Polyanion sodium-containing positive electrode material, preparation method therefor, positive electrode sheet, battery and electrical apparatus

Abstract

A polyanion sodium-containing positive electrode material, a preparation method therefor, a positive electrode sheet, a battery and an electrical apparatus. The polyanion sodium-containing positive electrode material is NaxRyPmOn, where 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 0.4-0.9, and the porosity thereof is 0.01-0.14. The polyanion sodium-containing positive electrode material exhibits both a high degree of sphericity and a low porosity, 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. 202410494565.3, 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 0.4-0.9, and the porosity is 0.01-0.14.

[0007] In the technical solution of this application embodiment, the polyanionic sodium-containing cathode material is used to achieve both high sphericity and low porosity, thereby effectively improving the powder compaction density of the polyanionic sodium-containing cathode material.

[0008] In some embodiments, the sphericity of the polyanionic sodium-containing cathode material is 0.5-0.9; and / or, the porosity of the polyanionic sodium-containing cathode material is 0.03-0.1. Controlling the sphericity and porosity of the polyanionic sodium-containing cathode material within the above ranges is beneficial for further improving the powder compaction density of the polyanionic sodium-containing cathode material.

[0009] In some embodiments, the volumetric particle size distribution Dv50 of the polyanionic sodium-containing cathode material is 0.5-3 μm, and the volumetric particle size distribution Dv90 is 2 μm-6 μm. By controlling the volumetric particle size distribution of the polyanionic sodium-containing cathode material within the above range, the particle size of the polyanionic sodium-containing cathode material is refined, which helps to reduce the number of large particles and the porosity of large particles, reduces the gap between particles, and improves the compaction density of the material powder.

[0010] In some embodiments, the specific surface area of ​​the polyanionic sodium-containing cathode material is 6 m². 2 / g-11m 2 / g. By controlling the specific surface area of ​​the polyanionic sodium-containing cathode material within the above range, it is beneficial to reduce the particle size of existing large-particle polyanionic sodium-containing cathode materials and reduce the porosity of large particles, which in turn helps to reduce the gap between particles and improve the compaction density of the powder.

[0011] 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 -2.3g / cm 3 By controlling the polyanionic sodium-containing cathode material to achieve both low porosity and high sphericity, its powder compaction density at 3T can reach 1.9 g / cm³. 3 -2.3g / cm 3 This allows it to maintain high powder compaction density.

[0012] In some embodiments, 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. 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 , 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m<4, 14.5≤n≤15.5.

[0016] The aforementioned sodium ferric pyrophosphate exhibits superior electrochemical performance.

[0017] In some embodiments, the surface of the polyanionic sodium-containing cathode material is coated with a carbon coating layer. This carbon coating layer helps to improve the conductivity and electrochemical performance of the polyanionic sodium-containing cathode material.

[0018] Secondly, this application provides a method for preparing a polyanionic sodium-containing cathode material, comprising:

[0019] A sodium-containing polyanionic substrate is placed in a shaping cavity, and airflow shaping is performed for at least 1 hour under an airflow pressure of 0.35 MPa or higher, to obtain a first powder that is sent to the vicinity of the classifier by the rising airflow and carried out and collected by the airflow, and a second powder that remains in the shaping cavity.

[0020] By combining the first powder and the second powder, a sodium-containing polyanionic cathode material is obtained.

[0021] The second powder accounts for 15%-85% of the mass of the polyanionic sodium-containing cathode material; 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≤4.2, 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 preparation method provided in this application involves airflow shaping of a polyanionic sodium-containing substrate. By precisely controlling the airflow pressure, airflow shaping time, and the mass of the second powder remaining in the shaping cavity after shaping, the porosity of the polyanionic sodium-containing substrate is reduced and its sphericity is improved. Simultaneously, the ratio of the first powder to the second powder is controlled, resulting in a combined effect that increases the powder compaction density of the polyanionic sodium-containing cathode material.

[0022] In some embodiments, the preparation method satisfies one or more of (b1)-(b2):

[0023] (b1) The airflow pressure is 0.35 MPa - 0.9 MPa;

[0024] (b2) The airflow shaping time is 1h-4h.

[0025] By controlling the preparation method to meet at least one of the above requirements, it is beneficial to improve the powder compaction density of the material.

[0026] In some embodiments, the volumetric particle size distribution Dv50 of the first powder is 0.5 μm-1.5 μm, and the volumetric particle size distribution Dv90 is 2 μm-4 μm; and / or,

[0027] The volumetric particle size distribution Dv50 of the second powder is 1.8μm-5.0μm, and the volumetric particle size distribution Dv90 is 4μm-6μm.

[0028] By controlling the volume particle size distribution of the first and second powders within the aforementioned range, it is beneficial to obtain a polyanionic sodium-containing cathode material with high sphericity and low porosity after mixing the two, thereby effectively improving the powder compaction density.

[0029] In some embodiments, the shaping cavity is cylindrical, and the ratio of its axial height to its diameter is 5-10:1. By increasing the axial height to prolong the residence time of large particles in the shaping cavity, the mass of the second powder after airflow shaping is increased. This not only facilitates operation but also helps to obtain polyanionic sodium-containing cathode materials with high sphericity and low porosity.

[0030] In some embodiments, the polyanionic sodium-containing substrate has a volumetric particle size distribution Dv50 of 1.8 μm-4.5 μm, a volumetric particle size distribution Dv90 of 4 μm-6 μm, a sphericity of 0.35-0.45, and a porosity of 0.11-0.3.

[0031] In some embodiments, the polyanionic sodium-containing cathode material includes sodium iron pyrophosphate, wherein the chemical formula of sodium iron pyrophosphate is (c1) or (c2):

[0032] (c1)Na x Fe y (PO4)2P2O7, 3.5≤x≤4.5, 2.75≤y≤3.25;

[0033] (c2)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.

[0034] The aforementioned sodium ferric pyrophosphate exhibits superior electrochemical performance.

[0035] In some embodiments, the polyanionic sodium-containing substrate is carbon-coated sodium iron pyrophosphate, which is prepared by the following method:

[0036] Sodium salt, iron source, phosphorus source, and organic carbon source are wet-mixed according to the chemical formula, dried to obtain raw material, which is then sintered under an inert atmosphere. The resulting carbon-coated sodium pyrophosphate sintered product is then pulverized. The carbon-coated iron pyrophosphate sodium prepared by the above method exhibits superior electrochemical performance.

[0037] In some embodiments, the raw materials are crushed 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.

[0038] Thirdly, this application provides a positive electrode sheet, which includes the polyanionic sodium-containing positive electrode material in the above embodiments.

[0039] Fourthly, this application provides a battery that includes the positive electrode sheet in the above embodiments.

[0040] Fifthly, this application provides an electrical device that includes the battery described in the above embodiments, the battery being used to provide electrical energy.

[0041] 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

[0042] 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:

[0043] Figure 1 is a schematic diagram of the vehicle structure according to some embodiments of this application;

[0044] Figure 2 is an exploded structural diagram of a battery according to some embodiments of this application;

[0045] Figure 3 is an exploded structural diagram of a battery cell according to some embodiments of this application;

[0046] Figure 4 is a SEM image of the sodium iron pyrophosphate base material used before airflow shaping in Example 1 of this application;

[0047] Figure 5 is a SEM image of the sodium iron pyrophosphate cathode material obtained after airflow shaping in Example 1 of this application.

[0048] The reference numerals in the detailed embodiments are as follows:

[0049] 1000 - Vehicles;

[0050] 100 - Battery; 200 - Controller; 300 - Motor;

[0051] 10-Box body; 11-First part; 12-Second part;

[0052] 20-Battery cell; 21-Casing; 22-Electrode assembly; 23-Electrode terminal; 24-Pressure relief structure;

[0053] 211-Shell; 212-Cover. Detailed Implementation

[0054] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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).

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] To address the technical problem of low compaction density in existing polyanionic sodium-containing cathode materials, airflow shaping is employed for physical shaping. This method helps to open closed pores in the material, smooth surface pores, effectively reduce the gaps between particles, and also rounds the particle surface, improving its sphericity. This results in polyanionic sodium-containing cathode materials with high sphericity and low porosity, thereby increasing the compaction density of the powder.

[0065] Based on the above considerations, 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 the polyanionic sodium-containing cathode material is 0.4-0.9, and the porosity is 0.01-0.14.

[0066] The polyanionic sodium-containing cathode material provided in this application, by taking into account both high sphericity and low porosity, 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] Battery cell 20 refers to the smallest unit that makes up battery 100.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] In one embodiment, 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 or the like may 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.

[0082] 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.

[0083] 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).

[0084] As one implementation method, 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.

[0085] In one embodiment, 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).

[0086] In one implementation, 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.

[0087] As one implementation, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0088] 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.

[0089] As one implementation method, the material of the separator can be selected from at least one of glass fiber, non-woven 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.

[0090] 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.

[0091] 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).

[0092] The positive electrode active material layer includes a positive electrode material, which includes a polyanionic sodium-containing positive electrode material. This positive electrode material provides Na+ that can travel between the positive and negative electrode plates during reversible charge and discharge processes. + .

[0093] In one embodiment, 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), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin.

[0094] In one implementation, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0095] 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 the polyanionic sodium-containing cathode material is 0.4-0.9, and the porosity is 0.01-0.14.

[0096] 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 polyanion-based sodium-containing cathode materials to 0.4-0.9, 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 polyanion-based 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 polyanion-based sodium-containing cathode material.

[0097] For example, the sphericity of the polyanionic sodium-containing cathode material is any value of 0.40, 0.46, 0.48, 0.51, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, or 0.90, or between any two values.

[0098] Porosity refers to the proportion of pores within the apparent volume of a granular material to its total volume. Porosity can be measured using a specific surface area and porosity analyzer according to GB / T21650.2-2008. Reducing the porosity of polyanionic sodium-containing cathode materials to between 0.01 and 0.14 is beneficial for increasing the compaction density of the electrode powder and improving the volumetric energy density of the battery. For example, the porosity of polyanionic sodium-containing cathode materials can be any value from 0.01, 0.05, 0.08, 0.09, 0.10, 0.12, and 0.14, or between any two values.

[0099] It should be noted that the sphericity and porosity measurements are for secondary particles, which are aggregates of primary particles.

[0100] The polyanionic sodium-containing cathode material provided in this application, by combining high sphericity and low porosity, effectively improves the powder compaction density of the polyanionic sodium-containing cathode material, thereby contributing to an increase in 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. According to some embodiments of this application, the sphericity of the polyanionic sodium-containing cathode material is 0.5-0.9; and / or,

[0101] The porosity of polyanionic sodium-containing cathode materials is 0.03-0.1.

[0102] Controlling the sphericity and porosity of polyanionic sodium-containing cathode materials within the above-mentioned range is beneficial to effectively improve the powder compaction density of polyanionic sodium-containing cathode materials.

[0103] For example, the sphericity of the polyanionic sodium-containing cathode material is any value of 0.50, 0.55, 0.65, 0.68, 0.70, 0.73, 0.75, 0.80, 0.83, 0.85, or 0.90, or between any two values. For example, the porosity of the polyanionic sodium-containing cathode material is any value of 0.03, 0.05, 0.08, 0.09, 0.95, or 0.10, or between any two values.

[0104] According to some embodiments of this application, the volumetric particle size distribution Dv50 of the polyanionic sodium-containing cathode material is 0.5-3 μm, and the volumetric particle size distribution Dv90 is 2 μm-6 μm.

[0105] 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 is as follows: first, the polyanionic sodium-containing cathode material (i.e., the powder obtained directly after ball milling and shaping) is ultrasonically dispersed, and then particle size distribution is measured 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 method after ultrasonic dispersion. Specifically, you can refer to standard GB / T 19077-2016 and use a laser diffraction scattering particle size analyzer for measurement.

[0106] Among them, the volumetric particle size distribution Dv50 and volumetric particle size distribution Dv90 measure secondary particles, which are aggregates of primary particles.

[0107] By controlling the volumetric particle size distribution of the polyanionic sodium-containing cathode material within the aforementioned range, the particle size of the polyanionic sodium-containing cathode material is refined, which helps to reduce the number of large particles and the porosity of large particles, further reducing the gap between particles and improving the compaction density of the material powder.

[0108] Understandably, with sphericity and porosity remaining constant, smaller particle size results in smaller gaps between particles, which is beneficial for increasing powder compaction density.

[0109] For example, the volumetric particle size distribution Dv50 of the polyanionic sodium-containing cathode material is any value of 0.5μm, 0.7μm, 0.8μm, 1.0μm, 1.1μm, 1.3μm, 1.5μm, 1.8μm, 2.0μm, 2.1μm, 3μm or between any two values, and the volumetric particle size distribution Dv90 is any value of 2.0μm, 2.5μm, 3.0μm, 3.5μm, 4.0μm, 4.5μm, 5.0μm, 5.5μm, 6.0μm or between any two values.

[0110] Optionally, the volumetric particle size distribution Dv50 of the polyanionic sodium-containing cathode material is 1μm-2.5μm, and the volumetric particle size distribution Dv90 is 2μm-5.2μm.

[0111] By controlling the volume particle size distribution of the polyanionic sodium-containing cathode material within the above-mentioned range, it is beneficial to further refine the particle size, further reduce the gap between particles, and further improve the compaction density of the material powder.

[0112] According to some embodiments of this application, the specific surface area of ​​the polyanionic sodium-containing cathode material is 6m². 2 / g-11m 2 / g.

[0113] 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. The specific surface area measured is for secondary particles, which are aggregates of primary particles.

[0114] By controlling the specific surface area, sphericity, and porosity of the particles within the above-mentioned ranges, it is beneficial to improve the compaction density of the powder.

[0115] For example, the specific surface area of ​​the polyanionic sodium-containing cathode material is 6m². 2 / g、7m 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.

[0116] 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 -2.3g / cm 3 .

[0117] Among them, the compaction density of powder can be tested using a powder compaction density meter.

[0118] This application achieves a powder compaction density of 1.9 g / cm³ under 3T pressure by controlling the particle morphology, porosity, and particle size of the polyanionic sodium-containing cathode material. 3 -2.3g / cm 3 This gives it a high powder compaction density.

[0119] For example, the compacted density of the polyanionic sodium-containing cathode material under a pressure of 3T is 1.9 g / cm³. 3 2.0g / cm 3 2.1g / cm 3 2.2g / cm 3 2.3g / cm 3 It can be any value in the range or any two values ​​in between.

[0120] According to some embodiments of this application, 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.

[0121] Polyanionic sodium-containing cathode materials exhibit excellent electrochemical and rate performance.

[0122] 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):

[0123] (a1)Na x Fe y (PO4)2P2O7, 3.5≤x≤4.5, 2.75≤y≤3.25.

[0124] The aforementioned sodium iron pyrophosphate exhibits excellent electrochemical and rate performance, and has a wide range of applications.

[0125] Alternatively, 3.9 ≤ x ≤ 4.2, 2.8 ≤ y ≤ 3.1.

[0126] For example, the chemical formula of sodium iron pyrophosphate is: Na 4.1 Fe 2.95 (PO4)2P2O7 or Na4Fe3(PO4)2P2O7.

[0127] (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.

[0128] 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.

[0129] 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.

[0130] Among them, the surface of the polyanionic sodium-containing cathode material can be coated with a coating layer according to actual needs, and the composition of the coating layer includes, but is not limited to, carbon.

[0131] According to some embodiments of this application, the surface of the polyanionic sodium-containing cathode material has a carbon coating layer.

[0132] The introduction of a carbon coating layer can improve the conductivity and electrochemical performance of polyanionic sodium-containing cathode materials.

[0133] Optionally, the carbon content in the polyanionic sodium-containing cathode material is 1wt%-3.5wt%, and / or the thickness of the carbon coating layer is 2-30nm. By controlling the carbon content in the cathode material within the above-mentioned suitable range and / or the carbon coating layer 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.

[0134] According to some embodiments of this application, this application also provides a method for preparing polyanionic sodium-containing cathode materials, which includes:

[0135] A sodium-containing polyanionic substrate is placed in a shaping cavity, and airflow shaping is performed for at least 1 hour under an airflow pressure of 0.35 MPa or higher, to obtain a first powder that is sent to the vicinity of the classifier by the rising airflow and carried out and collected by the airflow, and a second powder that remains in the shaping cavity.

[0136] By combining the first powder and the second powder, a sodium-containing polyanionic cathode material is obtained.

[0137] The second powder component accounts for 15%-85% of the mass of the polyanionic sodium-containing cathode material, and the polyanionic sodium-containing cathode material is Na... x R y P m On 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.

[0138] 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.

[0139] 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.

[0140] It should be noted that airflow shaping is carried out inside an airflow shaping machine. Its similarity to the principle of airflow pulverization lies in the fact that the supersonic jet generated by the rapid expansion and acceleration of compressed air through the pulverizing nozzle forms a centripetal reverse jet flow field in the lower part of the pulverizing chamber / shaping chamber. Under the action of pressure difference, the material at the bottom is fluidized. The accelerated material converges at the intersection of multiple nozzles, generating violent impact, collision, and friction to pulverize it. However, in current large-scale production applications, the residence time of the material in the pulverizing chamber during the airflow pulverization stage is very short, generally not exceeding 5-10 minutes. It will then be screened by the upper classifying wheel and collected by the bag collector as qualified material. Therefore, the particles of sodium iron pyrophosphate phosphate substrate have a large number of pores. Airflow pulverization cannot completely eliminate the surface pores of the micro particles, and may even lead to particle damage, making the particle surface uneven.

[0141] The difference between airflow shaping and airflow pulverization lies in the following: In airflow shaping, the pulverized material moves with the rising airflow to a certain height in the upper part of the pulverizing chamber. Under the action of gravity, the coarse particles fall back to the lower part of the grinding chamber along the wall of the grinding chamber, while the fine powder moves with the airflow to the upper classifying wheel. The purpose of the classifying wheel is no longer to screen and collect qualified fine powder, but to keep as much material as possible in the shaping chamber and prolong the shaping time.

[0142] Therefore, this application uses airflow to shape the polyanionic sodium-containing substrate by airflow collision for at least 1 hour under an airflow pressure of 0.35 MPa or higher. After the shaping is completed, the second powder remaining in the shaping cavity accounts for 15%-85% of the mass of the polyanionic sodium-containing cathode material. Through the combined action of the above steps, the polyanionic sodium-containing substrate can be repeatedly colliding and shaped in the cavity, and can be fully shaped and crushed. This grinds the surface of the polyanionic sodium-containing substrate particles to a smooth surface, reduces the gap between particles, and effectively improves the shaping effect.

[0143] If the airflow pressure is too low, the kinetic energy delivered by the gas to the material particles is insufficient to break down their morphology. Even with extended shaping time, the shaping effect remains insignificant. Therefore, limiting the airflow pressure to 0.35 MPa or higher is beneficial for further breaking down large particles. Since large particles contain pores, breaking them down into smaller particles also helps reduce the porosity of the polyanion-based sodium-containing cathode material, decreasing the gaps between particles and effectively improving the powder compaction density of the material. For example, the airflow pressure can be any value from 0.35 MPa, 0.40 MPa, 0.45 MPa, 0.50 MPa, 0.55 MPa, 0.60 MPa, 0.65 MPa, 0.70 MPa, 0.80 MPa, 0.90 MPa, or any two values ​​between them.

[0144] If the shaping time is too short, the material will stay in the shaping chamber for a very short time, which will not be enough to achieve sufficient shaping. At the same time, if the mass of the second powder remaining in the shaping chamber after shaping is too small, there is a problem that the material will be collected before it is fully shaped, which will also not achieve sufficient shaping. Therefore, the above-mentioned substrate is limited to airflow shaping under a specific airflow pressure for at least 1 hour, and the second powder accounts for 15%-85% of the mass of the polyanionic sodium-containing cathode material. This is conducive to fully breaking down the large particles of the polyanionic sodium-containing substrate, smoothing the particle surface, reducing the gap between particles, improving sphericity and reducing porosity.

[0145] For example, the airflow shaping time is any one of 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, or between any two values. For example, the second powder accounts for any one of 15%, 20%, 30%, 40%, 50%, 60%, 80%, 85% of the mass of the polyanionic sodium-containing cathode material, or between any two values.

[0146] If the second powder constitutes too small or too large a proportion of the mass of the polyanionic sodium-containing cathode material, the powder compaction density cannot be effectively improved. Therefore, limiting the proportion of the second powder to 15%-85% of the mass of the polyanionic sodium-containing cathode material is, on the one hand, to ensure that the substrate can be fully shaped within the aforementioned airflow shaping time range, thereby improving sphericity and reducing porosity, making it easy to determine whether the shaping has been sufficient. On the other hand, the proportion of the second powder to the mass of the polyanionic sodium-containing cathode material affects the ratio of the first and second powders. By limiting the proportion of the second powder to 15%-85% of the mass of the polyanionic sodium-containing cathode material, it is beneficial to improve the powder compaction density.

[0147] In summary, the preparation method provided in this application reduces the porosity and improves the sphericity of the polyanionic sodium-containing substrate by airflow shaping of the substrate, precisely controlling the airflow pressure, airflow shaping time, and the mass of the second powder remaining in the shaping cavity after shaping. At the same time, the mass of the second powder remaining in the shaping cavity after shaping controls the ratio of the first powder and the second powder, thereby improving the powder compaction density of the polyanionic sodium-containing cathode material.

[0148] Optionally, the sphericity of the polyanionic sodium-containing cathode material is 0.4-0.9, and the porosity is 0.01-0.14. By utilizing the polyanionic sodium-containing cathode material to achieve both high sphericity and low porosity, the powder compaction density of the polyanionic sodium-containing cathode material can be effectively improved.

[0149] According to some embodiments of this application, the preparation method satisfies at least one of (b1)-(b2):

[0150] (b1) The airflow pressure is 0.35 MPa - 0.9 MPa;

[0151] By controlling the airflow pressure within the aforementioned range, sufficient energy can be provided to break up large particles, reduce the porosity of the polyanion-based sodium-containing cathode material, and decrease the gap between particles, thereby increasing the powder compaction density of the material.

[0152] For example, the airflow pressure is any value of 0.35MPa, 0.40MPa, 0.45MPa, 0.50MPa, 0.55MPa, 0.60MPa, 0.65MPa, 0.70MPa, 0.80MPa, or 0.90MPa, or between any two values.

[0153] Optionally, the airflow pressure is 0.4 MPa to 0.9 MPa.

[0154] (b2) The airflow shaping time is 1h-4h.

[0155] By controlling the shaping time within the above range, it is beneficial to fully shape the sodium iron pyrophosphate substrate, improve sphericity, and reduce porosity.

[0156] For example, the airflow shaping time is any value of 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h or between any two values.

[0157] It is understandable that by airflow shaping of the polyanionic sodium-containing substrate within the aforementioned specific parameter range, the particle size distribution of the first and second powders can be controlled. By mixing the first and second powders with reasonable particle size distributions, a polyanionic sodium-containing cathode material with high sphericity and low porosity can be obtained, thereby effectively improving the powder compaction density.

[0158] According to some embodiments of this application, the volumetric particle size distribution Dv50 of the first powder is 0.5 μm-1.5 μm, and the volumetric particle size distribution Dv90 is 2 μm-4 μm; and / or,

[0159] The volumetric particle size distribution Dv50 of the second powder is 1.8μm-5.0μm, and the volumetric particle size distribution Dv90 is 4μm-6μm.

[0160] By controlling the volume particle size distribution of the first and second powders after airflow shaping to be within the above range, it is beneficial to obtain a polyanionic sodium-containing cathode material with smaller particle size, higher sphericity and lower porosity after mixing the two, thereby effectively improving the powder compaction density.

[0161] For example, the volumetric particle size distribution Dv50 of the first powder is any value of 0.5μm, 0.6μm, 0.7μm, 0.8μm, 1.0μm, 1.2μm, 1.5μm or between any two values; for example, the volumetric particle size distribution Dv90 of the first powder is any value of 2μm, 2.5μm, 3μm, 3.5μm, 4μm or between any two values.

[0162] For example, the volumetric particle size distribution of the second powder is any value of 0.8μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm or between any two values; for example, the volumetric particle size distribution Dv90 of the second powder is any value of 4μm, 4.5μm, 5μm, 5.5μm, 6μm or between any two values.

[0163] According to some embodiments of this application, the shaping cavity is cylindrical, and the ratio of the axial height to the diameter of the shaping cavity is 5-10:1.

[0164] It should be noted that when placing the sodium-containing polyanionic substrate in the shaping chamber of an existing airflow shaping machine, it is difficult to achieve a second powder content of 15%-85% of the mass of the sodium-containing polyanionic cathode material after airflow shaping at a pressure of 0.35 MPa or higher for at least 1 hour. Therefore, this application controls the ratio of the axial height to the diameter of the shaping chamber to be 5-10:1. By increasing the axial height, the residence time of large particles in the shaping chamber is extended, thereby increasing the mass of the second powder after airflow shaping. This not only makes the operation convenient but also helps to obtain sodium-containing polyanionic cathode materials with high sphericity and low porosity.

[0165] For example, the ratio of the axial height to the diameter of the shaping cavity is any one of 5:1, 6:1, 6.5:1, 7:1, 8:1, 9:1, 10:1 or between any two of these values.

[0166] According to some embodiments of this application, the volumetric particle size distribution Dv50 of the polyanionic sodium-containing substrate is 1.8 μm-4.5 μm, the volumetric particle size distribution Dv90 is 4 μm-6 μm, the sphericity is 0.35-0.45, and the porosity is 0.11-0.3.

[0167] Existing methods of mechanical crushing or air jet milling are used to crush sintered products that are agglomerated or directly in the form of hard blocks into powder. However, because the surface pores of micro-particles cannot be completely eliminated, a large number of pores still exist on the surface of the particles in the substrate. In some cases, some particles are even destroyed, making the surface uneven. The resulting substrate typically has the low sphericity or porosity parameters shown above.

[0168] 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.

[0169] The above-mentioned polyanionic sodium-containing cathode material structure exhibits excellent electrochemical performance and rate performance.

[0170] 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 (c1) or (c2):

[0171] (c1)Na x Fe y(PO4)2P2O7, 3.5≤x≤4.5, 2.75≤y≤3.25.

[0172] The aforementioned sodium iron pyrophosphate exhibits excellent electrochemical and rate performance, and has a wide range of applications.

[0173] Alternatively, 3.9 ≤ x ≤ 4.2, 2.8 ≤ y ≤ 3.1.

[0174] For example, the chemical formula of sodium iron pyrophosphate is: Na 4.1 Fe 2.95 (PO4)2P2O7 or Na4Fe3(PO4)2P2O7.

[0175] (c2)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.

[0176] 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.

[0177] 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 under a reducing atmosphere or an inert atmosphere, and the obtained carbon-coated sodium pyrophosphate sintered product is pulverized.

[0178] 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:

[0179] 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.

[0180] The carbon-coated iron pyrophosphate sodium prepared by the above method has better electrochemical performance.

[0181] 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.

[0182] 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.

[0183] By way of example, drying includes, but is not limited to, spray drying.

[0184] For example, the sintering temperature is 400℃-600℃ and the sintering time is 6h-24h.

[0185] According to some embodiments of this application, the raw material is crushed to a volumetric particle size distribution D before sintering in an inert atmosphere. V 50 is 0.5μm-4μm.

[0186] 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.

[0187] According to some embodiments of this application, this application also provides a positive electrode sheet, including any of the above-described polyanionic sodium-containing positive electrode materials.

[0188] According to some embodiments of this application, this application also provides a battery including a positive electrode sheet of any of the above schemes.

[0189] 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.

[0190] The electrical device can be any of the aforementioned battery-powered devices or systems.

[0191] The following specific embodiments are provided to better illustrate this application.

[0192] The sodium iron pyrophosphate substrate is prepared by the following method:

[0193] 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.

[0194] 2. Mix the carbon solution and the initial mixed solution, and stir to obtain a mixed solution.

[0195] 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.

[0196] 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 sintered at 550°C at a heating rate of 2°C for 10 hours to obtain carbon-coated sodium iron pyrophosphate sinter.

[0197] 5. The carbon-coated iron sodium pyrophosphate sinter is pulverized to obtain carbon-coated iron sodium pyrophosphate substrate, hereinafter referred to as substrate 1, wherein the chemical formula of iron sodium pyrophosphate is: Na4Fe3(PO4)2P2O7.

[0198] The above-mentioned substrate 1 was divided into multiple parts, which were used as the substrates in Examples 1-8 and Comparative Examples 1-5.

[0199] The preparation method of the substrate used in Example 10 is as follows:

[0200] 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 the initial mixed slurry.

[0201] 2. Spray dry the above mixed solution at an inlet air temperature of 220°C and an outlet air temperature of 109°C to obtain a powdered precursor.

[0202] 3. 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 sintered at 550°C at a heating rate of 2°C for 10 hours to obtain sodium iron pyrophosphate sinter.

[0203] 4. The sodium iron pyrophosphate sintered material is crushed to obtain sodium iron pyrophosphate base material, wherein the chemical formula of sodium iron pyrophosphate is: Na4Fe3(PO4)2P2O7.

[0204] In the following embodiments and comparative examples, the testing methods for each parameter 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] The nitrogen adsorption specific surface area was tested using a method that yielded the result using the 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] Porosity

[0212] Porosity was tested using a specific surface area and porosity tester in accordance with GB / T 21650.2-2008.

[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] Example 1

[0216] 6 kg of the above-mentioned substrate was weighed and placed in the shaping chamber of the airflow shaping machine. The shaping chamber was cylindrical and the axial height and diameter of the shaping chamber were shown in Table 1. Under the condition of airflow pressure of 0.4 MPa as shown in Table 1, airflow collision was used to shape the substrate for 2 hours. The first powder was sent to the vicinity of the classifier by the rising airflow and carried out by the airflow for collection, and the second powder remained in the shaping chamber. The second powder accounted for 72% or more of the mass of the polyanionic sodium-containing cathode material. The first powder and the second powder were combined to obtain the polyanionic sodium-containing cathode material.

[0217] Figure 4 shows the SEM image of the substrate, and Figure 5 shows the SEM image of the sodium iron pyrophosphate cathode material after airflow shaping in Example 1. Comparing Figures 4 and 5, it can be seen that the airflow shaping machine has significant pulverizing and shaping capabilities. After shaping, the large particles are significantly reduced, and the particles become rounder and more uniform. 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.

[0218] Examples 2-10 and Comparative Examples 1-5

[0219] Examples 1-8 and Comparative Examples 1-5 all used the same substrate, which was substrate 1. The only difference between Examples 1-8 and Comparative Examples 2-5 was the preparation process.

[0220] The only difference between Example 9 and Example 3 is that the substrate used is carbon-coated sodium iron pyrophosphate (Na). 4.1 Fe 2.95 (PO4)2P2O7 is used as the substrate, and the preparation method of the substrate is the same as that of substrate 1.

[0221] The only difference between Example 10 and Example 3 is that Na4Fe3(PO4)2P2O7 without carbon coating is used as the substrate.

[0222] Comparative Example 1 uses substrate 1 as the product and does not perform airflow shaping.

[0223] Specifically, the differences in compacted density, specific surface area, sphericity, and porosity of the substrates before airflow shaping in each embodiment and the comparative example are shown in Table 1. The process parameters for airflow shaping and the particle size parameters of the substrates before shaping are shown in Table 2. The differences in compacted density, specific surface area, sphericity, and porosity of the products after airflow shaping are shown in Table 3.

[0224] Table 1. Differences in compacted density, specific surface area, sphericity, and porosity of substrates before airflow shaping.

[0225]

[0226] The differences in process parameters for airflow shaping are shown in Table 2.

[0227] Table 2. Airflow shaping process parameters and particle size parameters of shaped powder.

[0228] In Table 2, the yield of the second powder (%) refers to the mass percentage of the second powder in the shaped sodium iron pyrophosphate cathode material.

[0229] It should be noted that the volumetric particle size distribution Dv50 of the first powder obtained by airflow shaping in Examples 1-10 and Comparative Examples 2 and 5 is 0.5μm-1.5μm, and the volumetric particle size distribution Dv90 is 2μm-4μm; the volumetric particle size distribution Dv50 of the second powder is 1.8μm-5.0μm, and the volumetric particle size distribution Dv90 is 4μm-6μm.

[0230] Table 3. Differences in compaction density, specific surface area, sphericity, and porosity of sodium iron pyrophosphate cathode materials after airflow shaping.

[0231]

[0232] Based on Tables 1, 2, and 3, and according to Examples 1-10 and Comparative Examples 1-5, it can be seen that physical shaping can effectively refine the particle size, resulting in sodium iron pyrophosphate cathode materials that combine high sphericity and low porosity, which is beneficial for improving the powder compaction density of the material.

[0233] As can be seen from Examples 1 and 4, the reason why the compaction density of Example 1 is greater than that of Example 4 is that, under the premise that the sphericity is the same and the porosity of Example 4 is 0.009 higher than that of Example 1, the reason is that, under the premise that the difference in porosity between the two is small, the volume particle size distribution Dv50 of Example 4 is significantly reduced compared with Example 1, thereby resulting in its powder compaction density being higher than that of Example 1.

[0234] According to Examples 2, 6-7, and Comparative Example 2, under the condition that the airflow pressure and the axial height and diameter ratio of the shaping cavity are consistent, the airflow shaping time will affect the yield and compaction density of the second powder obtained after shaping. The yield of the second powder first decreases and then increases with the increase of the airflow shaping time, and the compaction density of the powder also first decreases and then increases with the increase of the airflow shaping time. When the airflow shaping time is at least 1 hour, the compaction density of the sodium iron pyrophosphate cathode material at 3T pressure is greater than or equal to 1.9 g / cm³. 3 Optionally, the airflow shaping time is 1-4 hours, and the sodium iron pyrophosphate cathode material has a better powder compaction density.

[0235] As can be seen from Example 5 and Comparative Example 3, under the condition that the airflow pressure and shaping time are the same, the ratio of the axial height to the diameter of the shaping cavity will affect the percentage of the second powder in the mass of the sodium iron pyrophosphate cathode material. If the ratio of the axial height to the diameter of the shaping cavity is too small, the percentage of the second powder in the mass of the sodium iron pyrophosphate cathode material will be too large, resulting in the inability to effectively improve the powder compaction density. The ratio of the axial height to the diameter of the shaping cavity in the range of 5-10:1 has a better shaping effect and can effectively improve the powder compaction density.

[0236] As can be seen from Examples 1 and 9-10, even if the composition ratio of sodium iron pyrophosphate changes or carbon coating is not performed, the above-mentioned airflow shaping can still be used to effectively improve its sphericity and reduce porosity, thereby increasing the compaction density of the powder.

[0237] 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 0.4-0.9, and the porosity is 0.01-0.

14.

2. The polyanionic sodium-containing cathode material according to claim 1, wherein, The sphericity of the polyanionic sodium-containing cathode material is 0.5-0.9; and / or, The porosity of the polyanionic sodium-containing cathode material is 0.03-0.

1.

3. The polyanionic sodium-containing cathode material according to claim 1 or 2, wherein, The volumetric particle size distribution Dv50 of the polyanionic sodium-containing cathode material is 0.5-3 μm, and the volumetric particle size distribution Dv90 is 2 μm-6 μm.

4. The polyanionic sodium-containing cathode material according to any one of claims 1-3, wherein, The specific surface area of ​​the polyanionic sodium-containing cathode material is 6m². 2 / g-11m 2 / g.

5. The polyanionic sodium-containing cathode material according to any one of claims 1-4, wherein, Under a pressure of 3T, the compacted density of the polyanionic sodium-containing cathode material powder is 1.9 g / cm³. 3 -2.3g / cm 3 .

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 ,in, 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 Feb y Q m O n ,3.5≤x≤4.5,2.5≤y≤3.5,3.7<m<4,14.5≤n≤15.5。 8. The polyanionic sodium-containing cathode material according to any one of claims 1-7, wherein, The surface of the polyanionic sodium-containing cathode material is coated with a carbon layer.

9. A method for preparing a polyanionic sodium-containing cathode material, wherein, include: The sodium-containing polyanionic substrate is placed in the shaping cavity; Under conditions of airflow pressure of 0.35MPa or above, airflow collision is used to shape the airflow for at least 1 hour to obtain a first powder that is sent to the vicinity of the classifier by the rising airflow and carried out and collected by the airflow, and a second powder that remains in the shaping cavity. The first powder and the second powder are combined to obtain the polyanionic sodium-containing cathode material; The second powder comprises 15%-85% of the mass of the polyanionic sodium-containing cathode material; 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.

10. The preparation method according to claim 9, wherein, The preparation method satisfies one or more of (b1)-(b2): (b1) The airflow pressure is 0.35 MPa - 0.9 MPa; (b2) The airflow shaping time is 1h-4h.

11. The preparation method according to claim 9 or 10, wherein, The first powder has a volumetric particle size distribution Dv50 of 0.5 μm-1.5 μm and a volumetric particle size distribution Dv90 of 2 μm-4 μm; and / or, The second powder has a volumetric particle size distribution Dv50 of 1.8μm-5.0μm and a volumetric particle size distribution Dv90 of 4μm-6μm.

12. The preparation method according to any one of claims 9-11, wherein, The shaping cavity is cylindrical, and the ratio of its axial height to its diameter is 5-10:

1.

13. The preparation method according to any one of claims 9-12, wherein, The polyanionic sodium-containing substrate has a volumetric particle size distribution Dv50 of 1.8 μm-4.5 μm, a volumetric particle size distribution Dv90 of 4 μm-6 μm, a sphericity of 0.35-0.45, and a porosity of 0.11-0.

3.

14. The preparation method according to any one of claims 9-13, wherein, The polyanionic sodium-containing cathode material includes sodium iron pyrophosphate, wherein the chemical formula of sodium iron pyrophosphate is (c1) or (c2): (c1)Na x Fe y (PO4)2P2O7,3.5≤x≤4.5,2.75≤y≤3.25; (c2)In x Fe y P m Oh n ,3.5≤x≤4.5,2.5≤y≤3.5,3.7<m<4,14.5≤n≤15.5。 15. The preparation method according to any one of claims 9-14, wherein, The polyanionic sodium-containing substrate is carbon-coated sodium iron pyrophosphate, 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 carbon-coated sodium pyrophosphate sintered product is pulverized.

16. The preparation method according to claim 15, wherein, Before sintering the raw material under an inert atmosphere, it is crushed to a volumetric particle size distribution D. V 50 is 0.5μm-4μm.

17. A positive electrode plate, wherein, This includes the polyanionic sodium-containing cathode material according to any one of claims 1-8 or the polyanionic sodium-containing cathode material prepared by the preparation method according to any one of claims 9-16.

18. A battery, wherein, It includes the positive electrode as described in claim 17.

19. An electrical appliance, wherein, It includes the battery as described in claim 18.

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