Secondary battery and electric device

Abstract

The application discloses a secondary battery and an electric device, comprising an electrode assembly, a first conductive piece and a first adapter. The electrode assembly comprises a plurality of pole pieces and a separator. The plurality of pole pieces comprises a first pole piece, and the first pole piece is located at the outermost layer of the electrode assembly. The secondary battery further comprises a first tab, the first pole piece comprises a first current collector and a first active material layer, the first tab is connected to the first current collector, and the first active material layer is arranged on the first current collector. The first tab is provided with a first through hole extending along the thickness direction of the first tab. The first conductive piece is arranged in the first through hole, and the first adapter is connected to the first conductive piece. The secondary battery further comprises a first coating layer, the first coating layer has conductivity, the first coating layer separates the first tab from a second tab, separates the first tab from the first conductive piece, and separates the first tab from the first adapter, and the first coating layer is in contact with the first conductive piece. The secondary battery is beneficial to reducing the possibility of lithium precipitation of the first pole piece.

Description

TECHNICAL FIELD

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

[0002] The outermost electrode group of the electrode assembly in the secondary battery is usually coated with an active material layer on only one side of the current collector, and the inner electrode group is coated with an active material layer on both sides of the current collector, so as to fully utilize the active material layer, reduce the material cost, and improve the energy density of the battery. SUMMARY

[0003] For the secondary battery in the prior art, the inventors find that, since the outermost electrode group is coated with a single layer, and the inner electrode group is coated with a double layer, and the proportions of various substances in the active material layers of the inner and outer electrode groups are generally the same, the electrical conductivity of the outermost electrode group is greater than that of the inner electrode group, the current density of the outermost electrode group is significantly higher than that of the inner electrode group, and the consumption speed of the electrolyte at the outermost electrode group is faster during the cycle of the secondary battery, so that lithium is easily deposited on the outermost electrode group, resulting in the decrease of the cycle performance and the safety performance of the secondary battery.

[0004] In view of the above situation, it is necessary to provide a secondary battery capable of reducing the current density of the outermost electrode group of the electrode assembly, so as to reduce lithium deposition.

[0005] A first aspect of embodiments of the present application provides a secondary battery, comprising an electrode assembly, a first conductive member, and a first adapter. The electrode assembly comprises a plurality of electrode sheets and a separator, the plurality of electrode sheets are stacked along a first direction, any two adjacent electrode sheets have opposite polarities, and the separator is arranged between any two adjacent electrode sheets; the first direction is the thickness direction of the electrode sheets. The plurality of electrode sheets comprises a first electrode sheet with the same polarity, at least one second electrode sheet, and a third electrode sheet, the first electrode sheet and the third electrode sheet are respectively located at the two outermost layers of the electrode assembly, and the second electrode sheet is located between the first electrode sheet and the third electrode sheet. The secondary battery further comprises a first tab, a second tab, and a third tab. The first electrode sheet comprises a first current collector and a first active material layer, the first tab is connected to the first current collector, the first active material layer is arranged on the first current collector, and the first active material layer faces the inside of the electrode assembly. The second electrode sheet comprises a second current collector and two second active material layers, the second tab is connected to the second current collector, and the two second active material layers are respectively arranged on the two surfaces of the second current collector which are oppositely arranged along the first direction. The third tab is connected to the third electrode sheet. The first tab, the second tab, and the third tab are stacked, and the first tab is provided with a first through hole extending along the thickness direction thereof. The first conductive member is arranged in the first through hole, and the first conductive member is electrically connected to all the second tabs and the third tab. The first adapter is connected to the first conductive member. The first tab has a first surface and a second surface oppositely arranged along the thickness direction thereof, the first surface faces the second tab, and the first adapter is located on the side of the first tab with the second surface. The secondary battery further comprises a first coating layer, the first coating layer has electrical conductivity, and the first coating layer comprises a first portion, a second portion, and a third portion connected to each other. The first portion is arranged on the first surface to separate the first tab from the second tab. The second portion covers the surrounding wall of the first through hole to separate the first tab from the first conductive member. The third portion is arranged on the second surface to separate the first tab from the first adapter. The first coating layer contacts the first conductive member.

[0006] In the secondary battery, the first tab is provided with the first through hole to accommodate the first conductive member, the first coating layer connects the first tab and the first conductive member, and the first coating layer separates the first tab from the second tab, separates the first tab from the first conductive member, and separates the first tab from the first adapter, so that the secondary battery forms a series connection of the first tab and the first coating layer, and the whole of the first tab and the first coating layer is connected in parallel with the second tab and the third tab, thereby facilitating the reduction of the current density through the first electrode sheet, slowing down the consumption speed of the electrolyte, and reducing the possibility of lithium precipitation in the first electrode sheet.

[0007] In an optional embodiment of the application, the secondary battery comprises a second conductive member, the third tab is provided with a second through hole extending in the first direction, and the second conductive member is arranged in the second through hole and electrically connected to all the second tabs. The third tab has a third surface and a fourth surface oppositely arranged in the first direction, and the fourth surface faces the second tab. The electrode assembly further comprises a second coating layer having electrical conductivity, and the second coating layer comprises a fourth portion and a fifth portion connected to each other; the fourth portion is arranged on the fourth surface to separate the third tab from the second tab; and the fifth portion covers the surrounding wall of the second through hole to separate the third tab from the second conductive member, and the second coating layer contacts the second conductive member. In this way, the second coating layer is connected in series with the third tab, and the third tab, the whole of the second coating layer, the second tab, the whole of the first tab and the first coating layer are connected in parallel, thereby facilitating reduction of the current density of the third tab to reduce the possibility of lithium precipitation in the third tab.

[0008] A second aspect of the application provides a secondary battery comprising an electrode assembly, a first conductive member and a first adapter. The electrode assembly comprises a plurality of tabs and a separator, the plurality of tabs are arranged in a stack in a first direction, any two adjacent tabs have opposite polarities, and a separator is arranged between any two adjacent tabs; the first direction is the thickness direction of the tabs. The plurality of tabs comprises a first tab having the same polarity, at least one second tab and a third tab, the first tab and the third tab are respectively located at the two outermost layers of the electrode assembly, and the second tab is located between the first tab and the second tab. The electrode assembly further comprises a first tab, a second tab and a third tab, the first tab comprises a first current collector and a first active material layer, the first tab is connected to the first current collector, the first active material layer is arranged on the first current collector, and the first active material layer faces the inside of the electrode assembly; the second tab comprises a second current collector and a second active material layer, the second tab is connected to the second current collector, and the second active material layer is arranged on two surfaces of the second current collector oppositely arranged in the first direction; the third tab is connected to the third tab. The first tab, the second tab and the third tab are arranged in a stack, and the first tab is provided with a first through hole extending in the thickness direction thereof. The first conductive member is arranged in the first through hole, and the first conductive member is electrically connected to all the second tabs and the third tabs; the first adapter is connected to the third tab. The first tab has a first surface and a second surface oppositely arranged in the thickness direction thereof, and the first surface faces the second tab. The electrode assembly further comprises a first coating layer having electrical conductivity, and the first coating layer comprises a first portion and a second portion connected to each other; the first portion is arranged on the first surface to separate the first tab from the second tab; the second portion covers the surrounding wall of the first through hole to separate the first tab from the first conductive member; and the first coating layer contacts the first conductive member.

[0009] In the secondary battery, the first tab is provided with a first through hole to accommodate the first conductive member, the first coating connects the first tab and the first conductive member, and the first coating also separates the first tab and the second tab, so that the secondary battery forms a series connection of the first tab and the first coating, and the whole of the first tab and the first coating is connected in parallel with the second tab and the third tab, thereby facilitating the reduction of the current density through the first tab, slowing down the consumption rate of the electrolyte, and reducing the possibility of lithium precipitation on the first tab.

[0010] In an optional embodiment of the present application, the thickness of the first portion is T1, and 3pm≤T1≤10pm. By setting T1≥3pm, the thickness of the first portion is not too small, which facilitates the reduction of process difficulty, and the resistance of the first portion is not too large, which facilitates the reduction of the heat generated by the first portion during the use of the secondary battery, thereby improving safety and the discharge capacity of the secondary battery; by setting T1≤10pm, the thickness of the first portion is not too large, which on the one hand facilitates the reduction of the space occupied by the first portion in the shell, thereby reducing the impact on the energy density of the secondary battery, and on the other hand, facilitates the improvement of the resistance of the first portion.

[0011] In an optional embodiment of the present application, the first current collector includes a fifth surface and a sixth surface oppositely arranged along the first direction, the first active material layer is arranged on the fifth surface, and the first coating covers at least part of the surface of the sixth surface. By arranging the first coating on at least part of the surface of the sixth surface, the strength of the first tab is improved, and the curling of the first tab is reduced or eliminated.

[0012] In an optional embodiment of the present application, the total resistance of the first tab and the first current collector is R1, the resistance of the first coating is R2, and R1≤R2≤20R1. By setting R2≥R1, the resistance of the first coating relative to the first tab and the first current collector is not too small, which facilitates the reduction of the current density of the first tab and the reduction of lithium precipitation; by setting R2≤20R1, the resistance of the first coating relative to the first tab and the first current collector is not too large, which on the one hand facilitates the reduction of the difficulty of material selection of the first coating, and on the other hand, the thickness of the first coating is not too thin, which facilitates the reduction of process difficulty, and also facilitates the reduction of the loss of electric energy of the first coating and the improvement of the discharge capacity of the secondary battery.

[0013] In an optional embodiment of the present application, 5R1≤R2≤10R1. R2≥5R1 is set, the resistance of the first coating layer relative to the first tab and the first current collector is not too small, which is conducive to further reducing the current density of the first tab and reducing lithium precipitation; R2≤20R1 is set, the resistance of the first coating layer relative to the first tab and the first current collector is not too large, on the one hand, it is conducive to further reducing the difficulty of material selection of the first coating layer, on the other hand, the thickness of the first coating layer is not too thin, which is conducive to further reducing the process difficulty and further improving the discharge capacity of the secondary battery.

[0014] In an optional embodiment of the present application, 1mΩ≤R1≤10mΩ. R1≥1mΩ is set, the value of R1 is not too small, which is conducive to reducing the difficulty of material selection and preparation, and reducing the current density of the first tab; R1≤10mΩ is set, the value of R1 is not too large, which is conducive to reducing the energy consumption and heat generation inside the secondary battery and improving the efficiency of the secondary battery.

[0015] In an optional embodiment of the present application, the total resistance of the first tab, the first tab and the first coating layer is R3, the total resistance of any second tab and the second tab corresponding to it is R4, and 0.65R4≤R3≤15R4. R3≥0.65R4 is set, the total resistance of the first tab, the first tab and the first coating layer is not too small, which is conducive to reducing the current density of the first tab, thereby reducing the possibility of lithium precipitation of the first tab; R3≤15R4 is set, the total resistance of the first tab, the first tab and the first coating layer is not too large, which is conducive to the release of the capacity of the first tab, thereby improving the discharge capacity of the secondary battery.

[0016] In an optional embodiment of the present application, the material of the first coating layer includes a main material; the material of the main material includes at least one of silicon dioxide, aluminum oxide, zinc oxide, tin oxide, indium tin oxide, titanium oxide, iron oxide, silicon nitride, titanium nitride, aluminum nitride, silicon carbide, tungsten carbide and titanium carbide.

[0017] In an optional embodiment of the present application, the first coating layer includes a third part, and the third part is arranged on the second surface. The first conductive part includes a first connecting part and a second connecting part, the first connecting part is arranged through the first through hole, and the second connecting part is located on the side of the first tab having the second surface. The second connecting part and the third part are arranged in a stacked manner along the thickness direction of the first tab. By arranging the second connecting part and the third part in a stacked manner, a stable electrical connection is formed between the first conductive part and the first coating layer, which is conducive to stably reducing the current density of the first tab and reducing the possibility of lithium precipitation of the first tab.

[0018] The third aspect of the embodiments of the present application provides a kind of electric equipment, including the secondary battery as described in any one of the preceding embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a schematic view of a structure of a secondary battery in one embodiment of the present application.

[0020] Figure 2 is Figure 1 is a schematic view of a cross-sectional structure at II-II in FIG. 1.

[0021] Figure 3 is Figure 1 is a schematic view of a cross-sectional structure at III-III in FIG. 1.

[0022] Figure 4 is Figure 2 is an enlarged view of A in FIG. 1.

[0023] Figure 5 is a schematic view of a partial structure of a secondary battery in one embodiment of the present application.

[0024] Figure 6 is a schematic view of a structure of a first conductive member in one embodiment of the present application.

[0025] Figure 7 is a schematic view of a structure of a first electrode sheet in one embodiment of the present application.

[0026] Figure 8 is Figure 7 is a schematic view of a cross-sectional structure at VIII-VIII in FIG. 1.

[0027] Figure 9 is a schematic view of a structure of an electric device in one embodiment of the present application.

[0028] Explanation of Main Element Symbols

[0029] 100, secondary battery; 10, case; 20, electrode assembly; 21, electrode sheet; 210, positive electrode sheet; 211, positive current collector; 212, positive active material layer; 213, insulating layer; 220, negative electrode sheet; 221, negative current collector; 222, negative active material layer; 201, first electrode sheet; 2011, first current collector; 2011a, fifth surface; 2011b, sixth surface; 2012, first active material layer; 202, second electrode sheet; 2021, second current collector; 2022, second active material layer; 203, third electrode sheet; 22, separator; 30, tab; 31, positive tab; 32, negative tab; 301, first tab; 301a, first surface; 301b, second surface; 3011, first through-hole; 302, second tab; 303, third tab; 303a, third surface; 303b, fourth surface; 3031, second through-hole; 40, first conductive member; 41, first connecting portion; 42, second connecting portion; 50, first relay member; 60, first coating layer; 61, first portion; 62, second portion; 63, third portion; 70, second relay member; 80, second conductive member; 90, second coating layer; 91, fourth portion; 92, fifth portion; 1000, electric device; X, first direction.

[0030] The following detailed description will further describe the present application with reference to the above drawings. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments of the present application.

[0032] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element or can exist with a middle element. When an element is considered to be "provided" on another element, it can be directly provided on the other element or can exist with a middle element. The specific meanings of the above terms in the present application can be understood by those skilled in the art according to the specific circumstances.

[0033] 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 herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application.

[0034] In the description of the embodiments of the present application, the technical terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0035] In the description of the embodiments of the present application, the term "vertical" is used to describe the ideal state between two components. In the actual production or use state, there can be a state similar to vertical between the two components. The two components described as "vertical" can not be an absolute straight line, plane, but can be approximately a straight line or plane, and as a whole, the overall extension direction is a straight line or plane, which can be considered as a "straight line" or "plane".

[0036] Reference herein to "an 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 occurrence of the phrase in various places in the specification is not necessarily all referring to the same embodiment, nor is it necessarily referring to a separate or alternative embodiment, provided it does not contradict itself. The various embodiments in the present application can be combined with each other, provided they do not conflict.

[0037] A first aspect of embodiments of the present application provides a secondary battery, comprising an electrode assembly, a first conductive member and a first adapter. The electrode assembly comprises a plurality of electrode sheets and a separator, the plurality of electrode sheets are arranged in a stack along a first direction, any two adjacent electrode sheets have opposite polarities, and the separator is arranged between any two adjacent electrode sheets; the first direction is a thickness direction of the electrode sheets. The plurality of electrode sheets comprises a first electrode sheet, at least one second electrode sheet and a third electrode sheet, the first electrode sheet and the third electrode sheet are respectively located at two outermost layers of the electrode assembly, and the second electrode sheet is located between the first electrode sheet and the third electrode sheet. The secondary battery further comprises a first tab, a second tab and a third tab, the first electrode sheet comprises a first current collector and a first active material layer, the first tab is connected to the first current collector, the first active material layer is arranged on the first current collector, and the first active material layer faces an inside of the electrode assembly; the second electrode sheet comprises a second current collector and two second active material layers, the second tab is connected to the second current collector, and the two second active material layers are respectively arranged on two surfaces of the second current collector which are oppositely arranged along the first direction; and the third tab is connected to the third electrode sheet. The first tab, the second tab and the third tab are arranged in a stack, the first tab is provided with a first through hole extending along a thickness direction of the first tab. The first conductive member is arranged in the first through hole, and the first conductive member is electrically connected to all the second tabs and the third tab. The first adapter is connected to the first conductive member. The first tab has a first surface and a second surface which are oppositely arranged along the thickness direction of the first tab, the first surface faces the second tab, and the first adapter is located on a side of the first tab having the second surface. The secondary battery further comprises a first coating layer, the first coating layer has electrical conductivity, and the first coating layer comprises a first portion, a second portion and a third portion which are connected to each other. The first portion is arranged on the first surface to separate the first tab from the second tab. The second portion covers a surrounding wall of the first through hole to separate the first tab from the first conductive member. The third portion is arranged on the second surface to separate the first tab from the first adapter. The first coating layer contacts the first conductive member.

[0038] In the secondary battery, the first tab is provided with the first through hole to accommodate the first conductive member, the first coating layer connects the first tab and the first conductive member, and the first coating layer separates the first tab from the second tab, separates the first tab from the first conductive member, and separates the first tab from the first adapter, so that the secondary battery forms an electrical connection structure in which the first tab and the first coating layer are connected in series, and the whole of the first tab and the first coating layer and the second tab and the third tab are connected in parallel, thereby facilitating reduction of the current density passing through the first electrode sheet, slowing down the consumption speed of the electrolyte, and reducing the possibility of lithium precipitation in the first electrode sheet.

[0039] Embodiments of the present application will be further described below with reference to the drawings.

[0040] As Figure 1 and Figure 2As shown, the embodiments of the present application provide a secondary battery 100, which comprises a shell 10 and an electrode assembly 20, the electrode assembly 20 is accommodated in the shell 10.

[0041] In some embodiments, the shell 10 is a flexible packaging bag, for example, an aluminum plastic film. In other embodiments, the shell 10 is a hard shell, for example, a plastic shell, and for example, a metal shell comprising at least one of a steel alloy, an aluminum alloy, a copper alloy.

[0042] In some embodiments, as shown, Figure 2 The electrode assembly 20 comprises a plurality of pole pieces 21 and a separator film 22, the plurality of pole pieces 21 are stacked along a first direction X, any two adjacent pole pieces 21 have opposite polarities, and a separator film 22 is arranged between any two adjacent pole pieces 21, and the first direction X is the thickness direction of the pole piece 21. Specifically, according to the different polarities, part of the plurality of pole pieces 21 are positive pole pieces 210, and the other part are negative pole pieces 220.

[0043] In some embodiments, the pole piece 21 comprises a current collector and an active material layer. For the pole piece 21 located at the outermost layer of the electrode assembly 20, the active material layer is arranged on one surface of the current collector along the first direction X, and the active material layer faces the inside of the electrode assembly 20; for the pole piece 21 located between the two outermost pole pieces 21, the active material layer is arranged on both surfaces of the current collector along the first direction X. Among them, according to the different polarities of the pole piece 21, the current collector is divided into positive current collector 211 and negative current collector 221, and the active material layer is divided into positive active material layer 212 and negative active material layer 222.

[0044] In the foregoing, the determination of "the outermost layer" is determined according to the mutual positional relationship between the plurality of pole pieces 21, in other words, the relative positional relationship between the separator film 22 and the pole piece 21 is not considered. For example, the outer side of the outermost pole piece 21 can also be provided with a separator film 22.

[0045] Specifically, as shown, Figure 2 The positive pole piece 210 comprises a positive current collector 211 and a positive active material layer 212, and the positive active material layer 212 is arranged on one side or both sides of the positive current collector 211 along the first direction X. The negative pole piece 220 comprises a negative current collector 221 and a negative active material layer 222, and the negative active material layer 222 is arranged on one side or both sides of the negative current collector 221 along the first direction X.

[0046] In some embodiments, at least one of the positive current collector 211 and the negative current collector 221 is a metal layer. As an exemplary example, the positive current collector 211 can be a metal layer comprising at least one of aluminum, nickel, tantalum, titanium, for example, an aluminum foil. The negative current collector 221 can be a metal layer comprising at least one of copper, nickel, tantalum, titanium, for example, a copper foil.

[0047] In some embodiments, at least one of the positive current collector 211 and the negative current collector 221 is a composite current collector.

[0048] In some embodiments, the positive active material layer 212 includes a positive active material. The positive active material includes 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.

[0049] In some embodiments, the negative active material layer 222 includes a negative active material. The negative active material includes at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen material, silicon-carbon material.

[0050] In some embodiments, as shown in FIG. 2, the positive tab 210 further includes an insulating layer 213 disposed on the edge of the positive current collector 211 connecting the positive lug 31, to reduce the possibility of the burr of the edge of the positive current collector 211 puncturing the separator film 22 to cause short circuit between the positive tab 210 and the negative tab 220. Figure 2

[0051] In some embodiments, the material of the insulating layer 213 includes a ceramic material and a binding agent.

[0052] In some embodiments, the ceramic material includes at least one of aluminum oxide, magnesium oxide, silicon nitride, silicon carbide, boehmite.

[0053] In some embodiments, as shown in FIG. 2, the secondary battery 100 further includes a plurality of lugs 30, each of which is connected to one of the tabs 21. Specifically, according to the polarity of the tab 21 connected, the lugs 30 are divided into positive lugs 31 and negative lugs 32, the positive lugs 31 being connected to the positive tab 210, and the negative lugs 32 being connected to the negative tab 220. Figure 2 Figure 3

[0054] In some embodiments, the separator film 22 is a polyethylene film, a polypropylene film, a polyester film, or a polyimide film, etc. capable of insulation.

[0055] In some embodiments, the secondary battery 100 includes an electrolyte (not shown in the figure), which is contained in the housing 10.

[0056] In some embodiments, the electrolyte includes an electrolyte salt. The electrolyte salt includes at least one of an organic lithium salt or an inorganic lithium salt.

[0057] ​​​In some embodiments, the electrolyte salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium hexafluorocesium oxide (LiCsF6), lithium perchlorate (LiClO4), or lithium trifluoromethanesulfonate (LiCF3SO3).

[0058] In some embodiments, such as Figure 2 As shown, the plurality of electrode plates 21 include a first electrode plate 201 with the same polarity, at least one second electrode plate 202 and a third electrode plate 203. The first electrode plate 201 and the third electrode plate 203 are respectively located on the two outermost layers of the electrode assembly 20, and the second electrode plate 202 is located between the first electrode plate 201 and the second electrode plate 202. The plurality of tabs 30 include a first tab 301, a second tab 302, and a third tab 303. The first electrode 201 includes a first current collector 2011 and a first active material layer 2012. The first tab 301 is connected to the first current collector 2011, and the first active material layer 2012 is disposed on the first current collector 2011, facing inwards towards the interior of the electrode assembly 20. The second electrode 202 includes a second current collector 2021 and a second active material layer 2022. The second tab 302 is connected to the second current collector 2021. Two second active material layers 2022 are provided, respectively disposed on two opposing surfaces of the second current collector 2021 along a first direction X. The third tab 303 is connected to the third electrode 203. The first tab 301, second tab 302, and third tab 303 are stacked. The first tab 301 has a first through hole 3011 extending along its thickness direction.

[0059] In some embodiments, such as Figure 4 and Figure 5As shown, the secondary battery 100 further comprises a first conductive member 40, a first adapter member 50, and a first coating layer 60. The first conductive member 40 is arranged in the first through hole 3011, and the first conductive member 40 is electrically connected to all the second tabs 302 and the third tabs 303. The first adapter member 50 is connected to the first conductive member 40. The first tab 301 has a first surface 301a and a second surface 301b arranged oppositely along the thickness direction of the first tab 301. The first surface 301a faces the second tab 302. The first adapter member 50 is located on the side of the first tab 301 having the second surface 301b. The first coating layer 60 has electrical conductivity. The first coating layer 60 comprises a first portion 61, a second portion 62, and a third portion 63 connected to each other. The first portion 61 is arranged on the first surface 301a to separate the first tab 301 from the second tab 302. The second portion 62 covers the surrounding wall of the first through hole 3011 to separate the first tab 301 from the first conductive member 40. The third portion 63 is arranged on the second surface 301b to separate the first tab 301 from the first adapter member 50. The first coating layer 60 contacts the first conductive member 40.

[0060] In this embodiment, taking the first tab 201, the second tab 202, and the third tab 203 as examples of the positive electrode tab 210, the path of the current is as follows: the current flows from the first adapter member 50 to the first conductive member 40, and then flows to the electrode tab 21 through three parallel paths. One of the paths is that the current flows from the first conductive member 40 to the first coating layer 60, and then flows to the first tab 301 and the first tab 201 in sequence. Another of the paths is that the current flows from the first conductive member 40 to the second tab 302 and the second tab 202 in sequence. The third of the paths is that the current flows from the first conductive member 40 to the third tab 303 and the third tab 203. It can be seen that the first coating layer 60 and the first tab 301 are in series connection, and the total resistance of the first tab 301 and the first coating layer 60 is higher than the resistance value of the first tab 301. Compared with the state without the first coating layer 60, the current density of the first tab 201 decreases.

[0061] In this embodiment, the first tab 301 is provided with the first through hole 3011 to accommodate the first conductive member 40. The first coating layer 60 separates the first tab 301 from the second tab 302, separates the first tab 301 from the first conductive member 40, and separates the first tab 301 from the first adapter member 50. As a result, the secondary battery 100 forms the electric connection structure in which the first tab 301 and the first coating layer 60 are in series connection, and the whole of the first tab 301 and the first coating layer 60 and the second tab 302 and the third tab 303 are in parallel connection. This is conducive to reducing the current density through the first tab 201 and slowing down the consumption speed of the electrolyte, so as to reduce the possibility of lithium precipitation in the first tab 201.

[0062] In some embodiments, asFigure 2 and Figure 5 As shown in FIG. 1, the secondary battery 100 includes the second conductive member 80, the third tab 303 is provided with a second through hole 3031 extending along the first direction X, the second conductive member 80 is disposed through the second through hole 3031, and the second conductive member 80 is electrically connected to all the second tabs 302. The third tab 303 has a third surface 303a and a fourth surface 303b oppositely arranged along the first direction X, and the fourth surface 303b faces the second tab 302. The electrode assembly 20 further includes a second coating layer 90 having electrical conductivity, the second coating layer 90 includes a fourth portion 91 and a fifth portion 92 connected to each other; the fourth portion 91 is arranged on the fourth surface 303b to separate the third tab 303 from the second tab 302; and the fifth portion 92 covers the surrounding wall of the second through hole 3031 to separate the third tab 303 from the second conductive member 80, and the second coating layer contacts the second conductive member 80. In this way, the second coating layer is connected in series with the third tab 303, and the third tab 303 and the whole of the second coating layer, the second tab 302, and the whole of the first tab 301 and the first coating layer 60 are connected in parallel, thereby facilitating the reduction of the current density of the third tab 203 to reduce the possibility of lithium precipitation on the third tab 203.

[0063] In some embodiments, the secondary battery 100 further includes a first conductive member 40, a first adapter 50, and a first coating layer 60. The first conductive member 40 is disposed through the first through hole 3011, and the first conductive member 40 is electrically connected to all the second tabs 302 and the third tab 303; the first adapter 50 is connected to the third tab 303. The first tab 301 has a first surface 301a and a second surface 301b oppositely arranged along the thickness direction thereof, and the first surface 301a faces the second tab 302. The electrode assembly 20 further includes the first coating layer 60 having electrical conductivity, the first coating layer 60 includes a first portion 61 and a second portion 62 connected to each other; the first portion 61 is arranged on the first surface 301a to separate the first tab 301 from the second tab 302; the second portion 62 covers the surrounding wall of the first through hole 3011 to separate the first tab 301 from the first conductive member 40; and the first coating layer 60 contacts the first conductive member 40.

[0064] In this embodiment, taking the first tab 201, the second tab 202 and the third tab 203 as the positive electrode tab 210 as an example, the path of the current is: the current flows from the first adapter 50 to the third lug 303, the second lug 302 and the first conductive piece 40, at this time, the second lug 302 and the third lug 303 are in a parallel state, and the current of the first conductive piece 40 flows to the first lug 301 through the first coating layer 60. It can be known that the first coating layer 60 and the first lug 301 are in a series state, and the whole of the first lug 301 and the first coating layer 60 is in parallel with the second lug 302 and the third lug 303. Since the first coating layer 60 and the first lug 301 are in a series state, the total resistance of the first lug 301 and the first coating layer 60 is higher than the resistance value of the first lug 301, and compared with the state without the first coating layer 60, the current density of the first tab 201 decreases.

[0065] In this embodiment, the first lug 301 is provided with a first through hole 3011 for accommodating the first conductive piece 40, the first coating layer 60 connects the first lug 301 and the first conductive piece 40, and the first coating layer 60 also separates the first lug 301 and the second lug 302, so that the two secondary batteries 100 form an electrical connection structure in which the first lug 301 and the first coating layer 60 are in series, and the whole of the first lug 301 and the first coating layer 60 is in parallel with the second lug 302 and the third lug 303, thereby facilitating the reduction of the current density through the first tab 201, slowing down the consumption speed of the electrolyte, and reducing the possibility of lithium precipitation in the first tab 201.

[0066] In some embodiments, as shown in Figure 4 to Figure 6 The first coating layer 60 includes a third portion 63, and the third portion 63 is arranged on the second surface 301b. The first conductive piece 40 includes a first connecting portion 41 and a second connecting portion 42, the first connecting portion 41 is arranged through the first through hole 3011, and the second connecting portion 42 is located on the side of the first lug 301 having the second surface 301b. The second connecting portion 42 and the third portion 63 are arranged in a stacked manner along the thickness direction of the first lug 301. In order to facilitate the insertion of the first connecting portion 41 into the first through hole 3011, the size of the first connecting portion 41 is usually slightly smaller than the size of the remaining space of the first through hole 3011 covered by the second portion 62, and the electrical connection between the first connecting portion 41 and the second portion 62 may not be stable enough. By arranging the second connecting portion 42 and the third portion 63 in a stacked manner, it is beneficial to form a stable electrical connection between the first conductive piece 40 and the first coating layer 60, thereby stably reducing the current density through the first tab 201 and reducing the possibility of lithium precipitation in the first tab 201.

[0067] In some embodiments, as shown in Figure 6As shown, the first connecting portion 41 is cylindrical to fit the shape of the first through hole 3011. This helps to increase the contact area between the first connecting portion 41 and the second portion 62, thereby improving the stability of the electrical connection between them.

[0068] In some embodiments, the first connecting portion 41 is a hollow cylinder to save materials.

[0069] In some embodiments, such as Figure 6 As shown, the second connecting portion 42 is flat and cylindrical. The center of the second connecting portion 42 is approximately collinear with the center of the first through hole 3011, and the radius of the second connecting portion 42 is larger than the radius of the first through hole 3011. Thus, when connecting the first tab 301 and the first conductive element 40, after inserting the first connecting portion 41 into the first through hole 3011, the second connecting portion 42 can initially limit the position of the first conductive element 40, thereby reducing the difficulty of connection operations.

[0070] In some embodiments, the structure of the second conductive element 80 is the same as that of the first conductive element 40.

[0071] In some embodiments, the first conductive element 40, the first tab 301, the second tab 302, and the third tab 303 are welded together. Specific welding methods include, but are not limited to, laser welding and ultrasonic welding.

[0072] In some embodiments, such as Figure 2 As shown, the first tab 301, the second tab 302 and the third tab 303 are stacked and bent into a "U" shape to reduce the space occupied by the first tab 301 in the casing 10 of the secondary battery 100.

[0073] In some embodiments, the first adapter 50 is a flat, elongated metal piece, and a portion of the first adapter 50 extends out of the housing 10 to facilitate electrical connection of the secondary battery 100 to an external device.

[0074] In some embodiments, the first coating 60 covers the entire surface of the first tab 301. Thus, on the one hand, applying the first coating 60 to the entire surface of the first tab 301 without distinction reduces the difficulty of applying the first coating 60; on the other hand, it improves the coating quality of the first coating 60 and increases the resistance value that the first coating 60 can provide.

[0075] In some embodiments, the material of the first coating 60 includes a main material, which includes at least one of silicon dioxide, aluminum oxide, zinc oxide, tin oxide, indium tin oxide, titanium oxide, iron oxide, silicon nitride, titanium nitride, aluminum nitride, silicon carbide, tungsten carbide, and titanium carbide.

[0076] In some embodiments, the first coating 60 is coated on the surface of the first tab 301 by magnetron sputtering or vapor deposition.

[0077] In some embodiments, the material of the coating further comprises an adhesive.

[0078] In some embodiments, the thickness of the first portion 61 is T1, 3 μm≤T1≤10 μm. T1≥3 μm is set to prevent the thickness of the first portion 61 from being too small, which is conducive to reducing the process difficulty, and the resistance of the first portion 61 is not too large, which is conducive to reducing the heat generated by the first portion 61 during the use of the secondary battery 100, on the one hand, improving safety, and on the other hand, improving the discharge capacity of the secondary battery 100; T1≤10 μm is set to prevent the thickness of the first portion 61 from being too large, on the one hand, which is conducive to reducing the space occupied by the first portion 61 in the shell 10, so as to reduce the impact on the energy density of the secondary battery 100, and on the other hand, which is conducive to improving the resistance of the first portion 61.

[0079] In some embodiments, as shown in FIGS. 1A and 1B, the first coating 60 is coated on the surface of the first tab 301. Figure 7 and Figure 8 In some embodiments, as shown in FIGS. 1A and 1B, the first coating 60 is coated on the surface of the first tab 301.

[0080] In some embodiments, the total resistance of the first tab 301 and the first current collector 2011 is R1, the resistance of the first coating 60 is R2, and R1≤R2≤20R1. R2≥R1 is set to prevent the resistance of the first coating 60 relative to the first tab 301 and the first current collector 2011 from being too small, which is conducive to reducing the current density of the first tab 201 and reducing lithium precipitation; R2≤20R1 is set to prevent the resistance of the first coating 60 relative to the first tab 301 and the first current collector 2011 from being too large, on the one hand, which is conducive to reducing the difficulty of selecting the material of the first coating 60, and on the other hand, the thickness of the first coating 60 is not too thin, which is conducive to reducing the process difficulty, and also conducive to reducing the loss of electric energy of the first coating 60 and improving the discharge capacity of the secondary battery 100.

[0081] The measurement method of R1 and R2 is as follows:

[0082] Take the first pole piece 201, and the first pole piece 201 remains connected to the first tab 301 and the first coating layer 60;

[0083] Remove the first active material layer 2012 of the first pole piece 201;

[0084] Connect the first current collector 2011, the first tab 301, and the first coating layer 60 to a resistance measuring device (such as a multimeter). When connected, one connection terminal of the resistance measuring device is connected to the first current collector 2011, and the other terminal is connected to the first coating layer 60, so that the first current collector 2011, the first tab 301, and the first coating layer 60 are in series. Read the measurement result as R;

[0085] Remove the first coating layer 60, and connect the first current collector 2011 and the first tab 301 to a resistance measuring device (such as a multimeter). When connected, one connection terminal of the resistance measuring device is connected to the first current collector 2011, and the other terminal is connected to the first tab 301. Read the measurement result as R1;

[0086] Calculate R2, R2 = R - R1.

[0087] In some embodiments, 5R1≤R2≤10R1. R2≥5R1 is set so that the resistance of the first coating layer 60 relative to the first tab 301 and the first current collector 2011 is not too small, which is conducive to further reducing the current density of the first pole piece 201 and reducing lithium precipitation. R2≤20R1 is set so that the resistance of the first coating layer 60 relative to the first tab 301 and the first current collector 2011 is not too large, which is conducive to further reducing the difficulty of material selection of the first coating layer 60 on the one hand, and the thickness of the first coating layer 60 is not too thin on the other hand, which is conducive to further reducing the process difficulty and further improving the discharge capacity of the secondary battery 100.

[0088] In some embodiments, 1mΩ≤R1≤10mΩ. R1≥1mΩ is set so that the value of R1 is not too small, which is conducive to reducing the difficulty of material selection and preparation, and reducing the current density at the first pole piece 201; R1≤10mΩ is set so that the value of R1 is not too large, which is conducive to reducing the energy consumption and heat generation inside the secondary battery 100 and improving the efficiency of the secondary battery 100.

[0089] In some embodiments, the total resistance value of the first tab 201, the first lug 301 and the first coating layer 60 is R3, the total resistance value of any second tab 202 and the second lug 302 connected therewith is R4, and 0.65R4≤R3≤15R4. R3≥0.65R4 is set so that the total resistance value of the first tab 201, the first lug 301 and the first coating layer 60 is not too small, which is conducive to reducing the current density of the first tab 201 and thus reducing the possibility of lithium precipitation of the first tab 201; R3≤15R4 is set so that the total resistance value of the first tab 201, the first lug 301 and the first coating layer 60 is not too large, which is conducive to the release of the capacity of the first tab 201 and thus conducive to improving the discharge capacity of the secondary battery 100.

[0090] The measurement method of R3 and R4 is as follows:

[0091] Take the first tab 201, and the first tab 201 remains in a connected state with the first lug 301 and the first coating layer 60;

[0092] Connect the first tab 201, the first lug 301 and the first coating layer 60 to a resistance measuring device (e.g., a multimeter), and when connected, one connection terminal of the resistance measuring device is connected to the first active material layer 2012, and the other terminal is connected to the first coating layer 60, so that the first current collector 2011, the first active material layer 2012, the first lug 301 and the first coating layer 60 are in a series connection state, and the measurement result is recorded as R3;

[0093] Take a second tab 202, and the second tab 202 remains in a connected state with the second lug 302;

[0094] Connect the second tab 202 and the second lug 302 to a resistance measuring device (e.g., a multimeter), and when connected, one connection terminal of the resistance measuring device is connected to the second active material layer 2022, and the other terminal is connected to the second lug 302, so that the second current collector 2021, the second active material layer 2022 and the second lug 302 are in a series connection state, and the measurement result is recorded as R4.

[0095] As shown in Figure 9 The embodiments of the present application also provide a use electric device 1000, which comprises the secondary battery 100 according to any one of the foregoing embodiments.

[0096] To verify the influence of the scheme provided by the embodiments of the present application on the degree of lithium precipitation of the outermost tab 21 of the secondary battery 100, the inventors conducted the following experiments. The experiments include one group of comparative examples and nine groups of embodiments, and each group of comparative examples and each group of embodiments includes 21 secondary batteries 100.

[0097] The preparation process of the secondary battery 100 in Example 1 includes the following steps:

[0098] (1) Preparation of the positive electrode sheet 210: The active material lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), CNT (carbon nanotube), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:0.5:0.5:1.5, and N-methyl pyrrolidone (NMP) was added as a solvent to prepare a positive electrode active material having a solid content of 75 wt%, which was then stirred uniformly for use. An aluminum foil having a thickness of 10 μm was used as the positive electrode current collector 211. The above active material was uniformly coated on one surface of the positive electrode current collector 211 in the thickness direction thereof using a slot coater, and then dried at 90°C to obtain a positive electrode sheet 210 having the positive electrode active material coated on one surface. At this time, the thickness of the positive electrode active material layer 212 in the thickness direction of the positive electrode current collector 211 was 50 μm. The above coating step was repeated on the other surface of the positive electrode current collector 211 in the thickness direction thereof. The coated positive electrode sheet 210 was then cold-pressed, and the thickness of the positive electrode active material layer 212 after cold-pressing was 35 μm. The region of the positive electrode current collector 211 not covered by the positive electrode active material layer 212 was a positive electrode empty foil region, and the positive electrode empty foil region was die-cut to obtain the positive electrode tab 31. A plurality of positive electrode sheets 210 were prepared, two of which were positive electrode sheets 210 having the positive electrode active material layer 212 coated on one surface, and the remaining number was positive electrode sheets 210 having the positive electrode active material layer 212 coated on both surfaces. The positive electrode tab 31 of one of the positive electrode sheets 210 having the positive electrode active material layer 212 coated on one surface was provided with a first through-hole 3011, and the entire surface of the positive electrode tab 31 was coated with a first coating layer 60.

[0099] (2) Preparation of the negative electrode sheet 220: The active material artificial graphite, conductive carbon black (Super P), butadiene rubber (SBR), and CMC (sodium carboxymethyl cellulose) were mixed in a weight ratio of 97:0.5:1.3:1.2, deionized water was added as a solvent, and a negative electrode active material with a weight percentage of 50wt% was prepared and stirred uniformly for standby use. A copper foil with a thickness of 10μm was used as the negative electrode current collector 221. The above-mentioned negative electrode active material was uniformly coated on one surface of the negative electrode current collector 221 in the thickness direction thereof using a slot coater, and then dried at 110°C to obtain a negative electrode sheet 220 with a negative electrode active material layer 222 coated on one surface. At this time, the thickness of the negative electrode active material layer 222 in the thickness direction of the negative electrode current collector 221 was 55μm. The above-mentioned step was repeated on the other surface of the negative electrode current collector 221 in the thickness direction thereof. The coated negative electrode sheet 220 was then cold-pressed, and the thickness of the negative electrode active material layer 222 after cold-pressing was 45μm. The area of the negative electrode current collector 221 not covered by the negative electrode active material layer 222 was a negative electrode empty foil area, and the negative electrode empty foil area was die-cut to obtain the negative electrode tab 32. A plurality of negative electrode sheets 220 were prepared, and each was a negative electrode sheet 220 with a negative electrode active material layer 222 coated on both surfaces.

[0100] (3) Preparation of the electrolyte: In a dry argon atmosphere, first, ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC: EMC: DEC = 30:50:20 to form a base organic solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the base organic solvent to dissolve and mix uniformly to obtain an electrolyte with a lithium salt concentration of 1.15mol / L.

[0101] (4) Preparation of the separator film 22: A 7μm-thick polyethylene porous polymer film was used as the separator film 22.

[0102] (5) Preparation of the electrode assembly 20: The positive electrode sheet 210, the separator film 22, and the negative electrode sheet 220 were alternately stacked in the first direction X to obtain the electrode assembly 20. In the stacking structure of the electrode assembly 20, the two outermost electrode sheets 21 were both positive electrode sheets 210 with a positive electrode active material layer 212 coated on one surface, and thus, in the experiments of the present application, the first electrode sheet 201, the second electrode sheet 202, and the third electrode sheet 203 were positive electrode sheets 210. One first conductive member 40 and one first adapter member 50 were taken, the positive electrode tabs 31 were gathered to form a positive electrode tab bundle, the first conductive member 40 was placed in the first through hole 3011, and the first adapter member 50, the first conductive member 40, and the positive electrode tab bundle were welded. One second adapter member 70 was taken, the negative electrode tabs 32 were gathered to form a negative electrode tab bundle, and the second adapter member 70 was welded to the negative electrode tab bundle.

[0103] (6) Assembly of the secondary battery 100: Place the punched aluminum plastic film into the assembly jig with the pit surface facing up, place the electrode assembly 20 into the pit, and press tightly by applying an external force. Then place another punched aluminum plastic film with the pit surface facing down on the electrode assembly 20, heat seal the three edges of the two aluminum plastic films by hot pressing, and the unsealed edge is the side where the first adapter 50 and the second adapter 70 extend out of the shell 10. Then inject the electrolyte through the unsealed edge, and go through the processes of vacuum packaging, standing, hot pressing, shaping, etc., to obtain the secondary battery 100.

[0104] The preparation process of the secondary battery 100 in Comparative Example 1 is basically the same as that in Example 1, and the difference is that the positive electrode tab 31 of the positive electrode sheet 210 of the outermost layer of the secondary battery 100 in Comparative Example 1 is not provided with the first through hole 3011, and is not coated with the first coating layer 60.

[0105] The preparation process of the secondary battery 100 in Examples 2-9 is basically the same as that in Example 1, and the difference is that the parameters of the secondary battery 100 in Examples 2-9 are different from those in Example 1, and the different parameters are listed in Table 1.

[0106] After the preparation of the secondary battery 100 in the comparative examples and examples, for each experimental group, 20 secondary batteries 100 are randomly selected for long cycle test, and the remaining one secondary battery 100 is used for capacity retention test.

[0107] The specific process of the long cycle test is as follows:

[0108] 1) Maintain the test temperature at 25°C;

[0109] 2) Let the secondary battery 100 stand for 30 min;

[0110] 3) 1.3C constant current charging to 4.1V, and then constant voltage charging to 1C;

[0111] 4) 1C constant current charging to 4.2V, and then constant voltage charging to 0.7C;

[0112] 5) 0.7C constant current charging to 4.3V, and then constant voltage charging to 0.025V;

[0113] 6) Stand for 5 min;

[0114] 7) 0.7C constant current discharging to 3V;

[0115] 8) Stand for 5 min;

[0116] 9) Cycle steps 3-8 for 800 times;

[0117] 10) Disassemble the secondary battery 100, observe the morphology of the surface of the pole piece using a scanning electron microscope (SEM), and detect whether there is lithium metal deposition. Use an X-ray diffractometer (XRD) to analyze the composition of the surface of the pole piece, and confirm whether there is lithium metal to determine whether lithium deposition occurs on the first pole piece 201. Count the number of secondary batteries 100 in each group in which lithium deposition does not occur on the first pole piece 201, and record the experimental data in Table 1.

[0118] The specific process of the capacity retention rate test is as follows:

[0119] First, measure the initial capacity of the secondary battery in Comparative Example 1 as a1, and then measure the initial capacity of the secondary battery in the other experimental groups as a2. The capacity retention rate is (a1-a2) / a1, and the result is expressed as a percentage and recorded in Table 1.

[0120] The test steps of the initial capacity are as follows:

[0121] 1) Maintain the test temperature at 25°C;

[0122] 2) Place the secondary battery 100 for 60 min;

[0123] 3) Discharge at 0.5C constant current to 3V;

[0124] 4) Stand for 60 min;

[0125] 5) Charge at 0.7C constant current to 4.50V, and charge at constant voltage to 0.025C;

[0126] 6) Stand for 10 min to obtain the initial capacity.

[0127] The experimental results of the long cycle test and the initial capacity test are recorded in Table 1.

[0128] Table 1

[0129]

[0130] Note: In Table 1, " / " means no data, T1 is in units of μm, and R1 and R2 are in units of mΩ.

[0131] From Table 1, it can be seen that in Examples 1 to 9, the secondary battery 100 is provided with the first coating layer 60, while in Comparative Example 1, the first coating layer 60 is not provided. Compared with Comparative Example 1, the cycle test pass rate of the secondary battery 100 in Examples 1 to 9 is higher. It can be seen that in Examples 1 to 9, by providing the first coating layer 60 and connecting the first coating layer 60 in series with the first pole piece 201 and the first tab 301, it is beneficial to reduce the current density of the first pole piece 201, thereby slowing down the consumption speed of the electrolyte, so as to reduce the possibility of lithium deposition on the first pole piece 201.

[0132] In Embodiments 2 to 9, the secondary battery 100 satisfies T1≤10 μm, and the secondary battery 100 in Embodiments 2 to 9 has a higher pass rate in the cycle test than the secondary battery 100 in Embodiment 1. It can be seen that, by setting T1≥10 μm, the thickness of the first portion 61 is not too large, and the resistance value of the first coating layer 60 is not too high, which is conducive to reducing the current density of the first tab 201 and reducing lithium precipitation. The secondary battery 100 in Embodiments 1 to 8 satisfies T1≥3 μm, and the capacity retention rate of the secondary battery 100 in Embodiments 1 to 8 is higher than that in Embodiment 9. It can be seen that, by setting T1≥3 μm, the thickness of the first portion 61 is not too small, and the resistance value of the first coating layer 60 is not too high, which is conducive to reducing the loss of the first coating layer 60 to electrical energy and improving the discharge capacity of the secondary battery 100.

[0133] In Embodiments 2 to 9, the secondary battery 100 satisfies R2≥R1, and the secondary battery 100 in Embodiments 2 to 9 has a higher pass rate in the cycle test than the secondary battery 100 in Embodiment 1. It can be seen that, by setting R2≥R1, the resistance of the first coating layer 60 relative to the first lug 301 and the first current collector 2011 is not too small, which is conducive to reducing the current density of the first tab 201 and reducing lithium precipitation. In Embodiments 1 to 8, the secondary battery 100 satisfies R2≤20R1, and the capacity retention rate of the secondary battery 100 in Embodiments 1 to 8 is higher than that in Embodiment 9. It can be seen that, by setting R2≤20R1, the resistance of the first coating layer 60 relative to the first lug 301 and the first current collector 2011 is not too large, which is conducive to reducing the loss of the first coating layer 60 to electrical energy and improving the discharge capacity of the secondary battery 100.

[0134] In Embodiments 4 to 9, the secondary battery 100 satisfies R2≥5R1, and the secondary battery 100 in Embodiments 4 to 9 has a higher pass rate in the cycle test than the secondary battery 100 in Embodiments 2 and 3. It can be seen that, by setting R2≥5R1, it is conducive to further reducing the current density of the first tab 201 and reducing lithium precipitation. In Embodiments 1 to 6, the secondary battery 100 satisfies R2≤20R1, and the capacity retention rate of the secondary battery 100 in Embodiments 1 to 6 is higher than that in Embodiments 7 and 8. It can be seen that, by setting R2≤20R1, it is conducive to further reducing the loss of the first coating layer 60 to electrical energy and improving the discharge capacity of the secondary battery 100.

[0135] In Embodiments 2 to 9, the secondary battery 100 satisfies R3≥0.65R4, and the secondary battery 100 in Embodiments 2 to 9 has a higher pass rate in the cycle test than the secondary battery 100 in Embodiment 1, which shows that setting R3≥0.65R4, the total resistance value of the first tab 201, the first tab 301, and the first coating layer 60 is not too small, which is conducive to reducing the current density of the first tab 201, thereby reducing the possibility of lithium precipitation of the first tab 201. In Embodiments 1 to 8, the secondary battery 100 satisfies R3≤15R4, and the capacity retention rate of the secondary battery 100 in Embodiments 1 to 8 is higher than that in Embodiment 9, which shows that setting R3≤15R4, the total resistance value of the first tab 201, the first tab 301, and the first coating layer 60 is not too large, which is conducive to the release of the capacity of the first tab 201, thereby being conducive to improving the discharge capacity of the secondary battery 100.

[0136] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application, and are not used as a limitation to the present application, and any appropriate changes and variations made to the above embodiments within the spirit and principles of the present application fall within the disclosure range of the present application.

Claims

1. A secondary battery characterized by comprising: The electrode assembly, the first conductive member, and the first adapter; The electrode assembly includes a plurality of electrode pieces and a separator, the plurality of electrode pieces are stacked along a first direction, any two adjacent electrode pieces have opposite polarities, and the separator is arranged between any two adjacent electrode pieces; the first direction is the thickness direction of the electrode pieces; The plurality of electrode pieces includes a first electrode piece with the same polarity, at least one second electrode piece, and a third electrode piece, the first electrode piece and the third electrode piece are respectively located at the two outermost layers of the electrode assembly, and the second electrode piece is located between the first electrode piece and the second electrode piece; The secondary battery further includes a first tab, a second tab, and a third tab, the first electrode piece includes a first current collector and a first active material layer, the first tab is connected to the first current collector, the first active material layer is arranged on the first current collector, and the first active material layer faces the inside of the electrode assembly; the second electrode piece includes a second current collector and a second active material layer, the second tab is connected to the second current collector, and the second active material layer is arranged on two surfaces of the second current collector which are oppositely arranged along the first direction; the third tab is connected to the third electrode piece; The first tab, the second tab, and the third tab are stacked, the first tab is provided with a first through hole extending along the thickness direction of the first tab; The first conductive member is arranged in the first through hole, and the first conductive member is electrically connected to all the second tabs and the third tab, and the first adapter is connected to the first conductive member; The first tab has a first surface and a second surface oppositely arranged along the thickness direction of the first tab, the first surface faces the second tab, and the first adapter is located on the side of the first tab with the second surface; The secondary battery further includes a first coating layer, the first coating layer has electrical conductivity, the first coating layer includes a first part, a second part, and a third part connected to each other; the first part is arranged on the first surface to separate the first tab from the second tab; The second part covers the surrounding wall of the first through hole to separate the first tab from the first conductive member; The third part is arranged on the second surface to separate the first tab from the first adapter; The first coating layer contacts the first conductive member.

2. The secondary battery according to claim 1, wherein The secondary battery includes a second conductive member, the third tab is provided with a second through hole extending along the first direction, the second conductive member is arranged in the second through hole, and the second conductive member is electrically connected to all the second tabs; The third tab has a third surface and a fourth surface oppositely arranged along the first direction, and the fourth surface faces the second tab; The electrode assembly further includes a second coating layer, the second coating layer has electrical conductivity, and the second coating layer includes a fourth part and a fifth part connected to each other; The fourth part is arranged on the fourth surface to separate the third tab from the second tab; The fifth part covers the surrounding wall of the second through hole to separate the third tab from the second conductive member, and the second coating contacts the second conductive member.

3. A secondary battery characterized by comprising: The electrode assembly, the first conductive member, and the first adapter are provided. The electrode assembly includes a plurality of electrode sheets and a separator, the plurality of electrode sheets are arranged in a first direction, the polarity of any two adjacent electrode sheets is opposite, and the separator is arranged between any two adjacent electrode sheets; the first direction is the thickness direction of the electrode sheet. The plurality of electrode sheets includes a first electrode sheet with the same polarity, at least one second electrode sheet, and a third electrode sheet, the first electrode sheet and the third electrode sheet are respectively located at the two outermost layers of the electrode assembly, and the second electrode sheet is located between the first electrode sheet and the second electrode sheet. The electrode assembly further includes a first tab, a second tab, and a third tab, the first electrode sheet includes a first current collector and a first active material layer, the first tab is connected to the first current collector, the first active material layer is arranged on the first current collector, and the first active material layer faces the inside of the electrode assembly; the second electrode sheet includes a second current collector and a second active material layer, the second tab is connected to the second current collector, and the second active material layer is arranged on two surfaces of the second current collector which are oppositely arranged along the first direction; the third tab is connected to the third electrode sheet. The first tab, the second tab, and the third tab are arranged in layers, the first tab has a first through hole extending along the thickness direction thereof; The first conductive member is arranged in the first through hole, and the first conductive member is electrically connected to all the second tabs and the third tab; the first adapter is connected to the third tab; The first tab has a first surface and a second surface oppositely arranged along the thickness direction thereof, and the first surface faces the second tab; The electrode assembly further includes a first coating layer, the first coating layer has electrical conductivity, the first coating layer includes a first part and a second part connected to each other; the first part is arranged on the first surface to separate the first tab from the second tab; The second part covers the surrounding wall of the first through hole to separate the first tab from the first conductive member; The first coating layer contacts the first conductive member.

4. The secondary battery according to claim 1 or 3, wherein The thickness of the first part is T1, and 3 μm ≤ T1 ≤ 10 μm.

5. The secondary battery according to claim 1 or 3, wherein The first current collector includes a fifth surface and a sixth surface oppositely arranged along the first direction, the first active material layer is arranged on the fifth surface, and the first coating layer covers at least part of the surface of the sixth surface.

6. The secondary battery according to claim 1 or 3, wherein The total resistance value of the first tab and the first current collector is R1, the resistance value of the first coating layer is R2, and R1 ≤ R2 ≤ 20R1.

7. The secondary battery according to claim 6, wherein 5R1 ≤ R2 ≤ 10R1.

8. The secondary battery according to claim 6, wherein 1 mΩ ≤ R1 ≤ 10 mΩ.

9. The secondary battery according to claim 1 or 3, wherein The total resistance value of the first electrode sheet, the first tab, and the first coating layer is R3, the total resistance value of any second electrode sheet and the second tab connected thereto is R4, and 0.65R4 ≤ R3 ≤ 15R4.

10. The secondary battery according to claim 1 or 3, wherein The material of the first coating layer includes a main material; the material of the main material includes at least one of silicon dioxide, aluminum oxide, zinc oxide, tin oxide, indium tin oxide, titanium oxide, iron oxide, silicon nitride, titanium nitride, aluminum nitride, silicon carbide, tungsten carbide, and titanium carbide.

11. The secondary battery according to claim 1 or 3, wherein The first coating layer includes a third portion, and the third portion is disposed on the second surface; The first conductive member includes a first connecting portion and a second connecting portion, the first connecting portion is disposed through the first through hole, and the second connecting portion is located on the side of the first tab having the second surface; The second connecting portion and the third portion are stacked along the thickness direction of the first tab.

12. An electrical device, characterized by A secondary battery including any one of the secondary batteries according to claims 1 to 11.

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