Dry electrode sheet and method for manufacturing the same, sodium-ion battery

Abstract

The application discloses a dry electrode sheet, a preparation method thereof and a sodium ion battery. The dry electrode sheet comprises a current collector and a positive active material layer arranged on at least one surface of the current collector. The positive active material layer comprises a positive material, a carboxyl-modified conductive agent and a conductive binder. The mass ratio of the positive material, the carboxyl-modified conductive agent and the conductive binder is 85-99.25:0.25-1:0.5-32. The dry electrode sheet has good electrolyte wettability, the contact angle between the dry electrode sheet and the electrolyte is 35-42 degrees, and the membrane resistance of the dry electrode sheet is 5-7 ohms, so that the sodium ion battery comprising the dry electrode sheet has good rate performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to dry electrode sheets and their preparation methods, and sodium-ion batteries. Background Technology

[0002] The specific capacity of sodium-ion battery cathode materials is significantly lower than that of lithium-ion battery cathode materials, resulting in a lower energy density for the prepared full cell. Increasing the areal density of the positive and negative electrodes is an important means to improve the energy density of the full cell. However, using wet methods to prepare positive / negative electrode sheets with high areal density presents challenges such as coating difficulties, and excessively thick active material layers are prone to cracking during baking due to the different evaporation rates of the solvent on the surface and inside. Furthermore, problems such as powder shedding during rolling, low peel strength, and high film resistance also exist. Compared to wet electrode preparation, dry electrode sheets do not require solvents or baking processes, avoiding the problem of baking cracking, and can further reduce the production cost of sodium-ion batteries.

[0003] However, the dry-process electrode sheets currently prepared for sodium-ion batteries still suffer from the drawback of high film resistance, leading to an increase in the DC impedance of the entire cell and affecting the rate performance of the battery. Therefore, to solve the above problems, a novel dry-process electrode sheet and its preparation method, as well as a sodium-ion battery, are proposed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a dry electrode sheet that can solve the problems of high film resistance and poor battery rate performance by adding carboxyl-modified conductive agents and conductive binders.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] The first aspect of the present invention provides a dry electrode sheet, comprising a current collector and a positive electrode active material layer disposed on at least one surface of the current collector, wherein the positive electrode active material layer comprises a positive electrode material, a carboxyl-modified conductive agent and a conductive binder.

[0007] In some embodiments of the present invention, the mass ratio of the positive electrode material, the carboxyl-modified conductive agent, and the conductive binder is 85–99.25:0.25–1:0.5–32.

[0008] In some embodiments of the present invention, the current collector is selected from aluminum foil, nickel foil, or a polymer conductive film; preferably, the current collector is aluminum foil.

[0009] In some embodiments of the present invention, the conductive adhesive is PMS:PEDOT, wherein PMS is poly(methacryloyl-3,4-dihydroxy-L-phenylalanine-co-3-sulfopropyl methacrylate) and PEDOT is polyethylene dioxythiophene.

[0010] In some embodiments of the present invention, the conductive agent is selected from one or more of SuperP, Ketjen black, carbon nanotubes, carbon nanofibers, graphene, and conductive carbon.

[0011] In some embodiments of the present invention, the positive electrode material is a sodium-ion battery layered oxide material, and the molecular formula of the sodium-ion battery layered oxide material is Na x AO2, where 0.6 < x ≤ 1, A is one or more transition metal elements or other doping elements, and the other doping elements are selected from Li, B, Mg, Al, K, Ca, or Sn.

[0012] In some embodiments of the present invention, the dry electrode sheet 100 includes a current collector 1, a first positive electrode active material layer 21, and a second positive electrode active material layer 22. The current collector 1 has a first surface 11 and a second surface 12 facing away from each other in the thickness direction. The first positive electrode active material layer 21 is disposed on the first surface 11, and the second positive electrode active material layer 22 is disposed on the second surface 12.

[0013] In some embodiments of the present invention, the thickness of the positive electrode active material layer is 100 - 180 μm.

[0014] In some embodiments of the present invention, when performing an electrolyte wettability test on the dry electrode sheet, the contact angle between the dry electrode sheet and the electrolyte is 35° - 42°.

[0015] In some embodiments of the present invention, in the thickness direction of the dry electrode sheet, the sheet resistance of the dry electrode sheet is 5 - 7 Ω.

[0016] The second aspect of the present invention provides a method for preparing a dry electrode sheet, including the following steps:

[0017] Mix the positive electrode material, carboxyl-modified conductive agent, and conductive binder to obtain a mixed powder;

[0018] Add a solvent to the mixed powder and mix, and stir to obtain a wetted mixed powder;

[0019] Add a solvent to the wetted mixed powder and mix, and perform fibrillation treatment on the wetted mixed powder after mixing the solvents to obtain a fibrillated mixture;

[0020] Place the fibrillated mixture in an extruder and extrude to form an initial film;

[0021] Roll the initial film to obtain a finished film;

[0022] Thermally roll and laminate the finished film and the current collector to obtain a dry electrode sheet.

[0023] In some embodiments of the present invention, the cathode material is a layered oxide material for a sodium-ion battery, and the molecular formula of the layered oxide material for the sodium-ion battery is Na x AO2, where 0.6 < x ≤ 1, A is one or more transition metal elements or other doping elements, and the other doping elements are selected from Li, B, Mg, Al, K, Ca or Sn.

[0024] In some embodiments of the present invention, the carboxyl-modified conductive agent is prepared by the following steps:

[0025] Mix the conductive agent with water evenly to obtain a conductive agent aqueous dispersion;

[0026] Add a hydrogen peroxide solution to the conductive agent aqueous dispersion to obtain a conductive agent aqueous solution;

[0027] Introduce a mixed gas of ozone and oxygen, and perform water bath ultrasonic treatment to obtain a conductive agent aqueous solution modified with carboxyl functional groups;

[0028] Introduce an inert gas and perform freeze-drying to obtain the carboxyl-modified conductive agent.

[0029] In some embodiments of the present invention, in the step of mixing the conductive agent with water evenly to obtain a conductive agent aqueous dispersion, the conductive agent is selected from one or more of SuperP, Ketjenblack, carbon nanotubes, carbon nanofibers, graphene, and conductive carbon.

[0030] In some embodiments of the present invention, in the step of mixing the conductive agent with water evenly to obtain a conductive agent aqueous dispersion, the mass concentration of the conductive agent aqueous dispersion is 20 - 80 g / L.

[0031] In some embodiments of the present invention, in the step of adding a hydrogen peroxide solution to the conductive agent aqueous dispersion to obtain a conductive agent aqueous solution, the volume ratio of the conductive agent aqueous dispersion to the hydrogen peroxide solution is 1:0.2 - 0.5.

[0032] In some embodiments of the present invention, in the step of introducing a mixed gas of ozone and oxygen and performing water bath ultrasonic treatment to obtain a conductive agent aqueous solution modified with carboxyl functional groups, the gas flow rate of the mixed gas is 200 - 500 mL / min, and the ozone concentration in the mixed gas of ozone and oxygen is 20 - 100 g / m 3 .

[0033] In some embodiments of the present invention, in the step of introducing a mixed gas of ozone and oxygen and performing water bath ultrasonic treatment to obtain a conductive agent aqueous solution modified with carboxyl functional groups, the water bath ultrasonic temperature is 25°C - 50°C, and the water bath ultrasonic time is 0.5 - 3 h.

[0034] In some embodiments of the present invention, in the step of introducing an inert gas and freeze-drying to obtain a carboxyl-modified conductive agent, the inert gas is selected from nitrogen and / or argon, and the time for introducing the inert gas is 15 to 45 minutes.

[0035] In some embodiments of the present invention, in the step of introducing an inert gas and freeze-drying to obtain a carboxyl-modified conductive agent, the freeze-drying temperature is -40 to -70°C and the freeze-drying time is 5 to 12 hours.

[0036] In some embodiments of the present invention, the conductive adhesive is PMS:PEDOT.

[0037] In some embodiments of the present invention, in the step of mixing the positive electrode material, the carboxyl-modified conductive agent and the conductive binder to obtain a mixed powder, the mass ratio of the positive electrode material, the carboxyl-modified conductive agent and the conductive binder is 85-99.25:0.25-1:0.5-3.

[0038] In some embodiments of the present invention, in the step of mixing the positive electrode material, the carboxyl-modified conductive agent and the conductive binder to obtain a mixed powder, the mixing is carried out in a mixing tank, the mixing speed is 100-300 r / min, the mixing time is 0.5-2 h, and the mixing temperature is room temperature.

[0039] In some embodiments of the present invention, in the step of adding a solvent to the mixed powder, mixing and stirring to obtain a wetted mixed powder, the solvent is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, and ethylene glycol dimethyl ether.

[0040] In some embodiments of the present invention, in the step of adding solvent to the mixed powder and stirring to obtain a wetted mixed powder, the solid content of the wetted mixed powder is 96.5-98%. Adding solvent can cause the conductive binder to swell, so that the conductive binder, positive electrode material and carboxyl-modified conductive agent are mixed evenly.

[0041] In some embodiments of the present invention, in the step of adding solvent to the mixed powder, mixing and stirring to obtain a wetted mixed powder, the stirring is carried out in a stirring tank, the stirring speed is 1000-3500 r / min, the stirring time is 1-3 h, and the stirring temperature is room temperature.

[0042] In some embodiments of the present invention, in the step of adding a solvent to a moist mixed powder, mixing, and then performing a fibrosis treatment on the moist mixed powder after solvent mixing to obtain a fibrous mixture, the solvent is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, and ethylene glycol dimethyl ether.

[0043] In some embodiments of the present invention, in the step of adding a solvent to a moist mixed powder and mixing, and then performing a fiberization treatment on the moist mixed powder after solvent mixing to obtain a fiberized mixture, the solid content of the fiberized mixture is 90-95%. Adding a solvent can further swell the conductive adhesive, thereby facilitating the fiberization of the conductive adhesive.

[0044] In some embodiments of the present invention, in the step of adding a solvent to a moist mixed powder and mixing, and then performing a fiberization treatment on the moist mixed powder after solvent mixing to obtain a fiberized mixture, the fiberization treatment is carried out in a mixing tank, with a stirring speed of 4500-6000 r / min, a stirring time of 0.5-2 h, and a stirring temperature of 20-50 °C.

[0045] In some embodiments of the present invention, in the step of placing the fibrous mixture in an extruder and extruding it to obtain an initial film, the extrusion temperature is 40–120°C.

[0046] In some embodiments of the present invention, in the step of placing the fibrous mixture in an extruder and extruding it to obtain an initial film, the thickness of the initial film is 250–400 μm.

[0047] In some embodiments of the present invention, in the step of rolling the initial film to obtain the finished film, the rolling temperature is 80-150°C.

[0048] In some embodiments of the present invention, in the step of rolling the initial film to obtain the finished film, the thickness of the finished film is 120-200 μm.

[0049] In some embodiments of the present invention, in the step of obtaining a dry electrode sheet by hot rolling composite film and current collector, the temperature of hot rolling composite is 100-200°C.

[0050] In some embodiments of the present invention, the step of hot-rolling composite film and current collector to obtain dry electrode sheet includes hot-rolling composite of one film product to one side of the current collector or hot-rolling composite of two film products to one side of the current collector respectively.

[0051] A third aspect of the present invention provides a sodium-ion battery comprising the aforementioned dry electrode sheet.

[0052] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0053] This invention introduces a conductive binder PMS:PEDOT and a carboxylic acid-modified conductive agent into dry electrode sheets, which has the following advantages:

[0054] The conductive binder PMS:PEDOT is a fully organic polymer with strong adhesion, high flexibility, and good biocompatibility with organic solvents. With a conductivity as high as 250 S / m, PMS:PEDOT is applied to dry electrodes. Due to its high electronic conductivity, it becomes fibrous after fiberization treatment. When mixed with conductive agents, it forms a good conductive network, thereby reducing the amount of conductive agent used and improving battery energy density.

[0055] Due to the poor air stability of layered oxide materials, their surfaces are often covered by residual sodium-containing compounds (Na₂CO₃, NaOH, NaHCO₃, etc.). Over time, this gradually forms a dense resistive layer, hindering ion transport between the positive electrode and the electrolyte, as well as electron conduction between the positive electrode and the conductive carbon. Introducing a conductive agent modified with carboxyl functional groups allows the acidic carboxyl functional groups to react with the residual alkaline compounds (Na₂CO₃, NaOH, NaHCO₃, etc.) on the surface of the layered oxide material, reducing the content of alkaline compounds in the resistive layer. This disrupts the structure of the surface resistive layer, making it easier for the electrolyte to penetrate and wet the positive electrode active material. This improves electrolyte wettability and reduces membrane resistance, thereby enhancing battery rate performance. Furthermore, using highly polar carboxyl functional group-modified conductive agents, and applying these agents to dry-process electrode sheets, can increase the polarity of the dry-process electrode sheets, further improving the wettability of the electrolyte on the dry-process electrode sheets.

[0056] The dry electrode preparation process does not require the addition of toxic organic solvent NMP, and there is no emission of any toxic gases, resulting in no pollution or residue. It also eliminates the need for the oven drying process required in the wet electrode coating process, effectively reducing the cost of sodium-ion battery preparation and truly conforming to the concepts of "green" and "environmentally friendly". Attached Figure Description

[0057] Figure 1 The image shown is a scanning electron microscope (SEM) image of the dry electrode sheet prepared in Example 1.

[0058] Figure 2 This is a schematic diagram of the dry electrode sheet prepared in Example 1.

[0059] Figure 3 This is a schematic diagram of the contact angle test for electrolyte and dry electrode sheet.

[0060] The reference numerals in the attached figures are explained as follows:

[0061] 100. Dry electrode sheet; 1. Current collector; 11. First surface; 12. Second surface; 2. Positive electrode active material layer; 21. First positive electrode active material layer; 22. Second positive electrode active material layer; 4. Electrolyte; Line A is a dashed line perpendicular to the dry electrode sheet; Line B is the tangent of the electrolyte droplet, and Line B and the surface of the dry electrode sheet form a contact angle θ. Detailed Implementation

[0062] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0063] As one of the important cathode materials for sodium-ion batteries, layered oxides often have problems such as poor air stability. Their surface is usually covered with residual sodium compounds, which gradually form a dense resistive layer over time. This hinders ion transport between the cathode material and the electrolyte, as well as electron conduction between the cathode material and the conductive agent, thus limiting their practical application.

[0064] To address the aforementioned problems associated with layered oxides, this invention provides a dry-process electrode sheet. By adding a carboxylic acid-modified conductive agent and a conductive binder to the dry-process electrode sheet, they are uniformly distributed between the positive electrode material (layered oxide). The carboxylic acid groups on the surface of the conductive agent can react with the sodium compounds remaining on the surface of the layered oxide, disrupting the structure of the resistive layer. This allows the electrolyte to penetrate and wet the layered oxide material, thereby improving electrolyte wettability and reducing the interfacial resistance between the electrolyte and the electrode sheet. The conductive binder PMS:PEDOT (PEDOT is polyethylene dioxythiophene, a polymer of EDOT (3,4-ethylene dioxythiophene monomer), and PMS is poly(methacryloyl-3,4-dihydroxy-L-phenylalanine-co-3-sulfopropyl methacrylate)) has a conductivity as high as 250 S / m. When applied to dry electrodes, due to its high electronic conductivity, after fiberization treatment, it can be mixed with conductive agents to form a good conductive network, improving the conductivity between the positive electrode material and the current collector. The synergistic effect of the carboxylic acid modified conductive agent and the conductive binder PMS:PEDOT can achieve the purpose of improving the rate performance of the battery.

[0065] The present invention provides a dry electrode sheet 100, which includes a current collector 1 and a positive electrode active material layer 2 disposed on at least one surface of the current collector 1.

[0066] In some embodiments, the dry electrode sheet 100 includes a current collector 1, a first positive electrode active material layer 21, and a second positive electrode active material layer 22.

[0067] In some embodiments, the current collector 1 is selected from one of aluminum foil, nickel foil or a polymer conductive film; preferably, the current collector 1 is aluminum foil.

[0068] In some embodiments, the current collector 1 has a first surface 11 and a second surface 12 facing away from each other in the thickness direction, the first positive electrode active material layer 21 is disposed on the first surface 11, and the second positive electrode active material layer 22 is disposed on the second surface 12 (as Figure 3 shown).

[0069] In some embodiments, the positive electrode active material layer 2 includes a positive electrode material, a carboxyl-modified conductive agent and a conductive binder. Among them, the positive electrode material is a sodium-ion battery layered oxide material, and the molecular formula of the sodium-ion battery layered oxide material is Na x AO2, where 0.6 < x ≤ 1, A is one or more transition metal elements or other doping elements, and the other doping elements are selected from Li, B, Mg, Al, K, Ca or Sn. There is residual alkali on the surface of the sodium-ion battery layered oxide material, and the residual alkali forms a resistance layer on the surface of the positive electrode material, resulting in the problem of high film resistance, which is commonly present in the layered oxide material.

[0070] In some embodiments, the layered oxide Na x AO2 is a P2-phase layered oxide, 0.6 < x ≤ 0.8.

[0071] In some embodiments, the layered oxide Na x AO2 is an O3-phase layered oxide, 0.8 < x ≤ 1.

[0072] In a preferred embodiment of the present invention, the molecular formula of the sodium-ion battery layered oxide material is NaNi i Fe j Mn k M m O2, where M is one or more of Li, B, Mg, Al, K, Ca, Co, V, Cr, Cu, Zn, Zr, Nb and Sn; 0 < i < 1, 0 < j < 1, 0 < k < 1, 0 < m < 1, and i + j + k + m = 1. For example, i = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or j = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or k = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.6, 0.7, 0.8, 0.9, or m = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, etc.

[0073] In some embodiments, the sodium-ion battery layered oxide material can be used in the form of particles of any shape, such as spherical, sheet-like, or irregular particles. Furthermore, the layered oxide particles can be in the form of primary or secondary particles. The size of the layered oxide particles can be any size commonly used in the prior art.

[0074] The layered oxide powder for sodium-ion batteries can be prepared using conventional methods in the field, such as solid-state sintering, and this invention does not impose any limitations.

[0075] In some embodiments, the conductive agent in the carboxyl-modified conductive agent is selected from one or more of SuperP, Ketjen Black, carbon nanotubes, carbon nanofibers, graphene, and conductive carbon, preferably carbon nanotubes or carbon nanofibers.

[0076] In some embodiments, the conductive adhesive is PMS:PEDOT.

[0077] In some embodiments, the mass ratio of the positive electrode material, the carboxyl-modified conductive agent, and the conductive binder is 85–99.25:0.25–1:0.5–32.

[0078] In some embodiments, the thickness of the positive electrode active material layer is 100–180 μm.

[0079] In some embodiments, when performing an electrolyte wettability test on a dry electrode sheet, the contact angle between the dry electrode sheet and the electrolyte is 35° to 42°.

[0080] In some embodiments, the film resistance of the dry electrode sheet is 5 to 7 Ω in the thickness direction of the dry electrode sheet.

[0081] This invention also discloses a method for preparing the above-mentioned dry electrode sheet, comprising the following steps:

[0082] S1. Mix the conductive agent with water until homogeneous to obtain an aqueous dispersion of the conductive agent;

[0083] Step S1 includes the following steps: mixing the conductive agent with water in a stirrer to obtain an aqueous dispersion of the conductive agent; wherein the conductive agent is selected from one or more of SuperP, Ketjen Black, carbon nanotubes, carbon nanofibers, graphene, and conductive carbon; preferably, the conductive agent is selected from carbon nanotubes and / or carbon nanofibers. The mass concentration of the aqueous dispersion of the conductive agent is 20-80 g / L, for example, 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, etc.

[0084] S2. Add hydrogen peroxide solution to the aqueous dispersion of the conductive agent to obtain an aqueous solution of the conductive agent; introduce a mixture of ozone and oxygen gas into the aqueous solution of the conductive agent and sonicate in a water bath to obtain an aqueous solution of the carboxyl-modified conductive agent; introduce an inert gas into the aqueous solution of the carboxyl-modified conductive agent and freeze-dry to obtain the carboxyl-modified conductive agent;

[0085] Step S2 includes the following steps: adding a certain amount of hydrogen peroxide solution to the conductive agent aqueous dispersion to obtain a conductive agent aqueous solution, controlling the volume ratio of the conductive agent aqueous dispersion to the hydrogen peroxide solution to be 1:0.2 to 0.5, for example, 1:0.2, 1:0.3, 1:0.4, 1:0.5, etc.; and introducing a gas with a flow rate of 200 to 500 mL / min and an ozone concentration of 20 to 100 g / m³ into the conductive agent aqueous solution. 3 A mixture of ozone and oxygen gas is subjected to ultrasonic treatment in a water bath at 25℃~50℃ for 0.5~3h to obtain an aqueous solution of carboxyl-modified conductive agent. This step can be carried out in an ultrasonic cleaner, where carboxyl groups are generated on the surface of the conductive agent by hydrogen peroxide-ozone-ultrasonic oxidation. The number of carboxyl groups generated on the surface of the conductive agent can be controlled by adjusting the amount of hydrogen peroxide added, the flow rate and concentration of the ozone and oxygen gas mixture, and the ultrasonic treatment time.

[0086] An inert gas is introduced into the aqueous solution of the carboxyl-modified conductive agent for 15–45 min to remove residual ozone from the aqueous solution. The inert gas is selected from nitrogen and / or argon.

[0087] Aqueous solutions of carboxyl-modified conductive agents for ozone removal are freeze-dried. Compared to conventional drying, freeze-drying makes the physical and chemical structure of the material more stable and better preserves its inherent mechanistic advantages. The freeze-drying temperature is controlled between -40 and -70°C, for example, 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C; the freeze-drying time is controlled between 5 and 12 hours, for example, 5 hours, 6 hours, 7.5 hours, 8.5 hours, 9 hours, 10.5 hours, and 12 hours.

[0088] S3. Place the positive electrode material, carboxyl-modified conductive agent, and conductive binder in a mixing tank and stir to mix evenly to obtain a mixed powder; add an appropriate amount of solvent to the mixed powder and stir to obtain a wetted mixed powder; perform a fiberization treatment on the wetted mixed powder by adding an appropriate amount of solvent to the wetted mixed powder and stirring to obtain a fiberized mixture;

[0089] In step S3, the positive electrode material is a sodium-ion battery layered oxide material, and the molecular formula of the sodium-ion battery layered oxide material is Na. xAO₂, where 0.6 < x ≤ 1, A is one or more transition metal elements or other doping elements, and the other doping elements are selected from Li, B, Mg, Al, K, Ca or Sn. Preferably, the layered oxide Na x AO₂ is NaNi i Fe j Mn k M m O₂, where M is one or more of Li, B, Mg, Al, K, Ca, Co, V, Cr, Cu, Zn, Zr, Nb and Sn; 0 < i < 1, 0 < j < 1, 0 < k < 1, 0 < m < 1, and i + j + k + m = 1.

[0090] The carboxyl - modified conductive agent is prepared by the above step 2.

[0091] The conductive binder is PMS:PEDOT, which is a conductive polymer. It can be synthesized by thermal - initiated free - radical polymerization of N - methacryloyl - 3,4 - bis(tert - butyldimethylsilyloxy) - L - phenylalanine and 3 - sulfopropyl methacrylate to obtain poly(N - methacryloyl - 3,4 - bis(tert - butyl - dimethylsilyloxy) - L - phenylalanine - 3 - sulfopropyl methacrylate) (PMTS). Then, in an aqueous solution of PMTS, 3,4 - ethylenedioxythiophene (EDOT) monomers are polymerized by oxidative polymerization to obtain a PMTS:PEDOT solution. Finally, the silyl protecting group is removed by adding HCl to obtain PMS:PEDOT. PMS:PEDOT has a high electronic conductivity (the conductivity is up to 250 S / m). When used as a binder in a dry electrode, it can improve the film resistance of the dry electrode sheet.

[0092] In step S3, it includes the following steps: placing the cathode material, the carboxyl - modified conductive agent and the conductive binder in a stirring tank according to a certain mass ratio and stirring and mixing them evenly. The mass ratio of the cathode material, the carboxyl - modified conductive agent and the conductive binder is preferably 85 - 99.25:0.25 - 1:0.5 - 3, such as 97:0.8:2.2, 97.5:05:2, 98:0.75:1.25, 98.5:0.25:1.25, etc.; the rotation speed of stirring and mixing is controlled at 100 - 300 r / min, such as 100 r / min, 150 r / min, 200 r / min, 250 r / min, 300 r / min, etc.; the time of stirring and dispersion is controlled at 0.5 - 2 h, such as 0.5 h, 1 h, 1.5 h, 2 h, etc.; the temperature of stirring and dispersion is at room temperature.

[0093] After thorough mixing, a mixed powder is obtained. An appropriate amount of solvent is added, and the mixing speed is increased to disperse the powder and wet it. The solvent is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, and ethylene glycol dimethyl ether. The solid content of the wetted mixed powder is controlled to be 96.5%–98%, for example, 96.5%, 97%, 97.5%, 98%, etc. An appropriate amount of solvent is added to swell the conductive binder. The conductive binder, positive electrode material, and carboxyl-modified conductive agent are then thoroughly mixed through stirring and dispersion. The stirring speed is controlled to be 1000–3500 r / min, for example, 1000 r / min, 1500 r / min, 2000 r / min, 2500 r / min, 3000 r / min, etc. The stirring and dispersion time is controlled to be 1–3 h, for example, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, etc. The stirring and dispersion temperature is room temperature.

[0094] After stirring and dispersing, a moistened mixed powder is obtained. An appropriate amount of solvent is added again, and the stirring temperature, speed, and time are controlled. The high-speed shear force generated by high-intensity stirring ensures the mixed powder is uniformly dispersed, achieving a fibrous effect and resulting in a fibrous mixture. The solvent is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, and ethylene glycol dimethyl ether. The solid content of the fibrous mixture is controlled to be 90-95%, for example, 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, etc. Adding an appropriate amount of solvent further swells the conductive binder, thus facilitating the fibrosis of the mixed powder through the high-speed shear force generated by high-intensity stirring. Fiberization treatment can enable conductive binders to form a cross-network structure. Conductive binders with a cross-network structure can adhere to the uniformly mixed positive electrode material and conductive agent. On the one hand, the conductive binder with a cross-network structure plays a bonding role during the subsequent hot rolling composite current collector; on the other hand, due to the high conductivity of the conductive binder itself and its own cross-network structure, a good conductive network can be formed between conductive binders, between conductive binders and positive electrode materials, and between conductive binders and conductive agents, thereby reducing the film resistance.

[0095] The stirring speed is controlled between 4500 and 6000 r / min, for example, 4500 r / min, 5000 r / min, 5500 r / min, 6000 r / min, etc.; the stirring time is controlled between 0.5 and 2 hours, for example, 0.5 hours, 1 hour, 1.5 hours, 2 hours, etc.; the stirring temperature is controlled between 20 and 50 degrees Celsius, for example, 25 degrees Celsius, 30 degrees Celsius, 35 degrees Celsius, 40 degrees Celsius, 45 degrees Celsius, 50 degrees Celsius, etc.

[0096] S4. The fibrous mixture is placed in an extruder and extruded to obtain an initial film; the initial film is rolled to obtain a finished film; the finished film and the current collector are hot rolled together to obtain a dry electrode sheet.

[0097] Step S4 includes the following steps: extruding the fibrous mixture using an extruder to prepare an initial film, wherein the extrusion temperature is controlled between 40 and 120°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 70°C, 80°C, 85°C, 100°C, 115°C, etc.; and the thickness of the initial film is between 250 and 400 μm, for example, 250 μm, 300 μm, 350 μm, 400 μm, etc. After extrusion molding, the initial film is rolled to obtain the finished film. The rolling temperature is 80–150℃, for example, 80℃, 85℃, 95℃, 100℃, 115℃, etc. The thickness of the finished film is 120–200μm, for example, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, etc. Finally, the finished film and the current collector are hot-rolled together. The hot-rolling temperature is 100–200℃, for example, 100℃, 115℃, 130℃, 145℃, 155℃, 170℃, 185℃, 200℃, etc. After hot-rolling, a dry electrode sheet is obtained.

[0098] The above-described steps of hot-rolling composite of the diaphragm and the current collector include hot-rolling composite of one diaphragm onto one side of the current collector (single-sided composite) or hot-rolling composite of two diaphragms onto one side of the current collector respectively (double-sided composite). After hot-rolling composite of the diaphragm and the current collector, a dry electrode sheet is obtained. The diaphragm forms the positive active material layer on the surface of the dry electrode sheet. The thickness of the positive active material layer can be obtained by adjusting the thickness of the diaphragm and the rolling pressure of the hot-rolling composite, according to actual needs. Adjusting the rolling pressure of the hot-rolling composite to control the thickness of the positive active material layer is a conventional operation method in this field.

[0099] The type of current collector is not specifically limited and can be selected according to actual needs. For example, the current collector can be aluminum foil, nickel foil or polymer conductive film. Preferably, the current collector is aluminum foil.

[0100] Based on the above-mentioned dry electrode sheet, the present invention also provides a sodium-ion battery, including a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is configured to isolate the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet is the above-mentioned dry electrode sheet of the present invention or the dry electrode sheet obtained by the above-mentioned preparation method of the present invention.

[0101] In the aforementioned sodium-ion batteries, the type of separator is not specifically limited and can be any separator material used in existing batteries, such as polyethylene, polypropylene, polyvinylidene fluoride, non-woven fabric, their multilayer composite membranes, and modified separators such as ceramic modification and PVDF modification, but not limited to these.

[0102] In the aforementioned sodium-ion battery, the electrolyte can be one or more of the following: organic liquid electrolyte, organic solid electrolyte, solid ceramic electrolyte, and gel electrolyte. Preferably, the electrolyte is an organic liquid electrolyte, which is obtained by dissolving a sodium salt in a non-aqueous organic solvent; wherein the sodium salt may include one or more of sodium difluorophosphate (NaPO2F2), sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSi), and sodium difluorooxalate borate (NaDFOB). The aforementioned non-aqueous organic solvent may include one or more of cyclic carbonates, chain carbonates, and carboxylic acid esters. Cyclic carbonates may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate, and γ-butyrolactone; chain carbonates may be selected from one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), methyl acetate (MA), ethyl acetate (EA), and ethyl propionate (EP).

[0103] In some embodiments, a certain amount of additives may be added to the organic liquid electrolyte. The additives may include one or more of the following: vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), vinyl sulfite (ES), methylene disulfonate (MMDS), 1,3-propanesulfonate lactone (PS), propylene sulfonate lactone (PES), propylene sulfate (TMS), trimethylsilane phosphate (TMSP), trimethylsilane borate (TMSB), and fluoroethylene carbonate (FEC).

[0104] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0105] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0106] 1. SEM Testing Methods

[0107] First, apply a layer of conductive adhesive to the sample holder, then attach the cut dry electrode sheet to the conductive adhesive, and observe it under a scanning electron microscope.

[0108] 2. Electrolyte wettability test: The dry-process electrode sheet, after hot-roll pressing and lamination, was cut into rectangles approximately 5cm × 10cm and placed on the test stage. 20μL of electrolyte was dropped onto the dry-process electrode sheet using a pipette. After 2 minutes, a photograph was taken and the contact angle was measured. The electrolyte was 1M sodium hexafluorophosphate dissolved in a solvent with a volume ratio of EC:DEC = 1:1 + 5% FEC. A schematic diagram of the contact angle test for electrolyte 4 and dry-process electrode sheet 100 is shown below. Figure 2 As shown, a contact angle θ is formed between the tangent of the electrolyte 4 droplet and the interface of the dry electrode 100. The smaller the contact angle θ, the better the wettability of the electrolyte 4 on the dry electrode 100.

[0109] 3. Diaphragm Resistance Test: The dry-process electrode sheet after hot-rolling lamination is cut into rectangular samples of approximately 5cm × 10cm. The sample is placed between the two electrodes of the diaphragm resistance meter. The test pressure and holding time parameters are set on the MRMS software, and the test is started. The software automatically reads data such as diaphragm thickness, resistance, resistivity, and conductivity. Ten locations are randomly selected for testing on each sample, and the average value is calculated.

[0110] 4. Assembly and testing of pouch cells

[0111] The dry electrode sheet prepared using the method described in this application is used as the positive electrode. Next, the negative electrode hard carbon material, conductive agent SuperP, and CMC are weighed according to a mass ratio of 97:1.5:1.5, dissolved in a certain amount of water, stirred, coated, dried, and cut to prepare the negative electrode. The electrode sheet is prepared using a winding process. The separator is wound 5 / 6 turns first, then the positive electrode and the negative electrode are wound sequentially, for a total of 8 turns. Finally, the positive electrode is wound up, ensuring that the negative electrode is completely encapsulated within the positive electrode. The prepared core is welded with tabs and glued, then sealed with aluminum-plastic film, baked in a vacuum oven for 40–120 hours, and then removed. The water content is tested (H2O < 200 ppm is required). Then, electrolyte is injected according to a certain injection coefficient and ratio, sealed, aged, formed, and tested for capacity. The electrolyte used is 1M sodium hexafluorophosphate dissolved in a solvent with a volume ratio of EC:DEC = 1:1 + 5% FEC.

[0112] Capacity testing method: Place the sized pouch battery on the Xinwei Battery Testing Cabinet CTE-4064, first charge it with a constant current of 1C to 4V, then charge it with a constant voltage of 4V until the current is ≤0.05C, then discharge it with 1C to 2V, and then discharge it with 0.1C to 2V. Collect the test data to obtain the discharge capacity of the pouch battery, that is, the discharge specific capacity of 1C+0.1C, in mAh / g.

[0113] Rate performance test: The capacity-graded pouch batteries were placed on the Xinwei Battery Testing Cabinet CTE-4064. The charge and discharge voltage range was 2.0 to 4.0V. For the first week, a 2C rate was used for 5 weeks of charge and discharge testing. The average value of each cycle of 2C rate charge and discharge during this period was recorded as the 2C discharge capacity. Starting from the 6th week, a 4C rate was used for 5 weeks of charge and discharge testing. The average value of each cycle of 4C rate charge and discharge during this period was recorded as the 4C discharge capacity. Starting from the 11th week, a 5C rate was used for 5 weeks of charge and discharge testing. The average value of each cycle of 5C rate charge and discharge during this period was recorded as the 5C discharge capacity. The unit is mAh / g.

[0114] Example 1

[0115] (1) A conductive agent aqueous dispersion with a concentration of 50 g / L was prepared by uniformly mixing carbon nanotubes and water. Hydrogen peroxide with a volume ratio of 0.2:1 (hydrogen peroxide: conductive agent aqueous dispersion) was added to the conductive agent aqueous dispersion, and ozone with a concentration of 50 g / m³ was introduced. 3 A mixture of ozone and oxygen gas was prepared at a flow rate of 350 mL / min and ultrasonicated in a water bath at 35°C for 1 hour. Then, an inert gas (a mixture of argon and nitrogen) was introduced to purge the reaction system for 20 minutes to remove residual ozone. After freeze-drying, a carboxyl-modified conductive agent was obtained.

[0116] (2) O3-NaNi 0.34 Fe 0.33 Mn 0.33 O2, carboxyl-modified conductive agent, and conductive binder (PMS:PEDOT) were placed in a mixing tank at a mass percentage of 98%, 0.75%, and 1.25%, respectively, and mixed at 200 rpm for 1.5 hours to obtain a uniformly mixed dry powder. An appropriate amount of solvent was added to wet the dry powder particles, and the mixture was stirred and dispersed for 2 hours at a stirring speed of 2000 rpm to fully mix the solvent-wetted powder particles. A second appropriate amount of solvent was added, and the stirring temperature was controlled at 55℃. The stirring speed was adjusted to 5500 rpm, and the high-speed shear force generated by the high-intensity stirring was used to uniformly disperse the positive electrode material, conductive agent, and binder for 1.5 hours to achieve a fibrous effect.

[0117] (3) The fibrous powder was extruded at 80°C to obtain a sheet with a thickness of 350 μm; the obtained sheet was rolled at 120°C to form an electrode film with a thickness of 180 μm; finally, the positive electrode film and the aluminum foil current collector were hot-rolled and laminated at 150°C to obtain a dry electrode sheet (double-sided composite) for sodium-ion batteries. The structural schematic diagram of the dry electrode sheet is shown below. Figure 3 As shown.

[0118] Example 2

[0119] (1) A conductive agent aqueous dispersion with a concentration of 50 g / L was prepared by uniformly mixing carbon nanotubes and water. Hydrogen peroxide with a volume ratio of 0.2:1 (hydrogen peroxide: conductive agent aqueous dispersion) was added to the conductive agent aqueous dispersion, and ozone with a concentration of 50 g / m³ was introduced. 3 An ozone / oxygen mixture was prepared at a flow rate of 350 mL / min and ultrasonicated in a water bath at 35°C for 1 hour. The ozone remaining in the reaction system was then removed by blowing with an inert gas (a mixture of argon and nitrogen) for 20 minutes. After freeze-drying, a conductive agent modified with carboxyl functional groups was obtained.

[0120] (2) P2-Na 0.67 Ni 0.33 Mn 0.67 O2, a carboxyl functional group modified conductive agent, and a conductive binder (PMS:PEDOT) were placed in a mixing tank at a mass percentage of 98%, 0.75%, and 1.25%, respectively, and mixed at 200 r / min for 1.5 h to obtain a uniformly mixed dry powder. An appropriate amount of solvent was added to wet the dry powder particles, and the mixture was stirred and dispersed for 2 h at a stirring speed of 2000 r / min to fully mix the solvent-wetted powder particles. A second appropriate amount of solvent was added, and the stirring temperature was controlled at 55℃. The stirring speed was adjusted to 5500 r / min. The high-speed shear force generated by the high-intensity stirring was used to uniformly disperse the positive electrode material, conductive agent, and binder for 1.5 h to achieve a fibrous effect.

[0121] (3) The fibrous powder is extruded at 80°C to form a sheet with a thickness of 350μm; the sheet is rolled at 120°C to form an electrode film with a thickness of 180μm; finally, the positive electrode film and the aluminum foil current collector are hot rolled and compounded at 150°C to obtain a dry electrode sheet (double-sided composite) for sodium-ion batteries.

[0122] Example 3

[0123] (1) A conductive agent aqueous dispersion with a concentration of 50 g / L was prepared by uniformly mixing carbon nanotubes and water. Hydrogen peroxide with a volume ratio of 0.2:1 (hydrogen peroxide: conductive agent aqueous dispersion) was added to the conductive agent aqueous dispersion, and ozone with a concentration of 50 g / m³ was introduced. 3 An ozone / oxygen mixture was prepared at a flow rate of 350 mL / min and ultrasonicated in a water bath at 35°C for 1 hour. The ozone remaining in the reaction system was then removed by blowing with an inert gas (a mixture of argon and nitrogen) for 20 minutes. After freeze-drying, a conductive agent modified with carboxyl functional groups was obtained.

[0124] (2) O3-NaNi 0.34 Fe 0.33 Mn 0.33O2, a carboxyl functional group modified conductive agent, and a conductive binder (PMS:PEDOT) were placed in a mixing tank at a mass percentage of 98.5%, 0.25%, and 1.25%, respectively, and mixed at 200 r / min for 1.5 h to obtain a uniformly mixed dry powder. An appropriate amount of solvent was added to wet the dry powder particles, and the mixture was stirred and dispersed for 2 h at a stirring speed of 2000 r / min to fully mix the solvent-wetted powder particles. A second appropriate amount of solvent was added, and the stirring temperature was controlled at 55℃. The stirring speed was adjusted to 5500 r / min. The high-speed shear force generated by the high-intensity stirring was used to uniformly disperse the positive electrode material, conductive agent, and binder for 1.5 h to achieve a fibrous effect.

[0125] (3) The fibrous powder is extruded at 80°C to form a sheet with a thickness of 350μm; the sheet is rolled at 120°C to form an electrode film with a thickness of 180μm; finally, the positive electrode film and the aluminum foil current collector are hot rolled and compounded at 150°C to obtain a dry electrode sheet (double-sided composite) for sodium-ion batteries.

[0126] Example 4

[0127] (1) A conductive agent aqueous dispersion with a concentration of 50 g / L was prepared by uniformly mixing carbon nanotubes and water. Hydrogen peroxide with a volume ratio of 0.2:1 (hydrogen peroxide: conductive agent aqueous dispersion) was added to the conductive agent aqueous dispersion, and ozone with a concentration of 50 g / m³ was introduced. 3 An ozone / oxygen mixture was prepared at a flow rate of 350 mL / min and ultrasonicated in a water bath at 35°C for 1 hour. The ozone remaining in the reaction system was then removed by blowing with an inert gas (a mixture of argon and nitrogen) for 20 minutes. After freeze-drying, a conductive agent modified with carboxyl functional groups was obtained.

[0128] (2) O3-NaNi 0.34 Fe 0.33 Mn 0.33 O2, a carboxyl functional group modified conductive agent, and a conductive binder (PMS:PEDOT) were placed in a mixing tank at a mass percentage of 97.5%, 0.5%, and 2% respectively, and mixed at 200 r / min for 1.5 h to obtain a uniformly mixed dry powder. An appropriate amount of solvent was added to wet the dry powder particles, and the mixture was stirred and dispersed for 2 h at a stirring speed of 2000 r / min to fully mix the solvent-wetted powder particles. A second appropriate amount of solvent was added, and the stirring temperature was controlled at 55℃. The stirring speed was adjusted to 5500 r / min. The high-speed shear force generated by the high-intensity stirring was used to uniformly disperse the positive electrode material, conductive agent, and binder for 1.5 h to achieve a fibrous effect.

[0129] (3) The fibrous powder is extruded at 80°C to form a sheet with a thickness of 350μm; the sheet is rolled at 120°C to form an electrode film with a thickness of 180μm; finally, the positive electrode film and the aluminum foil current collector are hot rolled and compounded at 150°C to obtain a dry electrode sheet (double-sided composite) for sodium-ion batteries.

[0130] Comparative Example 1

[0131] (1) O3-NaNi 0.34 Fe 0.33 Mn 0.33 O2, conductive agent (carbon nanotubes), and binder (PTFE) are placed in a mixing tank at a mass percentage of 98%, 0.75%, and 1.25%, respectively, and mixed at 200 rpm for 1.5 hours to obtain a uniformly mixed dry powder. An appropriate amount of solvent is added to wet the dry powder particles, and the mixture is stirred and dispersed for 2 hours at a stirring speed of 2000 rpm to fully mix the solvent-wetted powder particles. A second appropriate amount of solvent is added, and the stirring temperature is controlled at 55℃ while the stirring speed is adjusted to 5500 rpm. The high-speed shear force generated by the high-intensity stirring ensures that the positive electrode material, conductive agent, and binder are uniformly dispersed for 1.5 hours to achieve a fibrous effect.

[0132] (2) The fibrous powder is extruded at 80°C to form a sheet with a thickness of 350μm; the sheet is rolled at 120°C to form an electrode film with a thickness of 180μm; finally, the positive electrode film and the aluminum foil current collector are hot rolled and compounded at 150°C to obtain a dry electrode sheet (double-sided composite) for sodium-ion batteries.

[0133] Comparative Example 2

[0134] (1) O3-NaNi 0.34 Fe 0.33 Mn 0.33 O2, conductive agent (carbon nanotubes), and conductive binder (PMS:PEDOT) were placed in a mixing tank at a mass percentage of 98%, 0.75%, and 1.25%, respectively, and mixed at 200 rpm for 1.5 hours to obtain a uniformly mixed dry powder. An appropriate amount of solvent was added to wet the dry powder particles, and the mixture was stirred and dispersed for 2 hours at a stirring speed of 2000 rpm to fully mix the solvent-wetted powder particles. A second appropriate amount of solvent was added, and the stirring temperature was controlled at 55℃. The stirring speed was adjusted to 5500 rpm, and the high-speed shear force generated by the high-intensity stirring was used to uniformly disperse the positive electrode material, conductive agent, and binder for 1.5 hours to achieve a fibrous effect.

[0135] (2) The fibrous powder is extruded at 80°C to form a sheet with a thickness of 350μm; the sheet is rolled at 120°C to form an electrode film with a thickness of 180μm; finally, the positive electrode film and the aluminum foil current collector are hot rolled and compounded at 150°C to obtain a dry electrode sheet (double-sided composite) for sodium-ion batteries.

[0136] Comparative Example 3

[0137] (1) P2-Na 0.67 Ni 0.33 Mn 0.67 O2, conductive agent (carbon nanotubes), and conductive binder (PMS:PEDOT) were placed in a mixing tank at a mass percentage of 98%, 0.75%, and 1.25%, respectively, and mixed at 200 rpm for 1.5 hours to obtain a uniformly mixed dry powder. An appropriate amount of solvent was added to wet the dry powder particles, and the mixture was stirred and dispersed for 2 hours at a stirring speed of 2000 rpm to fully mix the solvent-wetted powder particles. A second appropriate amount of solvent was added, and the stirring temperature was controlled at 55℃. The stirring speed was adjusted to 5500 rpm, and the high-speed shear force generated by the high-intensity stirring was used to uniformly disperse the positive electrode material, conductive agent, and binder for 1.5 hours to achieve a fibrous effect.

[0138] (2) The fibrous powder is extruded at 80°C to form a sheet with a thickness of 350μm; the sheet is rolled at 120°C to form an electrode film with a thickness of 180μm; finally, the positive electrode film and the aluminum foil current collector are hot rolled and compounded at 150°C to obtain a dry electrode sheet (double-sided composite) for sodium-ion batteries.

[0139] Comparative Example 4

[0140] (1) A conductive agent aqueous dispersion with a concentration of 50 g / L was prepared by uniformly mixing carbon nanotubes and water. Hydrogen peroxide with a volume ratio of 0.2:1 (hydrogen peroxide: conductive agent aqueous dispersion) was added to the conductive agent aqueous dispersion, and ozone with a concentration of 50 g / m³ was introduced. 3 An ozone / oxygen mixture was prepared at a flow rate of 350 mL / min and ultrasonicated in a water bath at 35°C for 1 hour. The ozone remaining in the reaction system was then removed by blowing with an inert gas (a mixture of argon and nitrogen) for 20 minutes. After freeze-drying, a conductive agent modified with carboxyl functional groups was obtained.

[0141] (2) O3-NaNi 0.34 Fe 0.33 Mn 0.33O2, a carboxyl functional group modified conductive agent, and a conductive binder (PTFE) were placed in a mixing tank at a mass percentage of 98.5%, 0.25%, and 1.25%, respectively, and mixed at 200 r / min for 1.5 h to obtain a uniformly mixed dry powder. An appropriate amount of solvent was added to wet the dry powder particles, and the mixture was stirred and dispersed for 2 h at a stirring speed of 2000 r / min to fully mix the solvent-wetted powder particles. A second appropriate amount of solvent was added, and the stirring temperature was controlled at 55℃. The stirring speed was adjusted to 5500 r / min. The high-speed shear force generated by the high-intensity stirring was used to uniformly disperse the positive electrode material, conductive agent, and binder for 1.5 h to achieve a fibrous effect.

[0142] (3) The fibrous powder is extruded at 80°C to form a sheet with a thickness of 350μm; the sheet is rolled at 120°C to form an electrode film with a thickness of 180μm; finally, the positive electrode film and the aluminum foil current collector are hot rolled and compounded at 150°C to obtain a dry electrode sheet (double-sided composite) for sodium-ion batteries.

[0143] Comparative Example 5

[0144] (1) A conductive agent aqueous dispersion with a concentration of 50 g / L was prepared by uniformly mixing carbon nanotubes and water. Hydrogen peroxide with a volume ratio of 0.2:1 (hydrogen peroxide: conductive agent aqueous dispersion) was added to the conductive agent aqueous dispersion, and ozone with a concentration of 50 g / m³ was introduced. 3 A mixture of ozone and oxygen gas was prepared at a flow rate of 350 mL / min and ultrasonicated in a water bath at 35°C for 1 hour. Then, an inert gas (a mixture of argon and nitrogen) was introduced to purge the reaction system for 20 minutes to remove residual ozone. After freeze-drying, a carboxyl-modified conductive agent was obtained.

[0145] (2) O3-NaNi 0.34 Fe 0.33 Mn 0.33 O2, carboxyl-modified conductive agent, and conductive binder (PTFE) are placed in a mixing tank at a mass percentage of 98%, 0.75%, and 1.25%, respectively, and mixed at 200 rpm for 1.5 hours to obtain a uniformly mixed dry powder. An appropriate amount of solvent is added to wet the dry powder particles, and the mixture is stirred and dispersed for 2 hours at a stirring speed of 2000 rpm to fully mix the solvent-wetted powder particles. A second appropriate amount of solvent is added, and the stirring temperature is controlled at 55℃ while the stirring speed is adjusted to 5500 rpm. The high-speed shear force generated by the high-intensity stirring ensures that the positive electrode material, conductive agent, and binder are uniformly dispersed for 1.5 hours to achieve a fibrous effect.

[0146] (3) The fibrous powder is extruded at 80°C to form a sheet with a thickness of 350μm; the sheet is rolled at 120°C to form an electrode film with a thickness of 180μm; finally, the positive electrode film and the aluminum foil current collector are hot rolled and compounded at 150°C to obtain a dry electrode sheet (double-sided composite) for sodium-ion batteries.

[0147] Material characterization

[0148] Characterization tests were performed on the dry electrode sheets prepared in the examples. Figure 1 The image shows a scanning electron microscope (SEM) image of the dry electrode sheet prepared in Example 1. Figure 1 It can be seen that the conductive binder PMS:PEDOT is distributed in a fibrous manner on the dry electrode sheet. Due to its high conductivity, it can form a good conductive network.

[0149] Performance testing

[0150] The electrolyte wettability test and membrane resistance test results of the dry electrode sheets of each embodiment and comparative example are shown in Table 1.

[0151] Table 1

[0152] Group Electrolyte contact angle (°) Diaphragm resistance (Ω) Example 1 37.5° 5.6 Example 2 35.1° 5.9 Example 3 40.5° 6.5 Example 4 38.2° 6.2 Comparative Example 1 58.2° 10.7 Comparative Example 2 57.3° 7.7 Comparative Example 3 59.0° 7.5 Comparative Example 4 37.2° 8.6 Comparative Example 5 36.1° 8.3

[0153] The test results of the 1C+0.1C discharge specific capacity and the 2C, 4C, and 5C discharge specific capacity of the sodium-ion soft-pack batteries assembled with dry electrode sheets in each embodiment and comparative example are shown in Table 2.

[0154] Table 2

[0155]

[0156] The positive electrode materials in Example 1 and Comparative Example 1 are the same, the difference being that Example 1 uses a conductive binder PMS:PEDOT and a conductive agent modified with carboxyl functional groups, while Comparative Example 1 uses polytetrafluoroethylene (PTFE) as the binder and an unmodified conductive agent. Table 1 shows that the dry electrode sheet prepared in Example 1 using the all-organic polymer conductive binder PMS:PEDOT and the functional group-modified conductive agent has a contact angle between the electrolyte and the electrode sheet of only 37.5° and a film resistance of only 5.6Ω, which is a significant improvement compared to Comparative Example 1. Table 2 shows that the dry electrode sheet prepared using the carboxyl-modified conductive agent and the conductive binder PMS:PEDOT has better rate performance.

[0157] The positive electrode materials and binders used in Examples 1 and 2, and Examples 2 and 3, were the same. The difference was that Examples 1 and 2 used conductive agents modified with carboxyl functional groups, while Comparative Examples 2 and 3 used conductive agents without carboxyl functional group modification. Referring to Tables 1 and 2, it can be seen that the dry-process electrode sheets exhibited excellent film resistance and wettability with the carboxyl functional group-modified conductive agent, resulting in a certain improvement in rate performance. This indicates that the addition of functional group-modified conductive agents can effectively improve the wetting effect of the electrolyte on the dry-process electrode sheets and reduce the film resistance of the electrode sheets.

[0158] The positive electrode materials and conductive agents of Examples 1 and 5, and Examples 3 and 5 are the same. The difference is that Examples 1 and 3 use the conductive binder PMS:PEDOT, while Comparative Examples 4 and 5 use the conventional binder polytetrafluoroethylene (PTFE). As can be seen from Table 1, because polytetrafluoroethylene (PTFE) does not have conductivity and the proportion of conductive agent is relatively small, its film resistance increases.

[0159] In summary, this invention uses the all-organic polymer conductive binder PMS:PEDOT in combination with a carboxyl functional group modified conductive agent to prepare dry electrode sheets. The addition of the highly polar carboxyl functional group modified conductive agent can effectively improve the wettability of the electrolyte. The carboxyl functional group can react with the sodium compounds remaining on the surface of the positive electrode material, weakening the influence of the resistive layer. In conjunction with the all-organic polymer conductive binder PMS:PEDOT, the film resistance of the electrode sheet can be significantly reduced and the rate performance of the battery can be improved.

[0160] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A dry electrode sheet (100), characterized in that, It includes a current collector (1) and a positive electrode active material layer (2) provided on at least one surface of the current collector. The positive electrode active material layer (2) includes a positive electrode material, a carboxyl-modified conductive agent, and a conductive binder. The conductive binder is PMS:PEDOT, where PMS is poly(methacryloyl-3,4-dihydroxy-L-phenylalanine-co-3-sulfopropyl methacrylate), and PEDOT is polyethylenedioxythiophene.

2. The dry-process electrode sheet according to claim 1, characterized in that, The mass ratio of the positive electrode material, the carboxyl-modified conductive agent, and the conductive binder is 85-99.25:0.25-1:0.5-32.

3. The dry-process electrode sheet according to claim 1, characterized in that, The conductive agent is selected from one or more of SuperP, Ketjen black, carbon nanotubes, carbon nanofibers, and graphene.

4. A dry-process electrode sheet according to claim 1, characterized in that, The positive electrode material is a sodium-ion battery layered oxide material. The molecular formula of the sodium-ion battery layered oxide material is NaxAO2, where 0.6 < x ≤ 1, and A is one or more transition metal elements or other doping elements. The other doping elements are selected from Li, B, Mg, Al, K, Ca, or Sn.

5. A dry-process electrode sheet according to claim 1, characterized in that, The dry electrode sheet (100) includes a current collector (1), a first positive electrode active material layer (21), and a second positive electrode active material layer (22). The current collector has a first surface (11) and a second surface (12) facing away from each other in the thickness direction. The first positive electrode active material layer (21) is provided on the first surface (11), and the second positive electrode active material layer (22) is provided on the second surface (12).

6. A dry-process electrode sheet according to claim 1, characterized in that, The thickness of the positive electrode active material layer is 100-180 μm.

7. A dry-process electrode sheet according to claim 1, characterized in that, When performing an electrolyte wettability test on the dry electrode sheet, the contact angle between the dry electrode sheet and the electrolyte is 35°-42°.

8. A dry-process electrode sheet according to claim 1, characterized in that, In the thickness direction of the dry electrode sheet, the film resistance of the dry electrode sheet is 5-7 Ω.

9. A method for preparing a dry electrode sheet as described in any one of claims 1-8, characterized in that, It includes the following steps: Provide a positive electrode material, a carboxyl-modified conductive agent, and a conductive binder; Mix the positive electrode material, the carboxyl-modified conductive agent, and the conductive binder according to a mass ratio of 85-99.25:0.25-1:0.5-3 to obtain a mixed powder; Add a solvent to the mixed powder and stir to obtain a wetted mixed powder; Add a solvent to the wetted mixed powder, perform fiberization treatment on the wetted mixed powder after mixing the solvents to obtain a fibrillated mixture; Place the fibrillated mixture in an extruder and extrude it at a temperature of 40-120 °C to obtain an initial film; Roll the initial film at 80-150 °C to obtain a finished film; Thermally roll and laminate the finished film and the current collector at a temperature of 100-200 °C to obtain the dry electrode sheet.

10. The method for preparing a dry electrode sheet according to claim 9, characterized in that, The carboxyl-modified conductive agent is prepared through the following steps: Mix the conductive agent and water evenly to prepare a conductive agent aqueous dispersion with a concentration of 20-80 g / L. The conductive agent is selected from one or more of SuperP, Ketjen black, carbon nanotubes, carbon nanofibers, and graphene; Hydrogen peroxide solution is added to the aqueous dispersion of the conductive agent to obtain an aqueous solution of the conductive agent; the volume ratio of the aqueous dispersion of the conductive agent to the hydrogen peroxide solution is 1:0.2 to 0.

5. A mixture of ozone and oxygen gas with a flow rate of 200-500 mL / min and an ozone concentration of 20-100 g / m3 is introduced into the conductive agent aqueous solution, and the solution is ultrasonically treated in a water bath at 25℃-50℃ for 0.5-3 h to obtain a conductive agent aqueous solution modified with carboxyl functional groups. An inert gas is introduced into the aqueous solution of the conductive agent modified with carboxyl functional groups for 15–45 min, and then freeze-dried at -40 to -70°C for 5–12 h to obtain the carboxyl-modified conductive agent.

11. The method for preparing a dry electrode sheet according to claim 9, characterized in that, The step of mixing the positive electrode material, the carboxyl-modified conductive agent, and the conductive binder specifically involves placing the positive electrode material, the carboxyl-modified conductive agent, and the conductive binder in a mixing tank and mixing them at a speed of 100–300 r / min for 0.5–2 h. In the step of adding solvent to the mixed powder and stirring to obtain a wetted mixed powder, the stirring speed is 1000-3500 r / min and the stirring time is 1-3 h; In the step of adding a solvent to the wetted mixed powder and mixing, and then performing a fiberization treatment on the wetted mixed powder after solvent mixing, the fiberization treatment is performed at a temperature of 20-50°C and a stirring speed of 4500-6000 r / min for 0.5-2 h.

12. The method for preparing a dry electrode sheet according to claim 9, characterized in that, The solid content of the wetted mixed powder is 96.5%–98%; the solid content of the fibrous mixture is 90%–95%.

13. The method for preparing a dry electrode sheet according to claim 9, characterized in that, The conductive adhesive is PMS:PEDOT, wherein PMS is poly(methacryloyl-3,4-dihydroxy-L-phenylalanine-co-3-sulfopropyl methacrylate) and PEDOT is polyethylene dioxythiophene; the solvent is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, and ethylene glycol dimethyl ether.

14. A sodium-ion battery, characterized in that, Includes the dry electrode sheet as described in any one of claims 1-8.

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