Polyanion sodium-containing positive electrode material and preparation method therefor, positive electrode sheet, battery, and electric device

Abstract

A polyanion sodium-containing positive electrode material and a preparation method therefor, a positive electrode sheet, a battery, and an electric device, relating to the field of batteries. The polyanion sodium-containing positive electrode material is NaxRyPmOn, wherein 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m≤ 4.2, 14.5≤n≤15.5, and R comprises at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb; the degree of sphericity of the polyanion sodium-containing positive electrode material is 0.44-0.9, and the average pore diameter is 5 nm to 35 nm. The polyanion sodium-containing positive electrode material has both relatively high degree of sphericity and a low average pore diameter, thereby effectively improving the powder compaction density of the polyanion sodium-containing positive electrode material.

Description

Polyanionic sodium-containing cathode materials and their preparation methods, cathode sheets, batteries and electrical devices Cross-references

[0001] This application claims priority to Chinese Patent Application No. 202410494833.1, filed on April 23, 2024, entitled “Polyanionic Sodium-Containing Cathode Material and Preparation Method Thereof, Cathode Sheet, Battery and Electrical Device Thereof”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of batteries, and more specifically, to a polyanionic sodium-containing cathode material and its preparation method, cathode sheet, battery, and electrical device. Background Technology

[0003] Cathode materials play a crucial role in the electrochemical performance of sodium-ion batteries. Taking sodium iron pyrophosphate as an example, polyanionic sodium-containing cathode materials can shorten the pores for sodium ion insertion and extraction, and improve the ion diffusion rate of the material, thereby obtaining good electrochemical performance and rate performance.

[0004] However, since the surface of existing polyanionic sodium-containing cathode materials is usually covered with pores, the compaction density of the powder is severely reduced, which is not conducive to improving the volumetric energy density of the battery cell and greatly restricts the application of sodium iron pyrophosphate. Summary of the Invention

[0005] In view of the above problems, this application provides a polyanionic sodium-containing cathode material and its preparation method, cathode sheet, battery and power device, which can improve the technical problem of low compaction density of existing polyanionic sodium-containing cathode material powder.

[0006] In a first aspect, embodiments of this application provide a polyanionic sodium-containing cathode material, wherein the polyanionic sodium-containing cathode material is Na x R y P m O n Wherein, 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m≤4.2, 14.5≤n≤15.5, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb; the sphericity of the polyanionic sodium-containing cathode material is 0.44-0.9, and the average pore size is 5nm-35nm.

[0007] In the technical solution of this application embodiment, by taking into account both high sphericity and low average pore size, the powder compaction density of polyanionic sodium-containing cathode material is effectively improved, which is conducive to improving the volumetric energy density after battery processing and effectively enhancing the material performance competitiveness of polyanionic sodium-containing cathode material in the sodium battery cathode material industry.

[0008] In some embodiments, the sphericity is 0.45-0.9; and / or the average pore size is 15nm-32nm. By controlling the sphericity and average pore size within the above ranges, it is beneficial to improve the powder compaction density of polyanionic sodium-containing cathode materials.

[0009] In some embodiments, the specific surface area of ​​the polyanionic sodium-containing cathode material is 7 m². 2 / g-11m 2 / g; and / or, the volumetric particle size distribution Dv50 of the polyanionic sodium-containing cathode material is 0.7μm-3μm, and the volumetric particle size distribution Dv90 is 4μm-6μm. By controlling the specific surface area and / or volumetric particle size distribution within the above ranges, it is beneficial to further improve the powder compaction density.

[0010] In some embodiments, the compacted density of the polyanionic sodium-containing cathode material powder is 1.9 g / cm³ under a pressure of 3T. 3 -2.1g / cm 3 By controlling the particle morphology, average pore size, and particle size of polyanionic sodium-containing cathode materials, it is possible to achieve high powder compaction density under 3T pressure.

[0011] In some embodiments, the surface of the polyanionic sodium-containing cathode material is coated with a carbon coating layer. The introduction of the carbon coating layer helps to improve the conductivity and electrochemical performance of the polyanionic sodium-containing cathode material.

[0012] In some embodiments, the polyanionic sodium-containing cathode material is Na x R y P m O n Wherein, 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m<4, 14.5≤n≤15.5, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb. The above-mentioned polyanionic sodium-containing cathode materials exhibit superior electrochemical performance.

[0013] In some embodiments, the polyanionic sodium-containing cathode material includes sodium iron pyrophosphate, wherein the chemical formula of sodium iron pyrophosphate is (a1) or (a2):

[0014] (a1)Na x Fe y (PO4)2P2O7, 3.5≤x≤4.5, 2.75≤y≤3.25;

[0015] (a2)Na x Fe y P m O n The following parameters are given: 3.5 ≤ x ≤ 4.5, 2.5 ≤ y ≤ 3.5, 3.7 < m < 4, 14.5 ≤ n ≤ 15.5. The above-mentioned sodium iron pyrophosphate exhibits superior electrochemical performance.

[0016] Secondly, embodiments of this application provide a method for preparing a polyanionic sodium-containing cathode material, comprising:

[0017] The sodium-containing polyanionic substrate and grinding balls were placed together in a ball milling jar, and dry ball milling was carried out in an inert atmosphere inside the ball milling jar.

[0018] Polyanionic sodium-containing cathode materials are Na x R y P m O n Wherein, 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m≤4.2, 14.5≤n≤15.5, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb. The sphericity of the polyanionic sodium-containing cathode material is 0.44-0.9, and the average pore size is 5nm-35nm. The polyanionic sodium-containing cathode material provided in this application reduces the average pore size of the polyanionic sodium-containing material and improves its sphericity to a certain extent by ball milling and shaping the polyanionic sodium-containing substrate, thereby increasing the powder compaction density of the polyanionic sodium-containing cathode material.

[0019] In some embodiments, the rotational speed of the ball mill jar is 150 RPM-1000 RPM, and the dry ball milling time is at least 1 hour. By controlling the rotational speed of the ball mill jar and the ball milling time within the above range, it is beneficial to improve the powder compaction density of the polyanionic sodium-containing cathode material.

[0020] In some embodiments, the grinding balls include a first grinding ball, a second grinding ball, and a third grinding ball. The diameter of the first grinding ball is 3-6 mm, the diameter of the second grinding ball is ≤9 mm (6 mm < 2 mm), and the diameter of the third grinding ball is ≤15 mm (9 mm < 3 mm). By selecting first, second, and third grinding balls of different specifications to work together, the shaping efficiency and effect are effectively improved, the average pore size is effectively reduced, and the sphericity is improved, which is beneficial to increasing the powder compaction density of polyanionic sodium-containing cathode materials.

[0021] In some embodiments, the mass ratio of the first grinding ball, the second grinding ball, and the third grinding ball is 1-3:1-2:1. Controlling the mass ratio within the above range is beneficial for improving the shaping efficiency and the compaction density of the shaped polyanionic sodium-containing cathode material powder.

[0022] In some embodiments, the volume ratio of the polyanionic sodium-containing substrate to the grinding balls is 2-3:1; and / or,

[0023] The temperature of dry ball milling should not exceed 80°C. Controlling the ball-to-material volume ratio within this range is beneficial for improving the compaction density of the shaped polyanionic sodium-containing cathode material powder. Controlling the dry ball milling temperature to no more than 80°C helps to suppress the potential generation of byproducts that could affect the capacity of the polyanionic sodium-containing cathode material if the temperature is too high during dry ball milling. In some embodiments, the total volume of the grinding balls and the polyanionic sodium-containing substrate does not exceed 80% of the volume of the ball mill jar. This configuration facilitates thorough ball milling and shaping.

[0024] In some embodiments, the polyanionic sodium-containing substrate has a Dv50 of 1.8 μm-4.5 μm, a Dv90 of 4 μm-6 μm, a sphericity of 0.35-0.45, and an average pore size of 5 nm-80 nm.

[0025] In some embodiments, the polyanionic sodium-containing substrate includes sodium iron pyrophosphate, wherein the chemical formula of sodium iron pyrophosphate is (b1) or (b2):

[0026] (b1)Na x Fe y (PO4)2P2O7, 3.5≤x≤4.5, 2.75≤y≤3.25;

[0027] (b2)Na x Fe y P m O n , 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m<4, 14.5≤n≤15.5.

[0028] The aforementioned sodium ferric pyrophosphate exhibits superior electrochemical performance.

[0029] In some embodiments, the polyanionic sodium-containing substrate is a carbon-coated sodium iron pyrophosphate substrate, which is prepared by the following method:

[0030] Sodium salt, iron source, phosphorus source and organic carbon source are wet-mixed according to chemical formula, dried to obtain raw material, sintered under an inert atmosphere, and the obtained sintered product is pulverized; the carbon-coated iron pyrophosphate sodium prepared by the above preparation method has better electrochemical performance.

[0031] In some embodiments, the raw material is pulverized to a volumetric particle size distribution D before sintering in an inert atmosphere. V 50 has a particle size of 0.5μm-4μm. Adding a crushing process to the raw materials before sintering helps to improve the powder compaction density of the material.

[0032] Thirdly, this application provides a positive electrode sheet, which includes the polyanionic sodium-containing positive electrode material in the above embodiments.

[0033] Fourthly, this application provides a battery that includes the positive electrode sheet in the above embodiments.

[0034] Fifthly, this application provides an electrical device that includes the battery described in the above embodiments, the battery being used to provide electrical energy.

[0035] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0036] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0037] Figure 1 is a schematic diagram of the vehicle structure according to some embodiments of this application;

[0038] Figure 2 is an exploded structural diagram of a battery according to some embodiments of this application;

[0039] Figure 3 is an exploded structural diagram of a battery cell according to some embodiments of this application;

[0040] Figure 4 is a SEM image of the base material 1 used before ball milling and shaping in Example 1 of this application;

[0041] Figure 5 is a SEM image of the sodium iron pyrophosphate cathode material obtained after ball milling and shaping in Example 1 of this application.

[0042] The reference numerals in the detailed embodiments are as follows:

[0043] 1000 - Vehicles;

[0044] 100 - Battery; 200 - Controller; 300 - Motor;

[0045] 10-Box body; 11-First part; 12-Second part;

[0046] 20-Battery cell; 21-Casing; 22-Electrode assembly; 23-Electrode terminal; 24-Pressure relief structure;

[0047] 211-Shell; 212-Cover. Detailed Implementation

[0048] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0050] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0051] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0052] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0053] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0054] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0055] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0056] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0057] Cathode materials play a crucial role in the electrochemical performance of sodium-ion batteries. However, existing polyanionic sodium-containing cathode materials, such as sodium iron pyrophosphate and sodium vanadium phosphate, typically have pores on their microparticle surfaces, which leads to a significant reduction in powder compaction density. This is detrimental to improving the volumetric energy density of the battery cell and greatly restricts the application of polyanionic sodium-containing cathode materials.

[0058] To address the technical problem of low compaction density in existing polyanionic sodium-containing cathode materials, ball milling is used to physically shape the polyanionic sodium-containing materials. This method helps to open closed pores, smooth surface pores, reduce the average pore size, and effectively reduce the gap between particles, thereby effectively improving the compaction density of the powder. Furthermore, the ball milling method also helps to make the particle surface more rounded, which is also conducive to further improving the compaction density of the powder.

[0059] Therefore, in order to alleviate the technical problem of low powder compaction density in existing polyanionic sodium-containing cathode materials, this application provides a polyanionic sodium-containing cathode material, wherein the polyanionic sodium-containing cathode material is Na x R y P m O n Wherein, 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m≤4.2, 14.5≤n≤15.5, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb; the sphericity of this polyanionic sodium-containing cathode material is 0.44-0.9, and the average pore size is 5nm-35nm.

[0060] The polyanionic sodium-containing cathode material provided in this application, by taking into account both high sphericity and low average pore size, effectively improves the powder compaction density of the polyanionic sodium-containing cathode material, thereby helping to improve the volumetric energy density after battery processing and effectively enhancing the material performance competitiveness of the polyanionic sodium-containing cathode material in the sodium battery cathode material industry.

[0061] The batteries disclosed in this application can be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft. A power system comprising such an electrical device can be used, incorporating batteries disclosed in this application. This helps to alleviate and improve the powder compaction density of polyanionic sodium-containing cathode materials, thereby increasing the volumetric energy density of the battery.

[0062] This application provides an electrical device that uses a battery as a power source. The electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0063] For ease of explanation, the following embodiments will be described using a vehicle 1000 as an example of an electrical device according to an embodiment of this application.

[0064] Please refer to Figure 1, which is a structural schematic diagram of a vehicle 1000 provided in some embodiments of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 100 is disposed inside the vehicle 1000, and the battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0065] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0066] In this application, battery 100 refers to a single physical module including one or more battery cells 20 to provide a certain voltage and capacity. It can be in the form of battery pack, battery module, etc. Battery 100 may also include a housing 10 for encapsulating one or more battery cells 20. The housing 10 can prevent liquids or other foreign objects from affecting the charging or discharging of the battery cells 20.

[0067] Please refer to Figure 2, which is an exploded view of a battery 100 provided in some embodiments of this application. The battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 provides a space for the battery cell 20 and can have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, jointly defining a space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 jointly define the space. Alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one open side, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can have various shapes, such as a cylinder, a cuboid, etc.

[0068] In battery 100, there can be multiple battery cells 20, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, battery 100 can also be composed of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the housing 10. Battery 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 20.

[0069] Battery cell 20 refers to the smallest unit that makes up battery 100.

[0070] Please refer to Figure 3, which is an exploded structural diagram of a battery cell 20 provided in some embodiments of this application. Referring to Figure 3, the battery cell 20 may include a housing 21, an electrode assembly 22, and an electrolyte, with the electrode assembly 22 and the electrolyte both housed within the housing 21.

[0071] The outer casing 21 may include a housing 211 and a cover 212. The housing 211 is an assembly that fits with the cover 212 to form an internal sealed space for the battery cell 20, wherein the formed sealed space can accommodate the electrode assembly 22, electrolyte, and other components. The cover 212 is a component that covers the opening of the housing 211 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the cover 212 may be adapted to the shape of the housing 211 to fit the housing 211, and the cover 212 may also be provided with functional components such as electrode terminals 23 and pressure relief structures 24. A sealing ring may be provided between the opening of the housing 211 and the cover 212 to achieve a seal between the housing 211 and the cover 212.

[0072] The housing 211 and cover 212 can be of various shapes and sizes, such as cuboids, cylinders, and hexagonal prisms. Specifically, the shapes of the housing 211 and cover 212 can be determined according to the specific shape and size of the electrode assembly 22. The materials of the housing 211 and cover 212 can be various, such as, but not limited to, metals like copper, iron, aluminum, stainless steel, and aluminum alloys. The materials of the sealing ring can be various, such as, but not limited to, materials resistant to electrolyte corrosion, high toughness, and fatigue resistance, such as PP (polypropylene), PC (polycarbonate), and PET (polyethylene terephthalate). A plating layer can be formed on the outer surface of the housing 211, and the plating layer material can be various, such as, but not limited to, corrosion-resistant materials like Ni and Cr.

[0073] The battery cell 20 can also be in a pouch form, such as a bag-type pouch. The material of the pouch can be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0074] The electrode assembly 22 includes a negative electrode, a separator, and a positive electrode. The battery cell 20 primarily functions by the movement of metal ions between the positive and negative electrodes. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through. The electrode assembly 22 can be a wound structure or a stacked structure; this embodiment is not limited to either.

[0075] The negative electrode sheet includes a negative current collector, a negative electrode tab, and a negative active material layer. The negative active material layer is disposed on at least one side of the negative current collector, and a base coating layer may also be disposed between the negative current collector and the negative active material layer. The negative electrode tab protrudes from the negative current collector and is located, for example, at one end of the negative current collector or at opposite ends.

[0076] In one implementation, the negative electrode sheet includes a negative current collector and a base coating, but does not contain a negative active material layer.

[0077] The negative electrode current collector can be a metal foil or a composite current collector. For example, the materials of the negative electrode current collector and the negative electrode tab can be copper. The composite current collector can include a polymer material base layer and a metal layer formed on at least one side of the polymer material powder. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material powder (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc. powder).

[0078] In some embodiments, the negative electrode material in the negative electrode active material layer includes, but is not limited to, at least one of hard carbon, soft carbon, graphite, silicon, silicon-carbon negative electrode materials, etc.

[0079] In some embodiments, the negative electrode active material 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).

[0080] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0081] 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)).

[0082] The separator is located between the positive electrode and the negative electrode, and plays a role in isolation. The embodiments of this application do not have any particular restrictions on the type of separator, and any well-known porous structure separator with good chemical and mechanical stability can be selected.

[0083] 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.

[0084] The positive electrode sheet includes a positive current collector, a positive electrode tab, and a positive active material layer. The positive active material layer is disposed on at least one side of the positive current collector, and an undercoating layer may also be disposed between the positive active material layer and the positive current collector. The positive electrode tab protrudes from the positive current collector and is located, for example, at one end of the positive current collector or at opposite ends.

[0085] The positive current collector can be a metal foil or a composite current collector. For example, the materials of the positive current collector and the positive electrode tab can be aluminum. The composite current collector may include a polymer material base layer and a metal layer formed on at least one side of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material powder (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc. powder).

[0086] The positive electrode active material layer includes a positive electrode material, which includes a polyanionic sodium-containing positive electrode material.

[0087] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0088] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0089] According to some embodiments of this application, this application provides a polyanionic sodium-containing cathode material, wherein the polyanionic sodium-containing cathode material is Na x R y P m O n Wherein, 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m≤4.2, 14.5≤n≤15.5, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb; the sphericity of this polyanionic sodium-containing cathode material is 0.44-0.9, and the average pore size is 5nm-35nm.

[0090] Sphericity measures the degree to which particles tend towards a spherical shape. A higher sphericity indicates a more spherical structure. By controlling the sphericity of polyanionic sodium-containing cathode materials to 0.44-0.9, compared to particles with uneven surfaces, it helps reduce the gaps between particles, increases the compaction density of the electrode powder, and thus improves the volumetric energy density of the battery. Sphericity can be determined by using a scanning electron microscope (SEM) to capture images of the polyanionic sodium-containing cathode material, importing them into IPP software for segmentation, and calculating the ratio of the particle's perimeter equivalent diameter to its area equivalent diameter using the software's calculation function. The average sphericity is then used as the sphericity of the sodium iron pyrophosphate cathode material.

[0091] For example, the sphericity of the polyanionic sodium-containing cathode material is any value of 0.44, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.80, or 0.90, or between any two values.

[0092] The average aperture can be obtained by analyzing high-resolution transmission electron microscopy. Representative areas of the magnified electron image are selected, the apertures of the through holes are counted, and the average aperture of more than 10 representative areas is taken to obtain the average aperture.

[0093] By controlling the average pore size of the polyanionic sodium-containing cathode material to be between 5 nm and 35 nm, it is beneficial to improve the compaction density of the electrode powder and enhance the volumetric energy density of the battery. The average pore size can be determined by analyzing a representative region in a magnified electron microscope image using high-resolution transmission electron microscopy, statistically analyzing the percentage of through-holes, and selecting at least 10 representative regions, for example, by averaging the values ​​of 10 regions. For example, the average pore size of the polyanionic sodium-containing cathode material can be any value from 5 nm, 15 nm, 20 nm, 25 nm, 30 nm, or 35 nm, or between any two values.

[0094] It should be noted that the sphericity and average pore size measurements are for secondary particles, which are aggregates of primary particles.

[0095] In summary, the polyanionic sodium-containing cathode material provided in this application, by combining high sphericity and low average pore size, effectively improves the powder compaction density of the polyanionic sodium-containing cathode material, thereby helping to improve the volumetric energy density after battery processing and effectively enhancing the material performance competitiveness of the polyanionic sodium-containing cathode material in the sodium battery cathode material industry.

[0096] According to some embodiments of this application, the sphericity is 0.45-0.9; and / or,

[0097] The average pore size is 15nm-32nm.

[0098] By controlling the sphericity of the polyanionic sodium-containing cathode material within the above-mentioned range, and / or controlling the average pore size of the polyanionic sodium-containing cathode material within the above-mentioned range, it is beneficial to improve the powder compaction density of the polyanionic sodium-containing cathode material.

[0099] For example, the sphericity of the polyanionic sodium-containing cathode material is any value of 0.45, 0.46, 0.50, 0.55, 0.60, 0.61, 0.65, or 0.90, or between any two values.

[0100] For example, the average pore size of the polyanionic sodium-containing cathode material is any value of 15nm, 18nm, 20nm, 21nm, 22nm, 25nm, 30nm, or 32nm, or between any two values.

[0101] According to some embodiments of this application, the specific surface area of ​​the polyanionic sodium-containing cathode material is 7m². 2 / g-11m 2 / g; and / or, the volumetric particle size distribution Dv50 of the polyanionic sodium-containing cathode material is 0.7μm-3μm, and the volumetric particle size distribution Dv90 is 4μm-6μm.

[0102] Specific surface area refers to the total surface area per unit mass of a substance. Specific surface area can be measured using instruments and methods known in the art, such as nitrogen adsorption specific surface area analysis and calculated using the BET method.

[0103] Both volumetric particle size distribution Dv50 and volumetric particle size distribution Dv90 refer to particle size distribution parameters determined by particle size distribution measurements. In this application, the testing of volumetric particle size distribution Dv50 and volumetric particle size distribution Dv90 involves: firstly, ultrasonically dispersing the polyanionic sodium-containing cathode material, and then measuring the particle size distribution to obtain the volumetric particle size distribution Dv50 and volumetric particle size distribution Dv90. For example, both volumetric particle size distribution Dv50 and volumetric particle size distribution Dv90 are determined by particle size analyzer-laser diffraction after ultrasonic dispersion. Specifically, refer to standard GB / T 19077-2016, which uses a laser diffraction scattering particle size analyzer for measurement.

[0104] It should be noted that the specific surface area and volumetric particle size distribution measurements are for secondary particles, which are aggregates of primary particles.

[0105] By controlling the specific surface area of ​​the polyanionic sodium-containing cathode material within the above-mentioned range, and / or the volumetric particle size distribution within the above-mentioned range, it is beneficial to further improve the powder compaction density.

[0106] For example, the specific surface area of ​​the polyanionic sodium-containing cathode material is 7m². 2 / g、8m 2 / g、9m 2 / g, 9.5m 2 / g, 10m 2 / g, 10.5m 2 / g、11m 2 Any value in / g or between any two values.

[0107] For example, the volumetric particle size distribution Dv50 of the polyanionic sodium-containing cathode material is any value of 0.9μm, 1μm, 1.3μm, 1.5μm, 1.7μm, 2.0μm, 2.3μm, 2.5μm, 2.7μm, 3.0μm or between any two values, and the volumetric particle size distribution Dv90 is any value of 4.0μm, 4.5μm, 5.0μm, 5.5μm, 5.8μm, 6.0μm or between any two values.

[0108] Understandably, with sphericity and average pore size remaining constant, smaller particle size results in smaller gaps between particles, which is more conducive to increasing powder compaction density.

[0109] According to some embodiments of this application, the compaction density of the polyanionic sodium-containing cathode material powder is 1.9 g / cm³ under 3T pressure. 3 -2.1g / cm 3 .

[0110] Among them, the compaction density of powder can be tested using a powder compaction density meter.

[0111] This application achieves a powder compaction density of 1.9 g / cm³ under 3T pressure by controlling the particle morphology, average pore size, and particle size of the polyanionic sodium-containing cathode material. 3 This gives it a high powder compaction density.

[0112] For example, the compacted density of the polyanionic sodium-containing cathode material under a pressure of 3T is 1.90 g / cm³. 3 1.95g / cm 3 2.00g / cm 3 2.05g / cm 3 2.10 g / cm 3 It can be any value in the range or any two values ​​in between.

[0113] It should be noted that the polyanionic sodium-containing cathode material can be composed entirely of polyanionic sodium-containing material, or it can have a polyanionic sodium-containing material as the core and a coating layer on the surface, wherein the composition of the coating layer includes, but is not limited to, carbon.

[0114] According to some embodiments of this application, the surface of the polyanionic sodium-containing cathode material has a carbon coating layer.

[0115] The introduction of carbon coating is beneficial to improving the conductivity and electrochemical performance of polyanionic sodium-containing cathode materials.

[0116] Optionally, the carbon content in the polyanionic sodium-containing cathode material is 1wt%-3.5wt%, and / or the thickness of the carbon layer is 2.5nm-30nm. By controlling the carbon content in the cathode material within the above-mentioned suitable range and / or the carbon coating within the above-mentioned suitable thickness range, it is beneficial to improve the conductivity of the cathode material and the electrochemical performance of the cathode material.

[0117] According to some embodiments of this application, the polyanionic sodium-containing cathode material is Na. x R y P m O nWherein, 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m<4, 14.5≤n≤15.5, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0118] The above-mentioned polyanionic sodium-containing cathode material structure exhibits excellent electrochemical performance and rate performance.

[0119] According to some embodiments of this application, the polyanionic sodium-containing cathode material includes sodium iron pyrophosphate, wherein the chemical formula of sodium iron pyrophosphate is (a1) or (a2):

[0120] (a1)Na x Fe y (PO4)2P2O7, 3.5≤x≤4.5, 2.75≤y≤3.25.

[0121] The aforementioned sodium iron pyrophosphate exhibits excellent electrochemical and rate performance, and has a wide range of applications.

[0122] Alternatively, 3.9 ≤ x ≤ 4.2, 2.8 ≤ y ≤ 3.1.

[0123] For example, the chemical formula of sodium iron pyrophosphate is: Na 4.1 Fe 2.95 (PO4)2P2O7 or Na4Fe3(PO4)2P2O7.

[0124] (a2)Na x Fe y P m O n , 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m<4, 14.5≤n≤15.5.

[0125] Introducing phosphorus vacancies facilitates the growth of its crystal lattice along the (602) crystal plane, shortening the Na... + The transmission path improves Na + The diffusion rate is beneficial to the rate performance and initial coulombic efficiency of the battery.

[0126] It should be noted that during the charging and discharging process of the battery, Na undergoes insertion / extraction and consumption, resulting in different molar Na contents at different discharge states. In the chemical formula of the polyanionic sodium-containing cathode material in this application, the molar Na content represents the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the molar Na content changes after charge-discharge cycles. The molar O content is only a theoretical value; lattice oxygen release causes changes in the molar O content, resulting in fluctuations in the actual molar O content.

[0127] According to some embodiments of this application, this application also provides a method for preparing a polyanionic sodium-containing cathode material, which includes:

[0128] The sodium-containing polyanionic substrate and grinding balls were placed together in a ball milling jar, and dry ball milling was carried out in an inert atmosphere inside the ball milling jar.

[0129] Polyanionic sodium-containing cathode materials are Na x R y P m O n Wherein, 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m≤4.2, 14.5≤n≤15.5, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb. The sphericity of the polyanionic sodium-containing cathode material is 0.44-0.9, and the average pore size is 5nm-35nm.

[0130] Among them, the polyanionic sodium-containing substrate (hereinafter referred to as substrate) refers to the raw material obtained by mixing the corresponding raw materials according to the chemical formula during the mass production process. After the raw material is sintered, the sintered product that shrinks into a slab or directly into a hard block is crushed into powder. It can be purchased directly or prepared by itself, and there is no limitation here. Usually, the raw material obtained by mixing the corresponding raw materials according to the chemical formula is obtained by sand milling and drying the corresponding raw materials. As a result, the sodium-containing raw materials dissolve in water during the sand milling process and are easy to solidify into a whole after drying. Thus, the polyanionic sodium-containing substrate after sintering contains pores caused by the exhaust gas during sintering.

[0131] It should be noted that the purpose of pulverization is only to crush sintered products that are hardened or directly in the form of hard blocks into powder. It cannot effectively eliminate the surface pores of micro particles, so that a large number of pores still exist on the surface of the particles of the substrate, and some particles may even be damaged, making the surface uneven.

[0132] Dry ball milling effectively utilizes the high-speed movement and collision of grinding balls in the milling jar to mechanically crush and physically shape the substrate. This process breaks down large particles, opens closed pores in the substrate particles, smooths surface pores, significantly reduces the average pore size, and effectively reduces the gap between particles. As a result, high sphericity and low average pore size polyanionic sodium-containing cathode materials are obtained, which in turn effectively improves the powder compaction density of polyanionic sodium-containing cathode materials.

[0133] It should be noted that when the sodium-containing polyanionic substrate is sodium iron pyrophosphate substrate, it contains divalent iron. Therefore, in order to suppress its oxidation during the ball milling process and affect its electrochemical performance, the ball milling and shaping is carried out in an inert atmosphere in the ball milling jar. The inert atmosphere includes, but is not limited to, at least one of argon and nitrogen.

[0134] Dry ball milling refers to the process where only sodium-containing polyanionic substrates and grinding balls are present in the milling jar. Compared to wet ball milling, this method avoids the dissolution of sodium ions during the milling process, thus maintaining a high capacity for the sodium-containing polyanionic cathode material.

[0135] In summary, the polyanionic sodium-containing cathode material provided in this application reduces the average pore size of the polyanionic sodium-containing substrate and improves its sphericity to a certain extent by ball milling and shaping the polyanionic sodium-containing substrate, thereby increasing the powder compaction density of the polyanionic sodium-containing cathode material.

[0136] Among them, the ball milling method includes, but is not limited to, at least one of planetary ball mills, grid ball mills, and vertical ball mills.

[0137] According to some embodiments of this application, the rotation speed of the ball mill jar is 150RPM-1000RPM, and the dry ball milling time is at least 1 hour.

[0138] Within the aforementioned range, it is beneficial to fully utilize the crushing effect and improve the efficiency and effectiveness of the procedure.

[0139] For example, the rotational speed of the ball mill jar is any value of 150 RPM, 200 RPM, 250 RPM, 300 RPM, 500 RPM, 800 RPM, 1000 RPM, or between any two values.

[0140] For example, the dry ball milling time is any value of 1h, 1.5h, 2h, 3h, 4h or between any two values.

[0141] Optionally, the rotation speed of the ball mill jar is 200RPM-1000RPM, and the dry ball milling time is 1h-4h.

[0142] Among these, a grinding ball diameter of less than 15mm is also beneficial for improving the grinding effect.

[0143] According to some embodiments of this application, the grinding ball includes a first grinding ball, a second grinding ball, and a third grinding ball. The diameter of the first grinding ball is 3-6 mm, 6 mm < the diameter of the second grinding ball is ≤9 mm, and 9 mm < the diameter of the third grinding ball is ≤15 mm.

[0144] Larger grinding balls generate more energy during the operation of the grinding jar, enabling rapid pulverization of the sample. Smaller grinding balls, on the other hand, can improve the precision and consistency of grinding. By selecting different sizes of first, second, and third grinding balls in combination, the shaping efficiency and effect can be effectively improved, the average pore size can be reduced, and the sphericity can be increased, which is beneficial to increasing the powder compaction density of polyanionic sodium-containing cathode materials.

[0145] For example, the diameter of the first grinding ball is 6 mm, the diameter of the second grinding ball is 8 mm, and the diameter of the third grinding ball is 10 mm.

[0146] According to some embodiments of this application, the mass ratio of the first grinding ball, the second grinding ball, and the third grinding ball is 1-3:1-2:1.

[0147] By controlling the mass ratio of the first grinding ball, the second grinding ball, and the third grinding ball within the above-mentioned range, it is beneficial to improve the shaping efficiency and the compaction density of the shaped polyanionic sodium-containing cathode material.

[0148] For example, the mass ratio of the first grinding ball, the second grinding ball, and the third grinding ball is any one of 1:1:1, 1:2:3, 2:1:1, 2:2:1, 3:2:2, or 3:1:1, or between any two of them.

[0149] Grinding balls, depending on their material, include, but are not limited to, metal balls such as stainless steel and cast iron, or ceramic balls such as zirconium oxide and alumina.

[0150] Optionally, the first, second, and third grinding balls are all made of zirconium oxide.

[0151] Understandably, during ball milling, the total volume of the grinding balls and the polyanionic sodium-containing substrate is smaller than the volume of the grinding jar.

[0152] According to some embodiments of this application, the volume ratio of the polyanionic sodium-containing substrate to the grinding balls is 2-3:1; and / or,

[0153] The temperature of dry ball milling should not exceed 80℃.

[0154] If the ball-to-material volume ratio is too small, the number of grinding balls is too low, resulting in fewer impacts and grinding cycles, leading to low ball milling efficiency. If the ball-to-material volume ratio is too large, the excessive number of grinding balls affects the impact between the grinding balls, failing to fully utilize the crushing effect. Therefore, the ball-to-material volume ratio should be controlled at 2-3:1. For example, the ball-to-material ratio can be any value from 2:1, 3:1, 5:2, or 5:3, or between any two values.

[0155] Controlling the temperature of dry ball milling to no more than 80℃ helps to suppress the problem that byproducts may be generated during the dry ball milling process if the temperature is too high, which could affect the capacity of polyanionic sodium-containing cathode materials.

[0156] According to some embodiments of this application, the total volume of the grinding balls and the polyanionic sodium-containing substrate does not exceed 80% of the volume of the grinding jar.

[0157] The above settings are conducive to fully shaping the ball mill.

[0158] For example, the total volume of the grinding balls and the polyanionic sodium-containing substrate is 40%, 50%, 60%, 70%, or 80% of the volume of the grinding jar.

[0159] Optionally, the total volume of the grinding balls and the polyanionic sodium-containing substrate is 40%-60% of the volume of the grinding jar.

[0160] According to some embodiments of this application, the Dv50 of the polyanionic sodium-containing substrate is 1.8μm-4.5μm, the Dv90 is 4μm-6μm, the sphericity is 0.35-0.45, and the average pore size is 5nm-80nm.

[0161] The purpose of pulverization is merely to crush sintered products that are either hardened or in the form of solid blocks into powder. It cannot completely eliminate the microscopic surface pores of the particles, resulting in a large number of pores remaining on the surface of the particles in the substrate. In some cases, the particles are even damaged, causing the surface to be uneven, resulting in a substrate material with low sphericity and high average pore size.

[0162] Optionally, the polyanionic sodium-containing cathode material is Na x R y P m O n Wherein, 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m<4, 14.5≤n≤15.5, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0163] The above-mentioned polyanionic sodium-containing cathode material structure exhibits excellent electrochemical performance and rate performance.

[0164] According to some embodiments of this application, the polyanionic sodium-containing cathode material includes sodium iron pyrophosphate, wherein the chemical formula of sodium iron pyrophosphate is (b1) or (b2):

[0165] (b1)Na x Fe y (PO4)2P2O7, 3.5≤x≤4.5, 2.75≤y≤3.25.

[0166] The aforementioned sodium ferric pyrophosphate exhibits superior electrochemical performance and has a wide range of applications.

[0167] Alternatively, 3.9 ≤ x ≤ 4.2, 2.8 ≤ y ≤ 3.1.

[0168] For example, the chemical formula of sodium iron pyrophosphate is: Na 4.1 Fe 2.95 (PO4)2P2O7 or Na4Fe3(PO4)2P2O7.

[0169] (b2)Na x Fe y P m O n , 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m<4, 14.5≤n≤15.5.

[0170] Introducing phosphorus vacancies facilitates the growth of its crystal lattice along the (602) crystal plane, shortening the Na... + The transmission path improves Na + The diffusion rate is beneficial to the rate performance and initial coulombic efficiency of the battery.

[0171] Among them, the polyanionic sodium-containing substrate can be sodium iron pyrophosphate without a surface coating. In this case, it is prepared by the following method: the sodium salt, iron source and phosphorus source are wet-mixed according to the chemical formula, dried to obtain raw material, the raw material is sintered in a reducing atmosphere, and the obtained carbon-coated sodium pyrophosphate sintered product is pulverized.

[0172] According to some embodiments of this application, the polyanionic sodium-containing substrate is carbon-coated sodium iron pyrophosphate, which is prepared by the following method:

[0173] Sodium salt, iron source, phosphorus source and organic carbon source are wet-mixed according to chemical formula, dried to obtain raw material, sintered under an inert atmosphere, and the obtained carbon-coated sodium pyrophosphate sintered product is pulverized.

[0174] The carbon-coated polyanionic sodium-containing compounds prepared by the above method exhibit superior electrochemical performance.

[0175] Exemplarily, the sodium salt includes, but is not limited to, one or more of sodium acetate, sodium carbonate, sodium citrate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, sodium carbonate, sodium nitrate, sodium oxalate, sodium acetate, sodium sulfate, sodium hydroxide, sodium formate, sodium citrate, sodium pyrophosphate, sodium dihydrogen pyrophosphate, and sodium chloride. The phosphorus source includes, but is not limited to, one or more of ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, phosphoric acid, ferric phosphate, triammonium phosphate, pyrophosphate, ferric pyrophosphate, sodium pyrophosphate, and sodium dihydrogen pyrophosphate. The iron source includes, but is not limited to, one or more of ferric phosphate, iron(III) oxide, ferric oxide, ferric oxalate, and ferrous oxalate; the organic carbon source includes, but is not limited to, one or more of sucrose, glucose, citric acid, starch, cyclodextrin, and polyethylene glycol.

[0176] For example, wet mixing includes at least one of wet ball milling or sand milling, and the solvent that may be used in wet mixing includes water.

[0177] By way of example, drying includes, but is not limited to, spray drying.

[0178] For example, the sintering temperature is 400℃-600℃ and the sintering time is 6h-24h.

[0179] According to some embodiments of this application, the raw material is pulverized to a volume particle size distribution D before sintering in an inert atmosphere. V 50 is 0.5μm-4μm.

[0180] A pulverization process is added to the raw materials before sintering. This pre-sintering pulverization yields particles with smaller, more uniform size and a larger specific surface area. Furthermore, the raw materials have not undergone a high-temperature solid-phase reaction at this stage; after pulverization (to a volumetric particle size distribution D...), the raw materials are further pulverized. V The material is 0.5μm-4μm in size and then subjected to high-temperature solid-state reaction sintering. This process makes it less likely for gas to be generated during the high-temperature solid-state reaction sintering process. As a result, it is easier to obtain smaller and more uniform particles after sintering, which is beneficial to improving the powder compaction density of the material. This can improve the specific capacity and initial coulombic efficiency of the positive electrode active material, thereby effectively improving the volumetric energy density of the battery.

[0181] According to some embodiments of this application, this application also provides a positive electrode sheet, which includes a polyanionic sodium-containing positive electrode material of any of the above schemes.

[0182] According to some embodiments of this application, this application also provides an electrical device including a battery of any of the above-described schemes, and the battery is used to provide electrical energy to the electrical device.

[0183] The electrical device can be any of the aforementioned battery-powered devices or systems.

[0184] The following specific embodiments are provided to better illustrate this application.

[0185] The following sodium iron pyrophosphate substrate (referred to as substrate 1) is prepared by the following method:

[0186] 1. Dissolve sodium pyrophosphate (Na4P2O7), ferrous oxalate, and ferric phosphate in deionized water at a molar ratio of 1.02:0.5:2, and stir continuously at room temperature for 30 minutes to obtain an initial mixed slurry. Dissolve Super P and glucose in deionized water and mix to obtain a carbon solution.

[0187] 2. Mix the carbon solution and the initial mixed solution, and stir to obtain a mixed solution.

[0188] 3. Spray dry the above mixed solution with an inlet air temperature of 220°C and an outlet air temperature of 109°C to obtain a powdered precursor.

[0189] 4. The powdered precursor is heated to 320°C in a N2 atmosphere at a heating rate of 2°C and held for 4 hours. Then, it is heated to 550°C at a heating rate of 2°C for a first sintering of 10 hours to obtain carbon-coated iron phosphate pyrophosphate sintered material that shrinks into a slab.

[0190] 5. The carbon-coated iron sodium pyrophosphate sinter is pulverized to obtain carbon-coated Na4Fe3(PO4)2P2O7, hereinafter referred to as the substrate.

[0191] The substrate has a compacted density of 1.856 g / cm³ in 3T powder. 3 The volumetric particle size distribution Dv50 is 2.879 μm, the volumetric particle size distribution Dv90 is 5.891 μm, the specific surface area is 7.89, the sphericity is 0.41, and the average pore size is 45 nm.

[0192] The above-mentioned substrate was divided into multiple portions, and the following embodiments and comparative examples were implemented respectively.

[0193] Example 1

[0194] The substrate and grinding balls were placed in a ball milling jar according to the ball-to-material volume ratio shown in Table 1. The total volume of the substrate and grinding balls was 80% of the volume of the ball milling jar. The jar was then dry-milled for 1 hour under a nitrogen atmosphere and a rotation speed of 200 RPM to obtain sodium iron pyrophosphate cathode material.

[0195] The grinding balls are made of zirconium dioxide and consist of a first grinding ball with a diameter of 6 mm, a second grinding ball with a diameter of 8 mm, and a third grinding ball with a diameter of 10 mm, arranged in a mass ratio of 1:1:1. The temperature of dry ball milling does not exceed 80℃.

[0196] Figure 4 shows the SEM image of the substrate, and Figure 5 shows the SEM image of the sodium iron pyrophosphate cathode material after ball milling in Example 1. Comparing Figures 4 and 5, it can be seen that ball milling has significant pulverizing and shaping capabilities. After shaping, the material exhibits significantly fewer large particles, and the particles become rounded and uniform with no obvious pores on the surface, reducing the average pore size. In other words, the method provided in this application can smooth the surface of the substrate particles and reduce the gaps between particles, greatly increasing the powder compaction density of the material and improving the volumetric energy density after battery processing. This is beneficial for enhancing the material performance competitiveness of polyanion-based sodium-containing cathode materials in the sodium battery cathode material industry.

[0197] Examples 2-6 and Comparative Examples 1-2

[0198] The only difference between Examples 1-6 is the preparation process.

[0199] The substrate was used as Comparative Example 1.

[0200] The only difference between Comparative Example 2 and Example 1 is that the substrate was placed in a vibratory mill and vibrated for 1 hour at a frequency of 100 Hz.

[0201] The main differences in the processes of each embodiment and comparative example are shown in Table 1.

[0202] Table 1. Differences in Processes

[0203]

[0204] Performance tests were conducted on the final products obtained from each embodiment and the comparative example, and the test methods are as follows:

[0205] Particle size distribution

[0206] 1g of sample was dispersed in 30ml of water and ultrasonically dispersed for 33s at an ultrasonic power of 120w. The particle size distribution was measured using a Malvern laser particle size analyzer according to standard GB / T19077-2016.

[0207] Specific surface area

[0208] GB / T 19587-2004 Determination of surface area of ​​solid substances by gas adsorption BET method.

[0209] Sphericity

[0210] Scanning electron microscope (SEM) images of sodium-containing polyanionic cathode materials were captured, imported into IPP software for segmentation, and the ratio of the equivalent diameter of the particle perimeter to the equivalent diameter of the particle area was calculated based on the software's calculation function. The average sphericity was then obtained as the sphericity of the sodium iron pyrophosphate cathode material.

[0211] Average pore size

[0212] Analysis was performed using a high-resolution transmission electron microscope (TEM, model Talos F200X) at an operating voltage of 120 kV. Representative areas from the magnified electron images were selected, and the diameters of the through-holes were statistically analyzed. The average diameter was obtained by averaging the diameters of at least 10 representative areas.

[0213] [Powder compaction density]

[0214] Using a powder compactor, place a 10g sample into the compactor, measure the volume after compaction under a pressure of 3T, and calculate the powder compaction density.

[0215] The test results are shown in Table 2.

[0216] Table 2 Test Results

[0217]

[0218] As shown in Table 2, the sphericity of the carbon-coated iron pyrophosphate after shaping is 0.44 or higher, and the average pore size of the carbon-coated iron pyrophosphate is 15nm-35nm. Further, the sphericity is 0.45-0.65; and / or the average pore size is 15nm-32nm. The compaction density of the carbon-coated iron pyrophosphate powder is maintained within a good range.

[0219] Based on Tables 1 and 2, and according to Examples 1-6 and the comparative examples, it can be seen that using ball milling to shape carbon-coated iron pyrophosphate sodium can effectively improve sphericity, reduce average pore size, and increase powder compaction density.

[0220] Comparative Example 2, due to the use of a vibratory mill for shaping, resulted in a limited increase in the compaction density of the shaped product powder, leading to a lower compaction density of the shaped powder compared to Examples 1-6 using the same substrate. This indicates that ball milling is more effective than vibratory milling.

[0221] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A polyanionic sodium-containing cathode material, wherein, The polyanionic sodium-containing cathode material is Na. x R y P m O n Wherein, 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m≤4.2, 14.5≤n≤15.5, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb; The sphericity of the polyanionic sodium-containing cathode material is 0.44-0.9, and the average pore size is 5nm-35nm.

2. The polyanionic sodium-containing cathode material according to claim 1, wherein, The sphericity is 0.45-0.9; and / or, The average pore size is 15nm-32nm.

3. The polyanionic sodium-containing cathode material according to claim 1, wherein, The specific surface area of ​​the polyanionic sodium-containing cathode material is 7m². 2 / g-11m 2 / g; and / or, The volumetric particle size distribution Dv50 of the polyanionic sodium-containing cathode material is 0.7 μm-3 μm, and the volumetric particle size distribution Dv90 is 4 μm-6 μm.

4. The polyanionic sodium-containing cathode material according to any one of claims 1-3, wherein, Under a pressure of 3T, the compacted density of the polyanionic sodium-containing cathode material powder is 1.9 g / cm³. 3 -2.1g / cm 3 .

5. The polyanionic sodium-containing cathode material according to any one of claims 1-4, wherein, The surface of the polyanionic sodium-containing cathode material is coated with a carbon layer.

6. The polyanionic sodium-containing cathode material according to any one of claims 1-5, wherein, The polyanionic sodium-containing cathode material is Na. x R y P m O n Wherein, 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m<4, 14.5≤n≤15.5, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

7. The polyanionic sodium-containing cathode material according to any one of claims 1-5, wherein, The polyanionic sodium-containing cathode material includes sodium iron pyrophosphate, wherein the chemical formula of sodium iron pyrophosphate is (a1) or (a2): (a1)Na x Fe y (PO4)2P2O7, 3.5≤x≤4.5, 2.75≤y≤3.25; (a2)Na x Fe y P m O n , 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m<4, 14.5≤n≤15.

5.

8. A method for preparing a polyanionic sodium-containing cathode material, wherein, include: The polyanionic sodium-containing substrate and grinding balls are placed together in a ball milling jar, and dry ball milling is carried out in the ball milling jar under an inert atmosphere. The polyanionic sodium-containing cathode material is Na. x R y P m O n Wherein, 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m≤4.2, 14.5≤n≤15.5, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb; the sphericity of the polyanionic sodium-containing cathode material is 0.44-0.9, and the average pore size is 5nm-35nm.

9. The preparation method according to claim 8, wherein, The rotational speed of the ball mill jar is 150 RPM-1000 RPM, and the dry ball milling time is at least 1 hour.

10. The preparation method according to claim 9, wherein, The grinding balls include a first grinding ball, a second grinding ball, and a third grinding ball. The diameter of the first grinding ball is 3-6 mm, 6 mm < the diameter of the second grinding ball is ≤9 mm, and 9 mm < the diameter of the third grinding ball is ≤15 mm.

11. The preparation method according to claim 10, wherein, The mass ratio of the first grinding ball, the second grinding ball, and the third grinding ball is 1-3:1-2:

1.

12. The preparation method according to any one of claims 8-11, wherein, The volume ratio of the polyanionic sodium-containing substrate to the grinding balls is 2-3:1; and / or, The temperature of the dry ball milling process does not exceed 80°C.

13. The preparation method according to any one of claims 8-12, wherein, The total volume of the grinding balls and the polyanionic sodium-containing substrate does not exceed 80% of the volume of the grinding jar.

14. The preparation method according to any one of claims 8-13, wherein, The polyanionic sodium-containing substrate has a Dv50 of 1.8μm-4.5μm, a Dv90 of 4μm-6μm, a sphericity of 0.35-0.45, and an average pore size of 5nm-80nm.

15. The preparation method according to any one of claims 8-14, wherein, The polyanionic sodium-containing cathode material includes sodium iron pyrophosphate, and the chemical formula of the sodium iron pyrophosphate is (b1) or (b2): (b1)Na x Fe y (PO4)2P2O7, 3.5≤x≤4.5, 2.75≤y≤3.25; (b2)Na x Fe y P m O n , 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m<4, 14.5≤n≤15.

5.

16. The preparation method according to any one of claims 8-15, wherein, The polyanionic sodium-containing substrate is a carbon-coated sodium iron pyrophosphate substrate, which is prepared by the following method: Sodium salt, iron source, phosphorus source and organic carbon source are wet-mixed according to chemical formula, dried to obtain raw material, the raw material is sintered under an inert atmosphere, and the obtained sintered product is pulverized.

17. The preparation method according to claim 16, wherein, Before sintering the raw material under an inert atmosphere, it is pulverized to a particle size distribution D. V 50 is 0.5μm-4μm.

18. A positive electrode plate, wherein, This includes the polyanionic sodium-containing cathode material according to any one of claims 1-7 or the polyanionic sodium-containing cathode material prepared by the preparation method according to claims 8-17.

19. A battery, wherein, It includes the positive electrode as described in claim 18.

20. An electrical appliance, wherein, It includes the battery as described in claim 19.

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