A dry electrode sheet preparation process, a dry electrode sheet, and a battery

Abstract

The application relates to the technical field of battery material preparation, and discloses a dry-method electrode sheet preparation process, a dry-method electrode sheet and a battery. The method comprises the following steps: mixing active material and conductive agent by low-high-low-high alternating mixing at 10-15 DEG C; uniformly dispersing a binder by low-high-low-high alternating mixing at 10-15 DEG C; increasing the temperature of the system by using the friction heat generated by the mixed materials; fixing a fiber network by gradually reducing the speed from 25-30 m / s to 5-10 m / s in stages; and the low-high-low-high alternating mixing is alternating mixing of low linear velocity of 5-10 m / s and high linear velocity of 20-25 m / s. Through the low-high alternating mixing, the friction heat excitation fiberization and the synergistic effect between the stepwise temperature reduction, the technical problems of binder agglomeration, uneven fiberization and impedance increase in the dry-method electrode preparation are solved.

Description

Technical Field

[0001] This invention relates to the field of battery material preparation technology, specifically to a dry electrode sheet preparation process, an electrode sheet, and a battery. Background Technology

[0002] Against the backdrop of the rapid development of the new energy industry, the limitations of traditional wet electrode fabrication processes are becoming increasingly apparent, posing a bottleneck to the further industrialization of lithium-ion batteries. Traditional wet electrode fabrication processes involve complex and energy-intensive steps such as slurry preparation, wet coating, electrode drying, and solvent recovery. Drying and solvent recovery processes alone account for approximately 48% of total energy consumption. Furthermore, the organic solvents used, such as N-methylpyrrolidone (NMP), are toxic and volatile, requiring expensive recovery systems to prevent environmental pollution, significantly increasing equipment investment and operating costs. From a technical perspective, solvent evaporation during drying triggers capillary action, causing binders and conductive agents to migrate and aggregate to the electrode surface, while active materials settle, resulting in delamination of the electrode microstructure, impairing the uniformity of the conductive network, and weakening the bond between the active material and the current collector. In addition, electrodes fabricated using wet processes commonly suffer from cracks and poor flexibility, especially when fabricating thick electrodes required for high energy density, where these defects are more pronounced, limiting the improvement of battery performance.

[0003] Dry electrode technology, as an alternative, demonstrates great potential in energy saving, process simplification, environmental friendliness, and cost reduction due to its outstanding advantages of being solvent-free and requiring no drying throughout the entire process. However, the core technical challenge of dry electrodes lies in controlling the fiberization process of the binder. Taking polytetrafluoroethylene (PTFE) as an example, its fiberization process (i.e., stretching to form a microfiber network under external force) is extremely sensitive to temperature and shear force: if the temperature is too low (e.g., below 19°C), the molecular chains are rigid and difficult to fiberize; improper control of temperature and shear force can easily lead to insufficient fiberization (failure to form a film) or excessive / uniform fiberization (binder agglomeration), both of which will significantly increase electrode impedance and reduce mechanical strength.

[0004] Chinese invention patent application CN115881888A discloses a method for controlling dry electrode fiberization. However, the control method in this patent is too general and lacks a precise strategy for the staged coordinated control of temperature and shear force, which are crucial to the fiberization process. It cannot effectively solve the core problems such as binder agglomeration and uneven fiberization caused by temperature runaway and uneven mixing. At the same time, it may have shortcomings in terms of process feasibility, stability and repeatability. Summary of the Invention

[0005] This invention provides a dry electrode fabrication process, electrode sheet, and battery to solve the problems of uneven fiberization and binder agglomeration caused by temperature runaway and uneven mixing in the existing dry electrode manufacturing process.

[0006] In a first aspect, the present invention provides a dry electrode sheet preparation process, comprising:

[0007] Mix at 10-15℃ using alternating low-high-low-high speeds to thoroughly mix the active material and conductive agent;

[0008] Mix the adhesive at 10-15℃ using alternating low-high-low-high speeds to disperse the binder;

[0009] Fiberization involves heating the system using the frictional heat of the mixed materials;

[0010] Cooling is achieved by gradually reducing the speed from 25-30 m / s to 5-10 m / s in stages, using a stepped reduction method to relax and fix the fiber network.

[0011] The alternating low-high-low-high speed mixing refers to the alternating mixing of low linear velocity of 5-10 m / s and high linear velocity of 20-25 m / s.

[0012] In one alternative implementation, the following steps are included:

[0013] S0 premix: Add the dried negative electrode active material and conductive agent to the mixer in proportion;

[0014] S1 mixing: At 10-15℃, mix at a low linear velocity of 5-10m / s for 60-180s and mix at a high linear velocity of 20-25m / s for 60-180s alternately.

[0015] S2 Mixing: Add adhesive, and mix at 10-15℃ with a low linear speed of 5-10m / s for 60-180s and a high linear speed of 20-25m / s for 60-180s alternately.

[0016] S3 fiberization: First, mix at a linear velocity of 20-25 m / s. When the material temperature reaches 50-60℃, increase the linear velocity to 30-40 m / s and shear at 80-120℃.

[0017] S4 Cooling: Staged speed reduction, gradually reducing the linear velocity from 25-30m / s to 5-10m / s in stages until the material temperature drops below 30℃;

[0018] S5 pre-discharge dispersion: At a linear velocity of 15-20 m / s, the material is rapidly dispersed to break up soft agglomerates;

[0019] S6 film-forming composite: The fibrous material obtained in S5 is calendered into a film and then hot-pressed on both sides to obtain a dry electrode sheet.

[0020] In one optional implementation, S3 involves mixing at a linear velocity of 20-25 m / s for 180-300 s, shearing for 180-300 s; S5 involves rapid dispersion for 10-60 s; and / or

[0021] In one optional implementation, the S4 staged deceleration procedure is as follows: 25-30 m / s held for 60-90 seconds → 20-25 m / s held for 60-90 seconds → 15-20 m / s held for 60-90 seconds → 10-15 m / s held for 60-90 seconds → 5-10 m / s until the material temperature is below 30°C; and / or

[0022] The S6 calendering film forming temperature is 80-120℃, and the pressure is 10-30T.

[0023] In one optional embodiment, the particle size of the negative electrode active material is 8-14 μm, and the particle size of the binder is 300-430 μm.

[0024] Optionally, S3 fiberization forms an interwoven three-dimensional fiber network structure that encapsulates the active material particles, wherein the aspect ratio of the three-dimensional fiber network structure is 50:1 to 1000:1.

[0025] In one optional embodiment, the negative electrode active material is graphite, silicon carbide, silicon suboxide, lithium-silicon alloy, and / or lithium powder; or

[0026] The conductive agent is acetylene black, superconducting carbon black, carbon nanotubes, carbon fibers, Ketjen black, and / or graphene; or

[0027] The adhesive is a fiber-forming adhesive selected from polytetrafluoroethylene, styrene-butadiene rubber, polypropylene, polyethylene and / or ethylene-vinyl acetate copolymer.

[0028] In one optional embodiment, the process uses the following raw material components in weight percentages to prepare dry electrode sheets: 94%-98% negative electrode active material, 1%-3% conductive agent, and 1%-3% binder;

[0029] In one alternative implementation, the cooling is achieved via a circulating cooling water system in the mixer jacket; and / or

[0030] The mixer is a 10L high-speed shear mixer or a 10L plow-type mixer. In the S0 premixing stage, the material is controlled to occupy 40%-60% of the total volume of the mixer's hopper.

[0031] Secondly, the present invention also provides a dry electrode sheet, which is prepared by the above-mentioned dry electrode mixing process.

[0032] In one optional embodiment, the raw material components by weight percentage are: 94%-98% negative electrode active material, 1%-3% conductive agent, and 1%-3% binder.

[0033] In one optional implementation, the raw material components by mass percentage are:

[0034] Graphite comprises 94%; a composite conductive agent consisting of acetylene black and carbon nanotubes at a mass ratio of 3:1 comprises 3%; a composite binder consisting of polytetrafluoroethylene and styrene-butadiene rubber at a mass ratio of 2:1 comprises 3%; or

[0035] The composite negative electrode active material, composed of silicon suboxide and lithium powder at a mass ratio of 2:3, accounts for 98%; the composite conductive agent, composed of conductive carbon black and carbon fiber at a mass ratio of 1:1, accounts for 1%; and the composite binder, composed of polypropylene and polyethylene at a mass ratio of 2:1, accounts for 1%; or

[0036] The composite negative electrode active material, composed of graphite / silicon-carbon at a mass ratio of 3:1, accounts for 96%; graphene accounts for 1.5%; and the composite binder, composed of polyethylene / EVA (ethylene-vinyl acetate copolymer) at a mass ratio of 1:2, accounts for 2.5%; or

[0037] The composite negative electrode active material, composed of lithium silicon alloy and hard carbon in a mass ratio of 3:2, accounts for 95%; the composite conductive agent, composed of Ketjen black and conductive carbon black in a mass ratio of 3:1, accounts for 3%; and the composite binder, composed of styrene-butadiene rubber and polypropylene in a mass ratio of 3:1, accounts for 2%.

[0038] Thirdly, the present invention also provides a battery comprising the aforementioned dry electrode sheet.

[0039] The technical solution of this invention has the following advantages:

[0040] 1. The dry electrode sheet preparation process provided by this invention adopts an alternating rotation speed strategy of "low-high-low-high" combined with low temperature (10-15℃). This avoids material agglomeration or uneven binder distribution caused by local overheating or uneven shearing, thereby promoting the uniform dispersion of active materials, conductive agents, and binders, forming a more stable composite structure. The low temperature environment (10-15℃) is close to or slightly higher than the glass transition temperature of the binder. At this temperature, the binder is in a "hard and tough" state, possessing both strength and the potential to be stretched. This avoids the binder becoming excessively soft, sticky, and agglomerated at excessively high temperatures, and also prevents the binder from becoming too brittle and difficult to fiberize at excessively low temperatures. The low temperature also inhibits premature runaway of frictional heat. The alternating high and low rotation speeds allow the binder to be uniformly stretched and extended into an adhesive layer. The initial thin film or short fiber network on the surface of the active material and conductive agent is formed. During the fiberization stage, the material spontaneously heats up due to frictional heat, avoiding the temperature gradient or energy consumption that may be caused by external heating. This makes the fiberization process of the binder more natural and uniform. The stepped speed reduction design (gradually decreasing from 25-30m / s to 5-10m / s) allows the fiber network to be gradually fixed during the relaxation process, reducing internal stress and forming a fiber network with good three-dimensional connectivity and high mechanical strength. This is beneficial to the flexibility and bonding strength of the electrode. The uniform conductive network and stable fiber structure help improve the electronic conductivity and ion transport efficiency of the electrode, thereby improving the rate performance and cycle stability of the battery. It also avoids structural damage to the active material caused by high temperature or excessive shear, maintains the integrity of the material, and is beneficial to capacity retention and lifespan improvement.

[0041] 2. The dry electrode sheet fabrication process provided by this invention refines the process into six specific steps, S0 to S6. Its advantage lies in providing a complete closed-loop process and operability. In particular, it clarifies the temperature range for "frictional heating" to raise the system temperature to (50-60℃) and the temperature range for fiber shearing (80-120℃), as well as the starting point for "staged rate reduction" (25-30 m / s). This makes the entire process control points clearer, enhancing the controllability and repeatability of the process.

[0042] 3. In the premixing stage of the dry electrode preparation process provided by this invention, the material accounts for 40%-60% of the silo volume, balancing equipment utilization and mixing space. Too much material will lead to uneven mixing, while too little will result in low efficiency. The mixing / shearing time of key steps is limited, achieving quantitative control of energy input (shear work) and the reaction process. The alternating total mixing time (240-720s) and fiberization time (180-300s) ensure an optimal balance between material mixing uniformity and fiberization degree. This avoids uneven mixing or incomplete fiberization due to insufficient time, and also prevents energy waste or excessive shearing damage to the fiber network due to excessive time. Rapid dispersion (10-60s) breaks up slight agglomerations that may be formed due to static electricity before discharge, ensuring the looseness and flowability of the material, which is beneficial for subsequent rolling. High-speed shearing at 80-120℃ puts the formed polymer fibers (such as PTFE, PE, EVA, etc.) in an ideal thermoplastic state, enhancing their molecular chain segment mobility. Under pressure of 10-30T, the contact points between fibers and between fibers and active material / conductive agent particles undergo localized softening, deformation, and fusion, forming numerous strong "thermal welding points." This greatly enhances the cohesion of the network and the anchoring force for the active particles, resulting in extremely high peel strength and cohesion of the electrode film. Under the combined action of heat and pressure, the previously formed three-dimensional fiber network is densified rather than destroyed. The fibers are compressed and interwoven more tightly in a thermoplastic state, but their long-range continuous topology is preserved, ultimately forming a "high-density, high-toughness, and high-conductivity" composite structure. This allows the electrode film to have both high mechanical strength to withstand rolling and slitting, and sufficient flexibility and elasticity to buffer volume changes during charging and discharging.

[0043] 4. The dry electrode fabrication process provided by this invention specifies a step-down rate reduction procedure (25-30 m / s held for 60-90 seconds → 20-25 m / s held for 60-90 seconds → 15-20 m / s held for 60-90 seconds → 10-15 m / s held for 60-90 seconds → 5-10 m / s until the material temperature is below 30°C), providing an optimal rate reduction curve to ensure the fiber network is fully relaxed, thereby achieving optimal toughness and strength; it also limits the negative electrode active material (8-14 μm). The particle size range of active materials (300-430 μm) and binder is optimized to improve the matching and filling properties between particles. The active material with a moderate particle size is conducive to the formation of high-density electrodes, while the binder particles with a specific particle size are more easily stretched into fibers with a high aspect ratio under shear. The combination of the two makes the fiber network achieve the best effect of wrapping and bonding the active particles. The aspect ratio range of the fiber network (50:1~1000:1) is given, which emphasizes the deterministic structural results that the process can achieve. This is direct microscopic evidence of the high performance of the electrode.

[0044] 5. The dry electrode sheet preparation process provided by this invention limits the specific materials and clarifies the broad material compatibility and technical universality of this process. The process is not only applicable to conventional graphite anodes, but also particularly applicable to high-capacity anode systems with huge volume expansion such as silicon-carbon, silicon suboxide, and lithium silicon alloy. It is also compatible with various mainstream conductive agents and fiber-forming binders, demonstrating strong technical inclusiveness.

[0045] 6. The dry electrode preparation process provided by this invention limits the weight ratio of the electrode formulation (94%-98% active material, 1%-3% conductive agent, and 1%-3% binder), determining the optimal composition window for achieving high-performance dry electrodes. The high content of active materials ensures high energy density, while an extremely low content (1-3%) of binder can form an effective network, highlighting the advantage of this method in binder utilization efficiency and helping to reduce the proportion of inactive materials. It also limits the cooling method (jacketed circulating water) and equipment selection (10L high-speed shear or plow-type mixer), and supplements the requirement that the premixed material content accounts for 40%-60% of the material submitted to the silo, providing clear equipment conditions and operating parameters for industrial implementation. This provides clear engineering guidance for the process to move from the laboratory to pilot-scale amplification, enhancing the industrial implementability of the patent.

[0046] 7. The dry electrode sheet provided by the present invention has extremely high mechanical strength, excellent flexibility, good electronic conductivity, and can be directly used for subsequent battery assembly.

[0047] 8. The raw material ratio design of the dry electrode sheet provided by this invention synergistically solves the problem of balancing high energy density, high conductivity, and high mechanical strength in the preparation of dry electrodes; the proportion of 94%-98% highly active materials directly increases the unit mass capacity of the electrode, enabling the electrode sheet to store more charge in a limited space; although the proportion of 1%-3% conductive agent is low, through the alternating mixing of "low-high-low-high" in the process, a uniform three-dimensional conductive network is formed, which reduces the internal resistance of the electrode; the 1%-3% binder forms a dense three-dimensional network after fiberization, which encapsulates the active material and endows the electrode with high peel strength and flexibility.

[0048] 9. The dry electrode sheets provided by this invention demonstrate the best performance that can be achieved by the technology of this invention through specific and optimized embodiments. These formulations cover a variety of systems from traditional graphite to advanced silicon-based and lithium metal composite materials, proving the specific application and excellent effect of the technology of this invention in the preparation of next-generation high-energy-density battery anodes.

[0049] 10. The dry-process negative electrode battery provided by this invention integrates all the advantages of dry-process electrode sheets, achieving significant results in high performance, high reliability, and high process stability. This battery is suitable for demanding applications such as 5G communication and the Internet of Things, demonstrating the complete technical advantages of this invention from materials to devices. Attached Figure Description

[0050] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0051] Figure 1 This is a scanning electron microscope image of the negative electrode powder after the graphite, conductive agent, and binder in the raw material formulation of Example 1 have been thoroughly mixed and fiberized.

[0052] Figure 2 This is a photograph of the dry negative electrode sheet prepared in Example 1;

[0053] Figure 3 This is a scanning electron microscope image of the surface of the dry negative electrode sheet prepared in Example 1;

[0054] Figure 4 This is a scanning electron microscope (SEM) image of the cross-section of the dry negative electrode sheet prepared in Example 1;

[0055] Figure 5 This is a scanning electron microscope image of the surface of the dry negative electrode sheet prepared in Example 3;

[0056] Figure 6 This is a scanning electron microscope (SEM) image of the negative electrode powder after the graphite, conductive agent, and binder in the raw material formulation of Example 1 have been thoroughly mixed and fiberized at 60°C. Detailed Implementation

[0057] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0058] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0059] Raw material preparation and pretreatment

[0060] Raw material specifications: Anode active materials: graphite (D50=8-14μm), silicon carbide, hard carbon, silicon suboxide, lithium silicon alloy, lithium powder.

[0061] Conductive agents: acetylene black, conductive carbon black, carbon nanotubes, carbon fiber, Ketjen black, graphene.

[0062] Adhesives: Fiberizable adhesives, such as polytetrafluoroethylene (PTFE, model F-106C, particle size 300-430μm), styrene-butadiene rubber, polypropylene, polyethylene, and ethylene-vinyl acetate copolymer (EVA).

[0063] The mass ratios of raw material components in Examples 1-4 are shown in Table 1.

[0064] Table 1. Raw material component ratios (mass ratio, mass percentage) for Examples 1-4

[0065]

[0066] Example 1

[0067] S0 feeding stage: First, dry the negative electrode active material graphite in an 80℃ vacuum oven for more than 12 hours to remove moisture. Then, use a 10L high-speed shear mixer to add 5kg of dried graphite, conductive agent acetylene black and carbon nanotubes (mass ratio 3:1) in sequence, controlling the premix to occupy 60% of the total volume of the silo.

[0068] S1 Dispersion Stage: Start the mixer, turn on the circulating cooling water system, control the temperature of the mixing chamber at 10℃, mix at a low linear velocity of 5m / s for 60s, switch to a high linear velocity of 25m / s for 180s, then mix at a low linear velocity of 10m / s for 90s, and then mix at a high linear velocity of 20m / s for 100s.

[0069] S2 Mixing Stage: Add the weighed binder polytetrafluoroethylene and styrene-butadiene rubber (mass ratio 2:1) to the material in step S1 and continue mixing. Mix at a low linear speed of 8m / s for 60s, switch to a high linear speed of 23m / s for 90s, then mix at a low linear speed of 10m / s for 180s, and then mix at a high linear speed of 23m / s for 160s. The temperature of the entire process is controlled at 10℃ by circulating cooling water.

[0070] S3 Fiberization Stage: The circulating cooling water system is shut off, and the mixture is mixed at a linear velocity of 25 m / s for 200 s, relying on the frictional heat of the mixture to allow the temperature to rise naturally and slowly. When the material temperature reaches 50℃, the linear velocity is increased to 35 m / s in one go, and the material from step S2 is fiberized through high-speed shearing. High-speed shearing is performed at 80℃ for 280 seconds to form a uniformly interwoven three-dimensional fiber network structure. The three-dimensional fiber network structure encapsulates the active material particles, with the binder length ranging from 1-10 μm and the diameter ranging from 10-20 nm.

[0071] S4 Cooling Stage: Restart the cooling system and use a phased rate reduction: 30m / s for 90s → 20m / s for 60s → 18m / s for 80s → 12m / s for 90s → 5m / s until the material temperature is below 30℃.

[0072] S5 pre-discharge stage: At a linear velocity of 20 m / s, the fibrous material obtained in step S4 is rapidly dispersed for 40 seconds.

[0073] S6 Roller Pressing Stage: The fibrous material obtained in S5 is fed to a multi-stage calendering roll press and calendered into a self-supporting film at 120℃ and 10T pressure. Then, this film is hot-pressed and laminated with a copper foil current collector on both sides to prepare a dry electrode sheet with a dense structure and a strong bond with the current collector.

[0074] Example 2

[0075] Compared with Example 1, Example 2 has the same process steps, but the composition and ratio of raw materials are different (see Table 1 for details), and the detailed process parameters are also different. The detailed process parameters for each step are as follows:

[0076] S0 feeding stage: The total weight of the negative electrode active material is 4kg, and the premixed material is controlled to account for 50% of the total volume of the silo;

[0077] S1 Dispersion Stage: Control the mixing chamber temperature at 15℃. Mix at a low linear velocity of 10m / s for 180s, switch to a high linear velocity of 20m / s for 60s, then mix at a low linear velocity of 5m / s for 60s, and then mix at a high linear velocity of 25m / s for 120s.

[0078] S2 Mixing Stage: Material mixing, low linear speed 5m / s mixing for 180s, switch to high linear speed 25m / s mixing for 120s, then low linear speed 7m / s mixing for 60s, high linear speed 25m / s mixing for 120s, control the temperature at 15℃ throughout the process;

[0079] S3 fiberization stage: First, mix at a linear speed of 25m / s for 200s. When the material temperature rises to 50℃, increase the linear speed to 35m / s in one go and shear at high speed at 120℃ for 280 seconds; the three-dimensional fiber network structure encapsulates the active material particles, with the binder length in the range of 1-10um and the diameter in the range of 10-20nm.

[0080] S4 Cooling Stage: Staged speed reduction and cooling process: 25m / s held for 60s → 20m / s held for 60s → 15m / s held for 90s → 10m / s held for 60s → 5m / s held until the material temperature is below 30℃.

[0081] S5 pre-discharge stage: rapid dispersion for 60 seconds at a linear velocity of 15m / s;

[0082] S6 Roller Pressing Stage: The film is rolled into a self-supporting film at 80℃ and 10T pressure.

[0083] Example 3

[0084] Compared with Example 1, this embodiment has the same process steps, but the composition and ratio of raw materials are different (see Table 1 for details), and the detailed process parameters are also different. The detailed process parameters for each step are as follows:

[0085] S0 feeding stage: The total weight of the negative electrode active material is 3.5 kg, and the premixed material accounts for 40% of the total volume of the silo;

[0086] S1 Dispersion Stage: Control the mixing chamber temperature at 12℃. Mix at a low linear velocity of 8m / s for 150s, switch to a high linear velocity of 21m / s for 100s, then mix at a low linear velocity of 9m / s for 180s, and then mix at a high linear velocity of 24m / s for 60s.

[0087] S2 Mixing Stage: Mix the materials, mix at a low linear speed of 10m / s for 80s, switch to a high linear speed of 20m / s for 180s, then mix at a low linear speed of 5m / s for 70s, and then mix at a high linear speed of 20m / s for 60s, controlling the temperature at 12℃ throughout the process;

[0088] S3 fiberization stage: First, mix at a linear velocity of 25m / s for 190s. When the material temperature rises to 50℃, increase the linear velocity to 35m / s in one go and shear at high speed at 100℃ for 300 seconds. The three-dimensional fiber network structure encapsulates the active material particles. The binder length is in the range of 1-10um and the diameter is in the range of 10-20nm.

[0089] S4 Cooling Stage: Staged speed reduction and cooling process, 28m / s held for 90s → 22m / s held for 60s → 18m / s held for 90s → 13m / s held for 70s → 9m / s held until the material temperature is below 30℃;

[0090] S5 pre-discharge stage: Rapidly disperse for 10 seconds at a linear velocity of 20m / s;

[0091] S6 Roller Pressing Stage: The film is rolled into a self-supporting membrane at 120℃ and 30T pressure.

[0092] Example 4

[0093] Compared with Example 1, this embodiment has the same process steps, but the composition and ratio of raw materials are different (see Table 1 for details), and the detailed process parameters are also different. The detailed process parameters for each step are as follows:

[0094] S0 feeding stage: The total weight of the negative electrode active material is 3kg, and the premixed material accounts for 45% of the total volume of the silo;

[0095] S1 Dispersion Stage: Control the mixing chamber temperature at 13℃. Mix at a low linear velocity of 7m / s for 110s, switch to a high linear velocity of 21m / s for 120s, then mix at a low linear velocity of 8m / s for 130s, and then mix at a high linear velocity of 23m / s for 140s;

[0096] S2 Mixing Stage: Mix the materials, mix at a low linear speed of 10m / s for 130s, switch to a high linear speed of 24m / s for 60s, then mix at a low linear speed of 10m / s for 70s, and then mix at a high linear speed of 22m / s for 180s. The temperature of the entire process is controlled at 14℃ by circulating cooling water.

[0097] S3 fiberization stage: mixing at a linear velocity of 23m / s for 300s; when the material temperature rises to 50℃, the linear velocity is increased to 40m / s in one go, and high-speed shearing is performed at 110℃ for 260 seconds; the three-dimensional fiber network structure encapsulates the active material particles, with the binder length in the range of 1-10um and the diameter in the range of 10-20nm.

[0098] S4 Cooling Stage: Staged speed reduction and cooling process: 26m / s held for 80s → 21m / s held for 90s → 19m / s held for 60s → 14m / s held for 80s → 6m / s held until the material temperature is below 30℃.

[0099] S5 pre-discharge stage: Rapidly disperse for 50 seconds at a linear velocity of 20m / s;

[0100] S6 Roller Pressing Stage: The film is rolled into a self-supporting membrane at 100℃ and 15T pressure.

[0101] Comparative Example 1

[0102] The electrode sheet was prepared according to the method of Example 1 of Chinese Invention Patent Application Publication No. CN115881888A. The fiberization control method of that patent lacks staged temperature control and shear force coordinated control.

[0103] Experimental Example 1

[0104] Electrode performance data of Examples 1-4 and Comparative Example 1

[0105] This experimental example uses a pouch cell for testing. The positive electrode of the pouch cell is made with the following proportions: positive electrode active material NCM811 (NCM represents its main components nickel, cobalt, and manganese, while 811 represents the ratio of the three components 8:1:1) 92% by weight, conductive agent SP 2% by weight, conductive agent activated carbon 2% by weight, and binder PTFE 4% by weight. It is combined with the negative electrode of Examples 1-4 and Comparative Example 1 to make a small pouch cell (including 2 single-sided positive electrode sheets, 1 double-sided negative electrode sheet, and conventional commercially available electrolyte).

[0106] The testing standards are as follows:

[0107] Peel strength: ASTM D903, unit N / m.

[0108] Ionic conductivity: measured by electrochemical impedance spectroscopy (EIS), unit S / cm.

[0109] First-time efficiency and capacity: Soft-pack battery test (voltage range 2.75-4.2V, current 0.1C), first-time efficiency = first discharge capacity / first charge capacity × 100%.

[0110] Internal resistance: AC impedance method, unit mΩ.

[0111] Table 2 Performance data of pouch cells made from electrode sheets of Examples 1-4 and Comparative Example 1

[0112]

[0113] Table 2 shows the following:

[0114] The peel strength of the pouch cells made from the electrode sheets of Examples 1-4 (27.4-30.6 N / m) is significantly higher than that of the pouch cell made from the electrode sheet of Comparative Example 1 (20.1 N / m), an improvement of over 36%. This indicates that the present invention, through a staged temperature control and shear force synergistic strategy, enables the PTFE binder to form a uniform and dense three-dimensional fiber network structure, greatly enhancing the bonding force between the active material and the current collector.

[0115] The ionic conductivity of the pouch cells made from the electrode sheets of Examples 1-4 (8.68-10.32 S / cm) is approximately 53%-82% higher than that of Comparative Example 1 (5.66 S / cm). The alternating "low-high-low-high" linear velocity mixing strategy in the S1 / S2 stages of this invention ensures that the conductive agents (such as carbon nanotubes and Ketjen Black) are uniformly dispersed in the active material, forming a continuous conductive network. Furthermore, the pouch cell made from the electrode sheets of Comparative Example 1 suffers from uneven fibrosis, leading to binder agglomeration and hindering ion transport pathways.

[0116] The pouch cells made from the electrode sheets of Examples 1-4 exhibit higher initial efficiency (82.98%-84.76%) and capacity (255-262mAh) than the pouch cells made from the electrode sheets of Comparative Example 1 (81.20%, 247mAh). The process of this invention avoids the damage to the active material structure caused by excessive fiberization (such as cracking of graphite particles), reduces side reactions, and improves lithium-ion insertion / extraction efficiency.

[0117] The internal resistance (60.8-69.5 mΩ) of the pouch cells made from the electrode sheets of Examples 1-4 is significantly lower than that of the pouch cell made from the electrode sheet of Comparative Example 1 (89.7 mΩ), a reduction of approximately 30%. This further verifies the superiority of the conductive network in the electrodes of the present invention.

[0118] Experimental Example 2. Process Stability and Repeatability

[0119] The standard deviation of the performance data (e.g., peel strength ±0.5 N / m) of the pouch cells made from the electrode sheets of Examples 1-4 is extremely small, indicating that the present invention achieves batch-to-batch stability by precisely controlling temperature, linear velocity and time parameters, thus meeting the requirements of industrial production.

[0120] Experimental Example 3. Selection of shear temperature during the fiberization stage and analysis of the attached data:

[0121] If the temperature is too low, the adhesive will agglomerate significantly, resulting in insufficient fiberization and uneven adhesive distribution. Figure 6 The image shows an electron microscope image of the binder at 60℃. The red box indicates that the binder has large agglomerations, meaning that the binder has not been fully fiberized and there is no obvious uniform fiberization. Excessive temperature, exceeding 120℃, leads to longer mixing time and higher energy consumption. It also reduces the electrode peel strength by 12-18 N / m.

[0122] Chart data analysis:

[0123] Figure 1 The uniform fine filaments observed in the scanning electron microscope indicate that PTFE is evenly distributed after the graphite negative electrode is fiberized, which helps to achieve uniform bonding between powders and between powders and current collectors after rolling. At the same time, no obvious agglomeration of conductive agent was observed, indicating that the material is relatively uniformly dispersed. Overall, this helps to improve the consistency of the electrode sheet.

[0124] from Figure 2 The photo shows that the electrode surface is clean and without any abnormalities or defects, indicating that the electrode rolling and current collector are well combined and the electrode has high consistency.

[0125] Figure 3The uniform fine filaments in the scanning electron microscope images indicate that PTFE is evenly distributed on the electrode surface, suggesting good lateral bonding between the electrode sheets; at the same time, no agglomeration of conductive agent was observed, indicating that the material is relatively uniformly dispersed; overall, this helps to improve the consistency of the electrode sheets.

[0126] Figure 4 The uniform fine filaments in the cross-sectional scanning electron microscope image indicate that PTFE is evenly distributed in the longitudinal direction of the electrode sheets, indicating good bonding between the electrode sheets in the longitudinal direction and good bonding with the current collector interface; at the same time, no agglomeration of conductive agent was observed, indicating that the material is relatively uniformly dispersed; overall, this helps to improve the consistency of the electrode sheets.

[0127] Figure 5 The uniform fine filaments in the scanning electron microscope image of the electrode surface indicate that PTFE is evenly distributed on the electrode surface, indicating good lateral bonding between the electrodes; at the same time, no agglomeration of conductive agent was observed, indicating that the material is relatively uniformly dispersed; overall, this helps to improve the consistency of the electrode.

[0128] Figure 6 The fiberization temperature of the scanning electron microscope image is 60℃. The red box in the scanning electron microscope shows that the binder agglomerates are relatively large, indicating that the binder is not fully fiberized and there is no obvious uniform fiberization phenomenon.

[0129] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A dry electrode sheet fabrication process, characterized in that, include: Mix at 10-15℃ using alternating low-high-low-high speeds to thoroughly mix the active material and conductive agent; Mix the adhesive at 10-15℃ using alternating low-high-low-high speeds to disperse the binder; Fiberization involves heating the system using the frictional heat of the mixed materials; Cooling is achieved by gradually reducing the speed from 25-30 m / s to 5-10 m / s in stages to relax and fix the fiber network. The alternating low-high-low-high speed mixing is a mixture of low linear velocity of 5-10 m / s and high linear velocity of 20-25 m / s. Follow these steps: S0 premix: The dried negative electrode active material and conductive agent are added to the mixer for premixing; S1 mixing: At 10-15℃, mix at a low linear velocity of 5-10m / s for 60-180s and mix at a high linear velocity of 20-25m / s for 60-180s alternately. S2 Mixing: Add adhesive, and mix at 10-15℃ with a low linear speed of 5-10m / s for 60-180s and a high linear speed of 20-25m / s for 60-180s alternately. S3 fiberization: First, mix at a linear velocity of 20-25 m / s. When the material temperature reaches 50-60℃, increase the linear velocity to 30-40 m / s and shear at 80-120℃. S4 Cooling: Staged speed reduction, gradually reducing the linear velocity from 25-30m / s to 5-10m / s, continuing until the material temperature drops below 30℃; S5 pre-discharge dispersion: disperse S4 material at a linear velocity of 15-20 m / s; S6 film lamination: The material obtained in S5 is calendered into a film and then hot-pressed on both sides for lamination. S3 is mixed at a linear velocity of 20-25 m / s for 180-300 s, and sheared for 180-300 s; and / or The dispersion time described in S5 is 10-60 seconds; and / or The temperature for S6 calendering film formation is 80-120℃, and the pressure is 10-30T. The phased speed reduction procedure described in S4 is as follows: 25-30m / s held for 60-90 seconds → 20-25m / s held for 60-90 seconds → 15-20m / s held for 60-90 seconds → 10-15m / s held for 60-90 seconds → 5-10m / s until the material temperature is below 30℃. The particle size of the negative electrode active material is 8-14 μm, and the particle size of the binder is 300-430 μm. S3 binder is fiberized to form an interwoven three-dimensional fiber network structure, which encapsulates the active material. The aspect ratio of the three-dimensional fiber network structure is 50:1 to 1000:

1.

2. The process according to claim 1, characterized in that, The negative electrode active material is graphite, silicon carbide, silicon suboxide, lithium-silicon alloy, and / or lithium powder; and / or The conductive agent is acetylene black, superconducting carbon black, carbon nanotubes, carbon fibers, Ketjen black, and / or graphene; and / or The adhesive is a fiber-forming adhesive selected from polytetrafluoroethylene, styrene-butadiene rubber, polypropylene, polyethylene and / or ethylene-vinyl acetate copolymer.

3. The process according to claim 2, characterized in that, The process uses the following raw material components by mass percentage to prepare dry electrode sheets: negative electrode active material 94%-98%, conductive agent 1%-3%, and binder 1%-3%; Cooling is achieved through a circulating cooling water system in the mixer jacket; and / or The mixer is a 10L high-speed shear mixer or a 10L plow-type mixer, and the material in the S0 premixing stage accounts for 40%-60% of the bin volume.

4. A dry-process electrode sheet, characterized in that, It is prepared by the process described in any one of claims 1 to 3.

5. The dry electrode sheet according to claim 4, characterized in that, The raw material composition by weight percentage is: 94%-98% negative electrode active material, 1%-3% conductive agent, and 1%-3% binder.

6. The dry electrode sheet according to claim 5, characterized in that, The raw material components by mass percentage are as follows: Graphite comprises 94%; a composite conductive agent consisting of acetylene black and carbon nanotubes at a mass ratio of 3:1 comprises 3%; a composite binder consisting of polytetrafluoroethylene and styrene-butadiene rubber at a mass ratio of 2:1 comprises 3%; or The composite negative electrode active material, composed of silicon suboxide and lithium powder at a mass ratio of 2:3, accounts for 98%; the composite conductive agent, composed of conductive carbon black and carbon fiber at a mass ratio of 1:1, accounts for 1%; and the composite binder, composed of polypropylene and polyethylene at a mass ratio of 2:1, accounts for 1%; or The composite negative electrode active material, composed of graphite / silicon-carbon at a mass ratio of 3:1, accounts for 96%; graphene accounts for 1.5%; and the composite binder, composed of polyethylene / EVA (ethylene-vinyl acetate copolymer) at a mass ratio of 1:2, accounts for 2.5%; or The composite negative electrode active material, composed of lithium silicon alloy and hard carbon in a mass ratio of 3:2, accounts for 95%; the composite conductive agent, composed of Ketjen black and conductive carbon black in a mass ratio of 3:1, accounts for 3%; and the composite binder, composed of styrene-butadiene rubber and polypropylene in a mass ratio of 3:1, accounts for 2%.

7. A battery, characterized in that, It includes a dry electrode sheet as described in any one of claims 4-6.

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