Positive electrode active material and preparation method thereof, positive electrode plate, battery and electric equipment

Abstract

The invention discloses a positive electrode active material and a preparation method thereof, a positive electrode plate, a battery and electric equipment, the positive electrode active material comprises an inner core and a coating layer, the inner core comprises a sodium ion transition metal oxide containing an iron element and / or a nickel element, in the sodium ion transition metal oxide, the molar weight of the iron element is recorded as b, and the molar weight of the nickel element is recorded as b; b is more than or equal to 0 and less than or equal to 0.4, and c is more than or equal to 0 and less than or equal to 0.4; the coating layer is arranged on at least one part of the surface of the inner core, and the coating layer contains an alkaline sodium compound. The positive electrode active material is stable in structure under high voltage, so that the cycling stability and the energy density of the battery containing the positive electrode active material under the high voltage are improved.

Description

[0001] This application is a divisional application of the invention patent application with application number 202310735567.2, application date June 20, 2023, entitled "Positive electrode active material and preparation method thereof, positive electrode sheet, battery and electrical device". Technical Field

[0002] This application belongs to the field of secondary battery technology, specifically relating to a positive electrode active material and its preparation method, a positive electrode sheet, a battery, and an electrical device. Background Technology

[0003] Secondary batteries are widely used in various consumer electronics products and electric vehicles due to their outstanding characteristics such as light weight, no pollution, and no memory effect.

[0004] Sodium-ion batteries are a type of rechargeable battery, and layered transition metal oxides (LTMOs) are commonly used positive electrode active materials. At high voltages, LTMOs can deintercalate and intercalate more sodium ions, resulting in higher specific capacity. However, existing LTMOs exhibit structural instability at high voltages, leading to lower cycle stability of the battery at these voltages.

[0005] Public content In view of the technical problems existing in the background art, this application provides a positive electrode active material, which aims to solve the problem of structural instability of positive electrode active materials under high voltage, thereby improving the cycle stability and energy density of batteries containing it under high voltage.

[0006] To achieve the above objectives, a first aspect of this application provides a positive electrode active material, the positive electrode active material comprising: The core comprises a sodium ion transition metal oxide containing iron and / or nickel, wherein the molar amount of iron in the sodium ion transition metal oxide is denoted as b, the molar amount of nickel is denoted as c, and 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4. A coating layer is disposed on at least a portion of the surface of the core, the coating layer containing an alkaline sodium compound.

[0007] The positive electrode active material of this application has a stable structure under high voltage, thereby improving the high-voltage cycle stability and energy density of batteries containing it.

[0008] In some embodiments, the mass percentage of the alkaline sodium compound is w%, based on the total amount of the positive electrode active material, and satisfies: 0.1 ≤ (b+c) / w ≤ 0.5, optionally 0.2 ≤ (b+c) / w ≤ 0.4. This improves the structural stability of the positive electrode active material under high voltage, thereby enhancing the high-voltage cycle stability and energy density of batteries containing it.

[0009] In some embodiments, the mass percentage w% of the alkaline sodium compound is 0.3 wt% - 5 wt%, optionally 0.5 wt% - 2 wt%. Thereby, the structural stability of the positive electrode active material at high voltages can be improved, and thus the cycle stability and energy density of the battery containing the same at high voltages can be improved.

[0010] In some embodiments, the alkaline sodium compound includes at least one of sodium hydroxide and sodium carbonate, optionally sodium carbonate. Thereby, the structural stability of the positive electrode active material at high voltages can be improved, and thus the cycle stability and energy density of the battery containing the same at high voltages can be improved.

[0011] In some embodiments, based on the total mass of the coating layer, the mass percentage of the sodium carbonate is higher than or equal to 80%. Thereby, the structural stability of the positive electrode active material at high voltages can be improved, and thus the cycle stability and energy density of the battery containing the same at high voltages can be improved.

[0012] In some embodiments, based on the total mass of the coating layer, the mass percentage of the sodium hydroxide is lower than or equal to 10%. Thereby, the structural stability of the positive electrode active material at high voltages can be improved, and thus the cycle stability and energy density of the battery containing the same at high voltages can be improved.

[0013] In some embodiments, the sodium ion transition metal oxide includes: Na x Mn a Fe b Ni c Q d O 2-e+δ F e , 0.5 ≤ x ≤ 1.2, 0 < a, 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4, 0 ≤ d, a + b + c + d = 1, 0 ≤ e ≤ 0.2, -0.1 ≤ δ ≤ 0.1, and Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi.

[0014] In some embodiments, the sodium ion transition metal oxide includes: Na x Mn a Fe b Ni c Q d O 2-e+δ F e, 0.7 ≤ x ≤ 1.2, 0 < a, 0.1 ≤ b ≤ 0.4, 0.1 ≤ c ≤ 0.4, 0 ≤ d ≤ 0.3, a + b + c + d = 1, 0 ≤ e ≤ 0.2, -0.1 ≤ δ ≤ 0.1, Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi, optionally at least one of B, Mg, Al, Si, Ca, Ti, Co, Cu, Zn, Zr, Nb, Mo, La, and Bi. Based on the total amount of the positive electrode active material, the mass ratio of the alkaline sodium compound is 1 wt% - 2 wt%. Thereby, the structural stability of the positive electrode active material at high voltages can be improved, and thus the cycle stability and energy density of the battery containing the same at high voltages can be improved.

[0015] In some embodiments, at least one of the following conditions is satisfied: 0.3 ≤ a ≤ 0.6; 0.15 ≤ b ≤ 0.35; 0.15 ≤ c ≤ 0.35; 0.1 ≤ d ≤ 0.2.

[0016] In some embodiments, 0.5 ≤ (b + c) / a ≤ 2, optionally 0.5 ≤ (b + c) / a ≤ 1.5. Thereby, the structural stability of the positive electrode active material at high voltages can be improved, and thus the cycle stability and energy density of the battery containing the same at high voltages can be improved.

[0017] In some embodiments, the phase of the sodium ion transition metal oxide includes the O3 phase, and the space group includes , and the layer spacing is 0.53 nm - 0.55 nm. Thereby, the capacity of the battery can be improved.

[0018] In some embodiments, the sodium ion transition metal oxide includes: Na x Mn a Ni c Q d O 2-e+δ F e, 0.5 ≤ x ≤ 1.2, 0 < a, 0.1 ≤ c ≤ 0.3, 0 ≤ d ≤ 0.3, a + c + d = 1, 0 ≤ e ≤ 0.2, -0.1 ≤ δ ≤ 0.1, Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi, optionally at least one of B, Mg, Al, Si, Ca, Ti, Co, Cu, Zn, Zr, Nb, Mo, La, and Bi. Based on the total amount of the positive electrode active material, the mass ratio of the alkaline sodium compound is 0.5 wt% - 1.5 wt%. Thus, the structural stability of the positive electrode active material at high voltages can be improved, thereby enhancing the cycle stability and energy density of the battery containing it.

[0019] In some embodiments, at least one of the following conditions is satisfied: 0.5 ≤ a ≤ 0.8; 0.15 ≤ c ≤ 0.25; 0.05 ≤ d ≤ 0.15.

[0020] In some embodiments, 0.125 ≤ c / a ≤ 0.45, optionally 0.2 ≤ c / a ≤ 0.3. Thus, the structural stability of the positive electrode active material at high voltages can be improved, thereby enhancing the cycle stability and energy density of the battery containing it.

[0021] In some embodiments, the phase of the sodium ion transition metal oxide includes the P2 phase, the space group includes P63 / mmc, and the layer spacing is 0.55 nm - 0.57 nm. Thus, the rate performance and cycle stability of the battery can be improved.

[0022] In some embodiments, the BET specific surface area of the positive electrode active material is Sm 2 / g, and S and w satisfy the relationship: 0.3 ≤ w / S ≤ 3, optionally 0.5 ≤ w / S ≤ 2. Thus, the cycle stability of the battery can be improved.

[0023] In some embodiments, the positive electrode active material satisfies at least one of the following conditions: the D v 50 of the positive electrode active material is 2 μm - 20 μm, optionally 4 μm - 15 μm; the BET specific surface area of the positive electrode active material is 0.2 m 2 / g - 2 m 2 / g, optionally 0.3 m 2 / g - 2 m 2 / g; the tap density of the positive electrode active material under a pressure of 300 MPa is 3.1 g / cm 3 - 3.8 g / cm 3 ,optionally 3.2 g / cm 3 - 3.6 g / cm 3.

[0024] Therefore, when the D of the positive electrode active material v 50. When at least one of the specific surface area and the compaction density at 300 MPa pressure is within the above range, the conduction distance of Na ions in the positive electrode active material is small and the surface side reactions are few, which promotes the positive electrode active material to exert its specific capacity and improves the capacity retention rate of the battery containing it.

[0025] The second aspect of this application provides a method for preparing the positive electrode active material described in the first aspect, comprising: A sodium ion transition metal oxide containing iron and / or nickel is provided, wherein the molar amount of iron in the sodium ion transition metal oxide is denoted as b, the molar amount of nickel is denoted as c, and 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4. The sodium ion transition metal oxide and the basic sodium compound are mixed and sintered to obtain the positive electrode active material. Wherein, based on the total amount of the positive electrode active material, the mass percentage of the alkaline sodium compound is w%, and 0.1≤(b+c) / w≤0.5.

[0026] Therefore, this application can prepare the above-mentioned positive electrode active material with stable structure under high voltage, thereby improving the high-voltage cycle stability and energy density of batteries containing it.

[0027] A third aspect of this application provides a positive electrode sheet comprising the positive active material described in the first aspect of this application or the positive active material prepared by the method described in the second aspect of this application.

[0028] A fourth aspect of this application provides a battery comprising the positive electrode sheet described in the third aspect of this application.

[0029] The fifth aspect of this application provides an electrical device that includes the battery described in the fourth aspect.

[0030] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0031] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the alternative embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a cross-sectional view of the positive electrode active material according to an embodiment of this application; Figure 2This is a schematic diagram of the structure of a battery according to one embodiment of this application; Figure 3 This is a schematic diagram of the structure of a battery module according to one embodiment of this application; Figure 4 This is a schematic diagram of the structure of a battery pack according to one embodiment of this application; Figure 5 yes Figure 4 Exploded view; Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a battery as a power source; Figure 7 The surface morphology of the positive electrode active material prepared in Example 1 is shown in the image. Figure 8 The surface morphology of the positive electrode active material prepared in Comparative Example 1 is shown. Figure 9 This is a surface morphology diagram of the positive electrode active material after disassembly of the coin cell of Example 1 after 50 cycles. Figure 10 This is a surface morphology image of the positive electrode active material after disassembling the coin cell of Comparative Example 1 after 50 cycles.

[0032] Explanation of reference numerals in the attached figures: 1000: Positive electrode active material; 100: Core; 200: Coating layer; 1: Secondary battery; 2: Battery module; 3: Battery pack; 4: Upper casing; 5: Lower casing. Detailed Implementation

[0033] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0034] 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.

[0035] For the sake of brevity, this article only discloses some specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0036] 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.

[0037] 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, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0038] Secondary batteries are not only used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. Sodium-ion batteries have a strong price advantage over traditional lithium-ion batteries and have broad application prospects in large-scale energy storage systems.

[0039] Layered transition metal oxides (LTMOs) have become a popular cathode active material for sodium-ion batteries due to their high conductivity, high energy density, large capacity, and long cycle life. Under high-voltage charging conditions, a significant amount of sodium ions are released from LTMOs, resulting in a high specific capacity. However, this also leads to high oxygen reactivity in LTMOs. This highly reactive oxygen readily reacts with the metals in the transition metal oxide, causing metal migration into the electrolyte. Furthermore, the highly reactive oxygen readily reacts with the electrolyte, leading to metal dissolution and oxygen loss from the transition metal oxide. This causes cracks in the LTMO, reducing its structural stability and resulting in lower cycle stability of the battery at high voltages.

[0040] In this application, the positive electrode active material includes a core and a coating layer disposed on at least a portion of the surface of the core. The core includes a sodium-ion transition metal oxide containing iron and / or nickel, wherein the molar amount of iron is denoted as b, the molar amount of nickel is denoted as c, and 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4. Since nickel and iron in the sodium-ion transition metal oxide have high activity, they easily induce an increase in the activity of oxygen at adjacent oxygen sites. Therefore, this application controls the molar amounts of iron (b) and nickel (c) within the above-mentioned ranges to reduce the content of highly active oxygen in the transition metal oxide. Simultaneously, the coating layer contains an alkaline sodium compound. The core and coating layer, satisfying this composition, can improve the specific capacity of the positive electrode active material while reducing the surface activity of the sodium-ion transition metal oxide. Furthermore, the coating layer can effectively isolate the sodium-ion transition metal oxide from contact with the electrolyte, reducing side reactions between the electrolyte and the transition metal oxide surface, reducing metal dissolution and oxygen loss, and improving the structural stability of the positive electrode active material under high voltage, thereby improving the high-voltage cycle stability and energy density of the battery containing it.

[0041] The positive electrode active material disclosed in this application is suitable for secondary batteries, and the battery disclosed in this application can be used in electrical devices that use batteries as a power source or in various energy storage systems that use batteries as energy storage elements. Electrical devices may include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys may include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0042] The first aspect of this application discloses a positive electrode active material, referring to... Figure 1 The positive electrode active material 1000 includes a core 100 and a coating layer 200. The core 100 includes a sodium ion transition metal oxide containing iron and / or nickel. In the sodium ion transition metal oxide, the molar amount of iron is denoted as b, and the molar amount of nickel is denoted as c, where 0 ≤ b ≤ 0.4 and 0 ≤ c ≤ 0.4. The coating layer 200 is disposed on at least a portion of the surface of the core 100, and the coating layer 200 contains an alkaline sodium compound.

[0043] The positive electrode active material 1000 of this application includes a core 100 and a coating layer 200 disposed on at least a portion of the surface of the core 100. The core 100 includes a sodium ion transition metal oxide containing iron and / or nickel, wherein the molar amount of iron is denoted as b and the molar amount of nickel is denoted as c, 0≤b≤0.4 and 0≤c≤0.4. Since nickel and iron in sodium ion transition metal oxide have high activity, they can easily induce an increase in the activity of oxygen at adjacent oxygen sites. Therefore, this application controls the molar amounts of iron b and nickel c to be within the above range, which can reduce the content of highly active oxygen in the transition metal oxide. Meanwhile, the coating layer 200 contains an alkaline sodium compound. The core 100 and the coating layer 200, which meet this composition, can reduce the surface activity of sodium ion transition metal oxides while increasing the specific capacity of the positive electrode active material 1000. Furthermore, the coating layer 200 can effectively isolate sodium ion transition metal oxides from contacting the electrolyte, reduce side reactions between the electrolyte and the surface of sodium ion transition metal oxides, reduce metal dissolution and oxygen loss, and improve the structural stability of the positive electrode active material 1000 under high voltage, thereby improving the high-voltage cycle stability and energy density of the battery containing it.

[0044] In some embodiments of this application, the core 100 comprises a sodium ion transition metal oxide containing iron and / or nickel. In this sodium ion transition metal oxide, the molar amount of iron is denoted as b, and the molar amount of nickel is denoted as c, where 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4, for example, 0.001 ≤ b ≤ 0.4, 0.005 ≤ b ≤ 0.4, 0.01 ≤ b ≤ 0.4, 0.015 ≤ b ≤ 0.4, 0.02 ≤ b ≤ 0.4, 0.05 ≤ b ≤ 0.4, 0.07 ≤ b ≤ 0.4, 0.1 ≤ b ≤ 0.4, 0.12 ≤ b ≤ 0.4, 0.15 ≤ b ≤ 0.4, 0.17 ≤ b ≤ 0.4, 0.2 ≤ b ≤ 0.4, 0.22 ≤ b ≤ 0.4, 0.25 ≤ b ≤ 0.4, 0.27 ≤ b ≤0.4, 0.3≤b≤0.4, 0.32≤b≤0.4, 0.35≤b≤0.4, 0.37≤b≤0.4, etc.; 0.001≤c≤0.4, 0.005≤c≤0.4, 0.01≤c≤0.4, 0.015≤c≤0.4, 0.02≤c≤0.4, 0.05≤c≤0.4, 0.07≤c≤0.4, The values ​​are 0.1≤c≤0.4, 0.12≤c≤0.4, 0.15≤c≤0.4, 0.17≤c≤0.4, 0.2≤c≤0.4, 0.22≤c≤0.4, 0.25≤c≤0.4, 0.27≤c≤0.4, 0.3≤c≤0.4, 0.32≤c≤0.4, 0.35≤c≤0.4, 0.37≤c≤0.4, etc. Specifically, since nickel and iron in sodium ion transition metal oxides are highly reactive, they easily induce an increase in the oxygen activity at adjacent oxygen sites. Therefore, this application controls the molar amounts of iron (b) and nickel (c) within the above ranges to reduce the content of highly reactive oxygen in transition metal oxides, thereby reducing metal dissolution and oxygen deficiency in transition metal oxides and improving the structural stability of the positive electrode active material 1000 under high voltage.

[0045] In some embodiments of this application, based on the total amount of the positive electrode active material 1000, the mass percentage of the alkaline sodium compound is w%, and the iron and / or nickel elements in the sodium ion transition metal oxide in the core 100 and the alkaline sodium compound in the coating layer 200 satisfy the following: 0.1 ≤ (b+c) / w ≤ 0.5, for example 0.15 ≤ (b+c) / w ≤ 0.45, 0.2 ≤ (b+c) / w ≤ 0.4, 0.25 ≤ (b+c) / w ≤ 0.35, 0.25 ≤ (b+c) / w ≤ 0.3, etc. In other embodiments of this application, the mass percentage of the alkaline sodium compound is w%, satisfying 0.2 ≤ (b+c) / w ≤ 0.4. Therefore, the core 100 and the coating layer 200 that meet this composition can reduce the surface activity of sodium ion transition metal oxide while increasing the specific capacity of the positive electrode active material 1000. In addition, the coating layer 200 can also effectively isolate the sodium ion transition metal oxide from contacting the electrolyte, reduce the side reactions between the electrolyte and the surface of the sodium ion transition metal oxide, reduce metal dissolution and oxygen loss, improve the structural stability of the positive electrode active material 1000 under high voltage, and thus improve the cycle stability and energy density of the battery containing it under high voltage.

[0046] In some embodiments of this application, the mass percentage (w%) of the alkaline sodium compound is 0.3wt%-5wt%, for example, 0.5wt%-4.5wt%, 0.8wt%-4.2wt%, 1wt%-4wt%, 1.2wt%-3.7wt%, 1.5wt%-3.5wt%, 1.8wt%-3.2wt%, 2wt%-3wt%, 2.2wt%-2.8wt%, 2.5wt%-2.7wt%, etc. In other embodiments of this application, the mass percentage (w%) of the alkaline sodium compound is 0.5wt%-2wt%. Therefore, the mass percentage of the alkaline sodium compound in the coating layer 200 of the positive electrode active material 1000 of this application meets the above ranges, which can effectively isolate sodium ion transition metal oxide from contact with the electrolyte, reduce side reactions on the surface of the electrolyte and sodium ion transition metal oxide, reduce metal dissolution and oxygen loss, improve the structural stability of the positive electrode active material 1000 under high voltage, and thus improve the high-voltage cycle stability and energy density of the battery containing it.

[0047] In some embodiments of this application, the alkaline sodium compound includes at least one of sodium hydroxide and sodium carbonate. In other embodiments of this application, the alkaline sodium compound includes sodium carbonate. Therefore, the coating layer 200 comprising the above-mentioned alkaline sodium compound can effectively isolate sodium ion transition metal oxides from contact with the electrolyte, reduce side reactions between the electrolyte and the surface of sodium ion transition metal oxides, reduce metal dissolution and oxygen loss, and improve the structural stability of the positive electrode active material 1000 under high voltage, thereby improving the high-voltage cycle stability and energy density of the battery containing it.

[0048] In some embodiments of this application, based on the total mass of the coating layer 200, the mass percentage of sodium carbonate is greater than or equal to 80%, for example, 80%-100%, 82%-98%, 85%-95%, 87%-92%, 90%-92%, etc. Thus, the coating layer 200 includes the aforementioned amount of sodium carbonate, which is more uniformly distributed on the surface of the core 100, and the resulting coating layer 200 is more uniform. This effectively isolates sodium ion transition metal oxides from contacting the electrolyte, reduces side reactions between the electrolyte and the surface of sodium ion transition metal oxides, reduces metal dissolution and oxygen loss, and improves the structural stability of the positive electrode active material 1000 under high voltage, thereby improving the high-voltage cycle stability and energy density of the battery containing it.

[0049] In some embodiments of this application, based on the total mass of the coating layer 200, the mass percentage of sodium hydroxide is less than or equal to 10%, for example, 9%-10%, 8%-8.5%, 7%-7.8%, 6%-6.8%, 5%-5.8%, 4%-4.8%, 3%-3.8%, 2%-2.8%, 1%-1.8%, 0%-1%, etc. Specifically, sodium hydroxide in the coating layer 200 easily undergoes side reactions with the binder in the positive electrode slurry, causing severe gelation of the slurry. Furthermore, sodium hydroxide readily generates water molecules during the conversion to form the coating layer 200. These water molecules react with sodium hexafluorophosphate (HF), the lithium salt in the battery electrolyte, and are easily converted into HF, thereby reducing the cycle stability of the battery. Therefore, the mass percentage of sodium hydroxide in the coating layer 200 of this application is within the above-mentioned range, which can reduce the gelation of the positive electrode slurry while improving the high-voltage cycle stability of the battery containing it.

[0050] In some embodiments of this application, the sodium ion transition metal oxide described in the core 100 above includes: Na x Mn a Fe b Ni c Q d O 2-e+δ F e , 0.5 ≤ x ≤ 1.2, 0 < a, 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4, 0 ≤ d, a + b + c + d = 1, 0 ≤ e ≤ 0.2, -0.1 ≤ δ ≤ 0.1, and Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi.

[0051] In some specific embodiments of the present application, the sodium ion transition metal oxide in the above-mentioned core 100 includes: Na x Mn a Fe b Ni c Q d O 2-e+δ F e , 0.7 ≤ x ≤ 1.2, 0 < a, 0.1 ≤ b ≤ 0.4, 0.1 ≤ c ≤ 0.4, 0 ≤ d ≤ 0.3, a + b + c + d = 1, 0 ≤ e ≤ 0.2, -0.1 ≤ δ ≤ 0.1, Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi, optionally at least one of B, Mg, Al, Si, Ca, Ti, Co, Cu, Zn, Zr, Nb, Mo, La, and Bi. Based on the total amount of the positive electrode active material 1000, the mass ratio of the basic sodium compound is 1 wt% - 2 wt%, such as 1.2 wt% - 2 wt%, 1.5 wt% - 2 wt%, 1.8 wt% - 2 wt%, etc. Thus, the mass ratio of the basic sodium compound in the coating layer 200 on the surface of the sodium ion transition metal oxide core 100 composed in the present application satisfies the above range, which can effectively isolate the sodium ion transition metal oxide from contacting the electrolyte, reduce the side reaction between the electrolyte and the surface of the sodium ion transition metal oxide, reduce metal dissolution and oxygen deficiency, improve the structural stability of the positive electrode active material 1000 at high voltage, and thus improve the cycle stability and energy density of the battery containing the same at high voltage.

[0052] In some embodiments of the present application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F eIn this case, x can take values ​​of 0.7 ≤ x ≤ 1.2, such as 0.7 ≤ x ≤ 1.1, 0.8 ≤ x ≤ 1, 0.85 ≤ x ≤ 1, 0.88 ≤ x ≤ 1, 0.9 ≤ x ≤ 1, 0.95 ≤ x ≤ 1, 0.98 ≤ x ≤ 1, etc. Therefore, this sodium-ion transition metal oxide contains this amount of sodium, resulting in a high battery capacity.

[0053] It should be noted that in the positive electrode, battery, or electrical device, sodium ions are consumed during the formation and cycling processes, resulting in a measured sodium content (x) in the transition metal oxide containing sodium ions being less than 1. Conversely, if sodium replenishment agents are used on both the positive and negative electrodes, the measured sodium content (x) in the transition metal oxide containing sodium ions will be greater than 1 after the battery undergoes formation and cycling.

[0054] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e In this case, 'a' can be greater than 0, for example, 0.001 ≤ a < 1, 0.005 ≤ a ≤ 0.9, 0.1 ≤ a ≤ 0.8, 0.2 ≤ a ≤ 0.7, 0.3 ≤ a ≤ 0.6, 0.4 ≤ a ≤ 0.5, etc. Therefore, including this amount of manganese in the sodium ion transition metal oxide can effectively improve the structural stability of the sodium ion transition metal oxide and improve the cycle stability of batteries containing it. In other embodiments of this application, the above-mentioned sodium ion transition metal oxide Na... x Mn a Fe b Ni c Q d O 2-e+δ F e In this case, 'a' can take values ​​of 0.3 ≤ a ≤ 0.6.

[0055] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e In this case, b can take values ​​of 0.1 ≤ b ≤ 0.4, for example, 0.1 ≤ b ≤ 0.35, 0.15 ≤ b ≤ 0.3, 0.2 ≤ b ≤ 0.25, 0.22 ≤ b ≤ 0.25, etc. Therefore, this sodium ion transition metal oxide Na... x Mn a Fe b Ni cQ d O 2-e+δ F e The inclusion of this amount of Fe not only reduces the content of highly reactive oxygen species in sodium ion transition metal oxides but also increases the specific capacity of the positive electrode active material 1000. In other embodiments of this application, the aforementioned sodium ion transition metal oxide Na... x Mn a Fe b Ni c Q d O 2-e+δ F e In this case, b can be 0.15 ≤ b ≤ 0.35.

[0056] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e In this case, c takes values ​​of 0.1 ≤ c ≤ 0.40, for example, 0.1 ≤ c ≤ 0.35, 0.15 ≤ c ≤ 0.3, 0.2 ≤ c ≤ 0.25, 0.22 ≤ c ≤ 0.25, etc. Therefore, this sodium ion transition metal oxide Na... x Mn a Fe b Ni c Q d O 2-e+δ F e Including this amount of Ni not only reduces the content of highly reactive oxygen species in sodium ion transition metal oxides, but also increases the specific capacity of the positive electrode active material 1000. In other embodiments of this application, the aforementioned sodium ion transition metal oxide Na... x Mn a Fe b Ni c Q d O 2-e+δ F e In this case, c is set to 0.15 ≤ c ≤ 0.35.

[0057] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F eQ includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi. In other embodiments of this application, the above-mentioned sodium ion transition metal oxide Na... x Mn a Fe b Ni c Q d O 2-e+δ F e Q includes at least one of B, Mg, Al, Si, Ca, Ti, Co, Cu, Zn, Zr, Nb, Mo, La, and Bi.

[0058] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e In this case, d takes values ​​of 0 ≤ d ≤ 0.3, for example, 0.001 ≤ d ≤ 0.3, 0.005 ≤ d ≤ 0.3, 0.01 ≤ d ≤ 0.3, 0.05 ≤ d ≤ 0.3, 0.1 ≤ d ≤ 0.3, 0.15 ≤ d ≤ 0.3, 0.17 ≤ d ≤ 0.27, 0.2 ≤ d ≤ 0.25, 0.2 ≤ d ≤ 0.22, etc. Therefore, this sodium ion transition metal oxide Na... x Mn a Fe b Ni c Q d O 2-e+δ F e Including this amount of Q element can improve the structural stability of the positive electrode active material 1000. In other embodiments of this application, the above-mentioned sodium ion transition metal oxide Na... x Mn a Fe b Ni c Q d O 2-e+δ F e In this case, d is taken as 0.1≤d≤0.2.

[0059] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F eIn this case, δ takes the value -0.1≤δ≤0.1, and e takes the value 0≤e≤0.2. For example, -0.09≤δ≤0.09, -0.08≤δ≤0.08, -0.07≤δ≤0.07, -0.06≤δ≤0.06, -0.05≤δ≤0.05, -0.04≤δ≤0.04, -0.03≤δ≤0.03, -0.02≤δ≤0.02, -0.01≤δ≤0.01, -0.01≤δ≤0, 0≤δ≤0.01, etc., 0.01≤e≤0.2, 0.02≤e≤0.18, 0.05≤e≤0.15, 0.08≤e≤0.12, 0.1≤e≤0.12, etc.

[0060] Specifically, the sodium ion transition metal oxide Na in this application x Mn a Fe b Ni c Q d O 2-e+δ F e Doping the oxygen sites with this amount of F can effectively stabilize the oxygen in sodium ion transition metal oxides, thereby reducing the structural damage caused by lattice oxygen release in sodium ion transition metal oxides, improving the stability of the positive electrode active material 1000, and thus improving the cycle stability of the battery.

[0061] It should be noted that in positive electrode plates, batteries, or electrical devices, due to the cycling process, oxygen elements in sodium ion transition metal oxides are lost, which may result in the measured oxygen content 2+δ-e in sodium ion transition metal oxides being less than 2.

[0062] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e In this application, 0.5 ≤ (b+c) / a ≤ 2, for example, 0.8 ≤ (b+c) / a ≤ 2, 1 ≤ (b+c) / a ≤ 1.8, 1.2 ≤ (b+c) / a ≤ 1.6, 1.5 ≤ (b+c) / a ≤ 1.6, etc. In other embodiments of this application, the above-mentioned sodium ion transition metal oxide Na... x Mn a Fe b Ni c Q d O 2-e+δ F eIn this application, 0.5 ≤ (b+c) / a ≤ 1.5. Specifically, Ni contributes to capacity, but the changing valence of Fe and Ni can easily lead to structural instability. Mn, on the other hand, can stabilize the structure of sodium-ion transition metal oxides. Therefore, the molar amount of Mn (a) in the sodium-ion transition metal oxide of this application satisfies the above-mentioned relationship with the molar amounts of Fe (b) and Ni (c). This can improve the specific capacity of sodium-ion transition metal oxides while enhancing their structural stability at high voltage, thereby improving the high-voltage cycle stability and energy density of batteries containing them.

[0063] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e The phase states include the O3 phase, and the space group includes... The interlayer spacing is 0.53nm-0.55nm, for example, it can be 0.532nm-0.55nm, 0.535nm-0.548nm, 0.537nm-0.545nm, 0.540nm-0.542nm, etc. Specifically, the high sodium ion transition metal oxide (Na) content in the formed O3 phase results in a high battery capacity.

[0064] It should be noted that the sodium ion transition metal oxide Na in this application x Mn a Fe b Ni c Q d O 2-e+δ F e The phase state, space group, and interlayer spacing can be characterized using X-ray diffraction.

[0065] Specifically, sodium ions in transition metal oxides (Na) x Mn a Fe b Ni c Q d O 2-e+δ F e The interlayer spacing d of the 003 crystal plane 003 The space group testing method includes: grinding the sample to be tested in an agate mortar and pestle in a drying room or glove box, then passing it through a 350-mesh sieve. A suitable amount of the sieved sample is placed in the center of the sample holder groove, ensuring the loose sample powder is slightly higher than the sample holder plane. A glass slide is then gently pressed against the sample surface to level it with the frame plane, and excess powder is scraped off. After sample preparation, a Brucker D8A_A25 X-ray powder diffractometer from Brucker AxS (Germany) is used with CuK...α The X-rays are used as the radiation source, with the X-ray wavelength λ = 1.5406 Å. The scanning range of the 2θ angle is 5° - 60°, and the scanning rate is 4° / min for testing. After the test is completed, based on the angle corresponding to the 003 crystal plane, according to the Bragg equation 2d•sinθ = λ, and since each unit cell of the 003 crystal plane contains three layers of transition metal layers, the interlayer spacing d of the 003 crystal plane can be obtained. 003 By comparing the XRD diffraction peaks of the sample with the standard cards of the XRD analysis software, the space group and crystal phase of the sample can be confirmed.

[0066] In some further specific embodiments of the present application, the sodium ion transition metal oxide in the above core 100 includes: Na x Mn a Ni c Q d O 2-e+δ F e , 0.5 ≤ x ≤ 1.2, 0 < a, 0.1 ≤ c ≤ 0.3, 0 ≤ d ≤ 0.3, a + c + d = 1, 0 ≤ e ≤ 0.2, -0.1 ≤ δ ≤ 0.1, Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi, optionally at least one of B, Mg, Al, Si, Ca, Ti, Co, Cu, Zn, Zr, Nb, Mo, La, and Bi. Based on the total amount of the positive electrode active material 1000, the mass ratio of the alkaline sodium compound is 0.5 wt% - 1.5 wt%, such as 0.5 wt% - 1.3 wt%, 0.7 wt% - 1 wt%, 0.9 wt% - 1 wt%, etc. Thus, the mass ratio of the alkaline sodium compound in the coating layer 200 on the surface of the sodium ion transition metal oxide core 100 formed in the present application satisfies the above range, which can effectively isolate the sodium ion transition metal oxide from contacting with the electrolyte, reduce the side reaction between the electrolyte and the surface of the sodium ion transition metal oxide, reduce metal dissolution and oxygen deficiency, improve the structural stability of the positive electrode active material 1000, and thereby improve the cycle stability and energy density of the battery containing it at high voltages.

[0067] In some embodiments of the present application, the above sodium ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F eIn this case, x can take values ​​of 0.5 ≤ x ≤ 1.2, such as 0.5 ≤ x ≤ 1.1, 0.6 ≤ x ≤ 1.1, 0.8 ≤ x ≤ 1, 0.85 ≤ x ≤ 1, 0.88 ≤ x ≤ 1, 0.9 ≤ x ≤ 1, 0.95 ≤ x ≤ 1, 0.98 ≤ x ≤ 1, etc. Therefore, this sodium-ion transition metal oxide contains this amount of sodium, resulting in a high battery capacity.

[0068] It should be noted that in the positive electrode, battery, or electrical device, sodium ions are consumed during the formation and cycling processes, resulting in a measured sodium content (x) in the transition metal oxide containing sodium ions being less than 1. Conversely, if sodium replenishment agents are used on both the positive and negative electrodes, the measured sodium content (x) in the transition metal oxide containing sodium ions will be greater than 1 after the battery undergoes formation and cycling.

[0069] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F e In this case, 'a' can be greater than 0, for example, 0.001 ≤ a < 1, 0.005 ≤ a ≤ 0.9, 0.1 ≤ a ≤ 0.8, 0.2 ≤ a ≤ 0.7, 0.3 ≤ a ≤ 0.6, 0.4 ≤ a ≤ 0.5, etc. Therefore, including this amount of manganese in the sodium ion transition metal oxide can effectively improve the structural stability of the sodium ion transition metal oxide and improve the cycle stability of batteries containing it. In other embodiments of this application, the above-mentioned sodium ion transition metal oxide Na... x Mn a Ni c Q d O 2-e+δ F e In this case, 'a' can be 0.5 ≤ a ≤ 0.8.

[0070] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F e In this case, c takes values ​​of 0.1 ≤ c ≤ 0.3, for example, 0.15 ≤ c ≤ 0.3, 0.2 ≤ c ≤ 0.25, 0.22 ≤ c ≤ 0.25, etc. Therefore, this sodium ion transition metal oxide Na... x Mn a Fe b Ni c Q d O 2-e+δ F eIncluding this amount of Ni not only reduces the content of highly reactive oxygen species in sodium ion transition metal oxides, but also increases the specific capacity of the positive electrode active material 1000. In other embodiments of this application, the aforementioned sodium ion transition metal oxide Na... x Mn a Ni c Q d O 2-e+δ F e In this case, c is set to 0.15 ≤ c ≤ 0.25.

[0071] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F e Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi. In other embodiments of this application, the above-mentioned sodium ion transition metal oxide Na... x Mn a Ni c Q d O 2-e+δ F e Q includes at least one of B, Mg, Al, Si, Ca, Ti, Co, Cu, Zn, Zr, Nb, Mo, La, and Bi.

[0072] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F e In this case, d takes values ​​of 0 ≤ d ≤ 0.3, for example, 0.001 ≤ d ≤ 0.3, 0.005 ≤ d ≤ 0.3, 0.01 ≤ d ≤ 0.3, 0.05 ≤ d ≤ 0.3, 0.1 ≤ d ≤ 0.3, 0.15 ≤ d ≤ 0.3, 0.17 ≤ d ≤ 0.27, 0.2 ≤ d ≤ 0.25, 0.2 ≤ d ≤ 0.22, etc. Therefore, this sodium ion transition metal oxide Na... x Mn a Ni c Q d O 2-e+δ F e Including this amount of Q element can improve the structural stability of the positive electrode active material 1000. In other embodiments of this application, the above-mentioned sodium ion transition metal oxide Na... x Mn aNi c Q d O 2-e+δ F e In this case, d is taken as 0.05≤d≤0.15.

[0073] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F e In this case, δ takes the value -0.1≤δ≤0.1, and e takes the value 0≤e≤0.2. For example, -0.09≤δ≤0.09, -0.08≤δ≤0.08, -0.07≤δ≤0.07, -0.06≤δ≤0.06, -0.05≤δ≤0.05, -0.04≤δ≤0.04, -0.03≤δ≤0.03, -0.02≤δ≤0.02, -0.01≤δ≤0.01, -0.01≤δ≤0, 0≤δ≤0.01, etc., 0.01≤e≤0.2, 0.02≤e≤0.18, 0.05≤e≤0.15, 0.08≤e≤0.12, 0.1≤e≤0.12, etc.

[0074] Specifically, the sodium ion transition metal oxide Na in this application x Mn a Ni c Q d O 2-e+δ F e Doping the oxygen sites with this amount of F can effectively stabilize the oxygen in sodium ion transition metal oxides, thereby reducing the structural damage caused by lattice oxygen release in sodium ion transition metal oxides, improving the stability of the positive electrode active material 1000, and thus improving the cycle stability of the battery.

[0075] It should be noted that in positive electrode plates, batteries, or electrical devices, due to the cycling process, oxygen elements in sodium ion transition metal oxides are lost, which may result in the measured oxygen content 2+δ-e in sodium ion transition metal oxides being less than 2.

[0076] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F eIn this application, the sodium ion transition metal oxide Na... (The text abruptly ends here, so the translation stops as well.) x Mn a Ni c Q d O 2-e+δ F e In this application, 0.2 ≤ c / a ≤ 0.3. Specifically, Ni contributes to capacity, but Ni's valence changes can easily lead to structural instability. Mn, on the other hand, can stabilize the structure of sodium-ion transition metal oxides. Therefore, the molar amount of Mn, a, and the molar amount of Ni, c, in the sodium-ion transition metal oxide satisfy the above relationship. This can improve the specific capacity of the sodium-ion transition metal oxide while simultaneously enhancing its structural stability at high voltage, thereby improving the high-voltage cycle stability and energy density of batteries containing it.

[0077] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F e The phase states include P2 phase, the space group includes P63 / mmc, and the interlayer spacing is 0.55nm-0.57nm, for example, the interlayer spacing can be 0.552nm-0.57nm, 0.555nm-0.568nm, 0.557nm-0.565nm, 0.56nm-0.562nm, etc. Specifically, the large interlayer spacing of the formed P2 phase sodium ion transition metal oxide can improve the Na ion transport rate, maintain the integrity of the layered structure, and enable the battery to have excellent rate performance and cycle performance.

[0078] It should be noted that the sodium ion transition metal oxide Na in this application x Mn a Ni c Q d O 2-e+δ F e The phase state, space group, and interlayer spacing can be characterized using X-ray diffraction.

[0079] Specifically, sodium ions in transition metal oxides (Na) x Mn a Ni c Q d O 2-e+δ Fe The interlayer spacing d of the 003 crystal plane 003 The space group testing method includes: grinding the sample to be tested in an agate mortar and pestle in a drying room or glove box, then passing it through a 350-mesh sieve. A suitable amount of the sieved sample is placed in the center of the sample holder groove, ensuring the loose sample powder is slightly higher than the sample holder plane. A glass slide is then gently pressed against the sample surface to level it with the frame plane, and excess powder is scraped off. After sample preparation, a Brucker D8A_A25 X-ray powder diffractometer from Brucker AxS (Germany) is used with CuK... α The radiation source is X-ray with a wavelength of λ = 1.5406 Å. The scanning angle range is 5°-60°, and the scanning rate is 4° / min. After the test, the interlayer spacing d of the 003 crystal plane can be obtained by passing the angle corresponding to the 003 crystal plane, according to Bragg's equation 2d•sinθ = λ, and the fact that each unit cell of the 003 crystal plane contains three transition metal layers. 003 By comparing the XRD diffraction peaks of the sample with the standard card of the XRD analysis software, the space group and crystal phase of the sample can be confirmed.

[0080] In some embodiments of this application, the BET specific surface area of ​​the positive electrode active material 1000 is Sm. 2 The S and W in the positive electrode active material 1000 satisfy the following relationship: 0.3 ≤ w / S ≤ 3, for example, 0.5 ≤ w / S ≤ 2.8, 0.7 ≤ w / S ≤ 2.5, 1 ≤ w / S ≤ 2.2, 1.3 ≤ w / S ≤ 2, 1.5 ≤ w / S ≤ 1.8, etc. In some other embodiments of this application, the S and W in the positive electrode active material 1000 satisfy the following relationship: 0.5 ≤ w / S ≤ 2. Therefore, the S and W in the positive electrode active material 1000 of this application satisfy the above relationship, which can effectively isolate sodium ions from contacting the transition metal oxide with the electrolyte while improving the specific capacity of the positive electrode, reducing the side reactions between the electrolyte and the surface of the transition metal oxide, reducing metal dissolution and oxygen loss, improving the structural stability of the positive electrode active material 1000, and thus improving the high-voltage cycle stability and energy density of the battery containing it.

[0081] In some embodiments of this application, the D of the positive electrode active material 1000 v 50 is 2μm-20μm, for example, the D of the positive electrode active material v 50 can be 2μm-19μm, 4μm-18μm, 5μm-15μm, 6μm-14μm, 8μm-13μm, 9μm-12μm, 10μm-11μm, etc. In other embodiments of this application, the D of the positive electrode active material 1000 is... v 50 is 4μm-15μm.

[0082] In this application, D v50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50%, for example, measured using a laser particle size analyzer (e.g., Malvern Master Size 3000) according to standard GB / T 19077-2016.

[0083] In some embodiments of this application, the BET specific surface area of ​​the positive electrode active material 1000 is 0.2 m². 2 / g-2m 2 / g, for example, the specific surface area of ​​the positive electrode active material can be 0.2m². 2 / g-1.5m 2 / g, 0.2m 2 / g-1m 2 / g, 0.3m 2 / g-0.8m 2 / g, 0.3m 2 / g-0.5m 2 / g, etc. In some other embodiments of this application, the specific surface area of ​​the positive electrode active material 1000 is 0.3m². 2 / g-2m 2 / g.

[0084] In this application, the BET specific surface area of ​​the positive electrode active material 1000 has a meaning known in the art and can be measured using instruments and methods known in the art. For example, it can be tested using the following method: using a US-made multi-station fully automated specific surface area and porosity analyzer Gemini VII2390, take about 7g of sample and put it into a 9cc long tube with a bulb, degas at 200°C for 2 hours, and then put it into the main unit to test and obtain the BET specific surface area data of the positive electrode active material 1000.

[0085] In some embodiments of this application, the compaction density of the positive electrode active material 1000 under a pressure of 300 MPa is 3.1 g / cm³. 3 -3.8g / cm 3 For example, the compaction density of positive electrode active material 1000 under a pressure of 300 MPa can be 3.0 g / cm³. 3 -3.8g / cm 3 3.2g / cm 3 -3.5g / cm 3 3.2g / cm 3 -3.4g / cm 3 In some embodiments of this application, the compaction density of the positive electrode active material 1000 under a pressure of 300 MPa is 3.2 g / cm³. 3 -3.6g / cm 3 .

[0086] In this application, "compacted density" has a well-known meaning in the art and can be determined using instruments and methods well-known in the art. For example, the following test method can be used: a quantitative amount of powder m is placed in a compaction mold, the mold is placed on a compaction density instrument, a pressure of 300 MPa is set, the thickness and volume v of the powder under the pressure of 300 MPa are measured on the instrument, and the compacted density is calculated by using density = mass m / volume v; (refer to GB / T24533-2009 for details).

[0087] Specifically, when the positive electrode active material 1000 of this application has a D v 50. When at least one of the specific surface area and the compaction density under 300 MPa pressure is within the above range, the conduction distance within the positive electrode active material 1000 is small and the surface side reactions are few, which promotes the positive electrode active material to exert its specific capacity and improves the capacity retention rate of the battery containing it.

[0088] In this application, the elemental composition of the positive electrode active material 1000 can be determined using instruments and methods known in the art, such as inductively coupled plasma atomic emission spectrometry (ICP-AES). The instrument standard reference is EPA 6010D-2014, "Inductively Coupled Plasma Atomic Emission Spectrometry". The sample is chemically treated and digested into a solution, then atomized into plasma to excite characteristic spectral lines of the elements. The elemental content is qualitatively and quantitatively analyzed based on the wavelength and intensity of the spectral lines (which are proportional to the concentration).

[0089] The content of alkaline sodium compound Na2CO3 in the coating layer 200 of the positive electrode active material 1000 can be determined using instruments and methods known in the art, such as referring to the GB / T 9736-2008 standard. Under a carbon dioxide-free atmosphere, 30g of the obtained positive electrode active material powder is weighed, 100ml of pure water is added and stirred for 30min, allowed to stand for 10min, filtered, and a certain amount of filtrate is taken. Titration is performed using 0.05mol / L hydrochloric acid standard solution, and the instrument used is a Mettler T5 titrator.

[0090] The content of alkaline sodium compound (NaOH) in the coating layer 200 of the positive electrode active material 1000 can be determined using instruments and methods known in the art, such as referring to the GB / T 9736-2008 standard. Under a dehumidified atmosphere free of carbon dioxide, 30g of the obtained layered oxide powder was weighed, 100ml of anhydrous ethanol was added and stirred for 30min, allowed to stand for 10min, filtered, and 10mL of the filtrate was transferred. This filtrate was then diluted with 50mL of ultrapure water, and subsequently titrated with 0.05mol / L hydrochloric acid standard solution using a Mettler T5 titrator.

[0091] In this application, the content of sodium element in the sodium-ion transition metal oxide in the core 100 can be calculated by subtracting the total amount of alkaline sodium compounds NaOH and Na2CO3 in the coating layer obtained by the above-mentioned inductively coupled plasma emission spectrometry from the total amount of sodium element obtained by the above-mentioned test method. The content of other elements in the composition of the sodium-ion transition metal oxide can be obtained by the above-mentioned inductively coupled plasma emission spectrometry, and thus the composition of the sodium-ion transition metal oxide can be obtained. The mass percentage w% of the alkaline sodium compound in the above-mentioned positive electrode active material 1000 can be obtained by adding the contents of the alkaline sodium compounds NaOH and Na2CO3 in the above-mentioned coating layer.

[0092] In the second aspect of this application, a method for preparing the positive electrode active material described in the first aspect is provided, including: S100: Provide a sodium-ion transition metal oxide containing iron element and / or nickel element In some embodiments of this application, in the sodium-ion transition metal oxide, the molar amount of iron element is denoted as b, the molar amount of nickel element is denoted as c, 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4.

[0093] In this application, the sodium-ion transition metal oxide may include: Na x Mn a Fe b Ni c Q d O 2-e+δ F e , for example, the sodium-ion transition metal oxide includes the above-mentioned Na x Mn a Fe b Ni c Q d O 2-e+δ F e , 0.7 ≤ x ≤ 1.2, 0 < a, 0.1 ≤ b ≤ 0.4, 0.1 ≤ c ≤ 0.4, 0 ≤ d ≤ 0.3, a + b + c + d = 1, 0 ≤ e ≤ 0.2, -0.1 ≤ δ ≤ 0.1, Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W and Bi; or for example, the sodium-ion transition metal oxide includes the above-mentioned Na x Mn a Ni c Q d O 2-e+δ F e, 0.5 ≤ x ≤ 1.2, 0 < a, 0.1 ≤ c ≤ 0.3, 0 ≤ d ≤ 0.3, a + c + d = 1, 0 ≤ e ≤ 0.2, -0.1 ≤ δ ≤ 0.1, and Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi.

[0094] In some embodiments of the present application, the preparation method of the above sodium ion transition metal oxide may include: mixing the Na source, Fe source, Mn source, Ni source, and Q source according to the composition of the above sodium ion transition metal oxide, pre-grinding them in an agate mortar, and then adding them to a planetary ball mill for ball milling for 1 h - 8 h, such as 2 h - 7 h, 3 h - 6 h, 4 h - 5 h, etc., to obtain the precursor mixture I. Then, the obtained precursor mixture I is evenly placed in an open crucible, and then heated in a muffle furnace from room temperature to 900°C - 1000°C at a heating rate of 2°C / min - 5°C / min (such as 2°C / min - 3°C / min, 2°C / min - 3°C / min, etc.), such as 910°C - 990°C, 920°C - 980°C, 930°C - 970°C, 940°C - 960°C, 940°C - 950°C Dengfeng, and kept at a constant temperature for 10 h - 20 h, such as 11 h - 19 h, 12 h - 18 h, 13 h - 17 h, 14 h - 16 h, 14 h - 15 h, etc. The atmosphere used is air dehumidified and carbon dioxide removed, and the sodium ion transition metal oxide is obtained after natural cooling.

[0095] It should be noted that due to the loss of the Na source during the subsequent calcination process, the addition amount of Na will be slightly higher than the content of Na required in the composition of the above sodium ion transition metal oxide.

[0096] The Na source, Fe source, Mn source, Ni source, and Q source in the present application are conventional materials in the art, and those skilled in the art can select according to the actual situation. For example, the Na source may include at least one of Na2CO3, NaHCO3, NaOH, and Na2O2; the Fe source may include at least one of FeO, Fe2O3, and Fe3O4; the Mn source may include at least one of Mn2O3, Mn3O4, MnO, and MnO2; the Ni source may include NiO; the Q source may include at least one of oxides of Q, salts containing Q, and other compounds.

[0097] It should be noted that if it is necessary to dope the F element in the cathode active material, at least one of the Na source, Fe source, Mn source, Ni source, and Q source adopts at least one of its corresponding fluorinated salts and other compounds, such as sodium fluoride, iron fluoride, manganese fluoride, fluorinated Ni, and fluorinated Q (fluorinated salt of Q).

[0098] S200: The sodium ion transition metal oxide and the basic sodium compound are mixed and sintered. In some embodiments of this application, the sodium ion transition metal oxide and basic sodium compound are mixed according to 0.1≤(b+c) / w≤0.5 (in the sodium ion transition metal oxide, the molar amount of iron is denoted as b, the molar amount of nickel is denoted as c, and the mass percentage of the basic sodium compound is w% based on the total amount of the positive electrode active material), pre-ground in an agate mortar, and then added to a planetary ball mill for ball milling for 1h-8h, for example 2h-7h, 3h-6h, 4h-5h, etc., to obtain precursor mixture II. The obtained precursor mixture II is then... The catalyst mixture II is uniformly placed in an open crucible, and then heated in a muffle furnace from room temperature to 300℃-600℃ at a heating rate of 2℃ / min-5℃ / min (e.g., 2℃ / min-3℃ / min, 2℃ / min-3℃ / min, etc.), such as 350℃-550℃, 400℃-500℃, 450℃-500℃, etc., and held at this temperature for 1h-3h, such as 1h-2h, 2h-3h, 1h-1.5h, etc., using dehumidified and carbon dioxide-free air. After natural cooling, the positive electrode active material is obtained. This sintering process allows the alkaline sodium compound to be more uniformly distributed and better bonded on the surface of the sodium ion transition metal oxide, thereby forming a stable coating layer on the surface of the sodium ion transition metal oxide, improving the structural stability of the positive electrode active material under high voltage, and thus improving the high-voltage cycle stability and energy density of the battery containing it.

[0099] Therefore, the method of this application can be used to prepare the above-mentioned positive electrode active material with stable structure under high voltage, thereby improving the high-voltage cycle stability and energy density of batteries containing it.

[0100] A third aspect of this application provides a positive electrode sheet comprising the positive active material described in the first aspect of this application or the positive active material prepared by the method described in the second aspect of this application.

[0101] The positive electrode typically includes a positive current collector and a positive active material layer disposed on the positive current collector, wherein the positive active material layer includes a positive active material.

[0102] The positive electrode current collector can be a conventional metal foil or a composite current collector (a composite current collector can be formed by setting metal materials on a polymer substrate). As an example, the positive electrode current collector may include at least one of copper foil, aluminum foil, nickel foil, stainless steel foil, stainless steel mesh, and carbon-coated aluminum foil.

[0103] The positive electrode active material layer may also optionally include a conductive agent and a binder. The conductive agent is used to improve the conductivity of the positive electrode active material layer, and the binder is used to firmly bond the positive electrode active material and the binder to the positive electrode current collector. This application does not specifically limit the types of conductive agents and binders, and they can be selected according to actual needs.

[0104] As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder may include at least one of styrene-butadiene rubber (SBR), water-based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), and polyvinyl alcohol (PVA).

[0105] These materials can all be obtained through commercial means.

[0106] A fourth aspect of this application provides a battery comprising the positive electrode described in the third aspect of this application. Consequently, this battery exhibits excellent cycle stability and energy density at high voltages.

[0107] A battery is a device that can be recharged after being discharged, allowing its active materials to be reactivated and continue to be used.

[0108] It is understood that the battery proposed in this application is a sodium-ion battery.

[0109] Typically, a battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The separator, positioned between the positive and negative electrodes, serves as a barrier. The electrolyte, acting as a conductor of ions, lies between the positive and negative electrodes.

[0110] [Negative electrode plate] In a battery, the negative electrode typically includes a negative current collector and a negative active material layer disposed on the negative current collector, wherein the negative active material layer includes a negative active material.

[0111] The negative electrode current collector can be a conventional metal foil or a composite current collector (for example, a metal material can be disposed on a polymer substrate to form a composite current collector). As an example, the negative electrode current collector can be a copper foil.

[0112] The specific type of the negative electrode active material is not limited; any active material known in the art that can be used as a negative electrode in sodium-ion batteries can be used. Those skilled in the art can select according to actual needs. As an example, the negative electrode active material may include, but is not limited to, at least one of sodium metal, carbon materials, alloy materials, transition metal oxides and / or sulfides, phosphorus-based materials, and titanate materials. Specifically, the carbon material may include at least one of hard carbon, soft carbon, amorphous carbon, and nanostructured carbon materials; the alloy material may include an alloy material formed from at least one of Si, Ge, Sn, Pb, and Sb; the general formula of the transition metal oxides and sulfides is M. x N y M includes at least one of Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V, and N includes O or S; the phosphorus-based material may include at least one of red phosphorus, white phosphorus, and black phosphorus; the titanate material may include Na2Ti3O7 or Na2Ti6O7. 13 Na4Ti5O 12 Li4Ti5O 12 At least one of NaTi2(PO4)3. These materials are all commercially available.

[0113] The negative electrode active material layer may also optionally include a binder and a conductive agent. The conductive agent is used to improve the conductivity of the negative electrode active material layer, and the binder is used to firmly bond the negative electrode active material and the binder to the negative electrode current collector. This application does not specifically limit the types of conductive agents and binders, which can be selected according to actual needs.

[0114] As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0115] As an example, the adhesive may include at least one of styrene-butadiene rubber (SBR), styrene-butadiene rubber (SBCs), water-based acrylic resin, and carboxymethyl cellulose (CMC).

[0116] The negative electrode active material layer may also optionally include a thickener, such as carboxymethyl cellulose (CMC). However, this application is not limited to this, and other materials that can be used as thickeners for sodium-ion battery negative electrode sheets may also be used.

[0117] Electrolyte The electrolyte may include an electrolyte salt and a solvent.

[0118] As an example, the electrolyte sodium salt may include at least one of sodium hexafluorophosphate, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium dioxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonyl)imide.

[0119] As an example, the solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0120] In some embodiments, the electrolyte also includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0121] [Isolation membrane] As for the aforementioned separator, this application does not have any particular limitations. Any known porous structure separator with electrochemical and mechanical stability can be selected according to actual needs. For example, it may include a single-layer or multi-layer film containing at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0122] This application does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. Figure 2 This is an example of a square-structured secondary battery 1.

[0123] In some embodiments, the battery may include an outer packaging. This outer packaging is used to encapsulate the positive electrode, the negative electrode, and the electrolyte.

[0124] In some embodiments, the outer packaging may include a shell and a cover. The shell may include a base plate and side plates attached to the base plate, the base plate and side plates enclosing a receiving cavity. The shell has an opening communicating with the receiving cavity, and the cover can be placed over the opening to close the receiving cavity.

[0125] The positive electrode, negative electrode, and separator can be formed into an electrode assembly using a winding or stacking process. The electrode assembly is encapsulated within the receiving cavity. The number of electrode assemblies contained in the battery can be one or more, and can be adjusted as needed.

[0126] In some implementations, the outer packaging of the battery may include a rigid shell, such as a rigid plastic shell, an aluminum shell, or a steel shell.

[0127] The outer packaging of the battery may also include a pouch, such as a soft pouch. The material of the pouch may be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0128] In some implementations, batteries can be assembled into battery modules, and the number of batteries contained in a battery module can be multiple, with the specific number adjustable according to the application and capacity of the battery module.

[0129] Figure 3 This is battery module 2 as an example. (See reference...) Figure 3 In battery module 2, multiple secondary batteries 1 can be arranged sequentially along the length of battery module 2. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 1 can be fixed in place using fasteners.

[0130] The battery module 2 may also include a housing with a receiving space in which multiple secondary batteries 1 are housed. In some embodiments, the battery modules may also be assembled into a battery pack, the number of battery modules contained in the battery pack being adjustable according to the application and capacity of the battery pack.

[0131] Figure 4 and 5 This is battery pack 3 as an example. (See reference...) Figure 4 and 5 The battery pack 3 may include a battery box and multiple battery modules 2 disposed within the battery box. The battery box includes an upper body 4 and a lower body 5, with the upper body 4 covering the lower body 5 to form a closed space for accommodating the battery modules 2. The multiple battery modules 2 can be arranged in any manner within the battery box.

[0132] This application provides a fifth aspect of an electrical device that includes the battery described in the fourth aspect. Specifically, the battery can serve as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships and satellites, and energy storage systems.

[0133] Figure 6 This is an example of an electrical appliance. The electrical appliance includes pure electric vehicles, hybrid electric vehicles, or plug-in hybrid electric vehicles.

[0134] Another example of a power-consuming device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and may use batteries as their power source.

[0135] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0136] Example 1 [Preparation of positive electrode active materials].

[0137] A total of 30g of sample was weighed, consisting of Na₂CO₃, Mn₂O₃, Fe₂O₃, and NiO in a molar ratio of Na:Mn:Fe:Ni of 1:0.4:0.3:0.3. The sample was pre-ground in an agate mortar and then ball-milled in a planetary ball mill for 1 hour to obtain precursor mixture I. Precursor mixture I was then uniformly placed in an open crucible and heated from room temperature to 950℃ in a muffle furnace at a heating rate of 5℃ / min, and held at 950℃ for 15 hours in a dehumidified and carbon dioxide-free atmosphere. After natural cooling, a sample with the composition Na₂CO₃ was obtained. 0.89 Mn 0.4 Fe 0.3 Ni 0.3 Sodium ion transition metal oxide of O2 is obtained, and the resulting sodium ion transition metal oxide is pre-ground with 0.5g Na2CO3 in an agate mortar and then ball-milled in a planetary ball mill for 1h to obtain precursor mixture II. The obtained precursor mixture II is then evenly placed in an open crucible and heated from room temperature to 500℃ in a muffle furnace at a heating rate of 5℃ / min, and held at 500℃ for 2h in a dehumidified and carbon dioxide-free atmosphere. After natural cooling, a positive electrode active material with a coating layer on the surface is obtained.

[0138] Preparation of the positive electrode sheet The above-obtained positive electrode active material, conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are thoroughly mixed in solvent NMP (N-methylpyrrolidone) at a mass ratio of 80:15:5 to form a uniform positive electrode slurry. The positive electrode slurry is then uniformly coated on the upper and lower surfaces of the positive electrode current collector aluminum foil. After drying and cold pressing, it is punched into a circular sheet with a diameter of 14 mm to obtain the positive electrode sheet.

[0139] Preparation of the negative electrode sheet The negative electrode is made of metallic sodium.

[0140] Preparation of Electrolyte Equal volumes of ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed to obtain an organic solvent. NaClO4 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0141]

Isolation Film

[0142] [Preparation of button cells] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The prepared electrolyte is then added to obtain a coin cell.

[0143] The coin cells containing positive electrode active materials in Examples 2-30 are the same as those in Example 1, except that the parameters in the preparation of the positive electrode active material are different (see Tables 1-6). Element Q is added as an oxide of Q, and the F source is added in the form of sodium source NaF.

[0144] The coin cell containing positive electrode active material in Comparative Example 1 is the same as that in Example 1, except that the process of preparing the positive electrode active material is different.

[0145] The preparation process of the positive electrode active material in Comparative Example 1 included: weighing a total of 30g of Na₂CO₃, Mn₂O₃, Fe₂O₃, and NiO in a molar ratio of Na:Mn:Fe:Ni of 1:0.4:0.3:0.3; pre-grinding the sample in an agate mortar and then ball-milling it in a planetary ball mill for 1 hour to obtain precursor mixture I; uniformly placing precursor mixture I in an open crucible; subsequently heating it from room temperature to 950℃ in a muffle furnace at a heating rate of 5℃ / min; maintaining the temperature at 950℃ for 15 hours in a dehumidified and carbon dioxide-free atmosphere; and after natural cooling, obtaining a sample with the composition Na₂CO₃, Mn₂O₃, Fe₂O₃, and NiO. 0.89 Mn 0.4 Fe 0.3 Ni 0.3 O2 is the positive electrode active material.

[0146] The coin cells containing positive electrode active materials in Comparative Examples 2-3 and 6 are the same as those in Comparative Example 1, except for the different parameters in the preparation of the positive electrode active material (see Table 1-6). Element Q is added as an oxide of Q, and the F source is added in the form of sodium source NaF.

[0147] The coin cells containing positive electrode active materials in Comparative Examples 4-5 are the same as those in Example 1, except for the different parameters in the preparation of the positive electrode active material (see Tables 1-6).

[0148] Considering the loss of sodium during sintering, to obtain a sodium ion transition metal oxide with a Na subscript of 1, the Na source needs to be in excess by 0.05-0.2% during the mixing stage. For example, to obtain NaMn... 0.4 Fe 0.3 Ni 0.3 For sodium ion transition metal oxides of O2, Na2CO3, Mn2O3, Fe2O3, and NiO are prepared in a molar ratio of Na:Mn:Fe:Ni of 1.05-1.2:0.4:0.3:0.3. It should also be noted that the alkaline sodium compounds in Examples 1-30 and Comparative Examples 4-5 all use sodium carbonate.

[0149] The composition of the positive electrode active material in the batteries of Examples 1-30 and Comparative Examples 1-6 of this application is shown in Tables 1-6.

[0150] Table 1

[0151] Table 2

[0152] Table 3

[0153] Table 4

[0154] Table 5

[0155] Table 6

[0156] Table 7

[0157] The surface morphology, BET specific surface area, composition, phase state, space group and interlayer spacing, and proportion of alkaline sodium compounds of the positive electrode active materials in Examples 1-30 and Comparative Examples 1-6 were characterized. The characterization results are shown in Tables 1-6. The first-cycle discharge specific capacity and coin cell cycle performance of the positive electrode active materials obtained in Examples 1-30 and Comparative Examples 1-6 were also characterized. The characterization results are shown in Table 7.

[0158] Testing methods: (1) Characterization of the surface morphology of the positive electrode active material: The surface morphology of the positive electrode active material was characterized by scanning electron microscopy (SEM). For example, the surface morphology of the positive electrode active material was characterized by field emission scanning electron microscopy (Zeiss Gemini 360) according to the JY / T010-1996 standard.

[0159] (2) Characterization of the BET specific surface area of ​​the positive electrode active material: Using a US-made Gemini VII2390 multi-station fully automated surface area and porosity analyzer, approximately 7g of sample was placed in a 9cc long tube with a bulb, degassed at 200℃ for 2 hours, and then placed in the main unit for testing to obtain the BET surface area data of the positive electrode active material 1000.

[0160] (3) Compositional characterization of sodium ion transition metal oxides: Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for testing: the instrument standard referenced was EPA 6010D-2014, "Inductively Coupled Plasma Atomic Emission Spectrometry". The sample was chemically treated and digested into a solution, then atomized and injected into the plasma to elicit characteristic spectral lines of the elements. The elemental content was qualitatively and quantitatively analyzed based on the wavelength and intensity of the spectral lines (which are proportional to the concentration).

[0161] The content of alkaline sodium compound Na2CO3 in the coating layer of the positive electrode active material can be determined using instruments and methods known in the art, such as referring to the GB / T 9736-2008 standard. Under a carbon dioxide-free atmosphere, 30g of the obtained positive electrode active material powder was weighed, 100ml of pure water was added and stirred for 30min, allowed to stand for 10min, filtered, and a certain amount of filtrate was transferred and titrated with 0.05mol / L hydrochloric acid standard solution using a Mettler T5 titrator.

[0162] The content of alkaline sodium compounds (NaOH) in the coating layer of the positive electrode active material can be determined using instruments and methods known in the art, such as referring to the GB / T 9736-2008 standard. Under a dehumidified atmosphere free of carbon dioxide, 30g of the obtained layered oxide powder was weighed, 100ml of anhydrous ethanol was added, and the mixture was stirred for 30min. After standing for 10min, the mixture was filtered, and 10mL of the filtrate was transferred and diluted with 50mL of ultrapure water. Then, a 0.05mol / L hydrochloric acid standard solution was used for titration using a Mettler T5 titrator.

[0163] The sodium content in the composition of sodium ion transition metal oxides can be calculated by subtracting the total amount of basic sodium compounds NaOH and Na2CO3 in the coating layer obtained by the above-mentioned inductively coupled plasma atomic emission spectrometry (ICP-AES). The contents of other elements in the composition of sodium ion transition metal oxides can be obtained by the above-mentioned inductively coupled plasma atomic emission spectrometry (ICP-AES). Thus, the composition of sodium ion transition metal oxides can be obtained.

[0164] (4) Test of the mass percentage w% of alkaline sodium compounds in the positive electrode active material: The content of alkaline sodium compounds NaOH and Na2CO3 in the above coating layer is added together to obtain the result.

[0165] (5) The phase state of sodium ion transition metal oxides and the interlayer spacing d of the 003 crystal plane 003 and space group testing: Grind the sample to be tested into a fine powder in an agate mortar and pestle in a drying room or glove box, then pass it through a 350-mesh sieve. Take an appropriate amount of the sieved sample and place it in the center of the sample holder groove, ensuring the loose sample powder is slightly higher than the sample holder plane. Gently press a glass slide onto the sample surface to level it with the frame plane, and scrape off any excess powder. After sample preparation, use a Brucker D8A_A25 X-ray powder diffractometer (Brucker AxS, Germany) with CuK... α The radiation source is X-ray with a wavelength of λ = 1.5406 Å. The scanning angle range is 5°-60°, and the scanning rate is 4° / min. After the test, the interlayer spacing d of the 003 crystal plane can be obtained by passing the angle corresponding to the 003 crystal plane, according to Bragg's equation 2d•sinθ = λ, and the fact that each unit cell of the 003 crystal plane contains three transition metal layers. 003 By comparing the XRD diffraction peaks of the sample with the standard card of the XRD analysis software, the space group and crystal phase of the sample can be confirmed.

[0166] (6) Initial discharge specific capacity and battery cycle performance testing of positive electrode active material At 25℃, the coin cell was charged to 4.2V at a constant current density of 10mA / g, and then discharged to 1.5V at a constant current density of 10mA / g to obtain the initial discharge specific capacity C0 of the coin cell. Subsequently, it underwent 50 charge-discharge cycles at a constant current density of 10mA / g, and the discharge specific capacity C1 of the 50th cycle was recorded. The capacity retention rate of the battery after 50 cycles = C1 / C0 × 100%.

[0167] Figure 7 The image shows the surface morphology of the positive electrode active material prepared in Example 1. Figure 8 The image shows the surface morphology of the positive electrode active material prepared in Comparative Example 1. Figure 7-8 It can be seen that the surface of the positive electrode active material in Example 1 has a uniform coating layer, while the surface of the positive electrode active material in Comparative Example 1 is relatively clean and does not have a clearly continuous coating layer. Furthermore, the surfaces of the positive electrode active materials in Comparative Examples 2-3 and 6 do not have a clearly continuous coating layer. Figure 9 This is a surface morphology image of the positive electrode active material after disassembling the coin cell of Example 1 after 50 cycles. Figure 10 This is a surface morphology image of the positive electrode active material after disassembling the coin cell of Comparative Example 1 after 50 cycles. Figure 9-10 It can be seen that after 50 cycles, the positive electrode active material of the coin cell in Example 1 still has a uniform coating layer and no obvious cracks, while the positive electrode active material of the coin cell in Comparative Example 1 shows obvious cracks after 50 cycles. This indicates that the positive electrode active material of Example 1 has higher structural stability under high voltage than the positive electrode active material of Comparative Example 1, thereby improving the cycle performance and energy density of the battery in Example 1.

[0168] Table 8

[0169] Conclusion: As shown in Tables 1-6, sodium carbonate and sodium hydroxide were detected in the positive electrode active materials of Examples 1-31 and Comparative Examples 5-7. The sodium hydroxide likely originated from the water absorption reaction of sodium oxide on the surface of the positive electrode active material. Sodium carbonate and sodium hydroxide were also detected in the positive electrode active materials of Comparative Examples 1-4. The sodium carbonate originated from the sodium source during the mixing process, and the sodium hydroxide likely originated from the water absorption reaction of sodium oxide on the surface of the positive electrode active material. As shown in Table 7, the batteries of Examples 1-30 exhibited superior capacity retention at high voltage compared to those of Comparative Examples 1-6, indicating that the positive electrode active material of this application can improve the cycle stability of the battery. Furthermore, the initial discharge specific capacity of the positive electrode active materials of Examples 1-30 of this application is not less than 158 mAh / g, indicating that the battery of this application has excellent energy density at high voltage. In summary, the positive electrode active material of this application can simultaneously improve the cycle stability and energy density of the battery at high voltage.

[0170] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A positive electrode active material, characterized in that, Comprising: A core, the core comprising a sodium-ion transition metal oxide containing iron element and / or nickel element, in the sodium-ion transition metal oxide, the molar amount of iron element is denoted as b, the molar amount of nickel element is denoted as c, 0≤b≤0.4, 0≤c≤0.4; A coating layer, the coating layer being provided on at least a part of the surface of the core, and the coating layer contains an alkaline sodium compound.

2. The positive electrode active material according to claim 1, characterized in that, Based on the total amount of the positive electrode active material, the mass proportion of the alkaline sodium compound is w%, and it satisfies: 0.1≤(b + c) / w≤0.5, optionally 0.2≤(b + c) / w≤0.

4.

3. The positive electrode active material according to claim 2, characterized in that, The mass proportion w% of the alkaline sodium compound is 0.3wt%-5wt%, optionally 0.5wt%-2wt%.

4. The positive electrode active material according to any one of claims 1-3, characterized in that, The alkaline sodium compound includes at least one of sodium hydroxide and sodium carbonate, optionally sodium carbonate.

5. The positive electrode active material according to claim 4, based on the total mass of the coating layer, the mass proportion of the sodium carbonate is higher than or equal to 80%.

6. The positive electrode active material according to claim 4 or 5, based on the total mass of the coating layer, the mass proportion of the sodium hydroxide is lower than or equal to 10%.

7. The positive electrode active material according to any one of claims 1-6, the sodium-ion transition metal oxide includes: So x Mr a Feb b Ni c Q d O 2-e+δ F e , 0.5≤x≤1.2, 0 < a, 0≤b≤0.4, 0≤c≤0.4, 0≤d, a + b + c + d = 1, 0≤e≤0.2, -0.1≤δ≤0.1, Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W and Bi.

8. The positive electrode active material according to any one of claims 1-7, characterized in that, The sodium-ion transition metal oxide includes: So x Mr a Feb b Ni c Q d O 2-e+δ F e , 0.7≤x≤1.2, 0 < a, 0.1≤b≤0.4, 0.1≤c≤0.4, 0≤d≤0.3, a + b + c + d = 1, 0≤e≤0.2, -0.1≤δ≤0.1, Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W and Bi, optionally at least one of B, Mg, Al, Si, Ca, Ti, Co, Cu, Zn, Zr, Nb, Mo, La and Bi, Based on the total amount of the positive electrode active material, the mass proportion of the alkaline sodium compound is 1wt%-2wt%.

9. The positive electrode active material according to claim 8, characterized in that, Satisfying at least one of the following conditions: 0.3≤a≤0.6； 0.15≤b≤0.35； 0.15≤c≤0.35； 0.1≤d≤0.2。 10. The positive electrode active material according to claim 8 or 9, characterized in that, 0.5≤(b + c) / a≤2, optionally 0.5≤(b + c) / a≤1.

5.

11. The positive electrode active material according to any one of claims 8-10, characterized in that, The sodium ion transition metal oxide includes the O3 phase in the following phases, and its space group is [space group number missing]. The interlayer spacing is 0.53nm-0.55nm.

12. The positive electrode active material according to any one of claims 1-7, characterized in that, The sodium-ion transition metal oxide includes: That x Mn a By c Q d Or 2-e+δ F e , 0.5 ≤ x ≤ 1.2, 0 < a, 0.1 ≤ c ≤ 0.3, 0 ≤ d ≤ 0.3, a + c + d = 1, 0 ≤ e ≤ 0.2, -0.1 ≤ δ ≤ 0.1, Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W and Bi, and optionally includes at least one of B, Mg, Al, Si, Ca, Ti, Co, Cu, Zn, Zr, Nb, Mo, La and Bi. Based on the total amount of the positive electrode active material, the mass ratio of the alkaline sodium compound is 0.5 wt% - 1.5 wt%.

13. The positive electrode active material according to claim 12, characterized in that, Meet at least one of the following conditions: 0.5≤a≤0.8； 0.15≤c≤0.25； 0.05≤d≤0.15。 14. The positive electrode active material according to claim 12 or 13, characterized in that, 0.125 ≤ c / a ≤ 0.45, optionally 0.2 ≤ c / a ≤ 0.

3.

15. The positive electrode active material according to any one of claims 11-14, characterized in that, The phase of the sodium ion transition metal oxide includes the P2 phase, the space group includes P63 / mmc, and the layer spacing is 0.55 nm - 0.57 nm.

16. The positive electrode active material according to any one of claims 1-15, characterized in that, The BET specific surface area of ​​the positive electrode active material is Sm 2 / g, S and w satisfy the relationship: 0.3≤w / S≤3, or 0.5≤w / S≤2.

17. The positive electrode active material according to any one of claims 1-16, characterized in that, The positive electrode active material meets at least one of the following conditions: The positive electrode active material D v 50 is available in sizes ranging from 2μm to 20μm, with options for 4μm to 15μm. The BET specific surface area of ​​the positive electrode active material is 0.2 m². 2 / g-2m 2 / g, optionally 0.3m 2 / g-2m 2 / g; The compaction density of the positive electrode active material under a pressure of 300 MPa is 3.1 g / cm³. 3 -3.8g / cm 3 3.2g / cm³ is an option. 3 -3.6g / cm 3 .

18. A method for preparing a positive electrode active material, characterized in that, Includes: Provide a sodium ion transition metal oxide containing iron element and / or nickel element. In the sodium ion transition metal oxide, the molar amount of the iron element is denoted as b, the molar amount of the nickel element is denoted as c, 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.

4. Mix and sinter the sodium ion transition metal oxide and the alkaline sodium compound to obtain a positive electrode active material. Where, based on the total amount of the positive electrode active material, the mass ratio of the alkaline sodium compound is w%, and 0.1 ≤ (b + c) / w ≤ 0.

5.

19. A positive electrode plate, characterized in that, The positive electrode sheet includes the positive electrode active material described in any one of claims 1 - 17 or the positive electrode active material prepared by the method described in claim 18.

20. A battery, characterized in that, The battery includes the positive electrode sheet described in claim 19.

21. An electrical appliance, characterized in that, Includes the battery described in claim 20.

Images