Positive electrode material and preparation method therefor, positive electrode sheet and sodium-ion battery

Abstract

The present application relates to the technical field of batteries, and in particular relates to a positive electrode material and a preparation method therefor, a positive electrode sheet and a sodium-ion battery. The chemical general formula of the positive electrode material is NaaNibZncFedMneXfO2, wherein 0.85≤a≤1.1, 0.1≤b≤0.4, 0.05≤c≤0.4, 0.1≤d≤0.4, 0.1≤e≤0.5, 0≤f≤0.02, and X is at least one element of Ti, Al, Ta, Nb, Ge, Y, Nb, W, Zr, B, Ce, Ca, V, Si, Sr, Mg and Mo. In an X-ray diffraction pattern of the positive electrode material, there is no diffraction peak when the 2θ value of a diffraction angle is within at least one range of 31º-32º and 34º-35º. The present application can solve the problem of rapid attenuation during the cycling of the positive electrode material.

Description

Positive electrode material and preparation method thereof, positive electrode sheet and sodium ion battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on June 29, 2023, with application number CN202310781322.3 and application name “Positive electrode material and preparation method thereof, positive electrode sheet and sodium ion battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to positive electrode materials and preparation methods thereof, positive electrode sheets and sodium ion batteries. Background Art

[0003] With the rapid development of new energy, the industry is increasingly demanding cost controls, and the development and application of sodium-ion batteries are attracting increasing attention. Single-crystal layered cathode materials, with their low cost and high voltage characteristics, are attracting more research.

[0004] However, after the positive electrode material is prepared using a zinc-containing precursor as the main raw material, the positive electrode material will experience the problem of rapid cycle attenuation.

[0005] Summary of the Invention

[0006] Based on this, the present application provides a positive electrode material and a preparation method thereof, a positive electrode plate and a sodium ion battery to improve the problem of rapid attenuation of the positive electrode material during cycling.

[0007] In a first aspect, the present application provides a positive electrode material, the technical solution of which is as follows:

[0008] A positive electrode material with the general chemical formula Na a Ni b Zn c Fe d Mn e X f O2, wherein 0.85≤a≤1.1, 0.1≤b≤0.4, 0.05≤c≤0.4, 0.1≤d≤0.4, 0.1≤e≤0.5, 0≤f≤0.02, and X is at least one element selected from Ti, Al, Ta, Nb, Ge, Y, Nb, W, Zr, B, Ce, Ca, V, Si, Sr, Mg, and Mo;

[0009] In the X-ray diffraction pattern of the positive electrode material, the diffraction angle 2θ value has no diffraction peak within at least one of the ranges of 31° to 32° and 34° to 35°.

[0010] In some embodiments, the positive electrode material satisfies at least one of the following conditions:

[0011] (1)0.95≤a≤1.1; (2)0.2≤b≤0.3; (3)0.05≤c≤0.2; (4)0.2≤d ≤0.4; (5)0.2≤e≤0.4.

[0012] In some embodiments, the particle size of the positive electrode material satisfies: (D90-D10) / D50≥0.7.

[0013] In some embodiments, the tap density of the positive electrode material satisfies: TD ≥ 1.95 g / cm 3 .

[0014] The second aspect of the present application provides a method for preparing a positive electrode material, the technical solution of which is as follows:

[0015] A method for preparing a positive electrode material comprises the following steps:

[0016] According to the molar ratio of Na element to precursor, a:1 Na source and a chemical formula of Ni b Zn c Fe d Mn e (OH)2 precursor to obtain a mixture, wherein 0.85≤a≤1.1, 0.1≤b≤0.4, 0.05≤c≤0.4, 0.1≤d≤0.4, 0.1≤e≤0.5;

[0017] The mixture is subjected to a solid solution reaction at a temperature of 700° C. or higher for at least 2 hours to obtain an intermediate product;

[0018] The intermediate product is sintered until the X-ray diffraction pattern of the sintered product has no diffraction peak at a diffraction angle 2θ value within at least one of a range of 31° to 32° and 34° to 35°, and the chemical formula is Na a Ni b Zn c Fe d Mn e O2 positive electrode material.

[0019] In some embodiments, preparing the mixture further comprises the following steps:

[0020] An additive is added according to a molar ratio of element X to the precursor of f:1, wherein the additive is selected from an oxide or hydroxide containing element X; the element X is at least one element selected from Ti, Al, Ta, Nb, Ge, Y, Nb, W, Zr, B, Ce, Ca, V, Si, Sr, Mg and Mo, wherein 0≤f≤0.02.

[0021] In some embodiments, the solid solution reaction and sintering satisfy at least one of the following conditions:

[0022] (1) The temperature of the solid solution reaction is 700°C to 850°C;

[0023] (2) The solid solution reaction time is 2h to 5h;

[0024] (3) The sintering temperature is not less than 930°C;

[0025] (4) The sintering time is 10 hours to 14 hours.

[0026] In some embodiments, the particle size of the precursor satisfies: (D90-D10) / D50≥0.7.

[0027] In some embodiments, the method for preparing the precursor comprises the following steps:

[0028] According to the chemical formula of the precursor, preparing a first metal salt solution and a second metal salt solution;

[0029] Mixing a first metal salt solution, a precipitant, and a complexing agent, and reacting them under alkaline conditions to obtain seed crystals with a D50 of 1 μm to 3 μm;

[0030] The seed crystal and the second metal salt solution are mixed and reacted under alkaline conditions to obtain the precursor.

[0031] In some embodiments, the Na source is selected from at least one of Na2CO3 and NaHCO3.

[0032] The third aspect of the present application provides a positive electrode plate, the technical solution of which is as follows:

[0033] A positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer arranged on the surface of the positive electrode current collector, wherein the material of the positive electrode active layer comprises the above-mentioned positive electrode material or the positive electrode material prepared by the above-mentioned preparation method, a conductive agent and a binder.

[0034] In some embodiments, the ultimate compaction density of the positive electrode sheet is 3.1 g / cm 3 ~3.5g / cm 3 .

[0035] In some embodiments, the conductive agent is one or more of acetylene black, conductive carbon black and conductive graphite; and / or

[0036] The binder is one or more of polyvinylidene fluoride and N-methylpyrrolidone.

[0037] A fourth aspect of the present application provides a sodium ion battery, the technical solution of which is as follows:

[0038] A sodium ion battery comprises the above-mentioned positive electrode material, the positive electrode material prepared by the above-mentioned preparation method, or the above-mentioned positive electrode plate.

[0039] Compared with traditional solutions, this application has the following beneficial effects:

[0040] Through the applicant's research, it was found that the problem of rapid cycle decay of the positive electrode material is mainly related to the presence of a zinc oxide phase in the structure of the positive electrode material. Specifically, since a zinc-containing precursor is used as the main raw material when preparing the positive electrode material, it is easy for the structure of the prepared positive electrode material to contain a zinc oxide phase that is difficult to fuse with other oxides, making it difficult to form a uniform phase with consistent structure, resulting in a decrease in the crystalline phase. During the cycle, due to anisotropy, problems such as cycle drop and increased internal resistance are prone to occur, which manifests as rapid cycle decay of the positive electrode material. Based on the above findings, the present application provides a positive electrode material containing zinc but with no zinc oxide phase, which has a high cycle capacity retention rate.

[0041] In addition, since the positive electrode material does not contain zinc oxide phase, the crystalline phase in the structure is relatively high, the release of active oxygen during the cycle is small, the possibility of material surface failure is small, the risk of thermal runaway is small, and the safety is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present application and to more fully understand the present application and its beneficial effects, the following is a brief introduction to the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present application. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0043] FIG1 is a SEM image of the precursors of Example 1 and Example 6;

[0044] FIG2 is a SEM image of the positive electrode materials of each embodiment and comparative example;

[0045] FIG3 is an XRD diagram of the positive electrode materials of Examples 1 to 4;

[0046] FIG4 is an XRD diagram of the positive electrode materials of Examples 5 to 8;

[0047] FIG5 is an XRD diagram of the positive electrode materials of each comparative example. DETAILED DESCRIPTION

[0048] The present application will be further described in detail below with reference to specific embodiments. The present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the present application's disclosure.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0050] the term

[0051] Unless otherwise specified or incompatible herewith, the terms and phrases used herein shall have the following meanings:

[0052] In this application, the selection range involving "and / or", "or / and", and "and / or" includes any one of two or more related listed items, and also includes any and all combinations of the related listed items, and the said any and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected by at least two conjunctions selected from "and / or", "or / and", and "and / or", it should be understood that the technical solution undoubtedly includes technical solutions that are all connected by "logical and", and undoubtedly includes technical solutions that are all connected by "logical or". For example, "A and / or B" includes three parallel solutions of A, B and A+B. For example, the technical solution of "A, and / or, B, and / or, C, and / or, D" includes any one of A, B, C, and D (that is, the technical solution of all being connected by "logical OR"), and also includes any and all combinations of A, B, C, and D, that is, the combination of any two or any three of A, B, C, and D, and also includes the four-item combination of A, B, C, and D (that is, the technical solution of all being connected by "logical AND").

[0053] In this application, "plurality", "multiple", "multiple times", "multiples", etc., unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or more than or equal to two.

[0054] In this application, the terms "preferred", "better", "more preferred" and "suitable" are only used to describe implementation methods or examples with better effects. It should be understood that they do not constitute limitations on the scope of protection of this application.

[0055] In this application, the terms “further”, “further”, “particularly”, etc. are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of this application.

[0056] In this application, the terms "optionally," "optional," and "optional" refer to options that are optional and may or may not be present, i.e., to the selection of either option from the two parallel options of "with" or "without." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or constraints, each "option" is independent.

[0057] In this application, the terms "first," "second," "third," "fourth," etc., in the "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be understood as indicating or implying relative importance or quantity, nor as implicitly indicating the importance or quantity of the indicated technical features. Furthermore, "first," "second," "third," "fourth," etc., are only used for non-exhaustive enumeration and description purposes, and should be understood not to constitute a closed-ended limitation on quantity.

[0058] In this application, when referring to a numerical interval (i.e., a numerical range), unless otherwise specified, the optional numerical distribution is considered continuous within the above numerical interval and includes the two numerical endpoints of the numerical range (i.e., the minimum and maximum values), as well as each numerical value between the two numerical endpoints. Unless otherwise specified, when a numerical interval refers only to integers within the numerical interval, it includes the two endpoint integers of the numerical range, as well as each integer between the two endpoints. In this article, it is equivalent to directly listing each integer, such as t is an integer selected from 1 to 10, indicating that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be merged. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges included therein.

[0059] Unless otherwise specified, the temperature parameters in this application allow for both constant temperature treatment and temperature fluctuations within a certain temperature range. It should be understood that the constant temperature treatment allows for temperature fluctuations within the accuracy range of instrument control. Fluctuations within ranges such as ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are permitted.

[0060] In this application, when referring to percentage content, unless otherwise specified, for solid-liquid mixing and solid-solid mixing, it refers to mass percentage, and for liquid-liquid mixing, it refers to volume percentage.

[0061] In this application, references to percentage concentrations, unless otherwise specified, refer to final concentrations, which are the percentage of an added component in the system after the addition of that component.

[0062] The applicant's research found that the problem of rapid cycle decay of the positive electrode material is mainly related to the presence of zinc oxide phase in the structure of the positive electrode material. Specifically, since the precursor containing zinc element is used as the main raw material when preparing the positive electrode material, it is easy for the structure of the prepared positive electrode material to contain zinc oxide phase that is difficult to fuse with other oxides, making it difficult to form a uniform phase with consistent structure, resulting in a decrease in the crystalline phase. Due to anisotropy, the cycle is prone to cycle jump and internal resistance increase, which manifests as rapid cycle decay of the positive electrode material. Based on the above findings, one embodiment of the present application provides a positive electrode material, whose general chemical formula is Na a Ni b Zn c Fe d Mn e X f O2, wherein 0.85≤a≤1.1, 0.1≤b≤0.4, 0.05≤c≤0.4, 0.1≤d≤0.4, 0.1≤e≤0.5, 0≤f≤0.02, and X is at least one element selected from Ti, Al, Ta, Nb, Ge, Y, Nb, W, Zr, B, Ce, Ca, V, Si, Sr, Mg, and Mo; and in the X-ray diffraction pattern of the positive electrode material, the diffraction angle 2θ value has no diffraction peak between at least one of the ranges of 31° to 32° and 34° to 35°.

[0063] The above-mentioned cathode material has a high cycle capacity retention rate. In addition, because the cathode material does not contain zinc oxide phase and has a high crystalline phase in the structure, the release of active oxygen during the cycle is low, the possibility of material surface failure is low, the risk of thermal runaway is low, and the safety is high.

[0064] In this embodiment, the diffraction angle 2θ value has no diffraction peak within at least one of the ranges of 31° to 32° and 34° to 35°, indicating that the zinc oxide phase has disappeared from the positive electrode material structure. The positive electrode material of this embodiment has a high cycle capacity retention rate. Furthermore, the diffraction angle 2θ value has no diffraction peak within at least one of the ranges of 31° to 32° and 34° to 35°.

[0065] It can be understood that within at least one of the ranges of 31° to 32° and 34° to 35° means within the range of 31° to 32°, or within the range of 34° to 35°, or within both the ranges of 31° to 32° and 34° to 35°.

[0066] It can be understood that a can be 0.85, 0.88, 0.9, 0.93, 0.95, 0.99, 1.0, or 1.1. Preferably, 0.95≤a≤1.1;

[0067] b can be 0.1, 0.2, 0.3, or 0.4. Preferably, 0.2≤b≤0.3;

[0068] c can be 0.05, 0.1, 0.2, 0.3, or 0.4. Preferably, 0.05≤c≤0.2;

[0069] d can be 0.1, 0.2, 0.3, or 0.4. Preferably, 0.2≤d≤0.4;

[0070] e can be 0.1, 0.2, 0.3, 0.4, or 0.5. Preferably, 0.2≤e≤0.4;

[0071] f can be 0, 0.001, 0.005, 0.01, 0.015, 0.02.

[0072] Optionally, the particle size of the positive electrode material satisfies: (D90-D10) / D50≥0.7. Using a positive electrode material that satisfies the above particle size distribution is conducive to preparing a positive electrode sheet with a higher compaction density.

[0073] It can be understood that (D90-D10) / D50 can be 0.7, 0.8, 0.9, 1, 1.5, or 2.

[0074] Generally speaking, the higher the ultimate compaction density of the positive electrode sheet, the higher the energy density of the battery. Therefore, improving the ultimate compaction density of the positive electrode sheet is also a research hotspot for R&D and manufacturing personnel. At present, the ultimate compaction density of the positive electrode sheet has reached 3.0g / cm 3 This is already a very high level and it is difficult to improve it further on the existing basis. In this embodiment, the use of positive electrode materials that meet the above-mentioned wide particle size distribution is conducive to improving the compaction performance of the subsequent positive electrode sheet, and the ultimate compaction density of the positive electrode sheet can be increased to 3.1g / cm 3 ~3.5g / cm 3 , which is beneficial to improving the energy density of the battery.

[0075] Further optionally, the tap density of the positive electrode material satisfies: TD ≥ 1.95 g / cm 3 In addition to having a wide particle size distribution, the positive electrode material that meets the above tap density is basically free of agglomeration, which is beneficial to improving the electrochemical performance of the battery, such as the first efficiency.

[0076] In summary, the positive electrode material of this embodiment has a high cycle capacity retention rate, is beneficial to improving the ultimate compaction density of the positive electrode sheet, is beneficial to improving the electrochemical performance of the battery, and is also beneficial to reducing the risk of thermal runaway of the battery.

[0077] In one embodiment of the present application, a method for preparing a positive electrode material is further provided, comprising the following steps:

[0078] According to the molar ratio of Na element to precursor, a:1 Na source and a chemical formula of Ni b Zn c Fe d Mn e (OH)2 precursor to obtain a mixture, wherein 0.85≤a≤1.1, 0.1≤b≤0.4, 0.05≤c≤0.4, 0.1≤d≤0.4, 0.1≤e≤0.5;

[0079] The mixture is subjected to a solid solution reaction at a temperature of 700° C. or higher for at least 2 hours to obtain an intermediate product;

[0080] The intermediate product is sintered until the X-ray diffraction pattern of the sintered product has no diffraction peak at a diffraction angle 2θ value within at least one of a range of 31° to 32° and 34° to 35°, and the chemical formula is Na a Ni b Zn c Fe d Mn e O2 positive electrode material.

[0081] Different from directly sintering the mixture of Na source and precursor, in this embodiment, the mixture is first subjected to a solid solution reaction, through which the diffusion of the Na source and the fusion of zinc are promoted, thereby eliminating a portion of the zinc oxide phase. The intermediate product is then sintered to further eliminate the zinc oxide phase, thereby obtaining a layered positive electrode material with a stable structure and excellent comprehensive performance.

[0082] Optionally, preparing the mixture further comprises the following steps:

[0083] An additive is added according to a molar ratio of element X to the precursor of f:1, wherein the additive is selected from an oxide or hydroxide containing element X; the element X is at least one element selected from Ti, Al, Ta, Nb, Ge, Y, Nb, W, Zr, B, Ce, Ca, V, Si, Sr, Mg and Mo, wherein 0≤f≤0.02.

[0084] In this embodiment, the solid solution reaction temperature is too low or the time is too short, the zinc in the structure is not completely integrated, and a large amount of zinc oxide phase remains.

[0085] Optionally, the temperature of the solid solution reaction is lower than the sintering temperature.

[0086] Optionally, the temperature of the solid solution reaction is 700° C. to 850° C. It is understood that the temperature of the solid solution reaction includes but is not limited to 700° C., 750° C., 800° C., and 850° C.

[0087] Optionally, the solid solution reaction time is 2 hours to 5 hours. It is understandable that the solid solution reaction time includes but is not limited to 2 hours, 3 hours, 4 hours, and 5 hours.

[0088] In this embodiment, the temperature of the solid solution reaction is too high or the time is too long, which easily causes the agglomeration of the particles of the positive electrode material, resulting in a tap density of the positive electrode material of less than 1.95 g / cm 3 .

[0089] Optionally, the sintering temperature is not less than 930° C. Further optionally, the sintering temperature is 930° C. to 1000° C. It is understood that the sintering temperature includes but is not limited to 930° C., 940° C., 950° C., 960° C., 970° C., 980° C., 990° C., and 1000° C.

[0090] Optionally, the sintering time is 10 hours to 14 hours. It is understandable that the sintering time includes but is not limited to 10 hours, 11 hours, 12 hours, 13 hours, and 14 hours.

[0091] In this embodiment, if the sintering temperature is too low or the sintering time is too short, the structural uniformity of the positive electrode material will be reduced. If the temperature is too high or the sintering time is too long, the positive electrode material particles will easily agglomerate, resulting in a tap density of the positive electrode material less than 1.95 g / cm.

[0092] The solid solution reaction and sintering described above eliminate the zinc oxide phase from the cathode material structure, producing a cathode material with good structural uniformity and high cycle capacity retention. Sintering also improves the roundness of the cathode material particles, which helps to increase the ultimate compaction density of the subsequent cathode sheet.

[0093] It is understandable that after sintering, the sintered product is further subjected to steps such as crushing, screening, iron removal and packaging.

[0094] The particle size distribution of the positive electrode material is mainly affected by the particle size distribution of the precursor. Optionally, the particle size of the precursor satisfies: (D90-D10) / D50≥0.7.

[0095] Alternatively, the precursor can be prepared by a continuous process. Compared to batch-wise preparation of the precursor, the continuous process has a wider particle size distribution, which is beneficial for preparing cathode materials with a wider particle size distribution and for preparing cathode plates with a higher ultimate compaction density.

[0096] Optionally, preparing the precursor by a continuous process comprises the following steps:

[0097] According to the chemical formula of the precursor, preparing a first metal salt solution and a second metal salt solution;

[0098] Mixing a first metal salt solution, a precipitant, and a complexing agent, and reacting them under alkaline conditions to obtain seed crystals with a D50 of 1 μm to 3 μm;

[0099] The seed crystal and the second metal salt solution are mixed and reacted under alkaline conditions to obtain the precursor.

[0100] Optionally, the metal elements in the first metal salt solution and the second metal salt solution are selected from one or more of Ni, Zn, Fe and Mn.

[0101] Optionally, the precipitant and the complexing agent are commonly used reagents for preparing precursors, for example, the precipitant may be NaOH, and the complexing agent may be aqueous ammonia, without particular limitation.

[0102] Optionally, the first metal salt solution, the precipitant and the complexing agent may react at a temperature of 50° C. to 70° C., a pH of 11.3 to 12.0, and an ammonia value of 3.3 g / L to 3.7 g / L.

[0103] Optionally, the seed crystal and the second metal salt solution can react at a temperature of 50° C. to 70° C., a pH of 11.3 to 12.0, and an ammonia value of 3.3 g / L to 3.7 g / L. After the reaction, the precursor can be filtered and dried.

[0104] Optionally, the Na source is selected from at least one of Na2CO3 and NaHCO3.

[0105] The above preparation method can improve the cycle capacity retention rate of the positive electrode material, increase the ultimate compaction density of the positive electrode sheet, improve the initial efficiency of the battery, and reduce the risk of thermal runaway. The preparation method is simple and is conducive to rapid commercialization.

[0106] One embodiment of the present application further provides a positive electrode plate, comprising a positive electrode current collector and a positive electrode active layer disposed on the surface of the positive electrode current collector, wherein the material of the positive electrode active layer comprises the above-mentioned positive electrode material, a conductive agent and a binder.

[0107] The above-mentioned positive electrode plate has all the advantages of the above-mentioned positive electrode materials, which will not be repeated here.

[0108] Optionally, the ultimate compaction density of the positive electrode sheet is 3.1 g / cm 3 ~3.5g / cm 3 The positive electrode sheet of this embodiment has a high ultimate compaction density, which is beneficial to improving the energy density of the battery.

[0109] Optionally, the conductive agent is selected from one or more of acetylene black, conductive carbon black and conductive graphite.

[0110] Optionally, the binder is selected from one or more of polyvinylidene fluoride and N-methylpyrrolidone.

[0111] One embodiment of the present application further provides a sodium ion battery, comprising the above-mentioned positive electrode material or the positive electrode material prepared by the above-mentioned preparation method or the above-mentioned positive electrode plate.

[0112] Optionally, the sodium ion battery further includes a negative electrode plate, an electrolyte and a separator.

[0113] The following is further described in conjunction with specific examples and comparative examples. Unless otherwise specified, the raw materials involved in the following specific examples and comparative examples can be sourced from commercial sources. The instruments used can be sourced from commercial sources unless otherwise specified. The processes involved can be selected conventionally by those skilled in the art unless otherwise specified.

[0114] Example 1

[0115] This embodiment provides a positive electrode material and a preparation method thereof, the steps are as follows:

[0116] Step 1: Prepare the precursor

[0117] A nickel sulfate aqueous solution, a zinc sulfate aqueous solution, an iron sulfate aqueous solution, and a manganese sulfate aqueous solution were prepared according to the molar ratio of Ni, Zn, Fe, and Mn of 0.23:0.1:0.33:0.33.

[0118] A portion of an aqueous nickel sulfate solution, a portion of an aqueous zinc sulfate solution, a portion of an aqueous iron sulfate solution, a portion of an aqueous manganese sulfate solution, a precipitant NaOH, and a complexing agent, aqueous ammonia, were mixed and reacted at a temperature of 60° C., a pH of 11.5, and an ammonia value of 3.5 g / L to obtain seed crystals with a D50 of 1 μm to 3 μm;

[0119] The seed crystals and the remaining nickel sulfate aqueous solution, the remaining zinc sulfate aqueous solution, the remaining iron sulfate aqueous solution and the remaining manganese sulfate aqueous solution were reacted at a temperature of 60°C, a pH of 11.5 and an ammonia value of 3.5 g / L. After the reaction, the mixture was filtered and dried to obtain a product having the general chemical formula Ni 0.23 Zn 0.10 Fe 0.33 Mn 0.33 Precursor of (OH)2.

[0120] Step 2: Add 10 kg of Ni obtained in step 1 to a 4 L high-pressure mixer. 0.23 Zn 0.10 Fe 0.33 Mn 0.33 Sodium carbonate was added to the (OH)2 precursor at a molar ratio of Na element to the precursor of 1:1, and the mixture was transferred to a 100 L high-speed mixer and stirred at 800 rpm for 20 minutes to obtain a mixture.

[0121] Step 3: Place the mixture obtained in step 2 into a sagger, introduce air atmosphere, heat to 750°C at a rate of 2°C / min, and keep warm for 3 hours to perform a solid solution reaction to obtain an intermediate product.

[0122] Step 4: The intermediate product obtained in step 3 is further heated to 950°C at a rate of 2°C / min and sintered for 12 hours, cooled to room temperature to obtain a layered positive electrode material, and then pulverized, sieved, deironed, and packaged using a jet mill to obtain positive electrode material particles.

[0123] Example 2

[0124] This embodiment provides a positive electrode material and a preparation method thereof, the steps are as follows:

[0125] Step 1 is the same as in Example 1.

[0126] Step 2 is the same as in Example 1.

[0127] Step 3: Place the mixture obtained in step 2 into a sagger, introduce air atmosphere, heat to 705°C at a rate of 2°C / min, and keep warm for 2h to perform a solid solution reaction to obtain an intermediate product.

[0128] Step 4: The intermediate product obtained in step 3 is further heated to 950°C at a rate of 2°C / min and sintered for 12 hours, cooled to room temperature to obtain a layered positive electrode material, and then pulverized, sieved, deironed, and packaged using a jet mill to obtain positive electrode material particles.

[0129] Example 3

[0130] This embodiment provides a positive electrode material and a preparation method thereof, the steps are as follows:

[0131] Step 1 is the same as in Example 1.

[0132] Step 2 is the same as in Example 1.

[0133] Step 3: Place the mixture obtained in step 2 into a sagger, introduce air atmosphere, heat to 845°C at a rate of 2°C / min, and keep warm for 5 hours to perform a solid solution reaction to obtain an intermediate product.

[0134] Step 4: The intermediate product obtained in step 3 is further heated to 950°C at a rate of 2°C / min and sintered for 12 hours, cooled to room temperature to obtain a layered positive electrode material, and then pulverized, sieved, deironed, and packaged using a jet mill to obtain positive electrode material particles.

[0135] Example 4

[0136] This embodiment provides a positive electrode material and a preparation method thereof, the steps are as follows:

[0137] Step 1 is the same as in Example 1.

[0138] Step 2 is the same as in Example 1.

[0139] Step 3: Place the mixture obtained in step 2 into a sagger, introduce air atmosphere, heat to 750°C at a rate of 2°C / min, and keep warm for 3 hours to perform a solid solution reaction to obtain an intermediate product.

[0140] Step 4: The intermediate product obtained in step 3 is further heated to 935°C at a rate of 2°C / min and sintered for 10 hours, cooled to room temperature to obtain a layered positive electrode material, and then pulverized, sieved, deironed, and packaged using a jet mill to obtain positive electrode material particles.

[0141] Example 5

[0142] This embodiment provides a positive electrode material and a preparation method thereof, the steps are as follows:

[0143] Step 1 is the same as in Example 1.

[0144] Step 2 is the same as in Example 1.

[0145] Step 3: Place the mixture obtained in step 2 into a sagger, introduce air atmosphere, heat to 750°C at a rate of 2°C / min, and keep warm for 3 hours to perform a solid solution reaction to obtain an intermediate product.

[0146] Step 4: The intermediate product obtained in step 3 is further heated to 995°C at a rate of 2°C / min and sintered for 14 hours, cooled to room temperature to obtain a layered positive electrode material, and then pulverized, sieved, deironed, and packaged using a jet mill to obtain positive electrode material particles.

[0147] Example 6

[0148] This embodiment provides a positive electrode material and a preparation method thereof, the steps are as follows:

[0149] Step 1: Prepare the precursor

[0150] A nickel sulfate aqueous solution, a zinc sulfate aqueous solution, an iron sulfate aqueous solution, and a manganese sulfate aqueous solution were prepared according to the molar ratio of Ni, Zn, Fe, and Mn of 0.23:0.1:0.33:0.33.

[0151] A nickel sulfate aqueous solution, a zinc sulfate aqueous solution, an iron sulfate aqueous solution, a manganese sulfate aqueous solution, a precipitant NaOH and a complexing agent ammonia solution were mixed and reacted at a temperature of 60°C, a pH of 11.5 and an ammonia value of 3.5 g / L to obtain a material with a chemical formula of Ni with a D50 of 3 μm to 7 μm. 0.23 Zn 0.10 Fe 0.33 Mn 0.33 Precursor of (OH)2.

[0152] Steps 2-4 are the same as those in Example 1.

[0153] Example 7

[0154] This comparative example provides a positive electrode material and a preparation method thereof, the steps are as follows:

[0155] Step 1 is the same as in Example 1.

[0156] Step 2 is the same as in Example 1.

[0157] Step 3: Place the mixture obtained in step 2 into a sagger, introduce air atmosphere, and heat to 750°C at a rate of 2°C / min and keep warm for 3 hours to carry out a solid solution reaction.

[0158] Step 4: The intermediate product obtained in step 3 is further heated to 1050°C at a rate of 2°C / min and sintered for 12 hours, cooled to room temperature to obtain a layered positive electrode material, and then pulverized, sieved, deironed, and packaged using a jet mill to obtain positive electrode material particles.

[0159] Example 8

[0160] This comparative example provides a positive electrode material and a preparation method thereof, the steps are as follows:

[0161] Step 1 is the same as in Example 1.

[0162] Step 2 is the same as in Example 1.

[0163] Step 3: Place the mixture obtained in step 2 into a sagger, introduce air atmosphere, and heat to 900°C at a rate of 2°C / min and keep warm for 3 hours to carry out a solid solution reaction.

[0164] Step 4: The intermediate product obtained in step 3 is further heated to 950°C at a rate of 2°C / min and sintered for 12 hours, cooled to room temperature to obtain a layered positive electrode material, and then pulverized, sieved, deironed, and packaged using a jet mill to obtain positive electrode material particles.

[0165] Comparative Example 1

[0166] This comparative example provides a positive electrode material and a preparation method thereof, the steps are as follows:

[0167] Step 1: Sodium carbonate, nickel oxide, zinc oxide, iron oxide and manganese tetraoxide were added to a 4L high-speed mixer at a molar ratio of Na, Ni, Zn, Fe and Mn of 1:0.23:0.1:0.33:0.33, and the mixture was transferred to a 100L high-speed mixer and stirred at 800 rpm for 20 minutes to obtain a mixture.

[0168] Step 2: Place the mixture obtained in step 1 into a sagger, introduce air atmosphere, and heat to 750°C at a rate of 2°C / min and keep warm for 3 hours to carry out a solid solution reaction.

[0169] Step 3: The intermediate product obtained in step 2 is further heated to 995°C at a rate of 2°C / min and sintered for 14 hours, cooled to room temperature to obtain a layered positive electrode material, and then pulverized, sieved, deironed, and packaged using a jet mill to obtain positive electrode material particles.

[0170] Comparative Example 2

[0171] This comparative example provides a positive electrode material and a preparation method thereof, the steps are as follows:

[0172] Step 1 is the same as in Example 1.

[0173] Step 2 is the same as in Example 1.

[0174] Step 3: Place the mixture obtained in step 2 into a sagger, introduce air atmosphere, heat to 950°C at a rate of 2°C / min, sinter for 12 hours, cool to room temperature, and obtain a layered positive electrode material. Then, use a jet mill to crush, sieve, remove iron, and package to obtain positive electrode material particles.

[0175] Comparative Example 3

[0176] This comparative example provides a positive electrode material and a preparation method thereof, the steps are as follows:

[0177] Step 1 is the same as in Example 1.

[0178] Step 2 is the same as in Example 1.

[0179] Step 3: Place the mixture obtained in step 2 into a sagger, introduce air atmosphere, and heat to 750°C at a rate of 2°C / min and keep warm for 3 hours to carry out a solid solution reaction.

[0180] Step 4: The intermediate product obtained in step 3 is further heated to 900°C at a rate of 2°C / min and sintered for 12 hours, cooled to room temperature to obtain a layered positive electrode material, and then pulverized, sieved, deironed, and packaged using a jet mill to obtain positive electrode material particles.

[0181] Comparative Example 4

[0182] This comparative example provides a positive electrode material and a preparation method thereof, the steps are as follows:

[0183] Step 1 is the same as in Example 1.

[0184] Step 2 is the same as in Example 1.

[0185] Step 3: Place the mixture obtained in step 2 into a sagger, introduce air atmosphere, and heat to 650°C at a rate of 2°C / min and keep warm for 3 hours to carry out a solid solution reaction.

[0186] Step 4: The intermediate product obtained in step 3 is further heated to 950°C at a rate of 2°C / min and sintered for 12 hours, cooled to room temperature to obtain a layered positive electrode material, and then pulverized, sieved, deironed, and packaged using a jet mill to obtain positive electrode material particles.

[0187] Test items

[0188] Item 1: The morphologies of the precursors obtained in step 1 of Example 1 and Example 6 were tested, as shown in Figure 1 . Figure 1a is a SEM image of the precursor of Example 6, and Figure 1b is a SEM image of the precursor of Example 1. It can be seen that the particle size distribution of the precursor of Example 1 is wider, while the particle size distribution of the precursor of Example 6 is more concentrated.

[0189] Item 2: Test the (D90-D10) / D50 of the precursors of Example 1 and Example 6, as well as the (D90-D10) / D50 of the positive electrode material particles of Example 1 and Example 6. The method is: using Malvern Master Size 2000 instrumentation, using pure water as a dispersant, performing internal ultrasound before the test, with an intensity of 10 and a time of 10s, adding about 0.5g of sample powder to 800L of water with a sample spoon, the speed of the stirrer is 2600rpm, the shading degree is 8-12%, and the laser particle size is tested. The results are shown in Table 1. It can be seen that the particle size distribution of the positive electrode material particles mainly depends on the particle size distribution of the precursor. Compared with Example 6, the particle size distribution of Example 1 is wider, which is beneficial to improving the compaction density of the electrode.

[0190] Item 3. Test the morphology of the positive electrode material particles of each embodiment and comparative example, as shown in Figure 2, Figure 2a is an SEM image of the positive electrode material particles of Example 1, Figure 2b is an SEM image of the positive electrode material particles of Example 2, Figure 2c is an SEM image of the positive electrode material particles of Example 3, Figure 2d is an SEM image of the positive electrode material particles of Example 4, Figure 2e is an SEM image of the positive electrode material particles of Example 5, Figure 2f is an SEM image of the positive electrode material particles of Example 6, Figure 2g is an SEM image of the positive electrode material particles of Example 7, Figure 2h is an SEM image of the positive electrode material particles of Example 8, Figure 2i is an SEM image of the positive electrode material particles of Comparative Example 1, Figure 2j is an SEM image of the positive electrode material particles of Comparative Example 2, Figure 2k is an SEM image of the positive electrode material particles of Comparative Example 3, and Figure 2l is an SEM image of the positive electrode material particles of Comparative Example 4. As can be seen, Example 6 has a relatively concentrated particle size distribution with no small particles; Examples 7 and 8 exhibit agglomeration; and Comparative Examples 1 to 3 exhibit agglomeration. Combining the tap density and electrochemical performance reported in Table 1, it can be seen that when the positive electrode material particles lack small particles or exhibit agglomeration, the tap density is less than 1.95 g / cm, which is detrimental to their electrochemical performance.

[0191] Project 4: The tap density of the positive electrode material particles of each Example and Comparative Example was measured. Using a Dandong Better (BT-301) instrument, 20 g of the material was placed in a 25 mL graduated cylinder and vibrated 2000 times at a rate of 2000 vibrations / min. The tap density (TD) was calculated using the formula (TD = m / V). The results are shown in Table 1.

[0192] Item 5. X-ray diffraction test was performed on the positive electrode material particles of each embodiment and comparative example, as shown in Figures 3, 4 and 5, Figure 3a is the XRD diagram of the positive electrode material particles of Example 1, Figure 3b is the XRD diagram of the positive electrode material particles of Example 2, Figure 3c is the XRD diagram of the positive electrode material particles of Example 3, Figure 3d is the XRD diagram of the positive electrode material particles of Example 4, Figure 4e is the XRD diagram of the positive electrode material particles of Example 5, Figure 4f is the XRD diagram of the positive electrode material particles of Example 6, Figure 4g is the XRD diagram of the positive electrode material particles of Example 7, Figure 4h is the XRD diagram of the positive electrode material particles of Example 8, Figure 5i is the XRD diagram of the positive electrode material particles of Comparative Example 1, Figure 5j is the XRD diagram of the positive electrode material particles of Comparative Example 2, Figure 5k is the XRD diagram of the positive electrode material particles of Comparative Example 3, and Figure 5l is the XRD diagram of the positive electrode material particles of Comparative Example 4. Compared with the standard card of ZnO, it can be seen that the positive electrode material particles of Examples 1-8 do not contain ZnO, while the positive electrode material particles of Comparative Examples 1-4 have a ZnO diffraction peak with an intensity exceeding 200.

[0193] Project 6: Prepare the positive electrode material particles from each example and comparative example into positive electrode sheets and assemble them into button cells. The specific method is as follows: weigh the positive electrode material, acetylene black, and polyvinylidene fluoride (PVDF) in a 90:5:5 mass ratio, mix them evenly, add NMP and stir for 2 hours to form a viscous slurry, evenly coat the slurry on a 15μm thick aluminum foil, then vacuum bake at 80°C, press the sheet, and cut the positive electrode discs with a diameter of 14mm. A pure sodium sheet with a diameter of 16mm was used as the negative electrode sheet, Tianci ENA-18 was used as the electrolyte, and a PP / PE / PP composite separator was used. The button cells were assembled in an argon-filled glove box.

[0194] 6.1 The ultimate compaction density of the positive electrode sheets of each embodiment and comparative example was tested. The specific method was: fold the sheet in half and observe whether there were holes. The compaction corresponding to the appearance of holes was called the ultimate compaction. The results are shown in Table 1.

[0195] 6.2 The button-type batteries of each Example and Comparative Example were tested for their initial discharge capacity, initial efficiency, and cycle capacity retention. The specific method employed was: a voltage range of 2-4 V, a nominal gram capacity of 150 mAh / g, and a test procedure of 0.1 / 0.1C charge and discharge for two weeks, with a constant voltage cutoff current of 0.05C. The charge and discharge gram capacities were measured, and the initial efficiency was calculated. The results are shown in Table 1.

[0196] 6.3 The positive electrode material particles from each example and comparative example were prepared into positive electrode sheets and assembled into full batteries. Specifically, the positive electrode material, conductive carbon black SP, conductive graphite KS-6, and binder PVDF were mixed in a mass ratio of 94.5%:2%:1%:2.5% NMP (N-methylpyrrolidone) to prepare a positive electrode slurry. The positive electrode sheets were then fabricated through coating and roller pressing. The positive electrode sheets were then assembled with the negative electrode (hard carbon), separator, and electrolyte (1 mol / L NaPF6 + DEC / EC (volume ratio 1:1)) into a 503048 model full battery with a capacity of approximately 400 mAh, which was then used for testing.

[0197] Cyclic performance test: using Xinwei test cabinet (CT3008-5V3A-A1), at 45℃, with a cycle voltage of 4-2V, a constant voltage cut-off current of 20mA, and 300 cycles.

[0198] The results of the 7-day thermal runaway gas production test at 45°C are shown in Table 1.

[0199] The DCR growth rate was tested 300 times at 45°C. The results are shown in Table 1.

[0200] Table 1

[0201] It can be seen that the cycle performance of the positive electrode materials of each embodiment is good, especially the positive electrode materials of Examples 1-5, which have no ZnO phase. In addition to the high cycle capacity retention rate, low thermal runaway gas production, and small DCR growth rate, the prepared positive electrode sheets have a high ultimate compaction density and a large tap density, and the other electrochemical properties of the prepared batteries are all good.

[0202] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0203] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A positive electrode material, wherein: Its chemical formula is Na a Ni b Zn c Fe d Mn e X f O2, wherein 0.85≤a≤1.1, 0.1≤b≤0.4, 0.05≤c≤0.4, 0.1≤d≤0.4, 0.1≤e≤0.5, 0≤f≤0.02, and X is at least one element selected from Ti, Al, Ta, Nb, Ge, Y, Nb, W, Zr, B, Ce, Ca, V, Si, Sr, Mg and Mo; In the X-ray diffraction spectrum of the positive electrode material, there is no diffraction peak when the diffraction angle 2θ value is within at least one of the ranges of 31° to 32° and 34° to 35°.

2. The positive electrode material according to claim 1, wherein The positive electrode material satisfies at least one of the following conditions: (1) 0.95≤a≤1.1; (2) 0.2≤b≤0.3; (3) 0.05≤c≤0.2; (4) 0.2≤d≤0.4; (5) 0.2≤e≤0.

4.

3. The positive electrode material according to claim 1 or claim 2, wherein The particle size of the positive electrode material satisfies: (D90-D10) / D50≥0.

7.

4. The positive electrode material according to claim 3, wherein The tap density of the positive electrode material satisfies: TD ≥ 1.95 g / cm 3 .

5. A method for preparing a positive electrode material, wherein: The following steps are involved: According to the molar ratio of Na element to precursor, a mixture of Na source and chemical formula Ni b Zn c Fe d Mn e (OH)2 precursor, to obtain a mixture, wherein 0.85≤a≤1.1, 0.1≤b≤0.4, 0.05≤c≤0.4, 0.1≤d≤0.4, 0.1≤e≤0.5; The mixture is subjected to a solid solution reaction at a temperature of 700° C. or higher for not less than 2 hours to obtain an intermediate product; The intermediate product is sintered until the X-ray diffraction spectrum of the sintered product has no diffraction peak at a diffraction angle 2θ value within at least one of a range of 31° to 32° and 34° to 35°, and the chemical formula is Na a Ni b Zn c Fe d Mn e O2 positive electrode material.

6. The method for preparing the positive electrode material according to claim 5, wherein: The preparation of the mixed material also includes the following steps: An additive is added according to a molar ratio of element X to the precursor of f:1, wherein the additive is selected from oxides or hydroxides containing element X; the element X is at least one of Ti, Al, Ta, Nb, Ge, Y, Nb, W, Zr, B, Ce, Ca, V, Si, Sr, Mg and Mo, wherein 0≤f≤0.

02.

7. The method for preparing the positive electrode material according to claim 5 or claim 6, wherein: The solid solution reaction and sintering satisfy at least one of the following conditions: (1) The temperature of the solid solution reaction is 700° C. to 850° C.; (2) The solid solution reaction time is 2h to 5h; (3) The sintering temperature is not less than 930° C.; (4) The sintering time is 10 h to 14 h.

8. The method for preparing the positive electrode material according to claim 5 or claim 6, wherein: The particle size of the precursor satisfies: (D90-D10) / D50≥0.

7.

9. The method for preparing the positive electrode material according to claim 8, wherein: The preparation method of the precursor comprises the following steps: According to the chemical formula of the precursor, preparing a first metal salt solution and a second metal salt solution; Mixing a first metal salt solution, a precipitant and a complexing agent, and reacting them under alkaline conditions to obtain seed crystals with a D50 of 1 μm to 3 μm; The seed crystal and the second metal salt solution are mixed and reacted under alkaline conditions to obtain the precursor.

10. The method for preparing a positive electrode material according to claim 9, wherein: The metal elements in the first metal salt solution and the second metal salt solution are selected from one or more of Ni, Zn, Fe and Mn elements.

11. The method for preparing a positive electrode material according to claim 9 or 10, wherein: The first metal salt solution, the precipitant and the complexing agent react under the conditions of a temperature of 50° C. to 70° C., a pH of 11.3 to 12.0, and an ammonia value of 3.3 g / L to 3.7 g / L.

12. The method for preparing a positive electrode material according to any one of claims 9 to 11, wherein: The seed crystal and the second metal salt solution react under the conditions of a temperature of 50° C. to 70° C., a pH of 11.3 to 12.0, and an ammonia value of 3.3 g / L to 3.7 g / L.

13. The method for preparing the positive electrode material according to any one of claims 5, 6, and 9 to 12, wherein: The Na source is selected from at least one of Na2CO3 and NaHCO3.

14. A positive electrode sheet, comprising a positive electrode current collector and a positive electrode active layer arranged on the surface of the positive electrode current collector, wherein the material of the positive electrode active layer comprises the positive electrode material according to any one of claims 1 to 4 or the positive electrode material prepared by the preparation method according to any one of claims 5 to 13, a conductive agent and a binder.

15. The positive electrode sheet according to claim 14, wherein: The ultimate compaction density of the positive electrode sheet is 3.1 g / cm 3 ~3.5g / cm 3 .

16. The positive electrode sheet according to any one of claims 14 to 15, wherein: The conductive agent is one or more of acetylene black, conductive carbon black and conductive graphite.

17. The positive electrode sheet according to any one of claims 14 to 16, wherein: The binder is one or more of polyvinylidene fluoride and N-methylpyrrolidone.

18. A sodium ion battery, wherein: The invention comprises the positive electrode material according to any one of claims 1 to 4, the positive electrode material prepared by the preparation method according to any one of claims 5 to 13, or the positive electrode sheet according to any one of claims 14 to 17.

19. The sodium ion battery according to claim 18, wherein: It also includes a negative electrode plate, an electrolyte and a separator.

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