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 NaxNiaFebMncM1dM2eO2 + delta-fFf, M1 comprises rare earth elements, M2 comprises at least one of IA group elements, IIA group elements, IIIA group elements, IVA group elements, VA group elements, VIA group elements and transition elements, 0.6 < = x < = 1.2, 0 < a < = 0.5, 0 < b < = 0.5, 0 < c < = 0.5, and 0 < d < = 0.5. 0 < b < = 0.4, 0.3 < = c < = 0.75, 0.001 < = d < = 0.05, 0 < = e < = 0.3,-0.1 < = delta < = 0.1, 0 < = f < = 0.1, 0.005 < = d / c < = 0.05, and a + b + c + d + e = 1.

Description

[0001] This application is a divisional application of the invention patent application with application number 202310736859.8, 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 relates to the field of secondary battery technology, specifically 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 not only used in energy storage power systems such as 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 and other fields.

[0004] Sodium-ion batteries are a type of rechargeable battery, and layered transition metal oxides are commonly used positive electrode active materials in sodium-ion batteries. However, existing sodium-ion batteries containing layered transition metal oxides have relatively low capacity retention.

[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 low capacity retention of batteries containing it.

[0006] To achieve the above objectives, a first aspect of this application provides a positive electrode active material, the positive electrode active material comprising: Na x Ni a Fe b Mn c M1 d M2 e O 2+δ-f F f , Wherein, M1 includes rare earth elements, and M2 includes at least one of Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group VIA and transition elements, 0.6≤x≤1.2, 0<a≤0.5, 0<b≤0.4, 0.3≤c≤0.75, 0.001≤d≤0.05, 0≤e≤0.3, -0.1≤δ≤0.1, 0≤f≤0.1, 0.005≤d / c≤0.05, and a+b+c+d+e=1.

[0007] This application includes at least the following beneficial effects: The main material of the positive electrode active material of this application includes NiFeMn, and is doped with rare earth elements M1 and M2. The Fe content mentioned above can improve the specific capacity of the material. Rare earth element M1 has a large radius and forms a dense and uniform doped layer on the surface of the positive electrode active material. The doped layer can effectively block the intrusion of water vapor from the surface of the positive electrode active material into the bulk phase, improving the structural stability of the material. During high-voltage charging, the doped layer can also inhibit the evolution of lattice oxygen and the penetration of electrolyte into the material, improving the structural stability of the material, thereby improving the capacity retention rate of the battery containing it. Doped element M2 is distributed in the bulk phase of the positive electrode active material and can form strong chemical bonds with O in the positive electrode active material, inhibiting the extraction of Na ions from the bulk phase of the positive electrode active material, and can reduce the interlayer spacing change of the positive electrode active material, delaying the occurrence of phase transition, improving the cycle stability of the positive electrode active material, thereby improving the capacity retention rate of the battery. Furthermore, when the ratio d / c of ​​rare earth elements M1 to Mn in the positive electrode active material is within the above range, it is beneficial to improve the air stability and cycle stability of the positive electrode active material, thereby improving the capacity retention rate of the battery containing it.

[0008] In some embodiments of this application, the rare earth element includes at least one selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Therefore, by employing at least one of the aforementioned rare earth elements, M1 can form a dense and uniform doped layer on the surface of the positive electrode active material, reducing the probability of phase transition in the positive electrode active material, improving the cycle performance of the positive electrode active material, and thus enhancing the capacity retention rate of the battery containing it.

[0009] In some embodiments of this application, M2 includes at least one of B, Mg, Al, Si, K, Ca, Ga, Ge, Se, Rb, Sr, In, Sn, Sb, Te, Sc, Ti, V, Cr, Co, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, and Au. Thus, element M2 is uniformly distributed in the bulk phase of the positive electrode active material, and can form strong chemical bonds with O in the positive electrode active material, inhibiting the release of Na from the bulk phase, improving the air stability of the positive electrode active material, and thereby improving the capacity retention rate of the battery containing it.

[0010] In some embodiments of this application, 0.01 ≤ d / c ≤ 0.03, which is beneficial to improving the air stability and cycle stability of the positive electrode active material, thereby improving the capacity retention of the battery containing it.

[0011] In some embodiments of this application, the positive electrode active material satisfies at least one of the following conditions: 0.1≤a≤0.4, optionally 0.15≤a≤0.3; 0.1≤b≤0.35, optionally 0.15≤b≤0.35; 0.35≤c≤0.6, optionally 0.35≤c≤0.5.

[0012] In some embodiments of this application, 1.75 ≤ (a+b+c) / b ≤ 9.5, optionally, 2 ≤ (a+b+c) / b ≤ 9.5, and more preferably, 2 ≤ (a+b+c) / b ≤ 6.3. Therefore, in the positive electrode active material, the ratio of the sum of the contents of Ni, Fe, and Mn to the Fe content is within the above range, which is beneficial to improving the air stability and cycle stability of the positive electrode active material, thereby improving the capacity retention rate of the battery containing it.

[0013] In some embodiments of this application, 0.8 < x ≤ 1.0, the phase state of the positive electrode active material includes the O3 phase, and the space group includes The interlayer spacing is 0.53nm-0.55nm. Therefore, within the above range, the O3 phase positive electrode active material formed has a high Na content, which can improve the battery capacity.

[0014] In some embodiments of this application, 0.6 ≤ x ≤ 0.8, the phase state of the positive electrode active material includes the P2 phase, the space group includes P63 / mmc, and the interlayer spacing is 0.54 nm-0.57 nm. Therefore, when x is within the above range, the interlayer spacing of the P2 phase positive electrode active material is large, which can improve the rate performance and cycle performance of the battery.

[0015] In some embodiments of this application, the pH value of the soaking solution of the positive electrode active material is less than or equal to 13; optionally, the pH value of the soaking solution of the positive electrode active material is less than or equal to 12.7; more preferably, the pH value of the soaking solution of the positive electrode active material is 11.0 ≤ pH ≤ 12.7.

[0016] In some embodiments of this application, the positive electrode active material satisfies at least one of the following conditions: The positive electrode active material D v 50 is 3μm-30μm, and can be selected as 5μm-15μm; The specific surface area of ​​the positive electrode active material is 0.1 m². 2 / g-5m 2 / g, optionally 0.3m 2 / g-3m 2 / g; The tap density of the positive electrode active material is 1 g / cm³. 3 -3g / cm 3 1.5g / cm³ is an optional value.3 -2.5g / cm 3 ; The compaction density of the positive electrode active material under a pressure of 300 MPa is 3.0 g / cm³. 3 -4.0g / cm 3 .

[0017] Therefore, when the D of the positive electrode active material v 50. When at least one of the specific surface area, tap density, and compaction density under 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.

[0018] The second aspect of this application provides a method for preparing the positive electrode active material described in the first aspect, comprising: The precursor was obtained by mixing Na source, Ni source, Fe source, Mn source, M1 source and M2 source; The precursor is calcined to obtain the positive electrode active material.

[0019] Therefore, the positive electrode active material prepared in this application has excellent air stability and cycle stability, and the battery containing it has excellent capacity retention.

[0020] A third aspect of this application provides another method for preparing the positive electrode active material described in the first aspect, comprising: A mixed solution was obtained by mixing Ni source, Fe source, Mn source, M1 source and M2 source with water; The solution is reacted with a precipitant to obtain a precursor; The precursor was mixed with a Na source and then calcined to obtain the positive electrode active material.

[0021] Therefore, the positive electrode active material prepared in this application has excellent air stability and cycle stability, and the battery containing it has excellent capacity retention.

[0022] The fourth aspect of this application provides a positive electrode sheet, which includes the positive electrode active material described in the first aspect of this application, the positive electrode active material prepared by the method described in the second aspect, or the positive electrode active material prepared by the method described in the third aspect.

[0023] A fifth aspect of this application provides a battery comprising the positive electrode sheet described in the fourth aspect of this application. Consequently, the battery exhibits excellent capacity retention.

[0024] The sixth aspect of this application provides an electrical device that includes the battery described in the fifth aspect.

[0025] 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

[0026] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred 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 schematic diagram of the structure of a battery according to one embodiment of this application; Figure 2 This is a schematic diagram of the structure of a battery module according to one embodiment of this application; Figure 3 This is a schematic diagram of the structure of a battery pack according to one embodiment of this application; Figure 4 yes Figure 3 Exploded view; Figure 5 This is a schematic diagram of one embodiment of an electrical device that uses a battery as a power source; Figure 6 These are the XRD patterns of the positive electrode active materials of Example 1 and Comparative Example 1 of this application; Figure 7 These are the XRD patterns of the positive electrode active materials of Example 1 and Comparative Example 2 of this application; Figure 8 This is a charging and discharging diagram of the positive electrode of Embodiment 1 of this application at 1.5-4.2 / 4.2-1.5V; Figure 9 This is a comparison chart of the capacity retention rates of the batteries in Example 1 and Comparative Example 4 of this application.

[0027] Explanation of reference numerals in the attached figures: 1: Secondary battery; 2: Battery module; 3: Battery pack; 4: Upper casing; 5: Lower casing. Detailed Implementation

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] With the technological advancements and increasing demands for electric vehicles and rechargeable mobile devices, secondary batteries, as a representative of the new energy field, have seen rapid development in related research. Sodium-ion batteries offer a significant price advantage over traditional lithium-ion batteries and have broad application prospects in large-scale energy storage systems.

[0034] Layered transition metal oxides have become one of the popular positive electrode active materials for sodium-ion batteries due to their high conductivity, high energy density, large capacity and long cycle life.

[0035] However, existing layered transition metal oxides have the following problems: Firstly, moisture in the air can penetrate from the surface of the layered transition metal oxide into the bulk phase, causing its structure to be easily damaged after prolonged exposure to air. Secondly, during high-voltage charging, the oxygen coordinated with the metal in the layered transition metal oxide also undergoes an oxidation reaction, i.e., lattice oxygen release, leading to structural damage. Thirdly, during high-voltage charging, the phase transition accompanying the extraction of sodium ions in the layered transition metal oxide can create cracks, allowing the electrolyte to seep into the material and react, further deteriorating the material's structure. The destruction of the layered transition metal oxide material structure leads to decreased material stability, directly resulting in a lower battery capacity retention rate.

[0036] In this application, the positive electrode active material is based on NiFeMn and doped with rare earth elements M1 and M2, with the ratio of M1 to Mn controlled. On the one hand, the large radius of rare earth element M1 allows it to remain on the surface of the positive electrode active material, forming a dense and uniform doped layer. This doped layer effectively blocks moisture from penetrating the bulk phase from the surface of the positive electrode active material, improving the structural stability of the material. Furthermore, during high-voltage charging, the doped layer can also suppress the evolution of lattice oxygen and the penetration of electrolyte into the material, improving the structural stability and thus enhancing the capacity retention of the battery containing it. On the other hand, doped element M2 is distributed in the bulk phase of the positive electrode active material, forming strong chemical bonds with O in the positive electrode active material, inhibiting the release of Na ions from the bulk phase, reducing the interlayer spacing change, delaying phase transition, and improving the cycle stability of the positive electrode active material. In addition, the ratio d / c of ​​rare earth elements M1 to Mn in the positive electrode active material in this application is controlled at 0.005-0.05, which is beneficial to improving the air stability and cycle stability of the positive electrode active material, thereby improving the capacity retention rate of the battery containing it.

[0037] 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.

[0038] The first aspect of this application discloses a positive electrode active material, said positive electrode active material comprising: Na x Ni aFe b Mn c M1 d M2 e O 2+δ-f F f , Wherein, M1 includes rare earth elements, and M2 includes at least one of Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group VIA and transition elements, 0.6≤x≤1.2, 0<a≤0.5, 0<b≤0.4, 0.3≤c≤0.75, 0.001≤d≤0.05, 0≤e≤0.3, -0.1≤δ≤0.1, 0≤f≤0.1, 0.005≤d / c≤0.05, and a+b+c+d+e=1.

[0039] This application includes at least the following beneficial effects: The main material of the positive electrode active material of this application includes NiFeMn, and is doped with rare earth elements M1 and M2. The Fe content mentioned above can improve the specific capacity of the positive electrode active material. Rare earth element M1 has a large radius and forms a dense and uniform doped layer on the surface of the positive electrode active material. The doped layer can effectively block the intrusion of water vapor from the surface of the positive electrode active material into the bulk phase, thereby improving the structural stability of the material. During high-voltage charging, the doped layer can also inhibit the evolution of lattice oxygen and the penetration of electrolyte into the material, improving the structural stability of the material and thus improving the capacity retention rate of the battery containing it. Doped element M2 is distributed in the bulk phase of the positive electrode active material and can form strong chemical bonds with O in the positive electrode active material, inhibiting the extraction of Na ions from the bulk phase of the positive electrode active material, and can reduce the interlayer spacing change of the positive electrode active material, delaying the occurrence of phase transition, improving the cycle stability of the positive electrode active material, thereby improving the capacity retention rate of the battery.

[0040] Furthermore, when the ratio d / c of ​​rare earth elements M1 to Mn in the positive electrode active material is within the above-mentioned range, it can reduce the formation of impurity phases caused by insufficient solid solubility between rare earth elements and Mn on the surface of the positive electrode active material. At the same time, it reduces the probability of failing to form a rare earth doped layer due to insufficient rare earth elements. This is conducive to the formation of a dense and uniform rare earth doped layer on the surface of the positive electrode active material, effectively blocking the intrusion of water vapor from the surface of the positive electrode active material into the bulk phase. It can also inhibit the evolution of lattice oxygen and the penetration of electrolyte into the bulk phase, improve the air stability and cycle stability of the positive electrode active material, thereby improving the capacity retention rate of the battery containing it.

[0041] In summary, the main materials in the positive electrode active material include NiFeMn, and it is doped with rare earth elements M1 and M2. The doping amount and d / c of ​​each element are controlled. These features work together to improve the specific capacity of the positive electrode active material.

[0042] In some embodiments of this application, the above-mentioned positive electrode active material Na x Ni a Fe b Mn c M1 d M2 e O 2+δ-f F f In this case, x can take values ​​of 0.6 ≤ x ≤ 1.2, such as 0.7 ≤ x ≤ 1.1, 0.8 ≤ x ≤ 1, 0.9 ≤ x ≤ 1.1, 1 ≤ x ≤ 1.1, etc. Therefore, the inclusion of this amount of sodium in the positive electrode active material results in a higher battery capacity.

[0043] It should be noted that in the positive electrode, battery, or electrical device, sodium ions are consumed during the formation and cycling processes, which may result in the measured sodium content (x) in the positive electrode active material being less than 1. Conversely, if sodium replenishment agents are used in both the positive and negative electrode plates, the measured sodium content (x) in the positive electrode active material may be greater than 1 after the battery undergoes formation and cycling.

[0044] In some embodiments of this application, the above-mentioned positive electrode active material Na x Ni a Fe b Mn c M1 d M2 e O 2+δ-f F f In this context, 'a' can take values ​​of 0 < a ≤ 0.5, for example, 0.001 ≤ a ≤ 0.5, 0.005 ≤ a ≤ 0.5, 0.1 ≤ a ≤ 0.5, 0.15 ≤ a ≤ 0.45, 0.2 ≤ a ≤ 0.4, 0.25 ≤ a ≤ 0.35, 0.25 ≤ a ≤ 0.3, etc. Therefore, including this amount of nickel in the positive electrode active material can improve the energy density of the battery. In other embodiments of this application, the above-mentioned positive electrode active material Na... x Ni a Fe b Mn c M1 d M2 e O 2+δ-f F f In this case, 'a' can take values ​​of 0.1 ≤ a ≤ 0.4, for example, 0.15 ≤ a ≤ 0.3.

[0045] In some embodiments of this application, the above-mentioned positive electrode active material Na x Ni a Fe b Mn c M1 d M2 e O 2+δ-fF f In this context, b can take values ​​of 0 < b ≤ 0.4, for example, 0.001 ≤ a ≤ 0.4, 0.005 ≤ a ≤ 0.4, 0.1 ≤ a ≤ 0.4, 0.15 ≤ a ≤ 0.35, 0.2 ≤ a ≤ 0.35, 0.25 ≤ a ≤ 0.35, 0.3 ≤ a ≤ 0.35, etc. Therefore, during the process of Na ions being extracted from the material, Fe, as a charge-compensating metal element, will oxidize from a trivalent state to a tetravalent state. When Na ions are reinserted into the material, Fe will be reduced from a tetravalent state back to a trivalent state. Including this amount of Fe in the positive electrode active material can improve the specific capacity of the material. In other embodiments of this application, the above-mentioned positive electrode active material Na... x Ni a Fe b Mn c M1 d M2 e O 2+δ-f F f In this case, b can take values ​​of 0.1 ≤ b ≤ 0.35, for example, 0.15 ≤ b ≤ 0.35.

[0046] In some embodiments of this application, the above-mentioned positive electrode active material Na x Ni a Fe b Mn c M1 d M2 e O 2+δ-f F f The concentration of Mn can be 0.3 ≤ c ≤ 0.75, for example, 0.35 ≤ c ≤ 0.75, 0.4 ≤ c ≤ 0.7, 0.45 ≤ c ≤ 0.65, 0.5 ≤ c ≤ 0.6, 0.55 ≤ c ≤ 0.6, etc. Therefore, this concentration of Mn can react with rare earth element M1 to form a uniform and dense doped layer on the surface of the positive electrode active material, improving the structural stability of the positive electrode active material and thus enhancing the capacity retention rate of the battery containing it. In other embodiments of this application, the above-mentioned positive electrode active material Na... x Ni a Fe b Mn c M1 d M2 e O 2+δ-f F f In this case, c can be 0.35≤c≤0.6, for example, 0.35≤c≤0.5.

[0047] In some embodiments of this application, the above-mentioned positive electrode active material Na x Ni a Fe b Mn c M1 d M2 e O2+δ-f F f M1 comprises at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Therefore, this composition of M1 can form a dense and uniform doped layer on the surface of the positive electrode active material, effectively preventing moisture from penetrating from the surface of the positive electrode active material into the bulk phase, thus improving the structural stability of the material. Simultaneously, during high-voltage charging, this doped layer can also suppress the evolution of lattice oxygen and the penetration of electrolyte into the material interior, improving the structural stability of the material and thereby enhancing the capacity retention rate of batteries containing it.

[0048] In addition, M1 uses at least one of the above elements, making it environmentally friendly and less polluting.

[0049] In some embodiments of this application, the above-mentioned positive electrode active material Na x Ni a Fe b Mn c M1 d M2 e O 2+δ-f F f In this case, d can be 0.001≤d≤0.05, for example, 0.005≤d≤0.05, 0.01≤d≤0.05, 0.015≤d≤0.045, 0.02≤d≤0.04, 0.025≤d≤0.035, 0.03≤d≤0.035, etc. Therefore, including this amount of M1 element in the positive electrode active material can form a dense and uniform doped layer on the surface of the positive electrode active material, effectively preventing moisture from penetrating from the surface of the positive electrode active material into the bulk phase, thus improving the structural stability of the material. Simultaneously, during high-voltage charging, this doped layer can also inhibit the evolution of lattice oxygen and the penetration of electrolyte into the material interior, improving the structural stability of the material and thereby enhancing the capacity retention rate of the battery containing it.

[0050] In some embodiments of this application, the above-mentioned positive electrode active material Na x Ni a Fe b Mn c M1 d M2 e O 2+δ-f F fThe contents of rare earth elements M1 and Mn satisfy the following relationship: 0.005≤d / c≤0.05, for example 0.01≤d / c≤0.05, 0.015≤d / c≤0.045, 0.02≤d / c≤0.04, 0.025≤d / c≤0.035, 0.03≤d / c≤0.035. When the ratio d / c of ​​rare earth elements M1 to Mn in the positive electrode active material is within the above-mentioned range, it can reduce the agglomeration of rare earth elements on the surface of the positive electrode active material due to insufficient solid solubility between rare earth elements and Mn, thus forming a heterogeneous phase. Simultaneously, it reduces the probability of failing to form a rare earth doped layer due to insufficient rare earth elements, which is beneficial for the formation of a dense and uniform rare earth doped layer on the surface of the positive electrode active material. This effectively prevents moisture from penetrating from the surface of the positive electrode active material into the bulk phase, and also inhibits the evolution of lattice oxygen and the penetration of electrolyte into the bulk phase, improving the air stability and cycle stability of the positive electrode active material, thereby enhancing the capacity retention rate of the battery containing it. In other embodiments of this application, the above-mentioned positive electrode active material Na... x Ni a Fe b Mn c M1 d M2 e O 2+δ-f F f The content of rare earth elements M1 and Mn satisfies the following relationship: 0.01≤d / c≤0.03. This is beneficial to improving the air stability and cycle stability of the positive electrode active material, thereby improving the capacity retention rate of the battery containing it.

[0051] In some embodiments of this application, the above-mentioned positive electrode active material Na x Ni a Fe b Mn c M1 d M2 e O 2+δ-f F f M2 includes at least one of B, Mg, Al, Si, K, Ca, Ga, Ge, Se, Rb, Sr, In, Sn, Sb, Te, Sc, Ti, V, Cr, Co, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, and Au. Specifically, in the positive electrode active material, element M2 is uniformly distributed in its bulk phase, and M2 can form strong chemical bonds with O in the positive electrode active material. This chemical bond, on the one hand, inhibits the extraction of Na from the bulk phase in the positive electrode active material, and on the other hand, stabilizes the structure of the metal layer of the positive electrode active material, reduces the change in the interlayer spacing of the positive electrode active material, reduces the occurrence of phase transition, and improves the cycle performance of the positive electrode active material, thereby improving the capacity retention rate of the battery containing it.

[0052] In some embodiments, the above-mentioned positive electrode active material Na x Ni a Fe b Mn c M1 d M2 e O 2+δ-f F f In this case, δ and f satisfy the following conditions: -0.1≤δ≤0.1, 0≤f≤0.1, 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≤f≤0.09, 0.02≤f≤0.08, 0.03≤f≤0.07, 0.04≤f≤0.06, 0.05≤f≤0.06, etc. Specifically, the oxygen sites in the positive electrode active material of this application are doped with this amount of F, which can effectively stabilize the oxygen in the positive electrode active material, thereby reducing the structural damage caused by the release of oxygen from the lattice in the positive electrode active material, improving the stability of the material, and thus improving the capacity retention rate of the battery.

[0053] It should be noted that in positive electrode sheets, batteries, or electrical devices, due to the cycling process, oxygen elements in the positive electrode active material are lost, which may result in the measured oxygen content 2+δ-f in the positive electrode active material being less than 2.

[0054] In some embodiments of this application, the above-mentioned positive electrode active material Na x Ni a Fe b Mn c M1 d M2 e O 2+δ-f F f1.75≤(a+b+c) / b≤9.5, for example, 1.8≤(a+b+c) / b≤9.5, 1.9≤(a+b+c) / b≤9.4, 2 ≤(a+b+c) / b≤9.3, 2.1≤(a+b+c) / b≤9.2, 2.2≤(a+b+c) / b≤9.1, 2.3≤(a+b+ c) / b≤9, 2.5≤(a+b+c) / b≤8.5, 3≤(a+b+c) / b≤8, 3.5≤(a+b+c) / b≤7.5, 4≤( a+b+c) / b≤7, 4.5≤(a+b+c) / b≤6.5, 5≤(a+b+c) / b≤6, 5≤(a+b+c) / b≤5.5, etc. Specifically, controlling the sum of Ni, Fe, and Mn content to the Fe content in the aforementioned positive electrode active material within the above-mentioned range reduces the amount of Na ions that can be extracted from the positive electrode active material due to insufficient Fe content, thus giving the positive electrode active material excellent specific capacity. On the other hand, it reduces the large amount of Fe migrating to the Na ion layer due to excessive Fe content in the positive electrode active material, thereby affecting the insertion and extraction of Na ions, improving the cycle performance of the positive electrode active material, and thus improving the capacity retention rate of the battery containing it.

[0055] In some embodiments of this application, the above-mentioned positive electrode active material Na x Ni a Fe b Mn c M1 d M2 e O 2+δ-f F f In the case where 0.8 < x ≤ 1.0, the phase state of the positive electrode active material includes the O3 phase, and the space group includes... The interlayer spacing is 0.53nm-0.55nm. For example, x can be 0.82-1.0, 0.85-0.95, 0.88-0.90, etc., and the interlayer spacing can be 0.53nm-0.545nm, 0.535nm-0.54nm, 0.536nm-0.539nm, etc. Specifically, when x is within the above range, the resulting O3 phase positive electrode active material has a high Na content, which can release more Na ions, resulting in a higher battery capacity.

[0056] In some embodiments of this application, 0.6 ≤ x ≤ 0.8, the phase state of the positive electrode active material includes the P2 phase, the space group includes P63 / mmc, and the interlayer spacing is 0.54 nm-0.57 nm. For example, x can be 0.6-0.78, 0.65-0.75, 0.68-0.7, etc., and the interlayer spacing can be 0.54 nm-0.565 nm, 0.545 nm-0.56 nm, 0.55 nm-0.555 nm, etc. Specifically, when x is within the above range, the interlayer spacing of the P2 phase positive electrode active material is large, which 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.

[0057] It should be noted that the characterization methods for the phase state, space group, and interlayer spacing of the positive electrode active material in this application can include X-ray diffraction, scanning electron microscopy, transmission electron microscopy, etc. Specifically, in the X-ray diffraction pattern, the characteristic peaks in the range of 40.5° to 42.5° indicate that the positive electrode active material is in the O3 phase, and the space group includes... The characteristic peaks in the range of 48° to 50° indicate that the positive electrode active material is a P2 phase, and the space group includes P63 / mmc. The interlayer spacing of the positive electrode active material of the O3 phase can be calculated by the position of the (003) peak of X-ray diffraction. The interlayer spacing of the positive electrode active material of the P2 phase can be calculated by the position of the (002) peak of X-ray diffraction.

[0058] In some embodiments of this application, the pH value of the soaking solution for the positive electrode active material is less than or equal to 13. For example, the pH value of the soaking solution for the positive electrode active material can be 7-13, 7.2-13, 7.5-13, 8-13, 8.5-13, 9-13, 10-12.9, 10.5-12.7, 11.0-12.7, 11.2-12.5, 11.5-12.3, 11.7-12.0, etc. Controlling the pH value of the soaking solution for the positive electrode active material within the above range can reduce the formation of gel during the slurry preparation process and facilitate the subsequent slurry preparation and coating of the positive electrode active material. In other embodiments of this application, the pH value of the soaking solution for the positive electrode active material is less than or equal to 12.7. For example, the pH value of the soaking solution for the positive electrode active material is 11.0 ≤ pH ≤ 12.7.

[0059] Specifically, the pH value of the immersion solution for the positive electrode active material can be measured using the following method: The positive electrode active material is dispersed in pure water and soaked. The solution is filtered to obtain the soaking solution, and the soaking solution is measured and titrated with standard hydrochloric acid solution.

[0060] In some embodiments of this application, the D of the positive electrode active material v 50 is 3μm-30μm, for example, the D of the positive electrode active materialv 50 can be 3μm-29μm, 4μm-28μm, 5μm-15μm, 6μm-14μm, 8μm-13μm, 9μm-12μm, 10μm-11μm, etc. In some other embodiments of this application, the D of the positive electrode active material... v 50 is 5μm-15μm.

[0061] In this application, D v 50 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.

[0062] In some embodiments of this application, the specific surface area of ​​the positive electrode active material is 0.1 m². 2 / g-5m 2 / g, for example, the specific surface area of ​​the positive electrode active material can be 0.1m². 2 / g-4.5m 2 / g, 0.2m 2 / g-4m 2 / g, 0.3m 2 / g-3m 2 / g, 0.5m 2 / g-2.5m 2 / g, 1m 2 / g-2m 2 / g, 1.2m 2 / g-1.8m 2 / g, etc. In some other embodiments of this application, the specific surface area of ​​the positive electrode active material is 0.3m². 2 / g-3m 2 / g.

[0063] In this application, the specific surface area of ​​the positive electrode active material can be obtained by the following method: using a US-made Gemini VII2390 multi-station fully automated specific surface area and porosity analyzer, take about 7g of sample and put it into a 9cc long tube with a bulb, degas at 200℃ for 2h, and then put it into the main unit to test and obtain the BET (specific surface area) data of the positive electrode active material.

[0064] In some embodiments of this application, the tap density of the positive electrode active material is 1 g / cm³. 3 -3g / cm 3 For example, the tap density of the positive electrode active material can be 1 g / cm³. 3 -2.8g / cm 3 1.5g / cm 3 -2.5g / cm3 1.7g / cm 3 -2.4g / cm 3 1.8g / cm 3 -2 g / cm 3 In other embodiments of this application, the tap density of the positive electrode active material is 1.5 g / cm³. 3 -2.5g / cm 3 .

[0065] In this application, tap density refers to the mass per unit volume of powder in a container after tapping under specified conditions. The method for determining the tap density of positive electrode active materials is as follows: The weighed positive electrode active material is loaded into the graduated cylinder of the tapping device, and the graduated cylinder is fixed on the support. Rotating the cam causes the guide rod to slide the support up and down, striking the anvil. The device vibrates at 250±15 times per minute for 12 minutes. The volume of the positive electrode active material in the graduated cylinder is measured; the ratio of the mass of the positive electrode active material to its volume is the tap density of the positive electrode active material.

[0066] The formula for calculating tap density is: ρbt = m0 / V Where ρbt is the tap density, in g / cm³. 3 m0 — Mass of the positive electrode active material, in grams V – Volume of the positive electrode active material after tapping (volume of the measuring cup), cm 3 .

[0067] In some embodiments of this application, the compaction density of the positive electrode active material under a pressure of 300 MPa is 3.0 g / cm³. 3 -4.0g / cm 3 For example, the compaction density of the positive electrode active material under a pressure of 300 MPa can be 3.0 g / cm³. 3 -3.9g / cm 3 3.1g / cm 3 -3.8g / cm 3 3.2g / cm 3 -3.7g / cm 3 3.3g / cm 3 -3.6g / cm 3 3.4g / cm 3 -3.5g / cm 3 wait.

[0068] In some embodiments of this application, compaction density refers to the compaction density of the electrode sheet after the material is formed. Compaction density = areal density / (thickness of the electrode sheet after compaction - thickness of the current collector). Specifically, the method for determining the compaction density of the positive electrode active material under a pressure of 300 MPa is as follows: Take the rolled electrode sheet, cut off a section with an area of ​​s (circular or square), measure its thickness as a, and weigh it as m1. Wash away the positive electrode material with an acetone-alcohol mixture and dry it. Weigh the remaining aluminum foil as m2 and measure its thickness as b. Divide the difference in weight between the two by the area s of the circle or square to calculate the areal density, i.e., areal density = (m1 - m2) / s. Divide the areal density by the thickness difference to obtain the compacted density, i.e., compacted density = (m1 - m2) / [s(ab)].

[0069] Specifically, when the D of the positive electrode active material of this application v 50. When at least one of the specific surface area, tap density, and compaction density under 300 MPa pressure is within the above range, the conduction distance within 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.

[0070] The second aspect of this application provides a method for preparing the positive electrode active material described in the first aspect, comprising: S100: A precursor is obtained by mixing Na source, Ni source, Fe source, Mn source, M1 source and M2 source. In some embodiments of this application, the Na source, Ni source, Fe source, Mn source, M1 source and M2 source are mixed according to the above-described positive electrode active material composition.

[0071] It should be noted that the Na source, Ni source, Fe source, Mn source, M1 source, and M2 source in this application are conventional materials in the art, and those skilled in the art can select them according to actual needs. For example, the Na source may include at least one of Na2CO3, NaHCO3, NaOH, and Na2O2; the Ni source may include NiO; 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 M1 source may include at least one of oxides of M1, salts containing M1, and other compounds; and the M2 source may include at least one of oxides of M2, salts containing M2, and other compounds.

[0072] It should be noted that if F element needs to be doped in the positive electrode active material, at least one of the Na source, Ni source, Fe source, Mn source, M1 source and M2 source shall be at least one of its corresponding fluorine salt and other compounds, such as sodium fluoride, nickel fluoride, iron fluoride, manganese fluoride, M1 fluoride (fluoride salt of M1) and M2 fluoride (fluoride salt of M2).

[0073] S200: Calcine the precursor. In some embodiments of this application, the precursor obtained above is placed in a muffle furnace and calcined in an air atmosphere, then cooled to room temperature, and mechanically pulverized to obtain the positive electrode active material. The calcination temperature can be 600℃-1200℃, for example, 600℃-1100℃, 700℃-1000℃, 800℃-900℃, etc., and the holding time is 10h-20h, for example, 10h-19h, 11h-18h, 12h-17h, 13h-16h, 14h-15h, etc.

[0074] In addition, the precursor can be pre-calcined and kept at a certain temperature before calcining, as needed. The pre-calcination temperature can be 600℃-900℃, for example, 600℃-850℃, 650℃-800℃, 600℃-750℃, 550℃-700℃, 500℃-650℃, 550℃-600℃, etc. The holding time is 10h-20h, for example, 10h-19h, 11h-18h, 12h-17h, 13h-16h, 14h-15h, etc.

[0075] Therefore, the above-mentioned positive electrode active material with excellent air stability and cycle stability can be prepared by using the solid-state method, thereby improving the capacity retention rate of the battery.

[0076] A third aspect of this application provides another method for preparing the positive electrode active material described in the first aspect, comprising: Sa: A mixed solution is obtained by mixing Ni source, Fe source, Mn source, M1 source and M2 source with water. In some embodiments of this application, a Ni source, Fe source, Mn source, M1 source and M2 source are mixed with water according to the above-described positive electrode active material composition to obtain a mixed solution.

[0077] It should be noted that the Ni source, Fe source, Mn source, M1 source, and M2 source in this application are conventional materials in the art, and those skilled in the art can select them according to actual needs. For example, the Ni source may include at least one of nickel chloride, nickel sulfate, nickel nitrate, and nickel oxalate; the Fe source may include at least one of ferric chloride, ferric sulfate, ferric nitrate, and ferric oxalate; the Mn source may include at least one of manganese chloride, manganese sulfate, manganese nitrate, and manganese oxalate; the M1 source may include at least one of the chloride, sulfate, nitrate, and oxalate of M1; and the M2 source may include at least one of the chloride, sulfate, nitrate, oxalate, and other compounds of M2.

[0078] Sb: The precursor is obtained by reacting the solution with a precipitant. In some embodiments of this application, the solution obtained in step Sa is reacted with a solution containing a precipitant to obtain a precursor, wherein the solution containing the precipitant includes at least one of ammonia, carbonic acid, and oxalic acid.

[0079] Sc: The precursor is mixed with the Na source and then calcined. In some embodiments of this application, the obtained precursor and Na source are mixed evenly by ball milling or mechanical stirring according to the above-mentioned positive electrode active material composition, then placed in a muffle furnace for calcination, then cooled to room temperature, and mechanically pulverized to obtain the positive electrode active material. The calcination temperature is 600℃-1200℃, for example, 700℃-1100℃, 800℃-1000℃, 900℃-950℃, etc. The calcination atmosphere can be air or oxygen atmosphere, and the holding time is 10h-20h, for example, 10h-19h, 11h-18h, 12h-17h, 13h-16h, 14h-15h, etc.

[0080] It should be noted that, as needed, before mixing and calcining the precursor and Na source, the precursor and Na source can be pre-calcined and held at a specific temperature. The pre-calcination temperature can be 600℃-900℃, for example, 600℃-850℃, 650℃-800℃, 600℃-750℃, 550℃-700℃, 500℃-650℃, 550℃-600℃, etc. The holding time can be 10h-20h, for example, 10h-19h, 11h-18h, 12h-17h, 13h-16h, 14h-15h, etc. The Na source can include at least one of Na2CO3, NaHCO3, NaOH, and Na2O2.

[0081] It should be noted that if F element needs to be doped in the positive electrode active material, at least one of the Na source, Ni source, Fe source, Mn source, M1 source and M2 source shall be at least one of its corresponding fluorine salt and other compounds, such as sodium fluoride, nickel fluoride, iron fluoride, manganese fluoride, M1 fluoride (fluoride salt of M1) and M2 fluoride (fluoride salt of M2).

[0082] Therefore, the co-precipitation method can be used to prepare the above-mentioned positive electrode active material with excellent air stability and cycle stability, thereby improving the capacity retention rate of the battery.

[0083] The fourth aspect of this application provides a positive electrode sheet, which includes the positive electrode active material described in the first aspect of this application, the positive electrode active material prepared by the method described in the second aspect, or the positive electrode active material prepared by the method described in the third aspect.

[0084] 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.

[0085] 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.

[0086] The positive electrode active material includes the positive electrode active material described in the first aspect of this application, the positive electrode active material prepared by the method described in the second aspect, or the positive electrode active material prepared by the method described in the third aspect.

[0087] 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.

[0088] 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).

[0089] These materials can all be obtained through commercial means.

[0090] A fifth aspect of this application provides a battery comprising the positive electrode sheet described in the fourth aspect of this application. Consequently, the battery exhibits excellent capacity retention.

[0091] A battery is a device that can be recharged after being discharged, allowing its active materials to be reactivated and continue to be used.

[0092] It is understood that the battery proposed in this application is a sodium-ion battery.

[0093] 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.

[0094] [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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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).

[0100] 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.

[0101] Electrolyte The electrolyte may include an electrolyte salt and a solvent.

[0102] 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.

[0103] 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).

[0104] 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.

[0105] [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.

[0106] 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 1 This is a square-structured battery 1 used as an example.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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).

[0112] 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.

[0113] Figure 2 This is battery module 2 as an example. (See reference...) Figure 2 In battery module 2, multiple batteries 1 can be arranged sequentially along the length of battery module 2. Of course, they can also be arranged in any other way. Furthermore, these multiple batteries 1 can be fixed in place using fasteners.

[0114] The battery module 2 may also include a housing with a receiving space in which multiple 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.

[0115] Figure 3 and 4 This is battery pack 3 as an example. (See reference...) Figure 3 and 4 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.

[0116] A sixth aspect of this application provides an electrical device comprising the battery described in the fifth 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.

[0117] Figure 5 This is an example of an electrical appliance. The electrical appliance includes pure electric vehicles, hybrid electric vehicles, or plug-in hybrid electric vehicles.

[0118] 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.

[0119] 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.

[0120] Example 1 NaNi 0.2 Fe 0.2 Mn 0.5 La 0.02 Cu 0.08 O2 preparation The raw materials were mixed according to the stoichiometric ratio of their molecular formulas: 23.666 g of Na₂CO₃, 6.672 g of NiO, 7.131 g of Fe₂O₃, 17.627 g of Mn₂O₃, 1.455 g of La₂O₃, and 2.841 g of CuO (molar ratio of Na, Ni, Fe, Mn, La, and Cu was 1:0.2:0.2:0.5:0.02:0.08). The mixture was placed in the agate ball mill jar of a planetary ball mill and ground at 600 r / min. The mixture was then calcined in a muffle furnace at a heating rate of 5 °C / min to 950 °C, held at that temperature for 15 h, and then allowed to cool naturally to room temperature to obtain the black positive electrode active material NaNi. 0.2 Fe 0.2 Mn 0.5 La 0.02 Cu 0.08 O2.

[0121] Preparation of the positive electrode sheet The NaNi prepared above 0.2 Fe 0.2 Mn 0.5 La 0.02 Cu 0.08 O2, conductive carbon black, binder polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) are mixed evenly in a weight ratio of 60:5:5:30 to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto a positive electrode aluminum foil current collector, and after drying, cold pressing, and slitting, a positive electrode sheet is obtained.

[0122] Preparation of the negative electrode sheet The negative electrode is made of metallic sodium.

[0123] Preparation of Electrolyte In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly at a volume ratio of 3 / 7 to obtain a mixed solvent. Then, NaPF6 was dissolved in the mixed solvent and stirred evenly to obtain an electrolyte with a sodium salt concentration of 1 mol / L.

[0124]

Isolation Film

[0125] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up. The electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried secondary battery. After vacuum sealing, settling, formation, and shaping, the secondary battery is obtained.

[0126] The secondary batteries containing positive electrode active materials in Examples 2-24 and Comparative Examples 1-4 are the same as those in Example 1, except for the different parameters (see Table 1).

[0127] The composition of the positive electrode active material in the batteries of Examples 1-24 and Comparative Examples 1-4 of this application is shown in Table 1.

[0128] Table 1

[0129] The D of the positive electrode active material in Examples 1-24 and Comparative Examples 1-4 v 50. The specific surface area, tap density, compaction density under 300 MPa pressure, pH value of the soaking solution, phase state, space group and interlayer spacing, as well as the capacity and capacity retention of the obtained sodium-ion battery were characterized. The characterization results are shown in Table 2.

[0130] Performance testing: 1. Phase, space group, and interlayer spacing test of positive electrode active material: XRD pattern of positive electrode active material is performed. The phase and space group of positive electrode active material are determined according to the position of characteristic peaks in the XRD pattern. The interlayer spacing d of positive electrode active material is calculated according to the position of (003) peak or (002) peak of X-ray diffraction and the corresponding peaks and the formula d=λ / (2sinθ). In the formula d=λ / (2sinθ), the X-ray wavelength λ=1.5406Å. Characteristic peaks with a scanning 2θ angle in the range of 40.5° to 42.5° indicate that the positive electrode active material is in the O3 phase. The space group includes The characteristic peaks in the range of 48° to 50° when scanning the 2θ angle indicate that the positive electrode active material is the P2 phase, and the space group includes P63 / mmc.

[0131] 2. D of the positive electrode active material v 50 Determination: The determination was performed using a Malvern Master Size 3000 laser particle size analyzer, in accordance with GB / T 19077-2016.

[0132] 3. Tap Density Measurement: The weighed positive electrode active material is loaded into the graduated cylinder of the tapping device, and the cylinder is fixed to the support. Rotating the cam causes the guide rod to slide the support up and down, impacting the anvil. Vibrate 250±15 times per minute for 12 minutes. Measure the volume of the positive electrode active material in the graduated cylinder; the ratio of the mass of the positive electrode active material to its volume is the tap density of the positive electrode active material.

[0133] The formula for calculating tap density is: ρbt = m0 / V Where ρbt is the tap density, in g / cm³. 3 m0 — Mass of the positive electrode active material, in grams V – Volume of the positive electrode active material after tapping (volume of the measuring cup), cm 3 .

[0134] 4. Compacted density of the positive electrode active material under 300MPa pressure: Take the rolled electrode sheet, cut off a region with an area of ​​s using a circular or square cutter, measure the thickness as a, and weigh it as m1. Wash away the positive electrode material with an acetone-alcohol mixture and blow dry. Weigh the remaining aluminum foil as m2 and measure the thickness of the aluminum foil as b. Divide the difference in weight between the two by the area of ​​the circle or square as s to calculate the surface density, i.e., surface density = (m1-m2) / s. Divide the surface density by the thickness difference to get the compacted density, i.e., compacted density = (m1-m2) / [s(ab)].

[0135] 5. pH value determination of the soaking solution of positive electrode active material: Disperse the positive electrode active material in pure water and soak it. Filter to obtain the soaking solution. Measure the soaking solution and titrate it with standard hydrochloric acid solution.

[0136] 6. Capacity testing of positive electrode: Fabricate positive and negative electrode sheets, punch molds, weigh them, and match the quality of positive and negative electrode sheets according to the types of positive and negative electrode materials. Then place them in a glove box for 2 hours. Assemble the button cells in the glove box, clamp the completed button cells on the electrochemical testing cabinet, and calculate the charge and discharge current according to the test rate (0.2C, 1C, 3C, 5C). Current = Rate × Theoretical specific capacity × (M2-M1) × ω% Where: Theoretical specific capacity - determined according to the theoretical specific capacity of the positive electrode material; M2 – The actual weight of the electrode; M1—The average weight of the current collector; ω% — Actual mass fraction of active substance 7. Battery capacity retention test: Taking Example 1 as an example, at 25°C, the secondary battery was charged at a constant current rate of 0.1C to the charging cutoff voltage of 4.2V, then discharged at 0.1C to 1.5V, left to stand for 5 minutes, and then discharged at a constant current rate of 0.5C to the discharge cutoff voltage of 2.8V, left to stand for 5 minutes. The battery discharge capacity C0 at this point was recorded. The battery was subjected to 500 charge-discharge cycles using this method, and the battery discharge capacity after 500 cycles was recorded as C1.

[0137] The cycle capacity retention rate of a secondary battery = C1 / C0 × 100%.

[0138] The testing procedures for the capacity retention of the secondary batteries in Examples 2-24 and Comparative Examples 1-4 were the same as those described above.

[0139] The XRD patterns of the positive electrode active materials of Example 1, Comparative Example 1, and Comparative Example 2 are shown below. Figure 6 and Figure 7 As shown, compared with Example 1, the ratio d / c of ​​rare earth elements M1 to Mn in the positive electrode active material of Comparative Example 1 is 0.004, which is less than 0.005. The peaks between 10 and 20 in the positive electrode active material are not obvious, while the impurity peaks between 30 and 40 are more obvious. It can be seen that too few rare earth elements are not conducive to improving the air stability and cycle stability of the positive electrode active material. Compared with Example 1, the ratio d / c of ​​rare earth elements M1 to Mn in the positive electrode active material of Comparative Example 2 is 0.06, which is greater than 0.05. The positive electrode active material has obvious impurity peaks. It can be seen that too many rare earth elements result in insufficient solid solubility between rare earth elements and Mn, which leads to the agglomeration of rare earth elements on the surface of the positive electrode active material and the formation of impurity phases.

[0140] Figure 8The charge-discharge curve of the sodium-ion battery prepared in Example 1 at 0.1C in the first cycle shows that the battery's operating voltage range is 1.5V-4.2V.

[0141] The capacity retention ratio comparison chart of Example 1 and Comparative Example 4 is shown below. Figure 9 As shown, the capacity retention rate of Example 1 of this application is significantly better than that of Comparative Example 4.

[0142] Table 2

[0143] As shown in Table 2, in the embodiments of this application, using NiFeMn as the main material and doping with rare earth elements M1 and M2 while controlling the ratio of rare earth elements M1 and Mn can improve the air stability and cycle stability of the positive electrode active material, thereby improving the capacity retention rate of the battery containing it. Compared with the embodiments, the d / c values ​​in Comparative Examples 1 and 2 are not within the range of the embodiments of this application, and the Mn content c values ​​in Comparative Examples 3 and 4 are not within the range of the embodiments of this application. The capacity retention rate and capacity of the batteries containing them are significantly reduced.

[0144] 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, The positive electrode active material includes: So x Ni a Feb b Mr c M1 d M2 e O 2+δ-f F f , Wherein, M1 includes rare earth elements, and M2 includes at least one of Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group VIA and transition elements, 0.6≤x≤1.2, 0<a≤0.5, 0<b≤0.4, 0.3≤c≤0.75, 0.001≤d≤0.0375, 0≤e≤0.3, -0.1≤δ≤0.1, 0≤f≤0.1, 0.005≤d / c≤0.05, and a+b+c+d+e=1.

2. The positive electrode active material according to claim 1, characterized in that, The rare earth elements include at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

3. The positive electrode active material according to claim 1 or 2, characterized in that, The M2 includes at least one of B, Mg, Al, Si, K, Ca, Ga, Ge, Se, Rb, Sr, In, Sn, Sb, Te, Sc, Ti, V, Cr, Co, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, and Au.

4. The positive electrode active material according to any one of claims 1-3, characterized in that, 0.01≤d / c≤0.

03.

5. The positive electrode active material according to any one of claims 1-4, characterized in that, The positive electrode active material satisfies at least one of the following conditions: 0.1≤a≤0.4, can be replaced by 0.15≤a≤0.3; 0.1≤b≤0.35, can be replaced with 0.15≤b≤0.35; 0.35≤c≤0.6, can be replaced with 0.35≤c≤0.

5.

6. The positive electrode active material according to any one of claims 1-5, characterized in that, 1.75≤(a+b+c) / b≤9.5, optionally, 2≤(a+b+c) / b≤9.5, more optionally, 2≤(a+b+c) / b≤6.

3.

7. The positive electrode active material according to any one of claims 1-6, characterized in that, 0.8 < x ≤ 1.0, the phase state of the positive electrode active material includes O3 phase, and the space group includes The interlayer spacing is 0.53nm-0.55nm.

8. The positive electrode active material according to any one of claims 1-6, characterized in that, 0.6≤x≤0.8, the phase state of the positive electrode active material includes P2 phase, the space group includes P63 / mmc, and the interlayer spacing is 0.54nm-0.57nm.

9. The positive electrode active material according to any one of claims 1-8, characterized in that, The pH value of the soaking solution of the positive electrode active material is less than or equal to 13. Optionally, the pH value of the soaking solution of the positive electrode active material is less than or equal to 12.

7. More preferably, the pH value of the soaking solution of the positive electrode active material is 11.0≤pH≤12.

7.

10. The positive electrode active material according to any one of claims 1-9, characterized in that, The positive electrode active material satisfies at least one of the following conditions: The positive electrode active material D v 50 is 3μm-30μm, and can be selected as 5μm-15μm; The specific surface area of ​​the positive electrode active material is 0.1 m². 2 / g-5m 2 / g, optional 0.3m 2 / g-3m 2 / g; The tap density of the positive electrode active material is 1 g / cm³. 3 -3g / cm 3 1.5g / cm³ is an optional value. 3 -2.5g / cm 3 ; The compaction density of the positive electrode active material under a pressure of 300 MPa is 3.0 g / cm³. 3 -4.0g / cm 3 .

11. A method for preparing the positive electrode active material according to any one of claims 1-10, characterized in that, include: The precursor was obtained by mixing Na source, Ni source, Fe source, Mn source, M1 source and M2 source; The precursor is calcined to obtain the positive electrode active material.

12. A method for preparing the positive electrode active material according to any one of claims 1-10, characterized in that, include: A mixed solution was obtained by mixing Ni source, Fe source, Mn source, M1 source and M2 source with water; The solution was reacted with a precipitant to obtain a precursor; The precursor was mixed with a Na source and then calcined to obtain the positive electrode active material.

13. A positive electrode plate, characterized in that, The positive electrode sheet comprises the positive active material according to any one of claims 1-10 or the positive active material prepared by the method according to claim 11 or 12.

14. A battery, characterized in that, The battery includes the positive electrode sheet as described in claim 13.

15. An electrical appliance, characterized in that, Includes the battery as described in claim 14.

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