Dense battery pole piece preparation process and battery pole piece hot-pressing and cold-extracting equipment

Abstract

The invention provides a densified battery pole piece preparation process and battery pole piece hot-pressing and cold-extracting equipment, and the densified battery pole piece preparation process comprises the following steps: rolling and heating a battery pole piece to obtain a high-elastic pole piece; carrying out first cooling on the high-elastic-state pole piece through liquid nitrogen injection so as to obtain a slowly-frozen pole piece; the slowly-frozen pole piece is placed in a normal-temperature environment to be buffered and then rolled and softened through a multi-roller assembly, and a softened pole piece is obtained; performing secondary cooling on the softened pole piece through liquid nitrogen injection to obtain a cold extraction pole piece; and putting the cold-extracted pole piece into a constant-temperature environment to release stress so as to obtain the densified battery pole piece. The structure of the pole piece is frozen, stabilized and solidified through cooperation of high-elastic-state rolling and cold extraction, the compaction density is improved, springback is inhibited, and therefore the densified battery pole piece is obtained; through the buffering step and the intermediate rolling softening step, the defect of generating microcracks is reduced, and the structural stability and the electrochemical performance are improved.

Description

Technical Field

[0001] This disclosure relates to the technical field of lithium batteries, and in particular to a process for preparing dense battery electrodes and a hot-pressing and cold-extraction apparatus for battery electrodes. Background Technology

[0002] In the manufacturing process of lithium-ion batteries, electrode rolling is a key step in improving electrode energy density. With the development of high-energy-density batteries, thick electrode systems such as silicon-based anodes and high-nickel cathodes place higher demands on the rolling process.

[0003] During the rolling process, due to the elastic properties of the polymer binder and the release of internal stress, the rolled electrodes exhibit significant springback during rest or subsequent processing, leading to a decrease in electrode density and a severe reduction in the volume ratio of active material. Furthermore, high-pressure rolling damages the electrode's microporous structure, increasing the tortuosity of ion transport paths by 20% to 40%, significantly increasing the battery's internal resistance. While hot rolling enhances binder fluidity by raising the temperature, simple heating cannot suppress the stress springback problem during material cooling, thus causing a decrease in electrode density.

[0004] For example, the powder-spreading hot-pressing dry electrode manufacturing equipment and method disclosed in prior art CN202410716241.X first controls the movement of the current collector through a winding and unwinding device, then spreads the electrode powder material onto the current collector using an automatic feeding roller spreading device, then preheats the electrode powder material through a preheating device, and finally processes the electrode powder material through a hot rolling device by heating and pressurizing to obtain a high-density, compact lithium-ion battery electrode sheet. This method obtains lithium-ion battery electrode sheets through a hot rolling process, but it cannot suppress the stress rebound problem during the material cooling process, thus leading to a decrease in electrode density. Summary of the Invention

[0005] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide a process for preparing denser battery electrodes that compacts density and suppresses springback, as well as a hot-pressing and cold-extraction apparatus for battery electrodes.

[0006] The purpose of this disclosure is achieved through the following technical solution: A process for fabricating denser battery electrodes includes the following steps: The battery electrode sheets are rolled and heated to obtain highly elastic electrode sheets; The high-elasticity electrode is first cooled to 0°C by liquid nitrogen injection to obtain a slow-frozen electrode. The slow-freezing electrode is placed in a room temperature environment for buffering, and then the slow-freezing electrode is introduced into a multi-roller assembly for rolling and softening to obtain a softened electrode. The softened electrode sheet is cooled a second time by liquid nitrogen injection to below -30°C to obtain a cold-extracted electrode sheet. The cold-extracted electrode is placed in a constant-temperature environment to release stress, thereby obtaining a densified battery electrode.

[0007] In one embodiment, the cooling rate is 40°C / s-50°C / s, and the cooling rate of the cold extraction is 50°C / s-100°C / s.

[0008] In one embodiment, the liquid nitrogen injection pressure is 0.5 MPa-1.5 MPa.

[0009] In one embodiment, the binder for the battery electrode is at least one of polyvinylidene fluoride-hexafluoropropylene, polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0010] In one embodiment, the rolling pressure is 5MPa-15MPa, and the heating temperature is 80℃-120℃.

[0011] In one embodiment, the slowly frozen electrode is placed in a room temperature environment for buffering, and then the slowly frozen electrode is softened by passing it through multiple rollers to obtain a softened electrode, including the following steps: The slow-freezing electrode at 0℃ is placed in a room temperature environment of 17℃-23℃ for buffering, and the buffering time is 10s-60s. The buffered, slow-freezing electrode sheet is introduced into a multi-roller softening assembly, and the buffered electrode sheet passes through multiple rollers spaced apart in an S-shaped path in sequence.

[0012] In one embodiment, the liquid nitrogen flow rate of the liquid nitrogen injection conforms to the following relationship: Q = k × (ΔT / Δt) × S; Where Q is the flow rate, k is the correction coefficient (k=0.8-1.2), ΔT / Δt is the measured cooling rate, and S is the electrode area.

[0013] A battery electrode hot-pressing and cold-extraction device is used to implement the densification battery electrode preparation process described in any of the above embodiments, including a hot-pressing module, a cold-extraction module, and a pressure leveling module. The hot pressing module is used to roll and heat the battery electrode sheets; The cold extraction module includes a slow-freezing chamber, a room-temperature drying chamber, and a cold extraction chamber arranged in sequence. The slow-freezing chamber and the cold extraction chamber are respectively equipped with liquid nitrogen injection components for spraying liquid nitrogen. The room-temperature drying chamber is equipped with a multi-roller assembly with multiple pairs of rollers. The slow-freezing chamber is connected to the outlet of the hot-pressing module. The pressure leveling module is connected to the outlet of the cold extraction chamber and is used to provide a constant temperature environment. In this embodiment, the electrode first enters the hot pressing module. Under a set heating temperature of 80℃-120℃ and a roller pressing pressure of 5MPa-15MPa, the coating components of the electrode enter a highly elastic state with excellent plasticity, achieving preliminary densification. The processed highly elastic electrode is continuously output to the cold extraction module. After entering the cold extraction module, the electrode is rapidly cooled by a liquid nitrogen spray component at a rate of 40-50℃ / s, and the temperature drops to about 0℃, causing the electrode coating components to undergo a preliminary glass transition, preventing the electrode coating from rebounding and forming a slowly frozen electrode. The slowly frozen electrode enters the ambient temperature drying chamber and stays briefly in an ambient temperature drying environment of 17-23℃ for 10-60 seconds to achieve temperature uniformity and stress buffering. In one embodiment, the liquid nitrogen injection assembly includes a condenser tube and a porous injection plate, the porous injection plate being connected to the condenser tube. In this embodiment, In one embodiment, the distance between the outlet of the porous spray plate and the electrode to be cooled is 10mm-30mm, and the spray angle of the outlet of the porous spray plate is 60°-90°. In this embodiment, Compared with the prior art, this disclosure has at least the following advantages: The aforementioned densified battery electrode preparation process, through the synergistic effect of high-elasticity rolling and deep glass transition during cold extraction, freezes and stabilizes the high-density microstructure of the electrode, increasing the electrode compaction density and completely suppressing the springback of the electrode coating material, thereby obtaining a densified battery electrode. Through staged temperature control and rolling steps, the active material, conductive agent, and binder are fully rearranged and bonded in a plastically enhanced state, strengthening the interfacial bonding between components. Uniform reheating eliminates thermal stress, improving the uniformity and consistency of the overall electrode structure. Buffering alleviates internal stress caused by rapid cooling, and rolling softening further compacts the coating material in a plastic state, significantly reducing defects such as microcracks caused by material brittleness, ensuring the integrity of the electrode structure, and thus improving the structural stability and electrochemical performance of the battery electrode. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a flowchart illustrating the steps of a process for fabricating a dense battery electrode according to one embodiment. Figure 2 Scatter plot of capacity retention after 200 cycles for the examples and comparative examples; Figure 3 Scatter plots showing the 5C discharge capacity retention rates of the examples and comparative examples; Figure 4 This is a schematic diagram of a battery electrode hot-pressing and cold-extraction device according to one embodiment. Detailed Implementation

[0016] To facilitate understanding of this disclosure, a more complete description will be given below with reference to the accompanying drawings, which illustrate preferred embodiments of the present disclosure. However, this disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure.

[0017] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0019] To better understand the technical solutions and beneficial effects of this disclosure, the following detailed description is provided in conjunction with specific embodiments: Please see Figure 1 The present invention provides a process for preparing a dense battery electrode, comprising the following steps: S101 involves rolling and heating the battery electrode to obtain a highly elastic electrode. It is understood that when the active material, conductive agent, binder, and current collector in the electrode coating enter a highly elastic state, the plasticity of the material is significantly enhanced, making it easier to undergo plastic deformation and facilitating subsequent densification.

[0020] S103 involves initial cooling of the elastic electrode to 0°C using liquid nitrogen injection to obtain a slow-frozen electrode. This process involves rapidly cooling the elastic electrode to 0°C using liquid nitrogen injection, freezing the electrode coating to prevent rebound, and causing the high-molecular-weight binder and other components within the electrode to undergo a glass transition or harden, thus initially improving overall rigidity.

[0021] S105, the slowly frozen electrode sheet is placed in a room temperature environment for buffering, and then the slowly frozen electrode sheet is introduced into a multi-roll assembly for rolling and softening to obtain a softened electrode sheet. It can be understood that placing the slowly frozen electrode sheet in a room temperature environment for a short buffering period allows its overall temperature to become more uniform, alleviating the surface and internal temperature difference stress caused by rapid cooling. Rolling further compacts the material, while reducing the risk of microcracks caused by the material being too brittle.

[0022] S107, the softened electrode is subjected to a second cooling process using liquid nitrogen spray, lowering the temperature to below -30°C to obtain a cold-extracted electrode. It is understood that after the second cooling, the amorphous components such as the polymer binder in the softened electrode coating undergo a deep glass transition, thereby freezing the highly dense microstructure of the softened electrode after roll pressing, making it an irreversibly stable structure and suppressing any elastic or viscoelastic recovery that may occur after the roll pressing stress is removed.

[0023] S109, the cold-extracted electrode is placed in a constant-temperature environment to release stress. It is understood that transferring the cold-extracted electrode to a constant and uniform temperature environment allows it to slowly and evenly reheat, eliminating thermal stress caused by differences in the coefficients of thermal expansion between different materials within the electrode during the reheating process. This allows the electrode material to recover from its glassy state to a more stable state, stabilizing the mechanical properties of the final product and ensuring its reliability in subsequent battery assembly and use.

[0024] The aforementioned densified battery electrode preparation process, through the synergistic effect of high-elasticity rolling and deep glass transition during cold extraction, freezes and stabilizes the high-density microstructure of the electrode, increasing the electrode compaction density and completely suppressing the springback of the electrode coating material, thereby obtaining a densified battery electrode. Through staged temperature control and rolling steps, the active material, conductive agent, and binder are fully rearranged and bonded in a plastically enhanced state, strengthening the interfacial bonding between components. Uniform reheating eliminates thermal stress, improving the uniformity and consistency of the overall electrode structure. Buffering alleviates internal stress caused by rapid cooling, and rolling softening further compacts the coating material in a plastic state, significantly reducing defects such as microcracks caused by material brittleness, ensuring the integrity of the electrode structure, and thus improving the structural stability and electrochemical performance of the battery electrode.

[0025] In one embodiment, the cooling rate is 40℃ / s-50℃ / s, and the cooling rate of the cold extraction is 50℃ / s-100℃ / s. In this embodiment, the first cooling uses a relatively fast rate of 40-50℃ / s, allowing the elastic electrode to quickly pass through the glass transition zone of the polymer material, achieving initial freezing and solidification of the coating, effectively preventing initial rebound. The first cooling rate is optimized to avoid the risk of increased surface embrittlement due to excessively rapid cooling, creating suitable material conditions for subsequent buffering and rolling softening. The second cooling uses an even higher rapid deep cooling of 50℃ / s-100℃ / s, which allows the softened electrode to instantly reach a deep glass transition state, completely locking the high-density microstructure after rolling, making the density increase irreversible. The second ultra-high-speed cooling is carried out while the electrode is softened and compacted, thereby quickly crossing the brittle temperature range and minimizing microcracks and internal stress caused by low-temperature dwell or excessive temperature difference.

[0026] In one embodiment, the liquid nitrogen injection pressure is 0.5 MPa-1.5 MPa. In this embodiment, with the liquid nitrogen injection pressure in the range of 0.5 MPa-1.5 MPa, the liquid nitrogen is fully atomized and forms a uniform and fine jet flow field, quickly covering the electrode surface to achieve efficient heat exchange. This allows the electrode to reach the target temperature synchronously and quickly in both the lateral and thickness directions, avoiding stress concentration or uneven deformation caused by excessive local temperature differences. A liquid nitrogen injection pressure less than 1.5 MPa avoids direct physical impact or vibration to the electrode coating due to excessive injection pressure, preventing microcracks or peeling of the already formed dense microstructure. A liquid nitrogen injection pressure greater than 0.5 MPa ensures that the liquid nitrogen jet has sufficient penetration and coverage, preventing uneven cooling, localized rebound, or incomplete glass transition due to insufficient pressure, thereby ensuring consistent overall curing effect.

[0027] In one embodiment, the adhesive for the battery electrode is at least one of polyvinylidene fluoride-hexafluoropropylene, polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber. In this embodiment, the van der Waals forces and mechanical interlocking of polyvinylidene fluoride-hexafluoropropylene, the strong polar bonding of polyacrylic acid and sodium carboxymethyl cellulose, and the elastic bonding of styrene-butadiene rubber provide balanced cohesion, interfacial adhesion, and flexibility for the electrode coating, effectively buffering thermal and mechanical stress and preventing the coating from cracking or peeling off from the current collector. The adhesive has a defined glass transition temperature and viscoelastic property range, thereby responding to the multi-stage temperature control process of heating to a high elastic state, then slow-freezing to 0°C, and then deep-cooling to below -30°C, ensuring that the expected plastic flow, initial hardening, and deep glass transition occur at each step, thereby achieving step-by-step structural locking. Furthermore, in one embodiment, the binder for the battery electrode is polyvinylidene fluoride-hexafluoropropylene (PVDF-HFA). In this embodiment, PVDF-HFA, as a copolymer of PVDF, has reduced crystallinity and more pronounced glass transition characteristics. During the heating and rolling stage, it can enter and stabilize in a highly elastic state with good plasticity earlier. The Tg range of PVDF-HFA coincides with the subsequent 0°C slow freezing and -30°C cryogenic temperature points, making its state transition smooth and controllable during multi-stage heat treatment. The hexafluoropropylene segments of PVDF-HFA introduce stronger flexibility, providing sufficient support to transmit pressure and achieve densification when softened by rolling. It can also uniformly disperse stress through moderate extension of the molecular chains, significantly reducing the sensitivity to microcracks during high-pressure compaction and rapid cooling. PVDF-HFA has a high proportion of amorphous regions, enabling faster and more thorough deep glass transition under liquid nitrogen cryogenic conditions.

[0028] In one embodiment, the rolling pressure is 5MPa-15MPa, and the heating temperature is 80℃-120℃. In this embodiment, the heating temperature is controlled between 80℃ and 120℃, which fully activates the molecular chain segment movement of the binder such as polyvinylidene fluoride-hexafluoropropylene, but does not reach a molten flow state. The composite system of active materials, conductive agents and binders in the coating exhibits a highly elastic state with significantly enhanced plasticity and reduced deformation resistance, while remaining below the heat distortion temperature of the current collector, thus maintaining the stability of the electrode substrate. At a temperature of 80℃-120℃, the rolling pressure is 5MPa-15MPa. The highly elastic coating material can undergo sufficient and uniform plastic flow and rearrangement, thereby efficiently filling the gaps between particles and significantly improving the initial compaction density. The rolling pressure is greater than 5MPa to ensure the compactness of the coating material, and less than 15MPa to avoid excessive stretching or microscopic damage to the current collector in a thermoplastic state due to excessive pressure, preventing the electrode coating particles from being crushed. While increasing the density, the microstructural integrity of the electrode is maintained to the maximum extent.

[0029] In one embodiment, the slowly frozen electrode is placed in a room temperature environment for buffering, and then the slowly frozen electrode is softened by passing it through multiple rollers to obtain a softened electrode, including the following steps: The slow-freezing electrode at 0℃ is placed in a room temperature environment of 17℃-23℃ for buffering, and the buffering time is 10s-60s. The buffered, slowly frozen electrode sheet is introduced into a multi-roller softening assembly. The buffered electrode sheet passes sequentially through multiple rollers spaced apart in an S-shaped path within the multi-roller softening assembly. In this embodiment, the slowly frozen electrode sheet at 0°C is placed in a room temperature environment of 17°C-23°C and maintained for 10s-60s to achieve thermal equilibrium and stress relaxation. This homogenizes the temperature difference between the electrode sheet surface and interior, alleviating the thermal shock stress caused by rapid cooling with liquid nitrogen. This reduces the brittleness of components such as polymer binders and slightly increases their toughness, thus creating a safe window for subsequent mechanical rolling and reducing the risk of microcracks directly occurring in the initial stage of rolling due to the material's brittleness. The buffered electrode sheet is guided through the multi-roller softening assembly and travels along an S-shaped path for gradual rolling softening. This allows the slowly frozen electrode sheet to undergo multiple small-scale cumulative plastic deformations as it passes through multiple pairs of rollers, effectively dispersing the rolling stress and achieving gradual and gentle densification of the slowly frozen electrode sheet.

[0030] Furthermore, in one embodiment, the surface temperature of the rollers in the multi-roller softening assembly is controlled between 25°C and 40°C. In this embodiment, the roller surface temperature is slightly higher than the buffer ambient temperature. When the slowly frozen electrode contacts the roller electrode, the temperature transfer ensures that the coating of the electrode remains within a softening window with moderate plasticity and good toughness, preventing the electrode surface from becoming brittle again due to contact with an excessively cold roller, and also preventing the adhesive from becoming overly softened or sticking to the roller due to excessively high roller temperature.

[0031] In one embodiment, the liquid nitrogen flow rate of the liquid nitrogen injection conforms to the following relationship: Q = k × (ΔT / Δt) × S; Where Q is the flow rate, k is the correction coefficient (k=0.8-1.2), ΔT / Δt is the measured cooling rate, and S is the electrode area. In this embodiment, by establishing this flow control relationship based on a physical model, quantitative and adaptive precise management of the cooling process is achieved. The liquid nitrogen flow rate Q is directly correlated with the core thermodynamic target ΔT / Δt of the process, namely the preset 40-50℃ / s or 50-100℃ / s, and the basic production variable electrode area S. The system can dynamically calculate the precise cold input required to achieve the target cooling rate, thereby ensuring that the cooling curves of slow freezing and cold extraction can be repeatedly executed, overcoming the problem of uneven cooling or substandard rate caused by differences in electrode size, initial temperature, or heat capacity under the fixed flow rate mode.

[0032] Understandably, a lower limit of 0.8 for the correction coefficient k provides a safety margin for system heat loss, atomization efficiency, and nozzle variability, ensuring the reliability of the cooling effect. An upper limit of 1.2 for the coefficient k prevents excessive spraying in pursuit of speed, avoiding excessive local stress, brittle material damage, and ineffective consumption of liquid nitrogen.

[0033] Understandably, the combined effect of flow control and injection pressure of 0.5MPa-1.5MPa ensures that the atomization quality of liquid nitrogen and the jet impact intensity form a uniform cooling medium field, enabling the electrode to achieve stable and uniform instantaneous heat exchange in both width and direction of travel.

[0034] Furthermore, in one embodiment, when the cold-extracted electrode is placed in a constant-temperature environment to release stress, dry air with a dew point below -40°C is introduced for dehumidification. In this embodiment, the dry air with a dew point below -40°C is dry air cooled to below -40°C, at which point water vapor will begin to condense into liquid water. The surface temperature of the cold-extracted electrode, taken out from below -30°C, is still extremely low. Introducing dry air with a dew point below -40°C creates an absolutely dry local atmosphere, ensuring that no moisture condenses on the surface or in the pores of the electrode during the entire process of slowly warming it to room temperature. This prevents water vapor from intruding into the high-density microstructure and causing expansion stress, interfacial corrosion, or side reactions. The flowing dry low-temperature air with a dew point below -40°C provides uniform and gentle heat exchange, promoting the gradual release of stress.

[0035] This application also provides a battery electrode hot-pressing and cold-extraction device 10, used to implement the densification battery electrode preparation process in any of the above embodiments, including a hot-pressing module 100, a cold-extraction module 200, and a pressure leveling module 300. The hot pressing module 100 is used to roll and heat the battery electrode sheets; The cold extraction module 200 includes a slow-freezing chamber 210, a room temperature drying chamber 220 and a cold extraction chamber 230 arranged in sequence. The slow-freezing chamber 210 and the cold extraction chamber 230 are respectively provided with liquid nitrogen injection components 211 for spraying liquid nitrogen. The room temperature drying chamber 220 is provided with a multi-roller softening component 221. The slow-freezing chamber 210 is connected to the outlet of the hot pressing module 100. The pressure leveling module 300 is connected to the outlet of the cold extraction chamber 230, and the pressure leveling module 300 is used to provide a constant temperature environment. In this embodiment, the battery electrode enters the hot pressing module 100 and is rolled at a preset temperature of 80℃-120℃ and a pressure of 5-15MPa. The coating components of the battery electrode enter a highly elastic state with good plasticity, completing the initial densification and obtaining a highly elastic electrode. The highly elastic electrode enters the cold extraction module 200 and passes through the slow freezing chamber 210, the ambient temperature drying chamber 220, and the cold extraction chamber 230 in sequence. The highly elastic electrode is rapidly cooled in the slow freezing chamber 210, and the liquid nitrogen spraying component cools the electrode to about 0℃ at a rate of 40℃ / s-50℃ / s. The coating of the highly elastic electrode undergoes a preliminary glass transition, forming a slow-frozen electrode. The slow-frozen electrode is then dried in the ambient temperature drying chamber 220 at 7℃-23℃. The electrode is buffered in a dry environment for 10-60 seconds, and then uniformly heated before entering the multi-roller softening assembly 221 for softening and densification, reducing the generation of microcracks. After the softened electrode enters the cold extraction chamber 230, the liquid nitrogen injection assembly 211 deeply cools it to below -30°C at a rate of 50°C / s-100°C / s, causing a deep glass transition in the coating of the electrode, and the structure of the coating is frozen to form a cold-extracted electrode. The cold-extracted electrode enters the constant temperature environment of the pressure balancing module 300, where it slowly and uniformly warms up. Dry air with a dew point below -40°C can be introduced to prevent condensation. The residual stress inside the cold-extracted electrode is fully released in the constant temperature environment, thereby obtaining a finished high-density electrode with stable dimensions and performance.

[0036] Understandably, the battery electrode hot-pressing and cold-extraction equipment 10 integrates hot rolling plasticizing and ultra-low temperature cryogenics into a continuous production line. The direct connection between the hot pressing module 100 and the slow-freezing chamber 210 enables the instantaneous transition of the electrode coating from a plastic state to a frozen state, effectively suppressing elastic rebound. The ambient temperature drying chamber 220 buffers the electrode to make the temperature and stress tend to be uniform. The liquid nitrogen injection component 211 adaptively regulates the flow rate to precisely control the cooling rate of the electrode. The multi-roller softening component 221 performs heat-assisted progressive rolling, avoiding the problem of easy cracking of low-temperature materials under direct pressure, and achieving a safe and controllable transition between the electrode freezing process and the densification process.

[0037] Furthermore, in one embodiment, the multi-roller softening assembly 221 includes a plurality of spaced rollers 2211, with the gap between adjacent rollers decreasing along the traveling direction of the softened electrode. In this embodiment, as the electrode travels along an S-shaped path, the reduction rate experienced by the electrode gradually and slightly increases, allowing the coating material to flow, rearrange, and collapse voids fully and gently during multiple, small-incremental plastic deformations, thereby effectively reducing microcracks inside the electrode.

[0038] Furthermore, in one embodiment, the linear pressure applied to the electrode by the multi-roller softening assembly 221 is 0.5 kN / cm to 2 kN / cm. In this embodiment, the pressure of the multi-roller softening component is lower than the initial heating roller pressure level, thereby performing restorative compaction and plastic softening on the slowly frozen electrode. The roller pressure is greater than 0.5 kN / cm, ensuring further rearrangement and micropore collapse of the coating, achieving an effective increase in density. The roller pressure is less than 2 kN / cm, which strictly limits the maximum stress of a single roller press, avoiding excessive pressure that could cause new microcracks in the already embrittled coating or peeling from the current collector, achieving a balance between compaction and no damage. The target deformation of the electrode thickness is controlled by the decreasing gap between adjacent rollers, and the required force intensity for this deformation is achieved by controlling the roller pressure, allowing the multi-roller softening component to safely drive the material to deform along the preset deformation path. Furthermore, the roller surface temperature provides thermal softening conditions for the material, reducing deformation resistance and ensuring that the material can undergo sufficient plastic flow in the thermally softened state, synergistically achieving gradual and gentle densification of the electrode material.

[0039] In one embodiment, the liquid nitrogen injection assembly 211 includes a condenser tube 2111 and a porous injection plate 2112, the porous injection plate 2112 being connected to the condenser tube 2111. In this embodiment, the condenser tube 2111 serves as a buffer unit for liquid nitrogen delivery and pressure stabilization, providing a uniform medium for injection; the precisely distributed micropore array on the porous injection plate 2112 disperses the liquid nitrogen into a uniformly distributed fine cryogenic jet, ensuring that the heat exchange intensity remains consistent at any position on the electrode surface within the slow-freezing chamber 210 and the cold extraction chamber 230, eliminating problems such as lateral temperature differences, local stress concentration, or uneven glass transition degrees caused by uneven cooling.

[0040] In one embodiment, a first infrared thermometer 212 is installed inside the slow-freezing chamber 210, and a second infrared thermometer 232 is installed inside the cold extraction chamber 230. In this embodiment, the first infrared thermometer 212 is electrically connected to the control system of the liquid nitrogen injection assembly of the slow-freezing chamber 210, and the second infrared thermometer 232 is electrically connected to the control system of the liquid nitrogen injection assembly of the cold extraction chamber 230, thereby dynamically adjusting the liquid nitrogen injection pressure or flow rate for real-time compensation and correction.

[0041] In one embodiment, the ambient temperature drying chamber 220 is provided with a first drying air channel 2201; the pressure leveling module 300 is provided with a second drying air channel 301. In this embodiment, both the first drying air channel 2201 and the second drying air channel 301 are used to introduce dry air with a dew point below -40°C for dehumidification.

[0042] In one embodiment, the distance between the outlet of the porous spray plate 2112 and the electrode to be cooled is 10mm-30mm, and the spray angle of the outlet of the porous spray plate is 60°-90°. In this embodiment, when the distance between the outlet of the porous spray plate and the electrode to be cooled is less than 10 mm, the jet impact force is too strong, interfering with the smooth movement of the electrode and causing mechanical impact on the fragile coating. When the distance between the outlet of the porous spray plate 2112 and the electrode to be cooled is greater than 30 mm, the liquid nitrogen droplets are excessively vaporized and dispersed, and the cooling intensity and uniformity decrease significantly. When the distance between the outlet of the porous spray plate 2112 and the electrode to be cooled is 10 mm to 30 mm, the atomized liquid nitrogen maintains sufficient kinetic energy and cold density when it reaches the surface of the electrode to be cooled, thereby forming a continuous and consistent cooling coverage in the width of the electrode and the direction of travel. The spray angle determines the direction of action and energy distribution of the cooling medium. The spray angle is 60° to 90°, which makes the cooling medium form a stable low-temperature air curtain above the electrode, isolating it from environmental thermal interference. The combination of spray distance, angle, constant spray pressure and flow control constitutes a defined cooling space geometry and medium input conditions, enhancing the repeatability of the process and ensuring a high degree of consistency in the glass transition process of the electrode between batches.

[0043] Compared with the prior art, this disclosure has at least the following advantages: The aforementioned densified battery electrode preparation process, through the synergistic effect of high-elasticity rolling and deep glass transition during cold extraction, freezes and stabilizes the high-density microstructure of the electrode, increasing the electrode compaction density and completely suppressing the springback of the electrode coating material, thereby obtaining a densified battery electrode. Through staged temperature control and rolling steps, the active material, conductive agent, and binder are fully rearranged and bonded in a plastically enhanced state, strengthening the interfacial bonding between components. Uniform reheating eliminates thermal stress, improving the uniformity and consistency of the overall electrode structure. Buffering alleviates internal stress caused by rapid cooling, and rolling softening further compacts the coating material in a plastic state, significantly reducing defects such as microcracks caused by material brittleness, ensuring the integrity of the electrode structure, and thus improving the structural stability and electrochemical performance of the battery electrode.

[0044] The following are some specific examples. When %, it refers to a percentage by weight. It should be noted that the following examples do not exhaustively list all possible scenarios, and unless otherwise specified, the materials used in the following examples are commercially available.

[0045] Example 1 Lithium nickel cobalt manganese oxide (NCM811), polyvinylidene fluoride-hexafluoropropylene, and conductive agent SP were mixed at a mass ratio of 96:2:2 and coated onto aluminum foil. After drying, a battery electrode sheet with a thickness of 200 μm was obtained. The battery electrode sheet was then introduced into a battery electrode sheet hot-pressing and cold-extraction equipment, where it underwent constant-temperature hot rolling pressing at a temperature of 115°C and a rolling pressure of 10 MPa, resulting in a highly elastic electrode sheet. The rolled highly elastic electrode sheet was then introduced into a slow-freezing chamber, where a porous spray plate sprayed liquid nitrogen onto the highly elastic electrode sheet at a pressure of 0.5 MPa and a cooling rate of 40°C / s, causing the temperature of the highly elastic electrode sheet to drop to 0°C within 3 seconds, thus obtaining a slow-frozen electrode sheet. The slowly frozen electrode is softened by multiple rollers in a room temperature drying chamber to obtain a softened electrode. The softened electrode then enters a cold quenching chamber, where a multi-hole spray plate sprays liquid nitrogen onto the softened electrode at a spray pressure of 1 MPa, causing the temperature of the softened electrode to drop to -40°C within 2 seconds to obtain a cold-extracted electrode. Finally, the cold-extracted electrode is introduced into a stress balancing module for room temperature drying and held for 80 seconds to balance the stress of the electrode and obtain a dense battery electrode.

[0046] Example 2 Silicon carbon graphite, polyacrylic acid (PAA), and conductive agent (SP) were mixed in a 90:5:5 ratio and coated onto copper foil. After drying, a battery electrode sheet with a thickness of 200 μm was obtained. The battery electrode sheet was then introduced into a hot-pressing and cold-extraction equipment, where it underwent constant-temperature hot rolling pressing at 80°C and 8 MPa, resulting in a highly elastic electrode sheet. The rolled highly elastic electrode sheet was then introduced into a slow-freezing chamber, where a porous spray plate sprayed liquid nitrogen onto it at a pressure of 0.4 MPa and a cooling rate of 40°C / s, causing the temperature of the highly elastic electrode sheet to drop to 0°C within 2 seconds, thus obtaining a slow-frozen electrode sheet. The slowly frozen electrode is softened by multiple rollers in a room temperature drying chamber to obtain a softened electrode. The softened electrode then enters a cold quenching chamber, where a multi-hole spray plate sprays liquid nitrogen onto the softened electrode at a spray pressure of 0.8 MPa, causing the temperature of the softened electrode to drop to -30°C within 2 seconds to obtain a cold-extracted electrode. Finally, the cold-extracted electrode is introduced into a stress balancing module for room temperature drying and held for 90 seconds to balance the stress of the electrode and obtain a dense battery electrode.

[0047] Example 3 Lithium iron phosphate, polyvinylidene fluoride-hexafluoropropylene, and conductive agent SP were mixed in a ratio of 92:5:3 and coated onto aluminum foil. After drying, a battery electrode sheet with a thickness of 300 μm was obtained. The battery electrode sheet was then introduced into a hot-pressing and cold-extraction equipment, where it underwent constant-temperature hot rolling pressing at a temperature of 120°C and a pressing pressure of 12 MPa, resulting in a highly elastic electrode sheet. The rolled highly elastic electrode sheet was then introduced into a slow-freezing chamber, where a porous spray plate sprayed liquid nitrogen onto the highly elastic electrode sheet at a pressure of 0.6 MPa and a cooling rate of 40°C / s, causing the temperature of the highly elastic electrode sheet to drop to 0°C within 3 seconds, thus obtaining a slow-frozen electrode sheet. The slowly frozen electrode is softened by multiple rollers in a room temperature drying chamber to obtain a softened electrode. The softened electrode then enters a cold quenching chamber, where a multi-hole spray plate sprays liquid nitrogen at a pressure of 1.2 MPa onto the softened electrode, causing the temperature of the softened electrode to drop to -50°C within 2 seconds to obtain a cold-extracted electrode. Finally, the cold-extracted electrode is introduced into a stress balancing module and dried at room temperature for 120 seconds to balance the stress of the electrode and obtain a dense battery electrode.

[0048] Comparative Example 1 Lithium nickel cobalt manganese oxide (NCM811), polyvinylidene fluoride-hexafluoropropylene, and conductive agent SP were mixed at a mass ratio of 96:2:2, coated on aluminum foil, and dried to obtain a battery electrode sheet with a thickness of 200 μm. After being rolled at 80 MPa, the electrode sheet was directly wound up.

[0049] Comparative Example 2 Lithium nickel cobalt manganese oxide (NCM811), polyvinylidene fluoride-hexafluoropropylene, and conductive agent SP were mixed at a mass ratio of 96:2:2 and coated onto aluminum foil. After drying, a battery electrode with a thickness of 200 μm was obtained. After rolling at 80 MPa, it was directly wound up. A constant-temperature hot rolling process was then performed at 165℃ and a rolling pressure of 10 MPa. After hot rolling, the electrode was allowed to cool naturally without cold quenching.

[0050] Table 1 Performance Tests of Examples and Comparative Examples It should be noted that: the compaction density after 24 hours was measured after the electrode was placed in a constant temperature and humidity environment for 24 hours; the porosity was measured using a mercury porosimeter; the first-cycle coulombic efficiency was tested under the set charge-discharge conditions of 0.1C; the 200-cycle capacity test was conducted under 1C constant current charge-discharge conditions within the voltage range for 200 consecutive cycles; and the 5C discharge capacity was tested under the same voltage range, under 5C constant current charge-discharge conditions for several cycles until the capacity stabilized.

[0051] From above Figure 2 , Figure 3As shown in Table 1, compared with Comparative Examples 1-2, the compaction density fluctuation rate of Comparative Examples 1-2 was 6.5%-7.4%, and the electrodes of Comparative Examples 1 and 2 had serious springback problems. The compaction density fluctuation rate of Example 1 was 0.6%-0.7%. This indicates that the electrode preparation process of the densified battery electrode freezes the high-density microstructure of the electrode by cold extraction, which not only increases the compaction density of the electrode but also suppresses the material springback and improves the long-term stability of the electrode pore structure, thereby obtaining a stable and uniform densified electrode.

[0052] The discharge capacity retention rates of Examples 1-3 are higher than those of Comparative Examples 1 and 2. Comparative Example 1 is prone to local over-compaction and microcracks under high-pressure rolling conditions, which leads to cycle decay. This shows that the electrode prepared by the densification battery electrode preparation process can form a uniform, interconnected and structurally stable pore structure while increasing the density.

[0053] The compaction density fluctuation rate, 200-cycle capacity retention rate and discharge capacity retention rate of Examples 1-3 are small, indicating that the three electrode materials have achieved low fluctuation rate, high rate performance and good cycle stability after being processed by the densification battery electrode preparation process.

[0054] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the disclosed patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A process for preparing denser battery electrodes, characterized in that, Includes the following steps: The battery electrode sheets are rolled and heated to obtain highly elastic electrode sheets; The high-elasticity electrode is first cooled to 0°C by liquid nitrogen injection to obtain a slow-frozen electrode. The slow-freezing electrode is placed in a room temperature environment for buffering, and then the slow-freezing electrode is introduced into a multi-roller assembly for rolling and softening to obtain a softened electrode. The softened electrode sheet is cooled a second time by liquid nitrogen injection to below -30°C to obtain a cold-extracted electrode sheet. The cold-extracted electrode is placed in a constant-temperature environment to release stress, thereby obtaining a densified battery electrode.

2. The process for preparing dense battery electrodes according to claim 1, characterized in that, The cooling rate is 40℃ / s-50℃ / s, and the cooling rate of the cold extraction is 50℃ / s-100℃ / s.

3. The process for preparing dense battery electrodes according to claim 1, characterized in that, The liquid nitrogen injection pressure is 0.5MPa-1.5MPa.

4. The process for preparing dense battery electrodes according to claim 1, characterized in that, The binder for the battery electrode is at least one of polyvinylidene fluoride-hexafluoropropylene, polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

5. The process for preparing dense battery electrodes according to claim 1, characterized in that, The roller pressing pressure is 5MPa-15MPa, and the heating temperature is 80℃-120℃.

6. The process for preparing dense battery electrodes according to claim 1, characterized in that, The slow-freezing electrode sheet is placed in a room temperature environment for buffering, and then the slow-freezing electrode sheet is softened by passing it through multiple rollers to obtain a softened electrode sheet, including the following steps: The slow-freezing electrode at 0℃ is placed in a room temperature environment of 17℃-23℃ for buffering, and the buffering time is 10s-60s. The buffered, slow-freezing electrode sheet is introduced into a multi-roller softening assembly, and the buffered electrode sheet passes through multiple rollers spaced apart in an S-shaped path in sequence.

7. The process for preparing dense battery electrodes according to claim 1, characterized in that, The liquid nitrogen flow rate of the liquid nitrogen injection conforms to the following relationship: Q = k × (ΔT / Δt) × S; Where Q is the flow rate, k is the correction coefficient (k=0.8-1.2), ΔT / Δt is the measured cooling rate, and S is the electrode area.

8. A hot-pressing and cold-extraction device for battery electrodes, characterized in that, The process for preparing dense battery electrode sheets according to any one of claims 1-7 includes a hot pressing module, a cold extraction module, and a pressure leveling module. The hot pressing module is used to roll and heat the battery electrode sheets; The cold extraction module includes a slow-freezing chamber, a room-temperature drying chamber, and a cold extraction chamber arranged in sequence. The slow-freezing chamber and the cold extraction chamber are respectively equipped with liquid nitrogen injection components for injecting liquid nitrogen. The room-temperature drying chamber is equipped with a multi-roller assembly. The slow-freezing chamber is connected to the outlet of the hot-pressing module. The pressure leveling module is connected to the outlet of the cold extraction chamber and is used to provide a constant temperature environment.

9. The battery electrode hot-pressing and cold-extraction equipment according to claim 8, characterized in that, The liquid nitrogen injection assembly includes a condenser tube and a porous injection plate, the porous injection plate being connected to the condenser tube.

10. The battery electrode hot-pressing and cold-extraction equipment according to claim 9, characterized in that, The distance between the outlet of the porous spray plate and the electrode to be cooled is 10mm-30mm, and the spray angle of the outlet of the porous spray plate is 60°-90°.

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