Electrochemical device and electronic device comprising the same

Abstract

The application provides an electrochemical device and an electronic device comprising the same. The electrochemical device comprises a packaging shell, a separator, a first electrode assembly and a second electrode assembly. The separator comprises an encapsulation part and a main body part. The encapsulation part is connected with the packaging shell and defines a first cavity and a second cavity on two sides of the separator, respectively. The tensile ratio of the separator is greater than or equal to 10%. The first electrode assembly and the second electrode assembly are arranged in the first cavity and the second cavity, respectively. The electrochemical device and the electronic device have good expansion performance, energy density and safety performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemistry, in particular to an electrochemical device and an electronic device comprising the same. BACKGROUND

[0002] Lithium ion batteries are used in electrical appliances. As the remaining space for accommodating lithium ion batteries in electrical appliances is getting smaller, the rear cover of the electrical appliance is in close contact with the outer wall of the lithium ion battery. If the lithium ion battery is slightly swollen and deformed, the rear cover of the electrical appliance cannot be closed, and the electrical appliance cannot be used normally. In addition, the lithium ion battery with an aluminum plastic film as a packaging shell cannot withstand the strong internal pressure generated therein. The swelling and deformation of the lithium ion battery will increase the risk of liquid leakage. Therefore, the swelling phenomenon is an important factor affecting the qualification rate and safety performance of lithium ion batteries.

[0003] In order to overcome this problem, the existing lithium ion battery usually uses a packaging shell with a relatively large size to accommodate the swelling of the electrode assembly. The dead volume (volume reserved for accommodating swelling) is usually about 15% to about 20% of the total volume of the lithium ion battery. The existence of such dead volume will reduce the volumetric energy density of the lithium ion battery. SUMMARY

[0004] The present application provides an electrochemical device and an electronic device comprising the same to improve the energy density of the electrochemical device.

[0005] The first aspect of the present application provides an electrochemical device, comprising a packaging shell; a separator, the separator comprising an encapsulation part and a main body part, the encapsulation part being connected with the packaging shell and defining a first cavity and a second cavity on both sides of the separator respectively; the tensile ratio δ of the separator is ≥10%; a first electrode assembly and a second electrode assembly, the first electrode assembly being arranged in the first cavity, and the second electrode assembly being arranged in the second cavity.

[0006] The electrochemical device of the embodiments of the present application uses a separator with a tensile ratio δ≥10%, so that in the case of different expansion of the first electrode assembly and the second electrode assembly during the cycle, the first electrode assembly with a larger expansion ratio can be extruded to the side of the second electrode assembly with a smaller expansion ratio due to the ductility of the separator, occupying the cavity space originally used to accommodate the second electrode assembly with a smaller expansion ratio. Therefore, on the one hand, the cavity space of the packaging shell can be flexibly used by the electrode assembly after expansion, without excessively increasing the volume of the entire electrochemical device, so that the energy density of the electrochemical device is improved. On the other hand, due to the ductility of the separator, the expansion of the electrode assembly will not adversely affect the sealed connection of the separator and the packaging shell, ensuring the reliability of the seal and improving the safety performance of the electrochemical device. In addition, when the electrochemical device falls, the separator with ductility can buffer the electrode assembly, preventing the sealed connection of the separator and the packaging shell from being damaged under stress, and improving the drop pass rate of the electrochemical device.

[0007] In some embodiments of the present application, the main body part is provided with a pre-deformation structure, which includes at least one of an arc-shaped structure, a wave-shaped structure or a groove-shaped structure. The provision of the above-mentioned pre-deformation structure can increase the tensile ratio of the separator, which is beneficial to the full use of the cavity space of the packaging shell by the first electrode assembly with a larger expansion ratio without increasing the volume of the electrochemical device, thereby improving the energy density thereof.

[0008] In some embodiments of the present application, the electrochemical device further comprises an encapsulation layer arranged on the edge of the surface of the separator or on the entire surface of the separator. Thus, the separator can be sealed and connected with the sealing edge of the first packaging body and the sealing edge of the second packaging body, so that the overall sealing performance of the electrochemical device is better, thereby further improving the encapsulation reliability of the electrochemical device.

[0009] In some embodiments of the present application, the encapsulation layer is arranged on the encapsulation part of the separator. In this way, the encapsulation part is sealed and connected with the packaging shell through the encapsulation layer, while the main body part is thinned due to the absence of the encapsulation layer, providing more accommodation space for the electrode assembly and the electrolyte, and improving the energy density of the electrochemical device.

[0010] In some embodiments of the present application, the material of the separator includes at least one of a high molecular material or a metal material, the high molecular material including at least one of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyether ether ketone, polyimide, polyamide, polyethylene glycol, polyamide-imide, polycarbonate, cyclic polyolefin, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, poly methylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-trifluorochloroethylene), silicone, vinylon, polypropylene, anhydride-modified polypropylene, polyethylene, ethylene and a copolymer thereof, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene ether, polyester, polysulfone, amorphous α-olefin copolymer, and a derivative thereof, and the metal material including at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Co, Cr, W, Mo, Al, Mg, K, Na, Ca, Sr, Ba, Si, Ge, Sb, Pb, In, Zn, stainless steel (SUS), and an alloy thereof. The separator made of the above-mentioned high molecular material and metal material not only has an ion insulating property, but also has good ductility, so that it can be stretched and deformed according to the swelling of the electrode assembly, thereby making it possible to flexibly use the cavity space of the electrode assembly and preventing the sealing connection of the separator and the packaging case from being damaged, and improving the packaging reliability.

[0011] In some embodiments of the present application, the material of the packaging layer includes at least one of polypropylene, anhydride-modified polypropylene, polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-ethylene vinyl alcohol copolymer, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyamide, polyester, amorphous α-olefin copolymer, and a derivative thereof. The above-mentioned material is easily heat-sealed and bonded to the inner surface of the packaging case, thereby effectively improving the sealing property of the separator and the packaging case, and improving the packaging reliability of the electrochemical device.

[0012] In some embodiments of the present application, the tensile ratio δ of the separator satisfies 10%≤δ≤40%. The tensile ratio of the separator in the above-mentioned range can improve the energy density and safety of the electrochemical device without affecting the structural stability of the electrochemical device.

[0013] In some embodiments of the present application, the thickness of the separator is 10 μm to 100 μm. The thickness of the separator in the above-mentioned range can improve the energy density and safety of the electrochemical device.

[0014] In some embodiments of the present application, the thickness of the separator is 10 μm to 30 μm, and the thickness of the packaging layer is 20 μm to 40 μm.

[0015] In some embodiments of the present application, the ratio of the expansion rate of the first electrode assembly to the expansion rate of the second electrode assembly is k, 1 < k ≤ 5. Limiting the expansion rate of the two electrode assemblies to a specific ratio range avoids the expansion rate of the first electrode assembly being too large, which causes the first electrode assembly to excessively press the second cavity beyond the extension capacity of the separator, resulting in the destruction of the sealed connection of the separator.

[0016] The second aspect of the present application provides an electronic device comprising the electrochemical device provided by the first aspect of the present application. Therefore, the electronic device has good expansion performance and energy density. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application and the prior art, the drawings needed to be used in the embodiments and the prior art are briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application.

[0018] Figure 1 The exploded structural view of the electrochemical device of some embodiments of the present application;

[0019] Figure 2 The top view of the separator structure of some embodiments of the present application;

[0020] Figure 3 The front view of the separator structure of some embodiments of the present application;

[0021] Figure 4 The top view of the separator structure of some embodiments of the present application;

[0022] Figure 5 The front view of the separator structure of some embodiments of the present application;

[0023] Figure 6 The top view of the separator structure of some embodiments of the present application;

[0024] Figure 7 The front view of the separator structure of some embodiments of the present application;

[0025] Figure 8 The structural view of the separator of some embodiments of the present application.

[0026] Reference signs: 001. Electrochemical device; 11. First electrode assembly; 12. Second electrode assembly; 20. Separator; 21. Encapsulation part; 22. Main body part; 30. Encapsulation layer; 40. Packaging shell; 41. First packaging body; 42. Second packaging body. DETAILED DESCRIPTION

[0027] For the purposes of the present application, the technical solutions and advantages thereof are more clearly apparent, further detailed description is made below with reference to the drawings and examples. Obviously, the described examples are only a part of the examples of the present application, but not all the examples. Based on the examples in the present application, all other technical solutions obtained by those skilled in the art belong to the scope of protection of the present application.

[0028] It should be noted that the content of the present application is explained by taking lithium ion battery as an example of electrochemical device, but the electrochemical device of the present application is not limited to lithium ion battery. The specific technical solutions are as follows:

[0029] As shown in Figure 1 and Figure 2 , the embodiment of the first aspect of the present application provides an electrochemical device 001, which comprises a packaging shell 40, a separator 20, a first electrode assembly 11 and a second electrode assembly 12; the separator 20 comprises an encapsulation part 21 and a main body part 22, the encapsulation part 21 is connected with the packaging shell 40 so as to define a first cavity (not shown in the figure) and a second cavity (not shown in the figure) on both sides of the separator 20, respectively, the first electrode assembly 11 is arranged in the first cavity, and the second electrode assembly 12 is arranged in the second cavity.

[0030] In some embodiments of the present application, the tensile ratio δ of the separator 20 is ≥10%; during the cycle process of the electrochemical device 001, due to the ductility of the separator 20, when the expansion ratio of the first electrode assembly 11 is greater than that of the second electrode assembly 12, the first electrode assembly 11 with larger expansion ratio can be extruded to one side of the second electrode assembly 12 with smaller expansion ratio, occupying the cavity space originally used to accommodate the second electrode assembly 12 with smaller expansion ratio. Therefore, on the one hand, the cavity space of the packaging shell 40 can be flexibly used by the electrode assembly after expansion, without excessively increasing the volume of the entire electrochemical device 001, so that the energy density of the electrochemical device 001 is improved. On the other hand, the expansion of the first electrode assembly 11 and / or the second electrode assembly 12 will not adversely affect the sealed connection of the separator 20 and the packaging shell 40, ensuring the reliability of the sealing and improving the safety performance of the electrochemical device 001. In addition, when the electrochemical device 001 is dropped, the separator 20 with ductility can produce a buffering effect on the electrode assembly, preventing the sealed connection of the separator 20 and the packaging shell 40 from being damaged under stress, and improving the drop pass rate of the electrochemical device 001.

[0031] It should be noted that, in view of the upper limit of the expansion rate of the electrode assembly and the simulated scenario of the drop test, the upper limit of the stretch rate of the separator 20 is not particularly limited in the present application, as long as the stretch rate δ of the separator 20 is greater than or equal to 10%, the purpose of the present application can be achieved. Preferably, the stretch rate δ of the separator is less than or equal to 40%, so as to avoid that the stretch rate is too large, which affects the structural stability of the electrode assembly in the packaging shell during use of the electrochemical device.

[0032] In some embodiments of the present application, in order to achieve the stretch rate δ of the separator 20 greater than or equal to 10%, the material of the separator 20 includes at least one of a polymer material or a metal material.

[0033] In some embodiments of the present application, the material of the separator 20 includes a polymer material, which has a small density and can reduce the weight of the separator 20, thereby improving the energy density of the electrochemical device 001. Moreover, in the case of mechanical abuse (for example, nail penetration, impact, extrusion, etc.), the polymer material has a smaller probability of generating debris and a better wrapping effect on the mechanically damaged surface, which can improve the safety performance in the above-mentioned mechanical abuse, thereby improving the safety test pass rate and further improving the safety performance of the electrochemical device 001. For example, the polymer material can include at least one of polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polyether ether ketone, polyimide, polyamide, polyethylene glycol, polyamide-imide, polycarbonate, cyclic polyolefin, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, poly methylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene, acid anhydride modified polypropylene, polyethylene, ethylene and its copolymer, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene ether, polyester, polysulfone, amorphous α-olefin copolymer, and derivatives thereof.

[0034] In some embodiments of the present application, the material of the separator 20 includes a metal material, which has strong isolation reliability, good toughness and density, and can be processed to a thinner thickness, thereby improving the energy density of the electrochemical device 001. For example, the metal material can include at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Co, Cr, W, Mo, Al, Mg, K, Na, Ca, Sr, Ba, Si, Ge, Sb, Pb, In, Zn, stainless steel (SUS), and alloys thereof.

[0035] In some embodiments of the present application, the material of the separator 20 includes a composite material of a polymer material and a metal material. For example, the composite material can include Ni metal composite PP, Ag metal composite PET, etc.

[0036] In some embodiments of the present application, as shown in Figure 2 The structure of the separator 20 can be flat, and the above-mentioned polymer material and metal material can achieve the ductility of the separator 20.

[0037] In some embodiments of the present application, the ductility of the separator 20 is achieved by changing the shape of the separator 20. In the present application, the separator 20 includes a packaging portion 21 and a main body portion 22. The packaging portion 21 is sealingly connected to the packaging shell 40. In order to ensure the packaging reliability of the packaging portion 21 and the packaging shell 40, the packaging portion 21 needs to maintain its flatness to achieve a tight connection with the packaging shell 40. The main body portion 22 achieves the ductility of the separator 20 by providing a pre-deformation structure. The pre-deformation structure provides additional accommodation space for the expansion of the electrode assembly, thereby preventing the electrode assembly from being pulled by the packaging portion 21 due to expansion, which can cause sealing failure.

[0038] As shown in Figures 3 to 7 In some embodiments of the present application, the pre-deformation structure includes Figure 3 an arc-shaped structure, Figure 5 a wave-shaped structure, or Figure 7 a groove-shaped structure, etc. Those skilled in the art can understand that the above-mentioned pre-deformation structure can also include other shapes, as long as it is beneficial to the improvement of the tensile rate δ of the separator, and it is within the scope of the present application. The provision of the above-mentioned pre-deformation structure can increase the tensile rate δ of the separator 20, provide additional space for the expansion of the electrode assembly, thereby effectively relieving the expansion of the electrochemical device 001 and improving the expansion performance of the electrochemical device 001.

[0039] The method for preparing the pre-deformation structure is not particularly limited in the present application, as long as it can achieve the purpose of the present application. For example, the arc-shaped structure, the wave-shaped structure, or the groove-shaped structure, etc. can be obtained by hot pressing a mold on the main body portion 22.

[0040] In some embodiments of the present application, as shown in Figure 8 The electrochemical device 001 further includes a packaging layer 30, which is arranged at the four peripheral edges of the surface of the separator 20 or on the entire surface of the separator 20. In this way, the separator 20 can be sealingly connected to the sealing edge of the first packaging body 41 and the sealing edge of the second packaging body 42, so that the overall sealing performance of the electrochemical device 001 is better, thereby further improving the packaging reliability of the electrochemical device 001.

[0041] In some embodiments of the present application, the encapsulation layer 30 is arranged on the encapsulation portion 21 of the separator 20. In this way, the encapsulation portion 21 is sealedly connected with the sealing edges of the upper packaging body 41 and the lower packaging body 42 respectively through the encapsulation layer 30, so that the overall sealing performance of the electrochemical device 001 is better. Further, the main body portion 22 does not need to be provided with the encapsulation layer 30, so that the thickness of the separator 20 can be made thinner, thereby providing more accommodation space for the electrode assembly, so as to reduce the volume of the electrochemical device 001, thereby improving the energy density of the electrochemical device 001.

[0042] In some embodiments of the present application, the material of the encapsulation layer 30 includes at least one of polypropylene, anhydride-modified polypropylene, polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-vinyl alcohol copolymer, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyamide, polyester, amorphous alpha-olefin copolymer and derivatives thereof. The above-mentioned materials are easy to be heat-sealed and bonded together with the inner surface of the packaging shell 40 such as an aluminum plastic film, thereby effectively improving the sealing performance of the separator 20 and the packaging shell 40, thereby improving the encapsulation reliability of the electrochemical device 001. It should be noted that the present application does not have special restrictions on the encapsulation temperature, encapsulation time and encapsulation pressure, as long as the purpose of the present application can be achieved. For example, when the encapsulation material is polypropylene, the encapsulation temperature is 180°C to 195°C, the encapsulation time is 2s to 4s, and the encapsulation pressure is 0.2MPa to 0.5MPa.

[0043] In some embodiments of the present application, the thickness of the separator 20 is at least 10μm, preferably 10μm to 30μm, and in some embodiments, the thickness of the separator 20 is preferably 30μm to 60μm. In some embodiments, the thickness of the separator 20 can include any one of the following values: 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm or 100μm, etc. When the thickness of the separator 20 is too thin (for example, less than 10μm), the barrier property of the separator 20 to the electrolyte will be affected, and the electrolyte in the first cavity and the second cavity on both sides of the separator 20 is easy to penetrate the separator 20, thereby affecting the electrochemical performance of the electrochemical device 001. When the thickness of the separator 20 is too thick (for example, greater than 100μm), the volume of the electrochemical device 001 is increased, thereby reducing the energy density of the electrochemical device 001.

[0044] In some embodiments of the present application, the thickness of the encapsulation layer 30 is 20-40 μm. For example, the lower limit of the thickness of the encapsulation layer 30 can include any of the following values: 20 μm, 25 μm, or 30 μm, etc.; the upper limit of the thickness of the encapsulation layer 30 can include any of the following values: 32 μm, 36 μm, or 40 μm, etc. When the thickness of the encapsulation layer 30 is too thin (e.g., less than 20 μm), the sealing effect between the separator 20 and the packaging shell 40 will be affected, thereby affecting the encapsulation reliability of the electrochemical device 001; when the thickness of the encapsulation layer 30 is too thick (e.g., greater than 40 μm), the sealing edge of the electrochemical device 001 is too thick, which is not conducive to the folding processing of the sealing edge, thereby affecting the encapsulation reliability of the electrochemical device 001, and the sealing edge is too thick, which increases the volume of the electrochemical device 001, and causes the energy density of the electrochemical device 001 to decrease.

[0045] It should be understood that the thickness of the encapsulation layer in the present application refers to the thickness of the encapsulation layer located on the surface of one side of the separator. The thickness of the separator refers to the thickness when the separator is in a flat state. For the separator provided with a pre-deformation structure, the thickness of the separator refers to the thickness when the separator is in a flat state before the pre-deformation structure is provided.

[0046] In some embodiments of the present application, the ratio of the expansion rate of the first electrode assembly 11 to the expansion rate of the second electrode assembly 12 is k, and 1 < k ≤ 5. During the charging and discharging process of the electrochemical device 001, the first electrode assembly 11 and the second electrode assembly 12 will expand to different degrees due to reasons such as electrode tab rebound or gas release, and the expansion rate of the second electrode assembly 12 is less than that of the first electrode assembly 11. The first electrode assembly 11 with a larger expansion rate can press the side of the second electrode assembly 12 with a smaller expansion rate, occupying the cavity space originally used to accommodate the second electrode assembly 12 with a smaller expansion rate, thereby preventing the increase of the overall expansion rate of the electrochemical device 001, and effectively improving the expansion performance of the electrochemical device 001. In this way, the volume of the electrochemical device 001 can also be prevented from increasing, thereby improving the energy density of the electrochemical device 001.

[0047] The present application does not particularly limit the expansion rate of the first electrode assembly 11 and the second electrode assembly 12, as long as it is less than 10%, which can achieve the purpose of the present application. For example, the expansion rate of the first electrode assembly 11 can be 5-10%, and the expansion rate of the second electrode assembly 12 can be 1-5%. When the expansion rate is greater than 10%, the expanded electrode assembly will exceed the encapsulation strength of the separator and the packaging shell, causing the sealing performance of the separator and the packaging shell to be damaged, which adversely affects the safety of the electrochemical device.

[0048] In the present application, the structure of the electrode assembly is not particularly limited as long as the object of the present application can be achieved. For example, the structure of the electrode assembly can include at least one of a roll structure or a stack structure.

[0049] The electrochemical device 001 of the present application can further include other devices that generate electrochemical reactions, such as a lithium metal secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery, etc.

[0050] The present application is not particularly limited in the process of preparing the electrochemical device 001 as long as the object of the present application can be achieved. For example, the electrochemical device 001 can be prepared by overlapping the positive electrode sheet and the negative electrode sheet via the separator, and placing them in the package case 40 after performing operations such as winding or folding as necessary, injecting an electrolyte into the package case 40, and sealing. In addition, a current overflow prevention element, a guide plate, etc. can be placed in the case as necessary, thereby preventing the pressure inside the electrochemical device 001 from rising, overcharging, or overdischarging.

[0051] The second aspect of the present application provides an electronic device including the electrochemical device 001 provided by the first aspect of the present application. The electronic device has good energy density and safety performance.

[0052] The electronic device of the present application is not particularly limited, and can include, but is not limited to, a notebook computer, a pen input type computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, an illuminating appliance, a toy, a game machine, a clock, an electric tool, a flash, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0053] The terms used in the present application are generally terms commonly used by those skilled in the art, and if they are inconsistent with commonly used terms, the terms in the present application are used.

[0054] Hereinafter, embodiments of the present application will be more specifically described by citing examples and comparative examples. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0055] Test methods and apparatuses:

[0056] Test of tensile ratio δ:

[0057] Turn on the power of the high-tension pull tester, confirm that the upper and lower clamps of the pull tester are in the horizontal position, the pull rod can move up and down normally, and the speed control of the pull tester is 50 mm / min; cut a sample with a width of 15 mm and a length of 100 mm using a cutter, prepare at least two parallel samples for each type of spacer, and adjust the upper and lower fixed clamps to be aligned on the same vertical plane; turn on the upper fixed clamp, clamp one end of the sample in the upper fixed clamp, and clamp the other end of the sample in the lower fixed clamp, make sure that the sample does not slip after being clamped in the upper fixed clamp, and fix the sample after being aligned; click the zero and run buttons to start the test, and the final tensile strength determination results are as follows: after the tensile test is completed, the machine will automatically stop, and the pull tester output force, displacement, and time are recorded;

[0058] Tensile rate calculation: tensile rate δ = ΔL / L x 100%, ΔL is the difference between the output displacement of the pull tester and the original gauge length, and L is the original gauge length.

[0059] Spacer thickness test:

[0060] The thickness of each layer was tested by scanning electron microscopy (SEM). A rectangular sample was cut from the center of the spacer material, and the sample was placed in an ion polishing machine for polishing. After polishing, the sample was placed under an SEM for observation. The thickness of the spacer was observed.

[0061] Expansion rate test:

[0062] A lithium ion battery with SOC = 50% was measured for thickness on a battery thickness tester (model PPG650gf, Shenzhen Automee). The thickness was recorded as T1. Then, the battery was charged to 4.35V at 0.5C and discharged to 3.0V at 0.5C, which was one charge-discharge cycle (Cycle). The battery thickness was measured every 50 cycles until the battery was tested to 500 cycles. The final battery thickness was recorded as T500.

[0063] Expansion rate = (T500 - T1) / T1 x 100%.

[0064] Energy density calculation:

[0065] After charging the lithium ion battery to 4.45V at 25℃, the length, width, and height of the lithium ion battery were measured using a laser thickness tester to obtain the volume (V) of the lithium ion battery. Then, the lithium ion battery was discharged at 0.2C to 3V to obtain the discharge capacity (C) and average voltage platform (U). The volumetric energy density (ED) can be calculated by the following formula: ED = C x U / V.

[0066] Example 1

[0067] Preparation of electrode assembly

[0068] Preparation of a first electrode assembly and a second electrode assembly, select one of the first electrode assembly to prepare the first battery, select one of the second electrode assembly to prepare the second battery, then the first battery and the second battery are respectively tested to calculate the expansion rate, the expansion rate of the first battery is considered as the expansion rate of the first electrode assembly, which is 10%, and the expansion rate of the second battery is considered as the expansion rate of the second electrode assembly, which is 2%.

[0069] <Preparation of the separator>

[0070] The encapsulation layer material PP is uniformly dispersed in the dispersing agent N-methyl pyrrolidone (NMP) to prepare a suspension of the encapsulation layer material. The encapsulation layer material with a thickness of 20 μm is coated on the encapsulation part of both surfaces of the Al foil separator with a thickness of 10 μm by using a glue coating machine. The dispersing agent NMP in the suspension of the encapsulation layer material is dried at 130°C, and the preparation of the separator is completed. The tensile rate δ of the separator is 14% after testing.

[0071] <Preparation of the lithium ion battery>

[0072] The second packaging body (aluminum plastic film with a thickness of 88 μm) shaped by punching is placed in the assembly fixture with the pit surface facing up, and the second electrode assembly (with an expansion rate of 2%) is placed in the pit, and one positive electrode tab and one negative electrode tab are drawn from the second electrode assembly. Among them, the second electrode assembly and the electrode assembly in the second battery tested are of the same batch.

[0073] Then, the separator is placed on the second electrode assembly, and the first electrode assembly (with an expansion rate of 10%) is placed on the separator, and one positive electrode tab and one negative electrode tab are drawn from the first electrode assembly. Among them, the first electrode assembly and the electrode assembly in the first battery tested are of the same batch. Then, the first packaging body (aluminum plastic film with a thickness of 88 μm) is covered on the first electrode assembly with the pit surface facing down, leaving the injection port and the area where the tabs are stretched out, and the other positions of the packaging shell are heat sealed, so as to form two independent first and second cavities on both sides of the separator, thereby obtaining the assembled electrode assembly. Among them, the heat sealing temperature is 180°C, and the heat sealing pressure is 0.5 MPa.

[0074] The electrolyte is separately injected into the two cavities of the assembled electrode assembly, and the injection port is sealed after injection.

[0075] Then, the negative electrode tab of the second electrode assembly and the positive electrode tab of the first electrode assembly are welded together by laser welding, so as to be connected in series. In the charging and discharging process, only the positive electrode tab of the second electrode assembly and the negative electrode tab of the first electrode assembly need to be connected.

[0076] Example 2

[0077] The rest is the same as Example 1 except that the thickness of the separator is 20 μm and the tensile ratio δ = 25% in the <Preparation of the separator>.

[0078] Example 3

[0079] <Preparation of the separator>

[0080] The separator prepared in Example 1 was heat-pressed in an arc-shaped mold to obtain a separator having an arc-shaped main body part, and the tensile ratio δ = 14% of the separator.

[0081] The rest is the same as Example 1.

[0082] Example 4

[0083] The rest is the same as Example 3 except that the material of the separator is PET, the thickness of the separator is 30 μm, and the tensile ratio δ = 37% of the separator in the <Preparation of the separator>.

[0084] Example 5

[0085] The rest is the same as Example 3 except that the mold is wave-shaped, the thickness of the separator is 20 μm, and the tensile ratio δ = 15% of the separator in the <Preparation of the separator>.

[0086] Example 6

[0087] The rest is the same as Example 4 except that the mold is wave-shaped and the tensile ratio δ = 25% of the separator in the <Preparation of the separator>.

[0088] Example 7

[0089] The rest is the same as Example 5 except that the material of the separator is Ti and the tensile ratio δ = 20% of the separator.

[0090] Example 8

[0091] The rest is the same as Example 5 except that the mold is groove-shaped, the thickness of the separator is 30 μm, and the tensile ratio δ = 15% of the separator in the <Preparation of the separator>.

[0092] Example 9

[0093] The rest is the same as Example 8 except that the material of the separator is PET and the tensile ratio δ = 35% of the separator.

[0094] Example 10

[0095] The rest is the same as Example 8 except that the material of the separator is Ti and the tensile ratio δ = 16% of the separator.

[0096] Example 11

[0097] The rest is the same as Example 10 except that in the <preparation of the separator>, the mold is arc-shaped, the thickness of the separator is 20 μm, and the tensile ratio δ of the separator is 20%.

[0098] Example 12

[0099] The rest is the same as Example 11 except that in the <preparation of the separator>, the thickness of the separator is 15 μm, and the tensile ratio δ of the separator is 22%.

[0100] Comparative Example 1

[0101] The rest is the same as Example 1 except that in the <preparation of the separator>, the material of the separator is stainless steel, the thickness of the separator is 20 μm, and the tensile ratio δ of the separator is 6%.

[0102] Comparative Example 2

[0103] The rest is the same as Comparative Example 1 except that in the <preparation of the separator>, the mold is arc-shaped, and the tensile ratio δ of the separator is 6%.

[0104] Comparative Example 3

[0105] The rest is the same as Example 7 except that in the <preparation of the separator>, the mold is groove-shaped, and the tensile ratio δ of the separator is 5%.

[0106] The preparation parameters and performance parameters of Examples 1 to 12 and Comparative Examples 1 to 3 are shown in Table 1:

[0107]

[0108] As can be seen from Examples 1, 2 and Comparative Example 1, by selecting a separator with a tensile ratio δ within the scope of the present application, the expansion performance of the electrochemical device can be effectively improved, thereby improving the energy density of the electrochemical device.

[0109] As can be seen from Examples 3 to 12 and Comparative Examples 2 and 3, by selecting a separator material and a pre-deformation structure on the main body of the separator, the tensile ratio δ of the separator is within the scope of the present application, which can significantly improve the expansion performance of the electrochemical device, thereby improving the energy density of the electrochemical device.

[0110] From the above analysis, it can be seen that the electrochemical device provided by the application selects the separator with a tensile ratio δ≥10%, so that in the case of different expansion of the first electrode assembly and the second electrode assembly in the cycle process, the first electrode assembly with a larger expansion rate can be extruded to one side of the second electrode assembly with a smaller expansion rate, occupying the cavity space originally used to accommodate the second electrode assembly with a smaller expansion rate, effectively improving the expansion performance of the electrochemical device, so that the volume of the electrochemical device does not increase too much, and the energy density of the electrochemical device is improved. It can also improve the sealing reliability of the separator and the packaging shell, and further improve the safety performance of the electrochemical device.

[0111] It should be noted that in this paper, relational terms such as "first" and "second" are only used to distinguish one entity from another, and do not necessarily require or imply any such actual relationship or order between the entities. Moreover, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or includes elements inherent to such article or device.

[0112] The above is only the preferred embodiment of the application, and is not used to limit the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. An electrochemical device, characterized in that, include: Packaging shell; A partition, comprising a sealing portion and a main body portion, wherein the sealing portion is connected to the packaging shell and defines a first cavity and a second cavity on both sides of the partition; the tensile strength of the partition is 40% ≥ δ ≥ 10%; A first electrode assembly is disposed in the first cavity; and The second electrode assembly is disposed in the second cavity; The main body is formed with a pre-deformation structure, which is selected from an arc-shaped structure, a wave-shaped structure, or a groove-shaped structure. The ratio of the expansion rate of the first electrode assembly to the expansion rate of the second electrode assembly is k, where 1 < k ≤ 5; The electrochemical device further includes an encapsulation layer disposed in the encapsulation portion of the separator; and The thickness of the partition is 10 μm to 30 μm, and the thickness of the encapsulation layer is 20 μm to 40 μm.

2. The electrochemical device according to claim 1, characterized in that, The material of the partition includes at least one of polymeric materials or metallic materials. The polymeric materials include at least one of polyetheretherketone, polyimide, polyamide, polyethylene glycol, polyamide-imide, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-trifluorochloroethylene), silicone, vinylon, polypropylene, anhydride-modified polypropylene, polyethylene and its copolymers, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene ether, polyester, polysulfone, amorphous α-olefin copolymers and their derivatives. The metallic materials include at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Co, Cr, W, Mo, Al, Mg, K, Na, Ca, Sr, Ba, Si, Ge, Sb, Pb, In, Zn and their alloys.

3. The electrochemical device according to claim 2, characterized in that, The polyester is at least one of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, and polypropylene carbonate.

4. The electrochemical device according to claim 2, characterized in that, The metal material is stainless steel.

5. The electrochemical device according to claim 1, characterized in that, The material of the partition includes cyclic polyolefins.

6. The electrochemical device according to claim 1, characterized in that, The encapsulation layer is made of at least one of the following materials: polypropylene, anhydride-modified polypropylene, polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-vinyl alcohol copolymer, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyamide, polyester, amorphous α-olefin copolymer and its derivatives.

7. An electronic device, characterized in that, The electrochemical device includes any one of claims 1 to 6.

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