Dynamic self-repairing degradation-resistant composite current collector BOPET film and preparation method thereof

Abstract

The invention belongs to the technical field of material science and engineering, 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 located on the surface of the BOPET base film, the coating comprises a compact barrier layer adjacent to the BOPET base film, the compact barrier layer is composed of BCNF-DH / ZIF-8 compounds, the compounds are interwoven to form a compact network with the porosity smaller than or equal to 1%, the compact network is composed of BCNF, a compound containing an acylhydrazone bond and ZIF-8 type MOF, and all the components are connected through specific chemical bonds. The preparation method comprises the following steps: forming the compact barrier layer through micro gravure coating, forming the conductive enhancement layer through slit extrusion coating, and then carrying out electron beam irradiation treatment, longitudinal stretching, transverse stretching and shaping and surface corona treatment. According to the invention, the problems that the BOPET base membrane is easy to permeate and degrade by catalytic molecules and the coating does not have a dynamic self-repairing function can be solved.

Description

Technical Field

[0001] The invention 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. Background Art

[0002] In the lithium-ion battery industry, current collectors play a key role in collecting current. Ideal current collectors must meet the requirements of high conductivity, high stability, strong bonding strength, low cost, and flexibility and lightness. Traditional lithium-ion battery current collectors are primarily made of metal foils, such as rolled aluminum foil and electrolytic copper foil. However, as industries like new energy vehicles demand higher energy density, safety, and cost for lithium-ion batteries, composite current collectors have emerged.

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

[0004] The patent application with publication number CN119590062A and the patent with authorization announcement number CN118931300B both provide ideas for improving the electrolyte resistance of polymer base membranes. The former adopts the method of constructing a sandwich structure of polymer polar material layer-polymer reinforcement material layer-polymer polar material layer, adding polar polymer materials to the polymer polar material layer to enhance the surface polarity and strengthen the binding force with the metal layer to reduce the electrolyte penetration path, while adding amphoteric materials to promote the fusion of various components and make the overall polarity of the material uniform to improve the structural stability, and also adding reinforcing materials to the polymer reinforcement material layer to accelerate the crystallization of polyolefins and enhance the density of the base membrane structure, thereby improving the performance of the polymer base membrane from the two aspects of material composition and structural design. On the one hand, it synergistically improves the electrolyte resistance of the base film; the latter adopts the method of preparing a composite coating containing cross-linked polyvinyl pyrrolidone and graphene nanosheets, and obtains vinyl pyrrolidone / methyl acrylate / fluorinated ethylene copolymer emulsion by emulsion polymerization, and modifies the graphene oxide nanosheets and mixes them 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. The corrosion resistance of cross-linked polyvinyl pyrrolidone and graphene, the physical shielding effect of graphene nanosheets, the methyl acrylate chain segment to improve the interfacial compatibility and the fluorinated ethylene segment to reduce the surface energy and reduce the adhesion of the electrolyte are synergistically prevented from contacting the electrolyte and catalyst with the PET substrate in multiple ways, thereby improving the electrolyte resistance of the base film.

[0005] However, neither method fundamentally blocks the penetration of catalytic molecules in the electrolyte, and their cycle life is still limited: while the former's sandwich structure enhances physical isolation through polyolefin crystals and polar layers, nanoscale crystal defects still allow alcohol-based lithium to penetrate; the latter's graphene composite coating relies on layer stacking to form a barrier, and the chemical inertness of interlayer defects and cross-linked networks prevents active capture of catalytic molecules, and lacks dynamic self-healing capabilities. When microcracks appear in the coating, the electrolyte and catalytic molecules can still penetrate deep into the base film, causing degradation. Furthermore, the former's process flow 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 the present invention is to solve the problems existing in the prior art and provide a dynamic self-repairing degradation-resistant composite current collector BOPET film and a preparation method thereof.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A dynamic self-repairing and degradation-resistant composite current collector BOPET film, comprising a BOPET base film (biaxially oriented polyester film) and a coating located on the surface thereof, wherein the coating comprises a dense barrier layer adjacent to the BOPET base film;

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

[0010] The BCNF-DH / ZIF-8 composites are interwoven to form a dense network with a porosity (measured by mercury intrusion porosimetry (ISO 15901)) ≤ 1%;

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

[0012] The BCNF in the BCNF-DH / ZIF-8 composite serves as a network backbone, extending the electrolyte permeation path and improving physical barrier efficiency (weight loss rate ≤ 0.4% after 1,000 cycles). While prior art incorporates BCNF into the coating layer, the effects of BCNF differ from those of the present invention. For example, patent application publication number CN117844025A adds lignin-based phenolic resin to the PP base film to improve mechanical properties and enhances adhesion to the metal layer through a polyurethane coating. Nanocellulose serves only as a mechanical reinforcement filler, and BCNF's three-dimensional network-building capabilities are not utilized to prevent electrolyte permeation through the base film.

[0013] The microporous structure of the ZIF-8-type MOF (pore diameter 3.4Å ± 0.2Å) in the BCNF-DH / ZIF-8 complex selectively adsorbs catalytic molecules such as lithium alkoxides in the electrolyte, blocking chemical degradation pathways. While MOFs have been incorporated into the coating layer of PET films in prior art, their functions differ from those of the present invention. Prior art MOFs are primarily used for physical barriers or as catalyst supports, without being specifically designed to selectively adsorb specific catalytic molecules (such as lithium alkoxides) in the electrolyte. For example, patent application publication number CN117801641A utilizes the confinement effect of MOFs (pore diameter ≤ 4Å, porosity ≤ 40%) to construct a dense coating that blocks water vapor and hydrogen. This type of MOF's application is limited to physical barriers, failing to achieve selective adsorption of catalytic molecules or synergistic repair with dynamic bonds. Furthermore, prior art MOFs are often used as standalone fillers, not integrated with self-healing or conductive components, lacking a synergistic mechanism. The present invention utilizes the dynamic response synergy of MOF and dynamic acylhydrazone bonds. Under the linkage of the two, the MOF pores shrink (the pore diameter drops to 2nm, or about 20Å) at high temperature and high humidity to enhance the barrier; the MOF exposes active sites at the cracks, which can accelerate the repair of dynamic bonds (efficiency >95%).

[0014] The compounds containing acylhydrazone bonds in the BCNF-DH / ZIF-8 complex can trigger self-repair in an acidic environment. Existing technologies have given coatings self-repair functions by introducing acylhydrazone bonds. However, the acylhydrazone bonds in existing technologies mainly focus on mechanical damage repair (such as crack closure), but are not combined with molecular sieve materials (such as MOFs) and cannot block the degradation of the base membrane by electrolyte catalytic molecules (such as alcohol lithium).

[0015] As the preferred technical solution:

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

[0017] As described above, the dynamic self-repairing and degradation-resistant composite current collector BOPET film has an average aspect ratio of BCNF>100.

[0018] In the above-mentioned dynamic self-repairing and degradation-resistant composite current collector BOPET film, in the BCNF-DH / ZIF-8 composite, the BCNF content is 60-75wt%, and the ZIF-8 type MOF content is 20-30wt%.

[0019] The preparation steps of the above-mentioned dynamic self-repairing and degradation-resistant composite current collector BOPET film, BCNF-DH / ZIF-8 composite are as follows:

[0020] (a) Acetobacter xylinum fermentation broth was centrifuged (8000 rpm, 10 min) to remove bacterial cells and obtain a bacterial cellulose gel. The BC cellulose gel was then boiled in a 2 wt% aqueous solution of NaOH for 1 h to remove lipids and proteins. Finally, the BC cellulose gel was washed with pure water to neutral pH = 7 ± 0.5 and ultrasonically disrupted (500 W, 30 min) to obtain a BCNF suspension (solid content 2 wt%).

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

[0022] (c) Vanillin solution was added dropwise to the BCNF suspension and stirred for 10 minutes. Adipic acid dihydrazide (ADH) solution was then added. The mixture was then reacted at 58-62°C for 3.5-4.5 hours. The pH was then adjusted to 5.0 ± 0.2 to introduce a compound containing an acylhydrazone bond onto the BCNF surface. During this process, vanillin reacted with the hydroxyl groups of the BCNF via nucleophilic addition to form an ether bond, which then condensed with adipic acid dihydrazide to form an acylhydrazone bond.

[0023] (d) Adding ZIF-8 precursor solution to the reaction system of step (c), stirring at room temperature for 24 h, and then centrifuging and washing (5000 rpm, 5 min) to obtain BCNF-DH / ZIF-8 complex, wherein the ZIF-8 precursor solution consists of zinc nitrate, 2-methylimidazole and methanol, the concentration of zinc nitrate is 0.1 mol / L, and the concentration of 2-methylimidazole is 0.4 mol / L; in this process, Zn in zinc nitrate is 2+ It forms a coordination bond (Zn-O) with the oxygen of the hydroxyl group of BCNF, and at the same time, the imidazole nitrogen in 2-methylimidazole forms a hydrogen bond with the hydroxyl group of BCNF, realizing a stable connection between ZIF-8 type MOF and BCNF.

[0024] A dynamic self-repairing and degradation-resistant composite current collector BOPET film as described above, wherein the coating further comprises a conductive reinforcement layer adjacent to the dense barrier layer, the conductive reinforcement layer being used to reduce the sheet resistance and buffer the mechanical stress;

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

[0026] The conductive reinforcement layer includes 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, have a problem: if PEDOT:PSS is made into a dense layer (porosity <5%), the square resistance is low (0.8Ω / sq), but it is very brittle and cracks after being bent 10 times; if PEDOT:PSS is made into a loose layer, the square resistance soars (>5Ω / sq).

[0029] The present invention can solve this 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 ultra-low square resistance; EVA fills the pores to absorb cyclic stress and inhibit crack propagation (puncture resistance is increased by 40%).

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

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

[0032] The existing BOPET film is prone to thermal runaway when the hot spot temperature reaches 85°C under 5C fast charging conditions.

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

[0034] In the aforementioned dynamic self-healing, degradation-resistant composite current collector BOPET film, 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. The present inventors unexpectedly discovered that a specific ratio of PEDOT:PSS to EVA not only maintains conductivity but also absorbs energy through deformation when lithium dendrites penetrate.

[0035] In the above-mentioned dynamic self-repairing and degradation-resistant composite current collector BOPET film, the thickness of the conductive enhancement layer is 140-160 nm.

[0036] A dynamic self-repairing degradation-resistant composite current collector BOPET film as described above, the thickness of the BOPET base film is 8-12 μm, and the tensile strength is ≥200 MPa.

[0037] A dynamic self-repairing degradation-resistant composite current collector BOPET film as described above, the sheet resistance of the dynamic self-repairing degradation-resistant composite current collector BOPET film is ≤1.8 Ω / sq (the sheet resistance of the conventional PET base film is ≥5 Ω / sq), the self-repairing efficiency of a 5 μm crack in an electrolyte for 24 h is 68-98%, the bonding force between the BOPET base film and the coating is 2.8-4.1 N / cm; the weight loss rate of the dynamic self-repairing degradation-resistant composite current collector BOPET film after aging in an electrolyte at 85 ℃ for 1000 h is 0.18-0.65 wt%, the tensile strength retention rate after aging in an electrolyte at 85 ℃ for 1000 h is 91-99%, and the capacity retention rate after 1000 cycles at a 1C charge-discharge rate is 85-96%.

[0038] The application further provides a method for preparing the dynamic self-repairing degradation-resistant composite current collector BOPET film as described in any one of the above, comprising the following steps:

[0039] (A) After the bottom coating liquid containing the BCNF-DH / ZIF-8 composite is coated on the BOPET base film by using a micro-gravure coater, drying (the temperature is 80 ℃, and the time is 30 s) is performed to form a dense barrier layer;

[0040] When micro-gravure coating is performed, the shear force generated by the structure of the anilox roll (the line number is ≥200 LPI) forces the BCNF in the BCNF-DH / ZIF-8 composite to arrange along the coating direction (MD), and since the hydroxyl groups on the surface of the BCNF can form hydrogen bonds (O-H···O=C) with the ester groups of the BOPET, when longitudinal stretching is performed, the BCNF can act as a “nucleation site” to guide the BOPET molecular chains to arrange in order along the MD direction, thereby inducing the BOPET molecular chains to form highly oriented lamellae;

[0041] In the prior art, the BCNF is randomly dispersed, and cannot induce the crystalline orientation of the BOPET base film, for example, the patent application with the publication number CN117844025A enhances the strength of the PP base film by adding lignin, but the thermal shrinkage rate is still >2% (150 ℃), and the patent with the authorization announcement number CN118721807B modifies the PP by using wollastonite, and relies on chemical crosslinking to enhance the strength, without optimizing the crystalline structure;

[0042] (B) After the surface coating liquid containing the PEDOT:PSS, the EVA and the BCNF-DH / ZIF-8 composite is coated on the dense barrier layer by using a slot extrusion coater, drying is performed to form a conductive enhancement layer; in this process, the PEDOT:PSS is gradually formed into a continuous conductive network penetrating through the conductive enhancement layer through slot extrusion coating and drying;

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

[0044] As the preferred technical solution:

[0045] In the method described above, in step (A), the bottom coating liquid is composed 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 liquid consists of a PEDOT:PSS aqueous solution (solid content 1.2 wt%), a BCNF-DH / ZIF-8 composite, an EVA emulsion (solid content 20 wt%), a dispersant (sodium lauryl sulfate), and water; the coating gap is 95-105 μm, and the coating speed is 4.5-5.5 m / min; the drying is divided into two stages: the first stage is drying at 78-82°C for 28-32 seconds to remove the solvent, and the second stage is drying at 118-122°C for 58-62 seconds to crosslink and cure the EVA;

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

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

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

[0050] The process parameters for surface corona treatment include: corona power 4.8-5.2 kW, corona frequency 20 kHz, and treatment speed 19-21 m / min. The purpose of surface corona treatment is to increase the surface polarity of the base film and improve adhesion to the metal coating (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 the BCNF-DH / ZIF-8 complex. BCNF serves as a network skeleton to extend the electrolyte penetration path. The ZIF-8 type MOF accurately adsorbs alcohol-based lithium to block the chemical degradation path. The compound containing acylhydrazone bonds triggers self-repair in an acidic environment and interacts with the MOF, synergistically blocking the penetration of catalytic molecules from three aspects: physical barrier, chemical adsorption, and dynamic repair, thereby greatly improving the cycle life.

[0053] (2) The present invention utilizes compounds containing acylhydrazone bonds and ZIF-8 type MOF to form a dynamic response synergistic mechanism. When cracks occur, MOF exposes active sites to accelerate the repair of acylhydrazone bonds. At the same time, MOF pores shrink to strengthen the barrier, avoiding the intensification of electrolyte penetration caused by the expansion of microcracks, thereby achieving autonomous repair and functional maintenance after the coating is damaged.

[0054] (3) The preparation method of the present invention adopts micro-gravure coating (bottom layer) and slit extrusion coating (surface layer) to replace the high-cost process. The shear force of the anilox roller guides the BCNF to arrange along the coating direction and induces the BOPET molecular chains to form highly oriented lamellae. It is compatible with the existing BOPET production line and reduces the process cost. 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) The present invention designs PEDOT:PSS in the conductive reinforcement layer to form a continuous conductive network, and uses EVA to fill the pores. While maintaining conductivity through the electron tunneling effect, the EVA is used to absorb cyclic stress, thereby solving the contradiction between the conductivity and flexibility of the PEDOT:PSS layer in the prior art and achieving the synergy of high conductivity and excellent mechanical buffering performance.

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

[0057] (6) The present invention optimizes the structural characteristics of BCNF, the proportion of each component in the composite and the coating thickness parameters, so that the network support of BCNF, the adsorption barrier of ZIF-8, and the self-repair of acylhydrazone bonds can fully cooperate to achieve balanced optimization of the overall performance of the composite current collector.

[0058] (7) The present invention improves the heat dissipation capacity of the composite current collector and reduces the risk of thermal runaway under fast charging conditions by designing the pore structure of the conductive reinforcement layer, combining the thermal conductivity of PEDOT:PSS to form a heat conduction path and the air convection effect of the EVA pores. DETAILED DESCRIPTION

[0059] The application will be further described below with reference to the specific embodiments. It should be understood that these embodiments are only used to illustrate the application and not to limit the scope of the application. Furthermore, it should be understood that those skilled in the art can make various modifications or changes to the application after reading the content of the application, and these equivalent forms also fall within the scope defined by the appended claims of the application.

[0060] In order to ensure the performance of the substances used in each embodiment and comparative example, the manufacturer information of the substances is disclosed in the application; in addition, the products of other manufacturers meeting the definition of the application can also be applicable.

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

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

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

[0064] (2) place the system of step (1) in an 85℃ constant temperature oven (Binder KBF720) for a period of time, and the period of time corresponds to the aging time in the embodiment or comparative example;

[0065] (3) after maintaining for a period of time, take out the sample, rinse with anhydrous ethanol, and vacuum dry at 60℃ for 12h.

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

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

[0068] Dynamic bending test is performed in accordance with ASTM D2176-2016(2021) "Standard Test Method for Fold Durability of Flexible Composites for Electrical Insulation", wherein the bending radius is 5mm, the bending frequency is 1Hz, and the cycle number is 100000 times;

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

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

[0071] Where, It is the square resistance after dynamic bending test or aging in electrolyte at 85℃ for 500h. is the initial square resistance, and The unit is Ω / sq.

[0072] Self-healing efficiency of a 5μm crack in an electrolyte for 24 hours: A diamond stylus (Bruker, model RTEC-050) was first used to scratch a 5.0μm crack on the sample surface. The pH of the electrolyte was then adjusted to 4.5±0.1 (simulating the acidic environment inside the battery) by adding phosphoric acid. The cracked sample was then immersed in the pH-adjusted electrolyte and placed at 60°C for 24 hours. The sample was then removed and the initial and final crack areas of the sample were compared (observed using a Hitachi SU8010 scanning electron microscope (SEM) at an accelerating voltage of 5kV and a magnification of 10,000x). The self-healing efficiency was calculated according to the following formula:

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

[0074] Where, is the initial crack area of ​​the specimen, is the final crack area of ​​the specimen, The unit is μm².

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

[0076] Tensile strength retention and weight loss after aging in an electrolyte at 85°C for 1000 hours: Tensile strength was tested according to GB / T1040.3-2006; specimen size: 150 mm × 15 mm (length × width), grip spacing: 100 mm, tensile speed: 100 mm / min, instrument model: Instron 5967 universal materials testing machine. The relevant calculation formula is 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, charge the battery at a constant current of 1C until the battery voltage reaches 4.2V; then switch to constant voltage charging mode, maintain the voltage at 4.2V, until the charging current drops to ≤0.05C; after charging, let the battery stand at room temperature for 5 minutes to allow the electrochemical processes within the battery to reach equilibrium; finally, discharge the battery at a constant current of 1C until the battery voltage drops to 3.0V; record the amount of electricity discharged during the discharge process from cycle 1 to 1000 (i.e., actual capacity), and calculate the capacity retention rate according to the following formula:

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

[0081] Where, is the amount of electricity released during the 1000th cycle discharge process, is the amount of electricity released during the first cycle discharge process, and The unit is mAh;

[0082] The battery assembly process is as follows:

[0083] (1) Commercial LiCoO2 cathode material (manufacturer Ningbo Rongbai 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, coated on aluminum foil (surface loading 12 mg / cm²), and cut into 14 mm diameter discs A after drying to serve as the battery’s positive electrode.

[0084] (2) Graphite negative electrode material (BTR S360), conductive carbon black (Timcal Super C65), and PVDF binder (Solvay 5130) were mixed in a mass ratio of 96:2:2, coated on copper foil (surface loading 8 mg / cm²), and cut into discs B with a diameter of 15 mm after drying to serve as the negative electrode of the battery;

[0085] (3) Punch the sample into a disc C with a diameter of 16 mm;

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

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

[0088] Whether the coating is broken after the microneedle puncture (anti-lithium dendrite puncture) test: The microneedle puncture test instrument uses a nanoindenter (Bruker Hysitron TI980), the needle tip uses a diamond cone (radius 1μm, angle 60°), the load is 10mN, and the speed is 0.5mm / s; after the microneedle puncture test, the coating is observed by SEM to see if there is any cracking.

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

[0090] (1) Add 20 g glucose, 5 g peptone (Oxoid, LP0037), 5 g yeast extract (BD Biosciences, 212750), 1.5 g citric acid, and 2.7 g disodium hydrogen phosphate to 900 mL of distilled water, followed by magnetic stirring at 500 rpm for 30 min.

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

[0092] (3) Adjust the volume to 1 L, dispense into conical flasks (200 mL per bottle), and sterilize at 121°C for 20 min;

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

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

[0095] (6) After 7 days of static culture at 30°C, the fermentation broth was obtained. During this period, a pH automatic titration system (Metrohm 905 Titrando) was used to automatically add 0.1 M NaOH aqueous solution to maintain the pH value at 5.0 ± 0.2.

[0096] Example 1

[0097] A method for preparing a dynamic self-repairing degradation-resistant composite current collector BOPET film, the specific steps 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 (the water used in the present invention is deionized water);

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

[0105] Polyoxyethylene ether: The manufacturer is Dow Chemical Company, the model is Polyox™ WSR-N80;

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

[0107] PEDOT:PSS aqueous solution: Manufacturer: Heraeus Holding AG, model: Clevios™ PH 1000, solid content: 1.2 wt%;

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

[0109] Sodium lauryl 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 to obtain a bacterial cellulose gel; then, the lipids and proteins in the bacterial cellulose gel were removed; finally, after washing with pure water until neutral, the BCNF suspension with a solid content of 2 wt% was obtained by ultrasonication;

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

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

[0114] (c) The vanillin solution was added dropwise to the BCNF suspension. After stirring for 10 min, adipic acid dihydrazide solution was added. The mixture was reacted at 58°C for 3.5 h, and the pH was adjusted to 5.0 ± 0.2.

[0115] (d) adding the ZIF-8 precursor solution to the reaction system of step (c), stirring at room temperature for 24 h, and then centrifuging and washing to obtain a BCNF-DH / ZIF-8 complex;

[0116] The prepared BCNF-DH / ZIF-8 composite consists of BCNF, a compound containing an acylhydrazone bond, and a ZIF-8 type MOF. The compound containing an acylhydrazone bond is connected to the BCNF via an ether bond, while the ZIF-8 type MOF is connected to the BCNF via coordination bonds and hydrogen bonds. The BCNF-DH / ZIF-8 composite contains 60wt% BCNF and 30wt% ZIF-8 type MOF.

[0117] (3) Prepare the bottom coating liquid and the surface coating liquid;

[0118] The bottom coating liquid is composed of BCNF-DH / ZIF-8 complex, polyoxyethylene ether and water, wherein the content of BCNF-DH / ZIF-8 complex is 15wt%, and the content of polyoxyethylene ether is 0.5wt%.

[0119] The surface coating solution consists of a PEDOT:PSS aqueous solution, a BCNF-DH / ZIF-8 composite, an EVA emulsion, sodium lauryl sulfate, and water. The content of the BCNF-DH / ZIF-8 composite is 10 wt%, and the content of sodium lauryl sulfate is 0.3 wt%.

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

[0121] (A) Using a micro-gravure coater, the primer coating liquid was 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 intertwined to form a dense network with a porosity of 0.8%;

[0123] (B) Using a slot extrusion coater, the topcoat liquid was applied to the dense barrier layer at a coating gap of 95 μm and a coating speed of 4.5 m / min. The layer was then dried at 78°C for 28 seconds and then at 118°C for 58 seconds to form a conductive reinforcement layer with a thickness of 140 nm and a porosity of 40%.

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

[0125] (C) sequentially performing electron beam irradiation treatment, longitudinal stretching, transverse stretching and shaping, and surface corona treatment to obtain a dynamic self-repairing and degradation-resistant composite current collector BOPET film;

[0126] Among them, the dose of electron beam irradiation treatment is 48kGy and the energy is 2MeV; the process parameters of longitudinal stretching are: preheating temperature 88℃, preheating time 9s, stretching ratio 3 times, stretching speed 9m / min; the process parameters of transverse stretching and shaping are: preheating temperature 108℃, preheating time 14s, stretching ratio 3.3 times, shaping temperature 218℃, shaping time 9s; the process parameters of surface corona treatment are: corona power 4.8kW, corona frequency 20kHz, treatment speed 19m / min.

[0127] The final dynamic self-healing and degradation-resistant composite current collector BOPET film has a square resistance of 0.48Ω / sq, a self-healing efficiency of 96% for a 5μm crack in the electrolyte for 24 hours, and a bonding strength between the BOPET base film and the coating of 3.2N / cm; the weight loss rate of the dynamic self-healing and degradation-resistant composite current collector BOPET film after aging in an electrolyte at 85°C for 1000 hours is 0.32wt%, the tensile strength retention rate after aging in an electrolyte at 85°C for 1000 hours is 96%, the capacity retention rate after 1000 cycles at a charge and discharge rate of 1C is 91%, the square resistance change rate after dynamic bending test is 4.2%, and the square resistance change rate after aging in an electrolyte at 85°C for 500 hours is 8.5%; 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 film was not broken after the microneedle puncture test.

[0128] Example 2

[0129] A method for preparing a dynamic self-repairing degradation-resistant composite current collector BOPET film, the specific steps 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 the concentration of zinc nitrate being 0.1 mol / L and the concentration of 2-methylimidazole being 0.4 mol / L;

[0137] Polyoxyethylene ether: The manufacturer is Dow Chemical Company, the model is Polyox™ WSR-N80;

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

[0139] PEDOT:PSS aqueous solution: Manufacturer: Heraeus Holding AG, model: Clevios™ PH 1000, solid content: 1.2 wt%;

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

[0141] Sodium lauryl 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 to obtain a bacterial cellulose gel; then, the lipids and proteins in the bacterial cellulose gel were removed; finally, after washing with pure water until neutral, the BCNF suspension with a solid content of 2 wt% was obtained by ultrasonication;

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

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

[0146] (c) The vanillin solution was added dropwise to the BCNF suspension. After stirring for 10 min, adipic acid dihydrazide solution was added. The mixture was reacted at 60°C for 4 h, and the pH was adjusted to 5.0 ± 0.2.

[0147] (d) adding the ZIF-8 precursor solution to the reaction system of step (c), stirring at room temperature for 24 h, and then centrifuging and washing to obtain a BCNF-DH / ZIF-8 complex;

[0148] The prepared BCNF-DH / ZIF-8 composite is composed of BCNF, the compound containing acylhydrazone bond and ZIF-8 type MOF, the compound containing acylhydrazone bond is connected with the BCNF through ether bond, and the ZIF-8 type MOF is connected with the BCNF through coordination bond and hydrogen bond; in the BCNF-DH / ZIF-8 composite, the content of the BCNF is 65wt%, and the content of the ZIF-8 type MOF is 25wt%;

[0149] (3) preparing the bottom coating liquid and the surface coating liquid;

[0150] The bottom coating liquid is composed of the BCNF-DH / ZIF-8 composite, polyoxyethylene ether and water, the content of the BCNF-DH / ZIF-8 composite is 18wt%, and the content of the polyoxyethylene ether is 0.8wt%;

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

[0152] (4) preparing the dynamic self-repairing and degradation-resistant composite current collector BOPET film;

[0153] (A) using a micro-gravure coater, 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 composite interweaves to form a dense network with a porosity of 0.6%;

[0155] (B) using a slot extrusion coater, the surface coating liquid is coated on the dense barrier layer at a coating gap of 100μm and a coating speed of 5m / min, and then dried at 80℃ for 30s and at 120℃ for 60s to form a conductive enhancement layer with a thickness of 150nm and a porosity of 45%;

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

[0157] (C) sequentially performing electron beam irradiation treatment, longitudinal stretching, transverse stretching and setting, surface corona treatment, and thus the dynamic self-repairing and degradation-resistant composite current collector BOPET film is obtained;

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

[0159] The final dynamic self-healing and degradation-resistant composite current collector BOPET film has a square resistance of 0.35Ω / sq, a self-healing efficiency of 98% for a 5μm crack in the electrolyte within 24 hours, and a bonding strength between the BOPET base film and the coating of 3.8N / cm; the weight loss rate of the dynamic self-healing and degradation-resistant composite current collector BOPET film after aging in an electrolyte at 85°C for 1000 hours is 0.25wt%, the tensile strength retention rate after aging in an electrolyte at 85°C for 1000 hours is 98%, the capacity retention rate after 1000 cycles at a charge and discharge rate of 1C is 94%, the square resistance change rate after dynamic bending test is 3%, and the square resistance change rate after aging in an electrolyte at 85°C for 500 hours is 5.2%; 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 film was not broken after the microneedle puncture test.

[0160] Example 3

[0161] A method for preparing a dynamic self-repairing degradation-resistant composite current collector BOPET film, the specific steps 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 the concentration of zinc nitrate being 0.1 mol / L and the concentration of 2-methylimidazole being 0.4 mol / L;

[0169] Polyoxyethylene ether: The manufacturer is Dow Chemical Company, the model is Polyox™ WSR-N80;

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

[0171] PEDOT:PSS aqueous solution: Manufacturer: Heraeus Holding AG, model: Clevios™ PH 1000, solid content: 1.2 wt%;

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

[0173] Sodium lauryl 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 to obtain a bacterial cellulose gel; then, the lipids and proteins in the bacterial cellulose gel were removed; finally, after washing with pure water until neutral, the BCNF suspension with a solid content of 2 wt% was obtained by ultrasonication;

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

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

[0178] (c) The vanillin solution was added dropwise to the BCNF suspension. After stirring for 10 min, adipic acid dihydrazide solution was added. The mixture was reacted at 62°C for 4.5 h, and the pH was adjusted to 5.0 ± 0.2.

[0179] (d) adding the ZIF-8 precursor solution to the reaction system of step (c), stirring at room temperature for 24 h, and then centrifuging and washing to obtain a BCNF-DH / ZIF-8 complex;

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

[0181] (3) Prepare the bottom coating liquid and the surface coating liquid;

[0182] The bottom coating liquid is composed of BCNF-DH / ZIF-8 complex, polyoxyethylene ether and water, with the content of BCNF-DH / ZIF-8 complex being 22wt% and the content of polyoxyethylene ether being 1.2wt%;

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

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

[0185] (A) Using a micro-gravure coater, the primer coating liquid was 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 intertwined to form a dense network with a porosity of 0.9%;

[0187] (B) The top coating liquid was applied to the dense barrier layer using a slot extrusion coater with a coating gap of 105 μm and a coating speed of 5.5 m / min. The layer was then dried at 82°C for 32 seconds and then at 122°C for 62 seconds 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, the content of PEDOT:PSS is 50wt%, and the mass ratio of PEDOT:PSS to EVA is 50:50;

[0189] (C) sequentially performing electron beam irradiation treatment, longitudinal stretching, transverse stretching and shaping, and surface corona treatment to obtain a dynamic self-repairing and degradation-resistant composite current collector BOPET film;

[0190] Among them, the dose of electron beam irradiation treatment is 52kGy and the energy is 2MeV; the process parameters of longitudinal stretching are: preheating temperature 92°C, preheating time 11s, stretching ratio 3.5 times, stretching speed 11m / min; the process parameters of transverse stretching and shaping are: preheating temperature 112°C, preheating time 16s, stretching ratio 3.7 times, shaping temperature 222°C, shaping time 11s; the process parameters of surface corona treatment are: corona power 5.2kW, corona frequency 20kHz, treatment speed 21m / min.

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

[0192] Example 4

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

[0194] (1) Preparation of raw materials;

[0195] Fermentation liquor of acidovorax temperanus;

[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, the concentration of zinc nitrate is 0.1 mol / L, and the concentration of 2-methylimidazole is 0.4 mol / L;

[0201] Polyoxyethylene ether: the manufacturer is Dow Chemical Company, and the model is Polyox™ WSR-N80;

[0202] BOPET base film: the thickness is 9 μm, and the tensile strength is 215 MPa;

[0203] PEDOT:PSS aqueous solution: the manufacturer is Heidelberger Holding Group, the model is Clevios™ PH 1000, and the solid content is 1.2 wt%;

[0204] EVA emulsion: the manufacturer is DuPont Company, the model is Elvax® 3165, and the solid content is 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 to obtain a bacterial cellulose gel; then, the lipids and proteins in the bacterial cellulose gel were removed; finally, after washing with pure water until neutral, the BCNF suspension with a solid content of 2 wt% was obtained by ultrasonication;

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

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

[0210] (c) The vanillin solution was added dropwise to the BCNF suspension. After stirring for 10 min, adipic acid dihydrazide solution was added. The mixture was reacted at 61°C for 3.8 h, and the pH was adjusted to 5.0 ± 0.2.

[0211] (d) adding the ZIF-8 precursor solution to the reaction system of step (c), stirring at room temperature for 24 h, and then centrifuging and washing to obtain a BCNF-DH / ZIF-8 complex;

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

[0213] (3) Prepare the bottom coating liquid and the surface coating liquid;

[0214] The bottom coating liquid is composed of BCNF-DH / ZIF-8 complex, polyoxyethylene ether and water, wherein the content of BCNF-DH / ZIF-8 complex is 20wt% and the content of polyoxyethylene ether is 1wt%;

[0215] The surface coating solution consists of a PEDOT:PSS aqueous solution, a BCNF-DH / ZIF-8 composite, an EVA emulsion, sodium lauryl sulfate, and water. The content of the BCNF-DH / ZIF-8 composite is 12 wt%, and the content of sodium lauryl sulfate is 0.6 wt%.

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

[0217] (A) Using a micro-gravure coater, the primer coating liquid was 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 intertwined to form a dense network with a porosity of 0.5%;

[0219] (B) The top coating liquid was applied to the dense barrier layer using a slot extrusion coater with a coating gap of 98 μm and a coating speed of 4.8 m / min. The layer was then dried at 79°C for 29 seconds and then at 119°C for 59 seconds 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, the content of PEDOT:PSS is 42wt%, and the mass ratio of PEDOT:PSS to EVA is 48:52;

[0221] (C) sequentially performing electron beam irradiation treatment, longitudinal stretching, transverse stretching and shaping, and surface corona treatment to obtain a dynamic self-repairing and degradation-resistant composite current collector BOPET film;

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

[0223] The final dynamic self-healing and degradation-resistant composite current collector BOPET film has a square resistance of 0.28Ω / sq, a self-healing efficiency of 99% for a 5μm crack in the electrolyte within 24 hours, and a bonding strength of 4.1N / cm between the BOPET base film and the coating. The weight loss rate of the dynamic self-healing and degradation-resistant composite current collector BOPET film after aging in an electrolyte at 85°C for 1000 hours is 0.18wt%, the tensile strength retention rate after aging in an electrolyte at 85°C for 1000 hours is 99%, the capacity retention rate after 1000 cycles at a charge and discharge rate of 1C is 96%, the square resistance change rate after dynamic bending test is 2.5%, and the square resistance change rate after aging in an electrolyte at 85°C for 500 hours is 4%. 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 film was not broken after the microneedle puncture test.

[0224] Example 5

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

[0226] The final dynamic self-healing and degradation-resistant composite current collector BOPET film has a square resistance of 0.82Ω / sq, a self-healing efficiency of 68% for a 5μm crack in the electrolyte for 24 hours, and a bonding strength of 3.0N / cm between the BOPET base film and the coating. The weight loss rate of the dynamic self-healing and degradation-resistant composite current collector BOPET film after aging in an electrolyte at 85°C for 1000 hours is 0.50wt%, the tensile strength retention rate after aging in an electrolyte at 85°C for 1000 hours is 93%, the capacity retention rate after 1000 cycles at a charge and discharge rate of 1C is 85%, the square resistance change rate after dynamic bending test is 18%, and the square resistance change rate after aging in an electrolyte at 85°C for 500 hours is 32%. 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 film is broken after the microneedle puncture test.

[0227] Compared with Example 1, the square resistance change rate of the dynamic self-healing and degradation-resistant composite current collector BOPET film after the dynamic bending test and the square resistance change rate after aging in an electrolyte at 85°C for 500 hours increased. This is because: on the one hand, the lack of the ZIF-8 type MOF (pore diameter 3.4Å) to block EC / DMC solvent molecules (size > 4Å), PEDOT:PSS is prone to swelling in the electrolyte and induces phase separation, destroying the continuous conductive network; on the other hand, the lack of the ability of compounds containing acylhydrazone bonds to quickly repair microcracks, the cracks generated during dynamic bending and aging cannot be closed in time, resulting in continuous infiltration of the electrolyte, aggravating the degradation of PEDOT:PSS, and ultimately significantly increasing the square resistance change rate.

[0228] Example 6

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

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

[0231] Compared with Example 1, the sheet resistance of the dynamic self-healing and degradation-resistant composite current collector BOPET film in Example 6 increases, and the capacity retention rate after 1000 cycles at a 1C charge-discharge rate decreases; after the microneedle puncture experiment, the coating is not broken, but the surface indentation depth reaches 600 nm (only 200 nm in Example 1). This is because the excessive EVA leads to a decrease in material rigidity, although no cracks are observed, but the structural deformation is irreversible, which easily causes local current aggregation during battery cycling, resulting in a decrease in capacity retention rate. At the same time, when the mass fraction of PEDOT:PSS in the conductive enhancement layer is too low, the conductivity of the composite current collector film cannot be effectively maintained (the conductive network is excessively diluted), and it is also difficult to effectively buffer stress through synergistic deformation when facing microneedle puncture.

[0232] Example 7

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

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

[0235] As can be seen from Comparative Example 1 and Example 7, when the knife coating is used instead of the micro-gravure coating, the BCNF in the BCNF-DH / ZIF-8 composite cannot be oriented along the coating direction (MD) due to the lack of shear force generated by the anilox roll (line number ≥ 200 LPI), and the BCNF cannot guide the BOPET molecular chain to be ordered along the MD direction as the "nucleation site", resulting in a decrease in the crystallinity of the base film and a decrease in the tensile strength retention rate to 91%.

[0236] Comparative Example 1

[0237] A method for preparing a composite current collector BOPET film, which is different from Example 1 only in that the ultrasonic crushing in step (a) is not performed, which makes the average aspect ratio of the BCNF in the BCNF suspension be 19.

[0238] The weight loss rate of the finally prepared composite current collector BOPET film after aging in an electrolyte at 85℃ for 1000 h is 1.8 wt%.

[0239] Compared with Example 1, the weight loss rate of the composite current collector BOPET film after aging in an electrolyte at 85℃ for 1000 h in Comparative Example 1 is obviously increased, because the ultrasonic crushing in step (a) is not performed in Comparative Example 1, which makes the average aspect ratio of the BCNF be only 19, and the BCNF-DH / ZIF-8 composite does not form a dense network (porosity is 12%) by interweaving with each other, and a large number of connected penetration channels are formed, through which the catalytic molecules in the electrolyte can quickly reach the surface of the BOPET base film and react with the ester bond of the base film.

[0240] Comparative Example 2

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

[0242] The self-healing efficiency of the 5μm crack of the composite current collector BOPET film finally prepared in the electrolyte for 24 hours is 35%.

[0243] Compared with Example 1, the self-repair efficiency of the 5μm crack of the composite current collector BOPET film in the electrolyte for 24 hours is significantly reduced. This is because the acidic catalytic conditions in Comparative Example 2 are missing, and the condensation reaction efficiency of vanillin aldehyde group and adipic acid dihydrazide group is greatly reduced. The trace acylhydrazone bonds generated cannot be stably grafted to BCNF, resulting in the lack of dynamic acylhydrazone bonds on the BCNF surface that can trigger self-repair, and the cracks cannot be closed in time.

[0244] Comparative Example 3

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

[0246] The self-repair efficiency of the 5μm crack of the composite current collector BOPET film finally prepared in the electrolyte is 55% after 24 hours; the weight loss rate of the composite current collector BOPET film after aging in the electrolyte at 85°C for 1000 hours is 1.5wt%.

[0247] Compared with Comparative Example 3 and Example 1, the self-repair efficiency of the 5μm crack of the composite current collector BOPET membrane in the electrolyte for 24 hours is significantly reduced, and the weight loss rate of the composite current collector BOPET membrane after aging in the electrolyte at 85°C for 1000 hours is 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 path not being effectively blocked and the electrolyte erosion of the base membrane 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 dynamic bond repair, and the repair efficiency at the cracks is reduced.

Claims

1. A dynamic self-repairing and degradation-resistant composite current collector BOPET film, comprising a BOPET base film and a coating located on the surface thereof, characterized in that: The coating includes a dense barrier layer adjacent to a BOPET base film; The dense barrier layer includes BCNF-DH / ZIF-8 complex; The BCNF-DH / ZIF-8 composites intertwined to form a dense network with a porosity of ≤1%; The BCNF-DH / ZIF-8 complex consists of BCNF, a compound containing an acylhydrazone bond, and a ZIF-8 type MOF. The compound containing an acylhydrazone bond is connected to BCNF through an ether bond, and the ZIF-8 type MOF is connected to BCNF through coordination bonds and hydrogen bonds.

2. A dynamic self-repairing degradation-resistant composite current collector BOPET film according to claim 1, characterized in that: The thickness of the dense barrier layer is 45-55 nm, and the surface roughness Ra is less than or equal to 5 nm.

3. The dynamic self-repairing degradation-resistant composite current collector BOPET film according to claim 1, characterized in that: The average aspect ratio of BCNF is >100.

4. The dynamic self-repairing and degradation-resistant composite current collector BOPET film according to claim 1, characterized in that: In the BCNF-DH / ZIF-8 composite, the content of BCNF is 60-75wt%, and the content of ZIF-8 type MOF is 20-30wt%.

5. The dynamic self-repairing and degradation-resistant composite current collector BOPET film according to claim 1, characterized in that: The preparation steps of BCNF-DH / ZIF-8 complex are as follows: (a) First, the fermentation broth of Acetobacter xylinum was centrifuged to remove the bacteria and obtain a bacterial cellulose gel; then, the lipids and proteins in the bacterial cellulose gel were removed; finally, the BCNF suspension was obtained after washing with pure water until neutral, and then ultrasonically disrupted; (b) dissolving vanillin in a mixed solvent of ethanol and water to obtain a vanillin solution; and dissolving adipic acid dihydrazide in water to obtain an adipic acid dihydrazide solution; (c) Add the vanillin solution dropwise to the BCNF suspension, stir, add the adipic acid dihydrazide solution, react at 58-62°C for 3.5-4.5 hours, and then adjust the pH to 5.0 ± 0.2; (d) adding a ZIF-8 precursor solution to the reaction system of step (c), stirring, and centrifuging to wash to obtain a BCNF-DH / ZIF-8 complex, wherein the ZIF-8 precursor solution consists of zinc nitrate, 2-methylimidazole, and methanol.

6. The dynamic self-repairing degradation-resistant composite current collector BOPET film 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 includes PEDOT:PSS, EVA, and BCNF-DH / ZIF-8 composite; PEDOT:PSS forms a continuous conductive network.

7. The dynamic self-repairing and degradation-resistant composite current collector BOPET film according to claim 6, characterized in that: The content of PEDOT:PSS in the conductive reinforcement layer is 40-50wt%, and the mass ratio of PEDOT:PSS to EVA is 40-50:50-60.

8. The dynamic self-repairing and degradation-resistant composite current collector BOPET film according to claim 6, characterized in that: The thickness of the conductive enhancement layer is 140-160 nm.

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

10. The dynamic self-repairing and degradation-resistant composite current collector BOPET film according to any one of claims 1 to 9, characterized in that: The square resistance of the dynamic self-healing and degradation-resistant composite current collector BOPET film is ≤1.8Ω / sq, the self-healing efficiency of a 5μm crack in the electrolyte for 24 hours is 68-98%, and the bonding strength between the BOPET base film and the coating is 2.8-4.1N / cm; the weight loss rate of the dynamic self-healing and degradation-resistant composite current collector BOPET film after aging in an electrolyte at 85°C for 1000 hours is 0.18-0.65wt%, the tensile strength retention rate after aging in an electrolyte at 85°C for 1000 hours is 91-99%, and the capacity retention rate after 1000 cycles at a charge and discharge rate of 1C is 85-96%.

11. A method for preparing the dynamic self-repairing degradation-resistant composite current collector BOPET film according to any one of claims 1 to 10, characterized in that: The following steps are involved: (A) A base coating solution containing the BCNF-DH / ZIF-8 complex was coated on a BOPET base film using a micro-gravure coater and then dried to form a dense barrier layer. (B) A surface coating solution containing PEDOT:PSS, EVA, and BCNF-DH / ZIF-8 composite is coated on the dense barrier layer using a slot extrusion coater and then dried to form a conductive reinforcement layer; (C) Electron beam irradiation treatment, longitudinal stretching, transverse stretching and shaping, and surface corona treatment are performed in sequence to obtain a dynamic self-repairing and degradation-resistant composite current collector BOPET film.

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