Binder for positive pole piece as well as preparation method and application of binder

Abstract

The invention discloses a binder for a positive pole piece as well as a preparation method and application of the binder. The adhesive comprises a rigid framework component, a flexible link component and an interface anchoring component, and is a composite adhesive system with a three-dimensional network structure. The preparation method comprises the following steps: uniformly dispersing the rigid framework component in water, sequentially adding the flexible linking component and the interface anchoring component, and uniformly mixing to obtain the adhesive. The binder can be applied to the Prussian blue type positive pole piece, the Prussian blue type positive pole piece comprises a current collector and an active substance layer coated on at least one side surface of the current collector, and the active substance layer comprises a Prussian blue type positive pole material, a conductive agent and the binder. The binder provided by the invention solves the problems of low peeling strength, poor flexibility, easy layering during baking and the like of the Prussian blue positive pole piece, and the prepared positive pole piece has excellent mechanical properties and electrochemical properties, and is suitable for the field of sodium ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a binder for positive electrode sheets, its preparation method, and its application. Background Technology

[0002] Prussian blue and its analogues (PBAs) are considered promising cathode materials for sodium-ion batteries due to their open framework structure, high theoretical specific capacity (approximately 170 mAh / g), and abundant raw material sources. Their applications in lithium-ion batteries are also being explored. PBAs have a face-centered cubic crystal structure and the chemical formula is A. h M[Fe(CN)6] y ·zH2O, where A is an alkali metal ion and M is a transition metal ion. However, Prussian blue materials have significant defects in electrode preparation: (1) Crystal structure defects: PBAs prepared by traditional co-precipitation method have a large number of [Fe(CN)6] vacancy defects and lattice water molecules, which lead to structural instability and capacity decay; (2) Poor mechanical properties of the electrode: The peel strength of the electrode is extremely low, usually in the range of 3~5 N / m, which is far lower than the requirements of conventional lithium-ion battery positive electrode (usually >10 N / m); Poor flexibility: The electrode is brittle and is prone to microcracks during rolling, cutting and battery winding; Severe delamination after baking: During the baking and drying process of the electrode, internal stress is generated due to solvent evaporation, and the traditional binders such as polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) composite water-based binder (CMC / SBR) have poor compatibility with the Prussian blue surface and weak adhesion, which easily leads to the active material layer peeling off from the aluminum foil current collector; (3) Electrochemical performance limitations: Lattice water molecules not only occupy Na + Site, also related to Na + Competition gap space, increase Na + Migration barrier: During charging and discharging, lattice water molecules may migrate into the organic electrolyte, triggering electrochemical decomposition side reactions. The main reason for this is that traditional linear binders cannot form a strong and resilient interface between Prussian blue particles and between them and the current collector. Currently, the industry attempts to mitigate this by optimizing the rolling process or slightly increasing the binder content, but the effects are limited and often come at the cost of energy density.

[0003] In summary, existing technologies suffer from several technical problems, including low peel strength and poor flexibility of Prussian blue cathode sheets, easy delamination after baking, poor electrochemical performance and cycle stability of Prussian blue materials, and environmentally unfriendly and costly aqueous preparation processes. Summary of the Invention

[0004] The main objective of this invention is to provide a binder for positive electrode sheets, its preparation method, and its application, in order to overcome the shortcomings of the prior art.

[0005] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0006] The first aspect of the present invention provides a binder for a positive electrode sheet, comprising a rigid skeleton component, a flexible link component, and an interface anchoring component, wherein the binder is a composite bonding system having a three-dimensional network structure.

[0007] A second aspect of the present invention provides a method for preparing the binder for the positive electrode sheet, comprising: uniformly dispersing a rigid skeleton component in water, then sequentially adding a flexible linking component and an interface anchoring component, mixing them evenly, and obtaining the binder.

[0008] A third aspect of the invention provides the use of the binder for positive electrode sheets in the preparation of Prussian blue-based positive electrode sheets.

[0009] A fourth aspect of the present invention provides a Prussian blue-based positive electrode sheet comprising a current collector and an active material layer coated on at least one side surface of the current collector, the active material layer comprising a Prussian blue-based positive electrode material, a conductive agent, and the binder for the positive electrode sheet.

[0010] A fifth aspect of the present invention provides a method for preparing the Prussian blue-type positive electrode sheet, comprising:

[0011] Provide the binder for the positive electrode sheet;

[0012] A mixed slurry containing Prussian blue cathode material, conductive agent and binder is uniformly coated on at least one side of the current collector, baked at a gradient temperature, and then rolled to obtain a Prussian blue cathode electrode.

[0013] A sixth aspect of the present invention provides a sodium-ion battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode is a Prussian blue type positive electrode.

[0014] Compared with the prior art, the present invention has at least the following beneficial effects:

[0015] (1) Excellent mechanical properties: Prussian blue positive electrode sheet peel strength ≥14N / m, with the best reaching 24N / m; no cracks after 180° folding, exhibiting excellent flexibility, and fundamentally eliminating the risk of delamination during baking and use.

[0016] (2) Excellent structural stability: The three-dimensional network structure in the binder effectively buffers volume changes; inhibits the pulverization and shedding of active material particles; and maintains the long-term integrity of the positive electrode structure.

[0017] (3) Significantly improved electrochemical performance: The sodium-ion battery containing the binder provided by the present invention has a first-cycle discharge specific capacity of ≥148mAh / g (0.1C), a capacity retention rate of ≥88% after 1000 cycles, excellent rate performance, and a capacity retention rate of ≥78% at 5C.

[0018] (4) Green and cost-effective: The binder preparation method provided by this invention adopts a water-based process throughout, avoiding the use of toxic solvents such as NMP; moreover, the raw materials are abundant, and the manufacturing cost of Prussian blue positive electrode sheet is reduced by 30-50% compared with the traditional PVDF bonding system. The preparation process is simple and suitable for large-scale industrial production. Detailed Implementation

[0019] In view of the problems existing in the prior art, the inventors of this invention have conducted extensive and in-depth research and have provided a binder for positive electrode sheets, its preparation method and application.

[0020] The following will provide a further explanation of the technical solution, its implementation process, and its principles.

[0021] The first aspect of the present invention provides a binder for a positive electrode sheet comprising a rigid skeleton component, a flexible link component, and an interface anchoring component, wherein the binder is a composite bonding system having a three-dimensional network structure.

[0022] In some implementations, the mass ratio of the rigid skeleton component, the flexible link component, and the interface anchoring component is (1~5):(2~8):(0.1~2).

[0023] In some embodiments, the rigid framework component is a one-dimensional or two-dimensional nanofiber material.

[0024] Furthermore, the rigid framework component includes at least one of nanocellulose, sodium alginate, carboxymethyl cellulose, etc., but is not limited to this.

[0025] In some embodiments, the flexible linking component is an elastic polymer emulsion with a glass transition temperature below -20°C.

[0026] Furthermore, the flexible link component includes at least one of polyacrylate emulsion, aqueous polyurethane emulsion, styrene-butadiene rubber emulsion, etc., but is not limited to this.

[0027] In some embodiments, the interface anchoring component is a natural or synthetic molecular compound containing a catechol or lysine structure.

[0028] Furthermore, the interface anchoring component includes at least one of tannic acid, dopamine, polydopamine, polyethyleneimine-dopamine copolymer, etc., but is not limited to this.

[0029] Furthermore, the nanocellulose has a molecular weight of 50,000~200,000 Da, a crystallinity of ≥80%, a diameter of 5~50 nm, and a length of 1~10 μm.

[0030] Furthermore, the sodium alginate has a molecular weight of 100,000 to 500,000 Da, and the ratio of guluronic acid to mannulic acid in the sodium alginate is 0.5 to 2.0:1.

[0031] Furthermore, the sodium carboxymethyl cellulose has a molecular weight of 250,000 to 700,000 Da and a degree of substitution of 0.7 to 1.2.

[0032] Furthermore, the glass transition temperature of the polyacrylate emulsion is -40°C to -60°C, the particle size is 100~500 nm, and the solid content is 40~50%.

[0033] Furthermore, the waterborne polyurethane emulsion has a glass transition temperature of -30°C to -50°C, a particle size of 50~300 nm, and a solid content of 30~45%.

[0034] Furthermore, the glass transition temperature of the styrene-butadiene rubber latex is -25°C to -45°C, the particle size is 150~400nm, and the solid content is 40~60%.

[0035] The second aspect of the present invention provides a method for preparing the binder for the positive electrode sheet, comprising: uniformly dispersing a rigid skeleton component in water, then sequentially adding a flexible linking component and an interface anchoring component, mixing them evenly, and obtaining the binder.

[0036] In some embodiments, the method for preparing the adhesive specifically includes:

[0037] The rigid framework component is uniformly dispersed in water and stirred at high speed of 2000~4000 rpm for 2~4 hours to form a homogeneous gel, wherein the solid content of the homogeneous gel is controlled at 1~3%;

[0038] Then, the flexible linking component is added, and the mixture is sheared and mixed at 2000-4000 rpm for 10-20 min. Next, the interface anchoring component is added, and the mixture is stirred at 500-1000 rpm for 30-60 min to obtain the adhesive.

[0039] A third aspect of the invention provides the use of the binder for positive electrode sheets in the preparation of Prussian blue-based positive electrode sheets.

[0040] A fourth aspect of the present invention provides a Prussian blue-based positive electrode sheet comprising a current collector and an active material layer coated on at least one side surface of the current collector, the active material layer comprising a Prussian blue-based positive electrode material, a conductive agent, and the binder for the positive electrode sheet.

[0041] In some embodiments, the total mass of the binder accounts for 3-7% of the total mass of the active material layer, the total mass of the Prussian blue cathode material accounts for 85-95 wt% of the total mass of the active material layer, and the total mass of the conductive agent accounts for 2-8 wt% of the total mass of the active material layer.

[0042] In some embodiments, the conductive agent includes at least one of carbon black, multi-walled carbon nanotubes, single-walled carbon nanotubes, fumed carbon fibers, Ketjen black, graphene, etc., but is not limited thereto.

[0043] In some embodiments, the Prussian blue-type cathode material is A h M[Fe(CN)6] y ·zH2O, where A is an alkali metal ion, M is a transition metal ion, h takes the value 0 < h < 2, y takes the value 0 < y ≤ 1, and z takes the value ≥ 0.

[0044] The method for preparing the Prussian blue-type positive electrode sheet provided in the fifth aspect of the present invention includes:

[0045] Provide the adhesive;

[0046] A mixed slurry containing Prussian blue cathode material, conductive agent and binder is uniformly coated on at least one side of the current collector, baked at a gradient temperature, and then rolled to obtain a Prussian blue cathode electrode.

[0047] In some implementations, the gradient temperature baking specifically includes: a first stage of baking at 60~80℃ for 5~15 min; a second stage of baking at 100~120℃ for 10~30 min; and a third stage of vacuum baking at 80~100℃ for 5~10 min.

[0048] In some implementations, the mass ratio of the Prussian blue-based cathode material, the conductive agent, and the binder is 85~95:2~8:3~7.

[0049] In some embodiments, the areal density of the mixed slurry coated on the surface of the current collector is 150~250 g / m². 2 .

[0050] In some embodiments, during the electrode rolling process, the porosity of the electrode is controlled to be 25% to 35%, and the compaction density is 1.2 to 1.8 g / cm³.

[0051] In some more specific embodiments, the method for preparing the Prussian blue-based positive electrode sheet may include the following steps:

[0052] Step 1: Preparation of composite adhesive

[0053] S1.1 The rigid framework component is dispersed in deionized water and stirred at high speed of 2000~4000 rpm for 2~4 hours to form a homogeneous gel with a solid content controlled at 1~3%;

[0054] S1.2 The flexible linking component is then added and the mixture is high-speed sheared at 2000-4000 rpm for 10-20 minutes;

[0055] Finally, add the interface anchoring component in step S1.3 and stir at 500-1000 rpm for 30-60 minutes to obtain the composite binder.

[0056] Step 2: Electrode paste preparation

[0057] Prussian blue cathode material, conductive agent and the above composite binder are mixed in a vacuum mixer in proportion to form a uniform slurry, wherein the Prussian blue cathode material is 85-95 wt%, the conductive agent is 2-8 wt% and the composite binder is 3-7 wt%.

[0058] Step 3: Electrode Coating and Gradient Baking

[0059] S3.1 The slurry is coated onto the aluminum foil current collector, with a coating surface density of 150~250 g / m². 2 ;

[0060] S3.2 Perform gradient temperature baking: The first stage is baking at 60~80℃ for 5~15 minutes to allow most of the solvent to evaporate slowly; the second stage is baking at 100~120℃ for 10~30 minutes to allow the adhesive system to fully cure and form a three-dimensional network structure; the third stage is vacuum baking at 80~100℃ for 5~10 minutes to remove residual moisture.

[0061] Step 4: Electrode Rolling

[0062] The baked electrode sheets are rolled at room temperature to control the porosity of the electrode sheets to be 25%~35% and the compaction density to be 1.2~1.8 g / cm³.

[0063] Specifically, the adhesive of the present invention achieves excellent performance through the following synergistic mechanism:

[0064] (1) Construction of three-dimensional network structure. The rigid skeleton component forms a three-dimensional network skeleton, providing extremely high bulk strength and modulus, which is the basis for high peel strength; the flexible link component acts as an efficient stress buffer, dispersing and absorbing the stress generated during baking, rolling and electrochemical cycling; the interface anchoring component forms strong coordination bonds and hydrogen bonds with the metal ions on the Prussian blue surface and the alumina layer on the aluminum foil surface through its catechol groups.

[0065] (2) Chemical bonding mechanism. The bonding between catechol groups and the surface of metal oxides includes: coordinate bonds; the hydroxyl oxygen of catechol forms coordinate bonds with metal atoms, and the bond energy can reach 50% of that of covalent bonds; hydrogen bonds: phenolic hydroxyl groups form a hydrogen bond network with surface hydroxyl groups; π-π stacking; interaction between aromatic rings and the π-electron system of conductive carbon black; Michael addition; oxidized quinones covalently bond with surface amino groups.

[0066] (3) Stress dispersion mechanism. The three-dimensional network structure can effectively disperse the internal stress during the electrode preparation process; buffer the volume change during electrochemical cycling; and inhibit the initiation and propagation of cracks.

[0067] A sixth aspect of the present invention provides a sodium-ion battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode is a Prussian blue type positive electrode.

[0068] In summary, the adhesive provided by this invention consists of a rigid skeleton component, a flexible linking component, and an interface anchoring component, forming a three-dimensional network structure. This composite adhesive system provides mechanical strength through the rigid skeleton, buffers stress through the flexible linking component, and enhances interfacial bonding through interface anchoring, synergistically solving technical problems such as low peel strength, poor flexibility, and easy delamination during baking of Prussian blue positive electrode sheets.

[0069] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0070] For experiments not specifically described in the examples, the procedures or conditions can be performed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available. Other unmentioned raw materials and instruments are all conventionally chosen and do not involve the core technical means of this invention.

[0071] Example 1

[0072] S1. Disperse 1.0g of nanocellulose (molecular weight 100000Da, crystallinity 85%, diameter 10nm, length 3μm) in 98g of deionized water and stir at high speed of about 2000 rpm for 2 hours to form a transparent gel.

[0073] S2. Add 4.0g of polyacrylate emulsion (T) to the above gel. g =-40℃, particle size 200nm, solid content 40%), sheared and mixed at 3000rpm for 10 minutes.

[0074] S3. Add 0.5g of tannic acid and continue stirring for 30 minutes to obtain the binder.

[0075] S4. Add 90g of Prussian blue cathode material (Na) 1.85 Mn[Fe(CN)6] 0.94 ·2.1H2O), 5g of conductive carbon black SuperP and 100g of the above binder (solid content about 3.0%) were mixed in a vacuum planetary mixer to obtain a uniform slurry.

[0076] S5. Coat the slurry onto a 20μm thick aluminum foil, with an areal density of approximately 200 g / m². 2 Place in an 80℃ oven for 10 minutes, then transfer to a 110℃ vacuum oven for 20 minutes.

[0077] S6. Finally, the electrode is rolled at 5 MPa pressure at room temperature. The porosity of the electrode is about 30% and the compaction density is about 1.5 g / cm³, thus obtaining the positive electrode.

[0078] Example 2

[0079] S1. Dissolve 2.0g of sodium alginate (molecular weight 250000Da, M / G=1.2) in 97g of deionized water to form a homogeneous solution.

[0080] S2. Add 3.0g of waterborne polyurethane emulsion (T g =35℃, particle size 150nm, solid content 30%), sheared and mixed at 2500rpm for 15 minutes.

[0081] S3. Add 0.1g of dopamine and stir until dissolved to obtain the adhesive.

[0082] S4. The preparation process is the same as in Example 1.

[0083] S5. The preparation process is the same as in Example 1.

[0084] S6. The preparation process is the same as in Example 1.

[0085] Example 3

[0086] S1. Disperse 1.5g of sodium carboxymethyl cellulose (degree of substitution 0.9, molecular weight 400000Da) in 96.5g of deionized water.

[0087] S2. Add 5.0g of styrene-butadiene rubber latex (T g =30℃, particle size 300nm, solid content 40%), sheared and mixed at 3500rpm for 12 minutes.

[0088] S3. Add 0.3g of polydopamine (molecular weight 50000Da) and continue stirring for 45 minutes to obtain the binder.

[0089] S4. Add 92g of Prussian blue cathode material (Na) 1.72 Fe[Fe(CN)6] 0.98 Mix 1.8H2O, 3g of carbon nanotubes with 100g of the above binder (solid content about 3.0%).

[0090] S5. The preparation process is the same as in Example 1.

[0091] S6. The preparation process is the same as in Example 1.

[0092] Example 4

[0093] The difference between this embodiment and Embodiment 1 is that:

[0094] The mass ratio of nanocellulose, polyacrylate emulsion and polydopamine is 5:8:2, that is, 5g of nanocellulose, 8g of polyacrylate emulsion and 2g of polydopamine, and the rest is the same as in Example 1.

[0095] Example 5

[0096] The difference between this embodiment and Embodiment 1 is that:

[0097] The mass ratio of nanocellulose, polyacrylate emulsion and polyethyleneimine-dopamine copolymer is 1:2:0.5, that is, 1g of nanocellulose, 2g of polyacrylate emulsion and 0.5g of polyethyleneimine-dopamine copolymer, and the rest is the same as in Example 1.

[0098] Example 6

[0099] The difference between this embodiment and Embodiment 1 is that:

[0100] S4. Add 85g of Prussian blue cathode material (Na) 1.85 Mn[Fe(CN)6] 0.94 • 2,1H2O), 8g of conductive carbon black SuperP, and 230g of the above binder (solid content approximately 3%) were mixed in a vacuum planetary mixer to obtain a homogeneous slurry. The rest was the same as in Example 1.

[0101] Example 7

[0102] The difference between this embodiment and Embodiment 1 is that:

[0103] S4. Add 95g of Prussian blue cathode material (Na) 1.85 Mn[Fe(CN)6] 0.94 • 2.1H2O), 2g of conductive carbon black SuperP, and 150g of the above binder (solid content approximately 3%) were mixed in a vacuum planetary mixer to obtain a homogeneous slurry. The rest was the same as in Example 1.

[0104] Comparative Example 1

[0105] The traditional PVDF system was adopted. 92g of Prussian blue cathode material, 4g of SuperP, 4g of PVDF binder and 100g of NMP solvent were mixed to form a slurry, coated and vacuum baked at 120℃ for 2 hours, and then rolled.

[0106] Comparative Example 2

[0107] A single carboxymethyl cellulose (CMC) binder was used. 90g of Prussian blue cathode material, 5g of conductive agent SuperP, 5g of CMC and 100g of deionized water were mixed to form a slurry, and the coating and baking process was the same as in Example 1.

[0108] Comparative Example 3

[0109] The difference between this comparative example and Example 1 is that tannic acid is not added; otherwise, they are the same as in Example 1.

[0110] Comparative Example 4

[0111] The difference between this comparative example and Example 1 is that no polyacrylate emulsion was added; otherwise, they are the same as in Example 1.

[0112] Comparative Example 5

[0113] The difference between this comparative example and Example 1 is that no nanocellulose was added; otherwise, they are the same as in Example 1.

[0114] Performance testing and results

[0115] (1) Mechanical property test of the Prussian blue positive electrode sheet of the present invention:

[0116] Peel strength test: According to GB / T2792-2014 standard, the Prussian blue positive electrode sheet was tested by peeling at 180° with a peeling speed of 100mm / min;

[0117] Flexibility test: The Prussian blue positive electrode sheet was folded 180° to test the surface cracks.

[0118] (2) The positive electrode of the sodium-ion battery is a Prussian blue positive electrode containing the binder of the present invention. Electrochemical performance tests were conducted on the sodium-ion battery:

[0119] The first-cycle discharge capacity, 1000-cycle retention rate, and 5C rate retention rate of sodium-ion batteries containing the binder of this invention were tested.

[0120] The performance test results of Examples 1-7 and Comparative Examples 1-5 of the present invention are shown in Table 1.

[0121] Table 1. Performance test results of Examples 1-7 and Comparative Examples 1-5

[0122] As can be seen from Table 1, the composite binder system of the present invention exhibits comprehensive and significant performance advantages in Prussian blue cathode sheets. Examples 1-7 are significantly superior to Comparative Examples 1-5 in terms of peel strength, flexibility, first-cycle discharge capacity, cycle retention, and rate performance, confirming the effectiveness and universality of the described three-dimensional network structure binder system.

[0123] As can be seen from Table 1, the mechanical properties of the Prussian blue cathode sheet containing the binder of this invention are significantly improved, completely solving the problems of delamination and brittleness. The peel strength of Examples 1-7 is between 14.0 and 24.0 N / m, which is far superior to Comparative Example 1 (4.1 N / m) and Comparative Example 2 (6.8 N / m).

[0124] Examples 1-7 showed no cracks in the 180° folding test, while Comparative Examples 1-5 showed obvious or slight cracks. This proves that the adhesive system greatly enhances the flexibility and structural integrity of the electrode, fundamentally eliminating the risk of delamination during baking and use.

[0125] Furthermore, the sodium-ion batteries incorporating the binder of this invention exhibit excellent electrochemical performance, balancing high capacity with long cycle stability. The first-cycle discharge capacity of Examples 1-7 remained between 150.0 and 158.0 mAh / g, higher than that of Comparative Examples 1-5 (138.0 to 145.2 mAh / g). Regarding cycle performance, Examples 1-7 achieved a capacity retention of 88.0% to 94.3% after 1000 cycles, significantly better than Comparative Examples 1-5 (50.0% to 72.8%). In terms of 5C rate retention, Examples 1-7 achieved 78.0% to 85.7%, while Comparative Examples 1-5 were all below 65%, indicating that this binder system possesses a good ion and electron transport network, supporting rapid charge and discharge.

[0126] Moreover, the rigid framework component, flexible linking component, and interface anchoring component all work synergistically and are indispensable. Comparative Example 3 (without interface anchoring component) showed a peel strength of only 5.0 N / m and a significant decrease in capacity retention, demonstrating that interface anchoring is crucial for enhancing the bond between the adhesive and the active material and current collector. Comparative Example 4 (without flexible linking component) had a higher peel strength (10.0 N / m) than Comparative Example 3, but it was still far lower than Examples 1-7, and its flexibility was poor, indicating that the flexible linking component is indispensable for buffering stress and preventing brittle fracture. Comparative Example 5 (without rigid framework component) had the worst overall performance (peel strength 3.0 N / m, capacity retention 50.0%), confirming that the rigid framework is the foundation for constructing the three-dimensional network and providing mechanical support.

[0127] Furthermore, as shown in Table 1, Example 4 (rigid:flexible:anchoring = 5:8:2) exhibited the highest peel strength (24.0 N / m), indicating that increasing the content of rigid skeleton and flexible link can further enhance mechanical properties. Example 5 (rigid:flexible:anchoring = 1:2:0.5) still maintained good overall performance, indicating that the three-dimensional network structure can still function effectively even at low dosages. Examples 6-7 demonstrated that excellent mechanical and electrochemical properties can be achieved with binder dosages ranging from 3% to 7%, reflecting the flexibility and process tolerance of the formulation of this invention.

[0128] In summary, the biomimetic three-dimensional network binder system provided by this invention, through the synergistic effect of the rigid skeleton, flexible link, and interface anchoring components, significantly improves the mechanical properties and structural stability of Prussian blue cathode sheets while maintaining high electrochemical performance. It effectively solves the problems of low peel strength, poor flexibility, and easy delamination during baking of Prussian blue cathode sheets, demonstrating excellent comprehensive performance in Prussian blue cathode sheets and possessing significant practical application value and industrialization prospects.

[0129] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0130] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. A binder for a positive electrode sheet, characterized in that, include: The adhesive comprises a rigid skeleton component, a flexible link component, and an interface anchoring component, and is a composite adhesive system with a three-dimensional network structure.

2. The adhesive according to claim 1, characterized in that: The mass ratio of the rigid skeleton component, the flexible link component, and the interface anchoring component is (1~5):(2~8):(0.1~2). And / or, the rigid framework component is a one-dimensional or two-dimensional nanofiber material; Preferably, the rigid framework component includes at least one of nanocellulose, sodium alginate, and carboxymethyl cellulose; And / or, the flexible linking component is an elastic polymer emulsion with a glass transition temperature below -20°C; Preferably, the flexible link component includes at least one of polyacrylate emulsion, aqueous polyurethane emulsion, and styrene-butadiene rubber emulsion; And / or, the interface anchoring component is a natural or synthetic molecular compound containing a catechol or lysine structure; Preferably, the interface anchoring component includes at least one of tannic acid, dopamine, polydopamine, and polyethyleneimine-dopamine copolymer.

3. The adhesive according to claim 2, characterized in that: The nanocellulose has a molecular weight of 50,000~200,000 Da, a crystallinity of ≥80%, a diameter of 5~50 nm, and a length of 1~10 μm; And / or, the sodium alginate has a molecular weight of 100,000 to 500,000 Da, and the ratio of guluronic acid to mannulic acid in the sodium alginate is 0.5 to 2.0:1; And / or, the sodium carboxymethyl cellulose has a molecular weight of 250,000 to 700,000 Da and a degree of substitution of 0.7 to 1.2; And / or, the glass transition temperature of the polyacrylate emulsion is -40°C to -60°C, the particle size is 100~500 nm, and the solid content is 40~50%; And / or, the waterborne polyurethane emulsion has a glass transition temperature of -30°C to -50°C, a particle size of 50~300 nm, and a solid content of 30~45%; And / or, the glass transition temperature of the styrene-butadiene rubber latex is -25°C to -45°C, the particle size is 150~400 nm, and the solid content is 40~60%.

4. The method for preparing the binder for the positive electrode sheet according to any one of claims 1-3, characterized in that, include: The rigid skeleton component is uniformly dispersed in water, and then the flexible linking component and the interface anchoring component are added in sequence and mixed evenly to obtain the adhesive.

5. The preparation method according to claim 4, characterized in that, Specifically, it includes: The rigid framework component is uniformly dispersed in water and stirred at high speed of 2000~4000 rpm for 2~4 hours to form a homogeneous gel, wherein the solid content of the homogeneous gel is controlled at 1~3%; Then, the flexible linking component is added, and the mixture is sheared and mixed at 2000-4000 rpm for 10-20 min. Next, the interface anchoring component is added, and the mixture is stirred at 500-1000 rpm for 30-60 min to obtain the adhesive.

6. The use of the binder for positive electrode sheets according to any one of claims 1-3 in the preparation of Prussian blue-based positive electrode sheets.

7. A Prussian blue-type positive electrode sheet, characterized in that, It includes a current collector and an active material layer coated on at least one side of the current collector, said active material layer comprising a Prussian blue-based cathode material, a conductive agent, and a binder for the cathode sheet according to any one of claims 1-3; Preferably, the total mass of the binder accounts for 3-7% of the total mass of the active material layer, the total mass of the Prussian blue-based cathode material accounts for 85-95 wt% of the total mass of the active material layer, and the total mass of the conductive agent accounts for 2-8 wt% of the total mass of the active material layer. Preferably, the conductive agent includes at least one of carbon black, multi-walled carbon nanotubes, single-walled carbon nanotubes, fumed carbon fibers, Ketjen black, and graphene. Preferably, the Prussian blue cathode material is A. h M[Fe(CN)6] y ·zH2O, where A is an alkali metal ion, M is a transition metal ion, h takes the value 0 < h < 2, y takes the value 0 < y ≤ 1, and z takes the value ≥ 0.

8. The method for preparing the Prussian blue-type positive electrode sheet according to claim 7, characterized in that, include: Provides a binder for a positive electrode sheet according to any one of claims 1-3; A mixed slurry containing Prussian blue cathode material, conductive agent and binder is uniformly coated on at least one side of the current collector, baked at a gradient temperature, and then rolled to obtain a Prussian blue cathode electrode.

9. The preparation method according to claim 8, characterized in that, The gradient heating baking process specifically includes: a first stage of baking at 60-80℃ for 5-15 min; a second stage of baking at 100-120℃ for 10-30 min; and a third stage of vacuum baking at 80-100℃ for 5-10 min. And / or, the mass ratio of the Prussian blue-based cathode material, conductive agent, and binder is 85~95:2~8:3~7; And / or, the areal density of the mixed slurry coated on the surface of the current collector is 150~250 g / m². 2 ; And / or, when performing the electrode rolling, the porosity of the electrode is controlled at 25%~35%, and the compaction density is 1.2~1.8 g / cm³.

10. A sodium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode is the Prussian blue type positive electrode as described in claim 7.

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