A positive electrode active material, a manufacturing method, a secondary battery, and an electric device

Abstract

The present application relates to a positive electrode active material comprising a boron-doped Prussian blue analogue; the chemical formula A of the Prussian blue analogue a M b M' c (CN)6·dH2O, wherein A comprises at least one of an alkali metal cation, an alkaline earth metal cation, Zn 2+ , Al 3+ , M and M' each independently comprise at least one of a Ni ion, a Cu ion, a Fe ion, a Mn ion, a Co ion and a Zn ion, H2O is a coordination water, 0

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of materials, in particular to a positive electrode active material, a preparation method, a secondary battery and an electric device. BACKGROUND

[0002] In recent years, with the application range of secondary batteries becoming more and more extensive, secondary batteries are widely used in energy storage power supply systems such as hydraulic, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. Due to the great development of secondary batteries, higher requirements are put forward for their energy density, cycle performance and safety performance, etc.

[0003] Prussian blue analogues have become promising positive electrode active materials for many next-generation metal-ion batteries due to their excellent electrochemical performance. Prussian blue analogues as positive electrode active materials, in their preparation process, some use borohydride as a reducing agent. The borohydride will react with water under high-temperature heating, releasing a large amount of hydrogen, thereby causing a large safety hazard; moreover, the strong base generated by the reaction will react with the prussian blue analogue to cause part of the metal elements in it to precipitate, thereby destroying the structural stability of the prussian blue analogue, resulting in a significant decrease in its electrical performance. Therefore, the existing prussian blue analogues still need to be improved. SUMMARY

[0004] The present application is carried out in view of the above-mentioned problems, and aims to provide a positive electrode active material which includes a boron-doped prussian blue analogue, improves the stability of the positive electrode active material, thereby improving the cycle performance of the corresponding secondary battery; the preparation method is simple to operate, the reaction conditions are mild, and is convenient for industrial application.

[0005] In order to achieve the above-mentioned purpose, the present application provides a positive electrode active material, a preparation method, a secondary battery and an electric device.

[0006] The first aspect of the present application provides a positive electrode active material comprising a boron-doped prussian blue analogue;

[0007] The chemical formula A of the prussian blue analogue a M b M' c (CN)6·dH2O, wherein A comprises at least one of an alkali metal cation, an alkaline earth metal cation, Zn 2+ , Al 3+ , M and M' each independently comprise at least one of Ni ion, Cu ion, Fe ion, Mn ion, Co ion and Zn ion, H2O is coordination water, 0

[0008] The positive electrode active material of this application includes a boron-doped Prussian blue analogue, in which the carbon element is replaced by the boron element, resulting in the localization of electrons in the boron-nitrogen bond to the nitrogen element, which increases the surface charge, increases the overlap of M-nitrogen chemical bond orbitals, decreases the bond length, and increases covalentness, thereby improving the stability of the positive electrode active material and thus improving the cycle performance of the corresponding secondary battery.

[0009] In any embodiment, the boron content is 0.001%-20% based on the weight of the positive electrode active material, optionally 2%-15.5%. Thus, by limiting the boron content, the stability of the positive electrode active material is further improved, thereby enhancing the cycle performance of the corresponding secondary battery.

[0010] In any embodiment, the molar ratio of boron to M in the positive electrode active material is (0.001-2):1, optionally (0.1-0.8):1. Therefore, by limiting the molar ratio of boron to M, the stability of the positive electrode active material is further improved, thereby enhancing the cycle performance of the corresponding secondary battery.

[0011] In any embodiment, the weight ratio of boron to carbon in the positive electrode active material is (0.001-800):1, optionally (0.1-8):1. Therefore, by limiting the weight ratio of boron to carbon, the stability of the positive electrode active material is further improved, thereby enhancing the cycle performance of the corresponding secondary battery.

[0012] In any embodiment, A in the positive electrode active material includes at least one of sodium ions, magnesium ions, and potassium ions. This further improves the stability of the positive electrode active material, thereby enhancing the cycle performance of the corresponding secondary battery.

[0013] In any embodiment, the positive electrode active material satisfies at least one of the following characteristics:

[0014] Specific surface area is 2m² 2 / g-5m 2 / g, optional 3m 2 / g-4m 2 / g; and

[0015] Average volumetric particle size D v50 The range is 1.5μm-5μm, and can be selected as 2μm-3.5μm.

[0016] This further improves the stability of the positive electrode active material, thereby enhancing the cycle performance of the corresponding secondary battery.

[0017] A second aspect of this application provides a method for preparing a positive electrode active material, comprising:

[0018] (1) Add the Prussian blue analogue to the mixed solvent to obtain a solution containing the Prussian blue analogue;

[0019] (2) Add a boron-containing compound to the solution containing the Prussian blue analogue, mix, and obtain a mixture;

[0020] (3) The mixture is filtered and dried to obtain a positive electrode active material;

[0021] The positive electrode active material contains a boron-doped Prussian blue analogue;

[0022] The chemical formula of the Prussian blue analogue is A a M b M' c (CN)6·dH2O, where A includes alkali metal cations, alkaline earth metal cations, and Zn. 2+ Al 3+ At least one of the following, M and M' each independently include at least one of Ni ion, Cu ion, Fe ion, Mn ion, Co ion and Zn ion, H2O is coordinated water, 0 <a≤2,0<b≤1,0<c≤1,0≤d≤2。

[0023] Therefore, the preparation method is simple to operate, the reaction conditions are mild, and it is easy to apply industrially. The boron-containing compound used can reduce the oxidized high-valence metal ions (e.g., M or M') in Prussian blue analogues, thereby avoiding the loss of A ions and further improving the stability of the positive electrode active material.

[0024] In any embodiment, in step (1), the mixed solvent is a mixture of water and an organic solvent miscible with water. This further enhances the stability of the prepared positive electrode active material.

[0025] In any embodiment, the volume ratio of water to the organic solvent is (0.001-3):1. This further enhances the stability of the prepared positive electrode active material.

[0026] In any embodiment, in step (2), the boron-containing compound is of formula Q(BH4). x The compound contains alkali metal ions, alkaline earth metal ions, aluminum ions, and zinc ions, where Q is an alkali metal ion, alkaline earth metal ion, aluminum ion, or zinc ion, and x is the valence state of Q. This further enhances the stability of the prepared positive electrode active material.

[0027] In any embodiment, in step (2), the molar ratio of the boron-containing compound to the Prussian blue analogue is (0.5-2):1, optionally (0.5-1):1. This further enhances the stability of the prepared positive electrode active material.

[0028] In any embodiment, in step (2), the mixing temperature is -10°C to 30°C, optionally 0°C to 25°C; and

[0029] The mixing time is 0 to 2 hours, optionally 0.5 to 1.5 hours. This further improves the stability of the prepared positive electrode active material.

[0030] A third aspect of this application provides a secondary battery, characterized in that it comprises the positive electrode active material described in the first aspect of this application or the positive electrode active material prepared according to the method described in the second aspect of this application. Therefore, the secondary battery exhibits excellent cycle performance.

[0031] In any embodiment, it is a sodium-ion secondary battery.

[0032] A fourth aspect of this application provides an electrical device, characterized in that it includes a secondary battery as described in any one of claims 13-14.

[0033] The positive electrode active material of this application improves the stability of the positive electrode active material by including boron-doped Prussian blue analogues, thereby improving the cycle performance of the corresponding secondary battery; the preparation method is simple to operate, the reaction conditions are mild, and it is easy to apply industrially. Attached Figure Description

[0034] Figure 1 This is a comparison of the cycle stability of the battery of Embodiment 1 and the battery of Comparative Example 1; where the black curve represents Embodiment 1 and the gray curve represents Comparative Example 1.

[0035] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0036] Figure 3 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0037] Figure 4 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0038] Explanation of reference numerals in the attached figures:

[0039] 5. Secondary battery; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. Detailed Implementation

[0040] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its preparation method, secondary battery, and power application device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0041] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0042] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0043] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0044] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0045] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0046] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0047] Prussian blue analogues have become promising cathode active materials for many next-generation metal-ion batteries due to their excellent electrochemical performance. However, the preparation of Prussian blue analogues as cathode active materials often involves the use of borohydrides as reducing agents. These borohydrides react with water at high temperatures, releasing large amounts of hydrogen gas, posing significant safety hazards. Furthermore, the strong alkali generated in the reaction reacts with the Prussian blue analogue, causing some of the metal elements to precipitate, thus compromising the structural stability of the Prussian blue analogue and resulting in a significant decrease in its electrical performance. Therefore, existing Prussian blue analogues still require improvement. Through extensive research, the inventors have discovered that using boron-doped Prussian blue analogues as cathode active materials can improve the stability of the cathode active material, thereby enhancing the cycle performance of the corresponding secondary batteries. Moreover, the preparation method is simple, the reaction conditions are mild, and it is easy to apply industrially.

[0048] Positive electrode active material

[0049] In some embodiments, the first aspect of this application provides a positive electrode active material comprising a boron-doped Prussian blue analogue;

[0050] The chemical formula of the Prussian blue analogue is A. a M b M' c(CN)6·dH2O, where A includes alkali metal cations, alkaline earth metal cations, and Zn. 2+ Al 3+ At least one of the following, M and M' each independently include at least one of Ni ion, Cu ion, Fe ion, Mn ion, Co ion and Zn ion, H2O is coordinated water, 0 <a≤2,0<b≤1,0<c≤1,0≤d≤2。

[0051] The positive electrode active material of this application includes a boron-doped Prussian blue analogue, in which the carbon element is replaced by the boron element, resulting in the localization of electrons in the boron-nitrogen bond to the nitrogen element, which increases the surface charge, increases the overlap of M-nitrogen chemical bond orbitals, decreases the bond length, and increases covalentness, thereby improving the stability of the positive electrode active material and thus improving the cycle performance of the corresponding secondary battery.

[0052] In some embodiments, "boron" typically refers to the element boron (B). "Doping" means that the B element can adhere to the surface of the Prussian analogue or penetrate into the structure of the Prussian analogue, for example, by doping into the bulk structure of the Prussian analogue.

[0053] In some embodiments, the boron content is 0.001%-20% based on the weight of the positive electrode active material, optionally 2%-15.5%, and further optionally 3.0%-7.5%. Thus, by limiting the boron content, the stability of the positive electrode active material is further improved, thereby enhancing the cycle performance of the corresponding secondary battery.

[0054] In this application, unless otherwise specified, the content of each element mentioned refers to its percentage of the weight of the positive electrode active material, determined by inductively coupled plasma atomic emission spectrometry.

[0055] In some embodiments, the molar ratio of boron to M in the positive electrode active material is 0.001-2:1, optionally 0.1-0.8:1, and further optionally 0.4-0.6:1, as determined by inductively coupled plasma atomic emission spectrometry. Thus, by limiting the molar ratio of boron to M, the stability of the positive electrode active material is further improved, thereby enhancing the cycle performance of the corresponding secondary battery.

[0056] In some embodiments, the weight ratio of boron to carbon in the positive electrode active material is (0.001-800):1, optionally (0.1-8):1, optionally (0.1-0.9):1, and further optionally (0.7-0.9):1. Therefore, by limiting the weight ratio of boron to carbon, the stability of the positive electrode active material is further improved, thereby enhancing the cycle performance of the corresponding secondary battery.

[0057] In some embodiments, the carbon content in the positive electrode active material is 2%-23%, optionally 5%-21%, and further optionally 10%-14%, based on the weight of the positive electrode active material.

[0058] In some embodiments, the nitrogen content in the positive electrode active material is 26%-27%, based on the weight of the positive electrode active material.

[0059] In some embodiments, A in the positive electrode active material includes at least one of sodium ions, magnesium ions, and potassium ions, and may be selected as sodium ions or potassium ions. This further improves the stability of the positive electrode active material, thereby improving the cycle performance of the corresponding secondary battery. In some embodiments, M in the positive electrode active material includes at least one of Fe and Mn; M' includes at least one of Fe and Mn. M and M' may be the same or different, but are preferably the same.

[0060] In some embodiments, the Prussian blue analogues in the positive electrode active material include Na2NiFe(CN)6, Na2ZnFe(CN)6, Na2CoFe(CN)6, Na2FeFe(CN)6, and Na2MnFe(CN). 6、 K2NiFe(CN)6, K2ZnFe(CN)6, K2CoFe(CN)6, K2FeFe(CN)6, K2MnFe(CN) 6、 At least one of Li2NiFe(CN)6, Li2ZnFe(CN)6, Li2CoFe(CN)6, Li2FeFe(CN)6, and Li2MnFe(CN)6, optionally including at least one of Na2FeFe(CN)6, K2FeFe(CN)6, and Li2FeFe(CN)6.

[0061] In some embodiments, the positive electrode active material satisfies at least one of the following characteristics:

[0062] Specific surface area is 2m² 2 / g-5m 2 / g, optional 3m 2 / g-4m 2 / g; and

[0063] Average volumetric particle size D v50 The range is 1.5μm-5μm, and can be selected as 2μm-3.5μm.

[0064] This further improves the stability of the positive electrode active material, thereby enhancing the cycle performance of the corresponding secondary battery.

[0065] In this application, the term "average volume particle size D" is used.v50 "The meaning is well known in the art, and can be determined using instruments and methods known in the art. For example, it can be determined using a laser particle size analyzer (e.g., Master Size 3000) in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method."

[0066] A second aspect of this application provides a method for preparing a positive electrode active material, comprising:

[0067] (1) Add the Prussian blue analogue to the mixed solvent to obtain a solution containing the Prussian blue analogue;

[0068] (2) Add a boron-containing compound to the solution containing the Prussian blue analogue, mix, and obtain a mixture;

[0069] (3) The mixture is filtered and dried to obtain a positive electrode active material;

[0070] The positive electrode active material contains a boron-doped Prussian blue analogue;

[0071] The chemical formula of the Prussian blue analogue is A a M b M' c (CN)6·dH2O, where A includes alkali metal cations, alkaline earth metal cations, and Zn. 2+ Al 3+ At least one of the following, M and M' each independently include at least one of Ni ion, Cu ion, Fe ion, Mn ion, Co ion and Zn ion, H2O is coordinated water, 0 <a≤2,0<b≤1,0<c≤1,0≤d≤2。

[0072] Therefore, the preparation method is simple to operate, the reaction conditions are mild, and it is easy to apply industrially. The boron-containing compound used can reduce the oxidized high-valence metal ions (e.g., M or M') in Prussian blue analogues, thereby avoiding the loss of A ions and further improving the stability of the positive electrode active material.

[0073] The Prussian blue analogues described herein are subject to the technical features described in the first aspect of this application regarding Prussian blue analogues and their composition. Similarly, the positive electrode active material is subject to the technical features described above regarding positive electrode active materials.

[0074] In some embodiments, in step (1), the mixed solvent is a mixture of water and an organic solvent miscible with water. This further enhances the stability of the prepared positive electrode active material.

[0075] In some embodiments, the organic solvent is typically any water-miscible compound known to those skilled in the art, including but not limited to at least one of methanol, ethanol, acetonitrile, ethylene glycol, acetone, diethyl ether, tetrahydrofuran, methyltetrahydrofuran, pyridine, 1,4-dioxane, N-methylpyrrolidone, and N,N-dimethylformamide. Optionally, it may include at least one of ethanol, methanol, tetrahydrofuran, and methyltetrahydrofuran, and may further be ethanol, methanol, or combinations thereof.

[0076] In some embodiments, the volume ratio of water to the organic solvent is (0.001-3):1. This further enhances the stability of the prepared positive electrode active material.

[0077] In some embodiments, in step (2), the boron-containing compound is a compound of formula Q(BH4)x, wherein Q includes at least one of alkali metal ions, alkaline earth metal ions, aluminum ions, and zinc ions, and optionally includes at least one of alkali metal ions and alkaline earth metal ions, and x is the valence state of Q. This further improves the stability of the prepared positive electrode active material.

[0078] In some embodiments, the Q ion in the boron-containing compound is the same as the A ion in the Prussian blue analogue. For example, in Prussian blue analogues having the chemical formula Na... a M b M' c In the case of (CN)6·dH2O (where a, M, b, M', c, and d have the above definitions), the boron-containing compound used is sodium borohydride. This further reduces the unnecessary incorporation of metal ions into the positive electrode active material or secondary battery.

[0079] In some embodiments, the boron-containing compound includes at least one of NaBH4, KBH4, Al(BH4)3, Ca(BH4)2, and Mg(BH4)2, and optionally NaBH4, KBH4, or a combination thereof.

[0080] In some embodiments, in step (2), the molar ratio of the boron-containing compound to the Prussian blue analogue is (0.5-2):1, optionally (0.5-1):1. This further enhances the stability of the prepared positive electrode active material.

[0081] In some embodiments, in step (2), the mixing temperature is -10°C to 30°C, optionally 0°C to 25°C; and

[0082] The mixing time is 0 to 2 hours, optionally 0.5 to 1.5 hours. This further improves the stability of the prepared positive electrode active material.

[0083] A third aspect of this application provides a secondary battery, characterized in that it comprises the positive electrode active material described in the first aspect of this application or the positive electrode active material prepared according to the method described in the second aspect of this application. Therefore, the secondary battery exhibits excellent cycle performance.

[0084] In some embodiments, the secondary battery is a metal ion secondary battery, including but not limited to at least one of sodium ion batteries, lithium ion batteries, potassium ion batteries, magnesium ion batteries, aluminum ion batteries, and zinc ion batteries.

[0085] In some preferred embodiments, the secondary battery is a sodium-ion secondary battery or a potassium-ion secondary battery, and may be selected as a sodium-ion secondary battery.

[0086] A fourth aspect of this application provides an electrical device, characterized in that it includes the secondary battery described in the third aspect of this application.

[0087] The secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0088] Unless otherwise specified, the battery components, material types or contents mentioned apply to all ion batteries.

[0089] In one embodiment of this application, a secondary battery is provided.

[0090] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0091] Positive electrode sheet

[0092] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0093] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0094] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on the polymer material substrate. The metal material includes, but is not limited to, aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material substrate may be (e.g., polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0095] In some embodiments, the positive electrode active material may also include positive electrode active materials known in the art for use in batteries.

[0096] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. The binder constitutes 0-20% by weight of the positive electrode film layer, based on the total weight of the positive electrode film layer.

[0097] In some embodiments, the positive electrode film may optionally include other conductive agents. As an example, the other conductive agents may include at least one of superconducting carbon, carbon black (e.g., acetylene black or Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The other conductive agents constitute 0-20% by weight of the positive electrode film, based on the total weight of the positive electrode film.

[0098] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, wherein the solid content of the positive electrode slurry is 40-80 wt%, and the viscosity at room temperature is adjusted to 5000-25000 mPa·s. The positive electrode slurry is then coated onto the surface of the positive current collector, dried, and cold-pressed using a cold rolling mill to form the positive electrode sheet; the compacted density of the positive electrode sheet is 2.0-3.6 g / cm³. 3 The concentration can be selected as 2.3-3.5 g / cm³. 3 .

[0099] Negative electrode sheet

[0100] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0101] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0102] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on the polymer material substrate. The metal material includes, but is not limited to, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material substrate includes, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE). The thickness of the negative electrode current collector is typically from 3 μm to 15 μm.

[0103] In some embodiments, the negative electrode active material of the secondary battery may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, acetylene black, mesophase carbon microspheres (MCMB), soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0104] The negative electrode active material accounts for 70-100% by weight in the negative electrode film, based on the total weight of the negative electrode film.

[0105] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The binder accounts for 0-30% by weight of the negative electrode film layer, based on the total weight of the negative electrode film layer.

[0106] In some embodiments, the negative electrode film may optionally include other conductive agents. These other conductive agents may be selected from at least one of superconducting carbon, carbon black (e.g., acetylene black or Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The other conductive agents constitute 0-20% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0107] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). The other additives constitute 0-15% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0108] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry, wherein the solid content of the negative electrode slurry is 30-70 wt%, and the viscosity at room temperature is adjusted to 2000-10000 mPa·s; the obtained negative electrode slurry is coated onto a negative electrode current collector, and after a drying process, it is cold-pressed, for example, by rollers, to obtain the negative electrode sheet. The compacted density of the negative electrode sheet is 1.2-2.0 g / m³. 3 .

[0109] electrolytes

[0110] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0111] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0112] In some embodiments, the electrolyte salt of the lithium-ion battery may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte salt is typically 0.5-5 mol / L.

[0113] The electrolyte salt for sodium-ion batteries can be selected from one or more of the following: sodium hexafluorophosphate, sodium difluorosulfonamide, sodium ditrifluoromethanesulfonamide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, sodium perchlorate, and sodium chloride.

[0114] The electrolyte salts used in other metal-ion batteries are basically compatible with the electrolyte salts used in the lithium-ion or sodium-ion batteries mentioned above; only the corresponding metal cations need to be replaced with the original cations.

[0115] In some embodiments, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), 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), 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).

[0116] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0117] Separating membrane

[0118] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0119] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0120] In some embodiments, the thickness of the isolation membrane is 6-40 μm, optionally 12-20 μm.

[0121] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0122] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0123] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0124] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 5.

[0125] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0126] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0127] In the battery module, multiple secondary batteries 5 can be arranged sequentially along the length of the battery module. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be secured with fasteners.

[0128] Optionally, the battery module may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0129] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0130] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0131] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary 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 may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0132] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0133] Figure 4 This is an example of an electrical device. The device could be 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 the secondary battery for this device, a battery pack or battery module can be used.

[0134] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0135] Example

[0136] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. 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 in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0137] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0138] I. Preparation of Positive Electrode Active Materials

[0139] Preparation Example 1

[0140] 1. Provide Prussian blue analogues

[0141] (1.1) Sodium ferrocyanide Na4Fe(CN)6·10H2O (a 0.4 mol / L aqueous solution), a cyanide of transition metal M', was mixed with FeSO4 (a 0.4 mol / L aqueous solution), a compound containing transition metal M, at a stoichiometric ratio of 1:1. The mixture was heated and stirred at 80 °C for 5 h to obtain a suspension of Prussian blue analogue. After cooling to room temperature, the suspension was washed three times with deionized water, filtered, and dried to obtain a Prussian blue analogue with the chemical formula Na2FeFe(CN)6·2H2O.

[0142] 2. Preparation of positive electrode active materials

[0143] (2.1) Dissolve 17.5 g of Prussian blue analogue with the chemical formula Na2FeFe(CN)6·2H2O in 500 mL of a mixed solvent of water and ethanol (volume ratio of 1:1) to obtain a solution containing Prussian blue analogue with a concentration of 0.1 mol / L.

[0144] (2.2) At 25°C, add 0.19 g of sodium borohydride (molar ratio of 0.1:1 to the Prussian blue analogue) to the solution obtained in step 2.1, stir for 1 hour, filter, and vacuum dry at 150°C for 10 hours to obtain the positive electrode active material.

[0145] Table 1 shows the different conditions and product parameters for preparing the positive electrode active material.

[0146] Examples 2-5

[0147] Repeat the steps of Example 1, except that in step 2.2, the amount of sodium borohydride is changed, as shown in Table 1.

[0148] Example 6: Potassium ions

[0149] 1. Provide Prussian blue analogues

[0150] (1.1) Potassium ferrocyanide K4Fe(CN)6·10H2O (a 0.4 mol / L aqueous solution), a cyanide of transition metal M', was mixed with FeSO4 (a 0.4 mol / L aqueous solution), a compound containing transition metal M, at a stoichiometric ratio of 1:1. The mixture was heated and stirred at 80 °C for 5 h to obtain a suspension of Prussian blue analogue. After cooling to room temperature, the suspension was washed three times with deionized water, filtered, and dried to obtain a Prussian blue analogue with the chemical formula K2FeFe(CN)6·2H2O.

[0151] 2. Preparation of positive electrode active materials

[0152] (2.1) Dissolve 19.1 g of the Prussian blue analogue with the chemical formula K2FeFe(CN)6·2H2O in 500 mL of a mixed solvent of water and ethanol (volume ratio of 1:1) to obtain a solution containing the Prussian blue analogue with a concentration of 0.1 mol / L.

[0153] (2.2) At 25°C, add 1.35g of potassium borohydride (molar ratio of 0.5:1 to the Prussian blue analogue) to the solution obtained in step 2.1, stir for 1 hour, filter, and vacuum dry at 150°C for 10 hours to obtain the positive electrode active material.

[0154] Table 1 shows the different conditions and product parameters for preparing the positive electrode active material.

[0155] Example 7

[0156] The difference from Example 1 is that the boron-containing compound and Prussian blue are similarly different, see Table 1.

[0157] Example 8: Magnesium ions

[0158] 1. Provide Prussian blue analogues

[0159] (1.1) Magnesium ferrocyanide Mg4Fe(CN)6·10H2O (a 0.4 mol / L aqueous solution) of the cyanide of transition metal M' was mixed with FeSO4 (a 0.4 mol / L aqueous solution) containing transition metal M at a stoichiometric ratio of 1:1. The mixture was heated and stirred at 80 °C for 5 h to obtain a suspension of Prussian blue analogue. After cooling to room temperature, the suspension was washed three times with deionized water, filtered, and dried to obtain a Prussian blue analogue with the chemical formula MgFeFe(CN)6·2H2O.

[0160] 2. Preparation of positive electrode active materials

[0161] (2.1) 17.6 g of the Prussian blue analogue with the chemical formula MgFeFe(CN)6·2H2O was dissolved in 500 mL of a mixed solvent of water and ethanol (volume ratio of 1:1) to obtain a solution containing the Prussian blue analogue with a concentration of 0.1 mol / L.

[0162] (2.2) At 25°C, add 0.675 g of magnesium borohydride (molar ratio of 0.25:1 to the Prussian blue analogue) to the solution obtained in step 2.1, stir for 1 hour, filter, and vacuum dry at 150°C for 10 hours to obtain the positive electrode active material.

[0163] Table 1 shows the different conditions and product parameters for preparing the positive electrode active material.

[0164] Examples 9-11

[0165] The steps of Example 1 were repeated, except that in step 2.2, sodium borohydride was added at -10°C, 10°C, and 30°C, respectively.

[0166] Examples 12-14

[0167] The steps of Example 1 were repeated, except that in step 2.1, the volume ratio of water to ethanol was adjusted to 0.5:1, 2:1, and 3:1, respectively.

[0168] Examples 15-16

[0169] The steps of Example 1 were repeated, except that in step 2.2, the stirring time was 0.5 hours and 1.5 hours, respectively.

[0170] Comparative Example 1

[0171] Sodium ferrocyanide Na4Fe(CN)6·10H2O (a 0.4 mol / L aqueous solution), a cyanide of transition metal M', was mixed with FeSO4 (a 0.4 mol / L aqueous solution), a compound containing transition metal M, at a stoichiometric ratio of 1:1. The mixture was heated and stirred at 80°C for 5 h to obtain a suspension of Prussian blue analogue. After cooling to room temperature, the suspension was washed three times with deionized water, filtered, and dried to obtain a Prussian blue analogue with the chemical formula Na2FeFe(CN)6·2H2O.

[0172] The main preparation conditions and product parameters of each embodiment and comparative example are detailed in Table 1.

[0173] Table 1. Main preparation conditions and product parameters for each example and comparative example.

[0174]

[0175] II. Application Examples

[0176] Example 1

[0177] 1) Preparation of positive electrode sheet

[0178] The positive electrode active material, conductive carbon black SP, and binder PVDF prepared in Example 1 were dispersed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 90:10:10 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto a positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained, with a coating weight of 0.27 g / 1540.25 mm². 2 .

[0179] 2) Preparation of negative electrode sheet

[0180] Hard carbon (negative electrode active material), carbon black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were dissolved in deionized water at a weight ratio of 97.2:0.8:0.8:1.2. The resulting negative electrode slurry was prepared under vacuum stirring. This slurry was then uniformly coated onto copper foil. After drying the copper foil at room temperature, it was transferred to a 120°C oven and dried for 1 hour. The foil was then cold-pressed and slit to obtain the negative electrode sheet, with a coating weight of 0.17 g / 1540.25 mm². 2 .

[0181] 3) Separating membrane

[0182] A 12μm thick glass fiber membrane with a porosity of 50% was selected.

[0183] 4) Preparation of electrolyte

[0184] The organic solvent was a mixture containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC), with a volume ratio of EC:EMC of 3:7. In an argon-atmosphere glove box (H₂O < 0.1 ppm, O₂ < 0.1 ppm), 12.5% ​​thoroughly dried NaPF₆ was dissolved in the organic solvent and mixed thoroughly to obtain the electrolyte. The concentration of lithium salt was 1 mol / L.

[0185] 5) Battery manufacturing

[0186] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. After being wound into a square bare cell, it is placed in an aluminum-plastic film, baked at 80°C to remove water, and then 10g of the corresponding non-aqueous electrolyte is injected and sealed. After processes such as standing, hot and cold pressing, formation, clamping, and capacity testing, a finished battery with a capacity of 4000mAh is obtained.

[0187] Examples 2-16 and Comparative Example 1

[0188] Its secondary battery is prepared in a similar manner to the secondary battery in Example 1, but uses the positive electrode active material of the corresponding preparation example.

[0189] III. Battery Cycle Performance Test

[0190] At 25°C, the battery corresponding to Example 1 was charged to 4.0V with a constant current of 1C, then charged to a current of 0.05C with a constant voltage of 4.0V, left to rest for 5 minutes, and then discharged to 1.5V with 1C. The resulting capacity was recorded as the initial capacity C0. The above steps were repeated for the same battery, and the discharge capacity Cn of the battery after the nth cycle was recorded. The battery capacity retention rate after each cycle, Pn = Cn / C0 * 100%, was calculated. Using the 400 points P1, P2...P400 as the ordinate and the corresponding number of cycles as the abscissa, the following results were obtained: Figure 1 The graph shown is a curve of battery capacity retention versus cycle number corresponding to the positive electrode active material of Preparation Example 1.

[0191] During this test, the first cycle corresponds to n=1, the second cycle to n=2, ..., the 400th cycle to n=400. The battery capacity retention rate corresponding to Example 1 in Table 2 is the data measured after 400 cycles under the above test conditions, i.e., the value of P400. The test process for Comparative Example 1 and other examples is the same as above.

[0192] Batteries for each embodiment and comparative example were prepared according to the above method, and cycle performance parameters were measured. The results are shown in Table 2 below.

[0193] Table 2 shows the cycle performance of the batteries in each embodiment and comparative example.

[0194] Example number Cycling performance P400 Comparative example 1 80.0％ Example 1 93.5％ Example 2 97.2％ Example 3 99.6％ Example 4 95.3％ Example 5 84.5％ Example 6 89.0％ Example 7 98.2％ Example 8 83％ Example 9 93.6％ Example 10 95.7％ Example 11 99.1％ Example 12 98.2％ Example 13 97.9％ Example 14 91.2％ Example 15 98.9％ Example 16 98.2％

[0195] As can be seen from the above embodiments and comparative examples, the positive electrode active material of this application, by doping with boron, has a stable structure when the boron content reaches the range of this invention, so that the corresponding battery can achieve a high level of capacity retention after 400 cycles, for example, up to 99.6%.

[0196] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode active material comprising a boron-doped Prussian blue analogue; wherein, in the boron-doped Prussian blue analogue, carbon is replaced by boron. The chemical formula of the Prussian blue analogue is A a M b M' c (CN)6·dH2O, where A includes alkali metal cations, alkaline earth metal cations, and Zn. 2+ Al 3+ At least one of the following, M and M' each independently include at least one of Ni ion, Cu ion, Fe ion, Mn ion, Co ion and Zn ion, H2O is coordinated water, 0 <a≤2,0<b≤1,0<c≤1,0≤d≤2。 2. The positive electrode active material according to claim 1, characterized in that, Based on the weight of the positive electrode active material, the boron content is 0.001%-20%.

3. The positive electrode active material according to claim 1 or 2, characterized in that, Based on the weight of the positive electrode active material, the boron content is 2%-15.5%.

4. The positive electrode active material according to any one of claims 1-3, characterized in that, In the positive electrode active material, the molar ratio of boron to M is (0.001-2):

1.

5. The positive electrode active material according to any one of claims 1-4, characterized in that, In the positive electrode active material, the molar ratio of boron to M is (0.1-0.8):

1.

6. The positive electrode active material according to any one of claims 1-5, characterized in that, In the positive electrode active material, the weight ratio of boron to carbon is (0.001-800):

1.

7. The positive electrode active material according to any one of claims 1-6, characterized in that, In the positive electrode active material, the weight ratio of boron to carbon is (0.1-8):

1.

8. The positive electrode active material according to any one of claims 1-7, characterized in that, In the positive electrode active material, A includes at least one of sodium ions, magnesium ions, and potassium ions.

9. The positive electrode active material according to any one of claims 1-8, characterized in that, The positive electrode active material satisfies at least one of the following characteristics: Specific surface area is 2m² 2 / g-5m 2 / g; and Average volumetric particle size D v50 The range is 1.5μm-5μm.

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 characteristics: Specific surface area is 3m² 2 / g-4m 2 / g; and Average volumetric particle size D v50 The range is 2μm-3.5μm.

11. A method for preparing a positive electrode active material, comprising: (1) Add the Prussian blue analogue to the mixed solvent to obtain a solution containing the Prussian blue analogue; (2) Add a boron-containing compound to the solution containing the Prussian blue analogue, mix, and obtain a mixture; (3) The mixture is filtered and dried to obtain a positive electrode active material; The positive electrode active material comprises a boron-doped Prussian blue analogue; in the boron-doped Prussian blue analogue, the carbon element in the Prussian blue analogue is replaced by the boron element. The chemical formula of the Prussian blue analogue is A a M b M' c (CN)6·dH2O, where A includes alkali metal cations, alkaline earth metal cations, and Zn. 2+ Al 3+ At least one of the following, M and M' each independently include at least one of Ni ion, Cu ion, Fe ion, Mn ion, Co ion and Zn ion, H2O is coordinated water, 0 <a≤2,0<b≤1,0<c≤1,0≤d≤2。 12. The method according to claim 11, characterized in that, In step (1), the mixed solvent is a mixture of water and an organic solvent miscible with water.

13. The method according to claim 12, characterized in that, The volume ratio of water to organic solvent is (0.001-3):

1.

14. The method according to any one of claims 11-13, characterized in that, In step (2), the boron-containing compound is of formula Q(BH4). x The compound, where Q is an alkali metal ion, alkaline earth metal ion, aluminum ion, zinc ion, and x is the valence state of Q.

15. The method according to any one of claims 11-14, characterized in that, In step (2), the molar ratio of the boron-containing compound to the Prussian blue analogue is (0.5-2):

1.

16. The method according to any one of claims 11-15, characterized in that, In step (2), the molar ratio of the boron-containing compound to the Prussian blue analogue is (0.5-1):

1.

17. The method according to any one of claims 11-16, characterized in that, In step (2), the mixing temperature is from -10°C to 30°C; and The mixing time is 0 to 2 hours.

18. The method according to claim 17, characterized in that, In step (2), the mixing temperature is 0°C to 25°C.

19. The method according to any one of claims 17-18, characterized in that, In step (2), the mixing time is 0.5 to 1.5 hours.

20. A secondary battery, characterized in that, The positive electrode active material includes any one of claims 1-10 or the positive electrode active material prepared by the method according to any one of claims 11-19.

21. The secondary battery according to claim 20, characterized in that, The secondary battery is a sodium-ion secondary battery.

22. An electrical appliance, characterized in that, The secondary battery includes any one of claims 20-21.

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