Electrode assembly, secondary battery and electric device

Abstract

The present application relates to the field of battery technology, and relates to an electrode assembly, a secondary battery and an electric device, wherein the secondary battery comprises an electrode assembly, the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a diaphragm, the diaphragm is arranged between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet, the diaphragm and the negative electrode sheet are wound and arranged; the diaphragm comprises a first diaphragm section and a second diaphragm section connected to each other, the first diaphragm section is located at the center of the electrode assembly, the first diaphragm section comprises a first base film and a first coating provided on at least one side of the first base film, the first coating comprises first particles, the second diaphragm section comprises a second base film and a second coating provided on at least one side of the second base film, the second coating comprises second particles; the particle size of the second particles is smaller than that of the first particles. The technical solution of the present application can ensure that the internal gas is discharged in time, thereby improving the cycle performance of the secondary battery.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an electrode assembly, a secondary battery and an electrical device. Background Art

[0002] The electrode assembly is the part where the electrochemical reaction occurs in the secondary battery. The electrode assembly can be processed into a roll structure by winding two pole pieces with opposite polarities and a diaphragm separating the two pole pieces. However, in the related art, the problem of poor exhaust inside the electrode assembly is prone to occur, which in turn affects the cycle performance of the secondary battery. Summary of the invention

[0003] The main purpose of the present application is to propose an electrode assembly, a secondary battery and an electrical device, aiming to solve the problem of poor exhaust inside the electrode assembly and ensure the cycle performance of the secondary battery.

[0004] To achieve the above-mentioned purpose, the first aspect of the present application provides a secondary battery, the secondary battery comprising an electrode assembly, the electrode assembly comprising a positive electrode sheet, a negative electrode sheet and a separator, the separator is arranged between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet, the separator and the negative electrode sheet are wound; the separator comprises a first separator segment and a second separator segment connected to each other, the first separator segment is located at the center of the electrode assembly, the first separator segment comprises a first base film and a first coating disposed on at least one side of the first base film, the first coating comprises first particles, the second separator segment comprises a second base film and a second coating disposed on at least one side of the second base film, the second coating comprises second particles; the particle size of the second particles is smaller than the particle size of the first particles. In some embodiments, the second separator segment comprises a second base film and a second coating disposed on at least one side of the second base film, the second coating comprises second particles.

[0005] In the secondary battery provided in the present application, the electrode assembly is formed by winding a positive electrode sheet, a diaphragm and a negative electrode sheet, wherein the diaphragm includes a first diaphragm segment and a second diaphragm segment connected to each other, the particle size of the first particles contained in the first coating of the first diaphragm segment is larger than the particle size of the second particles contained in the second coating of the second diaphragm segment, that is, the first coating of the first diaphragm segment located at the center of the electrode assembly is set to include first particles of larger size, then the pores formed in the area of ​​the electrode assembly corresponding to the first diaphragm segment (i.e., the center position area) are relatively large, and the pores formed in the area of ​​the electrode assembly corresponding to the second diaphragm segment (i.e., the middle position area) are relatively small, and the pores formed in the above two areas both provide exhaust channels for internal gas production, and most of the gas generated internally is discharged from the larger pores, and a small part is discharged from the smaller pores, thereby effectively ensuring that the gas generated inside the electrode assembly is discharged in time, thereby improving the cycle performance of the secondary battery.

[0006] In some embodiments, the volume particle size distribution D of the first particles V 50 is 10μm-50μm.

[0007] The large-sized first particles contained in the first coating of the present application are selected to be of appropriate size, thereby forming larger pores at the center of the electrode assembly, which is more conducive to the smooth discharge of gas and the rapid infiltration of electrolyte, thereby improving the cycle performance of the secondary battery and improving the black spot phenomenon.

[0008] In some embodiments, the volume particle size distribution D of the second particles V 50 is 2 μm-10 μm. The present application selects the second particles with appropriate particle size, which can ensure that the pores formed in the region of the electrode assembly corresponding to the second diaphragm segment have appropriate size, which is more conducive to gas discharge and electrolyte infiltration, and can ensure good transmission performance of active ions.

[0009] In some embodiments, the material of the first particles includes a high molecular polymer.

[0010] The present application uses first particles made of high molecular polymer material, which is beneficial to the discharge of gas and the infiltration of electrolyte, and can also enhance the bonding force between the first coating and the first base film.

[0011] In some embodiments, the thermal shrinkage of the first particles is 1%-5%.

[0012] The present application selects first particles with a lower thermal shrinkage rate, which can effectively suppress the internal deformation of the electrode assembly, thereby effectively ensuring the reliability of gas discharge and electrolyte infiltration.

[0013] In some embodiments, the length of the first diaphragm segment is 0.5 cm-100 cm.

[0014] The present application selects a first diaphragm segment of appropriate length, so that the pore size formed in the central area of ​​the electrode assembly is relatively appropriate, which can further facilitate the timely discharge of gas and the infiltration of electrolyte.

[0015] In some embodiments, the porosity of the first diaphragm segment is 50%-70%.

[0016] Since the particle size of the first particles of the first diaphragm segment is relatively large, the porosity of the first diaphragm segment is relatively large, which is more conducive to gas discharge and electrolyte infiltration.

[0017] In some embodiments, the first diaphragm segment is configured as a double-layer structure; and / or the number of turns of the first diaphragm segment is 1-2.

[0018] The first diaphragm segment of the present application is provided with a double-layer structure and / or the number of turns of the first diaphragm segment is limited to 1-2, thereby further increasing the pores formed in the central area of ​​the electrode assembly, more effectively ensuring the timely discharge of internal gas production, and improving the cycle performance of the secondary battery; at the same time, it also further improves the electrolyte infiltration performance and more effectively improves the phenomenon of black spots or lithium precipitation.

[0019] In some embodiments, the diaphragm further comprises a third diaphragm segment, the third diaphragm segment is connected to a side of the second diaphragm segment away from the first diaphragm segment, and is located at an edge of the electrode assembly; the third diaphragm segment comprises a third base film and a third coating disposed on at least one side of the third base film, the third coating comprising third particles, and the volume particle size distribution D of the third particles is V 50 is 10μm-50μm.

[0020] There are three gas discharge pathways in the present application, namely, the pores formed in the region of the electrode assembly corresponding to the first diaphragm segment (i.e., the central position region), the pores formed in the region of the electrode assembly corresponding to the second diaphragm segment (i.e., the middle position region), and the pores formed in the region of the electrode assembly corresponding to the third diaphragm segment (i.e., the edge position region). Correspondingly, the electrolyte infiltration channel also includes the pores formed in the above three regions, thereby more effectively ensuring timely gas discharge and sufficient electrolyte infiltration, thereby more effectively improving the cycle performance of the secondary battery and more effectively improving the phenomenon of black spots or lithium precipitation.

[0021] In some embodiments, the third diaphragm segment is configured as a double-layer structure; and / or the number of turns of the third diaphragm segment is 1-2.

[0022] The third diaphragm segment of the present invention is provided with a double-layer structure and / or the number of turns of the third diaphragm segment is limited to 1-2, thereby further increasing the pores formed in the edge area of ​​the electrode assembly, more effectively ensuring timely discharge of gas and improving the cycle performance of the secondary battery; at the same time, it also further improves the electrolyte infiltration performance and more effectively improves the phenomenon of black spots or lithium precipitation.

[0023] The second aspect of the present application further provides an electrode assembly, which is the electrode assembly included in the secondary battery provided in the first aspect of the present application.

[0024] The third aspect of the present application further provides an electrical device, which includes the secondary battery provided in the first aspect of the present application.

[0025] In the secondary battery provided in the present application, the electrode assembly is formed by winding a positive electrode sheet, a diaphragm and a negative electrode sheet, wherein the diaphragm includes a first diaphragm segment and a second diaphragm segment connected to each other, the particle size of the first particles contained in the first coating of the first diaphragm segment is larger than the particle size of the second particles contained in the second coating of the second diaphragm segment, that is, the first coating of the first diaphragm segment located at the center of the electrode assembly is set to include first particles of larger size, then the pores formed in the area of ​​the electrode assembly corresponding to the first diaphragm segment (i.e., the center position area) are relatively large, and the pores formed in the area of ​​the electrode assembly corresponding to the second diaphragm segment (i.e., the middle position area) are relatively small, and the pores formed in the above two areas both provide exhaust channels for internal gas production, and most of the gas generated internally is discharged from the larger pores, and a small part is discharged from the smaller pores, thereby effectively ensuring that the gas generated inside the electrode assembly is discharged in time, thereby improving the cycle performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0027] Figure 1 A schematic diagram of a secondary battery according to an embodiment of the present application;

[0028] Figure 2 for Figure 1 An exploded schematic diagram of a secondary battery according to an embodiment of the present application is shown;

[0029] Figure 3 is a schematic diagram of an electrode assembly according to an embodiment of the present application;

[0030] Figure 4 for Figure 3 A schematic diagram showing another perspective of the first diaphragm segment in the electrode assembly of one embodiment of the present application is shown.

[0031] Description of Figure Numbers:

[0032] 5. Secondary battery; 51. Shell; 52. Electrode assembly; 521. Positive electrode plate; 522. Diaphragm; 522a. First diaphragm segment; 522b. Second diaphragm segment; 522c. Third diaphragm segment; 5221. First particle; 523. Negative electrode plate; 53. End cap assembly.

[0033] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0035] The electrode assembly, secondary battery and electrical device of the present application are specifically disclosed below with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions 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.

[0036] "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.

[0037] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0038] 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.

[0039] 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.

[0040] The electrode assembly is a component in a secondary battery where electrochemical reactions occur. The electrode assembly can be formed into a roll structure by winding two pole pieces with opposite polarities and a separator separating the two pole pieces.

[0041] Electrode assemblies generate gas during the processes of formation, aging, circulation and storage. The electrode assemblies expand and close together, which compresses the internal space and narrows the channel for gas discharge, making it difficult for the gas to be discharged in time, thereby causing the cycle performance of the secondary battery to deteriorate.

[0042] In response to the above technical problems, the first aspect of the present application provides a secondary battery, which aims to solve the problem of poor exhaust inside the electrode assembly and ensure the cycle performance of the secondary battery.

[0043] See also Figures 1 to 4 In some embodiments, the secondary battery 5 includes an electrode assembly 52, the electrode assembly 52 includes a positive electrode sheet 521, a negative electrode sheet 523 and a separator 522, the separator 522 is arranged between the positive electrode sheet 521 and the negative electrode sheet 523, the positive electrode sheet 521, the separator 522 and the negative electrode sheet 523 are wound; the separator 522 includes a first separator segment 522a and a second separator segment 522b connected to each other, the first separator segment 522a is located at the center of the electrode assembly 52, the first separator segment 522a includes a first base film and a first coating provided on at least one side of the first base film, the first coating includes first particles 5221, and the volume particle size distribution D of the first particles 5221 is V 50 is 10μm-50μm.

[0044] In the present application, the electrode assembly 52 is a wound electrode assembly, and the first diaphragm segment 522a of the diaphragm 522 is located at the center of the wound electrode assembly, that is, located on the inner side of the second diaphragm segment 522b. The first diaphragm segment 522a includes a first base film and a first coating, and the first coating includes large-sized first particles 5221. The internal pores formed in the center area of ​​the electrode assembly are relatively large, and the pores formed in the center area provide an exhaust channel for the internal gas production, thereby effectively ensuring that the gas produced inside the electrode assembly 52 is discharged in time, thereby improving the cycle performance of the secondary battery 5.

[0045] Moreover, in addition to generating gas during the formation, aging, circulation and storage processes of the electrode assembly 52, liquid absorption is also required in the above processes to ensure that the electrolyte can fully infiltrate the electrode material and the diaphragm 522. If other gases are difficult to discharge, on the one hand, the space where the electrolyte was originally located will be occupied, causing reflux and back-absorption to be unsmooth, resulting in insufficient electrolyte, black spots, and even lithium precipitation, which seriously affects the cycle life and safety performance of the secondary battery 5; on the other hand, gas accumulation will also interfere with or even block the normal transmission path of active ions (such as lithium ions), resulting in active ion (such as lithium ion) bridge breaking, resulting in increased internal resistance and capacity decay of the secondary battery 5.

[0046] The present application sets the first coating of the first diaphragm segment 522a located in the center area of ​​the electrode assembly 52 to include large-sized first particles 5221, so that the larger internal pores formed in the center area also constitute the electrolyte reflux and reabsorption path, thereby effectively improving the phenomenon of black spots and even lithium precipitation caused by insufficient electrolyte, ensuring the cycle life and safety performance of the secondary battery 5. At the same time, it also effectively solves the problem of active ion (such as lithium ion) bridge breaking caused by gas accumulation, thereby ensuring the lower internal resistance and higher capacity of the secondary battery 5.

[0047] In addition, a large amount of gas will be generated during the operation of the secondary battery 5, especially under abnormal conditions such as overcharging and short circuit. Since the present application sets the first coating of the first diaphragm segment 522a located at the center of the electrode assembly 52 to include large-sized first particles 5221, the above-mentioned gas can be discharged in time from the larger internal pores formed by the electrode assembly 52, effectively avoiding the explosion caused by excessive internal pressure of the secondary battery 5, and thus improving the safety performance of the secondary battery 5.

[0048] Generally, during the charge and discharge process of the secondary battery 5, active ions are embedded and extracted back and forth between the positive electrode sheet 521 and the negative electrode sheet 523. The electrolyte plays a role in conducting ions between the positive electrode sheet 521 and the negative electrode sheet 523. The separator 522 is arranged between the positive electrode sheet 521 and the negative electrode sheet 523, mainly playing a role in preventing the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0049] [Diaphragm]

[0050] The present application has no particular limitation on the type of the diaphragm 522 , and any known porous structure diaphragm with good chemical stability and mechanical stability may be selected.

[0051] In some embodiments, the diaphragm 522 adopts a split structure, that is, it includes a first diaphragm segment 522a and a second diaphragm segment 522b connected to each other, wherein the first diaphragm segment 522a is located at the center of the electrode assembly 52, that is, the first diaphragm segment 522a is located on the inner side of the second diaphragm segment 522b, and the first diaphragm segment 522a includes a first base film and a first coating provided on at least one side of the first base film. The first coating includes first particles 5221, and the volume particle size distribution D of the first particles 5221 is V 50 is 10μm-50μm (such as 10μm, 20μm, 30μm, 40μm, 50μm and the interval between any two endpoint values), that is, the first coating includes large-sized first particles 5221, thereby forming larger pores at the center of the electrode assembly 52, which is conducive to the smooth discharge of gas and the rapid infiltration of electrolyte, thereby improving the cycle performance of the secondary battery and improving the black spot phenomenon.

[0052] The volume particle size distribution Dv50 refers to the particle size corresponding to 50% of the first particle volume distribution.

[0053] In some embodiments, the first base membrane is a porous structure base membrane, and its specific type is not particularly limited, and any known porous structure base membrane with good chemical stability and mechanical stability can be selected. The material of the first base membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The first base membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the first base membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0054] In some embodiments, the first particles 5221 include but are not limited to at least one of inorganic particles and organic particles. The first coating layer of the present application may be formed by spraying a slurry including a plurality of first particles 5221 using a spraying device.

[0055] In some embodiments, the first diaphragm segment 522a includes a first base film and a first coating disposed on both side surfaces of the first base film, the first coating containing large-sized first particles 5221, thereby the internal pores formed by the electrode assembly 52 are larger, which can further more effectively ensure that the internal gas is discharged more timely, thereby improving the cycle performance of the secondary battery.

[0056] In some embodiments, the first coating comprises a plurality of first particles 5221, and the plurality of first particles 5221 are distributed at intervals. As an example, the plurality of first particles 5221 are distributed in an array, so that the internal pores formed by the electrode assembly 52 are more regular, which is more conducive to the discharge of gas and the infiltration of electrolyte.

[0057] In some embodiments, the first coating layer further includes a binder, and the setting of the binder can enhance the bonding force between the base film layer and the positive electrode sheet and the negative electrode sheet. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0058] In some embodiments, the first diaphragm segment 522a is exposed on the positive electrode plate 521 and the negative electrode plate 523, that is, the first diaphragm segment 522a is the inner multi-rolled portion of the diaphragm 522, thereby further increasing the pores in the central area of ​​the electrode assembly 52, which is conducive to smooth gas discharge and rapid electrolyte infiltration, thereby improving the cycle performance of the secondary battery. At the same time, it can also effectively prevent the positive electrode plate 521 from contacting the negative electrode plate 523 and causing a short circuit, thereby improving the safety performance of the secondary battery.

[0059] In some embodiments, the second diaphragm segment 522b is located between the positive electrode sheet 521 and the negative electrode sheet 523. The second diaphragm segment 522b may be provided with second particles or may not be provided with second particles. When the second diaphragm segment 522b is not provided with second particles, the second diaphragm segment 522b is a porous structure diaphragm. The material of the second diaphragm segment 522b may be the same as the material of the first base film or may be different, which is not limited here. As an example, the material of the second diaphragm segment 522b is the same as the material of the first base film, and the two are an integrated structure, which can facilitate the processing and manufacturing of the diaphragm and simplify the manufacturing process.

[0060] When the second particles are set in the second diaphragm segment 522b, the second diaphragm segment 522b includes a second base film and a second coating provided on at least one side of the second base film, and the second coating contains second particles. Thus, internal pores are also formed in the area of ​​the electrode assembly 52 corresponding to the second diaphragm segment 522b, and the internal gas production also provides an exhaust channel, which can further and more effectively ensure the timely discharge of the internal gas production and the infiltration of the electrolyte, thereby improving the cycle performance of the secondary battery.

[0061] In some embodiments, the material of the second base film can be the same as that of the first base film, or it can be different, which is not limited here. As an example, the material of the second base film is the same as that of the first base film, and the two are an integrated structure, which can facilitate the processing and production of the diaphragm and simplify the production process. Of course, the first base film and the second base film can be separate structures, bonded together by an adhesive.

[0062] The material of the second particles may be the same as or different from the material of the first particles 5221 , and is not limited here.

[0063] In some embodiments, the first diaphragm segment 522a includes a first base film and a first coating layer including first particles 5221, and the second diaphragm segment 522b includes a second base film and a second coating layer including second particles. The electrode assembly 52 has pores formed in the region corresponding to the first diaphragm segment 522a (i.e., the central region) and the region corresponding to the second diaphragm segment 522b, and the pores formed in the above two regions provide exhaust channels for internal gas production, thereby more effectively ensuring that the internal gas production is discharged in a timely manner, thereby improving the cycle performance of the secondary battery. At the same time, the pores formed in the above two regions are also electrolyte channels and ion channels, which are more conducive to the infiltration of the electrolyte and the increase of ion channels.

[0064] It should be noted that the first coating layer can be provided on one side surface of the first base film, or on both sides of the first base film, the first coating layer contains first particles, and can be formed by spraying a slurry containing the first particles 5221 through a spraying device. Of course, the second coating layer can be provided on one side surface of the second base film, or on both sides of the second base film, the second coating layer contains second particles, and can be formed by spraying a slurry containing the second particles through a spraying device.

[0065] In some embodiments, the particle size of the second particles is larger than the particle size of the first particles 5221, and the pores formed in the area of ​​the electrode assembly 52 corresponding to the first diaphragm segment 522a (i.e., the central position area) are relatively large, and the pores formed in the area of ​​the electrode assembly 52 corresponding to the second diaphragm segment 522b are relatively small. Most of the gas generated inside is discharged from the larger pores, and a small part is discharged from the smaller pores, which is more conducive to the discharge of gas and the infiltration of electrolyte; at the same time, since the particle size of the second particles is small, it can ensure good transmission performance of active ions.

[0066] In some embodiments, the first base film has a first starting end and a second terminal opposite to the second starting end in its length direction, and the first coating extends from the first starting end of the first base film along its length direction toward the first terminal opposite to the first starting end; the second base film has a second starting end and a second terminal opposite to the second starting end in its length direction, and the second coating extends from the second starting end of the second base film along its length direction toward the second terminal opposite to the second starting end. The first terminal and the second starting end are the same end. In some embodiments, the above extensions of the first coating and the second coating are continuous and uninterrupted, which is conducive to enhancing the bonding force with the base film and / or the pole piece.

[0067] In some embodiments, the volume particle size distribution Dv50 of the second particles is 2 μm-10 μm (e.g., 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, and interval values ​​between any two end points). The present application selects second particles of appropriate particle size to ensure that the pores formed in the region of the electrode assembly 52 corresponding to the second diaphragm segment 522b have an appropriate size, which is more conducive to gas discharge and electrolyte infiltration, and can ensure good transmission performance of active ions.

[0068] It should be noted that in the embodiment where the first diaphragm segment 522a is provided with the first particles 5221 and the second diaphragm segment 522b is provided with the second particles, the thickness difference between the first diaphragm segment 522a and the second diaphragm segment 522b is the thickness difference between the first particles 5221 and the second particles. Optionally, the thickness of the second diaphragm segment 522b is 13 μm-50 μm (for example, 13 μm, 20 μm, 30 μm, 40 μm, 50 μm, and an interval value between any two end values).

[0069] In some embodiments, the distance between two adjacent first particles 5221 is 1 μm-300 μm (such as 1 μm, 10 μm, 100 μm, 200 μm, 300 μm and the interval between any two endpoint values). In the present application, the first particles 5221 are designed with a suitable distance, so that the pore size formed at the center of the electrode assembly 52 is more suitable, which is more conducive to the discharge of gas and the infiltration of electrolyte.

[0070] In some embodiments, the material of the first particles 5221 includes a polymer, and the polymer includes but is not limited to at least one of polyvinylidene fluoride (PVDF), polyethyl acrylate, and polybutyl acrylate (PAB). The present application selects the first particles 5221 made of a polymer material, which is conducive to the discharge of gas and the infiltration of electrolyte, and can also enhance the bonding force between the first coating and the first base film.

[0071] In some embodiments, the material of the second particles includes but is not limited to at least one of polyethyl acrylate, polybutyl acrylate (PAB), butadiene and isobutyl acrylate copolymers. Among them, polyethyl acrylate and polybutyl acrylate (PAB) can have different particle sizes at different polymerization degrees, so they can be selected for the first coating and the second coating based on the different particle sizes. The second particles of high molecular polymer material are selected in this application, which is conducive to the discharge of gas, the infiltration of electrolyte and the increase of ion channels, and can also enhance the bonding force between the second coating and the second base film.

[0072] In some embodiments, the thermal shrinkage of the first particles is 1%-5% (e.g., 1%, 2%, 3%, 4%, 5%, and any interval between the two end points). The present application uses first particles with a lower thermal shrinkage to effectively suppress deformation inside the electrode assembly, thereby effectively ensuring the reliability of gas discharge and electrolyte infiltration.

[0073] In some embodiments, the thermal shrinkage rate of the second particles is 0.1%-1% (such as 0.1%, 0.2%, 0.5%, 0.8%, 1% and any interval between the two end points). Since the second particles are located between the diaphragm and the pole piece, the present application sets a smaller shrinkage rate for the second particles, which can more effectively suppress the deformation of the electrode assembly and affect the performance of the secondary battery while ensuring gas discharge and electrolyte infiltration.

[0074] In some embodiments, the length of the first diaphragm segment 522a is 0.5 cm-100 cm (e.g., 0.5 cm, 1 cm, 10 cm, 50 cm, 100 cm, and interval values ​​between any two end points). The present application selects a first diaphragm segment 522a of a suitable length, so that the pore size formed in the center area of ​​the electrode assembly is relatively suitable, which can further facilitate the timely discharge of gas and the infiltration of electrolyte.

[0075] In some embodiments, the width of the first diaphragm segment 522a is 0.5cm-100cm (such as 0.5cm, 1cm, 10cm, 50cm, 100cm and an interval between any two end points). The width of the first diaphragm segment 522a is the size of the wound electrode assembly, and the specific selection can be determined according to actual needs.

[0076] In some embodiments, the porosity of the first diaphragm segment 522a is 50%-70% (e.g., 50%, 60%, 70%, and interval values ​​between any two end points). Since the particle size of the first particles 5221 of the first diaphragm segment 522a is relatively large, the porosity of the first diaphragm segment 522a is relatively large, which is more conducive to gas discharge and electrolyte infiltration.

[0077] In some embodiments, the porosity of the second diaphragm segment 522b is 30%-50% (for example, 30%, 40%, 50% and an interval value between any two end points). Since the second particle size of the second diaphragm segment 522b is relatively small, the porosity of the second diaphragm segment 522b is relatively small, so most of the gas generated inside is discharged from the first diaphragm segment 522a, and a small amount of gas is discharged from the second diaphragm segment 522b, which can also ensure that the internal gas is discharged in time, thereby improving the cycle performance of the secondary battery; at the same time, it can also improve the electrolyte infiltration performance and improve the phenomenon of black spots or lithium precipitation.

[0078] In some embodiments, the first diaphragm segment 522a is set to a double-layer structure. The present application adopts a double-layer structure of the first diaphragm segment 522a design, which can further increase the pores formed in the central area of ​​the electrode assembly 52, more effectively ensure that the internal gas is discharged in time, and improve the cycle performance of the secondary battery; at the same time, it also further improves the electrolyte infiltration performance and more effectively improves the phenomenon of black spots.

[0079] In some embodiments, the number of turns of the first diaphragm segment 522a is 1-2 (such as 1 turn, 1.5 turns, 2 turns, and any interval between the end points). This can further increase the pores formed in the center area of ​​the electrode assembly 52, more effectively ensure that the internal gas is discharged in time, and improve the cycle performance of the secondary battery; at the same time, it can also further improve the electrolyte infiltration performance and more effectively improve the phenomenon of black spots or lithium precipitation.

[0080] Please refer again Figure 3 In some embodiments, the diaphragm 522 further includes a third diaphragm segment 522c, which is connected to a side of the second diaphragm segment 522b away from the first diaphragm segment 522a and is located at the edge of the electrode assembly 52; the third diaphragm segment 522c includes a third base film and a third coating disposed on at least one side of the third base film, the third coating includes third particles, and the volume particle size distribution of the third particles is D V 50 is 10μm-50μm.

[0081] The third diaphragm segment 522c is located outside the second diaphragm segment 522b, that is, at the edge of the electrode assembly 52. ​​The third diaphragm segment 522c includes a third base film and a third coating. The third coating includes third particles. The volume particle size distribution of the third particles is D V 50 is 10 μm-50 μm (such as 10 μm, 20 μm, 30 μm, 40 μm, 50 μm and an interval value between any two endpoint values), that is, the third particle is a large particle.

[0082] In the present application, the third coating of the third diaphragm segment 522c located at the edge of the electrode assembly 52 is set to contain large-sized third particles, thereby forming larger pores at the edge of the electrode assembly 52, which is conducive to the smooth discharge of gas and the rapid infiltration of electrolyte, thereby improving the cycle performance of the secondary battery and improving the black spot phenomenon.

[0083] In some embodiments, there are three gas discharge pathways in the present application, namely, the pores formed in the area of ​​the electrode assembly 52 corresponding to the first diaphragm segment 522a (i.e., the center position area), the pores formed in the area of ​​the electrode assembly 52 corresponding to the second diaphragm segment 522b (i.e., the middle position area), and the pores formed in the area of ​​the electrode assembly 52 corresponding to the third diaphragm segment 522c (i.e., the edge position area). Correspondingly, the electrolyte infiltration channel also includes the pores formed in the above three areas, thereby more effectively ensuring timely gas discharge and sufficient electrolyte infiltration, thereby more effectively improving the cycle performance of the secondary battery and more effectively improving the phenomenon of black spots or lithium precipitation.

[0084] In some embodiments, the material of the third particles is the same as that of the first particles, the particle size of the third particles is the same as that of the first particles, and the distribution of the third particles is the same as that of the first particles. For details, please refer to the above embodiments and will not be repeated here.

[0085] In some embodiments, the first base film, the second base film, and the third base film are made of the same material and are an integrated film structure, thereby facilitating the manufacture of the diaphragm 522 .

[0086] In some embodiments, the third diaphragm segment 522c is exposed outside the positive electrode sheet 521 and the negative electrode sheet 523, that is, the third diaphragm segment 522c is the outer multi-rolled portion of the diaphragm 522, thereby further increasing the pores in the edge area of ​​the electrode assembly 52, which is conducive to smooth gas discharge and rapid electrolyte infiltration, thereby improving the cycle performance of the secondary battery. At the same time, it can also effectively prevent the positive electrode sheet 521 from contacting the negative electrode sheet 523 and causing a short circuit, thereby improving the safety performance of the secondary battery.

[0087] In some embodiments, the length of the third diaphragm segment 522c is 0.5 cm-100 cm (e.g., 0.5 cm, 1 cm, 10 cm, 50 cm, 100 cm, and any interval between the two end points). The present application selects a third diaphragm segment 522c of appropriate length, and the pore size formed by the edge area of ​​the electrode assembly is relatively appropriate, which is more conducive to gas discharge and electrolyte infiltration.

[0088] In some embodiments, the third diaphragm segment 522c is configured as a double-layer structure. The present application uses a double-layer structure for the third diaphragm segment 522c, that is, the third diaphragm segment 522c is configured as a double-layer structure, thereby further increasing the pores formed in the edge area of ​​the electrode assembly, more effectively ensuring timely gas discharge, and improving the cycle performance of the secondary battery; at the same time, it also further improves the electrolyte infiltration performance and more effectively improves the phenomenon of black spots.

[0089] In some embodiments, the number of turns of the third diaphragm segment 522c is 1-2 (such as 1 turn, 1.5 turns, 2 turns, and any interval between the end points). This can further increase the pores formed in the edge area of ​​the electrode assembly 52, more effectively ensure that the internal gas is discharged in time, and improve the cycle performance of the secondary battery; at the same time, it can also further improve the electrolyte infiltration performance and more effectively improve the phenomenon of black spots.

[0090] [Positive electrode]

[0091] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode material.

[0092] 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.

[0093] 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.).

[0094] In some embodiments, the secondary battery is a lithium-ion battery, and the positive electrode active material may adopt the positive electrode active material for lithium-ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, 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 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0095] In some embodiments, the secondary battery is a sodium ion battery, and the positive electrode active material in the positive electrode slurry can be a positive electrode active material for sodium ion batteries known in the art.

[0096] As an optional embodiment of the present invention, in the sodium transition metal oxide, the transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. The sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0097] As an optional embodiment of the present invention, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, and Y can be at least one of P, S and Si; n represents (YO4) n- valence state.

[0098] Polyanionic compounds can also be those with sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds of anion units and halogen anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, and Y can be at least one of P, S and Si; n represents (YO4) n- valence state; the halogen may be at least one of F, Cl and Br.

[0099] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anionic unit, tetrahedral unit (ZO y ) m+ and an optional halogen anion, Y may be at least one of P, S and Si; n represents (YO4) n- valence state; Z represents a transition metal, which may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; m represents (ZO y ) m+ valence state; the halogen may be at least one of F, Cl and Br.

[0100] Prussian blue compounds can be sodium ions, transition metal ions and cyanide ions (CN - ). The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Prussian blue compounds are, for example, Na a Me b Me' c(CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0101] In some embodiments, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0102] In some embodiments, the positive electrode active material layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0103] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0104] [Negative electrode]

[0105] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0106] 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 either or both of the two facing surfaces of the negative electrode current collector.

[0107] 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.).

[0108] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one 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. These negative electrode active materials may be used alone or in combination of two or more.

[0109] In some embodiments, the negative electrode active material layer may further include a binder, which may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0110] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0111] In some embodiments, the negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0112] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0113] [Electrolytes]

[0114] 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.

[0115] In some embodiments, the electrolyte may be an electrolyte solution including an electrolyte salt and a solvent.

[0116] In some embodiments, the electrolyte includes lithium hexafluorophosphate or a mixture of lithium hexafluorophosphate and 1 other lithium salt, and the other lithium 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.

[0117] 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.

[0118] 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.

[0119] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0120] 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.

[0121] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 1 The secondary battery 5 is a square structure as an example.

[0122] In some embodiments, again referring to Figure 2 , the outer package may include a shell 51 and an end cover assembly 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a accommodating cavity. The shell 51 has an opening connected to the accommodating cavity, and the end cover assembly 53 can be covered on the opening to close the accommodating cavity. The positive electrode sheet 521, the negative electrode sheet 523 and the separator 522 can form an electrode assembly 52 through a winding process. The electrode assembly 52 is encapsulated in the accommodating cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0123] The second aspect of the present application further provides an electrode assembly, which is the electrode assembly described in the secondary battery provided in the first aspect of the present application. Its specific structural configuration can refer to the above embodiment and is not limited here.

[0124] The third aspect of the present application further provides an electrical device, which includes the secondary battery provided in the first aspect of the present application. The electrical device of the present application has at least all the beneficial effects of the above-mentioned secondary battery, which will not be repeated here. The secondary battery can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device 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 to these.

[0125] As an example, the electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, a mobile phone, a tablet computer, a laptop computer, etc.

[0126] Example

[0127] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0128] Example 1

[0129] (1) Production of diaphragm

[0130] A polypropylene film is used as a base film, and a first coating, a second coating and a third coating are sequentially coated from one end to the other end of the base film to form a first diaphragm segment, a second diaphragm segment and a third diaphragm which are sequentially connected. The first coating contains first particles, the second coating contains second particles, and the third coating contains third particles. The first particles, the second particles and the third particles are all made of polyvinylidene fluoride (PVDF), wherein the volume particle size distribution Dv50 of the first particles is 10μm, the volume particle size distribution Dv50 of the second particles is 2μm, and the volume particle size distribution Dv50 of the third particles is 10μm. The length of the first diaphragm segment is 0.5cm, and the length of the third diaphragm segment is 0.5cm; the porosity of the first diaphragm segment is 50%, the porosity of the second diaphragm segment is 30%, and the porosity of the third diaphragm segment is 50%.

[0131] (2) Production of positive electrode

[0132] The positive electrode slurry is applied on the surface of the current collector to form a positive electrode active material layer, thus obtaining a positive electrode sheet, wherein the positive electrode slurry includes a positive electrode active material, a conductive agent, a binder, a dispersant and a solvent, N-methylpyrrolidone. In terms of mass parts, the positive electrode active material is 9 parts, the conductive agent is 2 parts, the binder is 3 parts, the dispersant is 2 parts, and the solvent is 3 parts.

[0133] (3) Production of negative electrode

[0134] The negative electrode slurry is applied on the surface of the current collector to form a negative electrode active material layer, that is, a negative electrode sheet is obtained, wherein the negative electrode slurry includes a negative electrode active material, a conductive agent, a binder, a dispersant and a solvent water. In terms of mass parts, the negative electrode active material is 90 parts, the conductive agent is 2 parts, the binder is 3 parts, the dispersant is 2 parts, and the solvent is 3 parts.

[0135] (4) Preparation of electrolyte

[0136] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), 1 mol / L lithium hexafluorophosphate was dissolved in an organic solvent, the organic solvent comprising: a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1, 10% by volume of fluoroethylene carbonate and 2% by volume of vinylene carbonate were added to the mixed solvent, and the mixture was stirred evenly to obtain an electrolyte.

[0137] (5) Battery assembly

[0138] The positive electrode sheet, the separator, and the negative electrode sheet are wound in sequence, so that the separator is between the positive electrode sheet and the negative electrode sheet to obtain an electrode assembly, and the electrolyte is added to assemble into a soft-pack battery. The first separator segment is located at the center of the electrode assembly and exposed to the positive electrode sheet and the negative electrode sheet, which is the inner multi-roll separator section, and the third separator segment is located at the edge of the electrode assembly and exposed to the positive electrode sheet and the negative electrode sheet, which is the outer multi-roll separator section.

[0139] Example 2

[0140] The difference between Example 2 and Example 1 is that the Dv50 of the first particle is 20 μm, the Dv50 of the second particle is 5 μm, and the Dv50 of the third particle is 20 μm. The rest is the same as Example 1.

[0141] Example 3

[0142] The difference between Example 3 and Example 1 is that the Dv50 of the first particle is 50 μm, the Dv50 of the second particle is 10 μm, and the Dv50 of the third particle is 50 μm. The rest is the same as Example 1.

[0143] Example 4

[0144] The difference between Example 4 and Example 1 is that the length of the first diaphragm segment is 10 cm, the length of the third diaphragm segment is 10 cm, and the rest is the same as Example 1.

[0145] Example 5

[0146] The difference between Example 5 and Example 1 is that the length of the first diaphragm segment is 100 cm, the length of the third diaphragm segment is 100 cm, and the rest is the same as Example 1.

[0147] Example 6

[0148] The difference between Example 6 and Example 1 is that the porosity of the first diaphragm segment is 60%, the porosity of the second diaphragm segment is 40%, and the porosity of the third diaphragm segment is 60%. The rest is the same as Example 1.

[0149] Example 7

[0150] The difference between Example 7 and Example 1 is that the porosity of the first diaphragm segment is 70%, the porosity of the second diaphragm segment is 50%, and the porosity of the third diaphragm segment is 70%. The rest is the same as Example 1.

[0151] Example 8

[0152] The difference between Example 8 and Example 1 is that the first diaphragm segment adopts a double-layer structure, the third diaphragm segment adopts a double-layer structure, and the rest is the same as Example 1.

[0153] Comparative Example 1

[0154] The difference between Comparative Example 1 and Example 1 is that the diaphragm directly adopts a polypropylene film, and the rest is the same as Example 1.

[0155] Performance Testing

[0156] In an environment of 25±0.5℃, charge the battery at a constant current-constant voltage of 4C until the battery reaches full charge, then discharge at a constant current of 0.5C until the electrochemical device is completely depleted, let stand for 3 minutes, and then repeat the above operation. Take the capacity of the third cycle as the reference value, test the capacity retention rate after 600 cycles, and record it; the battery in the cycle is disassembled in the fully charged state after the 200th, 400th, and 600th cycles, and observe whether there are black spots in the second bend section of the negative electrode sheet. Statistical data is recorded in the following table.

[0157] Table 1 Performance data of various embodiments and comparative examples

[0158]

[0159] Among them, cls represents the number of cycles.

[0160] It can be seen from Table 1 that, compared with Comparative Example 1, the capacity retention rates of the batteries of Examples 1 to 8 of the present application are all increased, and the proportion of the black spot area is all reduced. This shows that the embodiments of the present application improve the cycle performance of the secondary battery, and also effectively improve the interface problems on the surface of the negative electrode plate.

[0161] In summary, the present application sets the first coating of the first diaphragm segment located at the center of the electrode assembly to contain large-sized first particles, so that the internal pores formed in the center area of ​​the electrode assembly are relatively large, and the pores formed in the center area provide an exhaust channel for the internal gas production, thereby effectively ensuring that the gas produced inside the electrode assembly is discharged in time, thereby improving the cycle performance of the secondary battery. At the same time, the larger internal pores formed in the center area also constitute an electrolyte reflux and reabsorption path, which can effectively improve the electrolyte infiltration effect on the electrode assembly and improve the phenomenon of black spots.

[0162] The above description is only an exemplary embodiment of the present application and does not limit the patent scope of the present application. All equivalent structural changes made by using the contents of the present application specification and drawings under the technical concept of the present application, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A secondary battery, characterized in that: The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet, the separator and the negative electrode sheet are wound; The diaphragm includes a first diaphragm segment and a second diaphragm segment connected to each other, the first diaphragm segment is located at the center of the electrode assembly, the first diaphragm segment is exposed to the positive electrode sheet and the negative electrode sheet, the second diaphragm segment is located between the positive electrode sheet and the negative electrode sheet, the first diaphragm segment includes a first base film and a first coating provided on at least one side of the first base film, the first coating includes first particles, the second diaphragm segment includes a second base film and a second coating provided on at least one side of the second base film, the second coating includes second particles; The particle size of the second particles is smaller than that of the first particles.

2. The secondary battery according to claim 1, wherein: The volume particle size distribution D of the first particles V 50 is 10μm-50μm.

3. The secondary battery according to claim 1, wherein: The volume particle size distribution D of the second particles V 50 is 2μm-10μm.

4. The secondary battery according to claim 1, wherein: The material of the first particles includes high molecular polymer.

5. The secondary battery according to claim 1, wherein: The thermal shrinkage rate of the first particles is 1%-5%.

6. The secondary battery according to claim 1, wherein: The length of the first diaphragm segment is 0.5 cm-100 cm.

7. The secondary battery according to claim 1, wherein: The porosity of the first diaphragm segment is 50%-70%.

8. The secondary battery according to claim 1, wherein: The first diaphragm segment is configured as a double-layer structure; and / or, The number of turns of the first diaphragm segment is 1-2.

9. The secondary battery according to any one of claims 1 to 8, characterized in that: The diaphragm further comprises a third diaphragm segment, the third diaphragm segment is connected to a side of the second diaphragm segment away from the first diaphragm segment and is located at an edge of the electrode assembly; The third diaphragm segment includes a third base membrane and a third coating disposed on at least one side of the third base membrane, wherein the third coating contains third particles, and the volume particle size distribution of the third particles is V 50 is 10μm-50μm.

10. The secondary battery according to claim 9, characterized in that The third diaphragm segment is configured as a double-layer structure; and / or, The number of turns of the third diaphragm segment is 1-2.

11. An electrode assembly, characterized in that: The electrode assembly is an electrode assembly included in the secondary battery according to any one of claims 1 to 10.

12. An electrical device, characterized in that: The electric device comprises the secondary battery according to any one of claims 1 to 10.

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