Electrochemical device and electric equipment

Abstract

The application discloses an electrochemical device and an electric equipment, comprising an electrode assembly and a first discharge controller, the electrode assembly comprises a plurality of negative electrode sheets. The plurality of negative electrode sheets comprises at least one first negative electrode sheet and at least one second negative electrode sheet. Each first negative electrode sheet comprises a first negative electrode active material layer, the mass percentage of silicon in the first negative electrode active material layer is N1, and N1 is greater than or equal to 0. Each second negative electrode sheet comprises a second negative electrode active material layer, the mass percentage of silicon in the second negative electrode active material layer is N2, and N2 is greater than N1. A second negative electrode tab is electrically connected to the first discharge controller, the first discharge controller is preset with a first cut-off voltage, and the first discharge controller is configured to disconnect the electrical connection between the second negative electrode tab and an external load when the discharge voltage of the electrode assembly is equal to or less than the first cut-off voltage. The electrochemical device is beneficial to improve 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 such as 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 increasingly 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 into traditional negative electrode materials in a certain proportion as negative electrode active materials 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, which affects 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 the traditional negative electrode material 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] A first aspect of embodiments of the present application provides an electrochemical device, comprising an electrode assembly, the electrode assembly comprising a plurality of positive electrode sheets, a plurality of negative electrode sheets and a plurality of separator films, the plurality of positive electrode sheets, the plurality of separator films and the plurality of negative electrode sheets being stacked to form a laminated structure, and each of adjacent positive electrode sheets and negative electrode sheets being provided with a separator film. Each of the positive electrode sheets comprises a positive electrode current collector, a positive electrode active material layer and a positive electrode tab, the positive electrode active material layer being provided on at least one surface of the positive electrode current collector along a thickness direction of the positive electrode sheet, and one end of the positive electrode tab being electrically connected to the positive electrode current collector. The plurality of negative electrode sheets comprises 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 tab, the first negative electrode active material layer being provided on at least one surface of the first negative electrode current collector along a thickness direction of the first negative electrode sheet, the mass percentage of silicon in the first negative electrode active material layer being N1, and N1≥0, and one end of the first negative electrode tab being 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 tab, the second negative electrode active material layer being provided on at least one surface of the second negative electrode current collector along a thickness direction of the second negative electrode sheet, the mass percentage of silicon in the second negative electrode active material layer being N2, and N2>N1, and one end of the second negative electrode tab being 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 comprises at least one of artificial graphite, natural graphite, hard carbon, soft carbon and lithium titanate. The electrochemical device further comprises a first discharge controller, the other end of the second negative electrode tab being electrically connected to an input end of the first discharge controller, and the first discharge controller further having an output end. The first discharge controller is configured to disconnect the electrical connection between the second negative electrode tab and the output end of the first discharge controller when a discharge voltage of the electrode assembly is equal to or less than a first cut-off voltage U1, and the unit of U1 is V.

[0005] In the 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, and in the charging and discharging 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 conducive 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. After the second negative electrode sheet stops discharging, the first negative electrode sheet and the positive electrode sheet with a lower content of silicon can continue to discharge, which can further release the energy of the second active material layer in the first negative electrode sheet, and is conducive 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 conducive to improving the capacity of the electrochemical device, and setting N1≤3wt% is conducive to reducing the influence of the volume change of the first negative electrode sheet in the charging and discharging 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 conducive to further reducing the impact of the volume change of the first negative tab during the charging and discharging 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 conducive to improving the capacity of the electrochemical device, and setting N2≤ 25wt% is conducive to reducing the impact of the volume change of the second negative tab during the charging and discharging 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 conducive to improving the capacity of the electrochemical device, and setting N2≤ 13wt% is conducive to reducing the impact of the volume change of the first negative tab during the charging and discharging process on the cycle life of the electrochemical device.

[0010] In an optional embodiment of the present application, the total number of the first negative tabs is A1, the total number of the negative tabs is A, and 10%≤ A1 / A≤ 80%. Setting A1 / A≥ 10% is conducive to improving the discharge capacity of the electrochemical device by not making the number of the first negative tabs too small; in order to make the total silicon content of the negative tabs reach a certain target value, the more the number of the first negative tabs, the higher the silicon content required by the second negative tab, and the probability of the electrochemical device having problems in long cycle tends to increase, thus, setting A1 / A≤ 80% is conducive to reducing the impact of the volume change of the second negative tab during the charging and discharging process on the cycle life of the electrochemical device by not making the number of the first negative tabs too large and the silicon content of the second negative tab too high.

[0011] In an optional embodiment of the present application, 3.1V≤ U1≤ 3.4V. Setting U1≥ 3.1V is conducive to reducing the impact of the volume change of the second negative tab during the charging and discharging process on the cycle life of the electrochemical device by not making the first cut-off voltage too low; and setting U1≤ 3.4V is conducive to improving the discharge capacity of the electrochemical device by not making the first cut-off voltage too high.

[0012] In an optional embodiment of the present application, the electrochemical device comprises a second discharge controller, the other end of the first negative tab 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 tab 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, U2 is in V, and U2 < U1. By setting the second discharge controller, the electrochemical device stops discharging 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, wherein the other end of the positive tab is electrically connected to an input of the second discharge controller, and the second discharge controller also has an output. The second discharge controller is configured to disconnect the positive tab from the output of the second discharge voltage controller when the discharge voltage of the electrode assembly is equal to or less than a second cutoff voltage U2, where U2 is expressed in V and U2 < U1. The provision of the second discharge controller allows the electrochemical device to cease discharge when the voltage drops to the second cutoff voltage, thereby 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. Setting U2≥3.0V prevents the second cut-off voltage from being too low, thereby reducing the possibility of over-discharge of the electrochemical device; setting U2≤3.3V prevents the second cut-off voltage from being too high, thereby 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 beneficial for simplifying 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 provision of the first adapter can facilitate the connection of the first negative electrode sheet to an external load, the provision of the second adapter can facilitate the connection of the second negative electrode sheet to the first discharge controller, and the provision of the third adapter can facilitate the connection of the positive electrode sheet to an external load.

[0017] A second aspect of the embodiments 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 structural diagram of an electrode assembly in one embodiment of the present application.

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

[0023] Description of 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 electrode ear 1213

[0032] Negative electrode 122

[0033] 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] 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] First discharge controller 20

[0046] 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 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. 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.

[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 pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0051] In the description of the embodiments of this application, the technical terms "first," "second," etc. are used only to distinguish different objects and should not be understood to indicate or imply relative importance or to implicitly indicate the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise specifically defined.

[0052] In the description of the embodiments of this application, the term "perpendicular" is used to describe an ideal state between two components. In actual production or use, two components may be approximately perpendicular to each other. Two components described as "perpendicular" do not necessarily need to be absolutely straight lines or planes; they can also be approximately straight lines or planes. From a macroscopic perspective, the components are considered "straight" or "planar" if their overall extension direction is a straight line or plane.

[0053] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present application. The appearance of such phrases in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. The various embodiments of the present application may be combined with each other unless there is a conflict.

[0054] A first aspect of an embodiment of the present application provides an electrochemical device comprising an electrode assembly, the electrode assembly comprising 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, with separators interposed between adjacent positive and negative electrode sheets. Each positive electrode sheet comprises a positive current collector, a positive active material layer, and a positive tab. The positive active material layer is disposed on at least one surface of the positive current collector along the thickness direction of the positive electrode sheet, and one end of the positive tab is electrically connected to the positive current collector. The plurality of negative electrode sheets comprises at least one first negative electrode sheet and at least one second negative electrode sheet. Each first negative electrode sheet comprises a first negative electrode collector, a first negative active material layer, and a first negative tab. The first negative active material layer is disposed on at least one surface of the first negative electrode collector along the thickness direction of the first negative electrode sheet, and the mass percentage of silicon in the first negative active material layer is N1, where N1 ≥ 0. One end of the first negative tab is electrically connected to the first negative 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 tab. 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, where N2>N1. One end of the second negative electrode tab is electrically connected to the second negative electrode current collector. Both the first negative electrode active material layer and the second negative electrode active material layer contain a second active material, which 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 tab is electrically connected to an input terminal of the first discharge controller, which also has an output terminal. The first discharge controller is configured to disconnect the second negative electrode tab from the output terminal of the first discharge controller when the discharge voltage of the electrode assembly is equal to or less than a first cutoff voltage U1, where U1 is expressed in volts.

[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 impact 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 with reference to 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, as Figure 2 As shown, the shell 11 is a packaging bag obtained by packaging with a packaging film, such as aluminum-plastic film, 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, as Figure 3 As shown, the electrode assembly 12 includes multiple positive electrode sheets 121, multiple negative electrode sheets 122 and multiple isolation membranes 123. The multiple positive electrode sheets 121, multiple isolation membranes 123 and multiple negative electrode sheets 122 are stacked to form a laminated structure, and isolation membranes 123 are provided between adjacent positive electrode sheets 121 and negative electrode sheets 122.

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

[0062] In some embodiments, as Figure 3 As shown, the multiple 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 tab 12213. The first negative electrode active material layer 12212 is provided on at least one surface of the first negative electrode current collector 12211 along the thickness direction of the first negative electrode sheet 12211. The mass percentage of silicon element in the first negative electrode active material layer 12212 is N1, and N1 ≥ 0. One end of the first negative electrode tab 12213 is electrically connected to the first negative electrode current collector 12211, and the first negative electrode tab 12213 is used to electrically connect to an external load. Each second negative electrode sheet 1222 includes a second negative electrode current 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 current 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 current 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, as 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 the thickness direction of the first negative electrode sheet 1221 .

[0065] In some embodiments, as Figure 1 As shown, the electrochemical device 100 further includes a first discharge controller 20. The other end of the second negative electrode tab 12223 is electrically connected to the input terminal of the first discharge controller 20. The first discharge controller 20 also has an output terminal. The second negative electrode tab 12223 is configured to be electrically connected to an external load through the output terminal of the first discharge controller 20. The first discharge controller 20 is preset with a first cutoff voltage U1, where the unit of U1 is V. The first discharge controller 20 is configured to disconnect the electrical connection with the output terminal of the first discharge controller 20 when the discharge voltage of the electrode assembly 12 is equal to or less than the first cutoff 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 helps to reduce 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. Moreover, 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 helps to improve 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 example, the negative electrode current collector can 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, which includes one or more of pure silicon, silicon-carbon, silicon-oxygen, silicon-oxygen-carbon, and a silicon alloy. In some embodiments, the first negative electrode active material layer 12212 and the second negative electrode active material layer 12222 further contain a second active material, which 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 further 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 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 one 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.

[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 to a case where the negative electrode active layer of each negative electrode sheet 122 comprises a silicon-based material, only some of the negative electrode sheets 122 contain silicon. This increases the capacity of the electrochemical device 100 while also minimizing 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, 0 wt % ≤ N1 ≤ 1 wt %. Setting N1 ≤ 1 wt % is beneficial for further 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 .

[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 7 wt%, 9 wt%, 11 wt%, 13 wt%, 15 wt%, 17 wt%, 19 wt%, 21 wt%, and 23 wt%.

[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 first negative electrode sheets 1221 is A1, the total number of negative electrode sheets 122 is A, and 10% ≤ A1 / A ≤ 80%. Setting A1 / A ≥ 10% prevents the number of first negative electrode sheets 1221 from being too small, which is beneficial for improving the discharge capacity of the electrochemical device 100. To achieve a target total silicon content of the negative electrode sheets 122, a larger number of first negative electrode sheets 1221 requires a higher silicon content in the second negative electrode sheets 1222, which increases the probability of problems with the electrochemical device 100 during long cycles. Therefore, setting A1 / A ≤ 80% prevents an excessive number of first negative electrode sheets 1221 and an excessively high silicon content in the second negative electrode sheets 1222, which is beneficial for reducing the impact of volume changes in the second negative electrode sheets 1222 during charge and discharge on the cycle life of the electrochemical device 100.

[0088] In some embodiments, 3.1V≤U1≤3.4V. Setting U1≥3.1V prevents the first cutoff voltage from being too low, which helps 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. Setting U1≤3.4V prevents the first cutoff voltage from being too high, which helps improve the discharge capacity of the electrochemical device 100.

[0089] In some embodiments, as Figure 1 As shown, the electrochemical device 100 includes a second discharge controller 30. The other end of the first negative electrode tab 12213 is electrically connected to the output terminal of the second discharge controller 30. The second discharge controller also has an output terminal. The first negative electrode tab 12213 is configured to be electrically connected to an external load via the output terminal of the second discharge controller 30. The second discharge controller 30 is preset with a second cutoff voltage U2, where U2 is expressed in volts. The second discharge controller 30 is configured to disconnect the first negative electrode tab 12213 from the output terminal of the second discharge controller 30 when the discharge voltage of the electrode assembly 12 is equal to or less than the second cutoff voltage U2. The second cutoff voltage U2 is less than the first cutoff voltage U1. The provision of the second discharge controller 30 allows the electrochemical device 100 to cease discharge when the voltage drops to the second cutoff voltage, thereby 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 tab 1213 is electrically connected to the second discharge controller 30. The second discharge controller 30 also has an output terminal. The positive tab 1213 is configured to be electrically connected to an external load through the second discharge controller 30. The second discharge controller 30 is preset with a second cutoff voltage U2, where U2 is expressed in volts. The second discharge controller 30 is configured to disconnect the positive tab 1213 from the output terminal of the second discharge controller 30 when the discharge voltage of the electrode assembly 12 is equal to or less than the second cutoff voltage U2. The second cutoff voltage U2 is less than the first cutoff voltage U1. By providing the second discharge controller 30, discharge of the electrochemical device 100 is stopped when the voltage drops to the second cutoff voltage, which helps reduce the possibility of over-discharge of the electrochemical device 100.

[0091] In the embodiment 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 further described here.

[0092] In some embodiments, 3.0 V ≤ U2 ≤ 3.3 V. Setting U2 ≥ 3.0 V prevents the second cutoff voltage from being too low, thereby reducing the possibility of over-discharging of the electrochemical device 100. Setting U2 ≤ 3.3 V prevents the second cutoff voltage from being too high, thereby increasing the discharge capacity of the electrochemical device 100.

[0093] In some embodiments, as 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 tabs 12213 are connected to form a first negative electrode tab bundle, and the first adapter 13 is electrically connected to the first negative electrode tab bundle (such as Figure 3 ); all 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 via the second adapter 14; all 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 provision of the first adapter 13 facilitates connection of the first negative electrode sheet 1221 to an external load, the provision of the second adapter 14 facilitates connection of the second negative electrode sheet 1222 to the first discharge controller 20, and the provision of the third adapter 15 facilitates connection of the positive electrode sheet 121 to an external load.

[0094] like Figure 5 As shown, an embodiment of the present application further provides an electrical device 1000 , which 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] To verify the effects 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 experiments.

[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 Examples 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 The negative electrode sheets 122 in each electrode assembly 12 in the comparative example have the same silicon content by mass. In the embodiment, a portion of the 20 negative electrode sheets 122 in each electrode assembly 12 are first negative electrode sheets 1221 having a silicon content by mass of N1, and the remaining portion are second negative electrode sheets 1222 having a silicon content by mass of N2. The capacity of each negative electrode sheet 122 in the comparative example is the same as that of each negative electrode sheet 122 in the embodiment. The capacity of each positive electrode sheet 121 in the comparative example is the same as that of each positive electrode sheet 121 in the embodiment. The capacity of each first negative electrode sheet 1221 and each second negative electrode sheet 1222 in each embodiment is also the same. The capacity of the negative electrode sheet 122 is adjusted by varying the coating thickness based on 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 different thicknesses of negative electrode active material layers based on 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, 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 in a vacuum mixer until a solid content of 75wt% and a uniform positive electrode slurry is obtained. An aluminum foil with a thickness of 8μm is selected as the positive electrode current collector 1211, and the aluminum foil is cut to form the positive electrode inner tab. The positive electrode slurry is evenly coated on one surface of the aluminum foil of the positive electrode current collector 1211 and dried at 110°C to obtain a positive electrode sheet 121 with a single-sided positive electrode active material layer 1212 (thickness 80μm). Thereafter, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet 121 with a double-sided positive electrode active material layer 1212.

[0101] 2. Preparation of negative electrode sheet 122

[0102] The negative electrode active materials graphite powder, silicon powder, conductive carbon black (Super P), and binder styrene-butadiene rubber (SBR) are mixed in a certain mass ratio. Deionized water is then added as a solvent to prepare a negative electrode slurry with a solid content of 50 wt%, and the mixture is stirred evenly. A copper foil with a thickness of 5 μm is selected as the negative electrode current collector, and the copper foil is cut to form the negative electrode inner tab. 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. The above steps are then repeated on the other surface of the negative electrode sheet 122 to obtain a negative electrode sheet 122 coated with a negative electrode active material layer 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. Electrolyte Preparation

[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 uniformly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0107] 5. Preparation of Secondary Batteries

[0108] The separator 123, positive electrode sheet 121, separator 123, and negative electrode sheet 122 prepared above are stacked in order to form a laminated structure. The outermost electrode sheets at both ends of the laminated structure are both positive electrode sheets 121. The electrode assembly 12 is hot pressed at a pressure of 5 MPa, a temperature of 65°C, and a holding time of 10 seconds. All the negative tabs are connected to form a negative tab bundle, and an adapter is connected to the negative tab bundle. The adapter is also connected to all the positive tabs 1213 to form a positive tab 1213 bundle, and an adapter is connected to the positive tab 1213 bundle. The electrode assembly 12 is placed in an aluminum-plastic film packaging bag, with the two aforementioned adapters extending from the top seal of the packaging bag. After dehydration at 80°C, the electrolyte is injected and the package is sealed.

[0109] 6. Connect the discharge controller

[0110] Connect the discharge controller 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 of the comparative example. The difference is 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 silicon content of the first negative electrode sheet 1221 and the silicon content of the second negative electrode sheet 1222 are the same value; the negative electrode sheet 122 in the embodiment is obtained from two types of negative electrode sheets 122 with different silicon content according to the different mixing ratios of the negative electrode active materials, among which 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, namely the first adapter 13 mentioned above, all the second negative electrode sheets 1222 are connected to an adapter, namely the second adapter 14 mentioned above, all the positive electrode sheets 121 are connected to an adapter, namely 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 thermostat at 25°C ± 2°C for 30 minutes to allow the secondary battery 10 to reach a constant temperature. The device 100, once at a constant temperature, was charged at a constant current of 0.5C to the full charge voltage. The device was then charged at a constant current of 0.05C at the full charge voltage and discharged at a 0.2C rate until the discharge controller activated. The discharge capacity was recorded. The electrochemical device 100 in the comparative example had only one discharge controller, and its cutoff voltage is recorded in the second cutoff 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, and the 500th discharge capacity was recorded. The 500th discharge capacity was divided by the first discharge capacity to obtain the capacity retention rate after 500 cycles.

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

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

[0119] (2) After the discharge capacity test 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 data were 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 such data is not available. 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] Comparing Comparative Example 1 with Examples 1-18 shows that by providing the first voltage controller, the first negative electrode sheet 1221 and the positive electrode sheet 121 can continue to discharge after the second negative electrode sheet 1222 stops discharging, which is beneficial for improving the discharge capacity of the electrochemical device 100. Comparing Comparative Example 2 with Examples 1-18 shows 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 cutoff voltages, which is beneficial for improving the cutoff voltage of the electrochemical device 100 while also ensuring the capacity retention and expansion ratio of the electrochemical device 100 after long cycles.

[0125] Comparing Comparative Example 1 with Examples 1-4 shows that when the second cutoff voltage U2 satisfies 3.0V≤U2≤3.3V, the discharge capacity of the electrochemical device 100 further increases compared to Comparative Example 1 as the value of U2 decreases. The capacity retention rate after 500 cl / s and the expansion ratio after 500 cl / s do not change significantly compared to the Comparative Example. Therefore, setting U2≥3.0V prevents the second cutoff voltage from being too low, which helps reduce the possibility of over-discharge of the electrochemical device 100. Setting U2≤3.3V prevents the second cutoff voltage from being too high, which helps increase the discharge capacity of the electrochemical device 100. Comparing Comparative Example 1 with Examples 4-7 shows that when the first cutoff voltage U1 satisfies 3.1V≤U1≤3.4V, the discharge capacity of the electrochemical device 100 further increases compared to the Comparative Example. Furthermore, as the value of V1 decreases, the capacity retention rate after 500 cl / s decreases slightly, and the expansion ratio after 500 cl / s increases slightly. As can be seen, setting U1 ≥ 3.1V prevents the first cutoff voltage from being too low, which helps reduce the impact of the volume change of the second negative electrode sheet 1222 during charge and discharge on the cycle life of the electrochemical device 100. Setting U1 ≤ 3.4V prevents the first cutoff voltage from being too high, which helps improve the discharge capacity of the electrochemical device 100. A comparison between Example 4 and Examples 8-10 shows 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 500 cl s of cycling gradually decreases, and the expansion ratio after 500 cl s of cycling gradually increases. Therefore, setting N1 ≥ 0wt% helps improve the capacity of the electrochemical device 100, while setting N1 ≤ 3wt% helps reduce the impact of the volume change of the first negative electrode sheet 1221 during charge and discharge on the cycle life of the electrochemical device 100. When N1 satisfies 0wt% ≤ N1 ≤ 1wt%, the electrochemical device exhibits excellent capacity, cyclability, and expansion performance.

[0126] As can be seen from the comparison of Example 4 and Examples 11-17, 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 is constant, when N2 satisfies N2≤25wt%, as the value of N2 increases, the number of the second negative electrode sheet 1222 decreases, the number of the first negative electrode sheet 1221 increases, more negative electrode sheets 122 can be discharged to the second cut-off voltage, the discharge capacity of the electrochemical device 100 has a trend of increasing, the capacity retention rate after 500 cl s of cycling has a trend of decreasing, and the expansion ratio of 500 cl s of cycling has a trend of increasing. It can be seen that setting N2≤25wt% is beneficial to reducing the influence of the volume change of the first negative electrode sheet 1221 in the charging and discharging process on the cycle life of the electrochemical device 100. When N2 satisfies 8wt%≤N2≤12wt%, the capacity, cycle performance, and expansion performance of the electrochemical device are all good.

[0127] As can be seen from the comparison of Example 4 and Examples 11-18, 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 is constant, when the ratio of the total number of the first negative electrode sheet 1221 to the total number of the negative electrode sheet 122 satisfies 10%≤A1 / A≤80%, as the number of the first negative electrode sheet 1221 increases, the number of the second negative electrode sheet 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 has a trend of increasing, the capacity retention rate after 500 cl s of cycling has a trend of decreasing, and the expansion ratio of 500 cl s of cycling has a trend of increasing. It can be seen that setting A1 / A≥10% is beneficial to increasing the discharge capacity of the electrochemical device 100 by not making the number of the first negative electrode sheet 1221 too small; in order to make the total silicon content of the negative electrode sheet 122 reach a certain target value, the more the number of the first negative electrode sheet 1221, the higher the silicon content required by the second negative electrode sheet 1222, and the electrochemical device 100 has a trend of increasing the probability of problems in long cycling. Therefore, setting A1 / A≤80% is beneficial to reducing the influence of the volume change of the second negative electrode sheet 1222 in the charging and discharging process on the cycle life of the electrochemical device 100 by not making the number of the first negative electrode sheet 1221 too large and the silicon content of the second negative electrode sheet 1222 too high.

[0128] Those skilled in the art should understand that the above embodiments are only used to illustrate the present application, and are not used as a limitation to the present application, and as long as the above embodiments are within the spirit and scope of the present application, any suitable changes and modifications made to the above embodiments are within the disclosure range of the present application.

Claims

1. An electrochemical device comprising an electrode assembly, characterized in that: The electrode assembly includes 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 the separators are provided 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. 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. 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 includes a first negative electrode current collector, a first negative electrode active material layer, and a first negative electrode tab; 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, and N1 ≥ 0; one end of the first negative electrode tab is electrically connected to the first negative electrode current collector; Each of the second negative electrode sheets includes a second negative electrode current collector, a second negative electrode active material layer, and a second negative electrode tab, wherein the second negative electrode active material layer is provided 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 tab 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, wherein 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, wherein 0wt%≤N1≤3wt%.

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

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

5. The electrochemical device according to claim 4, wherein 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, wherein 3.1V≤U1≤3.4V.

8. The electrochemical device according to any one of claims 1 to 7, wherein 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, where the unit of U2 is V and U2 < U1.

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

10. The electrochemical device according to claim 9, wherein 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 tabs being connected to form a first negative electrode tab bundle, and the first adapter being electrically connected to the first negative electrode tab bundle; a second adapter, the other ends of the second negative tabs being connected to form a second negative tab bundle, the second adapter being electrically connected to the second negative tab bundle, and the second negative electrode sheet being electrically connected to the first discharge controller via 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, wherein: 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, where the unit of U2 is V, and U2 < U1.

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

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