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

Abstract

The invention discloses a positive electrode active material and a preparation method thereof, a positive electrode plate, a battery and an electric device, the positive electrode active material comprises Na4-xKyFe3-pMq (PO4) 2P2O7, M comprises at least one of Ni, Co, Mn, V, Ti, Mo, Nb, W, Cr, Zn, Zr, Ca, Mg, Cu, Sr, Y or A1, x is more than 0 and less than or equal to 0.4, y is more than 0 and less than or equal to 0.4, p is more than 0 and less than or equal to 0.3, and q is more than 0 and less than or equal to 0.3.

Description

Positive electrode active material and preparation method thereof, positive electrode sheet, battery and electrical device Technical Field

[0001] The present application belongs to the field of batteries, and specifically relates to a positive electrode active material and a preparation method thereof, a positive electrode sheet, a battery and an electrical device. Background Art

[0002] Lithium batteries face significant challenges due to the increasing scarcity of lithium resources, rising upstream material prices, lagging recycling technology development, and low recycling rates for older batteries. Sodium batteries utilize the intercalation and deintercalation of sodium ions between the positive and negative electrodes to achieve charge and discharge. Furthermore, sodium resources are far more abundant and widely distributed than lithium, and their cost is significantly lower. Therefore, sodium-ion batteries have become a promising next-generation electrochemical system to replace lithium secondary batteries. However, existing sodium batteries suffer from low energy density and rate performance.

[0003] Summary of the Invention

[0004] In view of the technical problems existing in the background technology, the present application provides a positive electrode active material, aiming to improve the energy density and rate performance of the sodium battery containing the positive electrode active material.

[0005] In order to achieve the above-mentioned object, the present application provides a positive electrode active material in one aspect, wherein the positive electrode active material comprises: Na 4-x K y Fe 3-p M q (PO4)2P2O7, wherein the M comprises at least one of Ni, Co, Mn, V, Ti, Mo, Nb, W, Cr, Zn, Zr, Ca, Mg, Cu, Sr, Y or Al, 0<x≤0.4, 0 <y≤0.4,0<p≤0.3,0<q≤0.3。

[0006] Compared with the prior art, the present application has at least the following beneficial effects: the present application performs dual-site doping in the positive electrode active material by doping K element at the Na site and metal element M at the Fe site, thereby improving the ionic conductivity and electronic conductivity of the positive electrode active material and thus improving the energy density and rate performance of the battery.

[0007] In some embodiments of the present application, in the positive electrode active material, the values ​​of x, y, p, and q satisfy at least one of the following conditions: 0.1≤x≤0.2; 0.05≤y≤0.15; 0.05≤p≤0.2; 0.05≤q≤0.15; p≥q. This can improve the energy density and rate performance of the battery.

[0008] In some embodiments of the present application, in the positive electrode active material, 4-x+y≤4. This can improve the ion conductivity of the positive electrode material, thereby facilitating the battery capacity and improving the energy density and rate performance of the material.

[0009] In some embodiments of the present application, in the positive electrode active material, 3-p+q<3. This can improve the phase purity of the positive electrode active material, thereby increasing the specific capacity of the material and the energy density of the battery.

[0010] In some embodiments of the present application, in the positive electrode active material, 0.02≤y / q≤80, preferably 0.1≤y / q≤40, and more preferably 0.2≤y / q≤10. This can increase the ionic conductivity and electronic conductivity of the positive electrode active material, improve the phase purity, and thus enhance the energy density and rate performance of the battery.

[0011] In some embodiments of the present application, in the positive electrode active material, M includes at least one of Ni, Co, Mn, V, Ca, Mg, Cu, Sr, Y, or Al. This can improve the phase purity and conductivity of the positive electrode active material, thereby increasing the energy density and rate capability of the battery.

[0012] In some embodiments of the present application, the positive electrode active material further comprises carbon, thereby improving the phase purity and conductivity of the positive electrode active material and enhancing the energy density and rate performance of the battery.

[0013] In some embodiments of the present application, the carbon content is 0.5% to 6%, preferably 1% to 3.6%, based on the total mass of the positive electrode active material. This can improve the phase purity and conductivity of the positive electrode active material, thereby improving the energy density and rate performance of the battery.

[0014] In some embodiments of the present application, the positive electrode active material satisfies at least one of the following conditions: the volume average particle size Dv50 of the positive electrode active material is 0.9 μm-8 μm, optionally 1.2 μm-3.5 μm; the BET specific surface area of ​​the positive electrode active material is 4 m 2 / g-13m 2 / g, optional 5.5m 2 / g-10m 2 / g.

[0015] The second aspect of the present application provides a method for preparing the above-mentioned positive electrode active material, comprising:

[0016] Mixing a sodium source, a potassium source, an iron source, a phosphorus source, and an M source to obtain a precursor material;

[0017] The precursor material is sintered to obtain a positive electrode active material.

[0018] Therefore, the method can be used to prepare the above-mentioned positive electrode active material with excellent ionic conductivity and electronic conductivity, thereby improving the energy density and rate performance of the battery.

[0019] In some embodiments of the present application, the sintering temperature is 200° C.-600° C., and the holding time is 11 h-16 h.

[0020] In some embodiments of the present application, the sodium source, potassium source, iron source, phosphorus source, M source, and first carbon source are mixed to improve the phase purity and conductivity of the positive electrode active material, thereby improving the energy density and rate performance of the battery.

[0021] In some embodiments of the present application, the method for preparing a positive electrode active material further includes: mixing the positive electrode active material with a second carbon source and sintering the mixture to form a carbon coating layer on the surface of the positive electrode active material. This can improve the conductivity of the positive electrode active material and enhance the energy density and rate capability of the battery.

[0022] In some embodiments of the present application, the temperature for sintering the mixed cathode active material and the second carbon source is 500° C.-600° C., and the holding time is 3 h-5 h.

[0023] In a third aspect, the present application provides a positive electrode sheet comprising the above-mentioned positive electrode active material or the positive electrode active material obtained by the above-mentioned method. Thus, the positive electrode sheet has excellent ionic conductivity and electronic conductivity, thereby improving the energy density and rate performance of the battery.

[0024] A fourth aspect of the present application provides a battery comprising the above-mentioned positive electrode sheet, thereby having excellent energy density and rate performance.

[0025] A fifth aspect of the present application provides an electrical device, which includes the above-mentioned battery.

[0026] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0028] FIG1 is a schematic structural diagram of a battery according to an embodiment of the present application;

[0029] FIG2 is a schematic structural diagram of a battery module according to an embodiment of the present application;

[0030] FIG3 is a schematic structural diagram of a battery pack according to an embodiment of the present application;

[0031] FIG4 is an exploded view of FIG3 ;

[0032] FIG5 is a schematic diagram of an embodiment of an electric device using a battery as a power source.

[0033] Explanation of reference numerals: 1: secondary battery; 2: battery module; 3: battery pack; 4: upper case; 5: lower case. DETAILED DESCRIPTION

[0034] The following embodiments of the technical solution of the present application are described in detail. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only used as examples and are not intended to limit the scope of protection of the present application.

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

[0036] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0037] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0039] With the technological advancements and increasing demand for electric vehicles and rechargeable mobile devices, secondary batteries, as a representative of the new energy sector, are experiencing rapid growth in research. Sodium-ion batteries offer significant price advantages over traditional lithium-ion batteries and hold broad application prospects in large-scale energy storage systems.

[0040] The iron-based polyanion phosphate positive electrode material Na4Fe3(PO4)2P2O7 has become one of the popular positive electrode active materials for sodium-ion batteries because of its abundant resources, environmental friendliness, easy large-scale production, open sodium ion diffusion channels, and good thermal stability and cycle stability.

[0041] However, this material still has the following problems: on the one hand, the material itself has poor electrical conductivity, which causes it to exhibit strong polarization when used in batteries, thereby reducing the battery's capacity and worsening the battery's rate performance; on the other hand, a small amount of impurities exist in the material during the synthesis process, which is difficult to remove, resulting in the material's gram capacity failing to reach the expected level, affecting the battery's energy density.

[0042] Therefore, in one aspect of the present application, a positive electrode active material is proposed, wherein the positive electrode active material comprises: Na 4-x K y Fe 3-p M q (PO4)2P2O7, wherein the M comprises at least one of Ni, Co, Mn, V, Ti, Mo, Nb, W, Cr, Zn, Zr, Ca, Mg, Cu, Sr, Y or Al, 0<x≤0.4, 0 <y≤0.4,0<p≤0.3,0<q≤0.3。

[0043] It should be noted that the ratio of each element in the positive electrode active material in this application refers to the ratio of each element in the positive electrode active material before the positive electrode sheet made of the positive electrode active material is assembled into a battery for formation. Those skilled in the art can understand that in the positive electrode sheet, battery or electrical device, due to processes such as formation and cycling, some elements will be consumed. Even if the measured ratio of the corresponding elements in the positive electrode active material is not within the above range, it should still fall within the scope of this application. For example, batteries on the market usually undergo cyclic aging after assembling the battery. Thus, in the positive electrode active material, the situation where x > 0.4 may occur for x, and / or the situation where p > 0.3 may occur for p, and / or the atomic ratio of the P element and the O element may be a non-integer ratio.

[0044] Without wishing to be bound by any theory, in this application, the K element (0 < y ≤ 0.4) is doped at the Na site of the positive electrode active material, and the metal element M (0 < q ≤ 0.3) is doped at the Fe site, realizing double-site doping at the sodium site and iron site in the material lattice. Since the radius of the K ion is larger than that of the Na ion, after doping the above content of K ions at the Na site, the lattice structure will undergo a slight deformation, expanding the Na ion transport channel, which is beneficial to the rapid insertion and extraction of Na ions. At the same time, after doping the above content of K ions at the Na site, the migration barrier of Na ions can be reduced, thereby increasing the ionic conductivity and improving the rate performance of the battery. After doping the above content of the metal element M at the Fe site, the formation of impurity phases such as sodium iron pyrophosphate and sodium iron phosphate can be inhibited, promoting the formation of polyanionic phosphate products, thereby improving the phase purity of the positive electrode material, increasing the specific capacity of the material, and提高 the energy density of the battery. In addition, doping the metal element M at the Fe site will also improve the ionic conductivity and electronic conductivity of the material, reduce the electron transport impedance in the battery, reduce the battery polarization, improve the reversibility of sodium ion insertion and extraction, and further improve the rate performance of the battery. Thus, by performing double-site doping on the positive electrode active material in this application, the ionic conductivity and electronic conductivity of the positive electrode active material can be提高, thereby improving the energy density and rate performance of the battery.

[0045] In some embodiments, the above positive electrode active material Na 4-x K y Fe 3-p [[ID=第十二条]]M q (PO4)2P2O7, M includes at least one of Ni, Co, Mn, V, Ti, Mo, Nb, W, Cr, Zn, Zr, Ca, Mg, Cu, Sr, Y or Al. Thus, the metal element M of this composition can not only reduce the impurity phase in the positive electrode active material, but also improve the conductivity of the positive electrode active material, thereby improving the energy density and rate performance of the battery. In other embodiments, M in the above positive electrode active material includes at least one of Ni, Co, Mn, V, Ca, Mg, Cu, Sr, Y or Al.

[0046] In some embodiments, the above compound Na 4-x K y Fe 3-p M q In (PO4)2P2O7, x can be 0 < x ≤ 0.4, such as 0.01-0.4, 0.03-0.38, 0.05-0.35, 0.1-0.32, 0.12-0.3, 0.15-0.28, 0.18-0.25, 0.2-0.22, etc. In other embodiments, 0.1 ≤ x ≤ 0.2. Thus, the inclusion of this content of sodium ions in the positive electrode active material enables the battery to have a higher capacity.

[0047] In some embodiments, the above compound Na 4-x K y Fe 3-p M q In (PO4)2P2O7, y can be 0<y≤0.4, such as 0.01-0.4, 0.03-0.38, 0.05-0.35, 0.1-0.32, 0.12-0.3, 0.15-0.28, 0.18-0.25, 0.2-0.22, etc. In other embodiments, 0.05≤y≤0.15. Thus, by doping the Na site of the positive electrode active material with this content of K ions, since the radius of K ions is larger than that of Na ions, after the K ions of this content are doped at the Na site, the lattice structure will be slightly deformed, thereby expanding the Na ion transmission channel, which is conducive to the rapid deintercalation of Na ions. At the same time, after the K ions of this content are doped at the Na site, the Na ion migration barrier can be reduced, thereby increasing the ionic conductivity and improving the battery rate performance.

[0048] In some embodiments, the positive electrode active material Na 4-x K y Fe 3-p M q In (PO4)2P2O7, x and y satisfy 4-x+y≤4, for example, 3.8≤4-x+y≤4, 3.85≤4-x+y≤3.95, and 3.9≤4-x+y≤3.95. Thus, the Na ions and K ions in the positive electrode active material act synergistically to improve the capacity and rate performance of the battery.

[0049] In some embodiments, the above compound Na 4-x K y Fe 3-p M qIn (PO4)2P2O7, p can be 0 < p ≤ 0.3, such as 0.01-0.3, 0.03-0.28, 0.05-0.25, 0.1-0.22, 0.12-0.2, 0.15-0.18, etc. In other embodiments, 0.05 ≤ p ≤ 0.2. Therefore, including this amount of Fe in the positive electrode active material can improve the thermal stability of the positive electrode material.

[0050] In some embodiments, the above compound Na 4-x K y Fe 3-p M q In (PO4)2P2O7, q can be 0<q≤0.3, such as 0.01-0.3, 0.03-0.28, 0.05-0.25, 0.1-0.22, 0.12-0.2, 0.15-0.18, etc. In other embodiments, 0.05≤q≤0.15. Thus, by doping the Fe site in the above-mentioned positive electrode material with the metal element M of this content, the formation of impurities such as sodium iron pyrophosphate and sodium iron phosphate can be suppressed, and the formation of polyanion phosphate products can be promoted, thereby improving the physical purity of the positive electrode material, increasing the gram capacity of the material, and increasing the energy density of the battery. In addition, the metal element M doped at the Fe site of this content will also improve the ionic conductivity and electronic conductivity of the material, reduce the electron transfer impedance in the battery, reduce the battery polarization, improve the reversibility of sodium ion insertion and extraction, and thus improve the rate performance of the battery.

[0051] In some embodiments, the positive electrode active material Na 4-x K y Fe 3-p M q In (PO4)2P2O7, p and q satisfy p≥q, i.e., 3-p+q≤3, for example, 2.8<3-p+q≤3, 2.85≤3-p+q≤2.95, and 2.9≤3-p+q≤2.95. In other embodiments, 3-p+q<3. Thus, the Fe and M elements in the above-mentioned positive electrode active material work synergistically to improve the battery's rate performance and energy density.

[0052] In some embodiments, the positive electrode active material Na 4-x K y Fe 3-p M q (PO4)2P2O7 0.02≤y / q≤80, such as 0.1-80, 0.5-80, 1-78, 5-75, 10-70, 20-60, 30-50, 30-40, etc. In other embodiments, the above-mentioned positive electrode active material Na 4-x K y Fe 3-p Mq In (PO4)2P2O7, 0.1≤y / q≤40 and 0.2≤y / q≤10. Specifically, K ion doping increases the impurity phase sodium iron phosphate in the positive electrode active material, while the metal element M can inhibit the formation of impurity phases in the positive electrode active material. This application adopts a ratio of the K ion doping amount to the metal element M doping amount within the above-mentioned range of this application. The K ions and the metal element M play a synergistic role, which can reduce the impurity phase sodium iron phosphate in the positive electrode active material while improving the structural stability of the material, improving the ionic conductivity and electronic conductivity of the positive electrode active material, thereby improving the energy density and rate performance of the battery.

[0053] In some embodiments, the above-mentioned positive electrode active material further includes carbon, for example, carbon can be mixed inside the positive electrode active material and / or coated on at least part of the surface of the positive electrode active material particles. Specifically, the carbon mixed inside the positive electrode active material can improve the phase purity of the material, reduce the content of impurities in the material, increase the gram capacity of the material, and also improve the conductivity of the positive electrode active material. The carbon coated on the surface of the positive electrode active material, that is, forming a carbon coating layer on the surface of the positive electrode active material particles, can not only improve the conductivity of the material, but also reduce the contact area between the positive electrode active material and the electrolyte in the battery, reduce the side reactions of the positive electrode active material, and facilitate the use of the material capacity.

[0054] In some embodiments, based on the total mass of the positive electrode active material, the carbon content of the positive electrode active material is 0.5%-6%, for example, 1%-6%, 1%-5.5%, 1%-4%, 1%-3.6%, 1.2%-3.4%, 1.4%-3.2%, 1.6%-3%, 1.8%-2.8%, 2%-2.6%, 2.2%-2.4%, etc. In other embodiments, based on the total mass of the positive electrode active material, the carbon content of the positive electrode active material is 1%-3.6%. Specifically, if carbon is mixed within the positive electrode active material, the carbon content here refers to the carbon content mixed within the positive electrode active material; if carbon is coated on the surface of the positive electrode active material, the carbon content here refers to the carbon content of the coating layer formed on the surface of the positive electrode active material; if carbon is both mixed within the positive electrode active material and coated on the surface of the positive electrode active material, the carbon content here refers to the sum of the carbon content mixed within the positive electrode active material and the carbon content coated on the surface of the positive electrode active material. Within the above ratio range of the total mass of the positive electrode active material in this application, the conductivity and gram capacity of the positive electrode active material can be improved.

[0055] In some embodiments, the positive electrode active material includes Na 3.95 K 0.05 Fe 2.9 V 0.1 (PO4)2P2O7、Na 3.95 K0.05 Fe 2.9 You 0.1 (PO4)2P2O7、Na 3.9 K 0.1 Fe 2.94 Mo 0.02 (PO4)2P2O7、Na 3.9 K 0.1 Fe 2.95 Nb 0.02 (PO4)2P2O7、Na 3.9 K 0.1 Fe 2.94 W 0.02 (PO4)2P2O7、Na 3.95 K 0.05 Fe 2.9 Cr 0.02 (PO4)2P2O7、Na 3.9 K 0.1 Fe 2.99 Zn 0.01 (PO4)2P2O7、Na 3.9 K 0.1 Fe 2.9 Zr 0.1 (PO4)2P2O7、Na 3.98 K 0.01 Fe 2.85 Mg 0.05 (PO4)2P2O7、Na 3.94 K 0.02 Fe 2.85 Mg 0.05 (PO4)2P2O7、Na 3.9 K 0.1 Fe 2.85 Mg 0.05 (PO4)2P2O7、Na 3.85 K 0.1 Fe 2.85 Mg 0.05 (PO4)2P2O7、Na 3.8 K 0.1 Fe 2.85 Mg 0.05 (PO4)2P2O7、Na 3.7 K 0.1 Fe 2.85 Mg 0.05 (PO4)2P2O7、Na 3.6 K 0.1 Fe 2.85 Mg 0.05 (PO4)2P2O7、Na 3.85 K 0.15 Fe2.85 Mg 0.05 (PO4)2P2O7、Na 3.6 K 0.3 Fe 2.85 Mg 0.05 (PO4)2P2O7、Na 3.7 K 0.25 Fe 2.85 M 0.05 (PO4)2P2O7、Na 3.6 K 0.4 Fe 2.85 Mg 0.05 (PO4)2P2O7、Na 3.85 K 0.05 Fe 2.85 Mg 0.05 (PO4)2P2O7、Na 3.6 K 0.4 Fe 2.85 Mg 0.005 (PO4)2P2O7、Na 3.6 K 0.4 Fe 2.85 Mg 0.006 (PO4)2P2O7、Na 3.6 K 0.4 Fe 2.85 Mg 0.01 (PO4)2P2O7、Na 3.6 K 0.4 Fe 2.85 Mg 0.02 (PO4)2P2O7、Na 3.85 K 0.05 Fe 2.7 Mg 0.25 (PO4)2P2O7、Na 3.85 K 0.004 Fe 2.75 Mg 0.2 (PO4)2P2O7、Na 3.95 K 0.05 Fe 2.95 Ni 0.03 (PO4)2P2O7、Na 3.95 K 0.05 Fe 2.9 Co 0.05 (PO4)2P2O7、Na 3.95 K 0.0.05 Fe 2.8 Ca 0.1 (PO4)2P2O7、Na 3.85 K 0.1 Fe 2.98 Mg0.1 (PO4)2P2O7、Na 3.85 K 0.1 Fe 2.95 Mg 0.02 (PO4)2P2O7、Na 3.85 K 0.1 Fe 2.9 Mg 0.05 (PO4)2P2O7、Na 3.85 K 0.1 Fe 2.85 Mg 0.1 (PO4)2P2O7、Na 3.85 K 0.1 Fe 2.85 Mg 0.15 (PO4)2P2O7、Na 3.85 K 0.1 Fe 2.8 Mg 0.15 (PO4)2P2O7、Na 3.85 K 0.1 Fe 2.7 Mg 0.15 (PO4)2P2O7、Na 3.85 K 0.1 Fe 2.7 Mg 0.2 (PO4)2P2O7、Na 3.85 K 0.1 Fe 2.7 Mg 0.3 (PO4)2P2O7、Na 3.85 K 0.1 Fe 2.95 Mn 0.05 (PO4)2P2O7、Na 3.85 K 0.1 Fe 2.9 Al 0.01 (PO4)2P2O7、Na 3.85 K 0.1 Fe 2.85 Mn 0.05 Mg 0.05 (PO4)2P2O7、Na 3.85 K 0.1 Fe 2.85 Co 0.04 Al 0.02 (PO4)2P2O7、、Na 3.9 K 0.1 Fe 2.88 Cu 0.1 (PO4)2P2O7、Na 3.95 K 0.05 Fe2.85 Sr 0.1 (PO4)2P2O7、Na 3.9 K 0.1 Fe 2.825 Y 0.05 (PO4)2P2O7、Na 3.9 K 0.1 Fe 2.88 Cu 0.07 Mg 0.03 (PO4)2P2O7、Na 3.95 K 0.05 Fe 2.85 Sr 0.05 Mg 0.05 (PO4)2P2O7、Na 3.9 K 0.1 Fe 2.87 Y 0.02 Mg 0.03 At least one of (PO4)2P2O7.

[0056] In some embodiments, the volume average particle size Dv50 of the positive electrode active material is 0.9 μm-8 μm, for example, 1 μm-7.8 μm, 1.2 μm-7.5 μm, 1.5 μm-7.2 μm, 1.7 μm-7 μm, 2 μm-6.5 μm, 2.5 μm-6 μm, 3 μm-5.5 μm, 3.5 μm-5 μm, 4 μm-4.5 μm. In other embodiments, the Dv50 of the positive electrode active material is 1.2 μm-3.5 μm.

[0057] In the present application, Dv50 refers to the particle size corresponding to when the cumulative volume distribution percentage reaches 50%, for example, with reference to the standard GB / T 19077-2016, and is measured using a laser particle size analyzer (such as Malvern Master Size 3000).

[0058] In some embodiments, the BET specific surface area of ​​the positive electrode active material is 4 m 2 / g-13m 2 / g, for example 4.2m 2 / g-12.8m 2 / g,4.5m 2 / g-12.5m 2 / g,4.7m 2 / g-12.2m 2 / g,5m 2 / g-12m 2 / g,5.5m 2 / g-11.5m 2 / g,6m 2 / g-11m2 / g,6.5m 2 / g-10.5m 2 / g,7m 2 / g-10m 2 / g,7.5m 2 / g-9.5m 2 / g,8m 2 / g-9m 2 In other embodiments, the BET specific surface area of ​​the positive electrode active material is 5.5 m 2 / g-10m 2 / g.

[0059] In this application, the BET specific surface area of ​​the positive electrode active material can be tested by referring to the following method: using the American Microelectronics multi-station fully automatic specific surface area and pore analyzer GeminiVII2390, 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 host to test to obtain the BET (specific surface area) data of the positive electrode active material.

[0060] Therefore, the positive electrode active material of the present application has excellent ionic conductivity and electronic conductivity, thereby improving the energy density and rate performance of the battery.

[0061] The second aspect of the present application provides a method for preparing the above-mentioned positive electrode active material, comprising:

[0062] S100: Mix sodium source, potassium source, iron source, phosphorus source and M source

[0063] In some embodiments, the sodium source, potassium source, iron source, phosphorus source and M source are mixed and added into water, stirred and ground to obtain a mixed slurry, and then the slurry is dried to obtain a precursor material.

[0064] It should be noted that the sodium source, potassium source, iron source, phosphorus source and M source are conventional materials in the field, and those skilled in the art can select them according to actual conditions. For example, the sodium source includes at least one of sodium pyrophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, sodium acetate and sodium oxalate; the potassium source includes at least one of potassium pyrophosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, potassium phosphate, potassium metaphosphate, potassium citrate, potassium carbonate, potassium bicarbonate, potassium oxalate and potassium acetate; the iron source includes at least one of ferric nitrate, ferric chloride, ferric oxide, ferric phosphate and ferrous oxalate; the phosphorus source includes at least one of sodium pyrophosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, ferric phosphate, phosphoric acid and pyrophosphoric acid; and the M source includes at least one of the chloride, oxide, acetate and nitrate of the M element.

[0065] In some embodiments, if carbon is to be mixed into the positive electrode active material, a sodium source, a potassium source, an iron source, a phosphorus source, an M source, and a first carbon source are mixed. It should be noted that the first carbon source includes at least one of sucrose, tannic acid, polyethylene glycol, polyvinyl pyrrolidone, glucose, ascorbic acid, conductive carbon black, carbon nanotubes, graphene, and citric acid.

[0066] S200: Sintering the precursor powder

[0067] In some embodiments, the precursor material including the sodium source, potassium source, iron source, phosphorus source and M source obtained above is placed in a tube furnace for sintering. Specifically, a reducing agent can be added during the sintering process, for example, sintering is carried out in a mixed atmosphere of hydrogen and argon (the volume ratio of hydrogen and argon is 3-7:93-97, for example, 3-7:94-96, 3-7:95, 4-6:93-97, 5:93-97), and the sintering temperature of the sintering process can be 200℃-600℃, and the holding time can be 11h-16h. For example, multi-step sintering can be adopted, for example, two-step sintering is adopted, the temperature of the first step sintering is 200℃-300℃, for example, 220℃-280℃, 240℃-260℃, and the holding time is 3h-4h, for example, 3.5h-4h, and the temperature of the second step sintering is 500℃-600℃, for example, 520℃-580℃, 540℃-560℃, and the holding time is 8h-12h, for example, 9h-11h, 10h-11h.

[0068] In some embodiments, if the precursor material obtained above including the sodium source, potassium source, iron source, phosphorus source, M source and the first carbon source is placed in a tubular furnace for sintering, nitrogen can be used as a protective gas during the sintering process. During the sintering process, the first carbon source is thermally decomposed and used as a reducing agent. The sintering conditions are the same as described above and will not be repeated here.

[0069] In some embodiments, if a positive electrode active material having a carbon coating layer is desired, the positive electrode active material obtained in the above step is mixed with a second carbon source and then sintered. Specifically, the positive electrode active material and the second carbon source can be directly mixed and then sintered, or the positive electrode active material and the second carbon source can be dissolved in a solvent and mixed into a slurry, and the slurry is then dried and sintered. The mixture including the positive electrode active material and the second carbon source is placed in a tube furnace, nitrogen is passed through as a protective gas, and the temperature is raised to 500°C-600°C, for example, 520°C-580°C, 540°C-560°C, and the temperature is maintained for 3h-5h, for example, 4h, and sintered. As the non-carbon elements in the second carbon source are released, a carbon-containing coating is formed on the surface of the positive electrode active material.

[0070] In some embodiments, if a composite material with internal mixed carbon and surface coated carbon is required, the precursor material including the sodium source, potassium source, iron source, phosphorus source, M source and the first carbon source is first sintered under a nitrogen atmosphere, and then the obtained positive electrode active material is mixed with the second carbon source and sintered under a nitrogen atmosphere.

[0071] It should be noted that the second carbon source includes at least one of sucrose, tannic acid, polyethylene glycol, polyacrylonitrile, cellulose, polyvinyl pyrrolidone, glucose, ascorbic acid, conductive carbon black, carbon nanotubes, graphene and citric acid. In the above preparation process, the mixing ratio of the sodium source, potassium source, iron source, phosphorus source, M source, the first carbon source and the second carbon source is based on the composition of the above positive electrode active material compound. 4-x K y Fe 3-p M q (PO4)2P2O7 is the standard and will not be repeated here.

[0072] A third aspect of the present application provides a positive electrode sheet comprising the positive electrode active material of the first aspect or the positive electrode active material obtained by the method of the second aspect. Thus, the positive electrode sheet has excellent ionic and electronic conductivity, thereby improving the energy density and rate performance of the battery.

[0073] In a sodium ion battery, the positive electrode sheet generally includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0074] The positive electrode current collector may be a conventional metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the positive electrode current collector may include one or more of copper foil, aluminum foil, nickel foil, stainless steel foil, stainless steel mesh, and carbon-coated aluminum foil.

[0075] In addition to the aforementioned positive electrode active material, 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 agent and binder, and they can be selected based on actual needs.

[0076] As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers; the binder may be one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA) and polyvinyl alcohol (PVA).

[0077] As an example, the binder may include one or more of styrene-butadiene rubber (SBR), styrene-butadiene rubber (SBCs), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and carboxymethyl cellulose (CMC).

[0078] These materials are all commercially available.

[0079] A fourth aspect of the present application provides a battery comprising the above-mentioned positive electrode sheet, thereby having excellent energy density and rate performance.

[0080] A battery is a battery that can be recharged to activate the active materials after discharge and continue to be used.

[0081] It can be understood that the battery proposed in this application can be a sodium ion battery.

[0082] Typically, a battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The separator is placed between the positive and negative electrodes to isolate them. The electrolyte conducts ions between the positive and negative electrodes.

[0083] [Negative electrode]

[0084] In a sodium ion battery, the negative electrode plate generally includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0085] The negative electrode sheet may also include only a negative electrode current collector, i.e., without the negative electrode active material. Alternatively, the negative electrode sheet may include a pre-deposited metal phase on the negative electrode current collector. The negative electrode current collector may be made of materials such as conventional metal foil, carbon-coated metal foil, or porous metal sheet. For example, the negative electrode current collector may be copper foil or aluminum foil.

[0086] There is no limitation on the specific type of the negative electrode active material, and active materials known in the art that can be used for the negative electrode of sodium ion batteries can be used, and those skilled in the art can choose according to actual needs. As an example, the negative electrode active material may include but is not limited to one or more of sodium metal, carbon material, alloy material, transition metal oxide and / or sulfide, phosphorus-based material, and titanate material. Specifically, the carbon material may include one or more of hard carbon, soft carbon, amorphous carbon, and nanostructured carbon material; the alloy material may include an alloy material formed by one or more of Si, Ge, Sn, Pb, and Sb; the general formula of the transition metal oxide and sulfide is M x N y, wherein M includes one or more of Fe, Co, Ni, Mn, Sn, Mo, Sb, and V, and N includes O or S; the phosphorus-based material may include one or more of red phosphorus, white phosphorus, and black phosphorus; the titanate material may include Na2Ti3O7, Na2Ti6O 13 、Na4Ti5O 12 、Li4Ti5O 12 , NaTi2(PO4)3. These materials can be obtained through commercial channels.

[0087] The negative electrode active material layer typically also optionally includes 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 agent and binder, and they can be selected according to actual needs.

[0088] As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0089] As an example, the binder may include one or more of styrene-butadiene rubber (SBR), styrene-butadiene rubber (SBCs), water-based acrylic resin, and carboxymethyl cellulose (CMC).

[0090] The negative electrode active material layer may also optionally include a thickener, such as carboxymethyl cellulose (CMC). However, the present application is not limited thereto, and other materials that can be used as thickeners for sodium ion battery negative electrode sheets may also be used in the present application.

[0091] [Isolation film]

[0092] As the above-mentioned isolation membrane, the present application has no special restrictions, and any well-known porous structure isolation membrane with electrochemical stability and mechanical stability can be selected according to actual needs. For example, it can be a single-layer or multi-layer film containing one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0093] [Electrolyte]

[0094] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The electrolyte may include an electrolyte salt and a solvent.

[0095] As an example, the electrolyte sodium salt includes at least one of sodium hexafluorophosphate, sodium difluorooxalatoborate, sodium tetrafluoroborate, sodium bisoxalatoborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethylsulfonyl)imide.

[0096] As an example, the solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene 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), ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, tetrahydropyran, ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0097] In some embodiments, the electrolyte further includes additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives capable of improving certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0098] The embodiment of the present application has no particular limitation on the shape of the sodium ion battery, which can be cylindrical, square or any other shape. FIG1 shows a secondary battery 1 with a square structure as an example.

[0099] In some embodiments, the secondary battery may include an outer packaging for encapsulating the positive electrode sheet, the negative electrode sheet, and the electrolyte.

[0100] In some embodiments, the outer packaging may include a housing and a cover. The housing may include a bottom plate and side plates connected to the bottom plate, with the bottom plate and side plates enclosing a receiving cavity. The housing may have an opening communicating with the receiving cavity, and the cover may be positioned over the opening to seal the receiving cavity.

[0101] The positive electrode sheet, negative electrode sheet, and separator can be wound or laminated to form an electrode assembly. The electrode assembly is encapsulated in the housing. The electrolyte can be an electrolyte solution, which is impregnated into the electrode assembly. The number of electrode assemblies in a sodium-ion battery can be one or more, and can be adjusted according to demand.

[0102] In some embodiments, the outer packaging of the sodium ion battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell.

[0103] The outer packaging of the sodium ion battery can also be a soft bag, such as a bag-type soft bag. The material of the soft bag can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0104] In some embodiments, sodium ion batteries can be assembled into a battery module. The battery module can contain multiple sodium ion batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0105] Figure 2 shows an example battery module 2. Referring to Figure 2 , within the battery module 2, multiple secondary batteries 1 may be arranged sequentially along the length of the battery module 2. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 1 may be secured together using fasteners.

[0106] The battery module 2 may further include a housing having a housing space, wherein the housing space accommodates a plurality of secondary batteries 1. In some embodiments, the battery modules may be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0107] Figures 3 and 4 illustrate an example battery pack 3. Referring to Figures 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 comprises an upper case 4 and a lower case 5. The upper case 4 can be placed over the lower case 5 to form an enclosed space for accommodating the battery modules 2. The multiple battery modules 2 can be arranged in any manner within the battery box.

[0108] [Electrical devices]

[0109] The present application also provides an electrical device, which includes at least one of the sodium ion battery, battery module and battery pack. The sodium ion battery, battery module or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck), an electric train, a ship and a satellite, and an energy storage system.

[0110] The electrical device can select a sodium ion battery, a battery module or a battery pack according to its usage requirements.

[0111] Figure 5 shows an example of an electric device. This device includes a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of sodium-ion batteries, a battery pack or battery module can be used.

[0112] As another example, electric devices may include mobile phones, tablet computers, and laptop computers. These electric devices are generally required to be lightweight and thin, and may use sodium ion batteries as power sources.

[0113] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0114] Example 1

[0115] 1. Preparation of positive electrode active materials

[0116] (1) Sodium pyrophosphate, potassium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, nitrate M (nitrate of M) and glucose were mixed according to the Na in Table 1. 4-x K y Fe 3-p M q (PO4)2P2O7 was added into deionized water after the composition ratio was reached, and the mixture was ground with a sand mill for 10 hours to obtain a mixed slurry, and then the mixed slurry was dried by a spray drying device to obtain a dry precursor powder;

[0117] (2) The dried precursor was placed in a tubular furnace, nitrogen was passed as a protective gas, the temperature was raised to 300°C, and the temperature was kept for 4 hours for the first step of sintering, and then the temperature was raised to 550°C and the temperature was kept for 12 hours for the second step of sintering to obtain the positive electrode active material.

[0118] 2. Preparation of positive electrode sheet

[0119] The polyvinylidene fluoride binder is fully dissolved in N-methylpyrrolidone, and a carbon black conductive agent and the above-mentioned positive electrode active material are added to prepare a uniformly dispersed positive electrode slurry (the mass ratio of polyvinylidene fluoride binder, carbon black conductive agent and positive electrode active material is 10:10:80). The positive electrode slurry is evenly coated on the upper and lower surfaces of the aluminum foil, and then transferred to a vacuum drying oven for complete drying. The obtained electrode sheet is rolled and then punched to obtain the positive electrode sheet.

[0120] 3. Preparation of negative electrode sheet

[0121] The carbon nanotube material and the binder sodium carboxymethyl cellulose are added to water in a mass ratio of 4:1.6 and stirred to form a uniform negative electrode slurry. The negative electrode slurry is coated on the upper and lower surfaces of the copper foil, and then transferred to a vacuum drying oven for complete drying, and then punched to obtain the negative electrode sheet.

[0122] 4. Preparation of electrolyte

[0123] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), sodium hexafluorophosphate NaPF6 was dissolved in an organic solvent, ethylene glycol dimethyl ether (DME), and stirred evenly to obtain an electrolyte with a sodium salt concentration of 1 mol / L.

[0124] 5. Isolation film

[0125] Polypropylene film is used as the isolation film.

[0126] 6. Preparation of button batteries

[0127] The prepared positive electrode sheet is pressed into a circular electrode sheet, and then a small circular sodium sheet is used as a counter electrode, a Celgard 2400 isolation membrane is used, and an electrolyte is injected to assemble a button battery.

[0128] 7. Preparation of sodium ion batteries

[0129] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to play an isolating role, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried sodium ion battery. After vacuum packaging, standing, formation, and shaping processes, a sodium ion battery is obtained.

[0130] The preparation methods of the sodium ion batteries and button batteries of Examples 2-41 and 44-49 and Comparative Examples 1-3 are the same as those of Example 1, except that the ratios of the elements in the prepared positive electrode active materials are different, as shown in Table 1-6.

[0131] Example 42

[0132] The difference from Example 1 is that the preparation of the positive electrode active material in Example 1 further includes placing the obtained positive electrode active material and glucose mixture into a tubular furnace, passing nitrogen as a protective gas, heating to 550°C, and keeping the temperature for 4 hours for sintering, thereby forming a carbon coating layer on the surface of the positive electrode active material. The other differences are shown in Table 5.

[0133] Example 43

[0134] The difference from Example 1 is that glucose is not added during the preparation of the positive electrode active material, and the sintering is carried out in a mixed atmosphere of hydrogen and argon (the volume ratio of hydrogen to argon is 5:95). The other differences are shown in Table 5.

[0135]

[0136]

[0137]

[0138]

[0139] Table 6

[0140] The performance of the button batteries obtained in Examples 1-49 and Comparative Examples 1-3 and the rate performance of the sodium ion batteries were characterized. The characterization results are shown in Table 7.

[0141] Button cell performance test: At 25°C and normal pressure, charge the button cell at a constant current rate of 0.1C to a voltage of 3.75V. Then charge it at a constant voltage of 3.75V until the current drops to 0.05C. Record the charge specific capacity at this time, which is the first sodium removal capacity. Then discharge it at a constant current rate of 0.1C to a voltage of 1.5V. Record the discharge specific capacity at this time, which is the first sodium insertion capacity. The gram capacity of the positive electrode active material is the first sodium insertion capacity.

[0142] Sodium ion battery rate performance test: At 25°C, the prepared sodium ion battery was placed in a 25°C constant temperature box and allowed to stand for 30 minutes to allow the battery to reach a constant temperature. The battery that reached a constant temperature was charged to 3.7V at 25°C at a constant current of 0.33C, charged to 0.05C at a constant voltage at 3.7V, allowed to stand for 5 minutes, and then discharged to 1.5V at a constant current of 0.33C, allowed to stand for 5 minutes, and the capacity C1 of 0.33C discharge was obtained; then the battery was charged to 3.7V at a constant current of 0.33C, charged to 0.05C at a constant voltage at 3.7V, allowed to stand for 5 minutes, and then discharged to 1.5V at a constant current of 3C, allowed to stand for 5 minutes, and the capacity C2 of 3C discharge was obtained. The capacity retention rate at the 3C rate is R=C2 / C1×100%.

[0143] Table 7

[0144] Conclusion: The positive electrode active material of Example 1-49 has a higher gram capacity than that of Comparative Examples 1-3, and the sodium ion battery of Example 1-49 has an excellent capacity retention rate at a 3C rate compared with Comparative Examples 1-3, indicating that the positive electrode active material composed of the present application can improve the energy density and rate performance of the sodium ion battery. At the same time, the positive electrode materials of Examples 1-42 and Examples 44-49 contain carbon, while the positive electrode material of Example 43 does not include carbon. By comparison, the positive electrode materials of Examples 1-42 and Examples 44-49 have higher gram capacity than the positive electrode material of Example 43, and the sodium ion batteries of Examples 1-42 and Examples 44-49 have excellent capacity retention at a 3C rate compared with the sodium ion battery of Example 43, indicating that the carbon mixed inside the positive electrode active material can improve the phase purity of the material and reduce the content of impurities in the material, thereby improving the gram capacity of the positive electrode active material, and can improve the conductivity of the positive electrode active material, thereby improving the capacity retention rate of the sodium ion battery at a 3C rate.

[0145] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0146] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A positive electrode active material, wherein The positive electrode active material includes: Na 4-x K y Fe 3-p M q (PO4)2P2O7, Wherein, M includes at least one of Ni, Co, Mn, V, Ti, Mo, Nb, W, Cr, Zn, Zr, Ca, Mg, Cu, Sr, Y or Al, 0<x≤0.4, 0 <y≤0.4,0<p≤0.3,0<q≤0.3。 2. The positive electrode active material according to claim 1, wherein The values ​​of x, y, p and q satisfy at least one of the following conditions: 0.1≤x≤0.2; 0.05≤y≤0.15; 0.05≤p≤0.2; 0.05≤q≤0.15; p≥q.

3. The positive electrode active material according to claim 1 or 2, wherein 4-x+y≤4.

4. The positive electrode active material according to any one of claims 1 to 3, wherein 3-p+q<3.

5. The positive electrode active material according to any one of claims 1 to 4, wherein 0.02≤y / q≤80, preferably 0.1≤y / q≤40, more preferably 0.2≤y / q≤10.

6. The positive electrode active material according to any one of claims 1 to 5, wherein The M includes at least one of Ni, Co, Mn, V, Ca, Mg, Cu, Sr, Y or Al.

7. The positive electrode active material according to any one of claims 1 to 6, wherein The positive electrode active material further includes carbon.

8. The positive electrode active material according to claim 7, wherein Based on the total mass of the positive electrode active material, the carbon content accounts for 0.5%-6%, preferably 1%-3.6%.

9. The positive electrode active material according to any one of claims 1 to 8, wherein The positive electrode active material satisfies at least one of the following conditions: The volume average particle size Dv50 of the positive electrode active material is 0.9 μm-8 μm, and can be 1.2 μm-3.5 μm; The BET specific surface area of ​​the positive electrode active material is 4 m 2 / g-13m 2 / g, optional 5.5m 2 / g-10m 2 / g.

10. A method for preparing the positive electrode active material according to any one of claims 1 to 9, wherein: include: Mixing a sodium source, a potassium source, an iron source, a phosphorus source and an M source to obtain a precursor material; The precursor material is sintered to obtain a positive electrode active material.

11. The method according to claim 10, wherein: The sintering temperature is 200° C.-600° C., and the heat preservation time is 11 h-16 h.

12. The method according to claim 10 or 11, wherein: The sodium source, potassium source, iron source, phosphorus source, M source and the first carbon source are mixed.

13. The method according to any one of claims 9 to 12, wherein: Further including: The positive electrode active material is mixed with a second carbon source and sintered to form a carbon coating on the surface of the positive electrode active material. layer.

14. The method according to claim 13, wherein: The temperature for sintering the positive electrode active material and the second carbon source is 500° C.-600° C., and the heat preservation time is 3 h-5 h. 15 . A positive electrode sheet, comprising the positive electrode active material according to claim 1 or the positive electrode active material obtained by the method according to claim 10 . A battery comprising the positive electrode sheet according to claim 15 .

17. An electrical device comprising the battery according to claim 16.

Images