Thick-electrode positive electrode sheet and preparation method therefor, and primary battery

Abstract

Provided in the present application are a thick-electrode positive electrode sheet and a preparation method therefor, and a primary battery. The method comprises: firstly, mixing a positive electrode active substance, an electrically conductive agent and a binder resin, so as to obtain a mixed material; subjecting the mixed material to a fibration treatment, so as to obtain a fiberized mixed material; then subjecting the fiberized mixed material and a granulating agent to a granulation treatment, so as to obtain a precursor material; and finally, subjecting the precursor material to a rolling film-forming treatment, so as to obtain the thick-electrode positive electrode sheet.

Description

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

[0001] This application claims priority to the Chinese patent application No. 2024119997665, filed on December 31, 2024, with the Chinese Patent Office, the content of which is incorporated herein by reference in its entirety.

[0002] TECHNICAL FIELD

[0003] The present application relates to the technical field of batteries, in particular to a thick-electrode positive electrode sheet, a preparation method thereof and a primary battery.

[0004] BACKGROUND

[0005] In the battery manufacturing process, cylindrical batteries usually adopt a winding method to manufacture the battery core, specifically, the positive electrode, the separator and the negative electrode are sequentially stacked and wound to manufacture the winding core, which not only can increase the effective area of the electrode sheet, but also can improve the energy density of the battery. Among them, for the rechargeable secondary battery, the positive electrode and the negative electrode are mostly coated with slurry on both sides of the current collector foil (such as aluminum foil or copper foil) in a coating manner, so as to form a long strip-shaped electrode sheet. However, due to the irreversible chemical reaction of the primary battery, the primary battery mainly adopts the method of filling as many active substances as possible on the mesh current collector to further improve the capacity of the battery. This structural design makes the thickness of the electrode sheet thicker, i.e., up to 500 μm, under the same high compaction density.

[0006] For example, a lithium manganese dioxide battery is a battery with electrolytic manganese dioxide as the positive electrode and lithium metal as the negative electrode, and the specific electrochemical reaction formula is: MnO2+xLi→Li x MnO2. The preparation of the positive electrode sheet of the lithium manganese dioxide cylindrical battery usually adopts a slurry drawing method, which includes configuring manganese dioxide, a conductive agent and a binder into a positive electrode active material slurry, then slowly passing the current collecting net through the positive electrode active material slurry pool, so that the slurry is uniformly hung on the net, and then the slurry is dried and precision pressed, to finally form the positive electrode sheet. The above preparation process has defects such as high slurry requirement, high production energy consumption, high powder falling rate of the prepared positive electrode sheet and inability to manufacture a positive electrode sheet with high compaction density.

[0007] For example, lithium thionyl chloride batteries have high specific energy (up to 590 Wh / kg), high rated voltage (3.6 V), low self-discharge rate (≤1%) and wide operating temperature range (-55°C to 85°C), etc. Therefore, it is the highest specific energy battery in current commercial applications. The working principle of lithium thionyl chloride battery is based on the chemical reaction of lithium and thionyl chloride (SOCl2). The battery is composed of metal lithium as negative electrode, carbon as positive electrode, SOCl2 solution of anhydrous lithium tetrachloroaluminate as electrolyte and positive active material. The electrochemical reaction formula is: 4Li + 2SOCl2→ 4LiCl + S↓ + SO2.

[0008] In lithium thionyl chloride cylindrical batteries, power batteries usually adopt a winding structure. Specifically, acetylene black, polytetrafluoroethylene emulsion and ethanol or isopropyl alcohol are mixed to form a powder, which is then uniformly coated on a nickel mesh, and then the mesh is wound with a separator and a negative electrode to form an integrated structure. Alternatively, the powder is prepared into a self-supporting film by kneading and rolling multiple times, and then the self-supporting film is attached to the nickel mesh for compounding.

[0009] Technical problem

[0010] In fact, the thickness of the power battery electrode is large and acetylene black is used as the conductive agent. The density and particle size of acetylene black are usually small, which makes it difficult to form a slurry suitable for coating production equipment. In addition, the form of self-supporting acetylene black film attached to the mesh cannot realize automatic and continuous production, and the preparation form of powder-pressed mesh will result in a high powder loss rate, so both production methods have certain shortcomings.

[0011] In recent years, in order to further produce thick electrode sheets and improve the energy density of the battery, dry electrode technology has attracted widespread attention. The core of this dry electrode technology is to utilize the fiberization ability of polytetrafluoroethylene (PTFE) binder, and then disperse the PTFE into a fibrous structure, and mix it with active material and conductive agent to form a self-supporting or non-self-supporting electrode film. This process does not require the use of solvents, thereby avoiding the defects of solvent residues in traditional wet process, while having the advantages of environmental protection, low cost and high production efficiency. However, the production of this dry electrode technology is difficult, and the fiberization degree of polytetrafluoroethylene is high. In addition, since no solvent is added, the formed fibers are prone to breakage during the dispersion process, and the active material particles also produce stress accumulation during film formation, resulting in uneven thickness of the formed film.

[0012] Therefore, it is urgent to develop a method for optimizing the fiberization process of PTFE to improve its mechanical strength and stability, and to solve the problem of insufficient adhesion between the current collector and the dry electrode film.

[0013] Technical solution

[0014] The application provides a thick electrode positive plate and a preparation method thereof and a primary battery. The preparation method provided by the application can be universally applied to a battery system that needs to use a current collecting grid to manufacture a thick electrode (>500 μm), and solves the defects of the thick electrode plate using the current collecting grid, such as difficulty in continuous automatic production, high powder falling rate of the plate and uneven thickness.

[0015] In a first aspect, the application provides a method for preparing a thick electrode positive plate, the method comprising the following steps:

[0016] S1. mixing a positive active material, a conductive agent and a binder resin to obtain a mixture;

[0017] S2. performing a fiberization treatment on the mixture to obtain a fiberized mixture;

[0018] 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;

[0019] S4. performing a film forming treatment on the precursor material by rolling to obtain the thick electrode positive plate.

[0020] In a second aspect, the application provides a thick electrode positive plate, which is prepared by the method for preparing a thick electrode positive plate according to the first aspect.

[0021] In a third aspect, the application provides a primary battery, which comprises a positive plate, a negative plate, an electrolyte and a separator, and the positive plate comprises the thick electrode positive plate according to the second aspect.

[0022] Advantages

[0023] Compared with the related art, the application has the following advantages:

[0024] The application provides a method for preparing a thick electrode positive electrode sheet. In one aspect, the application uses a binder resin for dispersion treatment, which is subjected to shear fiberization treatment, thereby forming a three-dimensional fiber network to adhere positive electrode active material particles. This is because the molecular weight of the binder resin is larger than that of the binder emulsion, so more fibers can be generated during fiberization. These fibers can better bind the positive electrode active material particles, ultimately improving the bonding strength and electrochemical performance of the positive electrode material. In another aspect, the application granulates the fiberized mixture with a granulating agent, so that the liquid material that can volatilize at room temperature can wrap the binder fibers and help granulation. During granulation, the material particles are further subjected to secondary fiberization, forming rubber-like particles with certain strength, thereby improving the film strength in the later stage. At the same time, a small amount of granulating agent can make the positive electrode active material move more easily during rolling, thereby avoiding the accumulation of lines caused by stress on the film, and improving the uniformity of its thickness.

[0025] Compared with the wet coating process in the related art, the preparation method provided by the application reduces the amount of solvent used, eliminates the traditional front film forming process, and does not need to additionally coat the binder on the surface of the current collector, thereby realizing continuous winding, which greatly improves the automation level of the production line and avoids errors caused by manual intervention in the production process. At the same time, the preparation method provided by the application has high adjustability, which can adjust the compaction density, liquid absorption rate and electrical conductivity of the film by adjusting the rolling film forming process parameters, the content of the granulating agent and the content of the binder, thereby adapting to the production of battery electrode sheets of different models.

[0026] In addition, the thick electrode positive electrode sheet prepared by the application has the advantages of high strength and low powder dropping rate.

[0027] Other aspects can become apparent from a review of the drawings and detailed description.

[0028] BRIEF DESCRIPTION OF DRAWINGS

[0029] FIG. 1 is a structural schematic diagram of a four-roller pressing device provided by some embodiments of the application.

[0030] FIG. 2 is a structural schematic diagram of an eight-roller pressing device provided by some embodiments of the application.

[0031] FIG. 3 is a structural schematic diagram of a ten-roller pressing device provided by some embodiments of the application.

[0032] FIG. 4 is a structural schematic diagram of a thick electrode positive electrode sheet provided by some embodiments of the application.

[0033] Among them, 1-electrode sheet, 2-current collecting net, 3-electrode film.

[0034] Embodiments of the application

[0035] In a first aspect, the present application provides a method for preparing a thick electrode positive electrode sheet, the method comprising the following steps:

[0036] S1. mixing a positive electrode active material, a conductive agent, and a binder resin to obtain a mixture;

[0037] S2. performing a fiberization treatment on the mixture to obtain a fiberized mixture;

[0038] 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 less than 0.2 mmHg;

[0039] S4. performing a roll-to-film treatment on the precursor material to obtain the thick electrode positive electrode sheet.

[0040] It should be noted that the granulating agent in the present application is a liquid with a vapor pressure not less than 0.2 mmHg at room temperature, for example, 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.

[0041] On the one hand, the present application uses a binder resin for dispersion treatment, which is subjected to shear fiberization treatment to form a three-dimensional fiber network to adhere positive electrode active material particles. This is because the molecular weight of the binder resin is larger than that of the binder emulsion, so more fibers can be generated during the fiberization process. These fibers can 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, the present application performs a granulation treatment on the fiberized mixture and a granulating agent, so that the liquid material that can volatilize at room temperature can wrap the binder fibers and help granulation. During the granulation process, the material particles are further subjected to secondary fiberization to form rubber-like particles with certain strength, thereby improving the film strength in the later stage. At the same time, a small amount of granulating agent can make the positive electrode active material move more easily during the rolling process, thereby avoiding the accumulation of lines due to stress on the film and improving the uniformity of its thickness.

[0042] Optionally, the positive electrode active material in step S1 includes manganese dioxide and / or acetylene black.

[0043] Optionally, the binder resin in step S1 includes polytetrafluoroethylene.

[0044] Optionally, when the positive active material in step S1 is manganese dioxide, the mass percentage of the binder resin in step S1 is 1wt.%-5wt.% based on the total mass of the mixture, which can be 1.5wt.%-2.5wt.% for example, such as 1wt.%, 1.2wt.%, 1.5wt.%, 1.8wt.%, 2wt.%, 2.2wt.%, 2.5wt.%, 2.8wt.%, 3wt.%, 3.2wt.%, 3.5wt.%, 3.8wt.%, 4wt.%, 4.2wt.%, 4.5wt.%, 4.8wt.%, 5wt.% and the like. The present application controls the mass percentage of the binder resin to fully expand the binder fibers to form a three-dimensional network to bind the positive active material particles, thereby controlling the formation of the electrode sheet. If a lower mass percentage of the binder resin is used, the positive active material cannot be fully bound, which can cause the film to be broken or unable to be transferred during the film rolling process, and the powder dropping rate of the prepared positive electrode sheet is high, which ultimately affects the electrical performance of the primary battery. If a higher mass percentage of the binder resin is used, the film resistance of the positive electrode sheet increases, which further affects the internal resistance and discharge performance of the assembled primary battery.

[0045] Optionally, when the positive active material in step S1 is acetylene black, the mass percentage of the binder resin in step S1 is 5wt.%-15wt.% based on the total mass of the mixture, which can be 6wt.%-8wt.% for example. The present application controls the mass percentage of the binder resin to fully expand the binder fibers to form a three-dimensional network to bind the positive active material particles, thereby controlling the formation of the electrode sheet. If a lower mass percentage of the binder resin is used, the positive active material cannot be fully bound, which can cause the film to be broken or unable to be transferred during the film rolling process, and the powder dropping rate of the prepared positive electrode sheet is high, which ultimately affects the electrical performance of the primary battery. If a higher mass percentage of the binder resin is used, the film resistance of the positive electrode sheet increases, which further affects the internal resistance and discharge performance of the assembled primary battery.

[0046] Optionally, the mixing in step S1 is performed by gravity-free mixing.

[0047] Optionally, the temperature for the mixing in step S1 is lower than 19℃, such as -10℃, -5℃, 0℃, 5℃, 10℃, 15℃ and the like.

[0048] The present application further controls the mixing method and temperature to avoid the binder resin being fiberized in advance during the mixing process.

[0049] Optionally, the device for the fiberization treatment in step S2 includes a high-speed mixer and / or an air jet mill.

[0050] Optionally, the linear speed of the high-speed mixer is 50 m / s-150 m / s, for example, it can be 50 m / s, 60 m / s, 70 m / s, 80 m / s, 90 m / s, 100 m / s, 110 m / s, 120 m / s, 130 m / s, 140 m / s, 150 m / s, etc.

[0051] Optionally, the air pressure of the jet mill is 0.75 MPa-0.85 MPa, for example, it can be 0.75 MPa, 0.78 MPa, 0.8 MPa, 0.82 MPa, 0.85 MPa, etc.

[0052] Optionally, 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, isomeric alkanes, paraffin oil, or pure water.

[0053] Optionally, when the positive electrode active material is manganese dioxide, the mass percentage of the granulating agent in step S3 is 10wt.%-30wt.% based on the total mass of the granulating material, which can be 15wt.%-25wt.%, for example, it can be 10wt.%, 12wt.%, 15wt.%, 18wt.%, 20wt.%, 22wt.%, 25wt.%, 28wt.%, 30wt.%, etc. By adjusting the mass percentage of the granulating agent, the fibrous mixture can be made into precursor material particles with uniform size, good sphericity, and good flowability, which facilitates uniform feeding during the roll-to-film process, thereby controlling the thickness uniformity of the film. If a lower mass percentage of the granulating agent is used, the granulating agent cannot completely coat the fibrous mixture, resulting in granulation failure; if a higher mass percentage of the granulating agent is used, the particle size of the precursor material particles is too large or the powder cannot be granulated (e.g., lumping or caking).

[0054] Optionally, when the positive electrode active material is acetylene black, the mass percentage of the granulating agent in step S3 is 30wt.%-70wt.% based on the total mass of the granulating material, which can be 50wt.%-60wt.%, for example, it can be 30wt.%, 40wt.%, 50wt.%, 52wt.%, 55wt.%, 60wt.%, 62wt.%, 65wt.%, 68wt.%, 70wt.%, etc. Since the density of acetylene black material is low, the content of the added granulating agent is high.

[0055] Optionally, the roll-to-film method in step S4 includes differential temperature film forming and / or differential speed film forming, which can be differential temperature film forming.

[0056] Compared with the differential speed film forming mode, the differential temperature film forming mode does not cause stress accumulation between particles in the film forming process and causes the accumulation lines of the film, thereby making the thickness, surface density uniformity and consistency of the film better.

[0057] Optionally, the differential temperature film forming device comprises a differential temperature film forming roller system.

[0058] Optionally, 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 between the first pressing roller and the second pressing roller, a second feeding port is formed above between 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.

[0059] Optionally, 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.

[0060] Optionally, 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 application controls the temperature of the first pressing roller and the fourth pressing roller to be higher than the temperature of the second pressing roller and the third pressing roller, because temperature has an influence on molecular motion and adhesion, which is specifically manifested as: the molecular motion on the surface of an object slows down at low temperature, resulting in an increase in the contact area between molecules, thereby enhancing the adhesion. On the contrary, the molecular motion on the surface of an object speeds up at high temperature, the contact area between molecules decreases, resulting in a decrease in the adhesion. Therefore, the low-temperature roller can better maintain the adhesion of the object, so that the film is more easily attached to the low-temperature roller.

[0061] Optionally, the temperature of the first pressing roller and the fourth pressing roller is 50-105℃, for example, it can be 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 105℃, etc.

[0062] Optionally, the temperature of the second pressing roller and the third pressing roller is 20-60℃, for example, it can be 20℃, 30℃, 40℃, 50℃, 60℃, etc.

[0063] Optionally, the temperature difference between the first pressing roller and the second pressing roller is 10-90℃, optionally 30-50℃, for example, it can be 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, etc. The application controls the temperature difference between the first pressing roller and the second pressing roller, so that the precursor material particles are adhered to one side of the second pressing roller after rolling, and then transferred to the gap between the second pressing roller and the third pressing roller for preparation of the positive electrode sheet.

[0064] Optionally, the temperature difference between the fourth press roller and the third press roller is 10-90°C, optionally 30-50°C, for example, it can be 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, etc. The present application controls the temperature difference between the fourth press roller and the third press roller, so that the precursor material particles adhere to one side of the third press roller after rolling, and then are transferred to the gap between the second press roller and the third press roller for the preparation of the positive electrode sheet.

[0065] In the present application, the diameters of the first press roller, the second press roller, the third press roller and the fourth press roller are the same.

[0066] In the present application, the centers of the first press roller, the second press roller, the third press roller and the fourth press roller are located on the same horizontal line.

[0067] In the present application, the linear speeds of the first press roller, the second press roller, the third press roller and the fourth press roller are the same.

[0068] As an optional technical solution of the present application, the precursor material prepared by the above granulation step is put into the gap between the first press roller and the second press roller of a four-roller press device, and into the gap between the third press roller and the fourth press roller, and the structure of the four-roller press device is shown in FIG. 1 (in the figure, 1 is the electrode sheet, 2 is the current collector, and the arrow represents the feeding position), wherein the leftmost is the first press roller, from left to right are the second press roller, the third press roller and the fourth press roller, the first press roller and the third press roller rotate clockwise, and the second press roller and the fourth press roller rotate counterclockwise.

[0069] The present application uses differential temperature rolling technology to make the precursor material particles form independent films during the rolling process and adhere to the low-temperature roller. The thickness of the film is controlled by the size of the gap between the first press roller and the second press roller and the gap between the third press roller and the fourth press roller, and the thickness of the electrode sheet is controlled by the size of the gap between the second press roller and the third press roller. During the lamination of the current collector, the film needs to be uniformly attached to the roller, so the film does not need to be self-supporting during this process. In addition, the uniformity of the film thickness will be affected by factors such as the particle size, specific surface area or microtopography of the active material. In order to improve the uniformity of the film thickness, a device with more rollers can be used, for example, an eight-roller press device or a ten-roller press device (as shown in FIG. 2 and FIG. 3, in FIG. 2 and FIG. 3, 1 is the electrode sheet, 2 is the current collector, and the arrow represents the feeding position). These devices can more effectively control the thickness distribution of the film by increasing the number of rollers, thereby improving the thickness consistency.

[0070] In the present application, the surface of the pole piece prepared by using differential temperature film forming technology is more smooth, and the area density is higher.

[0071] Optionally, the rolling temperature of the differential film forming is 40-110℃, for example, it can be 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, etc.

[0072] Optionally, the differential film forming device comprises a differential film forming roller system.

[0073] Optionally, the differential 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, 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 piece.

[0074] Optionally, the gap between adjacent rollers in the differential film forming roller system is 0.10-0.60mm, 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.

[0075] Specifically, when the positive electrode active material is manganese dioxide, the gap between adjacent rollers in the differential film forming roller system is 0.20-0.50mm; when the positive electrode active material is acetylene black, the gap between adjacent rollers in the differential film forming roller system is 0.10-0.60mm.

[0076] Optionally, 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.

[0077] Optionally, the linear speed of the first pressing roller and the fourth pressing roller is less than the linear speed of the second pressing roller and the third pressing roller.

[0078] Optionally, the linear speed of the first pressing roller and the linear speed of the fourth pressing roller are the same.

[0079] Optionally, the linear speed of the second pressing roller and the linear speed of the third pressing roller are the same.

[0080] Optionally, 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). 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. By adjusting the linear speed ratio of the first and / or fourth compression roller to the second and / or third compression roller, the precursor material particles are subjected to greater shear force during the rolling process, thereby further improving the film strength and reducing the powder drop rate of the positive electrode sheet. If the linear speed of the first and / or fourth compression roller is too high, the film sheet may be broken during the rolling process.

[0081] Specifically, when the temperature of the differential speed film forming and rolling is 40-80℃, the linear speed ratio of the first and / or fourth compression roller to the second and / or third compression roller is 1:(1.2-1.3); when the temperature of the differential speed film forming and rolling is 90-100℃, the linear speed ratio of the first and / or fourth compression roller to the second and / or third compression roller is 1:(1.1-1.3); when the temperature of the differential speed film forming and rolling is 110℃, 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).

[0082] In the present application, the diameters of the first, second, third and fourth compression rollers are the same.

[0083] In the present application, the centers of the first, second, third and fourth compression rollers are located on the same horizontal line.

[0084] As an optional technical solution of the present application, the precursor material prepared by the above granulation step is fed into the gap between the first and second compression rollers and the gap between the third and fourth compression rollers of a four-roller compression device, and the structure of the four-roller compression device is shown in FIG. 1 (FIG. 1 is an electrode sheet, FIG. 2 is a current collector, and the arrow represents the feeding position), wherein the leftmost is the first compression roller, from left to right are the second, third and fourth compression rollers, the first and third compression rollers rotate clockwise, and the second and fourth compression rollers rotate counterclockwise.

[0085] The application utilizes differential roller pressing technology to make the precursor material particles independently form a film during the roller pressing process and adhere to the fast roller. Specifically, the linear speed value of the second pressing roller and the third pressing roller is greater than the linear speed value of the first pressing roller and the fourth pressing roller, and the linear speed value of the second pressing roller is equal to the linear speed value of the third pressing roller, and the thickness of the film is controlled by adjusting the size of the gap between the first pressing roller and the second pressing roller and the gap between the third pressing roller and the fourth pressing roller.

[0086] In the application, the pole piece prepared by using the differential film forming technology has higher strength and better peeling force.

[0087] In the application, the process of roller pressing film in step S4 includes: feeding the precursor material prepared in the granulation step into the feeding port of the four-roller pressing device, and after differential temperature film forming and / or differential speed film forming, the film is converged between the gap between the second pressing roller or the second pressing roller and the third pressing roller or the third pressing roller, during which the current collector is inserted from the gap between the second pressing roller or the second pressing roller and the third pressing roller or the third pressing roller, and finally a sandwich structure (as shown in FIG. 4) of the positive active material film (electrode film 3 in FIG. 4) on both sides and the current collector (current collector 2 in FIG. 4) in the middle is formed. After drying and precision pressing, it is collected in a roll to obtain the thick electrode positive pole piece.

[0088] In a second aspect, the application provides a thick electrode positive pole piece, which is prepared by the method for preparing a thick electrode positive pole piece according to the first aspect.

[0089] In a third aspect, the application provides a primary battery, which includes a positive pole piece, a negative pole piece, an electrolyte and a separator, and the positive pole piece includes the thick electrode positive pole piece according to the second aspect.

[0090] The numerical range described in the application includes not only the point values exemplified above, but also any point values between the above numerical ranges that are not exemplified. Due to the limited space and for the sake of simplicity, the application does not enumerate the specific point values included in the range.

[0091] The technical solutions of the application will be further described below by combining the drawings and specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the application and should not be regarded as specific limitations of the application.

[0092] Firstly, the application discusses the influence of the types and contents of polytetrafluoroethylene bonding resins and granulating agents on the performance of the prepared thick electrode positive pole piece, which is specifically described in combination with the following embodiments: Example 1

[0093] The embodiment provides a thick electrode positive electrode sheet and a preparation method thereof, and the preparation method comprises the following steps.

[0094] S1. Manganese dioxide powder, conductive agent Super P powder and polytetrafluoroethylene resin are mixed in a gravity-free mixer at a temperature lower than 19 DEG C to obtain a mixture, wherein the mass percentage of the polytetrafluoroethylene resin in the total mass of the mixture is 3 wt.%; and

[0095] 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;

[0096] S3. The fiberized mixture is subjected to airflow grinding treatment to obtain a ground material; and then the ground material and dimethyl silicone oil granulating agent are subjected to stirring granulation treatment in a high-speed stirring granulator to obtain the precursor material, wherein the mass percentage of the dimethyl silicone oil granulating agent in the total mass of the granulation-treated material is 20 wt.%;

[0097] S4. The precursor material is put into the feeding port of a four-roll pressing device, and subjected to film forming treatment through a differential temperature film forming roller system, and is converged into a film opposite to each other at the gap between the second pressing roller and the third pressing roller, during which the current collector grid is also inserted from the gap between the second pressing roller and the third pressing roller, and finally a positive electrode sheet with a sandwich structure of positive electrode active material film on both sides and a current collector in the middle is formed, and after drying and fine pressing, the thick electrode positive electrode sheet is collected in a roll to obtain the thick electrode positive electrode sheet. The specific process of the differential temperature film forming comprises: using the precursor material prepared in the granulation step to be put into the gap between the first pressing roller and the second pressing roller and the gap between the third pressing roller and the fourth pressing roller of the four-roll pressing device, and the second pressing roller and the third pressing roller can press the put powder into a continuous film.

[0098] The structure diagram of the four-roll pressing device is shown in FIG. 1 (in the figure, 1 is an electrode sheet, 2 is a current collector grid, and the arrow represents the feeding position), wherein the leftmost 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 diameters of the first pressing roller, the second pressing roller, the third pressing roller and the fourth pressing roller are the same, 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, the first pressing roller and the third pressing roller rotate clockwise, and the second pressing roller and the fourth pressing roller rotate counterclockwise. In addition, the temperature of the first pressing roller is 110 DEG C, the temperature of the second pressing roller is 60 DEG C, the temperature of the third pressing roller is 60 DEG C, and the temperature of the fourth pressing roller is 110 DEG C. The linear velocities of the first pressing roller, the second pressing roller, the third pressing roller and the fourth pressing roller are the same. Embodiment 2

[0099] The difference between this embodiment and embodiment 1 is that step S3 is adjusted as follows: the milling agent and the N-methylpyrrolidone granulating agent are subjected to stirring granulation treatment in a high-speed stirring granulator to obtain the precursor material, wherein the mass percentage of N-methylpyrrolidone is 15wt.% based on the total mass of the granulation-treated material, and the others are the same as in embodiment 1. Embodiment 3

[0100] The difference between this embodiment and embodiment 1 is that step S3 is adjusted as follows: the milling agent and the polyethylene glycol granulating agent are subjected to stirring granulation treatment in a high-speed stirring granulator to obtain the precursor material, wherein the mass percentage of polyethylene glycol is 25wt.% based on the total mass of the granulation-treated material, and the others are the same as in embodiment 1. Embodiment 4

[0101] The embodiment provides a thick electrode positive electrode sheet and a preparation method thereof, and the preparation method comprises the following steps:

[0102] S1. Acetylene black, conductive agent Super P powder and polytetrafluoroethylene resin are mixed in a gravity-free mixer at a temperature lower than 19℃ to obtain a mixture, wherein the mass percentage of polytetrafluoroethylene resin is 10wt.% based on the total mass of the mixture;

[0103] S2. The mixture is subjected to fiberization treatment in an airflow mill at a gas pressure of 0.8MPa to obtain a fiberized mixture;

[0104] S3. The fiberized mixture and dimethyl silicone oil granulating agent are subjected to stirring granulation treatment in a high-speed stirring granulator to obtain the precursor material, wherein the mass percentage of dimethyl silicone oil granulating agent is 50wt.% based on the total mass of the granulation-treated material;

[0105] S4. The precursor material is put into the feeding port of a four-roll pressing device, and subjected to film forming treatment by a differential temperature film forming roller system, and the positive electrode active material film pieces on both sides and the current collector in the middle are converged into a sandwich structure of the positive electrode sheet at the gap between the second pressing roller and the third pressing roller, during which the current collector is also inserted from the gap between the second pressing roller and the third pressing roller, and finally the thick electrode positive electrode sheet is formed, which is collected in a roll after drying and precision pressing. The specific process of differential temperature film forming comprises: using the precursor material prepared in the above granulation step to be put into the gap between the first pressing roller and the second pressing roller and the gap between the third pressing roller and the fourth pressing roller of the four-roll pressing device, and the second pressing roller and the third pressing roller can press the powder into a continuous film piece.

[0106] The structure of the quadruple roller pressing device is shown in FIG. 1 (1 represents the pole piece, 2 represents the current collector, and the arrow represents the feeding position). The leftmost 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 diameters of the first pressing roller, the second pressing roller, the third pressing roller, and the fourth pressing roller are the same, and 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. The first pressing roller and the third pressing roller rotate clockwise, and the second pressing roller and the fourth pressing roller rotate counterclockwise. In addition, the temperature of the first pressing roller is 110°C, the temperature of the second pressing roller is 60°C, the temperature of the third pressing roller is 60°C, and the temperature of the fourth pressing roller is 110°C. The linear speeds of the first pressing roller, the second pressing roller, the third pressing roller, and the fourth pressing roller are the same. Example 5

[0107] The difference between this example and Example 1 is that the dimethyl silicone oil granulating agent in step S3 is replaced by an equal amount of isopropyl alcohol, and the others are the same as Example 1. Example 6

[0108] The difference between this example and Example 1 is that the mass percentage content of the dimethyl silicone oil granulating agent in step S3 is 5wt.% based on the total mass of the granulating material being 100%, and the others are the same as Example 1. Example 7

[0109] The difference between this example and Example 1 is that the mass percentage content of the dimethyl silicone oil granulating agent in step S3 is 35wt.% based on the total mass of the granulating material being 100%, and the others are the same as Example 1. Comparative Example 1

[0110] The difference between this example and Example 1 is that step S3 is adjusted to: no dimethyl silicone oil granulating agent is added, and only the step of treating the fiberized mixed material by airflow grinding to obtain a ground material is retained, and the others are the same as Example 1. Comparative Example 2

[0111] The difference between this example and Example 1 is that step S1 is adjusted to: the polytetrafluoroethylene resin is replaced by an equal amount of polytetrafluoroethylene emulsion; and step S3 is adjusted to: no dimethyl silicone oil granulating agent is added, and only the step of treating the fiberized mixed material by airflow grinding to obtain a ground material is retained, and the others are the same as Example 1.

[0112] The thick electrode positive pole pieces prepared in Examples 1-7 and Comparative Examples 1-2 were tested for performance, and the test method was as follows:

[0113] (1) Thickness consistency: On the prepared positive electrode roll material, every 20 cm, use the electrode piece sampler to cut a 5 cm diameter electrode piece, a total of 20 samples, use a micrometer (accurate to 0.001 mm) to measure each sample, and calculate the relative standard deviation of the collected 20 sample thickness values, the relative standard deviation calculation formula is: , x is the sample thickness.

[0114] (2) Initial positive electrode piece peeling force: Take 20 pieces of 400 mm x 20 mm electrode pieces from the prepared positive electrode roll material, test on a universal tensile testing machine, and take the average value.

[0115] (3) Positive electrode piece area density: Measure the weight of the sample measured for thickness consistency, calculate the electrode piece area density, and take the average value, the area density calculation formula is: , m is the sample weight, and s is the sample area.

[0116] The test results are shown in Table 1:

[0117]

[0118] As can be seen from Table 1, comparing Examples 1-4 and Comparative Examples 1-2, it can be seen that the step of granulating the fiberized mixture material with the granulating agent is crucial to improving the thickness consistency, peeling force, and area density of the thick electrode positive electrode piece.

[0119] Comparing Example 1 and Example 5, the application can wrap the binder fibers with a liquid material that can volatilize at room temperature, and help granulation, thereby improving the film strength in the later stage, avoiding the accumulation of lines due to stress in the film, and improving the uniformity of its thickness, but the isopropyl alcohol disclosed in the related art cannot achieve the above technical effects.

[0120] Comparing Example 1 and Examples 6-7, if the content of the granulating agent is not within the preferred content range of the application, it will affect the final granulation effect, so that the precursor material particles cannot complete the film transfer step during the rolling process. At the same time, under the premise of ensuring a certain granulation effect, the higher the content of the added granulating agent, the lower the area density of the prepared positive electrode piece, because the granulating agent leaves pores in the interior of the positive electrode piece after drying, thus causing the overall density of the positive electrode piece to be low.

[0121] Comparing Example 1 and Comparative Example 2, the polytetrafluoroethylene emulsion disclosed in the related art can also have a fiberizing effect to some extent, but it is obvious that the thickness consistency, peeling force, and area density of the positive electrode piece prepared using the polytetrafluoroethylene emulsion are not as good as those of the positive electrode piece provided in Example 1.

[0122] Secondly, the application aims to explore the influence of the differential temperature film forming method and its specific parameters on the performance of the thick electrode positive plate. This will be explained in detail in combination with Examples 8-18 shown in Table 2. Examples 8-18 are the same as Example 1 except for the conditions in Table 2.

[0123] As can be seen from Table 2, by adjusting the lowest temperature of the low-temperature roller and the temperature difference between the high-temperature roller and the low-temperature roller in the differential temperature film forming process, the quality of the prepared positive plate is improved.

[0124] As can be seen from the comparison between Comparative Example 1 and Examples 16-18, when the temperature of the low-temperature roller is relatively high (e.g. higher than 60℃), the temperature difference between the low-temperature roller and the high-temperature roller is not obvious, and the granulating agent is prone to evaporate during the rolling process, making it difficult for the film to complete the transfer film forming. On the contrary, as the temperature difference between the low-temperature roller and the high-temperature roller increases, the film forming process of the film becomes easier, thereby increasing the areal density of the positive plate, but the thickness consistency of the positive plate gradually deteriorates due to the evaporation of the granulating agent. Therefore, all aspects need to be considered during the production of the positive plate to further improve the comprehensive performance of the positive plate.

[0125] Finally, the application aims to explore the influence of the differential speed film forming method and its specific parameters on the performance of the thick electrode positive plate. This will be explained in detail in combination with Examples 19-33 shown in Table 3. Examples 19-33 are the same as Example 1 except for the conditions in Table 3.

[0126] As can be seen from Table 3, by adjusting the film forming temperature in the differential speed film forming process and the synergistic effect between the linear speed ratio of the slow roller and the fast roller, the film forming strength is further improved, and the powder dropping rate of the positive plate is reduced. Examples 19-23 show that when the rolling temperature is relatively low (e.g. 70℃) and the linear speed ratio of the slow roller and the fast roller is low (e.g. 1:1.1), the shear force is insufficient to transfer the film to the side of the fast roller. When the linear speed ratio of the slow roller and the fast roller is high (e.g. 1:1.5), the film will be broken during the transfer process. At the same rolling temperature, the greater the linear speed ratio of the slow roller and the fast roller, the greater the shear force during the rolling process, resulting in a greater peel force of the prepared positive plate, but the areal density of the film decreases.

Claims

1. A method for preparing a thick electrode positive plate, comprising 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 mixed material to obtain a fiberized mixed material; S3, granulating the fiberized mixture and a granulating agent to obtain a precursor material, wherein the granulating agent is a liquid having a vapor pressure of not less than 0.2 mmhg; S4. The precursor material is subjected to a roll-pressing film-forming process to obtain the thick electrode positive plate.

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

3. The method according to claim 1 or 2, wherein: The binder resin in step S1 includes polytetrafluoroethylene.

4. The method according to any one of claims 1 to 3, wherein: When the positive electrode active material in step S1 is manganese dioxide, based on the total mass of the mixture being 100%, the mass percentage of the binder resin in step S1 is 1 wt.%-5 wt.%, and can be optionally 1.5 wt.%-2.5 wt.%.

5. The method according to any one of claims 1 to 3, wherein: When the positive electrode active material in step S1 is acetylene black, based on the total mass of the mixture being 100%, the mass percentage of the binder resin in step S1 is 5 wt.%-15 wt.%, and can be optionally 6 wt.%-8 wt.%.

6. The method according to any one of claims 1 to 5, wherein: The mixing method in step S1 is zero-gravity mixing; Optionally, the mixing temperature in step S1 is lower than 19°C.

7. The method according to any one of claims 1 to 6, wherein: The equipment for the fiberization treatment in step S2 includes a high-speed mixer and / or a jet mill; Optionally, the linear speed of the high-speed mixer is 50m / s-150m / s; Optionally, the air pressure of the air jet mill is 0.75 MPa-0.85 MPa.

8. The method according to any one of claims 1 to 7, wherein: 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; Optionally, 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.%, optionally 15wt.%-25wt.%; Optionally, when the positive electrode active material is acetylene black, based on the total mass of the granulated material being 100%, the mass percentage of the granulating agent in step S3 is 30wt.%-70wt.%, optionally 50wt.%-60wt.%.

9. The method according to any one of claims 1 to 8, wherein: The roll-pressing film forming method in step S4 includes differential temperature film forming and / or differential speed film forming, and differential temperature film forming can be selected.

10. The method according to claim 9, wherein: The differential temperature film forming equipment includes a differential temperature film forming roller system.

11. The method according to claim 10, wherein: 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 first pressing roller and the second pressing roller, and a second feed inlet is formed above the third pressing roller and the fourth pressing roller, and the second pressing roller and the third pressing roller are capable of pressing powder fed into the first feed inlet and the second feed inlet into a continuous film sheet; Optionally, the rolling directions of the first pressing roller and the third pressing roller are opposite to the rolling directions of the second pressing roller and the fourth pressing roller; Optionally, 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; Optionally, the temperature of the first pressing roller and the fourth pressing roller are both 50° C.-105° C.; Optionally, the temperature of the second pressing roller and the third pressing roller are both 20° C.-60° C.; Optionally, the temperature difference between the first pressing roller and the second pressing roller is 10°C-90°C, optionally 30°C-50°C; Optionally, the temperature difference between the fourth pressing roller and the third pressing roller is 10°C-90°C, optionally 30°C-50°C.

12. The method according to claim 9, wherein The roller pressing temperature of the differential film forming is 40°C-110°C; Optionally, the differential film forming device includes a differential film forming roller system; Optionally, the differential-speed 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 being formed above the first pressing roller and the second pressing roller, and a second feed inlet being formed above the third pressing roller and the fourth pressing roller, and the second pressing roller and the third pressing roller are capable of pressing powders fed into the first feed inlet and the second feed inlet into a continuous film sheet; Optionally, the gap between adjacent rollers in the differential film-making roller system is 0.10 mm to 0.60 mm.

13. The method according to claim 12, wherein: The rolling directions of the first pressing roller and the third pressing roller are opposite to the rolling directions of the second pressing roller and the fourth pressing roller; Optionally, the linear speed of the first pressing roller and the fourth pressing roller is smaller than the linear speed of the second pressing roller and the third pressing roller; Optionally, the linear speed of the first pressing roller is the same as the linear speed of the fourth pressing roller; Optionally, the linear speed of the second pressing roller is the same as the linear speed of the third pressing roller; Optionally, the ratio of the linear speed of the Ith pressing roller and / or the IVth pressing roller to the linear speed of the IIth pressing roller and / or the IIIth pressing roller is 1:(1.1-2).

14. A thick electrode positive plate, wherein: The thick electrode positive electrode sheet is prepared by the method for preparing a thick electrode positive electrode sheet according to any one of claims 1 to 13. 15 . A primary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the positive electrode sheet comprises the thick electrode positive electrode sheet according to claim 14 .

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