Electrochemical device and electric device

Abstract

The application discloses an electrochemical device, comprising a first electrode assembly of a laminated structure, a second electrode assembly of a laminated structure and a separator. The first electrode assembly comprises a first negative electrode. The second electrode assembly comprises a second negative electrode. The first negative electrode comprises a first negative electrode active material, and the second negative electrode comprises a second negative electrode active material. The graphitization degree G1 of the first negative electrode active material and the graphitization degree G2 of the second negative electrode active material satisfy: G2-G1 >= 0.5%. The separator comprises a plurality of isolation portions and a plurality of bending portions. Any two adjacent electrodes are provided with an isolation portion, and any two adjacent isolation portions are connected through a bending portion. Through the above mode, the electrochemical device has excellent structural stability while taking into account high energy density and high rate charge and discharge capability, and can improve the use safety of the electrochemical device.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to an electrochemical device and an electrical device. Background Technology

[0002] With the development of technology, electronic products such as mobile phones, laptops, and drones have greatly enriched people's daily lives. Lithium-ion batteries, with their advantages of high energy density, high operating voltage, and long lifespan, are widely used in electronic products. On the one hand, people expect lithium-ion batteries to have high energy density to meet the requirements of long battery life; on the other hand, they also expect lithium-ion batteries to have good high-rate charge and discharge capabilities to meet the needs of emergency charging and high-rate applications. Summary of the Invention

[0003] The purpose of this application is to provide an electrochemical device and an electrical device that, while taking into account the high energy density and high rate charge / discharge capability of the electrochemical device, improve the structural stability of the electrochemical device.

[0004] In a first aspect, this application provides an electrochemical device comprising a first electrode assembly with a stacked structure, a second electrode assembly with a stacked structure, and a separator. The first electrode assembly includes a first positive electrode and a first negative electrode. The second electrode assembly includes a second positive electrode and a second negative electrode. Along a first direction, the first positive electrode and the first negative electrode are stacked sequentially, and the second positive electrode and the second negative electrode are stacked sequentially. The first negative electrode includes a first negative electrode active material, and the second negative electrode includes a second negative electrode active material. The graphitization degree G1 of the first negative electrode active material and the graphitization degree G2 of the second negative electrode active material satisfy: G2-G1≥0.5%. The separator includes multiple insulating portions and multiple bent portions. An insulating portion is disposed between any two adjacent electrodes, and any two adjacent insulating portions are connected by a bent portion.

[0005] The lower the graphitization degree of the negative electrode active material, the faster its lithium-ion insertion and extraction rates. Therefore, the first electrode assembly can accommodate a higher charge / discharge rate compared to the second electrode assembly. In other words, the first electrode assembly can function as a fast-charging system, while the second electrode assembly can function as a slow-charging system. The fast-charging system can meet the needs of emergency charging in critical situations and high-rate discharge in high-rate applications; the slow-charging system can meet the needs of regular use and ensure that the electrochemical device has a high capacity, thus meeting the long-term battery life requirements of electrical devices. Furthermore, by using a single separator membrane to assemble the first and second electrode assemblies into a single unit through Z-shaped folding, misalignment and displacement of the first and second electrode assemblies under external impact can be suppressed, thereby improving the stability of the internal structure of the electrochemical device and reducing the risk of internal short circuits. Simultaneously, since no additional adhesive methods are needed to fix the first and second electrode assemblies, the assembly difficulty of the first and second electrode assemblies is reduced, and manufacturing efficiency is improved.

[0006] In some embodiments, the first electrode assembly includes a first single-sided electrode. The first single-sided electrode is located on the side of the first electrode assembly closest to the second electrode assembly and has a first surface uncoated with an active material layer. The second electrode assembly includes a second single-sided electrode with the same polarity as the first single-sided electrode. The second single-sided electrode is located on the side of the second electrode assembly closest to the first electrode assembly and has a second surface uncoated with an active material layer. Along a first direction, the second surface and the first surface are disposed opposite each other. The fact that adjacent first and second single-sided electrodes in the first and second electrode assemblies have the same polarity reduces the risk of internal short circuits when the first and second electrode assemblies come into contact due to misalignment caused by external impact, thereby improving the safety of the electrochemical device.

[0007] In some implementations, the electrochemical device satisfies G1≤95%. In this case, the first electrode assembly can adapt to a larger charge and discharge rate, thereby better meeting the needs of emergency charging in emergency situations and high-rate discharge in high-rate applications.

[0008] In some implementations, the electrochemical device satisfies G2≥95.5%. In this case, the second negative electrode active material has a high degree of regularity, which can provide more lithium ion storage sites, thereby enabling the electrochemical device to have a high energy density and better meet the long-endurance requirements of electrical devices.

[0009] In some embodiments, the bonding strength between the isolator and the electrode satisfies: F ≥ 5 N / m. In this case, when the electrochemical device is subjected to external impact, the isolator can better suppress misalignment and movement between the electrodes, thereby further reducing the risk of internal short circuits in the electrochemical device.

[0010] In some embodiments, the isolation portion and the bending portion are integrally formed, which helps to ensure the overall structural strength of the isolation membrane, thereby better suppressing the misalignment and movement between the first electrode assembly and the second electrode assembly, as well as between electrodes, and improving the stability of the internal structure of the electrochemical device.

[0011] In some embodiments, the number of first electrode assemblies is at least two. The number of second electrode assemblies is at least one. Along the first direction, a second electrode assembly is sandwiched between two adjacent first electrode assemblies. Thus, when the first electrode assemblies are subjected to high-rate charge and discharge, the second electrode assembly can promote the dissipation of heat from the first electrode assemblies, thereby reducing the local temperature rise of the electrochemical device and improving the safety of the electrochemical device.

[0012] In some embodiments, the number of first electrode components is at least one. The number of second electrode components is at least two, with a first electrode component sandwiched between two adjacent second electrode components along the first direction. Therefore, when the first electrode components are subjected to high-rate charge and discharge, the heat generated by the first electrode components is facilitated to diffuse to adjacent sides, thereby reducing the local temperature rise of the electrochemical device and improving the safety of the electrochemical device.

[0013] In some embodiments, the electrochemical device further includes a third negative electrode plate disposed between the first electrode assembly and the second electrode assembly. The first electrode assembly includes a first positive electrode plate adjacent to the third negative electrode plate, the first positive electrode plate including a first positive current collector and a first positive active layer located on two surfaces of the first positive current collector opposite each other along a first direction; the second electrode assembly includes a second positive electrode plate adjacent to the third negative electrode plate, the second positive electrode plate including a second positive current collector and a second positive active layer located on two surfaces of the second positive current collector opposite each other along a first direction. An isolation portion is provided between the third negative electrode plate and the first electrode assembly. An isolation portion is provided between the third negative electrode plate and the second electrode assembly. The third negative electrode plate includes a third negative current collector, a third negative active layer, and a fourth negative active layer. The third negative active layer is located on the side of the third negative current collector closer to the first electrode assembly. The third negative active layer includes a third negative active material. The fourth negative electrode active layer is located on the side of the third negative electrode current collector closest to the second electrode assembly. The fourth negative electrode active layer comprises a fourth negative electrode active material. The graphitization degree G3 of the third negative electrode active material and the graphitization degree G4 of the fourth negative electrode active material satisfy: |G4-G2|≤0.2%, |G3-G1|≤0.2%. Since there is no longer a single-sided electrode between the first and second electrode assemblies, space waste is reduced, which is beneficial for improving the energy density of the electrochemical device.

[0014] In some embodiments, the electrochemical device further includes a housing. A first electrode assembly, a second electrode assembly, and a separator are housed within the housing. A first negative electrode includes a first negative electrode tab. A second negative electrode includes a second negative electrode tab. The first and second negative electrode tabs are electrically connected within the housing.

[0015] In some embodiments, the electrochemical device further includes a housing. A first electrode assembly, a second electrode assembly, a third negative electrode, and a separator are housed within the housing. The first negative electrode includes a first negative electrode tab. The second negative electrode includes a second negative electrode tab. The third negative electrode includes a third negative electrode tab. The first, second, and third negative electrode tabs are electrically connected within the housing.

[0016] The first negative electrode tab, the second negative electrode tab, and the optional third negative electrode tab are electrically connected inside the housing. Compared to connecting outside the housing, when subjected to external impact, they can suppress misalignment and movement between the first electrode assembly, the second electrode assembly, and the optional third negative electrode, thereby improving the stability of the internal structure of the electrochemical device and reducing the risk of internal short circuits.

[0017] In some embodiments, the electrochemical device satisfies the condition that, when viewed along a first direction, the projections of the first negative electrode tab and the second negative electrode tab at least partially overlap, so as to facilitate connection of the first negative electrode tab and the second negative electrode tab.

[0018] In some embodiments, the electrochemical device further includes a first adapter tab. The first adapter tab is connected within the housing and extends out of the housing, along with a first negative electrode tab and a second negative electrode tab. By leading out the polarity through a single first adapter tab, the space occupied by the first and second negative electrode tabs can be reduced, thereby increasing the energy density of the electrochemical device.

[0019] In some embodiments, the first positive electrode includes a first positive electrode tab. The second positive electrode includes a second positive electrode tab. The electrochemical device also includes a second adapter tab and a third adapter tab. The second adapter tab is connected to the first positive electrode tab within the housing and extends out of the housing, and the third adapter tab is connected to the second positive electrode tab within the housing and extends out of the housing. This structural design reduces the space occupied by the first and second positive electrode tabs, thereby increasing the energy density of the electrochemical device.

[0020] In some embodiments, the separator includes a substrate layer, a ceramic layer, and an adhesive layer.

[0021] In some embodiments, the ceramic layer is located on the surface of the substrate layer.

[0022] In some embodiments, the ceramic layer comprises inorganic particles and a binder.

[0023] In some embodiments, the inorganic particles include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate.

[0024] In some embodiments, the adhesive includes at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene, or polyhexafluoropropylene.

[0025] In some embodiments, the adhesive layer is located on the surface of the substrate layer and / or the ceramic layer.

[0026] In some embodiments, the adhesive layer comprises at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or a copolymer of polyvinylidene fluoride and hexafluoropropylene.

[0027] In a second aspect, this application provides an electrical device, including the electrochemical device described above. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the specific embodiments of this application, the accompanying drawings used in the description of the specific embodiments will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0029] Figure 1 This is a schematic diagram of the structure of an electrochemical device provided in the first embodiment of this application;

[0030] Figure 2 for Figure 1 The diagram shown is an exploded view of the electrochemical device.

[0031] Figure 3 for Figure 1 Cross-sectional views of the first electrode assembly, the second electrode assembly, and the separator membrane of the electrochemical device shown.

[0032] Figure 4 A cross-sectional view of the first electrode assembly, the second electrode assembly, and the separator in another electrochemical device provided in the first embodiment of this application;

[0033] Figure 5 A cross-sectional view of a first electrode assembly, a second electrode assembly, a third negative electrode, and a separator in an electrochemical device provided for the second embodiment of this application;

[0034] Figure 6 A cross-sectional view of the first electrode assembly, the second electrode assembly, the third negative electrode, and the separator in another electrochemical device provided in the second embodiment of this application. Detailed Implementation

[0035] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present application or its application or use. All other embodiments obtained based on the embodiments in this application are within the scope of protection of this application.

[0036] In the description of this application, it should be noted that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is usually based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0037] In the description of this application, it should be noted that the use of terms such as "first" and "second" to define the components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this application.

[0038] Please see Figure 1 The example shown, Figure 1 This is a schematic diagram of an electrochemical device provided in the first embodiment of this application; the electrochemical device can be any device capable of undergoing an electrochemical reaction, that is, the electrochemical device can be a primary battery or a secondary battery. For example, the secondary battery can be a lithium metal secondary battery, a lithium-ion secondary battery, a lithium polymer secondary battery, a solid-state battery, or a lithium-ion polymer secondary battery, etc.

[0039] Please combine Figure 3 See also Figure 2 , Figure 2 for Figure 1 The exploded view of the electrochemical device shown is as follows. Figure 3 for Figure 1The diagram shows a cross-sectional view of the first electrode assembly, the second electrode assembly, and the separator of an electrochemical device. The electrochemical device includes a housing 10, a stacked first electrode assembly 20, a stacked second electrode assembly 30, and a separator 40. For ease of explanation, [the diagram is shown using...]. Figure 1 The coordinate system in the diagram defines the directions of the electrochemical device. The coordinate axis W represents the first direction, which is the relative arrangement direction of the first electrode assembly 20 and the second electrode assembly 30, and also the thickness direction of the electrochemical device. The coordinate axis H represents the second direction, which is the direction in which each tab of the first electrode assembly 20 and / or the second electrode assembly 30 extends out of the housing 10, and also the height direction of the electrochemical device. The coordinate axis L represents the third direction, which is the width direction of the electrochemical device, and is perpendicular to the coordinate axes W and H, i.e., perpendicular to both the first direction W and the second direction H. The housing 10 has a cavity in which the first electrode assembly 20 and the second electrode assembly 30 are housed, and are stacked along the first direction W. A separator 40 is sandwiched between adjacent electrodes to separate them. Furthermore, the electrochemical device includes an electrolyte contained within the cavity, in which the first electrode assembly 20, the second electrode assembly 30, and the separator 40 are all immersed. The first electrode assembly 20 includes a first positive electrode 23 and a first negative electrode 24, and the second electrode assembly 30 includes a second positive electrode 33 and a second negative electrode 34. Along the first direction W, the first positive electrode 23 and the first negative electrode 24 are stacked sequentially, and the second positive electrode 33 and the second negative electrode 34 are also stacked sequentially. The first negative electrode 24 includes a first negative active material, and the second negative electrode 34 includes a second negative active material. The graphitization degree G1 of the first negative active material in the first negative electrode 24 and the graphitization degree G2 of the second negative active material in the second negative electrode 34 satisfy: G2 - G1 ≥ 0.5%. It should be noted that the negative active materials in the first electrode assembly 20 and the second electrode assembly 30 include carbon materials, such as natural graphite, artificial graphite, hard carbon, or soft carbon. Graphitization degree is used to measure the degree to which the crystal structure of a carbon material approximates ideal graphite. Among them, carbon materials with lower graphitization have more lithium insertion sites on their surface than carbon materials with higher graphitization. At the same time, the lithium ion diffusion path in carbon materials with lower graphitization is smaller than that in carbon materials with higher graphitization. Therefore, carbon materials with lower graphitization have a faster lithium ion insertion and extraction rate and can adapt to higher charge and discharge rates.

[0040] Therefore, the first electrode assembly 20 can adapt to a higher charge and discharge rate than the second electrode assembly 30. That is, the first electrode assembly 20 can be used as a fast charging system, and the second electrode assembly 30 can be used as a slow charging system. The fast charging system can meet the emergency charging needs in emergency situations and the discharge needs under high-rate applications; the slow charging system can meet the needs of normal use and can ensure that the electrochemical device has a high capacity, thereby meeting the needs of the electrical device for long battery life.

[0041] For the aforementioned separator membrane 40, please refer to Figure 3 In the example shown, in this embodiment of the application, the separator 40 includes a plurality of separator portions 41 and a plurality of bends 42. A separator portion 41 is provided between any two adjacent electrodes to separate them. Any two adjacent separator portions 41 are connected by a bend 42. By using a single separator 40 and assembling the first electrode assembly 20 and the second electrode assembly 30 into a single unit through Z-shaped folding, misalignment and displacement of the first electrode assembly 20 and the second electrode assembly 30 under external impact can be suppressed, thereby improving the stability of the internal structure of the electrochemical device and reducing the risk of internal short circuits. Simultaneously, since no additional adhesive method is needed to fix the first electrode assembly 20 and the second electrode assembly 30 together, the assembly difficulty of the first electrode assembly 20 and the second electrode assembly 30 is reduced, and manufacturing efficiency is improved. It should be noted that the electrodes here include the first positive electrode 23 and the first negative electrode 24 in the first electrode assembly 20, and the second positive electrode 33 and the second negative electrode 34 in the second electrode assembly 30.

[0042] In some embodiments, the multiple isolation portions 41 and the multiple bending portions 42 are integrally formed, which helps to ensure the overall structural strength of the isolation membrane 40, thereby better suppressing the misalignment and movement between the first electrode assembly 20 and the second electrode assembly 30, as well as between the positive electrode and the negative electrode, and improving the stability of the internal structure of the electrochemical device.

[0043] Furthermore, in some embodiments, the graphitization degree G1 of the first negative electrode active material in the first negative electrode 24 satisfies: G1≤95%. In this case, the first electrode assembly 20 can adapt to a larger charge / discharge rate, thereby better meeting the needs of emergency charging in emergency situations and discharge under high-rate applications. In some embodiments, the graphitization degree G2 of the second negative electrode active material in the second negative electrode 34 satisfies: G2≥95.5%. In this case, the second negative electrode active material has a higher degree of regularity, providing more lithium-ion storage sites, thereby enabling the electrochemical device to have a higher energy density and better meeting the long-range requirements of the device. Even further, the graphitization degree G1 of the first negative electrode active material satisfies: 94%≤G1≤95%, and the graphitization degree G2 of the second negative electrode active material satisfies: 95.5%≤G2≤96.5%.

[0044] For the aforementioned housing 10, as Figure 2 As shown, in this embodiment of the application, the housing 10 includes a first housing 11 and a second housing 12, with the first housing 11 connected to the second housing 12, forming the aforementioned cavity between them. Exemplarily, the first housing 11 and the second housing 12 can be heat-sealed together. It is understood that in other embodiments of this application, the first housing 11 and the second housing 12 may not be limited to being connected by welding.

[0045] Furthermore, the embodiments of this application do not specifically limit the material and shape of the housing 10, and can be adapted to meet actual usage requirements. For example, the housing 10 may be a soft housing 10, not limited to aluminum-plastic film or steel-plastic film, or the housing 10 may be a rigid housing 10, not limited to aluminum or steel.

[0046] Both the first electrode assembly 20 and the second electrode assembly 30 described above are stacked structures, such as... Figure 3 As shown in this embodiment, the first electrode assembly 20 includes a first single-sided electrode 22, a third single-sided electrode 21, and at least one double-sided first positive electrode 232 and / or at least one double-sided first negative electrode 242 located between the first single-sided electrode 22 and the third single-sided electrode 21. The third single-sided electrode 21 is located on the side of the first electrode assembly 20 away from the second electrode assembly 30, and the third single-sided electrode 21 has a third surface (not shown) without an active material layer. The first single-sided electrode 22 is located on the side of the first electrode assembly 20 close to the second electrode assembly 30, and the first single-sided electrode 22 has a first surface (not shown) without an active material layer, and the first surface is disposed opposite to the second single-sided electrode 32 of the second electrode assembly 30. At least one double-sided first positive electrode 232 and / or at least one double-sided first negative electrode 242 are located between the third single-sided electrode 21 and the first single-sided electrode 22. Based on this, the polarity of the third single-sided electrode 21 and the first single-sided electrode 22 is the same as that of the first negative electrode 24, that is, the third single-sided electrode 21, the first single-sided electrode 22 and any double-sided first negative electrode 242 all include the first negative electrode active material in the first negative electrode 24.

[0047] Specifically, each first negative electrode 24 includes a first negative electrode tab 241, which is located in the middle of the first electrode assembly 20. One end of the first negative electrode tab 241 is connected to the current collector of the corresponding first negative electrode 24, and the other end of the first negative electrode tab 241 is electrically connected to the first adapter tab 51 of the electrochemical device. Exemplarily, each first negative electrode tab 241 is integrally formed with the current collector of the corresponding first negative electrode 24; that is, the first negative electrode 24 is a negative electrode obtained by die-cutting, and the first negative electrode tab 241 is a die-cut tab. The other end of the first negative electrode tab 241 can be welded to the first adapter tab 51. Of course, the first negative electrode tab 241 may also be connected to the current collector of the first negative electrode 24 by welding or bonding with conductive adhesives, and this embodiment does not specifically limit this.

[0048] Each first positive electrode 23 includes a first positive electrode tab 231. Both the first positive electrode tab 231 and the first negative electrode tab 241 are located within the cavity of the housing 10, separated from the first negative electrode tab 241 along a third direction L. One end of the first positive electrode tab 231 is connected to the current collector of the corresponding first positive electrode 23, and the other end is electrically connected to the second adapter tab 52 of the electrochemical device. Exemplarily, each first positive electrode tab 231 is integrally formed with the current collector of the corresponding first positive electrode 23; that is, the first positive electrode 23 is a die-cut electrode, and the first positive electrode tab 231 is a die-cut tab. The other end of the first positive electrode tab 231 can be welded to the second adapter tab 52. Of course, the first positive electrode tab 231 may also be connected to the current collector of the first positive electrode plate 23 by welding or conductive adhesive, and the embodiments of this application do not specifically limit this.

[0049] Please continue reading. Figure 3The second electrode assembly 30 includes a fourth single-sided electrode 31, a second single-sided electrode 32, and at least one double-sided second positive electrode 332 and / or at least one double-sided second negative electrode 342 located between the second single-sided electrode 32 and the fourth single-sided electrode 31. The fourth single-sided electrode 31 is located on the side of the second electrode assembly 30 away from the first electrode assembly 20, and has a fourth surface (not shown) without an active material layer. The second single-sided electrode 32 is located on the side of the second electrode assembly 30 closer to the first electrode assembly 20, and has a second surface (not shown) without an active material layer, which is disposed opposite to the first surface of the first single-sided electrode 22. At least one double-sided second positive electrode 332 and / or at least one double-sided second negative electrode 342 are located between the fourth single-sided electrode 31 and the second single-sided electrode 32. Based on this, the polarity of the fourth single-sided electrode 31 and the second single-sided electrode 32 is the same as the polarity of the double-sided second negative electrode 342. That is, the fourth single-sided electrode 31, the second single-sided electrode 32, and any double-sided second negative electrode 342 all include the second negative electrode active material in the aforementioned second negative electrode 34. It should be noted that the first single-sided electrode 22, the second single-sided electrode 32, the third single-sided electrode 21, and the fourth single-sided electrode 31 in the embodiments of this application are all relative to the double-sided electrode with active material layers coated on both opposite surfaces of the current collector. They are electrodes formed after coating an active material layer only on one surface of the current collector.

[0050] Specifically, each of the second negative electrode plates 34 includes a second negative electrode tab 341. One end of the second negative electrode tab 341 is connected to the current collector of the corresponding second negative electrode plate 34, and the other end of the second negative electrode tab 341 is used for electrical connection with the first adapter tab 51 of the electrochemical device. Exemplarily, each second negative electrode tab 341 is integrally formed with the current collector of the corresponding second negative electrode plate 34, that is, the second negative electrode plate 34 is a die-cut electrode plate, and the second negative electrode tab 341 is a die-cut tab. The other end of the second negative electrode tab 341 can be welded to the first adapter tab 51. Of course, the second negative electrode tab 341 is not limited to being connected to the current collector of the second negative electrode plate 34 by welding or bonding with conductive adhesives; this embodiment does not specifically limit this.

[0051] Furthermore, when viewed along the first direction W, the projections of the second negative electrode tab 341 and the first negative electrode tab 241 at least partially overlap, which facilitates the connection of the first negative electrode tab 241 and the second negative electrode tab 341 and improves the reliability of the connection.

[0052] Each second positive electrode 33 includes a second positive electrode tab 331. Both the second positive electrode tab 331 and the second negative electrode tab 341 are located within the cavity of the housing 10, separated from the second negative electrode tab 341 along a third direction L. One end of the second positive electrode tab 331 is connected to the current collector of the corresponding second positive electrode 33, and the other end is used for electrical connection to the third adapter tab 53 of the electrochemical device. Exemplarily, each second positive electrode tab 331 is integrally formed with the current collector of the corresponding second positive electrode 33; that is, the second positive electrode 33 is a die-cut electrode, and the second positive electrode tab is a die-cut tab. The other end of the second positive electrode tab 331 can be welded to the third adapter tab 53. Of course, the second positive electrode tab 331 may also be connected to the current collector of the second positive electrode plate 33 by welding or bonding with conductive adhesive, and the embodiments of this application do not specifically limit this.

[0053] One end of the third adapter tab 53, the second adapter tab 52, and the first adapter tab 51 extends outside the housing 10. The third adapter tab 53 and / or the second adapter tab 52 and the first adapter tab 51 can be electrically connected to an external device to supply power to the external device.

[0054] It is understood that the specific construction of the first electrode assembly 20 and the second electrode assembly 30 is not limited to this. In other embodiments of this application, the difference from the specific construction of the first electrode assembly 20 is that both the third single-sided electrode 21 and the first single-sided electrode 22 are first positive electrode 23. In other embodiments of this application, the difference from the specific construction of the first electrode assembly 20 is that the polarities of the third single-sided electrode 21 and the first single-sided electrode 22 are different. Similarly, in other embodiments of this application, the difference from the specific construction of the second electrode assembly 30 is that both the fourth single-sided electrode 31 and the second single-sided electrode 32 are second positive electrode 33. In other embodiments of this application, the difference from the specific construction of the second electrode assembly 30 is that the polarities of the fourth single-sided electrode 31 and the second single-sided electrode 32 are different.

[0055] like Figure 3 As shown in the embodiments of this application, the first single-sided electrode 22 and the second single-sided electrode 32 have the same polarity. The fact that adjacent first single-sided electrodes 22 and second single-sided electrodes 32 between the first electrode assembly 20 and the second electrode assembly 30 have the same polarity reduces the risk of internal short circuits when the first electrode assembly 20 and the second electrode assembly 30 are misaligned due to external impact, thereby improving the safety of the electrochemical device.

[0056] To mitigate the risk of lithium plating or short circuits caused by misalignment of oppositely polarized electrodes in the first electrode assembly 20 and / or the second electrode assembly 30 within the separator 40, thereby ensuring the safety of the electrochemical device, the separator 40 may optionally possess adhesive properties. For example, in embodiments of this application, the separator 40 may include a substrate layer, which may be a nonwoven fabric, membrane, or composite membrane with a porous structure. The substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Exemplarily, the substrate layer may be a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane. Thus, the separator 40 may possess a certain degree of adhesiveness after hot pressing. Of course, in other embodiments of this application, the separator 40 may further include an adhesive layer coated on the outer surface of the substrate layer. The adhesive layer may be a polymer layer of at least one polymer selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene). Thus, the separator 40 may be inherently adhesive due to the presence of an adhesive coating. Further, the separator 40 may also include a ceramic layer sandwiched between the substrate layer and the adhesive layer. The ceramic layer comprises inorganic particles and a binder, wherein the inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The adhesive is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

[0057] Furthermore, the adhesion strength F between any isolation portion 41 of the separator 40 and its adjacent electrode satisfies: F ≥ 5 N / m. Therefore, when the electrochemical device is subjected to external impact, the isolation portion can better suppress misalignment and movement between the electrodes, thereby further reducing the risk of lithium plating or internal short circuits in the electrochemical device and improving its safety. Even further, 5 N / m ≤ F ≤ 25 N / m.

[0058] Please continue reading. Figure 4 The example shown, Figure 4This is a cross-sectional view of a first electrode assembly, a second electrode assembly, and a separator in another electrochemical device provided in the first embodiment of this application; the difference from the electrochemical device structure in the aforementioned embodiment is that, in this embodiment, the number of first electrode assemblies 20 is at least two, and the number of second electrode assemblies 30 is at least one. Along the first direction W, a first electrode assembly 20 is stacked on each of the two opposite sides of a second electrode assembly 30, i.e., the electrochemical device is a fast charging + slow charging + fast charging system. Therefore, when the fast charging system of the electrochemical device is charged and discharged at a high rate, the heat generated by the fast charging system on both sides can be rapidly diffused outward, thereby reducing the local temperature rise of the electrochemical device and improving the safety of the electrochemical device.

[0059] Alternatively, the number of first electrode components 20 is at least one, and the number of second electrode components 30 is at least two. Along the first direction W, a second electrode component 30 is stacked on each of the two opposite sides of a first electrode component 20. That is, the electrochemical device is a slow charging + fast charging + slow charging system. Thus, when the fast charging system of the electrochemical device is charged and discharged at a high rate, the slow charging system on both sides can disperse the heat generated by the fast charging system, thereby improving the local temperature rise of the electrochemical device and thus improving the safety of the electrochemical device.

[0060] Please continue reading. Figure 5 The example shown, Figure 5 This is a cross-sectional view of a first electrode assembly, a second electrode assembly, a third negative electrode, and a separator in an electrochemical device according to a second embodiment of this application. The first electrode assembly 20' still includes a third single-sided electrode 21', at least one double-sided first positive electrode 232', and / or at least one double-sided first negative electrode 242', and the second electrode assembly 30' still includes a fourth single-sided electrode 31', at least one double-sided second positive electrode 332', and / or at least one double-sided second negative electrode 342'. The difference between this embodiment and the first embodiment is that the first electrode assembly 20' no longer includes a first single-sided electrode, and the second electrode assembly 30' no longer includes a second single-sided electrode. Instead, the electrochemical device also includes a third negative electrode 60.

[0061] The third negative electrode 60 includes a third negative current collector 61, a third negative active layer 62, and a fourth negative active layer 63. The third negative electrode 60 is sandwiched between the first electrode assembly 20' and the second electrode assembly 30'. The third negative active layer 62 is coated on the side of the third negative current collector 61 closest to the first electrode assembly 20'. The third negative active layer 62 and the first positive electrode 23' adjacent to the third negative electrode 60 in the first electrode assembly 20' are separated by an insulating portion of a separator. The fourth negative active layer 63 is coated on the side of the third current collector closest to the second electrode assembly 30'. The fourth negative active layer 63 and the second positive electrode 33' adjacent to the third negative electrode 60 in the second electrode assembly 30' are separated by an insulating portion of a separator. Wherein, |G4-G2|≤0.2%, |G3-G1|≤0.2%. The advantage of this configuration is that the third negative electrode 60 can be combined with the first electrode assembly 20' as a fast charging system, or with the second electrode assembly 30' as a slow charging system. Furthermore, the graphitization degree G3 of the third negative electrode active material in the third negative electrode active layer 62 satisfies: G3≤95%, and the graphitization degree G4 of the fourth negative electrode active material in the fourth negative electrode active layer 63 satisfies: G4≥95.5%. Even further, the graphitization degree G3 of the third negative electrode active material satisfies: 94%≤G3≤95%, and the graphitization degree G4 of the fourth negative electrode active material satisfies: 95.5%≤G4≤96.5%.

[0062] Compared to the electrochemical device provided in the first embodiment, since there are no longer single-sided electrodes inside the first electrode assembly 20' and the second electrode assembly 30', space waste can be reduced, which is beneficial to improving the energy density of the electrochemical device.

[0063] In some embodiments of this application, the graphitization degree G3 of the third negative electrode active material in the third negative electrode active layer 62 and the graphitization degree G4 of the fourth negative electrode active material in the fourth negative electrode active material layer 63 satisfy: G4-G3≥0.5%.

[0064] Furthermore, the third negative electrode 60 may also include a third negative electrode tab (not shown) housed within the housing cavity, one end of which is connected to the third negative current collector 61, and the other end of which may be electrically connected to the first adapter tab within the housing cavity.

[0065] It is understood that the specific construction of the first electrode assembly 20' and the second electrode assembly 30' is not limited to this. In some other embodiments of this application, the specific construction of the first electrode assembly 20' differs from that described above, in that the third single-sided electrode 21' is the first positive electrode 23'. Similarly, in some other embodiments of this application, the specific construction of the second electrode assembly 30' differs from that described above, in that the fourth single-sided electrode 31' is the second positive electrode 33'. Furthermore, in some other embodiments of this application, the specific construction of the electrochemical device differs from that described above, in that a third positive electrode is used instead of the third negative electrode 60, and the third positive electrode and the first negative electrode 24' adjacent to the third positive electrode in the first electrode assembly 20' are separated by the isolation portion of the separator, and the third positive electrode and the second negative electrode 34' adjacent to the third positive electrode in the second electrode assembly 30' are separated by the isolation portion of the separator, which can also achieve the technical effects described above.

[0066] Please continue reading. Figure 6 The example shown, Figure 6 The cross-sectional view of the first electrode assembly, second electrode assembly, third negative electrode, and separator in another electrochemical device provided in the second embodiment of this application differs from the structure of the electrochemical device in the aforementioned embodiments. In this embodiment, the number of first electrode assemblies 20' and third negative electrode 60 is at least two, and the number of second electrode assemblies 30' is at least one. Along the first direction, a first electrode assembly 20' is stacked on each of the two opposite sides of a second electrode assembly 30', and a third negative electrode 60 is sandwiched between a second electrode assembly 30' and a first electrode assembly 20'. That is, the electrochemical device is a fast charging + slow charging + fast charging system. Therefore, when the fast charging system of the electrochemical device is charged and discharged at a high rate, the heat generated by the fast charging system on both sides can be rapidly diffused outward, thereby reducing the local temperature rise of the electrochemical device and improving the safety of the electrochemical device.

[0067] Alternatively, the number of first electrode components 20' is at least one, and the number of second electrode components 30' and third negative electrode 60 is at least two. Along the first direction, a second electrode component 30' is stacked on each of the two opposite sides of a first electrode component 20', and a third negative electrode 60 is sandwiched between a first electrode component 20' and a second electrode component 30'. That is, the electrochemical device is a slow charging + fast charging + slow charging system. Thus, when the fast charging system of the electrochemical device is charged and discharged at a high rate, the slow charging system on both sides can disperse the heat generated by the fast charging system, thereby improving the local temperature rise of the electrochemical device and thus improving the safety of the electrochemical device.

[0068] In the embodiments of this application, lithium-ion batteries with fast charging + slow charging system and fast charging + slow charging + fast charging system are used as examples to conduct charging temperature rise test and drop test.

[0069] Preparation of lithium-ion batteries

[0070] Example 1

[0071] (1) Preparation of negative electrode sheets for fast-charging and slow-charging systems: For the fast-charging system, artificial graphite with a graphitization degree G1 of 94.8% was selected as the negative electrode active material, and for the slow-charging system, artificial graphite with a graphitization degree G2 of 95.5% was selected as the negative electrode active material. The artificial graphite, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC) thickener were mixed in a weight ratio of 96:2:2, and deionized water was added as a solvent to prepare a slurry with a solid content of 70wt%, which was then stirred evenly. The slurry was uniformly coated on one surface of a 10μm thick copper foil current collector for negative electrode, and dried to obtain a negative electrode sheet with a single-sided negative electrode active layer. The above steps were repeated on the other surface of the copper foil current collector to obtain a negative electrode sheet with a double-sided negative electrode active layer. After cold pressing, the negative electrode sheet was cut into 41mm×61mm sizes for later use.

[0072] (2) Preparation of the positive electrode sheet: Lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%, and the mixture was stirred evenly. The slurry was uniformly coated on one surface of a 12 μm thick aluminum foil for the positive electrode current collector, and dried to obtain a positive electrode sheet with a single-sided positive electrode active layer. The above steps were repeated on the other surface of the aluminum foil for the positive electrode current collector to obtain a positive electrode sheet with a double-sided positive electrode active layer. After cold pressing, the positive electrode sheet was cut into 38 mm × 58 mm sizes for later use.

[0073] (3) Preparation of electrolyte: In dry argon gas, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a LiPF6 mass concentration of 12.5%.

[0074] (4) Preparation of the separator: A porous polyethylene membrane is used as the substrate layer, and a ceramic layer containing alumina ceramic and PVDF binder is coated on one side of the substrate layer as the separator (CCS). The mass percentage of alumina ceramic in the ceramic layer is 95%.

[0075] (5) Preparation of electrode assembly: The separator is folded in a Z-shape, and the positive and negative electrode sheets of the fast charging system are stacked in sequence to form the first electrode assembly of the fast charging system. Then, the positive and negative electrode sheets of the slow charging system are stacked in sequence to form the second electrode assembly of the slow charging system. The isolation part of the separator is located between two adjacent electrode sheets. Both sides of the first electrode assembly of the fast charging system and the second electrode assembly of the slow charging system are single-sided positive electrode sheets. The end of the separator is rolled up to wrap the entire electrode assembly to form a stacked electrode assembly for later use.

[0076] (6) Assembly of electrode assembly: Place the punched aluminum-plastic film in the assembly fixture with the punched surface facing up, place the electrode assembly in the punch, and then place multiple negative electrode tabs, multiple positive electrode tabs, multiple negative electrode tabs, and multiple positive electrode tabs of the fast charging system electrode assembly, the slow charging system electrode assembly, and the slow charging system electrode assembly together by laser welding, and then transfer the electrode tabs out. Then, cover the electrode assembly with another punched aluminum-plastic film with the punched surface facing down, and heat seal the four sides by hot pressing to obtain the assembled electrode assembly.

[0077] (7) Liquid injection and encapsulation: Electrolyte is injected into the assembled electrode assembly, and after vacuum encapsulation, standing, hot pressing formation, shaping and other processes, a lithium-ion battery is obtained.

[0078] The difference between Example 2 and Example 1 is that the first electrode assembly of the fast charging system and the second electrode assembly of the slow charging system both have their internal single-sided positive electrode removed and replaced with a third negative electrode. The side of the third negative electrode facing the first electrode assembly is coated with the negative active layer of the fast charging system, and the side facing the second electrode assembly is coated with the negative active layer of the slow charging system.

[0079] The difference between Example 3 and Example 1 is that the positive and negative electrode plates of the fast charging system are further stacked sequentially on the second electrode plate assembly of the slow charging system to form the third electrode plate assembly of the fast charging system. Both sides of the third electrode plate assembly are also single-sided positive electrode plates.

[0080] The difference between Example 4 and Example 1 is that the fast charging system uses artificial graphite with a graphitization degree G1 of 94.1% as the negative electrode active material; in the preparation of the separator, the mass percentage of alumina ceramic in the ceramic layer is 40% (PCCS).

[0081] The difference between Example 5 and Example 1 is that the fast charging system uses artificial graphite with a graphitization degree G1 of 94.1% as the negative electrode active material, while the slow charging system uses artificial graphite with a graphitization degree G2 of 96.1% as the negative electrode active material; in the preparation of the separator, the ceramic layer is replaced by an adhesive layer (PCS) containing only PVDF.

[0082] The difference between Example 6 and Example 1 is that the fast-charging system uses artificial graphite with a graphitization degree G1 of 94.0% as the negative electrode active material, while the slow-charging system uses artificial graphite with a graphitization degree G2 of 96.1% as the negative electrode active material. In the preparation of the separator, the mass percentage of alumina ceramic in the ceramic layer is 85%.

[0083] The difference between Example 7 and Example 2 is that the fast-charging system uses artificial graphite with a graphitization degree G1 of 94.2% as the negative electrode active material, while the slow-charging system uses artificial graphite with a graphitization degree G2 of 96.2% as the negative electrode active material. In the preparation of the separator, the ceramic layer is replaced with an adhesive layer (PCS) containing only PVDF.

[0084] The difference between Example 8 and Example 3 is that the fast charging system uses artificial graphite with a graphitization degree G1 of 94.5% as the negative electrode active material, while the slow charging system uses artificial graphite with a graphitization degree G2 of 95.8% as the negative electrode active material.

[0085] The difference between Example 9 and Example 1 is that, in the assembly of the electrode assembly, multiple negative electrode tabs of the fast charging system electrode assembly and the slow charging system electrode assembly overlap, and the overlapping negative electrode tabs are laser welded together and then led out by the adapter tab.

[0086] The difference between Comparative Example 1 and Example 1 lies in the preparation of the electrode assembly. First, a separator film is Z-folded and placed between the stacked negative and positive electrodes of the fast-charging system. The end of the separator film is then rolled up to wrap the entire electrode assembly, forming a stacked fast-charging system electrode assembly for later use. Then, another separator film is Z-folded and placed between the stacked negative and positive electrodes of the slow-charging system. The end of the separator film is then rolled up to wrap the entire electrode assembly, forming a stacked slow-charging system electrode assembly for later use. During the assembly of the electrode assembly, the fast-charging system electrode assembly is first placed in the pit, and then the slow-charging system electrode assembly is placed on top of the fast-charging system electrode assembly, aligning the edges, and then external force is applied to press it firmly. Next, the multiple negative electrode tabs overlapping in the fast charging system electrode assembly, the multiple positive electrode tabs overlapping in the fast charging system electrode assembly, the multiple negative electrode tabs overlapping in the slow charging system electrode assembly, and the multiple positive electrode tabs overlapping in the slow charging system electrode assembly are laser welded together, and the electrode tabs are led out separately. Then, another aluminum-plastic film with a dented surface is placed on the electrode assembly with the dented surface facing down, and the four sides are heat-sealed by hot pressing to obtain the assembled electrode assembly.

[0087] Test methods

[0088] Fast charging temperature rise test: The fast charging system was charged at 25°C with a constant current of 10C to 4.45V and a constant voltage of 0.05C, and the maximum temperature rise on the battery surface was monitored during the charging process.

[0089] Slow charging temperature rise test: The slow charging system was charged at 25°C with a constant current of 1C to 4.45V and a constant voltage of 0.02C, and the maximum temperature rise on the battery surface was monitored during the charging process.

[0090] Graphitization degree testing: XRD testing was performed using a Bruker instrument, with the XRD reference standard being JIS K0131-1996 "General rules of X-ray diffractometric analysis". During testing, the mass ratio of silicon powder to the graphite anode active material was 1:5. The target material was Cu Kα, the voltage was 40 kV, the current was 40 mA, the scanning angle range was 52° to 58°, the scanning step size was 0.008°, and the step time was 0.3 s.

[0091] Drop test: On a concrete drop surface, the battery is dropped from a height of 1m along all six sides once and from the four corners once, for a total of 5 rounds of testing; Judgment criteria: Misalignment in the width direction between electrode modules ≤ 0.2mm is judged as no misalignment; 0.2mm < misalignment in the width direction between electrode modules ≤ 0.5mm is judged as slight misalignment; 0.5mm < misalignment in the width direction between electrode modules ≤ 1.0mm is judged as moderate misalignment; misalignment in the width direction between electrode modules > 1.0mm is judged as severe misalignment.

[0092] Bonding strength test: ① Preparation before testing: Turn on the power of the high-speed rail tensile testing machine, confirm that the upper and lower clamps of the tensile testing machine are in a horizontal position, and that the tension rod can move up and down normally. Confirm that the speed control of the tensile testing machine is 50mm / min; ② Sample preparation: Cut a sample of the bonding area with a width of W; ③ Place the sample on the clamp, with the clamp holding the material on both sides of the bonding area sample; ④ Tensile test: Click the zeroing and run buttons to start the test, output the tensile value P, and then the bonding strength F = P / W.

[0093] The test results are shown in Table 1.

[0094] Table 1

[0095]

[0096]

[0097] Based on the above test results, it can be found that the graphitization degree G1 of the negative electrode active material in the fast charging system is less than that of the graphitization degree G2 of the negative electrode active material in the slow charging system. Furthermore, in conjunction with Examples 1-9, it can be seen that when G2-G1≥0.5%, the fast charging and slow charging requirements of the electrochemical device can be met.

[0098] Furthermore, when G1 ≤ 95% and / or G2 ≥ 95.5%, the battery temperature rise is relatively small when fast charging the electrode assembly of the fast charging system and slow charging the electrode assembly of the slow charging system. Even further, within the range of 94% ≤ G1 ≤ 95% and / or 95.5% ≤ G2 ≤ ​​96.5%, the battery temperature rise under both fast and slow charging conditions can achieve optimal results.

[0099] Furthermore, in the drop test, based on Examples 1-9 and Comparative Example 1, it can be seen that, compared with the non-integrated Comparative Example 1, Examples 1-9, which integrate the separator through Z-folding, show a significant reduction in the misalignment of the fast-charging system electrode assembly and the slow-charging system electrode assembly during the drop test. This indicates that using a single separator to assemble the fast-charging system electrode assembly and the slow-charging system electrode assembly into a whole through Z-folding can suppress misalignment and movement of the two during a drop, thereby improving the stability of the internal structure of the lithium-ion battery and reducing the risk of internal short circuits.

[0100] As shown in Examples 1 and 4-6, when the bonding strength F between the electrode and the separator is ≥7.8 N / m, misalignment and movement between the electrodes can be further suppressed, thereby further reducing the risk of internal short circuits in the lithium-ion battery. As shown in Examples 1 and 9, welding the negative electrode tabs of the fast-charging and slow-charging electrode assemblies together within the casing can further suppress misalignment during drop tests, thereby reducing the risk of internal short circuits and improving the safety of the lithium-ion battery.

[0101] Based on the same technical concept, a third aspect of this application also provides an electrical device, including the electrochemical device described in any of the above embodiments. It is understood that the electrical device in the embodiments of this application is not particularly limited, and can be any electrical device known in the prior art. For example, the electrical device includes, but is not limited to, Bluetooth headsets, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc.

[0102] The above description is merely an embodiment of this application and does not limit the scope of protection of this application. Any equivalent structural or procedural transformations made based on the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of protection of this application.

Claims

1. An electrochemical device, comprising a first electrode assembly of a stack structure, a second electrode assembly of a stack structure, and a separator, the first electrode assembly comprising a first positive electrode and a first negative electrode, the second electrode assembly comprising a second positive electrode and a second negative electrode; in a first direction, the first positive electrode and the first negative electrode are sequentially stacked, and the second positive electrode and the second negative electrode are sequentially stacked; the first negative electrode comprises a first negative active material, and the second negative electrode comprises a second negative active material, characterized in that: a graphitization degree G1 of the first negative active material and a graphitization degree G2 of the second negative active material satisfy: G2-G1≥0.5%; the separator comprises a plurality of separation portions and a plurality of bending portions, the separation portion is arranged between any two adjacent electrodes, and any two adjacent separation portions are connected by a bending portion; the electrochemical device further comprises a third negative electrode, the third negative electrode is arranged between the first electrode assembly and the second electrode assembly; the first electrode assembly comprises a first positive electrode adjacent to the third negative electrode, the first positive electrode adjacent to the third negative electrode comprises a first positive current collector and a first positive active layer located on two opposite surfaces of the first positive current collector in the first direction; the second electrode assembly comprises a second positive electrode adjacent to the third negative electrode, the second positive electrode adjacent to the third negative electrode comprises a second positive current collector and a second positive active layer located on two opposite surfaces of the second positive current collector in the first direction; the separation portion is arranged between the third negative electrode and the first electrode assembly, and the separation portion is arranged between the third negative electrode and the second electrode assembly; the third negative electrode comprises a third negative current collector, a third negative active layer and a fourth negative active layer, the third negative active layer is located on a side of the third negative current collector close to the first electrode assembly, and the third negative active layer comprises a third negative active material; the fourth negative active layer is located on a side of the third negative current collector close to the second electrode assembly, and the fourth negative active layer comprises a fourth negative active material, a graphitization degree G3 of the third negative active material and a graphitization degree G4 of the fourth negative active material satisfy: |G4-G2|≤0.2%, |G3-G1|≤0.2%; the electrochemical device further comprises a housing, the first electrode assembly, the second electrode assembly, the third negative electrode and the separator are accommodated in the housing; the first negative electrode comprises a first negative tab, the second negative electrode comprises a second negative tab, the third negative electrode comprises a third negative tab, and the first negative tab, the second negative tab and the third negative tab are electrically connected in the housing. The electrochemical device satisfies at least one of the following conditions: (1) the first negative active material and the second negative active material are different; (2) the first negative active material and the third negative active material are different; (3) the adhesion strength F between the separation portion and the electrode satisfies: F≥5N / m. ​ ​ ​ ​ 2. The electrochemical device of claim 1, wherein ​ （1）G1≤95%； （2）G2≥95.5%； ​ (4) The isolation portion is integrally formed with the bending portion.

3. The electrochemical device of claim 2, wherein 94%≤G1≤95%;and / or 95.5%≤G2≤96.5%.

4. The electrochemical device of claim 1, wherein The number of the first pole piece assemblies is at least two, the number of the second pole piece assemblies is at least one, and the second pole piece assembly is arranged between any two adjacent first pole piece assemblies along the first direction; or, The number of the first pole piece assemblies is at least one, the number of the second pole piece assemblies is at least two, and the first pole piece assembly is arranged between any two adjacent second pole piece assemblies along the first direction.

5. The electrochemical device of claim 1, wherein The electrochemical device satisfies at least one of the following conditions: (1) The projections of the first negative tab and the second negative tab at least partially overlap along the first direction; (2) The electrochemical device further comprises a first adapter tab, the first adapter tab is connected with the first negative tab and the second negative tab in the shell and extends out of the shell; (3) The first positive pole piece comprises a first positive tab, the second positive pole piece comprises a second positive tab, the electrochemical device further comprises a second adapter tab and a third adapter tab, the second adapter tab is connected with the first positive tab in the shell and extends out of the shell, and the third adapter tab is connected with the second positive tab in the shell and extends out of the shell.

6. The electrochemical device of claim 1, wherein The isolation film comprises a substrate layer, a ceramic layer and a bonding layer, and at least one of the following conditions is satisfied: (1) The substrate layer comprises at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide; (2) The ceramic layer is located on the surface of the substrate layer; (3) The ceramic layer comprises inorganic particles and a bonding agent, the inorganic particles comprise at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate; the bonding agent comprises at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene or polyhexafluoropropylene; (4) The bonding layer is located on the surface of the substrate layer and / or the ceramic layer; (5) The bonding layer comprises at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or a copolymer of vinylidene fluoride-hexafluoropropylene.

7. An electrical device, characterized by The power utilization device comprises the electrochemical device according to any one of claims 1-6.

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