Electrochemical apparatus and electrical device

Abstract

The present application discloses an electrochemical apparatus and an electrical device. The electrochemical apparatus comprises an electrode assembly and a first discharge controller, the electrode assembly comprising a plurality of negative electrode sheets. The plurality of negative electrode sheets comprise 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 substance layer, and the mass percentage of the element silicon in the first negative electrode active substance layer is N1, where N1≥0. Each second negative electrode sheet comprises a second negative electrode active substance layer, and the mass percentage of the element silicon in the second negative electrode active substance layer is N2, where N2>N1. A second negative tab is electrically connected to the first discharge controller. The first discharge controller is preset to have a first cut-off voltage. The first discharge controller is configured to disconnect an electrical connection between the second negative 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 apparatus is beneficial for improving discharge capacity.

Description

Electrochemical device and electric equipment TECHNICAL FIELD

[0001] The present application belongs to the technical field of energy storage, and particularly relates to an electrochemical device and an electric equipment. BACKGROUND

[0002] With the wide application of electrochemical devices such as lithium ion secondary batteries and sodium ion secondary batteries in various electronic products, electric vehicles, electric tools and other terminals, users have put forward higher and higher requirements for the energy density of electrochemical devices. Since silicon-based materials have a specific capacity of up to 4200 mAh / g, which is several times that of traditional negative electrode materials such as graphite and hard carbon, silicon-based materials have begun to be doped in traditional negative electrode materials at a certain proportion as negative active materials to improve the energy density of electrochemical devices. Since the silicon-based negative active material will have a large volume expansion in the charge and discharge cycle, affecting the cycle life of the lithium ion battery, the prior art often uses a higher discharge cycle to improve the cycle life of the battery of the silicon-doped negative active material, such as increasing the discharge cut-off voltage to above 3.5V. This method can improve the cycle expansion problem of the battery of the silicon-doped negative active material, but it loses part of the capacity of the traditional negative electrode material and sacrifices the energy density. SUMMARY

[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 the 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 comprises a second discharge controller, the other end of the positive tab is electrically connected to an input end of the second discharge controller, the second discharge controller further has an output end, and the second discharge controller is configured to disconnect the electrical connection between the positive tab and the output end of the second discharge voltage 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 providing the second discharge controller, the discharge of the electrochemical device is stopped when the voltage of the electrochemical device 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, and 3.0 V ≤ U2 ≤ 3.3 V. By setting U2 ≥ 3.0 V, the second cut-off voltage is not too low, which is conducive to reducing the possibility of over-discharge of the electrochemical device; by setting U2 ≤ 3.3 V, the second cut-off voltage is not too high, which is conducive to improving the discharge capacity of the electrochemical device.

[0015] In an optional embodiment of the present application, the output end of the first discharge controller is electrically connected to the input end of the second discharge controller. In this way, the electrical connection structure of the electrochemical device is simplified.

[0016] In an optional embodiment of the present application, the electrochemical device comprises a first adapter, a second adapter and a third adapter. The other end of the first negative tab is connected to form a first negative tab bundle, and the first adapter is electrically connected to the first negative tab bundle. The other end of the second negative tab is connected to form a second negative tab bundle, the second adapter is electrically connected to the second negative tab bundle, and the second negative tab is electrically connected to the first discharge controller through the second adapter. The other end of the positive tab is connected to form a positive tab bundle, and the third adapter is electrically connected to the positive tab bundle. By providing the first adapter, the first negative tab can be conveniently connected to an external load; by providing the second adapter, the second negative tab can be conveniently connected to the first discharge controller; and by providing the third adapter, the positive tab can be conveniently connected to an external load.

[0017] The second aspect of the embodiments of the present application provides a power utilization device comprising the electrochemical device according to any one of the preceding embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0018] FIG. 1 is a structural schematic diagram of an electrochemical device according to an embodiment of the present application.

[0019] FIG. 2 is a structural schematic diagram of a secondary battery of an electrochemical device according to an embodiment of the present application.

[0020] FIG. 3 is a sectional view of I-I in FIG. 2.

[0021] FIG. 4 is a structural schematic diagram of an electrode assembly according to an embodiment of the present application.

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

[0023] Main element symbol Explanation Electrochemical device 100 Secondary battery 10 Case 11 Electrode assembly 12 Positive electrode sheet 121 Positive electrode current collector 1211 Positive electrode active material layer 1212 Positive electrode tab 1213 Negative electrode sheet 122 First negative electrode sheet 1221 First negative electrode current collector 12211 First negative electrode active material layer 12212 First negative electrode tab 12213 Second negative electrode sheet 1222 Second negative electrode current collector 12221 Second negative electrode active material layer 12222 Second negative electrode tab 12223 Separation film 123 First adapter 13 Second adapter 14 Third adapter 15 First discharge controller 20 Second discharge controller 30

[0024] The following detailed description will further explain the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0025] With reference to the drawings and the embodiments described herein, it will be understood that the drawings are diagrammatic and are not drawn to scale, and that they are merely intended to conceptually illustrate the features of the application. Like reference numerals have been used in different drawings to imply like features.

[0026] It is to be noted that when an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements can be present. When an element is referred to as being "positioned on" another element, it can be directly positioned on the other element or intervening elements can be present.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0028] In the description of the embodiments of the 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 application, the meaning of "a plurality of" is two or more, unless otherwise explicitly specified.

[0029] In the description of the embodiments of the application, the term "vertical" is used to describe the ideal state between two components. In the actual production or use state, there can be an approximate vertical state between the two components. The two components described as "vertical" can not be an absolute straight line, plane, but can be approximately straight or planar, and the overall extension direction is straight or planar from a macroscopic point of view, which can be considered as "straight line" or "plane".

[0030] Reference herein to "embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearance of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of other embodiments. Various features that are described in the specification can be combined together in any combination.

[0031] 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 the 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.

[0032] 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.

[0033] Embodiments of the present application are further described below with reference to the accompanying drawings.

[0034] As shown in FIGS. 1-3, embodiments of the present application provide an electrochemical device 100, including a secondary battery 10, the secondary battery 10 including a housing 11 and an electrode assembly 12, the electrode assembly 12 being disposed inside the housing 11.

[0035] In some embodiments, as shown in FIG. 2, the housing 11 is a packaging bag obtained by packaging with a packaging film, such as an aluminum-plastic film, a steel-plastic film, etc.

[0036] In some embodiments, the housing 11 can be a metal housing 11, such as a steel shell, an aluminum shell, etc.

[0037] In some embodiments, as shown in FIG. 3, the electrode assembly 12 includes a plurality of positive electrode sheets 121, a plurality of negative electrode sheets 122, and a plurality of separator films 123, the plurality of positive electrode sheets 121, the plurality of separator films 123, and the plurality of negative electrode sheets 122 being stacked to form a laminated structure, and the separator film 123 being provided between adjacent positive electrode sheets 121 and negative electrode sheets 122.

[0038] In some embodiments, as shown in FIG. 3, each positive electrode sheet 121 includes a positive electrode current collector 1211, a positive electrode active material layer 1212, and a positive electrode tab 1213, the positive electrode active material layer 1212 being provided on at least one surface of the positive electrode current collector 1211 along the thickness direction of the positive electrode sheet 121, and one end of the positive electrode tab 1213 being electrically connected to the positive electrode current collector 1211, the positive electrode tab 1213 being used for electrically connecting an external load.

[0039] In some embodiments, as shown in FIG. 3, the plurality of negative electrode sheets 122 includes 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 being provided on at least one surface of the first negative electrode current collector 12211 along the thickness direction of the first negative electrode sheet 1221, the mass percentage of silicon in the first negative electrode active material layer 12212 being N1, and N1≥0; one end of the first negative electrode tab 12213 being electrically connected to the first negative electrode current collector 12211, and the first negative electrode tab 12213 being used for electrically connecting 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 tab 12223, the second negative electrode active material layer 12222 being provided 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 in the second negative electrode active material layer 12222 being N2, and N2>N1; and one end of the second negative electrode tab 12223 being electrically connected to the second negative electrode current collector 12221.

[0040] In some embodiments, the plurality of first negative electrode tabs 1221 are sequentially stacked on at least one side of the electrode assembly 12 in the thickness direction of the first negative electrode tab 1221, and the plurality of second negative electrode tabs 1222 are sequentially stacked on the other side or the middle of the electrode assembly 12.

[0041] In some embodiments, as shown in FIG. 4, the plurality of first negative electrode tabs 1221 and the plurality of second negative electrode tabs 1222 are alternately stacked in the thickness direction of the first negative electrode tab 1221.

[0042] In some embodiments, as shown in FIG. 1, 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 end of the first discharge controller 20, the first discharge controller 20 further has an output end, and the second negative electrode tab 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 be disconnected from 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.

[0043] In the electrochemical device 100, the mass percentage of silicon element in the second negative electrode active material layer 12222 is greater than the mass percentage of silicon element in the first negative electrode active material layer 12212, and the volume change amount of the second negative electrode tab 1222 is greater than that of the first negative electrode tab 1221 during the charge and discharge process of the electrochemical device 100, and the second negative electrode tab 1222 stops discharging after discharging to the first cut-off voltage, which is conducive to reducing the influence of the volume change of the second negative electrode tab 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 tab 1222 stops discharging, the first negative electrode tab 1221 with low silicon element content and the positive electrode tab 121 can continue to discharge, which can further release the energy of the second active material layer in the first negative electrode tab 1221, and is conducive to improving the discharge capacity of the electrochemical device 100.

[0044] In some embodiments, the first negative electrode current collector 12211 and the second negative electrode current collector 12221 are both metal layers. As an exemplary example, the negative electrode current collector can be a metal layer including at least one of copper, nickel, tantalum, and titanium, such as a copper foil.

[0045] In some embodiments, the first negative electrode current collector 12211 and the second negative electrode current collector 12221 are both composite current collectors.

[0046] 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 including 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 further contain a second active material including at least one of artificial graphite, natural graphite, hard carbon, and lithium titanate.

[0047] 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 including at least one of conductive carbon black, carbon nanotube, carbon fiber, or graphene, and a binder including at least one of styrene-butadiene rubber, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylic acid, or sodium carboxymethyl cellulose, etc.

[0048] In some embodiments, the positive electrode current collector 1211 is a metal layer. As an illustrative example, the positive electrode current collector 1211 can be a metal layer including at least one of aluminum, nickel, tantalum, and titanium, such as an aluminum foil.

[0049] In some embodiments, the positive electrode current collector 1211 is a composite current collector.

[0050] In some embodiments, the positive electrode active material layer 1212 includes a positive electrode active material including at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganate.

[0051] In some embodiments, the separator 123 is an insulating film material such as a polyethylene film, a polypropylene film, a polyester film, or a polyimide film.

[0052] In some embodiments, the electrochemical device 100 further includes an electrolyte contained in the housing 11.

[0053] In some embodiments, the electrolyte is in any one of a gel state, a solid state, and a liquid state.

[0054] In some embodiments, the electrolyte includes a lithium salt and a nonaqueous solvent.

[0055] 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.

[0056] 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 solvent, etc. For example, the carbonate compound can include at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, or trifluoromethyl ethylene carbonate, etc.

[0057] In some embodiments, N1=0. In this case, the first negative active material layer 12212 does not contain silicon elements. Compared with the case where each negative tab 122 contains silicon-based materials, only part of the negative tabs 122 contain silicon elements, which can increase the capacity of the electrochemical device 100 while taking into account the influence of silicon elements on the cycle life of the electrochemical device 100.

[0058] In some embodiments, 0wt%≤N1≤3wt%. Setting N1≥0wt% is conducive to increasing 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 tab 1221 during charging and discharging on the cycle life of the electrochemical device 100.

[0059] In some embodiments, the value of N1 is one of 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%.

[0060] In some embodiments, 0wt%≤N1≤1wt%. Setting N1≤1wt% is conducive to further reducing the influence of the volume change of the first negative tab 1221 during charging and discharging on the cycle life of the electrochemical device 100.

[0061] In some embodiments, 5wt%≤N2≤25wt%. Setting N2≥1wt% is conducive to increasing the capacity of the electrochemical device 100, and setting N2≤25wt% is conducive to reducing the influence of the volume change of the second negative tab 1222 during charging and discharging on the cycle life of the electrochemical device 100.

[0062] In some embodiments, N2 is one of 7 wt%, 9 wt%, 11 wt%, 13 wt%, 15 wt%, 17 wt%, 19 wt%, 21 wt%, 23 wt%.

[0063] In some embodiments, 8 wt%≤N2≤13 wt%. Setting N2≥8 wt% is conducive to improving the capacity of the electrochemical device 100, and setting N2≤13 wt% is conducive to further reducing the influence of the volume change of the second negative tab 1222 during the charging and discharging process on the cycle life of the electrochemical device 100.

[0064] In some embodiments, the total number of the first negative tabs 1221 is A1, the total number of the negative tabs 122 is A, and 10%≤A1 / A≤80%. Setting A1 / A≥10% is conducive to improving the discharging capacity of the electrochemical device 100, and setting A1 / A≤80% is conducive to reducing the influence of the volume change of the second negative tab 1222 during the charging and discharging process on the cycle life of the electrochemical device 100.

[0065] In some embodiments, 3.1V≤U1≤3.4V. Setting U1≥3.1V is conducive to reducing the influence of the volume change of the second negative tab 1222 during the charging and discharging process on the cycle life of the electrochemical device 100, and setting U1≤3.4V is conducive to improving the discharging capacity of the electrochemical device 100.

[0066] In some embodiments, as shown in FIG. 1, the electrochemical device 100 includes a second discharging controller 30, the other end of the first negative lug 12213 is electrically connected to the output end of the second discharging controller 30, and the second discharging controller further has an output end. The first negative lug 12213 is configured to be electrically connected to an external load through the output end of the second discharging controller 30, and the second discharging controller 30 is pre-set with a second cut-off voltage U2, and the unit of U2 is V. The second discharging controller 30 is configured to disconnect the electrical connection between the first negative lug 12213 and the output end of the second discharging controller 30 when the discharging 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 discharging controller 30, the electrochemical device 100 stops discharging when the voltage drops to the second cut-off voltage, which is conducive to reducing the possibility of over-discharging of the electrochemical device 100.

[0067] In some embodiments, the electrochemical device 100 comprises 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 further has an output end, 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 cut-off voltage U2, the unit of U2 is V. The second discharge controller 30 is configured to disconnect the electrical connection between the positive tab 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 of the electrochemical device 100 drops to the second cut-off voltage, which is beneficial to reduce the possibility of over-discharge of the electrochemical device 100.

[0068] In the embodiments of the present application, the first discharge controller 20 and the second discharge controller 30 can both adopt conventional designs in the prior art, which will not be described here.

[0069] In some embodiments, 3.0V≤U2≤3.3V. 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.

[0070] In some embodiments, as shown in FIG. 2, the electrochemical device 100 further comprises a first adapter 13, a second adapter 14 and a third adapter 15. All the first negative tabs 12213 are connected to form a first negative tab bundle, the first adapter 13 is electrically connected to the first negative tab bundle (as shown in FIG. 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 plate 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 configured to facilitate the connection of the first negative plate 1221 to an external load, the second adapter 14 is configured to facilitate the connection of the second negative plate 1222 to the first discharge controller 20, and the third adapter 15 is configured to facilitate the connection of the positive plate 121 to an external load.

[0071] As shown in FIG. 5, the embodiments of the present application further provide a power-using device 1000, which comprises the electrochemical device 100 according to any one of the preceding embodiments.

[0072] In some embodiments, the power-using device 1000 includes but is not limited to a notebook computer, a mobile phone, a power tool, and a power toy.

[0073] To verify the effects of the settings 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.

[0074] The experiments included 2 groups of comparative examples and 18 groups of embodiments, each group of comparative examples and each group of embodiments including 20 electrochemical devices 100, the electrochemical devices 100 in the embodiments 1-18 each including two discharge controllers, i.e., the first discharge controller 20 and the second discharge controller 30, the first discharge controller 20 being electrically connected to all the second negative electrode sheets 1222, and the second discharge controller 30 being electrically connected to all the positive electrode sheets 121; the electrochemical devices 100 in the comparative examples each including only one discharge controller, the discharge controller being electrically connected to all the positive electrode sheets 121, the electrode assemblies 12 of the electrochemical devices 100 in each group of comparative examples and each group of embodiments each including 21 positive electrode sheets 121 and 20 negative electrode sheets 122, the 20 negative electrode sheets 122 in each electrode assembly 12 in the comparative examples each having the same mass content of silicon element, the 20 negative electrode sheets 122 in each electrode assembly 12 in the embodiments each including a number of first negative electrode sheets 1221 having a mass content of silicon element of N1 and a number of second negative electrode sheets 1222 having a mass content of silicon element of N2, each negative electrode sheet 122 in the comparative examples and each negative electrode sheet 122 in the embodiments each having the same capacity, each positive electrode sheet 121 in the comparative examples and each positive electrode sheet 121 in the embodiments each having the same capacity, and each first negative electrode sheet 1221 and each second negative electrode sheet 1222 in each embodiment each having the same capacity. The capacity of the negative electrode sheets 122 was adjusted by changing the coating thickness of the negative electrode active material layer according to the gram capacity of the negative electrode active material in the negative electrode active material layer, in other words, the different negative electrode sheets 122 had negative electrode active material layers with different thicknesses according to the different contents of silicon element. Moreover, in each embodiment and comparative example, the content of silicon element in the secondary battery 10 was the same, i.e., the total mass of silicon element in all the negative electrode sheets 122 (the first negative electrode sheets 1221 and the second negative electrode sheets 1222) accounted for the same proportion of the total mass of the active material layer of all the negative electrode sheets 122 (the first negative electrode sheets 1221 and the second negative electrode sheets 1222).

[0075] In the comparative examples, the preparation process of the electrochemical device 100 included the following steps:

[0076] 1. Preparation of the positive electrode sheets 121:

[0077] 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 x 10 5) The positive electrode active material, the conductive agent, and the binder were mixed in a mass ratio of 94:3:3, N-methylpyrrolidone (NMP) was added as a solvent, and the positive electrode slurry was stirred in a vacuum stirrer until the solid content was 75 wt% and the system was uniform. An aluminum foil with a thickness of 8 μm was selected as the positive electrode current collector 1211, and the positive electrode inner tab was cut out of the aluminum foil. The positive electrode slurry was uniformly coated on one surface of the positive electrode current collector 1211 aluminum foil, and was dried at 110°C to obtain a positive electrode sheet 121 with a single-sided coated positive electrode active material layer 1212 (thickness 80 μm). Then, the above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet 121 with a double-sided coated positive electrode active material layer 1212.

[0078] 2. Preparation of the negative electrode sheet 122

[0079] The negative electrode active material graphite powder, silicon powder, conductive agent conductive carbon black (Super P), and binder styrene-butadiene rubber (SBR) were mixed in a certain mass ratio, and then deionized water was added as a solvent to prepare a negative electrode slurry with a solid content of 50 wt% and to stir uniformly. A copper foil with a thickness of 5 μm was selected as the negative electrode current collector, and the negative electrode inner tab was cut out of the copper foil. The negative electrode slurry was uniformly coated on one surface of the negative electrode current collector copper foil, and was dried at 90°C to obtain a single-sided negative electrode sheet 122. Then, the above steps were repeated on the other surface of the negative electrode sheet 122 to obtain a negative electrode sheet 122 with a double-sided coated negative electrode active material layer.

[0080] 3. Preparation of the separator film

[0081] A polyethylene (PE) porous film with a thickness of 8 μm was used as the separator film 123.

[0082] 4. Preparation of the electrolyte

[0083] In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solution, and then lithium salt lithium hexafluorophosphate was dissolved and mixed uniformly in the organic solvent to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0084] 5. Preparation of the secondary battery

[0085] The isolation film 123, the positive electrode sheet 121, the isolation film 123, and the negative electrode sheet 122 prepared above are stacked in order to form a laminated structure, and the outermost electrode sheet at both ends of the laminated structure is the positive electrode sheet 121. The electrode assembly 12 is hot-pressed at a pressure of 5 MPa and a temperature of 65°C for 10 s. The negative tabs are connected to form a negative tab bundle, and the positive tabs 1213 are connected to form a positive tab bundle 1213. The electrode assembly 12 is placed in an aluminum-plastic film packaging bag, and the two adapters mentioned above protrude from the top sealing edge of the packaging bag. After removing the moisture at 80°C, the electrolyte is injected and packaged.

[0086] 6. Connecting the discharge controller

[0087] The discharge controller is connected to the adapter connecting the positive tabs 1213.

[0088] The preparation process of the electrochemical device 100 in the examples is basically the same as that of the comparative examples. The difference is that the content of silicon element in each negative electrode sheet 122 in the comparative examples is the same, which is recorded as the silicon content of the first negative electrode sheet 1221 and the silicon content of the second negative electrode sheet 1222 in Table 1. The negative electrode sheets 122 in the examples have two kinds of silicon content according to the different mixing proportions of the negative electrode active material, wherein the first negative electrode sheet 1221 has a lower mass content of silicon element, and the second negative electrode sheet 1222 has a higher mass content of silicon element. 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 (the first discharge controller 20), and the third adapter 15 is connected to a discharge controller (the second discharge controller 30).

[0089] After the preparation of the electrochemical device 100 in the comparative examples and the examples, each electrochemical device 100 is subjected to discharge capacity test, capacity retention rate test after 500 cls, and lithium battery expansion ratio test after 500 cls.

[0090] The process of the discharge capacity test is as follows:

[0091] The electrochemical device 100 was placed in a constant temperature oven at 25℃±2℃ for 30 minutes to allow the secondary battery 10 to reach a constant temperature. The electrochemical device 100 reaching a constant temperature was charged at a constant current of 0.5C to a voltage of a full charge voltage, and then charged at a constant voltage of the full charge voltage to a current of 0.05C, and discharged at 0.2C to a voltage of a discharge controller start, and the discharge capacity was recorded. Among them, the electrochemical device 100 in the comparative example only has one discharge controller, and the cut-off voltage is recorded in the second cut-off voltage column in Table 1.

[0092] The process of the capacity retention rate test after 500 cycles is as follows:

[0093] The process of the discharge capacity test described above was repeated 500 times, and the discharge capacity of the 500th time was recorded. The discharge capacity of the 500th time was divided by the value of the discharge capacity of the first time to obtain the capacity retention rate after 500 cycles.

[0094] The process of the expansion ratio after 500 cycles is as follows:

[0095] (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 the condition of a force of 700g;

[0096] (2) After the discharge capacity test after 500 cycles, the thickness of the secondary battery 10 in the electrochemical device 100 was measured again using a flat plate thickness gauge (PPG) under the condition of a force of 700g.

[0097] After the experiment, the following Table 1 was obtained, and the values of the discharge capacity, the capacity retention rate after 500 cycles, and the expansion ratio after 500 cycles in Table 1 are the average values of the corresponding parameters of 20 electrochemical devices in the same group.

[0098] Table 1 Note: " / " in Table 1 means no data. N1: mass content of silicon element in the first negative active material layer; N2: mass content of silicon element in the second negative active material layer.

[0099] From the comparison between Comparative Example 1 and Examples 1-18, it can be seen that by setting the first voltage controller, the first negative tab 1221 and the positive tab 121 can continue to discharge after the second negative tab 1222 stops discharging, which is conducive to improving the discharge capacity of the electrochemical device 100. From the comparison between Comparative Example 2 and Examples 1-18, it can be seen that by setting the first voltage controller and the second voltage controller, the first negative tab 1221 and the second negative tab 1222 are discharged to different cut-off voltages, which is conducive to improving the cut-off voltage of the electrochemical device 100 while taking into account the capacity retention rate and the expansion ratio of the electrochemical device 100 after long cycles.

[0100] From the comparison between Comparative Example 1 and Examples 1-4, it can be seen that when the second cut-off voltage U2 satisfies 3.0 V≤U2≤3.3 V, the discharge capacity of the electrochemical device 100 is further improved compared with Comparative Example 1 as the value of U2 decreases, and the capacity retention rate after 500 cycles and the expansion ratio of 500 cycles have no obvious change compared with Comparative Example 1. It can be seen that setting U2≥3.0 V, the second cut-off voltage is not too low, which is conducive to reducing the possibility of over-discharge of the electrochemical device 100; setting U2≤3.3 V, the second cut-off voltage is not too high, which is conducive to improving the discharge capacity of the electrochemical device 100. From the comparison between Comparative Example 1 and Examples 4-7, it can be seen that when the first cut-off voltage U1 satisfies 3.1 V≤U1≤3.4 V, the discharge capacity of the electrochemical device 100 is further improved compared with Comparative Example 1, and as the value of U1 decreases, the capacity retention rate after 500 cycles decreases slightly, and the expansion ratio of 500 cycles increases slightly. It can be seen that setting U1≥3.1 V, 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 charging and discharging process on the cycle life of the electrochemical device 100; setting U1≤3.4 V, the first cut-off voltage is not too high, which is conducive to improving the discharge capacity of the electrochemical device 100. From the comparison between Example 4 and Examples 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 500 cycles gradually decreases, and the expansion ratio of 500 cycles gradually increases. It can be seen that setting N1≥0wt%, which is conducive to improving the capacity of the electrochemical device 100, and setting N1≤3wt%, which is conducive to reducing the influence of the volume change of the first negative electrode sheet 1221 during the charging and discharging process on the cycle life of the electrochemical device 100. When N1 satisfies 0wt%≤N1≤1wt%, the capacity, cycle performance, and expansion performance of the electrochemical device are all good.

[0101] 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 cycles has a trend of decreasing, and the expansion ratio after 500 cycles 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 during charging and discharging 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.

[0102] 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 cycles has a trend of decreasing, and the expansion ratio after 500 cycles 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 probability of problems occurring in the electrochemical device 100 during long cycles has a trend of increasing. Therefore, setting A1 / A≤80% is beneficial to reducing the influence of the volume change of the second negative electrode sheet 1222 during charging and discharging 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.

[0103] 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 by, The electrode assembly comprises 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 are stacked to form a laminated structure, and the separator film is arranged between adjacent positive electrode sheets and 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 arranged 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 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 is arranged 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 in the first negative electrode active material layer is N1, N1≥0, and 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 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 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 in the second negative electrode active material layer is N2, N2>N1, and 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, 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 is electrically connected to the input end of the first discharge controller, the first discharge controller further has an output end, and 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 the discharge voltage of the electrode assembly is equal to or less than a first cutoff voltage U1, and the unit of U1 is V.

2. The electrochemical device of claim 1, wherein, 0wt%≤N1≤3wt%.

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

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

5. The electrochemical device of claim 4, wherein 8wt%≤N2≤13wt%.

6. The electrochemical device of 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 of claim 1, wherein 3.1V≤U1≤3.4V.

8. The electrochemical device of any one of claims 1-7, wherein, The electrochemical device comprises a second discharge controller, the other end of the first negative electrode tab is electrically connected to the input end of the second discharge controller, the second discharge controller further has an output end, the second discharge controller is configured to disconnect the electrical connection between the first negative electrode 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 cutoff voltage U2, the unit of U2 is V, and U2 9. The electrochemical device of claim 8, wherein, The second cutoff voltage is U2, and 3.0V≤U2≤3.3V.

10. The electrochemical device of 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 of claim 1, wherein, The electrochemical device comprises: a first adapter, the other end of the first negative tab being connected to form a first negative tab bundle, the first adapter electrically connecting the first negative tab bundle; a second adapter, the other end of the second negative tab being connected to form a second negative tab bundle, the second adapter electrically connecting the second negative tab bundle, the second negative tab being electrically connected to the first discharge controller through the second adapter; a third adapter, the other end of the positive tab being connected to form a positive tab bundle, the third adapter electrically connecting the positive tab bundle.

12. The electrochemical device of any one of claims 1-7, wherein, the electrochemical device comprising a second discharge controller, the other end of the positive tab being electrically connected to an input end of the second discharge controller, the second discharge controller further having an output end; the second discharge controller being configured to disconnect the electrical connection between the positive 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 being in units of V, and U2 < U1.

13. An electrical device, characterized by an electrochemical device as claimed in any one of claims 1 to 12.

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