Preparation method of positive pole piece of sodium ion battery, positive pole piece and battery

Abstract

The invention discloses a preparation method of a positive pole piece of a sodium ion battery, the positive pole piece and the battery, and the method comprises the following steps: coating two sides of a conductive substrate with first active slurry, and drying at a first preset temperature to obtain a first positive pole piece, the first active slurry comprising a first sodium ion layered oxide; the two sides of the first positive pole piece are coated with second active slurry, drying is conducted at a second preset temperature, a second positive pole piece is obtained, the second active slurry comprises second sodium ion layered oxide, and the mass fraction of sodium in the first sodium ion layered oxide is different from the mass fraction of sodium in the second sodium ion layered oxide; and rolling the second positive pole piece to obtain the sodium ion battery positive pole piece. One of the first active slurry and the second active slurry can provide main body capacity and ion rapid transmission and enhance rate capability, and the other one can be used as a functional protection layer to improve interface stability and realize functional synergy of capacity supply and interface protection.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a method for preparing a positive electrode of a sodium-ion battery, the positive electrode of a sodium-ion battery, and a sodium-ion battery. Background Technology

[0002] Sodium-ion battery layered cathode materials stand out among many cathode materials due to their simple preparation methods, easy technology transfer, high energy density, high reversible specific capacity, high rate performance, and reversible sodium-ion intercalation / deintercalation capabilities. However, single sodium-ion layered cathode materials still have many problems. For example, O3-type Ni-Fe-Mn layered oxides have a high theoretical capacity. Summary of the Invention

[0003] This application provides a method for preparing a positive electrode sheet for a sodium-ion battery, a positive electrode sheet for a sodium-ion battery, and a sodium-ion battery, which can solve at least one of the above-mentioned technical problems.

[0004] In a first aspect, one embodiment of this application discloses a method for preparing the positive electrode sheet of a sodium-ion battery, comprising: A first active paste is coated on both sides of a conductive substrate and dried at a first preset temperature to obtain a first positive electrode sheet. The first active paste includes a first sodium ion layered oxide. The second active slurry is coated on both sides of the first positive electrode sheet and dried at the second preset temperature to obtain the second positive electrode sheet. The second active slurry includes a second sodium ion layered oxide, and the mass fraction of sodium in the first sodium ion layered oxide and the second sodium ion layered oxide are different. The second positive electrode sheet is rolled to obtain a sodium-ion battery positive electrode sheet.

[0005] Secondly, one embodiment of the positive electrode sheet of this application includes: Conductive substrate; The first positive electrode is formed by coating both sides of the conductive substrate with a first active paste, wherein the first active paste includes a first sodium ion layered oxide. The second positive electrode is formed by coating both sides of the first positive electrode with a second active slurry. The second active slurry includes a second sodium ion layered oxide, and the mass fraction of sodium in the first sodium ion layered oxide and the second sodium ion layered oxide are different.

[0006] Thirdly, one embodiment of the sodium-ion battery of this application includes: The positive electrode sheet described in any of the above embodiments; and Negative electrode plate; Diaphragm; The electrolyte, the negative electrode, the separator, and the positive electrode are all disposed in the electrolyte.

[0007] The method for preparing the positive electrode sheet of a sodium-ion battery, the positive electrode sheet of the sodium-ion battery, and the sodium-ion battery according to embodiments of this application are as follows: A first positive electrode sheet is obtained by coating a first active slurry onto both sides of a conductive substrate and drying it at a first preset temperature. The first active slurry includes a first sodium-ion layered oxide. A second active slurry is coated onto both sides of the first positive electrode sheet and dried at a second preset temperature to obtain a second positive electrode sheet. The second active slurry includes a second sodium-ion layered oxide. The mass fraction of sodium in the first sodium-ion layered oxide and the second sodium-ion layered oxide are different. The second positive electrode sheet is then rolled to obtain the positive electrode sheet of the sodium-ion battery. The first active slurry including the first sodium-ion layered oxide and the second active slurry including the second sodium-ion layered oxide are sequentially coated onto both sides of the conductive substrate. One of the first and second active slurries can provide bulk capacity and rapid ion transport, enhancing rate performance, while the other can serve as a functional protective layer, improving interface stability and achieving synergistic function of capacity supply and interface protection.

[0008] Additional aspects and advantages of embodiments of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of this application. Attached Figure Description

[0009] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, wherein: Figure 1 This is a schematic diagram illustrating the application scenarios of sodium-ion batteries according to certain embodiments of this application; Figure 2 This is a schematic flowchart of a method for preparing the positive electrode of a sodium-ion battery according to certain embodiments of this application; Figure 3 This is a schematic diagram of a method for preparing the positive electrode of a sodium-ion battery according to certain embodiments of this application; Figure 4 This is a schematic diagram of the positive electrode of a sodium-ion battery according to certain embodiments of this application; Figure 5 This is a schematic diagram illustrating a method for preparing the positive electrode of a sodium-ion battery according to certain embodiments of this application. Detailed Implementation

[0010] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0011] The flowchart shown in the attached diagram is for illustrative purposes only and does not necessarily include all content and operations / steps, nor does it necessarily have to be performed in the order described. For example, some operations / steps can be broken down, combined, or partially merged, so the actual execution order may change depending on the actual situation.

[0012] It should be understood that, in order to clearly describe the technical solutions of the embodiments of the present invention, the terms "first" and "second" are used in the embodiments of the present invention to distinguish identical or similar items with essentially the same function and effect. Those skilled in the art will understand that the terms "first" and "second" do not limit the quantity or execution order, and the terms "first" and "second" are not necessarily different.

[0013] It should be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0014] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0015] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0016] To facilitate understanding of this application, the background technology of this application will be further explained below: With the development and utilization of lithium resources, the Earth's lithium resources cannot meet the rapidly growing demand, leading to high costs and thus limiting the development and use of lithium-ion batteries. Sodium is the sixth most abundant element in the Earth's crust, and sodium resources have the advantages of low cost and abundant reserves. Sodium-ion batteries (SIBs), due to their high sodium content, are considered the most promising large-scale supplementary energy storage system.

[0017] Sodium-ion battery layered cathode materials stand out among many cathode materials due to their simple preparation methods, easy technology transfer, high energy density, high reversible specific capacity, high rate performance, and reversible sodium-ion intercalation / deintercalation capabilities. However, single sodium-ion layered cathode materials still have many problems. For example, O3-type Ni-Fe-Mn layered oxides have a high theoretical capacity.

[0018] However, their poor cycle life and air stability greatly limit their practical applications. P2-type transition layered oxides offer better cycle life but lower energy density. Therefore, traditional single-layer coatings tend to result in very limited cycle stability and rate performance of the cell, leading to chaotic material interfaces, obstructed ion migration pathways, exacerbated electrode-electrolyte side reactions, and decreased cycle life. This hinders their rapid commercial application in SIBs.

[0019] To address the aforementioned technical problems, this application provides a method for preparing a positive electrode sheet for a sodium-ion battery, a positive electrode sheet for a sodium-ion battery, and a sodium-ion battery. The method for preparing the positive electrode sheet for a sodium-ion battery can be applied to the positive electrode sheet. When the positive electrode sheet is applied to a sodium-ion battery, it can optimize the electrode pore structure and improve the stability of the paste interface, thereby effectively improving the rate performance and cycle performance of the sodium-ion battery.

[0020] The following provides a detailed description of the preparation method of the positive electrode sheet of the sodium-ion battery according to the embodiments of this application. Please refer to [link / reference needed]. Figure 1 , Figure 1 This diagram illustrates the application scenario of the positive electrode sheet of a sodium-ion battery prepared by the method for preparing the positive electrode sheet of a sodium-ion battery provided in the embodiments of this application, when applied to a sodium-ion battery 100. Figure 2 This is a schematic flowchart illustrating a method for preparing the positive electrode of a sodium-ion battery according to an embodiment of this application. It should be noted that the steps shown may be performed in a different logical order than that shown in the flowchart. The method may include the following steps: Step 011: Coat the first active paste on both sides of the conductive substrate and dry it at a first preset temperature to obtain the first positive electrode sheet. The first active paste includes a first sodium ion layered oxide.

[0021] Optionally, the first sodium ion layered oxide includes either an O3-type sodium ion layered oxide or a P2-type sodium ion layered oxide; the second sodium ion layered oxide includes the other of the O3-type sodium ion layered oxide or the P2-type sodium ion layered oxide, wherein the first sodium ion layered oxide and the second sodium ion layered oxide are different. For example, the first sodium ion layered oxide includes an O3-type sodium ion layered oxide, and the second sodium ion layered oxide includes a P2-type sodium ion layered oxide; or, the first sodium ion layered oxide includes a P2-type sodium ion layered oxide, and the second sodium ion layered oxide includes an O3-type sodium ion layered oxide.

[0022] Optionally, the first sodium ion layered oxide is expressed in the chemical formula of either NaxMyO2 or NazMyO2, and the second sodium ion layered oxide is expressed in the chemical formula of either NaxMyO2 or NazMyO2, wherein M is at least one of manganese, nickel, iron, copper, cobalt, titanium, magnesium or lithium, and 0.5≦x≦0.8, 0≦y≦1, 0.9≦z≦1.

[0023] In the x-region, a thick and unstable electrode-electrolyte interface film (CEI film) easily forms on the surface of the sodium layer, while the sodium layer in the z-region can serve as an interface protective layer. Its ordered crystal structure optimizes the interface environment between the electrode and electrolyte, suppressing excessive reactions between the underlying material and the electrolyte, reducing abnormal growth of the CEI film and structural collapse of the active material, thereby lowering the rate of increase in battery internal resistance and improving structural stability during charge and discharge. The first and second sodium-ion layered oxides have different mass fractions of sodium, but both have layered oxide crystal structures. Their physical properties (such as density and particle size compatibility) and chemical compatibility (compatibility with conductive agents, binders, and solvents) are consistent, ensuring that the coating process parameters (such as solid content, viscosity, and drying temperature) of the two slurries can be uniformly controlled. This avoids process problems such as interlayer delamination and uneven coating caused by differences in material properties, ensuring the stability and yield of the bilayer electrode fabrication.

[0024] Optionally, the first active slurry further includes a conductive agent and a binder, wherein the mass percentage of the first sodium ion layered oxide in the first active slurry ranges from [90%, 95%], the mass percentage of the conductive agent in the first active slurry ranges from [1.0%, 4.0%], and the mass percentage of the binder in the first active slurry ranges from [1%, 3%]; The second active slurry also includes a conductive agent and a binder. The mass percentage of the second sodium ion layered oxide in the second active slurry ranges from [90%, 95%], the mass percentage of the conductive agent in the second active slurry ranges from [1.0%, 4.0%], and the mass percentage of the binder in the second active slurry ranges from [1%, 3%].

[0025] The conductive agent includes one or more of the following: superconducting carbon black (SuperP), acetylene black, carbon nanotubes (CNTs), multi-walled carbon nanotubes (MWCNTs), and graphene. The binder includes polyvinylidene fluoride (PVDF).

[0026] Optionally, the method further includes: Step 014: Add the first sodium ion layered oxide, conductive agent and binder to N-methyl-2-pyrrolidone solvent (NMP) and mix evenly to obtain the first active slurry.

[0027] The first active slurry can be a slurry comprising a positive electrode active material of P2-type sodium ion layered oxide or a slurry comprising a positive electrode active material of O3-type sodium ion layered oxide. For example, the first active slurry may include a positive electrode active material of P2-type sodium ion layered oxide, a conductive agent, and a binder. The first active slurry is obtained by uniformly mixing the positive electrode active material of P2-type sodium ion layered oxide, the conductive agent, and the binder and dispersing them in an N-methyl-2-pyrrolidone (NMP) solvent. As another example, the first active slurry may include a positive electrode active material of O3-type sodium ion layered oxide, a conductive agent, and a binder. The first active slurry is obtained by uniformly mixing the positive electrode active material of P2-type sodium ion layered oxide, the conductive agent, and the binder and dispersing them in an N-methyl-2-pyrrolidone (NMP) solvent.

[0028] The first preset temperature range includes any value within [80℃, 130℃], for example, it can be 80℃, 85℃, 90℃, 100℃, 110℃, 120℃, or 130℃. Within the first preset temperature range, it can be used to remove NMP solvent from the first active slurry, allowing the first sodium ion layered oxide to firmly adhere to the surface of the conductive substrate. Optionally, the conductive substrate can be a carrier substrate for the electrode active material, or a current collector including aluminum foil, used for conducting electrons and supporting the electrode structure. Optionally, the conductive substrate includes aluminum foil, and the thickness of the conductive substrate includes 12μm.

[0029] The first positive electrode sheet coated with the first sodium ion layered oxide can be obtained by coating a first active slurry, including a first sodium ion layered oxide, onto the surface of a conductive substrate and drying it at a first preset temperature.

[0030] Step 012: Coat both sides of the first positive electrode sheet with the second active slurry and dry it at a second preset temperature to obtain the second positive electrode sheet. The second active slurry includes a second sodium ion layered oxide, and the mass fraction of sodium in the first sodium ion layered oxide and the second sodium ion layered oxide is different.

[0031] The second preset temperature range includes any one of [80℃, 130℃], for example, it can be 80℃, 85℃, 90℃, 100℃, 110℃, 120℃ or 130℃, etc.

[0032] At the drying temperature of the first preset temperature or the second preset temperature, the NMP solvent in the slurry can be efficiently removed (avoiding residual solvent from affecting the stability of the electrolyte), while ensuring the bonding performance of the binder (such as PVDF), so that the active material, conductive agent and current collector form a firmly bonded whole, while avoiding the destruction of the material's crystal structure due to high temperature.

[0033] Optionally, the method further includes: Step 015: Add the second sodium ion layered oxide, conductive agent and binder to N-methyl-2-pyrrolidone solvent and mix evenly to obtain the second active slurry.

[0034] The second active slurry can be a slurry comprising a P2-type sodium ion layered oxide positive electrode active material or an O3-type sodium ion layered oxide positive electrode active material. For example, the second active slurry may include a P2-type sodium ion layered oxide positive electrode active material, a conductive agent, and a binder. This is achieved by uniformly mixing the P2-type sodium ion layered oxide positive electrode active material, the conductive agent, and the binder, and dispersing them in an N-methyl-2-pyrrolidone (NMP) solvent. Alternatively, the second active slurry may include an O3-type sodium ion layered oxide positive electrode active material, a conductive agent, and a binder. This is achieved by uniformly mixing the P2-type sodium ion layered oxide positive electrode active material, the conductive agent, and the binder, and dispersing them in an N-methyl-2-pyrrolidone (NMP) solvent. For ease of explanation, this application uses an example where the first sodium ion layered oxide comprises a P2-type sodium ion layered oxide, and the second sodium ion layered oxide comprises an O3-type sodium ion layered oxide.

[0035] Specifically, please refer to Figure 3A second positive electrode sheet coated with the first sodium ion layered oxide and the second sodium ion layered oxide can be obtained by coating a second active slurry, including the second sodium ion layered oxide, onto both sides of the first positive electrode sheet and drying it at a second preset temperature.

[0036] Step 013: Roll the second positive electrode sheet to obtain the positive electrode sheet for sodium-ion batteries.

[0037] Optionally, the areal density of the sodium-ion battery positive electrode sheet ranges from [8 mg / cm² to 37.2 mg / cm²], and the areal density is the ratio between the sum of the masses of the first sodium-ion layered oxide and the second sodium-ion layered oxide and the coating area of ​​the first or second active slurry coated on the conductive substrate.

[0038] It is understandable that areal density determines the total amount of active material per unit area of ​​the battery, thus affecting the battery capacity. At an areal density of 8 mg / cm², the active material layer is thinner, the ion migration path is shorter, and the high-rate discharge capability can be further enhanced. At an areal density of 37.2 mg / cm², the active material is sufficient, which can increase the capacity of individual battery cells and is suitable for long-term energy storage scenarios. Moreover, thanks to the interface protection function of the O3 layer, even with the increase in areal density, ion transport obstruction and side reactions can be avoided. Therefore, by setting an areal density range of 8 mg / cm² to 37.2 mg / cm², the areal density can be adapted to the energy storage scenario to cover the capacity and power requirements of the entire scenario.

[0039] Optionally, when the first sodium ion layered oxide includes a P2-type sodium ion layered oxide and the second sodium ion layered oxide includes an O3-type sodium ion layered oxide, the coating thickness of the first active slurry ranges from [55 micrometers to 65 micrometers], and the coating thickness of the second active slurry ranges from [40 micrometers to 50 micrometers]; and / or, The solid content of the first active slurry ranges from [51%, 56%], and the viscosity ranges from [4000 mPa·s, 7000 mPa·s]. The solid content of the second active slurry ranges from [51%, 56%], and the viscosity ranges from [4000 mPa·s, 7000 mPa·s].

[0040] The P2 layer (55μm to 65μm) serves as the bottom layer, ensuring sufficient reserves of active materials to provide the battery with its main capacity and continuous fast ion channels, preventing rate performance degradation caused by an excessively thin bottom layer. Simultaneously, the 55μm to 65μm thickness range achieves a balance between ion transport efficiency and capacity supply, avoiding both excessive thickness increasing ion migration resistance and excessive thinness sacrificing cycle stability. The O3 layer (40μm to 50μm) serves as the top layer, ensuring the formation of a complete protective interface. It fully covers the surface of the P2 layer, suppressing side reactions between the P2 layer and the electrolyte, generating a thin and dense CEI film. At the same time, it avoids the elongation of ion migration paths caused by an excessively thick top layer, ensuring ion transport rates at high rates and achieving a balance between protective function and rate performance.

[0041] Specifically, by setting the solid content of the first active slurry to a range of [51%, 56%], the proportion of active material in the electrode is ensured, while the proportion of inactive components such as binders and conductive agents is reduced, thereby improving the battery's energy density. Simultaneously, it avoids problems such as uneven dispersion and screen clogging during coating caused by viscous slurry, ensuring that the slurry can uniformly cover the surface of the current collector layer, forming a smooth and dense active material layer. Furthermore, the consistent solid content of the two slurry layers ensures synchronized solvent evaporation rates during drying, further reducing interlayer stress and improving electrode flatness.

[0042] By setting the viscosity range to [4000 mPa·s, 7000 mPa·s], production efficiency is improved, ensuring that the slurry does not drip and has a uniform thickness during thick coating. Simultaneously, the consistent viscosity of the two slurry layers prevents the bottom layer from being penetrated by the surface slurry or the two layers from separating due to viscosity differences during coating, thus ensuring the integrity of the double-layer structure. Furthermore, matching the viscosity with the solid content ensures that the slurry maintains its shape stability after coating, forming an electrode with uniform porosity after drying, thus optimizing the ion transport channels.

[0043] Specifically, after obtaining the second positive electrode sheet, it can be rolled using methods such as rolling to optimize the electrode pore structure and compaction density, thereby obtaining the positive electrode sheet for sodium-ion batteries. P2-type sodium-ion layered oxides exhibit good cycle stability and fast ion transport rates, but have low energy density and are prone to forming thick and unstable electrode-electrolyte interface (CEI) films on their surface, leading to sodium ion loss. O3-type sodium-ion layered oxides have high theoretical capacity and ordered ion channels, and can form thin and dense CEI films on their surface, reducing interfacial impedance, but have limited cycle life. Therefore, by sequentially coating an active slurry comprising P2-type and O3-type sodium-ion layered oxides onto both sides of a conductive substrate, a synergistic function of capacity supply and interface protection is achieved. Rolling can adjust the porosity and compaction density of the electrode, reducing void obstruction in the ion migration path, improving ion conductivity, and simultaneously enhancing the interfacial bonding between the P2 and O3 layers, and between the active material and the current collector, preventing interlayer delamination during charging and discharging, and improving the stability of the electrode structure. In other words, double-layer coating avoids the interface chaos caused by single-material coating. The synergistic effect of the P2 layer and O3 layer makes the ion migration path more orderly. The interlayer bonding force is further enhanced after rolling, which effectively prevents electrode peeling and pulverization during charging and discharging, and improves the long-term reliability of the battery.

[0044] Thus, by coating a first active slurry onto both sides of a conductive substrate and drying it at a first preset temperature, a first positive electrode sheet is obtained. The first active slurry includes a first sodium ion layered oxide. A second active slurry is then coated onto both sides of the first positive electrode sheet and dried at a second preset temperature to obtain a second positive electrode sheet. The second active slurry includes a second sodium ion layered oxide, and the mass fraction of sodium in the first and second sodium ion layered oxides differs. The second positive electrode sheet is then rolled to obtain a sodium-ion battery positive electrode sheet. By sequentially coating the first active slurry including the first sodium ion layered oxide and the second active slurry including the second sodium ion layered oxide onto both sides of the conductive substrate, a synergistic function of capacity supply and interface protection is achieved. One of the first and second active slurries can provide the main capacity and rapid ion transport, enhancing rate performance, while the other can serve as a functional protective layer, improving interface stability.

[0045] Please refer to it again. Figure 3 and Figure 4 This application also proposes a positive electrode sheet for a sodium-ion battery, comprising: conductive substrate, The first positive electrode is formed by coating both sides of a conductive substrate with a first active paste, the first active paste comprising a first sodium ion layered oxide. The second positive electrode is formed by coating both sides of the first positive electrode with a second active slurry. The second active slurry includes a second sodium ion layered oxide, and the mass fraction of sodium in the first sodium ion layered oxide and the second sodium ion layered oxide are different.

[0046] Please see Figure 1 This application also proposes a sodium-ion battery 100, comprising: The positive electrode sheet described above in any of the above embodiments; and Negative electrode plate; Diaphragm; The electrolyte, negative electrode, separator, and positive electrode are all disposed in the electrolyte.

[0047] Optionally, the negative electrode includes an active material, which may be one of hard carbon or sodium titanate.

[0048] Optionally, a negative electrode slurry can be obtained by uniformly dispersing the negative electrode active material, conductive agent, and binder in deionized water, coating the negative electrode slurry onto the surface of aluminum foil, drying it at 110°C after coating, and then rolling it to obtain a negative electrode sheet.

[0049] Optionally, the electrolyte includes an electrolyte solvent and a solute. The electrolyte solvent includes one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. The sodium salt includes one or more of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), and sodium bis(fluorosulfonyl)imide (NaFSI).

[0050] Optionally, the separator is a separator known in the art or that will emerge in the future suitable for sodium-ion batteries.

[0051] Optionally, positive electrode sheets, negative electrode sheets, and electrolyte are prepared separately. Then, the die-cut positive and negative electrode sheets and separator are wound sequentially. After winding, the core is tied with 2-5 strands, aluminum tabs are welded, and aluminum-plastic film is used for encapsulation. After baking to remove moisture, the electrolyte is injected. After formation, secondary sealing, and capacity testing, a high-rate sodium-ion battery with layered oxygen sodium ion is obtained.

[0052] For ease of understanding, this application takes a sodium-ion battery with a thickness ≤3.8mm, width ≤52mm, and length ≤88mm as an example, and proposes further comparisons through the following embodiments and comparative cases.

[0053] Example 1: Preparation of positive electrode sheet: The active material Na 2 / 3 Ni 1 / 3MnO2, superconducting carbon black, PVDF, and carbon nanotubes were mixed uniformly in a mass ratio of 90.0%:5.0%:2.0%:3.0% and dispersed in N-methyl-2-pyrrolidone solvent to obtain a positive electrode active material P2 slurry. This P2 slurry was coated onto both sides of an aluminum foil and dried at 120°C to obtain a positive electrode sheet coated with the active material P2 layer. Na... 2 / 3 Ni 1 / 3 The particle size D50 of MnO2 is 8 μm.

[0054] The active material NaNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, superconducting carbon black, PVDF, and carbon nanotubes are mixed uniformly in a mass ratio of 90.0%:5.0%:2.0%:3.0% and dispersed in N-methyl-2-pyrrolidone solvent to obtain a positive electrode active material O3 slurry, wherein NaNi 1 / 3 Mn 1 / 3 Co 1 / 3 The particle size D50 of O2 is 11 μm. The positive electrode active material O3 slurry is coated on the surface of the active material layer P2, and then dried at 120°C to obtain the double-coated positive electrode sheet, which is then rolled.

[0055] The double-layer thickness of the active material layer P2 is 65 μm, and the double-layer thickness of the active material layer O3 is 25 μm. The areal density of the positive electrode is 13 ± 0.4 mg / cm².

[0056] Preparation of the negative electrode sheet: Hard carbon, superconducting carbon black, SBR, and CMC were mixed uniformly in a mass ratio of 91.0%:4.0%:2.0%:3.0% and dispersed in deionized water to obtain a negative electrode slurry. This negative electrode slurry was coated on both sides of an aluminum foil, dried at 100℃, rolled, and die-cut to obtain the negative electrode sheet. The areal density of the negative electrode on both sides was 6.28±0.4 mg / cm².

[0057] The above-mentioned positive electrode, negative electrode and separator are wound together to form a 385288 (960mAh) type soft pack battery.

[0058] Example 2: Unlike Example 1, the double layer thickness of active material layer P2 is 55 μm, and the double layer thickness of active material layer O3 is 35 μm.

[0059] Example 3: Unlike Example 1, the double layer thickness of active material layer P2 is 45 μm, and the double layer thickness of active material layer O3 is 45 μm.

[0060] Example 4: Unlike Example 1, the double layer thickness of active material layer P2 is 35 μm, and the double layer thickness of active material layer O3 is 55 μm.

[0061] Comparative Case 1: Adding active substance Na 2 / 3 Ni 1 / 3 MnO2, superconducting carbon black, PVDF, and carbon nanotubes were mixed uniformly in a mass ratio of 93.0%:3.0%:2.0%:2.0% and dispersed in N-methyl-2-pyrrolidone solvent to obtain a positive electrode active material P2 slurry. This P2 slurry was coated onto both sides of an aluminum foil to a thickness of 90 μm (excluding the foil thickness) and dried at 120℃ to obtain a positive electrode sheet coated with the active material P2 layer. Na... 2 / 3 Ni 1 / 3 The particle size D50 of MnO2 is 8 μm.

[0062] Preparation of the negative electrode sheet: Hard carbon, superconducting carbon black, SBR, and CMC were mixed uniformly in a mass ratio of 90.0%:5.0%:2.0%:3.0% and dispersed in deionized water to obtain a negative electrode slurry. This negative electrode slurry was coated on both sides of an aluminum foil, dried at 100℃, rolled, and die-cut to obtain the negative electrode sheet. The areal density of the negative electrode on both sides was 6.28±0.4 mg / cm².

[0063] The above-mentioned positive electrode, negative electrode and separator are wound together to form a 385288 (960mAh) type soft pack battery.

[0064] It's understandable that pouch batteries are typically numbered based on the thickness, width, and height of their battery design. For example, a pouch battery with a thickness of 6.5 mm, a width of 67 mm, and a height of 100 mm would be designated as type 6567100. Similarly, type 385288 indicates a pouch battery with a thickness of 3.8 mm, a width of 52 mm, and a height of 88 mm.

[0065] Comparative Case 2: Using the active material NaNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, superconducting carbon black, PVDF, and carbon nanotubes are mixed uniformly in a mass ratio of 90.0%:5.0%:2.0%:3.0% and dispersed in N-methyl-2-pyrrolidone solvent to obtain a positive electrode active material O3 slurry, wherein NaNi 1 / 3 Mn 1 / 3 Co 1 / 3 The particle size D50 of O2 is 11 μm. The positive electrode active material O3 slurry is coated on both sides of aluminum foil with a coating thickness of 90 μm (excluding the foil thickness). After coating, it is dried at a temperature of 120°C to obtain a double-coated positive electrode sheet, which is then rolled.

[0066] Preparation of the negative electrode sheet: Hard carbon, superconducting carbon black, SBR, and CMC were mixed uniformly in a mass ratio of 91.0%:4.0%:2.0%:3.0% and dispersed in deionized water to obtain a negative electrode slurry. This negative electrode slurry was coated on both sides of an aluminum foil, dried at 100℃, rolled, and die-cut to obtain the negative electrode sheet. The areal density of the negative electrode on both sides was 6.28±0.4 mg / cm².

[0067] The above-mentioned positive electrode, negative electrode and separator are wound together to form a 385288 (960mAh) type soft pack battery.

[0068] Battery performance was tested using the above embodiments and comparative cases. Before each continuous discharge rate, the sample was charged to 3.65V using a charging device. The digital thermometer probe was placed firmly against the center of the sample's front surface. The sample was correctly connected to the load cell. Initial voltage, internal resistance, and temperature were recorded. Test parameters were set, and the load cell was started. (See [link to relevant documentation]). Figure 5 The test data obtained are as follows: The discharge capacities of Examples 1, 2, 3, and 4 at 70C are 883.303, 866.077, 851.901, and 841.455 mAh, respectively. The discharge capacities of Comparative Examples 1 and 2 at 70C are 813.694 and 802.865 mAh, respectively.

[0069] It should be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. It should be understood that when an element or layer is referred to as “on,” “adjacent to,” “connected to,” or “coupled to” other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as “directly on,” “directly adjacent to,” “directly connected to,” or “directly coupled to” other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or portions, these elements, components, areas, layers, and / or portions should not be limited by these terms. These terms are merely used to distinguish one element, component, area, layer, or portion from another element, component, area, layer, or portion. Therefore, without departing from the teachings of this application, the first element, component, area, layer, or portion discussed below may be referred to as a second element, component, area, layer, or portion.

[0070] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein for convenience of description to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, then the element or feature described as “below,” “under,” or “below” other elements or features will be oriented “above” other elements or features. Therefore, the exemplary terms “below” and “under” can include both above and below orientations. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptive terms used herein will be interpreted accordingly.

[0071] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0072] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0073] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a positive electrode sheet for a sodium-ion battery, characterized in that, include: A first active paste is coated on both sides of a conductive substrate and dried at a first preset temperature to obtain a first positive electrode sheet. The first active paste includes a first sodium ion layered oxide. The second active slurry is coated on both sides of the first positive electrode sheet and dried at a second preset temperature to obtain the second positive electrode sheet. The second active slurry includes a second sodium ion layered oxide, and the mass fraction of sodium in the first sodium ion layered oxide and the second sodium ion layered oxide are different. The second positive electrode sheet is rolled to obtain a sodium-ion battery positive electrode sheet.

2. The method for preparing the positive electrode of a sodium-ion battery according to claim 1, characterized in that, The first sodium ion layered oxide has the chemical formula of either NaxMyO2 or NazMyO2, and the second sodium ion layered oxide has the chemical formula of either NaxMyO2 or NazMyO2, wherein M is at least one of manganese, nickel, iron, copper, cobalt, titanium, magnesium or lithium, and 0.5≦x≦0.8, 0≦y≦1, 0.9≦z≦1.

3. The method for preparing the positive electrode of a sodium-ion battery according to claim 1 or 2, characterized in that, The first sodium ion layered oxide includes an O3-type sodium ion layered oxide, and the second sodium ion layered oxide includes a P2-type sodium ion layered oxide; or, the first sodium ion layered oxide includes a P2-type sodium ion layered oxide, and the second sodium ion layered oxide includes an O3-type sodium ion layered oxide.

4. The method for preparing the positive electrode of a sodium-ion battery according to claim 1, characterized in that, The areal density range of the sodium-ion battery positive electrode sheet includes [8 mg / cm², 37.2 mg / cm²], and the areal density is the ratio between the sum of the masses of the first sodium-ion layered oxide and the second sodium-ion layered oxide and the coating area of ​​the first active slurry or the second active slurry coated on the conductive substrate.

5. The method for preparing the positive electrode of a sodium-ion battery according to claim 4, characterized in that, When the first sodium ion layered oxide includes a P2-type sodium ion layered oxide and the second sodium ion layered oxide includes an O3-type sodium ion layered oxide, the coating thickness of the first active slurry ranges from [55 micrometers to 65 micrometers], and the coating thickness of the second active slurry ranges from [40 micrometers to 50 micrometers]; and / or, The solid content of the first active slurry ranges from [51%, 56%], and the viscosity ranges from [4000 mPa·s, 7000 mPa·s]. The solid content of the second active slurry ranges from [51%, 56%], and the viscosity ranges from [4000 mPa·s, 7000 mPa·s].

6. The method for preparing the positive electrode of a sodium-ion battery according to any one of claims 1-5, characterized in that, The first active slurry further includes a conductive agent and a binder. The mass percentage of the first sodium ion layered oxide in the first active slurry ranges from [90%, 95%], the mass percentage of the conductive agent in the first active slurry ranges from [1.0%, 4.0%], and the mass percentage of the binder in the first active slurry ranges from [1%, 3%]; The second active slurry further includes a conductive agent and a binder. The mass percentage of the second sodium ion layered oxide in the second active slurry ranges from [90%, 95%], the mass percentage of the conductive agent in the second active slurry ranges from [1.0%, 4.0%], and the mass percentage of the binder in the second active slurry ranges from [1%, 3%].

7. The method for preparing the positive electrode of a sodium-ion battery according to claim 6, characterized in that, The conductive agent includes at least one of superconducting carbon black, acetylene black, carbon nanotubes or multi-walled carbon nanotubes graphene, and the binder includes polyvinylidene fluoride.

8. The method for preparing the positive electrode of a sodium-ion battery according to claim 6 or 7, characterized in that, The method further includes: The first sodium ion layered oxide, conductive agent, and binder are added to N-methyl-2-pyrrolidone solvent and mixed evenly to obtain the first active slurry; The second sodium ion layered oxide, conductive agent, and binder are added to N-methyl-2-pyrrolidone solvent and mixed evenly to obtain the second active slurry.

9. The method for preparing the positive electrode of a sodium-ion battery according to claim 1, characterized in that, The first preset temperature and the second preset temperature range from [80℃ to 130℃]; the conductive substrate includes aluminum foil; the thickness of the conductive substrate includes 12μm.

10. A positive electrode sheet for a sodium-ion battery, characterized in that, include: Conductive substrate; The first positive electrode is formed by coating both sides of the conductive substrate with a first active paste, wherein the first active paste includes a first sodium ion layered oxide. The second positive electrode is formed by coating both sides of the first positive electrode with a second active slurry. The second active slurry includes a second sodium ion layered oxide, and the mass fraction of sodium in the first sodium ion layered oxide and the second sodium ion layered oxide are different.

11. A sodium-ion battery, characterized in that, include: The positive electrode sheet as described in claim 10; and Negative electrode plate; Diaphragm; The electrolyte, the negative electrode, the separator, and the positive electrode are all disposed in the electrolyte.

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