Electrode slurry dynamic curing method and application

Abstract

The invention discloses an electrode slurry dynamic curing method. Rapidly heating a current collector-slurry interface to 100-120 DEG C by adopting electromagnetic induction, and triggering adhesive crosslinking and thermal expansion microspheres to generate pre-compressive stress; stress is relieved through phase change microcapsules in the hot air drying process of 70-90 DEG C; and finally, curing is completed at the temperature of 110-130 DEG C. The electrode slurry comprises thermal expansion microspheres and phase change microcapsules; the initial expansion temperature of the thermal expansion microspheres is 75-105 DEG C, and the phase change temperature of the phase change microcapsules is 45-65 DEG C; by reversing a traditional curing path and combining thermal expansion microspheres and phase change microcapsules with specific temperature response, the problems of demolding and cracking caused by negative electrode drying stress are solved, the interface integrity is remarkably improved, and the cycle life is remarkably prolonged.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery electrode manufacturing technology, and in particular to a dynamic curing method and application of electrode slurry based on dynamic curing process to achieve extremely high interface integrity. Background Technology

[0002] Drying stress during the fabrication of high-capacity silicon-carbon anodes is a key bottleneck restricting their structural integrity and electrochemical performance. In traditional hot air or oven curing processes, heat is transferred from the surface inwards, causing the solvent on the slurry surface to evaporate first and rapidly form a dense solid film. This surface cured layer acts like a "hard shell," not only hindering the continued outward diffusion and evaporation of internal solvents but also accumulating significant drying shrinkage stress within the slurry and at the interface. Since the binder polymer chains at the interface are not yet fully cross-linked and the network structure strength is insufficient, this concentrated stress easily induces micro-cracks between the active material layer and the current collector, localized delamination (i.e., "mold release"), and the collapse of the internal pore structure. These microstructural defects severely damage the electrode's conductive network, exacerbating interfacial side reactions during subsequent battery cycles and becoming initial stress concentration points for silicon particle volume expansion. Ultimately, this manifests as macroscopic electrode warping and active material shedding, leading to rapid capacity decay and a sharp decline in cycle life.

[0003] Existing improvement strategies mostly focus on "passive" optimization of slurry formulations, such as increasing the amount of binder, using highly elastic binders, or introducing single-function fillers. While these methods can enhance interfacial adhesion or provide limited buffer space to some extent, they are all remedial measures and fail to fundamentally change the non-uniform "outside-in" curing kinetics driven by external heat sources. As long as the curing process still relies on external heat conduction, the problem of inconsistent drying rates and shrinkage paces between the slurry surface and interior, and between the interface and bulk phase, cannot be avoided, and stress concentration phenomena are difficult to eliminate at their root.

[0004] Therefore, there is an urgent need in this field for an electrode fabrication technology that can innovate from the fundamental perspective of curing kinetics, overturning the traditional "outside-in" drying and curing mode and reconstructing the drying and curing path "inside-out." The ideal solution should be able to actively intervene in the phase transition process within the slurry, for example, by introducing an internal stress compensation mechanism or achieving precise internal energy supply, so that the slurry-current collector interface region or the interior of the slurry body preferentially reaches the curing conditions, thereby transforming the area most prone to defects into the structurally most stable region. This fundamental path shift can suppress the generation and accumulation of drying shrinkage stress at its source, achieving stress self-cancellation and self-homogenization. This is not only a key breakthrough in improving the interface stability of silicon-carbon anodes, but also provides a revolutionary new method and path for the electrode manufacturing of next-generation high-energy-density, high-yield lithium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a dynamic curing method for electrode slurries. This invention designs a multi-stage dynamic curing process comprising "electromagnetic induction interface preferential curing," "hot air drying and stress offsetting," and "final curing." Combined with a binder and additive system, this process first forms a strong cross-linked network at the current collector-slurry interface. It then utilizes the properties of thermally expanding microspheres and phase change microcapsules as additives to actively offset shrinkage stress. This type of process possesses the ability to actively manage internal stress. By controlling the temperature field distribution and introducing electromagnetic induction heating, the interface near the substrate is preferentially heated and cured, thereby reversing the stress transmission direction during drying and curing and reducing interface stress. Furthermore, segmented programmed drying or the introduction of an additive system with internal stress buffering creates a more uniform stress dissipation channel in the early stages of curing, enabling the fabrication of composite negative electrodes with no demolding and long lifespan on general-purpose current collectors.

[0006] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for dynamic curing of electrode slurry, comprising the following steps: S1: The electrode paste is coated onto the current collector substrate to obtain a pre-coated current collector; S2: Electromagnetic induction is used to heat the pre-coated current collector, raising the temperature of the current collector substrate-slurry interface to 100 ℃ ~ 120 ℃; S3: Dry in a hot air environment at 70℃~90℃ for 60~180 seconds; S4: Curing at 110℃~130℃ for 120~300 seconds; The electrode slurry comprises thermally expandable microspheres and phase change microcapsules; the initial expansion temperature of the thermally expandable microspheres is 75℃~105℃, and the phase change temperature of the phase change microcapsules is 45~65℃.

[0007] This invention provides a dynamic curing method for electrode slurry. The invention employs a multi-stage dynamic curing process comprising "electromagnetic induction interface-prioritized curing," "hot air drying and stress relief," and "final curing." First, a strong and tough cross-linked network is formed at the current collector substrate-slurry interface. Electromagnetic induction concentrates heat energy at the current collector-slurry interface, rapidly heating it to 100℃~120℃. This promotes rapid cross-linking of the binder in this area, forming a strong and tough initial three-dimensional network structure. This fundamentally reverses the heat and stress transfer direction from the surface to the interior in traditional drying processes, achieving enhanced anchoring of the current collector substrate. Subsequently, in a mild hot air stage at 70℃~90℃, the remaining solvent steadily evaporates. Furthermore, within this temperature range, the characteristics of the electrode slurry system are utilized to actively counteract and dissipate the internal stress generated by solvent evaporation and slurry drying, effectively preventing crack formation and interface delamination. Finally, in the final curing stage at 110℃~130℃, the entire slurry undergoes full cross-linking, constructing a dense and tough overall network.

[0008] Simultaneously, this invention also adds thermally expandable microspheres with an initial expansion temperature of 75℃~105℃ and phase change microcapsules with a phase change temperature of 45~65℃ to the electrode slurry. During the first step of heating the pre-coated current collector using electromagnetic induction, the interface region between the current collector substrate and the slurry rapidly heats up to 100℃~120℃. At this point, the surface layer of the slurry remains below 50℃ due to lag in heat conduction. Under this specific temperature field, the binder at the interface rapidly cross-links, forming an early-stage reinforced network, achieving "interface anchoring." Simultaneously, because the temperature rapidly rises to 100~120℃, exceeding the initial expansion temperature of the thermally expandable microspheres, the interfacial heat triggers the expansion of the microspheres at the interface, generating pre-compression stress. The overall drying shrinkage stress generated by the second-stage hot air treatment is partially offset by the peak value of the pre-compression stress generated in the previous stage. Since the hot air treatment temperature is limited to 70℃~90℃, and the phase change temperature of the phase change microcapsules is lower than this temperature, the melting and heat absorption within this temperature range significantly reduces the temperature gradient inside the slurry (especially in the thickness direction) and fills the interparticle gaps, further alleviating stress concentration caused by uneven drying. In the third stage of high-temperature thermal curing, complete solvent removal is ensured, and the binder within the electrode bulk phase is fully cross-linked. At this point, the thermally expanding microspheres located in the slurry layer begin to expand, generating pre-compression stress, further offsetting the shrinkage stress of the slurry on the surface and inside the substrate during the drying and curing process.

[0009] This combined process successfully produced composite negative electrode sheets with strong interfacial bonding, intact coating, no risk of mold release, and high cycle life on general current collectors, providing an effective solution to overcome the problem of lifespan degradation caused by volume effect in high-capacity electrode materials.

[0010] As a further option, the duration of electromagnetic induction in S2 is 3~10s.

[0011] This invention further limits the duration of electromagnetic induction, enabling the current collector-slurry interface temperature to rise to 100°C~120°C within a short time. This avoids excessive heat diffusion to the slurry surface caused by prolonged electromagnetic induction, thus consolidating the advantage of preferential interface curing. Conversely, if the duration is too short, the interface temperature will not reach the critical threshold required for binder crosslinking, making it difficult to form a sufficiently strong initial network and weakening the foundation of stress management in this process. Controlling the electromagnetic induction time to 3~10 seconds also effectively prevents side reactions such as solvent boiling, bubble generation, and even binder degradation that may be caused by instantaneous overheating of the interface, ensuring a dense and uniform microstructure in the interface region. This precise control of instantaneous energy input is a process guarantee for achieving high-strength, highly consistent interface bonding, laying a reliable foundation for stress mitigation and final curing in subsequent stages.

[0012] As a further embodiment, the frequency of the electromagnetic induction in S2 is 50 kHz to 200 kHz, and the power density of the electromagnetic induction is 5 to 20 W / cm². 2 .

[0013] This invention further optimizes the frequency and power density of electromagnetic induction heating within a certain range, utilizing the eddy current effect of the current collector to rapidly raise the temperature of its interface with the slurry to 100℃~120℃ within a short time. At this point, the surface layer of the slurry remains below 50℃ due to delayed heat conduction. Under this specific temperature field, the binder at the interface rapidly cross-links, forming an early-stage reinforced network, achieving "interface anchoring".

[0014] As a further embodiment, the hot air velocity in S3 is 1.5 m / s ~ 3.0 m / s.

[0015] This invention further optimizes the hot air velocity within this specific range to achieve synergistic control of drying kinetics and stress evolution. Excessive air velocity significantly weakens convective heat transfer efficiency and slows the escape rate of solvent vapor from the electrode surface, prolonging the necessary drying time and potentially leading to uneven solvent residue in the middle and surface layers of the slurry, causing uneven shrinkage stress during subsequent curing. Conversely, excessive air velocity induces rapid solvent evaporation and drastic drying shrinkage on the slurry surface. Although the interface layer has initially cured, rapid surface hardening blocks the escape channels of internal solvent and may generate significant shear stress between the surface layer and the cured interface layer, inducing microcracks. Therefore, precisely controlling the air velocity within the range of 1.5 m / s to 3.0 m / s ensures a relatively mild and uniform bulk drying environment, which aligns perfectly with the dual objectives of "steady solvent evaporation" and "active stress mitigation" at this stage. Through synergy with the additive system, it creates better conditions for the orderly dissipation of internal stress.

[0016] As a further embodiment, the electrode paste also includes active materials, conductive agents, and binders.

[0017] As a further embodiment, the conductive agent is selected from one or more of conductive carbon black, graphene, carbon nanotubes, acetylene black, activated carbon, conductive carbon spheres, conductive carbon fibers, reduced graphene oxide, and Ketjen black.

[0018] As a further embodiment, the active material includes at least one of hard carbon, soft carbon, graphite, graphite / hard carbon composite material, nano-silicon carbon composite material, and silicon suboxide carbon composite material.

[0019] As a further embodiment, the adhesive includes at least one of halogenated olefins and their copolymers, polyacrylic acid and acrylic resins, and cellulose compounds; As a further example, the halogenated olefins and their copolymers include at least one of polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of vinylidene fluoride-tetrafluoroethylene, copolymers of vinylidene fluoride-trifluoroethylene, copolymers of vinylidene fluoride-trichloroethylene, copolymers of vinylidene fluoride-fluorinated ethylene, and copolymers of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene. As a further example, the polyacrylic acid and acrylic resins include at least one of polyacrylic acid, vinyl acrylate resin, methyl acrylate resin, butyl acrylate resin, styrene acrylate resin, acrylate resin, acrylate copolymer resin, acrylic resin, and acrylic emulsion resin; As a further example, the cellulose compound is selected from one or more of carboxymethyl cellulose, carboxyethyl cellulose, methyl cellulose, methyl hydroxypropyl cellulose, and lithium carboxymethyl cellulose.

[0020] As a further preferred embodiment, the adhesive is polyacrylic acid.

[0021] The present invention further preferably uses polyacrylic acid as the binder, a choice that creates a synergistic effect with the dynamic curing process. Due to the abundance of carboxyl groups (-COOH) and double bond functional groups on the polyacrylic acid molecular chain, it can rapidly undergo cross-linking reactions with other components in the slurry when the interface temperature reaches 100℃~120℃ during the electromagnetic induction stage, thereby constructing a dense and tough three-dimensional network structure at the current collector-slurry interface. This rapid interfacial cross-linking is the chemical basis for achieving the "interfacial anchoring" strategy. The polyacrylic acid-based binder system exhibits excellent internal stress management capabilities in the subsequent hot air drying stage. Its molecular chains themselves possess a certain degree of flexibility, and the cross-linked network structure can dissipate some stress through the movement of flexible chain segments. Finally, during the final curing at 110℃~130℃, the PAA binder network is further deepened and strengthened, forming a stable and elastic overall network that runs through the entire electrode coating. This network not only provides extremely high bonding strength to prevent active materials from peeling off, but its own deformation capacity can also buffer the huge volume expansion and contraction of silicon-based materials during battery cycling, thus jointly creating a more superior structural integrity and ultra-long cycle life for the electrode sheets.

[0022] As a further embodiment, the electrode slurry comprises 1.0 wt% to 2.5 wt% of binder, 1.0 wt% to 2.0 wt% of thermally expandable microspheres, and 0.5 wt% to 1.0 wt% of phase change paraffin microcapsules, based on the total dry matter mass of the slurry.

[0023] As a further embodiment, the thermally expandable microspheres have a core-shell structure, wherein the outer shell of the thermally expandable microspheres is a thermoplastic polymer, and the core of the thermally expandable microspheres is a low-boiling-point liquid hydrocarbon encapsulated within the outer shell, and the initial expansion temperature of the thermally expandable microspheres is 75℃~100℃; the phase change microcapsules have a core-shell structure, wherein the shell layer of the phase change microcapsules is a dense polymer resin material, the core layer is a phase change material, the phase change melting temperature of the core layer is 55℃~65℃, and the phase change enthalpy is ≥150 J / g.

[0024] Both the thermally expandable microspheres and the phase change microcapsules in this invention are commercially available or can be obtained through common preparation methods. The thermally expandable microspheres can be exemplarily purchased from the Expancel® microspheres series of Matsumoto Yushi Pharmaceutical Co., Ltd. of Japan, and the phase change microcapsules can be exemplarily purchased from the MPCM series of phase change paraffin microcapsules of Shanghai Rushang New Energy Materials Co., Ltd.

[0025] This invention further defines the core-shell structure of the thermally expandable microspheres and specifies the initial expansion temperature range based on temperature changes during electrode preparation, ensuring effective triggering during the early stages of electrode curing, i.e., the initial cross-linking stage of the binder. Simultaneously, the phase change temperature of the phase change microcapsules in this invention is lower than the initial expansion temperature of the thermally expandable microspheres and falls within the typical temperature range for electrode drying. During electrode drying, the phase change microcapsules absorb a large amount of heat near the phase change temperature, thereby slowing down the heating rate of the slurry surface and significantly reducing the temperature gradient inside the electrode (especially in the thickness direction). The uniform temperature field avoids the large internal stress caused by asynchronous drying shrinkage, preventing crack formation. The phase change material in the core layer, after melting, is in a liquid state and can slightly seep out or transmit pressure through the shell, providing instantaneous lubrication between active material particles. This helps the active material particles to make micro-adjustments under stress, avoiding stress concentration, and filling tiny gaps after cooling and solidification. Therefore, the thermally expanded microspheres and phase change microcapsules form a dynamic stress buffering synergistic mechanism inside the electrode: During the drying process, the phase change microcapsules first melt in the lower temperature range of 55℃~65℃, absorbing a large amount of latent heat to delay the temperature rise of the electrode surface and reduce the temperature gradient in the thickness direction, thereby avoiding local shrinkage stress caused by uneven drying; at the same time, its molten core layer can temporarily lubricate the active material particles, promoting the micro-adjustment and rearrangement of particles under stress. Subsequently, when the temperature rises to 110℃~130℃ and enters the curing stage, the thermally expanded microspheres expand due to heat, and their volume increases significantly. The resulting inward pre-compression stress directly counteracts the tensile stress generated by the shrinkage of the slurry during curing, effectively suppressing the tendency of microcracks and curling in the coating. During battery cycling, the phase change microcapsules continuously dissipate the mechanical energy generated by the volume change of silicon particles through reversible solid-liquid phase change and homogenize the heat distribution during charging and discharging; while the elastic residual structure formed by the thermally expanded microspheres after the first expansion can serve as a durable support point, dispersing cyclic stress and delaying the fatigue aging of the binder network. The two are closely complementary in terms of time sequence and function, and are strongly adhered to the chemically active interface layer on the surface of the current collector, thus constructing a multi-level protection system from interface chemical bonding to bulk physical buffering, which together ensures the structural integrity and electrochemical stability of the high silicon content electrode during preparation and long-term cycling.

[0026] As a further preferred embodiment, the outer shell of the thermally expandable microspheres is selected from one or more alkene copolymers, the core of the thermally expandable microspheres is selected from one or more alkanes of C2 to C4; the phase change material in the phase change microcapsules is selected from one or more alkanes of C15 or higher, and the shell layer of the phase change microcapsules is selected from one or more amine-aldehyde resins.

[0027] As a further preferred embodiment, the outer shell of the thermally expandable microspheres is polyvinylidene chloride-acrylonitrile copolymer, and the core is isobutane; the shell layer of the phase change microcapsules is melamine-formaldehyde resin, and the core layer is n-eicosane.

[0028] As an example, when the outer shell of the thermally expandable microsphere is polyvinylidene chloride-acrylonitrile copolymer and the core is isobutane, the thermally expandable microsphere can be Nouryon Expansionl series 031 WUF 40, with an initial expansion temperature of 80°C.

[0029] As an example, when the shell of the phase change microcapsule is melamine-formaldehyde resin and the core is n-eicosane, the phase change microcapsule can be MPCM60 from the MPCM series of Shanghai Rushang New Energy Materials, with a phase change temperature of 60℃ and a phase change enthalpy of 190~200J / g.

[0030] As a further preferred embodiment, the particle size D50 of the thermally expandable microspheres is 5μm~20μm; the particle size D50 of the phase change microcapsules is 1μm~10μm.

[0031] As a further embodiment, in the S2 stage, the surface temperature of the electrode slurry is ≤50℃, and the thermally expanding microspheres expand due to heat, generating a pre-compression stress of 0.05 ~ 0.2 MPa inside the electrode; the pre-compression stress in the S2 stage offsets 15% ~ 35% of the drying shrinkage tensile stress in the S3 stage.

[0032] As a further preferred embodiment, the temperature gradient inside the electrode slurry in the S3 stage is <10 ℃ / μm.

[0033] Secondly, the present invention provides an electrode sheet prepared by a dynamic curing method for electrode slurry.

[0034] Thirdly, the present invention provides a lithium-ion battery, including an electrode sheet prepared by a dynamic curing method for electrode slurry.

[0035] The beneficial effects of this invention are: (1) Revolutionary curing path: Curing is achieved from the inside out through electromagnetic induction, which first strengthens the weakest interface area, fundamentally changing the path of stress generation and transmission, and effectively preventing demolding.

[0036] (2) Active stress management: The expansion behavior of thermal expansion microspheres is precisely controlled during the interface curing stage, so that the pre-compression stress generated can actively and timely offset the subsequent drying shrinkage stress, forming a "stress shield".

[0037] (3) Excellent process synergy: The rapid and localized characteristics of electromagnetic induction heating are perfectly matched with the crosslinking temperature of PAA, the triggering temperature of thermal expansion microspheres and the buffer zone of phase change microcapsules, forming a dynamic stress management system with precise timing and complementary functions.

[0038] (4) Universality and efficiency: This method has relaxed requirements for the pretreatment of the current collector, but can achieve an interface bonding effect that far exceeds that of traditional processes, making it suitable for industrial continuous production. Detailed Implementation

[0039] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0040] As a specific example of the implementation of this invention, detailed cases are provided below.

[0041] Example 1: The negative electrode sheet was prepared using the following steps: Step 1: A composite vapor was used as the process gas to perform plasma treatment on the current collector, introducing activated functional groups on its surface; the composite vapor included 7% ammonia, 85% argon, and 8% oxygen by volume; the plasma treatment power was 250 W, the plasma treatment pressure was 150 Pa, and the treatment time was 2 s, so that the substrate had activated functional groups bonded to the chemically active interface layer, resulting in an activated current collector; Step 2: The catecholamine polymer precursor solution is directly coated onto the activated current collector prepared in Step 1 for 20 seconds to complete the chemical reaction. It is then dried at 70°C for 15 seconds to form a chemically active interface layer, resulting in a current collector with a chemically active interface layer. The catecholamine polymer precursor is an alkaline aqueous solution of dopamine hydrochloride with a concentration of 1.5 g / L and a pH of 8.5. Step 3: Coat the electrode slurry onto the current collector with the active interface layer prepared above. The slurry, by dry matter mass percentage, comprises: 93.25 wt% silicon-carbon graphite active material, 2 wt% conductive agent graphene, 2.5 wt% polyacrylic acid, 1.5 wt% thermally expandable microspheres, and 0.75% phase change microcapsules; thus obtaining the pre-coated current collector. The outer shell of the thermally expanded microspheres is a polyvinylidene chloride-acrylonitrile copolymer; the core is isobutane. The outer shell of the phase change microcapsule is melamine-formaldehyde resin, and the core is n-eicosane; The D50 of thermally expanded microspheres is 15 μm; the D50 of phase change microcapsules is 5 μm. The thermal expansion microspheres are Nouryon Expansion series 031 WUF 40, with an initial expansion temperature of 80℃; The phase change microcapsules are MPCM60 from the MPCM series of Shanghai Rushang New Energy Materials, with a phase change temperature of 60℃ and a phase change enthalpy of 190~200J / g. Step 4: The pre-coated current collector is heated using electromagnetic induction to raise the interface temperature between the current collector substrate and the slurry to 110 ℃; the electromagnetic induction duration is 5 s, the electromagnetic induction frequency is 80 kHz, and the electromagnetic induction power density is 8 W / cm². 2 ; Step 5: Place the electrode obtained in Step 4 in a hot air environment at 80 ℃ for 120 seconds to dry it. The hot air velocity is 2 m / s. Step 6: Place the electrode obtained in Step 5 at 120 °C for 210 seconds to cure.

[0042] Example 2: Unlike Example 1, step 4 involves heating the pre-coated current collector using electromagnetic induction to raise the interface temperature between the current collector substrate and the slurry to 110 °C; the electromagnetic induction duration is 3 seconds, the frequency is 200 kHz, and the power density is 6 W / cm². 2 .

[0043] Example 3: Unlike Example 1, step 4 involves heating the pre-coated current collector using electromagnetic induction to raise the temperature of the current collector substrate-slurry interface to 110 °C; the electromagnetic induction duration is 10 s, the electromagnetic induction frequency is 50 kHz, and the electromagnetic induction power density is 20 W / cm². 2 .

[0044] Example 4: Unlike Example 1, step 5: The electrode obtained in step 4 is placed in a hot air environment at 80 ℃ and dried for 120 seconds, with a hot air velocity of 1.5 m / s.

[0045] Example 5: Unlike Example 1, step 5: The electrode obtained in step 4 is placed in a hot air environment at 80 ℃ and dried for 120 seconds, with a hot air velocity of 3 m / s.

[0046] Example 6: Unlike Example 1, an electrode slurry was coated onto the current collector with the active interface layer prepared above. The slurry, by dry matter mass percentage, contained: 93.5 wt% silicon-carbon graphite active material, 2 wt% conductive agent graphene, 2.5 wt% polyacrylic acid, 1 wt% thermally expandable microspheres, and 1% phase change microcapsules; thus, a pre-coated current collector was obtained.

[0047] Example 7: Unlike Example 1, an electrode slurry was coated onto the current collector with the active interface layer prepared above. The slurry, by dry matter mass percentage, contained: 93 wt% silicon-carbon graphite active material, 2 wt% conductive agent graphene, 2.5 wt% polyacrylic acid, 2 wt% thermally expandable microspheres, and 0.5% phase change microcapsules; thus, a pre-coated current collector was obtained.

[0048] Example 8: Unlike Example 1, in step 4: electromagnetic induction is used to heat the pre-coated current collector, raising the temperature of the current collector substrate-slurry interface to 100 °C; the electromagnetic induction duration is 30 s, the electromagnetic induction frequency is 45 kHz, and the electromagnetic induction power density is 4 W / cm². 2 .

[0049] Example 9: Unlike Example 1, the 2.5 wt% polyacrylic acid in step 4 was replaced with 2.5 wt% polyvinylidene fluoride.

[0050] Example 10: Unlike Example 1, the outer shell of the thermally expandable microspheres is made of acrylic resin and the core is made of isobutane, with an initial expansion temperature of 105°C; the phase change microcapsules are the same as in Example 1.

[0051] Example 11: The difference from Example 1 is that the thermally expandable microspheres are the same as in Example 1. The outer shell of the phase change microcapsule is melamine urea-formaldehyde resin, and the core is n-octadecane, with a phase change temperature of 45°C.

[0052] Example 12: Unlike Example 1, the D50 of the thermally expanded microspheres is 5 μm; the D50 of the phase change microcapsules is 1 μm.

[0053] Example 13: Unlike Example 1, the D50 of the thermally expanded microspheres is 20 μm; the D50 of the phase change microcapsules is 10 μm.

[0054] Comparative Example 1: Unlike Example 1, step 4 was not performed; steps 5 and 6 were performed directly.

[0055] Comparative Example 2: Unlike Example 1, an electrode slurry was coated onto the current collector with the active interface layer prepared above. The slurry, by dry matter mass percentage, contained: 95 wt% silicon-carbon graphite active material, 2.5 wt% conductive agent graphene, and 2.5 wt% polyacrylic acid; thus, a pre-coated current collector was obtained.

[0056] Comparative Example 3: Unlike Example 1, in step 4: electromagnetic induction was used to heat the pre-coated current collector, raising the temperature of the current collector substrate-slurry interface to 140 °C. The duration of electromagnetic induction was 5 s, the frequency was 300 kHz, and the power density was 30 W / cm². 2 .

[0057] Comparative Example 4: Unlike Example 1, the initial expansion temperature of the thermally expandable microspheres is 120°C, and the phase change temperature of the phase change microcapsules is 20°C. The thermally expandable microspheres used have a core-shell structure, with the outer shell being polyvinylidene chloride-acrylonitrile copolymer and the core being isobutane; the phase change microcapsules have a shell layer of melamine-formaldehyde resin and a core layer of n-eicosane.

[0058] Lithium-ion batteries were assembled using the negative electrode sheets prepared in Examples 1-13 and Comparative Examples 1-4. The specific preparation methods are as follows: 1. Cathode preparation Positive electrode active material (such as LiNi) 0.8 Co 0.1 Mn 0.1 O2), conductive agent (such as Super P) and binder (such as polyvinylidene fluoride, PVDF) are mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent at a mass ratio of 96.5:1.5:2.0 to prepare a uniform positive electrode slurry; The slurry is coated onto an aluminum foil current collector, dried, rolled, and then punched into a positive electrode sheet of the required size. 2. Negative electrode preparation The negative electrode sheets prepared in the examples and comparative examples were punched into sheets with an area slightly larger than that of the positive electrode; 3. Electrolyte LiPF6 of 1.15 mol / L was used as the lithium salt, and the solvent was a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) (volume ratio of 1:1:1), and fluoroethylene carbonate (FEC) of 2.0% of the total mass of the electrolyte was added as an additive. 4. Battery Assembly In a dry environment with a dew point ≤ -40℃, the positive electrode sheet, the separator (such as a PP / PE / PP three-layer composite film) and the negative electrode sheet are stacked in sequence and packed into an aluminum-plastic packaging shell. Inject sufficient electrolyte and perform vacuum sealing; The packaged cells are subjected to standard processes such as settling, formation, venting, and final sealing to produce lithium-ion pouch cells.

[0059] The following tests were performed on Examples 1-13 and Comparative Examples 1-4: (1) Half-electric rebound rate of electrode sheet (%): Half-electric rebound rate refers to the ratio between the thickness of the electrode sheet after rolling and the thickness of the electrode sheet measured after the battery has undergone its first charge and discharge (formation and capacity testing) at 50% state of charge (half-electric, SOC=50%). (2) Cycle capacity retention (%): Constant current charge-discharge test: After activation at 0.1C rate for 3 weeks, the coin cell was subjected to long-term cycle testing at 0.5C rate. Capacity retention = (Discharge capacity in week N / Discharge capacity in week 3) × 100%; (3) Peel strength (N / m): 180° peel test: The prepared electrode was cut into strips 20 mm wide and 100 mm long. The slurry surface of the electrode was fixed to a flat steel plate using strong double-sided adhesive tape. The current collector was peeled 180° at a speed of 50 mm / min using a tensile testing machine, and the average force F during the stable peeling stage was recorded. Peel strength = F / electrode width; (4) Drying Stress Mitigation Rate (%): This is a calculated value used to quantify the effectiveness of stress management. Two key data points need to be measured: 1. Pre-compression stress (σ_pre): Measured directly during the electromagnetic induction curing stage using a miniature stress sensor attached to the back of the current collector. 2. Total drying shrinkage stress (σ_total): The maximum shrinkage tensile stress measured using the same sensor throughout the entire curing process without electromagnetic induction. Drying stress mitigation rate = (σ_pre / σ_total) × 100%; (5) Electrode interface impedance: The electrode under test was assembled with a lithium sheet to form a symmetrical battery. At the open circuit potential, an AC perturbation with an amplitude of 10 mV was applied, with a frequency range from 100 kHz to 0.1 Hz. The obtained Nyquist plot was fitted with equivalent circuit using ZView software, where the diameter of the semicircle in the high-frequency region is the electrode interface impedance.

[0060] The results of the above tests are shown in Table 1 below:

[0061] As can be seen from the comparison of Examples 1-13 and Comparative Examples 1-4, the present invention, through a multi-stage dynamic curing process including "electromagnetic induction interface preferential curing", "hot air drying and stress offsetting" and "final curing", combined with the binder and additive system, successfully reverses the traditional surface-to-inside drying path, fundamentally strengthens the interface bonding and actively offsets the internal stress, thereby preparing a composite negative electrode with high peel strength, low interface impedance, excellent cycle stability and low expansion rate on a general current collector. The overall performance is significantly better than that of the traditional process.

[0062] As can be seen from Comparative Example 1, when the crucial "electromagnetic induction interface preferential curing" step is missing, the interfacial bonding strength (peel strength only 109 N / m) and cycle life (capacity retention of 82.3% after 100 cycles) of the electrode decrease significantly, while the electrode rebound rate and interfacial impedance increase sharply. This fully demonstrates that traditional hot air drying and curing alone cannot reverse the "from the surface to the interior" drying path. The slurry-current collector interface becomes a weak link of stress concentration because it fails to form a strong and tough network first, ultimately leading to poor interfacial integrity, increased impedance, and accelerated failure of active materials during cycling. This, in turn, verifies the indispensable key role of the core process steps of this invention in achieving extremely high interfacial integrity.

[0063] As can be seen from Comparative Example 2, when the key internal stress active management components of thermally expanded microspheres and phase change microcapsules are not introduced into the slurry system, although the electromagnetic induction interface curing step is retained, the drying stress offset rate is only about 1%, the rebound rate of the electrode during cycling is as high as 39.6%, and the cycling stability and interface bonding strength are not ideal. This clearly shows that although a single "inside-out" heat path can strengthen the interface, it cannot fully cope with the shrinkage stress and volume change stress generated by the bulk phase of the slurry during drying and cycling; without the pre-compression stress generated by the thermally expanded microspheres for active offsetting, and the temperature homogenization and instantaneous lubrication effect of the phase change microcapsules, stress sufficient to cause microstructural damage will still accumulate inside the electrode, thus limiting further improvement in overall performance. This result strongly demonstrates the synergistic necessity of the multi-stage dynamic curing process and the specific additive system of this invention in achieving active stress management; neither can be dispensed with.

[0064] As can be seen from Comparative Example 3, when the electromagnetic induction heating parameters far exceed the limits defined in this invention, although the peel strength and cycle performance of the electrode are stronger than those of Comparative Example 1, its overall performance is significantly deteriorated compared to Example 1, and the drying stress offset rate is significantly lower. This indicates that excessively high interfacial heating intensity and excessively fast heating rate may lead to local boiling of the solvent at the interface, resulting in micropores, premature cross-linking or partial degradation of the binder, which in turn damages the density and uniformity of the interfacial network. At the same time, excessively severe thermal shock may also cause the stress buffering behavior of additives such as thermally expanded microspheres to not adapt well to the curing process, and thus fail to effectively exert a synergistic effect under the correct timing. This result proves that the electromagnetic induction process parameter window set in this invention is crucial for achieving efficient and uniform interfacial curing and precise stress management. Only within the optimized parameter range can the best synergy between each process step and the material system be achieved.

[0065] As can be seen from Examples 1-3, this invention further optimizes the frequency and power density of electromagnetic induction heating within a certain range, utilizing the eddy current effect of the current collector to rapidly raise the temperature of the interface region with the slurry to 100℃~120℃ within a short time. At this time, the surface layer of the slurry remains below 50℃ due to lag in heat conduction. Under this specific temperature field, the binder at the interface rapidly cross-links first, forming an early-stage strengthening network and achieving "interface anchoring". Therefore, the optimized electromagnetic induction parameters can trigger sufficient cross-linking of the binder and effective activation of thermally expanded microspheres in the interface region, while avoiding incomplete interface strengthening due to insufficient heating or potential microstructure damage caused by overheating for too long. Therefore, the precise setting of the electromagnetic induction parameters is a key optimization for achieving efficient synergy between "interface anchoring" and "stress cancellation".

[0066] As can be seen from Examples 1 and 4-5, this invention further limits the hot air velocity to achieve synergistic control of drying kinetics and stress evolution. Excessive air velocity significantly weakens convective heat transfer efficiency and slows the escape rate of solvent vapor on the electrode surface, not only prolonging the necessary drying time but also potentially leading to uneven solvent residue in the middle and surface layers of the slurry, causing uneven shrinkage stress during subsequent curing. Conversely, excessive air velocity causes rapid solvent evaporation and drastic drying shrinkage on the slurry surface. Although the interface layer has initially solidified, excessive surface hardening blocks the channels for internal solvent escape and may generate huge shear stress between the surface layer and the solidified interface layer, thus inducing microcracks. Therefore, precisely controlling the air velocity within the range of 1.5 m / s to 3.0 m / s ensures a relatively mild and uniform bulk drying environment, which highly aligns with the dual objectives of "steady solvent evaporation" and "active stress mitigation" at this stage. Through synergy with the additive system, it creates better conditions for the orderly dissipation of internal stress. Therefore, a moderate air velocity can ensure effective solvent evaporation while avoiding uneven drying due to excessively low air velocity or excessive surface shrinkage and stress concentration caused by excessively high air velocity. This is most conducive to achieving uniform densification of the bulk structure on the solidified strong interface and protecting the interface bonding from damage. This result highlights the importance of precise coordination of process parameters at each stage in a multi-stage dynamic curing process for obtaining high-performance electrodes.

[0067] A comparison of Examples 1 and 6-7 shows that the present invention further limits the dosage of thermally expandable microspheres and phase change microcapsules. At this point, the two functional additives achieve an optimal volume ratio and spatial configuration with the active material, conductive agent, and binder. When the content of thermally expandable microspheres is 1.5 wt%~2.0 wt% and the content of phase change microcapsules is 0.5 wt%~1.0 wt%, the system achieves a better balance between stress buffering efficiency and the basic electrochemical performance of the electrode. Specifically, within this dosage range, the thermally expandable microspheres, after thermal expansion, can form moderately and uniformly distributed elastic support points inside the electrode. The pre-compression stress generated is sufficient to offset most of the drying shrinkage stress, while avoiding the disruption of the conductive network continuity due to excessive addition leading to an excessively low proportion of active material or the formation of excessively large pores. Similarly, the phase change microcapsules at this dosage provide sufficient total phase change enthalpy to effectively homogenize the temperature field and dissipate mechanical energy, while ensuring their dispersibility in the slurry, avoiding increased ion migration resistance that may be caused by excessive local agglomeration. Example 1 exhibits superior overall performance, indicating that the synergistic effect of the two additives is further enhanced under this preferred ratio: the macroscopic pre-stress framework constructed by the thermally expanded microspheres and the microscopic stress buffering and thermal management achieved by the phase change microcapsules work seamlessly together to maintain the structural dynamic equilibrium of the electrode under drastic volume changes. Therefore, precise control of the dosage of functional additives is a key step in ensuring that the multi-level synergistic stress buffering system of this invention can operate efficiently without compromising the electrode energy density.

[0068] A comparison of Examples 1 and 8 shows that precise optimization of electromagnetic induction heating parameters is key to achieving efficient interface curing. Excessive heat diffusion caused by prolonged heating time and low frequency significantly increases the surface temperature of the slurry, weakening the "interface-priority curing" effect. Therefore, the method and rate of achieving this temperature are also of significant optimization importance. This invention further achieves efficient and stable reversal of the curing path from "outside to inside" to "inside to outside" through coordinated control of key electromagnetic induction parameters (action time, frequency, and power density).

[0069] A comparison of Examples 1 and 9 shows that the correct selection of the binder system is crucial for achieving the overall effect of the dynamic curing process. Example 1, using polyacrylic acid (PAA) as the binder, exhibits superior overall electrode performance. In contrast, Example 9, under identical process conditions but with the binder replaced by traditional polyvinylidene fluoride (PVDF), shows inferior electrode peel strength and cycle stability compared to Example 1. This clearly demonstrates that the carboxyl functional groups on the PAA molecular chain can rapidly undergo cross-linking reactions within a specific temperature window during the electromagnetic induction stage, further strengthening the current "interface anchoring." Therefore, the chemical-physical synergy between the binder and the dynamic curing process further enhances the stress buffering effect of this invention and improves the overall performance of the battery.

[0070] As can be seen from the comparison of Examples 1, 10-11, and Comparative Example 4, the present invention can further optimize the types of thermally expandable microspheres and phase change microcapsules. The selected thermally expandable microspheres and phase change microcapsules are more perfectly matched with the temperature sequence of electromagnetic induction interface curing and hot air drying, achieving precise synergy at key nodes such as binder crosslinking, solvent evaporation, and stress generation and mitigation, thus exhibiting superior interface integrity and cycle stability. This indicates that the temperature response characteristics of functional additives must be matched with the dynamic curing process to maximize the synergistic effect of the multi-level stress management system.

[0071] A comparison of Examples 1 and 12-13 shows that the invention further precisely controls the physical morphology of the thermally expanded microspheres and phase change microcapsules. This avoids the problem that excessively small additive particle sizes may lead to agglomeration in the slurry and difficulty in forming effective stress buffer points inside the electrode; while excessively large particle sizes may disrupt the uniformity of the electrode coating, causing localized stress concentration and affecting the continuity of the conductive network. Therefore, selecting additives with appropriate particle sizes ensures good dispersion in the slurry and forms a suitable spatial match with the active material particles, thereby constructing a uniform and efficient multi-level stress buffer network in the most critical interface region and within the bulk phase.

[0072] In step 4 of the preparation method in Example 1, the eddy current effect of the current collector is utilized to rapidly heat the interface region between it and the slurry within 5 seconds. At this time, the surface layer of the slurry remains below 50°C due to lag in heat conduction. Under this specific temperature field, the PAA binder at the interface rapidly crosslinks first, forming an early-stage reinforced network and achieving "interface anchoring." Simultaneously, the interfacial heat triggers the expansion of the thermally expanding microspheres, generating a pre-compression stress of 0.05 ~ 0.2 MPa. The overall drying shrinkage tensile stress generated in step 5 is offset by 15% ~ 35% of the peak value of the pre-compression stress generated in step 4. The phase change microcapsules melt and absorb heat within this temperature range, significantly reducing the temperature gradient inside the slurry (especially in the thickness direction) to <10 °C / μm and filling the interparticle gaps, further alleviating stress concentration caused by uneven drying.

[0073] In summary, the composite anode preparation method based on dynamic curing technology provided by this invention successfully solves the problems of stress accumulation and interface failure in the drying and curing process of high-capacity silicon-carbon anodes through multi-stage synergistic curing path design and precise control of the responsive characteristics of functional additives. The core innovation of this method lies in utilizing electromagnetic induction heating to achieve preferential interface curing "from the inside out," combined with the pre-compression stress generated by thermally expanded microspheres and the temperature buffering effect of phase change microcapsules, thus constructing a dynamic stress offsetting mechanism. This provides a cathode solution with strong interface integrity and long cycle life for high-energy-density lithium-ion batteries, and its process compatibility and parameter controllability lay a solid foundation for industrial applications.

[0074] The technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions, and variations to the above embodiments within the scope of the present invention. Furthermore, without contradiction, those skilled in the art can combine and integrate different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A method of dynamic curing of electrode paste, characterized by, The method comprises the following steps: S1: applying an electrode slurry on a current collector substrate to obtain a pretreated coated current collector; S2: heating the pretreated coated current collector by electromagnetic induction to raise the temperature of the current collector substrate-slush interface to 100-120 ℃; S3: drying in a hot air environment at 70-90 ℃ for 60-180 seconds; S4: curing at 110-130 ℃ for 120-300 seconds. The electrode slurry comprises thermally expandable microspheres and phase change microcapsules; the thermally expandable microspheres have an initial expansion temperature of 75-105 ℃, and the phase change microcapsules have a phase change temperature of 45-65 ℃.

2. The method of dynamically solidifying an electrode paste of claim 1 wherein, The electromagnetic induction in S2 has an action time of 3-10 seconds. Preferably, the frequency of the electromagnetic induction in S2 is 50 kHz~200 kHz, and the power density of the electromagnetic induction is 5~20 W / cm 2 .

3. The method of dynamically solidifying an electrode paste of claim 1 wherein, The hot air speed in S3 is 1.5-3.0 m / s.

4. The method of dynamically solidifying an electrode paste of claim 1 wherein, The electrode slurry further comprises an active material, a conductive agent and a binder; Preferably, the conductive agent is selected from one or more of conductive carbon black, graphene, carbon nanotubes, acetylene black, activated carbon, conductive carbon spheres, conductive carbon fibers, reduced graphene oxide and Ketjen black; Preferably, the active material comprises at least one of hard carbon, soft carbon, graphite, graphite / hard carbon composite, nano-silicon carbon composite and silicon monoxide carbon composite; Preferably, the binder comprises at least one of halogen-containing olefins and copolymers thereof, polyacrylic acid and acrylic resin, and cellulose compounds; Further preferably, the binder is polyacrylic acid.

5. The method of dynamically solidifying an electrode paste of claim 1 wherein, The electrode slurry comprises 1.0-2.5 wt% of the binder, 1.0-2.0 wt% of the thermally expandable microspheres and 0.5-1.0 wt% of the phase change paraffin microcapsules, based on the total mass of the dry matter of the slurry.

6. The method of dynamically solidifying an electrode paste of claim 1 wherein, The thermally expandable microspheres have a core-shell structure, the shell of the thermally expandable microspheres is a thermoplastic polymer, the core of the thermally expandable microspheres is a low-boiling liquid hydrocarbon wrapped in the shell, and the thermally expandable microspheres have an initial expansion temperature of 75-100 ℃; the phase change microcapsules have a core-shell structure, the shell layer of the phase change microcapsules is a dense high molecular resin material, and the core layer is a phase change material, the phase change melting temperature of the core layer is 55-65 ℃, and the phase change enthalpy value is ≥150 J / g; Preferably, the shell of the thermally expandable microspheres is selected from one or more of olefin polymers, the core of the thermally expandable microspheres is selected from one or more of C2-C4 alkanes, the phase change material in the phase change microcapsules is selected from one or more of C15+ alkanes, and the shell layer of the phase change microcapsules is selected from one or more of amine-aldehyde resins.

7. The method of dynamically solidifying an electrode paste of claim 1 wherein, The shell of the thermally expandable microspheres is polyvinylidene chloride-acrylonitrile copolymer, and the core is isobutane; the shell layer of the phase change microcapsules is melamine-formaldehyde resin, and the core layer is n-eicosane; Preferably, the particle size D50 of the thermally expandable microspheres is 5-20 μm, and the particle size D50 of the phase change microcapsules is 1-10 μm.

8. The method of dynamically solidifying an electrode paste of claim 1 wherein, The surface layer temperature of the electrode paste in the S2 stage is ≤50℃, the thermal expansion microspheres are expanded by heat, and a pre-stress of 0.05-0.2 MPa is generated in the electrode; the pre-stress in the S2 stage offsets 15%-35% of the drying shrinkage tensile stress in the S3 stage. Preferably, the temperature gradient in the interior of the electrode paste in the S3 stage is <10 ℃ / μm.

9. An electrode plate prepared by the electrode paste dynamic curing method according to any one of claims 1-8.

10. A lithium-ion battery, characterized by, An electrode plate prepared by the electrode paste dynamic curing method according to any one of claims 1-8.

Images