High-compact sodium iron pyrophosphate phosphate cathode material, electrode sheet, preparation method and application thereof

Abstract

The present invention relates to the technical field of cathode materials for sodium-ion batteries. The present invention discloses a high-compactness sodium iron pyrophosphate phosphate cathode material, an electrode sheet, and a preparation method and application thereof. The preparation method includes: selecting sodium iron pyrophosphate phosphate A and sodium iron pyrophosphate phosphate B according to particle size conditions, and then calculating the mass ratio of the two based on the true density and compactness density of the sodium iron pyrophosphate phosphate A and sodium iron pyrophosphate phosphate B materials, and mixing them to obtain a high-compactness sodium iron pyrophosphate phosphate cathode material. The compactness density of the prepared sodium iron pyrophosphate phosphate cathode material is significantly increased, and the compactness density can reach 2.36 g / cm 3 or more. The electrode sheet and battery prepared by using it also show better processing performance and higher cycle stability. It is suitable for application in the preparation of cathode sheets for sodium-ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of cathode materials for sodium-ion batteries, and particularly to a high-compactness sodium iron pyrophosphate phosphate cathode material, an electrode sheet, and a preparation method and application thereof. More particularly, the present invention relates to a preparation method of a high-compactness sodium iron pyrophosphate phosphate cathode material, and other sodium iron pyrophosphate phosphate cathode materials and cathode electrode sheets prepared by using this method. Background Art

[0002] The statements in this section only provide background information related to the disclosure of the present application and may not constitute prior art.

[0003] Sodium-ion batteries have developed rapidly in recent years due to their high safety and long life characteristics, as well as low cost, easy availability of materials, environmental protection, and sustainability. Poly-anion compounds are commonly used cathode materials for sodium-ion batteries. Sodium iron pyrophosphate phosphate is a typical poly-anion structure material, but its tap density is low, and it is not easy to form a dense packing between powder particles. Currently, the tap density of most prepared electrode sheets is difficult to exceed 2.2 g / cm 3 , resulting in a low energy density of the final battery and hindering the application of this material.

[0004] To improve the energy density of the battery, it is almost a consensus in the industry to develop a high-compactness sodium iron pyrophosphate phosphate cathode material.

[0005] However, when improving the tap density of the material, it often leads to a sharp decline in other properties of the material or difficult processing.

[0006] A prior art preparation method and application of a cathode material for a sodium-ion battery provide a method of dispersing a sodium source compound, an iron source mixture, and a carbon source compound in water according to a certain ratio and stirring to obtain a dispersion liquid, controlling the ratio of the sodium source compound and the iron source mixture, and preparing a cathode material for a sodium-ion battery with a higher tap density and energy density. When the tap density of the sodium iron pyrophosphate phosphate prepared by this prior art reaches 2.25, the battery prepared has a discharge capacity of 106 mAh / g at a current density of 0.1C and a voltage range of 2.0 - 4.0V; when the tap density reaches 2.29, the battery prepared has a discharge capacity of 105 mAh / g at a current density of 0.1C and a voltage range of 2.0 - 4.0V. This prior art improves from the perspective of the preparation raw materials of sodium iron pyrophosphate phosphate to prepare sodium iron pyrophosphate phosphate with a higher tap density. However, improving from the raw material level has problems such as a long preparation cycle, complex technology, difficulty in rapid application, and poor technical flexibility. Summary of the Invention

[0007] The object of the present invention is to provide a high-tap-density sodium iron pyrophosphate cathode material, a pole piece, a preparation method and an application thereof, aiming at the problems of low tap density and long production cycle of the current sodium iron pyrophosphate cathode material. The tap density of the sodium iron pyrophosphate cathode material is improved through particle size matching, and the tap density can reach 2.36 g / cm 3 or more. At the same time, while ensuring the high tap density of the material, it also has excellent electrochemical performance and processing performance.

[0008] The technical solution of the present invention is as follows:

[0009] On the one hand, the present invention provides a preparation method of a high-tap-density sodium iron pyrophosphate cathode material, comprising the following steps:

[0010] Step S1: Sodium iron pyrophosphate A and sodium iron pyrophosphate B are screened according to the following conditions:

[0011] The particle size of the material satisfies the following formula:

[0012] ≤0.3, ≤0.3, and ≤35 μm;

[0013] In the formula, , and are the particle sizes of the sodium iron pyrophosphate A material corresponding to the cumulative volume distribution percentage of the material reaching 50%, 90%, and 100% respectively;

[0014] , and are the particle sizes of the sodium iron pyrophosphate B material corresponding to the cumulative volume distribution percentage of the material reaching 50%, 90%, and 100% respectively.

[0015] Step S2: The sodium iron pyrophosphate A and sodium iron pyrophosphate B screened in step S1 are compounded according to the following mass ratio:

[0016] ;

[0017] In the formula, in the formula, is the mass of the sodium iron pyrophosphate A material; is the mass of the sodium iron pyrophosphate B material;

[0018] is the true density of the sodium iron pyrophosphate B material;

[0019] and are the powder tap densities of the sodium iron pyrophosphate A material and the sodium iron pyrophosphate B material respectively;

[0020] γ is an empirical parameter, 0 < γ <0.15.

[0021] Preferably, there are two peaks in the particle size distribution of the sodium iron pyrophosphate phosphate cathode material.

[0022] Another aspect of the present invention provides the application of the high tap density sodium iron pyrophosphate phosphate cathode material as described above in the preparation of a positive electrode sheet for a sodium ion battery.

[0023] Another aspect of the present invention provides the application of the high tap density sodium iron pyrophosphate phosphate cathode material as described above in the preparation of a sodium ion battery.

[0024] Another aspect of the present invention provides a positive electrode sheet for a sodium ion battery, which includes a positive electrode current collector and a positive electrode active material layer coated on the surface of the positive electrode current collector. The positive electrode active material layer includes the high tap density sodium iron pyrophosphate phosphate cathode material as described above, as well as a conductive agent and a binder.

[0025] The positive electrode active material layer is formed by coating a slurry prepared from the high tap density sodium iron pyrophosphate phosphate cathode material, a conductive agent, a binder, and a solvent as described above on the surface of the positive electrode current collector; wherein, the solvent can be one or more of N-methylpyrrolidone (NMP), acetone, and dimethylacetamide (DMAC). The positive electrode current collector includes any one of aluminum foil, carbon-coated aluminum foil, and perforated aluminum foil. The conductive agent includes, but is not limited to, one or more of carbon nanotubes, graphene, carbon black, and carbon fiber. The binder includes, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyacrylonitrile (PAN).

[0026] Preferably, the high tap density sodium iron pyrophosphate phosphate cathode material, the conductive agent, and the binder are configured according to the conventional ratio in the art.

[0027] According to a preferred embodiment, the maximum tap density of the positive electrode sheet for a sodium ion battery is not less than 2.35 g / cm 3 . In some embodiments, the maximum tap density of the electrode sheet can reach 2.46 g / cm 3 or more.

[0028] Another aspect of the present invention provides a sodium ion battery, which includes a positive electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on the surface of the positive electrode current collector. The positive electrode active material layer includes the high tap density sodium iron pyrophosphate phosphate cathode material as described above, as well as a conductive agent and a binder.

[0029] Compared with the existing technology, the beneficial effects of the present invention are:

[0030] 1. The high-compaction sodium iron pyrophosphate phosphate cathode material, the prepared material not only has a high compaction density, but also can maintain a large energy density. When the current density is 0.1C and the voltage range is 2.0 - 4.0V, the compaction density increases from 2.285 g / cm 3 to 2.327 g / cm 3 and the discharge capacity also increases; it combines the two major elements of compaction density and performance, which helps to comprehensively improve the competitiveness of sodium iron pyrophosphate phosphate products;

[0031] 2. Provide a preparation method of the high-compaction sodium iron pyrophosphate phosphate cathode material. By grading two materials with different particle sizes, its compaction density is improved, and the data of the true density and powder compaction density of the material are innovatively used to confirm the weight ratio of the material. The method is novel, effective and has universality, and is suitable for popularization and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 SEM images of the positive electrode sheets prepared in Example 1, Example 3, Comparative Example 1 and Comparative Example 3;

[0033] Figure 2 Particle size distribution curves of the high-compaction sodium iron pyrophosphate phosphate cathode materials prepared in Example 1 and Example 3;

[0034] Figure 3 Charge-discharge curves of the positive electrode materials prepared in Example 1 and Example 3 at a current of 0.1 C;

[0035] Figure 4 Rate performance and long cycle performance of the positive electrode materials prepared in Example 2 and Example 5. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The specific embodiments listed in the present invention are only examples of the present invention, and the present invention is not limited to the specific embodiments described below. For those skilled in the art, any equivalent modifications and substitutions to the embodiments described below are also within the scope of the present invention. Therefore, equivalent transformations and modifications made without departing from the spirit and scope of the present invention should be covered within the scope of the present invention. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. All reagents or instruments not specified by the manufacturer are conventional products that can be purchased commercially. In order to better illustrate the present invention, numerous specific details are given in the following detailed description. Those skilled in the art should understand that the present invention can still be implemented without some specific details. In other embodiments, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the gist of the present invention.

[0037] Unless otherwise defined, all technical and scientific terms used herein shall have the same meaning as commonly understood by those of ordinary skill in the art. Unless otherwise specified, the units used in this specification are all international standard units, and the numerical values and ranges of numerical values appearing in the present invention shall be understood to include the systematic errors inevitable in industrial production.

[0038] The features and properties of the present invention will be further described in detail below in conjunction with the embodiments.

[0039] Example 1

[0040] A method for preparing a high-compact sodium iron pyrophosphate phosphate cathode material, comprising the following steps:

[0041] Step S1: Sodium iron pyrophosphate A and sodium iron pyrophosphate B are screened according to the following conditions:

[0042] Select sodium iron pyrophosphate A, and measure its particle sizes to be = 1.939 μm, = 4.443 μm, = 9.907 μm; select sodium iron pyrophosphate B, and measure its particle sizes to be = 10.510 μm, = 21.064 μm, = 33.535 μm. After calculation, = 0.184, = 0.219, and or ≤ 35 μm, satisfying the foregoing relationship.

[0043] Step S2: Calculate the grading ratio of materials A and B according to the density parameters of sodium iron pyrophosphate A and sodium iron pyrophosphate B. After measurement, the powder compact densities of materials A and B are respectively = 2.203 g / cm 3 , = 2.185 g / cm 3 , and the true density of material B is = 2.998 g / cm 3 . After calculation, = 0.273. Therefore, the optimized mass ratio of the composite of materials A and B is 0.273 ≤ ≤ 0.423.

[0044] Step S3: Sodium iron pyrophosphate A and sodium iron pyrophosphate B are weighted according to the mass ratios of 0.28:1, 0.38:1 and 0.42:1 respectively, and are mixed evenly by a horizontal tank mill to obtain high tap density sodium iron pyrophosphate cathode materials C1, C2 and C3. The tap densities of the powders of the high tap density sodium iron pyrophosphate cathode materials C1, C2 and C3 are measured to be 2.278 g / cm 3 、2.327 g / cm 3 、2.330 g / cm 3 respectively.

[0045] Step S4: The above cathode active materials are made into cathode plates. Weigh a certain mass of high tap density sodium iron pyrophosphate cathode material C, Super-P and PVDF powder according to the mass ratio of 95:2.5:2.5, add an appropriate amount of N-methylpyrrolidone (NMP) thereto, control the solid content of the slurry to be about 50 wt.%, and obtain a cathode slurry after mixing evenly by a centrifuge; coat both sides of the aluminum foil with the cathode slurry and obtain a cathode plate after drying. Test the maximum tap density of the cathode plate without particle breakage. The maximum tap densities of the cathode plates using C1, C2 and C3 as cathode materials are 2.375 g / cm 3 、2.415 g / cm 3 、2.417 g / cm 3 respectively.

[0046] Example 2

[0047] A preparation method of a high tap density sodium iron pyrophosphate cathode material, comprising the following steps:

[0048] Step S1: Sodium iron pyrophosphate A and sodium iron pyrophosphate B are screened according to the following conditions:

[0049] Select sodium iron pyrophosphate A, and its particle sizes are measured to be =1.476μm, =3.896μm, =9.076μm; select sodium iron pyrophosphate B, and its particle sizes are measured to be =10.510μm, =21.064μm, =33.535μm. After calculation, =0.140; 0.184. The particle sizes of sodium iron pyrophosphate A and sodium iron pyrophosphate B satisfy the aforementioned relationship.

[0050] Step S2: Calculate the optimized proportion of the grading of materials A and B according to the density parameters of sodium iron pyrophosphate A and sodium iron pyrophosphate B. After measurement, the powder compaction densities of materials A and B are respectively = 2.163 g / cm 3 , = 2.185 g / cm 3 , and the true density of material B is = 2.998 g / cm 3 .

[0051] According to the aforementioned relationship, the optimized mass ratio of the composite of materials A and B is 0.268 ≤ ≤ 0.418.

[0052] Step S3: Weigh materials A and B according to the mass ratios of 0.27:1, 0.35:1, and 0.41:1 respectively, and use a horizontal tank mill to mix them evenly to obtain high-compaction sodium iron pyrophosphate cathode materials C1, C2, and C3. The measured powder compaction densities of the high-compaction sodium iron pyrophosphate cathode materials C1, C2, and C3 are 2.313 g / cm 3 , 2.361 g / cm 3 , and 2.353 g / cm 3 .

[0053] Step S4: The same as Example 1. After measurement, the compaction densities of the electrode sheets made of C1, C2, and C3 are 2.392 g / cm 3 , 2.457 g / cm 3 , and 2.435 g / cm 3 .

[0054] Example 3

[0055] A preparation method of a high-compaction sodium iron pyrophosphate cathode material, comprising the following steps:

[0056] Step S1: Select sodium iron pyrophosphate A, and measure its particle sizes to be respectively = 1.079 μm, = 2.976 μm, = 7.093 μm; select sodium iron pyrophosphate B, and measure its particle sizes to be respectively = 5.490 μm, 11.779 μm, 20.534 μm. = 0.196; = 0.252; After calculation, the particle sizes of materials A and B satisfy the aforementioned relationship.

[0057] Step S2: Calculate the optimized proportion of the gradation of Material A and Material B according to the density parameters of Material A and Material B. After measurement, the powder compaction densities of Material A and Material B are respectively = 2.208 g / cm 3 , = 1.987 g / cm 3 , and the true density of Material B is = 3.085 g / cm 3 .

[0058] According to the aforementioned relationship, the optimized mass ratio of the composite of Material A and Material B is 0.396 ≤ ≤ 0.546.

[0059] Step S3: Weigh Material A and Material B according to a mass ratio of 0.45:1, and use a horizontal tank mill to mix them evenly to obtain the high-compaction sodium iron pyrophosphate phosphate cathode material C. The powder compaction density of the high-compaction sodium iron pyrophosphate phosphate cathode material C is measured to be 2.285 g / cm 3 .

[0060] Step S4: The same as Example 1. After measurement, the pole piece compaction density is 2.353 g / cm 3 .

[0061] Example 4

[0062] A preparation method of a high-compaction sodium iron pyrophosphate phosphate cathode material, comprising the following steps:

[0063] Step S1: Select sodium iron pyrophosphate phosphate A, and measure its particle sizes to be respectively = 1.079 μm, = 2.976 μm, = 7.093 μm; select sodium iron pyrophosphate phosphate B, and measure its particle sizes to be respectively = 9.781 μm, = 18.064 μm, = 25.535 μm. After calculation, = 0.110, = 0.164, and or ≤ 35 μm, meeting the aforementioned relationship.

[0064] Step S2: Calculate the optimized proportion of the gradation of Material A and Material B according to the density parameters of Material A and Material B. After measurement, the powder compaction densities of Material A and Material B are respectively = 2.208 g / cm 3 , = 2.215 g / cm 3 , and the true density of Material B is = 2.960 g / cm 3 。

[0065] According to the foregoing relationship, the optimized mass ratio of the composite of Material A and Material B is 0.251 ≤ ≤ 0.401.

[0066] Step S3: Weigh Material A and Material B according to a mass ratio of 0.40:1, and use a horizontal tank mill to mix them evenly to obtain the high-compactness sodium pyrophosphate iron phosphate cathode material C. The powder tap density of the high-compactness sodium pyrophosphate iron phosphate cathode material C is measured to be 2.304 g / cm 3 。

[0067] Step S4: The same as in Example 1. After measurement, the tap density of the electrode sheet is 2.363 g / cm 3 。

[0068] Example 5

[0069] A preparation method of a high-compactness sodium pyrophosphate iron phosphate cathode material, comprising the following steps:

[0070] Step S1: Select sodium pyrophosphate iron phosphate A, and measure its particle sizes to be = 1.177 μm, = 3.076 μm, = 6.093 μm; select sodium pyrophosphate iron phosphate B, and measure its particle sizes to be = 7.512 μm, = 12.113 μm, = 18.815 μm. After calculation, = 0.157, = 0.253, and or ≤ 35 μm, meeting the foregoing relationship.

[0071] Step S2: Calculate the optimized ratio of the grading of Material A and Material B according to the density parameters of Material A and Material B. After measurement, the powder tap densities of Material A and Material B are respectively = 2.130 g / cm 3 , = 2.105 g / cm 3 , and the true density of Material B is = 2.973 g / cm 3 。According to the foregoing relationship, the optimized mass ratio of the composite of Material A and Material B is 0.295 ≤ ≤ 0.445.

[0072] Step S3: Weigh material A and material B according to the mass ratio of 0.38:1, and use a horizontal tank mill to mix them evenly to obtain the high-compactness sodium pyrophosphate iron phosphate cathode material C. The powder tap density of the high-compactness sodium pyrophosphate iron phosphate cathode material C is measured to be 2.286 g / cm 3 .

[0073] Step S4: The same as Example 1. After measurement, the tap density of the electrode sheet is 2.369 g / cm 3 .

[0074] Comparative Example 1

[0075] A preparation method of a high-compactness sodium pyrophosphate iron phosphate cathode material includes the following steps:

[0076] It is basically similar to Example 1, and the difference between the two is that sodium pyrophosphate iron phosphate A and sodium pyrophosphate iron phosphate B are mixed according to the mass ratio of 0.18:1. After measurement, the tap density of the prepared high-compactness sodium pyrophosphate iron phosphate cathode material is 2.197 g / cm 3 , and the tap density of the electrode sheet is 2.255 g / cm 3 .

[0077] Comparative Example 2

[0078] A preparation method of a high-compactness sodium pyrophosphate iron phosphate cathode material includes the following steps:

[0079] It is basically similar to Example 2, and the difference between the two is that sodium pyrophosphate iron phosphate A and sodium pyrophosphate iron phosphate B are mixed according to the mass ratio of 0.11:1. After measurement, the tap density of the prepared high-compactness sodium pyrophosphate iron phosphate cathode material is 2.119 g / cm 3 , and the tap density of the electrode sheet is 2.207 g / cm 3 .

[0080] Comparative Example 3

[0081] A preparation method of a high-compactness sodium pyrophosphate iron phosphate cathode material includes the following steps:

[0082] It is basically similar to Example 3, and the difference between the two is that sodium pyrophosphate iron phosphate A and sodium pyrophosphate iron phosphate B are mixed according to the mass ratio of 4:1. After measurement, the tap density of the material is 2.035 g / cm 3 , and the tap density of the electrode sheet is 2.113 g / cm 3 .

[0083] Comparative Example 4

[0084] A preparation method of a high-compactness sodium pyrophosphate iron phosphate cathode material includes the following steps:

[0085] Step S1: Select sodium iron pyrophosphate A, and measure its particle sizes as = 5.490 μm, = 11.779 μm, = 20.534 μm. Select sodium iron pyrophosphate B, and measure its particle sizes as = 10.510 μm, = 21.064 μm, = 33.535 μm. After calculation, = 0.522, 0.558, which does not satisfy the foregoing relationship.

[0086] Step S2: The tap density of material A is = 1.978 g / cm 3 , = 2.203 g / cm 3 and the true density is: = 3.023 g / cm 3 .

[0087] According to the foregoing relationship, the optimized mass ratio of the composite of materials A and B is 0.245 ≤ ≤ 0.394.

[0088] Step S3: Weigh materials A and B according to a mass ratio of 0.3:1, and use a horizontal tank mill to mix them evenly to obtain a high-tap-density sodium iron pyrophosphate cathode material C. The measured tap density of the powder of the high-tap-density sodium iron pyrophosphate cathode material C is 2.142 g / cm 3 .

[0089] Step S4: The same as Example 1. After measurement, the tap density of the electrode is 2.204 g / cm 3 .

[0090] Comparative Example 5

[0091] A preparation method of a high-tap-density sodium iron pyrophosphate cathode material, comprising the following steps:

[0092] Step S1: Select sodium iron pyrophosphate A, and measure its particle sizes as = 4.030 μm, = 10.479 μm, = 20.534 μm. Select sodium iron pyrophosphate B, and measure its particle sizes as = 5.990 μm, 12.779 μm, = 26.944 μm. After calculation, = 0.734, = 0.890, which does not satisfy the aforementioned relationship.

[0093] Step S2: The compacted density of Material A is = 1.815 g / cm 3 , = 2.211 g / cm 3 and the true density is: = 3.015 g / cm 3 .

[0094] According to the aforementioned relationship, the optimized mass ratio of the composite of Materials A and B is 0.219 ≤ ≤ 0.370.

[0095] Step S3: Weigh Materials A and B according to a mass ratio of 0.3:1, and use a horizontal tank mill to mix them evenly to obtain the high-compaction sodium pyrophosphate iron phosphate cathode material C. The measured powder compacted density of the high-compaction sodium pyrophosphate iron phosphate cathode material C is 1.937 g / cm 3 .

[0096] Step S4: The same as in Example 1. After measurement, the compacted density of the electrode sheet is 2.077 g / cm 3 .

[0097] The compacted densities of the high-compaction sodium pyrophosphate iron phosphate cathode materials prepared in Examples 1-5 and Comparative Examples 1-5 were detected, and the results shown in Table 1 below were obtained:

[0098] Table 1: Compacted densities of the high-compaction sodium pyrophosphate iron phosphate cathode materials and electrode sheets prepared in Examples 1-5 and Comparative Examples 1-5

[0099]

[0100] As Figure 1 shown by the comparison between Example 1, Example 3 and Comparative Example 1 and Comparative Example 3, it can be seen with the naked eye that Examples 1 and 3 have fewer pores and higher compacted densities.

[0101] Figure 2 Shown below is the particle size comparison between Example 1 and Example 3. It can be seen from the figure that Example 1 with a higher compacted density has a particle size distribution with two peaks.

[0102] Figure 3The charge-discharge curves of the cathode materials prepared in Example 1 and Example 3 at a current of 0.1 C are shown. As can be seen from the figure, the discharge capacity of the cathode material in Example 1 at a current of 0.1 C is 105.3 mAh / g, and the discharge capacity of the cathode material in Example 3 at a current of 0.1 C is 101.5 mAh / g. Comparing the data in Table 2, it is not difficult to find that after compound modification, compared with the original material, the capacity and first Coulomb efficiency of the material hardly decay.

[0103] Figure 4 The rate performance and long cycle performance of the cathode materials prepared in Example 2 and Example 5 are shown. As can be seen from the figure, Example 2 and Example 5 exhibit excellent rate performance. The retention rates of both at a current of 1 C are greater than 90%, and the capacity retention rates at a large current of 2 C are greater than 80%, showing good rate performance. After cycling 50 times at a current of 1 C, the capacity retention rates of both are greater than 99%, showing good cycle characteristics.

[0104] The states of the cathode electrode sheets prepared in Example 1 of this application under different bending conditions show that under the condition of double-sided high compaction, the electrode sheets do not show fracture behavior after being folded in half twice, showing strong practical performance.

[0105] Sodium ion batteries are assembled from the cathode electrode sheets prepared in Examples 1-5 and Comparative Examples 1-5. The specific preparation method is as follows: in a glove box filled with nitrogen, the back of the cathode electrode sheets prepared in Examples 1-5 and Comparative Examples 1-5 of this application and the cathode electrode sheets prepared from the original materials sodium pyrophosphate iron A and sodium pyrophosphate iron B are closely attached to the center of the CR2016 cathode case. 50 μL of electrolyte is dropped to infiltrate the front of the cathode electrode sheet. Subsequently, a glass fiber separator is placed on the cathode sheet, and 100 μL of electrolyte is dropped again to infiltrate the separator. A commercial sodium sheet is placed on the separator, and the CR2016 negative electrode case is buckled. Finally, the battery is encapsulated with an automatic sealing machine to obtain a sodium ion battery. The performance parameters of the sodium ion batteries prepared from different cathode electrode sheets are as shown in Table 2 below:

[0106] Table 2: Performance parameters of sodium ion batteries assembled from different cathode electrode sheets prepared in Examples 1-5 and Comparative Examples 1-5

[0107]

[0108] The above-described embodiments only represent the specific implementation manners of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the protection scope of this application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the technical solution of this application, several deformations and improvements can still be made, and these all belong to the protection scope of this application.

Claims

1. A preparation method of a high-compactness sodium iron pyrophosphate phosphate cathode material, characterized in that It includes the following steps: Step S1: Sodium iron pyrophosphate A and sodium iron pyrophosphate B are screened and obtained according to the following conditions: The particle size of the material satisfies the following formula: ≤ 0.3, ≤ 0.3, and ≤ 35 μm; In the formula, , and are the particle sizes of the sodium iron pyrophosphate A material corresponding to the material when the cumulative volume distribution percentage of the material reaches 50%, 90% and 100% respectively. , and are the particle sizes of the sodium iron pyrophosphate phosphate B material corresponding to the material when the cumulative volume distribution percentage of the material reaches 50%, 90% and 100% respectively. Step S2: Sodium iron pyrophosphate A and sodium iron pyrophosphate B screened in Step S1 are compounded according to the following mass ratio: ； In the formula, is the mass of sodium acid pyrophosphate iron A material; is the mass of sodium acid pyrophosphate iron B material; is the true density of the sodium acid pyrophosphate iron B material; and are the powder compaction densities of sodium acid pyrophosphate iron A material and sodium acid pyrophosphate iron B material, respectively; γ is an empirical parameter, 0 < γ < 0.

15.

2. A high-compaction sodium iron pyrophosphate phosphate cathode material, characterized in that, It is prepared by using the preparation method described in Claim 1.

3. Application of a high-compactness sodium iron pyrophosphate phosphate cathode material in preparing a cathode pole piece of a sodium ion battery, characterized in that, The high-compactness sodium iron pyrophosphate cathode material is the high-compactness sodium iron pyrophosphate cathode material described in Claim 2.

4. Application of a high-compactness sodium iron pyrophosphate phosphate cathode material in preparing a sodium-ion battery, characterized in that, The high-compactness sodium iron pyrophosphate cathode material is the high-compactness sodium iron pyrophosphate cathode material described in Claim 2.

5. A positive electrode sheet of a sodium-ion battery, characterized in that, It includes a positive current collector and a positive active material layer coated on the surface of the positive current collector. The positive active material layer includes the high-compactness sodium iron pyrophosphate cathode material described in Claim 2, as well as a conductive agent and a binder.

6. The positive electrode sheet of a sodium-ion battery according to claim 5, characterized in that, The positive current collector is any one of aluminum foil, carbon-coated aluminum foil, and perforated aluminum foil; the conductive agent is one or more of carbon nanotubes, graphene, carbon black, and carbon fiber; the binder is one or more of polyvinylidene fluoride, polytetrafluoroethylene, and polyacrylonitrile.

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