Positive electrode active material and preparation method therefor, electrode sheet, battery, and electric device

Abstract

A positive electrode active material and a preparation method therefor, an electrode sheet, a battery, and an electric device. A positive electrode active material, wherein the positive electrode active material is a compound of Na4+xR3-yP4O15 and C, wherein 0≤x<0.8, 0≤y≤0.8, 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; and the porosity of the positive electrode active material is 0.69-1.7%. The positive electrode active material is beneficial to increasing the material compaction density, thereby helping to increase the volumetric energy density of the battery.

Description

Positive electrode active material and preparation method thereof, electrode sheet, battery, and electrical equipment Cross-references

[0001] This application claims priority to the Chinese invention patent application with application number 202410382465.1 filed on March 29, 2024, and invention name “Positive electrode active material and preparation method thereof, pole piece, battery, and electrical equipment”; and this application claims priority to the Chinese invention patent application with application number 202410523826.X filed on April 28, 2024, and invention name “Positive electrode active material and preparation method thereof, pole piece, battery, and electrical equipment”, the contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to a positive electrode active material and a preparation method thereof, a pole piece, a battery, and an electrical device. Background Art

[0003] In recent years, with the development of secondary battery technology, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As secondary batteries have achieved great development, higher requirements have been placed on their volumetric energy density. Summary of the Invention

[0004] The purpose of this application is to provide a positive electrode active material and a preparation method thereof, a pole piece, a battery, and an electrical device.

[0005] The embodiment of the present application is implemented as follows:

[0006] In the first aspect, the present invention provides a positive electrode active material, wherein the positive electrode active material is Na 4+x R 3-y P4O 15 / C;

[0007] Among them, 0≤x<0.8, 0≤y≤0.8, 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 porosity of the positive electrode active material is 0.69%-1.7%.

[0008] In the above technical solution, the porosity of the positive electrode active material is 0.69%-1.7%, which can increase the powder compaction density of the positive electrode active material, and can increase the gram capacity and first coulombic efficiency of the positive electrode active material; further conducive to improving the volume energy density of the battery.

[0009] In some alternative embodiments, the porosity of the positive electrode active material is 0.69%-1.3%.

[0010] The above technical solution further limits the porosity of the positive electrode active material to 0.69%-1.3%, which is further beneficial to improving the compaction density of the material, thereby helping to improve the volume energy density of the battery.

[0011] In some optional embodiments, the D of the positive electrode active material V 50 is 0.663μm~1.593μm.

[0012] In the above technical solution, the positive electrode active material D V 50 is 0.663μm~1.593μm, which can improve the gram capacity and the first coulomb efficiency of the positive electrode active material; further conducive to improving the volume energy density of the battery.

[0013] In some optional embodiments, the D of the positive electrode active material V 50 is 0.663μm~1.309μm.

[0014] The above technical solution further limits the D V 50 is 0.663μm~1.309μm, which can further improve the gram capacity and the first coulombic efficiency of the positive electrode active material; and further help to improve the volume energy density of the battery.

[0015] In some optional embodiments, the D of the positive electrode active material V 90 is 1.89μm~5.82μm.

[0016] In some optional embodiments, the D of the positive electrode active material V 90 is 1.89μm~2.74μm.

[0017] In some optional embodiments, the average pore size of the positive electrode active material is 9 nm to 45 nm.

[0018] In some optional embodiments, the average pore size of the positive electrode active material is 9 nm to 15 nm.

[0019] In some optional embodiments, the powder compaction density of the positive electrode active material tested under a pressure of 29400N is greater than or equal to 1.894g / cm 3 .

[0020] In the above technical solution, the powder compaction density of the positive electrode active material tested under a pressure of 29400N is greater than or equal to 1.894g / cm 3 ; It is further beneficial to improve the volume energy density of the battery.

[0021] In some optional embodiments, the powder compaction density of the positive electrode active material tested under a pressure of 29400N is 2.055g / cm 3 ~2.205g / cm 3 .

[0022] In the above technical solution, the powder compaction density of the positive electrode active material tested under a pressure of 29400N is 2.055g / cm 3 ~2.205g / cm 3 ; It is further beneficial to improve the volume energy density of the battery.

[0023] In some optional embodiments, the positive electrode active material is Na 4+x R 3-y P4O 15 / C;

[0024] Among them, 0≤x<0.5, 0≤y≤0.5, 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.

[0025] In some optional embodiments, the specific surface area of ​​the positive electrode active material is 5m 2 / g~7.98m 2 / g.

[0026] In some optional embodiments, the specific surface area of ​​the positive electrode active material is 5m 2 / g~5.70m 2 / g.

[0027] In the above technical solution, the specific surface area of ​​the positive electrode active material is within the above range; this is further beneficial to improving the volume energy density of the battery.

[0028] In a second aspect, an embodiment of the present application provides a method for preparing a positive electrode active material, comprising:

[0029] mixing raw materials of the positive electrode active material to obtain a mixed solution;

[0030] drying the mixed solution to obtain raw material powder;

[0031] The raw material powder is first sintered at a temperature below 400°C to obtain a first sintered material; the D of the first sintered material is V 50 is 10μm~12μm;

[0032] The first sintering material is crushed to D V 50 is 0.5 μm to 2 μm; obtaining the first raw material;

[0033] The first raw material is used for the second sintering.

[0034] In the above technical solution, the raw material powder is first sintered at a temperature below 400°C (low temperature sintering without phase change reaction), so that the D V 50 is 10μm~12μm, and then the first sintered material is crushed to D V 50 is 0.5 μm to 2 μm; a first raw material is obtained; and the first raw material is used for a second sintering. The above two sintering methods can effectively increase the compaction density of the positive electrode active material, increase the gram capacity and the first coulombic efficiency of the positive electrode active material, and thus increase the volume energy density of the battery.

[0035] In some optional embodiments, the raw material powder is sintered for the first time to obtain a first sintered material; the D of the first sintered material is V 50 is 10μm~12μm, including:

[0036] The raw material powder is sintered for the first time at 300℃~400℃.

[0037] In the above technical solution, the raw material powder is first sintered at 300℃~400℃. Sintering at this relatively low temperature can make the material degas. Since it is a low temperature sintering, the material does not undergo phase change reaction, and it is not easy to produce large pores, which is not easy to affect the reduction of the compaction density of the material. Furthermore, since it is a low temperature baking, the material does not undergo phase change reaction, the hardness of the raw material is low, and it is easy to crush. Therefore, after the first low temperature sintering, the first sintered material can be crushed to obtain D V 50 is the first raw material of 0.5μm to 2μm; and using this D V The high-temperature sintering of the first raw material with a diameter of 0.5 μm to 2 μm reduces the particle size of the primary particles before high-temperature sintering, increases the specific surface area, increases the exhaust area of ​​the high-temperature reaction, and reduces the exhaust pores of the primary particles, thereby increasing the compaction density of the positive electrode active material, which is beneficial to improving the volume energy density of the battery.

[0038] In some optional embodiments, the raw material powder is sintered for the first time to obtain a first sintered material; the D of the first sintered material is V 50 is 10μm~12μm, including:

[0039] The raw material powder is first sintered at 300°C to 400°C for 4h to 8h.

[0040] In the above technical solution, the raw material powder is first sintered at 300℃~400℃ for 4h~8h, and then the obtained first sintered material is crushed to easily obtain DV 50 is the first sintered material with a diameter of 10 μm to 12 μm. This first sintered material has a low hardness and is easy to be crushed to obtain D V 50 is a first raw material with a diameter of 0.5μm to 2μm; using this first raw material for the second sintering (high-temperature sintering) reduces the particle size of the primary particles before high-temperature sintering, increases the specific surface area, increases the exhaust area of ​​the high-temperature reaction, reduces the exhaust pores of the primary particles, and is beneficial to improving the compaction density of the material; and further helps to improve the volume energy density of the battery.

[0041] In some optional embodiments, the first sintering material is crushed to D V 50 is 0.5μm~2μm, including:

[0042] The first sintered material is pulverized using a first pulverizing gas pressure of 0.6 MPa or less.

[0043] In the above technical solution, since the first sintering material does not undergo phase change reaction and has a low hardness, it can be crushed using a first crushing pressure below 0.6 MPa to obtain D V The first raw material with a particle size of 0.5 μm to 2 μm not only saves energy, but also uses this first sintered material for the second sintering (high-temperature sintering), which makes it easy to obtain particles with smaller and more uniform particle size, which is beneficial to improving the compaction density of the material; and further, it is beneficial to improving the volume energy density of the battery.

[0044] In some optional embodiments, drying the mixed solution to obtain raw material powder comprises:

[0045] The mixed solution was spray dried to obtain D V 50 is raw material powder of 10μm-30μm.

[0046] In some optional embodiments, the second sintering is performed using the first raw material, comprising:

[0047] The first raw material is used for the second sintering at 450°C to 600°C.

[0048] In a third aspect, an embodiment of the present application provides an electrode sheet, comprising the positive electrode active material provided in the first aspect; or the electrode sheet comprises the positive electrode active material prepared by the preparation method of the positive electrode active material provided in the second aspect.

[0049] In the above technical solution, the electrode sheet can effectively improve the volume energy density of the battery by setting the positive electrode active material provided by the first aspect, or by setting the positive electrode active material prepared by the preparation method of the positive electrode active material provided by the second aspect.

[0050] In a fourth aspect, an embodiment of the present application provides a battery, which includes the electrode provided in the third aspect.

[0051] In the above technical solution, the battery is helpful in improving the volume energy density of the battery by setting the electrode provided by the third aspect.

[0052] In a fifth aspect, an embodiment of the present application provides an electrical device, which includes the battery provided in the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0054] FIG1 is a schematic structural diagram of a vehicle provided in some embodiments of the present application;

[0055] FIG2 is an exploded view of a battery provided in some embodiments of the present application;

[0056] FIG3 is an exploded view of the battery cell shown in FIG2 ;

[0057] FIG4 is a schematic diagram of a partial structure of an electrode assembly provided in some embodiments of the present application;

[0058] FIG5 is a schematic diagram of a partial structure of a positive electrode sheet provided in some embodiments of the present application;

[0059] FIG6 is a scanning electron microscope image of the positive electrode active material prepared in Example 1;

[0060] FIG7 is a scanning electron microscope image of the positive electrode active material prepared in Comparative Example 1;

[0061] FIG8 is a flow chart of the preparation of the positive electrode active material prepared in Example 1;

[0062] FIG9 is a flow chart of the preparation of the positive electrode active material prepared in Comparative Example 1.

[0063] icon:

[0064] Vehicles 1000;

[0065] Battery 100; Controller 200; Motor 300;

[0066] Box body 10; first part 11; second part 12; accommodating space 13;

[0067] Battery cell 20; housing 21; electrode assembly 22; electrode terminal 23; pressure relief structure 24;

[0068] Housing 211; cover 212; positive electrode sheet 221; negative electrode sheet 222; isolation film 223;

[0069] Negative electrode current collector 2221; Negative electrode active material layer 2222;

[0070] Positive electrode current collector 2211 ; positive electrode active material layer 2212 . DETAILED DESCRIPTION

[0071] 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.

[0072] 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.

[0073] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0074] In the description of the embodiments of the present application, the orientations or positional relationships indicated by technical terms such as "inside" and "outside" are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the embodiments of the present application.

[0075] In the description of the embodiments of this application, unless otherwise specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; they can refer to direct connections or indirect connections through an intermediate medium. Those skilled in the art will understand the specific meanings of the above terms in the embodiments of this application based on specific circumstances.

[0076] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0077] In the embodiments of this application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components in different embodiments are omitted. It should be understood that the heights, lengths, widths, and other dimensions of the various components in the embodiments of this application, as well as the overall heights, lengths, widths, and other dimensions of the integrated device shown in the drawings are merely illustrative and do not constitute any limitation on this application.

[0078] During the sintering process, gas is generated inside the primary particles of the raw material of the sodium ferric pyrophosphate positive electrode material, which will be exhausted between 300-400°C. Direct high-temperature sintering will cause many exhaust holes in the primary particles during the reaction exhaust process, making the microscopic surface of the primary particles after being fired easy to be full of pores, which seriously reduces the compaction density of the positive electrode material and is not conducive to improving the volume energy density of the battery (the compaction density of the porous sodium ferric pyrophosphate positive electrode material tested at a pressure of 29400N after firing is 1.6g / cm 3 -1.8g / cm 3 ).

[0079] The present invention provides a positive electrode active material, the positive electrode active material is Na 4+x R 3-y P4O 15 / C;

[0080] Among them, 0≤x<0.8, 0≤y≤0.8, 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 porosity of the positive electrode active material is 0.69%-1.7%.

[0081] In the above technical solution, the porosity of the positive electrode active material is 0.69%-1.7%, which can effectively increase the powder compaction density of the positive electrode active material, and can increase the gram capacity and first coulombic efficiency of the positive electrode active material; further conducive to improving the volume energy density of the battery.

[0082] As an optional technical method of the present application, the polyanionic compound can be Na 4+x R 3-y P4O 15 / C; wherein, 0≤x<0.5, 0≤y≤0.5, 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.

[0083] As an optional technical method of the present application, the polyanionic compound can be Na x-a A a V y-b M b (PO4)2(DO4)2F z - d Q d , wherein the A element represents an alkali metal element doped to replace the Na element, the M element represents a metal element replacing the V element, the D element represents a doping element replacing the P element, and the Q element represents a doping element replacing the F element. The D element includes at least one of Si and S, and the Q element includes at least one of Cl and O. 3.5≤x≤4.5, 0≤a≤0.15x, 0.8≤y≤1.1, 0≤b≤0.3y, 0.8≤z≤1.1, and 0≤d≤0.2z. Optionally, the A element includes at least one of K and Li; and the M element includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0084] The present application provides a pole piece, comprising the aforementioned positive electrode active material.

[0085] The electrode sheet can improve the volume energy density of the battery by disposing the positive electrode active material provided by the aforementioned embodiment.

[0086] The present application provides a battery, comprising the aforementioned electrode.

[0087] The battery is provided with the pole piece provided by the aforementioned embodiment, which is beneficial to improving the volume energy density of the battery.

[0088] The present application provides an electrical device, comprising the aforementioned battery.

[0089] The electrical equipment has improved comprehensive performance by being provided with the battery provided in the aforementioned embodiment.

[0090] Refer to Figure 1, which is a structural schematic diagram of a vehicle 1000 provided in some embodiments of the present application. The vehicle 1000 can be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A battery 100 is provided inside the vehicle 1000, and the battery 100 can be provided at the bottom, head or tail of the vehicle 1000. The battery 100 can be used to power the vehicle 1000. For example, the battery 100 can serve as an 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 power the motor 300, for example, for starting, navigating and driving the vehicle 1000.

[0091] In some embodiments of the present application, the battery 100 can not only serve as the operating power source of the vehicle 1000, but also serve as the driving power source of the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0092] In this application, battery 100 refers to a single physical module that includes one or more battery cells 20 to provide voltage and capacity. Battery 100 generally includes a housing 10 for enclosing one or more battery cells 20. Housing 10 prevents liquids or other foreign matter from affecting the charging or discharging of battery cells 20.

[0093] Referring to Figure 2, which is an exploded view of a battery 100 provided in some embodiments of the present application, the battery 100 may include a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 is used to house the battery cell 20 and may have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other and together define a storage space 13 for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one end open, and the first portion 11 may be a plate-like structure, which overlaps the open side of the second portion 12 to form the housing 10 with the storage space 13. Alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one end open, with the open side of the first portion 11 overlapping the open side of the second portion 12 to form the housing 10 with the storage space 13. Of course, the first portion 11 and the second portion 12 may have various shapes, such as a cylinder, a rectangular parallelepiped, etc.

[0094] In the battery 100, there can be one or more battery cells 20. If there are multiple battery cells 20, the multiple battery cells 20 can be connected in series, in parallel, or in a mixed connection. Mixed connection means that the multiple battery cells 20 are connected in series and in parallel. The multiple battery cells 20 can be directly connected in series, in parallel, or in a mixed connection, and then the whole formed by the multiple battery cells 20 is accommodated in the case 10. Alternatively, multiple battery cells 20 can be first connected in series, in parallel, or in a mixed connection to form a module, and the multiple modules are then connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in the case 10. The battery 100 can also include other structures. For example, the multiple battery cells 20 can be electrically connected through a busbar component to achieve parallel, series, or mixed connection of the multiple battery cells 20.

[0095] Referring to Figure 3 , which is an exploded view of the battery cell 20 shown in Figure 2 , the battery cell 20 is the smallest unit that makes up the battery 100. The battery cell 20 may include a housing 21 , an electrode assembly 22 , and an electrolyte, with both the electrode assembly 22 and the electrolyte being housed within the housing 21 .

[0096] The outer shell 21 may include a shell 211 and a cover 212. The shell 211 is a component used to cooperate with the cover 212 to form an internal sealed space of the battery cell 20, wherein the formed sealed space can be used to accommodate the electrode assembly 22, electrolyte and other components. The cover 212 refers to a component that covers the opening of the shell 211 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the cover 212 can be adapted to the shape of the shell 211 to cooperate with the shell 211. Functional components such as electrode terminals 23 and pressure relief structures 24 can also be provided on the cover 212. A sealing ring can be configured between the opening of the shell 211 and the cover 212 to achieve sealing between the shell 211 and the cover 212.

[0097] The shell 211 and the cover 212 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shapes of the shell 211 and the cover 212 can be determined according to the specific shape and size of the electrode assembly 22. The material of the shell 211 and the cover 212 can be various, such as but not limited to metals such as copper, iron, aluminum, stainless steel, and aluminum alloy. The material of the sealing ring can be various, such as but not limited to PP (polypropylene), PC (polycarbonate), PET (polyethylene terephthalate) and other materials that are resistant to electrolyte corrosion, high toughness and fatigue resistance. A coating can be formed on the outer surface of the shell 211, and the material of the coating can be various, such as but not limited to corrosion-resistant materials such as Ni and Cr.

[0098] Referring to Figure 4 , the electrode assembly 22 may be composed of a positive electrode sheet 221, a negative electrode sheet 222, and a separator 223. The separator 223 is located between the positive electrode sheet 221 and the negative electrode sheet 222 to provide isolation. The electrode assembly 22 may be a wound or laminated structure, but the present invention is not limited thereto.

[0099] 5 , the negative electrode sheet 222 includes a negative electrode current collector 2221 and a negative electrode active material layer 2222. The negative electrode current collector 2221 may be made of copper, and the negative electrode active material layer 2222 includes a negative electrode active material. The negative electrode active material includes at least one of graphite, silicon, a silicon alloy, or a tin alloy.

[0100] 5 , the positive electrode sheet 221 includes a positive electrode current collector 2211 and a positive electrode active material layer 2212 . Taking a battery cell as an example, the positive electrode current collector 2211 may be made of aluminum. The positive electrode active material layer 2212 includes positive electrode active material.

[0101] In some embodiments of the present application, the chemical formula of the positive electrode active material includes: Na 4+x R 3-y P4O 15 / C;

[0102] Among them, 0≤x<0.8, 0≤y≤0.8, 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 porosity of the positive electrode active material is 0.69%-1.7%.

[0103] In the above technical solution, the porosity of the positive electrode active material is 0.69%-1.7%, which can increase the powder compaction density of the positive electrode active material, and can increase the gram capacity and first coulombic efficiency of the positive electrode active material; further conducive to improving the volume energy density of the battery.

[0104] In some alternative embodiments, the porosity of the positive electrode active material is 0.69%-1.3%.

[0105] The above technical solution further limits the porosity of the positive electrode active material to 0.69%-1.3%, which is further beneficial to improving the compaction density of the material, thereby helping to improve the volume energy density of the battery.

[0106] Illustratively, in some embodiments of the present application, the porosity of the positive electrode active material is 0.69%, 0.70%, 0.71%, 0.72%, 0.75%, 0.78%, 0.80%, 0.82%, 0.85%, 0.88%, 0.90%, 0.94%, 0.98%, 1%, 1.1%, 1.2%, 1.3% or a range between any two of the foregoing values.

[0107] In the above technical solution, the porosity refers to the percentage of the volume of pores in the positive electrode active material that can be measured by nitrogen to the total volume of the positive electrode active material in its natural state.

[0108] Furthermore, in some embodiments of the present application, the porosity of the positive electrode active material is tested as follows:

[0109] Using a surface area and porosity tester, place an accurately weighed, pre-treated sample in a sample tube. First, vacuum the tube to degas it, then bring the entire system to the desired vacuum level. The tube is then immersed in a liquid nitrogen bath and filled with nitrogen. Adsorption of the gas by the adsorbent causes a pressure drop. Once adsorption equilibrium is reached, the equilibrium pressure is measured. The adsorption capacity is calculated based on the pressure change before and after adsorption. Repeat this process by gradually increasing the amount of adsorbate gas added to the system to change the pressure, and test the adsorption-desorption isotherm. A theoretical model is then used to determine the porosity of the sample.

[0110] Furthermore, the above Na 4+x R 3-y P4O 15 / C is Na 4+x R 3-y P4O 15 and a complex of C.

[0111] In some embodiments of the present application, the positive electrode active material is Na 4+x R 3-y P4O 15 / C;

[0112] Among them, 0≤x<0.5, 0≤y≤0.5, 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.

[0113] Further, illustratively, in some embodiments of the present application, the chemical formula of the positive electrode active material is: Na4Fe3(PO4)2P2O7, Na 4.1 Fe 2.8 (PO4) 2.1 P2O7、Na 4.2 Fe 2.9(PO4)2P2O7 or Na4Fe 2.8 (PO4)2P2O7.

[0114] The battery is accompanied by the deintercalation and consumption of Na during the charge and discharge process, and the molar content of Na is different when the battery is discharged to different states.

[0115] In the list of positive electrode active materials in this application, the molar content of O is only a theoretical value. Oxygen release from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate. For example, Na m Fe x (PO4) y The molar content of the O element in P2O7 is not strictly 7.

[0116] Furthermore, in some embodiments of the present application, the D of the positive electrode active material V 50 is 0.663μm~1.593μm.

[0117] In the above technical solution, the positive electrode active material D V 50 is 0.663μm~1.593μm, which can improve the gram capacity and the first coulomb efficiency of the positive electrode active material; further conducive to improving the volume energy density of the battery.

[0118] In some optional embodiments, the D of the positive electrode active material V 50 is 0.663μm~1.309μm.

[0119] The above technical solution further limits the D V 50 is 0.663μm~1.309μm, which can further improve the gram capacity and the first coulombic efficiency of the positive electrode active material; and further help to improve the volume energy density of the battery.

[0120] For example, in some embodiments of the present application, the D of the positive electrode active material is V 50 is 0.663 μm, 0.665 μm, 0.670 μm, 0.680 μm, 0.690 μm, 0.710 μm, 0.750 μm, 0.810 μm, 0.850 μm, 0.950 μm, 1.250 μm, 1.350 μm, 1.550 μm, 1.593 μm or the range between any two of the foregoing values.

[0121] In the embodiment of the present application, the volume distribution particle size D of the positive electrode active material is vThe term "50" is generally known in the art and represents the particle size corresponding to the 50% cumulative volume distribution percentage of the material. This can be measured using instruments and methods known in the art. For example, the measurement can be performed using a laser particle size analyzer, as described in GB / T 19077-2016. The testing instrument may be the Mastersizer 3000 laser particle size analyzer manufactured by Malvern Instruments Ltd., UK.

[0122] Furthermore, in some embodiments of the present application, the D of the positive electrode active material V 90 is 1.89μm~5.82μm.

[0123] Further optionally, in some embodiments of the present application, the D of the positive electrode active material V 90 is 1.89μm~2.74μm.

[0124] For example, in some embodiments of the present application, the D of the positive electrode active material is V 90 is 1.89 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm or a range between any two of the foregoing values.

[0125] In the embodiment of the present application, the volume distribution particle size D of the positive electrode active material is V The term "90" is generally known in the art and represents the particle size corresponding to the 90% cumulative volume distribution percentage of the material. This can be measured using instruments and methods known in the art. For example, the measurement can be performed using a laser particle size analyzer, as per GB / T 19077-2016. The testing instrument may be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0126] Furthermore, in some embodiments of the present application, the average pore diameter of the positive electrode active material is 9 nm-45 nm.

[0127] Illustratively, in some embodiments of the present application, the average pore size of the positive electrode active material is 9 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 36 nm, 37 nm, 38 nm, 39 nm, 40 nm, 41 nm, 42 nm, 43 nm, 44 nm, 45 nm, or a range between any two of the foregoing values.

[0128] In the above technical solution, the average pore diameter refers to the average pore diameter value of the through pores in the above positive electrode active material.

[0129] Furthermore, in some embodiments of the present application, the average pore size of the positive electrode active material is determined by analysis using a high-resolution transmission electron microscope (TEM, Talos F200X) at an operating voltage of 120 kV. The proportion of through-pores is determined by a statistical method: representative areas of the electron magnification image are selected, and the percentage of through-pores is calculated. The average value of the number of through-pores in at least 10 representative areas is taken.

[0130] Furthermore, in some embodiments of the present application, the average pore diameter of the positive electrode active material is 9 nm-15 nm.

[0131] Illustratively, in some embodiments of the present application, the average pore diameter of the positive electrode active material is 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, or a range between any two of the foregoing values.

[0132] Furthermore, in some embodiments of the present application, the powder compaction density of the positive electrode active material tested under a pressure of 29400N is greater than or equal to 1.894g / cm 3 .

[0133] In the above technical solution, the powder compaction density of the positive electrode active material tested under a pressure of 29400N is greater than or equal to 1.894g / cm 3 ; It is further beneficial to improve the volume energy density of the battery.

[0134] In this application, the powder compaction density of the positive electrode active material has a meaning well known in the art and can be tested using methods known in the art. For example, an electronic pressure testing machine (such as UTM7305) can be used for testing: a certain amount M of the powder sample to be tested is placed on a special compaction mold (bottom area S), different pressures are set (29400N can be used in this application), the pressure is maintained for 30s, the pressure is released, and the thickness H of the powder after compaction under the pressure is read on the device. The compaction density under the pressure can be calculated, and the powder compaction density of the positive electrode active material under the pressure = M / (H*S).

[0135] Furthermore, in some embodiments of the present application, the powder compaction density of the positive electrode active material tested under a pressure of 29400N is 2.055g / cm 3 ~2.205g / cm 3 .

[0136] In the above technical solution, the powder compaction density of the positive electrode active material tested under a pressure of 29400N is 2.055g / cm 3 ~2.205g / cm 3 ; It can improve the gram capacity and first coulombic efficiency of the positive electrode active material; further help to improve the volume energy density of the battery.

[0137] Further, illustratively, in some embodiments of the present application, the powder compaction density of the positive electrode active material tested under a pressure of 29400N is 2.055g / cm 3 , 2.056g / cm 3 , 2.086g / cm 3 , 2.124g / cm 3 , 2.150g / cm 3 , 2.205g / cm 3 Or the range between any two of the above values.

[0138] Furthermore, in some embodiments of the present application, the specific surface area of ​​the positive electrode active material is 5m 2 / g~7.98m 2 / g.

[0139] In the above technical solution, by setting the specific surface area of ​​the positive electrode active material to 5m 2 / g~7.98m 2 / g; further helps to improve the volume energy density of the battery.

[0140] For example, in some embodiments of the present application, the specific surface area of ​​the positive electrode active material is 5m 2 / g, 5.1m 2 / g, 5.2m 2 / g, 5.3m 2 / g, 5.4m 2 / g, 5.5m 2 / g, 5.6m 2 / g, 5.7m 2 / g, 5.8m 2 / g, 5.9m 2 / g、6m 2 / g, 6.2m 2 / g, 6.5m 2 / g, 6.8m 2 / g、7m 2 / g, 7.2m 2 / g, 7.5m 2 / g, 7.8m 2 / g, 7.98m 2 / g or the range between any two of the above values.

[0141] Furthermore, in some embodiments of the present application, the specific surface area of ​​the positive electrode active material is 5m 2 / g~5.70m 2 / g.

[0142] In the above technical solution, by setting the specific surface area of ​​the positive electrode active material to 5m 2 / g~5.70m 2 / g, which is further beneficial to improving the volume energy density of the battery.

[0143] In this application, the specific surface area of ​​the positive electrode active material has a meaning well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis test method in accordance with GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be a Tri-Star 3020 specific surface area pore size analyzer from Micromeritics, Inc., USA.

[0144] Some embodiments of the present application provide a method for preparing a positive electrode active material, comprising:

[0145] mixing raw materials of the positive electrode active material to obtain a mixed solution;

[0146] drying the mixed solution to obtain raw material powder;

[0147] The raw material powder is first sintered at a temperature below 400°C to obtain a first sintered material; the D of the first sintered material is V 50 is 10μm~12μm;

[0148] The first sintering material is crushed to D V 50 is 0.5 μm to 2 μm; obtaining the first raw material;

[0149] Using the first raw material to carry out the second sintering;

[0150] Wherein, the positive electrode active material is Na 4+x R 3-y P4O 15 / C;

[0151] Wherein, 0≤x<0.8, 0≤y≤0.8, 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; and the porosity of the positive electrode active material is 0.69%-1.7%.

[0152] In the above technical solution, by adopting the secondary sintering method, the raw material powder is first sintered at below 400°C (low temperature sintering, no phase change reaction occurs) to obtain the first sintered material; the D of the first sintered material is V 50 is 10μm~12μm; then the first sintered material is crushed to D V50 is 0.5 μm to 2 μm; a first raw material is obtained; and the first raw material is used for a second sintering. This can increase the compaction density of the positive electrode active material, increase the gram capacity and the first coulombic efficiency of the positive electrode active material, and thus increase the volume energy density of the battery.

[0153] Furthermore, the first sintered material after the raw material powder is first sintered at below 400°C (no high temperature phase reaction occurs) has a low hardness and is easy to crush. Microscopic primary small particles with uniform particle size and large specific surface area can be obtained before the high temperature solid phase reaction. Then, a sodium iron phosphate pyrophosphate material with uniform particle size is obtained by a second sintering through a high temperature solid phase reaction. After sintering, there is no need for air flow crushing again to obtain sodium iron phosphate pyrophosphate particles with smaller and more uniform particle size. The surface morphology of the microscopic primary particles of the material obtained by the above technical solution is smoother, the porosity is greatly reduced, the compaction density of the material is improved, and it is beneficial to improve the volume energy density of the battery.

[0154] Usually, the raw material powder of the sodium iron phosphate pyrophosphate positive electrode material is dried (not crushed before sintering) and then directly sintered. The sintered material obtained in this way is agglomerated or aggregated together, which is difficult to crush. Usually, the particle size of the primary particles (D V 50) Crushed to micron size; typically 5 μm. This grade of sodium iron phosphate pyrophosphate cathode material has a low compaction density and has limited impact on improving the battery's volumetric energy density.

[0155] Compared with this direct sintering method, the technical solution in the above embodiment of the present application adds a first low-temperature sintering process before high-temperature phase change sintering to obtain a first sintered material with lower hardness (the hardness of the first sintered material at this time is significantly lower than the hardness of the sintered material and is easier to crush). After crushing the first sintered material, a smaller, more uniform and larger specific surface area primary particle is obtained. And at this time, the raw material has not undergone high-temperature solid phase reaction. After being crushed (crushed to D V 50 is 0.5μm~2μm), and then high-temperature solid-phase reaction sintering is carried out, so that the material is not easy to generate gas during the high-temperature solid-phase reaction sintering process; thereby it is easy to obtain primary particles with fewer pores after sintering, and there is no need to crush them after high-temperature solid-phase sintering (the hardness is too high, the crushing is difficult, and it is difficult to crush them to a smaller particle size), which is beneficial to improving the powder compaction density of the material and the volume energy density of the battery.

[0156] The above technical solution reduces the need to grind the sodium iron pyrophosphate cathode material obtained after sintering by low temperature sintering the raw material before high temperature solid phase reaction sintering, greatly reduces the grinding difficulty, and is expected to make the particle size of the material (D V50) to a suitable range, the powder compaction density of the positive electrode active material can be increased, and the gram capacity and the first coulombic efficiency of the positive electrode active material can be increased; thereby, the volume energy density of the battery can be effectively improved.

[0157] Further optionally, for example, in some embodiments of the present application, the raw material powder is sintered for the first time to obtain a first sintered material; the D of the first sintered material is V 50 is 10 μm, 10.5 μm, 11 μm, 11.5 μm, 11.8 μm, 12 μm or a range between any two of the foregoing values.

[0158] Further, in some embodiments of the present application, illustratively, the first sintering material is crushed to D V 50 is 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.2μm, 1.3μm, 1.5μm, 1.8μm, 1.9μm, 2μm or a range between any two of the foregoing values.

[0159] Furthermore, in some embodiments of the present application, the raw material powder is sintered for the first time to obtain a first sintered material; the D of the first sintered material is V 50 is 10μm~12μm, including:

[0160] The raw material powder is sintered for the first time at 300℃~400℃.

[0161] In the above technical solution, the raw material powder is first sintered at 300℃~400℃. Sintering at this relatively low temperature can make the material degas. Since it is a low temperature sintering, the material does not undergo phase change reaction, and it is not easy to produce large pores, which is not easy to affect the reduction of the compaction density of the material. Furthermore, since it is a low temperature baking, the material does not undergo phase change reaction, the hardness of the raw material is low, and it is easy to crush. Therefore, after the first low temperature sintering, the first sintered material can be crushed to obtain D V 50 is the first raw material of 0.5μm to 2μm; and using this D V The first raw material with a particle size of 0.5 μm to 2 μm is sintered at a high temperature, which makes it easy to obtain a positive electrode active material with a smaller and more uniform particle size, thereby increasing the compaction density of the positive electrode active material, and further contributing to increasing the volume energy density of the battery.

[0162] Further, illustratively, in some embodiments of the present application, the raw material powder is sintered for the first time to obtain a first sintered material; the D of the first sintered material is V 50 is 10μm~12μm, including:

[0163] The raw material powder is first sintered at a temperature of 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C or a temperature within a range between any two of the foregoing values.

[0164] Furthermore, in some embodiments of the present application, the raw material powder is sintered for the first time to obtain a first sintered material; the D of the first sintered material is V 50 is 10μm~12μm, including:

[0165] The raw material powder is first sintered at 300°C to 400°C for 4h to 8h.

[0166] In the above technical solution, the raw material powder is first sintered at 300℃~400℃ for 4h~8h, and then the obtained first sintered material is crushed to easily obtain D V 50 is the first sintered material with a diameter of 10 μm to 12 μm. This first sintered material has a low hardness and is easy to be crushed to obtain D V 50 is a first raw material with a size of 0.5 μm to 2 μm; using this first raw material for the second sintering (high temperature sintering) can easily obtain particles with smaller and more uniform particle size, which is beneficial to improving the compaction density of the material; and further beneficial to improving the volume energy density of the battery.

[0167] Furthermore, in some embodiments of the present application, the first sintering material is crushed to D V 50 is 0.5μm~2μm, including:

[0168] The first sintered material is pulverized using a first pulverizing gas pressure of 0.6 MPa or less.

[0169] In the above technical solution, since the first sintering material does not undergo phase change reaction and has a low hardness, it can be crushed using a first crushing pressure below 0.6 MPa to obtain D V The first raw material with a particle size of 0.5 μm to 2 μm not only saves energy, but also uses this first sintered material for the second sintering (high-temperature sintering), which makes it easy to obtain particles with smaller and more uniform particle size, which is beneficial to improving the compaction density of the material; and further, it is beneficial to improving the volume energy density of the battery.

[0170] Further, for example, in some embodiments of the present application, the first sintering material is crushed to D V 50 is 0.5μm~2μm, including:

[0171] The first sintered material was pulverized using first pulverizing gas pressures of 0.5 MPa, 0.51 MPa, 0.52 MPa, 0.53 MPa, 0.54 MPa, 0.55 MPa, 0.56 MPa, 0.57 MPa, 0.58 MPa, and 0.59 MPa.

[0172] Furthermore, in some embodiments of the present application, the Dv90 of the first sintered material is 23.98 μm to 24.87 μm. For example, the Dv90 of the first sintered material is 23.98 μm, 24 μm, 24.1 μm, 24.2 μm, 24.5 μm, 24.8 μm, 24.87 μm, or a range between any two of the foregoing values.

[0173] Furthermore, in some embodiments of the present application, the Dv9 of the first raw material is 1.78 μm to 5.78 μm. For example, the Dv9 of the first raw material is 1.78 μm, 1.8 μm, 1.85 μm, 1.88 μm, 1.89 μm, 1.9 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 5.78 μm, or a range between any two of the foregoing values.

[0174] Furthermore, in some embodiments of the present application, the first sintering material is pulverized using a first pulverizing gas pressure of 0.6 MPa or less, comprising:

[0175] Use a classifier with a frequency of 45Hz to 50Hz to crush the first sintered material to D V 50 is 0.5μm~2μm.

[0176] In the above technical solution, a classifier with a frequency of 45Hz to 50Hz is used, which is beneficial for crushing the first sintering material powder to D V 50 is 0.5μm~2μm; it can improve the gram capacity and the first coulomb efficiency of the positive electrode active material; it is beneficial to improve the compaction density of the positive electrode active material, thereby helping to improve the volume energy density of the battery.

[0177] Illustratively, in some embodiments of the present application, crushing the first sintering material includes:

[0178] The first sintered material is crushed to D using a classifier with a frequency of 45 Hz, 46 Hz, 47 Hz, 48 Hz, 49 Hz, 50 Hz or a frequency range between any two of the above values. V 50 is 0.5μm~2μm.

[0179] Furthermore, in some embodiments of the present application, drying the mixed solution to obtain raw material powder comprises:

[0180] The mixed solution was spray dried to obtain D V 50 is raw material powder of 10μm-30μm.

[0181] In the above technical solution, the mixed solution can be effectively dried to D by spray drying. V 50 is a raw material powder with a size of 10 μm-30 μm. This is beneficial to improving the compaction density of the positive electrode active material, and can improve the gram capacity and the first coulombic efficiency of the positive electrode active material; thus, it is beneficial to improving the volume energy density of the battery.

[0182] Furthermore, in some embodiments of the present application, drying the mixed solution to obtain raw material powder comprises:

[0183] The mixed solution is spray-dried at an air inlet temperature of 200°C to 250°C and an air outlet temperature of 100°C to 110°C.

[0184] In the above technical solution, the mixed solution is spray-dried at an air inlet temperature of 200℃~250℃ and an air outlet temperature of 100℃~110℃, which can effectively dry the mixed solution into D V 50 is a raw material powder with a size of 10 μm-30 μm. This is beneficial to improving the compaction density of the positive electrode active material, and can improve the gram capacity and the first coulombic efficiency of the positive electrode active material; thus, it is beneficial to improving the volume energy density of the battery.

[0185] For example, in some embodiments of the present application, drying the mixed solution to obtain raw material powder comprises:

[0186] The mixed solution is spray-dried at an inlet air temperature of 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C, 235°C, 225°C, 250°C or a temperature range between any two of the foregoing values; and an outlet air temperature of 100°C, 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107°C, 108°C, 109°C, 110°C or a temperature range between any two of the foregoing values.

[0187] Furthermore, in some embodiments of the present application, the second sintering is performed using the first raw material, comprising:

[0188] The first raw material is used for the second sintering at 450°C to 600°C.

[0189] Furthermore, in some embodiments of the present application, the second sintering is performed using the first raw material, comprising:

[0190] Keep the first raw material at 280℃~350℃ for 4h~8h; raise the temperature to 450℃~600℃ and keep it for 5~20h.

[0191] For example, in some embodiments of the present application, the second sintering is performed using the first raw material, including:

[0192] The first raw material is kept at a temperature of 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C or a range between any two of the aforementioned values ​​for 4h, 5h, 6h, 7h, 8h or a range between any two of the aforementioned values; the temperature is raised to 450°C, 460°C, 470°C, 480°C, 500°C, 520°C, 550°C, 580°C, 600°C or a range between any two of the aforementioned values; and the temperature is kept for 5h, 8h, 10h, 15h, 18h, 20h or a range between any two of the aforementioned values.

[0193] Furthermore, in some embodiments of the present application, the raw materials of the positive electrode active material include: a sodium source, an iron source, and a phosphorus source.

[0194] In some embodiments of the present application, raw materials of the positive electrode active material are mixed to obtain a mixed solution, comprising:

[0195] A sodium source, an iron source and a phosphorus source are prepared according to a molar ratio of sodium element, iron element and phosphorus element of (4-4.2): (2.8-3): (4-4.1) to obtain a first solution.

[0196] Furthermore, in some embodiments of the present application, the raw material of the positive electrode active material also includes a carbon source; and the carbon source is prepared as a carbon source solution.

[0197] Furthermore, in some embodiments of the present application, raw materials of the positive electrode active material are mixed to obtain a mixed solution, comprising:

[0198] The first solution prepared above is mixed with the carbon source solution to obtain a mixed solution.

[0199] Furthermore, in some embodiments of the present application, the sodium source may be selected from at least one of a sodium salt, sodium hydroxide, or sodium oxide. Furthermore, in some embodiments of the present application, the phosphorus source may include at least one of a phosphate or phosphoric acid. Furthermore, in some embodiments of the present application, the iron source may include at least one of an iron salt, oxide, or hydroxide.

[0200] Illustratively, in some embodiments of the present application, the iron source is ferrous oxalate; the phosphorus source is ferric phosphate.

[0201] Further optionally, in some embodiments of the present application, the carbon source is selected from at least one of conductive carbon black Super P, glucose, sucrose, fructose, cellulose, acetylene black, pitch, carbon nanotubes, starch, citric acid, polyacrylic acid or dopamine.

[0202] [Positive electrode]

[0203] In some embodiments of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0204] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0205] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0206] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0207] In some embodiments, the positive electrode film layer may further include a conductive agent. For 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.

[0208] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0209] [Negative electrode]

[0210] In some embodiments of the present application, the specific type of the negative electrode active material in the film layer is not limited. Active materials known in the art for use in sodium ion battery negative electrodes can be used, and those skilled in the art can select them according to actual needs. As an example, the negative electrode active material can include but is not limited to carbon materials, including but not limited to at least one of hard carbon, soft carbon, amorphous carbon, and nanostructured carbon materials, all of which can be obtained through commercial channels.

[0211] For example, the negative electrode active material may include one or more of hard carbon, soft carbon, artificial graphite, and natural graphite.

[0212] In some embodiments, the current collector of the negative electrode plate may also generally include a current collector body and an undercoat layer. The undercoat layer may be disposed on at least one side of the current collector body. The undercoat layer substantially contains no negative electrode active material and may include a small amount of carbon material. However, the carbon material coating is thin and cannot function as a negative electrode active material. In this embodiment, the negative electrode plate may be a plate without a negative electrode active material layer. For negative electrode plates without a negative electrode active material layer, when the current collector of the negative electrode plate does not include an undercoat layer, the film layer may be disposed on at least one side of the current collector. When the current collector of the negative electrode plate includes an undercoat layer, the film layer may be disposed on the surface of the undercoat layer on the side away from the current collector.

[0213] In some embodiments, the film layer may further include a binder for fixing the additive to the negative electrode plate. The type of the binder is not particularly limited and can be flexibly selected by those skilled in the art based on actual needs.

[0214] [Electrolytes]

[0215] In some embodiments, the electrolyte acts as a conductive medium between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte may be selected based on specific needs. For example, the electrolyte may be liquid, gel, or solid.

[0216] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0217] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0218] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0219] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0220] [Isolation film]

[0221] In some embodiments, the battery cell further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0222] In some embodiments, 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.

[0223] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0224]

[0225] Some specific embodiments are listed below to better illustrate the present application.

[0226] Example 1

[0227] A positive electrode active material is provided, and as shown in FIG8 , the positive electrode active material is prepared according to the following steps:

[0228] Step S1, based on the stoichiometric ratio of Na4Fe3(PO4)2P2O7, sodium pyrophosphate, ferrous oxalate and ferric phosphate are mixed according to the molar ratio of Na element in sodium pyrophosphate, total Fe element in ferrous oxalate and ferric phosphate, and P element in ferric phosphate of 4:3:4 to obtain a mixture; the mixture is dissolved in deionized water and stirred continuously at room temperature for 30 minutes to obtain an initial mixed slurry; then conductive carbon black Super P and glucose are dissolved in deionized water and mixed to obtain a carbon solution; the amount of conductive carbon black Super P added to the mixture is 0.5wt%, and the amount of glucose added to the mixture is 2.5wt%.

[0229] Step S2: Mix the carbon solution obtained in step S1 and the initial mixed slurry obtained in step S1, and stir them evenly to obtain a mixed solution.

[0230] Step S3: spray-dry the mixed solution obtained in step S2 with an air inlet temperature of 220°C and an air outlet temperature of 109°C to obtain raw material powder; raw material powder D V 50 is 20μm.

[0231] Step S4: sinter the raw material powder obtained in step S3 at 350°C for 6 hours to obtain a first sintered material; D of the first sintered material V 50 is 10μm.

[0232] Step S5: Place the first sintered material obtained in step S4 in a jet mill with a classifier at a frequency of 48 Hz and a crushing pressure of 0.55 MPa to obtain a first raw material; D of the first raw material V 50 is 0.8μm.

[0233] Step S6: placing the first raw material obtained in step S5 in a N2 atmosphere, heating it to 320°C at a heating rate of 2°C and keeping it for 4 hours, and then heating it to 550°C at a heating rate of 2°C and keeping it for 10 hours to obtain sodium iron pyrophosphate positive electrode active material.

[0234] Examples 2-9

[0235] A positive electrode active material is provided, and the preparation method is the same as that of Example 1, except for the selection of preparation process parameters, as shown in Table 1.

[0236] The powder compaction density, D V 50. The average pore size, porosity and specific surface area are shown in Table 2.

[0237] Comparative Example 1

[0238] A positive electrode active material is provided, and as shown in FIG9 , the material is prepared according to the following steps:

[0239] Step S1: Based on the stoichiometric ratio of Na4Fe3(PO4)2P2O7, sodium pyrophosphate, ferrous oxalate, and ferric phosphate are mixed in a molar ratio of 4:3:4 (Na in sodium hydroxide, total Fe in ferrous oxalate and ferric phosphate, and P in ferric phosphate) to obtain a mixture. The mixture is dissolved in deionized water and stirred continuously at room temperature for 30 minutes to obtain an initial mixed slurry. Conductive carbon black Super P and glucose are then dissolved in deionized water and mixed to obtain a carbon solution; the conductive carbon black Super P is added in an amount of 0.5wt% of the mixture, and the glucose is added in an amount of 2.5wt% of the mixture.

[0240] Step S2: Mix the carbon solution obtained in step S1 and the initial mixed slurry obtained in step S1, and stir them evenly to obtain a mixed solution.

[0241] Step S3: spray-dry the mixed solution obtained in step S2 at an air inlet temperature of 220°C and an air outlet temperature of 109°C to obtain raw material powder. V 50 is 20μm.

[0242] Step S4: placing the raw material powder obtained in step S3 in a N2 atmosphere, heating it to 320°C at a heating rate of 2°C and keeping it warm for 4 hours, and then heating it to 550°C at a heating rate of 2°C and keeping it warm for 10 hours to obtain sodium ferric pyrophosphate.

[0243] Step S5: Place the sodium iron phosphate pyrophosphate obtained in step S4 in an air flow mill, using a classifier with a frequency of 48 Hz; use a crushing air pressure of 0.55 MPa; and crush to obtain a positive electrode active material.

[0244] The powder compaction density of the positive electrode active material of Comparative Example 1 tested under a pressure of 29400N is 1.856g / cm 3 、D V 50 is 2.879 μm, and the specific surface area is m 2 / g, see Table 2 for details.

[0245]

Material micromorphology detection

[0246] Scanning electron microscopy was used to examine the micromorphology of the positive electrode active materials.

[0247] The scanning electron microscope image of the positive electrode active material prepared in Example 1 is shown in FIG6 .

[0248] The scanning electron microscope image of the positive electrode active material prepared in Comparative Example 1 is shown in FIG7 .

[0249] As can be seen from Figure 6, the positive electrode active material prepared in Example 1 is a single crystal particle. As can be seen from Figure 7, the positive electrode active material prepared in Comparative Example 1 has agglomerated spheres. The positive electrode active material prepared in Example 1 has a smaller particle size.

[0250] From the comparison of Figures 6 and 7 , it can be seen that the primary particles of Example 1 have significantly fewer pores on their surfaces, while the primary particles of Comparative Example 1 have a large number of pores on their surfaces. This indicates that the porosity of the positive electrode active material of Example 1 is significantly lower than that of the positive electrode active material of Comparative Example 1.

[0251] Furthermore, the positive electrode active material of Example 1 has a smaller particle size, fewer pores on the surface of the primary particles, and a lower porosity, which indicates that the compaction density of the positive electrode material of Example 1 is significantly higher than that of the positive electrode active material of Comparative Example 1.

[0252]

Material parameter test method

[0253] 1. Average pore size (nm)

[0254] Analysis was performed using a high-resolution transmission electron microscope (TEM, Talos F200X) operating at 120 kV. The proportion of through-holes was determined using a statistical method: representative areas of the electron magnification image were selected, and the percentage of through-holes was calculated. The average of at least 10 representative areas was taken.

[0255] 2. Porosity (%)

[0256] Refer to pages 2-3 of GB / T 24586-2009, "Determination of Apparent Density, True Density, and Porosity of Iron Ore." Using a surface area and porosity tester, place an accurately weighed, pretreated sample in a sample tube. First, evacuate and degas the sample, then bring the entire system to the desired vacuum level. Then, immerse the sample tube in a liquid nitrogen bath and fill it with a known amount of gas. Adsorption of the gas by the adsorbent causes a pressure drop. Once adsorption equilibrium is reached, measure the equilibrium pressure and calculate the adsorbed amount based on the pressure change before and after adsorption. Repeat this process by gradually increasing the amount of adsorbate gas in the system to change the pressure, and measure the adsorption-desorption isotherm. The porosity of the sample can then be equivalently calculated using a theoretical model.

[0257] 3. Specific surface area (m 2 / g)

[0258] Surface area analysis was performed using nitrogen adsorption according to GB / T 19587-2017 and calculated using the Brunauer Emmett Teller (BET) method. The test instrument was a Micromeritics Tri-Star 3020 surface area pore size analyzer.

[0259] 4. Residual alkali content NaHCO3 (wt%)

[0260] Refer to pages 6-8 of GBT 41704-2022, "Test methods for positive electrode materials for lithium-ion batteries - Determination of magnetic foreign matter content and residual alkali content." The test instrument can be a Metrohm 905 potentiometric titrator.

[0261] The test results of each embodiment or comparative example are shown in Table 2.

[0262]

Performance test method

[0263] 1. Powder compaction density:

[0264] Test using an electronic pressure testing machine (such as UTM7305): Place a certain amount M of the powder sample to be tested prepared in each embodiment or comparative example on a special compaction mold (bottom area S), set a pressure of 29400N, maintain the pressure for 30 seconds, release the pressure, wait for 10 seconds, and read the thickness H of the powder after compaction under the pressure on the equipment. The compaction density under the pressure can be calculated. The powder compaction density of the positive electrode active material under the pressure = M / (H*S).

[0265] 2. Electrochemical properties of button batteries:

[0266] The positive electrode active material powder prepared in each embodiment or comparative example was respectively mixed with the conductive agent carbon black (Super P), the binder polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 and the solvent N-methylpyrrolidone (NMP) to form a slurry; the prepared slurry was coated on the surface of the positive electrode current collector aluminum foil, dried in an oven and set aside; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then NaPF6 was dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L; then, a metal sodium sheet was used as a counter electrode, a polyethylene (PE) film was used as an isolation membrane, and the above electrolyte was assembled into a CR2430 button battery in an argon-protected glove box.

[0267] (1) 0.1C rate first charge capacity

[0268] The CR2430 button batteries assembled from the aforementioned embodiments or comparative examples were used for testing:

[0269] After the obtained button battery was allowed to stand for 12 hours, the battery was charged at a constant current of 0.1C at 25°C to a voltage of 5V, and the charge capacity was recorded; the ratio of the charge capacity to the sample mass is the gram capacity of the corresponding positive electrode active material.

[0270] The test results of each embodiment or comparative example are shown in Table 2.

[0271] (2) First Coulomb efficiency

[0272] The CR2430 button batteries assembled from the aforementioned embodiments or comparative examples were used for testing:

[0273] After the obtained button battery was allowed to stand for 12 hours, it was charged at a constant current of 0.1C to a voltage of 5V at 25°C, and then charged at a constant voltage of 5V to a current of 0.02C. After standing for 5 minutes, the battery was discharged at a constant current of 0.1C to a voltage of 3.0V. This is a charge and discharge cycle process; the gram capacity of the first discharge and the first charge were recorded respectively, and the first coulombic efficiency (ICE) = first discharge capacity / first charge capacity × 100%.

[0274] The test results of each embodiment or comparative example are shown in Table 2.

[0275] Table 1

[0276] Table 2

[0277] From the above table data we can see that:

[0278] The powder compaction density of the positive electrode active material of each embodiment is higher than the powder compaction density of the positive electrode active material of Comparative Example 1, which shows that the embodiment of the present application can effectively improve the powder compaction density of the positive electrode active material, thereby facilitating the improvement of energy density.

[0279] The residual alkali content of the positive electrode active materials of each embodiment is significantly lower than that of the positive electrode active material of Comparative Example 1, indicating that the positive electrode active materials provided in this application can effectively reduce the residual alkali content.

[0280] The 0.1C rate first charge gram capacity of the positive electrode active materials of each embodiment is significantly higher than the 0.1C rate first charge gram capacity of the positive electrode active material of Comparative Example 1, indicating that the positive electrode active material provided in this application can effectively improve the 0.1C rate first charge gram capacity.

[0281] The first coulombic efficiency of the positive electrode active materials of each embodiment is significantly higher than the first coulombic efficiency of the positive electrode active material of Comparative Example 1, indicating that the positive electrode active material provided in this application can effectively improve the first coulombic efficiency.

[0282] The reasons for the performance improvement of this application solution include:

[0283] Comparative Example 1 uses direct high-temperature sintering to prepare sodium ferric pyrophosphate. However, direct high-temperature sintering results in the generation of numerous exhaust pores in the primary particles during the material reaction and exhaust process, ultimately leading to a low compaction density of the positive electrode active material powder, which is detrimental to energy density. The present application, on the other hand, performs low-temperature sintering first and then pulverizes the material before high-temperature sintering. This reduces the particle size of the primary particles before high-temperature sintering, increases the specific surface area, increases the exhaust area for high-temperature reactions, reduces the exhaust pores in the primary particles, and reduces the porosity of the material, thereby increasing the compaction density of the material after high-temperature sintering and contributing to an increase in energy density.

[0284] Furthermore, in Comparative Example 1, sodium iron phosphate pyrophosphate is obtained by high-temperature sintering and then crushed. The crushing causes the single crystal particles to break, the surface carbon coating layer to be damaged, the residual alkali of the positive electrode active material to increase, the charging gram capacity to decrease, and the coulombic efficiency to decrease; while the embodiment of the present application is sintered at a low temperature first (at this time, the carbon source and the raw material have not reacted) and then crushed in advance, and then sintered at a high temperature, so that the carbon coating is more complete, the residual alkali of the positive electrode active material is lower, the charging gram capacity is higher, and the coulombic efficiency is higher.

[0285] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A positive electrode active material, characterized in that The positive electrode active material is Na 4+x R 3-y P4O 15 / C; Wherein, 0≤x<0.8, 0≤y≤0.8, 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; and the porosity of the positive electrode active material is 0.69%-1.7%.

2. The positive electrode active material according to claim 1, characterized in that The porosity of the positive electrode active material is 0.69%-1.3%.

3. The positive electrode active material according to any one of claims 1 to 2, characterized in that The positive electrode active material D V 50 is 0.663μm~1.593μm.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that The positive electrode active material D V 50 is 0.663μm~1.309μm.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that The positive electrode active material D V 90 is 1.89μm~5.82μm.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that The positive electrode active material D V 90 is 1.89μm~2.74μm.

7. The positive electrode active material according to any one of claims 1 to 6, characterized in that The average pore diameter of the positive electrode active material is 9 nm to 45 nm.

8. The positive electrode active material according to any one of claims 1 to 7, characterized in that The average pore diameter of the positive electrode active material is 9 nm to 15 nm.

9. The positive electrode active material according to any one of claims 1 to 8, characterized in that The powder compaction density of the positive electrode active material tested under a pressure of 29400N is greater than or equal to 1.894g / cm 3 .

10. The positive electrode active material according to any one of claims 1 to 9, characterized in that The powder compaction density of the positive electrode active material tested under a pressure of 29400N is 2.055g / cm 3 ~2.205g / cm 3 .

11. The positive electrode active material according to any one of claims 1 to 10, characterized in that: The positive electrode active material is Na 4+x R 3-y P4O 15 / C; Among them, 0≤x<0.5, 0≤y≤0.5, 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.

12. The positive electrode active material according to any one of claims 1 to 11, characterized in that: The specific surface area of ​​the positive electrode active material is 5m 2 / g~7.98m 2 / g.

13. The positive electrode active material according to any one of claims 1 to 12, characterized in that: The specific surface area of ​​the positive electrode active material is 5m 2 / g~5.70m 2 / g.

14. A method for preparing a positive electrode active material, characterized in that: include: mixing the raw materials of the positive electrode active material to obtain a mixed solution; drying the mixed solution to obtain raw material powder; The raw material powder is first sintered at a temperature below 400° C. to obtain a first sintered material; and the D of the first sintered material is V 50 is 10μm~12μm; The first sintering material is crushed to D V 50 is 0.5 μm to 2 μm; obtaining the first raw material; Using the first raw material to perform a second sintering; Wherein, the positive electrode active material is Na 4+x R 3-y P4O 15 / C; Wherein, 0≤x<0.8, 0≤y≤0.8, 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; and the porosity of the positive electrode active material is 0.69%-1.7%.

15. The method for preparing a positive electrode active material according to claim 14, characterized in that: The raw material powder is sintered for the first time to obtain a first sintered material; the D of the first sintered material is V 50 is 10μm~12μm, including: The raw material powder is first sintered at 300° C. to 400° C.

16. The method for preparing a positive electrode active material according to claim 14 or 15, characterized in that: The raw material powder is sintered for the first time to obtain a first sintered material; the D of the first sintered material is V 50 is 10μm~12μm, including: The raw material powder is first sintered at 300° C. to 400° C. for 4 h to 8 h.

17. The method for preparing a positive electrode active material according to any one of claims 14 to 16, characterized in that: The first sintering material is crushed to D V 50 is 0.5μm~2μm, including: The first sintering material is pulverized using a first pulverizing gas pressure of 0.6 MPa or less.

18. The method for preparing a positive electrode active material according to any one of claims 14 to 17, characterized in that: The Dv90 of the first sintering material is 23.98 μm to 24.87 μm.

19. The method for preparing a positive electrode active material according to any one of claims 14 to 18, characterized in that: The Dv90 of the first raw material is 1.78 μm to 5.78 μm.

20. The method for preparing a positive electrode active material according to any one of claims 14 to 19, characterized in that: The step of drying the mixed solution to obtain raw material powder comprises: The mixed solution is spray-dried to obtain D V 50 is raw material powder of 10μm-30μm.

21. The method for preparing a positive electrode active material according to any one of claims 14 to 20, characterized in that: The second sintering using the first raw material comprises: The first raw material is used to perform a second sintering at 450° C. to 600° C.

22. A pole piece, characterized in that: The positive electrode active material comprises the positive electrode active material according to any one of claims 1 to 13; or the electrode sheet comprises the positive electrode active material prepared by the preparation method of the positive electrode active material according to any one of claims 14 to 21.

23. A battery, characterized in that: The battery comprises the pole piece according to claim 22.

24. An electrical device, characterized in that: The electric device comprises the battery according to claim 23.

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