Secondary battery and electric device

Abstract

The invention discloses a secondary battery and electric equipment. The secondary battery comprises an electrode assembly, a first conductive part and a first adapter, the electrode assembly includes a plurality of pole pieces and an isolation membrane. The plurality of pole pieces comprise a first pole piece, and the first pole piece is located on 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 substance layer, the first tab is connected with the first current collector, and the first active substance 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 penetrates through the first through hole, and the first adapter is connected with the first conductive piece. The secondary battery further comprises a first coating, the first coating has conductivity, and the first coating is used for separating the first tab from the second tab, separating the first tab from the first conductive piece and separating the first tab from the first adapter; the first coating contacts the first conductive member. 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 field of energy storage technology, and in particular relates to a secondary battery and electrical equipment. Background Art

[0002] The outermost electrode sheet of the stacked electrode assembly in a secondary battery is usually coated with an active material layer only on one side of the current collector, while the inner electrode sheet is coated with an active material layer on both sides of the current collector to fully utilize the active material layer, reduce material costs, and increase the energy density of the battery. Summary of the invention

[0003] For the secondary battery in the prior art, the inventors found that since the outermost electrode sheet is coated with a single layer and the inner electrode sheet is coated with double layers, and the ratio of various materials in the active material layers of the inner and outer electrode sheets is generally the same, this makes the conductivity of the outermost electrode sheet of the electrode assembly greater than the conductivity of the inner electrode sheet, and the current density of the outermost electrode sheet is significantly higher than the current density of the inner electrode sheet. During the cycle of the secondary battery, the electrolyte at the outermost electrode sheet is consumed faster, making it easy for lithium deposition to occur on the outermost electrode sheet, resulting in a decrease in the cycle performance of the secondary battery and a decrease in safety performance.

[0004] In view of the above situation, it is necessary to provide a secondary battery that can reduce the current density of the outermost electrode sheet of the electrode assembly to reduce lithium plating.

[0005] The first aspect of the embodiment of the present application provides a secondary battery, including an electrode assembly, a first conductive member and a first adapter. The electrode assembly includes a plurality of pole pieces and a separator, the plurality of pole pieces are stacked along a first direction, the polarities of any two adjacent pole pieces are opposite, and a separator is provided between any two adjacent pole pieces; the first direction is the thickness direction of the pole piece. The plurality of pole pieces include a first pole piece, at least one second pole piece and a third pole piece with the same polarity, the first pole piece and the third pole piece are respectively located at the two outermost layers of the electrode assembly, and the second pole piece is located between the first pole piece and the second pole piece. The secondary battery also includes a first pole piece, a second pole piece and a third pole piece, the first pole piece includes a first current collector and a first active material layer, the first pole piece is connected to the first current collector, the first active material layer is provided on the first current collector, and the first active material layer faces the inside of the electrode assembly; the second pole piece includes a second current collector and a second active material layer, the second pole piece is connected to the second current collector, the second active material layer is provided with two, and is respectively provided on the two surfaces of the second current collector oppositely arranged along the first direction; the third pole piece is connected to the third pole piece. The first pole lug, the second pole lug and the third pole lug are stacked, and the first pole lug is provided with a first through hole extending in the thickness direction thereof. The first conductive member is passed through the first through hole, and the first conductive member is electrically connected to all the second pole lugs and the third pole lugs, and the first adapter is connected to the first conductive member; the first pole lug has a first surface and a second surface arranged opposite to each other in the thickness direction thereof, the first surface faces the second pole lug, and the first adapter is located on the side of the first pole lug having the second surface; the secondary battery also includes a first coating, the first coating has conductivity, and the first coating 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 pole lug from the second pole lug; the second part covers the surrounding wall of the first through hole to separate the first pole lug from the first conductive member; the third part is arranged on the second surface to separate the first pole lug from the first adapter; the first coating contacts the first conductive member.

[0006] In this secondary battery, the first pole ear is provided with a first through hole to accommodate the first conductive member, the first coating connects the first pole ear and the first conductive member, and the first coating separates the first pole ear from the second pole ear, separates the first pole ear from the first conductive member, and separates the first pole ear from the first adapter, so that this secondary battery forms an electrical connection structure in which the first pole ear and the first coating are connected in series, and the first pole ear and the first coating as a whole are connected in parallel with the second pole ear and the third pole ear, thereby helping to reduce the current density passing through the first pole sheet, slowing down the consumption rate of the electrolyte, and reducing the possibility of lithium deposition in the first pole sheet.

[0007] In an optional embodiment of the present application, the secondary battery includes a second conductive member, the third pole ear is provided with a second through hole extending in the first direction, the second conductive member is inserted into the second through hole, and the second conductive member is electrically connected to all the second pole ears. The third pole ear has a third face and a fourth face arranged opposite to each other in the first direction, and the fourth face faces the second pole ear. The electrode assembly also includes a second coating, the second coating is conductive, and the second coating includes a fourth part and a fifth part connected to each other; the fourth part is arranged on the fourth face to separate the third pole ear from the second pole ear; the fifth part covers the surrounding wall of the second through hole to separate the third pole ear from the second conductive member, and the second coating contacts the second conductive member. In this way, the second coating is connected in series with the third pole ear, and the third pole ear and the entirety of the second coating, the second pole ear, and the first pole ear and the entirety of the first coating are connected in parallel, which is conducive to reducing the current density of the third pole sheet to reduce the possibility of lithium deposition in the third pole sheet.

[0008] The second aspect of the present application provides a secondary battery, including an electrode assembly, a first conductive member and a first adapter. The electrode assembly includes a plurality of pole pieces and a separator, the plurality of pole pieces are stacked along a first direction, the polarities of any two adjacent pole pieces are opposite, and a separator is provided between any two adjacent pole pieces; the first direction is the thickness direction of the pole piece. The plurality of pole pieces include a first pole piece, at least one second pole piece and a third pole piece with the same polarity, the first pole piece and the third pole piece are respectively located at the two outermost layers of the electrode assembly, and the second pole piece is located between the first pole piece and the second pole piece. The electrode assembly also includes a first pole piece, a second pole piece and a third pole piece, the first pole piece includes a first current collector and a first active material layer, the first pole piece is connected to the first current collector, the first active material layer is provided on the first current collector, and the first active material layer faces the inside of the electrode assembly; the second pole piece includes a second current collector and a second active material layer, the second pole piece is connected to the second current collector, the second active material layer is provided with two, and is respectively provided on the two surfaces of the second current collector arranged oppositely along the first direction; the third pole piece is connected to the third pole piece. The first pole lug, the second pole lug and the third pole lug are stacked, and the first pole lug is provided with a first through hole extending in the thickness direction thereof. The first conductive member is passed through the first through hole, and the first conductive member electrically connects all the second pole lugs and the third pole lugs; the first adapter is connected to the third pole lug. The first pole lug has a first surface and a second surface arranged opposite to each other in the thickness direction thereof, and the first surface faces the second pole lug. The electrode assembly also includes a first coating, the first coating is conductive, and the first coating includes a first part and a second part connected to each other; the first part is provided on the first surface to separate the first pole lug from the second pole lug; the second part covers the surrounding wall of the first through hole to separate the first pole lug from the first conductive member; the first coating contacts the first conductive member.

[0009] In this secondary battery, the first pole ear is provided with a first through hole to accommodate the first conductive member, the first coating connects the first pole ear and the first conductive member, and the first coating also separates the first pole ear from the second pole ear, so that this secondary battery forms an electrical connection structure in which the first pole ear and the first coating are connected in series, and the first pole ear and the first coating as a whole are connected in parallel with the second pole ear and the third pole ear, thereby helping to reduce the current density passing through the first pole sheet, slowing down the consumption rate of the electrolyte, and reducing the possibility of lithium deposition in the first pole sheet.

[0010] In an optional embodiment of the present application, the thickness of the first part is T1, 3μm≤T1≤10μm. When T1≥3μm is set, the thickness of the first part is not too small, which is conducive to reducing the difficulty of the process, and the resistance value of the first part is not too large, which is conducive to reducing the heat generated by the first part during the use of the secondary battery, on the one hand, improving safety, and on the other hand, improving the discharge capacity of the secondary battery; when T1≤10μm is set, the thickness of the first part is not too large, on the one hand, it is conducive to reducing the space occupied by its setting in the shell, so as to reduce the impact on the energy density of the secondary battery, and on the other hand, it is conducive to increasing the resistance value of the first part.

[0011] In an optional embodiment of the present application, the first current collector includes a fifth surface and a sixth surface arranged opposite to each other along the first direction, the first active material layer is arranged on the fifth surface, and the first coating layer covers at least a portion of the surface of the sixth surface. By providing the first coating layer on at least a portion of the surface of the sixth surface, it is beneficial to improve the strength of the first pole piece and reduce or eliminate the curling of the first pole piece.

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

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

[0014] In an optional embodiment of the present application, 1mΩ≤R1≤10mΩ. Setting R1≥1mΩ, the value of R1 is not too small, which is conducive to reducing the difficulty of material selection and preparation, and is conducive to reducing the current density at the first pole piece; setting R1≤10mΩ, 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 value of the first pole piece, the first pole lug and the first coating is R3, and the total resistance value of any second pole piece and the second pole lug connected thereto is R4, 0.65R4≤R3≤15R4. When R3≥0.65R4 is set, the total resistance value of the first pole piece, the first pole lug and the first coating is not too small, which is beneficial to reduce the current density of the first pole piece, thereby reducing the possibility of lithium precipitation of the first pole piece; when R3≤15R4 is set, the total resistance value of the first pole piece, the first pole lug and the first coating is not too large, which is beneficial to the release of the capacity of the first pole piece, thereby facilitating the improvement of the discharge capacity of the secondary battery.

[0016] In an optional embodiment of the present application, the material of the first coating 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 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 pole piece having the second surface. Along the thickness direction of the first pole piece, the second connecting portion and the third portion are stacked. By stacking the second connecting portion and the third portion, it is beneficial to form a stable electrical connection between the first conductive member and the first coating, so as to stably reduce the current density of the first pole piece and reduce the possibility of lithium deposition in the first pole piece.

[0018] A third aspect of the embodiments of the present application provides an electrical device, comprising a secondary battery as described in any of the aforementioned embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0020] Figure 2 yes Figure 1 Schematic diagram of the cross-sectional structure at II-II.

[0021] Figure 3 yes Figure 1 Schematic diagram of the cross-sectional structure at III-III in the figure.

[0022] Figure 4 yes Figure 2 Enlarged view of point A in the middle.

[0023] Figure 5 It is a partial structural schematic diagram of a secondary battery in one embodiment of the present application.

[0024] Figure 6 It is a schematic structural diagram of the first conductive member in an embodiment of the present application.

[0025] Figure 7 It is a schematic diagram of the structure of the first pole piece in an embodiment of the present application.

[0026] Figure 8 yes Figure 7 Schematic diagram of the cross-sectional structure at VIII-VIII.

[0027] Fig. 9 It is a schematic diagram of the structure of an electrical device in an embodiment of the present application.

[0028] Main component symbols 100, secondary battery; 10, shell; 20, electrode assembly; 21, pole piece; 210, positive pole piece; 211, positive current collector; 212, positive active material layer; 213, insulating layer; 220, negative pole piece; 221, negative current collector; 222, negative active material layer; 201, first pole piece; 2011, first current collector; 2011a, fifth side; 2011b, sixth side; 2012, first active material layer; 202, second pole piece; 2021, second current collector; 2022, second active material layer; 203, third pole piece; 22, separator; 30, pole ear; 31, positive pole ear; 32, Negative electrode ear; 301, first electrode ear; 301a, first surface; 301b, second surface; 3011, first through hole; 302, second electrode ear; 303, third electrode ear; 303a, third surface; 303b, fourth surface; 3031, second through hole; 40, first conductive member; 41, first connecting portion; 42, second connecting portion; 50, first adapter; 60, first coating; 61, first part; 62, second part; 63, third part; 70, second adapter; 80, second conductive member; 90, second coating; 91, fourth part; 92, fifth part; 1000, electrical equipment; X, first direction.

[0029] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0031] It should be noted that when an element is considered to be "connected" to another element, it may be directly connected to the other element or there may be a centrally disposed element at the same time. When an element is considered to be "disposed on" another element, it may be directly disposed on the other element or there may be a centrally disposed element at the same time. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0033] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0034] In the description of the embodiments of the present application, the term "perpendicular" is used to describe an ideal state between two components. In actual production or use, there may be a state that is approximately perpendicular between the two components. The two components described as "perpendicular" may not be absolutely straight lines or planes, but may be roughly straight lines or planes. From a macroscopic point of view, if the overall extension direction is a straight line or a plane, the components can be considered to be "straight lines" or "planes".

[0035] Reference to "embodiment" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. The various embodiments in the present application may be combined with each other in the absence of conflict.

[0036] The first aspect of the embodiment of the present application provides a secondary battery, including an electrode assembly, a first conductive member and a first adapter. The electrode assembly includes a plurality of pole pieces and a separator, the plurality of pole pieces are stacked along a first direction, the polarities of any two adjacent pole pieces are opposite, and a separator is provided between any two adjacent pole pieces; the first direction is the thickness direction of the pole piece. The plurality of pole pieces include a first pole piece, at least one second pole piece and a third pole piece with the same polarity, the first pole piece and the third pole piece are respectively located at the two outermost layers of the electrode assembly, and the second pole piece is located between the first pole piece and the second pole piece. The secondary battery also includes a first pole piece, a second pole piece and a third pole piece, the first pole piece includes a first current collector and a first active material layer, the first pole piece is connected to the first current collector, the first active material layer is provided on the first current collector, and the first active material layer faces the inside of the electrode assembly; the second pole piece includes a second current collector and a second active material layer, the second pole piece is connected to the second current collector, the second active material layer is provided with two, and is respectively provided on the two surfaces of the second current collector oppositely arranged along the first direction; the third pole piece is connected to the third pole piece. The first pole lug, the second pole lug and the third pole lug are stacked, and the first pole lug is provided with a first through hole extending in the thickness direction thereof. The first conductive member is passed through the first through hole, and the first conductive member is electrically connected to all the second pole lugs and the third pole lugs, and the first adapter is connected to the first conductive member; the first pole lug has a first surface and a second surface arranged opposite to each other in the thickness direction thereof, the first surface faces the second pole lug, and the first adapter is located on the side of the first pole lug having the second surface; the secondary battery also includes a first coating, the first coating has conductivity, and the first coating 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 pole lug from the second pole lug; the second part covers the surrounding wall of the first through hole to separate the first pole lug from the first conductive member; the third part is arranged on the second surface to separate the first pole lug from the first adapter; the first coating contacts the first conductive member.

[0037] In this secondary battery, the first pole ear is provided with a first through hole to accommodate the first conductive member, the first coating connects the first pole ear and the first conductive member, and the first coating separates the first pole ear from the second pole ear, separates the first pole ear from the first conductive member, and separates the first pole ear from the first adapter, so that this secondary battery forms an electrical connection structure in which the first pole ear and the first coating are connected in series, and the first pole ear and the first coating as a whole are connected in parallel with the second pole ear and the third pole ear, thereby helping to reduce the current density passing through the first pole sheet, slowing down the consumption rate of the electrolyte, and reducing the possibility of lithium deposition in the first pole sheet.

[0038] The embodiments of the present application are further described below in conjunction with the accompanying drawings.

[0039] like Figure 1 and Figure 2As shown, an embodiment of the present application provides a secondary battery 100 , which includes a housing 10 and an electrode assembly 20 , wherein the electrode assembly 20 is accommodated in the housing 10 .

[0040] In some embodiments, the housing 10 is a flexible packaging bag, such as an aluminum-plastic film. In other embodiments, the housing 10 is a hard shell, such as a plastic shell, or a metal shell including at least one of a steel alloy, an aluminum alloy, and a copper alloy.

[0041] In some embodiments, Figure 2 As shown, the electrode assembly 20 includes a plurality of pole pieces 21 and a separator 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 22 is disposed between any two adjacent pole pieces 21, and the first direction X is the thickness direction of the pole pieces 21. Specifically, according to different polarities, a portion of the plurality of pole pieces 21 is a positive pole piece 210, and another portion is a negative pole piece 220.

[0042] In some embodiments, the pole piece 21 includes 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 disposed on a 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 disposed on both surfaces of the current collector along the first direction X. According to the different polarities of the pole piece 21, the current collector is divided into a positive current collector 211 and a negative current collector 221, and the active material layer is divided into a positive active material layer 212 and a negative active material layer 222.

[0043] In the above content, the "outermost layer" is determined by the relative positional relationship between the plurality of pole pieces 21, in other words, the relative positional relationship between the isolation film 22 and the pole piece 21 is not considered. For example, the outer side of the outermost pole piece 21 may also be provided with an isolation film 22.

[0044] Specifically, Figure 2 As shown, the positive electrode sheet 210 includes a positive electrode collector 211 and a positive electrode active material layer 212, and the positive electrode active material layer 212 is disposed on one or both sides of the positive electrode collector 211 along the first direction X. The negative electrode sheet 220 includes a negative electrode collector 221 and a negative electrode active material layer 222, and the negative electrode active material layer 222 is disposed on one or both sides of the negative electrode collector 221 along the first direction X.

[0045] In some embodiments, at least one of the positive electrode current collector 211 and the negative electrode current collector 221 is a metal layer. As an illustrative example, the positive electrode current collector 211 may be a metal layer including at least one of aluminum, nickel, tantalum, and titanium, such as aluminum foil. The negative electrode current collector 221 may be a metal layer including at least one of copper, nickel, tantalum, and titanium, such as copper foil.

[0046] In some embodiments, at least one of the positive electrode current collector 211 and the negative electrode current collector 221 is a composite current collector.

[0047] In some embodiments, the positive electrode active material layer 212 includes a positive electrode active material, which includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganese oxide.

[0048] In some embodiments, the negative electrode active material layer 222 includes a negative electrode active material, and the negative electrode active material includes at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen material, and silicon-carbon material.

[0049] In some embodiments, Figure 2 As shown, the positive electrode sheet 210 also includes an insulating layer 213, which is arranged at the edge of the positive electrode collector 211 connected to the positive electrode ear 31 to reduce the possibility that the burrs on the edge of the positive electrode collector 211 pierce the isolation film 22 and cause a short circuit between the positive electrode sheet 210 and the negative electrode sheet 220.

[0050] In some embodiments, the material of the insulating layer 213 includes a ceramic material and a binder.

[0051] In some embodiments, the ceramic material includes at least one of aluminum oxide, magnesium oxide, silicon nitride, silicon carbide, and boehmite.

[0052] In some embodiments, Figure 2 and Figure 3 As shown, the secondary battery 100 further includes a plurality of tabs 30, and each pole piece 21 is connected to a tab 30. Specifically, according to the polarity of the connected pole piece 21, the tabs 30 are divided into positive tabs 31 and negative tabs 32, the positive tabs 31 are connected to the positive pole piece 210, and the negative tabs 32 are connected to the negative pole piece 220.

[0053] In some embodiments, the isolation film 22 is made of insulating film materials such as polyethylene film, polypropylene film, polyester film or polyimide film.

[0054] In some embodiments, the secondary battery 100 includes an electrolyte (not shown), which is contained in the housing 10 .

[0055] 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.

[0056] In some embodiments, the electrolyte salt includes but is not limited to at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)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).

[0057] In some embodiments, Figure 2 As shown, the multiple pole pieces 21 include a first pole piece 201, at least one second pole piece 202 and a third pole piece 203 with the same polarity. The first pole piece 201 and the third pole piece 203 are respectively located at the two outermost layers of the electrode assembly 20, and the second pole piece 202 is located between the first pole piece 201 and the second pole piece 202. The plurality of pole tabs 30 include a first pole tab 301, a second pole tab 302, and a third pole tab 303. The first pole sheet 201 includes a first current collector 2011 and a first active material layer 2012. The first pole tab 301 is connected to the first current collector 2011. The first active material layer 2012 is disposed on the first current collector 2011, and the first active material layer 2012 faces the interior of the electrode assembly 20. The second pole sheet 202 includes a second current collector 2021 and a second active material layer 2022. The second pole tab 302 is connected to the second current collector 2021. Two second active material layers 2022 are provided, and are respectively provided on two surfaces of the second current collector 2021 that are oppositely disposed along the first direction X. The third pole tab 303 is connected to the third pole sheet 203. The first pole tab 301, the second pole tab 302, and the third pole tab 303 are stacked, and the first pole tab 301 is provided with a first through hole 3011 extending along its thickness direction.

[0058] In some embodiments, Figure 4 and Figure 5As shown, the secondary battery 100 further includes a first conductive member 40, a first adapter 50 and a first coating 60. The first conductive member 40 is disposed 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 50 is connected to the first conductive member 40. The first tab 301 has a first surface 301a and a second surface 301b that are arranged opposite to each other along the thickness direction thereof, the first surface 301a faces the second tab 302, and the first adapter 50 is located on the side of the first tab 301 having the second surface 301b. The first coating 60 is conductive, and includes a first portion 61, a second portion 62, and a third portion 63 that are connected to each other; the first portion 61 is disposed on the first surface 301a to separate the first pole ear 301 from the second pole ear 302; the second portion 62 covers the surrounding wall of the first through hole 3011 to separate the first pole ear 301 from the first conductive component 40; the third portion 63 is disposed on the second surface 301b to separate the first pole ear 301 from the first adapter 50; the first coating 60 contacts the first conductive component 40.

[0059] In this embodiment, taking the first pole piece 201, the second pole piece 202 and the third pole piece 203 as the positive pole piece 210 as an example, the current path is: the current flows from the first adapter 50 to the first conductive member 40, and then flows from the first conductive layer to the pole piece 21 in three parallel paths, first, the current flows from the first conductive member 40 to the first coating 60, and then from the first coating 60 to the first pole ear 301 and the first pole piece 201 in sequence, second, the current flows from the first conductive member 40 to the second pole ear 302 and the second pole piece 202 in sequence, and third, the current flows from the first conductive member 40 to the third pole ear 303 and the third pole piece 203. It can be seen that the first coating 60 and the first pole ear 301 are in a series state, and the total resistance of the first pole ear 301 and the first coating 60 is higher than the resistance value of the first pole ear 301. Compared with the state where the first coating 60 is not provided, the current density of the first pole piece 201 decreases.

[0060] In this embodiment, the first pole ear 301 is provided with a first through hole 3011 to accommodate the first conductive member 40, and the first coating 60 connects the first pole ear 301 and the first conductive member 40, and the first coating 60 separates the first pole ear 301 from the second pole ear 302, separates the first pole ear 301 from the first conductive member 40, and separates the first pole ear 301 from the first adapter 50, so that this secondary battery 100 forms an electrical connection structure in which the first pole ear 301 and the first coating 60 are connected in series, and the first pole ear 301 and the first coating 60 are connected in parallel with the second pole ear 302 and the third pole ear 303 as a whole, thereby facilitating reducing the current density passing through the first pole sheet 201, slowing down the consumption rate of the electrolyte, and reducing the possibility of lithium deposition in the first pole sheet 201.

[0061] In some embodiments, Figure 2 and Figure 5 As shown, the secondary battery 100 includes a second conductive member 80, the third pole tab 303 is provided with a second through hole 3031 extending along the first direction X, the second conductive member 80 is penetrated in the second through hole 3031, and the second conductive member 80 is electrically connected to all the second pole tabs 302. The third pole tab 303 has a third surface 303a and a fourth surface 303b arranged opposite to each other along the first direction X, and the fourth surface 303b faces the second pole tab 302. The electrode assembly 20 also includes a second coating 90, the second coating 90 is conductive, and the second coating 90 includes a fourth portion 91 and a fifth portion 92 connected to each other; the fourth portion 91 is provided on the fourth surface 303b to separate the third pole tab 303 from the second pole tab 302; the fifth portion 92 covers the surrounding wall of the second through hole 3031 to separate the third pole tab 303 from the second conductive member 80, and the second coating contacts the second conductive member 80. In this way, the second coating is connected in series with the third pole ear 303, and the third pole ear 303 and the entire second coating, the second pole ear 302, the first pole ear 301 and the entire first coating 60 are connected in parallel, which is beneficial to reduce the current density of the third pole piece 203 to reduce the possibility of lithium deposition in the third pole piece 203.

[0062] In some embodiments, the secondary battery 100 further includes a first conductive member 40, a first adapter 50, and a first coating 60. The first conductive member 40 is disposed in the first through hole 3011, and the first conductive member 40 electrically connects all the second pole tabs 302 and the third pole tabs 303; the first adapter 50 connects the third pole tab 303. The first pole tab 301 has a first surface 301a and a second surface 301b disposed opposite to each other along its thickness direction, and the first surface 301a faces the second pole tab 302. The electrode assembly 20 further includes a first coating 60, the first coating 60 is conductive, and the first coating 60 includes a first portion 61 and a second portion 62 connected to each other; the first portion 61 is disposed on the first surface 301a to separate the first pole tab 301 from the second pole tab 302; the second portion 62 covers the surrounding wall of the first through hole 3011 to separate the first pole tab 301 from the first conductive member 40; the first coating 60 contacts the first conductive member 40.

[0063] In this embodiment, taking the first pole piece 201, the second pole piece 202 and the third pole piece 203 as the positive pole piece 210 as an example, the path of the current is: the current flows from the first adapter 50 to the third pole ear 303, the second pole ear 302 and the first conductive member 40. At this time, the second pole ear 302 and the third pole ear 303 are in parallel, and the current of the first conductive member 40 flows to the first pole ear 301 through the first coating 60. It can be seen that the first coating 60 and the first pole ear 301 are in series, and the first pole ear 301 and the first coating 60 are in parallel with the second pole ear 302 and the third pole ear 303. Since the first coating 60 and the first pole ear 301 are in series, the total resistance of the first pole ear 301 and the first coating 60 is higher than the resistance value of the first pole ear 301, and compared with the state where the first coating 60 is not provided, the current density of the first pole piece 201 decreases.

[0064] In this embodiment, the first pole ear 301 is provided with a first through hole 3011 to accommodate the first conductive member 40, the first coating 60 connects the first pole ear 301 and the first conductive member 40, and the first coating 60 also separates the first pole ear 301 from the second pole ear 302, so that the secondary battery 100 forms an electrical connection structure in which the first pole ear 301 and the first coating 60 are connected in series, and the first pole ear 301 and the first coating 60 are connected in parallel with the second pole ear 302 and the third pole ear 303 as a whole, thereby facilitating reducing the current density passing through the first pole piece 201 and slowing down the consumption rate of the electrolyte, so as to reduce the possibility of lithium deposition in the first pole piece 201.

[0065] In some embodiments, Figures 4 to 6 As shown, the first coating 60 includes a third portion 63, and the third portion 63 is arranged on the second surface 301b. The first conductive member 40 includes a first connecting portion 41 and a second connecting portion 42, the first connecting portion 41 is arranged in the first through hole 3011, and the second connecting portion 42 is located on the side of the first pole ear 301 having the second surface 301b. Along the thickness direction of the first pole ear 301, the second connecting portion 42 and the third portion 63 are stacked. 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 set to be slightly smaller than the size of the remaining space of the first through hole 3011 after being 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 stacking the second connecting portion 42 and the third portion 63, it is beneficial to form a stable electrical connection between the first conductive member 40 and the first coating 60, so as to stably reduce the current density passing through the first pole piece 201 and reduce the possibility of lithium deposition in the first pole piece 201.

[0066] In some embodiments, Figure 6As shown, the first connection portion 41 is cylindrical to match the shape of the first through hole 3011. This is beneficial to increase the contact area between the first connection portion 41 and the second portion 62, so as to improve the stability of the electrical connection between the two.

[0067] In some embodiments, the first connecting portion 41 is in a hollow cylindrical shape to save material.

[0068] In some embodiments, Figure 6 As shown, the second connection portion 42 is in the shape of a flat cylinder, the center of the second connection portion 42 is substantially colinear with the center of the first through hole 3011, and the radius of the second connection portion 42 is greater than the radius of the first through hole 3011. In this way, when connecting the first tab 301 and the first conductive member 40, after the first connection portion 41 is inserted into the first through hole 3011, the second connection portion 42 can initially limit the position of the first conductive member 40 to reduce the difficulty of operation during connection.

[0069] In some embodiments, the structure of the second conductive member 80 is the same as that of the first conductive member 40 .

[0070] In some embodiments, the first conductive member 40, the first electrode tab 301, the second electrode tab 302 and the third electrode tab 303 are welded. Specific welding methods include but are not limited to laser welding and ultrasonic welding.

[0071] In some embodiments, Figure 2 As shown, the first electrode tab 301, the second electrode tab 302 and the third electrode tab 303 are stacked and bent into a "U" shape to reduce the occupation of the head space in the shell 10 of the secondary battery 100.

[0072] In some embodiments, the first adapter 50 is a flat, long metal piece, and a portion of the first adapter 50 extends out of the housing 10 to facilitate electrical connection between the secondary battery 100 and an external device.

[0073] In some embodiments, the first coating 60 covers the entire surface of the first pole tab 301. Thus, on the one hand, the first coating 60 is provided on the surface of the first pole tab 301 without distinction, which is conducive to reducing the difficulty of providing the first coating 60, and on the other hand, it is conducive to improving the coating quality of the first coating 60 and improving the resistance value that the first coating 60 can provide.

[0074] In some embodiments, the material of the first coating 60 includes a main material, and 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.

[0075] In some embodiments, the first coating 60 is coated on the surface of the first electrode tab 301 by magnetron sputtering or vapor deposition.

[0076] In some embodiments, the coating material further includes a binder.

[0077] In some embodiments, the thickness of the first part 61 is T1, 3μm≤T1≤10μm. When T1≥3μm is set, the thickness of the first part 61 is not too small, which is conducive to reducing the difficulty of the process, and the resistance value of the first part 61 is not too large, which is conducive to reducing the heat generated by the first part 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; when T1≤10μm is set, the thickness of the first part 61 is not too large, on the one hand, it is conducive to reducing the occupation of the space in the housing 10 by its setting, so as to reduce the impact on the energy density of the secondary battery 100, and on the other hand, it is conducive to increasing the resistance value of the first part 61.

[0078] In some embodiments, Figure 7 and Figure 8 As shown, the first current collector 2011 includes a fifth surface 2011a and a sixth surface 2011b arranged relatively along the first direction X, the first active material layer 2012 is arranged on the fifth surface 2011a, and the first coating 60 covers at least a portion of the surface of the sixth surface 2011b. After the pole pieces 21 in the electrode assembly 20 are stacked, the electrode assembly 20 needs to be pressurized. During this process, part of the active material layer material will be embedded in the gap of the current collector, resulting in internal stress in the pole piece 21. Since the first pole piece 201 is coated with the active material layer only on one side of the first current collector 2011, the generation of internal stress makes the first pole piece 201 prone to curling. By providing the first coating 60 on at least a portion of the surface of the sixth surface 2011b, it is beneficial to improve the strength of the first pole piece 201 and reduce or eliminate the curling of the first pole piece 201.

[0079] In some embodiments, the total resistance of the first pole tab 301 and the first current collector 2011 is R1, and the resistance of the first coating 60 is R2, R1≤R2≤20R1. By setting R2≥R1, the resistance of the first coating 60 relative to the first pole tab 301 and the first current collector 2011 is not too small, which is conducive to reducing the current density of the first pole sheet 201 and reducing lithium precipitation; by setting R2≤20R1, the resistance of the first coating 60 relative to the first pole tab 301 and the first current collector 2011 is not too large, which is conducive to reducing the difficulty of material selection for the first coating 60 on the one hand, and on the other hand, the thickness of the first coating 60 is not too thin, which is conducive to reducing the difficulty of the process, and is also conducive to reducing the loss of electric energy by the first coating 60 and improving the discharge capacity of the secondary battery 100.

[0080] Among them, the measurement method of R1 and R2 is: Take the first pole piece 201, and keep the first pole piece 201 connected with the first pole tab 301 and the first coating 60; Removing the first active material layer 2012 of the first electrode sheet 201; Connect the first current collector 2011, the first electrode tab 301 and the first coating 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 60, so that the first current collector 2011, the first electrode tab 301 and the first coating 60 are in series connection. The measurement result is read and recorded as R; Remove the first coating 60, connect the first current collector 2011 and the first electrode tab 301 to a resistance measuring device (such as a multimeter), when connected, one connecting terminal of the resistance measuring device is connected to the first current collector 2011, and the other terminal is connected to the first electrode tab 301, and the measurement result is read and recorded as R1; Calculate R2, R2=R-R1.

[0081] In some embodiments, 5R1≤R2≤10R1. When R2≥5R1 is set, the resistance of the first coating 60 relative to the first pole 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; when R2≤20R1 is set, the resistance of the first coating 60 relative to the first pole tab 301 and the first current collector 2011 is not too large, which is conducive to further reducing the difficulty of material selection for the first coating 60 on the one hand, and on the other hand, the thickness of the first coating 60 is not too thin, which is conducive to further reducing the process difficulty and further improving the discharge capacity of the secondary battery 100.

[0082] In some embodiments, 1mΩ≤R1≤10mΩ. Setting R1≥1mΩ, the value of R1 is not too small, which is conducive to reducing the difficulty of material selection and preparation, and is conducive to reducing the current density at the first pole piece 201; setting R1≤10mΩ, 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.

[0083] In some embodiments, the total resistance of the first pole piece 201, the first pole tab 301 and the first coating 60 is R3, and the total resistance of any second pole piece 202 and the second pole tab 302 connected thereto is R4, and 0.65R4≤R3≤15R4. When R3≥0.65R4 is set, the total resistance of the first pole piece 201, the first pole tab 301 and the first coating 60 is not too small, which is conducive to reducing the current density of the first pole piece 201, thereby reducing the possibility of lithium precipitation of the first pole piece 201; when R3≤15R4 is set, the total resistance of the first pole piece 201, the first pole tab 301 and the first coating 60 is not too large, which is conducive to the release of the capacity of the first pole piece 201, thereby facilitating the improvement of the discharge capacity of the secondary battery 100.

[0084] Among them, the measurement method of R3 and R4 is: Take the first pole piece 201, and keep the first pole piece 201 connected with the first pole tab 301 and the first coating 60; Connect the first electrode sheet 201, the first electrode tab 301 and the first coating 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 active material layer 2012, and the other terminal is connected to the first coating 60, so that the first current collector 2011, the first active material layer 2012, the first electrode tab 301 and the first coating 60 are connected in series. The measurement result is read and recorded as R3; Take a second pole piece 202, and keep the second pole piece 202 and the second pole ear 302 connected; The second electrode sheet 202 and the second electrode tab 302 are connected to a resistance measuring device (such as a multimeter). 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 electrode tab 302, so that the second current collector 2021, the second active material layer 2022 and the second electrode tab 302 are in series connection. The measurement result is read and recorded as R4.

[0085] like Fig. 9 As shown, an embodiment of the present application further provides an electric device 1000 , which includes the secondary battery 100 involved in any of the aforementioned embodiments.

[0086] To verify the effect of the solution provided in the embodiment of the present application on the lithium deposition degree of the outermost electrode 21 of the secondary battery 100, the inventor conducted the following experiment. The experiment includes a group of comparative examples and 9 groups of embodiments, each group of comparative examples and each group of embodiments includes 21 secondary batteries 100.

[0087] The preparation process of the secondary battery 100 in Example 1 includes the following steps: (1) Preparation of positive electrode sheet 210: Active materials lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), CNT (carbon nanotube), polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:0.5:0.5:1.5, N-methylpyrrolidone (NMP) is added as a solvent, and a positive electrode active material with a solid content of 75wt% is prepared, and the mixture is stirred evenly for use. Aluminum foil with a thickness of 10μm is used as the positive electrode current collector 211. The above active material is evenly coated on one surface of the positive electrode current collector 211 along its thickness direction using a slit coater, and then dried at 90°C to obtain a positive electrode sheet 210 coated with a positive electrode active material on one side. At this time, the thickness of the positive electrode active material layer 212 along the thickness direction of the positive electrode current collector 211 is 50μm. The above coating steps are then repeated on the other surface of the positive electrode current collector 211 along its thickness direction. The coated positive electrode sheet 210 is then cold pressed. After cold pressing, the thickness of the positive electrode active material layer 212 is 35 μm. The area of ​​the positive electrode current collector 211 not covered by the positive electrode active material layer 212 is the positive electrode empty foil area, and the positive electrode empty foil area is die-cut to obtain the positive electrode ear 31. A plurality of positive electrode sheets 210 are prepared, two of which are positive electrode sheets 210 coated with a positive electrode active material layer 212 on one side, and the remaining number are positive electrode sheets 210 coated with a positive electrode active material layer 212 on both sides. The positive electrode ear 31 of one of the positive electrode sheets 210 coated with a positive electrode active material layer 212 on one side is provided with a first through hole 3011, and the entire surface of the positive electrode ear 31 is coated with a first coating 60.

[0088] (2) Preparation of negative electrode sheet 220: Active materials artificial graphite, conductive carbon black (Super P), styrene-butadiene rubber (SBR), and CMC (sodium carboxymethyl cellulose) are mixed in a weight ratio of 97:0.5:1.3:1.2, and deionized water is added as a solvent to prepare a negative electrode active material material with a weight percentage of 50wt%, and stirred evenly for use. A copper foil with a thickness of 10μm is used as the negative electrode current collector 221. The above negative electrode active material is evenly coated on one surface of the negative electrode current collector 221 along its thickness direction using a slit coater, and then dried at 110°C to obtain a negative electrode sheet 220 coated with a negative electrode active material layer 222 on one side. At this time, the thickness of the negative electrode active material layer 222 along the thickness direction of the negative electrode current collector 221 is 55μm. Then repeat the above steps on the other surface of the negative electrode current collector 221 along its thickness direction. The coated negative electrode sheet 220 is then cold pressed, and the thickness of the negative electrode active material layer 222 after cold pressing is 45 μm. The area of ​​the negative electrode current collector 221 not covered by the negative electrode active material layer 222 is the negative electrode empty foil area, and the negative electrode empty foil area is die-cut to obtain the negative electrode ear 32. A plurality of negative electrode sheets 220 are prepared, and all of them are negative electrode sheets 220 coated with the negative electrode active material layer 222 on both sides.

[0089] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) was added to the basic organic solvent to dissolve and mix well to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0090] (4) Preparation of the isolation membrane 22: A 7 μm thick polyethylene porous polymer film was used as the isolation membrane 22.

[0091] (5) Preparation of electrode assembly 20: Alternately stack the positive electrode sheet 210, the separator 22 and the negative electrode sheet 220 along the first direction X to obtain the electrode assembly 20. In the stacked structure of the electrode assembly 20, the two outermost electrode sheets 21 are both positive electrode sheets 210 coated with a positive electrode active material layer 212 on one side. Therefore, in the experiment of the present application, the first electrode sheet 201, the second electrode sheet 202 and the third electrode sheet 203 are positive electrode sheets 210. Take a first conductive member 40 and a first adapter 50, gather all the positive electrode ears 31 to form a positive electrode ear 31 bundle, put the first conductive member 40 into the first through hole 3011, and weld the first adapter 50, the first conductive member 40 and the positive electrode ear 31 bundle. Take a second adapter 70, gather all the negative electrode ears 32 to form a negative electrode ear 32 bundle, and weld the second adapter 70 to the negative electrode ear 32 bundle.

[0092] (6) Assembly of secondary battery 100: Place the aluminum-plastic film with holes punched and formed in an assembly fixture, with the holes facing upward, place the electrode assembly 20 in the holes, and apply external force to press it. Then, cover the electrode assembly 20 with another aluminum-plastic film with holes punched and formed, with the holes facing downward. Heat-seal the three edges of the two aluminum-plastic films by hot pressing. The unsealed edge is the side where the first adapter 50 and the second adapter 70 extend out of the shell 10. Then, inject electrolyte through the unsealed edge, and after vacuum packaging, standing, hot pressing, shaping and other processes, the secondary battery 100 is manufactured.

[0093] The preparation process of the secondary battery 100 in comparative example 1 is substantially the same as that in embodiment 1, except that the positive electrode tab 31 of the outermost positive electrode sheet 210 of the secondary battery 100 in comparative example 1 does not have a first through hole 3011 and is not coated with a first coating 60 .

[0094] The preparation process of the secondary battery 100 in Examples 2-9 is substantially the same as that in Example 1, except that some parameters of the secondary battery 100 in Examples 2-9 are different from those in Example 1. The different parameters are listed in Table 1.

[0095] After the secondary batteries 100 in the comparative example and the embodiment are prepared, for each experimental group, 20 secondary batteries 100 are randomly selected to perform a long cycle test, and the remaining one secondary battery 100 is tested for capacity retention rate.

[0096] The specific process of the long cycle test is: 1) Maintain the test temperature at 25°C; 2) The secondary battery 100 was left to stand for 30 min; 3) 1.3C constant current charging to 4.1V, then constant voltage charging to 1C; 4) 1C constant current charge to 4.2V, then constant voltage charge to 0.7C; 5) 0.7C constant current charge to 4.3V, then constant voltage charge to 0.025V; 6) Let stand for 5 minutes; 7) 0.7C constant current discharge to 3V; 8) Let stand for 5 minutes; 9) Repeat steps 3 to 8 800 times; 10) Disassemble the secondary battery 100, and use a scanning electron microscope (SEM) to observe the morphology of the electrode surface to detect whether there is metal lithium deposition. Use an X-ray diffractometer (XRD) to analyze the material composition of the electrode surface to confirm whether there is metal lithium, so as to determine whether lithium deposition occurs in the first electrode 201. Count the number of secondary batteries 100 in each group whose first electrode 201 does not have lithium deposition, and record the experimental data in Table 1.

[0097] (II) The specific process of capacity retention rate test is as follows: First, the initial capacity of the secondary battery in comparative example 1 is measured as a1, and then the initial capacity of the secondary batteries in other experimental groups is measured as a2. The capacity retention rate is (a1-a2) / a1. The results are expressed as percentages and recorded in Table 1.

[0098] The initial capacity test steps are as follows: 1) Maintain the test temperature at 25°C; 2) The secondary battery 100 was left to stand for 60 min; 3) 0.5C constant current discharge to 3V; 4) Let stand for 60 minutes; 5) 0.7C constant current charging to 4.50V, constant voltage charging to 0.025C; 6) Let stand for 10 minutes to obtain the initial capacity.

[0099] The experimental results of the long cycle test and initial capacity test are recorded in Table 1.

[0100] Table 1 Note: In Table 1, “ / ” indicates that there is no such data. The unit of T1 is μm, and the unit of R1 and R2 is mΩ.

[0101] As can be seen from Table 1, in Examples 1 to 9, the secondary battery 100 is provided with a first coating 60, while in Comparative Example 1, the first coating 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 60 and connecting the first coating 60 in series with the first pole piece 201 and the first pole tab 301, it is beneficial to reduce the current density of the first pole piece 201, thereby slowing down the consumption rate of the electrolyte, so as to reduce the possibility of lithium deposition in the first pole piece 201.

[0102] In Examples 2 to 9, the secondary battery 100 satisfies T1 ≤ 10 μm. Compared with Example 1, the secondary battery 100 in Examples 2 to 9 has a higher pass rate in the cycle test. It can be seen that when T1 ≥ 10 μm is set, the thickness of the first part 61 is not too large, and the resistance value of the first coating 60 is not too high, which is conducive to reducing the current density of the first pole piece 201 and reducing lithium precipitation. The secondary battery 100 in Examples 1 to 8 satisfies T1 ≥ 3 μm. Compared with Example 9, the capacity retention rate of the secondary battery 100 in Examples 1 to 8 is higher. It can be seen that when T1 ≥ 3 μm is set, the thickness of the first part 61 is not too small, and the resistance value of the first coating 60 is not too high, which is conducive to reducing the loss of electric energy by the first coating 60 and improving the discharge capacity of the secondary battery 100.

[0103] In Examples 2 to 9, the secondary battery 100 satisfies R2≥R1. Compared with Example 1, the secondary battery 100 in Examples 2 to 9 has a higher pass rate in the cycle test. It can be seen that by setting R2≥R1, the resistance of the first coating 60 relative to the first pole ear 301 and the first current collector 2011 is not too small, which is beneficial to reduce the current density of the first pole piece 201 and reduce lithium precipitation. In Examples 1 to 8, the secondary battery 100 satisfies R2≤20R1. Compared with Example 9, the capacity retention rate of the secondary battery 100 in Examples 1 to 8 is higher. It can be seen that by setting R2≤20R1, the resistance of the first coating 60 relative to the first pole ear 301 and the first current collector 2011 is not too large, which is beneficial to reduce the loss of electric energy by the first coating 60 and improve the discharge capacity of the secondary battery 100.

[0104] In Examples 4 to 9, the secondary battery 100 satisfies R2≥5R1. Compared with Examples 2 and 3, the secondary battery 100 in Examples 4 to 9 has a higher pass rate in the cycle test. It can be seen that setting R2≥5R1 is conducive to further reducing the current density of the first electrode 201 and reducing lithium plating. In Examples 1 to 6, the secondary battery 100 satisfies R2≤20R1. Compared with Examples 7 and 8, the capacity retention rate of the secondary battery 100 in Examples 1 to 6 is higher. It can be seen that setting R2≤20R1 is conducive to further reducing the loss of electric energy by the first coating 60 and improving the discharge capacity of the secondary battery 100.

[0105] In Examples 2 to 9, the secondary battery 100 satisfies R3≥0.65R4. Compared with Example 1, the secondary battery 100 in Examples 2 to 9 has a higher pass rate in the cycle test. It can be seen that by setting R3≥0.65R4, the total resistance value of the first pole piece 201, the first pole ear 301 and the first coating 60 will not be too small, which is conducive to reducing the current density of the first pole piece 201, thereby reducing the possibility of lithium deposition in the first pole piece 201. In Examples 1 to 8, the secondary battery 100 satisfies R3≤15R4. Compared with Example 9, the capacity retention rate of the secondary battery 100 in Examples 1 to 8 is higher. It can be seen that by setting R3≤15R4, the total resistance value of the first pole piece 201, the first pole ear 301 and the first coating 60 will not be too large, which is conducive to the release of the capacity of the first pole piece 201, thereby facilitating the improvement of the discharge capacity of the secondary battery 100.

[0106] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application and are not intended to be limiting of the present application. As long as they are within the spirit and scope of the present application, appropriate changes and modifications to the above embodiments are within the scope of the present application.

Claims

1. A secondary battery, characterized in that: It includes an electrode assembly, a first conductive member and a first adapter; The electrode assembly comprises a plurality of pole pieces and a separation film, wherein the plurality of pole pieces are stacked along a first direction, any two adjacent pole pieces have opposite polarities, and the separation film is disposed between any two adjacent pole pieces; the first direction is a thickness direction of the pole pieces; The plurality of pole pieces include a first pole piece, at least one second pole piece and a third pole piece with the same polarity, the first pole piece and the third pole piece are respectively located at two outermost layers of the electrode assembly, and the second pole piece is located between the first pole piece and the second pole piece; The secondary battery further comprises a first pole tab, a second pole tab and a third pole tab, the first pole sheet comprises a first current collector and a first active material layer, the first pole 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 pole sheet comprises a second current collector and a second active material layer, the second pole tab is connected to the second current collector, two second active material layers are provided, and are respectively arranged on two surfaces of the second current collector arranged oppositely along the first direction; the third pole tab is connected to the third pole sheet; The first pole tab, the second pole tab and the third pole tab are stacked, and the first pole tab is provided with a first through hole extending along the thickness direction thereof; The first conductive member is inserted into the first through hole, and the first conductive member is electrically connected to all the second tabs and the third tabs, and the first adapter is connected to the first conductive member; The first pole tab has a first surface and a second surface that are oppositely disposed along a thickness direction thereof, the first surface faces the second pole tab, and the first adapter is located on a side of the first pole tab having the second surface; The secondary battery further includes a first coating layer, the first coating layer is conductive, and the first coating layer includes a first portion, a second portion, and a third portion connected to each other; the first portion is disposed on the first surface to separate the first electrode tab from the second electrode tab; The second portion covers the surrounding wall of the first through hole to separate the first electrode tab from the first conductive member; The third portion is disposed on the second surface to separate the first electrode 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 electrode tab is provided with a second through hole extending along the first direction, the second conductive member is passed through the second through hole, and the second conductive member is electrically connected to all the second electrode tabs; The third pole tab has a third surface and a fourth surface that are arranged opposite to each other along the first direction, and the fourth surface faces the second pole tab; The electrode assembly further includes a second coating layer, the second coating layer is conductive, and the second coating layer includes a fourth portion and a fifth portion connected to each other; The fourth portion is disposed on the fourth surface to separate the third electrode tab from the second electrode tab; The fifth portion covers a peripheral wall of the second through hole to separate the third electrode tab from the second conductive member, and the second coating layer contacts the second conductive member.

3. A secondary battery, characterized in that: It includes an electrode assembly, a first conductive member and a first adapter; The electrode assembly comprises a plurality of pole pieces and a separation film, wherein the plurality of pole pieces are stacked along a first direction, any two adjacent pole pieces have opposite polarities, and the separation film is disposed between any two adjacent pole pieces; the first direction is a thickness direction of the pole pieces; The plurality of pole pieces include a first pole piece, at least one second pole piece and a third pole piece with the same polarity, the first pole piece and the third pole piece are respectively located at two outermost layers of the electrode assembly, and the second pole piece is located between the first pole piece and the second pole piece; The electrode assembly further includes a first electrode tab, a second electrode tab and a third electrode tab, the first electrode sheet includes a first current collector and a first active material layer, the first electrode 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 electrode tab is connected to the second current collector, two second active material layers are provided, and are respectively arranged on two surfaces of the second current collector arranged oppositely along the first direction; the third electrode tab is connected to the third electrode sheet; The first pole tab, the second pole tab and the third pole tab are stacked, and the first pole tab is provided with a first through hole extending along the thickness direction thereof; The first conductive member is inserted into the first through hole, and the first conductive member is electrically connected to all the second pole tabs and the third pole tabs; the first adapter is connected to the third pole tab; The first electrode tab has a first surface and a second surface arranged opposite to each other along a thickness direction thereof, and the first surface faces the second electrode tab; The electrode assembly further includes a first coating layer, the first coating layer is conductive, and the first coating layer includes a first portion and a second portion connected to each other; the first portion is disposed on the first surface to separate the first electrode tab from the second electrode tab; The second portion covers the surrounding wall of the first through hole to separate the first electrode 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, characterized in that: The thickness of the first portion is T1, 3 μm≤T1≤10 μm.

5. The secondary battery according to claim 1 or 3, characterized in that: The first current collector includes a fifth surface and a sixth surface arranged opposite to each other along the first direction, the first active material layer is arranged on the fifth surface, and the first coating layer covers at least a portion of the surface of the sixth surface.

6. The secondary battery according to claim 1 or 3, characterized in that: The total resistance value of the first electrode 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, characterized in that: 5R1≤R2≤10R1.

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

9. The secondary battery according to claim 1 or 3, characterized in that: The total resistance value of the first pole piece, the first pole lug and the first coating is R3, the total resistance value of any second pole piece and the second pole lug connected thereto is R4, and 0.65R4≤R3≤15R4.

10. The secondary battery according to claim 1 or 3, characterized in that: The material of the first coating 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, characterized in that: The first coating 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 inserted into the first through hole, and the second connecting portion is located on a side of the first electrode tab having the second surface; The second connecting portion and the third portion are stacked along a thickness direction of the first electrode tab.

12. An electrical device, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 11.

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