Positive electrode sheet and preparation method thereof, battery and energy storage device

Abstract

The present application provides a positive electrode plate and a preparation method thereof, a battery, and an energy storage device. The positive electrode plate of the present application includes: a positive electrode current collector having a preset surface; and a positive electrode active layer, the positive electrode active layer being disposed on the preset surface of the positive electrode current collector, the positive electrode active layer including positive electrode particles, the positive electrode particles being partially embedded in the positive electrode current collector, the positive electrode particles being sodium ferric phosphate pyrophosphate, and the positive electrode particles being spherical or spherical; the positive electrode plate satisfies the relationship: b≤c·α / 180°; wherein b is the depth of the positive electrode particles embedded in the positive electrode current collector, α is the angle between the tangents of the two points on the intersection line of the positive electrode particles and the preset surface that are farthest apart, and c is the distance from the intersection point of the tangents of the two points on the intersection line of the positive electrode particles and the preset surface to the preset surface.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and specifically to a positive electrode plate and a preparation method thereof, a battery, and an energy storage device. Background Art

[0002] Sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2(P2O7), which has a three-dimensional sodium ion diffusion channel and a sodium superion conductor structure, has a high voltage platform, high capacity, and excellent rate and cycling stability. It has great potential as a large-scale production cathode material for sodium-ion batteries. However, the compaction density of existing Na4Fe3(PO4)2(P2O7) is still relatively low. Summary of the Invention

[0003] The embodiment of the present application provides a positive electrode plate having a high compaction density and good mechanical properties.

[0004] In a first aspect, an embodiment of the present application provides a positive electrode plate, the positive electrode plate comprising:

[0005] a positive electrode current collector having a predetermined surface; and

[0006] A positive electrode active layer, the positive electrode active layer being disposed on the predetermined surface of the positive electrode current collector, the positive electrode active layer comprising positive electrode particles, the positive electrode particles being partially embedded in the positive electrode current collector, the positive electrode particles being sodium iron pyrophosphate, and the positive electrode particles being spherical or spherical;

[0007] The positive electrode sheet satisfies the relationship: b≤c·α / 180°;

[0008] Wherein, b is the depth of the positive electrode particles embedded in the positive electrode current collector, α is the angle between the tangents of the two points on the intersection line of the positive electrode particles and the preset surface that are farthest apart, and c is the distance between the intersection point of the tangents of the two points on the intersection line of the positive electrode particles and the preset surface and the preset surface.

[0009] Furthermore, the positive electrode plate also satisfies the relationship: b / a≤1 / 3, wherein a is the thickness of the positive electrode current collector.

[0010] Furthermore, the depth b of the positive electrode particles embedded in the positive electrode current collector is in the range of b≤6 μm.

[0011] Furthermore, the range of the angle α between the tangent lines of the two points on the intersection line between the positive electrode particles and the predetermined surface that are farthest apart is: 45°≤α≤120°.

[0012] Furthermore, a distance c between an intersection point of tangent lines of two points on an intersection line between the positive electrode particles and the preset surface that are farthest apart and the preset surface is in the range of: c≤18 μm.

[0013] Furthermore, the average sphericity of the positive electrode particles is greater than or equal to 0.9.

[0014] Furthermore, the molar ratio Na / Fe of the sodium element to the iron element in the positive electrode particles is in the range of 1.34≤Na / Fe≤1.5.

[0015] Furthermore, the molar ratio of iron to phosphorus in the positive electrode particles, Fe / P, is in the range of 0.70≤Fe / P≤0.745.

[0016] In a second aspect, the present application provides a method for preparing a positive electrode sheet, which comprises:

[0017] Providing a positive electrode current collector and a positive electrode slurry, wherein the positive electrode current collector has a predetermined surface, the positive electrode slurry comprises positive electrode particles, and the positive electrode particles are sodium iron pyrophosphate;

[0018] coating the positive electrode slurry on the predetermined surface of the positive electrode current collector, and removing the solvent of the positive electrode slurry to form a positive electrode active layer; and

[0019] Roll-pressing the positive electrode current collector having the positive electrode active layer so that the positive electrode particles are partially embedded in the positive electrode current collector to obtain a positive electrode sheet;

[0020] Wherein, the positive electrode sheet satisfies the relationship: b<c·α / 180°;

[0021] Wherein, b is the depth of the positive electrode particles embedded in the positive electrode current collector, α is the angle between the tangents of the two points on the intersection line of the positive electrode particles and the preset surface that are farthest apart, and c is the distance between the intersection point of the tangents of the two points on the intersection line of the positive electrode particles and the preset surface and the preset surface.

[0022] Furthermore, the positive electrode current collector having the positive electrode active layer is roll-pressed so that the positive electrode particles are partially embedded in the positive electrode current collector to obtain a positive electrode sheet, comprising:

[0023] The positive electrode current collector having the positive electrode active layer is roll-pressed with a rolling pressure P of 70 tons ≤ P ≤ 150 tons, so that the positive electrode particles are partially embedded in the positive electrode current collector to obtain a positive electrode sheet.

[0024] In a third aspect, the present application provides a battery comprising:

[0025] electrolyte;

[0026] The positive electrode sheet described in the embodiment of the present application;

[0027] a diaphragm located on one side of the positive electrode plate, and

[0028] A negative electrode plate is provided on a side of the diaphragm away from the positive electrode plate.

[0029] In a fourth aspect, the present application provides an energy storage device, comprising:

[0030] cabinet; and

[0031] A plurality of batteries according to the embodiments of the present application are housed in the box.

[0032] The positive electrode particles of the positive electrode sheet of the embodiment of the present application are partially embedded in the positive electrode current collector. The positive electrode particles are embedded in the positive electrode current collector, occupying part of the space in the positive electrode current collector, and the positive electrode particles are more densely packed, thereby improving the compaction density of the positive electrode sheet. In addition, due to the compression of the positive electrode active layer, the positive electrode current collector itself is also made more dense, increasing the compaction density of the positive electrode sheet, thereby enabling the positive electrode sheet to have a higher energy density and specific capacity, and also reducing the resistance of the positive electrode sheet. In addition, the shape and protrusion of the positive electrode particles embedded in the positive electrode current collector have a significant impact on the winding process of the positive electrode sheet. When the positive electrode particles embedded in the positive electrode current collector are irregular in shape and relatively protruding, tip cracks are formed at the embedded foil (i.e., the location where the positive electrode current collector is embedded), making the positive electrode sheet prone to breakage during the winding process. The present application prepares quasi-spherical or spherical sodium iron pyrophosphate particles, and makes the positive electrode sheet satisfy the relationship: b≤c·α / 180°, so that the positive electrode sheet has a high compaction density while the part of the positive electrode particles embedded in the positive electrode current collector is not too protruding, thereby better avoiding the formation of tip cracks at the position where the positive electrode particles are embedded in the positive electrode current collector, making the positive electrode current collector less likely to break during the winding process, and having a better winding process. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. 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 creative work.

[0034] Figure 1 It is a structural schematic diagram of the positive electrode plate of an embodiment of the present application.

[0035] Figure 2 The positive electrode of one embodiment of the present application is along the Figure 1Schematic diagram of the cross-sectional structure in the AA direction.

[0036] Figure 3 It is a schematic flow chart of a method for preparing a positive electrode sheet according to an embodiment of the present application.

[0037] Figure 4 This is a scanning electron microscope image (SEM image) of the cross-section of the positive electrode sheet of Example 1 of the present application.

[0038] Figure 5 Schematic diagram of the structure of a battery according to an embodiment of the present application.

[0039] Figure 6 The battery of one embodiment of the present application is Figure 5 Schematic diagram of the cross-sectional structure in the middle BB direction.

[0040] Figure 7 Schematic diagram of the structure of the negative electrode sheet of one embodiment of the present application.

[0041] Figure 8 It is a structural diagram of an energy storage device according to an embodiment of the present application.

[0042] Description of reference numerals:

[0043] 100-positive electrode sheet, 10-positive electrode current collector, 11-preset surface, 20-positive electrode active layer, 21-positive electrode particles, 300-battery, 320-separator, 330-negative electrode sheet, 331-negative electrode current collector, 332-negative electrode active layer, 340-shell, 350-end cover assembly, 400-energy storage device, 410-case. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0045] The terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish between different objects, not to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0046] The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings.

[0047] It should be noted that, for the convenience of explanation, in the embodiments of the present application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0048] Sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2(P2O7), which has a three-dimensional sodium ion diffusion channel and a sodium superion conductor structure, has a high voltage platform, high capacity, and excellent rate and cycling stability. It has great potential as a large-scale production cathode material for sodium-ion batteries. However, the compaction density of existing Na4Fe3(PO4)2(P2O7) is still relatively low.

[0049] Figure 1 Schematic diagram of the structure of the positive electrode plate 100 according to an embodiment of the present application. Figure 2 The positive electrode sheet 100 of one embodiment of the present application is Figure 1 Schematic diagram of the cross-sectional structure in the AA direction.

[0050] See Figure 1 and Figure 2 The embodiment of the present application provides a positive electrode sheet 100, the positive electrode sheet 100 comprising a positive electrode current collector 10 and a positive electrode active layer 20, the positive electrode current collector 10 having a predetermined surface 11; the positive electrode active layer 20 being disposed on the predetermined surface 11 of the positive electrode current collector 10, the positive electrode active layer 20 comprising positive electrode particles 21, the positive electrode particles 21 being partially embedded in the positive electrode current collector 10, the positive electrode particles 21 being sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2(P2O 7), the positive electrode particles 21 are spherical or spherical; the positive electrode plate 100 satisfies the relationship: b≤c·α / 180°; wherein b is the depth of the positive electrode particles 21 embedded in the positive electrode current collector 10, α is the angle between the tangents of the two points on the intersection line of the positive electrode particles 21 and the preset surface 11 that are farthest apart, and c is the distance between the intersection point of the tangents of the two points on the intersection line of the positive electrode particles 21 and the preset surface 11 and the preset surface 11.

[0051] The positive electrode sheet 100 of the embodiment of the present application can be applied to batteries, such as sodium ion batteries.

[0052] It can be understood that the positive electrode active layer 20 includes a plurality of positive electrode particles 21, some of the positive electrode particles 21 are close to the positive electrode current collector 10, some of the positive electrode particles 21 are away from the positive electrode current collector 10, and among the positive electrode particles 21 close to the positive electrode current collector 10, a portion of some of the positive electrode particles 21 is embedded in the positive electrode current collector 10.

[0053] It should be noted that the "predetermined surface 11" can be one or more surfaces of all the surfaces of the positive electrode current collector 10, or a portion of a surface of the positive electrode current collector 10. For example, the positive electrode active layer 20 covers a portion of each of two opposite surfaces of the positive electrode current collector 10. In the schematic diagram of this embodiment, the predetermined surface 11 is illustrated as two opposite surfaces of the positive electrode current collector 10, and this should not be construed as limiting the positive electrode sheet 100 provided in this embodiment of the application.

[0054] Optionally, the positive electrode current collector 10 is stacked with the positive electrode active layer 20 . The positive electrode active layer 20 is stacked on one or both of the two opposite surfaces of the positive electrode current collector 10 .

[0055] Optionally, the material of the positive electrode current collector 10 may be, but is not limited to, at least one of aluminum foil, aluminum sheet, and the like.

[0056] Optionally, the positive electrode active layer 20 further includes a positive electrode conductor, a positive electrode binder, a positive electrode thickener, and the like.

[0057] It is understood that the positive electrode sheet 100 satisfies the relationship: c·α / b ≥ 180°. Specifically, c·α / b can be, but is not limited to, 180°, 195°, 210°, 225°, 240°, 255°, 270°, 285°, 300°, etc. If c·α / b is too small, the positive electrode particles 21 will protrude too much when embedded in the positive electrode current collector 10, easily forming tip cracks at the embedding point between the positive electrode particles 21 and the positive electrode current collector 10, and thus making the positive electrode sheet 100 susceptible to breakage during the winding process.

[0058] Optionally, c>b.

[0059] The positive electrode particles 21 of the positive electrode sheet 100 of the embodiment of the present application are partially embedded in the positive electrode current collector 10. The positive electrode particles 21 are embedded in the positive electrode current collector 10, occupying part of the space in the positive electrode current collector 10. The positive electrode particles 21 are more densely packed together, thereby increasing the compaction density of the positive electrode sheet 100. Furthermore, due to the compression of the positive electrode active layer 20, the positive electrode current collector 10 itself is also made more dense, increasing the compaction density of the positive electrode sheet 100. This results in the positive electrode sheet 100 having a higher energy density and specific capacity, and also reduces the resistance of the positive electrode sheet 100. Furthermore, the shape and protrusion of the positive electrode particles 21 embedded in the positive electrode current collector 10 significantly affect the winding process of the positive electrode sheet 100. When the positive electrode particles 21 embedded in the positive electrode current collector 10 are irregular in shape and protrude significantly, tip cracks form at the foil embedding point (i.e., the location where they are embedded in the positive electrode current collector 10), making the positive electrode sheet 100 susceptible to breakage during the winding process. The present application prepares spherical or spherical sodium iron phosphate pyrophosphate particles, and makes the positive electrode plate 100 satisfy the relationship: b≤c·α / 180°, so that the positive electrode plate 100 has a high compaction density while the portion of the positive electrode particles 21 embedded in the positive electrode current collector 10 does not protrude too much, thereby better avoiding the formation of tip cracks at the position where the positive electrode particles 21 are embedded in the positive electrode current collector 10, making the positive electrode current collector 10 less likely to break during the winding process, and having a better winding process.

[0060] In some embodiments, the positive electrode sheet 100 further satisfies the relationship: b / a ≤ 1 / 3, where a is the thickness of the positive current collector 10. That is, the ratio b / a of the depth b of the positive electrode particles 21 embedded in the positive current collector 10 to the thickness a of the positive current collector 10 satisfies: b / a ≤ 1 / 3.

[0061] Specifically, b / a can be, but is not limited to, 0.03, 0.05, 0.1, 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, 0.3, 0.33, etc.

[0062] In this embodiment, if b / a is too large, the depth of the positive electrode particles 21 embedded in the positive electrode current collector 10 is too deep, which easily makes the positive electrode current collector 10 at the embedding position of the positive electrode particles 21 too thin, thereby reducing the mechanical properties of the positive electrode sheet 100, making the positive electrode sheet 100 brittle, and easily causing brittle fracture during the bending process, which is not conducive to the winding and subsequent preparation of the positive electrode sheet 100.

[0063] Optionally, the thickness a of the positive electrode current collector 10 is in the range of 10 μm ≤ a ≤ 18 μm. Specifically, the thickness a of the positive electrode current collector 10 may be, but is not limited to, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, etc. If the thickness a of the positive electrode current collector 10 is too thin, the mechanical strength of the positive electrode current collector 10 is reduced; if the thickness a of the positive electrode current collector 10 is too thick, the internal resistance of the battery is increased, resulting in energy loss and reduced efficiency of the battery.

[0064] In some embodiments, the depth b of the positive electrode particles 21 embedded in the positive electrode current collector 10 is in the range of b≤6 μm.

[0065] Specifically, the depth b of the positive electrode particles 21 embedded in the positive electrode current collector 10 may be, but is not limited to, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, etc.

[0066] In this embodiment, if the depth b of the positive electrode particles 21 embedded in the positive electrode current collector 10 is too small, the improvement of the compaction density of the positive electrode sheet 100 is limited; if the depth b of the positive electrode particles 21 embedded in the positive electrode current collector 10 is too large, the positive electrode current collector 10 at the embedding position of the positive electrode particles 21 is likely to be too thin, thereby reducing the mechanical properties of the positive electrode sheet 100, making the positive electrode sheet 100 brittle, and easily causing brittle fracture during the bending process, which is not conducive to the winding and subsequent preparation of the positive electrode sheet 100.

[0067] Furthermore, the depth b of the positive electrode particles 21 embedded in the positive electrode current collector 10 is in the range of 1 μm ≤ b ≤ 6 μm. This allows the positive electrode sheet 100 to have a higher compaction density and better mechanical strength, which is beneficial for the winding and subsequent preparation of the positive electrode sheet 100.

[0068] In some embodiments, the angle α between the tangent lines of the two points on the intersection line between the positive electrode particles 21 and the predetermined surface 11 that are farthest apart is in the range of 45°≤α≤120°.

[0069] Specifically, the angle α between the tangents of the two points farthest apart on the intersection line of the positive electrode particles 21 and the preset surface 11 can be, but is not limited to, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 90°, 95°, 100°, 105°, 110°, 115°, 120°, etc.

[0070] In this embodiment, if the angle α between the tangents of the two points on the intersection line of the positive electrode particles 21 and the preset surface 11 that are farthest apart is too small, then when the positive electrode particles 21 are embedded in the positive electrode current collector 10, the indentation caused to the positive electrode current collector 10 will be more abrupt and discontinuous, which will reduce the bending strength of the positive electrode current collector 10 and is not conducive to the subsequent winding of the positive electrode sheet 100; if the angle α between the tangents of the two points on the intersection line of the positive electrode particles 21 and the preset surface 11 is too large, then the depth of the positive electrode particles 21 embedded in the positive electrode current collector 10 is too shallow, the phenomenon of embedding in the positive electrode current collector 10 is not obvious, and the improvement of the compaction density of the positive electrode sheet 100 is limited.

[0071] In some embodiments, a distance c between an intersection of two tangent lines of the positive electrode particles 21 and the predetermined surface 11 at the two points on the intersection line between the positive electrode particles 21 and the predetermined surface 11 and the predetermined surface 11 is in the range of c≤18 μm.

[0072] Specifically, the distance c between the intersection of the tangents of the two farthest points on the intersection line of the positive electrode particles 21 and the preset surface 11 and the preset surface 11 can be, but is not limited to, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, etc.

[0073] In this embodiment, if the distance between the intersection of the tangents of the two points on the intersection line of the positive electrode particles 21 and the preset surface 11 and the preset surface 11 is too small, the depth of the positive electrode particles 21 embedded in the positive electrode current collector 10 is too small, and the improvement of the compaction density of the positive electrode plate 100 is limited; if the distance between the intersection of the tangents of the two points on the intersection line of the positive electrode particles 21 and the preset surface 11 and the preset surface 11 is too large, the depth of the positive electrode particles 21 embedded in the positive electrode current collector 10 is too large, thereby reducing the mechanical properties of the positive electrode plate 100, making the positive electrode plate 100 brittle, and easily causing brittle fracture during bending, which is not conducive to the winding and subsequent preparation of the positive electrode plate 100.

[0074] Furthermore, the distance c between the intersection of the tangent lines of the two points on the intersection line of the positive electrode particles 21 and the predetermined surface 11, and the predetermined surface 11, is in the range of 1 μm ≤ c ≤ 17 μm. This allows the positive electrode sheet 100 to have both a high compaction density and high mechanical properties.

[0075] Furthermore, the distance c between the intersection of the tangent lines of the two points on the intersection line of the positive electrode particles 21 and the predetermined surface 11, and the predetermined surface 11, is in the range of 2 μm ≤ c ≤ 15 μm. This allows the positive electrode sheet 100 to have both a high compaction density and high mechanical properties.

[0076] In some embodiments, the average sphericity of the positive electrode particles 21 is greater than or equal to 0.9.

[0077] In the embodiments of the present application, when a numerical value range of m to n is involved, unless otherwise specified, it means that the numerical value can be any numerical value between m and n, including the endpoint numerical value m and the endpoint numerical value n.

[0078] The sphericity of the present application is calculated in the following way: make two mathematical circles for the spherical Na4Fe3(PO4)2(P2O7) particles (phosphorus positive electrode particles 21), one is the minimum circumscribed circle of Na4Fe3(PO4)2(P2O7) (radius is R1), and the other is the maximum inscribed circle of Na4Fe3(PO4)2(P2O7) (radius is R2). The sphericity of the particle = R1 / R2. Take n particles (for example, more than 100 particles from a scanning electron microscope (SEM) image) and calculate the average sphericity of these particles.

[0079] It can be understood that the average sphericity of the positive electrode particles 21 ranges from 0.9 to 1.

[0080] Specifically, the average sphericity of the positive electrode particles 21 may be, but is not limited to, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, or the like.

[0081] When preparing the positive electrode sheet 100, the positive electrode particles 21 need to be slurried and coated on the positive electrode current collector 10, and then the positive electrode sheet 100 is rolled. When the sphericity of the positive electrode particles 21 is too low, the positive electrode particles 21 with lower sphericity have prominent edges and corners, which will hinder the movement and rolling of the positive electrode material during the rolling process. Therefore, some positive electrode particles 21 may be stuck in a local area, and eventually the surface of the positive electrode sheet 100 will crack or even break, thereby reducing the processing performance and compaction density of the positive electrode material. The positive electrode particles 21 of this embodiment have a high average sphericity. When the positive electrode particles 21 are used to prepare the positive electrode sheet 100, during the rolling process of the positive electrode sheet 100, the positive electrode particles 21 with a high sphericity are easy to move and can be more evenly deposited on the positive electrode collector 10 of the positive electrode sheet 100. In addition, smaller positive electrode particles 21 are more likely to move to the gaps between larger positive electrode particles 21, and the particles can be more densely deposited, so that the positive electrode sheet 100 has a higher compaction density and better processing performance.

[0082] In some embodiments, the molar ratio Na / Fe of the sodium element to the iron element in the positive electrode particles 21 is in the range of 1.34≤Na / Fe≤1.5.

[0083] It should be noted that the molecular formula of the sodium iron phosphate pyrophosphate in the present application, Na4Fe3(PO4)2(P2O7), is only a theoretical molecular formula obtained based on the valence state of each element. The ratio of sodium element to iron element and the ratio of sodium element to phosphorus element in the positive electrode particles 21 of the present application should not be understood as the quantitative ratio in the molecular formula. The ratio of sodium element to iron element and the ratio of iron element to phosphorus element in the positive electrode particles 21 of the present application shall be based on the specific description in the corresponding embodiment of the present application. The molecular formula should not be understood as a limitation on the specific elemental composition of the sodium iron phosphate pyrophosphate positive electrode material of the present application.

[0084] Specifically, the molar ratio Na / Fe of sodium to iron in the positive electrode particles 21 may be, but is not limited to, 1.36, 1.37, 1.38, 1.39, 1.40, 1.41, 1.42, 1.43, 1.44, 1.45, 1.46, 1.47, 1.48, 1.49, 1.5, etc.

[0085] In this embodiment, if the molar ratio Na / Fe of the sodium element to the iron element in the positive electrode particles 21 is too high, the positive electrode particles 21 are likely to form a sodium iron pyrophosphate miscella phase during the preparation process, reducing the gram capacity of the positive electrode particles 21. In addition, the sodium iron pyrophosphate miscella phase does not match the main phase of sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2(P2O7)), thereby reducing the degree of sphericity of the prepared positive electrode particles 21. If the molar ratio Na / Fe of the sodium element to the iron element in the positive electrode particles 21 is too low, the sodium iron phosphate miscella phase is likely to form during the preparation process of the positive electrode particles 21, also reducing the gram capacity of the sodium iron phosphate pyrophosphate positive electrode particles 21. In addition, the sodium iron phosphate miscella phase does not match the main phase of sodium iron phosphate pyrophosphate, thereby reducing the degree of sphericity of the prepared sodium iron phosphate pyrophosphate positive electrode particles 21. When the molar ratio Na / Fe of the sodium element to the iron element in the positive electrode particles 21 is in the range of 1.34≤Na / Fe≤1.5, the amount of sodium iron pyrophosphate impurity phase and sodium iron phosphate impurity phase in the sodium iron pyrophosphate positive electrode particles 21 can be made as small as possible, so that the positive electrode particles 21 have higher sphericity, thereby having higher compaction density and processing performance.

[0086] In some embodiments, the molar ratio of iron to phosphorus in the positive electrode particles 21 is Fe / P in a range of 0.70≤Fe / P≤0.745.

[0087] Specifically, the molar ratio of iron to phosphorus in the positive electrode particles 21 , Fe / P, may be, but is not limited to, 0.70, 0.705, 0.71, 0.715, 0.72, 0.725, 0.73, 0.735, 0.74, 0.745, etc.

[0088] In this embodiment, if the molar ratio (Fe / P) of iron to phosphorus in the positive electrode particles 21 is too low, the positive electrode particles 21 are insufficiently iron-rich, which can easily lead to the formation of inactive impurity phases in the positive electrode particles 21. This not only reduces the gram capacity of the positive electrode particles 21, but also reduces the sphericity of the positive electrode particles 21, thereby reducing the compaction density of the positive electrode sheet 100. If the molar ratio (Fe / P) of iron to phosphorus in the positive electrode particles 21 is too high, the inactive iron in the positive electrode particles 21 increases, reducing the volumetric energy density and mass energy density of the positive electrode particles 21. When used in a battery, this reduces the gram capacity of the battery. Furthermore, the increase in inactive iron impurity phases also reduces the sphericity of the positive electrode particles 21, thereby reducing the compaction density of the positive electrode sheet 100.

[0089] The amounts of iron, sodium, and phosphorus in the embodiments of the present application can be measured using an inductively coupled plasma optical emission spectrometer (ICP-OES).

[0090] The compaction density of the sodium iron pyrophosphate positive electrode plate 100 of the embodiment of the present application is in the range of 2.15 g / cm 3 Up to 2.45g / cm 3 Specifically, the compaction density of the sodium iron pyrophosphate positive electrode plate 100 can be, but is not limited to, 2.15 g / cm 3 , 2.2g / cm 3 , 2.25g / cm 3 , 2.3g / cm 3 , 2.35g / cm 3 , 2.4g / cm 3 , 2.45g / cm 3 wait.

[0091] The mass specific capacity of the positive electrode sheet 100 of the embodiment of the present application at 0.1C ranges from 108 mAh / g to 112 mAh / g. Specifically, the mass specific capacity of the positive electrode sheet 100 at 0.1C can be, but is not limited to, 108 mAh / g, 109 mAh / g, 110 mAh / g, 111 mAh / g, 112 mAh / g, etc.

[0092] The resistance of the positive electrode sheet 100 of the embodiment of the present application ranges from 40mΩ to 100mΩ. Specifically, the resistance of the positive electrode sheet 100 can be, but is not limited to, 40mΩ, 50mΩ, 60mΩ, 70mΩ, 80mΩ, 90mΩ, 100mΩ, etc. Under the premise that the formula of the positive electrode sheet 100 is fixed, the resistivity of the positive electrode sheet 100 is generally a constant value, and the relationship between resistance and resistivity is: resistance = resistivity × thickness / area). Under the condition of the same load, the thickness of the positive electrode sheet 100 with a high compaction density is thinner. Under the condition that the area of ​​the positive electrode sheet 100 is equal, the resistance of the positive electrode sheet 100 will be lower.

[0093] The peel force of the positive electrode sheet 100 of the embodiment of the present application ranges from 7 N·m to 12 N·m. Specifically, the peel force of the positive electrode sheet 100 can be, but is not limited to, 7 N·m, 8 N·m, 9 N·m, 10 N·m, 11 N·m, 12 N·m, etc. In the positive electrode sheet 100 of the present application, a portion of the positive electrode particles 21 is embedded in the positive electrode current collector 10, thereby increasing the contact area between the positive electrode active layer 20 and the positive electrode current collector 10, thereby achieving a higher peel force for the positive electrode sheet 100.

[0094] Peel strength test SOP: Cut the positive electrode sheet 100 into strips 25mm wide and longer than 20cm. Attach 20mm*100mm 3M double-sided tape to the center of a steel plate, leaving one-third of the back of the plate blank. Lay the cut positive electrode sheet 100, with both sides slightly wider than the 3M double-sided tape, parallel to the other side of the tape. Manually peel the positive electrode sheet 100 from the bottom to the center. Then, perform a tensile strength test using a tensile testing machine at a speed of 50mm / min. The peel strength value is obtained after the test.

[0095] The positive electrode sheet 100 of the embodiment of the present application can be prepared by the method described in the following embodiments of the present application. In addition, it can also be prepared by other methods. The preparation method of the embodiment of the present application is only one or more preparation methods of the positive electrode sheet 100 of the present application and should not be understood as a limitation on the positive electrode sheet 100 provided in the embodiment of the present application.

[0096] Figure 3 1 is a flow chart of a method for preparing a positive electrode plate 100 according to an embodiment of the present application.

[0097] See Figure 3 The present application also provides a method for preparing a positive electrode sheet 100, which includes:

[0098] S201, providing a positive electrode current collector 10 and a positive electrode slurry, wherein the positive electrode current collector 10 has a predetermined surface 11, the positive electrode slurry includes positive electrode particles 21, and the positive electrode particles 21 are sodium iron phosphate pyrophosphate;

[0099] Optionally, the positive electrode particles 21 , the positive electrode conductive agent, the positive electrode binder and the solvent are mixed uniformly in a tank mixer to obtain a positive electrode slurry.

[0100] Optionally, the positive electrode conductive agent may be, but is not limited to, at least one of acetylene black, conductive carbon black (Super P), carbon nanotubes, graphene, and the like.

[0101] Optionally, the positive electrode binder may be, but is not limited to, polyvinylidene fluoride (PVDF).

[0102] Alternatively, the solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0103] S202 , coating the positive electrode slurry on the predetermined surface 11 of the positive electrode current collector 10 , and removing the solvent of the positive electrode slurry to form a positive electrode active layer 20 ; and

[0104] Optionally, the positive electrode slurry is coated on the upper and lower surfaces (ie, the predetermined surface 11 ) of the positive electrode current collector 10 , and then dried in an oven to remove the solvent in the positive electrode slurry to obtain the positive electrode active layer 20 .

[0105] Optionally, the drying temperature may be 80° C. to 120° C. Specifically, the drying temperature may be, but is not limited to, 80° C., 90° C., 100° C., 110° C., 120° C., and the like.

[0106] Optionally, the drying is carried out under vacuum, i.e., negative pressure.

[0107] Optionally, the coating thickness of the positive electrode slurry ranges from 100 μm to 300 μm. Specifically, the coating thickness of the positive electrode slurry is 100 μm, 130 μm, 150 μm, 180 μm, 200 μm, 230 μm, 250 μm, 280 μm, 300 μm, etc. If the coating thickness of the positive electrode slurry is too thin, the areal loading of the positive electrode sheet 100 is too low, resulting in an area specific capacity of the positive electrode sheet 100 being too low; if the coating thickness of the positive electrode slurry is too thick, the mechanical properties of the positive electrode sheet 100 deteriorate, making the positive electrode sheet 100 prone to slagging.

[0108] S203 , rolling the positive electrode current collector 10 having the positive electrode active layer 20 so that the positive electrode particles 21 are partially embedded in the positive electrode current collector 10 , thereby obtaining a positive electrode sheet 100 ;

[0109] The positive electrode sheet 100 satisfies the relationship: b<c·α / 180°;

[0110] Among them, b is the depth of the positive electrode particles 21 embedded in the positive electrode current collector 10, α is the angle between the tangents of the two points on the intersection line of the positive electrode particles 21 and the preset surface 11 that are farthest apart, and c is the distance between the intersection point of the tangents of the two points on the intersection line of the positive electrode particles 21 and the preset surface 11 and the preset surface 11.

[0111] Optionally, the mass fraction of the positive electrode particles 21 in the positive electrode active layer 20 ranges from 88% to 97%. Specifically, the mass fraction of the positive electrode particles 21 in the positive electrode active layer 20 may be, but is not limited to, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, etc. If the mass fraction of the positive electrode particles 21 in the positive electrode active layer 20 is too low, it indicates that the content of the positive electrode conductive agent and the positive electrode binder is too high, which reduces the proportion of active material and the compaction density of the positive electrode sheet 100. If the mass fraction of the positive electrode particles 21 in the positive electrode active layer 20 is too high, the content of the positive electrode conductive agent and the positive electrode binder is too low, which reduces the conductivity of the positive electrode sheet 100 and the bonding between the positive current collector 10 and the positive electrode active layer 20. This makes it easy for the positive electrode sheet 100 to delaminate during winding, thereby reducing the mechanical properties of the positive electrode sheet 100.

[0112] Furthermore, the mass fraction of the positive electrode particles 21 in the positive electrode active layer 20 is in the range of 93% to 96%. This allows the positive electrode sheet 100 to have a higher compaction density and energy density, as well as better electrical conductivity and mechanical properties.

[0113] The positive electrode particles 21 of the positive electrode sheet 100 prepared by the preparation method of the positive electrode sheet 100 in the embodiment of the present application are partially embedded in the positive electrode collector 10. The positive electrode particles 21 are embedded in the positive electrode collector 10, occupying part of the space of the positive electrode collector 10, and the positive electrode particles 21 are more densely packed, thereby improving the compaction density of the positive electrode sheet 100; in addition, due to the squeezing effect of the positive active layer 20, the positive electrode collector 10 itself will also be made denser, thereby improving the compaction density of the positive electrode sheet 100, so that the positive electrode sheet 100 has a higher energy density and specific capacity, and also reduces the resistance of the positive electrode sheet 100. In addition, the shape and protrusion of the positive electrode particles 21 embedded in the positive electrode current collector 10 will have a great impact on the winding process of the positive electrode plate 100. When the positive electrode particles 21 embedded in the positive electrode current collector 10 are irregular in shape and relatively protruding, a tip crack is formed at the embedded foil (i.e., the position where the positive electrode current collector 10 is embedded), making the positive electrode plate 100 prone to breakage during the winding process. The present application prepares spherical or spherical sodium iron pyrophosphate particles, and makes the positive electrode plate 100 satisfy the relationship: b≤c·α / 180°, so that the positive electrode plate 100 has a high compaction density while the part where the positive electrode particles 21 are embedded in the positive electrode current collector 10 is not too protruding, thereby better avoiding the formation of tip cracks at the position where the positive electrode particles 21 are embedded in the positive electrode current collector 10, making the positive electrode current collector 10 less likely to break during the winding process, and having a better winding process.

[0114] In some embodiments, the positive electrode current collector 10 having the positive electrode active layer 20 is rolled so that the positive electrode particles 21 are partially embedded in the positive electrode current collector 10 to obtain the positive electrode sheet 100, including:

[0115] The positive electrode collector 10 having the positive electrode active layer 20 is roll-pressed with a roll-pressing pressure P of 70 tons ≤ P ≤ 150 tons, so that the positive electrode particles 21 are partially embedded in the positive electrode collector 10 to obtain a positive electrode sheet 100 .

[0116] Specifically, the rolling pressure P can be, but is not limited to, 70 tons, 80 tons, 90 tons, 100 tons, 105 tons, 110 tons, 115 tons, 120 tons, 130 tons, 140 tons, 150 tons, etc.

[0117] In this embodiment, if the rolling pressure is too low, the positive electrode particles 21 will be too little embedded in the positive electrode current collector 10, or even not embedded at all, making it difficult to effectively increase the compaction density of the positive electrode current collector 10. If the rolling pressure is too high, too many positive electrode particles 21 will be embedded in the positive electrode current collector 10, resulting in poor processing performance of the positive electrode sheet 100 and making the positive electrode sheet 100 itself brittle, which is not conducive to subsequent winding and processing of the positive electrode sheet 100. In addition, if the rolling pressure is too high, the compaction density of the positive electrode sheet 100 is too high, making electrolyte infiltration difficult and resulting in reduced capacity. In this embodiment, by taking advantage of the plasticity and relatively low compressive strength of the positive electrode current collector 10, and the good sphericity, high hardness, and compressive strength of the positive electrode particles 21, the rolling pressure is increased, resulting in a positive electrode sheet 100 with a higher compaction density, higher area specific capacity, lower resistance, and greater peeling force, as well as better mechanical properties and processing performance.

[0118] Furthermore, the rolling pressure P is 100 tons ≤ P ≤ 120 tons, which can make the positive electrode sheet 100 have a higher compaction density while having better mechanical properties and processing properties.

[0119] The positive electrode plate 100 of the embodiment of the present application is further described below through specific examples.

[0120] Example 1 to Example 5

[0121] The positive electrode sheet 100 of this embodiment is prepared by the following steps:

[0122] (1) 1.9 kg of Na4Fe3(PO4)2(P2O7) powder, 50 g of conductive carbon black (Super P, positive electrode conductive agent), 50 g of polyvinylidene fluoride (PVDF, positive electrode binder) and 5 kg of N-methylpyrrolidone (NMP, solvent) were stirred into a uniform positive electrode slurry, and aluminum foil was provided as the positive electrode current collector 10;

[0123] (2) coating the positive electrode slurry on the upper and lower surfaces of the positive electrode current collector 10, with a coating thickness of 200 μm on each surface;

[0124] (3) drying the positive electrode current collector 10 coated with the positive electrode slurry in a vacuum oven at 105° C. for 24 hours to obtain a positive electrode current collector 10 having a positive electrode active layer 20; and

[0125] (4) The positive electrode current collector 10 having the positive electrode active layer 20 was rolled using a double-roller machine. The rolling pressure of each example is shown in Table 1 below.

[0126] After the positive electrode sheet 100 of Example 1 is cut, the scanning electron microscope image (SEM image) of the cut surface is as follows: Figure 4 As shown by Figure 4 It can be seen that the positive electrode particles 21 of the present application are partially embedded in the positive electrode current collector 10 .

[0127] Comparative Example 1

[0128] The difference between this comparative example and Example 1 is that the roller pressing pressure is 30 tons.

[0129] Comparative Example 2

[0130] The difference between this comparative example and Example 1 is that the roller pressing pressure is 200 tons.

[0131] Comparative Example 3

[0132] The difference between this comparative example and Example 1 is that the mass fraction of the positive electrode particles 21 in the positive electrode active layer 20 is 80%.

[0133] Comparative Example 4

[0134] The difference between this comparative example and Example 1 is that the mass fraction of the positive electrode particles 21 in the positive electrode active layer 20 is 99%.

[0135] Comparative Example 5

[0136] The difference between this comparative example and Example 1 is that the coating thickness of the positive electrode slurry is 50 μm.

[0137] Comparative Example 6

[0138] The difference between this comparative example and Example 1 is that the coating thickness of the positive electrode slurry is 400 μm.

[0139] Comparative Example 7

[0140] The difference between this comparative example and Example 1 is that the positive electrode particles 21 are non-spherical, and b>c·α / 180°.

[0141] Various performance tests were performed on the positive electrode sheets 100 of the embodiments and comparative examples, and the test results are shown in Tables 1 and 2 below.

[0142] (1) Test method for the compaction density of the positive electrode sheet 100: Measure the thickness and mass of a 12 mm aluminum foil disc (positive electrode current collector 10), then measure the thickness of the positive electrode sheet 100 made from the positive electrode active material of each embodiment and comparative example, cut the positive electrode sheet 100 into 12 mm discs and weigh the mass, thereby calculating the mass and volume of the positive electrode active material on the positive electrode sheet 100, and then calculate the compaction density of the positive electrode active material after making the positive electrode sheet 100.

[0143] (2) Test method for the mass specific capacity of 100% positive electrode sheet: Cut the positive electrode sheet 100 into discs with a diameter of 12 mm and weigh the mass, subtract the mass of the positive electrode current collector 10 to obtain the mass of the positive electrode active material; assemble the cut positive electrode sheet 100 discs into a button battery using a 2032 model button battery shell (wherein a 14 mm metal sodium sheet is used as the negative electrode, the electrolyte is 1M NaClO4 dissolved in ethylene carbonate / diethyl carbonate (abbreviated as EC / DEC), and the diaphragm is a glass fiber diaphragm); the test process is: let it stand for 10 hours, charge to 3.5V at a rate of 0.1C, let it stand for 10 minutes, and then discharge to 1.5V at a rate of 0.1C to obtain the mass specific capacity.

[0144] (3) Area specific capacity of 100 pieces of positive electrode sheet = mass specific capacity × mass of positive electrode active material ÷ 1.131.

[0145] (4) Peel strength test: Cut the positive electrode sheet 100 into strips 25 mm wide and longer than 20 cm. Attach 20 mm*100 mm 3M double-sided tape to the center of a steel plate, leaving one-third of the back end of the steel plate blank. Attach the cut positive electrode sheet 100, with both sides slightly wider than the 3M double-sided tape, parallel to the other side of the 3M double-sided tape. Manually peel the positive electrode sheet 100 from the bottom to the center, and then perform a tensile strength test on it using a tensile testing machine at a tensile speed of 50 mm / min. The peel strength value can be obtained after the test.

[0146] Table 1 Performance parameters of the positive electrode sheet 100 of each embodiment and comparative example

[0147]

[0148] Table 2 Performance parameters of the positive electrode sheet 100 of each embodiment and comparative example

[0149]

[0150] From the test results of Examples 1 to 5 in Tables 1 and 2, it can be seen that the positive electrode sheet 100 of the embodiment of the present application has a higher compaction density, a higher mass specific capacity and area specific capacity, and has both lower resistance and higher peeling force.

[0151] It can be seen from the test results of Example 1 and Comparative Example 1 that when the rolling pressure is too small, the compaction density of the positive electrode sheet 100 is greatly reduced, and the mass specific capacity and area specific capacity are also greatly reduced. In addition, the resistance of the positive electrode sheet 100 is greatly increased and the peeling force is reduced.

[0152] The test results of Example 1 and Comparative Example 2 show that when the rolling pressure is too high, the compaction density of the positive electrode sheet 100 increases, the resistance decreases, and the peel force increases. However, the mass-specific capacity and area-specific capacity decrease slightly. This is because the excessive rolling pressure increases the compaction density of the positive electrode sheet 100, making electrolyte infiltration difficult and resulting in reduced capacity. In addition, the positive electrode sheet 100 is prone to brittle fracture and material loss during winding, significantly reducing processing performance.

[0153] It can be seen from the test results of Example 1, Comparative Example 3 and Comparative Example 4 that when the mass fraction of the positive electrode particles 21 in the positive electrode active layer 20 is too low (Comparative Example 3), the compaction density and area specific capacity of the positive electrode sheet 100 will be reduced, and the resistance and peeling force of the positive electrode sheet 100 will be slightly increased; when the mass fraction of the positive electrode particles 21 in the positive electrode active layer 20 is too high (Comparative Example 4), although the compaction density of the positive electrode sheet 100 is slightly increased, the mass specific capacity and area specific capacity are both reduced, and the resistance of the positive electrode sheet 100 is greatly increased, and the peeling force is greatly reduced; in addition, it also makes the positive electrode sheet 100 easy to fall off, which is not conducive to the cycle stability of the positive electrode sheet 100.

[0154] From the test results of Example 1, Comparative Example 5 and Comparative Example 6, it can be seen that when the coating thickness of the positive electrode slurry is too thin (Comparative Example 5), the area specific capacity of the positive electrode sheet 100 is greatly reduced, and the resistance and peeling force are also reduced; when the coating thickness of the positive electrode slurry is too thick (Comparative Example 6), the mass specific capacity of the positive electrode sheet 100 is reduced and the area specific capacity is increased, but the positive electrode sheet 100 is easy to break and the material is easy to fall off during winding, and the resistance is greatly increased, and the peeling force is also reduced.

[0155] It can be seen from the test results of Example 1 and Comparative Example 7 that when the morphology of the positive electrode particles 21 is non-spherical, under the same other conditions, the compaction density of the positive electrode plate 100 is greatly reduced, and the area specific capacity is also greatly reduced. In addition, the positive electrode plate is prone to brittle segments and the mechanical strength is reduced.

[0156] Figure 5 3 is a schematic structural diagram of a battery 300 according to an embodiment of the present application. Figure 6 The battery 300 of one embodiment of the present application is Figure 5 Schematic diagram of the cross-sectional structure in the middle BB direction.

[0157] See Figure 5 and Figure 6 , an embodiment of the present application further provides a battery 300, which includes an electrolyte, the positive electrode plate 100 described in the embodiment of the present application, the positive electrode plate 100 is immersed in the electrolyte; a diaphragm 320, the diaphragm is located on one side of the positive electrode plate 100 and is immersed in the electrolyte, and a negative electrode plate 330, the negative electrode plate 330 is arranged on the side of the diaphragm 320 away from the positive electrode plate 100 and is immersed in the electrolyte.

[0158] The battery 300 in the embodiment of the present application may be, but is not limited to, a sodium ion battery 300.

[0159] Optionally, the electrolyte includes a solvent and an electrolyte salt.

[0160] Figure 7 Schematic diagram of the structure of the negative electrode plate 330 according to an embodiment of the present application.

[0161] See Figure 7 Optionally, the negative electrode sheet 330 includes a negative electrode current collector 331 and a negative electrode active layer 332. The negative electrode current collector 331 may be, but is not limited to, copper foil or copper sheet. Optionally, the negative electrode active layer 332 includes a negative electrode active material, a second conductive agent, a second binder, and a second thickener.

[0162] Optionally, the diaphragm 320 may be, but is not limited to, at least one of a polypropylene film (PP film for short), a polyethylene film (PE film for short), a ceramic diaphragm 320 , and the like.

[0163] Optionally, the battery 300 further includes a housing 340 and an end cap assembly 350. The housing 340 and the end cap assembly 350 enclose a closed receiving chamber (not shown) for accommodating the electrolyte, the positive electrode sheet 100, the separator 320, and the negative electrode sheet 330. It is understood that the end cap assembly 350 electrically connects the positive electrode sheet 100 and the negative electrode sheet 330, respectively, and leads the positive electrode sheet 100 and the negative electrode sheet 330 out for electrical connection to external devices or other batteries 300.

[0164] Figure 8 4 is a schematic structural diagram of an energy storage device 400 according to an embodiment of the present application.

[0165] See Figure 8 The embodiment of the present application further provides an energy storage device 400 , which includes a box 410 and the battery 300 described in the embodiment of the present application, wherein the multiple batteries 300 are accommodated in the box 410 .

[0166] The energy storage device 400 of the present application can be applied to, but is not limited to, energy storage on the power generation side, energy storage on the grid side, and energy storage on the power consumption side.

[0167] The term "plurality" means greater than or equal to two.

[0168] It can be understood that the multiple batteries 300 of the energy storage device 400 can be connected in parallel with each other; or in series with each other; or partially in parallel and partially in series (in other words, mixed connection). This application does not specifically limit the connection method of the multiple batteries 300 of the same energy storage device 400.

[0169] It is understood that the housing 410 has a receiving cavity (not shown) in which multiple batteries 300 are received. In some embodiments, each receiving cavity receives one battery 300. In other embodiments, each receiving cavity receives multiple batteries 300.

[0170] Optionally, the energy storage device 400 may include, but is not limited to, a battery module, a battery pack, a battery system, and the like. The energy storage device 400 provided in the embodiments of this application may be, but is not limited to, the products listed above, or may be implemented in other forms. The embodiments of this application do not impose strict limitations on the application of the energy storage device 400. The embodiments of this application illustrate the energy storage device 400 as a multi-core battery 300, and this should not be construed as limiting the energy storage device 400 in the embodiments of this application.

[0171] References to "embodiments" and "implementation methods" in this application mean that the specific features, structures or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrases in various locations in the specification does not necessarily refer to the same embodiment, nor are they independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood explicitly and implicitly by those skilled in the art that the embodiments described in this application can be combined with other embodiments. In addition, it should be understood that the features, structures or characteristics described in the various embodiments of this application can be arbitrarily combined to form another embodiment that does not deviate from the spirit and scope of the technical solution of this application, unless there is a contradiction between them.

[0172] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the above preferred implementation modes, ordinary technicians in this field should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A positive electrode plate, characterized in that: The positive electrode plate comprises: a positive electrode current collector having a predetermined surface; and A positive electrode active layer, the positive electrode active layer being disposed on the predetermined surface of the positive electrode current collector, the positive electrode active layer comprising positive electrode particles, the positive electrode particles being partially embedded in the positive electrode current collector, the positive electrode particles being sodium iron pyrophosphate, and the positive electrode particles being spherical or spherical; The positive electrode sheet satisfies the relationship: b≤c•α / 180°; Wherein, b is the depth of the positive electrode particles embedded in the positive electrode current collector, α is the angle between the tangents of the two points on the intersection line of the positive electrode particles and the preset surface that are farthest apart, and c is the distance between the intersection point of the tangents of the two points on the intersection line of the positive electrode particles and the preset surface and the preset surface.

2. The positive electrode sheet according to claim 1, characterized in that: The positive electrode sheet also satisfies the relationship: b / a≤1 / 3, where a is the thickness of the positive electrode current collector.

3. The positive electrode sheet according to claim 1, characterized in that: The depth b of the positive electrode particles embedded in the positive electrode current collector is in the range of b≤6 μm.

4. The positive electrode sheet according to claim 1, characterized in that: The range of the angle α between the tangent lines of the two points on the intersection line between the positive electrode particles and the preset surface that are farthest apart is: 45°≤α≤120°.

5. The positive electrode sheet according to claim 1, characterized in that: The range of the distance c between the intersection point of the tangent lines of the two points on the intersection line between the positive electrode particles and the preset surface and the preset surface is: c≤18 μm.

6. The positive electrode sheet according to claim 1, characterized in that: The average sphericity of the positive electrode particles is greater than or equal to 0.

9.

7. The positive electrode sheet according to claim 1, characterized in that: The molar ratio Na / Fe of the sodium element to the iron element in the positive electrode particles is in the range of 1.34≤Na / Fe≤1.

5.

8. The positive electrode sheet according to claim 1, characterized in that: The molar ratio of iron to phosphorus in the positive electrode particles is Fe / P in a range of 0.70≤Fe / P≤0.

745.

9. A method for preparing a positive electrode sheet, characterized in that: include: Providing a positive electrode current collector and a positive electrode slurry, wherein the positive electrode current collector has a predetermined surface, the positive electrode slurry comprises positive electrode particles, the positive electrode particles are sodium ferric pyrophosphate, and the positive electrode particles are spherical or spherical; coating the positive electrode slurry on the predetermined surface of the positive electrode current collector, and removing the solvent of the positive electrode slurry to form a positive electrode active layer; and Roll-pressing the positive electrode current collector having the positive electrode active layer so that the positive electrode particles are partially embedded in the positive electrode current collector to obtain a positive electrode sheet; Wherein, the positive electrode sheet satisfies the relationship: b<c•α / 180°; Wherein, b is the depth of the positive electrode particles embedded in the positive electrode current collector, α is the angle between the tangents of the two points on the intersection line of the positive electrode particles and the preset surface that are farthest apart, and c is the distance between the intersection point of the tangents of the two points on the intersection line of the positive electrode particles and the preset surface and the preset surface.

10. The method for preparing a positive electrode sheet according to claim 9, wherein: The positive electrode current collector having the positive electrode active layer is rolled to partially embed the positive electrode particles into the positive electrode current collector to obtain a positive electrode sheet, comprising: The positive electrode current collector having the positive electrode active layer is roll-pressed with a rolling pressure P of 70 tons ≤ P ≤ 150 tons, so that the positive electrode particles are partially embedded in the positive electrode current collector to obtain a positive electrode sheet.

11. A battery, characterized in that: include: electrolyte; A positive electrode sheet, wherein the positive electrode sheet is the positive electrode sheet according to any one of claims 1 to 8 or the positive electrode sheet prepared by the preparation method of the positive electrode sheet according to claim 9 or 10; a diaphragm located on one side of the positive electrode plate, and A negative electrode plate is provided on a side of the diaphragm away from the positive electrode plate.

12. An energy storage device, characterized in that: include: Box; as well as A plurality of batteries according to claim 11, wherein the plurality of batteries are housed in the casing.

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