A method for preparing a high-strength thick electrode with a gradient pore

Abstract

The application relates to the technical field of battery electrode material preparation, and discloses a gradient-pore preparation method of a thick electrode with high bonding strength, which comprises the following steps: mixing poly-p-phenyleneterephthalamide fine fibers and natural cellulose coarse fibers to form a double-fiber composite binder skeleton, adding a silanol-containing active solution to the double-fiber composite binder skeleton to stir and modify the double-fiber composite binder skeleton to obtain a modified binder solution; mixing electrode active material, conductive material and the modified binder solution to obtain a base slurry; adding porous frame materials into the base slurry respectively to mix, so that a plurality of slurry systems with concentration gradients of the porous frame materials are obtained; coating the plurality of slurry systems on the surface of a current collector in the order of the volume fraction of the porous frame materials from low to high to form an electrode preform; and performing segmented heat pressing and curing on the electrode preform, and performing a breathing type pressure change and exhaust operation in the segmented heat pressing and curing stage to obtain a thick electrode. The application improves the cohesive strength of the thick electrode and improves the problem of insufficient deep electrolyte infiltration.

Description

Technical Field

[0001] This invention relates to the field of battery electrode material preparation technology, specifically a method for preparing gradient pores in a thick electrode with high bonding strength. Background Technology

[0002] As battery energy density requirements increase, increasing electrode thickness has become a common design approach. However, existing thick electrodes have significant drawbacks in their fabrication and use.

[0003] Existing polymer binders mostly rely on physical entanglement to connect active material particles. Thick electrodes undergo significant volume expansion during charging and discharging, and a single physical network cannot withstand the enormous internal stress, causing the mechanical conduction in the thickness direction to be interrupted. This results in low overall cohesive strength and peel strength of the electrode, making it easy for active particles to detach.

[0004] Meanwhile, as the electrode thickness increases, the resistance to electrolyte penetration into the deeper layers of the electrode also increases. The internal pores of thick electrodes prepared by conventional methods are often randomly distributed, failing to provide the necessary traction force for electrolyte penetration. This results in the deeper regions of the electrode remaining in a state of insufficient electrolyte wetting for extended periods, thereby lengthening the ion diffusion path and increasing ion transport resistance.

[0005] Furthermore, during the thermosetting or pore-forming process of thick electrodes, the gases generated by the thermal decomposition of the internal materials are trapped inside the thick electrode sheet and cannot escape through the surface. The gases remaining inside the electrode sheet can form localized micropores and bubbles, disrupting the smoothness and density of the internal structure of the electrode sheet and severely affecting the overall performance of the battery. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing gradient pores in thick electrodes with high bonding strength. This method solves the problems that existing thick electrodes are prone to encounter during preparation and cycling, such as insufficient bonding strength leading to electrode detachment, uneven internal pore distribution causing ion transport obstruction, and difficulty in venting internal gas, resulting in structural expansion and interface defects.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing gradient pores in a thick electrode with high bonding strength, comprising the following steps: Poly(p-phenylene terephthalamide) fine fibers are mixed with natural cellulose coarse fibers to form a dual-fiber composite binder skeleton. The dual-fiber composite binder skeleton is added to an active solution containing silanol and stirred for modification to obtain a modified binder solution. Electrode active material, conductive material and modified binder solution are mixed to obtain base slurry; Porous framework materials were added to the substrate slurry and mixed to prepare multiple slurry systems with a concentration gradient of porous framework materials. Multiple slurry systems are sequentially coated onto the surface of the current collector in order of increasing volume fraction of porous framework material to form an electrode preform. The electrode preform is subjected to segmented hot-press curing, and a breathing-type variable pressure exhaust operation is performed during the segmented hot-press curing stage to obtain a thick electrode with high bonding strength.

[0008] By adopting the above technical solution, and by using a dual-fiber composite system combined with silanol crosslinking modification, gradient coating, and pressure swing venting processes, the following effects are achieved: Regarding the binder mechanism, poly(p-phenylene terephthalamide), as an aramid-based rigid polymer, possesses high tensile strength and modulus, enabling it to withstand the volume expansion stress generated during the charging and discharging of thick electrodes. Natural cellulose provides abundant surface hydroxyl groups and flexibility. The silanol groups undergo a dehydration condensation reaction with the hydroxyl groups on the surface of natural cellulose, transforming the originally physically entangled fiber skeleton into a three-dimensional cross-linked network structure with chemical covalent bonds. This three-dimensional cross-linked network structure not only anchors the electrode active material particles but also provides a continuous mechanical conduction path along the thickness direction of the thick electrode, enhancing the overall cohesive strength.

[0009] In terms of pore structure construction, porous framework materials are coated sequentially in ascending order of volume fraction. The region near the bottom of the current collector has the lowest proportion of porous framework material, resulting in high solid density, which increases the physical contact area between the electrode material and the current collector surface, improves peel strength, and prevents the thick electrode from detaching from the substrate. The region near the electrode surface has the highest proportion of porous framework material, which provides electrolyte wetting channels after pore formation, shortens the diffusion path of lithium ions inside the thick electrode, reduces diffusion resistance, and solves the problem of poor dynamic performance of thick electrodes.

[0010] In the thick electrode molding and curing process, a segmented hot-pressing curing method combined with a breathing-style pressure-variable venting operation is used. The high-pressure state promotes the dense rearrangement of particles inside the electrode. Subsequently, pressure is released to create an outward pressure difference within the thick electrode. The negative pressure suction effect extracts the gases and residual solvents generated by the thermal decomposition of the porous framework material. Then, pressure is reapplied for structural shaping. This alternating pressure change overcomes the limitation of conventional constant-pressure curing where gases tend to accumulate and form defects inside the electrode, ensuring a smooth and dense interface between electrode layers.

[0011] Preferably, the diameter of the poly(p-phenylene terephthalamide) fine fibers is 0.1µm to 0.5µm, and the crystallinity is 70% to 85%; the diameter of the natural cellulose coarse fibers is 2µm to 5µm, and the degree of polymerization is 500 to 800; the mass ratio of the poly(p-phenylene terephthalamide) fine fibers to the natural cellulose coarse fibers is 2:1 to 4:1.

[0012] By employing the above technical solution, a multi-scale microstructure with a combination of coarse and fine fibers is constructed. Natural cellulose coarse fibers serve as the main support network, while poly(p-phenylene terephthalamide) fine fibers interweave and overlap between the coarse fibers to form a secondary network. A crystallinity of 70% to 85% endows the fine fibers with tensile strength, limiting the elongation of the electrode sheet during compaction. A mass ratio of 2:1 to 4:1 achieves a balance between rigid support and flexible buffering, preventing the coating from cracking due to an overly rigid framework or the thick electrode from collapsing due to an overly soft framework.

[0013] Preferably, the step of adding the dual-fiber composite binder skeleton to a silanol-containing active solution for stirring modification includes: adding 0.5% to 1.5% of the total mass of the dual-fiber composite binder skeleton to a mixed solvent composed of deionized water and N-methylpyrrolidone in a mass ratio of 1:99 to 5:95, and hydrolyzing to generate a silanol-containing active solution; adding the dual-fiber composite binder skeleton to the silanol-containing active solution, adjusting the amount of mixed solvent added to control the mass fraction of the solid component in the modified binder solution to be 5% to 10%, and stirring modification at a temperature of 50°C to 70°C for 1 to 2 hours.

[0014] By adopting the above technical solution, the crosslinking modification reaction mechanism includes the following steps: The first step is the hydrolysis reaction of the silane coupling agent. In the presence of deionized water, the alkoxy group at the end of the γ-aminopropyltriethoxysilane molecule undergoes hydrolysis to generate an intermediate containing an active silanol group.

[0015] The second step involves dehydration condensation and grafting reactions. Driven by thermodynamics at 50°C to 70°C, the silanol groups undergo dehydration condensation with the hydroxyl groups on the surface of natural cellulose, forming Si-OC covalent bonds. This reaction consumes the hydrophilic hydroxyl groups on the cellulose surface, reducing the risk of the electrode swelling due to water absorption later on. Simultaneously, the γ-aminopropyl terminals remain free in the binder solution, forming secondary chemical bonds with the surface of the subsequently added current collector metal.

[0016] Preferably, the electrode active material is lithium iron phosphate or artificial graphite; the conductive material is conductive carbon black; and the mass ratio of the electrode active material, the conductive material and the solid component in the modified binder solution in the substrate slurry is 90:6:4 to 96:2:2.

[0017] By adopting the above technical solution, the mass ratio boundaries of the active material, conductive network, and binder framework were clarified. These mass ratios ensure that the modified binder solution has sufficient solids to coat the lithium iron phosphate or artificial graphite particles without affecting the overall energy density, thus maintaining the electronic conductivity and mechanical integrity of the electrode.

[0018] Preferably, the porous framework material is one of ammonium oxalate, polystyrene microspheres, polymethyl methacrylate microspheres, and sodium bicarbonate; the weight-average molecular weight of the polystyrene microspheres is in the range of 150,000 to 250,000, and the weight-average molecular weight of the polymethyl methacrylate microspheres is in the range of 80,000 to 120,000; the number of multiple slurry systems is 3 to 5; the particle size of the porous framework material in the multiple slurry systems increases sequentially, and the particle size of the porous framework material is 0.5µm to 20µm.

[0019] By employing the above technical solution, the porous framework material possesses the characteristics of thermal decomposition or softening and shrinkage. The sequentially increasing particle size, combined with the increasing volume fraction, constructs a pore network within the thick electrode, with the pore size expanding from the bottom to the surface. The large pores on the surface provide channels for electrolyte entry, while the small pores at the bottom generate capillary forces that draw the electrolyte inward, improving the problem of insufficient electrolyte wetting in the deeper regions of the thick electrode.

[0020] Preferably, the multiple slurry systems are arranged in order of increasing volume fraction of porous framework material, including a first slurry system and subsequent slurry systems; in the first slurry system, the volume of porous framework material accounts for 10% to 20% of the total volume of all solid components in the first slurry system, and in subsequent slurry systems, the proportion of porous framework material to the total volume of all solid components in the slurry system increases sequentially by 5% to 15%; the current collector is an aluminum foil current collector or a copper foil current collector.

[0021] By adopting the above technical solution, a progressive gradient of porosity is defined. The low pore-forming agent content at the bottom (10% to 20%) retains sufficient binder area for contact with the aluminum or copper foil; the progressive increase of 5% to 15% avoids stress concentration surfaces caused by abrupt changes in porosity between adjacent layers, reducing the risk of peeling within the coating.

[0022] Preferably, after sequentially coating multiple slurry systems onto the surface of the current collector to form an electrode preform, and before performing segmented hot-pressing curing on the electrode preform, a pretreatment step is further included, comprising: applying a pressure of 10MPa to 20MPa to pre-press the electrode preform for 1 min to 2 min; and activating the surface of the pre-pressed electrode preform using a plasma treatment device to obtain an activated electrode preform; the processing power of the plasma treatment device is 100W to 300W, and the processing time is 30s to 60s.

[0023] By adopting the above technical solutions, the pre-pressing treatment at room temperature eliminates the interlayer gaps generated during the surface drying stage of multi-layer coating, and promotes the initial physical interlocking of particles on adjacent slurry layers. The plasma surface activation treatment uses particle bombardment of the electrode surface to remove organic contaminants and introduce oxygen-containing polar functional groups, increasing the surface energy of the preform surface layer, providing a highly active fusion interface for subsequent high-temperature hot pressing, and inhibiting the initiation of surface microcracks.

[0024] Preferably, the activated electrode preform is subjected to segmented hot-press curing, which includes: a first stage: heating to 80°C to 120°C, applying a pressure of 10MPa to 20MPa, and maintaining the temperature and pressure at a constant level for 10 to 20 minutes; a second stage: heating to 120°C to 160°C, applying a pressure of 20MPa to 30MPa, and maintaining the temperature and pressure at a constant level for 15 to 25 minutes; and a third stage: heating to 160°C to 180°C, applying a base pressure of 30MPa to 35MPa, with a total holding time of 5 to 10 minutes at the temperature and base pressure in the third stage.

[0025] By adopting the above technical solution, the curing process is highly matched with the physicochemical transformation of the material. The first stage removes moisture and low-boiling-point solvents; the second stage promotes thermal motion and rearrangement of macromolecular chain segments in the modified binder solution, and the porous framework material begins to decompose or shrink and deform; the third stage completes the volatilization of residual high-boiling-point solvents, the thermal curing and shaping of cross-linked networks, and the compaction and curing of overall density under high temperature of 160℃ to 180℃ and high pressure of 30MPa to 35MPa, preventing the release of internal stress in thick electrodes under a single temperature rise condition.

[0026] Preferably, the breathing-type pressure-changing exhaust operation is performed in the third stage. The breathing-type pressure-changing exhaust operation includes performing 3 to 5 pressure-changing exhaust cycles continuously. Each pressure-changing exhaust cycle includes: pressurizing to 30MPa to 35MPa and maintaining it for 1 to 2 minutes, depressurizing to 3MPa to 5MPa and maintaining it for 5 to 15 seconds, and then repressurizing to 30MPa to 35MPa.

[0027] By employing the above technical solution, in the high-temperature environment of the third stage, the gas generated by the decomposition or contraction of the porous framework material is in an expanded state. Pressurization to 30MPa to 35MPa ensures that the matrix does not expand; subsequently, depressurization is performed to 3MPa to 5MPa within 5 to 15 seconds, utilizing the pressure difference to induce deep gas accumulation and discharge to the outside of the electrode through interconnected micropores; high pressure is then restored to compact and close the cavity left after venting. Multiple pressure-changing venting cycles reduce the residual rate of pores and bubbles inside the thick electrode.

[0028] Preferably, after performing the breathing-type pressure-changing exhaust operation, the process further includes deep drying the activated electrode preform at a temperature of 100°C to 120°C and a vacuum of -0.099MPa to -0.090MPa for 2 to 4 hours.

[0029] By employing the above technical solution, vacuum negative pressure conditions combined with high temperature are used to remove residual liquid phase molecules that have recondensed or adsorbed during the initial hot pressing process. The dehydration and volatile matter removal operations prevent side reactions and gas generation during the charge-discharge phase after the thick electrodes are assembled into a battery, thus improving the stability of the electrochemical reaction system.

[0030] This invention provides a method for preparing gradient pores in a thick electrode with high bonding strength. It has the following beneficial effects: 1. This invention involves mixing poly(p-phenylene terephthalamide) fine fibers with natural cellulose coarse fibers to form a dual-fiber composite binder skeleton, and then adding the dual-fiber composite binder skeleton to an active solution containing silanol for cross-linking modification. The silanol groups undergo a dehydration condensation reaction with the hydroxyl groups on the surface of natural cellulose to form a three-dimensional cross-linked network structure with chemical covalent bonds. The three-dimensional cross-linked network structure enhances the anchoring effect on the electrode active material particles and establishes a continuous mechanical conduction path in the thickness direction of the thick electrode, thereby improving the overall cohesive strength and peel strength of the thick electrode and preventing the electrode from falling off during charging and discharging.

[0031] 2. This invention involves preparing multiple slurry systems with a concentration gradient of porous framework material and coating them sequentially onto the surface of the current collector according to the volume fraction and particle size of the porous framework material from low to high. This constructs a gradient pore network with pore size expanding from the bottom to the surface inside the thick electrode. The large pore structure on the surface provides channels for electrolyte entry, while the small pore structure at the bottom generates capillary force to pull the electrolyte to penetrate deeper. This improves the defect of insufficient electrolyte wetting in the deep region of the thick electrode, shortens the ion diffusion path, and reduces transport resistance.

[0032] 3. This invention performs segmented hot-press curing on the electrode preform and introduces a breathing-type pressure-variable venting operation with alternating pressurization and depressurization during the high-temperature and high-pressure stage of segmented hot-press curing. The pressure difference generated by depressurization causes the gas generated by the decomposition or contraction of the porous framework material inside the thick electrode to be discharged outward. The repressurization action compacts and closes the cavity left after venting. Multiple pressure-variable venting cycles eliminate residual air bubbles and micropores inside the thick electrode, ensuring the flatness and density of the internal structure of the thick electrode. Attached Figure Description

[0033] Figure 1 This is a comprehensive comparison chart of the electrode thickness expansion rate and the electrolyte complete wetting time of the present invention; Figure 2 This is a bidirectional horizontal bar comparison diagram of the multi-level interfacial bonding strength of the electrode sheet of the present invention. Figure 3 This is a comparison chart of the high-rate discharge performance of the full battery of the present invention; Figure 4 This is a diagram showing the evaluation of the microchemical stability of the full cell after long-term cycling according to the present invention. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings, examples, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] raw material: The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0036] Polystyrene, CAS No.: 9003-53-6, weight average molecular weight range: 150,000-250,000; Polymethyl methacrylate, CAS No.: 9011-14-7, with a weight-average molecular weight range of 80,000-120,000.

[0037] Examples 1-7: Example 1: This embodiment provides a method for preparing gradient pores in a thick electrode with high bonding strength, including the following steps: Poly(p-phenylene terephthalamide) (PPTA) fine fibers (0.1µm in diameter, 70% crystallinity) and natural cellulose coarse fibers (2µm in diameter, 500 degree of polymerization) were mixed at a mass ratio of 2:1 to form the skeleton of the dual-fiber composite binder.

[0038] In a mixed solvent consisting of deionized water and N-methylpyrrolidone at a mass ratio of 1:99, γ-aminopropyltriethoxysilane (KH550) was first added at a mass of 0.5% of the total mass of the dual-fiber composite binder skeleton. The deionized water in the mixed solvent was used to hydrolyze the γ-aminopropyltriethoxysilane to generate an active solution containing silanol. Subsequently, the dual-fiber composite binder skeleton was added to the active solution. By adjusting the amount of mixed solvent added, a binder solution with a solid component mass fraction of 5% was prepared. The solution was then modified by stirring at 50°C for 1 hour to obtain the modified binder solution.

[0039] Lithium iron phosphate, conductive carbon black, and modified binder solution are mixed to form a mixture, and the mass ratio of lithium iron phosphate, conductive carbon black, and solid components in the modified binder solution in the mixture is controlled to be 90:6:4 to obtain the base slurry.

[0040] Ammonium oxalate of different particle sizes was used as a porous framework material and added to an equal mass of base slurry and mixed evenly to prepare a first slurry system, a second slurry system, a third slurry system, a fourth slurry system, and a fifth slurry system. The particle sizes of ammonium oxalate used in the first to fifth slurry systems were 0.5µm, 3µm, 5µm, 8µm, and 10µm, respectively. The volume of the porous framework material in the first slurry system accounted for 10% of the total volume of all solid components in the first slurry system, and the proportion of the volume of the porous framework material in the total volume of all solid components in the second to fifth slurry systems increased by 5% sequentially (i.e., 15%, 20%, 25%, and 30%, respectively).

[0041] A multilayer coating machine was used to sequentially coat the five slurry systems onto the surface of the aluminum foil current collector in order of increasing porous framework material volume fraction. After each coating layer was applied, the surface was dried in a hot air environment at 75°C to form an initial electrode preform with a 5-layer structure.

[0042] To enhance the adhesion between coating layers, the initial electrode preform with a 5-layer structure was pre-compressed at 10 MPa for 1 minute at room temperature to obtain a pre-compressed electrode preform. After pre-compression, the surface of the pre-compressed electrode preform was activated using a plasma treatment device with a power of 100 W and a treatment time of 30 seconds to obtain an activated electrode preform.

[0043] The activated electrode preform is placed in a hot press with a vented textured pad and subjected to segmented hot pressing curing: First stage: Heat to 80℃, apply pressure of 10MPa, and maintain constant temperature and pressure for 10min; Second stage: Heat to 120℃, apply pressure of 20MPa, and maintain constant temperature and pressure for 15min; The third stage: heat up to 160℃, apply a base pressure of 30MPa, and hold at this temperature and base pressure for a total of 5 minutes.

[0044] To facilitate the smooth escape of gases generated by the thermal decomposition of porous framework materials, a breathing-type pressure-variable exhaust operation is performed during the holding period: pressurize to 30MPa and maintain for 1 minute, then instantly depressurize to 3MPa and maintain for 5 seconds, and then repressurize to 30MPa. The process of pressurization, depressurization and repressurization is a pressure-variable exhaust cycle, and the pressure-variable exhaust cycle is executed continuously 3 times.

[0045] The hot-pressed and cured electrodes were cut and placed in a vacuum drying oven for deep drying at 100℃ and -0.090MPa for 2 hours. The final product was a thick electrode with a thickness of 150µm.

[0046] Example 2: This embodiment provides a method for preparing gradient pores in a thick electrode with high bonding strength, including the following steps: PPTA fine fibers (0.3µm in diameter, 78% crystallinity) and natural cellulose coarse fibers (3.5µm in diameter, 650 degree of polymerization) were mixed at a mass ratio of 3:1 to form the skeleton of the dual-fiber composite binder.

[0047] In a mixed solvent consisting of deionized water and N-methylpyrrolidone in a mass ratio of 3:97, KH550, at a mass of 1.0% of the total mass of the dual-fiber composite binder skeleton, was first added to hydrolyze it to generate an active solution containing silanol. Subsequently, the dual-fiber composite binder skeleton was added to the active solution. By adjusting the amount of mixed solvent added, an binder solution with a solid component mass fraction of 8% was prepared. The solution was then modified by constant temperature stirring at 60°C for 1.5 h to obtain the modified binder solution.

[0048] Subsequently, lithium iron phosphate, conductive carbon black and modified binder solution are mixed to form a mixture, and the mass ratio of lithium iron phosphate, conductive carbon black and solid components in the modified binder solution in the mixture is controlled to be 93:4:3 to obtain the base slurry.

[0049] Ammonium oxalate of different particle sizes was used as a porous framework material and added to an equal mass of base slurry and mixed evenly to prepare a first slurry system, a second slurry system, a third slurry system, and a fourth slurry system. The particle sizes of the ammonium oxalate used in the first to fourth slurry systems were 2µm, 6µm, 10µm, and 15µm, respectively. The volume of the porous framework material in the first slurry system accounted for 15% of the total volume of all solid components in the first slurry system, and the proportion of the volume of the porous framework material in the second, third, and fourth slurry systems increased by 10% sequentially (i.e., 25%, 35%, and 45%, respectively).

[0050] The first, second, third, and fourth slurry systems were sequentially coated onto the surface of the aluminum foil current collector in order of increasing porous framework material volume fraction. After each coating layer, the surface was dried in a hot air environment at 85°C to form an initial electrode preform with a four-layer structure.

[0051] To enhance the adhesion between coating layers, the initial electrode preform with a 4-layer structure was pre-compressed at 15 MPa for 1.5 min at room temperature to obtain a pre-compressed electrode preform. After pre-compression, the surface of the pre-compressed electrode preform was activated using a plasma treatment device with a power of 200 W and a treatment time of 45 s to obtain an activated electrode preform.

[0052] The activated electrode preform is placed in a hot press with a vented textured pad and subjected to segmented hot pressing curing: First stage: Heat to 100℃, apply pressure of 15MPa, and maintain constant temperature and pressure for 15min; Second stage: Heat to 140℃, apply pressure of 25MPa, and maintain constant temperature and pressure for 20min; The third stage: the temperature is raised to 170℃, and a base pressure of 33MPa is applied. The total holding time at this temperature and base pressure is 8 minutes.

[0053] To facilitate the smooth escape of gases generated by the thermal decomposition of porous framework materials, a breathing-type pressure-variable venting operation is performed during the holding period: pressurize to 33MPa and maintain for 1.5min, instantly depressurize to 4MPa and maintain for 10s, and then repressurize to 33MPa. The process of pressurization, depressurization and repressurization is a pressure-variable venting cycle, and the pressure-variable venting cycle is executed continuously 4 times.

[0054] The hot-pressed and cured electrodes were cut and placed in a vacuum drying oven for deep drying at 110℃ and a vacuum of -0.095MPa for 3 hours. The final product was a thick electrode with a thickness of 350µm.

[0055] Example 3: This embodiment provides a method for preparing gradient pores in a thick electrode with high bonding strength, including the following steps: PPTA fine fibers (0.5µm in diameter, 85% crystallinity) and natural cellulose coarse fibers (5µm in diameter, 800 degree of polymerization) were mixed at a mass ratio of 4:1 to form the skeleton of the dual-fiber composite binder.

[0056] In a mixed solvent consisting of deionized water and N-methylpyrrolidone at a mass ratio of 5:95, KH550, accounting for 1.5% of the total mass of the dual-fiber composite binder skeleton, was first added to hydrolyze it to generate an active solution containing silanol. Subsequently, the dual-fiber composite binder skeleton was added to the active solution. By adjusting the amount of mixed solvent added, an binder solution with a solid component mass fraction of 10% was prepared. The solution was then modified by constant temperature stirring at 70°C for 2 hours to obtain a modified binder solution.

[0057] Lithium iron phosphate, conductive carbon black, and modified binder solution are mixed to form a mixture, and the mass ratio of lithium iron phosphate, conductive carbon black, and solid components in the modified binder solution in the mixture is controlled to be 96:2:2 to obtain the base slurry.

[0058] Ammonium oxalate of different particle sizes was used as a porous framework material and added to an equal mass of base slurry and mixed evenly to prepare a first slurry system, a second slurry system, and a third slurry system. The particle sizes of ammonium oxalate used in the first to third slurry systems were 5µm, 12µm, and 20µm, respectively. The volume of the porous framework material in the first slurry system accounted for 20% of the total volume of all solid components in the first slurry system, and the proportion of the volume of the porous framework material in the second and third slurry systems increased by 15% sequentially (i.e., 35% and 50%, respectively).

[0059] The first, second, and third slurry systems were sequentially coated onto the surface of the aluminum foil current collector in order of increasing volume fraction of porous framework material. After each layer was coated, the surface was dried in a hot air environment at 95°C to form an initial electrode preform with a three-layer structure.

[0060] To enhance the adhesion between coating layers, the initial electrode preform with a three-layer structure was pre-compressed at 20 MPa for 2 minutes at room temperature to obtain a pre-compressed electrode preform. After pre-compression, the surface of the pre-compressed electrode preform was activated using a plasma treatment device with a power of 300 W and a treatment time of 60 s to obtain an activated electrode preform.

[0061] The activated electrode preform is placed in a hot press with a vented textured pad and subjected to segmented hot pressing curing: First stage: Heat to 120℃, apply pressure of 20MPa, and maintain constant temperature and pressure for 20min; Second stage: Heat to 160℃, apply pressure of 30MPa, and maintain constant temperature and pressure for 25 minutes; The third stage: heat up to 180℃, apply a base pressure of 35MPa, and hold at this temperature and base pressure for a total of 10 minutes.

[0062] To facilitate the smooth escape of gases generated by the thermal decomposition of porous framework materials, a breathing-type pressure-variable exhaust operation is performed during the holding period: pressurize to 35MPa and maintain for 2 minutes, instantly depressurize to 5MPa and maintain for 15 seconds, and then repressurize to 35MPa. The process of pressurization, depressurization and repressurization is a pressure-variable exhaust cycle, and the pressure-variable exhaust cycle is executed continuously 5 times.

[0063] The hot-pressed and cured electrodes were cut and placed in a vacuum drying oven for deep drying at 120℃ and a vacuum of -0.099MPa for 4 hours. The final product was a thick electrode with a thickness of 600µm.

[0064] Example 4: This embodiment provides a method for preparing gradient pores in a thick electrode with high bonding strength. The basic steps are the same as in Embodiment 2, with the only difference being: The porous framework material was replaced with polystyrene microspheres (weight-average molecular weight in the range of 150,000-250,000). In the third stage of hot-press curing, the polystyrene microspheres underwent significant softening shrinkage and melting deformation at high temperature. The residual air and low-molecular-weight volatiles in the space freed up by the shrinkage of the microspheres were extracted using the suction effect of the breathing-type pressure-variable venting operation, thereby achieving the final shaping of the pore structure.

[0065] The remaining preparation steps and parameters are completely consistent with those in Example 2.

[0066] Example 5: This embodiment provides a method for preparing gradient pores in a thick electrode with high bonding strength. The basic steps are the same as in Embodiment 2, with the only difference being: Artificial graphite, conductive carbon black, and modified binder solution are mixed to form a mixture, and the mass ratio of solid components in the mixture to the modified binder solution is controlled to be 93:4:3 to obtain a base slurry.

[0067] Using a multilayer coating machine, the four slurry systems were sequentially coated onto the surface of the copper foil current collector in order of increasing volume fraction of porous framework material.

[0068] The remaining preparation steps and parameters are completely consistent with those in Example 2.

[0069] Example 6: This embodiment provides a method for preparing gradient pores in a thick electrode with high bonding strength. The basic steps are the same as in Embodiment 2, with the only difference being: The porous framework material was replaced with polymethyl methacrylate microspheres (weight-average molecular weight in the range of 80,000-120,000).

[0070] To match the thermal decomposition characteristics of polymethyl methacrylate (PMMA) microspheres, the parameters for segmented hot-pressing curing were adjusted: the second stage was heated to 150°C to soften the PMMA microspheres and induce partial thermal degradation; the third stage was heated to 175°C, and the holding time at this temperature and base pressure was adjusted to a total of 10 minutes. A breathing-type pressure swing venting operation was used to assist the rapid escape of thermal degradation products and free gases, and the pressure swing venting cycle was continuously executed 5 times to achieve the shaping of the pore structure.

[0071] The unmentioned segmented hot-pressing curing parameters and other preparation steps are completely consistent with those in Example 2.

[0072] Example 7: This embodiment provides a method for preparing gradient pores for a thick electrode with high bonding strength. The basic steps are the same as in Embodiment 2, except that the porous framework material is completely replaced by an equal volume of sodium bicarbonate instead of ammonium oxalate.

[0073] The remaining preparation steps and parameters are completely consistent with those in Example 2.

[0074] Comparative Examples 1-4: Comparative Example 1: Compared to Example 2, the difference lies in that: instead of preparing four slurry systems with concentration gradients, an equal amount of porous framework material is completely and uniformly mixed into the overall substrate slurry to form a mixed slurry of a single concentration. This slurry is then coated to the target thickness using a single-layer coating method, resulting in a homogeneous porosity distribution within the electrode. All other aspects remain the same.

[0075] Comparative Example 2: Compared to Example 6, the difference lies in that: in the third stage of hot-press curing, the breathing-type pressure-variable exhaust operation is completely eliminated, and the pressure is directly maintained at a constant level of 175°C and 33MPa for 10 minutes. All other aspects are the same.

[0076] Comparative Example 3: Compared to Example 2, the difference is that after the pre-compression treatment is completed by applying pressure at room temperature, the plasma activation treatment step is skipped, and the pre-compressed electrode preform is directly placed in a hot press for hot-press curing. All other aspects are the same.

[0077] Comparative Example 4: Compared to Example 2, the difference lies in the following: the dual-fiber composite binder skeleton composed of poly(p-phenylene terephthalamide) fine fibers and natural cellulose coarse fibers is omitted, and γ-aminopropyltriethoxysilane is not added for modification. Instead, it is directly replaced by an equal mass of conventional pure polyvinylidene fluoride as the single binder in the base slurry. All other aspects are the same.

[0078] Test Example 1-3: Test Example 1: Comprehensive Evaluation of Macroscopic Physicochemical Forming and Wetting Kinetics of Electrodes Test steps: The initial electrode preforms and finished electrodes prepared in Examples 1 to 6, as well as Comparative Examples 1 and 2, were selected as test objects.

[0079] Using a micrometer with an accuracy of 0.001 mm, the thickness of the initial electrode preform before hot-pressing curing was measured at five points in a matrix at 25°C. The average thickness of the geometric center and four corner regions was calculated. After the hot-pressing curing and deep drying processes, the finished electrode was placed on a reference surface for re-measurement to obtain the average thickness of the electrode sheet after hot pressing. The thickness expansion rate of each test object was calculated by dividing the thickness difference before and after measurement by the thickness of the preform before hot pressing. The macroscopic structural integrity of the surface layer of the finished electrode sheet was observed and recorded by the naked eye under a standard light source.

[0080] The finished electrodes for each test object were cut into 20mm × 20mm square samples and placed horizontally on a temperature-controlled glove box operating table with a dew point temperature below -50℃. Using a microsyringe, 5 μL of standard commercial electrolyte was drawn and vertically dropped onto the center area of ​​the square sample from a height of 2mm above the electrode surface. Simultaneously, the high-frequency camera mode of the contact angle measuring instrument was activated, capturing the time from the moment the droplet made contact with the electrode surface until the electrode surface completely lost its specular reflective properties. This time span was recorded as the electrolyte complete wetting time.

[0081] Test data: Table 1. Test data on macroscopic thickness expansion rate of electrode sheet and electrolyte wetting time

[0082] Test conclusion: Combining the physical measurements and macroscopic appearance characteristics recorded in Table 1, and Figure 1 The grayscale histograms on the left axis show that the thickness expansion rate of the example group was controlled within a reasonable range, and the macroscopic physical appearance maintained molding stability. In the early stages of thick electrode prototyping in the laboratory, polymer microspheres or inorganic framework materials decompose and release free gases and oligomer segments when exposed to thermodynamic environments above 150°C. If these gaseous products are confined within a closed, high-pressure physical boundary, they will induce local accumulation, thereby tearing the interlayer bonding network from the inside. This was confirmed in the test feedback of Comparative Example 2, corresponding to the localized blistering and bulging phenomenon with slight edge cracking described in Table 1. This study provides another approach by adjusting the curing parameters. The pressure-changing operation introduced in the examples physically breaks the closed-loop state inside the electrode, and the reaction waste gas is extracted by the pressure difference driven by the instantaneous pressure relief.

[0083] Further observation of the data from Supplementary Examples 1, 3, and 5 reveals that the preparation method of this application possesses excellent cross-scale and cross-system applicability. Example 1, as a relatively thin electrode of 150µm, exhibits a weak internal gas accumulation effect, an extremely low thickness expansion rate of only 0.75%, and an electrolyte wetting time as low as 5.24 seconds. In contrast, Example 3, when challenging the extreme physical thickness of 600µm, shows an exponential increase in venting difficulty. However, under the intervention of multiple variable-pressure venting cycles, the expansion rate is still effectively controlled at 1.40%, and the wetting time remains at a reasonable 12.68 seconds, demonstrating the stability of the concentration gradient pore-forming process across extremely large thickness spans. Meanwhile, Example 5, employing an artificial graphite system, also exhibits a smooth appearance and good macroscopic physicochemical characteristics, confirming the universality of this pore construction mechanism in negative electrode applications.

[0084] Besides structural integrity, the permeation kinetics of the electrolyte are also directly controlled by the pore distribution. Comparative Example 1, which possesses a pore-forming structure but lacks a concentration gradient, shows a significant increase in surface droplet penetration time, delayed to 19.53 seconds. The root cause of this time difference lies in the difference in the physical channels created by the volume fraction of the porous material in the longitudinal dimension. While the capillary resistance to liquid in the depth direction remains essentially constant in homogeneous pores, the example exhibits a high proportion of large-pore networks oriented and enriched on the electrode surface. These open mesoscopic physical spaces reduce the capillary resistance that hinders liquid penetration, thereby shortening the initial time for droplet penetration.

[0085] Test Example 2: Comparative Test of Multi-level Interfacial Bonding Strength of Electrodes

[0086] Test steps: The finished electrodes prepared in Examples 1, 2, 3, 5, Comparative Examples 1, 3, and 4 were selected as the test and analysis objects for evaluating mechanical properties in this group of experiments.

[0087] To minimize testing errors caused by edge effects, the selected finished electrodes were cut into strips 20 mm wide and 150 mm long standard samples along the coating extension direction. High-strength double-sided tape was used to flatly fix one side of the metal foil substrate of the sample to the surface of the stainless steel test plate, applying moderate pressure during fixing to ensure a tight fit and no air bubbles.

[0088] Under an ambient temperature of 25℃, a 180-degree peel test was performed using a microcomputer-controlled electronic universal testing machine. One end of the sample was peeled off, a stainless steel substrate was fixed by a clamp on one side, and the peeling end was pulled by a clamp on the other side. A constant tensile rate of 50 mm / min was set for continuous reverse peeling. This rate was chosen mainly because it can better simulate the dynamic mechanical strain that the electrode sheet is subjected to during the assembly process.

[0089] During the test, the peel force and displacement data were collected in real time using the mechanical sensors of the testing machine. Based on the observed fracture interface location of the sample, the complete peeling of the coating and current collector interface and the cohesive failure between layers within the coating were distinguished. The load data during the stable peeling stage were extracted and integrated to calculate and record the average peel force of the primer and the average peel force between internal layers.

[0090] Simultaneously, a tensile testing machine with a dedicated stainless steel test fixture was used to perform a vertical tensile test on the finished electrode. The test specimen area was 10mm × 10mm. High-strength epoxy resin was used to bond the upper and lower surfaces of the specimen to the upper and lower fixtures, respectively. A constant tensile rate of 5mm / min was set, and the maximum tensile force at which the coating fractured with the current collector or within the coating was recorded. The electrode tensile bond strength (N / mm²) was calculated by dividing the maximum tensile force by the test area. 2 ).

[0091] Test data: Table 2. Test data on the bonding strength of multi-level interfaces of electrodes

[0092] Test conclusion: Based on the data recorded in Table 2, Figure 2 A bidirectional extending structure with the central zero axis as the boundary was adopted. The dark gray stripe extending to the left represents the peel force between the coating and the current collector, while the light gray stripe extending to the right represents the interlayer peel force within the electrode. In the data analysis process, both the left and right horizontal stripes are indispensable, forming a complete mechanical evaluation loop. The mechanical failure modes of multilayer thick electrodes are complex. Simply evaluating the adhesion between the coating and the substrate or only testing the internal interlayer cohesion cannot truly reflect the overall stability of the electrode under actual working stress. Only by combining and comparing the data from the left side, representing the bottom interface, with the data from the right side, representing the interlayer interface, can the specific mechanical weaknesses caused by different preparation processes be accurately located, thus revealing the definite dependence of the multilayer coating structure on specific preparation process steps.

[0093] Example 2 showed that the peel strength of the primer and the peel strength of the interlayer were 35.62 N / m and 42.15 N / m, respectively, and the electrode tensile bond strength reached 1.72 N / mm. 2 This indicates that it has reliable structural stability at all interfaces.

[0094] During the cyclic testing of thick electrodes in the laboratory, the multilayer system faces an engineering bottleneck due to the easy peeling and slippage of the interlayer interfaces, which directly induces an irreversible surge in the battery's internal resistance. The test feedback of Comparative Example 3 confirms this failure mechanism; after canceling the plasma surface activation treatment, the internal interlayer peeling force showed a significant decrease, dropping to 18.45 N / m. This performance decline is mainly due to the inherent chemical inertness of the polymer surface layer; the lack of oxygen-containing groups leads to the degradation of the coating layers into a weak physical stacking state.

[0095] Comparing Examples 1, 2, and 3 clarifies the objective influence of the absolute thickness of the electrode sheet on the bonding strength of multi-level interfaces. As the electrode thickness jumps from 150µm to 600µm, the residual internal stress accumulated within the material increases significantly, causing the interlayer peel force to gradually decrease from 44.26 N / m to 40.12 N / m, and the primer peel force to slightly decrease from 38.15 N / m to 33.52 N / m. The data indicates that in multi-layer, ultra-thick electrode systems, the superposition of physical stress inevitably leads to a certain degree of adhesion loss. However, thanks to the synergistic chemical anchoring of the dual-fiber composite skeleton and plasma activation, even in the ultra-thick condition of 600µm in Example 3, all bonding strength indicators remain locked within the stable range of high-resistance ductile tearing, without mechanical collapse or fracture, and the tensile bonding strength remains at 1.61 N / mm. 2 The above. Furthermore, the test data for the artificial graphite anode in Example 5 of Table 2 also show that after replacing the main powder material system, the peel strength of the primer and interlayer remains at 34.68 N / m and 41.35 N / m, respectively, confirming that this multi-level reinforcement structure can also provide sufficient and reliable mechanical protection for the anode sheet (its tensile bond strength is stable at 1.68 N / mm). 2 ).

[0096] Comparative Example 1, employing a homogeneous integral mixed coating process, showed a lower undercoat peel strength of 21.83 N / m compared to Example 2. When large-sized pore-forming materials are uniformly distributed in the undercoat area close to the metal foil, the pore-forming process inevitably erodes the effective contact area between the electrode skeleton and the metal surface. The examples, relying on the construction of a slurry concentration gradient, suppressed the porosity of the underlying layer to a low level, maximizing the preservation of van der Waals forces and mechanical anchoring points between interfaces. Further investigation into the tear resistance source within the electrode sheet revealed that in Comparative Example 4, all indicators plummeted after the removal of the dual-fiber composite skeleton. The microscopic adhesion points provided by nanoscale fine fibers, combined with the three-dimensional support skeleton constructed by micron-scale coarse fibers, intertwine to form a localized mechanical reinforcement network within the electrode sheet, effectively offsetting the weakening effect of the porous structure on the overall strength.

[0097] Test Example 3: Comprehensive Verification of High-Rate Electrochemical and Chemical Microscopic Stability of Full Cells

[0098] Test steps: The finished electrodes prepared in Examples 2, 7 and Comparative Example 1 were selected and assembled into soft-pack full cells with the same rated capacity in a constant temperature glove box with extremely low dew point temperature, along with commercial graphite anodes, polyolefin microporous membranes and standard lithium hexafluorophosphate electrolyte. These cells were used as the analytical objects for electrochemical and chemical microscopic detection in this group.

[0099] The assembled full cells were transferred to a multi-channel battery testing system for formation and capacity assessment in a controlled environment at 25°C. The cells were charged to the cutoff voltage using a constant current of 0.3C. After stabilization, discharge tests were conducted at constant high-rate currents of 1C, 3C, 5C, and 10C. The actual discharge capacity of each cell at different rates was recorded, and the discharge capacity retention rate at each rate was calculated based on the standard capacity at 0.3C to evaluate the macroscopic mass transfer capability of the electrodes.

[0100] To assess the long-term microchemical stability of full cells, full cells from Examples 2, 7, and Comparative Example 1 were subjected to rigorous 10C high-rate charge-discharge cycles under the same environmental conditions. Capacity decay data was recorded after 1000 cycles, and long-term capacity retention was calculated.

[0101] After the cycle test, the full battery was destructively disassembled under inert gas protection. Residual electrolyte components inside the electrodes and separator were extracted using deionized water and a special eluent. The concentration of residual free hydrofluoric acid in the extract was precisely determined using ion chromatography. Simultaneously, a fixed area of ​​the cycled graphite negative electrode was cut, and the solid electrolyte interface film and metal substances deposited on its surface were completely dissolved by acid. The amount of iron ions deposited on the negative electrode side was detected and quantified using inductively coupled plasma atomic emission spectrometry.

[0102] Test data: Table 3. Comprehensive test data of mass transfer and microchemical stability of full-cell at multiple rates

[0103] Test conclusion: According to the data in Table 3, the spatial distribution pattern of the pore structure directly affects the mass transfer efficiency of the full cell under extreme conditions. Combined with... Figure 3As can be seen, the figure clearly characterizes the decay trajectory of the macroscopic electrochemical capacity of the battery under constant current discharge conditions of different intensities, and compares the differences in physical mass transfer between Example 2, Comparative Example 5, which have asymmetric pore structures, and Comparative Example 1, which has homogeneous pore characteristics. In the specific observation of the high-rate electrochemical characteristics of the electrode, Example 2 still maintained a capacity retention rate of 78.42% under a high current discharge condition of 10C. The dark gray broken line in the figure shows strong support at the end, while the capacity retention rate of Comparative Example 1, which adopts a homogeneous pore design, dropped sharply to 38.71% under the same test environment.

[0104] Thick electrodes suffer from severe ion transport obstruction, a long-standing physical bottleneck restricting the rate performance of high-energy-density batteries. This embodiment precisely constructs a concentration gradient in a porous framework material, directionally cultivating a highly interconnected macroporous network on the electrode surface. This asymmetric, heterogeneous porous mesostructure effectively alleviates the wetting resistance of the electrolyte deep within the electrode, shortening the diffusion path of lithium ions in the liquid and solid phases. When faced with the severe concentration polarization caused by high-rate charging and discharging, the abundant physical channels on the surface ensure rapid ion replenishment, thus exhibiting excellent capacity-free performance in macroscopic data.

[0105] Now that the physical mass transfer pathways have been established, the challenges to long-term microscopic stability at the chemical level are equally significant. After extending the testing period to 1000 high-intensity cycles, the interfacial chemical evolution induced by different pore-forming agent systems gradually became apparent. Combined with... Figure 4 As can be seen, this figure visually quantifies the concentration of free hydrofluoric acid accumulated in the internal polarized environment and the associated iron ion deposition on the negative electrode side of the full cells of Example 2, Comparative Example 1, and Comparative Example 5 after 1000 extreme cycle disassembly, verifying the long-term intervention effect of specific pore-forming framework materials on the chemical stability of the system. In specific measurement and analysis, it was found that the system of Example 2, which conventionally uses ammonium oxalate for pore formation, accumulated 185.64 mg / L of hydrofluoric acid, and the iron ion deposition on the negative electrode surface also reached 246.38 mg / L. Observing the comparison between the leftmost and middle bars of the chart, it can be found that Comparative Example 1, which also uses ammonium oxalate but exhibits homogeneous physical pores, had even higher free acid and iron dissolution rates of 192.11 mg / L and 258.42 mg / L, respectively. These highly similar deterioration data indicate that simple physical structure adjustments are completely unable to resist chemical corrosion. Comparative Example 5, which introduced sodium bicarbonate as a pore-forming material in the testing phase, not only demonstrated a level of high-rate discharge capability highly similar to that of Example 2, but also saw a significant reduction in the concentration of free hydrofluoric acid to 28.75 mg / L after thousands of cycles, while the amount of iron ion dissolution was simultaneously suppressed to an extremely low level of 41.52 mg / L.

[0106] Further analysis during testing confirmed that sodium bicarbonate decomposes during the hot-pressing curing stage, and the resulting weakly alkaline sodium carbonate irreversibly remains in situ and deposits on the inner side of the pore walls. Throughout the long electrochemical cycle, these uniformly distributed alkaline sites on the mesopore walls act as solid acid scavengers, actively neutralizing the strong acid produced by the hydrolysis of lithium hexafluorophosphate in the electrolyte. This active defense mechanism at the microscopic chemical level cuts off the continuous erosion of the lithium iron phosphate active lattice by strong acid, fundamentally ensuring the structural integrity of the electrode during its long cycle life.

Claims

1. A method for preparing gradient pores in a thick electrode with high bonding strength, characterized in that, Includes the following steps: Poly(p-phenylene terephthalamide) fine fibers are mixed with natural cellulose coarse fibers to form a dual-fiber composite binder skeleton. The dual-fiber composite binder skeleton is added to an active solution containing silanol and stirred for modification to obtain a modified binder solution. The electrode active material, conductive material and the modified binder solution are mixed to obtain a base slurry; The porous framework material is added to the substrate slurry and mixed to prepare multiple slurry systems with the concentration gradient of the porous framework material. The multiple slurry systems are sequentially coated onto the surface of the current collector in order of increasing volume fraction of the porous framework material to form an electrode preform. The electrode preform is subjected to segmented hot-press curing, and a breathing-type variable pressure exhaust operation is performed during the segmented hot-press curing stage to obtain a thick electrode with high bonding strength.

2. The method for preparing gradient pores of a thick electrode with high bonding strength according to claim 1, characterized in that, The poly(p-phenylene terephthalamide) fine fibers have a diameter of 0.1 µm to 0.5 µm and a crystallinity of 70% to 85%. The diameter of the natural cellulose crude fiber is 2µm to 5µm, and the degree of polymerization is 500 to 800; The mass ratio of the poly(p-phenylene terephthalamide) fine fibers to the natural cellulose coarse fibers is 2:1 to 4:

1.

3. The method for preparing gradient pores of a thick electrode with high bonding strength according to claim 1, characterized in that, The specific steps for adding the dual-fiber composite binder skeleton to the silanol-containing active solution for stirring modification are as follows: In a mixed solvent consisting of deionized water and N-methylpyrrolidone in a mass ratio of 1:99 to 5:95, γ-aminopropyltriethoxysilane is added at a mass ratio of 0.5% to 1.5% of the total mass of the dual-fiber composite binder skeleton, and hydrolyzed to generate the silanol-containing active solution. The dual-fiber composite binder skeleton is added to the silanol-containing active solution, and the amount of mixed solvent added is adjusted to control the mass fraction of the solid component in the modified binder solution to be 5% to 10%. The mixture is stirred and modified at a temperature of 50°C to 70°C for 1 to 2 hours.

4. The method for preparing gradient pores of a thick electrode with high bonding strength according to claim 1, characterized in that, The electrode active material is lithium iron phosphate or artificial graphite, and the conductive material is conductive carbon black; In the substrate slurry, the mass ratio of the electrode active material, the conductive material, and the solid component in the modified binder solution is 90:6:4 to 96:2:

2.

5. The method for preparing gradient pores of a thick electrode with high bonding strength according to claim 1, characterized in that, The porous framework material is one of ammonium oxalate, polystyrene microspheres, polymethyl methacrylate microspheres, and sodium bicarbonate. The weight-average molecular weight of the polystyrene microspheres is in the range of 150,000 to 250,000, and the weight-average molecular weight of the polymethyl methacrylate microspheres is in the range of 80,000 to 120,000. The number of the multiple slurry systems is 3 to 5; The particle size of the porous framework material in the plurality of slurry systems increases sequentially, and the particle size of the porous framework material is from 0.5µm to 20µm.

6. The method for preparing gradient pores of a thick electrode with high bonding strength according to claim 1, characterized in that, The plurality of slurry systems are arranged in order of increasing volume fraction of the porous framework material, including a first slurry system and subsequent slurry systems; In the first slurry system, the volume of the porous framework material accounts for 10% to 20% of the total volume of all solid components in the first slurry system, and in each subsequent slurry system, the proportion of the volume of the porous framework material to the total volume of all solid components in the slurry system increases sequentially by 5% to 15%. The current collector is an aluminum foil current collector or a copper foil current collector.

7. The method for preparing gradient pores of a thick electrode with high bonding strength according to claim 1, characterized in that, After sequentially coating the plurality of slurry systems onto the surface of the current collector to form an electrode preform, and before performing segmented hot-pressing curing on the electrode preform, the process further includes a pretreatment step for the electrode preform, comprising: The electrode preform is pre-compressed for 1 to 2 minutes by applying a pressure of 10 MPa to 20 MPa. The surface of the pre-pressed electrode preform is activated using a plasma treatment device to obtain an activated electrode preform. The plasma treatment device has a processing power of 100W to 300W and a processing time of 30s to 60s.

8. The method for preparing gradient pores of a thick electrode with high bonding strength according to claim 7, characterized in that, The segmented thermosetting curing is performed on the activated electrode preform, the segmented thermosetting curing comprising: First stage: Heat to 80℃ to 120℃, apply pressure of 10MPa to 20MPa, and maintain constant temperature and pressure for 10min to 20min; Second stage: Heat to 120℃ to 160℃, apply pressure of 20MPa to 30MPa, and maintain constant temperature and pressure for 15min to 25min. The third stage involves heating to 160°C to 180°C and applying a base pressure of 30MPa to 35MPa. The total holding time at the temperature and base pressure in the third stage is 5 to 10 minutes.

9. The method for preparing gradient pores of a thick electrode with high bonding strength according to claim 8, characterized in that, The breathing-type pressure-changing exhaust operation is performed during the third stage, and the breathing-type pressure-changing exhaust operation includes performing 3 to 5 consecutive pressure-changing exhaust cycles, each of which includes: Pressurize to 30MPa to 35MPa and maintain for 1 to 2 minutes, depressurize to 3MPa to 5MPa and maintain for 5 to 15 seconds, then pressurize again to 30MPa to 35MPa.

10. The method for preparing gradient pores of a thick electrode with high bonding strength according to claim 9, characterized in that, After performing the breathing-type pressure-changing exhaust operation, the activated electrode preform is further subjected to deep drying for 2 to 4 hours at a temperature of 100°C to 120°C and a vacuum of -0.099 MPa to -0.090 MPa.

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