A sodium-ion battery dry method electrode and a preparation method and application thereof

Abstract

The embodiment of the present application relates to a kind of sodium ion battery dry electrode and its preparation method and application, preparation method includes: positive active material, conductive agent, binder and composite sacrificial salt are stirred and mixed uniformly, then under the action of shearing, binder fibrillation is obtained, and fiberized mixture is obtained;The fiberized mixture is carried out heat calendering treatment, and self-supporting film embryo is obtained;Self-supporting film embryo is carried out heat roller pressing treatment, and self-supporting electrode film is obtained;Self-supporting electrode film is hotly compounded with current collector, and dry electrode electrode piece is obtained;Composite sacrificial salt is heated and decomposed in heat calendering and / or heat roller pressing process, and gas and sodium-containing solid product are generated;Gas builds multistage pore structure in the process of escaping in self-supporting electrode film;Sodium-containing solid product releases sodium ion when battery is charged for the first time, and is used to compensate the sodium consumed by negative electrode solid electrolyte interface film formation.The present application realizes the integration of sodium supplement and pore making, and the prepared electrode electrode piece has low resistivity, and battery cycle life is long.

Description

Technical Field

[0001] This invention relates to the field of dry electrode technology, and in particular to a dry electrode for sodium-ion batteries, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries have great development potential in large-scale energy storage, power, and other fields due to the abundant and uniform distribution of sodium resources, low cost, and similar working principle to lithium-ion batteries. Compared with lithium-ion batteries, sodium-ion batteries have certain advantages in low-temperature performance, rate performance, safety performance, and cost. Among various cathode material systems, layered oxide materials have become the mainstream approach for sodium-ion battery cathode materials due to their superior overall performance.

[0003] Currently, sodium-ion battery cathode sheets are mainly prepared using a wet coating process. However, the wet process has inherent drawbacks: the use of organic solvents increases costs and environmental pressures; layered oxide materials are sensitive to moisture and are prone to surface alkali accumulation during slurry preparation, forming a dense resistive layer that hinders ion transport; furthermore, in the application of sacrificial salt sodium replenishment technology in the wet process, the decomposition temperature of most sacrificial salts is much higher than the wet drying temperature, and electrochemical decomposition requires a high voltage, which can easily exceed the electrolyte stability window and trigger side reactions. Moreover, the gases released by the decomposition of sacrificial salts can easily lead to quality problems such as coating blistering and cracking.

[0004] To address these issues, dry electrode technology emerged. The dry process completely eliminates the use of solvents, resulting in electrodes with higher compaction density and superior mechanical strength, making it particularly suitable for moisture-sensitive layered oxide materials.

[0005] However, dry electrode technology still faces the following challenges: First, while the dry process increases the electrode's high compaction density, it also tends to result in a simple internal pore structure and poor connectivity, which is not conducive to electrolyte wetting and rapid sodium ion conduction.

[0006] Second, there is a clear technological bias in the existing technology regarding the application of sacrificial salts. Specifically, in wet electrode processes, the gases released from the decomposition of sacrificial salts often cause blistering and cracking of the coating, which are considered defects that need to be suppressed. This understanding is reasonable in wet processes. Due to the long-term influence of this technological inertia, those skilled in the art generally believe that gas generation by sacrificial salts during electrode preparation is harmful and should be avoided. This bias leads existing technologies to focus only on the sodium replenishment function of sacrificial salts, viewing their gas generation behavior as a side reaction that needs to be suppressed, while failing to recognize the potential value of this process in dry electrodes for actively optimizing pore structure.

[0007] Therefore, developing a technical solution that is compatible with dry processes, can efficiently replenish sodium, and can actively optimize the electrode pore structure is of great significance for preparing dry electrode sheets for sodium-ion batteries with low resistivity, and thus obtaining sodium-ion batteries with long cycle life. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by providing a dry electrode for sodium-ion batteries, its preparation method, and its application. By utilizing a composite sacrificial salt, sodium replenishment and pore formation are integrated, resulting in an electrode sheet with low resistivity and a long battery cycle life. To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a dry electrode for a sodium-ion battery, the method comprising the following steps: The positive electrode active material, conductive agent, binder and composite sacrificial salt are stirred and mixed evenly, and then the binder is fibrillated under shearing to form a three-dimensional network structure, thus obtaining a fibrous mixture; The fibrous mixture is subjected to hot calendering to obtain a self-supporting membrane preform; The self-supporting membrane preform is subjected to hot roll pressing to obtain a self-supporting electrode membrane; The self-supporting electrode film is thermally combined with the current collector to obtain a dry electrode sheet; The composite sacrificial salt is thermally decomposed during the hot rolling and / or hot rolling process to generate gas and sodium-containing solid products. During the escape process, the gas constructs a multi-level pore structure inside the self-supporting electrode film. The sodium-containing solid products release sodium ions during the first charge of the battery to compensate for the sodium consumed in the formation of the negative electrode solid electrolyte interface film.

[0009] Preferably, the mass ratio of the positive electrode active material, the conductive agent, the binder and the composite sacrificial salt is 90-98:0.2-5:0.2-10:0.5-10.

[0010] Preferably, the positive electrode active material is a layered oxide, including one or more of sodium nickel iron manganate, P2-sodium nickel manganate, sodium iron manganate, sodium nickel manganate, or high-entropy layered oxides. The conductive agent includes one or more of the following: acetylene black, Super P, carbon nanotubes, carbon fibers, Ketjen black, conductive graphite, or graphene. The adhesive includes one or more of polytetrafluoroethylene or tetrafluoroethylene copolymers.

[0011] Preferably, the composite sacrificial salt comprises one or more of sodium citrate, sodium oxalate, or sodium bicarbonate.

[0012] Preferably, the rotation speed for fibrillating the adhesive is 4000rpm-8000rpm and the time is 3min-30min.

[0013] Preferably, the temperature of the hot rolling process is 100℃-240℃ and the pressure is 20MPa-80MPa.

[0014] Preferably, the temperature of the hot roller pressing process is 70℃-250℃, and the pressure is 10T-200T.

[0015] Preferably, in the step of thermally combining the self-supporting electrode film with the current collector, the composite temperature is 70℃-250℃ and the composite pressure is 2T-30T.

[0016] In a second aspect, the present invention provides a dry electrode for a sodium-ion battery, wherein the dry electrode for a sodium-ion battery is prepared by the preparation method described in the first aspect above.

[0017] Thirdly, the present invention provides a sodium-ion battery, the sodium-ion battery comprising a sodium-ion battery dry electrode prepared by the preparation method described in the first aspect above, or comprising a sodium-ion battery dry electrode described in the second aspect above.

[0018] The preparation method provided by this invention involves, under dry, solvent-free conditions, in-situ fiberization of the binder to form a three-dimensional network structure through high-speed shearing, followed by hot calendering, hot rolling, and hot composite treatment to finally obtain a dry electrode sheet. During the hot calendering and / or hot rolling process, the composite sacrificial salt decomposes thermally, and the generated gas actively constructs a multi-level porous structure inside the electrode film upon escape, improving electrolyte wettability and sodium ion transport channels, thereby significantly reducing the resistivity of the electrode sheet. Simultaneously, the residual sodium-containing solid products (such as Na2CO3) from the decomposition are uniformly distributed in the electrode film. When this dry electrode sheet is assembled into a sodium-ion battery and undergoes its first charge, it decomposes and releases sodium ions under electrochemical conditions, compensating for the sodium consumed in the formation of the solid electrolyte interphase (SEI) film at the negative electrode, thereby improving the cycle stability of the battery.

[0019] The method for preparing a dry electrode for sodium-ion batteries provided in this invention breaks through the technical prejudice of "sacrificing salt to produce gas is harmful" in the prior art. It actively uses the gas escape behavior, which was originally regarded as a defect, to construct a multi-level pore structure, realizing the integration of sodium replenishment and pore formation. This avoids the complex process of adding additional pore-forming agents, simplifies the production process and reduces costs. Finally, a dry electrode sheet for sodium-ion batteries with low resistivity is obtained, as well as a sodium-ion battery with long cycle life assembled from it, which is suitable for mass production. Attached Figure Description

[0020] Figure 1A flowchart illustrating the preparation method of a dry electrode for a sodium-ion battery provided in an embodiment of the present invention; Figure 2 This is a photograph of the self-supporting membrane embryo prepared in Example 2 of the present invention. Figure 3 The graph shows the cycle capacity retention rate of the sodium-ion battery assembled with dry electrode according to Embodiment 2 of the present invention. Detailed Implementation

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0022] The reagents and materials used in the following examples and comparative examples are all commercially available conventional reagent products, or can be prepared by conventional methods. Where specific experimental steps or conditions are not specified in the examples, they were performed according to conventional experimental steps and conditions in the art. Unless otherwise specified, all equipment used is conventional equipment currently available in the art.

[0023] This invention provides a method for preparing a dry electrode for a sodium-ion battery, such as... Figure 1 As shown, the preparation method includes the following steps: Step 110: The positive electrode active material, conductive agent, binder and composite sacrificial salt are stirred and mixed evenly. Then, under shearing action, the binder is fibrillated to form a three-dimensional network structure, resulting in a fibrillated mixture.

[0024] In this step, the positive electrode active material, conductive agent, binder, and composite sacrificial salt are first weighed according to a predetermined mass ratio. Preferably, the mass ratio of the positive electrode active material, conductive agent, binder, and composite sacrificial salt is 90-98:0.2-5:0.2-10:0.5-10.

[0025] Preferably, the positive electrode active material is a layered oxide, including but not limited to one or more of sodium nickel manganese oxide, P2-sodium nickel manganese oxide, sodium iron manganese oxide, sodium nickel manganese oxide, or high-entropy layered oxides.

[0026] Preferably, the conductive agent includes, but is not limited to, one or more of acetylene black, Super P, carbon nanotubes, carbon fibers, Ketjen black, conductive graphite, or graphene.

[0027] Preferably, the adhesive is a fibrillable adhesive, specifically a fibrillable fluorinated resin, including but not limited to one or more of polytetrafluoroethylene or tetrafluoroethylene copolymers.

[0028] Preferably, the composite sacrificial salt includes one or more of sodium citrate, sodium oxalate, or sodium bicarbonate.

[0029] The components are added to a dry mixing device (such as a high-speed mixer, air jet mill, or dedicated dry mixing granulator) under solvent-free conditions and stirred at 1000-3000 rpm for 20-80 minutes to ensure initial uniform dispersion. Subsequently, a high-speed shearing process is performed at 4000-8000 rpm for 3-30 minutes. Under shearing, the binder particles undergo plastic deformation and are stretched into slender fibers. These fibers cross-link and entangle, forming a three-dimensional network structure to obtain a fibrous mixture. During this process, the material temperature rises due to shear heat generation and is typically controlled below a temperature that prevents significant decomposition of the composite sacrificial salt (e.g., 50℃-110℃) to avoid premature decomposition of the composite sacrificial salt.

[0030] Step 120: The fibrous mixture is subjected to hot calendering to obtain a self-supporting membrane preform.

[0031] The fibrous mixture obtained in step 110 is placed into a hot calendering device (such as a twin-roll hot calender). The temperature of the rollers and the pressure between the rollers are adjusted, with the hot calendering temperature set to 100℃-240℃, the hot calendering pressure set to 20MPa-80MPa, and the calendering speed controlled at 5m / min-10m / min. After the fibrous mixture enters the gap between the two rollers, it is subjected to the combined action of heat and pressure, and is continuously extruded into a film with a certain thickness and width, i.e., a self-supporting preform.

[0032] During this hot calendering process, two main changes occur: First, the binder fiber network further softens and compresses under heat and pressure, giving the membrane preform sufficient mechanical strength and self-supporting ability; second, the composite sacrificial salt decomposes thermally. When the temperature reaches the decomposition initiation temperature of the composite sacrificial salt, it decomposes into sodium-containing solid products (such as sodium carbonate, sodium oxide, etc.) and gases (such as carbon dioxide, water vapor, etc.). At this time, the membrane preform is still in a viscoelastic state. The gases form bubbles inside and gradually grow, then escape outward, leaving a large number of interconnected channels inside the membrane preform, initially forming a multi-level pore structure. The sodium-containing solid products remain uniformly in the membrane preform, serving as a sodium source for subsequent sodium replenishment.

[0033] Step 130: Perform hot rolling treatment on the self-supporting membrane preform to obtain a self-supporting electrode membrane.

[0034] The self-supporting preform obtained in step 120 is fed into a film-forming and thinning device (such as a multi-stage roller calender) for further hot rolling thinning. The process parameters for this step are controlled as follows: rolling temperature 70℃-250℃, rolling pressure adjustable stepwise according to the target thickness and areal density, typically 10T-200T, and calendering speed 5m / min-10m / min. After being extruded and stretched by one or more stages of rollers, the thickness of the self-supporting preform is gradually reduced to the target thickness, while the width and density of the preform are controlled, ultimately yielding a self-supporting electrode film.

[0035] This step primarily serves the following purposes: By controlling the gap and pressure between the rollers, the self-supporting preform is gradually thinned to the target areal density of 10 mg / cm². 2 -30mg / cm 2 .

[0036] The composite sacrificial salt that was not completely decomposed in step 120 will continue to decompose and generate gas in this step, further enriching the pore structure. Simultaneously, the mechanical compression of the hot roller compactor compacts the already formed pore walls, preventing pore collapse and creating stable, well-connected hierarchical channels. This hierarchical channel structure facilitates rapid electrolyte wetting and shortens the solid-phase diffusion distance of sodium ions.

[0037] Hot rolling makes the contact between conductive agent particles and between conductive agent and active material particles more compact and sufficient. At the same time, the three-dimensional network structure shrinks and cross-links under heat, locking the entire electrode structure in a low-resistance continuous conductive framework, thereby significantly reducing the electronic resistivity of the electrode.

[0038] Step 140: The self-supporting electrode film is thermally combined with the current collector to obtain a dry electrode sheet.

[0039] The self-supporting electrode film obtained in step 130 is then subjected to a hot-pressing composite process with the current collector. This step utilizes a hot-pressing composite device (such as a hot roller laminating machine).

[0040] Preferably, the current collector is a carbon-coated aluminum foil with a thickness of 10μm-20μm.

[0041] During the thermal bonding process, if the temperature is too low, the binder will not soften sufficiently, resulting in insufficient bonding strength and making the electrode prone to film detachment in subsequent processes; if the temperature is too high, it may cause the multi-level porous structure inside the electrode film to collapse. Preferably, the bonding temperature is 70℃-250℃.

[0042] The composite pressure is used to expel residual air between the interfaces, ensuring tight contact between the electrode film and the current collector, and obtaining the maximum effective composite area. Too low a pressure will result in weak localized composite bonding, while too high a pressure may crush the positive electrode active material particles or excessively compact the electrode film. Preferably, the composite pressure is 2T-30T.

[0043] After thermal bonding, the electrode sheet can be subjected to final rolling (leveling treatment) as needed, and then wound up to obtain the finished dry electrode sheet with a double-sided density of 20 mg / cm³. 2 -60mg / cm 2 The electrode compaction density reaches 2.8 g / cm³. 3 -3.2g / cm 3 .

[0044] The preparation method provided by this invention involves, under dry, solvent-free conditions, in-situ fiberization of the binder to form a three-dimensional network structure through high-speed shearing, followed by hot calendering, hot rolling, and hot composite treatment to finally obtain the electrode sheet. During the hot calendering and / or hot rolling process, the composite sacrificial salt decomposes thermally, and the generated gas actively constructs a multi-level porous structure inside the electrode film upon escape, improving electrolyte wettability and sodium ion transport channels, thereby significantly reducing the resistivity of the electrode sheet. Simultaneously, the residual sodium-containing solid products (such as Na2CO3) from the decomposition are uniformly distributed in the electrode film. When this dry-process electrode sheet is assembled into a sodium-ion battery and undergoes its first charge, it decomposes and releases sodium ions under electrochemical conditions, compensating for the sodium consumed in the formation of the solid electrolyte interphase (SEI) film at the negative electrode, thereby improving the cycle stability of the battery.

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0046] Example 1 1. Weigh sodium nickel iron manganese oxide, carbon nanotubes, polytetrafluoroethylene (PTFE), and sodium citrate in a mass ratio of 93.5:2:2:2.5. Add these materials to a high-speed mixer and mix at 2250 rpm for 1 hour, then shear at 4500 rpm for 15 minutes to fibrillate the PTFE, obtaining a fibrous mixture. During this process, maintain the material temperature at 88℃.

[0047] 2. The fibrous mixture is incorporated into a two-roll hot calender, with the temperature set at 180℃, the pressure at 30 MPa, and the speed at 6 m / min to obtain a self-supporting film preform.

[0048] 3. The self-supporting preform is fed into a multi-stage double-roll calender, with the temperature set at 250℃, the pressure at 20T, and the speed at 7m / min to obtain the self-supporting electrode film.

[0049] 4. The self-supporting electrode film is laminated with 16μm carbon-coated aluminum foil in a thermal laminating machine at a laminating temperature of 150℃ and a laminating pressure of 15T to obtain a dry-process positive electrode sheet.

[0050] Example 2 1. Weigh sodium nickel iron manganese oxide, carbon nanotubes, conductive graphite, graphene, polytetrafluoroethylene (PTFE), and sodium citrate according to a mass ratio of 92:1:1:1:2:3. Add these materials to a high-speed mixer and mix at 3000 rpm for 0.5 hours, then shear at 5000 rpm for 12 minutes to fibrillate the PTFE, obtaining a fibrous mixture. During this process, maintain the material temperature at 100℃.

[0051] 2. The fibrous mixture is incorporated into a two-roll hot calender, with the temperature set at 190℃, the pressure at 30 MPa, and the speed at 10 m / min, to obtain a self-supporting film preform.

[0052] 3. The self-supporting preform is fed into a multi-stage double-roll calender, with the temperature set at 200℃, the pressure at 5T, and the speed at 8m / min to obtain the self-supporting electrode film.

[0053] 4. The self-supporting electrode film is laminated with 16μm carbon-coated aluminum foil in a thermal laminating machine at a laminating temperature of 100℃ and a laminating pressure of 15T to obtain a dry-process positive electrode sheet.

[0054] Figure 2 This is a photograph of the self-supporting preform prepared in Example 2. Figure 2 It can be seen that by using the preparation method provided by the present invention, a self-supporting preform with complete film formation and uniform surface can be obtained.

[0055] Figure 3 This is a cycle capacity retention curve of a sodium-ion battery assembled with a dry electrode according to Embodiment 3 of the present invention. Figure 3 It can be seen that the dry positive electrode sheet prepared by the preparation method provided by the present invention, after being assembled into a sodium-ion battery, has a retention rate of 90.4% after 200 cycles.

[0056] Example 3 1. Weigh sodium nickel iron manganese oxide, carbon nanotubes, conductive graphite, graphene, polytetrafluoroethylene (PTFE), and sodium citrate in a mass ratio of 90:1.5:1:1:2.5:4. Add these materials to a high-speed mixer and mix at 2500 rpm for 70 minutes, then shear at 4000 rpm for 30 minutes to fibrillate the PTFE, obtaining a fibrous mixture. During this process, maintain the material temperature at 100℃.

[0057] 2. The fibrous mixture is incorporated into a two-roll hot calender, with the temperature set at 200℃, the pressure at 50 MPa, and the speed at 8 m / min to obtain a self-supporting film preform.

[0058] 3. The self-supporting preform is fed into a multi-stage double-roll calender, with the temperature set at 70℃, the pressure at 10T, and the speed at 5m / min to obtain the self-supporting electrode film.

[0059] 4. The self-supporting electrode film is laminated with 16μm carbon-coated aluminum foil in a thermal laminating machine at a laminating temperature of 250℃ and a laminating pressure of 10T to obtain a dry-process positive electrode sheet.

[0060] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the pressure during the hot rolling process is 10 MPa.

[0061] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that sodium citrate is not added.

[0062] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that sodium citrate in Example 1 is replaced with sodium carbonate.

[0063] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that sodium citrate in Example 1 is replaced with ammonium bicarbonate.

[0064] Next, electrochemical tests were performed on the electrode sheets prepared in the above embodiments and comparative examples.

[0065] Resistivity test: The resistivity of the electrode was tested using the two-probe method. A 10cm circular sample after rolling was taken. 2 For the electrode, place the sample to be tested on the lower metal terminal of the resistivity meter, click to start the resistivity test, apply a pressure of 5 MPa to both sides of the sample on the upper metal terminal, hold the pressure for 5 seconds, collect 6 points for each electrode, and take the average value as the resistivity value of the electrode.

[0066] Peel strength test: Referring to GB / T 2792-2014 standard, the peel strength of the electrode was tested using the 180° peel method. The prepared electrode was cut into 15mm × 150mm samples. A thin steel plate 17cm long and 5cm wide was prepared. A strip of double-sided tape was applied to the center of the steel plate (ensuring the tape length was greater than the sample test length and the same width as the electrode). The plate was then flattened using a roller. The prepared electrode was then attached to the double-sided tape and flattened again using a roller. The steel plate with the attached electrode was inserted into the lower clamp and fixed horizontally. The electrode without tape was inserted into the upper clamp and fixed at a 90° angle to the electrode in the lower clamp. The peel length and width, test force (50N), and peel speed (25cm / min) were input to start the test, obtaining the peel strength curve and peel strength value.

[0067] Cyclic capacity retention test: The prepared positive electrode sheet was die-cut and the tabs were welded on. A 9μm thick ceramic-coated polyethylene separator was used to stack the positive electrode sheet, separator, and negative electrode sheet in a "sandwich" structure to assemble a soft-pack cell, which was then placed in an aluminum-plastic film casing. Electrolyte was injected into the cell (2g / Ah), followed by vacuum sealing. The sealed cell was then placed in an inert atmosphere glove box for 48 hours to allow the electrolyte to fully wet the electrodes and separator. After the standing period, the cell underwent formation (initial constant current and constant voltage charging activation), followed by vacuum degassing (second sealing), ultimately yielding a sodium-ion soft-pack full battery.

[0068] Electrochemical performance testing: The assembled pouch cells were placed in a charge-discharge tester and subjected to cyclic charge-discharge tests at the set voltage window and charge-discharge rate. The discharge capacity of each cycle was recorded, and the capacity retention rate was calculated. The test temperature was 25℃, and the voltage window was 0V-2.5V. Cycle capacity retention rate: The ratio of the specific capacity after 200 cycles to the specific capacity after the first cycle is the 200-cycle capacity retention rate. Detailed test data are shown in Table 1.

[0069] Table 1 As can be seen from the data comparison in Table 1, Examples 1-3 (with sodium citrate added as a composite sacrificial salt) all successfully formed films, and their resistivity, peel strength and cycle retention were all superior to those of Comparative Examples 1-4.

[0070] Comparative Example 1 failed to form a film due to insufficient calendering pressure (10 MPa), indicating that sufficient calendering pressure is a prerequisite for the formation of a self-supporting film. Comparative Example 2 (without any sacrificial salt added) had the highest resistivity, but the lowest peel strength and cycle retention, indicating that the electrode performance was the worst without sodium replenishment and pore formation.

[0071] Comparative Example 3 (using sodium carbonate instead of sodium citrate, only adding sodium without creating pores) and Comparative Example 4 (using ammonium bicarbonate instead of sodium citrate, only creating pores without adding sodium) showed similar performance but were significantly worse than Example 1, indicating that neither sodium addition nor pore creation alone could achieve a synergistic effect. Only by adding a composite sacrificial salt to simultaneously achieve sodium compensation and multi-level pore construction can resistivity be effectively reduced, peel strength improved, and cycle life extended.

[0072] Furthermore, Examples 2 and 3, which use a combination of three conductive agents, outperform Example 1, which uses only a single conductive agent, demonstrating that multidimensional conductive networks can further improve electrode performance.

[0073] The above comparisons fully demonstrate that only by synergistically combining "gas generation and pore formation" with "sodium replenishment" can excellent conductivity, mechanical strength, and cycle stability be simultaneously achieved. This invention integrates sodium replenishment and pore formation through a dry process combined with composite sacrificial salts. Furthermore, by combining various conductive agents, it yields sodium-ion battery positive electrode sheets with low resistance, high peel strength, and long cycle life. This effectively overcomes the technical prejudice that "gas generation from sacrificial salts is harmful," achieving significantly superior technical results compared to solutions that do not add sacrificial salts, only replenish sodium, or only form pores.

[0074] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a dry electrode for a sodium-ion battery, characterized in that, The preparation method includes the following steps: The positive electrode active material, conductive agent, binder and composite sacrificial salt are stirred and mixed evenly, and then the binder is fibrillated under shearing to form a three-dimensional network structure, thus obtaining a fibrillated mixture; The fibrous mixture is subjected to hot calendering to obtain a self-supporting membrane preform; The self-supporting membrane preform is subjected to hot roll pressing to obtain a self-supporting electrode membrane; The self-supporting electrode film is thermally combined with the current collector to obtain a dry electrode sheet; The composite sacrificial salt is thermally decomposed during the hot rolling and / or hot rolling process to generate gas and sodium-containing solid products. During the escape process, the gas constructs a multi-level pore structure inside the self-supporting electrode film. The sodium-containing solid products release sodium ions during the first charge of the battery to compensate for the sodium consumed in the formation of the negative electrode solid electrolyte interface film.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the positive electrode active material, the conductive agent, the binder, and the composite sacrificial salt is 90-98:0.2-5:0.2-10:0.5-10.

3. The preparation method according to claim 1, characterized in that, The positive electrode active material is a layered oxide, including one or more of sodium nickel manganese oxide, P2-sodium nickel manganese oxide, sodium iron manganese oxide, sodium nickel manganese oxide, or high-entropy layered oxides. The conductive agent includes one or more of the following: acetylene black, Super P, carbon nanotubes, carbon fibers, Ketjen black, conductive graphite, or graphene. The adhesive includes one or more of polytetrafluoroethylene or tetrafluoroethylene copolymers.

4. The preparation method according to claim 1, characterized in that, The composite sacrificial salt includes one or more of sodium citrate, sodium oxalate, or sodium bicarbonate.

5. The preparation method according to claim 1, characterized in that, The adhesive is fibrillated at a speed of 4000 rpm to 8000 rpm for 3 min to 30 min.

6. The preparation method according to claim 1, characterized in that, The hot rolling process is carried out at a temperature of 100℃-240℃ and a pressure of 20MPa-80MPa.

7. The preparation method according to claim 1, characterized in that, The temperature of the hot roller pressing process is 70℃-250℃, and the pressure is 10T-200T.

8. The preparation method according to claim 1, characterized in that, In the step of thermally combining the self-supporting electrode film with the current collector, the composite temperature is 70℃-250℃ and the composite pressure is 2T-30T.

9. A dry electrode for a sodium-ion battery, characterized in that, The sodium-ion battery dry electrode is prepared by any one of the preparation methods described in claims 1-8.

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes a sodium-ion battery dry electrode prepared by any of the preparation methods described in claims 1-8, or includes a sodium-ion battery dry electrode described in claim 9.

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