Electrochemical devices and electronic devices

Abstract

An electrochemical device includes a packaging shell, a separator, and a plurality of electrode assemblies, wherein the electrode assemblies are respectively arranged in cavities separated by the separator in the packaging shell, and at least two electrode assemblies are connected in series; the electrode assemblies include a plurality of positive electrode sheets, a plurality of negative electrode sheets, and a Z-shaped separator. The present application also provides an electronic device. The electrochemical device of the present application improves safety and reliability during use.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and in particular to an electrochemical device and an electronic device. Background Art

[0002] Electrochemical devices (such as lithium-ion batteries) are widely used in consumer electronics, power tools and other electronic devices. In existing electrochemical device systems, the operating voltage of electrochemical devices is difficult to exceed 5V due to the limitations of the system in the electrochemical device (such as the limited voltage difference between the positive and negative active materials, the limited antioxidant capacity of the electrolyte, etc.).

[0003] However, in actual demand, there are many scenarios where the voltage of electrochemical devices exceeds 5V (such as automobiles, power tools, energy storage, etc.). Specifically, in the consumer electronics market, in order to meet the needs of fast charging, the open circuit voltage of electrochemical devices needs to be increased.

[0004] Currently, the method of connecting multiple finished lithium-ion batteries in series externally is generally used to increase the output voltage. However, there are many problems with connecting multiple lithium-ion batteries in series, such as: the series wires introduce additional electronic resistance, which generates heat and wastes energy; the higher the voltage, the more lithium-ion batteries are required, the lower the reliability of the battery series connection, and the more difficult it is to manage; the proportion of inactive substances (such as packaging shells) is further increased, resulting in energy density loss. Summary of the invention

[0005] In view of this, it is necessary to provide an electrochemical device with high energy density and high reliability.

[0006] In addition, it is also necessary to provide an electronic device.

[0007] In a first aspect of the present application, an electrochemical device is provided, comprising a packaging shell, a separator and a plurality of electrode assemblies, wherein the electrode assemblies are respectively arranged in cavities separated by the separators in the packaging shell, and at least two electrode assemblies are connected in series; the electrode assemblies comprise a plurality of positive electrode sheets, a plurality of negative electrode sheets and a Z-shaped separator.

[0008] In some embodiments, the Z-shaped separator includes a Z-shaped folded portion and a rolled portion, and the Z-shaped folded portion separates adjacent positive electrode sheets from negative electrode sheets.

[0009] In some embodiments, a plurality of positive electrode sheets, a plurality of negative electrode sheets and the Z-shaped folded portion form a stacking assembly, and the winding portion surrounds the stacking assembly.

[0010] The open circuit voltage of the electrochemical device can be increased by arranging electrode assemblies in series inside the packaging shell; in addition, the pole ears extending in the same direction in the two electrode assemblies can be directly connected in series, which can avoid the additional connection of the wires used for series connection, that is, it can reduce unnecessary resistance and cause heating of the electrochemical device, thereby reducing unnecessary energy loss; the electrode assemblies connected in series are arranged in the same packaging shell, which can also reduce unnecessary packaging to reduce the loss of the overall energy density of the electrochemical device; furthermore, the Z-shaped folding portion in the Z-shaped diaphragm is conducive to limiting the relative position between the positive and negative electrode sheets, and can increase the manufacturing rate of the electrode assembly, and the winding portion further fastens the stacked assembly as a whole, thereby reducing the risk of movement between the electrode sheets during the falling process. At the same time, the end bending structure of the Z-shaped folding portion can provide a buffering effect for the electrode assembly, thereby improving the safety and reliability of the electrochemical device. In addition, the end bending structure of the Z-shaped folding portion can improve the liquid retention capacity of the electrode assembly, thereby improving the cycle life of the electrochemical device and reducing the risk of liquid swelling in the electrochemical device.

[0011] In some embodiments, along the stacking direction of the multiple positive electrode sheets, the stacking assembly has a thickness H; along the winding direction of the Z-type separator, the stacking assembly has a length L, and the length of the winding portion is l; the thickness H, length L, and length l satisfy: 2(L+H)<l≤4(L+H)+0.5×L, thereby improving the energy density of the electrochemical device while ensuring the safety and reliability of the electrochemical device.

[0012] In some embodiments, the bonding force F between the electrode assembly and the packaging shell, and / or between the electrode assembly and the separator, satisfies: F ≥ 5 N / m. In some embodiments, 5 N / m ≤ F ≤ 300 N / m. By setting the bonding force F between the electrode assembly located inside the packaging shell and the packaging shell, and / or between the electrode assembly and the separator to satisfy: F ≥ 5 N / m, the electrode assembly is prevented from shaking inside the packaging shell, thereby improving the safety and reliability of the electrochemical device during assembly and use.

[0013] In some embodiments, the bonding force F' between the Z-shaped folded portion and the positive electrode sheet or the negative electrode sheet satisfies: 0.5N / m≤F'≤50N / m, which can not only improve the safety and reliability of the electrochemical device, but also improve the interface consistency and ensure the uniformity of the current density.

[0014] In some embodiments, the capacity ratio A between any two electrode assemblies connected in series satisfies: 0.95≤A≤1.05, so as to ensure the consistency of the capacity between any two electrode assemblies connected in series and avoid excessive difference in the capacity of the two electrode assemblies connected in series, resulting in energy density loss of the electrochemical device.

[0015] In some embodiments, the winding portion includes an end portion, and a tape is provided on the end portion. The tape bonds the end portion and the surface of the winding portion facing the end portion, further making the positive electrode sheet, the Z-shaped separator and the negative electrode sheet a tight whole, thereby improving the safety and reliability of the electrode assembly.

[0016] In some embodiments, the Z-shaped folded portion and the winding portion are integrally formed, which helps to ensure the integrity of the electrode assembly.

[0017] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material covering the surface of the positive electrode current collector. The area of ​​the positive electrode current collector along a plane perpendicular to the stacking direction of the plurality of positive electrode sheets is S 正 The area of ​​the positive electrode current collector surface covered with positive electrode active material is S1, S 正 Satisfy with S1: 80% ≤ S1 / S 正 <100%.

[0018] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material covering the surface of the negative electrode current collector. The area of ​​the negative electrode current collector along the plane perpendicular to the stacking direction of the multiple negative electrode sheets is S 负 The area of ​​the negative electrode current collector surface covered with negative electrode active material is S2, S 负 Satisfy with S2: 80% ≤ S2 / S 负 <100%.

[0019] In some embodiments, S2 and S1 satisfy: 100%≤S2 / S1≤120%.

[0020] In some embodiments, a ratio B of the orthographic projection areas of two adjacent electrode assemblies on the separator between the two adjacent electrode assemblies satisfies: 0.95≤B≤1.05.

[0021] In a second aspect of the present application, an electronic device is provided, comprising the electrochemical device provided in the first aspect.

[0022] The electrochemical device of the present application arranges the electrode assemblies connected in series in the same packaging shell and fixes the positive and negative electrode sheets through a Z-shaped separator, thereby improving the energy density while ensuring the safety and reliability of the electrochemical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the overall structure of an electrochemical device provided in one embodiment of the present application.

[0024] Figure 2 for Figure 1 Exploded view of the electrochemical device shown.

[0025] Figure 3 for Figure 2Schematic diagram of the structure of the electrode assembly shown.

[0026] Figure 4 for Figure 3 The schematic diagram of the structure of the electrode assembly shown is when the winding portion of the Z-type diaphragm is not wound around the stacking assembly.

[0027] Figure 5 for Figure 3 The cross-sectional schematic diagram of the electrode assembly along the VV direction is shown.

[0028] Figure 6 A schematic diagram of the structure of an electronic device provided in one embodiment of the present application.

[0029] Main component symbols

[0030]

[0031]

[0032] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0033] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the present application is described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other. In the following description, many specific details are set forth to facilitate a full understanding of the present application, and the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes all and any combination of one or more related listed items.

[0035] In the embodiments of the present application, for the convenience of description and not to limit the present application, the term "connection" used in the patent application specification and claims of the present application is not limited to physical or mechanical connection, whether direct or indirect. "Up", "down", "above", "below", "left", "right", etc. are only used to indicate relative position relationship. When the absolute position of the described object changes, the relative position relationship also changes accordingly.

[0036] See also Figure 1, the embodiment of the present application provides an electrochemical device 100, and the electrochemical device 100 includes all devices capable of electrochemical reactions. Specifically, the electrochemical device 100 includes all kinds of primary batteries and secondary batteries. Optionally, the electrochemical device 100 can be a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, a solid-state battery, and a lithium ion polymer secondary battery.

[0037] Please also read Figure 2 The electrochemical device 100 includes a packaging shell 10, a separator 30, and a plurality of electrode assemblies 20. The electrode assemblies 20 are respectively arranged in cavities separated by the separator 30 in the packaging shell 10, and at least two electrode assemblies 20 are connected in series to increase the voltage of the electrochemical device 100. The electrode assembly 20 encapsulated in the packaging shell 10 is connected to an external circuit through a tab 12 to achieve the charge and discharge function of the electrode assembly 20. The tab 12 of each electrode assembly 20 includes a positive tab 122 and a negative tab 124. The positive tab 122 and the negative tab 124 can be in the same direction or in different directions. The open circuit voltage of the electrochemical device 100 is increased by arranging the electrode assemblies 20 connected in series inside the same packaging shell 10; in addition, the tabs extending in the same direction in the two electrode assemblies 20 can be directly connected in series, which can avoid the additional connection of the wires used for series connection, that is, it can reduce unnecessary resistance and cause heating of the electrochemical device 100, thereby reducing unnecessary energy loss; arranging the electrode assemblies 20 connected in series in the same packaging shell 10 can also reduce unnecessary packaging to prevent the overall energy density of the electrochemical device 100 from decreasing.

[0038] The electrode assembly 20 includes a stack of sheets.

[0039] See also Figure 3 , Figure 4 as well as Figure 5 In this embodiment, the electrode assembly 20 is a laminated type. The electrode assembly 20 includes a plurality of stacked positive electrode sheets 22, a plurality of negative electrode sheets 24, and a Z-shaped separator 26. Figure 5 The Z-shaped separator 26 includes a Z-shaped folded portion 262 and a winding portion 264. The Z-shaped folded portion 262 separates the adjacent positive electrode sheet 22 from the negative electrode sheet 24. The stacked plurality of positive electrode sheets 22, the plurality of negative electrode sheets 24 and the Z-shaped folded portion 262 form a stack assembly 28 (see Figure 4 ), the winding portion 264 winds the laminate assembly 28. The winding portion 264 winds the positive electrode sheet 22, the negative electrode sheet 24 and the Z-shaped folding portion 262 to form a whole, thereby ensuring the integrity and reliability of the laminated electrode assembly 20 and preventing the positive electrode sheet 22 and / or the negative electrode sheet 24 from being separated from the Z-shaped separator 26.

[0040] In some embodiments, along the stacking direction L1 of the plurality of positive electrode sheets 22, the stack assembly 28 has a thickness H (see Figure 5 ); along the winding direction L2 of the Z-type diaphragm 26, the laminate assembly 28 has a length L, the length of the winding portion 264 is l (see Figure 4 ); thickness H, length L, length l satisfy: 2(L+H)<l≤4(L+H)+0.5×L. Among them, 2(L+H) means winding the laminate assembly 28 for one cycle; l≤4(L+H)+0.5×L is based on the consideration of the overall energy density of the electrochemical device 100. On the premise of ensuring that the laminate assembly 28 is a tight whole, the Z-type separator 26 is prevented from being too long, resulting in invalid occupation of the space of the electrode assembly 20, thereby reducing the energy density of the electrochemical device 100.

[0041] In some embodiments, the thickness H, the length L, and the length l satisfy: 2(L+H)+0.1×L≤l≤3(L+H)+0.5×L.

[0042] In some embodiments, the bonding force F between the electrode assembly 20 and the packaging shell 10, and / or between the electrode assembly 20 and the separator 30 satisfies: F ≥ 5 N / m, so as to improve the safety and reliability of the electrochemical device 100, and prevent the electrode assembly 20 from shaking in the packaging shell 10, causing the pole ear 12 to be pulled and damaged, thereby reducing the safety and reliability of the electrochemical device 100. In some embodiments, 5 N / m ≤ F ≤ 300 N / m. The bonding force F can be tested by a tensile machine, and the bonding force is calculated by taking the tensile force value f when the curve is flat, F = f / x, where x is the test specimen width, unit: N / m.

[0043] Specifically, the number of electrode assemblies 20 is N1, N1 ≥ 2. In some embodiments, a plurality of electrode assemblies 20 may be arranged in the direction of the thickness of the electrode assembly 20. In order to achieve bonding between the electrode assembly 20 and the packaging shell 10 and / or the separator 30, any one of the following methods or a combination thereof may be used, such as hot melt adhesive, light curing adhesive, pressure sensitive adhesive, etc. If hot melt adhesive is used for bonding, it has a certain elasticity while ensuring sufficient bonding force. When the electrochemical device 100 is subjected to external forces such as impact and falling, the hot melt adhesive also has a buffering force to prevent damage to the electrode assembly 20.

[0044] For the sake of distinction, it is defined that there is an adhesive force F1 between the electrode assembly 20 and the packaging shell 10, and there is an adhesive force F2 between the electrode assembly 20 and the partition 30. In some embodiments, there is an adhesive force F between the electrode assembly 20 and the partition 30. At this time, a glue layer can be set on the partition 30, such as applying hot melt adhesive on the surface of the partition or directly integrating a polymer with hot melt properties on the surface of the partition to form a whole, so as to improve processing efficiency. In some embodiments, there is an adhesive force F between the electrode assembly 20 and the packaging shell 10. At this time, the glue layer is set between the packaging shell 10 and the electrode assembly 20. In this case, during an external impact (such as falling), the force applied to the electrode assembly 20 can be dispersed to the packaging shell 10 through the glue layer to reduce the impact on the electrode assembly 20.

[0045] See also Figure 2 In some embodiments, the electrochemical device 100 further includes a separator 32, which is located between the cavities and fixed to the packaging case 10. The separator 32 includes an encapsulation layer 32 and an ion insulating layer 34.

[0046] The encapsulation layer 32 is located at the periphery of the ion insulating layer 34, and is used to connect the ion insulating layer 34 to the packaging shell 10. The material of the encapsulation layer 32 can be selected from polymer materials such as polypropylene (PP), p-hydroxybenzaldehyde (PHBA), polyester, etc. The melting point of the material of the encapsulation layer 32 can be 100°C-200°C, for example, 110°C-180°C, 120°C-160°C, etc., so that the encapsulation layer 32 can fix the ion insulating layer 34 to the packaging shell 10 under a more suitable temperature condition without damaging the ion insulating layer 34 and the packaging shell 10.

[0047] The ion insulating layer 34 is used to achieve ion insulation between the electrode assemblies 20 in different cavities. The material of the ion insulating layer 34 can be selected from single-layer or multi-layer composite materials such as polyhydrocarbons, polyesters, polyurethanes, polyimides, metals, inorganic salt layers, etc. In the same embodiment, the melting point of the ion insulating layer 34 is greater than the melting point of the encapsulation layer 32. In some embodiments, the melting point of the ion insulating layer 34 can be greater than or equal to 165°C.

[0048] The Z-type separator 26 has a certain degree of adhesion after hot pressing. The Z-type separator 26 can be a Z-type separator 26 that has adhesiveness itself, and it can be a Z-type separator 26 that has been treated with an adhesive coating. The bonding force F' between the Z-type folded portion 262 of the Z-type separator 26 and the positive electrode sheet 22 or the negative electrode sheet 24 satisfies: 0.5N / m≤F'≤50N / m. It can not only ensure the reliability of the electrode assembly 20, prevent the misalignment of the positive electrode sheet 22 and / or the negative electrode sheet 24 in the stacked electrode assembly 20, and cause safety hazards such as lithium precipitation; it can also ensure good interface consistency and uniformity of current density; and it can ensure the effective transfer of lithium ions while shortening the lithium ion transmission path; in addition, especially for high output voltages, the reliability and interface consistency of a single electrode assembly 20 are particularly important.

[0049] In some embodiments, the bonding force F′ between the Z-shaped folded portion 262 of the Z-shaped separator 26 and the positive electrode sheet 22 or the negative electrode sheet 24 satisfies: 1 N / m≤F′≤25 N / m, thereby further ensuring the reliability and interface consistency of the single electrode assembly 20 .

[0050] In some embodiments, the capacity ratio A between any two electrode assemblies 20 connected in series satisfies: 0.95≤A≤1.05, so as to ensure the consistency of the capacity between any two electrode assemblies 20 connected in series and avoid excessive difference in the capacity of the two electrode assemblies 20 connected in series, resulting in energy density loss of the electrochemical device 100.

[0051] The plurality of electrode assemblies 20 may be identical or different. The structure of the plurality of electrode assemblies 20 may be symmetrical or asymmetrical.

[0052] In some embodiments, the ratio B of the orthographic projection areas of any two adjacent electrode assemblies 20 on the partition 30 between the two adjacent electrode assemblies 20 satisfies: 0.95≤B≤1.05, that is, the size difference between the two adjacent electrode assemblies 20 is small, so as to ensure the close fit between the two adjacent electrode assemblies 20 and make full use of the space in the internal cavity of the packaging shell 10, which can improve the energy density of the electrochemical device 100 and the use reliability and packaging reliability of the electrode assembly 20.

[0053] In some embodiments, the winding portion 264 includes an end portion 2644, and the end portion 2644 is provided with a tape 265, and the tape 265 is used to bond the end portion 2644 and the surface of the winding portion 264 facing the end portion 2644, so as to further make the positive electrode sheet 22, the Z-type separator 26 and the negative electrode sheet 24 become a tight whole, thereby improving the safety and reliability of the electrode assembly 20.

[0054] In some embodiments, the positive electrode sheet 22 includes a positive electrode current collector and a positive electrode active material covering the surface of the positive electrode current collector. Along a plane perpendicular to the stacking direction L1 of the plurality of positive electrode sheets 22, the area of ​​the positive electrode current collector is S 正 The area of ​​the positive electrode current collector surface covered with positive electrode active material is S1, S 正 Satisfy with S1: 80% ≤ S1 / S 正 <100%, thereby maximizing the utilization rate of the positive electrode current collector and avoiding the waste of the positive electrode current collector area and thus reducing the energy density of the electrochemical device 100.

[0055] In some embodiments, the negative electrode sheet 24 includes a negative electrode current collector and a negative electrode active material covering the surface of the negative electrode current collector. Along a plane perpendicular to the stacking direction L1 of the plurality of negative electrode sheets 24, the area of ​​the negative electrode current collector is S 负 The area of ​​the negative electrode current collector surface covered with negative electrode active material is S2, S 负 Satisfy with S2: 80% ≤ S2 / S 负 <100%, thereby maximizing the utilization rate of the negative electrode current collector and avoiding the waste of the negative electrode current collector area which would lead to a decrease in the energy density of the electrochemical device 100.

[0056] In some embodiments, S2 and S1 satisfy: 100%≤S2 / S1≤120%, so as to ensure the utilization rate of the negative electrode active material as much as possible, avoid the waste of the negative electrode active material and cause the energy density of the electrochemical device 100 to be reduced. At the same time, it can ensure that the negative electrode has sufficient sites for lithium ion embedding, prevent the occurrence of lithium precipitation problems, and reduce safety hazards.

[0057] In some embodiments, the Z-shaped folded portion 262 and the winding portion 264 are integrally formed, thereby facilitating ensuring the integrity of the electrode assembly 20 .

[0058] The electrode assembly 20 also includes an electrolyte (not shown), and the electrolyte infiltrates the Z-shaped separator 26. Two adjacent electrode assemblies 20 are separated by a separator 32, and the ion insulating layer 34 in the separator 32 can isolate the ion conduction between the two adjacent cavities to avoid internal short circuits of positive and negative electrodes with different potentials under liquid conditions; at the same time, it can also avoid the decomposition failure of conventional liquid electrolytes under high voltage.

[0059] In some embodiments, the electrode assemblies 20 connected in series are realized by welding the pole tabs 12 of different polarities between the multiple electrode assemblies 20, and only one pole tab 12 of different polarities is led out of the packaging shell 10 or all pole tabs 12 are led out of the packaging shell 10, wherein one positive pole tab 122 and one negative pole tab 124 are connected to the external circuit, and the remaining pole tabs 12 can serve to monitor the voltage of each electrode assembly 20.

[0060] The inventors of this case found that under the same conditions, the overall performance of the laminated electrode assembly 20 is better than that of the wound electrode assembly 20. This is because the capacity difference of the wound electrode assembly 20 is greater than that of the laminated electrode assembly 20, and the manufacturing rate and safety reliability of the wound electrode assembly 20 are also lower than those of the laminated electrode assembly 20, which will lead to a low capacity of the entire high output voltage electrochemical device 100, a loss of energy density, and a high safety risk.

[0061] The specific reason is that the winding tension in the corner bending area of ​​the wound electrode assembly 20 is uneven, which causes the diaphragm or the electrode sheet (including the positive electrode sheet 22 and the negative electrode sheet 24) to bend or wrinkle, and some positive and negative electrode areas cannot be effectively contacted, and the capacity is reduced; in the case of severe bending in the corner area, the electrode sheet has local powder loss and cannot function normally, resulting in a large difference in capacity between different electrode assemblies 20. Therefore, the actual energy density of the high output voltage electrochemical device 100 based on the series connection of the wound electrode assemblies 20 is far from the design value. In addition, the safety risk of the wound electrode assembly 20 is large. Due to the different radii of the corner semicircle, the corresponding positive and negative active materials have different contents. When the total capacity of the positive electrode sheet 22 is greater than the total capacity of the negative electrode sheet 24, the lithium ions cannot be completely embedded in the negative electrode sheet 24, and will precipitate on the surface of the negative electrode sheet 24, causing lithium precipitation; abnormalities in the corner area, such as wrinkles in the electrode sheet / diaphragm 26, will also hinder the smooth embedding of lithium ions in the negative electrode sheet 24, and lithium ions will precipitate on the surface of the diaphragm 26 / negative electrode sheet 24, which has huge safety hazards. Powder loss of the electrode sheet will also cause safety problems such as short circuit. In addition, there are problems with the manufacturing reliability of the wound electrode assembly 20. The diaphragm 26 has tension during the winding process of the electrode assembly 20. After the electrode assembly 20 is wound, the stress at the edge of the diaphragm 26 cannot be offset and released, so the electrode assembly 20 is deformed, which is not conducive to the packaging of multiple electrode assemblies 20 in the same packaging bag. In addition, the electrode assembly 20 is prone to abnormal problems such as thickening and swelling during use, resulting in reduced reliability.

[0062] The laminated electrode assembly 20 can avoid the above problems, it has no corners and tension, and has good manufacturability; the laminated electrode assembly 20 has a flat surface, good contact with the Z-type diaphragm 26, uniform interface reaction, and uniform current distribution, which can fully utilize the capacity of the active material and effectively ensure the consistency of the capacity of the electrode assembly 20; in addition, unlike the wound electrode assembly 20 with severe temperature gradient distribution, that is, the internal temperature is high, the external temperature is low, and the heat cannot be evenly and effectively diffused, the laminated electrode assembly 20 has good internal diffusion performance, which ensures its safety performance; the laminated electrode assembly 20 is a multi-electrode ear 12 structure, which is suitable for high-power discharge requirements; the laminated electrode assembly 20 has high manufacturing flexibility, and can be designed according to the diversified needs of today's products. High-output voltage electrochemical devices 100 of different shapes and sizes can be designed to meet the needs of various electronic products.

[0063] The positive electrode active material is selected from any material that can be used for the positive electrode material of the electrode assembly 20, including but not limited to at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate and lithium titanate.

[0064] The negative electrode active material is selected from any material that can be used for the negative electrode material of the electrode assembly 20, including but not limited to at least one of graphite, hard carbon, soft carbon, silicon, silicon carbon and silicon oxide.

[0065] The electrolyte can use any electrolyte known in the art, and can be any one of a gel state, a solid state, and a liquid state. For example, in some embodiments, the liquid electrolyte includes a lithium salt and a non-aqueous solvent. The lithium salt can be selected from at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, or LiPO2F2; the non-aqueous solvent can be selected from at least one of organic solvents such as carbonate compounds, carboxylate compounds, ether compounds, and nitrile compounds. Among them, the carbonate compound may include at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate and trifluoromethylethylene carbonate.

[0066] The present application also provides an electronic device 200, which includes the electrochemical device 100. The electronic device 200 may be a consumer electronic product (such as a mobile communication device, a tablet computer, a laptop computer, a wearable device, etc.), an electric tool, a drone, an energy storage device, a power device, etc. Figure 6 In one embodiment, the electronic device 200 is a mobile communication device.

[0067] The present application is described below through specific examples and comparative examples.

[0068] Example 1

[0069] Preparation of negative electrode sheet 24

[0070] Graphite (negative electrode active material), conductive carbon black (conductive agent), and styrene-butadiene rubber (binder) were mixed in a mass ratio of 96:1.5:2.5, and deionized water was added to prepare a slurry with a solid content of 0.7, and stirred evenly. The slurry was evenly coated on the negative electrode current collector copper foil, dried at 110°C, and cut into (80mm×60mm) specifications to obtain a single-sided negative electrode sheet 24.

[0071] The negative electrode active material is coated on both sides of the negative electrode current collector copper foil in the same manner to obtain a double-sided negative electrode sheet 24 .

[0072] Preparation of positive electrode sheet 22

[0073] Lithium cobalt oxide (LiCoO2, positive electrode active material), conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF, binder) are mixed at a mass 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 0.75, and stirred evenly. The slurry is evenly coated on the positive electrode current collector aluminum foil, dried at 90°C, and cut into (78mm×58mm) specifications to obtain a single-sided positive electrode sheet 22.

[0074] The positive electrode active material is coated on both sides of the positive electrode current collector aluminum foil in the same manner to obtain a double-sided positive electrode sheet 22 .

[0075] Preparation of electrolyte

[0076] In a dry argon atmosphere, organic solvents 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, and then lithium salt lithium hexafluorophosphate (LiPF6) is added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15M.

[0077] Preparation of electrode assembly 20

[0078] The prepared positive electrode sheet 22, negative electrode sheet 24, Z-type separator 26 and other components are stacked into a laminated electrode assembly 20 in the form of a single-sided negative electrode sheet 24, a Z-type separator 26, a double-sided positive electrode sheet 22, a Z-type separator 26, a double-sided negative electrode sheet 24, a Z-type separator 26, a double-sided positive electrode sheet 22... Z-type separator 26, a single-sided negative electrode sheet 24, and the positive electrode tabs, the negative electrode tabs, the positive electrode aluminum transition tabs 122 and the negative electrode nickel transition tabs 124 are connected by laser welding, and the positive and negative tabs are in the same direction.

[0079] Part of the Z-shaped separator 26 (i.e., the Z-shaped folded portion 262) is folded in a "Z" shape between the positive electrode sheet 22 and the negative electrode sheet 24 to form a laminate assembly 28, and part of the Z-shaped separator 26 (i.e., the winding portion 264) is wound around the laminate assembly 28 to form a laminated electrode assembly 20. The bonding force F' between the Z-shaped folded portion 262 and the positive electrode sheet is 15N / m. Among them, the length l of the winding portion 264 is 194mm, the thickness H of the laminate assembly 28 is 5mm, and the length L of the laminate assembly 28 is 80mm, that is, l=2×(L+H)+0.3L.

[0080] Assembly of the electrochemical device 100

[0081] Assembly of two electrode assemblies 20: Place the punched packaging shell 10 (aluminum-plastic film with a thickness of 150 μm) in the assembly fixture with the pit facing upward. Place the first electrode assembly 20 in the pit, then place the partition 32 on the first electrode assembly 20 and apply external force to press it. Place the semi-finished product assembled above in the assembly fixture with the exposed surface of the partition 32 facing upward, place the second electrode assembly 20 on the partition 32 and apply external force to press it. Then cover the surface of the second electrode assembly 20 with another piece of packaging shell 10 with the pit facing downward, and heat seal it around.

[0082] Liquid injection and packaging: Liquid is injected into the two cavities of the assembled electrode assembly 20 separately, and then the surroundings are packaged after the liquid injection, wherein the surroundings of the separator 32 are all sealed in the seal. At this time, the two electrode assemblies 20 are divided into two independent sealed cavities by the separator 32, and there is no ion exchange between them.

[0083] Series connection: The negative electrode tab 124 of the first electrode assembly 20 is connected to the positive electrode tab 122 of the second electrode assembly 20 by welding (laser welding, ultrasonic welding or resistance welding) to achieve series conduction between the two electrode assemblies 20, and then all the tabs are led out of the packaging bag from the same side, and the series electrochemical device 100 is assembled.

[0084] The number of electrode assemblies 20 is 2, the number of tabs 12 extending out of the packaging shell 10 is 4, and the winding portion 264 is not provided in the Z-shaped separator 26 of the electrode assembly 20. There is no bonding force between the packaging shell 10 and the electrode assembly 20. There is no bonding force between the separator 32 and the electrode assembly 20. S1 / S 正 =0.95, S2 / S 负 =0.95, S2 / S1=1.05, the capacity ratio A between the two electrode assemblies 20=0.95; the ratio B of the projected areas of the two electrode assemblies 20 on the plane along the stacking direction L1 of the plurality of positive electrode sheets 22=0.98. The material of the encapsulation layer 32 of the separator 32 is PP with a melting point of 150°C; the material of the ion insulating layer 34 is PI with a melting point of 334°C.

[0085] The charge and discharge process only requires connecting the positive electrode tab 122 of the first electrode assembly 20 and the negative electrode tab 124 of the second electrode assembly 20; the series-connected tabs are used to monitor the voltage.

[0086] Example 2

[0087] The difference from the first embodiment is that the number of electrode assemblies 20 is 3.

[0088] Example 3

[0089] The difference from the first embodiment is that the number of the electrode tabs 12 extending out of the packaging shell 10 is two.

[0090] Example 4

[0091] The difference from the first embodiment is that the length l of the winding portion 264 of the Z-type separator 26 is 178 mm, that is, l=2×(L+H)+0.1L.

[0092] Example 5

[0093] The difference from the first embodiment is that the length l of the winding portion 264 of the Z-type separator 26 is 234 mm, that is, l=2×(L+H)+0.8L.

[0094] Example 6

[0095] The difference from the first embodiment is that the length l of the winding portion 264 of the Z-type separator 26 is 380 mm, that is, l=4×(L+H)+0.5L.

[0096] Example 7

[0097] The difference from Example 1 is that the bonding force F1 between the packaging case 10 and the electrode assembly 20 is 100 N / m.

[0098] Example 8

[0099] The difference from Example 1 is that the bonding force F1 between the packaging case 10 and the electrode assembly 20 is 5 N / m.

[0100] Example 9

[0101] The difference from Example 1 is that the bonding force F1 between the packaging case 10 and the electrode assembly 20 is 20 N / m.

[0102] Example 10

[0103] The difference from Example 1 is that the bonding force F1 between the packaging case 10 and the electrode assembly 20 is 50 N / m.

[0104] Embodiment 11

[0105] The difference from Example 1 is that the bonding force F1 between the packaging case 10 and the electrode assembly 20 is 300 N / m.

[0106] Example 12

[0107] The difference from Example 1 is that the bonding force F2 between the separator and the electrode assembly 20 is 100 N / m.

[0108] Embodiment 13

[0109] The difference from the seventh embodiment is that the bonding force F′ between the Z-shaped folded portion 262 and the positive electrode sheet 22 is 0.5 N / m.

[0110] Embodiment 14

[0111] The difference from the first embodiment is that the bonding force F′ between the Z-shaped folded portion 262 and the positive electrode sheet 22 is 1 N / m.

[0112] Embodiment 15

[0113] The difference from the first embodiment is that the bonding force F′ between the Z-shaped folded portion 262 and the positive electrode sheet 22 is 25 N / m.

[0114] Example 16

[0115] The difference from the first embodiment is that the bonding force F′ between the Z-shaped folded portion 262 and the positive electrode sheet 22 is 50 N / m.

[0116] Comparative Example 1

[0117] The difference from the first embodiment is that the two electrode assemblies 20 are not provided with separators 32 .

[0118] Comparative Example 2

[0119] The difference from the first embodiment is that the separator in the electrode assembly 20 is not a Z-shaped separator, but a plurality of rectangular separators respectively arranged between the positive electrode sheet 22 and the negative electrode sheet 24, and the separator size is larger than the negative electrode sheet size.

[0120] Comparative Example 3

[0121] The difference from Example 1 is that a wound electrode assembly is prepared during the preparation of the electrode assembly 20 .

[0122] The electrochemical device 100 is tested, and the test items include the voltage of the electrochemical device 100, the discharge energy density at a current density of 0.1C, the capacity retention rate at a current density of 2C charge / 0.2C discharge, whether lithium is deposited at the corners, and the drop test pass rate.

[0123] Please refer to Table 1, which is a summary of some of the different conditions and performance test results of Comparative Examples 1-3 and Examples 1-16.

[0124] Table 1

[0125]

[0126]

[0127]

[0128] From the difference conditions and performance test results in Table 1, it can be seen from the comparison with Comparative Examples 1-3 that: when comparing Example 1-16 with Comparative Example 1, no separator 32 is provided between the two electrode assemblies 20 in Comparative Example 1, a short circuit occurs between the two electrode assemblies 20, and the battery cannot be used, and the purpose of high output voltage cannot be achieved. When comparing Example 1-16 with Comparative Example 2, the separator in the electrode assembly 20 in Comparative Example 2 is not a Z-type separator, but a plurality of rectangular separators, the manufacturing rate and efficiency of the battery cell will be reduced; in addition, the components (positive electrode, negative electrode, separator) in the electrode assembly are prone to misalignment, resulting in capacity loss, or even short circuit, and high safety risks; the plurality of rectangular separators have no curved end design, which reduces the amount of electrolyte in the battery cell, and thus causes a loss in the electrical performance of the electrochemical device 100. Comparing Examples 1-16 with Comparative Example 3, the electrode assembly 20 in Comparative Example 3 is of a wound type. Compared with the laminated electrode assembly 20, there is tension in the diaphragm during its manufacturing process, which can easily cause deformation of the electrochemical device 100. In addition, the wound electrode assembly has corner areas, poor interface consistency, and poor dynamics, so there is a risk of lithium plating, and it will also bring about capacity loss. Therefore, it is not conducive to high-output voltage batteries with high consistency requirements for multiple electrode assemblies.

[0129] In addition, Example 2 effectively improves the voltage and energy density by increasing the number of electrode assemblies 20, while the capacity retention rate and drop performance test are basically unaffected. It is shown that improving the adhesion between the electrode assembly and the external device is also applicable in the multi-electrode assembly system, which can effectively improve the safety performance of the lithium-ion battery. Example 3 effectively improves the energy density by reducing the number of tabs, while maintaining excellent capacity retention rate and drop performance. Examples 4-6 regulate the length of the Z-type diaphragm winding portion to stabilize the electrode assembly as a whole, and are used to improve the drop test performance under the premise of limited energy density loss. At the same time, the output voltage and capacity retention rate of the lithium-ion battery are maintained. In Examples 7-16, adding an adhesive material (such as hot melt adhesive) between the electrode assembly and the packaging bag and (or) the separator can effectively construct the integrity of the electrochemical device 100, and can prevent the electrode assembly 20 from shaking in the packaging shell 10 and causing pulling and damage to the tab 12, thereby reducing the safety problem of failure of the electrochemical device 100 during mechanical abuse such as falling.

[0130] Embodiment 17

[0131] The difference from Example 7 is that the area S1 of the positive active material covered on the surface of a single positive current collector is equal to the area S 正 The ratio (S1 / S 正 ) is 0.90; the area S2 of the negative electrode active material covered on the surface of a single negative electrode current collector is equal to the area S 负 The ratio (S2 / S 负 ) is 0.90.

[0132] Embodiment 18

[0133] The difference from Example 7 is that the area S1 of the positive active material covered on the surface of a single positive current collector is equal to the area S 正 The ratio (S1 / S 正 ) is 0.98; the area S2 of the negative electrode active material covered on the surface of a single negative electrode current collector is equal to the area S 负 The ratio (S2 / S 负 ) is 0.98.

[0134] Embodiment 19

[0135] The difference from Example 18 is that: S2 / S1=1.20.

[0136] Embodiment 20

[0137] The difference from Example 18 is that the capacity ratio A between the two electrode assemblies 20 is 1.

[0138] Embodiment 21

[0139] The difference from Example 20 is that the ratio B of the projected areas of the two electrode assemblies 20 on the plane along the stacking direction L1 of the plurality of positive electrode sheets 22 is 0.95.

[0140] Embodiment 22

[0141] The difference from Example 20 is that the ratio B of the projected areas of the two electrode assemblies 20 on the plane along the stacking direction L1 of the plurality of positive electrode sheets 22 is 1.

[0142] Embodiment 23

[0143] The difference from Example 22 is that the material of the encapsulation layer 32 of the partition 32 is polystyrene, and the melting point is 240°C.

[0144] Embodiment 24

[0145] The difference from Example 22 is that the material of the ion insulating layer 34 is stainless steel with a melting point of 1440°C.

[0146] Embodiment 25

[0147] The difference from Example 22 is that the pole ear 12 comes out from the opposite side.

[0148] Please refer to Table 2 for a summary of the different conditions and performance test results of Examples 17-25.

[0149] Table 2

[0150]

[0151] From the comparison between the different conditions and performance test results in Table 2 and those in Comparative Example 1-2, it can be seen that by adjusting S1 / S 正 、S2 / S 负 , S2 / S1, A, B, the material and melting point of the encapsulation layer 32 of the separator 32, the material and melting point of the ion insulating layer 34 of the separator 32, and the extension direction of the electrode ear 12 can further improve the drop pass rate of the electrochemical device 100 while ensuring good energy density and capacity retention rate and controlling safety risks.

[0152] The above implementation modes are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the present application has been described in detail with reference to the above preferred implementation modes, a person skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. An electrochemical device, characterized in that: include: Packaging shell, separator and multiple electrode assemblies; The electrode assemblies are respectively arranged in cavities separated by the separators in the packaging shell, and at least two of the electrode assemblies are connected in series; The electrode assembly includes a plurality of positive electrode sheets, a plurality of negative electrode sheets and a Z-shaped separator, wherein the Z-shaped separator includes a Z-shaped folded portion and a winding portion, and the Z-shaped folded portion separates the adjacent positive electrode sheets from the negative electrode sheets; The bonding force F between the electrode assembly and the packaging shell, and / or between the electrode assembly and the separator satisfies: F≥5N / m; The bonding force F' between the Z-shaped folded portion and the positive electrode sheet or the negative electrode sheet satisfies: 0.5 N / m≤F'≤50 N / m.

2. The electrochemical device according to claim 1, characterized in that The plurality of positive electrode sheets, the plurality of negative electrode sheets and the Z-shaped folded portion form a laminate assembly, and the winding portion surrounds the laminate assembly.

3. The electrochemical device according to claim 2, characterized in that Along the stacking direction of the multiple positive plates, the stacking assembly has a thickness H; along the winding direction of the Z-type separator, the stacking assembly has a length L, and the length of the winding portion is l; the thickness H, the length L, and the length l satisfy: 2(L+H)<l≤4(L+H)+0.5×L.

4. The electrochemical device according to claim 1, characterized in that The capacity ratio A between any two of the electrode assemblies connected in series satisfies: 0.95≤A≤1.

05.

5. The electrochemical device according to claim 1, characterized in that The winding portion includes an end portion, and an adhesive tape is provided on the end portion. The adhesive tape bonds the end portion and a surface of the winding portion facing the end portion.

6. The electrochemical device according to claim 1, characterized in that The Z-shaped folded portion and the winding portion are integrally formed.

7. The electrochemical device according to claim 1, characterized in that The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material covering the surface of the positive electrode current collector. Along a plane perpendicular to the stacking direction of the plurality of positive electrode sheets, the area of ​​the positive electrode current collector is S 正 The area of ​​the positive electrode current collector surface covered with the positive electrode active material is S1, and the S 正 Satisfy the S1: 80%≤S1 / S 正 <100%; The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material covering the surface of the negative electrode current collector. The area of ​​the negative electrode current collector along a plane perpendicular to the stacking direction of the plurality of negative electrode sheets is S 负 The area of ​​the negative electrode current collector surface covered with the negative electrode active material is S2, and the S 负 The S2 meets the following requirements: 80% ≤ S2 / S 负 <100%.

8. The electrochemical device according to claim 7, characterized in that The S2 and the S1 satisfy: 100%≤S2 / S1≤120%.

9. The electrochemical device according to claim 1, characterized in that A ratio B of the orthographic projection areas of two adjacent electrode assemblies on the separator between the two adjacent electrode assemblies satisfies: 0.95≤B≤1.

05.

10. An electronic device, characterized in that: An electrochemical device comprising any one of claims 1 to 9.

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