygen concentration in the atmosphere of the heating stage I is 10-100 vol%, which means that the oxygen concentration in the atmosphere of the heating stage II is higher than the oxygen concentration in the atmosphere of the heating stage I, and the difference between the two is 10-100 vol%; the difference between the heating rate of the heating stage I and the heating rate of the heating stage II is 2-15°C / min, which means that the heating rate of the heating stage I is higher than the heating rate of the heating stage II, and the difference between the two is 2-15°C / min.

[0078] In the present invention, unless otherwise specified, the difference between the oxygen concentration in the atmosphere of the heating stage II and the oxygen concentration in the atmosphere of the heating stage I is 10-100 vol%, which means that the oxygen concentration in the atmosphere of the heating stage II is higher than the oxygen concentration in the atmosphere of the heating stage I, and the difference between the two is 10-100 vol%; the difference between the heating rate of the heating stage I and the heating rate of the heating stage II is 2-15°C / min, which means that the heating rate of the heating stage I is higher than the heating rate of the heating stage II, and the difference between the two is 2-15°C / min.

[0079] In some embodiments of the present invention, preferably, the conditions of the heating stage I include: heating to T1' at a heating rate of v1' in an oxygen-depleted atmosphere with an oxygen concentration ≤10 vol%; the conditions of the heating stage II include: heating to T2' at a heating rate of v2' in an atmosphere with an oxygen concentration ≥20 vol%; the conditions of the constant temperature stage include: keeping warm for t' in a temperature range of (T2'-10)≤T'≤(T2'+10); wherein, v1'≥3°C / min, v2'≤1°C / min, T1' is selected from 600-800°C, T2' is selected from 900-1100°C; and t' is selected from 5-15h.

[0080] In some embodiments of the present invention, preferably, in step (2), the method further comprises: cooling, crushing, and sieving the calcined product in sequence to obtain the positive electrode material.

[0081] In the present invention, the cathode material prepared by the preparation method provided by the present invention has a composition shown in Formula I: Na a (Ni x Fe y Mn z M m M' n )O2 (I), wherein 0.8≤a≤1.1, 0≤x≤0.5, 0≤y≤0.5, 0≤z≤0.5, 0≤m≤0.5, 0≤n≤0.2, 0.05≤m+n≤0.5, m and n are not simultaneously 0, and x+y+z+m+n=1; M and M' are each independently selected from at least one element of Li, Cu, Co, V, Cr, Ti, Mg, Sn, Zn, Al, Zr, Sr, Nb, B, Y, W, and La; Further preferably, in Formula I, 0.85≤a≤1.05, M is selected from at least one element of Cu, Co, V, Cr, Ti, Mg, Sn, Zn, Al, Zr, Nb, Y, W and La, and M' is selected from at least one element of Li, Al, Mg, Ti, Zr, Sr, La, Nb, B and W; more preferably, in Formula I, 0.93≤a≤1.03, and M and M' are different.

[0082] The third aspect of the present invention provides a sodium ion battery containing the positive electrode material provided by the first aspect, or the positive electrode material prepared by the preparation method provided by the second aspect.

[0083] In the present invention, the positive electrode material is used in a sodium ion battery, which can effectively improve the electrochemical performance of the sodium ion battery, especially the rate performance, cycle performance and volume energy density.

[0084] The present invention will be described in detail below through examples.

[0085] (1) The compositions of the precursor, pre-calcined precursor, and cathode material were measured using the ICP method. The instrument used was a PE Optima 7000DV. The test conditions were as follows: 0.1 g of sample was completely dissolved in a mixed acid solution of 3 mL HNO3 + 9 mL HCl and diluted to 250 mL for testing.

[0086] (2) The morphology of the material was observed by scanning electron microscopy (SEM), using a scanning electron microscope S-4800 from Hitachi, Japan;

[0087] (3) The particle size of the precursor and cathode materials was measured using a Malvern particle size analyzer;

[0088] (4) The crystal structure of the cathode material was tested by XRD; the instrument used was an X-ray diffractometer (Smart Lab 9KW, Rigaku), and the test conditions were: the X-ray source was Cu Kα radiation, the scanning range was 10°-80°, the scanning rate was 1.2° / min, and the sampling width was 0.02°;

[0089] (5) The compaction density of the positive electrode material was measured by powder compaction method; the instrument used was a powder compactor (MCP-PD51) and the test condition was 20 kN;

[0090] (6) The tap density of the precursor is measured using the fixed mass method; the specific surface area of ​​the precursor is measured using the BET specific surface area test method;

[0091] (7) Crystallite size ratio D A / D B The following method is used to measure: fill the cathode material into a dedicated substrate, use a CuKα ray source at a diffraction angle of 2θ A =15-19° and 2θ B=39-44°, with a sampling width of 0.02° and a scanning speed of 1.2° / min, half-spectrum measurements were performed to obtain the powder X-ray diffraction patterns of peak A and peak B, respectively. Using the powder X-ray diffraction pattern comprehensive analysis software JADE 6.5, the half-peak widths were calculated for peak A appearing in the range of 2θ = 16.5 ± 1° and peak B appearing in the range of 2θ = 41.5 ± 1° from the powder X-ray diffraction patterns obtained by the powder X-ray diffraction measurement. Using the obtained half-peak widths, the crystallite size D was calculated according to the Scherrer formula. A and crystallite size D B , and then the crystallite size ratio is obtained.

[0092] (8) Electrochemical performance test: In the following examples and comparative examples, the electrochemical performance of the positive electrode materials was tested using R2025 button-type sodium ion batteries.

[0093] The preparation process of sodium ion batteries is as follows:

[0094] Pole sheet preparation: The sodium ion battery positive electrode material, conductive agent SuperP and polyvinylidene fluoride (PVDF) are fully mixed with an appropriate amount of N-methylpyrrolidone (NMP) in a mass ratio of 90:5:5 to form a uniform slurry. The slurry is coated on aluminum foil and dried at 120°C for 12 hours. It is then stamped into a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm using a pressure of 100 MPa.

[0095] Battery Assembly: In an argon-filled glove box with water and oxygen contents less than 5 ppm, the positive electrode, separator, negative electrode, and electrolyte were assembled into an R2025 button-type sodium-ion battery and allowed to rest for 6 hours. The negative electrode used a 14 mm diameter, 1 mm thick sodium metal sheet; the separator used a 25 μm thick rubber-coated separator; and the electrolyte used a 4:6 mixture of 1 mol / L NaPF6, ethyl methyl carbonate (EMC), and propylene carbonate (PC).

[0096] Electrochemical performance test:

[0097] In the following examples and comparative examples, electrochemical performance tests were conducted on R2025 button-type sodium-ion batteries using a Shenzhen Xinweier Battery Testing System (CT3008). The initial charge and discharge capacity test conditions were 0.1C @ 2-4.0V, 25°C, and a constant voltage cutoff current of 0.02C. The cycling performance test conditions were 1.0C @ 2-4.0V, 25°C. Constant current charge and discharge tests were conducted on the button-type sodium-ion batteries at 0.1C and 1C, respectively, to evaluate the charge and discharge specific capacity, cycling performance, and volumetric energy density of the sodium-ion battery cathode material. A higher capacity retention rate during cycling indicates greater material stability and better cycling performance of the battery system.

[0098] Example 1

[0099] S1. Dissolve nickel sulfate, iron sulfate, manganese sulfate, and copper sulfate in a molar ratio of nickel, iron, manganese, and copper of 20:30:40:10 to obtain a 2 mol / L mixed metal salt solution; dissolve sodium hydroxide to obtain a precipitant solution with a concentration of 8 mol / L; and dissolve ammonia water to obtain a complexing agent solution with a concentration of 10.4 mol / L.

[0100] The 100 L mixed metal salt solution, the precipitant solution, and the complexing agent solution were introduced into a reactor in parallel to carry out a co-precipitation reaction. Then, under the protection of an argon atmosphere, the precipitate crystals were continuously controlled to grow in an overflow device until the average particle size of the particles reached 8 μm. The precursor slurry was filtered and washed, and the filter cake was dried at 120° C. and sieved to obtain a precursor (the composition and physical properties are listed in Table 1).

[0101] The conditions of the above coprecipitation reaction include: temperature of 60°C, pH of 12.38;

[0102] S2. Pre-calcining the precursor, and naturally cooling the obtained pre-calcined product to obtain a pre-calcined precursor (composition see Table 1);

[0103] The conditions of the first heating stage included: heating from 25°C to T1 = 250°C at a heating rate of v1 = 6°C / min in an oxygen-poor atmosphere with an oxygen concentration of 10 vol%;

[0104] The conditions of the second heating stage include: heating from 250°C to T2 = 550°C at a heating rate of v2 = 2°C / min in an atmosphere with an oxygen concentration of 20 vol%;

[0105] The conditions of the holding stage include: holding in the temperature range of T = 540-560°C for t = 4h;

[0106] S3, calcining the above-mentioned pre-calcined precursor with Na2CO3, cooling, crushing, and screening to obtain O3 type single crystal positive electrode material S1 (composition, crystal form, and physical properties are listed in Table 1);

[0107] The amounts of the above-mentioned pre-calcined precursor and Na source satisfy n(Ni+Fe+Mn+Cu):n(Na)=1:0.96;

[0108] The conditions of the heating stage I include: heating from 25°C to T1′=700°C at a heating rate of v1′=3°C / min in an oxygen-depleted atmosphere with an oxygen concentration of 10 vol%;

[0109] The conditions of the heating stage II include: heating from 700°C to T2′=950°C at a heating rate of v2′=1°C / min in an atmosphere with an oxygen concentration of 20 vol%;

[0110] The conditions of the constant temperature stage include: keeping the temperature within the range of T'=950°C for t'=15h.

[0111] Example 2

[0112] According to the method of Example 1, the difference is that

[0113] In step S2, the temperature in the second heating stage is T2 = 450°C; the temperature in the heat preservation stage is T = 440-460°C;

[0114] The remaining conditions are the same, and the O3 type single crystal positive electrode material S2 is obtained.

[0115] Example 3

[0116] According to the method of Example 1, the difference is that

[0117] In step S3, the precursor, Na2CO3 and Al2O3 are calcined, cooled, crushed and sieved to obtain the positive electrode material S3 (composition, crystal form and physical properties are listed in Table 1);

[0118] The amount of Al2O3 mentioned above satisfies n(Al):n(Ni+Fe+Mn+Cu+Al)=0.05;

[0119] The remaining conditions are the same, and the O3 type single crystal positive electrode material S3 is obtained.

[0120] Example 4

[0121] According to the method of Example 1, the difference is that

[0122] In step S2, the time in the heat preservation stage is t=10h;

[0123] The remaining conditions are the same, and the O3 type single crystal positive electrode material S4 is obtained.

[0124] Example 5

[0125] According to the method of Example 1, the difference is that

[0126] In step S2, the heating rate v1 in the first heating stage is 10°C / min, and the heating rate v2 in the second heating stage is 1°C / min;

[0127] The remaining conditions were the same, and the O3-type single crystal positive electrode material S5 was obtained.

[0128] Example 6

[0129] According to the method of Example 1, the difference is that

[0130] In step S1, the particle size distribution K of the precursor is adjusted by regulating the crystal growth of the precipitate. 90 =(D 90 -D 10 ) / D 50 =1;

[0131] The remaining conditions were the same, and O3-type single crystal positive electrode material S6 was obtained.

[0132] Example 7

[0133] According to the method of Example 1, the difference is that

[0134] In step S1, nickel sulfate, iron sulfate, manganese sulfate, and copper sulfate are dissolved in a molar ratio of nickel, iron, manganese, and copper of 22:25:42:11 to obtain a 2 mol / L mixed salt solution;

[0135] The remaining conditions were the same, and the O3-type single crystal positive electrode material S7 was obtained.

[0136] Example 8

[0137] According to the method of Example 1, the difference is that

[0138] In step S1, the particle size distribution K of the precursor is adjusted by regulating the crystal growth of the precipitate. 90 =(D 90 -D 10 ) / D 50 =0.8;

[0139] The remaining conditions were the same, and O3-type single crystal positive electrode material S8 was obtained.

[0140] Comparative Example 1

[0141] The method of Example 1 is the same as that of Example 1, except that there is no step S2.

[0142] That is, the precursor prepared in step S1 is directly subjected to the calcination treatment in step S3.

[0143] The other conditions were the same, and the O3 type single crystal positive electrode material DS1 was obtained.

[0144] Comparative Example 2

[0145] According to the method of Example 1, the difference is that

[0146] In step S2, the temperature in the second heating stage is T2 = 300°C; the temperature in the heat preservation stage is T = 290-310°C;

[0147] The other conditions were the same, and the O3-type single crystal positive electrode material DS2 was obtained.

[0148] Comparative Example 3

[0149] The method of Example 1 is as follows, except that

[0150] In step S2, the temperature in the second heating stage is T2 = 1000°C; the temperature in the heat preservation stage is T = 990-1010°C;

[0151] The other conditions were the same, and the O3 type single crystal positive electrode material DS3 was obtained.

[0152] Comparative Example 4

[0153] The method of Example 1 is as follows, except that

[0154] In step S2, the time in the heat preservation stage is t=1h;

[0155] The other conditions were the same, and the O3 type single crystal positive electrode material DS4 was obtained.

[0156] Comparative Example 5

[0157] The method of Example 1 is as follows, except that

[0158] In step S2, the heating rate of the second heating stage is v2 = 10°C / min;

[0159] The other conditions were the same, and the O3-type single crystal positive electrode material DS5 was obtained.

[0160] Comparative Example 6

[0161] The method of Example 1 is as follows, except that

[0162] In step S2, there is no first heating stage, that is, the precursor is directly heated from 25°C to T2 = 550°C at a heating rate of v2 = 2°C / min in an atmosphere with an oxygen concentration of 20 vol%, and then kept in the temperature range of T = 540-560°C for t = 4h;

[0163] The other conditions were the same, and the O3-type single crystal positive electrode material DS6 was obtained.

[0164] Table 1 Note: K 90 =(D 90 -D 10 ) / D 50 .

[0165] Table 1

[0166] Table 1 Note: 1- refers to the amount of Na source and pre-fired precursor satisfying n(Na):n(Ni+Fe+Mn+Cu); 2- refers to the amount of dopant satisfying n(M'):n(Ni+Fe+Mn+M+M').

[0167] Table 1

[0168] Table 1

[0169] From the results in Table 1, it can be seen that compared with Comparative Examples 1-6, the positive electrode materials prepared by the method provided by the present invention in Examples 1-8 meet the requirement of 1.3≤D A / D B ≤2.5, especially 1.3≤D A / D B ≤2, and the c value is selected from

[0170] Compared with Example 8, the particle size distribution of the precursors in Examples 1-7 is regulated to meet the following requirements: 1≤(D 90 -D 10 ) / D 50 ≤1.5, which more effectively improves the compaction density of the positive electrode material and the volume energy density of the electrode made of the positive electrode material.

[0171] Test Case

[0172] (1) Morphology test

[0173] The present invention tests the scanning electron microscope images of the precursors, pre-calcined precursors and O3 type single crystal positive electrode materials prepared in the above-mentioned embodiments and comparative examples, and exemplarily provides SEM images of the precursor, pre-calcined precursor and O3 type single crystal positive electrode material S1 prepared in Example 1. The results are shown in Figures 1 to 3, respectively. As can be seen from Figure 1, the particle size distribution of the above-mentioned precursor is wide, and the surfaces of large and small particles are dense; as can be seen from Figure 2, the pre-calcined precursor still maintains the sphericity and wide distribution of the precursor, and its surface is more rounded and dense; as can be seen from Figure 3, the surfaces of large and small single crystal particles of the O3 type single crystal positive electrode material S1 are smooth and round, and the particle size distribution is wide, small particles are filled between large particles, and have good grading performance.

[0174] (2) Physical property testing

[0175] The present invention tests the XRD of the precursor, pre-calcined precursor and O3 type single crystal positive electrode material S1 in the above examples and comparative examples, and provides the XRD images of the precursor, pre-calcined precursor and O3 type single crystal positive electrode material S1 prepared in Example 1 as an example. The results are shown in Figures 4-6 respectively. As can be seen from Figure 4, the phase of the precursor is 1 / 4 (Ni 0.2Fe 0.3 Mn 0.4 Cu 0.1 )OOH@3 / 4(Ni 0.2 Fe 0.3 Mn 0.4 Cu 0.1 )O 4 / 3 Composite phase; As can be seen from Figure 5, the phase of the pre-fired precursor is (Ni 0.2 Fe 0.3 Mn 0.4 Cu 0.1 )3O4 pure phase; As can be seen from Figure 6, the phase of the single crystal cathode material S1 is a sodium-ion O3 type layered oxide (Na 0.96 Ni 0.2 Fe 0.3 Mn 0.4 Cu 0.1 O2).

[0176] The O3-type single crystal cathode material samples prepared in the above examples and comparative examples were simultaneously exposed to air at a relative humidity of 45% for 0-6 hours. The precise moisture content, residual alkali content, and XRD characteristic diffraction peak parameters are shown in Table 2.

[0177] Water increment Δ(H2O)=H2O(t x -t0) / H2O(t0), 0h<t x ≤6h, t0=0h;

[0178] Residual alkali conversion Δ(Na2CO3+NaOH)=Na2CO3(t x -t0) / Na2CO3(t0)+NaOH(t x -t0) / NaOH(t0), 0h<t x ≤6h, t0=0h.

[0179] Table 2

[0180] Table 2

[0181] Table 2

[0182] Table 2

[0183] Table 2

[0184] Table 2

[0185] Table 2

[0186] It can be seen from the data in Table 2 that, compared with Comparative Examples 1-6, the positive electrode materials prepared by the preparation method provided by Examples 1-8 absorb less water in the air, and the conversion amount of Na2CO3 and NaOH is less, less Na is released by reacting with water and carbon dioxide in the air, and the interlayer spacing changes less, showing that the peak position of the characteristic diffraction peak A of the (003) crystal plane does not shift significantly.

[0187] Compared with Example 1, Comparative Example 1 adopts the technical solution of directly calcining the precursor, and the obtained positive electrode material absorbs a greater degree of water in the air, and the conversion amount of Na2CO3 and NaOH is relatively large.

[0188] By comparing Example 1 and Comparative Examples 2-6, it can be seen that by adjusting the sintering conditions, that is, the sintering temperature, the heating rate and the sintering time, the water content increase and the residual alkali conversion rate of the positive electrode material can be adjusted.

[0189] (3) Electrochemical performance test

[0190] The present invention tests the electrochemical properties of the sodium ion battery positive electrode materials prepared in the above embodiments and comparative examples, including 0.1C first discharge specific capacity, 0.1C first discharge specific capacity, rate performance, cycle performance and volume energy density. The specific test results are shown in Table 3.

[0191] Table 3

[0192] From the data in Table 3, it can be seen that in the sodium ion battery positive electrode material provided by the present invention, after the precursor is sintered by a specific sintering process, in particular, the particle size distribution of the precursor is regulated to meet 1≤(D 90 -D 10 ) / D 50 ≤1.5, the obtained pre-calcined precursor has better structural stability and reaction activity; at the same time, the positive electrode material made from the pre-calcined precursor has better air stability and structural stability. It can greatly improve the rate performance and cycle performance of the positive electrode material of sodium ion battery, especially by further limiting the median particle size D of the precursor. 50 and particle size distribution K 90 It can further improve the compaction density of sodium-ion positive electrode materials and increase the volume energy density; in addition, by doping elements, the rate performance and cycle performance of sodium-ion battery positive electrode materials can be further improved.

[0193] Comparison of Example 1 and Comparative Example 1 shows that after the precursor is pre-sintered, the cathode material produced has better rate performance and cycle performance. In other words, the pre-sintering scheme provided by the present invention is conducive to improving the structural stability and reactivity of the material. Compared with the sodium cathode material directly produced from the precursor without pre-sintering treatment, the sodium cathode material produced has the comprehensive performance of high capacity, high rate and long cycle.

[0194] Comparison of Example 1 and Comparative Examples 2-3 shows that when the pre-firing temperature is within the preferred range, the positive electrode material prepared therefrom has better rate performance, cycle performance and air stability.

[0195] By comparing Example 1 and Comparative Example 4, it can be seen that when the pre-burning time is within the preferred range, the structural stability of the sodium ion battery positive electrode material can be further enhanced, and its rate performance, cycle performance and air stability can be further improved.

[0196] By comparing Example 1, Example 5 and Comparative Example 5, it can be seen that when the pre-calcination heating rate is within the preferred range, the structural stability of the sodium ion battery positive electrode material can be further enhanced, and its rate performance, cycle performance and air stability can be further improved.

[0197] Comparison of Example 1 and Comparative Example 6 shows that, compared with the one-stage pre-firing treatment of the precursor, the rate performance, cycle performance and air stability after the two-stage pre-firing treatment are much better.

[0198] Comparing the test results of Example 1 and Example 3, it can be seen that different types of doping elements in the sodium ion battery positive electrode material can further enhance the stability of the single crystal structure and further improve the cycle performance and rate performance of the sodium ion battery positive electrode material.

[0199] Comparing the test results of Example 1 and Example 8, it can be seen that when the particle size distribution of the precursor A is outside the preferred range, the compaction density of its sodium ion battery positive electrode material will be significantly reduced, and the volume energy density will also be reduced.

[0200] By comparing the crystallite size ratio D of the embodiment and the comparative example A / D B As can be seen from the results of the unit cell parameter c value, the positive electrode material prepared within the preferred condition range has a crystallite size larger than D A / D B In the range of 1.3-2.5 and c value selected from 16-16.1, the composite exhibits better rate performance and significantly improved air stability compared to the comparative example.

[0201] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A sodium ion battery positive electrode material, characterized in that: In the XRD spectrum of the positive electrode material, there are characteristic diffraction peaks A and B of the (003) crystal plane and the (104) crystal plane at 2θ of 15-19° and 39-44°, respectively; wherein the crystallite size D of the characteristic diffraction peak A is A and the crystallite size D of the characteristic diffraction peak B B Satisfy: 1.3≤D A / D B ≤2.5, where D A and D B These correspond to the crystallite sizes in the directions perpendicular to the (003) and (104) crystal planes, respectively.

2. The positive electrode material according to claim 1, wherein The positive electrode material has an O3 type single crystal structure, and the c value is selected from And / or, in the XRD spectrum of the positive electrode material, the 2θ of the characteristic diffraction peak A is 16.5±1°, and the 2θ of the characteristic diffraction peak B is 41.5±1°; And / or, the crystallite size D of the characteristic diffraction peak A A and the crystallite size D of the characteristic diffraction peak B B Satisfy: 1.3≤D A / D B ≤2.

3. The positive electrode material according to claim 1 or 2, wherein The positive electrode material has a composition shown in Formula I: And a (You x Fe y Mn z I m I n )O2 (I), In formula I, 0.8≤a≤1.1, 0≤x≤0.5, 0≤y≤0.5, 0≤z≤0.5, 0≤m≤0.5, 0≤n≤0.2, 0.05≤m+n≤0.5, m and n are not 0 at the same time, x+y+z+m+n=1; M and M' are each independently selected from at least one element of Li, Cu, Co, V, Cr, Ti, Mg, Sn, Zn, Al, Zr, Sr, Nb, B, Y, W and La; Preferably, in Formula I, 0.85≤a≤1.05; further preferably, 0.93≤a≤1.03; Preferably, in Formula I, M is selected from at least one element of Cu, Co, V, Cr, Ti, Mg, Sn, Zn, Al, Zr, Nb, Y, W and La, and M' is selected from at least one element of Li, Al, Mg, Ti, Zr, Sr, La, Nb, B and W; further preferably, M and M' are different.

4. The positive electrode material according to any one of claims 1 to 3, wherein The average particle size D of the positive electrode material 50 7-20 μm, preferably 8-16 μm, more preferably 9-12 μm; And / or, the particle size distribution of the positive electrode material satisfies: 1.2≤(D 90 -D 10 ) / D 50 ≤1.8, preferably 1.4≤(D 90 -D 10 ) / D 50 ≤1.6; And / or, the compaction density of the positive electrode material is 3-3.6 g / cm 3 , preferably 3.3-3.6 g / cm 3 ; And / or, the water increment of the positive electrode material Δ(H2O)=H2O(t x -t0) / H2O(t0), 0h<t x ≤6h, t0=0h, satisfying: 0%≤Δ(H2O)≤120%, preferably 0%≤Δ(H2O)≤100%; And / or, the residual alkali conversion rate of the positive electrode material Δ(Na2CO3+NaOH)=Na2CO3(t x -t0) / Na2CO3(t0)+NaOH(t x -t0) / NaOH(t0), 0h<t x ≤6h, t0=0h, satisfying: 0%≤Δ(Na2CO3+NaOH)≤200%, preferably 0%≤Δ(Na2CO3+NaOH)≤150%.

5. A method for preparing a positive electrode material for a sodium ion battery, characterized in that: The preparation method comprises the following steps: (1) Ni α Fe β Mn γ M δ O a H b (II) pre-calcining a precursor with the composition shown in FIG. 1 to obtain a pre-calcined precursor; (2) mixing the pre-calcined precursor, the Na source and an optional dopant containing M' and calcining the mixture to obtain a positive electrode material; wherein M and M' in the positive electrode material are not simultaneously 0; Wherein, in formula II, 0≤α≤0.5, 0≤β≤0.5, 0≤γ≤0.5, 0≤δ≤0.5, 1≤a≤2, 0≤b≤2, α+β+γ+δ=1, M and M' are each independently selected from at least one element of Li, Cu, Co, V, Cr, Ti, Mg, Sn, Zn, Al, Zr, Sr, Nb, B, Y, W and La; The pre-burning includes a first heating stage, a second heating stage and a heat preservation stage. The conditions of the first heating stage include: heating to T1 at a heating rate of v1 in an oxygen-poor atmosphere with an oxygen concentration of ≤10 vol%; the conditions of the second heating stage include: heating to T2 at a heating rate of v2 in an oxygen-poor atmosphere with an oxygen concentration of ≤20 vol%; the conditions of the heat preservation stage include: heat preservation for t in a temperature range of (T2-10)≤T≤(T2+10); Wherein, v1 is selected from 5-10°C / min, v2 is selected from 1-3°C / min, T1 is selected from 200-300°C, T2 is selected from 450-750°C; and t is selected from 3-10h.

6. The preparation method according to claim 5, wherein: In step (1), the average particle size D of the precursor is 50 7.5-8.5μm, particle size distribution satisfies: 1≤(D 90 -D 10 ) / D 50 ≤1.5; And / or, the tap density of the precursor is 0.7-1.5 g / cm 3 , with a specific surface area of ​​30-100m 2 / g; And / or, the precursor is prepared by the following method: in a non-oxidizing atmosphere, a mixed metal salt solution containing a Ni source, a Fe source, a Mn source and an M source, a precipitant solution and a complexing agent solution are subjected to a co-precipitation reaction to obtain the precursor; And / or, the precursor and the pre-fired precursor each independently have a spherical structure.

7. The preparation method according to claim 5 or 6, wherein: In step (2), the amount of the pre-calcined precursor and the Na source satisfies n(Ni+Fe+Mn+M):n(Na)=0.8-1.1:1, preferably satisfies n(Ni+Fe+Mn+M):n(Na)=0.85-1.05:1, and more preferably satisfies n(Ni+Fe+Mn+M):n(Na)=0.93-1.03:1; And / or, the amount of component C satisfies: n(M'):n(Ni+Fe+Mn+M+M')=0-0.2:1; And / or, the dopant is selected from at least one of oxides, phosphates, carbonates, fluorides, chlorides, hydroxides and silicides containing the element M', preferably selected from at least one of Li2CO3, Al2O3, AlPO4, AlCl3, MgO, Mg3(PO4)2, MgCO3, MgSi2, MgF2, MgCl2, TiO2, ZrO, Zr(HPO4)2, ZrSi2, Sr(OH)2, SrCO3, SrSi2, SrF2, SrCl2, La2O3, Nb2O5, B2O3 and WO3.

8. The preparation method according to any one of claims 5 to 7, wherein: In step (2), the calcination conditions include: a temperature selected from 900-1100° C.; a time selected from 5-15 h; And / or, the roasting comprises: a heating stage I, a heating stage II and a constant temperature stage, wherein the heating stage II The difference between the oxygen concentration in the atmosphere of the heating stage I and the oxygen concentration in the atmosphere of the heating stage I is 10-100 vol%, and the difference between the heating rate of the heating stage I and the heating rate of the heating stage II is 2-15°C / min; Preferably, the conditions of the heating stage I include: heating to T1' at a heating rate of v1' in an oxygen-depleted atmosphere with an oxygen concentration of ≤10 vol%; the conditions of the heating stage II include: heating to T2' at a heating rate of v2' in an atmosphere with an oxygen concentration of ≥20 vol%; the conditions of the constant temperature stage include: keeping warm for t' in a temperature range of (T2'-10)≤T'≤(T2'+10); wherein v1'≥3°C / min, v2'≤1°C / min, T1' is selected from 600-800°C, T2' is selected from 900-1100°C; t' is selected from 5-15h.

9. The preparation method according to any one of claims 5 to 8, wherein: The positive electrode material has a composition shown in Formula I: And a (You x Fe y Mn z I m I n )O2 (I), In formula I, 0.8≤a≤1.1, 0≤x≤0.5, 0≤y≤0.5, 0≤z≤0.5, 0≤m≤0.5, 0≤n≤0.2, 0.05≤m+n≤0.5, m and n are not 0 at the same time, x+y+z+m+n=1; M and M' are each independently selected from at least one element of Li, Cu, Co, V, Cr, Ti, Mg, Sn, Zn, Al, Zr, Sr, Nb, B, Y, W and La; Preferably, in Formula I, 0.85≤a≤1.05; further preferably, in Formula I, 0.93≤a≤1.03; Preferably, in Formula I, M is selected from at least one element of Cu, Co, V, Cr, Ti, Mg, Sn, Zn, Al, Zr, Nb, Y, W and La, and M' is selected from at least one element of Li, Al, Mg, Ti, Zr, Sr, La, Nb, B and W; further preferably, M and M' are different.

10. A sodium ion battery, characterized in that: The sodium ion battery has the positive electrode material described in any one of claims 1 to 5, or the positive electrode material prepared by the preparation method described in any one of claims 6 to 9.

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