Sodium ion positive electrode sheet, preparation method thereof, and sodium ion battery

Abstract

The present application provides a sodium-ion positive electrode sheet, a preparation method thereof, and a sodium-ion battery. The above-mentioned sodium-ion positive electrode sheet comprises the following parts by mass: 90 to 98 parts of a positive electrode active material; 1 to 3 parts of a binder; 0.5 to 3 parts of a composite conductive agent; 0.5 to 4 parts of a solid sodium electrolyte; 120 to 150 parts of N-methylpyrrolidone; wherein, the solid sodium electrolyte is selected from Na 1+ x Zr2Si x P 3‑x O 12 , where 0 ≤ x ≤ 3. The above-mentioned sodium-ion positive electrode sheet, by compounding and using the composite conductive agent and Na 1+x Zr2Si x P 3‑x O 12 , where 0 ≤ x ≤ 3, the conductive network structure of the positive electrode active material is made more perfect, thereby improving the electronic conductivity of the sodium-ion electrode sheet, further improving the rate performance and cycling performance of the sodium-ion battery, effectively reducing the usage amount of the composite conductive agent, increasing more active materials within a limited volume, thereby improving the volumetric energy density of the battery, so as to better achieve a higher energy density of the sodium-ion positive electrode sheet.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and particularly to a sodium ion positive electrode sheet, a preparation method thereof, and a sodium ion battery. Background Art

[0002] Lithium ion batteries have been widely used in the fields of mobile phones, laptop computers, digital cameras, power tools, etc. due to their outstanding advantages such as high energy density, high working voltage, long cycle life, low self-discharge rate, and environmental friendliness, and are gradually expanding into the fields of new energy vehicles and energy storage. However, the high cost of lithium ion batteries and the shortage of lithium resources have limited their large-scale application in the fields of new energy vehicles and energy storage to a certain extent.

[0003] In recent years, the sodium ion battery system has received extensive attention because of its rich resources, low price, environmental friendliness, and electrochemical properties similar to those of lithium ion batteries, providing a new option for electrochemical energy storage. At present, the positive electrode materials of sodium ion batteries mainly include layered transition metal oxides, Prussian blue-based, Prussian white-based, and polyanion-type compounds.

[0004] However, these sodium ion positive electrode sheets generally have low energy density, poor power performance and cycle stability. Therefore, how to improve the energy density of the battery in a limited space and meet the requirements of power performance and cycle performance is an important problem faced by the development of sodium ion batteries. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art, and to provide a sodium ion positive electrode sheet, a preparation method thereof, and a sodium ion battery, which can improve the rate performance, high temperature storage and cycle performance of sodium ion batteries, reduce the usage amount of composite conductive agents, and achieve higher energy density of sodium ion positive electrode sheets.

[0006] The purpose of the present invention is achieved by the following technical solutions:

[0007] A sodium ion positive electrode sheet comprises the following parts by mass:

[0008]

[0009] Among them, the solid sodium electrolyte is selected from Na 1+x Zr2Si x P 3-x O 12 , and 0 ≤ x ≤ 3 in the selected solid sodium electrolyte.

[0010] In some other embodiments, the positive electrode active material includes NaFeO2, Na 2 / 3 MnO2, Na 2 / 3 Mn1 / 2 Fe 1 / 2 O2, Na 7 / 9 Cu 2 / 9 Mn 2 / 3 Fe 1 / 3 At least one of O2, Na2MnP2O7, Na2FeP2O7, Na3V2(PO4)3, Na3V2(PO4)2F3, NaFePO4, Na2MnFe(CN)6 and Na2CoFe(CN)6.

[0011] In some other embodiments, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride - hexafluoropropylene copolymer, polyimide, polyacrylonitrile and polyacrylate.

[0012] In some other embodiments, the composite conductive agent is a mixture of single - walled carbon nanotubes, multi - walled carbon nanotubes and conductive carbon black.

[0013] In some other embodiments, the mass ratio of the single - walled carbon nanotubes, the multi - walled carbon nanotubes and the conductive carbon black is (0.01 - 0.1):(0.1 - 1):(1 - 3).

[0014] A method for preparing a sodium - ion positive electrode sheet, which is used to prepare the sodium - ion positive electrode sheet in any of the above - mentioned embodiments. The method for preparing the sodium - ion positive electrode sheet includes the following steps:

[0015] Add single - walled carbon nanotubes, multi - walled carbon nanotubes, conductive carbon black and part of N - methylpyrrolidone to a ball mill for the first ball - milling operation to obtain a composite conductive paste;

[0016] Add a solid - state sodium electrolyte to the composite conductive paste for the second ball - milling operation to obtain a mixed dispersion;

[0017] Mix the positive electrode active material and the binder evenly to obtain a premix;

[0018] Add the mixed dispersion and the remaining N - methylpyrrolidone to the premix for mixing to obtain a positive electrode paste;

[0019] Coat the positive electrode paste on the surface of an aluminum foil sheet to obtain a semi - finished sodium - ion positive electrode sheet;

[0020] Dry the semi - finished sodium - ion positive electrode sheet to obtain a sodium - ion positive electrode sheet.

[0021] In some other embodiments, the time of the first ball - milling operation is 30 min - 60 min.

[0022] In some other embodiments, the time of the second ball milling operation is 20 min to 30 min.

[0023] In some other embodiments, the time of the second ball milling operation is less than that of the first ball milling operation.

[0024] A sodium-ion battery includes the sodium-ion positive electrode sheet obtained by using the preparation method of the sodium-ion positive electrode sheet described in any one of the above.

[0025] Compared with the prior art, the present invention has at least the following advantages:

[0026] 1. For the above-mentioned sodium-ion positive electrode sheet, since a composite conductive agent is introduced into the sodium-ion positive electrode sheet, the conductive network structure of the positive electrode active material is more perfect, thereby improving the electronic conductivity of the sodium-ion electrode sheet, further improving the rate performance and cycle performance of the sodium-ion battery. At the same time, the composite conductive agent contains single-walled carbon nanotubes, which can enhance the toughness of the sodium-ion positive electrode sheet, effectively avoid the phenomenon that the ion positive electrode sheet is prone to fracture, and is beneficial to the subsequent user to assemble the sodium-ion positive electrode sheet, thereby improving the production efficiency of the lithium battery.

[0027] 2. For the above-mentioned sodium-ion positive electrode sheet, since Na 1+x Zr2Si x P 3-x O 12 , where 0 ≤ x ≤ 3 is a solid-state sodium electrolyte, which has good framework structure, chemical stability and conductivity, can effectively shorten the sodium-ion transfer path, improve the sodium-ion conductivity, and thus effectively improve the rate performance, high-temperature storage and cycle performance of the sodium-ion battery. In addition, by compounding and using the composite conductive agent and Na 1+x Zr2Si x P 3-x O 12 , where 0 ≤ x ≤ 3, under the condition of ensuring the improvement of the rate performance, high-temperature storage and cycle performance of the sodium-ion positive electrode sheet, the usage amount of the composite conductive agent is effectively reduced, and more active materials are added within a limited volume, thereby improving the volume energy density of the battery, that is, a thinner and better-structured conductive network structure can be formed on the aluminum foil sheet to better achieve a higher energy density of the sodium-ion positive electrode sheet, and thus better adapt to the development of the market. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0029] Figure 1 Flow chart of the preparation method of the sodium ion positive electrode sheet according to an embodiment of the present invention;

[0030] Figure 2 For the sodium ion batteries of Example 1 of the present invention, Comparative Document 1 and Comparative Document 2, at 45 °C, cycling 300 times at 1C / 1C, the battery capacity retention rate graph was obtained;

[0031] Figure 3 Pictures of various curling structures of single-walled carbon nanotubes of the present invention. a represents the structure diagram of armchair single-walled carbon nanotubes, b represents the structure diagram of zigzag single-walled carbon nanotubes, and c represents the structure diagram of chiral single-walled carbon nanotubes. Detailed implementation manners

[0032] For ease of understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided so that the disclosure of the present invention can be understood more thoroughly and comprehensively.

[0033] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or there can also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only embodiments.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0035] This application provides a sodium ion positive electrode sheet, including the following parts by mass: 90 to 98 parts of a positive electrode active material; 1 to 3 parts of a binder; 0.5 to 3 parts of a composite conductive agent; 0.5 to 4 parts of a solid sodium electrolyte; 120 to 150 parts of N-methylpyrrolidone; wherein, the solid sodium electrolyte is selected from Na 1+x Zr2Si x P 3-x O 12 , where 0 ≤ x ≤ 3.

[0036] The above-mentioned sodium ion positive electrode sheet, due to the introduction of a composite conductive agent in the sodium ion positive electrode sheet, makes the conductive network structure of the positive electrode active material more perfect, thereby improving the electronic conductivity of the sodium ion electrode sheet, further improving the rate performance and cycling performance of the sodium ion battery. At the same time, the composite conductive agent contains single-walled carbon nanotubes, which can enhance the toughness of the sodium ion positive electrode sheet, effectively avoid the phenomenon that the ion positive electrode sheet is prone to fracture, and is beneficial to the subsequent assembly of the sodium ion positive electrode sheet by users, thereby improving the production efficiency of lithium batteries. Further, due to Na 1+x Zr2Si x P 3-x O 12 , where 0 ≤ x ≤ 3 is a solid-state sodium electrolyte, which has good framework structure, chemical stability and conductivity, can effectively shorten the sodium ion transfer path, improve the sodium ion conductivity, and thus effectively improve the rate performance, high-temperature storage and cycling performance of the sodium ion battery. In addition, by compounding and using the composite conductive agent and Na 1+x Zr2Si x P 3-x O 12 , where 0 ≤ x ≤ 3, under the condition of ensuring the improvement of the rate performance, high-temperature storage and cycling performance of the sodium ion positive electrode sheet, the usage amount of the composite conductive agent is effectively reduced, and more active materials are added within a limited volume, thereby increasing the volume energy density of the battery, that is, a thinner and better-structured conductive network structure can be formed on the aluminum foil sheet to better achieve a higher energy density of the sodium ion positive electrode sheet, and thus better adapt to the development of the market.

[0037] To better understand the technical solutions and beneficial effects of the present application, the following further elaborates on the present application in combination with specific embodiments:

[0038] A sodium ion positive electrode sheet of an embodiment includes the following parts by mass: 90 to 98 parts of positive electrode active material; 1 to 3 parts of binder; 0.5 to 3 parts of composite conductive agent; 0.5 to 4 parts of solid-state sodium electrolyte; 120 to 150 parts of N-methylpyrrolidone; wherein, the solid-state sodium electrolyte is selected from Na 1+x Zr2Si x P 3-x O 12 , where 0 ≤ x ≤ 3.

[0039] The above-mentioned sodium-ion positive electrode sheet, due to the introduction of a composite conductive agent in the sodium-ion positive electrode sheet, makes the conductive network structure of the positive electrode active material more perfect, thereby improving the electronic conductivity of the sodium-ion electrode sheet, further improving the rate performance and cycling performance of the sodium-ion battery. At the same time, the composite conductive agent contains single-walled carbon nanotubes, which can enhance the toughness of the sodium-ion positive electrode sheet, effectively avoid the phenomenon that the ion positive electrode sheet is prone to breakage, and is beneficial to the subsequent assembly of the sodium-ion positive electrode sheet by users, thereby improving the production efficiency of lithium batteries.

[0040] Furthermore, due to Na 1+x Zr2Si x P 3-x O 12 , where 0 ≤ x ≤ 3 is a solid-state sodium electrolyte, which has a good framework structure, chemical stability and conductivity, can effectively shorten the sodium-ion transfer path, improve the sodium-ion conductivity, and thus effectively improve the rate performance, high-temperature storage and cycling performance of the sodium-ion battery. In addition, by compounding and using the composite conductive agent and Na 1+ x Zr2Si x P 3-x O 12 , where 0 ≤ x ≤ 3, under the condition of ensuring the improvement of the rate performance, high-temperature storage and cycling performance of the sodium-ion positive electrode sheet, the usage amount of the composite conductive agent is effectively reduced, and more active materials are added within a limited volume, thereby improving the volume energy density of the battery, that is, a thinner and better-structured conductive network structure can be formed on the aluminum foil sheet to better achieve a higher energy density of the sodium-ion positive electrode sheet, and thus better adapt to the development of the market.

[0041] In some other embodiments, the positive electrode active material includes at least one of NaFeO2, Na 2 / 3 MnO2, Na 2 / 3 Mn 1 / 2 Fe 1 / 2 O2, Na 7 / 9 Cu 2 / 9 Mn 2 / 3 Fe 1 / 3 O2, Na2MnP2O7, Na2FeP2O7, Na3V2(PO4)3, Na3V2(PO4)2F3, NaFePO4, Na2MnFe(CN)6 and Na2CoFe(CN)6.

[0042] In some other embodiments, the adhesive includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylonitrile and polyacrylate to improve the adhesion of the positive electrode active material, composite conductive agent and solid sodium electrolyte to the aluminum foil to ensure that the prepared sodium ion positive electrode sheet is not easy to fall off.

[0043] In some other embodiments, the composite conductive agent is a mixture of single-walled carbon nanotubes, multi-walled carbon nanotubes and conductive carbon black. It can be understood that since single-walled carbon nanotubes are formed by curling a single layer of graphite into a tubular network structure, single-walled carbon nanotubes have excellent toughness and conductivity. Since multi-walled carbon nanotubes are usually carbon nanotubes formed by stacking multiple layers of coaxial graphite cylinders, they have higher strength. Since conductive carbon black has the characteristics of large specific surface area and high structure, conductive carbon black has a lower resistivity, that is, better conductivity. Therefore, the present application can enhance the toughness and strength of the composite conductive agent by compounding single-walled carbon nanotubes, conductive carbon black and conductive carbon black, so that a more complete network tubular conductive network structure with higher structural strength and more stacking numbers can be formed in the positive electrode active material.

[0044] like Figure 3 As shown, in some other embodiments, the single-walled carbon nanotube is a zigzag single-walled carbon nanotube. It can be understood that single-walled carbon nanotubes can be divided into armrest-type single-walled carbon nanotubes, zigzag single-walled carbon nanotubes and chiral single-walled carbon nanotubes according to the curling method. Since the curled end of the zigzag single-walled carbon nanotube can form a more uniform zigzag structure, the zigzag single-walled carbon nanotube can be better embedded in the multi-walled carbon nanotubes and conductive carbon black to form a network tubular composite conductive agent with high structural strength and a large number of stacking layers, thereby ensuring that the conductive network structure of the positive electrode active material has a large number of stacking layers, and also ensuring that the strength of the formed conductive network structure is high and the connection strength is good, so that the sodium ion positive electrode sheet has a good structural strength and shape, and at the same time cooperates with Na 1+x Zr2Si x P 3-x O 12 , where 0≤x≤3, so that the added Na 1+x Zr2Si x P 3-x O 12 , where 0≤x≤3, can effectively reduce the amount of composite conductive agent used while ensuring the improvement of the rate performance, high-temperature storage and cycle performance of the sodium ion positive electrode sheet, and add more active materials within a limited volume, thereby improving the volume energy density of the battery, that is, a thinner and structurally strong conductive network structure can be formed on the aluminum foil to better achieve a higher energy density of the sodium ion positive electrode sheet, thereby better adapting to market development.

[0045] Further, in some other embodiments, the mass ratio of the single-walled carbon nanotubes, the multi-walled carbon nanotubes, and the conductive carbon black is (0.01 to 0.1):(0.1 to 1):(1 to 3).

[0046] It should be noted that, compared with traditional sodium-ion batteries, the usage amount of the conductive agent in the sodium-ion positive electrode sheet is relatively high, that is, the usage amount of the conductive agent is usually 5.7 parts, so as to enable the sodium-ion battery to achieve better electrical conductivity and improve the cycle performance of the sodium-ion battery. However, due to the relatively high usage amount of the conductive agent, the thickness of the active material layer finally coated on the surface of the aluminum foil sheet is relatively thick, and thus it is impossible to ensure that the sodium-ion positive electrode sheet can achieve a thinner and higher energy density, and thus it cannot better adapt to the development of the market. Therefore, in the present application, by using (0.01 to 0.1) single-walled carbon nanotubes, (0.1 to 1) multi-walled carbon nanotubes, and (1 to 3) conductive carbon black, that is, the total usage amount of the composite conductive agent is 1.11 to 4.1 parts, it can achieve better electrical conductivity, rate performance, high-temperature storage, and cycle performance than traditional ones, and has good structural strength, so that the sodium-ion positive electrode sheet is not easily deformed and collapsed during the cyclic use process, so as to ensure that the sodium-ion battery can maintain a good structural form during the cyclic use process. Thus, under the condition of ensuring the improvement of the rate performance, high-temperature storage, and cycle performance of the sodium-ion positive electrode sheet, the usage amount of the composite conductive agent can be reduced, and more active materials can be added within a limited volume, thereby increasing the volume energy density of the battery, that is, a thinner and better-structured conductive network structure can be formed on the aluminum foil sheet to better achieve a higher and thinner energy density of the sodium-ion positive electrode sheet, and thus better adapt to the development of the market.

[0047] It is worth mentioning that in the present application, by compounding the composite conductive agent with Na 1+x Zr2Si x P 3-x O 12 , where 0 ≤ x ≤ 3, after compounding and using, the usage amounts of the single-walled carbon nanotubes and the multi-walled carbon nanotubes can be effectively reduced, especially the usage amount of the single-walled carbon nanotubes is smaller, that is, only a trace amount is required to build the conductive network structure to form a composite conductive agent with a higher structural strength and a larger number of stacked network tubes, so as to prepare a sodium-ion positive electrode sheet with an ultra-thin and higher energy density to better adapt to the development of the market.

[0048] In some other embodiments, 1.8 ≤ x ≤ 2.3. When 1.8 ≤ x ≤ 2.3, Na 1+x Zr2Si x P 3-x O 12 is in the monoclinic phase. Due to the monoclinic Na1+x Zr2Si x P 3-x O 12 There is a new high-energy Na position, which can significantly improve the bulk and total ionic conductivity, further effectively shorten the sodium ion transfer path, increase the sodium ion conductivity, thereby effectively improving the rate performance, high-temperature storage and cycling performance of sodium ion batteries, so as to further increase the high energy density of sodium ion positive electrode sheets. In addition, monoclinic Na 1+x Zr2Si x P 3-x O 12 can be well embedded in the network tubes of the composite conductive agent to form a sodium ion positive electrode sheet with good structural strength, firm connection and high conductivity, so as to avoid the phenomenon of easy deformation and collapse of the sodium ion positive electrode sheet during the recycling process, so that the sodium ion battery can maintain a good structural form during the recycling process, that is, provide a relatively stable transport channel for sodium ions.

[0049] In a preferred embodiment, Na 1+x Zr2Si x P 3-x O 12 is Na3Zr2Si2PO 12 so that there is a new high-energy Na5 in Na3Zr2Si2PO 12 to more effectively shorten the sodium ion transfer path and increase the sodium ion conductivity, thereby more effectively improving the rate performance, high-temperature storage and cycling performance of sodium ion batteries.

[0050] This application also provides a preparation method of a sodium ion positive electrode sheet. The preparation method of the sodium ion positive electrode sheet is used to prepare the sodium ion positive electrode sheet described in any of the above embodiments. The preparation method of the sodium ion positive electrode sheet includes the following steps: adding single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black and part of N-methylpyrrolidone to a ball mill for the first ball milling operation to obtain a composite conductive paste; adding a solid-state sodium electrolyte to the composite conductive paste for the second ball milling operation to obtain a mixed dispersion; mixing the positive electrode active material and the binder evenly to obtain a premix; adding the mixed dispersion and the remaining N-methylpyrrolidone to the premix for mixing operation to obtain a positive electrode paste; coating the positive electrode paste on the surface of an aluminum foil sheet to obtain a semi-finished sodium ion positive electrode sheet; drying the semi-finished sodium ion positive electrode sheet to obtain a sodium ion positive electrode sheet.

[0051] The above method for preparing the sodium ion positive electrode sheet first uses a part of N-methylpyrrolidone to perform the first ball milling operation on single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive carbon black, so that on the one hand, N-methylpyrrolidone can effectively remove the moisture inside the single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive carbon black to improve the conductivity of the sodium ion positive electrode sheet. On the other hand, since N-methylpyrrolidone is a cyclic aliphatic amide, N-methylpyrrolidone can form a denser network tubular composite conductive paste with single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive carbon black, so as to better coat the positive active material and form a sodium ion positive electrode with a more perfect conductive network structure. Then, the composite conductive paste and the solid sodium electrolyte are subjected to a second ball milling operation, so that the solid sodium electrolyte can be well dispersed in the network tubular composite conductive paste to prepare a mixed dispersion liquid with good structural strength, firm connection, high conductivity, and good dispersibility. Then, the well-dispersed mixed dispersion liquid and the remaining N-methylpyrrolidone are added to the premix for mixing operation, so as to obtain a uniformly mixed positive electrode paste, so as to coat an ultra-thin sodium ion positive electrode sheet with good structural strength, firm connection, and high conductivity on the aluminum foil sheet, so that a sodium ion battery with good rate performance, high-temperature storage, and cycling performance can be prepared subsequently.

[0052] Please refer to Figure 1 , to better understand the technical solutions and beneficial effects of the present application, the following further describes the present application in detail with specific embodiments. The method for preparing the sodium ion positive electrode sheet in one embodiment includes some or all of the following steps:

[0053] S110. Add single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, and a part of N-methylpyrrolidone to a ball mill for the first ball milling operation to obtain a composite conductive paste.

[0054] It should be noted that single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive carbon black all have a high specific surface area and porous structure, which causes the composite conductive agent to absorb moisture, resulting in a certain amount of water molecules in the composite conductive agent. The composite conductive agent with a high water content will reduce the conductivity of the sodium ion positive electrode sheet, thereby affecting the rate performance and cycling performance of the sodium ion battery. Since N-methylpyrrolidone is a cyclic aliphatic amide, an organic liquid with strong hygroscopicity and solubility, in this application, part of the N-methylpyrrolidone is subjected to a first ball milling operation with single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive carbon black, so that the N-methylpyrrolidone can better penetrate into the interior of single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive carbon black under the action of external force, thereby ensuring that the N-methylpyrrolidone can better adsorb the water molecules inside single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive carbon black, effectively removing the water content inside the composite conductive agent, thereby improving the conductivity of the sodium ion positive electrode sheet, and further improving the rate performance and cycling performance of the sodium ion battery. At the same time, because N-methylpyrrolidone is a cyclic aliphatic amide, the N-methylpyrrolidone can form a denser network tubular composite conductive slurry with single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive carbon black, so as to better coat the positive active material in the conductive network structure, making the conductive network structure more perfect, and further improving the conductivity and cycling performance of the sodium ion positive electrode sheet.

[0055] It should also be noted that due to the relatively small amount of single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive carbon black used, the N-methylpyrrolidone can more quickly remove the water content inside the composite conductive agent, and obtain a composite conductive slurry with a smaller and more uniform particle size. At the same time, adding part of the N-methylpyrrolidone can improve the dispersibility of the composite conductive agent, so as to achieve a better mixing effect with the positive active material in the subsequent process, and obtain a homogeneous positive electrode slurry with good dispersibility.

[0056] S120. Add a solid sodium electrolyte to the composite conductive slurry and perform a second ball milling operation to obtain a mixed dispersion.

[0057] It can be understood that since the solid sodium electrolyte has a good framework structure, in order to enable the solid sodium electrolyte to form a conductive network with better structural strength by combining with the network tubes in the composite conductive slurry. Therefore, in this application, the solid sodium electrolyte is added to the composite conductive slurry for a second ball milling operation, so that the monoclinic solid sodium electrolyte can better form a more perfect conductive network with the network tubular composite conductive agent, so as to prepare a mixed dispersion with good structural strength, firm connection, high conductivity, and good dispersibility.

[0058] S130. Mix the positive electrode active material and the binder evenly to obtain a premix, so as to better mix with the mixed dispersion liquid subsequently to obtain a uniformly dispersed premix.

[0059] S140. Add the mixed dispersion liquid and the remaining N-methylpyrrolidone to the premix for mixing operation to obtain a positive electrode slurry.

[0060] It can be understood that the remaining N-methylpyrrolidone can dissolve the premix well, so that the premix and the mixed dispersion liquid can have a better mixing operation, that is, the remaining N-methylpyrrolidone has good compatibility with part of the N-methylpyrrolidone in the mixed dispersion liquid, so that the composite conductive agent and the solid sodium electrolyte can be well dispersed and dissolved to obtain a positive electrode slurry with good uniformity and conductivity.

[0061] S150. Coat the positive electrode slurry on the surface of the aluminum foil sheet so that the active material, the composite conductive agent, the solid sodium electrolyte and N-methylpyrrolidone can adhere well to the surface of the aluminum foil sheet, thereby forming a semi-finished sodium ion positive electrode sheet with good structural strength and high conductivity on the surface of the aluminum foil sheet.

[0062] S160. Dry the semi-finished sodium ion positive electrode sheet to effectively remove the water molecules in the semi-finished sodium ion positive electrode sheet to obtain a sodium ion positive electrode sheet with less water content, thereby improving the conductivity and cycle performance of the sodium ion positive electrode sheet.

[0063] For the above preparation method of the sodium ion positive electrode sheet, first use part of the N-methylpyrrolidone to perform the first ball milling operation on single-walled carbon nanotubes, multi-walled carbon nanotubes and conductive carbon black, so that on the one hand, N-methylpyrrolidone can effectively remove the moisture inside the single-walled carbon nanotubes, multi-walled carbon nanotubes and conductive carbon black to improve the conductivity of the sodium ion positive electrode sheet. On the other hand, since N-methylpyrrolidone is a cyclic aliphatic amide, N-methylpyrrolidone can form a denser network tubular composite conductive slurry with single-walled carbon nanotubes, multi-walled carbon nanotubes and conductive carbon black, so as to better coat the positive electrode active material to form a sodium ion positive electrode with a more perfect conductive network structure. Then perform the second ball milling operation on the composite conductive slurry and the solid sodium electrolyte so that the solid sodium electrolyte can be well dispersed in the network tubular composite conductive slurry to prepare a mixed dispersion liquid with good structural strength, firm connection, high conductivity and good dispersibility. Then add the well-dispersed mixed dispersion liquid and the remaining N-methylpyrrolidone to the premix for mixing operation, thereby obtaining a uniformly mixed positive electrode slurry, so as to coat on the aluminum foil sheet to obtain an ultra-thin sodium ion positive electrode sheet with good structural strength, firm connection and high conductivity, so as to subsequently prepare a sodium ion battery with good rate performance, high-temperature storage and cycle performance.

[0064] In some other embodiments, the time of the first ball milling operation is 30 min to 60 min. It can be understood that if the time of the first ball milling operation is less than 30 min, it is impossible to ensure a more comprehensive mixing and uniformity effect of single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, and N-methylpyrrolidone. If the time of the first ball milling operation is less than 60 min, the strength of the network tubular structure of the composite conductive agent will be weakened, and thus it is impossible to ensure the formation of a conductive network with high structural strength and high conductivity in the positive electrode active material. Therefore, in this application, by controlling the ball milling operation time to be 30 min to 60 min, a more comprehensive mixing and uniformity effect of single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, and N-methylpyrrolidone can be ensured, so that a denser network tubular composite conductive paste can be formed, in order to better coat the positive electrode active material within the conductive network structure, thereby making the conductive network structure more perfect, and further improving the conductivity and cycle performance of the sodium ion positive electrode sheet.

[0065] In some other embodiments, the time of the second ball milling operation is 20 min to 30 min. It can be understood that by controlling the time of the second ball milling operation to be 20 min to 30 min, the solid-state sodium electrolyte can more comprehensively combine with the network tubes in the composite conductive paste to form a conductive network with good structural strength, so as to form a more perfect conductive network, thereby improving the conductivity and cycle performance of the sodium ion positive electrode sheet.

[0066] In some other embodiments, the time of the second ball milling operation is less than the time of the first ball milling operation. It can be understood that by setting a longer first ball milling operation time, the single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive carbon black can be mixed more uniformly, so as to better mix with the solid-state sodium electrolyte, improve the dispersion of the composite conductive agent in the positive electrode active material, and form a positive electrode paste with better dispersion, thereby enabling the formation of an ultra-thin sodium ion positive electrode sheet with good structural strength, firm connection, and high conductivity.

[0067] This application also provides a sodium ion battery, including the sodium ion positive electrode sheet obtained by using the sodium ion positive electrode sheet preparation method described in any one of the above. It can be understood that by using the sodium ion positive electrode sheet preparation method of the present invention, a conductive network structure with high structural strength, good conductivity, and firm connection can be prepared. Thus, while ensuring the improvement of the rate performance, high-temperature storage, and cycle performance of the sodium ion positive electrode sheet, the usage amount of the composite conductive agent is effectively reduced. Within a limited volume, more active materials can be added, thereby improving the volume energy density of the battery, that is, a thinner and better-structured conductive layer can be formed on the aluminum foil sheet to better achieve a higher energy density of the sodium ion positive electrode sheet, and further better adapt to the development of the market.

[0068] Compared with the prior art, the present invention has at least the following advantages:

[0069] 1. For the above-mentioned sodium ion positive electrode sheet, due to the introduction of a composite conductive agent into the sodium ion positive electrode sheet, the conductive network structure of the positive electrode active material is more perfect, thereby improving the electronic conductivity of the sodium ion electrode sheet, further enhancing the rate performance and cycling performance of the sodium ion battery. At the same time, the composite conductive agent contains single-walled carbon nanotubes, which can enhance the toughness of the sodium ion positive electrode sheet, effectively avoid the phenomenon that the ion positive electrode sheet is prone to breakage, and is beneficial to the subsequent assembly of the sodium ion positive electrode sheet by users, thus improving the production efficiency of lithium batteries.

[0070] 2. For the above-mentioned sodium ion positive electrode sheet, due to Na 1+x Zr2Si x P 3-x O 12 , where 0 ≤ x ≤ 3 is a solid sodium electrolyte, which has a good framework structure, chemical stability and conductivity, can effectively shorten the sodium ion transfer path, improve the sodium ion conductivity, and thus effectively improve the rate performance, high-temperature storage and cycling performance of the sodium ion battery. In addition, due to the addition of Na 1+x Zr2Si x P 3-x O 12 , where 0 ≤ x ≤ 3, while ensuring the improvement of the rate performance, high-temperature storage and cycling performance of the sodium ion positive electrode sheet, the usage amount of the composite conductive agent is effectively reduced, and more active materials can be added within a limited volume, thereby increasing the volume energy density of the battery, that is, a thinner and better-structured conductive network structure can be formed on the aluminum foil sheet to better achieve a higher energy density of the sodium ion positive electrode sheet, and thus better adapt to the development of the market.

[0071] The following are some specific examples. If "% " is mentioned, it means by weight percentage. It should be noted that the following examples do not exhaust all possible situations, and the materials used in the following examples can be obtained from commercial channels without special instructions.

[0072] Example 1

[0073] Add 0.05 kg of sawtooth single-walled carbon nanotubes, 0.329 kg of multi-walled carbon nanotubes, 1.658 kg of conductive carbon black and 20 mL of N-methylpyrrolidone to a ball mill for the first ball milling operation for 60 min to obtain a composite conductive slurry, and then add 1 kg of Na3Zr2Si2PO 12 for the second ball milling operation for 25 min to obtain a mixed dispersion; Add 96 kg of Na 2 / 3Mn 1 / 2 Fe 1 / 2Add 2 kg of O₂ and polyvinylidene fluoride to a stirrer and mix evenly to obtain a premix. Add the prepared mixed dispersion to the stirrer, continue stirring and mixing, then add 100 mL of N-methylpyrrolidone, and continue stirring for 3 h to obtain a positive electrode paste. Coat the positive electrode paste on the surface of an aluminum foil sheet to obtain a semi-finished sodium ion positive electrode sheet; dry the semi-finished sodium ion positive electrode sheet to obtain a sodium ion positive electrode sheet.

[0074] Example 2

[0075] Add 0.013 kg of single-walled carbon nanotubes, 0.222 kg of multi-walled carbon nanotubes, 1.041 kg of conductive carbon black, and 15 mL of N-methylpyrrolidone to a ball mill for the first ball milling operation for 50 min to obtain a composite conductive paste, and then add 0.5 kg of Na1Zr2Si0P3O 12 Perform the second ball milling operation for 20 min to obtain a mixed dispersion; add 90 kg of Na 2 / 3Mn 1 / 2 Fe 1 / 2 Add 0.013 kg of single-walled carbon nanotubes, 0.222 kg of multi-walled carbon nanotubes, 1.041 kg of conductive carbon black, 1 kg of O₂ and polytetrafluoroethylene to a stirrer and mix evenly to obtain a premix. Add the prepared mixed dispersion and 115 mL of N-methylpyrrolidone to the stirrer and continue stirring for 2 h to obtain a positive electrode paste. Coat the positive electrode paste on the surface of an aluminum foil sheet to obtain a semi-finished sodium ion positive electrode sheet; dry the semi-finished sodium ion positive electrode sheet to obtain a sodium ion positive electrode sheet.

[0076] Example 3

[0077] Add 0.1 kg of single-walled carbon nanotubes, 1 kg of multi-walled carbon nanotubes, 3 kg of conductive carbon black, and 30 mL of N-methylpyrrolidone to a ball mill for the first ball milling operation for 30 min to obtain a composite conductive paste, and then add 4 kg of Na4Zr2Si3P0O 12 Perform the first ball milling operation for 30 min to obtain a mixed dispersion; add 98 kg of Na 2 / 3Mn 1 / 2 Fe 1 / 2 Add 0.1 kg of single-walled carbon nanotubes, 1 kg of multi-walled carbon nanotubes, 3 kg of conductive carbon black, 3 kg of O₂ and polyvinylidene fluoride-hexafluoropropylene copolymer to a stirrer and mix evenly to obtain a premix. Add the prepared mixed dispersion and 120 mL of N-methylpyrrolidone to the stirrer and continue stirring for 3 h to obtain a positive electrode paste. Coat the positive electrode paste on the surface of an aluminum foil sheet to obtain a semi-finished sodium ion positive electrode sheet; dry the semi-finished sodium ion positive electrode sheet to obtain a sodium ion positive electrode sheet.

[0078] Example 4

[0079] Add 0.023 kg of single-walled carbon nanotubes, 0.226 kg of multi-walled carbon nanotubes, 1.752 kg of conductive carbon black, and 20 mL of N-methylpyrrolidone to a ball mill for the first ball milling operation for 60 min to obtain a composite conductive paste, and then add 0.5 kg of Na3Zr2Si2PO 12 Perform the second ball milling operation for 30 min to obtain a mixed dispersion; add 46.5 kg of Na 2 / 3 Mn 1 / 2 Fe 1 / 2 O2, 50 kg of Na2MnFe(CN)6, and 2 kg of polyvinylidene fluoride to a stirrer, mix evenly to obtain a premix, add the prepared mixed dispersion and 100 mL of N-methylpyrrolidone to the stirrer, and continue stirring for 3 h to obtain a positive electrode paste. Coat the positive electrode paste on the surface of an aluminum foil sheet to obtain a semi-finished sodium ion positive electrode sheet; dry the semi-finished sodium ion positive electrode sheet to obtain a sodium ion positive electrode sheet.

[0080] Example 5

[0081] Add 0.023 kg of single-walled carbon nanotubes, 0.226 kg of multi-walled carbon nanotubes, 1.752 kg of conductive carbon black, and 20 mL of N-methylpyrrolidone to a ball mill for the first ball milling operation for 60 min to obtain a composite conductive paste, and then add 1.5 kg of Na3Zr2Si2PO 12 Perform the second ball milling operation for 30 min to obtain a mixed dispersion; add 95.5 kg of Na 2 / 3Mn 1 / 2 Fe 1 / 2 O2, 2 kg of polyvinylidene fluoride, and 1 kg of polyacrylonitrile to a stirrer, mix evenly to obtain a premix, add the prepared mixed dispersion and 100 mL of N-methylpyrrolidone to the stirrer, and continue stirring for 3 h to obtain a positive electrode paste. Coat the positive electrode paste on the surface of an aluminum foil sheet to obtain a semi-finished sodium ion positive electrode sheet; dry the semi-finished sodium ion positive electrode sheet to obtain a sodium ion positive electrode sheet.

[0082] Example 6

[0083] Add 0.023 kg of single-walled carbon nanotubes, 0.226 kg of multi-walled carbon nanotubes, 1.752 kg of conductive carbon black, and 20 mL of N-methylpyrrolidone to a ball mill for the first ball milling operation for 60 min to obtain a composite conductive paste, and then add 3 kg of Na3Zr2Si2PO 12 Perform the second ball milling operation for 30 min to obtain a mixed dispersion; add 95 kg of Na 2 / 3 Mn 1 / 2Fe 1 / 2Add 2 kg of O₂ and polyvinylidene fluoride to a stirrer, mix evenly to obtain a premix. Add the prepared mixed dispersion and 100 mL of N-methylpyrrolidone to the stirrer, and continue stirring for 3 h to obtain a positive electrode slurry. Coat the positive electrode slurry on the surface of an aluminum foil sheet to obtain a semi-finished sodium-ion positive electrode sheet; dry the semi-finished sodium-ion positive electrode sheet to obtain a sodium-ion positive electrode sheet.

[0084] Example 7

[0085] Add 0.023 kg of single-walled carbon nanotubes, 0.226 kg of multi-walled carbon nanotubes, 1.752 kg of conductive carbon black, and 20 mL of N-methylpyrrolidone to a ball mill for the first ball milling operation for 60 min to obtain a composite conductive slurry. Then add 1 kg of Na₃Zr₂Si₂PO 12 Conduct a second ball milling operation for 30 min to obtain a mixed dispersion; add 96 kg of Na₃V₂(PO₄)₂F₃ and 2 kg of polyvinylidene fluoride to a stirrer, mix evenly to obtain a premix. Add the prepared mixed dispersion to the stirrer, continue stirring and mixing, then add 100 mL of N-methylpyrrolidone, and continue stirring for 3 h to obtain a positive electrode slurry. Coat the positive electrode slurry on the surface of an aluminum foil sheet to obtain a semi-finished sodium-ion positive electrode sheet; dry the semi-finished sodium-ion positive electrode sheet to obtain a sodium-ion positive electrode sheet.

[0086] Comparative Example 1

[0087] It is different from Example 2 in that the amount of Na₁Zr₂Si₀P₃O added is not added, and the rest remains unchanged. 12 The usage amount remains unchanged.

[0088] Comparative Example 2

[0089] It is different from Example 2 in that the amount of single-walled carbon nanotubes added is not added, that is, replace 0.013 kg of single-walled carbon nanotubes, 0.222 kg of multi-walled carbon nanotubes, and 1.041 kg of conductive carbon black in Example 2 with 0.235 kg of multi-walled carbon nanotubes and 1.041 kg of conductive carbon black, and the rest remains unchanged.

[0090] Comparative Example 3

[0091] It is different from Example 2 in that the amount of multi-walled carbon nanotubes added is not added, that is, replace 0.013 kg of single-walled carbon nanotubes, 0.222 kg of multi-walled carbon nanotubes, and 1.041 kg of conductive carbon black in Example 2 with 0.235 kg of single-walled carbon nanotubes and 1.041 kg of conductive carbon black, and the rest remains unchanged.

[0092] Comparative Example 4

[0093] It is different from Example 2 in that the amount of conductive carbon black added is not used, that is, 0.013 kg of single-walled carbon nanotubes, 0.222 kg of multi-walled carbon nanotubes, and 1.041 kg of conductive carbon black in Example 2 are replaced with 0.235 kg of single-walled carbon nanotubes and 1.041 kg of multi-walled carbon nanotubes, and the rest remains unchanged.

[0094] Comparative Example 5

[0095] It is different from Example 2 in the preparation method, that is, 0.013 kg of single-walled carbon nanotubes, 0.222 kg of multi-walled carbon nanotubes, 1.041 kg of conductive carbon black, 15 mL of N-methylpyrrolidone, and 0.5 kg of Na1Zr2Si0P3O 12 Perform ball milling operation for 70 min to obtain a mixed dispersion; add 90 kg of Na 2 / 3 Mn 1 / 2 Fe 1 / 2 O2 and 1 kg of polytetrafluoroethylene are added to the stirrer and mixed evenly to obtain a premix. The prepared mixed dispersion and 115 mL of N-methylpyrrolidone are added to the stirrer and stirred for another 2 h to obtain a positive electrode paste. The positive electrode paste is coated on the surface of an aluminum foil sheet to obtain a semi-finished sodium ion positive electrode sheet; the semi-finished sodium ion positive electrode sheet is dried to obtain a sodium ion positive electrode sheet.

[0096] Test items

[0097] Assemble the sodium ion positive electrode sheets obtained in the above Examples 1 to 4 and Comparative Examples 1 to 5 into a sodium ion battery, and perform high-temperature cycle performance detection on the sodium ion batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 5.

[0098] Detection conditions: At 45 °C, cycle 300 times at 1C / 1C, and the battery capacity retention rates are as follows in the table:

[0099]

[0100] It can be seen from the table that the sodium ion batteries prepared in Examples 1 to 4, under the condition of 45 °C, the sodium ion batteries in Examples 1 to 4 are cycled 300 times at 1C / 1C, and the battery capacity retention rate is as high as over 96.3%, which is significantly better than the battery capacity retention rates of Comparative Examples 1 to 5. Further, please refer to Figure 2 It can be seen that the battery capacity retention rate of Example 1 is as high as over 98.2%, which is significantly better than the battery capacity retention rates of Comparative Example 1 and Comparative Example 2. That is, the effect of Example 1 is the best, that is, using serrated single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, and Na3Zr2Si2PO 12For composite use, a sodium ion positive electrode sheet with a thinner thickness and good structural strength can be prepared, so that the conductive network structure of the positive electrode active material is more perfect, and the sodium ion transfer path is effectively shortened, the sodium ion conductivity is improved, thereby effectively improving the rate performance, high-temperature storage and cycling performance of the sodium ion battery, and thus better meeting the market demand.

[0101] The above embodiments only represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A sodium ion positive electrode sheet, characterized in that, It includes the following parts by mass: 90 to 98 parts of positive electrode active material; 1 to 3 parts of binder; 0.5 to 3 parts of composite conductive agent; 0.5 to 4 parts of solid sodium electrolyte; 120 to 150 parts of N-methylpyrrolidone; Among them, the solid sodium electrolyte is selected from Na 1+x Zr2Si x P 3-x O 12 , where 1.8 ≤ x ≤ 2.3; The composite conductive agent is a mixed solution of single-walled carbon nanotubes, multi-walled carbon nanotubes and conductive carbon black; and the mass ratio of the single-walled carbon nanotubes, the multi-walled carbon nanotubes and the conductive carbon black is (0.01 to 0.1):(0.1 to 1):(1 to 3); The preparation method of the sodium ion positive electrode sheet includes the following steps: Add single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black and part of N-methylpyrrolidone to a ball mill for the first ball milling operation to obtain a composite conductive paste; Add the solid sodium electrolyte to the composite conductive paste for the second ball milling operation to obtain a mixed dispersion; Mix the positive electrode active material and the binder evenly to obtain a premix; Add the mixed dispersion and the remaining N-methylpyrrolidone to the premix for mixing to obtain a positive electrode paste; Coat the positive electrode paste on the surface of an aluminum foil sheet to obtain a semi-finished sodium ion positive electrode sheet; Dry the semi-finished sodium ion positive electrode sheet to obtain the sodium ion positive electrode sheet.

2. The sodium ion positive electrode sheet according to claim 1, wherein, The positive electrode active material includes NaFeO2, Na 2 / 3 MnO2, Na 2 / 3 Mn 1 / 2 Fe 1 / 2 O2, Na 7 / 9 Cu 2 / 9 Mn 2 / 3 Fe 1 / 3 O2, at least one of Na2MnP2O7, Na2FeP2O7, Na3V2(PO4)3, Na3V2(PO4)2F3, NaFePO4, Na2MnFe(CN)6 and Na2CoFe(CN)6.

3. The sodium ion positive electrode sheet according to claim 1, wherein The binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylonitrile and polyacrylate.

4. The preparation method of the sodium ion positive electrode sheet according to claim 1, characterized in that, The time of the first ball milling operation is 30 min to 60 min.

5. The preparation method of the sodium ion positive electrode sheet according to claim 1, characterized in that, The time of the second ball milling operation is 20 min to 30 min.

6. The preparation method of the sodium ion positive electrode sheet according to claim 1, wherein The time of the second ball milling operation is less than the time of the first ball milling operation.

7. A sodium-ion battery, characterized in that, It includes the sodium ion positive electrode sheet obtained by using the preparation method of the sodium ion positive electrode sheet described in any one of claims 1 to 6.

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