Secondary battery and electric device

Abstract

The invention discloses a secondary battery and electric equipment. The secondary battery comprises a shell and an electrode assembly accommodated in the shell, the electrode assembly comprises a first pole piece and a second pole piece which are opposite in polarity, and a diaphragm for separating the first pole piece and the second pole piece. The first pole piece comprises a first current collector and a first active material layer, the first current collector comprises a first folding part, a connecting part and a second folding part which are sequentially connected, the first folding part comprises a first straight section and a first bent section which are alternately connected, and the second folding part comprises a second straight section and a second bent section which are alternately connected. In the first direction, the second straight section connected to the connecting part comprises a first part exceeding the first straight section, and the first part is provided with an empty foil area electrically connected with the shell. Along the second direction, the second pole piece is arranged between any two adjacent straight sections, and the first active material layer is arranged between the first current collector and the second pole piece. The internal resistance of the secondary battery is reduced, and the charge-discharge rate and the energy density of the secondary battery are improved.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to a secondary battery and electrical equipment. Background Art

[0002] In the prior art, a steel case battery includes a housing and an electrode assembly, wherein the electrode assembly includes an anode electrode sheet, a cathode electrode sheet and a diaphragm, wherein the diaphragm separates the anode electrode sheet from the cathode electrode sheet. In order to lead the electrical properties of the anode electrode sheet to the housing, the anode electrode sheet is provided with a plurality of anode tabs, and the plurality of anode tabs need to be gathered to form a tab bundle. Summary of the invention

[0003] For secondary batteries in the prior art, the inventors found that multiple anode tabs need to be bent and then stacked together to form a tab group, and then the tab group is welded to form a tab bundle. When the secondary battery falls or vibrates, the anode tab is prone to breakage. Especially when the number of anode tabs is large, the anode tab is bent more and more prone to breakage, resulting in poor electrical connection between the shell and the anode pole piece. The gathering of multiple anode tabs to form a tab bundle requires a certain amount of space inside the shell, resulting in a loss of energy density of the secondary battery. In addition, the internal resistance of the secondary battery is usually large, and the charge and discharge rate is not high when the secondary battery is charged and discharged.

[0004] In view of the above situation, it is necessary to provide a secondary battery that is conducive to reducing internal resistance, improving charging and discharging rate and energy density.

[0005] The first aspect of the present application provides a secondary battery, comprising a housing and an electrode assembly, wherein the electrode assembly is contained in the housing. The electrode assembly comprises a first electrode sheet, a second electrode sheet and a diaphragm, wherein the polarity of the second electrode sheet is opposite to that of the first electrode sheet, and the diaphragm separates the first electrode sheet from the second electrode sheet. The first electrode sheet comprises a first current collector and a first active material layer, wherein the first current collector comprises a first folding portion, a connecting portion and a second folding portion connected in sequence, wherein the first folding portion comprises a plurality of first straight sections and a first bending section connected alternately, and the second folding portion comprises a plurality of second straight sections and a second bending section connected alternately. Along the first direction, the second straight section connected to the connecting portion comprises a first portion extending beyond the first straight section, and a hollow foil region is provided on a side of the first portion facing the first folding portion, and the hollow foil region of the first portion is electrically connected to the housing. Along the second direction, the second electrode sheet is disposed between two adjacent arbitrary straight sections, and the first active material layer is disposed between the arbitrary straight section and the second electrode sheet. The first direction is perpendicular to the second direction, and the second direction is the thickness direction of the electrode assembly.

[0006] In the secondary battery of the present application, the side of the first part facing the first folding portion is an empty foil area, and the empty foil area of ​​the first part is electrically connected to the shell, so that the first electrode sheet can be directly electrically connected to the shell, which can shorten the charge and discharge path of the secondary battery, thereby helping to reduce the internal resistance of the secondary battery and improve the charge and discharge rate of the secondary battery. In addition, the empty foil area of ​​the first part is electrically connected to the shell, which can reduce the space occupied by the tab group inside the shell, thereby helping to improve the energy density of the secondary battery.

[0007] In one or more of the above embodiments, the first pole piece is an anode pole piece, and the second pole piece is a cathode pole piece.

[0008] In the above embodiment, compared with the case where the first pole piece is a cathode pole piece, the first pole piece is an anode pole piece, which is beneficial to reduce the potential difference between the first pole piece and the shell, thereby helping to reduce the risk of electrochemical corrosion in the electrolyte. In addition, if the first pole piece is a cathode pole piece and is electrically connected to the shell, the requirements for the shell are higher. For example, if the cathode pole piece is made of conventional aluminum material, the shell needs to be an aluminum shell, and the strength of the aluminum shell is relatively low. Under the same strength requirements for the shell, the aluminum shell needs to be thicker. Therefore, compared with the case where the first pole piece is a cathode pole piece, the first pole piece is an anode pole piece, which is beneficial to reduce the loss of energy density of the secondary battery.

[0009] In one or more of the above embodiments, along the second direction, at the first folded portion, the projection of the first straight section covers the projection of the second pole piece, and at the second folded portion, the projection of the second straight section covers the projection of the second pole piece.

[0010] In the above embodiment, it is helpful to reduce the space occupied by the electrode assembly in the direction perpendicular to the second direction. When the first pole piece is an anode pole piece and the second pole piece is a cathode pole piece, it is helpful to alleviate the lithium deposition phenomenon at the connection between the first straight section and the second straight section. In addition, it is also helpful to reduce the risk of short circuit caused by the second pole piece contacting the shell.

[0011] In one or more of the above embodiments, the number of first straight segments is m, and the number of second straight segments is n. Along the first direction, the size of the first straight segment is a, and the size of the second straight segment is b, 0.1≤(m×a) / (m×a+n×b)≤0.9.

[0012] In the above embodiment, the difference between the charge and discharge path from the first portion through the first folded portion and the charge and discharge path from the first portion through the second folded portion is small, which is beneficial to further reduce the internal resistance of the secondary battery and further improve the charge and discharge rate of the secondary battery.

[0013] In one or more of the above embodiments, 0.25≤a / b≤0.75.

[0014] In the above embodiment, when a / b is less than 0.25, the size a of the first straight section will be smaller. To satisfy 0.1≤(m×a) / (m×a+n×b)≤0.9, the number m of the first straight sections will be larger, resulting in a longer size of the first folded portion along the second direction, thereby making the secondary battery less resistant to deformation. Therefore, by setting 0.25≤a / b, it is helpful to ensure the resistant to deformation of the secondary battery. By setting a / b≤0.75, along the first direction, the size of the first straight section is not longer than the size of the second straight section, so that the first part can have a larger empty foil area to be electrically connected to the shell, which is helpful to improve the stability of the electrical connection between the empty foil area and the shell.

[0015] In one or more of the above embodiments, the secondary battery further comprises a conductive member, and the conductive member is disposed between the outer shell and the empty foil area along the second direction. The empty foil area and the outer shell are electrically connected through the conductive member.

[0016] In the above embodiment, the conductive member is helpful to improve the convenience of electrical connection between the empty foil area and the shell.

[0017] In one or more of the above embodiments, the conductive member includes a protrusion, and the protrusion is integrally formed with the housing.

[0018] The above embodiment is helpful to reduce the space required for the conductive member in the housing, thereby helping to reduce the loss of secondary battery energy density caused by the provision of the conductive member.

[0019] In one or more of the above embodiments, the conductive member includes a metal spring sheet, and along the second direction, the metal spring sheet is in a compressed state between the housing and the first part.

[0020] In the above embodiment, the metal spring has a small resistance, which is conducive to improving the conductive efficiency between the first part and the shell. In addition, the metal spring in a compressed state can abut against the shell and the first part respectively, which is conducive to improving the stability of the electrical connection between the first part and the shell.

[0021] In one or more of the above embodiments, the conductive member includes conductive glue, and the hollow foil area is further bonded to the housing through the conductive glue.

[0022] In the above embodiment, the empty foil area is electrically connected and bonded to the shell by conductive glue, which can reduce the possibility of movement of the electrode assembly relative to the shell, and is beneficial to reducing the risk of deformation of the shell due to falling, etc., resulting in failure of the electrical connection between the shell and the empty foil area.

[0023] In one or more of the above embodiments, along the second direction, a side of the first straight section farthest from the second folded portion facing away from the first portion is provided with an empty foil area, and is electrically connected to the housing.

[0024] In the above embodiment, based on the electrical connection between the empty foil area of ​​the first part and the outer shell, the first electrode can also be electrically connected to the outer shell through an additional empty foil area, which is beneficial to further shorten the charge and discharge path of the secondary battery, thereby further reducing the internal resistance of the secondary battery and further improving the charge and discharge rate of the secondary battery.

[0025] In one or more of the above embodiments, along the second direction, a side of the second straight section farthest from the first folded portion facing away from the first portion is provided with an empty foil area and is electrically connected to the housing.

[0026] In the above embodiment, based on the electrical connection between the empty foil area of ​​the first part and the outer shell, the first electrode can also be electrically connected to the outer shell through an additional empty foil area, which is beneficial to further shorten the charge and discharge path of the secondary battery, thereby further reducing the internal resistance of the secondary battery and further improving the charge and discharge rate of the secondary battery.

[0027] In one or more of the above embodiments, the diaphragm includes a first diaphragm and a second diaphragm, which are respectively arranged on two opposite sides of the first current collector along the thickness direction, and the first diaphragm and the second diaphragm are respectively continuous at the first bending section and the second bending section.

[0028] In the above embodiment, in the first bending section and the second bending section, the first diaphragm and the second diaphragm can also separate the second pole piece from the first pole piece, which is beneficial to reduce the risk of short circuit caused by contact between the second pole piece and the first pole piece.

[0029] In one or more of the above embodiments, along the first direction, the sizes of the plurality of first straight sections are all equal. And / or, along the first direction, the sizes of the plurality of second straight sections are all equal.

[0030] In the above embodiment, the first current collector can be made more regular as a whole, so that the electrode assembly can be made more regular as a whole, which is beneficial to improving the utilization of the space in the shell by the electrode assembly, thereby improving the energy density of the secondary battery. In addition, the shell and the electrode assembly can be better contoured, which is beneficial to improving the convenience of processing the shell.

[0031] The second aspect of the present application provides an electric device, comprising the secondary battery of the first aspect of the present application. The secondary battery has a low internal resistance and a high charge and discharge rate, which is conducive to improving the charge and discharge rate of the electric device. The secondary battery has a high energy density, which is conducive to improving the endurance of the electric device. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A front view of a secondary battery provided in accordance with an embodiment of the present application.

[0033] Figure 2A top view of a secondary battery provided in accordance with an embodiment of the present application.

[0034] Figure 3 For an embodiment of the present application Figure 1 Cross-section along the midline AA.

[0035] Figure 4 For an embodiment of the present application Figure 2 Cross-section along section line BB.

[0036] Figure 5 An overall schematic diagram of an electrical device provided in one embodiment of the present application.

[0037] Main component symbols

[0038] Electrical equipment 1000

[0039] Secondary battery 100

[0040] Housing 10

[0041] Accommodation chamber 101

[0042] Step portion 102

[0043] First Wall 1021

[0044] Second Wall 1022

[0045] Housing 11

[0046] Bottom wall 111

[0047] Side wall 112

[0048] Shell cover 12

[0049] Electrode assembly 20

[0050] First straight section 2011

[0051] The second straight section 2012

[0052] First bending section 2021

[0053] Second bending section 2022

[0054] The first pole piece 21

[0055] First current collector 211

[0056] First folding portion 2111

[0057] Connection 2112

[0058] Second folding portion 2113

[0059] Part I2113a

[0060] First active material layer 212

[0061] The second pole piece 22

[0062] Second fluid collector 221

[0063] Second active material layer 222

[0064] Diaphragm 23

[0065] The first diaphragm 231

[0066] Second diaphragm 232

[0067] Tab 30

[0068] Tab bundle 40

[0069] Pole 50

[0070] Insulation 60

[0071] First direction X

[0072] Second direction Y

[0073] The third direction Z. DETAILED DESCRIPTION

[0074] 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.

[0075] 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.

[0076] Unless otherwise specified, the term "plurality" as used herein means two or more than two.

[0077] The terms "first", "second", etc. are only used to distinguish different objects and shall not be understood as indicating or implying relative importance or implying the quantity, specific order or primary and secondary relationship of the technical features indicated.

[0078] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0079] It should be understood that, considering the actual processing tolerance factors, in the technical solution of the present application, when the two elements are arranged parallel / vertically and in the same direction, there may be a certain angle between the two elements, and a tolerance of 0-±10% is allowed between the two elements. A tolerance of 0-±10% is allowed between the two elements greater than, equal to or less than.

[0080] The embodiment of the present application provides a secondary battery, including a shell and an electrode assembly, wherein the electrode assembly is contained in the shell. The electrode assembly includes a first pole piece, a second pole piece and a diaphragm, wherein the polarity of the second pole piece is opposite to that of the first pole piece, and the diaphragm separates the first pole piece from the second pole piece. The first pole piece includes a first current collector and a first active material layer, wherein the first current collector includes a first folding portion, a connecting portion and a second folding portion connected in sequence, wherein the first folding portion includes a plurality of first straight sections and a first bending section connected alternately, and the second folding portion includes a plurality of second straight sections and a second bending section connected alternately. Along the first direction, the second straight section connected to the connecting portion includes a first portion extending beyond the first straight section, and a hollow foil area is provided on one side of the first portion facing the first folding portion, and the hollow foil area of ​​the first portion is electrically connected to the shell. Along the second direction, the second pole piece is disposed between two adjacent first straight sections, between the adjacent first straight section and the second straight section, and between two adjacent second straight sections, and the first active material layer is disposed between the first current collector and the second pole piece. The first direction is perpendicular to the second direction, and the second direction is the thickness direction of the electrode assembly.

[0081] In the secondary battery of the present application, a hollow foil area is provided on one side of the first part facing the first folding portion, and the hollow foil area of ​​the first part is electrically connected to the shell, so that the first electrode sheet can be directly electrically connected to the shell, which can shorten the charge and discharge path of the secondary battery, thereby facilitating the reduction of the internal resistance of the secondary battery and improving the charge and discharge rate of the secondary battery. In addition, the hollow foil area of ​​the first part is electrically connected to the shell, which can reduce the space occupied by the tab group inside the shell, thereby facilitating the improvement of the energy density of the secondary battery.

[0082] Some embodiments of the present application will be described below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0083] Please refer to Figures 1 to 4An embodiment of the present application provides a secondary battery 100 , including a housing 10 and an electrode assembly 20 , wherein the electrode assembly 20 is accommodated in the housing 10 .

[0084] In some embodiments, see Figure 3 and Figure 4 The housing 10 is provided with a receiving cavity 101 , and the electrode assembly 20 is disposed in the receiving cavity 101 .

[0085] In some embodiments, the housing 10 includes a housing 11 and a housing cover 12 . The housing 11 is recessed in a direction away from the housing cover 12 . The housing cover 12 is connected to the housing 11 to form a receiving cavity 101 .

[0086] In some embodiments, the housing 10 is a metal housing, and the material of the housing 10 includes at least one of steel alloy, aluminum alloy and copper alloy. The material of the housing 11 and the housing cover 12 includes at least one of steel alloy, aluminum alloy and copper alloy. In some embodiments, the housing cover 12 is welded to the housing 11.

[0087] In some embodiments, the housing 11 includes a bottom wall 111 and a side wall 112 . The side wall 112 is disposed around the periphery of the bottom wall 111 , and the housing cover 12 covers the side wall 112 .

[0088] See also Figure 3 The electrode assembly 20 includes a first electrode piece 21 , a second electrode piece 22 and a diaphragm 23 . The second electrode piece 22 has a polarity opposite to that of the first electrode piece 21 . The diaphragm 23 separates the first electrode piece 21 from the second electrode piece 22 .

[0089] In some embodiments, the first electrode sheet 21 includes a first current collector 211 and a first active material layer 212, the first current collector 211 includes a first folded portion 2111, a connecting portion 2112, and a second folded portion 2113 connected in sequence, the first folded portion 2111 includes a plurality of first straight segments 2011 and a first bent segment 2021 connected alternately, and the second folded portion 2113 includes a plurality of second straight segments 2012 and a second bent segment 2022 connected alternately. Along the first direction X, the second straight segment 2012 exceeds the first straight segment 2011, and the first direction X is perpendicular to the thickness direction of the electrode assembly 20. The so-called several may refer to one, two, three or more.

[0090] In some embodiments, the first straight section 2011 and the two adjacent first bent sections 2021 connected to the first straight section 2011, as well as the second straight section 2012 and the two adjacent second bent sections 2022 connected to the second straight section 2012 are roughly in a "Z" shape, wherein the preceding first bent section 2021 and the succeeding first bent section 2021 connected to the first straight section 2011 are respectively connected to different ends of the first straight section 2011, and the preceding second bent section 2022 and the succeeding second bent section 2022 connected to the second straight section 2012 are respectively connected to different ends of the second straight section 2012.

[0091] In some embodiments, the first bent segment 2021 and the two adjacent first straight segments 2011 connected to the first bent segment 2021, and the second bent segment 2022 and the two adjacent second straight segments 2012 connected to the second bent segment 2022 are roughly in a "U" shape, wherein the preceding first straight segment 2011 and the succeeding first straight segment 2011 connected to the first bent segment 2021 are respectively connected to different ends of the first bent segment 2021, and the preceding second straight segment 2012 and the succeeding second straight segment 2012 connected to the second bent segment 2022 are respectively connected to different ends of the second bent segment 2022.

[0092] See also Figure 3 , along the second direction Y, the second pole piece 22 is disposed between two adjacent first straight sections 2011, between adjacent first straight sections 2011 and second straight sections 2012, and between two adjacent second straight sections 2012, and the second direction Y is the thickness direction of the electrode assembly 20. The first direction X is perpendicular to the second direction Y. In some embodiments, the second pole piece 22 includes a second current collector 221 and a second active material layer 222.

[0093] In some embodiments, the first current collector 211 and the second current collector 221 are metal layers. As an illustrative example, the first current collector 211 may be a metal layer including at least one of copper, nickel, tantalum, and titanium, such as a copper foil. The second current collector 221 may be a metal layer including at least one of aluminum, nickel, tantalum, and titanium, such as an aluminum foil.

[0094] See also Figure 3, along the second direction Y, the first active material layer 212 is disposed between the first current collector 211 and the second pole piece 22, and the second active material layer 222 is disposed between the first active material layer 212 and the second current collector 221. In some embodiments, the first active material layer 212 includes a first active material, and the second active material layer 222 includes a second active material. As an illustrative example, the first active material includes at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen material, and silicon-carbon material. The second active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganese oxide.

[0095] See also Figure 3 , along the first direction X, the second straight section 2012 connected to the connecting portion 2112 includes a first portion 2113a that exceeds the first straight section 2011, and a hollow foil area is provided on one side of the first portion 2113a facing the first folded portion 2111, and the hollow foil area of ​​the first portion 2113a is electrically connected to the housing 10. In this case, the first electrode sheet 21 can be directly electrically connected to the housing 10, which can shorten the charge and discharge path of the secondary battery 100, thereby facilitating the reduction of the internal resistance of the secondary battery 100 and improving the charge and discharge rate of the secondary battery 100. In addition, the hollow foil area of ​​the first portion 2113a is electrically connected to the housing 10 to reduce the space occupied by the tab group inside the housing 10, thereby facilitating the improvement of the energy density of the secondary battery 100. The so-called hollow foil area is not provided with the first active material layer 212.

[0096] In some embodiments, the first active material layer 212 may be pre-set on one side of the first portion 2113a facing the first folding portion 2111, and a hollow foil area is formed by laser cleaning the one side of the first portion 2113a facing the first folding portion 2111. In this case, a small amount of the first active material may exist in the hollow foil area of ​​the first portion 2113a in consideration of the processing error of the actual process.

[0097] In some embodiments, the first portion 2113a has an empty foil area on one side facing the first folding portion 2111 , which can make the empty foil area of ​​the first portion 2113a larger and help improve the stability of the electrical connection between the empty foil area of ​​the first portion 2113a and the housing 10 .

[0098] In some embodiments, along the second direction Y, a first straight section 2011 that is farthest from the second folded portion 2113 has a hollow foil area on a side facing away from the first portion 2113a, and is electrically connected to the housing 10. In this way, on the basis of the hollow foil area of ​​the first portion 2113a being electrically connected to the housing 10, the first electrode sheet 21 can also be electrically connected to the housing 10 through the additional hollow foil area, which is beneficial to further shorten the charge and discharge path of the secondary battery 100, thereby further reducing the internal resistance of the secondary battery 100 and further improving the charge and discharge rate of the secondary battery 100.

[0099] In some embodiments, along the second direction Y, a second straight section 2012 that is farthest from the first folded portion 2111 is provided with an empty foil area on a side away from the first portion 2113a, and is electrically connected to the housing 10. In this way, on the basis of the empty foil area of ​​the first portion 2113a being electrically connected to the housing 10, the first electrode sheet 21 can also be electrically connected to the housing 10 through the additional empty foil area, which is beneficial to further shorten the charge and discharge path of the secondary battery 100, thereby further reducing the internal resistance of the secondary battery 100 and further improving the charge and discharge rate of the secondary battery 100.

[0100] In some embodiments, the secondary battery 100 includes a conductive member (not shown), which is disposed between the housing 10 and the empty foil area along the second direction Y. The empty foil area is electrically connected to the housing 10 through the conductive member. The conductive member is conducive to improving the convenience of electrical connection between the empty foil area and the housing 10.

[0101] In some embodiments, the conductive member includes a protrusion, and the protrusion is integrally formed with the housing 10. In this case, it is beneficial to reduce the space required for the conductive member in the housing 10, thereby reducing the loss of energy density of the secondary battery 100 caused by the provision of the conductive member. In some embodiments, the housing 10 is laser roughened to form a protrusion on the housing 10.

[0102] In some embodiments, the conductive member includes a metal spring, and the metal spring is in a compressed state between the housing 10 and the first portion 2113a along the second direction Y. The metal spring has a small resistance, which is beneficial to improving the conductive efficiency between the first portion 2113a and the housing 10. In addition, the metal spring in a compressed state can abut against the housing 10 and the first portion 2113a, respectively, which is beneficial to improving the stability of the electrical connection between the first portion 2113a and the housing 10.

[0103] In some embodiments, the conductive member includes a conductive adhesive, and the hollow foil area is also bonded to the housing 10 through the conductive adhesive. In this case, the hollow foil area is electrically connected and bonded to the housing 10 through the conductive adhesive, which can reduce the possibility of the electrode assembly 20 moving relative to the housing 10, and is conducive to reducing the risk of deformation of the housing 10 due to falling, etc., resulting in failure of the electrical connection between the housing 10 and the hollow foil area.

[0104] In some embodiments, along the first direction X, the sizes of the plurality of first straight sections 2011 are all equal. In some embodiments, the sizes of the plurality of second straight sections 2012 are all equal. In this case, the first current collector 211 can be made more regular as a whole, so that the electrode assembly 20 can be made more regular as a whole, which is beneficial to improve the utilization of the space in the housing 10 by the electrode assembly 20, thereby facilitating the improvement of the energy density of the secondary battery 100. In addition, the housing 10 and the electrode assembly 20 can be better contoured, which is beneficial to improving the convenience of processing the housing 10. The sizes of the plurality of first straight sections 2011 are all equal, but not absolutely equal, and a tolerance of ±10% is allowed for the sizes of the first straight sections 2011. The sizes of the plurality of second straight sections 2012 are all equal, but not absolutely equal, and a tolerance of ±10% is allowed for the sizes of the second straight sections 2012.

[0105] In some embodiments, along the first direction X, the sizes of the plurality of first straight segments 2011 may be unequal, and the sizes of the plurality of second straight segments 2012 may be unequal. However, along the first direction X, the size of the second straight segment 2012 connected to the connecting portion 2112 is greater than the largest size of the plurality of first straight segments 2011.

[0106] In some embodiments, see Figure 3 , the housing 10 includes a step portion 102, and the step portion 102 includes a first wall 1021 and a second wall 1022 connected to the first wall 1021. Along the first direction X, the projection of the first wall 1021 is separated from the projection of the second folded portion 2113. Along the second direction Y, the projection of the second wall 1022 is separated from the projection of the first folded portion 2111. In this case, it is beneficial for the housing 10 to conform to the electrode assembly 20, thereby facilitating the improvement of the energy density of the secondary battery 100.

[0107] In some embodiments, the housing cover 12 includes a step portion 102, which can facilitate electrical connection between the housing cover 12 and the empty foil area of ​​the first portion 2113a.

[0108] In some embodiments, along the second direction Y, at the first folding portion 2111, the projection of the first straight section 2011 covers the projection of the second electrode sheet 22, and at the second folding portion 2113, the projection of the second straight section 2012 covers the projection of the second electrode sheet 22. In this case, it is helpful to reduce the space occupied by the electrode assembly 20 in a direction perpendicular to the second direction Y. When the first electrode sheet 21 is an anode electrode sheet and the second electrode sheet 22 is a cathode electrode sheet, it is helpful to alleviate the lithium deposition phenomenon on the first straight section 2011 and the second straight section 2012. In addition, it is also helpful to reduce the risk of short circuit caused by the second electrode sheet 22 contacting the housing 10.

[0109] In some embodiments, along the first direction X, the size of the second pole piece 22 located at the second folded portion 2113 is larger than the size of the second pole piece 22 located at the first folded portion 2111. This is beneficial to fully utilize the surplus space of the second straight section 2012 beyond the first straight section 2011 along the first direction X, thereby facilitating the improvement of the energy density of the secondary battery 100.

[0110] In some embodiments, the number of the first straight segments 2011 is m, and the number of the second straight segments 2012 is n. Along the first direction X, the size of the first straight segment 2011 is a, the size of the second straight segment 2012 is b, and 0.1≤(m×a) / (m×a+n×b)≤0.9. For example, the value of (m×a) / (m×a+n×b) is 0.1, 0.3, 0.5, 0.7 or 0.9. In this case, the difference between the charge and discharge path from the first portion 2113a through the first folded portion 2111 and the charge and discharge path from the first portion 2113a through the second folded portion 2113 is small, which is conducive to further reducing the internal resistance of the secondary battery 100 and further improving the charge and discharge rate of the secondary battery 100.

[0111] It should be noted that the formula “(m×a) / (m×a+n×b)” actually intends to characterize the proportion of the total size of the first folded portion 2111 along the first direction X in the total size of the first current collector 211 along the first direction X when the electrode assembly 20 is flattened along the first direction X. Since the size of the first bent section 2021 in the present application is much smaller than the size of the first straight section 2011, and the size of the second bent section 2022 is much smaller than the size of the second straight section 2012, the sizes of the first bent section 2021 and the second bent section 2022 are negligible in the formula “(m×a) / (m×a+n×b)”. However, if the size of the first bent section 2021 is close to the size of the first straight section 2011, and the size of the second bent section 2022 is close to the size of the second straight section 2012, the sizes of the first bent section 2021 and the second bent section 2022 should be considered in the formula “(m×a) / (m×a+n×b)”.

[0112] In order to verify the influence of the value of (m×a) / (m×a+n×b) of the present application on the internal resistance and charge and discharge rate of the secondary battery 100, the inventors of the present application conducted the following experiment, which included 6 groups of comparative examples and 5 groups of exemplary embodiments. The first electrode plate 21 of the secondary battery 100 used in the comparative examples and exemplary embodiments is the anode electrode plate.

[0113] Table 1 - Relationship between (m×a) / (m×a+n×b) and internal resistance of secondary battery 100 and charging time

[0114]

[0115] In Table 1, the nominal capacity of the secondary battery 100 is 2800 mAh, the internal resistance of the secondary battery 100 is the internal resistance measured at a measurement current of 1000 Hz, and the charging time of the secondary battery 100 is the time required to charge the secondary battery 100 from 3.5 V to 4.52 V at room temperature using a constant current of 6 A, and then fully charge the secondary battery 100 using a constant voltage of 4.52 V. It should be understood that if the charging time of the secondary battery 100 is shorter, the charging rate of the secondary battery 100 is higher, and similarly, the discharge rate of the secondary battery 100 is also higher.

[0116] It can be seen from Comparative Examples 1 to 3, and from Comparative Examples 4 to 6 that when the values ​​of (m×a) / (m×a+n×b) are equal, the number m of the first straight segments 2011, the number n of the second straight segments 2012, the size a of the first straight segments 2011, and the size b of the second straight segments 2012 have little effect on the internal resistance and charging time of the secondary battery 100.

[0117] According to Comparative Examples 1 to 6 and Examples 1 to 5, it can be seen that when 0.1<(m×a) / (m×a+n×b) or (m×a) / (m×a+n×b)>0.9, the internal resistance of the secondary battery 100 in Comparative Examples 1 to 6 is greater than the internal resistance of the secondary battery 100 in Examples 1 to 5, and the charging time of the secondary battery 100 in Comparative Examples 1 to 6 is greater than the charging time of the secondary battery 100 in Examples 1 to 5. Moreover, according to Comparative Examples 1 to 3 and Example 1, and according to Comparative Examples 4 to 6 and Example 5, when 0.1<(m×a) / (m×a+n×b) or (m×a) / (m×a+n×b)>0.9, a slight change in (m×a) / (m×a+n×b) will lead to a significant increase in the internal resistance and charging time of the secondary battery 100. That is to say, by setting 0.1≤(m×a) / (m×a+n×b)≤0.9, it is beneficial to further reduce the internal resistance of the secondary battery 100 and further improve the charge and discharge rate of the secondary battery 100 .

[0118] In some embodiments, 0.25≤a / b≤0.75. When a / b<0.25, the size a of the first straight section 2011 will be smaller. To satisfy 0.1≤(m×a) / (m×a+n×b)≤0.9, the number m of the first straight sections 2011 will be larger, resulting in a longer size of the first folded portion 2111 along the second direction Y, thereby making the deformation resistance of the secondary battery 100 poor. Therefore, by setting 0.25≤a / b, it is helpful to ensure the deformation resistance of the secondary battery 100. By setting a / b≤0.75, along the first direction X, the size of the first straight section 2011 is not longer than the size of the second straight section 2012, so that the first part 2113a can have a larger empty foil area to be electrically connected to the shell 10, which is helpful to improve the stability of the electrical connection between the empty foil area and the shell 10.

[0119] In some embodiments, the first bending section 2021 and the second bending section 2022 are not provided with the first active material layer 212 , which is beneficial to reduce the space occupied by the first active material layer 212 and further improve the energy density of the secondary battery 100 .

[0120] In some embodiments, see Figure 3 The first current collector 211 is integrally formed, and a first folding portion 2111, a connecting portion 2112, and a second folding portion 2113 are formed by reciprocatingly bending the first current collector 211 in a flat state.

[0121] In some embodiments, the second pole piece 22 is insulated and connected to the housing 10. Figure 4 The second current collector 221 is provided with a tab 30 , which is connected to the second current collector 221 and extends out of the second current collector 221 along the third direction Z. A plurality of tabs 30 are stacked in sequence along the second direction Y and welded to form a tab bundle 40 .

[0122] In some embodiments, see Figure 4 The secondary battery 100 includes a pole 50 , which is insulated and fixed to the housing 10 , and the tab bundle 40 is bent in a direction opposite to the second direction Y and connected to the pole 50 .

[0123] In some embodiments, the tab bundle 40 is connected to the pole 50 through an adapter (not shown). The adapter is made of one or more conductive materials such as copper, aluminum, nickel, and nickel alloy.

[0124] In some embodiments, the pole 50 is insulated and fixed to the side wall 112 of the housing 11. Figure 4 The secondary battery 100 includes an insulating member 60 , which is disposed on the side wall 112 of the housing 11 . Along the second direction Y and the third direction Z, at least a portion of the insulating member 60 is located between the pole 50 and the side wall 112 .

[0125] In some embodiments, the first pole piece 21 is an anode pole piece, and the second pole piece 22 is a cathode pole piece. Compared with the case where the first pole piece 21 is a cathode pole piece, the first pole piece 21 is an anode pole piece, which is beneficial to reduce the potential difference between the first pole piece 21 and the shell 10, thereby reducing the risk of electrochemical corrosion in the electrolyte. In addition, if the first pole piece 21 is a cathode pole piece and is electrically connected to the shell 10, the requirements for the shell 10 are higher. For example, if the cathode pole piece adopts conventional aluminum material, the shell 10 needs to be an aluminum shell, and the strength of the aluminum shell is low. Under the same strength requirements for the shell 10, the aluminum shell needs a greater thickness, so compared with the case where the first pole piece 21 is a cathode pole piece, the first pole piece 21 is an anode pole piece, which is beneficial to reduce the loss of energy density of the secondary battery 100. In some other embodiments, the first pole piece 21 is a cathode pole piece, and the second pole piece 22 is an anode pole piece.

[0126] In some embodiments, along the first direction X, the projection of the anode electrode piece covers the projection of the cathode electrode piece. This is beneficial to reduce the occurrence of lithium deposition and improve the service life of the secondary battery 100. In addition, when the first electrode piece 21 is an anode electrode piece, the contact area of ​​the first electrode piece 21 that can be electrically connected to the housing 10 is larger, which is beneficial to improve the stability of the electrical connection between the first electrode piece 21 and the housing 10.

[0127] In some embodiments, along the second direction Y, the separator 23 is disposed between the first active material layer 212 and the second active material layer 222 , and separates the first active material layer 212 from the second active material layer 222 .

[0128] In some embodiments, the diaphragm 23 is an insulating film material such as a polyethylene film, a polypropylene film, a polyester film, or a polyimide film.

[0129] In some embodiments, the diaphragm 23 is interrupted in the empty foil area, which is beneficial to facilitate the electrical connection between the empty foil area and the housing 10 .

[0130] In some embodiments, see Figure 3 , the diaphragm 23 includes a first diaphragm 231 and a second diaphragm 232, and the first diaphragm 231 and the second diaphragm 232 are respectively arranged on two opposite sides of the first current collector 211 in the thickness direction. The first diaphragm 231 and the second diaphragm 232 are respectively continuous at the first bending section 2021 and the second bending section 2022. In this case, the first diaphragm 231 and the second diaphragm 232 can also separate the second pole piece 22 from the first pole piece 21 in the size of the first bending section 2021 and the second bending section 2022, which is conducive to reducing the risk of short circuit caused by the second pole piece 22 contacting the first pole piece 21.

[0131] exist Figure 3 In the illustrated embodiment, the first separator 231 and the second separator 232 are respectively compounded on two opposite surfaces of the first current collector 211 along the thickness direction.

[0132] In some embodiments, the secondary battery 100 includes an electrolyte (not shown), which is disposed in the receiving cavity 101. The electrolyte facilitates ion conduction between the first active material layer 212 and the second active material layer 222.

[0133] See also Figure 5 One embodiment of the present application provides an electric device 1000, comprising the secondary battery 100 as described above. The secondary battery 100 has a low internal resistance and a high charge and discharge rate, which is beneficial to improving the charge and discharge rate of the electric device 1000. The secondary battery 100 has a high energy density, which is beneficial to improving the endurance of the electric device 1000. The electric device 1000 includes but is not limited to electronic devices such as mobile phones, tablet computers, and laptop computers.

[0134] In addition, those skilled in the art should recognize that the above embodiments are only used to illustrate the present application, and are not intended to limit the present application. As long as they are within the essential scope of the present application, appropriate changes and modifications to the above embodiments are within the scope disclosed in the present application.

Claims

1. A secondary battery, characterized in that: It comprises a housing and an electrode assembly, wherein the electrode assembly is accommodated in the housing; The electrode assembly comprises a first electrode sheet, a second electrode sheet and a separator, the polarity of the second electrode sheet is opposite to that of the first electrode sheet, and the separator separates the first electrode sheet from the second electrode sheet; the first electrode sheet comprises a first current collector and a first active material layer, the first current collector comprises a first folding portion, a connecting portion and a second folding portion connected in sequence, the first folding portion comprises a plurality of first straight sections and a first bent section connected alternately, and the second folding portion comprises a plurality of second straight sections and a second bent section connected alternately; Along the first direction, the second straight segment connected to the connecting portion includes a first portion extending beyond the first straight segment, a hollow foil area is provided on a side of the first portion facing the first folding portion, and the hollow foil area of ​​the first portion is electrically connected to the outer shell; along the second direction, the second pole piece is provided between two adjacent first straight segments, between adjacent first straight segments and the second straight segments, and between the two adjacent second straight segments, and the first active material layer is provided between the first current collector and the second pole piece; the first direction is perpendicular to the second direction, and the second direction is the thickness direction of the electrode assembly.

2. The secondary battery according to claim 1, characterized in that: The first pole piece is an anode pole piece, and the second pole piece is a cathode pole piece.

3. The secondary battery according to claim 2, characterized in that: Along the second direction, at the first folded portion, the projection of the first straight section covers the projection of the second pole piece, and at the second folded portion, the projection of the second straight section covers the projection of the second pole piece.

4. The secondary battery according to claim 1, characterized in that: The number of the first straight segments is m, and the number of the second straight segments is n; along the first direction, the size of the first straight segment is a, and the size of the second straight segment is b, 0.1≤(m×a) / (m×a+n×b)≤0.

9.

5. The secondary battery according to claim 4, characterized in that: 0.25≤a / b≤0.

75.

6. The secondary battery according to claim 1, characterized in that: The secondary battery further comprises a conductive member, which is disposed between the outer shell and the empty foil area along the second direction; the empty foil area and the outer shell are electrically connected via the conductive member.

7. The secondary battery according to claim 6, characterized in that: The conductive member includes a protrusion, and the protrusion is integrally formed with the housing.

8. The secondary battery according to claim 6, characterized in that: The conductive member includes a metal spring sheet, and along the second direction, the metal spring sheet is in a compressed state between the housing and the first part.

9. The secondary battery according to claim 6, characterized in that: The conductive member includes conductive glue, and the hollow foil area is also bonded to the shell through the conductive glue.

10. The secondary battery according to claim 1, characterized in that: Along the second direction, a side of the first straight section farthest from the second folded portion facing away from the first portion is provided with an empty foil area, and is electrically connected to the housing.

11. The secondary battery according to claim 1 or 10, characterized in that: Along the second direction, a side of the second straight section farthest from the first folded portion facing away from the first portion is provided with an empty foil area, and is electrically connected to the housing.

12. The secondary battery according to claim 1, characterized in that: The separator includes a first separator and a second separator. The first separator and the second separator are respectively arranged on two opposite surfaces of the first current collector along the thickness direction. The first separator and the second separator are respectively continuous at the first bending section and the second bending section.

13. The secondary battery according to claim 1, characterized in that: Along the first direction, the sizes of the plurality of first straight sections are all equal; and / or, along the first direction, the sizes of the plurality of second straight sections are all equal.

14. An electrical device, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 13.

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