WO2024087068A1

WO2024087068A1 - Electrochemical apparatus and electronic device

Info

Publication number: WO2024087068A1
Application number: PCT/CN2022/127770
Authority: WO
Inventors: 郝慧; 黄矗; 尤裕哲; 林森
Original assignee: 宁德新能源科技有限公司
Priority date: 2022-10-26
Filing date: 2022-10-26
Publication date: 2024-05-02
Also published as: CN116888793A

Abstract

The present application discloses an electrochemical apparatus, comprising a housing, a first electrode assembly, and a second electrode assembly. The first electrode assembly comprises a first electrode sheet assembly, a first tab, and a third tab, the first electrode sheet assembly comprises a first negative electrode sheet, and the degree of graphitization of a first negative electrode active material of the first negative electrode sheet is G1. The second electrode assembly comprises a second electrode sheet assembly, a second tab, and a fourth tab, the second electrode sheet assembly comprises a second negative electrode sheet, the degree of graphitization of a second negative electrode active material of the second negative electrode sheet is G2, and the relation G2-G1≥0.5% is satisfied. The first tab and the second tab have the same polarity, and the first tab and the second tab are electrically connected in the housing. The electrochemical apparatus of the present application has high energy density and fast-charge performance, and can have excellent structural stability, so that the risk of an internal short circuit is reduced.

Description

Electrochemical devices and electronic devices

Technical Field

The present application relates to the field of battery technology, and in particular to an electrochemical device and an electronic device.

Background technique

With the development of science and technology, electronic products such as mobile phones, laptops, and drones have greatly enriched people's daily lives. Lithium-ion batteries are also widely used in electronic products due to their advantages such as high energy density, high operating voltage, and long service life. However, with the diversification of application scenarios, lithium-ion batteries with excellent comprehensive performance such as high energy density, fast charging performance, and high structural stability are urgently needed.

Summary of the invention

The present application aims to provide an electrochemical device and an electronic device, so as to at least improve the structural stability of the electrochemical device while taking into account the high energy density and fast charging performance of the electrochemical device.

In the first aspect, the present application proposes an electrochemical device, including a shell, a first electrode assembly and a second electrode assembly. The first electrode assembly includes a first electrode sheet assembly and a first electrode tab and a third electrode tab connected to the first electrode sheet assembly, the first electrode sheet assembly is accommodated in the shell, the first electrode sheet assembly includes a first negative electrode sheet, the first negative electrode sheet includes a first negative electrode active material, and the graphitization degree of the first negative electrode active material is G1. The second electrode assembly includes a second electrode sheet assembly and a second electrode tab and a fourth electrode tab connected to the second electrode sheet assembly, the second electrode sheet assembly is accommodated in the shell, the second electrode sheet assembly includes a second negative electrode sheet, the second negative electrode sheet includes a second negative electrode active material, and the graphitization degree of the second negative electrode active material is G2, satisfying: G2-G1≥0.5%. The polarity of the first electrode tab is the same as that of the second electrode tab, the polarity of the third electrode tab is the same as that of the fourth electrode tab, and the first electrode tab and the second electrode tab are electrically connected in the shell.

In the above technical solution, the graphitization degree G1 of the first negative electrode active material of the first electrode assembly is less than the graphitization degree G2 of the second negative electrode active material of the second electrode assembly, so that the first electrode assembly can have a larger maximum charge and discharge rate, that is, the first electrode assembly can be used as a fast charging system, and the second electrode assembly can be used as a slow charging system. The fast charging system can meet the emergency charging needs in emergency situations and the high-rate discharge needs under high-rate applications; the slow charging system can meet conventional use and ensure that the electrochemical device has a higher capacity. In addition, the first pole piece assembly and the second pole piece assembly are accommodated in the same shell, and when the first electrode assembly is charged and discharged at a high rate, the local temperature rise of the electrochemical device can be effectively reduced, thereby improving the safety of the electrochemical device. In addition, the first pole ear and the second pole ear are electrically connected inside the shell. Compared with being electrically connected outside the shell, when subjected to external impact, the first pole piece assembly and the second pole piece assembly can be suppressed from dislocation and movement, thereby improving the stability of the internal structure of the electrochemical device and reducing the risk of internal short circuit; at the same time, compared with being electrically connected outside the shell, the wires used for connection are reduced, space is saved, and the energy density of the electrochemical device can be improved while reducing the manufacturing cost.

In some embodiments, the first electrode assembly and the second electrode assembly are stacked, and when viewed along the stacking direction of the first electrode assembly and the second electrode assembly, the projections of the first electrode tab and the second electrode tab at least partially overlap, so that the first electrode tab and the second electrode tab can be easily electrically connected in the accommodating cavity of the shell.

In some embodiments, the first electrode assembly includes a plurality of the first pole tabs, the second electrode assembly includes a plurality of the second pole tabs, and the electrochemical device further includes a first transfer pole tab, which is connected to the plurality of the first pole tabs and the plurality of the second pole tabs in the housing and extends out of the housing. The polarity is drawn out through a first transfer pole tab, which can reduce the space occupied by the first pole tab and the second pole tab, thereby improving the energy density of the electrochemical device; at the same time, the first transfer pole tab can be used as a positive or negative contact point when the electrochemical device is charged and discharged, so as to facilitate the connection of the electrochemical device with an external circuit.

In some embodiments, the first electrode assembly includes a plurality of the third tabs, the second electrode assembly includes a plurality of the fourth tabs, the electrochemical device further includes a second transfer tab and a third transfer tab, the second transfer tab is connected to the plurality of the third tabs in the housing and extends out of the housing, and the third transfer tab is connected to the plurality of the fourth tabs in the housing and extends out of the housing. This structural design can reduce the space occupied by the third tab and the fourth tab, thereby improving the energy density of the electrochemical device.

In some embodiments, the first pole piece assembly is selected from a stacked structure or a wound structure.

In some embodiments, the second pole piece assembly is selected from a stacked structure or a wound structure.

In some embodiments, the internal resistance of the first electrode assembly is R1, and the internal resistance of the second electrode assembly is R2, satisfying R1<R2.

In some embodiments, the electrochemical device satisfies: G1≤95%, and/or G2≥95.5%. Further, the electrochemical device satisfies: 94%≤G1≤95%; and/or 95.5%≤G2≤96.5%.

In some embodiments, the electrochemical device further comprises a first connecting member, wherein the first connecting member connects the first pole piece assembly and the second pole piece assembly. In this case, the first pole piece assembly and the second pole piece assembly can be connected and fixed, thereby suppressing the misalignment and movement between the two and improving the stability of the internal structure of the electrochemical device.

In some embodiments, the first connecting component includes a first adhesive portion, a second adhesive portion, and a third adhesive portion. The first adhesive portion and the third adhesive portion are relatively arranged at two ends of the second adhesive portion, and the first pole piece assembly and the second pole piece assembly are located between the first adhesive portion and the third adhesive portion. In this case, the connection and fixing effect between the first pole piece assembly and the second pole piece assembly can be improved.

In some embodiments, the first pole piece assembly includes a first surface, a second surface, and a third surface connected to each other, the first surface and the third surface are arranged opposite to each other along the stacking direction of the first electrode assembly and the second electrode assembly, and the second surface is connected between the first surface and the third surface. The second pole piece assembly includes a fourth surface, a fifth surface, and a sixth surface connected to each other, the fourth surface and the sixth surface are arranged opposite to each other along the stacking direction of the first electrode assembly and the second electrode assembly, and the fifth surface is connected between the fourth surface and the sixth surface. The first bonding portion is bonded to the first surface, the second bonding portion is bonded to the second surface and the fifth surface, and the third bonding portion is bonded to the sixth surface. The first connecting component adopts the above-mentioned bending connection structure, which can suppress the misalignment and movement between the first pole piece assembly and the second pole piece assembly, and improve the stability of the internal structure of the electrochemical device.

In some embodiments, the first pole piece assembly includes a first diaphragm, the second pole piece assembly includes a second diaphragm, and the first pole piece assembly and the second pole piece assembly are connected via the first diaphragm and the second diaphragm. By connecting the first diaphragm and the second diaphragm, the first pole piece assembly and the second pole piece assembly are connected and fixed, and no additional connection assembly is required, which can save space and improve the energy density of the electrochemical device.

In some embodiments, a second connecting component is provided between the first pole piece assembly and the second pole piece assembly, and the first pole piece assembly and the second pole piece assembly are connected via the second connecting component. The second connecting component is located between the first pole piece assembly and the second pole piece assembly, which can better suppress the misalignment and movement between the first pole piece assembly and the second pole piece assembly, thereby reducing the risk of internal short circuit.

In some embodiments, the bonding strength between the first electrode assembly and the second electrode assembly is F, which satisfies: F ≥ 5 N/m. In this case, the connection stability between the first electrode assembly and the second electrode assembly is good, and the misalignment and movement between the two can be better suppressed.

In some embodiments, the first electrode assembly is a laminate structure, the first diaphragm includes a first Z-shaped folded portion and a first winding portion, the first electrode assembly also includes a first positive electrode sheet, the first Z-shaped folded portion is disposed between the adjacent first positive electrode sheet and the first negative electrode sheet, and the first winding portion is wound around the outer ring of the laminate structure. The use of the first diaphragm including the first Z-shaped folded portion and the first winding portion can better suppress the misalignment and movement between the first positive electrode sheet and the first negative electrode sheet, thereby reducing the risk of internal short circuit.

In some embodiments, the second pole piece assembly is a laminate structure, the second diaphragm includes a second Z-shaped folded portion and a second winding portion, the second pole piece assembly also includes a second positive pole piece, the second Z-shaped folded portion is disposed between the adjacent second positive pole piece and the second negative pole piece, and the second winding portion is wound around the outer ring of the laminate structure. The use of the second diaphragm including the second Z-shaped folded portion and the second winding portion can better suppress the misalignment and movement between the second positive pole piece and the second negative pole piece, thereby reducing the risk of internal short circuit.

In some embodiments, the first separator and the second separator each independently include a substrate layer, an optional ceramic layer, and an optional bonding layer.

In some embodiments, the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide.

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

In some embodiments, the ceramic layer includes inorganic particles and a binder.

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.

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

In some embodiments, the bonding layer is located on the surface of the substrate layer and/or the ceramic layer.

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

In some embodiments, the electrochemical device includes at least two of the first electrode assemblies and at least one of the second electrode assemblies, and the second electrode assembly is arranged between two adjacent first electrode assemblies. The first electrode assembly is a fast charging system, and a second electrode assembly is arranged between the first electrode assemblies of the fast charging system. When high-rate charging and discharging are performed through the first electrode assembly, it is possible to facilitate the diffusion of heat of the first electrode assembly of the fast charging system, thereby reducing the local temperature rise of the electrochemical device and improving the safety of the electrochemical device. Alternatively, the electrochemical device includes at least one of the first electrode assemblies and at least two of the second electrode assemblies, and the first electrode assembly is arranged between two adjacent second electrode assemblies. The first electrode assembly of the fast charging system is arranged in the middle, which is conducive to the diffusion of heat generated by the electrode assembly of the fast charging system to the left and right sides.

In a second aspect, the present application also proposes an electronic device, comprising any electrochemical device as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments are exemplarily described by corresponding drawings, which do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings represent similar elements, and the figures in the drawings do not constitute proportional limitations unless otherwise stated.

FIG1 is a schematic diagram of the structure of an electrochemical device according to some embodiments of the present application;

FIG2 is an exploded view of an electrochemical device according to some embodiments of the present application;

FIG3 is a schematic diagram of the structure of a first pole piece assembly and a second pole piece assembly in some embodiments of the present application;

FIG4 is a schematic diagram of a winding structure of a first pole piece assembly in some embodiments of the present application;

FIG5 is a schematic diagram of the structure of a first negative electrode plate in some embodiments of the present application;

FIG6 is a schematic diagram of stacking a first electrode assembly and a second electrode assembly according to some embodiments of the present application;

FIG7 is an exploded view of an electrochemical device according to some embodiments of the present application;

8 is a schematic diagram of a structure in which a first connecting component connects a first pole piece assembly and a second pole piece assembly according to some embodiments of the present application;

FIG. 9 is a schematic diagram of a structure in which a first connecting component connects a first pole piece assembly and a second pole piece assembly in some embodiments of the present application.

FIG10 is a schematic diagram of the structure of a first pole piece assembly and a second pole piece assembly in some embodiments of the present application;

FIG11 is a schematic diagram of the structure of a first pole piece assembly and a second pole piece assembly in some embodiments of the present application;

FIG. 12 is an exploded view of an electrochemical device according to some embodiments of the present application.

Description of reference numerals:

100. Electrochemical device;

10. Shell; 11. First shell; 111. First cavity; 12. Second shell;

20. First electrode assembly; 21. First electrode sheet assembly; 211. First positive electrode sheet; 212. First negative electrode sheet; 2121. First negative electrode current collector; 2122. First negative electrode active layer; 213. First separator; 2131. First Z-shaped folded portion; 2132. First winding portion; 22. First pole ear; 23. Third pole ear; 24. First surface; 25. Second surface; 26. Third surface; 27. First single-sided positive electrode sheet;

30. second electrode assembly; 31. second electrode sheet assembly; 311. second positive electrode sheet; 312. second negative electrode sheet; 313. second separator; 3131. second Z-shaped folded portion; 3132. second winding portion; 32. second electrode tab; 33. fourth electrode tab; 34. fourth surface; 35. fifth surface; 36. sixth surface; 37. second single-sided positive electrode sheet;

40. a first transfer tab;

50. Second transfer tab;

60. The third transfer tab;

70, first connecting member; 71, first bonding portion; 72, second bonding portion; 73, third bonding portion;

80. Second connecting component.

Detailed ways

The following embodiments of the technical solution of the present application will be described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

In the description of the embodiments of the present application, the term "and/or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships, for example, A and/or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character "/" in this article generally indicates that the associated objects before and after are in an "or" relationship.

Reference to "embodiment" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments.

In a first aspect, an embodiment of the present application provides an electrochemical device 100 , which is a place for realizing the conversion of electrical energy and chemical energy. Referring to FIG. 1 and FIG. 2 , the electrochemical device 100 includes a housing 10 , a first electrode assembly 20 , and a second electrode assembly 30 .

For the above-mentioned shell 10, the shell 10 is used to package the above-mentioned first electrode assembly 20 and the second electrode assembly 30. Referring to Figures 1 and 2, the shell 10 encloses a receiving cavity (not shown in the figure), and the above-mentioned first electrode assembly 20 and the second electrode assembly 30 can be accommodated in the receiving cavity. Optionally, the shell 10 is a square structure as a whole, and the thickness of each side wall of the shell 10 can be set to 40 microns to 200 microns; the shell 10 includes a first shell 11 and a second shell 12, the first shell 11 is recessed with a first cavity 111, and the second shell 12 is recessed with a second cavity (not shown in the figure), the first shell 11 and the second shell 12 are spliced and the edges of the first shell 11 and the second shell 12 are heat-sealed, so that the first shell 11 and the second shell 12 are connected to the shell 10, wherein the first cavity 111 is communicated with the second cavity to form a receiving cavity. The shell 10 can be a multi-layer composite film containing a metal layer or a stainless steel shell, for example, an aluminum-plastic film containing a PP layer and an aluminum layer stacked structure is used to fully improve the energy density of the electrochemical device 100 while playing a packaging role.

Regarding the first electrode assembly 20 , please refer to FIG. 2 . The first electrode assembly 20 includes a first electrode sheet assembly 21 , a first electrode tab 22 and a third electrode tab 23 .

For the above-mentioned first electrode sheet assembly 21, please refer to Figures 3 and 4. The first electrode sheet assembly 21 includes a first positive electrode sheet 211, a first negative electrode sheet 212 and a first separator 213. The first electrode sheet assembly 21 can adopt a laminated structure, that is, the first positive electrode sheet 211, the first separator 213 and the first negative electrode sheet 212 are stacked, and Figure 3 shows the stacked structure of the first electrode sheet assembly 21. The first electrode sheet assembly 21 can also adopt a winding structure, that is, the first positive electrode sheet 211, the first separator 213 and the first negative electrode sheet 212 are stacked and wound, and Figure 4 shows the winding structure of the first electrode sheet assembly 21. Please further refer to Figure 5. The first negative electrode sheet 212 includes a first negative current collector 2121 and a first negative active layer 2122. The first negative active layer 2122 is coated on at least one surface of the first negative current collector 2121. The first negative electrode active layer 2122 includes a first negative electrode active material, a binder, and an optional conductive agent, etc., wherein the first negative electrode active material includes graphite, and the graphitization degree of the first negative electrode active material is G1.

For the above-mentioned first pole ear 22 and third pole ear 23, please refer to Figures 2 and 3. The first pole ear 22 and the third pole ear 23 are both connected to the first pole piece assembly 21. The first pole ear 22 and the third pole ear 23 are metal conductors that lead out the positive and negative poles of the first pole piece assembly 21. For example, the first pole ear 22 is connected to the first negative pole piece 212, and the second pole ear 32 is connected to the first positive pole piece 211; in other embodiments, the first pole ear 22 can also be connected to the first positive pole piece 211, and the second pole ear 32 is connected to the first negative pole piece 212.

Regarding the second electrode assembly 30 , please refer to FIG. 2 . The second electrode assembly 30 includes a second electrode sheet assembly 31 , a second electrode tab 32 and a fourth electrode tab 33 .

For the above-mentioned second electrode sheet assembly 31, please refer to FIG. 3. The second electrode sheet assembly 31 includes a second positive electrode sheet 311, a second negative electrode sheet 312 and a second separator 313. The second electrode sheet assembly 31 can adopt a laminated structure, that is, the second positive electrode sheet 311, the second separator 313 and the second negative electrode sheet 312 are stacked; the second electrode sheet assembly 31 can also adopt a winding structure, that is, the second positive electrode sheet 311, the second separator 313 and the second negative electrode sheet 312 are stacked and wound. Among them, the second negative electrode sheet 312 includes a second negative electrode collector (not shown in the figure) and a second negative electrode active layer (not shown in the figure), and the second negative electrode active layer is coated on at least one surface of the second negative electrode collector. The second negative electrode active layer includes a second negative electrode active material, a binder and an optional conductive agent, etc.; wherein, the second negative electrode active material includes graphite, and the graphitization degree of the second negative electrode active material is G2, wherein G2-G1≥0.5%.

The lower the graphitization degree of the negative electrode active material, the higher the maximum charge and discharge rate of the corresponding electrode assembly can be set. Therefore, in the electrochemical device 100 of the present application, the maximum charge and discharge rate of the first electrode assembly 20 (the maximum charge and discharge rate that the electrode assembly can accept, for example, does not cause lithium precipitation at the maximum charge rate) can be set to be greater than the maximum charge and discharge rate of the second electrode assembly 30, that is, the first electrode assembly 20 is a fast charging system, and the second electrode assembly 30 is a slow charging system. The fast charging system can meet the emergency charging needs in emergency situations and the high-rate discharge needs under high-rate applications, but its capacity in the fully charged state is usually low; while the slow charging system can meet conventional use and can increase the overall capacity of the electrochemical device 100. For example, the maximum charging rate of the first electrode assembly 20 is greater than 2C, and the full charge capacity is ≤2000mAh. In an emergency, the fast charging system can be partially charged to meet emergency needs; the maximum charging rate of the second electrode assembly 30 is ≤2C, and the full charge capacity is ≥3000mAh. Under the condition of meeting conventional use, the electrochemical device 100 can be guaranteed to have a higher capacity as a whole. Furthermore, the first electrode assembly 21 and the second electrode assembly 31 are housed in the same housing 10. When the first electrode assembly 20 is charged and discharged at a high rate, the local temperature rise of the electrochemical device 100 can be effectively reduced, thereby improving the safety of the electrochemical device 100.

Specifically, in some embodiments, the degree of graphitization G1 of the first negative electrode active material is ≤95%, and/or the degree of graphitization G2 of the second negative electrode active material is ≥95.5%; further, the degree of graphitization G1 of the first negative electrode active material satisfies: 94%≤G1≤95%, and/or the degree of graphitization G2 of the second negative electrode active material satisfies: 95.5%≤G2≤96.5%.

For the above-mentioned second pole lug 32 and fourth pole lug 33, please refer to Figures 2 and 3. The second pole lug 32 and the fourth pole lug 33 are both connected to the second pole piece assembly 31. The second pole lug 32 and the fourth pole lug 33 are metal conductors that lead out the positive and negative poles of the second pole piece assembly 31. For example, the second pole lug 32 is connected to the second negative pole piece 312, and the fourth pole lug 33 is connected to the second positive pole piece 311; in other embodiments, the second pole lug 32 can also be connected to the second positive pole piece 311, and the fourth pole lug 33 is connected to the second negative pole piece 312.

The first pole tab 22 and the second pole tab 32 have the same polarity, and the third pole tab 23 and the fourth pole tab 33 have the same polarity. For example, the first pole tab 22 and the second pole tab 32 are both negative pole tabs; or, the first pole tab 22 and the second pole tab 32 are both positive pole tabs. The first pole tab 22 and the second pole tab 32 are electrically connected in the accommodating cavity of the shell 10. The first pole tab 22 and the second pole tab 32 are electrically connected in the accommodating cavity of the shell 10. Compared with being electrically connected outside the shell 10, when subjected to external impact, the first pole tab 22 and the second pole tab 32 can suppress the misalignment and movement between the first pole tab assembly 21 and the second pole tab assembly 31, thereby improving the stability of the internal structure of the electrochemical device 100 and reducing the risk of internal short circuit.

Specifically, as shown in Figure 2, the first electrode assembly 20 is stacked below the second electrode assembly 30, the first pole ear 22 and the third pole ear 23 are arranged near the upper edge of the first electrode assembly 20, and the second pole ear 32 and the fourth pole ear 33 are arranged near the lower edge of the second electrode assembly 30, so that the first pole ear 22 and the second pole ear 32 are stacked and connected.

In some embodiments, please refer to FIG. 6 , the first electrode assembly 20 and the second electrode assembly 30 are stacked, and the projections of the first pole tab 22 and the second pole tab 32 at least partially overlap when viewed along the stacking direction of the first electrode assembly 20 and the second electrode assembly 30. This structure can facilitate the connection of the first pole tab 22 and the second pole tab 32 in the accommodating cavity of the housing 10. For example, along the stacking direction of the first electrode assembly 20 and the second electrode assembly 30, laser welding is used to weld the stacked body of the first pole tab 22 and the second pole tab 32 into a whole, which can improve the stability of the connection between the first electrode assembly 20 and the second electrode assembly 30.

In some embodiments, please refer to FIG. 1 and FIG. 7 , the first electrode assembly 20 includes a plurality of first tabs 22, the second electrode assembly 30 includes a plurality of second tabs 32, and the electrochemical device 100 further includes a first transfer tab 40. One end of the first transfer tab 40 is disposed in the accommodating cavity of the housing 10 and connected to the plurality of first tabs 22 and the plurality of second tabs 32, and the other end of the first transfer tab 40 extends out of the housing 10. The first tab 22 and the second tab 32 have the same polarity, and the polarity is led out through a first transfer tab 40, which can reduce the space occupied by the first tab 22 and the second tab 32, thereby improving the energy density of the electrochemical device 100; at the same time, the first transfer tab 40 can be used as a positive or negative contact point of the electrochemical device 100 during charging and discharging, so as to facilitate the connection of the electrochemical device 100 with an external circuit.

Optionally, referring to FIG. 1 and FIG. 7 , the first electrode assembly 20 includes a plurality of third pole tabs 23, the second electrode assembly 30 includes a plurality of fourth pole tabs 33, and the electrochemical device 100 further includes a second transfer pole tab 50 and a third transfer pole tab 60. One end of the second transfer pole tab 50 is connected to the plurality of third pole tabs 23 in the accommodating cavity of the shell 10, and the other end of the second transfer pole tab 50 extends out of the shell 10 to serve as a contact point connected to an external circuit. One end of the third transfer pole tab 60 is connected to the plurality of fourth pole tabs 33 in the accommodating cavity of the shell 10, and the other end of the third transfer pole tab 60 extends out of the shell 10 to serve as a contact point connected to an external circuit. In this embodiment, this structural design can reduce the space occupied by the third pole tab 23 and the fourth pole tab 33, thereby improving the energy density of the electrochemical device 100.

In some embodiments, the first adapter tab 40 is welded to the first tabs 22 and the second tabs 32 , the second adapter tab 50 is welded to the third tabs 23 , and the third adapter tab 60 is welded to the fourth tabs 33 .

In some embodiments, the internal resistance of the first electrode assembly 20 is R1, and the internal resistance of the second electrode assembly 30 is R2, satisfying R1<R2. Optionally, R2-R1≤30mΩ. By setting the internal resistance of the first electrode assembly 20 to be smaller than the internal resistance of the second electrode assembly 30, the current passing through the first electrode assembly 20 is increased to meet the fast charging requirement.

In order to further fix the first electrode assembly 20 and the second electrode assembly 30, in an embodiment of the present application, please refer to Figure 8, the electrochemical device 100 also includes a first connecting component 70, and the first connecting component 70 connects the first pole piece assembly 21 and the second pole piece assembly 31 to connect and fix the first pole piece assembly 21 and the second pole piece assembly 31 to inhibit the misalignment and movement between the two, thereby reducing the risk of internal short circuit.

Optionally, referring to Figures 8 and 9, the first connecting member 70 includes a first adhesive portion 71, a second adhesive portion 72, and a third adhesive portion 73. The first adhesive portion 71 and the third adhesive portion 73 are relatively arranged at two ends of the second adhesive portion 72, and the first pole piece assembly 21 and the second pole piece assembly 31 are located between the first adhesive portion 71 and the third adhesive portion 73.

Specifically, referring to FIG8 and FIG9, the first pole piece assembly 21 includes a first surface 24, a second surface 25 and a third surface 26 connected to each other, the first surface 24 and the third surface 26 are arranged opposite to each other along the stacking direction of the first electrode assembly 20 and the second electrode assembly 30, and the second surface 25 is connected between the first surface 24 and the third surface 26. The second pole piece assembly 31 includes a fourth surface 34, a fifth surface 35 and a sixth surface 36 connected to each other, the fourth surface 34 and the sixth surface 36 are arranged opposite to each other along the stacking direction of the first electrode assembly 20 and the second electrode assembly 30, and the fifth surface 35 is connected between the fourth surface 34 and the sixth surface 36. The first bonding portion 71 is bonded to the first surface 24, the second bonding portion 72 is bonded to the second surface 25 and the fifth surface 35, and the third bonding portion 73 is bonded to the sixth surface 36. In this embodiment, the two ends of the first connecting member 70 are bent to form a U-shaped structure, so that the first bonding portion 71 is bonded to the first surface 24 of the first electrode assembly 20, the third bonding portion 73 is bonded to the sixth surface 36 of the second electrode assembly 30, and the second bonding portion 72 is bonded to the second surface 25 of the first electrode assembly 20 and the fourth surface 34 of the second electrode assembly 30, so that the first electrode assembly 20 and the second electrode assembly 30 are connected as a whole, which can inhibit the misalignment and movement between the first pole piece assembly 21 and the second pole piece assembly 31, and improve the stability of the connection. In this embodiment, the first connecting member 70 can be an adhesive tape. At this time, the thickness of the first connecting member 70 is relatively thin, which can reduce the space occupied by the first connecting member 70, and facilitate the improvement of the energy density of the electrochemical device 100.

In some embodiments, please refer to FIG. 3 , the end surface of the first pole piece assembly 21 facing the second pole piece assembly 31 is provided with a first diaphragm 213, and the end surface of the second pole piece assembly 31 facing the first pole piece assembly 21 is provided with a second diaphragm 313, and the first diaphragm 213 and the second diaphragm 313 each independently include a substrate layer, an optional ceramic layer, and an optional bonding layer, and the first pole piece assembly 21 and the second pole piece assembly 31 are connected through the first diaphragm 213 and the second diaphragm 313. Specifically, the first diaphragm 213 and the second diaphragm 313 can be bonded between the first pole piece assembly 21 and the second pole piece assembly 31 by hot pressing. In this embodiment, the first pole piece assembly 21 and the second pole piece assembly 31 are bonded and connected through the first diaphragm 213 and the second diaphragm 313 by direct hot pressing, and no additional bonding components are required, which can save space, so as to improve the energy density of the electrochemical device 100. It can be understood that the first diaphragm 213 or the second diaphragm 313 of different materials and structures provide different bonding forces during hot pressing. In the embodiment of the present application, the first diaphragm 213 and the second diaphragm 313 of suitable materials and structures can be selected according to the specific situation. In some embodiments, the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. In some embodiments, the ceramic layer is located on the surface of the substrate layer. In some embodiments, the ceramic layer includes inorganic particles and a binder. In some embodiments, the inorganic particles include 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. In some embodiments, the binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene or polyhexafluoropropylene. In some embodiments, the bonding layer is located on the surface of the substrate layer and/or the ceramic layer, and in this case, the bonding layer can promote the bonding between the first pole piece assembly 21 and the second pole piece assembly 31. In some embodiments, the bonding layer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or a copolymer of vinylidene fluoride and hexafluoropropylene.

Optionally, referring to FIG. 10 , a second connecting component 80 is provided between the first pole piece assembly 21 and the second pole piece assembly 31, and the first pole piece assembly 21 and the second pole piece assembly 31 are connected via the second connecting component 80. In this embodiment, the first pole piece assembly 21 and the second pole piece assembly 31 are connected via the second connecting component 80. As required, the second connecting component 80 with different viscosities can be selected to bond the first pole piece assembly 21 and the second pole piece assembly 31, for example, a strong adhesive tape is used to improve the stability of bonding the first pole piece assembly 21 and the second pole piece assembly 31.

In some embodiments, the bonding force between the first pole piece assembly 21 and the second pole piece assembly 31 is F, which satisfies: F ≥ 5 N. At this time, the connection stability between the first pole piece assembly 21 and the second pole piece assembly 31 is good, and the misalignment and movement between the two can be better suppressed.

Optionally, referring to FIG. 10 and FIG. 11 , the first electrode assembly 21 is a laminate structure, the first diaphragm 213 includes a first Z-shaped folded portion 2131 and a first winding portion 2132, the first electrode assembly 21 includes a plurality of first positive electrode sheets 211 and a plurality of first negative electrode sheets 212, the first Z-shaped folded portion 2131 is disposed between adjacent first positive electrode sheets 211 and first negative electrode sheets 212 to isolate the adjacent first positive electrode sheets 211 from the first negative electrode sheets 212, and the first winding portion 2132 is wound around the outer ring of the laminate structure. The use of the first diaphragm 213 including the first Z-shaped folded portion 2131 and the first winding portion 2132 can better suppress the misalignment and movement between the first positive electrode sheet 211 and the first negative electrode sheet 212, thereby reducing the risk of internal short circuit.

Further, the second electrode assembly 31 is a laminate structure, the second diaphragm 313 includes a second Z-shaped folded portion 3131 and a second winding portion 3132, the second electrode assembly 31 includes a plurality of second positive electrode sheets 311 and a plurality of second negative electrode sheets 312, the second Z-shaped folded portion 3131 is disposed between adjacent second positive electrode sheets 311 and second negative electrode sheets 312 to isolate the adjacent second positive electrode sheets 311 from the second negative electrode sheets 312, and the second winding portion 3132 is wound around the outer ring of the laminate structure. The second diaphragm 313 including the second Z-shaped folded portion 3131 and the second winding portion 3132 can better suppress the misalignment and movement between the second positive electrode sheet 311 and the second negative electrode sheet 312, thereby reducing the risk of internal short circuit.

Please refer to Figure 11. The outermost layer of the first pole piece assembly 21 is the first single-sided positive electrode plate 27, that is, the outermost first positive electrode collector is coated with a positive electrode active layer only on one side, and the positive electrode active layer faces the inner layer of the first pole piece assembly 21; similarly, the outermost layer of the second pole piece assembly 31 is the second single-sided positive electrode plate 37. This structure can make full use of each active layer to improve the energy density of the electrochemical device 100.

According to some embodiments of the present application, there are at least two first electrode assemblies 20, at least one second electrode assembly 30, and a second electrode assembly 30 is disposed between two adjacent first electrode assemblies 20. The first electrode assembly 20 is a fast charging system, and a second electrode assembly 30 is disposed between the first electrode assemblies 20 of the fast charging system. When the first electrode assembly 20 is charged and discharged at a high rate, the heat diffusion of the first electrode assembly 20 of the fast charging system can be facilitated, thereby reducing the local temperature rise of the electrochemical device 100 and improving the safety of the electrochemical device 100. According to some embodiments of the present application, there is at least one first electrode assembly 20, at least two second electrode assemblies 30, and a first electrode assembly 20 is disposed between two adjacent second electrode assemblies 30. The first electrode assembly 20 of the fast charging system is disposed in the middle, and the heat generated by the first electrode assembly 20 of the fast charging system can be easily diffused to the left and right sides. For example, please refer to Figure 12, there are two first electrode assemblies 20, and a second electrode assembly 30 is sandwiched between the two first electrode assemblies 20.

In the embodiments of the present application, taking lithium-ion batteries of three systems of fast charge + slow charge, fast charge + slow charge + fast charge, and slow charge + fast charge + slow charge as examples, charge and discharge tests, graphitization tests, drop tests, and bonding strength tests were performed on them.

Preparation of lithium-ion batteries

Example 1

(1) Preparation of negative electrode sheets for fast charging system and slow charging system: artificial graphite with a graphitization degree G1 of 94.8% is selected as the negative electrode active material for the fast charging system, and artificial graphite with a graphitization degree G2 of 95.5% is selected as the negative electrode active material for the slow charging system. The negative electrode active material artificial graphite, binder styrene butadiene rubber (SBR) and thickener sodium carboxymethyl cellulose (CMC) are mixed according to a weight ratio of 96:2:2, deionized water is added as a solvent, and a slurry with a solid content of 70wt% is prepared and stirred evenly. The slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 10μm, and dried to obtain a negative electrode sheet coated with a negative electrode active layer on one side. On the other surface of the negative electrode current collector copper foil, the above steps are repeated to obtain a negative electrode sheet coated with a negative electrode active layer on both sides. After cold pressing, the negative electrode sheet is cut into a specification of 41mm×61mm for standby use.

(2) Preparation of positive electrode sheet: The positive electrode active material lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%, and stirred evenly. The slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12μm, and dried to obtain a positive electrode sheet coated with a positive electrode active layer on one side. On the other surface of the positive electrode current collector aluminum foil, the above steps are repeated to obtain a positive electrode sheet coated with a positive electrode active layer on both sides. After cold pressing, the positive electrode sheet is cut into a specification of 38mm×58mm for standby use.

(3) Preparation of electrolyte: In a dry argon atmosphere, 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, and 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%.

(4) Preparation of isolation membrane: A polyethylene porous membrane is used as a substrate layer, and a ceramic layer containing alumina ceramics and a PVDF binder is coated on one surface of the substrate layer as a separator (CCS), wherein the mass percentage of alumina ceramics in the ceramic layer is 95%.

(5) Preparation of fast-charging system electrode assemblies and slow-charging system electrode assemblies: The separator is folded in a Z shape and placed between the stacked negative electrode sheets and the stacked positive electrode sheets. The tail end of the separator is wound around the entire electrode assembly to form a stacked structure electrode assembly for later use.

(6) Assembly of the fast-charging system electrode assembly and the slow-charging system electrode assembly: Place the aluminum-plastic film formed by punching holes in an assembly fixture with the pit side facing upward, place the fast-charging system electrode assembly in the pit, and then place the slow-charging system electrode assembly on the fast-charging system electrode assembly so that the edges are aligned and pressed tightly with external force, wherein the 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 the tabs are connected and led out. Then, the multiple overlapping positive electrode tabs of the fast-charging system electrode assembly and the multiple overlapping positive electrode tabs of the slow-charging system electrode assembly are laser welded together, and the tabs are connected and led out. Then, another aluminum-plastic film formed by punching holes is covered on the slow-charging system electrode assembly with the pit side facing downward, and heat-sealed on all sides by hot pressing to obtain an assembled electrode assembly.

(7) Liquid injection packaging: The assembled electrode assembly is injected with electrolyte, and after vacuum packaging, static standing, hot pressing, shaping and other processes, a lithium-ion battery is produced.

The difference between Example 2 and Example 1 is that the fast charging system selects artificial graphite with a graphitization degree G1 of 94.6% as the negative electrode active material. In the preparation of the separator, the mass percentage of alumina ceramic in the ceramic layer is 90%.

The difference between Example 3 and Example 1 is that the fast charging system selects artificial graphite with a graphitization degree G1 of 94.4% as the negative electrode active material. In the preparation of the separator, the mass percentage of alumina ceramic in the ceramic layer is 85%.

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

The difference between Example 5 and Example 1 is that the fast charging system selects artificial graphite with a graphitization degree G1 of 94.1% as the negative electrode active material, and the slow charging system selects artificial graphite with a graphitization degree G2 of 96.1% as the negative electrode active material; in the preparation of the isolation membrane, the ceramic layer is replaced by a bonding layer (PCS) containing only PVDF.

The difference between Example 6 and Example 3 is that the fast charging system selects artificial graphite with a graphitization degree G1 of 94.0% as the negative electrode active material, and the slow charging system selects artificial graphite with a graphitization degree G2 of 96.1% as the negative electrode active material. In the assembly steps of the fast charging system electrode assembly and the slow charging system electrode assembly, adhesive tape is first used as the first connecting component, the fast charging system electrode assembly and the slow charging system electrode assembly are stacked and bonded, and then placed in the pit of the aluminum-plastic film.

The difference between Example 7 and Example 5 is that the fast charging system selects artificial graphite with a graphitization degree G1 of 94.2% as the negative electrode active material, and the slow charging system selects artificial graphite with a graphitization degree G2 of 96.2% as the negative electrode active material. In the assembly steps of the fast charging system electrode assembly and the slow charging system electrode assembly, adhesive tape is first used as the first connecting component, the fast charging system electrode assembly and the slow charging system electrode assembly are stacked and bonded, and then placed in the pit of the aluminum-plastic film.

The difference between Example 8 and Example 2 is that the fast charging system selects artificial graphite with a graphitization degree G1 of 94.5% as the negative electrode active material, and the slow charging system selects artificial graphite with a graphitization degree G2 of 95.8% as the negative electrode active material. In the assembly step of the fast charging system electrode assembly and the slow charging system electrode assembly, a fast charging electrode assembly is further placed on the slow charging system electrode assembly to form a fast charging + slow charging + fast charging structure.

The difference between Example 9 and Example 1 is that the fast charging system selects artificial graphite with a graphitization degree G1 of 94.3% as the negative electrode active material, and the slow charging system selects artificial graphite with a graphitization degree G2 of 95.9% as the negative electrode active material. In the assembly steps of the fast charging system electrode assembly and the slow charging system electrode assembly, adhesive tape is used as the second connecting component, which is arranged between the fast charging system electrode assembly and the slow charging system electrode assembly, and is stacked and bonded to form a fast charging + slow charging + fast charging structure, and then placed in the pit of the aluminum-plastic film.

The difference between Example 10 and Example 7 is that the fast charging system selects artificial graphite with a graphitization degree G1 of 94.6% as the negative electrode active material, and the slow charging system selects artificial graphite with a graphitization degree G2 of 96.0% as the negative electrode active material. In the assembly step of the fast charging system electrode assembly and the slow charging system electrode assembly, a fast charging + slow charging + fast charging structure is formed.

The difference between Example 11 and Example 10 is that the fast charging system selects artificial graphite with a graphitization degree G1 of 94.8% as the negative electrode active material, and the slow charging system selects artificial graphite with a graphitization degree G2 of 95.7% as the negative electrode active material. In the assembly steps of the fast charging system electrode assembly and the slow charging system electrode assembly, a slow charging + fast charging + slow charging structure is formed.

The difference between Comparative Example 1 and Example 1 is that in the assembly steps of the fast-charging system electrode assembly and the slow-charging system electrode assembly, the multiple negative electrode tabs of the fast-charging system electrode assembly and the multiple negative electrode tabs of the slow-charging system electrode assembly are respectively laser welded together and the tabs are respectively connected and led out.

Test Methods

Fast charging temperature rise test: Charge the electrode components of the fast charging system at 25°C, charge to 4.45V at a constant current of 10C, and charge to 0.05C at a constant voltage, and monitor the maximum temperature rise of the battery surface during the charging process.

Slow charging temperature rise test: Charge the electrode components of the slow charging system at 25°C, charge to 4.45V at a constant current rate of 1C, and charge to 0.02C at a constant voltage, and monitor the maximum temperature rise of the battery surface during the charging process.

Graphitization degree test: XRD test was performed using Bruker test instrument, where the XRD reference standard was JIS K 0131-1996 "General rules of X-ray diffractometric analysis". During the test, the mass ratio of silicon powder to the graphite negative electrode active material to be tested was 1:5. The target material was Cu Kα, the voltage was 40KV, the current was 40mA, the scanning angle range was 52° to 58°, the scanning step length was 0.008°, and the duration of each step was 0.3s.

Drop test: On a cement drop floor, drop the battery from a height of 1m along 6 sides once and 4 corners once, for a total of 5 rounds of testing; judgment criteria: if the width misalignment between electrode assemblies is ≤0.2mm, it is judged as no misalignment; if the width misalignment between electrode assemblies is 0.2mm＜0.5mm, it is judged as mild misalignment; if the width misalignment between electrode assemblies is 0.5mm＜1.0mm, it is judged as moderate misalignment; if the width misalignment between electrode assemblies is >1.0mm, it is judged as severe misalignment.

Bond strength test: ①Preparation before the test, turn on the power of the high-speed rail tensile testing machine, confirm whether the upper and lower clamps of the tensile testing machine are in a horizontal position, whether the tension rod can move up and down normally, and confirm that the speed control of the tensile testing machine is 50mm/min; ②Make samples, cut the bonding area samples with a width of W; ③Put the clamps on the samples, and the clamps clamp the materials on both sides of the bonding area samples; ④Tensile test, click the reset and run buttons to start the test, output the tensile value P, then the bonding strength F = P/W.

The test results are shown in Table 1 below.

Table 1

According to the above test results, it can be found that the graphitization degree G1 of the fast charging system electrode assembly is less than the graphitization degree G2 of the slow charging system electrode assembly, and, in combination with Examples 1 to 11, it can be seen that when G2-G1≥0.5%, the fast charging and slow charging requirements of the electrochemical device 100 can be met.

Furthermore, when G1≤95%, and/or G2≥95.5%, the battery temperature rise is small when the fast charging system electrode assembly is fast charged and the slow charging system electrode assembly is slow charged. Further, 94%≤G1≤95%; and/or 95.5%≤G2≤96.5%, within this range, the battery temperature rise under fast charging and slow charging conditions can achieve better results.

In addition, in the drop test, in combination with Examples 1 to 11 and Comparative Example 1, it can be seen that the negative pole tabs of the fast-charging system electrode assembly and the slow-charging system electrode assembly are welded and connected in the shell, which can suppress the degree of misalignment during the drop test, thereby reducing the risk of internal short circuit. In combination with Examples 1 to 5 and Examples 6 to 7, it can be seen that when the first connecting component 70 is used to connect and fix each electrode assembly, the degree of misalignment during the drop test can be further reduced. Therefore, in the embodiments of the present application, the structure in which the first pole tab 22 and the second pole tab 32 are connected in the accommodating cavity is preferably adopted. Further, the first electrode assembly 20 and the second electrode assembly 30 are bonded by hot pressing bonding of the first diaphragm 213 and the second diaphragm 313, and the first electrode assembly 20 and the second electrode assembly 30 are connected as a whole by a first connecting component 70, thereby suppressing the misalignment between the first electrode assembly 20 and the second electrode assembly 30, and reducing the risk of short circuit inside the electrochemical device 100.

The embodiment of the present application also proposes an electronic device, including the electrochemical device 100 described in any of the above embodiments. The electronic device of the embodiment of the present application is not particularly limited, and it can be any electronic device known in the prior art. For example, the electronic device includes but is not limited to Bluetooth headsets, mobile phones, tablets, laptops, electric toys, electric tools, battery cars, electric cars, ships, spacecraft, etc.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Under the concept of the present application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes in different aspects of the present application as described above, which are not provided in detail for the sake of simplicity. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some of the technical features can be replaced by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

An electrochemical device, comprising:

case;

A first electrode assembly, comprising a first electrode sheet assembly and a first electrode tab and a third electrode tab connected to the first electrode sheet assembly, wherein the first electrode sheet assembly is accommodated in the housing, the first electrode sheet assembly comprises a first negative electrode sheet, the first negative electrode sheet comprises a first negative electrode active material, and the graphitization degree of the first negative electrode active material is G1;

A second electrode assembly includes a second electrode sheet assembly and a second electrode tab and a fourth electrode tab connected to the second electrode sheet assembly, wherein the second electrode sheet assembly is accommodated in the housing, the second electrode sheet assembly includes a second negative electrode sheet, the second negative electrode sheet includes a second negative electrode active material, and the graphitization degree of the second negative electrode active material is G2, satisfying: G2-G1≥0.5%;

The first pole tab and the second pole tab have the same polarity, the third pole tab and the fourth pole tab have the same polarity, and the first pole tab and the second pole tab are electrically connected in the housing.
The electrochemical device according to claim 1, characterized in that the electrochemical device satisfies at least one of the following conditions:

(1) The first electrode assembly and the second electrode assembly are stacked, and when viewed along the stacking direction of the first electrode assembly and the second electrode assembly, the projections of the first electrode tab and the second electrode tab at least partially overlap;

(2) The first electrode assembly includes a plurality of the first electrode tabs, the second electrode assembly includes a plurality of the second electrode tabs, and the electrochemical device further includes a first transfer tab, wherein the first transfer tab is connected to the plurality of the first electrode tabs and the plurality of the second electrode tabs in the housing and extends out of the housing;

(3) The first electrode assembly includes a plurality of the third electrode tabs, the second electrode assembly includes a plurality of the fourth electrode tabs, and the electrochemical device further includes a second transfer tab and a third transfer tab, the second transfer tab and the plurality of the third electrode tabs are connected in the shell and extend out of the shell, and the third transfer tab and the plurality of the fourth electrode tabs are connected in the shell and extend out of the shell;

(4) The first pole piece assembly is selected from a laminated structure or a wound structure;

(5) The second pole piece assembly is selected from a laminated structure or a wound structure;

(6) The internal resistance of the first electrode assembly is R1, and the internal resistance of the second electrode assembly is R2, satisfying R1<R2.
The electrochemical device according to claim 1, characterized in that the electrochemical device satisfies: G1≤95%, and/or G2≥95.5%.
The electrochemical device according to claim 3 is characterized in that the electrochemical device satisfies: 94%≤G1≤95%; and/or 95.5%≤G2≤96.5%.
The electrochemical device according to claim 1 is characterized in that the electrochemical device further comprises a first connecting component, wherein the first connecting component connects the first pole piece assembly and the second pole piece assembly.
The electrochemical device according to claim 5, characterized in that the first connecting member includes a first bonding portion, a second bonding portion and a third bonding portion;

The first adhesive portion and the third adhesive portion are arranged at two ends of the second adhesive portion opposite to each other, and the first pole piece assembly and the second pole piece assembly are located between the first adhesive portion and the third adhesive portion.
The electrochemical device according to claim 6, characterized in that

The first electrode assembly comprises a first surface, a second surface and a third surface connected to each other, the first surface and the third surface are arranged opposite to each other along the stacking direction of the first electrode assembly and the second electrode assembly, and the second surface is connected between the first surface and the third surface;

The second electrode assembly comprises a fourth surface, a fifth surface and a sixth surface connected to each other, the fourth surface and the sixth surface are arranged opposite to each other along the stacking direction of the first electrode assembly and the second electrode assembly, and the fifth surface is connected between the fourth surface and the sixth surface;

The first adhesive portion is adhered to the first surface, the second adhesive portion is adhered to the second surface and the fifth surface, and the third adhesive portion is adhered to the sixth surface.
The electrochemical device according to claim 1, characterized in that the electrochemical device satisfies at least one of the following conditions:

(1) The first pole piece assembly includes a first diaphragm, the second pole piece assembly includes a second diaphragm, and the first pole piece assembly and the second pole piece assembly are connected via the first diaphragm and the second diaphragm;

(2) A second connecting component is provided between the first pole piece assembly and the second pole piece assembly, and the first pole piece assembly and the second pole piece assembly are connected via the second connecting component.
The electrochemical device according to claim 8, characterized in that the electrochemical device satisfies at least one of the following conditions:

(1) The bonding strength between the first pole piece assembly and the second pole piece assembly is F, satisfying: F ≥ 5 N/m;

(2) The first electrode sheet assembly is a laminate structure, the first diaphragm includes a first Z-shaped folded portion and a first winding portion, the first electrode sheet assembly also includes a first positive electrode sheet, the first Z-shaped folded portion is arranged between the adjacent first positive electrode sheet and the first negative electrode sheet, and the first winding portion is wound around the outer ring of the laminate structure;

(3) The second pole piece assembly is a laminate structure, the second diaphragm includes a second Z-shaped folded portion and a second winding portion, the second pole piece assembly also includes a second positive pole piece, the second Z-shaped folded portion is arranged between the adjacent second positive pole piece and the second negative pole piece, and the second winding portion is wound around the outer ring of the laminate structure;

(4) The first separator and the second separator each independently include a substrate layer, an optional ceramic layer, and an optional bonding layer.
The electrochemical device according to claim 1, characterized in that the electrochemical device comprises at least two first electrode assemblies and at least one second electrode assembly, and the second electrode assembly is disposed between two adjacent first electrode assemblies; or

The electrochemical device includes at least one first electrode assembly and at least two second electrode assemblies, and the first electrode assembly is disposed between two adjacent second electrode assemblies.
An electronic device, characterized by comprising the electrochemical device according to any one of claims 1 to 10.