Thick-electrode positive plate, preparation method thereof and primary battery

Abstract

The invention provides a thick-electrode positive plate, a preparation method thereof and a primary battery. The method comprises the following steps: firstly, mixing a positive active material, a conductive agent and binder resin to obtain a mixture; carrying out fibration treatment on the mixed material to obtain a fibration mixed material; then, the fiberized mixed material and a granulating agent are subjected to granulation treatment, a precursor material is obtained, and the granulating agent is liquid with the vapor pressure not lower than 0.2 mmhg; finally, the precursor material is subjected to rolling film forming treatment, and the thick electrode positive plate is obtained. The preparation method provided by the invention can be widely applied to a battery system in which the thick electrode (greater than 500 microns) needs to be manufactured by using the current collecting net, and solves the problems that the thick electrode pole piece using the current collecting net is difficult to continuously and automatically produce, the powder falling rate of the pole piece is high, the thickness is not uniform and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a thick electrode positive plate and a preparation method thereof, and a primary battery. Background Art

[0002] In the battery manufacturing process, cylindrical batteries usually use a winding method to make battery cells. Specifically, the positive electrode, separator and negative electrode are stacked and wound in sequence to make a winding core. This can not only increase the effective area of ​​the electrode sheet, but also improve the energy density of the battery. Among them, for rechargeable secondary batteries, both the positive and negative electrodes are coated with slurry on both sides of the collector foil (such as aluminum foil or copper foil) to form a long strip of pole piece. However, due to the irreversible chemical reaction of primary batteries, the main method of filling as much active material as possible on the mesh collector is to further increase the capacity of the battery. This structural design makes the thickness of the pole piece thicker under the same high compaction density, that is, it can reach 500μm.

[0003] For example: Lithium manganese dioxide battery is a battery with electrolytic manganese dioxide as the positive electrode and lithium metal as the negative electrode. The specific electrochemical reaction formula is: MnO2+xLi→Li x MnO2. The positive electrode sheet of lithium manganese dioxide columnar battery is usually prepared by slurry pulling. This process includes configuring manganese dioxide, conductive agent and binder into positive electrode active material slurry, and then slowly passing through the positive electrode active material slurry pool through the current collecting net, so that the slurry is evenly hung on the net, and then dried and fine pressed to finally form the positive electrode sheet. The above preparation process has problems such as high slurry requirements, high production energy consumption, high powder loss rate of the prepared positive electrode sheet, and inability to produce positive electrode sheets with high compaction density.

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

[0005] In lithium thionyl chloride column batteries, power type batteries usually adopt a winding structure, specifically, acetylene black, polytetrafluoroethylene emulsion and ethanol or isopropanol are mixed into powder, and then evenly coated on the nickel mesh (such as Chinese invention patent: CN104733738A), and then wound with the separator and the negative electrode in turn into an integrated structure. Alternatively, after mixing into powder, it is kneaded and rolled several times to prepare a self-supporting film, and finally the self-supporting film is coated on the nickel mesh for compounding.

[0006] In fact, power battery pole pieces are thick and require acetylene black as a conductive agent, but the density and particle size of acetylene black are usually small, which makes it difficult to make it into a slurry suitable for coating production equipment. In addition, the use of self-supporting acetylene black film pasting mesh cannot achieve automated and continuous production, and the preparation of powder pressing mesh will lead to a high powder loss rate, so both production methods have certain shortcomings.

[0007] In recent years, in order to further produce thick electrode sheets to improve the energy density of batteries, the dry electrode process has received widespread attention. The core of the dry electrode process is to utilize the fiberization ability of polytetrafluoroethylene (PTFE) binder, and then disperse the PTFE into a fibrous structure, and mix it with active substances and conductive agents to form a self-supporting or non-self-supporting electrode film. This process does not require the use of solvents, thereby avoiding the problem of solvent residues in traditional wet processes, and has the advantages of environmental protection, low cost and high production efficiency. However, the production difficulty of the dry electrode process is relatively high, and the fiberization degree of polytetrafluoroethylene is required to be high. Because no solvent is added, the formed fibers are very easy to break during the dispersion process. At the same time, the active material particles will produce stress accumulation during film formation, resulting in uneven thickness of the formed diaphragm.

[0008] Therefore, it is urgent to develop a method to optimize the fiberization process of PTFE to improve its mechanical strength and stability, and to solve the adhesion problem between the current collector and the dry electrode membrane. Summary of the invention

[0009] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a thick electrode positive plate and a preparation method thereof and a primary battery. The preparation method provided by the present invention can be generally applied to battery systems that require the use of a current collector to make thick electrodes (>500 μm), and solves the problems of the difficulty of continuous automatic production of thick electrode plates using a current collector, high powder loss rate of the plates, and uneven thickness.

[0010] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

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

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

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

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

[0015] S4. The precursor material is subjected to a roll-pressing film-forming process to obtain the thick electrode positive plate.

[0016] It should be noted that the granulating agent described in the present invention is a liquid with a vapor pressure of not less than 0.2 mmhg, which specifically means that the vapor pressure at room temperature is not less than 0.2 mmhg, 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 the one hand, the present invention uses a binder resin for dispersion treatment, so that it is subjected to shear fiberization treatment, thereby forming a three-dimensional fiber network to adhere the 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 produced during the fiberization process. These fibers can better bond the positive electrode active material particles, ultimately improving the bonding strength and electrochemical properties of the positive electrode material. On the other hand, the present invention granulates the fiberized mixture with a granulating agent so that the liquid material that can volatilize at room temperature wraps the binder fiber and helps it granulate. During the granulation process, the material particles further undergo secondary fiberization to form rubber-like particles with a certain strength, thereby improving the film-forming strength of the latter stage. At the same time, a small amount of granulating agent can make the positive electrode active material easier to move during the rolling process, thereby avoiding the accumulation lines of the diaphragm caused by stress and improving the uniformity of its thickness.

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

[0019] Preferably, the binder resin in step S1 includes polytetrafluoroethylene.

[0020] Preferably, when the positive electrode active material in step S1 is manganese dioxide, based on the total mass of the mixture as 100%, the mass percentage of the binder resin in step S1 is 1wt.%-5wt.%, preferably 1.5wt.%-2.5wt.%, for example, it can be 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.%, etc. The present invention controls the mass percentage of the binder resin so that the binder fibers are fully expanded, thereby forming a three-dimensional network to bind the positive electrode active material particles, thereby controlling the pole piece molding. If a binder resin with a lower mass percentage is used, it will not be able to fully bond the positive electrode active material, causing the film to break or be unable to transfer during the rolling film forming process, and a high powder loss rate after the positive electrode sheet is made, ultimately affecting the electrical performance of the primary battery; if a binder resin with a higher mass percentage is used, the membrane resistance of the positive electrode sheet will increase, thereby affecting 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 5wt.%-15wt.%, preferably 6wt.%-8wt.%, based on the total mass of the mixture as 100%. The present invention controls the mass percentage of the binder resin so that the binder fibers are fully expanded to form a three-dimensional network to bind the positive electrode active material particles, thereby controlling the electrode sheet forming. If a binder resin with a lower mass percentage is used, the positive electrode active material cannot be fully bonded, resulting in the film being broken or unable to be transferred during the rolling film forming process, and the powder loss rate after the positive electrode sheet is made is high, which ultimately affects the electrical performance of the primary battery; if a binder resin with a higher mass percentage is used, the membrane 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 zero-gravity mixing.

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

[0024] The present invention further regulates the material mixing method and temperature to avoid premature fiberization of the binder resin during the mixing process.

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

[0026] Preferably, 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.

[0027] Preferably, the air pressure of the air flow 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.

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

[0029] Preferably, when the positive electrode active material is manganese dioxide, the mass percentage of the granulating agent in step S3 is 10wt.%-30wt.%, preferably 15wt.%-25wt.%, based on the total mass of the granulated material as 100%, for example, it can be 10wt.%, 12wt.%, 15wt.%, 18wt.%, 20wt.%, 22wt.%, 25wt.%, 28wt.%, 30wt.%, etc. The present invention adjusts the mass percentage of the granulating agent so that the fibrous mixture can be made into precursor material particles with uniform size, good sphericity and good fluidity, so as to facilitate uniform feeding during the roller film forming process, and further control the thickness uniformity of the membrane. If a granulating agent with a lower mass percentage is used, the granulating agent will not be able to completely cover the fiberized mixed material, resulting in granulation failure; if a granulating agent with a higher mass percentage is used, the granulation mesh size of the precursor material particles will be too large or the powder will not be able to be granulated (for example, forming agglomerates or lumps).

[0030] Preferably, when the positive electrode active material is acetylene black, 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. Since the density of the acetylene black material is relatively low, the content of the added granulating agent is relatively high.

[0031] Preferably, the roll-pressing film forming method in step S4 includes differential temperature film forming and / or differential speed film forming, preferably differential temperature film forming.

[0032] Compared with the differential film forming method, the method of forming a membrane using differential temperature film forming will not cause stress accumulation between particles during the film forming process, nor will it cause accumulation lines on the membrane, thereby making the thickness and surface density of the membrane more uniform and consistent.

[0033] Preferably, the differential temperature film forming equipment comprises 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 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 can press the powder put into the first feed inlet and the second feed inlet into a continuous film sheet.

[0035] Preferably, 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.

[0036] Preferably, the temperature of the first pressing roller and the fourth pressing roller is higher than that of the second pressing roller and the third pressing roller. The present invention regulates the temperature of the first pressing roller and the fourth pressing roller to be higher than that of the second pressing roller and the third pressing roller. This is because temperature has an influence on molecular motion and adhesion, which is specifically manifested as follows: at low temperatures, the molecular motion on the surface of an object slows down, resulting in an increase in the contact area between molecules, thereby enhancing the adhesion. On the contrary, at high temperatures, the molecular motion on the surface of an object accelerates, the contact area between molecules decreases, and the adhesion decreases. Therefore, the low-temperature roller can better maintain the adhesion of the object, making it easier for the film to adhere to the low-temperature roller.

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

[0038] Preferably, the temperature of the second pressing roller and the third pressing roller are both 20°C-60°C, for example, 20°C, 30°C, 40°C, 50°C, 60°C, etc.

[0039] Preferably, the temperature difference between the first pressing roller and the second pressing roller is 10°C-90°C, preferably 30°C-50°C, for example, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, etc. In the present invention, by adjusting the temperature difference between the first pressing roller and the second pressing roller, the precursor material particles adhere to one side of the second pressing roller after rolling, and are subsequently transferred to the gap between the second pressing roller and the third pressing roller to prepare the positive electrode sheet.

[0040] Preferably, the temperature difference between the fourth pressing roller and the third pressing roller is 10°C-90°C, preferably 30°C-50°C, for example, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, etc. In the present invention, by adjusting the temperature difference between the fourth pressing roller and the third pressing roller, the precursor material particles adhere to one side of the third pressing roller after rolling, and are subsequently transferred to the gap between the second pressing roller and the third pressing roller to prepare the positive electrode sheet.

[0041] In the present invention, the diameters of the first pressing roller, the second pressing roller, the third pressing roller, and the fourth pressing roller are the same.

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

[0043] In the present invention, the linear speeds of the first pressing roller, the second pressing roller, the third pressing roller and the fourth pressing roller are the same.

[0044] As a preferred technical solution of the present invention, the present invention puts the precursor material obtained by the above granulation step into the gap between the first pressing roller and the second pressing roller of the quadruple roller pressing device, and into the gap between the third pressing roller and the fourth pressing roller. The structural schematic diagram of the quadruple roller pressing device is shown in Figure 1 As shown, the leftmost one is the first pressing roller, and from left to right are the second pressing roller, the third pressing roller and the fourth pressing roller respectively. The first pressing roller and the third pressing roller rotate clockwise, while the second pressing roller and the fourth pressing roller rotate counterclockwise.

[0045] The present invention uses differential temperature rolling technology to make the precursor material particles independently form films during the rolling process and adhere to the low-temperature roller. The thickness of the diaphragm is controlled by 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, while the thickness of the pole piece is controlled by the size of the gap between the second pressing roller and the third pressing roller. During the lamination of the collecting network, the diaphragm needs to be evenly attached to the roller, so the diaphragm does not need to be self-supporting during this process. In addition, since the uniformity of the thickness of the diaphragm will be affected by factors such as the particle size, specific surface area or micromorphology of the active material. In order to improve the uniformity of the diaphragm thickness, equipment with more rollers can be used, such as an eight-roller pressing equipment or a ten-roller pressing equipment (such as Figure 2 and Figure 3 These devices can more effectively control the thickness distribution of the film by increasing the number of rollers, thereby improving thickness consistency.

[0046] In the present invention, the surface of the pole piece prepared by using the differential temperature film forming technology is smoother and has a higher surface density.

[0047] Preferably, the roller pressing temperature of the differential film forming is 40°C-110°C, for example, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, etc.

[0048] Preferably, the differential speed film forming device comprises a differential speed film forming roller system.

[0049] Preferably, the differential film-making 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 port is formed above the first pressing roller and the second pressing roller, and a second feed 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 powders put into the first feed port and the second feed port into a continuous film sheet.

[0050] Preferably, the gap between adjacent rollers in the differential film-making 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 0.20 mm-0.50 mm; when the positive electrode active material is acetylene black, the gap between adjacent rollers in the differential film-forming roller system is 0.10 mm-0.60 mm.

[0052] Preferably, the rolling direction of the I-th pressing roller and the III-th pressing roller is opposite to the rolling direction of the II-th pressing roller and the IV-th pressing roller.

[0053] Preferably, the linear speeds of the I-th pressing roller and the IV-th pressing roller are smaller than the linear speeds of the II-th pressing roller and the III-th pressing roller.

[0054] Preferably, the linear speed of the Ith pressing roller is the same as the linear speed of the IVth pressing roller.

[0055] Preferably, the linear speed of the II pressing roller is the same as the linear speed of the III pressing roller.

[0056] Preferably, the ratio of the linear speed of the I pressing roller and / or the IV pressing roller to the linear speed of the II pressing roller and / or the III 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. The present invention regulates the linear speed of the I pressing roller and / or the IV pressing roller to the linear speed of the II pressing roller and / or the III pressing roller, so that the precursor material particles are subjected to greater shear force during the rolling process, thereby further improving the film strength and reducing the powder loss rate of the positive electrode sheet. If the linear speed of the I pressing roller and / or the IV pressing roller is high, it will cause the film to break during the rolling process.

[0057] Specifically, when the temperature of the roller pressure in differential film forming is 40℃-80℃, 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:(1.2-1.3); when the temperature of the roller pressure in differential film forming is 90℃-100℃, 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:(1.1-1.3); when the temperature of the roller pressure in differential film forming is 110℃, 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).

[0058] In the present invention, the diameters of the Ith pressing roller, the IIth pressing roller, the IIIth pressing roller and the IVth pressing roller are the same.

[0059] In the present invention, the center of the circle of the I-th pressing roller, the center of the circle of the II-th pressing roller, the center of the circle of the III-th pressing roller and the center of the circle of the IV-th pressing roller are located on the same horizontal line.

[0060] As a preferred technical solution of the present invention, the present invention puts the precursor material obtained by the above granulation step into the gap between the first pressing roller and the second pressing roller of the four-roll pressing device, and into the gap between the third pressing roller and the fourth pressing roller. The structural schematic diagram of the four-roll pressing device is as follows: Figure 1 As shown, the leftmost one is the I pressing roller, and from left to right are the II pressing roller, the III pressing roller and the IV pressing roller. The I pressing roller and the III pressing roller rotate clockwise, while the II pressing roller and the IV pressing roller rotate counterclockwise.

[0061] The present invention utilizes differential rolling technology to enable precursor material particles to independently form films during the rolling process and adhere to a fast roller. Specifically, the linear speed values ​​of the second pressing roller and the third pressing roller are greater than the linear speed values ​​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. 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 are regulated to control the thickness of the membrane.

[0062] In the present invention, the pole piece prepared by using the differential film forming technology has higher strength and better peeling force.

[0063] In the present invention, the roller-pressing film forming process in step S4 includes: feeding the precursor material obtained in the granulation step into the feed port of the quadruple roller pressing device, so that it forms a film at a differential temperature / or a differential speed, and then merges into a film at the gap between the second pressing roller or the second pressing roller and the third pressing roller or the third pressing roller, respectively. During this period, the current collecting network is also 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 forms a sandwich structure with positive electrode active material membranes on both sides and a current collector in the middle (such as Figure 4 As shown), after drying and precision pressing, the thick electrode positive plate is collected into a roll to obtain the thick electrode positive plate.

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

[0065] In a third aspect, the present invention provides 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 the second aspect.

[0066] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

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

[0068] The present invention provides a method for preparing a thick electrode positive plate. On the one hand, the present invention uses a binder resin for dispersion treatment, so that it 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 produced during the fiberization process. These fibers can better bond the positive electrode active material particles, ultimately improving the bonding strength and electrochemical properties of the positive electrode material. On the other hand, the present invention granulates the fiberized mixed material with a granulating agent so that the liquid material that can volatilize at room temperature wraps the binder fiber and helps it granulate. During the granulation process, the material particles further undergo secondary fiberization to form rubber-like particles with a certain strength, thereby improving the film-forming strength of the latter stage. At the same time, a small amount of granulating agent can make the positive electrode active material easier to move during the rolling process, thereby avoiding the accumulation lines of the diaphragm due to stress and improving the uniformity of its thickness.

[0069] Compared with the wet coating process in the prior art, the preparation method provided by the present invention reduces the amount of solvent used, eliminates the traditional front-end film-making process, and does not require additional coating of a binder on the current collector surface, thereby enabling continuous winding, which greatly improves the automation level of the production line and avoids errors caused by manual intervention during the production process. At the same time, the preparation method provided by the present invention has high adjustability, and can adjust the compaction density, liquid absorption rate, conductivity and other parameters of the membrane by adjusting the roller-pressing film-forming process parameters, the content of the granulating agent and the content of the binder, thereby adapting to the production of different types of battery pole pieces.

[0070] In addition, the thick electrode positive plate prepared by the present invention has the advantages of high strength and low powder loss rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 It is a structural schematic diagram of the quadruple roller pressing equipment provided by the present invention.

[0072] Figure 2 It is a structural schematic diagram of the eight-roller pressing equipment provided by the present invention.

[0073] Figure 3 It is a structural schematic diagram of the ten-roller pressing equipment provided by the present invention.

[0074] Figure 4 It is a schematic structural diagram of the thick electrode positive plate provided by the present invention. DETAILED DESCRIPTION

[0075] The technical solution of the present invention is further described below by combining the accompanying drawings and specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0076] First, the present invention discusses the effects of the types and contents of polytetrafluoroethylene binder resin and granulating agent on the performance of the prepared thick electrode positive plate, which is specifically described in conjunction with the following examples:

[0077] Example 1

[0078] This embodiment provides a thick electrode positive plate and a preparation method thereof, the preparation method comprising the following steps:

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

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

[0081] S3. The fiberized mixture is subjected to air flow grinding to obtain a grind; the grind and the dimethyl silicone oil granulating agent are then subjected to stirring and granulation in a high-speed stirring granulator to obtain the precursor material, wherein the mass percentage of the dimethyl silicone oil granulating agent is 20wt.% based on the total mass of the granulated material as 100%;

[0082] S4. The precursor material is put into the feed port of the four-roll pressing device, and the film is formed through the differential temperature film-forming roller system, and the two materials are respectively merged into a film at the gap between the second pressing roller and the third pressing roller. During this period, the current collecting net 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 membranes on both sides and a current collector in the middle is formed. After drying and precision pressing, the positive electrode sheet is collected into a roll to obtain the thick electrode positive electrode sheet. Among them, the specific process of differential temperature film formation includes: the precursor material obtained by the above-mentioned granulation step is put into the gap between the first pressing roller and the second pressing roller of the four-roll pressing device, and the gap between the third pressing roller and the fourth pressing roller. The second pressing roller and the third pressing roller can press the put powder into a continuous film.

[0083] The structural diagram of the four-roller pressing equipment is as follows Figure 1As shown, 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, and the first pressing roller and the third pressing roller both rotate clockwise, while the second pressing roller and the fourth pressing roller both 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.

[0084] Example 2

[0085] The difference between this embodiment and embodiment 1 is that step S3 is adjusted as follows: the ground material and N-methylpyrrolidone granulating agent are stirred and granulated 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 granulated material being 100%, and the rest is the same as in embodiment 1.

[0086] Example 3

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

[0088] Example 4

[0089] This embodiment provides a thick electrode positive plate and a preparation method thereof, the preparation method comprising the following steps:

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

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

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

[0093] S4. The precursor material is put into the feed port of the four-roll pressing device, and the film is formed through the differential temperature film-forming roller system, and the two materials are respectively merged into a film at the gap between the second pressing roller and the third pressing roller. During this period, the current collecting net 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 membranes on both sides and a current collector in the middle is formed. After drying and precision pressing, the positive electrode sheet is collected into a roll to obtain the thick electrode positive electrode sheet. Among them, the specific process of differential temperature film formation includes: the precursor material obtained by the above-mentioned granulation step is put into the gap between the first pressing roller and the second pressing roller of the four-roll pressing device, and the gap between the third pressing roller and the fourth pressing roller. The second pressing roller and the third pressing roller can press the put powder into a continuous film.

[0094] The structural diagram of the four-roller pressing equipment is as follows Figure 1 As shown, 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, and the first pressing roller and the third pressing roller both rotate clockwise, while the second pressing roller and the fourth pressing roller both 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.

[0095] Example 5

[0096] The difference between this embodiment and embodiment 1 is that the dimethyl silicone oil granulating agent in step S3 is replaced by isopropanol of the same content, and the rest is the same as embodiment 1.

[0097] Example 6

[0098] The difference between this embodiment and embodiment 1 is that, based on the total mass of the granulated material being 100%, the mass percentage content of the dimethyl silicone oil granulating agent in step S3 is 5 wt.%, and the rest is the same as embodiment 1.

[0099] Example 7

[0100] The difference between this embodiment and embodiment 1 is that, based on the total mass of the granulated material being 100%, the mass percentage content of the dimethyl silicone oil granulating agent in step S3 is 35wt.%, and the rest is the same as embodiment 1.

[0101] Comparative Example 1

[0102] The difference between this embodiment and embodiment 1 is that step S3 is adjusted as follows: no dimethyl silicone oil granulating agent is added, and only the step of subjecting the fiberized mixture to airflow grinding to obtain the ground material is retained, and the rest is the same as embodiment 1.

[0103] Comparative Example 2

[0104] The difference between this embodiment and embodiment 1 is that step S1 is adjusted as follows: polytetrafluoroethylene resin is replaced by polytetrafluoroethylene emulsion with an equal content; and step S3 is adjusted as follows: no dimethyl silicone oil granulating agent is added, and only the step of subjecting the fiberized mixture to airflow grinding to obtain the ground material is retained, and the rest is the same as embodiment 1.

[0105] The thick electrode positive plates prepared in Examples 1 to 7 and Comparative Examples 1 to 2 were subjected to performance tests, and the test methods were as follows:

[0106] (1) Thickness consistency: On the prepared positive electrode coil, use a pole piece sampler to cut pole pieces with a diameter of 5 cm every 20 cm, and take 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 thickness values ​​of the 20 samples collected. The relative standard deviation calculation formula is: x is the sample thickness.

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

[0108] (3) Positive electrode surface density: Measure the weight of the sample for measuring the consistency of the electrode thickness, calculate the electrode surface density, and take the average value. The surface 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, by comparing Examples 1-4 and Comparative Examples 1-2, the step of granulating the fiberized mixture with the granulating agent is crucial to improving the thickness consistency, peeling force and surface density of the thick electrode positive plate.

[0114] By comparing Example 1 with Example 5, it can be seen that the present invention wraps the binder fibers with a liquid material that is preferably volatile at room temperature and helps them to granulate, thereby improving the strength of the subsequent film-forming stage, avoiding the accumulation lines of the diaphragm due to stress, and improving the uniformity of its thickness. However, the isopropyl alcohol disclosed in the prior art cannot achieve the above technical effects.

[0115] Comparing Example 1 with Example 6-Example 7, it can be seen that if the content of the granulating agent is not within the preferred content range of the present invention, it is easy to 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, if the content of the added granulating agent is higher, the surface density of the prepared positive electrode sheet will decrease accordingly. This is because the granulating agent leaves pores inside the positive electrode sheet after drying, thus causing the overall density of the positive electrode sheet to become lower.

[0116] By comparing Example 1 with Comparative Example 2, it can be seen that the polytetrafluoroethylene emulsion disclosed in the prior art can also achieve a fiberizing effect to a certain extent, but it is obvious that the thickness consistency, peeling force and surface density of the positive electrode sheet prepared using the polytetrafluoroethylene emulsion are not as good as those of the positive electrode sheet provided in Example 1.

[0117] Secondly, the present invention discusses the influence of the differential temperature film forming method and its specific parameters on the performance of the obtained thick electrode positive plate, and specifically describes it in conjunction with Examples 8 to 18 shown in Table 2 below. Except for the conditions in Table 2 that are different from those in Example 1, Examples 8 to 18 are the same as Example 1:

[0118] Table 2

[0119]

[0120]

[0121] It can be seen from Table 2 that the present invention improves the quality of the prepared positive electrode sheet by regulating 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 forming process.

[0122] Comparing Example 1 with Example 16-Example 18, it can be seen that when the temperature of the low-temperature roller is high (for example, higher than 60°C), the temperature difference between it and the high-temperature roller is not obvious, and the granulating agent is easy to evaporate during the rolling process, making it difficult for the film to complete the transfer film. On the contrary, as the temperature difference between the low-temperature roller and the high-temperature roller continues to increase, the film forming process of the film is easier to carry out, thereby increasing the surface density of the positive electrode sheet, but the thickness consistency of the positive electrode sheet will gradually deteriorate due to the evaporation of the granulating agent, so it is necessary to consider all aspects in the production process of the positive electrode sheet to further improve the comprehensive performance of the positive electrode sheet.

[0123] Finally, the present invention discusses the influence of the differential film forming method and its specific parameters on the performance of the obtained thick electrode positive plate, and specifically describes it in conjunction with Examples 19 to 33 shown in Table 3 below. Except for the different conditions in Table 3, Examples 19 to 33 are the same as Example 1:

[0124] Table 3

[0125]

[0126]

[0127] As can be seen from Table 3, the present invention further improves the film strength and reduces the powder loss rate of the positive electrode sheet by regulating the film forming temperature in the differential film forming process and the synergistic effect between the linear speed ratio between the slow roller and the fast roller. Example 19-Example 23 shows that when the rolling temperature is low (for example, 70°C), the linear speed between the slow roller and the fast roller is relatively low (Example 1: 1.1), which will cause insufficient shear force and make it impossible to transfer the film to the side of the fast roller. When the linear speed between the slow roller and the fast roller is relatively high (Example 1: 1.5), the film will break during the transfer process. At the same time, under the same rolling temperature conditions, the greater the linear speed ratio between the slow roller and the fast roller, the greater the shear force during the rolling process, so that the peeling force of the prepared positive electrode sheet is greater, but the surface density of the film is reduced accordingly.

[0128] The applicant declares that the above is only a specific implementation mode 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 thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a thick electrode positive plate, characterized in that: The method comprises the following steps: S1. Mixing the positive electrode active material, the conductive agent and the binder resin to obtain a mixture; S2. The mixture is subjected to fiberization treatment to obtain a fiberized mixture; S3. The fiberized mixture and the granulating agent are granulated 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, characterized in that The positive electrode active material in step S1 includes manganese dioxide and / or acetylene black; Preferably, the binder resin in step S1 includes polytetrafluoroethylene; Preferably, when the positive electrode active material in step S1 is manganese dioxide, based on the total mass of the mixture as 100%, the mass percentage of the binder resin in step S1 is 1wt.%-5wt.%, preferably 1.5wt.%-2.5wt.%; Preferably, when the positive electrode active material in step S1 is acetylene black, based on the total mass of the mixture as 100%, the mass percentage of the binder resin in step S1 is 5wt.%-15wt.%, preferably 6wt.%-8wt.%; Preferably, the mixing method in step S1 is zero-gravity mixing; Preferably, the mixing temperature in step S1 is lower than 19°C.

3. The method according to claim 1 or 2, characterized in that: The equipment for the fiberization treatment in step S2 includes a high-speed mixer and / or a jet mill; Preferably, the linear speed of the high-speed mixer is 50m / s-150m / s; Preferably, the air pressure of the air flow mill is 0.75 MPa-0.85 MPa.

4. The method according to any one of claims 1 to 3, characterized in that: 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; Preferably, when the positive electrode active material is manganese dioxide, the mass percentage of the granulating agent in step S3 is 10wt.%-30wt.%, preferably 15wt.%-25wt.%, based on the total mass of the granulated material as 100%; Preferably, 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.%, preferably 50wt.%-60wt.%.

5. The method according to any one of claims 1 to 4, characterized in that: The roll-pressing film forming method in step S4 includes differential temperature film forming and / or differential speed film forming, preferably differential temperature film forming.

6. The method according to claim 5, characterized in that The differential temperature film forming equipment comprises a differential temperature film forming roller system; Preferably, 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 which are 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 the powder put into the first feed inlet and the second feed inlet into a continuous film sheet; Preferably, 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; Preferably, 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; Preferably, the temperature of the first pressing roller and the fourth pressing roller are both 50°C-105°C; Preferably, the temperature of the second pressing roller and the third pressing roller are both 20°C-60°C; Preferably, the temperature difference between the first pressing roller and the second pressing roller is 10°C-90°C, preferably 30°C-50°C; Preferably, the temperature difference between the fourth pressing roller and the third pressing roller is 10°C-90°C, preferably 30°C-50°C.

7. The method according to claim 5, characterized in that The roller pressing temperature of the differential film forming is 40°C-110°C; Preferably, the differential film forming device comprises a differential film forming roller system; Preferably, the differential film-making roller system comprises a first pressing roller, a second pressing roller, a third pressing roller and a fourth pressing roller which are 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 the powder put into the first feed inlet and the second feed inlet into a continuous film sheet; Preferably, the gap between adjacent rollers in the differential film-making roller system is 0.10 mm-0.60 mm.

8. The method according to claim 7, characterized in that 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; Preferably, the linear speeds of the first pressing roller and the fourth pressing roller are smaller than the linear speeds of the second pressing roller and the third pressing roller; Preferably, the linear speed of the first pressing roller is the same as the linear speed of the fourth pressing roller; Preferably, the linear speed of the second pressing roller is the same as the linear speed of the third pressing roller; Preferably, 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).

9. A thick electrode positive plate, characterized in that: 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 1-8.

10. A primary battery, characterized in that: The primary battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, and the positive electrode sheet comprises the thick electrode positive electrode sheet according to claim 9.

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