Secondary battery, positive electrode sheet, positive electrode active material, production method, and electric device

Abstract

This application relates to a secondary battery, a positive electrode sheet, a positive electrode active material, a preparation method, and an electrical device. The secondary battery includes a positive electrode sheet containing a positive electrode active material. The positive electrode active material includes a core and a coating layer covering at least a portion of the surface of the core. The core contains a porous Prussian blue-like compound, and the coating layer contains a conductive polymer. By employing a porous Prussian blue-like compound with a porous structure and coating the outer surface of the porous Prussian blue with a conductive polymer, the ionic conductivity, electronic conductivity, and structural stability of the positive electrode active material can be improved, thereby enhancing the rate performance and cycle performance of the positive electrode active material, and consequently improving the rate performance and cycle performance of the secondary battery using this positive electrode active material.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a secondary battery, a positive electrode sheet, a positive electrode active material, a preparation method, and an electrical device. Background Technology

[0002] In recent years, with the increasingly widespread application of rechargeable batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Sodium-ion batteries have attracted widespread attention due to their excellent energy storage capacity, low cost, and environmental friendliness. Especially in large-scale energy storage systems, sodium-ion batteries are considered a highly promising energy storage technology due to the abundant reserves and wide distribution of sodium in the Earth's crust.

[0003] Prussian blue compounds are commonly used as positive electrode active materials in sodium-ion batteries, but sodium-ion batteries using Prussian blue compounds as positive electrode active materials suffer from poor rate performance. Summary of the Invention

[0004] This application provides a secondary battery, a positive electrode sheet, a positive electrode active material, a preparation method, and an electrical device to improve the rate performance of the secondary battery.

[0005] To achieve the above objectives, a first aspect of this application provides a secondary battery, including a positive electrode sheet, said positive electrode sheet comprising a positive electrode active material, said positive electrode active material comprising:

[0006] The core, comprising porous Prussian blue compounds; and

[0007] A coating layer covering at least a portion of the surface of the core, the coating layer comprising a conductive polymer.

[0008] Therefore, the core of the positive electrode active material contains Prussian blue compounds with porous structures. Under capillary action, the electrolyte can enter the porous structure of the Prussian blue compounds, thus increasing the effective reaction area of ​​the Prussian blue compounds while shortening the reaction time of Na+. +The diffusion path of the transport pathway improves the ionic conductivity of Prussian blue compounds. The conductive polymer coating the outer surface of the core enhances the electronic conductivity of the Prussian blue compounds. Furthermore, the flexible interface of the conductive polymer suppresses structural deformation and even collapse caused by lattice strain during charging and discharging, thus improving the structural stability of the cathode active material. In summary, by employing porous Prussian blue compounds with a porous structure and coating the outer surface of the porous Prussian blue with a conductive polymer, the ionic conductivity, electronic conductivity, and structural stability of the cathode active material can be improved, thereby enhancing its rate performance and cycle performance, and consequently, improving the rate performance and cycle performance of the secondary battery using this cathode active material.

[0009] In some embodiments of this application, the porous Prussian blue compound has a pore structure comprising macropores and mesopores. This facilitates electrolyte entry into the pore structure, increases the effective reaction area of ​​the Prussian blue compound, and shortens the reaction time of Na+. + The diffusion path of transport improves the ionic conductivity of Prussian blue compounds, thereby enhancing the rate performance of the positive electrode active material and consequently improving the rate performance of the secondary battery.

[0010] In some embodiments of this application, the average pore size of the pore structure is 3nm-30nm. This facilitates the entry of the electrolyte into the pore structure through capillary action, increasing the effective reaction area of ​​Prussian blue compounds while shortening the reaction time of Na+. + The diffusion path of transport improves the ionic conductivity of Prussian blue compounds, thereby enhancing the rate performance of the positive electrode active material and consequently improving the rate performance of the secondary battery.

[0011] In some embodiments of this application, the average pore size of the pore structure is 3nm-25nm.

[0012] In some embodiments of this application, the Dv80 of the positive electrode active material is 1 μm-1.15 μm. This reduces the interfacial area between the positive electrode active material and the electrolyte, decreases side reactions, and increases the compaction density of the positive electrode active material, thereby improving the capacity and cycle performance of the secondary battery.

[0013] In some embodiments of this application, the Dv80 of the positive electrode active material is 1.05 μm-1.15 μm.

[0014] In some embodiments of this application, the porous Prussian blue compound has the chemical formula Na2M[Fe(CN)6], where M includes one or more of Fe, Mn, Co, Ni, Cu, and Zn.

[0015] In some embodiments of this application, the main chain of the conductive polymer has a conjugated structure and π delocalized electrons.

[0016] In some embodiments of this application, the conductive polymer includes one or more of polyaniline and its derivatives, polypyrrole and its derivatives, polyacetylene and its derivatives, polythiophene and its derivatives, and polythiazole and its derivatives.

[0017] In some embodiments of this application, the polythiophene derivative includes poly3,4-ethylenedioxythiophene.

[0018] In some embodiments of this application, the thickness of the coating layer is 10 nm-50 nm. This is beneficial for improving the electronic conductivity of the positive electrode active material, thereby improving the rate performance of the secondary battery.

[0019] In some embodiments of this application, the thickness of the coating layer is 10nm-20nm.

[0020] In some embodiments of this application, the secondary battery is a sodium-ion battery.

[0021] A second aspect of this application also provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising:

[0022] The core, comprising porous Prussian blue compounds; and

[0023] A coating layer covering at least a portion of the surface of the core, the coating layer comprising a conductive polymer.

[0024] In some embodiments of this application, the positive electrode is the positive electrode in the secondary battery of the first aspect of this application.

[0025] A third aspect of this application provides a positive electrode active material, the positive electrode active material comprising:

[0026] The core, comprising porous Prussian blue compounds; and

[0027] A coating layer covering at least a portion of the surface of the core, the coating layer comprising a conductive polymer.

[0028] In some embodiments of this application, the positive electrode active material is the positive electrode active material in the secondary battery of the first aspect of this application.

[0029] The fourth aspect of this application provides a method for preparing a positive electrode active material, comprising the following steps:

[0030] Porous Prussian blue compounds were prepared by thermally reacting a mixture of Prussian blue compounds, polyvinylpyrrolidone, and an acidic solution.

[0031] The positive electrode active material is prepared by oxidative polymerization of a solution containing the porous Prussian blue compound, a polymer monomer, and an oxidant to coat at least a portion of the surface of the porous Prussian blue compound with a conductive polymer.

[0032] In some embodiments of this application, the molar concentration of the acidic solution is 0.5 mol / L to 1.5 mol / L. Consequently, the porous Prussian blue compounds prepared have a suitable pore size, which facilitates the entry of electrolyte into the pore structure, increases the effective reaction area of ​​the porous Prussian blue compounds, shortens the diffusion path of Na+ transport, and improves the ionic conductivity of the material, thereby enhancing the rate performance of the battery.

[0033] In some embodiments of this application, the ratio of the Prussian blue compound, povidone, and the acidic solution is 1 g:(5-25) g:(1-5) L. This avoids damaging the crystallinity of the Prussian blue compound while promoting the formation of mesopores and macropores.

[0034] In some embodiments of this application, the temperature of the thermal reaction is 100°C-200°C, and the time is 20-30 hours. This facilitates the formation of porous Prussian blue compounds with both mesopores and macropores.

[0035] In some embodiments of this application, the acidic substance contained in the acidic solution includes one or more of hydrochloric acid and sulfuric acid.

[0036] In some embodiments of this application, the polymer monomer includes one or more of aniline and its derivatives, pyrrole and its derivatives, acetylene and its derivatives, thiophene and its derivatives, and thiazole and its derivatives.

[0037] In some embodiments of this application, the mass-to-volume ratio of the porous Prussian blue compound to the polymer monomer is 2 g:(1-4) mL.

[0038] In some embodiments of this application, the mass-to-volume ratio of ferric chloride to the polymer monomer is 2 g: (1-4) mL.

[0039] The fifth aspect of this application provides an electrical device, including a secondary battery of the first aspect of this application, a positive electrode sheet of the second aspect, or a positive electrode active material of the third aspect.

[0040] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0041] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0042] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0043] Figure 2 for Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0044] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0045] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0046] Figure 5 for Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0047] Figure 6 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.

[0048] Explanation of reference numerals in the attached figures:

[0049] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Electrical device. Detailed Implementation

[0050] The following describes in detail, with appropriate reference to the accompanying drawings, some embodiments of the secondary battery, positive electrode sheet, positive electrode active material, preparation method, and electrical device of this application. However, some 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 to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0051] The "range" disclosed in this application can be defined in the form of 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; any endpoint can be independently included or excluded, and they can be combined arbitrarily, meaning 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 ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also 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" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when describing a parameter as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 for that parameter. For instance, when describing a parameter as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0052] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0053] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0054] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0055] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can 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.

[0056] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0057] Prussian blue compounds possess an open framework structure and abundant redox active sites, exhibiting strong structural stability. In particular, their large ion channels and interstitial spaces within the crystal lattice are among the few capable of accommodating larger basic cations, such as Na+. + Prussian blue is one of the host materials for sodium-ion batteries, facilitating reversible insertion reactions. Therefore, Prussian blue compounds are commonly used as positive electrode active materials in sodium-ion batteries. However, on the one hand, Prussian blue compounds have relatively large particle sizes, resulting in longer diffusion paths and poor ionic conductivity; on the other hand, Prussian blue compounds themselves have high electrical conductivity but poor electronic conductivity. This leads to poor rate performance in sodium-ion batteries using Prussian blue compounds as positive electrode active materials.

[0058] This application uses an acid etching method to prepare porous Prussian blue compounds with a porous structure, and coats at least a portion of the surface of the porous Prussian blue compounds with a conductive polymer, which can improve the ionic conductivity, electronic conductivity and structural stability of the positive electrode active material, thereby improving the rate performance and cycle performance of the positive electrode active material, and further improving the rate performance and cycle performance of the secondary battery using the positive electrode active material.

[0059] One or more embodiments of this application provide a secondary battery, the secondary battery including a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising a core and a coating layer covering at least a portion of the surface of the core; the core comprising a porous Prussian blue compound, and the coating layer comprising a conductive polymer.

[0060] It should be noted that the porous Prussian blue compounds mentioned in the context refer to Prussian blue compounds with porous structures.

[0061] Understandably, the core of the positive electrode active material contains Prussian blue compounds with porous structures. Under capillary action, the electrolyte can enter the porous structure of the Prussian blue compounds, thus increasing the effective reaction area of ​​the Prussian blue compounds while shortening the reaction time of Na+. + The diffusion path of the transport pathway improves the ionic conductivity of Prussian blue compounds. The conductive polymer coating the outer surface of the core enhances the electronic conductivity of the Prussian blue compounds. Furthermore, the flexible interface of the conductive polymer suppresses structural deformation and even collapse caused by lattice strain during charging and discharging, thus improving the structural stability of the cathode active material. In summary, by employing porous Prussian blue compounds with a porous structure and coating the outer surface of the porous Prussian blue with a conductive polymer, the ionic conductivity, electronic conductivity, and structural stability of the cathode active material can be improved, thereby enhancing its rate performance and cycle performance, and consequently, improving the rate performance and cycle performance of the secondary battery using this cathode active material.

[0062] As an example, the structural characteristics of the positive electrode active material mentioned in the context can be determined by the following method: disassemble the secondary battery, scrape the powder from the positive electrode sheet, disperse the powder in anhydrous ethanol, and sonicate for half an hour; drop the sonicated solution onto the carbon film, dry it, and then perform TEM characterization to obtain the structural characteristics of the positive electrode active material.

[0063] The specific materials contained in the core and coating of the positive electrode active material mentioned in the context can be determined by the following method: disassemble the secondary battery, scrape the powder from the positive electrode sheet, and use X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) to determine the specific materials contained in the core and coating.

[0064] It is easy to understand that the technical solution of this application does not exclude the possibility that at least one of the core and the covering layer includes other materials.

[0065] It should be noted that the core and the coating layer may each independently include other materials, but their content should not make them the main components, so as to avoid affecting the coating of the conductive polymer with porous Prussian blue compounds.

[0066] In some implementations, the core mainly comprises or contains only porous Prussian blue compounds, and the coating mainly comprises or contains only conductive polymers.

[0067] In some embodiments, the conductive polymer is directly coated on at least a portion of the surface of the porous Prussian blue compound.

[0068] In some embodiments, the porous Prussian blue compounds have a pore structure comprising one or more macropores and mesopores. This facilitates electrolyte entry into the pore structure, increases the effective reaction area of ​​the Prussian blue compounds, and shortens the reaction time of Na+. + The diffusion path of transport improves the ionic conductivity of Prussian blue compounds, thereby enhancing the rate performance of the positive electrode active material and consequently improving the rate performance of the secondary battery.

[0069] It should be noted that, in this context, "macropores" refers to pores with a diameter greater than 50 nm, while "mesopores" refers to pores with a diameter between 2 nm and 50 nm.

[0070] As one possible implementation, the average pore size of the pore structure is 3nm-30nm; for example, it can be, but is not limited to, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm, 30nm, or any range between two of the above average pore sizes. When the average pore size of the pore structure is within the above range, it is more conducive to the electrolyte entering the pore structure under capillary action, increasing the effective reaction area of ​​Prussian blue compounds while shortening the reaction time of Na. + The diffusion path of transport improves the ionic conductivity of Prussian blue compounds, thereby enhancing the rate performance of the positive electrode active material and consequently improving the rate performance of the secondary battery.

[0071] In some alternative implementations, the average pore size of the pore structure is 3nm-25nm.

[0072] As an example, the type of pore structure and the average pore size mentioned in the context can be determined by the following method: First, obtain nitrogen adsorption isotherms using a nitrogen adsorption-desorption apparatus. Then, calculate the pore size distribution according to the Barrett-Joyner-Halenda (BJH) method to obtain the average pore size and determine the type of pore structure. As an example, a NOVA 1000e nitrogen adsorption-desorption apparatus from Quanta Instruments, Inc. can be used.

[0073] In some optional embodiments, the Dv80 of the positive electrode active material is 1 μm-1.15 μm. For example, it can be, but is not limited to, 1 μm, 1.01 μm, 1.02 μm, 1.03 μm, 1.04 μm, 1.05 μm, 1.06 μm, 1.07 μm, 1.08 μm, 1.09 μm, 1.1 μm, 1.11 μm, 1.12 μm, 1.13 μm, 1.14 μm, 1.15 μm, or any range between two of the above Dv80 values. When the Dv80 of the positive electrode active material is within the above range, it reduces the interfacial area between the positive electrode active material and the electrolyte, reduces the occurrence of side reactions, and can also increase the compaction density of the positive electrode active material, thereby improving the capacity and cycle performance of the secondary battery.

[0074] In some embodiments of this application, the Dv80 of the positive electrode active material is 1.05 μm-1.15 μm.

[0075] It should be noted that Dv80 mentioned in the context refers to the particle size corresponding to 80% of the volume distribution. As an example, Dv80 can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, according to GB / T 19077-2016, Particle Size Distribution by Laser Diffraction. Specifically, the following method can be used: Place 0.036g-0.039g of the sample to be tested at the bottom of a beaker, add 1mL of surfactant (20% polyvinylpyrrolidone aqueous solution), pre-sonicate at 180W, 53kHz for 30s, then add 20mL of anhydrous ethanol and sonicate for 3min, finally using a laser particle size analyzer for measurement.

[0076] In some embodiments, the porous Prussian blue compound has the chemical formula Na2M[Fe(CN)6], where M includes one or more of Fe, Mn, Co, Ni, Cu, and Zn.

[0077] As one possible implementation, the main chain of the conductive polymer has a conjugated structure and π delocalized electrons.

[0078] In some alternative embodiments, the conductive polymer includes one or more of polyaniline and its derivatives, polypyrrole and its derivatives, polyacetylene and its derivatives, polythiophene and its derivatives, and polythiazole and its derivatives.

[0079] In some exemplary embodiments, the polythiophene derivative includes poly3,4-ethylenedioxythiophene.

[0080] In some embodiments, the thickness of the coating layer is 10nm-50nm; for example, it can be, but is not limited to, 10nm, 12nm, 14nm, 16nm, 18nm, 20nm, 22nm, 24nm, 26nm, 28nm, 30nm, 32nm, 34nm, 36nm, 38nm, 40nm, 42nm, 44nm, 46nm, 48nm, 50nm, or any range between two of the above thicknesses. A coating layer thickness within the above range is beneficial for improving the electronic conductivity of the positive electrode active material, thereby improving the rate performance of the secondary battery.

[0081] In some alternative implementations, the thickness of the coating layer is 10 nm to 20 nm.

[0082] In some of these embodiments, the thickness of the coating layer is 20nm-50nm.

[0083] As an example, the thickness of the coating layer mentioned in the context can be determined by the following method: disassemble the secondary battery, scrape off the powder from the positive electrode, disperse the powder in anhydrous ethanol, and sonicate for half an hour; drop the sonicated solution onto the carbon film, let it dry, and then perform TEM characterization to measure the coating layer thickness.

[0084] In some implementations, the secondary battery is a sodium-ion battery.

[0085] As one possible implementation, the positive electrode includes a positive current collector and a positive active material layer located on at least one side of the positive current collector, the positive active material layer containing the aforementioned positive active material.

[0086] As a non-limiting example, the positive electrode current collector has two surfaces opposite each other in its own thickness direction, and a positive electrode active material layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector, the positive electrode active material layer comprising the aforementioned positive electrode active material.

[0087] As an example, the positive electrode active material may also include one or more of the following materials: sodium transition metal oxides and polyanionic compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0088] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. A non-limiting example of a sodium transition metal oxide is Na. x QO2, where Q may include one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0089] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be one or more of P, S, and Si; n represents (YO4). n- The price state.

[0090] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds consisting of anionic units and halide anions. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be one or more of P, S, and Si, and n represents (YO4). n- The valence state; halogens can be one or more of F, Cl and Br.

[0091] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be one or more of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; halogens can be one or more of F, Cl and Br.

[0092] Polyanionic compounds can include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F and Na3(VO y )2(PO4)2F 3-2y One or more of (0≤y≤1). Among them, M' in NaM'PO4F can include one or more of V, Fe, Mn and Ni.

[0093] In some embodiments, the positive electrode 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 polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on a polymeric material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0094] In some embodiments, the positive electrode active material layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0095] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As a non-limiting 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.

[0096] 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 electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt%-80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s-25000 mPa·s. When coating the positive electrode slurry, the coating areal density per unit area (dry weight, minus solvent) can be 15 mg / cm³. 2 -35mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 g / cm³. 3 -3.6 g / cm 33.3g / cm³ is an option. 3 -3.5 g / cm 3 .

[0097] One or more embodiments of this application provide a positive electrode sheet comprising a positive active material including a core and a coating layer covering at least a portion of the surface of the core; the core comprises a porous Prussian blue compound and the coating layer comprises a conductive polymer.

[0098] In some embodiments, a conductive polymer is present in the porous Prussian blue compound's pore structure.

[0099] It is easy to understand that the technical solution of this application does not exclude the possibility that at least one of the core and the covering layer includes other materials.

[0100] It should be noted that the core and the coating layer may each independently include other materials, but their content should not make them the main components, so as to avoid affecting the coating of the conductive polymer with porous Prussian blue compounds.

[0101] In some implementations, the core mainly comprises or contains only porous Prussian blue compounds, and the coating mainly comprises or contains only conductive polymers.

[0102] In some embodiments, the conductive polymer is directly coated on at least a portion of the surface of the porous Prussian blue compound.

[0103] In some embodiments, the porous Prussian blue compounds have a pore structure comprising one or more macropores and mesopores. This facilitates electrolyte entry into the pore structure, increases the effective reaction area of ​​the Prussian blue compounds, and shortens the reaction time of Na+. + The diffusion path of transport improves the ionic conductivity of Prussian blue compounds, thereby enhancing the rate performance of the positive electrode active material and consequently improving the rate performance of the secondary battery.

[0104] As one possible implementation, the average pore size of the pore structure is 3nm-30nm; for example, it can be, but is not limited to, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm, 30nm, or any range between two of the above average pore sizes. This makes it more advantageous for the electrolyte to enter the pore structure under capillary action, increasing the effective reaction area of ​​Prussian blue compounds while shortening the reaction time of Na. +The diffusion path of transport improves the ionic conductivity of Prussian blue compounds, thereby enhancing the rate performance of the positive electrode active material and consequently improving the rate performance of the secondary battery.

[0105] In some alternative implementations, the average pore size of the pore structure is 3nm-25nm.

[0106] In some optional embodiments, the Dv80 of the positive electrode active material is 1 μm-1.15 μm. For example, it can be, but is not limited to, 1 μm, 1.01 μm, 1.02 μm, 1.03 μm, 1.04 μm, 1.05 μm, 1.06 μm, 1.07 μm, 1.08 μm, 1.09 μm, 1.1 μm, 1.11 μm, 1.12 μm, 1.13 μm, 1.14 μm, 1.15 μm, or any range between two of the above Dv80 values. Therefore, by reducing the interfacial area between the positive electrode active material and the electrolyte, the occurrence of side reactions is reduced, and the compaction density of the positive electrode active material can be increased, thereby improving the capacity and cycle performance of the secondary battery.

[0107] In some embodiments of this application, the Dv80 of the positive electrode active material is 1.05 μm-1.15 μm.

[0108] In some embodiments, the porous Prussian blue compound has the chemical formula Na2M[Fe(CN)6], where M includes one or more of Fe, Mn, Co, Ni, Cu, and Zn.

[0109] As one possible implementation, the main chain of the conductive polymer has a continuous conjugated structure and π delocalized electrons.

[0110] In some alternative embodiments, the conductive polymer includes one or more of polyaniline and its derivatives, polypyrrole and its derivatives, polyacetylene and its derivatives, polythiophene and its derivatives, and polythiazole and its derivatives.

[0111] In some exemplary embodiments, the polythiophene derivative includes poly3,4-ethylenedioxythiophene.

[0112] In some embodiments, the thickness of the coating layer is 10nm-50nm; for example, it can be, but is not limited to, 10nm, 12nm, 14nm, 16nm, 18nm, 20nm, 22nm, 24nm, 26nm, 28nm, 30nm, 32nm, 34nm, 36nm, 38nm, 40nm, 42nm, 44nm, 46nm, 48nm, 50nm, or any range between two of the above thicknesses. This is beneficial for improving the electronic conductivity of the positive electrode active material, thereby improving the rate performance of the secondary battery.

[0113] In some alternative implementations, the thickness of the coating layer is 10 nm to 20 nm.

[0114] In some of these embodiments, the thickness of the coating layer is 20nm-50nm.

[0115] One or more embodiments of this application provide a positive electrode active material comprising a core and a coating layer covering at least a portion of the surface of the core; the core comprises a porous Prussian blue compound, and the coating layer comprises a conductive polymer.

[0116] In some embodiments, a conductive polymer is present in the porous Prussian blue compound's pore structure.

[0117] It is easy to understand that the technical solution of this application does not exclude the possibility that at least one of the core and the covering layer includes other materials.

[0118] It should be noted that the core and the coating layer may each independently include other materials, but their content should not make them the main components, so as to avoid affecting the coating of the conductive polymer with porous Prussian blue compounds.

[0119] In some implementations, the core mainly comprises or contains only porous Prussian blue compounds, and the coating mainly comprises or contains only conductive polymers.

[0120] In some embodiments, the conductive polymer is directly coated on at least a portion of the surface of the porous Prussian blue compound.

[0121] In some embodiments, the porous Prussian blue compounds have a pore structure comprising one or more macropores and mesopores. This facilitates electrolyte entry into the pore structure, increases the effective reaction area of ​​the Prussian blue compounds, and shortens the reaction time of Na+. + The diffusion path of transport improves the ionic conductivity of Prussian blue compounds, thereby enhancing the rate performance of the positive electrode active material and consequently improving the rate performance of the secondary battery.

[0122] As one possible implementation, the average pore size of the pore structure is 3nm-30nm; for example, it can be, but is not limited to, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm, 30nm, or any range between two of the above average pore sizes. This makes it more advantageous for the electrolyte to enter the pore structure under capillary action, increasing the effective reaction area of ​​Prussian blue compounds while shortening the reaction time of Na.+ The diffusion path of transport improves the ionic conductivity of Prussian blue compounds, thereby enhancing the rate performance of the positive electrode active material and consequently improving the rate performance of the secondary battery.

[0123] In some alternative implementations, the average pore size of the pore structure is 3nm-25nm.

[0124] In some optional embodiments, the Dv80 of the positive electrode active material is 1 μm-1.15 μm. For example, it can be, but is not limited to, 1 μm, 1.01 μm, 1.02 μm, 1.03 μm, 1.04 μm, 1.05 μm, 1.06 μm, 1.07 μm, 1.08 μm, 1.09 μm, 1.1 μm, 1.11 μm, 1.12 μm, 1.13 μm, 1.14 μm, 1.15 μm, or any range between two of the above Dv80 values. Therefore, by reducing the interfacial area between the positive electrode active material and the electrolyte, the occurrence of side reactions is reduced, and the compaction density of the positive electrode active material can be increased, thereby improving the capacity and cycle performance of the secondary battery.

[0125] In some embodiments of this application, the Dv80 of the positive electrode active material is 1.05 μm-1.15 μm.

[0126] In some embodiments, the porous Prussian blue compound has the chemical formula Na2M[Fe(CN)6], where M includes one or more of Fe, Mn, Co, Ni, Cu, and Zn.

[0127] As one possible implementation, the main chain of the conductive polymer has a continuous conjugated structure and π delocalized electrons.

[0128] In some alternative embodiments, the conductive polymer includes one or more of polyaniline and its derivatives, polypyrrole and its derivatives, polyacetylene and its derivatives, polythiophene and its derivatives, and polythiazole and its derivatives.

[0129] In some exemplary embodiments, the polythiophene derivative includes poly3,4-ethylenedioxythiophene.

[0130] In some embodiments, the thickness of the coating layer is 10nm-50nm; for example, it can be, but is not limited to, 10nm, 12nm, 14nm, 16nm, 18nm, 20nm, 22nm, 24nm, 26nm, 28nm, 30nm, 32nm, 34nm, 36nm, 38nm, 40nm, 42nm, 44nm, 46nm, 48nm, 50nm, or any range between two of the above thicknesses. This is beneficial for improving the electronic conductivity of the positive electrode active material, thereby improving the rate performance of the secondary battery.

[0131] In some alternative implementations, the thickness of the coating layer is 10 nm to 20 nm.

[0132] In some of these embodiments, the thickness of the coating layer is 20nm-50nm.

[0133] One or more embodiments of this application provide a method for preparing a positive electrode active material, characterized by comprising the following steps:

[0134] A porous Prussian blue compound is prepared by thermally reacting a mixture of Prussian blue compound, polyvinylpyrrolidone, and an acidic solution. An oxidative polymerization reaction is then carried out on a solution containing the porous Prussian blue compound, a polymer monomer, and an oxidant to coat at least a portion of the surface of the porous Prussian blue compound with a conductive polymer, thereby preparing a positive electrode active material.

[0135] Porous Prussian blue compounds with porous structures were prepared by acid etching, which increased the effective reaction area of ​​the Prussian blue compounds and shortened the reaction time of Na+. + The diffusion path of the transport pathway improves the ionic conductivity of Prussian blue compounds. Then, coating the porous Prussian blue compounds with a conductive polymer not only improves their electronic conductivity but also suppresses structural deformation or even collapse caused by lattice strain during charge and discharge, thus enhancing the structural stability of the cathode active material. In summary, the cathode active material prepared by this method exhibits excellent ionic conductivity, electronic conductivity, and structural stability, thereby improving the rate performance and cycle performance of the cathode active material, and consequently, the rate performance and cycle performance of the secondary battery using this cathode active material.

[0136] In some embodiments, the oxidant includes ferric chloride and / or ferric chloride hexahydrate.

[0137] In some embodiments, the molar concentration of the acidic solution is 0.5 mol / L to 1.5 mol / L; for example, it can be, but is not limited to, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, or any range between two of the above concentrations. When the molar concentration of the acidic solution is within the above range, the porous Prussian blue compound prepared has a suitable pore size, which facilitates the entry of the electrolyte into the pore structure, increases the effective reaction area of ​​the porous Prussian blue compound, and shortens the Na+ condensation time. + The diffusion path of the transport increases the ionic conductivity of the material, thereby improving the rate performance of the battery.

[0138] In some embodiments, the ratio of Prussian blue compound, povidone, and acidic solution is 1 g:(5-25) g:(1-5) L; for example, but not limited to 1 g:(5-25) g:(1-5) L, 1 g:(6-23) g:(1-4.5) L, 1 g:(7-20) g:(1-4) L, 1 g:(7-17) g:(1-3.5) L, 1 g:(7-15) g:(1-3) L, or 1 g:(7-13) g:(1-2.5) L, etc. This avoids damaging the crystallinity of the Prussian blue compound while promoting the formation of mesopores and macropores.

[0139] In some embodiments, the temperature of the thermal reaction is 100°C-200°C; for example, it can be, but is not limited to, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, or any range between the above temperatures.

[0140] As one possible implementation, the thermal reaction time is 20h-30h; for example, it can be, but is not limited to, 20h, 21h, 22h, 23h, 24h, 25h, 26h, 27h, 28h, 29h, 30h or any range between two of the above times.

[0141] When the temperature and time of the thermal reaction are within the above-mentioned ranges, it is beneficial to form porous Prussian blue compounds with mesopores and macropores.

[0142] In some embodiments, the acidic substance contained in the acidic solution includes one or more of hydrochloric acid and sulfuric acid.

[0143] In some embodiments, the polymer monomer includes one or more of aniline and its derivatives, pyrrole and its derivatives, acetylene and its derivatives, thiophene and its derivatives, and thiazole and its derivatives.

[0144] As one possible implementation, the mass-to-volume ratio of the porous Prussian blue compound to the polymer monomer is 2 g:(1-4) mL; for example, it can be, but is not limited to, 2 g:1 mL, 2 g:1.5 mL, 2 g:2 mL, 2 g:2.5 mL, 2 g:3 mL, 2 g:3.5 mL, 2 g:4 mL, or any range between two of the above mass-to-volume ratios. This facilitates the coating of the porous Prussian blue compound with a conductive polymer, improving the electronic conductivity of the material and thus enhancing its rate performance.

[0145] In some embodiments, the mass-to-volume ratio of ferric chloride to the polymer monomer is 2g:(1-4)mL; for example, it can be, but is not limited to, 2g:1mL, 2g:2mL, 2g:3mL, 2g:4mL, or any range between the two of the above ratios.

[0146] In some embodiments, the porous Prussian blue compound has the chemical formula Na2M[Fe(CN)6], where M includes one or more of Fe, Mn, Co, Ni, Cu, and Zn.

[0147] In some embodiments, the preparation method of Prussian blue compounds includes the following steps:

[0148] Prussian blue compounds were prepared by mixing solution A containing Na4Fe(CN)6·10H2O and solution B containing the precursor, trisodium citrate, and sodium chloride.

[0149] In some embodiments, the precursor includes one or more of FeSO4·7H2O, CoCl2, MnSO4·H2O, NiCl2, ZnCl2, and CuCl2.

[0150] One or more embodiments of this application provide an electrical device, including the above-described secondary battery, the above-described positive electrode sheet, or the above-described positive electrode active material.

[0151] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0152] Typically, a secondary battery includes 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. The positive electrode can be one of the aforementioned types.

[0153] Negative electrode sheet

[0154] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer including a negative active material.

[0155] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0156] 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 polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0157] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more 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.

[0158] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may include one or more 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).

[0159] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. 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.

[0160] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0161] 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 (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, and other processes. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt%-60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s-10000mPa·s. When coating the negative electrode slurry, the coating unit areal density (dry weight, minus solvent) can be 75g / m³. 2 -220g / m 2 The compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 -1.8g / cm 3 .

[0162] electrolytes

[0163] Electrolytes function to conduct ions between the positive and negative electrode plates. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0164] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0165] In some embodiments, the electrolyte salt may include one or more of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorophosphate (NaPO2F2), sodium difluorooxalate borate (NaDFOB), sodium di(oxalate borate) (NaBOB), sodium difluorodi(oxalate phosphate) (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0166] In some embodiments, the solvent may include 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), butylene carbonate ( One or more of the following: fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0167] 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.

[0168] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), etc.

[0169] Separating membrane

[0170] 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.

[0171] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0172] In some embodiments, the thickness of the isolation membrane is 6μm-40μm, and optionally 12μm-20μm.

[0173] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0174] 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.

[0175] In some embodiments, the outer packaging of the secondary battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0176] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0177] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0178] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0179] In some of these embodiments, reference is made to Figure 2 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. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to actual needs.

[0180] The secondary battery can be either battery module 4 or battery pack 1.

[0181] A battery module includes at least one battery cell. The number of battery cells in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0182] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0183] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0184] 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. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0185] Figure 4 and Figure 5This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0186] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0187] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0188] Figure 6 Here is an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0189] 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.

[0190] Example

[0191] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where the technology or conditions are not specified in the embodiments, they are performed according to the technology or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0192] Preparation of primary and secondary batteries

[0193] Example 1

[0194] 1. Preparation of positive electrode sheet

[0195] Step S1: Weigh 3 mmol Na4Fe(CN)6·10H2O and slowly dissolve it in 50 mL of deionized water to prepare solution A; weigh 3 mmol FeSO4·7H2O, 10 mmol 0.01 mol trisodium citrate (TSC), and 12 mmol NaCl, and slowly dissolve them in 50 mL of deionized water to prepare solution B. At room temperature, while stirring, simultaneously add solutions A and B dropwise into 50 mL of deionized water and let stand for 24 h. Then, wash the reaction product five times with deionized water and ethanol, and dry the washed product in a vacuum drying oven at 60 °C for 24 h to obtain the Prussian blue compound Na2Fe[Fe(CN)6].

[0196] Step S2: A mixture containing 20 mg of the Prussian blue cathode material obtained in step S1 and 100 mg of polyvinyl ketone was added to a 1 mol / L hydrochloric acid solution. After mechanical stirring until homogeneous, the solution was transferred to a polytetrafluoroethylene-lined stainless steel high-pressure reactor and reacted at 140 °C for 4 h. After naturally cooling to room temperature, the product was washed three times with deionized water and ethanol, and finally dried in a vacuum drying oven at 60 °C for 24 h to obtain the porous Prussian blue compound Na2Fe[Fe(CN)6].

[0197] Step S3: Dissolve 0.2g of the porous Prussian blue-based cathode material Na2Fe[Fe(CN)6] obtained in step S2 in 30mL of deionized water. After mechanical stirring for 1 hour, add 100μL of thiophene monomer to the solution and stir for 0.5 hours. Then, add 20mL of 0.2g FeCl3·6H2O solution to the above solution and oxidize and polymerize at 25℃ for 24 hours. Wash the product three times with deionized water and ethanol, and finally dry it in a vacuum drying oven at 60℃ for 24 hours to coat the surface of the porous Prussian blue-based compound Na2Fe[Fe(CN)6] with the conductive polymer polythiophene, thus obtaining the cathode active material.

[0198] Step S4: Dissolve the above-prepared positive electrode active material, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) in solvent N-methylpyrrolidone at a mass ratio of 70:20:10. After thorough stirring and mixing, a positive electrode slurry is obtained. Then, the positive electrode slurry is uniformly coated onto the positive electrode current collector aluminum foil, and then dried, cold-pressed, and slit to obtain a positive electrode sheet.

[0199] 2. The negative electrode is a sodium negative electrode.

[0200] 3. Preparation of electrolyte

[0201] An equal volume of ethylene carbonate was dissolved in propylene carbonate, and then an appropriate amount of sodium perchlorate was dissolved in the mixed solvent to obtain the electrolyte. The concentration of the sodium salt was 1 mol / L.

[0202] 4. Preparation of the separating membrane

[0203] Glass fiber SiO2 was selected as the separator.

[0204] 5. Battery manufacturing

[0205] Battery assembly is carried out inside a glove box, which is continuously cleaned with argon gas to ensure that the water and oxygen content is less than 0.1 ppm. The specific process is as follows: the glass fiber separator is cut into 15 mm diameter discs and placed on the sodium negative electrode; 200 μL of electrolyte is added, the positive electrode is placed on the separator, and gaskets and springs are added. The positive electrode shell is then covered, and the battery is pressed tightly using a pressing machine.

[0206] Example 2

[0207] The secondary battery in Example 2 is prepared in a similar manner to the secondary battery in Example 1, except that the amount of thiophene monomer added in step S3 is 200 μL when preparing the positive electrode sheet, while all other steps are the same.

[0208] Example 3

[0209] The secondary battery in Example 3 is prepared in a similar manner to the secondary battery in Example 1, except that the amount of thiophene monomer added in step S3 is 400 μL when preparing the positive electrode sheet, while all other steps are the same.

[0210] Example 4

[0211] The secondary battery in Example 4 is prepared in a similar manner to the secondary battery in Example 2, except that the molar concentration of the hydrochloric acid solution in step S2 is 0.5 mol / L when preparing the positive electrode sheet, while all other aspects are the same.

[0212] Example 5

[0213] The secondary battery in Example 5 is prepared in a similar manner to the secondary battery in Example 2, except that the molar concentration of the hydrochloric acid solution in step S2 is 1.5 mol / L when preparing the positive electrode sheet, while all other aspects are the same.

[0214] Example 6

[0215] The preparation method of the secondary battery in Example 6 is similar to that of the secondary battery in Example 2, except that: when preparing the positive electrode active material, the precursor used in step S1 is CoCl2 in an amount equal to FeSO4·7H2O, and the obtained material is a Prussian blue compound Na2Co[Fe(CN)6]. All other aspects are the same.

[0216] Example 7

[0217] The preparation method of the secondary battery in Example 7 is similar to that of the secondary battery in Example 2, except that: when preparing the positive electrode active material, the precursor used in step S1 is MnSO4·H2O in an amount equal to FeSO4·7H2O, and the obtained product is Prussian blue compound Na2Mn[Fe(CN)6]. All other aspects are the same.

[0218] Implementation 8

[0219] The secondary battery in Example 8 is prepared in a similar manner to the secondary battery in Example 2, except that: when preparing the positive electrode active material, the precursor used in step S1 is NiCl2 in an amount equal to FeSO4·7H2O, and the obtained material is a Prussian blue compound Na2Ni[Fe(CN)6]. All other aspects are the same.

[0220] Example 9

[0221] The preparation method of the secondary battery in Example 9 is similar to that of the secondary battery in Example 2, except that: when preparing the positive electrode active material, the precursor used in step S1 is ZnCl2 in an amount equal to FeSO4·7H2O, and the obtained material is a Prussian blue compound Na2Zn[Fe(CN)6]. All other aspects are the same.

[0222] Example 10

[0223] The secondary battery of Example 10 is prepared in a similar manner to the secondary battery of Example 2, except that: when preparing the positive electrode active material, the precursor used in step S1 is CuCl2 in an amount equal to FeSO4·7H2O, and the obtained material is a Prussian blue compound Na2Cu[Fe(CN)6]. All other aspects are the same.

[0224] Example 11

[0225] The secondary battery in Example 11 is prepared in a similar manner to the secondary battery in Example 2, except that in the preparation of the positive electrode active material, an equal amount of aniline monomer is used to replace the thiophene monomer in step S3, while all other steps are the same.

[0226] Example 12

[0227] The secondary battery in Example 12 is prepared in a similar manner to the secondary battery in Example 2, except that in the preparation of the positive electrode active material, an equal amount of pyrrole monomer is used to replace the thiophene monomer in step S3, while all other steps are the same.

[0228] Example 13

[0229] The secondary battery in Example 13 is prepared in a similar manner to the secondary battery in Example 2, except that in the preparation of the positive electrode active material, an equal amount of acetylene monomer is used to replace the thiophene monomer in step S3, while all other steps are the same.

[0230] Example 14

[0231] The secondary battery in Example 14 is prepared in a similar manner to the secondary battery in Example 2, except that in the preparation of the positive electrode active material, an equal amount of thiazole monomer is used to replace thiophene monomer in step S3, while all other steps are the same.

[0232] Example 15

[0233] The secondary battery of Example 15 is prepared in a similar manner to the secondary battery of Example 2, except that in the preparation of the positive electrode active material, an equal amount of 3,4-ethylenedioxythiophene monomer is used to replace the thiophene monomer in step S3, while all other steps are the same.

[0234] Comparative Example 1

[0235] The preparation method of the secondary battery in Comparative Example 1 is similar to that of the secondary battery in Example 2, except that: when preparing the positive electrode active material, the Prussian blue compound Na2Fe[Fe(CN)6] obtained in step S1 is directly used in step S4 to prepare the positive electrode sheet, and all other aspects are the same.

[0236] Comparative Example 2

[0237] The secondary battery of Comparative Example 2 is similar to the secondary battery of Example 4 in that the preparation method is different in that step S3 is not performed when preparing the positive electrode active material, and the porous Prussian blue compound Na2Fe[Fe(CN)6] prepared in step S2 is directly used in step S4 to prepare the positive electrode sheet. All other aspects are the same.

[0238] Comparative Example 3

[0239] The secondary battery of Comparative Example 3 is similar to the secondary battery of Example 2 in that the preparation method is different in that step S3 is not performed when preparing the positive electrode active material, and the porous Prussian blue compound Na2Fe[Fe(CN)6] prepared in step S2 is directly used in step S4 to prepare the positive electrode sheet. All other aspects are the same.

[0240] Comparative Example 4

[0241] The preparation method of the secondary battery in Comparative Example 4 is similar to that of the secondary battery in Example 5, except that step S3 was not performed when preparing the positive electrode active material, and the porous Prussian blue compound Na2Fe[Fe(CN)6] prepared in step S2 was directly used in step S4 to prepare the positive electrode sheet. All other steps are the same.

[0242] Comparative Example 5

[0243] The secondary battery of Comparative Example 5 is similar to the secondary battery of Example 2 in that the preparation method is similar, except that step S3 is not performed when preparing the positive electrode active material, the molar concentration of hydrochloric acid solution in step S2 is 2 mol / L, and the porous Prussian blue compound Na2Fe[Fe(CN)6] prepared in step S2 is directly used in step S4 to prepare the positive electrode sheet. All other aspects are the same.

[0244] Comparative Example 6

[0245] The secondary battery of Comparative Example 6 is prepared in a similar manner to the secondary battery of Example 2, except that step S2 is not performed when preparing the positive electrode active material, and the Prussian blue compound Na2Fe[Fe(CN)6] prepared in step S1 is directly used to coat the conductive polymer in step S3. All other aspects are the same.

[0246] The secondary batteries prepared in the above embodiments and comparative examples were subjected to parameter tests including at least the following:

[0247] The Dv80 of the positive electrode active material, the average pore size of the porous Prussian blue compound pore structure, and the thickness of the coating layer of the positive electrode active material were measured. The test results are shown in Table 1.

[0248] The different preparation parameters mentioned in the above embodiments and comparative examples are shown in Table 1.

[0249] Table 1

[0250]

[0251] In Table 1, concentration refers to the solubility of the acidic solution, and n refers to the mass-volume ratio of porous Prussian blue compounds and polymer monomers in step S3 of the positive electrode preparation process.

[0252] It should be noted that the average pore size of the porous Prussian blue compounds in Table 1 was determined using the following method:

[0253] First, nitrogen adsorption isotherms were obtained using a nitrogen adsorption-desorption apparatus. Then, the pore size distribution was calculated according to the Barrett-Joyner-Halenda (BJH) method to obtain the average pore size of the pore structure and determine the type of pore structure. The nitrogen adsorption-desorption apparatus used was the NOVA 1000e nitrogen adsorption-desorption apparatus from Quanta Instruments, Inc.

[0254] The coating thickness of the positive electrode active material in Table 1 was determined by the following method: the secondary battery was disassembled, powder was scraped from the positive electrode sheet, the powder was dispersed in anhydrous ethanol and sonicated for half an hour; the sonicated solution was dropped onto the carbon film, dried, and then characterized by TEM to measure the coating thickness.

[0255] The Dv80 of the positive electrode active material in Table 1 was determined by the following method: 0.036g of the sample to be tested was placed at the bottom of a beaker, 1mL of surfactant (20% polyvinylpyrrolidone aqueous solution) was added, and the sample was pre-sonicated at 180W and 53KHz for 30s. Then, 20mL of anhydrous ethanol was added and sonicated for 3min. Finally, the particle size was determined using a Mastersizer 2000E laser particle size analyzer.

[0256] II. Performance Testing

[0257] The rate performance and cycle performance of the secondary batteries in the above embodiments and comparative examples were tested using the Xinwei CT-4008Tn battery testing system. The battery voltage test window was 2.0V-4.2V vs. Li+ / Li, and the batteries were tested at 25°C, where 1C = 100 mA / g. The test methods are as follows:

[0258] Rate performance testing: The capacitor was charged at a constant current rate of 0.33C to a cutoff voltage of 4.2V, allowed to stand for 5 minutes, and then discharged at a rate of 0.33C to a cutoff voltage of 2.0V, allowed to stand for 5 minutes. This charging and discharging cycle was repeated 10 times, and the average value was used to obtain the discharge specific capacity at 0.33C. The discharge specific capacity was then measured using the same method at rates of 1C, 3C, 6C, and 10C.

[0259] Cyclic performance test: After activating the battery at a rate of 0.1C for 3 cycles, charge it at a constant current rate of 0.33C to the cutoff voltage of 4.2V, and let it rest for 5 minutes; then discharge it at a rate of 0.33C to the cutoff voltage of 2.0V, and let it rest for 5 minutes; calculate C. n / C0*100 is the number of revolutions at 80%.

[0260] The performance test results of the above embodiments and comparative examples are shown in Table 2.

[0261] Table 2

[0262]

[0263] As can be seen from the comparison of the results of Examples 1-15 and Comparative Examples 1-6 in Table 2, by using porous Prussian blue compounds with porous structures and coating the surface of porous Prussian blue with conductive polymers, the ionic conductivity, electronic conductivity and structural stability of the positive electrode active material can be improved, thereby improving the rate performance and cycle performance of the positive electrode active material, and further improving the rate performance and cycle performance of the secondary battery using the positive electrode active material.

[0264] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0265] 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 secondary battery, characterized in that, The positive electrode includes a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising: The core, comprising porous Prussian blue compounds; and A coating layer covering at least a portion of the surface of the core, the coating layer comprising a conductive polymer.

2. The secondary battery as described in claim 1, characterized in that, The porous Prussian blue compounds have pore structures including one or more of macropores and mesopores.

3. The secondary battery according to any one of claims 1 to 2, characterized in that, The average pore size of the pore structure is 3nm-30nm.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The Dv80 of the positive electrode active material is 1μm-1.15μm.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The porous Prussian blue compound has the chemical formula Na2M[Fe(CN)6], where M is one or more of Fe, Mn, Co, Ni, Cu, and Zn.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The conductive polymer has a conjugated structure and π delocalized electrons on its main chain.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The conductive polymer includes one or more of polyaniline and its derivatives, polypyrrole and its derivatives, polyacetylene and its derivatives, polythiophene and its derivatives, and polythiazole and its derivatives.

8. The secondary battery as described in claim 7, characterized in that, The polythiophene derivatives include poly(3,4-ethylenedioxythiophene).

9. The secondary battery according to any one of claims 1 to 8, characterized in that, The thickness of the coating layer is 10nm-50nm.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, The secondary battery is a sodium-ion battery.

11. A positive electrode plate, characterized in that, The positive electrode sheet comprises a positive electrode active material, which includes: The core, comprising porous Prussian blue compounds; and A coating layer covering at least a portion of the surface of the core, the coating layer comprising a conductive polymer.

12. The positive electrode sheet as described in claim 11, characterized in that, The positive electrode sheet in the secondary battery according to any one of claims 2 to 9.

13. A positive electrode active material, characterized in that, The positive electrode active material includes: The core, comprising porous Prussian blue compounds; and A coating layer covering at least a portion of the surface of the core, the coating layer comprising a conductive polymer.

14. The positive electrode active material as described in claim 13, characterized in that, The positive electrode active material in the secondary battery according to any one of claims 2 to 9.

15. A method for preparing a positive electrode active material, characterized in that, Includes the following steps: Porous Prussian blue compounds were prepared by thermally reacting a mixture of Prussian blue compounds, polyvinylpyrrolidone, and an acidic solution. The positive electrode active material is prepared by oxidative polymerization of a solution containing the porous Prussian blue compound, a polymer monomer, and an oxidant to coat at least a portion of the surface of the porous Prussian blue compound with a conductive polymer.

16. The preparation method according to claim 15, characterized in that, The molar concentration of the acidic solution is 0.5 mol / L to 1.5 mol / L.

17. The preparation method according to claim 16, characterized in that, The ratio of the Prussian blue compound, povidone, and acidic solution is 1 g:(5-25) g:(1-5) L.

18. The preparation method according to any one of claims 15 to 17, characterized in that, The temperature of the thermal reaction is 100℃-200℃, and the time is 20h-30h.

19. The preparation method according to any one of claims 15 to 18, characterized in that, The acidic substances contained in the acidic solution include one or more of hydrochloric acid and sulfuric acid.

20. The preparation method according to any one of claims 15 to 19, characterized in that, The polymer monomers include one or more of aniline and its derivatives, pyrrole and its derivatives, acetylene and its derivatives, thiophene and its derivatives, and thiazole and its derivatives.

21. The preparation method according to claim 20, characterized in that, The mass-to-volume ratio of the porous Prussian blue compound to the polymer monomer is 2 g:(1-4) mL.

22. An electrical appliance, characterized in that, It includes the secondary battery according to any one of claims 1 to 10, the positive electrode sheet according to any one of claims 11 to 12, or the positive electrode active material according to any one of claims 13 to 14.

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