Positive electrode materials and their preparation methods, electrode sheets and batteries

Abstract

This application relates to a positive electrode material, its preparation method, an electrode sheet, and a battery. The positive electrode material includes an active material with the chemical formula Na4Fe3(PO4)2P2O7. The active material has multiple pores, including multiple first micropores. The pore size D1 of the first micropores satisfies the range D1≤500nm, and the percentage α of the first micropores relative to the total number of pores ranges from 85%≤α≤98%.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly relates to a cathode material, a preparation method thereof, an electrode sheet, and a battery. Background Art

[0002] With the continuous development of energy storage technologies, sodium-ion batteries have attracted much attention due to their high stability and safety. Na4Fe3(PO4)2P2O7 (NFPP), as an iron-based phosphate polyanion material, has three-dimensional sodium-ion diffusion channels and a relatively high theoretical specific capacity. However, the powder tap density of NFPP is relatively low, and when NFPP is applied to the cathode sheet, the tap density of the cathode sheet is also low, which limits the improvement of the energy density of the battery. Summary of the Invention

[0003] In view of this, this application provides a cathode material, a preparation method thereof, an electrode sheet, and a battery, and the cathode material has a relatively high tap density.

[0004] This application provides a cathode material, which includes an active material. The chemical formula of the active material is Na4Fe3(PO4)2P2O7. The active material has multiple pores, and the pores include multiple first fine pores. The pore diameter D1 of the first fine pores satisfies the range D1 ≤ 500 nm, and the percentage α of the number of the first fine pores in the pores satisfies the range: 85% ≤ α ≤ 98%.

[0005] Further, the multiple first fine pores include first sub-pores and second sub-pores. The pore diameter D2 of the first sub-pores satisfies the range: 0 < D2 ≤ 50 nm, the pore diameter D3 of the second sub-pores satisfies the range: 50 nm < D3 ≤ 500 nm, and the ratio β of the number of the first sub-pores to the number of the second sub-pores satisfies the relationship: 1 ≤ β ≤ 2.

[0006] Further, the active material further includes second fine pores. The pore diameter D4 of the second fine pores satisfies the range 500 nm < D4 ≤ 1000 nm, and the percentage γ of the number of the second fine pores in the pores satisfies the range: 0 < γ < 10%.

[0007] Further, the active material further includes third fine pores. The pore diameter D5 of the third fine pores satisfies the range D5 > 1000 nm, and the percentage δ of the number of the third fine pores in the pores satisfies the range: 0 ≤ δ < 5%.

[0008] Further, the tap density ρ of the cathode material satisfies the range: 2.0 g / cm 3 ≤ ρ ≤ 2.3 g / cm 3 . [[ID=3�]]

[0009] Furthermore, the positive electrode material includes a plurality of positive electrode particles, each positive electrode particle including a coating layer and the active material, the coating layer covering the outer periphery of the active material, and the mass fraction w of the coating layer in the positive electrode particles satisfying the range: 1% ≤ w ≤ 4%.

[0010] Furthermore, the median particle size D50 of the cathode material satisfies the range: 2μm≤D50≤10μm.

[0011] This application provides a method for preparing a cathode material. The method includes: providing a sodium source, an iron source, a phosphorus source, and a carbon source; dispersing the sodium source, iron source, phosphorus source, and carbon source in a solvent; adding acetic acid to mix and obtain a slurry; wherein the pH of the slurry satisfies the range: 2 ≤ pH < 6; milling and spray drying the slurry to obtain intermediate particles; and sintering the intermediate particles to obtain the cathode material. The cathode material includes an active material with the chemical formula Na4Fe3(PO4)2P2O7. The active material has multiple pores, including multiple first micropores. The pore size D1 of the first micropores satisfies the range D1 ≤ 500 nm, and the percentage α of the first micropores in the total number of pores is in the range: 85% ≤ α ≤ 98%.

[0012] Further, the process of milling and spray drying the slurry to obtain intermediate particles includes: milling the slurry to obtain a refined slurry, the refined slurry including precursor particles, the precursor particles having a particle size D6 range of D6 < 700 nm; and spray drying the refined slurry to obtain the intermediate particles.

[0013] Furthermore, the temperature at which the refined slurry is spray-dried is T1, and T1 satisfies the range: 250℃≤T1≤300℃.

[0014] Furthermore, the sintering temperature of the intermediate particles is T2, and T2 satisfies the range: 450℃≤T2≤550℃; the sintering time of the intermediate particles is t, and t satisfies the range: 8h≤t≤16h.

[0015] This application provides a positive electrode sheet, which includes: a positive current collector; and a positive electrode material layer disposed on the surface of the positive current collector. The positive electrode material layer includes the positive electrode material provided in this application, or the positive electrode material prepared by the method for preparing the positive electrode material provided in this application.

[0016] This application provides a battery comprising: an electrolyte, a negative electrode, a separator, and a positive electrode provided in this application. The negative electrode is at least partially immersed in the electrolyte; the separator is located on one side of the negative electrode and is at least partially immersed in the electrolyte; the positive electrode is disposed on the side of the separator opposite to the positive electrode and is at least partially immersed in the electrolyte.

[0017] In the cathode material provided in this application, the pore size D1 of the first micropore satisfies the range D1≤500nm, and the percentage α of the first micropore in the total pores satisfies the range 85%≤α≤98%. Therefore, the majority of the pores in the cathode material are first micropores, and these first micropores have small pore sizes and a narrow pore size distribution, resulting in strong compressive strength of the cathode material. Compared to cathode materials where the majority of pores have pore sizes greater than 500nm, the cathode material provided in this application is less prone to breakage under the same pressure. In other words, the pores occupy a smaller volume fraction in the cathode material, resulting in a higher compaction density. When the cathode material is applied to a cathode electrode sheet and assembled into a battery, the cathode electrode sheet has a high compaction density, and the battery has a high energy density. When the percentage α of the first fine pores in the total number of pores is too small, the positive electrode material contains a large number of pores with a diameter greater than 500 nm. Consequently, the pores account for a larger volume fraction of the positive electrode material, making the positive electrode material still easily broken and resulting in a low compaction density. When the positive electrode material is applied to a positive electrode sheet and assembled into a battery, both the compaction density of the positive electrode sheet and the energy density of the battery are low. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the implementation will be briefly introduced below. Obviously, the drawings described below are some implementations of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of a battery according to an embodiment of this application;

[0020] Figure 2 This is a schematic diagram of the structure of a positive electrode sheet according to an embodiment of this application;

[0021] Figure 3 This is a schematic flowchart of a method for preparing a positive electrode material according to an embodiment of this application;

[0022] Figure 4 This is a schematic flowchart illustrating a method for preparing a cathode material according to another embodiment of this application.

[0023] Figure 5 The image shows the SEM spectrum of the cathode material in Comparative Example 2.

[0024] Figure 6 The image shows the SEM image of the cross-section of the cathode material in Comparative Example 2.

[0025] Figure 7 The image shows the SEM spectrum of the cathode material in Example 7.

[0026] Figure 8 The image shows the SEM image of the cross-section of the cathode material in Example 7.

[0027] Explanation of reference numerals in the attached figures:

[0028] 100 - Positive electrode material, 200 - Positive electrode sheet, 210 - Positive electrode current collector, 220 - Positive electrode material layer, 300 - Battery, 310 - Electrolyte, 320 - Negative electrode sheet, 330 - Separator. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0030] 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.

[0031] In this document, references to "embodiment" or "implementation" mean that a particular feature, structure, or characteristic described in connection with an embodiment or implementation may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0032] With the continuous development of energy storage technology, sodium-ion batteries have attracted much attention due to their high stability and safety. Na4Fe3(PO4)2P2O7 (NFPP), as an iron-based phosphate polyanionic material, has three-dimensional sodium ion diffusion channels and a high theoretical specific capacity. However, NFPP has a low powder compaction density, and when NFPP is applied to the positive electrode, the compaction density of the positive electrode is also low, which limits the improvement of the battery's energy density.

[0033] During the sintering process of NFPP, due to the decomposition and gas generation of acid radicals from sodium and iron sources, as well as the interactions between grains, NFPP contains numerous pores, most of which have a pore size greater than 500 nm. When the pore size is too large, it weakens the compressive strength of NFPP. That is, under the same pressure, NFPP particles with large pores are more prone to breakage than those with small pores, resulting in a lower compaction density. Therefore, the pore size within NFPP particles has a significant impact on their compaction density.

[0034] Please see Figure 1 This application provides a battery 300, which includes: an electrolyte 310, a negative electrode 320, a separator 330, and a positive electrode 200 provided in this application. The negative electrode 320 is at least partially immersed in the electrolyte 310; the separator 330 is located on one side of the negative electrode 320 and is at least partially immersed in the electrolyte 310; the positive electrode 200 is disposed on the side of the separator 330 opposite to the positive electrode 200 and is at least partially immersed in the electrolyte 310.

[0035] Understandably, the positive electrode 200, the separator 330, and the negative electrode 320 are stacked sequentially.

[0036] In this embodiment, the battery 300 includes a positive electrode 200 provided in this application, and the positive electrode material layer 220 of the positive electrode 200 includes a positive electrode material 100 provided in this application. The positive electrode material 100 includes an active material, and in the active material, the percentage α of the first fine pores in the number of pores is in the range of 85% ≤ α ≤ 98%, which makes the positive electrode material 100 have a large compaction density, thereby making the positive electrode 200 have a large compaction density, and the battery 300 has a large energy density.

[0037] Optionally, the battery 300 can be one of a cylindrical battery, a prismatic battery, or a pouch battery. When the battery 300 is a cylindrical battery 300, the negative electrode 320, the separator 330, and the positive electrode 200 do not need to be pressed together.

[0038] Optionally, the battery 300 may be a sodium-ion battery.

[0039] Please see Figure 2 This application provides a positive electrode 200, which includes: a positive current collector 210; and a positive electrode material layer 220, which is disposed on the surface of the positive current collector 210. The positive electrode material layer 220 includes the positive electrode material 100 provided in this application, or the positive electrode material 100 prepared by the preparation method of the positive electrode material 100 provided in this application.

[0040] Optionally, in some embodiments, the positive electrode material layer 220 is disposed on one surface of the positive electrode current collector 210; in other embodiments, the positive electrode material layer 220 is disposed on two opposite surfaces of the positive electrode current collector 210.

[0041] Optionally, the positive current collector 210 is selected from foil materials.

[0042] In this embodiment, the positive electrode material layer 220 includes the positive electrode material 100 provided in this application, or the positive electrode material 100 prepared by the preparation method of the positive electrode material 100 provided in this application. The positive electrode material 100 includes an active material, and in the active material, the percentage α of the first fine pores in the number of pores is in the range of 85% ≤ α ≤ 98%, which makes the positive electrode material 100 have a large compaction density, thereby making the positive electrode sheet 200 have a large compaction density. When the positive electrode sheet 200 is assembled into the battery 300, the battery 300 has a large energy density.

[0043] Optionally, the positive electrode material layer 220 further includes a conductive agent and a binder, wherein the conductive agent is used to improve the conductivity of the positive electrode material layer 220, and the binder is used to bond the positive electrode material 100.

[0044] Optionally, the conductive agent is selected from one or more of acetylene black, conductive carbon black, carbon nanotubes, carbon fibers, graphene, etc.

[0045] Optionally, the adhesive is selected from polyvinylidene fluoride (PVDF).

[0046] This application provides a positive electrode material 100, which includes an active material with the chemical formula Na4Fe3(PO4)2P2O7. The active material has a plurality of pores, including a plurality of first micropores. The pore size D1 of the first micropores satisfies the range D1≤500nm, and the percentage α of the number of the first micropores in the pores is in the range of 85%≤α≤98%.

[0047] Specifically, the aperture D1 of the first fine hole can be, but is not limited to, 1nm, 5nm, 8nm, 10nm, 12nm, 15nm, 18nm, 20nm, 22nm, 25nm, 28nm, 30nm, 32nm, 35nm, 38nm, 40nm, 42nm, 45nm, 48nm, 50nm, 55nm, 80nm, 100nm, 120nm, 150nm, 180nm, 200nm, 220nm, 250nm, 280nm, 300nm, 330nm, 350nm, 380nm, 400nm, 420nm, 450nm, 480nm, 490nm, and 500nm.

[0048] Specifically, the percentage α of the first fine pores to the total number of pores can be, but is not limited to, 85%, 85.5%, 86%, 86.5%, 87%, 87.5%, 88%, 88.5%, 89%, 89.5%, 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, and 98%.

[0049] Understandably, the percentage α of the first pores to the total number of pores can be the ratio of the number of the first pores to the number of pores in the positive electrode material 100.

[0050] Understandably, all of the pores are open holes.

[0051] In the positive electrode material 100 provided in this embodiment, the pore size D1 of the first fine pores satisfies the range D1≤500nm, and the percentage α of the number of the first fine pores in the pores satisfies the range: 85%≤α≤98%. Therefore, the majority of the pores in the positive electrode material 100 are first fine pores, and the pore size of the first fine pores is small, and the pore size distribution of the pores is narrow. Thus, the positive electrode material 100 has strong compressive strength. Compared to a positive electrode material 100 where the pore size of most pores is greater than 500nm, under the same pressure, the positive electrode material 100 provided in this application is less likely to break. In other words, the pores occupy a smaller volume fraction in the positive electrode material 100, resulting in a higher compaction density. When the positive electrode material 100 is applied to the positive electrode sheet 200 and assembled in the battery 300, the positive electrode sheet 200 has a higher compaction density, and the battery 300 has a higher energy density. When the percentage α of the first fine pores in the total number of pores is too small, the positive electrode material 100 contains a large number of pores with a diameter greater than 500 nm. Consequently, the volume fraction of these pores in the positive electrode material 100 is larger, making the positive electrode material 100 still easily broken and resulting in a low compaction density. When the positive electrode material 100 is applied to the positive electrode sheet 200 and assembled into the battery 300, both the compaction density of the positive electrode sheet 200 and the energy density of the battery 300 are low.

[0052] In the terminology of this application, "multiple" means two or more, and can be, but is not limited to, five, ten, twenty, fifty, eighty, one hundred, five hundred, and one thousand.

[0053] In some embodiments, the plurality of first micropores include first sub-pores and second sub-pores. The aperture D2 of the first sub-pore satisfies the range: 0 < D2 ≤ 50 nm. The aperture D3 of the second sub-pore satisfies the range: 50 nm < D3 ≤ 500 nm. The ratio β of the number of first sub-pores to the number of second sub-pores satisfies the relationship: 1 ≤ β ≤ 2.

[0054] Specifically, the aperture D2 of the first sub-aperture can be, but is not limited to, 1nm, 5nm, 8nm, 10nm, 12nm, 15nm, 18nm, 20nm, 22nm, 25nm, 28nm, 30nm, 32nm, 35nm, 38nm, 40nm, 42nm, 45nm, 48nm, and 50nm.

[0055] Specifically, the aperture D3 of the second sub-aperture can be, but is not limited to, 55nm, 80nm, 100nm, 120nm, 150nm, 180nm, 200nm, 220nm, 250nm, 280nm, 300nm, 330nm, 350nm, 380nm, 400nm, 420nm, 450nm, 480nm, 490nm, and 500nm.

[0056] Specifically, the value of β, the ratio of the number of the first sub-holes to the number of the second sub-holes, can be, but is not limited to, 1, 1.02, 1.05, 1.1, 1.15, 1.18, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, and 2.

[0057] Understandably, the diameter of the first sub-hole is smaller than the diameter of the second sub-hole, and in the first fine hole, the number of the first sub-hole is equal to or greater than the number of the second sub-hole.

[0058] In this embodiment, the plurality of first micropores include first sub-pores and second sub-pores. The pore diameter D2 of the first sub-pores satisfies the range: 0 < D2 ≤ 50 nm, and the pore diameter D3 of the second sub-pores satisfies the range: 50 nm < D3 ≤ 500 nm. The pore diameter of the first sub-pores is smaller than that of the second sub-pores, and the ratio β of the number of the first sub-pores to the number of the second sub-pores satisfies the relational expression: 1 ≤ β ≤ 2, so the number of the first sub-pores is equal to or greater than the number of the second sub-pores. Among the plurality of first micropores, the first sub-pores with smaller pore diameters account for the majority of the first micropores, which is beneficial to reducing the volume fraction of the plurality of first micropores in the positive electrode material 100, and then further reducing the volume fraction of the pores occupying the positive electrode material 100. During the compaction process of the positive electrode material 100, the positive electrode material 100 is less likely to break, which is beneficial to improving the compaction density of the positive electrode material 100. When the positive electrode material 100 is applied to the positive electrode sheet 200 and assembled in the battery 300, the compaction density of the positive electrode sheet 200 and the energy density of the battery 300 are both high. When the ratio β of the number of the first sub-pores to the number of the second sub-pores is too large, among the first micropores, the number of the first sub-pores is much larger than that of the second sub-pores. Although the first sub-pores can reduce the volume fraction of the pores occupying the positive electrode material 100 to improve the compaction density of the positive electrode material 100, correspondingly, the volume fraction of the pores occupying the positive electrode material 100 in the positive electrode material 100 is too small, making it difficult for the positive electrode material 100 to absorb the electrolyte 310, which will cause the hindrance of the transmission of active ions inside the battery 300, thus affecting the charge-discharge efficiency and cycle performance of the battery 300. When the ratio β of the number of the first sub-pores to the number of the second sub-pores is too small, among the first micropores, the number of the first sub-pores is much smaller than that of the second sub-pores. Then, among the first micropores, the second sub-pores with larger pore diameters account for the majority of the first micropores, making the volume fraction of the first micropores in the positive electrode material 100 still large, and then making the volume fraction of the pores occupying the positive electrode material 100 large. During the compaction process of the positive electrode material 100, the positive electrode material 100 is easy to break, resulting in smaller compaction density of the positive electrode material 100, compaction density of the positive electrode sheet 200, and energy density of the battery 300.

[0059] In some embodiments, the active material further includes second micropores. The pore diameter D4 of the second micropores satisfies the range 500 nm < D4 ≤ 1000 nm, and the percentage γ of the number of the second micropores in the pores satisfies the range: 0 < γ < 10%.

[0060] Specifically, the value of the aperture D4 of the second fine hole can be, but is not limited to, 500nm, 520nm, 550nm, 580nm, 600nm, 620nm, 680nm, 700nm, 750nm, 780nm, 800nm, 820nm, 850nm, 880nm, 900nm, 920nm, 950nm, 980nm and 1000nm.

[0061] Specifically, the percentage γ of the second fine pores to the total number of pores can be, but is not limited to, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 2%, 2.5%, 2.8%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.2%, and 9.9%.

[0062] Understandably, the diameter of the second fine hole is larger than the diameter of the first fine hole; in other words, the diameter of the second fine hole is larger than the diameter of the first sub-hole and also larger than the diameter of the second sub-hole.

[0063] Understandably, in the pores, the number of the second pores is less than the number of the first pores.

[0064] In this embodiment, the active material includes first fine pores and second fine pores. The pore diameter D4 of the second fine pores satisfies the range 500 nm < D4 ≤ 1000 nm. Then, the pore diameter of the second fine pores is larger than that of the first fine pores, and the percentage γ of the number of the second fine pores in the pores satisfies the range: 0 < γ < 10%. Then, in the pores, the number of the second fine pores is much smaller than that of the first fine pores. The percentage γ of the number of the second fine pores in the pores is within a reasonable range. On the one hand, the number of the second fine pores is less than that of the first fine pores, which can avoid increasing the volume fraction of the pores in the positive electrode material 100 due to the excessive number of the second fine pores, thereby improving the tap density of the positive electrode material 100. When the positive electrode material 100 is applied to the positive electrode plate 200 and assembled in the battery 300, the tap density of the positive electrode plate 200 and the energy density of the battery 300 are both relatively high. On the other hand, there are second fine pores with larger pore diameters in the pores. When the positive electrode material 100 is applied to the positive electrode plate 200 and assembled in the battery 300, the performance of the positive electrode material 100 to absorb the electrolyte 310 can be improved, and the blocking of the insertion and extraction of active ions inside the battery 300 in the positive electrode material 100 can be avoided, so that the battery 300 has both a relatively high energy density and excellent cycle performance. When the percentage γ of the number of the second fine pores in the pores is too large, then in the pores, the number of the second fine pores with larger pore diameters is excessive, resulting in an increase in the volume fraction of the pores in the positive electrode material 100, so that the tap density of the positive electrode material 100 is too small. When the positive electrode material 100 is applied to the positive electrode plate 200 and assembled in the battery 300, the tap density of the positive electrode plate 200 and the energy density of the battery 300 are too small.

[0065] In some embodiments, the active material further includes third fine pores. The pore diameter D5 of the third fine pores satisfies the range D5 > 1000 nm, and the percentage δ of the number of the third fine pores in the pores satisfies the range: 0 ≤ δ < 5%.

[0066] Specifically, the value of the pore diameter D5 of the third fine pores can be, but is not limited to, 1050 nm, 1080 nm, 1100 nm, 1150 nm, 1200 nm, 1250 nm, 1300 nm, 1350 nm, etc.

[0067] Specifically, the value of the percentage δ of the number of the third fine pores in the pores can be, but is not limited to, 0, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.7%, 4%, 4.2%, 4.5%, 4.7%, 4.8%, 4.9%, etc.

[0068] Preferably, the percentage δ of the number of pores to the third micropore is 0; in other words, the pores do not include the third micropore.

[0069] Understandably, in the pores of the positive electrode material 100, the diameters of the first fine pore, the second fine pore, and the third fine pore increase sequentially; in other words, the diameters of the first sub-pore, the second sub-pore, the second fine pore, and the third fine pore increase sequentially.

[0070] In this embodiment, the active material includes a first micropore, a second micropore, and a third micropore, and the pore diameter D5 of the third micropore satisfies the range D5 > 1000 nm. The pore diameters of the first, second, and third micropores increase sequentially. The percentage δ of the third micropores in the total number of pores satisfies the range 0 ≤ δ < 5%. Therefore, the number of the larger-diameter third micropores in the pores is much smaller than the number of the first micropores, and they only occupy a very small portion of the pores. This avoids increasing the volume fraction of pores in the positive electrode material 100 due to an excessive number of third micropores, thereby improving the compaction density of the positive electrode material 100. When the positive electrode material 100 is applied to the positive electrode sheet 200 and assembled in the battery 300, both the compaction density of the positive electrode sheet 200 and the energy density of the battery 300 are high. When the percentage δ of the third fine pores in the total number of pores is too large, the number of the third fine pores with the largest pore size is excessive, increasing the volume fraction of pores in the positive electrode material 100, thereby resulting in an insufficient compaction density of the positive electrode material 100. When the positive electrode material 100 is applied to the positive electrode sheet 200 and assembled in the battery 300, both the compaction density of the positive electrode sheet 200 and the energy density of the battery 300 are insufficient.

[0071] Optionally, in some embodiments, the number of the first pores, the number of the second pores, and the number of the third pores in the pores of the positive electrode material 100 decrease sequentially; in other words, the number of the first sub-pores, the number of the second sub-pores, the number of the second pores, and the number of the third pores decrease sequentially. In other embodiments, the number of the first pores is greater than the number of the second pores, and the number of the second pores is greater than the number of the third pores; in other words, the number of the second pores may be greater than or equal to the number of the third pores, or it may be less than the number of the third pores.

[0072] Optionally, when the pores include a first pore, a second pore, and a third pore, the percentage of the first pore in the total number of pores, α, the percentage of the second pore in the total number of pores, and the percentage of the third pore in the total number of pores, δ, satisfy the relationship: α > γ > δ.

[0073] In this embodiment, the number of the first pore, the number of the second pore, and the number of the third pore decrease sequentially. Thus, the first pore, the second pore, and the third pore exhibit a gradient distribution in the pores. The first pore with the smallest pore size is used to reduce the compaction density of the positive electrode material 100, while the second pore with a moderate pore size and the third pore with the largest pore size are used to improve the absorption performance of the positive electrode material 100 of the electrolyte 310, thereby avoiding obstruction of the transport of active ions inside the battery 300. This allows the battery 300 to have both high energy density and good charge and discharge performance.

[0074] In some embodiments, the compaction density ρ of the positive electrode material 100 satisfies the range of 2.0 g / cm³. 3 ≤ρ≤2.3g / cm 3 .

[0075] Specifically, the compaction density ρ of the positive electrode material 100 can be, but is not limited to, 2.0 g / cm³. 3 2.03 g / cm 3 2.05g / cm 3 2.08 g / cm 3 2.1g / cm 3 2.11 g / cm 3 2.13 g / cm 3 2.15g / cm 3 2.18 g / cm 3 2.2g / cm 3 2.22 g / cm 3 2.25g / cm 3 2.28g / cm 3 and 3g / cm 3 wait.

[0076] In this embodiment, the compaction density ρ of the positive electrode material 100 satisfies the range of 2.0 g / cm³. 3 ≤ρ≤2.3g / cm 3 The pores include first, second, and third micropores with different pore sizes. The first micropores, with the smallest pore size, constitute the largest percentage of the pores, significantly reducing the volume fraction of pores in the cathode material 100. This results in the cathode material 100 exhibiting strong compressive strength, thereby increasing its compaction density to within the range of 2.0 g / cm³. 3 ≤ρ≤2.3g / cm 3 .

[0077] In some embodiments, the positive electrode material 100 includes a plurality of positive electrode particles, each positive electrode particle including a coating layer and the active material, the coating layer covering the outer periphery of the active material, and the mass fraction w of the coating layer in the positive electrode particles satisfying the range: 1% ≤ w ≤ 4%.

[0078] Specifically, the mass fraction w of the coating layer can be, but is not limited to, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.6%, 2.8%, 3%, 3.2%, 3.3%, 3.5%, 3.7%, 3.8%, 3.9%, and 4%.

[0079] Understandably, the mass fraction of the coating layer is the ratio of the mass of the coating layer to the mass of the positive electrode particle.

[0080] In this embodiment, when the mass fraction w of the coating layer satisfies the range of 1% ≤ w ≤ 4%, the value of the mass fraction of the coating layer is within a reasonable range.

[0081] When the positive electrode particles are applied to the positive electrode sheet 200 and assembled in the battery 300, the coating layer can improve the conductivity of the positive electrode material 100. The porosity of the active material is relatively small, which is beneficial for the positive electrode particles to have both good conductivity and high compaction density. When the positive electrode particles are applied to the positive electrode sheet 200 and assembled in the battery 300, the positive electrode sheet 200 has both good conductivity and high compaction density, and the battery 300 has both high charge / discharge efficiency and high energy density. When the mass fraction of the coating layer is too large, the mass fraction of the active material in the positive electrode particles is correspondingly too small. When the positive electrode particles are applied to the positive electrode sheet 200 and assembled in the battery 300, the capacity of the battery 300 is reduced, and the electrochemical performance of the battery 300 is poor. When the mass fraction of the coating layer is too small, the mass content of the coating layer in the positive electrode particles is too small, resulting in poor conductivity of the positive electrode particles. When the positive electrode particles are applied to the positive electrode sheet 200 and assembled into the battery 300, the charging and discharging efficiency of the battery 300 is low.

[0082] In some embodiments, the median particle size D50 of the cathode material 100 satisfies the range: 2μm≤D50≤10μm.

[0083] Specifically, the median particle size D50 of the cathode material 100 can be, but is not limited to, 2μm, 2.2μm, 2.3μm, 2.5μm, 2.8μm, 3μm, 3.2μm, 3.5μm, 4μm, 4.5μm, 4.8μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, and 10μm.

[0084] Understandably, the median particle size of the positive electrode material 100 is such that the number of positive electrode particles with a particle size greater than the median particle size accounts for 50% of the total number of positive electrode particles, and the number of positive electrode particles with a particle size less than the median particle size accounts for 50% of the total number of positive electrode particles.

[0085] In this embodiment, the positive electrode particle includes a coating layer and the active material, and the coating layer covers the outer periphery of the active material to improve the conductivity of the positive electrode particle. When the median particle size D50 of the positive electrode material 100 meets the range of 2μm≤D50≤10μm, the median particle size D50 of the positive electrode material 100 is within a reasonable range. When the positive electrode material 100 is applied to the positive electrode sheet 200, on the one hand, it can avoid the compaction density of the positive electrode sheet 200 being too small due to the median particle size of the positive electrode material 100, thereby making the battery 300 have a high energy density when the positive electrode sheet 200 is assembled. On the other hand, it can avoid the surface of the positive electrode sheet 200 being uneven due to the median particle size of the positive electrode material 100 being too large, thereby improving the processing performance of the positive electrode particles applied to the positive electrode sheet 200 and reducing the processing difficulty of the positive electrode particles applied to the positive electrode sheet 200, so that the battery 300 has good cycle performance when the positive electrode sheet 200 is applied to the battery 300. When the median particle size of the positive electrode material 100 is too large, large particles still protrude when the positive electrode material 100 is coated on the surface of the positive electrode current collector 210 during the application of the positive electrode material 100 to the positive electrode sheet 200. This increases the processing difficulty of applying the positive electrode material 100 to the positive electrode sheet 200 and reduces the processing performance of the positive electrode sheet 200. Consequently, when the positive electrode sheet 200 is applied to the battery 300, the internal resistance of the battery 300 increases, reducing the cycle performance of the battery 300. When the median particle size of the positive electrode material 100 is too small, although the positive electrode material 100 has a large compaction density, the small particle size of the positive electrode particles after application to the positive electrode sheet 200 still results in a low compaction density of the positive electrode sheet 200, thereby reducing the energy density of the battery 300 when the positive electrode sheet 200 is assembled into the battery 300.

[0086] Please see Figure 3This application provides a method for preparing a cathode material 100, the method being used to prepare the cathode material 100 provided in this application, the method comprising:

[0087] S101 provides a sodium source, an iron source, a phosphorus source, and a carbon source. The sodium source, iron source, phosphorus source, and carbon source are dispersed in a solvent, and acetic acid is added to mix them to obtain a slurry. The pH of the slurry satisfies the range: 2 ≤ pH < 6.

[0088] Specifically, the pH value of the slurry can be, but is not limited to, 2, 2.2, 2.3, 2.5, 2.8, 3, 3.1, 3.3, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.6, 5.8 and 5.9.

[0089] Optionally, the sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, sodium acetate, sodium hydroxide, and sodium nitrate.

[0090] Optionally, the iron source is selected from at least one of metallic iron, ferric phosphate, ferrous oxalate, ferric nitrate, metallic iron, iron oxide, and iron(II,III) oxide.

[0091] Optionally, the phosphorus source is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium pyrophosphate.

[0092] Optionally, the carbon source is selected from at least one of glucose, citric acid, oxalic acid, acetic acid, carboxymethyl cellulose, polypropylene, polystyrene, polyacrylonitrile, chitosan, ascorbic acid, polyethylene glycol, acetylene black, graphene, carbon nanotubes, sucrose, and starch.

[0093] Understandably, the chemical formula for acetic acid is CH3COOH.

[0094] Optionally, in some embodiments, the solvent is water.

[0095] S102, the slurry is sand-milled and spray-dried to obtain intermediate particles.

[0096] Understandably, sand milling can further mix the slurry obtained by mixing the sodium source, iron source, phosphorus source and carbon source, thereby improving the uniformity and stability of the mixture in the slurry and improving the overall quality and performance of the mixture in the slurry.

[0097] S103, the intermediate particles are sintered to obtain a positive electrode material 100; the positive electrode material 100 includes an active material with the chemical formula Na4Fe3(PO4)2P2O7, the active material has multiple pores, the pores include multiple first micropores, the pore size D1 of the first micropores satisfies the range D1≤500nm, and the percentage α of the number of the first micropores in the pores is in the range of 85%≤α≤98%.

[0098] In this embodiment, intermediate particles are formed by mixing, milling, and spray drying the provided sodium, iron, phosphorus, and carbon sources. These intermediate particles are then sintered to form the active material, Na4Fe3(PO4)2P2O7, from which the sodium, iron, and phosphorus sources are formed. The carbon source is carbonized to form the coating layer, which coats the outer periphery of the active material and improves the conductivity of the positive electrode particles. Understandably, both the sodium and phosphorus sources contain acid radicals, such as CO32-. 2- C2O4 2- PO4 3- HPO4 2- NO3 3- During the sintering process of the intermediate particles, the anions in the sodium and phosphorus sources decompose and generate a large amount of gas, thereby hindering the fusion of grains in the intermediate particles. This results in the active material having numerous pores with excessively large pore sizes, thus reducing the compaction density of the active material. In this embodiment, after dispersing the sodium, iron, phosphorus, and carbon sources in water, acetic acid is added to mix and obtain a slurry. Acetic acid provides H₂ to the slurry. + H + In the slurry, some acid radicals are released and combine with those from the sodium and phosphorus sources to form acids. The volatilization temperature of these acids is lower than the decomposition temperature of the corresponding salts, such as CO3 in sodium carbonate. 2- With H in the slurry +After conversion to carbonic acid, the volatilization temperature of carbonic acid is lower than the decomposition temperature of sodium carbonate. Furthermore, during the spray drying process of the slurry, most of the anions in the sodium and phosphorus sources can form acids with hydrogen ions, reducing the anion content in the sodium and phosphorus sources. This reduces the gas generated by the decomposition of anions in the sodium and phosphorus sources during the sintering of the intermediate particles, thereby reducing the pore size in the cathode material 100. Specifically, the pores include first micropores with a pore size D1 ≤ 500 nm, and the percentage of first micropores in the pores is relatively large. The percentage α of the first micropores in the pores ranges from 85% to 98%, and the number of first micropores is greater than the number of second and third micropores. This results in the cathode material 100 prepared by the method having a high compaction density. When the cathode material 100 is applied to the cathode electrode 200 and assembled in the battery 300, the battery 300 has a high energy density. When the spray drying temperature of the slurry reaches the boiling point of acetic acid, the acetic acid will evaporate, thus avoiding acetic acid residue.

[0099] In this embodiment, the acid used to adjust the pH of the slurry is acetic acid. Compared to other acids such as sulfuric acid, acetic acid is more volatile and does not introduce new impurity elements. During the drying process of the slurry, the acetic acid volatilizes to avoid introducing other impurities into the intermediate particles. Sulfuric acid, chloric acid, and nitric acid contain sulfur, chlorine, and nitrogen elements, respectively. Compared to sulfuric acid, chloric acid, and nitric acid, they introduce new impurity elements. Acetic acid, however, is composed of carbon, hydrogen, and oxygen, and its volatilization or decomposition during sintering does not introduce new impurity elements. When the pH of the slurry meets the range 2 ≤ pH < 6, the pH of the slurry is within a reasonable range. On the one hand, the H in the slurry... +When the concentration of the sodium and phosphorus sources is within a reasonable range, most of the anions in the sodium and phosphorus sources react with hydrogen ions to form acids, reducing the anion content in the sodium and phosphorus sources. During the spray drying process of the slurry, a small portion of the anions in the sodium and phosphorus sources react with hydrogen ions to form acids, which then volatilize and produce gas. This reduces the amount of gas produced by the volatilization of anions in the sodium and phosphorus sources during the sintering of the intermediate particles, resulting in a smaller pore size in the sintered cathode material 100. In other words, the percentage α of the first fine pores in the pores satisfies the range: 85% ≤ α < 98%, thus resulting in a higher compaction density of the prepared cathode material 100. Furthermore, the rate at which the anions in the sodium and phosphorus sources form acids with hydrogen ions is relatively fast, and the pH of the slurry is easily adjustable, thereby improving the efficiency of the preparation method for preparing the cathode material 100. When the pH of the slurry is too high, the acidity of the slurry is too weak; in other words, the H+ in the slurry... + If the concentration of the sodium and phosphorus sources is too low, only a small portion of the anions in the sodium and phosphorus sources will form acid with hydrogen ions in the slurry. Therefore, the content of anions in the sodium and phosphorus sources will still be high. During the spray drying process, the spray drying temperature is lower than the temperature required to decompose the anions in the sodium and phosphorus sources. Only a small portion of the anions in the sodium and phosphorus sources will form acid and volatilize. Consequently, during the sintering of the intermediate particles, most of the anions in the sodium and phosphorus sources will decompose and produce gas. This results in excessively large pore sizes in the sintered cathode material 100. In other words, the percentage of the first fine pores in the total pores may be less than 85%, leading to a low compaction density of the prepared cathode material 100. On the other hand, if the acidity of the slurry is too weak, it may reduce the rate at which the anions in the sodium and phosphorus sources form acid with hydrogen ions, thereby reducing the efficiency of the preparation method for the cathode material 100. Furthermore, acetic acid is a weak acid, and its pH is difficult to reach below 1 under normal circumstances. It requires special methods such as electrolysis or the use of strong acid catalysts to achieve this, which increases the difficulty of adjusting the pH, thereby increasing the preparation cost of the preparation method and reducing the efficiency of preparing the positive electrode material 100.

[0100] Understandably, the temperature at which the slurry is spray-dried is lower than the temperature at which the intermediate particles are sintered.

[0101] Understandably, the spray drying temperature of the slurry is higher than the volatilization temperature of the acetic acid, so that the acetic acid volatilizes during the spray drying process of the slurry, thus avoiding the introduction of impurities into the intermediate particles.

[0102] Optionally, the acetic acid has a volatilization temperature of 117.9°C.

[0103] More preferably, the pH of the slurry meets the range: 2 ≤ pH ≤ 4.

[0104] Specifically, the pH value of the slurry can be, but is not limited to, 2, 2.2, 2.3, 2.5, 2.8, 3, 3.1, 3.3, 3.5, 3.8 and 4.

[0105] Optionally, in some embodiments, the amount of acetic acid added is related to the amount of CO3 in the slurry. 2- C2O4 2- PO4 3- HPO4 2- NO3 3- The amount of acetic acid added is related to the concentration of the anion, and the relationship is: n(CH3COOH)=6n(CO3) 2- )+6n(C2O4 2- )+7n(PO4 3- )+6n(HPO4 2- )+5n(NO3 3- ), where n is the amount of substance corresponding to the acid radical ion or acetic acid within the parentheses, and n satisfies n≥0. When n=0, the acid radical ion or acetic acid within the parentheses does not exist.

[0106] In this embodiment, when the amount of acetic acid added is within a reasonable range, the acid radicals in the sodium source and phosphorus source can be fully mixed and as much acid as possible can be generated so that they can volatilize and generate gas during the drying process of the slurry. This reduces the increase in porosity of the cathode material 100 caused by the gas generation of acid radicals in the sodium source and phosphorus source during the sintering stage, thereby making the cathode material 100 have a higher compaction density.

[0107] Optionally, the sintering of the intermediate particles to obtain the cathode material 100 further includes: sieving the sintered cathode material 100 through a sieve of 200 to 600 mesh, so that the median particle size D50 of the cathode material 100 meets the range: 2μm≤D50≤10μm.

[0108] In this embodiment, after the intermediate particles are sintered, the cathode material 100 may agglomerate into a large mass. By sieving the cathode material 100 through a 200-600 mesh sieve, the median particle size D50 of the cathode material 100 can be made to meet a reasonable range. When the cathode material 100 is applied to the cathode electrode 200 and assembled into the battery 300, on the one hand, it can avoid the cathode material 100 having an excessively large median particle size, which would increase the processing difficulty of the cathode electrode 200; on the other hand, it can avoid the cathode material 100 having an excessively small median particle size, which would reduce the compaction density of the cathode electrode 200. Thus, the cathode material 100 prepared by the above preparation method has excellent performance.

[0109] Please see Figure 4 In some embodiments, the process of milling and spray drying the slurry to obtain intermediate particles includes:

[0110] S1021, the slurry is sand-milled to obtain a refined slurry, the refined slurry comprising precursor particles, the particle size D6 of the precursor particles being in the range of: D6 < 700 nm.

[0111] Specifically, the particle size D6 of the precursor particles can be, but is not limited to, 500nm, 550nm, 580nm, 590nm, 600nm, 620nm, 650nm, 670nm, 680nm, and 700nm.

[0112] S1022, the refined slurry is spray-dried to obtain the intermediate particles.

[0113] In this embodiment, the slurry is milled to obtain a refined slurry including precursor particles, thereby improving the uniformity and stability of the refined slurry, enhancing its overall performance, and resulting in better uniformity of the iron-based phosphate material in the final cathode particles, thus giving the cathode particles superior performance. In this embodiment, the particle size D6 of the precursor particles satisfies the range D6 < 700 nm. This ensures that adjacent precursor particles in the refined slurry can make sufficient and uniform contact, preventing the formation of other impurity phases from the sodium, phosphorus, and iron sources in the slurry during further sintering. This improves the purity of the final cathode material 100, thereby enhancing the charge-discharge cycle performance of the battery 300 when the cathode material 100 is applied to the cathode electrode 200 and assembled into the battery 300.

[0114] In some embodiments, the temperature at which the refined slurry is spray-dried is T1, and T1 satisfies the range: 250℃≤T1≤300℃.

[0115] Specifically, the temperature T1 for spray drying the refined slurry can be, but is not limited to, 250°C, 255°C, 260°C, 265°C, 270°C, 275°C, 280°C, 285°C, 290°C, 295°C, and 300°C.

[0116] In this embodiment, the refined slurry is spray-dried to remove water from it. When the spray-drying temperature T1 of the refined slurry meets the range of 250℃≤T1≤300℃, the spray-drying temperature is within a reasonable range. The temperature T1 reaches the volatilization temperature of the acid formed by the combination of acid radicals in the sodium and phosphorus sources with hydrogen ions in acetic acid. This causes the sodium and phosphorus sources to generate a large amount of gas and volatilize during the spray-drying process, thereby reducing the content of acid radicals in the sodium and phosphorus sources. Furthermore, during the sintering process of the intermediate particles, the gas generated by the decomposition of the remaining acid radicals in the sodium and phosphorus sources decreases, thereby reducing the pore size in the cathode material 100. This means that the percentage of the first fine pores in the pores is relatively large, and the percentage α of the first fine pores in the pores is within the range of 85% ≤ α ≤ 98%, reducing the volume fraction of pores in the cathode material 100, thus resulting in a higher compaction density of the cathode material 100. When the cathode material 100 is applied to the cathode electrode 200 and assembled into the battery 300, the battery 300 has a high energy density. However, if the spray drying temperature T1 of the refined slurry is too high, on the one hand, the sodium, iron, and phosphorus sources may undergo other side reactions. For example, the carbon in the carbon source and the iron ions in the iron source may undergo oxidation reactions, resulting in more impurities in the generated active material. This may increase the internal resistance of the battery 300, thereby affecting the cycle performance of the battery 300. On the other hand, after the refined slurry is spray-dried, a large amount of heat remains in the intermediate particles, which may cause the intermediate particles to melt or decompose due to heat absorption, leading to deterioration of the intermediate particles and reducing the performance of the preparation method for the cathode material 100. When the spray-drying temperature T1 of the refined slurry is too low, on the one hand, the spray-drying temperature is insufficient to completely dry the water in the refined slurry, leaving some solvent in the refined slurry. This causes the intermediate particles to become concentrated and viscous, which may lead to agglomeration of the intermediate particles during further sintering, thereby reducing the yield of the cathode material 100 prepared by the preparation method. On the other hand, the spray-drying temperature of the refined slurry is unlikely to reach the volatilization temperature of acetic acid, making it difficult for acetic acid to volatilize. This may result in the formation of other impurities in the cathode material 100, which may increase the internal resistance of the battery 300 and thus affect the cycle performance of the battery 300. On the other hand, during the spray drying process of the refined slurry, the temperature T1 is difficult to reach the volatilization temperature of the acid formed by the combination of the acid radical ions in the sodium source and the phosphorus source with the hydrogen ions in the acetic acid, so that most of the acid radical ions are still in the sodium source and the phosphorus source.Furthermore, during the sintering process of the intermediate particles, excessive gas is generated from the decomposition of acid radicals in the sodium and phosphorus sources. This results in excessively large pore sizes in the cathode material 100, meaning the percentage of the first fine pores in the total pore size is too small. This increases the volume fraction of pores in the cathode material 100, leading to a lower compaction density. When the cathode material 100 is applied to the cathode electrode 200 and assembled into the battery 300, the battery 300 exhibits a higher energy density.

[0117] Understandably, the temperature T1 for spray drying the refined slurry is the inlet temperature of the drying airflow entering the radiator. Then, the temperature of the drying airflow when it exits the radiator after spray drying the refined slurry is the outlet temperature T3. The outlet temperature T3 satisfies the range: 95℃≤T3≤110℃.

[0118] Specifically, the value of the outlet air temperature T3 can be, but is not limited to, 95℃, 96℃, 97℃, 98℃, 100℃, 101℃, 102℃, 103℃, 104℃, 105℃, 106℃, 107℃, 108℃, 109℃, and 110℃.

[0119] When the outlet air temperature T3 meets the range of 95℃≤T3≤110℃, the moisture in the refined slurry can be further dried to improve the dryness of the intermediate particles and ultimately improve the performance of the preparation method for preparing the cathode material 100.

[0120] In some embodiments, the sintering temperature of the intermediate particles is T2, and T2 satisfies the range: 450℃≤T2≤550℃.

[0121] Specifically, the value of the sintering temperature T2 for the intermediate particles can be, but is not limited to, 450°C, 455°C, 460°C, 465°C, 470°C, 480°C, 490°C, 500°C, 505°C, 510°C, 520°C, 530°C, 535°C, 540°C, and 550°C.

[0122] In this embodiment, during the sintering of the intermediate particles, the sodium source, phosphorus source, and iron source react to generate active material. When the sintering temperature T2 of the intermediate particles meets the range of 450℃≤T2≤550℃, as the temperature T2 increases, the atomic diffusion energy inside the active material becomes stronger, and the formation and growth rate of the sintering neck becomes faster, which is beneficial to the mutual fusion between grains. This results in the pore size of the pores in the active material becoming smaller and smaller, and ultimately the percentage α of the first fine pores in the pores meets the range of 85%≤α≤98%, which is beneficial to improving the compaction density of the cathode material 100. When the sintering temperature T2 of the intermediate particles is too high, the degree of mutual fusion between grains in the active material is too large, resulting in too small pores in the active material. This reduces the absorption performance of the active material of electrolyte 310 to a certain extent, which will hinder the transport of active ions inside the battery 300, thereby affecting the charge and discharge efficiency and cycle performance of the battery 300. When the sintering temperature T2 of the intermediate particles is too low, the degree of fusion between the grains in the active material is too small, resulting in excessively large pore sizes within the active material. In other words, the percentage α of the first fine pores in the total number of pores may be less than 85%, leading to an excessively large volume fraction of pores in the cathode material 100. Consequently, the cathode material 100 remains easily broken, resulting in a low compaction density. When the cathode material 100 is applied to the cathode electrode 200 and assembled into the battery 300, both the compaction density of the cathode electrode 200 and the energy density of the battery 300 are low.

[0123] Optionally, the sintering time for the intermediate particles is t, where t satisfies the range: 8h ≤ t ≤ 16h.

[0124] Specifically, the sintering time t for the intermediate particles can be, but is not limited to, 8h, 8.2h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h, 12h, 12.5h, 13h, 13.5h, 14h, 15h, and 16h.

[0125] In this embodiment, during the sintering of the intermediate particles, the sodium source, the phosphorus source, and the iron source react to generate active material. When the sintering temperature T2 of the intermediate particles meets the range of 450℃≤T2≤550℃ and the sintering time t of the intermediate particles meets the range of 8h≤t≤16h, as time t increases, atoms inside the active material continuously diffuse, sintering necks continuously form and grow, and the grains inside the active material continuously fuse with each other, thereby making the pore size of the pores in the active material smaller and smaller, and ultimately making the percentage α of the first fine pores in the pores meet the range of 85%≤α≤98%, which is beneficial to improving the compaction density of the positive electrode material 100. When the sintering time t of the intermediate particles is too long, the degree of fusion between the grains in the active material is too sufficient, making the pores in the active material too small, which to some extent reduces the performance of the active material in absorbing electrolyte 310, and will lead to the obstruction of active ion transport inside the battery 300, thereby affecting the charge and discharge efficiency and cycle performance of the battery 300. When the sintering time t of the intermediate particles is too short, the degree of fusion between the grains in the active material is insufficient, resulting in excessively large pore sizes within the active material. In other words, the percentage α of the first fine pores in the total number of pores may be less than 85%, leading to an excessively large volume fraction of pores in the cathode material 100. Consequently, the cathode material 100 remains easily broken, resulting in a low compaction density. When the cathode material 100 is applied to the cathode electrode 200 and assembled into the battery 300, both the compaction density of the cathode electrode 200 and the energy density of the battery 300 are low.

[0126] Optionally, the molar ratio A1 of iron in the iron source and sodium in the sodium source is in the range of 0.55≤A1≤0.75, and the molar ratio A2 of iron in the iron source and phosphorus in the phosphorus source is in the range of 0.55≤A2≤0.75, so as to facilitate the formation of the active material, and the chemical formula of the active material is Na4Fe3(PO4)2P2O7.

[0127] Specifically, the molar ratio A1 of iron in the iron source and sodium in the sodium source can be, but is not limited to, 0.55, 0.56, 0.57, 0.58, 0.59, 0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.68, 0.7, 0.71, 0.72, 0.73, 0.74, and 0.75.

[0128] Specifically, the molar ratio A2 of iron in the iron source and phosphorus in the phosphorus source can be, but is not limited to, 0.55, 0.56, 0.57, 0.58, 0.59, 0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.68, 0.7, 0.71, 0.72, 0.73, 0.74, and 0.75.

[0129] The technical solution of this application will be further described below with reference to several embodiments.

[0130] Examples 1 to 8, Comparative Example 1 and Comparative Example 2:

[0131] 1. Preparation and measurement of cathode material 100:

[0132] (1) Preparation steps of cathode material 100:

[0133] Step 1: In the preparation process of the cathode material 100 in Examples 1 to 8 and Comparative Example 1: Sodium source, iron source, phosphorus source and carbon source are provided, and the sodium source, iron source, phosphorus source and carbon source are dispersed in water, and acetic acid is added to mix and obtain a slurry; In the preparation process of the cathode material 100 in Comparative Example 2, sodium source, iron source, phosphorus source and carbon source are provided, and the sodium source, iron source, phosphorus source and carbon source are dispersed in water to obtain a slurry, that is, in the preparation process of the cathode material 100 in Comparative Example 2, acetic acid is not added to adjust the pH of the slurry.

[0134] The pH values ​​of the slurry in the preparation process of the positive electrode material 100 of Examples 1 to 8, Comparative Examples 1 and 2 are shown in Table 1.

[0135] In the preparation process of the positive electrode material 100 in Examples 1 to 8, Comparative Examples 1 and 2: the molar ratio A1 of iron element in the iron source and sodium element in the sodium source is in the range of 0.55≤A1≤0.75; the molar ratio A2 of iron element in the iron source and phosphorus element in the phosphorus source is in the range of 0.55≤A2≤0.75, and is not limited here.

[0136] Step 2: The slurry is sand-milled to obtain a refined slurry, which includes precursor particles with a particle size D6 range of D6 < 700 nm; the refined slurry is then spray-dried to obtain the intermediate particles.

[0137] The temperature at which the refined slurry is spray-dried is T1. The values ​​of T1 for the cathode material 100 in Examples 1 to 8, Comparative Examples 1 and 2 during the preparation process are shown in Table 1.

[0138] Step 3: Sinter the intermediate particles to obtain cathode material 100; wherein, the sintering temperature of the intermediate particles is T2, and the sintering time of the intermediate particles is t. The values ​​of T2 and t in the preparation process of cathode material 100 in Examples 1 to 8, Comparative Example 1 and Comparative Example 2 are shown in Table 1.

[0139] (2) Measurement of the porosity inside the positive electrode material 100:

[0140] The cross-sections of the positive electrode materials 100 obtained in Examples 1 to 8, Comparative Examples 1 and 2 obtained in the above steps were examined using a scanning electron microscope (SEM). In the active material, the percentage of the first sub-pores in the total number of pores is a1, the percentage of the second sub-pores in the total number of pores is a2, then the percentage of the first fine pores in the total number of pores α satisfies the relationship: α = a1 + a2, the ratio β of the number of the first sub-pores to the number of the second sub-pores satisfies the relationship: β = a1 / a2, the percentage of the second fine pores in the total number of pores is γ, and the percentage of the third fine pores in the total number of pores is δ.

[0141] The values ​​of a1, a2, α, β, γ and δ in Examples 1 to 8, Comparative Examples 1 and 2 are shown in Table 2.

[0142] (3) Measurement of the compaction density ρ of cathode material 100:

[0143] The compaction density ρ of the cathode material 100 was tested using the decompression method. The compaction densities ρ of the cathode materials 100 in Examples 1 to 8, Comparative Examples 1 and 2 are shown in Table 2.

[0144] 2. Preparation of positive electrode 200:

[0145] A positive electrode slurry was prepared according to the mass ratio of positive electrode material 100: polyvinylidene fluoride: acetylene black = 8:1:1. The slurry was coated onto the positive electrode current collector 210 (e.g., aluminum foil) and then cut into sheets to form the positive electrode sheets 200 of Examples 1 to 8, Comparative Examples 1 and 2.

[0146] Table 1: Preparation parameters of cathode material 100 in Examples 1 to 8, Comparative Examples 1 and 2.

[0147]

[0148] Table 2: Structural parameters of cathode materials 100 in Examples 1 to 8, Comparative Examples 1 and 2.

[0149] Comparative examples and embodiments a1 a2 α β γ δ <![CDATA[ρ(g / cm 3 )]]> Comparative Example 1 45 30 75 1.5 15 10 1.95 Comparative Example 2 35 33 68 1.06 22 10 1.9 Example 1 45 42 87 1.07 9 4 2.05 Example 2 50 39 89 1.23 8 3 2.11 Example 3 52 38 90 1.27 8 2 2.16 Example 4 50 40 90 1.25 9 1 2.20 Example 5 53 40 93 1.33 7 0 2.25 Example 6 57 38 96 1.5 5 0 2.29 Example 7 58 38 96 1.53 5 0 2.3 Example 8 58 37 95 1.57 5 0 2.29

[0150] Please refer to Tables 1 and 2. During the preparation of the cathode material 100, the slurry pH in Comparative Example 1 was 6, while in Comparative Example 2, no acetic acid was added to adjust the slurry pH, resulting in a pH of 6.2. In Examples 1 to 8, the slurry pH satisfied the range 2 ≤ pH < 6, causing the α values ​​in Examples 1 to 8 to be greater than those in Comparative Examples 1 and 2, the γ values ​​in Examples 1 to 8 to be less than those in Comparative Examples 1 and 2, and the δ values ​​in Examples 1 to 8 to be less than those in Comparative Examples 1 and 2. Furthermore, the compaction density of the cathode material 100 in Examples 1 to 8 was greater than that in Comparative Examples 1 and 2. This is because: when the slurry pH satisfied the range 2 ≤ pH < 6, the slurry pH was within a reasonable range. On the one hand, the H in the slurry... + When the concentration is within a reasonable range, most of the anions in the sodium and phosphorus sources in the slurry react with hydrogen ions to form acids, reducing the anion content in the sodium and phosphorus sources. During the spray drying process of the slurry, a small portion of the anions in the sodium and phosphorus sources react with hydrogen ions to form acids, which then volatilize and produce gas. This reduces the amount of gas produced by the decomposition of anions in the sodium and phosphorus sources during the sintering of the intermediate particles. Consequently, the pore size of the sintered cathode material 100 decreases, making the values ​​of α in Examples 1 to 8 greater than those in Comparative Examples 1 and 2. This ultimately affects the compaction density of the cathode material 100, making the compaction density of the cathode material 100 in Examples 1 to 8 greater than that in Comparative Examples 1 and 2. Furthermore, the spray drying temperature T1 of the refined slurry in Examples 1 to 8, Comparative Examples 1 and 2 all met the range of 250℃≤T1≤300℃, the sintering temperature T2 of the intermediate particles all met the range of 450℃≤T2≤550℃, and the sintering time t of the intermediate particles all met the range of 8h≤t≤16h. However, the pH of the slurry in Comparative Examples 1 and 2 did not meet the range of 2≤pH<6, resulting in a lower compaction density of the cathode material 100 in Comparative Examples 1 and 2. This indicates that even if the spray drying temperature, the sintering time and temperature of the intermediate particles meet reasonable ranges, if the pH of the slurry is not adjusted by acetic acid, the pore size of the prepared cathode material 100 cannot be reduced, resulting in a lower compaction density of the cathode material 100 in Comparative Examples 1 and 2.

[0151] Furthermore, in Examples 1 to 8, as the pH of the slurry continuously decreased, the H in the slurry... +As the concentration of the sodium and phosphorus sources gradually increases, most of the anions in the sodium and phosphorus sources react with hydrogen ions to form acids in the slurry, thus reducing the content of anions in the sodium and phosphorus sources. During the spray drying process of the slurry, most of the acids formed by the anions and hydrogen ions in the sodium and phosphorus sources volatilize, and the resulting gas evaporates. This reduces the amount of anion decomposition and gas production in the sodium and phosphorus sources during the sintering of the intermediate particles, resulting in smaller pore sizes in the sintered cathode material 100. In other words, in Examples 1 to 8, the percentage of the first fine pores in the total pores gradually increases, thereby gradually increasing the compaction density of the cathode material 100 in Examples 1 to 8. Furthermore, in Example 7, the compaction density of the cathode material 100 reaches its maximum value of 2.3 g / cm³. 3 .

[0152] Please see Figures 5 to 8 , Figure 5 The image shows the SEM spectrum of cathode material 100 in Comparative Example 2. Figure 6 This is a SEM image of the cross-section of the cathode material 100 in Comparative Example 2. Figure 7 This is the SEM spectrum of the cathode material 100 in Example 7. Figure 8 The image shown is a cross-sectional SEM image of the cathode material 100 in Example 7, for comparison. Figure 5 and Figure 6 It can be seen that by adding acetic acid to the slurry and adjusting the pH of the slurry, acetic acid provides H+ to the slurry. + H + In the slurry, some of the acid radicals in the sodium and phosphorus sources are free and combine with hydrogen ions to form acids. Furthermore, during the spray drying process of the slurry, most of the acid radicals in the sodium and phosphorus sources can combine with hydrogen ions to form acids, thereby reducing the content of acid radicals in the sodium and phosphorus sources. This reduces the amount of gas generated by the decomposition of acid radicals in the sodium and phosphorus sources during the sintering of the intermediate particles, and consequently significantly reduces the pore size of the cathode material 100.

[0153] 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 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.

[0154] 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 material, characterized in that, The positive electrode material includes an active material, the chemical formula of the active material is Na4Fe3(PO4)2P2O7, the active material has a plurality of pores, the pores include a plurality of first fine pores, the pore diameter D1 of the first fine pores satisfies the range D1≤500 nm, and the percentage α of the number of the first fine pores in the pores satisfies the range: 85%≤α≤98%; the plurality of first fine pores include first sub-pores and second sub-pores, the pore diameter D2 of the first sub-pores satisfies the range: 0<D2≤50 nm, the pore diameter D3 of the second sub-pores satisfies the range: 50 nm<D3≤500 nm, and the ratio β of the number of the first sub-pores to the number of the second sub-pores satisfies the relationship: 1≤β≤2.

2. The cathode material according to claim 1, characterized in that, The active material further includes second fine pores, the pore diameter D4 of the second fine pores satisfies the range 500 nm<D4≤1000 nm, and the percentage γ of the number of the second fine pores in the pores satisfies the range: 0<γ<10%.

3. The cathode material according to claim 2, characterized in that, The active material further includes third fine pores, the pore diameter D5 of the third fine pores satisfies the range D5>1000 nm, and the percentage δ of the number of the third fine pores in the pores satisfies the range: 0≤δ<5%.

4. The cathode material according to any one of claims 1 to 3, characterized in that, The compaction density ρ of the cathode material satisfies the range of 2.0 g / cm³. 3 ≤ρ≤2.3g / cm 3 .

5. The positive electrode material according to claim 4, characterized in that, The positive electrode material includes a plurality of positive electrode particles, the positive electrode particles include a coating layer and the active material, the coating layer coats the outer periphery of the active material, and in the positive electrode particles, the mass fraction w of the coating layer satisfies the range: 1%≤w≤4%.

6. The cathode material according to claim 5, characterized in that, The median particle size D50 of the positive electrode material satisfies the range: 2 μm≤D50≤10 μm.

7. A method for preparing a positive electrode material, characterized in that, For preparing the positive electrode material according to any one of claims 1 to 6, the preparation method includes: Providing a sodium source, an iron source, a phosphorus source and a carbon source, dispersing the sodium source, the iron source, the phosphorus source and the carbon source in a solvent, and adding acetic acid to mix to obtain a slurry, wherein the pH of the slurry satisfies the range: 2≤pH<6; Performing sand grinding and spray drying on the slurry to obtain intermediate particles; and Sintering the intermediate particles to obtain a positive electrode material; the positive electrode material includes an active material, the chemical formula of the active material is Na4Fe3(PO4)2P2O7, the active material has a plurality of pores, the pores include a plurality of first fine pores, the pore diameter D1 of the first fine pores satisfies the range D1≤500 nm, and the percentage α of the number of the first fine pores in the pores satisfies the range: 85%≤α≤98%; the plurality of first fine pores include first sub-pores and second sub-pores, the pore diameter D2 of the first sub-pores satisfies the range: 0<D2≤50 nm, the pore diameter D3 of the second sub-pores satisfies the range: 50 nm<D3≤500 nm, and the ratio β of the number of the first sub-pores to the number of the second sub-pores satisfies the relationship: 1≤β≤2.

8. The preparation method according to claim 7, characterized in that, Performing sand grinding and spray drying on the slurry to obtain intermediate particles includes: Performing sand grinding on the slurry to obtain a refined slurry, the refined slurry includes precursor particles, and the particle size D6 of the precursor particles satisfies the range: D6<700 nm; and Performing spray drying on the refined slurry to obtain the intermediate particles.

9. The preparation method according to claim 8, characterized in that, The temperature at which the refined slurry is spray-dried is T1, and T1 satisfies the range: 250℃≤T1≤300℃.

10. The preparation method according to claim 7, characterized in that, The sintering temperature of the intermediate particles is T2, and T2 satisfies the range: 450℃≤T2≤550℃; the sintering time of the intermediate particles is t, and t satisfies the range: 8h≤t≤16h.

11. A positive electrode plate, characterized in that, The positive electrode sheet includes: Positive current collector; and A positive electrode material layer is disposed on the surface of the positive electrode current collector, and the positive electrode material layer includes the positive electrode material according to any one of claims 1 to 6, or the positive electrode material prepared by the preparation method of the positive electrode material according to any one of claims 7 to 10.

12. A battery, characterized in that, The battery includes: Electrolyte: A negative electrode sheet, wherein the negative electrode sheet is at least partially immersed in the electrolyte; A separator, located on one side of the negative electrode, and at least partially immersed in the electrolyte; and The positive electrode sheet of claim 11, wherein the positive electrode sheet is disposed on the side of the diaphragm opposite to the positive electrode sheet and is at least partially immersed in the electrolyte.

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