Metal oxide precursor, and preparation method therefor and use thereof

Abstract

Disclosed are a metal oxide precursor, and a preparation method therefor and a use thereof. The metal oxide precursor has a single crystal structure, and the crystal is of an incompletely developed octahedron-like structure; and the incompletely developed octahedron-like structure is simulated as a fully developed regular octahedron structure for reference, a crystal development degree θ of the octahedron-like structure is 33-95%, and θ=L1 / L2, wherein L1 is the edge length of any crystal development edge in the octahedron-like structure, and L2 is the edge length of the crystal edge when the corresponding crystal development edge is simulated into a complete development state. The metal oxide precursor has an octahedron-like structure, and is used for preparing a positive electrode material, so that the structural stability and the energy density can be increased, and a battery has excellent cycle stability.

Description

Metal oxide precursor and preparation method and application thereof

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 29, 2023, with application number 202311867450.6 and invention name “Metal oxide precursors, preparation methods and applications thereof”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a metal oxide precursor and a preparation method and application thereof. Background Art

[0003] The statements herein only provide background information related to the present application and do not necessarily constitute prior art. The precursor synthesized by the coprecipitation method is usually a polycrystalline structure. Due to the presence of multiple grains and grain boundaries in the polycrystalline structure, the grains are not only loosely arranged, but also have many grain boundaries and defects. On the one hand, this leads to low crystallinity of the sintered positive electrode material and uneven grain size, which is easily crushed during the compaction process. In addition, cations are easily destroyed in the insertion and removal process. The structure of the positive electrode material is poorly stable, thereby affecting the cycle life and stability of the battery. On the other hand, the diffusion path of cations in the lattice is long, which affects the migration rate of cations and the discharge rate of the battery.

[0004] The precursor prepared by the traditional spray pyrolysis process is usually a regular octahedral structure (as shown in C in Figure 1, the crystal structure is fully developed). Although this structure has high stability, it has low activity and requires higher energy when sintering the positive electrode, which puts higher requirements and challenges on the production process and energy consumption.

[0005] Application Contents

[0006] One of the purposes of the embodiments of the present application is to provide a metal oxide precursor and its preparation method and application, aiming to solve the problem that the precursor prepared by the traditional spray pyrolysis process is usually a regular octahedral structure, which has low activity and requires higher energy when sintering the positive electrode, which puts higher requirements and challenges on the production process and energy consumption.

[0007] The technical solution adopted in the embodiment of this application is:

[0008] In the first aspect, a metal oxide precursor is provided, which has a single crystal structure and the crystal is an incompletely developed octahedral structure. The incompletely developed octahedral structure is simulated into a fully developed regular octahedral structure as a reference. The crystal development degree θ of the octahedral structure is 33%-95%, θ=L1 / L2, wherein L1 is the edge length of any crystal development edge in the octahedral structure, and L2 is the edge length of the crystal edge when the corresponding crystal development edge is simulated to be fully developed, that is, L2 is the edge length of the crystal edge in the regular octahedral structure corresponding to the L1 crystal development edge.

[0009] In one embodiment, L1 is 0.1 μm-4.3 μm.

[0010] In one embodiment, the single crystal particle growth rate η of the metal oxide precursor is L1 / H1, wherein L1 is the edge length of any crystal development edge in the octahedral-like structure, and H1 is the single crystal particle size of the octahedral-like structure.

[0011] In one embodiment, the single crystal particle growth rate of the metal oxide precursor is 23%-67%.

[0012] In one embodiment, the single crystal particle growth rate of the metal oxide precursor is 38%-58%.

[0013] In one embodiment, the single crystal particle growth rate of the metal oxide precursor is 35%-63%.

[0014] In one embodiment, the single crystal particle size of the metal oxide precursor is 0.43 μm-6.43 μm.

[0015] In one embodiment, the crystal surface area of ​​the metal oxide precursor accounts for 88.72% to 99.99% of the crystal surface area of ​​the metal oxide precursor when the crystal development degree is 100%.

[0016] In one embodiment, the crystal volume of the metal oxide precursor accounts for 95.23%-99.99% of the crystal volume of the metal oxide precursor when the crystal development degree is 100%.

[0017] In one embodiment, the ratio of the crystal surface area to the crystal volume of the metal oxide precursor is 1.62 μm -1 -26.03μm -1 .

[0018] In one embodiment, the metal oxide precursor includes a first crystal and / or a second crystal, the crystal development degree of the first crystal is 33%≤θ1≤65%, and the crystal development degree of the second crystal is 65%<θ2≤95%.

[0019] In one embodiment, the metal oxide precursor includes a first crystal and / or a second crystal, the length of the edge developed in the first crystal is 0.1 μm-2.95 μm, and the length of the edge developed in the second crystal is 0.2 μm-4.3 μm.

[0020] In one embodiment, the metal oxide precursor includes a first crystal and / or a second crystal, and the ratio of the crystal surface area to the crystal volume of the first crystal is 1.63 μm -1 -26.03μm -1 The ratio of the crystal surface area to the crystal volume in the second crystal is 1.62 μm -1 -24.48μm -1 .

[0021] In one embodiment, the chemical formula of the metal oxide precursor is represented by A x M y O2, wherein 0.9≤x≤1, 0≤y≤0.1, A is selected from at least one of Ni, Fe, Cu, Mn, and Co, and M is selected from at least one of Mg, Al, Sn, Ca, W, Ti, Zn, Li, Na, Mo, La, and Zr.

[0022] In a second aspect, a method for preparing the metal oxide precursor as described above is provided, wherein the preparation method is selected from spray pyrolysis.

[0023] In one embodiment, the pyrolysis temperature of the spray pyrolysis method is 460°C-1110°C.

[0024] In one embodiment, the pyrolysis time of the spray pyrolysis method is 1 min-30 min.

[0025] In a third aspect, a positive electrode material is provided which is prepared from the metal oxide precursor described above or the metal oxide precursor prepared by the method described above.

[0026] In a fourth aspect, a positive electrode sheet is provided, comprising a positive electrode current collector and a positive electrode material layer disposed on a surface of the positive electrode current collector, wherein the positive electrode material layer comprises the positive electrode material as described above.

[0027] In a fifth aspect, a secondary battery is provided, comprising the positive electrode sheet as described above.

[0028] The beneficial effect of the metal oxide precursor provided in the embodiment of the present application is that: the ratio of the edge length of the crystal development edge in the octahedral structure to the edge length of the crystal edge in the theoretically developed complete regular octahedral structure is used to evaluate the development degree of the metal oxide precursor. When the development degree of the metal oxide precursor is 33%-95%, the metal oxide precursor has an overall structure that is highly similar to a regular octahedron. At the same time, the six corners of the regular octahedron are incompletely developed, forming six unsaturated development facets, so that the metal oxide precursor has a fourteen-faced octahedral structure. On the one hand, the metal oxide precursor has high symmetry, an ordered lattice, and good structural stability. It can maintain good crystallinity during the preparation of the positive electrode material, which is beneficial to improving the structural stability of the positive electrode material and the cycle stability of the battery; on the other hand, the diffusion path of cations in the octahedral structure of the metal oxide precursor is short, which is beneficial to increasing the migration rate of cations, thereby increasing the reserve and providing a higher energy density for the positive electrode material. In addition, the metal oxide precursors of the embodiments of the present application not only improve structural stability, but also overcome the defects of traditional octahedral structure precursors such as low activity, high difficulty in preparing positive electrodes, and high cost, and have high market application potential.

[0029] The beneficial effect of the method for preparing a metal oxide precursor provided in the embodiments of the present application is that, through spray pyrolysis, single crystal particles of a metal oxide precursor with an incompletely developed octahedral structure can be produced. Using a fully developed octahedral structure as a reference, the crystal development degree θ of the octahedral structure is 33%-95%. These structural characteristics give the resulting metal oxide precursor high symmetry, lattice order, and structural stability, thereby improving the structural stability of the positive electrode material and the cycling stability of the battery. Furthermore, the reactive specific surface area of ​​the metal oxide precursor is increased, shortening the ion diffusion path, thereby improving the electrochemical properties of the positive electrode material, such as ion migration efficiency and storage capacity.

[0030] The beneficial effect of the positive electrode material provided in the embodiments of the present application is that using the above-mentioned metal oxide precursor to prepare the positive electrode material can not only improve the crystallinity of the positive electrode material, but also make the positive electrode material have a higher energy density, which is beneficial to improving the cycle performance of the battery.

[0031] The beneficial effect of the positive electrode sheet provided in the embodiment of the present application is that applying a positive electrode material with high energy density, cycle stability and other characteristics to the positive electrode sheet can improve the electrochemical properties of the positive electrode sheet, such as energy density and cycle stability.

[0032] The beneficial effect of the secondary battery provided by the embodiment of the present application is that applying a positive electrode sheet having characteristics such as high energy density and cycle stability to the secondary battery can improve the electrochemical properties of the secondary battery such as cycle stability and cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or exemplary technical descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0034] Figure 1 is a schematic diagram of the crystal structure of a metal oxide precursor, wherein A is a schematic diagram of the octahedral structure of the first crystal, B is a schematic diagram of the octahedral structure of the second crystal, and C is a schematic diagram of a simulated fully developed regular octahedral structure; L1 is the edge length of any crystal development edge in the octahedral structure of the first crystal or the second crystal, and L2 is the edge length of the crystal edge when the corresponding crystal development edge is simulated to be fully developed; that is, L2 is the edge length of the crystal edge in the regular octahedral structure corresponding to the L1 crystal development edge;

[0035] FIG2 is a scanning electron microscope image of the metal oxide precursor prepared in Example 1 of the present application;

[0036] FIG3 is a scanning electron microscope image of the metal oxide precursor prepared in Example 3 of the present application;

[0037] FIG4 is a scanning electron microscope image of the metal oxide precursor prepared in Example 6 of the present application;

[0038] FIG5 is a scanning electron microscope image of the metal oxide precursor prepared in Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit this application.

[0040] It should be noted that when a component is referred to as being "fixed on" or "disposed on" another component, it may be directly on the other component or indirectly on the other component. When a component is referred to as being "connected to" another component, it may be directly or indirectly connected to the other component. The terms "upper", "lower", "left", "right", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of 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 this application. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances. The terms "first" and "second" are only used for the purpose of convenience of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0041] In order to illustrate the technical solution described in this application, the following is a detailed description with reference to specific drawings and embodiments.

[0042] Some embodiments of the present application provide a metal oxide precursor, which has a single crystal structure and an incompletely developed octahedral structure. In combination with Figure 1, the incompletely developed octahedral structure (as shown in A and B in Figure 1) is simulated into a fully developed regular octahedral structure (as shown in C in Figure 1) as a reference. The crystal development degree θ of the octahedral structure is 33%-95%, θ=L1 / L2, wherein L1 is the edge length of any crystal development edge in the octahedral structure, and L2 is the edge length of the crystal edge when the corresponding crystal development edge is simulated to be fully developed, that is, L2 is the edge length of the crystal edge corresponding to the L1 crystal development edge in the regular octahedral structure.

[0043] It should be noted that the edge length of the fully developed crystal is equivalent to the edge length of the metal oxide precursor crystal when the crystal development degree is 100% (i.e., developed to a regular octahedral structure), which is the theoretical edge length. The metal oxide precursor crystals of the present embodiment have an incomplete octahedral structure that is easily inherited by the positive electrode material.

[0044] The embodiment of the present application uses the ratio of the edge length of the crystal development edge in the octahedral structure to the edge length of the crystal edge in the theoretically fully developed regular octahedral structure to evaluate the development degree of the metal oxide precursor. When the development degree of the metal oxide precursor is 33%-95%, the octahedral structure of the metal oxide precursor has an overall structure that is highly inclined to the regular octahedron. At the same time, the six corners in the octahedral structure are incompletely developed, forming six unsaturated development facets, thereby making the metal oxide precursor an octahedral structure with fourteen faces. In this case, the metal oxide precursor of the embodiment of the present application has at least the following performance advantages:

[0045] On the one hand, the octahedral structure of the metal oxide precursor has a high tendency toward a regular octahedral structure, which ensures that its crystal structure still has high symmetry, an ordered lattice, and good structural stability. This allows it to maintain good crystallinity during the preparation of the cathode material, which is beneficial for improving the structural stability of the cathode material and the cycling stability of the battery. On the other hand, the octahedral structure of the metal oxide precursor has fourteen faces, which increases its active specific surface area. The diffusion path of cations in the octahedral structure of the metal oxide precursor is shorter, which is beneficial for increasing the migration rate of cations, thereby increasing the energy storage capacity and providing a higher energy density for the cathode material. If the crystal growth degree of the octahedral structure is less than 33%, the structural stability, symmetry, and lattice order of the octahedral structure will be destroyed, which is not conducive to improving the electrochemical performance of the cathode material, such as structural stability and cycling stability. If the crystal growth degree of the octahedral structure is greater than 95%, the effect of increasing the reactive specific surface area of ​​the metal oxide precursor is not good, which is not conducive to shortening the ion diffusion path, and thus is not conducive to improving the electrochemical performance of the cathode material, such as ion migration efficiency and energy storage capacity.

[0046] For example, the crystal development degree θ of the octahedral structure can be any typical but non-limiting point value such as 33%, 35%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or an interval value between any two point values.

[0047] Since the incompletely developed octahedral structure in the metal oxide precursor of the embodiment of the present application is simulated as a fully developed regular octahedral structure as a reference, the edge length L1 of any crystal development edge in the octahedral structure will be lower than the edge length L2 of the crystal edge corresponding to the L1 crystal development edge in the regular octahedral structure.

[0048] In some embodiments, the edge length L2 of the crystal edge in the fully developed regular octahedron structure is 0.105 μm to 13.03 μm.

[0049] In some embodiments, the length L1 of any crystal development edge in the octahedral-like structure is 0.1 μm to 4.3 μm. In this case, the degree of crystal development of the octahedral-like structure is calculated according to the formula θ = L1 / L2, and the degree of crystal development of the octahedral-like structure in the metal oxide precursor is 33% to 95%. In this case, the symmetry, lattice order, and structural stability of the octahedral-like structure are maintained, which is beneficial for improving the structural stability of the positive electrode material and the cycle stability of the battery. The octahedral-like structure also has fourteen faces, which increases its active specific surface area and can increase the migration rate of cations.

[0050] For example, the edge length L1 of any crystal development edge in the octahedral structure can be 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 4 μm, 4.3 μm, or any other typical but non-restrictive point value or an interval value between any two point values.

[0051] Since the crystal development degree of the metal oxide precursor in the embodiment of the present application is 33%-95%, the single crystal particle size of the metal oxide precursor is also lower than the single crystal particle size of the metal oxide precursor when the crystal development degree is 100% (i.e., regular octahedral structure).

[0052] In some embodiments, the size of the single crystal particles of the regular octahedral structure is 0.148 μm to 18.43 μm.

[0053] In some embodiments, the single crystal particle size of the metal oxide precursor (i.e., the single crystal particle size of the octahedral structure) is 0.43 μm-6.43 μm. Under the condition of the single crystal particle size, within this range, the single crystal particle size belongs to a medium particle size, which can strike a balance between electrochemical performance and mechanical stability, and provide good overall performance. If the particle size is too large: the ion transmission path is long, which reduces the charge and discharge rate; the specific surface area is low, which reduces the electrochemical reaction rate and affects the capacity and power density of the battery; too large a size can also easily make the electrode structure uneven. If the particle size is too small: it is easy to cause particle agglomeration and rupture during the charge and discharge process, affecting the cycle performance; although the small size increases the reaction sites, it also increases side reactions, which will also affect the stability and life of the battery; too small particles will also reduce conductivity.

[0054] For example, the single crystal particle size of the metal oxide precursor (i.e., the single crystal particle size of the octahedral structure) can be 0.43 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 6.43 μm, or any other typical but non-limiting point value or an interval value between any two point values.

[0055] In some embodiments, the single crystal particle growth rate of the octahedral-like structure in the metal oxide precursor of the present embodiment can be calculated by measuring the edge length of the crystal development edge and the single crystal particle size. The single crystal particle growth rate of the metal oxide precursor can be expressed by the ratio of the edge length L1 of any crystal development edge in the octahedral-like structure to the single crystal particle size H1. The single crystal particle growth rate is calculated as η, where η = L1 / H1. For example, when the edge length L1 of the crystal development edge in the metal oxide precursor is 0.1 μm to 4.3 μm and the single crystal particle size H1 is 0.43 μm to 6.43 μm, the calculated single crystal particle growth rate η is 23% to 67%.

[0056] In other embodiments, the growth rate of single crystal particles of the octahedral structure in the metal oxide precursor of the present invention can also be estimated by the relationship between the single crystal particle size of the metal oxide precursor when the crystal development degree is 100% under ideal conditions and the single crystal particle size of the incompletely developed metal oxide precursor. For example, under ideal conditions, when the crystal development degree is 100%, the metal oxide precursor has a regular octahedral structure composed of 8 equilateral triangles, and its single crystal particle size is calculated as H2. The single crystal particle size of the incompletely developed metal oxide precursor is H1=H2×(1+θ) / 2, so The calculated single crystal particle growth rate is 35%-63%.

[0057] For example, the growth rate of single crystal particles of octahedral structure in the metal oxide precursor can be 23%, 30%, 35%, 38%, 40%, 45%, 50%, 55%, 58%, 60%, 63%, 67%, or any other typical but non-limiting point value or an interval value between any two point values.

[0058] In some embodiments, the single crystal particle growth rate of the metal oxide precursor is 38%-58%. In this case, the single crystal particle growth rate is higher, its development is more advanced, the structure is extremely stable, and it is more difficult and energy-consuming to fire the positive electrode. If the growth rate is too low, it indicates that the single crystal particle is not fully developed, resulting in poor crystallinity and increased crystal defects, which will reduce the electrochemical activity of the material and lead to reduced battery capacity.

[0059] Considering that the crystal development degree of the metal oxide precursors in the embodiments of the present application is 33%-95%, compared with the metal oxide precursors with a crystal development degree of 100%, the metal oxide precursors in the embodiments of the present application also have certain differences in crystal surface area and crystal volume.

[0060] In some embodiments, the crystal surface area of ​​the metal oxide precursor accounts for 88.72% to 99.99% of the crystal surface area of ​​the metal oxide precursor when the crystal development level is 100%. That is, based on the crystal surface area of ​​the regular octahedral structure as 100%, the crystal surface area of ​​the octahedral-like structure in the metal oxide precursor accounts for 88.72% to 99.99% of the crystal surface area of ​​the regular octahedral structure. In this case, it is beneficial to maintain the structural stability, symmetry, lattice order and other characteristics of the octahedral-like structure, while also increasing the reactive specific surface area of ​​the metal oxide precursor and shortening the ion diffusion path, thereby improving the electrochemical properties of the positive electrode material, such as ion migration efficiency and storage.

[0061] For example, when the crystal surface area of ​​the metal oxide precursor accounts for 100% of the crystal development degree, the crystal surface area of ​​the metal oxide precursor can be 88.72%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.99% or other typical but non-limiting arbitrary point values ​​or an interval value between any two point values.

[0062] In some embodiments, the crystal volume of the metal oxide precursor accounts for 95.23% to 99.99% of the crystal volume of the metal oxide precursor when the crystal development level is 100%. That is, based on the crystal volume of the regular octahedral structure as 100%, the crystal volume of the octahedral-like structure in the metal oxide precursor accounts for 95.23% to 99.99% of the crystal volume of the regular octahedral structure. In this case, it is beneficial to maintain the structural stability, symmetry, lattice order and other characteristics of the octahedral-like structure, while also increasing the reactive specific surface area of ​​the metal oxide precursor and shortening the ion diffusion path, thereby improving the electrochemical properties of the positive electrode material, such as ion migration efficiency and storage.

[0063] For example, when the crystal volume of the metal oxide precursor accounts for 100% of the crystal development degree, the crystal volume of the metal oxide precursor can be 95.23%, 96%, 97%, 98%, 99%, 99.99% or other typical but non-limiting arbitrary point values ​​or an interval value between any two point values.

[0064] In some embodiments, the ratio of the crystal surface area to the crystal volume of the metal oxide precursor is taken as the relative surface area, and the relative surface area is 1.62 μm -1 -26.03μm -1 That is, in the metal oxide precursor, the ratio of the crystal surface area to the crystal volume of the octahedral structure is 1.62 μm -1 -26.03μm -1 . In this case, the degree of development increases, and the corresponding surface area and volume of the crystal also increase, but the ratio of the two will decrease. A smaller ratio: means that the particles are larger, the structure is more stable, and it can also reduce the occurrence of side reactions and extend battery life. A ratio that is too low will result in too few active sites, limiting the reaction rate and rate performance of the battery. A larger ratio: indicates that there are more active sites, which is beneficial to improving the electrochemical reaction rate of the electrode material and can shorten the transmission path of ions and electrons inside the material. A ratio that is too high may make it easier for volume changes to occur during the cycle, resulting in structural instability and increasing side reactions. The ratio of crystal surface area to volume is 1.62μm -1 -26.03μm -1 Only within this range can the macroscopic geometric characteristics of the octahedral structure described in the present invention be met, thereby increasing the reaction rate and improving the cycle stability.

[0065] For example, the ratio of the crystal surface area to the crystal volume of the metal oxide precursor is used as the relative surface area. In this case, the relative surface area can be 1.62 μm -1 , 2μm -1 , 5μm -1 , 10μm -1 , 12μm -1 , 15μm -1 , 18μm -1 , 20μm -1 , 22μm -1 , 24μm -1 , 26μm -1 , 26.03μm -1 Typical but non-restrictive values ​​are any point value or interval value between any two point values.

[0066] The metal oxide precursor of the embodiment of the present application has a specific relative surface area while meeting the crystal development degree of 33%-95%. It also has a specific crystal surface area ratio and a specific crystal volume ratio with the metal oxide precursor with a crystal development degree of 100%. By limiting the structure of the metal oxide precursor of the embodiment of the present application, it is beneficial to improve the structural stability of the positive electrode material and the cycle stability of the battery, thereby improving the electrical performance.

[0067] It should be noted that the crystal surface area of ​​the metal oxide precursor when the crystal development degree is 100% is the theoretical crystal surface area; the crystal volume of the metal oxide precursor when the crystal development degree is 100% is the theoretical crystal volume.

[0068] In some embodiments, as shown in Figure 1, the metal oxide precursor includes a first crystal and / or a second crystal, and the first crystal and the second crystal have different degrees of crystal development. As shown in Figure 1A, the lower the degree of crystal development, the larger and more obvious the six unsaturated development cross-sections formed; as shown in Figure 1B, the higher the degree of crystal development, the smaller the area of ​​the six unsaturated development cross-sections formed, and they tend to form sharp corners.

[0069] In some embodiments, the metal oxide precursor includes a first crystal and / or a second crystal, the crystal development degree of the first crystal is 33%≤θ1≤65%, and the crystal development degree of the second crystal is 65%<θ2≤95%. In this case, if the crystallinity is too high, the sintering activity of the precursor is reduced, the sintering is more difficult, and the sintering temperature required is higher. There will be risks of grain growth and agglomeration, which will affect the electrochemical performance. If the crystallinity is too low, the structure is unstable and it is difficult to sinter into a stable single crystal positive electrode structure. The first crystal with a development degree of 33%≤θ1≤65% has a relatively low development degree, a low crystal crystallinity, and a high reactivity, which helps to form a uniform single crystal structure during the sintering process. The second crystal with a development degree of 65%<θ2≤95% has a relatively high development degree, a higher crystal crystallinity, and an improved structural stability of the material, making it more stable during the charge and discharge process, reducing capacity decay, and extending battery life.

[0070] In some embodiments, the metal oxide precursor includes first crystals and / or second crystals, wherein the length of the developed edges in the first crystals is 0.1 μm to 2.95 μm, and the length of the developed edges in the second crystals is 0.2 μm to 4.3 μm. In this case, the first crystals having developed edges with an edge length of 0.1 μm to 2.95 μm indicate a lower degree of crystal development, a more spherical crystal structure, a larger contact area with the electrolyte, and improved rate performance. In addition, the sintering temperature is lower, reducing energy consumption. The second crystals having developed edges with an edge length of 0.2 μm to 4.3 μm indicate a higher degree of crystal development, a more regular octahedral crystal structure, and a higher degree of crystallinity, which helps improve electronic and ionic conductivity and provides better structural stability during charge and discharge.

[0071] In some embodiments, the metal oxide precursor includes a first crystal and / or a second crystal, and the ratio of the crystal surface area to the crystal volume of the first crystal, that is, the relative surface area of ​​the first crystal is 1.63 μm -1 -26.03μm -1 , the ratio of the crystal surface area to the crystal volume in the second crystal, that is, the relative surface area of ​​the second crystal is 1.62 μm -1 -24.48μm -1 In this case, the relative surface area is 1.63 μm -1 -26.03μm -1 The first crystal has a low degree of development, ranging from 33% to 65%. The precursor with a low degree of development has a higher relative surface area and more active sites, which helps to improve the initial capacity and charge and discharge rate performance, and the positive electrode firing process is easier to control. The relative surface area is 1.62μm -1 -24.48μm -1The second crystal has a higher degree of development, ranging from 65% to 95%. The precursor with a higher degree of development has a higher crystallinity, which is easy to improve the conductivity and structural stability of the material.

[0072] In some specific embodiments, the metal oxide precursor comprises only the first crystal or the second crystal. In the embodiments of the present application, the metal oxide precursor may be mainly composed of the first crystal or the second crystal.

[0073] In other specific embodiments, the metal oxide precursor contains both first and second crystals. In this case, mixing the first and second crystals at different developmental stages can improve the material's conductivity and structural stability. This also results in higher reactivity, easier sintering of a uniform single crystal cathode, lower energy consumption, and a more controllable sintering process. Furthermore, crystals at different developmental stages often have different particle sizes. The coexistence of large and small particles can improve tap density, thereby increasing the potting capacity and reducing sintering costs.

[0074] When the first crystal and the second crystal are mixed and distributed in the metal oxide precursor, the present embodiment does not limit the distribution ratio of the first crystal and the second crystal. For example, the ratio of the first crystal to the second crystal can be 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, or any other typical but non-limiting value or an interval between any two values.

[0075] In some embodiments, the metal oxide precursor has the general chemical formula A x M y O2, wherein 0.9≤x≤1, 0≤y≤0.1, x+y=1, A is selected from at least one of Ni, Fe, Cu, Mn, and Co, and M is selected from at least one of Mg, Al, Sn, Ca, W, Ti, Zn, Li, Na, Mo, La, and Zr. It is understood that the metal oxide precursor in the embodiment of the present application can be a binary metal oxide, a ternary metal oxide, or a quaternary metal oxide, etc., and the embodiment of the present application is not limited thereto.

[0076] The embodiment of the present application provides a method for preparing the above metal oxide precursor, and the preparation method is selected from the spray pyrolysis method.

[0077] In the present embodiment, a spray pyrolysis method can be used to produce single crystal particles of metal oxide precursors with an incompletely developed octahedral structure. Using a fully developed octahedral structure as a reference, the crystal development degree θ of the octahedral structure ranges from 33% to 95%. These structural characteristics impart high symmetry, lattice order, and structural stability to the resulting metal oxide precursor, improving the structural stability of the cathode material and the cycling stability of the battery. Furthermore, the reactive specific surface area of ​​the metal oxide precursor is increased, shortening the ion diffusion path, thereby enhancing the electrochemical properties of the cathode material, such as ion migration efficiency and storage capacity.

[0078] It should be noted that the specific operation of the spray pyrolysis method can refer to the existing method, and the embodiments of the present application will not be described in detail.

[0079] In some embodiments, the pyrolysis temperature of the spray pyrolysis method is 460°C-1110°C; under such pyrolysis temperature conditions, when the pyrolysis temperature is low, the decomposition and crystallization processes are relatively slow, the particle development degree is low, the size is small, the development edge length is shorter, and this type of octahedral structure is closer to a spherical shape. As the pyrolysis temperature increases, the decomposition rate accelerates, the particles grow and gradually approach the optimal thermodynamic equilibrium state, the development degree is high, the development edge length is shorter, and this type of octahedral structure is closer to a regular octahedron. Within this pyrolysis temperature range, the degree of crystal development is moderate, while improving the conductivity and structural stability of the material, it is easier to sinter into a single crystal positive electrode, and the sintering process is easier to control.

[0080] It should be noted that the pyrolysis temperature is the operating temperature of the pyrolysis device.

[0081] In some embodiments, the spray pyrolysis method has a pyrolysis time of 1 min to 30 min. Under these pyrolysis time conditions, as the pyrolysis time increases, the pyrolysis is more complete, the crystallinity is higher, and the degree of development is higher. That is, the longer the edge length is, the closer the crystal structure is to a regular octahedral structure. Under these pyrolysis time conditions, the precursor has a higher reactivity, the sintering process of the positive electrode is easier to control, and it helps to improve the capacity and cycle stability.

[0082] Exemplarily, the pyrolysis temperature of the spray pyrolysis method can be 460°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, etc., which are typical but non-limiting values ​​at any point or an interval between any two values; the pyrolysis time can be 1 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, etc., which are typical but non-limiting values ​​at any point or an interval between any two values.

[0083] By adjusting the temperature and time of spray pyrolysis, it is beneficial to control the degree of crystal development of the metal oxide precursor, so that the metal oxide precursor can inherit the advantages of the octahedral structure while avoiding its complete development, which is conducive to the formation of an octahedral-like structure with fourteen faces, thereby achieving controllable development of the metal oxide precursor.

[0084] The embodiments of the present application also provide a positive electrode material prepared from the above metal oxide precursor.

[0085] Using the metal oxide precursor of the embodiment of the present application to prepare the positive electrode material can not only improve the crystallinity of the positive electrode material, but also make the positive electrode material have a higher energy density, which is beneficial to improving the cycle performance of the battery.

[0086] It should be noted that the preparation method of the positive electrode material refers to the existing method, and the embodiments of this application will not be repeated here.

[0087] An embodiment of the present application further provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode material layer disposed on the surface of the positive electrode current collector, wherein the positive electrode material layer comprises the above-mentioned positive electrode material.

[0088] In the embodiment of the present application, the positive electrode material with high energy density, cycle stability and other characteristics is applied to the positive electrode sheet, which can improve the electrochemical properties of the positive electrode sheet, such as energy density and cycle stability.

[0089] An embodiment of the present application further provides a secondary battery, comprising the above-mentioned positive electrode sheet.

[0090] The embodiments of the present application apply a positive electrode sheet having characteristics such as high energy density and cycle stability to a secondary battery, which can improve the electrochemical properties of the secondary battery, such as cycle stability and cycle life.

[0091] Exemplarily, the secondary battery may be a sodium ion battery.

[0092] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector, for example, aluminum foil is used as the metal foil; the composite current collector may be formed by forming a metal material on a polymer material substrate, wherein the metal material includes but is not limited to at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, and the polymer material substrate includes but is not limited to at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0093] It can be understood that the positive electrode material layer also includes a binder and a conductive agent, wherein the binder can be any commercially available binder for positive electrode sheets, including but not limited to polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-fluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin, or a binder prepared by any known method, which is not limited to the examples of the present application; the conductive agent can be any commercially available conductive agent for sodium ion batteries, such as carbon black, graphite, etc.

[0094] The following specific examples will be used to illustrate the metal oxide precursors, their preparation methods, and applications. However, those skilled in the art will understand that the following examples are only used to illustrate the embodiments of the present application and should not be considered to limit the scope of the embodiments of the present application. Where specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are followed. Reagents or instruments used where the manufacturer is not specified are all commercially available conventional products.

[0095] Example 1

[0096] Nickel nitrate, copper nitrate, iron nitrate, and manganese nitrate were dissolved in pure water at a metal atomic molar ratio of 25:5:35:35 to prepare a mixed metal salt solution with a concentration of 200 g / L. The mixed metal salt solution was first atomized with an atomization pressure of 0.4 MPa and an atomization angle of 45°, and then pyrolyzed at 460°C for 5 minutes to obtain a metal oxide precursor. The obtained metal oxide precursor product is represented by the simplified formula NCFM25 / 5 / 35 / 35.

[0097] The surface morphology of the metal oxide precursor prepared in this embodiment is shown in Figure 2. It can be seen that the metal oxide precursor has a single crystal structure, and its morphology is an octahedral structure with six unsaturated development cross sections, and the area of ​​the unsaturated development cross sections is large, indicating that the degree of crystal development under the spray pyrolysis process is at a low level.

[0098] Testing revealed that the single crystal particle size of the metal oxide precursor was approximately 0.68 μm, and the edge length L1 of the developed edge in the crystal was approximately 0.48 μm. Based on a calculated theoretical edge length of approximately 1.33 μm, the metal oxide precursor had a crystal development degree θ of approximately 36%, and a grain growth rate of approximately 31.6%. At this crystal development degree, the ratio of the metal oxide precursor's crystal surface area to the theoretical crystal surface area was approximately 86.2%, the ratio of the metal oxide precursor's crystal volume to the theoretical crystal volume was approximately 90.3%, and the relative surface area of ​​the metal oxide precursor was approximately 1.87.

[0099] Example 2

[0100] Nickel chloride and manganese chloride were dissolved in pure water at a metal atomic molar ratio of 35:65 to prepare a mixed metal salt solution with a concentration of 180 g / L. The mixed metal salt solution was first atomized with an atomization pressure of 0.5 MPa and an atomization angle of 50°, and then pyrolyzed at 800°C for 15 minutes to obtain a metal oxide precursor. The obtained metal oxide precursor product is represented by the simple formula FM35 / 65.

[0101] SEM testing shows that the metal oxide precursor prepared in this embodiment is a single crystal structure, and its morphology is an octahedral structure with six unsaturated development facets, and the area of ​​the unsaturated development facets is smaller than that in Example 1, indicating that the degree of crystal development under the spray pyrolysis process is higher than that in Example 1.

[0102] Testing revealed that the single crystal particle size of the metal oxide precursor was approximately 2.8 μm, and the edge length L1 of the developed edge in the crystal was approximately 1.98 μm. Based on a calculated theoretical edge length of approximately 3.6 μm, the metal oxide precursor had a crystal development degree θ of approximately 55% and a grain growth rate of approximately 38.89%. At this crystal development degree, the ratio of the metal oxide precursor's crystal surface area to the theoretical crystal surface area was approximately 91.7%, the ratio of the metal oxide precursor's crystal volume to the theoretical crystal volume was approximately 93.83%, and the metal oxide precursor had a relative surface area of ​​approximately 6.72.

[0103] Example 3

[0104] Nickel sulfate and manganese sulfate were dissolved in pure water at a metal atomic molar ratio of 25:75 to prepare a mixed metal salt solution with a concentration of 230 g / L. The mixed metal salt solution was first atomized with an atomization pressure of 0.6 MPa and an atomization angle of 42°, and then pyrolyzed at 1100°C for 25 minutes to obtain a metal oxide precursor. The obtained metal oxide precursor product is represented by the simplified formula NM25 / 75.

[0105] The surface morphology of the metal oxide precursor prepared in this example is shown in FIG3 . It can be seen that the metal oxide precursor has a single crystal structure, the area of ​​the unsaturated development section in the structure is small, and its morphology is close to a regular octahedron structure, indicating that the degree of crystal development under the spray pyrolysis process is at a high level.

[0106] Testing revealed that the single crystal particle size of the metal oxide precursor was approximately 5.6 μm, and the edge length L1 of the developed edge in the crystal was approximately 3.96 μm. Based on a calculated theoretical edge length of approximately 4.26 μm, the metal oxide precursor had a crystal development degree θ of approximately 93% and a grain growth rate of approximately 65.77%. At this crystal development degree, the ratio of the metal oxide precursor's crystal surface area to the theoretical crystal surface area was approximately 97.8%, the ratio of the metal oxide precursor's crystal volume to the theoretical crystal volume was approximately 99.3%, and the relative surface area of ​​the metal oxide precursor was approximately 24.21.

[0107] Example 4

[0108] Nickel nitrate, cobalt nitrate, and manganese nitrate were dissolved in pure water at a metal atomic molar ratio of 83:12:5 to prepare a mixed metal salt solution with a concentration of 220 g / L. The mixed metal salt solution was first atomized with an atomization pressure of 0.5 MPa and an atomization angle of 48°, and then pyrolyzed at 500°C for 2 minutes to obtain a metal oxide precursor. The obtained metal oxide precursor product is represented by the simple formula NCM83 / 12 / 5.

[0109] Testing revealed that the single crystal particle size of the metal oxide precursor was approximately 0.71 μm, and the edge length L1 of the developed edge in the crystal was approximately 0.25 μm. Based on a calculated theoretical edge length of approximately 0.76 μm, the metal oxide precursor had a crystal development degree θ of approximately 33% and a grain growth rate of approximately 35.1%. At this crystal development degree, the ratio of the metal oxide precursor's crystal surface area to the theoretical crystal surface area was approximately 66.33%, the ratio of the metal oxide precursor's crystal volume to the theoretical crystal volume was approximately 88.72%, and the metal oxide precursor had a relative surface area of ​​approximately 7.25.

[0110] Example 5

[0111] Nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in pure water at a metal atomic molar ratio of 65:15:20 to prepare a mixed metal salt solution with a concentration of 250 g / L. The mixed metal salt solution was first atomized with an atomization pressure of 0.7 MPa and an atomization angle of 55°, and then pyrolyzed at 1100°C for 30 minutes to obtain a metal oxide precursor. The obtained metal oxide precursor product is represented by the simple formula NCM65 / 15 / 20.

[0112] Testing revealed that the single crystal particle size of the metal oxide precursor was approximately 6.24 μm, and the edge length L1 of the developed edge in the crystal was approximately 4.3 μm. Based on a calculated theoretical edge length of approximately 4.53 μm, the metal oxide precursor had a crystal development degree θ of approximately 95% and a grain growth rate of approximately 68.9%. At this crystal development degree, the ratio of the metal oxide precursor's crystal surface area to the theoretical crystal surface area was approximately 99.81%, the ratio of the metal oxide precursor's crystal volume to the theoretical crystal volume was approximately 99.9%, and the relative surface area of ​​the metal oxide precursor was approximately 1.62.

[0113] Example 6

[0114] Nickel acetate, cobalt acetate, and manganese acetate were dissolved in pure water at a metal atomic molar ratio of 60:10:30 to prepare a mixed metal salt solution with a concentration of 210 g / L. The mixed metal salt solution was first atomized at an atomization pressure of 0.6 MPa and an atomization angle of 50°, and then pyrolyzed at 550°C for 5 minutes to produce the first crystal. While keeping other conditions unchanged, the pyrolysis temperature was changed to 780°C and the pyrolysis time was changed to 18 minutes to produce the second crystal. The two first crystals with different development levels were mixed with the second crystals in a ratio of 60:40, and the resulting metal oxide precursor product was represented by the simplified formula of NCM60 / 10 / 30.

[0115] The surface morphology of the metal oxide precursor prepared in this embodiment is shown in FIG4 , which shows the single crystal structure of the metal oxide precursor, and contains two octahedral structures with different development degrees and particle sizes, among which the crystals with larger particle sizes have a higher degree of development, and the crystals with smaller particle sizes have a lower degree of development.

[0116] Testing revealed that the single crystal particle size of the first crystal in the metal oxide precursor was approximately 2.48 μm, and the edge length L1 of the developed edge in the crystal was approximately 1.02 μm. Based on a calculated theoretical edge length of approximately 2.49 μm, the metal oxide precursor had a crystal development degree θ of approximately 41% and a grain growth rate of approximately 41.1%. At this crystal development degree, the ratio of the metal oxide precursor's crystal surface area to the theoretical crystal surface area was approximately 73.89%, the ratio of the metal oxide precursor's crystal volume to the theoretical crystal volume was approximately 92.3%, and the metal oxide precursor had a relative surface area of ​​approximately 2.37.

[0117] The single crystal particle size of the second crystal in the metal oxide precursor is approximately 5.09 μm, and the edge length L1 of the developed edge in the crystal is approximately 3.39 μm. Based on a calculated theoretical edge length of approximately 3.81 μm, the metal oxide precursor has a crystal development degree θ of approximately 89% and a grain growth rate of approximately 66.6%. At this crystal development degree, the ratio of the crystal surface area of ​​the metal oxide precursor to the theoretical crystal surface area is approximately 99.09%, the ratio of the crystal volume of the metal oxide precursor to the theoretical crystal volume is approximately 99.95%, and the relative surface area of ​​the metal oxide precursor is approximately 1.91.

[0118] Comparative Example 1

[0119] The difference between Comparative Example 1 and Example 1 is that the pyrolysis temperature is 380° C. and the pyrolysis time is 50 s.

[0120] Because the metal oxide precursor was not fully decomposed under these pyrolysis conditions, the crystal development was too low, resulting in a nearly spherical single crystal structure with little prismatic structure. Furthermore, the particle size was highly uneven. Testing revealed that the single crystal particle size of this metal oxide precursor was approximately 0.38 μm, with a development level of less than 25%.

[0121] Comparative Example 2

[0122] The difference between Comparative Example 2 and Example 2 is that the pyrolysis temperature is 1200° C. and the pyrolysis time is 40 s.

[0123] Due to the full reaction of the metal oxide precursor under these pyrolysis conditions, the crystals developed completely, the single crystal structure exhibited a substantially complete regular octahedral structure, and the particle size increased significantly. Testing revealed that the single crystal particle size of the metal oxide precursor was approximately 9.62 μm, and the edge length L1 of the developed edge in the crystal was approximately 6.8 μm. Based on the calculated theoretical edge length of approximately 6.83 μm, the crystal development degree θ of the metal oxide precursor was approximately 99.5%, and the grain growth rate was approximately 70.7%. At this crystal development degree, the ratio of the crystal surface area of ​​the metal oxide precursor to the theoretical crystal surface area was approximately 99.99%, the ratio of the crystal volume of the metal oxide precursor to the theoretical crystal volume was approximately 99.99%, and the relative surface area of ​​the metal oxide precursor was approximately 1.08.

[0124] Comparative Example 3

[0125] Nickel salt and manganese salt were prepared into a mixed metal salt solution in a metal atomic molar ratio of 25:75 and placed in a reactor. Then, sodium hydroxide solution and ammonia solution were added and nitrogen was introduced. The reaction temperature was controlled at 60°C, the pH value was 10.5, and the stirring rate was 500 r / min. The coprecipitation reaction was carried out for 13 hours, and then the metal hydroxide precursor was obtained by centrifugal washing and drying.

[0126] The surface morphology of the metal hydroxide precursor prepared in this comparative example is shown in FIG5 , which shows that the metal hydroxide precursor is a secondary particle composed of strip-shaped or flake-shaped primary particles aggregated together, presenting a polycrystalline structure, and the particle size is very uneven, distributed between 5 μm and 20 μm.

[0127] Comparative Example 4

[0128] The difference between Comparative Example 4 and Example 4 is that the pyrolysis temperature is 430° C. and the pyrolysis time is 2 min.

[0129] Because the metal oxide precursor cannot fully react under the pyrolysis conditions, the degree of crystal development is too low, the octahedral structure of the single crystal structure is no longer very obvious, and it presents a spherical structure. The particle size is extremely small and the agglomeration phenomenon is serious.

[0130] The single crystal particle size of the metal oxide precursor is approximately 3.18 μm, and the edge length L1 of the developed edge in the crystal is approximately 1.09 μm. Based on a calculated theoretical edge length of approximately 3.39 μm, the crystal development degree θ of the metal oxide precursor is approximately 32%, and the grain growth rate is approximately 34.3%. At this crystal development degree, the ratio of the crystal surface area of ​​the metal oxide precursor to the theoretical crystal surface area is approximately 65.32%, the ratio of the crystal volume of the metal oxide precursor to the theoretical crystal volume is approximately 88.2%, and the relative surface area of ​​the metal oxide precursor is approximately 1.61.

[0131] Comparative Example 5

[0132] The difference between Comparative Example 5 and Example 5 is that the pyrolysis temperature is 1200° C. and the pyrolysis time is 30 min.

[0133] Due to the full reaction of the metal oxide precursor under these pyrolysis conditions, the crystals developed completely, the single crystal structure exhibited a substantially complete regular octahedral structure, and the particle size increased significantly. Testing revealed that the single crystal particle size of the metal oxide precursor was approximately 6.49 μm, and the edge length L1 of the developed edge in the crystal was approximately 4.5 μm. Based on the calculated theoretical edge length of approximately 4.69 μm, the crystal development degree θ of the metal oxide precursor was approximately 96%, and the grain growth rate was approximately 69.3%. At this crystal development degree, the ratio of the crystal surface area of ​​the metal oxide precursor to the theoretical crystal surface area was approximately 99.88%, the ratio of the crystal volume of the metal oxide precursor to the theoretical crystal volume was approximately 99.99%, and the relative surface area of ​​the metal oxide precursor was approximately 1.57.

[0134] Application Examples

[0135] The precursors prepared in Examples 1-3 and Comparative Examples 1-3 were mixed with sodium carbonate in a molar ratio of 1:1, and then placed in a muffle furnace. In an air atmosphere, the temperature was raised to 900°C at a heating rate of 5°C / min. After constant temperature sintering for 15 hours, the mixture was naturally cooled, crushed, and sieved to obtain a positive electrode material.

[0136] The precursors prepared in Example 4-6 and Comparative Example 4-5 were mixed with lithium carbonate in a molar ratio of 1:1.05, and then placed in a muffle furnace. Under an air atmosphere, the temperature was raised to 950°C at a heating rate of 5°C / min. After constant temperature sintering for 15 hours, the mixture was naturally cooled, crushed and sieved to obtain a positive electrode material.

[0137] The positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-3 were made into sodium ion button batteries, and the discharge specific capacity and the capacity retention rate after 50 cycles were tested under the voltage conditions of 2V-4.2V. The positive electrode materials prepared in Examples 4-6 and Comparative Examples 4-5 were made into lithium ion button batteries, and the discharge specific capacity and the capacity retention rate after 50 cycles were tested under the voltage conditions of 2V-4.0V. The test results are shown in Table 1.

[0138] Table 1

[0139] As shown in Table 1, the metal oxide precursors prepared in Examples 1-3 exhibit good cycling stability as positive electrode materials for sodium-ion batteries. However, the cycling stability of Comparative Examples 1-3 is lower than that of Examples 1-3, particularly Comparative Example 3, where the capacity retention after 50 cycles is as low as 86.7%, indicating poor cycling stability.

[0140] Since the energy density is calculated based on the capacity and average voltage formula of the battery: mass energy density (Whkg) = capacity (Ah / kg) × average voltage (V), the positive electrode specific capacity is proportional to the mass energy density. According to the discharge specific capacity test results, the metal oxide precursors prepared in Examples 1-3 and Comparative Examples 1-3 are used to prepare positive electrode materials for sodium ion batteries, and the positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-3 are assembled into soft-pack batteries according to the same method. Under the same voltage conditions, Example 1-3 has a higher energy density than Comparative Example 1-3.

[0141] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0142] The above are merely optional embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included within the scope of the claims of the present application.

Claims

1. A metal oxide precursor, characterized in that, The metal oxide precursor has a single crystal structure, and the crystal has an incompletely developed octahedron-like structure. The incompletely developed octahedron-like structure is simulated as a completely developed regular octahedron structure as a reference. The crystal development degree θ of the octahedron-like structure is 33%-95%, and θ = L1 / L2, where L1 is the edge length of any crystal development edge in the octahedron-like structure, and L2 is the edge length of the crystal edge when the corresponding crystal development edge is simulated to be completely developed, that is, L2 is the edge length of the crystal edge corresponding to the L1 crystal development edge in the regular octahedron structure.

2. The metal oxide precursor according to claim 1, wherein L1 is 0.1 μm - 4.3 μm.

3. The metal oxide precursor according to claim 1, wherein The single crystal particle size of the metal oxide precursor is 0.43 μm - 6.43 μm.

4. The metal oxide precursor according to any one of claims 1, characterized in that The single crystal particle growth rate η of the metal oxide precursor = L1 / H1, where L1 is the edge length of any crystal development edge in the octahedron-like structure, and H1 is the single crystal particle size of the octahedron-like structure.

5. The metal oxide precursor according to any one of claims 4, characterized in that, The single crystal particle growth rate of the metal oxide precursor is 23%-67%.

6. The metal oxide precursor according to any one of claims 5, characterized in that, The single crystal particle growth rate of the metal oxide precursor is 35%-63%.

7. The metal oxide precursor according to any one of claims 6, characterized in that, The single crystal particle growth rate of the metal oxide precursor is 38%-58%.

8. The metal oxide precursor according to claim 1, wherein The crystal surface area of the metal oxide precursor accounts for 88.72%-99.99% of the crystal surface area of the metal oxide precursor when the crystal development degree is 100%.

9. The metal oxide precursor according to claim 1, wherein The crystal volume of the metal oxide precursor accounts for 95.23%-99.99% of the crystal volume of the metal oxide precursor when the crystal development degree is 100%.

10. The metal oxide precursor according to claim 1, characterized in that, The ratio of the crystal surface area to the crystal volume of the metal oxide precursor is 1.62 μm -1 -26.03 μm -1 .

11. The metal oxide precursor according to any one of claims 1-10, characterized in that, The metal oxide precursor includes a first crystal and / or a second crystal. The crystal development degree of the first crystal is 33% ≤ θ1 ≤ 65%, and the crystal development degree of the second crystal is 65% < θ2 ≤ 95%.

12. The metal oxide precursor according to any one of claims 1-10, characterized in that, The metal oxide precursor includes a first crystal and / or a second crystal. The edge length of the development edge in the first crystal is 0.1 μm - 2.95 μm, and the edge length of the development edge in the second crystal is 0.2 μm - 4.3 μm.

13. The metal oxide precursor according to any one of claims 1-10, characterized in that, The metal oxide precursor includes a first crystal and / or a second crystal, and the ratio of the crystal surface area to the crystal volume in the first crystal is 1.63 μm -1 -26.03 μm -1 , and the ratio of the crystal surface area to the crystal volume in the second crystal is 1.62 μm -1 -24.48 μm -1 .

14. The metal oxide precursor according to claim 1, wherein The chemical general formula of the metal oxide precursor is expressed as A x M y O2, where 0.9 ≤ x ≤ 1, 0 ≤ y ≤ 0.1, A is selected from at least one of Ni, Fe, Cu, Mn, and Co, and M is selected from at least one of Mg, Al, Sn, Ca, W, Ti, Zn, Li, Na, Mo, La, and Zr.

15. A method for preparing a metal oxide precursor according to any one of claims 1-14, characterized in that, The preparation method is selected from spray pyrolysis.

16. The method for preparing the metal oxide precursor according to claim 15, wherein, The pyrolysis temperature of the spray pyrolysis is 460°C - 1110°C.

17. The method for preparing a metal oxide precursor according to claim 15, wherein, The pyrolysis time of the spray pyrolysis is 1 min - 30 min.

18. A positive electrode material prepared from the metal oxide precursor according to any one of claims 1-14 or the metal oxide precursor prepared by the method according to any one of claims 15-17.

19. A positive electrode sheet, characterized in that, It includes a positive electrode current collector and a positive electrode material layer provided on the surface of the positive electrode current collector. The positive electrode material layer includes the positive electrode material according to claim 18.

20. A secondary battery, characterized in that, It includes the positive electrode sheet according to claim 19.

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