CN114667625A - Electrochemical device and electronic device - Google Patents

Abstract

An electrochemical device, comprising a packaging shell, a separator and a plurality of electrode assemblies, 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 assembly includes a plurality of electrode assemblies. A positive electrode sheet, a plurality of negative electrode sheets and a Z-type separator. The present application also provides an electronic device. The electrochemical device of the present application improves the safety and reliability during use.

Description

Electrochemical devices and electronic devices

technical field

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

Background technique

Electrochemical devices, such as lithium-ion batteries, have a wide range of applications in consumer electronics, power tools, and other electronic devices. In the existing electrochemical device system, 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.), the operating voltage of the electrochemical device is difficult to exceed 5V .

However, in actual demand, there are many scenarios where the voltage of electrochemical devices exceeds 5V (such as automatic vehicles, power tools, energy storage, etc.). Specifically, in the consumer electronics market, in order to meet demands such as fast charging, it is necessary to increase the open circuit voltage of the electrochemical device.

At present, the method of external series connection of multiple finished lithium-ion batteries is generally used to increase the output voltage, but there are many problems in the series connection of multiple lithium-ion batteries, such as the introduction of additional electronic resistance by the wires in series, which wastes energy due to heat generation; the higher the voltage, the more The greater the number of lithium-ion batteries, the lower the reliability of battery series connection, and the greater the difficulty in management; the proportion of inactive materials (such as packaging shells) is further increased, resulting in a loss of energy density.

SUMMARY OF THE INVENTION

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

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

In a first aspect of the present application, an electrochemical device is provided, comprising a packaging case, a separator, and a plurality of electrode assemblies, wherein the electrode assemblies are respectively disposed in cavities separated by the separators in the packaging case, and between at least two electrode assemblies In series; the electrode assembly includes a plurality of positive electrode sheets, a plurality of negative electrode sheets and a Z-shaped separator.

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.

In some embodiments, a plurality of positive electrode sheets, a plurality of negative electrode sheets and a Z-folded portion constitute a laminated sheet assembly, and the winding portion surrounds the laminated sheet assembly.

The open-circuit voltage of the electrochemical device can be increased by arranging the electrode assemblies in series inside the packaging shell; in addition, the tabs extending in the same direction in the two electrode assemblies can be directly connected in series, which can avoid additionally connecting wires for series connection. Reduce unnecessary resistance to cause heating of electrochemical devices, thereby reducing unnecessary energy loss; arranging series-connected electrode assemblies in the same packaging shell can also reduce unnecessary packaging and reduce the loss of overall energy density of electrochemical devices Furthermore, the Z-shaped folded part in the Z-shaped separator is beneficial to limit the relative position between the positive and negative electrode sheets, and can improve the manufacturing rate of the electrode assembly, and the winding part further tightens the laminated sheet assembly as a whole, Therefore, the risk of movement between the pole pieces during the drop process is reduced. At the same time, the end bending structure of the Z-shaped folded part can provide a buffering effect for the electrode assembly, thereby improving the safety and reliability of the electrochemical device. In addition, the Z-shaped folded part The curved end structure 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 of the electrochemical device.

In some embodiments, along the stacking direction of the plurality of positive electrode sheets, the stacked sheet assembly has a thickness H; along the winding direction of the Z-shaped separator, the stacked sheet 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. On the premise of ensuring the safety and reliability of the electrochemical device, the energy density of the electrochemical device is improved.

In some embodiments, the adhesive force F between the electrode assembly and the packaging case, and/or between the electrode assembly and the separator, satisfies: F≥5N/m. In some embodiments, 5N/m≤F≤300N/m. By setting the bonding force F between the electrode assembly inside the packaging case and the packaging case, and/or between the electrode assembly and the separator to satisfy: F≥5N/m, to prevent the electrode assembly from shaking inside the packaging case, thereby improving the Safety and reliability of electrochemical devices during assembly and use.

In some embodiments, the adhesive force F' between the Z-shaped folded part 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 It can improve the interface consistency and ensure the uniformity of the current density.

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

In some embodiments, the winding portion includes an end portion, and the end portion is provided with a tape, and the tape adheres 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 fastened Overall, the safety and reliability of the electrode assembly are improved.

In some embodiments, the Z-shaped folded portion and the winding portion are integrally formed, which is beneficial to ensure the integrity of the electrode assembly.

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, 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 _positive , and the surface of the positive electrode current collector is covered The area with positive active material is S ₁ , S _{is positive} and S ₁ satisfies: 80%≦S ₁ /S _positive <100%.

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. Along a plane perpendicular to the stacking direction of the plurality of negative electrode sheets, the area of the negative electrode current collector is S _negative , and the surface of the negative electrode current collector is covered with the area of the negative electrode active material. For S ₂ , S _negative and S ₂ satisfy: 80%≤S ₂ /S _negative <100%.

In some embodiments, S ₂ and S ₁ satisfy: 100%≦S ₂ /S ₁ ≦120%.

In some embodiments, the 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.

In a second aspect of the present application, an electronic device is provided, including the electrochemical device provided in the first aspect.

In the electrochemical device of the present application, by arranging the electrode assemblies connected in series in the same packaging shell, and fixing the positive and negative electrode sheets through the Z-type diaphragm, the safety and reliability of the electrochemical device are ensured while improving the energy density. .

Description of drawings

FIG. 1 is a schematic diagram of the overall structure of an electrochemical device according to an embodiment of the present application.

FIG. 2 is an exploded view of the electrochemical device shown in FIG. 1 .

FIG. 3 is a schematic structural diagram of the electrode assembly shown in FIG. 2 .

FIG. 4 is a schematic structural diagram of the electrode assembly shown in FIG. 3 when the winding portion of the Z-shaped separator is not wound around the lamination assembly.

FIG. 5 is a schematic cross-sectional view of the electrode assembly shown in FIG. 3 along the V-V direction.

FIG. 6 is a schematic structural diagram of an electronic device according to an embodiment of the present application.

Description of main component symbols

The following specific embodiments will further illustrate the present application in conjunction with the above drawings.

Detailed ways

In order to more clearly understand the above objects, features and advantages of the present application, the present application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features of the embodiments may be combined with each other unless there is conflict. Many specific details are set forth in the following description to facilitate a full understanding of the present application, and the described embodiments are only a part of the embodiments of the present application, but not all of the embodiments.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terms used herein in the specification of the present application are for the purpose of describing particular embodiments only, and are not intended to limit the present application. As used herein, the term "and/or" includes all and any combinations of one or more of the associated listed items.

In each embodiment of the present application, for the convenience of description rather than limitation of the present application, the term "connection" used in the description of the patent application and the claims of the present application is not limited to physical or mechanical connection, whether direct or indirect of. "Up", "Down", "Above", "Down", "Left", "Right", etc. are only used to indicate the relative positional relationship. When the absolute position of the described object changes, the relative positional relationship will also correspond accordingly. Change.

Referring to FIG. 1 , an embodiment of the present application provides an electrochemical device 100 . The electrochemical device 100 includes all devices capable of generating electrochemical reactions. Specifically, the electrochemical device 100 includes all kinds of primary batteries and secondary batteries. Alternatively, the electrochemical device 100 may 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.

Please also refer to FIG. 2 , the electrochemical device 100 includes a packaging case 10 , a separator 30 and a plurality of electrode assemblies 20 . The electrode assemblies 20 are respectively disposed in the cavities separated by the separators 30 in the packaging case 10 . At least two The electrode assemblies 20 are connected in series to increase the voltage of the electrochemical device 100 . The electrode assembly 20 encapsulated in the packaging case 10 is connected to an external circuit through the tab 12 , so as to realize the charging and discharging function of the electrode assembly 20 . The tabs 12 of each electrode assembly 20 include positive tabs 122 and negative tabs 124, and the positive tabs 122 and the negative tabs 124 may be in the same direction or opposite. The open circuit voltage of the electrochemical device 100 can be 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 additional connections for series connection It can reduce unnecessary resistance and cause the electrochemical device 100 to generate heat, 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 A reduction in the overall energy density of the electrochemical device 100 .

The electrode assembly 20 includes a laminated type.

Please refer to FIG. 3 , FIG. 4 and FIG. 5 , in this embodiment, the electrode assembly 20 is of a laminated type. The electrode assembly 20 includes a plurality of positive electrode sheets 22 , a plurality of negative electrode sheets 24 , and a Z-shaped separator 26 arranged in layers. Referring to FIG. 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 sheets 22 from the negative electrode sheets 24; a plurality of stacked positive electrode sheets 22, a plurality of The negative electrode sheet 24 and the Z-shaped folded portion 262 form the laminated sheet assembly 28 (please refer to FIG. 4 ), and the winding portion 264 winds the laminated sheet assembly 28 . The winding portion 264 winds the positive electrode sheet 22, the negative electrode sheet 24 and the Z-folded portion 262 to form a whole, thereby ensuring the integrity and reliability of the laminated electrode assembly 20, preventing the positive electrode sheet 22 and/or the negative electrode Sheet 24 is disengaged from Z-diaphragm 26 .

In some embodiments, along the lamination direction L ₁ of the plurality of positive electrode sheets 22 , the lamination assembly 28 has a thickness H (refer to FIG. 5 ); along the winding direction L ₂ of the Z-shaped separator 26 , the lamination assembly 28 has A length L, the length of the winding portion 264 is l (refer to FIG. 4 ); the thickness H, the length L, and the length l satisfy: 2(L+H)<1≤4(L+H)+0.5×L. Among them, 2(L+H) is to wind the laminated assembly 28 once; l≤4(L+H)+0.5×L, it is based on the consideration of the overall energy density of the electrochemical device 100, in order to ensure the laminated assembly On the premise that 28 is a tightened whole, the Z-shaped diaphragm 26 is prevented from being too long, which will lead to ineffectively occupying the space of the electrode assembly 20 , thereby reducing the energy density of the electrochemical device 100 .

In some embodiments, the thickness H, the length L, and the length l satisfy: 2(L+H)+0.1×L≤1≤3(L+H)+0.5×L.

In some embodiments, the adhesive force F between the electrode assembly 20 and the packaging case 10 and/or between the electrode assembly 20 and the separator 30 satisfies: F≥5N/m, so as to improve the safety and reliability of the electrochemical device 100 It can prevent the electrode assembly 20 from shaking in the packaging case 10 and cause pulling and damage to the tab 12 , thereby reducing the safety and reliability of the electrochemical device 100 . In some embodiments, 5N/m≤F≤300N/m. The adhesive force F can be tested by a tensile machine, and the adhesive force is calculated by taking the value of the tensile force f when the curve travels, F=f/x, where x is the width of the test specimen, unit: N/m.

Specifically, the number of electrode assemblies 20 is N ₁ , and N ₁ ≥2. In some embodiments, a plurality of electrode assemblies 20 may be arranged in the direction of the thickness of the electrode assemblies 20 . In order to realize the bonding between the electrode assembly 20 and the packaging shell 10 and/or the separator 30, any one or a combination of the following methods can be used, such as hot melt adhesive, light-curing adhesive, pressure-sensitive adhesive, etc. The hot-melt adhesive is used for bonding, and it also has a certain elasticity under the condition that the bonding force is sufficient. When the electrochemical device 100 is subjected to external forces such as impact, drop, etc., the hot-melt adhesive also has a buffering force to prevent the electrode Component 20 is damaged.

For the convenience of distinction, it is defined that the electrode assembly 20 and the packaging case 10 have an adhesive force F ₁ , and the electrode assembly 20 and the separator 30 have an adhesive force F ₂ . In some embodiments, there is an adhesive force F between the electrode assembly 20 and the separator 30. At this time, an adhesive layer can be arranged on the separator 30, such as applying hot melt glue on the surface of the separator or applying a hot melt adhesive to the separator. The polymer is directly integrated on the surface of the separator to form a whole to improve processing efficiency. In some embodiments, there is an adhesive force F between the electrode assembly 20 and the packaging case 10 , and at this time, the adhesive layer is provided between the packaging case 10 and the electrode assembly 20 , then during an external impact (eg, falling), it is applied to the The force on the electrode assembly 20 can be dispersed to the packaging case 10 through the adhesive layer, so as to reduce the impact on the electrode assembly 20 .

Referring to FIG. 2 , in some embodiments, the electrochemical device 100 further includes a separator 32 , and the separator 32 is located between the cavities and fixed on the packaging case 10 . Separator 32 includes encapsulation layer 32 and ion insulating layer 34 .

The encapsulation layer 32 is located on the periphery of the ion insulating layer 34 for connecting the ion insulating layer 34 with 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, can be 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 case 10 under suitable temperature conditions without damaging the ion insulating layer 34 and the packaging case 10 .

The ionic insulation layer 34 is used to achieve ionic 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 polyhydrocarbon, polyester, polyurethane, polyimide, metal, and inorganic salt layer. 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 may be greater than or equal to 165°C.

The Z-shaped diaphragm 26 has certain adhesiveness after being hot-pressed. The Z-type diaphragm 26 may be an adhesive Z-type diaphragm 26 itself, which may be a Z-type diaphragm 26 treated with an adhesive coating. The adhesive 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: 0.5N/m≤F'≤50N/m. It can not only ensure the reliability of the use of the electrode assembly 20, but also prevent the dislocation of the positive electrode sheet 22 and/or the negative electrode sheet 24 in the laminated electrode assembly 20, causing potential safety hazards such as lithium precipitation; it can also ensure good interface consistency and high current density. Uniformity; and 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.

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

In some embodiments, the capacity ratio A between any two electrode assemblies 20 in series satisfies: 0.95≤A≤1.05, so as to ensure the consistency of the capacity between any two electrode assemblies 20 in series, and avoid two electrode assemblies in series The capacity difference of 20 is too large, resulting in a loss of energy density of the electrochemical device 100 .

The plurality of electrode assemblies 20 may or may not be the same. The structure of the plurality of electrode assemblies 20 may be symmetrical or asymmetrical.

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

In some embodiments, the winding portion 264 includes an end portion 2644 provided with a tape 265 for bonding the end portion 2644 and the surface of the winding portion 264 toward the end portion 2644 to further bond the positive electrode sheet 22 , the Z-shaped diaphragm 26 and the negative electrode sheet 24 form a fastened whole, which improves the safety and reliability of the electrode assembly 20 .

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 _positive , and the positive electrode The area of the current collector covered with the positive active material is S ₁ , and S _{is positive} and S ₁ satisfies: 80%≤S ₁ /S _positive <100%, which maximizes the utilization rate of the positive current collector and avoids the area of the positive current collector waste, resulting in a decrease in the energy density of the electrochemical device 100 .

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 _negative , and the negative electrode The area of the current collector covered with the negative active material is S ₂ , and S _negative and S ₂ satisfy: 80%≤S ₂ /S _negative <100%, which maximizes the utilization rate of the negative current collector and avoids the area of the negative current collector. waste, resulting in a decrease in the energy density of the electrochemical device 100 .

In some embodiments, S ₂ and S ₁ satisfy: 100%≤S ₂ /S ₁ ≤120%, so as to ensure the utilization rate of the negative electrode active material as much as possible, and avoid the waste of negative electrode active material leading to the energy density of the electrochemical device 100 decrease. At the same time, it can ensure that the negative electrode has sufficient sites to intercalate lithium ions, prevent the occurrence of lithium precipitation problems, and reduce safety hazards.

In some embodiments, the Z-shaped folding portion 262 and the winding portion 264 are integrally formed, so as to help ensure the integrity of the electrode assembly 20 .

The electrode assembly 20 further includes an electrolyte solution (not shown), and the electrolyte solution infiltrates the Z-shaped separator 26 . The two adjacent electrode assemblies 20 are separated by the separator 32, and the ionic insulating layer 34 in the separator 32 can isolate the ion conduction between the two adjacent cavities, so as to avoid the internal short circuit of the positive and negative electrodes of different potentials under liquid conditions. At the same time, it can also avoid the decomposition failure of conventional liquid electrolyte under high voltage.

In some embodiments, the electrode assemblies 20 connected in series are realized by welding electrodes 12 of different polarities among a plurality of electrode assemblies 20, and only one of the tabs 12 of different polarities is led out of the package shell 10 or all of them are led out of the package In the case 10 , one positive tab 122 and one negative tab 124 are in communication with the external circuit, and the remaining tabs 12 can play the role of monitoring the voltage of each electrode assembly 20 .

The inventor of the present application 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 difference in capacity of the wound electrode assembly 20 is greater than that of the laminated electrode assembly 20, and the manufacturing yield and safety reliability of the wound electrode assembly 20 are also lower than those of the laminated electrode assembly 20, so the entire The electrochemical device 100 with high output voltage has low capacity performance, loss of energy density, and high safety risk.

The specific reason is: the winding electrode assembly 20 has uneven winding tension in the corner bending area, which causes bending or wrinkling of the separator or pole piece (including the positive electrode piece 22 and the negative electrode piece 24 ), and some positive and negative electrode areas cannot be Effective contact reduces the capacity exertion; in the case of severe bending in the corner area, the pole piece may partially drop powder, and the capacity cannot be exerted 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 high, and the content of the corresponding positive and negative active materials in the corner area is different due to the different radius of the corner semicircle. When the total capacity of the positive electrode sheet 22 is greater than the total capacity of the negative electrode sheet 24, lithium If the ions cannot be completely embedded in the negative electrode sheet 24, they will precipitate on the surface of the negative electrode sheet 24, resulting in lithium precipitation; abnormal corner areas, such as the folds of the polar sheet/diaphragm 26, etc., will also hinder the smooth insertion of lithium ions into the negative electrode sheet 24, and lithium ions will be in the separator. 26/The surface of the negative electrode sheet 24 is precipitated, which has a huge safety hazard. The powder drop of the pole piece can also cause safety problems such as short circuit. In addition, there is a problem with the manufacturing reliability of the wound electrode assembly 20. The separator 26 has tension during the winding process of the electrode assembly 20. After the electrode assembly 20 is wound, the stress on the edge of the separator 26 cannot be offset and released, so the electrode assembly 20 appears deformation, which is unfavorable for multiple electrode assemblies 20 to be packaged in the same packaging bag, and the electrode assemblies 20 are prone to abnormal problems such as thickening and liquid swelling during use, resulting in reduced reliability.

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

The positive 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, nickel cobalt lithium manganate, nickel cobalt aluminate lithium, lithium iron phosphate, lithium cobalt oxide, lithium manganate, lithium manganese iron phosphate and at least one of materials such as lithium titanate.

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 materials such as graphite, hard carbon, soft carbon, silicon, silicon carbon, and silicon oxide.

The electrolyte can be any electrolyte known in the art, and can be any one of gel state, solid state and liquid state. For example, in some embodiments, the liquid electrolyte includes a lithium salt and a non-aqueous solvent. The lithium salt may be selected from LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB(C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiC(SO ₂ CF ) ₃ ) At least one of ₃ or LiPO ₂ F ₂ , etc.; the non-aqueous solvent can be selected from at least one organic solvent such as carbonate compounds, carboxylate compounds, ether compounds, nitrile compounds and the like. Wherein, the carbonate compound may include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate Ester (MEC), Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), Vinyl Ethylene Carbonate (VEC), Fluoroethylene Carbonate (FEC), Carbonic Acid 1 ,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate -Fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluorocarbonate- At least one of 2-methylethylene and trifluoromethylethylene carbonate.

The present application also provides an electronic device 200 , and the electronic device 200 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 notebook computer, a wearable device, etc.), a power tool, an unmanned aerial vehicle, an energy storage device, a power device, and the like. Referring to FIG. 6 , in one embodiment, the electronic device 200 is a mobile communication device.

The present application will be described below through specific examples and comparative examples.

Example 1

Preparation of negative electrode sheet 24

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

Using the same method, the negative electrode active material was coated on both sides of the negative electrode current collector copper foil to obtain a double-sided negative electrode sheet 24 .

Preparation of positive electrode sheet 22

Lithium cobaltate (LiCoO ₂ , positive active material), conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF, binder) were mixed in a mass ratio of 97.5:1.0:1.5, and N-methylpyrrolidone was added. (NMP) was used as a solvent to prepare a slurry with a solid content of 0.75, and the mixture was uniformly stirred. The slurry was uniformly coated on the positive electrode current collector aluminum foil, dried at 90° C., and then cut into (78mm×58mm) specifications to obtain a single-sided positive electrode sheet 22 .

Using the same method, the positive electrode active material was coated on both sides of the positive electrode current collector aluminum foil to obtain the double-sided positive electrode sheet 22 .

Preparation of electrolyte

In a dry argon atmosphere, the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed in a mass ratio of EC:EMC:DEC=30:50:20, Then, lithium salt lithium hexafluorophosphate (LiPF ₆ ) is added to the organic solvent to dissolve and mix uniformly to obtain an electrolyte solution with a lithium salt concentration of 1.15M.

Preparation of Electrode Assembly 20

The prepared positive electrode sheet 22, negative electrode sheet 24, Z-type diaphragm 26 and other components are prepared with single-sided negative electrode sheet 24, Z-type diaphragm 26, double-sided positive electrode sheet 22, Z-type diaphragm 26, double-sided negative electrode sheet 24, Z-type diaphragm The separator 26, the double-sided positive electrode sheet 22... Z-shaped separator 26, and the single-sided negative electrode sheet 24 are stacked to form a laminated electrode assembly 20, and are connected to the positive electrode tab, the negative electrode tab, and the positive aluminum transfer electrode by laser welding. The tabs 122 and the negative nickel are connected to the tabs 124, and the directions of the positive and negative tabs are the same.

A portion of the Z-shaped separator 26 (ie, the Z-folded portion 262 ) is folded in a "Z" shape between the positive electrode sheet 22 and the negative electrode sheet 24 to form the laminate assembly 28 , and a portion of the Z-shaped separator 26 (ie, the winding portion 264 ) is rolled The laminated assembly 28 is wound to form the laminated electrode assembly 20 . The adhesive force F' between the Z-folded portion 262 and the positive electrode sheet was 15 N/m. The length l of the winding portion 264 is 194 mm, the thickness H of the lamination assembly 28 is 5 mm, and the length L of the lamination assembly 28 is 80 mm, that is, l=2×(L+H)+0.3L.

Assembly of Electrochemical Device 100

Assembly of the two electrode assemblies 20: Place the punched and formed packaging shell 10 (aluminum-plastic film with a thickness of 150 μm) into the assembly jig, with the pits facing upward. The first electrode assembly 20 is placed in the pit, and then the separator 32 is placed on the first electrode assembly 20 and pressed by an external force. The semi-finished product assembled above is placed in an assembly jig with the exposed side of the separator 32 facing upward, the second electrode assembly 20 is placed on the separator 32, and an external force is applied to press. Afterwards, cover the surface of the second electrode assembly 20 with another piece of packaging shell 10 facing down, and heat the surrounding area.

Liquid injection encapsulation: the assembled electrode assembly 20 is injected with liquid into the two cavities separately, and after the liquid injection, the four sides are encapsulated, and the four sides of the separator 32 are sealed in the seal. At this time, the two electrode assemblies 20 are divided into two independently sealed cavities by the separator 32, and there is no ion exchange between them.

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

The number of the electrode assemblies 20 is 2, the number of the tabs 12 extending out of the packaging case 10 is 4, and the Z-shaped separator 26 of the electrode assembly 20 is not provided with the winding portion 264 . There is no adhesive force between the packaging case 10 and the electrode assembly 20 . There is no adhesive force between the separator 32 and the electrode assembly 20 . S ₁ /S _positive = 0.95, S ₂ /S _negative = 0.95, S ₂ /S ₁ =1.05, the capacity ratio between the two electrode assemblies 20 A = 0.95; The ratio of the projected areas on the plane of the lamination direction L1 is B ₌ 0.98. The material of the encapsulation layer 32 of the separator 32 is PP, and the melting point is 150°C; the material of the ion insulating layer 34 is PI, and the melting point is 334°C.

The charging and discharging process only needs to connect 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.

Example 2

The difference from Embodiment 1 is that the number of electrode assemblies 20 is three.

Example 3

The difference from Embodiment 1 is that the number of tabs 12 protruding from the packaging shell 10 is two.

Example 4

The difference from Embodiment 1 is that the length l of the winding portion 264 of the Z-shaped diaphragm 26 is 178 mm, that is, l=2×(L+H)+0.1L.

Example 5

The difference from Embodiment 1 is that the length l of the winding portion 264 of the Z-shaped diaphragm 26 is 234 mm, that is, l=2×(L+H)+0.8L.

Example 6

The difference from Embodiment 1 is that the length l of the winding portion 264 of the Z-shaped diaphragm 26 is 380 mm, that is, l=4×(L+H)+0.5L.

Example 7

The difference from Example 1 is that the adhesive force between the packaging case 10 and the electrode assembly 20 is F ₁ =100 N/m.

Example 8

The difference from Example 1 is that the adhesive force between the packaging case 10 and the electrode assembly 20 is F ₁ =5 N/m.

Example 9

The difference from Example 1 is that the adhesive force between the packaging case 10 and the electrode assembly 20 is F ₁ =20 N/m.

Example 10

The difference from Example 1 is that the adhesive force between the packaging case 10 and the electrode assembly 20 is F ₁ =50 N/m.

Example 11

The difference from Example 1 is that the adhesive force between the packaging case 10 and the electrode assembly 20 is F ₁ =300 N/m.

Example 12

The difference from Example 1 is that the adhesive force between the separator and the electrode assembly 20 is F ₂ =100 N/m.

Example 13

The difference from Example 7 is that the adhesive force between the Z-shaped folded portion 262 and the positive electrode sheet 22 is F'=0.5 N/m.

Example 14

The difference from Embodiment 1 is that the adhesive force between the Z-folded portion 262 and the positive electrode sheet 22 is F'=1 N/m.

Example 15

The difference from Example 1 is that the adhesive force between the Z-folded portion 262 and the positive electrode sheet 22 is F'=25N/m.

Example 16

The difference from Embodiment 1 is that the adhesive force between the Z-folded portion 262 and the positive electrode sheet 22 is F'=50N/m.

Comparative Example 1

The difference from Embodiment 1 is that the separators 32 are not provided in the two electrode assemblies 20 .

Comparative Example 2

The difference from Embodiment 1 is that the separator in the electrode assembly 20 is not a Z-shaped separator, but a plurality of rectangular separators are respectively arranged between the positive electrode sheet 22 and the negative electrode sheet 24 , and the size of the separator is greater than the size of the negative electrode sheet.

Comparative Example 3

The difference from Example 1 is that in the preparation of the electrode assembly 20, a wound electrode assembly is prepared.

The above-mentioned 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, and whether the corners are lithium precipitation and drop test pass rate.

Please refer to Table 1 for a summary of the different conditions and performance test results of Comparative Examples 1-3 and Examples 1-16.

Table 1

It can be seen from the comparison of the difference conditions and performance test results in Table 1 with Comparative Examples 1-3: Comparing Examples 1-16 with Comparative Example 1, in Comparative Example 1, no separator is provided between the two electrode assemblies 20 32. There is a short circuit between the two electrode assemblies 20, which cannot be used, and the purpose of high output voltage cannot be achieved. Comparing Examples 1-16 with Comparative Example 2, in Comparative Example 2, the separator in the electrode assembly 20 is not a Z-shaped separator, but a plurality of rectangular separators, so the manufacturing yield and efficiency of the cell will be reduced; in addition, the electrode assembly The various components (positive electrode, negative electrode, separator) in the battery are prone to dislocation, resulting in capacity loss and even short circuit, and the safety risk is high; the multiple rectangular separators have no curved end design, which reduces the amount of electrolyte in the cell. Therefore, The electrical performance of the electrochemical device 100 will be lost. Comparing Examples 1 to 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 separator during the manufacturing process, which may easily lead to the electrochemical device 100. deformation; in addition, the wound electrode assembly has corner areas, poor interface consistency and poor kinetics, so there is a risk of lithium precipitation and capacity loss, so high output voltage batteries that require high consistency of multiple electrode assemblies is unfavorable.

In addition, by increasing the number of electrode assemblies 20 in Example 2, the voltage and energy density are effectively improved, and at the same time, the capacity retention rate and the drop performance test are basically not affected. It shows 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 and drop performance. In Examples 4-6, the length of the winding portion of the Z-shaped separator is regulated, which plays a role in stabilizing the electrode assembly as a whole, and is 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 a bonding material (such as hot melt adhesive) between the electrode assembly and the packaging bag and/or separator can effectively build the integrity of the electrochemical device 100 and prevent the electrode assembly 20 from The shaking in the packaging case 10 causes the tabs 12 to be pulled and damaged, thereby reducing the safety problem of the electrochemical device 100 failing during mechanical abuse such as falling.

Example 17

The difference from Example 7 is that the ratio of the area S ₁ of the positive active material covered on the surface of a single positive current collector to the area S _positive of the positive current collector (S ₁ /S _positive ) is 0.90; the negative electrode covered on the surface of a single negative current collector The ratio of the area S ₂ of the active material to the area S _negative of the negative electrode current collector (S ₂ /S _negative ) was 0.90.

Example 18

The difference from Example 7 is: the ratio of the area S ₁ of the positive active material covered on the surface of a single positive current collector to the area S _positive of the positive current collector (S ₁ /S _positive ) is 0.98; the negative electrode covered on the surface of a single negative current collector The ratio of the area S ₂ of the active material to the area S _negative of the negative electrode current collector (S ₂ /S _negative ) was 0.98.

Example 19

The difference from Example 18 is: S ₂ /S ₁ =1.20.

Example 20

The difference from Embodiment 18 is that the capacity ratio between the two electrode assemblies 20 is A=1.

Example 21

The difference from Example 20 is that the ratio 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 B=0.95.

Example 22

The difference from Embodiment 20 is that the ratio 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 B=1.

Example 23

The difference from Embodiment 22 is that the material of the encapsulation layer 32 of the separator 32 is polystyrene, and the melting point is 240°C.

Example 24

The difference from Embodiment 22 is that the material of the ion insulating layer 34 is stainless steel, and the melting point is 1440°C.

Example 25

The difference from Embodiment 22 is that the tabs 12 come out from opposite sides.

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

Table 2

It can be seen from the difference conditions and performance test results in Table 2 that compared with Comparative Examples 1-2: by adjusting S ₁ /S _positive , S ₂ /S _negative , S ₂ /S ₁ , A, B, separator 32 The material and melting point of the encapsulation layer 32, the material and melting point of the ion insulating layer 34 of the separator 32, and the extension direction of the tab 12 can be further improved on the premise of ensuring good energy density and capacity retention rate and controlling safety risks. The drop pass rate of the electrochemical device 100 .

The above embodiments are only used to illustrate the technical solutions of the present application rather than limitations. Although the present application has been described in detail with reference to the above preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or equivalently replaced. Neither should depart from the spirit and scope of the technical solutions of the present application.

Claims (13)

1. An electrochemical device, characterized in that, comprising: Packaging case, separator and multiple electrode assemblies; The electrode assemblies are respectively arranged in the 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. 2 . The electrochemical device according to claim 1 , wherein the Z-shaped separator comprises a Z-shaped folded part and a winding part, and the Z-shaped folded part connects the adjacent positive electrode sheet and the negative electrode sheet. 3 . separated. 3 . The electrochemical device according to claim 2 , wherein the plurality of positive electrode sheets, the plurality of negative electrode sheets and the Z-shaped folded part form a laminated assembly, and the winding part surrounds the Lamination assembly. 4 . The electrochemical device according to claim 3 , wherein, along the stacking direction of the plurality of positive electrode sheets, the stack assembly has a thickness H; along the winding direction of the Z-shaped separator, the The lamination 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. 5. The electrochemical device according to claim 1, wherein the adhesion force F between the electrode assembly and the packaging case, and/or between the electrode assembly and the separator satisfies: F≥5N/m. 6 . The electrochemical device according to claim 2 , wherein the adhesive force F′ between the Z-shaped folded portion and the positive electrode sheet or the negative electrode sheet satisfies: 0.5N/m≦F′ 6 . ≤50N/m. 7 . The electrochemical device according to claim 1 , wherein the capacity ratio A between any two of the electrode assemblies connected in series satisfies: 0.95≦A≦1.05. 8 . 8 . The electrochemical device according to claim 2 , wherein the winding portion comprises an end portion, the end portion is provided with an adhesive tape, and the adhesive tape adheres the end portion and the winding portion faces toward the end portion. 9 . the surface of the end. 9 . The electrochemical device according to claim 2 , wherein the Z-shaped folded portion and the winding portion are integrally formed. 10 . 10. The electrochemical device of claim 1, wherein 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. 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 _positive , and the positive electrode The area of the collector surface covered with the positive electrode active material is S ₁ , and the S _positive and the S ₁ satisfy: 80%≤S ₁ /S _positive <100%; 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. Along a plane perpendicular to the stacking direction of the plurality of negative electrode sheets, the area of the negative electrode current collector is S _negative , and the negative electrode The area of the current collector surface covered with the negative electrode active material is S ₂ , and the S _negative and the S ₂ satisfy: 80%≦S ₂ /S _negative <100%. 11 . The electrochemical device according to claim 10 , wherein the S ₂ and the S ₁ satisfy: 100%≦S ₂ /S ₁ ≦120%. 12 . 12 . The electrochemical device according to claim 1 , wherein the ratio B of the orthographic projection areas of the two adjacent electrode assemblies on the separator between the two adjacent electrode assemblies satisfies 12 . : 0.95≤B≤1.05. 13. An electronic device, characterized by comprising the electrochemical device according to any one of claims 1-12.

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