Positive electrode active material and preparation method therefor, positive electrode sheet, battery and electric device

Abstract

The present invention relates to the technical field of batteries, and provides a positive electrode active material and a preparation method therefor, a positive electrode sheet, a battery, and an electric device. In the positive electrode active material, the content change of Fe2+ satisfies Δn≥0.1, wherein Δn=n1-n2, where n1 is the content of Fe2+ in the positive electrode active material before charging; n2 is the content of Fe2+ in the positive electrode active material when the material is charged to 4.0 V; and the content of Fe2+ = the amount of substance of Fe2+ in the positive electrode active material / (the amount of substance of Fe2+ in the positive electrode active material + the amount of substance of Fe3+ in the positive electrode active material). Therefore, by means of the positive electrode active material, a battery loaded with same is allowed to have a good energy density.

Description

Positive electrode active material, preparation method thereof, positive electrode sheet, battery and electric device

[0001] Priority information

[0002] The present application claims priority to and the benefit of Chinese Patent Application No. 202410869502.1, filed on June 28, 2024, and which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application belongs to the field of batteries, and particularly relates to a positive electrode active material, a preparation method thereof, a positive electrode sheet, a battery and an electric device. BACKGROUND

[0004] In recent years, lithium ion batteries have developed rapidly and are widely used in new energy vehicles, energy storage power stations and digital 3C products. However, the price of lithium resources fluctuates greatly with market conditions. Under the current industry background, sodium ion batteries, with abundant sodium resources and low price, have the same working mechanism as lithium ion batteries, can greatly reduce the manufacturing cost of batteries, and are expected to be widely used in low-speed electric vehicles and energy storage fields.

[0005] In the sodium ion battery system, the positive electrode material is mainly divided into three types of layered oxides, polyanion and prussian blue. Among them, the layered oxide (Na x MO2) material has been first applied in the medium and low-end passenger car, energy storage system and other markets due to its high energy density, good low temperature performance, simple process and easy mass production.

[0006] However, with the decline of lithium price, the Na x MO2 material gradually loses the cost advantage and urgently needs to further improve the energy density and reduce the material watt-hour cost. Therefore, how to solve the above problems of the Na x MO2 material and improve the energy density of the material has become a subject to be studied and solved by the present application.

[0007] SUMMARY

[0008] The present application aims to at least partially solve one of the problems in the related art. To this end, one object of the present application is to provide a positive electrode active material, a preparation method thereof, a positive electrode sheet, a battery and an electric device, which has a high capacity and makes the battery containing the same have excellent energy density.

[0009] In one aspect of the present application, the present application provides a positive electrode active material, wherein the Fe 2+ content in the positive electrode active material changes by Δn≥0.1, Δn=n1-n2; wherein n1 is the Fe 2+content; n2 is the content of Fe in the positive electrode active material when charged to 4.0 V 2+ content; Fe 2+ content = Fe in the positive electrode active material 2+ amount of substance / Fe in the positive electrode active material 2+ amount of substance + Fe in the positive electrode active material 3+ amount of substance).

[0010] According to the positive electrode active material of the embodiments of the present application, during charging to 4.0 V, the change Δn of the content of Fe 2+ is ≥0.1, so that more Fe 2+ is converted into Fe 3+ , the change of the content of Fe 2+ is large, so that more electrons can be transferred during the charging process, improving the capacity of the positive electrode active material, and further improving the energy density of the battery containing it.

[0011] In addition, the positive electrode active material according to the above embodiments of the present application can also have the following additional technical features:

[0012] In some embodiments of the present application, Δn≥0.15.

[0013] In some embodiments of the present application, n1 is greater than 50%; preferably, n1 is greater than 70%; further preferably, n1 is greater than 80%.

[0014] In some embodiments of the present application, the positive electrode active material comprises:

[0015] Na a1 Ni x1 Fe y1 Mn z1 Zn m1 Ca n1 M p1 O2,

[0016] wherein 0.90≤a1≤1.10, 0≤x1≤0.5, 0

[0017] M comprises at least one of Cu, Ti, Mg, Sr, Sn, Sb, Zn, Zr, Nb, Y, W and La.

[0018] In some embodiments of the present application, a1:(x1+y1+z1+m1+n1+p1)=(0.90-1.05):1, preferably (0.95-1.05):1; further preferably (0.97-1.03):1.

[0019] In some embodiments of the present application, 0.01 < m1 < 0.2, preferably 0.05 < m1 < 0.1.

[0020] In some embodiments of the present application, 0.01 < n1 < 0.05.

[0021] In some embodiments of the present application, the ionic radius r(M) of M is greater than 0.06 nm.

[0022] In some embodiments of the present application, the positive electrode active material is a O3-type sodium-ion battery layered oxide.

[0023] In some embodiments of the present application, the D50 of the positive electrode active material is 3-12 μm, preferably 4-10 μm, and further preferably 5-8 μm. 50 In some embodiments of the present application, the particle size distribution of the positive electrode active material is 1.1 < (D

[0024] In some embodiments of the present application, the particle size distribution of the positive electrode active material is 1.1 < (D 90 -D 10 ) / D 50 < 1.6, preferably 1.2 < (D 90 -D 10 ) / D 50 < 1.4.

[0025] In a second aspect of the present application, a method for preparing the above positive electrode active material is provided, comprising:

[0026] mixing a Na source, a positive electrode active material precursor, optionally a Zn source, optionally a Ca source, and optionally a M source in a stoichiometric ratio to obtain a mixture, wherein the positive electrode active material precursor comprises Fe;

[0027] calcining the mixture in an oxidizing atmosphere, crushing, and sieving to obtain the positive electrode active material.

[0028] Thus, the above positive electrode active material can be prepared by using the method, and the Zn is added to the sodium-ion battery layered oxide, the initial Fe 2+ is higher, which is beneficial to transferring more electrons through Fe 2+ / Fe 3+ oxidation reaction during charging, providing more capacity, and further improving the energy density of the battery.

[0029] In some embodiments of the present application, the ratio of the amount of substance of Na to the sum of the amounts of substance of Ni, Fe, Mn, Zn, Ca, and M is 0.90-1.10, preferably 0.97-1.03.

[0030] In some embodiments of the present application, the calcination temperature is 900-1100°C.

[0031] In some embodiments of the present application, the calcination comprises a first temperature rising stage, a second temperature rising stage and a temperature holding stage, and the difference between the temperature rising rate of the first temperature rising stage and the temperature rising rate of the second temperature rising stage is 1℃ / min-10℃ / min.

[0032] In some embodiments of the present application, the calcination comprises: a first temperature rising stage: rising the temperature to T1 at a temperature rising rate of ≥3℃ / min; a second temperature rising stage: rising the temperature to T2 at a temperature rising rate of ≤2℃ / min; a temperature holding stage: holding the temperature at a temperature range of T2-10℃ to T2+10℃ for t1 hours; wherein, 600℃≤T1≤800℃, 900℃≤T2≤1100℃, 5h≤t1≤15h. Thus, when the conditions are met, the energy density and air stability of the positive electrode material are maximally compatible.

[0033] In some embodiments of the present application, the positive electrode active material precursor comprises:

[0034] Ni x2 Fe y2 Mn z2 Zn m2 O a H b ,

[0035] wherein, 0≤x2≤0.5, 0

[0036] In some embodiments of the present application, the D 50 particle size of the positive electrode active material precursor is 5μm-6μm,

[0037] In some embodiments of the present application, the particle size distribution of the positive electrode active material precursor is 1.1 90 -D 10 ) / D 50 < 1.6.

[0038] In some embodiments of the present application, the tap density of the positive electrode active material precursor is 1.50g / cm 3 -1.80g / cm 3 .

[0039] In some embodiments of the present application, the specific surface area of the positive electrode active material precursor is 10m 2 / g-20m 2 / g.

[0040] In a third aspect, the present application provides a positive electrode sheet, comprising the positive electrode active material according to the first aspect of the present application.

[0041] In a fourth aspect, the present application provides a battery, comprising the positive electrode sheet according to the third aspect of the present application. Thus, the battery has excellent electrochemical performance.

[0042] In a fifth aspect, the present application provides an electric device, comprising the battery according to the fourth aspect of the present application.

[0043] Additional aspects and advantages of the present application will be in part apparent and in part expressly stated in the description that follows. BRIEF DESCRIPTION OF DRAWINGS

[0044] FIG. 1 is a SEM image of the positive electrode active material precursor prepared in Example 1 of the present application;

[0045] FIG. 2 is a SEM image of the positive electrode active material prepared in Example 1 of the present application;

[0046] FIG. 3 is an XRD image of the positive electrode active material precursor prepared in Example 1 of the present application;

[0047] FIG. 4 is an XRD image of the positive electrode active material prepared in Example 1 of the present application;

[0048] FIG. 5 is an Fe element XPS image of the positive electrode active material prepared in Example 1 and Comparative Example 1 of the present application, before charging and after charging to 4.0 V;

[0049] FIG. 6 is a 0.1C first cycle charge-discharge curve of the positive electrode active material prepared in Example 1 and Comparative Example 1 of the present application, in a voltage window of 2.0-4.15 V. DETAILED DESCRIPTION

[0050] Embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by reference to the drawings are exemplary and are intended to explain the present application, and should not be understood as limiting the present application.

[0051] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges or values should be construed to be approximations that allow for significant variation. Various ranges of values that are stated herein are considered to be approximate values that can vary by a small amount. Endpoints of various ranges of values, endpoints of various ranges of values and individual point values, and individual point values can be combined with each other to form one or more new ranges of values, which should be considered to be specifically disclosed herein.

[0052] In one aspect of the present application, the present application provides a positive electrode active material, wherein the Fe 2+ content in the positive electrode active material changes by Δn≥0.1, Δn=n1-n2; wherein n1 is the Fe 2+ content in the positive electrode active material before charging; and n2 is the Fe 2+ content in the positive electrode active material when charged to 4.0 V. 2+ content in the positive electrode active material = Fe 2+ amount in the positive electrode active material / (Fe 2+ amount in the positive electrode active material + Fe 3+ amount in the positive electrode active material).

[0053] As an example, Δn can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, etc. According to other embodiments of the present application, Δn≥0.15.

[0054] The inventors have found that, in a layered oxide containing iron as a positive electrode active material, iron can provide a main capacity, and iron provides capacity through a change in valence state. When the Fe 2+ content in the above positive electrode active material changes by Δn≥0.1 before and after charging, more Fe 2+ is converted to Fe 3+ , and the Fe 2+ content changes greatly, so that more electrons can be transferred during charging, improving the capacity of the positive electrode active material, and further improving the energy density of a battery containing the same.

[0055] Embodiments of the present application can use XPS to test the Fe 2+ content of iron in different valence states in a sodium battery positive electrode active material, and use XPSPEAK41 software to analyze the data to obtain the Fe 2+ content. Wherein n1 is a test before charging and discharging of the positive electrode material, and n2 is that the positive electrode active material is prepared into a sodium ion battery according to a conventional method, charged to 4V at a current of 0.1C, and the positive electrode active material is subjected to XPS test. Further, the tests of n1 and n2 in the present application are measured in the first 20 weeks of the positive electrode material cycle.

[0056] It can be understood that XPS is X-ray photoelectron spectroscopy, which is a technique for analyzing the chemical composition of the surface of a material.

[0057] In the present application, more Fe 2+ is converted to Fe 3+ in the process of charging the sodium battery positive electrode active material to 4.0 V. 2+The content varies greatly, and more electrons can be transferred during the charging process to improve the battery capacity.

[0058] According to an embodiment of the present application, n1 is greater than 50%, for example, n1 can be 51%, 55%, 60%, 70%, 80%, 90%, 100%, etc., n1 is greater than 70%; further preferably, n1 is greater than 80%. In this way, the initial Fe 2+ content is high, on the one hand, during the charging process, by the oxidation reaction of Fe 2+ / Fe 3+ , electrons are transferred to provide capacity, and when charged to 4.0V, more Fe 2+ can be oxidized to Fe 3+ , more electrons can be transferred, and more capacity can be provided; on the other hand, the oxidation potential of O 2- / O - can be reduced, and the oxidation reaction of O 2- / O - that originally occurs between 4.10-4.15V of the material is promoted to occur at about 3.90V, and more capacity is provided in the voltage range of 2.0-4.0V.

[0059] According to an embodiment of the present application, the positive electrode active material comprises:

[0060] Na a1 Ni x1 Fe y1 Mn z1 Zn m1 Ca n1 M p1 O2,

[0061] wherein 0.90≤a1≤1.10, 0≤x1≤0.5, 0<y1≤0.5, 0≤z1≤0.5, 0<m1≤0.2, 0≤n1≤0.05, 0≤p1≤0.05;

[0062] M includes at least one of Cu, Ti, Mg, Sr, Sn, Sb, Zn, Zr, Nb, Y, W and La.

[0063] As an example, a1 can be 0.90, 0.95, 1.0, 1.05, 1.10, etc.; x1 can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, etc.; y1 can be 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, etc.; z1 can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, etc.; m1 can be 0.01, 0.05, 0.1, 0.15, 0.2, etc.; n1 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, etc.; p1 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, etc.

[0064] By regulating the proportion of Zn element in the positive active material composition in a suitable range, the capacity of the positive active material at low voltage (2.0-4.0V) can be greatly improved, and the average voltage can be raised, so that the energy density of the positive active material is greatly improved. In addition, the introduction of Zn element in the positive active material can make the average particle size of the positive active material larger, and the particle size of the positive active material increases more with the increase of the content of Zn element. Zn element helps to improve the single crystallization degree of the positive active material particles and improve the compaction density of the positive active material.

[0065] When n1 and / or p1 are not equal to 0, that is, Ca and / or M are doped in the positive active material, by introducing Ca doping, Ca can enter the sodium layer and transition metal layer in the positive active material to form a barrier to protect the Na in the structure from contacting water and carbon dioxide in the air, thereby improving the air stability of the positive active material. Further, by introducing a doping element M with a larger ionic radius than the main elements Ni, Fe, Mn, and regulating the appropriate doping amount, the interlayer spacing of the positive active material can be expanded, the rate performance can be improved, and the Na + The structural changes caused by the embedding / extraction process improve the structural stability of the positive active material.

[0066] According to an embodiment of the present application, x1+y1+z1+m1+n1+p1=1.

[0067] According to an embodiment of the present application, a1:(x1+y1+z1+m1+n1+p1)=(0.90-1.05):1, for example, can be 0.90:1, 0.95:1, 1.0:1, 1.05:1, etc. Preferably, a1:(x1+y1+z1+m1+n1+p1)=(0.95-1.05):1; further preferably (0.97-1.03):1, thereby the ratio of sodium ions and other metal ions is moderate, which can further improve the capacity of the positive active material, and further improve the energy density of the battery containing it.

[0068] According to an embodiment of the present application, 0.01 < m1 < 0.2, for example, m1 can be 0.01, 0.05, 0.1, 0.15, 0.2, etc., preferably 0.05 < m1 < 0.1, by controlling the content of Zn in the positive electrode active material within the above range, the capacity of the positive electrode active material at (2.0-4.0V) can be greatly improved, and the average voltage is raised, so that the energy density of the positive electrode active material is greatly improved; and the Zn element helps to improve the degree of single crystallization of the positive electrode active material particles, improve the compaction density of the positive electrode active material, and further improve the energy density.

[0069] According to an embodiment of the present application, 0.01 < n1 < 0.05, for example, it can be 0.01, 0.02, 0.03, 0.04, 0.05, etc. Thereby, the content of calcium in the positive electrode active material is controlled within the above range, which is further conducive to the entry of Ca into the sodium layer and the transition metal layer of the positive electrode active material to form a barrier to protect the Na in the structure from contacting water and carbon dioxide in the air, thereby improving the air stability of the positive electrode active material and enabling the battery containing the same to have excellent cycle performance.

[0070] According to an embodiment of the present application, the ionic radius r(M) of M is greater than 0.06 nm, for example, 0.065 nm, 0.07 nm, 0.08 nm, 0.09 nm, 0.1 nm, 0.15 nm, etc. The ionic radius of the M element within the above range can expand the interlayer spacing of the positive electrode active material, improve the rate performance, and alleviate the Na + The structural changes caused by the intercalation / deintercalation process improve the structural stability of the positive electrode active material, and further improve the cycle performance of the battery containing the same.

[0071] According to an embodiment of the present application, the positive electrode active material is an O3-type sodium ion battery layered oxide, so that the capacity of the positive electrode active material is high, the compaction density of the positive electrode active material is improved, and the volume energy density of the battery made therefrom is improved.

[0072] According to an embodiment of the present application, the D 50 The particle size is 3-12 μm, for example, the D 50 The particle size can be 3 μm, 5 μm, 7 μm, 9 μm, 10 μm, 12 μm, etc., preferably 4-10 μm; further preferably 5-8 μm. The D 50 The particle size is controlled within the above range, which can take into account the short migration path of sodium ions and the few side reactions of the positive electrode active material with the electrolyte, thereby improving the cycle performance of the battery containing the same.

[0073] In the present application, the D 50The particle size refers to the particle size corresponding to the cumulative volume distribution percentage of 50%, and is determined by using a laser particle size analyzer (for example, Malvern Master Size 3000) according to the standard GB / T 19077-2016.

[0074] According to an embodiment of the present application, the particle size distribution (K 90 ) of the positive electrode active material satisfies 1.1 < (D 90 -D 10 ) / D 50 < 1.6, preferably 1.2 < (D 90 -D 10 ) / D 50 < 1.4. For example, (D 90 -D 10 ) / D 50 may be 1.11, 1.2, 1.3, 1.4, 1.5, 1.59, etc., so that the particle size distribution of the positive electrode active material is wide, and the positive electrode active material has a high compaction density and a high volumetric energy density.

[0075] It can be understood that D 10 refers to the particle size corresponding to the cumulative volume distribution percentage of 10% of the positive electrode active material, D 50 refers to the particle size corresponding to the cumulative volume distribution percentage of 50% of the positive electrode active material, and D 90 refers to the particle size corresponding to the cumulative volume distribution percentage of 90% of the positive electrode active material, and the above particle sizes can be determined by using a laser particle size analyzer (for example, Malvern Master Size 3000).

[0076] In a second aspect of the present application, a method for preparing the positive electrode active material is provided. According to an embodiment of the present application, the method comprises:

[0077] S100: uniformly mixing a Na source, a positive electrode active material precursor, optionally a Zn source, optionally a Ca source, and optionally an M source in a stoichiometric ratio, to obtain a mixture, wherein the positive electrode active material precursor comprises Fe.

[0078] According to an embodiment of the present application, the Na source, the Zn source, the Ca source, and the M source can be commercially available products.

[0079] For example, the Na source comprises at least one of sodium carbonate, sodium hydroxide, sodium nitrate, and sodium oxide.

[0080] The Zn source comprises at least one of ZnO, ZnCO3, ZnCl2, Zn3(PO4)2, ZnF2, ZnCl2, Zn(OH)2, and ZnSi.

[0081] The Ca source includes at least one of an oxide of Ca, a carbonate of Ca, a phosphate of Ca, a fluoride of Ca, a chloride of Ca, a hydroxide of Ca, and a silicate of Ca.

[0082] The M source includes at least one of an oxide of M, a carbonate of M, a phosphate of M, a fluoride of M, a chloride of M, a hydroxide of M, and a silicate of M.

[0083] According to an embodiment of the present application, the ratio of the amount of substance of Na element to the sum of the amounts of substance of Ni, Fe, Mn, Zn, Ca, and M is 0.90-1.10, i.e., n(Na) / [n(Ni)+n(Fe)+n(Mn)+n(Zn)+n(Ca)+n(M)] = 0.90-1.10, which can be 0.90, 0.95, 1.0, 1.05, 1.10, etc., and is preferably 0.97-1.03. When the positive electrode active material is prepared, the ratio of the amount of substance of Na element to the sum of the amounts of substance of Ni, Fe, Mn, Zn, Ca, and M is controlled within the above range, which is beneficial to the prepared positive electrode active material. During charging to 4.0 V, Fe 2+ The change in content Δn≥0.1, so that more Fe 2+ is converted into Fe 3+ , the change in content of Fe 2+ is large, so that more electrons can be transferred during charging, which improves the capacity of the positive electrode active material and further improves the energy density of the battery containing the same.

[0084] According to an embodiment of the present application, the positive electrode active material precursor includes:

[0085] Ni x2 Fe y2 Mn z2 Zn m2 O a H b ,

[0086] wherein 0≤x2≤0.5, 0

[0087] As an example, x2 can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, etc.; y2 can be 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, etc.; z2 can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, etc.; m2 can be 0, 0.01, 0.05, 0.1, 0.15, 0.2, etc.; a can be 1, 1.2, 1.4, 1.5, 1.7, 2, etc.; and b can be 0, 0.5, 1, 1.5, 2, etc.

[0088] It can be understood that, in the preparation process of the positive active material, the Zn can be introduced when the positive active material precursor is prepared (at this time m2≠0); or the Zn can not be introduced when the positive active material precursor is prepared, but is introduced when the Na source, the positive active material precursor (at this time m2=0), the optional Zn source, the optional Ca source, and the optional M source are mixed, and the Zn source is added at the same time, and then calcined after mixing. Both of the two preparation methods are within the protection scope of the present application.

[0089] As an example, the zinc source compound is selected from at least one of ZnO, ZnCO3, ZnCl2, Zn3(PO4)2, ZnF2, ZnCl2, Zn(OH)2, and ZnSi.

[0090] According to an embodiment of the present application, the positive active material precursor can be prepared by the following method:

[0091] A mixed salt solution is prepared by mixing nickel salt, iron salt, manganese salt, and zinc salt with a concentration of 1.0-3.0 mol / L according to a molar ratio of Ni:Fe:Mn:Zn=x2:y2:z2:m2;

[0092] The mixed salt solution, the complexing agent, and the alkaline aqueous solution are used to synthesize a multi-element positive electrode material positive active material precursor slurry by a continuous method under the protection of argon, nitrogen, or other inert atmosphere;

[0093] The multi-element positive electrode material positive active material precursor slurry is filtered, washed, and dried to obtain the positive active material precursor.

[0094] According to an embodiment of the present application, the D50 of the positive active material precursor is 5-10 μm. 50 The particle size is 5 μm-6 μm, for example, can be 5 μm, 5.3 μm, 5.5 μm, 5.8 μm, 6 μm, etc. Controlling the particle size of the positive active material precursor within the above range can obtain a positive active material with a suitable particle size, which can take into account the short migration path of sodium ions and the few side reactions between the positive active material and the electrolyte, and improve the cycle performance of the battery containing the same.

[0095] According to an embodiment of the present application, the particle size distribution (K 90 ) of the positive active material precursor is 1.1 90 -D 10 ) / D 50 <1.6, for example, can be 1.11, 1.2, 1.3, 1.4, 1.5, 1.59, etc. In this way, the particle size distribution of the positive active material precursor is wide, and the particle size distribution of the positive active material prepared accordingly is wide, so that the positive active material has a high compaction density and a high volume energy density.

[0096] According to an embodiment of the present application, the tap density of the positive electrode active material precursor is 1.50 g / cm 3 -1.80 g / cm 3 , for example, can be 1.50 g / cm 3 , 1.55 g / cm 3 , 1.60 g / cm 3 , 1.65 g / cm 3 , 1.70 g / cm 3 , 1.75 g / cm 3 , 1.80 g / cm 3 , etc.

[0097] According to an embodiment of the present application, the specific surface area of the positive electrode active material precursor is 10 m 2 / g-20 m 2 / g. For example, can be 10 m 2 / g, 12 m 2 / g, 15 m 2 / g, 17 m 2 / g, 20 m 2 / g, etc.

[0098] S200: calcining the mixture under an oxidizing atmosphere, crushing and sieving to obtain a positive electrode active material.

[0099] According to an embodiment of the present application, the oxidizing atmosphere comprises oxygen or air.

[0100] According to an embodiment of the present application, the calcining temperature is 900-1100°C, for example, the calcining temperature can be 900°C, 950°C, 1000°C, 1050°C, 1100°C, etc.; thus, by making the calcining temperature in the above range, a positive electrode active material with high purity, stable structure and high capacity can be formed, and the cycle performance and energy density of the battery containing the same are improved.

[0101] According to an embodiment of the present application, the calcining comprises a first temperature rising stage, a second temperature rising stage and a holding stage, the difference between the temperature rising rate of the first temperature rising stage and the temperature rising rate of the second temperature rising stage is 1-10°C / min, for example, the difference between the temperature rising rate of the first temperature rising stage and the temperature rising rate of the second temperature rising stage is 1°C / min, 2°C / min, 5°C / min, 10°C / min, etc., thus, the energy density and air stability of the obtained positive electrode active material can be maximally compatible, and the energy density and cycle performance of the battery are improved.

[0102] According to an embodiment of the present application, the calcining comprises:

[0103] (a) a first temperature rising stage: rising temperature to T1 at a first temperature rising rate of ≥3℃ / min;

[0104] (b) a second temperature rising stage: rising temperature to T2 at a second temperature rising rate of ≤2℃ / min;

[0105] (c) a temperature holding stage: holding temperature at a temperature range of T2-10℃ to T2+10℃ for t1 hours;

[0106] wherein, T1 ranges from 600℃≤T1≤800℃; T2 is the first calcination temperature, 900℃≤T2≤1100℃; t1 is the holding calcination time, 5h≤t1≤15h;

[0107] For example, the temperature rising rate of the first temperature rising stage can be 3℃ / min, 5℃ / min, 8℃ / min, 10℃ / min, etc.; T1 can be 600℃, 650℃, 700℃, 750℃, 800℃, etc.; the temperature rising rate of the second temperature rising stage can be 0.5℃ / min, 1℃ / min, 1.5℃ / min, 2℃ / min, etc.; T2 can be 900℃, 950℃, 1000℃, 1050℃, 1100℃, etc., and t1 can be 5h, 8h, 10h, 15h, etc.

[0108] When the conditions are met, the energy density and air stability of the positive electrode active material are maximally compatible.

[0109] In summary, the positive electrode active material obtained by the above method can further improve the energy density and rate performance of the material, and greatly improve the problems of poor air stability and low cycle life of the material, compared with the existing nickel-iron-manganese ternary material.

[0110] In a third aspect of the present application, the present application provides a positive electrode sheet. According to embodiments of the present application, the positive electrode sheet comprises the positive electrode active material of the first aspect of the present application, or the positive electrode active material prepared by the method of the second aspect of the present application.

[0111] According to embodiments of the present application, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer comprises the positive electrode active material described above, wherein the positive electrode current collector can be a metal foil or a composite current collector (a metal material can be disposed on a polymer substrate to form a composite current collector), for example, the positive electrode current collector can be an aluminum foil.

[0112] According to some embodiments of the present application, the positive active material layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, or a fluorine-containing acrylate resin.

[0113] According to some embodiments of the present application, the positive active material layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0114] According to some embodiments of the present application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive current collector, and then drying, cold-pressing, or the like to obtain the positive electrode sheet.

[0115] It should be noted that the features and advantages described above for the positive active material and the method of preparing the same also apply to the positive electrode sheet, which will not be described again here.

[0116] In a fourth aspect of the present application, a battery is provided. According to embodiments of the present application, the battery includes at least one of the positive electrode sheet described in the third aspect.

[0117] As an example, the battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator membrane between the positive electrode sheet and the negative electrode sheet. During the charging and discharging of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator membrane is arranged between the positive electrode sheet and the negative electrode sheet, mainly serving to prevent short circuiting between the positive and negative electrodes, while allowing ions to pass through.

[0118] According to embodiments of the present application, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector, and the negative active material layer includes a negative active material. The negative current collector can be a metal foil or a composite current collector (a metal material can be disposed on a polymer substrate to form a composite current collector), for example, the positive current collector can be a copper foil.

[0119] According to some embodiments of the present application, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and sodium titanate, etc.

[0120] According to some embodiments of the present application, the negative active material layer can optionally further include a conductive agent. The conductive agent can include at least one of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0121] According to some embodiments of the present application, the negative active material layer can optionally further include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc.

[0122] According to some embodiments of the present application, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, and the binder, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector; and performing processes such as drying and cold pressing to obtain the negative electrode sheet.

[0123] According to further embodiments of the present application, the negative electrode sheet can include a metal sodium sheet or a sodium alloy, such as a sodium-indium alloy.

[0124] According to yet further embodiments of the present application, the type of the separator film is not particularly limited, and any known porous structure separator film having good chemical stability and mechanical stability can be used. As an example, the material of the separator film can include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0125] According to yet further embodiments of the present application, the type of the electrolyte is not particularly limited, and can be selected as needed. For example, the electrolyte can be in a gel state or a full solid state. According to some specific embodiments of the present application, the electrolyte uses an electrolyte solution including a sodium salt and a solvent.

[0126] According to some specific embodiments of the present application, the sodium salt can include at least one of sodium hexafluorophosphate, sodium difluoro oxalate borate, sodium tetrafluoroborate, sodium bisoxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethylsulfonate, or sodium bis(trifluoromethylsulfonyl)imide.

[0127] According to some specific embodiments of the present application, the solvent can include at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethylene glycol dimethyl ether, methyl ethyl sulfone, or diethyl sulfone.

[0128] In some embodiments of the present application, the electrolyte solution can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain performance of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature or low-temperature performance of the battery, etc.

[0129] It should be noted that the features and advantages described above in relation to the positive electrode sheet also apply to the solid-state battery, which will not be described again here.

[0130] In a fifth aspect of the present application, a power consuming device is provided. According to embodiments of the present application, the power consuming device includes the battery described above. According to embodiments of the present application, the power consuming device can include, but is not limited to, a mobile phone, a notebook computer, an electric vehicle, etc.

[0131] It should be noted that the features and advantages described above in relation to the battery also apply to the power consuming device, which will not be described again here.

[0132] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are intended to explain the present application only, and are not to be understood as limiting the present application. In the embodiments, specific techniques or conditions not mentioned are performed in accordance with techniques or conditions described in the literature in the art or in accordance with product instructions. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained commercially.

[0133] Example 1

[0134] S100: Nickel sulfate, iron sulfate, manganese sulfate, and zinc sulfate were dissolved in a ratio of 25:33:37:5 of nickel, iron, manganese, and zinc elements to obtain a mixed salt solution of 2 mol / L; sodium hydroxide was dissolved to obtain a precipitant solution with a concentration of 10 mol / L; ammonia water was dissolved to obtain a complexing agent solution with a concentration of 8 mol / L. 100 L of the mixed salt solution, the precipitant solution, and the complexing agent solution were introduced into a reaction kettle in a co-current manner at a temperature of 60°C and a pH value of 11.50, and then under the protection of a nitrogen atmosphere, the precipitate was continuously controlled to grow in an overflow device until the average particle size of the particles grew to 5 μm. The precursor slurry was suction filtered, washed, and the filter cake was dried at 120°C and then sieved to obtain a multi-element precursor A. The particle size distribution K of the precursor was D 90 = (D 90 -D 10 ) / D 50 = 1.3.

[0135] S200: The multi-element precursor A, CaO, yttrium oxide and Na2CO3 prepared in S1 are mixed in a molar ratio of Na / (Ni+Fe+Mn+Zn+Ca+Y)=1.01:1, wherein the molar ratio of Na / Ca=1.01:0.02, Na / Y=1.01:0.02, and the mixture is heated to 700°C at a heating rate of 3°C / min, and then heated to 1000°C at a heating rate of 1°C / min in an oxidizing atmosphere, and kept for 15h, and after cooling, crushing and sieving, an O3-type single crystal positive electrode active material is obtained.

[0136] Example 2

[0137] Except that the molar ratio of nickel, iron, manganese and zinc elements in step S100 is adjusted to 25:33:35:7, the rest of the preparation method and parameters are the same as those in Example 1.

[0138] Example 3

[0139] Except that the yttrium oxide in step S200 is replaced by magnesium oxide, the rest of the preparation method and parameters are the same as those in Example 1.

[0140] Example 4

[0141] Except that the molar ratio of Na / Ca in step S200 is adjusted to 1.01:0.05, the rest of the preparation method and parameters are the same as those in Example 1.

[0142] Example 5

[0143] Except that the molar ratio of Na / Y in step S200 is adjusted to 1.01:0.05, the rest of the preparation method and parameters are the same as those in Example 1.

[0144] Example 6

[0145] Except that the average particle size of the particles is grown to 8μm in step S100, the rest of the preparation method and parameters are the same as those in Example 1.

[0146] Example 7

[0147] Except that the yttrium oxide in step S200 is replaced by aluminum oxide, the rest of the preparation method and parameters are the same as those in Example 1.

[0148] Example 8

[0149] Except that the molar ratio of nickel, iron, manganese and zinc elements in step S100 is adjusted to 25:33:41:1, the rest of the preparation method and parameters are the same as those in Example 1.

[0150] Example 9

[0151] Except that no calcium oxide is added in step S200, i.e. the molar amount of calcium is 0, the rest of the preparation method and parameters are the same as those in Example 1.

[0152] Example 10

[0153] Except that the average particle size of the particles is grown to 14 μm in step S100, the rest of the preparation method and parameters are the same as in Example 1.

[0154] Example 11

[0155] Except that the precursor particle size distribution K 90 = (D 90 -D 10 ) / D 50 = 0.8 in step S100, the rest of the preparation method and parameters are the same as in Example 1. The precursor particle size distribution is different from that in Example 1, which is achieved by adjusting as follows: the prepared solution is added to the reaction kettle to the full kettle without passing through the overflow device, and when the precursor particle size in the kettle is grown to meet the requirements, the material in the kettle is completely discharged.

[0156] Example 12

[0157] Except that the molar ratio of nickel, iron, manganese, and zinc elements is adjusted to 25:33:27:15 in step S100, the rest of the preparation method and parameters are the same as in Example 1.

[0158] Example 13

[0159] Except that the molar ratio of nickel, iron, manganese, and zinc elements is adjusted to 25:33:32:10 in step S100, the rest of the preparation method and parameters are the same as in Example 1.

[0160] Comparative Example 1

[0161] Except that the molar ratio of nickel, iron, manganese, and zinc elements is adjusted to 25:33:42:0 (i.e., no zinc sulfate is added) in step S100, the rest of the preparation method and parameters are the same as in Example 1.

[0162] The compositions of the positive electrode active material precursors and the positive electrode active materials prepared in the above examples and comparative examples are shown in Table 1.

[0163] Table 1

[0164] (1) Morphology test

[0165] The present application tests the scanning electron microscope images of the positive electrode active material precursors and O3 type single crystal positive electrode active materials prepared in the above examples and comparative examples, and exemplarily provides the SEM pictures of the positive electrode active material precursors and O3 type single crystal positive electrode active materials prepared in Example 1, and the results are shown in Figures 1 and 2 respectively. As can be seen from Figure 1, the particle size distribution of the positive electrode active material precursor is wide, and the particle surface is dense; as can be seen from Figure 2, the size of the single crystal particle of the positive electrode active material is smooth, and the particle size distribution is wide, and the small particles are filled between the large particles, having good grading performance.

[0166] (2) Physical property test

[0167] The present application tests the XRD of the positive electrode active material precursors and O3 type single crystal positive electrode active materials in the above examples and comparative examples, and exemplarily provides the XRD images of the positive electrode active material precursors and O3 type single crystal positive electrode active materials prepared in Example 1, and the results are shown in Figures 3 and 4 respectively. As can be seen from Figure 3, the phase of the positive electrode active material precursor is (Ni 0.25 Fe 0.33 Mn 0.37 Zn 0.05 )O(OH); as can be seen from Figure 4, the phase of the sodium battery single crystal positive electrode active material of Example 1 of the present application is sodium battery O3 type layered oxide (Na 1.01 Ni 0.240 Fe 0.317 Mn 0.355 Zn 0.048 Ca 0.020 Y 0.020 O2).

[0168] The present application also tests the iron element of the O3 type single crystal positive electrode active material in the above examples and comparative examples by XPS, and exemplarily provides the Fe element XPS test fitting images of the sodium battery positive electrode active material before and after charging to 4.0V in Example 1 and Comparative Example 1, and the results are shown in Figure 5.

[0169] As can be seen from Figure 5a and Figure 5c, the molar ratio of Fe 2+ in Example 1 is much higher than that of Fe 2+ in Comparative Example 1. Further comparing the Fe element XPS images of the positive electrode active material of Example 1 before and after charging to 4.0V (Figure 5a, b), and the Fe element XPS images of the positive electrode active material of Comparative Example 1 before and after charging to 4.0V (Figure 5c, d), it can be found that the positive electrode active material of Example 1 has more Fe 2+ oxidized to Fe 3+ before and after charging to 4.0V, and this process can transfer more electrons to provide capacity.

[0170] (3) Hygroscopicity test

[0171] The O3-type single-crystal positive electrode active materials prepared in the above examples and comparative examples were exposed to air with a relative humidity of 45% for 0-6 h, and the precise moisture, residual alkali parameters were measured, as shown in Table 2.

[0172] Table 2

[0173] From the above results, it can be seen that the positive electrode active materials containing Ca doping other examples, compared with the example 9 without Ca doping, all show lower initial moisture, alcohol Na2CO3 and NaOH content, and when exposed to air for a long time, the water absorption degree, Na2CO3 and NaOH conversion amount are lower. The samples with Ca doping amount in the preferred range are far lower than the samples without Ca doping in the moisture increment (Δmoisture (%)) and residual alkali conversion rate (Δ(Na2CO3+NaOH) (%)), and show more excellent air stability.

[0174] wherein, Δmoisture = moisture (t x -t1) / moisture t1, 1≤x≤6; Δ(Na2CO3+NaOH) = (Na2CO3 (t x -t1)) / Na2CO3 (t1) + (NaOH (t x -t1) / NaOH (t1)).

[0175] (4) Particle size distribution K 90 and median particle size D 50 , compaction density and average particle size test

[0176] The present application tests the particle size distribution K 90 and median particle size D 50 of the positive electrode active material precursor prepared in the above examples and comparative examples, and the compaction density of the O3-type single-crystal positive electrode active material prepared, and the specific test results are shown in Table 3.

[0177] Table 3

[0178] From the above results, it can be seen that by using the method described in the present application, the K 90 of the positive electrode active material precursor obtained is greater than 1 (except for the K 90The particle size distribution is relatively wide. As can be further seen from Figure 1, the particle size distribution of the positive electrode active material precursor is relatively wide; and the morphology of the prepared positive electrode active material is also wide, as shown in Figure 2.

[0179] As can be seen by comparing the examples and comparative examples in Table 3, when the particle size distribution K 90 of the positive electrode active material precursor is within the preferred range, the sintered positive electrode active material still maintains a relatively wide particle size distribution, has a relatively high compaction density and volume energy density (corresponding to Table 5). Among them, the K 90 of the positive electrode active material precursor in Example 11 is within the preferred range, and the sintered positive electrode active material has a relatively wide particle size distribution, a relatively high compaction density and a relatively high volume energy density. a In addition, the present application measured the average particle size D a1 , 2, 8 and Comparative Example 1 can be found that the introduction of Zn element can make the average particle size of the prepared positive electrode material is larger, and with the increase of Zn element content, the particle size increases more, Zn element helps to improve the single crystallization degree of the particle, and improves the compaction density of the material.

[0180] The expression of the sodium battery positive electrode active material is as follows:

[0181] Na x1 Fe y1 Mn z1 Zn m1 Ca n1 M p1 )O2

[0182] (5) Ion radius of M, doping amount ratio, 2θ(003) value of positive electrode active material, n1 and Δn test

[0183] The ion radius (r (M) ) of the doping element M used in the positive electrode material of the examples and comparative examples, the doping amount ratio (p1 / (x1+y1+z1+m1+n1+p1)), the 2θ(003) value of the positive electrode active material were further counted; in addition, the amount of substance of iron element in the O3 type single crystal positive electrode active material in the above examples and comparative examples was tested by XPS, and the data was analyzed by fitting using XPSPEAK41 software, and the Fe 2+ ratio (Fe 2+ / (Fe2 + +Fe 3+ )) in the sodium battery positive electrode active material was characterized, as shown in Table 4.

[0184] Table 4

[0185] Comparing Example 1 and Example 7, it can be seen that the two samples have consistent M doping amounts, but the doped element M and its ionic radius in Example 7 are not within the preferred range, and the 2theta (003) value of the positive electrode active material prepared thereby is larger, indicating a smaller interlayer spacing; comparing Example 1 and Comparative Example 1, it can be seen that the Fe 2+ content in Example 1 containing Zn element is much higher than that in Comparative Example 1 without Zn element. 2+

[0186] From the above results, it can be seen that by doping an element M (r (M) >0.06 nm) with a large ionic radius and adjusting the M doping amount within the preferred range, the interlayer spacing of the positive electrode material can be expanded, which is expected to alleviate the structural changes caused by Na + insertion / extraction, and improve the structural stability of the material; in addition, the Zn-based positive electrode material has a higher initial Fe 2+ content, which is conducive to transferring more electrons through Fe 2+ / Fe 3+ oxidation reaction to provide more capacity.

[0187] (6) Electrochemical performance test of positive electrode active material and battery

[0188] Preparation method of battery:

[0189] The positive electrode active material prepared in each example, acetylene black and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:3:2 with an appropriate amount of N-methyl pyrrolidone (NMP) to form a uniform slurry, which was coated on an aluminum foil and dried at 120°C for 12h, and then punched into a positive electrode sheet with a diameter of 12mm and a thickness of 120μm using a pressure of 100MPa, wherein the loading amount of the positive electrode material was 15mg / cm 2 .

[0190] Assembly of battery: In an Ar glove box with water content and oxygen content less than 5ppm, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte were assembled into a 2025 type button cell and left for 6h. The negative electrode sheet used a metal sodium sheet with a diameter of 17mm and a thickness of 1mm; the separator used a Celgard 2325 porous membrane with a thickness of 25μm; the electrolyte used an equal amount of 1mol / L NaPF6, ethylene carbonate (EC) and diethyl carbonate (DEC) mixture.

[0191] Performance test method

[0192] The button cell was subjected to electrochemical test at 25°C using a new battery test system, and the charge / discharge current density of 0.1C was 140mA / g:​

[0193] 1. Test method of 0.1C initial charge-discharge specific capacity at 2.0-4.0V

[0194] The prepared button cell was subjected to charge-discharge test at 25℃, 2.0-4.0V, 0.1C to evaluate the 0.1C initial charge-discharge specific capacity of the material.

[0195] 2. Test method of average voltage of positive active material

[0196] The prepared button cell was subjected to charge-discharge test at 25℃, 2.0-4.0V, 0.1C to evaluate the 0.1C initial charge-discharge specific capacity of the material.

[0197] 3. Test method of rate performance

[0198] The prepared button cell was subjected to charge-discharge test at 25℃, 2.0-4.0V, 0.1C to evaluate the 0.1C initial charge-discharge specific capacity of the material.

[0199] 4. Test method of cycle performance

[0200] The prepared button cell was subjected to charge-discharge test at 25℃, 2.0-4.0V, 0.1C to evaluate the 0.1C initial charge-discharge specific capacity of the material.

[0201] 5. Test method of volume energy density

[0202] The 0.1C discharge specific capacity, average voltage and the corresponding compaction density of each example in Table 3 obtained by the above methods 1 and 2 were multiplied to obtain the volume energy density.

[0203] The test results are shown in Table 5.

[0204] Table 5

[0205] According to the data in Table 5, by comparing Example 1, 2 and Comparative Example 1, it can be seen that when the content of Zn in the positive active material is within the preferred range, higher charge-discharge capacity and average voltage can be achieved at 2.0-4.0V, and the energy density is higher. By comparing Example 1 and Example 7 and combining the data in Tables 4 and 5, it can be seen that the introduction of the doping element M (r (M)>0.06 nm) and satisfies the M doping amount in the preferred range, the interlayer spacing of the positive electrode material can be expanded, the rate performance can be improved, and Na + The structural changes caused by the embedding / extraction process improve the structural stability and cycle stability of the material.

[0206] Comparing Example 1 and Examples 10 and 6, when the particle size distribution K 90 of the positive electrode active material precursor is in the preferred range and D 50 is in the preferred range, the positive electrode material prepared therefrom has a higher compaction density and a higher volumetric energy density. The particle size D a of the positive electrode active material precursor of Example 10 is too large, resulting in a large particle size, a reduced compaction, and a lower energy density than Examples 1 and 6.

[0207] Comparing Example 1 and Example 12, the Zn content is too high, at 0.15, the Fe 2+ content increases slightly, and the other conditions are the same as in Example 1. The volumetric energy density changes little relative to Example 1, but the excessively high content leads to rapid cycle decay.

[0208] The sodium-ion battery positive electrode active material prepared from Example 1 and Comparative Example 1 was also tested. The 0.1C first cycle charge-discharge curve in the voltage window of 2.0-4.15 V is shown in FIG. 6. As shown by comparing the charge-discharge curves of Example 1 and Comparative Example 1, after Zn doping, a new inflection point (circled in FIG. 6) appears at 3.05 V in the charge curve, and the slope is slower (Fe 2+ / Fe 3+ oxidation reaction), and an upwardly inclined inflection point (O 2- / O - oxidation reaction) appears at about 3.90 V. In combination with the initial Fe 2+ content (Fe 2+ + Fe 3+ ) ratio in Table 4, it is shown that after Zn doping, the initial Fe 2+ content is increased, more electrons are transferred through the Fe 2+ / Fe 3+ oxidation reaction during the charging process, and more capacity is provided; on the other hand, the oxidation potential of O 2- / O - is reduced, and the O 2- / O - oxidation reaction originally occurring at 4.10-4.15 V is advanced to about 3.90 V, thereby providing more capacity in the voltage interval of 2.0-4.0 V. Therefore, the capacity of Example 1 is greatly improved relative to Comparative Example 1 in the voltage interval of 2.0-4.0 V.

[0209] It can be seen from the above results that the positive electrode material of the sodium ion battery has a particle size distribution K 90 and D 50 The Zn-based multi-component continuous process precursor in the preferred range, the first dopant Ca and the second dopant M(r (M) >0.06nm), according to the preferred doping ratio, are mixed, and after calcination treatment, the obtained positive electrode material has higher energy density and rate performance, and greatly improves the problems of poor air stability and low cycle life of the material.

[0210] In the description of the present specification, the description referring to the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. Furthermore, different embodiments or examples described in the present specification and the features of different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0211] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A positive electrode active material, wherein, Fe in the positive electrode active material 2+ The change in content Δn ≥ 0.1, Δn = n1 - n2; Wherein, n1 represents the Fe content in the positive electrode active material before charging. 2+ Content; n2 is the Fe content in the positive electrode active material when charged to 4.0V. 2+ content; Fe 2+ Content = Fe in the positive electrode active material 2+ Amount of substance / (Fe in the positive electrode active material) 2+ Amount of substance + Fe in the positive electrode active material 3+ Amount of substance.

2. The positive electrode active material according to claim 1, wherein, Δn ≥ 0.15; Optionally, n1 > 50%; preferably, n1 > 70%; more preferably, n1 > 80%.

3. The positive electrode active material according to claim 1 or 2, wherein, The positive electrode active material includes: Na a1 Ni x1 Fe y1 Mn z1 Zn m1 Ca n1 M p1 O2, Where 0.90 ≤ a1 ≤ 1.10, 0 ≤ x1 ≤ 0.5, 0 < y1 ≤ 0.5, 0 ≤ z1 ≤ 0.5, 0 < m1 ≤ 0.2, 0 ≤ n1 ≤ 0.05, 0 ≤ p1 ≤ 0.05; M includes at least one of Cu, Ti, Mg, Sr, Sn, Sb, Zn, Zr, Nb, Y, W, and La.

4. The positive electrode active material according to claim 3, wherein, a1:(x1 + y1 + z1 + m1 + n1 + p1) = (0.90 - 1.05):1; preferably (0.95 - 1.05):1; more preferably (0.97 - 1.03):1; Optionally, 0.01 < m1 ≤ 0.2, preferably 0.05 < m1 ≤ 0.1; Optionally, 0.01 < n1 ≤ 0.05; Optionally, the ionic radius r(M) of M > 0.06 nm; Optionally, the positive electrode active material is an O3-type sodium-ion battery layered oxide.

5. The positive electrode active material according to claim 1 or 2, wherein, The positive electrode active material D 50 The particle size is 3μm-12μm, preferably 4μm-10μm; more preferably 5μm-8μm. Optionally, the particle size distribution of the positive electrode active material is 1.1 < (D 90 -D 10 ) / D 50 <1.6, preferably 1.2<(D) 90 -D 10 ) / D 50 <1.

4.

6. A method for preparing the positive electrode active material according to any one of claims 1-5, wherein, Comprising: Taking a Na source, a positive electrode active material precursor, optionally a Zn source, optionally a Ca source, and optionally a M source in a stoichiometric ratio and mixing them uniformly to obtain a mixed material, wherein the positive electrode active material precursor includes Fe; Calcining the mixed material in an oxidizing atmosphere, pulverizing, and sieving to obtain a positive electrode active material.

7. The method according to claim 6, wherein, The ratio of the amount of substance of Na element to the sum of the amounts of substance of Ni, Fe, Mn, Zn, Ca, and M is 0.90 - 1.10, preferably 0.97 - 1.03; Optionally, the temperature of the calcination is 900 °C - 1100 °C; Optionally, the calcination includes a first heating stage, a second heating stage, and a heat preservation stage. The difference between the heating rate of the first heating stage and the heating rate of the second heating stage is 1 °C / min - 10 °C / min; Optionally, the calcination includes: First heating stage: heating at a heating rate of ≥ 3 °C / min to T1; Second heating stage: heating at a heating rate of ≤ 2 °C / min to T2; Heat preservation stage: heat preservation for t1 hours within the temperature range of T2 - 10 °C to T2 + 10 °C; Where 600 °C ≤ T1 ≤ 800 °C, 900 °C ≤ T2 ≤ 1100 °C, 5 h ≤ t1 ≤ 15 h.

8. The method according to claim 6, wherein, The positive electrode active material precursor includes: Ni x2 Fe y2 Mn z2 Zn m2 O a H b , Where 0 ≤ x2 ≤ 0.5, 0 < y2 ≤ 0.5, 0 ≤ z2 ≤ 0.5, 0 ≤ m2 ≤ 0.2, 1 ≤ a ≤ 2, 0 ≤ b ≤ 2, x2 + y2 + z2 + m2 = 1.

9. The method according to any one of claims 6-8, wherein, The D of the positive electrode active material precursor 50 The particle size is 5μm-6μm; Optionally, the particle size distribution of the positive electrode active material precursor is 1.1 < (D 90 -D 10 ) / D 50 <1.6; Optionally, the tap density of the positive electrode active material precursor is 1.50 g / cm³. 3 -1.80g / cm 3 ; Optionally, the specific surface area of ​​the positive electrode active material precursor is 10 m². 2 / g-20m 2 / g.

10. A positive electrode plate, wherein, Comprising the positive electrode active material according to any one of claims 1 - 5.

11. A battery, wherein, Comprising the positive electrode sheet according to claim 10.

12. An electrical appliance, wherein, Comprising the battery according to claim 11.

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