Electrode assembly, electrochemical device, and electronic device

Abstract

This utility model discloses an electrode assembly, including a positive electrode, a negative electrode, and a separator. The electrode assembly has a wound structure. The negative electrode includes a negative current collector and an active material layer disposed on at least one side of the negative current collector. The negative current collector includes a straight section and a corner section connected to each other. The straight section and the corner section are alternately arranged along the winding direction of the negative current collector. Foamed layers with a porous structure are disposed on both sides of the corner section. In addition, this application also discloses an electrochemical device and an electronic device. By providing a porous foamed layer in the corner section of the negative current collector, the stress concentration problem in the corner section is alleviated, while the electrolyte is absorbed and stored in the foamed layer. This continuously replenishes the electrolyte consumed during the cycle in the corner section, reduces the probability of lithium plating in the corner section, thereby improving the overall performance and service life of the electrochemical device and providing a more stable power supply to the electronic device.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and in particular to electrode components, electrochemical devices and electronic equipment. Background Technology

[0002] Due to their advantages such as compact structure, high energy density and mature technology, wound lithium batteries are widely used in portable electronic devices, electric vehicles and other fields.

[0003] However, in fast-charging scenarios, wound lithium batteries are prone to lithium plating at the negative electrode, a problem that severely impacts the battery's electrical performance, safety performance, and lifespan. Specifically, during the winding process, the radius of curvature of the negative electrode current collector corner changes, causing mechanical stress to concentrate at the corner. Simultaneously, during charging and discharging of the wound cell, the expansion coefficients of the copper foil (the negative electrode current collector) and the active material layer differ. These two factors work together to generate dynamic shear stress at the contact surface between the negative electrode current collector corner and the active material layer. Since the copper foil lacks the function of buffering stress at the corner, it cannot disperse or absorb this stress, leading to non-uniform deposition of lithium ions at the corner, ultimately causing lithium plating at the negative electrode corner of the wound cell.

[0004] Lithium plating on the negative electrode can reduce battery capacity and charge / discharge efficiency, and may also puncture the separator, causing internal short circuits and serious safety issues, which greatly limits the application of wound lithium batteries in the field of fast charging. Utility Model Content

[0005] The main objective of this application is to provide a negative electrode, an electrochemical device, and an electronic device, which aim to improve the overall performance and service life of the electrochemical device.

[0006] To achieve the above objectives, this application proposes an electrode assembly, including a positive electrode sheet, a negative electrode sheet, and a separator. The electrode assembly has a wound structure. The negative electrode sheet includes a negative current collector and an active material layer disposed on at least one side of the negative current collector. The negative current collector includes a straight section and a corner section connected to each other. The straight section and the corner section are alternately arranged along the winding direction of the negative current collector. Foaming layers are disposed on both sides of the corner section, and the foaming layers have a porous structure.

[0007] In some implementations, the length of the foamed layer along the length direction of the negative electrode current collector is A, and satisfies 2mm≤A≤15mm.

[0008] In some embodiments, the thickness of the foamed layer is B along the thickness direction of the negative electrode current collector, and the thickness of the negative electrode current collector is C, satisfying 0.5C≤B≤0.8C.

[0009] In some implementations, the thickness B of the foam layer ranges from 2µm to 9.6µm.

[0010] In some implementations, the thickness C of the negative electrode current collector ranges from 4 μm to 12 μm.

[0011] In some embodiments, the porosity of the foamed layer is in the range of 75% to 85%, and the pore size of the foamed layer is in the range of 5µm to 50µm.

[0012] In some embodiments, the foaming layer includes a bottom layer and a top layer disposed vertically, the bottom layer being in contact with the negative electrode current collector, and the top layer being located on the side of the bottom layer facing away from the negative electrode current collector.

[0013] In some implementations, the porosity of the bottom layer is 75%, and the pore size of the bottom layer is in the range of 20 μm to 50 μm; the porosity of the top layer is 85%, and the pore size of the top layer is in the range of 5 μm to 10 μm.

[0014] Another aspect of this application provides an electrochemical device comprising the electrode assembly described above.

[0015] This application also proposes an electronic device comprising the aforementioned electrochemical device.

[0016] This application proposes an electrode assembly, an electrochemical device, and an electronic device. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative current collector and an active material layer. By setting a porous foamed layer at the corner section of the negative current collector, not only can the stress concentration problem at the corner section be alleviated, but the electrolyte can also be absorbed and stored in the foamed layer. This continuously replenishes the electrolyte consumed during the cycle at the corner section, reducing the probability of lithium plating at the corner section. This improves the overall performance and service life of the electrochemical device and provides a more stable power supply to the electronic device. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the negative electrode sheet before it is wound in one embodiment of this application; Figure 2 This is a schematic diagram of the negative electrode current collector and the foaming layer in another embodiment of this application; Figure 3 This is a schematic diagram of the structure of the foamed layer in another embodiment of this application.

[0018] Explanation of reference numerals in the attached figures: Negative electrode 100; negative electrode current collector 110; straight section 111; corner section 112; active material layer 120; foaming layer 200; bottom layer 210; surface layer 220. Detailed Implementation

[0019] The 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 a part of the embodiments in this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0020] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0021] It should also be noted that when a component is described as "fixed to" or "set on" another component, it can be directly on the other component or there may be an intervening component present. When a component is described as "connected to" another component, it can be directly connected to the other component or there may be an intervening component present.

[0022] Furthermore, the use of terms such as "first" and "second" in this application is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed in this application.

[0023] Please see Figure 1 , Figure 1 This is a schematic diagram of the structure of the negative electrode 100 before winding in one embodiment of this application. This application provides an electrode assembly including a positive electrode, a negative electrode 100, and a separator. The electrode assembly has a wound structure. The negative electrode 100 includes a negative electrode current collector 110 and an active material layer 120 disposed on at least one side of the negative electrode current collector 110. The negative electrode current collector 110 includes a straight section 111 and a corner section 112 connected to each other. The straight section 111 and the corner section 112 are alternately arranged along the winding direction of the negative electrode current collector 110. Foamed layers 200 are disposed on both sides of the corner section 112, and the foamed layers 200 have a porous structure.

[0024] In this embodiment, the electrode assembly includes a positive electrode sheet, a negative electrode sheet 100, and a separator disposed between the positive and negative electrode sheets 100, all stacked and wound together. The negative electrode sheet 100 includes a negative current collector 110, an active material layer 120, and a foamed layer 200. Specifically, the negative current collector 110 is a copper foil and includes a straight section 111 and a corner section 112. Since the electrode assembly proposed in this application has a wound structure, when the negative electrode sheet 100 is wound, the negative current collector 110 inside the negative electrode sheet 100 will also be wound simultaneously. After the winding process, the corner section 112 of the negative current collector 110 will be located at the corner of the wound cell, while the straight section 111 will be located at the straight section of the wound cell.

[0025] During the winding process, the radius of curvature of the corner segment 112 of the negative electrode current collector 110 changes, causing mechanical stress to concentrate at the corner segment 112. Simultaneously, during the charging and discharging process of the wound cell, there is a difference in the coefficient of expansion between the copper foil (the negative electrode current collector 110) and the active material layer 120. Under the combined effect of these two factors, dynamic shear stress is generated at the contact surface between the corner segment 112 of the negative electrode current collector 110 and the active material layer 120. However, the copper foil itself does not have the function of buffering the stress at the corner segment 112, which leads to non-uniform deposition of lithium ions at the corner segment 112 of the negative electrode current collector 110, ultimately causing lithium plating at the corner of the wound cell. To improve this phenomenon, such as... Figure 1 As shown, foamed layers 200 are provided on both the upper and lower sides of the corner segment 112. In this embodiment, the foamed layers 200 can be formed on the corner segment 112 of the negative electrode current collector 110 by coating or dispensing. After the foamed layers 200 are formed on the negative electrode current collector 110, the active material layer 120 is then disposed on both sides of the negative electrode current collector 110. The foamed layers 200 are located between the active material layer 120 and the corner segment 112 of the negative electrode current collector 110, acting as a buffer between the two.

[0026] The foam layer 200 is formed of a porous polymer foam material. In this embodiment, the foam layer 200 can be made of polyvinylidene fluoride-hexafluoropropylene, which has good adhesion to the copper foil and is not easily detached. It is understood that in other embodiments, the foam layer 200 can also be made of any of the following porous polymers: thermoplastic polyurethane, styrene-butadiene rubber, soluble polyimide, etc., or a composite material formed from these materials, as long as the foam layer 200 has a buffering effect and exhibits a porous structure. Specifically, because such materials have good flexibility, they can effectively buffer the stress of the corner segment 112, thereby improving the lithium plating phenomenon at the corner segment 112. Furthermore, because the foam layer 200 has a porous structure, it can absorb and store electrolyte within the foam layer 200, continuously replenishing the electrolyte consumed during the cycle at the corner segment 112, further reducing the possibility of lithium plating at the corner segment 112, thereby improving the overall performance and lifespan of the battery.

[0027] like Figure 2 As shown, Figure 2 This is a schematic diagram of the negative electrode current collector 110 and the foamed layer 200 in one embodiment of this application. In some embodiments, the length of the foamed layer 200 along the length direction of the negative electrode current collector 110 is A, and satisfies 2mm≤A≤15mm.

[0028] In this embodiment, the dimension of the foamed layer 200 along the length of the negative electrode current collector 110 is denoted as the length of the foamed layer 200, and the length of the foamed layer 200 is defined as A, with the value of A set in the range of 2mm to 15mm. For example, in actual production, the length A of the foamed layer 200 can be set to different values ​​such as 2mm, 8mm, and 15mm according to different design requirements. In actual production, the value of the length A of the foamed layer 200 is adjusted according to the number of winding layers and the thickness of the wound cell. Its main purpose is to enable the foamed layer 200 to cover the corner section 112 of the negative electrode current collector 110, so as to achieve the functions of buffering stress and accumulating electrolyte. Specifically, setting the length A of the foam layer 200 to 2mm is to reduce the space occupied by the foam layer 200 in the negative electrode 100, thereby reducing the overall volume of the electrode assembly and increasing the energy density. Setting the length A of the foam layer 200 to 15mm is to ensure that the foam layer 200 can completely cover the corner section 112 and effectively reduce the stress concentration in the corner section 112. Setting the length A of the foam layer 200 to 8mm can reduce the volume while ensuring that the foam layer 200 covers the corner section 112, thereby increasing the energy density.

[0029] like Figure 2As shown, in some embodiments, along the thickness direction of the negative electrode current collector 110, the thickness of the foam layer 200 is B, the thickness of the negative electrode current collector 110 is C, and the condition 0.5C≤B≤0.8C is met.

[0030] In a preferred embodiment, the thickness B of the foam layer 200 ranges from 2 μm to 9.6 μm, and the thickness C of the negative electrode current collector 110 ranges from 4 μm to 12 μm.

[0031] In this embodiment, looking along the thickness direction of the negative electrode current collector 110, the thickness of the foamed layer 200 is denoted as B, and the thickness of the negative electrode current collector 110 is denoted as C. The value of the thickness B of the foamed layer 200 is set according to the thickness B of the negative electrode current collector 110, and satisfies 0.5C≤B≤0.8C. Specifically, the thickness C of the negative electrode current collector 110 can be set between 4µm and 12µm. In actual production, the thickness C of the negative electrode current collector 110 can be set to different values ​​such as 4µm, 10µm, and 12µm according to the specifications and performance of the battery to be produced. Specifically, taking the thickness C of the negative electrode current collector 110 as 4µm as an example, if the thickness C of the negative electrode current collector 110 is less than 4µm, the negative electrode current collector 110 is too thin and lacks mechanical strength. During the manufacturing process such as the winding of the negative electrode sheet 100 and battery packaging, the excessively thin negative electrode current collector 110 is prone to deformation and breakage, thereby affecting the yield. Taking a thickness C of 12µm for the negative electrode current collector 110 as an example, if the thickness C of the negative electrode current collector 110 is greater than 12µm, the negative electrode current collector 110 will be too thick, increasing the weight and volume of the negative electrode sheet 100 and reducing the energy density of the battery. This is detrimental to portable electronic devices and electric vehicles that pursue lightweight design and high energy density. On the other hand, although an excessively thick current collector has lower resistance, it increases the transport path of lithium ions between the current collector and the active material layer 120, increasing the resistance to lithium ion diffusion and affecting the lithium ion insertion and extraction process, leading to a decrease in the battery's charge and discharge performance. Taking a thickness C of 10µm for the negative electrode current collector 110 as an example, it is possible to ensure the structural strength of the negative electrode current collector 110 while maintaining the battery's energy density.

[0032] Here, since the thickness B of the foamed layer 200 is between 0.5 and 0.8 times the thickness C of the negative electrode current collector 110, the thickness B of the foamed layer 200 is set between 2 μm and 9.6 μm.

[0033] Specifically, if the thickness B of the foam layer 200 is less than 0.5 times the thickness C of the negative electrode current collector 110, the thickness of the foam layer 200 is too low, resulting in insufficient strength and inability to provide effective support for the corner segment 112 of the negative electrode current collector 110, leading to poor buffering effect. If the thickness B of the foam layer 200 is greater than 0.8 times the thickness C of the negative electrode current collector 110, the thickness of the foam layer 200 is too high, which will increase the overall volume of the electrode assembly and reduce the energy density.

[0034] In one specific embodiment, the thickness C of the negative electrode current collector 110 is set to 4 μm. In this case, the thickness B of the foamed layer 200 can be set between 2 μm and 3.2 μm, for example, 2 μm, 2.5 μm, or 3.2 μm. Specifically, setting the thickness C of the foamed layer 200 to 2 μm ensures that the foamed layer 200 can effectively buffer the stress concentrated at the corner segment 112; setting the thickness C of the foamed layer 200 to 3.2 μm ensures that the foamed layer 200 does not affect the overall volume of the electrode assembly, thus avoiding a decrease in energy density; setting the thickness C of the foamed layer 200 to 2.5 μm can alleviate the stress between the active material layer 120 and the corner segment 112 without affecting the energy density.

[0035] It is understood that, in another embodiment, when the thickness C of the negative electrode current collector 110 is set to 12 μm, the thickness C of the foamed layer 200 is set in the range of 6 μm to 9.6 μm; in yet another embodiment, when the thickness C of the negative electrode current collector 110 is set to 10 μm, the thickness C of the foamed layer 200 is set in the range of 5 to 8 μm; and so on, satisfying 0.5C ≤ B ≤ 0.8C. Therefore, by limiting the thickness B of the foamed layer 200 to between 0.5 and 0.8 times the thickness C of the negative electrode current collector 110, this application allows the foamed layer 200 to act as a buffer between the active material layer 120 and the corner segment 112 without affecting the energy density, thereby improving the lithium plating phenomenon at the corner segment 112 and improving the battery performance and lifespan.

[0036] In some embodiments, the porosity of the foam layer 200 is in the range of 75% to 85%, and the pore size of the foam layer 200 is in the range of 5µm to 50µm.

[0037] In this embodiment, the foamed layer 200 has a porous structure and is located between the corner segment 112 of the negative electrode current collector 110 and the active material layer 120. The porosity of the foamed layer 200 can be set in the range of 75% to 85%, for example, setting the porosity of the foamed layer 200 to different values ​​such as 75%, 80%, and 85%. Specifically, taking a porosity of 75% as an example, if the porosity is lower than 75%, the capacity of the foamed layer 200 to store electrolyte and its buffering effect will be reduced. Taking a porosity of 85% for the foam layer 200 as an example, if the porosity is higher than 85%, the mechanical strength of the foam layer 200 will decrease. During the winding process of the negative electrode sheet 100, it is prone to collapse, breakage, or peeling, generating dust or debris, which can lead to short circuits. Furthermore, the higher the porosity of the foam layer 200, the smaller its contact area with the negative electrode current collector 110. When the porosity is higher than 85%, the foam layer 200 is prone to detachment. Setting the porosity of the foam layer 200 to 80% can improve the stability of the connection between the foam layer 200 and the corner section 112 while ensuring the buffering effect.

[0038] In a preferred embodiment, along the direction from the corner segment 112 toward the active material layer 120, the porosity of the foamed layer 200 gradually increases from 75% to 85%, and the pore size of the foamed layer 200 gradually decreases from 50µm to 5µm. Specifically, the foamed layer 200 has a smaller porosity and larger pore size on the side closer to the corner segment 112, which can improve mechanical strength and prevent the current collector from breaking, thus affecting battery safety. The foamed layer 200 has a larger porosity and smaller pore size on the side closer to the active material layer 120, which can improve capillary adsorption force, absorb more electrolyte and store it in the foamed layer 200, continuously replenishing the electrolyte consumed by the corner segment 112 during the cycling process, thereby improving the lithium plating phenomenon of the corner segment 112.

[0039] like Figure 3 As shown, Figure 3 This is a schematic diagram of the structure of the foamed layer 200 in a preferred embodiment of this application. In this embodiment, the foamed layer 200 includes a bottom layer 210 and a top layer 220 disposed vertically. The bottom layer 210 is in contact with the negative electrode current collector 110, and the top layer 220 is located on the side of the bottom layer 210 facing away from the negative electrode current collector 110. The porosity of the bottom layer 210 is 75%, and the pore size of the bottom layer 210 is in the range of 20 μm to 50 μm; the porosity of the top layer 220 is 85%, and the pore size of the top layer 220 is in the range of 5 μm to 10 μm.

[0040] In this embodiment, the foamed layer 200 is divided into a bottom layer 210 and a top layer 220 arranged vertically. The bottom layer 210 is located on the side of the foamed layer 200 closer to the negative electrode current collector 110, and the top layer 220 is located on the side of the foamed layer 200 closer to the active material layer 120. The porosity of the bottom layer 210 is 75%, and the porosity of the top layer 220 is 85%. The pore size of the bottom layer 210 is larger than that of the top layer 220. This allows the bottom layer 210, closer to the negative electrode current collector 110, to store more electrolyte than the top layer 220, and provides sufficient deformation space when the corner section 112 of the negative electrode current collector 110 is under pressure, thereby improving the mechanical buffering effect of the foamed layer 200. The pore size of the bottom layer 210 can be set to different values ​​such as 20µm, 35µm, and 50µm. Taking a pore size of 20µm for the bottom layer 210 as an example, if the pore size is less than 20µm, the ability of the bottom layer 210 to store electrolyte will be weakened; taking a pore size of 50µm for the bottom layer 210 as an example, if the pore size is greater than 50µm, the mechanical support of the bottom layer 210 will be reduced, resulting in poor buffering effect; setting the pore size of the bottom layer 210 to 35µm can balance the buffering effect and electrolyte storage capacity of the bottom layer 210.

[0041] Furthermore, compared to the bottom layer 210, the surface layer 220 has a smaller pore size and higher porosity. This gives the surface layer 220 a stronger capillary adsorption force than the bottom layer 210, effectively attracting and locking in the electrolyte, preventing it from easily leaking out when the battery is shaken or squeezed. The pore size of the surface layer 220 can be set to different values ​​such as 5µm, 8µm, and 10µm. Taking a pore size of 5µm as an example, if the pore size is lower than 5µm, the electrolyte will be excessively locked in the surface layer 220, making it difficult for the foamed layer 200 to continuously provide electrolyte to the corner section 112. Taking a pore size of 10µm as an example, if the pore size is higher than 10µm, the electrolyte cannot be locked in, and it will leak out more quickly. Setting the pore size to 8µm can adsorb and lock in an appropriate amount of electrolyte, preventing the electrolyte from being excessively locked in or leaking out too quickly.

[0042] This application further proposes an electrochemical device including the aforementioned electrode assembly. The specific structure of the electrode assembly is as described in the above embodiments. Since the electrochemical device adopts all the technical solutions of all the above embodiments, it possesses at least all the technical effects brought about by the technical solutions of the above embodiments, which will not be elaborated upon here. The electrochemical device is a wound lithium battery.

[0043] This application further proposes an electronic device that includes the aforementioned electrochemical device for providing electrical energy to the electronic device.

[0044] In summary, this application proposes an electrode assembly, an electrochemical device, and an electronic device. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The negative electrode 100 includes a negative current collector 110 and an active material layer 120. By providing a porous foamed layer 200 at the corner section 112 of the negative current collector 110, the stress concentration problem at the corner section 112 can be alleviated. The electrolyte can also be absorbed and stored in the foamed layer 200, continuously replenishing the electrolyte consumed during the cycle at the corner section 112, reducing the possibility of lithium plating at the corner section 112, thereby improving the overall performance and service life of the electrochemical device and providing a more stable power supply to the electronic device.

[0045] The above description is only a part or preferred embodiment of this application. Neither the text nor the drawings should limit the scope of protection of this application. All equivalent structural transformations made using the content of this application's specification and drawings under the overall concept of this application, or direct / indirect applications in other related technical fields, are included within the scope of protection of this application.

Claims

1. An electrode assembly comprising a positive electrode, a negative electrode, and a separator, wherein the electrode assembly has a wound structure, and the negative electrode comprises a negative current collector and an active material layer disposed on at least one side of the negative current collector, characterized in that, The negative electrode current collector includes a straight section and a corner section connected to each other. The straight section and the corner section are alternately arranged along the winding direction of the negative electrode current collector. Foaming layers are provided on both sides of the corner section, and the foaming layers have a porous structure.

2. The electrode assembly according to claim 1, characterized in that, Along the length direction of the negative electrode current collector, the length of the foamed layer is A, and satisfies 2mm≤A≤15mm.

3. The electrode assembly according to claim 2, characterized in that, Along the thickness direction of the negative electrode current collector, the thickness of the foamed layer is B, the thickness of the negative electrode current collector is C, and the condition 0.5C≤B≤0.8C is met.

4. The electrode assembly according to claim 3, characterized in that, The thickness B of the foamed layer ranges from 2µm to 9.6µm.

5. The electrode assembly according to claim 4, characterized in that, The thickness C of the negative electrode current collector ranges from 4µm to 12µm.

6. The electrode assembly according to any one of claims 1 to 5, characterized in that, The porosity of the foamed layer is in the range of 75% to 85%, and the pore size of the foamed layer is in the range of 5µm to 50µm.

7. The electrode assembly according to claim 6, characterized in that, The foamed layer includes a bottom layer and a top layer distributed vertically. The bottom layer is in contact with the negative electrode current collector, and the top layer is located on the side of the bottom layer that faces away from the negative electrode current collector.

8. The electrode assembly according to claim 7, characterized in that, The porosity of the bottom layer is 75%, and the pore size of the bottom layer is in the range of 20um to 50um; the porosity of the surface layer is 85%, and the pore size of the surface layer is in the range of 5um to 10um.

9. An electrochemical device, characterized in that, Includes the electrode assembly according to any one of claims 1 to 8.

10. An electronic device, characterized in that, Includes the electrochemical device as described in claim 9.

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