Composite electrode tab, method of making and use thereof

Abstract

This application discloses a composite electrode, its preparation method, and its application. The composite electrode includes a current collector, a first material layer, and a second material layer. The first material layer is disposed on at least a portion of the surface of the current collector and includes an active material and a pore-forming agent. The active material includes a positive electrode active material or a negative electrode active material. The second material layer is disposed on at least a portion of the surface of the first material layer and includes ceramic. Both the second material layer and the first material layer have multiple pores formed by the thermal decomposition of at least a portion of the pore-forming agent on their interiors and surfaces. The composite electrode of this application, with a first material layer containing a pore-forming agent and an active material and a second material layer containing a safety-functional ceramic material sequentially disposed on the surface of the current collector, and both the first and second layers containing multiple pores, can improve the safety function and wettability of the electrode.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a composite electrode, its preparation method, and its application. Background Technology

[0002] With the increasing popularity of new energy vehicles, consumers are increasingly eager to alleviate range anxiety and charging anxiety, accelerating the development of battery products with higher energy density and fast charging capabilities. However, ensuring battery safety while meeting the demands for "fast charging" and "high energy density" is a primary challenge that battery technology professionals must address.

[0003] To improve battery safety, most solutions focus on the cell structure and battery pack design. For example, inverting the cells (with the explosion-proof valve facing downwards) can mitigate the damage to the vehicle in the event of thermal runaway, providing passengers or drivers with crucial escape time. Strengthening the battery pack structure and implementing thermal insulation designs enhances its overall safety. These measures effectively improve the safety of new energy vehicle batteries.

[0004] However, improving the intrinsic safety performance of batteries at the material or electrode level remains one of the most effective strategies. For example, designing solid-state batteries, using high-safety electrolytes, and employing cathode materials with lower oxygen release and better thermal stability are all effective means of improving the intrinsic safety of batteries.

[0005] Applying a safety coating is also a feasible strategy. For example, coating the separator with a layer of ceramic to prepare a ceramic composite separator can improve the separator's puncture resistance. Applying a ceramic coating with a width of 3-10 mm to the tab side of the positive electrode can prevent the tab from "inserting" and causing lithium plating, improve the tab membrane cutting burr, and reduce the risk of internal shorting. These safety coating measures can effectively improve the safety performance of the electrode and enhance the safety and reliability of the battery cell.

[0006] In addition, there are strategies that completely coat the electrode surface with a ceramic layer to thoroughly improve the cell's safety performance (such as patents CN118299674A and CN114141985B). However, the drawback of this approach is that, since the active material coating is completely covered by the ceramic safety coating, this significantly reduces the wetting effect between the active material coating and the electrolyte, affecting the wetting effect. This will inevitably lead to increased time consumption and process difficulty in processes such as electrolyte injection and high-temperature wetting (or aging). Poor wetting will ultimately cause black spots on the negative electrode and even lithium plating when the cell is fully charged, affecting the cell's electrochemical and safety performance. Summary of the Invention

[0007] In view of this, this application aims to provide a composite electrode sheet, wherein a first material layer containing a pore-forming agent and an active substance and a second material layer containing a ceramic material with safety function are sequentially disposed on the surface of the current collector, and both the first material layer and the second material layer contain multiple pores, which can improve the safety function and wettability of the electrode sheet.

[0008] Another object of this application is to provide a method for preparing composite electrodes.

[0009] Another object of this application is to provide a secondary battery.

[0010] Another object of this application is to provide an electrical device.

[0011] To achieve the above objectives, the first aspect of this application proposes a composite electrode, comprising:

[0012] current collector;

[0013] A first material layer is disposed on at least a portion of the surface of the current collector, the first material layer comprising an active material and a pore-forming agent, the active material comprising a positive electrode active material or a negative electrode active material;

[0014] A second material layer is disposed on at least a portion of the surface of the first material layer, the second material layer comprising ceramic; both the interior and surface of the second material layer and the first material layer are provided with a plurality of pores formed by the thermal decomposition of at least a portion of the pore-forming agent.

[0015] In some embodiments, the pore-forming agent includes at least one of ammonium carbonate, ammonium bicarbonate, azobisisobutyronitrile, and benzoyl peroxide.

[0016] In some embodiments, the particle size of the pore-forming agent ranges from 500 nm to 20 μm.

[0017] In some embodiments, the median particle size of the pore-forming agent is 1-5 μm.

[0018] In some embodiments, the pore-forming agent has a mass content of 0.1-3% in the first material layer.

[0019] In some embodiments, the positive electrode active material includes at least one of lithium iron phosphate, ternary materials, and lithium cobalt oxide.

[0020] In some embodiments, the negative electrode active material includes at least one of graphite, silicon-carbon composite material, silicon oxide, and silicon.

[0021] In some embodiments, the ceramic includes at least one of alumina ceramic and boehmite.

[0022] In some embodiments, the particle size of the ceramic ranges from 100 nm to 5 μm.

[0023] In some embodiments, the median particle size of the ceramic is 0.8-1.2 μm.

[0024] In some embodiments, when the active material includes a positive electrode active substance, the material of the first material layer comprises the following components in weight percentages: 94-97% positive electrode active substance, 0.5-2% first conductive agent, 1-3% first binder, and 0.1-3% pore-forming agent.

[0025] In some embodiments, when the active material includes a negative electrode active substance, the material of the first material layer comprises the following components in the following mass percentages: 94-97% negative electrode active substance, 0.5-2% second conductive agent, 0.7-2% thickener, 1-2% second binder, and 0.1-3% pore-forming agent.

[0026] In some embodiments, the material of the second material layer includes ceramic and a third adhesive.

[0027] In some embodiments, the first conductive agent includes at least one of conductive carbon black, Ketjen black, acetylene black, and carbon nanotubes.

[0028] In some embodiments, the first adhesive includes at least one of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0029] In some embodiments, the second conductive agent includes at least one of conductive carbon black, Ketjen black, and acetylene black.

[0030] In some embodiments, the thickener includes at least one of sodium carboxymethyl cellulose (CMC-Na), lithium carboxymethyl cellulose (CMC-Li), polyvinyl alcohol (PVA), and sodium polyacrylate (PAA-Na).

[0031] In some embodiments, the second adhesive includes at least one of styrene-butadiene latex (SBR) and polyacrylic acid (PAA).

[0032] In some embodiments, when the active material includes a positive electrode active substance, the third binder includes at least one of oil-based polyvinylidene fluoride resin (PVDF), polyacrylic acid (PAA), and polymethyl methacrylate (PMMA).

[0033] In some embodiments, when the active material includes a negative electrode active substance, the third binder includes at least one of aqueous polyvinylidene fluoride resin (PVDF), polyacrylic acid (PAA), and polymethyl methacrylate (PMMA).

[0034] In some embodiments, the mass ratio of the ceramic to the binder is (5-9):(5-1).

[0035] In some embodiments, when the active material includes a positive electrode active substance, the composite electrode is a positive electrode, and the porosity of the composite electrode is 30-40%.

[0036] In some embodiments, when the active material includes a negative electrode active substance, the composite electrode is a negative electrode, and the porosity of the composite electrode is 35-45%.

[0037] In some embodiments, the cohesive force of the composite electrode is greater than 25 N / m and less than 50 N / m.

[0038] In some embodiments, the thickness of the portion of the first material layer remaining on the current collector after a peel force test is less than 5 μm, and the peel force is a N / m, where 7 < a < 30.

[0039] In some embodiments, the areal density of the first material layer is 45-230 g / cm³. 2 .

[0040] In some embodiments, the areal density of the second material layer is 5-20 g / m³. 2 .

[0041] In some embodiments, the pore is a micro-nano pore channel with a diameter of less than 1 μm.

[0042] In some embodiments, the temperature of the thermal decomposition is 100-120°C.

[0043] In some embodiments, the current collector includes one of copper foil, aluminum foil, and carbon-coated aluminum foil.

[0044] In some embodiments, the thickness of the first material layer is 50-100 μm.

[0045] In some embodiments, the thickness of the second material layer is 5-20 μm.

[0046] In some embodiments, the mass ratio of the active material to the ceramic is (42.3-223.1):(2.5-18).

[0047] The second aspect of this application discloses a method for preparing a composite electrode, comprising:

[0048] A double-layer coating technology is used to simultaneously coat the first slurry and the second slurry onto the current collector, forming the first coating layer and the second coating layer respectively, resulting in a current collector containing a slurry layer;

[0049] The current collector containing the slurry layer is dried and rolled to obtain the composite electrode sheet;

[0050] The first slurry includes the material of the first material layer, and the second slurry includes the material of the second material layer.

[0051] In some embodiments, the first slurry further includes a first solvent, and when the active material includes a positive electrode active material, the first solvent includes N-methylpyrrolidone (NMP), or when the active material includes a negative electrode active material, the first solvent includes water.

[0052] In some embodiments, the second slurry further includes a second solvent, which includes at least one of water and N-methylpyrrolidone (NMP).

[0053] In some embodiments, when the active material includes a positive electrode active material, the positive electrode active material is lithium iron phosphate, the solid content of the first slurry is 60-64%, and the viscosity of the first slurry is 7000-11000 MPa·s; or, the positive electrode active material is a ternary material, the solid content of the first slurry is 70-74%, and the viscosity of the first slurry is 6000-10000 MPa·s; or, the positive electrode active material is lithium cobalt oxide, the solid content of the first slurry is 76-80%, and the viscosity of the first slurry is 3000-7000 MPa·s.

[0054] In some embodiments, when the active material includes a negative electrode active substance, the solid content of the first slurry is 52-56%, and the viscosity of the first slurry is 3000-7000 MPa·s.

[0055] In some embodiments, the solid content of the second slurry is 15-35%, and the viscosity of the second slurry is 3000-7000 MPa·s.

[0056] In some embodiments, the drying temperature is 100-120°C.

[0057] In some embodiments, the pore-forming agent decomposes at least partially during the baking process to generate gas, forming a plurality of pores inside and on the surface of the first and second coating layers.

[0058] A third aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, and a separator, wherein the positive electrode and / or the negative electrode are composite electrodes as described in this application or composite electrodes prepared by the method described in this application.

[0059] The fourth aspect of this application discloses an electrical device comprising the secondary battery described in this application.

[0060] The composite electrode described in this application can bring at least the following beneficial effects:

[0061] A first material layer containing a pore-forming agent and an active substance, and a second material layer containing a safety-functional ceramic, are sequentially disposed on the surface of the current collector. Both the first and second material layers contain multiple pores, which improves the safety function and wettability of the electrode. Specifically, the second material layer containing the safety-functional ceramic improves the thermal stability of the composite electrode, reducing or even avoiding the risk of fires, explosions, and other safety accidents caused by internal short circuits in batteries such as lithium batteries. At the same time, the pore-forming agent introduced into the first material layer near the current collector decomposes into gas upon heating, forming multiple pores both inside and on the surface of the first and second material layers. This in-situ increases the porosity of the electrode, thereby improving the wettability of the composite electrode and effectively mitigating the risk of decreased wettability caused by the ceramic safety coating.

[0062] The method for preparing the composite electrode described in this application can bring at least the following beneficial effects:

[0063] The dual-layer coating technology shortens the manufacturing process and reduces manufacturing costs. Furthermore, the in-situ fabrication of a safety ceramic coating (i.e., the second material layer) on the electrode improves the probability of lithium-ion batteries catching fire or exploding due to internal short circuits caused by lithium dendrite growth piercing the separator during charging and discharging, which can lead to direct contact between the positive and negative electrodes. Simultaneously, the introduction of a pore-forming agent into the first material layer near the current collector effectively mitigates the risk of decreased wettability caused by the ceramic coating adhering to the active material coating (i.e., the first material layer).

[0064] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0065] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings.

[0066] in:

[0067] Figure 1 This is a schematic diagram of the structure of a composite electrode shown in an exemplary embodiment of this application.

[0068] Figure 2 The flowchart illustrates a method for preparing a composite electrode in an exemplary embodiment of this application, wherein: the active material slurry is also known as the first slurry, and the ceramic safety coating slurry is also known as the second slurry.

[0069] Figure 3 Scanning electron microscope (SEM) image of the composite electrode prepared in Example 1.

[0070] Figure label:

[0071] 1-Current collector; 2-First material layer; 3-Second material layer; 4-Hole. Detailed Implementation

[0072] The embodiments of this application are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0073] In this application, the disclosure of numerical ranges includes all values ​​throughout the range and the disclosure of further subdivisions of the range, including the endpoints and subranges given for these ranges.

[0074] Unless otherwise specified, all raw materials and equipment involved in this application are self-made through commercial means or known methods; and all methods involved are conventional methods unless otherwise specified.

[0075] The following description, with reference to the accompanying drawings, describes an embodiment of this application of a composite electrode and a method for preparing the composite electrode.

[0076] <Composite Electrode>

[0077] Figure 1 This is a schematic diagram of the structure of a composite electrode shown in an exemplary embodiment of this application.

[0078] like Figure 1 As shown, the composite electrode of this application embodiment includes a current collector 1, a first material layer 2, and a second material layer 3. The first material layer 2 is disposed on at least a portion of the surface of the current collector 1, and the first material layer 2 includes an active material and a pore-forming agent. The active material includes a positive electrode active material or a negative electrode active material. The second material layer 3 is disposed on at least a portion of the surface of the first material layer 2, and the second material layer 3 includes ceramic. Both the interior and surface of the second material layer 3 and the first material layer 2 are provided with a plurality of pores 4 formed by the thermal decomposition of at least a portion of the pore-forming agent.

[0079] It is understood that in the embodiments of this application, the current collector, the first material layer, and the second material layer are stacked sequentially. When the active material includes a positive electrode active substance, the composite electrode is a positive electrode; when the active material includes a negative electrode active substance, the composite electrode is a negative electrode. Meanwhile, the first material layer, since it contains active material, can be understood as an active substance coating; the second material layer, since it contains ceramic, can be understood as a ceramic safety coating or a safety function coating, etc.

[0080] It should be noted that in the embodiments of this application, multiple pores are formed by the thermal decomposition of at least a portion of the pore-forming agent. Thermal decomposition refers to the thermal decomposition of the pore-forming agent during the preparation of the composite electrode itself, which at least partially forms multiple pores. Specifically, during the preparation of the composite electrode itself, after coating the current collector with a first slurry containing a first material layer (i.e., the first coating layer mentioned below) and a second slurry containing a second material layer (i.e., the second coating layer mentioned below), at least a portion of the pore-forming agent will be thermally decomposed during the drying (also known as baking) process to produce gases such as CO2, NH3, and N2, thereby leaving micro-nano pore channels in the internal space of the electrode - the electrode surface (i.e., the interior and surface of the first and second material layers), that is, multiple pores as described above.

[0081] In some embodiments, the pore-forming agent includes, but is not limited to, at least one of ammonium carbonate, ammonium bicarbonate, azobisisobutyronitrile, and benzoyl peroxide. Choosing these substances as pore-forming agents allows them to decompose thermally during composite electrode processing, generating gases such as CO2, NH3, and N2. This creates micro-nano pores on the electrode's internal space and surface, forming multiple small pores (i.e., pores 4) with a diameter <1 μm, thereby increasing the electrode's porosity. Furthermore, the residual pores in the first and second material layers increase the friction between them, enhancing the adhesion between the first and second material layers and the safety coating (second material layer).

[0082] In some embodiments, the particle size of the pore-forming agent ranges from 500 nm to 20 μm. In the embodiments of this application, when the particle size of the pore-forming agent is within the above range, a mesoporous structure with effective porosity can be obtained, and the wetting effect is significantly enhanced; if the particle size is less than 500 nm, the pore size is too small, and the wettability enhancement effect may be reduced; if the particle size is greater than 20 μm, the excessively large pore size may increase the risk of internal short circuits, which may increase the risk of safety failure.

[0083] For example, the particle size of the pore-forming agent includes, but is not limited to, 500nm, 1μm, 2μm, 3μm, 4μm, 5μm, 8μm, 10μm, 13μm, 15μm or 20μm.

[0084] In some embodiments, the median particle size of the pore-forming agent is 1-5 μm, including but not limited to 1 μm, 2 μm, 3 μm, 4 μm or 5 μm.

[0085] In some embodiments, the pore-forming agent has a mass content of 0.1-3% in the first material layer. In the embodiments of this application, when the mass content of the pore-forming agent in the first material layer is within the above range, a sufficiently controlled pore distribution can be obtained; if it is less than 0.1%, the pore distribution is sparse, and the effect on improving wettability is limited; if it is greater than 3%, the pore distribution is dense, affecting the final quality of the electrode, such as tensile strength and adhesion.

[0086] In some embodiments, the positive electrode active material includes, but is not limited to, at least one of lithium iron phosphate, ternary materials, and lithium cobalt oxide.

[0087] For example, ternary materials include, but are not limited to, those with the chemical formula LiNi. x Co y Mn 1-x-y Compounds of O2 (where 0 < x < 1, 0 < y < 1, 1 - xy > 0), such as at least one of NCM111, NCM523, NCM622, NCM811, etc.

[0088] In some embodiments, when the active material includes a positive electrode active substance, the material of the first material layer also includes a first conductive agent, a first binder, etc.

[0089] As an optional example, when the active material includes a positive electrode active substance, the material of the first material layer comprises the following components in the following mass percentages: 94-97% positive electrode active substance, 0.5-2% first conductive agent, 1-3% first binder, and 0.1-3% pore-forming agent.

[0090] For example, when the active material includes a positive electrode active substance, the mass content of the positive electrode active substance in the material of the first material layer includes, but is not limited to, 94%, 95%, 96%, or 97%.

[0091] For example, when the active material includes a positive electrode active substance, the mass content of the first conductive agent in the material of the first material layer includes, but is not limited to, 0.5%, 1%, 1.5%, or 2%.

[0092] For example, when the active material includes a positive electrode active substance, the mass content of the first binder in the material of the first material layer includes, but is not limited to, 1%, 1.5%, 2%, 2.5%, or 3%.

[0093] It should be noted that in the embodiments of this application, when the active material includes a positive electrode active material, the material of the first material layer also includes a first conductive agent, a first binder, etc. The ratio of the positive electrode active material, the first conductive agent, and the first binder is not limited to the above ratio. Since the material of the first material layer is equivalent to the positive electrode material of the positive electrode sheet of a secondary battery in this field, under the premise of ensuring that the mass content of the pore-forming agent is 0.1-3%, the positive electrode active material, the first conductive agent, and the first binder can also adopt a ratio well known in this field.

[0094] In some embodiments, the first conductive agent includes, but is not limited to, at least one of conductive carbon black (SP), Ketjen black, acetylene black, carbon nanotubes, etc.

[0095] In some embodiments, the first adhesive includes, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), etc.

[0096] In some embodiments, the negative electrode active material includes, but is not limited to, at least one of graphite, silicon-carbon composite material, silicon oxide, silicon, etc.

[0097] For example, silicon-carbon composite materials include, but are not limited to, at least one of Si / C (mass ratio Si:C = 9:1-1:9). Non-limitingly, the mass ratio of Si to C in Si / C is 8:1, 5:1, 3:1, 1:1, 1:2, 1:4, 1:6, or 1:8, etc.

[0098] For example, silicon oxides include, but are not limited to, SiO2. x Where 1 ≤ x ≤ 2. (Non-restrictive, SiO2) x The value of x can be, but is not limited to, 1.25, 1.5 or 1.75.

[0099] In some embodiments, when the active material includes a negative electrode active substance, the material of the first material layer also includes a second conductive agent, a thickener, a second binder, etc.

[0100] As an optional example, when the active material includes a negative electrode active substance, the material of the first material layer comprises the following components in the following mass percentages: 94-97% negative electrode active substance, 0.5-2% second conductive agent, 0.7-2% thickener, 1-2% second binder, and 0.1-3% pore-forming agent.

[0101] For example, when the active material includes a negative electrode active substance, the mass content of the negative electrode active substance in the material of the first material layer includes, but is not limited to, 94%, 95%, 96%, or 97%.

[0102] For example, when the active material includes a negative electrode active substance, the mass content of the second conductive agent in the material of the first material layer includes, but is not limited to, 0.5%, 1%, 1.5%, or 2%.

[0103] For example, when the active material includes a negative electrode active substance, the mass content of the thickener in the material of the first material layer includes, but is not limited to, 0.7%, 1%, 1.5% or 2%.

[0104] For example, when the active material includes a negative electrode active substance, the mass content of the second binder in the material of the first material layer includes, but is not limited to, 1%, 1.5%, or 2%.

[0105] It should be noted that in the embodiments of this application, when the active material includes a negative electrode active material, the material of the first material layer also includes a second conductive agent, a thickener, a second binder, etc. The ratio of the negative electrode active material, the second conductive agent, the thickener, and the second binder is not limited to the above ratio. Since the material of the first material layer is equivalent to the positive electrode material of the negative electrode sheet of a secondary battery in this field, under the premise of ensuring that the mass content of the pore-forming agent is 0.1-3%, the negative electrode active material, the second conductive agent, the thickener, and the second binder can also adopt a ratio well known in the art.

[0106] In some embodiments, the material of the second material layer includes ceramic and a third adhesive.

[0107] In some embodiments, the second conductive agent includes, but is not limited to, at least one of conductive carbon black (SP), Ketjen black, acetylene black, etc.

[0108] In some embodiments, the thickener includes, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC-Na), lithium carboxymethyl cellulose (CMC-Li), polyvinyl alcohol (PVA), and sodium polyacrylate (PAA-Na).

[0109] In some embodiments, the second adhesive includes, but is not limited to, at least one of styrene-butadiene latex (SBR), polyacrylic acid (PAA), etc.

[0110] In some embodiments, the ceramic includes, but is not limited to, at least one of alumina ceramics, boehmite, etc. In the embodiments of this application, boehmite is used as the ceramic, which has low cost, low water absorption, and good processing performance.

[0111] In some embodiments, the particle size of the ceramic ranges from 100 nm to 5 μm. In the embodiments of this application, a ceramic particle size within the above range can improve processing performance, reduce processing difficulty, and ensure coating quality; if the particle size is less than 100 nm, it is prone to agglomeration, difficult to disperse, and has a negative impact on mechanical properties; if the particle size is greater than 5 μm, the coating is prone to clogging, and the coating thickness and uniformity are difficult to control.

[0112] For example, the particle size of ceramics includes, but is not limited to, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, or 5μm.

[0113] In some embodiments, the median particle size of the ceramic is 0.8-1.2 μm, including but not limited to 0.8 μm, 0.9 μm, 1 μm, 1.1 μm or 1.2 μm, preferably 1 μm.

[0114] In some embodiments, when the active material includes a positive electrode active substance, the third binder includes, but is not limited to, at least one of oil-based polyvinylidene fluoride resin (PVDF), polyacrylic acid (PAA), polymethyl methacrylate (PMMA), etc.

[0115] In some embodiments, when the active material includes a negative electrode active substance, the third binder includes, but is not limited to, at least one of aqueous polyvinylidene fluoride resin (PVDF), polyacrylic acid (PAA), polymethyl methacrylate (PMMA), etc.

[0116] In some embodiments, the mass ratio of the ceramic to the binder is (5-9):(5-1), including but not limited to 5:5, 5:4, 5:3, 5:2, 5:1, 6:3, 6:1, 7:1, 7:3, 8:1, 8:3, 8:5, or 9:1.

[0117] In some embodiments, when the active material includes a positive electrode active substance, the composite electrode is a positive electrode, and the porosity of the composite electrode is 30-40%, including but not limited to 30%, 32.5%, 35%, 37.5% or 40%.

[0118] In some embodiments, when the active material includes a negative electrode active substance, the composite electrode is a negative electrode, and the porosity of the composite electrode is 35-45%, including but not limited to 35%, 37.5%, 40%, 42.5%, or 45%.

[0119] In some embodiments, the cohesive force of the composite electrode is greater than 25 N / m and less than 50 N / m, including but not limited to 25.5 N / m, 30 N / m, 35 N / m, 40 N / m, 45 N / m or 49.9 N / m.

[0120] In some embodiments, the thickness of the portion of the first material layer remaining on the current collector after a peel force test is less than 5 μm, and the peel force is a N / m, where a is greater than 7.

[0121] As an optional example, 7 < a < 30. Exemplary values ​​for a include, but are not limited to, 7.1, 8, 9, 10, 11, 12, 15, 20, 25, or 29.5. Preferably, when the composite electrode is a positive electrode, 7 < a < 30; when the composite electrode is a positive electrode, 7 < a < 25.

[0122] In some embodiments, the areal density of the first material layer is 45-230 g / m³. 2 including but not limited to 45g / m 2 75g / m 2100g / m 2 125g / m 2 150g / m 2 175g / m 2 Or 200g / m 2 wait.

[0123] In some embodiments, the areal density of the second material layer is 5-20 g / m³. 2 including but not limited to 5g / m 2 7.5g / m 2 10g / m 2 12.5g / m 2 15g / m 2 17.5g / m 2 Or 20g / m 2 wait.

[0124] In the embodiments of this application, the areal density of the first material layer is less than 45 g / cm³. 2 The density of the second material layer is less than 5 g / cm³. 2 All of these factors may increase manufacturing risks during the coating process, such as uneven mass distribution and foil leakage; the areal density of the first material layer is greater than 230 g / cm³. 2 The areal density of the second material layer is greater than 20 g / cm³. 2 This will increase the risk of negative effects such as uneven areal density distribution and electrode cracking.

[0125] In some implementations, the pore is a micro- or nano-sized channel.

[0126] In some embodiments, the diameter of the hole is less than 1 μm, including but not limited to 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm or 999 nm, preferably 400-800 nm.

[0127] In some embodiments, the thermal decomposition temperature is 100-120°C, including but not limited to 100°C, 105°C, 110°C, 115°C, or 120°C. As mentioned above, thermal decomposition here refers to the thermal decomposition of at least a portion of the pore-forming agent during the drying stage of the composite electrode preparation process, producing gases such as CO2, NH3, and N2.

[0128] In some embodiments, the current collector includes, but is not limited to, one of copper foil, aluminum foil, carbon-coated aluminum foil, etc.

[0129] In some embodiments, the thickness of the first material layer is 50-100 μm.

[0130] In some embodiments, the thickness of the second material layer is 5-20 μm.

[0131] In some embodiments, the mass ratio of the active material to the ceramic is (42.3-223.1):(2.5-18), including but not limited to 42.3:18, 42.3:10, 130:18, 130:2.5, or 130:10. In the embodiments of this application, the mass ratio of the active material to the ceramic is within the above range, which can maximize the reliability of the composite electrode manufacturing.

[0132] The composite electrode of this application embodiment has a first material layer containing a pore-forming agent and an active substance and a second material layer containing a safety-functional ceramic material sequentially disposed on the surface of the current collector. Both the first and second material layers contain multiple pores, which can improve the safety function and wettability of the electrode. Specifically, the second material layer containing the safety-functional ceramic material can improve the thermal stability of the composite electrode, reducing or even avoiding the risk of safety accidents such as fires and explosions caused by internal short circuits in batteries such as lithium batteries. At the same time, since the pore-forming agent is introduced into the first material layer near the current collector, the pore-forming agent decomposes into gas when heated, forming multiple pores in both the interior and surface of the first and second material layers, thereby increasing the porosity of the electrode in situ and improving the wettability of the composite electrode, effectively mitigating the risk of decreased wettability caused by the ceramic safety coating.

[0133] <Preparation Method of Composite Electrodes>

[0134] The method for preparing the composite electrode according to the embodiments of this application can be used to prepare the composite electrode according to the embodiments of this application.

[0135] Figure 2 This is a flowchart illustrating a method for preparing a composite electrode, which is an exemplary embodiment of this application.

[0136] like Figure 2 As shown, the preparation method includes the following steps:

[0137] S101. Using a double-layer coating technology, a first slurry and a second slurry are simultaneously coated onto the current collector to form a first coating layer and a second coating layer, respectively, to obtain a current collector containing a slurry layer; the first slurry includes the material of the first material layer, and the second slurry includes the material of the second material layer.

[0138] In some embodiments, the first slurry further includes a first solvent. In this case, the first slurry can be uniformly dispersed using a dual planetary mixer.

[0139] For example, when the active material includes a positive electrode active substance, the first solvent includes, but is not limited to, at least one of N-methylpyrrolidone (NMP), acetone, tetrahydrofuran, etc.

[0140] As an optional example, when the active material includes a positive electrode active material, the positive electrode active material is lithium iron phosphate, and the solid content of the first slurry is 60-64%, including but not limited to 60%, 61%, 62%, 63% or 64%; the viscosity of the first slurry is 7000-11000 MPa·s, including but not limited to 7000 MPa·s, 8000 MPa·s, 9000 MPa·s, 10000 MPa·s or 11000 MPa·s.

[0141] As another optional example, when the active material includes a positive electrode active material, the positive electrode active material is a ternary material, the solid content of the first slurry is 70-74%, including but not limited to 70%, 71%, 72%, 73% or 74%; the viscosity of the first slurry is 6000-10000 MPa·s, including but not limited to 6000 MPa·s, 7000 MPa·s, 8000 MPa·s, 9000 MPa·s or 10000 MPa·s.

[0142] As another alternative example, when the active material includes a positive electrode active material, the positive electrode active material is lithium cobalt oxide, and the solid content of the first slurry is 76-80%, including but not limited to 76%, 77%, 78%, 79% or 80%; the viscosity of the first slurry is 3000-7000 MPa·s, including but not limited to 3000 MPa·s, 4000 MPa·s, 5000 MPa·s, 6000 MPa·s or 7000 MPa·s.

[0143] For example, when the active material includes a negative electrode active substance, the first solvent includes at least one of water, ethanol, etc., preferably deionized water.

[0144] As an optional example, when the active material includes a negative electrode active substance, the solid content of the first slurry is 52-56%, including but not limited to 52%, 53%, 54%, 55% or 56%; the viscosity of the first slurry is 3000-7000 MPa·s, including but not limited to 3000 MPa·s, 4000 MPa·s, 5000 MPa·s, 6000 MPa·s or 7000 MPa·s.

[0145] In some embodiments, the second slurry further includes a second solvent. In this case, the second slurry can be uniformly dispersed using a dual planetary mixer.

[0146] In some embodiments, the second solvent includes, but is not limited to, at least one of water, N-methylpyrrolidone (NMP), etc.

[0147] As an alternative example, when the active material includes a positive electrode active substance, the second solvent is N-methylpyrrolidone (NMP) and the third binder is oil-based PVDF.

[0148] As another alternative example, when the active material includes a negative electrode active substance, the second solvent is deionized water and the third binder is aqueous PVDF.

[0149] In some embodiments, the solid content of the second slurry is 15-35%, including but not limited to 15%, 20%, 25%, 30% or 35%.

[0150] In some embodiments, the viscosity of the second slurry is 3000-7000 MPa·s, including but not limited to 3000 MPa·s, 4000 MPa·s, 5000 MPa·s, 6000 MPa·s or 7000 MPa·s.

[0151] As an optional example, a double-layer coating technique is used to simultaneously coat the first slurry and the second slurry onto the current collector, forming a first coating layer and a second coating layer respectively, resulting in a current collector containing a slurry layer, comprising:

[0152] The first slurry and the second slurry are pumped into the two chambers of the double-layer coating die through the feeding system of the double-layer coating machine. Through the double-layer coating technology, a current collector containing a slurry layer is prepared.

[0153] S102. The current collector containing the slurry layer is dried and rolled to obtain the composite electrode.

[0154] In some embodiments, the drying temperature is 100-120°C, including but not limited to 100°C, 105°C, 110°C, 115°C, or 120°C.

[0155] In the embodiments of this application, drying is also referred to as baking in some cases.

[0156] In some embodiments, the pore-forming agent decomposes at least partially during the baking process to generate gas, forming a plurality of pores inside and on the surface of the first and second coating layers.

[0157] For example, the pore-forming agent decomposes at least partially during the baking process to produce gases such as CO2, NH3, and N2.

[0158] In the embodiments of this application, during the drying process, the pore-forming agent in the first slurry achieves a pore-forming effect. Specifically, the pore-forming agent decomposes at 100-120℃ during the drying stage to produce gases such as CO2, NH3, and N2, leaving micro-nano pore channels (i.e., pores 4) in the internal space of the electrode and on the electrode surface (i.e., the first coating layer and the second coating layer, corresponding to the first material layer and the second material layer in the composite electrode). The pore diameter is <1μm, thereby increasing the porosity of the electrode. Furthermore, the residual pores in the first and second coating layers increase the friction between the first and second coating layers, enhancing the adhesion between the first coating layer and the safety coating (second coating layer).

[0159] The composite electrode preparation method of this application, through a double-layer coating technology, shortens the manufacturing process and reduces manufacturing costs. Furthermore, the in-situ processing of a safety ceramic coating (i.e., the second material layer) on the electrode improves the probability of lithium-ion batteries catching fire or exploding due to internal short circuits caused by lithium dendrite growth piercing the separator during charging and discharging, which could lead to direct contact between the positive and negative electrodes. Simultaneously, the introduction of a pore-forming agent into the first material layer near the current collector effectively mitigates the risk of decreased wettability caused by the ceramic coating adhering to the active material coating (i.e., the first material layer).

[0160] Secondary batteries

[0161] The secondary battery of this application embodiment includes a positive electrode, a negative electrode and a separator, wherein the positive electrode and / or the negative electrode are composite electrodes prepared by the method of preparing composite electrodes of this application embodiment.

[0162] It is understood that, in the composite electrode of this application embodiment, when the active material in the first material layer includes a positive electrode active material, the composite electrode is a positive electrode; when the active material in the first material layer includes a negative electrode active material, the composite electrode is a negative electrode. Therefore, in the secondary battery of this application embodiment, the positive electrode can be the electrode with the composite electrode of this application embodiment as the positive electrode, and the negative electrode can be the electrode with the composite electrode of this application embodiment as the negative electrode. Alternatively, electrodes with the composite electrode of this application embodiment as the positive electrode and electrodes with the composite electrode of this application embodiment as the negative electrode can be prepared separately and used simultaneously in the secondary battery of this application embodiment.

[0163] It should be noted that, depending on the type of active material in the first material layer of the composite electrode according to the embodiments of this application, the above-mentioned secondary battery can be different secondary batteries, such as lithium-ion battery, sodium-ion battery, potassium-ion battery, etc.

[0164] As a preferred example, the secondary battery in this application embodiment is a lithium-ion battery.

[0165] <Electrical Appliances>

[0166] The electrical device in this application includes the secondary battery in this application.

[0167] In some implementations, the aforementioned electrical devices include, but are not limited to, mobile phones, tablets, and new energy vehicles.

[0168] The following non-limiting embodiments further illustrate certain features of the present technology.

[0169] I. Examples and Comparative Examples

[0170] Example 1 (Negative Electrode)

[0171] (Preparation of composite electrodes)

[0172] The composite electrode in this embodiment is a negative electrode, and its preparation method includes the following steps:

[0173] (1) Preparation of the first slurry: The material of the first material layer is added to the first solvent, deionized water, and dispersed evenly by a double planetary mixer to obtain a first slurry with a solid content of 52% ± 2% and a viscosity of 5000 ± 2000 MP·s.

[0174] The first material layer is composed of the following components by mass percentage: 96.3% graphite, 0.8% carbon black, 1.2% CMC-Na, 1.6% SBR, and 0.1% ammonium carbonate. The ammonium carbonate has a particle size range of 500 nm to 2 μm, with a median particle size of 1 μm.

[0175] (2) Preparation of the second slurry: The material of the second material layer is added to the second solvent, deionized water, and dispersed evenly by a double planetary mixer to obtain a first slurry with a solid content of 20% ± 2% and a viscosity of 800 ± 200 MPa·s.

[0176] The second material layer is composed of the following components by mass percentage: 80% Al2O3 ceramic and 20% aqueous PVDF. The Al2O3 ceramic has a particle size range of 500 nm to 1.4 μm, with a median particle size of 0.9 μm.

[0177] (3) Using a double-layer coating technology, the first slurry obtained in step (1) is set as a slurry close to the current collector, and the second slurry obtained in step (2) is set as a slurry close to the first slurry but far away from the current collector. The two slurries are coated onto the current collector simultaneously using a double-layer coating machine. The first slurry is coated to form a first coating layer, and the second slurry is coated to form a second coating layer. The first coating layer is set on one surface of the current collector, and the second coating layer is set on the surface of the first coating layer. The current collector, the first coating layer, and the second coating layer are stacked in sequence to obtain a current collector containing a slurry layer.

[0178] The current collector uses a copper foil with a thickness of 6 μm; the areal density (single-sided) of the first coating layer is 95 g / m². 2 The density of the second coating layer (single-sided) is 10 g / m². 2 .

[0179] (4) The current collector containing the slurry layer obtained in step (3) is dried at 120°C. Ammonium carbonate decomposes to produce CO2 and NH3, forming multiple pores inside and on the surface of the first coating layer and the second coating layer. After rolling, the first coating layer becomes the first material layer and the second coating layer becomes the second material layer, thus obtaining a composite electrode sheet that improves the safety performance of lithium batteries, which is the composite electrode sheet of this embodiment.

[0180] Example 2 (positive electrode sheet, positive electrode active material is lithium iron phosphate)

[0181] This embodiment is basically the same as embodiment 1, except that:

[0182] In this embodiment, the composite electrode is a positive electrode. In step (1), the material of the first material layer is added to the first solvent NMP and dispersed evenly using a dual planetary mixer to obtain a first slurry with a solid content of 62% ± 2% and a viscosity of 9000 ± 2000 MPa·s. The material of the first material layer consists of the following components in the indicated mass percentages: 95.5% lithium iron phosphate, 1.5% SP, 2% PVDF, and 1% azobisisobutyronitrile (AIBN). The particle size range of AIBN is 800 nm to 5 μm, with a median particle size of 2 μm.

[0183] In step (2), the PVDF in the second material layer is oil-based PVDF.

[0184] In step (3), the current collector is made of aluminum foil with a thickness of 13 μm.

[0185] In step (4), the drying temperature is 100°C, and azobisisobutyronitrile decomposes to produce N2, forming multiple pores inside and on the surface of the first and second coating layers.

[0186] Example 3 (positive electrode sheet, positive electrode active material is ternary material)

[0187] This embodiment is basically the same as embodiment 1, except that:

[0188] In this embodiment, the composite electrode is a positive electrode. In step (1), the material of the first material layer is added to the first solvent NMP and dispersed evenly using a double planetary mixer to obtain a first slurry with a solid content of 72% ± 2% and a viscosity of 9000 ± 2000 MPa·s. The material of the first material layer consists of the following components by mass percentage: 95.5% ternary positive electrode material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 02), 1.5% SP, 2% PVDF, 1% azobisisobutyronitrile. The particle size range of azobisisobutyronitrile is 800nm-5μm, with a median particle size of 2μm.

[0189] In step (2), the PVDF in the second material layer is oil-based PVDF.

[0190] In step (3), the current collector is made of aluminum foil with a thickness of 13 μm.

[0191] In step (4), the drying temperature is 100°C, and azobisisobutyronitrile decomposes to produce N2, forming multiple pores inside and on the surface of the first and second coating layers.

[0192] Example 4 (ceramic content in ceramic slurry is at the upper limit of 90%)

[0193] This embodiment is basically the same as embodiment 1, except that:

[0194] In step (2), the material of the second material layer is composed of the following components by mass percentage: 90% Al2O3 ceramic and 10% PVDF.

[0195] Example 5 (ceramic slurry with a ceramic content of 70%)

[0196] This embodiment is basically the same as embodiment 1, except that:

[0197] In step (2), the material of the second material layer is composed of the following components in the following mass percentages: 70% Al2O3 ceramic, 30% PVDF.

[0198] Example 6 (Ceramic content in ceramic slurry is 60%)

[0199] This embodiment is basically the same as embodiment 1, except that:

[0200] In step (2), the material of the second material layer is composed of the following components in the following mass percentages: 60% Al2O3 ceramic and 40% PVDF.

[0201] Example 7 (ceramic content in ceramic slurry is the lower limit of 50%)

[0202] This embodiment is basically the same as embodiment 1, except that:

[0203] In step (2), the material of the second material layer is composed of the following components in the following mass percentages: 50% Al2O3 ceramic, 50% PVDF.

[0204] Example 8 (Lower limit of density of second coating layer 5 g / m) 2 )

[0205] This embodiment is basically the same as embodiment 1, except that:

[0206] In step (3), the density of the second coating layer (single-sided) is 5 g / m². 2 .

[0207] Example 9 (Second coating layer density, intermediate 8 g / m²) 2 )

[0208] This embodiment is basically the same as embodiment 1, except that:

[0209] In step (3), the density of the second coating layer (single-sided) is 8 g / m². 2 .

[0210] Example 10 (Second coating layer density, intermediate 13 g / m²) 2 )

[0211] This embodiment is basically the same as embodiment 1, except that:

[0212] In step (3), the density of the second coating layer (single-sided) is 13 g / m². 2 .

[0213] Example 11 (Second coating layer density, intermediate 15 g / m²) 2 )

[0214] This embodiment is basically the same as embodiment 1, except that:

[0215] In step (3), the density of the second coating layer (single-sided) is 15 g / m². 2 .

[0216] Example 12 (Upper limit of density of the second coating layer: 20 g / m²) 2 )

[0217] This embodiment is basically the same as embodiment 1, except that:

[0218] In step (3), the density of the second coating layer (single-sided) is 20 g / m². 2 .

[0219] Example 13 (Compared to Example 1, the pore-forming agent is benzoyl peroxide)

[0220] This embodiment is basically the same as embodiment 1, except that:

[0221] In step (1), ammonium carbonate is replaced with benzoyl peroxide; the particle size range of benzoyl peroxide is 1μm-10μm, and the median particle size is 4μm.

[0222] In step (4), the drying temperature is 120°C, and benzoyl peroxide decomposes to produce CO2, forming multiple pores inside and on the surface of the first and second coating layers.

[0223] Example 14 (Compared to Example 1, the pore-forming agent is a 1:1 mixture of ammonium bicarbonate and azobisisobutyronitrile)

[0224] This embodiment is basically the same as embodiment 1, except that:

[0225] In step (1), ammonium carbonate is replaced with a mixture of ammonium bicarbonate and benzoyl peroxide in a mass ratio of 1:1; the particle size range of ammonium bicarbonate is 1-20 μm, with a median particle size of 5 μm; the particle size range of benzoyl peroxide is 1 μm-10 μm, with a median particle size of 4 μm.

[0226] In step (4), the drying temperature is 120°C. Ammonium bicarbonate decomposes to produce CO2 and NH3, and azobisisobutyronitrile decomposes to produce N2. Multiple pores are formed inside and on the surface of the first coating layer and the second coating layer.

[0227] Example 15 (Compared to Example 2, the pore-forming agent is benzoyl peroxide)

[0228] This embodiment is basically the same as embodiment 2, except that:

[0229] In step (1), azobisisobutyronitrile is replaced with benzoyl peroxide; the particle size range of benzoyl peroxide is 1-10, and the median particle size is 4 μm.

[0230] In step (4), the drying temperature is 120°C, and benzoyl peroxide decomposes to produce CO2, forming multiple pores inside and on the surface of the first and second coating layers.

[0231] Example 16 (compared to Example 1, the pore-forming agent content is intermediate, 1.55%)

[0232] This embodiment is basically the same as embodiment 1, except that:

[0233] In step (1), the material of the first material layer is composed of the following components in the following mass percentages: 95% graphite, 0.8% carbon black, 1.15% CMC, 1.5% SBR, and 1.55% ammonium carbonate.

[0234] Example 17 (compared to Example 1, the pore-forming agent content is the upper limit of 3%)

[0235] This embodiment is basically the same as embodiment 1, except that:

[0236] In step (1), the material of the first material layer is composed of the following components by mass percentage: 94.35% graphite, 0.5% carbon black, 1.15% CMC, 1% SBR, and 3% ammonium carbonate.

[0237] Example 18 (compared to Example 2, the pore-forming agent content is the lower limit of 0.1%)

[0238] This embodiment is basically the same as embodiment 1, except that:

[0239] In step (1), the material of the first material layer is composed of the following components in the following mass percentages: 97% lithium iron phosphate, 1.5% SP, 1.4% PVDF, and 0.1% azobisisobutyronitrile.

[0240] Example 19 (compared to Example 2, the pore-forming agent content is intermediate, 1.55%)

[0241] In step (1), the material of the first material layer is composed of the following components in the following mass percentages: 94.95% lithium iron phosphate, 1.5% SP, 2% PVDF, and 1.55% azobisisobutyronitrile.

[0242] Example 20 (compared to Example 2, the pore-forming agent content is the upper limit of 3%)

[0243] In step (1), the material of the first material layer is composed of the following components in the following mass percentages: 94% lithium iron phosphate, 1.5% SP, 1.5% PVDF, and 3% azobisisobutyronitrile.

[0244] Example 21 (Compared to Example 1, the ceramic is boehmite)

[0245] This embodiment is basically the same as embodiment 1, except that:

[0246] In step (2), Al2O3 ceramic is replaced with boehmite.

[0247] Comparative Example 1

[0248] This comparative example provides a method for preparing a negative electrode sheet, and the specific preparation process is as follows:

[0249] Step 1: Add graphite, carbon black, SBR, and CMC to deionized water in a mass ratio of 96.4:0.8:1.6:1.2 to prepare a uniformly dispersed slurry with a solid content of 52%±4%, a viscosity of 3000-7000mPa·s, and a slurry fineness of <35μm.

[0250] Step 2: Using an extrusion coater, evenly coat the prepared slurry from Step 1 onto a 6μm copper foil. Adjust the coater and dry it to achieve a (single-sided) areal density of 95 g / m². 2 A negative electrode with a current collector.

[0251] Comparative Example 2

[0252] This comparative example provides a method for preparing a positive electrode sheet, and the specific preparation process is as follows:

[0253] Step 1: Add NMP to lithium iron phosphate material, SP, and PVDF in a mass ratio of 96.5%:1.5%:2% to prepare a slurry with a solid content of 62%±4%, a viscosity of 7000-11000mPa·s, and a slurry fineness of <35μm, which is uniformly dispersed.

[0254] Step 2: Using an extrusion coater, evenly coat the prepared slurry from Step 1 onto a 13μm carbon-coated aluminum foil. Adjust the coater and dry it to achieve a (single-sided) areal density of 210 g / m². 2 A positive electrode with a current collector.

[0255] Comparative Example 3

[0256] This comparative example provides a method for preparing a positive electrode sheet, and the specific preparation process is as follows:

[0257] Step 1: Add ternary material (NCM811), SP, and PVDF to deionized water in a mass ratio of 96.5%:1.5%:2% to prepare a slurry with a solid content of 72%±4%, a viscosity of 7000-11000mPa·s, and a slurry fineness of <35μm, which is uniformly dispersed.

[0258] Step 2: Using an extrusion coater, evenly coat the prepared slurry from Step 1 onto a 13μm carbon-coated aluminum foil. Adjust the coater and dry it to achieve a (single-sided) areal density of 160 g / m². 2 A positive electrode with a current collector.

[0259] Comparative Example 4

[0260] This comparative example is basically the same as Example 1, except that the pore-forming agent ammonium carbonate in step (1) is removed.

[0261] In step (1), the material of the first material layer is composed of the following components by mass percentage: 96.4% graphite, 0.8% carbon black, 1.2% CMC, and 1.6% SBR.

[0262] Comparative Example 5

[0263] This comparative example is basically the same as Example 2, except that the pore-forming agent azobisisobutyronitrile is removed in step (1).

[0264] In step (1), the material of the first material layer is composed of the following components by mass percentage: 96.5% lithium iron phosphate material, 1.5% SP, and 2% PVDF.

[0265] Comparative Example 6

[0266] This comparative example is basically the same as Example 3, except that the pore-forming agent azobisisobutyronitrile is removed in step (1).

[0267] In step (1), the material of the first material layer is composed of the following components by mass percentage: 96.5% ternary cathode material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 02), 1.5% SP, 2% PVDF.

[0268] II. Electrode Characterization and Performance Testing

[0269] 1. Electrode characterization and performance testing

[0270] (1) Polar characterization

[0271] The morphology of the electrodes in each example or comparative example was examined using scanning electron microscopy (SEM). The SEM image of the composite electrode prepared in Example 1 is shown below. Figure 3 As shown. According to Figure 3 It can be seen that the composite electrode has multiple pores.

[0272] (2) Electrode porosity test

[0273] The electrode porosity testing method is as follows: Electrodes prepared in each embodiment or comparative example are processed using a roller press. Depending on the type of active material in the first coating layer, electrodes with different compaction levels are prepared. The compacted electrodes (graphite, lithium iron phosphate, and ternary materials have a porosity of 1.6 g / cm³) are then pressed. 3 2.5g / cm 3 and 3.4g / cm 3 The negative electrode sheet, after being rolled, was cut into 100 small round pieces with a diameter of 14mm using a stamping machine. The thickness of the small round pieces was measured with a digital micrometer. The sample to be tested was placed in a fully automatic true density tester, and the density was determined using the formula: V = πR.2 hN is used to calculate the sample volume, where R is the radius of the disc (in mm), h is the thickness of the disc (in mm), N is the number of discs (in discs), and V is the sample volume (in cm³). 3 After setting all parameters for the true density test, select the porosity test, start the test, and obtain the electrode porosity.

[0274] (3) Electrode cohesion test

[0275] The test method for electrode cohesion is as follows: Electrodes prepared in each embodiment or comparative example are processed using a roller press. Depending on the type of active material in the first coating layer, electrodes with different compactions are prepared. The compacted electrodes (graphite, lithium iron phosphate, and ternary materials are compacted to 1.6 g / cm³) are then pressed. 3 2.5g / cm 3 and 3.4g / cm 3 After rolling, the electrode sheet is cut into strips of 2.5cm × 25cm. Double-sided adhesive tape is attached to the steel plate and rolled back and forth three times to ensure that the double-sided adhesive tape adheres tightly to the steel plate. Then, a layer of green adhesive is bonded to the negative electrode sheet. The green adhesive is clamped by a tensile testing machine and peeled off at 180° to remove the coating layer and the dressing layer. The data is read to obtain the cohesion.

[0276] (4) Electrode peeling force test

[0277] The test method for electrode peel strength is as follows: Electrodes prepared in each embodiment or comparative example are used, and depending on the type of active material in the first coating layer, electrodes with different compactions are prepared. After rolling, the compaction strength of the electrodes (graphite, lithium iron phosphate, and ternary materials are 1.6 g / cm³) is achieved. 3 2.5g / cm 3 and 3.4g / cm 3 After rolling, the electrode sheet is cut into strips of 2.5cm × 25cm. Double-sided adhesive tape is attached to the steel plate, and the strips are rolled back and forth three times to ensure a tight bond between the tape and the steel plate. Then, the cut electrode strips are attached to the steel plate using the double-sided adhesive tape, and the strips are rolled back and forth three times to ensure a tight bond. The steel plate is fixed on a peel testing machine, and the electrode sheet is kept at 180° to the peeling direction. The peeling force is then tested, and the data is recorded to obtain the peeling force.

[0278] (5) Electrode DSC thermal stability test

[0279] The method for DSC thermal stability testing of the electrode is as follows: the powder of the electrode prepared in each embodiment or comparative example is scraped off, and the thermal stability (decomposition temperature) of the electrode composite coating is tested using a differential scanning calorimeter (DSC). The test temperature range is 45℃-500℃.

[0280] 2. Safety performance and electrochemical performance testing

[0281] Battery fabrication:

[0282] Battery 1 fabrication: Battery 1 is fabricated by combining the positive electrode sheet prepared in each embodiment or comparative example, a commercially available negative electrode sheet (graphite system), and a separator. The specific fabrication method includes the following steps:

[0283] 1) Preparation of commercial negative electrode sheet (graphite system): same as the preparation method of negative electrode sheet in Comparative Example 1.

[0284] 2) Electrolyte preparation: EC / EMC / DMC = 30wt%:40wt%:30wt%, 0.5M LiPF6 + 0.5M LiFSI, 2.5%wt VC, 0.5%wt FEC, 0.5wt% DTD. Wherein, EC is ethylene carbonate, EMC is ethyl methyl carbonate, DMC is dimethyl carbonate, LiPF6 is lithium hexafluorophosphate, LiFSI is lithium bis(fluorosulfonyl)imide, VC is vinylene carbonate, FEC is fluoroethylene carbonate, and DTD is vinyl sulfate.

[0285] 3) Selection of diaphragm: 9μm PE single-sided coated diaphragm.

[0286] 4) Assembly: The positive electrode, separator and negative electrode prepared in each embodiment or comparative example are assembled according to an NP ratio or CB value (the ratio of negative electrode surface capacity to positive electrode surface capacity) of ≥1.05. Then, liquid is injected, and then the battery manufacturing process such as encapsulation, formation and capacity testing is carried out to prepare a square aluminum-cased battery.

[0287] Battery 2 Preparation: The negative electrode sheet prepared in each embodiment or comparative example, a commercially available positive electrode sheet (ternary 811 system or lithium iron phosphate system), and a separator are used to prepare battery 2 (Note: The batteries 2 shown in this application are all lithium iron phosphate-graphite or NCM811-graphite systems, but are not limited to these two systems in actual applications). The specific preparation method includes the following steps:

[0288] 1) Preparation of commercially available positive electrode sheets: preparation method of positive electrode sheet of ternary 811 system as in comparative example 3; preparation method of positive electrode sheet of lithium iron phosphate system as in comparative example 2.

[0289] 2) Electrolyte preparation: EC / EMC / DMC = 30wt%:40wt%:30wt%, 0.8M LiPF6 + 0.25M LiFSI, 2.5%wt VC, 0.5%wt FEC, 0.5wt% DTD. Wherein, EC is ethylene carbonate, EMC is ethyl methyl carbonate, DMC is dimethyl carbonate, LiPF6 is lithium hexafluorophosphate, LiFSI is lithium bis(fluorosulfonyl)imide, VC is vinylene carbonate, FEC is fluoroethylene carbonate, and DTD is vinyl sulfate.

[0290] 3) Selection of diaphragm: 9μm PE single-sided coated diaphragm.

[0291] 4) Assembly: The positive electrode, separator and negative electrode prepared in each embodiment or comparative example are assembled, followed by liquid injection, and then packaged, formed, and capacity tested to prepare a square aluminum-cased battery.

[0292] The safety and electrochemical performance of battery 1 or battery 2 corresponding to the composite electrodes prepared in each embodiment or comparative example were tested. Among them:

[0293] (1) Safety performance testing involves overcharge testing and nail penetration testing. Among them:

[0294] The overcharge test method is as follows: Charge the aluminum-cased battery at 0.33C to the cutoff voltage (voltage window for lithium iron phosphate-graphite system: 2.5-3.65V; voltage window for ternary NCM811-graphite system: 2.8-4.2V), then charge at a constant voltage until the current drops to 0.05C. Let it stand for 2 hours, then charge at 1C to 1.5 times the voltage or charge for 30 minutes and then stop charging. Observe whether thermal runaway occurs. If it occurs, record the state of charge (SOC) at the time of thermal runaway.

[0295] The needle penetration test method is as follows: charge the aluminum-cased battery at 0.33C to the cutoff voltage (voltage window of lithium iron phosphate graphite system: 2.5-3.65V; voltage window of ternary NCM811 graphite system: 2.8-4.2V), and then charge it at a constant voltage until the current drops to 0.05C. Use a φ5mm high-temperature resistant steel needle (the steel needle has a cone angle of 55°, a smooth surface, and is free of rust, oxide layer and oil stains), and penetrate it at a speed of (25)mm / s from a direction perpendicular to the battery plate. The penetration position should be close to the geometric center of the pierced surface. The steel needle stays in the battery and is observed for 1 hour after the test.

[0296] (2) Electrochemical performance testing

[0297] Cyclic testing method: The prepared square aluminum-cased battery was placed in a 25°C environment and cycled with 1 / 3C charging and 1C discharging. The specific steps were as follows: let stand for 1 hour, charge at a constant current of 1 / 3C to Umax, continue constant voltage charging until the current is less than 0.05C and then stop; let stand for 1 hour, discharge at a constant current of 1C to Umin; let stand for 1 hour. This constitutes one charge-discharge cycle of the battery. Repeat the above cycle until the battery capacity decays to 80% of the initial value, and record the number of cycles. (Note: For the lithium iron phosphate-graphite system, Umax = 3.65V, Umin = 2.5V; for the NCM811-graphite system, Umax = 4.2V, Umin = 2.8V).

[0298] Rate charging test method: Place the prepared square aluminum-cased battery in a 25℃ ambient temperature environment and let it stand for 2 hours. Charge it at 3C to Umax, continue constant voltage charging until the current is less than 0.05C, then stop charging. Let it stand for 1 hour, and discharge it at a constant current of 1C to Umin. Repeat the above steps 3 times. The ratio of the 3C charging capacity to the rated capacity on the third charge is recorded as the rate charging retention rate. Note: The rated capacity is the capacity discharged at a constant current of 1C to Umin at a temperature of 25℃. When the positive electrode is lithium iron phosphate and the negative electrode is graphite, Umax = 3.65V and Umin = 2.5V. When the positive electrode is NCM811 and the negative electrode is graphite, Umax = 4.2V and Umin = 2.8V.

[0299] The results of the DSC thermal stability and safety performance tests of the above electrodes are shown in Table 1, the results of the electrode porosity, cohesion and peel force tests are shown in Table 2, and the results of the electrochemical performance tests are shown in Table 3.

[0300] Table 1. Test results of electrode DSC thermal stability and safety performance.

[0301]

[0302]

[0303] As shown in Table 1:

[0304] Comparing Examples 1-3 and Comparative Examples 1-3, it is easy to see that, under the same active material, the decomposition temperature of the composite electrode provided in this application is higher than that of conventional electrode, which will help improve the thermal stability of the battery cell and enhance its safety.

[0305] Comparing Examples 1-3, we can see that this application provides a composite electrode preparation method, and the batteries prepared in Examples 1-3 all passed the nail penetration test. Example 3, due to the use of ternary material NCM811 for the positive electrode, experienced thermal runaway during overcharging. However, its SOC at the time of overcharge thermal runaway was 142.1%, significantly higher than the 113.2% of Comparative Example 3, increasing the difficulty of thermal runaway and improving safety. Furthermore, Comparative Examples 1-3 all failed the nail penetration test, indicating that compared to the electrode preparation methods of Comparative Examples 1-3, the method provided in this application can effectively improve the cell safety performance.

[0306] Comparing Examples 1 and 4-7, we found that as the ceramic content in the second slurry decreased, the ceramic content in the ceramic coating (i.e., the second material layer) also decreased, and the risk of overcharge runaway gradually increased. When the mass ratio of ceramic to binder (i.e., the third binder) decreased to 6:4, overcharge runaway occurred, and the failure SOC was 135.4%. Even so, this was still higher than the 114.5% SOC of Comparative Example 1 without ceramic coating when it failed due to overcharge runaway.

[0307] Comparing Examples 1 and 8-12, we found that as the density (thickness) of the second coating layer gradually decreases, the risk of thermal runaway gradually increases. When the density of the second coating layer decreases to 5 g / m², the risk increases further. 2 Its overcharge failure resulted in a failure SOC of 137.8%, which is much higher than the 114.5% SOC of the charge state that failed in Comparative Example 1.

[0308] As can be seen from Examples 1 and 13-14, and Comparative Examples 2 and 15, when the prepared composite electrode is a negative electrode, changing the type of pore-forming agent within the scope defined in this application has little impact on the thermal stability and safety performance of DSC. When the prepared composite electrode is a positive electrode, changing the type of pore-forming agent within the scope defined in this application will result in a change in the decomposition temperature. Specifically, benzoyl peroxide has a higher decomposition temperature than azobisisobutyronitrile, but the change in pore-forming agent does not affect the needle penetration test, and thermal runaway does not occur during overcharging.

[0309] Comparing Examples 1 and 16-17, and Examples 2 and 18-20, it can be seen that when the prepared composite electrode is a negative electrode, within the scope defined in this application, the thermal stability and safety performance of DSC are not significantly different with the increase of the pore-forming agent content. However, when the pore-forming agent content is the upper limit of 3%, the thermal decomposition temperature will decrease. When the prepared composite electrode is a positive electrode, within the scope defined in this application, the decomposition temperature gradually decreases with the increase of the pore-forming agent content, but all can pass the needle penetration test and will not experience thermal runaway.

[0310] Comparing Example 1 and Example 21, it can be seen that within the scope defined in this application, changing the type of ceramic has no impact on the thermal stability and safety performance of DSC.

[0311] Comparing Example 1 with Comparative Example 4, Comparative Example 2 with Comparative Example 5, and Comparative Example 3 with Comparative Example 6, it can be seen that the DSC thermal stability and safety performance of Example 1 with Comparative Example 4, Comparative Example 2 with Comparative Example 5, and Comparative Example 3 with Comparative Example 6 of this application are basically equivalent.

[0312] Table 2. Test results of electrode porosity, cohesion, and peel strength.

[0313]

[0314]

[0315] As shown in Table 2:

[0316] Comparing Examples 1-3 and Comparative Examples 4-6, it is evident that the composite electrodes prepared using this application exhibit higher porosity than electrodes with the same first coating layer type. Specifically, the porosity of the graphite negative electrode increases from 36.1% to 40.3%, the porosity of the lithium iron phosphate positive electrode increases from 31.3% to 35.2%, and the porosity of the ternary material NCM811 positive electrode increases from 33.4% to 37.4%. This demonstrates that this application effectively improves electrode porosity. Furthermore, the cohesive strength is also correspondingly enhanced, primarily due to the formation of pore channels, which increases the friction between the first and second material layers, indirectly improving the electrode's cohesive strength. The increase in peel strength is minimal, indicating no significant impact on the bonding effect at the current collector. Therefore, the composite electrode and its preparation method provided by this application can improve electrode porosity without weakening peel strength, while also providing safety features.

[0317] Comparing Examples 1 and 4-7, it can be seen that as the ceramic content in the second slurry decreases, the ceramic content in the ceramic coating (i.e., the second material layer) decreases, the porosity of the composite electrode gradually decreases, and the cohesion and peeling force gradually increase.

[0318] Comparing Examples 1 and 8-12, it can be seen that as the density (thickness) of the second coating layer gradually decreases, the porosity of the composite electrode gradually increases, while the cohesive force and peeling force gradually decrease.

[0319] As can be seen from Examples 1 and 13-14, and Comparative Examples 2 and 15, different pore-forming agents result in different porosities in the composite electrode, leading to differences in cohesive force and peel force, but all within the range defined in this application. Specifically: When the composite electrode is a negative electrode, under the same conditions, using a 1:1 mixture of ammonium bicarbonate and azobisisobutyronitrile (AIBN) or benzoyl peroxide and ammonium carbonate as the pore-forming agent, the porosity of the composite electrode gradually decreases, and both the cohesive force and peel force also gradually decrease. This is mainly because the pore-forming channels increase the friction between the first and second material layers, and between the first material layer and the current collector, indirectly improving the cohesive force of the electrode, the adhesion between the first and second material layers, and the adhesion between the first material layer and the current collector. The higher the porosity, the higher the cohesive force and peel force of the electrode. When the composite electrode is a positive electrode, under the same conditions, using benzoyl peroxide as the pore-forming agent yields higher porosity, cohesive force, and peel force compared to AIBN.

[0320] Comparing Examples 1 and 16-17, and Examples 2 and 18-20, it can be seen that within the scope defined in this application, as the content of the pore-forming agent increases, the porosity of the composite electrode gradually increases, while the cohesive force and peel force both increase first and then decrease. This indicates that the content of the pore-forming agent in this application has an optimal value within the defined range. At this value, the porosity is moderate, and the cohesive force and peel force are the highest. However, if the optimal value is exceeded, the porosity will increase further. But because the porosity is too high, the cohesive force and peel force may decrease (but the higher the porosity, the better the wettability of the electrolyte, and thus better battery electrochemical performance can be obtained, see Table 3 below for electrochemical performance test results).

[0321] Comparing Example 1 and Example 21, it can be seen that within the scope defined in this application, changing the type of ceramic has virtually no effect on porosity, cohesion, and peeling force.

[0322] Comparing Examples 1-3 and Comparative Examples 1-3, it can be seen that, under the same active material, the composite electrode of this application has higher porosity, cohesion and peel strength due to the presence of a pore-forming agent and a second material layer.

[0323] Table 3 Electrochemical performance test results

[0324]

[0325]

[0326] As can be seen from Table 3:

[0327] Comparing Examples 1-3 and Comparative Examples 4-6, it can be seen that the batteries assembled using the composite electrode prepared in this application have better electrochemical performance. This may be because the composite electrode prepared in this application has higher porosity, and higher porosity can improve the wettability of the electrolyte, thereby improving the battery's cycle capacity retention rate and rate charge capacity retention rate, among other electrochemical performance characteristics.

[0328] Comparing Examples 1 and 4-7, it can be seen that as the ceramic content in the second slurry decreases, the ceramic content in the ceramic coating (i.e., the second material layer) also decreases, leading to a gradual decrease in the battery's cycle capacity retention and rate charge capacity retention. This may be due to the gradual decrease in the porosity of the composite electrode, resulting in a gradual deterioration in the wettability of the electrolyte, and consequently a decline in electrochemical performance.

[0329] Comparing Examples 1 and 8-12, it can be seen that as the density (thickness) of the second coating layer gradually decreases, the cycle capacity retention rate and rate charge capacity retention rate of the battery generally show a gradually increasing trend. This may be because the porosity of the composite electrode gradually decreases, resulting in better electrolyte wettability and thus improved electrochemical performance.

[0330] As can be seen from Examples 1 and 13-14, and Comparative Examples 2 and 15, the porosity of the composite electrode varies with different pore-forming agents. Batteries with higher porosity have slightly higher cycle capacity retention and rate charge capacity retention.

[0331] Comparing Examples 1 and 16-17, and Examples 2 and 18-20, it can be seen that within the scope defined in this application, as the content of the pore-forming agent increases, the porosity of the composite electrode gradually increases, and the cycle capacity retention rate and rate charge capacity retention rate also gradually increase.

[0332] Comparing Example 1 and Example 21, it can be seen that within the scope defined in this application, changing the type of ceramic has virtually no impact on the cycle capacity retention rate and the rate charge capacity retention rate.

[0333] Comparing Examples 1-3 and Comparative Examples 1-3, it can be seen that, under the same active material, the present application exhibits higher cycle capacity retention and rate charge capacity retention due to the presence of a pore-forming agent and a second material layer. This may be because the porosity of the composite electrode gradually decreases, leading to a gradual deterioration in the wettability of the electrolyte and consequently a decline in electrochemical performance.

[0334] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0335] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0336] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A composite electrode, characterized in that, include: current collector; A first material layer is disposed on at least a portion of the surface of the current collector, the first material layer comprising an active material and a pore-forming agent, the active material comprising a positive electrode active material or a negative electrode active material; A second material layer is disposed on at least a portion of the surface of the first material layer, and the second material layer is a ceramic safety coating; the second material layer includes ceramic and a third binder, and does not contain the pore-forming agent; both the interior and surface of the second material layer and the first material layer are provided with a plurality of pores formed by the thermal decomposition of at least a portion of the pore-forming agent; The pore-forming agent has a mass content of 0.1-3% in the first material layer; the pore-forming agent includes at least one of ammonium carbonate, ammonium bicarbonate, azobisisobutyronitrile, and benzoyl peroxide; the particle size range of the pore-forming agent is 500 nm to 20 μm. The thickness of the first material layer is 50-100 μm; The thickness of the second material layer is 5-20 μm.

2. The composite electrode according to claim 1, characterized in that, The median particle size of the pore-forming agent is 1-5 μm.

3. The composite electrode according to claim 1, characterized in that, The positive electrode active material includes at least one of lithium iron phosphate, ternary materials, and lithium cobalt oxide; and / or, The negative electrode active material includes at least one of graphite, silicon-carbon composite material, silicon oxide compound, and silicon; and / or, The ceramic includes at least one of alumina ceramic and boehmite; and / or, The ceramic has a particle size range of 100 nm to 5 μm; and / or, The median particle size of the ceramic is 0.8-1.2 μm.

4. The composite electrode according to claim 1, characterized in that, When the active material includes a positive electrode active substance, the material of the first material layer comprises the following components in the following mass percentages: 94-97% positive electrode active substance, 0.5-2% first conductive agent, 1-3% first binder, 0.1-3% pore-forming agent; and / or, When the active material includes a negative electrode active substance, the material of the first material layer includes the following components in the following mass percentages: 94-97% negative electrode active substance, 0.5-2% second conductive agent, 0.7-2% thickener, 1-2% second binder, and 0.1-3% pore-forming agent.

5. The composite electrode according to claim 4, characterized in that, The first conductive agent includes at least one of conductive carbon black and carbon nanotubes; and / or, The first adhesive includes at least one of polyvinylidene fluoride resin and polytetrafluoroethylene; and / or, The second conductive agent includes conductive carbon black; and / or, The thickener includes at least one selected from sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyvinyl alcohol, and sodium polyacrylate; and / or, The second adhesive comprises at least one of styrene-butadiene latex and polyacrylic acid; and / or, When the active material includes a positive electrode active substance, the third binder includes at least one of oil-based polyvinylidene fluoride resin, polyacrylic acid, and polymethyl methacrylate; and / or, When the active material includes a negative electrode active substance, the third binder includes at least one of aqueous polyvinylidene fluoride resin, polyacrylic acid, and polymethyl methacrylate; and / or, The mass ratio of the ceramic to the third binder is (5-9):(5-1).

6. The composite electrode according to claim 1, characterized in that, When the active material includes a positive electrode active substance, the composite electrode is a positive electrode, and the porosity of the composite electrode is 30-40%; and / or, When the active material includes a negative electrode active substance, the composite electrode is a negative electrode, and the porosity of the composite electrode is 35-45%; and / or, The cohesive strength of the composite electrode is greater than 25 N / m and less than 50 N / m; and / or, The peel force of the first material layer, as tested by the peel force test, is a N / m, where 7 < a < 30; and / or, The areal density of the first material layer is 45-230 g / cm³. 2 ; and / or, The areal density of the second material layer is 5-20 g / m³. 2 ; and / or, The pores are micro-nano pore channels, with a diameter less than 1 μm; and / or, The temperature of the thermal decomposition is 100-120℃; and / or, The current collector includes one of copper foil and aluminum foil; and / or, The mass ratio of the active material to the ceramic is (42.3-223.1):(2.5-18).

7. A method for preparing a composite electrode as described in any one of claims 1 to 6, characterized in that, include: A double-layer coating technology is used to simultaneously coat the first slurry and the second slurry onto the current collector, forming the first coating layer and the second coating layer respectively, resulting in a current collector containing a slurry layer; The current collector containing the slurry layer is dried and rolled to obtain the composite electrode sheet; The first slurry includes the material of the first material layer, and the second slurry includes the material of the second material layer.

8. The preparation method according to claim 7, characterized in that, The first slurry further includes a first solvent, and when the active material includes a positive electrode active material, the first solvent includes N-methylpyrrolidone (NMP), or when the active material includes a negative electrode active material, the first solvent includes water; and / or, The second slurry further includes a second solvent, which comprises at least one of water, N-methylpyrrolidone (NMP); and / or, When the active material includes a positive electrode active material, the positive electrode active material is lithium iron phosphate, the solid content of the first slurry is 60-64%, and the viscosity of the first slurry is 7000-11000 MPa•s; or, the positive electrode active material is a ternary material, the solid content of the first slurry is 70-74%, and the viscosity of the first slurry is 6000-10000 MPa•s; or, the positive electrode active material is lithium cobalt oxide, the solid content of the first slurry is 76-80%, and the viscosity of the first slurry is 3000-7000 MPa•s; or... When the active material includes a negative electrode active substance, the solid content of the first slurry is 52-56%, and the viscosity of the first slurry is 3000-7000 MPa•s; and / or, The solid content of the second slurry is 15-35%, and the viscosity of the second slurry is 3000-7000 MPa•s; And / or, The drying temperature is 100-120℃; and / or, The pore-forming agent decomposes at least partially during the drying process to generate gas, forming a plurality of pores inside and on the surface of the first coating layer and the second coating layer.

9. A secondary battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that, The positive electrode and / or the negative electrode are composite electrodes as described in any one of claims 1 to 6 or composite electrodes prepared by the preparation method as described in any one of claims 7 or 8.

10. An electrical device, characterized in that, Includes the secondary battery as described in claim 9.

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