Secondary battery, battery pack, and electric device

Abstract

The invention discloses a secondary battery, a battery pack and electric equipment. The secondary battery comprises a shell, a plurality of electrode assemblies and a terminal assembly. The plurality of electrode assemblies are accommodated in the shell and are stacked in a first direction, and each electrode assembly comprises a tab; the terminal assembly comprises a plurality of electrode terminals, one end of each electrode terminal is located in the shell, the other end of each electrode terminal is located outside the shell, the plurality of electrode terminals are connected to the tabs of different electrode assemblies respectively, the plurality of electrode terminals are arranged in a stacked mode and are the same in polarity, the plurality of electrode terminals are welded to form a first welding part, and the first welding part is located outside the shell; wherein the rated capacity of the secondary battery is a Ah, the resistance between the adjacent electrode terminals is b m omega, a / b is 6 to 60, and a is 30 to 200. The secondary battery can have both high capacity and high use reliability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a secondary battery, a battery pack and an electric device. BACKGROUND

[0002] Secondary batteries are widely used in electronic devices, such as mobile phones, notebook computers, electric vehicles, electric cars, electric planes, electric ships and electric tools, etc.

[0003] How to improve the use reliability of secondary batteries is a research direction in the field of battery technology. SUMMARY

[0004] The present application provides a secondary battery, a battery pack and an electric device, which can have high capacity and high use reliability.

[0005] In a first aspect, the present application provides a secondary battery, which comprises a shell, a plurality of electrode assemblies and a terminal assembly. The plurality of electrode assemblies are accommodated in the shell and arranged in a stack along a first direction, each electrode assembly comprising a tab; the terminal assembly comprises a plurality of electrode terminals, one end of each electrode terminal being located in the shell and the other end being located outside the shell, the plurality of electrode terminals being connected to the tabs of different electrode assemblies respectively, the plurality of electrode terminals being arranged in a stack and having the same polarity, the plurality of electrode terminals being welded and forming a first welding portion, the first welding portion being located outside the shell; wherein the rated capacity of the secondary battery is a Ah, the resistance between adjacent electrode terminals is b mΩ, a / b is 6 to 60, and a is 30 to 200.

[0006] In the secondary battery of the present application, the plurality of electrode assemblies are accommodated in the shell and arranged in a stack along the first direction, each electrode assembly comprising a tab. The terminal assembly comprises a plurality of electrode terminals, one end of each electrode terminal being located in the shell and the other end being located outside the shell, the plurality of electrode terminals being connected to the tabs of different electrode assemblies respectively, the plurality of electrode terminals being arranged in a stack and having the same polarity, the plurality of electrode terminals being welded and forming a first welding portion. The first welding portion can constrain the plurality of electrode terminals to each other, thereby improving the strength of the terminal assembly as a whole. The first welding portion can also realize the electrical connection between the plurality of electrode terminals, which is conducive to simplifying the connection between the electrode terminals and the external conductive structure (such as a busbar). Compared with the resistance of the electrode terminals themselves, the resistance of the first welding portion is larger. When a is 30 to 200, by making the secondary battery satisfy a / b between 6 to 60, the current transmission between the electrode terminals can be hindered when the secondary battery is punctured or other accidents occur, the internal resistance of the secondary battery after short circuit is increased, the current transmitted to the short circuit position is reduced, and the surge of short circuit current is limited. In this way, the heat generation in the secondary battery can be reduced, the risk of local high temperature and thermal runaway can be reduced, and thus the secondary battery can have high capacity and high reliability.

[0007] In some embodiments, the electrode assembly includes a plurality of tabs, the plurality of tabs includes a positive tab, and the total number of layers of the positive tab stacked along the first direction in the secondary battery is 30-80. Thus, the secondary battery can have a higher capacity, and the number of internal short-circuit points in the secondary battery when the secondary battery is punctured is smaller, so that the secondary battery has both high capacity and high reliability.

[0008] In some embodiments, b is 0.5-5. Thus, the internal resistance of the secondary battery after a short circuit occurs can be increased, the heat generation in the secondary battery can be reduced, the risk of local high temperature and thermal runaway can be reduced, and the reliability of the secondary battery can be improved.

[0009] In some embodiments, the rated capacity of the electrode assembly is 15 Ah to 100 Ah. Thus, the internal resistance of a single electrode assembly is larger, and the short-circuit current that can be generated is limited, so that the short-circuit current of a single electrode assembly can be limited to a lower range. In this way, the short-circuit current of the secondary battery can be reduced, and the reliability of the secondary battery can be improved.

[0010] In some embodiments, the electrode assembly includes a plurality of tabs, the plurality of tabs includes a positive tab, and the total number of layers of the positive tab stacked along the first direction in the electrode assembly is 15-40. Thus, the number of internal short-circuit points in a single electrode assembly can be reduced, and the short-circuit current of a single electrode assembly can be reduced, so that the short-circuit current of the secondary battery can be reduced, and the reliability of the secondary battery can be improved.

[0011] In some embodiments, the area of the first welding portion is 60 mm 2 to 600 mm 2 . Thus, the normal electrical connection between each electrode terminal and the bus member can be allowed while effectively blocking the short-circuit current, so that the reliability of the secondary battery 1 in the case of puncture and the electrical performance of the secondary battery 1 in the normal working condition can be considered.

[0012] In some embodiments, the volume resistivity of the electrode terminal is 2×10 -8 Ω.m or more, and is optionally 4×10 -8 Ω.m to 1×10 -7 Ω.m. Thus, the higher resistance between adjacent electrode terminals and the current-carrying performance of the electrode terminal itself can be considered.

[0013] In some embodiments, the plurality of tabs includes a positive tab and a negative tab, and the plurality of terminal assemblies includes a portion connected to the positive tab and another portion connected to the negative tab.

[0014] In a second aspect, the present application provides a battery pack including a plurality of secondary batteries of any of the embodiments of the first aspect.

[0015] In some embodiments, the battery pack further comprises a plurality of busbar components electrically connecting the plurality of secondary batteries; and the at least one electrode terminal of the terminal assembly is welded to the busbar components and forms a second welding portion.

[0016] In some embodiments, the first welding portion and the second welding portion are separated. This facilitates improving the welding quality of the second welding portion, reducing welding defects, and improving the overcurrent capacity.

[0017] In a third aspect, the present application provides a power consuming device comprising the battery pack of any one of the first aspect. BRIEF DESCRIPTION OF DRAWINGS

[0018] Features, advantages, and technical effects of the exemplary embodiments of the present application will be described below with reference to the accompanying drawings.

[0019] FIG. 1 A structural schematic diagram of a secondary battery provided for some embodiments of the present application; FIG. 2 A partial sectional view schematic diagram of a secondary battery provided for some embodiments of the present application; FIG. 3 A schematic diagram of a battery pack provided for some embodiments of the present application; FIG. 4 A schematic diagram of a power consuming device provided for some embodiments of the present application.

[0020] Reference signs of the detailed description are as follows: 1, secondary battery; 10, electrode assembly; 11, electrode sheet; 11a, positive electrode sheet; 11b, negative electrode sheet; 12, tab; 13, separator; 20, shell; 21, packaging film; 30, terminal assembly; 31, electrode terminal; 32, first welding portion; 33, sealing member; 2, busbar component; 2a, second welding portion; 3, battery pack; 4, power consuming device; Z, first direction. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application.

[0022] The terms "first", "second", "third", and the like in the description and claims of this application or in the above summary of the application are used for distinguishing between similar elements and not necessarily for describing a specific sequential or chronological order. The terms "first", "second", "third", and the like are used anecdotally and are not construe as indicating a chronological or sequential order. In the description of the embodiments of the present application, like numbers refer to like elements throughout.

[0023] Reference to an "embodiment" in this application means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. The appearances of the phrase that an "embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive or alternative embodiments.

[0024] In the description of the application, it is necessary to explain that, unless otherwise explicitly specified and limited, the terms "mounting", "connection" and the like should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be directly connected, or indirectly connected through an intermediate medium, or the internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0025] In the embodiments of the present application, "parallel" not only includes the case of absolute parallel, but also includes the case of approximately parallel which is generally recognized in engineering; at the same time, "perpendicular" not only includes the case of absolute perpendicular, but also includes the case of approximately perpendicular which is generally recognized in engineering. Illustratively, the included angle between two directions is 80°-90°, which can be considered as the two directions being perpendicular; the included angle between two directions is 0°-10°, which can be considered as the two directions being parallel.

[0026] The battery pack of the present application will be described below with reference to the accompanying drawings.

[0027] With reference to FIG. 1 to FIG. 2 The embodiments of the present application provide a secondary battery 1. The secondary battery 1 can refer to a battery that can be used continuously by activating the active material through charging after discharging.

[0028] As an example, the secondary battery 1 can be a lithium ion battery, a sodium ion battery, a sodium lithium ion battery, a lithium metal battery, a sodium metal battery, a lithium sulfur battery, a magnesium ion battery, etc.

[0029] As an example, the secondary battery 1 can be a prismatic battery, a pouch battery, or a battery of other shapes, and the prismatic battery includes a square battery, a blade battery, a multi-prismatic battery, for example, a hexagonal prismatic battery, etc.

[0030] The secondary battery 1 includes a case 20 and an electrode assembly 10 accommodated in the case 20.

[0031] The electrode assembly 10 is a component in which electrochemical reactions occur in the secondary battery 1. One or more electrode assemblies 10 can be contained within the case 20. Exemplarily, the electrode assembly 10 can be in a jelly-roll structure or in a stack structure.

[0032] The electrode assembly 10 includes a positive electrode sheet 11a, a negative electrode sheet 11b, and a separator 13. The positive electrode sheet 11a and the negative electrode sheet 11b are opposite in polarity, and the separator 13 separates the positive electrode sheet 11a and the negative electrode sheet 11b. During charging and discharging of the secondary battery 1, active ions (e.g., lithium ions) are intercalated and deintercalated between the positive electrode sheet 11a and the negative electrode sheet 11b. The separator 13 is disposed between the positive electrode sheet 11a and the negative electrode sheet 11b, and can function to prevent short circuiting between the positive and negative electrodes while allowing the active ions to pass through.

[0033] The positive electrode sheet 11a includes a positive electrode current collector and a positive electrode active material layer disposed on a surface of the positive electrode current collector. The negative electrode sheet 11b includes a negative electrode current collector and a negative electrode active material layer disposed on a surface of the negative electrode current collector.

[0034] The positive electrode tab is connected to the positive electrode current collector. In some examples, the positive electrode tab and the positive electrode current collector are a unitary piece, e.g., a metal foil can be coated with a positive electrode active material layer on a surface thereof, and after the coating is complete, the positive electrode current collector and the positive electrode tab can be formed by die cutting the metal foil. In other examples, the positive electrode tab and the positive electrode current collector are separately formed and connected, e.g., the positive electrode tab and the positive electrode current collector can be welded.

[0035] The negative electrode tab is connected to the negative electrode current collector. In some examples, the negative electrode tab and the negative electrode current collector are a unitary piece, e.g., a metal foil can be coated with a negative electrode active material layer on a surface thereof, and after the coating is complete, the negative electrode current collector and the negative electrode tab can be formed by die cutting the metal foil. In other examples, the negative electrode tab and the negative electrode current collector are separately formed and connected, e.g., the negative electrode tab and the negative electrode current collector can be welded.

[0036] Optionally, the positive electrode current collector is an aluminum foil, and the negative electrode current collector is a copper foil.

[0037] In some embodiments, the secondary battery 1 is a pouch battery. A pouch battery can refer to a secondary battery 1 that uses a soft packaging film 21 (e.g., an aluminum-plastic film or the like) as the case 20. A pouch battery has the characteristics of a light structure weight and an easily diversified outer profile shape compared to a secondary battery 1 having a metal structured case 20.

[0038] The secondary battery 1 can have a rectangular shape, a square shape, or other irregular shapes.

[0039] In some embodiments, the case 20 includes two packaging films 21, and a receiving cavity is formed between the two packaging films 21, and the electrode assembly 10 is received in the receiving cavity.

[0040] In some embodiments, the two packaging films 21 are integrally formed. As an example, the two packaging films 21 can be formed by folding one sheet of the aluminum-plastic film.

[0041] In some alternative embodiments, the two packaging films 21 are separately formed. As an example, the two packaging films 21 are respectively two sheets of the aluminum-plastic film.

[0042] Each of the packaging films 21 includes an encapsulation layer, a metal layer, and a protective layer. The encapsulation layers of the two packaging films 21 are fused to form a closed accommodation cavity.

[0043] In some embodiments, the metal layer includes aluminum, and the encapsulation layer and the protective layer include a resin material.

[0044] In some embodiments, the encapsulation layer includes a polypropylene layer. The material of the protective layer includes one or more of nylon, polyethylene terephthalate.

[0045] In some embodiments, the secondary battery 1 includes a terminal assembly 30 including electrode terminals 31. One end of each of the electrode terminals 31 is located inside the case 20, and the other end is located outside the case 20. The electrode terminals 31 are connected to the tabs 12 (positive tabs or negative tabs). The electrode terminals 31 are used to connect with an external circuit to achieve charging and discharging of the secondary battery 1.

[0046] In some embodiments, the electrode terminals 31 are welded to the tabs 12.

[0047] In some embodiments, the terminal assembly 30 further includes a seal 33 surrounding the electrode terminals 31 and disposed between the electrode terminals 31 and the case 20. The seal 33 can be used to be fused with the encapsulation layer of the packaging film 21 to achieve a sealed connection between the terminal assembly 30 and the case 20.

[0048] In some embodiments, the terminal assembly 30 is multiple, and a part of the multiple terminal assemblies 30 are connected to the positive tabs, and another part of the multiple terminal assemblies 30 are connected to the negative tabs.

[0049] The secondary battery 1 of the present application includes a case 20, multiple electrode assemblies 10, and a terminal assembly 30.

[0050] The multiple electrode assemblies 10 are accommodated in the case 20 and arranged in a stack along a first direction Z. Each of the electrode assemblies 10 includes a tab 12. The terminal assembly 30 includes multiple electrode terminals 31. One end of each of the electrode terminals 31 is located inside the case 20, and the other end is located outside the case 20. The multiple electrode terminals 31 are respectively connected to the tabs 12 of different electrode assemblies 10. The multiple electrode terminals 31 are arranged in a stack and have the same polarity. The multiple electrode terminals 31 are welded to form a first welding portion 32, and the first welding portion 32 is located outside the case 20.

[0051] The rated capacity of the secondary battery 1 is a Ah, and the resistance between the adjacent electrode terminals 31 is b mΩ. a is 30 to 200, for example, the rated capacity of the secondary battery 1 can be selected as 30 Ah, 50 Ah, 70 Ah, 90 Ah, 100 Ah, 110 Ah, 130 Ah, 150 Ah, 170 Ah, 190 Ah, 200 Ah, or any numerical range between any two of them. And a / b is 6 to 60, for example, a / b can be selected as 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, or any numerical range between any two of them. Specifically, the rated capacity of the secondary battery 1 can be recorded in the outer packaging printed or product specification book when the secondary battery 1 is shipped.

[0052] The plurality of electrode terminals 31 can be welded by laser welding, ultrasonic welding, resistance welding, or other welding processes. As an example, the speed of laser welding can be 50 mm / s-100 mm / s, and the equivalent speed of resistance welding can be 10 mm / s-50 mm / s. The power of welding can be 100 W-500 W, the welding time can be 0.1 s-0.5 s, and the welding pressure can be 5 N-20 N.

[0053] When the secondary battery 1 is pierced by a sharp object such as a steel nail, the piercing object directly contacts the tab 11 of the secondary battery 1, which can form an electron channel and form a short circuit point, causing a short circuit inside the secondary battery 1. After the short circuit electron channel is formed, a short circuit current is generated inside the battery, which is then converted into Joule heat. Due to the limited heat dissipation rate of the secondary battery 1, if the heat generated by the short circuit is too large, it may cause local high temperature and thermal runaway inside the secondary battery 1, affecting the reliability of the secondary battery 1 and causing safety hazards.

[0054] In addition, with the development of the secondary battery 1, the requirement for its capacity is gradually increasing. However, with the increase of the capacity of the secondary battery 1, the content of active material inside increases, and the number of layers of the tab 11 increases. This leads to an increase in the short circuit current inside the secondary battery 1 when a puncture occurs, further exacerbating the safety hazards caused by the puncture.

[0055] In the secondary battery 1 of the present application, a plurality of electrode assemblies 10 are accommodated in the case 20 and arranged in a stacked manner along the first direction Z, each electrode assembly 10 including a tab 12. The terminal assembly 30 includes a plurality of electrode terminals 31, one end of each electrode terminal 31 being located inside the case 20 and the other end being located outside the case 20, the plurality of electrode terminals 31 being connected to the tabs 12 of different electrode assemblies 10 respectively, the plurality of electrode terminals 31 being arranged in a stacked manner and having the same polarity, and the plurality of electrode terminals 31 being welded and forming a first welding portion 32. The first welding portion 32 can constrain the plurality of electrode terminals 31 to each other, improving the strength of the terminal assembly 30 as a whole. The first welding portion 32 can also realize electrical connection between the plurality of electrode terminals 31, facilitating the connection of the electrode terminals 31 to an external conductive structure (e.g., the busbar 2). Compared with the electrical resistance of the electrode terminals 31 themselves, the first welding portion 32 has a larger electrical resistance. When a is 30 to 200, by making the secondary battery 1 satisfy a / b between 6 and 60, when the secondary battery 1 is subjected to a puncture or other accident, the electrical current transmission between the electrode terminals 31 can be impeded, the internal resistance of the secondary battery 1 after a short circuit is increased, the electrical current transmitted to the short circuit position is reduced, and the surge of the short circuit current is limited. Thus, the heat generation inside the secondary battery 1 can be reduced, the risk of local high temperature and thermal runaway is reduced, and thus the secondary battery 1 has both high capacity and high reliability.

[0056] By adjusting the area of the first welding portion 32, the material and thickness of the electrode terminals 31, and the welding process, the electrical resistance between adjacent electrode terminals 31 can be adjusted, and thus the value of a / b can be adjusted.

[0057] The electrical resistance between adjacent electrode terminals 31 can be tested by using a four-wire micro-ohmmeter. During the test, the current leads of the micro-ohmmeter can be connected to two surfaces of adjacent electrode terminals 31, and a stable small current (e.g., 1 A) can be applied. Then, the voltage leads can be connected to the two surfaces of adjacent electrode terminals 31, and the positions are as close to the current lead contact points as possible to accurately measure the voltage drop. After pressing the test button, the instrument will apply the current and measure the voltage drop, and automatically calculate the electrical resistance R between adjacent electrode terminals 31 according to the formula R=U / I, with the unit of mΩ. In the above formula, U represents the voltage drop with the unit of mV, and I represents the applied current with the unit of A. According to R, the value of b can be determined.

[0058] In some embodiments, the electrode assembly 10 includes a plurality of the pole pieces 11, and the tab 12 is connected to the pole pieces 11; the plurality of the pole pieces 11 includes the positive pole pieces 11a; in the secondary battery, the total number of layers of the positive pole pieces 11a stacked along the first direction Z is 30-80, for example, the total number of layers of the positive pole pieces 11a stacked along the first direction Z in the secondary battery 1 can be selected as 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 68, 70, 72, 74, 76, 78, 80, or a numerical range between any two of them.

[0059] The total number of layers of the positive pole pieces 11a stacked along the first direction Z in the secondary battery 1 meets the given range, which can make the secondary battery 1 have higher capacity, and also make the number of short-circuit points inside the secondary battery 1 when the secondary battery 1 is punctured be less, thereby facilitating the secondary battery 1 to have high capacity and high reliability.

[0060] In the embodiments of the present application, the total number of layers of the positive pole pieces 11a of the plurality of electrode assemblies 10 stacked along the first direction Z can be the same or different.

[0061] In some embodiments, in the electrode assembly 10, the total number of layers of the positive pole pieces 11a stacked along the first direction Z can be 15-40, for example, the total number of layers of the positive pole pieces 11a stacked along the first direction Z in the electrode assembly 10 can be selected as 15, 18, 20, 22, 24, 25, 28, 30, 32, 34, 35, 38, 40, or a numerical range between any two of them. Thus, in the case that the electrode assembly 10 is short-circuited when the secondary battery 1 is punctured, the number of short-circuit points inside a single electrode assembly 10 is less, and the short-circuit current is small, so that the short-circuit current of a single electrode assembly 10 can be reduced, thereby facilitating the reduction of the short-circuit current of the secondary battery 1 and improving the reliability of the secondary battery 1.

[0062] In some embodiments, the rated capacity of the electrode assembly 10 can be 15Ah-100Ah, for example, the rated capacity of the electrode assembly 10 can be selected as 15Ah, 20Ah, 25Ah, 30Ah, 35Ah, 40Ah, 45Ah, 50Ah, 55Ah, 60Ah, 65Ah, 70Ah, 75Ah, 80Ah, 85Ah, 90Ah, 95Ah, 100Ah, or a numerical range between any two of them.

[0063] The single electrode assembly 10 has a small rated capacity. When the secondary battery 1 is punctured, if the electrode assembly 10 is short-circuited, due to the large internal resistance, the short-circuit current that can be generated is limited, and the short-circuit current of the single electrode assembly 10 can be limited in a low range. Thus, under the limitation of the large resistance between the adjacent electrode terminals 31, the short-circuit current of the whole secondary battery 1 is also correspondingly low, so that the risk of local high temperature and thermal runaway of the secondary battery 1 can be reduced, and the reliability of the secondary battery 1 is improved.

[0064] In some embodiments, b can be 0.5-5, for example, the resistance between the adjacent electrode terminals 31 can be selected as 0.5 mΩ, 1 mΩ, 1.5 mΩ, 2 mΩ, 2.5 mΩ, 3 mΩ, 3.5 mΩ, 4 mΩ, 4.5 mΩ, 5 mΩ, or any numerical range between any two of them.

[0065] The resistance between the adjacent electrode terminals 31 is in the above range, which can effectively block the current collection between the electrode assemblies 10, increase the internal resistance of the secondary battery 1 after short-circuit, and limit the surge of short-circuit current. Further, the heat generation in the secondary battery 1 can be reduced, the risk of local high temperature and thermal runaway is reduced, and the reliability of the secondary battery 1 is improved.

[0066] In some embodiments, the area of the first welding portion 32 can be 60 mm 2 to 600 mm 2 , for example, it can be selected as 60 mm 2 , 100 mm 2 , 150 mm 2 , 200 mm 2 , 250 mm 2 , 300 mm 2 , 350 mm 2 , 400 mm 2 , 450 mm 2 , 500 mm 2 , 50 mm 2 , 600 mm 2 , or any numerical range between any two of them.

[0067] By making the area of the first welding portion 32 in the above range, the resistance between the adjacent electrode terminals 31 can be in a suitable range, and the electrode terminals 31 can also maintain good mechanical strength and current carrying performance. Thus, while effectively blocking the short-circuit current, the normal electrical connection between the electrode terminals 31 and the bus member 2 is allowed, so that the reliability of the secondary battery 1 under puncture and the electrical performance under normal working conditions are both considered.

[0068] In some embodiments, the volume resistivity of the electrode terminal 31 is 2 x 10 -8Ω.m and above, for example, 2×10 can be selected. -8 Ω.m, 2.7×10 -8 3.3×10 -8 4×10 -8 Ω.m, 4.7×10 -8 5.3×10 -8 6×10 -8 6.7×10 -8 7.3×10 -8 8×10 -8 8.7×10 -8 9.3×10 -8 9.7×10 -8 1×10 -7 Ω.m, or any range of values ​​between the two.

[0069] By keeping the volume resistivity of the electrode terminal 31 within the above range, it is possible to balance the high resistance between adjacent electrode terminals 31 with the current carrying capacity of the electrode terminal 31 itself.

[0070] Optionally, the volume resistivity of electrode terminal 31 is 4 × 10⁻⁶. -8 Ω.m to 1×10 -7 Ω.m, for example, can be selected as 4×10 -8 Ω.m, 4.5×10 -8 4.8×10 -8 5×10 -8 5.5×10 -8 5.8×10 -8 6×10 -8 6.5×10 -8 6.8×10 -8 7×10 -8 7.5×10 -8 7.8×10 -8 8×10 -8 8.5×10 -8 8.8×10 -8 9×10 -8 9.5×10 -8 9.8×10 -8 1×10 -7 Ω.m, or any range of values ​​between the two.

[0071] Optionally, the material of the electrode terminal 31 may be one or more of aluminum, nickel-plated copper, and nickel-copper alloy.

[0072] In some embodiments, there are multiple electrodes 12, and the multiple electrodes 12 include positive electrodes and negative electrodes.

[0073] The plurality of terminal assemblies 30 are connected to the positive electrode tab and the negative electrode tab.

[0074] For example, the terminal assembly 30 connected to the positive electrode tab is defined as a positive terminal assembly, and the terminal assembly 30 connected to the negative electrode tab is defined as a negative terminal assembly.

[0075] The positive terminal assembly and the negative terminal assembly can be led out from the same side of the shell 20, or can be led out from two sides of the shell 20 respectively. For example, as shown in FIG. 1 , two terminal assemblies 30 are led out from two sides of the shell 20 respectively.

[0076] According to a second aspect of the present application, referring to FIG. 3 , the present application also provides a battery pack 3 comprising a plurality of secondary batteries 1 according to any of the embodiments of the present application.

[0077] In some embodiments, the battery pack 3 further comprises a plurality of busbar components 2, and the plurality of busbar components 2 electrically connect the plurality of secondary batteries 1.

[0078] The plurality of busbar components 2 can connect the plurality of secondary batteries 1 in series, in parallel, or in a mixed manner, wherein the mixed manner means that there are both series connection and parallel connection.

[0079] In some embodiments, at least one electrode terminal 31 of the terminal assembly 30 is welded to the busbar component 2 and forms a second welding portion 2a.

[0080] In some examples, one electrode terminal 31 of the terminal assembly 30 is welded to the busbar component 2; in other examples, all electrode terminals 31 of the terminal assembly 30 are simultaneously welded to the same busbar component 2.

[0081] The electrode terminal 31 can be welded to the busbar component 2 by laser welding, ultrasonic welding, resistance welding, or other means.

[0082] Since the first welding portion 32 of the present embodiment electrically connects the plurality of electrode terminals 31, welding one electrode terminal 31 to the busbar component 2 can achieve electrical connection between the plurality of electrode assemblies 10 and the busbar component 2.

[0083] Of course, in order to improve the overcurrent capacity, a plurality of electrode terminals 31 can be simultaneously welded to the busbar component 2.

[0084] In some embodiments, the first welding portion 32 and the second welding portion 2a are separated, which is beneficial to improve the welding quality of the second welding portion 2a, reduce welding defects, and improve the overcurrent capacity.

[0085] The application also provides a battery pack 3, which includes the use of any of the foregoing embodiments. The battery pack 3 can provide power for the operation of the use of the electric device 4.

[0086] The use of the electric device 4 of the embodiments of the application can be a portable device, a notebook computer, an electric toy, a drone, an electric tool, an energy storage system, etc. The electric tool includes a metal cutting electric tool, a cleaning tool, etc., for example, an electric drill, an electric wrench, a dust collector, a sweeping robot, etc. The embodiments of the application do not make special restrictions on the above-mentioned use of the electric device 4.

[0087] Example The following examples more specifically describe the present disclosure, which are only used for illustrative purposes, because various modifications and changes within the scope of the present disclosure are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further treatment, and the instruments used in the examples are commercially available.

[0088] Example 1 Preparation of positive electrode sheet The positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), a positive electrode conductive agent carbon black (SP), a positive electrode conductive agent carbon nanotube (CNT), and a positive electrode binder polyvinylidene fluoride (PVDF) are dispersed in a solvent N-methyl pyrrolidone (NMP) according to a mass ratio of 96.4:1.4:0.8:1.4, mixed by fully stirring, and formulated into a positive electrode slurry one with a solid content of 65%; lithium iron manganese phosphate, a positive electrode conductive agent carbon black SP, a positive electrode conductive agent CNT, and a positive electrode binder PVDF are dispersed in a solvent NMP according to a mass ratio of 96.5:0.6:0.4:2.5, mixed by fully stirring, and formulated into a positive electrode slurry two with a solid content of 65%. The positive electrode slurry two is coated on one surface of a positive electrode current collector aluminum foil with a thickness of 13 μm, and then the positive electrode slurry one is coated on the positive electrode slurry two to form a double-layer slurry layer with the positive electrode slurry one on top and the positive electrode slurry two on the bottom, which is dried at 120°C to obtain a positive electrode sheet with a single-sided coated positive electrode material layer. In the single-sided positive electrode material layer, the mass ratio of NCM622 to lithium iron manganese phosphate is 7:3. Then, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coated positive electrode material layer. Then, after cold pressing, sheet cutting, and striping, the positive electrode sheet is formed with multiple die-cut tabs. The positive electrode sheet is dried under vacuum at 120°C for 10 min, and is ready for use. The single-sided coating weight of the positive electrode material layer is 17 mg / cm2.2 The thickness of the single-face positive electrode material layer is 57 μm.

[0089] Preparation of negative electrode sheet The negative active material artificial graphite, the negative conductive agent carbon black, the thickening agent sodium carboxymethyl cellulose (CMC-Na), and the negative binder styrene-butadiene rubber (SBR) were dispersed in deionized water at a mass ratio of 97.2:0.4:1:1.4, and were mixed by fully stirring to prepare a negative electrode slurry with a solid content of 40%. The negative electrode slurry was coated on the surface of a negative current collector copper foil with a thickness of 6 μm, and was dried at 100°C to obtain a negative electrode sheet with a single-face coated negative electrode material layer. Then, the above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-face coated negative electrode material layer. The negative electrode sheet was then formed with multiple die-cut tabs by cold pressing, sheet cutting, and striping. The negative electrode sheet was dried at 100°C under vacuum for 30 min, and was ready for use. The weight of the single-face coated negative electrode material layer was 8 mg / cm 2 The thickness of the single-face negative electrode material layer is 55 μm.

[0090] Preparation of electrolyte The dimethyl carbonate, diethyl carbonate, and ethylene carbonate were mixed at a mass ratio of 1:1:1 to obtain an organic solvent, and then the electrolyte salt LiPF6 was added to the organic solvent and mixed uniformly to obtain an electrolyte. The mass percentage of the electrolyte salt in the electrolyte was 12.5%, and the rest was the organic solvent.

[0091] Separator film A 10-μm-thick polyethylene film (provided by Celgard) was used as the separator film.

[0092] Preparation of secondary battery The prepared positive electrode sheet, negative electrode sheet, and separator film were wound to form an electrode assembly; the positive tabs of the two electrode assemblies were welded to the two electrode terminals (made of aluminum) of one terminal assembly, the two electrode terminals of the one terminal assembly were welded to form a first welded portion; the negative tabs of the two electrode assemblies were welded to the two electrode terminals (made of copper plated with nickel) of another terminal assembly, the two electrode terminals of the another terminal assembly were welded to form a first welded portion; the two electrode assemblies were loaded into an aluminum plastic film for top sealing and side sealing, and then the electrolyte was injected and sealed, followed by processes of standing, hot and cold pressing, formation, shaping, capacity testing, and the like, to obtain a secondary battery with a rated capacity a Ah of 30 Ah.

[0093] Example 2-5 The secondary battery was prepared in the same manner as in Example 1, except that the area of the first welded portion was adjusted according to the values shown in Table 1.

[0094] Example 6 The preparation of the secondary battery was the same as in Example 1, except that at least one of the thicknesses of the positive electrode material layer and the negative electrode material layer and the number of winding turns of the electrode assembly was adjusted to change the rated capacity of the secondary battery.

[0095] Examples 7-10 The preparation of the secondary battery was the same as in Example 1, except that at least one of the thicknesses of the positive electrode material layer and the negative electrode material layer and the number of winding turns of the electrode assembly was adjusted to change the rated capacity of the secondary battery.

[0096] Comparative Example 1 Preparation of secondary battery The prepared positive electrode sheet, negative electrode sheet, and separator were wound to form an electrode assembly; the positive electrode tab of the electrode assembly was welded to one electrode terminal, and the negative electrode tab was welded to another electrode terminal; the single electrode assembly was loaded into an aluminum plastic film for top sealing and side sealing, then electrolyte was injected and sealed, and then the electrode assembly was sequentially subjected to processes of standing, hot and cold pressing, formation, shaping, capacity testing, and the like, to obtain a secondary battery with a rated capacity of a Ah of 30 Ah.

[0097] Comparative Example 2 The preparation of the secondary battery was the same as in Comparative Example 1, except that the thicknesses of the positive electrode material layer and the negative electrode material layer and the number of winding turns of the electrode assembly were adjusted to change the rated capacity of the secondary battery.

[0098] Test section The secondary batteries in each of the examples and comparative examples were subjected to nail penetration testing. 100 of each of the examples and comparative examples were subjected to nail penetration testing at 25°C, charged at 0.5C to 4.3V, and then charged at 4.3V to 0.05C until the current cut-off.

[0099] The secondary batteries were subjected to nail penetration testing at 25°C, using a steel nail with a diameter of 5mm, a carbon steel material, a taper of 45mm, and a total length of 100mm, at a nail penetration speed of 25mm / s, and a nail penetration depth of the taper of the steel nail penetrating through the secondary battery. The state of the secondary battery during the testing was observed, and the secondary battery was determined to pass the nail penetration testing if it did not burn or explode, and the number of secondary batteries that passed the nail penetration testing was recorded. The reliability of the secondary battery was represented by the nail penetration testing pass rate. The higher the nail penetration testing pass rate, the better the reliability of the secondary battery.

[0100] The preparation parameters and test results of the examples and comparative examples are shown in Table 1. In Table 1, the positive electrode sheet layer number represents the total number of positive electrode sheets stacked along the first direction Z, for example, the positive electrode sheet layer number of Example 1 is “15&15”, which can represent that in two electrode assemblies of Example 1, the total number of positive electrode sheets stacked along the first direction Z in each electrode assembly is 15. a Ah represents the rated capacity of the secondary battery, b mΩ represents the resistance between adjacent electrode terminals, and “ / ” represents that there is no corresponding parameter.

[0101] Table 1

[0102] As can be seen from the test results in Table 1, when the rated capacity of the secondary battery is between 30 Ah and 200 Ah, by making the secondary battery include a plurality of electrode assemblies, a plurality of electrode terminals corresponding to the plurality of electrode assemblies are welded and form the first welding portion, and a / b is controlled to be 6 to 60, when the nail penetration test is performed, the current transmission between the electrode terminals can be hindered, the internal resistance of the secondary battery after short circuit is increased, the current transmitted to the short circuit position is reduced, and the surge of short circuit current is limited. Thus, the heat generation inside the secondary battery can be reduced, the risk of local high temperature and thermal runaway is reduced, so that the secondary battery has both high capacity and high reliability.

[0103] In this regard, Comparative Examples 1 and 2 are both secondary batteries containing only a single electrode assembly. During the nail penetration test, the steel nail directly contacts the electrode sheet of the secondary battery, and after short circuit, the current inside the secondary battery can be conducted through the electrode terminal, and the electrode terminal itself has a small resistance. Thus, the current in the secondary battery is easy to converge to the short circuit point, resulting in a surge of short circuit current. Therefore, the nail penetration pass rate of Comparative Examples 1 and 2 is low, and the secondary battery has poor reliability.

[0104] Although the present application has been described with reference to the preferred embodiments, various modifications can be made to it without departing from the scope of the application, and equivalent components can be substituted therefor, especially, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery, characterized in that, include: case; Multiple electrode assemblies are housed within the housing and stacked along a first direction, each electrode assembly including a tab; A terminal assembly includes multiple electrode terminals, one end of each electrode terminal being located inside the housing and the other end being located outside the housing. The multiple electrode terminals are respectively connected to the tabs of different electrode assemblies. The multiple electrode terminals are stacked and have the same polarity. The multiple electrode terminals are welded to form a first welded portion, which is located outside the housing. The rated capacity of the secondary battery is a Ah, the resistance between adjacent electrode terminals is b mΩ, a / b is 6 to 60, and a is 30 to 200.

2. The secondary battery according to claim 1, characterized in that, The electrode assembly includes an electrode plate, and the electrode tab is connected to the electrode plate; there are multiple electrode plates, and the multiple electrode plates include a positive electrode plate; In the secondary battery, the total number of positive electrode layers stacked along the first direction is 30-80.

3. The secondary battery according to any one of claims 1-2, characterized in that, b is 0.5-5.

4. The secondary battery according to any one of claims 1-3, characterized in that, The rated capacity of the electrode assembly is 15Ah to 100Ah; and / or, The electrode assembly includes an electrode sheet, and the tab is connected to the electrode sheet; there are multiple electrode sheets, and the multiple electrode sheets include a positive electrode sheet; in the electrode assembly, the total number of layers of the electrode sheets stacked along the first direction is 15-40.

5. The secondary battery according to any one of claims 1-4, characterized in that, The area of ​​the first welded part is 60mm. 2 Up to 600mm 2 .

6. The secondary battery according to any one of claims 1-5, characterized in that, The volume resistivity of the electrode terminals is 2×10⁻⁶. -8 For values ​​above Ω.m, 4×10 can be selected. -8 Ω.m to 1×10 -7 Ω.m.

7. The secondary battery according to any one of claims 1-6, characterized in that, The electrode tabs are multiple, and the multiple electrode tabs include positive electrode tabs and negative electrode tabs; The terminal assembly comprises multiple components, with a portion of each terminal assembly connected to the positive electrode tab and another portion of each terminal assembly connected to the negative electrode tab.

8. A battery pack, characterized in that, It includes multiple secondary batteries according to any one of claims 1-7.

9. The battery pack according to claim 8, characterized in that, The battery pack also includes multiple busbars that electrically connect multiple secondary batteries; At least one of the electrode terminals of the terminal assembly is welded to the busbar and forms a second welded portion.

10. The battery pack according to claim 9, characterized in that, The first welded part and the second welded part are separate.

11. An electrical appliance, characterized in that, Includes the battery pack according to any one of claims 8-10.

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