Layered oxide positive electrode active material and preparation method and application thereof

Abstract

The invention discloses a preparation method of a layered oxide positive electrode active material, which comprises the following steps: a, mixing a precursor metal salt solution with a precipitator and a complexing agent according to a designed ratio, and carrying out coprecipitation reaction to obtain a precursor; b, introducing a divalent metal salt solution into the precursor obtained in the step a, carrying out aging treatment, washing, filtering and drying to obtain a precursor containing a divalent metal coating layer; and c, mixing the precursor containing the divalent metal coating layer obtained in the step b, a sodium source and a tetravalent metal compound, and sintering to obtain the positive electrode active material. According to the method provided by the invention, the capacity of the positive electrode active material is effectively improved, irreversible phase change of the positive electrode active material in a high-voltage process is inhibited, and the stability of the positive electrode active material structure is improved.

Description

Technical Field

[0001] This application belongs to the field of secondary battery technology, specifically relating to a layered oxide positive electrode active material and its preparation method. Furthermore, this application also relates to a secondary battery and an electrical device. Background Technology

[0002] Lithium-ion batteries have been widely used in electric vehicles, 3C products, and other fields, permeating all aspects of people's lives. However, in the long run, lithium-ion batteries will face the problem of insufficient reserves, and their energy density drops significantly at low temperatures, making it difficult to meet the needs of some regions. Sodium-ion batteries work on a similar principle to lithium-ion batteries. Sodium resources are abundant in the Earth's crust, inexpensive, and have advantages over lithium-ion batteries in terms of low-temperature performance and safety. Therefore, developing structurally stable sodium-ion battery cathode active materials with high energy density is particularly important.

[0003] Sodium-ion battery cathode active materials have two structures: layered and tunnel. Among them, the structure and charge / discharge mechanism of layered oxide cathode active materials are similar to those of lithium-ion ternary materials, and they have a high discharge specific capacity. However, they also have problems such as severe irreversible phase transitions during high-voltage cycling, severe gas generation, high surface residual alkali, and difficulties in processing.

[0004] Therefore, it is necessary to conduct in-depth research and improvement on layered oxide cathode active materials in order to improve the electrochemical performance of cathode active materials under high voltage. Summary of the Invention

[0005] This application aims to at least partially address one of the technical problems in the related art. To this end, embodiments of this application propose a layered oxide positive electrode active material and its preparation method. During the synthesis of the positive electrode active material precursor, divalent metal ions are introduced in situ to form a coating layer, and tetravalent metal ions are doped during sintering. This not only effectively improves the capacity of the positive electrode active material but also suppresses the irreversible phase transition of the positive electrode active material during high voltage, thereby enhancing the structural stability of the positive electrode active material.

[0006] This application provides a method for preparing a layered oxide positive electrode active material, comprising the following steps:

[0007] a. Mix the precursor metal salt solution with the precipitant and complexing agent according to the designed ratio, and co-precipitate the precursor to obtain the precursor.

[0008] b. Pass a divalent metal salt solution into the precursor obtained in step a, perform aging treatment, and after washing, filtering and drying, obtain a precursor containing a divalent metal coating layer.

[0009] c. The precursor containing a divalent metal coating layer obtained in step b, the sodium source, and the tetravalent metal compound are mixed and sintered to obtain the positive electrode active material.

[0010] The advantages and technical effects of the preparation method of the layered oxide positive electrode active material in this application are as follows:

[0011] 1. In the method of this application embodiment, after the precursor metal salt is prepared by co-precipitation reaction, a divalent metal salt solution is introduced, and the divalent metal is uniformly precipitated on the surface of the precursor, thus coating the precursor in situ. Compared with the existing technology of sintering doping, a more uniform coating can be achieved.

[0012] 2. In the method of this application embodiment, some of the divalent metal elements in situ coated on the surface of the precursor enter the transition metal layer of the positive electrode active material after subsequent sintering, reducing the overall valence state of the transition metal and increasing the Na content in the positive electrode active material. + The proportion of divalent metals increases the capacity of the positive electrode active material; some divalent metals enter the Na layer, which can form a "pillar effect", which is beneficial to stabilizing the crystal structure and improving the stability of the positive electrode active material.

[0013] 3. In the method of this application embodiment, after forming a divalent metal coating layer in situ on the surface of the precursor, a tetravalent metal element is introduced for sintering doping. The introduction of the tetravalent metal element further stabilizes the crystal structure of the positive electrode active material and plays an important role in suppressing the irreversible phase transition of the positive electrode active material during high voltage. This is because the bond strength between the tetravalent metal and the O bond is greater than that of the main elements Ni-O, Fe-O and Mn-O, which can effectively suppress the oxidation of oxygen and oxygen escape, thereby delaying the side reactions and crystal structure decay of the positive electrode active material.

[0014] 4. The method in this application embodiment is simple and easy to apply. The obtained positive electrode active material not only has a high energy density, but also has a stable structure and excellent cycle performance under high voltage.

[0015] In some embodiments, in step a, the precursor metal salt solution includes nickel sulfate and manganese sulfate, and optionally, the precursor metal salt solution further includes ferric sulfate; the precipitant includes at least one of sodium hydroxide or sodium carbonate; and the complexing agent includes ammonia.

[0016] In some embodiments, in step a, the temperature of the coprecipitation reaction is 40–60°C, the pH is controlled at 9.50–10.20, and the reaction atmosphere is controlled as an inert atmosphere.

[0017] In some embodiments, in step a, the particle size D of the obtained precursor v50 The size is 3–15 μm.

[0018] 0.40≤K 90 ≤1.70, where K 90 =(D v90 -D v10 ) / D v50 .

[0019] In some embodiments, in step b, the divalent metal salt includes at least one of a divalent metal sulfate, nitrate, or chloride; optionally, the divalent metal ion includes Cu. 2+ Zn 2+ Mg 2+ Ca 2+ Ba 2+ 、Sr 2+ At least one of them.

[0020] In some embodiments, in step b, the flow rate of the divalent metal salt solution is 20-60 ml / min; the aging temperature is 40-60°C and the aging time is 0.5-5.0 h; the drying temperature is 90-110°C and the drying time is 4-10 h.

[0021] In some embodiments, in step c, the tetravalent metal compound includes at least one of a tetravalent metal oxide, carbonate, nitrate, or acetate; optionally, the tetravalent metal ion includes Ti. 4+ Zr 4+ 、Nb 4+ Sn 4+ Ru 4+ Ce 4+ At least one of them.

[0022] In some embodiments, in step c, the sodium source includes at least one of sodium carbonate, sodium bicarbonate, sodium nitrate, sodium oxalate, and sodium acetate.

[0023] In some embodiments, in step c, the mixing is performed by ball milling for a time of 0.5 h to 3 h.

[0024] In some embodiments, step c includes two sintering processes: the first sintering process includes heating to 750-800°C at a heating rate of 2-7°C / h and holding for 1-5 hours; the second sintering process includes heating to 800-1100°C at a heating rate of 2-7°C / h and holding for 10-17 hours.

[0025] In some embodiments, the chemical formula of the positive electrode active material obtained in step c is:

[0026] Na x Nia Fe b Mn c A e B (1-a-b-c-e) O2, where 0.50≤x≤1.10, 0.10≤a≤0.40, 0≤b≤0.40, 0.20≤c≤0.80, 0.001≤e≤0.30, and A contains divalent metal ions Cu. 2+ Zn 2+ Mg 2+ Ca 2+ Ba 2+ 、Sr 2+ At least one of them, B contains a tetravalent metal ion Ti 4+ Zr 4+ 、Nb 4+ Sn 4+ Ru 4+ Ce 4+ At least one of them.

[0027] This application also provides a layered oxide cathode active material, which is prepared using the preparation method of the layered oxide cathode active material described in the above embodiments of this application. The layered oxide cathode active material of this application introduces divalent and tetravalent metal elements. Some of the divalent metal elements enter the transition metal layer of the cathode active material, reducing the overall valence state of the transition metal and increasing the Na content in the cathode active material. + The proportion of divalent metal elements increases the capacity of the positive electrode active material; some divalent metal elements enter the Na layer, forming a "pillar effect", which is conducive to stabilizing the crystal structure and improving the stability of the positive electrode active material; the introduction of tetravalent metal elements effectively suppresses the irreversible phase transition of the positive electrode active material during high voltage, further stabilizing the crystal structure of the positive electrode active material, enabling the positive electrode active material to exhibit excellent cycle performance under high voltage.

[0028] This application also provides a secondary battery, which includes the layered oxide positive electrode active material of this application. The secondary battery of this application possesses all the advantages of the layered oxide positive electrode active material of this application, and will not be repeated here.

[0029] This application also provides an electrical device that includes the secondary battery described in this application. The electrical device of this application possesses all the advantages of the secondary battery described in this application, which will not be elaborated further here. Attached Figure Description

[0030] Figure 1 Here is a SEM image of the layered oxide positive electrode active material prepared in Example 1;

[0031] Figure 2 The cycling curves of the positive electrode active materials prepared in Example 1 and Comparative Example 1 after being assembled into a button cell at 2.0–4.1V are shown. Detailed Implementation

[0032] The embodiments of this application are described in detail below. The embodiments and accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0034] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0038] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0039] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0040] This application provides a method for preparing a layered oxide positive electrode active material, comprising the following steps:

[0041] a. Mix the precursor metal salt solution with the precipitant and complexing agent according to the designed ratio, and co-precipitate the precursor to obtain the precursor.

[0042] b. Pass a divalent metal salt solution into the precursor obtained in step a, perform aging treatment, and after washing, filtering and drying, obtain a precursor containing a divalent metal coating layer.

[0043] c. The precursor containing a divalent metal coating layer obtained in step b, the sodium source, and the tetravalent metal compound are mixed and sintered to obtain the positive electrode active material.

[0044] In the preparation method of the layered oxide positive electrode active material of this application embodiment, after the precursor metal salt is obtained by co-precipitation reaction, a divalent metal salt solution is introduced, and the divalent metal is uniformly precipitated on the surface of the precursor, thus coating the precursor in situ. Compared with the existing technology that uses sintering doping, a more uniform coating can be achieved.

[0045] In the preparation method of the layered oxide cathode active material of this application embodiment, some of the divalent metal elements in situ coated on the surface of the precursor enter the transition metal layer of the cathode active material after subsequent sintering, reducing the overall valence state of the transition metal and increasing the Na content in the cathode active material. + The proportion of divalent metals increases the capacity of the positive electrode active material; some divalent metals enter the Na layer, which can form a "pillar effect", which is beneficial to stabilizing the crystal structure and improving the stability of the positive electrode active material.

[0046] In the preparation method of the layered oxide positive electrode active material in this application embodiment, after forming a divalent metal coating layer in situ on the surface of the precursor, a tetravalent metal element is introduced for sintering doping. The introduction of the tetravalent metal element further stabilizes the crystal structure of the positive electrode active material and plays an important role in suppressing the irreversible phase transition of the positive electrode active material during high voltage. This is because the bond strength between the tetravalent metal and the O bond is greater than that of the main elements Ni-O, Fe-O and Mn-O, which can effectively suppress the oxidation of oxygen and oxygen escape, thereby delaying the side reactions and crystal structure decay of the positive electrode active material.

[0047] The preparation method of the layered oxide positive electrode active material in this application is simple and easy to apply. The obtained positive electrode active material not only has a high energy density, but also has a stable structure and excellent cycle performance under high voltage.

[0048] In some embodiments, in step a, the precursor metal salt solution includes nickel sulfate and manganese sulfate; optionally, the precursor metal salt solution further includes ferric sulfate; the precipitant includes at least one of sodium hydroxide or sodium carbonate; and the complexing agent includes ammonia. In this application embodiment, there are no particular limitations on the precipitant and complexing agent used for the co-precipitation reaction; any precipitant and complexing agent in the prior art capable of preparing the positive electrode active material precursor is applicable to this application embodiment.

[0049] In some embodiments, in step a, the temperature of the coprecipitation reaction is 40–60°C, the pH is controlled at 9.50–10.20, and the reaction atmosphere is controlled as an inert atmosphere. In the embodiments of this application, the coprecipitation reaction conditions are mild and easy to control.

[0050] In some embodiments, in step a, the particle size D of the obtained precursor v50 The size is 3–15 μm.

[0051] 0.40≤K 90 ≤1.70, where K 90 =(D v90 -D v10 ) / D v50 Optionally, D v50 =4~10μm, K 90 = 0.60~1.30. In the embodiments of this application, the precursor particle size D is controlled. v50 and K 90 This is beneficial for further improving the performance of the positive electrode active material.

[0052] In this embodiment of the application, D v10 This refers to the particle size at which the cumulative volume distribution percentage reaches 10%, meaning that the volume content of particles smaller than or equal to this size accounts for 10% of the total particle volume; D v50 This refers to the particle size at which the cumulative volume distribution percentage reaches 50%, meaning that particles smaller than or equal to this size account for 50% of the total particle volume; D v90 This refers to the particle size at which the cumulative volume distribution percentage reaches 90%, meaning that the volume content of particles smaller than or equal to this size accounts for 90% of the total particle volume.

[0053] In some embodiments, in step b, the divalent metal salt includes at least one of a divalent metal sulfate, nitrate, or chloride; optionally, the divalent metal ion includes Cu. 2+ Zn 2+ Mg 2+ Ca 2+ Ba 2+ 、Sr 2+At least one of them, and optionally, the divalent metal ion includes Cu. 2+ Zn 2+ Mg 2+ Ca 2+ At least one of the following. In the embodiments of this application, the selection of divalent metals is beneficial for the more uniform precipitation of divalent metals on the surface of the precursor, forming a more uniform coating layer. This is beneficial for some divalent metals to enter the transition metal layer after subsequent sintering, reducing the valence state of the transition metal, increasing the proportion of Na ions, and further improving the energy density of the positive electrode active material. At the same time, it is also beneficial for some divalent metal elements to enter the Na layer, forming a better pillar effect and improving the stability of the crystal structure.

[0054] In some embodiments, in step b, the flow rate of the divalent metal salt solution is 20-60 ml / min; the aging temperature is 40-60°C, and the aging time is 0.5-5.0 h; the drying temperature is 90-110°C, and the drying time is 4-10 h. In this embodiment, controlling the flow rate of the divalent metal salt solution facilitates the uniform precipitation of divalent metals on the precursor surface, forming a more uniform coating layer.

[0055] In some embodiments, in step c, the tetravalent metal compound includes at least one of a tetravalent metal oxide, carbonate, nitrate, or acetate; optionally, the tetravalent metal ion includes Ti. 4+ Zr 4+ 、Nb 4+ Sn 4+ Ru 4+ Ce 4+ At least one of the following. In the embodiments of this application, by selecting tetravalent metal elements, it is beneficial to further improve the suppression effect on the irreversible phase transition of the positive electrode active material during high voltage, and to improve the structural stability of the positive electrode active material, thereby improving the cycle performance of the positive electrode active material under high voltage.

[0056] In some embodiments, in step c, the sodium source includes at least one selected from sodium carbonate, sodium bicarbonate, sodium nitrate, sodium oxalate, and sodium acetate. In this application embodiment, there are no particular limitations on the sodium source used in the positive electrode active material; commonly used sodium sources in the prior art are applicable to the embodiments of this application.

[0057] In some embodiments, in step c, the mixing is performed by ball milling for 0.5 h to 3 h. In this embodiment, ball milling is beneficial for achieving uniform mixing of the raw materials to be sintered.

[0058] In some embodiments, step c, the sintering process includes two stages: the first stage includes heating to 750–800°C at a heating rate of 2–7°C / h and holding for 1–5 hours; the second stage includes further heating to 800–1100°C at a heating rate of 2–7°C / h and holding for 10–17 hours. Optionally, the heating rate for the first and second stages is controlled at 3–4°C / h, the temperature for the second stage is controlled at 880–990°C, and the holding time is controlled at 12–15 hours. In this embodiment, there are no particular limitations on the sintering process of the positive electrode active material; commonly used sintering processes in the prior art are applicable to this embodiment. The sintering process using the controlled conditions of this embodiment enables more uniform doping of divalent and tetravalent metal elements, further improving the energy density and cycle performance under high voltage of the positive electrode active material.

[0059] In some embodiments, the chemical formula of the positive electrode active material obtained in step c is:

[0060] Na x Ni a Fe b Mn c A e B (1-a-b-c-e) O2, where 0.50≤x≤1.10, 0.10≤a≤0.40, 0≤b≤0.40, 0.20≤c≤0.80, 0.001≤e≤0.30, and A contains divalent metal ions Cu. 2+ Zn 2+ Mg 2+ Ca 2+ Ba 2+ 、Sr 2+ At least one of them, B contains a tetravalent metal ion Ti 4+ Zr 4+ 、Nb 4+ Sn 4+ Ru 4+ Ce 4+ At least one of the following. In the embodiments of this application, selecting the chemical formula of the positive electrode active material is beneficial to further improve the energy density and cycle performance of the positive electrode active material.

[0061] This application also provides a layered oxide positive electrode active material, which is prepared by the preparation method of the layered oxide positive electrode active material of the above embodiments of this application.

[0062] The layered oxide cathode active material of this application introduces divalent and tetravalent metal elements. Some of the divalent metal elements enter the transition metal layer of the cathode active material, reducing the overall valence state of the transition metal and increasing the Na content in the cathode active material.+ The proportion of divalent metal elements increases the capacity of the positive electrode active material; some divalent metal elements enter the Na layer, forming a "pillar effect", which is conducive to stabilizing the crystal structure and improving the stability of the positive electrode active material; the introduction of tetravalent metal elements effectively suppresses the irreversible phase transition of the positive electrode active material during high voltage, further stabilizing the crystal structure of the positive electrode active material, enabling the positive electrode active material to exhibit excellent cycle performance under high voltage.

[0063] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0064] The volume particle size of the positive electrode active material in this embodiment was measured using a laser diffraction scattering particle size analyzer (Malvin 3000).

[0065] The morphology of the positive electrode active material in this application embodiment was characterized by observing the surface morphology of the material using a scanning electron microscope, specifically a Phenopro electron microscope.

[0066] Example 1

[0067] Preparation of positive electrode active material Na 0.82 Ni 0.221 Fe 0.2845 Mn 0.4142 Zn 0.0326 Ti 0.0477 O2

[0068] 1. Synthesis of precursors containing divalent metal coatings:

[0069] Step 1.1: According to the designed ratio, NiSO4 solution, FeSO4 solution and Mn(SO4)2 solution are mixed in a mixing tank and stirred for 30 min to prepare a 2 mol / L metal salt solution M1;

[0070] Prepare a 2 mol / L sodium hydroxide solution as a precipitant and a 2 mol / L ammonia solution as a complexing agent;

[0071] Weigh out ZnSO4 powder, dissolve it in deionized water, dissolve and stir in a mixing tank for 30 min to prepare a 0.5 mol / L divalent metal salt solution M2;

[0072] Step 1.2: Add 3 g / L ammonia solution as the base solution to the reactor. Heat the reactor to 50°C. Under a stirring speed of 800 rpm, simultaneously introduce the metal salt solution M1, NaOH solution, and ammonia solution into the reactor at a flow rate of 60 ml / min. Maintain the pH in the reactor at 10.05–10.10, and use nitrogen atmosphere. The current precursor particle size reaches D... v50 5–6 μm, K v90 When the concentration is ≤1.10, stop feeding the molten metal M1, NaOH solution and ammonia water to obtain the precursor;

[0073] Step 1.3: During the precursor aging process, metal solution M2 is slowly introduced into the reactor at a flow rate of 40 ml / min, while maintaining stirring and reaction temperature, and the reaction continues for 3.0 h. After that, the reaction solution is washed and filtered in a centrifuge, and the filter cake is dried in an oven at 100 °C for 5 h. After sieving, the Zn-coated precursor is obtained.

[0074] 2. Preparation of layered oxide positive electrode active materials

[0075] Step 2.1: Add the Zn-coated precursor, sodium carbonate and nano TiO2 powder obtained in Step 1 to a ball mill and mix for 60 min. Na:Me = 0.82:1 (molar ratio), where Me refers to the total molar amount of other metal elements in the positive electrode active material except Na.

[0076] Step 2.2: The uniformly milled mixture is loaded into a bowl and sintered in a roller kiln. The heating rate is controlled at 3℃ / h. The first sintering process involves heating to 780℃ and holding for 2 hours. The second sintering process involves heating to 900℃ and holding for 15 hours to complete the sintering process.

[0077] Step 2.3: After cooling the sintered positive electrode active material, it is pulverized by a roller mill and an air jet mill to dissociate the positive electrode active material into D... v50 =5~6μm, sieved to obtain layered oxide positive electrode active material Na 0.82 Ni 0.221 Fe 0.2845 Mn 0.4142 Zn 0.0326 Ti 0.0477 O2.

[0078] The SEM image of the layered oxide positive electrode active material prepared in this embodiment is shown below. Figure 1 As shown, the surface of the positive electrode active material is relatively smooth and free of abnormal particles, indicating that the coating material is uniformly attached to the surface of the positive electrode active material.

[0079] The median particle size D of the layered oxide positive electrode active material prepared in this embodiment is... v50 =5.7μm,Kv90 =1.02.

[0080] Example 2

[0081] The method is the same as in Example 1, except that the ratio of each metal element is different, and the chemical formula of the resulting positive electrode active material is Na. 0.80 Ni 0.222 Fe 0.3036 Mn 0.4118 Zn 0.0147 Ti 0.0479 O2.

[0082] The median particle size D of the positive electrode active material prepared in this embodiment is v50 =5.9μm,K v90 =1.01.

[0083] Example 3

[0084] The method is the same as in Example 1, except that the ratio of each metal element is different, and the chemical formula of the resulting positive electrode active material is Na. 0.80 Ni 0.2271 Fe 0.3105 Mn 0.4212 Zn 0.0153 Ti 0.0259 O2.

[0085] The median particle size Dv of the positive electrode active material prepared in this embodiment 50 =5.7μm,Kv 90 =1.01.

[0086] Example 4

[0087] Preparation of positive electrode active material Na 0.80 Ni 0.2264 Fe 0.3105 Mn 0.4212 Mg 0.0159 Ti 0.026 O2

[0088] 1. Synthesis of precursors containing divalent metal coatings:

[0089] Step 1.1: According to the designed ratio, NiSO4 solution, FeSO4 solution and Mn(SO4)2 solution are mixed in a mixing tank and stirred for 30 min to prepare a 2 mol / L metal salt solution M1;

[0090] Prepare a 2 mol / L sodium hydroxide solution as a precipitant and a 2 mol / L ammonia solution as a complexing agent;

[0091] Weigh out MgSO4 powder, dissolve it in deionized water, dissolve and stir in a mixing tank for 30 min to prepare a 0.3 mol / L divalent metal salt solution M2;

[0092] Step 1.2: Add 3 g / L ammonia solution as the base solution to the reactor. Heat the reactor to 50°C. Under a stirring speed of 800 rpm, simultaneously introduce the metal salt solution M1, NaOH solution, and ammonia solution into the reactor at a flow rate of 60 ml / min. Maintain the pH in the reactor at 10.05–10.10, and use nitrogen atmosphere. The current precursor particle size reaches D... v50 5–6 μm, K v90 When the concentration is ≤1.20, stop feeding the molten metal M1, NaOH solution and ammonia water to obtain the precursor;

[0093] Step 1.3: During the precursor aging process, metal solution M2 is slowly introduced into the reactor at a flow rate of 40 ml / min, while maintaining stirring and reaction temperature, and the reaction continues for 3.5 h. After that, the reaction solution is washed and filtered in a centrifuge, and the filter cake is dried in an oven at 100 °C for 7 h. After sieving, Mg-coated precursor is obtained.

[0094] 2. Preparation of layered oxide positive electrode active materials

[0095] Step 2.1: Add the Mg-coated precursor, sodium carbonate and nano TiO2 powder obtained in Step 1 to a ball mill and mix for 60 min. Na:Me = 0.80:1 (molar ratio), where Me refers to the total molar amount of other metal elements in the positive electrode active material except Na.

[0096] Step 2.2: The uniformly milled mixture is loaded into a bowl and sintered in a roller kiln. The heating rate is controlled at 3℃ / h. The first sintering process involves heating to 780℃ and holding for 2 hours. The second sintering process involves heating to 990℃ and holding for 15 hours to complete the sintering process.

[0097] Step 2.3: After cooling the sintered positive electrode active material, it is pulverized by a roller mill and an air jet mill to dissociate the positive electrode active material into D... v50 =5~6μm, sieved to obtain layered oxide positive electrode active material Na 0.80 Ni 0.2264 Fe 0.3105 Mn 0.421 2Mg 0.0159 Ti 0.026 O2.

[0098] The median particle size D of the positive electrode active material prepared in this embodiment is v50 =5.4μm,K v90 =1.05.

[0099] Example 5

[0100] Preparation of positive electrode active material Na 0.82 Ni 0.2267 Fe 0.2812 Mn 0.4139 Cu 0.0368 Ti 0.0414 O2

[0101] The method is the same as in Example 1, except that in step 1, the method for synthesizing a precursor containing a divalent metal coating is to replace ZnSO4 with CuSO4 to synthesize a Cu-coated precursor.

[0102] In this embodiment, a layered oxide positive electrode active material Na was prepared. 0.82 Ni 0.2267 Fe 0.2812 Mn 0.4139 Cu 0.0368 Ti 0.041 4O2, median particle size D v50 =5.6μm,K v90 =1.01.

[0103] Example 6

[0104] Preparation of positive electrode active material Na 0.82 Ni 0.2288 Fe 0.2803 Mn 0.4125 Ca 0.0365 Ti 0.0419 O2

[0105] The method is the same as in Example 1, except that in step 1, the method for synthesizing a precursor containing a divalent metal coating is to replace ZnSO4 with CaSO4 and use Na2CO3 as a precipitant to finally obtain a Ca-coated precursor material.

[0106] In this embodiment, a layered oxide positive electrode active material Na was prepared. 0.82 Ni 0.2288 Fe 0.2803 Mn 0.4125 Ca 0.0365 Ti 0.041 9O2, median particle size D v50 =5.4μm,K v90 =1.19.

[0107] Example 7

[0108] Preparation of positive electrode active material Na 0.82 Ni 0.2255 Fe 0.2884 Mn 0.4098Ba 0.0354 Ti 0.0409 O2

[0109] The method is the same as in Example 1, except that in step 1, the method for synthesizing the precursor containing a divalent metal coating is to replace ZnSO4 with BaSO4 and use Na2CO3 as a precipitant to finally obtain the Ba-coated precursor material.

[0110] In this embodiment, a layered oxide positive electrode active material Na was prepared. 0.82 Ni 0.2255 Fe 0.2884 Mn 0.4098 Ba 0.0354 Ti 0.040 9O2, median particle size D v50 =5.5μm,K v90 =1.06.

[0111] Example 8

[0112] Preparation of positive electrode active material Na 0.82 Ni 0.2261 Fe 0.2897 Mn 0.4080 Sr 0.0351 Ti 0.0411 O2

[0113] The method is the same as in Example 1, except that in step 1, the method for synthesizing the precursor containing a divalent metal coating is to replace ZnSO4 with SrSO4 and use Na2CO3 as a precipitant to finally obtain the Sr-coated precursor material.

[0114] In this embodiment, a layered oxide positive electrode active material Na was prepared. 0.82 Ni 0.2261 Fe 0.2897 Mn 0.4080 Sr 0.0351 Ti 0.041 1O2, median particle size D v50 =5.5μm,K v90 =1.07.

[0115] Example 9

[0116] Preparation of positive electrode active material Na 0.82 Ni 0.2207 Fe 0.2855 Mn 0.4135 Zn 0.0335 Zr 0.0468 O2

[0117] The method is the same as in Example 1, except that in step 2, nano ZrO2 powder is used instead of TiO2 powder.

[0118] In this embodiment, a layered oxide positive electrode active material Na was prepared. 0.82 Ni 0.2207 Fe 0.2855 Mn 0.4135 Zn 0.0335 Zr 0.046 8O2, median particle size D v50 =5.7μm,K v90 =1.07.

[0119] Example 10

[0120] The method is the same as in Example 1, except that in step 2, nano NbO2 powder is used instead of TiO2 powder.

[0121] In this embodiment, a layered oxide positive electrode active material Na was prepared. 0.82 Ni 0.2212 Fe 0.2846 Mn 0.4133 Zn 0.0337 Nb 0.047 2O2, median particle size D v50 =5.6μm,K v90 =1.06.

[0122] Example 11

[0123] The method is the same as in Example 1, except that in step 2, nano SnO2 powder is used instead of TiO2 powder.

[0124] In this embodiment, a layered oxide positive electrode active material Na was prepared. 0.82 Ni 0.2208 Fe 0.2851 Mn 0.4136 Zn 0.0335 Sn 0.047 0O2, median particle size D v50 =5.6μm,K v90 =1.06.

[0125] Example 12

[0126] The method is the same as in Example 1, except that in step 2, nano RuO2 powder is used instead of TiO2 powder.

[0127] In this embodiment, a layered oxide positive electrode active material Na was prepared. 0.82 Ni 0.2213 Fe 0.2846 Mn 0.4146 Zn 0.0338 Ru 0.045 7O2, median particle size D v50 =5.5μm,Kv90 =1.04.

[0128] Example 13

[0129] The method is the same as in Example 1, except that in step 2, nano CeO2 powder is used instead of TiO2 powder.

[0130] In this embodiment, a layered oxide positive electrode active material Na was prepared. 0.82 Ni 0.2209 Fe 0.2844 Mn 0.4149 Zn 0.0340 Ce 0.045 8O2, median particle size D v50 =5.5μm,K v90 =1.05.

[0131] Comparative Example 1

[0132] The method is the same as in Example 1, except that ZnSO4 solution is not introduced during the aging process of precursor synthesis in step 1, and the resulting precursor is a precursor without a coating layer, with a precursor particle size D. v50 =5.4μm, K v90 =1.01; No nano-TiO2 powder is introduced in step 2 during the preparation of the positive electrode active material.

[0133] The layered oxide positive electrode active material prepared in this comparative example is Na. 0.80 Ni 0.2431 Fe 0.3086 Mn 0.4483 O2.

[0134] The median particle size D of the positive electrode active material prepared in this comparative example v50 =5.9μm,K v90 =0.99.

[0135] Comparative Example 2

[0136] The method is the same as that of Comparative Example 1, except that step 2.1 in the preparation method of the positive electrode active material in step 2 is: the uncoated precursor, sodium carbonate, nano ZnO powder and nano TiO2 powder obtained in step 1 are ball-milled and mixed in a ball mill for 60 min.

[0137] The layered oxide positive electrode active material prepared in this comparative example is Na. 0.82 Ni 0.2215 Fe 0.2841 Mn 0.4157 Zn 0.0355 Ti 0.0432 O2.

[0138] The median particle size D of the positive electrode active material prepared in this comparative example v50 =5.4μm,K v90 =0.98.

[0139] Comparative Example 3

[0140] The method is the same as in Example 1, except that nano-TiO2 powder is not introduced in step 2 of the preparation of the positive electrode active material.

[0141] The layered oxide positive electrode active material prepared in this comparative example is Na. 0.82 Ni 0.231 Fe 0.2983 Mn 0.433 Zn 0.0377 O2.

[0142] The median particle size D of the positive electrode active material prepared in this comparative example v50 =5.5μm,K v90 =0.97.

[0143] Comparative Example 4

[0144] The method is the same as in Example 1, except that ZnSO4 solution is not introduced during the aging process of the precursor synthesis in step 1.

[0145] The layered oxide positive electrode active material prepared in this comparative example is Na. 0.80 Ni 0.2274 Fe 0.2938 Mn 0.4265 Ti 0.0523 O2.

[0146] The median particle size D of the positive electrode active material prepared in this comparative example v50 =5.6μm,K v90 =0.96.

[0147] The layered oxide positive electrode active materials synthesized in Examples 1-13 and Comparative Examples 1-4 and their preparation conditions are shown in Table 1.

[0148] Table 1

[0149] Group Positive electrode active material components Precipitator Precursor Synthesis Sintering treatment Example 1 <![CDATA[Na 0.82 Ni 0.2210 Fe 0.2845 Mn 0.4142 Zn 0.0326 The 0.0477 O2]]> Sodium hydroxide Zn coating Ti doping Example 2 <![CDATA[Na 0.80 Ni 0.2220 Fe 0.3036 Mn 0.4118 Zn 0.0147 The 0.0479 O2]]> Sodium hydroxide Zn coating Ti doping Example 3 <![CDATA[Na 0.80 Ni 0.2271 Fe 0.3105 Mn 0.4212 Zn 0.0153 The 0.0259 O2]]> Sodium hydroxide Zn coating Ti doping Example 4 <![CDATA[Na 0.80 In 0.2264 Want 0.3105 Mn 0.4212 Mg 0.0159 Of 0.026 O2]]> Sodium hydroxide Mg coating Ti doping Example 5 <![CDATA[Na 0.82 Aunt 0.2267 Fe 0.2812 Mn 0.4139 The 0.0368 Water 0.0414 O2]]> Sodium hydroxide Cu coating Ti doping Example 6 <![CDATA[Na 0.82 In 0.2288 Want 0.2803 Mn 0.4125 Ca 0.0365 Of 0.0419 O2]]> Sodium carbonate Ca coating Ti doping Example 7 <![CDATA[Na 0.82 In 0.2255 Want 0.2884 Mn 0.4098 Come on. 0.0354 Of 0.0409 O2]]> Sodium carbonate Ba coating Ti doping Example 8 <![CDATA[Na 0.82 Ni 0.2261 Fe 0.2897 Mn 0.4080 Sr 0.0351 The 0.0411 O2]]> Sodium carbonate Sr coating layer Ti doping Example 9 <![CDATA[Na 0.82 Ni 0.2207 Fe 0.2855 Mn 0.4135 Zn 0.0335 Zr 0.0468 O2]]> Sodium hydroxide Zn coating Zr doping Example 10 <![CDATA[Na 0.82 Ni 0.2212 Fe 0.2846 Mn 0.4133 Zn 0.0337 Nb 0.0472 O2]]> Sodium hydroxide Zn coating Nb doping Example 11 <![CDATA[Na 0.82 Ni 0.2208 Fe 0.2851 Mn 0.4136 Zn 0.0335 Sn 0.0470 O2]]> Sodium hydroxide Zn coating Sn doping Example 12 <![CDATA[Na 0.82 Ni 0.2213 Feb 0.2846 Mr 0.4146 Zn 0.0338 Ru 0.0457 O2]]> Sodium hydroxide Zn coating Ru doping Example 13 <![CDATA[Na 0.82 Ni 0.2209 Fe 0.2844 Mn 0.4149 Zn 0.0340 Ce 0.0458 O2]]> Sodium hydroxide Zn coating Ce doping Comparative Example 1 <![CDATA[Na 0.80 Ni 0.2431 Feb 0.3086 Mr 0.4483 O2]]> Sodium hydroxide Uncovered No dopant elements added Comparative Example 2 <![CDATA[Na 0.82 Ni 0.2215 Fe 0.2841 Mn 0.4157 Zn 0.0355 The 0.0432 O2]]> Sodium hydroxide Uncovered Ti and Zn doping Comparative Example 3 <![CDATA[Na 0.82 Ni 0.231 Fe 0.2983 Mn 0.433 Zn 0.0377 O2]]> Sodium hydroxide Zn coating No dopant elements added Comparative Example 4 <![CDATA[Na 0.80 In 0.2274 Want 0.2938 Mn 0.4265 Of 0.0523 O2]]> Sodium hydroxide Uncovered Ti doping

[0150] The positive electrode active materials prepared in Examples 1-13 and Comparative Examples 1-4 were tested using coin cells. The test results are shown in Table 2.

[0151] Assembly of the button electrode: The sodium-ion layered oxide positive electrode active material prepared according to the examples and comparative examples was mixed with conductive additives carbon black and polyvinylidene fluoride binder at a mass ratio of 70:20:10 to form a slurry, which was then uniformly coated onto aluminum foil. The slurry was then dried in a vacuum oven at 80℃ for 12 hours to obtain the working electrode, which has a diameter of 10 mm and an active material loading of 2.5-3.0 mg / cm³. 2 Finally, it is assembled into a button cell, the model number of which is CR2032.

[0152] Performance testing: The battery performance was tested using a Wuhan Landian CT2001A charge / discharge meter. Test conditions: nominal specific capacity of 130mAh / g, test voltage of 2.0-4.1V, test temperature of 25℃, the first cycle was 0.2C charge / discharge, followed by subsequent cycles of 1C charge / discharge, with a total of 100 cycles.

[0153] Cycle retention rate = 100 th specific capacity of coil discharge / 1 st The specific capacity of the coil discharge is 100%.

[0154] Table 2

[0155] Group <![CDATA[ 0.2C@2 0-4.1V initial discharge specific capacity]]> <![CDATA[ 1.0C@2.0~4.1V@100Cy .(%)]]> Example 1 141.2 96.2 Example 2 136.5 96.3 Example 3 138.9 94.6 Example 4 138.4 94.4 Example 5 140.6 95.8 Example 6 140.3 96.0 Example 7 139.9 95.7 Example 8 139.6 95.8 Example 9 140.2 95.5 Example 10 140.5 95.7 Example 11 140.7 95.4 Example 12 140.5 96.0 Example 13 140.1 95.6 Comparative Example 1 129.9 91.1 Comparative Example 2 138.6 93.4 Comparative Example 3 140.5 92.3 Comparative Example 4 124.4 93.1

[0156] As can be seen from Table 2, the sodium-ion layered oxide cathode active material prepared in the embodiments of this application has high capacity and cycle retention rate at a high voltage of 4.1V. The initial discharge specific capacity can reach more than 135mAh / g, and the capacity retention rate after 100 cycles at 1.0C can reach more than 94%, which shows excellent performance.

[0157] As shown in Table 2 and Figure 2 As shown, the positive electrode active material prepared in Comparative Example 1 did not use divalent metal elements to in-situ coat the precursor compared with Example 1, and it did not dop with tetravalent metal elements in the sintering stage. As a result, the structure of the positive electrode active material was unstable, and the discharge specific capacity and cycle performance under high voltage showed a significant decrease compared with Example 1.

[0158] Compared with Example 1, Comparative Example 2 differs in that it does not use divalent metal elements for in-situ coating during precursor synthesis. Instead, divalent metal elements are introduced together with tetravalent metal elements during the sintering stage for doping. The positive electrode active material prepared in Comparative Example 2 has lower discharge specific capacity and cycle retention rate under high voltage than that of Example 1. This is mainly because when Zn is in-situ coated on the surface of the precursor in Example 1, the distribution is more uniform after sintering, which is more conducive to the growth of Zn. 2+ The Zn enters the transition metal layer in the crystal structure, thereby reducing the overall valence state of the transition metal layer, increasing the occupancy of the Na layer, and thus increasing the capacity of the positive electrode active material; and some Zn... 2+Entering the Na layer, it exhibits a "pillar effect," thus demonstrating better crystal structure stability and improving cycling performance under high voltage.

[0159] Compared with Example 1, Comparative Example 3 did not introduce tetravalent metal elements in the sintering stage. Although the capacity difference of the positive electrode active material was small, the structural stability of the positive electrode active material was poor due to the lack of tetravalent metal doping. Compared with Example 1, the cycle performance under high voltage decreased significantly.

[0160] Compared with Example 2, Comparative Example 4 differs in that the divalent metal element Zn was not used for in-situ coating in the precursor synthesis. Instead, the tetravalent metal element Ti was introduced only in the sintering stage. The absence of Zn coating on the precursor resulted in a significant decrease in both the capacity and cycle performance of the positive electrode active material. This indicates that in-situ coating with Zn in the precursor synthesis can effectively improve the capacity of the positive electrode active material and enhance its cycle stability.

[0161] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing a layered oxide positive electrode active material, characterized in that, Includes the following steps: a. Mix the precursor metal salt solution with the precipitant and complexing agent according to the designed ratio, and co-precipitate the precursor to obtain the precursor. b. Pass a divalent metal salt solution into the precursor obtained in step a, perform aging treatment, and after washing, filtering and drying, obtain a precursor containing a divalent metal coating layer. c. The precursor containing a divalent metal coating layer obtained in step b, the sodium source, and the tetravalent metal compound are mixed and sintered to obtain the positive electrode active material.

2. The method for preparing the layered oxide positive electrode active material according to claim 1, characterized in that, In step a, the precursor metal salt solution includes nickel sulfate and manganese sulfate, and optionally, the precursor metal salt solution also includes ferric sulfate. And / or, the precipitant includes at least one of sodium hydroxide or sodium carbonate; And / or, the complexing agent includes ammonia; And / or, the temperature of the coprecipitation reaction is 40–60°C, the pH is controlled at 9.50–10.20, and the reaction atmosphere is controlled as an inert atmosphere; And / or, the particle size D of the obtained precursor v50 The micrometer range is 3–15 μm, and the K value is 0.40 ≤ K. 90 ≤1.70, where K 90 =(D v90 -D v10 ) / D v50 .

3. The method for preparing the layered oxide positive electrode active material according to claim 1, characterized in that, In step b, the divalent metal salt includes at least one of a sulfate, nitrate, or chloride salt of a divalent metal; and / or, the divalent metal ion includes Cu. 2+ Zn 2+ Mg 2+ Ca 2+ Ba 2+ 、Sr 2+ At least one of them.

4. The method for preparing the layered oxide positive electrode active material according to claim 1 or 3, characterized in that, In step b, the flow rate of the divalent metal salt solution is 20-60 ml / min; And / or, the aging temperature is 40–60°C, and the aging time is 0.5–5.0 h; And / or, the drying temperature is 90-110℃ and the drying time is 4-10h.

5. The method for preparing the layered oxide positive electrode active material according to claim 1, characterized in that, In step c, the tetravalent metal compound includes at least one of a tetravalent metal oxide, carbonate, nitrate, or acetate; and / or, the tetravalent metal ion includes Ti. 4+ Zr 4+ 、Nb 4+ Sn 4+ Ru 4+ Ce 4+ At least one of them.

6. The method for preparing the layered oxide positive electrode active material according to claim 1 or 5, characterized in that, In step c, the sodium source includes at least one of sodium carbonate, sodium bicarbonate, sodium nitrate, sodium oxalate, and sodium acetate. And / or, the mixing is performed by ball milling for a time of 0.5 h to 3 h; And / or, the sintering process includes two sintering processes: the first sintering process includes heating to 750-800°C at a heating rate of 2-7°C / h and holding at that temperature for 1-5 hours; the second sintering process includes continuing to heat to 800-1100°C at a heating rate of 2-7°C / h and holding at that temperature for 10-17 hours.

7. The method for preparing the layered oxide positive electrode active material according to claim 1, characterized in that, The chemical formula of the positive electrode active material obtained in step c is Na. x Ni a Fe b Mn c A e B (1-a-b-c-e) O2, where 0.50≤x≤1.10, 0.10≤a≤0.40, 0≤b≤0.40, 0.20≤c≤0.80, 0.001≤e≤0.30, and A contains divalent metal ions Cu. 2+ Zn 2+ Mg 2+ Ca 2+ Ba 2+ 、Sr 2+ At least one of them, B contains a tetravalent metal ion Ti 4+ Zr 4+ 、Nb 4+ Sn 4+ Ru 4+ Ce 4+ At least one of them.

8. A layered oxide positive electrode active material, characterized in that, It is prepared by any one of claims 1-7.

9. A secondary battery, characterized in that, Includes the layered oxide positive electrode active material as described in claim 8.

10. An electrical device, characterized in that, Includes the secondary battery as described in claim 9.

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