Electrochemical device and electric equipment

Abstract

The invention discloses an electrochemical device and electric equipment, the electrochemical device comprises an electrode assembly and a first discharge controller, and the electrode assembly comprises a plurality of negative plates. And the plurality of negative plates comprise at least one first negative plate and at least one second negative plate. Each first negative plate comprises a first negative active material layer, the mass percent of silicon in the first negative active material layer is N1, and N1 is greater than or equal to 0. And each second negative plate comprises a second negative active material layer, the mass percentage of the silicon element in the second negative active material layer is N2, and N2 is greater than N1. The second negative tab is electrically connected with a first discharge controller, a first cut-off voltage is preset in the first discharge controller, and the first discharge controller is configured to cut off the electric connection between the second negative tab and the external load when the discharge voltage of the electrode assembly is equal to or smaller than the first cut-off voltage. The electrochemical device is favorable for improving the discharge capacity.

Description

Technical Field

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

[0002] With the widespread application of electrochemical devices represented by lithium-ion secondary batteries and sodium-ion secondary batteries in various electronic products, electric vehicles, power tools and other terminals, users have also put forward higher and higher requirements for the energy density of electrochemical devices. Since silicon-based materials have a gram capacity of up to 4200mAh / g, which is several times the gram capacity of traditional negative electrode materials such as graphite and hard carbon, silicon-based materials have begun to be doped in traditional negative electrode materials as negative electrode active materials in a certain proportion to improve the energy density of electrochemical devices. Since silicon-based negative electrode active materials will have a large volume expansion during the charge and discharge cycle, affecting the cycle life of lithium-ion batteries, the existing technology often uses a higher discharge cycle to improve the cycle life of batteries doped with silicon-doped negative electrode active materials, such as increasing the discharge cut-off voltage to above 3.5V. This method can improve the cycle expansion problem of batteries doped with silicon-doped negative electrode active materials; however, this method loses part of the capacity of traditional negative electrode materials and sacrifices energy density. Summary of the invention

[0003] In view of the above situation, it is necessary to provide an electrochemical device to improve the discharge capacity of the electrochemical device.

[0004] The first aspect of the embodiment of the present application provides an electrochemical device, including an electrode assembly, the electrode assembly including a plurality of positive electrode sheets, a plurality of negative electrode sheets and a plurality of separators, the plurality of positive electrode sheets, the plurality of separators and the plurality of negative electrode sheets are stacked to form a laminated structure, and separators are provided between adjacent positive electrode sheets and negative electrode sheets. Each positive electrode sheet includes a positive electrode current collector, a positive electrode active material layer and a positive electrode ear, the positive electrode active material layer is provided on at least one surface of the positive electrode current collector along the thickness direction of the positive electrode sheet, and one end of the positive electrode ear is electrically connected to the positive electrode current collector. The plurality of negative electrode sheets include at least one first negative electrode sheet and at least one second negative electrode sheet. Each first negative electrode sheet includes a first negative electrode current collector, a first negative electrode active material layer and a first negative electrode ear; the first negative electrode active material layer is provided on at least one surface of the first negative electrode current collector along the thickness direction of the first negative electrode sheet, and the mass percentage of silicon element in the first negative electrode active material layer is N1, N1≥0; one end of the first negative electrode ear is electrically connected to the first negative electrode current collector. Each second negative electrode sheet includes a second negative electrode current collector, a second negative electrode active material layer and a second negative electrode ear. The second negative electrode active material layer is arranged on at least one surface of the second negative electrode current collector along the thickness direction of the second negative electrode sheet; the mass percentage of silicon element in the second negative electrode active material layer is N2, N2>N1; one end of the second negative electrode ear is electrically connected to the second negative electrode current collector. The first negative electrode active material layer and the second negative electrode active material layer both contain a second active material, and the second active material includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon, and lithium titanate. The electrochemical device also includes a first discharge controller, the other end of the second negative electrode ear is electrically connected to the input end of the first discharge controller, and the first discharge controller also has an output end; the first discharge controller is configured to disconnect the electrical connection between the second negative electrode ear and the output end of the first discharge controller when the discharge voltage of the electrode assembly is equal to or less than the first cut-off voltage U1, and the unit of U1 is V.

[0005] In this electrochemical device, the mass percentage of silicon in the second negative electrode active material layer is greater than the mass percentage of silicon in the first negative electrode active material layer. During the charge and discharge process of the electrochemical device, the volume change of the second negative electrode sheet is greater than that of the first negative electrode sheet, and the second negative electrode sheet stops discharging after discharging to the first cut-off voltage, which is beneficial to reducing the influence of the expansion of the second negative electrode sheet on the cycle life of the electrochemical device, thereby improving the cycle life of the electrochemical device; and after the second negative electrode sheet stops discharging, the first negative electrode sheet and the positive electrode sheet with lower silicon content can continue to discharge, which can further release the energy of the second active material layer in the first negative electrode sheet, which is beneficial to improving the discharge capacity of the electrochemical device.

[0006] In an optional embodiment of the present application, 0wt%≤N1≤3wt%. Setting N1≥0wt% is beneficial to increasing the capacity of the electrochemical device, and setting N1≤3wt% is beneficial to reducing the impact of the volume change of the first negative electrode sheet during the charge and discharge process on the cycle life of the electrochemical device.

[0007] In an optional embodiment of the present application, 0wt%<N1≤1wt%. Setting N1≤1wt% is beneficial to further reduce the influence of the volume change of the first negative electrode sheet during the charge and discharge process on the cycle life of the electrochemical device.

[0008] In an optional embodiment of the present application, 5wt%≤N2≤25wt%. Setting N2≥5wt% is beneficial to increasing the capacity of the electrochemical device, and setting N2≤25wt% is beneficial to reducing the impact of the volume change of the second negative electrode sheet during the charge and discharge process on the cycle life of the electrochemical device.

[0009] In an optional embodiment of the present application, 8wt%≤N2≤13wt%. Setting N2≥8wt% is beneficial to increasing the capacity of the electrochemical device, and setting N2≤13wt% is beneficial to reducing the impact of the volume change of the first negative electrode sheet during the charge and discharge process on the cycle life of the electrochemical device.

[0010] In an optional embodiment of the present application, the total number of first negative electrode sheets is A1, the total number of negative electrode sheets is A, 10%≤A1 / A≤80%. Setting A1 / A≥10% prevents the number of first negative electrode sheets from being too small, which is beneficial to improving the discharge capacity of the electrochemical device; in order to make the total silicon content of the negative electrode sheets reach a certain target value, the more the number of first negative electrode sheets, the higher the silicon content required for the second negative electrode sheets, and the probability of problems occurring in the electrochemical device in a long cycle tends to increase. Therefore, setting A1 / A≤80%, the number of first negative electrode sheets is not too large, and the silicon content of the second negative electrode sheet is not too high, which is beneficial to reducing the impact of the volume change of the second negative electrode sheet during the charge and discharge process on the cycle life of the electrochemical device.

[0011] In an optional embodiment of the present application, 3.1V≤U1≤3.4V. When U1≥3.1V is set, the first cut-off voltage is not too low, which is beneficial to reduce the impact of the volume change of the second negative electrode sheet during the charge and discharge process on the cycle life of the electrochemical device; when U1≤3.4V is set, the first cut-off voltage is not too high, which is beneficial to improve the discharge capacity of the electrochemical device.

[0012] In an optional embodiment of the present application, the electrochemical device includes a second discharge controller, the other end of the first negative electrode ear is electrically connected to the input end of the second discharge controller, and the second discharge controller is configured to disconnect the electrical connection between the first negative electrode ear and the output end of the second discharge controller when the discharge voltage of the electrode assembly is equal to or less than the second cut-off voltage U2, the unit of U2 is V, and U2 < U1. By setting the second discharge controller, the discharge of the electrochemical device is stopped when the voltage drops to the second cut-off voltage, which is conducive to reducing the possibility of over-discharge of the electrochemical device.

[0013] In an optional embodiment of the present application, the electrochemical device includes a second discharge controller, the other end of the positive electrode ear is electrically connected to the input end of the second discharge controller, and the second discharge controller also has an output end. The second discharge controller is configured to disconnect the electrical connection between the positive electrode ear and the output end of the second discharge voltage controller when the discharge voltage of the electrode assembly is equal to or less than the second cut-off voltage U2, where the unit of U2 is V, and U2 < U1. By setting the second discharge controller, the discharge of the electrochemical device is stopped when the voltage drops to the second cut-off voltage, which is conducive to reducing the possibility of over-discharge of the electrochemical device.

[0014] In an optional embodiment of the present application, the second cut-off voltage is U2, 3.0V≤U2≤3.3V. When U2≥3.0V is set, the second cut-off voltage is not too low, which is conducive to reducing the possibility of over-discharging of the electrochemical device; when U2≤3.3V is set, the second cut-off voltage is not too high, which is conducive to increasing the discharge capacity of the electrochemical device.

[0015] In an optional embodiment of the present application, the output terminal of the first discharge controller is electrically connected to the input terminal of the second discharge controller, which is helpful to simplify the electrical connection structure of the electrochemical device.

[0016] In an optional embodiment of the present application, the electrochemical device includes a first adapter, a second adapter, and a third adapter. The other end of the first negative electrode ear is connected to form a first negative electrode ear bundle, and the first adapter is electrically connected to the first negative electrode ear bundle. The other end of the second negative electrode ear is connected to form a second negative electrode ear bundle, and the second adapter is electrically connected to the second negative electrode ear bundle, and the second negative electrode sheet is electrically connected to the first discharge controller through the second adapter. The other end of the positive electrode ear is connected to form a positive electrode ear bundle, and the third adapter is electrically connected to the positive electrode ear bundle. The first adapter is provided to facilitate the connection of the first negative electrode sheet to an external load, the second adapter is provided to facilitate the connection of the second negative electrode sheet to the first discharge controller, and the third adapter is provided to facilitate the connection of the positive electrode sheet to an external load.

[0017] A second aspect of an embodiment of the present application provides an electrical device, which includes the electrochemical device involved in any of the aforementioned embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the structure of an electrochemical device in one embodiment of the present application.

[0019] Figure 2 Schematic diagram of the structure of a secondary battery of an electrochemical device in one embodiment of the present application.

[0020] Figure 3 yes Figure 2 Cross-sectional view at II in the middle.

[0021] Figure 4 It is a schematic diagram of the structure of an electrode assembly in one embodiment of the present application.

[0022] Figure 5 It is a schematic diagram of the structure of an electrical device in an embodiment of the present application.

[0023] Main component symbols

[0024] Electrochemical device 100

[0025] Secondary battery 10

[0026] Housing 11

[0027] Electrode assembly 12

[0028] Positive electrode 121

[0029] Positive electrode current collector 1211

[0030] Positive electrode active material layer 1212

[0031] Positive ear 1213

[0032] Negative electrode 122

[0033] The first negative electrode sheet 1221

[0034] First negative electrode current collector 12211

[0035] First negative electrode active material layer 12212

[0036] First negative electrode ear 12213

[0037] The second negative electrode sheet 1222

[0038] Second negative electrode current collector 12221

[0039] Second negative electrode active material layer 12222

[0040] Second negative electrode ear 12223

[0041] Isolation film 123

[0042] First adapter 13

[0043] Second adapter 14

[0044] The third adapter 15

[0045] The first discharge controller 20

[0046] The second discharge controller 30

[0047] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0049] It should be noted that when an element is considered to be "connected" to another element, it may be directly connected to the other element or there may be a centrally disposed element at the same time. When an element is considered to be "disposed on" another element, it may be directly disposed on the other element or there may be a centrally disposed element at the same time.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly 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.

[0051] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0052] In the description of the embodiments of the present application, the term "perpendicular" is used to describe an ideal state between two components. In actual production or use, there may be a state that is approximately perpendicular between the two components. The two components described as "perpendicular" may not be absolutely straight lines or planes, but may be roughly straight lines or planes. From a macroscopic point of view, if the overall extension direction is a straight line or a plane, the components can be considered to be "straight lines" or "planes".

[0053] Reference to "embodiment" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. The various embodiments in the present application may be combined with each other in the absence of conflict.

[0054] The first aspect of the embodiment of the present application provides an electrochemical device, including an electrode assembly, the electrode assembly including a plurality of positive electrode sheets, a plurality of negative electrode sheets and a plurality of separators, the plurality of positive electrode sheets, the plurality of separators and the plurality of negative electrode sheets are stacked to form a laminated structure, and separators are provided between adjacent positive electrode sheets and negative electrode sheets. Each positive electrode sheet includes a positive electrode current collector, a positive electrode active material layer and a positive electrode ear, the positive electrode active material layer is provided on at least one surface of the positive electrode current collector along the thickness direction of the positive electrode sheet, and one end of the positive electrode ear is electrically connected to the positive electrode current collector. The plurality of negative electrode sheets include at least one first negative electrode sheet and at least one second negative electrode sheet. Each first negative electrode sheet includes a first negative electrode current collector, a first negative electrode active material layer and a first negative electrode ear; the first negative electrode active material layer is provided on at least one surface of the first negative electrode current collector along the thickness direction of the first negative electrode sheet, and the mass percentage of silicon element in the first negative electrode active material layer is N1, N1≥0; one end of the first negative electrode ear is electrically connected to the first negative electrode current collector. Each second negative electrode sheet includes a second negative electrode current collector, a second negative electrode active material layer and a second negative electrode ear. The second negative electrode active material layer is arranged on at least one surface of the second negative electrode current collector along the thickness direction of the second negative electrode sheet; the mass percentage of silicon element in the second negative electrode active material layer is N2, N2>N1; one end of the second negative electrode ear is electrically connected to the second negative electrode current collector. The first negative electrode active material layer and the second negative electrode active material layer both contain a second active material, and the second active material includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon, and lithium titanate. The electrochemical device also includes a first discharge controller, the other end of the second negative electrode ear is electrically connected to the input end of the first discharge controller, and the first discharge controller also has an output end; the first discharge controller is configured to disconnect the electrical connection between the second negative electrode ear and the output end of the first discharge controller when the discharge voltage of the electrode assembly is equal to or less than the first cut-off voltage U1, and the unit of U1 is V.

[0055] In this electrochemical device, the mass percentage of silicon in the second negative electrode active material layer is greater than the mass percentage of silicon in the first negative electrode active material layer. During the charge and discharge process of the electrochemical device, the volume change of the second negative electrode sheet is greater than that of the first negative electrode sheet, and the second negative electrode sheet stops discharging after discharging to the first cut-off voltage, which is beneficial to reducing the influence of the expansion of the second negative electrode sheet on the cycle life of the electrochemical device, thereby improving the cycle life of the electrochemical device; and after the second negative electrode sheet stops discharging, the first negative electrode sheet and the positive electrode sheet with lower silicon content can continue to discharge, which can further release the energy of the second active material layer in the first negative electrode sheet, which is beneficial to improving the discharge capacity of the electrochemical device.

[0056] The embodiments of the present application are further described below in conjunction with the accompanying drawings.

[0057] like Figures 1 to 3As shown, an embodiment of the present application provides an electrochemical device 100 , including a secondary battery 10 . The secondary battery 10 includes a housing 11 and an electrode assembly 12 . The electrode assembly 12 is disposed inside the housing 11 .

[0058] In some embodiments, Figure 2 As shown, the shell 11 is a packaging bag packaged by a packaging film, such as an aluminum-plastic film, a steel-plastic film, etc.

[0059] In some embodiments, the housing 11 may be a metal housing 11 , such as a steel housing, an aluminum housing, or the like.

[0060] In some embodiments, Figure 3 As shown, the electrode assembly 12 includes multiple positive electrode sheets 121, multiple negative electrode sheets 122 and multiple isolation films 123. The multiple positive electrode sheets 121, multiple isolation films 123 and multiple negative electrode sheets 122 are stacked to form a stacked structure, and isolation films 123 are provided between adjacent positive electrode sheets 121 and negative electrode sheets 122.

[0061] In some embodiments, Figure 3 As shown, each positive electrode sheet 121 includes a positive electrode collector 1211, a positive electrode active material layer 1212 and a positive electrode ear 1213. The positive electrode active material layer 1212 is arranged on at least one surface of the positive electrode collector 1211 along the thickness direction of the positive electrode sheet 121. One end of the positive electrode ear 1213 is electrically connected to the positive electrode collector 1211, and the positive electrode ear 1213 is used to electrically connect to an external load.

[0062] In some embodiments, Figure 3 As shown, the plurality of negative electrode sheets 122 include at least one first negative electrode sheet 1221 and at least one second negative electrode sheet 1222. Each first negative electrode sheet 1221 includes a first negative electrode current collector 12211, a first negative electrode active material layer 12212 and a first negative electrode ear 12213; the first negative electrode active material layer 12212 is disposed on at least one surface of the first negative electrode current collector 12211 along the thickness direction of the first negative electrode sheet 1221, and the mass percentage of silicon element in the first negative electrode active material layer 12212 is N1, N1≥0; one end of the first negative electrode ear 12213 is electrically connected to the first negative electrode current collector 12211, and the first negative electrode ear 12213 is used to electrically connect to an external load. Each second negative electrode sheet 1222 includes a second negative electrode collector 12221, a second negative electrode active material layer 12222 and a second negative electrode ear 12223, the second negative electrode active material layer 12222 is arranged on at least one surface of the second negative electrode collector along the thickness direction of the second negative electrode sheet 1222; the mass percentage of silicon element in the second negative electrode active material layer 12222 is N2, N2>N1; one end of the second negative electrode ear 12223 is electrically connected to the second negative electrode collector 12221.

[0063] In some embodiments, in the thickness direction of the first negative electrode sheet 1221 , multiple first negative electrode sheets 1221 are stacked in sequence on at least one side of the electrode assembly 12 , and multiple second negative electrode sheets 1222 are stacked in sequence on the other side or in the middle of the electrode assembly 12 .

[0064] In some embodiments, Figure 4 As shown, a plurality of first negative electrode sheets 1221 and a plurality of second negative electrode sheets 1222 are alternately stacked in a thickness direction of the first negative electrode sheet 1221 .

[0065] In some embodiments, Figure 1 As shown, the electrochemical device 100 further includes a first discharge controller 20, the other end of the second negative electrode ear 12223 is electrically connected to the input end of the first discharge controller 20, and the first discharge controller 20 also has an output end, and the second negative electrode ear 12223 is configured to be electrically connected to an external load through the output end of the first discharge controller 20. The first discharge controller 20 is preset with a first cut-off voltage U1, and the unit of U1 is V. The first discharge controller 20 is configured to disconnect the electrical connection with the output end of the first discharge controller 20 when the discharge voltage of the electrode assembly 12 is equal to or less than the first cut-off voltage U1.

[0066] In this electrochemical device 100, the mass percentage of silicon in the second negative electrode active material layer 12222 is greater than the mass percentage of silicon in the first negative electrode active material layer 12212. During the charge and discharge process of the electrochemical device 100, the volume change of the second negative electrode sheet 1222 is greater than that of the first negative electrode sheet 1221. The second negative electrode sheet 1222 stops discharging after being discharged to the first cut-off voltage, which is beneficial to reducing the impact of the volume change of the second negative electrode sheet 1222 on the cycle life of the electrochemical device 100, thereby improving the cycle life of the electrochemical device 100; and after the second negative electrode sheet 1222 stops discharging, the first negative electrode sheet 1221 and the positive electrode sheet 121 with a lower silicon content can continue to discharge, which can further release the energy of the second active material layer in the first negative electrode sheet 1221, which is beneficial to improving the discharge capacity of the electrochemical device 100.

[0067] In some embodiments, the first negative electrode current collector 12211 and the second negative electrode current collector 12221 are both metal layers. As an illustrative example, the negative electrode current collector may be a metal layer including at least one of copper, nickel, tantalum, and titanium, such as copper foil.

[0068] In some embodiments, the first negative electrode current collector 12211 and the second negative electrode current collector 12221 are both composite current collectors.

[0069] In some embodiments, the first negative electrode active material layer 12212 and the second negative electrode active material layer 12222 contain a first active material, and the first active material includes one or more of pure silicon, silicon carbon, silicon oxygen, silicon oxygen carbon, and silicon alloy. In some embodiments, the first negative electrode active material layer 12212 and the second negative electrode active material layer 12222 also contain a second active material, and the second active material includes at least one of artificial graphite, natural graphite, hard carbon, and lithium titanate.

[0070] In some embodiments, the first negative electrode active material layer 12212 and the second negative electrode active material layer 12222 also include a conductive agent and a binder, the conductive agent includes at least one of conductive carbon black, carbon nanotubes, carbon fibers or graphene, and the binder includes at least one of styrene-butadiene rubber, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylic acid or sodium carboxymethyl cellulose.

[0071] In some embodiments, the positive electrode current collector 1211 is a metal layer. As an illustrative example, the positive electrode current collector 1211 may be a metal layer including at least one of aluminum, nickel, tantalum, and titanium, such as aluminum foil.

[0072] In some embodiments, the positive electrode current collector 1211 is a composite current collector.

[0073] In some embodiments, the positive active material layer 1212 includes a positive active material, and the positive active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganese oxide.

[0074] In some embodiments, the isolation film 123 is made of insulating film materials such as polyethylene film, polypropylene film, polyester film or polyimide film.

[0075] In some embodiments, the electrochemical device 100 further includes an electrolyte, which is contained in the housing 11 .

[0076] In some embodiments, the electrolyte is in any of a gel state, a solid state, and a liquid state.

[0077] In some embodiments, the electrolyte includes a lithium salt and a non-aqueous solvent.

[0078] In some embodiments, the lithium salt includes at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3 or LiPO2F2, etc.

[0079] In some embodiments, the non-aqueous solvent includes at least one of a carbonate compound, a carboxylate compound, an ether compound, a nitrile compound or other organic solvents, etc. For example, the carbonate compound may include at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene 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 or trifluoromethylethylene carbonate, etc.

[0080] In some embodiments, N1=0. In this case, the first negative electrode active material layer 12212 does not contain silicon. Compared with the case where the negative electrode active layer of each negative electrode sheet 122 contains silicon-based materials, only part of the negative electrode sheet 122 contains silicon, which increases the capacity of the electrochemical device 100 while taking into account the effect of silicon on the cycle life of the electrochemical device 100.

[0081] In some embodiments, 0wt%≤N1≤3wt%. Setting N1≥0wt% is beneficial to improving the capacity of the electrochemical device 100, and setting N1≤3wt% is beneficial to reducing the impact of the volume change of the first negative electrode sheet 1221 during the charge and discharge process on the cycle life of the electrochemical device 100.

[0082] In some embodiments, the value of N1 is one of 0.5 wt %, 1 wt %, 1.5 wt %, 2 wt %, and 2.5 wt %.

[0083] In some embodiments, 0wt%≤N1≤1wt%. Setting N1≤1wt% is beneficial to further reduce the influence of the volume change of the first negative electrode sheet 1221 during the charge and discharge process on the cycle life of the electrochemical device 100.

[0084] In some embodiments, 5wt%≤N2≤25wt%. Setting N2≥1wt% is beneficial to improving the capacity of the electrochemical device 100, and setting N2≤25wt% is beneficial to reducing the impact of the volume change of the second negative electrode sheet 1222 during the charge and discharge process on the cycle life of the electrochemical device 100.

[0085] In some embodiments, the value of N2 is one of 7wt%, 9wt%, 11wt%, 13wt%, 15wt%, 17wt%, 19wt%, 21wt%, and 23wt%.

[0086] In some embodiments, 8wt%≤N2≤13wt%. Setting N2≥8wt% is beneficial to improving the capacity of the electrochemical device 100, and setting N2≤13wt% is beneficial to further reducing the impact of the volume change of the second negative electrode sheet 1222 during the charge and discharge process on the cycle life of the electrochemical device 100.

[0087] In some embodiments, the total number of the first negative electrode sheets 1221 is A1, the total number of the negative electrode sheets 122 is A, and 10%≤A1 / A≤80%. By setting A1 / A≥10%, the number of the first negative electrode sheets 1221 is not too small, which is beneficial to improving the discharge capacity of the electrochemical device 100; in order to make the total silicon content of the negative electrode sheets 122 reach a certain target value, the more the number of the first negative electrode sheets 1221 is, the higher the silicon content required for the second negative electrode sheets 1222 is, and the probability of problems occurring in the electrochemical device 100 in a long cycle tends to increase. Therefore, by setting A1 / A≤80%, the number of the first negative electrode sheets 1221 is not too large, and the silicon content of the second negative electrode sheets 1222 is not too high, which is beneficial to reducing the impact of the volume change of the second negative electrode sheets 1222 during the charge and discharge process on the cycle life of the electrochemical device 100.

[0088] In some embodiments, 3.1V≤U1≤3.4V. When U1≥3.1V is set, the first cut-off voltage is not too low, which is beneficial to reduce the impact of the volume change of the second negative electrode sheet 1222 during the charge and discharge process on the cycle life of the electrochemical device 100; when U1≤3.4V is set, the first cut-off voltage is not too high, which is beneficial to improve the discharge capacity of the electrochemical device 100.

[0089] In some embodiments, Figure 1 As shown, the electrochemical device 100 includes a second discharge controller 30, the other end of the first negative electrode ear 12213 is electrically connected to the output end of the second discharge controller 30, and the second discharge controller also has an output end. The first negative electrode ear 12213 is configured to be electrically connected to an external load through the output end of the second discharge controller 30. The second discharge controller 30 is preset with a second cut-off voltage U2, and the unit of U2 is V. The second discharge controller 30 is configured to disconnect the electrical connection between the first negative electrode ear 12213 and the output end of the second discharge controller 30 when the discharge voltage of the electrode assembly 12 is equal to or less than the second cut-off voltage U2, and the second cut-off voltage U2 is less than the first cut-off voltage U1. By setting the second discharge controller 30, the discharge of the electrochemical device 100 is stopped when the voltage drops to the second cut-off voltage, which is conducive to reducing the possibility of over-discharge of the electrochemical device 100.

[0090] In some embodiments, the electrochemical device 100 includes a second discharge controller 30, the other end of the positive electrode ear 1213 is electrically connected to the second discharge controller 30, and the second discharge controller 30 also has an output end. The positive electrode ear 1213 is configured to be electrically connected to an external load through the second discharge controller 30, and the second discharge controller 30 is preset with a second cut-off voltage U2, and the unit of U2 is V. The second discharge controller 30 is configured to disconnect the electrical connection between the positive electrode ear 1213 and the output end of the second discharge controller 30 when the discharge voltage of the electrode assembly 12 is equal to or less than the second cut-off voltage U2, and the second cut-off voltage U2 is less than the first cut-off voltage U1. By setting the second discharge controller 30, the discharge of the electrochemical device 100 is stopped when the voltage drops to the second cut-off voltage, which is conducive to reducing the possibility of over-discharge of the electrochemical device 100.

[0091] In the embodiments of the present application, both the first discharge controller 20 and the second discharge controller 30 may adopt conventional designs in the prior art, which will not be described in detail here.

[0092] In some embodiments, 3.0 V ≤ U2 ≤ 3.3 V. When U2 ≥ 3.0 V is set, the second cut-off voltage is not too low, which is beneficial to reduce the possibility of over-discharging of the electrochemical device 100; when U2 ≤ 3.3 V is set, the second cut-off voltage is not too high, which is beneficial to increase the discharge capacity of the electrochemical device 100.

[0093] In some embodiments, Figure 2 As shown, the electrochemical device 100 further includes a first adapter 13, a second adapter 14, and a third adapter 15. All first negative electrode ears 12213 are connected to form a first negative electrode ear bundle, and the first adapter 13 is electrically connected to the first negative electrode ear bundle (such as Figure 3 ); all the second negative tabs 12223 are connected to form a second negative tab bundle, the second adapter 14 is electrically connected to the second negative tab bundle, and the second negative electrode sheet 1222 is electrically connected to the first discharge controller 20 through the second adapter 14; all the positive tabs 1213 are connected to form a positive tab bundle, and the third adapter 15 is electrically connected to the positive tab bundle. The first adapter 13 is provided to facilitate the connection of the first negative electrode sheet 1221 with an external load, the second adapter 14 is provided to facilitate the connection of the second negative electrode sheet 1222 with the first discharge controller 20, and the third adapter 15 is provided to facilitate the connection of the positive electrode sheet 121 with an external load.

[0094] like Figure 5 As shown, an embodiment of the present application further provides an electrical device 1000 , and the electrical device 1000 includes the electrochemical device 100 involved in any of the aforementioned embodiments.

[0095] In some embodiments, the electric device 1000 includes but is not limited to a laptop computer, a mobile phone, an electric tool, and an electric toy.

[0096] In order to verify the influence of the configuration of the first discharge controller 20 and the second discharge controller 30 on the discharge capacity, cycle life and expansion ratio after multiple cycles of the electrochemical device 100 , the inventors of the present application conducted the following experiment.

[0097] The experiment includes 2 groups of comparative examples and 18 groups of embodiments, each group of comparative examples and each group of embodiments includes 20 electrochemical devices 100, and the electrochemical devices 100 in embodiments 1-18 include two discharge controllers, namely a first discharge controller 20 and a second discharge controller 30, the first discharge controller 20 is electrically connected to all the second negative electrode sheets 1222, and the second discharge controller 30 is electrically connected to all the positive electrode sheets 121; the electrochemical device 100 in the comparative example includes only one discharge controller, which is electrically connected to all the positive electrode sheets 121, and the electrode assembly 12 of the electrochemical device 100 in each group of comparative examples and each group of embodiments includes 21 positive electrode sheets 121 and 20 Negative electrode sheet 122, the mass content of silicon element in 20 negative electrode sheets 122 in each electrode assembly 12 in the comparative example is the same, a portion of the 20 negative electrode sheets 122 in each electrode assembly 12 in the embodiment are first negative electrode sheets 1221 with a mass content of silicon element N1, and the remaining number of negative electrode sheets 122 are second negative electrode sheets 1222 with a mass content of silicon element N2, each negative electrode sheet 122 in the comparative example has the same capacity as each negative electrode sheet 122 in the embodiment, each positive electrode sheet 121 in the comparative example has the same capacity as each positive electrode sheet 121 in the embodiment, and each first negative electrode sheet 1221 and each second negative electrode sheet 1222 in each embodiment are also the same. The capacity of the negative electrode sheet 122 is adjusted by changing the coating thickness according to the gram capacity of the negative electrode active material in the negative electrode active material layer. In other words, different negative electrode sheets 122 have negative electrode active material layers of different thicknesses according to different silicon content. Moreover, in each embodiment and comparative example, the content of silicon in the secondary battery 10 is the same, that is, the total mass of silicon in all negative electrode sheets 122 (the first negative electrode sheet 1221 and the second negative electrode sheet 1222) accounts for the same proportion of the total mass of the active material layer of all negative electrode sheets 122 (the first negative electrode sheet 1221 and the second negative electrode sheet 1222).

[0098] In the comparative example, the preparation process of the electrochemical device 100 includes the following steps:

[0099] 1. Preparation of positive electrode sheet 121:

[0100] The positive electrode active material lithium iron phosphate, the positive electrode conductive agent acetylene black, and the positive electrode binder polyvinylidene fluoride (PVDF, weight average molecular weight 5×10 5) are mixed in a mass ratio of 94:3:3, N-methylpyrrolidone (NMP) is added as a solvent, and stirred under the action of a vacuum mixer until the solid content is 75wt% and the system is uniform. An aluminum foil with a thickness of 8μm is selected as the positive current collector 1211, and the aluminum foil is cut into positive electrode inner pole ears. The positive electrode slurry is evenly coated on one surface of the aluminum foil of the positive current collector 1211, and dried at 110°C to obtain a positive electrode sheet 121 with a single-sided coating of a positive electrode active material layer 1212 (thickness 80μm). Afterwards, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet 121 with a double-sided coating of a positive electrode active material layer 1212.

[0101] 2. Preparation of negative electrode sheet 122

[0102] The negative electrode active material graphite powder, silicon powder, conductive carbon black (Super P), and binder styrene-butadiene rubber (SBR) are mixed in a certain mass ratio, and then deionized water is added as a solvent to prepare a negative electrode slurry with a solid content of 50wt%, and stirred evenly. A copper foil with a thickness of 5μm is selected as the negative electrode current collector, and the copper foil is cut into negative electrode inner tabs. The negative electrode slurry is evenly coated on one surface of the negative electrode current collector copper foil, and dried at 90°C to obtain a single-sided negative electrode sheet 122. Afterwards, the above steps are repeated on the other surface of the negative electrode sheet 122 to obtain a negative electrode sheet 122 with a negative electrode active material layer coated on both sides.

[0103] 3. Preparation of Isolation Membrane

[0104] A polyethylene (PE) porous film with a thickness of 8 μm was used as the separator 123 .

[0105] 4. Preparation of Electrolyte

[0106] In a dry argon atmosphere, ethylene carbonate, ethyl methyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solution, and then lithium hexafluorophosphate was added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0107] 5. Preparation of Secondary Batteries

[0108] The prepared separator 123, positive electrode sheet 121, separator 123, and negative electrode sheet 122 are stacked in order to form a laminated structure. The outermost electrodes at both ends of the laminated structure are positive electrode sheets 121. The electrode assembly 12 is hot pressed at a pressure of 5MPa, a temperature of 65°C, and a holding time of 10s. All the negative ears are connected to form a negative ear bundle, and a converter is connected to the negative ear bundle. All the positive ears 1213 are connected to form a positive ear 1213 bundle, and a converter is connected to the positive ear 1213 bundle. The electrode assembly 12 is placed in the aluminum-plastic film of the packaging bag, and the two aforementioned converters extend from the top seal of the packaging bag. After dehydration at 80°C, the electrolyte is injected and packaged.

[0109] 6. Connect the discharge controller

[0110] A discharge controller is connected to the adapter connected to the positive electrode ear 1213 .

[0111] The preparation process of the electrochemical device 100 in the embodiment is basically the same as that in the comparative example, the difference lies in that the silicon content of each negative electrode sheet 122 in the comparative example is the same, which is recorded in Table 1 as the same value of the silicon content of the first negative electrode sheet 1221 and the silicon content of the second negative electrode sheet 1222; the negative electrode sheet 122 in the embodiment is obtained into two types of negative electrode sheets 122 with different silicon content according to different mixing ratios of the negative electrode active materials, wherein the first negative electrode sheet 1221 has a lower silicon content by mass, and the second negative electrode sheet 1222 has a higher silicon content by mass. All the first negative electrode sheets 1221 are connected to an adapter, i.e. the first adapter 13 mentioned above, all the second negative electrode sheets 1222 are connected to an adapter, i.e. the second adapter 14 mentioned above, all the positive electrode sheets 121 are connected to an adapter, i.e. the third adapter 15 mentioned above, the second adapter 14 is connected to a discharge controller (first discharge controller 20), and the third adapter 15 is connected to a discharge controller (second discharge controller 30).

[0112] After the electrochemical devices 100 in the comparative example and the embodiment were prepared, each electrochemical device 100 was subjected to a discharge capacity test, a capacity retention rate test after 500 cls, and a lithium battery expansion ratio test after 500 cls.

[0113] The process of discharge capacity test is:

[0114] The electrochemical device 100 was placed in a 25°C ± 2°C thermostat for 30 minutes to allow the secondary battery 10 to reach a constant temperature. The electrochemical device 100 that reached a constant temperature was charged at a constant current of 0.5C until the voltage reached the full charge voltage, then charged at the full charge voltage constant voltage until the current reached 0.05C, and discharged at 0.2C until the voltage reached the discharge controller, and the discharge capacity was recorded. Among them, the electrochemical device 100 in the comparative example was only provided with a discharge controller, and its cut-off voltage was recorded in the second cut-off voltage column in Table 1.

[0115] The process of capacity retention test after 500cls is as follows:

[0116] The above discharge capacity test process was repeated 500 times, the 500th discharge capacity was recorded, and the 500th discharge capacity was divided by the first discharge capacity to obtain the capacity retention rate after 500 cls of cycles.

[0117] The expansion ratio of the cycle 500cls is:

[0118] (1) Before the first discharge capacity test, the thickness of the secondary battery 10 in the electrochemical device 100 was measured using a flat plate thickness gauge (PPG) under a force of 700 g;

[0119] (2) After the discharge capacity test of the cycle of 500 cls, the thickness of the secondary battery 10 in the electrochemical device 100 was measured again using a flat plate thickness gauge (PPG) under a force of 700 g.

[0120] After the experiment, the results are summarized in Table 1. The values ​​of discharge capacity, capacity retention after 500 cl s of cycling, and expansion ratio after 500 cl s of cycling in Table 1 are the average values ​​of the corresponding parameters of 20 electrochemical devices in the same group.

[0121] Table 1

[0122]

[0123] Note: “ / ” in Table 1 indicates that there is no such data. N1: mass content of silicon in the first negative electrode active material layer; N2: mass content of silicon in the second negative electrode active material layer.

[0124] By comparing Comparative Example 1 with Examples 1-18, it can be seen that by providing the first voltage controller, after the second negative electrode sheet 1222 stops discharging, the first negative electrode sheet 1221 and the positive electrode sheet 121 can continue to discharge, which is beneficial to improving the discharge capacity of the electrochemical device 100. By comparing Comparative Example 2 with Examples 1-18, it can be seen that by providing the first voltage controller and the second voltage controller, the first negative electrode sheet 1221 and the second negative electrode sheet 1222 are discharged to different cut-off voltages, which is beneficial to improving the cut-off voltage of the electrochemical device 100 while taking into account the capacity retention rate and expansion ratio of the electrochemical device 100 after a long cycle.

[0125] By comparing Comparative Example 1 with Examples 1-4, it can be seen that when the second cut-off voltage U2 satisfies 3.0V≤U2≤3.3V, as the value of U2 decreases, the discharge capacity of the electrochemical device 100 is further improved compared with Comparative Example 1, and the capacity retention rate after 500cl s of cycling and the expansion ratio of 500cl s of cycling have no significant changes compared with the comparative example. It can be seen that by setting U2≥3.0V, the second cut-off voltage is not too low, which is beneficial to reduce the possibility of over-discharge of the electrochemical device 100; by setting U2≤3.3V, the second cut-off voltage is not too high, which is beneficial to improve the discharge capacity of the electrochemical device 100. By comparing Comparative Example 1 with Examples 4-7, it can be seen that when the first cut-off voltage U1 satisfies 3.1V≤U1≤3.4V, the discharge capacity of the electrochemical device 100 is further improved compared with the comparative example, and as the value of V1 decreases, the capacity retention rate after 500cl s of cycling decreases slightly, and the expansion ratio of 500cl s of cycling increases slightly. It can be seen that when U1≥3.1V is set, the first cut-off voltage is not too low, which is conducive to reducing the influence of the volume change of the second negative electrode sheet 1222 during the charge and discharge process on the cycle life of the electrochemical device 100; when U1≤3.4V is set, the first cut-off voltage is not too high, which is conducive to improving the discharge capacity of the electrochemical device 100. By comparing the embodiment 4 and the embodiments 8-10, it can be seen that when N1 satisfies 0wt%≤N1≤3wt%, as the value of N1 increases, the discharge capacity of the electrochemical device 100 gradually increases, the capacity retention rate after 500cl s of cycling gradually decreases, and the expansion ratio of 500cl s of cycling gradually increases. It can be seen that setting N1≥0wt% is conducive to improving the capacity of the electrochemical device 100, and setting N1≤3wt% is conducive to reducing the influence of the volume change of the first negative electrode sheet 1221 during the charge and discharge process on the cycle life of the electrochemical device 100. When N1 satisfies 0wt%≤N1≤1wt%, the capacity, cyclability and expansion performance of the electrochemical device are all good.

[0126] By comparing Example 4 and Examples 11-17, it can be seen that, under the premise that the silicon content of the electrochemical device 100 is constant and the silicon content of the first negative electrode sheet 1221 remains unchanged, when N2 satisfies N2≤25wt%, as the value of N2 increases, the number of the second negative electrode sheets 1222 decreases, the number of the first negative electrode sheets 1221 increases, more negative electrode sheets 122 can be discharged to the second cut-off voltage, the discharge capacity of the electrochemical device 100 tends to increase, the capacity retention rate after 500cl s of cycling tends to decrease, and the expansion ratio after 500cl s of cycling tends to increase. It can be seen that setting N2≤25wt% is conducive to reducing the impact of the volume change of the first negative electrode sheet 1221 during the charge and discharge process on the cycle life of the electrochemical device 100. When N2 satisfies 8wt%≤N2≤12wt%, the capacity, cyclability and expansion performance of the electrochemical device are all good.

[0127] By comparing Example 4 with Examples 11-18, it can be seen that, under the premise that the silicon content of the electrochemical device 100 is constant and the silicon content of the first negative electrode sheet 1221 remains unchanged, when the ratio of the total number of first negative electrode sheets 1221 A1 to the total number of negative electrode sheets 122 A satisfies 10%≤A1 / A≤80%, as the number of first negative electrode sheets 1221 increases, the number of second negative electrode sheets 1222 decreases and the silicon content increases, more negative electrode sheets 122 can be discharged to the first cut-off voltage, the discharge capacity of the electrochemical device 100 tends to increase, the capacity retention rate after cycling 500cl s tends to decrease, and the expansion ratio after cycling 500cl s tends to increase. It can be seen that by setting A1 / A≥10%, the number of first negative electrode sheets 1221 will not be too small, which is beneficial to improving the discharge capacity of the electrochemical device 100; in order to make the total silicon content of the negative electrode sheets 122 reach a certain target value, the more the number of first negative electrode sheets 1221 is, the higher the silicon content required for the second negative electrode sheet 1222 is, and the probability of problems occurring in the electrochemical device 100 in a long cycle tends to increase. Therefore, by setting A1 / A≤80%, the number of first negative electrode sheets 1221 will not be too large, and the silicon content of the second negative electrode sheet 1222 will not be too high, which is beneficial to reducing the impact of the volume change of the second negative electrode sheet 1222 during the charge and discharge process on the cycle life of the electrochemical device 100.

[0128] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application and are not intended to be limiting of the present application. As long as they are within the spirit and scope of the present application, appropriate changes and modifications to the above embodiments are within the scope of the present application.

Claims

1. An electrochemical device comprising an electrode assembly, characterized in that: The electrode assembly comprises a plurality of positive electrode sheets, a plurality of negative electrode sheets and a plurality of separators, wherein the plurality of positive electrode sheets, the plurality of separators and the plurality of negative electrode sheets are stacked to form a laminated structure, and the separators are disposed between adjacent positive electrode sheets and adjacent negative electrode sheets; Each of the positive electrode sheets comprises a positive electrode current collector, a positive electrode active material layer and a positive electrode tab, wherein the positive electrode active material layer is disposed on at least one surface of the positive electrode current collector along the thickness direction of the positive electrode sheet, and one end of the positive electrode tab is electrically connected to the positive electrode current collector; The plurality of negative electrode sheets include at least one first negative electrode sheet and at least one second negative electrode sheet; Each of the first negative electrode sheets comprises a first negative electrode current collector, a first negative electrode active material layer and a first negative electrode ear; the first negative electrode active material layer is provided on at least one surface of the first negative electrode current collector along the thickness direction of the first negative electrode sheet, the mass percentage of silicon element in the first negative electrode active material layer is N1, N1≥0; one end of the first negative electrode ear is electrically connected to the first negative electrode current collector; Each of the second negative electrode sheets comprises a second negative electrode current collector, a second negative electrode active material layer and a second negative electrode ear, wherein the second negative electrode active material layer is disposed on at least one surface of the second negative electrode current collector along the thickness direction of the second negative electrode sheet; The mass percentage of silicon in the second negative electrode active material layer is N2, N2>N1; one end of the second negative electrode ear is electrically connected to the second negative electrode current collector; The first negative electrode active material layer and the second negative electrode active material layer both contain a second active material, and the second active material includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon, and lithium titanate; The electrochemical device also includes a first discharge controller, the other end of the second negative electrode ear is electrically connected to the input end of the first discharge controller, and the first discharge controller also has an output end; the first discharge controller is configured to disconnect the electrical connection between the second negative electrode ear and the output end of the first discharge controller when the discharge voltage of the electrode assembly is equal to or less than a first cut-off voltage U1, where the unit of U1 is V.

2. The electrochemical device according to claim 1, characterized in that 0wt%≤N1≤3wt%.

3. The electrochemical device according to claim 2, characterized in that 0wt%<N1≤1wt%.

4. The electrochemical device according to claim 1, characterized in that 5wt%≤N2≤25wt%.

5. The electrochemical device according to claim 4, characterized in that 8wt%≤N2≤13wt%.

6. The electrochemical device according to claim 1, wherein: The total number of the first negative electrode sheets is A1, the total number of the negative electrode sheets is A, and 10%≤A1 / A≤80%.

7. The electrochemical device according to claim 1, characterized in that 3.1V≤U1≤3.4V.

8. The electrochemical device according to any one of claims 1 to 7, characterized in that The electrochemical device includes a second discharge controller, the other end of the first negative electrode ear is electrically connected to the input end of the second discharge controller, and the second discharge controller also has an output end; the second discharge controller is configured to disconnect the electrical connection between the first negative electrode ear and the output end of the second discharge controller when the discharge voltage of the electrode assembly is equal to or less than a second cut-off voltage U2, the unit of U2 is V, and U2<U1.

9. The electrochemical device according to claim 8, characterized in that The second cut-off voltage is U2, 3.0V≤U2≤3.3V.

10. The electrochemical device according to claim 9, characterized in that The output end of the first discharge controller is electrically connected to the input end of the second discharge controller.

11. The electrochemical device according to claim 1, wherein The electrochemical device comprises: a first adapter, the other ends of the first negative electrode ears are connected to form a first negative electrode ear bundle, and the first adapter is electrically connected to the first negative electrode ear bundle; a second adapter, the other ends of the second negative electrode ears are connected to form a second negative electrode ear bundle, the second adapter is electrically connected to the second negative electrode ear bundle, and the second negative electrode sheet is electrically connected to the first discharge controller through the second adapter; A third adapter, the other ends of the positive tabs are connected to form a positive tab bundle, and the third adapter is electrically connected to the positive tab bundle.

12. The electrochemical device according to any one of claims 1 to 7, characterized in that: The electrochemical device includes a second discharge controller, the other end of the positive electrode ear is electrically connected to the input end of the second discharge controller, and the second discharge controller also has an output end; the second discharge controller is configured to disconnect the electrical connection between the positive electrode ear and the output end of the second discharge controller when the discharge voltage of the electrode assembly is equal to or less than a second cut-off voltage U2, the unit of U2 is V, and U2<U1.

13. An electrical equipment, characterized in that: Comprising the electrochemical device according to any one of claims 1 to 12.

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