Method for preparing active material layer, active material layer, secondary battery, and electric device

Abstract

The invention relates to the field of batteries, and discloses a method for preparing an active material layer, the active material layer, a secondary battery and an electric device. The method for preparing the active material layer comprises the steps that an electrode diaphragm is smashed to obtain first powder, the electrode diaphragm comprises an active material, a binding agent and a conductive agent, the binding agent comprises a first binding agent and a second binding agent, and the first binding agent comprises polytetrafluoroethylene; the first powder and the second powder are mixed to obtain a mixture, the mixture is rolled to obtain the active material layer, the components of the second powder are the same as those of the first powder, and the fibrillation degree of the first binder in the second powder is lower than that of the first binder in the first powder. Therefore, the strength of the active material layer can be effectively improved, and the probability of breakage and tearing of the active material layer in the transfer process can be reduced.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular, to a method for preparing an active material layer, an active material layer, a secondary battery, and an electrical device. Background Art

[0002] The mainstream dry electrode process on the market now is to prepare a membrane of target weight by rolling and transferring the powder continuously for multiple times, and then laminate the membrane and the current collector together by rolling to obtain the electrode. If the strength of the membrane is insufficient, it will cause the membrane to break during the transfer process, and insufficient bonding between particles will cause the membrane to tear during the transfer process, affecting the continuity and quality rate of production. Summary of the invention

[0003] In view of the technical problems existing in the background technology, the present application provides a method for preparing an active material layer, aiming to improve the strength of a membrane prepared by a dry electrode process.

[0004] In one aspect of the present application, the present application proposes a method for preparing an active material layer. In some embodiments of the present application, the method for preparing an active material layer includes: pulverizing an electrode membrane to obtain a first powder, wherein the electrode membrane includes an active material, a binder and a conductive agent, wherein the binder includes a first binder and a second binder, wherein the first binder includes polytetrafluoroethylene, and the second binder includes one or more of polyvinylidene fluoride, polyacrylic acid, polyacrylamide, sodium carboxymethyl cellulose, and styrene-butadiene rubber; mixing the first powder with the second powder to obtain a mixture, and rolling the mixture to obtain an active material layer, wherein the components of the second powder are the same as those of the first powder, and the fibrillation degree of the first binder in the second powder is lower than the fibrillation degree of the first binder in the first powder.

[0005] On the one hand, the first binder in the electrode membrane has been fibrillated to a certain extent during the previous membrane preparation process. During the pulverization process and the subsequent rolling process, the first binder will be further fibrillated, locally strengthening the bonding effect on the active material and the conductive agent, thereby effectively improving the strength of the active material layer, which is beneficial to reduce the probability of the active material layer breaking or tearing during the transfer process. On the other hand, during the subsequent rolling process, the interaction between the second binder in the electrode membrane and the active material, the conductive agent, the second binder itself, and the first binder will also be enhanced, which is beneficial to further improve the strength of the active material layer. The first binder in the second powder can be fibrillated to a certain extent during the rolling process to bond the active material and / or conductive agent around it.

[0006] In some embodiments of the present application, based on the total mass of the electrode membrane, the mass percentage of the first binder is less than or equal to 5%, and / or the mass percentage of the second binder is less than or equal to 5%. This is conducive to improving the strength of the active material layer and improving the continuity and efficiency of production.

[0007] In some embodiments of the present application, based on the total mass of the electrode membrane, the mass percentage of the first binder is 0.1% to 4%, and / or the mass percentage of the second binder is 0.1% to 3%. This is conducive to further improving the strength of the active material layer and improving the continuity and efficiency of production.

[0008] In some embodiments of the present application, the first powder is sieved before rolling. The sieving process can remove particles with larger particle sizes, making the size of the first powder more uniform, which is conducive to obtaining an active material layer with excellent performance through subsequent rolling.

[0009] In some embodiments of the present application, the mesh number of the sieving process is 4 mesh to 400 mesh. The sieving process using the sieve with the above mesh number can obtain a powder with a suitable particle size, which is convenient for the subsequent preparation of the active material layer using a dry process.

[0010] In some embodiments of the present application, the mesh number of the sieving process is 6-35 meshes. This is conducive to preparing the active material layer by a dry process and is conducive to further improving the strength of the active material layer.

[0011] In some embodiments of the present application, the mass ratio of the first powder to the second powder is (1:10) to (100:1). The active material layer obtained by mixing the first powder and the second powder in the above ratio and subsequent rolling treatment has a higher strength.

[0012] In some embodiments of the present application, the pulverization process includes one or more of stirring crushing, granulation, and air flow pulverization. The pulverization process can pulverize the electrode membrane to form a relatively uniform powder.

[0013] In some embodiments of the present application, the linear speed of the stirring and crushing is less than or equal to 100 m / s, and / or the temperature of the stirring and crushing is -20°C to 150°C. Stirring and crushing the electrode membrane under the above conditions can form the electrode membrane into powder in a shorter time, and can improve the fibrillation degree of the first binder in the electrode membrane.

[0014] In some embodiments of the present application, the stirring and crushing linear speed is 5m / s-50m / s, and / or the stirring and crushing temperature is 0°C-110°C. Thus, the electrode membrane can be formed into powder and each substance in the electrode membrane can maintain good performance.

[0015] In some embodiments of the present application, the rolling process is performed 1 to 20 times. Single or multiple rolling processes can further fibrillate the first binder in the first powder, play a role in local strengthening, and fibrillate the first binder in the second powder, entangle the surrounding active materials and conductive agents.

[0016] In some embodiments of the present application, the rolling process satisfies at least one of the following conditions: temperature is 0°C to 150°C; speed is less than or equal to 150 m / min; pressure is less than or equal to 50 T; gap is less than or equal to 1000 μm. Thus, the powders can be bonded together by the rolling process to form an active material layer.

[0017] In some embodiments of the present application, the rolling process satisfies at least one of the following conditions: temperature is 10°C to 80°C; speed is 2m / min to 100m / min; pressure is 0.5T to 5T; gap is less than or equal to 500μm. This is conducive to the formation of the active material layer and to improving the strength of the active material layer.

[0018] In another aspect of the present application, the present application provides an active material layer. In some embodiments of the present application, the active material layer is an active material layer prepared by the method described above. Thus, the active material layer has a high strength and is not easy to break or tear during the transfer process.

[0019] In another aspect of the present application, the present application provides a secondary battery. In some embodiments of the present application, the secondary battery includes the active material layer described above. Thus, the active material layer in the secondary battery has high strength and good electrochemical properties, which is conducive to improving the stability of the secondary battery.

[0020] In another aspect of the present application, the present application provides an electric device. In some embodiments of the present application, the electric device includes the secondary battery described above. Therefore, the electric device has all the features and advantages of the secondary battery described above, which will not be repeated here.

[0021] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the optional embodiments below. The accompanying drawings are only used for the purpose of illustrating the optional embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings: Figure 1 is a flow chart of a method for preparing an active material layer according to an embodiment of the present application; Figure 2 It is a schematic diagram of the principle of forming a membrane by rolling the second powder; Figure 3 Schematic diagram of the principle of mixing the first powder and the second powder and then rolling to form an active material layer; Figure 4 is a schematic diagram of a battery cell according to an embodiment of the present application; Figure 5 yes Figure 4 An exploded view of a battery cell according to an embodiment of the present application is shown; Figure 6 is a schematic diagram of a battery module according to an embodiment of the present application; Figure 7 is a schematic diagram of a battery pack according to an embodiment of the present application; Figure 8 yes Figure 7 An exploded view of a battery pack according to an embodiment of the present application is shown; Fig. 9 is a schematic diagram of an electrical device according to an embodiment of the present application; Fig.10 is a comparison diagram of the tensile curves of the membranes in Example 1 and Comparative Example 1; Fig.11 This is a scanning electron microscope image of the new material in Comparative Example 1; Fig.12 This is a scanning electron microscope image of the waste powder in Example 1.

[0023] Description of reference numerals: 1 battery cell; 11 housing; 12 electrode assembly; 13 cover plate; 2 battery module; 3 battery pack; 31 upper case; 32 lower case; 40 active material; 51 first binder particles; 52 first fibers; 53 second fibers. DETAILED DESCRIPTION

[0024] The embodiments of the present application are described in detail below. Examples of the embodiments are shown in the drawings, but unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of actually identical structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0025] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by technicians in the technical field to which this application belongs; the terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application; unless otherwise specified, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the embodiments of this application).

[0026] The terms "including" and "having" in the specification and claims of the present application and any modifications thereof are open expressions, that is, including the contents specified in the present application but not excluding other contents.

[0027] In the description of this application, regardless of whether the words "about" or "approximately" are used, all the numbers disclosed herein are approximate values. The value of each number may differ by less than 10% or a reasonable difference considered by those skilled in the art, such as 1%, 2%, 3%, 4% or 5%.

[0028] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. "First feature" and "second feature" may include one or more of the features.

[0030] In the description of the present application, “plurality” means two or more.

[0031] In the description of the present application, "A and / or B" may include the case of A alone, the case of B alone, or any of the cases of A and B, where A and B are only used for examples and may be any technical feature connected by "and / or" in the present application.

[0032] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0033] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0034] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0035] The dry electrode process is used to prepare the membrane. If the strength of the membrane is insufficient, it will cause the membrane to break during the transfer process. Insufficient adhesion between particles will cause the membrane to tear during the transfer process, affecting the continuity and quality rate of production.

[0036] The present application obtains a first powder by pulverizing the electrode diaphragm, mixes the first powder and the second powder to obtain a mixture, and then prepares the mixture into an active material layer by rolling. On the one hand, the first binder in the electrode diaphragm has been fibrillated to a certain extent in the previous diaphragm preparation process. During the pulverization and subsequent rolling process, the first binder in the electrode diaphragm will be further fibrillated, and the bonding effect on the active material and the conductive agent will be locally strengthened, thereby effectively improving the strength of the active material layer, which is conducive to reducing the probability of fracture and tearing of the active material layer during the transfer process, improving the continuity of production and improving the yield. On the other hand, in the subsequent rolling process, the interaction between the second binder in the electrode diaphragm and the active material, the conductive agent, the second binder itself and the first binder will also be enhanced, which is conducive to further improving the strength of the active material layer. The fibrillation degree of the first binder in the second powder is lower than that of the first binder in the first powder. The first binder in the second powder will also undergo a certain degree of fibrillation during the rolling process, entangle the surrounding materials, and the second binder in the second powder can also bond the various surrounding materials through the rolling process.

[0037] The active material layer disclosed in the embodiment of the present application can be combined together by rolling with the current collector to form an electrode sheet, and the electrode sheet can be applied to a secondary battery. The secondary battery disclosed in the embodiment of the present application includes a lithium-ion battery, and the secondary battery disclosed in the embodiment of the present application can be used in an electrical device using a battery as a power source or various energy storage systems using a battery as an energy storage element. Electrical devices may include but are not limited to mobile phones, tablets, laptops, electric toys, electric tools, battery cars, electric cars, ships, spacecraft, and the like. Among them, electric toys may include fixed or mobile electric toys, for example, game consoles, electric car toys, electric ship toys, electric airplane toys, and the like, and spacecraft may include airplanes, rockets, space shuttles, spacecraft, and the like.

[0038] In one aspect of the present application, the present application provides a method for preparing a secondary battery. In some embodiments of the present application, reference is made to Figure 1 , the method for preparing a secondary battery may include the following steps: S10: crushing the electrode membrane to obtain a first powder.

[0039] In some embodiments of the present application, the electrode membrane includes an active material, a binder and a conductive agent, wherein the binder includes a first binder and a second binder, the first binder includes polytetrafluoroethylene (PTFE), and the second binder includes one or more of polyvinylidene fluoride (PVDF), polyacrylic acid, polyacrylamide, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0040] Polytetrafluoroethylene is a fibrillated binder. The first binder polytetrafluoroethylene in the electrode membrane has been fibrillated to a certain extent in the previous process (the preparation process of the electrode membrane). After the electrode membrane is crushed and then rolled, the first binder in the electrode membrane will be further fibrillated, locally strengthening the bonding effect, entangled the surrounding active materials and / or conductive agents together, and improving the strength of the active material layer and the bonding force between particles. The second binder such as polyvinylidene fluoride, polyacrylic acid, polyacrylamide, sodium carboxymethyl cellulose, styrene-butadiene rubber can bond the various substances together through physical interactions (such as mechanical riveting, etc.) and / or chemical interactions (such as covalent bonds, etc.). The second binder in the electrode membrane can also enhance the bonding force between various substances in the active material layer through the subsequent rolling process; in addition, the second binder in the electrode membrane can reduce the difficulty of the recycling process, improve the uniformity of the electrode membrane after crushing, and reduce the defects in the active material layer obtained by subsequent processing.

[0041] In some embodiments of the present application, based on the total mass of the electrode membrane, the mass percentage of the first binder is less than or equal to 5%, for example, the mass percentage of the first binder may be 0.1%, 1%, 2%, 3%, 4%, 5%, etc. The content of the first binder in the electrode membrane is within the above range, and further fibrillation can be achieved in the subsequent pulverization process and rolling process, thereby strengthening the bonding effect and facilitating improving the strength of the prepared active material layer.

[0042] In some embodiments of the present application, based on the total mass of the electrode membrane, the mass percentage of the first binder may be 0.1% to 4%, for example, the mass percentage of the first binder may be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc. The content of the first binder in the electrode membrane within the above range can meet the processing requirements and is conducive to increasing the capacity of the active material layer.

[0043] In some embodiments of the present application, based on the total mass of the electrode membrane, the mass percentage of the second binder is less than or equal to 5%, for example, the mass percentage of the second binder can be 0.05%, 0.1%, 1%, 2%, 3%, 4%, 5%, etc. This is conducive to improving the strength of the active material layer and improving the continuity and quality rate of production.

[0044] In some embodiments of the present application, based on the total mass of the electrode membrane, the mass percentage of the second binder may be 0.1% to 3%, for example, the mass percentage of the second binder in the electrode membrane may be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc. The content of the second binder in the electrode membrane within the above range can meet the processing requirements and is conducive to increasing the capacity of the active material layer.

[0045] In some embodiments of the present application, the substances and their contents in the electrode membrane can be tested by the following methods: thermogravimetric analysis, scanning electron microscopy and energy spectrum analysis, mass spectrometry, etc.

[0046] In the present application, the electrode membrane is formed by a rolling process, and the first binder in the electrode membrane has been fibrillated to a certain extent.

[0047] In the process of preparing the diaphragm by dry process, the edge of the diaphragm is cut off to ensure the flatness of the edge of the diaphragm and the alignment of the upper and lower surfaces of the diaphragm. If the cut diaphragm is directly scrapped, the production rate will be reduced and the production cost will be increased.

[0048] In some embodiments of the present application, the electrode membrane may be a waste membrane. In some embodiments, the waste membrane may include an edge portion cut from a membrane prepared using a dry process, and / or a dry process membrane that is torn or broken during the transfer process. In the preceding process, the membrane may be formed by powder mixing and rolling of active materials, conductive agents, binders, etc. The active material layer is prepared using waste membranes, and the waste membranes can be recycled, reducing material waste, which is beneficial to reducing production costs, and can improve the overall production quality rate.

[0049] In some embodiments of the present application, the edge of the membrane can be cut off by a scraper or a circular cutter, and the cut edge portion can be used as a waste membrane. The waste membrane is crushed and then rolled to form a high-strength active material layer to achieve the recycling of the waste membrane. The waste membrane is large in size and cannot be bitten into during the rolling process. By crushing it, a smaller powder can be obtained, which is conducive to the subsequent rolling process.

[0050] In some embodiments of the present application, the active material in the electrode membrane may be a positive electrode active material. In some embodiments of the present application, the positive electrode active material may include lithium iron phosphate (LiFePO4), lithium iron manganese phosphate, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 )), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2) or more.

[0051] Lithium-ion batteries are accompanied by Li deintercalation and consumption during the charge and discharge process. The molar content of Li in lithium-ion batteries is different when they are discharged to different states. In the list of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li will change after charge and discharge cycles.

[0052] In the list of positive electrode active materials in this application, the molar content of oxygen is only a theoretical value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of oxygen will fluctuate.

[0053] In some embodiments, based on the total mass of the electrode membrane, the mass percentage of the positive electrode active material can be 80%-99.5%. For example, the mass percentage of the positive electrode active material can be 80%, 83%, 85%, 88%, 90%, 92%, 95%, 97%, 99.5%, etc.

[0054] In other embodiments of the present application, the active material in the electrode membrane may be a negative electrode active material. In some embodiments, the negative electrode active material may be a negative electrode active material for a battery known in the art. As an example, the negative electrode active material may include one or more of the following materials: silicon-based materials, carbon-based materials (such as artificial graphite, natural graphite, soft carbon, hard carbon, etc.), tin-based materials, lithium titanate, etc. The tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used.

[0055] In some embodiments of the present application, based on the total mass of the electrode membrane, the mass percentage of the negative electrode active material can be 80%-99.5%. For example, the mass percentage of the negative electrode active material can be 80%, 83%, 85%, 88%, 90%, 92%, 95%, 97%, 99.5%, etc.

[0056] In some embodiments of the present application, the conductive agent in the electrode membrane may include, but is not limited to, one or more of conductive carbon, carbon nanotubes, and graphene.

[0057] In some embodiments of the present application, based on the total mass of the electrode membrane, the mass percentage of the conductive agent can be 0.1%-10%. For example, the mass percentage of the conductive agent in the electrode membrane can be 0.1%, 0.5%, 1%, 3%, 5%, 8%, 10%, etc.

[0058] In some embodiments of the present application, based on the total mass of the electrode membrane, the mass percentage of the active material can be 80%-99.5%, the mass percentage of the conductive agent can be 0.1%-10%, the mass percentage of the first binder is less than or equal to 5%, the mass percentage of the second binder is less than or equal to 5%, and the mass percentage of the first binder and the mass percentage of the second binder are both greater than 0.

[0059] In some embodiments of the present application, based on the total mass of the electrode membrane, the mass percentage of the active material can be 83%-99.5%, the mass percentage of the conductive agent can be 0.1%-10%, the mass percentage of the first binder can be 0.1%-4%, and the mass percentage of the second binder can be 0.1%-3%.

[0060] In some embodiments of the present application, the pulverization process may include one or more of stirring crushing, granulation, and air flow pulverization. The pulverization process may pulverize the electrode membrane to form a relatively uniform powder.

[0061] In some embodiments of the present application, the linear speed of stirring and crushing is less than or equal to 100 m / s, for example, the linear speed of stirring and crushing can be 1 m / s, 10 m / s, 50 m / s, 80 m / s, 100 m / s, etc. Thus, the electrode membrane can be quickly crushed, and the fibrillation degree of the first binder in the electrode membrane can be improved.

[0062] In some embodiments of the present application, the linear speed of stirring and crushing can be 5m / s to 50m / s, for example, the linear speed of stirring and crushing can be 5m / s, 10m / s, 15m / s, 20m / s, 25m / s, 30m / s, 35m / s, 40m / s, 45m / s, 50m / s, etc. The linear speed within the above range is more conducive to crushing the electrode membrane under relatively low equipment energy consumption conditions.

[0063] In some embodiments of the present application, the temperature of stirring and crushing can be -20°C to 150°C, for example, the temperature of stirring and crushing can be -20°C, -10°C, 0°C, 50°C, 100°C, 120°C, 150°C, etc. When the electrode membrane is stirred and crushed at the above temperature, the binder is not easy to melt or decompose, and the chemical structure of the binder can remain stable.

[0064] In some embodiments of the present application, the temperature of stirring and crushing can be 0°C to 110°C, for example, the temperature of stirring and crushing can be 0°C, 10°C, 20°C, 40°C, 60°C, 70°C, 90°C, 110°C, etc. The crushing effect is better when the temperature is within the above range, which can be specifically manifested in shortening the crushing time and improving the screening efficiency.

[0065] In other embodiments of the present application, the electrode membrane may be crushed by a granulation method. The specific conditions for granulation are not particularly limited in the present application.

[0066] In other embodiments of the present application, the electrode membrane may be pulverized by air flow pulverization. The specific conditions of air flow pulverization are not particularly limited in the present application.

[0067] S20: mixing the first powder material and the second powder material to obtain a mixed material, and rolling the mixed material to obtain an active material layer.

[0068] In some embodiments of the present application, the components of the second powder are the same as those of the first powder, and the fibrillation degree of the first binder in the second powder is lower than the fibrillation degree of the first binder in the first powder. By mixing the first powder with a higher fibrillation degree and the second powder with a lower fibrillation degree, and then rolling to obtain the active material layer, the strength of the active material layer can be significantly improved.

[0069] In the present application, the components of the second powder are the same as those of the first powder, which means that the types and proportions of the active material, binder, and conductive agent in the second powder and the first powder are the same. The components in the second powder are the same as those in the first powder, which is beneficial to control the proportions of the various substances in the final prepared active material layer, thereby facilitating the acquisition of an active material layer with better consistency.

[0070] In some embodiments of the present application, the mass ratio of the first powder to the second powder may be (1:10) to (100:1), for example, the mass ratio of the first powder to the second powder may be 1:10, 1:2, 1:1, 10:1, 20:1, 50:1, 80:1, 100:1, etc. The first powder and the second powder are mixed in the above ratio, and the active material layer obtained by subsequent rolling treatment has a higher strength. In addition, the use of the mixture in the above ratio to prepare the active material layer is conducive to improving the electrochemical performance of the active material layer, thereby helping to improve the overall performance of the battery.

[0071] In the present application, the first powder and the second powder can be mixed evenly by a method known in the art. In some embodiments, the first powder and the second powder can be mixed evenly by stirring to form a mixture.

[0072] In some embodiments of the present application, after the electrode membrane is crushed, the first powder may be sieved before the first powder is mixed with the second powder.

[0073] In some embodiments of the present application, the mesh number of the sieve for sieving can be 4 mesh to 400 mesh, for example, the mesh number of the sieve can be 4 mesh, 40 mesh, 100 mesh, 140 mesh, 170 mesh, 200 mesh, 230 mesh, 270 mesh, 325 mesh, 400 mesh, etc. The sieve with the above mesh number can be used for sieving to obtain a powder with a suitable particle size, which is convenient for preparing the active material layer through subsequent rolling treatment.

[0074] In some embodiments of the present application, the mesh number of the sieve for sieving can be 6 mesh to 35 mesh, for example, the mesh number of the sieve for sieving can be 6 mesh, 8 mesh, 10 mesh, 12 mesh, 14 mesh, 16 mesh, 18 mesh, 20 mesh, 25 mesh, 30 mesh, 35 mesh. Thus, it is beneficial to prepare the active material layer by rolling treatment, and it is beneficial to further improve the strength of the active material layer.

[0075] In some embodiments of the present application, the active material, the binder and the conductive agent may be mixed in a desired ratio to obtain a second powder. In some embodiments, the active material, the binder and the conductive agent forming the second powder may be purchased new materials (not subjected to rolling treatment). In some embodiments, the active material, the binder and the conductive agent may be stirred to form a second powder with uniform components.

[0076] In some embodiments, the active material, the binder and the conductive agent can be mixed in a desired ratio and sieved to obtain a second powder. In this step, the mesh number of the sieve for sieving can be 4 mesh to 400 mesh. In some embodiments, in this step, the mesh number of the sieve for sieving can be 6 mesh to 35 mesh. In some specific embodiments, the mesh number of the sieve used for sieving the second powder is the same as the mesh number of the sieve used after the electrode membrane is crushed, thereby maintaining good consistency in the particle size of the second powder and the first powder.

[0077] In some embodiments, the first binder in the second powder may be in a granular state without being fibrillated. During the rolling process of the mixed material, the first binder in the second powder may be fibrillated to a certain extent, entangled with the surrounding active material and conductive agent.

[0078] In some embodiments of the present application, the mixed material is subjected to a rolling process to obtain an active material layer, wherein the number of rolling processes may be 1 to 20 times, for example, the number of rolling processes may be 1, 3, 5, 8, 10, 15, 20, etc. Single or multiple rolling processes may further fibrillate the first binder in the first powder, thereby playing a role in local reinforcement, and may also enhance the bonding strength between the second binder in the first powder and the active material and the conductive agent. The first binder in the second powder may also be fibrillated to a certain extent, entangled with the surrounding materials. In addition, by single or multiple rolling processes, an active material layer having a coating amount (surface density or volume density) that meets the requirements may be obtained.

[0079] In some embodiments of the present application, the temperature of the rolling process may be 0°C to 150°C, for example, the temperature of the rolling process may be 0°C, 10°C, 20°C, 40°C, 50°C, 70°C, 80°C, 100°C, 130°C, 150°C, etc. The rolling process at the above temperature is beneficial to reducing energy consumption and equipment cost; the powder can maintain a certain fluidity, which is beneficial to improving the uniformity of the active material layer.

[0080] In some embodiments of the present application, the rolling temperature may be 10° C. to 80° C. Thus, the binder is not easily decomposed and can maintain good bonding performance; the first binder in the first powder can be further fibrillated during the rolling process to play a role in local strengthening.

[0081] In some embodiments of the present application, the speed of the rolling process is less than or equal to 150 m / min, for example, the speed of the rolling process may be 2 m / min, 5 m / min, 10 m / min, 30 m / min, 50 m / min, 70 m / min, 100 m / min, 120 m / min, 130 m / min, 150 m / min, etc. This is conducive to a more uniform distribution of the powder, thereby facilitating the formation of a membrane with better thickness consistency, uniform density, and fewer defects.

[0082] In some embodiments of the present application, the rolling speed may be 2 m / min to 100 m / min, thereby facilitating further fibrillation of the first binder in the first powder and fibrillation of the first binder in the second powder, thereby facilitating further improvement of the strength of the membrane.

[0083] In some embodiments of the present application, the pressure of the rolling process is less than or equal to 50T, for example, the pressure of the rolling process can be 0.5T, 1T, 2T, 3T, 4T, 5T, 10T, 20T, 30T, 40T, 50T, etc. The pressure of the rolling process is within the above range, which is conducive to reducing energy consumption, reducing production costs, and reducing defects of the diaphragm and improving the yield of the product.

[0084] In some embodiments of the present application, the pressure of the rolling process can be 0.5T~5T. This can significantly reduce energy consumption and cost, improve the uniformity of the thickness and density of the diaphragm, and reduce the defects of the diaphragm; and reduce the damage to the adhesive, so that the adhesive maintains good bonding performance.

[0085] In some embodiments of the present application, the gap of the rolling process is less than or equal to 1000 μm, for example, the gap of the rolling process can be 10 μm, 20 μm, 40 μm, 50 μm, 100 μm, 200 μm, 500 μm, 800 μm, 1000 μm, etc. Thus, an active material layer with a suitable thickness can be formed by the rolling process.

[0086] In some embodiments of the present application, the gap of the rolling process is less than or equal to 500 μm, for example, the gap of the rolling process can be 10 μm to 500 μm, thereby facilitating the acquisition of an active material layer with a suitable thickness and improving the strength of the active material layer.

[0087] The following describes the principle that the present application can improve the strength of the diaphragm in conjunction with the accompanying drawings: Figure 2 The figure is a schematic diagram of the principle of forming a membrane by rolling the second powder (taking new material as an example, the first binder in the new material has not been fibrillated). The second powder contains active material 40 and first binder particles 51. After rolling (one or more rollings), the first binder particles 51 are fibrillated and stretched into long strips of first fibers 52, which wrap the active material together to form a membrane. Figure 3 The schematic diagram of the principle of forming a membrane after the first powder and the second powder are mixed and then rolled. The second powder contains active material 40 and first binder particles 51, and the first powder contains active material 40 and first fibers 52 that have been stretched into long strips. After the second powder and the first powder are mixed and then rolled (one or more times), the first binder particles 51 in the second powder are fibrillated and stretched into fibers, and at least part of the first fibers 52 in the first powder are further fibrillated to form thinner second fibers 53, which play a role in local reinforcement. It should be noted that Figure 2 and Figure 3 Only the active material and the first binder are shown in the figure to illustrate the state change of the first binder after the rolling process.

[0088] In some embodiments, the diameter of the fiber formed by the first binder after rolling can be less than or equal to 1 μm, wherein the diameter of at least part of the fiber can be nanometer level, for example, the diameter of at least part of the fiber can be less than or equal to 200 nm. In some embodiments, the length of the fiber formed by the first binder after rolling can be less than or equal to 10 mm.

[0089] The active material layer of the present application can be used to form an electrode sheet. In some embodiments, after obtaining the active material layer, the active material layer is placed on at least one side of a current collector and subjected to a roller pressing process so that the active material layer and the current collector are pressed together to obtain an electrode sheet. The specific conditions of the roller pressing process are not particularly limited in the present application.

[0090] In this application, the electrode membrane is crushed to obtain a first powder, the first powder is mixed with the second powder, and the mixture is prepared into a new active material layer by rolling. On the one hand, the first binder in the electrode membrane has been fibrillated to a certain extent in the previous membrane preparation process. During the crushing process and the subsequent rolling process, the first binder will be further fibrillated, and the bonding effect on the active material and the conductive agent will be locally strengthened, thereby effectively improving the strength of the active material layer and the bonding force between the particles, thereby helping to reduce the probability of the active material layer breaking and tearing during the transfer process, improving the continuity of production, and improving the overall production rate. On the other hand, during the subsequent rolling process, the interaction between the second binder in the electrode membrane and the active material, the conductive agent, the second binder itself, and the first binder will also be enhanced to a certain extent, which is conducive to further improving the strength of the active material layer. In addition, this method does not require the introduction of other substances that will reduce the energy density. The first binder in the second powder will be stretched during the rolling process to form fibers, which play a role in bonding various substances. The second binder in the second powder can also bond the surrounding active materials or conductive agents through the rolling process.

[0091] It should be noted that the electrode diaphragm also undergoes powder mixing and rolling processes during the previous process, and the conditions of the rolling process can be similar to those of the mixed material rolling process. In some embodiments, the rolling process of the previous process can meet at least one of the following conditions: the number of rollings is 1 to 20 times; the temperature is 0°C to 150°C; the speed is less than or equal to 150m / min; the pressure is less than or equal to 50T; the gap is less than or equal to 1000μm. In other embodiments, the rolling process of the previous process can meet at least one of the following conditions: the number of rollings is 1 to 20 times; the temperature is 10°C to 80°C; the speed is 2m / min to 100m / min; the pressure is 0.5T to 5T; the gap is less than or equal to 500μm.

[0092] In another aspect of the present application, the present application proposes an active material layer. In some embodiments of the present application, the active material layer is an active material layer prepared by the method described above. As a result, the active material layer has a high mechanical strength and is not easily broken or torn during the transfer process.

[0093] In another aspect of the present application, the present application provides a secondary battery. In some embodiments of the present application, the secondary battery includes the active material layer described above. Thus, the active material layer in the secondary battery has high strength and good electrochemical properties, which is conducive to improving the stability of the secondary battery.

[0094] Generally, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery charging and discharging process, active ions are embedded and removed back and forth between the positive electrode and the negative electrode. The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The separator is set between the positive electrode and the negative electrode, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0095] [Positive electrode] In some embodiments, the active material layer (positive electrode active material layer) prepared by the method proposed in the present application can be used to form a positive electrode sheet. Specifically, the positive electrode active material layer can be arranged on at least one side of the positive electrode current collector, and a roll pressing process is performed to press the positive electrode active material layer and the positive electrode current collector together to obtain a positive electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector.

[0096] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on any one or both of the two facing surfaces of the positive electrode current collector.

[0097] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0098] [Negative electrode] In some embodiments, the active material layer (negative electrode active material layer) prepared by the method proposed in the present application can be used to form a negative electrode sheet. Specifically, the negative electrode active material layer can be arranged on at least one side of the negative electrode current collector, and a roll pressing process is performed to press the negative electrode active material layer and the negative electrode current collector together to obtain a negative electrode sheet. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer arranged on at least one side of the negative electrode current collector.

[0099] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on any one or both of the two facing surfaces of the negative electrode current collector.

[0100] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0101] [Electrolytes] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0102] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0103] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0104] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0105] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0106] [Isolation film] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0107] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0108] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0109] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0110] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0111] In some embodiments, the secondary battery of the present application includes a battery cell form, a battery module form, and a battery pack form.

[0112] The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. For example, Figure 4 The battery cell 1 is a square structure as an example.

[0113] In some embodiments, reference Figure 5The outer packaging may include a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the battery cell 1 can be one or more, and those skilled in the art can select according to specific actual needs.

[0114] In some embodiments, battery cells may be assembled into a battery module. The number of battery cells contained in the battery module may be one or more. The specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0115] Figure 6 2 is an example of a battery module 2. Figure 6 In the battery module 2, the plurality of battery cells 1 may be arranged in sequence along the length direction of the battery module 2. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 1 may be fixed by fasteners.

[0116] Optionally, the battery module 2 may further include a housing having a receiving space, and the plurality of battery cells 1 are received in the receiving space.

[0117] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0118] Figure 7 and Figure 8 The battery pack 3 is used as an example. Figure 7 and Figure 8 The battery pack 3 may include a battery box and a plurality of battery modules 2 disposed in the battery box. The battery box includes an upper box body 31 and a lower box body 32. The upper box body 31 can cover the lower box body 32 and form a closed space for accommodating the battery modules 2. The plurality of battery modules 2 can be arranged in the battery box in any manner.

[0119] In some embodiments, the battery cell, battery module or battery pack can be used as a power source for an electrical device or as an energy storage unit for an electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0120] The electrical device can select a battery cell, a battery module or a battery pack according to its usage requirements.

[0121] Fig. 9 The power consumption device is used as an example. The power consumption device may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module may be used.

[0122] As another example, the electric device may be a mobile phone, a tablet computer, a notebook computer, etc. The electric device is usually required to be light and thin, and a battery cell may be used as a power source.

[0123] In another aspect of the present application, the present application provides an electric device. In some embodiments of the present application, the electric device includes the secondary battery described above. Therefore, the electric device has all the features and advantages of the secondary battery described above, which will not be repeated here.

[0124] In some embodiments, electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0125] The scheme of the present application is described below by specific examples. It should be noted that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If no specific technology or conditions are specified in the examples, the technology or conditions described in the literature in this area or the product instructions are used. The reagents or instruments used are not specified by the manufacturer and are all conventional products that can be obtained commercially.

[0126] Example 1 (1) Crushing of discarded membranes The pre-rolling process parameters of the waste diaphragm are shown in Table 1. The edge of the rolled diaphragm is cut off by a scraper, and the edge part is recycled as a waste diaphragm. In the waste diaphragm, the active material is lithium nickel cobalt manganese oxide, the conductive agent is conductive carbon Super P, the first binder is PTFE, and the second binder is PVDF. The mass ratio of lithium nickel cobalt manganese oxide, conductive carbon, PTFE, and PVDF is 96:1.5:2:0.5.

[0127] The waste membrane sheets were stirred and crushed at a linear speed of 10 m / s and a temperature of 25° C. Afterwards, they were sieved with a 20-mesh sieve to obtain waste powder.

[0128] (2) Preparation of active material layer The waste powder and the new material (the new material and the waste powder have the same components. In this embodiment, the new material is obtained by mixing lithium nickel cobalt manganese oxide, conductive carbon, PTFE, and PVDF in a mass ratio of 96:1.5:2:0.5) are mixed evenly, wherein the mass ratio of the waste powder to the new material is 10:1; then, the powder is rolled to obtain an active material layer. The rolling process parameters are shown in Table 3.

[0129] The components of the waste membranes in each embodiment and comparative example are recorded in Table 1, the previous rolling process of the waste membranes, the conditions for the crushing of the waste membranes, and the mesh size of the sieve used for screening are all recorded in Table 2, and the mass ratio of the waste powder to the new material and the rolling process parameters after the waste powder and the new material are mixed are recorded in Table 3.

[0130] The membrane strength was tested by the following method: the electrode membrane (active material layer) was clamped between the upper and lower clamps of a universal mechanical testing machine and its strength was tested in a tensile mode. The test results are recorded in Table 3.

[0131] Table 1 Composition of waste membranes

[0132] Table 2 Pre-rolling process of waste diaphragms, crushing conditions of waste diaphragms and mesh size of sieves used for screening

[0133] Table 3 Mass ratio of waste powder to new material, rolling process parameters after mixing waste powder and new material, and fracture force

[0134] Fig.10 The tensile curves B1 and B2 of two parallel samples prepared in comparative example 1 and the tensile curves L1 and L2 of two parallel samples prepared in example 1 are shown, and the average value of the breaking force of the two parallel samples is taken as the breaking force of the sample. It can be seen that the strength of the diaphragm prepared by the method proposed in the present application is significantly improved, and the breaking force of the diaphragm is significantly higher than that of the comparative example (increased from 0.62N to 3.88N), indicating that the method can effectively improve the strength of the diaphragm.

[0135] Fig.11 The scanning electron microscope image of the new material obtained by mixing lithium nickel cobalt manganese oxide, conductive carbon, the first binder PTFE and the second binder PVDF in Comparative Example 1 is shown. Fig.11 There is no obvious fiber structure in the sample, indicating that PTFE is not fibrillated without rolling treatment. Fig.12 The scanning electron microscope image of the waste powder in Example 1 is shown. Fig.12 There are more fibers in the PTFE, which shows that the PTFE has been fibrillated after rolling.

[0136] It can be seen from Table 3 that, compared with Comparative Examples 1 and 2, the recycled waste film in Examples 1-25 is crushed and then mixed with new materials and then re-rolled into new film. In addition, the waste film contains both the first binder and the second binder, which can significantly improve the strength of the film. The waste film in Comparative Example 2 only uses the first binder, which is not crushed evenly during the crushing process, and the obtained powder is uneven. The surface of the film obtained by subsequent processing has many holes and defects, and the strength of the film is also low. The waste film in Examples 1-25 contains both the first binder and the second binder, which can reduce the difficulty of the recycling process. A uniform powder is obtained by crushing, and the surface of the film obtained by subsequent processing is flat without obvious defects, and the strength is significantly improved. There is no strength test data for Example 3 for the following reasons: In Example 3, the waste membrane and the new material do not contain the first binder, and the waste membrane sticks to the roller, and is scraped off and then subjected to subsequent process steps such as crushing. The waste powder and the new material are rolled through a dry process, and the powder still sticks to the roller and cannot be removed for use, and there is no way to test the strength.

[0137] In addition, the diaphragms prepared in the comparative examples are prone to breakage or tearing during the transfer process, while the active material layers prepared in the embodiments of the present application do not experience breakage or tearing during the transfer process. This also illustrates that the present application adopts a simple method to crush the electrode diaphragm, and the obtained first powder is rolled or the first powder is mixed with the second powder and then rolled, which can improve the strength of the diaphragm and make it less likely to break during the transfer process. The bonding force between the particles can also be effectively improved, making it less likely to tear during the transfer process, which is beneficial to improving production continuity and quality rate.

[0138] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "other embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0139] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for preparing an active material layer, characterized in that: include: The electrode membrane is crushed to obtain a first powder, wherein the electrode membrane comprises an active material, a binder and a conductive agent, wherein the binder comprises a first binder and a second binder, wherein the first binder comprises polytetrafluoroethylene, and the second binder comprises one or more of polyvinylidene fluoride, polyacrylic acid, polyacrylamide, sodium carboxymethyl cellulose, and styrene-butadiene rubber; The first powder and the second powder are mixed to obtain a mixture, and the mixture is rolled to obtain an active material layer, wherein the components of the second powder are the same as those of the first powder, and the fibrillation degree of the first binder in the second powder is lower than the fibrillation degree of the first binder in the first powder.

2. The method according to claim 1, characterized in that Based on the total mass of the electrode membrane, the mass percentage of the first binder is less than or equal to 5%, and / or the mass percentage of the second binder is less than or equal to 5%.

3. The method according to claim 2, characterized in that Based on the total mass of the electrode membrane, the mass percentage of the first binder is 0.1% to 4%, and / or the mass percentage of the second binder is 0.1% to 3%.

4. The method according to claim 1, characterized in that Before the first powder is subjected to the rolling process, the first powder is subjected to the sieving process.

5. The method according to claim 4, characterized in that The mesh number of the sieve for the sieving process is 4 mesh to 400 mesh.

6. The method according to claim 5, characterized in that The mesh number of the sieve for the sieving process is 6 mesh to 35 mesh.

7. The method according to claim 1, characterized in that The mass ratio of the first powder to the second powder is (1:10) to (100:1).

8. The method according to claim 1, characterized in that The pulverization process includes one or more of stirring crushing, granulation, and air flow pulverization.

9. The method according to claim 8, characterized in that The linear speed of the stirring and crushing is less than or equal to 100 m / s, and / or the temperature of the stirring and crushing is -20°C to 150°C.

10. The method according to claim 9, characterized in that The linear speed of the stirring and crushing is 5m / s~50m / s, and / or the temperature of the stirring and crushing is 0℃~110℃.

11. The method according to any one of claims 1 to 10, characterized in that The number of rolling treatments is 1 to 20 times.

12. The method according to any one of claims 1 to 10, characterized in that The rolling process satisfies at least one of the following conditions: Temperature: 0℃~150℃; Speed ​​less than or equal to 150m / min; The pressure is less than or equal to 50T; The gap is less than or equal to 1000 μm.

13. The method according to claim 12, characterized in that The rolling process satisfies at least one of the following conditions: Temperature: 10℃~80℃; Speed: 2m / min~100m / min; The pressure is 0.5T~5T; The gap is less than or equal to 500 μm.

14. An active material layer, characterized in that: The active material layer is an active material layer prepared by the method according to any one of claims 1 to 13.

15. A secondary battery, characterized in that: The secondary battery includes the active material layer of claim 14 .

16. An electrical device, characterized in that: The electric device comprises the secondary battery according to claim 15 .

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