Secondary battery and electronic device

Abstract

The invention discloses a secondary battery and electronic equipment, the secondary battery comprises a shell, an accommodating cavity is enclosed by the shell, the shell comprises a first wall part, the first wall part comprises a first wall surface deviating from the accommodating cavity and a second wall surface facing the accommodating cavity, the shell is provided with a pressure relief hole, and the pressure relief hole penetrates through the first wall surface and the second wall surface. The pressure relief assembly comprises a metal sheet and a sealing piece, the metal sheet comprises a first metal layer and a second metal layer which are arranged in a stacked mode, the sealing piece is bonded between the first metal layer and the first wall face, and the metal sheet covers the pressure relief hole. The thermal expansion coefficient of the first metal layer is G1, the thermal expansion coefficient of the second metal layer is G2, and G1 is greater than G2; or G1 is less than G2. The area of the pressure relief hole is Smm < 2 > when being observed in the direction from the first wall surface to the second wall surface; the specific bending nominal value coefficient of the metal sheet is K; the elastic modulus of the metal sheet is E Mpa; the thickness of the metal sheet is Dmm in the direction from the first wall face to the second wall face. And 0.5 * S + K * E * 100 * D2 is greater than or equal to 0.3, so that the risk of explosion of the secondary battery can be reduced.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to a secondary battery and an electronic device. Background Art

[0002] With the rapid development of new energy technologies, batteries have been widely used in fields such as mobile phones, laptops, and electric vehicles, and the quality and safety requirements for batteries are also getting higher and higher. However, when the battery is in a high-temperature environment or short-circuited, it is prone to cause thermal runaway of the battery, and the internal pressure of the battery gradually increases, which is likely to cause the battery to catch fire or even explode, posing a safety risk. Summary of the Invention

[0003] An object of an embodiment of this application is to provide a secondary battery and an electronic device to reduce the technical problem that secondary batteries are prone to explosion.

[0004] In a first aspect, an embodiment of this application provides a secondary battery, including a housing. The housing encloses a receiving cavity. The housing includes a first wall portion. The first wall portion includes a first wall surface facing away from the receiving cavity and a second wall surface facing the receiving cavity. The housing is provided with a pressure relief hole that penetrates the first wall surface and the second wall surface. The secondary battery further includes a pressure relief component, and the pressure relief component includes a metal sheet and a seal. Along the direction from the second wall surface to the first wall surface, the metal sheet includes a first metal layer and a second metal layer stacked on top of each other. The seal is bonded between the first metal layer and the first wall surface, and the metal sheet covers the pressure relief hole. The coefficient of thermal expansion of the first metal layer is G 1 , and the coefficient of thermal expansion of the second metal layer is G 2 , G 1 > G 2 ; or, G 1 < G 2 . When observed along the direction from the first wall surface to the second wall surface, the area of the pressure relief hole is S mm 2 ; the specific bending nominal value coefficient of the metal sheet is K; the elastic modulus of the metal sheet is E Mpa; along the direction from the first wall surface to the second wall surface, the thickness of the metal sheet is D mm. It satisfies: 0.5×S + K×E×100×D 2 ≥0.3.

[0005] In the above technical solution, when G 1 > G 2 , because the coefficient of thermal expansion of the first metal layer is larger, when an abnormal situation occurs in the secondary battery and the temperature rises, the first metal layer expands more, causing the edge of the first metal layer to bend and warp towards the second metal layer. As a result, the first metal layer is partially separated from the seal, weakening the adhesion between the metal sheet and the seal, making it easier for the seal to be washed away, thereby realizing the timely release of the internal pressure of the secondary battery and playing a role in timely pressure relief.

[0006] When G 1 <G 2 When the temperature rises due to an abnormal condition in the secondary battery, since the coefficient of thermal expansion of the second metal layer is greater, the second metal layer expands more. As a result, the center of the first metal layer bends towards the second metal layer and protrudes, causing the first metal layer to partially separate from the seal. This weakens the adhesion between the metal sheet and the seal, and some gas inside the housing can enter between the first metal layer and the seal, increasing the pressure-bearing area of the metal sheet, which is beneficial for the seal to be blown open, thereby realizing the timely release of the internal pressure of the secondary battery and playing a role in timely pressure relief.

[0007] Moreover, by defining 0.5×S + K×E×100×D 2 ≥0.3, the timely pressure relief of the secondary battery under abnormal working conditions can be achieved. In practical applications, the accuracy and reliability of the pressure relief of the secondary battery can be significantly improved. By calculating the relationship between the pressure relief hole area S, the specific bending nominal value coefficient K of the metal sheet, the elastic modulus E of the metal sheet, and the thickness D of the metal sheet, it is possible to more easily determine the optimal values of each parameter according to different design requirements and usage scenarios of the secondary battery, reduce unnecessary material waste and over-design, thereby reducing production costs, facilitating the timely and effective pressure relief of the secondary battery under abnormal working conditions (such as overcharging, short-circuiting, high temperature, etc.), and reducing the risks of explosion, fire, etc. of the secondary battery.

[0008] 0.5×S + K×E×100×D 2 represents the sum of the internal pressure of the battery and the pressure generated by the deformation of the bimetal sheet when the temperature reaches 125°C, and 0.3 is the adhesion of the seal when the temperature reaches 125°C. In some embodiments, 0.5×S + K×E×70×D 2 <20. This can reduce the risk of the pressure relief component being blown open prematurely.

[0009] In some embodiments, 0.04 mm ≤ D ≤ 0.5 mm, which is beneficial for the normal use of the secondary battery under normal working conditions, enables the secondary battery to have better sealing performance; and can respond to the temperature change of the secondary battery in a timely manner, reducing the opening or closing of the pressure relief component at inappropriate temperatures, which is beneficial for the timely pressure relief of the secondary battery under abnormal conditions.

[0010] In some embodiments, 5×10 -6 ≤ K ≤ 25×10 -6 , which is beneficial for the normal operation of the secondary battery under normal working conditions and is beneficial for the timely pressure relief of the secondary battery under abnormal working conditions.

[0011] In some embodiments, 40000 Mpa ≤ E ≤ 200000 Mpa, which can respond to the temperature change of the secondary battery in a timely manner and is more convenient for the secondary battery to relieve pressure in a timely manner under abnormal working conditions. Preferably, 100000 Mpa ≤ E ≤ 200000 Mpa.

[0012] In some embodiments, the diameter of the pressure relief hole is R 2 , R 2 , 0.5 mm ≤ R 2 ≤ 4 mm, which is beneficial to the timely pressure relief of the secondary battery under abnormal working conditions and can reduce the occurrence of liquid leakage.

[0013] In some embodiments, along the direction from the first wall surface to the second wall surface, the thickness of the first metal layer is D 11 , and the thickness of the second metal layer is D 12 , 1 ≤ D 11 / D 12 ≤ 5. It can reduce the excessive bending of the metal sheet, which is beneficial to the normal use of the secondary battery under normal working conditions, and at the same time can respond to the temperature change of the secondary battery in a timely manner, which is beneficial to the timely pressure relief of the secondary battery in case of abnormality.

[0014] In some embodiments, the material of the first metal layer includes at least one of nickel-chromium-iron alloy, nickel, copper, copper-tin-zinc alloy, copper-zinc alloy or alloy steel. The material of the second metal layer includes at least one of nickel-iron alloy, invar alloy, nickel-chromium-iron or manganese-copper-nickel. It can reduce the excessive bending of the metal sheet, which is beneficial to the normal use of the secondary battery under normal working conditions, and at the same time can respond to the temperature change of the secondary battery in a timely manner, which is beneficial to the timely pressure relief of the secondary battery in case of abnormality.

[0015] In some embodiments, 4 × 10 -6 / ℃ ≤ |G 1 -G 2 | ≤ 15 × 10 -6 / ℃, which is beneficial to the normal use of the secondary battery and can respond to the temperature change of the secondary battery in a timely manner, which is beneficial to the timely pressure relief of the secondary battery in case of abnormality.

[0016] In some embodiments, the housing further includes a connecting piece disposed on the first wall surface. The first wall portion is provided with a first through hole, and the connecting piece is provided with a second through hole. The second through hole communicates with the first through hole so that the first through hole and the second through hole together form a pressure relief hole. The sealing member is bonded between the connecting piece and the first metal layer, and the metal sheet covers the second through hole. During installation, the sealing member can be first bonded between the metal sheet and the connecting piece, and then the connecting piece can be connected to the housing, which can simplify the installation process and is beneficial to improving the installation accuracy. During disassembly, the entire pressure relief component can be removed from the housing by separating the connecting piece from the housing, which can make the pressure relief component have a high integrity and is beneficial to the reuse of the pressure relief component.

[0017] In some embodiments, along the direction from the first wall surface to the second wall surface, the connecting piece includes a fourth metal layer and a fifth metal layer arranged in a stacked manner. The second through hole penetrates through the fourth metal layer and the fifth metal layer. The fifth metal layer is connected to the housing, and the fourth metal layer is disposed between the seal and the fifth metal layer. The coefficient of thermal expansion of the fourth metal layer is G 4 , and the coefficient of thermal expansion of the fifth metal layer is G 5 , G 4 >G 5 .

[0018] Since the coefficient of thermal expansion of the fourth metal layer is larger, when an abnormal situation occurs in the secondary battery and the temperature rises, the fourth metal layer expands more. Due to the limitation of the first wall portion, the central part of the fourth metal layer will protrude in a direction away from the first wall portion, and then the fourth metal layer will be partially separated from the seal, so that the adhesion between the connecting piece and the seal is weakened, which is more conducive to the seal being washed open, thereby realizing the timely release of the internal pressure of the secondary battery and playing a role in pressure relief. Moreover, the bending direction of the connecting piece is opposite to that of the metal piece, which can further reduce the bonding area between the seal, the metal piece and the connecting piece, and further weaken the adhesion, which is beneficial to improving the sensitivity of the pressure relief component, and then can respond to the abnormal temperature change of the secondary battery in a timely manner.

[0019] In some embodiments, when observed along the direction from the first wall surface to the second wall surface, the connecting piece includes a first part overlapping with the first wall portion. The first part includes a first area fixed to the first wall portion and a second area not fixed to the first wall portion. The first area surrounds the second area, and the second area surrounds the first through hole. Only the first area near the edge of the connecting piece is fixed to the housing, and its central part is relatively free. This structural design provides a certain degree of flexibility for the pressure relief component. When the internal pressure of the secondary battery changes, since the central part of the connecting piece is not fixedly dead, it can better conform to the convex deformation of the connecting piece center outward, which is beneficial to timely pressure relief when the air pressure rises or the temperature changes.

[0020] In some embodiments, when observed along the direction from the first wall surface to the second wall surface, the connecting piece further includes a second part connected to the first part, and the second part covers a part of the first through hole. When the pressure inside the housing rises, it can make the gas impact the second part of a part of the connecting piece, which is more conducive to the second part driving the second area to protrude in a direction away from the housing, and then making the connecting piece partially separate from the seal.

[0021] In some embodiments, the width of the first area is W 1 , 0.1 mm ≤ W 1 ≤ 1 mm, and the width of the second area is W 2 , 1 / 10 ≤ W 1 / W2 ≤ 1 / 3, which can enable the secondary battery to have better sealing performance under normal working conditions, and is conducive to the second region protruding away from the first wall portion under abnormal working conditions of the secondary battery, which is more conducive to pushing open the seal, and can facilitate the timely pressure relief of the secondary battery.

[0022] In some embodiments, when observed along the direction from the first wall surface to the second wall surface, the connecting piece is circular, and the outer diameter of the connecting piece is R 1 , 1.5 mm ≤ R 1 ≤ 6 mm. This can reduce the impact on the energy density of the secondary battery, and can enable the connecting piece and the seal to have sufficient connection area, reduce the loosening or falling off of the connecting piece, and improve the reliability of the pressure relief component.

[0023] In some embodiments, the melting point of the seal is T, 90°C ≤ T ≤ 150°C. Within the normal operating temperature range of the secondary battery, the seal has better sealing performance and can seal the installation gap between the metal sheet and the housing. When the temperature reaches the melting point of the seal (90°C to 150°C), the seal begins to melt, enabling the pressure relief component to be opened in a timely manner and reducing the explosion caused by the excessive internal pressure of the secondary battery.

[0024] In some embodiments, the material of the seal includes at least one of polypropylene, polyethylene, polyvinylidene fluoride, or polytetrafluoroethylene.

[0025] In a second aspect, the present application also proposes an electronic device, including the secondary battery according to any one of the embodiments in the first aspect above.

[0026] The additional aspects and advantages of the embodiments of the present application will be partially described, shown, or explained through the implementation of the embodiments of the present application in the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic structural diagram of a secondary battery according to some embodiments of the present application;

[0028] Figure 2 is an explosion schematic diagram of a secondary battery according to some embodiments of the present application;

[0029] Figure 3 is a schematic structural diagram of a pressure relief component according to some embodiments of the present application;

[0030] Figure 4 is a schematic structural diagram of a pressure relief component according to some embodiments of the present application (pressure relief state);

[0031] Figure 5 is a schematic structural diagram of a pressure relief component according to some embodiments of the present application (pressure relief state);

[0032] Figure 6Explosion schematic diagram of a secondary battery according to some embodiments of the present application;

[0033] Figure 7 Structural schematic diagram of a pressure relief component according to some embodiments of the present application;

[0034] Figure 8 Structural schematic diagram of a pressure relief component according to some embodiments of the present application (pressure relief state);

[0035] Figure 9 Structural schematic diagram of a pressure relief component according to some embodiments of the present application (pressure relief state);

[0036] Figure 10 Structural schematic diagram of a pressure relief component according to some embodiments of the present application;

[0037] Figure 11 Structural schematic diagram of a pressure relief component according to some embodiments of the present application (pressure relief state);

[0038] Figure 12 Structural schematic diagram of a pressure relief component according to some embodiments of the present application (pressure relief state);

[0039] Figure 13 Front view of a secondary battery according to some embodiments of the present application (observed along a direction perpendicular to the first wall portion);

[0040] Figure 14 Structural schematic diagram of a pressure relief component according to some embodiments of the present application;

[0041] Figure 15 Structural schematic diagram of a pressure relief component according to some embodiments of the present application (pressure relief state);

[0042] Figure 16 Structural schematic diagram of a pressure relief component according to some embodiments of the present application (pressure relief state);

[0043] Figure 17 Partial structural schematic diagram of a secondary battery according to some embodiments of the present application.

[0044] Explanation of reference numerals:

[0045] 100, secondary battery;

[0046] 10, housing; 10a, main body portion; 10b, cover body; 11, accommodation cavity; 12, first wall portion; 121, first wall surface; 122, second wall surface; 123, first through hole; 13, pressure relief hole;

[0047] 20, electrode assembly;

[0048] 30, pole column;

[0049] 40, pressure relief component;

[0050] 41. Metal sheet; 411. First metal layer; 412. Second metal layer; 413. Third metal layer;

[0051] 42. Seal; 421. Third through-hole;

[0052] 43. Connecting piece; 43a. First part; 43a1. First region; 43a2. Second region; 43b. Second part; 431. Fourth metal layer; 432. Fifth metal layer; 433. Second through-hole;

[0053] 44. Protective layer;

[0054] X. First direction; Y. Second direction. Detailed implementation manners

[0055] 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 clearly described 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.

[0056] Referring to "embodiment" in the present application means that the specific features, structures, or characteristics described in connection with the embodiment may be included in at least one embodiment of the present application. The phrase appears in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments.

[0057] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order, or primary-secondary relationship of the indicated technical features. In the description of the embodiments of the present application, "a plurality of" means two or more, unless otherwise specifically defined.

[0058] In the description of the embodiments of the present application, the term " / and" is only a description of the association relationship of the associated objects, indicating that three relationships may exist. For example, A / and B may mean: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0059] The technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0060] In a first aspect, the present application provides a secondary battery 100. Please refer to Figure 1 and Figure 2, the secondary battery 100 includes a housing 10, an electrode assembly 20, a terminal 30, and a pressure relief assembly 40. The electrode assembly 20 is disposed within the housing 10. The housing 11 is provided with a pressure relief hole 13. One end of the terminal 30 is connected to the electrode assembly 20, and the other end protrudes from the housing 10. The terminal 30 is used to lead out one polarity of the secondary battery 100. The pressure relief assembly 40 is disposed within the housing 10, and the pressure relief assembly 40 can cover the pressure relief hole 13. When the air pressure within the housing 10 is relatively high, some of the gas within the housing 10 can be discharged outward through the pressure relief hole 13 and the pressure relief assembly 40.

[0061] For the above-mentioned housing 10, please refer to Figure 2 , the housing 10 encloses a receiving cavity 11. The receiving cavity 11 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure). The electrolyte wets the electrode assembly 20 within the receiving cavity 11, thereby causing an electrochemical reaction. In an embodiment of the present application, the housing 10 can be formed by punching a conductive metal layer. The thickness of the conductive metal layer can be set to 0.1 mm to 0.4 mm, such that the housing 10 has a relatively high punching strength.

[0062] Among them, the conductive metal layer can be made of materials such as aluminum, steel, stainless steel, nickel, copper, or magnesium alloy. The housing 10 can lead out a certain polarity of the secondary battery 100, and the above-mentioned terminal 30 can lead out the other polarity.

[0063] The housing 10 can be square, trapezoidal, cylindrical, etc. Taking the square housing 10 as an example. In some embodiments, please refer to Figure 1 and Figure 2 , the housing 10 includes a main body portion 10a and a cover body 10b. The main body portion 10a is provided with a pit cavity, and one end of the main body portion 10a is open. The above-mentioned electrode assembly 20 can be directly placed in the pit cavity through the opening. The cover body 10b is connected to the main body portion 10a and covers the pit cavity, thereby causing the pit cavity to form the receiving cavity 11.

[0064] Please further refer to Figure 3 , the housing 10 includes a first wall portion 12. The first wall portion 12 includes a first wall surface 121 facing away from the receiving cavity 11 and a second wall surface 122 facing the receiving cavity 11. The first wall portion 12 is provided with a first through hole 123. The first through hole 123 penetrates through the first wall surface 121 and the second wall surface 122, and the first through hole 123 communicates with the receiving cavity 11. When the air pressure within the housing 10 increases, some of the gas can be discharged outward through the first through hole 123, which can reduce the explosion risk of the secondary battery 100. When the gas is only discharged through the first through hole 123, the first through hole 123 is used as the pressure relief hole 13. The first through hole 123 can also be used as a liquid injection hole. During the assembly process of the secondary battery 100, after the cover body 10b is connected to and sealed with the main body portion 10a, the electrolyte can be directly injected into the receiving cavity 11 through the first through hole 123, which is convenient for the preparation of the secondary battery 100.

[0065] For the above-mentioned electrode assembly 20, the electrode assembly 20 is disposed in the accommodation cavity 11 of the housing 10, and the shape of the electrode assembly 20 can be set to be adapted to the housing 10, so as to make full use of the space of the accommodation cavity 11 of the housing 10 and improve the energy density of the secondary battery 100.

[0066] The electrode assembly 20 includes a positive electrode plate (not labeled in the figure), a negative electrode plate (not labeled in the figure), and a separator (not labeled in the figure). The positive electrode plate, the separator, and the negative electrode plate are stacked and wound to form a wound electrode assembly 20. Alternatively, a plurality of positive electrode plates and a plurality of negative electrode plates are alternately stacked, and a separator is disposed between adjacent positive and negative electrode plates to form a stacked electrode assembly 20.

[0067] The negative electrode plate of the electrode assembly 20 can be directly electrically connected to the housing 10, so that the housing 10 leads out the negative electrode, and the positive electrode plate of the electrode assembly 20 can be electrically connected to the pole column 30, so that the pole column 30 leads out the positive electrode. In some other embodiments, the housing 10 can also lead out the positive electrode, and the pole column 30 leads out the negative electrode.

[0068] For the above-mentioned pole column 30, please refer to Figure 1 and Figure 2 , the pole column 30 is disposed on the first wall portion 12. A part of the pole column 30 is electrically connected to the electrode assembly 20 in the accommodation cavity 11, and the other part protrudes from the first wall portion 12. In the embodiment of the present application, the polarity of the pole column 30 is opposite to that led out by the housing 10. An insulating member (not labeled in the figure) can be disposed between the pole column 30 and the housing 10 to reduce the occurrence of short circuits, and the insulating member can be bonded between the pole column 30 and the first wall portion 12. On the one hand, it can connect the pole column 30 and the housing 10, and on the other hand, it can seal the installation gap between the pole column 30 and the housing 10 to improve the sealing performance of the secondary battery 100.

[0069] For the above-mentioned pressure relief assembly 40, please refer to Figure 2 and Figure 3 , the pressure relief assembly 40 includes a metal sheet 41 and a seal 42. The seal 42 is bonded between the metal sheet 41 and the first wall surface 121. The metal sheet 41 covers the first through hole 123, and the seal 42 seals the installation gap between the metal sheet 41 and the first wall surface 121, which can improve the sealing performance of the housing 10.

[0070] When the secondary battery 100 is in a high-temperature environment or short circuits, the secondary battery 100 is prone to thermal runaway, and the internal air pressure of the housing 10 gradually increases and impacts the metal sheet 41 and the seal 42, which can cause the seal 42 to be flushed open, thereby forming a pressure relief channel connecting the accommodation cavity 11 and the outside, and reducing the explosion of the secondary battery 100. Among them, the seal 42 can also be provided with a third through hole 421, and the third through hole 421 communicates with the first through hole 123 to facilitate the seal 42 to be flushed open for pressure relief.

[0071] However, the inventors of the present application have discovered that it takes a long time and a high gas pressure for the gas inside the shell 10 to break through the seal 42. If the gas pressure in the shell 10 increases rapidly in a short period of time, the pressure relief assembly 40 may be difficult to respond in time, and there is also a risk of explosion of the secondary battery 100.

[0072] To reduce the above problems, in the embodiment of the present application, the metal sheet 41 may be made of a double metal layer memory alloy. Figure 3 and Figure 4 , along the direction from the second wall surface 122 to the first wall surface 121 (second direction Y), the metal sheet 41 includes a first metal layer 411 and a second metal layer 412 stacked, the seal 42 is bonded between the first metal layer 411 and the first wall surface 121, and the metal sheet 41 covers the first through hole 123. Among them, the thermal expansion coefficient of the first metal layer 411 is G 1 , the thermal expansion coefficient of the second metal layer 412 is G 2 , G 1 >G 2 .

[0073] The metal sheet 41 of the bimetallic memory alloy utilizes the difference in thermal expansion coefficients of the two metal layers to achieve its function. At normal temperature, the metal sheet 41 maintains a certain shape and cooperates with the seal 42 to maintain the sealing state of the secondary battery 100. When an abnormality occurs inside the secondary battery 100, such as overcharging, short circuit, etc., which causes the temperature to rise, the metal sheet 41 will change its shape due to the temperature change.

[0074] In the embodiment of the present application, because the thermal expansion coefficient of the first metal layer 411 is larger, when an abnormal situation occurs in the secondary battery 100 and causes the temperature to rise, the first metal layer 411 expands more, causing the edge of the first metal layer 411 to bend and lift toward the second metal layer 412, thereby partially separating the first metal layer 411 from the seal 42. The adhesion between the metal sheet 41 and the seal 42 is weakened, which is more conducive to the seal 42 being flushed open, thereby achieving the timely release of the internal pressure of the secondary battery 100 and achieving the effect of timely pressure relief.

[0075] Compared with the traditional pressure relief component, the bimetallic memory alloy in the embodiment of the present application is more sensitive to temperature changes and can respond to the temperature changes inside the secondary battery 100 in a timely manner, which helps to release the gas in time and reduce the explosion caused by the sharp rise in pressure inside the secondary battery 100. For example, in some high-temperature environment tests, when the temperature of the secondary battery 100 rises to a certain level, the metal sheet 41 of the bimetallic memory alloy will react quickly and can open the pressure relief channel earlier than the pressure relief component 40 made of ordinary materials.

[0076] Moreover, the shape memory property of the bimetallic layer memory alloy enables the metal sheet 41 to return to its original state after the temperature decreases. For example, when the abnormal situation inside the secondary battery 100 is resolved and the temperature drops, the metal sheet 41 of the bimetallic layer memory alloy will return to its original shape. To a certain extent, it can cooperate with the seal 42 again to restore the sealed state of the secondary battery 100, which is beneficial to the reuse of the pressure relief component 40.

[0077] In some other embodiments, G can also be used 2 >G 1 . Please further refer to Figure 5 , because the coefficient of thermal expansion of the second metal layer 412 is larger. When the temperature rises due to an abnormal situation in the secondary battery 100, the second metal layer 412 expands more, causing the center of the first metal layer 411 to bend and protrude towards the second metal layer 412. As a result, the first metal layer 411 is partially separated from the seal 42, weakening the adhesion between the metal sheet 41 and the seal 42. Moreover, some gas inside the housing 10 can enter between the first metal layer 411 and the seal 42, increasing the pressure-bearing area of the metal sheet 41, which is beneficial to the seal 42 being flushed open, thereby realizing the timely release of the internal pressure of the secondary battery 100 and playing a role in timely pressure relief.

[0078] The inventors of the present application found through research that a thrust F is generated when the metal sheet 41 deforms 1 , the internal pressure of the secondary battery 100 is F 2 (under abnormal working conditions), and the adhesion of the seal 42 is F 3 . When F 1 + F 2 ≥F 3 , the seal 42 can be flushed open, and then the pressure is relieved. Among them, when the temperature reaches 125 °C (for example, the normal temperature environment is 25 °C, then the temperature difference ΔT is 100 °C), the secondary battery 100 needs to be urgently pressure-relieved. The adhesion of the seal 42 changes with the temperature. Generally, when the temperature reaches 125 °C, F 3 is about 0.3 N.

[0079] The inventors of the present application also found through research that F 1 has a certain relationship with the elastic modulus E of the metal sheet 41, the specific bending nominal value coefficient K of the metal sheet 41, the thickness D of the metal sheet 41, and the temperature difference ΔT, and it is obtained that F 1 = K × E × ΔT × D 2 . Among them, ΔT is taken as 100 °C, that is, F 1 = K × E × 100 × D 2 .

[0080] The inventors of the present application found through research that F 2There is a certain relationship between the internal pressure P of the secondary battery 100 and the area S of the pressure relief hole 13, that is, F 2 = P × S. When the internal pressure reaches 0.5 Mpa, it reaches the pressure relief critical point. Therefore, P = 0.5 Mpa, and F 2 = 0.5 × S.

[0081] Therefore, when 0.5 × S + K × E × 100 × D 2 ≥ 0.3, timely pressure relief of the secondary battery 100 under abnormal conditions can be achieved. In the embodiments of the present application, by limiting 0.5 × S + K × E × 100 × D 2 ≥ 0.3, the accuracy and reliability of the pressure relief of the secondary battery 100 can be significantly improved in practical applications. By calculating the relationship between the area S of the pressure relief hole 13, the specific bending nominal value coefficient K of the metal sheet 41, the elastic modulus E of the metal sheet 41, and the thickness D of the metal sheet 41, it is possible to determine the optimal values of each parameter according to different design requirements and usage scenarios of the secondary battery 100. For example, on the basis of meeting the pressure relief conditions, reasonably select the material of the metal sheet 41 and determine the area of the pressure relief hole 13, etc., reduce unnecessary material waste and over-design, thereby reducing production costs, and facilitating the secondary battery 100 to be able to relieve pressure in a timely and effective manner under abnormal conditions (such as overcharging, short circuit, high temperature, etc.), and reducing the risks of explosion, fire, etc. of the secondary battery 100.

[0082] In some embodiments, 0.5 × S + K × E × 70 × D 2 < 20. During the use of the secondary battery, stricter control of the pressure relief of the secondary battery is required. When the usage environment of the secondary battery is less than 95°, the secondary battery does not relieve pressure. At this time, ΔT = 70°, and F 3 is about 20 N. Referring to the above formula, restricting 0.5 × S + K × E × 70 × D 2 < 20 can reduce the risk of premature pressure relief of the secondary battery.

[0083] In addition, the elastic modulus of the metal sheet 41 can be selected such that 40000 Mpa ≤ E ≤ 200000 Mpa, and any value within the range of 40000 Mpa to 200000 Mpa can be chosen. For example, 40000 Mpa, 50000 Mpa, 60000 Mpa, 70000 Mpa, 80000 Mpa, 90000 Mpa, 100000 Mpa, 110000 Mpa, 120000 Mpa, 130000 Mpa, 140000 Mpa, 150000 Mpa, 160000 Mpa, 170000 Mpa, 180000 Mpa, 190000 Mpa or 200000 Mpa can be selected. This is beneficial for promptly responding to the temperature change of the secondary battery 100 and is more convenient for the secondary battery 100 to relieve pressure in a timely manner under abnormal working conditions. Preferably, 100000 Mpa ≤ E ≤ 200000 Mpa.

[0084] Regarding the adjustment of the elastic modulus of the metal sheet 41, the adjustment of the elastic modulus of the metal sheet 41 can be mainly achieved by changing its chemical composition, performing heat treatment, controlling the processing technology, and introducing surface treatment and other methods. For example, adding specific elements to the metal can significantly change its elastic modulus. Exemplarily, adding elements such as chromium and nickel to steel can form an alloy that can improve the strength and elastic modulus of the steel; adding elements such as magnesium and silicon to aluminum can form an aluminum alloy that can improve the elastic modulus of the alloy to a certain extent through the solid solution strengthening mechanism. Quenching, tempering, and annealing can all adjust the elastic modulus. Furthermore, through cold working processes such as rolling and drawing, the grains of the metal sheet can be elongated along the processing direction to form a fibrous structure, and at the same time, work hardening occurs, increasing the dislocation density, thereby increasing the elastic modulus of the metal sheet. In addition, by chemical vapor deposition (CVD) and physical vapor deposition (PVD), a thin film with specific properties, such as titanium nitride and silicon carbide, is deposited on the metal surface, which can change the mechanical properties of the metal surface and thus adjust its overall elastic modulus.

[0085] Definition of the specific bending K: The specific bending K (unit: / ℃) is defined as: the curvature change amount (the displacement of the highest point after bending compared to the position of this point when it is not bent) generated at the free end of a thermal bimetal sheet with a unit thickness (mm) for a unit temperature change (1℃).

[0086] Measurement method (cantilever beam method):

[0087] Sample manufacturing: Cut a bimetal sheet with standard dimensions (such as length 100 mm × width 5 mm), and fix one end as a cantilever beam.

[0088] Temperature control: Place the sample in a constant temperature oven, stabilize the initial temperature at T1 (such as 25℃), and record the initial position of the free end.

[0089] Heating test: Heat up to T2 (such as 125 °C), and measure the displacement ΔH at the free end with a laser displacement sensor or a micrometer.

[0090] Calculate the K value: ΔH is the displacement at the free end, L is the length, ΔT is the temperature rise, and D is the thickness of the bimetal sheet. Substitute these values into the formula K = ΔH / (L×ΔT×D) for calculation, and repeat 3 times to take the average value to reduce errors.

[0091] The inventors of the present application have found through research that the specific bending nominal value coefficient K is relatively large. The specific bending nominal value coefficient is a parameter used to measure the degree of bending of the bimetal layer under a unit temperature difference, which means that the metal sheet 41 is extremely sensitive to temperature changes, and slight heating may cause the metal sheet 41 to malfunction, thereby triggering unnecessary pressure relief. If it is smaller, the response to temperature changes becomes sluggish, and it is difficult to generate sufficient bending deformation in time to trigger the pressure relief device. In the embodiments of the present application, 5×10 -6 ≤K≤25×10 -6 can be selected, and any value within 5×10 -6 to 25×10 -6 can be chosen, for example, 5×10 -6 , 6×10 -6 , 7×10 -6 , 8×10 -6 , 9×10 -6 or 10×10 -6 . This is beneficial to the normal operation of the secondary battery 100 under normal working conditions and is also beneficial to the timely pressure relief of the secondary battery 100 under abnormal working conditions.

[0092] Regarding the diameter of the metal sheet 41, a smaller diameter may result in a smaller deformation of the metal sheet 41, making it difficult to relieve pressure. A larger diameter may occupy the thickness of the secondary battery 100 and affect the energy density of the secondary battery 100. In the embodiments of the present application, 1.27 mm ≤ R ≤ 5 mm, and any value within 1.27 mm to 5 mm can be selected, such as 1.27 mm, 1.3 mm, 1.5 mm, 1.8 mm, 2 mm, 2.3 mm, 2.5 mm, 2.7 mm, 2.9 mm, 3 mm, 3.3 mm, 3.5 mm, 3.8 mm, 4 mm, 4.3 mm, 4.5 mm, 4.7 mm, 4.9 mm or 5 mm, etc. This is beneficial to the timely pressure relief of the secondary battery 100 and can reduce the influence of the metal sheet 41 on the energy density of the secondary battery 100. Preferably, 1.5 mm ≤ R ≤ 4 mm, which is beneficial to the secondary battery 100 to respond to temperature changes in a timely manner, enabling the secondary battery 100 to relieve pressure in a timely manner under abnormal working conditions and further reducing the influence on the energy density of the secondary battery 100.

[0093] Measurement of diameter R: Place the metal sheet 41 on a flat surface. Use a vernier caliper to measure the highest and lowest points of the metal sheet 41. Change the angle and repeat the measurement three times. Take the average value.

[0094] Regarding the diameter of the pressure relief hole 13, if the diameter of the pressure relief hole 13 is small, it may be difficult for the secondary battery 100 to relieve pressure in a timely manner. If the diameter of the pressure relief hole 13 is relatively large, there is a risk of liquid leakage. In the embodiments of the present application, the diameter of the pressure relief hole 13 is R 2 , 0.5mm ≤ R 2 ≤ 4mm, and any value between 0.5mm and 4mm can be selected, such as 0.5mm, 0.6mm, 0.8mm, 2mm, 2.2mm, 2.4mm, 2.6mm, 2.8mm, 3mm, 3.2mm, 3.4mm, 3.6mm, 3.8mm or 4mm, etc. This is beneficial for the secondary battery 100 to relieve pressure in a timely manner under abnormal working conditions and can reduce the occurrence of liquid leakage.

[0095] Among them, the terminal 30 and the pressure relief assembly 40 can both be arranged on the first wall portion 12. There is a large space between the terminal 30 and the electrode assembly 20, which is beneficial for the exhaust and pressure relief of the pressure relief assembly 40.

[0096] For the measurement of the thermal expansion coefficient of the metal layer, a dilatometer can be used for measurement. First, prepare a rectangular sample to ensure that the surface of the sample is smooth and defect-free. Use a dilatometer (DilatometeR1) to calibrate the equipment to ensure the accuracy of the measurement. Place the sample in the dilatometer and conduct tests in a controlled temperature environment. Slowly and evenly change the temperature and measure the dimensional changes of the sample. During the temperature change process, the dilatometer will record the length changes of the sample and record the length change data at different temperatures. Use the formula to calculate the linear thermal expansion coefficient G = ΔL / (L 0 × ΔT), where ΔL is the length change, L 0 is the initial length, and ΔT is the temperature change.

[0097] In the embodiments of the present application, please refer to Figure 3, along the direction from the first wall surface 121 to the second wall surface 122 (the first direction X), the thickness of the metal sheet 41 is D, where 0.04 mm ≤ D ≤ 0.5 mm, and any value within the range of 0.04 mm to 0.5 mm can be selected, such as 0.04 mm, 0.05 mm, 0.08 mm, 0.1 mm, 0.12 mm, 0.15 mm, 0.18 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, or 0.5 mm, etc. This is beneficial to the normal use of the secondary battery 100 under normal operating conditions, enabling the secondary battery 100 to have better sealing performance; and it can promptly respond to the temperature change of the secondary battery 100, reducing the opening or closing of the pressure relief component 40 at inappropriate temperatures, which is beneficial to the timely pressure relief of the secondary battery 100 in abnormal situations.

[0098] Regarding the thickness ratio of the first metal layer 411 to the second metal layer 412, if the thickness ratio is larger, the first metal layer 411 with a larger coefficient of thermal expansion has a greater thickness, which may cause the metal sheet 41 to bend excessively, easily leading to stress concentration. During the deformation process caused by temperature changes, relatively large stresses may be generated at the interface between the first metal layer 411 and the second metal layer 412, which may cause damage such as cracks or delamination in the metal sheet 41, affecting the service life of the pressure relief component 40 and being unfavorable for the reuse of the pressure relief component 40; moreover, a larger thickness ratio may also cause the metal sheet 41 to bend slightly when heated, which may affect the normal operation of the secondary battery. If the thickness ratio is smaller, that is, the thickness of the first metal layer 411 is smaller, the expansion or contraction effect during temperature changes is not obvious, and it may be difficult to drive the second metal layer 412 to deform and open the pressure relief channel, increasing the risk of explosion.

[0099] In the embodiment of the present application, along the direction from the first wall surface 121 to the second wall surface 122 (the first direction X), the thickness of the first metal layer 411 is D 11 , and the thickness of the second metal layer 412 is D 12 , 1 ≤ D 11 / D 12 ≤ 5, and any value within the range of 1 to 5 can be selected, such as 1, 2, 3, 4, or 5, etc. This can reduce the excessive bending of the metal sheet 41, which is beneficial to the normal use of the secondary battery 100 under normal operating conditions, and can reduce phenomena such as cracks or delamination in the metal sheet 41 due to excessive bending. At the same time, it can promptly respond to the temperature change of the secondary battery 100, which is beneficial to the timely pressure relief of the secondary battery 100 in abnormal situations.

[0100] In the embodiment of the present application, 4 × 10 -6 / ℃ ≤ |G 1 -G 2 | ≤ 15 × 10 -6 / ℃, and 4 × 10-6 / °C to 15×10 -6 / °C, for example, select 4×10 -6 / °C, 5×10 -6 / °C, 6×10 -6 / °C, 7×10 -6 / °C, 8×10 -6 / °C, 9×10 -6 / °C, 10×10 -6 / °C, 11×10 -6 / °C, 12×10 -6 / °C, 13×10 -6 / °C, 14×10 -6 / °C or 15×10 -6 / °C, etc. When the difference in thermal expansion coefficients of the two metal layers is less than 4×10 -6 / °C, the deformation of the metal sheet 41 during temperature change is relatively small. When the internal temperature of the secondary battery 100 rises, the speed at which the metal sheet 41 opens the pressure relief channel is relatively low, which may cause the internal pressure of the secondary battery 100 to be released slowly, increasing the safety risk of the secondary battery 100 under abnormal high temperatures. When the difference in thermal expansion coefficients is greater than 15×10 -6 / °C, the metal sheet 41 will be more sensitive to temperature fluctuations. Limiting 4×10 -6 / °C ≤ |G 1 -G 2 | ≤ 15×10 -6 / °C is beneficial to the normal use of the secondary battery 100 and can respond in a timely manner to the temperature change of the secondary battery 100, which is beneficial to the timely pressure relief of the secondary battery 100 under abnormal conditions.

[0101] Among them, the material of the first metal layer 411 includes at least one of nickel-chromium-iron alloy, nickel, copper, copper-tin-zinc alloy, copper-zinc alloy, or alloy steel, etc. The material of the second metal layer 412 includes at least one of nickel-iron alloy, invar alloy, nickel-chromium-iron, or manganese-copper-nickel, etc. It can enable the metal sheet 41 to work normally within the conventional temperature range (generally -20°C to 85°C) and deform at a temperature of 90°C to 150°C. For example, the metal sheet adopts combinations such as copper-nickel-chromium-iron, copper-zinc alloy-manganese-copper-nickel, copper-tin-zinc-invar alloy, etc., and its deformation temperature is within 90°C to 150°C, which is beneficial to the timely pressure relief of the secondary battery 100.

[0102] The synergistic effect among the above metal materials can effectively achieve the pressure relief function of the secondary battery 100. For example, when the internal temperature of the secondary battery 100 rises, due to the relatively large coefficient of thermal expansion of the first metal layer 411, it will expand relative to the second metal layer 412, causing the metal sheet 41 to bend and deform. This deformation acts on the seal 42. When the deformation reaches a certain degree, the seal 42 opens, and the pressure inside the secondary battery 100 can be released in time.

[0103] Regarding the adjustment of the coefficient of thermal expansion of various metal layers, it can be adjusted by adjusting the components of various metal layers. For example, for nickel-iron alloys, changing the ratio of nickel and iron will affect the coefficient of thermal expansion. An increase in the nickel content will reduce the coefficient of thermal expansion. Invar alloy, adding a small amount of other elements such as carbon, silicon, manganese, etc. to the Invar alloy will increase the expansion coefficient. Nickel-chromium-iron alloy, by adjusting the contents of nickel, chromium, iron and other alloying elements, the coefficient of thermal expansion of the alloy can be changed. Manganese-copper-nickel alloy, by changing the ratio of the three main elements of manganese, copper and nickel, the coefficient of thermal expansion can be adjusted. The above nickel-chromium-iron alloy, copper-tin-zinc alloy, copper-zinc alloy and alloy steel, etc. can all adjust the size of their coefficients of thermal expansion by adjusting the proportion of each component. For copper, nickel, etc., a small amount of other elements can also be added, such as adding molybdenum, tungsten, etc. In some other embodiments, the coefficient of thermal expansion of various metal layers can also be adjusted by heat treatment, adding trace elements and optimizing the processing technology, etc. For example, in different heat treatment states, the coefficient of thermal expansion will be different.

[0104] In some embodiments, please refer to Figures 6 to 9 , the pressure relief assembly 40 further includes a connecting piece 43. The connecting piece 43 is disposed on the first wall surface 121, and the connecting piece 43 is provided with a second through hole 433. The second through hole 433 communicates with the first through hole 123, so that the gas in the housing 10 can be discharged through the first through hole 123 and the second through hole 433. Among them, the connecting piece 43 can be connected to the housing 10 by welding, bonding or other means.

[0105] It can be understood that when the gas is discharged through the first through hole 123 and the second through hole 433, that is, the first through hole 123 and the second through hole 433 together form a pressure relief hole 13. The area of the pressure relief hole 13 is the smaller of the diameters of the first through hole 123 and the second through hole 433. That is, when the area of the first through hole 123 is smaller than the area of the second through hole 433, the area of the pressure relief hole 13 is the area of the first through hole 123. When the area of the first through hole 123 is larger than the area of the second through hole 433, the area of the pressure relief hole 13 is the area of the second through hole 433.

[0106] The seal 42 is bonded between the connecting piece 43 and the first metal layer 411. The metal piece 41 covers the second through hole 433, enabling the metal piece 41, the seal 42, and the connecting piece 43 to form an integral whole. During installation, the seal 42 can be first bonded between the metal piece 41 and the connecting piece 43, and then the connecting piece 43 can be connected to the housing 10, which can simplify the installation process and is beneficial to improving the installation accuracy. During disassembly, the entire pressure relief component 40 can be removed from the housing 10 by separating the connecting piece 43 from the housing 10, enabling the pressure relief component 40 to have a high integrity and being beneficial to the reuse of the pressure relief component 40.

[0107] The inventors of the present application found through research that the connecting piece 43 can also be made of a bimetallic layer shape memory alloy. Please refer to Figures 10 to 12 , in the direction from the first wall surface 121 to the second wall surface 122 (the first direction X), the connecting piece 43 includes a fourth metal layer 431 and a fifth metal layer 432 arranged in a stacked manner. The second through hole 433 penetrates through the fourth metal layer 431 and the fifth metal layer 432. The fifth metal layer 432 is connected to the housing 10, and the fourth metal layer 431 is disposed between the seal 42 and the fifth metal layer 432. The coefficient of thermal expansion of the fourth metal layer 431 is G 4 , and the coefficient of thermal expansion of the fifth metal layer 432 is G 5 , G 4 > G 5 .

[0108] In the embodiments of the present application, since the coefficient of thermal expansion of the fourth metal layer 431 is larger, when the secondary battery 100 undergoes an abnormal situation resulting in a temperature rise, the fourth metal layer 431 expands more. Due to the limitation of the first wall portion 12, the central part of the fourth metal layer 431 will protrude in a direction away from the first wall portion 12, thereby causing the fourth metal layer 431 to be partially separated from the seal 42, and then weakening the adhesive force between the connecting piece 43 and the seal 42, which is more conducive to the seal 42 being washed open, thus realizing the timely release of the internal pressure of the secondary battery 100 and playing a role in pressure relief. Moreover, the bending directions of the connecting piece 43 and the metal piece 41 are opposite, which can further reduce the bonding area between the seal 42, the metal piece 41, and the connecting piece 43, and further weaken the adhesive force, being beneficial to improving the sensitivity of the pressure relief component 40, and thus being able to respond to the abnormal temperature change of the secondary battery 100 in a timely manner.

[0109] Similar to the above-mentioned metal piece 41, among them, the material of the fourth metal layer 431 includes at least one of nickel-chromium-iron alloy, nickel, copper, copper-tin-zinc alloy, copper-zinc alloy, or alloy steel, etc. The material of the fifth metal layer 432 includes at least one of nickel-iron alloy, invar alloy, nickel-chromium-iron, or manganese-copper-nickel, etc. The synergistic effect between the various metal materials can effectively realize the pressure relief function of the secondary battery 100.

[0110] Please refer toFigures 13 to 16 When observed in the direction from the first wall surface 121 to the second wall surface 122 (the first direction X), the connecting piece 43 includes a first portion 43a overlapping with the first wall portion 12. The first portion 43a includes a first region 43a1 fixed to the first wall portion 12 and a second region 43a2 not fixed to the first wall portion 12. The second region 43a2 is located between the first region 43a1 and the first through hole 123. The first region 43a1 is disposed around the second region 43a2, and the second region 43a2 is disposed around the first through hole 123. For example, the first region 43a1 and the first wall portion 12 are fixed by welding, and the second region 43a2 does not need to perform any operation and directly fits with the first wall portion 12, or a partial gap space is preset between the second region 43a2 and the first wall portion 12.

[0111] In an embodiment of the present application, only the first region 43a1 near the edge of the connecting piece 43 is fixed to the housing 10, and its central portion (including the second region 43a2) is relatively free. This structural design provides a certain degree of flexibility for the pressure relief component 40. When the internal pressure of the secondary battery 100 changes, since the central portion of the connecting piece 43 is not fixedly held, it can better conform to the convex deformation of the center of the connecting piece 43 outward, which is beneficial to timely pressure relief when the air pressure rises or the temperature changes.

[0112] In some embodiments, when observed in the direction from the first wall surface 121 to the second wall surface 122 (the first direction X), the connecting piece 43 further includes a second portion 43b connected to the first portion 43a, and the second portion 43b covers a part of the first through hole 123. When the pressure inside the housing 10 rises, the gas can impact the second portion 43b of a part of the connecting piece 43, which is more conducive to the second portion 43b driving the second region 43a2 to protrude in a direction away from the housing 10, and further causing the connecting piece 43 to be partially separated from the seal 42, which is beneficial to timely respond to the pressure change inside the housing 10 and further reduce the risk of explosion of the secondary battery 100.

[0113] In some embodiments, please refer to Figure 15 and Figure 16 , the width of the first region 43a1 is W 1 , the width of the second region 43a2 is W 2 . The relatively small width of the second region 43a2 may make it difficult for the second region 43a2 to protrude in a direction away from the housing 10 in a timely manner, thereby making it difficult to relieve pressure in a timely manner. The relatively large width of the second region 43a2 may result in insufficient connection strength between the connecting piece 43 and the housing 10, affecting the sealing performance of the secondary battery 100. In an embodiment of the present application, it is defined that 0.1 mm ≤ W 1 ≤ 1 mm. For example, W 1Select 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, etc. And, it is defined that 1 / 10 ≤ W 1 / W 2 ≤ 1 / 3, for example 0.3 mm ≤ W 2 ≤ 3 mm, for example W 2 Select 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, etc. This can enable the secondary battery 100 to have better sealing performance under normal working conditions, and is beneficial for the second region 43a2 to protrude in a direction away from the first wall portion 12 under abnormal working conditions of the secondary battery 100, which is more conducive to pushing open the seal 42 and facilitating the timely pressure relief of the secondary battery 100. Among them, the width of the first region 43a1 can be the difference between the outer diameter and the inner diameter of the fitting circle where the first region 43a1 is located, and the second region 43a2 is similar.

[0114] In some embodiments, when observing along the direction from the first wall surface 121 to the second wall surface 122 (the first direction X), the connecting piece 43 is circular. A circular ring is a centrosymmetric figure, and no matter from which direction the pressure acts, the force can be evenly distributed on the circumference. When the circular ring-shaped connecting piece 43 is subjected to the force transmitted from the internal pressure of the secondary battery 100 and the deformation of the metal piece 41, it can achieve relatively uniform stress. For example, when the internal pressure of the secondary battery 100 increases and the gas generates an outward thrust on the connecting piece 43, the forces received by each point on the edge of the circular ring-shaped connecting piece 43 are basically the same. This reduces the situation of local stress concentration, enables the connecting piece 43 to withstand the pressure more stably, and is not prone to damage due to relatively large local stress.

[0115] And, the first through hole 123 is usually circular, and the circular ring-shaped connecting piece 43 can be well matched with it, enabling the circular ring-shaped connecting piece 43 to naturally cover around the first through hole 123. While improving the connection strength, it is easier to control the coverage degree of the first through hole 123 through reasonable design (such as setting the first part 43a and the second part 43b as described above) to ensure the timely response of the pressure relief function.

[0116] For the outer diameter of the connecting piece 43, a larger outer diameter will occupy more space of the secondary battery 100, affect the thickness of the secondary battery 100, and may cause energy density loss of the secondary battery 100. While a smaller outer diameter means a smaller connection area with the housing 10 and insufficient support for the seal 42. When the internal pressure of the secondary battery 100 changes, the tensile force and shear force on the connecting piece 43 may cause the connection point to loosen or fall off, thus affecting the normal operation of the pressure relief component 40.

[0117] In the embodiment of the present application, please refer to Figure 17 , the outer diameter of the connecting piece 43 is R 1 , 1 mm ≤ R 1 ≤ 6 mm, and any value between 1 mm and 6 mm can be selected, such as 1 mm, 1.2 mm, 1.5 mm, 1.7 mm, 1.9 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm or 6 mm, etc. It can reduce the influence on the energy density of the secondary battery 100 and can make the connecting piece 43 have a sufficient connection area with the seal 42, reduce the loosening or falling off of the connecting piece 43, and improve the reliability of the pressure relief component 40.

[0118] Preferably, 2 mm ≤ R 1 ≤ 5 mm, which can further reduce the risk of the connecting piece 43 loosening or falling off while reducing the influence on the energy density of the secondary battery 100, and improve the reliability of the pressure relief component 40.

[0119] For the diameter of the first through hole 123, a larger diameter makes the sealing more difficult, increases the risk of internal electrolyte leakage of the secondary battery 100, and may cause external air, moisture, etc. to enter the secondary battery 100, thus affecting the chemical properties of the electrolyte and may cause faults such as internal short circuit of the secondary battery 100. When the diameter of the first through hole 123 is smaller, the pressure relief efficiency is reduced. In the case of a sharp increase in the internal pressure of the secondary battery 100 (such as abnormal conditions such as battery thermal runaway, short circuit, etc.), the gas cannot be discharged in time, which may cause the housing 10 to rupture or even explode, seriously affecting the safety of the secondary battery 100.

[0120] In the embodiment of the present application, the diameter of the first through hole 123 is R 11 , 0.5 mm ≤ R 11 ≤ 5.5 mm, and any value between 0.5 mm and 5.5 mm can be selected, such as 0.5 mm, 0.7 mm, 0.9 mm, 1 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm or 5.5 mm, etc. It can not only reduce the entry of external air, moisture, etc. into the secondary battery 100, but also facilitate the timely discharge of gas.

[0121] As for the diameter of the second through-hole 433, if the diameter of the second through-hole 433 is relatively large, it will make it easier for external air, moisture, etc. to enter the secondary battery 100 through this second through-hole 433, increasing the risk of electrolyte leakage and internal short circuit of the secondary battery 100. If the diameter of the second through-hole 433 is relatively small, it will limit the gas discharge speed, resulting in reduced pressure relief efficiency and being prone to blockage. Impurities generated inside the secondary battery 100 (such as tiny particles of electrode material, solid substances generated by electrolyte decomposition, etc.) may accumulate at the second through-hole 433. Once blocked, gas cannot be discharged through this channel, resulting in the failure of the pressure relief function, thereby affecting the safety of the secondary battery 100.

[0122] In the embodiment of the present application, the diameter of the second through-hole 433 is R 12 , 0.1 mm ≤ R 12 ≤ 4 mm, and any value between 0.1 mm and 4 mm can be selected, such as 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.3 mm, 1.5 mm, 1.7 mm, 1.9 mm, 2 mm, 3 mm or 4 mm, etc. This can not only reduce the entry of external air, moisture, etc. into the secondary battery 100, but also reduce the risk of blockage of the second through-hole 433, and is more conducive to the timely discharge of gas. Preferably, 0.5 mm ≤ R 12 ≤ 4 mm.

[0123] Wherein, when observing in the direction from the first wall surface 121 to the second wall surface 122 (the first direction X), the area of the first through-hole 123 is S 1 , and the area of the second through-hole 433 is S 2 , S 2 <S 1 . The area of the second through-hole 433 being smaller than the area of the first through-hole 123 can, to a certain extent, regulate the pressure relief speed and reduce excessive pressure relief. During the normal operation of the secondary battery 100, a small amount of gas is generated inside. The generation and consumption of these gases occur in a balanced state. The smaller area of the second through-hole 433 can reduce the excessive loss of gas inside the secondary battery 100 under normal circumstances, helping to maintain the internal pressure of the secondary battery 100 within the normal range, thereby improving the performance stability of the secondary battery 100.

[0124] Moreover, the second through-hole 433 is relatively small, which can reduce the entry of external air, moisture, etc. into the secondary battery 100. During pressure relief, the connecting piece 43 can limit the contact opportunity between external substances and the electrolyte and electrode materials inside the secondary battery 100, enabling the chemical reactions inside the secondary battery 100 to occur in a relatively stable environment. The first through-hole 123 is made larger, which can also serve as a liquid injection hole to achieve liquid injection. If the first through-hole 123 is relatively small, it may be difficult to inject liquid.

[0125] For the above-mentioned seal 42, in the embodiments of the present application, the melting point of the seal 42 is T, where 90°C ≤ T ≤ 150°C. Any value between 90 and 150 can be selected, such as 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, or 150°C, etc.

[0126] Within the normal operating temperature range of the secondary battery 100 (generally -20°C to 85°C), the seal 42 can remain solid, having better sealing performance. It can seal the installation gap between the metal sheet 41 and the housing 10, effectively preventing the leakage of the electrolyte inside the secondary battery 100 and blocking the entry of external air and moisture into the secondary battery 100.

[0127] When an abnormal situation occurs in the secondary battery 100, such as overcharging, short-circuiting, or local overheating, the internal temperature of the secondary battery 100 will rise sharply. When the temperature reaches the melting point of the seal 42 (90°C to 150°C), the seal 42 begins to melt, enabling the pressure relief component 40 to be opened in a timely manner, reducing the risk of explosion due to excessive internal pressure in the secondary battery 100. Among them, the deformation temperature of the metal sheet 41 can be set to 90°C to 150°C. For example, the metal sheet 41 is made of combinations such as copper-nickel-chromium-iron, copper-zinc alloy-manganese-copper-nickel, or copper-tin-zinc-invar alloy, and their deformation temperatures are all within 90°C to 150°C, which can cooperate with the seal 42 and is beneficial to the timely pressure relief of the secondary battery 100.

[0128] Regarding the material of the seal 42, in the embodiments of the present application, the material of the seal 42 includes at least one of polypropylene, polyethylene, polyvinylidene fluoride, or polytetrafluoroethylene. Each material has good chemical stability, can withstand the erosion of the electrolyte, reduce the damage of the seal 42 caused by chemical corrosion, and thus improve the sealing performance of the seal 42. Moreover, each material has low permeability to gases and liquids, can reduce the leakage of the internal electrolyte, and prevent the entry of external air, moisture, etc. into the secondary battery 100, which is beneficial to maintaining the normal operation of the secondary battery 100.

[0129] Regarding the adjustment of the melting point of the seal 42:

[0130] The melting point of polypropylene can be adjusted by copolymerization modification: By copolymerizing with a small amount of other monomers, the melting point of polypropylene can be adjusted. For example, polypropylene modified by copolymerizing with ethylene to form ethylene-propylene rubber (EPR1). The introduction of ethylene monomers changes the molecular chain structure of polypropylene, reduces the regularity of the molecular chain, and decreases the crystallinity, thus lowering the melting point. The melting point of this modified polypropylene can be adjusted according to the content of ethylene. Generally, as the content of ethylene increases, the melting point gradually decreases.

[0131] The melting point of polyethylene can be adjusted by density regulation: Such as low-density polyethylene (LDPE), high-density polyethylene (HDPE), and linear low-density polyethylene (LLDPE), their melting points are also different.

[0132] The melting point of polyvinylidene fluoride can be adjusted by controlling crystallinity: By changing processing conditions, such as stretching, annealing and other processes, the crystallinity can be adjusted, thus affecting the melting point. For example, annealing treatment at an appropriate temperature can make the crystallization of polyvinylidene fluoride more perfect, increase the crystallinity, and the melting point also increases accordingly. On the contrary, processing methods such as rapid cooling may reduce the crystallinity, resulting in a decrease in the melting point. The melting point of polyvinylidene fluoride can be adjusted by copolymerization modification.

[0133] The melting point of polytetrafluoroethylene can be adjusted by adding fillers: For example, adding inorganic fillers such as glass fibers and carbon fibers, these fillers can change the thermal properties of the material, such as improving the thermal conductivity, making the temperature distribution of the material more uniform during heating, and thus may exhibit different thermal behaviors in practical applications, indirectly affecting its processing performance and service performance.

[0134] Regarding the thickness of the seal 42, if the thickness of the seal 42 is relatively large, it may increase the resistance to opening the pressure relief channel, easily leading to a delay in the pressure relief action. If the thickness is relatively small, it may not provide sufficient sealing force, possibly resulting in electrolyte leakage or the entry of external air and moisture into the battery interior.

[0135] In the embodiments of the present application, along the direction from the first wall surface 121 to the second wall surface 122 (the first direction X), the thickness of the seal 42 is D 3 ,0.01mm ≤ D 3 ≤ 0.5mm, any value between 0.01mm and 0.5mm can be selected, for example, 0.01mm, 0.02mm, 0.03mm, 0.04mm, 0.05mm, 0.06mm, 0.07mm, 0.08mm, 0.09mm, 0.1mm, 0.2mm, 0.3mm, 0.4mm or 0.5mm, etc. It can improve the sealing performance under the normal working conditions of the secondary battery 100, and can timely open the pressure relief channel under abnormal conditions (pressure increase or temperature increase) of the secondary battery 100.

[0136] In a second aspect, the present application also provides an electronic device, which includes a secondary battery 100 as in any embodiment of the first aspect above. The electronic device in the embodiments of the present application is not particularly limited, and it can be any electronic device known in the prior art. For example, the electronic device includes but is not limited to a Bluetooth headset, a mobile phone, a tablet, a laptop computer, an electric toy, an electric tool, an electric vehicle, an electric car, a ship, a spacecraft, etc. Among them, the electric toy can include a fixed or mobile electric toy, such as a game console, an electric vehicle toy, an electric ship toy, an electric aircraft toy, etc., and the spacecraft can include an airplane, a rocket, a space shuttle, a spaceship, etc.

[0137] Embodiment 1

[0138] Preparation of the positive electrode sheet:

[0139] Mix the positive electrode active material lithium iron phosphate, the positive electrode conductive agent acetylene black, and the positive electrode binder polyvinylidene fluoride (PVDF, weight average molecular weight is 5×10 5 ) in a mass ratio of 94:3:3, add N-methylpyrrolidone (NMP) as a solvent, and formulate a positive electrode slurry with a solid content of 75 wt%, and stir evenly under a vacuum mixer. Select an aluminum foil with a thickness of 8 μm and a length of 1000 mm as the positive electrode current collector, evenly coat the positive electrode slurry on one surface of the positive electrode current collector aluminum foil, and dry it at 110°C to obtain a positive electrode sheet with a single-sided coated positive electrode active material layer. Then, repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coated positive electrode active material layer.

[0140] Preparation of the negative electrode sheet:

[0141] Mix the negative electrode active material graphite powder, silicon powder, the conductive agent conductive carbon black (Super P), and the binder styrene-butadiene rubber (SD-3) in a weight ratio of 89.5:8:1:1.5, then add deionized water as a solvent, formulate a negative electrode slurry with a solid content of 50 wt%, and stir evenly. Select a copper foil with a thickness of 5 μm and a length of 1050 mm as the negative electrode current collector, evenly coat the negative electrode slurry on one surface of the negative electrode current collector copper foil, and dry it at 90°C to obtain a single-sided negative electrode sheet. After the above steps are completed, the single-sided coating of the negative electrode sheet is completed. Then, repeat the above steps on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a double-sided coated negative electrode active material layer. Clean out a second groove in one negative electrode active material layer through a laser cleaning process, and weld a part of the negative electrode tab to the negative electrode current collector in the second groove.

[0142] Preparation of the separator:

[0143] Polyethylene is selected as the 7-μm substrate layer, and polyvinylidene fluoride is selected as the adhesive layer. An alumina ceramic layer with a thickness of 2 μm is provided on the side of the adhesive layer facing away from the substrate layer to prepare a porous separator membrane.

[0144] Preparation of the electrolyte:

[0145] In a dry argon atmosphere, ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate are mixed in a mass ratio of 30:50:20 to obtain an organic solution. Then, lithium hexafluorophosphate is added to the organic solvent and dissolved and mixed uniformly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0146] Preparation of the metal sheet:

[0147] A copper-zinc alloy (brass) with a thickness D 11 of 0.025 mm is selected as the first metal layer, and a nickel-iron alloy with a thickness D 12 of 0.025 mm is selected as the second metal layer. The first metal layer and the second metal layer are stacked and bonded to form a metal sheet with a thickness D of 0.05 mm. The radius R of the metal sheet is 3 mm, the elastic modulus E of the metal sheet is 160,000 Mpa, and the specific bending nominal value coefficient K of the metal sheet is 5×10 -6 . The thermal expansion coefficient G 1 (18.5×10 -6 / °C) of the first metal layer is greater than the thermal expansion coefficient G 2 (9.5×10 -6 / °C) of the second metal layer.

[0148] Preparation of the lithium-ion secondary battery:

[0149] The above positive electrode plate is welded to the aluminum positive electrode tab, and the negative electrode plate is welded to the nickel negative electrode tab. The separator membrane, the positive electrode plate, the separator membrane, and the negative electrode plate are stacked in sequence and wound to obtain an electrode assembly. The electrode assembly is placed in a steel shell, the positive electrode tab is welded to the pole column on the shell, and the negative electrode tab is welded to the shell. Among them, the shell has a pressure relief hole with a diameter R 2 of 0.5 mm. After removing moisture at 80°C, the electrolyte is injected. Polypropylene is selected as the seal, and the metal sheet is bonded to the shell through the seal, and the metal sheet covers the first through hole. After processes such as encapsulation, formation, capacity testing, and voltage internal resistance testing, the lithium-ion battery is manufactured.

[0150] Different from Example 1, the relevant parameters in Examples 2 to 28 and Comparative Examples 1 to 4 are shown in Table 1 below. Among them, in Examples 6 and 7, the radius R of the metal sheet is 5 mm and 6 mm respectively. Among them, S is the area of the pressure relief hole,

[0151] The thermal shock test process is as follows:

[0152] First, set the test environment temperature to 23°C ± 2°C and let the test sample stand still for 5 minutes. Then, perform a charging operation on the lithium-ion battery sample, charging it at a constant current (DC) of 0.2C to a voltage of 3.0V. After completing the above charging operation, let the sample stand still for 5 minutes again to allow for a short period of stable adjustment inside the lithium-ion battery after charging.

[0153] Adjust the furnace temperature for testing to 37°C (±2°C) and let the lithium-ion battery sample stand still in this high-temperature environment for 2 hours to allow the sample to fully adapt to the high-temperature environment in order to observe the performance of the sample under this high-temperature condition and subsequent operations.

[0154] Then, charge at a constant current of 1.65C to a voltage of 4.1V, and then switch to a constant voltage (CV) charging mode until the current drops to 1.55C. Then, charge at a constant current of 1.55C to a voltage of 4.2V, and then switch to constant voltage charging until the current drops to 1.4C. Subsequently, charge at a constant current of 1.4C to a voltage of 4.24V, and then switch to constant voltage charging until the current drops to 1.1C. Then, charge at a constant current of 1.1C to a voltage of 4.27V, and then switch to constant voltage charging until the current drops to 0.7C. Finally, charge at a constant current of 0.7C to a voltage of 4.3V, and then switch to constant voltage charging until the current drops to 0.4C, and charge at a constant current of 0.4C to a voltage of 4.505V, and then switch to constant voltage charging until the current drops to 0.025C.

[0155] When completing the above series of complex charging operations, observe whether the pressure relief component of the secondary battery is blown open. If it is not blown open, let the lithium-ion secondary battery sample stand still for 5 minutes again and conduct the following tests:

[0156] Test process: ① Check the appearance and take photos before and after the test; ② The position where the temperature-sensing wire is attached is near the anode tab; ③ Place the lithium-ion battery sample horizontally in the box and heat it up to 130 ± 2°C at a heating rate of 5 ± 2°C and hold for 30 minutes; ④ Measurement frequency: For voltage and internal resistance measurement, use a 1KHz specification, measure after pretreatment and after the test; ⑤ Judgment criteria: No explosion, no smoking, no fire.

[0157] For each group of 20 lithium-ion secondary batteries, conduct routine tests and thermal shock tests. If failure occurs during any process, it is regarded as a test failure. The number of test failures is N, and the test failure rate is N / 20.

[0158] Table 1

[0159]

[0160]

[0161] According to the above Table 1, in combination with Examples 1 to 7 and Comparative Example 1, Examples 8 to 14 and Comparative Example 2, Examples 15 to 23 and Comparative Example 3, Examples 24 to 31 and Comparative Example 4, it can be seen that when 0.5×S + K×E×100×D 2 ≥0.3, the test failure rate can be reduced, which is beneficial to achieving timely pressure relief of the secondary battery under abnormal conditions, and can significantly improve the accuracy and reliability of the pressure relief of the secondary battery in practical applications. By reasonably selecting the material and size of the metal sheet, etc., it is convenient for the secondary battery to relieve pressure in a timely manner under abnormal conditions, and the accuracy and timeliness of the pressure relief are improved.

[0162] In Examples 1 to 7, the test failure rate is less than that of Comparative Example 1. In Example 7, R 2 is relatively large, so that the diameter R of the metal sheet is relatively large, which affects the energy density of the secondary battery, and the metal sheet needs to absorb more heat before it may deform, which is not conducive to timely responding to the temperature change of the secondary battery. In the embodiments of the present application, in combination with Examples 1 to 6, 0.5mm ≤ R 2 ≤ 4mm can be selected, which can reduce the influence on the energy density of the secondary battery and is beneficial to timely pressure relief.

[0163] In Example 3 and Examples 8 to 13, the test failure rate is less than that of Comparative Example 2, and in Example 3 and Examples 8 to 12, the test failure rate is further reduced. Therefore, in the embodiments of the present application, 5×10 -6 ≤ K ≤ 25×10 -6 can be selected, which is beneficial to the normal operation of the secondary battery at non-pressure relief temperatures and is beneficial to the timely pressure relief of the secondary battery under abnormal conditions.

[0164] In Example 3 and Examples 14 to 21, the test failure rate is less than that of Comparative Example 3, and in Example 3 and Examples 14 to 20, the test failure rate is less than that of Example 21. In the embodiments of the present application, 40000Mpa ≤ E ≤ 200000Mpa can be selected. In Example 3 and Examples 17 to 20, the test failure rate is further reduced, and 100000Mpa ≤ E ≤ 200000Mpa can be preferably selected.

[0165] In Example 3 and Examples 22 to 28, the test failure rate is less than that of Comparative Example 4, and in Example 3 and Examples 23 to 27, the test failure rate is less than that of Examples 22 and 28. The thickness of the metal sheet is relatively small, which may affect the sealing performance. For example, during the conventional working condition test of the secondary battery, the pressure relief component may be washed open, resulting in test failure. And when the thickness is relatively large, its deformation degree and bending force may also be relatively large. For example, it deforms severely after being heated, and may even open the pressure relief channel prematurely. In the embodiments of the present application, 0.04mm ≤ D ≤ 0.5mm can be selected.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than limiting them; under the idea of the present application, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order, and there are many other variations in different aspects of the present application as described above. For the sake of brevity, they are not provided in detail; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present application.

Claims

1. A secondary battery, comprising a shell, the shell enclosing a receiving cavity, the shell comprising a first wall portion, the first wall portion comprising a first wall surface away from the receiving cavity and a second wall surface facing the receiving cavity, the shell being provided with a pressure relief hole, the pressure relief hole penetrating the first wall surface and the second wall surface; characterized in that: The secondary battery further includes a pressure relief assembly, wherein the pressure relief assembly includes a metal sheet and a sealing member; Along the direction from the second wall surface to the first wall surface, the metal sheet includes a first metal layer and a second metal layer stacked together, the sealing member is bonded between the first metal layer and the first wall surface, and the metal sheet covers the pressure relief hole; The thermal expansion coefficient of the first metal layer is G1, the thermal expansion coefficient of the second metal layer is G2, G1>G2; or, G1<G2; Observed from the direction from the first wall surface to the second wall surface, the area of ​​the pressure relief hole is Smm 2 ; The specific bending nominal coefficient of the metal sheet is K; The elastic modulus of the metal sheet is E Mpa; The thickness of the metal sheet along the direction from the first wall to the second wall is Dmm; Satisfies: 0.5×S+K×E×100×D 2 ≥0.

3.

2. The secondary battery according to claim 1, characterized in that: 0.5×S+K×E×70×D 2 <20。 3. The secondary battery according to claim 1, characterized in that: At least one of the following conditions is met: (a), 0.04mm≤D≤0.5mm; (b)、5×10 -6 ≤K≤25×10 -6 ; (c), 40000Mpa≤E≤200000Mpa.

4. The secondary battery according to claim 3, characterized in that: 100000Mpa≤E≤200000Mpa.

5. The secondary battery according to claim 1, characterized in that: The diameter of the pressure relief hole is R2, 0.5mm≤R2≤4mm.

6. The secondary battery according to claim 1, characterized in that: Along the direction from the first wall surface to the second wall surface, the thickness of the first metal layer is D 11 , the thickness of the second metal layer is D 12 , 1≤D 11 / D 12 ≤5.

7. The secondary battery according to claim 1, characterized in that: The material of the first metal layer includes at least one of nickel-chromium-iron alloy, nickel, copper, copper-tin-zinc alloy, copper-zinc alloy or alloy steel; The material of the second metal layer includes at least one of nickel-iron alloy, Invar alloy, nickel-chromium-iron or manganese-copper-nickel.

8. The secondary battery according to any one of claims 1 to 7, characterized in that: 4×10 -6 / ℃≤|G1-G2|≤15×10 -6 / ℃。 9. The secondary battery according to claim 1, characterized in that: The shell also includes a connecting piece arranged on the first wall surface, the first wall portion is provided with a first through hole, the connecting piece is provided with a second through hole, the second through hole is communicated with the first through hole so that the first through hole and the second through hole together form the pressure relief hole, the sealing member is bonded between the connecting piece and the first metal layer, and the metal sheet covers the second through hole.

10. The secondary battery according to claim 9, characterized in that: Along the direction from the first wall surface to the second wall surface, the connecting sheet includes a fourth metal layer and a fifth metal layer which are stacked; The second through hole passes through the fourth metal layer and the fifth metal layer, the fifth metal layer is connected to the housing, and the fourth metal layer is arranged between the sealing member and the fifth metal layer; The thermal expansion coefficient of the fourth metal layer is G4, the thermal expansion coefficient of the fifth metal layer is G5, and G4>G5.

11. The secondary battery according to claim 10, characterized in that: When viewed from the direction from the first wall surface to the second wall surface, the connecting piece includes a first portion overlapping the first wall portion, and the first portion includes a first area fixed to the first wall portion and a second area not fixed to the first wall portion; The first area is disposed around the second area, and the second area is disposed around the first through hole.

12. The secondary battery according to claim 11, characterized in that: Observing from the direction from the first wall surface to the second wall surface, the connecting piece further includes a second portion connected to the first portion, and the second portion covers a portion of the first through hole.

13. The secondary battery according to claim 11, characterized in that: The width of the first region is W1, 0.1 mm≤W1≤1 mm, and the width of the second region is W2, 1 / 10≤W1 / W2≤1 / 3.

14. The secondary battery according to any one of claims 9 to 13, characterized in that: Observing from the direction from the first wall surface to the second wall surface, the connecting piece is in a circular ring shape, and the outer diameter of the connecting piece is R1, 1.5mm≤R1≤6mm.

15. The secondary battery according to claim 1, characterized in that: The melting point of the sealing member is T, 90°C≤T≤150°C.

16. The secondary battery according to claim 1, characterized in that: The material of the sealing element includes at least one of polypropylene, polyethylene, polyvinylidene fluoride or polytetrafluoroethylene.

17. An electronic device, characterized in that: Includes the secondary battery according to any one of claims 1 to 16.

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