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

Abstract

A positive electrode active material, comprising NaxRyPmOn, wherein 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m<4, 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, Nb, Mo, In, Ga, Sn, Hf, Ta, W and Pb. Due to the fact that the positive electrode active material is in a phosphorus-deficient state, the oriented growth of the crystal lattices thereof along the (602) crystal plane is facilitated, the transport path of Na+ is shortened, the diffusion rate of Na+ is increased, and therefore the rate capability and initial coulombic efficiency of a battery are improved. Moreover, small particles of the positive electrode active material are in a flat state, which is favorable for improving the density of the positive electrode active material, and thus improving the compaction density of a positive electrode active material layer.

Description

A positive electrode active material and its preparation method, a positive electrode sheet, a battery, and an electrical device thereof. Cross-references

[0001] This application claims priority to Chinese Patent Application No. 2024104945738, filed on April 23, 2024, entitled "A positive electrode active material and its preparation method, positive electrode sheet, battery and power device", the contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, and more specifically, to a positive electrode active material and its preparation method, a positive electrode sheet, a battery, and an electrical device. Background Technology

[0003] Sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7) type positive electrode active materials have advantages such as low cost, environmental friendliness, high theoretical capacity (129mAh / g), and high average operating voltage (3.1vs. Na + With characteristics such as low Na₂(PO₄)₂P₂O₇, it is considered the most promising cathode material for sodium-ion batteries. However, the Na₂(PO₄)₂P₂O₇ prepared so far... + The ion diffusion rate is slow, and the compaction density of the active material layer formed is low. Summary of the Invention

[0004] In view of the above problems, this application provides a positive electrode active material and its preparation method, a positive electrode sheet, a battery, and an electrical device, which can improve the performance of the positive electrode active material Na. x R y P m O n Na + It can improve the ion diffusion rate and enhance the compaction density of the active material layer formed therefrom.

[0005] In a first aspect, this application provides a positive electrode active material, said positive electrode active material comprising 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, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0006] In the technical solution of this application embodiment, by making the positive electrode active material Na x R y Pm O n 3.7 < m < 4, positive electrode active material Na x R y P m O n The presence of phosphorus deficiency is beneficial for its crystal lattice to grow along the (602) crystal plane, shortening the Na+ ionization period. + The transmission path improves Na + The diffusion rate is improved, which in turn benefits the battery's rate performance and initial coulombic efficiency. Simultaneously, it also improves the diffusion rate of the positive electrode active material Na... x R y P m O n The small particles are relatively flat, which helps to increase the density of the large particles formed by their aggregation, thereby increasing the compaction density of the formed active material layer.

[0007] In some embodiments, 3.8 ≤ m < 4.

[0008] In the above implementation process, by making the positive electrode active material Na x R y P m O n The condition 3.8 ≤ m < 4 allows the positive electrode active material to have a better specific capacity. Furthermore, it is more conducive to the lattice orientation growth along the (602) crystal plane, shortening the Na... + The transport path of this positive electrode active material enables batteries to have better rate performance and first-pass coulombic efficiency. Simultaneously, the relatively flat shape of its small particles helps increase the density of the large particles formed by aggregation, thereby resulting in a higher compaction density of the active material layer.

[0009] In some embodiments, the number of phosphorus vacancies is denoted as a, and the positive electrode active material includes Na. x R y P 4-a O n , 0 < a < 0.3.

[0010] In the above implementation process, through the positive electrode active material Na x R y P 4-a O n The formation of phosphorus vacancies in the lattice facilitates the orientation and growth of the crystal along the (602) crystal plane, shortening the Na+ lattice. + The transmission path improves Na + The diffusion rate is improved, which in turn benefits the battery's rate performance and initial coulombic efficiency. Simultaneously, it also improves the diffusion rate of the positive electrode active material Na... x R y P 4-a O nThe small particles are relatively flat, which helps to increase the density of the large particles formed by their aggregation, thereby increasing the compaction density of the formed active material layer.

[0011] In some embodiments, 0 < a ≤ 0.2.

[0012] In the above implementation process, by controlling 0 < a ≤ 0.2, it is more conducive to the growth of its crystal lattice along the (602) crystal plane and shortening the Na... + The transport path of this cathode active material allows batteries to exhibit better rate performance and initial coulombic efficiency. Simultaneously, the relatively flat shape of its small particles facilitates the increase in the density of the large particles formed through aggregation, resulting in a higher compaction density of the formed active material layer. Furthermore, the cathode active material also possesses good specific capacity.

[0013] In some embodiments, the chemical formula of the positive electrode active material is Na. x Fe y P m O n Among them, 3.9≤x≤4.2, 2.8≤y≤3.1, 3.8≤m<4, and 14.5≤n≤15.5.

[0014] In some embodiments, the relationship between the X-ray diffraction intensity I(602) of the (602) crystal plane and the X-ray diffraction intensity I(022) of the (022) crystal plane of the positive electrode active material satisfies: I(602) / I(022) = 1.12~1.15.

[0015] In the above embodiments, the ratio of the X-ray diffraction intensity I(602) of the positive electrode active material (602) crystal plane to the X-ray diffraction intensity I(022) of the (022) crystal plane is 1.12 to 1.15, which is beneficial to improving the Na + The diffusion rate is improved, which in turn benefits the battery's rate performance and initial coulombic efficiency. Simultaneously, it also improves the diffusion rate of the positive electrode active material Na... x R y P m O n The flatness of the small particles is within a good range, which helps to reduce the porosity in the large particles formed by their aggregation, while keeping the large particles relatively round and having good sphericity, thereby better improving the compaction density of the active material layer formed by them.

[0016] In some embodiments, the relationship between the X-ray diffraction intensity I(602) of the positive electrode active material (602) crystal plane and the X-ray diffraction intensity I(022) of the (022) crystal plane satisfies: I(602) / I(022)=1.13~1.14.

[0017] In some embodiments, the porosity of the positive electrode active material is 0.012–0.078 cm⁻¹. 3 / g.

[0018] In the above implementation process, the porosity of the positive electrode active material is controlled to be 0.012–0.078 cm⁻¹. 3 / g, which is beneficial to increasing the compaction density of the active material layer formed.

[0019] In some embodiments, the median particle size Dv50 of the positive electrode active material is 2–3 μm.

[0020] In the above implementation process, the smaller the particle size of the positive electrode active material, the more beneficial it is to the compaction density of the positive electrode active material layer, which in turn is beneficial to the volumetric energy density of the battery; while the larger the particle size of the positive electrode active material, the easier its preparation is, and the more beneficial it is to control its cost. By controlling the median particle size Dv50 of the positive electrode active material to 2-3 μm, both the volumetric energy density and cost of the battery can be balanced.

[0021] In some embodiments, the chemical formula of the positive electrode active material is Na. x R y P m O n / C, where 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, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0022] In the above implementation process, by using the positive electrode active material Na x R y P m O n Combining with C can reduce the Na content of the positive electrode active material. x R y P m O n During preparation and use, it comes into contact with water and other external environmental elements, thereby reducing the generation of residual alkali during preparation and use.

[0023] In some embodiments, the number of R vacancies is denoted as z, and the positive electrode active material includes Na. x R 3-z P m O n , 0≤z≤0.5.

[0024] In the above implementation process, by controlling 0≤z≤0.5, the content of impurity phases such as NaFePO4 in the positive electrode active material is reduced, thereby increasing the content of Na4R3(PO4)2P2O7, which is beneficial to improving the specific capacity of the positive electrode active material.

[0025] In some embodiments, 0 < z ≤ 0.2.

[0026] In the above implementation process, by controlling 0<z≤0.2, the content of impurity phases such as NaFePO4 in the positive electrode active material is further reduced, thereby increasing the content of Na4R3(PO4)2P2O7, which is more conducive to improving the specific capacity of the positive electrode active material.

[0027] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0028] (a) The initial coulombic efficiency of the positive electrode active material is ≥93%;

[0029] (b) The specific capacity of the positive electrode active material is 110–126 mAh / g;

[0030] (c) The mass content of residual alkali in the positive electrode active material is ≤0.36%.

[0031] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0032] (a) The initial coulombic efficiency of the positive electrode active material is ≥94%;

[0033] (b) The specific capacity of the positive electrode active material is 123.2 to 125.8 mAh / g.

[0034] In some embodiments, the compaction density of the positive electrode sheet is 2.15–2.25 g / cm³. 3 .

[0035] Secondly, this application provides a method for preparing a positive electrode active material, the method comprising:

[0036] Sodium source, R source and phosphorus source are mixed to obtain a mixture, wherein the molar ratio of Na, R and P in the mixture is 3.5-4.7:2.3-3.5:3.5-4, wherein R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, In, Ga, Sn, Hf, Ta, W and Pb;

[0037] The mixture is sintered to obtain a positive electrode active material, wherein the positive electrode active material includes Na. x R y Pm O n Among them, 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m<4, and 14.5≤n≤15.5.

[0038] In the technical solution of this application embodiment, by reducing the addition of phosphorus source during preparation, the proportion of phosphorus is made less than the theoretical value of 4, thereby making the positive electrode active material Na... x R y P m O n The presence of phosphorus deficiency is beneficial for its crystal lattice to grow along the (602) crystal plane, shortening the Na+ ionization period. + The transmission path improves Na + The diffusion rate is improved, which in turn benefits the battery's rate performance and initial coulombic efficiency. Simultaneously, it also improves the diffusion rate of the positive electrode active material Na... x R y P m O n The small particles are relatively flat, which helps to increase the density of the large particles formed by their aggregation, thereby increasing the compaction density of the formed active material layer.

[0039] In some embodiments, the mixture further includes a carbon source.

[0040] In some embodiments, the carbon source includes a first carbon source and a second carbon source, wherein the first carbon source includes an inorganic carbon source and the second carbon source includes an organic carbon source.

[0041] In the above implementation process, the simultaneous use of inorganic and organic carbon sources for coating facilitates the crystal growth of the positive electrode active material, resulting in higher lattice regularity. Simultaneously, it reduces the content of impurity phases in the positive electrode active material, thereby increasing its specific capacity. Furthermore, it achieves better coating of the positive electrode active material, reducing the possibility of Na4R3(PO4)2P2O7 reacting with water in the environment, which is beneficial to the cycle stability of the positive electrode active material.

[0042] In some embodiments, the first carbon source includes at least one selected from graphite, carbon black, carbon nanotubes, and graphene; and / or

[0043] The second carbon source includes at least one of sucrose, glucose, citric acid, starch, cyclodextrin, pitch, and PEG.

[0044] Thirdly, this application provides a positive electrode sheet, which includes a positive electrode active material layer, comprising the positive electrode active material provided in the first aspect or the positive electrode active material prepared by the method provided in the second aspect.

[0045] Fourthly, this application provides a battery, which includes the positive electrode provided in the third aspect.

[0046] Fifthly, this application provides an electrical device that includes the battery provided in the fourth aspect. Attached Figure Description

[0047] 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:

[0048] Figure 1 is a structural schematic diagram of a vehicle provided in some embodiments of this application;

[0049] Figure 2 is an exploded structural diagram of a secondary battery provided in some embodiments of this application;

[0050] Figure 3 is a schematic diagram of the structure of a battery cell provided in some embodiments of this application;

[0051] Figure 4 is an exploded view of a single battery cell provided in some embodiments of this application;

[0052] Figure 5 is a scanning electron microscope image of the positive electrode active material provided in some embodiments of this application;

[0053] Figure 6 is a flowchart of a method for preparing positive electrode active materials according to some embodiments of this application;

[0054] Figure 7 is a schematic diagram of the first structure of the positive electrode sheet provided in some embodiments of this application;

[0055] Figure 8 is a schematic diagram of the second structure of the positive electrode sheet provided in some embodiments of this application;

[0056] Figure 9 is a flowchart of the preparation process of a battery cell provided in some embodiments of this application;

[0057] Figure 10 is a scanning electron microscope image of the positive electrode active material provided in Comparative Example 2 of this application;

[0058] Figure 11 is a scanning electron microscope image of the positive electrode active material provided in Comparative Example 3 of this application;

[0059] Figure 12 is a scanning electron microscope image of the positive electrode active material provided in Example 3 of this application.

[0060] The reference numerals in the detailed embodiments are as follows:

[0061] 1000 - Vehicle; 100 - Secondary battery; 200 - Motor; 300 - Controller; 10 - Housing; 11 - Accommodation space; 12 - First part; 13 - Second part; 20 - Battery cell; 21 - Shell; 211 - Opening; 22 - End cap assembly; 221 - End cap; 222 - Electrode terminal; 23 - Electrode assembly; 231 - Positive electrode sheet; 2311 - Positive current collector; 2312 - Positive active material layer; 24 - Current collector component; 25 - Insulation protection component. Detailed Implementation

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0067] 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).

[0068] 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.

[0069] 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.

[0070] 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.

[0071] Sodium-ion batteries can be used as power batteries. Sodium is abundant, which can significantly reduce battery costs, thus giving sodium-ion batteries broad application prospects. For example, sodium-ion batteries can be used in portable electronic devices, electric vehicles, and other fields. Sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7) type positive electrode active materials have advantages such as low cost, environmental friendliness, high theoretical capacity (129mAh / g), and high average operating voltage (3.1Vs.Na2O7). + With characteristics such as low Na₂(PO₄)₂P₂O₇, it is considered the most promising cathode material for sodium-ion batteries. However, the Na₂(PO₄)₂P₂O₇ prepared so far... + The ion diffusion rate is slow, and the compaction density of the active material layer formed is low.

[0072] Based on the above considerations, in order to improve the Na+ of sodium iron pyrophosphate-based cathode active materials + To improve the ion diffusion rate and the compaction density of the formed active material layer, this application proposes a positive electrode active material, wherein the positive electrode active material includes 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, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0073] In such a positive electrode active material, by making the positive electrode active material Na x R y P m O n 3.7 < m < 4, which enables the use of Na as a positive electrode active material. x R y P m O n The presence of phosphorus deficiency is beneficial for its crystal lattice to grow along the (602) crystal plane, shortening the Na+ ionization period. + The transmission path improves Na + The diffusion rate is improved, which in turn benefits the battery's rate performance and initial coulombic efficiency. Simultaneously, it also improves the diffusion rate of the positive electrode active material Na... x R y P m O n The small particles are relatively flat, which helps to increase the density of the large particles formed by their aggregation, thereby giving the active material layer a higher compaction density.

[0074] This positive electrode active material can be used to prepare the positive electrode active material layer of a positive electrode sheet, which can be used to prepare an electrode assembly. This electrode assembly can be used, but is 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 or the like disclosed in this application.

[0075] 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.

[0076] 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.

[0077] 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 secondary battery 100 is installed inside the vehicle 1000, and the secondary battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The secondary battery 100 can be used to power the vehicle 1000; for example, the secondary battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 300 and a motor 200. The controller 300 is used to control the secondary battery 100 to supply power to the motor 200, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0078] In some embodiments of this application, the secondary 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.

[0079] In this application, the secondary battery 100 can refer to a single battery cell 20, or it can refer to a single physical module comprising multiple battery cells 20 to provide higher voltage and capacity, which can be in the form of a battery pack, battery module, etc. The secondary battery 100 may include a housing 10 for encapsulating multiple battery cells 20, and the housing 10 can prevent liquids or other foreign objects from affecting the charging or discharging of the battery cells 20.

[0080] Figure 2 is an exploded structural diagram of a secondary battery 100 provided in some embodiments of this application. Referring to Figure 2, the secondary battery 100 includes a housing 10 and battery cells 20, with the battery cells 20 housed within the housing 10.

[0081] The housing 10 provides a receiving space 11 for the battery cell 20. In some embodiments, the housing 10 may include a first portion 12 and a second portion 13, which overlap each other to define the receiving space 11 for accommodating the battery cell 20. Of course, the connection between the first portion 12 and the second portion 13 may be sealed by a sealant (not shown), such as a sealing ring, sealant, etc.

[0082] The first part 12 and the second part 13 can be of various shapes, such as cuboids, cylinders, etc. The first part 12 can be a hollow structure with one side open to form a cavity for accommodating the battery cell 20, and the second part 13 can also be a hollow structure with one side open to form a cavity for accommodating the battery cell 20. The opening side of the second part 13 covers the opening side of the first part 12, thus forming a box 10 with a accommodating space 11. Of course, as shown in Figure 2, the first part 12 can also be a hollow structure with one side open, and the second part 13 can be a plate-like structure. The second part 13 covers the opening side of the first part 12, thus forming a box 10 with a accommodating space 11.

[0083] In the secondary battery 100, there are multiple battery cells 20. These multiple battery cells 20 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. 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, multiple battery cells 20 can first be connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules can be connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the housing 10. The battery cell 20 can be cylindrical, flat, cuboid, or other shapes. Figure 2 illustrates an example of a square battery cell 20.

[0084] In some embodiments, the secondary battery 100 may further include a busbar (not shown), through which multiple battery cells 20 can be electrically connected to each other to achieve series, parallel, or mixed connection of multiple battery cells 20.

[0085] Figure 3 is a schematic diagram of the structure of a battery cell 20 provided in some embodiments of this application, and Figure 4 is an exploded view of a battery cell 20 provided in some embodiments of this application. Referring to Figures 3 and 4, the battery cell 20 may include a housing 21, an end cap assembly 22, and an electrode assembly 23. The housing 21 has an opening 211, the electrode assembly 23 is accommodated within the housing 21, and the end cap assembly 22 is used to seal the opening 211.

[0086] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 is a cuboid structure, the housing 21 can also be a cuboid structure. Figures 3 and 4 exemplarily show the case where the housing 21 and the electrode assembly 23 are square.

[0087] The outer shell 21 can also be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc. This application embodiment does not impose any special restrictions on this.

[0088] The end cap assembly 22 includes an end cap 221 and electrode terminals 222. The end cap assembly 22 is used to seal the opening 211 of the housing 21 to form a sealed mounting space (not shown) for accommodating the electrode assembly 23. The mounting space also accommodates an electrolyte, such as an electrolyte solution. As a component that outputs electrical energy to the electrode assembly 23, the end cap assembly 22 has electrode terminals 222 for electrical connection to the electrode assembly 23, specifically, the electrode terminals 222 are electrically connected to the tabs of the electrode assembly 23. For example, the electrode terminals 222 and the tabs are connected via a current collector 24 to achieve the electrical connection between the electrode terminals 222 and the tabs.

[0089] It should be noted that the opening 211 of the outer casing 21 can be one or two. If the outer casing 21 has one opening 211, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22. The two electrode terminals 222 are used to electrically connect to the positive electrode tab and the negative electrode tab of the electrode assembly 23, respectively. If the outer casing 21 has two openings 211, for example, the two openings 211 are located on opposite sides of the outer casing 21, the end cap assembly 22 can also be two, and the two end cap assemblies 22 respectively cover the two openings 211 of the outer casing 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal 222, used to electrically connect to the positive electrode tab of the electrode assembly 23; the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal 222, used to electrically connect to the negative electrode plate of the electrode assembly 23.

[0090] In some embodiments, as shown in FIG4, the battery cell 20 may further include an insulating protective member 25 fixed to the outer periphery of the electrode assembly 23. The insulating protective member 25 is used to insulate and isolate the electrode assembly 23 from the housing 21. Exemplarily, the insulating protective member 25 is an adhesive tape bonded to the outer periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 surrounds the outer periphery of multiple electrode assemblies 23, forming multiple electrode assemblies 23 into an integral structure to maintain the structural stability of the electrode assembly 23.

[0091] The electrode assembly 23 includes a positive electrode 231, a negative electrode 231, and a separator. The separator is located between the positive electrode 231 and the negative electrode 231 and serves as a separator. The electrode assembly 23 can be a wound structure or a stacked structure, and the embodiments of this application are not limited to these.

[0092] This application does not impose any particular restrictions on the positive electrode 231, the negative electrode, and the separator.

[0093] In some embodiments, the separator can be a PP (polypropylene) porous membrane, a PE (polyethylene) porous membrane, a polyimide porous membrane, or a porous membrane formed by a composite of various polymers.

[0094] In some embodiments, the positive electrode 231 includes a positive current collector 2311 and a positive active material layer 2312 covering at least one surface of the positive current collector 2311 in the thickness direction; the positive current collector 2311 without the positive active material layer 2312 protrudes from the positive current collector 2311 with the positive active material layer 2312 coated, and the positive current collector 2311 without the positive active material layer 2312 coated serves as a positive electrode tab. The material of the positive electrode current collector 2311 may include aluminum foil, aluminum foam, aluminum composite current collector (with a polymer support layer in the middle, and aluminum metal layers on both surfaces of the support layer), nickel foil, nickel foam, etc.; the positive electrode active material in the positive electrode active material layer 2312 includes one or a mixture of several of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium olivine-structured lithium phosphates, such as lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, etc.; positive electrode The binder in the active material layer 2312 is selected from at least one of vinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylate, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, ethylene-vinyl acetate copolymer, and ethylene-acrylic acid copolymer; the dispersant in the positive electrode active material layer 2312 is selected from polyvinylpyrrolidone, etc.; the conductive particles in the positive electrode active material layer 2312 are selected from at least one of conductive carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, graphene, activated carbon, graphite sheets, graphite particles, and mesophase carbon microspheres.

[0095] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet 231, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g. N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0096] In some embodiments, the negative electrode includes a negative current collector and a negative active material layer covering at least one surface of the negative current collector in the thickness direction; the negative current collector without the negative active material layer protrudes from the negative current collector with the negative active material layer, and the negative current collector without the negative active material layer serves as a negative electrode tab. The material of the negative current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or a polymer substrate coated with a conductive metal, wherein the conductive metal includes, but is not limited to, copper, nickel, or titanium, and the polymer substrate material includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene propylene copolymer, polyethylene terephthalate, polyethylene terephthalate, and poly(p-phenylene terephthalate); the negative active material in the negative active material layer includes carbon materials, elemental lithium, and alloys formed by lithium and other metallic or non-metallic elements, wherein the carbon materials include, but are not limited to, at least one of hard carbon, soft carbon, amorphous carbon, and nanostructured carbon materials, all of which are commercially available. Metallic elements include tin (Sn), zinc (Zn), aluminum (Al), magnesium (Mg), silver (Ag), gold (Au), gallium (Ga), indium (In), and tin foil (Pt), while non-metallic elements include boron (B), carbon (C), and silicon (Si).

[0097] In other embodiments, the current collector of the negative electrode sheet may also include a current collector body and a base coating. The base coating may be disposed on at least one side of the current collector body. The base coating basically does not contain negative electrode active material, but may contain a small amount of carbon material. However, the carbon material forms a thin coating and cannot function as a negative electrode active material. In this embodiment, the negative electrode sheet can be an electrode sheet without a negative electrode active material layer. For a negative electrode sheet without a negative electrode active material layer, when the current collector of the negative electrode sheet does not contain a base coating, the film layer of the negative electrode sheet can be disposed on the surface of at least one side of the current collector body; when the current collector of the negative electrode sheet includes a base coating, the film layer of the negative electrode sheet can be disposed on the surface of the base coating away from the current collector body.

[0098] In some embodiments, the electrolyte acts as a conductor of ions between the positive and negative electrode plates. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0099] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0100] 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 difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0101] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0102] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0103] Figure 5 is a scanning electron microscope image of a positive electrode active material provided in some embodiments of this application; referring to Figure 5, an embodiment of this application provides a positive electrode active material, the positive electrode active material including 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, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0104] The content of each element can be obtained by inductively coupled plasma atomic emission spectrometry (ICP).

[0105] By making the positive electrode active material Na x R y P m O n 3.7 < m < 4, which enables the use of Na as a positive electrode active material. x R y P m O n The presence of phosphorus deficiency is beneficial for its crystal lattice to grow along the (602) crystal plane, shortening the Na+ ionization period. + The transmission path improves Na + The diffusion rate is improved, which in turn benefits the battery's rate performance and initial coulombic efficiency. Simultaneously, it also improves the diffusion rate of the positive electrode active material Na... x R y P m O n The small particles are relatively flat, which helps to increase the density of the large particles formed by their aggregation, thereby giving the active material layer a higher compaction density.

[0106] It should be noted that the above limitation on x includes the molar content of Na under different charge and discharge states of the battery (typically the battery voltage is between 2-5V).

[0107] Understandably, sodium (Na) is intercalated and deintercalated during the charging and discharging process of a battery. The Na content in the positive electrode varies depending on the state of discharge. The Na content can be measured using molar content, but is not limited to this. Simultaneously, when a positive electrode material is applied to the positive electrode in a battery system, the Na content in the positive electrode material typically changes after charge-discharge cycles. In the examples of positive electrode materials listed in this application, unless otherwise specified, the Na content refers to the initial state of the material. Regarding "Na content refers to the initial state of the material," the initial state of the material refers to its state before being added to the positive electrode slurry. It is understood that new materials obtained by appropriately modifying the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for the positive electrode material; non-limiting examples include coating modification.

[0108] It is understandable that the molar content of R, y, and the molar content of Na are similar, so we will not elaborate on them here.

[0109] For example, Na x R y P m O n In this case, x can be 3.5, 3.55, 3.6, 3.65, 3.7, 3.75, 3.8, 3.85, 3.9, 3.95, 4, 4.05, 4.1, 4.15, 4.2, 4.25, 4.3, 4.35, 4.4, 4.45, or 4.5, or any value within the range of 3.5 to 4.5. Na x R y P m O n In this case, y can be 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, or 3.5, or any value within the range of 2.5 to 3.5. Na x R y P m O n In this case, m can be 3.7, 3.75, 3.8, 3.85, 3.9, 3.91, 3.92, 3.93, 3.94, 3.94, 3.95, 3.96, 3.97, 3.98, or 3.99, etc., or any value within the range of 3.7 to 4. Na x R y P m O nIn this case, n can be 14.5, 14.6, 14.7, 14.8, 14.9, 15, 15.1, 15.2, 15.3, 15.4 or 15.5, etc., or any value in the range of 14.5 to 15.5.

[0110] In some embodiments of this application, 3.8 ≤ m < 4. This is achieved by making the positive electrode active material Na... x R y P m O n The condition 3.8 ≤ m < 4 allows the positive electrode active material to have a better specific capacity. Furthermore, it is more conducive to the lattice orientation growth along the (602) crystal plane, shortening the Na... + The transport path of this positive electrode active material enables batteries to have better rate performance and first-pass coulombic efficiency. Simultaneously, the relatively flat shape of its small particles helps increase the density of the large particles formed by aggregation, thereby resulting in a higher compaction density of the active material layer.

[0111] In some embodiments of this application, the number of phosphorus vacancies is denoted as 'a', and the positive electrode active material includes Na. x R y P 4-a O n , 0 < a < 0.3.

[0112] A vacancy is a type of point defect, which in turn is a type of crystal defect that deviates from the normal arrangement of the crystal structure at or near a node. Point defects occur within one or more lattice constants in a crystal and are very small in size in all three dimensions. The number of vacancies refers to the difference between the theoretical and actual number of a certain element in the crystal lattice. The phosphorus vacancy number 'a' refers to the difference between the theoretical and actual number of phosphorus elements in the crystal lattice. For example, inductively coupled plasma atomic emission spectrometry (ICP) can be used to determine the content of each element in the entire positive electrode active material, and the impurity phase and its content in the positive electrode active material can be detected. Based on the chemical formula and content of the impurity phase, the content of each element in the impurity phase (e.g., NaRPO4) can be calculated. The content of each element in the impurity phase (e.g., NaRPO4) can be obtained by subtracting the content of each element in the impurity phase (e.g., NaRPO4) from the content of each element in the entire positive electrode active material. x R y P 4-a O n The chemical formula is obtained, and then the number of phosphorus vacancies a is obtained. The detection of impurity phases and their contents can be carried out by methods such as XRD.

[0113] Through the positive electrode active material Na x R y P 4-a O nThe formation of phosphorus vacancies in the lattice facilitates the orientation and growth of the crystal along the (602) crystal plane, shortening the Na+ lattice. + The transmission path improves Na + The diffusion rate is improved, which in turn benefits the battery's rate performance and initial coulombic efficiency. Simultaneously, it also improves the diffusion rate of the positive electrode active material Na... x R y P 4-a O n The small particles are relatively flat, which helps to increase the density of the large particles formed by their aggregation, thereby increasing the compaction density of the formed active material layer.

[0114] In some embodiments of this application, 0 < m ≤ 0.2. By controlling 0 < m ≤ 0.2, it is more beneficial for the crystal lattice to grow along the (602) crystal plane, shortening the Na... + The transport path of this material allows batteries using this positive electrode active material to exhibit better rate performance and initial coulombic efficiency. It also improves the performance of the positive electrode active material Na. x R y P m O n The small particles are relatively flat, which helps to increase the density of the large particles formed by their aggregation, and thus further enhances the compaction density of the active material layer formed by them.

[0115] In some embodiments of this application, the chemical formula of the positive electrode active material is Na. x Fe y P m O n Among them, 3.9≤x≤4.2, 2.8≤y≤3.1, 3.8≤m<4, and 14.5≤n≤15.5.

[0116] In some embodiments of this application, the relationship between the X-ray diffraction intensity I(602) of the (602) crystal plane and the X-ray diffraction intensity I(022) of the (022) crystal plane of the positive electrode active material satisfies: I(602) / I(022) = 1.12~1.15. A ratio of 1.12~1.15 between the X-ray diffraction intensity I(602) of the (602) crystal plane and the X-ray diffraction intensity I(022) of the (022) crystal plane of the positive electrode active material is beneficial for improving the performance of Na+. + The diffusion rate is improved, which in turn benefits the battery's rate performance and initial coulombic efficiency. Simultaneously, it also improves the diffusion rate of the positive electrode active material Na... x R y P m O n The flatness of the small particles is within a good range, which helps to reduce the porosity in the large particles formed by their aggregation, while keeping the large particles relatively round and having good sphericity, thereby better improving the compaction density of the active material layer formed by them.

[0117] For example, the ratio of the X-ray diffraction intensity I(602) of the positive electrode active material (602) crystal plane to the X-ray diffraction intensity I(022) of the (022) crystal plane, I(602) / I(022), can be 1.12, 1.13, 1.14 or 1.15, etc., or it can be any value in the range of 1.12 to 1.15.

[0118] In some embodiments of this application, the relationship between the X-ray diffraction intensity I(602) of the positive electrode active material (602) crystal plane and the X-ray diffraction intensity I(022) of the (022) crystal plane satisfies: I(602) / I(022)=1.13~1.14.

[0119] In some embodiments of this application, the porosity of the positive electrode active material is 0.012–0.078 cm⁻¹. 3 / g.

[0120] Porosity refers to the percentage of the nitrogen-measurable pore volume in the above-mentioned positive electrode active material to the total volume of the positive electrode active material under natural conditions.

[0121] The porosity test method can be as follows: Using a specific surface area and porosity tester, place an accurately weighed pretreated sample in a sample tube, first degas the sample by evacuation, then bring the entire system to the required vacuum level, then immerse the sample tube in a liquid nitrogen bath and fill it with nitrogen gas. The adsorbent adsorbs the gas, causing a pressure drop. After adsorption equilibrium is reached, measure the equilibrium pressure of the gas, and calculate the adsorption amount based on the pressure change of the system before and after adsorption. Gradually increase the amount of adsorbate gas in the system to change the pressure, repeat the above operation, and test the adsorption-desorption isotherms. Then, use a theoretical model to equivalently calculate the porosity of the sample being tested.

[0122] By controlling the porosity of the positive electrode active material to be 0.012–0.078 cm⁻¹ 3 / g, which is beneficial to increasing the compaction density of the active material layer formed therefrom.

[0123] For example, the porosity of the positive electrode active material can be 0.012 cm⁻¹. 3 / g, 0.02cm 3 / g, 0.03cm 3 / g, 0.04cm 3 / g, 0.05cm 3 / g, 0.06cm 3 / g, 0.07cm 3 / g or 0.078cm 3 / g, etc., can also be 0.012~0.078cm 3 Any value within the range / g.

[0124] In some embodiments of this application, the median particle size Dv50 of the positive electrode active material is 2-3 μm.

[0125] The median particle size Dv50 is the particle size corresponding to 50% of the cumulative amount in the volumetric particle size distribution map. The volumetric particle size distribution map, also known as the differential particle size distribution map, is a curve plotted with particle size on the x-axis and the differential distribution of particle size at different dimensions on the y-axis. It can accurately reflect the particle size distribution characteristics of a material. A laser particle size analyzer can be used to determine the volumetric particle size distribution of the material and plot the interval particle size distribution curve. When measuring the median particle size of the positive electrode active material in the active material layer of the electrode sheet, the positive electrode active material layer can be removed, immersed in the solvent NMP, and the binder in the positive electrode active material layer can be washed out to obtain the powder material of the positive electrode active material layer. After drying the powder material, a Mastersizer3000 laser particle size analyzer is used to detect the volumetric particle size distribution map. The median particle size of polycrystalline and single-crystal particles can be obtained from the peaks in the volumetric particle size distribution map.

[0126] The median particle size Dv50 of the positive electrode active material refers to the particle size when the positive electrode active material is accumulated from smallest to largest until it accounts for 50% of the total volume.

[0127] Smaller particle size of the positive electrode active material is more conducive to the compaction density of the positive electrode active material layer, which in turn is beneficial to the volumetric energy density of the battery; while larger particle size of the positive electrode active material is easier to manufacture and more conducive to cost control. By controlling the median particle size Dv50 of the positive electrode active material to 2-3 μm, both the volumetric energy density and cost of the battery can be balanced.

[0128] For example, the median particle size Dv50 of the positive electrode active material can be 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, 2.6μm, 2.7μm, 2.8μm, 2.9μm or 3μm, etc., or it can be any value in the range of 2 to 3μm.

[0129] In some embodiments of this application, the chemical formula of the positive electrode active material is Na. x R y P m O n / C, where 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, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0130] Na x R y P m O n / C refers to Na x R y P m O n A complex with C.

[0131] By using Na, the positive electrode active material x R y P m O n Combining with C can reduce the Na content of the positive electrode active material. x R y P m O n During preparation and use, it comes into contact with water and other external environmental elements, thereby reducing the generation of residual alkali during preparation and use.

[0132] In some embodiments of this application, the number of R vacancy numbers is denoted as z, and the positive electrode active material includes Na. x R 3-z P m O n , 0≤z≤0.5.

[0133] A vacancy is a type of point defect, which in turn is a type of crystal defect that deviates from the normal arrangement of the crystal structure at or near a node. Point defects occur within one or more lattice constants in a crystal and are very small in size in all three dimensions. The number of vacancies refers to the difference between the theoretical and actual number of a certain element in the lattice. The R-vacancy number z refers to the difference between the theoretical and actual number of element R in the lattice. For example, inductively coupled plasma atomic emission spectrometry (ICP) can be used to determine the content of each element in the entire positive electrode active material, and the impurity phase and its content in the positive electrode active material can be detected. Based on the chemical formula and content of the impurity phase, the content of each element in the impurity phase (e.g., NaRPO4) can be calculated. By subtracting the content of each element in the impurity phase (e.g., NaRPO4) from the content of each element in the entire positive electrode active material, the Na content can be obtained. x R 3-z P m O n The chemical formula is obtained, and then the number of R vacancies z is obtained. The detection of impurity phases and their content can be performed using methods such as XRD.

[0134] By controlling 0≤z≤0.5, the content of impurity phases such as NaFePO4 in the positive electrode active material is reduced, thereby increasing the content of Na4R3(PO4)2P2O7, which is beneficial to improving the specific capacity of the positive electrode active material.

[0135] In some embodiments of this application, 0 < z ≤ 0.2. By controlling 0 < z ≤ 0.2, the content of impurity phases such as NaFePO4 in the positive electrode active material is further reduced, thereby increasing the content of Na4R3(PO4)2P2O7, which is more conducive to improving the specific capacity of the positive electrode active material.

[0136] In some embodiments of this application, the positive electrode active material satisfies one or more of the following characteristics:

[0137] (a) The initial coulombic efficiency of the positive electrode active material is ≥93%;

[0138] (b) The specific capacity of the positive electrode active material is 110–126 mAh / g;

[0139] (c) The residual alkali content in the positive electrode active material is ≤0.36% by mass.

[0140] For example, the initial coulombic efficiency of the positive electrode active material can be 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.1%, 99.2%, 99.3%, 99.4%, or 99.5%, etc., or any value within the range >92.6%. The specific capacity of the positive electrode active material can be 110 mAh / g, 112 mAh / g, 115 mAh / g, 118 mAh / g, 121 mAh / g, 124 mAh / g, or 126 mAh / g, etc., or any value within the range of 110–126 mAh / g. The mass content of residual alkali in the positive electrode active material can be 0, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, or 0.36%, etc., or any value within the range ≤0.36%.

[0141] In some embodiments of this application, the positive electrode active material satisfies one or more of the following characteristics:

[0142] (a) The initial coulombic efficiency of the positive electrode active material is ≥94%;

[0143] (b) The specific capacity of the positive electrode active material is 123.2 to 125.8 mAh / g.

[0144] Figure 6 is a flowchart of a method for preparing a positive electrode active material according to some embodiments of this application. Referring to Figure 6, this application also provides a method for preparing a positive electrode active material, the method including:

[0145] S110. A sodium source, an R source, and a phosphorus source are mixed to obtain a mixture, wherein the molar ratio of Na, R, and P in the mixture is 3.5–4.7: 2.3–3.5: 3.5–4, wherein R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb;

[0146] The sodium source can be at least one of sodium salt, sodium hydroxide, or sodium oxide. The phosphorus source includes at least one of phosphate or phosphoric acid. The R source includes at least one of salt, oxide, or hydroxide of element R; the R source can also be an iron source.

[0147] In some embodiments of this application, the mixture further includes a carbon source.

[0148] In some embodiments of this application, the carbon source includes a first carbon source and a second carbon source. The first carbon source includes an inorganic carbon source, and the second carbon source includes an organic carbon source. By simultaneously employing both inorganic and organic carbon sources for coating, the crystal growth of the positive electrode active material is facilitated, resulting in higher lattice regularity. Simultaneously, it reduces the content of impurity phases in the positive electrode active material, thereby increasing its specific capacity. Furthermore, it achieves better coating of the positive electrode active material, reducing the possibility of Na4R3(PO4)2P2O7 reacting with water in the environment, which is beneficial to the cycle stability of the positive electrode active material.

[0149] The first carbon source includes at least one of graphite, carbon black, carbon nanotubes, and graphene; the second carbon source includes at least one of sucrose, glucose, citric acid, starch, cyclodextrin, pitch, and PEG.

[0150] S120. The mixture is sintered to obtain a positive electrode active material, wherein the positive electrode active material includes Na. x R y P m O n Among them, 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m<4, and 14.5≤n≤15.5.

[0151] It should be noted that, due to other losses of phosphorus during the preparation process, the amount of phosphorus added is greater than that of the final product, the positive electrode active material Na. x R y P m O n The amount of phosphorus added is understandable, and therefore the amount of phosphorus added is related to the final product's positive electrode active material, Na. x R y P m O nThe value of m in the equation will show a positive correlation to some extent.

[0152] This method reduces the amount of phosphorus added during preparation, making the phosphorus content less than the theoretical value of 4, thereby making the positive electrode active material Na... x R y P m O n The presence of phosphorus deficiency is beneficial for its crystal lattice to grow along the (602) crystal plane, shortening the Na+ ionization period. + The transmission path improves Na + The diffusion rate is improved, which in turn benefits the battery's rate performance and initial coulombic efficiency. Simultaneously, it also improves the diffusion rate of the positive electrode active material Na... x R y P m O n The small particles are relatively flat, which helps to increase the density of the large particles formed by their aggregation, thereby increasing the compaction density of the active material layer formed.

[0153] Figure 7 is a first structural schematic diagram of the positive electrode 231 provided in some embodiments of this application, and Figure 8 is a second structural schematic diagram of the positive electrode 231 provided in some embodiments of this application; please refer to Figures 7 and 8, the embodiments of this application provide a positive electrode 231, the positive electrode 231 includes a positive active material layer 2312, the positive active material layer 2312 includes the positive active material provided above.

[0154] In some embodiments of this application, the compaction density of the positive electrode sheet is 2.15–2.25 g / cm³. 3 .

[0155] For example, the compaction density of the positive electrode sheet can be 2.15 g / cm³. 3 2.16 g / cm 3 2.17 g / cm 3 2.18 g / cm 3 2.19 g / cm 3 2.2g / cm 3 2.21 g / cm 3 2.22 g / cm 3 2.23 g / cm 3 2.24 g / cm 3 Or 2.25g / cm 3 etc., its concentration can also be 2.15–2.25 g / cm³. 3 Any value within the range.

[0156] Please refer to Figure 7. The positive electrode active material layer 2312 can be disposed on one side of the positive electrode current collector. Please refer to Figure 8. The positive electrode active material layer 2312 can also be disposed on both sides of the positive electrode current collector. The material of the positive electrode current collector 2311 can be one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

[0157] Having introduced the materials and structure of the battery cell 20, the preparation method of the battery cell 20 will be described in detail below.

[0158] The preparation method of the battery cell 20 includes the following steps: mixing positive electrode active material, conductive agent and binder, and then mixing with solvent to prepare positive electrode active slurry; coating the positive electrode active slurry onto positive electrode current collector 2311 to obtain positive electrode sheet 231; after preparing positive electrode sheet 231, stacking positive electrode sheet 231, separator, negative electrode sheet, separator, and so on, to form stacked electrode assembly 23; then placing electrode assembly 23 in housing and injecting electrolyte to form battery cell 20.

[0159] Figure 9 is a flowchart of the preparation process of the battery cell 20 provided in some embodiments of this application. As shown in Figure 9, the specific process of preparing the battery cell 20 is as follows:

[0160] S210, Preparation of positive electrode active slurry: The positive electrode active material, binder, and conductive agent are dispersed in a solvent to form a positive electrode active slurry. The positive electrode active material used is the one provided above. Optionally, a small amount of other positive electrode active materials may be added.

[0161] The binder can be one or more of styrene-butadiene rubber, waterborne acrylic resin, carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, polyvinyl alcohol, and polyvinyl butyral. The conductive agent can be at least one of conductive carbon black, carbon fiber, carbon nanotubes, Ketjen black, graphene, or acetylene black. The solvent can be one or more of dimethyl glutarate and N-methylpyrrolidone. Leveling agents, dispersants, etc., can also be added to the positive electrode active slurry.

[0162] S220, Preparation of positive electrode active material layer 2312: The positive electrode active slurry is coated on the surface of the positive electrode current collector 2311 and then dried to form the positive electrode active material layer 2312. During coating, it can be applied to one or both surfaces of the positive electrode current collector 2311 as needed.

[0163] The coating method can be: scraping, roller coating, slot coating, etc., and this application does not limit it.

[0164] The positive electrode current collector 2311 can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0165] S230, roll-press the positive electrode active material layer 2312 to obtain the positive electrode sheet 231.

[0166] S240, positive electrode 231, separator, negative electrode, separator, and so on are stacked in sequence to form a stacked electrode assembly 23.

[0167] S250, the stacked electrode assembly 23 is assembled into a battery cell 20. This battery cell 20 can be used to prepare a secondary battery 100 and provide electrical energy to an electrical device.

[0168] The following examples will describe one or more embodiments in more detail. Of course, these examples do not limit the scope of the one or more embodiments.

[0169] Examples and Comparative Examples

[0170] Preparation of positive electrode active materials

[0171] Sodium, R, and phosphorus sources were dissolved in deionized water at a specific molar ratio and stirred continuously at room temperature for 30 minutes to obtain an initial mixed slurry. The first and second carbon sources were dissolved in deionized water and mixed to obtain a carbon solution. This carbon solution was then mixed with the initial mixed solution and stirred to obtain a mixed solution. The mixed solution was spray-dried at an inlet air temperature of 220°C and an outlet air temperature of 109°C to obtain a powdered precursor. Finally, in a N2 atmosphere, the temperature was increased to 320°C at a rate of 2°C and held for 4 hours, followed by a further increase to 550°C at a rate of 2°C and held for 10 hours. The sintered product was then subjected to air jet milling and sieved to obtain a uniformly sized positive electrode active material.

[0172] Preparation of the positive electrode sheet

[0173] 2.5 wt% of the binder polyvinylidene fluoride was fully dissolved in the solvent N-methylpyrrolidone. 2.0 wt% of super p and 1.0 wt% of CNT were added as conductive agents, and 94.5 wt% of the above-mentioned positive electrode active material were mixed to form a uniformly dispersed slurry. The slurry was uniformly coated onto the surface of the positive electrode current collector aluminum foil, and after drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0174] Preparation of the negative electrode sheet

[0175] Sodium metal sheet is used as the negative electrode.

[0176] Preparation of Electrolyte

[0177] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) / diethyl carbonate (DEC) / ethyl methyl carbonate (EMC) are mixed evenly in a volume ratio of 1 / 1 / 1. 1 mol / L NaPF6 sodium salt is added and dispersed evenly. Then, 5% fluoroethylene carbonate is dissolved in the above organic solvent and stirred evenly to obtain the electrolyte.

[0178]

Isolation Film

[0179] Polyethylene film is used as the separation membrane.

[0180] [Preparation of button cells]

[0181] The prepared positive electrode, negative electrode, separator and electrolyte are assembled into CR2430 button cell in an argon-protected glove box.

[0182] The main parameter controls for Examples 1 to 16 and Comparative Examples 1 to 2 are shown in the table below:

[0183] In the table, x', y', and m' refer to the molar ratios of sodium source, R source, and phosphorus source, respectively.

[0184] The " / " indicates that the material was not added or that the value does not exist.

[0185] The performance of the positive electrode active materials and batteries composed thereof provided in each embodiment and comparative example was tested. The performance testing specifically included:

[0186] Compacted density test: This test measures the mass (g / cm³) of the positive electrode active material layer per unit area on one side. 2 The density of the positive electrode active material layer (PD) is determined by the thickness (cm) of the positive electrode active material layer on one side (number of sampling points > 14). Specifically, the compaction density PD of the positive electrode active material layer is equal to the mass of the positive electrode active material layer on one side per unit area (g / cm³). 2 ) / Thickness of the positive electrode active material layer (cm).

[0187] Surface residual alkali quality test: An acid-base titration method was used. Sodium bicarbonate and sodium carbonate in the positive electrode material were titrated with a standard hydrochloric acid solution. A pH electrode was used as the indicator electrode, and the endpoint was determined by the sudden change in potential. The titration volume of the standard solution was determined based on the titration endpoint. The calculated masses of Na₂CO₃ and NaHCO₃ were divided by the mass of the positive electrode active material, and the sodium ion content was used as the residual alkali content of the positive electrode active material. The calculation formula is as follows:

[0188] Na2CO3%=(V2-V1)*C*106*100n / 1000m

[0189] NaHCO3%=V2*C*84*n*100 / 1000m

[0190] Na + %=V2*C*23*n*100 / 1000m.

[0191] Specific capacity test: After the battery is left to stand for 12 hours, it is discharged at a constant current of 0.05C until it reaches 0.005V, and then left to stand for 10 minutes. It is then discharged at a constant current of 50μA until it reaches 0.005V, and left to stand for 10 minutes. Finally, it is discharged at a constant current of 10μA until it reaches 0.005V. Then, it is charged at a constant current of 0.1C until it reaches 2V. The charging capacity is recorded. The ratio of the charging capacity to the weight of the positive electrode active material is the specific capacity of the prepared positive electrode active material.

[0192] Initial Coulombic Efficiency Test: The initial coulombic efficiency test process is as follows: At 25°C, the prepared battery is charged to 3.75V with a constant current of 1 / 5C, and then charged at a constant voltage of 3.75V until the current drops to 0.05C, obtaining the initial charge capacity (Cc1); then discharged to 1.5V with a constant current of 1 / 5C, obtaining the initial discharge capacity (Cd1), and the battery coulombic efficiency is calculated according to the following formula: Initial Coulombic Efficiency = Initial Discharge Capacity (Cd1) / Initial Charge Capacity (Cc1).

[0193] The test results are shown in Table 1 below:

[0194] As shown in the table above, the positive electrode active material prepared by the method provided in this application has a small porosity, thereby resulting in a high compaction density of the prepared active material layer. Simultaneously, this positive electrode active material exhibits a high initial coulombic efficiency.

[0195] Comparison of data from Examples 1 and 2 and Comparative Examples 1 and 3 shows that when the positive electrode active material is in a phosphorus-deficient state, its porosity decreases to some extent, while its initial coulombic efficiency increases to some extent. Furthermore, during the preparation process, as the amount of phosphorus source added decreases, i.e., the phosphorus deficiency of the positive electrode active material increases, the porosity of the positive electrode active material gradually decreases, and the compaction density of the corresponding positive electrode active material layer gradually increases, as does its initial coulombic efficiency, but its specific capacity gradually decreases. When the value of m is below 4, the positive electrode active material exhibits relatively low porosity, good specific capacity, and initial coulombic efficiency. Further, when the value of m is between 3.8 and 4, the flatness of the small particles of the positive electrode active material is within a favorable range, and it can form more effective active components, thus balancing performance such as compaction density, initial coulombic efficiency, and specific capacity, with a porosity of 0.028 cm⁻¹. 3 For materials with a specific capacity of less than 110.0 mAh / g and a specific capacity of more than 110.0 mAh / g, the corresponding compaction density of the formed positive electrode active material layer is 2.19 g / cm³. 3 The resulting battery has an initial coulombic efficiency of over 96.6%.

[0196] Comparison of data from Examples 5 to 7, Comparative Examples 1 and 2 shows that when iron defects exist in the positive electrode active material, its residual alkali content is significantly reduced, while its specific capacity is significantly increased. Furthermore, during the preparation process, as the amount of iron source added decreases, i.e., the iron defects in the positive electrode active material increase, the residual alkali content of the positive electrode active material exhibits a trend of first decreasing and then increasing. When the value of the iron defect y is below 0.5, the residual alkali content of the positive electrode active material is controlled within 0.22%. Further, when the value of the iron defect y is below 0.2, the residual alkali content of the positive electrode active material is controlled within 0.21%, while its porosity is controlled at 0.025 cm⁻¹. 3 Within / g, the positive electrode active material layer formed has a better compaction density. It is speculated that the reason is that the reduction of residual alkali is conducive to the control of its porosity, which in turn is conducive to the compaction density.

[0197] Data from Examples 3 and 8 to 9 show that selecting different R sources has essentially the same effect.

[0198] A comparison of the data from Examples 3 and 10 to 12 shows that using different carbon-coated raw materials can effectively control the residual alkali content while maintaining a good specific capacity. In particular, using two carbon sources allows for even better control of the residual alkali content and better maintenance of the specific capacity.

[0199] Electron microscopy scans were performed on the examples, comparative examples 2 and 3. Since the results of each example are similar, only the results of example 3 are selected for specific description. The test results of comparative examples 2, 3 and example 3 are shown in Figures 10 to 12 respectively.

[0200] The positive electrode active material in Comparative Example 2 is phosphorus-free. As shown in Figure 10, when phosphorus is not deficient, the small particles formed are relatively rounded, and the large particles that agglomerate have more pores. Consequently, the compaction density of the material is low, only 2.12 g / cm³. 3 .

[0201] The positive electrode active material of Comparative Example 3 is phosphorus deficient but not in the range of 3.7 < m < 4. As can be seen from Figure 11, the flatness of the small particles formed is too high, and the sphericity of the large particles formed by aggregation is poor. Therefore, the compaction density of the corresponding positive electrode active material layer is low.

[0202] In Example 3, the positive electrode active material is phosphorus deficient and in the range of 3.7 < m < 4. As can be seen from Figure 12, the flatness of the small particles formed is moderate, and the large particles formed by their aggregation are relatively round. Therefore, the compaction density of the corresponding positive electrode active material layer is high.

[0203] The rate performance of batteries composed of the positive electrode active materials provided in Examples 2, 3, and Comparative Example 2 was tested as follows:

[0204] Rate performance (5C capacity retention) test: The battery was tested at different discharge rates at room temperature (23℃). The charging rate was uniformly 0.5C, and the discharge rates were 0.5C and 5C respectively. The discharge capacity retention rate of 5C rate compared with 0.5C rate was calculated, which is the 5C capacity retention rate.

[0205] The results are shown in Table 2 below:

[0206] As can be seen from the table above, the positive electrode active material prepared by the method provided in the embodiments of this application has good rate performance.

[0207] The above are merely specific embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes 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, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

2. The positive electrode sheet according to claim 1, characterized in that, 3.8≤m＜4。 3. The positive electrode sheet according to any one of claims 1 to 2, characterized in that, The chemical formula of the positive electrode active material is Na. x Fe y P m O n Among them, 3.9≤x≤4.2, 2.8≤y≤3.1, 3.8≤m<4, and 14.5≤n≤15.

5.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, The relationship between the X-ray diffraction intensity I(602) of the (602) crystal plane and the X-ray diffraction intensity I(022) of the (022) crystal plane of the positive electrode active material satisfies: I(602) / I(022)=1.12~1.

15.

5. The positive electrode sheet according to claim 4, characterized in that, The relationship between the X-ray diffraction intensity I(602) of the (602) crystal plane and the X-ray diffraction intensity I(022) of the (022) crystal plane of the positive electrode active material satisfies: I(602) / I(022)=1.13~1.

14.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that, The porosity of the positive electrode active material is 0.012–0.078 cm⁻¹. 3 / g.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that, The chemical formula of the positive electrode active material is Na. x R y P m O n / C, where 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, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

8. The positive electrode sheet according to any one of claims 1 to 7, characterized in that, The positive electrode active material satisfies one or more of the following characteristics: (a) The initial coulombic efficiency of the positive electrode active material is ≥93%; (b) The specific capacity of the positive electrode active material is 110–126 mAh / g; (c) The residual alkali content in the positive electrode active material is ≤0.36% by mass.

9. The positive electrode sheet according to claim 8, characterized in that, The positive electrode active material satisfies one or more of the following characteristics: (a) The initial coulombic efficiency of the positive electrode active material is ≥94%; (b) The specific capacity of the positive electrode active material is 123.2 to 125.8 mAh / g.

10. The positive electrode sheet according to any one of claims 1 to 9, characterized in that, The compaction density of the positive electrode sheet is 2.15–2.25 g / cm³. 3 .

11. A battery, characterized in that, The battery includes the positive electrode sheet according to any one of claims 1 to 10.

12. A battery, characterized in that, The battery is a negative electrode-free battery, comprising the positive electrode sheet according to any one of claims 1 to 10.

13. An electrical appliance, characterized in that, The electrical device includes the battery as described in claim 11 or 12.

14. A positive electrode active material, characterized in that, The positive electrode active material includes 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, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

15. The positive electrode active material according to claim 14, characterized in that, The relationship between the X-ray diffraction intensity I(602) of the (602) crystal plane and the X-ray diffraction intensity I(022) of the (022) crystal plane of the positive electrode active material satisfies: I(602) / I(022)=1.12~1.

15.

16. A method for preparing a positive electrode active material, characterized in that, The method includes: Sodium source, R source and phosphorus source are mixed to obtain a mixture, wherein the molar ratio of Na, R and P in the mixture is 3.5-4.7:2.3-3.5:3.5-4, wherein R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, In, Ga, Sn, Hf, Ta, W and Pb; The mixture is sintered to obtain a positive electrode active material, wherein the positive electrode active material includes Na. x R y P m O n Among them, 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m<4, and 14.5≤n≤15.

5.

17. The method for preparing the positive electrode active material according to claim 16, characterized in that, The mixture also includes a carbon source.

18. The method for preparing the positive electrode active material according to claim 17, characterized in that, The carbon source includes a first carbon source and a second carbon source, wherein the first carbon source includes an inorganic carbon source and the second carbon source includes an organic carbon source.

19. The method for preparing the positive electrode active material according to claim 18, characterized in that, The first carbon source includes at least one of graphite, carbon black, carbon nanotubes, and graphene; and / or The second carbon source includes at least one of sucrose, glucose, citric acid, starch, cyclodextrin, pitch, and PEG.

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