Electrochemical device

Abstract

This disclosure provides an electrochemical device. At least one side of the silicon anode sheet in the electrochemical device is coated with a negative electrode slurry. The negative electrode slurry includes a silicon-based material and an aqueous fluorinated polyurethane conductive adhesive. The aqueous fluorinated polyurethane conductive adhesive is used to crosslink during low-temperature drying to form a connected three-dimensional continuous conductive framework of fluorinated polyurethane and a fluorinated protective film layer. The three-dimensional continuous conductive framework of fluorinated polyurethane is embedded inside the negative electrode slurry and encapsulates the silicon-based material. The fluorinated protective film layer is located on the surface of the negative electrode slurry and protects the silicon-based material and the three-dimensional continuous conductive framework of fluorinated polyurethane. The low-temperature drying temperature is 45℃~55℃, and the time is 120min~240min. This device reduces production energy consumption and the probability of yellowing and aging of the silicon-carbon anode sheet; it also achieves a self-healing effect, better resisting the expansion of the silicon-based anode material; and it effectively fills the interface defects of physically exfoliated single-walled carbon nanotubes.

Description

Technical Field

[0001] This disclosure relates to the field of electrochemical device technology, and in particular to an electrochemical device. Background Technology

[0002] An electrochemical device is a device that uses electrochemical reactions for energy conversion and material processing. With the continuous development of electrochemical devices, high-capacity negative electrode sheets have become one of the development goals. Therefore, silicon-carbon negative electrode sheets have appeared on the market.

[0003] In practical applications, silicon-carbon anode sheets experience significant internal stress during cycling due to silicon expansion, leading to structural collapse or cracking of the conductive mesh. To address this, some researchers have attempted to employ methods such as the silicon anode composite sheet fabrication method described in patent CN114824177A. This method, through the addition of a conductive buffer layer and the combined use of graphene-elastic resin materials, effectively reduces the likelihood of structural collapse or conductive mesh cracking in silicon-carbon anode sheets. However, the added conductive buffer layer tends to increase the thickness of the silicon-carbon anode sheet, hindering its development towards thinner and lighter designs. Furthermore, this method requires the additional fabrication of the conductive buffer layer, resulting in a complex and cumbersome process.

[0004] In response, some scholars have attempted to improve the performance of silicon-based anode materials for solid-state lithium batteries, as described in patent CN 109411725 A. This method improves the performance of silicon-based anode materials for solid-state lithium batteries by loading nano-monocrystalline silicon and metal particles onto fluorinated polyurethane. It also ensures that the nano-silicon particles loaded onto the fluorinated polyurethane have extremely high toughness, which can effectively suppress the stress of silicon expansion. At the same time, the added metal particles are uniformly dispersed inside the fluorinated polyurethane, which improves the conductivity of the anode material.

[0005] However, the silicon-based anode material in this literature still suffers from poor dispersibility due to the poor flowability of fluorinated glassy polyurethane, which makes it difficult to disperse effectively with aluminum chloride, elemental metals, and high-silicon zeolite rods. Furthermore, because the conductive mesh of the silicon-based anode material in this literature is composed of fluorinated graphene and elemental metals, and the crosslinking temperature of the fluorinated polyurethane is high, the final fluorinated polyurethane-loaded nanocrystalline silicon and metal particles are brittle and cannot effectively withstand the expansion of the silicon-based anode material, resulting in problems such as conductive mesh cracking or silicon-based material detachment. Moreover, the high crosslinking temperature (80℃~90℃) of the silicon-based anode material in this literature not only leads to high production energy consumption but also increases the probability of yellowing and aging of the silicon-carbon anode sheet. Summary of the Invention

[0006] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide an electrochemical device that not only reduces the high-temperature crosslinking temperature to reduce production energy consumption, but also reduces the probability of yellowing and aging of silicon-carbon anode sheets; it also achieves a self-healing effect to better resist the expansion of silicon-based anode materials and reduce the problems of conductive mesh cracking or silicon-based material detachment; and it ensures that the soft and hard microphase separation structure of the waterborne fluorinated polyurethane conductive adhesive can better fill the interface defects of physically exfoliated single-walled carbon nanotubes, which is conducive to the preparation of a uniform, stable, highly flexible, and highly conductive three-dimensional continuous conductive framework of fluorinated polyurethane, thereby improving the rate performance of the electrochemical device.

[0007] The purpose of this disclosure is achieved through the following technical solution:

[0008] An electrochemical device includes a positive electrode and a silicon negative electrode disposed separately, wherein at least one side of the silicon negative electrode is coated with a negative electrode paste.

[0009] The negative electrode slurry includes a silicon-based material and an aqueous fluorinated polyurethane conductive adhesive. The aqueous fluorinated polyurethane conductive adhesive is used to crosslink during low-temperature drying to form a connected three-dimensional continuous conductive framework of fluorinated polyurethane and a fluorinated protective film layer. The three-dimensional continuous conductive framework of fluorinated polyurethane is embedded inside the negative electrode slurry and is used to encapsulate the silicon-based material. The fluorinated protective film layer is located on the surface of the negative electrode slurry and is used to protect the silicon-based material and the three-dimensional continuous conductive framework of fluorinated polyurethane.

[0010] The low-temperature drying temperature is 45℃~55℃, and the time is 120min~240min;

[0011] The preparation method of the water-based fluorinated polyurethane conductive adhesive includes the following steps:

[0012] A super-dispersed single-walled carbon nanotube slurry is obtained by secondary exfoliation of the single-walled carbon nanotube dispersion using a mild physical method; wherein the single-walled carbon nanotube dispersion includes a dispersant, a mild viscosity reducer, water, and single-walled carbon nanotubes.

[0013] A first ultrasonic high-pressure homogenization operation was performed by adding sheet-like graphene to the ultradispersed single-walled carbon nanotube slurry to obtain a single-walled carbon nanotube / graphene composite slurry.

[0014] Aqueous fluorinated polyurethane emulsion is mixed with the single-walled carbon nanotube / graphene composite slurry and vacuum degassed to obtain the aqueous fluorinated polyurethane conductive adhesive; wherein the aqueous fluorinated polyurethane conductive adhesive forms a soft and hard microphase separation structure, and the hard segment region of the soft and hard microphase separation structure is used to spontaneously form a physical support skeleton at low temperature to reduce the drying temperature of the negative electrode slurry.

[0015] In one embodiment, the fluorinated polyurethane three-dimensional continuous conductive framework includes a fluorinated polyurethane main framework and a three-dimensional conductive mesh; the fluorinated polyurethane main framework includes connected hard segment regions and multiple soft segment regions, the hard segment regions and each of the soft segment regions form the soft-hard microphase separation structure, and the soft-hard microphase separation structure is connected to the silicon-based material through the three-dimensional conductive mesh.

[0016] In one embodiment, the coating thickness of the negative electrode slurry is 100μm~500μm.

[0017] In one embodiment, the solid content of the waterborne fluorinated polyurethane conductive adhesive is greater than 5% to 10%; and / or,

[0018] The silicon-based material content is 87%~93%; and / or,

[0019] The diameter of the single-walled carbon nanotubes is 10 nm to 20 nm.

[0020] In one embodiment, after the step of adding sheet-like graphene to the ultradispersed single-walled carbon nanotube slurry for a first ultrasonic high-pressure homogenization operation, and after the step of mixing the aqueous fluorinated polyurethane emulsion with the single-walled carbon nanotube / graphene composite slurry under vacuum degassing, the following step is further included:

[0021] Alicyclic diisocyanates were reacted with fluorinated diols at low temperature to obtain fluorinated prepolymers;

[0022] The fluorinated prepolymer is subjected to a chain extension reaction with polyether glycol and a catalyst;

[0023] The fluorinated prepolymer, after chain extension reaction, is neutralized with a salt-forming agent and then dispersed at high speed in water to obtain the waterborne fluorinated polyurethane emulsion.

[0024] In one embodiment, the alicyclic diisocyanate includes at least one of isophorone diisocyanate and aliphatic diisocyanate; and / or,

[0025] The fluorinated diol includes at least one selected from trifluoropropanediol, hexafluorobutanediol, and 2,2,3,3-tetrafluoro-1,4-butanediol; and / or...

[0026] The polyether glycol includes at least one of polytetrahydrofuran, polypropylene glycol, and polyethylene glycol.

[0027] In one embodiment, the alicyclic diisocyanate is used in an amount of 29% to 39% of the total amount added in the polymerization reaction; and / or,

[0028] The low-temperature heating reaction is carried out at a temperature of 60℃~80℃ for 2h~4h; and / or,

[0029] After the step of reacting the alicyclic diisocyanate with the fluorinated diol at low temperature and before the step of chain extension reaction of the fluorinated prepolymer with the polyether diol and the catalyst, the following step is also included:

[0030] The fluorinated prepolymer is cooled to 40℃~60℃.

[0031] In one embodiment, the step of gently physically exfoliating the single-walled carbon nanotubes from the dispersion includes the following specific steps:

[0032] The dispersant and the mild viscosity reducer are added to the water for a first high-speed dispersion operation to obtain a dispersion.

[0033] A second high-speed dispersion operation was performed by adding single-walled carbon nanotubes to the dispersion to obtain a single-walled carbon nanotube premix.

[0034] The premixed liquid of single-walled carbon nanotubes was subjected to a sand milling operation to obtain the dispersion of single-walled carbon nanotubes.

[0035] Ultrasonic high-pressure microfluidic homogenization was performed on the single-walled carbon nanotube dispersion to obtain an ultra-dispersed single-walled carbon nanotube slurry.

[0036] In one embodiment, the mass ratio of the single-walled carbon nanotubes to the sheet-like graphene is (0.5~1.5):(1~3); and / or,

[0037] The aspect ratio of the single-walled carbon nanotubes in the ultradispersed single-walled carbon nanotube slurry is 2500~4000; and / or,

[0038] The conditions for the first ultrasonic high-pressure homogenization operation are: ultrasonic power 100W~300W, pressure 20MPa~80MPa, and time 20min~60min.

[0039] In one embodiment, the mild viscosity reducer includes at least one of ammonia, sodium silicate, and polyacrylamide; and / or,

[0040] The mass ratio of the dispersant, the mild viscosity reducer, and the water is (0.3~1):(0.05~0.1):100.

[0041] Compared with the prior art, this disclosure has at least the following advantages:

[0042] 1) Since the three-dimensional continuous conductive framework of fluorinated polyurethane is mainly composed of single-walled carbon nanotubes and sheet graphene, without the use of inorganic metal elements, it effectively improves the stability of the interface between single-walled carbon nanotubes, graphene and fluorinated polyurethane, and reduces the brittleness of the three-dimensional continuous conductive framework of fluorinated polyurethane, so as to better resist the expansion of silicon-based anode materials and effectively avoid the problems of conductive mesh cracking or silicon-based material falling off.

[0043] 2) Because the hard segment region of the waterborne fluorinated polyurethane conductive adhesive, which has a soft-hard microphase separation structure, contains strongly polar groups (-NHCOO-, -CF3), the hard segment region of the waterborne fluorinated polyurethane conductive adhesive can spontaneously crosslink at a relatively low temperature of 45℃~55℃ to form a physical support skeleton. This eliminates the need for harsh high-temperature conditions to obtain the prototype of the fluorinated polyurethane three-dimensional continuous conductive skeleton, effectively reducing the heat generated during the low-temperature drying of the negative electrode slurry. This allows the waterborne fluorinated polyurethane conductive adhesive to fully complete the crosslinking reaction at a relatively low temperature of 45℃~55℃, enabling the formed fluorinated polyurethane three-dimensional continuous conductive skeleton to encapsulate and fix the silicon-based material. Furthermore, it forms a robust fluorinated protective film layer on the surface of the negative electrode slurry, effectively protecting the silicon-based material and the fluorinated polyurethane three-dimensional continuous conductive skeleton, reducing the damage caused by the external environment to the silicon-based material and the fluorinated polyurethane three-dimensional continuous conductive skeleton. This effectively reduces the drying temperature of the negative electrode slurry, not only lowering production energy consumption but also reducing the probability of yellowing and aging of the silicon-carbon negative electrode sheet. Furthermore, the soft segment region of the soft-hard microphase separation structure can absorb and release the stress of the volume expansion of the silicon-based material through its own reversible deformation, thus achieving a better self-healing effect. This further enhances the ability of the fluorinated polyurethane three-dimensional continuous conductive framework to resist the expansion of the silicon-based negative electrode material, thereby more effectively maintaining the structural integrity of the silicon negative electrode sheet during long-term cycling and further reducing the problems of conductive mesh cracking or silicon-based material shedding. Consequently, it improves the rate performance of the electrochemical device.

[0044] 3) Since the single-walled carbon nanotubes in the dispersion are peeled off by a gentle physical method without the use of strong acidic substances (hydrofluoric acid), the integrity of the single-walled carbon nanotube structure is preserved to the greatest extent, thereby effectively utilizing the conductivity of the single-walled carbon nanotubes and effectively reducing the amount of single-walled carbon nanotubes used.

[0045] 4) Although the single-walled carbon nanotubes in the dispersion can be peeled off by a gentle physical method to a certain extent, the integrity of the single-walled carbon nanotube structure can still be maintained to some extent. However, interface defects still exist at the ends and bends of the peeled single-walled carbon nanotubes. The soft and hard microphase separation structure of the waterborne fluorinated polyurethane conductive adhesive disclosed in this invention can better fill the interface defects of the physically peeled single-walled carbon nanotubes, which is beneficial for constructing a uniform, stable, highly flexible, and highly conductive three-dimensional continuous conductive framework of fluorinated polyurethane.

[0046] 5) Due to the low viscosity and good flowability of the waterborne fluorinated polyurethane emulsion, the single-walled carbon nanotube / graphene composite slurry can be uniformly distributed in the waterborne fluorinated polyurethane emulsion, reducing the agglomeration problem of single-walled carbon nanotubes and sheet graphene. Furthermore, the entire negative electrode slurry preparation does not use strong acidic substances (hydrofluoric acid), further reducing damage to single-walled carbon nanotubes and sheet graphene, which is conducive to constructing a uniform, stable, highly flexible, and highly conductive three-dimensional continuous conductive framework of fluorinated polyurethane. Attached Figure Description

[0047] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a flowchart of an embodiment of the waterborne fluorinated polyurethane conductive adhesive of the present invention.

[0049] Figure 2 The diagram shows the specific capacity at different magnifications for each embodiment and comparative example of the present invention.

[0050] Figure 3 The image shows a scanning electron microscope (SEM) image of the single-walled carbon nanotubes obtained by exfoliation in Example 3 of the present invention.

[0051] Figure 4 The image shows the electron microscope scan of the single-walled carbon nanotubes obtained by exfoliation in Comparative Example 1 of this invention.

[0052] Figure 5 This is a photograph of the actual process of testing the dispersibility of the ultradispersed single-walled carbon nanotube graphene conductive adhesive of Example 3 of the present invention after 180 days of storage. Detailed Implementation

[0053] To facilitate understanding of this disclosure, a more complete description will be given below with reference to the accompanying drawings, which illustrate preferred embodiments of the present disclosure. However, this disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure.

[0054] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0056] To better understand the technical solutions and beneficial effects of this disclosure, the following detailed description is provided in conjunction with specific embodiments.

[0057] An electrochemical device according to one embodiment includes a positive electrode and a silicon negative electrode disposed separately, wherein at least one side of the silicon negative electrode is coated with a negative electrode slurry, the negative electrode slurry comprising a silicon-based material and an aqueous fluorinated polyurethane conductive adhesive.

[0058] It is understood that because the hard segment region of the waterborne fluorinated polyurethane conductive adhesive, which has a soft-hard microphase separation structure, contains strongly polar groups (-NHCOO-, -CF3), the hard segment region of the waterborne fluorinated polyurethane conductive adhesive can spontaneously crosslink at a relatively low temperature of 45℃~55℃ to form a physical support skeleton. This eliminates the need for harsh high-temperature conditions to obtain the prototype of the fluorinated polyurethane three-dimensional continuous conductive skeleton, effectively reducing the heat required for low-temperature drying of the negative electrode slurry. This allows the waterborne fluorinated polyurethane conductive adhesive to fully complete the crosslinking reaction at a relatively low temperature of 45℃~55℃ and a drying time of 120min~240min. The resulting fluorinated polyurethane three-dimensional continuous conductive skeleton is embedded within the negative electrode slurry, enabling it to encapsulate and fix the silicon-based material. Furthermore, it forms a robust fluorinated protective film layer on the surface of the negative electrode slurry, effectively protecting the silicon-based material and the fluorinated polyurethane three-dimensional continuous conductive skeleton, reducing the damage caused by the external environment to both. This effectively reduces the drying temperature of the negative electrode slurry, not only lowering production energy consumption but also reducing the probability of yellowing and aging of the silicon-carbon negative electrode sheet. Furthermore, the soft segment region of the soft-hard microphase separation structure can absorb and release the stress of the volume expansion of the silicon-based material through its own reversible deformation, thus achieving a better self-healing effect. This further enhances the ability of the fluorinated polyurethane three-dimensional continuous conductive framework to resist the expansion of the silicon-based negative electrode material, thereby more effectively maintaining the structural integrity of the silicon negative electrode sheet during long-term cycling and further reducing the problems of conductive mesh cracking or silicon-based material shedding. Consequently, it improves the rate performance of the electrochemical device.

[0059] It is worth mentioning that the improved rate performance of the electrochemical device disclosed herein refers to improved cycling stability of the electrochemical device at low, medium, and high rates (0.1C-2C), meaning that the specific capacity will not experience a significant decline. For details, please refer to [reference needed]. Figure 2 .

[0060] It is also understandable that, since the water-based fluorinated polyurethane conductive adhesive is mainly composed of single-walled carbon nanotubes and sheet graphene, without the use of inorganic metal elements, it effectively improves the stability of the interface between single-walled carbon nanotubes, graphene and fluorinated polyurethane, and reduces the brittleness of the three-dimensional continuous conductive skeleton of fluorinated polyurethane, so as to better resist the expansion of silicon-based anode materials and effectively avoid the problems of conductive mesh cracking or silicon-based material falling off.

[0061] It is also understandable that, since the single-walled carbon nanotubes in the water-based fluorinated polyurethane conductive adhesive are obtained by gently and physically peeling the single-walled carbon nanotubes from the dispersion, without using strong acidic substances (hydrofluoric acid), the integrity of the single-walled carbon nanotube structure is preserved to the greatest extent, thereby effectively leveraging the conductivity of the single-walled carbon nanotubes and effectively reducing the amount of single-walled carbon nanotubes used.

[0062] It is also understandable that although the single-walled carbon nanotubes in the dispersion can be peeled off by a gentle physical method to a certain extent, the integrity of the single-walled carbon nanotube structure can still be maintained to some extent. However, interface defects still exist at the ends and bends of the peeled single-walled carbon nanotubes. The soft and hard microphase separation structure of the waterborne fluorinated polyurethane conductive adhesive disclosed in this invention can better fill the interface defects of the physically peeled single-walled carbon nanotubes. This is beneficial for constructing a uniform, stable, highly flexible, and highly conductive three-dimensional continuous conductive framework of fluorinated polyurethane, which is better suited for the application of thinner silicon anode sheets with high silicon content.

[0063] It is also understandable that the low viscosity and good flowability of the waterborne fluorinated polyurethane emulsion in the waterborne fluorinated polyurethane conductive adhesive allow the single-walled carbon nanotube / graphene composite slurry to be uniformly distributed in the waterborne fluorinated polyurethane emulsion, reducing the agglomeration problem of single-walled carbon nanotubes and sheet graphene. Furthermore, the entire negative electrode slurry preparation does not use strong acidic substances (hydrofluoric acid), further reducing damage to single-walled carbon nanotubes and sheet graphene, which is conducive to constructing a uniform, stable, highly flexible, and highly conductive three-dimensional continuous conductive framework of fluorinated polyurethane.

[0064] In one embodiment, the fluorinated polyurethane three-dimensional continuous conductive framework includes a fluorinated polyurethane main framework and a three-dimensional conductive mesh. The fluorinated polyurethane main framework includes interconnected hard segment regions and multiple soft segment regions. The hard segment regions and each of the soft segment regions form the soft-hard microphase separation structure. The soft-hard microphase separation structure is connected to the silicon-based material through the three-dimensional conductive mesh, so that the fluorinated polyurethane three-dimensional continuous conductive framework can better encapsulate the silicon-based material and achieve better conductivity with the silicon-based material. No additional conductive buffer layer is required, which is more conducive to the development of thinner silicon anode sheets.

[0065] In one embodiment, the coating thickness of the negative electrode slurry is 100μm~500μm to ensure that the thickness of the negative electrode slurry is relatively thin, which is beneficial to the preparation of a thin and light silicon negative electrode sheet with high energy density.

[0066] In one embodiment, the silicon-based material content is 87% to 93%, which is higher than that of traditional silicon-based materials. Because the waterborne fluorinated polyurethane conductive adhesive of this disclosure crosslinks to form a fluorinated polyurethane three-dimensional continuous conductive skeleton during low-temperature drying, it has a uniform, stable, highly flexible, and highly conductive fluorinated polyurethane three-dimensional continuous conductive skeleton. At the same time, with the use of a fluorinated protective film layer, the formed fluorinated polyurethane three-dimensional continuous conductive skeleton can better resist the expansion of silicon with high silicon content, so as to better adapt to the application of thinner, higher energy density, and higher silicon content silicon anode sheets.

[0067] In one embodiment, the negative electrode slurry also includes 2 to 8 parts of superconducting carbon black. The silicon-based material, water-based fluorinated polyurethane conductive adhesive and superconducting carbon black are simply stirred and mixed to obtain a uniform and stable negative electrode slurry.

[0068] In one embodiment, the mass ratio of silicon-based material, waterborne fluorinated polyurethane conductive adhesive, and superconducting carbon black is (87~93):(4~6):(3~7) to ensure that the product can be prepared using a small amount of waterborne fluorinated polyurethane conductive adhesive.

[0069] In this embodiment, the simple mixing conditions are: mixing for 20 to 30 minutes using a high-speed homogenizer at a speed of 1000 rpm to 2000 rpm.

[0070] In one embodiment, the solid content of the waterborne fluorinated polyurethane conductive adhesive is greater than 5% to 10%, which ensures that the solid content of the waterborne fluorinated polyurethane conductive adhesive not only meets the requirements for dispersion with silicon-based materials, but also helps to reduce the drying temperature of the negative electrode slurry, thereby further reducing the probability of yellowing and aging of the silicon negative electrode sheet.

[0071] It should be noted that the diameter of commercially available single-walled carbon nanotubes (SWCNTs) is currently 10nm~20nm, generally exceeding the standard value (1nm~2nm) for SWCNTs. This makes them difficult to disperse in the negative electrode slurry, resulting in a higher addition amount of SWCNTs and lower utilization rate. The traditional method involves high-speed dispersion with a dispersant and water, which is effective for smaller diameter SWCNTs (10nm~15nm). However, for SWCNTs with a diameter greater than 15nm and a length of 10μm~50μm, traditional high-speed dispersion with dispersants and water is insufficient. While some chemical-assisted dispersion methods exist, these require the addition of alkaline or acidic chemicals. However, these chemicals can damage the structure of the SWCNTs, compromising their structural integrity. Specifically, the diameter of single-walled carbon nanotubes can be 16nm, 17nm, 18nm, 18nm and 20nm.

[0072] Therefore, this disclosure provides a mild physical method for preparing an aqueous fluorinated polyurethane conductive adhesive. While using a small amount of mild viscosity reducer, it still achieves complete and intact exfoliation of single-walled carbon nanotubes, thereby preparing single-walled carbon nanotubes with fewer surface defects, good integrity, high tube diameter uniformity, high aspect ratio, and high purity. Furthermore, the added sheet-like graphene can be well adsorbed between the exfoliated single-walled carbon nanotubes under the first ultrasonic high-pressure homogenization operation, achieving spatial isolation of the single-walled carbon nanotubes and further preventing entanglement of the exfoliated single-walled carbon nanotubes. Thus, in... Using a small amount of mild viscosity reducer, it can effectively and stably prevent the unwrapped single-walled carbon nanotubes from entanglement, thus ensuring the stability of the dispersion of single-walled carbon nanotubes in the single-walled carbon nanotube / graphene composite slurry. This ensures that the single-walled carbon nanotubes in the single-walled carbon nanotube / graphene composite slurry will not delaminate or agglomerate even after long-term storage. Furthermore, the soft and hard microphase separation structure of the waterborne fluorinated polyurethane conductive adhesive can better fill the interface defects of physically unwrapped single-walled carbon nanotubes, which is beneficial for preparing a uniform, stable, highly flexible, and highly conductive three-dimensional continuous conductive framework of fluorinated polyurethane.

[0073] Please see Figure 1 One embodiment of the method for preparing an aqueous fluorinated polyurethane conductive adhesive includes some or all of the following steps:

[0074] S101. The single-walled carbon nanotubes in the single-walled carbon nanotube dispersion are peeled off by a mild physical method to obtain an ultra-dispersed single-walled carbon nanotube slurry; wherein the single-walled carbon nanotube dispersion includes a dispersant, a mild viscosity reducer, water and single-walled carbon nanotubes.

[0075] It is understandable that by gently and physically peeling the single-walled carbon nanotubes from the dispersion, using a mild viscosity reducer and physical dispersion methods, the integrity of the peeled single-walled carbon nanotubes is preserved to the greatest extent, thereby effectively leveraging the conductivity of the single-walled carbon nanotubes and thus effectively reducing the amount of single-walled carbon nanotubes used in the negative electrode slurry.

[0076] It should be noted that some scholars currently use patent CN 120903486 A, employing purely physical methods, such as a combination of premixing and microfluidic homogenization. However, in practical applications, high-speed stirring and dispersion can randomly break and peel off single-walled carbon nanotubes, resulting in poor size uniformity, low aspect ratio, and numerous surface defects in the peeled single-walled carbon nanotubes. Furthermore, after stirring or high-speed dispersion ceases, single-walled carbon nanotubes peeled off using purely physical methods tend to entangle and agglomerate, which is detrimental to subsequent dispersion with silicon-based materials. This entanglement and agglomeration also increases the viscosity of the single-walled carbon nanotube dispersion, further complicating the dispersion of the single-walled carbon nanotube dispersion with silicon-based materials. This entanglement and agglomeration is particularly pronounced for single-walled carbon nanotubes with large diameters and high aspect ratios. Specifically, single-walled carbon nanotubes with large diameters and high aspect ratios refer to those with diameters greater than 15 nm and lengths ranging from 10 μm to 50 μm.

[0077] To address the aforementioned technical issues, some researchers have attempted to improve the entanglement and aggregation of single-walled carbon nanotubes after exfoliation by adding a viscosity-reducing agent, as described in patent CN110473653A. However, the viscosity-reducing agent used in this paper is a strongly alkaline agent (pH>11) such as ethanolamine or piperazine, which easily damages the structure of the single-walled carbon nanotubes. This means it cannot effectively achieve complete exfoliation of the coarse single-walled carbon nanotubes, and therefore cannot prepare a uniform, stable, highly flexible, and highly conductive three-dimensional continuous conductive framework of fluorinated polyurethane. Furthermore, the high dosage (0.1~1%) of the strongly alkaline viscosity-reducing agent in patent CN110473653A results in a high cost.

[0078] Therefore, in this disclosure, a mild viscosity reducer is used directly instead of a strong alkaline viscosity reducer. This mild viscosity reducer effectively reduces damage to the exfoliated single-walled carbon nanotubes, ensuring the integrity of the exfoliated single-walled carbon nanotube structure. Furthermore, it effectively reduces the interfacial tension of the coarse single-walled carbon nanotubes, preventing entanglement and aggregation after exfoliation. This ensures that the mild viscosity reducer maintains the stability of the viscosity of the ultra-dispersed single-walled carbon nanotube slurry, facilitating dispersion and mixing with sheet-like graphene, thus benefiting subsequent coating operations and ensuring the preparation of a uniform, stable, highly flexible, and highly conductive three-dimensional continuous conductive framework of fluorinated polyurethane. Additionally, the mild viscosity reducer is used in conjunction with the dispersant, the mild viscosity reducer itself, and the water in a mass ratio of (0.3~1):(0.05~0.1):100, ensuring a lower dosage of the mild viscosity reducer and reducing its usage cost. Moreover, the interfacial layer formed by the mild viscosity reducer can buffer the direct impact of abrasive beads on the coarse single-walled carbon nanotubes, effectively reducing fracture caused by stress concentration.

[0079] In one embodiment, the mild viscosity reducer includes at least one of ammonia, sodium silicate, and polyacrylamide. Since ammonia is weakly alkaline and sodium silicate and polyacrylamide are neutral, this ensures that ammonia, sodium silicate, and polyacrylamide are all mild viscosity reducers.

[0080] In a preferred embodiment, the mild viscosity reducer is a mixture of ammonia and polyacrylamide.

[0081] In one embodiment, the mass ratio of ammonia to polyacrylamide is 1:2 to 1:8.

[0082] It is understandable that if the mass fraction of the dispersant is less than 0.3 parts, the amount of dispersant added is too small to achieve good dispersion of single-walled carbon nanotubes; if the mass fraction of the dispersant is greater than 1 part, the amount of dispersant added is too large and affects the conductivity of the single-walled carbon nanotube dispersion; if the mass fraction of the mild viscosity reducer is greater than 0.05 parts, it cannot effectively improve the viscosity rise problem of single-walled carbon nanotubes and cannot achieve more thorough exfoliation of single-walled carbon nanotubes; if the mass fraction of the mild viscosity reducer is greater than 0.1 parts, the amount of mild viscosity reducer used is too large and affects the purity of the finally exfoliated single-walled carbon nanotubes, thus affecting the conductivity of the single-walled carbon nanotube dispersion.

[0083] Therefore, in one embodiment, the mass ratio of the single-walled carbon nanotubes, the dispersant, the mild viscosity reducer, and the water is (0.5~1.5):(0.3~1):(0.05~0.1):100. In this way, while ensuring that the addition of a small amount of mild viscosity reducer does not affect the purity of the finally exfoliated single-walled carbon nanotubes, it can also achieve a more thorough and complete exfoliation of single-walled carbon nanotubes with large diameter and high aspect ratio. This is beneficial for preparing a uniform, stable, highly tough, and highly conductive fluorinated polyurethane three-dimensional continuous conductive framework.

[0084] In one embodiment, the mass ratio of the dispersant, the mild viscosity reducer, and the water is (0.3~0.8):(0.05~0.08):100, to ensure that a thorough and complete exfoliation of coarse-diameter, high aspect ratio single-walled carbon nanotubes can be achieved using less mild viscosity reducer.

[0085] In one embodiment, the dispersant includes at least one of CMC, SDS, and CTAB.

[0086] In one embodiment, the water is deionized water.

[0087] It should be noted that since a lower amount of mild viscosity reducer will reduce the contact area with single-walled carbon nanotubes, the traditional simple high-speed dispersion + homogenization operation cannot effectively achieve the desired effect of a low amount of mild viscosity reducer.

[0088] Therefore, in one embodiment, the step of peeling the single-walled carbon nanotubes from the single-walled carbon nanotube dispersion by a gentle physical method includes the following specific steps: First, the dispersant and the gentle viscosity reducer are added to the water for a first high-speed dispersion operation, so that the gentle viscosity reducer and the dispersant can be uniformly distributed in the water, resulting in a uniform, stable, and well-dispersed dispersion, which is beneficial to increasing the contact area between the gentle viscosity reducer and the single-walled carbon nanotubes; then, single-walled carbon nanotubes are added to the dispersion for a second high-speed dispersion operation to promote effective contact between the single-walled carbon nanotubes and the dispersant, the gentle viscosity reducer, and the water, resulting in a single-walled carbon nanotube premix, thereby ensuring that a smaller amount of gentle viscosity reducer is sufficient to meet the requirements of the entire peeling of the single-walled carbon nanotubes and viscosity control; next, the single-walled carbon nanotube premix is ​​subjected to a sand milling operation to achieve the primary peeling of the single-walled carbon nanotubes, thereby peeling and dispersing them. Single-walled carbon nanotubes (SUVs) are produced to form a SUV dispersion. The SUV dispersion is then subjected to ultrasonic high-pressure microjets for homogenization. This process generates directional resistance to van der Waals forces, allowing for secondary exfoliation of the SUVs. This achieves complete and thorough exfoliation of the SUVs, resulting in a gentle physical secondary exfoliation process. This ensures that the exfoliated SUVs have fewer surface defects, better integrity, higher diameter uniformity, and a higher aspect ratio, leading to a highly dispersed SUV slurry. This slurry facilitates the construction of a uniform, stable, highly tough, and highly conductive three-dimensional continuous conductive framework for fluorinated polyurethane. It effectively avoids the problems of incomplete exfoliation, low aspect ratio, and poor dimensional uniformity caused by large-diameter, high-length SUVs directly entering the exfoliation process, thus improving the utilization rate of the SUVs and reducing their usage.

[0089] It should be noted that by performing a sand milling operation on the premixed liquid of the single-walled carbon nanotubes, the interior of the single-walled carbon nanotubes can be better dispersed and loosened, which facilitates thorough and complete peeling in subsequent ultrasonic high-pressure microjet homogenization operations.

[0090] In one embodiment, the aspect ratio of the single-walled carbon nanotubes obtained by gently physical peeling off the single-walled carbon nanotube dispersion is 2500~4000; to ensure that single-walled carbon nanotubes with high aspect ratio are prepared.

[0091] In one embodiment, the stirring speed of the first high-speed dispersion operation is 100 rpm to 2000 rpm, and the time is 10 min to 30 min. Further, the stirring speed of the first high-speed dispersion operation is 1000 rpm to 2000 rpm, and the time is 20 min to 30 min.

[0092] In one embodiment, the stirring speed of the second high-speed dispersion operation is 100 rpm to 2000 rpm and the time is 10 min to 30 min.

[0093] In one embodiment, the grinding operation is performed at a speed of 500 rpm to 2000 rpm for a time of 60 min to 120 min.

[0094] In one embodiment, the ultrasonic high-pressure microjets homogenization of the single-walled carbon nanotube dispersion includes the following specific steps: first, the single-walled carbon nanotube dispersion is subjected to a second ultrasonic high-pressure homogenization, and then the single-walled carbon nanotube dispersion after the second ultrasonic high-pressure homogenization is subjected to a microjets homogenization, so as to achieve a directional, gentle, thorough and complete secondary exfoliation of the single-walled carbon nanotubes.

[0095] In one embodiment, the conditions for the second ultrasonic high-pressure homogenization operation are: ultrasonic power of 100W~300W, pressure of 20MPa~80MPa, and time of 20min~60min, to achieve a gentler initial exfoliation of the single-walled carbon nanotubes, thereby ensuring that the final exfoliated single-walled carbon nanotubes have an intact structure. Furthermore, the use of a mild viscosity reducer during the second ultrasonic high-pressure homogenization operation allows for sufficient contact with the exfoliated single-walled carbon nanotubes, ensuring that a smaller amount of mild viscosity reducer is sufficient to meet the requirements of the entire exfoliation process and viscosity control, while also effectively preventing the exfoliated single-walled carbon nanotubes from entangled.

[0096] It is understandable that if a large pressure is used to perform micro-jet homogenization operation on single-walled carbon nanotubes after the initial exfoliation, the exfoliated single-walled carbon nanotubes may break due to excessive pressure. This would not be able to ensure that the final exfoliated single-walled carbon nanotubes have fewer surface defects, better integrity, higher tube diameter uniformity, and a higher aspect ratio.

[0097] Therefore, in one embodiment, the microfluidic homogenization operation is performed under the following conditions: time 20-60 minutes, pressure 100-200 MPa. This ensures relatively low pressure during the microfluidic homogenization operation, thereby ensuring gentle directional exfoliation. Simultaneously, a mild viscosity reducer is used to achieve complete and thorough exfoliation of the initial single-walled carbon nanotubes. This effectively reduces the risk of breakage during directional exfoliation due to excessive pressure, ensuring that the final exfoliated product is a single-walled carbon nanotube with few surface defects, good integrity, high diameter uniformity, and a high aspect ratio. For details, please refer to [link to relevant documentation]. Figure 3 .

[0098] S102. Add sheet-like graphene to the ultradispersed single-walled carbon nanotube slurry and perform a first ultrasonic high-pressure homogenization operation to obtain a single-walled carbon nanotube / graphene composite slurry.

[0099] It is understandable that the added sheet-like graphene can be well adsorbed on the surface of the exfoliated single-walled carbon nanotubes under the first ultrasonic high-pressure homogenization operation, achieving spatial isolation of the single-walled carbon nanotubes and further preventing the exfoliated single-walled carbon nanotubes from entanglement. This better maintains the stability of the single-walled carbon nanotube / graphene composite slurry system, ensuring that the viscosity does not change too much. This effectively reduces the amount of mild viscosity reducer used, ensuring that the mild viscosity reducer used in this disclosure can still maintain the dispersion stability of the single-walled carbon nanotube / graphene composite slurry for a long time. This ensures that the single-walled carbon nanotube / graphene composite slurry will not have problems with stratification or agglomeration when stored for a long time. This is conducive to the long-term stable preservation of the single-walled carbon nanotube / graphene composite slurry, ensuring that a uniform, stable and well-dispersed negative electrode slurry can be prepared by simply stirring and mixing with silicon-based materials. This effectively saves the preparation time of the negative electrode slurry preparation process and greatly improves the production efficiency of the electrochemical device.

[0100] It is also understandable that the sheet-like graphene adsorbed on the single-walled carbon nanotubes can form a three-dimensional conductive network of vine petals with the peeled single-walled carbon nanotubes, which effectively improves the conductivity of the three-dimensional continuous conductive framework of fluorinated polyurethane, so as to ensure that high-energy-density silicon anode sheets can be prepared using a smaller amount of single-walled carbon nanotubes and sheet-like graphene.

[0101] In one embodiment, the size of the sheet graphene is 4μm to 10μm, and in particular, the mass ratio of the single-walled carbon nanotubes to the sheet graphene is (0.5~1.5):(1~3). This ensures that the added sheet graphene not only improves the conductivity of the fluorinated polyurethane three-dimensional continuous conductive framework, but also effectively prevents the stripped single-walled carbon nanotubes from entanglement.

[0102] In one embodiment, the conditions for the first ultrasonic high-pressure homogenization operation are: ultrasonic power of 100W~300W, pressure of 20MPa~80MPa, and time of 20min~60min, to ensure that the sheet graphene can be gently adsorbed on the surface of the stripped single-walled carbon nanotubes.

[0103] In one embodiment, both the first and second ultrasonic high-pressure homogenization operations are performed in an intermittent mode. Specifically, the intermittent mode duration is: the ultrasound is turned on for 3 seconds and then turned off for 5 seconds.

[0104] In one embodiment, an ultrasonic cell disruptor probe is incorporated into both the first and second ultrasonic high-pressure homogenization operations.

[0105] In one embodiment, both the high pressure and homogenization in the first and second ultrasonic high pressure homogenization operations are in continuous mode.

[0106] In one embodiment, the particle size of the single-walled carbon nanotube / graphene composite slurry is 1μm~15μm to ensure that the particle size of the prepared single-walled carbon nanotube / graphene composite conductive agent is suitable, avoiding the situation where the single-walled carbon nanotubes cannot effectively expand due to the excessively large sheet diameter of the graphene. This is beneficial to preparing a uniform, stable, highly flexible, and highly conductive three-dimensional continuous conductive framework of fluorinated polyurethane.

[0107] It is also understandable that, since the water-based fluorinated polyurethane conductive adhesive is mainly composed of single-walled carbon nanotubes and sheet graphene, without the use of inorganic metal elements, it effectively improves the stability of the interface between single-walled carbon nanotubes, graphene and fluorinated polyurethane, and reduces the brittleness of the three-dimensional continuous conductive skeleton of fluorinated polyurethane, so as to better resist the expansion of silicon-based anode materials and effectively avoid the problems of conductive mesh cracking or silicon-based material falling off.

[0108] In one embodiment, the mass ratio of the single-walled carbon nanotubes to the sheet graphene is (0.5~1.5):(1~3).

[0109] S103. The waterborne fluorinated polyurethane emulsion is mixed with the single-walled carbon nanotube / graphene composite slurry and vacuum degassed to obtain the waterborne fluorinated polyurethane conductive adhesive; wherein, the waterborne fluorinated polyurethane conductive adhesive forms a soft-hard microphase separation structure, and the hard segment region of the soft-hard microphase separation structure is used to spontaneously form a physical support framework at low temperature to reduce the drying temperature of the negative electrode slurry.

[0110] It is understood that, because the hard segment region of the waterborne fluorinated polyurethane conductive adhesive, which has a soft-hard microphase separation structure, contains strongly polar groups (-NHCOO-, -CF3), the hard segment region of the waterborne fluorinated polyurethane conductive adhesive can spontaneously crosslink at a relatively low temperature of 45℃~55℃ to form a physical support framework. This allows for the formation of a preliminary three-dimensional continuous conductive framework of fluorinated polyurethane without the need for harsh high-temperature conditions, effectively reducing the heat generated during the low-temperature drying of the negative electrode slurry. This enables the waterborne fluorinated polyurethane conductive adhesive to fully complete the crosslinking reaction at a relatively low temperature of 45℃~55℃, allowing the formed three-dimensional continuous conductive framework of fluorinated polyurethane to encapsulate and fix the silicon-based material. Furthermore, it forms a robust fluorinated protective film layer on the surface of the negative electrode slurry, effectively protecting the silicon-based material and the three-dimensional continuous conductive framework of fluorinated polyurethane, reducing the damage caused by the external environment to both. This effectively reduces the drying temperature of the negative electrode slurry, not only lowering production energy consumption but also reducing the probability of yellowing and aging of the silicon-carbon negative electrode sheet. Furthermore, the soft segment region of the soft-hard microphase separation structure can absorb and release the stress of the volume expansion of the silicon-based material through its own reversible deformation, thus achieving a better self-healing effect. This further enhances the ability of the fluorinated polyurethane three-dimensional continuous conductive framework to resist the expansion of the silicon-based negative electrode material, thereby more effectively maintaining the structural integrity of the silicon negative electrode sheet during long-term cycling and further reducing the problems of conductive mesh cracking or silicon-based material shedding. Consequently, it improves the rate performance of the electrochemical device.

[0111] It is also understandable that although the single-walled carbon nanotubes (SUVs) in the dispersion can be peeled off through a gentle physical method to a certain extent, ensuring the integrity of the SUV structure, interfacial defects are likely to exist at the ends and bends of the peeled SUVs. Therefore, the soft-hard microphase separation structure of the waterborne fluorinated polyurethane conductive adhesive disclosed in this invention can effectively fill the interfacial defects, such as those at the ends and bends, resulting from the physical peeling of SUVs; thus facilitating the construction of a uniform, stable, highly flexible, and highly conductive three-dimensional continuous conductive framework of fluorinated polyurethane.

[0112] In one embodiment, after the step of adding graphene to the ultradispersed single-walled carbon nanotube slurry for a first ultrasonic high-pressure homogenization operation, and after the step of mixing the aqueous fluorinated polyurethane emulsion with the single-walled carbon nanotube / graphene composite slurry under vacuum degassing, the following steps are further included: First, an alicyclic diisocyanate and a fluorinated diol are subjected to a low-temperature heating reaction to obtain a fluorinated prepolymer to prepare the hard segment region of the fluorinated polyurethane backbone; then, the fluorinated prepolymer is subjected to a chain extension reaction with a polyether glycol and a catalyst to prepare the soft segment region of the fluorinated polyurethane backbone, so that the small-branched polyether glycol can be better dispersed on the side of the fluorinated polyurethane backbone to form more branches, thereby achieving a better soft and hard microphase separation structure; then, the fluorinated prepolymer after the chain extension reaction is subjected to a neutralization reaction with a salting agent, and then dispersed at high speed in water to obtain the aqueous fluorinated polyurethane emulsion.

[0113] In one embodiment, the alicyclic diisocyanate includes at least one of isophorone diisocyanate and aliphatic diisocyanate; particularly in conjunction with the use of at least one of the fluorinated diols, including trifluoropropanediol, hexafluorobutanediol, and 2,2,3,3-tetrafluoro-1,4-butanediol; and the use of at least one of the polyether diols, including polytetrahydrofuran, polypropylene glycol, and polyethylene glycol, to ensure that the hard segment region of the soft-hard microphase separation structure can spontaneously form a physical support framework at low temperature. It is worth noting that the temperature at which the hard segment region can spontaneously form a physical support framework at low temperature is 30°C to 45°C, and those skilled in the art can select according to actual conditions, such as 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 40°C, 41°C, 42°C, 45°C, etc.

[0114] In one embodiment, the salt-forming agent includes at least one of triethylamine, pyridine, and ethanolamine.

[0115] In one embodiment, the catalyst includes at least one of dibutyltin dilaurate, bismuth triacetylacetonate, and zinc stearate.

[0116] In one embodiment, the low-temperature heating reaction is carried out at a temperature of 60°C to 80°C for 2 to 4 hours. This ensures that the pre-crosslinking of the alicyclic diisocyanate and the fluorinated diol is completed at a lower temperature, resulting in a lower degree of crosslinking of the fluorinated prepolymer. This ensures that the final waterborne fluorinated polyurethane emulsion has good fluidity, which is beneficial for achieving rapid and uniform dispersion of the waterborne fluorinated polyurethane emulsion and the single-walled carbon nanotube / graphene composite slurry. This effectively reduces the agglomeration problem of single-walled carbon nanotubes and graphene.

[0117] In one embodiment, after the step of reacting the alicyclic diisocyanate with the fluorinated diol at low temperature and before the step of reacting the fluorinated prepolymer with the polyether diol and the catalyst, the following step is also included: cooling the fluorinated prepolymer to 40°C to 60°C to suppress the side reactions of the fluorinated prepolymer and to provide a suitable environment for the subsequent adjustment of the catalyst activity, ensuring that the growth of the fluorinated polyurethane backbone is the dominant reaction, which is beneficial to preparing a soft and hard microphase separation structure with a hard segment region accounting for 40% to 60%.

[0118] It is understandable that if the proportion of the hard segment region is too high or too low, a highly flexible fluorinated polyurethane main framework cannot be formed. In one embodiment, the waterborne fluorinated polyurethane conductive adhesive forms a soft-hard microphase separation structure, with the hard segment region accounting for 40% to 60% of the structure. This ensures a suitable distribution ratio between the hard and soft segments, which helps to form a highly flexible fluorinated polyurethane main framework. Furthermore, a suitable distribution ratio between the hard and soft segments ensures that the amount of hard segment region spontaneously forming a physical support framework at low temperatures is appropriate. Thus, while satisfying the requirement to construct a prototype of a three-dimensional continuous conductive framework for fluorinated polyurethane, the waterborne fluorinated polyurethane conductive adhesive also ensures suitable fluidity, facilitating the preparation of a uniform, stable, and well-dispersed negative electrode slurry through simple stirring and mixing with subsequent silicon-based materials. This effectively saves preparation time in the preceding negative electrode slurry steps and significantly improves the production efficiency of the electrochemical device.

[0119] In one embodiment, the alicyclic diisocyanate is used in an amount of 29% to 39% of the total amount added to the polymerization reaction, so that the content of the alicyclic diisocyanate is higher than that of the fluorinated diol.

[0120] In one embodiment, the mass ratio of alicyclic diisocyanate, fluorinated diol, polyether diol, catalyst and salting agent is (29~39):(2~5):(48~52):(0.01~0.1):(1~4) to ensure that the proportion of hard segment regions with soft and hard microphase separation structure in the final prepared waterborne fluorinated polyurethane conductive adhesive is 40%~60%.

[0121] In one embodiment, the operating conditions for mixed vacuum degassing are: vacuum pressure of -90 kPa to -100 kPa and holding time of 10 min to 20 min, so as to effectively remove the bubbles remaining in the water-based fluorinated polyurethane conductive adhesive, which is beneficial to preparing silicon anode sheets with fewer pores and better uniformity.

[0122] The following are some specific examples. When %, it refers to a percentage by weight. It should be noted that the following examples do not exhaustively list all possible scenarios, and unless otherwise specified, the materials used in the examples are commercially available.

[0123] Example 1

[0124] S1. Add 0.9g of dispersant CMC and 0.15g of viscosity reducer (ammonia:polyacrylamide ratio of 1:2) to 300g of deionized water and perform a first high-speed dispersion operation (1000rpm, 20min) using a high-speed disperser to obtain a dispersion. Add 1.5g of single-walled carbon nanotubes (SWCNTs, diameter 16nm, length 28μm) powder to the dispersion and perform a second high-speed dispersion operation (100rpm, 10min) using a high-speed disperser to obtain a single-walled carbon nanotube premix. Then transfer the single-walled carbon nanotube premix to a sand mill and mill at 500rpm for 60min to obtain an SWCNT dispersion.

[0125] S2. The SWCNT dispersion from step S1 is transferred to a homogenizer for high-pressure homogenization. At the same time, an ultrasonic cell disruptor probe is added to the homogenizer cup. High-pressure homogenization and ultrasonication are combined for 20 minutes (ultrasonic power 100W, pressure 20MPa, ultrasonic on for 3 seconds and then off for 5 seconds). This completes the second ultrasonic high-pressure homogenization operation on the single-walled carbon nanotube dispersion. Then, it is transferred to a microfluidic homogenizer and homogenized at 100MPa for 60 minutes to obtain an ultra-dispersed SWCNT slurry.

[0126] S3. Add 3g of sheet graphene powder (sheet diameter 4μm) to the ultra-dispersed SWCNT slurry and disperse it. Then perform high-pressure homogenization and ultrasound (ultrasound power 100W, pressure 20MPa, ultrasound on for 3S and then off for 5S) to complete the first ultrasonic high-pressure homogenization operation. Stop the operation when the particle size of the single-walled carbon nanotube / graphene composite slurry reaches 3μm.

[0127] S4. Under an inert atmosphere, 58g of isophorone diisocyanate (IPDI) and 4g of trifluoropropane diol were reacted at 60°C for 2 hours to generate a fluorinated prepolymer. The prepolymer was then cooled to 40°C, and 96g of polytetrahydrofuran and 0.02g of catalyst (dibutyltin dilaurate) were added to initiate a chain extension reaction. Finally, 2g of salt-forming agent (triethylamine) was added for neutralization, and the mixture was then dispersed in deionized water using a high-speed disperser (1000 rpm, 120 min) to form a stable aqueous fluorinated polyurethane emulsion.

[0128] S5. The single-walled carbon nanotube / graphene composite slurry prepared in S3 is mixed with the waterborne fluorinated polyurethane emulsion prepared in S4 and then placed in a vacuum degassing machine for vacuum negative pressure mixing and degassing (-90 kPa, time 20 min) to finally obtain ultra-dispersed single-walled carbon nanotube graphene conductive adhesive (solid content 12.9%).

[0129] S6. Mix 500g of ultradispersed single-walled carbon nanotube graphene conductive adhesive, 1323g of silicon-based material (silicon content 92%), and 500g of Super P by simple stirring (1500rpm, 30min) to obtain a uniform and stable negative electrode slurry.

[0130] S7. Coat the negative electrode paste from S6 onto the negative current collector (copper foil) and control the coating thickness to be 200 μm to obtain silicon negative electrode a.

[0131] S8. Place the silicon anode sheet a from S7 in 45°C and dry for 180 min to obtain a thinner silicon anode sheet (active layer thickness is 150 μm).

[0132] S9. The thin silicon anode sheet and the positive electrode sheet are separated, and the electrolyte is 1M LiPF6 in EC:DEC=1:1 with 5% FEC to prepare an electrochemical device (solid state).

[0133] Example 2

[0134] S1. Add 3g of dispersant CMC and 0.3g of viscosity reducer (ammonia:polyacrylamide ratio of 1:8) to 300g of deionized water and perform a first high-speed dispersion operation (2000rpm, 30min) using a high-speed disperser to obtain a dispersion. Add 4.5g of single-walled carbon nanotubes (SWCNTs, diameter 17nm, length 32μm) powder to the dispersion and perform a second high-speed dispersion operation (2000rpm, 30min) using a high-speed disperser to obtain a single-walled carbon nanotube premix. Then transfer the single-walled carbon nanotube premix to a sand mill and mill at 2000rpm for 120min to obtain an SWCNT dispersion.

[0135] S2. The SWCNT dispersion from step S1 is transferred to a homogenizer for high-pressure homogenization. At the same time, an ultrasonic cell disruptor probe is added to the homogenizer cup. High-pressure homogenization and ultrasonication are combined for 60 minutes (ultrasonic power 300W, pressure 80MPa, ultrasonic on for 3 seconds and then off for 5 seconds). This completes the second ultrasonic high-pressure homogenization operation on the single-walled carbon nanotube dispersion. Then, it is transferred to a microfluidic homogenizer and homogenized at 100MPa for 60 minutes to obtain an ultra-dispersed SWCNT slurry.

[0136] S3. Add 9g of sheet graphene powder (sheet diameter 10μm) to the ultra-dispersed SWCNT slurry and disperse it. Then perform high-pressure homogenization and ultrasound (ultrasound power 100W, pressure 80MPa, ultrasound on for 3S and then off for 5S) to complete the first ultrasonic high-pressure homogenization operation. Stop the operation when the particle size of the single-walled carbon nanotube / graphene composite slurry reaches 12μm.

[0137] S4. Under an inert atmosphere, 78g of aliphatic diisocyanate and 10g of hexafluorobutylene glycol were reacted at 80°C for 2 hours to generate a fluorinated prepolymer. The prepolymer was then cooled to 40°C, and 104g of polyethylene glycol and 0.2g of catalyst (dibutyltin dilaurate) were added to initiate a chain extension reaction. Finally, 8g of salt-forming agent (triethylamine) was added for neutralization, and the mixture was then dispersed in deionized water using a high-speed disperser (1000rpm, 120min) to form a stable aqueous fluorinated polyurethane emulsion.

[0138] S5. The single-walled carbon nanotube / graphene composite slurry prepared in S3 is mixed with the waterborne fluorinated polyurethane emulsion prepared in S4 and then placed in a vacuum degassing machine for vacuum negative pressure mixing and degassing (-90 kPa, time 20 min) to finally obtain ultra-dispersed single-walled carbon nanotube graphene conductive adhesive (solid content 18.7%).

[0139] S6. Mix 500g of ultradispersed single-walled carbon nanotube graphene conductive adhesive, 1323g of silicon-based material (silicon content 92%), and 500g of Super P by simple stirring (1500rpm, 30min) to obtain a uniform and stable negative electrode slurry.

[0140] S7. Coat the negative electrode paste from S6 onto the negative current collector (copper foil) and control the coating thickness to be 200 μm to obtain silicon negative electrode a.

[0141] S8. Place the silicon anode sheet a from S7 in 55℃ and dry for 240 min to obtain a thinner silicon anode sheet (active layer thickness is 150 μm).

[0142] S9. The thin silicon anode sheet and the positive electrode sheet are separated, and the electrolyte is 1M LiPF6 in EC:DEC=1:1 with 5% FEC to prepare an electrochemical device (solid state).

[0143] Example 3

[0144] S1. Add 1.5g of dispersant CMC and 0.15g of viscosity reducer (ammonia:polyacrylamide ratio of 1:6) to 300g of deionized water and perform a first high-speed dispersion operation (1500rpm, 30min) using a high-speed disperser to obtain a dispersion; add 3g of single-walled carbon nanotubes (SWCNTs, 20nm diameter, 50μm length) powder to the dispersion and perform a second high-speed dispersion operation (1000rpm, 30min) using a high-speed disperser to obtain a single-walled carbon nanotube premix; then transfer the single-walled carbon nanotube premix to a sand mill and mill at 1500rpm for 100min to obtain an SWCNT dispersion;

[0145] S2. The SWCNT dispersion from step S1 is transferred to a homogenizer for high-pressure homogenization. At the same time, an ultrasonic cell disruptor probe is added to the homogenizer cup. High-pressure homogenization and ultrasonication are combined for 60 minutes (ultrasonic power 200W, pressure 60MPa, ultrasonic on for 3 seconds and then off for 5 seconds). This completes the second ultrasonic high-pressure homogenization operation on the single-walled carbon nanotube dispersion. Then, it is transferred to a microfluidic homogenizer and homogenized at 100MPa for 60 minutes to obtain an ultra-dispersed SWCNT slurry.

[0146] S3. Add 6g of sheet graphene powder (sheet diameter 8μm) to the ultra-dispersed SWCNT slurry, disperse it, and then perform high-pressure homogenization and ultrasound (ultrasound power 100W, pressure 60MPa, ultrasound on for 3S and then off for 5S) to complete the first ultrasonic high-pressure homogenization operation. Stop the operation when the particle size of the single-walled carbon nanotube / graphene composite slurry reaches 5μm.

[0147] S4. Under an inert atmosphere, 73g of isophorone diisocyanate (IPDI) and 9.6g of trifluoropropane diol were reacted at 70°C for 2 hours to generate a fluorinated prepolymer. The prepolymer was then cooled to 40°C, and 100g of polytetrahydrofuran and 0.1g of catalyst (dibutyltin dilaurate) were added to initiate a chain extension reaction. Finally, 6.06g of salt-forming agent (triethylamine) was added for neutralization, and the mixture was then dispersed in deionized water using a high-speed disperser (1000 rpm, 120 min) to form a stable aqueous fluorinated polyurethane emulsion.

[0148] S5. The single-walled carbon nanotube / graphene composite slurry prepared in S3 is mixed with the waterborne fluorinated polyurethane emulsion prepared in S4 and then placed in a vacuum degassing machine for vacuum negative pressure mixing and degassing (-90 kPa, time 20 min) to finally obtain ultra-dispersed single-walled carbon nanotube graphene conductive adhesive (solid content 15.8%).

[0149] S6. Mix 500g of ultradispersed single-walled carbon nanotube graphene conductive adhesive, 1323g of silicon-based material (silicon content 92%), and 500g of Super P by simple stirring (1500rpm, 30min) to obtain a uniform and stable negative electrode slurry.

[0150] S7. Coat the negative electrode paste from S6 onto the negative current collector (copper foil) and control the coating thickness to be 200 μm to obtain silicon negative electrode a.

[0151] S8. Place the silicon anode sheet a from S7 in 45°C and dry for 120 min to obtain a thinner silicon anode sheet (active layer thickness is 150 μm).

[0152] S9. The thin silicon anode sheet and the positive electrode sheet are separated, and the electrolyte is 1M LiPF6 in EC:DEC=1:1 with 5% FEC to prepare an electrochemical device (solid state).

[0153] Comparative Example 1

[0154] The difference from Example 3 is that the 0.15g viscosity reducer (ammonia: polyacrylamide in a ratio of 1:6) in S1 is replaced with 0.15g of a strong alkaline viscosity reducer (ethanolamine), while the rest remains the same.

[0155] Comparative Example 2

[0156] The difference from Example 3 is that the 3g of single-walled carbon nanotube (SWCNT, 20nm diameter, 50μm length) powder in S1 is replaced with 1g of single-walled carbon nanotube (SWCNT, 20nm diameter, 50μm length) powder, while the rest remains the same.

[0157] Comparative Example 3

[0158] The difference from Example 3 is that the 3g of single-walled carbon nanotube (SWCNT, 20nm diameter, 50μm length) powder in S1 is replaced with 5g of single-walled carbon nanotube (SWCNT, 20nm diameter, 50μm length) powder, while the rest remains the same.

[0159] Comparative Example 4

[0160] The difference from Example 3 is that the 6g of sheet graphene powder (8μm in diameter) in S3 is replaced with 2g of sheet graphene powder (11μm in diameter), while everything else remains the same.

[0161] Comparative Example 5

[0162] The difference from Example 3 is that the 6g of sheet graphene powder (8μm in diameter) in S3 is replaced with 9g of sheet graphene powder (3μm in diameter), while everything else remains the same.

[0163] Comparative Example 6

[0164] The difference from Example 3 is that 73g of isophorone diisocyanate (IPDI) in S4 is replaced with 57g of isophorone diisocyanate (IPDI), while the rest remains the same.

[0165] Comparative Example 7

[0166] The difference from Example 3 is that the vacuum degassing machine in S5 is used to perform vacuum negative pressure mixing and degassing (-90 kPa, time 20 min) instead of standing for 30 min, while the rest remains the same.

[0167] The stability of the ultradispersed single-walled carbon nanotube graphene conductive adhesives prepared in Examples 1-3 and Comparative Examples 1-7 was visually tested after 180 days of storage, and the data are shown in Table 1 below:

[0168] The stability assessment method involves: pouring the super-dispersed single-walled carbon nanotube graphene conductive adhesive, after 180 days of storage, into a transparent glass ring and observing for obvious layering or turbidity; then, pouring a portion of the super-dispersed single-walled carbon nanotube graphene conductive adhesive onto white paper and observing for visible particles; finally, pouring out the super-dispersed single-walled carbon nanotube graphene conductive adhesive and observing the bottom of the transparent glass ring for visible particles. If no visible particles are found, the adhesive is considered to be in a homogeneous and stable state. For more details, please refer to [reference needed]. Figure 5 .

[0169] Table 1

[0170]

[0171] As can be seen from the data in Table 1 above, because Examples 1-3 used a gentle physical method to peel off the single-walled carbon nanotubes from the dispersion and introduced a soft-hard microphase separation structure, the interfacial defects of the physically peeled single-walled carbon nanotubes were effectively filled, improving the structural integrity and conductivity of the single-walled carbon nanotubes. Please refer to [link to relevant documentation]. Figure 3 and Figure 4 This facilitates the construction of a uniform, stable, highly flexible, and highly conductive three-dimensional continuous conductive framework for fluorinated polyurethane. Furthermore, the use of sheet graphene with a size of 4μm~10μm and a mass ratio of single-walled carbon nanotubes to sheet graphene of 1:2 (0.5~1.5):(1~3) ensures that the prepared ultra-dispersed single-walled carbon nanotube graphene conductive adhesive will not exhibit delamination or agglomeration even after prolonged storage. Figure 5 As shown, to achieve long-term stable preservation, the stability of Examples 1-3 is significantly better than that of Comparative Examples 1-7.

[0172] The appearance of the thin silicon anode sheets prepared in Examples 1-3 and Comparative Examples 1-7 was inspected, and the data in Table 2 below were obtained:

[0173] Table 2

[0174]

[0175] As can be seen from Table 2 above, since a small amount of waterborne fluorinated polyurethane conductive adhesive was added in Examples 1-3, thin silicon anode sheets without yellowing and aging can be prepared. In particular, the mass ratio of silicon-based material, waterborne fluorinated polyurethane conductive adhesive and superconducting carbon black is (87-93): (4-6): (3-7), and the solid content of waterborne fluorinated polyurethane conductive adhesive is greater than 5%-10%. This ensures that the drying of the anode slurry can be completed at a lower temperature (45℃-55℃). As a result, the appearance performance of the thin silicon anode sheets of Examples 1-3 is significantly better than that of Comparative Examples 1-7, and the production energy consumption is reduced.

[0176] The rate performance of the electrochemical devices of Examples 1-3 and Comparative Examples 1-7 described above was tested to obtain... Figure 2 The data charts; among them, the rate performance testing method: the coin charge rate performance is tested according to the electrochemical performance testing method.

[0177] from Figure 2 As can be seen from Examples 1-3 and Comparative Example 1, since Examples 1-3 all use a weaker alkaline viscosity reducer, the damage to the structure of the single-walled carbon nanotubes is smaller. In contrast, Comparative Example 1 uses a stronger alkaline viscosity reducer, which causes greater damage to the structure of the single-walled carbon nanotubes. As a result, the rate performance stability of the electrochemical devices in Examples 1-3 is significantly better than that in Comparative Example 1. Among them, Example 3 has the best overall performance.

[0178] from Figure 2 As can be seen from Examples 3 and Comparative Examples 2-3, since the mass ratio of single-walled carbon nanotubes, dispersant, mild viscosity reducer and water in Example 3 is in the range of (0.5~1.5):(0.3~1):(0.05~0.1):100, it ensures that adding a small amount of mild viscosity reducer will not affect the purity of the finally peeled single-walled carbon nanotubes, while also achieving a more thorough and complete peeling of single-walled carbon nanotubes with large diameter and high aspect ratio. This is beneficial for preparing a uniform, stable, highly tough and highly conductive fluorinated polyurethane three-dimensional continuous conductive framework, making the rate performance stability of the electrochemical device in Example 3 significantly better than that in Comparative Examples 2-3.

[0179] from Figure 2 As can be seen from Examples 3 and Comparative Examples 4-5, since the size of the sheet graphene in Example 3 is between 4μm and 10μm, and the mass ratio of single-walled carbon nanotubes to sheet graphene is 1:2, which is in the range of (0.5~1.5):(1~3), the added sheet graphene not only improves the conductivity of the three-dimensional continuous conductive framework of fluorinated polyurethane, but also ensures that the added sheet graphene can better prevent the stripped single-walled carbon nanotubes from entanglement. As a result, the rate performance stability of the electrochemical device in Example 3 is significantly better than that in Comparative Examples 4-5.

[0180] from Figure 2 As can be seen from Examples 3 and Comparative Example 6, the electrochemical device of Example 3 exhibits significantly better rate performance stability than that of Comparative Example 6 because the mass ratio of the alicyclic diisocyanate (isophorone diisocyanate), fluorinated diol (trifluoropropane diol), polyether diol (polytetrahydrofuran), catalyst (dibutyltin dilaurate), and salt-forming agent (triethylamine) used in Example 3 is in the range of (29~39):(2~5):(48~52):(0.01~0.1):(1~4).

[0181] from Figure 2 As can be seen from Example 3 and Comparative Example 7, since Comparative Example 7 did not use vacuum negative pressure mixing and degassing operation, the overall performance of Comparative Example 7 was significantly worse than that of Example 3.

[0182] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the disclosed patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. An electrochemical device comprising a positive electrode and a silicon negative electrode disposed separately, wherein at least one side of the negative current collector of the silicon negative electrode is coated with a negative electrode slurry, characterized in that, The negative electrode slurry includes a silicon-based material and an aqueous fluorinated polyurethane conductive adhesive. The aqueous fluorinated polyurethane conductive adhesive is used to crosslink during low-temperature drying to form a connected three-dimensional continuous conductive framework of fluorinated polyurethane and a fluorinated protective film layer. The three-dimensional continuous conductive framework of fluorinated polyurethane is embedded inside the negative electrode slurry and is used to encapsulate the silicon-based material. The fluorinated protective film layer is located on the surface of the negative electrode slurry and is used to protect the silicon-based material and the three-dimensional continuous conductive framework of fluorinated polyurethane. The low-temperature drying temperature is 45℃~55℃, and the time is 120min~240min; The preparation method of the water-based fluorinated polyurethane conductive adhesive includes the following steps: A super-dispersed single-walled carbon nanotube slurry is obtained by physically peeling the single-walled carbon nanotubes from the dispersion. The single-walled carbon nanotube dispersion includes a dispersant, a mild viscosity reducer, water, and single-walled carbon nanotubes. The diameter of the single-walled carbon nanotubes is 10 nm to 20 nm. A first ultrasonic high-pressure homogenization operation was performed by adding sheet-like graphene to the ultradispersed single-walled carbon nanotube slurry to obtain a single-walled carbon nanotube / graphene composite slurry; wherein the conditions for the first ultrasonic high-pressure homogenization operation were: ultrasonic power 100W~300W, pressure 20MPa~80MPa, and time 20min~60min. The aqueous fluorinated polyurethane emulsion is mixed with the single-walled carbon nanotube / graphene composite slurry and vacuum degassed to obtain the aqueous fluorinated polyurethane conductive adhesive; wherein, the preparation method of the aqueous fluorinated polyurethane emulsion includes the following steps: A fluorinated prepolymer is obtained by reacting an alicyclic diisocyanate with a fluorinated diol at a low temperature; wherein the alicyclic diisocyanate includes at least one of isophorone diisocyanate and aliphatic diisocyanate. The fluorinated diols include at least one of trifluoropropanediol, hexafluorobutanediol and 2,2,3,3-tetrafluoro-1,4-butanediol; The low-temperature heating reaction is carried out at a temperature of 60℃~80℃ for 2h~4h. The fluorinated prepolymer is subjected to a chain extension reaction with a polyether glycol and a catalyst; wherein the polyether glycol includes at least one of polytetrahydrofuran, polypropylene glycol and polyethylene glycol. The catalyst includes at least one of dibutyltin dilaurate, bismuth triacetylacetonate, and zinc stearate; The fluorinated prepolymer, after chain extension reaction, is neutralized with a salt-forming agent and then dispersed at high speed in water to obtain the aqueous fluorinated polyurethane emulsion; wherein the salt-forming agent includes at least one of triethylamine, pyridine, and ethanolamine. The water-based fluorinated polyurethane conductive adhesive forms a soft and hard microphase separation structure. The hard segment region of the soft and hard microphase separation structure is used to spontaneously form a physical support skeleton at low temperature to reduce the drying temperature of the negative electrode slurry. The temperature at which the physical support skeleton is spontaneously formed at low temperature is 30℃~45℃.

2. The electrochemical device according to claim 1, characterized in that, The fluorinated polyurethane three-dimensional continuous conductive framework includes a fluorinated polyurethane main framework and a three-dimensional conductive mesh; the fluorinated polyurethane main framework includes connected hard segment regions and multiple soft segment regions, the hard segment regions and each of the soft segment regions form the soft-hard microphase separation structure, and the soft-hard microphase separation structure is connected to the silicon-based material through the three-dimensional conductive mesh.

3. The electrochemical device according to claim 1, characterized in that, The coating thickness of the negative electrode slurry is 100μm~500μm.

4. The electrochemical device according to claim 1, characterized in that, The solid content of the waterborne fluorinated polyurethane conductive adhesive is greater than 5% to 10%.

5. The electrochemical device according to claim 1, characterized in that, The content of the silicon-based material is 87% to 93%.

6. The electrochemical device according to claim 1, characterized in that, The amount of the alicyclic diisocyanate used is 29% to 39% of the total amount input for the polymerization reaction.

7. The electrochemical device according to claim 1, characterized in that, After the step of reacting the alicyclic diisocyanate with the fluorinated diol at low temperature and before the step of chain extension reaction of the fluorinated prepolymer with the polyether diol and the catalyst, the following step is also included: The fluorinated prepolymer is cooled to 40°C~60°C.

8. The electrochemical device according to claim 1, characterized in that, The step of physically exfoliating the single-walled carbon nanotubes in the dispersion includes the following specific steps: The dispersant and the mild viscosity reducer are added to the water for a first high-speed dispersion operation to obtain a dispersion. A second high-speed dispersion operation was performed by adding single-walled carbon nanotubes to the dispersion to obtain a single-walled carbon nanotube premix. The premixed liquid of single-walled carbon nanotubes was subjected to a sand milling operation to obtain the dispersion of single-walled carbon nanotubes. A single-walled carbon nanotube dispersion is subjected to ultrasonic high-pressure microfluidic homogenization to obtain an ultra-dispersed single-walled carbon nanotube slurry. The ultrasonic high-pressure microfluidic homogenization of the single-walled carbon nanotube dispersion includes the following specific steps: First, the single-walled carbon nanotube dispersion is subjected to a second ultrasonic high-pressure homogenization operation; then, the single-walled carbon nanotube dispersion after the second ultrasonic high-pressure homogenization operation is subjected to microfluidic homogenization operation. The conditions for the second ultrasonic high-pressure homogenization operation are: ultrasonic power 100W~300W, pressure 20MPa~80MPa, and time 20min~60min. The conditions for the microjet homogenization operation are a time of 20 min to 60 min and a pressure of 100 MPa to 200 MPa.

9. The electrochemical device according to claim 1, characterized in that, The mass ratio of the single-walled carbon nanotubes to the sheet-like graphene is (0.5~1.5):(1~3); and / or, The aspect ratio of the single-walled carbon nanotubes in the ultradispersed single-walled carbon nanotube slurry is 2500~4000.

10. The electrochemical device according to claim 1, characterized in that, The mild viscosity reducer includes at least one of ammonia, sodium silicate, and polyacrylamide; and / or, The mass ratio of the dispersant, the mild viscosity reducer, and the water is (0.3~1):(0.05~0.1):100.

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