Electrode assembly and secondary battery

Abstract

This application provides an electrode assembly and a secondary battery, particularly relating to an electrode assembly comprising at least one electrode sheet, the electrode sheet being wound to form a wound structure; the electrode sheet includes a current collector, an electrode film layer L1, and an electrode film layer L2, the current collector having two surfaces opposite each other in its own thickness direction, the electrode film layers L1 and L2 being respectively disposed on the two opposite surfaces; the electrode film layer L1 is located inside the electrode film layer L2 relative to the center of the wound structure; each of the electrode film layers L1 and L2 contains an electrode material; wherein the ultimate compaction density of the electrode material contained in the electrode film layer L1 is 0.05 g / cm³ higher than the ultimate compaction density of the electrode material contained in the electrode film layer L2. 3 ~1g / cm 3 .

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to an electrode assembly, a secondary battery, a battery module, a battery pack, and an electrical device. Background Technology

[0002] Secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0003] The electrodes of a secondary battery mainly consist of a current collector and an electrode film. The electrode film can be formed by coating or other methods using electrode materials, including electrode active materials, conductive agents, and binders. Currently, the manufacturing of secondary battery electrodes commonly employs a double-sided coating process. This involves coating both sides of the current collector with a slurry containing electrode materials, followed by drying, rolling, slitting, and die-cutting to produce positive and negative electrode sheets. These sheets are then wound or stacked to form bare battery cells. Due to its high production speed and yield, the winding method is widely used in battery cell manufacturing. Summary of the Invention

[0004] After the existing square hard-shell secondary battery electrodes are wound and hot-pressed, two planar areas and two corner areas are formed. The inner circle electrode in the corner area is prone to protrusion due to bending and compression, while the outer circle electrode is prone to cracking due to bending and stretching. The burrs at the protrusions and cracks may puncture the separator, causing a short circuit in the cell and thus leading to thermal runaway. On the other hand, lithium plating is more likely to occur in the corner area.

[0005] To address the above technical problems, this application provides an electrode assembly comprising a double-sided asymmetric coated electrode. The electrode is coated with an electrode material with a high ultimate compaction density on the inner surface of the current collector and an electrode material with a low ultimate compaction density on the outer surface of the current collector. While ensuring the matching of positive and negative electrode capacities, this can improve the problem that the electrode in the corner area of ​​a square hard-shell cell is prone to cracking due to bending stress, leading to lithium plating.

[0006] To achieve the above objectives, this application provides an electrode assembly, a secondary battery, a battery module, a battery pack, and an electrical device.

[0007] A first aspect of this application provides an electrode assembly including at least one electrode sheet, the electrode sheet being wound to form a wound structure; the electrode sheet comprising a current collector, an electrode film layer L1, and an electrode film layer L2, the current collector having two surfaces opposite each other in its own thickness direction, the electrode film layer L1 and the electrode film layer L2 being respectively disposed on the two opposite surfaces; the electrode film layer L1 is located inside the electrode film layer L2 relative to the center of the wound structure; the electrode film layers L1 and L2 each comprise an electrode material; wherein the ultimate compaction density of the electrode material comprised in the electrode film layer L1 is 0.05 g / cm³ higher than the ultimate compaction density of the electrode material comprised in the electrode film layer L2. 3 ~1g / cm 3 .

[0008] In some embodiments, the electrode sheet is a positive electrode sheet, the current collector is a positive current collector, and the electrode film layers L1 and L2 are positive electrode film layers LC1 and LC2, respectively; the positive electrode film layer LC1 contains positive electrode material C1, and the positive electrode film layer LC2 contains positive electrode material C2; wherein the limiting compaction density of the positive electrode material C1 is 0.05 g / cm³ higher than that of the positive electrode material C2. 3 ~1g / cm 3 In some implementation schemes, the height is 0.2 g / cm 3 ~0.5g / cm 3 .

[0009] In some embodiments, the thickness ratio of the positive electrode film LC1 to the positive electrode film LC2 is 1.1 to 1.2:1.

[0010] In some embodiments, the positive electrode material C1 and the positive electrode material C2 are coated to form the positive electrode film layers LC1 and LC2 on the two surfaces of the current collector, respectively.

[0011] In some embodiments, the coating weight Wc_1 of the positive electrode material C1 is 0-200 mg / 1540.25 mm higher than the coating weight Wc_2 of the positive electrode material C2. 2 In some implementations, the concentration is as high as 10 mg / 1540.25 mm. 2 ~40mg / 1540.25mm 2 .

[0012] In some embodiments, the electrode sheet is a negative electrode sheet, the current collector is a negative electrode current collector, and the electrode film layers L1 and L2 are negative electrode film layers LA1 and LA2, respectively; the negative electrode film layer LA1 contains negative electrode material A1, and the negative electrode film layer LA2 contains negative electrode material A2; wherein the limiting compaction density of the negative electrode material A1 is 0.05 g / cm³ higher than that of the negative electrode material A2. 3 ~1g / cm 3 In some implementation schemes, the height is 0.05 g / cm 3 ~0.15g / cm 3 .

[0013] In some embodiments, the thickness ratio of the negative electrode film LA1 to the negative electrode film LA2 is 1.05 to 1.2:1.

[0014] In some embodiments, the electrode assembly includes a positive electrode selected from any of the above definitions and a negative electrode selected from any of the above definitions.

[0015] A second aspect of this application provides a method for preparing an electrode assembly, comprising the following steps:

[0016] (1) Provide a positive electrode and a negative electrode; the positive electrode is selected from the positive electrode as defined in any of the above, and / or the negative electrode is selected from the negative electrode as defined in any of the above;

[0017] (2) The positive electrode and the negative electrode are wound together to form a wound structure, such that the positive electrode film LC1 is located inside the positive electrode film LC2 relative to the center of the wound structure, and / or the negative electrode film LA1 is located inside the negative electrode film LA2 relative to the center of the wound structure.

[0018] A third aspect of this application provides the use of a positive or negative electrode sheet as defined in any of the preceding claims in the fabrication of an electrode assembly; wherein the positive electrode sheet and / or the negative electrode sheet form a wound structure, the positive electrode film LC1 is located inside the positive electrode film LC2 relative to the center of the wound structure, and / or the negative electrode film LA1 is located inside the negative electrode film LA2 relative to the center of the wound structure.

[0019] The fourth aspect of this application provides a secondary battery including the electrode assembly provided in the first aspect of this application.

[0020] The fifth aspect of this application provides a battery module, including the electrode assembly provided in the first aspect of this application or the secondary battery provided in the fourth aspect of this application.

[0021] The sixth aspect of this application provides a battery pack, including the electrode assembly provided in the first aspect of this application, the secondary battery provided in the fourth aspect of this application, or the battery module provided in the fifth aspect of this application.

[0022] The seventh aspect of this application provides an electrical device, including the electrode assembly provided in the first aspect of this application, the secondary battery provided in the fourth aspect of this application, the battery module provided in the fifth aspect of this application, or the battery pack provided in the sixth aspect of this application.

[0023] This application sets materials with different flexibility on both sides of the current collector, and further allows the electrode layer thickness on both sides of the current collector to be different, exhibiting an asymmetrical distribution relative to the current collector. While ensuring the matching of positive and negative electrode capacities, it improves the problem that the corner electrode of the square hard-shell cell is prone to cracking due to bending stress, leading to lithium plating. Attached Figure Description

[0024] Figure 1 This is a cross-sectional view of an electrode assembly according to one embodiment of this application.

[0025] Figure 2 This is a schematic diagram of the layer structure of an electrode assembly according to one embodiment of this application.

[0026] Figure 3 This is a schematic diagram of a square-structured secondary battery according to one embodiment of this application.

[0027] Figure 4 yes Figure 3 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0028] Figure 5 This is a schematic diagram of a battery module according to one embodiment of this application.

[0029] Figure 6 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0030] Figure 7 yes Figure 6 An exploded view of a battery pack according to one embodiment of this application is shown.

[0031] Figures 3-7 The following are the labels in the attached drawings: 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly.

[0032] Figure 8 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application. Detailed Implementation

[0033] The following detailed description, with appropriate reference to the accompanying drawings, discloses the composite material and its preparation method, as well as embodiments of the positive electrode sheet, secondary battery, battery module, battery pack, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0034] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0036] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0037] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0038] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0039] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0040] [Electrode assemblies and electrode plates]

[0041] One embodiment of this application discloses an electrode assembly comprising at least one electrode sheet, the electrode sheet being wound to form a wound structure; the electrode sheet includes a current collector, an electrode film layer L1, and an electrode film layer L2, the current collector having two surfaces opposite each other in its own thickness direction, the electrode film layers L1 and L2 being respectively disposed on the two opposite surfaces; the electrode film layer L1 is located inside the electrode film layer L2 relative to the center of the wound structure; the electrode film layers L1 and L2 each contain electrode material; wherein the ultimate compaction density of the electrode material contained in the electrode film layer L1 is 0.05 g / cm³ higher than the ultimate compaction density of the electrode material contained in the electrode film layer L2. 3 ~1g / cm 3 (e.g., 0.05 g / cm) 3 ~0.07g / cm 3 0.07g / cm 3 ~0.1g / cm 3 0.1g / cm 3 ~0.2g / cm 3 0.2g / cm 3 ~0.3g / cm 3 0.3g / cm3 ~0.4g / cm 3 0.4g / cm 3 ~0.5g / cm 3 0.5g / cm 3 ~0.6g / cm 3 0.6g / cm 3 ~0.7g / cm 3 0.7g / cm 3 ~0.8g / cm 3 0.8g / cm 3 ~0.9g / cm 3 or 0.9g / cm 3 ~1.0g / cm 3 ).

[0042] In the electrode assembly provided in this application, at least one electrode sheet has electrode material asymmetrically disposed on both sides of the current collector (e.g., coated), that is, an electrode material with a higher limiting compaction density is disposed on the inner surface of the current collector (e.g., coated), and an electrode material with a lower limiting compaction density is disposed on the outer surface of the current collector (e.g., coated), thereby improving the problem that flat cells are prone to cracking in the corner area, which further leads to lithium plating.

[0043] In this application, the inner and outer ring surfaces are determined according to their distance from the center of the winding structure in the winding direction. For the same layer, the side of the current collector closer to the center of the winding structure is the inner ring surface, and the side farther away from the center of the winding structure is the outer ring surface.

[0044] The ultimate compaction density of the electrode material can be obtained through a folding and light transmission experiment. That is, under the condition of a set electrode material coating weight, the maximum compaction density at which the electrode sheet is folded twice without light transmission is measured. An exemplary measurement method includes the following steps:

[0045] 1. Prepare test samples and operating tools. The test samples include at least 5 electrodes, and the electrode size can be 4cm×25cm. The operating tools include a cylindrical roller (e.g., a 2kg cylindrical roller).

[0046] 2. Operating steps:

[0047] 1) Take the electrode to be tested and fold it in half along the width direction, centering it in half;

[0048] 2) Place the folded electrode sheet on a flat surface and roll it continuously in the center position 3 times with a cylindrical roller;

[0049] 3) After rolling, unfold the electrode sheet and observe whether the creases are translucent or broken;

[0050] 4) After completing the tests on all parallel samples, if no light transmission is observed in any of the parallel samples, the compaction density can be increased by 0.05 g / cm³. 3 ,

[0051] 5) Repeat steps 1-4) until the test sample shows light transmission or breaks. Take the compaction density of the previous test sample as the ultimate compaction density of this sample.

[0052] [Positive electrode plate]

[0053] In the electrode assembly of this application, the double-sided asymmetric coated electrode sheet can be a positive electrode sheet. In the positive electrode sheet, the current collector is a positive current collector, and the electrode film layers L1 and L2 are positive electrode film layers LC1 and LC2, respectively; the positive electrode film layer LC1 contains positive electrode material C1, and the positive electrode film layer LC2 contains positive electrode material C2. The inventors have discovered that if the difference in the ultimate compaction density of the positive electrode materials C1 and C2 is within a suitable range, it can significantly improve the cracking effect in the corner region of the electrode sheet, while simultaneously leveraging the energy density advantage of the positive electrode material C1, which has a higher ultimate compaction density. In some embodiments, the ultimate compaction density of the positive electrode material C1 is 0.05 g / cm³ higher than that of the positive electrode material C2. 3 ~1g / cm 3 In some embodiments, the limiting compaction density of the cathode material C1 is 0.2 g / cm³ higher than that of the cathode material C2. 3 ~0.5g / cm 3 (e.g., 0.2g / cm) 3 ~0.3g / cm 3 0.3g / cm 3 ~0.4g / cm 3 or 0.4g / cm 3 ~0.5g / cm 3 ).

[0054] In some implementations, the limiting compaction density of the cathode material C1 is ≥2.4 g / cm³. 3 The higher the ultimate compaction density, the better it is for improving the actual energy density of the electrode assembly.

[0055] As an improvement to this application, this application provides a thicker positive electrode material on the inner surface of the positive electrode current collector and a thinner positive electrode material on the outer surface, resulting in an asymmetrical thickness distribution on both sides of the positive electrode current collector. This utilizes the characteristic that thinner materials exhibit less tensile deformation for the same radius of curvature, further mitigating the drawback of easy cracking in corner areas and improving the safety of the secondary battery during cycling. In some embodiments, the thickness ratio of the positive electrode film LC1 to the positive electrode film LC2 is 1.1–1.2:1.

[0056] The positive current collector used for the positive electrode can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can 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.).

[0057] Cathode material C1 and cathode material C2 may each contain the same or different cathode active materials. In some embodiments, the cathode active material may be a cathode active material known in the art for use in batteries. As an example, the cathode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as cathode active materials for batteries may also be used. These cathode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05One or more of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. As an improvement of this application, the positive electrode active materials contained in positive electrode materials C1 and C2 are each independently selected from at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium cobalt oxide, lithium-rich manganese-based, and cobalt-free high-nickel. In some embodiments, the stoichiometric ratio of lithium to nickel in the active materials of positive electrode materials C1 or C2 can be adjusted to achieve a desired limiting compaction density. In some embodiments, the sum of the stoichiometric ratios of lithium to nickel in the positive electrode active materials is 1 to 1.8 (e.g., 1, 1.35, 1.4, 1.42, 1.5, 1.7, or 1.8). In some implementations, the particle size of the active material contained in the cathode material C1 or C2 can be adjusted to achieve the desired ultimate compaction density. In some embodiments, the active material contained in the cathode material C1 or C2 has a D10 of 0.4um to 6um (e.g., 0.4um to 1um, 1um to 2um, 2um to 3um, 3um to 4um, 4um to 5um or 5um to 6um), a D50 of 0.7um to 9um (e.g., 0.7um to 1um, 1um to 2um, 2um to 3um, 3um to 4um, 4um to 5um, 5um to 6um, 6um to 7um, 7um to 8um or 8um to 9um), and / or a D90 of 3um to 13um (e.g., 3um to 4um, 4um to 5um, 5um to 6um, 6um to 7um, 7um to 8um, 8um to 9um, 9um to 10um, 10um to 11um, 11um to 12um or 12um to 13um).

[0058] In some embodiments, cathode material C1 and cathode material C2 may each contain the same or different binders. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0059] Furthermore, cathode material C1 and cathode material C2 may each contain the same or different conductive agents. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0060] In some implementations, positive electrode material C1 and positive electrode material C2 each contain the same or different positive electrode active material, binder and conductive agent.

[0061] [Negative electrode plate]

[0062] In the electrode assembly of this application, the double-sided asymmetric coated electrode can also be a negative electrode. In the negative electrode, the current collector is a negative current collector, and the electrode film layers L1 and L2 are negative electrode film layers LA1 and LA2, respectively; the negative electrode film layer LA1 contains negative electrode material A1, and the negative electrode film layer LA2 contains negative electrode material A2. The inventors have discovered that if the difference in the ultimate compaction density of negative electrode materials A1 and A2 is within a suitable range, it can significantly improve the cracking effect in the corner region of the electrode, while simultaneously leveraging the energy density advantage of negative electrode material A1, which has a higher ultimate compaction density. In some embodiments, the ultimate compaction density of negative electrode material A1 is 0.05 g / cm³ higher than that of negative electrode material A2. 3 ~1g / cm 3 In some embodiments, the limiting compaction density of the negative electrode material A1 is 0.05 g / cm³ higher than that of the negative electrode material A2. 3 ~0.15g / cm 3 (e.g., 0.05 g / cm) 3 ~0.07g / cm 3 0.07g / cm 3 ~0.1g / cm 3 or 0.1g / cm 3 ~0.15g / cm 3 ).

[0063] In some implementations, the ultimate compaction density of the negative electrode material A1 is ≥1.5 g / cm³. 3 The higher the ultimate compaction density, the better it is for improving the actual energy density of the electrode assembly.

[0064] As an improvement to this application, this application provides a thicker negative electrode material on the inner surface of the negative electrode current collector and a thinner negative electrode material on the outer surface, resulting in an asymmetrical thickness distribution on both sides of the negative electrode current collector. This utilizes the characteristic that thinner materials exhibit less tensile deformation for the same radius of curvature, further mitigating the drawback of easy cracking in corner areas and improving the safety of the secondary battery during cycle time. In some embodiments, the thickness ratio of the negative electrode film LA1 to the negative electrode film LA2 is 1.05 to 1.2:1.

[0065] The negative electrode current collector used for the negative electrode sheet can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can 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.).

[0066] Negative electrode material A1 and negative electrode material A2 may each contain the same or different negative electrode active materials. In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from one or more of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional 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. As an improvement of this application, the negative electrode active materials contained in negative electrode material A1 and negative electrode material A2 are each independently selected from at least one of graphite, hard carbon, silicon-doped graphite, silicon oxide, silicon, and mesophase carbon microspheres. In some embodiments, the negative electrode active material contained in negative electrode materials A1 and A2 is graphite.

[0067] In some embodiments, the particle size of the active material contained in the negative electrode material A1 or A2 can be adjusted to achieve a desired limiting compaction density. In some embodiments, the active material contained in the negative electrode material A1 or A2 has a D10 of 2µm to 7µm (e.g., 2µm to 4µm, 4µm to 6µm, or 6µm to 7µm), a D50 of 12µm to 22µm (e.g., 12µm to 14µm, 14µm to 16µm, 16µm to 18µm, 18µm to 20µm, or 20µm to 22µm), and / or a D90 of 42µm to 45µm (e.g., 42µm, 43µm, 44µm, or 45µm). In some embodiments, the degree of graphitization of the graphite can also be adjusted to achieve a desired limiting compaction density. In some embodiments, the degree of graphitization is 93% to 99% (e.g., 93% to 95%, 95% to 97%, or 97% to 99%).

[0068] In some embodiments, negative electrode material A1 and negative electrode material A2 may each contain the same or different binders. The binder may be selected from one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), sodium carboxymethyl cellulose (CMC-Na), and carboxymethyl chitosan (CMCS).

[0069] Furthermore, negative electrode material A1 and negative electrode material A2 may each contain the same or different conductive agents. The conductive agent may be selected from one or more of superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0070] In some embodiments, the negative electrode film layer may optionally include other additives, such as thickeners.

[0071] In some implementations, negative electrode material A1 and negative electrode material A2 each contain the same or different negative electrode active material, binder and conductive agent.

[0072] [Preparation of Electrodes]

[0073] Positive electrode materials C1 and C2 can be coated to form positive electrode films LC1 and LC2 on the two surfaces of the positive electrode current collector, respectively, or negative electrode materials A1 and A2 can be coated to form negative electrode films LA1 and LA2 on the two surfaces of the negative electrode current collector, respectively.

[0074] In some embodiments, electrode sheets can be prepared by dispersing the components of the electrode material, such as electrode active material, conductive agent, and binder, in a solvent (e.g., N-methylpyrrolidone) to form a slurry; coating the slurry onto a current collector, and then subjecting it to processes such as drying, rolling, and slitting to obtain the electrode sheet. The coating method can be selected from at least one of transfer coating, extrusion coating, gravure coating, spray coating, and dip coating.

[0075] The coating weight of the electrode material is related to the type of material and the thickness of the current collector. Generally speaking, for the same material, the greater the current collector thickness, the greater the required coating weight.

[0076] The coating weights Wc_1 and Wc_2 of the cathode material C1 and C2 can be selected as needed to achieve a suitable difference between them. In some embodiments, the coating weight Wc_1 of the cathode material C1 is 0–200 mg / 1540.25 mm higher than the coating weight Wc_2 of the cathode material C2. 2 (For example, 0-10 mg / 1540.25 mm) 2 10mg / 1540.25mm2 ~40mg / 1540.25mm 2 40mg / 1540.25mm 2 ~100mg / 1540.25mm 2 100mg / 1540.25mm 2 ~150mg / 1540.25mm 2 Or 150mg / 1540.25mm 2 ~200mg / 1540.25mm 2 In some more preferred embodiments, the coating weight Wc_1 of the cathode material C1 is 10 mg / 1540.25 mm higher than the coating weight Wc_2 of the cathode material C2. 2 ~40mg / 1540.25mm 2 (e.g., 10mg / 1540.25mm) 2 ~20mg / 1540.25mm 2 20mg / 1540.25mm 2 ~30mg / 1540.25mm 2 Or 30mg / 1540.25mm 2 ~40mg / 1540.25mm 2 Within the above range, the thickness difference between the two sides of the electrode after roll forming is appropriate, which has a significant effect on improving corner cracks and can prevent wrinkles from forming at the electrode edge due to the large difference in shrinkage stress on both sides of the current collector during electrode drying.

[0077] In some implementations, the coating weight Wa of the negative electrode material can be determined according to formula (1).

[0078]

[0079] In the formula, Q a It is the initial charge capacity (unit: mAh / g) of the negative electrode material A1 or A2, wt a W is the mass percentage of negative electrode material A1 or A2 in the negative electrode film. a This refers to the coating weight of the negative electrode material A1 or A2 (unit: g / 1540.25mm). 2 );Q c It is the initial charge capacity (unit: mAh / g) of the cathode material C2 or C1, wt c It is the mass percentage of the positive electrode material C2 or C1 in the positive electrode film layer, W c This refers to the coating weight of the positive electrode material C2 or C1 (unit: g / 1540.25mm). 2 ); CB is the capacity ratio of the negative electrode to the positive electrode. Wherein, when the negative electrode material is Al, Qc wt c and W c These are the parameters of the positive electrode material C2. When the negative electrode material is A2, Q... c wt c and W c These are the parameters of the cathode material C1.

[0080] Furthermore, after coating the electrode material onto the current collector, it needs to be dried and rolled to form the electrode sheet. In some embodiments, the rolling thickness of an electrode film layer can be determined according to formula (2):

[0081]

[0082] In the formula, H is the roll thickness of one electrode film layer (unit: mm), and W is the coating weight of the electrode material forming the electrode film layer (unit: g / 1540.25 mm). 2 PD is the compaction density of the electrode material forming the electrode film (unit: g / cm³). 3 ), T cc The thickness of the current collector (unit: mm).

[0083] The compaction density is related to the composition of the electrode material (e.g., the types of active materials included in the electrode material, and the proportions of each component). The desired compaction density can be obtained by adjusting the slurry formulation.

[0084] As an improvement of this application, the length of the coating areas of positive electrode materials C1 and C2 can be 0.5m to 10m (e.g., 0.5m to 1m, 1m to 3m, 3m to 5m, 5m to 7m, 7m to 9m or 9m to 10m), and the length of the coating areas of negative electrode materials A1 and A2 can be 0.5m to 10m (e.g., 0.5m to 1m, 1m to 3m, 3m to 5m, 5m to 7m, 7m to 9m or 9m to 10m). The length of the head of the coating area of ​​the negative electrode material can be 10mm to 30mm longer than the coating area of ​​the positive electrode material (e.g., 10mm to 20mm or 20mm to 30mm), and the length of the tail can be 10mm to 30mm longer than the coating area of ​​the positive electrode material (e.g., 10mm to 20mm or 20mm to 30mm), thereby ensuring a sufficient negative electrode / positive electrode capacity ratio (CB).

[0085] As an improvement of this application, the width of the coating areas of positive electrode material C1 and positive electrode material C2 can be 10mm to 500mm (e.g., 10mm to 50mm, 50mm to 100mm, 100mm to 200mm, 200mm to 300mm, 300mm to 400mm, or 400mm to 500mm), and the width of the coating areas of negative electrode material A1 and negative electrode material A2 can be 10mm to 500mm (e.g., 10mm to 50mm). The width of the area coated with the negative electrode material can be 4mm to 10mm (e.g., 4mm to 6mm, 6mm to 8mm, or 8mm to 10mm) larger than that of the area coated with the positive electrode material, ensuring that the area coated with the negative electrode material is large enough to prevent lithium deposition at the electrode edge.

[0086] [Electrode assemblies and their fabrication methods]

[0087] In the electrode assembly provided in this application, the positive electrode sheet can be a positive electrode sheet with double-sided asymmetric coating as described above, and the negative electrode sheet can be a regular negative electrode sheet; or, the negative electrode sheet can be a negative electrode sheet with double-sided asymmetric coating as described above, and the positive electrode sheet can be a regular positive electrode sheet. In some preferred embodiments, the electrode assembly provided in this application includes a positive electrode sheet with double-sided asymmetric coating as described above and a negative electrode sheet with double-sided asymmetric coating as described above.

[0088] In some embodiments, the electrode assembly provided in this application further includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0089] In some embodiments, the material of the separator can be selected from one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0090] In this application, the positive electrode, the negative electrode, and the optional separator can be manufactured into an electrode assembly by a winding process, and optionally, the electrode assembly can also be made into a flat shape by hot pressing.

[0091] Therefore, this application also provides a method for preparing an electrode assembly, comprising the following steps:

[0092] (1) Provide a positive electrode and a negative electrode; the positive electrode is a positive electrode as defined in any of the preceding items, and / or the negative electrode is a negative electrode as defined in any of the preceding items;

[0093] (2) The positive electrode and the negative electrode are wound together to form a wound structure, such that the positive electrode film LC1 is located inside the positive electrode film LC2 relative to the center of the wound structure, and / or the negative electrode film LA1 is located inside the negative electrode film LA2 relative to the center of the wound structure.

[0094] Figure 1 This is a cross-sectional view of an electrode assembly according to an embodiment of this application, wherein the positive electrode, the negative electrode, and the separator form a wound structure.

[0095] Figure 2 This is a schematic diagram of the layer structure of an electrode assembly according to an embodiment of this application. In this embodiment, a positive electrode film layer LC1 containing positive electrode material C1 is disposed on the inner surface of the positive electrode current collector, and a positive electrode film layer LC2 containing positive electrode material C2 is disposed on the outer surface of the positive electrode current collector. The thickness of LC1 is less than the thickness of LC2. A negative electrode film layer LA1 containing negative electrode material A1 is disposed on the inner surface of the negative electrode current collector, and a negative electrode film layer LA2 containing negative electrode material A2 is disposed on the outer surface of the negative electrode current collector.

[0096] As an improvement of this application, the width of the separator can be 10mm to 500mm (e.g., 10mm to 50mm, 50mm to 100mm, 100mm to 200mm, 200mm to 300mm, 300mm to 400mm or 400mm to 500mm). The width of the separator can be 4mm to 10mm wider than the width of the negative electrode material coating area (e.g., 4mm to 6mm, 6mm to 8mm or 8mm to 10mm) to ensure that the positive and negative electrode material coating areas will not short-circuit due to contact.

[0097] [Applications of Electrode Plates]

[0098] This application also provides the use of a positive electrode sheet or a negative electrode sheet as defined in any of the preceding claims in the fabrication of an electrode assembly; wherein the positive electrode sheet and / or the negative electrode sheet form a wound structure, the positive electrode film LC1 is located inside the positive electrode film LC2 relative to the center of the wound structure, and / or the negative electrode film LA1 is located inside the negative electrode film LA2 relative to the center of the wound structure.

[0099] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0100] [Rechargeable Battery]

[0101] In one embodiment of this application, a secondary battery is provided, the secondary battery comprising at least one electrode assembly as described above.

[0102] Typically, secondary batteries also include an electrolyte. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. A separator is placed between the positive and negative electrodes, primarily to prevent short circuits while allowing ions to pass through.

[0103] [Electrolytes]

[0104] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0105] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0106] In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0107] In some embodiments, the solvent may be selected from one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0108] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0109] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0110] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0111] This application does not impose any particular restrictions on the shape of the secondary battery. For example, Figure 3 This is an example of a square-structured secondary battery 5.

[0112] In some implementations, refer to Figure 4 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0113] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0114] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0115] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0116] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0117] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0118] In addition, this application also provides an electrical device, which includes one or more of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0119] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0120] Figure 8 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0121] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0122] Example

[0123] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0124] Preparation of positive electrode sheet:

[0125] A uniformly stirred slurry containing cathode material C1 is applied to the inner surface of the cathode current collector by extrusion or transfer, with a coating weight of Wc_1. A uniformly stirred slurry containing cathode material C2 is applied to the outer surface of the cathode current collector by extrusion or transfer, with a coating weight of Wc_2. The cathode sheets are then dried, rolled, and slit to obtain the cathode material. The formulation of cathode material C1 is: 96% active material, 2.5% conductive agent (2% conductive carbon black, 0.5% conductive carbon nanotubes), and 1.5% binder (polyvinylidene fluoride). The formulation of cathode material C2 differs from that of cathode material C1 only in the composition of the active material. The cathode active materials in the examples and comparative examples are selected from lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium cobalt oxide, lithium-rich manganese-based, and cobalt-free high-nickel materials.

[0126] Negative electrode preparation:

[0127] The uniformly stirred slurry containing negative electrode material A1 is applied to the inner surface of the negative electrode current collector by extrusion or transfer, with a coating weight of Wa_1. The uniformly stirred slurry containing negative electrode material A2 is applied to the outer surface of the negative electrode current collector by extrusion or transfer, with a coating weight of Wa_2. After drying, rolling, and slitting, the negative electrode sheet is obtained. The formulation of negative electrode material A1 is: 97% active material, 1.5% conductive agent (conductive carbon black), and 1.5% binder (sodium carboxymethyl cellulose). The formulation of negative electrode material A2 differs from that of positive electrode material A1 only in the composition of the active material.

[0128] Preparation of Comparative Examples 1 and 2:

[0129] Preparation of positive electrode sheet:

[0130] A mixed slurry Sc_1 is prepared by mixing the uniformly stirred positive electrode materials C1 and C2 at a mass ratio of 1:1. This slurry is then coated onto both sides of the positive electrode current collector by extrusion or transfer coating, with a coating weight of W_Sc_1. After drying, rolling, and slitting, the positive electrode sheet is obtained. The formulation of positive electrode material C1 is: 96% active material, 2.5% conductive agent, and 1.5% binder. The composition of positive electrode material C2 differs from that of positive electrode material C1.

[0131] Negative electrode preparation:

[0132] A mixed slurry Sa_1 is prepared by mixing uniformly stirred negative electrode materials A1 and A2 at a mass ratio of 1:1. This slurry is then coated onto both sides of the negative electrode current collector by extrusion or transfer coating, with a coating weight of W_Sa_1. After drying, rolling, and slitting, the negative electrode sheet is obtained. The formulation of negative electrode material A1 is: 97% active material, 1.5% conductive agent, and 1.5% binder. The composition of negative electrode material A2 differs from that of negative electrode material A1.

[0133] Preparation of Comparative Example 3:

[0134] The only difference in the preparation of the positive electrode sheet is that the mass ratio of the positive electrode materials C1 and C2 is changed to 7:3; everything else is the same as in Comparative Example 1.

[0135] The preparation of the negative electrode sheet was the same as that of Comparative Example 1.

[0136] Electrode assembly fabrication:

[0137] The battery cell employs a winding method that uses two layers of separator film sandwiching the positive electrode sheet. First, the separator film is loosely wound around the winding needle once. Then, the negative electrode sheet is fed in and wound half a turn. Finally, the positive electrode sheet is fed in, and the separator film is loosely wound once more. After the winding is completed, the electrode assembly is hot-pressed and shaped before being encapsulated in an aluminum-plastic film. After liquid injection, formation, shaping, and capacity testing, the finished battery cell is produced.

[0138] In the following examples and comparative examples, unless otherwise specified, the CB value is assumed to be CB = 1.07, and the positive electrode T... cc =0.013mm, negative electrode T cc =0.006mm.

[0139] In the following examples and comparative examples, the electrode active materials were all commercially available. Particle sizes, expressed as D10, D50, and D90, represent inherent properties of the active materials. The degree of graphitization is an inherent property of the graphite material. The sum of the stoichiometric ratios of lithium and nickel can be determined through the material composition.

[0140] In the table below, the coating weight (W) c or W a The units for all values ​​are mg / 1540.25 mm. 2 The units for both ultimate compaction density (PDmax) and design compaction density (design PD) are g / cm³. 3 Coating weight (W) c or W a ) is a given value, and the roll forming thickness (H) c or H a The value can be calculated using formula (2) as described above. PDmax can be obtained using the test method described above. The ratio of inner and outer ring surface thickness is: (inner ring surface thickness / outer ring surface thickness) × 100%.

[0141] First charge capacity (Q) c Q a This can be measured using the following exemplary methods:

[0142] 1. Electrode production:

[0143] 1.1 Weighing

[0144] Positive electrode formulation:

[0145] Active material powder: conductive agent: binder = 90:5:5

[0146] Negative electrode formulation:

[0147] Active material powder: conductive agent: binder = 92:2:6

[0148] 1.2 Slurry Preparation

[0149] Positive electrode slurry: Add N-methylpyrrolidone to make a slurry with a solid content of 40-45%, stir slowly at 800 rpm for 1 minute and stir quickly at 800 rpm for 15 minutes.

[0150] Negative electrode slurry: Add deionized water to make a slurry with a solid content of 40-50%, stir quickly at 1800 rpm for 60 minutes, and then stir slowly at 1800 rpm for 10 minutes.

[0151] 1.3 Coating

[0152] Using a 120µm doctor blade at a speed of 2.5cm / s, the slurry is uniformly applied to the current collector.

[0153] 1.4 Drying

[0154] First, let the film air dry naturally for 3 minutes, then put it in a 100℃ drying oven for more than 2 hours.

[0155] 1.5 Cold Press

[0156] Adjust the parameters of the roller press to achieve a compaction density of 3.3–3.6 g / cm³ for the ternary cathode material. 3 Lithium iron phosphate reaches 2-2.2 g / cm³. 3 .

[0157] 1.6 punching and weighing

[0158] The electrode sheets were cut using a die with a diameter of 15mm and then weighed.

[0159] 1.7 Drying

[0160] Vacuum degree -0.1MPa, vacuum time 1~15h, drying temperature 105℃.

[0161] 2. Button assembly:

[0162] The positive electrode (or negative electrode) is assembled together with the casing, nickel mesh, electrolyte, lithium sheet, and separator to form a button cell.

[0163] 3. Testing:

[0164] Positive electrode: Let stand for 3 hours; charge at a constant current of 0.1C to the specified voltage, then charge at a constant voltage to 50uA (recorded as charging capacity); let stand for 5 minutes; discharge at a constant current of 0.1C to the specified voltage (recorded as discharge capacity).

[0165] Negative electrode: Let stand for 5 hours; discharge at 0.05C constant current to 5mV, discharge at 50uA constant current to 5mV (recorded as discharge capacity); let stand for 5 minutes; discharge at 10uA constant current to 5mV; let stand for 5 minutes; charge at 0.1C constant current to 2V (recorded as charging capacity).

[0166] The specific capacity is obtained by dividing the charge / discharge capacity obtained from the test by the mass of the positive electrode powder (or the mass of the negative electrode powder).

[0167] I. Positive Electrode Materials and Electrodes

[0168] Following the preparation method described above, positive electrode sheets Examples 1-4, as shown in Table 1, were prepared using the difference in the ultimate compaction density of the positive electrode materials as a variable. Positive electrode sheets Examples 5-7, as shown in Table 1, were prepared using the ratio of the inner and outer surface thicknesses of the positive electrode sheets as a variable. These were then combined with the negative electrode sheets shown in Table 5 to form an electrode assembly.

[0169] Table 1. Design of positive electrode examples

[0170]

[0171] Set up the following comparative examples according to Tables 2 and 3:

[0172] Comparative Example 1: Cathode material C1 and cathode material C2 were mixed into a slurry and coated on both sides of the current collector, with the inner and outer surfaces having the same thickness.

[0173] Comparative Example 2: Positive electrode material C1 and positive electrode material C2 were mixed into a slurry and coated on both sides of the current collector. The thickness ratio of the inner and outer ring surfaces was 110.1%, the same as in Examples 1-4 above.

[0174] Comparative Example 3: The ultimate compaction density of cathode material C1 is lower than that of cathode material C2. They are coated on both sides of the current collector, and the thickness ratio of the inner and outer ring surfaces is 110.1%, which is the same as in Examples 1-4 above.

[0175] Table 2 Comparative Design of Positive Electrode Sheets

[0176]

[0177] Table 3 Comparative Design of Positive Electrode Sheets

[0178]

[0179] The material properties of the positive electrode active material used in the positive electrode examples and comparative examples are shown in Table 4, and the negative electrode design and graphite properties are shown in Table 5.

[0180] Table 4. Material properties of the active materials in the positive electrode examples and comparative examples.

[0181]

[0182] Table 5. Negative electrode designs and graphite properties used in the positive electrode examples and comparative examples.

[0183]

[0184] Three batteries were selected for each embodiment or comparative example and subjected to 800 cycles of 1C constant current charge-discharge in a 25°C constant temperature chamber. After full charging, the batteries were disassembled. Each battery has 42 corners. The positive electrode was taken from the corner and the presence of lithium deposition was observed visually. The number of corners where lithium deposition occurred on the positive electrode of the three samples was counted and the average value was calculated. The statistical results are shown in Table 6.

[0185] Table 6. Lithium plating status of the positive electrode sheet.

[0186]

[0187] The results above show that, compared to the comparative example's positive electrode, the positive electrode of this embodiment exhibits fewer lithium plating corners. The limiting compaction density of positive electrode material C1 is 0.5 g / cm³ higher than that of positive electrode material C2. 3 ~1g / cm 3 In embodiments where the ratio of inner to outer ring surface thickness is 110% to 112%, fewer corners are affected by lithium plating.

[0188] II. Negative Electrode Materials and Electrodes

[0189] Following the preparation method described above, negative electrode sheets Examples 1-4, as shown in Table 7, were prepared using the difference in ultimate compaction density of the negative electrode material as a variable. Negative electrode sheets Examples 5-8, as shown in Table 7, were prepared using the ratio of the inner and outer ring surface thicknesses of the negative electrode sheet as a variable, and were then combined with the positive electrode sheets shown in Table 10 to form an electrode assembly.

[0190] Table 7. Design of negative electrode sheet examples

[0191]

[0192]

[0193] Set up the following comparative examples according to Tables 8 and 9:

[0194] Comparative Example 1: A mixed slurry of negative electrode material C1 and negative electrode material C2 was coated on both sides of the current collector, with the same thickness on the inner and outer surfaces.

[0195] Comparative Example 2: A mixed slurry of negative electrode material C1 and negative electrode material C2 was coated on both sides of the current collector. The thickness ratio of the inner and outer ring surfaces was 107%, the same as in Examples 5-8 above.

[0196] Comparative Example 3: The ultimate compaction density of negative electrode material C1 is lower than that of negative electrode material C2. They are coated on both sides of the current collector, and the thickness ratio of the inner and outer ring surfaces is 107%, which is the same as in Examples 5-8 above.

[0197] Table 8 Comparative Design of Negative Electrode Sheets

[0198]

[0199] Table 9 Comparative Design of Negative Electrode Sheets

[0200]

[0201] The material properties of the active material (graphite) used in the negative electrode examples and comparative examples are shown in Table 10, and the positive electrode design and material properties of the active material are shown in Table 11.

[0202] Table 10 Material properties of the active material (graphite) used in the negative electrode examples and comparative examples.

[0203]

[0204] Table 11 shows the positive electrode designs and material properties of the active materials used in the negative electrode examples and comparative examples.

[0205]

[0206] Three batteries were selected for each embodiment or comparative example and subjected to 800 cycles of 1C constant current charge-discharge in a 25°C constant temperature chamber. After full charging, the batteries were disassembled. Each battery has 42 corners. The negative electrode was taken from the corner and the presence of lithium was observed by visual inspection. The number of corners where lithium deposition occurred on the negative electrode of the three samples was counted and the average value was calculated. The statistical results are shown in Table 12.

[0207] Table 12 Lithium plating status of the negative electrode sheet

[0208]

[0209] In summary, by asymmetrically coating electrode films on both sides of the current collector, a positive or negative electrode material with a higher ultimate compaction density can be coated on the inner surface of the current collector, while a positive or negative electrode material with a lower ultimate compaction density can be coated on the outer surface. Furthermore, by utilizing the characteristic that thinner thicknesses result in less tensile deformation for the same radius of curvature, the problem of cracks easily forming in corner areas of flat cells, which can lead to lithium plating, can be mitigated, thereby improving the safety of secondary battery cycling.

[0210] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An electrode assembly comprising at least one electrode sheet, the electrode sheet being formed into a wound structure by winding; the electrode sheet comprising a current collector, an electrode film layer L1, and an electrode film layer L2, the current collector having two surfaces opposite each other in its own thickness direction, the electrode film layer L1 and the electrode film layer L2 being respectively disposed on the two opposite surfaces; the electrode film layer L1 being located inside the electrode film layer L2 relative to the center of the wound structure; the electrode film layers L1 and L2 each comprising an electrode material; wherein, The ultimate compaction density of the electrode material contained in electrode film layer L1 is 0.05 g / cm³ higher than that of the electrode material contained in electrode film layer L2. 3 ~1g / cm 3 .

2. The electrode assembly according to claim 1, wherein the electrode sheet is a positive electrode sheet, the current collector is a positive current collector, and the electrode film L1 and electrode film L2 are positive electrode film LC1 and positive electrode film LC2, respectively; the positive electrode film LC1 contains positive electrode material C1, and the positive electrode film LC2 contains positive electrode material C2; wherein, The limiting compaction density of cathode material C1 is 0.05 g / cm³ higher than that of cathode material C2. 3 ~1g / cm 3 .

3. The electrode assembly according to claim 2, wherein, The limiting compaction density of cathode material C1 is 0.2 g / cm³ higher than that of cathode material C2. 3 ~0.5g / cm 3 .

4. The electrode assembly according to claim 2, wherein, The thickness ratio of the positive electrode film LC1 to the positive electrode film LC2 is 1.1~1.2:

1.

5. The electrode assembly according to claim 2 or 3, wherein, The positive electrode material C1 and the positive electrode material C2 are coated to form the positive electrode film layers LC1 and LC2 on the two surfaces of the current collector, respectively.

6. The electrode assembly according to claim 5, wherein, The coating weight Wc_1 of the positive electrode material C1 is 0~200mg / 1540.25mm higher than the coating weight Wc_2 of the positive electrode material C2. 2 .

7. The electrode assembly according to claim 6, wherein, The coating weight Wc_1 of the positive electrode material C1 is 10 mg / 1540.25 mm higher than the coating weight Wc_2 of the positive electrode material C2. 2 ~40mg / 1540.25mm 2 .

8. The electrode assembly according to claim 1, wherein the electrode sheet is a negative electrode sheet, the current collector is a negative current collector, and the electrode film L1 and electrode film L2 are negative electrode film LA1 and negative electrode film LA2, respectively; the negative electrode film LA1 contains negative electrode material A1, and the negative electrode film LA2 contains negative electrode material A2; wherein, The ultimate compaction density of the negative electrode material A1 is 0.05 g / cm³ higher than that of the negative electrode material A2. 3 ~1g / cm 3 .

9. The electrode assembly according to claim 8, wherein, The ultimate compaction density of the negative electrode material A1 is 0.05 g / cm³ higher than that of the negative electrode material A2. 3 ~0.15g / cm 3 .

10. The electrode assembly according to claim 8 or 9, wherein, The thickness ratio of the negative electrode film LA1 to the negative electrode film LA2 is 1.05~1.2:

1.

11. An electrode assembly, the electrode assembly comprising at least one positive electrode sheet, the positive electrode sheet being formed into a wound structure by winding; the positive electrode sheet comprising a positive current collector, a positive electrode film layer LC1, and a positive electrode film layer LC2; the positive current collector having two surfaces opposite each other in its own thickness direction, the positive electrode film layer LC1 and the positive electrode film layer LC2 being respectively disposed on the two opposite surfaces; the positive electrode film layer LC1 being located inside the positive electrode film layer LC2 relative to the center of the wound structure; the positive electrode film layer LC1 comprising a positive electrode material C1, and the positive electrode film layer LC2 comprising a positive electrode material C2; wherein, The limiting compaction density of cathode material C1 is 0.05 g / cm³ higher than that of cathode material C2. 3 ~1g / cm 3 ; The electrode assembly further includes at least one negative electrode sheet, which is formed into a wound structure by winding. The negative electrode sheet comprises a negative current collector, a negative electrode film LA1, and a negative electrode film LA2. The negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film LA1 and negative electrode film LA2 are respectively disposed on the two opposite surfaces. The negative electrode film LA1 is located inside the negative electrode film LA2 relative to the center of the wound structure. The negative electrode film LA1 comprises a negative electrode material A1, and the negative electrode film LA2 comprises a negative electrode material A2. The limiting compaction density of the negative electrode material A1 is 0.05 g / cm³ higher than that of the negative electrode material A2. 3 ~1g / cm 3 .

12. The electrode assembly according to claim 11, wherein in the positive electrode sheet, the limiting compaction density of the positive electrode material C1 is 0.2 g / cm³ higher than the limiting compaction density of the positive electrode material C2. 3 ~0.5g / cm 3 .

13. The electrode assembly according to claim 11, wherein the thickness ratio of the positive electrode film LC1 to the positive electrode film LC2 in the positive electrode sheet is 1.1~1.2:

1.

14. The electrode assembly according to claim 11, wherein in the positive electrode sheet, the positive electrode material C1 and the positive electrode material C2 are respectively formed into the positive electrode film layers LC1 and LC2 on two surfaces of the current collector by coating; the coating weight Wc_1 of the positive electrode material C1 is 0~200 mg / 1540.25 mm higher than the coating weight Wc_2 of the positive electrode material C2. 2 .

15. The electrode assembly according to any one of claims 11-14, wherein in the negative electrode sheet, the limiting compaction density of the negative electrode material A1 is 0.05 g / cm³ higher than the limiting compaction density of the negative electrode material A2. 3 ~0.15g / cm 3 .

16. The electrode assembly according to any one of claims 11-14, wherein the thickness ratio of the negative electrode film LA1 to the negative electrode film LA2 in the negative electrode sheet is 1.05~1.2:

1.

17. A secondary battery comprising an electrode assembly according to any one of claims 1-16.

18. A battery module comprising an electrode assembly according to any one of claims 1-16 or a secondary battery according to claim 17.

19. A battery pack comprising an electrode assembly according to any one of claims 1-16, a secondary battery according to claim 17, or a battery module according to claim 18.

20. An electrical device comprising an electrode assembly according to any one of claims 1-16, a secondary battery according to claim 17, a battery module according to claim 18, or a battery pack according to claim 19.

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