A positive electrode sheet, a method for manufacturing the same, and a lithium ion battery

Abstract

The application belongs to the technical field of battery materials, and provides a positive electrode sheet, a preparation method thereof and a lithium ion battery. The positive electrode sheet comprises: a functional current collector; an inner functional layer arranged on at least one side surface of the functional current collector and comprising chemical capture groups and physical adsorption sites; a positive electrode active material layer arranged on a surface of the inner functional layer; and an outer functional layer arranged on a surface of the positive electrode active material layer and comprising voltage-responsive groups, the voltage-responsive groups being used for capturing and converting polymer monomers in an activated state. The application sets the voltage-responsive outer functional layer on the surface of the positive electrode active material layer, so that the monomers can be preferentially captured and converted; and sets the inner functional layer on the surface of the functional current collector, so that the residual monomers can be adsorbed and consumed. The two gradient synergies realize multi-level interception of residual monomers after in-situ polymerization of the gel-state polymer electrolyte, can inhibit the interface side reaction, reduce the interface impedance, prevent the active material from being precipitated, and effectively improve the electrochemical performance of the lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a positive electrode sheet, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the increasing demands for energy density, safety performance, and cycle life of lithium batteries from new energy vehicles and energy storage devices, composite current collectors (such as polymer-based film / metal layer composite structures) are widely used due to their lightweight and high conductivity. Meanwhile, gel-state polymer electrolytes combine the high ionic conductivity of liquid electrolytes with the excellent safety performance of solid electrolytes, becoming an important development direction for improving the overall performance of lithium-ion batteries. However, combining gel-state electrolytes with composite current collectors in high-performance lithium-ion battery systems still faces many technical challenges.

[0003] In actual preparation processes, gel-state polymer electrolytes are typically formed through in-situ polymerization. However, due to incomplete polymerization, unreacted monomers often remain in the system. These residual monomers are prone to oxidative decomposition at the high-voltage cathode interface, exacerbating side reactions at the cathode interface and compromising interfacial structural stability. Furthermore, their oxidation products accumulate on the cathode surface, significantly increasing interfacial impedance and hindering lithium-ion transport. In addition, residual monomers may induce the precipitation of active materials from the electrode surface, disrupting the integrity of the electrode structure and adversely affecting the battery's capacity retention, coulombic efficiency, and cycle stability.

[0004] Therefore, how to solve the problem of unreacted monomer residues after in-situ polymerization of gel-state polymer electrolytes, thereby suppressing side reactions at the cathode interface, reducing interfacial impedance and preventing the precipitation of active materials, is a technical challenge that urgently needs to be addressed. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a positive electrode sheet, its preparation method, and a lithium-ion battery. The present invention adds an external functional layer to the surface of the positive electrode active material layer. This external functional layer employs highly reactive but voltage-threshold-controlled voltage-responsive groups, which can preferentially capture and convert polymer monomers in the activated state. Residual or subsequently penetrating polymer monomers into the positive electrode active material layer can be further consumed and adsorbed by the internal functional layer on the surface of the functional current collector through chemically captured groups and physical adsorption sites. The two elements form a gradient synergistic effect in space, enabling multi-level interception and efficient consumption of unreacted monomers remaining after in-situ polymerization of the gel-state polymer electrolyte. This significantly suppresses the oxidative decomposition side reactions of monomers at the high-voltage positive electrode interface, reduces the positive electrode interface impedance, and prevents the precipitation of active materials, thereby effectively improving the battery's safety performance and cycle stability, and significantly improving the battery's overall electrochemical performance.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a positive electrode sheet, the positive electrode sheet comprising: Functional current collector.

[0007] An inner functional layer is disposed on at least one side surface of the functional current collector, and the inner functional layer includes chemical trapping groups and physical adsorption sites.

[0008] A positive electrode active material layer is disposed on the surface of the inner functional layer.

[0009] An external functional layer is disposed on the surface of the positive electrode active material layer. The external functional layer includes voltage-responsive groups, which are used to capture and convert polymer monomers in an activated state.

[0010] This invention adds an external functional layer to the surface of the positive electrode active material layer. This external functional layer employs highly reactive but voltage-threshold-controlled voltage-responsive groups, which can preferentially capture and convert polymer monomers in the activated state. Meanwhile, residual or subsequently penetrating polymer monomers into the positive electrode active material layer can be further consumed and adsorbed by the internal functional layer on the surface of the functional current collector through chemically captured groups and physical adsorption sites. The two layers form a gradient-like synergistic effect in space, enabling multi-level interception and efficient consumption of unreacted monomers remaining after in-situ polymerization of the gel-state polymer electrolyte. This significantly suppresses the oxidative decomposition side reactions of monomers at the high-voltage positive electrode interface, reduces the positive electrode interface impedance, and prevents the precipitation of active materials, thereby effectively improving the battery's safety performance and cycle stability, and significantly enhancing the battery's overall electrochemical performance.

[0011] Preferably, along a direction away from the functional current collector, the inner functional layer comprises a polymer reaction layer and a polymer adsorption layer stacked together.

[0012] In this invention, the polymer reaction layer consumes residual polymer monomers through chemical reaction, and the polymer adsorption layer covers the capture blind zone of the polymer reaction layer by physically adsorbing residual polymer monomers. The two work together to form a true "two-stage capture", avoiding the evacuation of monomers to the functional current collector and causing greater problems.

[0013] Preferably, in the polymer reaction layer, the chemically trapped groups include any one or a combination of at least two of the following: epoxy groups, amino groups, or thiol groups.

[0014] The groups provided by this invention can firmly anchor residual monomers and transform them into a stable cross-linked network structure, thereby completely eliminating residual monomers and cutting off their possibility of oxidation.

[0015] Preferably, the material of the polymer adsorption layer includes any one or a combination of at least two of metal oxides, metal fluorides, or boron-based oxides.

[0016] In the polymer adsorption layer provided by the present invention, the nano-metal particles supplement the coverage blind area of ​​the polymer reaction layer through physical / coordination adsorption (having the ability to adsorb electrophilic / hydrophobic monomers) and increase the interface roughness to improve adhesion.

[0017] Preferably, the metal oxide includes any one or a combination of at least two of ZrO2, TiO2, MgO, and Al2O3.

[0018] Preferably, the metal fluoride includes any one or a combination of at least two of AlF3, MgF2, or TiF4.

[0019] Preferably, the boron-based oxide includes B2O3.

[0020] Preferably, the thickness of one side of the polymer reaction layer is 10-100nm, for example, it can be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm, etc.

[0021] In this invention, a suitable polymer reaction layer thickness can ensure that it has sufficient chemically active sites to fully capture and transform residual polymer monomers (i.e., monomers that have not been fully polymerized by the electrolyte).

[0022] Preferably, the thickness of one side of the polymer adsorption layer is 10-50 nm, for example, it can be 10 nm, 20 nm, 30 nm, 40 nm or 50 nm.

[0023] In this invention, an appropriate polymer adsorption layer thickness can maintain good lithium-ion conductivity while ensuring sufficient physical adsorption effect.

[0024] Preferably, the thickness ratio of the polymer reaction layer to the polymer adsorption layer is 1:(1-10), for example, it can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, etc.

[0025] Preferably, the oxidation potential of the voltage-responsive group is >4.2V, for example, it can be 4.3V, 4.4V or 4.5V.

[0026] In this invention, the oxidation potential of the voltage-responsive group is >4.2V, indicating that it is inert at <4.2V and activated at >4.2V. This avoids interference with the normal chemical process of the electrode at low potentials, while providing additional protection when truly needed (high voltage stage) and reducing the monomers in direct contact with the electrode surface.

[0027] Preferably, the voltage-responsive group includes any one or a combination of at least two of the following: nitroxide radical group, quinone group, thioether group, or aromatic amine group.

[0028] Preferably, the thickness of one side of the outer functional layer is 100-300nm, for example, it can be 100nm, 150nm, 200nm, 250nm or 300nm.

[0029] In this invention, an appropriate thickness of the outer functional layer can ensure that it has sufficient voltage-responsive groups to efficiently capture and convert residual monomers, while avoiding the increase in interface impedance, poor thickness uniformity, and interface failure caused by an excessively thick functional layer. Conversely, an excessively thin functional layer can also lead to poor thickness uniformity and interface failure.

[0030] Preferably, the functional current collector includes a polymer base film and a metal layer disposed on at least one side surface of the polymer base film.

[0031] Preferably, the polymer-based film comprises any one or a combination of at least two of polyethylene terephthalate film (PET film), polyimide film (PI film), or polypropylene film (PP film).

[0032] Preferably, the metal layer comprises an Al layer.

[0033] In a second aspect, the present invention provides a method for preparing a positive electrode sheet as described in the first aspect, the method comprising the following steps: Prepare functional current collectors.

[0034] An inner functional layer, a positive electrode active material layer, and an outer functional layer are sequentially prepared on at least one side surface of the functional current collector to obtain the positive electrode sheet.

[0035] Preferably, before the inner functional layer is prepared, the functional current collector is subjected to surface activation treatment, the steps of which include: The functional current collector is soaked in alkaline solution, rinsed, and then dried.

[0036] The purpose of this invention to perform surface activation treatment on functional current collectors is to provide -Al-OH sites to facilitate the bonding of silanes or other coupling agents with aluminum, thereby improving coating quality.

[0037] Preferably, the alkaline solution comprises a sodium hydroxide solution.

[0038] Preferably, the concentration of the alkaline solution is 0.4-0.6 wt%, for example, it can be 0.4 wt%, 0.5 wt%, or 0.6 wt%.

[0039] Preferably, the soaking time is 10-30 seconds, for example, 10 seconds, 20 seconds, or 30 seconds.

[0040] Preferably, the preparation steps of the inner functional layer include: (a) Provide a reactive capture solution.

[0041] The functional current collector is immersed in the reactive capturing liquid and dried to form a polymer reaction layer.

[0042] (b) Provide an adsorbent capture solution.

[0043] The adsorbent capturing liquid is coated on the surface of the polymer reaction layer and dried to form a polymer adsorption layer.

[0044] Preferably, the preparation steps of the outer functional layer include: Provide the precursor solution for the outer functional layer.

[0045] The precursor solution of the outer functional layer is coated on the surface of the positive electrode active material layer and dried to form the outer functional layer.

[0046] Preferably, the concentration of the reactive capture solution is 0.5-2 wt%, for example, it can be 0.5 wt%, 1 wt%, 1.5 wt%, or 2 wt%.

[0047] Preferably, the reactive capture solution comprises any one or a combination of at least two of the following: ethylenediamine, tetraethylenepentamine, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, pentaerythritol tetramercaptoacetate, or polyethyleneimine.

[0048] It should be noted that the present invention does not specifically limit the solvent of the reactive capture liquid. For example, it can be an alcohol solvent, such as ethanol.

[0049] Preferably, the concentration of the adsorbent capturing liquid is 0.5-1 wt%, for example, it can be 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, or 1 wt%.

[0050] Preferably, the adsorbent capturing liquid includes any one or a combination of at least two of the following: metal oxide nanoparticles, metal fluoride nanoparticles, or boron-based oxide nanoparticles.

[0051] It should be noted that the present invention does not specifically limit the solvent of the adsorption capture liquid. For example, it can be an alcohol solvent, such as ethanol.

[0052] Preferably, the concentration of the outer functional layer precursor solution is 0.1-5 wt%, for example, it can be 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%.

[0053] Preferably, the outer functional layer precursor solution includes any one or a combination of at least two of tetramethylpiperidine oxide, benzoquinone, aniline, diphenylamine, pyridinium imine, or anisole.

[0054] It should be noted that the solvent of the precursor solution for the outer functional layer is not specifically limited in this invention. For example, it can be an alcohol solvent, such as ethanol or isopropanol.

[0055] Preferably, the preparation method includes the following steps: (1) Preparation of functional current collectors: Metal layers are deposited on both sides of the polymer base film to obtain the functional current collector.

[0056] The metal layer includes an Al layer; the thickness of the metal layer on one side is 400-2000 nm (for example, it can be 400 nm, 800 nm, 1200 nm, 1600 nm or 2000 nm, etc.).

[0057] (2) Preparation of the inner functional layer: (2-1) The functional current collector is surface activated and then immersed in a reactive trapping solution with a concentration of 0.5-2wt% for 1-10 min, and dried at 60-100℃ (e.g., 60℃, 70℃, 80℃, 90℃ or 100℃, etc.) for 3-10 min (e.g., 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min or 10 min, etc.) to obtain a polymer reaction layer with a single-sided thickness of 10-100 nm; wherein, the reactive trapping solution includes any one or a combination of at least two of ethylenediamine, tetraethylenepentamine, 3-aminopropyltriethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, pentaerythritol tetramercaptoacetate or polyethyleneimine.

[0058] (2-2) An adsorbent capturing liquid with a concentration of 0.5-1wt% is sprayed onto the surface of the polymer reaction layer and dried to form a polymer adsorption layer with a single-sided thickness of 10-50nm; wherein, the solute in the adsorbent capturing liquid is nanoparticles, and the nanoparticles include any one or a combination of at least two of metal oxide nanoparticles, metal fluoride nanoparticles or boron-based oxide nanoparticles; the particle size D50 of the nanoparticles is 20-100nm (for example, it can be 20nm, 40nm, 60nm, 80nm or 100nm, etc.).

[0059] (3) Preparation of the positive electrode active material layer: A positive electrode slurry is coated on the surface of the inner functional layer and dried to obtain a positive electrode active material layer. The solid content of the positive electrode slurry is 60-75 wt% (e.g., 60 wt%, 65 wt%, 70 wt%, or 75 wt%). The dry basis of the positive electrode slurry includes the following components by weight: 90-95 parts of positive electrode active material (e.g., 90, 91, 92, 93, 94, or 95 parts), 1-3 parts of conductive agent (e.g., 1, 2, or 3 parts), and 1-3 parts of binder (e.g., 1, 2, or 3 parts).

[0060] (4) Preparation of the outer functional layer: A 0.1-5 wt% external functional layer precursor solution is sprayed onto the surface of the positive electrode active material layer and dried to form an external functional layer with a single-sided thickness of 100-300 nm; wherein the external functional layer precursor solution includes any one or a combination of at least two of tetramethylpiperidine oxide, benzoquinone, aniline, diphenylamine, pyridinium imine, or anisole.

[0061] For example, the deposition method of the metal layer can be vapor deposition or magnetron sputtering, etc.

[0062] For example, the positive electrode active material can be lithium nickel cobalt manganese oxide, etc.

[0063] For example, the conductive agent may be graphite, etc.

[0064] For example, the adhesive may be polyvinylidene fluoride, etc.

[0065] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and a gel polymer electrolyte.

[0066] The positive electrode sheet is the positive electrode sheet described in the first aspect, or it is prepared by the preparation method described in the second aspect.

[0067] The gel-state polymer electrolyte is disposed on the surface of the side containing the inner functional layer of the positive electrode.

[0068] The gel-state polymer electrolyte includes polymer monomers, crosslinking agents, solvents, lithium salts, fast-response initiators, and slow-response initiators.

[0069] This invention introduces fast-response and slow-response initiators into gel-state polymer electrolytes to achieve a spatially selective curing effect: the fast-response initiator forms only a primary network backbone under low-dose UV conditions, keeping the system in a pre-critical gel or shallow gel state, allowing monomers to still migrate; the slow-response initiator remains relatively inert during the dispensing and initial curing stages, only gradually decomposing during subsequent heating or battery formation. At this point, the system has basically completed concentration homogenization, so the crosslinked network formed at this stage is more uniform, significantly reducing the probability of local monomer encapsulation.

[0070] Specifically, during the light irradiation stage, a fast-response initiator is used to preferentially form a highly cross-linked dense layer on the side near the light source, achieving rapid interface stabilization; unreacted monomers are retained in the low-cross-linked region, and then a thermally triggered slow-response initiator is used to gradually polymerize the remaining monomers, ultimately forming a gradient cross-linked structure; this avoids the possibility of internal residues being sealed and unprocessable due to one-time strong curing.

[0071] This invention emphasizes that the gel-state polymer electrolyte is disposed on the surface of the inner functional layer of the positive electrode, so that the gel-state polymer electrolyte first contacts the outer functional layer on the surface of the positive electrode active material layer, realizing the "in-situ capture" of residual unreacted monomers, while the inner functional layer between the functional current collector and the positive electrode active material layer is responsible for deep suppression of diffusion and side reactions.

[0072] Preferably, the mass fraction of the fast-response initiator in the gel polymer electrolyte is 0.2-1 wt%, for example, it can be 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%, or 1 wt%.

[0073] It should be noted that the fast-response initiator is selected from photoinitiators or thermal initiators with low decomposition temperatures, including but not limited to 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L), 2-hydroxy-2-methyl-1-phenyl-1-propanone (Irgacure 1173), bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure 819), or benzoyl peroxide, etc.

[0074] Preferably, the slow-response initiator in the gel polymer electrolyte has a mass fraction of 0.05-0.5 wt%, for example, it can be 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, or 0.5 wt%.

[0075] It should be noted that slow-response initiators are selected from thermal initiators with high decomposition temperatures, including but not limited to azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (V-65), or azobismethoxyisoheptanenitrile (V-70).

[0076] Preferably, in the gel-state polymer electrolyte, the polymer monomers include acrylate monomers and / or methacrylate monomers.

[0077] Preferably, the polymer monomer comprises any one or a combination of at least two of polyethylene glycol diacrylate (PEGDA), polyethylene glycol dimethacrylate (PEGDMA), hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate (HPMA), butyl acrylate (BA), ethyl acrylate (EA), or trimethylolpropane triacrylate (TMPTA).

[0078] Preferably, in the gel-state polymer electrolyte, the mass fraction of polymer monomers is 10-35 wt%, for example, it can be 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, or 35 wt%.

[0079] Preferably, the crosslinking agent comprises any one or a combination of at least two of trimethylolpropane triacrylate (TMPTA), ethoxylated trimethylolpropane triacrylate (ETPTA), or pentaerythritol triacrylate (PETA).

[0080] Preferably, in the gel polymer electrolyte, the mass fraction of the crosslinking agent is 0.5-5 wt%, for example, it can be...

[0081] Preferably, the solvent includes any one or a combination of at least two of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC).

[0082] Preferably, the mass fraction of the solvent in the gel polymer electrolyte is 40-75 wt%, for example, it can be 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, or 75 wt%.

[0083] Preferably, the lithium salt comprises lithium bisfluorosulfonylimide (LiFSI) and / or lithium bistrifluoromethylsulfonylimide (LiTFSI).

[0084] Preferably, the mass fraction of lithium salt in the gel polymer electrolyte is 5-20 wt%, for example, it can be 5 wt%, 10 wt%, 15 wt% or 20 wt%.

[0085] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0086] Compared with the prior art, the present invention has the following beneficial effects: This invention adds an external functional layer to the surface of the positive electrode active material layer. This external functional layer employs highly reactive but voltage-threshold-controlled voltage-responsive groups, which can preferentially capture and convert polymer monomers in the activated state. Meanwhile, residual or subsequently penetrating polymer monomers into the positive electrode active material layer can be further consumed and adsorbed by the internal functional layer on the surface of the functional current collector through chemically captured groups and physical adsorption sites. The two layers form a gradient-like synergistic effect in space, enabling multi-level interception and efficient consumption of unreacted monomers remaining after in-situ polymerization of the gel-state polymer electrolyte. This significantly suppresses the oxidative decomposition side reactions of monomers at the high-voltage positive electrode interface, reduces the positive electrode interface impedance, and prevents the precipitation of active materials, thereby effectively improving the battery's safety performance and cycle stability, and significantly enhancing the battery's overall electrochemical performance. Attached Figure Description

[0087] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet provided in Embodiment 1 of the present invention.

[0088] Among them, 1-functional current collector; 2-inner functional layer; 21-polymer reaction layer; 22-polymer adsorption layer; 3-positive electrode active material layer; 4-outer functional layer. Detailed Implementation

[0089] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0090] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0091] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" means a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this invention, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0092] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this invention. The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various locations throughout the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this invention can be combined with other embodiments that do not conflict with the technology. The ordinal numbers "first," "second," "third," and "fourth," etc., used in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect" in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0093] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined based on its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0094] Example 1 This embodiment provides a positive electrode sheet, the structural schematic diagram of which is shown below. Figure 1 As shown, the positive electrode includes: Functional current collector 1.

[0095] An inner functional layer 2 is disposed on both sides of the functional current collector 1. Along the direction away from the functional current collector 1, the inner functional layer 2 includes a polymer reaction layer 21 and a polymer adsorption layer 22 stacked together. In the polymer reaction layer 21, the chemically trapped groups are amino groups. The polymer adsorption layer 22 is made of Al2O3 nanoparticles.

[0096] Positive electrode active material layer 3 is disposed on the surface of the inner functional layer 2.

[0097] An external functional layer 4 is disposed on the surface of the positive electrode active material layer 3. The external functional layer 4 includes voltage-responsive groups, which are used to capture and convert polymer monomers in an activated state. The oxidation potential of the voltage-responsive groups is >4.2V, and the voltage-responsive groups are nitroxide free radical groups.

[0098] The polymer reaction layer 21 has a single-sided thickness of 50 nm, the polymer adsorption layer 22 has a single-sided thickness of 20 nm, and the thickness ratio of the polymer reaction layer 21 to the polymer adsorption layer 22 is 1:0.4; the external functional layer 4 has a single-sided thickness of 120 nm; the functional current collector 1 includes a PET film with a thickness of 4.5 μm and an Al layer disposed on both sides of the PET film, the Al layer having a thickness of 1200 nm.

[0099] This embodiment also provides a method for preparing the above-mentioned positive electrode sheet, the method comprising the following steps: (1) Preparation of functional current collectors: The functional current collector is obtained by depositing Al layers on both sides of a PET film using magnetron sputtering. The parameters of the magnetron sputtering method include: aluminum target (purity: 99.99%) as the target material, power of 2.8KW, argon flow rate of 70mL / min, coating vacuum of 0.1Pa, coating time of 100s, and cooling temperature of the main roller during the coating process of 0℃.

[0100] (2) Preparation of the inner functional layer: (2-1) The functional current collector is immersed in a 0.5 wt% sodium hydroxide solution for 20 s, rinsed with deionized water and dried with nitrogen to obtain a surface-activated functional current collector. Then it is immersed in a 1 wt% reactive trapping solution for 1.5 min. After that, it is dried in an 80°C hot air oven for 10 min to obtain a polymer reaction layer with a single-sided thickness of 50 nm. The reactive trapping solution includes 3-aminopropyltriethoxysilane and the solvent is ethanol.

[0101] (2-2) A 0.5 wt% adsorbent capture liquid is sprayed onto the surface of the polymer reaction layer and dried to form a polymer adsorption layer with a single-sided thickness of 20 nm; wherein, the adsorbent capture liquid is obtained by ultrasonically dispersing Al2O3 nanoparticles with a particle size D50 of 50 nm in ethanol for 10 min.

[0102] (3) Preparation of the positive electrode active material layer: First, NCM622, graphite, and polyvinylidene fluoride were added to N-methylpyrrolidone in a mass ratio of 94:3:3, and stirred at 500 rpm for 2 hours in a planetary mixer to obtain a positive electrode slurry with a solid content of 70 wt%. Then, the positive electrode slurry was coated onto the surface of the inner functional layer by a scraper to a thickness of 120 μm. After drying, it was rolled to obtain the positive electrode active material layer.

[0103] (4) Preparation of the outer functional layer: A 0.2 wt% external functional layer precursor solution was sprayed onto the surface of the positive electrode active material layer and dried at 60°C for 10 min to form the external functional layer with a single-sided thickness of 120 nm. The external functional layer precursor solution included 2,2,6,6-tetramethylpiperidine-1-oxy and anhydrous isopropanol as the solvent.

[0104] This embodiment also provides a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and a gel polymer electrolyte.

[0105] The positive electrode sheet is prepared using the method described above; the negative electrode sheet uses copper foil as the negative current collector and artificial graphite as the negative active material; the separator is a polyethylene separator coated with alumina ceramic with a thickness of 25 μm.

[0106] The gel-state polymer electrolyte is disposed on the surface of the inner functional layer of the positive electrode sheet; the gel-state polymer electrolyte comprises polymer monomers, crosslinking agents, lithium salts, fast-response initiators, and slow-response initiators in a mass ratio of 25:2:10:0.4:0.2; the polymer monomers comprise PEGDA and HEMA in a mass ratio of 1.5:1, the crosslinking agent is TMPTA, the solvent is composed of EC and DEC in a volume ratio of 1:1, the lithium salt is LiFSI, the fast-response initiator is TPO, and the slow-response initiator is AIBN.

[0107] The preparation method of the gel polymer electrolyte includes: PEGDA and HEMA were selected as polymer monomers, and TMPTA was selected as a crosslinking agent. Then, a solvent composed of EC and DEC was added, and lithium salt LiFSI was added. The mixture was stirred for 2 hours under nitrogen protection until the lithium salt was completely dissolved. TPO was used as a fast-response photoinitiator and AIBN was used as a slow-response thermal initiator. After adding these, the mixture was stirred for another 30 minutes to obtain a uniform gel-state polymer electrolyte.

[0108] Example 2 The difference between this embodiment and embodiment 1 is that the spraying process in step (4) is adjusted so that the single-sided thickness of the outer functional layer is 80nm.

[0109] The remaining preparation methods and parameters are consistent with those in Example 1.

[0110] Example 3 The difference between this embodiment and embodiment 1 is that the spraying process in step (4) is adjusted so that the single-sided thickness of the outer functional layer is 320nm.

[0111] The remaining preparation methods and parameters are consistent with those in Example 1.

[0112] Example 4 The difference between this embodiment and Embodiment 1 is that the concentration of the reactive capture solution is 0.1 wt%.

[0113] The remaining preparation methods and parameters are consistent with those in Example 1.

[0114] Example 5 The difference between this embodiment and Embodiment 1 is that the concentration of the reactive capture solution is 3 wt%.

[0115] The remaining preparation methods and parameters are consistent with those in Example 1.

[0116] Example 6 The difference between this embodiment and Embodiment 1 is that the concentration of the adsorbent capturing liquid is 0.1 wt%.

[0117] The remaining preparation methods and parameters are consistent with those in Example 1.

[0118] Example 7 The difference between this embodiment and Embodiment 1 is that the concentration of the adsorbent capturing liquid is 2 wt%.

[0119] The remaining preparation methods and parameters are consistent with those in Example 1.

[0120] Example 8 The difference between this embodiment and Embodiment 1 is that, in the gel polymer electrolyte, AIBN is replaced by TPO by mass.

[0121] The remaining preparation methods and parameters are consistent with those in Example 1.

[0122] Example 9 The difference between this embodiment and Embodiment 1 is that, in the gel polymer electrolyte, TPO is replaced by AIBN by mass.

[0123] The remaining preparation methods and parameters are consistent with those in Example 1.

[0124] Comparative Example 1 The difference between this comparative example and Example 1 is that step (2) is not performed, that is, no internal functional layer is set.

[0125] The remaining preparation methods and parameters are consistent with those in Example 1.

[0126] Comparative Example 2 The difference between this comparative example and Example 1 is that the inner functional layer is only a polymer reaction layer, that is, step (2-2) is not performed.

[0127] The remaining preparation methods and parameters are consistent with those in Example 1.

[0128] Comparative Example 3 The difference between this comparative example and Example 1 is that the inner functional layer is only a polymer adsorption layer, that is, step (2-1) is not performed.

[0129] The remaining preparation methods and parameters are consistent with those in Example 1.

[0130] Comparative Example 4 The difference between this comparative example and Example 1 is that step (4) is not performed, that is, no outer functional layer is set.

[0131] The remaining preparation methods and parameters are consistent with those in Example 1.

[0132] Performance testing The lithium-ion batteries provided in the above embodiments and comparative examples were subjected to staged curing, the steps of which included: applying light with a wavelength of 365 nm and an intensity of 12 mW / cm² from the positive electrode side. 2 After irradiation with ultraviolet light for 2 minutes, the battery was left to stand for 15 minutes, followed by heating at 70°C for 4 hours. Then, a formation process was performed, including: an initial charge at 0.1C (Note: During the initial charge, voltage-responsive groups in the outer functional layer of the positive electrode surface are activated, capturing residual unpolymerized monomers and active intermediates in the gel electrolyte, thereby forming a stable chemical anchoring structure in situ at the positive electrode interface), with a cutoff voltage set at 4.3V. After formation, the lithium-ion battery underwent the following tests: 1) High-voltage static expansion test: The battery is charged to 4.45V and placed in a 25℃ environment for 48 hours. Before and after static, the battery thickness change is measured with a micrometer and the thickness expansion rate is calculated. At the same time, the appearance of the battery is observed to determine whether there is an obvious bulging NG phenomenon.

[0133] 2) High voltage and high temperature static self-discharge test: The battery is charged to 4.45V and placed in a 60℃ environment for 24 hours. The voltage decay rate is measured.

[0134] 3) High voltage cycle performance: The battery is continuously cycled for 300 cycles at a 0.5C rate within the voltage range of 3-4.45V, and the capacity retention rate is calculated as the battery capacity after 300 cycles / the battery capacity at the first cycle × 100%.

[0135] 4) EIS impedance: After completing the normalization and target cycle, let the battery stand for 3 hours to allow polarization to balance. Use an electrochemical workstation to measure the AC impedance at 100kHz-10mHz and extract the Rct value.

[0136] The test results are shown in Table 1.

[0137] Table 1 analyze: As shown in Table 1, this invention adds an external functional layer to the surface of the positive electrode active material layer. This external functional layer employs highly reactive but voltage-threshold-controlled voltage-responsive groups, which can preferentially capture and convert polymer monomers in the activated state. Meanwhile, residual or subsequently penetrating polymer monomers into the positive electrode active material layer can be further adsorbed and / or consumed by the internal functional layer on the surface of the functional current collector through chemical polymer monomer capture groups and / or physical adsorption sites. The two elements form a gradient synergistic effect in space, enabling multi-level interception and efficient consumption of unreacted monomers remaining after in-situ polymerization of the gel-state polymer electrolyte. This significantly suppresses the oxidative decomposition side reactions of monomers at the high-voltage positive electrode interface, reduces the positive electrode interface impedance, and prevents the precipitation of active materials, thereby effectively improving the battery's safety performance and cycle stability, and significantly improving the battery's overall electrochemical performance.

[0138] As can be seen from the comparison between Example 1 and Examples 2-3, if the thickness of one side of the outer functional layer is too small, the thickness uniformity will be poor, and the polymer monomers that penetrate the positive electrode active material layer cannot be effectively captured and converted, resulting in interface failure. If the thickness of one side of the outer functional layer is too large, the interface impedance will increase, the thickness uniformity will be poor, the interface will fail, and the monomer penetration and side reactions will be aggravated.

[0139] As can be seen from the comparison between Example 1 and Examples 4-5, if the concentration of the reactive trapping liquid is too low, the number of chemical trapping groups in the inner functional layer will be insufficient, which will not be able to effectively consume the residual polymer monomers that penetrate the positive electrode active material layer, resulting in side reactions and an increase in the positive electrode interface impedance. If the concentration of the reactive trapping liquid is too high, it will hinder the normal transport of lithium ions, and excessive chemical trapping groups may damage the interface stability and reduce the electrochemical performance of the battery.

[0140] As can be seen from the comparison between Example 1 and Examples 6-7, if the concentration of the adsorbent capture liquid is too low, the distribution of physical adsorption sites in the inner functional layer is sparse and cannot cover the reaction blind zone of the chemical capture group, resulting in some monomers still being able to diffuse to the vicinity of the current collector; if the concentration of the adsorbent capture liquid is too high, it will increase the ion transport resistance, and the excessively thick adsorption layer is prone to structural collapse during the cycle, affecting the long-term stability of the inner functional layer.

[0141] As can be seen from the comparison between Example 1 and Examples 8-9, if the gel polymer electrolyte does not contain a slow-response initiator, the unreacted monomers inside the system are sealed in the highly cross-linked network and cannot polymerize further. During long-term cycling, these residual monomers slowly migrate to the positive electrode interface and are oxidized, resulting in an increase in impedance. If the gel polymer electrolyte does not contain a fast-response initiator, it lacks the rapid interface stabilization during the light exposure stage, which easily forms local highly cross-linked regions and uncured regions, resulting in poor interface contact and ultimately a decrease in battery performance.

[0142] As can be seen from the comparison between Example 1 and Comparative Example 1, if an inner functional layer is not provided, the polymer monomers that remain or penetrate the positive electrode active material layer cannot be further consumed and adsorbed, resulting in the problem of unreacted monomer residues in the gel-state polymer electrolyte after in-situ polymerization not being completely solved.

[0143] As can be seen from the comparison between Example 1 and Comparative Examples 2-3, if the inner functional layer is only a polymer monomer reaction layer, it cannot cover the capture blind zone of the polymer reaction layer, resulting in incomplete removal of residual polymer monomers. These monomers may still migrate to the surface of the functional current collector, causing corrosion or side reactions. If the inner functional layer is only a polymer monomer adsorption layer, the residual polymer monomers lack chemical reactions to consume or transform them. Under long-term cycling or high-temperature conditions, the adsorbed monomers may desorb and re-diffuse, failing to eliminate the risk of interface failure caused by the monomers.

[0144] As can be seen from the comparison between Example 1 and Comparative Example 4, if no external functional layer is provided, the polymer monomers that penetrate the positive electrode active material layer are directly exposed to the high-voltage positive electrode interface. The side reaction of monomer oxidation and decomposition is aggravated, resulting in a sharp increase in the positive electrode interface impedance, destruction of the active material structure, and a significant reduction in battery performance.

[0145] It should be noted that the present invention is illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes: Functional current collector; An inner functional layer is disposed on at least one side surface of the functional current collector, and the inner functional layer includes chemical trapping groups and physical adsorption sites; A positive electrode active material layer is disposed on the surface of the inner functional layer; An external functional layer is disposed on the surface of the positive electrode active material layer. The external functional layer includes voltage-responsive groups, which are used to capture and convert polymer monomers in an activated state.

2. The positive electrode sheet according to claim 1, characterized in that, Along a direction away from the functional current collector, the inner functional layer includes a polymer reaction layer and a polymer adsorption layer stacked together; In the polymer reaction layer, the chemically trapped groups include any one or a combination of at least two of epoxy groups, amino groups, or thiol groups; The polymer adsorption layer is made of any one or a combination of at least two of the following: metal oxides, metal fluorides, or boron-based oxides.

3. The positive electrode sheet according to claim 2, characterized in that, The thickness of the polymer reaction layer on one side is 10-100 nm; And / or, the thickness of one side of the polymer adsorption layer is 10-50 nm; And / or, the thickness ratio of the polymer reaction layer to the polymer adsorption layer is 1:(1-10).

4. The positive electrode sheet according to claim 1, characterized in that, The oxidation potential of the voltage-responsive group is >4.2V; And / or, the voltage-responsive group includes any one or a combination of at least two of the following: nitroxide radical group, quinone group, thioether group or aromatic amine group; And / or, the thickness of one side of the outer functional layer is 100-300 nm; And / or, the functional current collector includes a polymer base film and a metal layer disposed on at least one side surface of the polymer base film.

5. A method for preparing a positive electrode sheet as described in any one of claims 1-4, characterized in that, The preparation method includes the following steps: Preparation of functional current collectors; An inner functional layer, a positive electrode active material layer, and an outer functional layer are sequentially prepared on at least one side surface of the functional current collector to obtain the positive electrode sheet.

6. The preparation method according to claim 5, characterized in that, The preparation steps of the inner functional layer include: (a) Provide a reactive capture solution; The functional current collector is immersed in the reactive capturing liquid and dried to form a polymer reaction layer; (b) Provide an adsorbent capture solution; The adsorbent capturing liquid is coated on the surface of the polymer reaction layer and dried to form a polymer adsorption layer; And / or, the fabrication steps of the outer functional layer include: Provide precursor solution for outer functional layer; The precursor solution of the outer functional layer is coated on the surface of the positive electrode active material layer and dried to form the outer functional layer.

7. The preparation method according to claim 6, characterized in that, The concentration of the reactive capture solution is 0.5-2 wt%; And / or, the reactive capture solution includes any one or a combination of at least two of the following: ethylenediamine, tetraethylenepentamine, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, pentaerythritol tetramercaptoacetate, or polyethyleneimine. And / or, the concentration of the adsorbent capturing liquid is 0.5-1 wt%; And / or, the adsorbent capture liquid includes any one or a combination of at least two of the following: metal oxide nanoparticles, metal fluoride nanoparticles, or boron-based oxide nanoparticles; And / or, the concentration of the outer functional layer precursor solution is 0.1-5 wt%; And / or, the outer functional layer precursor solution includes any one or a combination of at least two of tetramethylpiperidine oxide, benzoquinone, aniline, diphenylamine, pyridinium imine, or anisole.

8. The preparation method according to claim 5, characterized in that, The preparation method includes the following steps: (1) Preparation of functional current collectors: Metal layers are deposited on both sides of the polymer-based film to obtain the functional current collector; The metal layer includes an Al layer; the thickness of the metal layer on one side is 400-2000 nm. (2) Preparation of the inner functional layer: (2-1) The functional current collector is subjected to surface activation treatment, and then immersed in a reactive trapping solution with a concentration of 0.5-2wt% for 1-10 min, and dried at 60-100℃ for 3-15 min to obtain a polymer reaction layer with a single-sided thickness of 10-100 nm; wherein, the reactive trapping solution includes any one or a combination of at least two of ethylenediamine, tetraethylenepentamine, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, pentaerythritol tetramercaptoacetate or polyethyleneimine; (2-2) An adsorbent capturing liquid with a concentration of 0.5-1wt% is sprayed onto the surface of the polymer reaction layer and dried to form a polymer adsorption layer with a single-sided thickness of 10-50nm; wherein, the solute in the adsorbent capturing liquid is nanoparticles, and the nanoparticles include any one or a combination of at least two of metal oxide nanoparticles, metal fluoride nanoparticles or boron-based oxide nanoparticles, and the particle size D50 of the nanoparticles is 20-100nm; (3) Preparation of the positive electrode active material layer: A positive electrode slurry is coated on the surface of the inner functional layer and dried to obtain a positive electrode active material layer; wherein, the solid content of the positive electrode slurry is 60-75 wt%, and the dry basis of the positive electrode slurry includes the following components by weight: 90-95 parts of positive electrode active material, 1-3 parts of conductive agent, and 1-3 parts of binder. (4) Preparation of the outer functional layer: A 0.1-5 wt% external functional layer precursor solution is sprayed onto the surface of the positive electrode active material layer and dried to form an external functional layer with a single-sided thickness of 100-300 nm; wherein the external functional layer precursor solution includes any one or a combination of at least two of tetramethylpiperidine oxide, benzoquinone, aniline, diphenylamine, pyridinium imine, or anisole.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and a gel polymer electrolyte; The positive electrode sheet is the positive electrode sheet according to any one of claims 1-4, or is prepared by the preparation method according to any one of claims 5-8; The gel-state polymer electrolyte is disposed on the surface of the side where the inner functional layer of the positive electrode sheet is located; The gel-state polymer electrolyte includes polymer monomers, crosslinking agents, solvents, lithium salts, fast-response initiators, and slow-response initiators.

10. The lithium-ion battery according to claim 9, characterized in that, In the gel-state polymer electrolyte, the mass fraction of the fast-response initiator is 0.2-1 wt%. And / or, in the gel polymer electrolyte, the mass fraction of the slow-response initiator is 0.05-0.5 wt%; And / or, in the gel-state polymer electrolyte, the polymer monomers include acrylate monomers and / or methacrylate monomers; And / or, in the gel-state polymer electrolyte, the mass fraction of the polymer monomer is 10-35 wt%.

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