Electrode assembly, method of manufacturing electrode assembly, and electrochemical device

Abstract

The application provides an electrode assembly, a manufacturing method of the electrode assembly and an electrochemical device. The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector. The positive electrode sheet, the separator and the negative electrode sheet are wound to form the electrode assembly. The positive electrode active material layer comprises a first positive electrode active material layer arranged on a positive electrode flat area and a second positive electrode active material layer arranged on a positive electrode corner area. The material of the first positive electrode active material layer comprises a positive electrode active material, and the material of the second positive electrode active material layer comprises a positive electrode active material and a lithium supplement agent. The mass percentage of the lithium supplement agent in the second positive electrode active material layer is x, wherein 0.1%≤x<3%, so that the battery impedance of the corner area is reduced, the kinetic performance of the corner area is improved, the lithium precipitation phenomenon of the corner area is sufficiently reduced, and the safety performance of the electrode assembly is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to an electrode assembly, a method for manufacturing the electrode assembly, and an electrochemical device. Background Technology

[0002] Lithium-ion battery cells can be classified into wound structure and stacked structure according to their structure. During the winding process, the wound cell structure will form a flat area and an arc-shaped corner area at both ends of the core. During long-term charge and discharge cycles, lithium plating is prone to occur in the arc-shaped corner area. Lithium plating has a significant impact on the safety performance of the cell, and the cell is prone to safety problems such as internal short circuit and thermal runaway. Summary of the Invention

[0003] This application provides an electrode assembly, a method for manufacturing the electrode assembly, and an electrochemical device to solve the above-mentioned technical problems.

[0004] The embodiments of this application are implemented as follows:

[0005] An electrode assembly includes a positive electrode, a negative electrode, and a separator. The positive electrode includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector. The separator is disposed between the positive and negative electrode, and the positive electrode, separator, and negative electrode are wound together to form the electrode assembly. The positive electrode has a straight positive region and a corner positive region in the wound structure of the electrode assembly. The positive active material layer includes a first positive active material layer and a second positive active material layer. The first positive active material layer is disposed in the straight positive region, and the second positive active material layer is disposed in the corner positive region. The material of the first positive active material layer includes a positive active material, and the material of the second positive active material layer includes a positive active material and a lithium supplement agent. The mass percentage of the lithium supplement agent in the second positive active material layer is x, where 0.1% ≤ x < 3%.

[0006] The electrode assembly of this application reduces the battery impedance in the corner region by adding a lithium replenishing agent to the active material layer in the positive electrode corner region and limiting the amount of lithium replenishing agent added to a specific range, thereby improving the dynamic performance of the corner region, significantly reducing lithium plating in the corner region, and enhancing the safety performance of the electrode assembly.

[0007] In one possible implementation: the thickness of the second positive electrode active material layer is less than the thickness of the first positive electrode active material layer.

[0008] In one possible implementation: the thickness of the first positive electrode active material layer is h1, and the thickness of the second positive electrode active material layer is h2, wherein 1μm≤(h1-h2)≤20μm.

[0009] Thus, by reducing the thickness of the second positive electrode active material layer, the capacity of the positive electrode active material in the corner region can be avoided, thereby preventing the CB value difference between the corner region and the straight region from increasing, and further reducing the risk of lithium plating.

[0010] In one possible implementation: the lithium supplement includes one or more of the following: lithium-rich manganese-based materials, lithium-rich lithium nickelate materials, lithium ferrite materials, lithium oxide materials, lithium fluoride materials, lithium sulfide materials, carbon-coated lithium sulfide materials, lithium nitride materials, and sacrificial lithium salts.

[0011] In one possible implementation: the negative electrode sheet includes a negative current collector and a negative active material layer, the negative active material layer being disposed on the surface of the negative current collector; in the winding structure of the electrode assembly, the negative electrode sheet includes a negative straight region and a negative corner region, and the positive electrode sheet covers the outside of the negative electrode sheet; along the winding direction of the electrode assembly, the size of the second positive active material layer in the positive corner region is larger than the size of the negative active material layer in the negative corner region, so as to prevent the offset caused by fluctuations in electrode sheet thickness, length tolerance and winding tolerance during the manufacturing process of the electrode assembly, which would result in the size of the positive corner region with added lithium supplement not completely covering the negative corner region.

[0012] In one possible implementation: the size of the second positive electrode active material layer in the positive electrode corner region is 0.5mm-5mm longer than the size of the negative electrode active material layer in the negative electrode corner region.

[0013] In one possible implementation: the positive electrode active material includes lithium iron phosphate, carbon nanotubes, conductive carbon black and polyvinylidene fluoride, so that the positive electrode active material has good electrical conductivity and kinetic properties.

[0014] Embodiments of this application also provide a method for manufacturing an electrode assembly, used to prepare the electrode assembly described in the above embodiments. The method for manufacturing the electrode assembly includes the following steps:

[0015] A slurry for preparing the first positive electrode active material layer, the slurry for the first positive electrode active material layer comprising positive electrode active material;

[0016] A slurry for preparing the second positive electrode active material layer is prepared. The slurry for the second positive electrode active material layer includes a positive electrode active material and a lithium supplementing agent. The mass percentage of the lithium supplementing agent in the second positive electrode active material layer is x, where 0.1% ≤ x < 3%.

[0017] A positive current collector is provided, and a slurry for coating a first positive active material layer is applied to the gaps on the surface of the positive current collector. The coating area of ​​the first positive active material layer is the positive straight area of ​​the positive electrode sheet, and the blank area between the coating areas of adjacent first positive active material layers is the positive corner area of ​​the positive electrode sheet.

[0018] A slurry containing a second positive electrode active material layer is coated onto a blank area on the positive electrode current collector to form a positive electrode sheet.

[0019] A negative electrode and a separator are provided. The separator is placed between the positive electrode and the negative electrode. The positive electrode, the separator and the negative electrode are wound together to form an electrode assembly.

[0020] In one possible implementation: the coating thickness of the second positive electrode active material layer is less than the coating thickness of the first positive electrode active material layer.

[0021] Embodiments of this application also provide an electrochemical device, including a packaging body and an electrode assembly as described in the above embodiments, wherein the electrode assembly is disposed within the packaging body. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a partial structural schematic diagram of an electrode assembly according to an embodiment of this application.

[0024] Figure 2 This is a flowchart illustrating a method for manufacturing an electrode assembly according to an embodiment of this application.

[0025] Figure 3 This is a flowchart illustrating a method for manufacturing an electrode assembly according to another embodiment of this application.

[0026] Figure 4 This is a partial structural diagram of an electrode assembly in a pair of proportions.

[0027] Figure 5 This is a partial structural diagram of the electrode assembly in another example.

[0028] Figure 6 This is a schematic diagram of the structure of an electrochemical device according to an embodiment of this application.

[0029] Explanation of key component symbols:

[0030] Electrode assemblies 100, 100a, 100b

[0031] Positive electrode plates 10, 10a, 10b

[0032] Positive flat region 101

[0033] Positive corner region 102

[0034] Positive current collectors 11, 11a, 11b

[0035] Positive electrode active material layers 12, 12a, 12b

[0036] First positive electrode active material layer 121

[0037] Second positive electrode active material layer 122

[0038] Negative electrode plates 20, 20a, 20b

[0039] Negative electrode flat region 201

[0040] Negative electrode corner area 202

[0041] Negative electrode current collectors 21, 21a, 21b

[0042] Negative electrode active material layers 22, 22a, 22b

[0043] Diaphragm 30, 30a, 30b

[0044] Electrochemical device 200

[0045] Packaging body 210

[0046] First electrode terminal 220

[0047] Second electrode terminal 230

[0048] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this application. Detailed Implementation

[0049] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0050] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component. When a component is said to be "set on" another component, it can be directly set on the other component or there may be an intervening component. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "or / and" as used herein includes any and all combinations of one or more of the associated listed items.

[0052] Some embodiments of this application are described in detail. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0053] See Figure 1 This embodiment provides an electrode assembly 100, including a positive electrode 10, a negative electrode 20, and a separator 30. The positive electrode 10 includes a positive current collector 11 and a positive active material layer 12 disposed on the surface of the positive current collector 11. The separator 30 is disposed between the positive electrode 10 and the negative electrode 20, and the positive electrode 10, the separator 30, and the negative electrode 20 are wound to form the electrode assembly 100. The positive electrode 10 has a straight positive electrode region 101 and a corner positive electrode region 102 in the wound structure of the electrode assembly 100. The positive active material layer 12 includes a first positive active material layer 121 and a second positive active material layer 122, the first positive active material layer 121 being disposed in the straight positive electrode region 101, and the second positive active material layer 122 being disposed in the corner positive electrode region 102. The first positive electrode active material layer 121 is made of positive electrode active material, and the second positive electrode active material layer 122 is made of positive electrode active material and lithium supplementation agent. The mass percentage of lithium supplementation agent in the second positive electrode active material layer 122 is x, where 0.1% ≤ x < 3%.

[0054] The electrode assembly 100 of this application adds a lithium replenishing agent to the active material layer in the positive electrode corner region 102, and limits the amount of the lithium replenishing agent to a specific range. This allows the lithium replenishing agent to act as an additional lithium source in the positive electrode corner region 102, slowing down the volume expansion and phase transition of the positive electrode active material material itself in the corner region, which is beneficial to maintaining the conductivity and stability of the material. At the same time, the addition of the lithium replenishing agent to the positive electrode corner region 102 also allows for a more uniform distribution of lithium ions, which helps the electrolyte to wet the electrode material, improves conductivity, and reduces the electrode impedance in the corner region. Based on this, the addition of a specific proportion of lithium replenishing agent to the active material layer in the positive electrode corner region 102 of the electrode assembly of this application effectively improves the kinetic performance of the corner region, thereby significantly reducing lithium plating in the corner region and improving the safety performance of the electrode assembly.

[0055] In addition, the lithium replenishing agent added to the positive electrode corner region 102 can replenish lithium ions in the battery system, which helps to reduce the consumption of lithium ions inside the system, reduce the decomposition of electrolyte, avoid unnecessary side reactions, effectively reduce the polarization phenomenon of electrode assembly 100, improve the black spot phenomenon in the corner region, and improve the service life of electrode assembly 100.

[0056] During the initial charging process, the lithium replenishing agent added to the positive electrode corner region 102 of the electrode assembly 100 can generate active oxygen and oxygen, which participate in the formation of the negative electrode SEI film, optimizing the structure of the negative electrode SEI film and making the inorganic-organic mixed structure of the SEI film more reasonable. The formation of the SEI film is mainly due to the reaction of reducing substances and oxides generated by the decomposition of solutes in the electrolyte during the charging and discharging process of the lithium-ion battery, forming a thin film on the electrode surface. This film has certain conductivity and stability, and can prevent further decomposition of solutes in the electrolyte, thereby protecting the electrode materials inside the battery. In this application, by adding a specific proportion of lithium replenishing agent to the positive electrode corner region 102, the structure of the SEI film can be optimized, which can regulate the ion transport rate inside the electrode assembly 100, further reduce the electrode impedance, and improve the cycle life of the electrode assembly.

[0057] In some embodiments, the mass percentage of the lithium replenisher includes, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.9%, or a range of any two of these values.

[0058] In some embodiments, the thickness h2 of the second positive electrode active material layer 122 is less than the thickness h1 of the first positive electrode active material layer 121. The lithium supplementer added to the second positive electrode active material layer 122 increases the specific capacity of the active material in the positive electrode corner region 102. By thinning the thickness of the second positive electrode active material layer 122, the increase in the positive electrode active material capacity in the positive electrode corner region 102 can be avoided, keeping the positive electrode active material capacity in the positive electrode corner region 102 as consistent as possible with the capacity without the addition of the lithium supplementer. This avoids an increase in the difference between the CB value of the corner region and the CB value of the straight region, thereby further reducing the risk of lithium plating.

[0059] In addition, the thickness h1 of the second positive electrode active material layer 122 is less than the thickness h2 of the first positive electrode active material layer 121, which can increase the gap between the positive electrode 10 and the negative electrode 20 in the corner area. The increased gap space can alleviate the compression and stress deformation between adjacent layers caused by the expansion of the electrode in the corner area, and can also enhance the wetting and reflux of the electrolyte in the corner area, further reduce the lithium plating problem, optimize the interface state in the later stage of the cycle at the corner position, and improve the life and safety of the electrode assembly 100.

[0060] Furthermore, the thickness difference between the second positive electrode active material layer 122 thickness h2 and the first positive electrode active material layer 121 thickness h1 is: 1μm≤(h1-h2)≤20μm, which keeps the gap space between adjacent electrodes in the corner region within a reasonable range. This can not only improve the stress deformation of the electrode assembly 100 in the corner region, but also reduce the mechanical performance degradation caused by the excessively thin positive electrode in the corner region, thus improving the overall performance of the electrode assembly 100.

[0061] In some embodiments, the lithium replenishing agent includes one or more of the following: lithium-rich manganese-based materials (LixNiyMnzOp), lithium-rich lithium nickelate materials (Li2NiO2), lithium ferrite materials (Li5FeO4), lithium oxide materials (LiO, Li2O2, Li2O), lithium fluoride materials (LiF), lithium sulfide materials (Li2S), carbon-coated lithium sulfide materials (Li2S@C), lithium nitride materials (Li3N), and sacrificial lithium salts. In other embodiments, the lithium replenishing agent of this application can also be a substance that modifies traditional lithium replenishing agents through surface modification, coating, doping with metal / non-metal elements, etc., to improve the stability, safety, economy, conductivity, impedance, and specific capacity of the lithium replenishing agent.

[0062] In some embodiments, such as Figure 1 As shown, in the winding structure of the electrode assembly 100, the negative electrode sheet 20 includes a negative current collector 21 and a negative active material layer 22, with the negative active material layer 22 disposed on the surface of the negative current collector 21. The negative electrode sheet 20 includes a negative straight region 201 and a negative corner region 202. The negative active material layers 22 of the negative straight region 201 and the negative corner region 202 are consistent. The positive electrode sheet 10 covers the outside of the negative electrode sheet 20. Along the winding direction of the electrode assembly 100, the size of the second positive active material layer 122 of the positive corner region 102 is larger than the size of the negative active material layer 22 of the negative corner region 202, to prevent the offset caused by fluctuations in electrode thickness, length tolerance, and winding tolerance during the manufacturing process of the electrode assembly 100, which would result in the size of the positive corner region 102 with added lithium supplement not completely covering the negative corner region 202.

[0063] Furthermore, the size of the second positive electrode active material layer 122 in the positive electrode corner region 102 is 0.5mm-5mm longer than the size of the negative electrode corner region 202 to ensure that the negative electrode corner region 202 can be fully covered by the positive electrode corner region 102. The difference between the size of the second positive electrode active material layer 122 in the positive electrode corner region 102 and the size of the negative electrode corner region 202 includes, but is not limited to, 0.5mm, 1.0mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, or any combination of these values.

[0064] In some embodiments, the positive electrode active material includes lithium iron phosphate, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride. The mass ratio of lithium iron phosphate, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride is (96-98):(0.5-1.5):(0.2-0.8):(1.0-2.0) to give the positive electrode active material good conductivity and kinetic properties. The material of the second positive electrode active layer 122 can be based on the positive electrode active material, with the addition of a specific proportion of lithium supplementer to form the coating material of the second positive electrode active layer 122. Thus, the main active material of the first positive electrode active layer 121 and the second positive electrode active layer 122 can be the same, which helps to reduce the configuration difficulty of the second positive electrode active layer 122 and reduce the manufacturing cost of the electrode assembly 100.

[0065] In other embodiments, in addition to the above-mentioned positive active material, the material of the first positive active material layer 121 may also include a lithium supplementing agent. In this case, the material of the second positive active material layer 122 may be a lithium supplementing agent slurry system with lower impedance than the first positive active material layer 121, so as to keep the specific capacity of the second positive active material layer 122 higher than that of the first positive active material layer 121 and the thickness thinner than that of the first positive active material layer 121.

[0066] Please see Figure 2 This application also provides a method for manufacturing an electrode assembly 100, used to prepare the electrode assembly 100 described in the above embodiments. The method for manufacturing the electrode assembly 100 of this application includes the following steps:

[0067] A slurry for preparing the first positive electrode active material layer 121, wherein the slurry for the first positive electrode active material layer 121 includes a positive electrode active material;

[0068] A slurry for preparing the second positive electrode active material layer 122 is prepared. The slurry for the second positive electrode active material layer 122 includes a positive electrode active material and a lithium supplementing agent. The mass percentage of the lithium supplementing agent in the second positive electrode active material layer is x, where 0.1% ≤ x < 3%.

[0069] A positive current collector 11 is provided, and a slurry of a first positive active material layer 121 is coated on the gap of the surface of the positive current collector 11. The coating area of ​​the first positive active material layer 121 is the positive straight region 101 of the positive electrode 10, and the blank area between the coating areas of adjacent first positive active material layers 121 is the positive corner region 102 of the positive electrode 10.

[0070] A slurry of the second positive electrode active material layer 122 is applied to the blank area on the positive electrode current collector 11 by intermittent coating to form the positive electrode sheet 10.

[0071] A negative electrode 20 and a separator 30 are provided. The separator is disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the separator 30 and the negative electrode 20 are wound to form an electrode assembly 100.

[0072] In some of the preparation methods, the mass percentage of the lithium replenishing agent includes, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, and 2.9%, or a range consisting of any two of these values. The composition and content ratio of the positive electrode active material are largely the same as in the aforementioned embodiments and will not be repeated here.

[0073] In some embodiments, when the first positive electrode active material layer 121 is intermittently coated onto the surface of the positive electrode current collector 11, the size of the blank area on the surface of the positive electrode current collector 11 is larger than the size of the corresponding negative electrode corner region 202 on the negative electrode sheet 20 along the winding direction of the electrode assembly. Specifically, the size of the blank area is 0.5mm-5mm longer than the size of the corresponding negative electrode corner region 202 on the negative electrode sheet 20, to ensure that the negative electrode corner region 202 can be fully covered by the positive electrode corner region 102. The difference between the size of the blank area and the size of the corresponding negative electrode corner region 202 includes, but is not limited to, 0.5mm, 1.0mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, or any combination of these values.

[0074] In some embodiments, the coating thickness of the second positive electrode active material layer 122 is less than the coating thickness of the first positive electrode active material layer 121, so as to avoid increasing the active material capacity at the positive electrode corner region 102, while increasing the gap space between adjacent electrodes in the corner region of the electrode assembly 100.

[0075] like Figure 3As shown, in one embodiment, after the preparation step of the slurry of the first positive electrode active material layer 121 is completed, the first positive electrode active material layer 121 can be intermittently coated on the positive electrode current collector 11, and then the slurry of the second positive electrode active material layer 122 can be prepared, and then the slurry of the second positive electrode active material layer 122 can be coated on the blank area of ​​the positive electrode current collector 11. Figure 3 The embodiments shown are merely examples. In some embodiments, the slurry preparation process of the first positive electrode active material layer 121 and the second positive electrode active material layer 122 can be alternated with the interstitial coating process of each slurry, and the preparation order can be adjusted according to production needs. This application is not limited to this.

[0076] In some embodiments, the method for manufacturing the electrode assembly further includes a drying step, wherein the electrode is dried after each gap coating process is completed to prevent mixing of different slurries or displacement of slurries during the secondary gap coating process.

[0077] In the embodiments of this application, the material of the positive current collector 11 is aluminum foil with a thickness of 10μm-15μm, preferably 13μm. In some embodiments, the thickness of the positive current collector 11 includes, but is not limited to, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or any combination of these values. In the process of preparing the positive electrode sheet 10, a large positive current collector master sheet can be provided first. A slurry of the first positive active material layer 121 and a slurry of the second positive active material layer 122 are coated on the positive current collector master sheet with gaps. After the drying process is completed, die-cutting and slitting are performed to cut the positive current collector master sheet coated with the slurry of the first positive active material layer 121 and the slurry of the second positive active material layer 122 into multiple positive electrode sheets 10, thereby improving the manufacturing efficiency of the positive electrode sheet 10.

[0078] In some embodiments, the preparation steps of the negative electrode sheet 20 include: preparing a slurry of a negative electrode active material layer 22; providing a negative electrode current collector 21; coating the slurry of the negative electrode active material layer 22 onto the negative electrode current collector 21 by continuous coating; and drying the coating to form the negative electrode sheet 20.

[0079] In the embodiments of this application, the material of the negative electrode current collector 21 is a copper foil with a thickness of 4μm-8μm, preferably 6μm. In some embodiments, the thickness of the negative electrode current collector 21 includes, but is not limited to, 4μm, 5μm, 6μm, 7μm, 8μm, or any combination of these values.

[0080] In the preparation process of the negative electrode sheet 20, a larger negative electrode current collector mother sheet can be provided first. A slurry of negative electrode active material layer 22 is coated on the negative electrode current collector mother sheet. After the drying process is completed, the positive electrode current collector mother sheet coated with negative electrode active material layer 22 slurry is die-cut and slited to cut multiple negative electrode sheets 20, thereby improving the manufacturing efficiency of the negative electrode sheet 20.

[0081] In some embodiments, the material of the negative electrode active material layer 22 includes graphite, conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose. The mass ratio of graphite:conductive carbon black:styrene-butadiene rubber:sodium carboxymethyl cellulose is (95-98):(0.5-1.5):(1.0-2.0):(0.5-1.5) to ensure that the negative electrode active material has good electrical conductivity and kinetic properties.

[0082] In some embodiments, the diaphragm 30 may be a polyethylene-based membrane diaphragm, which has good durability and flexibility.

[0083] The electrode assembly manufacturing method of this application is simple and does not require changes to existing production lines and processes. In the preparation of the positive electrode 10, only two slurries need to be prepared: one containing the positive electrode active material, and the other formed by adding a lithium supplement agent to the positive electrode active material slurry. No additional coating processes, methods, or procedures are required; only two intermittent coatings are needed to prepare the desired positive electrode 10. At the same time, the amount of lithium supplement agent used is very small, the cost is low, and the capacity of the positive electrode active material is not sacrificed, thus not reducing the energy density of the electrode assembly 100.

[0084] The following will describe the manufacturing method of the electrode assembly with reference to specific embodiments.

[0085] Example 1

[0086] The manufacturing method of electrode assembly 100 is as follows:

[0087] Preparation of positive electrode 10:

[0088] Preparation of the slurry for the first positive electrode active material layer 121: Lithium iron phosphate, carbon nanotubes, conductive carbon black and polyvinylidene fluoride are mixed evenly in a mass ratio of 97:1.0:0.5:1.5. The above mixed slurry is coated onto a 13μm positive electrode current collector aluminum foil through gap coating. The blank area of ​​the gap coating is a corner arc-shaped area, and the coated area of ​​the gap coating is a straight area. After coating, the electrode is dried. After drying, the thickness of the electrode in the coated area is 176.5μm.

[0089] Preparation of the slurry for the second positive electrode active material layer 122: Lithium iron phosphate, lithium supplementer Li5FeO4, carbon nanotubes, conductive carbon black and polyvinylidene fluoride are mixed evenly in a mass ratio of 96:1.0:1.0:0.5:1.5. The above mixed slurry is then coated onto the blank area of ​​the electrode formed by the above coating through gap coating. After drying, it is die-cut and slit to finally obtain the required positive electrode 10. The electrode thickness of the slurry coating area of ​​the second positive electrode active material layer 122 is 171 μm.

[0090] Preparation of negative electrode 20:

[0091] The negative electrode active materials graphite, conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed evenly in a mass ratio of 96.4:1.0:1.6:1.0. The mixed slurry was evenly coated on a 6µm negative electrode current collector copper foil, dried, and then die-cut and slit to obtain the negative electrode sheet 20.

[0092] Preparation of diaphragm 30: Diaphragm 30 is a polyethylene-based membrane. For example... Figure 1 and Figure 6 As shown, the positive electrode 10, the separator 30, and the negative electrode 20 are wound together to form an electrode assembly 100. The positive electrode 10 and the negative electrode 20 can also be connected to positive and negative tabs, respectively. After the electrode assembly 100 is placed into a packaging body 210, the positive and negative tabs can be appropriately cut. After the tabs are connected to the electrode terminals on the packaging body 210, they are sealed, and an electrolyte is injected into the packaging body 210 to wet the electrode assembly 100. Then, steps such as formation, capacity separation, degassing, and sealing are performed to obtain an electrochemical device 200 ready for use.

[0093] Example 2

[0094] In Example 2, the design of the positive electrode 10, negative electrode 20, separator 30, etc. is roughly the same as in Example 1. The difference is that in the slurry of the second positive electrode active material layer 122 in Example 2, the content of lithium supplementer is 1.5%, corresponding to a 0.5% reduction in the content of lithium iron phosphate, and the electrode thickness of the second positive electrode active material layer 122 on the positive electrode 10 is 167.3 μm.

[0095] Example 3

[0096] In Example 3, the design of the positive electrode 10, negative electrode 20, separator 30, etc. is roughly the same as in Example 1. The difference is that in the slurry of the second positive electrode active material layer 122 in Example 3, the content of lithium supplementer is 2.0%, which corresponds to a 1% reduction in the content of lithium iron phosphate. The electrode thickness of the second positive electrode active material layer 122 on the positive electrode 10 is 163.8 μm.

[0097] Example 4

[0098] In Example 4, the design of the positive electrode 10, negative electrode 20, separator 30, etc. is roughly the same as in Example 1. The difference is that in the slurry of the second positive electrode active material layer 122 in Example 4, the lithium supplementing agent is Li2S@C, and the electrode thickness of the second positive electrode active material layer 122 on the positive electrode 10 is 167.6μm.

[0099] Comparative Example 1

[0100] In Comparative Example 1, the design of the positive electrode 10, negative electrode 20, separator 30, etc. is roughly the same as that in Example 1. The difference is that in the slurry of the second positive electrode active material layer 122 in Comparative Example 1, the content of lithium supplementer is 3.0%, which corresponds to a 2% reduction in the content of lithium iron phosphate. The electrode thickness of the second positive electrode active material layer 122 on the positive electrode 10 is 157.3 μm.

[0101] Comparative Example 2

[0102] Please see Figure 4 , Figure 4 This is a partial structural schematic diagram of electrode assembly 100a in Comparative Example 2. The difference between Comparative Example 2 and Example 1 is that the positive electrode active material layer 12a in both the straight positive electrode region and the positive electrode corner region of the positive electrode 10a does not contain lithium replenishing agent. That is, the positive electrode active material layer 12a of the positive electrode 10a is an active region without lithium replenishing agent formed by continuous coating. The same active material layer is used in both the straight positive electrode region and the positive electrode corner region of the positive electrode 10a. Figure 4 As shown, the thickness of the positive electrode active material layer 12a remains consistent across all regions.

[0103] Comparative Example 3

[0104] Please see Figure 5 , Figure 5 This is a partial structural schematic diagram of electrode assembly 100b in Comparative Example 3. The difference between Comparative Example 3 and Example 1 is that in the positive electrode 10b, both the positive electrode active material layer 12b in the straight positive electrode region and the positive electrode corner region contain a lithium replenishing agent with a mass ratio of 1%. The material of the lithium replenishing agent is the same as in Example 1; that is, the positive electrode active material layer 12b of the positive electrode 10b is an active region containing the lithium replenishing agent formed by continuous coating. The same active material layer is used in both the straight positive electrode region and the positive electrode corner region of the positive electrode 10b. Figure 5 As shown, the thickness of the positive electrode active material layer 12b remains consistent across all regions.

[0105] The electrochemical devices containing electrode components prepared in Examples 1-4 and Comparative Examples 1-3 were subjected to cyclic testing as follows: at 25°C, they were charged to 3.65V at a constant current and constant voltage of 1C, cut off at 0.05C, and left to stand for 1 hour. Then, they were discharged to 2.0V at a constant current of 1C and left to stand for 1 hour. The above charge and discharge process was repeated 300 times. The test object was then disassembled, and the lithium plating state at the corner of the negative electrode was observed.

[0106] The test results for each embodiment and comparative example are shown in Table 1 below:

[0107] Table 1

[0108]

[0109] The degree of lithium plating in lithium-ion batteries can be judged according to the following criteria:

[0110] No lithium deposition: No lithium is deposited on the surface of the negative electrode corner;

[0111] Slight lithium plating: The lithium deposition area at the corner of the negative electrode is less than 10%;

[0112] Lithium deposition: The lithium deposition area at the corner of the negative electrode sheet is 10% to 25%;

[0113] Severe lithium plating: The lithium deposition area at the corner of the negative electrode sheet is greater than 25%.

[0114] As can be seen from the test results in Table 1, after adding an appropriate proportion of lithium replenishing agent to the active material layer in the positive electrode corner region, the lithium plating situation in the negative electrode corner region was significantly improved, which fully enhanced the safety performance of the electrode assembly. In addition, the capacity retention rate after 300 cycles was also significantly improved, proving that the dynamic performance and lifespan of the electrode assembly can be improved.

[0115] A comparison of the test results from Examples 1 and 4 shows that, with the same amount of lithium replenishing agent added, the capacity retention rate after 300 cycles is higher, and the dynamic performance and service life of the electrode assembly can be improved more significantly when using a lithium replenishing agent with better conductivity.

[0116] The test results of Comparative Example 1 show that 3% is the critical value for the amount of lithium replenishing agent added in the active material layer of the positive electrode corner. At this amount, lithium plating will occur in the negative electrode corner. The amount of lithium replenishing agent added in the active material layer of the positive electrode corner should be as small as possible to improve the safety performance of the electrode assembly.

[0117] The test results of Comparative Examples 2 and 3 show that using the same active material layer material in both the positive electrode corner region and the positive electrode straight region does not reduce the lithium plating problem in the negative electrode corner region. Although adding the same proportion of lithium replenishing agent to the active material layer material in both the positive electrode corner region and the positive electrode straight region improves the capacity retention after charge-discharge cycles to some extent, the lithium plating problem in the negative electrode corner region still exists. This fully demonstrates the importance of using different active material materials in the positive electrode straight region and the positive electrode corner region in this application, and the importance of adding a specific proportion of lithium replenishing agent in the positive electrode corner region for improving the lithium plating problem and enhancing the overall performance of the electrode assembly.

[0118] Please see Figure 6 This application also provides an electrochemical device 200, including but not limited to batteries, pouch cells, and other devices. The electrochemical device 200 includes a packaging body 210 and an electrode assembly 100 as described in the above embodiments. The electrode assembly 100 is disposed within the packaging body 210, which can be filled with an electrolyte. The electrochemical device 200 may further include a first electrode terminal 220 and a second electrode terminal 230. The first electrode terminal 220 is electrically connected to the positive electrode 10 of the electrode assembly 100, and the first electrode terminal 220 protrudes from the packaging body 210. The second electrode terminal 230 is electrically connected to the negative electrode 20 of the electrode assembly 100, and the second electrode terminal 230 protrudes from the packaging body 210. The first electrode terminal 220 and the second electrode terminal 230 are used to connect to an external charging and discharging circuit.

[0119] The electrode assembly 100, the method for manufacturing the electrode assembly, and the electrochemical device 200 of this application coat the positive electrode corner region 102 with an active material coating containing a lithium replenishing agent. The amount of lithium replenishing agent added is constrained within a specific range, and the main active material of the positive electrode straight region 101 and the active material of the positive electrode corner region 102 are the same. Utilizing the high specific capacity of the lithium replenishing agent, a lower coating thickness is achieved without reducing the capacity of the positive electrode active material in the positive electrode corner region 102. During cycling, the characteristics of the lithium replenishing agent reduce the impedance of the negative electrode. At the same time, the thinner coating thickness of the positive electrode sheet 10 can also mitigate the compression and stress deformation between adjacent layers caused by the expansion of the electrode sheet in the corner region. It can also enhance the wetting and reflux of the electrolyte in the corner region, greatly improve the lithium deposition phenomenon at the corner, optimize the interface state in the later stages of cycling at the corner position, and improve the life and safety of the electrode assembly.

[0120] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. An electrode assembly, characterized by, Comprise: a positive electrode tab comprising a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer being disposed on a surface of the positive electrode current collector; a negative electrode tab; and a separator disposed between the positive electrode tab and the negative electrode tab, the positive electrode tab, the separator, and the negative electrode tab being wound to form the electrode assembly; the positive electrode tab has a positive electrode flat area and a positive electrode corner area in a winding structure of the electrode assembly, the positive electrode active material layer comprises a first positive electrode active material layer and a second positive electrode active material layer, the first positive electrode active material layer is disposed on the positive electrode flat area, and the second positive electrode active material layer is disposed on the positive electrode corner area; the material of the first positive electrode active material layer comprises a positive electrode active material, the material of the second positive electrode active material layer comprises the positive electrode active material and a lithium supplement agent, the material of the second positive electrode active material layer is formed by adding the lithium supplement agent to the material of the first positive electrode active material layer, and the mass percentage of the lithium supplement agent in the second positive electrode active material layer is x, wherein 0.1%≤x<3%.

2. The electrode assembly according to claim 1, wherein: the thickness of the second positive electrode active material layer is less than the thickness of the first positive electrode active material layer.

3. The electrode assembly according to claim 2, wherein: the thickness of the first positive electrode active material layer is h1, and the thickness of the second positive electrode active material layer is h2, wherein 1 μm≤(h1-h2)≤20 μm.

4. The electrode assembly according to claim 1, wherein: the lithium supplement agent comprises one or more of a lithium-rich manganese-based material, a lithium-rich lithium nickelate material, a lithium ferrite material, a lithium oxide material, a lithium fluoride material, a lithium sulfide material, a carbon-coated lithium sulfide material, a lithium nitride material, and a sacrificial lithium salt.

5. The electrode assembly according to claim 1, wherein: the negative electrode tab comprises a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer being disposed on a surface of the negative electrode current collector; in the winding structure of the electrode assembly, the negative electrode tab comprises a negative electrode flat area and a negative electrode corner area, and the positive electrode tab is wrapped on the outside of the negative electrode tab; and along the winding direction of the electrode assembly, the size of the second positive electrode active material layer of the positive electrode corner area is greater than the size of the negative electrode active material layer of the negative electrode corner area.

6. The electrode assembly according to claim 5, wherein: the size of the second positive electrode active material layer of the positive electrode corner area is 0.5 mm-5 mm longer than the size of the negative electrode active material layer of the negative electrode corner area.

7. The electrode assembly according to claim 1, wherein: the positive electrode active material comprises lithium iron phosphate, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride. The method for manufacturing the electrode assembly comprises the steps of:

8. A method of manufacturing an electrode assembly for producing the electrode assembly according to any one of claims 1 to 7, characterized by, preparing a slurry of a first positive electrode active material layer, the slurry of the first positive electrode active material layer comprising a positive electrode active material; ​ A slurry for preparing a second positive electrode active material layer is prepared, the slurry for the second positive electrode active material layer including a positive electrode active material and a lithium supplement, the mass percentage of the lithium supplement in the second positive electrode active material layer being x, wherein 0.1%≤x<3%; the slurry for the second positive electrode active material layer is formed by adding the lithium supplement to the slurry for the first positive electrode active material layer; A positive electrode current collector is provided, and the slurry for the first positive electrode active material layer is coated on the surface gap of the positive electrode current collector, the coated area of the first positive electrode active material layer being a positive electrode flat area of the positive electrode sheet, and the blank area between adjacent coated areas of the first positive electrode active material layer being a positive electrode corner area of the positive electrode sheet; The slurry for the second positive electrode active material layer is coated on the blank area on the positive electrode current collector to form a positive electrode sheet; A negative electrode sheet and a separator are provided, 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 to form an electrode assembly.

9. The manufacturing method of the electrode assembly according to claim 8, wherein: The coating thickness of the second positive electrode active material layer is less than the coating thickness of the first positive electrode active material layer.

10. An electrochemical device, characterized by, The electrode assembly according to any one of claims 1-7 is arranged in the packaging body.

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