Positive electrode sheet, sodium battery and energy storage device

Abstract

This application provides a positive electrode sheet, a sodium battery, and an energy storage device. The positive electrode sheet of this application includes: a positive current collector; and a positive active layer disposed on the surface of the positive current collector. The positive active layer includes sodium iron pyrophosphate particles and a conductive agent, wherein the powder resistivity PR of the sodium iron pyrophosphate particles is in the range of 70 Ω·cm ≤ PR ≤ 800 Ω·cm.

Description

Technical Field

[0001] This application relates to the field of energy storage, specifically to a positive electrode, a sodium battery, and an energy storage device. Background Technology

[0002] Sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7), with its three-dimensional sodium ion diffusion channels and sodium superionic conductor structure, exhibits high voltage plateau, high capacity, excellent rate capability, and excellent cycle stability, making it a promising cathode material for large-scale production in sodium batteries. However, Na4Fe3(PO4)2P2O7 powder has high resistivity and poor conductivity, resulting in excessive internal resistance and reduced cycle life in sodium batteries. Related cathode technologies aim to reduce film resistivity by increasing the content of conductive carbon black and carbon nanotubes in the active layer. However, carbon nanotubes are very expensive, significantly increasing the cost of the cathode. Furthermore, increasing the content of conductive carbon black and carbon nanotubes reduces the capacity of the cathode. Summary of the Invention

[0003] This application provides a positive electrode sheet that has low film resistivity and high capacity without using a large amount of conductive agent.

[0004] In a first aspect, embodiments of this application provide a positive electrode sheet, the positive electrode sheet comprising:

[0005] Positive current collector; and

[0006] A positive electrode active layer is disposed on the surface of the positive electrode current collector. The positive electrode active layer includes sodium iron pyrophosphate particles and a conductive agent. The powder resistivity PR of the sodium iron pyrophosphate particles is in the range of 70 Ω·cm ≤ PR ≤ 800 Ω·cm.

[0007] Furthermore, the resistivity DR of the positive electrode film is in the range of 0.05Ω·m≤DR≤0.4Ω·m.

[0008] Furthermore, the conductive agent includes carbon nanotubes, and the mass fraction M1 of the carbon nanotubes in the positive electrode active layer is in the range of 0.2% ≤ M1 ≤ 1%.

[0009] Furthermore, the mass fraction M1 of the carbon nanotubes in the positive electrode active layer is in the range of 0.2% ≤ M1 ≤ 0.6%.

[0010] Furthermore, the conductive agent also includes conductive carbon black, and the mass fraction M2 of the conductive carbon black in the positive electrode active layer is in the range of 0.8% ≤ M2 ≤ 2.4%.

[0011] Furthermore, the mass fraction M2 of the conductive carbon black in the positive electrode active layer is in the range of 1.2% ≤ M2 ≤ 1.8%.

[0012] Furthermore, the positive electrode plate satisfies the following relationship:

[0013]

[0014] Wherein, K is a constant, DR is the film resistivity of the positive electrode sheet in Ω·m; PR is the powder resistivity of the sodium iron pyrophosphate particles in Ω·m; M1 is the mass fraction of the carbon nanotubes in the positive electrode active layer in wt%; and M2 is the mass fraction of the conductive carbon black in the positive electrode active layer in wt%.

[0015] Furthermore, the numerical range of K is: 5 × 10 -4 ≤K≤3×10 -3 .

[0016] Furthermore, the sodium iron pyrophosphate particles comprise a sodium iron pyrophosphate core and a carbon layer, wherein the carbon layer is wrapped around the surface of the sodium iron pyrophosphate core within the sodium iron pyrophosphate particles, and the mass fraction w of the carbon layer is in the range of 2.6% ≤ w ≤ 3.2%.

[0017] Secondly, embodiments of this application provide a sodium battery, which includes: an electrolyte, a positive electrode, a separator, and a negative electrode as described in embodiments of this application.

[0018] Thirdly, embodiments of this application provide an energy storage device, which includes:

[0019] include:

[0020] Box; and

[0021] The sodium battery described in this application embodiment is housed within the casing.

[0022] The positive electrode sheet of this application embodiment includes a positive current collector and a positive active layer. The positive active layer is disposed on the surface of the positive current collector and includes sodium iron pyrophosphate particles and a conductive agent. The powder resistivity (PR) of the sodium iron pyrophosphate particles is in the range of 70 Ω·cm ≤ PR ≤ 800 Ω·cm. The sodium iron pyrophosphate particles of this application embodiment have a low powder resistivity, thus allowing the positive electrode sheet to have a low film resistivity without using a large amount of conductive agent, reducing the amount of conductive agent used in the positive active layer, thereby reducing the cost of the positive electrode sheet. Furthermore, due to the reduced content of conductive agent in the positive active layer, more sodium iron pyrophosphate particles can be contained in the same volume of the positive active layer, resulting in a higher volumetric capacity. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet according to an embodiment of this application.

[0025] Figure 2 This is a schematic diagram of the structure of sodium iron pyrophosphate particles according to an embodiment of this application.

[0026] Figure 3 This is a schematic flowchart of a method for preparing sodium iron pyrophosphate particles according to an embodiment of this application.

[0027] Figure 4 This is a schematic diagram of the structure of a sodium battery according to an embodiment of this application.

[0028] Figure 5 This application describes a sodium battery according to an embodiment of the present application. Figure 4 A schematic diagram of the cross-sectional structure along the AA direction.

[0029] Figure 6 This is a schematic diagram of the structure of the negative electrode sheet according to an embodiment of this application.

[0030] Figure 7 This is a schematic diagram of the structure of an energy storage device according to an embodiment of this application.

[0031] Figure 8 This is a structural block diagram of an energy storage system according to an embodiment of this application.

[0032] Figure 9 This is an application scenario diagram of an energy storage system according to an embodiment of this application.

[0033] Explanation of reference numerals in the attached figures:

[0034] 100-Positive electrode sheet, 10-Positive current collector, 20-Positive active layer, 21-Sodium iron pyrophosphate particles, 211-Sodium iron pyrophosphate core, 212-Carbon layer, 300-Sodium battery, 320-Separator, 330-Negative electrode sheet, 331-Negative current collector, 332-Negative active layer, 340-Shell, 350-End cap assembly, 400-Energy storage device, 410-Box, 500-Energy storage system, 510-Power conversion device. Detailed Implementation

[0035] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0036] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0037] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0038] It should be noted that, for ease of explanation, the same reference numerals denote the same components in the embodiments of this application, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0039] Currently, the generation of green electricity generally relies on solar, wind, and hydropower. However, wind and solar power are generally characterized by strong intermittency and large fluctuations, which can cause grid instability, insufficient power during peak demand periods, and excessive power during off-peak periods. Unstable voltage can also damage the power grid. Therefore, insufficient electricity demand or insufficient grid capacity may lead to the problem of "wind and solar curtailment." Solving these problems requires energy storage. This involves converting electrical energy into other forms of energy through physical or chemical means and storing it. When needed, this energy can be converted back into electrical energy and released. Simply put, energy storage is like a large "power bank," storing electrical energy when solar and wind power are abundant and releasing the stored electricity when needed.

[0040] Batteries are the smallest energy storage unit in energy storage devices and systems, and their performance directly affects the performance and application of these devices and systems. Batteries include lithium batteries and sodium batteries.

[0041] Sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7), with its three-dimensional sodium ion diffusion channels and sodium superionic conductor structure, exhibits high voltage plateau, high capacity, excellent rate capability, and excellent cycle stability, making it a promising cathode material for large-scale production in sodium batteries. However, Na4Fe3(PO4)2P2O7 powder has high resistivity and poor conductivity, resulting in excessive internal resistance and reduced cycle life in sodium batteries. Related cathode technologies have attempted to reduce film resistivity by increasing the content of conductive carbon black and carbon nanotubes in the active layer. However, the high cost of carbon nanotubes significantly increases the cost of the cathode, and the increased content of conductive carbon black and carbon nanotubes reduces the cathode's capacity.

[0042] Please see Figure 1 This application provides a positive electrode 100, which includes a positive current collector 10 and a positive active layer 20. The positive active layer 20 is disposed on the surface of the positive current collector 10. The positive active layer 20 includes sodium iron pyrophosphate particles 21 and a conductive agent. The powder resistivity PR of the sodium iron pyrophosphate particles 21 is in the range of 70Ω·cm≤PR≤800Ω·cm.

[0043] The positive electrode 100 of this application embodiment can be applied to a sodium battery. Optionally, the sodium battery of this application embodiment can be, but is not limited to, at least one of sodium-ion batteries, sodium metal batteries, and lithium-sodium hybrid batteries.

[0044] It should be noted that sodium iron pyrophosphate particles 21 are used as the positive electrode active material of the positive electrode active layer 20.

[0045] It should be noted that the positive electrode active layer 20 can be disposed on one surface of the positive electrode current collector 10, or on two opposite surfaces of the positive electrode current collector 10. In the following embodiments and accompanying drawings of this application, the positive electrode sheet 100 is illustrated by way of having two positive electrode active layers 20 (i.e., the positive electrode current collector 10 has positive electrode active layers 20 on both opposite surfaces), and should not be construed as a limitation on the positive electrode sheet 100 of the embodiments of this application.

[0046] It should be noted that the powder resistivity PR of sodium iron pyrophosphate granules 21 in this embodiment of the application is measured using the two-probe method. Specifically, 2g to 3g of sodium iron pyrophosphate granules 21 powder is added to the mold of a powder resistivity instrument with a diameter of 13mm, and after being pressurized to 200MPa, the powder resistivity value is measured.

[0047] Specifically, the powder resistivity PR of the sodium iron pyrophosphate particles 21 can be, but is not limited to, 70 Ω·cm, 80 Ω·cm, 90 Ω·cm, 100 Ω·cm, 120 Ω·cm, 140 Ω·cm, 160 Ω·cm, 180 Ω·cm, 200 Ω·cm, 220 Ω·cm, 240 Ω·cm, 260 Ω·cm, 280 Ω·cm, 300 Ω·cm, 320 Ω·cm, 340 Ω·cm, 360 Ω·cm, 380 Ω·cm, etc. The resistivity values ​​are 400 Ω·cm, 420 Ω·cm, 440 Ω·cm, 460 Ω·cm, 480 Ω·cm, 500 Ω·cm, 520 Ω·cm, 540 Ω·cm, 560 Ω·cm, 580 Ω·cm, 600 Ω·cm, 620 Ω·cm, 640 Ω·cm, 660 Ω·cm, 680 Ω·cm, 700 Ω·cm, 720 Ω·cm, 740 Ω·cm, 760 Ω·cm, 780 Ω·cm, 800 Ω·cm, etc. In this embodiment, the powder resistivity PR of the sodium iron pyrophosphate particles 21 is too low. Therefore, a higher sintering temperature is required during the preparation of the sodium iron pyrophosphate particles 21 to achieve a lower powder resistivity. However, an excessively high sintering temperature will increase the proportion of sodium iron pyrophosphate decomposition, increase the generation of sodium iron phosphate impurities and sodium iron pyrophosphate impurities, and reduce the specific capacity of the sodium iron pyrophosphate particles 21. The powder resistivity PR of the sodium iron pyrophosphate particles 21 is too high. When the positive electrode 100 is used in a sodium battery, it results in excessive internal resistance of the sodium battery, reducing the cycle life of the sodium battery. Alternatively, more conductive agents such as carbon nanotubes and conductive carbon black are needed to make the positive electrode 100 have a lower film resistivity, thereby increasing the manufacturing cost of the positive electrode 100 and reducing the volumetric capacity of the sodium battery.

[0048] The positive electrode 100 of this embodiment includes a positive current collector 10 and a positive active layer 20. The positive active layer 20 is disposed on the surface of the positive current collector 10. The positive active layer 20 includes sodium iron pyrophosphate particles 21 and a conductive agent. The powder resistivity PR of the sodium iron pyrophosphate particles 21 is in the range of 70 Ω·cm ≤ PR ≤ 800 Ω·cm. The sodium iron pyrophosphate particles 21 of this embodiment have a low powder resistivity, so that the positive electrode 100 can have a low film resistivity without using a large amount of conductive agent, reducing the amount of conductive agent used in the positive active layer 20, thereby reducing the cost of the positive electrode 100. In addition, since the content of conductive agent in the positive active layer 20 is reduced, the positive active layer 20 can contain more sodium iron pyrophosphate particles 21 in the same volume, thereby giving the positive active layer 20 a higher volumetric capacity.

[0049] In some embodiments, the range of the film resistivity DR (i.e., the resistivity of the positive electrode active layer 20) of the positive electrode 100 is: 0.05Ω·m≤DR≤0.4Ω·m.

[0050] Specifically, the film resistivity DR of the positive electrode 100 can be, but is not limited to, 0.05Ω·m, 0.06Ω·m, 0.08Ω·m, 0.1Ω·m, 0.12Ω·m, 0.14Ω·m, 0.16Ω·m, 0.18Ω·m, 0.2Ω·m, 0.22Ω·m, 0.24Ω·m, 0.26Ω·m, 0.28Ω·m, 0.3Ω·m, 0.32Ω·m, 0.34Ω·m, 0.36Ω·m, 0.38Ω·m, 0.4Ω·m, etc.

[0051] Measurement of the film resistivity DR of the positive electrode 100: The positive electrode 100 coated with the positive active layer 20 on both sides is cut into 5 squares with a size of 5cm×5cm. The thickness of the positive electrode 100 is measured with a micrometer (the average value of the five measurements is taken). Then, the film resistance of each small positive electrode 100 square is measured with a resistance meter (the thickness value is entered and the measurement pressure is adjusted to be maintained at 0.4 tons). Finally, the average value of the film resistivity measurements of the five square positive electrode 100 is taken.

[0052] In this embodiment, if the film resistivity DR of the positive electrode 100 is too low, the sintering temperature during the preparation of sodium iron pyrophosphate particles 21 needs to be increased. This will increase the generation of sodium iron phosphate impurities and sodium iron pyrophosphate impurities, reducing the specific capacity of the sodium iron pyrophosphate particles 21 and the volumetric specific capacity of the positive electrode active layer 20. Alternatively, more conductive agent needs to be added to the positive electrode active layer 20, which will increase the preparation cost of the positive electrode 100 and reduce the volumetric specific capacity of the positive electrode active layer 20. If the film resistivity DR of the positive electrode 100 is too high, when the positive electrode 100 is applied to a sodium battery, it will increase the internal resistance of the sodium battery, affecting the specific capacity of the sodium battery and reducing the kinetic and cycle performance of the sodium battery.

[0053] In some embodiments, the conductive agent includes carbon nanotubes (CNTs), and the mass fraction M1 of the carbon nanotubes in the positive electrode active layer 20 is in the range of 0.2% ≤ M1 ≤ 1%.

[0054] Specifically, the mass fraction M1 of the carbon nanotubes in the positive electrode active layer 20 can be, but is not limited to, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0055] In this embodiment, if the mass fraction M1 of carbon nanotubes in the positive electrode active layer 20 is too low, the film resistivity of the positive electrode 100 will increase, resulting in excessive internal resistance of the sodium battery using the positive electrode 100, which will reduce the kinetic performance and cycle performance of the sodium battery. If the mass fraction M1 of carbon nanotubes in the positive electrode active layer 20 is too high, the manufacturing cost of the positive electrode 100 will increase, and the compaction density and specific capacity of the positive electrode 100 will decrease, which will reduce the cycle capacity retention rate of the sodium battery using the positive electrode 100.

[0056] Furthermore, the mass fraction M1 of the carbon nanotubes in the positive electrode active layer 20 is in the range of 0.2% ≤ M1 ≤ 0.6%. Specifically, the mass fraction M1 of the carbon nanotubes in the positive electrode active layer 20 can be, but is not limited to, 0.2%, 0.35%, 0.4%, 0.45%, 0.5%, 0.6%, etc. This allows the positive electrode 100 to have a higher specific capacity, lower film resistivity, and higher compaction density, resulting in sodium batteries using the positive electrode 100 having lower internal resistance, higher kinetic performance, and better cycle performance.

[0057] Furthermore, the mass fraction M1 of the carbon nanotubes in the positive electrode active layer 20 is in the range of 0.3% ≤ M1 ≤ 0.5%. Specifically, the mass fraction M1 of the carbon nanotubes in the positive electrode active layer 20 can be, but is not limited to, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, etc. This allows the positive electrode 100 to have a higher specific capacity, lower film resistivity, and higher compaction density, resulting in sodium batteries using the positive electrode 100 having lower internal resistance, higher kinetic performance, and better cycle performance.

[0058] In some embodiments, the conductive agent further includes conductive carbon black (SP), and the mass fraction M2 of the conductive carbon black in the positive electrode active layer 20 is in the range of 0.8% ≤ M2 ≤ 2.4%.

[0059] Specifically, the mass fraction M2 of the conductive carbon black in the positive electrode active layer 20 can be, but is not limited to, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, etc.

[0060] In this embodiment, if the mass fraction M2 of the conductive carbon black in the positive electrode active layer 20 is too low, the film resistivity of the positive electrode 100 will increase, resulting in excessive internal resistance of the sodium battery using the positive electrode 100, which will reduce the kinetic performance and cycle performance of the sodium battery. If the mass fraction M2 of the conductive carbon black in the positive electrode active layer 20 is too high, the manufacturing cost of the positive electrode 100 will increase, and the compaction density and specific capacity of the positive electrode 100 will decrease, which will reduce the cycle capacity retention rate of the sodium battery using the positive electrode 100.

[0061] Furthermore, the mass fraction M2 of the conductive carbon black in the positive electrode active layer 20 is in the range of 1.0% ≤ M2 ≤ 2.0%. This allows the positive electrode 100 to have a higher specific capacity, lower film resistivity, and higher compaction density, resulting in sodium batteries using the positive electrode 100 having lower internal resistance, higher kinetic performance, and better cycle performance.

[0062] Furthermore, the mass fraction M2 of the conductive carbon black in the positive electrode active layer 20 is in the range of 1.2% ≤ M2 ≤ 1.8%. This allows the positive electrode 100 to have a higher specific capacity, lower film resistivity, and higher compaction density, resulting in sodium batteries using the positive electrode 100 having lower internal resistance, higher kinetic performance, and better cycle performance.

[0063] It should be noted that the carbon nanotubes and conductive carbon black in the positive electrode active layer of this application can be detected and characterized by scanning electron microscopy (SEM) and quantitatively analyzed by Raman spectroscopy. Specifically, the presence of CNTs (two-dimensional fine line morphology) in the positive electrode active layer can be directly observed by SEM; the mass fraction M1 of carbon nanotubes and the mass fraction M2 of conductive carbon black in the positive electrode active layer are detected by Raman spectroscopy; in the Raman spectrum, carbon nanotubes have sharp G peaks and 2D peaks, while conductive carbon black has D peaks and G peaks with nearly equal and relatively broad peaks, and the signal peaks of the Raman spectrum are positively correlated with the content of the corresponding substances in the positive electrode active layer. The Raman spectrum of the positive electrode active layer is then quantitatively and parameterized: the 1520 cm⁻¹ spectrum is used for further analysis. -1 ~1640cm -1 The highest peak intensity within the range is defined as P. G 1290cm -1 ~1410cm -1 The highest peak intensity within the range is defined as P. D Therefore, the mass fraction of SP in the positive electrode active layer, M2, is 7 × 10⁻⁶. -5 ×P D The mass fraction of SP in the positive electrode active layer is M1 = 5 × 10⁻⁶ -6 ×P G -8.4×10 -6 ×PD .

[0064] In some embodiments, the positive electrode 100 satisfies equation (1):

[0065]

[0066] Wherein, K is a constant, DR is the film resistivity of the positive electrode 100 in Ω·m; PR is the powder resistivity of the sodium iron pyrophosphate particles 21 in Ω·m; M1 is the mass fraction of the carbon nanotubes in the positive electrode active layer 20 in wt%; and M2 is the mass fraction of the conductive carbon black in the positive electrode active layer 20 in wt%.

[0067] It should be noted that each parameter in relation (1) is a numerical value of the corresponding parameter, and none of the parameters in the relation are in units.

[0068] It should be noted that carbon nanotubes are one-dimensional conductive agents, while conductive carbon black is a zero-dimensional conductive agent. Therefore, the improvement of the film resistivity of the positive electrode 100 by carbon nanotubes is greater than that of the positive electrode 100 by conductive carbon black. Thus, in equation (1), DR is positively correlated with the -2 power of M1 and positively correlated with the -1 power of M2. This can better reflect the influence of carbon nanotubes and conductive carbon black on the film resistivity of the positive electrode 100, so that the theoretical calculation can better fit the experiment, thereby better guiding the experimental design through theoretical calculation and shortening the experimental time.

[0069] As can be seen from the above relationship (1), when the mass fraction M1 of the carbon nanotubes in the positive electrode active layer 20 and the mass fraction M2 of the conductive carbon black in the positive electrode active layer 20 remain unchanged, the film resistivity DR of the positive electrode 100 is positively correlated with the powder resistivity PR of the sodium iron pyrophosphate particles 21. When the powder resistivity PR of the sodium iron pyrophosphate particles 21 decreases, the film resistivity DR of the positive electrode 100 also decreases. Therefore, by preparing sodium iron pyrophosphate particles 21 with lower powder resistivity, the film resistivity of the positive electrode 100 can be significantly reduced.

[0070] As can be seen from the above relationship (1), when the mass fraction M2 of the conductive carbon black in the positive electrode active layer 20 remains constant, and the mass fraction M1 of the carbon nanotubes in the positive electrode active layer 20 decreases, the film resistivity DR of the positive electrode 100 increases. Furthermore, the greater the powder resistivity PR of the sodium iron pyrophosphate particles 21, the faster the increase in the film resistivity DR of the positive electrode 100. Similarly, when the mass fraction M2 of the conductive carbon black in the positive electrode active layer 20 remains constant, and the mass fraction M1 of the carbon nanotubes in the positive electrode active layer 20 increases, the film resistivity DR of the positive electrode 100 decreases. Furthermore, the greater the powder resistivity PR of the sodium iron pyrophosphate particles 21, the faster the increase in the film resistivity DR of the positive electrode 100. This indicates that at this point, the powder resistivity PR of sodium iron pyrophosphate particles 21 has a greater impact on the film resistivity DR of the positive electrode 100. Reducing the powder resistivity PR of sodium iron pyrophosphate particles 21 can reduce the film resistivity DR of the positive electrode 100 to a greater extent.

[0071] As can be seen from the above relationship (1), when the film resistivity DR of the same positive electrode 100 is maintained, reducing the powder resistivity PR of sodium iron pyrophosphate particles 21 can reduce the mass fraction M1 of carbon nanotubes in the positive electrode active layer 20, thereby reducing the preparation cost of the positive electrode 100.

[0072] When the mass fraction M1 of carbon nanotubes and the mass fraction M2 of conductive carbon black in the positive electrode active layer 20 are both too high, the compaction density of the positive electrode 100 and the volumetric specific capacity of the positive electrode active layer 20 will be reduced, thereby reducing the energy density of the sodium battery using the positive electrode 100. In addition, if the mass fractions of carbon nanotubes and conductive carbon black in the positive electrode active layer 20 are too high, the proportion of positive electrode active material in the positive electrode active layer 20 will be reduced, resulting in a loss of specific capacity of the positive electrode active layer 20.

[0073] It should be noted that the conductivity of the positive electrode 100 will affect the specific capacity of the positive electrode active material, especially significantly affecting the specific capacity of the positive electrode active material at low temperatures.

[0074] In this embodiment, when the measured value of the film resistivity of the positive electrode 100 is significantly higher than the calculated value of formula (1), it indicates that under a certain electrode processing state, the carbon nanotubes and conductive carbon black failed to form an effective conductive network, wasting the role of the conductive agent to a certain extent; when the measured value of the film resistivity of the positive electrode 100 is significantly lower than the calculated value of formula (1), the film resistivity of the positive electrode 100 is too low, indicating that there may be agglomeration of the conductive agent in the thickness direction of the positive electrode 100, and a separate conductive path belonging to the conductive agent, thus exhibiting an excessively low film resistivity of the positive electrode 100. However, this will lose the contribution of the conductive agent to the conductivity of the positive electrode active material, resulting in a deterioration in the capacity performance, a reduction in rate performance, and a deterioration in low-temperature performance of the sodium battery. Therefore, when the positive electrode 100 satisfies the relationship... When the carbon nanotubes and conductive carbon black contribute optimally to the conductivity of the positive electrode active material, the sodium battery using the positive electrode 100 exhibits higher kinetic performance, higher rate performance, and higher low-temperature performance. This relationship can be used to effectively measure the quality of the positive electrode 100, thereby providing better theoretical guidance for experiments, shortening experimental time, and reducing experimental costs.

[0075] In some embodiments, the numerical range of K is: 5 × 10 -4 ≤K≤3×10 -3 .

[0076] Specifically, the value of K can be, but is not limited to, 5 × 10. -4 6×10 -4 7×10 -4 8×10 -4 9×10 -4 1.0×10 -3 1.2×10 -3 1.4×10 -3 1.6×10 -3 1.8×10 -3 2.0×10 -3 2.2×10 -3 2.4×10 -3 2.6×10 -3 2.8×10 -3 3×10 -3 wait.

[0077] In this embodiment, the value of K is related to the processing technology of the positive electrode 100. When the value of K is too small, the positive electrode 100 requires greater pressure during rolling. Greater pressure increases the direct contact between the positive active material and the conductive agent in the positive active layer 20, thereby reducing the film resistivity of the positive electrode 100. However, excessive rolling pressure increases the hardness of the positive electrode 100, affecting its winding. Furthermore, excessive rolling pressure increases the elongation of the positive electrode 100, reducing its strength and making it prone to localized breakage during winding and bending. When the value of K is too large, the positive active layer 20 of the positive electrode 100 needs to be coated with a greater thickness. An excessively thick positive active layer 20, under the same rolling pressure, results in poor contact between the positive active material and the conductive agent, leading to a decrease in film resistivity of the positive electrode 100. Therefore, when the value range of K is: 5 × 10 -4 ≤K≤3×10 -3 This allows the positive electrode 100 to have both low film resistivity and good mechanical strength, making it less prone to breakage during winding and providing better winding performance.

[0078] Please see Figure 2 In some embodiments, the sodium iron pyrophosphate granules 21 include a sodium iron pyrophosphate core 211 and a carbon layer 212, wherein the carbon layer 212 is wrapped around the surface of the sodium iron pyrophosphate core 211, and the mass fraction w of the carbon layer 212 in the sodium iron pyrophosphate granules 21 ranges from 2.6% to 3.2%.

[0079] Understandably, the sodium iron pyrophosphate particles 21 have a core-shell structure. That is, sodium iron pyrophosphate forms the core, and the carbon layer 212 forms the outer shell. In other words, the positive electrode active material has a core-shell structure.

[0080] Specifically, the mass fraction w of the carbon layer 212 in the sodium iron pyrophosphate particles 21 can be, but is not limited to, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, etc. If the mass fraction w of the carbon layer 212 in the sodium iron pyrophosphate particles 21 is too low, the inhibition effect on the formation of sodium iron phosphate impurities and sodium iron pyrophosphate impurities will be poor during the synthesis of sodium iron pyrophosphate particles 21, thus reducing the specific capacity of sodium iron pyrophosphate particles 21. In addition, if the mass fraction w of the carbon layer 212 in the sodium iron pyrophosphate particles 21 is too low, the electron transport rate of sodium iron pyrophosphate particles 21 will be reduced, the powder resistivity of sodium iron pyrophosphate particles 21 will be increased, and the film resistivity of the positive electrode 100 will be increased. If the mass fraction w of carbon layer 212 in the sodium iron pyrophosphate particles 21 is too high, the inhibition effect on the formation of sodium iron phosphate impurities and sodium iron pyrophosphate impurities will not be improved during the synthesis of sodium iron phosphate particles 21. However, the excessive content of carbon layer 212 reduces the specific capacity, powder compaction density and electrode layer compaction density of sodium iron pyrophosphate particles 21.

[0081] Optionally, the positive current collector 10 can be, but is not limited to, aluminum foil or aluminum sheet.

[0082] Alternatively, the conductive agent may also include at least one of acetylene black, carbon fiber, graphene, etc.

[0083] Optionally, the positive electrode active layer 20 may also include a positive electrode binder.

[0084] Optionally, the positive electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), and polyhexafluoropropylene.

[0085] Optionally, the compaction density (referred to as electrode compaction density) of the positive electrode active layer 20 of the positive electrode 100 is in the range of 2.25 g / cm³. 3 Up to 2.45 g / cm 3 Specifically, it can be, but is not limited to, 2.25 g / cm³. 3 2.30g / cm 3 2.35g / cm 3 2.4g / cm 32.45g / cm 3 wait.

[0086] In the embodiments of this application, when the numerical range a to b is involved, unless otherwise specified, the numerical value can be any value between a and b, including the endpoint value a and the endpoint value b.

[0087] The method for testing the compaction density of the positive electrode active layer 20 in this application is as follows: the thickness of the aluminum foil and the mass of the aluminum foil cut into 12mm round pieces are measured in advance. Then, the thickness of the positive electrode sheet 100 made of the positive electrode active material is measured, and the positive electrode sheet 100 is cut into 12mm round pieces and weighed. The mass and volume of the positive electrode active material on the positive electrode sheet 100 are calculated, and then the compaction density of the positive electrode active layer 20 on the positive electrode sheet 100 is calculated.

[0088] The sodium ferric pyrophosphate granules 21 of this application embodiment can be prepared by the methods described in the following embodiments of this application. In addition, they can also be prepared by other methods. The preparation methods of this application embodiment are merely one or more preparation methods of the sodium ferric pyrophosphate granules 21 of this application and should not be construed as limiting the sodium ferric pyrophosphate granules 21 provided in the embodiments of this application.

[0089] Please see Figure 3 This application provides a method for preparing sodium iron pyrophosphate granules 21, which includes:

[0090] S201, providing raw material components, said raw material components including sodium source, phosphorus source, iron source and carbon source;

[0091] Optionally, the sodium source may include, but is not limited to, at least one of these compounds, such as sodium dihydrogen phosphate, sodium pyrophosphate, sodium carbonate, sodium acetate, and compounds containing water of crystallization.

[0092] Optionally, the phosphorus source may include, but is not limited to, at least one of these compounds, including sodium dihydrogen phosphate, sodium pyrophosphate, ammonium dihydrogen phosphate, and compounds containing water of crystallization.

[0093] Optionally, the iron source may include, but is not limited to, at least one of these compounds, including ferrous oxalate, ferric nitrate, ferrous sulfate, and compounds containing water of crystallization. For example, ferrous oxalate dihydrate.

[0094] Optionally, the carbon source is at least one of glucose, sucrose, starch, polyethylene glycol, ascorbic acid, citric acid, etc.

[0095] S202, sodium source, phosphorus source, iron source and carbon source are mixed in a solvent to obtain a slurry;

[0096] S203, the slurry is spray-dried to obtain precursor powder; and

[0097] S204, the precursor powder is sintered to obtain the sodium iron pyrophosphate particles 21. The sodium iron pyrophosphate particles 21 include a sodium iron pyrophosphate core 211 and a carbon layer 212. The carbon layer 212 is wrapped around the surface of the sodium iron pyrophosphate core 211. The powder resistivity PR of the sodium iron pyrophosphate particles 21 is in the range of 70Ω·cm≤PR≤800Ω·cm.

[0098] Optionally, the mass fraction w of the carbon layer 212 in the sodium iron pyrophosphate granules 21 ranges from 2.6% to 3.2%.

[0099] The preparation method of sodium iron pyrophosphate particles 21 described in this application embodiment controls the content of carbon source, thereby ensuring that the content of carbon layer 212 in sodium iron pyrophosphate particles 21 is 2.6% ≤ w ≤ 3.2%. This effectively suppresses the formation of sodium iron phosphate and sodium iron pyrophosphate impurities during the synthesis of sodium iron pyrophosphate particles 21, increases the decomposition temperature of sodium iron pyrophosphate, and improves the specific capacity of sodium iron pyrophosphate particles 21. Furthermore, the increased decomposition temperature of sodium iron pyrophosphate allows for the synthesis of sodium iron pyrophosphate particles 21 at higher temperatures, resulting in a higher degree of carbonization of the carbon layer 212 in the positive electrode active particles, leading to a higher electron transport rate and lower powder resistivity. Therefore, sodium iron pyrophosphate particles 21 exhibit both low powder resistivity and high specific capacity. Furthermore, since sodium iron pyrophosphate particles 21 have a lower powder resistivity, when sodium iron pyrophosphate particles 21 are applied to the positive electrode 100, the amount of expensive positive electrode conductive agents such as carbon nanotubes in the positive electrode active layer 20 of the positive electrode 100 can be reduced while ensuring that the resistivity of the positive electrode 100 remains unchanged, thereby greatly reducing the cost of the positive electrode 100.

[0100] In some embodiments, in S201, the mass fraction of the carbon source in the raw material component ranges from 3.7% to 38.9%.

[0101] Specifically, the mass fraction of the carbon source in the raw material components can be, but is not limited to, 3.7%, 4.0%, 4.2%, 4.6%, 5.0%, 5.2%, 5.5%, 6.0%, 6.4%, 6.8%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 38.9%, etc.

[0102] In this embodiment, if the mass fraction of the carbon source in the raw material composition is too low, the carbon source will have a poor inhibitory effect on the formation of sodium iron phosphate and sodium iron pyrophosphate impurities during sintering. This results in an excessively high content of sodium iron phosphate and sodium iron pyrophosphate impurities in the obtained sodium iron phosphate pyrophosphate particles 21, reducing the specific capacity of the sodium iron phosphate pyrophosphate particles 21. Furthermore, if the mass fraction w of the carbon layer 212 in the obtained sodium iron phosphate pyrophosphate particles 21 is too low, it will reduce the electron transport rate of the sodium iron phosphate pyrophosphate particles 21 and increase the powder resistivity of the sodium iron phosphate pyrophosphate particles 21. If the mass fraction of the carbon source in the raw material composition is too high, the inhibitory effect on the formation of sodium iron phosphate and sodium iron pyrophosphate impurities during sintering will not be further improved. However, the excessively high content of the carbon layer 212 in the obtained sodium iron phosphate pyrophosphate particles 21 will reduce the specific capacity, powder compaction density, and electrode layer compaction density of the sodium iron phosphate pyrophosphate particles 21.

[0103] In one specific embodiment, sodium pyrophosphate (Na4P2O7) is used as the sodium source and part of the phosphorus source, ammonium dihydrogen phosphate (NH4H2PO4) as the phosphorus source, ferrous oxalate dihydrate (FeC2O4 2H2O) as the iron source, and glucose as the carbon source. The mass fraction of the carbon source in the raw material components ranges from 5.2% to 6.4%. In one example, sodium iron pyrophosphate granules 21 are prepared using the preparation process of this embodiment with Na4P2O7 (172g), NH4H2PO4 (149g), FeC2O4 2H2O (339g), and glucose (45g, mass fraction 6.4%). The mass fraction of the carbon layer 212 in the prepared sodium iron pyrophosphate granules 21 is 3.2%.

[0104] In another specific embodiment, sodium pyrophosphate (Na4P2O7) is used as the sodium source and part of the phosphorus source, ammonium dihydrogen phosphate (NH4H2PO4) as the phosphorus source, ferrous oxalate dihydrate (FeC2O4·2H2O) as the iron source, and sucrose as the carbon source. The mass fraction of the carbon source in the raw material components ranges from 3.7% to 4.6%. In one example, Na4P2O7 (172g), NH4H2PO4 (149g), FeC2O4·2H2O (339g), and sucrose (35g to 32g) are used.

[0105] In another specific embodiment, sodium pyrophosphate (Na4P2O7) is used as the sodium source and part of the phosphorus source, ammonium dihydrogen phosphate (NH4H2PO4) as the phosphorus source, ferrous oxalate dihydrate (FeC2O4·2H2O) as the iron source, and starch as the carbon source. The mass fraction of the carbon source in the raw material components ranges from 5.5% to 6.8%. In one example, Na4P2O7 (172g), NH4H2PO4 (149g), FeC2O4·2H2O (339g), and starch (38g to 48g) are used.

[0106] In another specific embodiment, sodium pyrophosphate (Na4P2O7) is used as the sodium source and part of the phosphorus source, ammonium dihydrogen phosphate (NH4H2PO4) as the phosphorus source, ferrous oxalate dihydrate (FeC2O4·2H2O) as the iron source, and citric acid as the carbon source. The mass fraction of the carbon source in the raw material components ranges from 13.4% to 16.5%. In one example, Na4P2O7 (172g), NH4H2PO4 (149g), FeC2O4·2H2O (339g), and citric acid (102g to 130g) are used.

[0107] In another specific embodiment, sodium pyrophosphate (Na4P2O7) is used as the sodium source and part of the phosphorus source, ammonium dihydrogen phosphate (NH4H2PO4) as the phosphorus source, ferrous oxalate dihydrate (FeC2O4·2H2O) as the iron source, and polyvinyl alcohol as the carbon source. The mass fraction of the carbon source in the raw material components ranges from 31.6% to 38.9%. In one example, Na4P2O7 (172g), NH4H2PO4 (149g), FeC2O4·2H2O (339g), and polyvinyl alcohol (305g to 420g) are used.

[0108] In some embodiments, in S202, the step of mixing the sodium source, phosphorus source, iron source and carbon source in a solvent to obtain a slurry includes: mixing the sodium source, phosphorus source, iron source and carbon source in water and performing a sand milling process to obtain a slurry, wherein the sand milling time is 0.5h to 4h and the sand milling speed is 1000rpm to 4000rpm.

[0109] Understandably, the solvent may be, but is not limited to, water.

[0110] In this embodiment, before spray drying, the raw materials (i.e., sodium source, phosphorus source, iron source and carbon source) are first mixed by sand milling. Sand milling can reduce the particle size of the raw materials, providing a prerequisite for the formation of sodium iron pyrophosphate. In addition, sand milling can fully mix the soluble and insoluble substances in the raw materials, avoiding uneven mixing of the raw materials when there are multiple insoluble raw materials, which would increase the probability of impurity phases in the final sodium iron pyrophosphate.

[0111] It should be noted that when all raw material components are water-soluble, the grinding process can be omitted.

[0112] Specifically, the milling time can be, but is not limited to, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, etc. If the milling time is too short, the particle size of the insoluble raw materials in the sodium, phosphorus, iron, and carbon sources will be too large, resulting in localized growth and crystallization during the subsequent sintering process, which reduces the sphericity of the obtained sodium iron pyrophosphate 21 particles; if the milling time is too long, it will reduce production efficiency.

[0113] Specifically, the milling speed can be, but is not limited to, 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, 3500 rpm, 4000 rpm, etc. If the milling speed is too low, the particle size of the insoluble raw materials in the sodium, phosphorus, iron, and carbon sources will be too large, resulting in localized growth and crystallization during the subsequent sintering process, which reduces the sphericity of the obtained sodium iron pyrophosphate 21 particles; if the milling speed is too high, the slurry is prone to splashing.

[0114] In some embodiments, the solid content of the slurry ranges from 20% to 40%. Specifically, the solid content of the slurry can be, but is not limited to, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, etc. In this embodiment, if the solid content of the slurry is too low, the material cannot quickly and effectively shrink into a spherical shape during the spray drying stage, affecting the sphericity of the final obtained sodium iron pyrophosphate granules 21; if the solid content of the slurry is too high, it will cause great difficulties in the sand milling stage. In addition, if the material forms spheres too quickly during the spray drying stage, there is not enough time to form spheres with high sphericity, thereby reducing the sphericity of the obtained precursor powder, which in turn leads to a reduction in the sphericity of the final obtained sodium iron pyrophosphate granules 21.

[0115] In some embodiments, in S203, spray drying the slurry to obtain precursor powder includes: spray drying the slurry at a temperature of 102℃≤T1≤120℃ to obtain precursor powder.

[0116] Specifically, the spray drying temperature can be, but is not limited to, 102℃, 103℃, 104℃, 105℃, 106℃, 107℃, 108℃, 110℃, 112℃, 114℃, 116℃, 118℃, 119℃, 120℃, etc.

[0117] In this embodiment, if the spray drying temperature of the slurry is too low, the solvent (such as water) evaporates too slowly, resulting in a slow spherical formation rate of the precursor powder. This can easily lead to the formation of hollow or collapsed spherical morphologies, affecting the processing performance and compaction density of the final sodium iron pyrophosphate granules 21. If the spray drying temperature of the slurry is too high, the solvent (such as water) evaporates too quickly, resulting in a fast spherical formation rate of the precursor powder and a decrease in the sphericity of the formed precursor powder.

[0118] In some embodiments, in S204, sintering the precursor powder to obtain the sodium iron pyrophosphate particles 21 includes: sintering the precursor powder at a temperature of 580°C to 630°C to obtain the sodium iron pyrophosphate particles 21.

[0119] Optionally, sintering is carried out under an inert atmosphere. Optionally, the inert atmosphere includes at least one of helium, nitrogen, and argon.

[0120] Specifically, the sintering temperature of the precursor powder can be, but is not limited to, 580℃, 585℃, 590℃, 595℃, 300℃, 305℃, 610℃, 615℃, 620℃, 625℃, 630℃, etc. If the sintering temperature of the precursor powder is too low, the carbonization degree of the carbon layer 212 in the obtained sodium iron pyrophosphate particles 21 will be too low, and the resistivity of the sodium iron pyrophosphate particles 21 will be too high. When applied to sodium batteries, this will result in excessive internal resistance and reduce the cycle life of the sodium batteries. If the sintering temperature of the precursor powder is too high, the control of the mass fraction of the carbon layer 212 and the control of impurity elements (potassium, boron, sulfur) in the sodium, iron, and phosphorus sources will not be sufficient to inhibit the decomposition of sodium iron pyrophosphate at high temperatures. Sodium iron pyrophosphate will easily decompose to generate sodium iron phosphate impurity phase and sodium iron pyrophosphate impurity phase, thereby reducing the specific capacity of the sodium iron pyrophosphate particles 21.

[0121] Furthermore, the sintering temperature of the precursor powder is in the range of 600℃ to 610℃. This allows the carbon layer 212 of the prepared sodium iron pyrophosphate particles 21 to have a higher electron transport rate and the sodium iron pyrophosphate particles 21 to have a lower powder resistivity. At the same time, it also allows for a lower content of sodium iron phosphate impurities and sodium iron pyrophosphate impurities in the prepared positive electrode active particles, thereby achieving a higher specific capacity.

[0122] Optionally, the sintering time of the precursor powder can be from 2 hours to 48 hours. Specifically, the sintering time of the precursor powder can be, but is not limited to, 2 hours, 4 hours, 8 hours, 12 hours, 16 hours, 20 hours, 24 hours, 28 hours, 32 hours, 36 hours, 40 hours, 44 hours, 48 ​​hours, etc. If the sintering time of the precursor powder is too short, the carbonization degree of the carbon layer 212 of the obtained sodium iron pyrophosphate particles 21 will be too low, increasing the powder resistivity of the sodium iron pyrophosphate particles 21. If the sintering time of the precursor powder is too long, the probability of decomposition of sodium iron pyrophosphate will increase, increasing the content of sodium iron phosphate impurities and sodium iron pyrophosphate impurities in the sodium iron pyrophosphate particles 21, and reducing the specific capacity of the sodium iron pyrophosphate particles 21.

[0123] Please see Figure 4 and Figure 5 This application also provides a sodium battery 300, which includes: an electrolyte, a positive electrode 100, a separator 320 and a negative electrode 330 as described in this application embodiment.

[0124] It should be noted that the sodium battery 300 in this application embodiment can be, but is not limited to, at least one of sodium-ion batteries, sodium metal batteries, lithium-sodium hybrid batteries, etc.

[0125] Optionally, the sodium battery 300 may be, but is not limited to, at least one of cylindrical sodium batteries, prismatic sodium batteries, and blade sodium batteries. The accompanying drawings of this application merely illustrate one or more possible forms of the sodium battery 300 and should not be construed as limiting the sodium battery 300 of the embodiments of this application, nor should they be construed as limiting the sodium iron pyrophosphate particles 21 of the embodiments of this application.

[0126] Understandably, the positive electrode 100 and the negative electrode 330 are located on opposite sides of the separator 320, that is, the separator 320 is located between the positive electrode 100 and the negative electrode 330, separating the positive electrode 100 and the negative electrode 330.

[0127] It should be noted that the positive electrode 100, the separator 320, and the negative electrode 330 are all at least partially immersed in the electrolyte.

[0128] Optionally, the electrolyte includes an electrolyte salt, an organic solvent, and a film-forming additive.

[0129] Optionally, the electrolyte salt may include, but is not limited to, sodium salts. Optionally, the sodium salt may be, but is not limited to, at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalatoborate), sodium difluorodioxalatophosphate, sodium difluorooxalatoborate, sodium difluorophosphate (NaPO2F2), sodium trifluoromethanesulfonate (CF3SO3Na), etc.

[0130] Optionally, the organic solvent may include at least one of cyclic carbonates and chain carbonates. Optionally, the cyclic carbonate may include, but is not limited to, at least one of ethylene carbonate (EC) and propylene carbonate (PC). Ethylene carbonate has a much higher dielectric constant than propylene carbonate, and can better promote the formation of a solid electrolyte interface membrane (SEI). Optionally, the chain carbonate may include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). Optionally, the organic solvent may also include at least one of ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, γ-butyrolactone, and 2,2-difluoroethyl acetate.

[0131] Optionally, the film-forming additive may include, but is not limited to, at least one of the following: propargylbenzenesulfonic acid, vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), methanedisulfonate (MMDS), butyl sulfonate lactone (BS), and 1,3-propenyl sulfonate lactone (PST).

[0132] Optionally, the diaphragm 320 can be, but is not limited to, at least one of a polypropylene membrane (PP membrane), a polyethylene membrane (PE membrane), and a ceramic diaphragm 320. Optionally, the thickness of the diaphragm 320 is from 10 μm to 18 μm, specifically, the thickness of the diaphragm 320 can be, but is not limited to, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, and 18 μm.

[0133] Please see Figure 6 Optionally, the negative electrode 330 includes a negative current collector 331 and a negative active layer 332.

[0134] Optionally, the negative current collector 331 can be, but is not limited to, at least one of copper foil, copper sheet, aluminum foil, and aluminum sheet.

[0135] Optionally, the negative electrode active layer 332 includes a negative electrode active material, a negative electrode conductive agent, a negative electrode binder, and a negative electrode thickener.

[0136] Optionally, the negative electrode active material can be, but is not limited to, hard carbon.

[0137] Optionally, the negative electrode conductive agent may be, but is not limited to, at least one of conductive carbon black (SP), acetylene black, carbon nanotubes, carbon fibers, graphene, etc.

[0138] Optionally, the negative electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride, polyamide, polyacrylonitrile, polyacrylate, polyethylene ether, polymethyl methacrylate, polyhexafluoropropylene, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber, etc.

[0139] Optionally, the negative electrode thickener may be, but is not limited to, at least one of polyacrylamide (PAM) and polymethyl methacrylate (PMA).

[0140] Please see again Figure 4 and Figure 5 Optionally, the sodium battery 300 further includes a housing 340 and an end cap assembly 350, the housing 340 and the end cap assembly 350 forming a closed receiving cavity (not shown) for housing the electrolyte, the positive electrode 100, the separator 320, and the negative electrode 330. Understandably, the end cap assembly 350 electrically connects the positive electrode 100 and the negative electrode 330, respectively, leading out the positive electrode 100 and the negative electrode 330 for electrical connection to external devices or other sodium batteries 300.

[0141] The following specific embodiments further describe the positive electrode 100, sodium iron pyrophosphate particles 21, and sodium battery 300 of this application.

[0142] Example 1

[0143] The sodium iron pyrophosphate granules 21 in this embodiment are prepared by the following steps:

[0144] (1) 178g sodium pyrophosphate (sodium source, phosphorus source), 150g ammonium dihydrogen phosphate (phosphorus source), 340g ferrous oxalate dihydrate (iron source), 36g glucose (carbon source) and 2.5kg water (solvent) are stirred evenly to obtain a slurry, wherein the solid content of the slurry is 35%.

[0145] (2) The slurry was spray-dried at 105°C to obtain precursor powder;

[0146] (3) The precursor powder was sintered in a sintering furnace at a temperature of 610°C for 12 hours under nitrogen protection. After cooling, sodium iron pyrophosphate granules 21 were obtained.

[0147] Measurements showed that the mass fraction of carbon layer 212 in sodium iron pyrophosphate granules 21 of this embodiment was 2.6%.

[0148] The method for measuring the carbon layer 212 content in sodium iron pyrophosphate particles 21 of this application is as follows: 0.1g of sample is added to the crucible and tested using a carbon-sulfur content tester, and the average value is measured three times.

[0149] Preparation of the positive electrode 100 in this embodiment: Sodium iron pyrophosphate particles 21, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride prepared in this embodiment are mixed in a mass ratio of 96:0.4:1.5:2. 0.1% dispersant is added and dispersed in N-methylpyrrolidone (NMP). A defoamer is used to prepare the positive electrode slurry. The positive electrode slurry is uniformly coated onto two opposing surfaces of an aluminum foil current collector (positive electrode current collector 10) using a scraper. The coating amount of the positive electrode slurry is 17 mg / cm². 2 After vacuum drying, rolling, and cutting, positive electrode sheet 100 is obtained, where K = 0.002 and the rolling pressure is 40T.

[0150] Example 2

[0151] The difference between this embodiment and Embodiment 1 is that the mass of glucose in this embodiment is 37.4g.

[0152] Measurements showed that the mass fraction of carbon layer 212 in sodium iron pyrophosphate granules 21 of this embodiment was 2.7%.

[0153] Example 3

[0154] The difference between this embodiment and Embodiment 1 is that the mass of glucose in this embodiment is 38.9g.

[0155] Measurements showed that the mass fraction of carbon layer 212 in sodium iron pyrophosphate granules 21 of this embodiment was 2.8%.

[0156] Example 4

[0157] The difference between this embodiment and Embodiment 1 is that the mass of glucose in this embodiment is 40.7g.

[0158] Measurements showed that the mass fraction of carbon layer 212 in sodium iron pyrophosphate granules 21 of this embodiment was 2.9%.

[0159] Example 5

[0160] The difference between this embodiment and Embodiment 1 is that the mass of glucose in this embodiment is 42.2g.

[0161] Measurements showed that the mass fraction of carbon layer 212 in sodium iron pyrophosphate granules 21 of this embodiment was 3.0%.

[0162] Example 6

[0163] The difference between this embodiment and Embodiment 1 is that the mass of glucose in this embodiment is 44.3g.

[0164] Measurements showed that the mass fraction of carbon layer 212 in sodium iron pyrophosphate granules 21 of this embodiment was 3.1%.

[0165] Example 7

[0166] The difference between this embodiment and Embodiment 1 is that the mass of glucose in this embodiment is 46g.

[0167] Measurements showed that the mass fraction of carbon layer 212 in sodium iron pyrophosphate granules 21 of this embodiment was 3.2%.

[0168] Example 8

[0169] The difference between this embodiment and embodiment 6 is that the mass ratio of sodium iron phosphate pyrophosphate particles 21, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride in the positive electrode sheet 100 of this embodiment is 96.2:0.2:1.5:2.

[0170] Example 9

[0171] The difference between this embodiment and embodiment 6 is that the mass ratio of sodium iron phosphate pyrophosphate particles 21, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride in the positive electrode sheet 100 of this embodiment is 95.8:0.6:1.5:2.

[0172] Example 10

[0173] The difference between this embodiment and embodiment 6 is that the mass ratio of sodium iron phosphate pyrophosphate particles 21, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride in the positive electrode sheet 100 of this embodiment is 95.6:0.8:1.5:2.

[0174] Example 11

[0175] The difference between this embodiment and embodiment 6 is that the mass ratio of sodium iron phosphate pyrophosphate particles 21, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride in the positive electrode sheet 100 of this embodiment is 95.4:1.0:1.5:2.

[0176] Example 12

[0177] The difference between this embodiment and embodiment 6 is that the mass ratio of sodium iron phosphate pyrophosphate particles 21, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride in the positive electrode sheet 100 of this embodiment is 96.7:0.4:0.8:2.

[0178] Example 13

[0179] The difference between this embodiment and embodiment 6 is that the mass ratio of sodium iron phosphate pyrophosphate particles 21, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride in the positive electrode sheet 100 of this embodiment is 96.3:0.4:1.2:2.

[0180] Example 14

[0181] The difference between this embodiment and embodiment 6 is that the mass ratio of sodium iron phosphate pyrophosphate particles 21, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride in the positive electrode sheet 100 of this embodiment is 95.7:0.4:1.8:2.

[0182] Example 15

[0183] The difference between this embodiment and embodiment 6 is that the mass ratio of sodium iron phosphate pyrophosphate particles 21, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride in the positive electrode sheet 100 of this embodiment is 95.1:0.4:2.4:2.

[0184] Example 16

[0185] The difference between this embodiment and embodiment 6 is that K = 0.0008 and the roller pressure is 60T.

[0186] Example 17

[0187] The difference between this embodiment and Embodiment 6 is that K = 0.0024, and the coating amount of the positive electrode slurry is 19 mg / cm³. 2 .

[0188] Comparative Example 1

[0189] The difference between this comparative example and Example 1 is that the mass of glucose in this example is 26g.

[0190] Measurements showed that the mass fraction of carbon layer 212 in sodium iron pyrophosphate granules 21 of this embodiment was 1.2%.

[0191] Comparative Example 2

[0192] The difference between this comparative example and Example 1 is that the mass of glucose in this comparative example is 58g.

[0193] Measurements showed that the mass fraction of carbon layer 212 in the sodium iron pyrophosphate granules 21 of this comparative example was 3.8%.

[0194] Comparative Example 3

[0195] The difference between this comparative example and Example 6 is that the mass ratio of sodium iron pyrophosphate particles 21, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride in the positive electrode 100 of this comparative example is 96.35:0.05:1.5:2.

[0196] Comparative Example 4

[0197] The difference between this comparative example and Example 1 is that the mass ratio of sodium iron pyrophosphate particles 21, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride in the positive electrode 100 of this comparative example is 92.4:4:1.5:2.

[0198] Comparative Example 5

[0199] The difference between this comparative example and Example 1 is that the mass ratio of sodium iron pyrophosphate particles 21, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride in the positive electrode sheet 100 of this comparative example is 97.2:0.4:0.3:2.

[0200] Comparative Example 6

[0201] The difference between this comparative example and Example 1 is that the mass ratio of sodium iron pyrophosphate particles 21, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride in the positive electrode 100 of this comparative example is 91.5:0.4:6:2.

[0202] Comparative Example 7

[0203] The difference between this comparative example and Example 6 is that K = 0.0003 and the rolling pressure is 100T.

[0204] Comparative Example 8

[0205] The difference between this comparative example and Example 6 is that K = 0.01, and the coating amount of the positive electrode slurry is 25 mg / cm³. 2 .

[0206] The following performance tests were performed on the sodium iron pyrophosphate particles 21 and the positive electrode 100 of the embodiments and comparative examples.

[0207] (1) Powder resistivity test of sodium iron pyrophosphate granules 21: The two-probe method was used for measurement. Specifically, 2g to 3g of sodium iron pyrophosphate granules 21 powder was added to the mold of a powder resistivity instrument with a diameter of 13mm, and after being pressurized to 200MPa, the powder resistivity value was measured.

[0208] (2) Film resistivity of positive electrode 100: The positive electrode 100 coated with positive active layer 20 on both sides is cut into 5 squares with a size of 5cm×5cm. The thickness of the positive electrode 100 is measured with a micrometer (the average value of the five measurements is taken). Then, the film resistance of each small positive electrode 100 square is measured with a resistance meter (the thickness value is entered and the measurement pressure is adjusted to be kept at 0.4 tons). Finally, the average value of the film resistivity measurements of the five square positive electrode 100 is taken.

[0209] (3) Compacted density of positive electrode active layer 20 of positive electrode 100: aluminum foil is cut into aluminum foil discs with a diameter of 12 mm, and the thickness and weight of the aluminum foil discs are measured. The positive electrode slurry of each embodiment and comparative example is coated on the aluminum foil discs and dried to obtain positive electrode 100. The thickness and weight of positive electrode 100 are measured, and the compacted density of positive electrode active layer 20 of positive electrode 100 is calculated according to the formula: (thickness of positive electrode 100 - thickness of aluminum foil disc) / (volume of positive electrode 100 - volume of aluminum foil disc).

[0210] (4) Volumetric specific capacity of the positive electrode active layer 20: Using the positive electrode 100 of each embodiment and comparative example, with a sodium metal sheet as the counter electrode and a glass fiber membrane 320 as the separator, the positive electrode 100, separator 320, sodium sheet, electrolyte, and casing are assembled into a button cell sodium battery 300. Subsequently, the specific capacity of the sodium battery 300 is measured (tested in a temperature chamber at 25°C or -20°C respectively). Constant current charge and discharge tests are performed using a blue electric current tester with a current of 0.24mA and a test voltage range of 1.5V to 3.5V. The measured capacity value is divided by the volume of the positive electrode active layer 20 to obtain the volumetric specific capacity of the positive electrode active layer 20 (the positive electrode 100 can be uniformly made into a disc with a diameter of 12mm).

[0211] The performance parameters of sodium iron pyrophosphate particles 21 and positive electrode plates 100 in Examples 1 to 17 and Comparative Examples 1 to 8 are shown in Table 1 below.

[0212] Table 1 Performance parameters of sodium iron pyrophosphate particles 21 from Examples 1 to 17 and Comparative Examples 1 to 8

[0213]

[0214] Note: The DR values ​​in Table 1 are calculated based on the following formula. Perform the calculation.

[0215] The test results from Examples 1 to 7, Comparative Examples 1 and 2 show that as the mass fraction of carbon layer 212 in sodium iron pyrophosphate granules 21 increases, the powder resistivity PR of sodium iron pyrophosphate granules 21 gradually decreases, the film resistivity DR of positive electrode 100 gradually decreases, the compaction density of positive electrode 100 slightly decreases, and the volumetric specific capacity of positive electrode active layer 20 at low temperature (-20℃) and room temperature (25℃) first gradually increases and then gradually decreases.

[0216] The test results of Examples 6, 8 to 11, Comparative Example 3 and Comparative Example 4 show that as the mass fraction M1 of the carbon nanotubes in the positive electrode active layer 20 increases, the film resistivity DR of the positive electrode 100 gradually decreases, the compaction density of the positive electrode 100 decreases slightly, and the volumetric specific capacity of the positive electrode active layer 20 at low temperature (-20℃) and room temperature (25℃) first gradually increases and then gradually decreases.

[0217] The test results of Examples 6, 12 to 15, Comparative Examples 5 and 6 show that as the mass fraction M2 of the conductive carbon black in the positive electrode active layer 20 increases, the film resistivity DR of the positive electrode sheet 100 gradually decreases, the compaction density of the positive electrode sheet 100 decreases slightly, and the volumetric specific capacity of the positive electrode active layer 20 at low temperature (-20℃) and room temperature (25℃) first gradually increases and then gradually decreases.

[0218] The test results of Examples 6, 16, 17, Comparative Example 7 and Comparative Example 8 show that as the value of K increases, the film resistivity DR of the positive electrode 100 gradually increases, the compaction density of the positive electrode 100 decreases slightly, and the volumetric specific capacity of the positive electrode active layer 20 at low temperature (-20℃) and room temperature (25℃) first gradually increases and then gradually decreases.

[0219] The test results from Examples 1 and 17, and Comparative Examples 1 to 8 also show that the measured value of the film resistivity DR of the positive electrode 100 of this application is related to the following formula: The calculated values ​​are very close, illustrating the relationship in this application: It can be used to calculate the film resistivity of the positive electrode 100, thereby guiding the experiment through theoretical calculation, which can greatly shorten the experimental time, improve efficiency, and reduce research and development costs.

[0220] Please see Figure 7 This application embodiment also provides an energy storage device 400, which includes a housing 410 and a sodium battery 300 as described in this application embodiment, wherein the sodium battery 300 is housed within the housing 410.

[0221] The energy storage device 400 of this application can be applied to, but is not limited to, energy storage on the generation side, energy storage on the grid side, and energy storage on the consumption side.

[0222] Optionally, the energy storage device 400 may include, but is not limited to, sodium battery modules, sodium battery packs, sodium battery systems, energy storage boxes, energy storage cabinets, and energy storage containers. The actual application form of the energy storage device 400 provided in this application embodiment may be, but is not limited to, the listed products, and may also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 400. The accompanying drawings of this application embodiment are only illustrative of the energy storage device 400 including multiple sodium batteries 300, and should not be construed as limiting the energy storage device 400 of this application embodiment.

[0223] Optionally, the number of sodium batteries 300 can be, but is not limited to, one or more. When there are multiple sodium batteries 300, they are stacked within the housing 410. It is understood that the stacked arrangement of the multiple sodium batteries 300 can be either arranged sequentially abutting each other, or arranged sequentially with intervals between them. Furthermore, the multiple sodium batteries 300 can be stacked laterally (e.g., horizontally) or longitudinally (e.g., along the direction of gravity). The stacking method and direction of the multiple sodium batteries 300 can be designed according to actual conditions, and this application does not impose specific limitations.

[0224] The term "multiple" refers to two or more.

[0225] Understandably, the multiple sodium batteries 300 of the energy storage device 400 can be connected in parallel, or in series, 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 sodium batteries 300 of the same energy storage device 400.

[0226] Understandably, the housing 410 has a receiving cavity in which one or more sodium batteries 300 are received. In some embodiments, each receiving cavity receives one sodium battery 300. In other embodiments, each receiving cavity receives multiple sodium batteries 300.

[0227] Please see Figure 8 and Figure 9 This application also provides an energy storage system 500, which includes the energy storage device 400 described in this application embodiment; and an energy conversion device 510, wherein the energy conversion device 510 is electrically connected to the energy storage device 400, the energy conversion device 510 is used to convert other forms of energy into electrical energy, and the energy storage device 400 is used to store the electrical energy.

[0228] It should be noted that energy storage (i.e., energy storage) has a wide range of applications, including generation-side energy storage, grid-side energy storage, and consumption-side energy storage. This application's embodiment of the energy storage system 500 uses generation-side energy storage as an example for detailed description, and should not be construed as limiting the energy storage system 500, nor as limiting the energy storage device 400, sodium battery 300, and sodium iron pyrophosphate granules 21, etc., of this application.

[0229] During operation, the power conversion device 510 converts other forms of energy into electrical energy and stores it in the energy storage device 400. The electrical energy stored in the energy storage device 400 can be used to supply electrical loads such as streetlights and household appliances during peak electricity prices, or to supply power when the power grid experiences a power outage. The electrical energy generated by the power conversion device 510 can also be supplied to the power grid through high-voltage cables to alleviate the power supply pressure on the power grid during peak periods.

[0230] Optionally, the power conversion device 510 can convert at least one other form of energy, such as solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy, and mechanical energy, into electrical energy.

[0231] Optionally, the number of power conversion devices 510 can be one or more. When there are multiple power conversion devices 510, the multiple power conversion devices 510 can be connected in series, in parallel or in a mixed manner. This application does not make specific limitations.

[0232] Optionally, the power conversion device 510 can be, but is not limited to, at least one of photovoltaic panels, wind power generation devices, hydropower generation devices, etc.

[0233] Optionally, the number of energy storage devices 400 can be one or more. When there are multiple energy storage devices 400, the multiple energy storage devices 400 can be connected in series or in parallel. This application does not make specific limitations.

[0234] In this application, the terms "embodiment" and "implementation" mean that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of this application. The appearance of these phrases in various locations throughout the specification does not necessarily refer to the same embodiment, nor are they independent or alternative embodiments mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this application can be combined with other embodiments. Furthermore, it should be understood that the features, structures, or characteristics described in the various embodiments of this application can be arbitrarily combined to form yet another embodiment that does not depart from the spirit and scope of the technical solution of this application, provided there is no contradiction between them.

[0235] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes: Positive current collector; and A positive electrode active layer is disposed on the surface of the positive electrode current collector. The positive electrode active layer includes sodium iron pyrophosphate particles and a conductive agent. The powder resistivity PR of the sodium iron pyrophosphate particles is in the range of 70Ω·cm≤PR≤800Ω·cm. The resistivity DR of the positive electrode film is in the range of: 0.05Ω•m≤DR≤0.4Ω•m; The conductive agent includes carbon nanotubes and conductive carbon black, and the positive electrode sheet satisfies the following relationship: DR= ; Where K is a constant, DR is the film resistivity of the positive electrode sheet in Ω·m; PR is the powder resistivity of the sodium iron pyrophosphate particles in Ω·m; M1 is the mass fraction of carbon nanotubes in the positive electrode active layer in wt%; M2 is the mass fraction of conductive carbon black in the positive electrode active layer in wt%; and the value range of K is 5 × 10⁻⁶. -4 ≤K≤3×10 -3 .

2. The positive electrode sheet according to claim 1, characterized in that, The mass fraction M1 of the carbon nanotubes in the positive electrode active layer is in the range of 0.2% ≤ M1 ≤ 1%.

3. The positive electrode sheet according to claim 2, characterized in that, The mass fraction M1 of the carbon nanotubes in the positive electrode active layer is in the range of 0.2% ≤ M1 ≤ 0.6%.

4. The positive electrode sheet according to claim 1, characterized in that, The mass fraction M2 of the conductive carbon black in the positive electrode active layer is in the range of 0.8% ≤ M2 ≤ 2.4%.

5. The positive electrode sheet according to claim 4, characterized in that, The mass fraction M2 of the conductive carbon black in the positive electrode active layer is in the range of 1.2% ≤ M2 ≤ 1.8%.

6. The positive electrode sheet according to any one of claims 1-5, characterized in that, The sodium iron pyrophosphate particles comprise a sodium iron pyrophosphate core and a carbon layer, wherein the carbon layer coats the surface of the sodium iron pyrophosphate core, and the mass fraction w of the carbon layer in the sodium iron pyrophosphate particles ranges from 2.6% to 3.2%.

7. A sodium battery, characterized in that, include: Electrolyte, positive electrode, separator and negative electrode as described in any one of claims 1-6.

8. An energy storage device, characterized in that, include: Box; as well as The sodium battery of claim 7, wherein the sodium battery is housed within the casing.

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