Preparation method of battery ceramic slurry and preparation method of positive pole piece

Abstract

The invention discloses a preparation method of battery ceramic slurry, the ceramic slurry comprises the following components: a binder, ceramic powder and an organic solvent, the mass ratio of the binder to the ceramic powder is 4: 1-9: 1, the molecular weight of the binder is greater than or equal to 90 * 10 < 4 > Da, and the binder is selected from one of polyimide, polyacrylic acid, polyvinylidene fluoride and polytetrafluoroethylene; the preparation method of the battery ceramic slurry comprises the following steps: preparing a glue solution, namely preparing the glue solution from an organic solvent and a binder, wherein the solid content of the glue solution is 5-9%; ceramic slurry is prepared, wherein ceramic powder is divided into two parts, and the first part of ceramic powder is added into the glue solution to be mixed for the first time; the second part of ceramic powder is added for secondary mixing, ceramic slurry is obtained, and the solid content of the ceramic slurry is 25%-35%. The invention also discloses a preparation method of the battery positive pole piece. According to the invention, the problems of mutual dissolution and virtual edge abnormity of the ceramic slurry and the positive electrode slurry are effectively solved.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a method for preparing a battery ceramic slurry and a method for preparing a positive electrode sheet. Background Art

[0002] In the actual production process of batteries, metal burrs are prone to form on the edges of the pole pieces after die-cutting. If the burrs pierce the diaphragm, they will directly conduct with the negative pole piece, which may cause a short circuit between the positive and negative poles, and may also cause risks such as fire and explosion of the lithium battery. To solve this problem, in the coating process of the positive pole piece, more and more battery cell manufacturers usually apply a layer of ceramic coating with a width of 3 to 7 mm on the edge of the positive pole piece. After die-cutting, the positive pole piece will have a 2 to 5 mm wide ceramic coating remaining, making the width of the positive pole piece slightly larger than the width of the negative pole piece. Therefore, during the winding or lamination process, the edge of the negative pole is facing the residual ceramic coating of the positive pole, thereby effectively avoiding the safety risk of the positive and negative poles being connected through the die-cutting burrs. This not only improves the energy density, fast charging performance and safety performance of the battery, but also reduces manufacturing costs.

[0003] Among them, the common processes for coating ceramics on pole pieces are divided into built-in coating ceramic processes and external coating ceramic processes. The external coating ceramic process meets the requirements of different material area widths and tab blanking processes, but its mounting brackets are externally adjusted and fixed, and its anti-interference ability is weak, making it suitable for small-batch trial production lines. In contrast, the built-in coating ceramic process has a simple structure and strong anti-external interference ability, making it suitable for mass production lines. However, both built-in and external coating ceramic processes place extremely strict requirements on the coating process of the ceramic slurry.

[0004] Despite this, in the actual coating production process, mutual dissolution between the ceramic slurry and the positive electrode slurry is still inevitable, which leads to the interface between the positive electrode slurry and the ceramic slurry not being clearly visible, that is, the "virtual edge" problem occurs. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a method for preparing battery ceramic slurry and a method for preparing positive electrode sheets.

[0006] In the first aspect, the embodiment of the present invention discloses a method for preparing a battery ceramic slurry, wherein the components of the ceramic slurry include a binder, a ceramic powder and an organic solvent, the mass ratio of the binder to the ceramic powder is 4:1 to 9:1, and the molecular weight of the binder is ≥90*10 4 Da, the binder is selected from one of polyimide, polyacrylic acid, polyvinylidene fluoride and polytetrafluoroethylene; the preparation method of the battery ceramic slurry comprises the following steps:

[0007] Preparation of glue solution: preparing glue solution by combining the organic solvent and the binder, wherein the solid content of the glue solution is 5% to 9%;

[0008] Preparation of ceramic slurry: Ceramic powder is divided into two parts, the first part of ceramic powder is added to the glue and mixed once; then the second part of ceramic powder is added and mixed twice to obtain the ceramic slurry, wherein the solid content of the ceramic slurry is 25% to 35%.

[0009] By adopting the above technical solution, the mutual solubility and virtual edge problems between the ceramic slurry and the positive electrode slurry can be significantly improved by optimizing the formula of the ceramic slurry and optimizing the preparation method of the ceramic slurry.

[0010] Optionally, the particle size D of the ceramic powder 50 0.5μm~1.5μm.

[0011] Optionally, the viscosity of the ceramic slurry is 2000 mPa s to 4000 mPa s.

[0012] Optionally, the ceramic powder is selected from at least one of zirconium oxide, aluminum oxide, magnesium oxide and boehmite ceramics, and / or the organic solvent is at least one of ethyl acetate, methanol, ethanol, xylene, tetrahydrofuran, chlorobenzene, NMP and acetone.

[0013] Optionally, in the glue preparation step, the organic solvent and the binder are mixed at a revolution of 10 r / min to 20 r / min and a rotation of 500 r / min to 1000 r / min for a mixing time of 10 min to 30 min. After scraping the cylinder, they are mixed again at a revolution of 10 r / min to 20 r / min and a rotation of 800 r / min to 1500 r / min for a mixing time of 10 min to 30 min to prepare the glue.

[0014] Optionally, in the ceramic slurry preparation step, the primary mixing is carried out at a revolution of 10 r / min to 20 r / min and a rotation of 500 r / min to 1000 r / min, and the mixing time is 10 min to 30 min; the secondary mixing is carried out at a revolution of 10 r / min to 20 r / min and a rotation of 8000 r / min to 1500 r / min, and the mixing time is 10 min to 20 min, and then the cylinder is scraped, and then the mixing is carried out at a revolution of 10 r / min to 20 r / min, a rotation of 800 r / min to 1500 r / min, and a vacuum degree ≤-80 Kpa, and the mixing time is 120 min to 240 min.

[0015] In a second aspect, embodiments of the present application disclose a method for preparing a battery positive electrode sheet, the method for preparing the battery positive electrode sheet uses the method for preparing the battery ceramic slurry in any of the embodiments of the first aspect to prepare the ceramic slurry, the positive electrode sheet includes a current collector and tabs, the tabs are arranged on both sides of the current collector along a first direction, the current collector has opposite front and back surfaces, the front and back surfaces are respectively provided with a main material area and a ceramic area, the main material area of the front surface and the main material area of the back surface are arranged correspondingly, the ceramic area of the front surface and the ceramic area of the back surface are arranged correspondingly, and the ceramic area is arranged on both sides of the main material area along the first direction. The method for preparing the battery positive electrode sheet is prepared by using a coating machine, the coating machine includes a die and a convex back roller, the convex back roller includes a back roller and a convex part arranged on the back roller, and the method for preparing the battery positive electrode sheet includes the following steps:

[0016] Front surface coating: the positive electrode slurry is coated on the main material area of the front surface, the ceramic slurry is coated on the ceramic area of the front surface through the die, and the coating thickness of the ceramic slurry is less than the coating thickness of the positive electrode slurry;

[0017] Back surface coating: the current collector after the front surface coating is turned over, so that the coated front surface wraps around the outer periphery of the convex back roller, and the convex part and the coated ceramic area of the front surface abut; the convex part is used to elevate the ceramic area of the front surface, so that the radial distance between the main material area of the back surface and the center of the back roller is equal to the radial distance between the ceramic area of the back surface and the center of the back roller, the positive electrode slurry is coated on the main material area of the back surface, and the ceramic slurry is coated on the ceramic area of the back surface through the die;

[0018] Drying: the current collector after the back surface coating is dried to obtain the positive electrode sheet.

[0019] By using the above technical solution, the difference between the coating thickness of the positive electrode slurry after the front surface coating and the coating thickness of the ceramic slurry can be offset by the convex part, so that the distance between the die and the ceramic area of the back surface during the back surface coating process is always consistent, thereby further avoiding the problems of mutual solubility and virtual edge between the ceramic slurry and the positive electrode slurry on the back surface.

[0020] Optionally, in the drying step, the current collector after the back surface coating is placed in an oven for drying, the temperature of the oven is controlled to be 60-110°C, the air blowing frequency is controlled to be 10-40 Hz, and the air exhaust frequency is controlled to be 10-40 Hz.

[0021] Optionally, the drying step includes:

[0022] The oven includes a first temperature zone and a second temperature zone. The current collector is placed in the first temperature zone for drying. After maintaining a first drying time of 6s to 10s in the first temperature zone, the current collector is transferred to the second temperature zone and maintained for a second drying time of 6s to 10s. The temperature of the first temperature zone is 60°C to 70°C, and the temperature of the second temperature zone is 100°C to 110°C.

[0023] Or the oven includes a third temperature zone, a fourth temperature zone and a fifth temperature zone, the current collector is placed in the third temperature zone for drying, and after maintaining the third drying time of 6s to 10s in the third temperature zone, the current collector is transported to the fourth temperature zone and maintained for a fourth drying time of 6s to 10s, and then transported to the fifth temperature zone and maintained for a fifth drying time of 6s to 10s. The temperature of the third temperature zone is 100°C to 110°C, the temperature of the fourth temperature zone is 60°C to 90°C, and the temperature of the fifth temperature zone is 100°C to 110°C.

[0024] Optionally, the coating thickness of the ceramic slurry is 20 μm to 50 μm, the difference between the coating thickness of the positive electrode slurry and the coating thickness of the ceramic slurry is 50 μm to 110 μm, and the overlapping width of the ceramic area and the main material area along the first direction is ≤0.5 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic top view of a positive electrode sheet according to an embodiment of the present invention is shown;

[0026] Figure 2 A schematic top view of a convex back roller of the present invention is shown;

[0027] Figure 3 A schematic diagram showing a curve of the oven temperature in the preparation method of the positive electrode sheet of Example 1 and Example 2 of the present invention;

[0028] Figure 4 A schematic diagram showing a curve of the oven temperature in the method for preparing the positive electrode sheet according to Example 3 of the present invention;

[0029] Figure 5 A schematic diagram showing a curve of the oven temperature in the method for preparing the positive electrode sheet according to Example 4 of the present invention.

[0030] 1. Positive electrode sheet, 10. Tab, 11. Current collector, 110. Main material area, 111. Ceramic area, 2. Convex back roller, 20. Back roller, 21. Convex part DETAILED DESCRIPTION

[0031] The following is an explanation of the embodiments of the present invention by specific specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Although the description of the present invention will be introduced in conjunction with the preferred embodiment, this does not mean that the features of this invention are limited to this embodiment. On the contrary, the purpose of introducing the invention in conjunction with the embodiment is to cover other options or modifications that may be extended based on the claims of the present invention. In order to provide a deep understanding of the present invention, the following description will contain many specific details. The present invention can also be implemented without using these details. In addition, in order to avoid confusion or blurring the focus of the present invention, some specific details will be omitted in the description. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0032] It should be noted that in this specification, similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0033] The terms “first”, “second”, etc. are only used for distinguishing descriptions and should not be understood as indicating or implying relative importance.

[0034] In the description of this embodiment, it should be noted that, unless otherwise specified or limited, the terms "disposed," "connected," and "connected" should be understood broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this embodiment based on specific circumstances.

[0035] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0036] In the first aspect, the embodiments of the present invention disclose a method for preparing a battery ceramic slurry, wherein the components of the ceramic slurry include a binder, a ceramic powder, and an organic solvent. The binder is selected from one of polyimide, polyacrylic acid, polyvinylidene fluoride, and polytetrafluoroethylene, the mass ratio of the binder to the ceramic powder is 4:1 to 9:1, and the molecular weight of the binder is ≥90*10 4 Da.

[0037] It has been found through research that if the fluidity of the ceramic slurry is too strong and the adhesion is insufficient, during the coating process, the ceramic slurry will easily migrate to the positive electrode slurry area, thereby causing the mutual dissolution of the ceramic slurry and the positive electrode slurry, making the interface between the two unclear, forming the so-called "virtual edge" problem. Therefore, the present invention significantly reduces the migration of the ceramic slurry to the positive electrode slurry by the mutual coordination of the types, molecular weights and mass ratios of the above-mentioned binders. Specifically, the present invention first selects only one of polyimide, polyacrylic acid, polyvinylidene fluoride and polytetrafluoroethylene as a binder, avoiding the compatibility problems that may be caused by the mixing of multiple binders, and helping to better adjust the viscosity and fluidity of the ceramic slurry. At the same time, the present invention controls the mass ratio of the binder to the ceramic powder between 4:1 and 9:1. On the one hand, the ceramic slurry has suitable viscosity and fluidity; on the other hand, it can enhance the bonding effect between the ceramic slurry and the substrate (such as the current collector in the pole piece) to prevent the coating from falling off. In addition, the present invention also controls the molecular weight of the binder to be ≥90*10 4 Da, a molecular weight within this range ensures that the binder has sufficient molecular chain length and entanglement ability, further effectively enhancing the viscosity of the ceramic slurry and reducing its fluidity.

[0038] Based on the above, the preparation method of ceramic slurry includes the following steps:

[0039] Preparation of glue: An organic solvent and a binder are prepared into a glue, and the solid content of the glue is 5% to 9%. The organic solvent is at least one of ethyl acetate, methanol, ethanol, xylene, tetrahydrofuran, chlorobenzene, NMP (N-methylpyrrolidone), and acetone. In a specific embodiment of the present invention, the solid content of the glue refers to the mass percentage of the binder (i.e., solid matter) to the sum of the mass of the organic solvent and the binder. The solid content of the glue in this range ensures that the glue has appropriate viscosity and solubility, prevents agglomeration, and facilitates subsequent mixing of ceramic powders.

[0040] Preparation of ceramic slurry: Ceramic powder is divided into two portions. The first portion of ceramic powder is added to the adhesive solution and mixed once. The second portion of ceramic powder is then added and mixed again to obtain a ceramic slurry. The solid content of the ceramic slurry is 25% to 35%. In the specific embodiment of the present invention, the solid content of the ceramic slurry refers to the mass percentage of the sum of the mass of the binder and the ceramic powder (i.e., the solid matter) to the sum of the mass of the organic solvent, ceramic powder, and binder.

[0041] That is to say, the present invention obtains a ceramic slurry with a solid content of 25% to 35% and the above-mentioned formula through the mutual cooperation of the type, molecular weight, mass ratio of the binder and the above-mentioned preparation method. The viscosity of the prepared ceramic slurry is 2000mPa s to 4000mPa s. Specifically, on the basis of optimizing the formula of the ceramic slurry, the present invention further prepares and controls the solid content of each stage in the preparation method of the ceramic slurry in stages. Not only is the influence of the difference in solid content between the ceramic slurry and the positive electrode slurry effectively avoided, the migration of the ceramic slurry to the positive electrode slurry is further reduced; it also makes the ceramic slurry have a more suitable viscosity, thereby further reducing the migration of the ceramic slurry to the positive electrode slurry.

[0042] Therefore, by adopting the above technical solution, the present invention effectively solves the problems of mutual dissolution with the positive electrode slurry and virtual edges caused by the ceramic slurry itself by optimizing the formula of the ceramic slurry and optimizing the preparation method of the ceramic slurry.

[0043] Furthermore, the molecular weight of the binder is 90*10 4 Da~150*10 4 Da. In combination with the above, it can be seen that, on the one hand, the problem of too low viscosity and excessive fluidity of the ceramic slurry due to the low molecular weight of the binder is avoided. If the molecular weight of the binder is low, the fluidity of the ceramic slurry is enhanced, but its adhesion is insufficient. This will cause the ceramic slurry to easily migrate to the positive electrode slurry area during the coating process, seriously affecting the quality and performance of the coating. On the other hand, it also avoids the problem of excessive viscosity and reduced fluidity of the ceramic slurry due to excessively high molecular weight. If the molecular weight of the binder is too high, the viscosity of the ceramic slurry will increase significantly, the fluidity will be too poor, and it will be difficult to spread smoothly on the coating equipment. This will not only cause the ceramic slurry to be unable to be evenly distributed on the substrate, forming a coating with inconsistent thickness, but may also cause defects such as bubbles and streaks in the coating, affecting the uniformity and stability of the coating, thereby reducing the performance and safety of the battery.

[0044] In some other possible embodiments provided by the present invention, the particle size D of the ceramic powder is 50 The particle size is 0.5 μm to 1.5 μm. This allows the ceramic powder to be evenly distributed in the binder and organic solvent system, thereby further improving the uniformity of the ceramic slurry. On the other hand, it also helps to enhance the interfacial bonding between the ceramic slurry and the substrate, further preventing it from falling off.

[0045] Specifically, in the glue preparation step of the present invention, organic solvent and binding agent are mixed under revolution 10r / min~20r / min, rotation 500r / min~1000r / min, mixing time is 10min~30min, after scraping cylinder, again under revolution 10r / min~20r / min, rotation 800r / min~1500r / min, mixing time is 10min~30min, make glue. Thus, revolution and rotation speed combination ensures sufficient wetting and uniform dispersion of organic solvent and binding agent, avoids local concentration too high or agglomeration phenomenon, thereby improves the uniformity of glue. Secondly, appropriate mixing time (10min~30min) can both ensure that dissolving is sufficient, and can avoid molecular chain degradation caused by long-term high-speed shearing, maintain mechanical properties and bonding strength of binding agent. At the same time, the scraping cylinder operation further enhances the mixing efficiency and prevents the material from sticking to the wall and affecting the uniformity. Increasing the rotation speed (800r / min~1500r / min) after scraping the cylinder helps to further refine the glue structure, reduce the bubble content, and make the glue have more suitable viscosity and solid content.

[0046] In the ceramic slurry preparation step, the first mixing is carried out at a revolution of 10r / min to 20r / min and a rotation of 500r / min to 1000r / min, and the mixing time is 10min to 30min; the second mixing is carried out at a revolution of 10r / min to 20r / min and a rotation of 8000r / min to 1500r / min, and the mixing time is 10min to 20min, and then the cylinder is scraped, and then the cylinder is rotated at a revolution of 10r / min to 20r / min, a rotation of 800r / min to 1500r / min, and a vacuum degree of ≤-80Kpa, and the mixing time is 120min to 240min. Thus, through the first mixing and the second mixing, the dispersion of ceramic powder in the ceramic slurry can be better guaranteed. At the same time, scraping the cylinder in the second mixing can remove the material attached to the cylinder wall, avoid uneven mixing, and further ensure that all components are fully dispersed. In addition, long-term mixing (120min to 240min) under vacuum conditions of ≤-80KPa can inhibit the volatilization of organic solvents, which is beneficial to maintaining the stability of the solid content of the ceramic slurry and avoiding changes in the viscosity of the ceramic slurry due to loss of organic solvents. At the same time, the vacuum environment can effectively eliminate bubbles in the ceramic slurry and reduce pore defects in the ceramic slurry during the coating process.

[0047] In the second aspect, the embodiment of the present invention discloses a method for preparing a positive electrode sheet of a battery, wherein the method for preparing a positive electrode sheet of a battery adopts the method for preparing a battery ceramic slurry in any embodiment of the first aspect to prepare a ceramic slurry. Figure 1 and Figure 2As shown, the positive electrode plate 1 includes a current collector 11 and a tab 10. The tab 10 is arranged along a first direction (eg Figure 1 The current collector 11 has a front side and a back side opposite to each other, and the front side and the back side can also be understood as two opposite sides arranged along the thickness direction of the current collector 11. The front side and the back side are respectively provided with a main material area 110 and a ceramic area 111. The ceramic area 111 is arranged along the first direction (for example Figure 1 The positive electrode sheet is prepared using a coating machine comprising a die head and a convex back roller 2. The convex back roller 2 comprises a back roller 20 and a convex portion 21 provided on the back roller 20.

[0048] Specifically, the method for preparing the positive electrode sheet of a battery includes the following steps:

[0049] Front coating: The positive electrode slurry is coated on the main material area on the front side, and the ceramic slurry is coated on the ceramic area on the front side through the die head. The coating thickness of the ceramic slurry is less than the coating thickness of the positive electrode slurry. Among them, controlling the coating thickness of the ceramic slurry to be less than the coating thickness of the positive electrode slurry can not only ensure that the ceramic coating plays an insulating role, thereby effectively avoiding the safety risk of the positive and negative electrodes being connected through the die-cutting burrs, but also avoid the fact that the thickness of the ceramic coating is too thick and reduces the energy density of the battery. Preferably, the coating thickness of the ceramic slurry is 20μm to 50μm, and the difference between the coating thickness of the positive electrode slurry and the coating thickness of the ceramic slurry is 50μm to 110μm. More specifically, the back side of the current collector is wrapped around the periphery of a common back roller, the positive electrode slurry is coated on the main material area on the front side, and the ceramic slurry is coated on the ceramic area on the front side through the die head. The coating thickness of the ceramic slurry is less than the coating thickness of the positive electrode slurry.

[0050] Back coating: Flip the current collector 11 after coating on the front side so that the coated front side is wrapped around the outer periphery of the convex back roller 2. The convex portion 21 abuts against the ceramic area on the front side after coating, and the convex portion 21 is used to raise the ceramic area on the front side so that the radial distance between the main material area on the back side and the center of the back roller 20 is equal to the radial distance between the ceramic area on the back side and the center of the back roller 20. In other words, the radial height between the main material area on the back side and the center of the back roller 20 is equal to the radial height between the ceramic area on the back side and the center of the back roller 20. Alternatively, it can be understood that the thickness of the convex portion 21 is equal to the difference between the coating thickness of the positive electrode slurry and the coating thickness of the ceramic slurry. At this time, the positive electrode slurry is coated on the main material area on the back side, and the ceramic slurry is coated on the ceramic area on the back side through the die head.

[0051] Drying: The current collector after coating on the back side is dried to obtain the positive electrode sheet 1.

[0052] In the prior art, ordinary back rollers are usually used for front and back coating in the positive electrode tab coating process. However, due to the difference between the coating thickness of the ceramic slurry and the coating thickness of the positive electrode slurry, the ceramic area on the back surface will be uneven compared to the main area on the back surface when the coated front surface wraps around the outer periphery of the ordinary back roller, and even falls on the end of the main area on the back surface. During the back coating process, the spraying distance between the die head and the ceramic area on the back surface will become inconsistent due to the unevenness of the ceramic area on the back surface as the ordinary back roller rotates. This will also cause the ceramic slurry to splash onto the main area on the back surface, thereby causing the problem of mutual solubility between the positive electrode slurry and the ceramic slurry on the back surface of the current collector.

[0053] Therefore, by using a convex back roller in the back coating step, the convex portion 21 is used to elevate the ceramic area on the front surface, so that the radial distance between the main area on the back surface and the center of the back roller 20 is equal to the radial distance between the ceramic area on the back surface and the center of the back roller 20. That is, the present application offsets the difference between the coating thickness of the positive electrode slurry after front coating and the coating thickness of the ceramic slurry by the convex portion 21, so that the distance between the die head and the ceramic area on the back surface remains consistent during the back coating process, thereby further avoiding the problem of mutual solubility between the ceramic slurry and the positive electrode slurry on the back surface.

[0054] Further, the width of the overlap between the ceramic area and the main area in the first direction (e.g. Figure 1 x direction) is ≤0.5mm. Thus, the small overlap width can further prevent the problem of boundary blurring or mutual solubility between the ceramic slurry and the positive electrode slurry during the coating process.

[0055] In some other possible embodiments provided by the present application, in the drying step, the current collector 11 after back coating is placed in an oven for drying, the oven temperature is controlled to be 60-110°C, the air blowing frequency is controlled to be 10-40Hz, and the air exhaust frequency is controlled to be 10-40Hz. Thus, the appropriate temperature range (60-110°C) can ensure that the solvents in the ceramic slurry and the positive electrode slurry evaporate at an appropriate speed. Too high a temperature can cause the solvent to evaporate quickly, causing the surface of the slurry to dry quickly, while the internal solvent cannot escape in time, thereby causing bubbles or cracking; too low a temperature will prolong the drying time and reduce production efficiency. The control of the air blowing frequency and the air exhaust frequency forms a stable air circulation, avoiding the mixing of the slurry due to air turbulence. Therefore, by controlling the above drying conditions, the present application can further effectively prevent the problem of mutual solubility between the ceramic slurry and the positive electrode slurry while avoiding cracking of the positive electrode tab.

[0056] Specifically, the drying step comprises:

[0057] The oven includes a first temperature zone and a second temperature zone. The collector 11 after back coating is placed in the first temperature zone for drying. After maintaining the first drying time of 6s to 10s in the first temperature zone, the collector 11 is transported to the second temperature zone and maintained for the second drying time of 6s to 10s. The temperature of the first temperature zone is 60℃ to 70℃, and the temperature of the second temperature zone is 100℃ to 110℃.

[0058] Thus, after the current collector 11 is dried in the first temperature zone for 6s to 10s, it is dried in the second temperature zone for 6s to 10s. The drying temperature is controlled from the lower temperature of the first temperature zone to the temperature of the second temperature zone, which can avoid the internal stress concentration of the slurry caused by the rapid evaporation of the solvent. This drying method helps to further maintain the stability of the ceramic slurry and the positive electrode slurry during the drying process, and prevents the virtual edge mutual dissolution phenomenon caused by the intense thermal movement of the ceramic slurry. At the same time, through this drying process, it can ensure that the drying rate of each part of the coating is relatively consistent, reduce the stress difference caused by uneven drying, and thus effectively reduce the risk of cracking of the pole piece.

[0059] Alternatively, the oven includes a third temperature zone, a fourth temperature zone, and a fifth temperature zone. The current collector 11 after back coating is placed in the third temperature zone for drying. After maintaining the third drying time of 6s to 10s in the third temperature zone, the current collector 11 is transported to the fourth temperature zone and maintained for the fourth drying time of 6s to 10s, and then transported to the fifth temperature zone and maintained for the fifth drying time of 6s to 10s. The temperature of the third temperature zone is 100℃ to 110℃, the temperature of the fourth temperature zone is 60℃ to 90℃, and the temperature of the fifth temperature zone is 100℃ to 110℃.

[0060] Therefore, initially setting the third temperature zone to a higher temperature range can quickly initiate the solvent volatilization process, allowing the ceramic slurry and positive electrode slurry surfaces to initially dry, forming a relatively stable coating structure. Drying in the third temperature zone for 6 to 10 seconds avoids stress concentration within the coating caused by rapid solvent volatilization due to excessively high temperatures, thereby ensuring uniform drying of the coating surface. Subsequently, the current collector 11 is transferred to the fourth temperature zone. This cooling process helps relieve stress within the coating caused by the initial high-temperature drying and allows the solvent within the coating to evaporate more evenly. Drying in the fourth temperature zone at 60 to 90°C for 6 to 10 seconds further balances the drying rate within the coating, reducing the risk of cracking caused by uneven solvent volatilization. Furthermore, the lower fourth temperature reduces the fluidity of the ceramic slurry, further preventing the occurrence of virtual edge miscibility between the ceramic slurry and the positive electrode slurry during the drying process. Next, the current collector 11 is transferred to the fifth temperature zone to ensure complete volatilization of the solvent within the coating, forming a strong and uniform coating structure. Finally, drying in the fifth temperature zone at 100°C to 110°C for 6 to 10 seconds can further achieve the ideal drying state of the coating. Therefore, through the aforementioned zoned temperature control and drying time settings, the present invention optimizes the drying rate of the coating in different temperature zones, further and more effectively preventing problems such as virtual edge dissolution caused by the drying process or coating cracking caused by uneven drying.

[0061] The following will be described in conjunction with more specific implementation methods.

[0062] Example 1

[0063] The method for preparing the positive electrode sheet in Example 1 includes the following steps:

[0064] Preparation of glue: an organic solvent (N-methylpyrrolidone) and a binder (polyvinylidene fluoride) are prepared into a glue, and the solid content of the glue is 6%;

[0065] Preparation of ceramic slurry: Ceramic powder (boehmite ceramic) was divided into two parts. The first part of ceramic powder was added to the glue solution and mixed once. Then, the second part of ceramic powder was added and mixed again to obtain a ceramic slurry. The solid content of the ceramic slurry was 33%, and the viscosity of the ceramic slurry was 3000 mPa s.

[0066] Front coating: The back side is wrapped around the outer periphery of the ordinary backing roller, and the positive electrode slurry (lithium iron phosphate slurry) is coated on the main material area of ​​the front side. The ceramic slurry is coated on the ceramic area of ​​the front side through the die head. The coating thickness of the ceramic slurry is 32μm, and the coating thickness of the positive electrode slurry is 120μm.

[0067] Back coating: The current collector after coating on the front side is turned over so that the coated front side is wrapped around the outer periphery of the convex back roller, and the convex part abuts against the ceramic area on the coated front side; the convex part is used to raise the ceramic area on the front side so that the radial distance between the main material area on the back side and the center of the back roller is equal to the radial distance between the ceramic area on the back side and the center of the back roller, and the positive electrode slurry is coated on the main material area on the back side, and the ceramic slurry is coated on the ceramic area on the back side through the die head;

[0068] Drying: The oven includes the first temperature zone and the second temperature zone. The oven temperature curve is as follows: Figure 3 As shown, the back-coated current collector 11 is placed in the first temperature zone and dried at 65°C for 9 seconds. The current collector 11 is then transferred to the second temperature zone and dried at 110°C for 9 seconds to obtain a positive electrode sheet. The oven has a blast frequency of 10 Hz to 40 Hz, and an exhaust frequency of 10 Hz to 40 Hz.

[0069] The mass ratio of binder to ceramic powder is 85:15, and the molecular weight of binder is 95*10 4 Da.

[0070] Example 2

[0071] The difference from Example 1 is that in the back coating step, a convex back roller is not used, but a normal back roller is used.

[0072] Example 3

[0073] The difference from Example 1 is that the coating thickness of the ceramic slurry is 33 μm, and in the back coating step, a convex back roller is not used, but a normal back roller is used. In the drying step, the oven includes the third temperature zone, the fourth temperature zone and the fifth temperature zone. The oven temperature curve is as follows Figure 4 As shown, the current collector 11 after back coating is placed in the third temperature zone for drying. After drying for 9 seconds at a temperature of 110°C in the third temperature zone, the current collector 11 is transported to the fourth temperature zone and dried for 9 seconds at a temperature of 85°C in the fourth temperature zone. It is then transported to the fifth temperature zone and dried for 9 seconds at a temperature of 110°C in the fifth temperature zone.

[0074] Example 4

[0075] The difference from Example 1 is that the coating thickness of the ceramic slurry is 30 μm, and in the back coating step, a convex back roller is not used, but a normal back roller is used. In the drying step, the oven temperature curve is as follows: Figure 5 As shown, the back-coated current collector is placed in a 60°C temperature zone of an oven and dried for 9 seconds, then transferred to a 110°C temperature zone of an oven and dried for 9 seconds, and then transferred to a 70°C temperature zone of an oven and dried for 9 seconds.

[0076] After drying, the front edge, back edge, front cracking, and back cracking of Examples 1-4 were observed and scored accordingly. The scoring results are recorded in Table 1.

[0077] Table 1

[0078]

[0079] Among them, "0" indicates no miscibility, no virtual edges, and a clear interface between the cathode slurry and the ceramic slurry; or indicates no cracking. "1" indicates slight miscibility, slight virtual edges; or indicates slight cracking. "2" indicates moderate miscibility, moderate virtual edges; or indicates moderate cracking. "3" indicates moderate miscibility, moderate virtual edges; or indicates moderate cracking.

[0080] The front side of the positive electrode sheets of Examples 1-4 of the present invention effectively avoids the problems of mutual dissolution and virtual edges between the ceramic slurry and the positive electrode slurry before drying (i.e., during the coating process). According to Table 1, the front side of the positive electrode sheets of Examples 1-4 can still effectively avoid the problems of mutual dissolution and virtual edges between the ceramic slurry and the positive electrode slurry after drying. In addition, Examples 1-3 further optimize the process conditions in the drying step, and also effectively avoid the problem of cracking of the electrode sheet after drying. Furthermore, Example 1 uses a convex back roller in the back coating process, thereby completely solving the problems of mutual dissolution and virtual edges between the ceramic slurry and the positive electrode slurry.

[0081] Although the present invention has been illustrated and described with reference to certain preferred embodiments thereof, it should be understood by those skilled in the art that the above description is provided as a further detailed description of the present invention in conjunction with specific embodiments thereof, and that the specific implementation of the present invention is not limited to these descriptions. Those skilled in the art may make various changes in form and details, including simple deductions or substitutions, without departing from the spirit and scope of the present invention.

Claims

1. A method for preparing a battery ceramic slurry, characterized in that: The components of the ceramic slurry include a binder, ceramic powder and an organic solvent. The mass ratio of the binder to the ceramic powder is 4:1 to 9:

1. The molecular weight of the binder is ≥90*10 4 Da, the binder is selected from one of polyimide, polyacrylic acid, polyvinylidene fluoride and polytetrafluoroethylene; the preparation method of the battery ceramic slurry comprises the following steps: Preparation of glue solution: preparing glue solution by combining the organic solvent and the binder, wherein the solid content of the glue solution is 5% to 9%; Preparation of ceramic slurry: Ceramic powder is divided into two parts, the first part of ceramic powder is added to the glue and mixed once; then the second part of ceramic powder is added and mixed twice to obtain the ceramic slurry, wherein the solid content of the ceramic slurry is 25% to 35%.

2. The method for preparing a battery ceramic slurry according to claim 1, wherein: The particle size D of the ceramic powder 50 0.5μm~1.5μm.

3. The method for preparing a battery ceramic slurry according to claim 1, wherein: The viscosity of the ceramic slurry is 2000 mPa s to 4000 mPa s.

4. The method for preparing a battery ceramic slurry according to claim 1, wherein: The ceramic powder is selected from at least one of zirconium oxide, aluminum oxide, magnesium oxide and boehmite ceramics, and / or the organic solvent is at least one of ethyl acetate, methanol, ethanol, xylene, tetrahydrofuran, chlorobenzene, NMP and acetone.

5. The method for preparing a battery ceramic slurry according to claim 1, wherein: In the glue liquid preparation step, the organic solvent and the binder are mixed at a revolution of 10 r / min to 20 r / min and a rotation of 500 r / min to 1000 r / min for a mixing time of 10 min to 30 min. After scraping the cylinder, they are mixed again at a revolution of 10 r / min to 20 r / min and a rotation of 800 r / min to 1500 r / min for a mixing time of 10 min to 30 min to prepare the glue liquid.

6. The method for preparing a battery ceramic slurry according to claim 1, wherein: In the ceramic slurry preparation step, the primary mixing is carried out at a revolution of 10 r / min to 20 r / min and a rotation of 500 r / min to 1000 r / min, and the mixing time is 10 min to 30 min; the secondary mixing is carried out at a revolution of 10 r / min to 20 r / min and a rotation of 8000 r / min to 1500 r / min, and the mixing time is 10 min to 20 min, and then the cylinder is scraped, and then the mixing is carried out at a revolution of 10 r / min to 20 r / min, a rotation of 800 r / min to 1500 r / min, and a vacuum degree of ≤-80 Kpa, and the mixing time is 120 min to 240 min.

7. A method for preparing a positive electrode sheet of a battery, characterized in that: The method for preparing the battery positive electrode sheet adopts the method for preparing the battery ceramic slurry according to any one of claims 1 to 6 to prepare the ceramic slurry, the positive electrode sheet includes a current collector and a pole ear, the pole ear is arranged on both sides of the current collector along a first direction, the current collector has a relative front and back, the front and back are respectively provided with a main material area and a ceramic area, the main material area of ​​the front and the main material area of ​​the back are arranged correspondingly, the ceramic area of ​​the front and the ceramic area of ​​the back are arranged correspondingly, and the ceramic area is arranged on both sides of the main material area along the first direction. The method for preparing the battery positive electrode sheet adopts a coating machine, the coating machine includes a die head and a convex back roller, the convex back roller includes a back roller and a convex portion provided on the back roller, and the method for preparing the battery positive electrode sheet includes the following steps: Front coating: coating the positive electrode slurry on the main material area of ​​the front surface, and coating the ceramic slurry on the ceramic area of ​​the front surface through the die head, wherein the coating thickness of the ceramic slurry is less than the coating thickness of the positive electrode slurry; Back coating: flip the current collector after coating on the front side so that the coated front side is wrapped around the periphery of the convex back roller, and the convex portion abuts against the ceramic area on the coated front side; the convex portion is used to raise the ceramic area on the front side so that the radial distance between the main material area on the back side and the center of the back roller is equal to the radial distance between the ceramic area on the back side and the center of the back roller, and the positive electrode slurry is coated on the main material area on the back side, and the ceramic slurry is coated on the ceramic area on the back side through the die head; Drying: Drying the current collector after coating on the back side to obtain the positive electrode sheet.

8. The method for preparing a positive electrode sheet of a battery according to claim 7, wherein: In the drying step, the current collector after back coating is placed in an oven for drying, and the oven temperature is controlled to be 60° C. to 110° C., the blowing frequency is 10 Hz to 40 Hz, and the exhaust frequency is 10 Hz to 40 Hz.

9. The method for preparing a positive electrode sheet of a battery according to claim 8, wherein: The drying step comprises: The oven includes a first temperature zone and a second temperature zone. The current collector is placed in the first temperature zone for drying. After maintaining a first drying time of 6s to 10s in the first temperature zone, the current collector is transferred to the second temperature zone and maintained for a second drying time of 6s to 10s. The temperature of the first temperature zone is 60°C to 70°C, and the temperature of the second temperature zone is 100°C to 110°C. Or the oven includes a third temperature zone, a fourth temperature zone and a fifth temperature zone, the current collector is placed in the third temperature zone for drying, and after maintaining the third drying time of 6s to 10s in the third temperature zone, the current collector is transported to the fourth temperature zone and maintained for a fourth drying time of 6s to 10s, and then transported to the fifth temperature zone and maintained for a fifth drying time of 6s to 10s. The temperature of the third temperature zone is 100°C to 110°C, the temperature of the fourth temperature zone is 60°C to 90°C, and the temperature of the fifth temperature zone is 100°C to 110°C.

10. The method for preparing a positive electrode sheet of a battery according to claim 7, wherein: The coating thickness of the ceramic slurry is 20 μm to 50 μm, the difference between the coating thickness of the positive electrode slurry and the coating thickness of the ceramic slurry is 50 μm to 110 μm, and the overlapping width of the ceramic area and the main material area along the first direction is ≤0.5 mm.

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