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

Abstract

The application relates to a sodium ion battery dry-process electrode pole piece and a preparation method thereof. The preparation method is as follows: (1) mixing an electrode active material, a conductive agent, a thermoplastic material and a plasticizer to obtain uniformly mixed dry powder, and treating the uniformly mixed dry powder by high-speed shearing to obtain fibrous powder; (2) extruding the fibrous powder to obtain an initial film piece; (3) performing roll pressing treatment on the initial film piece to obtain an electrode film piece; and (4) performing hot roll pressing on the electrode film piece and a current collector to obtain the sodium ion battery dry-process electrode pole piece. The sodium ion battery dry-process electrode pole piece is designed by changing the amount and molecular weight of the thermoplastic material and reasonably using the plasticizer, the flexibility of the pole piece is improved, and the pole piece cracking in the dry-process electrode preparation process is relieved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery dry-process electrode plate and a preparation method thereof. Background Art

[0002] Dry electrode technology is an electrode preparation process in which the electrode active material, conductive agent and binder are stirred and mixed to obtain a fiberized electrode powder, and then the electrode sheet is obtained by continuous roll-forming and thermally compounding with the current collector. This method has the advantages of low production cost, high production efficiency and environmental friendliness. Applying dry electrode technology to the preparation process of sodium-ion batteries can significantly reduce the preparation cost of sodium-ion batteries. However, there are still some technical difficulties in the preparation of dry electrodes, such as poor flexibility of the electrode sheet due to the hardness of the material, and cracking of the electrode sheet. These problems need to be solved and optimized urgently. Summary of the Invention

[0003] To this end, the purpose of the present invention is to solve the technical problems in the prior art such as poor flexibility of the pole piece and cracking of the pole piece caused by material hardness.

[0004] To address the above technical issues, the present invention provides a method for preparing a sodium-ion battery dry-process electrode plate. This method designs the dry-process electrode plate for sodium-ion batteries based on the amount and molecular weight of the thermoplastic active material and the use of a plasticizer, improving the plate's flexibility and mitigating cracking during the dry-process electrode preparation process.

[0005] The first object of the present invention is to provide a method for preparing a dry-process electrode sheet for a sodium ion battery, comprising the following steps:

[0006] (1) mixing an electrode active material, a conductive agent, a thermoplastic material, and a plasticizer to obtain a uniformly mixed dry powder, and treating the uniformly mixed dry powder with a high-speed shearing method to obtain a fiberized powder; the thermoplastic material has a molecular weight of 1000 g / mol to 10000 g / mol;

[0007] (2) extruding the fiberized powder to obtain an initial membrane;

[0008] (3) rolling the initial membrane to obtain an electrode membrane;

[0009] (4) The electrode membrane and the current collector are hot rolled to obtain the sodium ion battery dry electrode sheet.

[0010] In one embodiment of the present invention, in step (1), the electrode active material has a particle size D50 of 8 μm to 20 μm and a specific surface area of ​​0.5 m 2 / g~10m 2 / g.

[0011] In one embodiment of the present invention, in step (1), the electrode active material includes a positive electrode active material or a negative electrode active material.

[0012] Furthermore, the positive electrode active material includes but is not limited to one or more of three-dimensional porous sodium vanadium phosphate, sodium vanadium phosphate, sodium iron phosphate, sodium iron pyrophosphate, Prussian blue, Prussian white, and sodium ion layered metal oxide.

[0013] Furthermore, the particle size D50 of the positive electrode active material satisfies D50=10 μm to 20 μm, and the specific surface area S is 0.5 m 2 / g~1.5m 2 / g.

[0014] Furthermore, the negative electrode active material includes but is not limited to hard carbon and / or soft carbon.

[0015] Furthermore, the particle size D50 of the negative electrode active material satisfies: D50=8μm-18μm, and the specific surface area S is 2m 2 / g~10m 2 / g.

[0016] In one embodiment of the present invention, in step (1), the amounts of the electrode active material, conductive agent, thermoplastic material and plasticizer are: 85wt% to 97.5wt%, conductive agent 0.5wt% to 5wt%, thermoplastic material powder 0.5wt% to 5wt%, and plasticizer 0.1wt% to 5wt%.

[0017] In one embodiment of the present invention, in step (1), the thermoplastic material is selected from one or more of polyvinylidene fluoride (PVDF), acrylic resin (PAA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyetheretherketone (PEEK), polyether block amide (PEBA), polyurethane (TPU) and polyhexamethylene adipamide (PA66).

[0018] In one embodiment of the present invention, in step (1), the plasticizer is dioctyl phthalate and / or isooctyl phthalate.

[0019] In one embodiment of the present invention, in step (1), the stirring speed of the mixing is 100 r / min to 300 r / min, the stirring time is 0.5 h to 2 h, and the stirring temperature is room temperature.

[0020] In one embodiment of the present invention, in step (1), the high-speed shearing is carried out by a mixer with a stirring speed of 4500 r / min to 6000 r / min, a stirring time of 0.5 h to 2 h, and a stirring temperature of 20° C. to 50° C.

[0021] In one embodiment of the present invention, in step (2), the extrusion molding temperature is 40° C. to 120° C.; and the thickness of the initial membrane is 250 μm to 400 μm.

[0022] In one embodiment of the present invention, in step (3), the temperature of the roller pressing treatment is 80° C. to 150° C.; and the thickness of the electrode membrane is 120 μm to 200 μm.

[0023] In one embodiment of the present invention, in step (4), the temperature of the hot rolling lamination is 100°C to 200°C.

[0024] In one embodiment of the present invention, in step (4), the current collector is selected from one or more of aluminum foil, carbon-coated aluminum foil, metal mesh current collector, surface-roughened aluminum foil, and composite current collector. Furthermore, carbon-coated aluminum foil, surface-roughened aluminum foil, or metal mesh current collector is preferred.

[0025] Furthermore, the specific processing steps of the surface roughened aluminum foil are: contacting at least one side of the surface of the aluminum foil with an alkaline solution for corrosion treatment, and then washing with water and anhydrous ethanol to remove surface residues.

[0026] Furthermore, the alkali solution is a sodium hydroxide solution with a concentration of 8wt% to 12wt%.

[0027] Furthermore, the corrosion treatment temperature is 40-50° C., and the time is 20-62 seconds.

[0028] In one embodiment of the present invention, in step (4), the peel strength of the electrode plate is 4.1 N / m to 7.2 N / m.

[0029] The second object of the present invention is to provide a sodium ion battery dry-process electrode plate, including a sodium ion battery dry-process electrode plate prepared by the preparation method.

[0030] The above technical solution of the present invention has the following advantages over the prior art:

[0031] This invention utilizes the dosage and molecular weight of thermoplastic materials and the rational use of plasticizers to design a dry-process electrode sheet for sodium-ion batteries. High-speed shearing fiberizes the thermoplastic material, forming a cross-mesh structure that is evenly distributed across the electrode sheet. The thermoplastic material's adhesive properties increase the contact area between the electrode sheet and the current collector, improving the peel strength of the electrode sheet. The addition of plasticizers also enhances the electrode sheet's flexibility, mitigating the risk of cracking. Furthermore, the design of the thermoplastic material's molecular weight further improves the sheet's peel strength.

[0032] The preparation method provided by the present invention does not require the addition of toxic organic solvents, is pollution-free and residue-free, and does not require an oven during the wet electrode coating process, effectively reducing the cost of the sodium ion battery preparation process and truly conforming to the concepts of "green" and "environmental protection". BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0034] Figure 1 This is a scanning electron microscope image of the electrode prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0035] In order to solve the technical problems in the prior art such as poor flexibility of the pole piece and cracking of the pole piece caused by material hardness, the present invention provides the following technical solutions:

[0036] The first object of the present invention is to provide a method for preparing a dry-process electrode sheet for a sodium ion battery, comprising the following steps:

[0037] (1) mixing the electrode active material, the conductive agent, the thermoplastic material and the plasticizer to obtain a uniformly mixed dry powder, and using high-speed shearing to uniformly disperse the wetted dry powder to obtain a fiberized powder;

[0038] (2) Extruding the fiberized powder into a mold to obtain an initial membrane;

[0039] (3) rolling the initial membrane to obtain an electrode membrane;

[0040] (4) The electrode membrane and the current collector are hot rolled to obtain the sodium ion battery dry electrode sheet.

[0041] In a specific embodiment, in step (1), the electrode active material has a particle size D50 of 8 μm to 20 μm and a specific surface area of ​​0.5 to 10 m 2 / g.

[0042] Furthermore, the electrode active material includes a positive electrode active material or a negative electrode active material.

[0043] The positive electrode active materials include but are not limited to three-dimensional porous sodium vanadium phosphate, sodium vanadium phosphate, sodium iron phosphate, sodium iron pyrophosphate, Prussian blue, Prussian white and layered metal oxide Na x Ni i Fe j Mn k M m One or more of O2.

[0044] Further, the layered metal oxide satisfies: 0 < i ≤ 0.4, 0 < j ≤ 0.5, 0 < k ≤ 0.6, 0 < m ≤ 0.2, and i + j + k + m = 1.

[0045] Furthermore, when 0.6 < x ≤ 0.8, the material is a P2-phase layered oxide; when 0.8 < x ≤ 1, the material is an O3-phase layered oxide.

[0046] In a specific embodiment, the particle size D50 of the positive electrode active material satisfies D50 = 10 μm to 20 μm, and the specific surface area S satisfies S = 0.5 m 2 / g to 1.5 m 2 / g.

[0047] In a specific embodiment, the negative electrode material includes, but is not limited to, hard carbon and / or soft carbon.

[0048] Further, the particle size D50 of the negative electrode active material satisfies: D50 = 8 μm to 18 μm, and the specific surface area S satisfies: S = 2 m 2 / g to 10 m 2 / g.

[0049] In a specific embodiment, the conductive agent is one or more of Super P, Ketjen black, carbon nanotubes, carbon nanofibers, graphene, and conductive carbon, preferably carbon nanotubes and / or carbon nanofibers.

[0050] In a specific embodiment, in step (1), the dosages of the electrode active material, conductive agent, thermoplastic material, and plasticizer are: 85 wt% to 97.5 wt%, conductive agent 0.5 wt% to 5 wt%, thermoplastic material powder 0.5 wt% to 5 wt%, and plasticizer 0.1 wt% to 5 wt%.

[0051] In a specific embodiment, in step (1), the thermoplastic material is selected from one or more of polyvinylidene fluoride (PVDF), acrylic resin (PAA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyether ether ketone (PEEK), polyether block amide (PEBA), polyurethane (TPU), and polyhexamethylene adipamide (PA66).

[0052] In a specific embodiment, in step (1), the molecular weight of the thermoplastic material is 1000 g / mol to 10000 g / mol. It can be 1000 g / mol to 5000 g / mol, 5000 g / mol to 8000 g / mol, or 8000 g / mol to 10000 g / mol. For example, it can be 1000 g / mol, 2000 g / mol, 3000 g / mol, 4000 g / mol, 5000 g / mol, 6000 g / mol, 7000 g / mol, 8000 g / mol, 9000 g / mol, 10000 g / mol, or any value between any two values.

[0053] In a specific embodiment, in step (1), the plasticizer is dioctyl phthalate and / or isooctyl phthalate.

[0054] In a specific embodiment, in step (1), the stirring speed of the mixing is 100 r / min to 300 r / min, the stirring time is 0.5 h to 2 h, and the stirring temperature is room temperature.

[0055] In a specific embodiment, in step (1), the high-speed shearing is performed using a stirrer at a stirring speed of 4500 r / min to 6000 r / min, a stirring time of 0.5 h to 2 h, and a stirring temperature of 20° C. to 50° C. When the speed is lower than 4500 r / min, the speed is too low to meet the fiberization requirements, and the thermoplastic material is difficult to form a cross-network structure, resulting in the thermoplastic material being unable to uniformly contact with the active material, the conductive agent, and the plasticizer, thereby affecting the performance of the electrode.

[0056] In a specific embodiment, in step (2), the extrusion molding temperature is 40° C. to 120° C.; and the thickness of the initial membrane is 250 μm to 400 μm.

[0057] In a specific embodiment, in step (3), the temperature of the roller pressing treatment is 80° C. to 150° C.; and the thickness of the electrode membrane is 120 μm to 200 μm.

[0058] In a specific embodiment, in step (4), the temperature of the hot rolling lamination is 100°C to 200°C.

[0059] In a specific embodiment, in step (4), the current collector is selected from one or more of aluminum foil, carbon-coated aluminum foil, metal mesh current collector, surface-roughened aluminum foil, and composite current collector. Furthermore, carbon-coated aluminum foil, surface-roughened aluminum foil, or metal mesh current collector is preferred.

[0060] Furthermore, the specific processing steps of the surface roughened aluminum foil are: contacting at least one side of the surface of the aluminum foil with an alkaline solution for corrosion treatment, and then washing with water and anhydrous ethanol to remove surface residues.

[0061] Furthermore, the alkali solution is a sodium hydroxide solution with a concentration of 8 wt% to 12 wt%. Furthermore, the corrosion treatment temperature is 40° C. to 50° C. and the treatment time is 20 s to 62 s.

[0062] In one embodiment of the present invention, in step (4), the peel strength of the electrode plate is 4.1 N / m to 7.2 N / m.

[0063] The second object of the present invention is to provide a sodium ion battery dry-process electrode plate, including a sodium ion battery dry-process electrode plate prepared by the preparation method.

[0064] 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 the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0065] Example 1

[0066] This embodiment provides a method for preparing a dry-process electrode plate, which can be used as a positive electrode of a sodium ion battery. The preparation method includes:

[0067] 1. The particle size D50 is 14.8 μm and the specific surface area S is 1.2 m 2 / g of sodium cathode material, a conductive agent, thermoplastic material powder polytetrafluoroethylene (PTFE, molecular weight of 1000g / mol) and a plasticizer dioctyl phthalate are placed in a stirring tank in the proportion of 85%, 5%, 5% and 5% by mass and mixed at a speed of 200r / min to obtain a uniformly mixed dry powder; then the mixture is fully mixed at a stirring speed of 2000r / min; finally, the stirring temperature is controlled at 55°C and the stirring speed is adjusted to 5500r / min, and the high-speed shear force generated by high-intensity stirring is used to uniformly disperse the sodium cathode material, the conductive agent, the thermoplastic material powder and the plasticizer, thereby achieving a fiberization effect and obtaining a fiberized powder.

[0068] 2. The fiberized powder is extruded into a sheet with a thickness of 350 μm at 80°C; the sheet is rolled into a 180 μm thick electrode film at 120°C; and finally, the positive electrode film and the surface-roughened aluminum foil current collector are hot-rolled at 150°C to obtain the sodium ion battery dry electrode positive electrode sheet.

[0069] Example 2

[0070] This embodiment provides a dry-process method for preparing an electrode sheet, which is used as the positive electrode of a sodium ion battery. The details are as follows:

[0071] The preparation steps are similar to those in Example 1, except that the mass percentages of the material components for preparing the positive electrode plate of the sodium ion battery dry electrode are different. The mass percentages of the positive electrode material, conductive agent, polytetrafluoroethylene (PTFE), and plasticizer dioctyl phthalate are 97.5%, 0.5%, 1%, and 1%, respectively.

[0072] Example 3

[0073] This embodiment provides a dry-process method for preparing an electrode sheet, which is used as the positive electrode of a sodium ion battery. The details are as follows:

[0074] The preparation steps are similar to those in Example 2, except that the molecular weight of polytetrafluoroethylene (PTFE) is 10,000 g / mol.

[0075] Example 4

[0076] This embodiment provides a dry-process method for preparing an electrode sheet, which is used as the positive electrode of a sodium ion battery. The details are as follows:

[0077] The preparation steps are the same as those in Example 1, except that the percentages of the components of the dry-process positive electrode for sodium ion batteries are different: the mass percentages of the positive electrode material, the conductive agent, the thermoplastic material polytetrafluoroethylene (PTFE), and the plasticizer dioctyl phthalate are 95.5%, 2.5%, 1.9%, and 0.1%, respectively. The obtained dry-process electrode was characterized, and the results are shown in FIG. Figure 1 .from Figure 1 It can be seen that the material has achieved fiberization and formed a cross-network structure.

[0078] Example 5

[0079] This embodiment provides a method for preparing a dry-process electrode plate, which is used as a positive electrode of a sodium ion battery. The preparation method includes:

[0080] 1. The particle size D50 is 13.6 μm and the specific surface area S is 1.35 m 2 / g of sodium cathode material, a conductive agent, polytetrafluoroethylene (PTFE, molecular weight of 1000g / mol) and a plasticizer, isooctyl phthalate, are placed in a stirring tank in the proportions of 85%, 5%, 5% and 5% by mass and mixed at a speed of 200r / min to obtain a uniformly mixed dry powder; the mixture is then fully mixed at a stirring speed of 2000r / min; and finally, the stirring temperature is controlled at 55°C and the stirring speed is adjusted to 5500r / min, and the high-speed shear force generated by high-intensity stirring is used to uniformly disperse the sodium cathode material, the conductive agent, the thermoplastic material powder and the plasticizer, thereby achieving a fiberization effect and obtaining a fiberized powder.

[0081] 2. The fiberized powder is extruded into a sheet with a thickness of 350 μm at 80°C; the sheet is rolled into a 180 μm thick electrode film at 120°C; and finally, the positive electrode film and the surface-roughened aluminum foil current collector are hot-rolled at 150°C to obtain the sodium ion battery dry electrode positive electrode sheet.

[0082] Example 6

[0083] This embodiment provides a method for preparing a dry-process electrode plate, which can be used as a negative electrode for a sodium ion battery. The preparation method includes:

[0084] 1. The particle size D50 is 9.3 μm and the specific surface area S is 4.5 m 2 / g of sodium negative electrode material, a conductive agent, polytetrafluoroethylene (PTFE, molecular weight of 8000g / mol) and a plasticizer isooctyl phthalate are placed in a stirring tank in the proportions of 85%, 5%, 5% and 5% by mass and mixed at a speed of 200r / min to obtain a uniformly mixed dry powder; then the mixture is fully mixed at a stirring speed of 2000r / min; finally, the stirring temperature is controlled at 55°C and the stirring speed is adjusted to 5500r / min, and the high-speed shear force generated by high-intensity stirring is used to uniformly disperse the sodium negative electrode material, the conductive agent, the thermoplastic material powder and the plasticizer, thereby achieving a fiberization effect and obtaining a fiberized powder.

[0085] 2. The fiberized powder is extruded into a sheet with a thickness of 300 μm at 80°C; the sheet is rolled into a 120 μm thick electrode film at 120°C; and finally, the negative electrode film and the surface-roughened aluminum foil current collector are hot-rolled at 130°C to obtain the sodium ion battery dry-process electrode negative electrode sheet.

[0086] Example 7

[0087] This embodiment provides a method for preparing a dry-process electrode plate, which can be used as a negative electrode for a sodium ion battery. The preparation method includes:

[0088] The preparation steps are the same as those in Example 6, except that the mass percentages of the material components for preparing the negative electrode sheet of the sodium ion battery dry electrode are different. The mass percentages of the negative electrode material, the conductive agent, polytetrafluoroethylene (PTFE, molecular weight 8000 g / mol), and the plasticizer isooctyl phthalate are 95.5%, 1.5%, 2.5%, and 0.5%, respectively.

[0089] Example 8

[0090] This embodiment provides a method for preparing a dry-process electrode plate, which can be used as a negative electrode for a sodium ion battery. The preparation method includes:

[0091] The preparation steps are the same as those in Example 6, except that the percentages of the material components for preparing the negative electrode sheet of the dry-process electrode for the sodium ion battery are different. The mass percentages of the negative electrode material, the conductive agent, polytetrafluoroethylene (PTFE, molecular weight 8000 g / mol), and the plasticizer isooctyl phthalate are 90%, 1.5%, 4.5%, and 4%, respectively.

[0092] Comparative Example 1

[0093] This comparative example provides a method for preparing a sodium ion battery dry-process positive electrode sheet. The difference from Example 1 is that the molecular weight of the thermoplastic powder in this comparative example is adjusted to 100 g / mol. Specifically, the preparation method includes:

[0094] 1. The particle size D50 is 14.8 μm and the specific surface area S is 1.2 m 2 / g of sodium battery positive electrode material, conductive agent, polytetrafluoroethylene (PTFE, molecular weight of 100g / mol), and plasticizer isooctyl phthalate are placed in a stirring tank according to mass percentages of 97.5%, 0.5%, 1%, and 1%, and mixed at a speed of 200r / min to obtain a uniformly mixed dry powder; then the mixture is fully mixed at a stirring speed of 2000r / min; finally, the stirring temperature is controlled at 55°C, and the stirring speed is adjusted to 5500r / min. The high-speed shear force generated by high-intensity stirring is used to uniformly disperse the conductive material, conductive agent, and thermoplastic material powders, thereby achieving a fiberization effect and obtaining a fiberized powder.

[0095] 2. The fiberized powder is extruded into a sheet with a thickness of 350 μm at 80°C; the sheet is rolled into a 180 μm thick electrode film at 120°C; and finally, the positive electrode film and the surface-roughened aluminum foil current collector are hot-rolled at 150°C to obtain the sodium ion battery dry electrode positive electrode sheet.

[0096] Comparative Example 2

[0097] This comparative example provides a method for preparing a sodium ion battery dry-process positive electrode sheet. The main difference from the embodiment is that this comparative example does not add a plasticizer. Specifically, the preparation method includes:

[0098] 1. The particle size D50 is 15.8 μm and the specific surface area S is 1.47 m 2 / g of sodium battery positive electrode material, conductive agent, and polytetrafluoroethylene (PTFE, molecular weight 8000g / mol) are placed in a stirring tank according to mass percentages of 90%, 5%, and 5%, respectively, and mixed at a speed of 200r / min, and then fully mixed at a stirring speed of 2000r / min; finally, the stirring temperature is controlled at 55°C, and the stirring speed is adjusted to 5500r / min. The high-speed shear force generated by high-intensity stirring is used to uniformly disperse the conductive material, conductive agent, and thermoplastic material powders, thereby achieving a fiberization effect and obtaining a fiberized powder.

[0099] 2. The fiberized powder is extruded into a sheet with a thickness of 350 μm at 80°C; the sheet is rolled into a 180 μm thick electrode film at 120°C; and finally, the positive electrode film and the surface-roughened aluminum foil current collector are hot-rolled at 150°C to obtain the sodium ion battery dry electrode positive electrode sheet.

[0100] Comparative Example 3

[0101] This comparative example provides a method for preparing a positive electrode sheet for a sodium ion battery. The difference from Example 4 is that the molecular weight of the thermoplastic powder in this comparative example is adjusted to 15,000 g / mol. Specifically, the preparation method includes:

[0102] 1. The sodium cathode material, a conductive agent, polytetrafluoroethylene (PTFE, molecular weight 15000g / mol), and a plasticizer dioctyl phthalate with a particle size D50 of 14.3 μm and a specific surface area S of 1.2 are placed in a stirring tank and mixed at a speed of 200 r / min to obtain a uniformly mixed dry powder; then the stirring speed is 2000 r / min to fully mix; finally, the stirring temperature is controlled at 55°C and the stirring speed is adjusted to 5500 r / min, and the high-speed shear force generated by high-intensity stirring is uniformly dispersed to achieve a fibrosis effect and obtain a fibrotic powder.

[0103] 2. The fiberized powder is extruded into a sheet with a thickness of 350 μm at 80°C; the sheet is rolled into a 180 μm thick electrode film at 120°C; and finally, the positive electrode film and the aluminum foil current collector are hot-rolled and composited at 150°C to obtain the sodium ion battery dry electrode positive electrode sheet.

[0104] Comparative Example 4

[0105] This comparative example provides a method for preparing a negative electrode sheet for a sodium ion battery. The difference from Example 8 is that no plasticizer is added in this comparative example. Specifically, the preparation method includes:

[0106] 1. The particle size D50 is 9.3 μm and the specific surface area S is 4.5 m 2 / g of sodium negative electrode material, a conductive agent, and polytetrafluoroethylene (PTFE, molecular weight of 8000g / mol) are placed in a stirring tank according to mass percentages of 90%, 5%, and 5%, and mixed at a speed of 200r / min to obtain a uniformly mixed dry powder; then the mixture is fully mixed at a stirring speed of 2000r / min; finally, the stirring temperature is controlled at 55°C, the stirring speed is adjusted to 5500r / min, and the high-speed shear force generated by high-intensity stirring is used to uniformly disperse the sodium negative electrode material, the conductive agent, and the thermoplastic material powders, thereby achieving a fiberization effect and obtaining a fiberized powder.

[0107] 2. The fiberized powder is extruded into a sheet with a thickness of 350 μm at 80°C; the sheet is rolled into a 180 μm thick electrode film at 120°C; and finally, the negative electrode film and the aluminum foil current collector are hot-rolled at 150°C to obtain the sodium ion battery dry electrode negative electrode sheet.

[0108] The types and amounts of raw materials used in the above examples and comparative examples are shown in Table 1, as follows:

[0109] Table 1

[0110]

[0111]

[0112] Performance Testing

[0113] The pole pieces obtained in Examples 1 to 8 and Comparative Examples 1 to 4 were subjected to performance tests of peel strength and flexibility.

[0114] Peel Strength Test Method: Peel strength tests were conducted on the positive and negative electrode sheets prepared in Examples 1-8 and Comparative Examples 1-4 in accordance with GB / T 2792-1998. The tests were conducted at room temperature (23°C ± 2°C) and relative humidity (65 ± 5%). The adhesive tape and adhered material (i.e., the test material) were allowed to stand under these conditions for at least 2 hours. The tape was peeled off, and the outer 3-5 layers were cut off. The tape was then evenly peeled off, leaving the tape bonded to one end of the adhered material at an angle greater than 30°. A polyester film approximately 200 mm long and 40 mm wide was placed under the other end of the adhered material. The sample was then rolled back and forth three times using the wheels of a rolling device under its own weight at a speed of approximately 120 mm / s. The free end of the sample was folded 180° (90° for the positive electrode and 180° for the negative electrode), and the adhesive surface was peeled back approximately 10 mm. The adhered material was clamped in the lower clamp, and the free end of the sample was clamped in the upper clamp. Keep the peeling surface aligned with the testing machine's force line. The testing machine continuously peels at a descending speed of 300 ± 10 mm / min. The effective peeling length of the adhesive surface is approximately 100 mm, and an automatic technical device provides peel strength and peel force data.

[0115] Flexibility test method: Cut the electrode into pieces 50mm wide and 200mm long. Wind the cut electrode 360° through steel needles of different diameters and observe whether the electrode has cracks or light transmission. If there are no cracks or light transmission after winding the electrode around the steel needle, the flexibility is qualified. The smaller the diameter of the steel needle that the electrode can pass, the better the flexibility of the electrode.

[0116] Table 2 Diaphragm extrusion molding state, electrode peeling strength and flexibility of Examples 1 to 8 and Comparative Examples 1 to 4

[0117]

[0118] As can be seen from Table 2, Examples 1 to 5 and Examples 6 to 8 are the extrusion molding state and electrode peeling strength of the positive and negative electrode membranes of the sodium ion battery, respectively; by using the dry electrode preparation method provided by the present invention, positive and negative electrode membranes with good extrusion molding state and positive and negative electrode sheets with high peeling strength are obtained.

[0119] The difference between Comparative Example 1 and Example 2 is that the molecular weight of the thermoplastic material is different. The plasticizer molecular weight of Comparative Example 1 is 100 g / mol (less than 1000 g / mol). The peel strength of the obtained film is much lower than that of Example 1, and the edges and center of the film are more severely cracked, indicating that by regulating the molecular weight of the plastic material, the peel strength of the material can be effectively improved, and the cracking of the film can be solved.

[0120] Compared with the embodiment, the other parameters of Comparative Example 2 are all within the range described in the present invention. The difference is that no plasticizer is added. The edge cracks of the diaphragm obtained in Comparative Example 2 are more serious and the flexibility is also relatively poor. This shows that the addition of plasticizer is beneficial to improving the flexibility of the dry electrode plate.

[0121] Compared with Example 4, the difference between Comparative Example 3 is that Comparative Example 3 uses PTFE with a larger molecular weight of thermoplastic material (greater than 10,000 g / mol). The material with too large a molecular weight is difficult to disperse, the processing performance deteriorates, the prepared slurry is non-uniformly fibrotic, and there is a problem of unstable bonding after thermally compounding it into a dry-process electrode pole piece. This shows that the molecular weight of the thermoplastic material needs to be within an appropriate range to obtain a dry-process electrode pole piece with excellent performance.

[0122] Compared with Example 8, the difference between Comparative Example 4 is that no plasticizer is added in Comparative Example 4, resulting in poor flexibility of the electrode and severe cracking at the edge of the diaphragm. This once again shows that the addition of plasticizer is beneficial to improving the flexibility of the dry electrode electrode and reducing the cracking of the diaphragm.

[0123] In summary, the present invention can effectively improve the flexibility and peel strength of the dry-process electrode plate and solve the problem of plate cracking by adjusting the amount and molecular weight of the thermoplastic material of the positive electrode material and rationally using the plasticizer.

[0124] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a dry-process electrode sheet for a sodium ion battery, characterized in that: The following steps are involved: (1) mixing an electrode active material, a conductive agent, a thermoplastic material, and a plasticizer to obtain a uniformly mixed dry powder, and treating the uniformly mixed dry powder with a high-speed shearing method to obtain a fiberized powder; the molecular weight of the thermoplastic material is 1000 g / mol to 10000 g / mol; The thermoplastic material is selected from one or more of polyvinylidene fluoride, acrylic resin, polytetrafluoroethylene, styrene-butadiene rubber, polyetheretherketone, polyether block amide, polyurethane and polyhexamethylene adipamide; the plasticizer is dioctyl phthalate and / or isooctyl phthalate; The amounts of the electrode active material, conductive agent, thermoplastic material and plasticizer are: 85wt%~97.5wt% of electrode active material, 0.5wt%~5wt% of conductive agent, 0.5wt%~5wt% of thermoplastic material powder, and 0.1wt%~5wt% of plasticizer; (2) Extruding the fiberized powder to obtain an initial membrane; (3) Roll-pressing the initial membrane to obtain an electrode membrane; (4) Hot rolling-compounding the electrode membrane and the current collector to obtain the sodium ion battery dry-process electrode sheet.

2. The preparation method according to claim 1, characterized in that In step (1), the electrode active material particle size D50 is 8 μm to 20 μm, and the specific surface area is 0.5 m 2 / g~10m 2 / g.

3. The preparation method according to claim 1, characterized in that The current collector is selected from one or more of aluminum foil, carbon-coated aluminum foil, metal mesh current collector, surface-roughened aluminum foil, and composite current collector.

4. The preparation method according to claim 1, characterized in that In step (1), The mixing speed is 100 r / min to 300 r / min, and the stirring time is 0.5 h to 2 h; The high-speed shearing is performed by a mixer with a stirring speed of 4500 r / min to 6000 r / min, a stirring time of 0.5 h to 2 h, and a stirring temperature of 20° C. to 50° C.

5. The preparation method according to claim 1, characterized in that In step (2), the extrusion molding temperature is 40°C to 120°C; and the thickness of the initial membrane is 250 μm to 400 μm.

6. The preparation method according to claim 1, characterized in that In step (3), the temperature of the rolling treatment is 80°C to 150°C; the thickness of the electrode membrane is 120μm to 200μm.

7. The preparation method according to claim 1, characterized in that In step (4), the temperature of the hot rolling compounding is 100°C to 200°C; and the peel strength of the electrode sheet is 4.1N / m to 7.2N / m.

8. A sodium ion battery dry electrode plate, characterized in that: The sodium ion battery dry electrode sheet is prepared by the preparation method according to any one of claims 1 to 7.

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