Diaphragm and preparation method and application thereof

Abstract

The invention provides a diaphragm and a preparation method and application thereof, the diaphragm comprises a base membrane and a functional coating, and the functional coating is located on the surface of at least one side of the base membrane; the functional coating comprises a modified first polymer and a second polymer; the modified first polymer comprises boric acid ester bonds and hydroxyl groups; the second polymer comprises at least one of polyvinylidene fluoride (PVDF) and a copolymer thereof, polyoxyethylene (PEO), polyurethane and polyvinyl butyral (PVB). According to the diaphragm provided by the invention, through a hydrogen bond and multiple bonding mechanism, rapid repair of microcracks on the surface of the diaphragm can be realized, and the diaphragm has excellent self-healing performance, mechanical stability, thermal stability and electrolyte infiltration performance, so that the electrochemical performance of a battery can be effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery separators and lithium battery technology, specifically relating to a separator, its preparation method, and its application. Background Technology

[0002] As an important electrochemical energy storage device, the performance and safety of lithium-ion batteries are highly dependent on the stability of their internal components. The separator, a key component of the battery, is primarily responsible for isolating the positive and negative electrodes to prevent short circuits, while allowing lithium ions to pass freely. To improve the wettability, thermal stability, and interfacial compatibility with the electrodes, functional coatings are often applied to the surface of the base film, such as polyolefin films.

[0003] Traditional coating technologies are mainly divided into two categories: single polymer coatings (such as polyvinylidene fluoride PVDF) and inorganic particle-reinforced composite coatings (such as alumina Al2O3, boehmite, and other inorganic particles as the main functional components). However, these traditional solutions have inherent defects: the physical adhesion or weak van der Waals forces between polymers such as PVDF and the base film result in insufficient adhesion, making the coating prone to delamination and peeling under long-term charge-discharge cycles or electrolyte immersion; while inorganic filler particles, due to the lack of an effective fixation mechanism, are easily detached during electrolyte scouring or volume changes, not only losing their original function but also increasing interfacial impedance, thus impairing the battery's rate performance and cycle life.

[0004] To overcome the limitations of static coatings, self-healing membrane technology with dynamic repair capabilities has emerged. However, while self-healing membrane technology shows potential in repairing battery coating cracks and improving cycle stability, it still has limitations, mainly in the following three aspects: (1) Insufficient efficiency and response speed of self-healing mechanisms: Existing technologies rely heavily on non-covalent dynamic bonding such as hydrogen bonds and ionic bonds. Although these bonding methods are reversible, their bond energies are low and their cohesive strength is limited. This results in their self-healing ability being mainly targeted at micron-level cracks, with limited effectiveness in repairing larger cracks or deep mechanical damage that may occur during cycling. The recovery rate of the mechanical properties and ionic conductivity of the coating after self-healing often falls short of ideal levels. More importantly, the self-healing process based on hydrogen bonds usually requires external energy stimulation (such as heating or specific wavelength light) to accelerate molecular chain movement and recombination, and the repair response time is long (several hours to several days), which cannot meet the demand for immediate and active repair in high-power batteries under rapid charge and discharge scenarios.

[0005] (2) Poor chemical and interfacial stability of the material system: Some organic materials introduced to achieve self-healing function (such as acrylate polymers containing a large number of ester groups or ether bonds) are prone to swelling, plasticization or even chemical degradation after long-term immersion in highly polar carbonate electrolytes, which leads to the gradual decline or even failure of the self-healing function with the increase of cycle number. In addition, inorganic nanoparticle fillers added to enhance mechanical properties or thermal stability are prone to detachment under interfacial stress if they fail to form a stable bond with the polymer matrix. This not only causes uneven coating function, but the detached particles may also migrate to the electrode surface, aggravating interfacial side reactions and causing the battery internal resistance to increase continuously.

[0006] (3) Complex preparation process and high production cost: Many high-performance self-healing coatings rely on precise multi-component compounding (such as A / B two-component reaction system), harsh synthesis conditions (such as anhydrous and oxygen-free), or complex post-coating treatment processes (such as UV curing and thermal crosslinking). The preparation process requires precise control of initiator dosage, reaction temperature and time, which increases the complexity of the process and uncontrollable factors, making it difficult to achieve large-scale, continuous and stable production. At the same time, the high cost of some key raw materials (such as specific dynamic crosslinking agents, high-strength polymers such as aramid) and advanced coating equipment (such as electrospinning equipment) significantly increases the final cost of the membrane, restricting its commercial application prospects. Summary of the Invention

[0007] To address the problems and shortcomings of existing technologies, this invention provides a separator, its preparation method, and its application. The separator provided by this invention can achieve rapid repair of microcracks on the separator surface through hydrogen bonding and multiple bonding mechanisms, and has excellent self-healing properties, mechanical stability, thermal stability, and electrolyte wetting properties, thus effectively improving the electrochemical performance of the battery.

[0008] According to a first aspect of the present invention, a diaphragm is provided, comprising a base membrane and a functional coating, the functional coating being located on at least one side of the surface of the base membrane; the functional coating comprising a modified first polymer and a second polymer; the modified first polymer comprising borate ester bonds and hydroxyl groups; the second polymer comprising at least one selected from polyvinylidene fluoride (PVDF) and its copolymers, polyethylene oxide (PEO), polyurethane, and polyvinyl butyral (PVB).

[0009] Preferably, the mass percentage of element B in the modified first polymer is 0.1-0.55%; and / or, the mass percentage of element B in the functional coating is 0.012-0.46%.

[0010] Preferably, the modified first polymer comprises a main chain structure based on the first polymer; the first polymer contains a 1,2-diol or 1,3-diol structure; preferably, the first polymer comprises at least one of polyvinyl alcohol (PVA) and its derivatives, polysaccharides and their derivatives; preferably, the first polymer is polyvinyl alcohol.

[0011] Preferably, the number average molecular weight of the first polymer is 2000-4000 g / mol.

[0012] Preferably, the functional coating further includes inorganic particles, which include at least one of Al2O3, MgO, TiO2, ZrO2, AlOOH (boehmite), Al(OH)3, BN, and AlN.

[0013] Preferably, the surface of the inorganic particles contains at least one of hydroxyl and carboxyl groups.

[0014] Preferably, the particle size of the inorganic particles is 0.1-0.5 μm. Preferably, the total thickness of the diaphragm is 10-18 μm. Preferably, the total thickness of the diaphragm is 10-12 μm.

[0015] Preferably, the thickness of the functional coating applied to one side of the base film is 6-13 μm.

[0016] Preferably, the functional coating is a self-healing functional coating.

[0017] Preferably, the base film is made of at least one of PE and PP.

[0018] According to a second aspect of the present invention, a method for preparing any of the above-mentioned diaphragms is provided, comprising the following steps: S1. Completely dissolving a first polymer in a first solvent, then adding a boric acid compound or a borate compound to the solvent at 60-80°C, stirring and reacting for 1-2 h to obtain a first mixed system, the first mixed system containing a modified first polymer; S2. Completely dissolving a second polymer in a second solvent to prepare a second polymer solution, adding the second polymer solution to the first mixed system, stirring and reacting for 2-3 h at 60-80°C to obtain a second mixed system; S3. Adding inorganic particulate powder to the second mixed system, mixing and stirring evenly to obtain a slurry; S4. Coating the slurry onto a base membrane, drying, to obtain a diaphragm.

[0019] Preferably, in step S1, the added compound is a borate compound. Preferably, the borate compound is a tetraborate compound. Preferably, the tetraborate compound is borax, i.e., Na₂B₄O₇·10H₂O or Na₂B₄O₇.

[0020] Preferably, in step S1, the mass of the boric acid compound or borate compound is 0.5% or more but less than 5% of the mass of the first polymer; and / or, the first solvent includes at least one of water, glycerol, phenol, and dimethyl sulfoxide. Preferably, the mass of the boric acid compound or borate compound is 1-3% of the mass of the first polymer. More preferably, the mass of the boric acid compound or borate compound is 1-2% of the mass of the first polymer.

[0021] Preferably, in step S1, the specific operation of completely dissolving the first polymer in the first solvent is to heat the first solvent to 60-80°C, add the first polymer, and stir until completely dissolved.

[0022] Preferably, in step S1, the modified first polymer is obtained by reacting the first polymer with a boric acid compound or a borate compound.

[0023] Preferably, in step S2, the mass ratio of the first polymer to the second polymer is (1-3):(7-9); and / or, the second solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0024] Preferably, in step S3, the mass of the inorganic particles is 10-30% of the total mass of the first polymer and the second polymer.

[0025] Preferably, in step S4, the drying process is divided into two stages; the first stage is processed at 40-50°C for 2-4 minutes; the second stage is processed at 80-90°C for 1-2 hours. The first stage is pre-drying, and the second stage is curing.

[0026] Preferably, in step S4, after the drying process, vacuum drying is also required at a pressure of -0.05 to 0.2 MPa. This vacuum drying step is for removing residual solvent.

[0027] According to a third aspect of the present invention, a battery is provided, comprising any of the above-described separators, or a separator prepared by any of the above-described preparation methods.

[0028] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: This invention introduces a functional coating with a specific structure into a membrane. This functional coating comprises a modified first polymer containing boronic acid ester bonds and abundant hydroxyl groups. The modified first polymer is composited with a second polymer to construct a multi-layered bonding network formed by the synergistic interaction of hydrogen bonds and boronic acid ester bonds. Specifically, some of the hydroxyl groups in the first polymer react with boric acid compounds or borate compounds to form boronic acid ester bonds, while others react with the second polymer to form hydrogen bonds. That is, the resulting modified first polymer molecular chain contains boronic acid ester bonds and can form hydrogen bonds with the second polymer.

[0029] Among these, boronic acid ester bonds provide a stable covalent cross-linked network for the coating, significantly improving its structural strength and durability. Simultaneously, based on the dynamic characteristics that boronic acid ester bonds may exhibit in the electrolyte environment, their synergy with the abundant hydrogen bonds in the system endows the coating with potential self-healing capabilities, enabling it to autonomously recover to a certain extent when micro-damage occurs, thereby further improving the reliability of the separator during long-term cycling. The synergistic effect of the aforementioned multiple bonding mechanisms of hydrogen bonds and boronic acid ester bonds allows the coating's self-healing process to be triggered and carried out primarily by the internal environmental conditions of the battery during operation (such as the electrolyte environment and operating temperature), significantly reducing dependence on strong external stimuli such as additional heating and light exposure, thus better aligning with actual battery usage scenarios.

[0030] Furthermore, the modified first polymer three-dimensional network formed by borate ester bonds provides a stable framework for the entire coating, while the second polymer, which runs through it, is tightly bonded to it via hydrogen bonds, forming an interpenetrating network structure. This structure not only endows the coating with excellent mechanical stability, thermal stability, and electrolyte wetting properties, but also effectively fixes the dynamic repair units (hydrogen bonds and / or borate ester bonds) in three-dimensional space, which can suppress the degradation of self-healing function caused by material swelling or migration. At the same time, this network can firmly anchor inorganic fillers, preventing them from falling off and ensuring that the composition and function of the coating remain uniform and intact even during repeated repair processes.

[0031] Therefore, by utilizing the rapid self-healing properties of the membrane surface coating, it is possible to promptly prevent interface deterioration and side reactions caused by the propagation of coating cracks, thus meeting the immediate protection requirements of the battery under dynamic operating conditions such as fast charging and discharging. This effectively improves various electrochemical performances of the battery, such as cycle performance. Moreover, the coating itself has higher mechanical stability, thermal stability, and strong wetting properties, which is also more conducive to further optimizing various performances of the battery. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the interpenetrating network structure formed by the modified first polymer generated from the reaction of borax and PVA and PVDF (second polymer) in Example 1.

[0033] Figure 2The graph shows (a) capacity and (b) capacity retention during 500 charge-discharge cycles of the battery in Example 1.

[0034] Figure 3 The comparison is before and after the diaphragm was damaged in Example 1; where (a) PVA:PVDF=1:9, (b) PVA:PVDF=2:8, (c) PVA:PVDF=3:7, (d) PVDF + inorganic filler (inorganic particles).

[0035] Figure 4 The graph shows (a) capacity and (b) capacity retention during 500 charge-discharge cycles of the battery in Example 2.

[0036] Figure 5 The comparison is shown before and after the diaphragm was damaged in Example 2; where (a) 1% borax, (b) 3% borax, (c) 5% borax, and (d) PVDF + inorganic filler.

[0037] Figure 6 The graph shows (a) capacity and (b) capacity retention during 500 charge-discharge cycles of the battery in Example 3.

[0038] Figure 7 The comparison is shown before and after the diaphragm was damaged in Example 3; where (a) S-0 (adhesive layer without inorganic particles), (b) S-10, (c) S-20, and (d) S-30.

[0039] Figure 8 The graph shows (a) capacity and (b) capacity retention during 500 charge-discharge cycles of the battery in Example 4.

[0040] Figure 9 The comparison is shown before and after the diaphragm was damaged in Example 4; where (a) D-0 (base membrane), (b) D-1, (c) D-3, and (d) D-5.

[0041] Figure 10 The infrared spectra of PVDF and PVA / PVDF in Example 4 are shown. Detailed Implementation

[0042] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0043] According to a first aspect of the present invention, a diaphragm is provided, comprising a base membrane and a functional coating, the functional coating being located on at least one side of the surface of the base membrane; the functional coating comprising a modified first polymer and a second polymer; the modified first polymer comprising borate ester bonds and hydroxyl groups; the second polymer comprising at least one selected from polyvinylidene fluoride (PVDF) and its copolymers, polyethylene oxide (PEO), polyurethane, and polyvinyl butyral (PVB).

[0044] The diaphragm provided by this invention comprises a modified first polymer with borate ester bonds and abundant hydroxyl groups in its functional coating. The modified first polymer is composited with a second polymer to construct a multi-layered bonding network formed by the synergistic interaction of hydrogen bonds and borate ester bonds. Specifically, some of the hydroxyl groups in the first polymer react with boric acid to form borate ester bonds, while others react with the second polymer to form hydrogen bonds. Therefore, the resulting modified first polymer molecular chain contains borate ester bonds and can form hydrogen bonds with the second polymer.

[0045] Among these, boronic acid ester bonds provide a stable covalent cross-linked network for the coating, significantly improving its structural strength and durability. Simultaneously, based on the dynamic characteristics that boronic acid ester bonds may exhibit in the electrolyte environment, their synergy with the abundant hydrogen bonds in the system endows the coating with potential self-healing capabilities, enabling it to autonomously recover to a certain extent when micro-damage occurs, thereby further improving the reliability of the separator during long-term cycling. The synergistic effect of the aforementioned multiple bonding mechanisms of hydrogen bonds and boronic acid ester bonds allows the coating's self-healing process to be triggered and carried out primarily by the internal environmental conditions of the battery during operation (such as the electrolyte environment and operating temperature), significantly reducing dependence on strong external stimuli such as additional heating and light exposure, thus better aligning with actual battery usage scenarios.

[0046] Furthermore, the modified first polymer forms a cross-linked network through borate ester bonds, which interpenetrates with the second polymer chain that runs through it via hydrogen bonds, forming a stable composite. This structure firmly fixes the dynamic repair active sites (borate ester bonds and hydrogen bonds) within a stable three-dimensional framework, inhibiting their deactivation due to material swelling and migration during long-term cycling or electrolyte immersion, thus ensuring the long-term effectiveness of the self-healing function. Moreover, this stable composite structure itself is also a highly effective binding network, significantly improving the coating's cohesion and adhesion to the base film, thereby helping to solve the problem of easy delamination in traditional coatings.

[0047] Furthermore, the hydroxyl groups retained in the modified first polymer endow the coating with durable and stable hydrophilicity, significantly improving the wettability of the separator to the electrolyte and helping to reduce the battery's internal resistance. The introduction of the second polymer provides the necessary mechanical strength and electrochemical inertness, and when used in combination with the modified first polymer, the coating maintains excellent overall durability while possessing dynamic repair properties.

[0048] Therefore, the separator provided by the present invention introduces a functional coating with excellent dynamic repair performance. This coating can not only actively, quickly and effectively repair cycle damage, but also simultaneously improve the adhesion, wettability and interface stability of the separator, providing a key separator solution for the development of advanced lithium batteries with long life and high safety.

[0049] Preferably, the mass percentage of element B in the modified first polymer is 0.1-0.55%. This range corresponds to the optimal reaction ratio between the boric acid compound crosslinking agent and the hydroxyl groups in the first polymer. Within this range, a complete and uniform boric acid ester crosslinking network can be formed, providing the necessary structural framework and mechanical strength for the coating. If the element B content is too low, there will be insufficient crosslinking points, resulting in a fragile network structure that cannot effectively improve the coating's adhesion and durability; if the content is too high, it may lead to over-crosslinking, affecting subsequent processing and lamination. Simultaneously, this moderate degree of crosslinking allows sufficient free hydroxyl groups to remain in the modified first polymer. These hydroxyl groups can not only form strong hydrogen bonds with the second polymer but also ensure good and lasting wettability of the coating to the electrolyte. And / or, the mass percentage of element B in the functional coating is 0.012-0.46%. Similarly, the mass percentage of element B in the functional coating is also within a certain range, which is more conducive to optimizing the overall performance of the functional coating and the diaphragm.

[0050] Preferably, the modified first polymer comprises a main chain structure based on the first polymer; the first polymer contains a 1,2-diol or 1,3-diol structure. Structures like 1,2-diol or 1,3-diol are ideal sites for the efficient and specific esterification reaction of boric acid compounds to form stable five- or six-membered cyclic borate esters, ensuring the efficiency and specificity of the modification reaction. This is a prerequisite for generating a robust three-dimensional covalent network sufficient to support the entire coating, and is beneficial for obtaining a stable coating framework structure.

[0051] Preferably, the first polymer comprises at least one of polyvinyl alcohol (PVA) and its derivatives, and polysaccharides and their derivatives. The preferred material types, such as PVA and its derivatives, and polysaccharides, are themselves polymers with good chemical stability. After crosslinking via borate ester bonds, the stability of its network structure is further enhanced, effectively resisting electrolyte swelling and degradation under long-term electrochemical conditions. This ensures the long-lasting effectiveness of the coating framework formed by this modified polymer and its dynamic repair potential throughout the battery's entire lifespan.

[0052] Preferably, the first polymer is polyvinyl alcohol.

[0053] Preferably, the number-average molecular weight of the first polymer is 2000-4000 g / mol. Molecular weight directly affects the length of the polymer chain and the distribution of reactive sites. Within this preferred range, the polymer chain is long enough to effectively support and space multiple crosslinking sites (hydroxyl groups), allowing the reaction with boric acid to form a spatially uniform three-dimensional network with a moderate crosslinking density. If the molecular weight is too low, the chain segments are too short, easily forming a brittle structure with localized over-crosslinking; if the molecular weight is too high, excessive chain entanglement may lead to decreased accessibility of reactive sites and an uneven network structure. This range effectively balances these two factors, providing a stable and flexible framework for the coating. Furthermore, within the aforementioned molecular weight range, the final modified polymer network possesses both good cohesive strength and a certain degree of chain segment flexibility. This ensures that the coating has sufficient mechanical strength to resist external force damage while avoiding excessive rigidity that could lead to excessive brittle cracks under volumetric stress during battery cycling. In addition, a suitable chain length facilitates effective stress dissipation and structural rearrangement during reversible breakage and recombination of dynamic bonds, thereby supporting and enhancing the coating's long-term dynamic self-healing capability.

[0054] Preferably, the functional coating further includes inorganic particles, including at least one selected from Al2O3, MgO, TiO2, ZrO2, AlOOH (boehmite), Al(OH)3, BN, and AlN. The introduction of these specific inorganic particles significantly enhances the coating's thermal stability, mechanical strength, and electrolyte affinity. Furthermore, it is noteworthy that because the molecular chains of the second polymer penetrate the modified first polymer to form an interpenetrating polymer network structure, this structure tightly encapsulates and anchors the inorganic particles, effectively "mechanically locking" them in place. This greatly reduces the risk of the inorganic particles detaching during charge-discharge cycles due to volume changes and electrolyte erosion, maintaining stable interfacial impedance.

[0055] Preferably, the surface of the inorganic particles contains at least one of hydroxyl and carboxyl groups. The presence of active groups such as hydroxyl and carboxyl groups on the surface of the inorganic particles enables them to form strong interactions such as hydrogen bonds with the hydroxyl groups of the modified first polymer. This allows the inorganic particles to be more firmly chemically anchored in the polymer interpenetrating network, effectively improving the problem of easy physical detachment of inorganic particles during cycling, ensuring the long-term uniformity and thermal stability of the coating structure, and enhancing the high durability of the functional coating.

[0056] Preferably, the inorganic particles have a particle size of 0.1~0.5μm. This particle size range ensures that the inorganic particles are highly uniformly dispersed in the polymer network, effectively preventing agglomeration, thereby optimizing the coating's pore structure and ensuring ionic conductivity. Simultaneously, particles of this size have a high specific surface area, enabling them to form a strong bond with the polymer network through surface functional groups, significantly improving their fixation and reinforcing effects, and maintaining excellent surface smoothness and structural density in thin-layer coatings.

[0057] Preferably, the total thickness of the diaphragm is 10-18 μm. More preferably, the total thickness of the diaphragm is 10-12 μm.

[0058] Preferably, the thickness of the functional coating applied to one side of the base film is 6-13 μm.

[0059] Preferably, the functional coating is a self-healing functional coating.

[0060] Preferably, the base film is made of at least one of PE and PP.

[0061] According to a second aspect of the present invention, a method for preparing any of the above-mentioned diaphragms is provided, comprising the following steps: S1. Completely dissolving a first polymer in a first solvent, then adding a boric acid compound to the solvent at 60-80°C, stirring and reacting for 1-2 h to obtain a first mixed system, the first mixed system containing a modified first polymer; S2. Completely dissolving a second polymer in a second solvent to prepare a second polymer solution, adding the second polymer solution to the first mixed system, stirring and reacting at 60-80°C for 2-3 h to obtain a second mixed system; S3. Adding inorganic particulate powder to the second mixed system, mixing and stirring evenly to obtain a slurry; S4. Coating the slurry onto a base membrane, drying to obtain a diaphragm. Firstly, the first polymer and boric acid compound are pre-reacted under mild conditions to preferentially form a three-dimensional network framework cross-linked by boric acid ester bonds; subsequently, the second polymer solution is introduced, and hydrogen bonds are formed and interpenetrated with molecular chains during continuous heating and stirring to construct a stable interpenetrating network structure; finally, inorganic particles are added to achieve uniform dispersion and fixation. The entire process is characterized by mild and controllable conditions, allowing for sufficient reaction of all components. It is also compatible with traditional coating processes, ensuring the reliable and efficient preparation of high-performance membranes.

[0062] Preferably, in step S1, the added compound is a borate compound. Preferably, the borate compound is a tetraborate compound. Preferably, the tetraborate compound is borax, i.e., Na₂B₄O₇·10H₂O or Na₂B₄O₇.

[0063] Preferably, in step S1, the amount of boric acid compound or borate compound is 0.5% or more but less than 5% of the mass of the first polymer. Preferably, in step S1, the mass of boric acid compound or borate compound is 1-3% of the mass of the first polymer. More preferably, in step S1, the mass of boric acid compound or borate compound is 1-2% of the mass of the first polymer.

[0064] Preferably, in step S1, the first solvent includes at least one of water, glycerol, phenol, and dimethyl sulfoxide.

[0065] Preferably, in step S1, the specific operation of completely dissolving the first polymer in the first solvent is to heat the first solvent to 60-80°C, add the first polymer, and stir until completely dissolved.

[0066] Preferably, in step S1, the modified first polymer is obtained by reacting the first polymer with a boric acid compound or a borate compound.

[0067] Preferably, in step S2, the mass ratio of the first polymer to the second polymer is 1-3:7-9. This mass ratio ensures that the second polymer provides the bulk strength and chemical stability as the continuous phase, while allowing the first polymer to form an effective cross-linked network throughout. This ratio effectively balances hydrogen bond density and cross-linking degree, providing sufficient dynamic bonding sites for self-healing while avoiding excessive cross-linking embrittlement or swelling due to an excess of the first polymer, and insufficient network strength due to an insufficient amount, thereby synergistically improving the coating's adhesion, wettability, and long-term cycling stability.

[0068] Preferably, in step S2, the second solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0069] Preferably, in step S3, the mass of the inorganic particles is 10-30% of the total mass of the first polymer and the second polymer. This dosage range ensures that the inorganic particles fully exert their function of enhancing thermal stability and mechanical strength, while preventing problems such as agglomeration, coating embrittlement, or pore blockage caused by excessive particles. Furthermore, it allows the particles to be effectively encapsulated and fixed by the polymer network, achieving an optimal balance between performance improvement and structural stability. More preferably, in step S3, the mass of the inorganic particles is 20-30% of the total mass of the first polymer and the second polymer.

[0070] Preferably, in step S4, the drying process is divided into two stages; the first stage is performed at 40-50°C for 2-4 minutes; the second stage is performed at 80-90°C for 1-2 hours. The first stage is pre-drying, and the second stage is curing. The first stage (pre-drying at 40-50°C) allows the solvent on the surface of the slurry to evaporate gently, initially fixing the coating morphology, preventing sagging, and avoiding bubbles or cracks caused by rapid drying. The second stage (curing at 80-90°C) promotes the complete evaporation of the solvent at a higher temperature, while simultaneously strengthening the thermal motion and arrangement of polymer chain segments. This facilitates the full formation and stabilization of interactions such as borate ester bonds and hydrogen bonds, thereby enhancing the coating's cohesiveness and its interfacial bonding with the base film, ultimately resulting in a dense and stable functional coating.

[0071] Preferably, in step S4, after the drying process, vacuum drying is also required at a pressure of -0.05 to -0.2 MPa. This vacuum drying step is for removing residual solvent.

[0072] According to a third aspect of the present invention, a battery is provided, comprising any of the above-described separators, or a separator prepared by any of the above-described preparation methods.

[0073] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: This invention introduces a functional coating with a specific structure into a membrane. This functional coating comprises a modified first polymer containing boronic acid ester bonds and abundant hydroxyl groups. The modified first polymer is composited with a second polymer to construct a multi-layered bonding network formed by the synergistic interaction of hydrogen bonds and boronic acid ester bonds. Specifically, some of the hydroxyl groups in the first polymer react with boric acid compounds or borate compounds to form boronic acid ester bonds, while others react with the second polymer to form hydrogen bonds. That is, the resulting modified first polymer molecular chain contains boronic acid ester bonds and can form hydrogen bonds with the second polymer.

[0074] Among these, boronic acid ester bonds provide a stable covalent cross-linked network for the coating, significantly improving its structural strength and durability. Simultaneously, based on the dynamic characteristics that boronic acid ester bonds may exhibit in the electrolyte environment, their synergy with the abundant hydrogen bonds in the system endows the coating with potential self-healing capabilities, enabling it to autonomously recover to a certain extent when micro-damage occurs, thereby further improving the reliability of the separator during long-term cycling. The synergistic effect of the aforementioned multiple bonding mechanisms of hydrogen bonds and boronic acid ester bonds allows the coating's self-healing process to be triggered and carried out primarily by the internal environmental conditions of the battery during operation (such as the electrolyte environment and operating temperature), significantly reducing dependence on strong external stimuli such as additional heating and light exposure, thus better aligning with actual battery usage scenarios.

[0075] Furthermore, the modified first polymer three-dimensional network formed by borate ester bonds provides a stable framework for the entire coating, while the second polymer, which runs through it, is tightly bonded to it via hydrogen bonds, forming an interpenetrating network structure. This structure not only endows the coating with excellent mechanical stability, thermal stability, and electrolyte wetting properties, but also effectively fixes the dynamic repair units (hydrogen bonds and / or borate ester bonds) in three-dimensional space, which can suppress the degradation of self-healing function caused by material swelling or migration. At the same time, this network can firmly anchor inorganic fillers, preventing them from falling off and ensuring that the composition and function of the coating remain uniform and intact even during repeated repair processes.

[0076] Therefore, by utilizing the rapid self-healing properties of the membrane surface coating, it is possible to promptly prevent interface deterioration and side reactions caused by the propagation of coating cracks, thus meeting the immediate protection requirements of the battery under dynamic operating conditions such as fast charging and discharging. This effectively improves various electrochemical performances of the battery, such as cycle performance. Moreover, the coating itself has higher mechanical stability, thermal stability, and strong wetting properties, which is also more conducive to further optimizing various performances of the battery.

[0077] To further illustrate the present invention, the following embodiments will be described in detail.

[0078] Example 1 This embodiment investigates the performance comparison of PVA:PVDF at different mass ratios with the same amount (1 wt%) of boric acid compound or borate compound (specifically borax, i.e., Na2B4O7·10H2O or Na2B4O7). The membrane preparation in this embodiment is as follows: 1. Preparation of slurry Experimental group: 1g, 2g, and 3g of PVA (number-average molecular weight of 3000 g / mol) were dissolved in 20g of water at 60-80℃, stirred until homogeneous, and then 1% (by mass) of borax was added. The mixture was stirred again until homogeneous, and these solutions were labeled A, B, and C, respectively. 9g, 8g, and 7g of PVDF were dissolved in 180g of NMP at 60-80℃, stirred until homogeneous, and these solutions were labeled E, F, and G, respectively. After mixing solutions A / E, B / F, and C / G until homogeneous, 2g of Al₂O₃ with a particle size of 0.3μm was added to each solution, and stirring continued until the slurry was uniformly mixed.

[0079] like Figure 1 As shown, it is a schematic diagram of the interpenetrating network structure formed by the modified first polymer generated by the reaction of borax and PVA and PVDF (second polymer).

[0080] Control group: 10g of PVDF was dissolved directly in 180g of NMP at 60-80℃ and stirred until homogeneous. This solution was labeled as H solution. Then, 2g of Al2O3 with a particle size of 0.3μm was added to the H solution and stirring was continued until the slurry was homogeneous. The control group slurry was obtained.

[0081] 2. Coating and Drying Coating: The slurry prepared above is uniformly coated on the surface of the PE base film (thickness 7-9 μm). The total thickness of the wet film after single-layer coating is 15-20 μm, and the total thickness of the diaphragm after drying is 10-12 μm. Segmented drying: First stage, pre-dry at 40-50℃ for 2-4 min; Second stage, cure at 80-90℃ for 1-2 h; followed by vacuum drying (-0.1 MPa) to remove residual solvent.

[0082] The membrane prepared in this embodiment was subjected to the following performance tests: (1) Adhesion: The adhesion of the sample was tested at a peeling speed of 100 mm / min and a temperature of 25℃. The peel strength between the coating and the PE base film was tested, and the average value of the sample was taken.

[0083] (2) Thermal stability (heat shrinkage rate): A square sample of 90 mm × 90 mm was prepared, placed in an oven at 180℃ for 1 hour, and then cooled to room temperature before measuring the heat shrinkage rate according to the formula (L0 L1) / L0×100% (L1 is the length after heating, L0 is the original length), calculate separately for the longitudinal and transverse directions (the results in the table are the longitudinal heat shrinkage).

[0084] (3) Self-healing performance: Take a 90 mm × 90 mm square sample and scratch the inorganic filler layer with a blade without damaging the base membrane. Soak the scratched diaphragm in DMC to simulate the state of soaking in electrolyte. First, place the diaphragm at 25℃ for 12 h, and then place the diaphragm at 40℃ for 12 h to observe the diaphragm healing phenomenon.

[0085] (4) Electrochemical performance: Ionic conductivity: The ionic conductivity of a LiFePO4 / Li half-cell assembled using a separator was measured by EIS at 25℃. The ionic impedance of the separator was obtained based on the transmission line model. σ is the ionic conductivity, L is the membrane thickness, R is the ionic impedance obtained from EIS testing, and A is the area of ​​the LiFePO4 electrode.

[0086] Electrolyte wettability: The absorbance rate of the diaphragm in the electrolyte is measured. The diaphragm is weighed before soaking and recorded as W0. It is weighed again after one hour of soaking and recorded as W1. The absorbance rate = (W1 - W0) / W0 reflects the wettability of the diaphragm.

[0087] Cyclic performance: After the LiFePO4 / graphite full cell is assembled and formed, it can cycle 500 times at 25℃: 1C CC (constant current charging) to 3.65V, 3.65V CV (constant voltage charging) to I (cutoff current) ≤0.05C, and 0.33C DC (constant current discharging) to 2.5V.

[0088] The results of the above-mentioned related tests are shown in Table 1 and... Figure 2 , 3 As shown.

[0089] Table 1. Relevant performance tests of the separator and battery in Example 1.

[0090] As shown in Table 1 and Figure 2 , Figure 3 As shown, in the separator provided by the present invention, the mass ratio of the first polymer (such as PVA) to the second polymer (such as PVDF) has a significant impact on the separator's self-healing performance, peel strength, thermal shrinkage rate, liquid absorption rate, as well as the battery's ionic conductivity and capacity retention rate.

[0091] Among these, when the mass ratio of the first polymer (such as PVA) to the second polymer (such as PVDF) is 3:7, the membrane's self-healing performance, peel strength, thermal shrinkage rate, liquid absorption rate, and the battery's ionic conductivity and capacity retention all reach their optimal levels. This is because the compatibility between the modified first polymer (the cross-linked network structure formed by the reaction of borax and PVA) and the second polymer is optimal at this point. Therefore, the synergistic effect of the cross-linked network structure of the modified first polymer and the hydrogen bond network structure formed by the modified first polymer and the second polymer is optimal, resulting in the most stable interpenetrating network structure in the final coating. This gives the coating the best performance, thereby maximizing the optimization of the various performance characteristics of the membrane and the battery.

[0092] When the mass ratio of the first polymer (e.g., PVA) to the second polymer (e.g., PVDF) is 1:9 or 2:8, the various properties of the separator decrease to varying degrees compared to the 3:7 ratio. Specifically, when the mass ratio of the first polymer (e.g., PVA) to the second polymer (e.g., PVDF) is 1:9, there is insufficient PVA, resulting in low hydrogen bond density and weak adhesion; PVDF dominates, exhibiting strong hydrophobicity but poor hydrophilicity. When the mass ratio of the first polymer (e.g., PVA) to the second polymer (e.g., PVDF) is 2:8, the hydrogen bond network begins to form, but the proportion of PVA is still relatively low, resulting in limited electrolyte wettability. Therefore, these factors lead to varying degrees of performance degradation in both the separator and the battery.

[0093] Furthermore, we can see that without the introduction of the modified first polymer, that is, without the introduction of the cross-linked network structure formed by the reaction of borax and PVA, it is obvious that the resulting separator cannot self-heal. Although it has a high liquid absorption rate, its peel strength and ionic conductivity are low, and its thermal shrinkage rate is high. After 500 cycles, the battery capacity and capacity retention are both low.

[0094] Example 2 This embodiment investigates the performance comparison of different amounts of boric acid compounds or borate compounds (specifically borax). The membrane in this embodiment is prepared as follows: 1. Preparation of slurry Experimental Group: 3g of PVA (number-average molecular weight 3000 g / mol) was dissolved in 20g of water at 60-80℃, stirred until homogeneous, and repeated three times to prepare three solutions. Then, 1%, 3%, and 5% (by mass of PVA) of borax were added to each of the three solutions respectively, and the mixtures were stirred again until homogeneous. These solutions were designated A, B, and C. 7g of PVDF was dissolved in 180g of NMP at 60-80℃, stirred until homogeneous, and this solution was designated D. Three solutions of D were prepared. The three solutions of D were added to solutions A, B, and C respectively, and stirred until homogeneous. Then, 2g of Al₂O₃ with a particle size of 0.3μm was added to each of the mixed solutions, and stirring continued until the slurry was homogeneous.

[0095] After conversion, the mass percentages of element B in the modified first polymer obtained from solutions A, B, and C are 0.112%, 0.330%, and 0.540%, respectively. Furthermore, in the subsequently dried functional coatings (functional coatings formed from the slurry), the mass percentages of element B in the functional coatings corresponding to solutions A, B, and C are 0.0283%, 0.0844%, and 0.14%, respectively.

[0096] Control group: 10g of PVDF was dissolved directly in 180g of NMP at 60-80℃ and stirred until homogeneous. This solution was labeled as H solution. Then, 2g of Al2O3 with a particle size of 0.3μm was added to the H solution and stirring was continued until the slurry was homogeneous. The control group slurry was obtained.

[0097] 2. Coating and Drying Coating: The slurry prepared above is uniformly coated on the surface of the PE base film (thickness 7-9μm). The total thickness of the single-layer wet film is 15-20μm, and the total thickness of the diaphragm after drying is 10-12μm. Segmented drying: First stage, pre-dry at 40-50℃ for 2-4 min; Second stage, cure at 80-90℃ for 1-2 h; followed by vacuum drying (-0.1 MPa) to remove residual solvent.

[0098] The membrane prepared in this embodiment was tested for adhesion, thermal stability and self-healing performance. At the same time, the electrochemical performance of the battery prepared using the membrane was tested. The specific test methods are the same as in Example 1.

[0099] The results of the above-mentioned related tests are shown in Table 2, and Figure 4 , 5 As shown.

[0100] Table 2. Relevant performance tests of the separator and battery in Example 2.

[0101] As shown in Table 2 and Figure 4 , Figure 5 As shown, in the separator provided by the present invention, the amount of borax added has a significant impact on the separator's self-healing performance, peel strength, thermal shrinkage rate, liquid absorption rate, as well as the battery's ionic conductivity and capacity retention rate.

[0102] It can be seen that when the amount of borax added is 1 wt% of PVA, the self-healing performance, peel strength, thermal shrinkage rate, liquid absorption rate of the separator, as well as the ionic conductivity and capacity retention rate of the battery, all reach their best performance.

[0103] As the amount of borax added gradually increases, the liquid absorption rate of the separator decreases, as does its self-healing ability. The battery exhibits a decrease in ionic conductivity, possibly because excessive borax leads to overly high cross-linking, which is detrimental to liquid absorption and self-healing, and can also cause blockage of ion transport channels. The amount of borax added has a relatively small effect on the thermal shrinkage rate of the separator.

[0104] Furthermore, it can be seen that without the addition of PVA and borax, i.e. without modification of the first polymer, the performance of the separator and the battery is significantly worse.

[0105] Example 3 This embodiment investigates the performance comparison of different amounts of inorganic particles (inorganic fillers). The preparation of the diaphragm in this embodiment is as follows: Experimental Group: 3g of PVA (number-average molecular weight 3000 g / mol) was dissolved in 20g of water at 60-80℃, stirred until homogeneous, and repeated three times to prepare three solutions. Then, 1% (by weight of PVA) of borax was added to each of the three solutions, and the mixture was stirred again until homogeneous. These solutions were designated A, B, and C. 7g of PVDF was dissolved in 180g of NMP at 60-80℃, stirred until homogeneous, and this solution was designated D. Three solutions of D were prepared. The three solutions of D were added to solutions A, B, and C respectively, and stirred until homogeneous. Then, 1g, 2g, and 3g of Al₂O₃ with a particle size of 0.3μm were added to the mixed solutions respectively, and the mixture was stirred until homogeneous. The three slurries prepared were designated as group S-10 (10%, 7 g PVDF + 1 g Al2O3 + 3 g PVA + 0.03 g borax), group S-20 (20%, 7 g PVDF + 2 g Al2O3 + 3 g PVA + 0.03 g borax), and group S-30 (30%, 7 g PVDF + 3 g Al2O3 + 3 g PVA + 0.03 g borax). In the above S-10, S-20, and S-30, 10%, 20%, and 30% respectively represent the amount of inorganic particles (Al2O3) used, which are 10%, 20%, and 30% of the total mass of the first polymer (PVDF) and the second polymer (PVA).

[0106] Control group: Dissolve 3g PVA (number average molecular weight of 3000 g / mol) in 20g of water at 60-80℃ and stir until homogeneous. Then add 1% borax by mass of PVA to the solution and stir until homogeneous. Dissolve 7g PVDF in 180g of NMP at 60-80℃ and stir until homogeneous to obtain the control group slurry, denoted as group S-0.

[0107] 2. Coating and Drying Coating: The slurry prepared above is uniformly coated on the surface of the PE base film (thickness 7-9μm). The total thickness of the wet film after single-layer coating is 15-20μm, and the total thickness of the diaphragm after drying is 10-12μm. Segmented drying: First stage, pre-dry at 40-50℃ for 2-4 min; Second stage, cure at 80-90℃ for 1-2 h; followed by vacuum drying (-0.1 MPa) to remove residual solvent.

[0108] The thermal stability and self-healing performance of the separators prepared in this embodiment (including the base membrane of the control group) were tested. The electrochemical performance of the batteries prepared using the separators was also tested, with specific testing methods referring to Example 1. The porosity, tensile strength, and puncture strength of the separators prepared in this embodiment (including the base membrane of the control group) were also tested. Porosity was tested using a weighing method. Specifically, a square separator with a side length of L was cut, and the dry mass m1 and thickness h of the separator were weighed. The mass m2 of the separator after fully absorbing n-hexadecane was also measured. Based on the density ρ of n-hexadecane, the volume of n-hexadecane absorbed by the separator, V2 = (m2 - m1) / ρ, was calculated. The ratio of this volume to the separator volume V1 = L * h, i.e., V2 / V1, is the porosity. Tensile strength: The tensile strength was tested at room temperature using a universal testing machine at a tensile rate of 50 mm / min. Puncture strength: A 1 mm diameter puncture needle was used for the puncture strength test, with a puncture speed set to 2 mm / s.

[0109] The results of the above-mentioned relevant tests are shown in Table 3, and Figure 6 , 7 As shown.

[0110] Table 3. Performance tests of the separator and battery in Example 3

[0111] From Table 3, and Figure 6 , 7 It is known that in the separator provided by the present invention, the amount of inorganic particles added has a significant impact on the separator's self-healing performance, porosity, thermal shrinkage rate, liquid absorption rate, tensile strength, puncture strength, as well as the battery's ionic conductivity and capacity retention rate.

[0112] It can be seen that when the amount of inorganic particles (Al2O3) is 20% of the total mass of the first polymer (PVA) and the second polymer (PVDF) (i.e., group S-20), the performance of the separator and the battery is optimal.

[0113] Compared to the S-20 group, the performance of the separator and battery in the S-10 and S-30 groups is reduced. Specifically, the S-10 group has fewer inorganic particles, resulting in limited improvement in thermal stability and mechanical strength. The S-30 group has more inorganic fillers, which easily aggregate and cause pore blockage, leading to decreased ionic conductivity and flexibility, reduced self-healing performance, and a significant decrease in battery cycle performance.

[0114] We can also see that the S-0 group has no inorganic particles in its coating, and it is similar to a base membrane directly coated with a glue layer. The properties of the S-0 group separator are similar to those of the base membrane. Therefore, the performance of batteries composed of S-0 group separators is relatively poor. However, thanks to the addition of PVA and borax to the glue layer, the separator has self-healing properties.

[0115] Example 4 This embodiment investigates the performance comparison of inorganic particles with different particle sizes. The membrane in this embodiment is prepared as follows: Experimental Group: 3g of PVA (number-average molecular weight 3000 g / mol) was dissolved in 20g of water at 60-80℃, stirred until homogeneous, and repeated three times to prepare three solutions. Then, 1% (by weight of PVA) of borax was added to each of the three solutions as a crosslinking agent, and the mixture was stirred again until homogeneous. These solutions were designated A, B, and C. 7g of PVDF was dissolved in 180g of NMP at 60-80℃, stirred until homogeneous, and this solution was designated D. Three solutions of D were prepared. The three solutions of D were added to solutions A, B, and C respectively, and stirred until homogeneous. Then, 2g of Al₂O₃ with particle sizes of 0.1μm, 0.3μm, and 0.5μm were added to the mixed solutions respectively, and stirring continued until the slurry was homogeneous. The three slurries prepared were designated as group D-1 (7 g PVDF + 2 g 0.1 μm Al2O3 + 3 g PVA + 0.03 g borax), group D-3 (7 g PVDF + 2 g 0.3 μm Al2O3 + 3 g PVA + 0.03 g borax), and group D-5 (7 g PVDF + 2 g 0.5 μm Al2O3 + 3 g PVA + 0.03 g borax).

[0116] Control group: The base membrane was used directly as the subsequent separator, and it was designated as group D-0 (no functional coating, and therefore no inorganic particles).

[0117] 2. Coating and Drying Coating: The slurry prepared above is uniformly coated on the surface of the PE base film (thickness 7-9μm). The total thickness of the wet film after single-layer coating is 15-20μm, and the total thickness of the diaphragm after drying is 10-12μm. Segmented drying: First stage, pre-dry at 40-50℃ for 2-4 min; Second stage, cure at 80-90℃ for 1-2 h; followed by vacuum drying (-0.1 MPa) to remove residual solvent.

[0118] The membranes prepared in this embodiment (including the base membrane of the control group) were tested for adhesion, thermal stability and self-healing performance. At the same time, the electrochemical performance of the batteries prepared using the membranes was tested. The specific test methods are referred to in Example 1.

[0119] The results of the above-mentioned related tests are shown in Table 4, and Figure 8 , 9 As shown.

[0120] Table 4. Performance tests of the separator and battery in Example 4

[0121] From Table 4, and Figure 8 , 9 As shown, in the separator provided by the present invention, the particle size of its inorganic particles has a significant impact on the separator's self-healing performance, thermal shrinkage rate, liquid absorption rate, as well as the battery's ionic conductivity and capacity retention rate.

[0122] It can be seen that when the particle size of inorganic particles (Al2O3) is 0.3μm (i.e., group D-3), the overall performance of the separator and the battery is the best.

[0123] Compared to group D-3, the peel strength and thermal shrinkage rate of the separators in groups D-1 and D-5 decreased, and the ionic conductivity and capacity retention of the batteries prepared with the separators also decreased.

[0124] Furthermore, it can be seen that using only the base membrane as the separator results in significantly worse performance of the separator and the battery compared to the D-3 group.

[0125] In addition, in this embodiment, infrared spectroscopy was performed on PVDF and the dried material (denoted as PVA / PVDF) of the D solution (modified interpenetrating network structure formed by the first polymer and the second polymer) prepared in D-3. The results are as follows. Figure 10 As shown. Figure 10 Infrared spectroscopy showed that PVA / PVDF at 3462 cm⁻¹ -1 The presence of a characteristic peak for -OH at this location indicates the formation of hydrogen bonds between -OH groups, thus broadening the characteristic peak. (1423 cm⁻¹) -1The characteristic peak of CF at 1453 cm⁻¹ shows a redshift compared to pure PVDF, indicating that hydrogen bonds are formed in the CF phase of PVA / PVDF. Therefore, infrared spectroscopy proves that the hydroxyl groups in the modified first polymer (such as those generated by the reaction of borax and PVA) and the second polymer (PVDF) form an effective hydrogen bond network, together constituting a stable interpenetrating network structure. This can effectively improve the performance of the separator and the battery, especially the self-healing performance, mechanical stability, thermal stability of the separator, and the cycle capacity retention of the battery.

[0126] Furthermore, as can be seen from Examples 1-4 above, taking the optimal experimental groups in each example (such as the PVA:PVDF mass ratio of 3:7 in Example 1, the borax addition of 1% in Example 2, the S-20 group in Example 3, and the D-3 group in Example 4) as examples, firstly, the peel strength of its separator reaches 55 N / m, far exceeding the 12.3 N / m of the pure base membrane and the 28 N / m of PVDF + inorganic filler. This result indicates that the hydrogen bond network formed by the hydroxyl groups of PVA and the fluorine atoms of PVDF, as well as the three-dimensional framework of PVA crosslinked by borax, significantly enhances the interfacial bonding force between the coating and the base membrane. High peel strength can effectively prevent coating peeling during cycling and improve the long-term stability of the battery.

[0127] Secondly, at a high temperature of 180℃, the thermal shrinkage rate of its separators is lower than that of the pure base membrane (65.2%) and the PVDF+inorganic filler (15.2%). This difference stems from the heat resistance of PVA and the synergistic effect of the inorganic fillers: the PVA cross-linking network inhibits the high-temperature migration of polymer chains, while fillers such as Al2O3 reduce separator shrinkage through physical support. The low thermal shrinkage rate significantly reduces the risk of high-temperature short circuits and improves battery safety.

[0128] Third, the ionic conductivity of its membrane is superior to that of the pure base membrane (0.78 × 10⁻⁶). -3 S / cm. The hydrophilic hydroxyl groups of PVA improve electrolyte wettability, while the hydrophobic microporous structure of PVDF maintains electrolyte stability; together, they synergistically optimize the lithium-ion transport channel. Higher conductivity reduces battery internal resistance and improves rate performance.

[0129] Fourth, after 500 cycles, the battery capacity retention rate of the membrane is higher than that of the pure base membrane by 72%. This advantage is due to multiple mechanisms: (1) Coating stability, the interpenetrating network structure fixes inorganic particles and reduces the increase in interfacial impedance caused by shedding; (2) Dendrite suppression, the uniform ion flow distribution suppresses lithium dendrite growth; (3) Electrolyte retention, the liquid absorption capacity of PVA delays the drying of the electrolyte.

[0130] Fifth, after determining the mass ratio of inorganic fillers and the ratio of PVA to PVDF, the different sizes of inorganic fillers have almost no effect on the self-healing performance of the diaphragm.

[0131] In summary, the separator provided by this invention possesses a multi-faceted superior functional coating. This functional coating, through hydrogen bonding crosslinking, interpenetrating network structure, and / or synergistic effects of inorganic fillers, comprehensively surpasses pure base membrane coatings in mechanical strength, thermal stability, and electrochemical performance, making it particularly suitable for power battery applications requiring high energy density and long cycle life. More importantly, due to the combined effect of borate ester bonds and hydrogen bonds in the functional coating, the separator can self-repair coating damage when heated or when swollen by the electrolyte, exhibiting excellent self-healing properties.

[0132] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A diaphragm, characterized in that: The system includes a base film and a functional coating, wherein the functional coating is located on at least one side of the surface of the base film; the functional coating includes a modified first polymer and a second polymer. The modified first polymer comprises boron ester bonds and hydroxyl groups; The second polymer includes at least one of polyvinylidene fluoride (PVDF) and its copolymers, polyethylene oxide (PEO), polyurethane, and polyvinyl butyral (PVB).

2. The diaphragm as described in claim 1, characterized in that: The mass percentage of element B in the modified first polymer is 0.1-0.55%; And / or, the mass percentage of element B in the functional coating is 0.012-0.46%.

3. The diaphragm as described in claim 1, characterized in that: The modified first polymer includes a main chain structure based on the first polymer; The first polymer contains a 1,2-diol or 1,3-diol structure; preferably, the first polymer includes at least one of polyvinyl alcohol (PVA) and its derivatives, polysaccharides and their derivatives; preferably, the first polymer is polyvinyl alcohol.

4. The diaphragm as described in claim 1, characterized in that: The number-average molecular weight of the first polymer is 2000-4000 g / mol.

5. The diaphragm as described in claim 1, characterized in that: The functional coating also includes inorganic particles, which include at least one of Al2O3, MgO, TiO2, ZrO2, AlOOH, Al(OH)3, BN, and AlN. And / or, the particle size of the inorganic particles is 0.1~0.5μm; And / or, the surface of the inorganic particles contains at least one of hydroxyl and carboxyl groups.

6. A method for preparing a diaphragm as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. The first polymer is completely dissolved in a first solvent, and then a boric acid compound or a borate compound is added to it at 60-80°C. The mixture is stirred for 1-2 h to obtain a first mixed system, wherein the first mixed system contains the modified first polymer. S2. Completely dissolve the second polymer in the second solvent to prepare a solution of the second polymer. Add the second polymer solution to the first mixture and stir the mixture at 60-80°C for 2-3 hours to obtain the second mixture. S3. Add the inorganic particulate powder to the second mixing system, mix and stir evenly to obtain a slurry; S4. The slurry is coated onto the base membrane and dried to obtain the diaphragm.

7. The method for preparing the diaphragm as described in claim 6, characterized in that: In step S1, the mass of the boric acid compound or the borate compound is 0.5% or more and less than 5% of the mass of the first polymer; And / or, the first solvent includes at least one of water, glycerol, phenol, and dimethyl sulfoxide.

8. The method for preparing the diaphragm as described in claim 6, characterized in that: In step S2, the mass ratio of the first polymer to the second polymer is (1-3):(7-9); And / or, the second solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

9. The method for preparing the diaphragm as described in claim 6, characterized in that: In step S3, the mass of the inorganic particles is 10-30% of the total mass of the first polymer and the second polymer.

10. A battery, characterized in that: It includes the diaphragm as described in any one of claims 1-5, or the diaphragm prepared by the preparation method as described in any one of claims 6-9.

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