High-safety composite pole piece, preparation method and application thereof

Abstract

This invention belongs to the field of battery material technology, and relates to a high-safety composite electrode, its preparation method, and its application. This electrode effectively addresses or mitigates cell safety issues, comprising a current collector and an active layer coated on the current collector, with a flame-retardant layer coated on the active layer. The active layer is located between the current collector and the flame-retardant layer, and the flame-retardant layer is composed of discrete lattice units. The flame-retardant layer contains a core-shell structured flame-retardant component, formed by a dispersant encapsulating the flame retardant. The dispersant has slow-release properties, allowing the flame retardant to be slowly released during cell heating. Applying this electrode to a battery imparts excellent electrical performance and thermal stability. This invention involves first preparing a glue solution, then mixing the glue solution with a flame retardant and a dispersant to prepare a flame-retardant slurry, and finally coating the slurry onto an electrode substrate to obtain the electrode. This method can be seamlessly integrated with existing electrode production processes, requires less flame retardant, has controllable costs, and is suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and relates to a high-safety composite electrode, its preparation method, and its application. Background Technology

[0002] Lithium-ion battery safety is directly related to the personal and property safety of users, and effectively preventing combustion and explosion accidents caused by thermal runaway is a hot research topic in the industry. Lithium-ion battery safety is a key prerequisite for the large-scale deployment of core scenarios such as new energy vehicles and energy storage power stations, and can ensure the steady development of the new energy industry.

[0003] In practical applications, millisecond-level instantaneous short circuits within a battery cell can trigger uncontrollable thermal runaway. Adding flame retardants to the battery cell can improve thermal runaway, reduce the risk of combustion and explosion, and enhance safety. Currently, there are several ways to add flame retardants to battery cells, including directly adding them to the electrolyte, adding them to the positive or negative electrode slurry, adding them to the positive electrode edge coating, or directly applying a functional flame retardant coating to the entire positive or negative electrode sheet.

[0004] Patent document CN115911552A discloses a flame-retardant electrolyte comprising: lithium salt, carbonate organic solvent, co-solvent, and flame-retardant additive; the concentration of lithium salt in the electrolyte composed of lithium salt and carbonate organic solvent is 0.5~5 mol / L; the volume ratio of carbonate electrolyte to flame-retardant additive is 100:(1~30); the volume ratio of co-solvent to flame-retardant additive is (4~120):(1~5); the co-solvent is a solvent capable of dissolving the flame-retardant additive, and the flame-retardant additive is a perfluorohexane derivative. This patent application proposes introducing a co-solvent that does not interact with lithium ions into the electrolyte, using the bridging effect of the co-solvent to introduce the insoluble flame retardant into the conventional electrolyte. Directly adding the flame retardant to the electrolyte is the most direct and convenient method, but it easily reduces capacity and cycle life, increases internal resistance, and affects the electrical performance of the battery cell.

[0005] Patent document CN111129467B discloses a positive electrode slurry comprising 85-97 parts by weight of a positive electrode active material, 1-6 parts by weight of a conductive agent, 1-5 parts by weight of a binder, 0.5-8 parts by weight of a flame retardant, and a solvent; wherein the flame retardant has a number average molecular weight of 10,000 to 500,000 and a general structural formula of [insert formula here]. In this context, R1 and R2 may be the same or different, independently representing C1-10 alkyl, C2-10 alkenyl, C2-10 alkynyl, C3-10 cycloalkyl, C3-10 cycloalkenyl, C6-15 aryl, or C5-15 heteroaryl. One or more hydrogen atoms in R1 and R2 may optionally be substituted with fluorine, C1-10 alkyl, or C6-15 aryl. Patent document CN109888264A discloses a high-energy lithium-ion battery negative electrode slurry, which includes a negative electrode active material, a conductive agent, a binder, a defoamer, a polymer additive, a dispersant additive, a thickener, a flame retardant, a buffer solution, and the balance being a solvent. The flame retardant is triphenyl phosphate and tetrabromophthalic anhydride, with a mass ratio of triphenyl phosphate to tetrabromophthalic anhydride of 3:1. Adding flame retardants to the positive or negative electrode slurry can achieve full-area flame retardancy by uniformly mixing the flame retardant with the active material, making it compatible with conventional coating processes. However, this reduces the proportion of active material, directly lowering the cell's specific capacity and energy density. It can also easily damage the positive and negative electrode interface film, inducing side reactions that lead to cycle decay. Furthermore, it is prone to incompatibility with the positive and negative electrode slurries, resulting in problems such as subsequent electrode powder shedding.

[0006] In addition, much research has focused on adding flame retardants to the edge coating of the positive electrode, specifically adding them only to the non-active areas at the electrode edges. This avoids encroaching on the space of the positive and negative electrode active materials, and the dosage is much lower than that used in the slurry, resulting in minimal impact on the overall production cost of the battery cell. However, the flame retardant coverage is limited, acting only on the electrode edges and failing to suppress the combustion reaction of the electrolyte and electrode body within the battery cell, thus limiting the overall flame retardant effect. Another area of ​​research involves directly applying a functional coating of flame retardant to the entire positive or negative electrode, improving battery cell safety through the action of the flame retardant. Commonly used nitrogen-based or phosphorus-based flame retardants typically improve safety by generating a large amount of inert gas to dilute oxygen. However, nitrogen- or phosphorus-containing compounds instantly generate a large amount of gas when they reach their decomposition point (150~400℃). In practical applications, this large amount of gas generates a significant impact on the battery cell, leading to internal core short circuits and more severe thermal runaway, further negatively impacting battery safety. Summary of the Invention

[0007] Based on this, the purpose of the present invention is to provide a high-safety composite electrode sheet, which has a flame-retardant layer coated on the surface of the positive electrode sheet or the negative electrode sheet. The flame-retardant layer contains flame-retardant slow-release components, which can specifically solve or mitigate the safety problems of the battery cell.

[0008] The present invention also provides a method for preparing the high-safety composite electrode, its application in batteries, and a high-safety battery.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] The present invention provides a high-safety composite electrode, comprising a current collector and an active layer coated on the current collector, wherein a flame-retardant layer is coated on the active layer; the active layer is located between the current collector and the flame-retardant layer, and the flame-retardant layer is composed of discrete lattice units.

[0011] Furthermore, the current collector includes aluminum foil or copper foil, wherein the active layer coated on the surface of the aluminum foil is a positive electrode coating, and the active layer coated on the surface of the copper foil is a negative electrode coating.

[0012] Furthermore, the positive electrode coating contains a positive electrode active material, a second binder, and a first conductive agent; preferably, the positive electrode active material includes lithium iron phosphate (LFP), the second binder includes polyvinylidene fluoride (PVDF), and the first conductive agent includes carbon black (SP) and / or carbon nanotubes (CNTs), and the mass ratio of the positive electrode active material, the second binder, and the first conductive agent is 96:2:2.

[0013] Furthermore, the negative electrode coating contains a negative electrode active material, a second conductive agent, and a third binder; preferably, the negative electrode active material includes graphite (Gr), the second conductive agent includes carbon black (SP), and the third binder includes carboxymethyl cellulose (CMC) and / or styrene-butadiene rubber (SBR), and the mass ratio of the negative electrode active material, the second conductive agent, and the third binder is 96:1:3.

[0014] Furthermore, the flame-retardant layer is coated on all or part of the surface of the active layer, and the electrode includes a stacked electrode or a wound electrode; the part includes the edge area and / or the area near the tab of the stacked electrode, or the core area and / or the tab side of the wound electrode.

[0015] Furthermore, the thickness of the flame-retardant layer is 5~25μm, and the dot matrix unit includes circular units with a diameter of 50~100μm and a spacing of 250~350μm. The density of the flame-retardant layer dot matrix can be adjusted according to the most critical points of safety issues in different types of battery cells.

[0016] Furthermore, the flame-retardant layer contains a core-shell structured flame-retardant component and a first binder, wherein the core-shell structured flame-retardant component is formed by a dispersant encapsulating the flame-retardant; the mass ratio of the flame-retardant, the first binder, and the dispersant is 70%~85%: 1.5%~3.5%: 13.5%~30%.

[0017] Further, the flame retardant comprises any one or more of aluminum diethylphosphonate (ADP), brominated epoxy, brominated polystyrene (BPS), tetrachlorophthalic anhydride (TCPA), bis(hexachlorocyclopentadiene)cyclooctane (DP), magnesium hydroxide, aluminum hydroxide, zinc borate, antimony trioxide, and mica, compounded to form a composite flame retardant; the first binder comprises polyacrylic acid (PAA), styrene-butadiene rubber (SBR), or polyvinylidene fluoride (PVDF), and the dispersant comprises hydroxypropyltrimethylammonium chloride chitosan (HTCC).

[0018] Preferably, the flame retardant is a composite flame retardant formed by compounding aluminum diethylphosphonate (ADP), antimony trioxide, and bis(hexachlorocyclopentadiene)cyclooctane (DP) in a certain proportion, wherein the mass ratio of aluminum diethylphosphonate (ADP), antimony trioxide, and bis(hexachlorocyclopentadiene)cyclooctane (DP) in the composite flame retardant is 1:1:1; its flame retardant effect is mainly achieved through the synergistic effect of gas phase flame retardancy and condensed phase flame retardancy, thus achieving a high-efficiency flame retardant effect.

[0019] This invention further provides a method for preparing the above-mentioned high-safety composite electrode sheet. First, an active slurry is coated onto a current collector to form an active layer. Then, a flame-retardant slurry is coated onto the active layer. After segmented drying to form a flame-retardant layer, the high-safety composite electrode sheet is obtained. The preparation process of the flame-retardant slurry includes: S1, mixing a first binder and a solvent in a certain proportion to obtain a colloid. The solvent includes deionized water, ethanol, or N-methylpyrrolidone (NMP), and the solid content of the colloid is 6%~7%. S2, mixing a flame retardant, the colloid from S1, and a dispersant in a certain proportion, and obtaining a flame-retardant slurry after degassing. The mass ratio of the flame retardant, the first binder, and the dispersant in the colloid is 70%~85%: 1.5%~3.5%: 13.5%~30%.

[0020] Furthermore, the segmented drying and heating process is as follows: the first stage is 70~80℃, the second stage is 100~120℃, and the third stage is 130~145℃.

[0021] Furthermore, the viscosity of the adhesive in S1 is 1500±500 mPa.s; the viscosity of the flame-retardant slurry before degassing in S2 is 5000~9000 mPa.s, and the slurry fineness is <25.

[0022] Preferably, in step S1, the first binder and solvent are added to a planetary mixer and stirred at a low speed of 300-500 r / min for 30-60 minutes to obtain a transparent and uniform adhesive solution; in step S2, the flame retardant, the adhesive solution described in step S1, and the dispersant are added to the planetary mixer and dispersed at a high speed of 1500-2500 r / min for 1-2 hours until a stable flame retardant slurry that is not prone to settling is formed; to ensure the coating effect, the stirring speed is reduced to 300-500 r / min after the viscosity reaches the standard before degassing.

[0023] This invention further provides an application of the above-mentioned high-safety composite electrode in a battery. Preferably, it is used in a lithium-ion battery.

[0024] Furthermore, the battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode and / or the negative electrode is the high-safety composite electrode.

[0025] The beneficial effects of this invention are:

[0026] This invention is based on coating the surface of the positive or negative electrode sheet with a dot-matrix arranged flame-retardant layer. This flame-retardant layer consists of an adhesive, a dispersant, and a flame retardant. Its unique dispersant, combined with an organic / inorganic composite flame retardant slurry, forms a flame-retardant slurry with a slow-release effect, effectively addressing or mitigating battery cell safety issues. This invention, while solving or mitigating battery cell safety problems, also offers several advantages:

[0027] 1. No sacrifice in electrochemical performance: The flame-retardant layer arranged in a dot matrix is ​​only coated in the local non-active areas or gaps of the electrode, without occupying the space of the positive and negative electrode active materials, and without damaging the integrity of the positive and negative electrode interface film. It has minimal impact on the cell capacity, cycle life and ion and electron conduction efficiency, and avoids the performance loss problem caused by adding flame retardants into the slurry.

[0028] 2. Flexible adjustment of flame retardant coverage: The dot matrix coating flame retardant can precisely cover the areas of the electrode sheet that are prone to safety risks. Its coverage is comprehensive and flexible (the coating position can be selected according to different stacking and winding, and the coating position can also be adjusted according to different prismatic, soft-pack and cylindrical cell structures. Depending on the situation, the dot matrix flame retardant layer can be concentrated on the tab side, the middle of the electrode sheet, the inside of the core or the end of the roll). With the help of the free radical quenching, inert gas release or carbon layer isolation effect of the flame retardant, the combustion chain reaction is blocked and the triggering and spread of thermal runaway is suppressed.

[0029] 3. Slow-release flame retardant coating reduces the impact of instantaneous gas generation: Utilizing the unique slow-release properties of hydroxypropyltrimethylammonium chloride chitosan (HTCC) dispersant, it acts on the surface of the flame retardant to form a core-shell structure, which can slowly release the flame retardant during the heating process of the battery cell. In addition, the different decomposition temperatures of the multiple composite flame retardants can effectively release the flame retardant gas in stages, avoiding the generation of a large amount of gas that would generate a huge impact on the battery cell, leading to a more serious thermal runaway caused by internal core short circuit. Attached Figure Description

[0030] To more clearly illustrate the technical solution of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the high-safety composite electrode structure in this invention. In the diagram, Figure A is a cross-sectional view and Figure B is a surface view.

[0032] Figure 2 This is a schematic diagram of the flame-retardant layer coating position in the high-safety composite electrode of the present invention. In the figure, A shows the dot matrix coating on the edge area of ​​the stacked electrode; B shows the dot matrix coating on the area of ​​the stacked electrode near the tab; C shows the dot matrix coating on the core area of ​​the wound electrode; and D shows the dot matrix coating on the tab side of the wound electrode.

[0033] Figure 3 This is a schematic diagram of the HTCC@flame retardant core-shell structure in the high-safety composite electrode flame retardant layer prepared in the embodiments of the present invention;

[0034] Figure 4 This is a schematic diagram of the preparation process of the high-safety composite electrode in this invention;

[0035] Figure 5 This is a summary table of electrode parameters and performance test results obtained in the embodiments and comparative examples of this invention;

[0036] Figure 6 This is a comparison chart of the discharge rate performance test results of batteries containing the electrodes prepared in the embodiments and comparative examples of this invention;

[0037] Figure 7 This is a comparison chart showing the capacity retention test results of batteries containing the electrodes prepared in the embodiments and comparative examples of this invention after 300 cycles at room temperature. Detailed Implementation

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All mentioned embodiments are implemented based on the technical solutions of the present invention, and detailed implementation processes are given. However, it should be stated that the scope of protection of the present invention is not limited to the following embodiments.

[0039] The following embodiments provide detailed implementation procedures for the technical solutions of the present invention. Unless otherwise specified, the experimental methods used in the following experimental examples are conventional methods; unless otherwise specified, the materials and reagents used are commercially available.

[0040] like Figure 1 As shown, the high-safety composite electrode of the present invention includes a current collector and an active layer coated on the current collector, and a flame-retardant layer is coated on the active layer; the active layer is located between the current collector and the flame-retardant layer. Figure 1 (Figure A in the diagram) The flame-retardant layer is composed of discrete lattice units. Figure 1 (See Figure B in the diagram). The flame-retardant layer has a thickness of 5-25 μm, and the lattice units include circular units with a diameter of 50-100 μm and a spacing of 250-350 μm. The density of the flame-retardant layer lattice can be adjusted according to the most critical points of safety issues in different types of battery cells. For example... Figure 2 As shown, the flame retardant layer is coated on all or part of the surface of the active layer, and the electrode includes a stacked electrode or a wound electrode; the local area includes the edge area and / or near the tab area of ​​the stacked electrode, or the core area and / or tab side of the wound electrode.

[0041] The current collector includes aluminum foil (positive electrode current collector) or copper foil (negative electrode current collector). The active layer coated on the surface of the aluminum foil is the positive electrode coating, and the active layer coated on the surface of the copper foil is the negative electrode coating. The positive electrode coating contains a positive electrode active material, a second binder, and a first conductive agent. Preferably, the positive electrode active material includes lithium iron phosphate (LFP), the second binder includes polyvinylidene fluoride (PVDF), and the first conductive agent includes carbon black (SP) and / or carbon nanotubes (CNTs), with a mass ratio of positive electrode active material, second binder, and first conductive agent of 96:2:2. The negative electrode coating contains a negative electrode active material, a second conductive agent, and a third binder. Preferably, the negative electrode active material includes graphite (Gr), the second conductive agent includes carbon black (SP), and the third binder includes carboxymethyl cellulose (CMC) and / or styrene-butadiene rubber (SBR), with a mass ratio of negative electrode active material, second conductive agent, and third binder of 96:1:3.

[0042] The flame-retardant layer contains a flame retardant, a first binder, and a dispersant, wherein the mass ratio of the flame retardant, the first binder, and the dispersant is 70%~85%: 1.5%~3.5%: 20%~30%. The flame retardant includes any one or more of aluminum diethylphosphinate (ADP), brominated epoxy, brominated polystyrene (BPS), tetrachlorophthalic anhydride (TCPA), bis(hexachlorocyclopentadiene)cyclooctane (DP), magnesium hydroxide, aluminum hydroxide, zinc borate, antimony trioxide, or mica, compounded to form a composite flame retardant. The first binder includes polyacrylic acid (PAA), styrene-butadiene rubber (SBR), or polyvinylidene fluoride (PVDF), and the dispersant includes hydroxypropyltrimethylammonium chloride chitosan (HTCC).

[0043] Preferably, the flame retardant is a composite flame retardant formed by compounding aluminum diethylphosphonate (ADP), antimony trioxide, and bis(hexachlorocyclopentadiene)cyclooctane (DP) in a certain proportion, wherein the mass ratio of aluminum diethylphosphonate (ADP), antimony trioxide, and bis(hexachlorocyclopentadiene)cyclooctane (DP) in the composite flame retardant is 1:1:1; its flame retardant effect is mainly achieved through the synergistic effect of gas-phase flame retardancy and condensed-phase flame retardancy, thus achieving a high-efficiency flame retardant effect. Figure 3 As shown, in the HTCC@flame retardant core-shell structure, the inner core consists of DP+ADP+antimony trioxide particles, and the outer shell is a physical layer formed by HTCC. It can be seen that the dispersant hydroxypropyltrimethylammonium chloride chitosan (HTCC) acts on the surface of the composite flame retardant (ADP+antimony trioxide+DP) to form a core-shell structure that can slowly release the flame retardant. Utilizing the unique slow-release properties of the hydroxypropyltrimethylammonium chloride chitosan dispersant, it acts on the surface of the flame retardant to form a core-shell structure, which can slowly release the flame retardant during the cell heating process. In addition, the different decomposition temperatures of the multiple composite flame retardants can effectively release the flame-retardant gas in stages, avoiding the generation of a large amount of gas that could generate a huge impact on the cell, leading to a more serious thermal runaway due to internal core short circuit.

[0044] like Figure 4 As shown, the process for preparing the high-safety composite electrode in this invention is as follows: First, an active slurry is coated onto a current collector to form an active layer, resulting in a positive or negative electrode substrate to be coated a second time; then, a flame-retardant slurry is coated (preferably using gravure coating for dot matrix coating) onto the active layer of the positive or negative electrode substrate, and after segmented drying to form a flame-retardant layer, a high-safety composite electrode (composite electrode coated with dot-matrix flame retardant) is obtained. The preparation process of the flame-retardant slurry is as follows: First, a binder and solvent are mixed in proportion to obtain a colloid; then, a flame retardant and a dispersant are added to the colloid, mixed in proportion, and after degassing, a flame-retardant slurry is obtained.

[0045] The embodiment of this invention completes the cell (i.e., battery) preparation through the following steps: preparation of positive and negative electrode slurries and flame retardant slurries, coating of positive and negative electrodes and flame retardant layers, roll pressing and slitting, cell winding, welding and assembly, baking, electrolyte injection 1, activation, formation, aging, electrolyte injection 2, sealing, and capacity testing. Then, the scheme is evaluated and assessed.

[0046] Example 1

[0047] The binder PAA and solvent NMP were added to a planetary mixer in a specific ratio and stirred at low speed for 60 minutes to produce a transparent and homogeneous slurry with a viscosity of 1500±500 mPa·s. The solid content of the slurry was 6.5%. Flame retardant ADP, antimony trioxide and DP (mass fraction ratio 1:1:1), the above slurry, and dispersant HTCC were dispersed at high speed (2500 r / min) in the planetary mixer for 2 hours at a specific ratio (flame retardant: binder: dispersant mass fraction ratio 76.5%:3.5%:20%). After the viscosity reached the standard (5000-9000 mPa·s), the stirring speed was reduced (500 r / min) to degas the slurry, forming the flame retardant slurry to be coated.

[0048] The positive electrode active material lithium iron phosphate (LFP), binder polyvinylidene fluoride (PVDF), conductive agent carbon black (SP), and conductive agent carbon nanotubes (CNTs) were uniformly dispersed in N-methylpyrrolidone (NMP) at a mass ratio of 96.0:2.0:1.2:0.8 to obtain the positive electrode slurry. The negative electrode active material graphite (Gr), conductive agent carbon black (SP), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were uniformly dispersed in deionized water at a mass ratio of 96.0:1.0:1.3:1.7 to obtain the negative electrode slurry. The positive electrode slurry was uniformly and stably coated on both sides of the prepared composite current collector, and the negative electrode slurry was uniformly and stably coated on both sides of the copper foil. The positive electrode coating surface density was 185 g / m². 2 The negative electrode coating surface density is 95 g / m². 2 After drying, the positive / negative electrode substrate to be coated is obtained.

[0049] Using a custom-designed gravure roller, the roller surface is laser-engraved to form the desired circular dot matrix, with a pit depth of 5μm, a diameter of 50μm, and a dot spacing of 300μm. The gravure plate is immersed in the aforementioned flame retardant slurry tank, and excess slurry is scraped off with a scraper, leaving only a measured amount of slurry in the pits. When the roller contacts the positive / negative electrode substrate to be coated, the slurry in the pits is transferred to the electrode surface under pressure, forming a discrete flame retardant dot matrix. The double-sided coated dot matrix flame retardant-coated composite electrode is then subjected to segmented heating and drying to complete the preparation of the high-safety dot matrix flame retardant-coated composite electrode.

[0050] Roll pressing and slitting yielded a matrix-shaped flame retardant-coated composite electrode sheet, with the positive electrode sheet having a compacted density of 2.40 g / m³. 3 The compaction density of the negative electrode sheet is 1.45 g / m³. 3 The positive and negative electrode sheets and separator are coated with a dot-matrix flame retardant and wound together. Then, the electrode tabs are flattened, welded and assembled, the cell is baked, and the electrolyte is injected for the first time (135g of electrolyte is injected, and the electrolyte formula mass fraction ratio is EC:DMC:LiPF6:VC:PS=23:57:10:5:5). The process includes activation, formation, aging, and a second electrolyte injection (15g of electrolyte is injected, and the electrolyte formula mass fraction ratio is EC:DMC:LiPF6:VC:PS=23:57:10:5:5). The process also includes sealing and capacity testing to obtain the 65150 lithium-ion cylindrical battery used in this invention (Note: 65150 is the cylindrical battery model).

[0051] Example 2

[0052] The difference between this embodiment and Embodiment 1 is that: a customized gravure roller is used, and the roller surface is laser-engraved to form the required circular dot matrix, with a pit depth of 10μm and a diameter of 50μm.

[0053] Example 3

[0054] The difference between this embodiment and Embodiment 1 is that: a customized gravure roller is used, and the roller surface is laser-engraved to form the required circular dot matrix, with a pit depth of 15μm and a diameter of 50μm.

[0055] Example 4

[0056] The difference between this embodiment and Embodiment 1 is that: a customized gravure roller is used, and the roller surface is laser-engraved to form the required circular dot matrix, with a pit depth of 20μm and a diameter of 50μm.

[0057] Example 5

[0058] The difference between this embodiment and Embodiment 1 is that a customized gravure roller is used, and the roller surface is laser-engraved to form the required circular dot matrix with a pit depth of 25 μm and a diameter of 50 μm. Everything else is the same as in Embodiment 1.

[0059] Example 6

[0060] The difference between this embodiment and Embodiment 1 is that a customized gravure roller is used, and the roller surface is laser-engraved to form the required circular dot matrix with a pit depth of 5μm and a diameter of 100μm. Everything else is the same as in Embodiment 1.

[0061] Example 7

[0062] The difference between this embodiment and Embodiment 1 is that a customized gravure roller is used, and the roller surface is laser-engraved to form the required circular dot matrix with a pit depth of 25μm and a diameter of 100μm. Everything else is the same as in Embodiment 1.

[0063] Comparative Example 1

[0064] The difference between this comparative example and Example 1 is that only the positive electrode is coated with a dot matrix flame retardant, while the negative electrode is not coated with a flame retardant.

[0065] Comparative Example 2

[0066] The difference between this embodiment and Embodiment 1 is that only the negative electrode sheet is coated with a dot matrix flame retardant, while the positive electrode is not coated with a flame retardant.

[0067] Comparative Example 3

[0068] The difference between this embodiment and Embodiment 1 is that neither the positive nor negative electrode plates are coated with flame retardant.

[0069] Implementation effect analysis

[0070] The electrodes and batteries prepared in Examples 1-7 and Comparative Examples 1-3 were subjected to the following tests, and the test results are as follows: Figures 5-6 As shown:

[0071] (1) Electrode internal resistance test: The resistivity of the electrode was tested at 25MPa using an electrode resistance meter.

[0072] (2) Battery internal resistance test: Use a battery AC internal resistance tester to test the battery's AC internal resistance (ACR).

[0073] (3) Battery thermal runaway performance test: The fully charged battery is heated according to the method in UL / 9540A until the cell thermal runaway occurs.

[0074] (4) Battery capacity retention rate at different discharge rates: At 25±5℃, three discharge rates were set as follows: 1C discharge capacity / 0.5C discharge capacity, denoted as 1C / 0.5C, 2C discharge capacity / 0.5C discharge capacity, denoted as 2C / 0.5C, and 3C discharge capacity / 0.5C discharge capacity, denoted as 3C / 0.5C.

[0075] (5) Battery cycle performance test: Capacity retention rate after 300 cycles at 0.5C discharge rate under 25±5℃. The charging rate and discharge rate are both set to 0.5C, and recorded as 0.5C / 0.5C; Capacity retention rate = 0.5C discharge capacity of the 300th cycle ÷ 0.5C discharge capacity of the 1st cycle.

[0076] Where C is the battery charge / discharge rate parameter, defined as the ratio of charging / discharging current to the battery's rated capacity. Its calculation follows the formula: charge / discharge rate = charging / discharging current (A) / rated capacity (Ah). For example, a battery with a rated capacity of 20Ah corresponds to a 0.5C rate when discharged at 10A.

[0077] Figure 5 Four major experimental items were compared for each modified experimental item in Examples 1-7 and Comparative Examples 1-3: flame retardant coating circle thickness, flame retardant coating circle diameter, flame retardant coating on a single positive electrode, and flame retardant coating on a single negative electrode. Applying flame retardant slightly increases electrode resistance; as electrode resistance increases, cell internal resistance also increases. The increase in electrode internal resistance changes with the thickness and area ratio of the flame retardant dot matrix coating. The cell's thermal runaway safety performance (according to UL 9540A) was tested. Figure 5 As demonstrated, flame retardants play a crucial role in the early stages of thermal runaway. They rapidly release free radical quenchers / form a char layer, blocking the combustion chain reaction and inhibiting heat spread within the cell. Externally, this results in the cell's surface temperature not exceeding 200°C. Furthermore, as the thickness and diameter of the flame retardant lattice increase, the maximum surface temperature of the cell can be effectively reduced to 78°C. In the comparative example, applying flame retardant only to the positive electrode and also to the negative electrode also improves battery safety performance; the highest surface temperature of the cell in the thermal runaway test was lower than that of the blank sample without flame retardant on the positive and negative electrodes.

[0078] Figure 6 as well as Figure 7 The figures compare the rate performance and cycle performance of batteries in Examples 1-7 and Comparative Examples 1-3. The figures demonstrate that the electrochemical performance of the embodiments of the present invention and the comparative examples is almost identical, proving the advantage of the present invention: it does not deteriorate the electrochemical performance of the battery cell, which is a significant advantage in practical applications. The dot-matrix coating method used in the present invention does not occupy space for active materials, does not hinder electrolyte wetting and ion conduction, and has no significant negative impact on cell capacity, cycle life, or internal resistance.

[0079] In summary, this invention forms a discrete functional protective layer by applying a core-shell structured flame retardant composite slurry to the surface of the positive and negative electrode sheets of a lithium-ion battery in a dot-matrix pattern. This layer combines three core functions: flame retardant protection, interface stabilization, and slow gas release. It addresses the technical pain points of traditional electrode protective layers (full coating / flame retardant incorporated into the slurry) that sacrifice electrochemical performance and have poor protective targeting, thus meeting the dual requirements of high safety and high energy density in lithium-ion battery cells. Through the optimization of this invention, the safety performance of the battery cell can be significantly improved while maintaining electrochemical performance. In particular, the core-shell structure and temperature-gradient gas release of this invention avoid internal short circuits in the battery cell caused by the instantaneous release of large amounts of gas from the flame retardant, which is of great significance for the future development of battery cells.

[0080] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-safety composite electrode, characterized in that, The device includes a current collector and an active layer coated on the current collector, the active layer being coated with a flame-retardant layer; the active layer is located between the current collector and the flame-retardant layer, the flame-retardant layer being composed of discrete lattice units; the flame-retardant layer contains a core-shell structured flame-retardant component and a first binder, the core-shell structured flame-retardant component being formed by a dispersant encapsulating the flame-retardant; the dispersant includes hydroxypropyltrimethylammonium chloride chitosan, the flame-retardant being formed by compounding aluminum diethylphosphonate, antimony trioxide, and bis(hexachlorocyclopentadiene)cyclooctane in a mass ratio of 1:1:1; the lattice units include circular units, the diameter of the circular units being 50~100μm and the spacing being 250~350μm; the flame-retardant layer is coated on all or part of the surface of the active layer, the electrode includes a wound electrode; the part includes the core area and / or the tab side of the wound electrode.

2. The high-safety composite electrode according to claim 1, characterized in that, The thickness of the flame-retardant layer is 5~25μm.

3. The high-safety composite electrode according to claim 1, characterized in that, The mass ratio of the flame retardant, the first binder, and the dispersant is 70%~85%: 1.5%~3.5%: 13.5%~30%.

4. The high-safety composite electrode according to claim 1, characterized in that, The first adhesive includes styrene-butadiene rubber (SBR) or polyvinylidene fluoride (PVDF).

5. A method for preparing a high-safety composite electrode according to any one of claims 1 to 4, characterized in that, First, an active slurry is coated onto the current collector to form an active layer. Then, a flame-retardant slurry is coated onto the active layer. After segmented drying to form a flame-retardant layer, a high-safety composite electrode is obtained. The flame-retardant slurry coating is a dot matrix coating, and the dot matrix coating adopts a gravure coating process. The segmented drying and heating process is as follows: the first stage is 70~80℃, the second stage is 100~120℃, and the third stage is 130~145℃. The preparation process of the flame-retardant slurry includes: S1, the first adhesive and solvent are mixed in a certain proportion to obtain an adhesive solution, wherein the solvent includes deionized water, ethanol or N-methylpyrrolidone, and the solid content of the adhesive solution is 6%~7%; S2, the flame retardant, the adhesive solution and dispersant mentioned in S1 are mixed in proportion, and after degassing, a flame retardant slurry is obtained. The mass ratio of the flame retardant, the first binder and the dispersant in the adhesive solution is 70%~85%: 1.5%~3.5%: 13.5%~30%. The viscosity of the adhesive in S1 is 1500±500 mPa.s; the viscosity of the flame-retardant slurry before degassing in S2 is 5000~9000 mPa.s, and the slurry fineness is <25.

6. The application of the high-safety composite electrode sheet according to any one of claims 1 to 4 in a battery.

7. The application of the high-safety composite electrode sheet according to claim 6 in a battery, characterized in that, The battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode and / or the negative electrode is the high-safety composite electrode.

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