Sodium battery positive plate, preparation method thereof and sodium battery

Abstract

The invention discloses a sodium battery positive plate and a preparation method thereof and a sodium battery, the preparation method of the sodium battery positive plate comprises the following steps: S1, a current collector is uniformly coated with positive slurry to obtain a coating, the positive slurry comprises NFPP, and the porosity of the current collector is 13-17%; s2, carrying out first hot rolling on the coating; the temperature of the first hot rolling is 190-210 DEG C, and the pressure of the first hot rolling is 290-310 MPa; s3, carrying out second hot rolling on the coating; the temperature of the second hot rolling is 245-255 DEG C, and the pressure of the second hot rolling is 340-360 MPa; s4, performing third hot rolling on the coating to obtain the sodium battery positive plate, wherein the temperature of the third hot rolling is 190-210 DEG C and the pressure is 290-310 MPa; the compaction density of the NFPP in the coating is greater than or equal to 2.20 g / cm < 3 >. According to the preparation method of the sodium battery positive plate provided by the invention, the interface bonding strength and the structural stability of the sodium battery positive plate are remarkably improved by controlling the pore ratio (13-17%) of the current collector and the synergistic effect of the three-stage gradient hot pressing process, and finally, the sodium battery achieves double breakthrough of high energy density and long cycle life.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium batteries, and particularly relates to a sodium battery positive plate, a preparation method thereof and a sodium battery. BACKGROUND

[0002] Sodium ion batteries have great application potential in large-scale energy storage and low-speed electric vehicles due to their abundant resources, low cost and high safety. Among them, polyanion type composite sodium iron phosphate (NFPP) positive materials have become a promising technology route in the energy storage field due to their stable three-dimensional framework structure, super-long cycle life and excellent wide-temperature performance.

[0003] However, the industrial application of NFPP materials still faces two key technical bottlenecks: 1. The compaction density of traditional NFPP materials is usually 1.9-1.95 g / cm 3 When it is increased to 2.20 g / cm 3 , the particle breakage rate exceeds 30%, resulting in micro-cracks in the electrode, which seriously hinders the ion transmission channel and affects the battery performance. 2. Under the condition that the compaction density exceeds 2.20 g / cm 3 , the capacity attenuation exceeds 40% after 500 cycles, and the main reason is that the particle breakage causes the interface side reaction to intensify, resulting in continuous decomposition of the electrolyte and consumption of active sodium, thereby accelerating the battery performance degradation; these technical bottlenecks seriously restrict the promotion of NFPP materials in high energy density and long cycle life application scenarios.

[0004] Therefore, there is an urgent need for a sodium battery positive plate, a preparation method thereof and a sodium battery to solve the problems of the prior art. SUMMARY

[0005] In view of the performance bottleneck of NFPP (Na4Fe3(PO4)2P2O7) materials in high energy density and long cycle life applications, the traditional optimization strategy usually relies on improving the porosity of the current collector. The high-porosity current collector can provide a buffer space for the expansion of NFPP particles, reduce mechanical stress concentration, thereby inhibiting particle breakage or peeling from the current collector, and prolonging the cycle life. However, this scheme faces significant challenges in practical applications: the Mohs hardness of NFPP is 4.2, while the mechanical strength of aluminum foil current collector is low, and the difference in mechanical properties between the two leads to insufficient interface bonding force, so that the rigidity of NFPP particles easily causes local deformation of the current collector during charging and discharging, intensifying the interface peeling phenomenon, and accelerating the capacity attenuation. Based on this, the purpose of the present application is to provide a sodium battery positive plate, a preparation method thereof and a sodium battery, which can enable the sodium battery to achieve a double breakthrough of high energy density and long cycle life.

[0006] To achieve the above object, the present application provides a preparation method of a sodium battery positive electrode sheet, comprising the following steps: S1, uniformly coating a positive electrode slurry on a current collector to obtain a coating layer, the positive electrode slurry comprising NFPP, and the current collector having a porosity of 13-17%; S2, performing first hot rolling on the coating layer, the first hot rolling being performed at a temperature of 190-210℃ and a pressure of 290-310MPa; S3, performing second hot rolling on the coating layer, the second hot rolling being performed at a temperature of 245-255℃ and a pressure of 340-360MPa; S4, performing third hot rolling on the coating layer to obtain the sodium battery positive electrode sheet, the third hot rolling being performed at a temperature of 190-210℃ and a pressure of 290-310MPa, and the NFPP in the coating layer having a compacted density of ≥2.20g / cm 3 .

[0007] Compared with the prior art, the present application controls the porosity of the current collector to be 13-17%, so that the current collector can withstand the high pressure of 340-360MPa in the second hot rolling stage, avoids microcracks caused by stress concentration at the edges of the pores, and retains sufficient ductility (elongation >5%) to buffer the expansion of particles during charging and discharging. In the three-stage gradient hot pressing process, the first stage (205-215℃ / 290-310MPa) uses low-temperature pre-pressing to make the pores of the current collector elastically expand and realize the shallow embedding of the 1-2μm surface layer of the NFPP particles, the second stage (245-255℃ / 340-360MPa) promotes the plastic flow of the NFPP particles to completely fill the gap between the pores of the current collector and eliminate the interface pores through high-temperature softening, and the third stage (190-210℃ / 290-310MPa) realizes the mechanical locking of the NFPP particles at the edges of the pores by the shrinkage of the current collector during cooling, thereby significantly improving the interface peeling strength and ensuring the compacted density of ≥2.2g / cm 3 . Therefore, the preparation method of the sodium battery positive electrode sheet provided by the present application realizes the significant improvement of the interface bonding strength and structural stability of the sodium battery positive electrode sheet through the synergistic effect of controlling the porosity of the current collector (13-17%) and the three-stage gradient hot pressing process, and finally realizes the breakthroughs of high energy density and long cycle life of the sodium battery.

[0008] Further, the current collector in step S1 of the present application is an aluminum foil.

[0009] Further, the particle size D50 of the NFPP in step S1 of the present application is 8.6-9.0μm, and the specific surface area BET of the NFPP is 4.4-4.5m 2 / g. Preferably, the specific surface area BET of the NFPP is 4.43 m 2 / g.

[0010] Further, the positive electrode slurry of the present application comprises, in mass fraction: 93~95 parts of NFPP (Na4Fe3(PO4)2P2O7), 1.8~2.6 parts of PVDF (polyvinylidene fluoride), 0.8~1.2 parts of SP (conductive carbon black), 0.8~1.2 parts of CNTS (carbon nanotubes). Specifically, the NFPP can be but is not limited to 93 parts, 94 parts, 95 parts; the PVDF can be but is not limited to 1.8 parts, 1.9 parts, 2.0 parts, 2.2 parts, 2.3 parts, 2.5 parts, 2.6 parts; the SP can be but is not limited to 0.8 parts, 0.9 parts, 1.0 parts, 1.1 parts, 1.2 parts; the CNTS can be but is not limited to 0.8 parts, 0.9 parts, 1.0 parts, 1.1 parts, 1.2 parts.

[0011] Further, the solid content of the positive electrode slurry of the present application is 58~62%. Specifically, the solid content of the positive electrode slurry can be but is not limited to 58%, 59%, 60%, 61%, 62%.

[0012] Further, the single-side coating density of the positive electrode slurry in step S1 of the present application is controlled to be 160~186 g / m2. 2 Specifically, the single-side coating density of the positive electrode slurry can be but is not limited to 160 g / m2, 163 g / m2, 165 g / m2, 168 g / m2, 170 g / m2, 175 g / m2, 180 g / m2, 183 g / m2, 185 g / m2, 186 g / m2. 2 2 2 2 2 2 2 2 2 2 .

[0013] Further, the thickness of the sodium battery positive electrode sheet obtained in step S4 of the present application is 168~174 μm. Specifically, the thickness of the sodium battery positive electrode sheet can be but is not limited to 168 μm, 170 μm, 171 μm, 172 μm, 173 μm, 174 μm.

[0014] Correspondingly, the second aspect of the present application provides a sodium battery positive electrode sheet, which is prepared by the above-mentioned preparation method of the sodium battery positive electrode sheet. The sodium battery positive electrode sheet has good interface bonding strength and structural stability.

[0015] Correspondingly, the third aspect of the present application provides a sodium battery, which comprises a positive electrode sheet, a negative electrode sheet, and the positive electrode sheet is the sodium battery positive electrode sheet prepared by the above-mentioned preparation method of the sodium battery positive electrode sheet or the above-mentioned sodium battery positive electrode sheet. The sodium battery has good high energy density and long cycle life.

[0016] ​​​​​​​​​Further, the active material of the negative electrode sheet of the present application is hard carbon material.

[0017] Further, the preparation of the negative electrode sheet of the present application comprises: (1) mixing hard carbon, conductive carbon black (SP), sodium carboxymethyl cellulose (CMC) and butadiene-styrene rubber (SBR) according to the mass ratio of 92~94:0.8~1.5:0.8~1.5:0.8~3.1 and adjusting the solid content to 47~50% to obtain negative electrode slurry; (2) uniformly coating the negative electrode slurry on the copper foil, controlling the single-side coating area density of the negative electrode slurry to be 60~69.5 g / m 2 ; (3) performing one-time conventional cold pressing on the coated aluminum foil, controlling the compaction density to be 0.95±0.02 g / cm 3 , and the thickness of the final negative electrode sheet to be 160±3 μm.

[0018] Further, the N / P ratio of the negative electrode sheet and the positive electrode sheet of the present application is 1.1~1.2. Preferably, the N / P ratio of the negative electrode sheet and the positive electrode sheet is 1.19.

[0019] Further, the preparation of the sodium battery of the present application comprises: preparing a roll core by winding the positive electrode sheet, the negative electrode sheet and the separator, and then performing the processes of packaging, liquid injection, high-temperature clamp formation, air extraction, shaping and capacity distribution to obtain the sodium battery. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of the current collector of the present application.

[0021] Figure 2 It is a schematic diagram of the interlocking of the NFPP and the holes on the current collector in the third gradient hot rolling in the preparation method of the present application. DETAILED DESCRIPTION

[0022] In order to better illustrate the purpose, technical scheme and beneficial effects of the present application, the present application will be further described below in combination with specific embodiments. It should be noted that the following implementation of the method is a further explanation and description of the present application, and should not be regarded as a limitation of the present application.

[0023] The first aspect of the present application provides a preparation method of a positive electrode sheet of a sodium battery, comprising the steps of: S1, uniformly coating a positive electrode slurry on a current collector to obtain a coating layer, the positive electrode slurry comprising NFPP, and the hole rate of the current collector being 13~17%; S2, performing first hot rolling on the coating layer; the temperature of the first hot rolling being 190~210℃, and the pressure being 290~310 MPa; S3, the second hot rolling is performed on the coating layer; the temperature of the second hot rolling is 245-255 DEG C, and the pressure is 340-360 MPa; S4, the third hot rolling is performed on the coating layer to obtain the sodium battery positive electrode sheet; the temperature of the third hot rolling is 190-210 DEG C, and the pressure is 290-310 MPa; the compaction density of the NFPP in the coating layer is ≥2.2 g / cm 3 .

[0024] Please refer to Figure 1 , the collective has a hole, the hole rate is 13-17%, and the hole rate of 13-17% is the balance point of the strength and flexibility of the current collector, and the hole rate of 13-17% makes the current collector withstand the pressure of 300 MPa without breaking and have sufficient ductility to allow the particles to be embedded.

[0025] Please refer to Figure 2 , in the first hot rolling (190-210 DEG C / 290-310 MPa): the low-temperature pre-pressing makes the current collector hole elastic expansion and realizes the shallow embedding of the NFPP particle surface layer of 1-2 μm. In the second hot rolling (245-255 DEG C / 340-360 MPa): the high-temperature softening promotes the plastic flow of the NFPP particles to completely fill the gap between the current collector holes and eliminate the interface pores. In the third hot rolling (190-210 DEG C / 290-310 MPa), the current collector is cooled and shrunk to realize the mechanical locking of the NFPP particles at the hole edge, so that the interface peeling strength is significantly improved and the compaction density is ≥2.20 g / cm 3 .

[0026] The application will be further described below with specific examples and comparative examples.

[0027] The aluminum foil current collector with a hole rate of 15% in examples 1-3, comparative example 3 and comparative example 4 is purchased from Jiangsu Zhongtian Technology, the model is ZT-AI-15H, the tensile strength is 200 MPa, the elongation at break is 6.2%, and the NFPP embedding depth is 2.1±0.4 μm.

[0028] The aluminum foil current collector with a hole rate of 10% in comparative example 1 is purchased from Japan JFE Mining, the model is JFA-10P, and meets the ISO / TS16949:2016 certification, the tensile strength is 255 MPa, the elongation at break is 8.5%, and the NFPP embedding depth is 0.8±0.3 μm.

[0029] The aluminum foil current collector with a hole rate of 20% in comparative example 2 is purchased from 3M Company in the United States, the model is 3M-Al-20E, and meets the UL certification E360789, the tensile strength is 165 MPa, the elongation at break is 3.1%, and the NFPP embedding depth is 3.5±0.7 μm.

[0030] The NFPP (composite sodium iron phosphate) in the positive electrode slurry in the examples and comparative examples is PN10 high compaction material of the company Prisec; the D50 is 8.8±0.2 μm; the BET is 4.43 m 2 / g.

[0031] Example 1 The present example provides a sodium battery positive electrode sheet, and the steps of the preparation method thereof include: S1, uniformly coating a positive electrode slurry on an aluminum foil current collector to obtain a coating layer, the single-sided coating density of the positive electrode slurry is 170 g / m 2 , the porosity of the current collector is 15%, wherein the positive electrode slurry includes, in mass parts: 95 parts of NFPP, 2.6 parts of PVDF, 1.2 parts of SP, and 1.2 parts of CNTS, and the solid content is 58%; S2, first heat rolling of the coating layer; the temperature of the first heat rolling is 200℃, and the pressure is 300 MPa; S3, second heat rolling of the coating layer; the temperature of the second heat rolling is 250℃, and the pressure is 350 MPa; S4, third heat rolling of the coating layer to a thickness of 170 μm to obtain a sodium battery positive electrode sheet, the temperature of the third heat rolling is 200℃, and the pressure is 300 MPa; the compaction density of the NFPP in the coating layer is 2.20 g / cm 3 .

[0032] Example 2 The present example provides a sodium battery positive electrode sheet, and the steps of the preparation method thereof include: S1, uniformly coating a positive electrode slurry on an aluminum foil current collector to obtain a coating layer, the single-sided coating density of the positive electrode slurry is 175 g / m 2 , the porosity of the current collector is 15%, wherein the positive electrode slurry includes, in mass parts: 93 parts of NFPP, 2.6 parts of PVDF, 1.1 parts of SP, and 1.2 parts of CNTS, and the solid content is 58%; S2, first heat rolling of the coating layer; the temperature of the first heat rolling is 198℃, and the pressure is 302 MPa; S3, second heat rolling of the coating layer; the temperature of the second heat rolling is 248℃, and the pressure is 355 MPa; S4, third heat rolling of the coating layer to a thickness of 170 μm to obtain a sodium battery positive electrode sheet, the temperature of the third heat rolling is 202℃, and the pressure is 301 MPa; the compaction density of the NFPP in the coating layer is 2.25 g / cm 3 .

[0033] Example 3 The present example provides a sodium battery positive electrode sheet, and the steps of the preparation method thereof include: S1, uniformly coating positive electrode slurry on an aluminum foil current collector to obtain a coating layer, the single-sided coating density of the positive electrode slurry being 180 g / m 2 , the porosity of the current collector being 15%, wherein the positive electrode slurry comprises, in mass fraction: 94 parts of NFPP, 2.5 parts of PVDF, 1.1 parts of SP, and 1.0 part of CNTS, and the solid content being 58%; S2, first heat rolling of the coating layer; the temperature of the first heat rolling being 202℃, and the pressure being 298 MPa; S3, second heat rolling of the coating layer; the temperature of the second heat rolling being 252℃, and the pressure being 348 MPa; S4, third heat rolling of the coating layer to a thickness of 171 μm to obtain a sodium battery positive electrode sheet, the temperature of the third heat rolling being 198℃, and the pressure being 298 MPa; the compaction density of the NFPP in the coating layer being 2.31 g / cm 3 .

[0034] Comparative Example 1 The present comparative example provides a sodium battery positive electrode sheet, the steps of the preparation method of which include: S1, uniformly coating positive electrode slurry on an aluminum foil current collector to obtain a coating layer, the single-sided coating density of the positive electrode slurry being 170 g / m 2 , the porosity of the current collector being 10%, wherein the positive electrode slurry comprises, in mass fraction: 95 parts of NFPP, 2.6 parts of PVDF, 1.2 parts of SP, and 1.2 part of CNTS, and the solid content being 58%; S2, first heat rolling of the coating layer; the temperature of the first heat rolling being 200℃, and the pressure being 300 MPa; S3, second heat rolling of the coating layer; the temperature of the second heat rolling being 250℃, and the pressure being 350 MPa; S4, third heat rolling of the coating layer to a thickness of 171 μm to obtain a sodium battery positive electrode sheet, the temperature of the third heat rolling being 200℃, and the pressure being 300 MPa; the compaction density of the NFPP in the coating layer being 2.18 g / cm 3 .

[0035] Comparative Example 2 The present comparative example provides a sodium battery positive electrode sheet, the steps of the preparation method of which include: S1, uniformly coating positive electrode slurry on an aluminum foil current collector to obtain a coating layer, the single-sided coating density of the positive electrode slurry being 170 g / m 2 , the porosity of the current collector being 20%, wherein the positive electrode slurry comprises, in mass fraction: 95 parts of NFPP, 2.6 parts of PVDF, 1.2 parts of SP, and 1.2 part of CNTS, and the solid content being 58%; S2, first heat rolling of the coating layer; the temperature of the first heat rolling being 200℃, and the pressure being 300 MPa; S3, second hot rolling is performed on the coating layer; the temperature of the second hot rolling is 250°C, and the pressure is 350 MPa; S4, third hot rolling is performed on the coating layer to obtain a sodium battery positive electrode sheet with a thickness of 167 μm; the temperature of the third hot rolling is 200°C, and the pressure is 300 MPa; the compacted density of the NFPP in the coating layer is 2.23 g / cm 3 .

[0036] Comparative Example 3 The present comparative example provides a sodium battery positive electrode sheet, and the steps of the preparation method thereof include: S1, uniformly coating a positive electrode slurry on an aluminum foil current collector to obtain a coating layer; the single-sided coating density of the positive electrode slurry is 170 g / m 2 ; the porosity of the current collector is 15%, wherein the positive electrode slurry includes, in mass parts: 95 parts of NFPP, 2.6 parts of PVDF, 1.2 parts of SP, and 1.2 parts of CNTS, and the solid content is 58%; S2, first hot rolling is performed on the coating layer; the temperature of the first hot rolling is 200°C, and the pressure is 300 MPa; S3, second hot rolling is performed on the coating layer to obtain a sodium battery positive electrode sheet with a thickness of 175 μm; the temperature of the second hot rolling is 250°C, and the pressure is 350 MPa; the compacted density of the NFPP in the coating layer is 2.12 g / cm 3 .

[0037] Comparative Example 4 The present comparative example provides a sodium battery positive electrode sheet, and the steps of the preparation method thereof include: S1, uniformly coating a positive electrode slurry on an aluminum foil current collector to obtain a coating layer; the single-sided coating density of the positive electrode slurry is 170 g / m 2 ; the porosity of the current collector is 15%, wherein the positive electrode slurry includes, in mass parts: 95 parts of NFPP, 2.6 parts of PVDF, 1.2 parts of SP, and 1.2 parts of CNTS, and the solid content is 58%; S2, first hot rolling is performed on the coating layer; the temperature of the first hot rolling is 200°C, and the pressure is 300 MPa; S3, second hot rolling is performed on the coating layer; the temperature of the second hot rolling is 250°C, and the pressure is 350 MPa; S4, third hot rolling is performed on the coating layer to obtain a sodium battery positive electrode sheet with a thickness of 171 μm; the temperature of the third hot rolling is 280°C, and the pressure is 350 MPa; the compacted density of the NFPP in the coating layer is 2.20 g / cm 3 .

[0038] The interface peeling strength of the sodium battery positive electrode sheet prepared from Example 1 to Example 3 and Comparative Example 1 to 4 was tested according to JIS K6854-1:2019, specifically, the test method and parameters are shown in Table 1, and the test results are shown in Table 2.

[0039] Table 1

[0040] Test procedure: 1. electrode cutting → 2. bonding polyimide film → 3. curing (80℃ / 2h) → 4. clamping peeling → 5 data recording analysis.

[0041] Table 2

[0042] The sodium battery positive electrode sheet prepared from Example 1 to Example 3 and Comparative Example 1 to 4 was applied in a sodium battery according to the following application method.

[0043] Preparation of sodium battery: (1) Preparation of negative electrode sheet: hard carbon, conductive carbon black (SP), sodium carboxymethyl cellulose (CMC) and butadiene-styrene rubber (SBR) were mixed in a mass ratio of 94:1.5:1.5:3 and the solid content was adjusted to 48% to obtain a negative electrode slurry; the negative electrode slurry was uniformly coated on a copper foil, and the single-sided coating density of the negative electrode slurry was controlled to be 69.5 g / m 2 ; the coated copper foil was subjected to one-time conventional cold pressing, and the compacted density was controlled to be 0.95 g / cm 3 , and the thickness of the final negative electrode sheet was 160 μm.

[0044] (2) The sodium battery positive electrode sheet, negative electrode sheet and separator were prepared into a roll core by winding, and then subjected to packaging, liquid injection, high-temperature fixture formation, air extraction, shaping and capacity distribution processes to obtain a sodium battery; wherein the N / P ratio of the negative electrode sheet and the positive electrode sheet in the examples and comparative examples was set as follows: the N / P ratio of Example 1 was 1.19, the N / P ratio of Example 2 was 1.15, the N / P ratio of Example 3 was 1.13, and the N / P ratio of Comparative Example 1 to 4 was all 1.19.

[0045] The cycle performance of the prepared sodium battery was tested according to GB / T37201-2018&IEC62660-1:2018, and the detailed test parameters are shown in Table 3, and the energy density calculated according to the design formula is shown in Table 4.

[0046] Table 3

[0047] Table 4

[0048] From the comparative results of Example 1 and Comparative Examples 1-2 in Tables 1-2, it can be seen that when the porosity of the current collector exceeds 17%, the porosity is too large, the current collector cannot withstand the high pressure of 340-360 MPa in the second hot rolling stage, the stress concentration at the edge of the hole causes micro-cracks, thereby causing the sodium battery positive plate interface bonding strength and structural stability to be unable to be significantly improved, and the micro-cracks expand during charging and discharging, causing the electrolyte to separate and thus the cycle performance to decrease. Correspondingly, when the porosity of the current collector is less than 13%, there is no buffer space for the expansion of the NFPP particles, thereby causing the cycle performance to decrease.

[0049] From the comparative results of Example 1 and Comparative Example 3 in Tables 1-2, it can be seen that removing the third hot rolling, the cumulative pressure is insufficient, the particle filling is incomplete, and the compaction density is not high, thereby causing the cycle performance to decrease.

[0050] From the comparative results of Example 1 and Comparative Example 4 in Tables 1-2, it can be seen that the third stage is still high temperature, for example, when the temperature of the third hot rolling is 280°C and the pressure is 350 MPa, the olivine structure of the NFPP crystal Fe-O bond breaks at greater than 260°C, causing irreversible loss of capacity, and at 280°C the tensile strength of the aluminum foil decreases to 150 MPa, which cannot withstand the compressive stress of 350 MPa, thereby causing the cycle performance to decrease.

[0051] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A method for preparing a sodium battery positive electrode sheet, characterized in that the steps include... include: S1. A positive electrode slurry is uniformly coated onto the current collector to obtain a coating, wherein the positive electrode slurry includes NFPP, and the porosity of the current collector is 13-17%. S2. The coating is subjected to a first hot rolling press; the temperature of the first hot rolling press is 190~210℃ and the pressure is 290~310MPa. S3. The coating is subjected to a second hot rolling process; The temperature of the second hot roller is 245~255℃, and the pressure is 340~360MPa; S4. The coating is subjected to a third hot rolling process to obtain a sodium battery positive electrode sheet. The temperature of the third hot rolling process is 190~210℃, and the pressure is 290~310MPa. The compaction density of NFPP in the coating is ≥2.20g / cm³. 3 .

2. The method for preparing the sodium battery positive electrode sheet as described in claim 1, characterized in that, The NFPP in step S1 has a particle size D50 of 8.6~9.0 μm and a specific surface area BET of 4.4~4.5 m². 2 / g.

3. The method for preparing the sodium battery positive electrode sheet as described in claim 1, characterized in that, The positive electrode slurry comprises, by weight, 93-95 parts NFPP, 1.8-2.6 parts PVDF, 0.8-1.2 parts SP, and 0.8-1.2 parts CNTS.

4. The method for preparing the sodium battery positive electrode sheet as described in claim 1, characterized in that, The solid content of the positive electrode slurry is 58-62%.

5. The method for preparing the sodium battery positive electrode sheet as described in claim 1, characterized in that, In step S1, the single-sided coating density of the positive electrode slurry is controlled to be 160~186 g / m². 2 .

6. The method for preparing the sodium battery positive electrode sheet as described in claim 1, characterized in that, The thickness of the sodium battery positive electrode obtained in step S4 is 168~174μm.

7. A sodium battery positive electrode sheet, characterized in that, It is prepared by the method for preparing sodium battery positive electrode sheet as described in any one of claims 1 to 6.

8. A sodium battery, comprising a positive electrode and a negative electrode, characterized in that, The positive electrode sheet is a sodium battery positive electrode sheet prepared by the method for preparing a sodium battery positive electrode sheet as described in any one of claims 1 to 6, or a sodium battery positive electrode sheet as described in claim 7.

9. The sodium battery as described in claim 8, characterized in that, The active material of the negative electrode is hard carbon material.

10. The sodium battery as described in claim 8, characterized in that, The N / P ratio of the negative electrode and the positive electrode is 1.1 to 1.2.

Images