A thick electrode positive electrode sheet, its preparation method, and a primary battery

Abstract

This invention provides a thick electrode positive electrode sheet, its preparation method, and a primary battery. The method includes the following steps: first, mixing a positive electrode active material, a conductive agent, and a binder resin to obtain a mixture; then, subjecting the mixture to fibrosis treatment to obtain a fibrous mixture; next, granulating the fibrous mixture with a granulating agent to obtain a precursor material, wherein the granulating agent is a liquid with a vapor pressure not less than 0.2 mmHg; finally, subjecting the precursor material to roll forming to obtain the thick electrode positive electrode sheet. The preparation method provided by this invention can be widely applied to battery systems that require the use of current collectors to fabricate thick electrodes (>500 μm), and solves problems such as the difficulty in continuous automated production of thick electrode sheets using current collectors, high electrode powder shedding rate, and uneven thickness.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a thick electrode positive electrode sheet, its preparation method, and a primary battery. Background Technology

[0002] In battery manufacturing, cylindrical batteries typically use a winding method to create the cells. Specifically, the positive electrode, separator, and negative electrode are stacked and wound sequentially to form a core. This not only increases the effective area of ​​the electrode sheets but also improves the battery's energy density. For rechargeable batteries, both the positive and negative electrodes are coated with a slurry onto both sides of a current collector foil (such as aluminum or copper foil) to form elongated electrode sheets. However, primary batteries, due to their irreversible chemical reactions, primarily utilize a mesh current collector filled with as much active material as possible to further increase battery capacity. This structural design allows for a thicker electrode sheet, reaching up to 500 μm, under the same high compaction density.

[0003] For example, a lithium manganese dioxide battery uses electrolytic manganese dioxide as the positive electrode and lithium metal as the negative electrode. The specific electrochemical reaction is: MnO2 + xLi → Li x MnO2. The preparation of positive electrode sheets for lithium manganese dioxide cylindrical batteries typically employs a slurry-drawing method. This process involves preparing a slurry of manganese dioxide, a conductive agent, and a binder, then slowly passing the slurry through a current collector to ensure uniform adhesion. Subsequent drying and fine pressing processes result in the final positive electrode sheet. This preparation process suffers from drawbacks, including high requirements for the slurry, high energy consumption, high powder shedding rate of the produced positive electrode sheet, and the inability to produce positive electrode sheets with high compaction density.

[0004] For example, lithium thionyl chloride batteries possess advantages such as high specific energy (up to 590Wh / kg), high rated voltage (3.6V), low self-discharge rate (≤1%), and a wide operating temperature range (-55℃ to 85℃), making them the batteries with the highest specific energy currently available in commercial applications. The working principle of lithium thionyl chloride batteries is based on the chemical reaction between lithium and thionyl chloride (SOCl2). This battery consists of metallic lithium as the negative electrode, carbon as the positive electrode, anhydrous lithium tetrachloroaluminate SOCl2 solution as the electrolyte, and the positive electrode active material. The electrochemical reaction is: 4Li + 2SOCl2 → 4LiCl + S↓ + SO2.

[0005] In lithium thionyl chloride cylindrical batteries, power cells typically employ a wound structure. Specifically, acetylene black, polytetrafluoroethylene emulsion, and ethanol or isopropanol are mixed to form a powder, which is then uniformly coated onto a nickel mesh (e.g., Chinese invention patent: CN104733738A). This powder is then sequentially wound with a separator and a negative electrode to form an integrated structure. Alternatively, the powder mixture is repeatedly kneaded and rolled to prepare a self-supporting membrane, which is then laminated onto the nickel mesh.

[0006] In fact, power battery electrodes are relatively thick and require the use of acetylene black as a conductive agent. However, acetylene black typically has a small density and particle size, making it difficult to formulate into a slurry suitable for coating production equipment. Furthermore, the self-supporting acetylene black film-on-screen method cannot achieve automated and continuous production, while the powder-pressed screen method results in a high powder shedding rate. Therefore, both of these production methods have certain shortcomings.

[0007] In recent years, dry electrode technology has received widespread attention in order to further produce thicker electrode sheets and thus improve the energy density of batteries. The core of this dry electrode technology lies in utilizing the fibrous ability of polytetrafluoroethylene (PTFE) binder. PTFE is subsequently dispersed into a fibrous structure and mixed with active materials and conductive agents to form self-supporting or non-self-supporting electrode films. This process eliminates the need for solvents, thus avoiding the solvent residue problems of traditional wet processes, and also offers advantages such as environmental friendliness, low cost, and high production efficiency. However, the dry electrode process is more difficult to produce and requires a higher degree of PTFE fibrosis. Furthermore, because no solvent is added, the fibers formed are highly susceptible to breakage during dispersion, and stress accumulation in the active material particles during film formation can lead to uneven film thickness.

[0008] Therefore, there is an urgent need to develop a method to optimize the fibrous process of PTFE to improve its mechanical strength and stability, as well as a method to solve the adhesion problem between the current collector and the dry electrode film. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a thick electrode positive electrode sheet, its preparation method, and a primary battery. The preparation method provided by this invention can be widely applied to battery systems requiring the use of current collectors to fabricate thick electrodes (>500 μm), and solves problems such as the difficulty in continuous automated production of thick electrode sheets using current collectors, high electrode powder shedding rate, and uneven thickness.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a method for preparing a thick electrode positive sheet, the method comprising the following steps:

[0012] S1. Mix the positive electrode active material, conductive agent and binder resin to obtain a mixture;

[0013] S2. The mixture is subjected to a fiberization treatment to obtain a fiberized mixture;

[0014] S3. The fibrous mixture and granulating agent are granulated to obtain a precursor material, wherein the granulating agent is a liquid with a vapor pressure of not less than 0.2 mmhg;

[0015] S4. The precursor material is rolled into a film to obtain the thick electrode positive electrode sheet.

[0016] It should be noted that the granulating agent mentioned in this invention is a liquid with a vapor pressure of not less than 0.2 mmhg, specifically referring to a vapor pressure of not less than 0.2 mmhg at room temperature. For example, it can be 0.2 mmhg, 0.4 mmhg, 0.6 mmhg, 0.8 mmhg, 1 mmhg, 1.2 mmhg, 1.5 mmhg, 1.8 mmhg, 2 mmhg, etc.

[0017] On one hand, this invention uses a binder resin for dispersion treatment, subjecting it to shear fibrillation to form a three-dimensional fiber network that adheres to the positive electrode active material particles. This is because the binder resin has a larger molecular weight than the binder emulsion, thus generating more fibers during the fibrillation process. These fibers better bind the positive electrode active material particles, ultimately improving the bonding strength and electrochemical performance of the positive electrode material. On the other hand, this invention granulates the fibrillated mixture with a granulating agent, allowing the room-temperature volatile liquid material to encapsulate the binder fibers and aid in granulation. During granulation, the material particles undergo further secondary fibrillation, forming rubber-like particles with a certain strength, thereby improving the film strength in the subsequent stages. Simultaneously, a small amount of granulating agent allows the positive electrode active material to move more easily during rolling, thus avoiding stress-induced build-up lines on the film and improving its thickness uniformity.

[0018] Preferably, the positive electrode active material in step S1 includes manganese dioxide and / or acetylene black.

[0019] Preferably, the adhesive resin in step S1 comprises polytetrafluoroethylene.

[0020] Preferably, when the positive electrode active material in step S1 is manganese dioxide, the mass percentage of the binder resin in step S1, based on the total mass of the mixture being 100%, is 1 wt.%-5 wt.%, preferably 1.5 wt.%-2.5 wt.%, for example, it can be 1 wt.%, 1.2 wt.%, 1.5 wt.%, 1.8 wt.%, 2 wt.%, 2.2 wt.%, 2.5 wt.%, 2.8 wt.%, 3 wt.%, 3.2 wt.%, 3.5 wt.%, 3.8 wt.%, 4 wt.%, 4.2 wt.%, 4.5 wt.%, 4.8 wt.%, 5 wt.%, etc. This invention controls the electrode sheet forming by adjusting the mass percentage of the binder resin, allowing the binder fibers to fully expand, thereby forming a three-dimensional network that binds the positive electrode active material particles. If a lower percentage of binder resin is used, the positive electrode active material will not be able to be fully bonded, resulting in film breakage or failure to transfer during the roll forming process, as well as a higher powder shedding rate after the positive electrode sheet is made, which ultimately affects the electrical performance of the primary battery. If a higher percentage of binder resin is used, the film resistance of the positive electrode sheet will increase, which in turn affects the internal resistance and discharge performance of the assembled primary battery.

[0021] Preferably, when the positive electrode active material in step S1 is acetylene black, the mass percentage of the binder resin in step S1 is 5 wt.%-15 wt.%, preferably 6 wt.%-8 wt.%, based on the total mass of the mixture as 100%. This invention controls the electrode sheet formation by adjusting the mass percentage of the binder resin, allowing the binder fibers to fully expand and form a three-dimensional network to bind the positive electrode active material particles. If a lower mass percentage of binder resin is used, the positive electrode active material cannot be fully bonded, resulting in film breakage or inability to transfer during the roll forming process, and a higher powder shedding rate after the positive electrode sheet is formed, ultimately affecting the electrical performance of the primary battery. If a higher mass percentage of binder resin is used, the film resistance of the positive electrode sheet will increase, thereby affecting the internal resistance and discharge performance of the assembled primary battery.

[0022] Preferably, the mixing method in step S1 is gravity-free mixing.

[0023] Preferably, the mixing temperature in step S1 is below 19°C, for example, it can be -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, etc.

[0024] This invention further controls the mixing method and temperature of the materials to prevent the binder resin from becoming fibrous in advance during the mixing process.

[0025] Preferably, the equipment for the fiberization process in step S2 includes a high-speed mixer and / or an air jet mill.

[0026] Preferably, the linear velocity of the high-speed mixer is 50m / s-150m / s, for example, it can be 50m / s, 60m / s, 70m / s, 80m / s, 90m / s, 100m / s, 110m / s, 120m / s, 130m / s, 140m / s, 150m / s, etc.

[0027] Preferably, the air pressure of the air jet mill is 0.75MPa-0.85MPa, for example, it can be 0.75MPa, 0.78MPa, 0.8MPa, 0.82MPa, 0.85MPa, etc.

[0028] Preferably, the granulating agent in step S3 includes any one or a combination of at least two of N-methylpyrrolidone, dimethyl silicone oil, polyethylene glycol, propylene glycol, isoparaffin, paraffin oil, or pure water.

[0029] Preferably, when the positive electrode active material is manganese dioxide, based on the total mass of the granulated material being 100%, the mass percentage of the granulating agent in step S3 is 10wt.%-30wt.%, preferably 15wt.%-25wt.%, for example, 10wt.%, 12wt.%, 15wt.%, 18wt.%, 20wt.%, 22wt.%, 25wt.%, 28wt.%, 30wt.%, etc. This invention, by controlling the mass percentage of the granulating agent, enables the fibrous mixture to be made into precursor material particles with uniform size, good sphericity, and good flowability, thereby facilitating uniform feeding during the roll forming process and controlling the thickness uniformity of the film. If a lower mass percentage of granulating agent is used, the granulating agent will not be able to completely coat the fibrous mixture, resulting in granulation failure; if a higher mass percentage of granulating agent is used, the precursor material particles will have an excessively large granulation mesh or the powder will not be granulated (e.g., clumping or agglomeration).

[0030] Preferably, when the positive electrode active material is acetylene black, based on the total mass of the granulated material as 100%, the mass percentage of the granulating agent in step S3 is 30wt.%-70wt.%, preferably 50wt.%-60wt.%, for example, 30wt.%, 40wt.%, 50wt.%, 52wt.%, 55wt.%, 60wt.%, 62wt.%, 65wt.%, 68wt.%, 70wt.%, etc. Because acetylene black has a low density, the content of the added granulating agent is relatively high.

[0031] Preferably, the rolling film forming method in step S4 includes differential temperature film forming and / or differential speed film forming, with differential temperature film forming being the preferred method.

[0032] Compared to differential film deposition, the method of forming films by differential temperature deposition does not cause stress accumulation between particles or deposition lines on the film during the film deposition process, thus resulting in better uniformity and consistency in film thickness and areal density.

[0033] Preferably, the differential temperature film forming equipment includes a differential temperature film forming roller system.

[0034] Preferably, the differential temperature film forming roller system includes a first pressing roller, a second pressing roller, a third pressing roller, and a fourth pressing roller arranged in sequence. A first feed inlet is formed above the space between the first pressing roller and the second pressing roller, and a second feed inlet is formed above the space between the third pressing roller and the fourth pressing roller. The second pressing roller and the third pressing roller are capable of pressing the powder fed into the first feed inlet and the second feed inlet into a continuous film.

[0035] Preferably, the rolling directions of the first and third pressing rollers are opposite to those of the second and fourth pressing rollers.

[0036] Preferably, the temperatures of the first and fourth pressure rollers are higher than those of the second and third pressure rollers. This invention regulates the temperatures of the first and fourth pressure rollers to be higher than those of the second and third pressure rollers because temperature affects molecular motion and adhesion. Specifically, at low temperatures, molecular motion on the surface of an object slows down, leading to an increase in the contact area between molecules, thereby enhancing adhesion. Conversely, at high temperatures, molecular motion on the surface of an object accelerates, reducing the contact area between molecules and thus decreasing adhesion. Therefore, the low-temperature rollers better maintain the adhesiveness of the object, making it easier for the film to adhere to the rollers.

[0037] Preferably, the temperature of the first pressing roller and the fourth pressing roller is 50℃-105℃, for example, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 105℃, etc.

[0038] Preferably, the temperature of the second and third pressing rollers is 20℃-60℃, for example, 20℃, 30℃, 40℃, 50℃, 60℃, etc.

[0039] Preferably, the temperature difference between the first pressing roller and the second pressing roller is 10℃-90℃, more preferably 30℃-50℃, and can be, for example, 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, etc. This invention, by controlling the temperature difference between the first and second pressing rollers, causes the precursor material particles to adhere to one side of the second pressing roller after being rolled, and subsequently transferred to the gap between the second and third pressing rollers for the preparation of the positive electrode sheet.

[0040] Preferably, the temperature difference between the fourth pressing roller and the third pressing roller is 10℃-90℃, more preferably 30℃-50℃, and can be, for example, 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, etc. This invention, by controlling the temperature difference between the fourth and third pressing rollers, causes the precursor material particles to adhere to one side of the third pressing roller after being rolled, and subsequently transferred to the gap between the second and third pressing rollers for the preparation of the positive electrode sheet.

[0041] In this invention, the first pressing roller, the second pressing roller, the third pressing roller, and the fourth pressing roller have the same diameter.

[0042] In this invention, the centers of the first pressing roller, the second pressing roller, the third pressing roller, and the fourth pressing roller are located on the same horizontal line.

[0043] In this invention, the first pressing roller, the second pressing roller, the third pressing roller, and the fourth pressing roller have the same linear velocity.

[0044] As a preferred embodiment of the present invention, the precursor material obtained by the above-described granulation step is fed into the gap between the first and second pressing rollers of a four-roll press, and into the gap between the third and fourth pressing rollers. A schematic diagram of the four-roll press is shown below. Figure 1 As shown, the leftmost roller is the first pressing roller, and from left to right are the second pressing roller, the third pressing roller, and the fourth pressing roller. The first and third pressing rollers rotate clockwise, while the second and fourth pressing rollers rotate counterclockwise.

[0045] This invention utilizes differential temperature rolling technology to independently form a film from precursor material particles during the rolling process, which then adheres to the low-temperature rollers. The film thickness is controlled by the size of the gaps between the first and second pressing rollers, and between the third and fourth pressing rollers, while the electrode thickness is controlled by the size of the gap between the second and third pressing rollers. During the bonding of the current collector, the film needs to adhere uniformly to the rollers; therefore, the film does not need to be self-supporting during this process. Furthermore, the uniformity of film thickness is affected by factors such as the particle size, specific surface area, or microstructure of the active material. To improve the uniformity of film thickness, equipment with more rollers can be used, such as an eight-roller pressing machine or a ten-roller pressing machine (e.g., ...). Figure 2 and Figure 3 (As shown). These devices, by increasing the number of rollers, can more effectively control the thickness distribution of the film, thereby improving thickness consistency.

[0046] In this invention, the electrode sheet prepared by differential temperature film formation technology has a smoother surface and a higher surface density.

[0047] Preferably, the roller pressing temperature for differential film formation is 40℃-110℃, for example, it can be 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, etc.

[0048] Preferably, the differential film forming equipment includes a differential film forming roller system.

[0049] Preferably, the differential film-forming roller system includes a first pressing roller, a second pressing roller, a third pressing roller, and a fourth pressing roller arranged in sequence. A first feed inlet is formed above the space between the first pressing roller and the second pressing roller, and a second feed inlet is formed above the space between the third pressing roller and the fourth pressing roller. The second pressing roller and the third pressing roller are capable of pressing the powder fed into the first feed inlet and the second feed inlet into a continuous film.

[0050] Preferably, the gap between adjacent rollers in the differential film-forming roller system is 0.10mm-0.60mm, for example, it can be 0.10mm, 0.12mm, 0.15mm, 0.18mm, 0.20mm, 0.22mm, 0.25mm, 0.28mm, 0.30mm, 0.32mm, 0.35mm, 0.38mm, 0.40mm, 0.42mm, 0.45mm, 0.48mm, 0.50mm, 0.52mm, 0.55mm, 0.58mm, 0.60mm, etc.

[0051] Specifically, when the positive electrode active material is manganese dioxide, the gap between adjacent rollers in the differential film-forming roller system is 0.20mm-0.50mm; when the positive electrode active material is acetylene black, the gap between adjacent rollers in the differential film-forming roller system is 0.10mm-0.60mm.

[0052] Preferably, the rolling direction of the first and third pressing rollers is opposite to that of the second and fourth pressing rollers.

[0053] Preferably, the linear velocity of the first and fourth pressing rollers is less than the linear velocity of the second and third pressing rollers.

[0054] Preferably, the linear velocity of the first pressing roller and the linear velocity of the fourth pressing roller are the same.

[0055] Preferably, the linear velocity of the second pressing roller is the same as that of the third pressing roller.

[0056] Preferably, the ratio of the linear velocity of the first and / or fourth pressing roller to the linear velocity of the second and / or third pressing roller is 1:(1.1-2). For example, it can be 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, etc. This invention, by adjusting the ratio of the linear velocity of the first and / or fourth pressing roller to the linear velocity of the second and / or third pressing roller, allows the precursor material particles to undergo greater shear force during the rolling process, thereby further improving film strength and reducing the powder shedding rate of the positive electrode sheet. If the linear velocity of the first and / or fourth pressing roller is too high, it will cause film breakage during the rolling process.

[0057] Specifically, when the temperature of the roller pressing in differential film formation is 40℃-80℃, the ratio of the linear velocity of the first pressing roller and / or the fourth pressing roller to the linear velocity of the second pressing roller and / or the third pressing roller is 1:(1.2-1.3); when the temperature of the roller pressing in differential film formation is 90℃-100℃, the ratio of the linear velocity of the first pressing roller and / or the fourth pressing roller to the linear velocity of the second pressing roller and / or the third pressing roller is 1:(1.1-1.3); when the temperature of the roller pressing in differential film formation is 110℃, the ratio of the linear velocity of the first pressing roller and / or the fourth pressing roller to the linear velocity of the second pressing roller and / or the third pressing roller is 1:(1.1-2).

[0058] In this invention, the first pressing roller, the second pressing roller, the third pressing roller, and the fourth pressing roller have the same diameter.

[0059] In this invention, the centers of the first pressing roller, the second pressing roller, the third pressing roller, and the fourth pressing roller are located on the same horizontal line.

[0060] As a preferred embodiment of the present invention, the precursor material obtained by the above-described granulation step is fed into the gap between the first and second pressing rollers of a four-roll press, and into the gap between the third and fourth pressing rollers. A schematic diagram of the four-roll press is shown below. Figure 1 As shown, the leftmost roller is the first pressing roller, and from left to right are the second, third, and fourth pressing rollers. The first and third pressing rollers rotate clockwise, while the second and fourth pressing rollers rotate counterclockwise.

[0061] This invention utilizes differential rolling technology to enable precursor material particles to form films independently during the rolling process and adhere to the high-speed rollers. Specifically, the linear velocity values ​​of the second and third pressing rollers are greater than those of the first and fourth pressing rollers, and the linear velocity value of the second pressing roller is equal to that of the third pressing roller. The thickness of the film is controlled by adjusting the size of the gap between the first and second pressing rollers and the gap between the third and fourth pressing rollers.

[0062] In this invention, the electrode sheet prepared using differential film formation technology has higher strength and better peel strength.

[0063] In this invention, the roll forming process in step S4 includes: feeding the precursor material obtained in the granulation step into the feed inlet of a four-roll press, allowing it to form a film through differential temperature / or differential speed film formation, and then converging them towards each other at the gap between the second or second-stage pressing roller and the third or third-stage pressing roller to form a film. During this period, a current collector is also inserted from the gap between the second or second-stage pressing roller and the third or third-stage pressing roller, ultimately forming a sandwich structure with positive electrode active material films on both sides and a current collector in the middle (e.g., ...). Figure 4 As shown in the figure, after drying and fine pressing, the thick electrode positive electrode sheet is collected in rolls to obtain the thick electrode positive electrode sheet.

[0064] In a second aspect, the present invention provides a thick electrode positive sheet, which is prepared by the method for preparing a thick electrode positive sheet according to the first aspect.

[0065] Thirdly, the present invention provides a primary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode comprises a thick electrode positive electrode as described in the second aspect.

[0066] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0067] Compared with the prior art, the present invention has the following beneficial effects:

[0068] This invention provides a method for preparing thick-film positive electrode sheets. On one hand, the invention uses a binder resin for dispersion treatment, subjecting it to shear fiberization to form a three-dimensional fiber network that adheres to the positive electrode active material particles. This is because the binder resin has a larger molecular weight than the binder emulsion, thus generating more fibers during the fiberization process. These fibers better bond the positive electrode active material particles, ultimately improving the bonding strength and electrochemical performance of the positive electrode material. On the other hand, the invention granulates the fiberized mixture with a granulating agent, allowing the room-temperature volatile liquid material to encapsulate the binder fibers and aid in granulation. During granulation, the material particles undergo further secondary fiberization, forming rubber-like particles with a certain strength, thereby improving the film strength in the subsequent stages. Simultaneously, a small amount of granulating agent allows the positive electrode active material to move more easily during rolling, thus avoiding stress-induced build-up lines on the film and improving its thickness uniformity.

[0069] Compared to existing wet coating processes, the preparation method provided by this invention reduces solvent usage, eliminates the traditional front-end film-forming process, and eliminates the need for additional binder coating on the current collector surface, thus enabling continuous winding. This significantly improves the automation level of the production line and avoids errors caused by manual intervention during production. Furthermore, the preparation method provided by this invention offers high adjustability, allowing for the control of parameters such as film compaction density, liquid absorption rate, and conductivity by adjusting the rolling film-forming process parameters, granulator content, and binder content, thereby adapting to the production of different battery electrode types.

[0070] Furthermore, the thick electrode positive sheet prepared by this invention has the advantages of high strength and low powder shedding rate. Attached Figure Description

[0071] Figure 1 This is a schematic diagram of the structure of the four-roller press provided by the present invention.

[0072] Figure 2 This is a schematic diagram of the structure of the eight-roller press provided by the present invention.

[0073] Figure 3 This is a schematic diagram of the structure of the ten-roller press provided by the present invention.

[0074] Figure 4 This is a schematic diagram of the structure of the thick electrode positive electrode sheet provided by the present invention. Detailed Implementation

[0075] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0076] First, this invention explores the influence of the type and content of polytetrafluoroethylene binder and granulator on the performance of the prepared thick electrode positive sheet, which is illustrated in the following examples:

[0077] Example 1

[0078] This embodiment provides a thick electrode positive electrode sheet and its preparation method, the preparation method including the following steps:

[0079] S1. Manganese dioxide powder, conductive agent Super P powder and polytetrafluoroethylene resin are mixed in a zero-gravity mixer at a temperature below 19°C to obtain a mixture, wherein the mass percentage of polytetrafluoroethylene resin is 3 wt.% based on the total mass of the mixture as 100%.

[0080] S2. The mixture is subjected to fiberization treatment in a high-speed mixer at a linear velocity of 100 m / s to obtain a fiberized mixture.

[0081] S3. The fibrous mixture is subjected to air jet milling to obtain abrasive material; then the abrasive material and dimethyl silicone oil granulator are stirred and granulated in a high-speed stirring granulator to obtain the precursor material, wherein, based on the total mass of the granulated material as 100%, the mass percentage of dimethyl silicone oil granulator is 20 wt.%.

[0082] S4. The precursor material is fed into the inlet of a four-roll press and subjected to film formation by a differential temperature film-forming roller system. The film is formed by the materials converging towards each other at the gap between the second and third pressing rollers. During this process, a current collector is also inserted through the gap between the second and third pressing rollers, ultimately forming a positive electrode sheet with a sandwich structure of positive active material films on both sides and a current collector in the middle. After drying and fine pressing, the material is rolled up and collected to obtain the thick electrode positive electrode sheet. The specific process of differential temperature film formation includes: feeding the precursor material obtained in the above granulation step into the gap between the first and second pressing rollers of the four-roll press, and into the gap between the third and fourth pressing rollers. The second and third pressing rollers can press the fed powder into a continuous film sheet.

[0083] A schematic diagram of the four-roller press is shown below. Figure 1As shown, the leftmost roller is the first pressure roller, and from left to right, they are the second, third, and fourth pressure rollers. The first, second, third, and fourth pressure rollers have the same diameter, and their centers are all on the same horizontal line. The first and third pressure rollers rotate clockwise, while the second and fourth rotate counter-clockwise. Furthermore, the temperature of the first and third pressure rollers is 110℃, the temperature of the second and third pressure rollers is 60℃, and the temperature of the fourth pressure roller is 110℃. The linear velocities of the first, second, third, and fourth pressure rollers are the same.

[0084] Example 2

[0085] The difference between this embodiment and Embodiment 1 is that step S3 is adjusted to: the grinding material and N-methylpyrrolidone granulating agent are stirred and granulated in a high-speed stirring granulator to obtain the precursor material, wherein, based on the total mass of the granulated material as 100%, the mass percentage of N-methylpyrrolidone is 15 wt.%, and all other aspects are the same as in Embodiment 1.

[0086] Example 3

[0087] The difference between this embodiment and Embodiment 1 is that step S3 is adjusted to: the grinding material and polyethylene glycol granulating agent are stirred and granulated in a high-speed stirring granulator to obtain the precursor material, wherein, based on the total mass of the granulated material as 100%, the mass percentage of polyethylene glycol is 25 wt.%, and all other aspects are the same as in Embodiment 1.

[0088] Example 4

[0089] This embodiment provides a thick electrode positive electrode sheet and its preparation method, the preparation method including the following steps:

[0090] S1. Acetylene black, conductive agent Super P powder and polytetrafluoroethylene resin are mixed in a zero-gravity mixer at a temperature below 19°C to obtain a mixture, wherein the mass percentage of polytetrafluoroethylene resin is 10 wt.% based on the total mass of the mixture as 100%.

[0091] S2. The mixture is subjected to fiberization treatment in an air jet mill at a pressure of 0.8 MPa to obtain a fiberized mixture;

[0092] S3. The fibrous mixture and dimethyl silicone oil granulator are mixed and granulated in a high-speed mixing granulator to obtain the precursor material, wherein the mass percentage of dimethyl silicone oil granulator is 50 wt.% based on the total mass of the granulated material as 100%.

[0093] S4. The precursor material is fed into the inlet of a four-roll press and subjected to film formation by a differential temperature film-forming roller system. The film is formed by the materials converging towards each other at the gap between the second and third pressing rollers. During this process, a current collector is also inserted through the gap between the second and third pressing rollers, ultimately forming a positive electrode sheet with a sandwich structure of positive active material films on both sides and a current collector in the middle. After drying and fine pressing, the material is rolled up and collected to obtain the thick electrode positive electrode sheet. The specific process of differential temperature film formation includes: feeding the precursor material obtained in the above granulation step into the gap between the first and second pressing rollers of the four-roll press, and into the gap between the third and fourth pressing rollers. The second and third pressing rollers can press the fed powder into a continuous film sheet.

[0094] A schematic diagram of the four-roller press is shown below. Figure 1 As shown, the leftmost roller is the first pressure roller, and from left to right, they are the second, third, and fourth pressure rollers. The first, second, third, and fourth pressure rollers have the same diameter, and their centers are all on the same horizontal line. The first and third pressure rollers rotate clockwise, while the second and fourth rotate counter-clockwise. Furthermore, the temperature of the first and third pressure rollers is 110℃, the temperature of the second and third pressure rollers is 60℃, and the temperature of the fourth pressure roller is 110℃. The linear velocities of the first, second, third, and fourth pressure rollers are the same.

[0095] Example 5

[0096] The difference between this embodiment and Embodiment 1 is that the dimethyl silicone oil granulator in step S3 is replaced with an equal amount of isopropanol, while all other aspects are the same as in Embodiment 1.

[0097] Example 6

[0098] The difference between this embodiment and Embodiment 1 is that, taking the total mass of the granulated material as 100%, the mass percentage of dimethyl silicone oil granulating agent in step S3 is 5 wt.%, while all other aspects are the same as in Embodiment 1.

[0099] Example 7

[0100] The difference between this embodiment and Embodiment 1 is that, taking the total mass of the granulated material as 100%, the mass percentage of dimethyl silicone oil granulating agent in step S3 is 35 wt.%, while all other aspects are the same as in Embodiment 1.

[0101] Comparative Example 1

[0102] The difference between this embodiment and Embodiment 1 is that step S3 is adjusted to: no dimethyl silicone oil granulating agent is added, only the step of processing the fibrous mixture by air jet milling to obtain the abrasive is retained, and all other steps are the same as in Embodiment 1.

[0103] Comparative Example 2

[0104] The difference between this embodiment and Embodiment 1 is that step S1 is adjusted to replace polytetrafluoroethylene resin with an equal amount of polytetrafluoroethylene emulsion; and step S3 is adjusted to not add dimethyl silicone oil granulating agent, only retaining the step of processing the fibrous mixture by air jet milling to obtain abrasive material, while all other steps are the same as in Embodiment 1.

[0105] The thick electrode positive plates prepared in Examples 1-7 and Comparative Examples 1-2 were subjected to performance testing. The testing methods are as follows:

[0106] (1) Thickness consistency: On the prepared positive electrode roll, electrode sheets with a diameter of 5cm were cut every 20cm using an electrode sampler, for a total of 20 samples. Each sample was measured using a micrometer (accurate to 0.001mm). The relative standard deviation of the thickness values ​​of the 20 collected samples was calculated. The formula for calculating the relative standard deviation is: x represents the sample thickness.

[0107] (2) Initial positive electrode peeling force: Take 20 400mm×20mm electrodes from the prepared positive electrode roll and test them on a universal tensile testing machine, and take the average value.

[0108] (3) Positive electrode sheet areal density: For samples with uniform electrode sheet thickness, measure their weight, calculate the electrode sheet areal density, and take the average value. The areal density calculation formula is: m is the sample weight, and s is the sample area.

[0109] The test results are shown in Table 1:

[0110] Table 1

[0111]

[0112]

[0113] As can be seen from Table 1, comparing Examples 1-4 and Comparative Examples 1-2, it is evident that the step of granulating the fibrous mixture with a granulating agent in this invention is crucial for improving the thickness uniformity, peel strength, and areal density of the thick electrode positive sheet.

[0114] Comparing Example 1 and Example 5, it can be seen that the present invention uses a liquid material that can evaporate at room temperature to encapsulate the binder fiber and help it granulate, thereby improving the film strength in the later stage, avoiding the accumulation lines caused by stress on the film, and improving the uniformity of its thickness. However, the isopropanol disclosed in the prior art cannot achieve the above technical effects.

[0115] Comparing Example 1 with Examples 6-7, it can be seen that if the content of the granulating agent is not within the preferred range of this invention, it easily affects the final granulation effect, thus preventing the precursor material particles from completing the film transfer step during the rolling process. Furthermore, while ensuring a certain granulation effect, a higher content of the added granulating agent results in a lower areal density of the prepared positive electrode sheet. This is because the granulating agent leaves pores inside the positive electrode sheet after drying, thus reducing the overall density of the positive electrode sheet.

[0116] Comparing Example 1 and Comparative Example 2, it can be seen that the polytetrafluoroethylene emulsion disclosed in the prior art can also achieve a certain degree of fiberization effect. However, it is obvious that the thickness uniformity, peel strength and areal density of the positive electrode sheet prepared using polytetrafluoroethylene emulsion are not as good as those of the positive electrode sheet provided in Example 1.

[0117] Secondly, this invention explores the influence of the differential temperature film formation method and its specific parameters on the performance of the resulting thick electrode positive sheet. This is specifically illustrated in Examples 8-18 shown in Table 2 below. Examples 8-18 are identical to Example 1 except for the conditions in Table 2.

[0118] Table 2

[0119]

[0120]

[0121] As can be seen from Table 2, the present invention improves the quality of the prepared positive electrode sheet by controlling the minimum temperature of the low-temperature roller and the temperature difference between the high-temperature roller and the low-temperature roller during the differential temperature film formation process.

[0122] Comparing Example 1 with Examples 16-18, it can be seen that when the temperature of the low-temperature roller is high (e.g., above 60°C), the temperature difference between it and the high-temperature roller is not significant, and the granulating agent is easily evaporated during the rolling process, making it difficult for the film to be transferred and formed. Conversely, as the temperature difference between the low-temperature roller and the high-temperature roller increases, the film formation process becomes easier, thereby increasing the areal density of the positive electrode sheet. However, the thickness uniformity of the positive electrode sheet gradually deteriorates due to the evaporation of the granulating agent. Therefore, a comprehensive consideration is needed in the production process of the positive electrode sheet to further improve its overall performance.

[0123] Finally, this invention explores the influence of differential film formation method and its specific parameters on the performance of the prepared thick electrode positive sheet, specifically illustrated in Examples 19-33 shown in Table 3 below. Examples 19-33 are identical to Example 1 except for the conditions shown in Table 3.

[0124] Table 3

[0125]

[0126]

[0127] As shown in Table 3, this invention further improves film strength and reduces the powder shedding rate of the positive electrode by controlling the film-forming temperature during the differential film-forming process and the synergistic effect between the linear velocity ratio of the slow and fast rollers. Examples 19-23 show that when the rolling temperature is low (e.g., 70°C), the linear velocity ratio between the slow and fast rollers is low (e.g., 1:1.1), resulting in insufficient shear force and preventing the film from transferring to the fast roller side. When the linear velocity ratio between the slow and fast rollers is high (e.g., 1:1.5), the film will break during the transfer process. Simultaneously, under the same rolling temperature conditions, the larger the linear velocity ratio between the slow and fast rollers, the greater the shear force during the rolling process, resulting in a greater peel force for the prepared positive electrode, but a decrease in the areal density of the film.

[0128] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for producing a thick-electrode positive electrode sheet, characterized by, The method comprises the following steps: S1. mixing a positive electrode active material, a conductive agent, and a binder resin to obtain a mixture; S2. performing a fiberization treatment on the mixture to obtain a fiberized mixture; S3. performing a granulation treatment on the fiberized mixture and a granulating agent to obtain a precursor material, wherein the granulating agent is a liquid with a vapor pressure not lower than 0.2 mmHg; S4. performing a roll-to-film treatment on the precursor material to obtain the thick electrode positive electrode sheet; The roll-to-film manner in step S4 comprises differential temperature film forming; The differential temperature film forming device comprises a differential temperature film forming roller system; The differential temperature film forming roller system comprises a first pressing roller, a second pressing roller, a third pressing roller, and a fourth pressing roller arranged in sequence, a first feeding port is formed above the first pressing roller and the second pressing roller, and a second feeding port is formed above the third pressing roller and the fourth pressing roller, and the second pressing roller and the third pressing roller can press the powder placed in the first feeding port and the second feeding port into a continuous film sheet; The rolling direction of the first pressing roller and the third pressing roller is opposite to the rolling direction of the second pressing roller and the fourth pressing roller; The temperature of the first pressing roller and the fourth pressing roller is higher than the temperature of the second pressing roller and the third pressing roller; The temperature of the first pressing roller and the fourth pressing roller is 50-105°C; The temperature of the second pressing roller and the third pressing roller is 20-60°C; The temperature difference between the first pressing roller and the second pressing roller is 10-90°C; The temperature difference between the fourth pressing roller and the third pressing roller is 10-90°C; The thickness of the thick electrode positive electrode sheet is >500 μm.

2. The method of claim 1, wherein, The positive electrode active material in step S1 comprises manganese dioxide and / or acetylene black.

3. The method of claim 1, wherein, The binder resin in step S1 comprises polytetrafluoroethylene.

4. The method of claim 1, wherein, When the positive electrode active material in step S1 is manganese dioxide, the mass percentage of the binder resin in step S1 is 1-5% based on the total mass of the mixture.

5. The method of claim 4, wherein, When the positive electrode active material in step S1 is manganese dioxide, the mass percentage of the binder resin in step S1 is 1.5-2.5% based on the total mass of the mixture.

6. The method of claim 1, wherein, When the positive electrode active material in step S1 is acetylene black, the mass percentage of the binder resin in step S1 is 5-15% based on the total mass of the mixture.

7. The method of claim 6, wherein, When the positive electrode active material in step S1 is acetylene black, the mass percentage of the binder resin in step S1 is 6-8% based on the total mass of the mixture.

8. The method of claim 1, wherein, The mixing manner in step S1 is gravity-free mixing.

9. The method of claim 1, wherein, The mixing temperature in step S1 is lower than 19°C.

10. The method of claim 1, wherein, The fiberization treatment device in step S2 comprises a high-speed mixer and / or an airflow mill.

11. The method of claim 10, wherein, The linear speed of the high-speed mixer is 50-150 m / s.

12. The method of claim 10, wherein, The air pressure of the jet mill is 0.75-0.85 MPa.

13. The method of claim 1, wherein, The granulating agent in step S3 includes any one or a combination of at least two of N-methyl pyrrolidone, dimethyl silicone oil, polyethylene glycol, propylene glycol, isoparaffin, paraffin oil or pure water.

14. The method of claim 1, wherein, When the positive active material is manganese dioxide, the mass percentage of the granulating agent in step S3 is 10-30 wt.% based on the total mass of the granulating material.

15. The method of claim 14, wherein, When the positive active material is manganese dioxide, the mass percentage of the granulating agent in step S3 is 15-25 wt.% based on the total mass of the granulating material.

16. The method of claim 1, wherein, When the positive active material is acetylene black, the mass percentage of the granulating agent in step S3 is 30-70 wt.% based on the total mass of the granulating material.

17. The method of claim 16, wherein, When the positive active material is acetylene black, the mass percentage of the granulating agent in step S3 is 50-60 wt.% based on the total mass of the granulating material.

18. The method of claim 1, wherein, The temperature difference between the first and second compression rollers is 30-50°C.

19. The method of claim 1, wherein, The temperature difference between the fourth and third compression rollers is 30-50°C.

20. The method of claim 1, wherein, The film-rolling method in step S4 includes differential temperature film rolling and differential speed film rolling.

21. The method of claim 20, wherein, The film-rolling temperature of the differential speed film rolling is 40-110°C.

22. The method of claim 20, wherein, The differential speed film rolling device includes a differential speed film rolling system.

23. The method of claim 22, wherein, The differential speed film rolling system includes a first compression roller, a second compression roller, a third compression roller and a fourth compression roller arranged in sequence, a first feeding port is formed above the first and second compression rollers, a second feeding port is formed above the third and fourth compression rollers, and the second and third compression rollers can roll the powder fed into the first and second feeding ports into a continuous film.

24. The method of claim 23, wherein, The gap between adjacent rollers in the differential speed film rolling system is 0.10-0.60 mm.

25. The method of claim 23, wherein, The rolling direction of the first and third compression rollers is opposite to that of the second and fourth compression rollers.

26. The method of claim 23, wherein, The linear speed of the first and fourth compression rollers is lower than that of the second and third compression rollers.

27. The method of claim 23, wherein, The linear speed of the first compression roller is the same as that of the fourth compression roller.

28. The method of claim 23, wherein, The linear speed of the second compression roller is the same as that of the third compression roller.

29. The method of claim 23, wherein, The linear speed ratio of the first and / or fourth compression roller to the second and / or third compression roller is 1:(1.1-2).

30. A thick electrode positive electrode sheet, characterized by The thick electrode positive plate is prepared by the method for preparing a thick electrode positive plate according to any one of claims 1-29.

31. A primary battery, characterized by comprising: The primary battery includes a positive plate, a negative plate, an electrolyte and a separator, and the positive plate includes the thick electrode positive plate according to claim 30.

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