Polytetrafluoroethylene binder with multistage core-shell structure, preparation method of polytetrafluoroethylene binder, pole piece, lithium ion battery and electric equipment

Abstract

The invention provides a polytetrafluoroethylene binder with a multistage core-shell structure, a preparation method of the polytetrafluoroethylene binder, a pole piece, a lithium ion battery and electric equipment, and relates to the field of lithium ion batteries. The polytetrafluoroethylene binder comprises an inner core, a coating layer arranged on the surface of the inner core, and a plurality of inorganic ceramic nanosheets interspersed in the coating layer and / or the inner core, the inner core comprises polytetrafluoroethylene; the coating layer comprises a first coating layer and a second coating layer, and the first coating layer is arranged between the inner core and the second coating layer; the first coating layer comprises polydopamine, and the second coating layer comprises a conductive polymer. According to the polytetrafluoroethylene adhesive, conductivity-mechanics synergistic enhancement is realized by constructing a hierarchical coating structure of polydopamine and a conductive polymer and supporting a rigid framework of an inorganic ceramic nanosheet; the conductive polymer (the second coating layer) provides an electronic path, so that the insulation defect of the traditional PTFE is counteracted; the inorganic ceramic nanosheet is used as a rigid framework, so that the shear strength of the fiber is improved.

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, and more particularly to a multi-level core-shell structured polytetrafluoroethylene binder and its preparation method, electrode sheets, lithium-ion batteries, and electrical devices. Background Technology

[0002] In the field of lithium-ion battery electrode fabrication, dry electrode technology has many advantages, but it also faces some key challenges. Currently, the mainstream binder for dry electrodes is polytetrafluoroethylene (PTFE). While PTFE can be fiberized under high temperature and high shear, allowing it to contact and bond with the active material in solvent-free conditions, it has significant drawbacks. Firstly, its relatively large particle size limits the bonding effect, and during battery cycling, the binder easily detaches from the surface of the active material, leading to decreased electrode structural stability and consequently affecting the battery's cycle life. Secondly, PTFE's insulating properties increase the internal resistance of the electrode, exacerbating polarization during high-current charge and discharge, thus reducing the battery's charge / discharge efficiency and rate performance. Furthermore, the solid-solid contact impedance problem is particularly prominent in dry electrodes, limiting ion migration within the electrode and affecting the overall battery performance.

[0003] Therefore, developing a new type of adhesive to overcome the above problems is of great practical significance. Summary of the Invention

[0004] The purpose of this application is to provide a multi-level core-shell structured polytetrafluoroethylene binder and its preparation method, as well as an electrode, a lithium-ion battery, and an electrical device, to solve the above-mentioned problems.

[0005] To achieve the above objectives, the first aspect of this application provides a multi-level core-shell structured polytetrafluoroethylene adhesive, comprising a core and a coating layer disposed on the surface of the core, and a plurality of inorganic ceramic nanosheets interspersed in the coating layer and / or the core. The core comprises polytetrafluoroethylene; The coating layer includes a first coating layer and a second coating layer, wherein the first coating layer is disposed between the core and the second coating layer; The first coating layer comprises polydopamine, and the second coating layer comprises a conductive polymer.

[0006] Optionally, the kernel has a particle size of 1-20 μm; And / or, the thickness of the first coating layer is 10-50 nm; And / or, the thickness of the second coating layer is 50-500 nm; And / or, the particle size of the inorganic ceramic nanosheets is 50-100 nm; And / or, the inorganic ceramic nanosheets comprise LLZO and / or LATP; And / or, the raw materials for the conductive polymer include polyaniline or poly3,4-ethylenedioxythiophene and poly(styrene sulfonic acid); When the conductive polymer comprises the poly(3,4-ethylenedioxythiophene) and the poly(styrenesulfonic acid), the mass ratio of the poly(3,4-ethylenedioxythiophene) and the poly(styrenesulfonic acid) is 1:2-10.

[0007] The second aspect of this application provides a method for preparing a multi-level core-shell structured polytetrafluoroethylene adhesive, comprising: Nitric acid, potassium permanganate and polytetrafluoroethylene are mixed to obtain a first mixture. The first mixture is then subjected to a first reaction and solid-liquid separation to obtain pretreated polytetrafluoroethylene. The pretreated polytetrafluoroethylene, first (hydroxymethyl)aminomethane hydrochloride, potassium permanganate and dopamine hydrochloride monomer are mixed and reacted in a second way to obtain polydopamine-coated polytetrafluoroethylene. The polydopamine-coated polytetrafluoroethylene and the second (hydroxymethyl)aminomethane hydrochloride are mixed in a third process to obtain a second mixture; the second mixture, the conductive polymer aqueous solution, and dimethyl sulfoxide are mixed in a fourth process to obtain a third mixture; the third mixture is subjected to a third reaction to obtain the conductive polymer-coated polytetrafluoroethylene. The conductive polymer-coated polytetrafluoroethylene and the inorganic ceramic nanosheet aqueous solution are mixed for a fifth time to obtain a fourth mixture; the fourth mixture is subjected to solid-liquid separation to obtain a solid material, which is then embedded in a supercritical CO2 environment to obtain a multi-level core-shell structured polytetrafluoroethylene binder.

[0008] It is also important to note that traditional PTFE binders have almost no ionic or electronic conductivity. The inert PTFE in the electrode system hinders electron transport and lithium-ion insertion / extraction, affecting battery performance. Furthermore, with increasing battery cycle count, volume changes in the electrode material during charge / discharge can cause the PTFE binder to gradually detach, weakening or even failing, leading to decreased electrode structural stability. This application first performs a hydrophilic pretreatment on the PTFE surface to improve the affinity and adhesion of PDA. Then, in an alkaline environment under the action of a strong oxidant, dopamine hydrochloride monomers undergo a polymerization reaction, forming a PDA coating layer on the PTFE surface. Maintaining a low-temperature environment slows down the polymerization rate, which is beneficial for forming a uniform and dense PDA coating layer on the PTFE surface. PDA and the conductive polymer PEDOT:PSS can undergo electrostatic bonding (dominant), hydrogen bonding, and π-π stacking. Under the synergistic effect of these multiple interactions, the PTFE modified with PDA exhibits a strong affinity for PEDOT:PSS, thereby enhancing the affinity of PDA for PEDOT:PSS. DOT:PSS can be uniformly and stably attached to the outer surface of the PDA. PTFE itself has electronic insulation properties, which can increase the internal resistance of the battery and affect its performance. However, the conductive polymer PEDOT:PSS coating layer can effectively increase the conductivity of PTFE, which is beneficial to reducing the internal resistance of the battery and improving the energy density and rate performance. Furthermore, through the diffusion effect of supercritical CO2, LATP or LLZO inorganic nanosheets are embedded into the PTFE surface. The high specific surface area of ​​LATP / LLZO nanosheets can provide a new transport path for lithium ions in the electrode. The rigid inorganic nanosheets can also improve the strength of PTFE, thereby helping to maintain the stability of the electrode and improve battery performance.

[0009] Optionally, the mass ratio of the nitric acid and the potassium permanganate in the first mixture is 1-5:1; And / or, in the second mixture, the molar ratio of the potassium permanganate to the dopamine hydrochloride monomer is 1:1.5-5; And / or, the solid-liquid ratio of the polydopamine-coated polytetrafluoroethylene and the (hydroxymethyl)aminomethane hydrochloride is 0.1g-10g:100mL; And / or, the mass concentration of the conductive polymer aqueous solution is 0.5-5%; And / or, the mass concentration of the dimethyl sulfoxide is 0-1%; And / or, the volume ratio of the second mixture to the aqueous solution of the poly(3,4-ethylenedioxythiophene-poly(styrenesulfonic acid)) is 1-10:1; And / or, the mass concentration of the inorganic ceramic nanosheet aqueous solution is 0.1-10%.

[0010] Optionally, the temperature of the first reaction is 40-80℃, and the time is 2-5 hours; And / or, the temperature of the second reaction is -5 to -10°C, and the time is 12 to 24 hours; And / or, the temperature of the third reaction is 0-50℃, and the time is 0.5-2h; And / or, the embedding process is carried out at a temperature of 25-100°C, a pressure of 20-60 MPa, and a time of 1-5 h.

[0011] Optionally, the pH value of the second reaction is 8.0-9.5; And / or, the pH of the first (hydroxymethyl)aminomethane hydrochloride is 8-9; And / or, the pH of the second (hydroxymethyl)aminomethane hydrochloride is 7.5-9; And / or, the pH of the third reaction is 7.5-9.

[0012] Optionally, after the second reaction is completed, the obtained reactants are washed and vacuum dried to obtain the polydopamine-coated polytetrafluoroethylene; The vacuum drying temperature is 80-120℃, and the time is 6-24h.

[0013] A third aspect of this application provides an electrode sheet comprising a polytetrafluoroethylene adhesive with a multi-level core-shell structure.

[0014] A fourth aspect of this application provides a lithium-ion battery, including the aforementioned electrode.

[0015] The fifth aspect of this application provides an electrical device including the aforementioned lithium-ion battery.

[0016] Compared with the prior art, the beneficial effects of this application include: The multi-level core-shell structured polytetrafluoroethylene (PTFE) adhesive provided in this application achieves synergistic enhancement of conductivity and mechanics by constructing a hierarchical coating structure of "polydopamine and conductive polymer" and a rigid framework support of inorganic ceramic nanosheets. The conductive polymer (second coating layer) provides electronic pathways, offsetting the insulation defects of traditional PTFE. The inorganic ceramic nanosheets, as a rigid framework, improve the shear strength of the fiber and also have high lithium-ion conductivity (>10). -4 (S / cm) can promote ion migration inside the electrode, compensate for the solid-solid contact impedance problem of dry electrode, and improve the performance of the binder.

[0017] The method for preparing a multi-level core-shell structured polytetrafluoroethylene (PTFE) adhesive provided in this application involves a first reaction that generates oxygen-containing polar groups on the PTFE surface, significantly enhancing the binding force of subsequent polydopamine (PDA). A second reaction promotes the oxidation of dopamine to generate a quinone structure, which anchors the PTFE surface through π-π stacking and hydrogen bonding, forming a dense PDA layer. A third reaction ensures full bonding and uniform coating between the PDA and the conductive polymer. The high diffusivity of supercritical CO2 facilitates the embedding of inorganic ceramic nanosheets into the micropores of the PTFE surface, enhancing interfacial mechanical interlocking, ultimately yielding a multi-level core-shell structured PTFE adhesive.

[0018] The electrode, lithium-ion battery, and electrical equipment provided in this application have excellent conductivity and good cycle performance. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, 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 application and should not be regarded as a limitation on the scope of this application.

[0020] Figure 1 A schematic diagram of the multi-level core-shell structured polytetrafluoroethylene adhesive provided in Example 1; Figure 2 This is a schematic diagram of the preparation method of the multi-level core-shell structured polytetrafluoroethylene adhesive provided in Example 1.

[0021] Explanation of key component symbols: 100-Polytetrafluoroethylene core; 200-Polydopamine coating layer; 300-Conductive polymer coating layer; 400-Inorganic ceramic nanosheets. Detailed Implementation

[0022] First, the solution provided in this application will be explained in more detail as follows: The first aspect of this application provides a multi-level core-shell structured polytetrafluoroethylene adhesive, including a core and a coating layer disposed on the surface of the core, and a plurality of inorganic ceramic nanosheets interspersed in the coating layer and / or the core; The core comprises polytetrafluoroethylene; The coating layer includes a first coating layer and a second coating layer, wherein the first coating layer is disposed between the core and the second coating layer; The first coating layer comprises polydopamine, and the second coating layer comprises a conductive polymer.

[0023] It should be noted that the first coating layer and the second coating layer have good affinity and bonding force, thus ensuring that the second coating layer can have a uniform and stable coating effect.

[0024] In some embodiments, the kernel has a particle size of 1-20 μm; Optionally, the kernel particle size can be any value between 1μm, 5μm, 10μm, 15μm, 20μm or 1-20μm; And / or, the thickness of the first coating layer is 10-50 nm; Optionally, the thickness of the first coating layer can be any value between 10nm, 20nm, 30nm, 40nm, 50nm or 10-50nm; And / or, the thickness of the second coating layer is 50-500 nm; Optionally, the thickness of the second coating layer can be any value between 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm or 50-500 nm. And / or, the particle size of the inorganic ceramic nanosheets is 50-100 nm; Optionally, the particle size of the inorganic ceramic nanosheets can be any value between 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm or 50-100 nm. And / or, the inorganic ceramic nanosheets comprise LLZO and / or LATP; And / or, the raw materials for the conductive polymer include polyaniline or poly3,4-ethylenedioxythiophene and poly(styrene sulfonic acid); When the conductive polymer comprises the poly(3,4-ethylenedioxythiophene) and the poly(styrene sulfonic acid) (PEDOT-PSS), the mass ratio of the poly(3,4-ethylenedioxythiophene) and the poly(styrene sulfonic acid) is 1:2-10.

[0025] When the conductive polymer includes the poly(3,4-ethylenedioxythiophene) and the poly(styrenesulfonic acid), the mass ratio of poly(3,4-ethylenedioxythiophene) to poly(styrenesulfonic acid) can be any value between 1:2, 1:4, 1:6, 1:8, 1:10 or 1:2-10.

[0026] The second aspect of this application provides a method for preparing a multi-level core-shell structured polytetrafluoroethylene adhesive, comprising: Nitric acid, potassium permanganate and polytetrafluoroethylene are mixed to obtain a first mixture. The first mixture is then subjected to a first reaction and solid-liquid separation to obtain pretreated polytetrafluoroethylene. It should be noted that nitric acid and potassium permanganate form hydrophilic manganese oxides or manganese hydroxides that cover the surface of PTFE particles; The pretreated polytetrafluoroethylene, first (hydroxymethyl)aminomethane hydrochloride, potassium permanganate and dopamine hydrochloride monomer are mixed and reacted in a second way to obtain polydopamine-coated polytetrafluoroethylene. The polydopamine-coated polytetrafluoroethylene and the second (hydroxymethyl)aminomethane hydrochloride are mixed in a third process to obtain a second mixture; the second mixture, the conductive polymer aqueous solution, and dimethyl sulfoxide are mixed in a fourth process to obtain a third mixture; the third mixture is subjected to a third reaction to obtain the conductive polymer-coated polytetrafluoroethylene. It should be noted that after polydopamine-coated polytetrafluoroethylene and the second (hydroxymethyl)aminomethane hydrochloride are mixed, for example, the mixture is stirred at 100 rpm for 30 minutes at 25°C to protonate the surface of polydopamine-coated polytetrafluoroethylene to form a stable positive charge layer. Dimethyl sulfoxide can enhance its conductivity. For example, an aqueous solution of conductive polymer and dimethyl sulfoxide are mixed, and the resulting mixture is ultrasonically dispersed at 40 kHz for 10 min. Undispersed particles are removed by filtration with 0.45 μm filter paper. The filtered PEDOT-PSS aqueous solution is slowly added dropwise to the filtered mixture at a rate of 1 mL / min to avoid excessive local concentration that could lead to PEDOT aggregation. The conductive polymer-coated polytetrafluoroethylene and the inorganic ceramic nanosheet aqueous solution are mixed for a fifth time to obtain a fourth mixture; the fourth mixture is subjected to solid-liquid separation to obtain a solid material, which is then embedded in a supercritical CO2 environment to obtain a multi-level core-shell structured polytetrafluoroethylene binder.

[0027] It should be noted that the preparation of the inorganic ceramic nanosheet aqueous solution includes: mixing the inorganic ceramic nanosheets and water, followed by ultrasonic treatment to ensure uniform dispersion of the nanosheets; In some embodiments, the mass ratio of the nitric acid to the potassium permanganate in the first mixture is 1-5:1; Optionally, the mass ratio of nitric acid to potassium permanganate in the first mixture can be any value between 1:1, 2:1, 3:1, 4:1, 5:1, or 1-5:1; And / or, in the second mixture, the molar ratio of the potassium permanganate to the dopamine hydrochloride monomer is 1:1.5-5; Optionally, in the second mixture, the molar ratio of potassium permanganate and dopamine hydrochloride monomer can be any value between 1:1.5, 1:2, 1:3, 1:4, 1:5, or 1:1.5-5; And / or, the solid-liquid ratio of the polydopamine-coated polytetrafluoroethylene and the (hydroxymethyl)aminomethane hydrochloride is 0.1g-10g:100mL; Optionally, the solid-liquid ratio of polydopamine-coated polytetrafluoroethylene and (hydroxymethyl)aminomethane hydrochloride can be 0.1 g: 100 mL, 1 g: 100 mL, 5 g: 100 mL, 10 g: 100 mL or any value between 0.1 and 10 g: 100 mL; And / or, the mass concentration of the conductive polymer aqueous solution is 0.5-5%; Optionally, the mass concentration of the conductive polymer aqueous solution can be 0.5%, 1%, 2%, 3%, 4%, 5%, or any value between 0.5% and 5%. And / or, the mass concentration of the dimethyl sulfoxide is 0-1%; Optionally, the mass concentration of dimethyl sulfoxide can be 0%, 0.5%, 1%, or any value between 0% and 1%. And / or, the volume ratio of the second mixture to the aqueous solution of the poly(3,4-ethylenedioxythiophene-poly(styrenesulfonic acid)) is 1-10:1; Optionally, the volume ratio of the second mixture to the aqueous solution of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) can be any value between 1:1, 5:1, 10:1 or 1-10:1; And / or, the mass concentration of the inorganic ceramic nanosheet aqueous solution is 0.1-10%.

[0028] Optionally, the mass concentration of the inorganic ceramic nanosheet aqueous solution can be 0.1%, 1%, 5%, 10%, or any value between 0.1% and 10%.

[0029] In some embodiments, the temperature of the first reaction is 40-80°C and the time is 2-5 hours; Optionally, the temperature of the first reaction can be any value between 40℃, 50℃, 60℃, 70℃, 80℃ or 40-80℃, and the time can be any value between 2h, 3h, 4h, 5h or 2-5h. And / or, the temperature of the second reaction is -5 to -10°C, and the time is 12 to 24 hours; Optionally, the temperature of the second reaction can be any value between -5°C, 0°C, 5°C, 10°C or 5-10°C, and the time can be any value between 12h, 18h, 24h or 12-24h. It should be noted that the low temperature conditions of the second reaction can suppress side reactions and ensure uniform coating of PDA; And / or, the temperature of the third reaction is 0-50℃, and the time is 0.5-2h; Optionally, the temperature of the third reaction can be any value between 0℃, 10℃, 20℃, 30℃, 40℃, 50℃ or 0-50℃, and the time can be any value between 0.5h, 1h, 1.5h, 2h or 0.5-2h. It should be noted that the first, second, and third reactions of this application are all carried out at relatively low temperatures, reducing energy consumption and avoiding the risk of thermal deformation of PTFE and modified materials (coating layer); And / or, the embedding process is carried out at a temperature of 25-100°C, a pressure of 20-60 MPa, and a time of 1-5 h.

[0030] Optionally, the embedding temperature can be any value between 25℃, 50℃, 75℃, 100℃ or 25-100℃, the pressure can be any value between 20 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa or 20-60 MPa, and the time can be any value between 1h, 2h, 3h, 4h, 5h or 1-5h.

[0031] In some embodiments, the pH value of the second reaction is 8-9; Optionally, the pH value of the second reaction can be any value between 8, 8.5, 9, or 8-9; Preferably, the pH value is sampled and tested every 20 minutes during the second reaction, and the pH value of the solution is finely adjusted with 0.1M HCl / NaOH to maintain the pH of the second reaction at around 8.5. At this time, the quinone / semiquinone ratio of PDA reaches its peak, and the electron affinity is high, which can enhance the electrostatic attraction with the anionic conductive polymer PEDOT:PSS and improve the bonding effect. At the end of the second reaction, the reactants are diluted with four times the amount of water to terminate the reaction, and the solid complex is collected by centrifugation at 8000 rpm, washed three times with ethanol / water (1:1), and then vacuum dried at 60°C for 12 h. And / or, the pH of the first (hydroxymethyl)aminomethane hydrochloride is 8-9; Optionally, the pH of the first (hydroxymethyl)aminomethane hydrochloride can be 8, 8.5, 9, or any value between 8 and 9; And / or, the pH of the second (hydroxymethyl)aminomethane hydrochloride is 7.5-9; Optionally, the pH of the second (hydroxymethyl)aminomethane hydrochloride can be 7.5, 8, 8.5, 9, or any value between 7.5 and 9; And / or, the pH of the third reaction is 7.5-9.

[0032] Optionally, the pH value of the third reaction can be 7.5, 8, 8.5, 9, or any value between 7.5 and 9.

[0033] It should be noted that PDA in a weakly alkaline environment is conducive to ensuring amino protonation (-NH3). + ), with PEDOT-PSS's -SO3 - It forms a strong static electricity effect.

[0034] In some embodiments, after the second reaction is completed, the resulting reactants are washed and vacuum dried to obtain the polydopamine-coated polytetrafluoroethylene; The vacuum drying temperature is 80-120℃, and the time is 6-24h.

[0035] Optionally, the vacuum drying temperature can be any value between 80℃, 90℃, 100℃, 110℃, 120℃ or 80-120℃, and the time can be any value between 6h, 12h, 18h, 24h or 6-24h.

[0036] It is important to note that after the second reaction is completed, the product is washed repeatedly with water 3-5 times until the filtrate is clear to completely remove unreacted monomers and impurities. Then, vacuum drying is performed to eliminate residual moisture and prevent the PDA layer from cracking, finally obtaining polydopamine-coated PTFE binder.

[0037] A third aspect of this application provides an electrode sheet comprising a polytetrafluoroethylene adhesive with a multi-level core-shell structure.

[0038] A fourth aspect of this application provides a lithium-ion battery, including the aforementioned electrode.

[0039] The fifth aspect of this application provides an electrical device including the aforementioned lithium-ion battery.

[0040] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0041] Example 1 This embodiment provides a multi-level core-shell structured PTFE adhesive, comprising a polytetrafluoroethylene core 100, a polydopamine coating layer 200 and a conductive polymer coating layer 300 sequentially disposed on the surface of the core, and a plurality of inorganic ceramic nanosheets 400 intercalated in the coating layers and / or the core, as shown in the specific structural diagram below. Figure 1 As shown; The core is made of polytetrafluoroethylene; The first coating layer is polydopamine, and the second coating layer is made of poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(styrene sulfonic acid) (PSS).

[0042] The core has a particle size of 10 μm, the first coating layer has a thickness of 20 nm, the second coating layer has a thickness of 100 nm, the molar ratio of poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonic acid) is 1:2; the inorganic ceramic nanosheets have a particle size of 50-60 nm; the inorganic ceramic nanosheets are LLZO.

[0043] The second aspect of this embodiment provides a method for preparing a multi-level core-shell structured PTFE adhesive, the preparation process of which is as follows: Figure 2 As shown, the specific preparation steps are as follows: S1: Dissolve 12.00g of potassium permanganate (KMnO4) in 200mL of distilled water, slowly add 68wt% concentrated nitric acid (HNO3) to prepare a mixed solution of KMnO4 and HNO3 in a mass ratio of 3:1, immerse 15g of PTFE particles in the mixed solution of KMnO4 and HNO3, and keep warm in a water bath at 60℃ for 3 hours; S2: The pretreated PTFE was added to a (hydroxymethyl)aminomethane (Tris-HCl) buffer (pH=8.5±0.1), followed by the addition of 0.04 mol potassium permanganate (KMnO4) and 0.027 mol dopamine hydrochloride monomer. The mixture was stirred at 1200 rpm for 24 hours at 0°C. After the reaction was complete, the product was washed three times with deionized water until the filtrate was clear. Then, it was vacuum dried at 100°C for 12 hours to obtain a dried PDA-grafted PTFE composite binder (polydopamine-coated polytetrafluoroethylene). S3: Weigh 1g of polydopamine-coated polytetrafluoroethylene and disperse it in 100mL of Tris-HCl buffer solution with pH 8.5. Stir at 100rpm for 30 minutes at 25℃ to obtain mixture A. Prepare a 1.5wt% aqueous solution of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid), add 0.1wt% dimethyl sulfoxide, and sonicate at 40KH power for 10min. Filter with 0.45μm filter paper to remove undispersed particles. Slowly add the filtered PEDOT-PSS aqueous solution to mixture A at a rate of 1mL / min. The volume ratio of PEDOT:PSS aqueous solution to mixture A is 1:5 to obtain mixture B. Stir mixture B in a 25℃ water bath at 300rpm for 2h. During this period, sample and test the pH value every 20min at 0.1M. The pH of the HCl / NaOH solution was fine-tuned to ensure that the pH of the mixture B was maintained at 8.5. After the time was up, four times the amount of deionized water was added to dilute the mixture B, and the solid complex was collected by centrifugation at 8000 rpm. It was washed three times with ethanol / water (1:1) and then vacuum dried at 60 °C for 12 h to obtain PEDOT:PSS-PTFE composite powder (conductive polymer coated with polytetrafluoroethylene). S4: Prepare an aqueous dispersion of 0.5 wt% LLZO nanosheets (particle size 50-60 nm), sonicate for 1 hour to ensure uniformity, add 1 g of PEDOT:PSS-PTFE composite powder to 150 mL of LLZO nanosheet dispersion, stir magnetically at 25 °C for 15 min, filter to obtain solid mixture C, wash with deionized water, and vacuum dry at 60 °C for 12 h; place solid mixture C in a supercritical reactor, inject liquid CO2 and heat to 40 °C and pressurize to 35 MPa, maintain for 2 hours to obtain solid composite D, add solid composite D to water / ethanol mixed solvent (volume ratio 1:1) at 5% solid content, and sonicate at 300 W for 15 min to finally obtain LLZO@PEDOT:PSS@PTFE composite modified PTFE binder (multi-level core-shell structure polytetrafluoroethylene binder).

[0044] Example 2 The difference from Example 1 is that in step S3, the pH of the Tris-HCl buffer is 9, and the pH of the reaction in this step is maintained at 9.

[0045] Example 3 The difference from Example 1 is as follows: In step S1, the mass ratio of KMnO4 to HNO3 is 4:1, and 10g of PTFE particles are immersed in a mixed solution of KMnO4 and HNO3; in step S4, the particle size of LLZO nanosheets is 50-100 nm, and the temperature of the liquid in the supercritical reactor is set to 45°C and the pressure is increased to 40MPa.

[0046] Example 4 The difference from Example 1 is that in step S3, the pH of the Tris-HCl buffer is 7.5, and the pH of the reaction in this step is maintained at 7.5.

[0047] Comparative Example 1 The difference from Example 1 is that step S4 is not performed, that is, the final product does not contain inorganic ceramic nanosheets.

[0048] Comparative Example 2 The difference from Example 1 is that steps S1 and S2 are not performed, that is, the first coating layer (polydopamine coating layer) is not set, and 1g of polydopamine-coated polytetrafluoroethylene is directly replaced with 1g of PTFE particles.

[0049] Comparative Example 3 The difference from Example 1 is that step S1 is not performed; that is, in step S2, the pretreated PTFE is replaced with an equal mass of PTFE particles.

[0050] Comparative Example 4 The difference from Example 1 is that step S2 is not performed. That is, in step S3, the polydopamine-coated polytetrafluoroethylene is replaced with an equal mass of pretreated PTFE prepared in step S1, and the final product does not have a first coating layer.

[0051] Comparative Example 5 The difference from Example 1 is that step S3 is not performed. That is, in step S4, the PEDOT:PSS-PTFE composite powder is replaced with polydopamine-coated polytetrafluoroethylene prepared in step S2, and the final product does not have a second coating layer (conductive polymer coating layer).

[0052] Comparative Example 6 The difference from Example 1 is that the order of steps S2 and S3 is replaced.

[0053] This application also uses the binder provided in the above embodiments and comparative examples to prepare battery electrode sheets, and the specific method is as follows: Weigh appropriate amounts of NCM811 ternary cathode material, Super-P conductive carbon black, and binders prepared in the above examples and comparative examples according to a mass ratio of 90:5:5. First, add NCM811 and Super-P to a high-speed mixer and stir at 1500 rpm for 20 minutes to premix the material. Then, add the binder and stir at 1500 rpm for 20 minutes at 10°C. Then, raise the temperature to 100°C and stir at 2000 rpm for 30 minutes to perform fiberization treatment. Roll the fiberized powder into a film using a roller press at 120°C and 5T pressure to obtain a dry cathode self-supporting film with a thickness of 80μm. The film and a 16μm thick carbon-coated aluminum foil are hot-pressed together using a hot roller press (temperature 120°C, pressure 8T) to form a dry electrode sheet.

[0054] This application also provides the assembly of lithium batteries, and the specific preparation method is as follows: The prepared dry cathodes were fabricated into small discs with a diameter of 16 mm. CR2032 battery cases were used, and the electrolyte was a 1 mol / L LiPF6 / EC+DEC solution (volume ratio 1:1). The cathodes were assembled in the following order: cathode case, spring sheet, gasket, cathode sheet, separator, electrolyte, lithium sheet, and anode case. All operations were performed in a glove box with an argon atmosphere containing less than 0.1 ppm of water and oxygen.

[0055] After the prepared button cells were left to stand for 24 hours, charge-discharge cycle tests were conducted at 0.5C rate and 2.5~4.3V. After 200 cycles, the specific test results are shown in Table 1.

[0056] Table 1 Charge-discharge cycle test

[0057] analyze: The test results show that the cycle data of the battery in the example is significantly better than that of the comparative example. In the comparative example, whether the first or second coating layer was removed, or the PTFE particles were not pretreated, the results were negatively affected. This is because the conductive polymer coated on the PTFE improves the conductivity of the PTFE, and the inorganic nanosheets enhance the ion transport capacity and improve the structural stability of the PTFE. In addition, the cycle data of the battery in Example 1 is the best. This is because within a suitable pH range, it is beneficial to form a uniform and stable coating layer on the PTFE surface, achieving the expected ideal effect and thus improving battery performance.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0059] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A multi-level core-shell structured polytetrafluoroethylene adhesive, characterized in that, It includes a core and a coating layer disposed on the surface of the core, as well as a plurality of inorganic ceramic nanosheets interspersed in the coating layer and / or the core; The core comprises polytetrafluoroethylene; The coating layer includes a first coating layer and a second coating layer, wherein the first coating layer is disposed between the core and the second coating layer; The first coating layer comprises polydopamine, and the second coating layer comprises a conductive polymer.

2. The multi-level core-shell structured polytetrafluoroethylene adhesive according to claim 1, characterized in that, The kernel has a particle size of 1-20 μm; And / or, the thickness of the first coating layer is 10-50 nm; And / or, the thickness of the second coating layer is 50-500 nm; And / or, the particle size of the inorganic ceramic nanosheets is 50-100 nm; And / or, the inorganic ceramic nanosheets comprise LLZO and / or LATP; And / or, the raw materials for the conductive polymer include polyaniline or poly3,4-ethylenedioxythiophene and poly(styrene sulfonic acid); When the conductive polymer comprises the poly(3,4-ethylenedioxythiophene) and the poly(styrenesulfonic acid), the mass ratio of the poly(3,4-ethylenedioxythiophene) and the poly(styrenesulfonic acid) is 1:2-10.

3. A method for preparing a multi-level core-shell structured polytetrafluoroethylene adhesive as described in claim 1 or 2, characterized in that, include: Nitric acid, potassium permanganate and polytetrafluoroethylene are mixed to obtain a first mixture. The first mixture is then subjected to a first reaction and solid-liquid separation to obtain pretreated polytetrafluoroethylene. The pretreated polytetrafluoroethylene, first (hydroxymethyl)aminomethane hydrochloride, potassium permanganate and dopamine hydrochloride monomer are mixed and reacted in a second way to obtain polydopamine-coated polytetrafluoroethylene. The polydopamine-coated polytetrafluoroethylene and the second (hydroxymethyl)aminomethane hydrochloride are mixed in a third process to obtain a second mixture; the second mixture, the conductive polymer aqueous solution, and dimethyl sulfoxide are mixed in a fourth process to obtain a third mixture; the third mixture is subjected to a third reaction to obtain the conductive polymer-coated polytetrafluoroethylene. The conductive polymer-coated polytetrafluoroethylene and the inorganic ceramic nanosheet aqueous solution are mixed for a fifth time to obtain a fourth mixture; the fourth mixture is subjected to solid-liquid separation to obtain a solid material, which is then embedded in a supercritical CO2 environment to obtain a multi-level core-shell structured polytetrafluoroethylene binder.

4. The method for preparing the multi-level core-shell structured polytetrafluoroethylene adhesive according to claim 3, characterized in that, The mass ratio of the nitric acid and the potassium permanganate in the first mixture is 1-5:1; And / or, in the second mixture, the molar ratio of the potassium permanganate to the dopamine hydrochloride monomer is 1:1.5-5; And / or, the solid-liquid ratio of the polydopamine-coated polytetrafluoroethylene and the (hydroxymethyl)aminomethane hydrochloride is 0.1g-10g:100mL; And / or, the mass concentration of the conductive polymer aqueous solution is 0.5-5%; And / or, the mass concentration of the dimethyl sulfoxide is 0-1%; And / or, the volume ratio of the second mixture to the aqueous solution of the poly(3,4-ethylenedioxythiophene-poly(styrenesulfonic acid)) is 1-10:1; And / or, the mass concentration of the inorganic ceramic nanosheet aqueous solution is 0.1-10%.

5. The method for preparing the multi-level core-shell structured polytetrafluoroethylene adhesive according to claim 3, characterized in that, The temperature of the first reaction is 40-80℃, and the time is 2-5 hours; And / or, the temperature of the second reaction is -5 to -10°C, and the time is 12 to 24 hours; And / or, the temperature of the third reaction is 0-50℃, and the time is 0.5-2h; And / or, the embedding process is carried out at a temperature of 25-100°C, a pressure of 20-60 MPa, and a time of 1-5 h.

6. The method for preparing the multi-level core-shell structured polytetrafluoroethylene adhesive according to claim 3, characterized in that, The pH value of the second reaction is 8.0-9.5; And / or, the pH of the first (hydroxymethyl)aminomethane hydrochloride is 8-9; And / or, the pH of the second (hydroxymethyl)aminomethane hydrochloride is 7.5-9; And / or, the pH of the third reaction is 7.5-9.

7. The method for preparing the multi-level core-shell structured polytetrafluoroethylene adhesive according to any one of claims 3-6, characterized in that, After the second reaction is completed, the resulting reactants are washed and vacuum dried to obtain the polydopamine-coated polytetrafluoroethylene. The vacuum drying temperature is 80-120℃, and the time is 6-24h.

8. An electrode sheet, characterized in that, The polytetrafluoroethylene adhesive includes the multi-level core-shell structure as described in claim 1 or 2.

9. A lithium-ion battery, characterized in that, Includes the electrode as described in claim 8.

10. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 9.

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