Dynamic self-healing degradation-resistant composite current collector bopet film and method of making

Abstract

The application belongs to the field of material science and engineering technology, and relates to a dynamic self-repairing degradation-resistant composite current collector BOPET film and a preparation method thereof.The BOPET film comprises a BOPET base film and a coating layer located on the surface of the BOPET base film, the coating layer comprises a dense barrier layer adjacent to the BOPET base film, the dense barrier layer is composed of a BCNF-DH / ZIF-8 composite, the composite is interwoven to form a dense network with a porosity of less than or equal to 1%, the dense network is composed of BCNF, a compound containing an acylhydrazone bond and a ZIF-8 type MOF, and the components are connected through specific chemical bonds.The preparation method comprises the following steps: forming the dense barrier layer by micro-gravure coating, forming a conductive reinforcing layer by slit extrusion coating, and then performing electron beam irradiation treatment, longitudinal stretching, transverse stretching and shaping, and surface corona treatment to obtain the BOPET film.The application can solve the problems that the BOPET base film is easily degraded by catalytic molecules and the coating layer has no dynamic self-repairing function.

Description

Technical Field

[0001] This invention belongs to the field of materials science and engineering technology, and relates to a dynamic self-healing and degradation-resistant composite current collector BOPET membrane and its preparation method. Background Technology

[0002] In the field of lithium batteries, current collectors play a crucial role in collecting current. An ideal current collector needs to meet conditions such as high conductivity, high stability, strong bonding force, low cost, and flexibility and thinness. Traditional lithium battery current collectors are mainly metal foils, such as rolled aluminum foil and electrolytic copper foil. However, with the increasing demands for energy density, safety, and cost of lithium batteries from industries such as new energy vehicles, composite current collectors have emerged.

[0003] Composite current collectors are typically sandwich structures consisting of "metal-polymer base film-metal". Among them, biaxially oriented polyester (BOPET) film has become the mainstream choice for polymer base film due to its low cost and high mechanical strength. However, its chemical stability in the electrolyte environment is insufficient, and it is easily degraded by catalytic molecules such as alcohol-based lithium, resulting in a short cycle life.

[0004] Patent application CN119590062A and patent CN118931300B both provide ideas for improving the electrolyte resistance of polymer base films. The former employs a sandwich structure of a polymer polar material layer, a polymer reinforcing material layer, and another polymer polar material layer. Polar polymers are added to the polymer polar material layer to increase surface polarity and enhance adhesion to the metal layer, thus reducing electrolyte penetration paths. Simultaneously, amphoteric materials are added to promote the fusion of components and ensure uniform overall polarity, thereby improving structural stability. Furthermore, reinforcing materials are added to the polymer reinforcing material layer to accelerate polyolefin crystallization and enhance the density of the base film structure. This approach addresses both material composition and structural design. The first method synergistically improves the electrolyte resistance of the base film. The second method uses a composite coating containing cross-linked polyvinylpyrrolidone and graphene nanosheets. A ethylene pyrrolidone / methyl acrylate / fluorinated vinyl copolymer emulsion is prepared by emulsion polymerization. After modifying the graphene oxide nanosheets, they are mixed with the copolymer emulsion. With the help of a cross-linking agent, the copolymer forms a three-dimensional network structure and the graphene nanosheets are chemically connected to it. By utilizing the corrosion resistance of cross-linked polyvinylpyrrolidone and graphene, the physical shielding effect of graphene nanosheets, the improved interfacial compatibility of methyl acrylate segments, and the reduced surface energy of fluorinated vinyl segments to reduce electrolyte adhesion, multiple pathways are synergistically prevent the electrolyte and catalyst from contacting the PET substrate, thereby improving the electrolyte resistance of the base film.

[0005] However, neither method fundamentally blocks the penetration of catalytic molecules from the electrolyte, limiting their cycle life: while the sandwich structure of the former enhances physical barrier through polyolefin crystallization and a polar layer, nanoscale crystal defects still allow alcohol-based lithium to penetrate; the graphene composite coating of the latter relies on layer stacking to form a barrier, but the chemical inertness of interlayer defects and cross-linked networks prevents the active capture of catalytic molecules, and it lacks dynamic self-healing capabilities—when microcracks appear in the coating, electrolyte and catalytic molecules can still penetrate deep into the base film, initiating degradation. Furthermore, the former's process is extremely complex, while the latter relies on chemical vapor deposition (CVD) or magnetron sputtering, resulting in high process costs. Summary of the Invention

[0006] The purpose of this invention is to solve the problems existing in the prior art and provide a dynamic self-healing and degradation-resistant composite current collector BOPET membrane and its preparation method.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A dynamic self-healing and degradation-resistant composite current collector BOPET membrane includes a BOPET base film (biaxially oriented polyester film) and a coating on its surface, the coating including a dense barrier layer adjacent to the BOPET base film.

[0009] The dense barrier layer includes a BCNF-DH / ZIF-8 complex;

[0010] The BCNF-DH / ZIF-8 complexes interweave to form a dense network with a porosity (tested by mercury porosimetry (ISO 15901)) ≤1%;

[0011] The BCNF-DH / ZIF-8 complex consists of BCNF (bacterial cellulose nanofibers), a compound containing acylhydrazone bonds (DH, pH-responsive dynamic covalent bonds), and ZIF-8 type MOF. The compound containing acylhydrazone bonds is connected to BCNF through ether bonds (COC), and the ZIF-8 type MOF is connected to BCNF through coordination bonds (Zn-O) and hydrogen bonds.

[0012] In the BCNF-DH / ZIF-8 composite, BCNF acts as a network framework, extending the electrolyte penetration path and improving physical barrier efficiency (weight loss ≤0.4% after 1000 cycles). While existing technologies incorporate BCNF into coating layers, the function of BCNF differs from that of this invention. For example, patent application CN117844025A adds lignin-based phenolic resin to the PP base membrane to enhance mechanical properties and strengthens the bond with the metal layer through a polyurethane coating. Nanocellulose is used only as a mechanically reinforcing filler and does not utilize the three-dimensional network construction ability of BCNF to block electrolyte penetration into the base membrane.

[0013] The microporous structure (pore size 3.4 Å ± 0.2 Å) of the ZIF-8 type MOF in the BCNF-DH / ZIF-8 composite allows for the selective adsorption of catalytic molecules such as ethanol-based lithium in the electrolyte, blocking chemical degradation pathways. While existing technologies incorporate MOFs into the coating layer of PET films, the function of these MOFs differs from that of this invention. Existing MOFs are primarily used for physical barrier functions or as catalyst supports, without specifically designed for the selective adsorption of particular catalytic molecules (such as ethanol-based lithium) in the electrolyte. For example, patent application CN117801641A utilizes the confinement effect of MOFs (pore size ≤ 4 Å, porosity ≤ 40%) to construct a dense coating, blocking water vapor and hydrogen. The application of this type of MOF is limited to physical barrier functions, failing to achieve selective adsorption of catalytic molecules and synergistic repair with dynamic bonds. Furthermore, in existing technologies, MOFs are often used as independent fillers, without linkage with self-healing or conductive components, lacking a synergistic mechanism. This invention utilizes the synergistic dynamic response of MOF and dynamic acylhydrazone bonds. Under the combined effect of the two, the MOF pores shrink (the pore size decreases to about 2nm, or about 20Å) at high temperature and high humidity to enhance the barrier; the MOF exposes active sites at the crack, which can accelerate the repair of dynamic bonds (efficiency >95%).

[0014] The acylhydrazone-containing compounds in the BCNF-DH / ZIF-8 complex can trigger self-healing under acidic conditions. Existing technologies have introduced acylhydrazone bonds to endow coatings with self-healing functions. However, the acylhydrazone bonds in existing technologies mainly focus on mechanical damage repair (such as crack closure) but do not bind to molecular sieve materials (such as MOFs) and cannot block the degradation of the base film by electrolyte catalytic molecules (such as lithium alcohols).

[0015] As a preferred technical solution:

[0016] The dynamic self-healing and degradation-resistant composite current collector BOPET membrane described above has a dense barrier layer with a thickness of 45-55 nm and a surface roughness Ra (tested by AFM (ISO 4287)) ≤ 5 nm.

[0017] The dynamic self-healing and degradation-resistant composite current collector BOPET membrane described above has an average aspect ratio of >100 for BCNF.

[0018] The dynamic self-healing and degradation-resistant composite current collector BOPET membrane described above has a BCNF-DH / ZIF-8 composite with a BCNF content of 60-75 wt% and a ZIF-8 type MOF content of 20-30 wt%.

[0019] The preparation steps of the BCNF-DH / ZIF-8 composite current collector BOPET membrane, as described above, are as follows:

[0020] (a) First, the Acetobacter xylinum fermentation broth was centrifuged (8000 rpm, 10 min) to remove the bacterial cells and obtain bacterial cellulose gel. Then, lipids and proteins in the bacterial cellulose gel were removed by boiling in a 2 wt% NaOH aqueous solution for 1 h. Finally, after washing with pure water until neutral (pH = 7 ± 0.5), the gel was ultrasonically disrupted (500 W, 30 min) to obtain a BCNF suspension (2 wt% solid content).

[0021] (b) Vanillin was dissolved in a mixed solvent of ethanol and water (volume ratio 3:7) to obtain a vanillin solution (concentration 0.2 mol / L); adipic acid dihydrazide (ADH) was dissolved in water to obtain an adipic acid dihydrazide solution (concentration 0.2 mol / L).

[0022] (c) Vanillin solution was added dropwise to BCNF suspension, stirred for 10 min, and then adipic acid dihydrazide (ADH) solution was added. The mixture was then reacted at 58-62℃ for 3.5-4.5 h, and the pH was adjusted to 5.0±0.2 to introduce compounds containing acylhydrazone bonds onto the surface of BCNF. During this process, vanillin and the hydroxyl group of BCNF formed an ether bond through nucleophilic addition, and then condensed with adipic acid dihydrazide to form an acylhydrazone bond.

[0023] (d) Add the ZIF-8 precursor solution to the reaction system of step (c), stir at room temperature for 24 h, and then centrifuge and wash (5000 rpm, 5 min) to obtain the BCNF-DH / ZIF-8 complex. The ZIF-8 precursor solution consists of zinc nitrate, 2-methylimidazole, and methanol, with a zinc nitrate concentration of 0.1 mol / L and a 2-methylimidazole concentration of 0.4 mol / L. During this process, the Zn in the zinc nitrate... 2+ A coordinate bond (Zn-O) is formed with the oxygen of the hydroxyl group in BCNF, while the imidazole nitrogen in 2-methylimidazolium forms a hydrogen bond with the hydroxyl group in BCNF, thus achieving a stable connection between the ZIF-8 type MOF and BCNF.

[0024] The dynamic self-healing and degradation-resistant composite current collector BOPET membrane described above further includes a conductive reinforcement layer adjacent to the dense barrier layer, which is used to reduce sheet resistance and buffer mechanical stress.

[0025] The porosity of the conductive reinforcement layer is 40-50%;

[0026] The conductive reinforcement layer comprises PEDOT:PSS (conductive polymer), EVA (plasticizer), and BCNF-DH / ZIF-8 composite.

[0027] PEDOT:PSS forms a continuous conductive network.

[0028] Existing technologies, such as the patent application with publication number CN119590062A, present a problem: if PEDOT:PSS is made into a dense layer (porosity <5%), the sheet resistance is low (0.8Ω / sq), but it is brittle and will crack after 10 bends; if PEDOT:PSS is made into a loose layer, the sheet resistance soars (>5Ω / sq).

[0029] This invention solves the problem because PEDOT:PSS forms a continuous conductive network (i.e., a through-type conductive island chain with an island spacing of ≤50nm), and the electron tunneling effect maintains an ultra-low sheet resistance; EVA fills the pores to absorb cyclic stress and inhibit crack propagation (increasing puncture resistance by 40%).

[0030] Existing technologies, such as the patent application with publication number CN117799203A, present a problem: PEDOT:PSS is prone to swelling in the electrolyte, leading to phase separation, and the sheet resistance increases by about 200% after 100 cycles.

[0031] This invention solves the problem because the conductive reinforcement layer of this invention contains both PEDOT:PSS and BCNF-DH / ZIF-8 complex. The ZIF-8 type MOF (pore size 3.4 Å) in the BCNF-DH / ZIF-8 complex can block EC / DMC solvent molecules (size > 4 Å) from contacting PEDOT:PSS. The acylhydrazone-containing compound in the BCNF-DH / ZIF-8 complex can quickly repair microcracks and prevent electrolyte penetration.

[0032] Under 5C fast charging conditions, existing BOPET films are prone to thermal runaway when the hot spot temperature reaches 85°C.

[0033] This invention can solve the problem because the high porosity of the conductive reinforcement layer is beneficial for heat dissipation. PEDOT:PSS has high thermal conductivity, and the continuous conductive network formed by PEDOT:PSS can form a heat conduction path. The pores of EVA can promote air convection heat dissipation.

[0034] The dynamically self-healing and degradation-resistant composite current collector BOPET film described above has a PEDOT:PSS content of 40-50 wt% in the conductive reinforcement layer, and a PEDOT:PSS to EVA mass ratio of 40-50:50-60. This invention unexpectedly discovered that, at a specific ratio, PEDOT:PSS and EVA not only maintain conductivity but also absorb energy through deformation during lithium dendrite penetration.

[0035] The BOPET membrane, described above, is a dynamic self-healing and degradation-resistant composite current collector with a conductive reinforcement layer thickness of 140-160 nm.

[0036] The dynamic self-healing and degradation-resistant composite current collector BOPET membrane described above has a BOPET base film thickness of 8-12 μm and a tensile strength ≥200 MPa.

[0037] The dynamically self-healing and degradation-resistant composite current collector BOPET membrane described above has a sheet resistance ≤1.8Ω / sq (compared to ≥5Ω / sq for traditional PET base membranes), a self-healing efficiency of 68-98% for 5μm cracks in electrolyte after 24 hours, and an adhesion strength of 2.8-4.1N / cm between the BOPET base membrane and the coating. The BOPET membrane exhibits a weight loss of 0.18-0.65wt% after aging in electrolyte at 85℃ for 1000 hours, a tensile strength retention rate of 91-99% after aging in electrolyte at 85℃ for 1000 hours, and a capacity retention rate of 85-96% after 1000 cycles at a 1C charge / discharge rate.

[0038] The present invention also provides a method for preparing a dynamic self-healing and degradation-resistant composite current collector BOPET membrane as described in any of the preceding claims, comprising the following steps:

[0039] (A) The bottom coating liquid containing the BCNF-DH / ZIF-8 composite was coated onto the BOPET base film using a micro-gravure coating machine and then dried (at a temperature of 80°C for 30 seconds) to form a dense barrier layer.

[0040] During microgravure coating, the anilox roller structure (line count ≥ 200 LPI) generates shear force that forces the BCNF in the BCNF-DH / ZIF-8 composite to align along the coating direction (MD). Since the hydroxyl groups on the surface of BCNF can form hydrogen bonds with the ester groups of BOPET (OH···O=C), BCNF can act as a "nucleation site" during longitudinal stretching, guiding the BOPET molecular chains to align in an orderly manner along the MD direction, thereby inducing the BOPET molecular chains to form highly oriented lamellar crystals.

[0041] In the prior art, BCNF is randomly dispersed and cannot induce the crystal orientation of BOPET base film. For example, the patent application with publication number CN117844025A enhances the strength of PP base film by adding lignin, but the heat shrinkage rate is still >2% (150℃). The patent with authorization publication number CN118721807B uses wollastonite to modify PP, which relies on chemical crosslinking to improve strength, but does not optimize the crystal structure.

[0042] (B) A surface coating liquid containing PEDOT:PSS, EVA and BCNF-DH / ZIF-8 composite is coated onto a dense barrier layer using a slot extrusion coating machine and then dried to form a conductive reinforcement layer. During this process, PEDOT:PSS gradually forms a continuous conductive network that penetrates the conductive reinforcement layer through slot extrusion coating and drying.

[0043] (C) Electron beam irradiation, longitudinal stretching, transverse stretching and shaping, and surface corona treatment are performed sequentially to obtain a dynamic self-healing and degradation-resistant composite current collector BOPET film.

[0044] As a preferred technical solution:

[0045] As described above, in step (A), the undercoating solution consists of a BCNF-DH / ZIF-8 composite, a leveling agent (polyoxyethylene ether), and water; the coating speed is 9-11 m / min.

[0046] In step (B), the surface coating solution consists of PEDOT:PSS aqueous solution (solid content 1.2wt%), BCNF-DH / ZIF-8 composite, EVA emulsion (solid content 20wt%), dispersant (sodium dodecyl sulfate) and water; the coating gap is 95-105μm, and the coating speed is 4.5-5.5m / min; the drying is divided into two stages, the first stage is drying at 78-82℃ for 28-32s to remove the solvent, and the second stage is drying at 118-122℃ for 58-62s to allow the EVA to crosslink and cure;

[0047] In step (C), the electron beam irradiation treatment dose is 48-52 kGy and the energy is 2 MeV; the purpose of electron beam irradiation treatment is to enhance the interfacial adhesion between the coating and the base film.

[0048] The process parameters for longitudinal stretching include: preheating temperature 88-92℃, preheating time 9-11s, stretching ratio 3.0-3.5 times, and stretching speed 9-11 m / min. The purpose of longitudinal stretching is to improve the orientation of the molecular chains of the base film, enhance mechanical strength, eliminate internal stress in the coating, and prevent cracking.

[0049] The process parameters for transverse stretching and setting include: preheating temperature 108-112℃, preheating time 14-16s, stretching ratio 3.3-3.7 times, setting temperature 218-222℃, and setting time 9-11s. The purpose of transverse stretching and setting is to further optimize the crystallinity of the base film, improve dimensional stability, and solidify the coating structure to prevent high-temperature shrinkage.

[0050] The process parameters for surface corona treatment include: corona power 4.8-5.2 kW, corona frequency 20kHz, and processing speed 19-21 m / min. The purpose of surface corona treatment is to increase the surface polarity of the base film, improve the adhesion to metal coatings (such as copper foil), eliminate static electricity, and avoid dust adsorption during the coating process.

[0051] Beneficial effects:

[0052] (1) The present invention achieves multiple synergistic protection through a dense barrier layer constructed by BCNF-DH / ZIF-8 complex. BCNF serves as a network skeleton to extend the electrolyte penetration path, and ZIF-8 type MOF precisely adsorbs alcohol-based lithium to block the chemical degradation path. Compounds containing acylhydrazone bonds trigger self-repair in acidic environment and are linked with MOF. It synergistically blocks the penetration of catalytic molecules from three aspects: physical barrier, chemical adsorption and dynamic repair, and greatly improves cycle life.

[0053] (2) This invention utilizes the dynamic response synergistic mechanism formed by the compound containing acylhydrazone bond and ZIF-8 type MOF. When cracks occur, the MOF exposes active sites to accelerate the repair of acylhydrazone bonds. At the same time, the MOF pore shrinks to strengthen the barrier, avoiding the aggravation of electrolyte penetration caused by microcrack propagation, and realizing the autonomous repair and functional maintenance of the coating after damage.

[0054] (3) The preparation method of the present invention uses microgravure coating (bottom layer) and slot extrusion coating (top layer) to replace the high-cost process. The shear force of the anilox roller guides BCNF to align along the coating direction and induces BOPET molecular chains to form highly oriented lamellar crystals. It is compatible with existing BOPET production lines and reduces process costs. At the same time, the gradient structure design (dense barrier layer + conductive reinforcement layer) avoids mutual restriction of performance and takes into account both degradation resistance and conductivity.

[0055] (4) This invention designs a continuous conductive network of PEDOT:PSS in the conductive reinforcement layer and fills the pores with EVA. By using the electron tunneling effect to maintain conductivity, it also uses EVA to absorb cyclic stress, thus solving the contradiction between conductivity and flexibility of the PEDOT:PSS layer in the prior art and achieving a synergy between high conductivity and excellent mechanical buffering performance.

[0056] (5) This invention introduces the BCNF-DH / ZIF-8 composite into the conductive reinforcement layer, utilizes the pore size of the ZIF-8 type MOF to selectively block solvent molecules from contacting PEDOT:PSS, and relies on the acylhydrazone bond to quickly repair microcracks, avoiding the failure of conductive materials caused by electrolyte infiltration, and ensuring the long-term stability of conductive performance.

[0057] (6) By optimizing the structural characteristics of BCNF, the proportion of each component in the composite and the coating thickness parameters, the present invention enables the network support of BCNF, the adsorption barrier of ZIF-8 and the self-repair of acylhydrazone bonds to work together, thereby achieving balanced optimization of the overall performance of the composite current collector.

[0058] (7) By designing the porous structure of the conductive reinforcement layer, the present invention combines the thermal conductivity of PEDOT:PSS to form a heat conduction path and the air convection effect of EVA pores, thereby improving the heat dissipation capacity of the composite current collector and reducing the risk of thermal runaway under fast charging conditions. Detailed Implementation

[0059] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0060] To ensure that the performance of the substances used in each embodiment and comparative example is fully disclosed, the manufacturer information of the substances is specified in this invention; in addition, products from other manufacturers that conform to the limitations of this invention are also applicable.

[0061] In the following examples and comparative examples, the electrolyte is composed of LiPF6, ethylene carbonate, dimethyl carbonate and lithium ethoxide, with a concentration of 1M for LiPF6, a concentration of 1wt% for lithium ethoxide, and a volume ratio of ethylene carbonate to dimethyl carbonate of 1:1.

[0062] In the following embodiments and comparative examples, the specific steps of the aging process are as follows:

[0063] (1) Immerse the 10cm×10cm sample (i.e. the final product of each example or comparative example) completely in the electrolyte;

[0064] (2) Place the system from step (1) in an 85°C constant temperature oven (Binder KBF720) for a period of time, the period of time corresponding to the aging time in the embodiment or comparative example;

[0065] (3) After keeping it for a period of time, take out the sample, rinse it with anhydrous ethanol, and vacuum dry it at 60°C for 12 hours.

[0066] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0067] Sheet resistance, sheet resistance change rate after dynamic bending test, and sheet resistance change rate after aging in electrolyte at 85℃ for 500h: Sheet resistance was tested according to GB / T 3048.3-2007; among which, the four-probe spacing was 1.0mm±0.01mm, the test pressure was 5N (constant), and the instrument model was BER2500 electrode resistance meter (Yuaneng Technology (Xiamen) Co., Ltd.).

[0068] The dynamic bending test was performed in accordance with ASTM D2176-2016(2021) "Standard test method for folding durability of flexible composite materials for electrical insulation", with a bending radius of 5 mm, a bending frequency of 1 Hz, and 100,000 cycles.

[0069] The formula for calculating the rate of change of sheet resistance is as follows:

[0070] Sheet resistance change rate (%) = ×100%;

[0071] In the formula, The sheet resistance is measured after dynamic bending testing or aging in an electrolyte at 85°C for 500 hours. For the initial resistance, and The units are all Ω / sq.

[0072] Self-healing efficiency of a 5μm crack in electrolyte for 24 hours: A 5.0μm wide crack was first formed on the sample surface using a diamond scribing needle (Bruker, model RTEC-050). The pH of the electrolyte was then adjusted to 4.5±0.1 (simulating the acidic environment inside a battery) by adding phosphoric acid. The cracked sample was then immersed in the pH-adjusted electrolyte and placed at 60℃ for 24 hours. After removal, the initial and final crack areas were compared (observed using a Hitachi SU8010 scanning electron microscope (SEM) at 5kV accelerating voltage and 10000x magnification). The self-healing efficiency was calculated using the following formula:

[0073] Self-repair efficiency (%) = ×100%;

[0074] In the formula, The initial crack area of ​​the sample is denoted as . This represents the final crack area of ​​the sample. The units are all μm².

[0075] The adhesion between the BOPET base film and the coating was tested according to ASTM D903-20; the peel angle was 90°, the peel speed was 100 mm / min, the sample size was 200 mm × 25 mm (copper foil bonding surface), and the instrument model was Instron 5967 (load sensor 50 N).

[0076] Tensile strength retention and weight loss after aging in an electrolyte at 85℃ for 1000 hours: Tensile strength was tested according to GB / T1040.3-2006; sample size: 150mm × 15mm (length × width); clamp spacing: 100mm; tensile speed: 100mm / min; instrument model: Instron 5967 universal testing machine; relevant calculation formulas are as follows:

[0077] Tensile strength retention rate (%) = ×100%;

[0078] Weight loss rate (%) = ×100%.

[0079] Capacity retention after 1000 cycles at a 1C charge / discharge rate: According to GB / T 18287-2013, the specific process of a single cycle is as follows: First, the battery is charged at a constant current of 1C until the battery voltage reaches 4.2V; then, it is switched to constant voltage charging mode, maintaining the voltage at 4.2V until the charging current drops to ≤0.05C; after charging, the battery is left to stand at room temperature for 5 minutes to allow the internal electrochemical processes to reach equilibrium; finally, the battery is discharged at a constant current of 1C until the battery voltage drops to 3.0V; the amount of electricity discharged during the first 1000 discharge cycles (i.e., the actual capacity) is recorded, and the capacity retention rate is calculated according to the following formula:

[0080] Capacity retention rate (%) = ×100%;

[0081] In the formula, This refers to the amount of electricity released during the 1000th discharge cycle. This refers to the amount of electricity released during the first discharge cycle. and The units are all in mAh;

[0082] The battery assembly process is as follows:

[0083] (1) A commercial LiCoO2 cathode material (manufacturer: Ningbo Ronbay New Energy Technology Co., Ltd., model S800 (NCM 811 series)), conductive carbon black (Timcal Super C65), and PVDF binder (Solvay 5130) were mixed in a mass ratio of 96:2:2 and coated onto an aluminum foil (area loading 12 mg / cm²). After drying, the mixture was cut into a 14 mm diameter disc A, which served as the cathode of the battery.

[0084] (2) The graphite anode material (BTR S360), conductive carbon black (Timcal Super C65), and PVDF binder (Solvay 5130) are mixed in a mass ratio of 96:2:2 and coated on copper foil (area loading 8mg / cm²). After drying, it is cut into a circular piece B with a diameter of 15mm, which serves as the anode of the battery.

[0085] (3) The sample is punched into a circular piece C with a diameter of 16 mm;

[0086] (4) Adjust the pH of the electrolyte to 4.5 ± 0.1 by adding phosphoric acid;

[0087] (5) In an argon atmosphere glove box (water oxygen content <0.1ppm), first place the negative electrode shell (as battery substrate), then lay disc B (coated side up) on the negative electrode shell, then add 40μL of electrolyte after pH adjustment to disc B, then cover disc C on disc B, then add 40μL of electrolyte after pH adjustment to disc C, then place disc A (coated side down) on disc C, place spring sheet (to provide pressure buffer) on disc A, and finally snap the positive electrode shell together. Use a button cell packaging machine (Hefei Kejing MSK-110) to seal it with 8MPa pressure to make a CR2032 button cell.

[0088] Whether the coating cracked after microneedle puncture (anti-lithium dendrite puncture) test: The microneedle puncture test instrument was a nanoindenter (Bruker Hysitron TI980), the needle tip was a diamond cone (radius 1μm, angle 60°), the load was 10mN, and the speed was 0.5mm / s; after the microneedle puncture test, the coating was observed for cracks by SEM.

[0089] In the following embodiments, the preparation process of the Acetobacter xylinum fermentation broth is as follows:

[0090] (1) Take 900mL of distilled water and add 20g glucose, 5g peptone (brand Oxoid, catalog number LP0037), 5g yeast extract (brand BD Biosciences, catalog number 212750), 1.5g citric acid, and 2.7g disodium hydrogen phosphate in sequence. Stir magnetically at 500rpm for 30min.

[0091] (2) The pH of the system in step (1) was adjusted to 6.0±0.1 using 0.1M NaOH aqueous solution to obtain liquid culture medium;

[0092] (3) Make up to 1L, dispense into conical flasks (200mL per flask), and sterilize at 121℃ for 20min;

[0093] (4) Inoculate Acetobacter xylinum (preservation number CGMCC No.2955) into solid culture medium (i.e. liquid culture medium + 15g / L agar) and incubate at 30℃ for 48h;

[0094] (5) Pick a single colony and inoculate it into 50 mL of liquid culture medium. After culturing in a shaker at 30°C and 150 rpm for 24 h, aseptically inoculate it at a volume ratio of 5% (10 mL seed liquid / 200 mL culture medium).

[0095] (6) After being cultured at 30℃ for 7 days, the fermentation broth was obtained. During this period, 0.1M NaOH aqueous solution was automatically added using a pH automatic titration system (Metrohm 905Titrando) to maintain the pH value at 5.0±0.2.

[0096] Example 1

[0097] A method for preparing a dynamic self-healing and degradation-resistant composite current collector BOPET membrane, the specific steps of which are as follows:

[0098] (1) Preparation of raw materials;

[0099] Acetobacter xylinum fermentation broth;

[0100] Vanillin;

[0101] Mixed solvent: composed of ethanol and water in a volume ratio of 3:7;

[0102] Adipic acid dihydrazide;

[0103] Water (all water used in this invention is deionized water);

[0104] ZIF-8 precursor solution: composed of zinc nitrate, 2-methylimidazole and methanol, with a zinc nitrate concentration of 0.1 mol / L and a 2-methylimidazole concentration of 0.4 mol / L;

[0105] Polyoxyethylene ether: Manufacturer: Dow Chemical Company, Model: Polyox™ WSR-N80;

[0106] BOPET base film: 8μm thick, tensile strength 205MPa;

[0107] PEDOT:PSS aqueous solution: manufactured by Heraeus Holding Group, product name Clevios™ PH 1000, solid content 1.2wt%;

[0108] EVA emulsion: manufactured by DuPont, model number Elvax® 3165, solid content 20 wt%;

[0109] Sodium dodecyl sulfate;

[0110] (2) Preparation of BCNF-DH / ZIF-8 complex;

[0111] (a) First, the fermentation broth of Acetobacter xylinum was centrifuged to remove the bacterial cells and obtain bacterial cellulose gel; then, lipids and proteins were removed from the bacterial cellulose gel; finally, after washing with pure water until neutral, it was ultrasonically broken to obtain a BCNF suspension with a solid content of 2wt%.

[0112] In the BCNF suspension, the average aspect ratio of BCNF is 120;

[0113] (b) Dissolve vanillin in a mixed solvent to obtain a vanillin solution with a concentration of 0.2 mol / L; dissolve adipic acid dihydrazide in water to obtain adipic acid dihydrazide solution with a concentration of 0.2 mol / L;

[0114] (c) Add vanillin solution dropwise to BCNF suspension, stir for 10 min, add adipic acid dihydrazide solution, react at 58 °C for 3.5 h, and then adjust the pH to 5.0 ± 0.2;

[0115] (d) Add ZIF-8 precursor solution to the reaction system of step (c), stir at room temperature for 24 h, centrifuge and wash to obtain BCNF-DH / ZIF-8 complex.

[0116] The prepared BCNF-DH / ZIF-8 complex consists of BCNF, an acylhydrazone-containing compound, and a ZIF-8 type MOF. The acylhydrazone-containing compound is linked to BCNF via ether bonds, while the ZIF-8 type MOF is linked to BCNF via coordinate and hydrogen bonds. In the BCNF-DH / ZIF-8 complex, the content of BCNF is 60 wt%, and the content of ZIF-8 type MOF is 30 wt%.

[0117] (3) Prepare the base coat liquid and the top coat liquid;

[0118] The base coat solution consists of BCNF-DH / ZIF-8 composite, polyoxyethylene ether, and water, with the BCNF-DH / ZIF-8 composite content being 15 wt% and the polyoxyethylene ether content being 0.5 wt%.

[0119] The surface coating solution consists of PEDOT:PSS aqueous solution, BCNF-DH / ZIF-8 complex, EVA emulsion, sodium dodecyl sulfate and water, with the BCNF-DH / ZIF-8 complex content being 10 wt% and the sodium dodecyl sulfate content being 0.3 wt%.

[0120] (4) Preparation of dynamic self-healing and degradation-resistant composite current collector BOPET membrane;

[0121] (A) Using a micro-gravure coating machine, the bottom coating liquid is coated on the BOPET base film at a coating speed of 9 m / min and then dried to form a dense barrier layer with a thickness of 45 nm and a surface roughness Ra of 4.2 nm.

[0122] In the dense barrier layer, the BCNF-DH / ZIF-8 composites interweave to form a dense network with a porosity of 0.8%;

[0123] (B) Using a slot extrusion coating machine, the surface coating liquid is coated on the dense barrier layer with a coating gap of 95μm and a coating speed of 4.5m / min. Then, it is dried at 78℃ for 28s and then dried at 118℃ for 58s to form a conductive reinforcement layer with a thickness of 140nm and a porosity of 40%.

[0124] In the conductive reinforcement layer, PEDOT:PSS forms a continuous conductive network, with a PEDOT:PSS content of 40wt% and a mass ratio of PEDOT:PSS to EVA of 40:60.

[0125] (C) Electron beam irradiation, longitudinal stretching, transverse stretching and shaping, and surface corona treatment are performed sequentially to obtain a dynamic self-healing and degradation-resistant composite current collector BOPET film.

[0126] The electron beam irradiation treatment had a dose of 48 kGy and an energy of 2 MeV. The longitudinal stretching process parameters were: preheating temperature 88℃, preheating time 9s, stretching ratio 3, and stretching speed 9m / min. The transverse stretching and shaping process parameters were: preheating temperature 108℃, preheating time 14s, stretching ratio 3.3, shaping temperature 218℃, and shaping time 9s. The surface corona treatment process parameters were: corona power 4.8kW, corona frequency 20kHz, and processing speed 19m / min.

[0127] The resulting dynamic self-healing and degradation-resistant composite current collector BOPET membrane has a sheet resistance of 0.48 Ω / sq, a self-healing efficiency of 96% for a 5μm crack after 24 hours in electrolyte, and an adhesion strength of 3.2 N / cm between the BOPET base film and the coating. The BOPET membrane exhibits a weight loss of 0.32 wt% after aging in electrolyte at 85℃ for 1000 hours, a tensile strength retention rate of 96% after aging in electrolyte at 85℃ for 1000 hours, a capacity retention rate of 91% after 1000 cycles at 1C charge-discharge rate, a sheet resistance change rate of 4.2% after dynamic bending testing, and a sheet resistance change rate of 8.5% after aging in electrolyte at 85℃ for 500 hours. The coating (i.e., the overall structure of the dense barrier layer and the conductive reinforcement layer) of the BOPET membrane did not crack after a microneedle puncture test.

[0128] Example 2

[0129] A method for preparing a dynamic self-healing and degradation-resistant composite current collector BOPET membrane, the specific steps of which are as follows:

[0130] (1) Preparation of raw materials;

[0131] Acetobacter xylinum fermentation broth;

[0132] Vanillin;

[0133] Mixed solvent: composed of ethanol and water in a volume ratio of 3:7;

[0134] Adipic acid dihydrazide;

[0135] water;

[0136] ZIF-8 precursor solution: composed of zinc nitrate, 2-methylimidazole and methanol, with a zinc nitrate concentration of 0.1 mol / L and a 2-methylimidazole concentration of 0.4 mol / L;

[0137] Polyoxyethylene ether: Manufacturer: Dow Chemical Company, Model: Polyox™ WSR-N80;

[0138] BOPET base film: 10μm thick, tensile strength 225MPa;

[0139] PEDOT:PSS aqueous solution: manufactured by Heraeus Holding Group, product name Clevios™ PH 1000, solid content 1.2wt%;

[0140] EVA emulsion: manufactured by DuPont, model number Elvax® 3165, solid content 20 wt%;

[0141] Sodium dodecyl sulfate;

[0142] (2) Preparation of BCNF-DH / ZIF-8 complex;

[0143] (a) First, the fermentation broth of Acetobacter xylinum was centrifuged to remove the bacterial cells and obtain bacterial cellulose gel; then, lipids and proteins were removed from the bacterial cellulose gel; finally, after washing with pure water until neutral, it was ultrasonically broken to obtain a BCNF suspension with a solid content of 2wt%.

[0144] In the BCNF suspension, the average aspect ratio of BCNF is 150;

[0145] (b) Dissolve vanillin in a mixed solvent to obtain a vanillin solution with a concentration of 0.2 mol / L; dissolve adipic acid dihydrazide in water to obtain adipic acid dihydrazide solution with a concentration of 0.2 mol / L;

[0146] (c) Add vanillin solution dropwise to BCNF suspension, stir for 10 min, add adipic acid dihydrazide solution, react at 60 °C for 4 h, and then adjust the pH to 5.0 ± 0.2;

[0147] (d) Add ZIF-8 precursor solution to the reaction system of step (c), stir at room temperature for 24 h, centrifuge and wash to obtain BCNF-DH / ZIF-8 complex.

[0148] The prepared BCNF-DH / ZIF-8 complex consists of BCNF, an acylhydrazone-containing compound, and a ZIF-8 type MOF. The acylhydrazone-containing compound is linked to BCNF via an ether bond, while the ZIF-8 type MOF is linked to BCNF via a coordinate bond and a hydrogen bond. In the BCNF-DH / ZIF-8 complex, the content of BCNF is 65 wt%, and the content of ZIF-8 type MOF is 25 wt%.

[0149] (3) Prepare the base coat liquid and the top coat liquid;

[0150] The base coat solution consists of BCNF-DH / ZIF-8 composite, polyoxyethylene ether, and water, with the BCNF-DH / ZIF-8 composite content being 18 wt% and the polyoxyethylene ether content being 0.8 wt%.

[0151] The surface coating solution consists of PEDOT:PSS aqueous solution, BCNF-DH / ZIF-8 complex, EVA emulsion, sodium dodecyl sulfate, and water. The content of BCNF-DH / ZIF-8 complex is 15 wt%, and the content of sodium dodecyl sulfate is 0.5 wt%.

[0152] (4) Preparation of dynamic self-healing and degradation-resistant composite current collector BOPET membrane;

[0153] (A) Using a micro-gravure coating machine, the bottom coating liquid is coated on the BOPET base film at a coating speed of 10m / min and then dried to form a dense barrier layer with a thickness of 50nm and a surface roughness Ra of 3.5nm.

[0154] In the dense barrier layer, the BCNF-DH / ZIF-8 composites interweave to form a dense network with a porosity of 0.6%;

[0155] (B) Using a slot extrusion coating machine, the surface coating liquid is coated on the dense barrier layer with a coating gap of 100 μm and a coating speed of 5 m / min. Then, it is dried at 80°C for 30 s and then dried at 120°C for 60 s to form a conductive reinforcement layer with a thickness of 150 nm and a porosity of 45%.

[0156] In the conductive reinforcement layer, PEDOT:PSS forms a continuous conductive network, with a PEDOT:PSS content of 45wt% and a PEDOT:PSS to EVA mass ratio of 45:55.

[0157] (C) Electron beam irradiation, longitudinal stretching, transverse stretching and shaping, and surface corona treatment are performed sequentially to obtain a dynamic self-healing and degradation-resistant composite current collector BOPET film.

[0158] The electron beam irradiation treatment had a dose of 50 kGy and an energy of 2 MeV. The longitudinal stretching process parameters were: preheating temperature 90℃, preheating time 10s, stretching ratio 3.3 times, and stretching speed 10m / min. The transverse stretching and shaping process parameters were: preheating temperature 110℃, preheating time 15s, stretching ratio 3.5 times, shaping temperature 220℃, and shaping time 10s. The surface corona treatment process parameters were: corona power 5kW, corona frequency 20kHz, and processing speed 20m / min.

[0159] The resulting dynamic self-healing and degradation-resistant composite current collector BOPET membrane has a sheet resistance of 0.35 Ω / sq, a self-healing efficiency of 98% for a 5 μm crack after 24 h in electrolyte, and an adhesion strength of 3.8 N / cm between the BOPET base film and the coating. The BOPET membrane exhibits a weight loss of 0.25 wt% after aging in electrolyte at 85℃ for 1000 h, a tensile strength retention rate of 98% after aging in electrolyte at 85℃ for 1000 h, a capacity retention rate of 94% after 1000 cycles at 1C charge-discharge rate, a sheet resistance change rate of 3% after dynamic bending testing, and a sheet resistance change rate of 5.2% after aging in electrolyte at 85℃ for 500 h. The coating (i.e., the overall structure of the dense barrier layer and the conductive reinforcement layer) of the BOPET membrane did not crack after a microneedle puncture test.

[0160] Example 3

[0161] A method for preparing a dynamic self-healing and degradation-resistant composite current collector BOPET membrane, the specific steps of which are as follows:

[0162] (1) Preparation of raw materials;

[0163] Acetobacter xylinum fermentation broth;

[0164] Vanillin;

[0165] Mixed solvent: composed of ethanol and water in a volume ratio of 3:7;

[0166] Adipic acid dihydrazide;

[0167] water;

[0168] ZIF-8 precursor solution: composed of zinc nitrate, 2-methylimidazole and methanol, with a zinc nitrate concentration of 0.1 mol / L and a 2-methylimidazole concentration of 0.4 mol / L;

[0169] Polyoxyethylene ether: Manufacturer: Dow Chemical Company, Model: Polyox™ WSR-N80;

[0170] BOPET base film: 12μm thick, tensile strength 230MPa;

[0171] PEDOT:PSS aqueous solution: manufactured by Heraeus Holding Group, product name Clevios™ PH 1000, solid content 1.2wt%;

[0172] EVA emulsion: manufactured by DuPont, model number Elvax® 3165, solid content 20 wt%;

[0173] Sodium dodecyl sulfate;

[0174] (2) Preparation of BCNF-DH / ZIF-8 complex;

[0175] (a) First, the fermentation broth of Acetobacter xylinum was centrifuged to remove the bacterial cells and obtain bacterial cellulose gel; then, lipids and proteins were removed from the bacterial cellulose gel; finally, after washing with pure water until neutral, it was ultrasonically broken to obtain a BCNF suspension with a solid content of 2wt%.

[0176] In the BCNF suspension, the average aspect ratio of BCNF is 180;

[0177] (b) Dissolve vanillin in a mixed solvent to obtain a vanillin solution with a concentration of 0.2 mol / L; dissolve adipic acid dihydrazide in water to obtain adipic acid dihydrazide solution with a concentration of 0.2 mol / L;

[0178] (c) Add vanillin solution dropwise to BCNF suspension, stir for 10 min, add adipic acid dihydrazide solution, react at 62 °C for 4.5 h, and then adjust the pH to 5.0 ± 0.2;

[0179] (d) Add ZIF-8 precursor solution to the reaction system of step (c), stir at room temperature for 24 h, centrifuge and wash to obtain BCNF-DH / ZIF-8 complex.

[0180] The prepared BCNF-DH / ZIF-8 complex consists of BCNF, an acylhydrazone-containing compound, and a ZIF-8 type MOF. The acylhydrazone-containing compound is linked to BCNF via an ether bond, while the ZIF-8 type MOF is linked to BCNF via coordinate and hydrogen bonds. In the BCNF-DH / ZIF-8 complex, the content of BCNF is 75 wt%, and the content of ZIF-8 type MOF is 20 wt%.

[0181] (3) Prepare the base coat liquid and the top coat liquid;

[0182] The base coat solution consists of BCNF-DH / ZIF-8 composite, polyoxyethylene ether, and water, with the BCNF-DH / ZIF-8 composite content being 22 wt% and the polyoxyethylene ether content being 1.2 wt%.

[0183] The surface coating solution consists of PEDOT:PSS aqueous solution, BCNF-DH / ZIF-8 complex, EVA emulsion, sodium dodecyl sulfate, and water. The content of BCNF-DH / ZIF-8 complex is 20 wt%, and the content of sodium dodecyl sulfate is 0.8 wt%.

[0184] (4) Preparation of dynamic self-healing and degradation-resistant composite current collector BOPET membrane;

[0185] (A) Using a micro-gravure coating machine, the bottom coating liquid is coated on the BOPET base film at a coating speed of 11 m / min and then dried to form a dense barrier layer with a thickness of 55 nm and a surface roughness Ra of 4.8 nm.

[0186] In the dense barrier layer, the BCNF-DH / ZIF-8 composites interweave to form a dense network with a porosity of 0.9%;

[0187] (B) Using a slot extrusion coating machine, the surface coating liquid is coated on the dense barrier layer with a coating gap of 105 μm and a coating speed of 5.5 m / min. Then, it is dried at 82°C for 32 s and then dried at 122°C for 62 s to form a conductive reinforcement layer with a thickness of 160 nm and a porosity of 50%.

[0188] In the conductive reinforcement layer, PEDOT:PSS forms a continuous conductive network, with a PEDOT:PSS content of 50wt% and a mass ratio of PEDOT:PSS to EVA of 50:50.

[0189] (C) Electron beam irradiation, longitudinal stretching, transverse stretching and shaping, and surface corona treatment are performed sequentially to obtain a dynamic self-healing and degradation-resistant composite current collector BOPET film.

[0190] The electron beam irradiation treatment had a dose of 52 kGy and an energy of 2 MeV. The longitudinal stretching process parameters were: preheating temperature 92℃, preheating time 11s, stretching ratio 3.5 times, and stretching speed 11m / min. The transverse stretching and shaping process parameters were: preheating temperature 112℃, preheating time 16s, stretching ratio 3.7 times, shaping temperature 222℃, and shaping time 11s. The surface corona treatment process parameters were: corona power 5.2kW, corona frequency 20kHz, and processing speed 21m / min.

[0191] The resulting dynamic self-healing and degradation-resistant composite current collector BOPET membrane has a sheet resistance of 0.42 Ω / sq, a self-healing efficiency of 97% for a 5 μm crack after 24 h in electrolyte, and an adhesion strength of 3.5 N / cm between the BOPET base film and the coating. The BOPET membrane exhibits a weight loss of 0.38 wt% after aging in electrolyte at 85℃ for 1000 h, a tensile strength retention rate of 97% after aging in electrolyte at 85℃ for 1000 h, a capacity retention rate of 92% after 1000 cycles at 1C charge-discharge rate, a sheet resistance change rate of 4.8% after dynamic bending testing, and a sheet resistance change rate of 9% after aging in electrolyte at 85℃ for 500 h. The coating (i.e., the overall structure of the dense barrier layer and the conductive reinforcement layer) of the BOPET membrane did not crack after a microneedle puncture test.

[0192] Example 4

[0193] A method for preparing a dynamic self-healing and degradation-resistant composite current collector BOPET membrane, the specific steps of which are as follows:

[0194] (1) Preparation of raw materials;

[0195] Acetobacter xylinum fermentation broth;

[0196] Vanillin;

[0197] Mixed solvent: composed of ethanol and water in a volume ratio of 3:7;

[0198] Adipic acid dihydrazide;

[0199] water;

[0200] ZIF-8 precursor solution: composed of zinc nitrate, 2-methylimidazole and methanol, with a zinc nitrate concentration of 0.1 mol / L and a 2-methylimidazole concentration of 0.4 mol / L;

[0201] Polyoxyethylene ether: Manufacturer: Dow Chemical Company, Model: Polyox™ WSR-N80;

[0202] BOPET base film: 9μm thick, tensile strength 215MPa;

[0203] PEDOT:PSS aqueous solution: manufactured by Heraeus Holding Group, product name Clevios™ PH 1000, solid content 1.2wt%;

[0204] EVA emulsion: manufactured by DuPont, model number Elvax® 3165, solid content 20 wt%;

[0205] Sodium dodecyl sulfate;

[0206] (2) Preparation of BCNF-DH / ZIF-8 complex;

[0207] (a) First, the fermentation broth of Acetobacter xylinum was centrifuged to remove the bacterial cells and obtain bacterial cellulose gel; then, lipids and proteins were removed from the bacterial cellulose gel; finally, after washing with pure water until neutral, it was ultrasonically broken to obtain a BCNF suspension with a solid content of 2wt%.

[0208] In the BCNF suspension, the average aspect ratio of BCNF is 110;

[0209] (b) Dissolve vanillin in a mixed solvent to obtain a vanillin solution with a concentration of 0.2 mol / L; dissolve adipic acid dihydrazide in water to obtain adipic acid dihydrazide solution with a concentration of 0.2 mol / L;

[0210] (c) Add vanillin solution dropwise to BCNF suspension, stir for 10 min, add adipic acid dihydrazide solution, react at 61 °C for 3.8 h, and then adjust the pH to 5.0 ± 0.2;

[0211] (d) Add ZIF-8 precursor solution to the reaction system of step (c), stir at room temperature for 24 h, centrifuge and wash to obtain BCNF-DH / ZIF-8 complex.

[0212] The prepared BCNF-DH / ZIF-8 complex consists of BCNF, an acylhydrazone-containing compound, and a ZIF-8 type MOF. The acylhydrazone-containing compound is linked to BCNF via an ether bond, while the ZIF-8 type MOF is linked to BCNF via coordinate and hydrogen bonds. In the BCNF-DH / ZIF-8 complex, the content of BCNF is 70 wt%, and the content of ZIF-8 type MOF is 22 wt%.

[0213] (3) Prepare the base coat liquid and the top coat liquid;

[0214] The base coat solution consists of BCNF-DH / ZIF-8 composite, polyoxyethylene ether, and water, with the BCNF-DH / ZIF-8 composite content being 20 wt% and the polyoxyethylene ether content being 1 wt%.

[0215] The surface coating solution consists of PEDOT:PSS aqueous solution, BCNF-DH / ZIF-8 complex, EVA emulsion, sodium dodecyl sulfate and water, with the BCNF-DH / ZIF-8 complex content being 12 wt% and the sodium dodecyl sulfate content being 0.6 wt%.

[0216] (4) Preparation of dynamic self-healing and degradation-resistant composite current collector BOPET membrane;

[0217] (A) Using a micro-gravure coating machine, the bottom coating liquid is coated on the BOPET base film at a coating speed of 9.5 m / min and then dried to form a dense barrier layer with a thickness of 48 nm and a surface roughness Ra of 2.9 nm.

[0218] In the dense barrier layer, the BCNF-DH / ZIF-8 composites interweave to form a dense network with a porosity of 0.5%;

[0219] (B) Using a slot extrusion coating machine, the surface coating liquid is coated on the dense barrier layer with a coating gap of 98 μm and a coating speed of 4.8 m / min. Then, it is dried at 79°C for 29 s and then dried at 119°C for 59 s to form a conductive reinforcement layer with a thickness of 145 nm and a porosity of 42%.

[0220] In the conductive reinforcement layer, PEDOT:PSS forms a continuous conductive network, with a PEDOT:PSS content of 42wt% and a PEDOT:PSS to EVA mass ratio of 48:52.

[0221] (C) Electron beam irradiation, longitudinal stretching, transverse stretching and shaping, and surface corona treatment are performed sequentially to obtain a dynamic self-healing and degradation-resistant composite current collector BOPET film.

[0222] The electron beam irradiation treatment had a dose of 49 kGy and an energy of 2 MeV. The longitudinal stretching process parameters were: preheating temperature 89℃, preheating time 9.5s, stretching ratio 3.2 times, and stretching speed 9.2m / min. The transverse stretching and shaping process parameters were: preheating temperature 109℃, preheating time 14.5s, stretching ratio 3.4 times, shaping temperature 219℃, and shaping time 9.5s. The surface corona treatment process parameters were: corona power 4.9kW, corona frequency 20kHz, and processing speed 19.5m / min.

[0223] The resulting dynamic self-healing and degradation-resistant composite current collector BOPET membrane has a sheet resistance of 0.28 Ω / sq, a self-healing efficiency of 99% for a 5μm crack after 24 hours in electrolyte, and an adhesion strength of 4.1 N / cm between the BOPET base film and the coating. The BOPET membrane exhibits a weight loss of 0.18 wt% after aging in electrolyte at 85℃ for 1000 hours, a tensile strength retention rate of 99% after aging in electrolyte at 85℃ for 1000 hours, a capacity retention rate of 96% after 1000 cycles at 1C charge-discharge rate, a sheet resistance change rate of 2.5% after dynamic bending testing, and a sheet resistance change rate of 4% after aging in electrolyte at 85℃ for 500 hours. The coating (i.e., the overall structure of the dense barrier layer and the conductive reinforcement layer) of the BOPET membrane did not crack after a microneedle puncture test.

[0224] Example 5

[0225] A method for preparing a dynamic self-healing and degradation-resistant composite current collector BOPET membrane differs from Example 1 only in that the surface coating solution does not contain the BCNF-DH / ZIF-8 composite.

[0226] The resulting dynamic self-healing and degradation-resistant composite current collector BOPET membrane has a sheet resistance of 0.82 Ω / sq, a self-healing efficiency of 68% for a 5 μm crack after 24 h in electrolyte, and an adhesion strength of 3.0 N / cm between the BOPET base film and the coating. The dynamic self-healing and degradation-resistant composite current collector BOPET membrane exhibits a weight loss of 0.50 wt% after aging in electrolyte at 85℃ for 1000 h, a tensile strength retention rate of 93% after aging in electrolyte at 85℃ for 1000 h, a capacity retention rate of 85% after 1000 cycles at 1C charge-discharge rate, a sheet resistance change rate of 18% after dynamic bending testing, and a sheet resistance change rate of 32% after aging in electrolyte at 85℃ for 500 h. The coating (i.e., the overall structure of the dense barrier layer and the conductive reinforcement layer) of the dynamic self-healing and degradation-resistant composite current collector BOPET membrane cracked after a microneedle puncture test.

[0227] Compared with Example 1, Example 5 showed an increase in the sheet resistance change rate of the dynamically self-healing and degradation-resistant composite current collector BOPET membrane after dynamic bending test and after aging in electrolyte at 85°C for 500 hours. This is because: on the one hand, the lack of ZIF-8 type MOF (pore size 3.4 Å) to block EC / DMC solvent molecules (size > 4 Å) makes PEDOT:PSS prone to swelling and phase separation in electrolyte, destroying the continuous conductive network; on the other hand, the lack of acylhydrazone-containing compounds to rapidly repair microcracks means that cracks generated during dynamic bending and aging cannot be closed in time, leading to continuous electrolyte penetration, aggravating the degradation of PEDOT:PSS, and ultimately causing a significant increase in the sheet resistance change rate.

[0228] Example 6

[0229] The preparation method of a dynamic self-healing and degradation-resistant composite current collector BOPET film differs from Example 1 only in that the mass ratio of PEDOT:PSS to EVA in the conductive reinforcement layer is 30:70.

[0230] The resulting dynamic self-healing and degradation-resistant composite current collector BOPET membrane has a sheet resistance of 1.8 Ω / sq, a self-healing efficiency of 95% for a 5 μm crack after 24 h in electrolyte, and an adhesion strength of 3.1 N / cm between the BOPET base film and the coating. The BOPET membrane exhibits a weight loss of 0.33 wt% after aging in electrolyte at 85℃ for 1000 h, a tensile strength retention rate of 94% after aging in electrolyte at 85℃ for 1000 h, a capacity retention rate of 87% after 1000 cycles at 1C charge-discharge rate, a sheet resistance change rate of 6.0% after dynamic bending testing, and a sheet resistance change rate of 9.0% after aging in electrolyte at 85℃ for 500 h. The coating (i.e., the overall structure of the dense barrier layer and the conductive reinforcement layer) of the BOPET membrane did not crack after a microneedle puncture test.

[0231] Compared to Example 1, Example 6 showed an increase in sheet resistance of the dynamically self-healing and degradation-resistant composite current collector BOPET film, and a decrease in capacity retention after 1000 cycles at a 1C charge-discharge rate. After microneedle puncture testing, although the coating did not crack, the surface indentation depth reached 600 nm (compared to only 200 nm in Example 1). This is because excessive EVA leads to a decrease in material rigidity; although no cracks were observed, the structural deformation is irreversible, easily causing localized current accumulation during battery cycling, resulting in a reduced capacity retention. Simultaneously, when the PEDOT:PSS mass ratio in the conductive reinforcement layer is too low, it cannot effectively maintain the conductivity of the composite current collector film (the conductive network is excessively diluted), and it is also difficult to effectively buffer stress through synergistic deformation when subjected to microneedle puncture.

[0232] Example 7

[0233] The preparation method of a dynamic self-healing and degradation-resistant composite current collector BOPET film differs from Example 1 only in that: in step (A), when coating the bottom coating liquid, a doctor blade coating is used, and the coating speed is 9m / min.

[0234] The resulting dynamic self-healing and degradation-resistant composite current collector BOPET membrane has a sheet resistance of 0.60 Ω / sq, a self-healing efficiency of 90% for a 5μm crack after 24 hours in electrolyte, and an adhesion strength of 2.8 N / cm between the BOPET base film and the coating. The dynamic self-healing and degradation-resistant composite current collector BOPET membrane exhibits a weight loss of 0.65 wt% after aging in electrolyte at 85℃ for 1000 hours, a tensile strength retention rate of 91% after aging in electrolyte at 85℃ for 1000 hours, a capacity retention rate of 86% after 1000 cycles at a 1C charge-discharge rate, a sheet resistance change rate of 15% after dynamic bending testing, and a sheet resistance change rate of 20% after aging in electrolyte at 85℃ for 500 hours. The coating (i.e., the overall structure of the dense barrier layer and the conductive reinforcement layer) of the dynamic self-healing and degradation-resistant composite current collector BOPET membrane cracked after a microneedle puncture test.

[0235] Comparing Examples 1 and 7, it can be seen that when blade coating is used instead of microgravure coating, due to the lack of shear force generated by the anilox roller (line count ≥ 200 LPI), the BCNF in the BCNF-DH / ZIF-8 composite cannot be oriented along the coating direction (MD). BCNF cannot serve as a "nucleation site" to guide the BOPET molecular chains to align in an orderly manner along the MD direction, resulting in a decrease in the crystallinity of the base film and a reduction in the tensile strength retention rate to 91%.

[0236] Comparative Example 1

[0237] A method for preparing a composite current collector BOPET membrane differs from Example 1 only in that ultrasonic disruption is not performed in step (a), which results in an average aspect ratio of 19 for BCNF in the BCNF suspension.

[0238] The final composite current collector BOPET membrane had a weight loss of 1.8 wt% after aging in an electrolyte at 85°C for 1000 h.

[0239] Compared with Example 1, the weight loss rate of the composite current collector BOPET membrane after aging in an electrolyte at 85°C for 1000 h increased significantly. This is because ultrasonic disruption was not performed in step (a) of Comparative Example 1, resulting in an average aspect ratio of only 19 for BCNF. The BCNF-DH / ZIF-8 composite did not interweave to form a dense network (porosity of 12%), but instead formed a large number of interconnected permeation channels. Catalytic molecules in the electrolyte could quickly reach the surface of the BOPET base membrane through these channels and undergo hydrolysis reactions with the ester bonds of the base membrane.

[0240] Comparative Example 2

[0241] A method for preparing a composite current collector BOPET membrane differs from Example 1 only in that: in step (c), the pH value is adjusted to 7.0±0.2, and the product in step (2) is actually a BCNF / ZIF-8 complex (the BCNF-DH / ZIF-8 complex does not contain compounds with acylhydrazone bonds).

[0242] The self-healing efficiency of the 5μm crack in the final composite current collector BOPET membrane was 35% after 24 hours in the electrolyte.

[0243] Compared with Example 1, the self-healing efficiency of the 5μm crack in the composite current collector BOPET membrane was significantly reduced after 24 hours in the electrolyte. This is because the acidic catalytic conditions were missing in Comparative Example 2, and the condensation reaction efficiency of vanillin aldehyde group and adipic acid dihydrazide group was greatly reduced. The generated trace amount of acylhydrazone bond could not be stably grafted onto BCNF, resulting in the lack of dynamic acylhydrazone bonds on the BCNF surface that could trigger self-healing, and the crack could not be closed in time.

[0244] Comparative Example 3

[0245] A method for preparing a composite current collector BOPET membrane differs from Example 1 only in that: the ZIF-8 precursor solution is replaced with the MIL-101(Cr) precursor solution, which is composed of terephthalic acid, chromium nitrate and water, with the concentration of terephthalic acid being 0.1 mol / L and the concentration of chromium nitrate being 0.1 mol / L; the product of step (2) is actually a BCNF-DH / MIL-101 composite (the ZIF-8 type MOF in the BCNF-DH / ZIF-8 composite is replaced with the MIL-101 type MOF).

[0246] The self-healing efficiency of the 5μm crack in the composite current collector BOPET membrane was 55% after 24 hours in the electrolyte; the weight loss of the composite current collector BOPET membrane after aging in the electrolyte at 85℃ for 1000 hours was 1.5wt.

[0247] Compared with Comparative Example 3 and Example 1, the self-healing efficiency of the 5μm crack in the composite current collector BOPET membrane after 24h in the electrolyte was significantly reduced, and the weight loss rate of the composite current collector BOPET membrane after aging in the electrolyte at 85℃ for 1000h was significantly increased. This is because the pore size of MIL-101(Cr) is too large, and it cannot selectively adsorb catalytic molecules such as lithium ethanol in the electrolyte, resulting in the chemical degradation pathway not being effectively blocked, and the erosion of the base film by the electrolyte being aggravated. At the same time, MIL-101(Cr) lacks synergistic effect with compounds containing acylhydrazone bonds, and its exposed active sites cannot efficiently accelerate the dynamic bond repair, resulting in a decrease in the repair efficiency at the crack.

Claims

1. A dynamic self-healing and degradation-resistant composite current collector BOPET membrane, comprising a BOPET base film and a coating on its surface, characterized in that, The coating includes a dense barrier layer adjacent to the BOPET base film; The dense barrier layer includes a BCNF-DH / ZIF-8 complex; The BCNF-DH / ZIF-8 complex interweaves to form a dense network with a porosity of ≤1%; The BCNF-DH / ZIF-8 complex consists of BCNF, an acylhydrazone-containing compound, and ZIF-8. The acylhydrazone-containing compound is linked to BCNF via an ether bond, while ZIF-8 is linked to BCNF via a coordinate bond and a hydrogen bond. The average aspect ratio of BCNF is >100; The preparation steps of the BCNF-DH / ZIF-8 complex are as follows: (a) First, the fermentation broth of Acetobacter xylinum was centrifuged to remove the bacterial cells and obtain bacterial cellulose gel; then, lipids and proteins in the bacterial cellulose gel were removed; finally, after washing with pure water until neutral, it was ultrasonically broken to obtain BCNF suspension. (b) Dissolve vanillin in a mixed solvent of ethanol and water to obtain a vanillin solution; dissolve adipic acid dihydrazide in water to obtain adipic acid dihydrazide solution; (c) Add vanillin solution dropwise to BCNF suspension, stir, add adipic acid dihydrazide solution, react at 58-62℃ for 3.5-4.5h, and then adjust the pH to 5.0±0.2; (d) Add ZIF-8 precursor solution to the reaction system of step (c), stir, centrifuge and wash to obtain BCNF-DH / ZIF-8 complex, wherein the ZIF-8 precursor solution is composed of zinc nitrate, 2-methylimidazole and methanol.

2. The dynamic self-healing and degradation-resistant composite current collector BOPET membrane according to claim 1, characterized in that, The thickness of the dense barrier layer is 45-55nm, and the surface roughness Ra≤5nm.

3. The dynamic self-healing and degradation-resistant composite current collector BOPET membrane according to claim 1, characterized in that, In the BCNF-DH / ZIF-8 complex, the content of BCNF is 60-75 wt%, and the content of ZIF-8 is 20-30 wt%.

4. The dynamic self-healing and degradation-resistant composite current collector BOPET membrane according to claim 1, characterized in that, The coating also includes a conductive reinforcement layer adjacent to the dense barrier layer; The porosity of the conductive reinforcement layer is 40-50%; The conductive reinforcement layer comprises PEDOT:PSS, EVA, and BCNF-DH / ZIF-8 composite. PEDOT:PSS forms a continuous conductive network.

5. The dynamic self-healing and degradation-resistant composite current collector BOPET membrane according to claim 4, characterized in that, The PEDOT:PSS content in the conductive reinforcement layer is 40-50wt%, and the mass ratio of PEDOT:PSS to EVA is 40-50:50-60.

6. The dynamic self-healing and degradation-resistant composite current collector BOPET membrane according to claim 4, characterized in that, The thickness of the conductive reinforcement layer is 140-160nm.

7. The dynamic self-healing and degradation-resistant composite current collector BOPET membrane according to claim 1, characterized in that, The thickness of the BOPET base film is 8-12μm, and the tensile strength is ≥200MPa.

8. A dynamic self-healing and degradation-resistant composite current collector BOPET membrane according to any one of claims 1 to 7, characterized in that, The sheet resistance of the dynamically self-healing and degradation-resistant composite current collector BOPET membrane is ≤1.8Ω / sq, and the self-healing efficiency of a 5μm crack in electrolyte for 24h is 68-98%. The adhesion between the BOPET base film and the coating is 2.8-4.1N / cm. The weight loss of the dynamically self-healing and degradation-resistant composite current collector BOPET membrane after aging in electrolyte at 85℃ for 1000h is 0.18-0.65wt%, the tensile strength retention rate after aging in electrolyte at 85℃ for 1000h is 91-99%, and the capacity retention rate after 1000 cycles at 1C charge-discharge rate is 85-96%.

9. A method for preparing a dynamic self-healing and degradation-resistant composite current collector BOPET membrane as described in any one of claims 1 to 8, characterized in that, Includes the following steps: (A) The bottom coating liquid containing the BCNF-DH / ZIF-8 composite was coated onto the BOPET base film using a micro-gravure coating machine and then dried to form a dense barrier layer. (B) A surface coating liquid containing PEDOT:PSS, EVA and BCNF-DH / ZIF-8 composite was applied to a dense barrier layer using a slot extrusion coating machine and then dried to form a conductive reinforcement layer. (C) Electron beam irradiation, longitudinal stretching, transverse stretching and shaping, and surface corona treatment are performed sequentially to obtain a dynamic self-healing and degradation-resistant composite current collector BOPET film.

10. The method according to claim 9, characterized in that, In step (A), the bottom coating solution consists of BCNF-DH / ZIF-8 complex, leveling agent and water; the coating speed is 9-11 m / min; In step (B), the surface coating solution consists of PEDOT:PSS aqueous solution, BCNF-DH / ZIF-8 complex, EVA emulsion, dispersant and water; the coating gap is 95-105μm and the coating speed is 4.5-5.5m / min; the drying is divided into two stages, the first stage is drying at 78-82℃ for 28-32s, and the second stage is drying at 118-122℃ for 58-62s. In step (C), the electron beam irradiation treatment dose is 48-52 kGy and the energy is 2 MeV; The process parameters for longitudinal stretching include: preheating temperature 88-92℃, preheating time 9-11s, stretching ratio 3.0-3.5 times, and stretching speed 9-11 m / min; The process parameters for transverse stretching and setting include: preheating temperature 108-112℃, preheating time 14-16s, stretching ratio 3.3-3.7 times, setting temperature 218-222℃, and setting time 9-11s. The process parameters for surface corona treatment include: corona power 4.8-5.2 kW, corona frequency 20 kHz, and processing speed 19-21 m / min.