Self-supporting membrane for dry-method electrode and preparation method of dry-method electrode

Abstract

The invention discloses a self-supporting membrane for a dry-method electrode and a preparation method of the dry-method electrode. In the preparation process of the self-supporting diaphragm for the dry-method electrode, the material mixing process of the self-supporting diaphragm comprises the steps of firstly carrying out medium-free mixing and then carrying out medium mixing; wherein the medium-free mixing refers to mixing depending on the low-strength shearing effect generated by material self-overturning and self-circulation caused by overall movement of a mixing cavity and mutual friction between materials in the mixing process; a material of the dry-method electrode is placed in the mixing cavity; the medium mixing means that a functional structural member used for stirring, shearing or colliding is arranged in the mixing cavity. According to the invention, a'stepped controllable mixing 'strategy is initiated for the first time, the root problem of non-uniform dispersion and fibrosis is solved, a traditional single and rough mixing mode is abandoned, medium-free mixing and medium mixing are innovatively and organically combined, and performance fluctuation caused by non-uniform mixing is completely eradicated from the source.

Description

Technical Field

[0001] This invention relates to the field of electrode materials technology, and in particular to a self-supporting film for dry electrode and a method for preparing dry electrode. Background Technology

[0002] As lithium-ion batteries and related electrochemical energy storage devices develop towards higher energy density and green manufacturing, dry electrode fabrication processes have attracted widespread attention due to their elimination of organic solvents, low energy consumption, and simplified procedures. In dry electrode systems, electrode materials are typically composed of active substances, conductive agents, and fibrous polymer binders, and the uniformity of their mixing has a decisive influence on the mechanical and electrochemical properties of the electrode.

[0003] Dry electrode fabrication is becoming an industry trend due to its solvent-free process, significantly reduced energy consumption, and reduced pollution. Unlike wet processes, the dispersion of components in dry processes relies entirely on mechanical mixing, especially the distribution of the binder during mixing, which directly affects the subsequent construction of the conductive-bonded network. However, current dry electrode fabrication suffers from uneven distribution of different components within the mixing chamber, and the binder is prone to agglomeration, ultimately leading to non-uniform internal electrode structure and poor performance consistency. These problems are particularly prominent in the fabrication of thick electrodes or high areal density electrodes, and have become significant factors restricting the stability and large-scale application of dry electrode processes.

[0004] Therefore, a new method for preparing dry electrodes is urgently needed to solve the problem of uneven material distribution in dry systems. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing a self-supporting membrane for dry electrodes and a dry electrode. This method ensures that all components (especially the binder) are highly uniformly dispersed at the microscale, enabling the stable preparation of a high-strength, tough, thick-film dry electrode.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a self-supporting membrane for dry electrode, wherein, in the preparation process of the self-supporting membrane for dry electrode, the material mixing process of the self-supporting membrane is first mixed without a medium, and then mixed with a medium.

[0008] Wherein, the medium-free mixing refers to mixing that relies on the overall movement of the mixing chamber to induce material self-turning, self-circulation, and low-intensity shearing action generated by mutual friction between materials; the mixing chamber contains the material of the dry electrode;

[0009] The term "medium-based mixing" refers to the presence of functional structural components within the mixing chamber for stirring, shearing, or collision.

[0010] In this process, after adding any type of material, mixing without a medium is performed first, followed by mixing with a medium. In this step, the materials are categorized as follows: conductive agent is one type of material, binder is another, and active substance is yet another. For example, even if two active substances are used, they are considered as one type of material.

[0011] The self-supporting membrane is made of conductive agents, binders, and active substances.

[0012] The material mixing process of the self-supporting membrane includes the following steps:

[0013] (1) The conductive agent and the binder are mixed without a medium to obtain mixture A;

[0014] (2) Mixture A is mixed with a medium to obtain mixture B;

[0015] (3) Mixture B with the active substance without a medium to obtain mixture C;

[0016] (4) Mixture C is mixed with a medium to obtain mixture D.

[0017] The media-free mixing is achieved through a mixing device with a closed mixing chamber. The interior of the mixing chamber is a hollow structure and does not contain any functional structural mixing components for stirring, shearing, or collision. The media-free mixing is achieved through the rolling, flipping, oscillating, planetary revolution, or a combination thereof of the mixing chamber.

[0018] The mixing equipment used for the medialess mixing is a ballless mixer;

[0019] And / or, the mixing of the medium is achieved using a high-speed mixer.

[0020] Preferably, the rotation speed of the ballless mixer in the medialess mixing is 200~600 rpm, and the medialess mixing time is 10~30 minutes;

[0021] The high-speed mixer rotates at 400-600 rpm, and the mixing time with the medium is 10-30 minutes.

[0022] The media-free mixing is segmented mixing, and the parameters of media-free mixing in different stages are not exactly the same.

[0023] The medium-mixing is segmented mixing, and the parameters of the medium-mixing in different stages are not exactly the same.

[0024] The method for preparing the dry electrode includes the following steps:

[0025] S1: Mix the materials of the dry electrode;

[0026] S2: The mixture obtained in step S1 is subjected to high shear force fiberization treatment; the high shear force fiberization treatment is achieved by air jet milling;

[0027] S3: The fibrous mixture obtained in step S2 is subjected to a film-forming process to obtain a self-supporting membrane;

[0028] S4: The dry electrode can be obtained by combining the self-supporting membrane obtained in step S3 onto the current collector.

[0029] Preferably, the high shear force fiberization treatment in step S2 is achieved by air jet milling, wherein the milling air pressure is 0.4~0.8MPa; and the feeding air pressure of the air jet milling is greater than the milling air pressure.

[0030] Preferably, the film-forming treatment specifically includes the following steps:

[0031] S31: Preliminary film-forming treatment: The fibrous mixture is rolled to form a preliminary film;

[0032] S32: Final film formation process: The film obtained in step S31 is thinned by multi-stage rolling to obtain a self-supporting film with a thickness of 30~300 μm.

[0033] Preferably, the preliminary film formation in step S31 is performed using a roller press, wherein the speed ratio of roller A to roller B of the roller press is 1:1, and the roller gap width is set to 500~1000 μm.

[0034] The thinning process employs a constant-speed multi-stage hot rolling process, where the speed ratio of roller A to roller B in the thinning process is 1:1, the rolling pressure is 1 to 30 tons, and the single roller speed is 0.1 to 10 r / min.

[0035] The dry electrode comprises a conductive agent, a binder, and an active material. The conductive agent is a conductive carbon black material, the binder is a fibrous polymer binder, and the active material is at least one of hard carbon, soft carbon, graphite, activated carbon, lithium iron phosphate, and ternary materials. The mass ratio of the binder to the conductive agent is 2:1 to 1:3.

[0036] The present invention also provides a method for preparing a dry electrode, which is to composite the self-supporting film obtained by the above-mentioned method for preparing a self-supporting film onto a current collector to obtain a dry electrode.

[0037] The beneficial effects of this invention are as follows:

[0038] (1) This invention pioneered the “step-by-step controllable mixing” strategy to solve the root cause of uneven dispersion and fiberization. It abandons the traditional single and crude mixing mode and innovatively combines media-free mixing and media-based mixing. In the media-free mixing stage, it breaks up material agglomeration throughout the entire area and avoids segregation. Under the premise of protecting the material structure, it achieves uniform pre-dispersion of each component, laying a homogeneous foundation for subsequent processing. Then, media-based mixing is used to ensure uniform mechanical action. Thus, the conductive agent uniformly and firmly coats the binder, and the binder fibers are initially uniformly formed, eliminating performance fluctuations caused by uneven mixing from the source.

[0039] (2) The preparation method of the dry electrode self-supporting film of the present invention further introduces the alternating forward and reverse operation mode to accurately adapt to the objectives of each process stage: (1) In the non-medium mixing stage, the uniform pre-dispersion of each component is achieved by alternating forward and reverse gentle shearing under the premise of protecting the material structure. (2) In the medium mixing stage, the alternating forward and reverse operation is adopted in the coating and pre-fiberization, and the flow field is periodically disturbed to ensure uniform mechanical action.

[0040] (3) The self-supporting membrane preparation method of the present invention achieves precise real-time control of binder content and micro-distribution. Through the above-mentioned fine mixing process, it is ensured that the binder can achieve uniform molecular-level distribution in the electrode at a preset content (1~10 wt%). The resulting continuous and uniform three-dimensional network skeleton simultaneously optimizes the mechanical integrity and electrochemical consistency of the electrode, solving the core pain point of PTFE distribution runaway.

[0041] (4) This invention further constructs a "mechanical-airflow" dual-stage fiberization synergistic process to achieve precise control of the network structure by adopting a synergistic combination of "mechanical shearing pre-fiberization" and "airflow pulverization deep fiberization". The former initiates and guides fiber formation under controlled conditions; the latter "combs" and homogenizes the fiber clusters through high-speed collisions. This dual-stage process achieves precise control of the morphology and network density of PTFE fibers, thereby constructing a strong and isotropic three-dimensional conductive bonded network;

[0042] (5) The dry electrode preparation method of the present invention implements green manufacturing throughout the entire process, completely eliminates solvent dependence, and does not require any organic solvents (such as NMP) throughout the entire production process. It completely eliminates the emission of volatile organic compounds, solvent recovery energy consumption and potential safety hazards from the source, which is in line with the green and sustainable development trend of high-end manufacturing industry. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the pre-coated material formed by the non-ball-bound mixing and coating treatment of the conductive agent and PTFE in Example 1.

[0044] Figure 2The photograph shows the morphology of the material after prefiberization and air jet milling in Example 1, which exhibits a good "flocculent" fibrous structure.

[0045] Figure 3 The image shows the final dry electrode obtained in Example 1, which has a smooth, continuous surface without cracks.

[0046] Figure 4 The image shown is a scanning electron microscope (SEM) image of the dry electrode prepared in Example 1, which shows that the PTFE fibers form a continuous three-dimensional network that tightly connects the active particles and the conductive agent.

[0047] Figure 5 The image shows the EDS surface scan pattern (C and F element distribution) of the dry electrode prepared in Example 1.

[0048] Figure 6 The image shows the elemental quantitative analysis results of the dry electrode prepared in Example 1. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0050] The inventors discovered that existing dry processes, especially systems using polytetrafluoroethylene (PTFE) as a binder, still face a series of unresolved key technical challenges:

[0051] (1) The mixing process is crude and cannot take into account both the uniformity of dispersion and the protection of material structure: The ideal dry mixing needs to achieve different purposes at different stages: the initial stage requires gentle dispersion to prevent damage to the material structure, and the later stage requires controlled shearing to induce fibrosis. Existing technologies mostly adopt a unidirectional, constant high-speed mixing mode, which has significant drawbacks. Unidirectional high-speed rotation easily forms a stable unidirectional flow field in the mixing chamber, causing light materials (such as carbon black) and heavy materials to stratify and aggregate in specific areas, making it impossible to achieve uniform pre-dispersion throughout the entire area. Omitting this gentle pre-dispersion step and directly entering high-shear mixing will seriously damage the chain structure of the conductive agent and promote the premature aggregation of PTFE. The lack of alternating forward and reverse operation makes it impossible for the material to be periodically disrupted and redistributed, which is one of the key process defects causing uneven dispersion in the initial stage;

[0052] (2) PTFE fiberization is difficult to control, resulting in an unsatisfactory three-dimensional network construction: PTFE fiberization is the core of its bonding network formation. Existing processes often rely on single high-shear spherical mixing to achieve fiberization, but the unidirectional shear force field is fixed in direction, which easily leads to excessive stretching and breakage of PTFE fibers in a single direction, or effective shearing only in local areas, while PTFE in other areas remains granular. This non-uniformity in the degree and direction of fiberization makes the formed three-dimensional network fragile and anisotropic, unable to provide uniform mechanical strength for the electrode film;

[0053] (3) Uneven component dispersion, especially the distribution of PTFE: The insulating properties of PTFE and its tendency to agglomerate make it difficult to disperse evenly in dry powder mixing. If it is directly mixed with active materials and conductive agents at high intensity, PTFE is prone to forming micron-sized agglomerates due to electrostatics or van der Waals forces. These agglomerates will become structural weaknesses in subsequent film formation, resulting in uneven electrode film density, pore defects, and significantly increased local impedance. More importantly, the content and distribution uniformity of PTFE directly determine the bonding strength of the electrode and the integrity of the conductive network. If the content is too low, it is not enough to form a continuous network, and the film is prone to pulverization; if the content is too high, it will be overly insulating and block ion transport channels. Existing technologies often only focus on the total content of PTFE and lack effective means to achieve uniform and controllable distribution of it at the microscale. This is one of the core bottlenecks restricting the consistency of dry electrode performance and yield.

[0054] (4) The influence of the mixing process on the material structure and dispersion basis is ignored: In the dry process, the initial contact state between the conductive agent and PTFE is crucial to the subsequent coating and fiberization effect. If the gentle pre-dispersion step is omitted and high-shear mixing is carried out directly, the strong external force may destroy the chain structure of the carbon black conductive agent, reduce the specific surface area, and impair the conductivity; at the same time, the PTFE particles may be prematurely compacted or form uncontrollable coarse fiber clusters, making it impossible to achieve the ideal structure of "conductive agent as the core and PTFE coating", which will create hidden dangers for the homogenization of the electrode.

[0055] (5) Thick films are difficult to calender and have low film formation rate: Due to the above-mentioned problems of fiberization and uneven dispersion, when preparing electrode films with a thickness greater than 100 μm, the internal stress distribution is extremely uneven, and macroscopic cracks or delamination are very likely to occur during the rolling process, making it difficult to achieve continuous and stable industrial production.

[0056] (6) Insufficient bonding strength between dry membrane and current collector: Uneven PTFE distribution also leads to large fluctuations in adhesion force at the interface between membrane and current collector, resulting in weak local adhesion. This can easily cause active material stripping during battery cycling, leading to accelerated capacity decay.

[0057] Therefore, the present invention provides a method for preparing a dry electrode, comprising the following steps:

[0058] 1) The conductive agent and polytetrafluoroethylene binder are mixed without a medium to obtain mixture A;

[0059] 2) Mixture A is mixed with a medium to obtain mixture B;

[0060] 3) Mixture B is mixed with the active substance without a medium to obtain mixture C;

[0061] 4) Mixture C is mixed with a medium to obtain mixture D;

[0062] 5) The mixture D is subjected to high shear force fiberization;

[0063] 6) The fibrous mixture D is initially formed into a film by roller pressing;

[0064] 7) The material after preliminary film formation is thinned by multi-stage roller pressing to obtain a self-supporting film with a thickness of 30~300 μm;

[0065] 8) Coating: The self-supporting film obtained in step 7) is hot-pressed onto a copper current collector, an aluminum current collector, or a current collector that has been coated with a primer to obtain a dry electrode.

[0066] As a preferred embodiment of the present invention, in step 1), the conductive agent is a conductive carbon black material. The binder is a fibrous polymer binder, more preferably polytetrafluoroethylene. The mass ratio of the binder to the conductive agent is 2:1 to 1:3.

[0067] The media-free mixing refers to the mixing stage without introducing grinding balls, grinding rods or other grinding media, stirring paddles, kneading components, screw extrusion components, and without any functional structural components for stirring, shearing, or collision within the mixing chamber. The mixing process relies solely on the material's self-turning and self-circulation caused by the overall movement of the mixing chamber, as well as the low-intensity shearing action generated by the friction between materials, to mix electrode raw materials containing at least a binder and a conductive agent, achieving uniform dispersion of the binder without significant fibrosis. By suppressing its structural evolution during the mixing stage, the binder maintains a good redispersible state, thereby avoiding the formation of irregular fibers or agglomerates before sufficient dispersion.

[0068] Preferably, the media-free mixing is achieved through a mixing device with a closed mixing chamber. The mixing chamber has a hollow structure and does not contain stirring paddles, plow blades, spiral blades, or other internal mixing components. Mixing can be achieved through the rolling, tumbling, oscillating, planetary revolution, or combinations thereof within the mixing chamber, causing the material to continuously change its position and stress state within the chamber under the influence of gravity and inertia, thereby achieving uniform mixing at both the macroscopic and microscopic scales.

[0069] The media-free mixing process does not introduce any mixing or grinding media, and the mixing equipment does not have any functional structural components for shearing or grinding; in one embodiment, the media-free mixing is achieved by a double planetary mixing device, but without installing stirring paddles, plow blades or spiral blades, and mixing is achieved solely by the movement of the device cavity.

[0070] The dielectric-free mixing method can be used for the premixing of conductive agents and binders, or for mixing of at least two components comprising an active substance, a conductive agent, and a binder.

[0071] Preferably, the mixing equipment used in the medialess mixing of the present invention can be a mixer without a stirring paddle, a bladeless mixer, a gravity-free mixer, a ballless ball mill, a ballless sand mill, etc.

[0072] This step preferentially employs a ball mill without balls, performing ball-free mixing at a speed of 200-600 rpm, with alternating forward and reverse rotation for 10-30 minutes. This ball-free mixing process aims to achieve initial uniform dispersion of the conductive agent and binder through gentle, low-shear forces, effectively avoiding material structural damage and secondary agglomeration, thus laying a homogeneous material foundation for subsequent coating treatment.

[0073] As a preferred embodiment of the present invention, in step 2), the binder coating treatment is carried out using a high-speed mixer at a mixing speed of 400-600 rpm, with alternating forward and reverse mixing modes, and grinding media is added for a mixing time of 10-30 minutes. This ball-mixing utilizes the impact and shearing action of the media to promote a firm and uniform coating of the conductive agent onto the surface of the PTFE particles. The resulting coating structure effectively compensates for the insulation properties of PTFE, reduces electrode internal resistance, and improves electron transport efficiency; at the same time, it prevents PTFE from agglomerating in subsequent processes, ensuring its uniform distribution in the electrode film.

[0074] As a preferred embodiment of the present invention, in step 3), the active material is at least one selected from hard carbon, soft carbon, graphite, activated carbon, lithium iron phosphate, and ternary materials. This step also employs a ball mill for ballless mixing at a speed of 200-600 rpm, alternating forward and reverse rotation for 10-30 minutes. This process ensures uniform mixing of the pre-coated material and the active material under mild conditions, avoiding structural damage and providing a homogeneous mixture for the subsequent fiberization process.

[0075] As a preferred embodiment of the present invention, the purpose of the media mixing in step 4) is to perform pre-fiberization treatment. This media mixing, i.e., pre-fiberization treatment, is carried out using a dual planetary high-speed mixer at a speed of 400-600 rpm, with alternating forward and reverse rotation for 10-30 minutes. This step initiates the fibrosis process of PTFE under controlled mechanical shear, forming a preliminary fiber network.

[0076] As a preferred embodiment of the present invention, the high-shear fiberization in step 5) is achieved through air jet milling. The milling air pressure is 0.4~0.8MPa; the feeding air pressure must be greater than the milling air pressure; and the feed rate is controlled to be no more than 10 kg / h. Through this air jet milling process, fiber agglomerates can be further broken down, achieving deep and uniform dispersion of active materials, conductive agents, and PTFE fibers at the nano-micron scale, and pre-constructing a stable conductive / bonding three-dimensional network, thereby improving the tensile strength and flexibility of the electrode film.

[0077] As a preferred technical solution of the present invention, in step 6), the preliminary film formation is carried out using a roller press, wherein the speed ratio of roller A to roller B is 1:1, and the roller gap width is set to 500~1000 μm.

[0078] As a preferred embodiment of the present invention, in step 7), the final film-forming process employs a constant-speed multi-stage hot rolling process. In this process, the speed ratio of roller A to roller B is 1:1, the rolling pressure is 1-30 tons, and the single-roller speed is 0.1-10 r / min. Through multiple passes of progressive thinning, the final film thickness is precisely controlled to be 30-300 μm. This process achieves uniform densification of the film material, effectively avoiding cracking caused by internal stress concentration. The resulting film has a smooth, flat surface, free from defects such as pores, cracks, and wrinkles.

[0079] As a preferred embodiment of the present invention, in step (8), the obtained self-supporting diaphragm is laminated onto the current collector or the current collector coated with a primer using a hot press. The hot pressing temperature is 50~120℃, and the hot pressing time is 20~60 seconds to ensure a strong bond between the diaphragm and the current collector.

[0080] The present invention also provides a dry electrode film prepared by the preparation method, wherein the active material can be selected from hard carbon, soft carbon, graphite, activated carbon, lithium iron phosphate, or ternary materials.

[0081] Example 1

[0082] This embodiment prepares a dry electrode of activated carbon cathode material, which is composed of the following components in the following mass ratio:

[0083] AC (activated carbon):PTFE (binder polytetrafluoroethylene):SP (conductive agent Super C) = 85:5:10.

[0084] The preparation method is as follows:

[0085] (1) One-time ballless mixing treatment: Weigh an appropriate amount of conductive agent Super C and binder polytetrafluoroethylene according to the above mass ratio, and then mix the conductive agent Super C and binder polytetrafluoroethylene in segments without balls. 1) Rotation speed 300 rpm, alternating forward and reverse rotation every 6 min, mix for 12 min; 2) Rotation speed 400 rpm, alternating forward and reverse rotation every 6 min, mix for 12 min; 3) Rotation speed 500 rpm, alternating forward and reverse rotation every 6 min, mix for 12 min, to obtain uniformly mixed PTFE and Super C;

[0086] (2) Adhesive coating treatment: Add the above mixture to the grinding balls, and mix in segments with the balls to obtain the pre-coated material. The ball-to-material ratio is 1:1. 1) Rotate at 400 rpm, and alternate between forward and reverse rotation every 6 minutes for 12 minutes. 2) Rotate at 500 rpm, and alternate between forward and reverse rotation every 6 minutes for 12 minutes for 12 minutes. Stir during the process to prevent compaction.

[0087] (3) Secondary ballless mixing treatment: The activated carbon (AC) and the pre-coated material obtained in step 2 are mixed according to the same three-stage ballless mixing procedure as in step 1;

[0088] (4) Pre-fiberization treatment: Add grinding balls to the mixture in step 3 and perform ball mixing according to the same procedure as in step 2 to achieve preliminary fiberization;

[0089] (5) Airflow pulverization: The material obtained in step (4) is subjected to airflow pulverization. The feeding airflow pressure is 0.8 MPa, the pulverization pressure is 0.7 MPa, and the feed rate is 6 kg / h.

[0090] (6) Film forming process: The material pulverized by airflow in step (5) is rolled into shape by a roller press, and then gradually thinned by a high-precision electric roller press. The roller pressing pressure is 20t, and the gap between the two hot rollers is gradually reduced by 0.01mm. The final film thickness of the rolled film is 80±5μm.

[0091] (7) Coating treatment: The film prepared in step (6) is hot-pressed onto the current collector by a hot press at a temperature of 120°C and a time of 30s.

[0092] Example 2

[0093] The dry electrode of the hard carbon anode material in this embodiment is composed of the following components in the following mass ratio:

[0094] HC (hard carbon):PTFE:SP = 90:5:5.

[0095] (1) One-time ballless mixing treatment: The conductive agent Super C and the binder polytetrafluoroethylene were mixed in segments without balls. 1) The rotation speed was 300 rpm, and the forward and reverse rotation were alternated every 6 min for 12 min. 2) The rotation speed was 400 rpm, and the forward and reverse rotation were alternated every 6 min for 12 min. 3) The rotation speed was 500 rpm, and the forward and reverse rotation were alternated every 6 min for 12 min for 12 min to obtain a uniformly mixed PTFE and Super C.

[0096] (2) Binder coating treatment: Add the above mixture to the grinding balls and mix in segments with balls. The ball-to-material ratio is 1:1. 1) Rotate at 400 rpm, alternating between forward and reverse rotation every 6 minutes, and mix for 12 minutes. 2) Rotate at 500 rpm, alternating between forward and reverse rotation every 6 minutes, and mix for 12 minutes. Stir during the process to prevent compaction.

[0097] (3) Secondary ballless mixing process: Hard carbon (HC) and the pre-coated material obtained in step 2 are mixed according to the same three-stage ballless mixing procedure as in step 1;

[0098] (4) Pre-fiberization treatment: Add grinding balls to the mixture in step 3 and perform ball mixing according to the same procedure as in step 2 to achieve preliminary fiberization;

[0099] (5) Fiberization treatment: The material obtained in step (4) is subjected to air jet milling with a feeding air pressure of 0.8 MPa, a milling pressure of 0.7 MPa, and a feed rate of 6 kg / h;

[0100] (6) Film forming process: The material pulverized by airflow in step (5) is rolled into shape by a roller press, and then gradually thinned by a high-precision electric roller press. The roller pressing pressure is 20t, and the gap between the two hot rollers is gradually reduced by 0.01mm. The final film thickness is 50±5μm.

[0101] (7) Coating treatment: The HC membrane prepared in step (6) is hot-pressed onto the current collector by a hot press machine. The hot pressing temperature is 60℃ and the hot pressing time is 20s.

[0102] Example 3

[0103] The raw material system used in this embodiment is the same as that in Embodiment 1, the only difference being that some process parameters are taken as the lower limit of the range defined in the claims.

[0104] (1) One-time media-free mixing treatment: The conductive agent Super C and polytetrafluoroethylene binder were added to the ball mill in the mass ratio of Example 1, and the media-free mixing was carried out at a speed of 200 rpm. The mixing mode was alternating forward and reverse rotation, and the mixing time was 10 min to obtain a preliminary mixture.

[0105] (2) Mixing with media (coating treatment): Add grinding balls to the mixture obtained in step (1) with a ball-to-material ratio of 1:1. Mix with media in a high-speed mixer at a speed of 400 rpm, alternating between forward and reverse rotation, for a mixing time of 10 min.

[0106] (3) Secondary medium-free mixing treatment: The material obtained in step (2) is mixed with the active substance and mixed without media at a speed of 200 rpm for 10 min;

[0107] (4) Pre-fiberization treatment: Add grinding balls to the mixture obtained in step (3) and perform media mixing at 400 rpm for 10 min;

[0108] (5) High-shear fiberization treatment: Fiberization treatment is carried out by air jet milling, wherein the milling air pressure is 0.4 MPa;

[0109] (6) Film forming process: The film is formed by constant speed multi-stage rolling process, with rolling pressure of 1 t and single roller speed of 0.1 r / min, and finally a self-supporting film with a thickness of about 200 μm is obtained.

[0110] The results show that, under the aforementioned lower limit of parameters, the resulting membrane can still be continuously formed, possessing basic mechanical integrity and operability, indicating that the lower limit of parameters defined in the claims is feasible.

[0111] Example 4

[0112] The raw material system used in this embodiment is the same as that in Embodiment 1, the only difference being that some process parameters are taken as the upper limit of the range defined in the claims.

[0113] (1) One-time media-free mixing treatment: The conductive agent Super C and polytetrafluoroethylene binder are added to the ball mill and mixed media-free at a speed of 600 rpm, with alternating forward and reverse rotation, and the mixing time is 30 min;

[0114] (2) Mixing with media (coating treatment): Add grinding balls to the mixture obtained in step (1) with a ball-to-material ratio of 1:1, and mix with media in a high-speed mixer at a speed of 600 rpm for 30 min;

[0115] (3) Secondary medium-free mixing treatment: The material obtained in step (2) is mixed with the active substance and mixed without media at a speed of 600 rpm for 30 min;

[0116] (4) Pre-fiberization treatment: Mixing with a medium at 600 rpm for 30 min to induce significant fiberization of polytetrafluoroethylene;

[0117] (5) High-shear fiberization treatment: Fiberization treatment is carried out by air jet milling, wherein the milling air pressure is 0.8 MPa;

[0118] (6) Film forming process: The film is formed by constant speed multi-stage hot rolling process. The rolling pressure is 30 t and the single roller speed is 10 r / min. Finally, a self-supporting film with a thickness of about 50 μm is obtained.

[0119] The results show that the self-supporting membrane structure obtained in the above embodiments is dense and has good continuity, with no obvious breakage or delamination.

[0120] Comparative Example 1 (without premixing step)

[0121] The formulation is the same as in Example 1. The ballless mixing steps 1 and 3 are omitted; the conductive agent, PTFE, and activated carbon are directly mixed in a single, ball-like process (equivalent to combining steps 2 and 4). Subsequent airflow pulverization, film formation, and coating steps are the same as in Example 1. The preparation method is as follows:

[0122] (1) Adhesive coating treatment: The adhesive polytetrafluoroethylene PTFE and the conductive agent Super C are mixed in segments and with balls. 1) The rotation speed is 400 rpm, and the forward and reverse rotation is alternated every 6 minutes for 12 minutes. 2) The rotation speed is 500 rpm, and the forward and reverse rotation is alternated every 6 minutes for 12 minutes. During the process, the mixture is stirred to prevent compaction.

[0123] (2) Pre-fiberization treatment: Add the active substance to the material uniformly mixed in step (1) for preliminary fiberization (with balls); 1) Rotation speed 400 rpm, alternating forward and reverse rotation every 6 min, mix for 12 minutes; 2) Rotation speed 500 rpm, alternating forward and reverse rotation every 6 min, mix for 12 minutes, stirring during the process to prevent compaction;

[0124] (3) The material obtained in step (2) is subjected to air jet milling. The feeding air pressure is 0.8 MPa, the milling pressure is 0.7 MPa, and the feed rate is 6 kg / h.

[0125] (4) The material pulverized by airflow in step (3) is rolled into shape by a dough rolling machine, and then gradually thinned by a high-precision electric roller press. The rolling pressure is 20t, and the gap between the two hot rollers is gradually reduced by 0.01mm. The final film thickness is 80±5μm.

[0126] (5) The membrane prepared in step (4) is hot-pressed onto the current collector by a hot press at a temperature of 120°C and a time of 30s.

[0127] Comparative Example 2 (without premixing step)

[0128] The formulation is the same as in Example 2. The ballless mixing steps 1 and 3 are omitted; the conductive agent, PTFE, and activated carbon are directly mixed in a single process with balls (equivalent to combining steps 2 and 4). Subsequent airflow pulverization, film formation, and coating steps are the same as in Example 2. The preparation method is as follows:

[0129] (1) Adhesive coating treatment: The adhesive polytetrafluoroethylene PTFE and the conductive agent Super C are mixed in segments and with balls. 1) The rotation speed is 400 rpm, and the forward and reverse rotation is alternated every 6 minutes for 12 minutes. 2) The rotation speed is 500 rpm, and the forward and reverse rotation is alternated every 6 minutes for 12 minutes. During the process, the mixture is stirred to prevent compaction.

[0130] (2) Pre-fiberization treatment: Add the active substance to the material uniformly mixed in step (1) for preliminary fiberization (with balls); 1) Rotation speed 400 rpm, alternating forward and reverse rotation every 6 min, mix for 12 minutes; 2) Rotation speed 500 rpm, alternating forward and reverse rotation every 6 min, mix for 12 minutes, stirring during the process to prevent compaction;

[0131] (3) The material obtained in step (2) is subjected to air jet milling. The feeding air pressure is 0.8 MPa, the milling pressure is 0.7 MPa, and the feed rate is 6 kg / h.

[0132] (4) The material pulverized by airflow in step (3) is rolled into shape by a dough rolling machine, and then gradually thinned by a high-precision electric roller press. The rolling pressure is 20t, and the gap between the two hot rollers is gradually reduced by 0.01mm. The final film thickness is 50±5μm.

[0133] (5) The membrane prepared in step (4) is hot-pressed onto the current collector by a hot press at a temperature of 60°C and a time of 30s.

[0134] Performance Testing and Result Analysis

[0135] The electrode sheets prepared in the above embodiments and comparative examples were subjected to morphological observation, elemental analysis, and half-cell electrochemical testing. The results are as follows:

[0136] The initial coulombic efficiency of the powders or hot-pressed electrode films prepared in Examples 1-2, as measured by scanning electron microscopy and assembled half-cell testing, is as follows: Figure 1-4 As shown in Table 1-4.

[0137] Figure 1 The morphology of the binder and conductive agent after ballless mixing is shown; from Figure 1 It can be seen that the binder and conductive agent are uniformly dispersed and there is no obvious agglomeration after being mixed without balls.

[0138] Figure 2 The image shows the material after being fiberized by strong shear force in Example 1. It can be seen that the material is "flocculated" at this time, with obvious fibrous material and a certain degree of viscosity, indicating that the binder has been successfully fiberized.

[0139] Figure 3 The image shows the film after rolling in Example 1. The results show that the electrode has good continuous film formation, a smooth and flat surface, uniform thickness, and no pore defects, which confirms the excellent quality of the film.

[0140] Figure 4 This is a planar scanning electron microscope image of the self-supporting membrane obtained in Example 1. It can be seen that the content of fibrous binder and conductive material is beneficial for forming a good three-dimensional cross-linked network structure inside the membrane. From... Figure 4 The fiber filaments are of moderate length and without breakage, tightly connecting the active particles and conductive agent to form an electrode film. In particular, the fine conductive carbon black particles connected in series in the fiber filaments significantly enhance the electronic conductivity of the electrode.

[0141] Figure 5 The image shows the EDS surface scan of the dry electrode prepared in Example 1. Figure 5 The EDS surface scan spectrum shows that C and F elements are highly uniformly distributed throughout the observation area, with no obvious enrichment or aggregation regions.

[0142] Figure 6 The image shows the elemental quantitative analysis results of the dry electrode prepared in Example 1. Figure 6 Quantitative analysis showed that the atomic content of carbon (C) in the electrode was 95.1%, and the atomic content of phosphorus (F) was 4.9%, which highly matched the mass ratio of carbonaceous materials (active materials and conductive agents) to PTFE binder in the raw material formulation. This fully demonstrates that the ballless mixing process provided by this invention can achieve uniform molecular-level dispersion of PTFE binder within the electrode, ensuring the consistency of the electrode at both the macroscopic and microscopic scales.

[0143] Table 1: Initial coulombic efficiency, 0.2C discharge specific capacity, and capacity retention after 3000 cycles at 20C obtained from the half-cell tests of the samples prepared in Example 1 and Comparative Example 1.

[0144]

[0145] Table 2. Elemental distribution and proportion of dry electrode films in Example 1 and Comparative Example 1.

[0146]

[0147] Table 3 shows the initial coulombic efficiency, 0.2C discharge specific capacity, and capacity retention rate after 300 cycles at 1C obtained from the half-cell tests of the samples prepared in Example 2 and Comparative Example 2.

[0148]

[0149] Table 4 shows the elemental distribution and proportion of the dry electrode films in Example 2 and Comparative Example 2.

[0150]

[0151] As can be seen from the test results in Table 1, the initial coulombic efficiency (97.2%), 0.2C specific capacity (62.5 mAh / g), and capacity retention (100%) after 3000 cycles at ultra-high rate (20C) of Example 1 (AC cathode) are significantly better than those of Comparative Example 1.

[0152] As can be seen from the test results in Table 3, the 0.2C specific capacity (329 mAh / g) and the capacity retention rate (90.1%) of Example 2 (HC anode) are also significantly higher than those of Comparative Example 2.

[0153] The elemental quantitative analysis in Tables 2 and 4 shows that the atomic percentages of C and F in the examples are highly consistent with the raw material ratio, confirming that the process of the present invention can achieve uniform dispersion of components at the molecular level; while the proportion of F in the comparative examples deviates from the theoretical value and fluctuates greatly, confirming its uneven dispersion.

[0154] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0155] The parts of this invention not described in detail are well-known in the art. The above embodiments are provided merely for the purpose of describing the invention and are not intended to limit the scope of the invention. The scope of the invention is defined by the appended claims. All equivalent substitutions and modifications made without departing from the spirit and principles of the invention should be covered within the scope of the invention.

Claims

1. A method for preparing a self-supporting film for dry electrodes, characterized in that, In the preparation process of the self-supporting membrane for dry electrode, the material mixing process of the self-supporting membrane is to first perform media-free mixing and then perform media-containing mixing. Wherein, the medium-free mixing refers to mixing that relies on the overall movement of the mixing chamber to induce material self-turning, self-circulation, and low-intensity shearing action generated by mutual friction between materials; the mixing chamber contains the material of the dry electrode; The term "medium-based mixing" refers to the provision of functional structural components within the mixing chamber for stirring, shearing, or collision.

2. The method for preparing a self-supporting film for a dry electrode according to claim 1, characterized in that, After adding any type of material, perform mixing without a medium first, and then perform mixing with a medium.

3. The method for preparing a self-supporting film for a dry electrode according to claim 2, characterized in that, The self-supporting membrane is made of conductive agents, binders, and active substances. The material mixing process of the self-supporting membrane includes the following steps: (1) The conductive agent and the binder are mixed without a medium to obtain mixture A; (2) Mixture A is mixed with a medium to obtain mixture B; (3) Mixture B with the active substance without a medium to obtain mixture C; (4) Mixture C is mixed with a medium to obtain mixture D.

4. The method for preparing a self-supporting film for a dry electrode according to claim 1, characterized in that, The media-free mixing is achieved through a mixing device with a closed mixing chamber. The interior of the mixing chamber is a hollow structure and does not contain any functional structural components for stirring, shearing, or collision. The media-free mixing is achieved through the rolling, flipping, oscillating, planetary revolution, or a combination thereof of the mixing chamber.

5. The method for preparing a self-supporting film for a dry electrode according to claim 4, characterized in that, The mixing equipment used for the medialess mixing is a ballless mixer; The mixing of the medium is achieved using a high-speed mixer.

6. The method for preparing a self-supporting diaphragm for a dry electrode according to claim 5, characterized in that, The rotation speed of the ballless mixer in the medium-free mixing process is 200~600 rpm, and the mixing time is 10~30 minutes. The high-speed mixer rotates at 400-600 rpm, and the mixing time with the medium is 10-30 minutes.

7. The method for preparing a self-supporting film for a dry electrode according to claim 1, characterized in that, The media-free mixing is a segmented mixing process, and the parameters of media-free mixing in different stages are not exactly the same. The medium-mixing is segmented mixing, and the parameters of the medium-mixing in different stages are not exactly the same.

8. The method for preparing a self-supporting film for a dry electrode according to any one of claims 1 to 7, characterized in that, The method for preparing the dry electrode includes the following steps: S1: Mix the materials of the dry electrode; S2: The mixture obtained in step S1 is subjected to high shear force fiberization treatment; the high shear force fiberization treatment is achieved by air jet milling; S3: The fibrous mixture obtained in step S2 is subjected to a film-forming process to obtain a self-supporting membrane; S4: The dry electrode can be obtained by combining the self-supporting membrane obtained in step S3 onto the current collector.

9. The method for preparing a self-supporting diaphragm for a dry electrode according to claim 1, characterized in that, The dry electrode comprises a conductive agent, a binder, and an active material. The conductive agent is a conductive carbon black material, the binder is a fibrous polymer binder, and the active material is at least one of hard carbon, soft carbon, graphite, activated carbon, lithium iron phosphate, and ternary materials. The mass ratio of the binder to the conductive agent is 2:1 to 1:

3.

10. A method for preparing a dry electrode, characterized in that, The dry electrode can be obtained by combining the self-supporting membrane obtained by the method of preparing a self-supporting membrane according to any one of claims 1 to 9 onto the current collector.

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