Secondary battery and electric device

Abstract

Disclosed are a secondary battery and an electric device. The secondary battery comprises a housing and an electrode assembly accommodated in the housing. The electrode assembly comprises a first electrode sheet and a second electrode sheet having opposite polarities, and a separator used for separating 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 which are connected in sequence; the first folding portion comprises first straight sections and first bent sections which are alternately connected; and the second folding portion comprises second straight sections and second bent sections which are alternately connected. In a first direction, each second straight section connected to the connecting portion comprises a first portion beyond the corresponding first straight section, and an empty foil region electrically connected to the housing is provided at each first portion. In a second direction, the second electrode sheet is arranged between any two adjacent straight sections, and the first active material layer is arranged between the first current collector and the second electrode sheet. The battery structure is conducive to reducing the internal resistance of the secondary battery, thereby improving the charge / discharge rate and the energy density of the secondary battery.

Description

Secondary batteries and electrical equipment

[0001] This application claims priority to Chinese Patent Application No. 202411985151.7, filed with the Chinese Patent Office on December 31, 2024, entitled "Secondary Battery and Electrical Equipment", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of energy storage technology, and in particular to a secondary battery and electrical equipment. Background Technology

[0003] In the prior art, a steel-cased battery includes a casing and an electrode assembly. The electrode assembly includes an anode electrode, a cathode electrode, and a separator, with the separator separating the anode electrode and the cathode electrode. To conduct the electrical charge from the anode electrode to the casing, the anode electrode has multiple anode tabs, which need to be gathered together to form a tab bundle. Summary of the Invention

[0004] Regarding existing secondary batteries, the inventors discovered that multiple anode tabs need to be bent and stacked together to form a tab group, which is then fused together to form a tab bundle. When the secondary battery is dropped or vibrated, the anode tabs are prone to breakage, especially when there are many anode tabs, as the bending degree of the anode tabs is greater and breakage is more likely, leading to poor electrical connection between the casing and the anode plates. The tab bundle formed by multiple anode tabs occupies a certain amount of internal space in the casing, resulting in a loss of energy density in the secondary battery. Furthermore, the internal resistance of secondary batteries is usually relatively high, resulting in a low charge / discharge rate.

[0005] In view of the above situation, it is necessary to provide a secondary battery that can reduce internal resistance, improve charge and discharge rate and energy density.

[0006] This application provides a secondary battery, including a casing and an electrode assembly housed within the casing. The electrode assembly includes a first electrode, a second electrode, and a separator. The polarity of the second electrode is opposite to that of the first electrode. The separator separates the first electrode from the second electrode. The first electrode includes a first current collector and a first active material layer. The first current collector includes a first folded portion, a connecting portion, and a second folded portion connected in sequence. The first folded portion includes a plurality of alternately connected first straight segments and first bent segments. The second folded portion includes a plurality of alternately connected second straight segments and second bent segments. Along a first direction, the second straight segment connected to the connecting portion includes a first portion extending beyond the first straight segment. The side of the first portion facing the first folded portion has an empty foil area, which is electrically connected to the casing. Along a second direction, the second electrode is disposed between two adjacent arbitrary straight segments, and the first active material layer is disposed between an arbitrary straight segment and the second electrode. The first direction is perpendicular to the second direction, which is the thickness direction of the electrode assembly.

[0007] In the secondary battery of this application, the side of the first portion facing the first fold is an empty foil area. This empty foil area is electrically connected to the outer casing, allowing the first electrode to be directly electrically connected to the outer casing. This shortens the charging and discharging path of the secondary battery, thereby reducing its internal resistance and increasing its charging and discharging rate. Furthermore, the electrical connection between the empty foil area and the outer casing reduces the space occupied by the tab group inside the casing, thus improving the energy density of the secondary battery.

[0008] In one or more of the above embodiments, the first electrode is an anode electrode and the second electrode is a cathode electrode.

[0009] In the above embodiments, compared to the case where the first electrode is a cathode electrode, using the first electrode as an anode electrode is beneficial for reducing the potential difference between the first electrode and the outer casing, thereby reducing the risk of electrochemical corrosion in the electrolyte. Furthermore, if the first electrode is a cathode electrode electrically connected to the outer casing, the requirements for the outer casing are higher. For example, if the cathode electrode is made of conventional aluminum, the outer casing must be an aluminum shell. Since aluminum shells have lower strength, to meet the same strength requirements, the aluminum shell needs to be thicker. Therefore, compared to the case where the first electrode is a cathode electrode, using the first electrode as an anode electrode is beneficial for reducing the energy density loss of the secondary battery.

[0010] In one or more of the above embodiments, along the second direction, in the first folded portion, the projection of the first straight segment covers the projection of the second electrode, and in the second folded portion, the projection of the second straight segment covers the projection of the second electrode.

[0011] In the above embodiments, it is beneficial to reduce the space occupied by the electrode assembly in the direction perpendicular to the second direction. When the first electrode is an anode electrode and the second electrode is a cathode electrode, it is beneficial to alleviate lithium plating at the connection between the first and second straight sections. Furthermore, it is also beneficial to reduce the risk of short circuits caused by the second electrode contacting the outer casing.

[0012] 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, the size of the second straight segment is b, and 0.1≤(m×a) / (m×a+n×b)≤0.9.

[0013] In the above embodiments, the difference between the charging and discharging path from the first part through the first fold and the charging and discharging path from the first part through the second fold is small, which is beneficial to further reduce the internal resistance of the secondary battery and further improve the charging and discharging rate of the secondary battery.

[0014] In one or more of the above embodiments, 0.25 ≤ a / b ≤ 0.75.

[0015] In the above embodiments, when a / b < 0.25, the dimension 'a' of the first straight segment will be relatively small. To satisfy 0.1 ≤ (m × a) / (m × a + n × b) ≤ 0.9, the number of first straight segments 'm' will be relatively large, resulting in a longer dimension of the first folded portion along the second direction, thus making the secondary battery less resistant to deformation. Therefore, setting 0.25 ≤ a / b helps to ensure the secondary battery's resistance to deformation. Setting a / b ≤ 0.75 ensures that the dimension of the first straight segment is not too long relative to the dimension of the second straight segment along the first direction, allowing the first part to have a larger empty foil area for electrical connection with the outer casing, which helps to improve the stability of the electrical connection between the empty foil area and the outer casing.

[0016] In one or more of the above embodiments, the secondary battery further includes a conductive element disposed between the outer casing and the empty foil area along the second direction. The empty foil area and the outer casing are electrically connected through the conductive element.

[0017] In the above embodiments, the use of conductive components facilitates the convenient electrical connection between the empty foil area and the outer casing.

[0018] In one or more of the above embodiments, the conductive element includes a protrusion, which is integrally formed with the outer shell.

[0019] In the above embodiments, it is beneficial to reduce the space required for conductive components within the casing, thereby reducing the loss of secondary battery energy density caused by the installation of conductive components.

[0020] In one or more of the above embodiments, the conductive element includes a metal spring, which is in a compressed state between the outer shell and the first part along the second direction.

[0021] In the above embodiments, the metal spring has low resistance, which helps to improve the conductivity between the first part and the outer shell. Furthermore, the compressed metal spring can abut against both the outer shell and the first part, which helps to improve the stability of the electrical connection between the first part and the outer shell.

[0022] In one or more of the above embodiments, the conductive component includes conductive adhesive, and the empty foil area is also bonded to the outer shell by conductive adhesive.

[0023] In the above embodiments, the empty foil area is electrically connected and bonded to the outer shell through conductive adhesive, which can reduce the possibility of the electrode assembly moving relative to the outer shell. This helps to reduce the risk of the outer shell deforming due to drops or other situations, which could lead to the failure of the electrical connection between the outer shell and the empty foil area.

[0024] In one or more of the above embodiments, along the second direction, the side of the first straight section furthest from the second fold portion that faces away from the first portion is provided with an empty foil area and is electrically connected to the outer casing.

[0025] In the above embodiments, based on the electrical connection between the empty foil area of ​​the first part and the outer casing, the first electrode can also be electrically connected to the outer casing through an additional empty foil area, which is beneficial to further shorten the charging and discharging path of the secondary battery, thereby further reducing the internal resistance of the secondary battery and further improving the charging and discharging rate of the secondary battery.

[0026] In one or more of the above embodiments, along the second direction, the side of the second straight section furthest from the first fold portion that faces away from the first portion is provided with an empty foil area and is electrically connected to the outer casing.

[0027] In the above embodiments, based on the electrical connection between the empty foil area of ​​the first part and the outer casing, the first electrode can also be electrically connected to the outer casing through an additional empty foil area, which is beneficial to further shorten the charging and discharging path of the secondary battery, thereby further reducing the internal resistance of the secondary battery and further improving the charging and discharging rate of the secondary battery.

[0028] In one or more of the above embodiments, the diaphragm includes a first diaphragm and a second diaphragm, which are respectively disposed on opposite sides of the first current collector along the thickness direction, and the first diaphragm and the second diaphragm are continuous at the first bending section and the second bending section, respectively.

[0029] In the above embodiments, the first diaphragm and the second diaphragm can also separate the second electrode from the first electrode in the first bending section and the second bending section, which helps to reduce the risk of short circuit when the second electrode and the first electrode come into contact.

[0030] In one or more of the above embodiments, the dimensions of the plurality of first straight segments are all equal along the first direction. And / or, the dimensions of the plurality of second straight segments are all equal along the first direction.

[0031] In the above embodiments, the first current collector can be made more regular in shape, which in turn makes the electrode assembly more regular in shape. This is beneficial for improving the utilization of the internal space of the electrode assembly, thereby improving the energy density of the secondary battery. Furthermore, it allows for better conformal matching between the outer casing and the electrode assembly, thus improving the ease of casing processing.

[0032] A second aspect of this application provides an electrical device including the secondary battery of the first aspect of this application. The secondary battery has low internal resistance and a high charge / discharge rate, which is beneficial for improving the charge / discharge rate of the electrical device. The secondary battery also has high energy density, which is beneficial for improving the battery life of the electrical device. Attached Figure Description

[0033] Figure 1 is a front view of a secondary battery provided in an embodiment of this application.

[0034] Figure 2 is a top view of a secondary battery provided in an embodiment of this application.

[0035] Figure 3 is a cross-sectional view along section line AA in Figure 1 according to an embodiment of this application.

[0036] Figure 4 is a cross-sectional view along section line BB in Figure 2 of an embodiment of this application.

[0037] Figure 5 is an overall schematic diagram of an electrical device provided in an embodiment of this application.

[0038] Key Component Symbols Explanation: Electrical Equipment 1000 Secondary Battery 100 Outer Shell 10 Receiving Cavity 101 Stepped Section 102 First Wall 1021 Second Wall 1022 Outer Shell 11 Bottom Wall 111 Side Wall 112 Shell Cover 12 Electrode Assembly 20 First Straight Section 2011 Second Straight Section 2012 First Bending Section 2021 Second Bending Section 2022 First Electrode 21 First Current Collector 211 First Folded Section 2111 Connecting Section 2112 Second Folded Section 2113 First Part 2113a First Active Material Layer 212 Second Electrode 22 Second Current Collector 221 Second Active Material Layer 222 Separator 23 First Separator 231 Second Separator 232 Tab 30 Tab Bundle 40 Terminal 50 Insulating Component 60 First Direction X Second Direction Y Third Direction Z Detailed Implementation

[0039] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0040] It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or may also have a component that is centrally located. When a component is considered to be "set" on another component, it can be directly set on the other component or may also have a component that is centrally located.

[0041] Unless otherwise stated, the term "multiple" as used herein refers to two or more.

[0042] The terms “first”, “second”, etc., are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implying the quantity, specific order, or primary and secondary relationship of the indicated technical features.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0044] It should be understood that, considering the actual machining tolerance, in the technical solution of this application, when the two components are set in parallel / perpendicular directions, they are set in the same direction, and there may be a certain angle between the two components. The tolerance between the two components is allowed to be 0-±10%, and the tolerance between the two components is allowed to be greater than, equal to or less than 0-±10%.

[0045] Embodiments of this application provide a secondary battery, including a casing and an electrode assembly housed within the casing. The electrode assembly includes a first electrode, a second electrode, and a separator. The polarity of the second electrode is opposite to that of the first electrode. The separator separates the first electrode and the second electrode. The first electrode includes a first current collector and a first active material layer. The first current collector includes a first folded portion, a connecting portion, and a second folded portion connected in sequence. The first folded portion includes a plurality of alternately connected first straight segments and first bent segments. The second folded portion includes a plurality of alternately connected second straight segments and second bent segments. Along a first direction, the second straight segment connected to the connecting portion includes a first portion extending beyond the first straight segment. The side of the first portion facing the first folded portion has an empty foil area, which is electrically connected to the casing. Along a second direction, the second electrode is disposed between two adjacent first straight segments, between adjacent first straight segments and second straight segments, and between two adjacent second straight segments. The first active material layer is disposed between the first current collector and the second electrode. The first direction is perpendicular to the second direction, which is the thickness direction of the electrode assembly.

[0046] In the secondary battery of this application, a hollow foil area is provided on the side of the first portion facing the first folded portion. The hollow foil area of ​​the first portion is electrically connected to the outer casing, which allows the first electrode to be directly electrically connected to the outer casing. This shortens the charging and discharging path of the secondary battery, thereby reducing the internal resistance of the secondary battery and improving the charging and discharging rate. Furthermore, the electrical connection between the hollow foil area of ​​the first portion and the outer casing reduces the space occupied by the tab group inside the outer casing, thereby improving the energy density of the secondary battery.

[0047] Some embodiments of this application will now be described with reference to the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0048] Referring to Figures 1 to 4, embodiments of this application provide a secondary battery 100, including a housing 10 and an electrode assembly 20, wherein the electrode assembly 20 is housed within the housing 10.

[0049] In some embodiments, please refer to Figures 3 and 4, the housing 10 is provided with a receiving cavity 101, and the electrode assembly 20 is disposed in the receiving cavity 101.

[0050] In some embodiments, the housing 10 includes a housing 11 and a cover 12, the housing 11 being recessed in a direction away from the cover 12, and the cover 12 being connected to the housing 11 to form a receiving cavity 101.

[0051] In some embodiments, the outer casing 10 is a metal casing, and the material of the outer casing 10 includes at least one selected from steel alloy, aluminum alloy, and copper alloy. The outer casing 11 and the cover 12 are made of at least one selected from steel alloy, aluminum alloy, and copper alloy. In some embodiments, the cover 12 is welded to the outer casing 11.

[0052] In some embodiments, the housing 11 includes a bottom wall 111 and a side wall 112, the side wall 112 surrounding the periphery of the bottom wall 111, and the housing cover 12 covering the side wall 112.

[0053] Please refer to Figure 3. The electrode assembly 20 includes a first electrode 21, a second electrode 22, and a diaphragm 23. The second electrode 22 has the opposite polarity to the first electrode 21, and the diaphragm 23 separates the first electrode 21 from the second electrode 22.

[0054] In some embodiments, the first electrode 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 alternately connected first straight segments 2011 and first bent segments 2021. The second folded portion 2113 includes a plurality of alternately connected second straight segments 2012 and second bent segments 2022. Along a first direction X, the second straight segments 2012 extend beyond the first straight segments 2011. The first direction X is perpendicular to the thickness direction of the electrode assembly 20. The term "a plurality of" can refer to one, two, three, or more.

[0055] In some embodiments, the first straight segment 2011 and two adjacent first bend segments 2021 connected to the first straight segment 2011, and the second straight segment 2012 and two adjacent second bend segments 2022 connected to the second straight segment 2012 are generally in a "Z" shape, wherein the preceding first bend segment 2021 and the following first bend segment 2021 connected to the first straight segment 2011 are respectively connected to different ends of the first straight segment 2011, and the preceding second bend segment 2022 and the following second bend segment 2022 connected to the second straight segment 2012 are respectively connected to different ends of the second straight segment 2012.

[0056] In some embodiments, the first bent segment 2021 and two adjacent first straight segments 2011 connected to the first bent segment 2021, and the second bent segment 2022 and two adjacent second straight segments 2012 connected to the second bent segment 2022 are generally U-shaped, wherein the preceding first straight segment 2011 and the following 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 following second straight segment 2012 connected to the second bent segment 2022 are respectively connected to different ends of the second bent segment 2022.

[0057] Referring to Figure 3, along the second direction Y, the second electrode 22 is disposed between two adjacent first straight segments 2011, between an adjacent first straight segment 2011 and a second straight segment 2012, and between two adjacent second straight segments 2012. 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 electrode 22 includes a second current collector 221 and a second active material layer 222.

[0058] In some embodiments, the first current collector 211 and the second current collector 221 are metal layers. As an example, the first current collector 211 may be a metal layer including at least one of copper, nickel, tantalum, and titanium, such as copper foil. The second current collector 221 may be a metal layer including at least one of aluminum, nickel, tantalum, and titanium, such as aluminum foil.

[0059] Referring to Figure 3, along the second direction Y, a first active material layer 212 is disposed between a first current collector 211 and a second electrode 22, and a 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 material, and the second active material layer 222 includes a second active material material. As an example, the first active material material includes at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen materials, and silicon-carbon materials. 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.

[0060] Referring to Figure 3, along the first direction X, the second straight section 2012 connected to the connecting portion 2112 includes a first portion 2113a extending beyond the first straight section 2011. The side of the first portion 2113a facing the first folded portion 2111 has an empty foil area, which is electrically connected to the outer casing 10. In this configuration, the first electrode 21 can be directly electrically connected to the outer casing 10, shortening the charging and discharging path of the secondary battery 100, thereby reducing the internal resistance of the secondary battery 100 and increasing its charging and discharging rate. Furthermore, the electrical connection of the empty foil area of ​​the first portion 2113a to the outer casing 10 reduces the space occupied by the tab group inside the outer casing 10, thus improving the energy density of the secondary battery 100. The empty foil area does not have a first active material layer 212.

[0061] In some embodiments, the side of the first portion 2113a facing the first fold 2111 may be pre-formed with a first active material layer 212, and an empty foil area is formed by laser cleaning of the side of the first portion 2113a facing the first fold 2111. In this case, considering the processing error of the actual process, a small amount of the first active material may be present in the empty foil area of ​​the first portion 2113a.

[0062] In some embodiments, the side of the first portion 2113a facing the first fold 2111 is provided with an empty foil area, which can make the area of ​​the empty foil area of ​​the first portion 2113a larger, which is beneficial to improving the stability of the electrical connection between the empty foil area of ​​the first portion 2113a and the outer shell 10.

[0063] In some embodiments, along the second direction Y, the side of the first straight segment 2011 furthest from the second fold 2113 opposite to the first portion 2113a has an empty foil area, which is electrically connected to the outer casing 10. Thus, in addition to the empty foil area of ​​the first portion 2113a being electrically connected to the outer casing 10, the first electrode 21 can also be electrically connected to the outer casing 10 through an additional empty foil area. This helps to further shorten the charging and discharging path of the secondary battery 100, thereby further reducing the internal resistance of the secondary battery 100 and further improving the charging and discharging rate of the secondary battery 100.

[0064] In some embodiments, along the second direction Y, the side of the second straight segment 2012 furthest from the first fold 2111 that faces away from the first portion 2113a has an empty foil area, which is electrically connected to the outer casing 10. Thus, in addition to the empty foil area of ​​the first portion 2113a being electrically connected to the outer casing 10, the first electrode 21 can also be electrically connected to the outer casing 10 through an additional empty foil area. This helps to further shorten the charging and discharging path of the secondary battery 100, thereby further reducing the internal resistance of the secondary battery 100 and further improving the charging and discharging rate of the secondary battery 100.

[0065] In some embodiments, the secondary battery 100 includes a conductive element (not shown) disposed between the outer casing 10 and the empty foil area along the second direction Y. The empty foil area and the outer casing 10 are electrically connected via the conductive element. The conductive element facilitates easier electrical connection between the empty foil area and the outer casing 10.

[0066] In some embodiments, the conductive element includes a protrusion integrally formed with the housing 10. This reduces the space required for the conductive element within the housing 10, thereby reducing energy density loss in the secondary battery 100 due to the conductive element. In some embodiments, the housing 10 is laser-textured to form the protrusion.

[0067] In some embodiments, the conductive element includes a metal spring that is compressed between the housing 10 and the first portion 2113a along the second direction Y. The metal spring has low resistance, which is beneficial for improving the conductivity between the first portion 2113a and the housing 10. Furthermore, the compressed metal spring can abut against both the housing 10 and the first portion 2113a, which is beneficial for improving the stability of the electrical connection between the first portion 2113a and the housing 10.

[0068] In some embodiments, the conductive element includes conductive adhesive, and the empty foil area is also bonded to the housing 10 via conductive adhesive. In this case, the empty foil area is electrically connected and bonded to the housing 10 via conductive adhesive, which can reduce the possibility of the electrode assembly 20 shifting relative to the housing 10, and help reduce the risk of the housing 10 deforming due to drops or other reasons, leading to the failure of the electrical connection between the housing 10 and the empty foil area.

[0069] In some embodiments, along the first direction X, the dimensions of a plurality of first straight segments 2011 are all equal. In some embodiments, the dimensions of a plurality of second straight segments 2012 are all equal. In this case, the first current collector 211 can be made more regular overall, thereby making the electrode assembly 20 more regular overall, which is beneficial to improving the utilization of the internal space of the casing 10 by the electrode assembly 20, thereby improving the energy density of the secondary battery 100. Furthermore, the casing 10 and the electrode assembly 20 can be better conformed, thereby improving the ease of processing the casing 10. The fact that the dimensions of the plurality of first straight segments 2011 are all equal is not completely absolute; a tolerance of ±10% is allowed in the dimensions of the first straight segments 2011. Similarly, the fact that the dimensions of the plurality of second straight segments 2012 are all equal is not completely absolute; a tolerance of ±10% is allowed in the dimensions of the second straight segments 2012.

[0070] In some embodiments, along the first direction X, the dimensions of the plurality of first straight segments 2011 may be unequal, and the dimensions of the plurality of second straight segments 2012 may be unequal. However, along the first direction X, the dimension of the second straight segment 2012 connected to the connecting portion 2112 is greater than the largest dimension among the plurality of first straight segments 2011.

[0071] In some embodiments, referring to FIG3, the housing 10 includes a stepped portion 102, which includes a first wall 1021 and a second wall 1022 connecting the first wall 1021. Along a first direction X, the projection of the first wall 1021 is separate from the projection of the second fold portion 2113. Along a second direction Y, the projection of the second wall 1022 is separate from the projection of the first fold portion 2111. In this case, it is advantageous for the housing 10 to conform to the electrode assembly 20, thereby improving the energy density of the secondary battery 100.

[0072] In some embodiments, the cover 12 includes a stepped portion 102, which facilitates electrical connection between the cover 12 and the empty foil area of ​​the first portion 2113a.

[0073] In some embodiments, along the second direction Y, in the first fold 2111, the projection of the first straight section 2011 covers the projection of the second electrode 22, and in the second fold 2113, the projection of the second straight section 2012 covers the projection of the second electrode 22. In this case, it is beneficial to reduce the space occupied by the electrode assembly 20 in the direction perpendicular to the second direction Y. When the first electrode 21 is an anode electrode and the second electrode 22 is a cathode electrode, it is beneficial to mitigate lithium plating on the first straight section 2011 and the second straight section 2012. Furthermore, it is also beneficial to reduce the risk of short circuit caused by the second electrode 22 contacting the housing 10.

[0074] In some embodiments, along the first direction X, the size of the second electrode 22 located in the second fold 2113 is larger than the size of the second electrode 22 located in the first fold 2111. This facilitates full utilization of the extra space in the second straight section 2012 that extends beyond the first straight section 2011 along the first direction X, thereby improving the energy density of the secondary battery 100.

[0075] In some embodiments, the number of first straight segments 2011 is m, and the number of second straight segments 2012 is n. Along the first direction X, the size of the first straight segment 2011 is a, and the size of the second straight segment 2012 is b, where 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 charging / discharging path from the first portion 2113a through the first fold 2111 and the charging / discharging path from the first portion 2113a through the second fold 2113 is small, which is beneficial for further reducing the internal resistance of the secondary battery 100 and further improving the charging / discharging rate of the secondary battery 100.

[0076] It should be noted that the formula “(m×a) / (m×a+n×b)” is actually intended to represent the proportion of the total dimension of the first folded portion 2111 along the first direction X in the total dimension of the first current collector 211 along the first direction X when the electrode assembly 20 is in a flattened state along the first direction X. However, since the size of the first bent segment 2021 is much smaller than the size of the first straight segment 2011 and the size of the second bent segment 2022 is much smaller than the size of the second straight segment 2012 in this application, the sizes of the first bent segment 2021 and the second bent segment 2022 are ignored in the formula “(m×a) / (m×a+n×b)”. However, if the dimensions of the first bent segment 2021 are similar to those of the first straight segment 2011, and the dimensions of the second bent segment 2022 are similar to those of the second straight segment 2012, then the dimensions of the first bent segment 2021 and the second bent segment 2022 should be considered in the formula “(m×a) / (m×a+n×b)”.

[0077] To verify the effect of the value of (m×a) / (m×a+n×b) on the internal resistance and charge / discharge rate of the secondary battery 100, the inventors of this application conducted the following experiments, which included 6 comparative examples and 5 implementation examples. The first electrode 21 of the secondary battery 100 used in the comparative examples and implementation examples was the anode electrode.

[0078] Table 1 – Relationship between (m×a) / (m×a+n×b) and the internal resistance and charging time of secondary battery 100

[0079] In Table 1, the nominal capacity of secondary battery 100 is 2800mAh. The internal resistance of secondary battery 100 is measured at a current of 1000Hz. The charging time of secondary battery 100 is the time required to charge it from 3.5V to 4.52V using a constant current of 6A at room temperature, and then fully charge it using a constant voltage of 4.52V. It should be understood that the shorter the charging time of secondary battery 100, the higher its charging rate; similarly, the higher its discharging rate.

[0080] Based on Comparative Examples 1 to 3, and Comparative Examples 4 to 6, it can be seen that when the value of (m×a) / (m×a+n×b) is equal, the changes in the number m of the first straight segment 2011, the number n of the second straight segment 2012, the size a of the first straight segment 2011, and the size b of the second straight segment 2012 have little effect on the internal resistance and charging time of the secondary battery 100.

[0081] As can be seen from Comparative Examples 1 to 6 and Examples 1 to 5, 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 that in Examples 1 to 5, and the charging time of the secondary battery 100 in Comparative Examples 1 to 6 is greater than that in Examples 1 to 5. Furthermore, 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, even a small change in (m×a) / (m×a+n×b) leads to a significant increase in the internal resistance and charging time of the secondary battery 100. In other words, 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 charging and discharging rate of the secondary battery 100.

[0082] In some embodiments, 0.25 ≤ a / b ≤ 0.75. When a / b < 0.25, the size a of the first straight segment 2011 will be small. To satisfy 0.1 ≤ (m×a) / (m×a+n×b) ≤ 0.9, the number m of the first straight segments 2011 will be large, resulting in a longer dimension of the first folded portion 2111 along the second direction Y, thus making the deformation resistance of the secondary battery 100 poor. Therefore, by setting 0.25 ≤ a / b, it is beneficial to ensure the deformation resistance of the secondary battery 100. Setting a / b ≤ 0.75, along the first direction X, the size of the first straight segment 2011 is not too long relative to the size of the second straight segment 2012, which allows the first part 2113a to have a larger empty foil area electrically connected to the outer casing 10, which is beneficial to improving the stability of the electrical connection between the empty foil area and the outer casing 10.

[0083] In some embodiments, the first bending segment 2021 and the second bending segment 2022 do not have the first active material layer 212. This helps to reduce the space occupied by the first active material layer 212 and further improve the energy density of the secondary battery 100.

[0084] In some embodiments, please refer to FIG3, the first current collector 211 is integrally formed, and by repeatedly bending the first current collector 211 in a flat state, a first folded portion 2111, a connecting portion 2112, and a second folded portion 2113 are formed.

[0085] In some embodiments, the second electrode 22 is insulated from the housing 10. Referring to FIG4, the second current collector 221 is provided with tabs 30, which are connected to the second current collector 221 and extend from the second current collector 221 in a third direction Z. A plurality of tabs 30 are stacked sequentially along a second direction Y and welded to form a tab bundle 40.

[0086] In some embodiments, please refer to FIG4, the secondary battery 100 includes a terminal post 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 terminal post 50.

[0087] In some embodiments, the tab bundle 40 is connected to the pole post 50 via an adapter (not shown). The adapter is made of one or more conductive materials such as copper, aluminum, nickel, and nickel alloys.

[0088] In some embodiments, the terminal 50 is insulated and fixed to the side wall 112 of the housing 11. Referring to FIG4, the secondary battery 100 includes an insulating member 60 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 terminal 50 and the side wall 112.

[0089] In some embodiments, the first electrode 21 is the anode electrode, and the second electrode 22 is the cathode electrode. Compared to the case where the first electrode 21 is the cathode electrode, using the first electrode 21 as the anode electrode is beneficial for reducing the potential difference between the first electrode 21 and the casing 10, thereby reducing the risk of electrochemical corrosion in the electrolyte. Furthermore, if the first electrode 21 is the cathode electrode and electrically connected to the casing 10, the requirements for the casing 10 are higher. For example, if the cathode electrode is made of conventional aluminum, the casing 10 needs to be an aluminum shell. Since aluminum shells have lower strength, to meet the same strength requirements for the casing 10, the aluminum shell needs to be thicker. Therefore, compared to the case where the first electrode 21 is the cathode electrode, using the first electrode 21 as the anode electrode is beneficial for reducing the energy density loss of the secondary battery 100. In other embodiments, the first electrode 21 is the cathode electrode, and the second electrode 22 is the anode electrode.

[0090] In some embodiments, along the first direction X, the projection of the anode electrode overlaps the projection of the cathode electrode. This helps reduce lithium plating and improves the lifespan of the secondary battery 100. Furthermore, when the first electrode 21 is the anode electrode, the contact area between the first electrode 21 and the housing 10 is larger, which helps improve the stability of the electrical connection between the first electrode 21 and the housing 10.

[0091] In some embodiments, along the second direction Y, a diaphragm 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 and the second active material layer 222.

[0092] In some embodiments, the diaphragm 23 is an insulating membrane material such as a polyethylene membrane, a polypropylene membrane, a polyester membrane, or a polyimide membrane.

[0093] In some embodiments, the diaphragm 23 is interrupted in the empty foil area. This facilitates electrical connection between the empty foil area and the housing 10.

[0094] In some embodiments, referring to FIG3, the diaphragm 23 includes a first diaphragm 231 and a second diaphragm 232, which are respectively disposed on opposite sides of the first current collector 211 along the thickness direction. The first diaphragm 231 and the second diaphragm 232 are continuous at the first bending section 2021 and the second bending section 2022, respectively. In this case, the dimensions of the first bending section 2021 and the second bending section 2022, as well as the first diaphragm 231 and the second diaphragm 232, can also separate the second electrode 22 from the first electrode 21, which helps to reduce the risk of short circuits caused by contact between the second electrode 22 and the first electrode 21.

[0095] In the embodiment shown in FIG3, the first diaphragm 231 and the second diaphragm 232 are respectively composited on opposite sides of the first current collector 211 along the thickness direction.

[0096] In some embodiments, the secondary battery 100 includes an electrolyte (not shown) 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.

[0097] Referring to Figure 5, one embodiment of this application provides an electrical device 1000, including the secondary battery 100 as described above. The secondary battery 100 has low internal resistance and a high charge / discharge rate, which is beneficial for improving the charge / discharge rate of the electrical device 1000. The secondary battery 100 has high energy density, which is beneficial for improving the battery life of the electrical device 1000. The electrical device 1000 includes, but is not limited to, electronic devices such as mobile phones, tablet computers, and laptop computers.

[0098] Furthermore, those skilled in the art should recognize that the above embodiments are merely illustrative of this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the substantive scope of this application fall within the scope of this application.

Claims

1. A secondary battery, characterized in that, It includes a housing and an electrode assembly, the electrode assembly being housed within the housing; The electrode assembly includes a first electrode, a second electrode, and a diaphragm. The polarity of the second electrode is opposite to that of the first electrode. The diaphragm separates the first electrode from the second electrode. The first electrode includes a first current collector and a first active material layer. The first current collector includes a first folded portion, a connecting portion, and a second folded portion connected in sequence. The first folded portion includes a plurality of alternately connected first straight segments and first bent segments. The second folded portion includes a plurality of alternately connected second straight segments and second bent segments. Along the first direction, the second straight section connected to the connecting portion includes a first portion extending beyond the first straight section. The side of the first portion facing the first folded portion has an empty foil area, and the empty foil area of ​​the first portion is electrically connected to the outer casing. Along the second direction, the second electrode is disposed between two adjacent first straight sections, between two adjacent first straight sections and the second straight section, and between two adjacent second straight sections. The first active material layer is disposed between the first current collector and the second electrode. 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 electrode is the anode electrode, and the second electrode is the cathode electrode.

3. The secondary battery according to claim 2, characterized in that, Along the second direction, at the first fold, the projection of the first straight segment covers the projection of the second electrode, and at the second fold, the projection of the second straight segment covers the projection of the second electrode.

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 also includes a conductive element, which is disposed between the outer casing and the empty foil area along the second direction; the empty foil area and the outer casing are electrically connected through the conductive element.

7. The secondary battery according to claim 6, characterized in that, The conductive element includes a protrusion, which is integrally formed with the outer shell.

8. The secondary battery according to claim 6, characterized in that, The conductive element includes a metal spring, which is compressed between the outer shell and the first part along the second direction.

9. The secondary battery according to claim 6, characterized in that, The conductive component includes conductive adhesive, and the empty foil area is also bonded to the outer shell by the conductive adhesive.

10. The secondary battery according to claim 1, characterized in that, Along the second direction, the side of the first straight section furthest from the second fold portion that faces away from the first part has an empty foil area and is electrically connected to the outer casing.

11. The secondary battery according to claim 1 or 10, characterized in that, Along the second direction, the side of the second straight section furthest from the first fold portion that faces away from the first portion has an empty foil area and is electrically connected to the outer casing.

12. The secondary battery according to claim 1, characterized in that, The diaphragm includes a first diaphragm and a second diaphragm, which are respectively disposed on opposite sides of the first current collector along the thickness direction. The first diaphragm and the second diaphragm are continuous at the first bending section and the second bending section, respectively.

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

14. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1 to 13.

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